Utility-based Almost Blank Subframe Optimization in Heterogeneous Cellular Networks

Heterogeneous cellular networks are expected to provide capacity enhancement and user offloading with cell range expansion. Under this circumstance, downlink cross-tier interference from macro base stations to pico mobile stations especially in the expanded range is a challenging problem. To mitigated this problem, the use of almost blank subframes (ABSs)has been proposed in 3GPP LTE-A systems. The issues are how many ABSs are configured, and how pico base stations schedule their pico mobile stations to configured ABSs. In this paper,we study the optimal number of ABSs along with pico mobile station scheduling in ABSs by formulating a utility maximization problem with constraints of minimum required data rate of picomobile stations in the expanded range. To solve the optimization problem, we first propose an algorithm for each pico base station to schedule pico mobile stations onto ABSs and non-ABSs, in away that if their local utility is maximized for a given number of ABSs, then the optimal number of ABSs is obtained by maximizing the network-wide utility. Through simulations, we demonstrated that the proposed scheme not only can improve the network-wide utility, can also provide fairness among mobile stations.