LEO NETWORK COMMUNCATIONS

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LEO NETWORK COMMUNCATIONS
Trina Dobson Paul Woolaver Bob Whynot
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INTRODUCTION

• Need for LEOs.
• Brief history.
• Characteristics.
• Design issues.
• Types of LEOs.
• Major players.
• Teledesic example.

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WHY LEO?

• Because most of the Earths surface has no access
  to terrestrial communication lines.
• Because GEOs cannot facilitate real-time
  applications.
• Because of an increasingly mobile workforce.

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BRIEF HISTORY

• 1984 U of Surrey launches UoSAT-2
• 1985 LEO network concept conceived by Motorola.
• 1988 Teledesic system conceived.
• 1990 Motorola plans to build Iridium.
• 1992 WARC-92
• 1995 FCC starts granting licenses to LEO
  companies
• 1997 Iridium launches 41 satellites.
• 1998 Motorola invests 750 M in Teledesic.

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CHARACTERISTICS

• 1/3 the delay of GEOs (and dropping).
• More in common with Terrestrial based cellular
  service.
• Autonomous network.
• Dynamic topology.
• Cheap compared to GEOs.
• The great packet switching network in the sky.

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DESIGN ISSUES

• Delay needs to be minimized.
• Tail charges need to be minimized.
• Processing needs to be minimized.
• Battery charge is limited.
• No upgrades after launch.
• Routing algorithms.
• Placement of ground terminals.

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TYPES OF LEOS

• Little LEO and Big LEO.
• Little LEO
• Slow data communications.
• Paging/store-and-forward, messaging.
• Communicate directly with ground stations.
• Weigh 50 to 100 kg.
• Frequencies
• Downlink 137 to 138 and 400.15 to 401 MHz
• Uplink 148 to 149.9 MHz.

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TYPES OF LEOS

• Big LEO (Broadband LEO)
• High speed communication.
• Voice, Data, Video, etc.
• Generally Utilize ISLs.
• Smart nodes.
• Weigh 350 500 kg.
• Frequencies
• 1610 1626.5 MHz.

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MAJOR PLAYERS

• Teledesic
• Iridium (???)
• Skybridge
• Globalstar
• Motorola
• Lockheed
• Boeing

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TELEDESIC EXAMPLE

• 288 satellite constellation.

• Each satellite makes a complete orbit in 100
  minutes.

• Use of unique ATM-like protocol.

• Utilize ISLs (Intersatellite Links) via lasers.

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TELEDESIC

• Plans to interface with IP, ISDN and ATM.
• Communication within the network is treated as
  streams of short, fixed-length packets
• HEADER destination address and sequence info
• ERROR CONTROL verify the integrity of the header
• PAYLOAD digitally encoded user data (voice,
  video, data, etc.)
• Conversion to and from packet form takes place on
  the edge of the network.
• Frequency license
• DOWNLINK 18.8 GHz to 19.3 GHz
• UPLINK 28.6 GHz to 29.1 GHz

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TELEDESIC

• Plans to offer two different connections
• PACKAGE 1 64 Mbps on the downlink and 2 Mbps on
  the uplink.
• PACKAGE 2 64 Mbps full duplex.
• Teledesic estimate that an antenna will have to
  switch satellites every 4 minutes!
• Routing algorithms originally used to manage
  congestion in ATM networks will be used
  frequently in the Teledesic system.
• Using ISLs Teledesic hopes to reduce delay from
  100 to 40 milliseconds.