  Intelligent reflecting surface (IRS) has been considered as a promising
technology to alleviate the blockage effect and enhance coverage in millimeter
wave (mmWave) communication. To explore the impact of IRS on the performance of
mmWave communication, we investigate a multi-IRS assisted mmWave communication
network and formulate a sum rate maximization problem by jointly optimizing the
active and passive beamforming and the set of IRSs for assistance. The
optimization problem is intractable due to the lack of convexity of the
objective function and the binary nature of the IRS selection variables. To
tackle the complex non-convex problem, an alternating iterative approach is
proposed. In particular, utilizing the fractional programming method to
optimize the active and passive beamforming and the optimization of IRS
selection is solved by enumerating. Simulation results demonstrate the
performance gain of our proposed approach.
