A Measuring Method of Multipath Delay and Doppler Frequency Shift in Underwater Acoustic Channel

Abstract

A method for measuring multipath time delay and Doppler frequency shift in an underwater acoustic channel relates to an underwater acoustic channel estimation method. The transmitting end generates N chirp signals and linearly superimposes them as channel estimation signals, and converts the channel estimation signals into acoustic waves through the transmitting transducer to propagate in the ocean underwater acoustic channel; The acoustic signal is received and converted into an electrical signal, and the digital signal is obtained after pre-amplification, filtering, and analog / digital conversion; the digital signal and the local reference signal are subjected to N times of fractional Fourier transform corresponding to the focus order and compared to obtain The peak position offsets of N different orders; according to the peak position offsets, the multipath time delay and Doppler frequency shift of each path in the channel are measured by the joint estimation method of time delay and frequency shift. The calculation process is simple and saves system overhead.

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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