Improved Turbo Equalization Schemes Robust to SNR Estimation Errors

Qiang LI  Wai Ho MOW  Zhongpei ZHANG  Shaoqian LI  

IEICE TRANSACTIONS on Communications   Vol.E90-B   No.6   pp.1454-1459
Publication Date: 2007/06/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.6.1454
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
turbo equalization,  SNR mismatch,  Scaled Max-Log-Map equalization,  switching equalization scheme,  soft information,  

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An improved Max-Log-Map (MLM) turbo equalization algorithm called Scaled Max-Log-Map (SMLM) iterative equalization is presented. Simulations show that the scheme can dramatically outperform the MLM besides it is insensitive to SNR mismatch. Unfortunately, its performance is still much worse than that of Log-Map (LM) with exact SNR over high-loss channels. Accordingly, we also propose a new SNR estimation algorithm based on the reliability values of soft output extrinsic information of SMLM decoder. Using the new scheme, we obtain good performance close to that of LM with ideal knowledge of SNR.