satellite communication fundamentals 1
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Satellite Communication
Fundamentals
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History of International
Communication 1850 - Submarine Telephone cable (UK & France)
1901 Transoceanic Long Wave Communication (Europe & America)
1926 Short wave communication (UK & Europe)
1945 Microwave Transmission System (Europe & America) 1945 Geo stationery Satellite concept by Arthur C Clarke
1956 Co-axial multi channel submarine cable (UK & USA)
1957First man made satellite Sputnik by USSR
1964 Formation of Intelsat Organization (UK, USA, Australia,Japan, Germany, Italy & France)
1965 First Communication Satellite (Intelsat - 1)
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Satellites
Arthur C. Clarkes vision:
3 Geostationary satellites illuminate theEarth
Illumination Lines
Satellite 1 Satellite 2
Satellite 3
17.4
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PolarOrbitInclined
Orbit
EquatorialOrbit
Equator
Satellites
Three Basic Orbits
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Satellites
What does Geostationary mean?
Geo = Earth, Stationary = Not Moving
Satellite is a Fixed Point in the Sky
Rotation of the Satellite = Rotation of the Earth(~24 Hrs/Rot)
Equatorial Plane (only possible orbit)
35,786 km above the Earths surface(only possible distance)
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Equatorial Plane
Station-keepingBox
42,16
5km
LongitudinalDrift+0.1
Variation due toOrbital Ellipticity
LatitudinalVariation
+0.1
NominalSatelliteLocation
Satellites
Geostationary Orbits
Satellite needs to stay within designated area:
Station-keeping box
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Transmit Antenna
Transponder(incl. Switching
Matrix)
Receive Antenna
Spinner
3-Axis Stabilized
Communications Satellites
What is a Communications Satellite?
ARadio Relayin the SkyReceives, amplifies and re-directs analog and digital
signals carried within a carrier frequency
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Electrical Power
CommunicationAntenna Payload
Spacecraft Control/Propulsion
Communications Satellites
What are the Satellite Components?
Main subsystems:
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Communication Satellite
Earth(M)
Satellite
(m)
Gravitational Force
GmM/R2
Centrifugal Force
mV2/R
At equilibration
mV2/R=GmM/R2
Since
V=R
R=(GM)1/3/ 2/3
Resolving
R=42,000 km
From Surface of Earth
R=42,000km-6,378km=35,786km
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Spin Stabilization
Three Axis Stabilization
Satellite Stabilization
wheel
motor
satellite
rotation
Motor applies torque to wheel (red)
Reaction torque on motor (green)causes satellite to rotate
Spin Stabilization For (cylindrical shape)
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Three Axis Stabilization (For cubical shape)
N
S
Satellite Position
(South - North Drift)
Orbital Path
Roll
Yaw
Pitch
Local Vertical
(East-West Drift)
Geostationary Orbits (especially 3-AxisStabilized S/C)
Station-keeping for East-West & North-South drift
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S
N
Sub Satellite Point
Longitude (Long=342 for IS-705)
Latitude (Lat=0 for all Intelsat Satellites)
Communications Satellites
What identifies a S/C? Each satellite is defined by its Sub Satellite Point (SSP)
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Satellite Architecture
Communications data passes through a satellite usinga signal path known as a Transponder.
Typically satellites have between 24 and 72transponders.
A single transponder is capable of handling up to 155million bits of information per second.
Simple voice or data to the most complex andbandwidth-intensive video, audio and Internet
content.
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Radio frequency bands
Band Frequency/(GHz)
UHF 0.3 1.0
L 1.0 1.5
S 1.5 3.9
C 3.9 8.0
X 8.0 12.5
Ku 12.5 18.0
K 18.0 26.5
Ka 26.5 40.0
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Communications Satellites
Why do we use satellites?
Global reach
Distance insensitive
Mobility and flexibility
Rapid deployment of ground equipment /ease of expansion
Bundling of applications
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Indian/APROcean Region
33E 64E 85E60E 66E 110.5 E62E 83E 157 E
AtlanticOcean Region
PacificOcean Region
304.5E 328.5E 340E307E 330.5E 342E310E 332.5E 359E325.5E 335.5E
174E 178E176E 180E
Communications Satellites
Where are the satellites located? Three Orbital Regions
AOR, IOR/APR, POR
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Co-located S/C
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Communications Satellites
How is simultaneous operation of satellitespossible?
Spacing (2-degree, 3-degree)
Coverage (different footprints)
Frequency (C-band, Ku-band, Ka-band )
How close can simultaneous satellites operate?
At different frequency bands:
Co-location: typically at 0.2 (~ 120 km)
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E/S
Distance between 2-degree Satellites:~ 1200 km
Distance between 3-degree Satellites:~ 1900 km
S/C 1
S/C 2
2
3S/C 3
Communications Satellites
Spacing
Why is the satellite spacing important?
Pointing error (E/S mispointing)
System margins (small error => BIG mistake)
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Spacing
Why is the satellite spacing important?(Continued)
Antenna size (radiation pattern) Small E/S (wide beam, low gain)
Large E/S (narrow beam, high gain)
What to keep in mind?
Interference margins (ASI)
Communications Satellites
Antenna Peak Gain
Large E/SSmall E/S
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Communications Satellites
Satellite Spacing:
Desired and un-desired
RADIO LINK
DESIRED
SATELLITE SPACING
UNWANTED SIGNALS
WANTED SIGNALS
SATELLITE ANTENNA
UNDESIREDSATELLITESPACING
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What is a Footprint?
