Transcript LEO NETWORK COMMUNCATIONS

LEO NETWORK
COMMUNCATIONS
Trina Dobson :: Paul Woolaver :: Bob Whynot
INTRODUCTION
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Need for LEOs.
Brief history.
Characteristics.
Design issues.
Types of LEOs.
Major players.
Teledesic example.
WHY LEO?
• Because most of the Earth’s surface
has no access to terrestrial
communication lines.
• Because GEOs cannot facilitate realtime applications.
• Because of an increasingly mobile
workforce.
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.
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.
DESIGN ISSUES
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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.
TYPES OF LEOS
• Little LEO and Big LEO.
• Little LEO:
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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.
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.
MAJOR PLAYERS
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Teledesic
Iridium (???)
Skybridge
Globalstar
Motorola
Lockheed
Boeing
TELEDESIC EXAMPLE
• 288 satellite
constellation.
• Each satellite
makes a complete
orbit in 100 minutes.
• Use of unique ATMlike protocol.
• Utilize ISLs
(Intersatellite Links) via
lasers.
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
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.