In the paper, the physical-layer security for reconfigurable intelligent surface (RIS) aided integrated sensing and communication (ISAC) system is studied. There is an active eavesdropper (AE) as well as a passive eavesdropper (PE), and they cooperate each other. By joint base station beamforming and RIS reflection design, we aim to achieve the best secure data communications with guaranteed sensing performance. Mathematically, taking the constraints on sensing performance and transmission power in consideration, the system secrecy rate maximization problem is formulated with respect to transmit beamforming, RIS reflection, and receive beamforming. The formulated problem is non-convex and is decomposed to three subproblems by applying the alternating optimization (AO). For the decomposed subproblem, we utilize the quadratic penalty method and successive convex approximation (SCA) for the solution derivation. Thereafter, an iterative numerical algorithm, referred to as the joint beamforming and reflection design (JBRD) algorithm, is proposed. Finally, numerical results demonstrate the effectiveness and superiority of the proposed algorithm.

翻译：本文研究了可重构智能表面（RIS）辅助的集成感知与通信（ISAC）系统的物理层安全问题。系统中同时存在主动窃听者（AE）与被动窃听者（PE），且两者相互协作。通过联合设计基站波束赋形与RIS反射系数，旨在实现保障感知性能条件下的最优安全数据传输。在数学建模上，考虑感知性能约束与发射功率限制，构建了关于发射波束赋形、RIS反射系数及接收波束赋形的系统保密率最大化问题。该问题具有非凸性，采用交替优化（AO）方法将其分解为三个子问题。针对每个子问题，分别利用二次惩罚法和连续凸近似（SCA）求解。进而提出一种迭代数值算法——联合波束赋形与反射设计（JBRD）算法。最后，数值结果验证了所提算法的有效性与优越性。