2. •
WHAT IS GPS?
ELEMENTS OF GPS
MAIN TECHNOLOGY
BEHIND IT
SOURCES OF ERRORS OF
GPS SIGNAL
GPS SIGNALS AND
FREQUENCIES
ADVANTAGES
PRESENT UPDATATION APPLICATIONS
INDEX
3. WHAT IS GPS?
The global positioning system is a Technology which provides unequal amount of
accuracy and flexibility of positioning for navigation and surveying.
It provides continuous 3D positioning 24 hours a day throughout the world
The concept of GPS was introduced by united state Department Of Defence(DOD)
GPS is a satellite based Navigation, Timing and Positioning System.
4. ELEMENTS OF GPS
GPS is divided into three
major components.
1.The space segment
2.The user segment
3.The control segment
5. CONTROL SEGMENT
The GPS Ground Segment (also referred to as Control Segment or Operational Control
System) is the responsible for the proper operation of the GPS system.
It has three components
1. Monitor station(MS).
2. Master Control Station(MCS).
3. Ground Antennas(GA) .
The tasks performed by the Control Station(cs) are
1. Monitoring and Control of Satellite orbital parameters.
2. Updating of parameters in the Navigation message(ephemeris, almanac and clock
corrections).
3. Activation of spare Satellites.
4. Passive tracking of Satellites.
5. Controlling health and status of Satellite substations.
6. Resolving satellite anomalies
6. MASTER CONTROL STATION
Master Control Station (MCS) is the central control node for the GPS satellite constellation.
It is located at Colorado Spring.
The major tasks performed by MCS are
1. Monitoring and management of Precise Positioning Service (PPS) Signal-In-Space (SIS)
performance in support of all performance standards.
2. Navigation message data upload operations as required to sustain performance in
accordance with accuracy and integrity performance standards.
3. Detecting and responding to PPS SIS failures.
7. MONITOR STATION
Monitoring stations keep the Global Positioning System running smoothly.
Some are located in the United States, and others are situated elsewhere around the
globe.
Monitoring stations have been installed on Kwajalein, an island group in the Pacific
Ocean; Diego Garcia, an atoll, or island, in the Indian Ocean; and Ascension Island, in
the South Atlantic Ocean, among other locations.
8. GROUND ANTENNAS
The Ground Antennas uplink data to the
satellites via S-band radio signals.
These data includes ephemerides and
clock correction information transmitted
within the Navigation Message, as well as
command telemetry from the MCS.
9. SPACE SEGMENT
It consists of a nominal constellation of 34
satellites that transmit one way signal that gives the
current GPS satellite position and time.
Each Satellote contains 4 precise atomic clocks(i.e
Rubidium and Cesium Standards) and has a
microprocessor on board for limited Self
Monitoring and Data processing.
The satellites are equipped with Thrusters which
can be used to modify their orbits.
10. USER SEGMENT
The GPS receiver is user segment of GPS.
It consists of a antenna preamplifier, radiosignal
based microprocessor control and display device,
data recording unit and power supply.
They are tuned to the frequencies transmitted by
the Satellites.
The GPS receiver decodes the timing signal from
thr ‘visible’ satellites and after calculating
distances from each satellite, computes its own
latitude, elevation, longitude and time.
12. GPS POSITIONING METHODS
METHODS OF GPS POSITIONING
NUMBER OF RECEIVERS
SINGLE POSITIONING
RELATIVE
POSITIONING
MOVEMENT OF RECEIVERS
STATIC KINEMATIC
PROCESSING
POST
PROCESSING REAL TIME
SINGLE RELATIVE
13. HOW GPS WORK
A. Distance from satellites used
B. Accurate clocks are used
C. Need to know satellite location
D. Correction of errors imposed on GPS signal due to
atmosphere and ionosphere
E. Remove S/A(Selective
availability)
14. STEP I
To compute a position in 3 dimension a
minimum of 4 satellites Is required.
15. a
STEP II
To triangulate, the GPS receiver
measures the distance using the
travel time of the radio
message(distance=travel time*
speed of light).
To calculate this travel time it
requires a very accurate clock.
Receiver do not have the atomic
clock, it is synced via the satellites
via another complex process.
16. STEP III
Once the distance from the
satellite is known then the
position of the satellite in space is
required.
This information is given by
Control Segment.
There is a two way link between
satellite and control segment.
17. STEP IV
As GPS signal is travelled through
ionosphere and the earth’s atmosphere,
the signal is delyed.
