| Summary: | 碩士 === 國立臺灣大學 === 電信工程學研究所 === 105 === Orthogonal frequency divsion multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA)have been adopted as a modulation technique in many wireless communication standards. However, OFDM-based systems are sensitive to synchronization errors, such as symbol timing o set (STO) and carrier frequency offset (CFO). These synchronization errors may cause intercarrier interference (ICI) among all subcarriers as well as intersymbol interference (ISI) between successive OFDM symbols. Therefore, accurate estimation and compensation of these synchronization errors are important. In this thesis, we study the blind estimation of STO and CFO in OFDM systems, and the blind estimation of multiple CFOs in uplink OFDMA systems. The thesis includes three parts. In the first part, we propose a new blind STO estimator for OFDM systems with constant modulus (CM) constellation. The proposed estimators can estimate STO with only one OFDM symbol. Besides, a low complexity implementation for the proposed estimator is derived. In the second part, we extend the proposed STO estimation to the blind joint estimation of CFO and STO. In the third part, we propose a blind CFO estimatior for uplink OFDMA systems with constant modulus (CM) constellation. The proposed estimator can estimate multiple CFOs under any kinds of subcarrier assignment, while most of existing methods can only work for the interleaved subcarrier assignment scheme. Moreover, unlike the existing methods which can work for non fully-loaded systems, our methods can work for fully-loaded and non fully-loaded systems. Numerical simulations are also provided to verify the performances of the proposed methods.
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