Wi-Fi that finds you

MIT's Chronos system has been shown to correctly distinguish individuals in a room or outside a store up to 97 percent of the time

There's a lot of buzz around "smart home" products and the convenience of advanced automation and mobile connectivity. However, new research may soon be able to add extra emphasis on "smart" by enhancing wireless technology with greater awareness. A team at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) has developed a system that enables a single wireless access point to accurately locate users down to a tenth of a meter, without any added sensors.

Wireless networks are good at quickly identifying devices that come within range. Once you link several access points together, it becomes possible to zero in on someone's position by triangulation. But this new wireless technology – dubbed "Chronos" – is capable of 20 times the accuracy of existing localization methods. Through experiments led by Professor Dina Katabi, Chronos has been shown to correctly distinguish individuals inside a store from those outside up to 97 percent of the time, which would make it easier for free Wi-Fi in coffee shops to be a customer-only affair, for example.

Chronos is able to achieve such accuracy by resolving the actual distance from a user to an access point – data's "time-of-flight" is multiplied by the speed of light. When computed with the angle, positions can be determined to the centimeter. By designing Chronos to quickly hop across different frequency channels, take measurements, and then "stitch" together the results, the team has enhanced commercial Wi-Fi with a high-level accuracy normally limited to expensive ultra-wideband radio.

The system had to be programmed to account for additional delays in the process. A Wi-Fi encoding method helps to distinguish packets of data from actual time-of-flight, and acknowledgements from data packets are used to cancel out "phase offsets" generated by all the band-hopping. The researchers also developed an algorithm to address bouncing signals and the separate delays experienced by each copy.

With Wi-Fi that can pinpoint other wireless devices, we can envision a future where drones maintain a safe distance from people or other drones, misplaced wireless devices may be recovered more efficiently, homes could identify individuals within and adapt heating and/or lighting accordingly, and wireless access can be extended exclusively to select rooms or living areas.

A paper on the research was recently presented at the USENIX Symposium on Networked Systems Design and Implementation (NSDI '16).

The video below shows a live demonstration of the Chronos system.

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