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Opleiding 2 cycli – Campus Paardenmarkt Paardenmarkt 92 – 2000 Antwerpen Academiejaar 2003 – 2004
Convergentie WLAN en UMTS
Eindwerk voorgedragen door Helsmoortel Carl tot het bekomen van de titel en de graad van Industrieel Ingenieur Elektronica optie Informatie- en communicatietechnieken
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Dankwoord Er zijn een aantal personen die ik zou willen bedanken. In de eerste plaats richt ik mijn dank aan mijn promotor tevens Hoogleraar aan de Hogeschool Antwerpen, ir. L. Pieters voor de nodige steun en advies tijdens het uitwerken van mijn eindwerk en het regelen van bedrijfsbezoeken. Ten tweede richt ik een woord van dank aan Ing. T. Dams en Ing. S. Deruyter, onderzoekers aan de Hogeschool Antwerpen, tevens voor de steun en advies. Het realiseren van een degelijk eindwerk kan niet bedacht worden zonder de nodige bedrijfsbezoeken. Hiervoor zou ik Luc Buntinx(Sinfilo), Jan Vercruysse(Option), Willem Peeters(Mobistar), Razvan Unguranu(Mobistar), Emmanuel Genbrugge(Mobistar), Oscar garcia(UPC) willen bedanken voor hun tijd en het beantwoorden van mijn vragen. De derdejaars studenten industrieel ingenieur elektronica Baart Annica, Giebens Kris, Peeters Michaël en Schmidt Gwyn zou ik tevens willen bedanken voor de uitvoerige uitwerking van het GPRS en EDGE deel. Als laatste wens ik mijn ouders, vriendin en vrienden te bedanken die onrechtstreeks deelgenomen hebben voor de nodige steun.
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Inhoudsopgave Dankwoord ................................................................................................................................. 1 Inhoudsopgave ........................................................................................................................... 2 Abstract Nederlands ................................................................................................................... 3 Abstract Engels .......................................................................................................................... 4 Inleiding ..................................................................................................................................... 5 1 Theoretische studie............................................................................................................. 6 1.1 Inleiding ..................................................................................................................... 6 1.2 Theoretische inhoud ................................................................................................... 6 1.2.1 GSM ................................................................................................................... 6 1.2.2 GPRS.................................................................................................................. 6 1.2.3 EDGE ................................................................................................................. 7 1.2.4 UMTS................................................................................................................. 7 1.2.5 Convergentie WLAN en UMTS ........................................................................ 7 2 Praktijk gedeelte................................................................................................................. 8 2.1 Bedrijfsbezoeken ........................................................................................................ 8 2.1.1 Introductie .......................................................................................................... 8 2.1.2 Sinfilo ................................................................................................................. 8 2.1.3 Option............................................................................................................... 10 2.1.4 Mobistar ........................................................................................................... 10 2.1.5 UPC .................................................................................................................. 10 2.1.6 Deelbesluit........................................................................................................ 11 2.2 GPRS_EDGE project ............................................................................................... 11 2.2.1 Inleiding ........................................................................................................... 11 2.2.2 Maatregelen vooraf .......................................................................................... 12 2.2.3 Onderwerp(en) ................................................................................................. 12 2.2.4 Vergaderingen .................................................................................................. 13 2.2.5 Deelbesluit........................................................................................................ 14 2.3 Erasmus project ........................................................................................................ 14 2.3.1 Inleiding ........................................................................................................... 14 2.3.2 Maatregelen vooraf .......................................................................................... 15 2.3.3 Onderwerp(en) ................................................................................................. 15 2.3.4 Vergaderingen .................................................................................................. 16 2.3.5 Deelbesluit........................................................................................................ 16 2.4 Mobile IP.................................................................................................................. 17 2.4.1 Inleiding ........................................................................................................... 17 2.4.2 Deelbesluit........................................................................................................ 18 Besluit....................................................................................................................................... 19 Bronnen .................................................................................................................................... 20 Bijlagen .................................................................................................................................... 21 Nieuwsberichten................................................................................................................... 21 Vergaderingen van het Erasmus project............................................................................... 27 Kort verslag convergentie WLAN en UMTS ...................................................................... 30 Opgestelde documenten ....................................................................................................... 42
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Abstract Nederlands Titel
:
Convergentie WLAN en UMTS
Student
:
Helsmoortel Carl – ICT
Bedrijf
:
Hogeschool Antwerpen dep. IWT 2 cycli
Promotor
:
ir. L. Pieters, ing. S. Deruyter, ing. T. Dams
HA promotor :
ir. L. Pieters
UMTS(3G) is een veelbelovende technologie die zich nog in zijn implementatie fase bevindt. UMTS zorgt voor een hoge data snelheid en de invoering van nieuwe diensten (multimedia,…). De voorganger van UMTS, GPRS(2.5G) kende een snelle introductie in de markt dankzij het hergebruik van het ‘Radio Access Network’ van het GSM(2G) netwerk. Deze implementatie zorgde ervoor dat de kosten niet al te hoog waren als men weet dat 80% van de investering naar het RAN gespendeerd wordt. UMTS zal eerst geïntroduceerd worden in de grote steden, men spreekt hier over een nieuw RAN, nl. UTRAN(UMTS Terrestrial RAN). Om ervoor te zorgen dat men een aantrekkelijk product kan aanbieden, zal men in omstreken EDGE implementeren in het GSM/GPRS netwerk. Deze software implementatie bestaat uit een aantal nieuwe modulatie technieken die ervoor zorgen dat men tot snelheden komt die 4 maal sneller zijn dan GPRS. WLAN biedt een hoge data snelheid, wat één van zijn sterke eigenschappen is in tegenstelling tot GPRS, EDGE, UMTS,... Mobile operatoren beschouwen deze technologie niet als mobiel, aangezien ze geen volledige dekking aanbieden. Door deze twee veelbelovende technologieën te integreren bekomt men een technologie die beide sterke eigenschappen bevatten(Mobiliteit en snelheid). Deze convergentie wordt ook wel ‘Beyond 3G’ genoemd die zal evolueren naar 4G(vierde generatie mobile technologieën) Momenteel wordt er nog veel gespeculeerd over 4G. Deze zal verschillende mobiele technologieën bevatten die samen geïntegreerd worden tot één technologie. Het staat vast dat de convergentie van WLAN en UMTS de ‘hot item’ wordt van de vierde generatie mobiele netwerken.
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Abstract Engels Title
:
Convergence WLAN and UMTS
Student
:
Helsmoortel Carl – ICT
Company
:
Hogeschool Antwerpen dep. IWT 2 cycli
Promoter
:
ir. L. Pieters, ing. S. Deruyter, ing. T. Dams
HA promoter :
ir. L. Pieters
UMTS(3G) is a promising technology which is still in its implementation phase for the mobile operators. UMTS provides high data rates and new services(Multimedia services,…) GPRS(2.5G) had an easy introduction to the market. This is due to the fact that this technology employs the RAN(Radio Access Network) of the GSM(2G) network. The introduction of GPRS didn’t have a big impact on the financial side of the mobile operators if you know that 80% of the investment is spend for the RAN. UMTS will be first introduced in the big cities. Comparing with GPRS, UMTS has a new RAN called UTRAN(UMTS Terrestrial RAN). To provide a plausible product, mobile operators will implement EDGE in the surroundings. EDGE is implemented as a kind of upgrade of the GSM/GPRS network. This software implementation/upgrade contains several new modulation techniques that will provide a data rate that is 4 times faster than the rate provide by GPRS. WLAN provides a much higher data rate then GPRS, EDGE, UMTS… This is one of the strong characteristic of WLAN. Mobile operators do not speak of a mobile technology because WLAN doesn’t provide a total coverage. We get a stronger technology by integrating these two technologies(WLAN and UMTS). This convergence sometimes called ‘Beyond 3G’ will evolve to 4G(fourth generation of mobile systems). There are a lot of speculations at this moment about 4G. This new system will integrate different mobile technologies. One thing is sure: the convergence of WLAN and UMTS will be the hot item of this fourth generation of mobile system.
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Inleiding Dit onderwerp werd mij voorgesteld naar aanleiding van het eindwerk over WLAN dat vorig jaar(2002-2003) uitgevoerd werd. Dit jaar werd het kenniscentrum over draadloze technologieën door Tim Dams en Sven Deruyter opgebouwd. WLAN omvat de draadloze wereld terwijl UMTS het mobiel gedeelte omvat. Tijdens hun studie merkten zij op dat een convergentie tussen beide technologieën weliswaar een nieuwe evolutie zou betekenen. Als eerste werd mij gevraagd om de nodige zaken te onderzoeken i.v.m deze convergentie. Aangezien mijn kennis omtrent de draadloze en mobiele netwerken niet uitgebreid was, kwam er een intensieve studie en onderzoek van beide technologieën tijdens de eerste maanden. De uiteindelijke bedoeling van dit eindwerk is om een deel van het kenniscentrum te vervolledigen op gebied van mobiele netwerken en de convergentie tussen WLAN en UMTS.
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1 Theoretische studie 1.1 Inleiding Elk eindwerk kent een theoretische studie fase, die voor mijn eindwerk in het eerste semester plaats vond. Al snel greep ik naar informatie omtrent de convergentie van WLAN en UMTS. Het was hier duidelijk dat dit te snel was, maar toch nodig om de bron van deze convergentie te achterhalen. Het onderzoek van het UMTS gedeelte leerde mij meer informatie te zoeken over het bestaande GSM/GPRS netwerk. Aangezien de ‘Core Network’ gebruikt wordt voor UMTS, vond ik het geschikt om hierover een studie te bouwen. Het EDGE gedeelte kwam pas later naar aanleiding van het bedrijfsbezoek bij Mobistar. De bespreking en de studie omtrent de convergentie van WLAN en UMTS eist een uitgebreide kennis van WLAN. Hiervoor heb ik mij voornamelijk gebaseerd op het eindwerk van Sven(IEEE 802.11 architecture).
1.2 Theoretische inhoud 1.2.1 GSM De bedoeling was om hier een uitgebreide studie rond te voeren(aangezien deze samenhangt met het GPRS netwerk). Tijdens het opzoekwerk i.v.m het GSM/GPRS netwerk, werd het al snel duidelijk dat dit niet noodzakelijk was om een uitgebreide kennis te verwerven i.v.m het GSM netwerk, aangezien dit niet sterk samenhangt met het UMTS netwerk. Een andere reden om hierover geen uitgebreide studie uit te voeren was het principe dat GSM het ‘Circuit Switched’ gedeelte voorstelt van het mobiel netwerk. Het deel over GSM behandelt de hardware componenten die door het UMTS en het GPRS netwerk gebruikt worden. Deze wordt beschreven en verwerkt in het GPRS deel.
1.2.2 GPRS Bedoeling van dit deel is om een algemene kennis te verwerven. Aangezien GPRS het ‘Packet Switched’ gedeelte voorstelt, zijn er veel gelijkenissen met UMTS. Dit deel behandelt de verschillende Hardware componenten. Deze werd opgedeeld in vier grote delen: • GPRS introductie: Wat is het, Principe van ‘slots’, hardware componenten, ‘planes’, ‘interfaces’,… • Fysieke laag • RLC/MAC laag
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• RRC laag Raadpleeg het ‘GPRS_EDGE project’ op blz. 11 voor meer informatie omtrent het GPRS onderzoek.
1.2.3 EDGE Aangezien EDGE een softwarematige aanpassing is van het bestaande GSM/GPRS netwerk, werd er voor dit deel aandacht besteed aan de modulatie technieken die toegepast worden. Twee belangrijke vragen werden hier gesteld: • Waardoor is EDGE 4 maal sneller dan GPRS? • Welke software implementatie zijn er nodig Raadpleeg het ‘GPRS_EDGE project’ op blz. 11 voor meer informatie omtrent het EDGE onderzoek.
1.2.4 UMTS Het UMTS gedeelte kreeg naast de convergentie, de grootste aandacht. Hierbij werd er voornamelijk aandacht besteed aan het nieuwe RAN, nl UTRAN en de samenhang met het reeds bestaande GSM/GPRS netwerk. Een ongeveer analoge studie zoals die voor GPRS, kwam hier van toepassing en werd opgedeeld in volgende delen: • Toegangsmethoden • Hardware componenten • Fysieke laag • MAC laag • RLC laag • RRC laag
1.2.5 Convergentie WLAN en UMTS Het is vereist om een algemene kennis te verwerven over WLAN en UMTS vooraleer men het deel convergentie tussen WLAN en UMTS bestudeert. Dit gedeelte behandelt ook de vierde generatie mobiele technologie in het kort. Deze reden hiertoe is dat dit de toekomst is en een eindwerk onderwerp. Verdere studie over de vierde generatie mobiele technologie is noodzakelijk…
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2 Praktijk gedeelte 2.1 Bedrijfsbezoeken 2.1.1 Introductie Bedrijfsbezoeken zijn van cruciaal belang voor het uitvoeren van een degelijk eindwerk. Naast de informatie die ik gekregen heb tijdens deze bezoeken, ben ik tot een belangrijke vaststelling gekomen. Er zijn namelijk veel artikels, papers geschreven over de volgende vraag: “Zijn WLAN en UMTS complementair of zijn ze concurrenten?” Het antwoord hierop zou een eindeloze discussie kunnen vormen tussen UMTS en WLAN goeroes. Mijn mening hierover na het bestuderen van deze materie is dat ze voor 100% complementair zijn, maar ook concurrenten. De concurrentie aspect kwam tijdens de bedrijfsbezoeken duidelijk naar voor. Het was opmerkelijk dat de pioniers in de convergentie van WLAN en UMTS hun product als utopisch beschouwen en de andere negeren, maar toch geven ze toe dat ze deze niet kunnen weg denken. Om dit beeld te verkrijgen heb ik bewust tijdens elk bedrijfsbezoek dezelfde vragen vooropgesteld, nl: 1. WLAN hotspots wordt soms wel eens gezien als een bedreiging voor UMTS en anderzijds als een complement. Wat is uw visie? 2. Interconnectie wel nodig? => financiële kant , toekomst, UMTS nog nodig? 3. Er zijn verschillende interconnecties mogelijk tussen WLAN en GPRS/UMTS netwerk elk met hun voor en nadelen. Uit welke criteria wordt zo’n interconnectie gekozen? 4. The beveiliging van WLAN is niet optimaal, zou een interconnectie(waarbij de beveiliging door UMTS opgenomen wordt) een oplossing zijn? In dit geval zou WLAN de slave netwerk zijn en UMTS de master netwerk. 5. Hoe zit het met de communicatie/contracten tussen enerzijds WiFi hotspots en mobiele netwerken(mobistar, proximus en base)?
2.1.2 Sinfilo
Bedrijf: Sinfilo (Siemens) Contactpersoon: Luc Buntinx 8
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Na het gesprek met Luc Buntix kon ik de volgende besluiten trekken: De convergentie van WLAN en UMTS zal zeker aangeboden worden aan de gebruikers. Er zijn niet alleen aanpassingen nodig aan de hardware kant (PHY en MAC) maar ook aan de applicatie laag. Men zou extra intelligentie moeten toevoegen aan deze laag. Wanneer men een zwaar bestand moet downloaden en we een connectie leggen via het UMTS of GPRS netwerk, zou extra software ervoor moeten zorgen dat hij deze later zal downloaden wanneer hij een WLAN Hotspots tegenkomt om zo de kosten te drukken. Onder mobiel netwerken verstaat men twee zaken: “Always on” en “on the move”. Momenteel zijn er niet zo veel antennes beschikbaar voor UMTS. UMTS biedt 2 Mbps (theoretisch). Dit is waar wanneer men vlak onder een UMTS-antenne zit en men niet beweegt. In-the-field tests hebben aangetoond dat de snelheid ver onder deze 2Mbps komt te liggen, snelheden van 500kbps (of minder) zijn realistischer. GSM operatoren hebben het moeilijk gehad om de GSM antennes te installeren (problemen met gemeente en dergelijke). GSM-antennes hebben een groter bereik dan UMTS antennes. Men moet zich even voorstellen hoeveel antennes men nodig heeft om dezelfde bedekking te hebben als GSM. WEP beveiligt het systeem (WLAN) niet genoeg. Een interconnectie tussen WLAN en UMTS waarbij WLAN het slave- en UMTS het master-netwerk is, is geen oplossing op gebied van beveiliging. De connectie tussen de device en het UMTS-netwerk is niet beveiligd. Oplossing via VPN dat vanaf de device de pakketten encrypteert. Een praktisch voorbeeld aangehaald door Luc Buntinx: (dit is een toekomstvoorbeeld, bestaat nog niet) Koeriers bij DHL verwerken veel gegevens wanneer ze “on-the-road” zijn. Dit gebeurde via GPRS. Het verzenden en ontvangen van berichten/pakketten gebeurde vrij traag en duur (negatieve kanten van GPRS). DHL heeft een WLAN-service geïnstalleerd in hun auto’s. Nu gebeurt het zenden en ontvangen niet direct, maar in de plaats hiervan wordt gewacht tot dat men een hotspot tegenkomt. Wanneer bvb de chauffeur met zijn auto een hotspot tegenkomt op de autosnelweg via een pompstation worden deze pakketen razendsnel verzonden en ontvangen. Dit heeft als gevolg dat deze service veel goedkoper is. Onze contactpersoon werkt voor Sinfilo. Sinfilo is een WISP. Samen met Megabeam zijn ze de twee enige WISPs in België. Wanneer ik mijn vragen stelde over de convergentie tussen WLAN en UMTS haalde hij telkens de positieve kanten van WLAN en de negatieve kanten van UMTS uit, waarbij hij achteraf duidelijk zei dat UMTS complementair is bij WLAN, samen zijn ze sterk. Ook had hij een bedenking over UMTS: deze is momenteel niet presterend en stabiel genoeg voor de nodige mobiliteit en de beloofde bandbreedte. Er zal waarschijnlijk een nieuwe technologie op de markt komen dat UMTS mogelijk zal vervangen. Alhoewel deze afspraak zeer interessant was, kwam er weinig aan bod i.v.m UMTS.
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2.1.3 Option
Bedrijf: Option 28/10 Contactpersoon: Jan Vercruysse Option beschikt over een testnetwerk(UMTS, GPRS, WLAN). Ze beschikken nl. over vijf ‘Base Stations’ die verbonden zijn met de verschillende netwerken. De WLAN/GPRS-kaartjes(Globetrotter) komen volgende maand (november 2003) in productie. Deze kaartjes bevat een SIM kaart nl. USIM voor UMTS. Op zo een USIM kaart staan alle services erop en is deze moeilijk te kraken (veilige manier) (EAP-SIM in 802.1x). Via een Master/Slave confguratie(WLAN: slave, UMTS: master)kan men het UMTS-netwerk gebruiken om AAA te verzorgen. De PCMCIA-kaartjes (WLAN/GPRS/UMTS) van Option worden (onder Windows) beschouwd als 3 verschillende devices. De software zal beslissen welk netwerk/device er gebruikt wordt. Volgend jaar (juli 2004) worden de nieuwe WLAN/GPRS/UMTS PCMCIA-kaartjes in productie genomen.
2.1.4 Mobistar
Bedrijf: Mobistar Contactpersoon: Peeters Willem en Unguranu Razvan Op 20 Oktober werd er contact opgenomen met Mobistar. Na tal van mails en telefonisch contacten ging het bedrijfsbezoek door op 11 februari. Aangezien ik hiervoor al veel had opgezocht en mijn kennis al ruim was, heb ik mijn gedachten en structuur voorgesteld. Het bedrijfbezoek was meer een gesprek dan een informatie verrijking. De vragen die ik stelde mochten zij ofwel niet beantwoorden ofwel wisten ze het zelf niet.
2.1.5 UPC
Bedrijf: Universiteit UPC te Barcelona 10
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Contactpersoon: Garcia Oscar Tijdens het jaarlijkse studie uitstap naar Barcelona bezochten we een aantal universiteiten. De universiteit UPC was in het bijzonder zeer interessant aangezien zij een groep onderzoekers hebben die de convergentie van WLAN en GPRS alsook UMTS bestuderen. Oscar Garcia besprak een aantal belangrijke zaken i.v.m de convergentie en de problemen. Deze convergentie test hij uit met een GPRS mobiele telefoon aangesloten op de seriële poort en een WLAN PCMCIA kaart. Hij had namelijk problemen met het simultaan ontvangen van het GPRS signaal en het WLAN signaal. Hij vertrok van het principe dat er sowieso GPRS ontvangst is en wanneer men een WLAN signaal ontvangt, zal men via WLAN een connectie leggen. Hiervoor verwees ik naar Option voor hun multimode PCMCIA kaarten. Het onverwacht bezoek zorgde ervoor dat wij beiden niet voorbereid waren om de nodige informatie uit te wisselen. Daardoor kwam men verder in contact via mail.
2.1.6 Deelbesluit Zoals vermeld in de inleiding worden beide technologieën als concurrenten beschouwd. Hierdoor was het niet eenvoudig om de juiste contacten te vinden.
2.2 GPRS_EDGE project 2.2.1 Inleiding Naar aanleiding van het Bachelor/Master programma dat van start zal gaan in 2005, werd er gevraagd om een project uit te voeren waarbij de nadruk lag op het Coachen, delegeren van een project. Het is voornamelijk de bedoeling om in het Master programma dit in te voeren om zo in aanraking te komen met het management gedeelte. Eindwerk studenten zullen een goed afgebakend onderwerp moeten opleggen aan studenten van het 3de jaar(laatste jaar Bachelor). Dit heeft als voordeel dat de studenten in het 3de jaar al in aanraking komen met een eindwerk waarbij zij het gevoel kunnen krijgen van de ernst van een eindwerk. Tevens heeft dit als groot voordeel dat de interne kennis vergroot wordt en dat eindwerk studenten zich kunnen concentreren op andere zaken. Structuur van dit project wordt weergegeven in figuur2.1:
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Figuur 2.1: Structuur
2.2.2 Maatregelen vooraf De taak van de eindwerkstudenten mag zeker niet onderschat worden. Ernstige afspraken moeten op voorhand gemaakt worden om ervoor te zorgen dat iedereen in goede banen werkt. Dit project werd in Maart ingevoerd waarbij de einddatum op 27 april stond. In de toekomst(2005), moet men ervan bewust zijn dat dit onmogelijk vroeger kan ingevoerd worden aangezien de eindwerkstudenten nog zelf kennis moeten aanschaffen en een goed onderwerp bedenken. Dit heeft als gevolg dat de Bachelor studenten op een korte tijd ongeveer dezelfde kennis moeten hebben van het eindwerk als de eindwerkstudenten. Het meegeven van links en boeken is dwaas, waarbij een subtiele aanpak nodig is. Het project werd voorgesteld tijdens de les Telematica(ir. L. Pieters) waarbij een algemene beschrijving werd gegeven over het eindwerk en het uit te voeren onderwerp. Wanneer het groepje samengesteld was(Baart Annica, Giebens Kris, Peeters Michaël, Schmidt Gwyn), werd deze presentatie tijdens de eerste vergadering overlopen. Rond de maand Oktober heb ik een kort(ongeveer 17blz) verslag geschreven i.v.m met de verschillende Mobiele netwerken en de convergentie van WLAN en UMTS. Deze is verstaanbaar voor studenten die nog geen kennis hebben over dit onderwerp(zie bijlage). Nadat deze werd bestudeerd door de studenten kon men aan de slag met het onderverdelen van het onderwerp. Het leveren van de geschreven documenten gebeurde aan de hand van een ‘Briefcase’(http://briefcase.yahoo.com/gprs_edge2004). Deze werden door mezelf verbeterd en achteraf via mail of tijdens een vergadering besproken.
2.2.3 Onderwerp(en) Als onderwerp heb ik gekozen om twee technologieën te bespreken, nl; GPRS en EDGE. De bedoeling van mijn eindwerk is om de nodige technologieën te bespreken die nodig zijn voor de bespreking van de convergentie. Aangezien UMTS een trage invoering zal kennen(in tegenstelling tot GPRS), zal het GPRS netwerk nog in gebruik genomen worden. Door middel van ‘multimode’ toestellen zal er indien geen UMTS dekking is, het GPRS netwerk in gebruik 12
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genomen worden. Om ervoor te zorgen dat de mobiele operatoren toch een degelijk product/technologie aanbieden aan hun klanten, zullen zij de EDGE technologie implementeren in het GPRS netwerk waar er nog geen UMTS dekking is. Deze software matige aanpassing zal ervoor zogen dat men tot snelheden komt die 4 maal hoger zijn dan wat GPRS vandaag aanbied. De GPRS technologie werd in zijn totaliteit besproken door drie studenten(Baart Annica, Giebens Kris, Schmidt Gwyn) met de nadruk op: • Transmission planes • Signalling plane • Protocols • Access methodes • Coding scheme • PHY laag • RLC laag • MAC laag EDGE is een software upgrade die door Peeters Michaël uitgevoerd werd. De nadruk lag hier vooral op twee vragen: • Waardoor is EDGE 4 maal sneller dan GPRS? • Wat zijn de wijzigingen die moeten gebracht worden in het GSM/GPRS netwerk?
2.2.4 Vergaderingen Deze verslagen kunnen terug gevonden worden in de bijlage. Ze bevatten voornamelijk kernwoorden. Deze werden gebruikt om tijdens de vergaderingen bepaalde zaken te bespreken. Na elke vergadering is er een korte beschrijving van het verloop.
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2.2.5 Deelbesluit Het EDGE gedeelte werd goed afgehandeld omdat dit een duidelijk afgebakend onderwerp was. Het GPRS, dat ook goed afgewerkt werd, was te algemeen en kende geen einde. Men moet hier een onderscheid maken tussen een afgebakend onderwerp dat een duidelijk begin en einde heeft en een eindwerk dat geen einde kent. Zoals in de inleiding beschreven werd, is het voornamelijk de bedoeling om de studenten van het 3de jaar in aanraking te laten komen met een eindwerk. Het zou hierbij nuttig zijn om bepaalde regels voor op te stellen zoals bvb. Tekst sjabloon, ‘deadlines’,… Als slot zou ik Baart Annica, Giebens Kris, Peeters Michaël en Schmidt Gwyn willen bedanken voor hun uitstekend werk dat ze hebben geleverd.
Figuur 2.2: Van links naar rechts : Baart Annica, Schmidt Gwyn, Giebens Kris. Zittend: Peeters Michaël
2.3 Erasmus project 2.3.1 Inleiding Dit jaar waren vier buitenlandse studenten in de opleiding elektronica aanwezig. Er werd mij gevraagd om drie van hen te coachen, nl Ana, Cesc en Mikko. De taak die mij werd opgelegd is ongeveer analoog aan het GPRS_EDGE project. Het onderwerp, ’Mesh networking’, werd door ir. L. Pieters, ing. T. Dams en ing S. Deryter vooropgelegd. Tijdens de eerste vergadering(samen met ir. L. Pieters, T. Dams en S. Deryter) werd het onderwerp uitgebreid en opgedeeld in volgende delen: • •
Onderzoek naar Mesh networking Onderzoek naar Simulatie software(in het bijzonder OPNET) 14
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•
Grid computers
Tijdens deze vergadering werd ook de opdeling gemaakt: Ana en Cesc kregen de opdracht om OPNET te analyseren en Mikko de opdracht om de Mesh networking te bespreken. Grid computers kreeg weinig aandacht(zie deelbesluit).
2.3.2 Maatregelen vooraf Voor dit project was een andere aanpak nodig dan voor het GPRS_EDGE project. De taak en het onderwerp werd mij meegedeeld vier dagen voor de start van het project. Aangezien ik hen moest coachen en ondersteunen, heb ik een klein onderzoek gedaan omtrent Mesh networking en simulatie programma’s. De nodige links en documentatie werd hen meegedeeld tijdens de eerste vergadering. Tevens werd er hier gebruik gemaakt van een yahoo “briefcase” om de documenten te “uploaden”. (http://Briefcase.yahoo.com/mesh_eras_2004, Paswoord : project2004)
2.3.3 Onderwerp(en)
2.3.3.1 Theorie Een mesh netwerk is een LAN waarbij elke node(desktop PCs en/of Laptops) met de andere nodes verbonden zijn. Figuur2.3 toont deze topologie aan waarbij vijf nodes met elkaar verbonden zijn.
Figuur 2.3: Mesh topologie
De connecties tussen de nodes kunnen bedraad of draadloos zijn. Dit laatste zorgt voor veel voordelen om een Mesh WLAN infrastructuur te creëren. De WLAN Access Points bieden een bedekking van ongeveer 50m. Deze bedekking kan vergroot worden door gebruik te maken van de Mesh topologie en de nodige protocols. Elke node communiceert direct met elkaar. Indien een node zich in een WLAN “cell” bevindt kan hij communiceren met een node die zich niet in een WLAN cell bevindt en op een bepaalde afstand van elkaar verwijderd zijn. De node die niet in de WLAN cell bevindt, kan op zijn beurt met een andere node communiceren die nog verder verwijderd is van de WLAN cell. Hierdoor is het mogelijk om er een ‘mesh’ van te maken en de bedekking van een WLAN Access Point te vergroten.
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OPNET is een simulatie programma. Met deze simulatie programma is het mogelijk om een uitgebreide analyse en beheer van een netwerk te vormen.
2.3.3.2 Uitvoering De eerste studiefase van Mesh was om het volledig theoretisch te behandelen. Aangezien Mesh een topologie is, was het hier voornamelijk de bedoeling om het principe te achterhalen van Wireless Mesh en de nieuwe wireless protocollen die hiervoor ontworpen zijn te bespreken. Nadat deze theoretisch behandeld werd, was het de bedoeling om de Mesh topologie te implementeren in een WLAN infrastructuur. Een node of access point dat met beide technologieen kan communiceren als Gateway tussen enerzijds Mesh ad-hoc topologie en anderzijds WLAN. Na de theoretische bespreking van OPNET, was het de bedoeling om een WLAN netwerk te simuleren alsook wireless mesh.
2.3.4 Vergaderingen Deze verslagen kunnen terug gevonden worden in de bijlage. Ze bevatten voornamelijk kernwoorden. Deze werden gebruikt om tijdens de vergaderingen bepaalde zaken te bespreken. Na elke vergadering is er een korte beschrijving van het verloop. De verslagen zijn in het engels om de communicatie met de Erasmus studenten te vergemakkelijken.
2.3.5 Deelbesluit Het coachen van de Erasmus studenten verliep niet even vlot als bij het GPRS_EDGE project. Dit heeft te maken met allerlei factoren. In eerste instantie had ik evenveel kennis als hen over het onderwerp, aangezien mijn onderzoek vier dagen heeft geduurd. De Erasmus studenten konden fulltime bezig zijn met dit project. De vergaderingen en besprekingen konden enkel op woensdag plaats vinden. Tijdens dit project moest ik zelf nog aan mijn eindwerk werken. In de toekomst zou het beter zijn om een onderdeel van een eindwerk als project te geven voor de Erasmus studenten. Dit zou het coachen vergemakkelijken en een goed afgebakend resultaat opleveren. Er werd gevraagd om informatie op te zoeken ivm Grid computers en link naar Wireless Mesh. Dit werd samen met ing. F. Van Der Schueren besproken waarna er geen verder onderzoek mogelijk was.
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Figuur 2.4: Van links naar rechts: Ana Pedraz, Cesc en Mikko
2.4 Mobile IP 2.4.1 Inleiding Een poging tot het implementeren van Mobile IP in het labo D32, werd samen met Ing. Vercauteren besproken. De reden tot het implementeren van deze technologie is om bij WLAN netwerken van het ene ESS naar het andere te gaan zoals afgebeeld op figuur2.5.
Figuur 2.5
Tevens wordt deze technologie gebruikt om een interconnectie te verzorgen tussen WLAN en UMTS.
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De bedoeling was hier om een PC(desktop of laptop)van het ene subnet naar het andere te verplaatsen met de nodige router configuratie Zoals afgebeeld op figuur2.6.
Figuur 2.6: Labo netwerk D32
Indien men het volledig mobiel wil doen, zou men in principe twee Access Point, één router en een laptop met WLAN kaart nodig moeten hebben. Dit heeft als gevolg dat het opzoeken naar fouten moeilijk wordt. Daarvoor werd de eerste fase tot een minimum herleidt, nl; Laptop of desktop PC van het ene subnetmask naar het andere te verplaatsen(niet draadloos).
2.4.2 Deelbesluit Dit project kon niet uitgevoerd worden aangezien de Nortel passport 1648 Router aanwezig in het labo lokaal D32 niet beschikt over de Mobile IP optie.
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Besluit Toen ik twee jaar geleden op de Hogeschool Antwerpen ben aangekomen, had ik weinig kennis van bedraade, draadloze en mobiele netwerken. Aangezien mijn vorige opleiding gebaseerd was op het software gedeelte van de ICT wereld, kon ik mijn kennis rond hardware/netwerken vergroten door deze opleiding te volgen. De kennis die ik dit jaar gevormd heb, heb ik te danken aan bepaalde gedoceerde vakken en dit eindwerk. Het eindwerk is naar mijn mening tot een goed einde gekomen. Na het bestuderen van diverse technologieën(WLAN, GPRS, UMTS, EDGE, GSM,…) heb ik ook het psychologisch aspect achtergehaald, wat tot interessante discussies kan leiden. Zoals hierboven vermeld, is dit eindwerk tot een duidelijk einde gekomen maar vereist nog verder onderzoek. Vermits UMTS op 13 mei 2004 gelanceerd wordt, zal men de zaken meer in details kunnen bestuderen en de speculaties van de voorbije jaren analyseren. Het aantal toenemende hotspots in België(en andere werelden) zal er tevens voor zorgen dat de convergentie tussen WLAN en UMTS een groot succes zal vormen. Ik heb kunnen vaststellen bij het afwerken van dit eindwerk dat de vele vragen die ik mij dit jaar gesteld heb, eindelijk antwoorden gevonden hebben. Eén van de grote moeilijkheden was het stellen van de grenzen van mijn onderwerp. Dit eindwerk sluit ik met veel respect en ik zal in de komende jaren deze convergentie en de introductie van UMTS in België op de voet blijven volgen.
