Robust RIS-Assisted MIMO Communication-Radar Coexistence: Joint Beamforming and Waveform Design

This paper addresses the problem of co-existence between a radar and a communication system that share the same frequency band. In particular, we investigate the role of a reconfigurable intelligent surface (RIS) in improving the performance of both systems and facilitating their co-existence. We consider the optimization problem of maximizing the radar signal to interference plus noise ratio (SINR) with respect to the active transmit beamformer at the radar, the passive RIS reflection coefficients, and the transmit covariance matrices of the communication system, subject to communication outage as well as radar and communication power constraints. This problem is solved through an alternating maximization procedure, first in the ideal scenario of perfect channel state information (CSI), and then in the case of incomplete CSI, using a statistical model of the CSI uncertainty. Numerical results demonstrate the effectiveness of our approach and quantify the beneficial effect of an RIS on the co-existence of a radar and a communication system.