Frekvenční a fázová synchronizace

Frekvenční a fázová synchronizace

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Proč je nutná synchronizace v mobilích sítích 1588v2 PTP, SyncE Master a Slave Clock, Boundary a Transparent Clock v systémech 1588v2, referenční body Stabilita obnovených hodin, měření wanderu a fáze

Frekvenční a fázová synchronizace Proč je nutná synchronizace v mobilních sítích Why do mobile basestations need frequency synchronisation? •Regulation and licensing of spectrum •Interference with other basestations •Handoff for mobiles moving between cells

Handset frequency acceptance ± 250ppb Basestation frequency accuracy ± 50ppb

•Quality of service

•Doppler effect

fc

frequency

Frekvenční a fázová synchronizace Doppler Shift f = fo . v c At 320km/h (200mph), f = 300ppb

At 160km/h (100mph), f = 150ppb

Frekvenční a fázová synchronizace Time Synchronisation GSM, UMTS (European 2G and 3G mobile standards): •no requirement for time synchronisation cdmaOne, cdma2000 (N. American 2G and 3G mobile standards): •Basestations must be within 3s of system time (10s holdover) •Required for “soft handoff” •Handset must see pilot signals from both basestations within a few microseconds of each other to handover properly

Company ±3s Confidential  ±1km

±3s  ±1km

Frekvenční a fázová synchronizace LTE Advanced: Small Cells Enhanced Inter-Cell Interference Co-ordination (eICIC) •Interference in small cell edge area •Solution: “Almost Blank Sub Frames” – macrocell reduces power temporarily so handsets can “hear” the small cell •Time synchronisation of ±1 to 5s required to co-ordinate ABSF

Frekvenční a fázová synchronizace LTE Advanced: CoMP Co-ordinated Multipoint (CoMP) Several techniques for improving throughput and performance:

•Joint Transmission or Reception •Co-ordinated Beamforming •Dynamic Point Selection •Dynamic Point Blanking All require time synchronisation in the order of ±1 to 5s

Frekvenční a fázová synchronizace LTE Synchronization Requirements

LTE (FDD)

±50 ppb

N/A

±16ppb (G.8261.1)

LTE (TDD)

±50 ppb

±1.5µs (< 3km radius) ±5µs (> 3km radius)

±16ppb (G.8261.1) ±1.1μs (G.8271.1)

LTE-A MBSFN

±50 ppb

LTE-A CoMP

±50 ppb

±1 to 5µs implementation dependent

±16ppb (G.8261.1) ±1.1μs (G.8271.1)

±33ppb ±1.1μs (G.8271.1) ±100ppb ±1.1μs (G.8271.1)

Network MIMO

LTE-A eICIC HetNet Coordination

±50 ppb

Small Cells

±100 ppb

N/A (FDD) ±1.5µs (TDD) ±1 to 5µs (eICIC)

Home Cells

±250 ppb

N/A (FDD) ±1.5µs (TDD)

Frekvenční a fázová synchronizace Frekvenční synchronizace – signály mají stejnou periodu, ale ne nutně fázi

Fázový posun mezi začátkem referenčního signálu Fázová synchronizace – signály začínají se stejný čas, ale ne nutně se stejnou periodou

Frekvenční a fázová synchronizace Mobile Backhaul Synchronization • Approach 1: Use the physical layer clock • SyncE clocks (EEC) made identical to SECs in performance terms Up to 10 SSUs

PRC

Up to 20 SECs or EECs

SSU


SSU

SSU

• Approach 2: Use a packet timing protocol • Packet timing protocols such as PTP or NTP used to deliver frequency


End Equipment

Up to 10 SSUs

M

PRC


SSU


SSU

SSU

Packet Network

S

Packet Master and Slave

End Equipment

Frekvenční a fázová synchronizace •Conventional timing (frequency) signal: •

A nominally periodic signal, generated by a clock: Significant instants

Timing jitter and wander

•Packet timing signal: •

A nominally periodic signal, generated by a packet master clock: Significant instants

F Payload Payload 4 H4 H

Packets



Packet Delay Variation


Frekvenční a fázová synchronizace G.8260: Definitions and Terminology for Synchronization in Packet Networks (includes PDV metrics)

Frequency Basic Aspects Network Requirements

Time/phase

G.8261: Timing and Synchronization Aspects in Packet Networks (Frequency) G.8261.1: PDV Network Limits Applicable to PacketBased Methods (Frequency)

G.8271: Time and Phase Synchronization Aspects in Packet Networks G.8271.1: Network Limits for Time/Phase (full timing support) G.8271.2: Network Limits for Time/Phase (partial timing support)

Clock Specifications

G.8262: Timing Characteristics of a Synchronous Ethernet Equipment Slave Clock (EEC)

