Intelligent reflecting surfaces (IRSs) have several prominent advantages, including improving the level of wireless communication security and privacy. In this work, we focus on the latter aspect and introduce a strategy to counteract the presence of passive eavesdroppers overhearing transmissions from a base station towards legitimate users that are facilitated by the presence of IRSs. Specifically, we envision a transmission scheme that cycles across a number of IRS-to-user assignments, and we select them in a near-optimal fashion, thus guaranteeing both a high data rate and a good secrecy rate. Unlike most of the existing works addressing passive eavesdropping, the strategy we envision has low complexity and is suitable for scenarios where nodes are equipped with a limited number of antennas. Through our performance evaluation, we highlight the trade-off between the legitimate users' data rate and secrecy rate, and how the system parameters affect such a trade-off.

翻译：智能反射面（IRSs）具有若干显著优势，包括提升无线通信安全与隐私保护水平。本文聚焦于隐私保护这一方面，针对被动窃听者监听基站通过IRS辅助向合法用户传输的场景，提出一种对抗策略。具体而言，我们设计了一种在多个IRS-用户分配方案间循环切换的传输机制，并以近最优方式选择这些分配方案，从而在保障高数据速率的同时实现良好的保密速率。与现有大多数针对被动窃听问题的研究不同，本文提出的策略复杂度低，尤其适用于节点配备有限数量天线的场景。通过性能评估，我们揭示了合法用户数据速率与保密速率之间的权衡关系，以及系统参数如何影响这种权衡。