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Tuesday, July 23, 2013

Hybrid location technologies: indoor/outdoor GPS/WiFi

As continued from our previous report: Smart phones commonly support Wi-Fi to connect to the Internet, a feature encouraged by network operators to offload the large amounts of cellular data a standard smart phone generates. In addition, the properties of the Wi-Fi technology can be exploited for location positioning, or combined with an existing GPS tracking system it can be used as a hybrid positioning system.

There are many different proprietary implementations of Wi-Fi positioning, including fingerprinting techniques, which take advantage of environments with high Wi-Fi access point (AP) density such as cities and buildings.

First, the device scans and sends information about the visible Wi-Fi APs—generally the strongest APs are rated in terms of received signal. Second, this information is reported to a server on the network. The server houses a database of APs associated with geo tags and other markers. A fingerprinting algorithm is applied to the input from the handset, which then provides an estimate of the mobile’s position.

The information doesn’t always have to be provided to the network. Instead, the network may provide a subset of its central database to the handset, which then can run the fingerprinting algorithm itself. The fingerprinting algorithm can only work if a sufficiently advanced central database of Wi-Fi APs for the location of interest is available. This database is created by:

  • Wardriving: Driving (or walking) in specific areas and using high-grade receivers to collect visible Wi-Fi AP data.
  • Crowd sourcing: Having a smart phone constantly report observed Wi-Fi APs along with a GPS location (if available) to location servers

In some cases the handsets are used to augment the database of Wi-Fi reference points; reporting or augmenting the position data for the device or handset that is mobile - while also 'wardriving' - reporting mobile position data and AP updates at the same time.  When done with the users knowlege, this can be helpful - but when done as 'secret' tracking then this can be potentially injurious to the user.