Objective: Over the last two decades, radar-based contactless monitoring of vital signs (heartbeat and respiration rate) has raised increasing interest as an emerging and added value to health care. However, until now, the flaws caused by indoor multipath propagation formed a fundamental hurdle for the adoption of such technology in practical healthcare applications where reliability and robustness are crucial. Multipath reflections, originated from one person, combine with the direct signals and multipaths of other people and stationary objects, thus jeopardizing individual vital signs extraction and localization. This work focuses on tackling indoor multipath propagation. Methods: We describe a methodology, based on accurate models of the indoor multipaths and of the radar signals, that enables separating the undesired multipaths from desired signals of multiple individuals, removing a key obstacle to real-world contactless vital signs monitoring and localization. Results: We also demonstrated it by accurately measure individual heart rates, respiration rates, and absolute distances (range information) of paired volunteers in a challenging real-world office setting. Conclusion: The approach, validated using a frequency-modulated continuous wave (FMCW) radar, was shown to function in an indoor environment where radar signals are severely affected by multipath reflections. Significance: Practical applications arise for health care, assisted living, geriatric and quarantine medicine, rescue and security purposes.

For remote vital signs and occupancy detection in many smart home/building applications, radar sensors are a preferred option over cameras, due to privacy preservation and robustness to ambient light conditions. These radars not only need to provide precise range and vital signs information over meters distance, but also preferably can operate on a battery up to a few months or even years, for cost and practical reasons (like smoke detectors). State-of-the-art remote vital-sign sensors typically use an impulse-radio UWB (IR-UWB) radar [1,2] because it provides a range resolution <20 cm. However, their power consumption is typically in the order of 100's of mW, preventing long-term maintenance-free battery-powered operations. Although mains power can be used to supply such radars, this is not always available, depending on the location and the building type, and the installation cost (e.g., power routing) is significantly higher than for battery-powered ones. In this work, a burst-chirp radar with an energy-efficient chirp generation is proposed, leading to a record-low power consumption of 680 μW.

This letter presents an ultrawideband (UWB) radar for occupancy and vital signs detection. The proposed burst-chirp operation achieves > 30\times power reduction and abundant margin for the UWB spectrum regulations. With the proposed Domino chirp generation and time-domain predistortion, the radar has a fast chirp slope of 0.7 GHz/40 μ \text{s} and a low RMS error of 0.5 MHz. Fabricated in a 40-nm CMOS process, the presented radar consumes a record-low power of 680 μ \text{W} and can detect human respiration and heartbeat up to 15 and 5 m, respectively.