  Intelligent reflect surface (IRS) is a potential technology to build
programmable wireless environment in future communication systems. In this
paper, we consider an IRS-assisted multi-base station (multi-BS) multi-user
millimeter wave (mmWave) downlink communication system, exploiting IRS to
extend mmWave signal coverage to blind spots. Considering the impact of IRS on
user association in multi-BS mmWave systems, we formulate a sum rate
maximization problem by jointly optimizing passive beamforming at IRS, power
allocation and user association. This leads to an intractable nonconvex
problem, for which to tackle we propose a computationally affordable iterative
algorithm, capitalizing on alternating optimization, sequential fractional
programming (SFP) and forward-reverse auction (FRA). In particular, passive
beamforming at IRS is optimized by utilizing the SFP method, power allocation
is solved through means of standard convex optimization method, and user
association is handled by the network optimization based FRA algorithm.
Simulation results demonstrate that the proposed algorithm can achieve
significant performance gains, e.g., it can provide up to 175% higher sum rate
compared with the benchmark and 140% higher energy efficiency compared with
amplify-and-forward relay.
