Design of the satellite link, friss transmission formula , up link , down link

1. Communication satellites bring the
world to you anywhere and any time…..
AJAL.A.J
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2. UNIVERSAL ENGINEERING COLLEGE, THRISSUR- 680123
Department of ECE
EC09 L05: Satellite Communication
Module 3
Satellite Link Design
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3. 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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6. ELIPTICAL ORBIT
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7. Applications

Traditionally
weather satellites
 radio and TV broadcast satellites
 military satellites
 satellites for navigation and localization (e.g., GPS)


Telecommunication
global telephone connections
replaced by fiber optics
 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)

8. Orbits
GEO (Inmarsat)
HEO
MEO (ICO)
LEO
(Globalstar,
Irdium)
inner and outer Van
Allen belts
earth
1000
10000
Van-Allen-Belts:
ionized particles
2000 - 6000 km and
15000 - 30000 km
above earth surface
35768
km

9. 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

10. LEO’S
Picture from [1]
• ISL Inter Satellite Link
• GWL – Gateway Link
• UML – User Mobile Link
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11. ISL (Inter Satellite Links)
• Intra-orbital links: connect consecutive
satellites on the same orbits
• Inter-orbital links: connect two satellites on
different orbits
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12. 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

13. 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

14. Classical satellite systems
Inter Satellite Link
(ISL)
Mobile User
Link (MUL)
Gateway Link
(GWL)
MUL
GWL
small cells
(spotbeams)
base station
or gateway
footprint
ISDN
PSTN: Public Switched
Telephone Network
PSTN
User data
GSM

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20. Design of the Satellite Link
Figure : Critical Elements of the Satellite Link
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21. 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.
Demodulator
A 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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22. • Modulation
The process of manipulating the frequency or
amplitude of a carrier in relation to an
incoming video, voice or data signal.
• Modulator
A 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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23. How Satellites are used
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
Service Types

Fixed Service Satellites (FSS)
•

Broadcast Service Satellites (BSS)
•
•

Example: Point to Point Communication
Example: Satellite Television/Radio
Also called Direct Broadcast Service (DBS).
Mobile Service Satellites (MSS)
•
Example: Satellite Phones

24. Elevation
Elevation:
angle ε between center of satellite beam
and surface
minimal elevation:
elevation needed at least
to communicate with the satellite
ε
foo
t
rin
tp
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25. Satellite Foot print
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26. 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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27. 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
Note: satellite signals are usually very weak –
requires careful link budget planning
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28. Free space path loss – transmit side
•
•
•
Free Space Path Losses (FSPL) due to dispersion of
Power flux in the direction of
EM wave energy
maximum radiation
Antenna used to focus the energy of the wave in the
PT GT
direction of the receiver
W=
Note: antenna gain is usually quoted in the direction
4πR 2
of radiation maximum. For other direction need to
use the actual radiation pattern
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31. Free space path loss – receive side
Received power
PR = W ⋅ Ae =
PT GT
⋅ Ae
2
4πR
Using
λ2
Ae =
⋅ GR
4π
One obtains
Effective antenna gain (effective aperture)
Ae = η A A
ηA – aperture efficiency of the antenna (50-90%)
PT GT GR
PR =
( 4πR / λ ) 2
FSPL equation
FSPL = ( 4πR / λ )
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32. 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
Link equation
PR = EiRP + GR − FSPL − AL
AL – additional losses
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33. Shannon capacity formula
•
•
Shannon capacity formula – establishes
fundamental limits on communication
In the case of AWGN channel
S

C = B ⋅ log 2 1 + 
 N
C – capacity of the channel in bits/sec
B – bandwidth of the channel in Hz
S/N – signal to noise ratio (linear)
Define γ = R/B - bandwidth utilization in bps/Hz,
where R is the information rate in bps.
 E R
C
= log 2 1 + b 
 N B
R
0


 E

γ ≤ log 2 1 + b ⋅ γ 
 N

0


Minimum energy per bit normalized to noise
power density that is required for a given
spectrum utilization
 Eb  2γ − 1
Eb
≥ min   =
N0
γ
 N0 
Note: γ is the fundamental measure
of spectrum utilization. Ultimate
goal of every wireless
communication system is to provide
largest γ for a give set of constraints.
γ≤
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35. EIRP
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37. Frequencies & Wavelengths
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38. Electromagnetic Spectrum
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39. RF Bands, Names & Users
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40. ELEVATION ANGLE
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42. Propagation Effects and their impact
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43. DVB-S
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50. Satellite Link Design
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51. Thank you

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