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Soft decision output decoder for decoding convolutionally encoded codewords

  • US 5,933,462 A
  • Filed: 11/06/1996
  • Issued: 08/03/1999
  • Est. Priority Date: 11/06/1996
  • Status: Expired due to Term
First Claim
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1. A system for decoding a sequence of signals output by an encoder and transmitted over a channel, said encoder output represented by a trellis having a block length T, said system comprising:

  • first means for Viterbi decoding said sequence of signals received over said channel during a forward iteration through said trellis, said first means providing a plurality of forward iteration state metrics (x for each state at each time interval over a window of length 2L, where L is a number of constraint lengths and 2L is less than block length T, wherein said forward iteration begins at an initial state t0 ;

    second means for Viterbi decoding said sequence of signals received over said channel during a backward iteration through said trellis, said second means providing a plurality of backward iteration state metrics β

    for each state at each time interval starting at a second time; and

    third means for performing a dual maxima computation at each state using the forward state metrics, the backward state metrics and the branch metrics for same to provide a measure of the likelihood that a particular sequence of data was transmitted by said encoder.

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