Communications Satellites
Composite Plot/IBN
1-dB Contour Plot
Composite Plot / Satellite Guide
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+
How to visualize a footprint?
Communications Satellites
Like Mountains Profile:
Antenna Radiation Pattern: Cartesian Representation
Full Gain Grid - 1 dB steps
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1000
100
10
1SkyTemperature
(DegreesKelvin)
0.5 5 10 50
Frequency GHz
GalacticBackground
MicrowaveWindow
Sky Temp(Total)
Water VaporResonance
22 GHz
OxygenResonance
60 GHz
AtmosphereAbsorption
(Ka-Band)
C-Band Ku-Band
Satellite Communication
Why C- and Ku-band? ITU-assigned frequency band: 1 - 30 GHz
Low rain degradation
Low sky noise
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What is Polarization? Linear (vertical / horizontal)
All Intelsat Ku-band
C-band on [email protected], APR-1@83E and [email protected]
=> When used Simultaneously: Double theBandwidth
Circular (left-hand / right-hand)C-band on most Intelsat satellites
=> When used Simultaneously: Double theBandwidth
Satellite Communication
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Horizontal Polarization
Vertical Polarization
Linear Polarization
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Circular Polarization
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Communications Satellites
Why do we need solar panels?
Convert sunlight into electric power
Primary power supply
Only 10% - 14% of sunlight can be converted
Charge satellite battery system
Ceases during eclipse
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Autumn
Summer
Spring
Winter
Communications Satellites
What is theimpact of aneclipse?
No solar power Error in earth
sensor
Service outages
Eclipse: 21 MarchMax. Outage = 70 min.+ preceding & following days
Eclipse: 23 September
Max. Outage = 70 min.+ preceding & following days
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Satellite Communication
What is the Communication Subsystem? Transponder satellite bandwidth
Receiver satellite antenna (G/T)
Amplifier TWTA/SSPA (wattage) Switching matrix connectivity
Transmitter transmit power (D/L e.i.r.p.)
Full Transponder Layout:
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Satellite Communication
Some typical carriers
Voice:8 kb/s
16 kb/s
64 kb/s
Data:64 kb/s
up to 155 Mb/s
Video:2 Mb/s
8 Mb/s
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What to keep in mind?
Time delay
One-way delay: location dependant
Sub-satellite point: 119.3 ms
Horizon: 138.9 ms
Path length:
Location dependant (elevation angle)
Sub-satellite point: 71,572 km
Horizon: 83,360 km
Dependant on actual elevation angle
C-band: ~200 dB
Ku-band: ~206 dB
Satellite Communication
SSP
Horizon
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Earth Station
Technology
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Earth Station Equipment For Data
U/C
HPA
IF COMB
RF COMB
MOD
U/C
HPA
IF COMB
RF COMB
MOD
D/C
LNA
IF DIV
RF DIV
DEMOD
D/C
LNA
IF DIV
RF DIV
DEMOD
RHCP LHCP RHCP LHCP
TRANSMIT PATH RECEIVE PATH
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Earth Station Equipment For TV
U/C
HPA
IF COMB
RF COMB
ENCODER
U/C
HPA
IF COMB
RF COMB
ENCODER
D/C
LNB
IF DIV
RF DIV
DECODER
D/C
LNB
IF DIV
RF DIV
DECODER
RHCP LHCP RHCP LHCP
TRANSMIT PATH RECEIVE PATH
T i l P t f E th
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Typical Parameters for EarthStation Antennas: C Band
IntelsatStandard
G/T (dB/K) AntennaDiameter(typical)
A 35 (35 + 20 Log f/4) 18 - 21 m
B 31.7 11 - 13 m
F3 29 9 10 m
F2 27 6.5 7.3 m
F1 22.7 3.7 4 m
H 22.1 for H4
18.3 for H3
15.1 for H2
3.7 m
2.4 m
1.8 m
T i l P t f E th
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Typical Parameters for EarthStation Antennas: Ku Band
IntelsatStandard
G/T (dB/deg K) AntennaDiameter(typical)
C 37 11 m
E3 34 7 - 8 m
E2 29 3.7 4.5 m
E1 25 2.4 - 3.7 m
K3 23.3 1.8 m
K2 19.8 1.2 1.5 m
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CASSEGRAIN FEED SYSTEM
PARAXIAL FOCUS
Earth Station Antenna Configurations
Common Antenna Feed Systems
FOCAL FEED PARABOLOID
HYPERBOLOID
GREGORIAN FEED SYSTEM
ELLIPSOID
SPHERICAL REFLECTOR
FEEDER PHOTO REQUIRED
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Prime Focus & Cassegrain Antenna Optics
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Antenna Radiation Pattern (1)
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Satellite Communication
Transmission via satellite Modulation (change of properties of an
electrical signal)
Coding (change an analog signal to a digital
signal)
Multiplexing (combine several signals)
Up/Down converter (change of frequency)
Amplifier (enhance signal strength) Multiple access techniques (procedure to access
the satellite)
T f P l i
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Types of Propulsion
Chemical Propulsion
Performance is energy limitedPropellant Selection
Electric Propulsion
ElectrostaticIon Engine
Electro thermalArc JetElectromagneticRail gun
Solar Sails
Would use large (1 sq. km.) reflective sail (made of thinplastic)
Light pushes on the sail to provide necessary force to changeorbit.
Still on the drawing board, but technologically possible!
Nuclear Thermal
L hi
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Vp Transfer orbit
Launching
Earth
Geo stationary orbit
Va
Parking orbit
Launching
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N
EWEquator
Orbital velocity
Velocity acceleratedby
Apogee motor
Geo St. velocity
Launching