Some Remarks about Entropy of Digital Filtered Signals

The finite numerical resolution of digital number representation has an impact on the properties of filters. Much effort has been done to develop efficient digital filters investigating the effects in the frequency response. However, it seems that there is less attention to the influence in the entropy by digital filtered signals due to the finite precision. To contribute in such a direction, this manuscript presents some remarks about the entropy of filtered signals. Three types of filters are investigated: Butterworth, Chebyshev, and elliptic. Using a boundary technique, the parameters of the filters are evaluated according to the word length of 16 or 32 bits. It has been shown that filtered signals have their entropy increased even if the filters are linear. A significant positive correlation (p < 0.05) was observed between order and Shannon entropy of the filtered signal using the elliptic filter. Comparing to signal-to-noise ratio, entropy seems more efficient at detecting the increasing of noise in a filtered signal. Such knowledge can be used as an additional condition for designing digital filters.

An Adaptive Filter Based on Local Slope by Adjusting Elliptic Filter Kernel for ICESat-2 Photon Counting Laser Altimetric Data

The Ice, Cloud and Land Elevation Satellite-2 (ICESat-2) was launched on September 15th, 2018, which continues to perform measurement tasks as the successor to ICESat. Unlike full waveform technology of ICESat, ICESat-2 employs micropulse photon counting technology, which provides higher accuracy, but produces plenty of noise. This paper proposes an adaptive filter based on local slope by adjusting elliptic filter kernel. The general approach is 1) data preprocessing, 2) Gaussian density calculation, 3) OTSU adaptive threshold calculation. This method is seen to be robust in identifying signal points from high background noise points and suitable for low density data caused by slope.

QUASI-ELLIPTIC MICROSTRIP FILTER

Currently, modern telecommunication and radio-electronic systems widely use wireless information transmission technologies over the radio channel. Therefore, an urgent task is to ensure electromagnetic compatibility of a large number of simultaneously operating radio facilities using high-selective bandpass filters. This paper presents circuit solutions for microstrip filters using incomplete inclusion of loads and communication elements. This construction makes it possible to obtain additional attenuation poles in the near zone of the stop band, which frequencies are determined by the load inclusion factor. It is proposed to include a capacitor in the middle of the microstrip communication line to improve the selective properties. This made it possible to increase the order of the filter at constant dimensions. The frequency characteristics of a high-selective quasi-elliptic filter are given.