Research On Fast Time-Varying Characteristics Of High Speed Rail Wireless Channel And Key Technology Of Channel Equalization

High-speed railway is a very important public transportation at present,and it is very important to ensure the safety and reliability of high-speed railway.The salient feature of the high-speed railway communication compared with general wireless communication is that the train moves at high speed,which causes the relative high-speed movement between the transmitting antennas and receiving antennas and the rapid changes in the surrounding environment during the train operation,and result in rapid changes of channel characteristics.The multipath effect and Doppler frequency shift cause the transmission signal fading,signal frequency deviation and severe Inter-symbol interference between subcarriers,affecting wireless communication performance.In order to meet the real-time,safety and reliability of wireless communication of high-speed trains,it is necessary to provide corresponding solutions for the fast time-varying characteristics of high-speed railway wireless channel transmission.In view of the fast time-varying characteristics of high-speed rail channels,this thesis just studies the wireless channel model of high-speed railway and analyzes the impact of wireless channel time-varying characteristics on high-speed rail wireless communication signal transmission.The high-speed movement of the train degrade the communication quality t.The performance can be evaluated by the Doppler frequency shift performance between the transmiter and receiver.Studying the Doppler frequency shift estimation and compensation methods for high-speed rail channels is of great practical significance for ensuring the reliability of high-speed rail wireless communications.The key to improve the communication quality is to improve the signal-to-interference ratio.In order to accurately estimate the frequency shift of the high-speed rail wireless channel,this thesis studies the Doppler instantaneous value estimation technology based on the repetitive structure training symbol and based on the conjugate structure training symbol,and the joint detection technology of carrier frequency shift and channel impulse response based on Taylor expansion.The estimation results are used to improve the signal-to-interference ratio by Doppler diversity compensation of frequency shift to achieve the purpose of improving communication quality and ensuring communication security.The superior performance demonstrated by the joint detection technology of carrier frequency shift and channel impulse response based on Taylor expansion will play an important role in promoting the development of frequency shift estimation and compensation technology in high-speed rail scenarios.In addition,in order to verify the above results,this thesis studies the Doppler diversity channel equalization algorithm and considers the situation where the three diversity branch interference signals are uncorrelated with each other to obtain more accurate frequency shift values.The results show that Doppler grading can effectively improve the signal-to-interference ratio of high-speed rail wireless communications and improve the safety and reliability of railway communications.