driving the ultra-mobile enterprise

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.

Assembled into a database of billions of signal data points, Skyhook’s software can take an arbitrary snapshot, find the associated access points, and perform a variety of proprietary calculations to determine an approximate location.

The company’s system takes in account that access points can move (it happens a lot), and associates additional data: every snapshot that’s sent to Skyhook’s servers for a lookup is also used to correct and supplement data they collect by driving.

GPS technology has been improved enormously in the last few years, with the time to acquire a location fix reduced from anywhere from 1 to 13 minutes down to from under a second to 35 seconds. But GPS still needs help or can’t function in typical urban environments in which tall buildings and lots of reflection prevent a quick, error-free lock-on to the 3 to 4 satellites signals required.

WiFi positioning can be used instead of GPS; to enhance GPS by providing a fast fix which is then updated with GPS-based coordinates when they’re available; or a hybrid approach in which GPS, WiFi, and cellular tower data are combined for more precision.

Skyhook’s WiFi positioning system was built into the iPhone 2.0 software, and is the only method the iPod touch has to find a location. A few laptop-recovery services have partnered with Skyhook, and the company has platform partnerships with three of the largest GPS chipmakers: Broadcom, Qualcomm, and SiRF.

As smartphones increasingly include WiFi as a basic feature, and as standalone GPS devices are more likely to require traffic and other updates that necessitate including WiFi, using WiFi as a position supplement or enhancement becomes ever more feasible.

Skyhook isn’t alone. Navizon offers a grassroots WiFi positioning system that relies on lightly rewarded volunteers gathering GPS-accurate location data. And Google recently said that they have their own WiFi location data, not from Skyhook, although the company won’t disclose its practices or data sources.

WiFi isn’t just for connections any more. Instead, it’s become part of the street signage of the wireless age. If you find yourself at the corner of “Free the Net” Blvd. and “linksys” Ave., take a right at the next intersection.