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


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)


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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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


Where are the satellites located? Three Orbital Regions

AOR, IOR/APR, POR


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Co-located S/C


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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


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)


Antenna Peak Gain

Large E/SSmall E/S


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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?


Composite Plot/IBN

1-dB Contour Plot

Composite Plot / Satellite Guide


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+

How to visualize a footprint?


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


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



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Horizontal Polarization

Vertical Polarization

Linear Polarization


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Circular Polarization


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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


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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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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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


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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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

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Satellite Communication Fundamentals 1