Secrecy performance analysis of NOMA-UWOC systems over a vertically stratified WGG oceanic turbulence channel

Underwater wireless optical communication (UWOC) has emerged as a promising solution for short-range high-speed underwater data transmission in recent years. For what is believed to be the first time, this work presents a comprehensive secrecy performance analysis of a downlink non-orthogonal multiple access (NOMA)-UWOC system over the composite vertically stratified Weibull-generalized gamma (WGG) oceanic fading channel, in which the impacts of path loss, underwater turbulence, pointing errors, and angle-of-arrival fluctuations are considered. Specifically, the closed-form expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the vertically stratified WGG fading channel coefficient are derived analytically. Then, on the basis of these derivations, analytical frameworks for the key secrecy performance metrics, including secrecy outage probability, strictly positive secrecy capacity, and effective secrecy throughput, are obtained, taking into account the residual interference from successive interference cancellation (SIC), which are validated through Monte Carlo simulations. Finally, the effects of the number of layers, the thermohaline gradient and air bubbles, the residual power factor of imperfect SIC, the transceiver misalignment, and the angle-of-arrival deviation are investigated on this UWOC system. The presented results give valuable insights into the practical aspects of deployment of UWOC networks.