presentation sattelite communication 2

7/31/2019 Presentation Sattelite Communication 2

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By Rajendra Kuma

http://powerpointpresentationon.blogspot.com
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Satellite

Communication


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What is satellite?

Satellite is a repeater in thesky.

Receives uplink frequencies and translates todownlink frequencies and transmits back to theearth station after

Amplification The translation is done to avoid +ve feed

back.Trying to

receive and transmit an amplified version of the sameuplink waveform at the same satellite will causeunwanted feedback, or ring around, from the downlinkantenna back into the receiver


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What is a communications satellite and how does it

work?

A communications satellite is a radio relay station in orbit above the earth thatreceives, amplifies, and redirects analog and digital signals carried on a specificradio frequency.In addition to communications satellites.

In satcom the satellite acts as a media for the data transfer between the source anddestination.Between the source and destination we use a pair of frequencies to communicate.The Satellite acts as a frequency translator and amplifier.


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What are the different kinds of orbits?

An orbit is the path that a satellite follows as it revolves around Earth. In terms ofcommercial satellites, there are three main categories of orbits:

500-2,000 km above the earth These orbits are much closer to the Earth, requiring satellites to travel at a very

high speed inorder to avoid being pulled out of orbit by Earth's gravity At LEO, a satellite can circle the Earth in approximately one and a half hours

LEO( Low Earth Orbit)


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MEO( Medium EarthOrbit)

8,000-20,000 km above the earth These orbits are primarily reserved for communications satellites that cover the

North andSouth Pole MEO's are placed in an elliptical (oval-shaped) orbit


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GEO( GeosynchronousOrbit)

35,786 km above the earth

Orbiting at the height of 22,282 miles above the equator (35,786 km), thesatellitetravels in the same direction and at the same speed as the Earth's rotation on itsaxis,taking 24 hours to complete a full trip around the globe. Thus, as long as asatellite ispositioned over the equator in an assigned orbital location, it will appear to be

"stationary" with respect to a specific location on the Earth. A single geostationary satellite can view approximately one third of the

Earth's surface.If three satellites are placed at the proper longitude, the height of this orbit allowsalmost all of the Earth's surface to be covered by the satellites.


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Polar OrbitingSatellite

These satellites orbit the earth in such a way as to cover the north and southpolar regions.

These satellites if in a low earth orbit have to travel at a very high speed.

These satellites can be kept in low earth orbit (800 -900 km) or at 36000kmapart.


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Geo-SynchronousSatellite

Orbit on the equatorial plane - appears stationary

Altitude of 36000 Kms.

Circular orbit around earth with period of 24 hours.

Coverage of about 1/3 of Earth.

2 deg. apart. Identified by Longitudinal position with ref. to

Greenwich.

Advantage Of GeostationarySatellite

Simple ground station trackingrequirements.

Removes Satellite hand-overproblems.

Negligible Doppler shift


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A disadvantage of Geostationary satellites is that points on Earthbeyond about 80 deg latitude are not visible.

Inclined orbits, on the other hand can provide visibility to thehighernorthern and southern latitudes, although they require earth stationsto continually track the satellite.

Inclined OrbitSatellite


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Geosynchronous

Transponder

Footprint

Frequency

Polarization

Path Propagation

Timing

Satellite Access

Link Performance

Technical

Term


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Geosynchronous

Geosynchronous means that the satellite is synchronized with the earth in time and

direction. It means that is time taken by a satellite to complete its orbit around earthis equal to the time taken by to earth rotates around its own axis.

Transponder

Frequency band on the satellite is divided into several channels. Each channels arecalled transponder Each transponder have 40 MHz.

Satellite Footprint

Coverage of entire surface of earth that is visible by thesatellite.


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Frequency Band Range

L-Band 1 to 1.5 GHz

S-Band 1 to 3.9 GHz

C-Band 3.9 to 8 GHzX-Band 8 to 12.5 GHz

Ku-Band 10.95 to 18 GHz

K-Band 18 to 26.5 GHz

Ka-Band 26.5 to 40 GHz

Frequency Bands use in SatelliteCommunication


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Advantages And Disadvantages of Different FrequencyBand

C-BandAdv. : Broad Footprint, little rain fadeDisadv. : Weak signals, interference, large antenna sizesand amplifiers

ExC-Band

Adv.. : Broad Footprint, little rain fade, less interferenceDisadv. : Week signals, large antenna sizes and amplifiers

Ku-BandAdv. : Focused Foot prints, no terrestrial interferencesmall antenna and amplifierDisadv. : Interference to rain.