G.8272: Timing Characteristics of Primary Reference Time Clocks (PRTC)

G.8263: Timing Characteristics of Packet-Based Equipment Clocks (PEC)

G.8273: Packet-Based Equipment Clocks for Time/Phase: Framework G.8273.1: Telecom Grandmaster (T-GM) G.8273.2: Telecom Boundary Clock (T-BC) G.8273.3: Telecom Transparent Clock (T-TC)

Methodds and Architecture

G.8264: Distribution of Timing Information through Packet Networks G.8265: Architecture and Requirements for Packet-Based Frequency Delivery

Profiles

G.8265.1: Precision Time Protocol Telecom Profile for Frequency Synchronization

G.8273.4: Telecom Time Slave Clock (T-TSC) G.8275: Architecture and Requirements for Packet-Based Time and Phase Delivery G.8275.1: PTP Profile for Time and Phase Synchronization (full timing support) G.8275.2: PTP Profile for Time and Phase Synchronization (partial timing support)

Published

1st version agreed

Under development

Options

Frekvenční a fázová synchronizace Synchronous Ethernet (SyncE) Účelem SyncE je distribuovat informaci o frekvenci od PRC (Primary Reference Clock) prostřednictvím ethernetových zařízení. Hlavní činností SyncE rozhraní je získat synchronizační frekvenci z přicházejícího bitového streamu a předat ji systémovým hodinám EEC (Ethernet Equipment Clock) routru nebo switche, které pak tuto informaci šíří dál k dalšímu zařízení.

Hlavní rozdíl mezi “klasickým“ ethernetem a SyncE je ve vysílání hodin na TX portu routru/switche.

Frekvenční a fázová synchronizace SyncE ITU-T G.8261 • Používá k synchronizaci fyzickou vrstvu • Získává hodinový signál “bit stream” • Každý uzel obnovuje “hodiny“

• Nezávislý na použité síti (data jsou oddělená od synchronizace) • EEC (Ethernet Equipment Clock)

Frekvenční a fázová synchronizace Synchronous Ethernet (SyncE) • Použitý vysoce stabilní interní oscilátor • Ethernet ‘Classic’: ±100ppm. • Synchronous Ethernet: ±4.6ppm

ITU-T Standardy • G.8261: Timing & Synchronisation in Packet Networks • G.8262: Timing Characteristics for Synchronous Ethernet Equipment • G.8264: Distribution of Timing Through Packet Networks (ESMC)

Frekvenční a fázová synchronizace Precision Time Protocol (PTP) - IEEE 1588v2 • Jakmile je ustanovena hierarchie Master/Slaver (BMCA) “Announce message“, může začít proces synchronizace hodin, pomocí výměny PTP zpráv, která se skládá ze dvou částí: • Změřením “propagation delay“ mezi Mastrem a Slavem. Sync Message obsahuje časovou značku kdy byla odeslaná Mastrem.

Delay_Req_Message je identická jako Sync Message, ale odeslaná Slavem, obsahuje časovou značku kdy byla odeslaná Slavem.

Delay_Resp_Message odeslaná Mastrem, obsahuje časovou značku kdy byla Delay_req_message doručená Mastru.

t1 = Master Time čas vyslání Sync Message. t2 = Slave Time čas přijetí Sync Message. t3 = Slave Time čas vyslání Delay_Req Message. t4 = Master Time čas přijetí Delay_Req Message.

Frekvenční a fázová synchronizace Master t1=10

Time = 10 s Time = 11 s

Slave Sync = 10s? Follow up = 10s

Time = 17 s

t4=19

Time = 5 s Time = 8 s

t2=8

Time = 11 s

t3=11

Delay Req= 11s

Time = 19 s

Delay Resp= 19s Time = 23 s Time = 24 s

Sync = 23s ? Follow up = 23s

Delay = [(t2-t1) + (t4-t3)]/2 = [(19-11) + (8-10)]/2 = 3 Offset = (t2-t1) – Delay = -5

Time = 17 s Time = 23 s Time = 24 s

Slave čas upravený o offset a delay

Zpráva Sync resp. Follow Up udávajá zpoždění Master->Slave (t-ms) Zprávay Delay_req a Delay_resp udávají zpoždění Slave->Master (t-sm) Jakákoliv asymetrie mezi (t-ms) a (t-sm) vnáší chybu do výpočtu korekce hodin!

Frekvenční a fázová synchronizace Time Error Source Constant Time Error (cTE) The fixed component is called Constant Time Error (cTE) and comes from Link asymmetries and Node (T-GM, T-BC, T-TSC) asymmetries.

