Underwater wireless optical communication in turbulent channels: a review

Significance Underwater wireless optical communication (UWOC) is considered as a vital technology for the future of ocean information transmission and sensing due to its large bandwidth, high data rates, and low latency. UWOC has significant application potential in fields such as ocean exploration, military communications, and the Internet of Underwater Things (IoUT). However, attenuation inherent to underwater channels, such as absorption and scattering, particularly the effects of oceanic turbulence caused by random temperature and salinity fluctuations, can lead to light intensity scintillation, phase distortion, and beam drift. These factors are key challenges that hinder the practical implementation of such systems. Therefore, a thorough investigation of underwater turbulent channel characteristics and exploration of effective anti-fading techniques are crucial for UWOC. This study aims to systematically review research progress on turbulent channels and their impact on communication systems.Progress First, the formation mechanisms and primary physical influences on ocean turbulence are elucidated by the study, and typical ocean refractive index power spectrums as well as optical wave characteristic parameters are introduced. Second, common turbulence statistical models for UWOC systems are summarized, and then analytical methods and recent research achievements regarding key performance metrics, including bit error rate (BER), outage probability (OP), and ergodic capacity (EC), are reviewed Furthermore, multiple anti-fading techniques are thoroughly discussed, including aperture averaging, adaptive optics, spatial diversity, relay cooperation, and deep learning, and moreover, their respective advantages, disadvantages, and research progress are analyzed. Finally, based on the current research landscape, future development trends in the UWOC field are explored in conclusion.Conclusions and Prospects This study provides a reference for understanding the mechanisms of turbulence, evaluating the performance of systems, and promoting anti-fading technologies. Consequently, it offers theoretical support for achieving reliable and efficient UWOC.