TOPIC :- GPS (GLOBAL POSITIONING SYSTEM)
PRESENTED BY:- SANDEEP KUMAR BAGARTI
GUIDED BY :- MR. GADADHAR SAHOO
ROLL NO. :- 5703U13033
Content
• INTRODUCTION
• WHY DO WE NEED GPS?
• SEGMENTS OF GPS
• HOW DOES THE GPS WORK?
• PARTS OF A GPS SYSTEM
• GPS APPLICATIONS
• GPS SETUP BLOCK DIAGRAM
• FACTORS THAT AFFECT GPS
• CONCLUSION
Global Positioning System
An easy to use technology for everyone.
What is GPS ?
• It Is a satellite based navigation system made up of a network of 24 satellites
placed into orbit.
•Developed and maintained by the US Department of Defense (DOD).
• Satellite Based
* 24 satellites
* 20,200 km high orbit
•The 24 satellites are orbiting the earth about 12000 miles above us and are
travelling at the speeds of roughly 7000 miles an hour.
•In 1978 the first experimental gps satellite was launched.
WHY DO WE NEED GPS?
• Trying to figure out where you are is probable man’s oldest pastime.
• Finally US Dept of Defense decided to form a worldwide positioning system.
• Also known as NAVSTAR ( Navigation Satellite Timing and Ranging Global
positioning system) provides instantaneous position, velocity and time
information.
HOW DOES THE GPS WORK?
• Requirements
• Triangulation from satellite
• Distance measurement through travel time of radio signals
• Very accurate timing required
• To measure distance the location of the satellite should also be known
Parts Of A GPS System:-
GPS Setup Block Diagram:-
Segments of GPS
1. Space Segment:-
A constellation of 24 satellites
2. Monitor Station:-
A network of earth-based facilities
3. Users & Equipment
The Space Segment
• There are four satellites in each of 6 orbital planes. Each plane is inclined
55 degrees relative to the equator, which means that satellites cross the
equator tilted at a 55 degree angle. The system is designed to maintain full
operational capability even if two of the 24 satellites fail. They orbit at
altitudes of about 12000, miles each, with orbital periods of 12 sidereal
hours (i.e., determined by or from the stars), or approximately one half of
the earth's periods, approximately 12 hours of 3-D position fixes.
• The User Segment
• The user segment is a total user and supplier community, both civilian and
military. The User Segment consists of all earth-based GPS receivers.
Receivers vary greatly in size and complexity, though the basic design is
rather simple. The typical receiver is
• composed of an antenna and preamplifier, radio signal microprocessor,
control and display device, data recording unit, and power supply.
GPS Monitoring Station:-
GPS APPLICATIONS
• Surveying and Mapping
• Navigation
• Remote Sensing and GIS
• Geodesy
• Military
FACTORS THAT AFFECT GPS
• Number of satellites - minimum number required
• Multipath - reflection of GPS signals near the antennae
• Ionosphere - change in the travel time of the signal
• Troposphere - change in the travel time of the signal
• Satellite Geometry - general distribution of the satellites
• Satellite Health - Availability of Signal
• Signal Strength - Quality of Signal
• Distance from the Reference Receiver
• Radio Frequency (RF) Interference
• Loss of Radio Transmission from Base
Determining GPS Position
• Suppose the distance from
Satellite A to our position is
+
Satellite A 11,000 miles
• At this point we could be located
anywhere on the specified sphere
+
Satellite B
• Next, let us take another measurement
from a second satellite, Satellite B
• Now our position is narrowed down to the
intersection of theses two sphere
Determining GPS Position
• Taking another measurement
+
Satellite A from a 3rd satellite narrows our
position down even further, to
the two points
+
+
Satellite B
Satellite C • These points are located where
the 3rd sphere cuts through the
the intersection of first two spheres
• So by ranging from 3 satellites we can
narrow our position to just two points in space
How do we decide which one is our
true location?
• We could make a 4th measurement
from another satellite to determine
+
Satellite A
the true point
OR
• We can eliminate one of the two
+ C
+
Satellite B
Satellite points that gives a ridiculous
answer
• The ridiculous point may be too
far from the earth
• However, GPS receivers use a 4th satellite to precisely
locate our position
Multipath:-
• Position Dilution of Precision
PDOP:-
• When GPS signals arrive at the receiver having traveled different paths.
Good PDOP Poor PDOP
SNR (signal-to-noise ratio):-
• SNR determines the signal strength relative to noise.
• GPS position is degraded if the SNR of one or more satellites in the constellation falls
below certain range.
Signal Strength
Indicators
MULTIPATHS
• Multipath effects arise when signals transmitted from the satellites
bounce off a reflective surface before getting to the receiver antenna.
When this happens, the receiver gets the signal in straight line path as
well as delayed path (multiple paths). The effect is similar to a ghost
or double image on a TV set.
• PDOP-
• GPS receivers usually report the quality of satellite geometry in terms of
Position Dilution of Precision, or PDOP. PDOP refers to horizontal (HDOP)
and vertical (VDOP) measurements (latitude, longitude and altitude).A low
DOP indicates a higher probability of accuracy, and a high DOP indicates a
lower probability of accuracy. A PDOP of 4 or less is excellent, a PDOP
between 5 AND 8 is acceptable, and a PDOP of 9 or greater is poor. TDOP or
Time Dilution of Precision refers to satellite clock offset.
CONCLUSION:-
• Barring significant new complications due to S/A (Selective
Availability) from DOD, the GPS industry is likely to
continue to develop in the civilian community.
• There are currently more than 50 manufacturers of GPS
receivers, with the trend continuing to be towards smaller,
less expensive, and more easily operated devices.
• Also INDIA in the future will do use this technology, not
only in the field of Defense, but also in civilian community
as this is not a scientific luxury but is the need of future.
