September 2004
doc.: IEEE 802.11-04/903-00-0000n
Partial Proposal:
Turbo Codes
Marie-Helene Hamon, Olivier Seller, John Benko
Claude Berrou
Jacky Tousch
Brian Edmonston
Submission
Slide 1
France Telecom
ENST Bretagne
TurboConcept
iCoding
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Outline
Part I: Turbo Codes
Part II: Turbo Codes for 802.11n
• Why TC for 802.11n?
• Flexibility
• Performance
Submission
Slide 2
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Outline
Part I: Turbo Codes
Part II: Turbo Codes for 802.11n
• Why TC for 802.11n?
• Flexibility
• Performance
Submission
Slide 3
France Telecom
September 2004
Known applications
of convolutional
turbo codes
Submission
doc.: IEEE 802.11-04/903-00-0000n
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
Slide 4
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Main progress in turbo coding/decoding since 1993
• Max-Log-MAP and Max*-Log-MAP algorithms
• Simplicity
• Sliding window
• Simplicity
• Duo-binary turbo codes
• Performance and simplicity
• Circular (tail-biting) encoding
• Performance
• Permutations
• Performance
• Parallelism
• Throughput
• Computation or estimation of Minimum Hamming
distances (MHDs)
• Maturity
• Stopping criterion
• Power consumption
• Bit-interleaved turbo coded modulation
• Performance and simplicity
Submission
Slide 5
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
The TCs used in practice
B
A
X
k b in a ry
d a at
k /2 b in a ry
c o u p le s
p e rm u taio n
Y 1
1
Y

p e rm u taio n

2
Y
( a)
( b)
Y 2
polynomia ls 15,13( or 13,15)
B
X
A
k b in a ry
d a at
k 2
/b in a ry
c o u p el s
Y
p e rm u taio n
1
Y 1

p e rm u taio n

Y 2
( c)
( d)
Y 2
polynomia ls 23,35( or 31,27)
Submission
Slide 6
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
The turbo code proposed for all sizes, all coding rates
systematic part
systematic part
A
B
A
B
1

+
circular (tail-biting)
encoding
Y
redundancy part
N = k/2
couples
of data
permutation
2
(N)
Y
puncturing
c
o
d
e
w
o
r
d
redundancy part
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)
• No ROM
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.
• Quasi-regular (no routing issue)
• Versatility
• Inherent parallelism
i = P0*j + P +1 mod. N
Submission
Slide 7
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Decoding
FER
5
Gaussian,
1504 bits,
R = 4/5
10-1
5
Max-Log-MAP algorithm
10-2
Sliding window
5
10-3
Full MAP
Max-Log-MAP
5
10-4
3
4
Eb/N0 (dB)
Theoretical limit
(sphere packing bound)
+ inherent parallelism, easy connectivity (quasi-regular permutation)
Submission
Slide 8
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Decoding complexity
Useful rate: 100 Mbps with 8 iterations
5-bit quantization (data and extrinsic)
Gates
RAM
• 164,000 @ Clock = 100 Mhz
Data input buffer
• 82,000 @ Clock = 200 Mhz
+
• 54,000 @ Clock = 400 Mhz
8.5xk for extrinsic information
For 0.18m CMOS
+ 4000 for sliding window
(example: 72,000 bits for 1000-byte block)
No ROM
Duo-binary TC decoders are already available from several providers
(iCoding Tech., TurboConcept, ECC, Xilinx, Altera, …)
Submission
Slide 9
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Outline
Part I: Turbo Codes
Part II: Turbo Codes for 802.11n
• Why TC for 802.11n?
• Flexibility
• Performance
Submission
Slide 10
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
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
Submission
Slide 11
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Duo-Binary Turbo Code
systematic part
A
s2
s1
s3
B
W
Y
redundancy part
systematic part
A
B
1
N = k/2 couples
of data
permutation
(k/2)

2
W1 or 2
Y1 or 2
puncturing
c
o
d
e
w
o
r
d
redundancy part
Submission
Slide 12
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
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
Submission
Slide 13
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
# of Iterations vs. Performance
The number of
iterations can
be adjusted for
better
performance –
complexity
trade-off
Submission
Slide 14
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
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
Submission
Slide 15
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Performance: AWGN
3.5-4 dB
gain over
802.11a CC
Submission
Slide 16
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Performance: model B
~3 dB
gain over
802.11a
CC
Submission
Slide 17
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Performance: model D
~3 dB
gain over
802.11a
CC
Submission
Slide 18
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
Performance: model E
~3 dB
gain over
802.11a
CC
Submission
Slide 19
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
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
Submission
Slide 20
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
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
Submission
Slide 21
France Telecom
September 2004
doc.: IEEE 802.11-04/903-00-0000n
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.
Submission
Slide 22
France Telecom