Tracking using 802.11
GPS is the ideal way to enable a mobile user where they are. But GPS has a number of limitations, It needs to see the sky to work. It is battery hungry and takes a significant amount of time to work out where it is when first turned on. There are ways to improve performance, but these take time and money.
Is there another way when you are just interested in getting rough location? Maybe. You see there are a huge number of 802.11 access points all over the place. In most cases, these access points will be installed, and stay where they are until they are replaced and thrown out. And these access points are constantly transmitting a unique serial number all the time saying that they are there.
Almost without exception, even secured access points transmit their MAC address even if they do not allow the general public to attach to the access point. So if it is possible to correlate the MAC address from Access Points to the GPS location of the access point then most of the problem will be solved.
It just so happens that AirSnort will accept GPS tracker information when mapping access points. The application logs to a database where the access point was heard. So then later on when a mobile station hears an access point, all they need to do is do a lookup of the MAC address and that will give an approximate location.
If more than one access point can be heard, statistical techniques can be used to work out a more accurate approximation for the current position.