Enabling Robust Radar-Based Localization and Vital Signs Monitoring in Multipath Propagation Environments

Abstract

Over the last two decades, radarbased 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.

Hallway Gait Monitoring Using Novel Radar Signal Processing and Unsupervised Learning

“…solutions for naturalistic settings (e.g., individual's homes, long-term care, and hospitals). One of the main challenges in such environments is the existence of stationary objects (i.e., clutter), creating multipath or ghosting effects [1]. Multipath occurs when a signal takes two or more paths from the transmitting antenna to the receiving antenna.…”

“…Multipath occurs when a signal takes two or more paths from the transmitting antenna to the receiving antenna. The number and particular behaviour of the multiple paths depends on the room structure and the presence of objects [1]. The multipath issue is more significant when people walk in the space since moving even a small object in an environment causes changes in multipath reflections [1].…”

Noncontact Respiratory Measurement for Multiple People at Arbitrary Locations Using Array Radar and Respiratory-Space Clustering

“…In real life situations, however, the effect of multipath propagation must be taken into account. Some studies reported radar-based physiological measurement techniques that work even in a multipath-rich environment [43]- [46]. It is important to improve the accuracy of the proposed method when it is applied to measurement data recorded in a multipath-rich environment.…”

Automatic radar-based 2-D localization exploiting vital signs signatures

“…This because, current approaches aim at directly extracting the Doppler signals from the received radar signals which are the overall results of the sums of reflections due to direct paths (desired information), multipath, and static reflectors (i.e., clutter, furniture, objects, etc), whose Doppler (phase) information combines non-linearly. In this condition, the radar may: (1) fail to determine the right number of subjects in the room; (2) erroneously conclude people being located elsewhere than the actual location; (3) detect a non-existing person (i.e., a radar ghost) or even represent a life-less object as alive (hence, static objects cannot be simply treated as stationary); (4) assign disturbed signals to an individual 42 .…”