Underwater Acoustic Communication Using a “virtual” Electronic Time-reversal Mirror Approach

This work presents a technique for reducing the intersymbol interference (ISI) in underwater coherent communications using time-reversal acoustics. The paper introduces a “virtual" time-reversal mirror (TRM) that is implemented electronically at the receiver array and simulates the kind of processing that would be done by an actual TRM during the reciprocal propagation stage. In both cases, a probe pulse sent by the transmitter/receiver located at the (physical or virtual) focal point and received at the array provides a template impulse response for undoing the effects of multipath by straightforward linear filtering. Very simple equalization algorithms may subsequently be used to decode the message. Channel variations between transmission of the probe and the actual message lead to mismatch that can impact the coherence of TRMs, and hence degrade the focusing power of the array. Computer simulations using a normal-mode propagation model in a reallistic shallow water scenario show that, even with high uncertainty in the transmitter and receiver relative positions, the virtual mirror can strongly reduce the effects of multipath. Although a multichannel equalizer attains a lower mean-square error, the "virtual" TRM can provide comparable results under low mismatch with much smaller complexity.