Noncoherent sequence demodulation for trellis coded M-DPSK

The maximum likelihood block decoder for trellis-coded noncoherent M-DPSK signals on the AWGN (additive white Gaussian noise) channel is outlined, first assuming that the decoder has no knowledge of the state of the encoder at the beginning of the block, and then assuming that it knows the state. Because these exhaustive decoders suffer from an exponential growth in complexity with blocklength, two simplified decoders are proposed that approach the performance of the exhaustive decoders with a much more manageable complexity. Through a union bound analysis and computer simulations, it is shown that it is possible to achieve large gains over uncoded systems with a very reasonable decoder complexity. Simulations of these noncoherent decoders show that in environments in which the random channel phase is slowly varying with respect to blocks on the order of 20-30 symbol periods, noncoherent sequence decoders like those presented are capable of gaining essentially all of the asymptotic coding gain of trellis codes used on a coherent link