The Effect Of Radio Propagation Characteristics To Digital Communication Systems For The High-speed Railway

Along with the spur of science and technology, the products of science and technology continue to change people’s lifestyle and livelihood-related civilian. Wireless communications greatly facilitate people’s social activities. The rapid development of wireless communications makes the wireless products continue to emerge, so that the wireless transmission quality becomes a growing topic of concern.The long range radio wave propagation plays a significant role in both mobile communication and research on environment conditions. The propagation of electromagnetic waves have not only its own characteristics of electromagnetic waves, but also have some characteristics by the impact of environmental factors, such as the obstacle in the path of electromagnetic wave propagation, multi-path effects, shadow effects, etc. All of those will change the received signal. This article is based on the Maxwell equations and started from the wave equation, then leads to the conclusion of parabolic equation approximation process after a careful derivation. In that process, with the using of Fourier algorithm for the numerical solution of parabolic equations, we predict the distribution of field characteristics of radio signals in long distance transmission and analysis electromagnetic characteristics of complex terrain.This paper selects two high-speed railway communication systems (GSM-R system and TETRA system) as the object of study, and then analyzes the bit error rate characteristics of the two communication systems in high-speed situation. The biggest difference between high-speed railway communication system and traditional communications systems is the relative motion of the train and the base station. And the most difficult point is the analysis of high-speed communication channel. Firstly, we use the method of equal interval to simulate the deterministic Gaussian process during the process of structure of the communication channel. Secondly, we analyze the affection of high-speed movement on signal, and thus according to the characteristics of the deterministic Gaussian process, we construct the Rice, Rayleigh and multi-path process. According to that we can construct the communication channel by using mathematical simulation. During the process of error rate calculation, we original calculate the field strength in space by using the parabolic equation method with the according to the situation of distribution of field intensity in space, and get the result of signal to noise ratio on any point in the space. Thirdly, according to the relationship between signal to noise ratio and bit error rate, we obtain the space distribution of bit error rate. Finally, we analyze the respective signal bit error rate of the GSM-R system and TETRA systems in different relatively movement speed and in different signal frequency, which is based on the channel structure in this paper. And we also conclude the affection of the speed or signal frequency to the bit error rate of signal.This paper estimates not only the error of the loss of signal between the SPE propagation model and the Hata model, but also analyzes the affection of deterministic Gaussian random process for high-speed signal. We use mathematical methods to achieve the Rice, Rayleigh and other multi-channels. According to the SPE propagation model we estimate the space signal to noise ratio to any point. Thereby we obtain the relationship between transmission distance or height and the space signal bit error rate. The analysis of the signal bit error rate of GSM-R system and TETRA system in multi-channels provides the characteristics of bit error rate to speed or the signal frequency of GSM-R system and TETRA communication system.