NOISE PROPERTY OF BREATHING AND HEARTBEAT INFORMATIVE SIGNALS

Abstract

Subject and Purpose. The subject of research is the flicker noise present in informative signals of search-and-rescue radars, specifically its properties and the effect it may have on algorithms for detecting and identifying manifestations of human breath and heartbeat processes during rescue operations. The work has been aimed at creating a suitable description of flicker noise for developing optimal algorithms of digital signal processing for quick detection and identification of informative signals during rescue missions.

Methods and Methodology. The low-frequency fl icker noise has been modeled within the polynomial equations technique, proceeding from an analysis of real data on noise components in the output signals from a coherent search-and-rescue radar. A comparative analysis is done for a variety of approximating functions suggested for representing the low frequency portion of the spectrum observed.

Results. For the low-frequency range wherein spectral components of the informative signal owing to respiration and heartbeat of humans are concentrated, an adequate model of the fluctuating interference is the flicker noise model built on the basis of polynomial equations. The problem of optimized model representation of the noise in digital signal processing algorithms has been analyzed for the case of a coherent search-and-rescue radar. A model of the fluctuating process has been suggested, based on a polynomial approximation for the spectral function in the low-frequency range of the signals observed at the radar output.

Conclusion. Spectral characteristics of both interference and informative signals have been investigated. A structural diagram has been proposed for a high sensitivity, coherent search-and-rescue radar implementing a signal storage algorithm based on the polynomial model of the fl uctuating process. Th e advantages and disadvantages of the radar are discussed, with examples given of real signal implementations and of noise spectrograms. Methods of effective estimation of Doppler signal phases are presented. The paper suggests an analysis of basic requirements as to parameters and performance characteristics of the rescue radar.

Keywords: polynomial model, flicker noise, algorithm, probe signals, low-frequency noise, Doppler-shifted signal, coherent search-and-rescue radar, opaque obstacles.

Manuscript submitted 23.05.2022

Radio phys. radio astron. 2022, 27(4): 284-288

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