Presented by
PRANAY MONDAL M.Tech. (Communication System Engg.)
ROLL - 1351015
GLOBAL POSITIONING SYSTEM
CONTENTS :- Introduction
What is GPS?
Basic principal of GPS
Information in a GPS signal
GPS segments
Errors in GPS
DGPS
GPS application
Conclusion
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
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.
BASIC PRINCIPAL OF GPS :-
Trilateration :
Trilateration (cont.) :-
2D & 3D Positioning by Satelites
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
GPS SEGMENTS :-
Space segment
Control Segment
User Segment
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.
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.
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.
CONTROL SEGMENT :-The CS consists of 3 entities:
i) Master Control Station , ii) Monitor Stations ,
iii) Ground Antennas
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.
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.
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.
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.
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 .
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.
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.
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!
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
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