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Different Channel Coding Options for MIMO-OFDM 802.11n

Different Channel Coding Options for MIMO-OFDM 802.11n. Ravi Mahadevappa, ravi@realtek-us.com Stephan ten Brink, stenbrink@realtek-us.com Realtek Semiconductors, Irvine, CA. Overview. Simulation environment/assumptions Different channel codes Comparison: Required SNR, selected cases

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Different Channel Coding Options for MIMO-OFDM 802.11n

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  1. Different Channel Coding Optionsfor MIMO-OFDM 802.11n Ravi Mahadevappa, ravi@realtek-us.com Stephan ten Brink, stenbrink@realtek-us.com Realtek Semiconductors, Irvine, CA Ravi Mahadevappa, Stephan ten Brink, Realtek

  2. Overview • Simulation environment/assumptions • Different channel codes • Comparison: Required SNR, selected cases • Observations and recommendations • Appendix: Rate/RX sensitivity tables for different channel coding options Ravi Mahadevappa, Stephan ten Brink, Realtek

  3. Simulation Environment • 802.11a PHY simulation environment, plus • Higher order QAM constellations • Higher/lower channel code rates • TX/RX diversity/MIMO OFDM • Alamouti with MRC • ZF detection and soft post processing Ravi Mahadevappa, Stephan ten Brink, Realtek

  4. Likely 802.11n Transmitter • Shown with 2 TX antennas channel encoder Ravi Mahadevappa, Stephan ten Brink, Realtek

  5. Likely 802.11n Receiver • Shown with 2 RX antennas channel decoder Ravi Mahadevappa, Stephan ten Brink, Realtek

  6. Simulation Assumptions • Perfect channel knowledge/synchronization • Idealized multipath MIMO channel • More optimistic than [3] • Sub-channels independent; exponential decay, Trms = 60ns • Quasi static (channel stays constant during one packet) • Packet length: 1000 bits and 10000 bits • 10dB noise figure (conservative [4]) • 5dB implementation margin (conservative [4]) • Not yet incorporated in results: • Channel estimation • Packet detection, synchronization • foff estimation • Clipping DAC/finite precision ADC • Front-end filtering Ravi Mahadevappa, Stephan ten Brink, Realtek

  7. Different Channel Codes • Convolutional code memory 6 (abbreviation CC6) • Convolutional code memory 8 (CC8) • Parallel concatenated code [9], UMTS turbo code memory 3 (PCC3), random bit interleaver (over packet), 8 iterations • Serially concatenated code [10], inner memory 1, outer memory 2 code (SCC2), random bit interleaver (over packet), 15 iterations • LDPCC, regular [11] (LDREG), random edge interleaver (over packet), 40 iterations (note: 1-Rate = dv/dc) • Rate 1/2: variable node degree dv=3, check node degree dc=6; rate 3/4: dv=3, dc=12; rate 7/8: dv=3, dc=24 • LDPCC, irregular [12] (LDIRR), random edge interleaver (over packet), 40 iterations • dv,1=3 (89.74% of variable nodes), dv,2=4 (2.78%), dv,3=16 (7.48%); rate 1/2: dc=8; rate 3/4: dc=16; rate 7/8: dc=32 Ravi Mahadevappa, Stephan ten Brink, Realtek

  8. Table C1, 802.11a, 1x1, different codes, AWGN, length 1000 bits • Required SNR at 10% PER • Difference between various channel coding options is about 1-2dB • Best: Turbo code of memory 3, PCC3 • Worst: Convolutional code of memory 6, CC6 • Memory 8 convolutional code CC8 gains about 0.5dB Ravi Mahadevappa, Stephan ten Brink, Realtek

  9. Table C1, 802.11a, 1x1, AWGN, length 10000 bits • Longer block length: CC6,CC8 have worse PER by about 1dB: Code does not become stronger, but packet error prob. increases • Longer block length: good for iterative decoding (stronger code) • Differences between codes more pronounced for longer block length • LDREG and LDIRR virtually identical for maxlog-decoding Ravi Mahadevappa, Stephan ten Brink, Realtek

  10. Table C2, 802.11a, 1x1, fading, length 10000 bits • Trms=60ns • Maxlog-decoding used for PCC3, SCC2 and LDREG • In fading, CC8 gains about 1dB over CC6 • PCC3 still best; gain of about 2-3.5dB over CC6 Ravi Mahadevappa, Stephan ten Brink, Realtek

  11. Table C3, 802.11a, 2x3, AMRC, length 10000 bits • AMRC, Alamouti space/time block code [8] with max. ratio combining at receiver • CC8 gains about 0.5dB over CC6 • PCC3 still best; gain of about 2-3dB over CC6 • SCC2 worse than PCC3; omitted in the following Ravi Mahadevappa, Stephan ten Brink, Realtek

  12. Table C4, High-rate, 2x3, SMX, length 10000 bits • SMX, spatial multiplexing [6,7] • Rate 7/8 PCC3 obtained by random puncturing of parity bits • CC8 gains about 0.5-1dB over CC6 • PCC3/LDPCC gain of about 2-3dB over CC6 for rate 3/4 • PCC3/LDPCC gain of about 4dB over CC6 for rate 7/8 Ravi Mahadevappa, Stephan ten Brink, Realtek

