| The earth with stable channel characteristic is used as transmission medium in through-the-earth communication. Through-the-earth communication plays an important role in the mine and geological disaster rescue because it is not easily influenced by these disasters.But the stratified earth channel is very complex and it can cause serious attenuation to the high frequency electromagnetic wave. Therefore, the low frequency wave is used to complete the transmission within limited channel bandwidth in through-the-earth communication. Moreover,through-the-earth communication will lead to signal fading.For the problem of narrow channel bandwidth and signal fading for through-the-earth communication, OFDM technology is adapted in this paper. However, due to the subcarrier orthogonality requirements, OFDM technology is very sensitive to synchronization error, timing deviation will bring inter-symbol interference. This topic mainly focuses on the synchronization of OFDM symbols.In this paper, the principle of OFDM communication system is introduced, the influence of OFDM synchronization error is analyzed, and the OFDM symbol timing synchronization algorithm is studied. In this paper the Schmidl & Cox algorithm, Minn algorithm and Park algorithm in the classical training sequence based synchronization algorithm are studied and simulated by MATLAB. Based on the characteristics of Minn algorithm and Park algorithm,an improved synchronous timing method based on Chirp sequence of Chirp sequence is proposed to implement OFDM system symbol timing synchronization. And the Zadoff-Chu sequence was used to construct the training sequence and simulated using MATLAB. The results show that the Chirp sequence construction training sequence is less affected by noise,and the training sequence correlation peak of the improved symbol synchronization algorithm is sharper and the starting position of the OFDM symbol can be located more accurately, MSE is less than 10-4. |
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