Researching On The Mobile Multi-path Channel Modeling For High-speed Railway Environment

In recent years,the rapid development of China's high-speed railway(HSR)has drawn much attention.Compared with other means of transportation,HSR has the features of high speed,environmentally friendly,low energy consumption and large passenger capacity.In order to provide high quality communication and data services for passengers,HSR communication has become a hot issue.Due to the high loss,high velocity and frequent cell switching in HSR environment,the traditional mobile communication system is facing severe challenges in signal coverage and data rate.Therefore,channel measurements and modeling need to be studied for HSR environment.In this paper,we research the mobile multi-path channel model in HSR environment from three aspects:field channel measurements,large-scale channel modeling,and multi-path channel modeling.The major work and contribution of this paper consist in:1.Dynamic channel modeling based on field channel measurementsWireless channel measurement is an important method to study the channel characteristics of HSR mobile communication system.In this paper,a measurement campaign at 1905 GHz is conducted in the HST network from Beijing to TianJin,and the large-scale channel modeling and multi-path channel modeling for HSR environment are conducted and combined with the measurement results.In order to improve the coverage of the signal,the antenna of base station is set in a high height,and the height can not be ignored in the channel modeling.In addition,in the actual HSR environment,the base station antenna has a certain downtilt angle,and there are different antenna gain in different directions.The traditional two-dimensional channel modeling can not accurately reflect the impact of the antennas of base station.Therefore,combining the antenna pattern of the actual base station,we use the three-dimensional channel modeling method to represent the dynamic channel modeling in HSR environment.2.Large-scale channel modeling based on a novel data processing algorithmIn the process of channel measurement,the position of the train changes rapidly because of the high velocity.The method for estimating the location of the train exsits error,which uses the latitude and longitude recorded by the scanner.In order to ensure the accuracy of large-scale channel modeling,a method based on Doppler frequency shift and delay is proposed to estimate the distance parameters during the train running.In addition,a new Median Average Filtering(MAF)algorithm is proposed to remove the multi-path effects in large-scale channel modeling.The performance of the MAF algorithm is evaluated and compared with the traditional local average algorithm by Kolmogorov-Smirnov tests.The results show that the MAF algorithm has higher passing rate and smaller root mean square error.3.Multi-path channel modeling based on multiple RRU cascade networkingCompared with deterministic model and empirical model,semi deterministic model can reduce the complexity of modeling and ensure the reliability of modeling.In this paper,a semi deterministic model based on geometric distribution is used for multi-path channel modeling in HSR environment.Different from traditional communication system,the train can communicate with several Radio Remote Units(RRU)at the same time in the LTE-R communication system,which means that there are many line-of-sight(LOS)clusters in the wireless channel.In order to further study the impact of the direct cluster and reduce the modeling complexity,we have proposed the pure LOS model(PLM)and the LOS and Scattering Clusters model(LSCM).Besides,the channel verification test is carried out.The results show that the LSCM model suit the channel characteristics of HSR environment better.Finally,based on the proposed multi-path channel models,a test platform for simulating HSR field environment is provided,which provides an experimental platform for further research and performance analysis in the HSR environment.