Secure Transmission for Active RIS-assisted THz ISAC Systems with Delay Alignment Modulation

In this paper, we study the secure transmission problem in the active reconfigurable intelligent surfaces (RIS)-assisted terahertz integrated sensing and communication system, where the delay alignment modulation technique is applied at the base station (BS). Meanwhile, the target is regarded as a potential eavesdropper. We aim to maximize the secrecy rate while guaranteeing the minimum illumination power of the target. Since the formulated optimization problem is non-convex and is difficult to be solved directly. Next, we propose an alternative optimization algorithm to solve the BS transmit beamforming and active RIS reflection coefficients alternatively based on the majorization-minimization and semidefinite program relaxation techniques. Finally, simulation results show the effectiveness of the proposed scheme.