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Partial Proposal: Turbo Codes

Partial Proposal: Turbo Codes. Marie-Helene Hamon, Olivier Seller, John Benko France Telecom Claude Berrou ENST Bretagne Jacky Tousch TurboConcept Brian Edmonston iCoding. Outline. Part I: Turbo Codes Part II: Turbo Codes for 802.11n Why TC for 802.11n? Flexibility

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Partial Proposal: Turbo Codes

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  1. Partial Proposal: Turbo Codes Marie-Helene Hamon, Olivier Seller, John Benko France Telecom Claude Berrou ENST Bretagne Jacky Tousch TurboConcept Brian Edmonston iCoding France Telecom

  2. Outline Part I: Turbo Codes Part II: Turbo Codes for 802.11n • Why TC for 802.11n? • Flexibility • Performance France Telecom

  3. Outline Part I: Turbo Codes Part II: Turbo Codes for 802.11n • Why TC for 802.11n? • Flexibility • Performance France Telecom

  4. Application turbo code termination polynomials rates CCSDS (deep space) binary, 16-state tail bits 23, 33, 25, 37 1/6, 1/4, 1/3, 1/2 UMTS, CDMA2000 (3G Mobile) binary, 8-state tail bits 13, 15, 17 1/4, 1/3, 1/2 DVB-RCS (Return Channel over Satellite) duo-binary, 8-state circular 15, 13 1/3 up to 6/7 DVB-RCT (Return Channel over Terrestrial) duo-binary, 8-state circular 15, 13 1/2, 3/4 Inmarsat (M4) binary, 16-state no 23, 35 1/2 Eutelsat (Skyplex) duo-binary, 8-state circular 15, 13 4/5, 6/7 IEEE 802.16 (WiMAX) duo-binary, 8-state circular 15, 13 1/2 up to 7/8 Known applications of convolutional turbo codes France Telecom

  5. Main progress in turbo coding/decoding since 1993 • Max-Log-MAP and Max*-Log-MAP algorithms • Sliding window • Duo-binary turbo codes • Circular (tail-biting) encoding • Permutations • Parallelism • Computation or estimation of Minimum Hamming distances (MHDs) • Stopping criterion • Bit-interleaved turbo coded modulation • Simplicity • Simplicity • Performance and simplicity • Performance • Performance • Throughput • Maturity • Power consumption • Performance and simplicity France Telecom

  6. The TCs used in practice France Telecom

  7. The turbo code proposed for all sizes, all coding rates Very simple algorithmic permutation: i =0, …, N-1, j = 0, ...N-1 level 1: if j mod. 2 = 0, let (A,B) = (B,A) (invert the couple) level 2: - if j mod. 4 = 0, then P = 0; - if j mod. 4 = 1, then P = N/2 + P1; - if j mod. 4 = 2, then P = P2; - if j mod. 4 = 3, then P = N/2 + P3. i = P0*j + P +1 mod. N • No ROM • Quasi-regular (no routing issue) • Versatility • Inherent parallelism France Telecom

  8. Decoding Max-Log-MAP algorithm Sliding window + inherent parallelism, easy connectivity (quasi-regular permutation) France Telecom

  9. Decoding complexity Useful rate: 100 Mbps with 8 iterations 5-bit quantization (data and extrinsic) • Gates • 164,000 @ Clock = 100 Mhz • 82,000 @ Clock = 200 Mhz • 54,000 @ Clock = 400 Mhz RAM Data input buffer + 8.5xk for extrinsic information + 4000 for sliding window (example: 72,000 bits for 1000-byte block) For 0.18m CMOS No ROM Duo-binary TC decoders are already available from several providers (iCoding Tech., TurboConcept, ECC, Xilinx, Altera, …) France Telecom

  10. Outline Part I: Turbo Codes Part II: Turbo Codes for 802.11n • Why TC for 802.11n? • Flexibility • Performance France Telecom

  11. Introduction • Purpose • Show the multiple benefits of TCs for 802.11n standard • Overview of duo-binary TCs • Comparison between TC and .11a Convolutional Code • High Flexibility • Complexity • Properties of Turbo Codes (TCs) • Rely on soft iterative decoding to achieve high coding gains • Good performance, near channel capacity for long blocks • Easy adaptation in the standard frame • (easy block size adaptation to the MAC layer) • Well controlled hardware development and complexity • TC advantages led to recent adoption in standards France Telecom

