Analysis of ergodic sum rate in RSMA with perfect and imperfect SIC: A multiple-antenna selection approach for optimizing UAV positioning

Rate-Splitting Multiple Access (RSMA) has emerged as a promising multiple access technique for next-generation wireless networks, enabling enhanced spectral efficiency and interference management. This paper analyzes the ergodic sum-rate performance of an RSMA-enabled unmanned aerial vehicle (UAV)-assisted communication system under both perfect and imperfect successive interference cancellation (SIC) scenarios. To optimize system performance, we propose an antenna selection strategy with multiple antennas at the UAV-based aerial base station (UAV-BS) and derive closed-form analytical expressions for the ergodic sum rate under various network configurations. Furthermore, an alternating optimization (AO)-based UAV-BS placement strategy is developed to maximize spectral efficiency. We also extend the analysis to the high-SNR regime, where asymptotic approximations offer insights into the impact of residual interference in imperfect SIC scenarios. Additionally, we introduce the energy-spectral efficiency (ESE) metric, which accounts for both spectral efficiency and total power consumption, including UAV propulsion, radio frequency (RF) transmission, and circuit power consumption. Simulation results demonstrate that RSMA significantly outperforms Non-Orthogonal Multiple Access (NOMA), particularly under imperfect SIC conditions, while achieving superior ESE through optimized power allocation and UAV positioning. These findings provide valuable design guidelines for robust and energy-efficient RSMA-enabled UAV-assisted networks in future wireless systems.