The document discusses the global positioning system (GPS) and how it has changed navigation worldwide. It provides details on the three segments of GPS - the space segment consisting of 24 satellites in orbit, the control segment of 5 ground stations that monitor the satellites, and the user segment of GPS receivers. GPS uses trilateration of radio signals from satellites to determine precise location and timing information for users. Its widespread applications now include navigation, tracking, mapping, and more.

1. Global Positioning System
A GADGET WHICH
CHANGED THE WAY THE
WORLD OPERATES
Seminar by:
B V Aparna
ECE
CMR College of Engg. And Tech

2. 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.

3. Four Basic Functions of GPS
 Position and coordinates.
 The distance and direction between any two waypoints,
or a position and a waypoint.
 Travel progress reports.
 Accurate time measurement.

4. 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
 Finally delays have to be corrected

5. GPS Satellite Signal:
 L1 freq. (1575.42 Mhz) carries the SPS code and the
navigation message.
 L2 freq. (1227.60 Mhz) used to measure
ionosphere delays by PPS receivers
 3 binary code shift L1 and/or L2 carrier phase
 The C/A code
 The P code
 The Navigation message which is a 50 Hz signal
consisting of GPs satellite orbits . Clock correction and
other system parameters

6. Signal generation in a GPS Satellite
L1
90
Q
1575Mhz
I
1.023
C/A code Mbps SUM
C/A + NAV
50 bps Multipliers
Navigation
message L1+P+C/A
+NAV
10.23 L1 output
P code Mbps P+NAV
L2 output
L2 I L2+P+NAV
1227 Mhz

7. Triangulation
 Position is
calculated from
distance
measurement
 Mathematically
we need four
satellites but
three are
sufficient by
rejecting the
ridiculous
answer

8. Measuring Distance
 Distance to a satellite is determined by measuring
how long a radio signal takes to reach us from the
satellite
 Assuming the satellite and receiver clocks are sync.
The delay of the code in the receiver multiplied by
the speed of light gives us the distance

9. Getting Perfect timing
 If the clocks are perfect
sync the satellite range will
intersect at a single point.
 But if imperfect the four
T satellite will not intersect
at the same point.
 The receiver looks for a
T+3 common correction that
will make all the satellite
intersect at the same point

10. Space Segment:
 24 GPS space
vehicles(SVs).
 Satellites orbit the
earth in 12 hrs.
 6 orbital planes
inclined at 55
degrees with the
equator.
 This constellation
provides 5 to 8 SVs
from any point on
the earth.

11. Control Segment:
 The control segment comprises of 5
stations.
 They measure the distances of the
overhead satellites every 1.5 seconds
and send the corrected data to Master
control.
 Here the satellite orbit, clock
performance and health of the satellite
are determined and determines
whether repositioning is required.
 This information is sent to the three
uplink stations

12. User Segment:
 It consists of receivers that decode the signals from
the satellites.
 The receiver performs following tasks:
 Selecting one or more satellites
 Acquiring GPS signals
 Measuring and tracking
 Recovering navigation data

13. User Segment:
There are two services SPS and PPS
The Standard Positioning Service
 SPS- is position accuracy based on GPS measurements on
single L1 frequency C/A code
The Precise Position Service
 PPS is the highest level of dynamic positioning based on the
dual freq P-code
 Only authorized users, this consists of SPS signal plus the P
code on L1 and L2 and carrier phase measurement on L2

14. User Segment
 Military.
 Search and rescue.
 Disaster relief.
 Surveying.
 Marine, aeronautical and terrestrial navigation.
 Remote controlled vehicle and robot guidance.
 Satellite positioning and tracking.
 Shipping.
 Geographic Information Systems (GIS).
 Recreation.

15. Three Segments of the GPS
GPS
Space Segment
Space Segment Control Segment User Segment
User Segment
Control Segment
Ground
Antennas
Master Station Monitor Stations

16. Errors in GPS
The GPS is designed as accurate as possible.However, there are
still errors and the most significant of these are discussed
below:
 Atmospheric conditions
 Ephemeris errors
 Clock drift/measurement noise
 Selective availability
 multipath

17. Sources of GPS Error
Standard Positioning Service (SPS ): Civilian Users
Source Amount of Error
 Satellite clocks: 1.5 to 3.6 meters
 Orbital errors: < 1 meter
 Ionosphere: 5.0 to 7.0 meters
 Troposphere: 0.5 to 0.7 meters
 Receiver noise: 0.3 to 1.5 meters
 Multipath: 0.6 to 1.2 meters
 User error: Up to a kilometer or more
 Errors are cumulative and increased by PDOP.

18. Errors due to geometry
 Poor GDOP
 When angles from the
receiver to the SVs
used are similar
 Good GDOP
 When the angles are
different

19. Sources of Signal Interference causing errors
Earth’s Atmosphere
Solid Structures
Metal Electro-magnetic Fields

20. DGPS
 Errors in one position
are similar to a local
area
 High performance GPS
receiver at a known
location.
 Computes errors in the
satellite info

21. DGPS
 Data Links
 Land Links
 MF,LF,UHF/VHF freq used
 Radiolocations,local FM, cellular telephones and marine radio
beacons
 Satellite links
 DGPS corrections on the L band of geostaionary satellites
 Corrections are determined from a network of reference Base
stations which are monitored by control centers like OmniSTAR
and skyFix

22. Applications of GPS system
 Tracking is useful because it enables a central point
to monitor the position of several vehicles or people,
in real time, without them needing to relay that
information explicitly. This can include children,
criminals, police and emergency vehicles or military
applications.
o GPS vehicle tracking is also used to locate stolen
cars, or stolen mobiles.
 Once we know our location, we can, of course, find
out where we are on a map, and GPS mapping and
navigation is perhaps the most well-known of all the
applications of GPS.

23. Applications of GPS system
 A tracking applications are not that much popular
as the navigation applications. But, so many people
take uses of them. It enables users to find a location
of any object that is tagged with a system.
 Navigation applications are the most famous GPS
applications. The latest releases of those applications
allow users to have much advanced features and
facilities.
 Other common applications:Car navigation,Hand
held ,Tracking,GIS,Survey ,Manufacturing,Military
Related 1%

24. Thank you