  12. Duo-Binary Turbo Code France Telecom

  13. Duo-Binary Turbo Code • Duo-binary input: • Reduction of Latency & Complexity (compared to binary TCs) • Complexity per decoded bit is 35 % lower than binary TCs. • Better convergence in the iterative decoding process • Circular Recursive Systematic Codes • Constituent codes • No trellis termination overhead! • Original permuter scheme • Larger minimum distance • Better asymptotic performance France Telecom

  14. Flexibility & Efficiency • All Coding Rates possible (no limitations) • Same encoder/decoder for: • any coding rate via simple puncturing adaptation • different block sizes via adjusting permutation parameters • 4 parameters are used per block size to define an interleaver • Higher PHY data rates enabled with TCs: • High coding gains over 802.11a CC ( =>lower PER) • More efficient transmission modes enabled more often. • Combination with higher-order constellations • Better system efficiency • ARQ algorithm used less frequently France Telecom

  15. # of Iterations vs. Performance The number of iterations can be adjusted for better performance – complexity trade-off France Telecom

  16. Simulation Environment • Both Turbo Codes and 802.11a CCs simulated • Simulation chain based on 802.11a PHY model • SISO configuration mainly • CC59 and CC67 followed • Simulated Channels: AWGN, models B, D, E • No PHY impairments • Packet size of 1000 bytes. • Minimum of 100 packet errors • Assume perfect channel estimation & synchronization • Turbo Code settings: • 8-state Duo-Binary Convolutional Turbo Codes • Max-Log-MAP decoding • 8 iterations France Telecom

  17. Performance: AWGN 3.5 - 4 dB gain over 802.11a CC France Telecom

  18. Performance: model B ~2.5 - 3 dB gain over 802.11a CC France Telecom

  19. Performance: model D ~2.5 - 3 dB gain over 802.11a CC France Telecom

  20. Performance: model E ~2.5 - 3 dB gain over 802.11a CC France Telecom

  21. Performance in MIMO system Spatial multiplexing, 2x2, MMSE receiver France Telecom

  22. Conclusions • Mature, stable, well established and implemented • Multiple Patents, but well defined licensing • All other advanced FECs also have patents • Complexity: • Show 35% decrease in complexity per decoded bit over binary TCs • Performance is slightly betterthan binary TCs • Significant performance gain over .11a CC: • 3.5 - 4 dB on AWGN channel • 2.5 - 3 dB on 802.11n channel models France Telecom

  23. References • [1] IEEE 802.11-04/003, "Turbo Codes for 802.11n", France Telecom R&D, ENST Bretagne, iCoding Technology, TurboConcept, January 2004. • [2] IEEE 802.11-04/243, "Turbo Codes for 802.11n", France Telecom R&D,iCoding Technology, May 2004. • [3] IEEE 802-04/256, "PCCC Turbo Codes for IEEE 802.11n", IMEC, March 2004. • [4] C. Berrou, A. Glavieux, P. Thitimajshima, "Near Shannon limit error-correcting coding and decoding: Turbo Codes", ICC93, vol. 2, pp. 1064-1070, May 93. • [5] C. Berrou, "The ten-year-old turbo codes are entering into service", IEEE Communications Magazine, vol. 41, pp. 110-116, August 03. • [6] C. Berrou, M. Jezequel, C. Douillard, S. Kerouedan, "The advantages of non-binary turbo codes", Proc IEEE ITW 2001, pp. 61-63, Sept. 01. • [7] TS25.212 : 3rd Generation Partnership Project (3GPP) ; Technical Specification Group (TSG) ; Radio Access Network (RAN) ; Working Group 1 (WG1); "Multiplexing and channel coding (FDD)". October 1999. • [8] EN 301 790 : Digital Video Broadcasting (DVB) "Interaction channel or satellite distribution systems". December 2000. • [9] EN 301 958 : Digital Video Broadcasting (DVB) "Specification of interaction channel for digital terrestrial TV including multiple access OFDM". March 2002. France Telecom

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