4
18. GPS communicated its all information with the receiver by using codes.
This information contains
I. The satellite orbital and clock message.
II. General system status message.
III. Ionospheric delay model.
GPS broadcasts two carrier waves which are modulated by information signals
It useses two carrier waves L1 and L2.
L1 signal broadcasted at 1575.42 MHZ.
L2 signal broadcasted at 1227.4MHZ.
L1 signals has two codes modulated on it
1. C/A code(The Coarse/Acquisition code).
2. P code(Precision code).
L2 signal has only one code modulated on it , P-code.
DIFFERENT FREQUENCIES USED BY GPS
19. TYPES OF ERRORS ENCOUNTERED IN GNSS
Satellites clock errors.
Any slide amount of errors in satellites clock results in significant amount of error in the
position calculated by receivers. For example, 10 nanoseconds of clock error results in 3 meters
of position error. The clocks in the satellites is monitored and updated by ground control
station.
Orbital errors
The orbits og GNSS satellite’s do vary small amount from its precise well known orbits. Also, like
the satellite clocks, a small variation in the orbit results in a significant error in the position
calculated. When the satellite orbit changes, the ground control system sends a correction to
the satellites and the satellite ephemeris is updated.
20. vsd
Multipath errors
When signals from GPS is reflected from walls of
building before receiving by GPS receiver then
multipath errors occur. The reflected signal
received at the receiver slide delay than the
direct signal. Long delay multipath errors are
typically handled by the GNSS receiver, while
short delay multipath errors are handled by the
GNSS antenna.
Ionospheric delays
This layer contains electrically charged particles called ions which delays the satellite signals
and can cause a significant amount of satellite position error . This makes it very difficult to
predict how much ionospheric delay is impacting the calculated position
21. DO WE HAVE OUR OWN NAVIGATION SATELLITE
SYSTEM
22. NAVIC (NAVIGATION WITH INDIAN CONSTELLATION)
The Indian Regional Navigation Satellite System (IRNSS), with an operational name
of NAVIC is an autonomous regional satellite navigation system that provides accurate real-
time positioning and timing services.
It covers India and a region extending 1,500 km (930 mi) around it.
The system at present consists of a constellation of seven satellites.
Out of which 3 are in geostationary orbit and four are in geosynchronous orbit.
NAVIC gives two kind of services 1. Standard Position Service(SPS).
2. Restricted service(RS)
23. COMPARISON BETWEEN GPS AND NAVIC
RESOLUTION
GPS has a resolution of 20m for the public, Navic alose has a resolution of 20m for the public. But for restricted service NAVIC
is also said to have an accuracy of 1m or less according to reports.
COVERAG
As the name suggests GPS has a global coverage, but NAVIC servers India and it’s neighboring countries.
SATELLITES
GPS has 33 satellites as of June 2018, while NAVIC has only 7 satellites.
TIMMING
Most of GPS satellites are located in low earth orbit hence signal takes less time than NAVIC signal whose satellites are
located in geostationary orbit(-36000km from earth) .
24. ADVANTAGES OF GPS
FREE AND INDEPENDENT OPERATION
One of the notable advantages of Global Positioning System technology is that it does not require a user to transmit data
from his or her device. It is also important to note that a key benefit of GPS is that it is free.
SAFETY
GPS tracking can be used by parents to keep tabs on their children. Spouses can also use similar technology to keep track
of their partners. Workers and others can also use GPS tracking for personal safety, so that their whereabouts are known if
there is an emergency.
EASY TO USE
Navigation using GPS is generally very easy and requires minimal skill or effort, certainly when compared to traditional
methods and technologies, such as map-reading.
LOW COST
The satellites behind GPS are paid for, maintained and upgraded by the US Department of Defense. That means that the
system is essentially free, although you may have to pay for a device and software to utilize it.
25. .
APPLICATIONS OF GPS
THERE ARE NUMEROUS APPLICATIONS OF GPS. AMONG THE SOME IMPORTANS ARE
AS FOLLOWS
1. Military.
2. Science.
3. Surveying.
4. Telecommunications
5. Seeking treasure.
6. Robotic field.
26. CONCLUSION
1.GPS, a global positioning satellite system is undoubtly a very essential
technology today.
There are many companies which are totally dependent on it.
.
2. Not only positioning but it has numerous other applications.
3. Its position pointing accuracy can also be increased by increasing
number of satellites.
4. Using of atomic clock indicates that very high quality of technology is
used here.
5. It can be accessed from any where in the world.
6. It cab be utilized to increase the performance of other technology.
