  Reconfigurable intelligent surface (RIS) refers to a signal reflection
surface containing a large number of low-cost passive reflecting elements. RIS
can improve the performance of radar and communication systems by dynamically
modulating the wireless channels. In this paper, we consider the co-design for
improving the co-existence between multiple-input-multiple-output (MIMO) radar
and MIMO communication system with the aid of RIS.The design purpose is to
improve the radar detection performance and guarantee the communication
capability. Due to the unimodular constraint on the RIS coefficients and the
constant-envelope constraint on the radar transmit waveforms, the associated
optimization problem is non-convex.To tackle this problem, we develop a cyclic
method based on minorization-maximization, semi-definite programming, and
alternating direction method of multipliers. Numerical examples verify the
effectiveness of the proposed algorithm.
