Orthogonal Frequency Division Multiplexing ( OFDM) system is sensitive to Carrier Frequency Offset ( CFO ). In this paper, traditional Maximum Likelihood Estimators (MLE) for CFO of OFDM are introduced first. Th...Orthogonal Frequency Division Multiplexing ( OFDM) system is sensitive to Carrier Frequency Offset ( CFO ). In this paper, traditional Maximum Likelihood Estimators (MLE) for CFO of OFDM are introduced first. Then, averaging method and a-filter are introduced as Low Pass Filter (LPF) to improve the performance of cyclic prefix estimator. The bandwith of LPF is determined by the coherence time of radio channel. Estimation performance in multipath channel is analyzed. Outlier picking-out scheme is proposed to improve performance further. Performance of close-loop structure is presented briefly, which is worse than that of open-loop structure. Finally, a parallel switch structure of frequency synchronizer is proposed for mobile OFDM systems. The scheme ezcploits training sequence and cyclic prefix. The proposed synchronizer has a wide acquisition range. It is accurate and robust in both AWGN channel and multipath channels. The complexity is low due to functionality of a-filter. A better performance of frequevlcy synchronization is obtained comparing to that of existing Maximum Likelihood Estimator( MLEs). We achieve these advantages without loss of bandwidth efficiency.展开更多
摘要Orthogonal Frequency Division Multiplexing ( OFDM) system is sensitive to Carrier Frequency Offset ( CFO ). In this paper, traditional Maximum Likelihood Estimators (MLE) for CFO of OFDM are introduced first. Then, averaging method and a-filter are introduced as Low Pass Filter (LPF) to improve the performance of cyclic prefix estimator. The bandwith of LPF is determined by the coherence time of radio channel. Estimation performance in multipath channel is analyzed. Outlier picking-out scheme is proposed to improve performance further. Performance of close-loop structure is presented briefly, which is worse than that of open-loop structure. Finally, a parallel switch structure of frequency synchronizer is proposed for mobile OFDM systems. The scheme ezcploits training sequence and cyclic prefix. The proposed synchronizer has a wide acquisition range. It is accurate and robust in both AWGN channel and multipath channels. The complexity is low due to functionality of a-filter. A better performance of frequevlcy synchronization is obtained comparing to that of existing Maximum Likelihood Estimator( MLEs). We achieve these advantages without loss of bandwidth efficiency.