Research On Location-tracking Handover Schemes In High-speed Railway Mobile Communication System

In recent years,with the rapid development of China’s high-speed railway field and the continuous improvement of train speed,the mobile communication system suitable for the current high-speed environment is also changing.An important technical process that high-speed train will inevitably experience when running is cross zone switching.The research on the handoff scheme of high-speed railway also puts forward higher requirements for high-speed railway wireless mobile communication system.Handoff refers to the process that the wireless communication signal of the train disconnects from the current service cell and establishes a connection with the next target cell,which runs through the beginning and end of high-speed rail operation.The smooth progress of the handover process will directly affect the operation safety of the train.Therefore,it is particularly necessary to study the handoff scheme suitable for the future high-speed rail mobile communication system.Based on the analysis of most high-speed rail handoff schemes at present,a handoff scheme based on beamforming and position tracking is designed from the perspective of improving the handoff success rate and reducing the handoff interruption rate;From the perspective of reducing the switching trigger delay and promoting the timely trigger of high-speed train,the switching parameter optimization scheme based on speed grade is designed.Both schemes aim to improve the switching performance of high-speed rail in the switching area.Firstly,the paper expounds the wireless channel fading often experienced during high-speed rail operation.According to the empirical formula,the simulation analysis of the channel fading of the train communication environment in different operating scenarios is carried out,which provides a research basis for the next handover scheme.Then,it describes in detail the handover technology,the network coverage method of high-speed rail operation,and many challenges that are often encountered during handover,such as Doppler effect,signal compartment penetration loss,frequent handovers that can easily lead to communication dropouts,etc.influence.Secondly,a switching scheme based on beamforming and position tracking is proposed.Using beamforming technology in the switching overlap area,the antenna changes from omnidirectional mode to beamforming mode to produce directional beams with different gain sizes.So as to ensure that the received signal strength reaches the set switching trigger threshold,so as to achieve smooth switching and prevent the occurrence of untimely switching,call drop,disconnection and other phenomena.The distributed antenna system arrangement ensures that the beam can accurately cover the on-board stations receiving signals in the overlapping area,so as to realize beam tracking.Through theoretical analysis and simulation experiments,the rationality of the scheme is verified.Finally,combined with the previously proposed handoff scheme,a handoff parameter optimization scheme based on speed classification is designed to simplify the handoff process.The scheme first divides three different speed levels according to the different train speeds when passing through the switching area,and then gives different beam forming gain values to the trains under different speed levels to assist the occurrence of switching.Finally,the switching hysteresis tolerance of the switching parameters commonly used in the switching decision stage is optimized.On the basis of the original fixed switching hysteresis,the speed factor is selected to consider,so that it can switch the hysteresis value according to the dynamic change of the current train speed,which is more suitable for the handoff under different speed levels to ensure the smooth occurrence of handoff.After mathematical theory analysis and simulation experiments,the rationality of the scheme is finally verified.