标题： 通过可重构智能表面对抗窃听攻击：一个新的威胁模型和保密速率优化 显示英文标题

标题： Counteracting Eavesdropper Attacks Through Reconfigurable Intelligent Surfaces: A New Threat Model and Secrecy Rate Optimization

摘要： 可重构智能表面（RISs）在节能和性能提升的无线通信中的潜力最近引起了显著的研究关注，促使它们被考虑用于各种$5$代（5G Advanced）及以后的应用。 在本文中，我们考虑一个具有多数据流的多输入多输出（MIMO）物理层安全（PLS）系统，包括一个合法的被动RIS和一个恶意的被动RIS，前者对多天线窃听者是透明的，而后者的存在在合法的多天线收发器中是未知的。 我们首先提出一种针对RIS增强的窃听系统的新型威胁模型，并设计了一个联合优化框架，用于窃听者的接收合并矩阵和恶意RIS的反射系数。 接下来，专注于保密率最大化问题，我们提出了一种RIS赋能的PLS方案，该方案联合设计了合法的预编码矩阵和数据流数量、人工噪声（AN）协方差矩阵、接收合并矩阵以及合法RIS的反射系数。 所提出的优化算法，其收敛到至少局部最优解已被证明，基于交替最大化、小化最大化和流形优化，包括优化变量的半闭式表达式。 我们对两种典型的系统设置进行了大量仿真结果表明，在没有合法RIS的情况下，收发器空间滤波和AN无法提供非零的保密速率，即使对于元素数量较少的恶意RIS也是如此。 然而，当部署一个$L$个元素的合法RIS时，可以保护机密通信免受拥有超过$5L$个元素的恶意RIS的窃听系统。 显示英文摘要

摘要： The potential of Reconfigurable Intelligent Surfaces (RISs) for energy-efficient and performance-boosted wireless communications is recently gaining remarkable research attention, motivating their consideration for various $5$-th Generation (5G) Advanced and beyond applications. In this paper, we consider a Multiple-Input Multiple-Output (MIMO) Physical Layer Security (PLS) system with multiple data streams including one legitimate passive RIS and one malicious passive RIS, with the former being transparent to the multi-antenna eavesdropper and the latter's presence being unknown at the legitimate multi-antenna transceivers. We first present a novel threat model for the RIS-boosted eavesdropping system and design a joint optimization framework for the eavesdropper's receive combining matrix and the reflection coefficients of the malicious RIS. Focusing next on the secrecy rate maximization problem, we present an RIS-empowered PLS scheme that jointly designs the legitimate precoding matrix and number of data streams, the Artificial Noise (AN) covariance matrix, the receive combining matrix, and the reflection coefficients of the legitimate RIS. The proposed optimization algorithms, whose convergence to at least local optimum points is proved, are based on alternating maximization, minorization-maximization, and manifold optimization, including semi-closed form expressions for the optimization variables. Our extensive simulation results for two representative system setups reveal that, in the absence of a legitimate RIS, transceiver spatial filtering and AN are incapable of offering non-zero secrecy rates, even for malicious RISs with small numbers of elements. However, when an $L$-element legitimate RIS is deployed, confidential communication can be safeguarded against eavesdropping systems possessing even more than a $5L$-element malicious RIS.