Ergodic Rate Characterization for Rate-Splitting Multiple Access Based Underwater Wireless Optical Communications

This paper introduces the rate-splitting multiple access (RSMA) to underwater wireless optical communications (UWOC) and investigates the ergodic rate metric for the RSMA-based UWOC system over turbulence-induced fading channels. Specifically, the model of the RSMA applied to UWOC is established, where an aggregated channel with the combined effects of absorption, scattering, and oceanic turbulence is considered. To quantify the ergodic rate of the RSMA-based UWOC system, an approximation of the instantaneous signal to interference plus noise ratio (SINR) is derived using the Fenton-Wilkinson moment matching method. With the approximated SINR, this paper further presents a high-accurate approximation of the ergodic rate in terms of the scaled complementary error function and Tayler series. Numerical results are demonstrated to evaluate the ergodic rate of the RSMA-based UWOC system and to validate the excellent match between the derived approximated analytical expression of ergodic rate and the results obtained from the original integral expression and Monte Carlo simulations.