Research Of The Characteristics Of The Radio Wave Propagations Around The High-Speed Railway

The developments of high-speed railway put forward higher requirement to railway mobile communication system that the railway mobile communication system should be able to meet the real time and reliability requirement of wireless data transmission with high frequency spectrum efficiency under high speed.However, under the high-speed railway environment, the performance of the wireless channel has the sudden change because of high-speed movement and the complex topographical condition. Also, the receive signals are affectd by the multi-path fading and Doppler shift. Since there are two choices which our country's railway of the new generation are facing that are GSM-R and TETRA, this article compares and analyses various digital mobile communication technologies, such as GSM-R and TETRA, combining with the existing status and future trends. Then the future railway mobile communication system structure and technical architecure are studied from the angle of the radio wave prppagation.Based on the research of former, this article first introduces the systematic characteristic property and respective advantage of GSM-R and TETRA, including system structure, economic factor, radio frequency, reality apply, and so on.Then the model of mobile receiver with high-speed are discussed in theory, including the characteristics of radio large-scale path loss and small-scale fading. The structure of model was confirmed in introduction step, based on the synthesis construe and discussion.Gaussian fading are simulated using the theory of sine summation.Meanwhile, the impact of speed on Gauss fading process and Rician fading process are studied which is the beding of the study of Bit error rate. Also, the relationship of the statistical properties of the fading channels which are the fading frequcency, the fading width and the fading depth and speed is discussed.Bit error rate is the most important part of this article. The model of mobile channel with high speed are based using the blocks of Matlab 7.0/Simulink. There are three ways of transmission that are studied which are general wireless transmission system, GSM-R and TETRA.The ways of simulation are single-block simulation and muti-blocks simulation. According to the modulation principle of every system which is BFSK modulation, GMSK modulation,Ï€/4DQPSK modulation, the signals pass the differert channels which are White Gaussian Noise Channel, Multipath Rayleigh Fading Channel, Rician Fading Channel and multi-blocks channel. Then we can get the curve of Bit error rate. The influence of speed to Bit error rate in high-speed movement is studied. Results indicated that speed plays a small part to Bit error rate. At the same time, the signal-to-noise ratio, the bit rate and the value of BT are simulated.We can find that GSM-R is good at anti-noise while TETRA is good at anti-multipath fading using simulation. In short that TETRA is suit for high speed railway which has serious multipath fading.Finally, the ways of improving are proposed.