  13. Observations • About 1-4dB gain possible with improved coding (LDPCC/PCC) for large block lengths • CC8 gains about 0.5-1dB over CC6; simple to implement • LDPCC similar performance as PCC3 • Concatenated codes with iterative decoding(PCC3, LDPCC) yield best performance, but implementation complexity high Ravi Mahadevappa, Stephan ten Brink, Realtek

  14. Recommendation Ravi Mahadevappa, Stephan ten Brink, Realtek

  15. Recommendation Ravi Mahadevappa, Stephan ten Brink, Realtek

  16. Recommendation Ravi Mahadevappa, Stephan ten Brink, Realtek

  17. Some References [1] J. M. Keenan, A. J. Motley, “Radio coverage in buildings”, British Telecom Technology Journal, vol. 8, no. 1, Jan. 1990, pp. 19-24 [2] J. Medbo, J.-E. Berg, “Simple and accurate path loss modeling at 5GHz in indoor environments with corridors”, Proc. VTC 2000, pp. 30-36 [3] J. P. Kermoal, L. Schumacher, K. I. Pedersen, P. E. Mogensen, F. Frederiksen, “A stochastic MIMO radio channel model with experimental validation”, IEEE Journ. Sel. Areas. Commun., vol. 20, no. 6, pp. 1211-1226, Aug. 2002 [4] IEEE Std 802.11a-1999, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, High-speed Physical Layer in the 5 GHz Band [5] J. H. Winters, J. Salz, R. D. Gitlin, “The impact of antenna diversity on the capacity of wireless communication systems”, IEEE Trans. Commun., vol. 42, no. 2/3/4, pp. 1740-1751, Feb./Mar./Apr. 1994 [6] G. J. Foschini, “Layered space-time architecture for wireless communication in a fading environment when using multi-element antennas”,Bell Labs. Tech. J., vol. 1, no. 2, pp. 41-59, 1996 [7] H. Sampath, S. Talwar, J. Tellado, V. Erceg, A. Paulraj, “A fourth-generation MIMO-OFDM broadband wireless system: Design, performance, and field trial results”, IEEE Commun. Mag., pp. 143-149, Sept. 2002 [8] S. M. Alamouti, “A simple transmit diversity technique for wireless communications”, IEEE J. on Select. Areas in Commun., vol. 16, pp. 1451-1458, Oct. 1998 [9] C. Berrou, A. Glavieux, P. Thitimajshima, “Near Shannon limit error-correcting coding and decoding: Turbo-codes”, in Proc. ICC, May 1993, pp. 1064-1070 [10] S. Benedetto, D. Divsalar, G. Montorsi, F. Pollara, “Serial concatenation of interleaved codes: Performance analysis, design and iterative decoding”, IEEE Trans. Inform. Theory, vol. 44, no. 3, pp. 909-926, May 1998 [11] R. G. Gallager, “Low-density parity-check codes”, IEEE Trans. Inform. Theory, vol. 8, pp. 21-28, Jan. 1962 [12] T. J. Richardson, A. Shokrollahi, R. L. Urbanke, “Design of capacity-approaching low-density parity-check codes”, IEEE Trans. Inform. Theory, vol. 47, no. 2, pp. 619-637, Feb. 2001 Ravi Mahadevappa, Stephan ten Brink, Realtek

  18. Appendix • Receiver sensitivity tables C1-C4 • Abbreviations, diversity/MIMO modes: • SEL: selection diversity at RX • AMRC: Alamouti Space/Time [8] with MRC at RX • SMX: spatial multiplexing (i.e. MIMO mode, [6,7]) • Abbreviations, MIMO detection algorithms • ZF: Zero Forcing with APP post processing • Abbreviations, channel coding options • CC6, CC8: convolutional codes of memory 6, 8 • PCC3: parallel concatenated code (memory 3) • SCC2: serially concatenated code (inner memory 1, outer memory 2) • LDREG, LDIRR: regular, irregular low-density parity-check code (LDPCC) Ravi Mahadevappa, Stephan ten Brink, Realtek

  19. Rate Table (C1) 802.11a, 1x1, Different Codes, AWGN AWGN channel Abbreviations: max = maxlog decoding; jac = jacobian logarihm decoding Ravi Mahadevappa, Stephan ten Brink, Realtek

  20. Rate Table (C2) 802.11a, 1x1, Different Codes Delay profile: Exp. decay Trms=60ns maxlog decoding used for all codes Ravi Mahadevappa, Stephan ten Brink, Realtek

  21. Rate Table (C3) 802.11a, 2x3, AMRC, Diff. Codes Delay profile: Exp. decay Trms=60ns maxlog decoding used for all codes Ravi Mahadevappa, Stephan ten Brink, Realtek

  22. Rate Table (C4) High-rate, 2x3, SMX, Diff. Codes ZF MIMO SMX detection Delay profile: Exp. decay Trms=60ns maxlog decoding used for all codes Ravi Mahadevappa, Stephan ten Brink, Realtek

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