Demodulation method for frequency-modulation acoustic communication system
A demodulation method and underwater acoustic communication technology, applied in the direction of frequency modulation carrier system, transmission system, electrical components, etc., can solve the problems of low frequency resolution and easy to be affected by Doppler in demodulation, and achieve simple algorithm, It is beneficial to correct demodulation and reduces the effect of Doppler frequency shift
Inactive Publication Date: 2013-06-19
XIAMEN UNIV
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[0015] The purpose of the present invention is to provide a windowed bilinear interpolation based on the deficiencies in the demodulation of the existing underwater acoustic FM system, such as low frequency resolution and being easily affected by Doppler. The demodulation method of the FM underwater acoustic communication system has the advantages of high frequency accuracy, stable demodulation decision window, etc., and can tolerate the influence of Doppler frequency deviation to the greatest extent, and improve the communication success rate of the underwater acoustic FM system.
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[0040] The demodulation and simulation of the underwater acoustic 4FSK signal is carried out by using the double linear interpolation FFT method of the present invention. Use 4FSK modulation in the simulation, the frequency range is 17 ~ 23kHz, according to Nesqui's sampling law, the sampling rate fs of the system is set to 50kHz. In order to resist the multi-channel effect in the underwater acoustic channel, the modulation method adopts FH-MFSK (Frequency Hopping Multi-Carrier Frequency Shift Keying), which divides the available bandwidth into multiple sub-bands, and uses 4FSK modulation in each sub-band, so the modulation frequency The width interval between is 0.25kHz, Gaussian white noise is used as the channel interference source, and the signal-to-noise ratio is 5dB.
[0041] For example, the experimental carrier frequency is 20.75kHz, and the width N of each symbol is set to 256. Smaller symbol width contains fewer data points, which is convenient for system operation....
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A demodulation method for a frequency-modulation acoustic communication system comprises the following steps: amplifying acoustic signals acquired from an energy converter to obtain a discrete signal sequence s(n) of N sampling points; constructing Hanning window function with length N, and windowing s(n) to obtain S'(n); conducting FFT (Fast Fourier Transform) algorithm on N points to obtain a frequency domain information sequence S(n); searching peak spectral lines and left and right side spectral lines from S(n); adopting double-linear interpolation correction method to carry out frequencyspectrum correction on the peak spectral lines and left and right side spectral lines, and obtaining a corrected peak position kmax; calculating a corrected frequency fmax from kmax according to the relation between frequency and sampling rate; and adopting frequency point best approximation algorithm to decode peak frequency f, and restoring original binary information. The method has the advantages of simplicity, practicality, fast calculation speed, high frequency-discrimination frequency, and stability in the demodulation and the judgment window; and the influence of Doppler shift can be maximally accommodated and the communication success rate for the acoustic communication system can be improved.
Description
technical field [0001] The invention belongs to the field of underwater acoustic communication, and in particular relates to a method for demodulating an underwater acoustic FSK (Frequency-shift keying, frequency-shift keying) signal in a windowed bilinear interpolation FFT (fast Fourier transform) mode. Background technique [0002] With the rapid development of modern information technology, underwater acoustic communication technology is an important technical component in the development of contemporary marine resources and the three-dimensional monitoring system of the marine environment. Especially widely used in underwater telemetry and remote control, pollution monitoring, marine resource investigation and development, it is one of the urgent research and development projects of my country's marine high technology. [0003] The underwater acoustic channel is an extremely complex channel with random time, space and frequency changes. Its main characteristics are: comp...
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IPC IPC(8): H04L27/14H04B13/02
Inventor 邹哲光许肖梅陶毅张小康彭阳明朱兆彤
Owner XIAMEN UNIV