Abstract: The inherent broadcast nature of wireless signals makes communication systems vulnerable to eavesdropping and interference threats. This is especially true in Integrated Sensing and Communication (ISAC) systems, where radar detection signals often convey sensitive information from communication users, complicating security concerns even further. To tackle this issue, this paper investigates a secure ISAC system supported by an Active Reconfigurable Intelligent Surface (RIS). It proposes a joint secure transmission mechanism that employs artificial noise (AN) to enhance physical layer security. In multiuser communication and sensing scenarios with a potential eavesdropper, we achieve coordinated optimization of communication, sensing, and security by jointly designing the base station (BS) precoding, AN interference signals, and RIS reflection coefficients. This approach minimizes the Cramér–Rao bound (CRB) for parameter estimation while satisfying the communication Quality of Service (QoS) requirements for legitimate users. To address the resulting multivariate coupled nonconvex problem, an efficient algorithm based on Alternating Optimization (AO), Semidefinite Relaxation (SDR), and Majorization Minimization (MM) is proposed. This method transforms the original problem into two subproblems for more efficient solutions. Simulation results indicate that, compared to the AN-free scheme, the proposed approach reduces the Signal-to-Interference-Plus-Noise Ratio (SINR) by approximately 20.3 dB (representing a decrease of about 99.07%) while sacrificing only around 0.5 dB (approximately 11.28%) in sensing performance , achieving a balance between security and sensing accuracy. Additionally, the active RIS-assisted approach markedly enhances security performance over passive RIS, validating the effectiveness of "enhancing physical layer security through perception" and providing a practical method for the secure design of ISAC systems.

摘要： 无线信号固有的广播特性使通信系统面临潜在的窃听与干扰威胁，尤其在通感一体化(ISAC)系统中，雷达探测信号中常同时承载着通信用户的机密信息，使其安全问题更为复杂。针对这一挑战，在本文中探讨一种有源可重构智能表面(RIS)辅助的安全ISAC系统，提出一种基于人工噪声(AN)的联合安全传输机制，用以增强物理层安全性。在存在潜在窃听者的多用户通信与感知场景中，通过联合设计基站(BS)发射预编码、AN干扰信号和RIS反射系数，在考虑合法用户通信质量的同时，最小化感知性能指标克拉美罗界(CRB)，从而实现通信、感知与安全的协同优化。为解决由此产生的多变量耦合非凸问题，提出基于交替优化(AO)、半定松弛(SDR)与主化最小化(MM)的高效算法，将原问题转化为两个子问题进行高效求解。仿真结果显示，与无AN方案相比，所提方案可使窃听信干噪比(SINR)降低约20.3 dB(下降约99.07%)，而感知性能仅损失约0.5 dB(约11.28%)，实现了安全性与感知精度之间的平衡。与无源RIS相比，所提有源RIS辅助方案在安全性能方面显著提升，并验证了“以感知增强物理层安全”的有效性，为ISAC系统的安全设计提供了可行的方法。