Smart Homes that Monitor Breathing and Heart Rate

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We introduce Vital Radio a new input device for tracking Vital Radio accurately tracks breathing patterns and heart. breathing and heartbeats without physical contact with the beats Over more than 200 two minute experiments our re. person s body Vital Radio works correctly in the presence sults show that. of multiple users in the environment and can track the vital Vital Radio can accurately track a person s breathing and. signs of the present users simultaneously Also Vital Radio heart rate without body contact even when the user is up. does not require the user to face the device or be aware of to 8 meters away from the device or behind a wall. its presence In fact the user can be sleeping watching TV Vital Radio s median accuracy for breathing is 99 3 er. typing on her laptop or checking her phone Furthermore ror of 0 09 breath minute and for heart rate is 98 5 0 95. Vital Radio can accurately track a user s breathing and heart beat minute when the person is 1 m away from the de. rate even if she is 8 meters away from the device or in a dif vice The accuracy decreases to 98 7 error of 0 15. ferent room breath minute and 98 3 1 1 beat minute when the per. Vital Radio works by using wireless signals to monitor the son is 8 m away from the device. minute movements due to inhaling exhaling and heartbeats In an area that spans 8 m 5 m Vital Radio can monitor the. Specifically it transmits a low power wireless signal and vital signs of up to three individuals with the same accuracy. measures the time it takes for the signal to reflect back to as for one person. the device The reflection time depends on the distance of the We also perform activity focused experiments to explore. reflector to the device and changes as the reflector moves Vital Radio s monitoring capabilities Specifically we. Fig 1 illustrates the impact of breathing on the signal s re demonstrate that Vital Radio can accurately measure users. flection time When the person inhales his chest expands breathing and heart rates while they are typing on their com. and moves forward reducing the reflection time In contrast puter or using their cell phones We also demonstrate that. when the person exhales his chest contracts moving away Vital Radio can track sharp changes in vital signs Specifi. from the device hence increasing the reflection time Gener cally we perform experiments where users are asked to exer. ally even when the person is not directly facing our device cise and show how Vital Radio accurately tracks the change. the wireless signal traverses his body and his vital signs cause in breathing and heart rates after exercising. periodic changes in the signal s reflection time Vital Radio. measures these changes and analyzes them to extract breath We believe Vital Radio takes a significant step toward en. ing and heartbeats abling smart homes that allow people to monitor their vital. signals and that its capabilities can have a significant impact. A key feature of Vital Radio is its ability to monitor the vital on our health awareness and our health care system. signs of multiple people and operate robustly without requir RELATED WORK. ing the users to lie still The main challenge in delivering this The desire for non contact monitoring of vital signs has oc. feature is that any motion in the environment can affect the cupied researchers since the late 70 s 29 Early work pre. wireless signal and hence interferes with tracking breathing sented a proof of concept that the wireless signal is affected. or heartbeats Past work addresses this challenge by requir by movements of the chest In these experiments the person. ing that only one person be present in front of the device and lies still on a bed and the sensor is placed only 3 cm away. that the person remains still In contrast Vital Radio recog from the apex of the heart The results are qualitative with no. nizes that one can address this problem by building on recent evaluation of accuracy. technologies that localize users using wireless signals 6. Specifically Vital Radio first localizes each user in the envi Subsequently military research explored the potential of. ronment then zooms in on the signal reflected from each user building radars that can detect human presence through walls. and analyzes variations in his reflection to extract his breath or under rubble by relying on the fact that breathing impacts. ing and heart rate By isolating a user s reflection Vital Radio wireless signals 42 47 26 45 Specifically because wire. also eliminates other sources of interference including noise less signals traverse obstacles they could be used to sense the. or extraneous motion in the environment which may other chest movements of a trapped victim through rubble or enable. wise mask the minute variations due to the user s vital signs SWAT teams to sense movement from behind an obstacle and. This enables Vital Radio to monitor multiple users breathing avoid being ambushed However since these systems target. and heart rates and to operate at distances up to 8 m from the the military they typically transmit at excessive power and. user or even from behind a wall use military reserved spectrum bands 47 45 which is not. feasible for consumer devices More importantly this line of. We built a real time prototype of Vital Radio and validated work generally focused on the detection of users by sensing. its capabilities by conducting experiments with 14 subjects motion due to their vital signs rather than estimating or mon. For baselines we use FDA approved breathing and heart rate itoring the vital signs themselves. monitors these include chest straps for monitoring the inhale. exhale motion and pulse oximeters placed on the subject s Recently the mounting interest in technologies for well being. finger to monitor their heart rate In our benchmark evalua has led researchers to investigate non contact methods for an. tion we ask the users to wear the baseline monitors while alyzing vital signs Current research on this topic can be di. Vital Radio monitors them remotely without any body con vided into two areas vision based techniques and wireless. tact We compare the output of Vital Radio with the ground systems Specifically advances in image processing allowed. truth from the FDA approved baselines demonstrating that researchers to amplify visual patterns in video feeds such as. color changes due to blood flow to detect breathing and heart. rate 8 44 however such video based techniques require the Bucket1 Bucket 2 Bucket 3 Bucket 4. user to face the camera and do not work when he she turns. around or is outside the camera s field of view Transmission. Similarly advances in wireless transmission systems and sig. nal processing have enabled researchers to detect and analyze. human vital signs Past proposals use one of the following. techniques Doppler radar 17 16 15 WiFi 34 27 or, ultra wideband radar 48 14 7 The key challenge in us Vital Radio. ing wireless signals to extract vital