Enhancing the Performance of the Aerial Relay System Through Rate-Splitting Multiple Access and Reconfigurable Intelligent Surface

This article presents a strategy to improve the performance of the aerial relay (AR) system by combining rate-splitting multiple access (RSMA) with reconfigurable intelligent surface (RIS) technologies. Our proposal is called an RIS-aided AR system with RSMA and abbreviated by the RIS-AR-RSMA system. Moreover, we analyze the outage probability (OP), system throughput (ST), and energy efficiency over Nakagami-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> channels, which are relevant for fifth-generation wireless communications. The system performance is also compared with that of an RIS-AR system utilizing nonorthogonal multiple access (NOMA), an AR-RSMA system without RIS, and an RSMA system without both RIS and AR, to verify the advantages of RSMA and RIS. Numerical results show a significant performance boost of the proposed RIS-AR-RSMA system. This improvement enables the RIS-AR-RSMA system to achieve the same target OP with notably lower transmit power than the AR-NOMA system. Furthermore, RSMA outperforms NOMA when the common rate substantially exceeds the private rate. We also comprehensively analyze the impacts of various parameters on OP and ST in the RIS-AR-RSMA system, including common rate, number of reflecting elements, AR positions, carrier frequency, and power allocation coefficients. By doing so, we propose recommendations to optimize the RIS-AR-NOMA system's performance. Monte-Carlo simulations validate the exactness of our analytical expressions and affirm the effectiveness of our proposed approach.