chapter 1 - satcom

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Module 1Module 1

INTRODUCTIONINTRODUCTION

SatelliteSatelliteCommunicationCommunication

SystemsSystems


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THE ORIGIN OF SATELLITE

COMMUNICATION SYSTEMS (SCS)

To achieve ever increasing ranges (distances) High data transmission capacity & large bandwidth

Lowest possible cost & maintenance

1. Objective behind their development :-

2. Much development after World War II :- Advances in missiles & microwaves (RADAR)

Expertise from combined use of these techniques

Research in communications & space technologies


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THE BIRTH OF SATELLITE


Satellite in the circular equatorial orbit at 42,242 km away has angular

velocity equal to that of the earth Hence by remaining always above the same spot on the ground, relaying

signals from most hemisphere

Three satellites spaced 120 apart would cover the whole world with some

overlapping regions

Electrical power required for satellite operation can be obtained from suns

radiations (solar energy)

Postulated by Arthur C. Clarke in 1945 :-Postulated by Arthur C. Clarke in 1945 :-


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satellitesatellite

11

satellitesatellite

22

satellitesatellite33

THE BIRTH OF SATELLITE


orbit at 42,242 kmorbit at 42,242 km

above earths surfaceabove earths surface

120120 angular separation angular separation

between the satellitesbetween the satellites


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EVOLUTION OF SATELLITE

COMMUNICATION SYSTEMS (SCS) I

1945 Postulated by Arthur C. Clarke (1917 2008)

1957 Russia (then USSR) launches Sputnik I, the first ever artificial satellite launched in space

1958 SCORE (signal communication by orbiting relay equipment) launched by the USA

1960 First ever communication satellites ECHO I & ECHO II launched as floating balloons (passive)

1962 Bell Laboratories launched the TELSTAR I

1963 First geostationary satellite named SYNCOM


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EVOLUTION OF SATELLITE

COMMUNICATION SYSTEMS (SCS) II

1965 First communication satellite INTELSAT I was launched with two 25 MHz transponders

1970s About 14 INTELSAT series 3 & 4 satellites were launched for climate & weather forecasting

1975 India launches Aryabhatta, its first satellite

1980s About 15 INTELSAT series 5 & 6 launched for TV transmission, multiple access, weather etc.

1990s INTELSAT series 7 & 8 launched in Ku band

2000s INTELSAT series 9 launched in the Ka band


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SATELLITE COMMUNICATION

SYSTEM (SCS) BLOCK DIAGRAM

USERUSER

USERUSER

TERRESTRIALTERRESTRIAL

NETWORKNETWORK

TERRESTRIALTERRESTRIALNETWORKNETWORK

EARTHEARTH

STATIONSTATION

EARTHEARTH

STATIONSTATIONCOMMUNICATIONCOMMUNICATION

SATELLITESATELLITE

downlink frequencydownlink frequencyuplinkuplink

frequencyfrequency


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User at Source & Destination (Tx & Rx)

Terrestrial Network at Transmitter & Receiver

Earth Station at Transmitter & Receiver

Transmitting & Receiving Antenna

Communications Satellite

Uplink & Downlink Frequencies

Contains the following main elements :-




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Satellite Communication Systems(SCS) by Jayen Modi9

Source & destination terminals on the earth

Transmits & receives the message/data signals

Connected to earth station by terrestrial network

Modulates/demodulates at lower frequencies (MHz)

Belongs to the ground segment category

Data/information can include these types :-

1. User at source & destination (Tx & Rx) :-

text/symbols/words speech/sound/audio pictures/images/video




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Intermediate link between the user & earth station

Relays data from user to satellite & vice versa

Wired/wireless network on the ground (terrestrial)

Wired links may include twisted pair, coaxial & OFC

Wireless links are short/medium distance RF links

Switching/multiplexing network or a dedicated one

2. Terrestrial network at Tx & Rx:-




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Intermediate link between the user & the satellite

Relays data from user to satellite & vice versa

Modulates/demodulates at high frequencies (GHz)

Contains highly directional dish/parabolic antennas

Works with uplink & downlink frequencies (6/4 GHz)

Modulated signal amplified by high power amplifier

Receiver earth station uses low noise amplifier

3. Earth Station at Tx & Rx:-




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Unidirectional antennas having high directive gain

Relays signals to & from the satellite & earth station

Transmits uplink frequencies from the earth station

Receives downlink frequencies from the satellite

Basically parabolic dish reflector antennas used

4. Transmitting & Receiving Antenna :-

types oftypes of

parabolicparabolic

reflectorsreflectors




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Spacecraft in placed in an orbit above the earth

Relays signals between two terrestrial users (earth)

Located in the space segment category

Satellite consists of the payload & the platform

Payload Tx & Rx antenna with electronic systems useful for data communication & transmission

Platform consists of all individual subsystems that allow the payload to operate efficiently

5. Communication Satellite :-




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Frequencies over which the communication occurs

Uplink from the earth station to the satellite

Downlink from the satellite to the earth station

6/4 GHz (C band) for commercial broadcasting

8/7 GHz (X band) for government use (special)

