Mobility performance enhancements for LTE-Advanced heterogeneous networks

Heterogeneous Networks (HetNets) has attracted considerable attention since they can improve the system capacity and user throughput in Long Term Evolution (LTE)-Advanced system. However, due to the different coverage sizes for macro eNodeB (eNB) and pico eNB, the handover performance of UE will be impacted especially when the user equipment (UE) moves in medium or high speed in HetNets. Three metrics are agreed in 3GPP RAN WG2 to evaluate the handover performance: radio link failure (RLF) rate, handover failure (HOF) rate, and short time of stay (short ToS). In this paper, firstly, based on the three metrics, the handover performance in HetNets is analyzed. Then, we propose two schemes to solve the issue of handover performance deterioration when UE moves in medium speed. One scheme is to optimize pico-macro handover, and the other is to optimize macro-pico handover. In other words, two schemes can separately optimize pico cell leaving and attaching. Furthermore, the two schemes can be used jointly to further improve the mobility robustness in HetNets. System level simulation is employed to present the handover performance improvement.