Research On Radio Channel Characteristics Of The High Speed Railway

With the Beijing to Guangzhou high speed railway (HSR) coming to service, the mileage of China’s HSR in operation has reached9339km. The HSR network has ini-tially formed. The speed of HSR train has exceeded300km/h. The high speed movement of the train brings many challenges to the control of the HSR network. The transmission of train control information requires a mobile communication system with high reliabili-ty and safety. As a result, railway mobile communication system has a higher quality of service (QoS) requirement, including connection establishment delay, end-to-end trans-mission delay, handoff time, the connection rate, etc. The study of channel characteristics plays a key role in wireless communications. The propagation scenarios of HSR are different from the public mobile communication scenarios. The channel characteristics change rapidly due to the high mobility of the train. Therefore, channel measurement and modeling in the typical HSR scenarios has a great significance for the network planning and performance improvement of railway mobile communication system.Based on a lot of measurements in HSR scenarios, and using radio wave propagation theory and statistical analysis methods, the dissertation studies the large scale propaga-tion characteristics, small scale fading envelope characteristics and small scale fading second order statistics of the HSR scenarios. The studied scenarios include viaduct s-cenario, cutting scenario and viaduct cutting hybrid scenario. The dissertation not only presents the results of channel parameters, such as path loss exponent, shadow fading standard deviation, Rice factor, level crossing rate (LCR), average fade duration (AFD), but also analyzes the influence of structural parameters of various scenarios on channel parameters. The main innovations of this dissertation are listed as follows:1) The dissertation studies the path loss in typical HSR scenarios and analyzes the influence of structural parameters on path loss. For viaduct scenario, the effect of viaduct height, relative height of the base station antenna and surrounding environment on path loss is analyzed. The results show that path loss exponent increases with viaduct height and decreases with relative height of the base station antenna. Meanwhile, higher path loss exponent is observed for viaduct with more scatters in the surrounding environment. For cutting scenario, a new parameter called equivalent slope height is defined to reflect the average slope height in cutting scenario. And the path loss exponent basically de- creases with the increase of equivalent slope height. In addition, a simplified geometric model for the overline bridge in cutting scenario is proposed. The proposed model can effectively estimate the location where the signal average power experiences a sudden de-crease. The power attenuation is found to be5-13dB. The proposed model can be used to design the handover parameters, such as window length for averaging the received mea-surement samples and handover threshold, thus is of vital significance for improving the handover quality of railway mobile communication system.2) The dissertation studies the small scale fading envelope characteristics in typical HSR scenarios and analyzes the variation of Rice factor with distance. By introducing the K-S (Kolmogorov-Smirnov) test, Rice distribution and Nakagami distribution are found to be optimum for describing the small scale fading envelope distribution in HSR scenari-o. The K-S test method is proved to be faster and more accurate than the usual way of comparing the figures. For viaduct scenario, a500m bounded piecewise linear regression model is proposed to analyze the variation of Rice factor with distance. For cutting sce-nario, a3-segment regression model is proposed to study the variation of Rice factor with distance. Then the influence of slope height on the variation of Rice factor is discussed. It turns out that Rice factor increases with decrease of slope height. For viaduct cutting hybrid scenario, the dissertation mainly analyzes the similarities and differences of Rice factor as a function of distance between viaduct to cutting scenario and cutting to viaduct scenario. The results show that Rice factor decreases with distance in viaduct to cutting scenario and increases with distance in cutting to viaduct scenario.3) The dissertation studies the second order statistics of HSR scenarios. The change characteristics of LCR and AFD with train speed are studied based on channel measure-ment data. LCR is found to increase with the train speed, while AFD is found to decrease with train speed. Then the measured results of LCR and AFD are compared with the prediction results of commonly used theoretical models. The comparison results indicate that Rice model generally fits the measured second order statistics accurately. At last, the normalized second order statistics for viaduct and cutting scenario are given. The results have important significance in the optimization of interleaver and error correcting codes, as well as Markov modeling of fading channels.