KINERJA SISTEM OFDM MELALUI KANAL HIGH
ALTITUDE PLATFORM STATION (HAPS)
LAPORAN TUGAS AKHIR
Oleh:
YUDY PUTRA AGUNG
NIM : 132 03 017
Program Studi : Teknik Elektro
SEKOLAH TEKNIK ELEKTRO DAN INFORMATIKA
INSTITUT TEKNOLOGI BANDUNG
2007
KINERJA SISTEM OFDM MELALUI KANAL HIGH
ALTITUDE PLATFORM STATION (HAPS)
Oleh :
Yudy Putra Agung
NIM : 132 03 017
Tugas Akhir ini telah diterima dan disahkan Sebagai persyaratan untuk memperoleh gelar SARJANA TEKNIK di
JALUR PILIHAN TEKNIK TELEKOMUNIKASI
PROGRAM STUDI TEKNIK ELEKTRO
SEKOLAH TEKNIK ELEKTRO DAN INFORMATIKA
INSTITUT TEKNOLOGI BANDUNG
Bandung, September 2007
Disetujui oleh :
Pembimbing
Dr. Iskandar, ST. MT
NIP: 132162435
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DAFTAR TABEL
Halaman Tabel 2.1 Karakteristik dasar terrestrial, satelit dan HAPS ........................................................... 9
Tabel 2.2 Parameter Rician K-factor ............................................................................................20
Tabel 3.1 Parameter lintasan .........................................................................................................48
Tabel 3.2 Parameter K - factor......................................................................................................49
Tabel 4.1 Perbandingan kinerja BER pada K factor 1.4 dengan bitrate yang berbeda .................51
Tabel 4.2 Perbandingan kinerja BER pada K factor 2.0 dengan bitrate yang berbeda .................52
Tabel 4.3 Perbandingan kinerja BER pada K factor 2.3 dengan bitrate yang berbeda .................53
Tabel 4.4 Perbandingan kinerja BER pada K factor 2.7 dengan bitrate yang berbeda .................54
Tabel 4.5 Perbandingan kinerja BER pada K factor 4.6 dengan bitrate yang berbeda .................55
Tabel 4.6 Perbandingan kinerja BER pada K factor 6.4 dengan bitrate yang berbeda .................56
Tabel 4.7 Perbandingan kinerja BER pada K factor 9.2 dengan bitrate yang berbeda .................57
Tabel 4.8 Perbandingan kinerja BER pada K factor 12.2 dengan bitrate yang berbeda ...............59
Tabel 4.9 Perbandingan kinerja BER pada K factor 16.8 dengan bitrate yang berbeda ...............60
Tabel 4.10 Perilaku kanal dengan bitrate yang berbeda ...............................................................62
Tabel 4.11 Perilaku kanal dengan frekuensi Doppler yang berbeda .............................................67
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ABSTRAK
KINERJA SISTEM OFDM MELALUI KANAL HIGH ALTITUDE PLATFORM (HAPS) Oleh
Yudy Putra Agung
NIM : 132 03 017
PROGRAM STUDI TEKNIK ELEKTRO
Menyediakan layanan komunikasi pita lebar pada HAPS merupakan ide baru dan layak untuk diperbincangkan. Salah satunya mengadopsi
teknik transmisi OFDM
sebagai media modulasi digital untuk diterapkan pada HAPS. Teknologi HAPS memiliki kelebihan yang dapat menutupi kekurangan dari teknologi terrestrial maupun satelit. Pada tugas akhir ini penulis mempelajari kinerja system OFDM pada kanal HAPS yang merupakan kanal Rician fading. Pada kondisi real di lapangan, daya yang diterima merupakan gabungan dari daya sinyal dominant/LOS dan daya sinyal multipath. Parameter yang menggambarkan perbandingan daya sinyal dominant dengan daya sinyal multipath disebut K factor. Bertambahnya sudut elevasi antara platform HAPS dengan user terminal mengakibatkan bertambahnya nilai K factor dan mempengaruhi kinerja system OFDM yang terpengaruh multipath fading. Hasil yang diperoleh memunjukkan semakin bertambahnya sudut elevasi (nilai K factor bertambah) maka kinerja system OFDM semain baik. Akan tetapi kinerja system OFDM memburuk seiring bertambahnya bitrate dan Doppler spread. Kata Kunci : HAPS, OFDM, sinyal dominant/ LOS, sinyal multipath, K factor, sudut elevasi, kinerja system, bitrate, Doppler spread.
