GPS
SEMINAR REPORT
ON
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GPS
Acknowledgement
We acknowledge our friend elder has directiy or indirectly
contribution in my project of gps.
My great full acknowledge the valuble subjection and
contribution from Miss Nirali and Sweta also thanks full to
my college aits last but not least thanks to our parents.
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GPS
ABSTRACT
Recently Technology is advancing quickly everyday in our lives.
New devices are being brought to the public to make our everyday
lives easier. With that in mind, one of the more recent, advancing
devices is the Global Positioning System.
I chose this topic of technology because I feel that it has
undoubtedly made a big impact in society. With all that it can
perform and accomplish for different people and groups, the GPS has
been a great advancement in technology
The GPS, also known as the NAVSTAR (Navigation Signal Timing
and Ranging Global Positioning System) Global Positioning System,
is a satellite-based radio-navigation network that provides a person's
location in all parts of the world at all times (Dixon 9).
The GPS is built and operated by the U.S. military on a system of
twenty-one satellites plus three spares which constantly orbit the
earth completely in twelve hours (Evans, Martin, and Poatsy 354).
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GPS
INDEX
Introduction
History
Defination
How it works
GPS satellite geometry
GPS satellite signals
GPS architecture
Application
Advantages
Disadvantages
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GPS
PROJECT PROFILE
Period of project work: may to December
Project guide: purvi patel
Developed by: parmar nirali
Ponkia sweta
Submitted to: Atmiya institude of technology and
science
Kalaward road. Rajkot
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GPS
Introduction
The Global Positioning System (GPS) is a location system
based on a constellation of about 24 satellites orbiting the
earth at altitudes of approximately 11,000 miles.
GPS was developed by the United States Department of
Defense (DOD), for its tremendous application as a military
locating utility. The DOD's investment in GPS is immense.
Billions and billions of dollars have been invested in
creating this technology for military uses. However, over
the past several years, GPS has proven to be a useful tool in
non-military mapping applications as well.
GPS satellites are orbited high enough to avoid the
problems associated with land based systems, yet can
provide accurate positioning 24 hours a day, anywhere in
the world.
Uncorrected positions determined from GPS satellite signals
produce accuracies in the range of 50 to 100 meters. When
using a technique called differential correction, users can get
positions accurate to within 5 meters or less.
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GPS
History
1969—Defense Navigation Satellite System (DNSS) formed
1973—NAVSTAR Global Positioning System developed
1978—first 4 satellites launched
1993—24th satellite launched; initial operational capability
1995—full operational capability
May 2000—Military accuracy available to all users
NavStar :
- Started development in 1973
- First four satellites launched in 1978
- Full Operational Capacity (FOC) reached on July
17, 1995
- System cost of $12 billion
Selective Availability (S/A) deactivated May 2000
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GPS
Definition
GPS, which stands for Global Positioning System, is
a radio navigation system that allows land, sea,
and airborne users to determine their exact
location, velocity, and time 24 hours a day, in all
weather conditions, anywhere in the world.
The capabilities of today’s system render other
well-known navigation and positioning
“technologies”—namely the magnetic compass, the
sextant, the chronometer, and radio-based
devices—impractical and obsolete.
GPS is used to support a broad range of military,
commercial, and consumer applications.
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GPS
How it works
All satellites have clocks set to exactly the same time.
All satellites know their exact position in space from data
sent to them from the systems controllers.
Each satellite transmits its position and a time signal.
The signals travel to the receiver delayed only by
distance traveled.
The receiver calculates the distance to each satellite and
trilaterates its own position
31 satellites currently active (9/2007)
Orbit 11,000 miles above Earth
6 visible sats from any point on Earth
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GPS
How it works (continue)
5 monitoring stations synchronize the atomic clocks on board
each satellite
distance from a satellite to a receiver in miles=(186,000 mi/sec)
x (signal travel time in seconds)
Pseudo-Random Code
• Complex signal
• Unique to each satellite
• All satellites use same frequency
• “Amplified” by information theory
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GPS
How it works (continue)
Distance to a satellite is determined by measuring how long a
radio signal takes to reach us from that satellite.
To make the measurement we assume that both the satellite and
our receiver are generating the same pseudo-random codes at
exactly the same time.
By comparing how late the satellite's pseudo-random code
appears compared to our receiver's code, we determine how long
it took to reach us.
Multiply that travel time by the speed of light and you've got
distance.
Accurate timing is the key to measuring distance to satellites.
Satellites are accurate because they have four atomic clocks
($100,000 each) on board.
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GPS
How it works (continue)
To use the satellites as references for range measurements we
need to know exactly where they are.
GPS satellites are so high up their orbits are very predictable.
