Joint load balancing and interference coordination on the downlink of a heterogeneous network

In a heterogeneous cellular network (HetNet) obtained by overlaying low-power picocells on a conventional macrocell network, two important problems on the downlink must be addressed in order to obtain significant capacity gains from the picocell deployment. These are inter-cell load balancing, i.e., determining which cell to assign each user to for service, and inter-cell interference coordination, i.e., determining when and for how long each macrocell must be silenced in order to mitigate interference to users served by nearby picocells. In this paper, we introduce a centralized optimization framework for these coupled problems, and propose a simple and computationally efficient (though, in general, suboptimal) solution based on the Frank-Wolfe convex optimization algorithm. Simulation results for a hotspot evaluation model show that the proposed algorithm has near-optimal performance, and can double the median user rate and triple the edge user rate (at sufficiently high picocell density), compared to a baseline HetNet with maximum-signal-strength-based association of users to cells and with all cells active all the time.