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Communication satellites bring the world to you anywhere and any time…..

AJAL.A.J

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Module 3 Satellite Link Design

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UNIVERSAL ENGINEERING COLLEGE, THRISSUR- 680123 Department of ECE

EC09 L05: Satellite Communication

History of satellite communication

1945 Arthur C. Clarke publishes an essay about „Extra Terrestrial Relays“

1957 first satellite SPUTNIK

1960 first reflecting communication satellite ECHO

1963 first geostationary satellite SYNCOM

1965 first commercial geostationary satellite Satellit „Early Bird“ (INTELSAT I): 240 duplex telephone channels or 1 TV

channel, 1.5 years lifetime

1976 three MARISAT satellites for maritime communication

1982 first mobile satellite telephone system INMARSAT-A

1988 first satellite system for mobile phones and data communication INMARSAT-C

1993 first digital satellite telephone system

1998 global satellite systems for small mobile phones

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ELIPTICAL ORBIT

Applications

Traditionally weather satellites radio and TV broadcast satellites military satellites satellites for navigation and localization (e.g., GPS)

Telecommunication global telephone connections backbone for global networks connections for communication in remote places or underdeveloped areas global mobile communication

satellite systems to extend cellular phone systems (e.g., GSM or AMPS)

replaced by fiber optics

Orbits

earth

km35768

10000

1000

LEO (Globalstar,

Irdium)

HEO

inner and outer VanAllen belts

MEO (ICO)

GEO (Inmarsat)

Van-Allen-Belts:ionized particles2000 - 6000 km and15000 - 30000 kmabove earth surface

LEO systems

Orbit 500 - 1500 km above earth surface visibility of a satellite ca. 10 - 40 minutes global radio coverage possible latency comparable with terrestrial long distance

connections, ca. 5 - 10 ms smaller footprints, better frequency reuse but now handover necessary from one satellite to another many satellites necessary for global coverage more complex systems due to moving satellites

Examples: Iridium (start 1998, 66 satellites)

Bankruptcy in 2000, deal with US DoD (free use, saving from “deorbiting”)

Globalstar (start 1999, 48 satellites) Not many customers (2001: 44000), low stand-by times for mobiles

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LEO’S

• ISL Inter Satellite Link• GWL – Gateway Link• UML – User Mobile Link

Picture from [1]

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ISL (Inter Satellite Links)• Intra-orbital links: connect consecutive

satellites on the same orbits• Inter-orbital links: connect two satellites on

different orbits

MEO systems

Orbit ca. 5000 - 12000 km above earth surface

comparison with LEO systems: slower moving satellites less satellites needed simpler system design for many connections no hand-over needed higher latency, ca. 70 - 80 ms higher sending power needed special antennas for small footprints needed

Example:

ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000 Bankruptcy, planned joint ventures with Teledesic, Ellipso – cancelled

again, start planned for 2003

Geostationary Earth Orbits (GEO)

Orbit 35,786 km distance to earth surface, orbit in equatorial plane (inclination 0°)

complete rotation exactly one day, satellite is synchronous to earth rotation

fix antenna positions, no adjusting necessary satellites typically have a large footprint (up to 34% of earth surface!),

therefore difficult to reuse frequencies bad elevations in areas with latitude above 60° due to fixed position

above the equator high transmit power needed high latency due to long distance (ca. 275 ms)

not useful for global coverage for small mobile phones and data transmission, typically used for radio and TV transmission

base stationor gateway

Classical satellite systems

Inter Satellite Link (ISL)

Mobile User Link (MUL) Gateway Link

(GWL)

footprint

small cells (spotbeams)

User data

PSTNISDN GSM

GWL

MUL

PSTN: Public Switched Telephone Network

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Design of the Satellite Link

Figure : Critical Elements of the Satellite Link

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LNB (LOW NOISE BLOCK DOWN CONVERTER) • A device mounted in the dish, designed to amplify the satellite signals and

convert them from a high frequency to a lower frequency. LNB can be controlled to receive signals with different polarization. The television signals can then be carried by a double-shielded aerial cable to the satellite receiver while retaining their high quality. A universal LNB is the present standard version, which can handle the entire frequency range from 10.7 to 12.75 GHz and receive signals with both vertical and horizontal polarization.

