# ‘No Wi-Fi beyond this point’: new tech could block access based on location

Imagine blocking your Wi-Fi network entirely from extending to anyone outside your home or business. This could provide a nice additional layer of security, and it’s becoming possible thanks to, among other things, the speed of light.

Chronos is a new system that allows a single Wi-Fi access point to physically locate connected users, meaning a router equipped with the system could block users just a few inches outside a cafe. (Nobody tell Starbucks about this, okay?)

A team led by professor Dina Katabi at the Massachusetts Institute of Technology (MIT) created the system, and then put it to the test. Experiments in a two-bedroom apartment show Chronos can figure out which room a resident is in 94 percent of the time. Another test, in a cafe, showed Chronos to be 97 percent accurate in determining whether someone was inside the store or not.

It’s always been possible for some Wi-Fi networks to track users — if a network uses three or more access points, that will be enough for triangulation. So how does Chronos work with only one access point? In part by calculating the “time-of-flight,” or the time it takes for data to make it from the router to a phone or laptop, with extreme accuracy. The team discovered a way to calculate time-of-flight with an average error of only 0.47 nanoseconds (a nanosecond is one billionth of a second, so yeah: that’s pretty accurate). Multiply that time-of-flight speed by the speed of light and you’ve got a precise idea of how far away the user is, within a couple of decimeters.

“Knowing both the distance and the angle allows you to compute the user’s position using just one access point,” said PhD candidate Deepak Vasish. “This is encouraging news for the many small businesses and consumers that don’t have the luxury of owning several access points.”

Combine this with an accurate calculation of the angle and you’ve got a pretty precise location.

So what could this be used for? Stopping people from outside a coffee shop from leaching the Wi-Fi, for one thing, but also to enable drones to stay away from smartphone-carrying humans.

“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 Wi-Fi in robotics, home automation and more,” said Vasish. “Designing a system that enables one Wi-Fi node to locate another is an important step for wireless technology.”

It’s a fascinating piece of tech that could come to a router near you. Go ahead and read MIT’s summary of the research if you want to learn more.

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