Wital: A COTS WiFi Devices Based Vital Signs Monitoring System Using
NLOS Sensing Model
Abstract
Vital sign (breathing and heartbeat) monitoring is essential for patient
care and sleep disease prevention. Most current solutions are based on
wearable sensors or cameras; however, the former could affect sleep
quality, while the latter often present privacy concerns. To address
these shortcomings, we propose Wital, a contactless vital sign
monitoring system based on low-cost and widespread commercial
off-the-shelf (COTS) Wi-Fi devices. There are two challenges that need
to be overcome. First, the torso deformations caused by
breathing/heartbeats are weak. How can such deformations be effectively
captured? Second, movements such as turning over affect the accuracy of
vital sign monitoring. How can such detrimental effects be avoided? For
the former, we propose a non-line-of-sight (NLOS) sensing model for
modeling the relationship between the energy ratio of line-of-sight
(LOS) to NLOS signals and the vital sign monitoring capability using
Ricean K theory and use this model to guide the system construction to
better capture the deformations caused by breathing/heartbeats. For the
latter, we propose a motion segmentation method based on motion
regularity detection that accurately distinguishes respiration from
other motions, and we remove periods that include movements such as
turning over to eliminate detrimental effects. We have implemented and
validated Wital on low-cost COTS devices. The experimental results
demonstrate the effectiveness of Wital in monitoring vital signs.