Research On Channel Estimation Technology Of Wireless Communication System In The High-speed Railway Scenario

With the rapid development of wireless communication technology,people's demand for broadband wireless communication is increasing.In order to provide more stable and reliable mobile communication services,it is necessary to conduct more in-depth research on wireless communication technology under complex conditions.In the high-speed railway environment,the complex scene environment and the high mobility of the receiver lead to the frequency selective fading and fast time-varying characteristics of the wireless channel.At this time,it is difficult for the receiver to obtain accurate channel state information,so it is necessary to take certain means to compensate the fading effect on the received data.Channel estimation is the key part of the receiver of OFDM system,which is the basis of correlation detection,demodulation and equalization in broadband wireless communication system,and directly affects the performance of the whole communication system.The accurate estimation of channel state information has a very important impact on the performance of the whole system,which promotes the extensive research of channel estimation in wireless communication system under complex conditions.In view of the above problems,the main research work of this paper includes:Firstly,the basic principles of OFDM technology and the propagation characteristics of the wireless channel are analyzed,and the fading characteristics of the wireless channel are analyzed.The multipath effect and Doppler effect caused by small-scale fading are mainly analyzed in the process of channel propagation.On this basis,the special propagation scenario of high-speed railway is analyzed.Its characteristics are that there are a certain number of multipaths and the high-speed operation of mobile terminal leads to the wireless channel shows the characteristics of fast time-varying.Secondly,the principle of traditional channel estimation algorithm based on pilot is deeply studied,including pilot insertion method,channel response estimation algorithm at pilot and interpolation algorithm at non-pilot data.In view of the shortcomings of the traditional algorithm,an improved algorithm is proposed.Based on the first rough estimation of LS and LMMSE estimation criteria,the threshold DFT algorithm is introduced.By setting the threshold value,the channel response of the rough estimation is judged,and the second estimation is completed to remove the noise and improve the estimation performance.The simulation results show that the denoising algorithm has good performance.Finally,because of the fast time-varying characteristics of the wireless channel in the high-speed railway environment,this paper uses BEM to model the channel,to achieve the fitting of the time-varying channel,and to transform the estimation of the channel parameters into a small number of basic function coefficients.Based on CE-BEM,P-BEM andDKL-BEM,this paper focuses on the analysis of the basic principles of these models,and discusses the performance of different BEM models in fitting time-varying channels,as well as the influence of different number of basis functions and different operation speed on BEM modeling.In order to reduce the influence of inter-carrier interference caused by high-speed movement on channel estimation,the pilot-group is used as the insertion pilot,and the calculation process of the base coefficient estimation by the LS and LMMSE criterion in BEM model is deduced.On this basis,Kalman filter technology is introduced as a time-varying channel estimation method,and the first-order autoregressive process is established to represent the change process of OFDM symbols in the transmission process,which can more effectively track the time-varying channel response.Finally,the performance of different estimation algorithms based on BEM modeling is verified by experimental simulation.