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MIT turns Wi-Fi Into Indoor GPS

New tech from CSAIL lab lets one Wi-Fi device locate another to within centimeters

3 min read
MIT turns Wi-Fi Into Indoor GPS
Illustration: iStockphoto

Global Positioning System (GPS) satellite technology comes in handy for tracking cruise missiles, doing in-car navigation, and finding secluded restaurants. But step inside an airport, museum, or mall, and you’re often relegated to studying a paper map or asking for directions.

There are positioning systems designed for indoors, but they rely either on GPS-like radio or magnetic beacons, or on mapping the ever-shifting morass of Wi-Fi access points. Such methods have proved expensive to install and difficult to scale. What’s more, these indoor GPS systems are far from accurate enough to let you do cool things like a have a robot follow or avoid you.

Now researchers at MIT’s Computer Science and Artificial Intelligence lab (CSAIL) have developed a way for adjacent Wi-Fi devices, including smartphones, to locate each other within centimeters. The technology, called Chronos, relies on making the devices emulate multi-gigahertz wideband radios.

imgImage: MIT CSAIL

Chronos starts by having two Wi-Fi devices, a transmitter and receiver, hop simultaneously between all 35 frequency bands in the 2.4 gigahertz to 5.8 GHz Wi-Fi range. At each frequency, the rate at which signals accumulate phase naturally varies. The transmitter skips between bands every 2 to 3 microseconds, with the receiver comparing the phase differences at each step. Chronos can then calculate the time of flight of signals—and thus the distance—between the devices.

If one of the devices has multiple Wi-Fi antennas, as do most modern smartphones and laptops, Chronos can also calculate the angle between the two devices, and locate them in space. In experiments in everyday environments like an apartment or coffee shop, Chronos was able to localize devices to within 65 cm (or about 10 times the accuracy of GPS) using only off-the-shelf Wi-Fi cards.

The MIT researchers, PhD student Deepak Vasisht and Professor Dina Katabi, envisage Chronos being used to count people in smart homes for lighting control, to offer password-free Wi-Fi in cafés (while excluding freeloaders outside), and for robots to operate safely around humans.

“Because Wi-Fi is widely used and in every cellphone, it would be good to use this amazing technology for as many applications as we can,” Katabi told IEEE Spectrum.

There are some limitations, however. Although Chronos can run on existing Wi-Fi devices using just an app (or a firmware upgrade for an access point), each device has to undergo a one-time distance calibration. And because Chronos takes around one-tenth of a second to sweep all the Wi-Fi bands, its accuracy plunges if the devices are moving relative to one another during this initial setup.

So, do you have to place your cellphone on a counter—or on a table in the food court if you’re at the mall—so it’ll be perfectly still? “Walking is fine, but we’re not talking about somebody in a car,” says Katabi. “However for a drone, it’s actually better if it moves. Because its movement is controlled and you know the speed, you can leverage that information in a feedback loop to boost your results.”

Vasisht and Katabi tested Chronos on an AscTec Hummingbird quadcopter fitted with an Intel 5300 Wi-Fi card and a Go-Pro camera. The drone was set to stay 1.4 meters from a netbook, shooting photos of the computer as it moved. Chronos was able to keep the drone within just 4 cm of its programmed distance.

The next step for Vasisht and Katabi is to improve the resolution of Chronos even further, and to start building functions such as geo-fencing, which sets virtual boundaries. The researchers are in discussions with MIT about commercializing the technology. If all goes well, using your phone to find the way to your departure gate, with your robotic carry-on following close behind, could be just a few years away.

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The Cellular Industry’s Clash Over the Movement to Remake Networks

The wireless industry is divided on Open RAN’s goal to make network components interoperable

13 min read
Image of workers working on a cellular tower.
Photo: George Frey/AFP/Getty Images
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We've all been told that 5G wireless is going to deliver amazing capabilities and services.But it won't come cheap. When all is said and done, 5G will cost almost US $1 trillion to deploy over the next half decade. That enormous expense will be borne mostly by network operators, companies like AT&T, China Mobile, Deutsche Telekom, Vodafone, and dozens more around the world that provide cellular service to their customers. Facing such an immense cost, these operators asked a very reasonable question: How can we make this cheaper and more flexible?

Their answer: Make it possible to mix and match network components from different companies, with the goal of fostering more competition and driving down prices. At the same time, they sparked a schism within the industry over how wireless networks should be built. Their opponents—and sometimes begrudging partners—are the handful of telecom-equipment vendors capable of providing the hardware the network operators have been buying and deploying for years.

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