| Summary: | 碩士 === 國立暨南國際大學 === 通訊工程研究所 === 97 === In recent years, orthogonal frequency division multiplexing (OFDM) technology has become the most attractive transmission scheme for wireless communications. A well-known problem in OFDM systems is the synchronization issues, including both time and frequency offset. The synchronization errors usually result in both inter-symbol interference (ISI) and inter-carrier interference (ICI) to distort transmission signal and degrade system performance. In general, timing synchronization is the major task to be completed in the receiver end. Most of all, the compensation of timing error is the first work to be done in synchronization scheme. Therefore, how to correctly estimate the error of timing shift in OFDM systems is crucial and significant.
Several specific training symbols or pilots have been employed in the symbol timing synchronization. In this thesis, various preamble patterns for timing synchronization would be introduced and investigated in wireless OFDM systems. Two proposed preamble patterns are given for reducing the computational complexity and improving the system performance. The modified Park's preamble is proposed to reduce computational complexity with insertion of zero padding to estimate the timing offset. The computational complexity can be reduced, but the performance would not be degraded seriously when zero symbols insertion is appropriate to be chosen. In addition, a hybrid estimation algorithm with a particular preamble pattern is developed for timing synchronization. If the weighting coefficient is chosen appropriately, then the system performance can be further enhanced. Finally, several simulation results are given to illustrate the advantages of the proposed schemes.
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