All GPS receivers have an almanac programmed into their
computers that tells them where in the sky each satellite is,
moment by moment.
Minor variations in their orbits are measured by the
Department of Defense.
The error information is sent to the satellites, to be transmitted
along with the timing signals.
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GPS
GPS Satellite Geometry
Satellite geometry can affect the quality of GPS signals and
accuracy of receiver trilateration.
Dilution of Precision (DOP) reflects each satellite’s position
relative to the other satellites being accessed by a receiver.
There are five distinct kinds of DOP.
Position Dilution of Precision (PDOP) is the DOP value used
most commonly in GPS to determine the quality of a
receiver’s position.
It’s usually up to the GPS receiver to pick satellites which
provide the best position triangulation.
More advanced GPS receivers can filter out poor DOP
values.
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GPS
Ideal Satellite Geometry
W E
S
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Poor Satellite Geometry
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GPS
GPS Satellite Signals
Atomic Clock (G, Rb) fundamental frequency - 10.23. MHz
L1 Carrier Signal - 154 X 10.23 MHz
L1 Frequency - 1575.42 MHz
L1 Wave length - 19.05 Cm
L2 Carrier Signal - 120 X 10.23 MHz
L2 Frequency - 1227.60 MHz
L2 Wave Length - 24.45 Cm
P-Code Frequency (Chipping Rate) - 10.23 MHz (Mbps)
P-Code Wavelength - 29.31 M
P-Code Period 267 days - 7 Days/Satellite
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GPS
C/A-Code Frequency (Chipping Rate) - 1.023 MHz (Mbps)
C/A-Code Wavelength - 293.1 M
C/A-Code Cycle Length - 1 Milisecond
Data Signal Frequency - 50 bps
Data Signal Cycle Length - 30 Seconds
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GPS
GPS Architecture
The GPS system is divided into three segments:
The Space Segment
The Control Segment
The User Segment
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GPS
1.The Space Segment
GPS uses more than two dozen operational satellites, with
an additional three satellites in orbit as redundant backup.
GPS uses NAVSTAR satellites manufactured by Rockwell
International. Each NAVSTAR satellite is approximately 5
meters wide (with solar panels extended) and weighs
approximately 900Kg.
GPS satellites orbit the earth at an altitude of approximately
20,200Km.
Each GPS satellite has an orbital period of 11 hours and 58
minutes. This means that each GPS satellite orbits the Earth
twice each day. Highly accurate atomic clocks are installed
on these satellites, operating at a fundamental frequency of
10.23MHz each. With the help of these clocks, signals are
generated from the satellite, to be broadcast to the Earth.
These twenty-four satellites orbit in six orbital planes, or
paths. This means that four GPS satellites operate in each
orbital plane.
Each of these six orbital planes is spaced sixty degrees
apart. All of these orbital planes are inclined fifty-five
degrees from the Equator.
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GPS
[space segment figure]
A visual example of theGPS constellation in motion with
the Earth rotating. Notice how the number of satellites in
view from a given point on the Earth's surface, in this
example at 45°N, changes with time.
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GPS
2.The Control Segment
The Control Segment is comprised of a master control
station, 5 monitor stations and 4 ground antennas. All of
these are strategically located along the Equator.
The Master Control Station (MCS) of the GPS system is
operated at Schriever Air Force Base in Colorado Springs,
Colorado. The United States Air Force maintains redundant
Master Control Stations in Rockville, Maryland and
Sunnyvale, California.
The Air Force also maintains monitoring stations in
Colorado Springs, Hawaii, The Ascension Islands, Diego
Garcia, and Kwajalein.
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GPS
Key Functions of the Control Segment
The Control Segment keeps track of the orbiting position of
the GPS satellites, calibrating and synchronizing their
clocks.
It also predicts the path of each satellite for the following 24
hours, and uploads this information to each satellite.
Communications with the space segment are conducted
through ground antennas in the Ascension Islands, Diego
Garcia, and Kwajalein. The satellite signals are read here
and the measurements sent to the Master Control Station in
Colorado. The signals are processed there to determine any
errors, and sent back to the four monitor stations with
ground antennas, after which the information is uploaded
back to the satellites.
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GPS
[control segment figure]
US Space Command
Cape Canaveral
Hawaii
Kwajalein Atoll
Diego Garcia
Ascension Is.
Master Control Station Monitor Station Ground Antenna
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GPS
3.The User Segment
This part consists of user receivers which are hand-held or,
can be placed in a vehicle.
All GPS receivers have an almanac programmed into their
computer, which tells them where each satellite is at any
given moment.
The GPS receivers detect, decode and process the signals
received from the satellites.
