Research On Mobility Management Algorithm In LTE-Hi System

Traditional LTE wireless cellular networks are mainly based on single layer structure. However, the conventional cellular systems are not sufficient to address the challenges of future mobile broadband systems, and there will be more UE distributed in indoor and hot spots in the future. Therefore, the international standard organization 3GPP in Release 12 proposed LTE-Hi (Hotspot/indoor LTE)technology. Due to the deployment of small cells in LTE-Hi heterogeneous network, small cells will be more intensive in the future. Compared with the traditional single layer network topology network, the mobility management technology of LTE-Hi network is facing more difficulties and challenges. This article mainly focuses on the mobility management algorithms in LTE-Hi system.First, this paper introduces the concept and key technology of LTE-Hi system.Second, it expounds the method of cell selection/reselection and summarizes the handover algorithms related to the existing LTE-Hi system. Third, the reasons for the handover failure is analyzed. And then, we put forward a new handover algorithm in LTE-Hi heterogeneous network and a new user association algorithm with dual connectivity in LTE-Hi network.About the handover algorithm in LTE-Hi network, we proposed a handover algorithm based on the state and speed of UE. The frequency of macro cells and small cells is different. We use the modified A2/A4 event for handover between different types of cells while using the traditional A3 event for handover between the same types of cells in order to improve the utilization rate of small cells and reduce the handover failure probability. The proposed handover algorithm also takes into account the effects of the speed factor. Simulation results show that the proposed algorithm can effectively reduce the number of handover, while improving the throughput of the user.In the matter of user association algorithm in LTE-Hi network with dual connectivity, a novel QoS aware user association algorithm for load balancing is proposed, where the best combination of macro cell and small cell for each user to associate is determined and the optimal traffic split between the macro cell and small cell is selected. Considering both guaranteed bit rate (GBR) users and Best Effort (BE) users, user association problem is formulated as a multi-objective optimization model. Furthermore, the objective function for GBR users is a joint optimization of the load balancing index and average load of the network, and the objective function for BE users is to maximize the utility function of the throughput of BE users. A decomposition method is presented to analyze the original model in consideration of the computational complexity and quality of service (QoS) priorities of different users. And then, we adopt the greedy algorithm to solve this problem. Simulation results demonstrate that the proposed algorithm can decrease call blocking probability and improve throughput of boundary BE users, while achieving better load balancing.