RSMA-Enhanced Secure Transmission Scheme for Active STAR-RIS-Aided Networks.

Abstract

In this letter, a secure transmission scheme is proposed for active simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided networks based on rate-splitting multiple access (RSMA). Specifically, we formulate a joint optimization problem which maximizes the minimum secrecy rate by simultaneously designing the base station beamforming vectors and the active STAR-RIS coefficient matrices. To tackle this challenging non-convexity joint optimization, we design an efficient alternating optimization algorithm, which leverages the weighted minimum mean square error method to reformulate legitimate user rates and applies successive convex approximation to handle eavesdropper rates. Simulation study shows that our proposed active STAR-RIS achieves superior security performance compared to its passive counterpart, while our RSMA strategy provides higher secrecy rates than both space-division multiple access and non-orthogonal multiple access schemes under the considered system setting.