Performance analysis of AUV-aided NOMA-based vertical UWOC system with cascaded WGG turbulence model

In this work, an autonomous underwater vehicles (AUVs) based downlink non-orthogonal multiple access (NOMA) vertical underwater wireless optical communication (UWOC) system has been investigated for the first time in detail, to the best of our knowledge. Specifically, assuming that the turbulence-induced fading over this vertical UWOC link is subject to Weibull generalized gamma (WGG) distribution, one N-layer composite cascaded statistical fading model is derived under the comprehensive impacts of oceanic turbulence, pointing errors, absorption, and scattering, in which each layer considers the vertically inhomogeneous nature of the underwater environment with different parameters. On the basis of this model, the analytical as well as asymptotic expression for outage probability is obtained in the form of Fox's H function, and the coverage probability and average achievable rate are derived for this UWOC system, which are all confirmed by Monte Carlo simulations. Moreover, the effects of the number of layers, water types, detection techniques, power allocation coefficient, pointing errors, and the residual power factor of imperfect successive interference cancellation are further analyzed on this system. This work would benefit the design and development of vertical UWOC systems.