A Cross-self-correlation Time Synchronization for OFDM Underwater Acoustic Communications

In this paper, an anti-multipath time synchronization method based on Hyperbolic Frequency Modulation (HFM) signal is proposed. It is common for underwater acoustic multipath channel that the first path is not the strongest one which brings difficulty to synchronization for Orthogonal Frequency Division Multiplexing (OFDM) system. In the proposed method, both crosscorrelation between received signals and sending HFM, and self-correlation between sending HFMs are obtained to arrive to the correlation coefficient as the statistics for synchronization. This method can help us to find the first path in multipath underwater channel which is important for synchronization. In addition, since the HFM is Doppler-insensitive, the time synchronization method is also Doppler-tolerant. Performance with simulations and experimental data sets shows that the proposed synchronization method reduces the bit error rate (BER) comparing with the traditional methods when the multipath effect is serious and Doppler is evident for underwater acoustic channel.