mmCG: Noncontact Millimeter-Wave Cardiography for Heart Rate Variability Monitoring

Heart rate variability (HRV) is an essential indicator of cardiovascular and nervous system function, with wide applications in health monitoring and disease management. Traditional contact-based methods like electrocardiograms (ECG) and photoplethysmography (PPG), while effective, face significant limitations in user experience, such as discomfort during prolonged use, and challenges in long-term, continuous monitoring. Meanwhile, contactless wireless sensing based on mmWave radar offers a promising alternative but is hindered by issues of directional sensing and noise interference. In this paper, we propose mmCG (mmWave Cardiac Gram), a contactless HRV monitoring system. Specifically, it integrates a heartbeat spatial localization method for directional sensing, which significantly improves the SNR, and a dynamic peak search algorithm that leverages heartbeat temporal correlations to effectively mitigate the impact of artifacts. Experimental results show that mmCG achieves advanced performance, reducing the IBI error to 9.44ms, a 51.29% improvement over existing methods. With its lightweight design and enhanced accuracy, mmCG offers a practical solution for daily HRV monitoring, with potential applications in stress management, personalized healthcare, and cardiovascular disease monitoring.