  In this paper, we investigate an intelligent reflect surface (IRS) assisted
multi-user millimeter wave (mmWave) downlink communication system, exploiting
IRS to alleviate the blockage effect and enhance the performance of the mmWave
system. Considering the impact of IRS on user association, we formulate a sum
rate maximization problem by jointly optimizing the passive beamforming at IRS
and user association, which is an intractable non-convex problem. Then an
alternating optimization algorithm is proposed to solve the problem
efficiently. In the proposed algorithm, passive beamforming at IRS is optimized
by utilizing the fractional programming method and user association is solved
through the network optimization based auction algorithm. We provide numerical
comparisons between the proposed algorithm and different reference algorithms.
Simulation results demonstrate that the proposed algorithm can achieve
significant gains in the sum rate of all users.
