Satellite Communication

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Satellite Communication
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Important Milestones (1950-1970)
Early Satellite Communication

• 1957 First satellite launched by former USSR
  (Sputnik, LEO)
• 1958 First US satellite launched (Explorer-1,
  LEO)
• 1960 First passive communication satellite
  launched (EchoIII)
• 1962 First active comm. satellite launched
  (Telstar, MEO)
• 1963 First satellite launched into geostationary
  orbit (Syncom1)
• 1964 Intelsat created
• 1965 First satellite launched into geostationary
  orbit for commercial use Early Bird (re-named
  Intelsat 1)

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Important Milestones (1970-1990)
GEO Applications Development

• 1972 First DOMSAT operational (Canada),
  Inter-Sputnik founded
• 1977 1979 Inmarsat established
• 1981 First reusable launch vehicle flight
• 1982 International maritime communications made
  operational
• 1984 First DBS operational (Japan)
• 1987 Successful trials of land mobile comm.
  (Inmarsat)
• 1989-90 Global mobile communication service
  extended to land mobile and aeronautical use
  (Inmarsat)

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Important Milestones (1990 - Current)

• NGSO development and GEO expansion
• 1990-95 NGSO systems proposed for mobile
  communications. Continuing growth of VSATs and
  DBS
• 1997 Launch of first batch of LEO for hand-held
  terminals (Iridium). Voice service
  telephone-and paging service- pocket size mobile
  terminals launched (Inmarsat)
• 1998 Iridium initiates services
• 1999 Globalstar Initiates Service
• 2000 ICO initiates Service.Iridium fails system
  sold to Boeing, Thuraya I launched into GEO for
  MSS
• 2003 Thuraya II launched into GEO

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Basic Satellite System Elements
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Satellite Footprints
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Communication Satellite Services

• Fixed Satellite Services (FSS)
• Broadcast Satellite Services (BSS)
• Mobile Satellite Services (MSS)
• - Aeronautical
• Maritime
• Land

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Development of Satellite Communication Systems
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Microwave Frequencies
Frequency Band Name
30 300 MHz VHF 300 MHz 1 GHz UHF 1 GHz
2 GHz L band 2 4 GHz S band 4 8 GHz
C band 8 12 GHz X band 12 18 GHz Ku
band 18 27 GHz K band 27 40 GHz Ka
band 40 50 GHz Q band 50 60 GHz U
band 60 80 GHz V band
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International Regulations
The radio spectrum is a limited natural resource,
which should be shared by all types of radio
services. International Telecommunication Union
(ITU) allocates the frequencies and also
specifies the power allowed for each type of
services on a global and regional basis. To
facilitate the planning the ITU has divide the
world into three regions 1. Europe, Africa,
Former SU, Mongolia, Middle-East 2. North and
South America and Greenland 3. Remainder of Asia,
Australia and the South-West Pacific
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Satellite Orbits

• Can be circular or elliptical
• Can orbit around the equator (equatorial orbit)
  or pass over the poles (polar orbit) or can be at
  any angle between these
• Lower height limit of about 300 km due to
  atmospheric drag

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Satellite Orbits

• Categorized as
• Low Earth Orbit (LEO)
• Medium Earth Orbit (MEO)
• Geostationary Earth Orbit (GEO)
• Non-Geostationary satellites are sometimes called
  orbital satellites (though all satellites are in
  orbit)

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Van Allen Belts

• Regions of high radiation that can damage
  satellites
• Extend from about 1500 to 5000 km and 10, 000 to
  25 000 km above the earth
• LEO satellites are below the first belt
• MEO satellites are between the two belts
• GEO satellites are above the belts

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LEO satellites

• Altitude 300 to 1500 km
• Many satellites needed for continuous coverage
• Short propagation distance leads to strong
  signals and short propagation times

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MEO Satellites

• Altitude from 8000 to 10 000 km
• Fewer required for complete coverage, but signals
  are weaker and propagation delays longer than for
  LEO

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GEO Satellites

• Altitude approx. 36 000 km
• Must have circular equatorial orbit and must
  orbit in same direction as earths rotation.
• Appear to remain stationary above a point on
  earth
• One satellite can cover almost an entire
  hemisphere
• Very large propagation distance leads to weak
  signals and long propagation time

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GEO Orbit

• Three satellites could cover entire globe EXCEPT
  polar regions
• Angle of elevation to satellite decreases near
  poles causing spreading of beam and reduced
  signal strength

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Propagation Time

• For a GEO satellite, the time for a signal to
  propagate to a satellite and return is approx.
  0.25 second
• This causes an inconvenient though not
  unacceptable delay in a telephone conversation
• Also can cause problems in data comm.

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The Spacecraft

• Communication considerations
• Type of service
• Communication capacity (Bandwidth, EIRP)
• Coverage area

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Transponders

• Transponder is the component of the communication
  subsystem of the satellite which receives
  signals, shifts it frequency for retransmission.
• Two types of transponders
• Bent Pipe
• Regenerative
• Beam Switching

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Bent Pipe Transponder
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Regenerative Transponder
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Cross Links

• Satellites that are in view of one another can
  communicate directly without going through an
  earth station

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Earth Station Antennas

• Since many GEO sats use the same frequency bands,
  earth station antennas must have narrow beamwidth
  of 2 degrees or less
• Smaller beamwidth is associated with higher gain
  and larger diameter. Some Intelsat earth stations
  use 0.1 degree.

