| Summary: | 碩士 === 國立臺灣大學 === 電信工程學研究所 === 107 === In recent years, the demand for high transmission efficiency is increasing, so adopting uplink multi-user transmission (UL MU) is more important. Orthogonal frequency-division multiplexing (OFDM) and orthogonal frequency-division multiple access (OFDMA) have been widely adopted in many wireless communication standards. However, the OFDMA-based systems are sensitive to the synchronization error, including carrier frequency offset (CFO) and symbol timing offset (STO), which destroys the orthogonality among the subcarriers. In this thesis, we focus on the estimation and compensation of the STO. At the receiver, the received signal is a superposition of signals from all active users with individual STO. The STO introduces both inter-carrier interference (ICI) and multi-user interference (MUI), which seriously degrade the performance of systems. Hence, the estimation and compensation of STO and interferences are challenging tasks in uplink OFDMA systems. In the thesis, we frst propose a ICI and MUI compensation algorithm which can improve the BER. Next, we propose a pilot-based joint STO and channel estimator. Moreover, we also propose a pilot structure to further improve the estimation performance. Simulations are carried out to verify the performance of the proposed methods.
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