| Orthogonal frequency division multiplexing (OFDM) has been applied in communication fields over a wide range, and will be the most promising technique in 4G mobile communication. However, synchronization techniques are of great importance since synchronization errors might introduce inter-symbol interference and inter-carrier interference, which result in the loss of orthogonality among sub-carriers.Most blind synchronization algorithms are proposed in additive white Gaussian noise channel, but can not be used in multi-path channel. A novel cost function is proposed in this paper to solve such a problem. This function has a stable peak which is suitable for synchronization with peak detection. For computational complexity reduction, adaptive searching is used in peak detection; however, its decreasing step-size method is suitable for convergence stage while constant step-size method is suitable for tracking stage. A gate value is used to combine both decreasing and constant step-size methods, which ensures a good performance in tracking stage as well as in convergence stage. A bidirectional search method is designed in the new algorithm to make the searching direction more stable. Meanwhile, multi-scale searching method is designed to make adaptive searching more stable and achieve estimation results with different resolutions.It is shown that the mean square errors of time and frequency offset estimates can be reduced to 0.9243 and 0.003 respectively with even a bad channel estimate. Simulation also shows that it takes only 10-20 symbols for the proposed algorithm to track the change of channel delay. |
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