A New LLR Approximation for BICM Systems with HARQ

Jin Whan KANG  Sang-Hyo KIM  Seokho YOON  Tae Hee HAN  Hyoung Kee CHOI  

Publication
IEICE TRANSACTIONS on Communications   Vol.E93-B    No.6    pp.1628-1632
Publication Date: 2010/06/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E93.B.1628
Print ISSN: 0916-8516
Type of Manuscript: LETTER
Category: Wireless Communication Technologies
Keyword: 
log-likelihood ratio,  BICM,  HARQ,  QAM,  demapper,  

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Summary: 
In this letter, a new approximation of log-likelihood ratio (LLR) for soft input channel decoding is proposed. Conventional simplified LLR using log-sum approximation can degrade the performance of bit interleaved coded modulation (BICM) systems employing hybrid automatic repeat request (HARQ) at low SNR. The proposed LLR performs as well as the exact LLR, and at the same time, requires only a small number of elementary operations.