Research On The Doppler Frequency Shift Algorithm In LTE Network For High-speed Railway

In recent years, with the rapid development of China’s transportation industry, the high-speed railway, developed rapidly by its high speed and low price, has become the first choice for people to travel. At the same time, with the continuous development of the intelligent terminal technology, the application of data communication for passengers the high-speed railway is also more frequent, which has also bought the new requirements on reliability and effectiveness of the high-speed wireless communication. In the environment of higher than 200km/h, how to ensure the quality of mobile communication and network becomes a new challenge to the high-level communication technology used in the high-speed railway.LTE, the new generation of communications technology, has become mature with the advantage of shorter delay, faster transmission rate, wider frequency band and less operating costs, and compatible with 3G communication technology and the evolution of 3G. LTE not only becomes the most concerned technology in the current mobile broadband communication technology, but also is the first choice for the next generation of high-speed railway communication network, which can ensure the calls and network quick and effective in the moving state of high speed.However, by the concept of the Doppler Effect, communication signals in high-speed moving will inevitably produce large Doppler frequency shift. But the uplink and downlink of LTE is very sensitive to frequency offset, Which will result in the problems of inter user’s transmission signal aliasing and user interference under the direct application. Therefore, to apply LTE into wireless communication coverage for high-speed railway, the problem of the frequency offset in Doppler Effect must be solved first.The dissertation firstly analyzes the LTE communication network and its key technologies based on the study of the Doppler frequency shift effect in high-speed moving and the fading characteristics of high-speed wireless channel, the dissertation has proposed a new Doppler frequency shift algorithm based on Toeplitz cyclic prefix, which uses the LTE cyclic prefix to extract channel information, and then calculates the more reliable frequency shift. In addition, since the high speed of the mobile terminal, the Doppler frequency shift is increased, which will cause serious inter-carrier-interference. So the dissertation also carries on the compensation to the signal frequency shift, so as to correct the transmission signal of users, so that the interference between the signals may be eliminated, and the signals can be restored itself to ensure the quality of the user’s communication services. At last, the software of MATLAB is used to build a simulation platform of high-speed railway communication system to verify the effectiveness of the frequency offset algorithm on the base of Ricean channel. Then the problems of the signal jumping and interference also be discussed.The simulation experiment results show that the algorithm is reliable and effective under the environment of high-speed railway, and the estimation of frequency shift algorithm is basically consistent with the real value. The maximum estimation error is less than 50 Hz, which is 2.5% of 2GHz carrier frequency parameter. In the transmission environment of high-speed railway large SNR, the estimated error is approximate to zero. After the effective compensation to the signal, the error in sending and receiving signals is close to zero. The algorithm can effectively improve the ability of anti-Doppler effect of LTE in high-speed railway, so as to ensure the communication quality of LTE networks in high speed railway.