It’s an experience everyone can relate with—eagerly trying to locate a WiFi signal. But will it not be a relief if, instead, the WiFi could locate us?
A research team led by Prof. Dina Katabi developed a system called Chronos, which enables a single WiFi access point to locate users to within tens of centimeters, without external sensors.
The new wireless technology could mean safer drones, smarter homes, and password-free WiFi to users. The system was demonstrated in an apartment and a cafe, while also presenting a drone that maintains a safe distance from its user with a margin of error of about four centimeters.
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“From developing drones that are safer for people to be around to tracking where family members are in your house, Chronos could open up new avenues for using WiFi in robotics, home automation, and more. Designing a system that enables one WiFi node to locate another is an important step for wireless technology,” says Deepak Vasisht, a PhD student who is a member of the team.
The device locates users by calculating the time-of-flight that is required for data to travel from the user to an access point. The system is 20 times more accurate than existing systems, computing time-of-flight with an average error of 0.47 nanoseconds or less than one-billionth of a second.
How It Works
At the moment, the system requires four or five WiFi access points. It is so because today’s WiFi devices don’t have enough bandwidth to measure time-of-flight, and so locating someone’s position will require triangulating multiple angles relative to the person.
This is where Chronos beats the localized system. It has the ability to calculate not just the angle but the actual distance from a user to an access point, as determined by multiplying the time-of-flight by the speed of light.
“Knowing both the distance and the angle allows you to compute the user’s position using just one access point,” says Vasisht. “This is encouraging news for the many small businesses and consumers that don’t have the luxury of owning several access points.”
Since WiFi allows users to hop on different frequency channels, the team programmed the system to jump from channel to channel, gathering many different measurements of the distance between access points and the user. Then Chronos automatically “stitches” together these measurements to determine the distance.
“By devising a method to rapidly hop across these channels that span almost one gigahertz of bandwidth, Chronos can measure time-of-flight with sub-nanosecond accuracy, emulating with commercial WiFi what has previously needed an expensive ultra-wideband radio,” says Venkat Padmanabhan, a principal researcher at Microsoft Research India. “This is an impressive breakthrough and promises to be a key enabler for applications such as high-accuracy indoor localization.”
It was thereafter hypothesized that the success of Chronos is an indication that WiFi-based positioning could help for other situations where there are limited or inaccessible sensors, like finding lost devices or controlling large fleets of drones.
“Imagine having a system like this at home that can continuously adapt the heating and cooling depending on number of people in the home and where they are” says Katabi. “Eliminating the need for cooperation between WiFi routers opens up many exciting new applications for localization.”