DemodulatorA satellite receiver circuit which extracts or "demodulates" the "wanted "signals from the received carrier.

Decoder• A box which, normally together with a viewing card, makes it possible to view

encrypted transmissions. If the transmissions are digital, the decoder is usually integrated in the receiver.

• recorded video information to be played back using a television receiver tuned to VHF channel 3 or 4.

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• ModulationThe process of manipulating the frequency or amplitude of a carrier in relation to an incoming video, voice or data signal.

• ModulatorA device which modulates a carrier. Modulators are found as components in broadcasting transmitters and in satellite transponders. Modulators are also used by CATV companies to place a baseband video television signal onto a desired VHF or UHF channel. Home video tape recorders also have built-in modulators which enable the

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How Satellites are used

Service Types

Fixed Service Satellites (FSS)• Example: Point to Point Communication

Broadcast Service Satellites (BSS)• Example: Satellite Television/Radio• Also called Direct Broadcast Service (DBS).

Mobile Service Satellites (MSS)• Example: Satellite Phones

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ElevationElevation:angle between center of satellite beam and surface

minimal elevation:elevation needed at leastto communicate with the satellite

footprint

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Satellite Foot print

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Objective of a link analysis• Link analysis determines properties of

satellite equipment (antennas, amplifiers, data rate, etc.)

• Two links need to be planned– Uplink – from ground to satellite– Downlink – from satellite to ground

• Two way communication – 4 links (two way maritime communications)

• One way communication – 2 links (example – TV broadcast)

• Two links are not at the same frequency • Two links may or may not be in the same

band– Fixed / broadcast satellite services –

usually same band– Mobile satellite services may use

different bands• In some systems satellite links may be

combined with terrestrial returns

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One way communication

Two way communication

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Elements of a satellite link• Transmit power• TX antenna gain• Path losses

– Free space– TX/RX antenna losses– Environmental losses

• RX antenna gain• RX properties

– Noise temperature– Sensitivity (S/N and ROC)

• Design margins required to guarantee certain reliability

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Note: satellite signals are usually very weak – requires careful link budget planning

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Free space path loss – transmit side

• Free Space Path Losses (FSPL) due to dispersion of EM wave energy

• Antenna used to focus the energy of the wave in the direction of the receiver

• Note: antenna gain is usually quoted in the direction of radiation maximum. For other direction need to use the actual radiation pattern

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24 R

GPW TT

Power flux in the direction of maximum radiation

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Free space path loss – receive side

Effective antenna gain (effective aperture)

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AA Ae A – aperture efficiency of the antenna (50-90%)

Received power

eTT

eR AR

GPAWP

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Using

Re GA 4

2

2/4 R

GGPP RTT

R

One obtains

FSPL equation

2/4 RFSPL

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Additional losses• Additional losses

– Misalignment of the antennas– Atmospheric losses– Radome losses

• The additional losses are taken into account through appropriate design margins

• Typical design margin 5-10dB– Component accuracy– Operating frequency– Required reliability

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ALFSPLEiRP RR GPLink equation

AL – additional losses

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Shannon capacity formula• Shannon capacity formula – establishes

fundamental limits on communication• In the case of AWGN channel

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N

SBC 1log2

C – capacity of the channel in bits/sec

B – bandwidth of the channel in Hz

S/N – signal to noise ratio (linear)

Define = R/B - bandwidth utilization in bps/Hz, where R is the information rate in bps.

02

02

1log

1log

N

E

BN

RE

R

C

b

b

Minimum energy per bit normalized to noise power density that is required for a given spectrum utilization

12min

00

N

E

N

E bb

Note: is the fundamental measure of spectrum utilization. Ultimate goal of every wireless communication system is to provide largest for a give set of constraints.

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EIRP

10/02/14

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37Freq

uenc

ies

& W

avel

engt

hs

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Electromagnetic Spectrum

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RF Bands, Names & Users

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ELEVATION ANGLE

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Propagation Effects and their impact

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DVB-S

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Satellite Link Design

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Thank you