GPS receivers look to the sky to plot their precise point on the globe at a precise point in time. But if you can’t see the sky, what good does have nearly three dozen satellites orbiting the earth do you?
That’s where WiFi positioning comes in. While not a new technology, a series of high-profile adoptions of WiFi positioning as a supplement to or alternative to GPS made 2008 the year that a device finding itself via WiFi network signals became as mainstream as GPS in a cellphone did just a couple years ago.
WiFi isn’t a precise technology, and it’s deployed on an ad-hoc basis: People, companies, government bodies, and institutions install WiFi gateways as they see fit, using unlicensed spectrum—which means no regulatory permission is required in advance to use certified devices.
WiFi positioning uses a property of WiFi networks to establish location. Nearly all WiFi networks are configured so that the access points that comprise them send out a frequent beacon, a message that allows WiFi network adapters to learn the name and unique adapter address of a base station. (Access points set to “closed” or “hidden” turn off the beacon.
Even though you only see the network name, even when the network has 3,000 unique access points, each of those access points’ unique BSSID (basic service set identifier) is broadcast. (The BSSID is equivalent to an Ethernet adapter’s Media Access Control or MAC address, using the same format.)
Skyhook Wireless was the first to take advantage of this characteristic. Starting years ago, the company began having drivers pass up and down every street in larger cities in the U.S. with a kit on board that recorded GPS coordinates and associated them with snapshots of the name, BSSID, and signal strength of each access point its WiFi radio could pick up. Read More »
