Wi-fi trick for Indoor Location Fixes accurate to 40 centimeters

The Wi-Fi equipment serving offices, airports, and other large buildings could be easily upgraded to allow mobile devices to get indoor location fixes to an accuracy of less than half a meter, Stanford researchers have shown. The technology, dubbed SpotFi, could lead to GPS-style maps for indoor spaces.

The new technique requires multiple Wi-Fi access points to get a location fix.

They are working on a variant of their technique that a device could use to get a rougher sense of its location from a single access point. That might help a drone being controlled by a smartphone, for example, he says. The Stanford group is also thinking about how to commercialize SpotFi for use in workplaces or other buildings with multiple Wi-Fi access points like malls and airports.

Indoor location technology based on Wi-Fi is already on the market. But the most accurate requires specialized hardware and is not widely deployed. Another method that works using existing Wi-Fi equipment can typically locate a device only to within a few meters or sometimes even less accurately, says Sachin Katti, an assistant professor at Stanford University whose research group developed SpotFi.

“We can use off-the-shelf, already deployed Wi-Fi infrastructure but get accuracy comparable to state-of-the-art systems that require specialized equipment or modifications,” says Katti. In tests, a Wi-Fi device could locate itself with a median accuracy of 40 centimeters (16 inches).

SpotFi: Decimeter Level Localization Using WiFi by Manikanta Kotaru, Kiran Joshi, Dinesh Bharadia, Sachin Katti of Stanford

SpotFi makes two key technical contributions. First, SpotFi incorporates super-resolution algorithms that can accurately compute the angle of arrival (AoA) of multipath components even when the access point (AP) has only three antennas. Second, it incorporates novel filtering and estimation techniques to identify AoA of direct path between the localization target and AP by assigning values for each path depending on how likely the particular path is the direct path. Our experiments in a multipath rich indoor environment show that SpotFi achieves a median accuracy of 40 cm and is robust to indoor hindrances such as obstacles and multipath


* should be able to localize any target device that has a commodity WiFi chip and nothing else. They should not require the target to have any other hardware, be it sensors such as accelerometers, gyroscopes, barometers, cameras, etc., or radios such as UWB, ultra-sound, Bluetooth LE, etc.

* should be accurate, ideally as accurate as the best known localization systems that use wireless signals (even including those that do not satisfy the above two requirements). To the best of our knowledge, the most accurate such localization systems are ArrayTrack [1]
and Ubicarse [2] and these systems achieve an accuracy ranging from 30–50 cm in office environments. Achieving such accuracy would be the target.