Environmental Model-Based Time-Reversal Underwater Communications

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.