| Summary: | 碩士 === 國立交通大學 === 電信工程系所 === 92 === Bandwidth efficiency and multipath immunity make orthogonal frequency division multiplexing (OFDM) an attractive modulation technique for modern high data rate communication systems. A major concern of OFDM systems is that symbol timing and frequency synchronization errors can seriously degrade the system performance. Therefore, it is important to obtain accurate estimate of time and frequency offsets. In this thesis, we focus on frame timing synchronization. Several cyclic prefix based techniques are investigated and two modified algorithms based on global search algorithm are proposed. In the local search algorithm, we only search the sample points near the estimated point of previous frame; this can increase the accuracy of estimated timing at high SNR. Another algorithm, called modified global search algorithm, yields a comparable performance and lower complexity compared with other techniques. Our proposed algorithms are all self-learning in the sense that they can automatically track slowly time varying channel conditions. The performance and complexity of our proposed algorithms will be compared with other cyclic prefix based algorithms from simulation results.
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