Optimal joint base station assignment and downlink beamforming for heterogeneous networks

Consider a MIMO heterogeneous network with multiple transmitters (including macro, pico and femto base stations) and many receivers (mobile users). The users are to be assigned to the base stations which then optimize their linear transmit beamformers accordingly. In this work, we consider the problem of joint base station assignment and linear beamformer design to maximize a system wide utility. We first establish the NP-hardness of the resulting optimization problem for a large family of α-fairness utility functions. Then, we propose an efficient algorithm to approximately solve this problem for the special case of sum rate maximization. The simulation results show that the algorithm improves the sum rate.