Performance analysis of dual-IRS-assisted NOMA for underwater visible light communication in turbulent channels

Underwater visible light communication (UVLC) has become a highly attractive solution for fast wireless underwater communications, given its high data transmission rates, low delay, and security associated with the physical layer. Nonetheless, it suffers from serious limitations resulting from absorption, scattering, and turbulence-induced fading. In this paper, we present a new dual IRS architecture for UVLC communication that utilizes Intelligent Reflecting Surface (IRS) and Non-orthogonal Multiple Access (NOMA) technology to enhance the reliability and spectral efficiency of the link. A unified channel model is developed, where both the direct and IRS-assisted paths are taken into account, including the impact of underwater absorption, scattering, and turbulence through the Exponential Generalized Gamma (EGG) distribution. Based on the proposed channel model, closed-form expressions for the cumulative distribution function (CDF) and probability density function (PDF) are derived in terms of the Meijer- G function. Furthermore, analytical expressions are developed for the outage probability and average bit error rate (ABER), while the ergodic capacity is evaluated to quantify the achievable spectral efficiency of the proposed system. An asymptotic outage analysis is also carried out to characterize the system behavior in the high-SNR regime. The proposed framework is evaluated under different underwater channel and system conditions, and the analytical results are validated through Monte Carlo simulations. The close agreement between the analytical and simulation results confirms the accuracy of the developed framework and demonstrates the performance benefits of the proposed dual-IRS-assisted NOMA-UVLC system.