This paper investigates the multi-antenna covert communications assisted by a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS). In particular, to shelter the existence of covert communications between a multi-antenna transmitter and a single-antenna receiver from a warden, a friendly full-duplex receiver with two antennas is leveraged to make contributions where one antenna is responsible for receiving the transmitted signals and the other one transmits the jamming signals with a varying power to confuse the warden. Considering the worst case, the closed-form expression of the minimum detection error probability (DEP) at the warden is derived and utilized in a covert constraint to guarantee the system performance. Then, we formulate an optimization problem maximizing the covert rate of the system under the covertness constraint and quality of service (QoS) constraint with communication outage analysis. To jointly design the active and passive beamforming of the transmitter and STAR-RIS, an iterative algorithm based on semi-definite relaxation (SDR) method and Dinkelbachs algorithm is proposed to effectively solve the non-convex optimization problem. Simulation results show that the proposed STAR-RIS-assisted scheme highly outperforms the case with conventional RIS, which validates the effectiveness of the proposed algorithm as well as the superiority of STAR-RIS in guaranteeing the covertness of wireless communications.

翻译：本文研究了由同时透射和反射可重构智能表面（STAR-RIS）辅助的多天线隐蔽通信。特别地，为隐藏多天线发射机与单天线接收机之间隐蔽通信的存在性，使其免于被监控者侦测，本文利用了一个配备两根天线的友好全双工接收机；其中一根天线负责接收发射信号，另一根则以可变功率发射干扰信号以迷惑监控者。在最坏情况下，推导了监控者处最小检测错误概率（DEP）的闭式表达式，并将其用于隐蔽约束以保证系统性能。随后，我们构建了一个优化问题，在通信中断分析下，以满足隐蔽约束和服务质量（QoS）约束为条件最大化系统隐蔽速率。为联合设计发射机和STAR-RIS的有源与无源波束成形，提出了一种基于半定松弛（SDR）方法和Dinkelbach算法的迭代算法，以有效求解该非凸优化问题。仿真结果表明，所提出的STAR-RIS辅助方案显著优于传统RIS方案，验证了所提算法的有效性以及STAR-RIS在保障无线通信隐蔽性方面的优越性。