• Node asymmetry • Link asymmetry • Route asymmetry

Dynamic Time Error (dTE) The time-varying component is called Dynamic Time Error (dTE) and comes primarily from Packet Delay Variation (PDV) caused by router queues, etc.

Frekvenční a fázová synchronizace Approaches to Time Distribution 1. “Full Timing Support” • •

Combined use of PTP for time and SyncE for frequency Every switch or router in the timing path must support PTP and SyncE (i.e. contain a Telecom Boundary Clock, T-BC)

2. “Assisted Partial Timing Support” • •

Use of GNSS for time, supported by PTP for protection Some switches or routers in the timing path may support PTP (i.e. contain a BC or TC), but this is not mandatory

3. “Partial Timing Support” • •

Use of PTP for both time and frequency distribution Some switches or routers in the timing path may support PTP (i.e. contain a BC or TC), but this is not mandatory


PTP with Full Timing Support GNSS Reference Point A

Reference Point B

Reference Point C

Reference Point D

all switch/routers on the path between T-GM and T-TSC contain a T-BC

T-GM

PRTC

Features

PTP Grandmaster

T-TSC

Packet Network

PTP Slave

End clock

•Every element in the path must be “PTP aware”

•T-BC case covered in standards, T-TC case under development •Uses a combination of SyncE and PTP, where SyncE provides the frequency and PTP the phase/time

Frekvenční a fázová synchronizace Boundary Clock

Slave

PTP

Master

Boundary Clocks reduce PDV accumulation by:

Master

Slave

SyncE

PTP

1pps SyncE

EEC G.8273.2 Telecom FrequencyClock Time/Phase Boundary (T-BC) (T1/E1/SyncE) (1pps)

•Terminating the PTP flow and recovering the reference time •Generating a new PTP flow using the recovered time •No direct transfer of PDV •Slave/Master combination Telecom BCs use SyncE to: •Improve stability •Improve holdover


Packet Interfaces

Packet Interfaces

Siwtch/router Switch/Router

Slave

PTP Messages

Master

Boundary Clock

PTP Messages

1pps SyncE

EEC

SyncE

Frekvenční a fázová synchronizace Transparent Clock Transparent Clocks reduce PDV by; Calculating the time a PTP packet resides in the TC device (in nsec) and insert the value into the CorrectionField. Using the CorrectionField, the Slave or terminating BC can effectively remove the PDV introduced by the TC.

Q1

Q2 Qn

Packet Delay in TC Device inserted into CorrectionField

TC CF Accuracy = 50ns (IEEE C 37.238)


PTP with Full Timing Support Benefits •Controlled, deterministic environment suitable for both frequency and time/phase transfer •“Building block” approach to network construction, with example time error budgets in G.8271.1 •Profile, architecture and clock performance defined by ITU-T, published May 2014 Challenges •All equipment in path needs to be PTP aware •No control of asymmetry in the network

Frekvenční a fázová synchronizace G.8275.2 “Partial Timing Support” Profile

GNSS

GNSS not all switch/routers on the path between T-GM and T-TSC contain a T-BC T-GM

PRTC

PTP Grandmaster

APTSC Packet Network

Combined End clock GPS/PTP Slave

Features •Objective is backup to GNSS, i.e. “assisted holdover” •Can use GNSS when in service to monitor PTP service quality and measure network asymmetry

•PTP can maintain timebase when GNSS is out of service (e.g. due to jamming or antenna failure)

Frekvenční a fázová synchronizace PTP with Assisted Partial Timing Support Benefits •Mutual co-operation between GNSS and PTP • • •

PTP provides an initial time fix to assist the GNSS during signal acquisition GNSS calibrates the PTP asymmetry, and monitors its suitability for service PTP can monitor GNSS timing quality, e.g. antenna failure, spoofing, jamming

•Operates over existing networks, including third party access networks that may not have built-in PTP support •Profile, architecture and clock performance under definition in ITU-T Challenges •Less deterministic path from T-GM to APTSC, because not every network element assists in the timing flow •May need constraints on traffic load and span of the packet network •Little agreement in ITU-T on the scope of the network, hence consent date keeps slipping

Frekvenční a fázová synchronizace Use case: In-building Small Cells

Features: •GNSS antenna on roof, supplies synchronization to building (and possibly neighbouring buildings) •Distributed to small cells using PTP over the building LAN •No timing support provided (e.g. BCs or TCs)

Frekvenční a fázová synchronizace PTP with Partial Timing Support GNSS not all switch/routers on the path between T-GM and T-TSC contain a T-BC

T-GM

PRTC

PTP Grandmaster

Packet Network

Features •Objective is to distribute time over a small PTP-unaware network •Small network, potentially only a single in-building network •Places GNSS source as close to the end clock as possible

