1. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 1 Interleaving for Reed Solomon Coding for the 802.11 MAC Joseph Lauer (jlauer@broadcom.com), Chris Hansen (chansen@broadcom.com), Raju Gubbi (rgubbi@broadcom.com), Matt Fischer (mfischer@broadcom.com) Broadcom Corporation

2. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 2 Overview Channel characterized by burst errors, corrupting multiple adjacent symbols Interleaving spreads burst errors across multiple Reed Solomon (RS) codewords –Increases maximum correctable burst length –Does not affect RS code design (N and K)

3. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 3 Application to 802.11 MAC Word aligned interleaving on body codewords Interleaver depth equals number of codewords (M) Header not encoded –Header contains only one RS codeword –Backward compatible with existing MAC RS EncoderInterleaver RS DecoderDeinterleaver MAC Frame Bodyto symbol mapping from demappingDecoded bytes

4. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 4 Burst Error Channel Model Bursts independent Start of a burst occurs with probability P b Description of burst –Burst length drawn uniformly from 1 to a maximum length –First and last bit of burst are in error –Other bits within burst drawn from (.5,.5) distribution

5. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 5 Row-Column Interleaver Write in words as rows Read out words as columns c i (j) = byte i of codeword j Each row is a Reed Solomon codeword Deinterleaver uses the same structure but writes words in as columns and reads words out as rows c 0 (0) c 1 (0),c 2 (0) c 3 (0), …,c N-2 (M-1) c N-1 (M-1) c 0 (0) c 1 (0) c N-2 (0) c N- 1 (0) c 0 (1) c 1 (1) c N-2 (1) c N- 1 (1) c 2 (0) c 3 (0) c 2 (1) c 3 (1) c 0 (M) c 1 (M) c N-2 (M) c N-1 (M) c 0 (M) c 1 (M) c 0 (0) c 1 (0),c 0 (1) c 1 (1), …,c N-2 (M-1) c N-1 (M-1)

6. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 6 Performance Maximum burst length 32 bits, M = 5 codewords, (224, 208) code

7. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 7 Performance Maximum burst length 32 bits, M = 5 codewords, (224, 208) code

8. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 8 Maximum burst length 48 bits, M = 5 codewords, (224, 208) code Performance

9. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 9 Maximum burst length 48 bits, M = 5 codewords, (224, 208) code Performance

10. doc.: IEEE 802.11-01/148 Submission March 2001 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, BroadcomSlide 10 Conclusions PHY layer errors will tend to occur in bursts Simple interleaving will greatly improve the ability of Reed Solomon coding to correct burst errors Interleaving should be part of the 802.11 MAC level FEC coding