3. INTRODUCTION
The Global Positioning System(GPS) is
a satellite-based navigation system
made up of a network of 24 satellites
placed into orbit by the U.S. Department
of Defence that continuously transmit
coded information, which makes it
possible to precisely identify locations
on earth.
4. HISTORY
In the old time, people have used Stars
and moon to get positions so that they
can travel..
5. NEED OF GPS
Where am I? Where am I going? Where
are you? What is the best way to get
there? When will I get there?
GPS technology can answer all these
questions.
6. WHERE IT CAME FROM
Funded and Controlled by U.S. DOD
Originally Designed for the Military
1978 First Block of Satellites launched
1989 Second Block of Satellites launched
1995 Fully Operational
Korean Flight 007 Crashed(1983)–
President Ronald Regan guaranteed all
GPS signals would be available to the world
7. HOW DOES THE GPS
WORK?
Triangulation from satellite
Distance measurement through travel
time of radio signals
Very accurate timing required
Along with distance, need to know exactly
where the satellites are in space
Finally delays have to be corrected
9. SPACE SEGMENT
24 Satellites in 6
orbital plane
4 satellites in each
plane
20,200km altitudes
Five to Eight Satellites visible at any time
Each satellite transmits data including both
current location and time
11. USER SEGMENT
GPS Receivers
• Decodes the signals
from Satellites.
• Calculate the distance.
• Triangulates the
position
• Triangulation?
12. CALCULATING DISTANCE
Velocity x Time = Distance
Radio waves travel at the speed of light, roughly
3,00,000km per second (kmps)
If it took 0.06 seconds to receive a signal
transmitted by a satellite floating directly
overhead, use this formula to find your distance
from the satellite.
3,00,000kmps x 0.06 seconds = 18,000km
17. TRIANGULATION(IN 2D)
A man says that he is at 500km from
Delhi.
Again he says, he is at 300km from
Lucknow.
He again says that he is 400km away
from Jaipur.
24. Standard Positioning System
• Data Transmitted on L1(1575.42 MHz)
Frequency
• For civil users
• Accuracy is degraded
Precise Positioning System
• Data Transmitted on L1(1575.42 MHz)
and L2(1227.60 MHz) Frequencies
• For Military users
• Highly Accurate
Modes of Operation
HA=100m
VA=156m
TA=340ns
HA=22m
VA=27.7m
TA=200ns
25. FACTORS THAT AFFECT
GPS
Clock Error
Relativity Error
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
Radio Frequency (RF) Interference
27. Sources of Signal Interference
Earth’s Atmosphere
Solid Structures
Metal Electro-magnetic Fields
28. SATELLITE GEOMETRY
When the satellites are all in the same part
of the sky, readings will be less accurate.
PDOP-Position Dilution of Precision
29. CLOCK ERROR
Time of the satellites and receivers must be
synchronized.
GPS satellites use Atomic Clocks.
Most of the GPS receivers do not use Atomic
clock because of expense.
So we get error in time , so error in position.
30. RELATIVE ERROR
According to Special Relativity-
on-board atomic clocks on the satellites
should fall behind clocks on the ground
by about 7 microseconds per day
because of the slower ticking rate due
to the time dilation effect of their
relative motion.
Means satellite clock=T-7us
31. RELATIVE ERROR Contd.
According to General Relativity-clocks
closer to a massive object will seem to tick
more slowly than those located further away.
A calculation using General Relativity
predicts that the clocks in each GPS satellite
should get ahead of ground-based clocks by
45 microseconds per day.
Means satellite clock=T+45us
On combining both. Time =T+45-7=T+38us.
32. RELATIVE ERROR Contd.
38us means error of 11 km per day
To overcome this error , satellite clock is
corrected generally after 2-4 hour.
35. WORLD WORK ON
NAVIGATION
GPS –by United States
GLONASS -by Russian
GALILEO-by European Union
Compass –by China
IRNSS(Indian Regional Navigation Satellite
System)-by INDIA
36. Indian Regional Navigation Satellite
System
Total satellites 7
First launch 1 July 2013
Last launch 28 April 2016
Orbital height 36,000 km
Precision 10 m (public) 0.1 m
(encrypted)
Coverage -Regional (up to 1,500 km from
borders)
38. REFERENCES
GPS primer “A Student
Guide”(Aerospace Corporation)
www.trimble.com
An Introduction – Global Positioning
system S. K. Upadhyaya, G. S.
Pettygrove, J.W. Oliveira, B. R. Jahn1
GPS Guide for Beginners(GARMIN
Corporation)
