Noncoherent sequence detection of coded linear modulations

New noncoherent sequence detection algorithms for combined demodulation and decoding of coded amplitude/phase modulations transmitted over additive white Gaussian noise (AWGN) channels are presented. Optimal noncoherent sequence detection requires a tree search and a complexity exponentially increasing with the duration of the transmission. In order to realize simple suboptimal receivers based on the Viterbi algorithm (VA), approximate schemes are proposed, characterized by a performance which approaches that of coherent detection. In the proposed schemes the tradeoff between complexity and performance is simply controlled by a parameter referred to as implicit phase memory and the number of trellis states. These schemes represent a significant improvement over previous results.