Joint Design for RIS-Aided Radar-Communication Coexistence With Space Spectral Compatibility

In this paper, we investigate a reconfigurable intelligent surface (RIS) aided spectrum sharing scheme between a multiple input multiple-output (MIMO) radar and MIMO multiuser communication system under non-homogeneous interference scenarios, including the interference from scattering points, the mutual interference between the two systems, and the interference among multiple users. We consider a flexibly-weighted framework for joint resource allocation, aiming at maximizing the mutual information of both the radar and the communication systems under the usual constraints on the transmit power and on the compatibility of the space spectral. To deal with the resulting triple degrees of freedom non-convex framework, a sub-optimal procedure, based on iterative alternating maximization of three suitably derived subproblems, is proposed and analyzed. Each yields a closed-form solution. In particular, to address the constant modulus constraint imposed by the RIS, we propose two different optimization strategies, based on the Minorization-Maximization framework in conjunction with the Alternating Direction Penalty Method and the Element Block Coordinate Descent formulations, namely, MM-ADPM and MM-EBCD, respectively. Finally, simulation results compare the effectiveness and advantages of the two algorithms.