Study On Mobility Strategy Of Heterogeneous Networks In LTE-Advanced System

In cellular mobile communication systems, the introduction of low power nodes forms a complex heterogeneous network environment. With the deployment of Marco eNodeB and low power nodes, the indoor and hotspots coverage can be optimized, and the cell capacity and user throughput can be improved. Because of the existence of multiple base station configuration in the heterogeneous network, the complexity of network topology is increased, which leads to serious interference. Compared to the homogeneous network, the mobile performance of the heterogeneous network in the cellular system is obviously deteriorated. With the rapid growth of service requirements, the research of mobile strategy has gradually become the key technology of the future development of LTE-A heterogeneous network. The user also puts forward higher requirements for mobility. Therefore, reasonable mobility strategies should be formulated to meet the users’ QoS requirements in the moving process, and ensure the quality of the user’s communication.This thesis mainly analyzes and studies the mobility strategy in LTE-A heterogeneous network. As the main embodiment of users’ mobility, the success or not of the cell selection and handover can be used to evaluate the performance of the whole heterogeneous network. Aiming at the main existing problems in heterogeneous networks, and based on the domestic and foreign research status of mobile strategy, this thesis analyzes the basic principle and implementation process of three kinds of key technologies of mobility strategy, such as cell selection algorithm, handover algorithm and DRX energy saving mechanism. The main contributions of this thesis are as follows.In order to solve the users’ high power consumption problem of traditional cell selection scheme, which is caused by the frequent interaction between the user and the network side, this paper proposes a cell selection scheme for the DRX state in LTE-A HetNet system. The scheme allocates the DRX cycle length for the user by taking the minimal cost function as the criterion at first, in order to balance the user’s power consumption and the average waiting delay. Then determine the type of the cells need to be measured by the user according to the user’s DRX cycle length and speed. The scheme can select the corresponding level of the cell as the target cell adaptively and reduce the number of adjacent cells need to be measured to a large extent, so as to reduce the interaction between the user and the network side and enhance the battery life of the terminal. The simulation results showed that when the speed of the user is 3km/h, the ping-pong rate of this scheme is reduced by 4.13%. When the user speed is 30km/h, the handover failure rate is reduced by 17.03%, and the radio link failure rate is reduced by 16.25%, and ping-pong rate is reduced by 7.54%. Compared to the traditional RSRP cell selection scheme, the handover performance and the communication quality of the users of this scheme are significantly improved.To solve the problem of too early handover, too late handover and ping-pong handover caused by the high handover delay of the user in the moving process, a handover scheme based on mobility prediction is proposed in this thesis. The proposed scheme chooses the effective prediction algorithm based on the user’s mobility rule in two different mobile scenarios, selecting the target cells and reserving the resources for the handover process of the user in advance, so the handover process can be shortened. Simulation results show that the accuracy rate of two mobile scenarios’mobility prediction algorithm is 98%. Compared to the traditional LTE-A handover scheme which selects the target cell based on the A3 event, the proposed handover scheme can improve the handover performance of LTE-A HetNet system, with the handover delay being reduced by 30ms or 60ms, the total handover frequency being decreased by 4.35%, and the handover failure rate being reduced by 7.44%.