Iterative decoding of compound codes by probability propagation in graphical models

  • Authors:
  • F. R. Kschischang;B. J. Frey

  • Affiliations:
  • Dept. of Electr. & Comput. Eng., Toronto Univ., Ont.;-

  • Venue:
  • IEEE Journal on Selected Areas in Communications
  • Year:
  • 2006

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Abstract

We present a unified graphical model framework for describing compound codes and deriving iterative decoding algorithms. After reviewing a variety of graphical models (Markov random fields, Tanner graphs, and Bayesian networks), we derive a general distributed marginalization algorithm for functions described by factor graphs. From this general algorithm, Pearl's (1986) belief propagation algorithm is easily derived as a special case. We point out that iterative decoding algorithms for various codes, including “turbo decoding” of parallel-concatenated convolutional codes, may be viewed as probability propagation in a graphical model of the code. We focus on Bayesian network descriptions of codes, which give a natural input/state/output/channel description of a code and channel, and we indicate how iterative decoders can be developed for parallel-and serially concatenated coding systems, product codes, and low-density parity-check codes