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Bronnen Boeken/Papers • • • •
SEURRE Emmanuel, SAVELLI Patrick, PIETRI Pierre-Jean, GPRS for mobile internet, ISBN: 1-58053-600-X PRASAD Ramjee, MUNOZ Luis, WLAN and WPANs toward 4G Wireless, ISBN : 158053-090-7 CLAPTON Alan, Future Mobile Networks: 3G and Beyond, ISBN 0-85296-983-X DERUYTER Sven, IEEE 802.11b architecture, Thesis van Industrieel Ingenieur Elektronica optie ICT, Antwerpen: Hogeschool Antwerpen, 2003
Artikels • • • • • • •
Van GSM naar UMTS, EOS jaargang18(2001) nr2 p.90-96 Bos Lieve, Leroy Suresh, WLAN en UMTS hand in hand?, Het ingenieursblad jaargang 71(2002) nr 11/12 p.37-42 Jos Limburg, Koppeling WiFi hotspots aan mobiele netwerken, 2002 Luc Blyaert, Wireless LAN fnuikt 3G, 2002 Jan-Frans Lemmens, Hotspots, het cybercafé heruitgevonden , network & telecom(2003), nr 41, p.20-22 Nieuwsbrieven van Datanews, www.datanews.be Nieuwsbrieven van Tweakers, www.tweakers.be
Internet • http://www.sciencedirect.com Databanken met betrouwbare informatie • http://www.ebsco.com Databanken met betrouwbare informatie • http://www.3gpp.org Specificaties van UMTS • http://www.umts-forum.org Website met algemene beschrijving van UMTS en andere technologieën • http://www.umtsworld.com Website met algemene beschrijving van UMTS en andere technologieën Bedrijfsbezoeken • • • •
Jan Vercruysse, Option te Leuven Willem Peeters, Razvan Unguranu , Emmanuel Genbrugge, Mobistar te Brussel-Evere Jan Buntix, Sinfilo te Hasselt Oscar Garcia, UPC te Barcelona
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Bijlagen Nieuwsberichten Aan de hand van artikels werd er een globaal overzicht verkregen omtrent de invoering en de psychologie achter UMTS. De artikels zijn chronologisch geordend en de moeilijke introductie en investering van UMTS in België is duidelijk waar te nemen. Tevens zijn de artikels vrij kritisch over de introductie van UMTS en zijn rivaal WLAN. De artikels komen voornamelijk van Datanews(http://www.vnunet.be/datanews) en Tweakers(http://www.tweakers.net). Aan de uitgeef datums is duidelijk te zien dat de regeling van UMTS al een tijdje voorbij is en het nu voornamelijk de taak is van de Mobile operatoren om deze technologie in te voeren. Artikels • Proximus lanceert eerste UMTS-netwerk in België(08/04/2004) Proximus wordt de eertse Belgische mobile operator die zijn UMTS-netwerk openstelt voor gebruik. Vanaf 13 mei gaat het bedrijf Vodafoon Mobile Connect 3G/GPRS datacard aanbieden, in combinatie met toegang via UMTS. • WiFi voor grote afstanden op komst(02/03/2004) Het onderscheid tussen draadloze netwerken, zoals wifi en 3G, gaat verdwijnen. Dat voorspelde Intel topman Paul Otellini op het 3GSM Congres in Cannes. Met name Wimax, wifi voor grote afstanden, zal voor die omwenteling moeten zorgen. Het bereik bedraagt zo'n 50 kilometer versus 100 meter voor huidige wifi-standaarden met 75 megabits per seconde als maximale bandbreedte. •
Proximus haalt in 2003 grotere omzetstijging maar kleinere winstgroei(30/01/2004) Bij mobiele Belgacom-dochter Proximus steeg de omzet in 2003 sterker dan het jaar voordien, maar bleef de winstgroei kleiner dan in 2002. Ook het marktaandeel van Proximus ging achteruit. De kleinere winstgroei in 2003 heeft mogelijk te maken met investeringen in nieuwe technologieen zoals UMTS of mobiele datadiensten • UMTS – tussen droom en realiteit(10/10/2003) Siemens Mobile zet zwaar in op telefonie van de derde generatie. Met de lancering van hun tweede UMTS-telefoon en met de voorstelling van een eerste commercieel project wil het aantonen dat UMTS realiteit wordt. • Orange licht tipje van 3G-sluier op(18-09-2003) De mobiele telefoniedochter van France Telecom heeft Alcatel, Nortel en Nokia uitverkoren tot leveranciers van zijn volgend jaar te bouwen Europese umts-netwerk. • Mobistar houdt WLAN hotspots af(05-03-2003) GSM-operator Mobistar is niet van plan om draadloze WLAN hotspots in zijn netwerk te installeren. Ook op een doorbraak van GPRS mobiele datatoepassingen is het mogelijk nog wachten tot 2004. 21
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• GSM-operatoren vragen opnieuw 3G-uitstel(07-10-2002) De drie Belgische GSM-operatoren vragen opnieuw uitstel voor de lancering van de nieuwe mobiele 3G-breedbandnetwerken, ook wel aangeduid als UMTS. Vorige week hebben ze de aanvraag in een brief aan telecomminister Rik Daems bezorgd. • Brussel wil delen 3G-netwerken toestaan(16-09-2002) De Europese Commissie heeft T-Mobile en mmO2 voorlopig het groene licht gegeven voor het samen gebruiken van onderdelen van elkaars 3G-netwerkinfrastructuur. • Eén jaar langer wachten op UMTS(11-02-2002) Minister van Telecommunicatie Daems heeft er mee ingestemd om de lancering van UMTS met één jaar uit te stellen. De eerder vooropgestelde datum was september 2002. • Drie UMTS-licenties eindelijk de deur uit(02-03-2001) Drie UMTS-licenties zijn geveild voor een totaal bedrag van 450,2 miljoen euro of een goeie 18 miljard BEF. Belgacom, KPN en Mobistar kunnen nu aan de verdere uitbouw en invulling van 3G-netwerken beginnen. • UMTS raakt maar niet geveild(27-02-2001) De veiling voor de Belgische UMTS-licenties wordt opnieuw verdaagd. De deelnemende operatoren dienden hun vragenlijsten pas op de valreep in. Het ministerie verplaatst het ganse gebeuren naar komende vrijdag. • Drie kandidaten voor vier UMTS-licenties(09-02-2001) Er zijn maar drie kandidaten, Proximus, Mobistar en KPN Orange, voor de vier Belgische UMTS-licenties. De opbrengst van de veiling zal daardoor slechts 18 miljard frank bedragen. Een tegenvaller voor de overheid en minister van Rik Daems. • Daems prikkelt UMTS-spelers(13-12-2000) Op 12/12/02 vond een tweede ontmoeting plaats tussen Minister Daems, het BIPT en de Belgische telecomoperatoren. Op de agenda stonden de wetgeving aangaande het telecombeleid, de rol van het BIPT en de planning voor de verdere deregulerisatie.
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Vergaderingen van het GPRS_EDGE project Groep : Baart Annica Giebens Kris Peeters Michaël Schmid Gwyn Vergadering 1 (04/03) Te bespreken tijdens vergadering: • Opfrissing presentatie • MAIL MOBISTAR!! • Doel uitleggen van dit project(coördinatie, vergaderingen,…) • Webruimte voorzien om de tijdelijke documenten te “Uploaden” Î http://briefcase.yahoo.com/gprs_edge2004 Î paswoord: “project2004” • Document WLAN_UMTS.doc bespreken(document om een overzicht te krijgen) • “Science direct”. Indeling document: • GPRS netwerk protocols Î “GPRS for mobile internet” ISBN 1-58053-600-X Î zelf geschreven documenten(zie briefcase yahoo) Î links Î QoS services Î Netwerk protocol(layers) (interfaces) Î lijst boeken GPRS: http://www.palowireless.com/bookshop/booksgprs.asp • EDGE modulatie technieken Î (zie uitleg invoering UMTS) Î Waardoor is EDGE 4 maal sneller dan GPRS Î Wat zijn de wijzigingen die moeten gebracht worden in het GSM/GPRS netwerk Î ISBN: 0470866942 •
Cursus telematica!
Verloop van de vergadering: • De punten hierboven werden allemaal besproken. • Doel is nu om de documenten te lezen en informatie op te zoeken. • Michael Î EDGE • Annica Î GPRS Gwyn Î GPRS Kris Î GPRS • deze indeling staat nog niet 100% vast. Volgende vergadering geplant op vrijdag 12/03 om 15u in de refter Vergadering 2 (11/03)
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Opmerking: De documentatie op de “briefcase” zijn bruikbaar. Te bespreken tijdens vergadering: • teksten schrijven in het engels • tegen 15/03: indeling werkjes binnenbrengen. + korte inhoudsopgave. • Bespreken EDGE documentatie “Implementation effects on GSM's EDGE Modulation”: goei documentje!! Bij modulatie technieken niet te veel wiskundige formules te gebruiken, meer met woorden uitleggen.(grafieken en figuren zijn altijd nuttig mits uitleg erbij) Paper van Nokia: Goede inleidende informatie "wireless communication solutions": ok • Bespreken EDGE indeling Momenteel modulatie technieken. • Bespreken GPRS documentatie Documenten op briefcase zijn te algemeen Zie boek GPRS • Bespreken GPRS indeling Verschillende lagen Interfaces Netwerk componenten • Boek GPRS • Bespreken kopies van het boek “Wireless IP”: geeft een kort overzicht van GPRS ivm protocols. • “glossary”: lijst bijhouden met afkortingen en definities, nuttig voor in de bijlage Verloop van de vergadering: • De punten hierboven werden allemaal besproken. • Doel: schrijven van de documentatie • De onderwerpen werden al verdeeld • Document van Ericsson Î Michaël • Volgende vergadering zo snel mogelijk om zeker te zijn dat de onderwerpen in goede banen geleid worden. • Vergadering nog plannen: mail sturen. UMTS documenten uploaden. Vergadering 3 (19/03) Te bespreken tijdens de vergadering: • • • •
Layout, presentatie, timing De introductie moet meer onderverdeelt zijn: QoS en class A en B De interface worden samen met de planes uitgelegd
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• • • •
• • •
document van Kris aan Michaël!! Bij UMTS spreekt men van Control planes en User planes maar bij GPRS spreekt men van signalling planes en transmission planes BTS en BSC worden gebruikt in het GPRS netwerk. het is hier niet de bedoeling om dit terug uit te leggen maar hiervoor verwijs ik naar het document WLAN_UMTS_verslag1.doc op p.12 Document Annica: Boek GPRS Of Specs 3GPP Zie opmerkingen in tekst Document Michael Zie opmerkingen in tekst + uitbreiden Document kris Nuttig voor Michaël! Zie opmerkingen in tekst Document Gwyn Geen protocols, enkel physical layer(+/- Michaël) Zie opmerkingen in tekst
Verloop van de vergadering: De vorige punten werden besproken. Er zal nu voornamelijk met de ‘briefcase’ gewerkt worden. Iedereen zal telkens zijn voorontwerp op de briefcase uploaden, waarbij deze achteraf verbeterd zal worden. Er is een vergadering geplant na de paasvakantie om de presentatie voor te bereiden. Er wordt verondersteld dat de werkjes(documenten) afgewerkt zullen zijn. Enkel nog layout en andere zullen nog aangepast worden.
Vergadering 4 (20/04) Te bespreken tijdens de vergadering: •
Presentatie Layout Indeling Ten laatste voor vrijdag 23/04 uploaden op de ‘Briefcase’ Structuur presentatie:
• •
Indeling(carl) Inleiding GPRS(carl) Î Evolutie 1G -> 3G Î GSM/GPRS netwerk Î Deel van Annica, Gwyn en Kris inleiden • Deel Annica • Deel Gwyn • Deel Kris 25
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•
Inleiding EDGE(carl) Î UMTS netwerk Î Coverage Î Invoering UMTS • Deel Michaël • Besluit(carl) Verloop van de vergadering: De vorige punten werden besproken. De verschillende documenten moeten nu samengevoegd worden(layout, …) De presentaties worden ten laatste op vrijdag doorgestuurd zodat het geheel nog eens besproken kan worden op maandag 26/04. Er werd nog gevraagd om wat meer uitleg te verkrijgen ivm de ‘Coding schemes’ van GPRS
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Vergaderingen van het Erasmus project Meeting 1 on Monday 1/03 • • • •
Yahoo Briefcase to put documents Briefcase.yahoo.com/mesh_eras_2004 Password : project2004 Routing proocols !!
What to do • • • •
theoretical paper : overview of different simulation tools OPNET Grid computer(is there a link with mesh networks?) Presentation about mesh network(simulation, topology, protocols, …) 3 of April
Ana en Cesc will work on OPNET and the overview of different simulation program. Mikko will work on the routing protocols. Meeting 2 on Wednesday 17/03 What to discus: • manuel OPNET(focussing on WLAN) • list + description of simulation program Î finished? • WLAN and Mesh in OPNET = support of WMR? • paper about wireless routing protocols?: Î Table-driven routing protocols Î DSDV Î CGSR Î WRP Î Source-initiated on-demand routing Î AODV Î DSR Î TORA Î ABR Î SSR Î DRP Î SRP • Practical part: IDEA: using(convergence) the infrastructured WLAN network with the mesh topology. 1. simulation in OPNET If possible with the academical version(ITGURU) 2. One AP and two nodes(laptop)
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•
Grid computers: Î Making a short theoretical paper about grid computer Idea: Connecting the different (grid) computers with each other using mesh protocols Problem: Connection between the different computers has to be fast. We will discus this with F. Van Der Schueren later…
What we discussed: • • • • •
Mesh connex Linux?? Mail to Zaballos for the full version of OPNET(Tim will do that) Still working on the protocols and simulation OPNET Focussing on other simulation programs(searching for a Free program??)
Preparation & discussion about the presentation of MESH The pupose of this presentation is mainly to explain the Mesh focussing on the different mesh protocols. Mikko will do the main part of this presentation because he worked on this item. Anna en Cesc will cover there item(simulator OPNET) very short because they will do an extended presentation on the 6 of Mai. So, for this presentation they only have to give a global overview of OPNET, just to be informed what we can do with OPNET. First draft of the presentation content: • •
•
• • • • •
Content of the presentation Situation of mesh Î What is it? Î Benefits Î WLAN & Mesh Mesh protocols Î Why new? Î List of protocols Î Most Important Overview of simulation programs OPNET Î Simulation example Grid computers What are we going to do… Conclusion
After discussing this content we finaly made the following one. The main purpose was to give a detailed explanation of Mesh itself. We aimed to give some information about Final presentation content
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Comment after the presentation Meeting 4 : Discussion for the presentation about OPNET
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Kort verslag convergentie WLAN en UMTS
Evolutie van mobile netwerken Evolutie van 1G naar 3G(kort) 1G (analoog) NMT-450 NMT-900 TACS AMPS
2G(Digitaal) GSM IS-95(CDMA) IS-136(TDMA)
2.5G(High-speed data) HSCSD GPRS EDGE 1xRTT
3G(Multimedia/IMT-2000) UMTS Cdma2000
Beschrijving van 2.5G mobiele netwerken Internet en GSM evolueerde sterk samen. De trage snelheid van GSM(14.4Kbps) was een harde klap voor de gebruikers. De bedoeling van het samen smelten van twee technologieën kwam tot stand: broadband en wireless. HSCSD(High speed circuit switched Data) Short term solution HSCSD biedt hogere bandbreedte(tot 64Kbps) aan de gebruiker, het is een concentratie van verschillende GSM data kanalen. HSCSD was bedoeld om een tijdelijke oplossing te geven dat vervangen zou worden door een andere toekomstige technologie. HSCSD lost het probleem van “always on” niet op(zoals GPRS). Naast deze problemen had HSCSD nog drie andere problemen: • De nodige veranderingen aan de mobiele stations waren te groot ten opzichte van de relatief lage veranderingen aan het mobiel netwerk. • De netwerk operatoren waren bezorgd bij het toekomstig gebruik van HSCSD. Het zou de gelimiteerde ‘Air interface’ volledig gebruiken. • Het ontwikkelen van bruikbare HSCSD netwerken en mobiele stations was te traag waarbij alternatieve voor high ‘speed mobile data’ al klaar voor ontwikkeling waren. GPRS(General Packet Radio System) GPRS heeft als doel(zoals HSCSD) om hogere bandbreedtes te bieden door ‘time slots’ te concentreren. In tegenstelling tot HSCSD was GPRS een echte innovatie. GPRS laat variabele ‘code rate settings’ toe. GPRS laat een transitie snelheid toe van 160Kbps. De belangrijkste innovatie van GPRS is niet de hogere bandbreedte maar de ‘packet switched’ karakteristieken. GPRS laat toe dat verschillende gebruikers dezelfde ‘time slots’ gebruiken. Î Resource on demand. Î Beter gebruik van network resources.
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EDGE(Enhanced Data Rate for GSM or Global Evolution) Er zijn verschillende variaties van EDGE : klassiek EDGE, Compact EDGE en UWC-136, GSM/EDGE Radio Access Network. Klassiek EDGE Klassiek EDGE is de logische stap voor het verder ontwikkelen van GPRS en HSCSD. Bij de introductie van klassiek EDGE evolueerde GPRS en HSCSD naar respectievelijk EGPRS(enhanced GPRS) en ECSD (enhanced CSD). Nieuwe modulatie technieken maken het mogelijk om een hogere snelheid te bereiken. Ö 480Kbps Compact EDGE en UWC-136 Compact EDGE is geen GSM standaard. Compact EDGE is een algemeen(overlay) netwerk voor IS-136(2G), dat gebaseerd is op EGPRS standaard. De GSM/EDGE Radio Access Network De GSM/EDGE Radio Access network is de samenvoeging van de bestaande en toekomstige GSM/GPRS/EGPRS access netwerken. Het netwerk switching subsysteem wordt de intelligente “core” netwerk, dat de meeste services biedt. Verschillende radio access netwerken(RANs), kunnen aan deze core gekoppeld worden.
Universal Mobile Telecommunication System en UTRAN UMTS is de oplossing van de GSM community aanvraag aan de ITU-T(International Telecommunication Union – Telecommunication sector) voor een derde generatie mobiele netwerk(3G). In het begin(1999) waren deze 3G in ITU-T Future Public Land Mobile Communication System(FPLMTS) genoemd, waarbij ze achteraf samengebracht werd onder de naam IMT/2000. UMTS radio access netwerk is de UTRAN(UMTS Terrestrial Radio Access Network). Ze wordt in twee versies beschreven: 1) De UTRA-FDD(‘frequency division duplex’) mode gebruikt ‘wideband code division multiple access’(W-CDMA met 5MHz carrier) als multiple access methode. -> 384Kbps 2) De UTRA-TDD(‘time division duplex’) mode gebruikt een combinatie van W-CDMA en TDMA. -> 2Mbps in semi-stationaire mode. UMTS biedt niet enkel hogere snelheid op het Air interface. Het concept van UMTS zal in het bijzonder het gebruik van ‘real-time’ applicaties mogelijk maken en van ‘packet swiched’ en ‘circuit switched’ diensten tegelijkertijd en flexiebel gebruik te maken.
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GPRS als een voorloper van 3G en UMTS GPRS heeft niet als doel om de transitie snelheid te verhogen of te optimaliseren. EDGE wel... GPRS heeft de volgende doel/hoofd functies: • ‘always on’ status: denk aan bv e-mail programma’s dat binnenkomende mails aanmeld, binnenhaald; • Applicaties dat in de achtergrond kunnen werken(“background traffic”): bv downloaden van e-mails en bestanden; • ‘App. that are based on push services in connection with location based services’: bv wanneer men een restaurant voorbij komt, krijgt men een berichtje van de speciale aanbiedingen. Probleem: wie betaalt deze services? • Interactieve Internet Applicaties. De meeste services van GPRS kunnen met een traditionele mobiele apparaat gebruikt worden. De meeste schermen van deze traditionele apparaten(de GSM zoals we ze kennen) zijn niet geschikt voor deze services, denk aan bv. de oude modellen van ericsson. Geschikte mobile apparaten zouden van een breed scherm moeten voorzien zijn. Men zou deze kunnen uitbreiden tot een traditionele PDA met spraak toepassingen. EDGE(of EGPRS, GPRS) zijn gebaseerd op de GSM karakteristieken en hebben geen doorbrekende technologie. Als we geen rekening houden met de lage snelheid(data rate) dan is een combinatie van GSM en GPRS de toekomstige UMTS
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Werking van een mobiele toestel PCS GSM CDMA TDMA Een mobiele telefoon is een extreem gesofistikeerde radio. Vroeger, mensen die echt mobiele telefoons nodig hadden, installeerde een “radio telefoon” in hun auto, huis,... voor deze “radio telefoon” systemen was er één grote antenne per stad met 25 kanalen. De telefoons die de gebruikers gebruikte, had een zeer krachtige zender, groot genoeg om 70km te bereiken. Het is duidelijk dat het gebruik weinig mensen aantrok, vanwege de gelimiteerde kanalen.
Wat is een cel De stad wordt opgesplitst in verschillende kleine cellen. Dit laat toe om frequenties te hergebruiken over de stad, gebied. Elke hexagonale cel heeft een grote van ongeveer 26 km2.
(figuur 1) Figuur 1 geeft ons een beeld van de opgedeelde cellen. De twee blauwe cellen kunnen dezelfde frequentie hergebruiken. Elke cel heeft een basis station dat uit een toren en een klein gebouw(met de nodige radio toestellen) bestaat. Eén cel in een analoog systeem gebruikt 1/7 van de voorziene duplex spraak kanalen: • Een mobiele telefoon krijgt 832 radio frequenties te gebruiken in één stad. • Elke mobiele telefoon gebruikt twee frequenties per oproep(een duplex kanaal), dus zijn er 395 spraak kanalen per carrier(de andere 42 frequenties worden gebruikt als controle kanalen ) • Hierdoor heeft elke cel 56 spraak kanalen. M.a.w., in elke cel kunnen 56 mensen tegelijkertijd bellen. Via digitale transmissie methodes, worden de aantal kanalen verhoogd. Met TDMA gebaseerde digitale systemen kunnen er 3 keer zoveel oproepen genomen worden in tegenstelling tot de analoge systemen. Mobiele telefoons hebben lage verbruiks zenders, dit neemt twee voordelen met zich mee: • De transmissie van een basis station en de telefoons in de cel gaan niet veel verder dan de afmeting van de cel. Hierdoor(figuur 1) kunnen de twee blauwe cellen de 56 frequenties hergebruiken • Klein verbruik betekent ook kleinere batterijen en dit is één van de redenen voor de doorbraak van de kleine mobiele telefoons/aparaten.
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Er zijn honderden torens geplaatst per stad(gezien het toenemende aantal gebruikers). Elke carrier in elke stad beschikt ook over een centrale genaamd Mobile Telephone Switching Office(MTSO). Deze vestiging regelt alle connecties tussen de mobiele telefoons en de normale analoge vaste telefoon lijnen en regelt ook alle basis stations in de regio.
Handover bij GSM Elke mobiele telefoon heeft een speciale code geassocieerd. Deze codes worden gebruikt om een telefoon, de gebruiker en de service provider te identificeren. Wat gebeurt er wanneer iemand u probeert te bereiken: • Wanneer de telefoon ingeschakeld wordt, luistert hij naar SID(System Identification Code is een unieke 5 digit nummer dat wordt geassocieerd aan elke carrier door de FCC) op de controle kanaal. De controle kanaal is een speciaal frequentie dat tussen basis station en mobiele telefoons gebruikt word om te kunnen communiceren. • Wanneer ze de SID krijgen, wordt deze vergeleken met de geprogrammeerde SID van de mobiele telefoon. • Naast de SID wordt er ook een ‘registration request’ verzonden. Vervolgens wordt de telefoon locatie opgeslagen in een database gelegen aan de MTSO. Zo kan de MTSO de inkomende oproepen doorverbinden naar de locatie opgeslagen in zijn database. • Wanneer een oproep binnenkomt gaat de MTSO de mobiele telefoon positie opzoeken in zijn database. • Vervolgens neemt de MTSO een frequentie paar dat de mobiele telefoon zal gebruiken tijdens het opnemen van de oproep in die cel. • De MTSO communiceert met de mobiele telefoon via de controle kanaal om de gebruikte frequentie mee te delen. Wanneer de mobiele telefoon en de toren naar deze frequenties ingesteld worden, wordt er via een ‘two-way’ radio gecommuniceerd. • Wanneer er een verzwakking is, zal de basis station dit opvatten als het verlaten van een cel. Tegelijkertijd zal de toren van een andere cel een signaal opvangen en zo een nieuwe connectie leggen in een nieuwe cel en nieuwe toren dankzij de MTSO.(zie figuur 2.1 en figuur 2.2)
(figuur 2.1)
(figuur 2.2)
Roaming bij GSM Wanneer de SID op de controle kanaal niet overeenkomt met de SID geprogrammeerd in de telefoon, dan herkent de telefoon dit als ‘roaming’. De MTSO van de cel waar je roaming nodig hebt contacteerd de MTSO van de gebruiker. Deze zal in zijn database controleren of je telefoon gevalideerd is.
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Circuit switched en Packet switched Alle telecommunicate netwerken zijn ofwel circuit switched of packet switched. Circuit switched worden vooral gebruikt voor de transmissie van spraak en packet switched voor transmissie van data. De laatste jaren is de proportie van het aantal data connectie drastisch verhoogd(door gebruik van internet en bedrijfsnetwerken). Het belangrijke is om deze twee technieken/netwerken aan mekaar te koppelen waarbij spraak en data over één netwerk getransporteerd wordt. Het probleem is dat ze sterk verschillende eigenschappen hebben. Circuit switched Problemen en eigenschappen: • • • • •
Wanneer gebruiker A een connectie wil aangaan met gebruiker B en er zijn geen resources aanwezig in één van de netwerk nodes, zal de gebruiker A geen verbinding krijgen. Alleen kleine aanvragen kunnen gemaakt worden. Vele applicaties in de telecommunicatie vragen een hogere snelheid tijdens hun transacties. De switched resources zijn continu beschikbaar …
Packet switched Packet switched heeft ongeveer dezelfde taken als circuit switched. Het grote verschil tussen circuit switched en packet switched is dat er geen vaste connectie is tussen de twee gebruikers(zogenaamde kanaal, tunnel). De informatie moet in verschillende pakketjes verdeeld worden en zo één voor één doorgestuurd worden Î Packet switched en circuit switched hebben elk hun voor en nadelen.
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Netwerk architectuur van de GSM(2G) Kort overzicht: Elk GSM netwerk kan opgedeeld worden in de base station subsystem BSS, network switching subsystem NSS en het mobiele station.
De BSS(base station subsystem) De BTS(base transceiver station) De BSS bestaat uit verschillende “Base transceiver stations”. Deze BTSen verzorgen de draadloze communicatie van het draadloos station naar het netwerk via de Um of air interface. De BTS verzorgt alle functies van de fysieke laag op gebied van communicatie tussen het mobiel station en het netwerk. Dit houdt in, channel coding, interleaving(alleen GSM, niet GPRS), en burst generatie. Alsook GMSK, modulatie en demodulatie. De BSC(base station controller) Alle BTSen van de BSS zijn geconcerteerd aan de BSC via de Abis interface. De BSC is een circuit switching exchange in tegenstelling tot de MSC(mobile service switching center). De BSC was ontworpen om alle draadloze taken van de MCS te ontdoen. Dit houdt in de evaluatie van het meet resultaat van de BTS en het mobiele station tijdens een live connectie en de handover(van BTS naar BTS). Bijkomende functies van de BSC zijn de peer functie van het mobiele station voor de radio resource management protocol(RR) en de resource administration voor de Abis en Air interface. De BSC is een hindernis voor GPRS. De exchange functies van de BSC zijn onbruikbaar voor packet switched services en bovendien is de RR protocol extreem moeilijk om aan de eisen van packet switched service te voldoen. Indien men het compatibel wil maken voor GPRS zal er een extensie van de BSC, een nieuw netwerk element of een aanpassing aan de BSC De TRAU(Transcoding Rate and Adoption Unit) De TRAU is het derde network element van de BSS. De belangrijkste taak van de TRAU is spraak compressie van 64Kbps naar 16Kbps of 8Kbps(full-of half rate). Werkt tevens comfort noice generation weg. De belangrijkste functie van de TRAU is de conversie van de inkomende informatie van de MSC in TRAU frames. Deze actie neemt plaats voor fax, data en spraak toepassing, dus voor betalen activiteiten tussen het mobiel station en de TRAU neemt plaats op de TRAU frames. De TRAU frames hebben een lengte van 320bits. Elke 20ms wordt er een TRAU frame verzonden of ontvangen. Positie van de TRAU is van groot belang. Indien men deze vóór de BSC plaatst wint men connectie snelheid, men spreekt van de remote TRAUs.
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De NSS(Network Switching Subsystem) De NSS bestaat uit één of meerdere HLR(Home Location Register) met de AuC(Authentication Center) en optioneel met de EIR(equipment Identity Register) en verschillende MSCs met een geconcerteerde VLR(Visitor Location Register). De HLR(Home Location Register) en de AuC(Autentication Center) De HLR is een statische database met informatie van duizenden abonnees(telefoonnummer, diensten, limieten). De HLR bevat ook informatie op welke VLR de abonnee momenteel geregistreerd is. De AuC is een intern deel van de HLR. Deze berekend de respectievelijke autenticatie resultaten(SRES) en ciphering keys(Kc). GPRS authenticiteit en activatie van de GPRS ciphering worden gecontroleerd door de SGSN. Hieruit volgt dat de een mobiel telefoon zich tweemaal kan registreren: in de VLR en de SGSN. De MSC(Mobile Services Switching Center) en VLR(Visitor Location Register) De MSC is voornamelijk een ISDN exchange voor de GSM dat gewijzigd werd voor gebruik van GSM-MSC. Een typisch GSM netwerk bevat verschillende MSCs. Slechts enkele daarvan hebben een interface naar andere netwerken, men spreekt van gateway MSCs(G-MSC). De netwerk operator beslist welke MSC deze interface bevatten. Naast deze G-MSC bevinden zich de IWF(Interworking Function). Deze heeft als functie rate adaption(RA) in connectie met andere data netwerken. GSM laat werking met andere netwerken toe: CSPDNs, PSPDNs, PSTN en ISDN. De EIR(Equipment Identity Register) De EIR is tevens een database(te vergelijken met de VLR en HLR). Deze houdt geen informatie bij van de abonnee zelf maar van de mobile telefoon zelf. De EIR is een optioneel netwerk element en wordt door netwerk operatoren zelden geïmplementeerd(wegens te hoge kosten).
Het mobiele GSM station en de SIM(Subscriber Identity Module) De GMSK modulatie techniek wordt gebruikt om met laag verbruik versterkers te werken. De GSM mobiele station bevat alle fysische laag functies zoals de BTS en de TRAU. Verschil GPRS/GSM station: • • • •
Nieuwe protocol Nieuwe channel coding processes Multislot transmission New MMI
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Het GSM/GPRS netwerk architectuur Bij een GSM netwerk wordt er 70%-80% voor de BSS geïnvesteerd, zowel hardware als software en andere. De overige investeringen gaan naar de NSS. GPRS is de overstap naar UMTS, veel operatoren hadden niet de mogelijk om enorm te investeren in zo’n netwerk. Door deze problemen wordt de BSS zonder bijzonder bijkomende hardware gebruikt, terwijl een nieuw packet switched netwerk nodig is. De verdeelde netwerken gebruiken allen dezelfde BSSs en dezelfde Air interface.
