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Design of the satellite link
 

Design of the satellite link

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

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

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    Design of the satellite link Design of the satellite link Presentation Transcript

    • Communication satellites bring the world to you anywhere and any time….. AJAL.A.J 1
    • UNIVERSAL ENGINEERING COLLEGE, THRISSUR- 680123 Department of ECE EC09 L05: Satellite Communication Module 3 Satellite Link Design 02/11/14 2
    • 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 02/11/14 6
    • 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)
    • 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
    • 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
    • LEO’S Picture from [1] • ISL Inter Satellite Link • GWL – Gateway Link • UML – User Mobile Link 02/11/14 10
    • ISL (Inter Satellite Links) • Intra-orbital links: connect consecutive satellites on the same orbits • Inter-orbital links: connect two satellites on different orbits 02/11/14 11
    • 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
    • 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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    • Design of the Satellite Link Figure : Critical Elements of the Satellite Link 20
    • 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. 02/11/14 21
    • • 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 02/11/14 22
    • How Satellites are used 23  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
    • 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 24
    • Satellite Foot print 02/11/14 25
    • 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 Page 26 One way communication Two way communication 26
    • 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 Page 27 27
    • 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 Page 28 28
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    • 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 ) Page 31 2 31
    • 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 Page 32 32
    • 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≤ Page 33 33
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    • EIRP 10/02/14 35
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    • Frequencies & Wavelengths 37
    • Electromagnetic Spectrum 38
    • RF Bands, Names & Users 39
    • ELEVATION ANGLE 40
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    • Propagation Effects and their impact 42
    • DVB-S 43
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    • Satellite Link Design 50
    • Thank you  51