Chapter 1 - Satcom
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Transcript of 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
COMMUNICATION SYSTEMS (SCS)
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
COMMUNICATION SYSTEMS (SCS)
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 :-
SATELLITE COMMUNICATION
SYSTEM (SCS) BLOCK DIAGRAM
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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
SATELLITE COMMUNICATION
SYSTEM (SCS) BLOCK DIAGRAM
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Satellite Communication Systems(SCS) by Jayen Modi10
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:-
SATELLITE COMMUNICATION
SYSTEM (SCS) BLOCK DIAGRAM
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Satellite Communication Systems(SCS) by Jayen Modi11
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:-
SATELLITE COMMUNICATION
SYSTEM (SCS) BLOCK DIAGRAM
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Satellite Communication Systems(SCS) by Jayen Modi12
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
SATELLITE COMMUNICATION
SYSTEM (SCS) BLOCK DIAGRAM
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Satellite Communication Systems(SCS) by Jayen Modi13
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 :-
SATELLITE COMMUNICATION
SYSTEM (SCS) BLOCK DIAGRAM
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Satellite Communication Systems(SCS) by Jayen Modi14
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 :-
SATELLITE COMMUNICATION
SYSTEM (SCS) BLOCK DIAGRAM
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Satellite Communication Systems(SCS) by Jayen Modi15
SATELLITE COMMUNICATION
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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Satellite Communication Systems(SCS) by Jayen Modi16
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 :-
SATELLITE COMMUNICATION
SYSTEM (SCS) CONFIGURATION
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Satellite Communication Systems(SCS) by Jayen Modi17
Satellite System Configuration
1. THE SPACE SEGMENT
intersatelliteintersatellite
communicationcommunication
(constellation)(constellation)SatelliteSatellite
11
SatelliteSatellite
22
SatelliteSatellite
33
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Satellite Communication Systems(SCS) by Jayen Modi18
Satellite System Configuration
1. THE SPACE SEGMENT
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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Satellite Communication Systems(SCS) by Jayen Modi19
Satellite System Configuration
1. THE SPACE SEGMENT
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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Satellite Communication Systems(SCS) by Jayen Modi21
Different Types of Payload
(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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Satellite Communication Systems(SCS) by Jayen Modi22
Different Types of Payload
(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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Satellite Communication Systems(SCS) by Jayen Modi23
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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Satellite Communication Systems
(SCS) by Jayen Modi25
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
Satellite System Configuration
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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Satellite Communication Systems
(SCS) by Jayen Modi27
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