September 2004
France TelecomSlide 1
doc.: IEEE 802.11-04/903-00-0000n
Submission
Partial Proposal: Turbo Codes
Marie-Helene Hamon, Olivier Seller, John Benko France TelecomClaude Berrou ENST BretagneJacky Tousch TurboConceptBrian Edmonston iCoding
September 2004
France TelecomSlide 2
doc.: IEEE 802.11-04/903-00-0000n
Submission
Outline
Part I: Turbo Codes
Part II: Turbo Codes for 802.11n • Why TC for 802.11n?• Flexibility• Performance
September 2004
France TelecomSlide 3
doc.: IEEE 802.11-04/903-00-0000n
Submission
Outline
Part I: Turbo Codes
Part II: Turbo Codes for 802.11n • Why TC for 802.11n?• Flexibility• Performance
September 2004
France TelecomSlide 4
doc.: IEEE 802.11-04/903-00-0000n
Submission
Known applications of convolutional
turbo codes
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
September 2004
France TelecomSlide 5
doc.: IEEE 802.11-04/903-00-0000n
Submission
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
September 2004
France TelecomSlide 6
doc.: IEEE 802.11-04/903-00-0000n
Submission
k binarydata
permutation
Y1
Y2
X
B
A
Y1
Y2
permutation
k/2 binarycouples
polynomials 15, 13 (or 13, 15)
k binarydata
permutation
Y1
Y2
XB
A
Y1
Y2
permutation
k/2 binarycouples
polynomials 23, 35 (or 31, 27)
(a) (b)
(c) (d)
The TCs used in practice
September 2004
France TelecomSlide 7
doc.: IEEE 802.11-04/903-00-0000n
Submission
The turbo code proposed for all sizes, all coding rates
permutation (N)N = k/2
couplesof data
codeword
systematic part
redundancy part
1
2punctu-ring
Y
A
B
AB
Y
systematic part
redundancy part +circular (tail-biting) encoding
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
September 2004
France TelecomSlide 8
doc.: IEEE 802.11-04/903-00-0000n
Submission
Decoding
Max-Log-MAP algorithm
Sliding window
FER
5
5
5
510-3
10-4
10-1
10-2
Eb/N0 (dB)3 4
Full MAP Max-Log-MAP
Theoretical limit(sphere packing bound)
Gaussian,1504 bits, R = 4/5
+ inherent parallelism, easy connectivity (quasi-regular permutation)
September 2004
France TelecomSlide 9
doc.: IEEE 802.11-04/903-00-0000n
Submission
Decoding complexityUseful 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)
No ROM
For 0.18m CMOS
Duo-binary TC decoders are already available from several providers (iCoding Tech., TurboConcept, ECC, Xilinx, Altera, …)
September 2004
France TelecomSlide 10
doc.: IEEE 802.11-04/903-00-0000n
Submission
Outline
Part I: Turbo Codes
Part II: Turbo Codes for 802.11n • Why TC for 802.11n?• Flexibility• Performance
September 2004
France TelecomSlide 11
doc.: IEEE 802.11-04/903-00-0000n
Submission
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
September 2004
France TelecomSlide 12
doc.: IEEE 802.11-04/903-00-0000n
Submission
Duo-Binary Turbo Code
s1 s3s2A
B
W
systematic part
redundancy partY
permutation (k/2)
N = k/2 couplesof data
codeword
systematic part
redundancy part
1
2
puncturing
Y1 or 2W1 or 2
A
B
September 2004
France TelecomSlide 13
doc.: IEEE 802.11-04/903-00-0000n
Submission
Duo-Binary Turbo Code
• Duo-binary input:– Reduction of Latency & Complexity (compared to UMTS TCs)– Complexity per decoded bit is 35 % lower than binary UMTS 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
September 2004
France TelecomSlide 14
doc.: IEEE 802.11-04/903-00-0000n
Submission
# of Iterations vs. Performance
The number of iterations can
be adjusted for better
performance – complexity trade-off
September 2004
France TelecomSlide 15
doc.: IEEE 802.11-04/903-00-0000n
Submission
Simulation Environment
• Both Turbo Codes and 802.11a CCs simulated
• Simulation chain based on 802.11a PHY model – SISO configuration– 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
September 2004
France TelecomSlide 16
doc.: IEEE 802.11-04/903-00-0000n
Submission
Performance: AWGN
3.5-4 dB gain over
802.11a CC
September 2004
France TelecomSlide 17
doc.: IEEE 802.11-04/903-00-0000n
Submission
Performance: model B
~3 dB gain over 802.11a
CC
September 2004
France TelecomSlide 18
doc.: IEEE 802.11-04/903-00-0000n
Submission
Performance: model D
~3 dB gain over 802.11a
CC
September 2004
France TelecomSlide 19
doc.: IEEE 802.11-04/903-00-0000n
Submission
Performance: model E
~3 dB gain over 802.11a
CC
September 2004
France TelecomSlide 20
doc.: IEEE 802.11-04/903-00-0000n
Submission
Flexibility
• 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
September 2004
France TelecomSlide 21
doc.: IEEE 802.11-04/903-00-0000n
Submission
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 UMTS TCs– Performance is slightly better than UMTS TCs
• Significant performance gain over .11a CC:– 3.5 - 4 dB on AWGN channel– 3 dB on 802.11n channel models
September 2004
France TelecomSlide 22
doc.: IEEE 802.11-04/903-00-0000n
Submission
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.