Wi-Fi used as in-town GPS

By John Cox
Network World, 06/20/05

A new service uses wireless LANs to act as a GPS-style location finder.

Skyhook Wireless has produced software that uses the signals being radiated by access points to discover the longitude and latitude of someone's position, accurate within 90 feet. This data can feed any number of applications: maps, routing and scheduling, fleet tracking, searching and advertising.

The idea, Skyhook executives say, is to create a GPS that relies on the growing number of 802.11 access points, instead of satellites.

The software is the brainchild of Kaveh Pahlavan. Skyhook's chief technical adviser, and a professor who specialises in computer networks and geolocation at Worcester Polytechnic Institute. "GPS signals perform very poorly in congested areas," says Ted Morgan, Skyhook's president and co-founder. GPS devices need a line of sight to the satellite, which can be blocked by a city's tall buildings. Once you enter a building, the signal is cutoff. Secondly, Morgan says, the radio phenomenon, called multi-path, bounces off buildings, vehicles and other objects, which results in many signals hitting the receiving antenna on a headset. Morgan says the handset can't sort out which signals to use to create the most precise location.

By contrast, Skyhook measures radio signal strength, whereas no line of sight is needed. There are two parts to Skyhook's setup. One is the client code, with proprietary algorithms that evaluate the signal strength from any WLAN access points within range.

Because the software, working with the client adapter, is listening but not connecting, it can pick up signals from almost 1,000 feet away, according to company executives. The software also captures the unique media access control address that each access point broadcasts.

The second part is a database of every access point in a given area. "We drove around and physically scanned every street within the Route 128 area" in metropolitan Boston," Morgan says. "We collected information on about 70,000 access points." Morgan says the company has so far done this road-by-road radio scan in the top 20 metro areas in the US, and will have the top 100 areas completed by year-end.

These access-point locations are packed into a database, which can be downloaded to any Windows or Windows Mobile client device, or accessed by the client, via a Web link, on servers maintained by Skyhook. The database is being ported to PalmOS this summer.

A user's device gathers the signal data from any surrounding access points, compares them with the database, and creates a latitude and longitude. Those figures can be called up by any software application that is programmed to call a GPS system for the same data, according to Morgan.

As the client software interacts with the database, new access points are identified, and those that have moved can be relocated. As a result the database is being continuously updated, Morgan says.

Skyhook is as an OEM supplier, licensing its software to other vendors, such as CyberAngel, which incorporates it into its own products. CyberAngel's software is loaded on laptops. If a laptop is stolen and then makes a network connection, the software transmits a secret message to the CyberAngel network operations center. There, staff collect data, such as the originating phone number and the IP address, and pass this information to local, state or federal police.

The Skyhook software currently covers 20 US cities, from Boston to San Francisco. Pricing varies with the type of application and the number of users.

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