What is the best place to sleep good night? Body Compass shows the way

MIT researchers use reflected wireless signals from a small device mounted on the wall of the bedroom to monitor a person’s sleeping posture (whether back, abdomen, or side) wirelessly privately. Developed the method.

The device, called the body compass, is the first wireless-based home wireless system to provide accurate sleep data without the need for a camera or sensor attached to the body, according to Shichao Yue, who will introduce the system at a presentation at UbiComp 2020. is. Meeting on September 15th. PhD students have been studying sleep stages and insomnia for several years using wireless sensing.

“I thought sleep posture was another high-impact application of the system,” said Yue, who worked on the project under the supervision of Professor Dina Katabi of the Computer Science and Artificial Intelligence Laboratory at MIT. .. Studies have shown that gastric sleep increases the risk of sudden death in people with epilepsy, and sleep postures deprive the patient of the ability to turn over in bed, so to measure the progression of Parkinson’s disease. Can also be used.

In the future, BodyCompass may be used to track your sleep habits and monitor your baby’s sleep, saying, “It could be either a medical device or a consumer product, depending on your needs. There is sex “

Other authors of conference papers published in ACM Minutes on Interactive, Mobile, Wearable and Ubiquitous TechnologyIncludes graduate students Yuzhe Yang and Hao Wang, and Hariharan Rahul, an affiliate of Katabi Lab. Katabi is a professor of electrical engineering and computer science at MIT, Andrew and Erna Viterbi.

Peaceful reflection

BodyCompass works by analyzing the reflection of radio signals reflected by objects in a room, including the human body. Similar to a Wi-Fi router mounted on the wall of a bedroom, the device sends and collects these signals and returns them via multiple paths. Researchers then map the paths of these signals and work backwards from the reflexes to determine body posture.

However, for this to work, we needed a way to understand which signals were bouncing off the sleepers and not from mattresses, nightstands, and overhead fans. Yue and his colleagues realized that their past work of decoding breathing patterns from radio signals could solve the problem.

They conclude that the signals that bounce off a person’s chest and abdomen are uniquely modulated by breathing. When the breathing signal is identified as a way to “tag” reflexes from the body, researchers analyze those reflexes against the position of the device to determine how a person lay in bed. I can do it. (For example, when a person is lying on his back, strong radio waves bouncing off his chest are directed at the ceiling and towards the device on the wall.) “By identifying the coding as breathing, the signal from the body can be separated. Environmental reflexes allow us to track where beneficial reflexes are, “says Yue.

The reflexes from the body are analyzed by a customized neural network to estimate the angle of the body during sleep. The neural network defines the sleep posture according to the angle, so the device can distinguish between a sleeper lying to the right and a sleeper leaning slightly to the right. This kind of fine-grained analysis is especially important for epilepsy patients whose prone position sleep correlates with sudden and unexpected death, Yue said.

BodyCompass has several advantages over other methods of monitoring sleep posture, such as installing a camera in a person’s bedroom or attaching a sensor directly to a person or bed. Yue said the sensors can be uncomfortable to sleep with, and the camera reduces a person’s privacy. “It is almost impossible for users to infer other activities from this data, as it only records important information to detect sleeping posture, such as the breathing signal of a sleeping person.”

Accurate compass

The research team tested the Body Compass accuracy of over 200 hours of sleep data from 26 healthy people sleeping in their bedrooms. At the beginning of the study, subjects taped two accelerometers (sensors that detect movement) to the chest and stomach and trained the device’s neural network with “ground truth” data about sleep posture.

BodyCompass was most accurate when the device was trained based on a week’s worth of data-94% of the time it predicted the correct body posture. One night’s training data gave accurate results in 87% of the time. BodyCompass was able to collect only 16 minutes of data and achieve 84% accuracy when the sleeper was required to take some normal sleeping postures in front of the wireless sensor.

In addition to epilepsy and Parkinson’s disease, BodyCompass may help treat patients who are vulnerable to bedridden or sleep apnea. This is because both conditions can be alleviated by changes in sleep posture. Yue is also interested in himself: he suffers from migraines that appear to be influenced by the way he sleeps. “The next day, I sleep on the right side to avoid headaches, but I’m not sure if there is a real correlation between sleeping posture and migraines. This may help to find out if there is any relationship. May. “

For now, BodyCompass is a monitoring tool, but one day it can be combined with alerts that warn sleepers to change their posture. “Researchers are working on mattresses that allow patients to rotate slowly to avoid dangerous sleeping postures,” says Yue. “In future work, sleep posture detectors and such mattresses can be combined to move epilepsy patients to a safer position, if desired.”

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