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Channel Coding in IEEE802.16e

Channel Coding in IEEE802.16e. Student: Po-Sheng Wu Advisor: David W. Lin. Reference. IEEE Std 802.16a-2003, April 2003 IEEE Std 802.16-2004, October 2004 IEEE Std 802.16e™-2005 and IEEE Std 802.16™-2004/Cor1-2005 IEEE Std 802.16e/D9, June 2005. Outline. Overview RS code

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Channel Coding in IEEE802.16e

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  1. Channel Coding in IEEE802.16e Student: Po-Sheng Wu Advisor: David W. Lin

  2. Reference • IEEE Std 802.16a-2003, April 2003 • IEEE Std 802.16-2004, October 2004 • IEEE Std 802.16e™-2005 and IEEE Std 802.16™-2004/Cor1-2005 • IEEE Std 802.16e/D9, June 2005

  3. Outline • Overview • RS code • Convolution code • LDPC code • Future Work

  4. Overview

  5. RS code • The RS code in 802.16a is derived from a systematic RS (N=255, K=239, T=8) code on GF(2^8)

  6. RS code

  7. RS code • This code then is shortened and punctured to enable variable block size and variable error-correction capability. • Shorten：(n, k) → (n-l, k-l) • Punctured： (n, k) → (n-l, k) • In general, the generator polynomial in IEEE802.16a h=0

  8. RS code • They are shortened to K’ data bytes and punctured to permit T’ bytes to be corrected. • When a block is shortened to K’, the first 239-K’ bytes of the encoder input shall be zero • When a codeword is punctured to permit T’ bytes to be corrected, only the first 2T’ of the total 16 parity bytes shall be employed.

  9. RS code • When shortened and punctured to (48,36,6) the first 203(239-36) information bytes are assigned 0. • And only the first 12(2*6) bytes of R(X) will be employed in the codeword.

  10. Shortened and Punctured

  11. RS code

  12. RS code • Decoding : The Euclid’s (Berlekamp) algorithm is a common decoding algorithm for RS code. • Four step: -compute the syndrome value -compute the error location polynomial -compute the error location -compute the error value

  13. Convolution code • Each RS code is encoded by a binary convolution encoder, which has native rate of ½, a constraint length equal to 7.

  14. Convolution code • “1” means a transmitted bit and “0” denotes a removed bit, note that the has been changed from that of the native convolution code with rate ½ .

  15. Convolution code • Decoding: Viterbi algorithm

  16. Convolution code • The convolution code in IEEE802.16a need to be terminated in a block, and thus become a block code. • Three method to achieve this termination • Direct truncation • Zero tail • Tail biting

  17. RS-CC code • Outer code: RS code • Inner code: convolution code • Input data streams are divided into RS blocks, then each RS block is encode by a tail-biting convolution code. • Between the convolution coder and modulator is a bit interleaver.

  18. RS-CC code

  19. LDPC code • low density parity checks matrix • LDPC codes also linear codes. The codeword can be expressed as the null space of H, Hx=0 • Low density enables efficient decoding • Better decoding performance to Turbo code • Close to the Shannon limit at long block length

  20. LDPC code • n is the length of the code, m is the number of parity check bit

  21. LDPC code • Base model

  22. LDPC code • if p(f,i,j) = -1 • replace by z*z zero matrix else • p(f,i,j) is the circular shift size

  23. LDPC code • Encoding [u p1 p2]

  24. LDPC code • Decoding • Tanner Graph • Sum Product Algorithm

  25. LDPC code • Tanner Graph

  26. LDPC code • Sum Product Algorithm

  27. LDPC code

  28. LDPC code

  29. Future Work • Realize these algorithm in computer • Find some decoding algorithm to speed up

  30. Thanks for your attention

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