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Improvements in SOVA-Based Decoding for Turbo-Coded Storage Channels.

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Title: Improvements in SOVA-Based Decoding for Turbo-Coded Storage Channels.
Authors: Ghrayeb, Ali1 aghrayeb@ece.concordia.ca, Chuan Xiu Huang1
Source: IEEE Transactions on Magnetics. Dec2005, Vol. 41 Issue 12, p4435-4442. 8p.
Subjects: Algorithms, Turbo languages (Computer program language), Decoders (Electronics), Decoders & decoding, Lorentz transformations, Mathematical analysis
Abstract: 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). We first identify the reason behind these exaggerated values and then propose a simple remedy for it. We argue that what leads to this optimistic extrinsic information is the inherent strong correlation between the intrinsic information (input to the SOVA) and extrinsic information (output of the SOVA). Our 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). We examine the modified SOYA (MSOVA) on idealized partial response (PR) channels and the Lorentzian channel equalized to a PR target. We consider both 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 1.6 dB at Pb = 10-5. Finally, we note that the proposed modifications, while they provide considerable performance improvements, introduce only two additional multipliers to the complexity of the SOVA algorithm, which is remarkable. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract: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). We first identify the reason behind these exaggerated values and then propose a simple remedy for it. We argue that what leads to this optimistic extrinsic information is the inherent strong correlation between the intrinsic information (input to the SOVA) and extrinsic information (output of the SOVA). Our 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). We examine the modified SOYA (MSOVA) on idealized partial response (PR) channels and the Lorentzian channel equalized to a PR target. We consider both 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 1.6 dB at Pb = 10-5. Finally, we note that the proposed modifications, while they provide considerable performance improvements, introduce only two additional multipliers to the complexity of the SOVA algorithm, which is remarkable. [ABSTRACT FROM AUTHOR]
ISSN:00189464
DOI:10.1109/TMAG.2005.857453