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ABSTRACT
THE PERFORMANCE OF OFDM SYSTEM THROUGH HIGH ALTITUDE
PLATFORM STATON (HAPS) CHANNEL
By
Yudy Putra Agung
NIM : 132 03 017
ELECTRICAL ENGINEERING STUDY PROGRAM
Providing broadband communication service in High Altitude Platform Station (HAPS) is a new idea that proper to be discussed. One of this services is adopting OFDM transmission technique as digital modulation medium applicable in HAPS. HAPS technology is an alternative that can be covered the lack of terrestrial and satellite technologies. In this final project, writer studies about the performance of OFDM system in HAPS channel, where it has known as Rician fading channel. In real condition, received power in HAPS channel is composite of dominant / LOS signal power and multipath signal power. The parameter that describe comparison of dominant signal power and multipath signal power is K factor. Elevation angle increase between HAPS platform and terminal user cause K factor value raising and affect the performance of OFDM in multipath fading condition. The result shows the increase of elevation of angle (in this case K factor is also increasing) makes system performance works better. However OFDM
system
performance is getting worse when bitrate and Doppler spread increased. Keywords: HAPS, OFDM, dominant/LOS signal, multipath signal, K factor, elevation angle, system performance, bitrate, Doppler spread
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DAFTAR GAMBAR
Halaman Gambar 2.1 Balon udara HAPS .................................................................................................... 7
Gambar 2.2 Arsitektur layanan teknologi HAPS .......................................................................... 8
Gambar 2.3 Grafik redaman oleh hujan,kabut, uap air dan oksigen sbg fungsi dari frekuensi . 11
Gambar 2.4 Grafik power delay profile persamaan Dovis ......................................................... 12
Gambar 2.5 Peristiwa Doppler Shift ........................................................................................... 14
Gambar 2.6 Komunikasi HAPS dengan perbedaan sudut elevasi ............................................. 16
Gambar 2.7 Grafik cumulative probabilities daya yang diterima pada frekuensi 2.4 GHz ........ 17
Gambar 2.8 Variasi statistic amplitude sinyal yang diterima dan K factor................................. 19
Gambar 2.9 Pengukuran K factor sebagai fungsi dari sudut elevasi .......................................... 20
Gambar 2.10 Kanal AWGN ....................................................................................................... 22
Gambar 2.11 Kharakteristik AWGN .......................................................................................... 22
Gambar 2.12 Diagram phasor sinyal Rician fading ................................................................... 23
Gambar 2.13 Pengalokasian simbol pilot pada frekuensi subcarrier tertentu ............................. 27
Gambar 2.14 Proses estimasi dengan teknik interpolasi ............................................................. 28
Gambar 2.15 Bagan dasar OFDM............................................................................................... 30
Gambar 2.16 Sinyal-sinyal orthogonal ...................................................................................... 31
Gambar 2.17 Penambahan Cyclic Prefix pada sinyal OFDM .................................................... 34
Gambar 2.18 Cyclic Prefix mencegah terjadinya ISI pada simbol OFDM ................................ 34
Gambar 3.1 Blok pemodelan simulasi ........................................................................................ 35
Gambar 3.2 Blok sistem pengiriman........................................................................................... 36
Gambar 3.3 Diagram konstelasi untuk modulasi QPSK ............................................................. 37
Gambar 3.4 Pengalokasian simbol pilot pada frekuensi subcarrier tertentu ............................... 40
Gambar 3.5 Blok sistem penerimaan ......................................................................................... 45
Gambar 4.1 Grafik kinerja BER terhadap SNR pada K factor 1.4 dengan bitrate berbeda ........ 51
Gambar 4.2 Grafik kinerja BER terhadap SNR pada K factor 2.0 dengan bitrate berbeda ........ 52
Gambar 4.3 Grafik kinerja BER terhadap SNR pada K factor 2.3 dengan bitrate berbeda ........ 53
Gambar 4.4 Grafik kinerja BER terhadap SNR pada K factor 2.7 dengan bitrate berbeda ........ 54
Gambar 4.5 Grafik kinerja BER terhadap SNR pada K factor 4.6 dengan bitrate berbeda ........ 55
