Global
Positioning
System
(GPS)
DELIVERING BY:
MOHAMMED MOIZUDDIN
ZEESHAN
UNDER THE GUIDANCE:
PROF. SHIVANAND S.
RUMMA
Department of Computer Science,
Gulbarga University, Kalaburagi
CONTENTS
HISTORY.
WHAT IS GPS?
GPS ELEMENTS.
HOW IT WORKS?
GPS SIGNALS & FREQUENCIES.
SOURCES OF GPS SIGNAL ERRORS.
HOW TO IMPROVE THE ACCURACY OF GPS.
APPLICATIONS(VEHICLE TRACKING).
FUTURE OF GPS.
LIMITATIONS.
CONCLUSION.
HISTORY OF
NAVIGATION
People first navigated only by means of landmarks mountains, trees, or leaving trails of stones.
This would only work within a local area and the environment
was subject to change due to environmental factors such as
natural disasters.
For travelling across the ocean a process called dead
reckoning, which used a magnetic compass and required the
calculation of how fast the ship was going, was applied.
The measurement tools were crude and inaccurate. It was
also a very complicated process.
HISTORY
Navigating by
measurements)
stars
(requires
clear
nights
and
careful
most widely used for centuries
The GPS project was developed in 1973 to overcome the
limitations of previous navigation systems.
GPS was created and realized by the U.S. Department of
Defense (DOD) and was originally run with 24 satellites.
It became fully operational in 1995. Bradford Parkinson, Roger
L. Easton, and Ivan A. Getting are credited with inventing it.
WHAT IS GPS?
Global Positioning System (GPS)
A space-based satellite navigation system provides accurate
location and time information 24 hours a day in all weather
anywhere in the world.
Maintained by the United States government and is freely
accessible by anyone with a GPS receiver.
GPS satellites also called NAVSTAR (Navigational Satellite
Timing And Ranging), the official U.S. Department of Defense
(DOD) name for GPS.
Official logo for
NAVSTAR GPS
Official name : Navigational Satellite Timing And Ranging
Global Positioning System (NAVSTAR GPS)
Consists of 30+ GPS satellites in medium Earth orbit
(2000km - 35,000km).
Made up of two dozen satellites working in harmony are
known as a satellite constellation.
Mainly used for navigation, map-making and surveying.
GPS SEGMENTS
GPS uses radio transmissions.
The
satellites
transmit
timing
information and satellite location
information.
The system can be separated into
three parts:
1. Space Segment
2. Control Segment
3. User Segment
Space Segment
Control
Segment
THE FOLLOWING FIGURE ILLUSTRATES
HOW THE THREE SEGMENTS FIT TOGETHER
SPACE SEGMENT
The space segment consists of the satellites
themselves.
According to the United States Naval
Observatory, there are currently 27 operational
GPS satellites about 11,000 miles up in space.
This constellation provides between five and
eight GPS satellites visible from any point on
the earth. The next scheduled launch is May
10, 2000.
It takes each satellite about twelve hours to
orbit the earth. There are six orbital planes with
at least four satellites in each plane.
CONTROL SEGMENT
Control
Segment
The control segment is a group of ground stations that monitor
and operate the GPS satellites.
There are monitoring stations spaced around the globe and
one Master Control Station located in Colorado Springs,
Colorado.
Each station sends information to the Control Station which
then updates and corrects the navigational message of the
satellites.
There are actually five major monitoring systems, the figure
below does not include the Hawaiian station.
USER SEGMENT
The user requires a GPS receiver in order to receive the
transmissions from the satellites.
The GPS receiver calculates the location based on signals
from the satellites.
The user does not transmit anything to the satellites and
therefore the satellites don't know the user is there.
The only data the satellites receive is from the Master Control
Station in Colorado. The users consist of both the military and
civilians.
WORKING PRINCIPLE
(HOW GPS DETERMINES LOCATION)
Things which need to be determined:
Current Locations of GPS Satellites
The Distance Between Receivers Position and the GPS
Satellites
CURRENT LOCATION
OF GPS SATELLITES
GPS satellites are orbiting the earth at an altitude of
11,000 miles.
The orbits, and the locations of the satellites, are
known in advance.
GPS receivers store this orbit information for all of the
GPS satellites in an ALMANAC*.
* the Almanac is a file which contains positional information for all of the GPS satellites
All 24 satellites are
divided into 6 parts.
There are 4 satellites
in each part.
A definite orbit is
defined for each part.
Each of these 3,000to 4,000-pound solarpowered satellites.
DISTANCE BETWEEN RECEIVERS
POSITION & THE GPS SATELLITES
To get the distance to each satellite,
By measuring the amount of time taken by radio
signal (the GPS signal) to travel from the satellite to
the receiver.