De Packet Control Unit De PCU is een onderdeel van de BSS(van de BSC). Men gebruikt dezelfde configuratie van de BSS. Omwille van financiële redenen wordt de configuratie van de BTS intact. De BSC wordt voorzien van een uitbreiding, de zogenaamde PCU. Deze PCU zijn kaarten met de nodige software. De plaats keuze van de PCU wordt beïnvloed door de TRAU
Taken van de PCU • •
Radio resource management functie in GPRS(Nieuwe protocol vergeleken met de RR in GSM) RLC/MAC protocol voor GPRS. De PCU is verantwoordelijk voor de lagere lagen van de GPRS protocol op de Air interface. Conversie van packet data in PCU frames. Transparant getransporteerd van de BSC naar BTS wanneer de PCU aan de SGSN zit. Deze PCU frames hebben dezelfde formaat als TRAU frames
Î Dankzij deze laatste functie is de combinatie van GSM/GPRS mogelijk. Deze functies van de PCU brengen een aantal gevolgen met zich mee: •
Data rates boven de 16Kbps: 16Kbps kanalen worden tussen TRAU en BSC gebruikt. • Coördinatie tussen BSC en PCU: Om te voorkomen dat de BSC en de PCU elk een time slot proberen te reserveren die al in gebruik is. • Leverancier afhankelijk: Het formaat van de TRAU frames in gebonden aan de leverancier -> de PCU moet van dezelfde leverancier komen als de BSS
De Serving GPRS Suport Node(SGSN) Maakt deel uit van de GPRS netwerk(zie figuur). De SGSN voor de GPRS netwerken neemt de functie over dat door de MSC en VLR worden uitgevoerd in GSM netwerk. In GPRS bestaat de link tussen MSC en VLR niet meer. De SGSN heeft nog andere functies: • Packet swiching • Transfer van short messages
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• • • •
Chipering in GPRS Data compresion in GPRS Charging SGSN handover
De Gateway GPRS Support Node(GGSN) De GGSN is de interface tussen de GPRS netwerk en de andere externe packet data netwerken(Internet). De GGSN lijkt op een router. De GGSN is Pachet switched en heeft de nodige modificaties nodig voor de GSM/GPRS netwerk. De GGSN heeft volgende taken/functies: • Setting up of PDP context • Anchor function • De GGSN en Charging • Types of GGSN Besluit: Er zijn interfaces nodig tussen de GSM netwerk elementen en de nieuwe GPRS netwerk elementen: Gc, Gd, Gf, Gr en Gs(optioneel) interfaces
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UMTS netwerk (zie figuur UMTS netwerk architectuur). De “Core” netwerk is idem als die van de GSM/GPRS netwerk. Deze core netwerk kunnen diensten leveren aan zowel de UTRAN en de GSM radio access netwerk. De core netwerk(zoals ze al besproken werd) bevat twee domeinen: CS(circuit switched) en PS(Packet switched). Het CS domein handelt de circuit-switched connecties en de ps domein handelt de packet transfers. CS wordt rond de MSC gebouwd en PS rond SGSN.
Core network (zie GSM/GPRS)
De UTRAN(UMTS Terrestrial Radio Access Network) De UTRAN is de nieuwe radio access netwerk speciaal ontworpen voor UMTS. De UTRAN bestaat uit verschillende RNC(radio network controllers) en Node Bs(base station). Deze twee vormen de RNS(radio network system. Intern(RNS) worden deze verbonden met de Iub interface(tussen Node B en RNC) en de Iur(tussen de verschillende RNCs) De RNC(Radio network controller) De RNC controleert één of meerdere Node Bs. Deze wordt gekoppeld via de Iu interface naar de MSC(IuCS interface) of naar de SGSN(IuPS). De interface tussen de RNCs(Iur) is een logische interface en een directe fysieke connectie bestaat er niet. (in GSM termen) De RNC kan vergeleken worden met de BSC in GSM netwerken. Functies van de RNC: • Iub transprot resource management • Controle van de Node B logische operaties en maintenance resources. • System information management en scheduling van system information. • Traffic management van common channels • Macro diversity combining/splitting of data streams transferred over several Node Bs • Modification to active sets -> soft handover • Allocation of DL channelization codes. • Uplink outerloop power control • DL power control • Admission control • Reporting management • Traffic management of shared channels De Node B De Node B kan vergeleken worden met de BTS van het GSM network. Deze kan verschillende vellen bedienen. Deze naam wordt in een logisch concept gebruikt, fysiek spreekt men van “base stations”
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Functies van de Node B: • …
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Opgestelde documenten Deze documenten kan men terug vinden onder de naam “Appendix: Convergence WLAN and UMTS”. Deze bevat een theoretische studie over GSM/GPRS, EDGE, UMTS en de convergentie tussen WLAN en UMTS.
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Opleiding 2 cycli – Campus Paardenmarkt Paardenmarkt 92 – 2000 Antwerpen Academiejaar 2003 – 2004
Convergence WLAN and UMTS
Eindwerk voorgedragen door Helsmoortel Carl tot het bekomen van de titel en de graad van Industrieel Ingenieur Elektronica optie Informatie- en communicatietechnieken
Introduction This paper is divided into three main parts. Part 1 covers the 2.5 Generation of Mobile Systems. This part explains the GPRS network and the introduction of EDGE in the GSM/GPRS network. Part 2 covers the 3 Generation of Mobile Systems in details. Finally part 3 covers the interconnection/convergence of WLAN and UMTS. The raison for this is that UMTS will be first introduced in the main cities whereby in the GSM/GPRS network will be upgraded with the EDGE technology to provide a good overall speed.
PART 1 General Packet Radio Service & Enhanced Data rates for GSM Evolution
Table of content Table of content.......................................................................................................................... 1 1 Introduction ........................................................................................................................ 3 1.1 Why GPRS? ............................................................................................................... 3 1.2 What is better about GPRS?....................................................................................... 3 1.3 What do we have to do for GPRS? ............................................................................ 4 1.3.1 For the provider .................................................................................................. 4 1.3.2 For the user......................................................................................................... 4 1.4 Quality of Service....................................................................................................... 5 2 GPRS network.................................................................................................................... 7 2.1 Mobile Station ............................................................................................................ 7 2.2 Base Station Subsystem ............................................................................................. 7 2.3 Packet Control Unit.................................................................................................... 8 2.4 Serving GPRS Support Node ................................................................................... 10 2.5 Gateway GPRS Support Node ................................................................................. 11 2.6 Databases.................................................................................................................. 11 2.6.1 Home Location Regeister(HLR) ...................................................................... 11 2.6.2 Visitor Location Register(VLR)....................................................................... 11 2.6.3 AuC .................................................................................................................. 12 2.6.4 EIR ................................................................................................................... 12 3 Planes and interfaces ........................................................................................................ 13 3.1 Transmission Plane .................................................................................................. 13 3.1.1 Um interface..................................................................................................... 14 3.1.2 Gb interface ...................................................................................................... 14 3.1.3 Gn/Gp interface ................................................................................................ 14 3.1.4 Interface between MS and SGSN..................................................................... 14 3.2 Signaling Plane......................................................................................................... 15 3.2.1 Between MS and SGSN ................................................................................... 15 3.2.2 Between two GSNs .......................................................................................... 16 3.2.3 New interfaces with the SS7 network .............................................................. 16 3.2.4 Gr interface....................................................................................................... 16 3.2.5 Gc interface ...................................................................................................... 17 3.2.6 Gf interface....................................................................................................... 18 3.2.7 Gs interface ...................................................................................................... 18 3.2.8 Gd interface ...................................................................................................... 19 3.2.9 Gi interface ....................................................................................................... 19 4 Physical layer: Principles. ................................................................................................ 20 4.1 Physical link layer (PLL) ......................................................................................... 20 4.1.1 Access scheme.................................................................................................. 20 4.1.2 Multislot classes ............................................................................................... 21 4.1.3 Channel coding................................................................................................. 23 4.2 RF physical layer...................................................................................................... 27 4.2.1 Modulation ....................................................................................................... 27 5 RLC LLC/MAC layers..................................................................................................... 29
1
5.1 Introduction .............................................................................................................. 29 5.2 RLC/MAC Block Structure...................................................................................... 29 5.2.1 Control Block ................................................................................................... 30 5.2.2 RLC Data Block ............................................................................................... 32 5.3 Broadcast information Management ........................................................................ 33 5.3.1 SI Message Scheduling .................................................................................... 33 5.3.2 MS Acquisition of Broadcast Information ....................................................... 35 5.3.3 Monitoring of PBBCH Information ................................................................. 36 5.3.4 Cell Reselection Parameter Acquisition........................................................... 37 5.3.5 Frequency parameters ...................................................................................... 37 5.3.6 Cell Allocation ................................................................................................. 38 5.3.7 Cell Reselection................................................................................................ 39 5.4 Measurements........................................................................................................... 40 5.4.1 In Packet Idle Mode ......................................................................................... 40 5.4.2 In Packet Transfer Mode .................................................................................. 40 5.5 RLC .......................................................................................................................... 41 5.5.1 Transmission Modes ........................................................................................ 42 5.5.2 Segmentation and Reassembly of LLC PDUs ................................................. 43 5.5.3 Transfer of RLC Data Blocks........................................................................... 44 6 EDGE ............................................................................................................................... 45 6.1 Introduction .............................................................................................................. 45 6.2 Modulation ............................................................................................................... 46 6.2.1 GSM Waveform ............................................................................................... 46 6.2.2 EDGE Waveform ............................................................................................. 48 6.3 Comparison of GSM and EDGE.............................................................................. 51 6.4 Link Adaptation........................................................................................................ 52 6.5 RLC/MAC Improvement ......................................................................................... 54 6.6 Implementation......................................................................................................... 54 Index......................................................................................................................................... 55
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1 Introduction 1.1 Why GPRS? The impressive growth of cellular mobile telephony as well as the number of Internet users promises an exciting potential for a market that combines both innovations: cellular wireless data services. Mobile telephony has been for many years the most popular application supported by mobile systems such as the Global System for Mobile communications (GSM). In the last few years, the use of mobile data applications such as the GSM Short Message Service (SMS) has gained popularity. However, the GSM system can only support data services up to 9.6 kbit/s, circuit switched and thus doesn’t fulfills the needs of users and providers. That is why some new packet data technologies have been developed. One of them is the General Packet Radio Service or GPRS. It is developed by the European Telecommunications Standards Institute (ETSI) and is a packet switched data service for GSM that can allow much higher bit rates.
1.2 What is better about GPRS? Like we said before, GPRS can allow much higher bit rates than GSM. In theory up to 170 kbit/s per user. However, commercial GPRS systems will be able to support rates up to 115 kbit/s. Because of the fact that GPRS is a packet switched service, it will result in a much better utilization of the traffic channels. This is because a channel will only be allocated when needed and will be released immediately after the transmission of the packets. With this principle, multiple users can share one physical channel (statistical multiplexing). Networks based on the Internet Protocol (IP) (e.g., the global Internet or private/corporate intranets) and X.25 networks are supported in the current version of GPRS. In addition, GPRS packet transmission offers a more user-friendly billing than that offered by circuit switched services. In circuit switched services, billing is based on the duration of the connection. This is unsuitable for applications with bursty traffic. The user must pay for the entire airtime, even for idle periods when no packets are sent (e.g., when the user reads a Web page). In contrast to this, with packet switched services, billing can be based on the amount of transmitted data. The advantage for the user is that he or she can be "online" over a long period of time but will be billed based on the transmitted data volume. To sum up, GPRS improves the utilization of the radio resources, offers volume-based billing, higher transfer rates, shorter access times, and simplifies the access to packet data networks.
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1.3 What do we have to do for GPRS? 1.3.1 For the provider GPRS is thus a step between GSM and 3G cellular networks. GPRS is a new technology so we have to adjust the GSM network and even add some new modules. In Figure 1 you can see the GSM network (blue) and the GPRS network (red). Some modules like BTS and BSC are used in both networks but other ones like SGSN are specific for the GPRS network. What these modules do, will be explained in the next section.
Figure 1
1.3.2 For the user If you want to use GPRS, you have to buy a new mobile telephone. These telephones support GPRS above the usual GSM. There are three classes: A,B and C. •
A Class A terminal supports GPRS and other GSM services (such as SMS and voice) simultaneously. This support includes simultaneous attach, activation, monitor, and traffic. As such, a Class A terminal can make or receive calls on two services simultaneously. In the presence of circuit-switched services, GPRS virtual circuits will be held or placed on busy rather than being cleared.
•
A Class B terminal can monitor GSM and GPRS channels simultaneously, but can support only one of these services at a time. Therefore, a Class B terminal can support simultaneous attach, activation, and monitor, but not simultaneous traffic. As with Class A, the GPRS virtual circuits will not be closed down when circuit-switched 4
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•
traffic is present. Instead, they will be switched to busy or held mode. Thus, users can make or receive calls on either a packet or a switched call type sequentially, but not simultaneously. A Class C terminal supports only nonsimultaneous attach. The user must select which service to connect to. Therefore, a Class C terminal can make or receive calls from only the manually (or default) selected service. The service that is not selected is not reachable. Finally, the GPRS specifications state that support of SMS is optional for Class C terminals.
1.4 Quality of Service The Quality of Service or QoS is a set of parameters describing a cost-based level of service. Mobile users have a choice on session quality, knowing that a better QoS is going to cost them more money. QoS requirements of typical mobile packet data applications are very diverse (e.g., consider real-time multimedia, Web browsing, and e-mail transfer). Support of different QoS classes, which can be specified for each individual session, is therefore an important feature. GPRS allows defining QoS profiles using the parameters service precedence, reliability, delay, and throughput. • •
The service precedence is the priority of a service in relation to another service. There exist three levels of priority: high, normal, and low. The reliability indicates the transmission characteristics required by an application. Three reliability classes are defined, which guarantee certain maximum values for the probability of loss, duplication, mis-sequencing, and corruption (an undetected error) of packets (see Tabel 1).
Tabel 1
•
The delay parameters define maximum values for the mean delay and the 95percentile delay (see Tabel 2). The latter is the maximum delay guaranteed in 95 percent of all transfers. The delay is defined as the end-to-end transfer time between two communicating mobile stations or between a mobile station and the Gi-interface to an external packet data network. This includes all delays within the GPRS network, e.g., the delay for request and assignment of radio resources and the transit delay in 5
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the GPRS backbone network. Transfer delays outside the GPRS network, e.g., in external transit networks, are not taken into account.
Tabel 2
•
The throughput specifies the maximum/peak bit rate and the mean bit rate.
Using these QoS classes, QoS profiles can be negotiated between the mobile user and the network for each session, depending on the QoS demand and the current available resources. The billing of the service is then based on the transmitted data volume, the type of service, and the chosen QoS profile.
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2 GPRS network In this section we will discuss all the modules for the GPRS network. We will explain what there has to be done in order to let the GPRS system work on the existing GSM network. The GPRS system architecture is given in figure 2.
Figure 2
2.1 Mobile Station Mobile Station (MS) is the combination of a Mobile Terminal (MT) and a Terminal Equipment (TE). The TE provides the user interface to the GPRS system for example a laptop, a palm computer,… To access GPRS services, a totally new subscriber terminal is required. These new terminals will be backward compatible with GSM for voice calls. The MT communicates with the base transceiver station (BTS) and TE. MT has to be equipped with GPRS functionality to be able to operate in GPRS network.
2.2 Base Station Subsystem Base Station Subsystem or BSS consists of several Base Transceiver Stations (BTS) and a Base Station Controller (BSC). The BTS receive and transmit the radio traffic between the transmitter and a MS. For the GPRS network, a software upgrade is required in the existing BTSs. The BSC controls its transceiver stations and takes care of the communication with the MS. Each BSC will require the installation of one or more PCUs and a software upgrade. The PCU provides a physical and logical data interface out of the base station system (BSS) for packet data traffic. 7
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When either voice or data traffic is originated at the subscriber terminal, it is transported over the air interface to the BTS, and from the BTS to the BSC in the same way as a standard GSM call. However, at the output of the BSC the traffic is separated; voice is sent to the mobile switching center (MSC) per standard GSM, and data is sent to a new device called the SGSN, via the PCU over a Frame Relay interface.
2.3 Packet Control Unit The Packet Control Unit or PCU stands for a logical entity that manages packet toward the radio interface. The PCU communicates with the Channel Codec Unit (CCU), positioned in the BTS. The PCU is in charge of RLC/MAC functions such as segmentation and reassembly of LLC frames, transfer of RLC blocks in acknowledged or unacknowledged mode, radio resource assignment, and radio channel management. An image of the task of the PCU is given in the next picture.
Figure 3
The CCU handles GSM layer 1 functions such as channel decoding, channel encoding, equalization, and radio channel measurements.
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Figure 4
As shown in figure 3, the PCU can be located either at the BTS site, the BSC site or on the SGSN site. When the PCU is located at the BSC or the SGSN site, it is referred to as being a remote PCU. If the PCU is located at the BSC, it could be implemented as an adjunct unit to the BSC. When the PCU is located at the SGSN side, the BSC is transparent for frames transmitted between the PCU and the CCU. This PCU location implies the implementation of a signaling protocol between the BSC and the PCU (e.g., for time slot management, access on CCCH management). A protocol is also needed when the PCU is located at the BTS side. In case of remote PCU, GPRS traffic between the PCU and the CCU are transferred through the A-bis interface. The A-bis interface in GSM is based on TRAU frames carrying speech data and having a fixed length of 320 bits (every 20 ms). This corresponds to a throughput of 16 Kbps per A-bis channel. As the PCU is supporting functions such as RLC block handling (retransmission, segmentation, and so forth) and access control, it needs to know the GSM radio interface timing. This implies in the case of a remote PCU the design of a synchronous interface between the PCU and the CCU. The PCU must be able to determine in which radio frames is sent an RLC/MAC block. In case of a PCU locates at the BTS side, the PCU knows the radio interface time. The remote PCU solution requires the sending of in-band information between the PCU and the CCU (for transmission power indication, channel coding indication, and synchronization between the CCU and the PCU). Below you have a list of the advantages and disadvantages for each place of the PCU: PCU at the BTS side:
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Advantages : Disadvantages:
There is an internal interface between the PCU ant the CCU. There is a low round-trip delay (the round-trip delay is the time between the transmission of a block and the reception of the answer). There is no waste of A-bis bandwidth due to retransmission of RLC blocks. There is a likely impact on the existing BTS hardware (when migrating from a circuit-switched network to a GPRS one). This is an important disadvantage considering the number of BTSs in the field.
PCU at the BSC side: Advantages:
There is an internal interface between the PCU and the BSC.
There are likely hardware impacts on the current BSC (however, the number of BSCs is lower compared with the number of BTSs). There is a greater round-trip delay. A synchronous protocol is needed between the PCU and the CCU. A-bis bandwidth is wasted in case of RLC blocks retransmission.
Disadvantage: PCU at the SGSN side Advantages: Disadvantages:
There is no hardware impact on the current GSM network (BTS, BSC). There is a smooth introduction of GPRS in the network. There is a greater round-trip delay (longer temporary block flow establishment). A synchronous protocol is needed between the PCU and the CCU. A-bis bandwidth is wasted in case of RLC blocks retransmission. A protocol is needed between the BSC and the PCU.
2.4 Serving GPRS Support Node Serving GPRS Support Node (SGSN) is a new element for the GPRS network. It can be viewed as a "packet-switched MSC"; it delivers packets to mobile stations (MSs) within its service area. SGSNs send queries to home location registers (HLRs) to obtain profile data of GPRS subscribers. SGSNs detect new GPRS MSs in a given service area, process registration 10
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of new mobile subscribers, and keep a record of their location inside a given area. Therefore, the SGSN performs mobility management functions such as mobile subscriber attach/detach and location management. The SGSN is connected to the base-station subsystem via a Frame Relay connection to the PCU in the BSC.
2.5 Gateway GPRS Support Node Gateway GPRS Support Node (GGSN) is also a new element in the GPRS network. GGSNs are used as interfaces to external IP networks such as the public Internet, other mobile service providers' GPRS services, or enterprise intranets. GGSNs maintain routing information that is necessary to tunnel the protocol data units (PDUs) to the SGSNs that service particular MSs. Other functions include network and subscriber screening and address mapping. One (or more) GGSNs may be provided to support multiple SGSNs.
2.6 Databases Visitor Location Register (VLR), Home Location Register (HLR), Equipment Identity Register (EIR) and Authentication Centre (AUC) are the databases of the GSM network. All these databases will require software upgrades to handle the new call models and functions introduced by GPRS.
2.6.1 Home Location Register(HLR) A Home Location Register (HLR) is a database that contains semi-permanent mobile subscriber information for a wireless carriers' entire subscriber base. HLR subscriber information includes the International Mobile Subscriber Identity (IMSI), service subscription information, location information (the identity of the currently serving Visitor Location Register (VLR) to enable the routing of mobile-terminated calls), service restrictions and supplementary services information. The HLR handles SS7 transactions with both Mobile Switching Centers (MSCs) and VLR nodes, which either request information from the HLR or update the information contained within the HLR. The HLR also initiates transactions with VLRs to complete incoming calls and to update subscriber data. Traditional wireless network design is based on the utilization of a single Home Location Register (HLR) for each wireless network, but growth considerations are prompting carriers to consider multiple HLR topologies.
2.6.2 Visitor Location Register(VLR) A Visitor Location Register (VLR) is a database which contains temporary information concerning the mobile subscribers that are currently located in a given MSC serving area, but whose Home Location Register (HLR) is elsewhere.
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When a mobile subscriber roams away from his home location and into a remote location, SS7 messages are used to obtain information about the subscriber from the HLR, and to create a temporary record for the subscriber in the VLR. There is usually one VLR per MSC.
2.6.3 AuC The AuC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world.
2.6.4 EIR The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node.
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3 Planes and interfaces The GPRS network deploys two separate planes : the transmission plane and the signaling plane. The first one is used for the transmission of user data and control functions. The second one is used to convey signaling info that controls and supports the transmission plane functions, to create, modify and delete GTP tunnels. In these planes, we will find al the components of the GPRS network. As we know, the GPRS network is based on the GSM network, so there is a need for new interfaces between the GSM network modules and the new modules of the GPRS network. These interfaces, that are also shown in figure 2, are called the Gc, Gd, Gf, Gr, Gs, Gb, Gn, Gi, Gp interfaces. In the next paragraph we will explain the two planes and the different interfaces that exist. The pictures will show you the protocol stack. For a detailed explanation of the protocols, read the paragraphs about the layers.
3.1 Transmission Plane The transmission plane consists of a layered protocol structure providing user data transfer, along with associated procedures that control the information transfer such as flow control, error detection, and error correction. The next figure illustrates the layered protocol structure between the MS and the GGSN.
Figure 5
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3.1.1 Um interface This interface is explained in the GSM network.
3.1.2 Gb interface This interface connects the BSC with the SGSN. It supports data transfer in the transmission plane. The Gb interface supports the following protocols: The BSS GPRS protocol (BSSGP). This layer conveys routing and QoS-related information between the BSS and SGSN. Network Service (NS). It transports BSSGP PDUs and is based on a frame relay connection between the BSS and SGSN. A relay function is implemented in the SGSN to relay the packet data protocol (PDP) PDUs between the Gb and Gn interfaces (IP PDUSs in figure 5).
3.1.3 Gn/Gp interface The Gn interface is located between two GSNs (SGSN or GGSN) within the same PLMN, while the Gp interface is between two GSNs in different PLMNs. PLMN stands for Public Land Mobile Network and is a generic name for all mobile wireless networks that use earth base stations rather than satellites. The mobile equivalent of the PSTN. The Gn/Gp interface supports the following protocols: GPRS Tunneling protocol (GTP). This protocol tunnels user data between the SGSN and GGSN in the GPRS backbone network. GTP operates on top of UDP over IP. The layers L1 and L2 of the Gn interface are not specified in the GSM/GPRS standard. User Datagram Protocol (UDP). It carries GTP packet data units (PDUs) in the GPRS Core Network for protocols that do not need a reliable data link (e.g. IP). Internet Protocol (IP). This is the protocol used for routing user data and control signaling within the GPRS backbone network.
3.1.4 Interface between MS and SGSN This interface supports the following protocols: SubNetwork-Dependent Convergence Protocol (SNDCP). This protocol maps the IP protocol to the underlying network. SNDCP also provides other functions such as compression, segmentation, and multiplexing of network layer messages. 14
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Logical Link Protocol (LLC). This layer provides a highly reliable logical link that is independent of the underlying radio interface protocols. LLC is also responsible for the GPRS ciphering.
3.2 Signaling Plane The signaling plane consists of protocols for control and support if the transmission plane functions. It controls both the access connections to the GPRS network (e.g. GPRS attach and GPRS detach) and the attributes of an established network access connection (e.g. activation of a PDP address), manages the routing of information for a dedicated network connection in order to support user mobility, adapts network resources depending on, the QoS parameters and provides supplementary services.
3.2.1 Between MS and SGSN
Figure 6
Figure 6 shows the signaling plane between the MS and the SGSN. This plane is made up of the following protocols: GMM. The GMM protocol supports mobility management functionalities such as GPRS attach, GPRS detach, security, RA update and location update. Session Management (SM). The SM protocol supports functionalities such as PDP context activation, PDP context modification and PDP context deactivation.
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3.2.2 Between two GSNs
Figure 7
The signaling plane between two GSNs is made up of the following protocols: • •
GTP for the control plane (GTP-C). This protocol tunnels signaling messages between SGSNs and GGSNs, and between SGSNs in the GPRS core network. UDP. This protocol transfers signaling messages between GSNs.
3.2.3 New interfaces with the SS7 network The various GSNs of the GPRS backbones network use a Signaling System No 7 (SS7) network to exchange information with GSM SS7 network nodes such as HLR, MSC/VLR, EIR and SMS-GMSC. The SS7 network provides facilities to quickly exchange messages between GPRS backbone network nodes irrespective of data transmission through the GPRS PLMN network. We will give a brief summary of the interfaces:
3.2.4 Gr interface The HLR stores the user profile, the current SGSN address, and the Packet Data Protocol (PDP) address(es) for each GPRS user in the PLMN. The Gr interface is used to exchange this information between HLR and SGSN.
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Figure 8
3.2.5 Gc interface This is the interface between a GGSN and a HLR.
Figure 9
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3.2.6 Gf interface This is the interface between a SGSN and an EIR.
Figure 10
3.2.7 Gs interface The Gs interface connects the data bases of SGSN and MSC/VLR.
Figure 11
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3.2.8 Gd interface To exchange messages of the short message service (SMS) via GPRS, the Gd interface is defined. It interconnects the SMS-Gateway MSC (SMS-GMSC) with the SGSN. It also connects the SMS-Interworking MSC (SMS-IWMSC).
Figure 12
3.2.9 Gi interface The Gi interface connects the PLMN with external public or private PDNs, such as the Internet or corporate intranets. Interfaces to IP (IPv4 and IPv6) and X.25 networks are supported.
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4 Physical layer: Principles. The physical layer of the OSI-model is a communication-oriented layer. This layer provides the mechanical, electrical and signalisation functions, necessary to make, maintain and abort a physical connection. Comparable to the OSI-model, GPRS has its own physical layer. Its network architecture is based on GSM in as much as the physical layer structure and air interface are preserved. The physical layer between MS and BSS is divided into the two sublayers: the physical link layer (PLL) and the physical RF Layer (RFL). The PLL provides a physical channel between the MS and the BSS. Its tasks include channel coding (detection of transmission errors, forward error correction (FEC), indication of uncorrectable code words), interleaving, and detection of physical link congestion. The RFL operates below the PLL. Among other things, it includes modulation and demodulation.
4.1 Physical link layer (PLL) 4.1.1 Access scheme There are different ways of sharing the physical resource among all the users in a radio system, called multiple-access method. The multiple-access scheme defines how simultaneous communications share the radio spectrum. The various multiple-access techniques in use in radio systems are FDMA, TDMA and CDMA. The access scheme upon which GPRS is based, is TDMA, with eight basic physical channels per carrier (TS 0 to 7). TDMA stands for; time division multiple access and is a digital transmission technology. It allows a number of users to access a single radio-frequency (RF) channel, without interference, by allocating unique time slots to each user within each channel. The TDMA digital transmission scheme multiplexes three signals over a single channel. The current TDMA standard for cellular divides a single channel into six time slots, with each signal using two slots, providing a 3 to 1 gain in capacity over advanced mobile-phone service (AMPS). Each caller is assigned a specific time slot for transmission. A physical channel uses a combination of frequency- and time-division multiplexing and is defined as a radio frequency channel and time slot pair. The physical channel that is used for packet logical channels is called a packet data channel (PDCH). PDCHs are dynamically allocated in the cell by the network. The PDCH is mapped on a 52-multiframe. This 52multiframe consists of 12 radio blocks of 4 consecutive TDMA frames and 4 idle frames.
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Like GSM, GPRS uses the concept of logical channels mapped on top of te physical channels. Two types of logical channels have been introduced, namely traffic channels and control channels. Three subtypes of control channels have been defined for GPRS: broadcast, common control and associated. The different packet data logical channels are: Packet broadcast control channel (PBCCH) Packet common control channel (PCCCH) Packet data traffic channel (PDTCH)
Figure 13
4.1.2 Multislot classes The concept of multislot classes allows for transmission in several time slots in the TDMA frame(see figure 13). The GPRS link level performance has been usually assessed considering the allocation of a single slot per TDMA frame. However, multiple slots may be allocated to a single user in order to increase the transmission bandwidth. One of the most important GPRS characteristics on the air interface is the possibility of increasing the achievable bit rate by grouping together several channels. In order to do so with a reasonable impact on the MS in terms of implementation complexity, it has been decided to allow the RF transmission on several slots of a TDMA frame, with a number of restrictions, as listed below: • •
Several bursts can be transmitted within a TDMA frame, but should all be on the same ARFC number. Depending on the mobile capability, delay constraints are needed between the transmission and reception of bursts, and between reception and transmission, to allow the mobile to perform the adjacent cell measurements, or monitoring.
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•
If there are m time slots allocated to an MS for reception and n time slots allocated for transmission, the system requires that min (m,n) reception and transmission time slots have the same time slot number within the TDMA frame.
Two types of MSs are defined: type 1 mobiles are not able to transmit and to receive at the same time, while type 2 mobiles are. For these two types, there exist different classes, depending on the capability of the MS in terms of complexity. The classes are called multislot classes since they refer to the ability of the mobile to support a communication on several time slots of the TDMA frame. For a given multislot class, the mobile is able to transmit on a maximum of Tx time slots, and to receive on a maximum of Rx time slots within a TDMA frame, but the sum Tx + Rx is limited. This means that the maximum of Tx slots and the maximum of Rx slots are not active at the same time(see figure 14). The definition of the type 1 multislot classes relies on the following time constraints: Tta is the maximum number of time slots allowed to the MS to measure an adjacent cell received signal and to get ready to transmit. This parameter is therefore used to set the minimum allowed delay between the end of a transmit or receive time slot and the next transmit time slot, with an adjacent cell measurement to be performed in between; Trb relates to the number of TS needed by the MS, prior to a receive time slot, when no adjacent cell measurement is performed. It is the minimum delay between the end of a transmit or receive TS and the first next receive TS. Tra is the minimum allowed delay in number of TS, between the end of a transmit or receive time slot and the next receive time slot, when an adjacent cell measurement is to be performed in between. Ttb is the minimum number of TS between the end of a receive or transmit TS and the first next transmit TS, without adjacent cell measurement in between. These constraints have been chosen to give the mobile enough time for the frequency change between a receive or transmit slot, and the next receive or transmit slot. It also allows some time to measure an adjacent cell received signal level, which requires a measurement window and two frequency changes.
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Figure 14
4.1.3 Channel coding. Channel coding is used to protect the transmitted data packets against errors. The channel coding technique in GPRS is quite similar to the one employed in conventional GSM. An outer block coding, an inner convolutional coding, and an interleaving scheme is used. Channel Scheme
Coding
CS-1
CS-2
CS-3
CS-4
3
6
6
12
Infobits without 181 USF
268
312
428
Parity bits BC
40
16
16
16
Tail bits
4
4
4
-
456
588
676
456
Punctured bits
0
132
220
-
Code rate
½
~2/3
~3/4
1
Data rate kbit/s
9.05
13.4
15.6
21.4
107.2 kb/s
124.8 kb/s
171.2 kb/s
Pre-cod. USF
Output encoder
conv
Maximum data speed with 8 72.4 kb/s time-slots
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The choice of coding scheme depends on the condition of the channel provided by the cellular network (quality of the radio link between cell phone and base station). If the channel is very noisy, the network may use CS-1 to ensure higher reliability; in this case the data transfer rate is only 9.05 kbit/s per GSM time slot used. If the channel is providing a good condition, the network could use CS-3 or CS-4 to obtain optimum speed, and would then have up to 21.4 kbit/s per GSM time slot. PDTCH Four coding schemes, CS-1 to CS-4, are used for the GPRS PDTCHs. They offer different levels of protection, and the CS to be used is chosen by the network according to the radio environment. If, for instance, the carrier to interference ratio is high, low protection is applied, to achieve a higher data rate, and if that ratio is low, the level of protection is increased, which leads to a lower data rate. This mechanism is called link adaptation. Coding schemes CS-1 to CS-4 are mandatory for MSs supporting GPRS, but with exception of CS-1 they may not be supported by the network. The first step of the coding procedure consists of adding a block check sequence coded on 16 bits for error detection. For CS-2, CS-3 and CS-4, the next step is the precoding of the USF field. The 3 bit field is mapped onto a 6 –bit word in CS-2 and CS-3, and on a 12-bit word in CS-4. The USF is used as a token for uplink multiplexing. It needs to be decoded with a very low error rate, by the different mobiles allocated on the same PDCH. That is why its coding is more robust than the rest of the block.
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Figure 15
For CS-1, CS-2 and CS-3, the next step involves adding four tail bits prior to a rate ½ convolutional encoding stage for error correction. This code is punctured to give the desired coding rate. The same convolutional code is used for the three coding schemes but with a different puncturing rate. The interest of the puncturing is to allow different coding rates with the same convolutional code. It consists on not transmitting some of the bits that are output by the encoder. At the reception, the hole positions are known by the receiver. They are filled with zero before the decoding. For CS-4 there is no convolutional coding. Note that after the convolutional encoding stage, the 3-bit USF field is mapped on a 12-bit word in CS-2, CS-3 and on a 6-bit word in CS-1. The coded data obtained is then interleaved over four bursts.
