Sub-Block Recovery Scheme for Iterative Decoding of Turbo Codes with the Sub-Block Structure

Chunlong BAI  Bartosz MIELCZAREK  Ivan J. FAIR  Witold A. KRZYMIE  

IEICE TRANSACTIONS on Communications   Vol.E91-B   No.5   pp.1375-1386
Publication Date: 2008/05/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e91-b.5.1375
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Fundamental Theories for Communications
turbo codes,  sub-block structure,  ML decoding,  SOVA,  Log-MAP,  

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Wireless communication systems usually employ a concatenated error control coding scheme consisting of an outer error detection code and an inner error correction code. Traditionally, these two codes are decoded separately. When the sub-block structure is used, each data block (input sequence) at the inner encoder consists of several sub-blocks and each of these sub-blocks is protected with the error detection code. The sub-block structure is used in the Wideband CDMA (WCDMA) system specified by the 3rd Generation Partnership Project (3GPP). In this paper, a sub-block recovery scheme is proposed for this concatenated error control coding scheme to utilize the error detection capability introduced by the outer code in the decoding of the inner code. We demonstrate that, if the inner code is a turbo code with a highly structured interleaver and iterative sub-optimal decoding is used, the sub-block recovery scheme is helpful in correcting a typical error pattern, which helps to improve the block error rate performance. We analyze the decoding performance when sub-block recovery is used together with the maximum likelihood (ML) algorithm as well as the log maximum-a-posteriori probability (Log-MAP) and the soft output Viterbi algorithm (SOVA) and demonstrate gains introduced by the sub-block recovery in the latter two cases using computer simulations.