Outage and Throughput Analysis of RSMA-Enabled Satellite Downlinks Over Shadowed Rician Fading

Abstract

Rate-splitting multiple access (RSMA) is a promising enabler for improving spectral efficiency, interference management, and user fairness in satellite downlink systems. Yet, most RSMA studies are either tailored to terrestrial settings or rely primarily on numerical optimization, offering limited analytical insight under satellite-realistic propagation such as shadowing. Motivated by geostationary Earth orbit (GEO) downlink operation, this paper provides a tractable performance analysis of an RSMA-enabled single-beam multiuser downlink over shadowed Rician fading. We consider a $K$-antenna GEO satellite serving $Q$ single-antenna users with maximum-ratio transmission (MRT)–based precoding and perfect successive interference cancellation (SIC). Closed-form expressions are derived for the distribution of the effective channel gain, leading to exact and high-SNR outage probability characterizations. The resulting formulas explicitly reveal the roles of the antenna count (defined as the number of satellite transmit antennas $K$), shadowed Rician parameters, and RSMA power allocation. Furthermore, the analysis yields simple feasibility conditions that delineate practical operating regions for common/private power splitting. We obtain user and system throughput expressions and identify that the achieved diversity order equals $K$. Monte Carlo simulations validate the analysis and benchmark RSMA against nonorthogonal multiple access (NOMA) under various shadowing levels and power-allocation settings, highlighting reliability–rate trade-offs and providing actionable guidance for GEO satellite downlink design.