A heterogeneous RIS-assisted all-optical ocean-air integrated network: Channel modelling and performance analysis

Abstract

This paper introduces a unified framework for an integrated underwater-to-air multihop optical network that combines reconfigurable intelligent surface (RIS)-assisted underwater wireless optical communication (UWOC) with differential technology (DT) and modulating retroreflector (MRR)-based free space optical (FSO) systems. The system utilizes unmanned aerial vehicles (UAVs) as mobile aerial base stations, transmitting signals from automatic underwater vehicles (AUVs) to destination UAVs through an offshore micro-buoy relay. The paper models pointing errors with RIS and modifies the corresponding probability density function. It adopts the decode-and-forward (DF) relaying protocols to derive expressions for outage probability (OP), average bit error rate (ABER), and average channel capacity (ACC). The analysis considers factors like bubble levels, temperature and salinity gradients, detection technology, pointing errors, and RIS deployment strategy. Monte Carlo simulation validates the analytical results. The deployment of RIS is demonstrated to mitigate underwater fading impairments, and DT is shown to improve the performance of both FSO and UWOC subsystems. In addition, we provide interesting deployment and engineering insights based on results. This work contributes to the design and research of high-bandwidth integrated space-air-ground-ocean Internet of Things (IoT) networks for 6 G applications.