Optimization of RIS-Assisted RSMA-Enabled Tethered-UAV Communications

Abstract

Several technologies have been driving the development of next-generation wireless networks, including unmanned aerial vehicles (UAVs), reconfigurable intelligent surfaces (RISs), and rate-splitting multiple access (RSMA). UAVs, in particular tethered UAVs (TUAVs), are seen as an enabler of ubiquitous and continuous cellular services. Similarly, RIS technology can improve spectral efficiency by smartly directing radio signals toward receivers, while RSMA emerged as an efficient multiple-access technique that controls interference to serve multiple users. To benefit from these paradigms, we explore here a RIS-assisted RSMA-enabled TUAV communication system and investigate the joint optimization of its parameters. Specifically, we formulate the joint TUAV placement, RIS phase-shift configuration, and RSMA parameters optimization problem to maximize the weighted sum data rate (WSR) of ground users. Due to the problem's complexity, we study the sub-problems of phase-shift optimization, RSMA precoding and rate-splitting, and TUAV placement. Through the combination of the proposed solutions, we present a novel exhaustive/alternating optimization-based algorithm. The obtained results illustrate the efficiency of our method in enhancing the WSR performance. Then, through an impact study of parameters such as TUAV altitude, RIS size, and location, we provide novel insights into the design of RIS-assisted RSMA-enabled TUAV systems.