User Association in Heterogeneous Cellular Networks Via the Hungarian Method

In heterogeneous cellular networks, traditional user association schemes based on reference signal power result in load imbalances between macro cell base stations (MBSs) and small cell base stations (SBSs). Meanwhile, offloading users to SBSs face the quality of service (QoS) degradation. In this paper, we propose a utility maximization framework to address the user association problem. In order to strike a tradeoff between load balancing and user QoS experiences, a bi-criterion optimization problem is formulated to solve the user association problem. The bi-criterion optimization problem is then linearized as a utility maximization problem with a tunable parameter. In addition, we show that the utility maximization problem can be reformulated as a maximum bi-partite matching problem and can be solved in polynomial time by using the Hungarian method. Simulation results show that our proposed method achieves load balancing and can strike tradeoffs between load balancing and user QoS by tuning the optimization parameter.