Research On Characteristics Of LTE-R Wireless Channel And Its Impact On System Performance

In recent years,high-speed railway(HSR)has become the first choice for daily transportation in China,and railway mobile communication has also played an increasingly important role in social transportation.Due to the narrow-band property of Global System for Mobile Communications for Railway(GSM-R),communication needs of railway are hard to be met.Therefore,a new-generation railway dedicated mobile communication system named Long Term Evolution for Railway(LTE-R)is proposed,based on the significant advantages of Long Term Evolution(LTE)technology of high rate,low latency,and a complete industrial chain.The new demands of bearing voice,data and video for dedicated railway communication can be met based on LTE-R.The first LTE-R test network has been deployed in 2018.Different from the public LTE network,the base stations of LTE-R railway mobile network are distributed along the railway line.The frequency band of LTE-R test network is 465 MHz.The bandwidth of LTE-R test network is 5MHz.The radio propagation scenarios of HSR are relatively special.When the trains run at a high speed,large Doppler shifts and Doppler spreads of the signal will be Formed.There are high reliability requirements for the railway communication system quality.Therefore,it is necessary to study the relationship between LTE-R network performance and channel characteristics to ensure the safety of railway operation.The system throughput test and wireless channel test of the LTE-R test network in the HSR are first carried out in this thesis.Based on the throughput data,it is found that the network throughput performance is poor in the cell edge areas.Then based on the wireless channel measurement data,the wireless channel transmission characteristics are analyzed.Finally,combining the two analysis results,a hardware-in-the-loop emulation platform is built in the laboratory to test and analyze the relationship between throughput performance and channel characteristics of LTE-R network.The main contributions of this thesis are as follows:(1)Performance measurement is performed in the LTE-R test network in the highspeed railway scenario.According to LTE-R throughput measurement data,the throughput of the LTE-R network is analyzed.The reference signal received power,signal-to-noise ratio and LTE-R system throughput are combined for accurate analysis.The thesis proposes the reasons that cause the decrease of downlink throughput of the LTE-R test network.(2)Wireless channel measurement is carried out in the LTE-R test network.The issue of extracting pilot signals based on channel test data is solved.The main steps are frequency offset estimation and correction,cell search and synchronization,OFDM demodulation,and pilot signal extraction.Based on the extracted pilot signals,the wireless channel characteristics such as path loss,large-scale fading,small-scale fading,noise and interference in rural scene are analyzed.(3)High-speed hardware-in-the-loop emulation platform of LTE-R system is built in the laboratory to dynamically simulate the HSR wireless channel environment.System performance measurement is conducted in the conditions of unresolved single-path,twopath,and three-path.It is based on the wireless channel parameters of large-scale fading,multipath delay,frequency shift,Rician factor.The degree to which throughput performance is affected by wireless channel characteristics is analyzed,which can provide a theoretical basis for optimizing LTE-R systems.