Joint Beamforming Design for Active RIS-Aided THz ISAC Systems With Delay Alignment Modulation

In this letter, we investigate a terahertz integrated sensing and communication system that employs active reconfigurable intelligent surfaces (RIS) and delay alignment modulation, where the signals of different paths can arrive the receiver simultaneously. This avoids to use the sophisticated channel equalization technique for mitigating the inter-symbol interference. We aim to maximize the target illumination power while guaranteeing the communication quality by jointly optimizing the dual-functional radar and communication base station beamforming and RIS beamforming. To tackle this issue, we decouple the original non-convex problem into two subproblems relying on the alternative optimization technique. Next, we transform each subproblem into the convex one by the quadratically constrained quadratic program and semidefinite program relaxation (SDR) techniques, and obtain the solutions by standard convex optimization technique. To reduce the complexity of SDR technique, a majorization-minimization technique-based iterative algorithm is proposed. Simulation results show the effectiveness of the proposed scheme.