Rearch On LTE-R Handover Algorithm For High Speed Railway

With the rapidly development of high-speed railway, Global System for Mobile Communications Railway(GSM-R) is increasingly unable to meet the high-speed train control and communication requirements in the handoff. Great security risk would be caused by the interruption of train-ground reliable communication, when the high-speed train handoff to a failure in the handoff. Therefore Long Term Evolution for Railway system(LTE-R) plays a pivotal role in ensuring the secure and efficient communication, especially in the handoff. In addition, the public mobile communication system technology, such as LTE, must meet the rules of rail transport, when it is applied in railway communication system. So it is significant to develop the LTE-R system and to find an advanced trigger handover algorithm ensuring the secure in the railway signal handoff.Main factors which influence the handover success rate are analyzed according to the structure of LTE-R system. The mathematical analysis result shows that the handover success rate can be improved by shorting handover delay. Based on the speed and the calls to database, the advance trigger handover algorithm is designed to shorting handoff delay. Then the validity of the algorithms are verified according to results of simulation and theoretical calculations.Firstly, the wireless protocol architecture of the LTE-R system is introduced. Main technical supports in LTE-R are elaborated, such as Orthogonal Frequency Division Multiplexing(OFDM) principle mechanism, multi-antenna technology, LTE-R system specifications and key parameters setting. Then high-speed wireless coverage schemes and switching mechanism of LTE-R are described in detail, which is theoretical basis for the following analysis algorithm.Secondly, mathematical models for handover are established on the handover flow signaling processes in LTE-R. The basic theory of how delays influencing the handover success rate in LTE-R is discussed by mathematical models, and the simulation results show that shorten delay can be improved by the handover success rate in LTE-R.Subsequently, the advance trigger handover algorithm based on the speed is apply to handover in LTE-R, it's designed to suppress communication interruption and dropped calls caused by that the signaling interaction and setting pre-bearer switching point get rise to handover too early or too late. The theoretical analysis is established in the signaling flow chart, and it is shown that the advance handover algorithm can shorten the handoff latency, and the simulation shows that compared with the conventional handover algorithm, the advance handover algorithm has a higher and more stable handover success rate.Finally, Evolved Universal Terrestrial Radio Acess Network Node(eNodeB) trouble and eNodeB working time-out may be happened when the train running on the railway. So it proposed an advanced trigger handover algorithm combination of the train speed and database weight invoked in eNode B abnormal situation. The superiority and effectiveness of improved algorithm and traditional algorithm are analyzed by mathematical and LTE-Sim Toolbox. Then compared to the respective voip packet loss ratio flows and average voip delay flows in simulation, improved switching algorithm can actually shorten the handover latency, and reduced system handover interruption rate. It provides a theoretical basis for the future railway private network applications with LTE-R.