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GEO Applications

• Television/radio broadcasting
• Fixed Telephony
• Data
• Shipboard and mobile communication

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Broadcasting

• Used for communication within TV networks, to
  CATV headends etc
• Now also used by individuals (DBSS)
• Uses transponders in C and Ku bands
• C band 6 GHz up, 4 GHz down
• Ku band 14 GHz up, 12 GHz down
• DBS uses high power satellites which uses of 200
  W per transponder

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Anik E-2 Footprint
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Satellite Telephony

• Not as high quality as fiber optic systems
  largely due to time delay
• Three main types
• Frequency division multiplexing - frequency
  modulation (FDM-FM)
• Single channel per carrier (SCPC)
• Time-division multiple access (TDMA)

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FDM-FM

• Whole transponder is used, with one main carrier,
  FM modulation
• A number of telephone signals are multiplexed
  using conventional SSB-FDM techniques, then the
  whole signal (with frequency content up to about
  8 MHz) is used to FM modulate the main carrier

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SCPC

• Transponder bandwidth is divided up and portions
  are given to service providers, which may be at
  different locations
• Each carrier is modulated by one voice signal
  using FM
• Allows small users but is less efficient of
  bandwidth
• Requires linear power amps on satellite

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TDMA

• Each earth station uses the whole transponder
  satellite for a portion of the time
• Efficient but complex timing is critical

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Satellite Data

• Conventional bent-pipe transponder can support
  many types of data
• One popular use is called Very Small Aperture
  Terminal system (VSAT)
• VSAT refers to the size of the dish at remote
  terminals (1.2 to 2.4 m, which is small for a
  non-DBS GEO satellite)

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VSAT

• VSAT networks are usually in the form of a star.
• Central hub has large dish (5 to 7 m) and
  transmits at 256 to 512 kb/s
• Remote terminals have lower data rate of about 12
  to 19.2 kb/s
• Most systems are two-way, one-way systems are
  also possible

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VSAT Applications

• Two-way
• Branch offices connect to head office
• Portable credit/bank card setups
• One-way
• Stock market information
• Wire services to radio stations

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Mobile GEO Systems

• Example
• Inmarsat
• Thuraya

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Inmarsat

• International Marine Satellite Organization
• Has 9 GEO sats, 4 used, 5 spares or leased to
  others
• Each sat. has one hemisphere beam and 5 spot
  beams
• Spot beams have about 48 dBW EIRP
• Operates in L Band (1.5/1.6 GHz)

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Inmarsat Services

• Services intended mainly for ships
• A service analog telephony
• B service digital telephony
• Portable service
• Uses spot beams mainly on land
• Notebook-size terminal with flat antenna

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LEO Systems

• These satellites have many uses. We concentrate
  on two telephony and related uses (Big LEOs)
  and paging and other related low-bandwidth
  applications (Little LEOS)

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Big LEOs

• Three contenders
• Iridium (went bankrupt but operating again)
• Globalstar (operating but still losing money)
• Teledesic (currently on hold)

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Iridium

• Uses 66 satellites with an elaborate system of
  crosslinks
• Complete worldwide coverage
• Voice, data at up to 10 kb/s using compression,
  using TDMA
• Flawed Marketing Strategy

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Iridium Phone
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Globalstar

• Simpler system than Iridium
• 48 satellites, simple bent-pipe type, no
  switching on sats and no crosslinks
• 25 gateways at present, 38 needed for worldwide
  coverage.
• Uses CDMA, now owned by Qualcomm.
• Converged collection of services voice, SMS,
  Roaming, Global positioning, Fax, Data upto 9600
  Kbps.

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Globalstar Coverage
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Globalstar Coverage
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Globalstar Phone
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Teledesic

• Aimed mainly at high speed data to fixed
  terminals.
• Will eventually have 288 satellites.
• Service was scheduled to begin in 2005, now
  postponed indefinitely.
• To support 64 Mbps and 2Mbps on the downlink and
  uplink.

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Little LEOs

• Used for low bandwidth services like paging and
  truck tracking
• Real-time connection not always needed so fewer
  satellites can be used

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MEO Systems

• Lower cost than LEO but still useful for portable
  telephony
• Two large systems in planning stages
• Ellipso
• ICO (Intermediate Circular Orbit)

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Ellipso

• Uses elliptical orbits to concentrate on northern
  hemisphere
• Also uses circular orbits
• Under construction, was to start in 2002
• US radio licence has been revoked due to slow
  buildup, presently appealing

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Ellipso Orbits
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ICO Global Communication

• Still in development
• To use 10 sats plus 2 spares
• Circular orbits at 45 degree angle to equator and
  height of 10 355 km
• Will have global coverage
• Filed for bankruptcy (Aug, 1999)
• ICO is now affiliated with Teledesic and
  Ellipso.

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Current and Future Trends

• Bigger, heavier, GEO satellites with multiple
  roles
• More direct broadcast TV and Radio satellites
• Expansion into Ka, Q, V bands
• Massive growth in data services fueled by
  Internet
• Mobile services and introduction of broadband
  PCS
• A number of LEO and MEO constellations
  operational
• Low cost phased array antennas for mobiles