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Figure 16
PCCCH For all GPRS packet control channels other than PRACH and PTCCH on uplink, the coding scheme CS-1 is always used. For ABs on PRACH, two coding schemes are defined: Packet AB that carries 8 information bits, the coding of which is the same as for GSM Extended packet AB that carries 11 information bits. The coding is the same as for the normal AB except that puncturing is used to increase the information field. The extended AB carries more information, which allows the mobile to give more information when requesting the establishment of a TBF. The use of normal AB or extended AB is controlled by a network parameter. PTCCH The PTCCH downlink channel coding is the same as for the GSM SACCH. In uplink, either packet ABs or extended packet ABs are sent depending on the network parameter. The information field is set to a fixed pattern.
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4.2 RF physical layer 4.2.1 Modulation GPRS is based on a modulation technique known as Gaussian minimum-shift keying (GMSK). Gaussian minimum shift keying is a form of continuous phase modulation, a technique that achieves smooth phase transitions between signal states, thereby reducing bandwidth requirements. With Gaussian minimum shift keying, input bits with rectangular (+1, -1) representation are converted to Gaussian (bell-shaped) pulses by a Gaussian filter before further smoothing by a frequency modulator. Also, in most cases, the Gaussian pulse is allowed to last longer than one bit time—the amount of time a binary 1 is in the "on" position. Consequently, the pulses overlap, giving rise to a phenomenon known as intersymbol interference. The extent of this overlap is determined by the product of the bandwidth of the Gaussian filter and the data-bit duration; the smaller the bandwidth–bit-time product, the more the data bits or pulses overlap. The resulting carrier signal is very smooth in phase—particularly in comparison to waveforms generated through standard binary or quarternary phase-shift keying. This is important because signals with smooth phase transitions require less bandwidth to transmit. On the other hand, this very smooth phase makes the receiver's job much harder. With Gaussian minimum shift keying, there are no well-defined phase transitions to detect for bit synchronization, and Measured data showing growth of sidelobes in the the energy from each bit is mixed power spectral density of offset quarternary phase-shift with the energy from several other keying. The pink curve indicates performance through bits. The transmitter output looks a standard (linear) amplifier, while the green curve nothing like the data input, and on shows the poorer performance though a saturated the receiver side, a special (nonlinear) amplifier. demodulator of increased complexity is needed to extract the data bits. For the receiver to achieve a given bit-error rate, the transmitter must generate more power to overcome the receiver noise in the presence of the intersymbol interference. In other words, the Gaussian minimum shift keying waveform is usually less power-efficient than more traditional waveforms such as binary phase-shift keying and requires a more complex receiver, but this potential reduction in power efficiency and increase in receiver complexity could be rewarded with a very significant enhancement of bandwidth efficiency. So, with
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Gaussian minimum shift keying, there is a trade-off between bandwidth efficiency and power efficiency. Gaussian minimum shift keying is not new—the technique has been used extensively in Europe for cell-phone applications with a bandwidth–bit-time product of 0.3. But system designs using very small bandwidth–bit-time products such as 1/5 or 1/8 are new—and challenging. Aerospace became interested in these smaller bandwidth–bit-time products because of their narrow bandwidth occupancy and the rapid roll-off of their power spectra. These two factors strongly influence the ability to pack many different channels into a limited amount of bandwidth. The Gaussian minimum shift keying waveform exhibits a steep power spectrum and therefore coexists well with adjacent channels in a frequency-division multipleaccess system.
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5 RLC LLC/MAC layers 5.1 Introduction The RLC/MAC layer is dedicated to the management of radio resources and can be compared to the “data link” layer in the OSI model. Before there is any useful communication possible between the mobile and the base station, the mobile must be granted resources for uplink and downlink transmission. MAC manages all the signaling necessary for their allocation, and release (TBF establishment). Another function of the MAC protocol is the mapping and multiplexing of data and signaling blocks onto different logical sub channels. The RLC protocol is in charge of the data transfer management during the TBF. It provides an acknowledged mode allowing selective retransmission of radio blocks as well as an unacknowledged mode of data transmission. For GPRS, the movement of the mobile trough the network is entirely managed by a procedure of cell reselection. The mobile can perform autonomous cell reselection or reselection can be controlled by the network. In any case, the RLC/MAC layer manages this process.
5.2 RLC/MAC Block Structure The RLC/MAC block is the basic transport unit on the air interface that is used to communicate between the mobile and the network. It is used to carry data and RLC/MAC signaling. A radio block is defined as an information block transmitted over four consecutive bursts on a PDCH, the four bursts are send using a TDMA procedure. One RLC data block is mapped onto one radio block, witch is always transmitted on a packet data sub channel (PDTCH). One RLC/MAC control block is transmitted into one radio block on a signaling sub channel (PACCH, PCCCH, PBCCH). The RLC/MAC control block is used to transmit RLC/MAC control messages, whereas the RLC data block contains data. A MAC header is added at the beginning of each type of radio block. A block check sequence (BCS) is added at the end of a radio block and is used for error control detection.
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5.2.1 Control Block The RLC/MAC control block is used for the transfer of control messages that are represented by a MAC header and a RLC/MAC control block. These blocks are send using the CS1 coding scheme. This means that the size of one RLC/MAC control block is 22 bytes in size, and the header takes up one additional byte.
Figure 17
5.2.1.1 Downlink RLC/MAC control block This is the type of RLC/MAC block send from the network to the MS. It consists of a “control message contents field” and an optional header. The MAC header consists of the following fields: • PT: Indicates whether it is a control –or data block. • USF: Used as an uplink multiplexing means when dynamic or extended dynamic allocation is used. It authorizes or refuses a transmission in the next block or set of four blocks following that received by the mobile. A number of mobile can thus share a given uplink PDCH, but only one Mobile can transmit on one block at any given time. When resources are allocated, a given USF is reserved for a mobile on a given PDCH. • RRBP: The “Relative reserved block period” indicates the number of frames that the mobile must wait before transmitting an RLC/MAC control block • S/P: The “Supplementary/Polling” field indicates whether the RRBP field is valid. The RLC/MAC header contains the following elements: • RBSN: “Reduces Block Sequence Number”. This gives the sequence number of the RLC/MAC control block. • RTI: The Radio transaction identifier is used to identify an RLC/MAC control message that has been segmented into two RLC/MAC control blocks. • FS: Indicates whether the RLC/MAC control block contains the FS of the segmented RLC/MAC control message. • AC: Tells the MS whether or not there are PR,TFI, and D fields present. If these bytes are present, then the message will be one byte larger. • TFI: The “temporary flow indicator” identifies a downlink or uplink TBF, as well as the ownership of the block. • D: Indicates the direction of the TBF identified by the TFI field. 30
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•
PR:
This two bit indicator tells gives the power reduction used by the BTS to transmit the current block.
5.2.1.2 Uplink RLC/MAC control block This block consists of an MAC header and a control message field. The MAC header contains: • PT: Indicates the type of data within the block (RLC data –or control block). • R: Indicates whether the mobile transmitted the message one time or more, during it’s most recent channel access.
Figure 18
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5.2.2 RLC Data Block The RLC/MAC block that is used for data transfer consists of a MAC header and an RLC data block. The RLC data block consists of an RLC header, an RLC data unit and spare bits. The size of the RLC block depends on the type of channel coding (CS-1->4), as listed below
Figure 19
5.2.2.1 Downlink RLC Data Block The explanation of the MAC header was given earlier and is common to the most RLC blocks. The downlink RLC data block has the following unique fields. •
FBI:
The “Final Block Indicator” indicates whether or not the RLC data block received is the last of the TBF. • BSN: Gives the sequence number of the RLC block in the TBF. • E: “Extension” indicates the presence of an optional byte. • M: “More” Indicates the presence of another LLC frame in the data unit part. • LI: “Length Indicator” Makes it possible to delimit LLC frames within an RLC data block by giving the length of the data in the RLC data block belonging to an LLC frame. The RLC data field can contain bytes for one or more LLC frames.
Figure 20
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5.2.2.2 Uplink RLC Data Block The MAC header contains the following fields, only the new ones are explained here. •
CV:
The “Countdown Value” gives the number of RLC blocks associated with the TBF remaining to be transmitted. • SI: “Stall Indicator” indicates an acknowledgement request from the mobile when the RLC protocol is stalled. • TLLI: This byte, “Temporary Logical Link Identity”, identifies a GPRS user. • TI: “TLLI indicator” is used to indicate the presence of the optional byte that contains the PFI. • PFI: Identifies the packet flow content. The “E” bit after the TFI field will be used in the future to indicate the presence of an additional byte due to an evolution in the protocol. If the number of bytes corresponding to one or more LLC frames in the RLC data unit field cannot fill the RLC frame completely, it is filled with spare bits.
Figure 21
5.3 Broadcast information Management In each cell, the BCCH and PBCCH, if present, continuously broadcast information on the serving cell and neighbor cells’ configuration. The serving cell and neighbor cell parameters are broadcast within messages called SI messages on BCCH and “Packet System Information” messages (PSI) on PBCCH. Based on this information, the MS is able to decide whether and how it may gain access to the system via the cell it is currently residing in.
5.3.1 SI Message Scheduling All information broadcast on the BCCH or PBCCH is carried in SI messages or PSI messages, respectively. 33
RLC LLC/MAC layers
As there are several SI and PSI message types having a different content, it is useful for the MS to know where these types of messages are located in a group of mutiframes. A variable TC was introduced in the GSM standard to facilitate the MS operation. Each type of SI of PSI message is associated with a TC value. TC = (FN/51) mod 8 A given SI message type is located on a specific 51 multiframe number equal to FN/51. All SI message types are associated with a fixed TC value. This means that all SI message types are scheduled in the same location within a group of 51 multiframes. This is a rule that is applied by all the network operators. On a PBCCH the occurrence of PSI message type is defined by the following formula: TC = (FN/52) mod PSIx_repeat_period Where PSx_repeat_period is a predefined number for the type of PSI message number, E.g. The PSI1 message type has a value between 1 and 16 Unlike with the SI message type, the other PSI message types are not associated with a predefined TC value fixed by the standard. This means there is an acquisition phase for the MS to determine the association between the PSI message type and the TC value when the MS is located on a new cell. The PSI message types other than the PSI1 message are divided into two categories: •
High repetition rate PSIs: These PSIs are broadcast on the PBCCH occurrences that are not used by the PSI1 messages, in a sequence determined by the network. This sequence is repeated at each TC that is equal to 0 every PS1_repeat_period of 52 multiframes. The PSI_COUNT_HR parameter broadcast by the network indicates the number of PSIs with high repetition rates. • Low repetition rate PSIs: This type of PSI messages are broadcast on the PBCCH occurrences that are not used by the PSI1 and high repetition rate PSIs. The sequence is again determined by the network, and is repeated at the beginning of the hyperframe when the FN is equal to 0. The PSI_COUNT_LR parameter broadcast by the network indicated the number of PSIs with low repetition rates. Important to know is that the PSI1_REPEAT_PERIOD, PSI_COUNT_HR, PSI_COUNT_LR parameters are broadcast in a PSI1 type message. The MS must read the configuration.
PSI1 message first, to understand the mapping in a given
34
RLC LLC/MAC layers
Figure 22
5.3.2 MS Acquisition of Broadcast Information The BCCH is used to broadcast both GSM and GPRS network parameters. These parameters are the frequencies that are used in the cell, the neighbor cell frequencies, the GSM and GPRS logical channel description, and the access control parameters. The mobile uses the broadcast serving cell frequencies to derive its frequency allocation during resource assignment. It uses the neighbor cell frequencies for measurement and cell reselection purposes. The logical channel description indicate how the different logical channels are multiplexed on the time slots. The network broadcasts access control parameters and puts constraints on the access channels in order to avoid congestion. All these parameters can be found in distinct SI messages (used for BCCH). • • • • •
SI type 1 messages: SI type 2 messages:
contain the serving frequency parameters. this category includes the SI type 2bis, and SI type 2ter messages. And contain the neighbor BCCH frequency list and access control parameters SI type 3 messages: contain control channel descriptions, cell options and cell selection parameters. SI type 4 messages: contain cell selection parameters and CBCH configuration. SI type 13 messages: contain GPRS cell options.
SI type 2, 3 and 4 messages are always broadcast, the 1, 2bis, 2ter, and 13 messages are optional. Other SI messages exist, but are not directly linked to GPRS, and therefore not discussed.
35
RLC LLC/MAC layers
Broadcast of the SI type 13 message in the cell indicates the availability of the GPRS service. The position of the SI type 13 message is indicated in either the SI type 3 or SI type 4 message. It the PBCCH is not present in the cell, the SI type 13 message gives the GPRS cell parameters such as cell reselection mode, power control programs, and the AB format to be used on the GPRS channels. If PBCCH is present, the SI type 13 message indicates the description of the PBCCH (position, radio channel description, training sequence code and PR of transmission compared to the BCCH). The MS attempts to decode the full BCCH data of the serving cell at least every 30 seconds in order to detect any changes in the network configuration. It also decodes the neighbor BCCH data block that contains the parameters affection the cell reselection for each of the six strongest neighbor cells at least every 5 minutes.
5.3.3 Monitoring of PBBCH Information The PBCCH broadcasts parameters relevant to both GSM and GPRS. When the PBCCH is present in the cell, it will be monitored by Mobile Stations that want to get GPRS attached and access to the GPRS service. A GPRS mobile that monitors the PBCCH does not have to monitor the BCCH, since the BCCH information is also broadcast on the PBCCH. This information can be found in the following messages (used by PBCCH) • • •
PSI type 1 message: contain the GPRS cell options, PCCCH description, and PRACH control parameters. PSI type 2 message: contain frequency parameters. PSI type 3 message: also includes the PSI type 3bis message, and contain the necessary cell reselection parameters of the serving cell and neighbor cells, as well as the neighbor cell BCCH information.
Other PSI messages are send optional by the network. The mobile attempts to regularly decode the PSI type 1 messages of it’s serving cell (at least every 30 seconds). Within the PSI type 1 message, the network indicates whether a change took place within one or more types of broadcast PSI messages. The network may indicate which family of PSI messages has changed by using the PSI_CHANGE_FIELD parameter in order to avoid having the MS rescan the complete PBCCH. Whenever a change took place, the MS must reread the new PSI messages within the next 10 seconds.
36
RLC LLC/MAC layers
Note that the MS may suspend it’s data transfer in order to decode the above information. However, in order to avoid data transfer interruption during packet transfer mode, the network can broadcast PSI in the PACCH.
5.3.4 Cell Reselection Parameter Acquisition For cell-reselection purpose, the mobile must acquire special parameters that are used for the evaluation of the cell-reselection criteria. Some are linked to the serving cell and others dedicated to neighbor cells. When there is no PBCCH in the serving cell, these parameters are broadcast by the network in the SI type 3 or 4 messages. In this case, each BCCH sends it’s own cell parameters for cell reselection. The mobile must decode the SI 3 and 4 messages on the six strongest neighbors’ BCCH in order to acquire these parameters. (The measurement is in terms of RXLEV) When the PBCCH is present however, the network broadcasts both the neighbor cell and serving cell parameters that are used for cell reselection on this channel. They can be found in PSI type 3 messages. The network may have to broadcast these parameters in several instances of the PSI 3 message depending on the number of neighbor cells. All in all, the acquisition time of neighbor cells parameters is much faster when PBCCH is present, since they are all transmitted on the same channel.
5.3.5 Frequency parameters When the network allocates radio resources to the mobile, It provides frequency parameters needed by the mobile to know its frequency channel allocated. The radio channel description used by the mobile consists of: •
One frequency in case of a non-hopping radio frequency channel.
•
A list of frequencies, a MAIO and HSN when frequency hopping is used.
The list of frequencies that is used by the mobile for GPRS transfer is called “GPRS mobile allocation”. The radio channel description is provided to the mobile during resource assignment. When frequency hopping is used in the cell, the size of the mobile allocation can be very large. In order to avoid sending the list of frequencies directly during the assignment phase, special mechanisms are defined.
37
RLC LLC/MAC layers
5.3.6 Cell Allocation The operator allocates a set of radio frequency channels to each cell. This set is defined as the cell allocation (CA). The CA defines the list of frequencies that can be assigned to the MS directly after the first resource assignment. Other radio frequencies can be assigned later, during the assignment phase. This CA is provided in a SI type 1 or 2 message, when there is a PBCCH in the cell. In a type 1 message, the CA is directly defined using ARFCN encoding. In a type 2 message, the network provides the mobile with reference frequency lists (RFLs). One RFL consists of a list of frequencies that are used in the cell. Up to 4 RFLs can be stored in a mobile. The GPRS mobile allocation (GPRS MA) is defined as a subset of either the CA or RFLs. It is deduced from the CA or RFLs using a bitmap. Different encoding mechanisms have been defined in order to provide frequency list within RFLs in PSI 2 messages or CA in SI type 1 messages. For GSM 900 the number of frequencies is limited to 124. The encoding mechanism resides in a bitmap (each bit representing an ARFCN from 1 to 124) indicating the frequencies of the list.
Figure 23
During the assignment, the network can provide the radio channel description with either: • •
One frequency in case of a non-hopping radio frequency channel. One GPRS MA number, one HSN, and one MAIO (referred to as “indirect encoding” in the GSM specifications). • A bitmap referring to one or more RFLs (broadcast on PBCCH) of the CA (broadcast on the BCCH or PBCCH), one HSN, and one MAIO (referred to as “direct encoding 1” in GSM specifications). • A list of frequencies, one MAIO, and one HSN (referred to as “direct encoding 2” in GSM specifications). Note that the drawback of the direct encodings 1 and 2 is the large amount of space required in the assignment message. If many frequencies are sent, it will be necessary to provide the assignment message in two radio blocks. This indicates the delay and complexity of the establishment. The drawback of the indirect encoding is that more space is required in the 38
RLC LLC/MAC layers
PSI 2 messages to broadcast the RFLs, leading to a lower repetition rate of some other PSI messages.
5.3.7 Cell Reselection The cell reselection can be controlled either autonomously by the mobile or the network. It is based on measurements performed by the mobile. The network can request these measurements to be reported periodically by the MS. Three cell reselection modes NC0, NC1 and NC2 have been defined. • • •
NC0: In this mode, the GPRS mobile performs autonomous cell reselection without sending measurement reports to the network. NC1: In this mode the GPRS mobile performs autonomous cell reselection and periodically sends measurement reports to the network. NC2: In this mode, the network controls the cell reselection. The mobile sends measurement reports to the network.
When the mobile performs autonomous cell reselection, it chooses a new cell and triggers a cell reselection on its own. The NC2 mode allows the network to control the mobility of GPRS users within the network. Two criteria are defined for autonomous cell reselection: one is based on the (C1, C2) criteria. It corresponds to the GSM cell-reselection criteria, except if the cell reselection parameters are sent explicitly to the mobile in one control message. The other, based on the (C’1, C31, C32) criteria, has been introduced for GPRS. All these criteria are based on “received signal level” (RXLEV) measurements in the serving cell and its neighbor cells.
Figure 24
39
RLC LLC/MAC layers
The mobile, or the network can decide to switch cells if they detect that the current cell is operating at full capacity or the data loss rate becomes too high, a downlink signaling failure has occurred, the serving cell has been barred, there is a neighboring cell that has better reception or equipment, more options, etc.
5.4 Measurements When the mobile resides on a cell, it receives the list of neighbor cells (identified by their BCCH frequencies and their BISCs) from the network. The mobile periodically measures the RXLEV on these neighbor BCCHs, and checks the BSIC of the BCCH carriers. These measurements are used in autonomous cell reselection mode, and reported back to the network in case of cell reselection controlled by the network and NC1 mode.
5.4.1 In Packet Idle Mode The mobile measures the RXLEV on the BCCH carrier of the serving cell and on each BCCH carrier of the neighboring cells. It calculates an average RXEV on each carrier, with at least 5 measurements during a maximum period of 5 seconds, or 5 consecutive paging blocks of the mobile. The mobile must perform at least one measurement on a cell every 4 seconds, with a maximum of 20 measurements a second. It must also decode the BSIC and BCCH of the six most powerful cells every 14 paging blocks or al least once every 10 seconds.
5.4.2 In Packet Transfer Mode This mode is identical to the measurements taken in Packet Idle Mode, except that the mobile performs additional measurements on each TDMA frame, for at least one of the given BCCH carriers. The decoding process is now taking place during the two idle frames of the 52multiframe. DRX mode In order to minimize the power consumption, the MS is not required to listen continuously to the amount of information provided by the network while it is in idle mode. The (P)PCH logical channels have been split into several paging sub channels. All paging messages addressed to an MS with a given IMSI are sent on the same paging sub channel. This feature is called DRX.
40
RLC LLC/MAC layers
Note that the DRX feature allows for an increase in battery lifetime, but at the expense of a small increase in time delay for the establishment of the circuit and GPRS incoming calls/ The method whereby paging sub channels are accessed is determined by either the network, in case of PCH channels, or by the MS, in the case of PPCH channels. Non DRX mode After a TBF release, or a measurement report in idle mode, the mobile reverts to the non DRX mode, in which it must decode all CCCH or PCCCH blocks, independently of its DRX period. If the network needs to initiate a new downlink TBF, it sends the downlink TBF allocation on any (P)CCCH related to the (P)CCCH_GROUP of the MS. The downlink TBF establishment is quicker for a MS in non DRX mode, because the network does not need to wait for the MS paging sub channel in order to send the paging message. After a TBF release, the non DRX period is equal to the smallest time given. One value is set by the network, and given on the broadcast channels. The other is set by the MS during the GPRS-attach procedure. At the end of a measurement report in idle mode, the non DRX period is equal to a value set by the network and given on broadcast channels. Note that: • There is a high probability that a new downlink TBF needs to be established a short time after the end on an up –or downlink TBF. In the case of a client server relation, a downlink TBF may occur shortly after an uplink TBF. • The non DRX mode has an impact on the MS autonomy in idle mode because in this period the MS must continuously decode the CCH or the PCCH blocks. The MS must perform a tradeoff between autonomy and downlink TBF establishment time when setting the NON_DRX_TIMER value.
5.5 RLC The RLC layer provides a reliable link between the BSS and the MS, allowing transmission of RLC blocks in acknowledged or unacknowledged mode. The RLC layer is responsible for the segmentation of LLC frames into RLC data blocks. Before being transmitted on the radio interface, these blocks are numbered by the transmitter so that the receiver is able to detect data blocks witch aren’t decoded. So that it can request for their retransmission. When all RLC data belonging to one LLC frame has been received, the RLC layer (at the receiving side) ensures the reassembly of the LLC frame. The RLC layer also provides a similar mechanism for the transmission of RLC/MAC control messages form the BSS to the mobile.
41
RLC LLC/MAC layers
5.5.1 Transmission Modes The RLC automatic repeat request (ARQ) functions support two modes of operation. • •
RLC acknowledged mode. RLC unacknowledged mode.
In RLC acknowledged mode, the RLC ensures the selective retransmission of RLC data blocks that have not been correctly decoded by the receiver. This mode is used to achieve a high reliability in LLC PDU sending. In RLC unacknowledged mode, RLC data blocks that have not been correctly decoded are not retransmitted by the sending entity. This mode is used for applications that are tolerant of error, and that request a constant throughput, such as streaming applications (e.g. video or audio streams.). In uplink, the requested RLC mode is indicated in the PACKET_RESOURCE_REQUEST when a two phase access is used. In case of a one phase access, it uses the default setting: RLC acknowledged mode. In downlink, the RLC mode is indicated within the assignment message by the RLC_MODE parameter. During the TBF, the RLC mode cannot be changed, any change in the RLC mode requires the release of the TBF.
42
RLC LLC/MAC layers
5.5.2 Segmentation and Reassembly of LLC PDUs
5.5.2.1 Segmentation of LLC PDUs into RLC data blocks The segmentation of LLC PDUs allows the transport through the radio interface of LLC PDUs, whose size can be much larger than the data unit length of a single RlC data block. The segmentation of LLC PDUs is done in a dynamic way. This means that a change of coding scheme, which normally results in a decrease or increase of the maximum size of one RLC data block, could happen at any time of the transmission. Depending on the CS used to encode the transmitted RLC data block, the LLC PDU will be segmented into variable size data units. The LLC PDUs are segmented in the same order as they are received by the transmit entity. Each RLC data block resulting from the segmentation of an LLC PDU is numbered using the BSN field of the RLC header. The BSN ranges from 0 to 127. For one TBF, the first segmented RLC data block of the first LLC frame is numbered with BSN = 0, the next BSN = 1 and so forth, the maximum BSN number is 127. When a LLC PDU gets segmented, it can occur that there is wasted space in the last segment of that message. To overcome this problem, it is possible to have more than one message in one radio block. E.g. the end of one and the beginning of another message can both be found on the same radio block. The LI, extension (E) and more (M) fields (see downlink RLC data block) are used to delimit the consecutive LLC PDUs within one RLC data block.
5.5.2.2 Reassembly of LLC PDUs from RLC data blocks After having received all the RLC data blocks belonging to an LLC PDU, the reassembly involves removing the RLC header from each RLC data block, and reassembling the data unit using the BSN sequencing. In case of RLC unacknowledged mode, some RLC data blocks may not have been decoded during the transfer. The RLC data units not received must be substituted with logical zeros.
43
RLC LLC/MAC layers
5.5.3 Transfer of RLC Data Blocks
5.5.3.1 Sliding Window Mechanism The transfer of RLC data blocks in the acknowledged RLC mode is controlled by a selective ARQ mechanism. This retransmission mechanism relies on the identification of each RLC data block, thanks to its BSN. The RLC protocol relies on a sliding window mechanism. The size of this window for GPRS is 65 blocks. The window ensures that the gap, in term of block number, between the oldest unacknowledged block and the next-in-sequence block to be transmitted is always lower then 64. The sending side is not allowed to transmit a new block when the BSN of the oldest unacknowledged block is 63 lower than the current. If this is the case, the RLC protocol is stalled. And the transmit entity is only allowed to retransmit the blocks that have not yet been acknowledged. Each time an acknowledgement message is received from the receiver, the transmitter updates its list of unacknowledged RLC blocks. It then may send a new block. The receiver maintains a table that contains the state of all the RLC data blocks within the window. At the beginning of the TBF, the receiver expects to receive the block with BSN=0. Since the RLC blocks are send in sequence by the sending side, the receiver can deduce all the previous sent blocks that have not been decoded. Whenever an RLC block is decoded, it is marked as decoded within the table.
44
EDGE
6 EDGE 6.1 Introduction EDGE is an enhancement to the GSM mobile cellular phone system. The name EDGE stands for Enhanced Data for GSM Evolution and it enables data to be sent over a GSM TDMA system at speeds up to 384 kbps. In some instances EDGE systems may also be known as EGPRS, or Enhanced General Packet Radio Service systems. Although strictly speaking a "2.5G" system, it is anticipated that it will be used to provide data services by operators who have not been able to secure the full 3G licences. So in big city’s operaters will implement UMTS and for regional locations they are planning on implementing EDGE because of the high cost it brings with it. In time edge will be substituted by UMTS. EDGE is intended to build on the enhancements provided by the addition of GPRS (General Packet Radio Service) where packet switching is applied to a network. It then enables a three fold increase in the speed at which data can be transferred by adopting a new form of modulation. GSM uses a form of modulation known as Gaussian Minimum Shift Keying (GMSK), but EDGE changes the modulation to 8PSK and thereby enabling a significant increase in data rate to be achieved. So we can state that there is no need for additional hardware too implement EDGE.
Figure 25
45
EDGE
6.2 Modulation 6.2.1 GSM Waveform GSM uses Gaussian Minimum Shift Keying (GMSK) modulation to transmit data symbols as shown in Figure 26. Incoming data bits, which can have a value of either 1 or –1, are alternately placed in I and Q. The I and Q data bits are then alternated with zeros. This symbol creation process is shown in Figure 27.
Figure 26
Figure 27
The symbols created by this process are then passed through the transmit filter. The impulse and frequency responses of this filter are shown in Figure 28 and Figure 29. The impulse response equals zero at ± 2 symbols from each transmitted data symbol. Since the I and Q data bits are sent in quadrature as shown in Figure 2, no inter-symbol interference is created on transmit.
46
EDGE
Figure 28
Figure 29
Figure 30 shows the I/Q diagram for the GSM waveform. The waveform is nearly constant envelope. The peak-to-average for this waveform is 0.52 dB with a minimum-to-maximum ratio of 1.07 dB. A nearly saturated amplifier can amplify this waveform without degradation in communication. Non-linear amplification will however cause spectrum mask problems.
47
EDGE
Figure 30
6.2.2 EDGE Waveform The EDGE requirement specifies 3π/8-shifted 8-PSK modulation using the linearized GMSK filter. The proposal defines the EDGE symbol pattern shown in Figure 31. Figure 32 displays the I/Q diagram for the EDGE waveform.
Figure 31
48
EDGE
Figure 32
This waveform has significant transmit inter-symbol interference. Figure 33 shows the result of sampling the transmit waveform at the peak of each transmit symbol impulse response. A review of Figure 28 shows that the transmit filter impulse response is down approximately 0.26 at ± 1 symbol. This means that every sampled symbol is corrupted by 0.26 times the proceeding and following symbol. This large amount of inter-symbol interference makes amplifier design more difficult.
Figure 33
Since the receiver knows the impulse response function of the transmitter and receives a known training sequence of symbols in each transmitted time division burst, the receiver can remove inter-symbol interference. The amplifier non-linear performance however can corrupt this process. Figure 34 show received symbols after correction in a perfectly linear system. Figure 35 shows the effects of a non-linear amplifier.
49
EDGE
Figure 34
Figure 35
The signal power cumulative probability density function for the EDGE waveform shown in Figure 33 is given in Figure 36. This waveform shows significant amplitude variation compared to GSM. The peak-to-average ratio for the Figure 8 waveform is 3.17 dB. The maximum to minimum ratio for the EDGE waveform is 16.37 dB.
50
EDGE
Figure 36
6.3 Comparison of GSM and EDGE EDGE is a significantly different waveform from the original GMSK waveform used in GSM. The GMSK waveform has miniscule amplitude variation. EDGE has peak-to-average ratio of 3.17 dB and a maximum-to-minimum ratio of 16.37 dB. Amplifier distortion has little effect on communication performance on GMSK but will have significant effect on EDGE performance. For example, an ideal amplifier capable of boosting a GSM signal to 40 Watts will boost an EDGE signal to only 21.4 Watts before the EVM becomes excessive. Imperfections in the amplifier will further reduce EDGE power level. Table 1 compares the maximum symbol rates and data rates between 8PSK and GMSK modulation as implemented in EDGE and GPRS. Table 1: Technical Data for GMSK and 8PSK Modulation
GMSK 8PSK 270 270 ksymbols/s Symbol Rate ksymbols/s 1 bit per 3 bits per Bits per Symbol symbol symbol Modulation Bit Rate 270 kbits/s 810 kbits/s Max Users Data Rate 20 kbit/s for 59.2 kbit/s for per TS CS4 MCS9
51
EDGE
6.4 Link Adaptation The EDGE air interface introduces nine modulation coding schemes (MCS), each employing different data coding (user payload) and channel coding (header and protection) rates with GMSK and 8PSK modulations (see Figure 37). Each MCS is designed to deliver the optimal throughput under different radio environments [carrier-to-interference ratio (C/I) and carrierto-noise ratio (C/N)]. It will be possible through the link adaptation feature to change the modulation and coding scheme during the communication to adapt to the changing radio environment. This enables a more efficient use of the spectrum and improves performance and robustness.
Figure 37: EDGE is equipped with nine modulation coding schemes.
As illustrated in Figure 37, EDGE coding scheme MCS-4 sports a user payload size that is a multiple of MCS-1. Likewise, MCS-2, MCS-5 and MCS-7 have payload sizes that are multiples of MCS2; and MCS-3, MCS-6 and MCS-9 have payload sizes that are multiples of MCS-3. These groupings of EDGE MCS are called "families." MCS-3, MCS-6 and MCS-8 are also considered one family when the user payload of MCS-3 and MCS-6 are reduced enabling multiple blocks of these coding schemes to fit in one block of MCS-8. The reduced payload of MCS-3 and MCS-6 will need to be padded before coding when transmitting as a member of this family. Table 2 illustrates the organization of MCS into families. With these configurations, EDGE allows for the re-segmentation of the original data block for retransmission using a different coding scheme than the original data block's MCS. However, the new MCS chosen for the retransmission is limited to one of the member of the same family of the originally transmitted data block's MCS. Table 2: MCS Families Family Name Modulation Coding Schemes A MSC-3, MSC-6, MSC-9 A with MCS-3, MCS-6, MCS-8 padding B MCS-2, MCS-5, MCS-7 C MCS-1 and MCS-4
User Payload (octets) 37, 2x37, 4x37 34+padding, 2x (34+padding), 4*34 28, 2x28, 4x28 22, 2x22
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EDGE
The network automatically adapts the coding scheme according to the radio link quality. This adaptation is done automatically for the downlink, and the network commands the mobile station (mobile phone) to use the optimum MCS for the uplink. In order to perform this adaptation, the mobile station (for downlink transfer) and the base transceiver station [BTS] (for uplink transfer) carry out the radio link quality measurements (LQM), which are transmitted to the packet control unit service node (PCUSN). According to the radio link quality, the PCUSN can trigger a modification of the coding scheme. In EDGE, the LQM consist of the mean bit error probability (MEAN-BEP) and the coefficient of variance of the bit error probability (CV-BEP). The measurements are performed on every radio block and can be reported back to the network for filtering and triggering of MCS changes with improved reactivity and accuracy compared to GPRS. The link quality measurements provide an excellent indication of the radio environment and, in particular, the C/I and C/N. With the knowledge of the estimated C/I, the networks can trigger MCS adaptation to deliver the maximum throughput for the environment. Figure 38 illustrates the mapping of C/I to MCS and achievable throughput.
