Simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) enable full-space coverage but also expose wireless transmissions to security from multiple spatial directions. This paper investigates a STAR-RIS-assisted secure RSMA system where both internal and external eavesdroppers may coexist in the transmission and reflection regions. In such a scenario, the RSMA common stream simultaneously serves legitimate users, impairs external eavesdroppers, and avoids assisting internal eavesdroppers, leading to a challenging trade-off between spectral efficiency and confidentiality. To address this issue, we formulate a max-min fairness problem under secrecy constraints and develop an iterative algorithm to jointly optimize transmit beamforming and STAR-RIS phase shifts. Simulation results demonstrate that the proposed scheme improves spectral efficiency while maintaining confidentiality.

翻译：同时透射与反射可重构智能表面（STAR-RIS）可实现全空间覆盖，但也使得无线传输面临多空间方向的安全威胁。本文研究STAR-RIS辅助的安全速率分割多址接入（RSMA）系统，其中透射区和反射区可能同时存在内部窃听者与外部窃听者。在此场景下，RSMA公共流同时服务于合法用户、干扰外部窃听者并避免协助内部窃听者，导致频谱效率与保密性之间呈现复杂权衡。为解决该问题，我们在保密约束下构建最大最小公平性优化问题，并提出迭代算法联合优化发射波束成形与STAR-RIS相位偏移。仿真结果表明，所提方案在维持保密性的同时能提升频谱效率。