Improving the accuracy of determining the singularity by the detail wavelet!coefficients of the reflectogram decomposition
I. V. Manonina, V. V. Shestakov · CyberDOI · 2018
When measuring communication lines with "classical" TDR and OTDR, the results obtained in the form of reflectograms contain certain errors. These errors depend on communication lines discontinuity, type of measured device, length of the measured line, parameters of the pilot pulse (wavelength, duration and pulse shape), dispersion of optical fiber, and methods for acquisition of the reflectogram on the screen and its further processing. An overview of modern methods of measuring communication lines has shown that known methodology and devices based on it make it possible to detect discontinuities and damage to communication lines with errors, therefore, it is necessary to improve the methods of measuring communication lines using modern methods of processing data from OTDRs that can significantly reduce the error of localization of damage. The method for determining the singularity of reflectograms based on the analysis of the detail coefficients of the wavelet decomposition of the reflectogram to improve measurement accuracy is proposed in the article, and it allows to significantly increase the localization of damages and discontinuities. The method is based on the mathematical processing of the signal with the determination of the points of discontinuity or changes in the regularity of the signal (finding the exact localization of the singularity) pointing to the places of damage, discontinuities or specialized connection (splitters) by the wavelet coefficients. The presence of a singularity is characterized by the Lipschitz exponent at a given point. Two types of typical damages (discontinuities, connection) were simulated as the analyzed signal, which were processed using different wavelets (Haar wavelet, Daubechies wavelet D4-D18, symmlets) and at the following comparison of the results for this type of discontinuities, the most accurate values for the location of damage were obtained using Daubechies wavelets D6-D10 having 3, 4 and 5 vanishing moment. To accurately define singularity, a procedure written in the MATLAB environment is used. In conclusion, an example of the application of the developed method for the real reflectogram is given for conducting a comparative analysis of the results obtained from the reflectometer and by the wavelet processing. The proposed method made it possible to improve the accuracy of instrumental methods for localizing damage and discontinuities (singularity) of communication lines by a factor of 1.5-2.