PSO-based Optimization of STAR-RIS aided NOMA Wireless Communication Networks

This paper considers a wireless communication system assisted by a Simultaneous Transmission and Reflection Reconfigurable Intelligent Surface (STAR-RIS) aided by Non-Orthogonal Multiple Access (NOMA) technique. The STAR-RIS is a new technology that, different from the traditional RIS, is capable of not only reflecting but also transmitting the incident signal. However, due to the large number of elements at the STAR-RIS, acquiring Channel State Information (CSI) may require considerable training overhead, which is limiting in practice. Therefore, we aim to jointly optimize the power allocation, the beamforming at the base station, and the STAR-RIS transmitting and reflecting beamforming vectors without full CSI, by maximizing the achievable sum rate, subject to a minimum achievable rate at each user. To solve this problem, a method based on the Particle Swarm Optimization (PSO) technique is proposed. Results show that the new solution outperforms STAR-RIS-assisted orthogonal multiple access (OMA) systems.