Adaptive multichannel combining and equalization for underwater acoustic communications

A theoretically optimal multichannel receiver for intersymbol interference communication channels is derived, and its suboptimal versions with linear and decision feedback equalizer are presented. A practical receiver based on any of these structures encounters difficulties in the underwater acoustic channels in which the extended time-varying multipath is accompanied by phase instabilities. A receiver that overcomes these problems by jointly performing adaptive mean-squared error diversity combining, multichannel carrier-phase synchronization and decision feedback equalization is proposed. Its performance is demonstrated on the experimental telemetry data from deep and shallow water long-range acoustic channels. Presented results indicate superior quality of coherent phase-shift keying (PSK) and quadrature amplitude modulation (QAM) reception obtained through joint equalization of very few channels.