Coherent detection of coded/uncoded MPSK sequences over the Gaussian channel with unknown carrier phase using a Viterbi decoder

Using the approach of simultaneous ML estimation of digital sequence and unknown carrier phase, the authors develop a new suboptimum ML soft decoder which achieves coherent detection performance if the carrier phase is time-invariant. This decoder does not require any explicit recovery of coherent references, involves only linear operations in the metric computation, and can be implemented efficiently using a Viterbi decoder structure. It is applied to the ML estimation of a convolutionally/trellis coded MPSK sequence, as well as an uncoded MPSK sequence