Study Of Wireless Channel Models Employed In High-speed Railways And System Performance Analysis

In high-speed railway systems, the communication environment may become very bad for wireless communications because of the high velocity of the trains. Although 3G networks cover widely in most areas of China, serious time selective fading and frequency selective fading could affect the signal propagation in physical layer. As the most random factor, propagation channel can cause directly affects towards communication quality and performance. In order to fight against performance degradation and sudden effects, it has been very necessary to analyze the existing problem in high-speed railway communication systems, especially channel models. However, existing channel models in high-speed railways are mostly experimental channel models that are based on measurement data, rarely theoretical models that are widely accepted and used exist. It’s not valid anymore to use the classic fading models which can represent very limited scenarios since high-speed railway scenarios vary frequently. Consequently, to select the best fading model which fits the high-speed scenarios and to evaluate its theoretical performance can have significant sense in towards both evaluations of high-speed railway wireless networks and optimal resource arrangements.To study the channel models in high-speed railways, we analyze the signal propagation model that fits the high-speed environment and evaluate the system performance using different channel models. Our main contributions in this paper are as follows:(1) We analyze the signal propagation character theoretically, introduce two generalized channel model and discuss the fitness in high-speed scenario. Moreover, some addition key problems in high-speed railways are discussed.(2) Applying different generalized models, we derive the system indices expressions in an accurate form, which includes outage probability, average bit error probability and average capacity. More significantly, we present possible asymptotic analysis at high-SNR regime in Chapter 3; To show the difference between different models, we derive outage probability using selection diversity and simulate the performance of average bit error probability in MATLAB. Note that all the expressions are novel in related investigation fields.(3) For the wireless communication systems which apply measurement data based channel model, we also derive the expressions of outage probability and average bit error probability of such system in consideration of both path-loss and small-scale fading.With the help of simulation platforms, all of our theoretical analysis results have errors within 10-6. In order to show the character of the variations of system indices, we present figures of the expressions with corresponding instructions as well. In conclusion, all the results are accurate and reliable, which can make important influences on modern channel modeling and system performance evaluation in high-speed railways.