August 2004 doc.: IEEE 802.11-04/0951r1 Submission S. Coffey, et al., WWiSE group Slide 1 WWiSE...
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S. Coffey, et al., WWiSE group Slide 1 August 2004 doc.: IEEE 802.11- 04/0951r1 Submissio n WWiSE Group Partial WWiSE Group Partial Proposal on Turbo Codes Proposal on Turbo Codes August 13, 2004 Airgo Networks, Bermai, Broadcom, Conexant, STMicroelectronics, Texas Instruments
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August 2004 doc.: IEEE /0951r1 Submission S. Coffey, et al., WWiSE group Slide 3 Contents Overview of partial proposal Motivation for advanced coding Specification of turbo code Performance results Summary
Transcript of August 2004 doc.: IEEE 802.11-04/0951r1 Submission S. Coffey, et al., WWiSE group Slide 1 WWiSE...
S. Coffey, et al., WWiSE groupSlide 1
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
WWiSE Group Partial Proposal on WWiSE Group Partial Proposal on Turbo CodesTurbo Codes
August 13, 2004
Airgo Networks, Bermai, Broadcom, Conexant, STMicroelectronics, Texas Instruments
S. Coffey, et al., WWiSE groupSlide 2
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
WWiSE contributors and contact WWiSE contributors and contact informationinformation
• Airgo Networks: VK Jones, [email protected]• Bermai: Neil Hamady, [email protected]• Broadcom: Jason Trachewsky, [email protected]• Conexant: Michael Seals, [email protected] • STMicroelectronics: George Vlantis,
[email protected]• Texas Instruments: Sean Coffey, [email protected]
S. Coffey, et al., WWiSE groupSlide 3
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
ContentsContents
• Overview of partial proposal• Motivation for advanced coding• Specification of turbo code• Performance results• Summary
S. Coffey, et al., WWiSE groupSlide 4
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Overview of partial proposalOverview of partial proposal
• The WWiSE complete proposal contains an optional LDPC code to enable maximum coverage and robustness
• FEC coding fits into the system design in a modular way, and in principle any high-performance code could be used instead of the LDPC code
• This partial proposal highlights an alternative choice for optional advanced code– The system proposed is identical to the WWiSE complete
proposal in all respects except that the optional LDPC code is replaced by the turbo code described here
S. Coffey, et al., WWiSE groupSlide 5
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Motivation for advanced codingMotivation for advanced coding• Advanced coding translates into higher achievable
throughput at the same robustness• In particular, in most configurations the BCC of rate ¾
and turbo code of rate 5/6 have approximately the same performance
• Thus advanced coding enables a rate increase from ¾ to 5/6 without robustness penalty
• At any given rate, advanced coding enhances coverage and robustness
• In addition, the modularity of the design means that the advantages carry over to every MIMO configuration and channel bandwidth
S. Coffey, et al., WWiSE groupSlide 6
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Transmitter block diagramTransmitter block diagram
Turbo encoder, puncturer
MIMO interleaver
Symbol mapper
Add pilots
D/AInterpol., filtering, limiter
Upconverter, amplifierIFFT
Add cyclic extension (guard)
S. Coffey, et al., WWiSE groupSlide 7
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Turbo encoderTurbo encoder
Parity bit 0
Parity bit 1
1+D +D3
1+D2+D3g(D)
=
Turbointerleav
er
1+D +D3
1+D2+D3g(D)
=
Systematic bit
These are the constituent codes used in the 3GPP/UMTS standard encoder
S. Coffey, et al., WWiSE groupSlide 8
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Turbo code frame formatTurbo code frame format
• The data payload is padded to reach a multiple of 512 bits
• The result is divided into blocks of 2048 bits and 512 bits– Number of 512 bit blocks is in the range 1-4
• All 512 bit blocks are placed at end of frame
• Each block is encoded as a separate turbo codeword
S. Coffey, et al., WWiSE groupSlide 9
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Turbo interleaver designTurbo interleaver design
• Two interleavers are proposed, one for each supported block size: 2048 and 512 bits
• Each interleaver is a contention-free inter-window shuffle interleaver– Designed to minimize memory contention when code is
decoded in parallel– Equivalent performance to 3GPP/UMTS interleavers
S. Coffey, et al., WWiSE groupSlide 10
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
PuncturerPuncturer
• Parity bits are punctured at regular intervals– Puncture intervals:
• Systematic & tail bits are not punctured; pad bits are punctured
• All code rates are easily derivable from mother code• Other puncturing patterns and setups also work well
Code rate Puncture interval
2/3 43/4 65/6 10
S. Coffey, et al., WWiSE groupSlide 11
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Puncturing tail codewordsPuncturing tail codewords
• Tailing codewords, i.e., codewords of length 512 information bits, are punctured differently, to a lower code rate– This facilitates low latency decoding: tail codeword
blocks are shorter and can be decoded with fewer iterations, without affecting operating point
• Puncture intervals for tail blocks: Code
ratePuncture interval
2/3 23/4 35/6 3
S. Coffey, et al., WWiSE groupSlide 12
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Parallelization of turbo decodersParallelization of turbo decoders
• Parallelization:– Divide trellis into a number of (possibly overlapping)
segments and decode each in parallel– Any reasonable number of iterations can be achieved without
affecting latency• End-of-packet latency:
– To achieve full gains of turbo or any iterative code, it is possible to taper codeword length and rate at end of packet
– High throughput naturally requires longer packets and Block Ack
Block 1Block 2
Block 3 . . .