signs is that any motion in. the environment affects the signal Since breathing and heart. beats are minute movements they can be easily masked by. interference from any other source of movement in the envi Figure 2 Separating Reflectors into Different Buckets Vital. ronment Furthermore the presence of multiple users even Radio uses a radar technique called FMCW to separate the reflec. if none of them moves prevents these systems from operat tions arriving from objects into different buckets depending on the. distance between these objects and the device, ing correctly since the wireless signal will be affected by the. combination of their vital signs making it hard to disentangle laptop reading a newspaper or sleeping Vital Radio can use. the vital signs of each individual Past proposals deal with this all of these intervals to monitor a user s vital signs and track. problem by ensuring that there is only one source of motion how they vary throughout the day. in the environment namely the vital signs of the monitored. individual Hence their experimental setup has one person THEORY OF OPERATION. who typically lies still in close proximity to the device 17 Vital Radio transmits a low power wireless signal and mea. 16 15 34 27 48 14 7 4 sures the time it takes its signal to travel to the human body. and reflect back to its antennas Knowing that wireless sig. In contrast to these past systems Vital Radio has an intrin nals travel at the speed of light we can use the reflection time. sic mechanism that enables it to separate different sources to compute the distance from the device to the human body. of motion in the environment To do so Vital Radio builds This distance varies slightly and periodically as the user in. on state of the art wireless localization techniques 6 which hales and exhales and his heart beats Vital Radio captures. can identify the distance between the device and different these minute changes in distance and uses them to extract the. moving objects Vital Radio however uses these methods user s vital signs. to disentangle the incoming signals based on distance rather. than estimate the actual location This allows it to separate However natural environments have a large number of re. signals reflected off different bodies and body parts It then flectors such as walls and furniture as well as multiple users. analyzes their motion independently to estimate the breathing whose bodies all reflect the wireless signal To address these. and heart rate of potentially multiple individuals issues Vital Radio s operation consists of three steps. CONTEXT AND SCOPE 1 Isolate reflections from different users and eliminate reflec. We envision that Vital Radio can be deployed in a smart home tions off furniture and static objects. to monitor its inhabitants breathing and heart rates without 2 For each user identify the signal variations that are due to. body instrumentation The device can monitor multiple users breathing and heartbeats and separate them from variations. vital signs simultaneously even if some of them are occluded due to body or limb motion. from the device by a wall or a piece of furniture A single de 3 Analyze signal variations to extract breathing and heart. vice can monitor users vital signs at distances up to 8 meters rates. and hence may be used to cover a studio or a small apart In what follows we describe how these steps enable us to. ment One can cover a larger home by deploying multiple monitor users vital signs using Vital Radio. Vital Radio devices in the environment Step 1 Isolate Reflections from Different Users and Elim. Vital Radio s algorithms run continuously separating signals inate Reflections off Furniture and Walls. from different users then analyzing the signal from each user To understand the operation of Vital Radio let us consider. independently to measure his her vital signs However when the scenario in Fig 2 where the device is placed behind the. a user walks or performs a large body motion the chest mo wall of a room that has two humans and a table When Vital. tion is mainly impacted by the walk and no longer represen Radio transmits a wireless signal part of that signal reflects. tative of the breathing and heart rate 1 At home there are off the wall the other part traverses the wall reflects off the. typically sufficient intervals when a user is quasi static these humans and the table inside the room and then traverses the. include scenarios where the user is watching TV typing on a wall back to the device. 1 To isolate signals reflected off different objects Vital Radio. The vast majority of vital signs monitors including chest bands. that monitor breathing and pulse oximeters that monitor heart rate uses a radar technique called FMCW Frequency Modulated. cannot provide accurate estimates when the user walks or moves Carrier Waves We refer the reader to 6 for a detailed de. a major limb 35 28 11 To prevent such motion from causing. errors in its vital signs estimates Vital Radio automatically detects scription of how FMCW works A key property of FMCW. periods during which the user is quasi static and computes estimates that we exploit in this paper is that it enables separating the. only during such intervals reflections from different objects into buckets based on their. reflection times Since wireless signals travel at the speed of Heartbeats. light signals reflected off objects at different distances would 0 8. Phase in radians,fall into different buckets 0 6, However in contrast to past work on localization which uses 0 2. 0 95 1 1 05 1 1 1 15 1 2 1 25 1 3 1 35 1 4,Phase in radians. FMCW to sense the amount of power arriving from different Time in minutes. distances to localize the users Vital Radio uses the FMCW 0 5. technique as a filter i e it uses it to isolate the reflected sig 0. nals arriving from different distances in the environment into. different buckets before it proceeds to analyze the signals in 0 5. each of these buckets to extract the vital signs step 2 below 1. Our implementation of FMCW follows the system in 6 1 5. 0 0 2 0 4 0 6 0 8 1 1 2 1 4 1 6 1 8 2, where the resolution of FMCW buckets is about 8 cm This Time in minutes.
has two implications Figure 3 Phase variation due to vital signs The figure shows. Reflections from two objects that are separated by at least the variations in phase due to breathing and heartbeats where peaks. 8 cm would fall into different buckets Hence two users and valleys in the phase correspond to exhale and inhale motions. that are few feet apart would naturally fall into different respectively also zooming in on the signal allows us to observe the. Smart Homes that Monitor Breathing and Heart Rate Fadel Adib Hongzi Mao Zachary Kabelac Dina Katabi Robert C Miller Massachusetts Institute of Technology 32 Vassar Street Cambridge MA 02139 ffadel hongzi zek dk rcmg mit edu ABSTRACT The evolution of ubiquitous sensing technologies has led to intelligent environments that can monitor and react to our daily activities such as adapting our

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