FMCW Millimeter-Wave Radar-Based Remote Monitoring of Vital Signs in Multiple Subjects

Traditional methods for measuring vital signs often require hospital visits and direct skin contact, making them costly and operationally inconvenient. However, advancements in millimeter-wave radar technology have enabled noncontact monitoring of vital signs, particularly in close-range, single-subject scenarios. Despite this progress, challenges persist in simultaneously monitoring multiple subjects over extended distances. This paper investigates the feasibility of long-range, multi-subject vital sign monitoring using frequency-modulated continuous-wave (FMCW) radar technology. In this study, we first determined the subject distances and angles through radar measurements. To enhance the accuracy of breathing rate (BR) and heart rate (HR) estimations, we coherently accumulated phase information from multiple subjects. Noise interference was mitigated using first-order difference and moving average filtering techniques. Adaptive filters were also developed to effectively separate the breathing and cardiac signals. Finally, spectral estimation algorithms were employed to accurately calculate BR and HR. Experimental results demonstrated that when subjects were positioned within 1.5 m, the root mean square error (RMSE) for both BR and HR remained below 2. At a distance of 3.0 m, the RMSE for BR and HR increased but remained below 4. By varying the subject-radar distances and angular configurations, the proposed method was validated for its effectiveness and precision in long-range, multi-subject monitoring scenarios.