PTP Slave

End clock

Frekvenční a fázová synchronizace PTP with Partial Timing Support Benefits •Simple deployment over existing networks •Operators do not need to own or manage the network •Can be leased from a third party, e.g. building owner

•Short network, so cable or fibre asymmetry small •Profile, architecture and clock performance under definition in ITU-T Challenges •Less deterministic path from T-GM to T-TSC, because not every network element assists in the timing flow •Switches/routers not designed with PTP asymmetry in mind, so device asymmetry is uncontrolled •May need constraints on traffic load and span of the packet network •Little agreement in ITU-T on the scope of the network

Frekvenční a fázová synchronizace G.8271.1: Reference Points GPS

Reference Point A

Reference Point B

Reference Point C

T-GM PRTC

PTP Grandmaster

Reference Point D

T-TSC Packet Network

PTP Slave End clock

Reference Point A:

• Time accuracy and stability at output of PRTC (defined in G.8272)

Reference Point B: • Packet timing interface at output of PTP GM (defined in G.8272; same as A)

Reference Point C: • Time accuracy and stability at input to end equipment (defined in G.8271.1)

Reference Point D: • End application requirements (e.g. air interface time/frequency specification)

Frekvenční a fázová synchronizace G.8271.1 Network Reference Points A, B

±100ns (PRTC/T-GM)

C ±200ns dTE (random network variation)

D

cTE uses up 70% of the network equipment budget ±550ns cTE (node asymmetry, ±50ns per node)

±250ns cTE (link asymmetry compensation)

Class A T-BCs: Class B T-BCs: ±420ns cTE (21 nodes, ±20ns per node)

±380ns cTE (link asymmetry compensation)

±1.1µs network equipment budget ±1.5µs end-to-end budget

±250ns (short term holdover) ±150ns (end application)

Frekvenční a fázová synchronizace - co je nutné měřit TIE – Time Interval Error (ns) Fázový rozdíl mezi referenčním signálem a testovaným signálem v určitém čase.

MTIE – Maximum Time Interval Error (ns) Maximální rozkmit testovaného signálu vůči referenčnímu signálu, během celého testu.

TDEV – Time Deviation (ns)

TIE (ns)

Phase Error (TIE) MTIE

časová stabilita fáze v závislosti na času měření.

t(1) t(2) t(3) t(4) t(5)

Observation time (n·t0)

Reference Clock

Test Signal

MTIE (ns)

*Faster playback is used to better explain the concept.

t (s)

Frekvenční a fázová synchronizace Clock Interface on Manufacturers’ Equipments Juniper ACX 1100

Juniper ACX 1100 has a SMC port which outputs 1pps signal

ZTE BS 8700

PIN 18 for 10MHz signal. PIN 16 for GND

Huawei BTS 3900

Frekvenční a fázová synchronizace Clock Interface on Manufacturers’ Equipments Ericsson SIU (Cell Site Router)

Symmetricom TP 2700 BNC port which outputs 1pps signal.

Huawei ATN CX600/950B

Huawei CX600 has both RJ45 and miniBNC port that output E1 and 1pps signal.

Frekvenční a fázová synchronizace TX300S, TX320,MTT320 RXT1200

Paragon - X

Sentinel

Frekvenční a fázová synchronizace (CSAC) Chip Scalled Atomic Clock

Frekvenční a fázová synchronizace MTT320 wander analysis

GPS

Reference Point A

Reference Point B

Reference Point C

TGM PRTC

PTP GM

Reference Point D

T-TSC Packet Network

PTP Slave

End clock

1PPS

Frekvenční a fázová synchronizace TX300 Master Slave emulation GPS Reference Point B

Reference Point C

Reference Point D

T-TSC

TX300 Master Emulation

Packet Network

PTP Slave

TX300 Slave

Frekvenční a fázová synchronizace Sentinel operating in Pseudo-Slave mode

Antenna

Sentinel Tester emulates PTP Pseudo-Slave

1588v2 GM 1G O/E or 100M E

eNodeB

RNC NETWORK

2MHz/10MH/1PPS from eNodeB

Cell Site Router or Switch

Base Station

Frekvenční a fázová synchronizace Sentinel operating in Monitor mode

Sentinel Tester in Transparent Mode

Antenna

1588v2 GM 1G O/E or 100M E

A RNC NETWORK

Cell Site Router or Switch

A

B

Taps or Splitter

B

eNodeB Base Station


Color TFT, 8.4” 800 x 600

Antenna

Frequency In/Out Ports

388mm

126mm

320mm Net Weight: < 6kg (13lb)

Packet Module Clock Module

Modular Design


•Master Slave Emulation gives highest accuracy and repeatability for test bed •Time Error measurements in CAT allow detailed insight into device performance.

Frekvenční a fázová synchronizace

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