BCJR algorithm

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The BCJR algorithm is an algorithm for maximum a posteriori decoding of error correcting codes defined on trellises (principally convolutional codes). The algorithm is named after its inventors: Bahl, Cocke, Jelinek and Raviv. This algorithm is critical to modern iteratively-decoded error-correcting codes including turbo codes and low-density parity-check codes.

Steps involved[edit]

Based on the trellis:

  • Compute forward probabilities <math>\alpha</math>
  • Compute backward probabilities <math>\beta</math>
  • Compute smoothed probabilities based on other information (i.e. noise variance for AWGN, bit crossover probability for binary symmetric channel)

Variations[edit]

SBGT BCJR[edit]

Berrou, Glavieux and Thitimajshima simplification.

Log-Map BCJR[edit]

Max-Log-Map BCJR[edit]

Implementations[edit]

See Also on BitcoinWiki[edit]

External links[edit]

Source[edit]

http://wikipedia.org/