Secure Transmission Design for Rate-splitting Empowered STAR-RIS-Aided Networks

Rate splitting multiple access (RSMA) empowered simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided networks have been extensively researched to enhance spectrum efficiency and coverage capability without considering eavesdropping. However, the 360∘ service coverage provided by STAR-RIS inevitably leads to comprehensive eavesdropping, posing more significant security risks for private information transmission compared to traditional reflection-only RIS. In this paper, we propose a secure transmission scheme for STAR-RIS aided downlink communication systems, which is empowered by a novel multiple access paradigm called RSMA. To address the security challenge, we study the proposed security transmission scheme by jointly designing active beamforming, passive beamforming, and common rate allocation to maximize the sum secrecy rate. To tackle the highly coupled non-convex optimization problem, we propose an efficient and low-complexity successive convex approximation-based penalization RSMA-STAR (PE-RSSTA) algorithm. The numerical results demonstrate that: i) the algorithm converges through iterations; ii)the proposed algorithm improves secrecy rate performance by 5.22% compared to the PE space division multiple access (SDMA) STAR algorithm and achieves a notable 27.37% improvement over the conventional RIS algorithm.