Research On Handover Optimization In High-speed Railway Wireless Communication System

In recent years,with the rapid development of high-speed railway,the system capacity of railway wireless communication system is increasing gradually.How to meet the increasing system capacity and improve the passenger’s communication experience has become the main focus of the development of the railway industry.Long term evolution for railway(LTE-R)has the advantages of high transmission rate and low delay due to its flat and IP-based network architecture,LTE-R has become the main development goal of railway communication system.Handover technology is an important part of LTE-R.When the train crosses the base station area,the communication between the train and the ground will be blocked due to the failure of the handover,and that will bring safety risks to the train and will reduce the quality of service(Qo S).Therefore,it is of great significance to develop efficient and fast handover algorithms for high-speed railway scenarios to reduce communication outage probability and handover failure rate,so as to ensure the service quality and train safety of railway communication system.In this thesis,the existing handover algorithms are analyzed first,and the handover problem is studied for two different railway networks.The main work are as follows:(1)A preloading handover scheme based on beamforming and distance is proposed,and the beamforming technology is used to improve the signal quality received by the train in the overlapping area of the base station,so as to improve the handover trigger rate.On this basis,the minimum trigger point is calculated by adjusting the handover hysteresis according to the train speed.When the train arrives at the point,the base station makes the handover decision based on the signal quality to avoid the wrong trigger.In addition,the base station starts the pre-loaded process before the minimum trigger location,reducing the handover time.The simulation results show that,compared with the traditional beamforming scheme,the proposed handover scheme can effectively improve the success rate of handover.(2)The control plane/user plane separation network architecture is introduced into the railway communication system,and a fast soft handover scheme is proposed,in which the control plane information is transmitted through the macro station in the low frequency,and the user plane information is transferred by the small base station in the high frequency band.The existing handover scheme improves the handover performance by using dual-antenna architecture,but the handover process is complicated because it involves control plane handover and user plane handover simultaneously.Therefore,in this thesis,based on the existing scheme,the small base station supporting user plane is deployed in the overlap area of the macro stations.In this way,the control plane handover and user plane handover are staggered,which simplifies the control plane handover process and realizes the fast handover.Simulation results show that the proposed scheme can effectively improve the handover success rate and reduce the communication outage probability.