Coherent equalization for underwater acoustic communications: A performance evaluation of adaptive MMSE and time-reversal techniques

Abstract

A simple analytical expression is presented for evaluating and comparing the performance of channel-estimate-based coherent equalizers. A channel-estimate-based equalizer is one whose filter coefficients are calculated as a function of an explicit estimate of the acoustic channel impulse response. This is in contrast to a direct adaptation equalizer whose coefficients are calculated directly as the solution to a data estimation error minimization problem. The equalizer performance expression is different from other commonly used expressions because it is formulated from the viewpoint of the estimate of the channel impulse response rather than the actual channel impulse response. The expression allows the dependence of the performance of coherent equalizers on channel complexity and the quality of the channel estimate to be separately evaluated. The expression is used to evaluate and compare the performance of adaptive MMSE and time-reversal equalizers. [Work supported by ONR Ocean Acoustics.]