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Free Space Optical Communication

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  • 1. FREE SPACE OPTICAL COMMUNICATION PRESENTED BYNIDHI P TIGGA & MRINAL
  • 2. Introduction to the concepts of Free Space Optics (FSO)   FSO was initially developed by NASA and US military. FSO is a line-of-sight technology which uses LASERS and Photo detectors to provide optical connections between two points—without the fiber.
  • 3. Introduction to the concepts of Free Space Optics (FSO)  It uses optical communication technology.  Uses invisible beams of light to provide optical bandwidth connections.  FSO can transmit data, voice or video at speeds capable of reaching 1.25 Gbps.
  • 4. How Free Space Optics / Laser Communications Works  It's based on connectivity between FSO- based optical wireless units.  Provide full-duplex (bi-directional) capability.  Each optical wireless unit uses an optical source, plus a lens or telescope.  Receiving lens or telescope connects to a high-sensitivity receiver via optical fiber.
  • 5. Free Space Optic Link Equation:      • Preceived = received power • Ptransmit = transmit power • Areceiver = receiver area • Div = beam divergence (in radians) • Range = link length
  • 6. Denver, Colorado Fog/Snowstorm Conditions
  • 7. Preventing Interception of the Signal
  • 8. Another view of the narrow beam divergence inherent in FSO transmission.
  • 9. Signal Propagation Impediments:  Fog: The primary way to counter fog when deploying FSO is through a network design that shortens FSO link distances and adds network redundancies.  Absorption: This causes a decrease in the power density (attenuation) of the FSO beam and directly affects the availability of a system.  Scattering: When the scatterer is smaller than the wavelength, this is known as Rayleigh scattering. When the scatterer is of comparable size to the wavelength, this is known as Mie scattering.
  • 10. Signal Propagation Impediments(contd):  Physical obstructions: Flying birds can temporarily block a single beam, but it tends to cause short interruptions, and transmissions are easily and automatically resumed.  Building sway/seismic activity: The movement of buildings can upset receiver and transmitter alignment.  Scintillation: Heated air rising from the earth or manmade devices such as heating ducts creates temperature variations among different air pockets. This can cause fluctuations in signal amplitude which leads to image fluctuations at the FSO receiver end.
  • 11. S.NO System Infrared Light (765 nm) Power Losses 1 Clear, still air -1 to -5 dB/km 2 Scintillation 0 to -3 dB/km 0 3 Birds or foliage Impenetrable 0 to -20 dB 4 Window (double-glazed) -3 to -1 dB 5 Light mist (visibility 400m) -25 to -1 dB/km 6 Medium fog (visibility 100m) -120 to -1 dB/km 7 Thick fog (visibility 40m) -1 to -300 dB/km 8 Light rain (25mm/hour) -1 to -10 dB/km 9 Heavy rain (150mm/hour) -25 to -40 dB/km
  • 12. ADVANTAGES OF FSO SYSTEMS  Installation cost is very low as compared to laying Fiber.  No sunk costs.  Highly secure transmission possible.  High data rates  Immunity to electromagnetic interference.  License free long-range operation (in contrast with radio communication)
  • 13. DISADVANTAGES OF FSO SYSTEMS  Beam dispersion  Atmospheric absorption  Rain  Fog (10..~100 dB/km attenuation)  Snow  Pollution / smog  Pointing stability in wind