Research On Handover Algorithm Methods In LTE-A High-speed Railway Environment

With the gradual development of the Chinese high-speed railway network and the continuous increase of railway line density,the requirements of wireless communication technology for high-speed trains have also improved accordingly.Long Term Evolution-Advanced(LTE-A)shows a great number of advantages in the next-generation high-speed railway communication system due to its low latency,high transmission rate,and flat network structure,and thus,it has been chosen as the development direction of railway wireless communication systems by the International Union of Railways.Handover is closely related to the train safety;therefore,handover is an essential part of high-speed railway wireless communication.The high mobility of high-speed railway leads to problems like frequent switching,Ping-Pong Switching and Doppler Shift in wireless communication systems.This thesis focuses on handover problems of high-speed railway wireless communication.To be specified,after summarizing and analyzing the existing handover approaches,the author proposes a handover algorithm based on the reference signal received power(RSRP)and assisted-beamforming.The key research points are as follows:(1)An improvement of the traditional A3 event based-handover algorithm.In the handover process of high-speed railway wireless communication,most of the LTE-A handover algorithms are focused on the optimization of train speed,but during the optimization process,there are still problems like failing to effectively guarantee the reference signal power(RSRP)of the train.The traditional handover algorithm is based on the received signal power difference between the two eNodeBs,which determines whether the handover hysteresis threshold is reached and then triggers handover.In this thesis,an improved handover algorithm is proposed.According to the real-time operating information that the train sends,supervision of signal receiving power is added which ensures the signal receiving power is maintained above the minimum signal receiving power when the train is moving.By setting the beamforming threshold,if the signal receiving power drops to a threshold during the high-speed train movement,the service cell will trigger the beamforming gain and sends a beamforming request to the target cell.When the train travels to the midpoint of the switching section,the beamforming gain of the target cell is changed,and the serving cell is restored to the primal signal transmission power.Until the end of the handover interval,the serving cell and the target cell are restored to the original signal transmission power.In this way,under the high-speed rail environment,the problem of low handover success rate caused by fast wireless signal changes and short handover time is solved.(2)Parameter optimization based on speed information.Based on the improved algorithm,the beamforming gain is adjusted by setting three different speed levels.Different train speeds are divided into three-speed levels: low speed,medium speed,and high speed.Based on ensuring that the received signal power can be maintained at the minimum receivable power,different beamforming gains are adopted for the corresponding speed levels.In the medium-speed class,the serving cell and the target cell only need to perform beamforming gain once,and in the low-speed class,only the serving cell needs to trigger the beamforming gain.This simplifies the complexity of the handover algorithm and makes the handover algorithm more widely applicable.(3)Based on the theoretical research,this thesis builds a simulation platform through MATLAB software,and reasonable simulation parameters are set.The improved algorithm is verified and analyzed.The simulation results are as follows:The handover algorithm Based on RSRP and assisted-beamforming allows both the serving base station and the target base station to provide better signal reception strength,advance the handover location appropriately,and improve the probability of handover success effectively.After dividing the speed class of the train,for the medium-speed and low-speed trains,the improved handover algorithm delays the handover triggering position,and makes the medium and low-speed trains still maintain approximately the handover performance of high-speed trains.The improved handover algorithm simplifies the complexity of the handover algorithm.