Wearable health-monitoring systems are becoming very popular, especially in enabling the noninvasive diagnosis of vital functions of the human body. Besides typical singular heartbeat or perspiration sensors, which have been commercially available in recent years, the deployment of a series of body-worn sensors can enable an effective health-monitoring mechanism. The combined information obtained from such systems can either be relayed directly to any health-monitoring personnel in the case of emergencies or can be logged and analyzed as a part of preventive health measures. However, the deployment of on-body nodes for humans must be performed with care, as they may interfere with the patients' regular movements. This is especially challenging because the relationship between the electromagnetic waves is influenced by the patient's movements, distance from the nearest base station, operating environment, etc. Additional challenges to the deployment of such mechanisms are also faced in situations where the nodes require additional on-body space, impose additional weight, or are not conformal enough to the patient's body. On the hardware design aspect, the sensory and communication functions on the electronic node have to be designed using special materials to avoid reliability issues or damage due to repeated or intense movements. Finally, and perhaps the most important aspect that needs to be addressed concerning such systems, is their electromagnetic safety level, which is defined by their specific absorption rates (SARs). This article aims to review the latest developments in body-worn wireless health-monitoring systems and their current challenges and limitations and to discuss future trends for such worn devices for these applications.

Innovative technology approaches have been increasingly investigated for the last two decades aiming at human-being long-term monitoring. However, current solutions suffer from critical limitations. In this paper, a complete system for contactless health-monitoring in home environment is presented. For the first time, radar, wireless communications, and data processing techniques are combined, enabling contactless fall detection and tagless localization. Practical limitations are considered and properly dealt with. Experimental tests, conducted with human volunteers in a realistic room setting, demonstrate an adequate detection of the target's absolute distance and a success rate of 94.3% in distinguishing fall events from normal movements. The volunteers were free to move about the whole room with no constraints in their movements.

A single-input and single-output (SISO) frequencymodulated continuous wave (FMCW) radar architecture is proposed and in vivo demonstrated for remote two-dimensional (2-D) localization (range and angular information) and vital signs monitoring of multiple subjects. The radar sensor integrates two frequency scanning antennas which allow angular separation and enable determining a 2-D map (range vs. angle) of a room environment from which people can be distinguished from objects and clutter. After technical tests to validate the functionality of the proposed architecture and data processing algorithm, a practical setup was successfully demonstrated to locate human volunteers, at different absolute distances and orientations, and to retrieve their respiratory and heart rate information. Experimental results show that this radar sensor can monitor accurately the vital signs of multiple subjects within typical room settings, reporting maximum mean absolute errors of 0.747 breaths-perminute and 2.645 beats-per-minute respectively for respiration rate and heartbeat. Practical applications arise for Internet of Things (IoT), ambient assisted living, healthcare, geriatric and quarantine medicine, automotive, rescue and security purposes.

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.

A continuous wave Doppler radar, operating as a phase-locked-loop in phase demodulator configuration, is proposed and in vivo demonstrated for noncontact vital signs monitoring. The radar architecture exhibits a unique precision in tracking the phase modulation caused by human cardiopulmonary activity from which heartbeat and respiration can simultaneously be extracted. The single mixer architecture is immune to the null point and does not require small-angle approximation conditions, which distinguishes it from pre-existing other approaches. This enables the proposed radar to behave highly linear, with very precise detection of phase modulations induced by any kind of movement, independently from amplitude and speed. After simulations and technical tests to validate functionality and safety of the proposed architecture, a practical setup was demonstrated on human volunteers. Wavelet independent component analysis was applied to successfully retrieve respiratory and heart rate information from the radar baseband signal.