多普勒问题（Doppler problem）.doc

多普勒问题（Doppler problem） With the continuous upgrading of Chinas railway, the railway after several large current speed, high-speed railway construction has reached a speed of 350 kilometers per hour, which marks Chinas high-speed railway has reached the world advanced level. To the mobile communication system, mobile terminal when the speed reaches 350 km / hour, you need to consider some new technical problems. First of all, the train speed makes the Doppler shift effect is obvious; second, switching and reselection system, some micro cellular system and low speed of switching has not suitable for such high-speed mobile carrier; third, increase the intensity of the high-speed train wave penetration loss also increases further. To solve these problems, three experts are from operators, equipment manufacturers recommendations. 1 Doppler frequency shift effect The communications industry newspaper (net): as the train generated by high speed Doppler effect makes the system of sending and receiving frequency offsets, the influence of Doppler effect on communication? How to overcome the Doppler effect in the construction of the communication network? Liu Jianmin: when the electromagnetic wave emission source and the receiver when the relative motion of the transmission frequency, will cause the received change. When the speed reaches a certain threshold, will significantly change the transmission frequency, which is called the Doppler shift. CDMA using coherent demodulation receiver demodulation and carrier carrier requirements of received signals with the same frequency and phase, affect the demodulation performance of carrier frequency jitter on receiver. CDMA20001X uses a Qualcomm CSM6700 chip, the frequency of 800MHz, CDMA20001X CSM6700, frequency shift of the maximum value of 1440Hz, CDMA20001XEVDORevA using Qualcomm CSM6800 chip, the working frequency of 800MHz for CDMA20001XEVDORevA, CSM6800, frequency shift of the maximum value of 960Hz, via Backstepping calculati