Figure 38: Throughput versus C/I for each MCS.
As indicated in Figure 38, MCS-9 does not provide the highest throughput in the entire range of C/I. In fact, each MCS is designed to deliver the optimal throughput in a range of C/I. In this respect, link adaptation (LA) provides the mechanism to optimize the end user throughput by selecting the most appropriate MCS scheme for the given radio conditions.
53
EDGE
To ensure a certain level of throughput at the cell edge, the network must provide the required level of C/I at cell edge. There would also be a similar requirement for C/N. Therefore, if the current network C/I and C/N design does not meet the required level of performance at the cell edge, then changes in site density and frequency planning are required to achieve the desired throughput. In practice, the network design and frequency plan would remain constant, and EDGE throughput at the cell edge and aggregate throughput throughout the entire cell will be based on the C/I and C/N distribution achieved with the current network design.
6.5 RLC/MAC Improvement The RLC/MAC layer is significantly improved with EDGE. In GPRS, the acknowledgement window used in the ARQ mechanism is limited to 64 RLC/MAC blocks. This limited window can quickly result in a stalling condition with handsets that support multiple time slots. The stalling condition occurs when an incorrectly received block has not been acknowledged before 64 new blocks have been transmitted. During the stalling condition, the transmitter stops transmitting new blocks until this oldest, unacknowledged block is successfully transmitted. Handsets capable of multiple time slots are more susceptible to this stalling condition because the 64-block buffer can quickly reach its limit with the increase in data rate capability. In EDGE this acknowledgement window size has been extended up to 1024 blocks depending on the MCS selected. This increase has significantly reduced the stalling window condition even for multiple time slots handset operating at higher MCS.
6.6 Implementation No new operator licenses are needed for EDGE and existing spectrum, carrier processes and cell planning can be used. Only one EDGE transceiver unit will need to be added to each cell. Software upgrades to the BSC and Base Stations can be carried out remotely. The new EDGE capable transceiver can also handle standard GSM traffic and will automatically switch to EDGE mode when needed. EDGE capable terminals will also be needed. Existing GSM terminals do not support the new modulation techniques and will need to be upgraded to use EDGE network functionality. Some EDGE capable terminals are expected to support high data rates in the downlink receiver only, whilst others will access EDGE in both uplink and downlinks and will therefore need greater terminal modifications to both the receiver and the transmitter parts. In addition, the TDMA industry association, the Universal Wireless Communications Corporation, has introduced what it calls EDGE Compact. This a spectrum efficient version of EDGE that will support the 384 kbits mandated packet data rates but will require only minimum spectral clearing and therefore could work for network operators with limited spectrum allocations. In fact, as a result of this, EDGE has been renamed Enhanced Data Rates for GSM and TDMA Evolution.
54
Index
Index 3π/8, 50 8PSK, 47
FDMA, 21 FEC, 21
A
G
ARFC, 22 ARFCN, 39 AUC, 11
Gateway GPRS Support Node, 11 Gb, 14 Gf, 19 GGSN, 11 GMSK, 28, 47, 48 Gn, 15 Gp, 15 GPRS MA, 40 Gr, 17 Gs, 19 GTP, 15 GTP-C, 17
B Base Station Subsystem, 7 Base Transceiver Stations, 7 BCCH, 35 BCS, 30 BSC, 7 BSS, 7 BSSGP, 14 BTS, 7
C C/I, 54 C/N, 54 CA, 39 CCU, 8 CDMA, 21 Class A, 4 Class B, 4 Class C, 5 CS-1, 25 CS-2, 25 CS-3, 25 CS-4, 25
D Downlink RLC, 34 Downlink RLC/MAC, 32
E EDGE, 47 EDGE Waveform, 50 EIR, 11 ETSI, 3
F
H HLR, 11 HSN, 39
I IMSI, 11 interfaces, 13 IP, 15
L LA, 56 LLC, 15
M MAIO, 39 MCS, 54 Multislot classes, 22
N NC0, 41 NC1, 41 NC2, 41 NS, 14
P PBCCH, 35 55
Index
PCCCH, 27 PCU, 7 PDTCH, 25, 30 Physical layer, 21 Planes, 13 PLL, 21 PSI, 35 PSI1, 36 PTCCH, 27
SACCH, 27 Serving GPRS Support Node, 10 SGSN, 9, 10 SI Message, 35 Signaling Plane, 15 SNDCP, 15 SS7, 11, 17
T
QoS, 5
TDMA, 21 Transmission Plane, 13 TRAU, 9
R
U
Reselection, 40 RFL, 21, 39 RLC, 43 RLC/MAC, 30 RXLEV, 42
UDP, 15 Um, 14 Uplink RLC, 34 Uplink RLC/MAC, 33
Q
S
V VLR, 11
56
PART 2 Universal Mobile Telecommunications System
Table of content Table of content.......................................................................................................................... 1 1 Introduction ........................................................................................................................ 3 2 WCDMA Radio Access ..................................................................................................... 4 2.1 Introduction ................................................................................................................ 4 2.1.1 FDMA ................................................................................................................ 4 2.1.2 TDMA ................................................................................................................ 5 2.1.3 CDMA................................................................................................................ 6 2.2 CDMA principles ....................................................................................................... 7 2.2.1 Spread spectrum ................................................................................................. 7 2.2.2 CDMA processing gain ...................................................................................... 8 2.2.3 Power control ..................................................................................................... 9 2.2.4 Soft handover ................................................................................................... 10 2.3 WCDMA .................................................................................................................. 10 2.3.1 Main parameters in WCDMA .......................................................................... 11 2.3.2 Discussion of the parameters............................................................................ 11 3 UMTS services and applications...................................................................................... 13 3.1 Bearer service........................................................................................................... 13 3.1.1 The End-to-End Service and UMTS Bearer Service ....................................... 14 3.1.2 Lower Level Bearer Services ........................................................................... 14 3.2 QoS classes............................................................................................................... 16 3.2.1 Conversational class ......................................................................................... 16 3.2.2 Streaming class................................................................................................. 18 3.2.3 Interactive class ................................................................................................ 18 3.2.4 Background class.............................................................................................. 20 3.3 Service capabilities with different terminal classes ................................................. 21 4 UMTS Architecture.......................................................................................................... 22 4.1 Introduction .............................................................................................................. 22 4.2 User Equipment........................................................................................................ 23 4.2.1 Mobile Equipment............................................................................................ 23 4.2.2 USIM................................................................................................................ 23 4.3 UTRAN architecture ................................................................................................ 24 4.3.1 Node B.............................................................................................................. 24 4.3.2 Radio Network Controller ................................................................................ 29 4.4 Core Network ........................................................................................................... 30 4.4.1 Serving Network Domain................................................................................. 31 4.4.2 Home Network Domain ................................................................................... 31 4.4.3 Transit Network Domain.................................................................................. 31 4.5 General Protocol Model for UTRAN terrestrial Interfaces...................................... 32 4.5.1 General ............................................................................................................. 32 4.5.2 Horizontal Layers............................................................................................. 32 4.5.3 Vertical planes.................................................................................................. 32 4.6 Iu, the UTRAN – CN interface ................................................................................ 34 4.6.1 Protocol Structure for Iu CS............................................................................. 34 Universal Mobile Telecommunication System
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4.6.2 Protocol Structure for Iu PS ............................................................................. 36 4.6.3 RANAP Protocol.............................................................................................. 37 4.6.4 Iu User Plane Protocol...................................................................................... 38 4.7 UTRAN Internal Interfaces ...................................................................................... 39 4.7.1 Iur Interface: RNC – RNC interface and the RNSAP signalling ..................... 39 4.7.2 Iub Interface: RNC – Node B interface and the NBAP signalling................... 41 5 UTRAN protocol LAYERS ............................................................................................. 42 5.1 Introduction .............................................................................................................. 42 5.1.1 Channels ........................................................................................................... 42 5.2 Air interface: 3G Physical layer ............................................................................... 44 5.2.1 Forward Error Correction encoding/decoding ................................................. 45 5.2.2 Radio measurement and indications to higher layers....................................... 47 5.2.3 Macro diversity distribution / combining and soft handover execution........... 48 5.2.4 Error detection on transport channel ................................................................ 48 5.2.5 Multiplexing transport channels and demultiplexing coded composite transport channels 48 5.2.6 Rate Matching .................................................................................................. 48 5.2.7 Mapping of CCTrCHs on physical channels.................................................... 49 5.2.8 Modulation/Demodulation ............................................................................... 50 5.2.9 Inner-loop power control.................................................................................. 50 5.2.10 RF processing................................................................................................... 51 5.3 Protocol Stack .......................................................................................................... 51 5.3.1 MAC layer........................................................................................................ 51 5.3.2 RLC .................................................................................................................. 60 5.3.3 RRC.................................................................................................................. 66 Index......................................................................................................................................... 68
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Introduction
1 Introduction UMTS(Universal Mobile Telecommunication System) also known as 3G, the third generation of mobile systems, is developed by ETSI within the ITU’s IMT-2000 framework. UMTS will offer the transmission of data rates up to 2 Mbit/s(micro cell). The support of 384 Kps for high-mobility applications in cellular environments is possible(macro cell). Packet data will be required to offer high data rate services in a spectrally efficient manner. Once UMTS will be fully implemented, terminals and UMTS phones will be constantly connected to the internet. It is expected that this year(2004) the mobile operators must have 30% of coverage. Every year they have to provide an increase of 10% whereby in 2007 there must be 80% of coverage. Until UMTS is fully implemented(real data not sure) , users will have a Dual mode(multi mode) device that switch to the currently available technology(mainly GPRS and EDGE) where UMTS is not (yet) implemented. These Dual mode devices are already available as a PCMCIA card(see figure 1.1). These multi-mode cards will perform transparent handover between UMTS and GSM/GPRS(EDGE)1 networks.
Figure 1.1: Multi mode UMTS/GPRS/GSM PCMCIA card.
UMTS has the support of many major telecommunications operators and manufacturers because it represents a unique opportunity to create a mass market for highly personalized and user-friendly mobile access to the Information Society. New mobile phones coexist in different forms. This paper doesn’t cover this item. The introduction of UMTS is a big investment. UMTS requires a new Radio Access Network which is interconnected with the GSM/GPRS Core Network(see UMTS architecture). This investments where also present for the implementation of the GSM network. The main difference here is that the licences of UMTS that are been sold are extremely high.
1 GSM/GPRS/(EDGE), EDGE is here put between brackets because we don’t speak about a new network. EDGE is an upgrade of the GPRS network
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WCDMA Radio Access
2 WCDMA Radio Access 2.1 Introduction The usage of the radio spectrum must be carefully controlled. Mobile cellular systems use various techniques to allow multiple users to access the same radio spectrum at the same time. In fact, many systems employ several techniques simultaneously, to have a hybrid access technique(see section about TDMA). In this section, different techniques will be explained. CDMA and WCDMA will be explained in more details afterwards. If you depict this abbreviation, the first word tells you what the access method is. The second word, ‘division’, lets you know that it splits calls based on that access method. The last part of each name is multiple access. This simply means that more than one user can utilize each cell. Figure shows the first three different Access method;
Figure 2.1: (a)FDMA, (b)TDMA, (c)CDMA
2.1.1 FDMA FDMA(Frequency Division Multiple Access) divides the spectrum available into several frequency channels. Each user is allocated 2 channels(one channel for the uplink direction and the other channel for the downlink direction). For example: A radio station sends its signal at different frequency within the available band. This Access technique is mainly for analogue transmission. While it is certainly capable of carrying digital information, FDMA is not considered to be an efficient method for digital transmission. The channel bandwidth used in most FDMA systems is typically low as each channel only needs to support a single user. FDMA is used as the primary subdivision of large allocated frequency bands and is used as part of most multi-channel systems. Figure 2.2 shows the allocation of bandwidth
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WCDMA Radio Access
Figure 2.2: Bandwidth allocation in FDMA
2.1.2 TDMA In TDMA(Time Division Multiple Access), the entire available bandwidth is used by one user, but only for short periods at a time. The frequency channel is divided into time slots, and these are periodically allocated to the same user so that other users can use other time slots. Separate time slots are needed for the uplink and the downlink.
Figure 2.3
GSM uses this access technology but in a somewhat different way. TDMA is used together with FDMA to subdivide the total available bandwidth into several channels(see figure 2.4). This is done to reduce the number of users per channel allowing a lower data rate to be used. This helps reduce the effect of delay spread on the transmission. The figure below shows the use of TDMA with FDMA. Each channel based on FDMA, is further subdivided using TDMA, so that several users can transmit of the one channel. This type of transmission technique is used by most digital second generation mobile phone systems. Consult the previous paper(GPRS & EDGE), for more information about the timeslot and Coding schemes.
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WCDMA Radio Access
Figure 2.4: hybrid FDMA/TDMA
2.1.3 CDMA Code Division Multiple Access (CDMA) is a spread spectrum technique. It doesn’t use frequency channels nor time slots like in FDMA and TDMA. With CDMA, the narrow band message is multiplied by a large bandwidth signal that is a pseudo random noise code (PN code). All users in a CDMA system use the same frequency band and transmit simultaneously. The transmitted signal is recovered by correlating the received signal with the PN code used by the transmitter. Figure 2.5 below shows the general use of the spectrum using CDMA.
Figure 2.5: CDMA
CDMA technology was originally developed by the military during World War II. For many years, spread spectrum technology was considered solely for military applications. However, with rapid developments in LSI and VLSI designs, commercial systems were starting to be used. Universal Mobile Telecommunication System
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WCDMA Radio Access
(If you dispose of the CD-rom of this paper, you can check out a short movie(55sec.) about CDMA.) The next section will discuss the CDMA access method in more details.
2.2 CDMA principles 2.2.1 Spread spectrum
2.2.1.1 Spreading Spread-spectrum transmission is a technique in which the user’s original signal is transformed into another form that occupies a larger bandwidth than the original signal would normally need. This transformation is known as spreading. The original data sequence is binary multiplied with a spreading code that typically has a much larger bandwidth than the original signal. This method is depicted in figure 2.6.
Figure 2.6: spreading of data with the spreading code
2.2.1.2 Despreading The bits in the spreading codes are called chips to differentiate them from the bits in the data sequence, which are called symbols. The term “chip” describes how the spreading operation chops up the original data stream into smaller parts, or chips. Each user has its own spreading code. The identical code is used in both transformations on each end of the radio channel, spreading the original signal to produce a wideband signal, and dispreading the wideband signal back to the original narrowband signal. This method is depicted in figure 2.7.
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WCDMA Radio Access
Figure 2.7: despreading of the spread signal with the spreading code
2.2.2 CDMA processing gain The ratio between the transmission bandwidth and the original bandwidth is called the processing gain.
Where BWRF is the transmitted bandwidth after the data is spread, and BWinfo is the bandwidth of the information data being sent. The spreading codes are unique, at least at the cell level. This means that once a user despreads the received wideband signal, the only component to despread is the one that had been spread with the same code in the transmitter. Two types of spreading codes are used in the UTRAN(UMTS Access Network, see later): orthogonal codes and pseudo-noise codes. Figure 2.8 below shows the process of a CDMA transmission. The data to be transmitted (a) is spread before transmission by modulating the data using a PN code. This broadens the spectrum as shown in (b). In this example the process gain is 125 as the spread spectrum bandwidth is 125 times greater the data bandwidth. Part (c) shows the received signal. This consists of the required signal, plus background noise, and any interference from other CDMA users or radio sources. The received signal is recovered by multiplying the signal by the original spreading code. This process causes the wanted received signal to be despread back to the original transmitted data. However, all other signals that are uncorrelated to the PN spreading code become more spread. The wanted signal in (d) is then filtered removing the wide spread interference and noise signals.
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WCDMA Radio Access
Figure 2.8: Basic CDMA transmission
The described multiple access fully distinguishes CDMA from other multiple access systems. This makes the radio resource management of CDMA very challenging, since there is no absolute upper limit on the number of users that can be supported in each cell. This feature of CDMA is also called soft capacity. If the users are allowed to enter the system without any restrictions, the interference may increase to intolerable levels, thus damaging the quality of reverse links by causing power outage of some terminals. This thesis tries to find an efficient way to limit the number of uplink calls in order to improve the performance of the system. In general, the maximum number of users depends on many factors. These include interference that is generated at the base station by all the uplinked signals from own cell and other cells, and the propagation conditions which consist of path loss, shadowing and fast-fading. The components of the total interference are cross-correlation interference of users' signals and background noise. Overall, the CDMA systems are interference limited. As described above, CDMA systems have limitations due to interference, and a brief summary is given next of the elements and technical solutions that are fundamental for the performance of a real CDMA network.
2.2.3 Power control Combats near-far problem. That is a situation, in which a mobile device close to a base station is received at higher power than a mobile located further away. Consequently, the reception of the mobile device's transmission is blocked. Power control solves this by increasing the output power as the mobile moves away from the base station, and by decreasing the transmit power as the mobile moves closer to the base station. Power control measures the signal-toUniversal Mobile Telecommunication System
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WCDMA Radio Access
interference ratio (SIR) and sends commands to the transmitter on the other end to adjust the transmission power accordingly. Power control is used in both directions in CDMA.
2.2.4 Soft handover Handover (handoff) is the action of switching a call in progress from one cell to another without interruption when a mobile station moves from one cell to another. Neighbouring cells in FDMA and TDMA cellular systems do not use the same frequencies. In those systems, a mobile station performs a hard handover when the signal strength of a neighbouring cell exceeds the signal strength of the current cell with some threshold. In CDMA systems, the universal frequency reuse with factor of one is used. Thus, the previous approach would cause excessive interference in the neighbouring cells. Neither is it feasible to perform an instantaneous handover, which would naturally solve this problem. The solution in CDMA systems is soft handover (soft handoff), in which a mobile user may receive and send the same call simultaneously from and to two or more base stations. In this way, the transmission power of a mobile can be controlled by the prevailing base station that receives the strongest signal.
2.3 WCDMA W-CDMA(Wideband Code Division Multiple Access) is one of the main technologies for the implementation of third-generation (3G) cellular systems. It is based on radio access technique proposed by ETSI Alpha group and the specifications was finalised 1999.
Figure 2.9: WCDMA
The implementation of W-CDMA will be a technical challenge because of it's complexity and versatility. The complexity of W-CDMA systems can be viewed from different angles: the Universal Mobile Telecommunication System
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WCDMA Radio Access
complexity of each single algorithm, the complexity of the overall system and the computational complexity of a receiver. W-CDMA link-level simulations are over 10 times more compute-intensive than current second-generation simulations. In W-CDMA interface different users can simultaneously transmit at different data rates and data rates can even vary in time. UMTS networks need to support all current second generation services and numerous new applications and services.
2.3.1 Main parameters in WCDMA The following table(2.1) gives a short list of the main parameters: Multiple access method Duplexing method Base station synchronization Chip rate Frame length Service multiplexing Multirate concept Detection Multi-user detection, antennas
DS-CDMA FDD / TDD Asynchronous operation 3.84 Mcps 10ms Multiple services with different quality of service requirements multiplexed on one connection Variable spreading factor Coherent using pilot symbols or common pilot smart Supported by the standard, optional in the implementation
Tabel 2.1: main parameters of WCDMA
2.3.2 Discussion of the parameters The following section gives a closer look to these parameters. WCDMA is a wideband Direct-sequence code division multiple access(DS-CDMA) system, i.e. user information bits is spread over a wide bandwidth by multiplying the user data with quasi-random bits(called chips) derived from CDMA spreading codes. In order to support very high bit rate(up to 2Mbps), the use of a variable spreading factor and multicode connection is supported. The chip rate of 3.84 Mcps2 used leads to a carrier bandwidth of approximately 5 Mhz. The inherently wide carrier bandwidth of WCDMA supports high user data rates and also has certain performance benefits, such as increased multipath diversity. Subject to this operating licence, the network operator can deploy multiple such 5Mhz carriers to increase capacity, possible in the form of hierarchical cell layer. WCDMA support highly variable user data rates, in other words the concept of obtaining Bandwidth on Demand(BoD) is well supported. Each user is allocated frames of 10 ms 2
Mega chip per second
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WCDMA Radio Access
duration, during which the user data rate is kept constant. However, the data capacity among the users can be change from frame to frame. WCDMA support two basic modes of operation: Frequency Division Duplex(FDD) and Time Division Duplex(TDD). In the FDD mode, separate 5Mhz carrier frequencies are used for the uplink and the downlink respectively, whereas in TDD only one 5Mhz is time-shared between uplink and downlink. Uplink is the connection from the mobile to the base station(node B), and downlink is that from the base station(Node B) to the mobile. The TDD mode is based heavily on FDD mode concept. WCDMA support the operation of asynchronous base stations, so that (unlike in the synchronous IS-95 system) there is no need for a global time reference, such as GPS. WCDMA employs coherent detection on uplink and downlink based on the use of pilot symbols or common pilot. The WCDMA air interface has been crafted in such a way that advanced CDMA receiver concept, such as multi-user detection and smart adaptive antennas, can be deployed by the network operator as a system option to increase capacity and or coverage. WCDMA is designed to be deployed in conjunction with GSM. Therefore, handovers between GSM and WCDMA are supported in order to be able to leverage the GSM coverage for the introduction of WCDMA.
Figure 2.10
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UMTS services and applications
3 UMTS services and applications 3.1 Bearer service Network Services are considered end-to-end, this means from a Terminal Equipment (TE) to another TE. An End-to-End Service may have a certain Quality of Service (QoS) which is provided for the user of a network service. It is the user that decides whether he is satisfied with the provided QoS or not. To realise a certain network QoS a Bearer Service with clearly defined characteristics and functionality is to be set up from the source to the destination of a service. A bearer service includes all aspects to enable the provision of a contracted QoS. These aspects are among others the control signalling, user plane transport and QoS management functionality. The layered architecture of a UMTS bearer service is depicted in figure 3.1; each bearer service on a specific layer offers its individual service using those provided by the layers below.
Figure 3.1: layered architecture of a UMTS bearer service
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UMTS services and applications
3.1.1 The End-to-End Service and UMTS Bearer Service
Figure 3.2
On its way from the TE to another TE the traffic has to pass different bearer services of the network. A TE is connected to the UMTS network by use of a Mobile Termination (MT). The End-to-End Service on the application level uses the bearer services of the underlying network. The End-to-End-Service used by the TE will be realised using a TE/MT Local Bearer Service, a UMTS Bearer Service, and an External Bearer Service(see figure). The UMTS operator offers services provided by UMTS Bearer Service. Thus, UMTS Bearer Service provides the UMTS QoS.
3.1.2 Lower Level Bearer Services
3.1.2.1 The Radio Access Bearer Service and the Core Network Bearer Service
Figure 3.3
The UMTS Bearer Service consists of two parts, the Radio Access Bearer Service and the Core Network Bearer Service. Both services reflects the optimised way to realise the UMTS Bearer Service over the respective cellular network topology taking into account such aspects as e.g. mobility and mobile subscriber profiles. The Radio Access Bearer Service provides confidential transport of signalling and user data between MT and CN Iu Edge Node with the QoS adequate to the negotiated UMTS Bearer Service or with the default QoS for signalling. This service is based on the characteristics of the radio interface and is maintained for a moving MT. Universal Mobile Telecommunication System
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UMTS services and applications
The Core Network Bearer Service of the UMTS core network connects the UMTS CN Iu Edge Node with the CN Gateway to the external network. The role of this service is to efficiently control and utilise the backbone network in order to provide the contracted UMTS bearer service. The UMTS packet core network shall support different backbone bearer services for variety of QoS.
3.1.2.2 The Radio Bearer Service and the Iu Bearer Service
Figure 3.4
The Radio Access Bearer Service is realised by a Radio Bearer Service and an Iu-Bearer Service. The role of the Radio Bearer Service is to cover all the aspects of the radio interface transport. This bearer service uses the UTRA FDD/TDD. The Iu-Bearer Service together with the Physical Bearer Service provides the transport between UTRAN and CN. Iu bearer services for packet traffic shall provide different bearer services for variety of QoS.
3.1.2.3 The Backbone Network Service
Figure 3.5
The Core Network Bearer Service uses a generic Backbone Network Service. The Backbone Network Service covers the layer 1/Layer2 functionality and is selected according to operator’s choice in order to fulfil the QoS requirements of the Core Network
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UMTS services and applications
Bearer Service. The Backbone Network Service is not specific to UMTS but may reuse an existing standard.
3.2 QoS classes When defining the UMTS QoS classes the restrictions and limitations of the air interface have to be taken into account. It is not reasonable to define complex mechanisms as have been in fixed networks due to different error characteristics of the air interface. The QoS mechanisms provided in the cellular network have to be robust and capable of providing reasonable QoS resolution. In the proposal there are four different QoS classes (or traffic classes): • • • •
Conversational class, Streaming class, Interactive class, Background class.
The main distinguishing factor between these classes is how delay sensitive the traffic is: Conversational class is meant for traffic which is very delay sensitive while Background class is the most delay insensitive traffic class. In the initial phase of UMTS the conversational and streaming classes will be transmitted as real-time connections over the WCDMA air interface, while the interactive and background classes are transmitted as scheduled non-real-time packet data.
3.2.1 Conversational class The best-known application of this class is speech service over circuit-switched bearers. With internet and multimedia, a number of new applications will require this type, for example voice over IP and video telephony. Real-time conversation is always performed between peers of live end-users. This is the only type of the four classes where the required characteristics are strictly imposed by human perception. Real-time conversation is characterised by the fact that the end-to-end delay is low and the traffic is symmetric or nearly symmetric. The maximum end-to-end delay is given by the human perception of video and audio conversation.
3.2.1.1 The AMR speech service The AMR speech coder consists of the multi-rate speech coder, a source controlled rate scheme including a voice activity detector and a comfort noise generation system, and an error concealment mechanism to combat the effects of transmission errors and lost packets. The multi-rate speech coder is a single integrated speech codec with eight source rates from 4.75 kbit/s to 12.2 kbit/s, and a low rate background noise encoding mode. The speech coder is capable of switching its bit-rate every 20 ms speech frame upon command. AMR adapts the error protection level to the local radio channel and traffic conditions so that it always selects the optimum channel and codec mode (speech and channel bit rates) to Universal Mobile Telecommunication System
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UMTS services and applications
deliver the best combination of speech quality and system capacity. AMR has 8 coded modes in UMTS system (in GSM AMR uses either 6 or 8 modes) and it is possible to operate on a set of up to 4 codec modes, which are selected at call setup phase or handover. AMR encoded bits are divided to three indicative classes according to their importance: A, B and C. Class A contains the bits that are most sensitive to errors and any kind of error in these bits typically results the in a corrupted speech frame which should not be decoded without applying appropriate error concealment. This class is protected by the CRC in AMR Auxiliary information. Class B and C contains bits where increasing error rates gradually reduce the speech quality, but the decoding of an erroneous speech frame is usually possible without annoying artifacts. As presented previously the AMR speech codec adapts its error protection level existing radio conditions and this flexibility provides a number of important benefits: • Improved speech quality in means of codec mode adaptation i.e. by varying the balance between speech and channel coding for the same gross bit-rate • The ability to trade speech quality and capacity smoothly and flexibly by a combination of channel and codec mode adaptation; this can be controlled by the network operator on a cell by cell basis • Improved robustness to channel errors under marginal radio signal conditions • Ability to tailor AMR operation to meet the different needs of operators • Potential for improved handover and power control resulting from additional signalling transmitted rapidly in-band Frame structure: AMR frame is divided into three parts: AMR header, AMR Auxiliary Information and AMR core frame. The AMR header part includes the Frame Types and the Frame Quality Indicator fields. The AMR Auxiliary information part includes the Mode Indication, Mode Request, and Codec CRC fields. The AMR Core Frame part consists of the speech parameter bits, or in case of a comfort noise frame, the comfort noise parameter bits. In case of a comfort noise frame, comfort noise parameters replace Class A bits of AMR Core Frame while Class B and C bits are omitted.
3.2.1.2 Video Telephony Video telephony has similar delay requirements to speech services. Due to the nature of video compression, the BER(Bit Error Rate) requirement is more stringent that of speech. UMTS has specidied that ITU-T Rec.H.324M should be used for video telephony in CS connections. At the moment there are two video telephony codecs for PS connections: ITU-T REC.H323 and IETF SIP.
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UMTS services and applications
3.2.2 Streaming class Multimedia streaming is a technique for transferring data such that it can be processed as a steady and continuous stream. Streaming technologies are becoming increasingly important with the growth of the internet because most users do not have fast enough access to download large multimedia files quickly. While streaming, the client browser or plug-in can start displaying the data before the entire file has been transmitted.
3.2.3 Interactive class When the end-user, either a machine or a human, is on line requesting data from remote equipment, this scheme applies. Interactive traffic is the other classical data communication scheme that is broadly characterised by the request response pattern of the end-user. At the message destination there is an entity expecting the message(response) within a certain time. Round-trip delay time is therefore one of the key attributes.
3.2.3.1 Location-based services UMTS networks will support location service features, to allow new and innovative location based services to be developed. It will be possible to identify and report in a standard format (e.g. geographical co-ordinates) the current location of the user's terminal and to make the information available to the user, ME, network operator, service provider, value added service providers and for PLMN3 internal operations. The location is provided to identify the likely location of specific MEs. This is meant to be used for charging, location-based services, lawful interception, emergency calls, etc., as well as the positioning services. Location Information consists of: • Geographic Location • Velocity (the combination of speed and heading ) • Quality of Service information (horizontal & vertical accuracy and response time) LCS Client: a software and/or hardware entity that interacts with a LCS Server for the purpose of obtaining location information for one or more Mobile Stations. LCS Clients subscribe to LCS in order to obtain location information. LCS Clients may or may not interact with human users. The LCS Client is responsible for formatting and presenting data and managing the user interface (dialogue). The LCS Client is identified by a unique international identification, e.g. E.164, number or Access Point Name (APN). 3
A way to group UMTS network elements is to devide them into sub-networks. The possibility of having several entities of the same type allows the division of the UMTS system into sub-networks that are operational either on their own or together with other sub-networks, an that are distinguished from each other with unique identities. Such a sub-network is called a UMTS PLMN(Public Land Mobile Network).
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UMTS services and applications
A LCS Client is a logical functional entity that makes a request to the PLMN LCS server for the location information of one or more than one target UEs. A LCS server consists of a number of location service components and bearers needed to serve the LCS clients. The LCS server shall provide a platform which will enable the support of location based services in parallel to other telecommunication services such as speech, data, messaging, other teleservices, user applications and supplementary services. Using the Location Service Request, an LCS client communicates with the LCS server to request the location information for one or more target UEs within a specified set of quality of service parameters. As shown in below, a location service may be specified as immediate or deferred. Request Type
Response Time
Number of responses
Immediate
Immediate
Single
Deferred
Delayed
One or More
Location Service Requests The LCS Server will provide, on request, the current or most recent Location Information (if available) of the Target UE or, if positioning fails, an error indication plus optional reason for the failure. For emergency services (where required by local regulatory requirements), the geographic location may be provided to an emergency services LCS Client either without any request from the client at certain points in an emergency services call (e.g. following receipt of the emergency call request, when the call is answered, when the call is released) or following an explicit request from the client. The former type of provision is referred to as a “push” while the latter is known as a “pull”. Type of access
Information Items
Push
Current Geographic Location (if available) MSISDN IMSI IMEI NA-ESRK NA-ESRD State of emergency call: – unanswered, answered, released
Pull
Geographic location, either: Current location - Initial location at start of emergency call
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The specification Release '99(see later) specifies the following LCS positioning methods: • Cell coverage based positioning method • Observed Time Difference Of Arrival (OTDOA) method with network configurable idle periods • Network assisted GPS methods
OTDOA Location Method
3.2.4 Background class Data traffic of application such as e-mail delivery, SMS, downloading of database and reception of measurement records can be delivered background since such applications do not require immediate action. The delay may be seconds, tens of seconds or even minutes. Background traffic is one of the classical data communication schemes that is broadly characterised by the fact that the destination is not expecting the data within a certain time. It is thus more or less intesitive to delivery time. Another characteristic is that the content of the packets does not need to be transparently transferred. Data to be transmitted has to be received error free.
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3.3 Service capabilities with different terminal classes WCDMA terminals shall tell the network, upon connection set up, larger set of parameters indicating the radio access capabilities of the particular terminal. For example what is the maximum user data rate supported in particular radio configuration. • • • • • •
32 kbps class: This is intended to provide basic speech service, including AMR speech as well as some limited data rate capabilities up to 32 kbps. 64 kbps class: This is intended to provide speech and data service, with also simultaneous data and AMR speech capability. 144 kbps class: This class has the air interface capability to provide for example video telephony or then various other data services. 384 kbps class 768 kbps class: This class has been defined as an intermediate step between 384 kbps and 2 Mbps class. 2 Mbps class: This class has been defined for downlink direction only.
These classes are defined so that a higher class has all the capabilities covered by a lower class.
