Gps by Jhasketan Sahu

7/31/2019 Gps by Jhasketan Sahu

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GLOBAL POSITIONING

SYSTEM

PRESENTED BY ::-

JHASKETAN SAHU

0801300154

CSE (3rd YEAR)

HI-TECH INSTITUTE OF TECHNOLOGY


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INTRODUCTION

o TheGPS is a satellite based Radio Navigation

system, that utilizes precise range measurements

from the GPS satellites to determine precise

position anywhere in the world.


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Globe Positioning System (GPS)

http://maic.jmu.edu/sic/glossary.htm#Projectio

n

o GPS is a Satellite NavigationSystem

o GPS is funded and controlledby the U. S. Department of

Defense (DOD). While thereare many thousands of civilusers of GPS world-wide, thesystem was designed for andis operated by the U. S.military.

o GPS provides specially codedsatellite signals that can beprocessed in a GPS receiver,enabling the receiver tocompute position, velocityand time.

o At least 4 satellites are usedto estimate 4 quantities:position in 3-D (X, Y, Z) and

GPSing time (T)

20,000 km


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Components of the GPS

S p a c e S

C o n t r o l

U s e r S e

G P S


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Space Segment:

o 24 GPS spacevehicles(SVs).

o Satellites orbit the

earth in 12 hrs.o 6 orbital planes

inclined at 55degrees with the

equator.o This constellation

provides 5 to 8SVs from any

point on the earth.


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Control Segment:

o The control segment comprises of 5stations.

o They measure the distances of the overheadsatellites every 1.5 seconds and send thecorrected data to Master control.

o Here the satellite orbit, clock performanceand health of the satellite are determinedand determines whether repositioning isrequired.

o

This information is sent to the three uplinkstations


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User Segment:

o There are two services SPS and PPSo The Standard Positioning Service

n SPS- is position accuracy based on GPS

measurements on single L1 frequencyC/A code

n C/A ( coarse /acquisition orclear/access) GPs code sequence of

1023 pseudo random bi phasemodulation on L1 freq


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User Segment:

o The Precise Position Servicen PPS is the highest level of dynamic

positioning based on the dual freq P-

coden The P-code is a very long pseudo-

random bi phase modulation on the GPScarrier which does not repeat for 267

daysn Only authorized users, this consists of

SPS signal plus the P code on L1 and L2and carrier phase measurement on L2


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GPS Satellite Signal:

o L1 freq. (1575.42 Mhz) carries the SPScode and the navigation message.

o L2 freq. (1227.60 Mhz) used to measure

ionosphere delays by PPS receiverso 3 binary code shift L1 and/or L2 carrier

phasen The C/A coden

The P coden The Navigation message which is a 50 Hz signal

consisting of GPs satellite orbits . Clockcorrection and other system parameters


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NAVIGATION

o Navigation is used forestimating the position of a

vehicle on sea, in air orand on land to ensure thatthe chosen route is

followed accurately.

o GPS satellitesconstellations orbitconsists of 24 satellitesorbiting in 6 orbits,4each.they are orbitingaround earth in every 12hours emitting continuousnavigation signals.


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HOW DOES IT WORK?

o GPS providesspecially codedsatellite signals thatcan be processed ina GPS receiver,

enabling the receiverto compute position,

velocity and time.

o Four GPS satellitesignals are used tocompute positions inthree dimensions

and the time offset

in the receiver clock.


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SATELLITE NAVIGATION

o This is based onmeasurement of the

times of arrival of the

time signals received

from 3 or more

orbiting satellites,

whose positional

coordinates in space

are also transmitted.

o The limiting pulses

are sent out by eachsatellite in the L-

Band, using spread

spectrum modulation

and are received by

the GPS Receivers in


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SATELLITE TRANSMISSION

o The space vehicles transmit two microwave

carrier signals. The L1 frequency ranging about

1575.42 MHz carries the navigation message and

the SPS code signals. The L2 frequency about

1227.60 MHz is used to measure the ionosphericdelay by PPS equipped receiver.

o Three types of binary codes are there which shifts

the L1 and/or L2 carrier phase.

The C/A Code (Coarse Acquisition) The P-Code (Precise) The Navigation Message


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RECEIVER POSITION, VELOCITY AND

TIME

GPS RECEIVER


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POSITION &TIME DETERMINATION


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RADIO NAVIGATION

o The basis of Global Navigation for an AGV isreliably gaining a co-ordinate of vectordescribing where the vehicle is in relation to afixed point on the globe.

o This point is generally taken to be theintersection of the Greenwich meridian and theequator line of latitude, at sea level - inaccordance with standard geographical practice.

o Using this position information, with referenceto a map or otherwise, a list of waypoints can begenerated and followed to allow the vehicle tonavigate between end points of a journey.


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WAYPOINT NAVIGATION

o A waypoint is an address whichdefines starting point, expected

destination point, a place to avoid or

sometimes the intermediate positionalong the way.

o The Destination Waypointo Routeso Mob (man over board) position waypointo Navigating To Single Way Point


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NASA Landsat-7 (ETM+)

launched 4/15/1999

SpectrumVisible

Near Infrared

Thermal Infrared

Bands8

Resolution (m)

15, 30, 60

705 km


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Terra satellite launched

on 12/18/1999

http://terra.nasa.gov/About/MODIS/modis_swath.html

SpectrumVisible

Near InfraredThermal Infrared

Bands36

Resolution (m)250, 500, 1000

705 km


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Global Geostationary Satellites

Europe andAfrica

N. & S.American Eastern

Pacific

Jap. Aus. W.Paci

C. Asia, India China, India

Earth radius 6,370 kmSatellite altitude 35,800 km


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Image processingand modeling

Imageprocessing

andmodeling

Soil

moistu

Surface

tempert

Rainf

all

E

T

Snow

and

Wat

er

Vegetati

on

Lan

d

The size of a cell we call image resolution,depending onSuch as 1 m, 30 m, 1 km, or 4 km


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http://www.geoplane.com/gpsneeds.html


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Errors

o Satellite errorsn Errors in modeling clock offsetn Errors in Keplerian representation of ephemerisn

Latency in trackingo Atmospheric propagation errors

n Through the ionosphere,carrier experiencesphase advance and the code experiences groupdelay

Dependent ono Geomagnetic latitudeo Time of the dayo Elevation of the satellite


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Errors

o Atmospheric errors can be removed byn Dual freq measurementlow freq get refracted more than high freq

thus by comparing delays of L1 and L2

errors can be eliminated

o Single freq users model the effects of

the ionosphere


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Errors

o Troposphere causes delays in code andcarrier

But they arent freq dependentBut the errors are successfullymodeledo Errors due to Multipatho Receiver noise


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Errors due to geometry

o Poor GDOPn When angles from

the receiver to the

SVs used aresimilar

o Good GDOPn

When the anglesare different


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CONCLUSION

o Though Navigation was someday anunsolved mystery but GPS made itpossible in all types of Navigation suchas Space, Ground and Marine

Navigations.

o further researches are making it day byday more useful and the prediction says

that all the problems regarding positionfixing and determination will be solvedby the development of GPS efficiency


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THANK YOU!!!

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Gps by Jhasketan Sahu