PRT Shaping Method for Heart Rate Variability Monitoring Using Phase- and Quadrature Self-Injection-Locked (PQSIL) Radar

This article proposes a PRT shaping algorithm, which is used in conjunction with a 2.4-GHz phase- and quadrature self-injection-locked (PQSIL) radar for noncontact heart rate variability (HRV) monitoring. To validate the demodulated signal measured from the radar system, experiments were conducted on actuators executing minute variable-frequency motions, which could be recovered without distortion. The PRT shaping algorithm for enhancing the heartbeat features and obtaining the HRV was processed in the time domain to avoid the tradeoff between the window length and frequency resolution typically encountered in frequency-domain analysis. Specifically, the breathing-related motion was first removed from the signal, and the heartbeat features were enhanced via autocorrelation. Subsequently, one-cycle segmentation was performed before using the PRT model to eliminate the initial peak deviation within a heartbeat cycle duration, based on the cardiac rhythm corresponding to the P, R, and T waves. The R peaks of the waveforms obtained after PRT shaping were compared with those of a reference electrocardiogram (ECG) signal. For experimental verification, noncontact HRV monitoring was performed for five subjects seated 1-m away from the radar. The feasibility of the proposed method was verified in terms of various evaluation indicators for HRV analysis, including an overall average mean relative error (MRE) of <2% and a 5 beats per minute (bpm) accuracy of 100%.