Directional Modulation Design of Radar-Communication System Assisted by Reconfigurable Intelligent Surface

To alleviate spectrum congestion and reduce hardware cost, radar and communication integrated waveform designs have been widely studied. In this paper, a symbol-level design is carried out by combining directional modulation (DM) and reconfigurable intelligent surface (RIS) technology. The modulated symbols in the communication directions are maintained, but scrambled in other directions to reduce the risk of eavesdropping. The deployment of discrete phase shifts of the RIS are considered, due to limited accuracy in practice implementation. A two-stage iterative optimization method has been proposed to solve the non-convex optimization problem. The key features of the radar waveform are selected as the first stage of design, followed by embedding symbols that satisfy service quality requirements in the communication directions. The proposed method has lower sidelobe levels compared to the benchmark scheme and is applicable to both radar-centric and communication-centric integrated waveform design with security. The simulation results have verified the effectiveness of the design.