On the secrecy rate trade-off analysis and secure precoding design for ISAC systems under dual eavesdropping threats

A single-station integrated sensing and communication (ISAC) system subject to dual eavesdropping threats was investigated. In this system, the base station communicates with a legitimate user and simultaneously receives the reflected echo signal from it for sensing. However, there is a communication eavesdropper (ComEve) that wiretaps communication information, and a sensing eavesdropper (SenEve) that passively eavesdrops on the legitimate user’s echo signal for sensing. Focusing on the sensing eavesdropping issue, the expression of sensing secrecy rate was derived, and a weighted optimization model of communication and sensing secrecy rates was formulated. This model helped to find the upper bound of system performance that balanced the security of both aspects. To enhance the security of practical ISAC systems, the optimization problems were established to maximize sensing or communication secrecy rate under different constraints, yielding optimal secure precoding designs for different requirements. Simulation results indicate that the proposed precoding scheme improves the overall system security performance by approximately 30% on average compared with the schemes that only consider the security of communication or sensing.