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Method of detecting DC-free sequences

  • US 5,910,969 A
  • Filed: 11/05/1996
  • Issued: 06/08/1999
  • Est. Priority Date: 11/05/1996
  • Status: Expired due to Term
First Claim
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1. A method of decoding a sequence of samples received over a communications channel representing a length k binary bit stream encoded as a sequence of bipolar symbols comprised of q groups of L symbols, each length L group of said symbols corresponding to one of 2m subwords having a predetermined block digital sum, said subwords having been encoded according to an inner rate m/L code and concatenated into blocks of complementary sign block digital sum according to an outer rate p/q code, where p is one part of said length k sequence and qm is the remaining part, comprising the steps of:

  • a. finding, for each group of L samples, the maximum likelihood paths through a trellis of said inner rate p/q code for said subwords having complementary sign block digital sums of +q and of -q;

    b. recording the cumulative state metrics and cumulative branch metrics for each of said paths; and

    c. identifying from said cumulative metrics for each said group of L samples a corresponding branch in a trellis for said outer rate m/L code to determine the order of concatenation of said subwords.

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