Research On Service Continuity For The 5G Multi-frequency Cooperative Hetnets

In order to satisfy the requirements on the ever-increasing number of user devices and network traffic,researches on key technologies of the 5th Generation mobile communication system such as millimeter-wave communication,coordinated beamforming and massive-mimo have been conducted intensely.In the meanwhile,due to the densification and randomness of deployment and the introduction of millimeter-wave,the 5G network will be denser and more random,and more complex.Therefore,this thesis focuses on technologies for 5G multi-frequency cooperative networks and the ultra-dense scenario.The main research contents are summarized as follows:First,focusing on the ultra-dense scenario of 5G multi-frequency cooperative HetNets,this thesis analyzes the challenges introduced by the ultra-dense deployment of millimeter-wave small base stations,then proposes a strategy on how to select coordinated beamforming base stations.Furthermore,we obtain the average distance between the nearest interference base station and a typical UE by employing a stochastic geometry approach.Besides,some performance metrics such as cell association probability,signal to interference plus noise ratio coverage probability and data rate coverage probability are obtained through theoretical derivation.Finally,we obtain the impacts of different coordinated beamforming base station cardinalities on the network performance under different deployment scenarios.This research provides some theoretical guidelines for network deployment and on how to guarantee the service continuity.Second,through analyzing some defects and unsuitability of applying traditional cell range expansion in 5G multi-frequency cooperative HetNets,this thesis proposes two new cell range expansion schemes for this scenario:a self-adaptive cell range expansion scheme and a dynamic cell range expansion scheme which considers cell edge performance.After analyzing the traditional Reference Signal Received Power based(RSRP-based)cell range expansion scheme and the features of millimeter-wave,we propose a Reference Signal Received Rate based(RSRR-based)cell range expansion scheme,the simulation results demonstrate the benefits of proposed scheme concerning network throughput and energy efficiency.Besides,in order to guarantee the throughput of cell edge user and whole network,we propose a dynamic cell range expansion scheme which can consider cell edge performance,and the results show that this new scheme effectively improve the network throughput on the basis of guaranteeing the quality of service of cell edge users.These schemes bring some suggestions for cell selection strategy and guaranteeing service continuity.In conclusion,this thesis conducts researches on coordinated beamforming analysis and cell selection strategies under 5G multi-frequency cooperative HetNets.The research results provide some guidelines and suggestions for cell selection,small base station deployment strategy and the optimal base station cardinality for coordinated beamforming.