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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!!!