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How channel fadings affect the system service of high speed railway communications

As the rapid development of high speed railway (HSR) all over the world, the very high data rate wideband communication on HSR attracts huge attention. Since there exists a dominant line of sight component in the communication channel in most cases, most of works in the literature employed the assumption that the transmission channel is with additive white Gaussian noise (AWGN), referred to the quasi-AWGN model. However, a small scale channel fading is always existing, which can be characterized by using the Nakagami model due to its flexibility with adaptive parameter m. In this paper, we shall investigate how the channel fading affect the mobile service of system in very high speed railway communication systems and try to answer when the quasi-AWGN approach model is valid. Some theoretical analysis and numeral results are presented. It will show that there exists a threshold. When fading parameter is larger than the value of threshold, the effect of fading can be neglected. Otherwise, the channel fading need to be taken into account when discussing the system design or making the railway communication system planning.