Respiratory Rate Estimation During Rehabilitation Exercise Using Continuous Wave Radar System

A bio-radar system for monitoring vital signs is proposed, and its applicability is evaluated in patients performing rehabilitation exercises in a clinical environment. The system employs Empirical Mode Decomposition (EMD), an adaptive signal decomposition technique, to separate motion artifacts and high-frequency noise from received signals and thereby extract respiratory information effectively. Cardiopulmonary exercise testing was conducted on four patients with cardiac disease, during which respiration was simultaneously measured using an in-house 5.8-GHz continuous-wave radar sensor and conventional contact-based medical equipment. The results show a Pearson correlation coefficient of 0.60～0.80 and a mean absolute error of 4.0～5.5 bpm. These outcomes demonstrate that the radar-based measurement can reliably reproduce the increasing and decreasing respiratory trends observed by contact-based devices and offer clinically acceptable stability even under high-intensity rehabilitation conditions.