Users association in small cell networks with massive MIMO

In this paper, an investigation of the effect of deploying massive MIMO in two-tier cellular networks is presented. In our model, the macrocell base station (BS) as well as femtocell access points (FAPs) are equipped with a very large number of antennas. Each mobile user will attempt to connect to the BS or FAPs. However, it is assumed that the users may be biased to connect to FAPs rather than the BS. A resource allocation problem is formulated to find the optimal bias that maximizes the total system capacity while keeping the transmitted power from the BS and the FAPs within a certain limit. An algorithm for solving the optimization problem is proposed and numerical results are presented to illustrate how deploying massive MIMO can affect the optimal bias value and the total capacity. In addition, the performance of our proposed scheme is evaluated when using different precoding schemes.