Covert communications assisted by simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) in non-orthogonal multiple access (NOMA) systems have been explored in this paper. In particular, the access point (AP) transmitter adopts NOMA to serve a downlink covert user and a public user. The minimum detection error probability (DEP) at the warden is derived considering the uncertainty of its background noise, which is used as a covertness constraint. We aim at maximizing the covert rate of the system by jointly optimizing APs transmit power and passive beamforming of STAR-RIS, under the covertness and quality of service (QoS) constraints. An iterative algorithm is proposed to effectively solve the non-convex optimization problem. Simulation results show that the proposed scheme significantly outperforms the conventional RIS-based scheme in ensuring system covert performance.

翻译：本文研究了非正交多址接入（NOMA）系统中由同步透射和反射可重构智能表面（STAR-RIS）辅助的隐蔽通信。具体而言，接入点（AP）发射机采用NOMA以服务一个下行链路隐蔽用户和一个公共用户。考虑监守者背景噪声的不确定性，推导了其最小检测错误概率（DEP），并将其作为隐蔽性约束条件。我们旨在在隐蔽性和服务质量（QoS）约束下，通过联合优化AP发射功率和STAR-RIS的无源波束成形，最大化系统的隐蔽速率。针对该非凸优化问题，提出了一种迭代算法以高效求解。仿真结果表明，所提方案在确保系统隐蔽性能方面显著优于传统基于RIS的方案。