On Linear Receivers for Digital Transmission Systems

Two main classes of receivers for data modems using linear modulation systems over time-dispersive channels have been investigated by many authors for both theoretical and practical purposes, 1) structure-constrained linear receivers, such as zeroforcing and mean-square-error tapped-delay-line equalizers, and 2) nonlinear receivers, such as decision-feedback equalizers and maximum likelihood sequence estimators. In this paper a linear receiver that turns out to be practical and optimum in the mean-square sense is analyzed in detail, and some interesting features of this receiver are stressed; for instance, it is shown that in the absence of noise it becomes a zero-forcing equalizer, provided that stability can be achieved. A comprehensive set of results is also presented, showing that conventional tapped-delay-line equalizers perform very close to the optimum.