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Channel combination strategies for acoustic communication with towed arrays

Acoustic communication experiments were carried out during multistatic submarine searches in a littoral area. The purpose of the communication is to send information from the active transmitter to bistatic receivers. After transmission with a low-frequency source, phase-shift keyed signals were recorded on various hydrophone arrays towed by remote platforms. Message recovery is complicated by ambient noise, a time-varying Doppler shift due to platform motion, and by severe intersymbol interference due to multipath propagation. The present paper considers several techniques to combine the hydrophone channels of the receive arrays: a conventional beamformer followed by a single channel receiver, an equalizer combiner applied to the hydrophone channels, and an equalizer combiner applied to a collection of beams. The best performance is obtained with the beams combiner, which allows a data rate of 1000 bit/s in a reverberant coastal area.