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There are two systems that the Prism TM uses outside of the Teletrac system. One is the Global
Positioning System, more commonly called GPS and the other is the General Packet Radio
System otherwise known as GPRS. The following pages will give you a basic introduction to
where these systems came from as well as how they work. At the end of this section will be a
summary of how Teletrac uses these two systems together to get the location of a vehicle.
G
P
LOBAL
OSITIONING
The following information was taken from information posted to the Teletrac Intranet. Included
here is the abridged version of GPS. The full text appears in Appendix A at the end of this
Information Guide.
A
I
N
NTRODUCTION TO
Global Positioning Systems
GPS uses "man-made stars" or satellites as reference points to calculate positions on Earth
accurate to within meters. In fact, with advanced forms of GPS you can make measurements to
better than a centimeter. In a sense, it's like giving every square meter on the planet a unique
address.
Since GPS receivers have been miniaturized to just a few integrated circuits and have become
very economical, the technology has become increasingly accessible.
Here's how GPS works in five logical steps:
Here is a summary of each of the steps involved with GPS in order to determine a location. This
is the first part of Teletrac finding the locations of vehicles using a Prism TM. Once a location is
determined then it is sent via another system. We'll explain each of the following points in the
next five sections.
1. The basis of GPS is "triangulation" from satellites.
2. To "triangulate," a GPS receiver measures distance using the travel time of radio
signals.
3. To measure travel time GPS needs very accurate timing, which it achieves with
some tricks.
1622-0300 B1 3/18/04
Teletrac, Inc. - Prism TM Information and Installation Guide
--------------Unit Two--------------
T
GPS
HE
AND
S
(GPS)
YSTEMS
G
P
LOBAL
OSITIONING
GPRS S
YSTEMS
S
S
ATELLITE
YSTEMS
9
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