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LEO NETWORK COMMUNCATIONS

LEO NETWORK COMMUNCATIONS. Trina Dobson :: Paul Woolaver :: Bob Whynot. INTRODUCTION. Need for LEOs. Brief history. Characteristics. Design issues. Types of LEOs. Major players. Teledesic example. WHY LEO?.

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LEO NETWORK COMMUNCATIONS

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  1. LEO NETWORK COMMUNCATIONS Trina Dobson :: Paul Woolaver :: Bob Whynot

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

  3. WHY LEO? • Because most of the Earth’s surface has no access to terrestrial communication lines. • Because GEOs cannot facilitate real-time applications. • Because of an increasingly mobile workforce.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. MAJOR PLAYERS • Teledesic • Iridium (???) • Skybridge • Globalstar • Motorola • Lockheed • Boeing

  10. 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.

  11. 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

  12. 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.

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