Joint Design of Waveform and Passive Beamforming for Dual-RIS-Assisted ISAC System

In the single-reconfigurable intelligent surface (RIS) assisted integrated sensing and communication (ISAC) system, the attainable performance gain is constrained by limited communication processing capability and restricted anti-interference performance. In this paper, a joint waveform and passive beamforming design is proposed for the dual-RIS-assisted ISAC system. This design targets enhancing sensing and communication capabilities by maximizing the sensing signal-to-interference-plus-noise ratio (SINR) and minimizing the communication multi-user interference (MUI). Furthermore, phase shift optimization functions for multi-RIS deployment are derived. By analyzing the strong coupling among optimization variables, multi-RIS deployment is shown to fail in yielding sustained performance gains and inducing optimization instability. The Alternating Conjugate Gradient Descent on Riemannian manifold (ACGRM) method is employed to address the optimization problem. Experimental results indicate that the dual-RIS system achieves 23.68% higher communication rates and 10.83% higher sensing SINR than single-RIS system.