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Efficient Algorithm for Decoding Concatenated Codes
Chang-Woo LEE
Publication
IEICE TRANSACTIONS on Communications
Vol.E87-B
No.11
pp.3180-3186 Publication Date: 2004/11/01 Online ISSN:
DOI: Print ISSN: 0916-8516 Type of Manuscript: PAPER Category: Fundamental Theories for Communications Keyword: concatenated codes, turbo codes, Max-Log-MAP, SOVA, efficient algorithm,
Full Text: PDF(465.5KB)>>
Summary:
The maximum a posteriori (MAP) algorithm is the optimum solution for decoding concatenated codes, such as turbo codes. Since the MAP algorithm is computationally complex, more efficient algorithms, such as the Max-Log-MAP algorithm and the soft-output Viterbi algorithm (SOVA), can be used as suboptimum solutions. Especially, the Max-Log-MAP algorithm is widely used, due to its near-optimum performance and lower complexity compared with the MAP algorithm. In this paper, we propose an efficient algorithm for decoding concatenated codes by modifying the Max-Log-MAP algorithm. The efficient implementation of the backward recursion and the log-likelihood ratio (LLR) update in the proposed algorithm improves its computational efficiency. Memory is utilized more efficiently if the sliding window algorithm is adopted. Computer simulations and analysis show that the proposed algorithm requires a considerably lower number of computations compared with the Max-Log-MAP algorithm, while providing the same overall performance.
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