Improvements in SOVA-based decoding for turbo-coded storage channels

Ali Ghrayeb, Chuan Xiu Huang

Research output: Contribution to journalArticle

7 Citations (Scopus)


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 SOVA (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 P b = 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.

Original languageEnglish
Pages (from-to)4435-4442
Number of pages8
JournalIEEE Transactions on Magnetics
Issue number12
Publication statusPublished - 1 Dec 2005



  • Concatenated codes
  • Iterative decoding
  • SOVA algorithm
  • Storage channels
  • Turbo codes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering

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