Constant Modulus Waveform Design for RIS-Aided ISAC System

Integrated sensing and communication (ISAC) technology is receiving more and more attention, and waveform design is an important research direction. In the ISAC system of multi-user communication and multi-target sensing, system performance requirements limit the freedom degree of the integrated waveform. This paper studies the joint waveform design and passive beamforming in the ISAC system aided by reconfigurable intelligent surface (RIS). We consider the practical constant modulus waveform design and study the minimization of weighted mean square cross-correlation pattern (MSCCP) under the unit modulus constraints of RIS reflection phase shift, target illumination power and multi-user interference (MUI) constraint. We decompose the original non-convex problem into multiple sub-problems for alternating optimization (AO). The redundant constraints are incorporated into the objective function of the subproblem as penalty terms to obtain a problem whose feasible region is manifold. Then, an efficient Riemannian conjugate gradient (RCG) algorithm is proposed to solve it. The simulation results show that under the constant modulus waveform constraint, the introduction of RIS can significantly improve the freedom of waveform design. The MSCCP between the beams transmitted by the BS can be reduced under the constraint of the target illumination power and MUI.