Noncontact Cardiorespiratory Feature Extraction Using Frequency Modulated Continuous Wave Radar: Opportunities and Challenges

Advances in noncontact vital sign detection have demonstrated its vast potential to supplant conventional contact sensors, not only within the established healthcare system but also across emerging domains such as smart homes, security systems, and in-cabin sensing. Noncontact cardiorespiratory measurements are among the most common, in part due to their relative ease of measurement using noncontact sensors. For this application, radar-based sensors have several advantages, including high accuracy measurement that is invariant to ambient lighting conditions, which are especially beneficial in non-clinical settings. Radar-based cardiorespiratory feature extraction architectures consist of two parts: the radar hardware design and the signal processing pipeline. However, the combined complexity of the hardware, the underlying physics and the scene itself, makes the signal processing requirements very challenging. To address this issue, we first review the recent trends in this domain, including the move towards Frequency Modulated Continuous Wave (FMCW) radar sensors, and then present an empirical investigation using a commercial FMCW radar to illustrate the unsolved real-world signal processing challenges for noncontact cardiorespiratory measurement. Additional in-depth analysis is used to interpret the underlying reasons behind the challenges, together with potential solutions. The work presented will benefit researchers and industrialists working on radar-based physiological measurement, facilitating a greater understanding of the problem, its benefits and challenges, and potential future research directions.