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OFDM based Applications

OFDM based Applications. DAB-OFDM  Digital Audio Broadcasting DVD-OFDM  Digital Video Broadcasting ADSL-OFDM  Asynchronous Digital Subscriber Line Wireless Local Area Network IEEE-802.11a, IEEE-802.11g ETSI BRAN (Hyperlan/2) Wireless MAN 802.16 Working Group of IEEE

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OFDM based Applications

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  1. OFDM based Applications • DAB-OFDM  Digital Audio Broadcasting • DVD-OFDM  Digital Video Broadcasting • ADSL-OFDM  Asynchronous Digital Subscriber Line • Wireless Local Area Network • IEEE-802.11a, IEEE-802.11g • ETSI BRAN (Hyperlan/2) • Wireless MAN 802.16 Working Group of IEEE • 802.16 -- 2 to 11 GHz

  2. OFDM Systems

  3. DAB • Standardized in 1995 by ETSI • Improved sound quality & high spectral efficiency • Single frequency by all transmitters – if tp < tg no ISI, ICI – diversity achieved • Sampling at 48 KHz, frame 24 ms, SOF – null symbol • Differentially encoded QPSK - ref, symbol tx. • Rate ¼ conv. Code CL = 7  8/9 by puncturing • Maximum data rate = 1536 x 2 x 8/(9 x 1.246 ms ) = 2.4 Mbps

  4. DAB transmission modes

  5. DVB - T • Standardized in 1997 • 2K mode • Size of IFFT , 1705 subcarriers • 8K mode • Size of IFFT , 6817 subcarriers, FFT interval 896 s , guard time – 28 to 224 s

  6. Input data Group of 188 bytes Scrambler RS outer code Outer interleave Conv. inner code Inner interleave Byte-wise Depth-12 Rate ½, 7 (2/3, ¾, 5/6, 7/8) (204,188,t=8) RF Tx. DAC Guard time insertion Pilot insertion QAM mapping QPSK 16-QAM 64-QAM 768 pilots/ 192 pilots, Position change every 4 OFDM symbols 28 to 224 s Block diagram of DVB-T

  7. Internet DSLAM downstream Central Office DSL modem upstream DSL modem Voice Switch LPF LPF Customer Premises Telephone Network DSLAM - Digital Subscriber Line Access Multiplexer LPF – Low Pass Filter Digital Subscriber Line (DSL) -Broadband Access

  8. Telephone line Telephone line Voice (+ ADSL leakage) Voice (only) Splitter Splitter Voice + ADSL Voice + ADSL ADSL (only) ADSL (only) ADSL Filter ADSL modem ADSL modem Phone Phone Phone Phone

  9. Selected DSL Standards Courtesy of Shawn McCaslin (Cicada Semiconductor, Austin, TX)

  10. Multicarrier Modulation • Divide channel into narrowband subchannels • No inter-symbol interference (ISI) in subchannels if constant gain within every subchannel and if ideal sampling • Discrete multitone modulation • Based on fast Fourier transform (FFT) • Standardized for ADSL • Proposed for VDSL pulse sinc DTFT-1 w k -wc wc channel carrier magnitude subchannel frequency Subchannels are 4.3 kHz wide in ADSL and DMT VDSL

  11. Discrete Multitone (DMT) • ADSL – Asymmetric DSL (G.DMT Standard) • Maximum data rates supported (ideal case) Echo cancelled: 14.94 Mbps downstream, 1.56 Mbps upstream Frequency division multiplexing: 13.38 Mbps downstream, 1.56 Mbps up • VDSL – Very High RateDSL (Proposed Standard) • Also has symmetric mode:13, 9, or 6 Mbps • Single carrier and DMT • DMT VDSL Higher speed G.DMT ADSL Frequency division multiplex 2m subcarriers m [8, 12]

  12. Echo Cancellation FDM Upstream Downstream Upstream Downstream POTS POTS Frequency 1 Mhz Frequency 1 Mhz Create Multiple Channel

  13. N/2 subchannels N real samples S/P quadrature amplitude modulation (QAM) encoder mirror data and N-IFFT add cyclic prefix P/S D/A + transmit filter Bits 00110 TRANSMITTER channel RECEIVER N/2 subchannels N real samples P/S time domain equalizer (FIR filter) QAM demoddecoder N-FFT and remove mirrored data S/P remove cyclic prefix receive filter + A/D invert channel = frequency domain equalizer conventional ADSL equalizer structure ADSL Transceiver

  14. Wireless LAN • IEEE 802.11  IEEE • Hyperlan/2  ETSI • MMAC (Multimedia Mobile Access Communication)  MPT • Phy & MAC standardized • Phy at 900 MHz, 2.5 GHz & 5 GHz

  15. OFDM Transceiver RF Tx DAC Binary Input Data Add Cyclic extension & Windowing QAM mapping Pilot Insertion S - P P - S Coding Interleaving IFFT FFT Remove Cyclic extension QAM demapping Channel Correction P - S S - P Decoding De-Interleaving Binary Output Data Timing & Freq. Sync. RF Rx ADC

  16. Typical PHY ConfigurationSmall differences exist in PHY for the three WLANs • Carrier frequency 5 GHz • 52 subcarriers (4 pilots)  64 point FT/IFFT • FFT period 3.2 µs • Guard time 800 ns • OFDM Symbol time 4 µs • Modulations  BPSK, QPSK, 16-QAM, 64-QAM • Coding rates 1/2,3/4,2/3 • Bit rates 6,9,12,18,24,36,48,54 Mbps • Subcarrier spacing 312.5 KHz • Channel spacing 20 MHz • 3-dB bandwidth 16.56 MHz • Tolerable delay spread about 250 ns at 24 Mbps

  17. Medium Access Control • IEEE 802.11 • CSMA / CA • Hyperlan/2 • Centralized & scheduled MAC • MMAC • Supports both MACs

  18. Wireless LANIEEE 802.11a/b/g/h/j/n • b : 1999 ~2.4 GHz ISM • a : 2002 – 2003 ~5.0 GHz ISM • g : 2002 – 2003 ~2.4 GHz ISM • h : 2003 – 2004 ~5.0 GHz ISM • j : 2004 ~5.0 GHz ISM • n : 2006

  19. Modulation & Filter type • b  DBPSK / DQPSK ( 11Mbps ) • Gaussian filter or vendor specific • a/g/h/j  upto 64 QAM on 52 OFDM • subcarriers, rectangular filter or • vendor specific (54 Mbps ) • n  upto 64 QAM on 108 OFDM • subcarriers, rectangular filter or • vendor specific ( > 100 Mbps ), MIMO

  20. WMAN – IEEE 802.16IEEE802.16e - WiMAX • Carrier • Fixed Access : < 11 GHz • Mobile Access : 2 to 6 GHz • MAC : TDMA • Modulation • Fixed Access : OFDM with BPSK, QPSK, 16-QAM, 64-QAM • Mobile Access : OFDMA with BPSK, QPSK, 16-QAM, 64-QAM • Channel spacing • Fixed Access : 1.25 to 20 MHz • Mobile Access : 1.25, 5, 10, 20 MHz • Single user data rate  upto 75 Mbps

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