Estimating mutual information for the underwater acoustic channel

Abstract

Estimates of the upper and lower bounds on the information rates attainable for acoustic communication systems with white Gaussian sources under uncertain channel conditions are provided that account for finite duration signaling and finite coherence time. For the case where the coherence time of the channel exceeds that of the packet duration the estimators are computationally efficient with the Levinson recursion and provide a means of tuning the accuracy of the estimates to fit a given computational budget. The reduction in the information rate relative to the known channel case is quantified in terms associated with the duration of signaling, the posterior covariance of the channel, and the prior covariance of the channel. For scenarios where the prior channel covariance is known exact bounds on the information rates are computable else the estimators provide confidence intervals for these rates. The estimators are tested on 18 kHz at sea data collected in shallow water north of Elba Italy on a 1.8-m aperture vertical array and on very shallow water sites at Keyport Washington. The effects of temporal coherence degradation as well as multi-path spread are quantified. [Work supported by the Office of Naval Research.]