Research On Improvement Of Handover Based On LTE-R

The terrain along the railway is complex and the wireless transmission environment is bad.It is very important to ensure the continuity and reliability of the train mobile communication system.As the next generation of railway mobile communication system,Long Term Evolution for Railway(LTE-R)has better performance than Global System for Mobile communications–Railway(GSM-R).Due to the banded distribution of base stations in the railway,trains need to ensure normal information transmission through frequent handover.With the construction of railway and the development of technology,the train speed has increased significantly,and the handover is more frequent.Therefore,the success of handover is of great significance to the continuity and reliability of train mobile communication system.By analyzing the LTE-R system architecture,handover principle and handover signaling process,considering the impact of handover execution time,handover hysteresis threshold,Reference Signal Receiving Power(RSRP),Signal to Interference plus Noise Ratio(SINR)and other factors on handover,the handover problem in LTE-R system is optimized and improved from many aspects to improve the performance of handover.Firstly,considering the influence of train speed and switching direction on the handover problem,an improved handover algorithm based on speed direction is proposed.The algorithm uses the cell synchronization process to obtain the Physical Cell ID(PCI)in advance,and monitors the access cell in real time according to the PCI to judge the direction and nature of the train triggering handover.When setting the handover hysteresis threshold,make the handover hysteresis threshold of the train triggering ping-pong handover higher than the handover hysteresis threshold triggering normal handover,and make it change dynamically with the speed,making it difficult for the train to switch to the cell accessed last time,so as to reduce the ping-pong handover probability.Secondly,from the perspective of shortening the handover execution time and optimizing RSRP,an early handover algorithm based on Grey Markov model is designed.The grey model is used to predict and process RSRP.In order to reduce the prediction error of grey model,Markov process is introduced to correct the error,and combined with preloading algorithm,the handover delay is shortened while improving the fluctuation of RSRP.Then,using beamforming,a key technology in LTE system,a Linearly Constrained Minimum Variance(LCMV)beamforming handover algorithm based on Direction Of Arrival(DOA)estimation is proposed.The base station uses the DOA estimation algorithm to obtain the incoming wave direction of the signal and judge the train position.When the train enters the handover overlap area,the Evolved Node B(e Node B)adopts the method of transmitting beamforming,and sets different beamforming gains in different ranges of the overlap area to improve the signal transmission power.The User Equipment(UE)end adopts LCMV beamforming algorithm,which not only ensures the receiving effect of RSRP,but also suppresses the interference of other signals and noise,improves the signal-to-noise ratio of the received signal,and can better adapt to the railway operation environment.Finally,the MATLAB platform is used to simulate the wireless channel environment suitable for the railway scene.In this environment,the three improved algorithms are simulated and analyzed from the aspects of handover success rate,interruption rate and ping-pong handover probability,and compared with the traditional algorithm,so as to verify the effectiveness of the improved algorithm in handover performance.