Vehicle locating system utilizing global positioning

DETAILED DESCRIPTION OF THE INVENTION FIG.
1 is a diagram of a prior art vehicle location system 100 which utilized a plurality of stationary location towers, herein after referred to as tracking stations 104, which provide tracking coverage for a predetermined geographic area 102.
The predetermined geographic area 102 can represent a city; small, medium, or large metropolitan area, county, an so forth.
A transceiver beacon, herein after referred to as beacon 108, is installed in vehicles to be protected, such as an automobile as shown.
The beacon 108 provides a radio frequency (RF) output of typically 4 watts which is used to track and locate a stolen vehicle when activated.
When a vehicle is stolen, the beacon 108 could be activated autonomously by a vehicle alarm, or by an beacon activation signal 110 that is sent from a central tracking station, hereinafter referred to as a tracking control station 106, once the owner of the vehicle reports the theft.
As shown in FIG.
1, the tracking stations 104 were typically deployed along the perimeter of and within the predetermined geographic area 102 within which vehicle location service was provided.
Each of the tracking stations 104 typically employed a circular array of half-wave dipole antennas that were used to determine the angle of arrival of the beacon signals 112 radiating from the stolen vehicle.
It will be appreciated that the resolution of such a tracking system was dependent upon the number of quadrants into which the circular array of antennas was divided.
To pinpoint the location of a stolen vehicle, the prior art vehicle location system 100 needed at least two of the tracking stations 104 to have received the beacon signals 112.
Those tracking stations 104 that received the beacon signals 112 sent relative direction information from the beacon 108 to a tracking control station 106.
The relative direction information corresponded to the antenna segment receiving the strongest beacon signal.
It will also be appreciated that the relative direction information could also have included a relative distance measurement, which would be derived from the actual received signal strength or from a bit error rate measurement, as is well known in the art