Abstract
To measure vital signs using Doppler radar, a common approach involves the use of time-varying echo phase. To acquire these measurements, clutter rejection is necessary because clutter power is often larger than echo power. To reject static clutter, several techniques have been proposed that assume relatively large phase rotation angles because many studies assume the measurement of the upper torso, where displacement is mainly caused by respiration. However, signals from other parts of the human body are known to have smaller displacements that exhibit small phase rotation angles, which make clutter rejection more difficult. Three clutter rejection techniques for measuring small displacements are compared and their performances are investigated. Using numerical analysis, one method is demonstrated to be the most effective, even for small displacements in noisy data. The best method successfully estimates the centre with an error of −13.4 and −24.0 dB, with a signal-to-noise ratio of 10 and 40 dB and the range of phase rotation angles of 90° and 15°.
Highlights
Contactless vital monitoring using Doppler radar is a promising technique for health care applications [1,2,3,4,5,6]
In realistic scenarios, radar signals contain static clutters that interfere with the time-dependent vital sign components
Clutter rejection is essential for accurate vital sign monitoring using Doppler radar [1,2,3,4,5,6]
Summary
Contactless vital monitoring using Doppler radar is a promising technique for health care applications [1,2,3,4,5,6]. Estimating the centre of the circle in the I–Q plane facilitates static clutter rejection. In this Letter, we compare and evaluate three methods – proposed by Park et al [5], Zakrzewski et al [1], and Hu et al [6] – and conclude that the Hu method has the most effective clutter rejection capability for signals with small phase rotations. In this figure, the actual centre was at (I, Q) = (2.0, 3.0). Only the Hu method correctly estimates the centre position, indicating that static clutter can only be rejected with their method in this simulation
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