Abstract:

Because of the complexity and variability of the underwater acoustic (UWA) channel, signal transmitting in the UWA channel is accompanied with multi-path timedelay and Doppler frequency shift, which are important parameters in UWA channel estimation. Based on the time-delay and frequency shift characteristics of fractional Fourier transform (FRFT), a novel method of UWA channel estimation is proposed, using multi-component linear frequency modulated (LFM) signals. By analyzing the shift of signal peak in the fractional Fourier domain (FRFD) and solving the time-delay and frequency shift errors equations of different orders, the time-delay and frequency shift values can be figured out. The theoretical derivation and simulation results show that the time-delay and frequency shift decrease to some extent with the increase of the number of LFM signals and the difference of frequency modulation rates using the proposed method, with low computational complexity. A pair of LFM signals with contrary frequency modulation rates is chosen to estimate the multi-path delay and Doppler frequency shift in the pool experiment, and the velocities of underwater moving targets are presented. The experiment results demonstrate the proposed method is simple, effective and practical in the multi-path time delay and Doppler frequencyshift estimation.