Study On Carrier Frequency Offset Estimation Algorithms In OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is a special multi-carrier modulation technique, which has high spectral efficiency, good robustness to multi-path interference and easily implementation. OFDM has already been widely used in various wireless communication systems such as wireless local area network (WLAN), digital audio broadcasting system (DAB), digital video broadcasting system (DVB) and so on, which has potential to the core technology of the next generation mobile communications. Compared with the single-carrier systems, OFDM systems have a serious problem, which are very sensitive to the carrier frequency offset, that is to say, a smaller carrier frequency offset will degrade the system performance severely. Therefore, research on efficient and accurate carrier frequency offset estimation algorithms are very important for OFDM systems.Recently, research on carrier frequency offset estimation algorithms about OFDM system at home and abroad. In this paper, some classical algorithms for carrier frequency offset estimation will be discussed in depth, including the content of the algorithms, the analysis of the performance of the algorithms and computer simulation. The primary content will be described as following:Firstly, the development history and application status of the OFDM, the background and the meaning of the carrier frequency offset estimation algorithms, the basic principle of the OFDM and the receiver architecture of the OFDM system are introduced in this paper. The carrier frequency offset affects the performance of the OFDM system are analyzed.Secondly, the carrier frequency offset estimation algorithms for OFDM system will be researched and analyzed in the presence of direct current offset in this paper, which include virtual sub-carriers based OFDM carrier frequency offset estimator (ME algorithm and ME-TDA algorithm), null space based OFDM carrier frequency offset estimator (NBE algorithm), maximum-likelihood estimator for carrier frequency offset (ML algorithm) and cp(cyclic prefix)-based carrier frequency offset estimator (CPE algorithm). First, we simply introduce these estimators, then theoretical analysis and computer simulation of these estimators are carried out, finally, we conclude the advantages and disadvantages of these estimators. Based on the CPE algorithm, a novel cp-based carrier frequency offset estimator for OFDM systems will be proposed. From the results of computer simulation, the proposed novel algorithm has superior system performance over the five algorithms.At last, IEEE802.11a preamble structure based OFDM carrier frequency offset estimators will be emphasis researched and analyzed, which include a low complexity carrier frequency offset estimation in the presence of direct current offset (Ho algorithm) and least squares based carrier frequency offset estimator (Lin algorithm). Based on the analysis of Ho algorithm and Lin algorithm, a novel subspace-based carrier frequency offset estimator is proposed. From the results of computer simulation, the proposed novel subspace-based estimator has better system performance than Ho algorithm or Lin algorithm, which is very close to the Cramer-Rao lower bound (CRB). The proposed novel algorithm has low complexity, which is easily implemented.