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