GPS-How does it work?
By Ethan Mann
Basic Information
• GPS is used to
find your exact
location on the
world, to help you
navigate.
• It is a complex
system developed
by the military for
their use.
What GPS is used for
• GPS is used in boats
for navigational
purposes.
• GPS is used in
airplanes for
navigation, and it plots
a course for the plane.
• It is also used in cars
for the same purposes.
• It is used for hikers in
the woods to give
them their location.
What GPS Needs to Work
• A receiver
• Three or four
satellites “visible”
for the GPS
receiver to use to
collect data
• The correct time
How GPS works
• The GPS satellites
send radio signals
to the GPS
receivers
• The signals are at
1575.42 MHz for
civilian receivers
• The radio signals
have information
for the receiver
The GPS Receiver
• It determines where
you are, as it works
with the satellites,
providing latitude,
longitude, and
altitude.
• It receives radio
signals from the
satellites to help get
this information.
The Satellite System
• There are 24 satellites in
use for the GPS system,
and at least three spares in
case of errors.
• They weigh 1 to 2 tons.
They orbit the earth twice a
day at an altitude of about
22,000 feet.
• They orbit in
geosynchronous orbits,
which means that they are
in the same position above
the Earth at all times.
The Radio Signals
• They are highfrequency, lowpower signals
transferred between
the satellite and the
receiver.
• They relay the
information such as
location to the
receiver, who then
makes a calculation.
What is in the Radio Signals
• (1) Pseudorandom
code, which is the
satellite’s ID.
• (2) Ephermis data,
which shows the
condition and time.
• (3) Almanac data,
where the satellite
should be in orbit
at any particular
time.
With the Radio Signals
• After the receiver gets the
radio signals from the
satellites, it then
determines where it is
using the principle of
triangulation.
• The data from the radio
signals leads the receiver
to a clue where all three
satellites meet. That is
where the triangulation
comes into play.
Triangulation-How GPS works
• Triangulation is the
mathematical principle
that explains how GPS
works.
• There are two types of
triangulation: 2-D and
3-D.
• GPS uses 3-D
triangulation. 3-D has
the capability to tell
altitude or height, while
2-D doesn’t have that
capability.
More about Triangulation
• Triangulation is what
the receiver does after
it gets the signal.
• The radio signals give
it the three possible
spherical locations.
• Then, with the
triangulation principle
in place, it determines
where you are, your
longitude, latitude and
altitude.
What Triangulation does for GPS
A
B
C
• Say you’re 10 miles from
Satellite A. You are in a
sphere with a radius 10
miles away from satellite A.
• If you’re 15 miles from
satellite B, then there is
another sphere drawn. And
the same for a third satellite
and its sphere. At the
common point of the
satellites is your location.
Once you get that….
• There should be a point
where all the spheres
meet from the
triangulation principle.
• Using the information
from the radio signal
and the triangulation,
the receiver can
determine your location
on Earth with latitude,
longitude, and altitude.
When it finds your location...
• The GPS receiver
knows it is the one on
the Earth’s surface.
• The Earth can act as a
fourth sphere, and this
also helps it find the
location on Earth and
not the one in space.
So in a Nutshell...
• The GPS receiver
receives radio signals
from three or more
satellites.
• The signal tells you
information from the
three satellites, which
helps the receiver to find
a common point from
where the signals meet.
This is where the
receiver and you are
located.
Deterrents to the Process
• Problems to the radio
signal (There are
several examples).
• SA, selective
availability.
• Inside buildings.
• Problems with the
radio signals can be
fixed with DGPS,
though.
Errors in Transmission
• Method of transmission
assumes that it will stay
at a constant speed.
• Speed is affected when
the signal travels
through the parts of the
atmosphere.
• Problems also occur
when signals bounce off
skyscrapers, which
makes the receiver think
it is in a different place.
SA
• SA stands for
Selective
Availability, which
is a weakening of
the GPS satellite
signal.
• This was made to
stop military
enemies from
using the highly
accurate and
available GPS.
DGPS
• Differential GPS (DGPS) help to
correct these problems.
• The stations for DGPS are located
in several different places.
• DGPS receivers are more accurate
than regular GPS receivers.
History of GPS
• Early 1970’s-The military begins
developing GPS
• 1995-Available for everyone to
use
• 2000-SA turned off
Ethan Mann
• I was born on March
4, 1991 in Whiteville,
NC.
• I moved to
Clemmons at age 6.
• I am a big sports fan,
especially of Duke.
• I am Jewish, and
had my Bar Mitzvah
on March 13, 2004.
Bibliography
• Brain, Marshall and Harris, Tom.
Howstuffworks.com. 1998-2004. HSW Media
Network. 27 April 2004.
<http://electronics.howstuffworks.com/gps.htm/pr
intable>
• Brown, Allison K. “Global Positioning System.”
World Book Encyclopedia. Chicago: World
Book Inc., 2003.
• Griffin, Darren. “How does GPS work?” 5th
Sept. 2002. Pocket GPS World. 27 April 2004.
<http://www.pocketgps.co.uk/howgpsworks.php>
• “What is GPS?” ESO/Sea and Space. 27 April
2004. ESA. 27 April 2004.
<http://www.eso.org/seaspace/navigation/navgps