Ka-BandAdv. : Focused Foot prints, large unusedbandwidthsDisadv. : Interference to rain.


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FREQUENCY BAND UPLINK DOWNLINK

C-Band 5.925-6.425 3.700-4.200

Ex.C-Band 6.725-7.025 4.500-4.800

Ku-Band 14.00-14.50 10.95-12.75

Ka-Band 30.00 20.00

Satellites Uplink And Downlink Frequency in DifferentBands

** all frequencies are inGHz.


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VSAT Technology in Satellite Communication

VSAT stands for Very Small Aperture Terminal

It is a two way satellite ground station.

VSATs are most commonly used to transmit narrowband data orbroadband data.

VSATs access satellites in geosynchronous orbit to relay data fromsmall remote

earth stations (terminals) to other terminals or master earth station "hubs.


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Remote VSAT1 Remote VSAT

2

Earth Station

(HUB)

UplinkDownlink

Satellite

SatelliteLink


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Topologie

s

Star Topology

As the Hub is a powerful receiver and retransmitter , the remote VSATsites are

comparatively small.

A central uplink site, such as a Network Operation Center (NOC), totransport

data back and forth to each VSAT terminal via satellite

VSATs communicate to Hub on Inroutes and the Hub Communicates to

VSATs onthe Outroute

VSAT SystemArchitecture


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Mesh Topology

Each VSAT terminal relays data via satellite to another terminal by acting asa hub, minimizing the need for a centralized uplink site.

VSATs are comparatively larger as they have to communicate directly witheach other

VSATs communicate directly with each other, Hub will be involved only forcall

setup and then fade out.( Hub will not be involved in permanent Circuits)


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Parts Of

VSATs

Antenna

Block Up Converter (BUC)

Low Noise Block Converter(LNB)

Orthomode Transducer(OMT)

Interfacility Link Cable (IFL)

Indoor Unit (IDU)


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Types OfAntenna

Prime FocusAntenna Single Reflector Antenna. Feed horn is placed at the Focal point

of the Reflector. Antenna Electronics are placed on

Feed. More susceptible to Interference fromLow elevation sources.

More Blockage because feed. Antenna Efficiency is in the range of

60%. Low Cost Antenna.

Primarily Used for Receive onlyapplications.


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CassagrainAntenna

Main reflector is Paraboloid Sub-Reflector is hyperboloid and

placed at Prime Focus Feed is Corrugated Horn and is

placed at Center of the MainReflectors.

The paraboloid converges towardsthe Sub Reflector ( prime focus),which is then reflected by Sub-Reflector to form a Spherical Waveconverging on the Feed.


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GregarionAntenna

Main reflector is Paraboloid Sub-Reflector is Paraboloid and

placed at Prime Focus Feed is Corrugated Horn and is

placed at Center of the MainReflectors.

The paraboloid converges towardsthe Sub Reflector ( prime focus),which is then reflected by Sub-Reflector to form a Spherical Waveconverging on the Feed.


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Offset FedAntenna

Used for Smaller Earth Stations. Main Reflector is a section of

Parabolic, cutoff above the axis. Feed is located below the axis

giving a completely unblockedAperture.

High Antenna efficiency.


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A BUC (Block Up-Converter) takes an L-Band input and transmits it upstream to thesatellite on Ka, Ku, or C band.

BUC's are rated according to their output

power. A low power Ka-Band BUC cantransmit with as little as 2 watts, while ahigh power C-Band BUC can transmit withas much as 200 watts.

Block Up-Converter(BUC)


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Low Noise BlockConverter(LNB)

It is typically mounted at the focal point ofthe

receiving parabolic dish.

It's primarily used to amplify and convertreceivedsatellite signals into frequencies compatible withthe satellite receiver.


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Orthomode Transducer(OMT)

OMT is 3-port microwave waveguidesystem that split input power into twoparts, allow the simultaneous operation oftwo outdoor radio units

OMT can be directly mounted on theantennas that have circular waveguide

connector.


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Interfacility Link Cable (IFL)

Interfacility Link (IFL) DistributionCable is an indoor rated,connectorizedcable assembly that is used within abuilding to connect a fiber feeder

splicepoint to an optical connectordistribution panel.

The cable can be terminated withconnectors at one or both ends inconjunction with various styles of fan-

out kits at any breakout length.


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Indoor Unit (IDU)

Its Satellite Modem consists of Modulatorand

Demodulator. The IDU also determines the access

schemesunder which the VSAT would operate. The IDU also interfaces with various end

userequipment, ranging from stand alonecomputers,LAN's, routers, multiplexes, telephone

instruments, EPABX as per the requirement.


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