Underwater acoustic communications with Viterbi detector

An efficient underwater acoustic communication system has to deal simultaneously with problems of noise, multipath propagation and non-stationary channel. The Viterbi algorithm, often used in radio communications, is deserted in underwater ones because of the channel impulse response length. The first part of the paper discusses the feasibility of using this processing in the sea. We distinguish deep and shallow water cases, short and long range transmissions. Adaptive beamforming or parametric transmission can be used to reduce the channel time-spreading. In the second part we give results obtained by applying the Viterbi algorithm with a self-optimised LMS filter used for channel identification. Through simulations we emphasize the influence of signal-to-noise ratio, channel shape (particularly non-minimum phase one), delays... . One Atlantic (Azores) transmission (60 km range) helped to show the superiority of Viterbi on a linear equalizer (even with adaptive step) processing, due to its ability to follow channel variations (interesting for moving transmitter-receivers). Its robustness is analysed