Method and apparatus for communicating digital data using trellis coded QAM

  • US 5,233,629 A
  • Filed: 07/26/1991
  • Issued: 08/03/1993
  • Est. Priority Date: 07/26/1991
  • Status: Expired due to Term
First Claim
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1. A method for communicating digital data using QAM transmission comprising the steps of:

  • dividing an N-bit QAM constellation pattern into four subsets, each subset including N/4 symbol points of said constellation pattern;

    assigning a different two-bit codeword to each of said four subsets;

    encoding a symbol to be transmitted by processing a first bit of said symbol with a rate 1/2 binary convolutional encoding algorithm to provide the two-bit codeword assigned to the subset in which said symbol resides in said constellation pattern;

    mapping said two-bit codeword with the remaining bit(s) of said symbol to provide a modulation function, wherein said two-bit codeword forms the least significant bits of said modulation function and defines the columns of a matrix of coordinates of said constellation pattern, and said remaining bit(s) form the most significant bits of said modulation function, correlate said symbol with one of the N/4 symbol points included in the subset defined by said codeword and determine the size of said constellation pattern; and

    modulating a carrier with said modulation function for transmission on a communication channel.

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