Wi-Fi Networks Know Where You Are

By Roland Piquepaille

It's a well-known fact that GPS devices perform better in rural areas than in urban ones, especially because their signals bounce upon buildings. This is not the case with Wi-Fi networks. So why not applying the concept of triangulation, central to GPS localization, to Wi-Fi? In "One more way to find yourself," the Boston Globe tells us the story of a start-up company, Skyhook Wireless, which is using Wi-Fi networks to provide location-based services (LBS). When you're walking or driving, your laptop or PDA can get the ID number of several Wi-Fi access points stored in Skyhook Wireless database, even if the signal is not strong enough to provide a connection. With these IDs, the company will plot a map of where you are. Neat idea, but will it work if people move from an area to another one, taking away their access points with them? Read more...

Let's start with a diagram comparing the relative performances of the GPS and Wi-Fi signals depending on the area where you are. (Credit: Skyhook Wireless)

Here is a general description of the idea behind the Skyhook Wireless concept.

Their idea: map all of the known WiFi networks in a metropolitan area, then create software that would calculate a user's location based on the WiFi networks his laptop (or any other WiFi-fluent device, like a PocketPC) could "see" at a given moment. [...] The more networks it can see simultaneously, the more accurate the locational fix. "If you can tune in to five to 10 access points, you can figure your accuracy within 20 to 30 meters," Morgan says one of the founders.

In a city such as Boston and its suburbs,the company already has identified more than 50,000 Wi-Fi networks, which should be enough to find several access points near your location.

Here is how the system works.

A user of Skyhook's software doesn't actually need to log on to any of the WiFi networks to figure her position, and some of the networks may well be password-protected. But every WiFi base station will send out an ID number when hit with a blast of radio-frequency energy from the WiFi card inside a laptop or hand-held computer. And even if the signal is too weak for a laptop to connect to, it can still get the ID, which it then compares to Skyhook's database and plots on a map.

Below is an illustration showing how the client part of the Skyhook Wireless system works. (Credit: Skyhook Wireless)

Here is how the company summarizes how the client part works: "Wireless device receives signals from Wi-Fi sites in range; Skyhook software compares these signals to its database of geographically known locations; and location data is used to direct safety services, provide driving directions and local information, etc."

You'll find larger images of these illustrations in the technology pages of Skyhook Wireless.

This new approach is certainly promising, but the company will need to constantly monitor the Wi-Fi networks to check for new ones or others which move from one location to another.

Anyway, I bet that we'll see a mix of several technologies to guide us: GPS devices, cellphones triangulation, and LGS based on Wi-Fi networks.

Sources: Scott Kirsner, for the Boston Globe, May 23, 2005; and Skyhook Wireless website

Related stories can be found in the following categories.

• Networking
  
• Privacy
  
• Security
  
• Wireless