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Global Satellite Services

Global Satellite Services. GEO, MEO and LEO Satellites, IntelSat, and Global Positioning Systems. What is a telecommunications satellite?. Telecommunications satellites. Space-based cluster of radio repeaters (called transponders) Link

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Global Satellite Services

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  1. Global Satellite Services GEO, MEO and LEO Satellites, IntelSat, and Global Positioning Systems

  2. What is a telecommunications satellite?

  3. Telecommunications satellites • Space-based cluster of radio repeaters (called transponders) • Link • terrestrial radio transmitters to satellite receiver (uplink) • Satellite transmitters to terrestrial receivers (downlink)

  4. Orbits • Mostly geostationary (GEO) • Circular orbit • 22,235 miles above earth • Fixed point above surface • Almost always a point on Equator • Must be separated by at least 4 degrees

  5. Satellite services • Wide Area Broadcasting • Single transmitter to multiple receivers • Wide Area Report-Back • Multiple transmitters to a single receiver • Example VSATs (very small aperture terminals) • Also have microwave transmitters and receivers • Allows for spot-beam transmission (point- to-point data communications) • Can switch between beams upon request (Demand Assigned Multiple Access –DAMA) • Multi-beam satellites link widely dispersed mobile and fixed point users

  6. Earth-based equipment • Original microwave transmitters and receivers were large installations • Dishes measuring 100 feet in diameter • Modern antennas about 3 feet in diameter

  7. A Modern GEO satellite (IntelSat 900 series) • May have more than 72 separate microwave transponders • Each transponder handles multiple simultaneous users (protocol called Time Division Multiple Access) • Transponder consists of • Receiver tuned to frequency of uplink • Frequency shifter (to lower frequency to that of transmitter) • Power amplifier

  8. IntelSat 902 (launched August 30, 2001)

  9. Frequency ranges • Most transponders operate in 36MHz bandwidth • Use this bandwidth for • voice telephony (400 2-way channels/transponder) • Data communication (120Mbs) • TV and FM Radio

  10. C-band, Ku-band, Ka-band • Most GEO satellites operate in the C-Band frequencies • Uplink at 6 GHz • Downlink at 4 GHz • Ku-band also used • Uplink at 14 GHz • Downlink at 11 GHz • Above bands best suited for minimal atmospheric attenuation • Few slots left… forcing companies to look at Ka band (uplink:30 GHZ , downlink: 20 GHz)

  11. Intelsat • Began as an inter-governmental consortium in 1964 • Launched world’s first commercial communication satellite in 1965 • By 1969, had a fleet • Broadcast live Neil Armstrong’s first steps on the moon • In 1974, establish the “hot-line” between the Kremlin and the White House • In mid-1980s, developed more powerful satellites – allowed smaller ground equipment for live broadcasts • In 1997, introduced pay-as-you-go, shared access satellite coverage for low demand, rural areas. • 2001 – became a private company providing turnkey connectivity solutions

  12. Intelsat’s fleet • 20 Geosynchronous satellites • Cover 200 countries • 4 nines reliability (99.997%) • 18000 earth stations, and millions of VSATs • Offer • Bandwidth-on-demand • Point-to-point • Point-to-multipoint • C- and Ku-band capacity

  13. Latest Satellites launched • Last of the Intelsat IX series launched Feb 15, 2003 (went live in March) • Offers more powerful C-band coverage for • Europe • Africa • The Americas • Ku spot beam coverage for Europe and Africa

  14. Global Positioning Satellites • 24 MEO satellites owned by US DoD (last launched in 1994) • 21 active, 3 spare • 11,000 miles above earth • Five control stations around the world make sure satellites operating correctly • Can tell your position within 300 feet • Possible to get as accurate as 3 feet using special calculations.

  15. How GPS works • 24 satellites, each takes 12 hours to orbit the earth • You can receive signals from 6 from any point on earth • Satellites have up to 4 cesium and rubidium clocks (accurate to 3 billionths of a second)

  16. The signals • GPS satellites transmit 2 low power radio signals – L1 and L2 (civilians can only use L1) • 25-50 watts (compare to 100,000 watts for an FM radio station) • L1 sends 3 pieces of data • Pseudorandom code (ID of transmitting satellite) • Ephemeris data (tells current data and time) • Almanac data (tells GPS receiver where every satellite should be at any time of day) • The data indicates when the signal was transmitted from the satellite • The receiver indicates when it was received. • It is now possible to calculate distance from satellite • Three more such signals and you can be pinpointed.

  17. Galileo • The EU wants to compete • Galileo will be under civilian control • 30 satellites (27+3 spare) • Inter-operable with GPS • Dual frequency design allows positioning within 1 meter.

  18. Then there was LEO • Iridium project • Initially began as a plan for 77 LEO satellites (atomic number 77 = Iridium) • Scaled down to 66 (should be called Dysporium) • Cost $5billion (Mostly Motorola) • Sold 2 years ago for $25 million

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