GPS Overview Part 1 - Introduction
The original theory behind Location-Based Services -
or LBS - is to help you find out where you are or where something
else is. There are several ways of determining location, including GPS,
cell locations, triangulation and other methods.
This overview describes the history and workings of the Global
Positioning System (GPS), as well as its uses and the future for it.
The Global Positioning System (GPS) is a network of
24 Navstar satellites orbiting Earth at 11,000
miles. Originally established by the U.S. Department of Defence (DOD) at a
cost of about US$13 billion, access to GPS is free to all users, including
those in other countries. The system’s positioning and timing data are
used for a variety of applications, including air, land and sea
navigation, vehicle and vessel tracking, surveying and mapping, and asset
and natural resource management. With military accuracy restrictions
partially lifted in March 1996 and fully lifted in May 2000, GPS can now
pinpoint the location of objects as small as a penny anywhere on the
earth’s surface.
The first GPS satellite was launched in 1978. The
first 10 satellites were development satellites, called Block I. From 1989
to 1993, 23 production satellites, called Block II were launched. The
launch of the 24th satellite in 1994 completed the system. The
DOD keeps 4 satellites in reserve to replace any destroyed or defective
satellites. The satellites are positioned so that signals from six of them
can be received nearly 100 percent of the time at any point on earth.
GPS provides specially coded satellite signals that
can be processed in a GPS receiver,
enabling the receiver to compute position, velocity and time. Basically
GPS works by using four GPS satellite signals to compute positions in
three dimensions (and the time offset) in the receiver clock. So by very
accurately measuring our distance from these satellites a user can
triangulate their position anywhere on earth.
GPS receivers have been miniaturised to just a few
integrated circuits and so are becoming very economical. And that makes
the technology accessible to virtually everyone. These days GPS is finding
its way into cars,
boats, planes, construction equipment, movie making gear, farm machinery,
even laptop computers. This report shows the various features of GPS and
the reasons why it may soon become almost as basic as the telephone.
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