Shifting the Sensing Versus Data-Security Tradeoff in ISAC Systems With Active RIS

Abstract

Integrated sensing and communication (ISAC) greatly alleviates the problem of spectrum congestion by sharing the hardware platform and spectrum resources. However, due to the broadcast characteristics of the wireless channels, a potential eavesdropping target may detect the confidential information sent to the communication users. In this paper, we focus on data-secure ISAC transmission where the sensing target it treated as a potential data-eavesdropper. We employ an active RIS to facilitate data security. Specifically, we use active RIS to manipulate the wireless propagation environments and amplify signals to overcome weak echo signals received by low-sensitivity ISAC receiver. By jointly designing the sensing and communication precoding matrix and the active RIS reflection coefficient matrix, we optimize the sensing performance in terms of Cramér-Rao Bound (CRB) subject to the requirements of signal-interference-plus-noise ratio (SINR) and secure transmission of communication users. We show that a well-designed sensing precoding matrix can also act as the artificial noise (AN) conceived for drowning out the eavesdropping channel with increased design degrees of freedom (DoF). An effective algorithm based on alternating optimization, semidefinite relaxation (SDR), and majorization-minimization (MM) is proposed to solve the complex non-convex problem. Simulation results show that employing active RIS in ISAC systems outperforms traditional passive RIS in terms of sensing performance, and the proposed scheme can achieve a better sensing vs data-security trade-off.