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UMTS Architecture
4 UMTS Architecture 4.1 Introduction The UMTS system utilises the same architecture/principle that has been used by all main second generation system and even by some first generation systems. The UMTS system consists of a number of logical network elements that each has a defined functionality. In the standards, network elements are defined at the logical level, but this quite often results in a similar physical implementation, especially since there are a defined to such a number of open interfaces. There are three kinds of interfaces in the UMTS/GSM network. The first category contains those interfaces that are truly open. This means that they are well-specified, and the specification is such that the equipment on different ends of the interface can be acquired from different manufacturers. The second category includes those interfaces that are specified at some level, but the interface is still proprietary. The equipment for such interfaces must come from the same manufacturer. The third category contains those interfaces for which there is no specification at all. Functionally the network elements are grouped into the UTRAN(UMTS Terrestrial Radio Access Network) and the CN(Core Network). The UTRAN handles all radio-related and mobility functionalities and the CN is responsible for switching and routing calls and data connections to external networks. Figure 4.1 shows a simplified UMTS architecture with its basic domains and external reference points and interfaces to the UTRAN. A basic architectural split is between the user equipment (terminals) and the infrastructure. This results in two domains (in this context a domain is the highest-level group of physical entities; reference points are defined between domains), the User Equipment domain and the Infrastructure domain.
Figure 4.1: UMTS-Architecture
User equipment is the equipment used by the user to access UMTS services. User equipment has a radio interface to the UTRAN, this interface is termed Uu reference point. Universal Mobile Telecommunication System
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The UTRAN is connected to the Core Network through the Iu reference point.
4.2 User Equipment This domain encompasses a variety of equipment types with different levels of functionality. These equipment types are referred to as user equipment4 (terminals), and they may also be compatible with one or more existing access (fixed or radio) interfaces e.g. dual mode UMTS/GPRS/GSM user equipment. The user equipment may include a removable smart card that may be used in different user equipment types. The user equipment is further subdivided in to the Mobile Equipment Domain (ME) and the User Services Identity Module Domain (USIM). The reference point between the ME and the USIM is termed the “Cu” reference point.
Figure 4.2: User Equipment
4.2.1 Mobile Equipment The Mobile Equipment performs radio transmission and contains applications. The mobile equipment may be further subdivided into several entities, e.g. the one which performs the radio transmission and related functions, Mobile Termination (MT), and the one which contains the end-to-end application (e.g. laptop connected to a mobile phone), Terminal Equipment (TE).
4.2.2 USIM The USIM contains data and procedures which identify itself. These functions are typically embedded in a stand alone smart card. This device is associated to a given user, and as such allows to identify this user regardless of the ME he uses.
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4.3 UTRAN architecture
Figure 4.3: UMTS architecture
The UTRAN consists of a set of Radio Network Subsystems (RNS), which are the access parts of the UMTS network (comparison to GSM: RNS is analogue to the Base Station System - BSS). A RNS offers the allocation and the release of specific radio resources to establish means of connection in between an UE and the UTRAN. A RNS is connected to the Core Network through the reference interconnection point Iu. Each RNS consists of a Radio Network Controller (RNC) and one or more Node Bs (the RNC has the same general function like a Base Station Controller(BSC) in GSM and a Node B could be compared with the Base Transceiver System(BTS) in GSM).
4.3.1 Node B A Node B is a logical node responsible for radio transmission / reception in one or more cells to / from the UE, in other words it can be considered as a network component which serves one cell. The term ‘Node B’ was initially adopted as a temporary term during the standardisation process, but the never changed.
4
Several names are used to indicate a mobile node, this paper will use UE.
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Figure 4.4: UMTS, GSM/GPRS network
As you can see in figure 4.4 , operators must install new base stations(node B) to perform UMTS. Some vendors are working on a multi-standard base station for GSM/GPRS and UMTS. This is not a problem for GPRS because it uses the same base station as GSM. The following section describes the importance to use/deploy a multi-standard base station.
4.3.1.1 Benefits Space requirement In a multi-standard environment GSM and UMTS share the same base station. Therefore it is possible to reduce the number of base station installed on site in line with the capacity needed on the air interface, thus cutting the initial investment required to deploy a mobile network. Operation Everyone trained to use the GSM BTS will feel at home with a multi-standard base station. This will cut maintenance and installation times, and reduce operating costs. Co-existence of UMTS and GSM Multi-standard equipment in which UMTS and GSM modules share the same base station ensures that all the problems have been studied and solved. Universal Mobile Telecommunication System
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Multi-standard site Designing a multi-standard base station leads to an “embedded” solution that makes optimal use of common equipment and batteries. This result in a multi-standard site on which GSM and UMTS equipment can coexist. Common modules The development of common modules allows both applications to benefit from the same technology at the same time.
4.3.1.2 Merging of two standards and technology challenge The features of the multi-standard base station architecture are: •
Merging of two standard(UMTS FDD and GSM/GPRS(EDGE)) into a common BTS: There are numerous existing GSM BTS. Thus there is a strong need for a multistandard GSM/UMTS base station that offers the same flexibility as the established GSM BTS. • Use of ATM for transport, with the option of evolution to IP as the transport protocol • Installing of UMTS modules in an exciting GSM BTS.
4.3.1.3 The multi-standard BTS architecture
Figure 4.5: multi-standard BTS Node B
Figure 4.5 shows all the interfaces that should be supported, taking into account all the possible environments for a multi-Standard Base Station in terms of applications and transport solutions. On the left side of the figure are the network interfaces and the logical interfaces to a common OMC(Operation and Maintenance Centre) for both standards. On the right side of the figure are the two air interfaces to the GSM mobile station and to the Universal Mobile Telecommunication System
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UMTS UE. In addition there is a local maintenance terminal connected to the multi-standard Base Station.
Figure 4.6
Figure 4.6 shows the main functions of the UMTS base station(Node B). The blue parts are UMTS elements while the multicoloured parts are multi-standard elements. Basic Telecom functions There are three main telecom related parts within a Node B: the transmission part to the outside world on the fixed line interface (Iu-b in UMTS), the transmission part to the user equipment via the air interface (Uu in UMTS) and the signal processing part between both interfaces. Node B could be viewed as a modem translating an incoming signal on one side to an outgoing signal on the other side. Basic architecture of the UMTS part
Figure 4.7
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Figure 4.7 shows the architecture of Node B in the multi-standard environment for transmit and receive diversity. On the left is the traffic independent Station Unit Module (SUM) which is responsible for central operations and maintenance of the base station (including GSM in the multi-standard configuration), clock generation and distribution, the external transmission interfaces (Iu-b and Abis) including circuit and ATM add/drop, and translation between the external and internal formats. The pure signal processing part, seen as a pool of processing resources, is realized in Base Band (BB) modules 1 to N, of which sufficient are equipped to support the required traffic capacity on the number of channels provided for this Node B. The main functional blocks of a BB module are: • • • •
frame protocol termination transmit/receive symbol processing transmit/receive chip processing higher layer protocol termination.
On the downlink, each BB module must be able to deliver the broadband signals for up to four carriers to support multi-carrier operation. Where there is a need to support only a very low traffic capacity, a low cost configuration can be realized by equipping just one BB board, as well as the common control channel functions for all the considered sectors (equivalent to one frequency or cell). In the case of UMTS, an Interconnection between the BB modules is required in the downlink direction: • •
At chip rate level after the transmit spreading function. Interconnection of transmission power control and transmit load control when processing of the shared downlink channel is allocated to another BB module as its associated dedicated channel.
In the uplink direction, each BB module needs physical access to the uplink BB signals of all receiver parts within the Antenna Network Receivers for UMTS (ANRU) of each sector (realized in the receive interconnection device) for the following reasons: • •
Receive antenna diversity: two receive functions in one ANRU. Softer handover: soft combining of BB signals from receivers which can belong to different ANRUs.
The radio part is subdivided Into two parts: • Transmitter Equipment for UMTS (TE U). • Antenna receiver for UMTS. The TEU is a multi-carrier module that supports a set of transmit paths. Including the diversity function. It handles all the functions on the downlink (transmit direction) from BB filtering to the RF frequency domain. Including power amplification. Similarly, the ANRU is a multi-carrier module, but it supports a set of receive paths, including the diversity function. It handles all the functions on the uplink (receive direction) Universal Mobile Telecommunication System
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from RF down to base band (two times available for diversity). In addition, the ANRU includes a duplexer to mix the transmit and receive paths on the same feeder. The GSM part is also shown in Figure 4.7 with its transceiver equipment and antenna network with combiner, which is part of the GSM module block. The GSM and UMTS parts use the same internal operations and maintenance interface, but different data interfaces between the Station Unit Module Universal (SUMU) and transceiver equipment or SUMU and BB because of the different bandwidth requirements.
4.3.2 Radio Network Controller The RNC(Radio Network Controller) has the overall control of the logical resources of its Node B’s and it is also responsible for the Handover decisions that require signalling to the UE. The Node B supporting the FDD mode can comprise an optional combining/splitting function to support macro diversity inside a Node B. A Node B is connected to the RNC through the Iub interface. Inside the UTRAN, the RNCs of the Radio Network Subsystems can be interconnected together through the Iur. Iur is a physical direct connection between RNCs. The Iur interface is needed to support Macro diversity. If this interface wasn’t implemented, it could be done through the core network. This is actually not the idea behind the RNC. The RNC is actually implemented to avoid mobility functionalities in the Core Network. Each RNS is responsible for the resources and transmission/reception in a set of cells. The RNC controlling one node B is indicating as the controlling RNC(CRNC) of the Node B. The controlling RNC is responsible for the load and congestion control of its own cells and also executes the admission control and code allocation for new radio links to be established in those cells. For each connection between a UE and the UTRAN, one RNS is the Serving RNC. The Serving RNS is in charge of the radio connection between a UE and the UTRAN. The Serving RNS terminates the Iu for this UE. When required, Drift RNSs support the Serving RNC by providing radio resources when the connection between the UTRAN and the UE need to use cell(s) controlled by this RNS is referred to as Drift RNS.
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Figure 4.8: Serving RNC and Drift RNC
4.4 Core Network The Core Network consists of the physical entities which provide support for the network features and telecommunication services. It is actually the Backbone that will rout the calls and the packets. The core network domain can be subdivided into the Home Network Domain, Serving Network Domain and the Transit Network Domain. Figure 4.10 shows the interface Zu between the Home Network Domain and the Serving Network Domain. Yu is the interface between Serving Network Domain and Transit Network Domain.
Figure 4.9: Core network
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After the implementation of the GPRS network, the CN can be subdivided in Packet Switched Domain(GPRS) and the Circuit Switched Domain(GSM). UEs can have both services implemented or only PS or CS.
4.4.1 Serving Network Domain The serving network domain is the part of the core network domain to which the access network domain that provides the user’s access is connected. It represents the core network functions that are local to the user’s access point and thus their location changes when the user moves. The serving network domain is responsible for routing calls and transport user data/information from source to destination. It has the ability to interact with the home domain to cater for user specific data/services and with the transit domain for non user specific data/services purposes.
4.4.2 Home Network Domain The home network domain represents the core network functions that are conducted at a permanent location regardless of the location of the user’s access point. The USIM is related by subscription to the home network domain. The home network domain therefore contains at least permanently user specific data and is responsible for management of subscription information. It may also handle home specific services, potentially not offered by the serving network domain.
4.4.3 Transit Network Domain The transit network domain is the core network part located on the communication path between the serving network domain and the remote part. If, for a given call, the remote part is located inside the same network as the originating UE, then no particular instance of the transit domain is activated.
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4.5 General Protocol Model for UTRAN terrestrial Interfaces 4.5.1 General The general protocol model for UTRAN Interfaces is shown in figure 4.10. The Layers and the planes are logically independent of each other. This has the advantage that protocol stacks and planes can be implemented to conform further requirements.
Figure 4.10: General Protocol Model for UTRAN Interfaces
4.5.2 Horizontal Layers Figure 4.10 shows two main layers: the Radio Network Layer and the Transport Network Layer. All UTRAN related issues are visible only in the Radio Network Layer, and the Transport Network Layer represents standard transport technology that is selected to be used for UTRAN.
4.5.3 Vertical planes The Vertical plane can be divided into two main parts: The control planes, which is responsible for the transmission of non-user data and the User Plane, which is responsible for the transmission of the user data, the information itself.
4.5.3.1 Control planes The Control Plane is used for all UMTS specific control signalling. The Control Plane Includes the Application Protocol(i.e. RANAP in Iu, RNSAP in Iur or NBAP in Iub, and the Universal Mobile Telecommunication System
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Signalling Bearer for transporting the Application Protocol messages). The application protocol is used, among other things, for setting up bearers to the UE. Transport Network Control Plane The Transport Network Control Plane is used for all control signalling within the Transport Layer. It does not include any Radio Network Layer information and is completely in the Transport Layer. It includes the ALCAP protocol that is needed to set up the transport bearers (Data Bearer) for the User Plane. It also includes the appropriate Signalling Bearer needed for the ALCAP protocol. The Transport Network Control Plane is a plane that acts between the control plane and the User Plane. The introduction of the Transport Network Control Plane makes it possible for the Application Protocol in the Radio Network Control Plane to be completely independent of technology selected for the Data Bearer in the User Plane. When the transport Network control plane is used, the transport bearers for the Data Bearer in the User Plane are set up in the following fashion. First there is a signalling transaction by the application protocol in the control plane, which triggers the setup of the Data Bearer by the ALCAP protocol that is specific for the User Plane technology. The independence of the Control Plane and the User Plane assumes that an ALCAP signalling transaction takes place. It should be noted that ALCAP might not be used for all types of Data Bearers. If there is no ALCAP signalling transaction, the Transport Network Control Plane is not used for setting up the signalling Bearer for the Application Protocol or for the ALCAP during real-time operation.
4.5.3.2 User planes All information sent and received by the user, such as the coded voice in a voice call or the packets in an internet connection, are transported via the User Plane. The User Plane Includes the Data Stream and the Data Bearer for the Data Stream. Each Data Stream is characterised by one or more frame protocols specified for that interface. Transport Network User Plane The Data Bearer in the User Plane and the Signalling Bearer for the Application Protocol, also belong to the Transport Network User Plane. The Data Bearers in the Transport Network User Plane are directly controlled by the Transport Network Control Plane during real-time operation, but the control actions required for setting up the Signalling Bearer for the application Protocol are considered O&M actions.
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4.6 Iu, the UTRAN – CN interface The Iu is the interface between the UTRAN and the CN. It is an open interface that devides the system into radio specific UTRAN and CN which handles switching, routing and service control. The Iu needs to have two types; the Iu CS and Iu PS. Both to connect respectively UTRAN to Circuit Switched CN(which was implemented for the GSM network) and UTRAN to Packet switched CN(which was an hardware upgrade of the GSM network).
4.6.1 Protocol Structure for Iu CS The three planes in the Iu interface share a common ATM(asynchronous transfer mode) transport which is used for all planes. ATM is a transmission procedure based on asynchronous time division multiplexing using small, fixed length packets. These data packets have a length of only 53 bytes5, of which 5 bytes are for the packet header and 48 bytes are reserved for the payload(the information itself). The fixed packet length makes it possible to use very efficient and fast packet switches. Filling up long ATM packets with speech samples yields delay, wich reduce the quality of real-time speech transmission. Thus, the shorter the packet, the better it suits speech transfer. However, pure non-real-time data transfer would be more efficient if longer packets were used. The length of 53 bytes was a suitable compromise as it allows real-time speech transmission, but doesn’t hamper data transmission speeds too much. Also, the 5 byte header doesn’t represent too mush overhead if the payload is 48 bytes. The physical layer is the interface to the physical medium. The Iu CS overall protocol is shown in figure 4.11 and are explained in the following sections. 5
The chosen packet length(53 bytes) was a comprise between the requirements of speech transfer and data transmission.
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Figure 4.11: Iu CS protocol structure
4.6.1.1 Iu CS Control Plane Protocol Stack The Control Plane protocol stack consists of RANAP on top of the Broad Band SS7 protocols which contains all the control information specified for the Radio Network Layer. Other layers are Signalling Connection Control Part(SCCP), Message Transfer Part (MTP3-b), Signalling ATM Adaptation Layer for Network to Network Interfaces (SAAL-NNI), Service Specific Co-ordination Function (SSCF), Service Specific Connection Oriented Protocol (SSCOP) and ATM Adaptation Layer 5 (AAL5). RANAP provides the signalling service between the UTRAN and the CN that is required to fulfil the RANAP functions(see 4.6.3 for more details). Two message transfer service classes are used in the SSCF layer: class 0 and class 2. Class 0 provides a connectionless service and class 2 a connection oriented service. The MTP provides message routing, discrimination and distribution, signalling link management and load sharing. SSCF and SSCOP layers are specifically designed for signalling transport in ATM networks, and take care of such functions as signalling connection management. The SSCOP defines mechanisms for the connection establishment, release and reliable exchange of signalling information between signalling entities. The SSCF protocol task maps the requirements of the higher layer to the requirements of the SSCOP. Universal Mobile Telecommunication System
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Above the ATM layer we find an ATM adaptation layer(AAL). Its function is to process the data from higher layers for ATM transmission. This means segmenting the data into 48-byte chunks and reassembling the original data frames on the receiving side. AAL5 is used for segmenting the data to ATM cells(fixed packets).
4.6.1.2 Iu CS Transport Network Control Plane Protocol Stack The Transport Network Control Plane protocol stack consists of signalling protocol for setting up AAL2 connections on top of BB SS7 protocols. AAL2 is designed for transmission of real-time data streams with variable bit rates. AAL5 fulfils the same requirements except the real-time parameter.
4.6.1.3 Iu CS User Plane Protocol stack User Plane protocol stack is on top of AAL2. The purpose of this protocol is to carry user data related to RABs over the Iu Interface. It has Transparent Mode and Support Mode. See later for more details.
4.6.2 Protocol Structure for Iu PS The Iu protocol structure is shown in figure 4.12. As explained above for the Iu CS protocol structure, a common ATM transport is applied for both User and Control Plane.
Figure 4.12: Iu PS protocol structure
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4.6.2.1 Iu PS Control Plane Protocol Stack The Control Plane protocol stack consists of RANAP and the same BB SS7-based signalling bearer. An IP based signalling bearer is specified which consists of M3UA (SS7 MTP3 - User adaptation Layer), SCTP (Simple Control Transmission Protocol), IP (Internet Protocol) and AAL5. The SCTP layer is specially designed for signalling transport in the internet. Specific adaptation layers are specified for different kinds of signalling protocols, such as M3UA for SS7-based signalling. The M3UA protocol support the transport of any SS7 MTP3-User signalling over IP using the services of the SCTP.
4.6.2.2 Iu PS Transport Network Control Plane Protocol Stack The Transport Network Control Plane is not applied to Iu PS. The setting up of the GTP tunnel requires only an identifier for the tunnel, and the IP addresses for both directions, and these already included in the RANAP RAB assignment messages. The same information elements that are used in Iu CS for addressing and identifying the AAL2 signalling are used for the Plane data in Iu CS.
4.6.2.3 Iu PS User Plane Protocol Stack In the Iu PS User Plane, multiple packet data flows are multiplexed on one or several AAL5 PVCs. GTP is the protocol between GPRS support nodes(GSN) in the UMTS/GPRS backbone network. It includes both the GTP signalling(GTP-C) and data transfer(GTP-U) procedures. GTP is defined for the Gn interface(interface between GSN within a PLMN) and the Gp interface between GSN in different PLMN. Only GTP-U is defined for the Iu interface between the SGSN in the PS domain ant the UTRAN. On the Iu interface, the RANAP protocol performs the control function for GTP-U. In the User plane, GTP uses a tunnelling mechanism(GTP-U) to provide a service for carrying packets.
4.6.3 RANAP Protocol This protocol layer provides UTRAN–specific signalling and control over the Iu. The functions of the RANAP are: •
Relocation. This function handles both SRNS relocation and Hard handover, including intersystem case to/from GSM: Î SRNS Relocation: the serving RNS functionality(see above SRNC) is relocated from one RNS to another without changing the radio resources and without interrupting the user data flow. The prerequisite for SRNS relocation is that all Radio Links are already in the same DRNC that is the target for the relocation.
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• • • •
• • •
• • • •
Î Inter RNS Hard handover: used to relocate the serving RNS functionality from one RNS to another and to change the radio resource correspondingly by a hard handover in the Uu interface. The prerequisite for hard handover is that the UE is at the border of the source and target cells. Overall radio access bearer (RAB) management, which includes the RAB’s setup, maintenance, and release Iu release. Release all resources from a given instance of Iu related to the specified UE Reporting unsuccessfully transmitted data. Common ID management. In this function the permanent identification of the UE is sent from the CN to UTRAN to allow paging coordination from possibly two different CN domains. Paging requests from the CN to the UE. Management of tracing. The CN may, for operation and maintenance purpose, request UTRAN to start recording all activity related to a specific UE-UTRAN connection. UE-CN signalling transfer. This functionality provides transparent transfer of UE-CN signalling messages that are not interpreted by UTRAN in three cases: Î transfer of the first UE message from UTRAN to UE Î Direct transfer(used for carrying all consecutive signalling messages) Î CN information broadcast(allows the CN to set system information to be broadcast respectively to all users in a specified area) Security mode control(used to set the ciphering or integrity checking on or off) Management of overload(used to control the load over the Iu interface) Reset(used to reset the CN or the UTRAN side of the Iu interface in error situations) Location reporting(allows the CN to receive information on the location of a given UE)
4.6.4 Iu User Plane Protocol The Iu User Plane protocol is in the Radio Network Layer of the Iu User Plane. One objective of the Iu User Plane protocol is to remain independent of the CN domain (Circuit Switched or Packet Switched) and to have limited or no dependency with the Transport Network Layer. Meeting this objective provides the flexibility to evolve services regardless of the CN domain and to migrate services across CN domains. The purpose of the User Plane protocol is to carry user data related to RABs over the Iu interface. Each RAB has its own instance of the protocol. The protocol performs either a fully transparent operation, or framing for the user data segments and some basic control signalling to be used for initialisation and online control. The Iu User Plane protocol has two modes: • Transparent mode: this mode does not perform any framing or control. • Support mode for predefined SDU(service data unit) sizes. This mode performs framing of the user data. The SDU size typically correspond to AMR speech frames.
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4.7 UTRAN Internal Interfaces 4.7.1 Iur Interface: RNC – RNC interface and the RNSAP signalling
Figure 4.13: Iur protocol stack
As explained in section 4.3.2, The Iur interface was initially designed to support the inter RNC soft handover(macro diversity), more features were added during the development of the standard. The Iur interface provides four distinct functions: • • • •
Support of basic Inter-RNC Mobility Support of dedicated Channels traffic Support of common channel traffic Support of global resource management
The Iur signalling protocol is divided into four different modules:
4.7.1.1 Iur1: Support of basic Inter-RNC Mobility This first module provides the functionality needed for the mobility of the user between the two RNCs, but does not support the exchange of any user data traffic. If this module is not implemented, the Iur interface as such does not exist and the only way for a user connected to UTRAN via the RNS1 to utilise a cell in RNS2 is to disconnect itself temporarily from UTRAN. Universal Mobile Telecommunication System
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In this case the User Plane and Transport Network Control Plane protocols are not needed because the functionality does not involve user data traffic across the Iur.
4.7.1.2 Iur2: Support of dedicated Channels traffic This functionality requires the dedicated channel module of RNSAP signalling and allows the dedicated channel traffic between two RNCs. The initial need for this functionality is to support the inter-RNC soft handover state. This module also allows the anchoring of the SRNC for all the time the user is utilising dedicated channels. This functionality requires also the User Plane frame protocol for the dedicated channel, plus the Transport Network Control Plane protocol(Q.2630.1)6 used for the setup of the transport connections(AAL2 connections). Each dedicated channel is conveyed over one transport connection, except the coordinated DCH(dedicated channel)7 used to obtain unequal error protection in the air interface. The Q.2150.1 protocol task is a converter between the ALCAP and the MPT3-B protocol.
4.7.1.3 Iur3: Support of common channel traffic This functionality allows the handling of common and shared channel data streams across the Iur interface. It requires the common transport channel modules of the RNSAP protocol and the Iur common transport channel frame protocol(CCH FP). The Q.2630.1 signalling protocol of the transport network control plane is also needed if signalled AAL2 connections are used.
4.7.1.4 Iur4: Support of global resource management This functionality provides signalling to support enhanced radio resource and O&M features across the Iur interface. This function is optional.
6
A generic name for this protocol is Access Link Control Application Part(ALCAP) The frame protocol for the dedicated channels(DCH FP) defines the structure of the data frames carrying the user data and the control frames used to exchange measurements and control information. 7
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4.7.1.5 Iub Interface: RNC – Node B interface and the NBAP signalling
Figure 4.14: Iub protocol stack
The Iub interface signalling is divided into two components: the common NBAP(that defines the signalling procedures across the common signalling link) and the dedicated NBAP(used in the dedicated signalling link) • • • • •
Management of common channels, common resources, and radio links Configuration management, such as cell configuration management Measurement handling and control Synchronization (TDD) Reporting of error situations
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5 UTRAN protocol LAYERS 5.1 Introduction Following the OSI protocol model, radio interface protocols in the UTRAN system can be described by using a layered Three-level protocol model(see figure 5.1). The lowest layer in this interface is the physical layer(PHY). Layer 2 consist of the medium access control(MAC), the radio link control(RLC), the broadcast multicast control(BMC), end the Packet Data convergence protocol(PDCP) sub layers. Layer 3 includes the following sub layers: RRC, mobility management(MM), GPRS mobility management(GMM), call control (C), supplementary services(SS), short message service(sms), session management(SM) and GPRS short messages service support(GSMS).
Figure 5.1
5.1.1 Channels There are three separate channel concepts in the UTRAN: logical, transport and physical channels. The mapping of the transport and physical channel will be explained in the physical layer part. The mapping of the logical and transport channel will be explained in the MAC layer part.
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Figure 5.2: channels
Logical channel defines what type of data is transferred. These channels defines the datatransfer services offered by the MAC layer. Transport channels defines how and with wich type of characteristics the data is transferred by the physical layer. These channels are used in the interface between the MAC and the PHY layers Physical channels defines the exact physical characteristics of the radio channels. These are the channels used below(the radio interface) the PHY layers. A further detailed explanation will be discussed in the following sections.
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5.2 Air interface: 3G Physical layer The physical layer is the lowest layer in the WCDMA air interface protocol model. It has to handle slightly different tasks depending on whether it is located in the UE or in the Node B. Like it is shown on figure 5.3, the physical layer has logical interfaces to both the MAC and RRC sub layer. The interface to the MAC in called PHY end it is used to transfer data(transport channels). The control PHY(CPHY) interface lies between the physical layer and the RRC, and is used for control and measurement information transfer. It is only used for layer 1 management.
Figure 5.3: logical interfaces
The UTRAN can operate in two modes: FDD and TDD, and these modes set slightly different requirements for layer 1 functionality. In the FDD mode, the uplink and downlink transmissions use different frequency bands. In TDD mode, the uplink and downlink transmissions are on the same frequency but in different time slots. A WCDMA-TDD system is actually a CDMA/TDMA system because of this time slicing components. The following list gives a short overview of the different task that must be performed by the physical layer: • • • • • • • • • • • •
Forward error correction (FEC) encoding/decoding Radio measurement and indications to higher layers Macro diversity distribution / combining and soft handover execution Error detection on transport channels Multiplexing of transport channels and demultiplexing of coded composite transport channels Rate matching Mapping of CCTrCHs on physical channels Modulation/demodulation Frequency and time synchronisation Closed loop power control Power weighting and combining of physical channels RF processing
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• •
Timing advance on uplink channels(TDD only) Support of uplink synchronisation
The following paragraphs list these tasks in more details:
5.2.1 Forward Error Correction encoding/decoding FEC schemes aim to reduce transmission errors. Error correction coding is also known as channel coding. The idea is to add redundancy to the transmitted bit stream. There are numerous error-control schemes available, each having different capabilities. The UTRAN employs two FEC schemes: convolutional codes and turbo codes. The convolutional coding can be used for low data rates while turbo codes can be used for higher data rates.
5.2.1.1 Convolutional codes FEC tent to fix the error, so when a receiver detects an error it will not ask for retransmission but will correct the code. The coded data must contain enough redundant information to make it possible to correct at least some of the detected errors that appear in the channel decoder without having to ask for repeat. Convolutional codes operate on streams of data. They also have a memory, which means that the output bits do not only depend on the current input bits, but also on several preceding input bits. A convolutional code can be described as the following format: (n, k, m), where n is the number of output bits per data word, k is the number of input bits and m is the length of the coder memory. The following figure gives an example of a convolution coder with the following format: (3, 1, 9).
Figure 5.4
In the end of the data sequence to be coded, the convolutional codes adds m – 1 zeros to the output sequence.
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5.2.1.2 Turbo codes The coder that is used in the UTRAN is called a Parallel Concatenated Convolution Code(PCCC). As you can see on the figure the turbo coder consist of two convolutional encoders in parallel separated by an interleaver. The interleaver randomize the data before it enters the second encoder. Figure 5.5 gives an example of a Turbo encoder:
Figure 5.5: Turbo encoder
Figure 5.6 shows two Soft-Input-Soft-Output(SISO) connected by interleaver and deinterleaver.
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Figure 5.6
Because there is more encoding taking place, it is more suited for high data rates. The UTRAN learns from the UE’s capability information whether the UE support turbo codes. In the UTRAN the channel coding is combined with the CRC error detection function to form a hybrid ARQ scheme. This means that the channel coding aims to fix as many errors as possible, and then the error detection function checks whether the result was correct. The retransmission of missing or corrupted packets belongs to RLC layer functionality.
5.2.2 Radio measurement and indications to higher layers Some measurement types are specific to either the UE or the Node B, but there are also measurements that are applicable to both. The radio measurement are typically controlled by the RRC layer(see section about RRC layer) in the UE. The RRC receives the necessary control information from the UTRAN in measurement control message. The RRC may explicitly ask the physical layer to perform to perform a certain measurement, or it can se certain conditions and the fulfilment of these then triggers the measurement process. There are a lot of measurement processes, some are used continuous and are performed periodically when the physical layer is in a certain state. The purpose of the measurements is different in IDLE mode and in connected mode. In IDLE mode, the measurements helps the UE in the cell-reselection process(finding the best available cell). These processes are also used in the connected mode but the purpose of the measurement taken in this mode is to maintain the optimal radio connection.
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5.2.3 Macro diversity distribution / combining and soft handover execution Macro diversity is a situation where the UE receives more than one signal from different sources. Similarly, an RNC may combine the same signal sent by the UE and received by several base stations. In the downlink the UE can receive as many macro diversity components as it has fingers in its RAKE receiver. Thus the more RAKE8 fingers the UE has, the more macro diversity components he can detect, the better the performance it has.
5.2.4 Error detection on transport channel The purpose is to find out whether a received block of data was recovered correctly. This is done using CRC(cyclic redundant check) method. There are five CRC polynomial lengths in use(0, 8, 12, 16 and 24 bits). The higher layer indicates which length should be used for a given transport channel. The sending entity calculates the CRC checksum over the whole message and attaches it to the end of the message. The receiving entity checks whether the CRC of the received message matches with the received CRC. In the UTRAN, the error detection is combined with the channel coding scheme to form a hybrid ARQ scheme. The channel coding has to reduce the amount of faulty packets before they get detected in the error-detection function.
5.2.5 Multiplexing transport channels and demultiplexing coded composite transport channels Each UE can have several transport channels in use simultaneously. Every 10ms, one radio frame from each transport channel is multiplexed into a coded composite transport channel(CCtrCH). This multiplexing is done serially, the frames are concatenated together. FDD mode: Each UE can have only one CCTrCH on the uplink TDD mode: Several CCTrCH is possible on the uplink.
5.2.6 Rate Matching The number of bits on a transport channel can vary with every transmission time interval. However, the physical channel radio frames must be completely filled. This means that some sort of adjusting must be done to match the two given rates.
8
A RAKE receiver is made of correlators, also known as RAKE fingers, each receiving a multipath signal.
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In the uplink: The total bit rate after transport channel multiplexing must match the total physical channel bit rate. This is done by deleting or repeating bits. This is done by a predefined scheme. In the downlink: The network can interrupt the transmission if the number of bits to be send is lower than the maximum available. This is called the discontinuous transmission(DTX) mode and it is done to reduce the overall interference in the radio path.
5.2.7 Mapping of CCTrCHs on physical channels When there are several physical channel in use, the bits in the CCTrCH must be divided among them. This is done by segmenting the input bits evenly for each physical channel. The last phase of mapping is the actual filling of radio frames with bits. In the uplink: All frames are completely filled if they are used. In downlink: All frames are also completely filled, but the DTX bits are not actually sent. The following textual figure gives the mapping of transport and physical channels:
Figure 5.7
The Broadcast Channel The Broadcast Channel (BCH) is a transport channel that is used to transmit information specific to the UTRA network or for a given cell. Universal Mobile Telecommunication System
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The Forward Access Channel (FACH) is a downlink transport channel that carries control information to terminals known to locate in the given cell. This is so, for example, after a random access message bas been received by the base station. It is also possible to transmit packet data on the FACH. The Paging Channel (PCH) is a downlink transport channel that carries data relevant to the paging procedure, that is, when the network wants to initial communication with the terminal. The simplest example is a speech call to the terminal: the network transmits the paging message to the terminal on the paging channel of those cells belonging to the location area that the terminal is expected to be in. The Random Access Channel (RACH) is an uplink transport channel intended to be used to carry control information from the terminal, such as requests to set up a connection. It can also be used to send small amounts of packet data from the terminal to the network. The uplink common packet channel (CPCH) is an extension to the RACH channel that is intended to carry packet-based user data in the uplink direction. The pair providing the data in the downlink direction is the FACH. In the physical layer, the main differences from the RACH are the use of fast power control, a physical layer based collision detection mechanism and a CPCH status monitoring procedure. The downlink shared channel (DSCH) is a transport channel intended to carry dedicated user data and/or control information; it can be shared by several users. In many respects it is similar to the forward access channel, but the shared channel supports the use of fast power control as well as variable bit rate on a frame-by-frame basis. The common transport channels needed for the basic network operation are RACH, FACH and PCH, while the use of DSCH and CPCH is optional and can be decided by the network.
