Integrated sensing and communication (ISAC) has already established itself as a promising solution to the spectrum scarcity problem, even more so when paired with a reconfigurable intelligent surface (RIS), as RISs can shape the propagation environment by adjusting their phase-shift coefficients. Albeit the potential performance gain, a RIS is also a potential security threat to the system. In this paper, we explore both the positive and negative sides of having a RIS in a multi-user multiple-input multiple-output (MIMO) ISAC network. We first develop an alternating optimization algorithm, obtaining the active and passive beamforming vectors that maximize the sensing signal-to-noise ratio (SNR) under minimum signal-to-interference-plus-noise ratio (SINR) constraints for the communication users and finite power budget. We also investigate the destructive potential of the RIS by devising a RIS phase-shift optimization algorithm that minimizes the sensing SNR while preserving the same minimum communication SINR previously guaranteed by the system. We further investigate the impact of the RIS's individual element failures on the system performance. The simulation results show that the RIS performance-boosting potential is as good as its destructive one and that both of our optimization strategies are hindered by the investigated impairments.

翻译：感知与通信一体化（ISAC）已被确立为解决频谱稀缺问题的有前景方案，当与可重构智能表面（RIS）结合时尤其如此，因为RIS可通过调整其相移系数来塑造传播环境。尽管存在潜在的性能增益，RIS也可能对系统构成安全威胁。本文探讨了在多用户多输入多输出（MIMO）ISAC网络中部署RIS的积极与消极影响。我们首先提出一种交替优化算法，在满足通信用户最低信号干扰噪声比（SINR）约束及有限功率预算的条件下，通过优化有源与无源波束成形向量来最大化感知信噪比（SNR）。同时，我们通过设计RIS相移优化算法来研究RIS的破坏潜力，该算法在保持系统先前保障的相同最低通信SINR前提下，最小化感知SNR。我们进一步分析了RIS单元故障对系统性能的影响。仿真结果表明，RIS的性能提升潜力与其破坏潜力同样显著，且我们所研究的损伤因素会同时制约两种优化策略的效果。