14/12 GHz (Ku band) in current operational use

30/20 GHz (Ka band) for high B/W & low interference

6. Uplink & Downlink Frequencies :-




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SYSTEM (SCS) CONFIGURATION

SPACESPACE

SEGMENTSEGMENT

GROUNDGROUND

SEGMENTSEGMENTCONTROLCONTROL

SEGMENTSEGMENT

to & from theto & from the

service providerservice providerTerrestrialTerrestrialNetworkNetwork

useruser

terminalterminal

useruser

terminalterminal

1.1. SPACE SEGMENTSPACE SEGMENT

Intersatellite linksIntersatellite links

2. GROUND SEGMENT2. GROUND SEGMENT

Interface StationInterface Station

User StationUser Station

Service StationService Station

3. CONTROL SEGMENT3. CONTROL SEGMENT TT&C StationTT&C Station

Network ManagementNetwork Management


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The Space Segment contains one or several active & spare satellites organized into a constellation

The Control Segment all ground facilities for the control & monitoring of satellites, called as TT&C (telemetry, tracking& command) stations & for the management of traffic & on board resources

The Ground Segment consisting of all the traffic earth stations viz. interface, user & service station

It consists of the following segments :-


SYSTEM (SCS) CONFIGURATION


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Satellite System Configuration

1. THE SPACE SEGMENT

intersatelliteintersatellite

communicationcommunication

(constellation)(constellation)SatelliteSatellite

11

SatelliteSatellite

22

SatelliteSatellite

33


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Payload Transparent & Regenerative Platform Different Subsystems

Satellite Coverage Area (Footprint)

The space segment encompasses :-

Beam CoverageBeam Coverage Area CoverageArea Coverage

SingleSingle

BeamBeam

MultipleMultiple

BeamBeam

InstantaneousInstantaneous Long TermLong Term


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Contains one or more active & spare type satellites arranged together

in a constellation

Satellite consists of payload & platform (basic type) Payload Tx & Rx antennas & all electronic systems or equipments

which supports transmission

Platform All the possible satellite subsystems that allow the satellite

to operate efficiently

Two main type of payload viz. Transparent Payload & Regenerative

Payload


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Different Types of Payload

(a) TRANSPARENT PAYLOAD

Also called as bent type payload, where the carrier power is amplified &

frequency is downconverted

Power gain is typically 100 130 dB & is required to raise power level from

few pW to few watts (W)

Frequency conversion required to increase isolation between receiving

input & transmitting output

Overall payload bandwidth is split into several type of sub-bands, carriers

in each sub-band amplified by a dedicated power amplifier, called

transponders


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(a) TRANSPARENT PAYLOAD (contd.)

Bandwidth splitting is achieved using a set of filters called the input

multiplexers (IMUX)

The amplified carriers are then later recombined in the outputmultiplexers (OMUX)

Transparent payload belongs to a single beam type of satellite where

Tx & Rx antenna have one beam

For multiple beam antennas, routing of carriers from one upbeam to

given downbeam achieved through transponder hopping


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(b) REGENERATIVE PAYLOAD

In multiple beam regenerative payload all the uplink carrier frequencies are

demodulated

Baseband signal availability allows onboard signal processing &information routing through OBS@B

Frequency conversion is achieved by modulating on board generated

carriers at the downlink frequency

The modulated carriers are amplified & delivered to the destination

downbeam


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1. The Space Segment

SATELLITE BEAM COVERAGE

In satellite single beam coverage, a small spot or the region of the earths

surface is covered by the beam

The same satellite can also illuminate multiple spots or regions on theearths surface in multi-beam

Instantaneous system coverage consists of the total at a given time of

coverage areas of all the satellites

Long term coverage refers to the areas of the earth scanned over time by

the antennas of the satellites


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Satellite Communication Systems

(SCS) by Jayen Modi24

1. The Space Segment

THE PLATFORM SUBSYSTEMS

Attitude & Orbit Control Subsystem (AOCS) Propulsion & Thrust System

Electrical Power Supply Subsystem

Telemetry, Tracking & Command (TT&C)

Thermal Control Subsystem

Structural Subsystem

Platform consists of following subsystems :-


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Interface Stations known as gateways, which are used to

interconnect the space segment to existing terrestrial network &

hence user terminals Service Stations such as hub or feeder stations for collecting

or distributing information from & to user stations via the space

segment

User Stations like handsets, portables & mobile stations with

very small aperture terminals (VSAT) allowing direct access tothe space segment


2. THE GROUND SEGMENT


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2. The Ground Segment

GENERAL BLOCK DIAGRAM

GROUND SEGMENTGROUND SEGMENT

INTERFACEINTERFACE

STATIONSTATION

GatewayGateway

USERUSER

STATIONSTATION

VSAT HandsetVSAT Handset

SERVICESERVICE

STATIONSTATION

uplinkuplink

frequencyfrequencydownlinkdownlink

frequencyfrequency

terrestrialterrestrial

networknetwork

useruser

terminalterminal

Hub OR FeederHub OR Feeder

to & fromto & fromserviceservice

providerprovider


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2. The Ground Segment

EARTH STATION BLOCK DIAGRAM

LOW NOISELOW NOISE

AMPLIFIERAMPLIFIERIFIF

DEMODULATORDEMODULATOR

HIGH POWERHIGH POWERAMPLIFIERAMPLIFIER

IFIFMODULATORMODULATOR

TELEMETRY &TELEMETRY &

TRACKINGTRACKINGCONTROL &CONTROL &

MONITORINGMONITORING

POWERPOWER

SUPPLYSUPPLY

DIPLEXERDIPLEXER

basebandbaseband

signalssignals

TO USERSTO USERS

FROM USERSFROM USERS

chapter 1 - satcom

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