5.2.8 Modulation/Demodulation The UTRAN uses the DS-CDMA(Direct Sequence) modulation technique. In Direct Sequence-CDMA, the original signal is multiplied directly by faster-rate spreading code. This resulting code then modulates the digital wideband carrier. The following list describe the most important modulation techniques for spreading the information signal: • (Frequency Hopping)FH-CDMA • (Time-Hopping)TH-CDMA • (Multicarrier)MC-CDMA
5.2.9 Inner-loop power control Power control comes in two forms, open and closed loop control. The closed loop control is based on the explicit power control commands received from the peer entity. In the open loop control the transmission the transmission entity estimates power level by itself from the received signal. These methods are both used in the UTRAN. The closed loop control can also further divided into two processes: the inner-loop and the outer-loop power control Universal Mobile Telecommunication System
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5.2.10
RF processing
Î The UE power classes There are 4 power classes for the UEs. The following table gives an overview of them: Power class 1 2 3 4
Maximum output power + 33dBm + 27dBm + 24 dBm + 21dBm
Î Frequency bands The total bandwidth for the 3G is divided between the FDD and the TDD modes. The paired band is allocated for the FDD mode and the smaller unpaired band for the TDD mode. The UTRA/FDD is designed to operate in the following paired bands:
5.3 Protocol Stack The unifying principle in the UTRAN development work has been to keep the mobility management(MM) and connection management(CM) layers independent of the AIR interface radio technology. This idea has been realized as the Access Stratum(AS) and the NonAccess Stratum(NAS)(see figure below). The AS is a functional entity that includes radio access protocols between the UE and the UTRAN. These protocols terminate in the UTRAN. The NAS includes core network protocols between the UE and the CN itself. These protocols are not terminated in the UTRAN, but in the CN. The UTRAN is transparent to the NAS. The MM and CM protocols are GSM CN protocols, the GPRS Mobility Management(GMM) and Session Management(SM) are GPRS CN protocols. Just as the NAS tries to be independent of the underlying radio techniques, so also have the MM, CM, GMM and SM protocols tried to remain independent of their underlying radio technologies.
5.3.1 MAC layer The UTRAN MAC is not the same protocol as the GPRS MAC, even though they both have similar names and handle similar tasks in similar ways. The UTRAN MAC can even contain different functionalities depending on whether it supports FDD, TDD, or both modes. The MAC is not a symmetric protocol; the entities in the UE and in the UTRAN are different. A MAC task contains several different functional entities:
5.3.1.1 MAC-b
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Figure 5.8 illustrates the connectivity of the MAC-b entity in a UE and in each cell of the UTRAN.
Figure 5.8: MAC-b
MAC-b is the control entity for the broadcast channel (BCH).There is one (current cell) or multiple (current and neighbour cells) MAC-b entities in each UE and one MAC-b in the UTRAN for each cell. The MAC Control SAP is used to transfer Control information to MAC-b. The MAC-b entity is located in the Node B.
5.3.1.2 MAC architecture - UE side The MAC-c/sh is responsible for the access of common transport channels, on the other hand, MAC-d is responsible for the access of dedicated transport channels. If logical channels of dedicated type are mapped to common channels then MAC-d passes the data to MAC-c/sh via connection between the functional entities(as illustrated in red in figure 5.9). The mapping of logical channels on transport channels depends on the multiplexing that is configured by RRC. The MAC Control SAP is used to transfer Control information to each MAC entity(illustrated in green). The following section will give a detailed explanation of these MAC UE entities.
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Figure 5.9
MAC-c/sh – UE side Figure 5.10 gives a detailed view of MAC-c/sh at the UE side.
Figure 5.10: MAC-c/sh at UE side
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•
TCTF MUX: Î The TCTF MUX is responsible for the handling of the TCTF field in the MAC header and the respective mapping between logical and transport channels. In other words, the insertion for uplink channels and detection and deletion for downlink channels. This TCPTF field indicates which type of common logical channel is used or which dedicated logical channel is used. • add/read UE Id: Î The UE Id is not added for every channel. This field is filled in only for Common Packet Channel(CPCH) and Random Access Channel(RACH) transmissions Î The UE id is read to associate the data to a certain UE. • UL-TF selection: Î In the uplink, the possibility of Transport Format(TF) selection exists. In case of CPCH transmission, a TF is selected based on TF availability determined from status information on the CPCH Status Indication Channel(CSICH); • ASC selection: Î For RACH, MAC indicates the ASC associated with the PDU to the physical layer. For CPCH, MAC may indicate the ASC associated with the PDU to the Physical Layer. This is to ensure that RACH and CPCH messages associated with a given Access Service Class (ASC) are sent on the appropriate signature(s) and time slot(s). MAC also applies the appropriate back-off parameter(s) associated with the given ASC. When sending an RRC CONNECTION REQUEST message, RRC will determine the ASC; in all other cases MAC selects the ASC; • Scheduling /priority handling Î This functionality is used to transmit the information received from MAC-d on RACH and CPCH based on logical channel priorities. This function is related to TF selection. • TFC selection The RLC provides RLC-PDUs to the MAC, which fit into the available transport blocks on the transport channels. There is one MAC-c/sh entity in each UE.
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MAC-d – UE side
Figure 5.11: MAC-d at UE side
•
• • • •
Transport Channel type switching Î This functionality is done in the MAC-d but it is actually based on decisions taken in the RRC layer. This is related to a change of radio resources. The RRC will request to the Mac to switch the mapping of one designated logical channel between dedicated transport channels and common transport channels. C/T MUX: Î The C/T MUX is used when multiplexing of several dedicated logical channels onto one transport channel is used Ciphering: Î MAC-d performs the Ciphering for transparent mode data. Deciphering: Î MAC-d deciphers the ciphered transparent mode data. UL-TFC selection:
The MAC-d entity is responsible for mapping dedicated logical channels for the uplink either onto dedicated transport channels or to transfer data to MAC-c/sh to be transmitted via common channels. One dedicated logical channel can be mapped simultaneously onto DCH and DSCH. Universal Mobile Telecommunication System
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The MAC-d entity has a connection to the MAC-c/sh entity. This connection is used to transfer data to the MAC-c/sh to transmit data on transport channels that are handled by MAC-c/sh (uplink) or to receive data from transport channels that are handled by MAC-c/sh (downlink).
5.3.1.3 MAC architecture – UTRAN side The architecture of the MAC UTRAN side is similar to the UE side with the exception that there will be one MAC-d for each UE and each UE (MAC-d) that is associated with a particular cell may be associated with that cell's MAC-c/sh(like indicated on figure 5.12). MAC-c/sh is located in the controlling RNC(CRNC) while MAC-d is located in the serving RNC(SRNC). The MAC Control SAP is used to transfer Control information to each MAC entity belongs to one UE.
Figure 5.12
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MAC-c/sh – UTRAN side
Figure 5.13: MAC-c/sh at UTRAN side
• • • • • •
The Scheduling – Priority Handling Î This function manages FACH and DSCH resources between the UEs and between data flows according to their priority. TCTF MUX Î (idem as UE side) UE Id Mux; Î This field is used to distinguish different UEs, for dedicated type logical channels. TFC selection: Î In the downlink, transport format combination selection is done for FACH and PCH and DSCHs. Demultiplex Î For TDD operation the demultiplex function is used to separate USCH data from different UEs, i.e. to be transferred to different MAC-d entities. DL code allocation Î This function is used to indicate the code used on the DSCH.
The RLC provides RLC-PDUs to the MAC, which fit into the available transport blocks on the transport channels. There is one MAC-c/sh entity in the UTRAN for each cell. Universal Mobile Telecommunication System
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MAC-d – UTRAN side
Figure 5.14
• • • • • •
•
Transport Channel type switching: Î (idem as UE side) C/T MUX box: Î The function includes the C/T field when multiplexing of several dedicated logical channels onto one transport channel is used. Priority setting: Î This function is responsible for priority setting on data received from DCCH / DTCH. Ciphering: Î (idem as UE side) Deciphering: Î (idem as UE side) DL Scheduling/Priority handling: Î In the downlink, scheduling and priority handling of transport channels is performed within the allowed transport format combinations of the TFCS assigned by the RRC. Flow Control:
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Î The flow control in the MAC-c/sh is needed to limit buffering between MAC-d and MAC-c/sh entities. This function is intended to limit layer 2 signalling latency and reduce discarded and retransmitted data as a result of FACH or DSCH congestion. A MAC-d entity using common channels is connected to a MAC-c/sh entity that handles the scheduling of the common channels to which the UE is assigned and DL (FACH) priority identification to MAC-c/sh. A MAC-d entity using downlink shared channel is connected to a MAC-c/sh entity that handles the shared channels to which the UE is assigned and indicates the level of priority of each PDU to MAC-c/sh. A MAC-d entity is responsible for mapping dedicated logical channels onto the available dedicated transport channels or routing the data received on a DCCH or DTCH to MAC-c/sh. One dedicated logical channel can be mapped simultaneously on DCH and DSCH. Different scheduling mechanisms apply for DCH and DSCH. There is one MAC-d entity in the UTRAN for each UE that has one or more dedicated logical channels to or from the UTRAN.
5.3.1.4 MAC-hs MAC-hs handles the HSDPA9 functionality. The HS-DSCH is a high-speed downlink shared channel. The UE has one MAC-hs if it is HSDPA-capable. The UTRAN has one MAC-hs for each cell that supports HS-DSCH. Note that a UE does not have to support HS-DSCH and DSCH reception simultaneously. MAC-hs is a bit of a special case among other functional entities because it works with 2ms sub frames, whereas the other entities use 10ms frames. This timing constraint also means that especially the HARQ function control cannot be handled via higher-layer protocols as usual, but must be handled directly from layer 1. The MAC operates on transport channels between the MAC and layer 1(as described in the introduction of this section). The logical channels are described between the MAC and RLC. The internal configuration of the MAC is controlled by the RRC.
5.3.1.5 MAC services The following lists the function of MAC for the upper layers: • Data transfer • Reallocation of radio resources and MAC parameters • Reporting of measurements to RRC 9
HSDPA stands for High Speed Data Packet and is introduced in 3G to enable higher data rates in downlink direction, so it will support the introduction of high bit rate data services and will increase network capacity, while minimizing operators’ investment. It can be compared with EDGE.
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5.3.1.6 MAC functions • • • • • • • • • • •
Mapping between logical channels and transport channels. Selection of appropriate Transport Format for each Transport Channel depending on instantaneous source rate. Priority handling between data flows of one UE. Priority handling between UEs by means of dynamic scheduling. Identification of UEs on common transport channels. Multiplexing/demultiplexing of upper layer PDUs into/from transport blocks delivered to/from the physical layer on common transport channels. Multiplexing/demultiplexing of upper layer PDUs into/from transport block sets delivered to/from the physical layer on dedicated transport channels. Traffic volume measurement. Transport Channel type switching. Ciphering for transparent mode RLC. Access Service Class selection for RACH and CPCH transmission.
5.3.2 RLC
5.3.2.1 RLC entities The RLC layer is in charge of the actual data packet transmission over the air interface. It makes sure that the data to be send over the radio interface is packed into suitably sized packets. The RLC task maintains a retransmission buffer, performs ciphering and routes the incoming data packets to the right destination task(RRC, BMC, PDCP or voice codec). One RLC task contains several different functional entities. For bearers using the transparent mode service or the unacknowledged mode (UM) service, there is one transmitting and one receiving entity for each bearer. For bearers using the acknowledged mode (AM) service, there is only one combined transmitting and receiving entity for each bearer. Different modes are used for different types of data. If the data is of an important nature, it needs lots of protection and AM service. On the other hand, some data is not suitable for AM service. For example, it is not good to use AM for voice. The AM retransmission protocol could guarantee that a voice packet does get through eventually, but a retransmitted voice packet cannot be used anymore because of the additional delay. A voice packet must be received in time without delays or it is worthless.
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Figure 5.15
The following gives a more detailed discussion about these modes.
5.3.2.2 Transparent mode(TM) – RLC entity The transparent mode is used for the BCCH, PCCH, SHCCH, DCCH, DTCH and CCCH channels. For the CCCH and SHCCH the transparent mode is only used in uplink direction. Transparent mode means that very little processing is done to the data in the RLC. It contains transmission and receiving buffers and also segmentation and reassembly functions. There is no header added to the data unit in the transparent mode. Figure 5.16 shows the model of two transparent RLC entities
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Figure 5.16
The transmitting TM-RLC entity receives RLC SDUs from upper layers through the TMSAP(service access point). All received RLC SDUs must be of a length that is a multiple of one of the valid TMD PDU lengths. If segmentation has been configured by upper layers and a RLC SDU is larger than the TMD PDU size used by the lower layer for that TTI, the transmitting TM RLC entity segments RLC SDUs to fit the TMD PDUs size without adding RLC headers. All the TMD PDUs carrying one RLC SDU are sent in the same TTI, and no segment from another RLC SDU are sent in this TTI. If segmentation has not been configured by upper layers, then more than one RLC SDU can be sent in one TTI by placing one RLC SDU in one TMD PDU. All TMD PDUs in one TTI must be of equal length. When the processing of a RLC SDU is complete, the resulting one or more TMD PDU(s) are/is submitted to the lower layer through either a BCCH, DCCH, PCCH, CCCH, SHCCH or a DTCH logical channel. The receiving TM-RLC entity receives TMD PDUs through the configured logical channels from the lower layer. If segmentation is configured by upper layers, all TMD PDUs received within one TTI are reassembled to form the RLC SDU. If segmentation is not configured by upper layers, each TMD PDU is treated as a RLC SDU. The receiving TM RLC entity delivers RLC SDUs to upper layers through the TM-SAP. Universal Mobile Telecommunication System
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5.3.2.3 Unacknowledged mode(UM) – RLC entity UM is used for the DCCH, DTCH, CTCH and the downlink SHCCH and CCCH channels. The RLC adds a header to the PDU and cipher/deciphers it. As in transparent mode, one instance is needed per direction and per bearer.
Figure 5.17
The transmitting UM-RLC entity receives RLC SDUs from upper layers through the UMSAP. The transmitting UM RLC entity segments the RLC SDU into UMD PDUs of appropriate size, if the RLC SDU is larger than the length of available space in the UMD PDU. The UMD PDU may contain segmented and/or concatenated RLC SDUs. UMD PDU may also contain padding to ensure that it is of a valid length. Length Indicators are used to define boundaries between RLC SDUs within UMD PDUs. Length Indicators are also used to define whether Padding is included in the UMD PDU. If ciphering is configured and started, an UMD PDU is ciphered (except for the UMD PDU header) before it is submitted to the lower layer. The transmitting UM RLC entity submits UMD PDUs to the lower layer through either a CCCH, SHCCH, DCCH, CTCH or a DTCH logical channel. The receiving UM-RLC entity receives UMD PDUs through the configured logical channels from the lower layer. The receiving UM RLC entity deciphers (if ciphering is configured and started) the received UMD PDUs (except for the UMD PDU header). It removes RLC headers from received UMD PDUs, and reassembles RLC SDUs (if segmentation and/or concatenation has been performed by the transmitting UM RLC entity). RLC SDUs are delivered by the receiving UM RLC entity to the upper layers through the UM-SAP. Universal Mobile Telecommunication System
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5.3.2.4 Acknowledged mode(AM) – RLC entity AM can be used for DCCH and DTCH channels. The SDU’s are segmented or concatenated onto the PDUs of fixed length. The multiplexer(MUX) chooses the PDUs and decides when they are delivered to the MAC. The MUX may for example send RLC control PDUs on one logical channel and data PDUs on another logical channel or it may send everything via one logical channel. If the data in AM mode does not fill the whole PDU, then padding is used to fill the rest of the PDU. There is only one AM entity per bearer in the UE that is common to both the uplink and the downlink.
Figure 5.18
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5.3.2.5 RLC Services • Transparent data transfer Service: The following functions are needed to support transparent data transfer: Î Segmentation and reassembly. Î Transfer of user data. Î SDU discard. • Unacknowledged data transfer Service: The following functions are needed to support unacknowledged data transfer: Î Segmentation and reassembly. Î Concatenation. Î Padding. Î Transfer of user data. Î Ciphering. Î Sequence number check. Î SDU discard. • Acknowledged data transfer Service: The following functions are needed to support acknowledged data transfer: Î Segmentation and reassembly. Î Concatenation. Î Padding. Î Transfer of user data. Î Error correction. Î In-sequence delivery of upper layer PDUs. Î Duplicate detection. Î Flow Control. Î Protocol error detection and recovery. Î Ciphering. Î SDU discard.
5.3.2.6 RLC functions • • • • • • • • • • •
Segmentation and reassembly. Concatenation. Padding. Transfer of user data. Error correction. In-sequence delivery of upper layer PDUs. Duplicate detection. Flow control. Sequence number check. Protocol error detection and recovery. Ciphering.
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•
SDU discard
5.3.3 RRC The RRC controls the configuration of the lower layers in the protocol stack and it has control interfaces to each of the lower layer(PDCP, BMC, RLC, MAC and layer 1). It is the constructor of the protocol stack
5.3.3.1 RRC services • General control: This is an information broadcast service. The information transferred is unacknowledged and it is broadcast to all mobiles within a certain area. • Notification: This includes paging and notification broadcast services. The paging service broadcasts paging information in a certain geographical area but it is addressed to a specific UE or UE’s. The notification broadcast service is defined to provide information broadcast to all UEs in a cell or cell. Note that the notification broadcast service seems to be quite similar to the general control service. • Dedicated control This service includes the establishment and release of a connection and the transfer of messages using this connection. These connections can be both point-to-point and group connections. Message transfers are acknowledged.
5.3.3.2 RRC functions • •
• • • • • • • 10
Initial cell selection and cell reselection Broadcast of information Î This information is about the system and the serving cell that is sent by the network in a point-to-multipoint manner. This information consists of messages called System Information Blocks(SIB). Reception of paging10 messages Establishment, maintenance and release of RRC connection Establishment, reconfiguration and release of radio bearer Assignment, reconfiguration and release of radio resources for the RRC connection, which includes such things as the assignment of codes and CPCH channels Handover, which include the preparation and execution of handovers and intersystem handovers. Measurement controls Outer-loop power control
Paging is a procedure that is used by the UTRAN to tell a mobile that there is an incoming call waiting.
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• • • •
Security mode control Routing of higher layer PDU’s Control of requested QoS Support of DRAC Î In the uplink, the spreading codes are not orthogonal, but pseudorandom. The user signals appear as interference to each other. To ease the situation in the uplink, the 3GPP has defined a scheme called dynamic resource allocation control(DRAC) • Contention resolution in the TDD mode • Timing advance in the TDD mode • Management of the CBS service Î Cell Broadcast Service. Cell broadcast messages are text messages that are broadcast to everybody in a cell.
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Index
Index A AAL, 37 AAL5, 37 acknowledged mode, 62 Air interface, 46 ALCAP, 35 AMR speech service, 17 ASC selection, 56 ATM, 36
B Background class, 17 BCH, 51 Bearer Service, 14 BER, 18 BMC, 44
C CCtrCH, 50 CCTrCH, 50 CDMA, 7 CDMA processing gain, 9 Channels, 44 chips, 8 CN, 33 Control planes, 34 Conversational class, 17 Convolutional codes, 47 CPCH, 51 CPHY, 46 CRC, 49 CRNC, 31
D Despreading, 8 Drift RNS, 31 DS-CDMA, 52 DSCH, 51
F FACH, 51 FDMA, 5 Universal Mobile Telecommunication System
G GMM, 44 GSMS, 44 GTP-C, 39 GTP-U, 39
H Handover, 11 Home Network Domain, 33 Horizontal Layers, 34 hybrid FDMA/TDMA, 7
I Interactive class, 17 Interfaces, 34 Iu, 35 Iu Bearer Service, 16 Iu CS, 36 Iu PS, 38 Iub, 42 Iur, 40 Iur1, 41 Iur2, 42 Iur3, 42 Iur4, 42
L LCS Client, 19 Location-based services, 19
M MAC, 53 MAC-b, 53 MAC-c/sh, 54 MAC-d, 56 MAC-hs, 61 macro cell, 3 Mapping, 50 micro cell, 3 MM, 44 Mobile Equipment, 24 MTP, 37 68
Index
multi-standard environment, 27
N NBAP, 34 Node B, 26
O OTDOA, 21
P PCH, 51 PDCP, 44 PHY, 44 planes, 34 PLMN, 19 Power control, 10
Q QoS, 14 QoS classes, 17
R RACH, 51 Radio Network Layer, 34 RAKE, 49 RANAP, 34, 37, 39 Rec.H.324M, 18 REC.H323, 18 RLC, 62 RNC, 31 RRC, 67
S SAAL-NNI, 37 SCCP, 37
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Serving Network Domain, 33 Serving RNC, 31 SIR, 11 Spread spectrum, 8 Spreading, 8 SS, 44 SS7, 37 SSCF, 37 SSCOP, 37 Streaming class, 17
T TCTF MUX, 56 TDMA, 6 TFC selection, 56 Transit Network Domain, 33 transport channels, 46 Transport Network Control Plane, 35 Transport Network Layer, 34 Transport Network User Plane, 35
U UL-TF, 56 UMTS, 3 UMTS-Architecture, 23 unacknowledged mode, 62 User Equipment, 24 User planes, 35
V Vertical planes, 34
W WCDMA, 11
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PART 3 Convergence WLAN and UMTS
Introduction
Table of content Table of content.......................................................................................................................... 1 1 Introduction ........................................................................................................................ 2 1.1 Comparing WLAN and UMTS .................................................................................. 2 1.1.1 Similarities ......................................................................................................... 2 1.1.2 Difference........................................................................................................... 3 1.2 Convergence............................................................................................................... 4 1.3 Possibility, requirements and triggering..................................................................... 6 2 Interworking System architecture ...................................................................................... 7 2.1 Interconnection between 3G-SGSN and WLAN AP by RNC-emulator ................... 8 2.2 Interconnection between GGSN and WLAN AP by 3G-SGSN-emulator............... 11 2.3 Interconnection between UMTS and WLAN through VAP .................................... 11 2.4 Interconnection between UMTS and WLAN via Mobility Gateway ...................... 13 2.5 Interconnection between UMTS and WLAN based on Mobile IP .......................... 15 2.6 Mobile IP.................................................................................................................. 15 2.6.1 Introduction ...................................................................................................... 15 2.6.2 The challenge for Mobile IP............................................................................. 16 2.6.3 Characteristic of the standard ........................................................................... 17 2.6.4 Network architecture with Mobile IP............................................................... 17 2.6.5 Handover Procedure......................................................................................... 18 2.6.6 Mobile IP Security ........................................................................................... 21 2.7 Pros and CONS of the different scenarios ............................................................... 23 3 Handover between WLAN and UMTS............................................................................ 26 3.1 Introduction .............................................................................................................. 26 3.2 Handover based on Mobile IP .................................................................................. 27 3.2.1 MN moving from WLAN to UMTS coverage................................................. 27 3.2.2 MN moving from UMTS to WLAN coverage................................................. 28 4 Handover between GSM/GPRS and UMTS .................................................................... 29 4.1 Measurements........................................................................................................... 29 4.1.1 Dual receiver .................................................................................................... 29 4.1.2 Compressed mode ............................................................................................ 29 4.2 Different maximum data rate ................................................................................... 29 5 Fourth Generation of Mobile Systems(4G)...................................................................... 31 5.1 4G architecture ......................................................................................................... 31 5.1.1 Multimode device............................................................................................. 31 5.1.2 Overlay network............................................................................................... 32 5.1.3 Common access protocol ................................................................................. 32 Index......................................................................................................................................... 34
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Introduction
1 Introduction Before we start with the introduction, it is important to know that when we speak about WLAN, we meant also WiFi.
Figure 1.1: WiFi logo
The Wi-Fi Alliance is a nonprofit international association formed in 1999 to certify interoperability of WLAN products based on IEEE 802.11 specification. The goal of the WiFi Alliance's members is to enhance the user experience through product interoperability. For more information about WLAN architecture and WLAN security, please check paper mentioned in the source.
1.1 Comparing WLAN and UMTS In this section the difference and similarities will be summed. After examined the previous paper (UMTS) and the paper about WLAN (Tim & Sven) it might appear that UMTS and WLAN address completely different user needs in quite distinct, non overlapping markets.
1.1.1 Similarities
1.1.1.1 Wireless UMTS and WLAN are wireless technologies which avoids the installation of cables. Avoiding installing cables reduces the cost and provides scalable infrastructures. This is off course from a user point of view. Wireless infrastructures may be developed more rapidly than wire line alternatives to respond to new market opportunities and changing demands. Compared to wire line technologies, it facilitates mobility. This includes two main items: The ability to move without any concern of cable or devices, which is a key advantage of WLAN over the wire line LAN. The ability to stay continuously connected over wider serving areas is a key advantage of UMTS. It is possible to cover a wide area with WLAN, but it is most offen deployed in local area with a few base stations (Access Point). Compared to this, UMTS will have more base stations (Node B) to cover a wide area.
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Introduction
1.1.1.2 Access technologies For UMTS, the wireless link is from the end user device to the cell base station which can be a distance of a few kilometre. For WLAN, the wireless link is a hundred meter from the end user device to the base station (AP). The rest of the hardware components is wire lined interconnected with each other. UMTS and WLAN are both access technologies, therefore we must consider the role of backbone wire line providers that provide connectivity to the rest of the internet and support transport within the core network. Three main parts can be distinguished: • The backbone • The second last km providers • The last km access facilities The wireless challenge here is the last km access facilities that provide the mobility procedures and services.
1.1.1.3 Broadband services UMTS and WLAN offer a high data rate. WLAN offers a data rate of approximately 11Mbps whereby UMTS offers less data rate, 2Mbps. It is important to know that the future wireless mobile technology will offer greater data rates, this will also be the case of WLAN and other wire line technologies. The fact is that UMTS and WLAN offer a sufficient bandwidth to support services that need high bandwidth like for example real-time voice, data, streaming media,… Off course the quality will increasing if these rates increases also. UMTS and WLAN will also support the “Always on” idea which is a very important aspect of broadband services.
1.1.2 Difference
1.1.2.1 Spectrum 3G and other mobile technologies(like GSM,…) use licensed spectrum while WLAN uses unlicensed shared spectrum. This is something important for the cost of service, the QoS, congestion management and industry structure. Mobile operators had to spend a big part of there investment on the cost of the licence which was approximately 150 million euros. On the other hand, WLAN uses the shared 2.4 GHz unlicensed spectrum. On the other hand while licensed spectrum is expensive, it does have the advantage of facilitating QoS management. With licensed spectrum, the licensee is protected from interference from other services providers. The unlicensed spectrum used by WLAN imposes strict power limits on users and forces users to accept interference from others. It is easier for a UMTS provider to give a predictable level of service and to support delay sensitive services.
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Introduction
1.1.2.2 Technology development The development of UMTS is growing very slowly. There are a number of reasons for this: The high cost of the license, new UMTS handsets needed, new important investment for the new UTRAN,… On the other hand WLAN can be installed very rapidly. This has mainly to do with the fact that the WLAN equipment has substantially lowered prices. WLAN is easy to use/install for non-technical home users. The embedded support of voice services is another important difference between UMTS and WLAN. UMTS was designed as an upgrade technology for wireless voice telephony networks, so voice services are an intrinsic part of UMTS. WLAN provides a lower layer data communication service that can be used as the substrate on which to layer services such as voice telephony(VoIP). UMTS over WLAN offers a better support for secure/private communication that does WLAN. Off course at the moment there is a limited operational experience with how secure UMTS communication is.
1.2 Convergence One of the main features of the next generation systems, usually referred to as systems beyond 3G(4G), is represented by the interoperation of different fixed and mobile networks. Contrary to horizontal handover which is forwarding of an active connection from one cell to another of the same radio access technologies, an intersystem handover implies switching from a serving cell of a given radio access technologies to another radio access technologies, e.g. UMTS FDD to WLAN. Depending on the level of integration that is necessary numerous approaches can be taken to combine different radio access technologies. When the integration between different technologies is close, the provisioning of the service is more efficient and the choice of the mode in order to find the best radio access is faster. This could, for example greatly affect real time flows. On the contrary, a higher level of integration means providing a greater effort in the definition of interfaces and mechanisms that are able to support the necessary exchange of data and signalling between radio access technologies. The interworking has been classified under two methods, i.e. Loose Coupling and Tight Coupling. From a macro point of view the main difference is how and where the WLAN is coupled to the UMTS network. The choice is mainly a trade-off between the required degree of modifications to standards, the seamlessness of interworking and amount of infrastructure in common. As you can see on figure 1.2 different couplings are possible. The following section gives an overview of these.
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Introduction
Figure 1.2: coupling scenarios
•
Open Coupling
This scenario is an open standard and is used for access and roaming. The term Open coupling indicates that there is no real integration between two or more access technologies. The WLAN and UMTS networks are considered as two independent systems that share a single billing scheme between them. Although a common database is used between the two; separate authentication procedures are used. Thus a current session in use will always have to be terminated as it enters to a new radio access network. Seamless handover will never be possible. •
Loose Coupling
In this scenario, there is a common customer database and an authentication procedure. In loose coupling the operator will still be able to utilize the same subscriber database for existing 3G clients and new radio access network (WLAN) clients, allowing centralized billing and maintenance for different technologies. However the new link AAA-HLR requires standardization. Loose coupling is defined as utilization of a generic RAT (WLAN in our case) as an access network complementary to current 3G access networks. It utilizes the common subscriber database without any user plane Iu interface. As at present this is regarded by many the most attractive solution. •
Tight Coupling
The key characteristic of this scenario includes the possibility of seamless handover between UMTS and a WLAN. As a consequence it requires additional standardization as opposed to the Loose and Open coupling. In tight coupling, the generic radio access technologies network is connected to the rest of the UMTS network (the core network) in the same manner as other UMTS radio access technologies (UTRAN, GERAN) using the Iu interfaces by means of Interworking Unit (IWU). One of the most relevant aspects of tight coupling interworking is that it foresees the definition of the Iu interface between different radio access technologies making vertical handover possible. •
Integration
This scenario is similar compared to the previous method regarding seamless handover. 5
Introduction
However in this case a WLAN can be viewed as a cell managed at the RNC level. This concept is not widespread because robust network planning is not pertinent for WLANs yet; owing to lack of geographical condensed presence of the system .i.e. interference levels are not considered because in common scenarios geographical spreading of AP (AP) ensures lack of interference from neighbouring cells. However it should be noted that this method would be the ideal case from the end user perspective.
1.3 Possibility, requirements and triggering UMTS utilizes a slotted transmission mode in the downlink, whereby a single-receiver mobile station can carry out measurements on other frequencies without affecting its normal data flow. The information which is normally transmitted during a 10ms frame is compressed in time, either by code puncturing or by reducing the spreading factor by a factor of 2. As a result an idle time period of 5ms is created within each frame, which is used for interfrequency measurement. WLAN too utilizes a similar method termed as the sleep mode. Terminals can be in one of sixteen sleep groups, each group having a different sleep periodicity, in which it carries out interfrequency measurements. The idle period parameter is non standardized and could be set to a desired level by the operator. Mobility (Handover UMTS - WLAN) should be supported. The user should be notified of any possible degradation of the provided Quality of Service (QoS) due to change of access network. Partnership or roaming agreements between a UMTS network operator and a WLAN network operator should give the user the same benefits as if the interworking was handled within one network operator. Subscriber Identification, Billing and Accounting between roaming partners must be handled. Inter System Handover may be triggered due to the following reasons. The first two are operator specific while the latter is user specific. • Coverage Expansion - at the initial roll out of UMTS coverage will be a limiting factor especially in the rural areas. • Load Balancing - when the traffic in UMTS increases it would be an advantageous to handover certain part of the load to an other radio access technologies. • QoS requirement - the user may demand a higher QoS for example at a higher price. If it is available the operator can then redirect it to another radio access technology which is capable of providing it.
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Interworking System Architecture
2 Interworking System architecture The following section will describe the previous discussed coupling in more details. As you can see on figure 2.1 there are five different scenarios. Each has pros and cons.
