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Differentially nonlinear convolutional channel coding with expanded set of signalling alphabets

DC
  • US 4,520,490 A
  • Filed: 08/05/1983
  • Issued: 05/28/1985
  • Est. Priority Date: 08/05/1983
  • Status: Expired due to Term
First Claim
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1. A method for transmitting a bit sequence by modulating a carrier signal to sequentially assume one of a plurality of pairs of discrete signal values, comprising the steps of:

  • (a) differentially encoding bits in each group of r bits in said sequence by rotating the values of bits in the previous differentially encoded r bit group in accordance with the values of bits in the current r bit group,(b) expanding each differentially encoded r bit group into a group of r+1 bits by a non-linear convolutional coding process utilizing m internal states, the current state of said convolutional code being determined by p stored bits, where 2p =m, said p stored bits being functions of the previous bits input to said convolutional encoder and affecting the output of said convolutional encoder,(c) selecting one of 2r+1 signalling alphabets from a signal constellation, each alphabet corresponding to a pair of discrete signal values, said selection being made as a function of the r+1 bit group so that 2r signalling alphabets correspond to all permitted transitions from each current internal state of said convolutional coding process to m possible next states of said convolutional coding process, and so that the 2r signalling alphabets have a larger minimum distance from each other than the minimum distance within the complete set of 2r+1 signalling alphabets, and(d) transmitting the pairs of discrete signal values corresponding to the selected signalling alphabets in sequence,wherein said signal constellation is arranged so that the same signal constellation is obtained when the original constellation is rotated by 90, 180 or 270 degrees, and whereinrotation of said constellation by 90, 180 or 270 degrees produces the same effect on said transmitted discrete signal values as rotation of said differentially encoded bits in each r bit group.

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