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On The Use Of Reed Solomon Codes For 802.11n

On The Use Of Reed Solomon Codes For 802.11n. Xuemei Ouyang, Monisha Ghosh Philips Research. Pen C. Li Philips Semiconductors. Past History with RS codes. Performance was evaluated only for AWGN channel: gain was about 2 dB at PER of 10%

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On The Use Of Reed Solomon Codes For 802.11n

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  1. On The Use Of Reed Solomon Codes For 802.11n Xuemei Ouyang, Monisha Ghosh Philips Research. Pen C. Li Philips Semiconductors Monisha Ghosh, et al., Philips

  2. Past History with RS codes • Performance was evaluated only for AWGN channel: gain was about 2 dB at PER of 10% • Protection only on MPDU, PHY header becomes the weakest point • RS codes were proposed for 802.11e, in the MAC layer, with no interleaving among codewords. • Was discarded, since the gains were not considered substantial enough, and wouldn’t help the robustness of the link Monisha Ghosh, et al., Philips

  3. 64QAM, 0.8us GI, 128 FFT, 40MHz Ch, RS(220,200), 3/4 CC 0 10 without RS with RS PER -1 10 -2 10 14 15 16 17 18 19 20 SNR (Es/No) dB Performance of RS(220,200) In AWGN Monisha Ghosh, et al., Philips

  4. RS Codes and MIMO • The question of RS codes needs to be revisited. • Channel model is no longer AWGN. • Can use RS codes in the PHY layer now, and hence some interleaving is possible • Question: What kind of performance gains are possible in a MIMO channel with multipath Rayleigh fading? • Answer:Substantial gains in 20ns and 50 ns channels, not so much in flat fading, as expected. Monisha Ghosh, et al., Philips

  5. Simulation Parameters For MIMO • 2 X 2 MIMO, 64 QAM, ¾ CC, 64 FFT, 0.8 ms guard interval. • 1000 data byte packets, RS(220,200) over GF(256): 5 RS codewords per packet. • Channel model: uncorrelated channels, exponential Rayleigh fading on each channel. • Data rate with RS coding: 98 Mbps (108 Mbps without RS). • Receiver: weighted zero-forcing. Monisha Ghosh, et al., Philips

  6. RS Performance For 2X2 MIMO Monisha Ghosh, et al., Philips

  7. Simulation Parameters For 40 Mhz • 64 QAM, ¾ CC, 128 FFT, 108 data carriers, 0.4 ms guard interval. • 1000 data byte packets, RS(220,200) over GF(256): 5 RS codewords per packet. • Channel model: exponential Rayleigh fading. • Data rate with RS coding: 123Mbps (135 Mbps without RS). • Receiver: weighted zero-forcing. Monisha Ghosh, et al., Philips

  8. RS Performance In 40Mhz channel Monisha Ghosh, et al., Philips

  9. Conclusions • RS codes can give substantial performance improvement, especially at low PERs, for both MIMO and double-bandwidth systems. • Interleaving among codewords can give an additional 1-1.5 dB gain. • The overhead penalty (~10%) can be made up by increasing the symbol length and/or reducing the guard interval. • Reducing the guard interval to 0.4 ms did not have any adverse performance effect with upto 50 ns delay spreads channels. Monisha Ghosh, et al., Philips

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