satellite communications ppt.pptx

7/30/2019 satellite communications ppt.pptx

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It is originated fromthe latin word satellit-meaning an attendant,one who is constantlyhovering around andattending to a master

or big man. A heavenly objectwhich revolves aroundsome heavenly body dueto gravitational force. A communication

satellite (COSMAT) is anartificial satellite sent tospace for the purpose oftelecommunications.


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Two stations on earth

want to communicatethrough radio broadcastbut are too far away to useconventional means.

The two stations can use asatellite as a relay station

for their communication.One earth station sends a

transmission to thesatellite. This is calledUPLINK. The satellitetransponder converts thesignal and sends it downto the second earthstation. This is calledDOWNLINK.


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The first artificial satellite

was SOVIET SPUTNIKlaunched on October 4

1957.

The first American satellite

to relay communications wasPROJECT SCORE in 1958.

TELSTAR was the first act

relay 1 launched on Dec 13

1962 and was first to transmit

across pacific.

India launched its first

artificial satellite in 1975.


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Satellites are mainly of twotypes:1.Active satellites

2.Passive satellites

Active satellites: These

satellites have a processing

equipment called

transponder and prevents

interference of signals.

Passive satellites: These are

relay stations in space ,they

include natural satellites

and artificial satellites.


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Based on satellite orbitsGeo stationary earth orbit(GEO) Low earth orbit(LEO)

Medium earth orbit(MEO)

Molniya orbit


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These satellites revolve in a orbit35,863 km above the earths surfacealong the equator. Objects in geostationary orbit revolvearound the earth at the same speed asthe earth revolves. So they are always in

a position relative to earth.GEO orbit is useful for communicationbecause ground antennas can be aimedat the satellite with out having to trackthe satellite motion which is veryinexpensive.

Satellite can not serve extreme northand south areasHeight of the orbitSignificant delay of 0.25 sec incommunications


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LEO satellites are much closer to earth than GEO

satellites ranging from 500 -1500 kms above the earth

surface and correspondingly a period of 90 minutes.

Leo satellites do not stay in a fixed position relative to

earth and are only visible for 15 -20 minutes each pass.

So ,for uninterrupted connectivity a network of LEO

satellites is necessary.

Due to the proximity to the ground, these do notrequire a high signal strength.

A group of satellites working in concert is known as

satellite constellation.Two such constellations intended

to provide satellite phone services to remote areas are

IRIDIUM and GLOBALSTAR systems. Another such wasTELEDESIC.

Discontinuity coverage


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Medium earth orbits(MEO) are at a

distance 2 -8000 kms above the earthssurface.

These satellites have a larger

coverage area than LEO satellites.

A MEO satellite longer duration of

visibility and wider footprint means

fewer satellites are needed in a MEO

network than a LEO network.

A MEO satellite s distance gives it alonger time delay and weaker signal

than a LE0 satellite, though not as bad

as a GEO satellite.


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Used by Russia for decades.This satellites are mainly designed tooperate in the areas of extreme northernand southern latitudes which is the main

drawback of GEO satellites.Molniya orbits are highly inclinedguaranteeing good elevation over selectedpositions during the northern portion ofthe orbit.Period of molniya satellite is half day. so

it is available for operation over the targetfor 6-9 hrs every revolution. So aconstellation of 3 molniya satellites canprovide an uninterrupted coverage.


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TELEPHONE:

The first and historical most important application for

communication satellites was an intercontinental long

distance telephony.

The fixed public switched telephone network

relays telephone calls from land line telephones to

an earth station, where they are then transmitted to a

geostationary satellite. The downlink follows an

analogous path.

With the evolution of fibre optics, the use of satellites

declined but they still serve the remote islands where no

submarine cables are in service.

Satellite phones connect directly to a constellation

either GEO or LEO satellites. calls are then forwarded to

satellite teleport connected to public switch telephone

network.


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Satellite often used as a weapon.A satellite itself neither military norcivil.

1)constellation of military satellites

managed by U.S air force2)provide wideband, narrow bandand protected militarycommunication systems. Wideband: high band width

transfers Protected: more sophisticatedsecurity like nuclear survivability

Narrow band: basic communication


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The advent of HRPT in the 19th

century allowed real time weatherforecasting to become a reality.

Small scale features (mesocyclones,

polar lows) as well as long scale

features (katabatic winds) could be

detected in infrared channel.

1.Lack of high performance

communication links.

2. Development and implementationof software to derive and visualize

products has been lagged.


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1. Payload:

Transponder : Transmit, Receive antennas

other equipments

Receives signals: multiplex, demultiplex , amplify andtransmit.

2. Support Subsystems :

Power Supply, Altitude, orbit control equipment.

Telemetry, Telecommand systems.


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Series of interconnected units

which forms a communication

channel between the receiving

and transmitting antennas.

Transponder is actually

composed of:

1. Input band limiting device

2. An input low noise amplifier

3. Frequency translator4. Output band pass filter

5. Power amplifier


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ADVANTAGES OF COMSAT OVERTERRESTRIAL COMMUNICATION

Coverage area of satellite greatly exceeds than that of

terrestrial system.

Satellite to satellite communication is very precise.

Higher bandwidths available.

Transmission cost of a satellite is independent of the distance

from the center of the coverage area.


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Launching satellite into orbit is

costly.

Satellite band width is graduallybecoming used up.

Failure of satellites during the

equinox period.


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ISRO is amongst the six largest government space agencies inthe world.Indias first satellite ARYABHATA was built by ISRO

First satellite launched by ISRO was SLV3

LAUNCH VEHICLE FLEET:SLV: 4 stage solid fuel light launcher. Intended to reach a

height of 500km.ASLV: 5 stage solid propellent rocket with the capability of

placing 150kg into LEO.

PSLV: 1. design to launch Indian remote sensing satellites.

2. It launched 10 satellites at once, breaking the world record of

Russia.

GSLV:

1.Developed to launch INSAT type vehicles.

2.It is the heaviest satellite launch vehicle of ISRO.

Comparison ofIndian carrierrockets. Left toright: SLV,ASLV,PSLV, GSLV, GSLV

III.
http://en.wikipedia.org/wiki/Satellite_Launch_Vehiclehttp://en.wikipedia.org/wiki/ASLVhttp://en.wikipedia.org/wiki/PSLVhttp://en.wikipedia.org/wiki/GSLVhttp://en.wikipedia.org/wiki/GSLV_IIIhttp://en.wikipedia.org/wiki/GSLV_IIIhttp://en.wikipedia.org/wiki/GSLV_IIIhttp://en.wikipedia.org/wiki/GSLV_IIIhttp://en.wikipedia.org/wiki/GSLVhttp://en.wikipedia.org/wiki/PSLVhttp://en.wikipedia.org/wiki/ASLVhttp://en.wikipedia.org/wiki/Satellite_Launch_Vehicle


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