  The performance of wireless communication systems is fundamentally
constrained by random and uncontrollable wireless channels. Recently,
reconfigurable intelligent surfaces (RIS) has emerged as a promising solution
to enhance wireless network performance by smartly reconfiguring the radio
propagation environment. While significant research has been conducted on
RIS-assisted wireless systems, this paper focuses specifically on the
deployment of RIS in a wideband millimeter wave (mmWave)
multiple-input-multiple-output (MIMO) system to achieve maximum sum-rate.
First, we derive the average user rate as well as the lower bound rate when the
covariance of the channel follows the Wishart distribution. Based on the lower
bound of users' rate, we propose a heuristic method that transforms the problem
of optimizing the RIS's orientation into maximizing the number of users served
by the RIS. Simulation results show that the proposed RIS deployment strategy
can effectively improve the sum-rate. Furthermore, the performance of the
proposed RIS deployment algorithm is only approximately 7.6\% lower on average
than that of the exhaustive search algorithm.
