Method for determining multipath time delay and Doppler frequency shift in underwater acoustic channel

Abstract

The invention provides a method for determining multipath time delay and Doppler frequency shift in an underwater acoustic channel, and relates to an underwater acoustic channel estimation method. A transmitting terminal generates N linear frequency modulation signals and the signals are linearly superposed to serve as channel estimation signals, and the channel estimation signals are converted into sound waves through a transmitting transducer to be spread in ocean acoustic channels; a receiving terminal receives acoustical signals spread in the ocean acoustic channels through a receiving transducer and converts the acoustical signals into electrical signals, and digital signals are obtained through pre-amplification, smoothing and analog / digital conversion; fractional Fourier transformation corresponding to focusing orders is conducted on the digital signals and local reference signals N times and N peak position offset quantities with different orders are obtained through comparison; the multipath time delay and the Doppler frequency shift of all paths of the channel are determined by the adoption of a time-delay and frequency-shift joint estimation method according to the peak position offset quantities. By means of the method, the computational process is simple and system overhead is saved.

Description

technical field [0001] The present invention relates to an underwater acoustic channel estimation method, in particular to a multipath time delay and Doppler frequency shift in an underwater acoustic channel which adopts multiple linear frequency modulation signals as channel estimation signals and uses fractional Fourier transform to simultaneously measure the signals method of measurement. Background technique [0002] The underwater acoustic channel is a double-diffusion channel with time delay and frequency shift. The reflection of the acoustic boundary in the water body, the refraction caused by the gradient of the sound velocity profile, and the scattering of substances such as fish and suspended particles will cause multipath propagation of the signal, resulting in the time expansion of the signal; The fluctuation and the scattering of particles will cause the Doppler frequency shift of the signal, resulting in the expansion of the frequency shift of the signal. Bot...

AI Technical Summary

Problems solved by technology

The reflection of the acoustic boundary in the water body, the refraction caused by the gradient of the sound velocity profile, and the scattering of fish and suspended particles will cause multipath propagation of the signal, resulting in the time expansion of the signal; The fluctuation and the scattering of particles will cause the Doppler frequency shift of the signal, resulting in the expansion of the frequency shift of the signal

Both will have a certain impact on the underwater acoustic communication system

[0004] Since the above method does not perform fractional-order Fourier transform on the focused order of the chirp signal, it needs to perform correlation operations after the transform, thus increasing the amount of calculation

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