A Survey on Underwater Acoustic Communications Under Information-Theoretic Constraints

Abstract

Underwater wireless communication is constrained by frequency-dependent attenuation, severe multipath propagation, slow acoustic propagation, Doppler-induced time scaling, and highly nonstationary noise. These effects make the usable bandwidth strongly dependent on distance and lead to a channel that is simultaneously bandwidth-limited and energy-limited. This paper summarizes the dominant physical and information-theoretic limitations of underwater links and reviews technical approaches for improving reliability and spectral efficiency. The discussion focuses on acoustic channel modeling, distance-dependent capacity, multicarrier and nonorthogonal access waveforms, channel coding, learningassisted receivers, and hybrid acoustic/optical/electromagnetic architectures. The survey indicates that future underwater networks will rely on adaptive cross-layer operation and multimodal link switching rather than a single universal physical layer.