Maximum-likelihood receiver for four-dimensional signaling schemes corrupted by ISI

A maximum-likelihood decision-directed receiver structure is derived for a data transmission system which employs quadrature-quadrature phase shift keying (Q/sup 2/PSK) as the modulation scheme. The receiver is derived by treating the problem of sequence decision, sample timing, and carrier phase as a composite estimation problem. It is shown that the resulting maximum-likelihood estimates (MLEs) are asymptotically unbiased, and the variances of these estimates are derived. In this receiver, symbol detection is carried out by means of a modified Viterbi algorithm (MVA) while a parallel synchronizer is used for carrier phase and delay recovery. As a measure of performance, an error-event probability bound is derived for the MVA. The effect of intersymbol interference, (ISI) present at the two matched filters' outputs, on the error bound is analyzed and illustrated. It is shown that the resulting MVA and the parallel estimator are well suited for systolic array implementation.<
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