Spatio-Temporal Focusing for Elimination of Multipath Effects in High Rate Acoustic Communications

High rate underwater communications have traditionally relied on equalization methods to overcome the intersymbol interference (ISI) caused by multipath propagation. An alternative technique has emerged in the form of time-reversal, which comes at virtually no cost in computational complexity, but sacrifices the data rate and relies on large arrays to reduce ISI. In this paperer, optimal multipath suppression using spatio-temporal processing is addressed analytically. A communication link between a single element and an array is considered in several scenarios: uplink and downlink transmission, with and without channel state information and varying implementation complexity. Transmit/receive techniques are designed which simultaneously maximize the data detection SNR and minimize the residual ISI, while maintaining maximal data rate in a given bandwidth and satisfying a constraint on transmitted energy. The performance of various techniques is compared on a shallow water channel operating in the 15 kHz band. Results demonstrate benefits of optimal focusing whose performance is not conditioned on the array size.