Comparative analysis of methods of recognition of signals from illegal radio equipment based on frequency transformations

DOI: 10.31673/2412-4338.2019.037182

Abstract

The methods of recognition of radio signals on the basis of frequency transformations of signals, such as the method of Fourier transform, the method of fast Fourier transform, window Fourier transform, the wavelet transformation, are compared. Practical examples of modeling in the Matlab environment shows the advantages and disadvantages of Fourier transform for the analysis of radio signals, considered the fast Fourier transform compared to the window Fourier transform, proposed a method for selecting window functions at a specified resolution, and specified dynamic range of signal change.
It is shown that the problem of calculating good windows is reduced to the mathematical problem of finding a time-bounded Fourier transform function that best approximates a function in frequency, i.e., they have a minimum of energy beyond a given frequency interval. It is shown that the wavelet transform method has all the advantages of the Fourier transform for recognition of radio signals. In addition, the advantage of wavelet transform over Fourier transform is that it allows to trace the change in the spectral properties of a signal over time and to indicate which frequencies (scales) dominate the signal. Considered the wavelet transform signal in terms of practical application for the analysis of short pulse signal. Presented graphic results obtained from modeling processes convert radio signals in Matlab environment in the context of a comparative analysis of different methods of signal conversion for their recognition. Attention is drawn to the pros and cons of the above methods of signal conversion in terms of the analysis of short-term, non-stationary and periodically repeated analog signals. The use of wavelet transform for the analysis of short-term signals on the amplitude-time (frequency) characteristics is justified in order to detect the operation of a digital radio-bug that works with the accumulation of information and transmits it in a short period.

Keywords: Fourier transform, wavelet transform, radio device, frequency conversion.

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