1 / 16

The Future of Satellite Communications

The Future of Satellite Communications. Joel Klooster ENGR 302 May, 2002. History. Sputnik - Russian (Oct 4, 1957) Only lasted 92 days in orbit Echo - 1st TV satellite (1960) Telstar - 1st active TV satellite (1962) Syncon - 1st earth synchronous (1964). Types of Orbits. Geosynchronous

aurelia-herrera
Download Presentation

The Future of Satellite Communications

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Future of Satellite Communications Joel Klooster ENGR 302 May, 2002

  2. History • Sputnik - Russian (Oct 4, 1957) • Only lasted 92 days in orbit • Echo - 1st TV satellite (1960) • Telstar - 1st active TV satellite (1962) • Syncon - 1st earth synchronous (1964)

  3. Types of Orbits • Geosynchronous • Same rotational velocity as earth • Maintains position relative to earth • Altitude - 35 786 km • Velocity - 11 300 km/hr • Asynchronous • Much lower altitude = much higher velocity • Position over earth constantly changing

  4. Operation of Satellites • Transmission • Reception • Low Noise Converter • Polarization • Tuner • Antennas

  5. Radio Signal Propagation • Free Space Propagation Model • Line-of-sight with no obstructions • Friis free space equation

  6. Path Loss (PL) • Fading of electromagnetic signal • Positive difference between received power and transmitted power (in dB)

  7. The Solution?? Lasers!!

  8. Advantages of Laser Communications • Frequencies 7 - 8x higher • Higher bandwidth • Smaller beam divergence • Smaller antennas • Higher data rates

  9. What type of Laser is used? • Neodymium: yttrium, aluminum, garnet (Nd:YAG) most common type • Rod of crystalline YAG lightly doped with Nd is used as the amplifier • Optical energy excites Nd atoms to higher energy state • Return to normal energy state emits energy at wavelength of 1.664 um

  10. Modulation • What actually drives the communication • Birefringence modulator most useful • Uses electric-field induced birefringence of the crystal to rotate polarized light

  11. Optical Detectors • Receiver must somehow convert the laser energy to an electric current • Photon-wave theory of light • Photons have some momentum that exerts a force on the receiver • Frees electrons from atoms of cathode • Photoelectrons attracted to anode, creating a current

  12. Optical Modulation Formats • Based on short energy pulses with a high peak power and low duty cycle • Three Types • Pulse Gated Binary Modulation (PGBM) • Pulse Polarization Binary Modulation (PPBM) • Pulse Interval Modulation (PIM)

  13. Pulse Interval Modulation • Most efficient type of modulation • N separate time slots in pulse interval • Transmit log2(N) bits per pulse • Pulse sent during one of these time slots • Time slot is value of the word • Translated in binary data

  14. Example of PIM

  15. Conclusion • Satellites very important for modern communications • Radio Frequency communication reaching the end of its usefulness • Laser Communications will eventually be the method of choice for satellites

  16. Questions

More Related