Environmental Model-Based Time-Reversal Underwater Communications

Abstract

This paper addresses channel compensation in underwater acoustic communications by proposing a method for inserting physical propagation modeling into a passive time-reversal (PTR) receiver. PTR is known as a low complexity channel equalizer that uses multichannel probing for time signal refocusing, reducing inter-symbol interference caused by multipath propagation. The proposed method aims to improve PTR communications performance by replacing the conventional noisy channel estimates with optimized and noiseless channel replicas computed by a numerical ray trace model. The optimization consists of environmental focalization in an “ a priori ” physical parameter search space to obtain “ a posteriori ” channel impulse response replicas that best match the observed data. The results obtained on two data sets acquired during the UAN’11 experiment in a shallow water fjord near Trondheim, in May 2011, show that the proposed method clearly outperformed the traditional PTR by a mean square error gain from 1 up to 4 dB. Channel tracking was effective despite a reduced physical parameter search space that could be exhaustively covered with a minimal computational effort. To the best of our knowledge, this is the first successful report on the usage of a physical parameter fed numerical model for underwater acoustic communications channel equalization with real transmitted data in a useful underwater modem frequency band.