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A simple remedy for the exaggerated extrinsic information produced by the SOVA algorithm

IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2006年第5期5卷 996-1002页

作者： Huang, Chuan Xiu Ghrayeb, Ali Concordia Univ Dept Elect & Comp Engn Montreal PQ Canada

In this paper, we propose a novel and simple approach for dealing with the exaggerated extrinsic information produced by the soft-output Viterbi algorithm (SOVA). The proposed remedy is based on mathematical analysis and it involves using two attenuators, one applied to the immediate output of the SOVA and another applied to the extrinsic information before it is passed to the other decoder (assuming iterative decoding). The use of these attenuators aims at reducing the inherent strong correlation between the intrinsic information (input to the SOVA) and extrinsic information (output of the SOVA). We examine the modified SOVA (MSOVA) on additive white Gaussian noise (AWGN) and flat fading channels for parallel concatenated codes (PCCs) and serial concatenated codes (SCCs). We show that the MSOVA provides substantial performance improvements over both channels. For example, it provides improvements of about 0.8 to 1.0 dB at P-b = 10(-5) in AWGN, and about 1.4 to 2.0 dB at P-b = 10(-5) on fading channels. We also show that there are cases where the MSOVA is superior to the a posteriori probability (app) algorithm. With this motivation, we extend the proposed modification to the app algorithm with favorable results. We demonstrate that the modified app (Mapp) provides performance improvements between 0.3 to 0.6 dB at P-b = 10(-5) relative to the app. We lastly mention that the proposed modifications, while they provide considerable performance improvements, keep the complexity of these decoders almost, the same, which is remarkable.

关键词： app algorithm extrinsic information fading channels turbo codes SOVA algorithm

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Serially concatenated continuous phase modulation with iterative decoding

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IEEE TRANSACTIONS ON COMMUNICATIONS 2001年第11期49卷 1901-1915页

作者： Moqvist, P Aulin, TM Chalmers Univ Technol Telecommun Theory Grp Dept Comp Engn SE-41296 Gothenburg Sweden Ericsson Mobile Data Design AB SE-41266 Gothenburg Sweden

Serially concatenated and interleaved continuous phase modulation (CPM) with iterative decoding is investigated. Ana posteriori probability (app) algorithm for CPM is developed based on the classic app algorithm for channel codes. The system is analyzed through upper bounds on the average bit error probability. For coded and interleaved minimum shift keying, the weight spectrum is computed, resulting in a transfer function bound. This is cumbersome for a general CPM system;instead, only the most significant error events contributing to the weight spectrum are identified. Simulations show that, firstly, these events give a satisfactory view of system performance when equal outer codes are used, and secondly, that remarkably good performance can be obtained for some simple systems. finally, power spectral densities and bandwidths are computed, allowing for a bandwidth/performance comparison of different combinations.

关键词： app algorithm concatenated codes continuous phase modulation iterative decoding serial concatenation

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