A sparse adaptive decision feedback equalization equipped with digital phase-locked loop on feedback filter for underwater acoustic communication with a fast-moving platform

Abstract Ocean survey systems using underwater robots, such as autonomous underwater vehicles, for exploring vast ocean areas have gained attention. However, mobile underwater acoustic communication (UWAC) channels present highly challenging doubly selective environments, necessitating advanced signal processing techniques. Recently, methods leveraging the physical characteristics of UWAC channels, particularly channel response sparsity, have garnered interest. This study proposes a signal processing method that applies a sparsity-constrained adaptive algorithm to a decision feedback equalizer, with digital phase-locked loops on the feedback filter taps to track Doppler shifts in multipaths. The method’s performance was evaluated through simulations in a high-speed mobile communication environment in shallow water, showing improved communication performance under severe conditions, such as low-signal to noise ratio (SNR) and high relative speed (15 kt) with significant delay-Doppler spread. Additionally, the communication performance bounds were analyzed parametrically based on channel characteristics, confirming near-optimal gains relative to SNR or signal-to-interference ratio.