Figure 2.1: different interconnections
These coupling/interconnection architectures involve minimum changes to the existing standards and technologies and especially for the MAC and PHY layer to ensure that existing standard and networks continue to function as before. The interconnection 1 and 2 will always have interaction between the Access point(AP) and the PS part of the UMTS CN. This means that the gateway to the IEEE 802.11 WLAN network is attached to the PS domain. This interconnection is possible through the GGSN and the 3G-SGSN entities. In this case the WLAN area seams to appear as a UMTS cell called routing area(RA). In this case the UMTS network will be the master and the WLAN network will be the slave. With this in mind, the mobility management and security will be handled by the UMTS network and the WLAN will be seen as a cell. The traffic will first reach the UMTS 3G-SGSN or GGSN before reaching its final destination even if the final destination is in the WLAN network. Interconnection 3 reverse the role of WLAN and UMTS as in 1 and 2 by using a VAP(Virtual Access Point). This is the scenario of a tight coupling because there is always interaction 7
Interworking System Architecture
between both networks. In this case the WLAN is the master network and the UMTS is the slave network. Mobility management is done by the WLAN network. Interconnection 4 is done by using a mobility gateway/mobile proxy(MG) between the UMTS network and the WLAN network. They are both peer-to-peer networks. The MG is a proxy that is implemented on either the UMTS or the WLAN sides and will handle the mobility and routing. The last(5) interconnection is based on MobileIP protocol. There is no coupling is this case and both networks are peers. MobileIP handles the mobility management. The following sections will handle these interconnections more in details.
2.1 Interconnection between 3G-SGSN and WLAN AP by RNCemulator
Figure 2.2: interconnection between 3G-SGSN and WLAN Access Point
This interconnection connects the IEEE 802.11 WLAN network on the UMTS core network via the Iu interface. The IEEE 802.11 WLAN-based RAN is connected via an interworking unit (IWU), which is an RNC emulator which is represented in figure 2.2. With this configuration, the WLAN network is now considered as an UMTS cell. The IWU is needed to exchange the packets between the WLAN network and the UMTS network. The IWU almost has the same function as an RNC in the UTRAN.
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Interworking System Architecture
The adapted UMTS bearer concept includes an appropriate location and mobility management for the terminals in the WLAN coverage area. The WLAN AP doesn’t cover a very large area, for that reason the WLAN AP is not directly connected to the UMTS core network. A distribution network connects the WLAN APs and enlarges the coverage area of this radio access form. In this case/interconnection the IEEE 802.11 WLAN is threaded as a routing area(RA), although it seems like an RNC for the UMTS network. The user that connects on the UMTS network or WLAN network will always be threaded as an UMTS user. The UMTS mobility management will have to maintain information about the user even when it is connected to a WLAN network. The IWU entity is the RNC emulator.
Figure 2.3: IWU protocol stack (UMTS)
Figure 2.4: IWU protocol stack (WLAN)
The RNC could be a LAN or an extra implemented UMTS hardware entity. Dual WLAN/UMTS mode MS is needed to use both networks. The roaming arises when the user is connected to the WLAN network. For this interconnection, the users have to interface to the UMTS network through the RNC emulator. UMTS specific protocol such as PDCP is on top of the IEEE 802.11 MAC and the PHY layers implemented. UMTS related signalling protocols are carried out between the protocols in the MS and the RNC emulator.
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Interworking System Architecture
Figure 2.5: WLAN/UMTS dual mode protocol stack of a Mobile Node
The RNC emulator is a black box that hides WLAN specific features from the UMTS network. IP is used to transfer PS data over the Iu-interface as well as in the CN. The GPRS Tunnelling Protocol for UMTS(GTP-U) on top of this transport IP layer provides a tunnelling services through the CN until the access network encapsulates the user data. But if IP packets are transmitted on the user level, two IP layers exist in the packet switched architecture. The WLAN coverage area is represented as one routing area for the CN. If a mobile node enters or leaves this routing area, an update message is send to the core network of UMTS. But, the 3G-SGSN can simply distinguish the different radio access networks via routing areas. Running IP sessions are not interrupted because the IP address of a terminal is not changed. The procedure is completely transparent to the user. However, if a mobile node leaves the WLAN area, the service quality will degrade, especially for those sessions that made use of the high throughput capabilities of IEEE 802.11 WLAN system. With this interconnection the mobility management, roaming, billing and location related issues are taken care of by the UMTS network(see figure below)
Figure 2.6: Mobility, security, billing UMTS side
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Interworking System Architecture
2.2 Interconnection between GGSN and WLAN AP by 3G-SGSNemulator This type of connection is an alternative of the connection between WLAN AP and 3GSGSN. The interface between WLAN and UMTS is now a 3G-SGSN-like device (a 3GSGSN emulator). In this interconnection the Iu interfaces and the protocol between 3G-SGSN and 3G-GGSN are not used and hence the functions supported by those protocols are not available. It is possible to bypass some of the RNC-related functionalities by using a 3GSGSN emulator, and mobility management is again handled by UMTS.
2.3 Interconnection between UMTS and WLAN through VAP
Figure 2.7: interconnection through VAP
The VAP(Virtual Access Point) reverses the role of WLAN and UMTS in the first two interconnections. The WLAN is now the master network and UMTS the slave network. The VAP replaces the RNC/3G-SGSN in the first two interconnections. The roaming that the WLAN observes is between different APs in the extended service set and the VAP that appears as yet another AP to the IEEE 802.11 WLAN. In this case the UMTS network is seen as a basic service or a Pico cell associated with another (VAP). The function of the VAP is to communicate with mobile stations connected through UMTS, deencapsulate their packets and transmit them on the LAN. After that the packet will reach his final destination through the router attached to the LAN. The protocol stack of the VAP is shown in the figure 2.8:
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Interworking System Architecture
Figure 2.8: VAP compared with the GGSN
The VAP based interconnection also requires some modification on the MS protocol stack:
Figure 2.9: protocol stack of the MS
In this interconnection the VAP become an adopted unit in the user plane protocol of the UMTS architecture. For this reason the IEEE 802.11 MAC protocol is implemented on top of the protocols of the UMTS GGSN part. This is done for both the MS and the VAP entity. From the GGSN part of the UMTS network all protocols up to GTP-U level will be mapped onto IEEE 802.3 MAC so that the WLAN network sees the VAP as an AP. On the VAP side the UDP/TCP is on top of the stack. The 802.11 MAC protocol that is implemented in the MS is a level below the UDP/TCP.
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Interworking System Architecture
2.4 Interconnection between UMTS and WLAN via Mobility Gateway
Figure 2.10: interconnection through Mobility Gateway. (1-3 Client Server communication, 2-4 Server to Client communication)
As you can see on the figure there is an intermediate server(Mobile proxy) placed on either the UMTS or the IEEE 802.11 WLAN side. The MG will handle the routing and mobility issues. When an MS is attached to an AP, the communication path between the MS and a host on the internet will be via the access server through the MG and a router(1a to 3). But when the MS is on the UMTS side the path between the MS and the host will be 2a to 4.(see figure 2.10) The links after the MG will never change, only the links in the WLAN and UMTS side will change(1 and 2), depending on where the MS is. Nothing changes on protocol stacks architecture of the WLAN network. The protocol architecture of the UMTS network is a modification in which the MG is placed next the GGSN part of the protocol stacks of the UMTS. On the MS there will be some protocols adopted if the user wants roaming between both networks when he or she is still in one of the networks. So this functionality does require a dual-mode stack implementation on the MS. The following figure shows the protocol stack of the MS and the MG.
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Interworking System Architecture
Figure 2.11: Protocol stack Mobile Station/Node
Figure 2.12: Protocol stack Mobile Station/Node
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2.5 Interconnection between UMTS and WLAN based on Mobile IP
Figure 2.13: interconnection based on Mobile IP
Mobile IP is employed to restructure connections when a mobile station roams from one data network to another. Outside of its home network, the MS is identified by a care-of address associated with its point of attachment, and a collocated foreign agent that manages deencapsulation and delivery packets. The MS registers its care-of address with Home Agent. The Home Agent resides in the home network of the MS and is responsible for intercepting datagrams addressed to the MSs home address as well as encapsulating them to the associated care-of address. The datagrams to an MS are always routed through the Home Agent. Datagrams from the MS are relayed along an optimal path by the internet routing system, though it is possible to employ reverse tunnelling through the Home Agent. The required dual-mode MS protocol stack is the same as the previous paragraph. Both networks are peer networks and the functionality of the Home Agent/Foreign Agent exists at the IP layer. To have a more detailed overview of Mobile IP, check the following section.
2.6 Mobile IP 2.6.1 Introduction MIP is a new proposed standard of the IETF designed to support mobile users. It is also a new internet standard for the web and private networks. There are currently two standard, one to support the current IPv4 and on for the upcoming IPv6. One of the big requirements on the new standard is that it should support both ordinary and wireless networks.
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Interworking System Architecture
MIP in wireless networks is intended to be a direct extension of the existing fixed/wire line networks with uniform end-to-end QoS guarantees. MIP will and is changing the way that everybody works. The internet of today lacks mechanisms for support of users travelling through the world. IP is the common base for thousands of applications and runs over dozens of different networks. This is the reason for supporting mobility at the layer IP.
2.6.2 The challenge for Mobile IP The IP address of a host consists of two parts: • The higher order bits of the address determine the network on which the host resides. In a class A network the first 8bits, in a class B the first 16bits and in a class C the first 32bits. • The remaining low-order bits determine the host number. In a class A network the last 32bits, in a class B the last 16bits and in a class C the last 8bits. IP decides the next-hop by determining the network information from the destination IP address of the packet. While trying to support mobility on the Internet under the existing protocol suite, we are faced with two mutually conflicting requirements: • A mobile node has to change its IP address whenever it changes its point of attachment, so that packets destined to the node are routed correctly, • Maintaining existing TCP connections, the mobile node has to keep its IP address the same. Changing the IP address will cause the connection to be lost. Mobile IP is designed to solve the problem mentioned above by allowing each mobile node to have two IP addresses and by transparently maintaining the binding between the two addresses. The main goals of Mobile IP are to make mobility transparent to the higher level protocols and to make minimum changes to the existing Internet infrastructure.
2.6.2.1 Advantages Some advantages of using MIP are listed below: • A user can move a mobile computer from a WLAN AP coverage to a UMTS cell coverage area(between two different IP networks). without losing the connection to the home network • It allows fast, continuous low-cost access to corporate networks in remote areas where there is no public telephone system or cellular coverage. • Mobile IP finds local IP routers and connects automatically. • The remaining routers and hosts will still use current IP. MIP layer leaves transport and higher protocols unaffected. • Authentication is performed to ensure that rights are being protected. • Users can be permanently connected to their internet provider and charged only for the data packets that are sent and received.
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Interworking System Architecture
2.6.2.2 Disadvantages Besides these advantages there are also some disadvantages: • There is a routing inefficiency problem caused by the “Triangle routing” formed by the home agent, correspondent host and the foreign agent. (see figure) • Security risks are the most important problem facing MIP. Besides the traditional security risks with IP, one has to worry about faked care-of addresses. By obtaining a mobile host’s care-of address and rerouting the data to itself, an attacker can obtain unauthorized information. Yet another issue related to the security is how to make MIP coexist with security features coming in use within the Internet.
2.6.3 Characteristic of the standard Compatibility, transparency, scalability, efficiency and security are the characteristics that should be considered as baseline requirements to be satisfied by any candidate for a Mobile IP. The following points will give some more explanation about these characteristic: • Compatibility: A new standard cannot require changes for applications or network protocols already in use. MIP has to remain compatible to all lower layers used for the standard IP. • Transparency: Mobility should remain “invisible” for many higher layer protocols and application. Besides maybe noticing a lower bandwidth and some interruptions in service, higher layers should continue to work even if the mobile changed its point of attachment to the network. • Scalability and efficiency: A new mechanism into the internet must not degrade the efficiency of the network. Due to the growth rates of mobile communication, it is clear that MIP must be scalable over a large number of participants in the whole internet. • Security: All messages used to transmit information to another node about the location of a mobile node must be authenticated to protect against remote redirection attacks.
2.6.4 Network architecture with Mobile IP
Figure 2.14: Mobile IP architecture
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Interworking System Architecture
The big issue is to solve the overlapping between different networks, a user must be able to move between different networks without packet losses. The solution is that the mobile node should use two IP addresses: a fixed home address and a care-of address, that changes at each point of attachment. This solution requires two additional components: the home agent and the foreign agent as you can see on the figure 2.12. The mobile host is then able to move between different networks, while keeping the same IP address. The home agent is paced on the user’s local network, while the foreign agent is placed on the host that the user is currently visiting.
2.6.5 Handover Procedure The following section describes the handover between two different IP networks. Section 3.2 describes the handover based on Mobile IP specifically between WLAN and UMTS. The following steps describe the use of MIP while moving to a different network: • Mobile Agents advertise their presence by sending agent advertisement messages.
Figure 2.15: Agent Advertisement message format
• • • •
A mobile host may solicit Mobile Agents by sending agent solicitation messages. A mobile host determine if it is on the home or the foreign network by using the Mobile Agent advertisements. When the host is on the home network, it acts normal(independently of the Home Agent) When a mobile host returns from a foreign network, it must deregister with the home agent through Registration Request and Registration Reply messages.
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Interworking System Architecture
Figure 2.16: Registration Reply Request message format
• • • •
When a mobile host finds it has moved to a new, foreign network, it obtains a care-of address from the foreign agent or from other means such as DHCP. When a mobile host on the foreign network obtains its care-of address, it registers the new care-of address with the home agent using Registration Request and Registration Reply. Datagrams sent to the home network are received by the Home Agent. They are encapsulated in a new datagram that contains the care-of address and are sent to the Foreign Agent or to the mobile host if it is acting without the aid of the home agent. Datagrams sent by the mobile host on the foreign network need not be returned to the Home Agent, but could be sent directly to the destination.
There are three major components of Mobile IP that are used for these above procedures: Agent discovery, Registration, Tunnelling.
2.6.5.1 Agent discovery The agent discovery procedure used in Mobile IP is based on the internet control message protocol(ICMP). During the agent discovery phase, Home Agents and Foreign Agents advertise their presence on their attached links by periodically multicasting or broadcasting messages called agent advertisements. Mobile nodes listen to these advertisements and determine if they are connected to their home link or a foreign link. Rather than waiting for agent advertisements, an mobile node can also send an agent solicitation. This solicitation forces any agents on the link to immediately send an agent advertisement. If an mobile node determines that it is connected to a foreign link, it acquires a care-of address. Two types of care-of addresses exist: •
•
Foreign Agent care-of address is a temporary, loaned IP address that the mobile node acquires from the Foreign Agent advertisement. This type of care-of address is the exit point of the tunnel from the Home Agent to the Foreign Agent. Collocated care-of address is an address temporarily assigned to an mobile node interface. This address is assigned by DHCP or by manual configuration.
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2.6.5.2 Registration After receiving a care-of address, the Mobile Node registers this address with its home agent through an exchange of messages. The home agent creates a mobility binding table that maps the home IP address of the mobile node to the current care-of address of the mobile node. An entry in this table is called a mobility binding. The main purpose of registration is to create, modify, or delete the mobility binding of a mobile node at its home agent. During registration, the mobile node also asks for service from the Foreign Agent. The Home Agent advertises reach ability to the home IP address of the mobile node, thereby attracting packets that are designated for that address. When a device on the Internet, called a corresponding node(a node that sends or receives a packet to a mobile node. The correspondent node may be another mobile node or a non-mobile Internet node), sends a packet to the mobile node, the packet is routed to the home network of the mobile node. The Home Agent intercepts the packet and tunnels it to the registered care-of address of the mobile node. At the care-of address, the foreign agent extracts the packet from the tunnel and delivers it to the mobile node. If the mobile node is sending registration requests through a Foreign Agent, he keeps track of all visiting mobile nodes by keeping a visitor list. The Foreign Agent relays the registration request directly to the Home Agent without the need for tunnelling. The Foreign Agent serves as the router for all packets sent by the visiting mobile node. When the mobile node powers down or determines that it is reconnected to its home link, it deregisters by sending a deregistration request to the home agent. The home agent then reclaims the mobile node. Registration in MIP must be made secure so that fraudulent registrations can be detected and rejected.(see security for more explanation)
2.6.5.3 Tunnelling
Figure 2.17: Tunnelling
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Interworking System Architecture
(You can see the tunnel between the home agent and the foreign agent on figure 2.17. The traffic is always passing through the home agent.) Because the major function of a Layer 3 protocol is routing, the major features of Mobile IP deal with how to route packets to users who are mobile. Mobile IP is a tunnelling-based solution that takes advantage of the Generic Routing Encapsulation (GRE) tunnelling technology and simpler IP-in-IP tunnelling protocol. The traffic destined for the mobile node is forwarded in a triangular manner(see disadvantages of mobile IP). When the corresponding node (a device on the Internet) sends a packet to the mobile node, the home agent redirects the packet by tunnelling to the care-of address (current location) of the mobile node on the foreign network. The foreign agent receives the packet from the home agent and forwards it locally to the mobile node. However, packets sent by the mobile node are routed directly to the corresponding node.
2.6.6 Mobile IP Security The implementation of mobile IP on the global scale does introduce some problems related to security (the main goal to be established) with the implementation of the authentication being the foremost amongst them. As the mobile node keeps changing its location frequently the issue of authentication becomes more obvious. Mobile IP provides the following guidelines on security between its components: • Communication between Mobile Node and Home Agent must be authenticated. • Communication between Mobile Node and Foreign Agent can optionally be authenticated. • Communication between Foreign Agent and Home Agent can optionally be authenticated. Also, communication between an active Home Agent and a standby Home Agent, as implemented when using the Home Agent redundancy feature, must be authenticated.
2.6.6.1 Mobile Node – Home Agent security In particular, the Mobile IP registration process is vulnerable to security attacks, because it informs the Home Agent where to tunnel packets to a travelling Mobile Node. An illegitimate node could send a bogus registration request to an Home Agent and cause all packets to be tunnelled to the illegitimate node instead of the MN. This type of attack, called a denial-ofservice attack, prevents the Mobile Node from receiving and sending any packets. To prevent denial-of-service attacks, Mobile IP requires that all registration messages between an Mobile Node and an Home Agent be authenticated. Message Digest 5 (MD5) is an algorithm that takes the registration message and a key to compute the smaller chunk of data, called a message digest, plus a secret key. The Mobile Node and HA both have a copy of the key, called a symmetric key, and authenticate each other by comparing the results of the computation. 21
Interworking System Architecture
The time stamp is an identifier in the message that ensures the origination of the registration request and the time it was sent, thereby preventing replay attacks. A replay attack occurs when an individual records an authentic message that was previously transmitted and replays it at a later time. The time stamp is also protected by MD5. This authentication process begins when a Mobile Node sends the registration request. The Mobile Node adds the time stamp, computes the message digest, and appends the MHAE to the registration request. The Home Agent receives the request, checks that the time stamp is valid, computes the message digest using the same key, and compares the message digest results. If the results match, the request is successfully authenticated. For the registration reply, the Home Agent adds the time stamp, computes the message digest, and appends the MHAE to the registration reply. The Mobile Node authenticates the registration reply upon arrival from the Home Agent.
2.6.6.2 Mobile Node – Foreign Agent The authentication is not required in Mobile IP between a Mobile Node and a Foreign Agent Most of the (Mobile IP) routers supports the Mobile-Foreign Authentication Extension (MFAE). MFAE will protect the communication between the Mobile Node and a Foreign Agent by generating and keeping a shared key between them.
2.6.6.3 Foreign Agent – Home Agent Like the security between a Mobile Node and a Foreign Agent, the standard Mobile IP does not require the authentication between an Foreign Agent and an Home Agent. Most of the (Mobile IP) routers support the Foreign-Home Authentication Extension (FHAE). FHAE will protect the communication between the Foreign Agent and the Home Agent by generating and keeping a shared key between them.
22
Interworking System Architecture
2.7 Pros and CONS of the different scenarios Lets take the first figure of this section and lets compare. The following table gives the pros and cons of the different scenarios.
Figure 2.18
1: Interconnection between 3G-SGSN and WLAN AP by emulating RNC 2: Interconnection between GGSN and WLAN AP by emulating 3G-SGSN 3: Interconnection between UMTS and WLAN through VAP 4: Interconnection between UMTS and WLAN through Mobility Gateway 5: Interconnection between UMTS and WLAN based on Mobile IP Interconnection between 3G-SGSN and WLAN AP by emulating RNC Advatanges • •
The mobility management, roaming, billing and location related issues are taken care by the UMTS network. The strong security provided in the UMTS network and QoS for real-time services may now be provided over WLAN.
23
Interworking System Architecture
Disadvatages • • •
The master-slave configuration is not optimal. Using PDCP frames over WLAN may create bottlenecks. The UMTS network may be a bottleneck for the WLAN traffic Modification to standard WLAN terminals. So speed and price will be no attractive with this interconnection.
Interconnection between GGSN and WLAN AP by emulating 3G-SGSN Advatanges •
The mobility management, roaming, billing and location related issues are taken care by the UMTS network.
Disadvatages •
Master-slave configuration is not optimal: bottlenecks and inefficient routing also exist in this interconnection.
Interconnection between UMTS and WLAN through VAP Advatanges •
No specific advantages over the other!
Disadvatages •
There is an overhead of the packets: Each packet will have twice the UDP/TCP and twice the IP/PPP headers. So there will be an IEEE 802.11 MAC header along with the UMTS-related headers.
Interconnection between UMTS and WLAN through Mobility Gateway Advatanges • •
The proxy architecture are scalable Proxies are already in place in many organizations. These can be reused for mobility management and intertechnology roaming
Disadvatages • • •
The proxy architecture is not standardized and therefore requires proprietary protocols for intertechnology roaming The performance of a proxy is poor There are still open issues in the development of protocols for mobility management with the proxy architecture 24
Interworking System Architecture
Interconnection between UMTS and WLAN based on Mobile IP Advatanges •
This interconnection is based on Mobile IP which makes the IP address mobile.
Disadvatages • •
The triangle routing of Mobile IP is not a good thing for real-time applications like video and audio transmission. (Databases of both network has to communicate with each other to overcome packet duplication)
25
Handover WLAN and UMTS
3 Handover between WLAN and UMTS 3.1 Introduction There are two types of handovers: the horizontal handover and the vertical handover. • Horizontal handover refers to handover between node B’s and APs that are using the same kind of network interface. • Vertical handover refers to handover between a node B and an AP or vice-versa that are employing different wireless technologies. There are two differences in this type of handover: Î Upward vertical handover, which occurs from IEEE 802.11 WLAN AP with small coverage to an UMTS Node B with wider coverage. Î Downward vertical handover, which occurs from UMTS Node B with wider coverage to IEEE 802.11 WLAN AP with small coverage. Upward vertical handover takes place when the Mobile Node moves out the WLAN coverage to UMTS services when it becomes available even though the user still has connection to the WLAN coverage. Downward vertical handover has to take place when coverage of a service with a smaller coverage becomes available when the user still has connection to the services with the UMTS coverage. The Mobile Node decides that the current network is not reachable and performs handover to the higher overlay UMTS network when several beacons from the serving WLAN service are not available. It instructs the WLAN to stop forwarding packets and routes this request via Mobile IP registration procedure through the UMTS core network. When it is connected to the UMTS network, the Mobile Node listen to the lower layer WLAN AP, and if several beacons are received successfully, it will connect to the WLAN network via Mobile IP registration process. The vertical handover decisions are made on the basis of the presence or absence of beacon packets.
Figure 3.1: Overlaying(UMTS) and underlying(WLAN) network
When an Mobile Node moves away from an AP or from a node B, the signal level degrades and there is a need to switch communications to another point of attachment that gives access to the IEEE 802.11 WLAN network or the UMTS network. Handover in an overlay UMTS
26
Handover WLAN and UMTS
and underlay WLAN means that the Mobile Node will check every n time if there is the possibility to enter the underlaying WLAN coverage to use the benefits of WLAN(speed). There must be a string handover algorithm in order to avoid unnecessary handovers. The method that is used is the RSS(Received Signal Strength) metric, which means that the handover initiation or the handover triggering is sensitive to these signals. The following algorithm shows the handover procedure between WLAN and UMTS:
Working in WLAN cell
Working in UMTS cell No
no Loosing ?
WLAN Beacon ? yes
Yes Handover
UMTS ? No
Yes
connect
Wait long
Wait
connect
HO WLAN HO UMTS
3.2 Handover based on Mobile IP An Mobile Node moving from the WLAN network coverage may suddenly experience severe degradation of service and will have to perform handover very quickly to maintain the higherlayer connection.
3.2.1 MN moving from WLAN to UMTS coverage •
At first, he signal received from the AP in the WLAN network is initially strong and the Mobile Node is connected to the WLAN network which is also the home network of the Mobile Node and also the Home Agent in this network.
27
Handover WLAN and UMTS
•
• •
•
If the Mobile Node if moving away from the coverage of WLAN, then the signal become weaker when the mobile moves away. The Mobile Node scans the air for an other AP. If there isn’t any AP replying or if this signal is not strong enough, then the procedure would take place(there are also other parameters where he can make a decision to make the handover). Connection procedure is initiated to activate the UMTS PCMCIA card. The handover algorithm in the Mobile Node decides to disassociate from the WLAN and associate with the UMTS network. The Foreign Agent is activated, used by the MS Dual PCMCIA card and the Mobile IP, and the Mobile Node gets care-of address for visiting the UMTS network as a foreign network. The Home Agent in the WLAN is informed about the new IP address through a Mobile IP registration procedure and it performs the proxy ARP(address Resolution protocol) and intercepts the datagram. The Home Agent encapsulated datagram tunnels any packets arriving for the MN to the Foreign Agent of the UMTS network. At the end of the delivery the Mobile Node will deencapsulate and get the datagrams.
In this case the handover algorithm determines that there is no local coverage available via WLAN and handover must be performed to the UMTS network assuming that a service is always available to the Mobile Node.
3.2.2 MN moving from UMTS to WLAN coverage Once the Mobile Node is attached to the UMTS, it will constantly monitor the air at repeated intervals to see whether or not a high data rate WLAN service is available(reception of beacons). As soon as such a service becomes available, the handover algorithm should initiate an associated procedure to the newly discovered AP. • • • • •
Initially, he signal from the WLAN AP is not detected. The Mobile Node then detects a beacon, which indicates that an underlay WLAN network is available. The Mobile Node decides to make the hand over from the UMTS network to the WLAN network. The Foreign Agent in the UMTS network is deactivated and updates by Mobile IP and the home IP address is used. The Home Agent in the WLAN network is instructed by the MN to no longer do a proxy ARP through the Mobile IP.
28
Handover GSM/GPRS and UMTS
4 Handover between GSM/GPRS and UMTS In the first stage, the introduction of UMTS will require hard handover between the UMTS UTRAN and the GSM/GPRS GERAN to provide the “always on” idea. It is offen called intersystem handover or interfrequency handover. This means that it provide the handover between two different Radio Access Technologies. Before such handover can be made, some procedures has to be taken. The first procedure deals with measurements. Before the Mobile Node can start any handover, it must measure the quality of the new cell.
4.1 Measurements First the Mobile Node must know the frequency in which the new cell in the other system is transmitting. This information must be relayed to the Mobile Node via the old cell. This information is typically sent within some kind of measurement control message. Second, the Mobile Node must be able to measure the signal strength of the new carrier or some other parameter on which the handover algorithm is based. This operation must be accomplished simultaneously with the operations of the old channel. It is very difficult in case of handover between GSM/GPRS and UMTS. This is because the Mobile Node in the UMTS UTRAN is receiving all the time and there are no idle slots in which to take measurements on the other frequency. This problem can be solved with two alternatives:
4.1.1 Dual receiver If the Mobile Node has two receivers, then one receiver can perform interfrequency measurements, while another receives the normal UTRAN transmission. If the used GSM/GPRS frequency band is 1800-1900Mhz, it may be so close to the UMTS band used that the intercarrier interference becomes a problem.
4.1.2 Compressed mode In compressed mode not all time slots in downlink are used for data transmission. If both frequencies use overlapping compressed mode gaps(idle slots) and the switch is done during such a gap, then the handover could be seamless. The use of compressed mode is mandatory for Mobile Node that do not have dual receivers.
4.2 Different maximum data rate
29
Handover GSM/GPRS and UMTS
The different maximum data rates is an additional problem when handover in the UMTS to GSM/GPRS direction is taking place. This procedure must cope with a situation in which the UMTS UTRAN connection was using close to 2Mbps data rates and after handover the new connection can only get a small part of this rate.(This could also be the problem in the handover between WLAN and UMTS). In the GSM/GPRS to UMTS direction the handover procedure is technically easier. A special problem with this handover is that synchronization to a UMTS cell requires a large amount of information about the cell and the system and relaying that information to the Mobile Node using an extended GSM/GPRS handover command would be impractical. The Mobile Node should download up to 16 predifined UMTS radio configurations. Once the handover takes place, the network indicates only the identity of the preconfiguration to be used and possibly some additional parameters in the GSM/GPRS handover command message.
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Fourth Generation of Mobile Systems
5 Fourth Generation of Mobile Systems(4G) 4G is for now one not very clear and a lot of annalists speculate about this new generation of mobile systems. One thing is sure, this 4G will include various wireless and mobile systems which will form one system. Which technology that is used will be transparent for the user. For example, from a cellular network to a satellite-based network to a high-bandwidth wireless LAN. With this feature, users will have access to different services, increased coverage, the convenience of a single device, one bill with reduced total access cost, and more reliable wireless access even with the failure or loss of one or more networks. 4G networks will also feature IP interoperability for seamless mobile Internet access and bit rates of 50 Mbps or more. Because deployment of 4G wireless technology is not expected until 2006 or even later, developers will hopefully have time to resolve issues involving multiple heterogeneous networks such as access, handoff, support for QoS, pricing and billing,…
5.1 4G architecture One of the major challenge in developing 4G systems is how to access different wireless and mobile systems. There are several(three) possible architectures for this challenge. The next section described these architecture at a high level.
5.1.1 Multimode device
Figure 5.1: multimode device
The above figure shows 4G architecture using a multimode device. The devices will have multiple interfaces(see blue spots on figure 4.1) to access services on different wireless networks. Early examples of this architecture include the existing AMPS/CDMA dualfunction cell phone, Iridium’s dual function satellite-cell phone, and the emerging 31
Fourth Generation of Mobile Systems
GSM/DECT dual-mode cordless phone, the UMTS/GPRS/EDGE cards. The multimode device architecture may improve call completion and expand effective coverage area. It should also provide reliable wireless coverage in case of network, link, or switch failure. The user, device, or network can initiate handoff between networks. The device itself incorporates most of the additional complexity without requiring wireless network modification or employing interworking devices. Each network can deploy a database that keeps track of user location, device capabilities, network conditions, and user preferences. The handling of (QoS) issues remains an open research question.
5.1.2 Overlay network
Figure 5.2: Overlay network
In this type of architecture, a user accesses an overlay network consisting of several universal AP(UAP) indicated with the pink squares on figure 4.2. These UAPs in turn select a wireless network based on availability, QoS specifications, and user defined choices. A UAP performs protocol and frequency translation, content adaptation, and QoS negotiation-renegotiation on behalf of users. The overlay network performs handoffs as the user moves from one UAP to another. A UAP stores user, network, and device information, capabilities, and preferences. Because UAPs can keep track of the various resources a caller uses, this architecture supports single billing and subscription.
5.1.3 Common access protocol
32
Fourth Generation of Mobile Systems
Figure 5.3: Common Access protocol
This protocol becomes viable if wireless networks can support one or two standard access protocols. One possible solution, which will require interworking between different networks, uses wireless ATM. To implement wireless ATM, every wireless network must allow transmission of ATM cells with additional headers or wireless ATM cells requiring changes in the wireless networks. One or more types of satellite-based networks might use one protocol while one or more terrestrial wireless networks use another protocol.
33
Index
Index 3G-SGSN, 8 3G-SGSN-emulator, 11 4G, 29
A Agent Advertisement message format, 18 Agent discovery, 19
C care-of address, 17 Common access protocol, 30 Compatibility, 17
D DHCP, 19
E efficiency, 17
F foreign network, 18
G GGSN, 12 GRE, 20 GSM/DECT, 30 GTP-U, 10
Loose Coupling, 5
M MAC, 12 MD5, 21 MFAE, 22 MG, 13 Mobile IP, 15 Mobility Gateway, 12 Multimode, 29
O Open Coupling, 5 Overlay network, 30
P PDCP, 9
R RA, 7, 9 Registration, 19 Registration Reply Request message format, 18 RNC, 8 RNC-emulator, 8 RSS, 27
S
Handover, 18, 26 home agent, 18
Scalability, 17 second last km, 3 Security, 17
I
T
H
IETF, 15 Integration, 5 interworking, 4 IPv4, 15 IPv6, 15 IWU, 8
Tight Coupling, 5 Transparency, 17 Tunnelling, 20
L
V
last km access, 3
U UDP/TCP, 12
VAP, 11 34
Index
VoIP, 4
WiFi, 2
35
6 Conclusion 4G could be the conclusion of this paper because the interconnection of WLAN and UMTS(3G) will be the hot item of 4G. Part 1 covers the important items at a high level because it is not sure how it will be developed and evolves in the future. The 3G is not yet in its last phase and is still growing. In Belgium the mobile operators must have a coverage growth of 10% each year. So within at least 4 years, there will be a full coverage of UMTS in Belgium(and other countries). Till now, the interworking between UMTS and WLAN will contains also the interworking between WLAN and GPRS to provide a global acceptable product/system. This paper covered also the use of Mobile IP for one of the five interconnections. The interconnection between WLAN and UMTS based on Mobile IP is the more suitable of the five interconnections presented in part 1. Finally, intersystem handover is a topic that will become more and more important in the evolutionary path toward UMTS and 4G wireless infrastructures.
