Research On Estimation Of Wireless Channel Parameters In High-speed Railway Systems

With the rapid development of high-speed railway in our country, the demand ofwireless train control and wireless broadband access.in high-speed mobileenvironment is increasing quickly. However, the propagation of radio waves in highspeed railway environment is very complex, and the mobile communicationsbusiness of high-speed railway is quite special, which make railway mobilecommunication system face many new challenges. As an important part of thecoherent reception, channel estimation performance plays a vital role on theperformance of the mobile communication system.This paper mainly discusses the path loss in viaduct scenairos of high speedrailway. Test scenarios and test parameters are given first, we measure receivedsignal power in high-speed railway viaduct from Zhengzhou to Xi’an undernarrowband large-scale tests.Then introduce the current Hata model applied to theGSM-R network and classic logarithmic normal shadow model. Compared with Hatamodel and Lognormal shadow model, the received signal power predicted by thelinear fitting path loss model using the received signal power measured is closer tothe measured received signal power. So the performance of path loss estimation oflinear fitting path loss model is better than empirical model based on lognormalshadow and Hata model.Then discuss the estimation algorithm, which exploits the autocorrelationfunction of the received signal envelope square to get the maximum Doppler shitfinformation. While the complexity of the algorithm is rather low，the maximumDoppler frequency shift value estimated by the algorithm is always bigger than the theoretical value, which indicates that the accuracy of estimation by the algoirthm isnot high. In order to improve the estimation accuracy of the Doppler shift andrespond to larger velocity of high-speed，we introduced another Doppler shitfestimation algorithm, which base on the received signal normalized autocorrelationifinction. The algorithm uses the autocorrelation of the received signal to getmaximum Doppler frequency shitf, which can be used to match the running speed ofhigh-speed railway, finally we can get a more precise maximum Doppler shitf.Simulation results show that the adaptive estimation algorithm is not affected bythe SNR, although it adds a rough estimate step of the maximum Doppler frequencyshitf， it does not cause an uncertain estimated time. At the same time，it can alsosignificantly improve the performance of the Doppler frequency shitf estimation.Therefore, the high-speed railway mobile communication system may consider applythe algorithm to estimate the maximum Doppler shitf.