The Method Of OFDM Frequency Offset Estimation In High Mobile Environment

Orthogonal frequency division multiplexing (OFDM) is a kind of multi-carrier modulation in wireless environment. In recent years, as the rapid development of the hardware technique, OFDM has been given more attention because of its efficiency of using the limited spectrum and its robustness against the effects of multi-path propagation which are main obstruction for mobile reception and realization of single frequency network. OFDM is a technique that we can use in the future mobile communication.While in the meantime, OFDM has its own shortcomings: its sensitivity to a frequency offset and the high peak-to-average ratio. How to eliminate the two problems is the main task of the research of OFDM. Meanwhile to the mobile communication system, the different mobile channel has the different effect to the system. In the high speed environment, the Doppler shift can destroy the orthogonal characteristic between the sub-carrier. It will affect the performance largely. How to overcome the influence of the Doppler shift will be a research direction in the future. The paper mainly researches the method of OFDM frequency synchronization in high mobile environment.The paper first introduces the basic theory of the OFDM system and the high mobile environment. Then it mainly researches the method of OFDM frequency offset estimation in high mobile environment, it includes the estimation of the carrier frequency offset and sample frequency offset. The paper especially researches the algorithm of the carrier frequency offset estimation. Usually there are two methods of the frequency offset estimation. The one is the method based on the data-aided, the other is the non data-aided. Compare with the non data-aided method, the data-aided method will reduce the transmission efficiency of the system, but it has high precision of the estimation and low computing. To the data-aided method, actually it can be separated into two methods. One is the method based on the cyclic prefix, the other based on the midamble. But actually these methods can get the good performance under the low speed. In the high speed environment, some methods can't get the good performance between the range and the precision of the frequency offset estimation. Based of these methods, the paper wants to research an algorithm of frequency offset estimation that can work in the high mobile environment. This algorithm use the iterative method, it not only can get the large range of the estimation, but also can get the high precision of the estimation. The performance is very good.Based on the above, the paper introduces the influence of the symbol synchronization to the frequency offset estimation. Because in the high mobile environment the symbol synchronization is the premise of the frequency offset estimation. Meanwhile the paper also researches the method of the frequency domain estimation. It includes the estimation of SNR and the speed.Finally, we realize the algorithm in the communication system. From the result of the simulation we can find that the algorithm can work well in the high speed mobile channel and it can be realized conveniently.