Global Positioning System Location Determination

The Global Positioning System (GPS) method of locating a wireless caller is just one of several that may be selected by wireless carriers to meet Phase II requirements by October, 2001. The Time Difference of Arrival, Angle of Arrival and location pattern matching methods are additional methods being considered. There are also hybrid location methods that use both TDOA and AOA technology. The TDOA, AOA and location pattern matching methods are network based, while the GPS method is handset based.

Using this technique:

• A wireless subscriber must use a handset specially equipped with GPS circuitry to make a 911 call. Either continuously or when a 911 call is placed, the GPS electronics determine the phone's latitude and longitude using data received from the satellites. Several companies, including SnapTrack and SiRF, offer additional electronics to increase the accuracy and reliability of the GPS fix.
• When the caller dials 911, the voice call and latitude and longitude data are sent to the wireless phone antennas.
• The antennas forward the voice and latitude and longitude data to the carrier's switch.
• The switch forwards the voice call and the latitude and longitude to the PSAP for use by the dispatcher, where it's displayed on a map.

Also check this Web page or this page for an explanation of general GPS technology.

Wireless 911 page