Wi-Fi Powers Metro Positioning System

By Eric Griffith

June 20, 2005

A Boston startup is indexing every access point it can find in 25 big U.S. cities to turn 802.11 signals into a tool to handle global positioning.

Positioning systems in the outdoors are usually powered by satellites, or at least cellular towers. Skyhook Wireless of Boston  (formerly Quarterscope when they first announced this tech) hopes to change that by putting 802.11 access points to work in tracking. Simply put, any Wi-Fi device using the service could pinpoint its own location exactly based on where it is in relation to the APs.

"There are so many access points in metropolitan areas that the signals overlap," says Skyhook founder and CEO Ted Morgan. "You can't find a place across such areas where you aren't covered when you factor in not just public access wireless LANs, but also the private kind, both corporate and at home.

"We take advantage of that by physically scanning every street in the top 25 metropolitan areas, building a reference database of all the access points in an area—that's 50,000 to 80,000 to cover that area—and use them as reference points for location tracking," says Morgan.

The system, which Skyhook calls Wi-Fi Positioning System (WPS), is being developed for others vendors to build into future products and services. WPS won't require any additional hardware to turn Wi-Fi devices into a 802.11-based GPS. It will work just as well indoors as out—the denser the number of APs, the better.

"We don't connect, we just get the identifier and compare," says Morgan. WPS  installed on a device will track the scan requests made to all APs in range. The MAC address ID number for each base station in range is returned, and checked against the WPS database. The comparison will tell the Wi-Fi device where it is in relation to the APs.

The company compares itself to location providers like Newbury Networks and Ekahau as only the most distant of cousins. Where those vendors create a controlled network for location and positioning, Skyhook is planning for entire urban areas to be the environment of choice.

Skyhook is planning to do a baseline scan—essentially a city-wide site survey—in its top markets every year to keep track of the inevitable changes as people and companies move and change equipment. In-between, the WPS software on client systems, will help manage some of the AP data. Comparison of the existing database to the scans made by devices can be uploaded occasionally so Skyhook can see where things are different.

"It's healing and maintaining [the database] during use," says Morgan.

The database of AP locations can be stored locally so it can still do location tracking even if the WPS device isn't online. The company is using a proprietary compression scheme to get its list of  1.5 million APs down to a manageable 7MB in size. Users can synchronize with Skyhook every month or so to get a refreshed listing.

The focus for now is on Wi-Fi because of the sheer number of existing APs, and there are more and more sold each month. Morgan says the amount of APs make 802.11 the most accurate technology for trying this, but says that WiMax and other wireless broadband technologies like EV-DO could work essentially the same way in the future. Right now, the AP list is only 802.11b/g. Skyhook isn't checking for 11a APs as yet, either.

The uses Morgan sees for WPS go far beyond individuals using it for finding ATM machines and the like. He hopes WPS will be key in enhanced 911 (e911) that is getting a lot of press now, especially as Wi-Fi phones become more and more prevalent. Shipping fleets doing asset tracking in dense urban areas that can lose satellite signals could use WPS as backup, switching back and forth between GPS and WPS.

"A lot of the indoor Wi-Fi tracking companies like Pango and Ekahau have ID tags," says Morgan. "Why put up another network [to track them]? Now I can track a truck in a warehouse and then across the country."

WPS is currently running on Windows XP and Windows Mobile products, and will move soon to Palm devices. Morgan says the goal is to be "embedded in as many devices as possible, to get companies like Google and Yahoo! to build it into their toolbars." He envisions a time when users will go to Google Maps and see not just satellite photos, but an image of where they are on that map.

The first customer of WPS is CyberAngels of Nashville, which provides notebook computer recovery systems (essentially a "LoJack" for laptops). In the past the company has relied on hidden software that the crooks didn't know about which would send out a signal if the laptop was online. CyberAngels would then get and IP address with which it would get a subpoena, and then go to the cops—an inexact science at best. With WPS, Morgan says they "can say the exact latitude and longitude at this very second."



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