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：同时发射和反射的可重构智能表面（STAR-RIS）能够实现全空间覆盖，但也使无线传输面临来自多个空间方向的安全威胁。本文研究了一个STAR-RIS辅助的安全速率分割多址接入（RSMA）系统，其中传输区和反射区可能同时存在内部和外部窃听者。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，并避免辅助内部窃听者，从而导致频谱效率与保密性之间复杂的权衡。为解决此问题，我们在保密约束下构建了一个最大最小公平性优化问题，并开发了一种迭代算法以联合优化发射波束成形和STAR-RIS相位偏移。仿真结果表明，所提方案在保持保密性的同时提高了频谱效率。