Radio waves travel at the speed of light, i.e. about
186,000 miles per second.
The distance from the satellite to the receiver can
be determined by the formula
distance = speed * time.
Distance measurements from two satellites
limits our location to the intersection of two
spheres, which is a circle.
A third
measurement
narrows our
location to just
two points.
A fourth
measurement
determines
which point is
our true
location
GPS ERROR BUDGET
Different errors can cause a deviation of +/- 50
-100meters from the actual GPS receiver position
which are:
ATMOSPHERIC CONDITIONS:
Speed of GPS signal is affected by ionosphere & troposphere.
Which cause a deviation of 0 to 30 m. from the actual position of
receiver.
EPHEMERIS ERRORS:
The predicted changes in the orbit of a satellite.
Which cause a deviation of 0 to 5 m. from the actual position of
receiver
CLOCK DRIFT:
Due to different code generations in satellite and receiver
simultaneously.
Which cause a deviation of 0 to 1.5m. from the actual position of
receiver
MULTIPATH:
Bouncing of GPS signal due to a reflecting surface before reaching
to receiver antenna.
Which cause a deviation of 0 to 1 m. from the actual position of
receiver
MEASURING GPS
ACCURACY
The geometry of the constellation is evaluated by
Dilution Of Precision, or DOP.
INCREASING
ACCURACY OF GPS
Differential correction provides accuracy within 1-5 m.
Coarse Acquisition receiver provides accuracy within 1-5m.
Carrier Phase receivers provides accuracy within 10-30 cm.
Dual-Frequency receivers are capable of providing subcentimeter GPS position accuracy.
APPLICATIONS
AVIATION
AGRICULTURE
MARINE
TIMING
SPACE
RAILWAYS
ROADWAYS
DISASTER RELIEF
APPLICATIONS OF
GPS
The applications of the Global Positioning System fall into five
categories:
Location
Navigation
Timing
Mapping, and
Tracking.
Each category contains uses for the military, industry,
transportation, recreation and science.
LOCATION
This category is for position determination and is the most
obvious use of the Global Positioning System.
GPS is the first system that can give accurate and precise
measurements anytime, anywhere and under any weather
conditions. Some examples of applications within this category
are:
Measuring the movement of volcanoes and glaciers.
Measuring the growth of mountains.
Measuring the location of icebergs - this is very valuable to
ship captains helping them to avoid possible disasters.
NAVIGATION
Navigation is the process of getting from one location to
another. This was the what the Global Positioning System was
designed for.
The GPS system allows us to navigate on water, air, or land.
It allows planes to land in the middle of mountains and helps
medical evacuation helicopters save precious time by taking
the best route.
TIMING
GPS brings precise timing to the us all.
Each satellite is equipped with an extremely precise atomic clock.
This is why we can all synchronize our watches so well and make
sure international events are actually happening at the same time.
MAPPING
This is used for creating maps by recording a series of
locations.
The best example is surveying where the DGPS technique is
applied but with a twist.
Instead of making error corrections in real time, both the
stationary and moving receivers calculate their positions
using the satellite signals.
Surveying: Surveyors use absolute locations
to make maps and determine property
boundaries.
Telematics: GPS technology integrated with
computers and mobile communications
technology in automotive navigation systems.
TRACKING
The applications in this category are ways of monitoring
people and things such as packages.
This has been used along with wireless communications to
keep track of some criminals.
The suspect agrees to keep a GPS receiver and transmitting
device with him at all times.
If he goes where he's not allowed to, the authorities will be
notified.
This can also be used to track animals.
VEHICLE TRACKING
MONITOR-TRACK-SPY
HOW IT WORKS?
Satellites orbiting the
earth tell the GPS locator
in the vehicle where it is.
Vehicle location and onboard information
is sent via GPRS over the cell phone
network every 2-10 minutes or when an
event takes place such as ignition
ON/OFF.
Customer computers are
updated continuously over
the internet.
Information is stored on the host server
usually at the secure remote location
LIMITATIONS
GPS can provide worldwide, three-dimensional positions, 24
hours a day, in any type of weather.
But, There must be a relatively clear "line of sight" between the
GPS antenna and four or more satellites.
Hence it becomes too difficult to ensure reliable positioning.
These difficulties are particularly prevalent in urban areas.
The GPS signal may bounce off nearby objects causing another
problem called multi path interference.
CONCLUSION
The technology of the Global Positioning System is allowing
for huge changes in society.
The applications using GPS are constantly growing.
The cost of the receivers is dropping while at the same time
the accuracy of the system is improving.
This affects everyone with things such as faster Internet speed
and safer plane landings.
ANY QUESTIONS ?
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