The document discusses the Global Positioning System (GPS). GPS is a satellite-based navigation system consisting of three segments - space, control, and user. The space segment includes 24 satellites that transmit radio signals used by GPS receivers to determine location, velocity, and time. The control segment monitors the satellites and updates their clocks. The user segment includes GPS receivers that calculate position by precisely timing signals from at least three satellites. Common sources of error and differential GPS for improving accuracy are also covered, as well as many applications of GPS technology.

1. GLOBAL POSITIONING SYSTEM
Presented by
PRANAY MONDAL
M.Tech. (Communication System Engg.)
ROLL - 1351015

2. CONTENTS :-
 Introduction
 What is GPS?
 Basic principal of GPS
 Information in a GPS signal
 GPS segments
 Errors in GPS
 DGPS
 GPS application
 Conclusion

3. INTRODUCTION :-
 Radio-based navigation system developed by U.S. Department of
Defense (DOD)
 Initial operation in 1993
 Fully operational Capability in 1995
 System is called NAVSTAR
 NAVigation with Satellite Timing And Ranging
 Referred to as GPS
 Provides specially coded radio signals that can be processed in a
GPS receiver.
– position
– velocity
– time

4.  What is GPS? :-
• Based on a constellation of about 24
satellites.
• Transmit coded radio signals that can be
processed in a GPS receiver by position,
velocity and time.
 The system measures the time delay
between the signal transmission and
signal reception of the GPS signal.
 The signals carry information about
the satellite’s location.
 Determines the position of, and
distance to, at least three satellites, to
reduce error.
 The receiver computes position using
trilateration.

5. BASIC PRINCIPAL OF GPS :-
Trilateration :

6. Trilateration (cont.) :-
2D & 3D Positioning by Satelites

7. INFORMATION IN A GPS SIGNAL :-
The GPS signal contains 2 types of data.
 Ephemeris data –
 status of the satellite
 current date
 time
 Almanac data -
 orbital information for that satellite and for every other
satellite

8. GPS SEGMENTS :-
 Space segment
 Control Segment
 User Segment

9. SPACE SEGMENT :-
 24 satellites that orbit the
earth at about 11,000
nautical miles, once every
12 hours.
 Each planes has about 55°
tilt relative to Earth's
equator in order to cover
the polar regions.
 Each satellite is identified
by number and broadcasts
a unique signal.

10. SPACE SEGMENT (CONT.) :-
 Satellite Signals-Code-Phasing Ranging
 Each satellite has a unique no & unique signal.
 It continuously broadcasts its signal and also sends out a
time signal every time it starts.
 The receiver has a copy of each satellite signal and
determines the distance by recording the time between when
the satellite says it starts its signal and when the signal
reaches the receiver.

11. SPACE SEGMENT (CONT.) :-
 Satellite Signals-Code-Phasing Ranging (cont.)
 Distance is calculated using the velocity equation.
Velocity = Distance/time
 Rearranging the equation for distance
Distance= velocity * time
 If the system knows the velocity of a signal and the
time it takes for the signal to travel from the sender to
the receiver, the distance between the sender and the
receiver can be determined.

12. CONTROL SEGMENT :-
The CS consists of 3 entities:
i) Master Control Station , ii) Monitor Stations ,
iii) Ground Antennas

13. CONTROL SEGMENT (CONT.) :-
 Master Control Station :
 responsible for overall management of the remote monitoring and
transmission sites.
 Monitor Stations :
 Each of the monitor stations checks the exact altitude, position,
speed, and overall health of the orbiting satellites.
 uses measurements collected by the monitor stations to predict
the behavior of each satellite's orbit and clock.
 The prediction data is up-linked, or transmitted, to the satellites
for transmission back to the users.
 ensures that the GPS satellite orbits and clocks remain within
acceptable limits.
 Ground Antennas :
 Ground antennas monitor and track the satellites from horizon
to horizon.
 They also transmit correction information to individual
satellites.

14. USER SEGMENT :-
 GPS receivers are generally
composed of an antenna, tuned to
the frequencies transmitted by the
satellites, receiver-processors, and
a highly-stable clock.
 They can also include a display
for showing location and speed
information to the user.

15. USER SEGMENT (CONT.) :-
 GPS receiver has to know two things:
 The location of atleast three satellites above one’s.
 The distance between us and each of those satellites
 A standard GPS receiver can give you several
information-
 How far you've travelled (odometer)
 How long you've been travelling
 Our current speed (speedometer)
 Our average speed
 A "bread crumb" trail showing us
exactly where we have travelled on
the map
 The estimated time of arrival at
our destination if you maintain
our current speed.

16. ERRORS IN GPS :-
 Selective Availability or SA –
hamper very precise positioning accuracy
 Ionosphere and troposphere delays-
Signal delayed upon going through the ionosphere and
troposphere.
 Receiver clock errors –
the receiver timing references will have some small error.
 Orbital errors -
Also known as ‘ephemeris errors’, these are inaccuracies in the
satellite’s reported position.

17. ERRORS IN GPS (CONT.) :-
 Multipath error – can produce large location errors.
 Signal attenuation -
Non-restricted GPS signals (1.575 GHz) are blocked by
steel and concrete structures .

18. DGPS :-
 Technique used to correct some of these errors.
 Referred to as “differential GPS” or DGPS.
 In DGPS, two GPS receivers are used.
 One receiver is located at an accurately surveyed point
referred to as the “base station”.
 A correction is calculated by comparing the known
location to the location determined by the GPS satellites.
 The correction is then applied to the other receiver’s
(known as the “rover”) calculated position.

19. DGPS METHODS :-
 Post-processing
 Corrections performed after the data is collected.
 Special software required .
 Real-time
 Corrections are performed while the data is being
collected.
 Need special equipment to receive the DGPS signal.

20. GPS APPLICATIONS :-
 GPS in the air
 GPS on land
 GPS in sea
 Military Uses for GPS
 GPS in scientific research
 Applications for your business
 Monitor Nuclear Explosions
 Every Day Life
 Set Your Watch!

21. CONCLUSION :-
 GPS will find more civilian uses
 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.
 DOD has promised to eliminate Selective Availability