| Summary: | 碩士 === 國立中正大學 === 通訊工程研究所 === 95 === In recent years, wireless communication technology has acquired widespread application in human life. Due to the growing necessity for multimedia, effectively employing the available bandwidth and improving the data rate are essential. Orthogonal frequency division multiplexing (OFDM) is a technique that employs several sub-carriers for modulation. Thus, by taking advantage of the orthogonality between different sub-carriers, OFDM systems can employ with useful bandwidth perfectly. Moreover, inter-symbol interference can be effectively reduced by adding a guard interval in each OFDM symbol.
In this thesis, we use a preamble in a WirelessMAN-OFDM system for symbol timing synchronization and carrier-frequency-offset estimation. The correlation between the repeated samples around the actual symbol timing is relatively large due to the repetitive characteristics of the conventional preamble used for symbol timing synchronization. The actual symbol timing of the conventional preamble does not exhibit a clear maximum value, and it interferes with the accuracy of synchronization. Hence, we present a novel preamble structure with symmetry characteristics. Based on the proposed preamble, two algorithms for symbol timing synchronization are proposed. The actual symbol timing of the proposed preamble shows a clear maximum value because of the use of the symmetry characteristics of the proposed preamble to estimate the symbol timing. Thus, the actual symbol timing can be easily obtained. The simulation results show that when the signal-to-noise ratio (SNR) is low, the efficiencies of the proposed algorithms are quite good. Thus, the superior performance of the proposed algorithms is demonstrated. Moreover, by determining the correct symbol timing, easy estimation of the carrier frequency offset and better accuracy can be achieved simultaneously.
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