Efficient Target Search and Detection in RIS-aided Integrated Sensing and Communications System

The integration of Reconfigurable Intelligent Surface (RIS) with the Dual-Functional Radar-Communication (DFRC) base station in a unified system has been a topic of growing interest. This study centers on a system augmented by RIS for both target sensing and multi-user communication purposes. Our primary objective is to enhance radar efficacy. To this end, we devise a framework to maximize radar detection probability, taking into account the combined aspects of transmit beamforming and RIS phase-shift vector formulation, ensuring we adhere to set standards for communication quality of service (QoS), transmit power limitations, and phase-shift parameters. Firstly, we obtain the target angle by maximum likelihood estimation. Then, we perform target tracking by solving a Quadratic Semidefinite Programming (QSDP) problem. Next, we maximize the detection probability for different scenarios, i.e., general case and special case respectively. In the special case, we obtain the explicit expression for the transmit beamforming and employ Semidefinite Relaxation (SDR) to determine the phase-shift vector of the RIS. Finally, we demonstrate simulation results that validate the performance of the proposed method and confirm the efficacy of the proposed Majorization-Minimization (MM) and Penalty-aided Block Coordinate Descent (PBCD) algorithm across various scenarios.