1. January 2004
Turbo Codes for IEEE n
Marie-Helene Hamon, Olivier Seller France Telecom R&D
Claude Berrou, Catherine Douillard, Sylvie Kerouedan ENST Bretagne
Brian Edmonston iCODING Technology Inc.

2. Contents TC for 802.11n Performance Granularity (Flexibility)
January 2004
Contents
TC for n
Performance
Granularity (Flexibility)
Complexity & latency
Conclusion

3. Turbo Codes: Iterative FEC for 802.11n
January 2004
Turbo Codes: Iterative FEC for n
Revolutionary form of error correcting, relying on soft iterative decoding to achieve high coding gains
Very good performance, near channel capacity for long blocks
TC advantages led to adoption in several recent digital communication standards: 3GPP UMTS (WCDMA), DVB-RCS, DVB-RCT, cdma2000 and consumer sattelite broadcast…
Hardware development and complexity well controlled

4. Turbo Codes: Iterative FEC for 802.11n
January 2004
Turbo Codes: Iterative FEC for n
High coding gains over classical convolutional code:
- Turbo Codes enable the use of more efficient transmission modes (coding rate and modulation) more often, to increase throughput
- Turbo Codes yield a lower PER: better system efficiency, as ARQ algorithm could be used less frequently
- Reasonable memory requirements

5. January 2004
Duo-Binary CTC

6. Advantages of this TC Duo-binary:
January 2004
Advantages of this TC
Duo-binary:
- reduction of the latency and complexity per decoded bit
- reduction of the path error density better convergence
Circular Revursive Systematic Codes as constituent codes no trellis termination overhead
Original permuter scheme larger minimum distance, better asymptotic performance

7. Performance on AWGN channel
January 2004
Performance on AWGN channel
Duo-Binary 8-state CTC
K=1600 bit, R=4/5
Max-Log-MAP decoding
8 iterations
At BER=10-5, 8-state CTC is dB from capacity

8. January 2004
Performance on AWGN

9. Block size Very good performance whatever the block size
January 2004
Block size
Very good performance whatever the block size
Two Duo-Binary CTC:
8-state for PER>10-4, 16-state for PER>10-7
Better performance than LDPC codes
- for any code rate
- for any block size <10000 bits
- for any BER <10-9
- for any associated modulation
Block sizes as small as 12 bytes (DVB-RCS) and 18 bytes (DVB-RCT) have been standardized

10. High Flexibility With the same encoder/decoder:
January 2004
High Flexibility
With the same encoder/decoder:
- several coding rates allowed through simple adaptation of the puncturing pattern (DVB-RCS: 7 coding rates)
- different block sizes enabled just by adjusting permutation parameters (DVB-RCS: 12 block sizes)
For the duo-binary Turbo Code, a set of 4 permutation parameters needs to be modified. Each set of parameters defines an interleaver for one block size, all coding rates.

11. High Flexibility Better granularity in block size and coding rate:
January 2004
High Flexibility
Better granularity in block size and coding rate:
FER (hardware measurements) for 8-state CTC, 8 iterations, 4-bit quantization at decoder input, Max-Log-MAP decoding

12. January 2004
High Flexibility
Turbo codes can adjust to all kinds of coding rates, block sizes and modulations

13. January 2004
Granularity
Modulation and Code rate are adjusted to keep actual performance close to capacity for any given SNR
The more granularity the greater the OVERALL performance
Low granularity substantially reduces the benefit of the advanced coding

14. January 2004
Granularity

15. January 2004
Complexity
The decoder of DVB-RCS is not more complex than any LDPC decoder
Terminals are equiped with both encoder and decoder
To enable high bit rates, decoding can be restricted to 4 iterations without significantly altering performance

16. TC Memory Requirements
January 2004
TC Memory Requirements
Rate 4/5, 1600 information bits (1600,2000)
6 bit samples
70,000 bits (approx) of RAM
160,000 soft information reads per 8 iterations
80,000 soft information reads per 4 iterations
Power consumption ~ total memory x iterations
Lower memory requirements and iterations -> less power consumption

17. LDPC Memory Comparison
January 2004
LDPC Memory Comparison
120 Kbits of memory
8 iterations minimum
274,285 soft decision read/write per frame

18. January 2004
Latency
The decoder has an inherent possibility of parallelism, thanks to the simple generic permutation. For example, with:
- parallelism of degree 4 (4 backward/forward processors)
- 250 MHz circuit clock
- k=500 information bits per block
- 4 iterations
about 250 Mbits/s data rate can be achieved with 2.5 μs decoding latency

19. January 2004
Conclusion
Duo-Binary Turbo Code enables large performance gains, for all block sizes and coding rates
Highly flexible solution
Minimizes memory access requirements
Mature technology, implemented in 3rd generation mobile phones & volume consumer satellite

20. January 2004
References
C. Berrou, A. Glavieux, P. Thitimajshima, "Near Shannon limit error-correcting coding and decoding: Turbo Codes", ICC93, vol. 2, pp , May 93.
C. Berrou, "The ten-year-old turbo codes are entering into service", IEEE Communications Magazine, vol. 41, pp , August 03.
TS : 3rd Generation Partnership Project (3GPP) ; Technical Specification Group (TSG) ; Radio Access Network (RAN) ; Working Group 1 (WG1); "Multiplexing and channel coding (FDD)". October 1999.
EN : Digital Video Broadcasting (DVB) "Interaction channel or satellite distribution systems". December 2000.
EN : Digital Video Broadcasting (DVB) "Specification of interaction channel for digital terrestrial TV including multiple access OFDM". March 2002.