Research On The Estimation Of Frequency Offset In OFDM System

OFDM system is one basic technique of the future wireless communication. It is paid attention more and more ,because of its performace for resisting multipath influence and its high efficiency of system bandwidth. So it is possible to be adopted in mobile communication in 4G However, the OFDM system is sensitive to frequency offset of carrier wave, which will make the property of the system deteriorate evidently. Therefore the investigation for frequency offset has turn into the one of the focuses in OFDM, which has signality to improve the system property. Hence, it is also the main work in this paper.In paper, some classical algorithm of frequency offset have been researched in depth, including the presentation of the algorithm content, the embedded analysis of the estimation performance of the algorithm. Based on these, the improvement is proposed to the algorithm. The primary content in this paper will be described as following:Firstly, it is introduced that the background, imperative issue, structure and the system mode of the OFDM. The infection of frequency offset is also described and analyzed simply.Secondly, The ML algorithm based on CP in being and its tracking performance are analyzed. The emphases is the improvement to the quondam algorithm, namely, the hybrid maximum-likelihood estimation algorithm based on the information of both CP and pilot subcarriers. Correspondingly, the ML function of quondam algorithm is re-derived. It all the same rely on the correlation and the function of ML, while importing imformation of pilot symbols which had been used originally to channel estimation. Because of using the information of pilot, the frequency offset is estimated by a shorter CP. Therefore, the spending of system is reduced. At one time, the precision of estimation is improved. Specially, on lower SNR, the precision can reach to the requirement of system. These strongpoints are confirmed by the emluator.Thirdly, the methods of the pilot insertion is firstly discussed. Following it, the corresponding algorithm are described. The algorithm based on comb-shaped pilot symbol, using distributing characteristic of energy diffusing of pilot, and its expansion are expatiated. Mainly analyze the algorithm of using quadrate pilot instead of the comb one. The algorithm improves the property because of the simple structure and well reliability of the quadrate pilot. Through the experimentation, the estimation performance of the quadrate pilot is better than the comb or the hexagon insertion assuredly.