Outage-aware cell association in heterogeneous cellular networks

In heterogeneous networks(HetNets), offloading mobile users to less congested small cells results in a degraded SINR for offloaded users and leads to a high probability of outage for these users. In this paper, we proposes a general framework to solve the cell association problem for load balancing while improving system outage performance in a downlink multi-tier HetNet. A bi-criterion optimization problem is formulated to strike a tradeoff between load balancing and outage performance. Our method inherits the utility maximization with proportional fairness objectives, and explicitly takes into account the outage probabilities for users. In addition, we show this combinatorial bi-criterion optimization problem can be reformulated as a submodular function maximization problem and propose a greedy lazy algorithm that offers a near optimal solution to the reformulated problem, which enforces single BS association for each user. Simulation results show that our proposed method achieves load balancing and improves system outage performance significantly.