In this paper, we consider the physical layer security of an RIS-assisted multiple-antenna communication system with randomly located eavesdroppers. The exact distributions of the received signal-to-noise-ratios (SNRs) at the legitimate user and the eavesdroppers located according to a Poisson point process (PPP) are derived, and a closed-form expression for the secrecy outage probability (SOP) is obtained. It is revealed that the secrecy performance is mainly affected by the number of RIS reflecting elements, and the impact of the transmit antennas and transmit power at the base station is marginal. In addition, when the locations of the randomly located eavesdroppers are unknown, deploying the RIS closer to the legitimate user rather than to the base station is shown to be more efficient. We also perform an analytical study demonstrating that the secrecy diversity order depends on the path loss exponent of the RIS-to-ground links. Finally, numerical simulations are conducted to verify the accuracy of these theoretical observations.

翻译：本文研究了RIS辅助多天线通信系统中存在随机分布窃听者时的物理层安全问题。推导了合法用户与遵循泊松点过程分布的窃听者处接收信噪比的精确分布，并获得了保密中断概率的闭式表达式。研究表明，保密性能主要受RIS反射单元数量影响，而基站发射天线数与发射功率的影响较小。此外，当随机窃听者的位置未知时，将RIS部署在更靠近合法用户而非基站的位置更为有效。理论分析还证明，保密分集阶数取决于RIS到地面链路的路径损耗指数。最后通过数值仿真验证了上述理论观察的准确性。