Performance Analysis of Underwater Optical Wireless Communication Using O-RIS and Fiber Optic Backhaul (Extended version)

TL;DR

The work introduces a resilient UWOC backbone by integrating underwater optical access points with a PON-based fiber backhaul and an Optical-RIS (O-RIS). It rigorously analyzes direct and RIS-assisted UWOC links under Gamma–Gamma and mEGG turbulence, employing hard switching and diversity combining (SC, MRC) to enhance reliability, and evaluates system capacity under a practical UWOC-WDM-PON architecture. The study provides closed-form outage and BER expressions, derives ergodic capacity with backhaul constraints, and validates findings via Monte Carlo simulations, highlighting the impact of RIS element count, placement, and configuration (passive vs active). Practical insights include RIS-enabled throughput gains, RIS placement caveats in linear regimes, and scalable backhaul integration suitable for real-world underwater networks. The results demonstrate a path toward high-throughput, low-latency, long-range underwater communications with robust operation in varying aquatic environments.

Abstract

This Letter presents a novel hybrid underwater wireless optical communication (UWOC) system that integrates underwater optical access points (UOAPs) with a passive optical network (PON)-based fiber-optic backhaul to provide a resilient backbone. A hard switching mechanism is employed between direct and optical reconfigurable intelligent surface (O-RIS)-assisted links to ensure reliable connectivity. Unlike previous studies, the proposed system is evaluated under both active and multiple passive O-RIS configurations. To enhance reliability, the Selection Combining (SC) and Maximal Ratio Combining (MRC) schemes are applied. Analytical and simulation results demonstrate that optimal O-RIS placement significantly enhances system performance. However, in the linear regime, placing it too close to the receiver causes degradation due to increased path loss and beam jitter in an identical water type. Moreover, increasing the number of O-RIS elements within practical limits further improves overall system performance and enhances adaptability to variations in the underwater channel.

Figures (4)

• Figure 1: Proposed research system model illustrating the unmanned underwater vehicles (UUV), transmitter (Tx), and receiver (Rx).
• Figure 2: (a) OP vs. average SNR ($\bar{\gamma}$) for $L_{sr}=L_{rd}=1\ \mathrm{m}$ under mEGG and G–G turbulence models. (b) OP vs. $\bar{\gamma}$ for various temperature and salinity levels. (c) OP vs. $\bar{\gamma}$ for $L_{sr}=L_{rd}=40\ \mathrm{m}$ and $\gamma_{th}=5$ dB under SC and MRC techniques. (d) OP comparison vs. $\bar{\gamma}$ for $L_{sr} = L_{rd} = 50\ \mathrm{m}$ with various O-RIS types. (e) BER vs. $\bar{\gamma}$ for different modulation types. (f) BER of BPSK vs. $L_{sd}$, with $L_{sr}=L_{rd}$ and $\bar{\gamma}=25~\mathrm{dB}$. (g) BER of BPSK vs. $(\frac{L_{sr}}{L_{sd}})$ for various water types, with $P_t = 20~\mathrm{dB}$ and $N_{\mathrm{O\text{-}RIS}} = 16$. (h) SOC vs. $\bar{\gamma}$ for under different $N_{O\text{-}RIS}$ and jitter conditions, with $L_{sr} = L_{rd} = 60\ \mathrm{m}$.
• Figure 3: (a) OP versus average SNR ($\bar{\gamma}$) for $L_{sr} = 90\,\mathrm{m}$, $L_{rd} = 60\,\mathrm{m}$, and $L_D = 140\,\mathrm{m}$. (b) Comparison of the CC under H.D. and IM/DD detection modes, considering a direct link with $L_D = 120$ m and an O-RIS–assisted link with $L_{sr} = 95$ m and $L_{rd} = 40$ m. (c) DO versus average SNR for $L_{sr} = L_{rd} = 60$ m. (d) 3D plot of DO as a function of $N_{\text{O-RIS}}$ and average SNR ($L_{sr} = L_{rd} = 40$ m). (e) 3D plot of SOC under the same setup. (f) 3D plot of BER versus $N_{\text{O-RIS}}$ and $L_{sd} \quad (L_{sr} = L_{rd})$. (g) 3D plot of CC versus $N_{\text{O-RIS}}$ and $L_{sd}$. (h) 3D plot of OP versus the same parameters.
• Figure 4: (a) E2E delay and throughput allocated to each UOAP vs. the number of UOAPs. (b) CC of the IM/DD for $\mathfrak{T}=2$ under hard switching, where the direct links $L_D$ are $90\,\mathrm{m}$ and the O-RIS links $L_{SR}=L_{RD}$ are $50\,\mathrm{m}$.