Multi-parameter estimation of underwater acoustic channel based on fractional Fourier transform

A novel estimation algorithm for multipath number, time delay and the Doppler shift in the underwater acoustic multipath channel is proposed. A double-chirp signal with a fixed time interval T is sent. And the fractional Fourier transform (FRFT) is applied to analyze the received signal. So at a specific order, a series of peaks will appear in the corresponding u domain. The relationships between the channel parameters with the intervals among the peaks are induced. Besides, it´s not necessary to search for the order of the received signal as the result of the invariant characteristic of the chirp rate, which greatly improve the algorithm efficient. The simulation results show the effectiveness of the algorithm.