Research On LTE-R Handover Algorithm In High Speed Railways

With the construction and development of China's high-speed railways,the railway mobile communication system has more stringent requirements for information transmission rate and bandwidth selection of train-ground,As a result of Long Term Evolution(LTE)(LTE)system has the advantages of high information transmission rate,variable bandwidth,and high spectrum efficiency,so that Internation Union of Railway(UIC)identified Long Term Evolution for Railway(LTE-R)as the next-generation railway mobile communication system in 2010.As an important part to ensure the uninterrupted communication between train and ground,handoffs have been studied in depth,which is of great significance for the reliability and security of information transmission between train and ground.Based on the analysis of the LTE-R system architecture and the factors that affect the handover success rate,an improved handover algorithm based on speed triggering and a handover algorithm based on fuzzy control are designed.The two algorithms separately consider the handover delay and the main factors which affect the handover process in order to increase the success rate of handoff,reduce the handoff rate of handoffs,ensure the continuity of vehicle-to-ground communications and verify the effectiveness of the algorithm through simulations.First,the overall architecture of the LTE system is introduced,the core network and the access network in the architecture are analyzed,and then the mechanism principles of the uplink multiple access technology,the downlink multiple access technology,and the Multi-antenna technology in the LTE system are described.The base station arrangement in the railway network,handover procedures,handover classification,and different handover signaling procedures of the two LTE-R interfaces are analyzed in detail to provide a theoretical basis for the subsequent design of the LTE-R handover algorithm.Then,an improved switching algorithm based on speed triggering is designed,and the pre-loading point of the handover is calculated by using the train running speed information and the base station cell measurement time,and calculated switching trigger delay according to the filtering factor of measurement period Tm and the reporting period Tu in the handover measurement process.Then analyzes and models the two interface signaling flows of the algorithm,and simulates the improved handover algorithm through Matlab to verify the effectiveness of the algorithm.Finally,considering the complex diversity of the high-speed railway in operating environment,in the traditional handoff decision process,only when the train receives the signal power of the base station as the only handover decision condition makes it easier to induce the handoff phenomenon in the process of handoff.A fuzzy control-based switching algorithm is designed to calculate the distance between the train and the base station and the signal power of the train receiving base station and the fuzzy control is used to handle intangibly the train speed,the distance between the train and the base station,and the signal power of the train receiving base station.The three factors that affect the handover decision are comprehensively considered to obtain the switching value after the fuzzy processing,thereby reducing the occurrence of call drop phenomenon in the handover,and the simulation is performed through Matlab to verify the effectiveness of the algorithm.