Research On Frequency Offset Estimation And Compensation For LTE System In High-speed Railway Environment

Currently, the speed of high-speed railway generally have reached 250km/h, and some even have exceeded 350km/h. The accelerated pace of the speed of high-speed railway brings a range of effects to high-speed railway communication system, and the most influential factor is Doppler effect. If measures are not taken to restrain Doppler, system performance will be very poor. So it is very important to research on the frequency offset estimation and compensation algorithm of LTE system in high-speed railway scene. The paper mainly does the following works:Firstly, based on the transmission characteristics of wireless channel and the characteristics of high-speed railway environment, the high-speed railway channel model is studied and the simulation platform of LTE system is built.Secondly, a comparison of data-aided frequency offset algorithm and non-data-aided frequency offset algorithm is made in the paper. Since the data-aided algorithm based on pilot has the advantages of fast acquisition and high precision, the paper makes a further research on two kinds of the algorithm, sub- frame non correlation algorithm and sub- frame correlation algorithm. The results show that the frequency offset estimation range of sub-frame correlation algorithm is larger, so it is more suitable for high-speed environment. However, when the high-speed railway communication link quality is poor, the frequency offset will be too large and too hard to track and correct in real time by sub- frame correlation algorithm. Especially, when Doppler frequency offset changes between the biggest positive value and the biggest negative value, the estimation accuracy will be seriously reduced.Finally, in order to adapt to rapid change of large Doppler frequency offset and solve the frequency hopping problem, an improved frequency offset estimation method based on the sub- frame correlation algorithm is proposed. Using frequency offset estimation algorithm based on single pilot to capture the range of initial value of frequency offset for pre-correction, and determining the frequency offset value by sub-frame correlation algorithm. According to the estimated frequency offset value to compensate between inter-symbol and intra-symbol. The simulation results show that the algorithm has high estimation precision and can track and correct the change of frequency offset in real time, which greatly improves the o verall performance of LTE system and makes LTE has the advantages of lower error rate and larger throughput.