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Sensors 2014, 14(2), 2595-2618; doi:10.3390/s140202595

Techniques for Clutter Suppression in the Presence of Body Movements during the Detection of Respiratory Activity through UWB Radars

Department of Electronic, Electric and Automatic Control Engineering, Universitat Rovira i Virgili (URV), Av. Països Catalans 26, Campus Sescelades, Tarragona 43007, Spain
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Received: 20 December 2013 / Revised: 16 January 2014 / Accepted: 24 January 2014 / Published: 7 February 2014
(This article belongs to the Special Issue Biomedical Sensors and Systems)
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Abstract

This paper focuses on the feasibility of tracking the chest wall movement of a human subject during respiration from the waveforms recorded using an impulse-radio (IR) ultra-wideband radar. The paper describes the signal processing to estimate sleep apnea detection and breathing rate. Some techniques to solve several problems in these types of measurements, such as the clutter suppression, body movement and body orientation detection are described. Clutter suppression is achieved using a moving averaging filter to dynamically estimate it. The artifacts caused by body movements are removed using a threshold method before analyzing the breathing signal. The motion is detected using the time delay that maximizes the received signal after a clutter removing algorithm is applied. The periods in which the standard deviations of the time delay exceed a threshold are considered macro-movements and they are neglected. The sleep apnea intervals are detected when the breathing signal is below a threshold. The breathing rate is determined from the robust spectrum estimation based on Lomb periodogram algorithm. On the other hand the breathing signal amplitude depends on the body orientation respect to the antennas, and this could be a problem. In this case, in order to maximize the signal-to-noise ratio, multiple sensors are proposed to ensure that the backscattered signal can be detected by at least one sensor, regardless of the direction the human subject is facing. The feasibility of the system is compared with signals recorded by a microphone.
Keywords: breathing monitoring; sleep apnea; vital signs; ultra-wideband radar breathing monitoring; sleep apnea; vital signs; ultra-wideband radar
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Lazaro, A.; Girbau, D.; Villarino, R. Techniques for Clutter Suppression in the Presence of Body Movements during the Detection of Respiratory Activity through UWB Radars. Sensors 2014, 14, 2595-2618.

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