March 2001 doc IEEE 802 11 01148 Interleaving
- Slides: 10
March 2001 doc. : IEEE 802. 11 -01/148 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 Submission 1 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 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) Submission 2 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 Application to 802. 11 MAC Frame Body RS Encoder Interleaver from demapping Deinterleaver RS Decoder to symbol mapping Decoded bytes • 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 Submission 3 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 Burst Error Channel Model • Bursts independent • Start of a burst occurs with probability Pb • 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 Submission 4 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 Row-Column Interleaver Write in words as rows c 0(0) c 1(0) c 2(0) c 3(0) c. N-2(0) c. N-1(0) c 0(1) c 1(1) c 2(1) c 3(1) c. N-2(1) c. N-1(1) c 0(M) c 1(M) c. N-2(M) c. N-1(M) c 0(0) c 1(0) , c 2(0) c 3(0), … , c. N-2(M-1) c. N-1(M-1) Read out words as columns c 0(0) c 1(0) , c 0(1) c 1(1), … , c. N-2(M-1) c. N-1(M-1) • ci(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 Submission 5 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 Performance Maximum burst length 32 bits, M = 5 codewords, (224, 208) code Submission 6 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 Performance Maximum burst length 32 bits, M = 5 codewords, (224, 208) code Submission 7 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 Performance Maximum burst length 48 bits, M = 5 codewords, (224, 208) code Submission 8 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 Performance Maximum burst length 48 bits, M = 5 codewords, (224, 208) code Submission 9 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
March 2001 doc. : IEEE 802. 11 -01/148 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 Submission 10 J. Lauer, C. Hansen, R. Gubbi, M. Fischer, Broadcom
