We explore the potential of a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) to enhance the performance of wireless surveillance systems. The STAR-RIS is deployed between a full-duplex (FD) multi-antenna legitimate eavesdropper (E) and a suspicious communication pair. It reflects the suspicious signal towards the suspicious receiver (SR), while simultaneously transmitting the same signal to E for interception purposes. Additionally, it enables the forwarding of a jamming signal from E to SR, which is located on the back side of the STAR-RIS. To enhance the eavesdropping non-outage probability, we formulate a non-convex joint optimization problem to design the beamforming vectors at E and reflection/transmission phase shift matrices at the STAR-RIS. We adopt the block coordinate descent (BCD) algorithm and propose an approach, mainly based on semi-definite relaxation (SDR) and successive convex approximation (SCA), for solving the resulting decoupled sub-problems. Finally, we compare the performance of the proposed design against low-complexity zero-forcing (ZF)-based beamforming designs.

翻译：我们探究了同时透射和反射可重构智能表面（STAR-RIS）在提升无线监视系统性能方面的潜力。STAR-RIS部署在全双工多天线合法窃听者（E）与可疑通信对之间：一方面将可疑信号反射至可疑接收端（SR），同时将相同信号透射给E进行拦截；另一方面，该表面能够将来自E的干扰信号转发至位于STAR-RIS背侧的SR。为提升窃听非中断概率，我们构建了一个非凸联合优化问题，用于设计E的波束赋形向量及STAR-RIS的反射/透射相移矩阵。采用块坐标下降（BCD）算法，提出了一种基于半定松弛（SDR）和逐次凸近似（SCA）的方法来求解解耦后的子问题。最后，我们将所提设计的性能与基于低复杂度迫零（ZF）的波束赋形方案进行了对比。