Multiple Intelligent Reflecting Surfaces Assisted Interference Coordination in Multi-Cell MU-MIMO Communications

In this paper, we investigate an multiple intelligent reflecting surfaces (IRSs) assisted interference coordination in multi-cell multi-user multi-input multi-output (MU-MIMO) downlink communication system, where the IRSs are dedicated deployed at cells boundary for coordinating the intra-cell and inter-cell interference. For this configuration, the weighted sum-rate (WSR) of all the users is maximized by optimizing the active transmit beamforming at the base stations (BSs) and passive reflective beamforming at the IRS cooperatively. We consider both general constraint case and the more practical constraint case at the IRS. Since the problem is non-convex, we first recast it into an equivalent form by using extended Lagrangian Dual Transform and Fractional Programming Transform, and then for general constraint case, we propose an efficient iterative alternately algorithm to find the optimal solution in closed-form. Moreover, we propose a low-complexity two-step algorithm based on the well-known Majorization-Minimization Algorithm and Nearest Point Projection Algorithm for optimizing the passive reflective beamforming under the more practical constraint case. Simulations results indicate that the IRS can significantly enhance the system performance through coordinating interference, and proposed jointly optimizing algorithms offer a substantial improvement performance gain over baseline schemes. Furthermore, we discuss some interesting issues related to the IRS-assisted communication system.