Towards robust adaptive acoustic communications

Modulation and detection techniques used for underwater acoustic communications include phase coherent (PSK and QAM) and noncoherent (FSK) techniques. The objective of this work is the development of algorithms that can select the best technique for a given channel. The system of interest operates in shallow water over several kilometers in the 10-15 kHz band. A wideband probe is used at the beginning of each data packet to measure the multipath and the Doppler spread, as well as the SNR. The choice of modulation is based on these measurements. The spread factor of the channel determines whether phase coherent communications are possible. If so, an equalizer is employed to combat any intersymbol interference. If the channel varies too rapidly, noncoherent signaling is chosen. Guard intervals are used to eliminate the effect of multipath. Computer simulations and theoretical analysis are presented to quantify the performance of candidate modulation methods for varying channel parameters.