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7/31/2019 Satellite Pre2

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Satellite Communications

Fahad Faraz Ahmad

Reg#2009-ee-470


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Overview

Basics of Satcom

Working of Satellite Modulation Schemes

Types & services

VSAT & GPS Frequency Bands

Satellite Communication

Organizations


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What is Satellite?

Satellite is a largemicrowave repeater in thespace.

It contains severaltransponders which listensto some portion of

spectrum, amplifies theincoming signal andbroadcasts it in anotherfrequency.


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Major Parts:

Altitude and Orbit Control System rocket to move satellite back to the correct orbit

keep antennas point toward earth

Operation center

TTC & M SSC - Satellite Control Center OCC - Operations Control Center SCF - Satellite Control Facility

Power system electrical power from solar cells

Communication subsystem

one or more antennas and a set of receivers and

transmitters (transponders)


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How do Satellites Work? Use a satellite as a relay

station.

One Earth Station sends atransmission to thesatellite. This is called aUplink.

The satellite Transponderconverts the signal andsends it down to the secondearth station. This is calleda Downlink.


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Transponders

Repeaters Carried by Communications Satellites

Low Noise Amplifier(LNA)

Heterodyning (frequency changing) High Power Amplifier(HPA)


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Factors in satellite communication

Elevation Angle: The angle ofthe horizontal of the earth surface

to the center line of the satellitetransmission beam.

Coverage Angle: A measure ofthe portion of the earth surface

visible to a satellite taking theminimum elevation angle intoaccount.


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Other Factors:

Propagation Delay

Free Space Loss

Satellite Footprint

Atmospheric Attenuation

Atmospheric absorption

Traveling ionosphericdisturbances

Cloud attenuation

Rain attenuation


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Propagation Delay:


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Modulation schemes:


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Satellite communication

services:Fixed Service Satellites

(FSS)

Example: Point to Point

CommunicationBroadcast Service

Satellites (BSS)

Example: SatelliteTelevision/Radio

Also called Direct BroadcastService (DBS).

Mobile Service Satellites(MSS)

Example: Satellite Phones


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Types of Satellite based Networks

GEO Geostationary Orbits

36,000 km above Earth

Commercial and militarysatellites

Three satellite are used for wholeearth coverage

MEO Medium Earth Orbits

From 5000 to 15000 km

Navigation satellites (GPS)

LEO

Low Earth Orbits 500 to 1000 km above Earth

Military intelligence satellites,weather satellites

HEO High Elliptical Orbits

Satellite Handover


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VSAT Network At the Very Small Aperture Terminala lower

performance microwave transceiver and lower

gain dish antenna (smaller size) is used.

Ideal for centralized networks with a central host(Banking institutions with branches all over the

country). Star configuration Mesh configuration Use the ALOHA and TDMA for communication


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VSAT Network Component: AVSAT network has

three components:

A central hub (MES)The satellite

A Number ofVSATearth stations invarious locations -across a country orcontinent


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Global Positioning System(GPS)

GPS is a space-based satellite navigationsystem that provides location and time

information in all weather, anywhere on or nearthe Earth

6 orbit and 24 or more GPS satellites

It is maintained by the United Statesgovernment

Freely accessible to anyone with a GPS receiver.
http://en.wikipedia.org/wiki/Satellite_navigationhttp://en.wikipedia.org/wiki/Positioning_systemhttp://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/GPS_receiverhttp://en.wikipedia.org/wiki/GPS_receiverhttp://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/Positioning_systemhttp://en.wikipedia.org/wiki/Satellite_navigation


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Basic concept of GPS A GPS receiver calculates

its position by precisely

timing the signals sent byGPS satellites high abovethe Earth. Each satellitecontinually transmits

messages that include the time the message was

transmitted

satellite position at timeof message transmission
http://en.wikipedia.org/wiki/Satelliteshttp://en.wikipedia.org/wiki/Satellites


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Components of GPS:

The current GPSconsists of three

major segments

Space segment (SS)

Control segment

(CS) User segment (US)


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MAC(Media Access Control)

protocols for satellite links ALOHA:

Every station can transmit any time

Very low efficiency 18- 36 %.

FDMA(Frequency Division Multiple Access):

It is the oldest and most common.

the available satellite channel bandwidth is

broken into frequency bands for differentearth stations.


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TDMA (Time Division Multiple Access

) : Each earth station gets to transmit in a fixed time

slot only. Requires time synchronization between the Earth

Stations. CDMA : (Code Division Multiple Access)

Combination of time/frequency multiplexing

( a form of spread spectrum modulation). It provides a decentralized way of providing

separate channels without timingsynchronization.


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Frequency Bands Different kinds of satellites use different

frequency bands. LBand: 1 to 2 GHz, used by MSS

S-Band: 2 to 4 GHz, used by MSS, NASA, deep spaceresearch

C-Band: 4 to 8 GHz, used by FSS

X-Band: 8 to 12.5 GHz, used by FSS and in terrestrialimaging, ex: military and meteorological satellites

Ku Band: 12 to 14.5 GHz

Ka Band: 17 to 31 GHz, The Ka and Ku bands arereserved exclusively for satellite communication butare subject to rain attenuation


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Advantages of SatelliteCommunication: The advantages of satellite communication over

terrestrial communication are:

The coverage area of a satellite greatly exceedsthat of a terrestrial system.

Transmission cost of a satellite is independent ofthe distance from the center of the coverage area.

Satellite to Satellite communication is veryprecise. Higher Bandwidths are available for use.


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Disadvantages of Satellitecommunication: The disadvantages of satellite communication:

Launching satellites into orbit is costly.

There is a larger propagation delay in satellitecommunication than in terrestrialcommunication.

Satellite bandwidth is gradually becomingused up.


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Satellite communication OrganizationsITSO previously known by the acronym, INTELSAT, global cooperation in satellite communications

ESA ESA is responsible for developing new technologyfor European space industries for the field ofsatellite communications

NATIONAL ORGANIZATIONS

National Aeronautics and Space Administration(NASA)

Japan Aerospace Exploration Agency(JAEA) China National Space Administration(CNSA) etc.


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Thank you

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