Measurements, Data Analysis And Modeling Of Broadband Wireless Channel In High Speed Railway Scenarios

The rapid development of high speed railway (HSR) has brought new opportunities and challenges for HSR wireless communication system. HSR communication system can not only provide real-time, flexible and fast wireless access, but also achieve the higher transmission rate, larger capacity and wider coverage for train-ground communications. It can provide passenger better experiences during their journeys. And it has spurred new chances for the realization of a more stable and reliable broadband train control system.In high speed railway scenarios, researches of broadband wireless channel models are based on the analysis of large quantities of practical measured data. Considering the security, railway departments all over the world strictly restrict the sending and receiving wireless signals along the railway lines. Therefore, in order to obtain the measured data in HSR environments, the proper coordination among the railway department, high-speed trains, base station, transceiver equipments and testing personnel should be made. For the restrictions of the above terms, the existing researches results on the HSR broadband channels are few. In consideration of the special requirements in the research, this dissertation is supported by the national science and technology project. We conducted broadband measurements at2.6GHz with the maximum bandwidth of20MHz in HSR scenarios, and then studied and researched with the first hand measured data and achieved some research results. Our research work follows the three steps:construction of the measurement system, optimization of data processing algorithms and channel modeling. For each step, our work is divided into four procedures, which are the research of the present work, analysis of the underlying problem, study the simulation results and the analysis of the actual measured data respectively.The main work and results of this dissertation are listed as follows.Chapter1summarizes the background, significance and necessities of the project. The characteristics of the environment in HSR wireless communications are concluded, which are different from that in traditional cellular. It leads to the special features of the channel. The current situation of the overseas and domestic research are introduced and analyzed. At last, research achievements and structures of the paper are given out.Propagation characteristics of the wireless channel are introduced in Chapter2. We described the fading properties in aspects of both large-scale fading and small-scale fading. The parameters of wireless channel are stated through time domain, frequency domain and spatial domain. Based on the channel characteristics in HSR, the special properties of HSR channel are introduced, which provide the foundation for the channel measurement and analysis of fading properties in the following chapters.Chapter3puts forward a measurement scheme and system applied in HSR scenarios. As the measurement system is to be implemented in the "HSR scenarios" based on "TD-LTE system", there are higher demands in the design of the bandwidth, maximum delay spread, Doppler shift, sample rate, storing velocity and coverage area in the scheme. In this chapter, the measurement scheme for the signal fetching, acquisition of the deviation of information and the choice of measurement sequence are all optimized. Then, we finish the construction of the system and solve the problem of system trigger and multiple sampling rates. Finally, with many simulation and verification, our system has been proved with higher measurement efficiency and better performance.Analysis of large-scale fading is stated in Chapter4. In the measurement process, the data may be influenced by the noise, interference, accidental error and the small-scale fading. According to these problems, our paper proposes some new methods and algorithms for optimization and improvement. Based on the wavelet transformation de-noising method algorithm, we establish a complete procedure for the data processing. This new issued process is verified to have better performances based on the simulation results and measurement results.Chapter5focuses on the data processing of small-scale fading and analysis of channel parameters. It is known that there are some problems in the traditional multipath separation algorithm. In this paper, we present a novel multipath separation algorithm which relies on the properties of channel distribution. It aims to solve the following two problems occurred in the traditional algorithm. The first one is the higher probability of false alarm and missed detection due to the decision of threshold. And the other problem is bigger error probability occurred in the dense multipath circumstance. We have done large quantities of simulations under different signal-to-noise ratio. Furthermore, simulations for the extraction and fitting of the parameters after the multipath separation have been done. The reliability of the algorithm has been verified through our simulation and measured data.In chapter6, based on the quantities of measured data under HSR, data analysis are done in the four main scenarios, including the urban area, the viaduct, hilly terrain, open area scenario. Path loss models are obtained through the data processing of large-scale channel parameters. In addition, based on the small-scale parameters, tapped-delay-line (TDL) channel models are established in detail for the four scenarios respectively. At last, the performance of the models are compared and analyzed. Conclusions are drawn in Chapter7. The later research fields are also stated in this section.