Joint User Scheduling and Phase Shift Optimization for STAR-RIS-Assisted Multicast Satellite Communications

Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS), capable of transmitting and reflecting incident signals, is an emerging technology for satellite communication (SatCom) systems to improve the network capacity and support
$360^{\circ }$
full-space coverage. This paper studies joint optimization of user scheduling and phase shift for multicast services in STAR-RIS-assisted SatCom systems. We establish a stochastic optimization problem with the objective of maximizing the average data rate with the constraints for ensuring target quality-of-service (QoS). To solve the problem, an algorithm is developed that jointly finds the optimal user set, phase shift values, and energy splitting ratios based on a dual approach. From the simulation results, it is observed that the proposed algorithm substantially enhances system performance while satisfying the target QoS requirement.