Joint load balancing and interference coordination can double heterogeneous network capacity

In a heterogeneous network (HetNet) obtained by overlaying low-power picocells on a conventional macrocell network, two important problems must be addressed in order to obtain significant downlink capacity gains. These are inter-cell load balancing, i.e., determining which cell must serve each user so as to utilize all cells effectively, and inter-cell interference coordination, i.e., determining when and for how long must each macrocell be silenced so as to mitigate interference caused to nearby picocell users. We formulate a centralized optimization framework for these coupled problems, and propose a simple solution to them based on convex relaxation and two applications of the Frank-Wolfe algorithm. Simulation results show that the proposed solution has near-optimal performance in a canonical “hotspot” network model, and can double both the 50th percentile and 5th percentile user rates, when compared to a baseline HetNet with no load balancing and no interference coordination. Further, both interference coordination and load balancing are necessary; each by itself yields much lower gains.