Experimental Demonstration of Equalization with Phase Lock Loops Against Doppler Shifts of Multipath Signals on Underwater Acoustic Communications

In mobile underwater acoustic (UWA) communication, such as communication between autonomous underwater and surface vehicles, the motion of terminals causes a time-varying phase shift to each multipath signal, degrading demodulation performance in a manner difficult to address through conventional signal processing. To suppress the effects of phase shifts, equalization with loops for the compensation of multipath signal phase shifts has previously been proposed. Although the improvement yielded by the proposed equalization has been confirmed through simulations in the previous study, the applicability of this approach to actual data in an at-sea experiment has never been reported. In this study, the proposed method's improvement yield was evaluated by application to acoustic data obtained in a prior marine experiment with an autonomous surface vehicle. Consequently, the equalization was demonstrated to improve demodulation performance in UWA channels with nonuniform Doppler shifts and multipath signals.