Integrated spatial-temporal detectors for asynchronous Gaussian multiple-access channels

The optimum (maximum likelihood) multi-element global sequence detector is derived for the multi-user communication channel. The resulting integrated array detector is composed of retro-directive beam-formers in the users’ directions followed by a bank of matched filters and a processor implementing a dynamic programming (Viterbi) algorithm. Suboptimal realizations of the multi-element detector are considered, offering reduced complexity as compared to the optimum solution. The performance of the multi-element detector is analysed in terms of error probability, detection asymptotic efficiency and near-far resistance. In particular, the effects of array beam-forming on the performance is discussed and shown to generalize existing results for the scalar (single channel) case. Processing which uses the additional dimension of space can result in significant improvements in performance over the scalar case. Following a general performance analysis, a comparison of several suboptimal multi element detectors is given. In particular, it is shown that a new combined spatial-temporal processing is always uniformly superior to that of using beam-formers which result in separation of signals, followed by single-user detectors.