"Catching a Breath – Wirelessly" is Catching On

Breathing signal strength
Research news from the SPAN lab, featured in a news release titled Catching a Breath – Wirelessly, has been written up on tech news sites such as Engadget, Popular Science, CNET, InformationWeek, PC World, New Scientist, LifeHacker, and Gizmodo. The news story has also been picked up by international press, by the Russian Compulenta, the German Pressetext, and the Hungarian HWSW. SPAN researchers have shown that standard wireless devices deployed around a person can be used to reliably detect breathing and accurately estimate the rate at which the person is breathing, and have submitted the research results for publication. While specialized RF devices have been proposed which can also detect and monitor breathing, the new research shows that a standard wireless network can be used for this purpose. A technical report, titled Monitoring Breathing via Signal Strength in Wireless Networks is under submission to the IEEE Transactions on Mobile Computing and is posted on arXiv.org.

To address some of the questions and misleading statements made in some press articles, here are some frequently asked questions and answers:

Q: Is it true that someone could spy on me using my WiFi router?

A: It is possible, but with current technology, not very likely. We showed that a single link, even with the wireless devices right next to a person's body, has only a small (<5%) chance of being able to detect the person's breathing. For someone to reliably detect your breathing, they would need many wireless devices, more than just your wireless router. We used 20 wireless devices.

Q: How accurate were the breathing rate estimates?

A: In tests using thirty seconds of data, we were able to estimate the true breathing rate within 0.3 breaths per minute. This is the root-mean-squared (RMS) error. The breathing rates we tested were 12.0, 15.0, and 19.0 breaths per minute.

Q: Is it true that you can measure lung capacity or volume of air exhaled?

A: Not with our technology. We can't estimate the change in size of the person's chest when they inhale or exhale. In fact, we can't measure that they've exhaled any air -- in obstructive apnea, some people move their chest up and down while no air is exhaled or inhaled.

Q: Is it true that you can measure heart rate?

A: Absolutely not. Some articles on the web have inexplicably replaced "breathing rate" with "heart rate". Your pulse does not cause enough change to be noticed by our system. However, some radar devices have been shown to be able to measure heart rate -- see the paper: N. Rivera, S. Venkatesh, C. Anderson, and R. Buehrer, Multi-target estimation of heart and respiration rates using ultra wide-band sensors, in Proc. of the 14th European Signal Processing Conference, 2006.

Q: Would these radio waves interfere with medical equipment in a hospital?

A: Other wireless devices that send signals at 2.4 GHz are already used in hospitals. In fact, devices that transmit Zigbee signals (the devices we used) are already used in hospitals to help keep track of critical medical equipment. Because our devices transmit very little information, and relatively infrequently, they can interoperate with other wireless devices that operate on the same band.

Q: Does the patient risk getting cancer from the radio waves?

A: We refer to the National Cancer Institute website for information summarizing the many, many studies of human exposure to radio waves. Further, these devices, in use in a future product, would probably be set to transmit 10,000 times less power than your laptop or cell phone transmits. Thus any exposure to the patient from these devices would be insignificant to the exposure already incurred from other wireless devices.