Research On Mobility Management Technology For Ultra-dense Heterogeneous Networks

With the continuously development of mobile communication technologies and the rapid increase of mobile communication services,cellular networks have experienced the explosive growth in mobile data traffic brought by mobile devices.In order to meet the growing demand for mobile data traffic,the deployment of low-power nodes(including the micro-cells,the pico-cells and the femtocells)has many advantages,which can enhance the coverage area and support more mobile devices.Different kinds of base stations are deployed together forming a multi-layer,heterogeneous hybrid network.This deployment strategy makes wireless network denser.The mobility management will play a more and more important role in the future.Thus,the main contributions are as follows:Aiming at the load imbalance and frequent cooperation among base stations in the Fifth Generation(5G)ultra-dense heterogeneous network,the thesis proposes a scheme to cluster cells.Firstly,the Gaussian similarity formula is used to calculate the similarity between base stations considering the distance,load condition and inter-base station interference.Secondly,in the intra-cluster base stations cooperation mechanism,the base stations can adjust its own state('active','sleep')by actively transferring the base station load.The simulation results show that the proposed scheme can significantly reduce system costs.Aiming at the continuous growth of mobile devices and the scarcity of spectrum in 5G ultra-dense heterogeneous networks,this thesis proposes a scheme to improve system capacity and spectrum utilization.In the scheme,the micro base stations use passive reception detection to enhance the wireless bands access opportunity.And the micro base stations jointly detect the deployment area of the macro users.The levy flight movement model is utilized to simulate the users' movement trajectory.Then the users'movement probability distribution is derived to describe whether the macro users will move to the micro cell coverage in next time slot.The simulation result shows that the scheme can improve the opportunities to access the wireless bands occupied by the micro base stations,and the throughput of the system is increased by more than 20%compared with the traditional scheme.Aiming at the degrading of the Quality of Services and high energy consumption introduced by the frequent handover in 5G ultra-dense network,the thesis proposes an algorithm which considers both the users'mobile state and the base stations'load state.Firstly,the l evy flight movement model is used to predict the mobile state of the users in the next time slot.And the signals received from the nearby base stations as well as the current load states of these base stations are calculated to make a joint handover decision.The simulation results show that the proposed scheme can save energy consumption by more than 10%compared with the traditional scheme.