Secure Beamforming and Radar Association in CoMP-NOMA Empowered Integrated Sensing and Communication Systems

Integrated sensing and communication (ISAC) has been regarded as an emerging technique to satisfy the sensing requirements for future 6G networks. However, the confidential communication information embedded in the probing waveform could be eavesdropped by the radar targets, which leads to insecurity issues for ISAC systems. To this end, we propose a coordinated multi-point transmission (CoMP) empowered secure ISAC system. Unlike existing work focusing on a single base station (BS), multiple BSs are coordinated to improve sensing performance and communication security. Specifically, non-orthogonal multiple access (NOMA) is employed to improve spectrum efficiency and facilitate spectrum sharing between sensing and communication functions. By importing the artificial noise (AN) to disrupt eavesdropper reception, a joint radar association and beamforming design optimization problem is formulated to maximize the minimum beampattern gain, subject to the maximum power constraint and secure communication requirements. The mixed-integer non-convex optimization problem is first transformed into more tractable forms. Then, a near-optimal solution is obtained by applying an accelerated stochastic coordinate descent algorithm for radar association and the penalty-based iterative algorithm for beamforming design. Moreover, the optimization problem is further extended to more practical cases with uncertain target directions. Our numerical results show: i) the proposed AN-aided COMP-NOMA empowered ISAC system can support much higher high-quality radar sensing, while simultaneously guaranteeing secure communication; ii) the proposed scheme significantly outperforms the relevant benchmark schemes in terms of the beampattern gain; iii) the proposed joint optimization algorithm can achieve high beampattern gain, even with uncertain target directions.