Gambar 4.6 Grafik kinerja BER terhadap SNR pada K factor 6.4 dengan bitrate berbeda ........ 56
Gambar 4.7 Grafik kinerja BER terhadap SNR pada K factor 9.2 dengan bitrate berbeda ........ 57
Gambar 4.8 Grafik kinerja BER terhadap SNR pada K factor 12.2 dengan bitrate berbeda ...... 58
Gambar 4.9 Grafik kinerja BER terhadap SNR pada K factor 16.8 dengan bitrate berbeda ...... 59
Gambar 4.10 Fading skala kecil berdasarkan Multipath time delay spread .............................. 60
Gambar 4.11 Grafik kinerja BER thdp frekuensi Doppler dgn variasi K factor, Rb= 1Mbps ... 64
Gambar 4.12 Grafik kinerja BER thdp frekuensi Doppler dgn variasi K factor, Rb= 2 Mbps... 65
Gambar 4.13 Grafik kinerja BER thdp frekuensi Doppler dgn variasi K factor, Rb= 4 Mbps... 65
Gambar 4.14 Fading skala kecil berdasarkan Doppler spread ................................................... 67
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DAFTAR ISI
HALAMAN PENGESAHAN……………………………………………………..i
ABSTRAK………………………………………………………………………...ii
ABSTRACT………………………………………………………………………iii
KATA PENGANTAR ........................................................................................... iv
DAFTAR ISI .......................................................................................................... vi
DAFTAR GAMBAR ............................................................................................. ix
DAFTAR TABEL ................................................................................................. xii
DAFTAR ISTILAH ............................................................................................. xiii
BAB I PENDAHULUAN ....................................................................................... 1
1.1. Latar Belakang Masalah............................................................................. 1
1.2. Tujuan Penelitian ....................................................................................... 2
1.3 Perumusan Masalah ................................................................................... 2
1.4. Batasan Masalah......................................................................................... 2
1.5. Metodologi Penelitian ................................................................................ 3
1.6. Sistematika Penulisan ................................................................................ 4
BAB II TEORI DASAR ......................................................................................... 6
2.1. Sistem Komunikasi HAPS ......................................................................... 6
2.2. Karakteristik Kanal Komunikasi HAPS .................................................. 10
2.2.1 Pendahuluan ......................................................................................... 10
2.2.2 Redaman Hujan (Rain Attenuation) ..................................................... 10
2.2.3 Delay Spread ........................................................................................ 11
2.2.4 Doppler Spread .................................................................................... 13
2.2.5 Sudut Elevasi antara Platform HAPS dengan Penerima ...................... 15
2.2.6 K Factor................................................................................................ 16
2.3. Model Kanal HAPS .................................................................................. 21
2.3.1 Kanal AWGN ..................................................................................... 21
2.3.2 Kanal Rician......................................................................................... 22
2.3.3 Model Respon Impuls Kanal Rician Fading........................................ 24
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2.3.4 Estimasi Kanal ..................................................................................... 26
2.4. OFDM (Orthogonal Frequency Division Multiplexing) ........................... 28
2.4.1 Prinsip Dasar OFDM ........................................................................... 29
2.4.2 Sifat Orthogonal ................................................................................... 30
2.4.3 Keunggulan OFDM.............................................................................. 31
2.4.4 Guard Interval...................................................................................... 33
BAB III PERANCANGAN MODEL DAN SIMULASI SISTEM ...................... 35
3.1 Pendahuluan ............................................................................................... 35
3.2 Blok Sistem Pengiriman............................................................................. 36
