Study On The Doppler Shift Estimation Algorithms In LTE Mobile Communication System

The rapid development of high-speed railway imposes higher requirements on railway mobile communication systems. Long Time Evolution(LTE) has drawn extensive attention in high-speed railway mobile communication, because it supports high-speed data rates, high efficiency on spectral resources and high mobility. However, new challenges are brought to LTE system because of high mobility. The large Doppler shift not only makes the channel change rapidly but also destructs orthogonality between sub carriers of OFDM systems, and inter carrier inference is produced, the communication quality of LTE system is decreased.Therefore, researching and resolving interference problems caused by Doppler dispersion has important scientific significance and application value in high-speed mobile scenarios.Firstly, transmission characteristics of wireless channel is analyzed. Based on that, the formation mechanism of high-speed railway mobile environment Doppler effect and how it affect on the wireless channel is analyzed.Secondly, several major traditional frequency estimation algorithm are studied, and concluded that campared with Doppler diversity mode and CFO joint estimation algorithms,two times frequency estimation method performes better in offset estimation range and accuracy, but it still can not be applied to the LTE uplink.Finally, focused on the shortcomings like small estimation range, low accuracy and poor traceability in the doppler frequency offset estimation of SC-FDMA system. An improved method is proposed in this paper to solve these problems, which reduces the effects of noise an interference on the accuracy of the Doppler frequency estimatiom. The autoregressive(AR)model is employed between the subframes in the improved method, which helps to reduce computational complexity.