Reliable downlink transmission for underwater optical wireless systems with energy harvesting and HARQ.

Given the limited bandwidth of radio frequency and acoustic waves, alongside the growing demand for high-speed data transmission in underwater applications, underwater wireless optical communication (UWOC) has emerged as a promising and viable alternative. Nevertheless, UWOC systems face significant challenges due to performance degradation attributed to underwater attenuation, oceanic turbulence, bubble-induced blockages, and uncertainty in receiver positioning. This paper proposes a protocol design for reliable and energy-efficient UWOC operation. Specifically, we introduce an incremental redundancy hybrid automatic repeat request scheme integrated with energy harvesting capabilities. Additionally, a comprehensive and realistic UWOC channel model is developed to accurately characterize environmental impairments. To assess the system performance, we present a Markov chain-based analytical framework capable of deriving key performance metrics including average bit error rate, average throughput, average packet delay, and packet loss probability. Theoretical analysis is validated through the Monte Carlo simulations, confirming the effectiveness of the proposed design compared to state-of-the-art solutions.