3.2.1 Pengirim Bit Informasi......................................................................... 36
3.2.2 Konversi Serial ke Paralel .................................................................... 37
3.2.3 Modulasi Sinyal ................................................................................... 39
3.2.4 Penyisipan Symbol Pilot ...................................................................... 39
3.2.5 Inverse Fast Fourier Transform (IFFT)............................................... 40
3.2.6 Penyisipan Guard Interval ................................................................... 40
3.2.7 Konversi Paralel ke Serial.................................................................... 41
3.3 Blok Kanal Transmisi ................................................................................ 41
3.4 Blok Sistem Penerimaan ............................................................................ 44
3.4.1 Konversi Serial ke Paralel .................................................................... 45
3.4.2 Pengeluaran Guard Interval ................................................................. 45
3.4.3 Fast Fourier Transform (FFT) ............................................................. 45
3.4.4 Pengeluaran Symbol Pilot .................................................................... 46
3.4.5 Estimasi Kanal ..................................................................................... 46
3.4.6 Demodulasi Sinyal ............................................................................... 46
3.4.7 Konversi Paralel ke Serial.................................................................... 46
3.5 Paramter-Parameter yang Digunakan dalam Pemodelan Simulasi............ 47
3.5.1 Parameter Sistem.................................................................................. 47
3.5.2 Parameter Kanal Rician ....................................................................... 48
BAB IV HASIL DAN ANALISIS........................................................................ 50
4.1.Pendahuluan .............................................................................................. 50
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4.2 Pengaruh K factor pada Kanal yang Dipengaruhi Time Delay Spread..... 50 4.2.1 K factor= 1.4 (Sudut Elevasi 100) ........................................................ 51
4.2.2 K factor= 2.0 (Sudut Elevasi 200) ........................................................ 52
4.2.3 K factor= 2.3 (Sudut Elevasi 300) ........................................................ 53
4.2.4 K factor= 2.7 (Sudut Elevasi 400) ........................................................ 54
4.2.5 K factor= 4.6 (Sudut Elevasi 500) ........................................................ 55
4.2.6 K factor= 6.4 (Sudut Elevasi 600) ........................................................ 56
4.2.7 K factor= 9.2 (Sudut Elevasi 700) ........................................................ 57
4.2.8 K factor= 12.2 (Sudut Elevasi 800) ...................................................... 58
4.2.9 K factor= 16.8 (Sudut Elevasi 900) ...................................................... 59
4.3 Pengaruh K factor pada Kanal yang Dipengaruhi Doppler Spread .......... 63
BAB V KESIMPULAN DAN SARAN................................................................ 68
5.1. Kesimpulan .............................................................................................. 68
5.2. Saran......................................................................................................... 70 DAFTAR PUSTAKA………………………………………………………… xiv LAMPIRAN ........................................................................................................ A-1
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DAFTAR ISTILAH
AWGN Bc BS BWA CP DAB fd FFT GI HAPS HDSL HDTV ICI IFFT ISI LAN LOS MAN OFDM PDF QPSK SNR Tm VHDSL WAN
:Additive White Gaussian Noise :Coherence Bandwidth :Base Station :Broadband Wireless Access : Cyclic Prefix : Digital Audio Broadcast :Doppler Shift : Fast Fourier Transform : Guard Interval :High altitude platform station :High Bit-rate Digital Subscriber Lines :High Definition Televisi :Inter-carrier Interference : Inverse Fast Fourier Transform :Inter Symbol Interference :Local Area Network :Line of Sight :Metropolitan Area Network :Orthogonal frequency division multiplexing :Probability Density Function :Quadrature Phase Shift Keying :Signal to Noise Ratio :Maksimum excess delay time :Very High Speed Digital Subscriber Line :Wide Area Network
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