S. Coffey, et al., WWiSE groupSlide 13
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
ComplexityComplexity• Compare to state complexity of 64-state BCC decoding
equivalent throughput• System assumptions: M-state constituent codes, I
iterations, soft-in soft-out algorithm extra cost factor of , BCC duty factor of
• Decoder must process 2 x 2 x I x trellis transitions (I iterations, 2 constituent codes, forward-backward for each, less duty factor), each of which costs M/64 as much– Overall complexity is 4I M/64 times as much as 64-state
code– E.g., with M = 8, I = 7, = 1.5, = 0.7, we have 3.675 times
the state complexity– This does not account for other differences such as memory
requirements and interleaver complexity
S. Coffey, et al., WWiSE groupSlide 14
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
Performance resultsPerformance results
S. Coffey, et al., WWiSE groupSlide 15
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Simulation setupSimulation setup
• All combinations of:– Channels B, D, AWGN– 20 MHz and 40 MHz– Rate ¾ and rate 5/6– BCC and turbo code
• All simulations under ideal conditions
S. Coffey, et al., WWiSE groupSlide 16
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Channel model B NLOS, 20 MHzChannel model B NLOS, 20 MHz
S. Coffey, et al., WWiSE groupSlide 17
August 2004 doc.: IEEE 802.11-04/0951r1
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Channel model B NLOS, 40 MHzChannel model B NLOS, 40 MHz
S. Coffey, et al., WWiSE groupSlide 18
August 2004 doc.: IEEE 802.11-04/0951r1
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Channel model D NLOS, 20 MHzChannel model D NLOS, 20 MHz
S. Coffey, et al., WWiSE groupSlide 19
August 2004 doc.: IEEE 802.11-04/0951r1
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Channel model D NLOS, 40 MHzChannel model D NLOS, 40 MHz
S. Coffey, et al., WWiSE groupSlide 20
August 2004 doc.: IEEE 802.11-04/0951r1
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AWGN, 20 MHzAWGN, 20 MHz
S. Coffey, et al., WWiSE groupSlide 21
August 2004 doc.: IEEE 802.11-04/0951r1
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AWGN, 40 MHzAWGN, 40 MHz
S. Coffey, et al., WWiSE groupSlide 22
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
ReferencesReferencesIEEE 802.11 documents:
• IEEE 802.11/04-0886-00-000n, “WWiSE group PHY and MAC specification,” M. Singh, B. Edwards et al.
• IEEE 802.11/04-0877-00-000n, “WWiSE proposal response to functional requirements and comparison criteria,” C. Hansen et al.
• IEEE 802.11/04-0952-00-000n, “WWiSE partial proposal on turbo codes: specification,” S. Pope et al.
Parallelization:
4. K. Blankenship, B. Classon, and V. Desai, “High-throughput turbo decoding techniques for 4G,” Int. Conf. on 3G Wireless & Beyond, 2002.
5. E. Yeo, B. Nikolic, and V. Anantharam, “Iterative decoder architectures,” IEEE Communications Magazine, August 2003, pp.132-140
S. Coffey, et al., WWiSE groupSlide 23
August 2004 doc.: IEEE 802.11-04/0951r1
Submission
References, contd.References, contd.6. Z. Wang, Z. Chi, and K. K. Parhi, “Area-efficient high-speed
decoding schemes for turbo decoders,” IEEE Trans. VLSI Systems, vol. 10, no. 6, pp. 902-912, Dec. 2002
7. S. Yoon and Y. Bar-Ness, “A parallel MAP algorithm for low latency turbo decoding,” IEEE Communications Letters, vol. 6, no. 7, pp. 288-290, July 2002
Interleavers:
8. A. Nimbalker, K. Blankenship, B. Classon, T. Fuja, and D. Costello, “Inter-window shuffle interleavers for high-throughput turbo decoding,” Proc. Int. Symp. on Turbo Codes, 2003.
9. A. Nimbalker, K. Blankenship, B. Classon , T. Fuja, and D. Costello, “Contention-free interleavers,” Proc. Int. Symp. on Info. Theory, 2004.