The receiver is usually used in conjunction with computer
software to output the information to the user in the form of
a map.
As the user does not have to communicate with the satellite
there can be unlimited users at one time.
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GPS
Three segment of the gps
Space Segment
User Segment
Control Segment
Ground
Antennas
Master Station Monitor Stations
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GPS
Applications
GPS has become a widely used and a useful tool for
commerce, scientific uses, tracking and surveillance.
GPS's accurate timing facilitates everyday activities such
as banking, mobile phone operations, and even the control
of power grids.
Farmers, surveyors, geologists and countless others
perform their work more efficiently, safely, economically,
and accurately
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GPS
Civilian
This antenna is mounted on the roof of a hut containing a
scientific experiment needing precise timing.
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GPS
The first civilian application of GPS was on large ships,
where the relatively high expense of the early GPS receivers
was not such a problem. As prices have fallen, GPS
receivers have become common on smaller vessels as well.
GPS receiver systems are now being incorporated into cars
as well. While they remain mostly curiosities in the US so
far, they have proven popular in Japan, where consumers are
more gadget-happy.
Such systems may interact with the car's CD-ROM player to
obtain map information and present it on a dashboard video
display.
Surveying: Surveyors use absolute locations to make
maps and determine property boundaries
Map-making: Both civilian and military cartographers use
GPS extensively.
Navigation: Navigators value digitally precise velocity
and orientation measurements.
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GPS
Advantages
fast speed
leads u in right direction
helps improve mapping skills
makes navagation easier
has panic buttons built in
you can be found easier if in danger or in accident
plugs into your car cigeratte lighter
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GPS
Fast speed
GPS receivers display speed and calculate the speed using
algorithms in the Kalman filter.
Most receivers compute speed by a combination of
movement per unit time and computing the doppler shift in
the pseudo range signals from the satellites.
The speed is smoothed and not instantaneous speed.
makes navigation easier
A GPS device is extremely handy.
When you are hiking, you can deviate from a path without
worrying about how you will find your way back.
When you are driving, GPS-based navigation systems can
provide you with turn-by-turn directions, a helpful feature in
a strange town.
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GPS
Search Nearby Area
Some GPS systems allow you to search the local area for
nearby amenities, such as hotels, restaurants and gas
stations.
This is extremely helpful in some situations.
For example, if you are driving cross-country and realize
there is a problem with your car, you can search for
nearby auto mechanics and select one that is along your
route.
Your GPS system will show you exactly how to get
there.
Ease of Navigation
A GPS device is extremely handy.
When you are hiking, you can deviate from a path without
worrying about how you will find your way back.
When you are driving, GPS-based navigation systems
can provide you with turn-by-turn directions, a helpful
feature in a strange town
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GPS
Water Navigation
GPS devices are perfect for water navigation. Since there
are no landmarks in large bodies of water, boaters in the
past had to use a compass and a map to determine if they
were on the right heading, with somewhat imprecise
results.
But the advent of GPS systems allowed boaters to figure
out their exact position on the map.
In situations where underwater hazards are a problem,
GPS devices allow boaters to steer around hidden dangers
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GPS
Disadvantages
cellular devices can track other cellular device users not
very cheap
people focus on GPS more than road = accidents
should be used as backup map but used as 1st resource -
Possible Failures
needs good care and handling
external power
needs batteries (handheld ones)
Inaccuracy
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GPS
Possible Failures
You need to carry a backup map and directions in case
your GPS fails for some reason.
For example, if you are driving down a city street, the
buildings may block the satellite signal, preventing you
from receiving position updates.
If you are hiking in the wilderness, your handheld GPS
receiver's battery may die, leaving you with no way to
navigate.
For hiking situations, it's a good idea to bring along a
compass as well.
Inaccuracy
GPS signals are not completely accurate.
Obstacles like buildings and trees can deflect the signal,
causing your position on the GPS screen to be off by as
much as 100 feet. Atmospheric conditions (such as
geomagnetic storms caused by solar activity) may also
affect GPS accuracy. For highway driving, this can cause
you to miss a turn or exit.
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GPS
Battery Life
GPS units that are not plugged into a power source, and
rely on batteries, which can drain quickly.
This can increase the cost of owning a GPS unit
significantly.
Cost
Purchasing a GPS based on price can be a major
disadvantage.
If you purchase a "bargain GPS," you will get what you pay
for, and features such as traffic and up-to-date maps could
be lacking.
Reception
GPS devices are limited by having clear access to the
satellites that provide the tracking.
In locations with tall buildings or sparse coverage,
reception can be poor.
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GPS
BIBLIOGRAPHY
jcovili@media.utah.edu
ajensen@stoller.com
www.stoller-eser.com
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