IRIDIUM

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IRIDIUM

• by
• David Lee 1012727
• Oana Stanoiu 1875108
• This report was prepared for Professor L.
  Orozco-Barbosa
• in partial fulfillment of the
• requirements
• for the course ELG/CEG 4183

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Outline

• Background
• System overview
• Geosynchronous vs. Leo (low-earth orbiting)
• Satellite configuration
• Frequencies Used
• Business Perspective
• IRIDIUM vs. other satellite telecommunication
  networks (GlobalStar, Odyssey)

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Background

• Why Iridium?
• Derived from the chemical element Iridium which
  has atomic number 77
• Initially there were supposed to be 77 satellites
• Driving forces Major players and their roles
• International consortium
• Motorola was the initiator of the project
• Based on GSM standards
• Siemens GSM technology links the satellites to
  the public telephone and data networks through a
  system of 15 gateway switching centers

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System overview

• System Architecture
• Composed of
• Satellite system of 66 LEO
• Operating in 6 orbital planes
• Altitude of 780 km
• Orbital period of 101 minutes
• Terestrial gateways
• Iridium handhelds

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GEO vs. LEO

• Geo-stationary Earth orbital satellite
• On a circular orbit in the equatorial plane at an
  altitude of 35786 km making 1 revolution in 24
  hours.
• Unable to service north or south latitudes gt 70
  degree and has long propagation delay (270ms, one
  way)
• Need huge antenna for low-powered mobile
  terminals
• No satellite tracking needed, relay communication
  24 hours a day
• Good for non RT, non-interactive application
  (i.e. TV broadcasting)

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GEO vs. LEO

• Low Earth Orbital satellites
• Excellent link feasibility with low delay due to
  low orbit
• Small coverage cell is obtainable with small
  on-board antenna
• Global coverage possible
• Require large number of spacecraft (satellites)
• Very complex space control system
• Frequent handovers (10 min between satellites,
  1-2 min between beams)
• Low minimum angle

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Technology Description

• Combination of TDMA and FDMA for the uplink and
  downlink to satellites
• Support full-duplex voice channels at 4800 bps
  and half-duplex data channels at 2400-bps

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TDMA frame structure
Guard Time
Framing
UL1
UL2
UL3
UL4
DL1
DL2
DL3
DL4
90ms
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FDMA Structure
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Channel Frequency Reuse

• Each IRIDIUM satellite has 3 phased array
  antennas with 16 spot beams
• 48 spot beams/satellite
• Spot beams are assigned a fraction of the
  available frequency channels
• Channels can be reused throughout the network by
  assigning them to cells that are far enough apart
  to minimize co-channel interference
• IRIDIUM network uses a cluster factor of 12

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Frequency Reuse Schema
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Link Strategy

• IRIDIUM has 2 Intra-Orbit ISL and 2 Inter-Orbit
  ISL
• Intra-Orbit ISLs connect satellites within the
  same orbit
• Inter-Orbit ISLs connect satellites on different
  orbits

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IRIDIUM satellite configuration
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Performance

• Cumulative outage
• Terrestrial based network outage averages at 24
  hours
• The benchmark for cumulative outage is 55 minutes
• IRIDIUM has a possible outage of 10 minutes

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Business Perspective

• Early model
• Need at least 1 million subscriber to break even
  (5 billion to build)
• 3000 handset 7.00/min Internet access _at_
  10kbps
• Current model (Iridium Satellite LLC)
• Major sectors Military (US 72 mil)
  Industry(mining, offshore drilling rugs, CNN,
  aviation, maritime, entertainment)
• Flat rate 1.5/min
• Voice, data, and pager services
• Satellite Lifetime (7 yrs), other competitors

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Business Perspective Cont.

• Major Competitors
• GlobalStar
• Also struggling (only 13000 subscribers with 2
  mil in revenue. October 2001 reported a 3rd
  quarter loss of gt 211 million)
• Voice and data, not truly global
• 500 satellite phones as part of security
  telecommunications network during the Olympic
  games
• Inmarsat
• UK based, use geosynchronous satellites
• Satellite communication for ships, video phone
  images

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IRIDIUM vs. other satellite telecommunication
network

• Geographical coverage
• Iridium truly global with 66 satellites Others
  focuses on regions in the mid-latitudes
  (Globalstar has 24 satellites, Odyssey has 9)
• Co-operation with terrestrial Networks
• Iridium uses 1 gateway Globalstar and Odyssey
  require maximum co-operation with terrestrial
  networks (no gateway, no service)

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IRIDIUM vs. other satellite telecommunication
network

• Propagation delay
• Satellite to Earth Iridium has the shortest
• Terrestrial Networks Iridium has the shortest
  since it has less terrestrial trail
• Processing delay due to transmission systems and
  on-board processing Iridium has the longest
• Voice coding and decoding time (system
  independent)

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IRIDIUM vs. other satellite telecommunication
network

• Frequency bands and multiple access techniques
• Iridium has a greater capacity (0.3 mErlang/km2)
  than the Globalstar (0.06 mErlang/km2) and
  Odyssey (0.2 mErlang/km2)
• Iridium uses TDMA access technique to coexist
  with the other systems while Globalstar and
  Odysseys S-band downlink is share with ISM
  applications leading to service degradation in
  populated urban area

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IRIDIUM vs. other satellite telecommunication
network

• Elevation angle and signal fading margin
• Iridium (15 degree) Globalstar and Odyssey (30
  degree 90 of the time)
• Iridium has a higher fading margin (16 dB for
  voice, 35 dB for pagaing) Globalstar and Odyssey
  has less than 10 dB for voice

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Questions

• 1) Why is LEO a better choice for global
  satellite telecommunication network than GEO
  (Geo-stationary Earth orbit)?
• 2) Who was the initiator of the IRIDIUM program?
• 3) Name two differences between IRIDIUM and
  GlobalStar satellite networks?
• 4) What was the cause of the initial failure of
  the IRDIUM program?
• 5) How many satellites are in the IRIDIUM
  satellite network?
• 6) Define Erlang.

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References

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• 2 Fossa, C. E., Raines, R.A., Gunsch, G.H., M.
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  Low Earth Orbit Satellite System with a Degraded
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