Free Space Optical Communication

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FREE SPACE OPTICAL COMM(FSO):

FREE SPACE OPTICAL COMM(FSO) PRESENTED BY PRAMOD KUMAR DWIVEDI 0903031077 EC-2

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September 11, 2001, New York

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Every thing was destroyed including normal fiber link Wall street stock market was closed because the communication was destroyed

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FSO vs RF RF 2.4 GHz systems were typically running at 2-4 Mbps due to interference issues in the unlicensed frequency ranges FSO provided 10 Mbps of throughput for less than unlicensed RF FSO is less cost, more secure, and seemed simpler

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Two of these units were used between building to re-establish a high speed communication link.

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Beams only a few meters in diameter at a kilometer Allows VERY close spacing of links without interference No side lobes Highly secure Efficient use of energy Ranges of 20m to more than 8km possible Why Free Space Optics?

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ADVANTAGE OF FSO No interference Unlicensed Easy to install Through the window (or from the rooftop) Fiber-like data rates Many deployment options High data rates, uptu 2.5 Gbps at present and 10 Gbps in the near future.

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FSO- A brief introduction Line-of-sight communication technology using optical range of the EM spectrum Medium of transmission is free space/air.

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How FSO Works 1 Network traffic converted into pulses of invisible light representing 1’s and 0’s 2 Transmitter projects the carefully aimed light pulses into the air 5 Reverse direction data transported the same way. Full duplex 3 A receiver at the other end of the link collects the light using lenses and/or mirrors 4 Received signal converted back into fiber or copper and connected to the network Anything that can be done in fiber can be done with FSO

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Application of FSO Connectivity Solutions 'Last-Mile' Network Solutions Temporary Network Provision Cable Free Connectivity CCTV Security Applications

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Air Force Its potential for low electromagnetic emanation when transferring sensitive data Navy Secure communication with submerged submarines. Military Application of FSO

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Industrial estates, Science parks and university campus environments typically exhibit a common problem – a number of separate buildings, separated by roads or other obstacles, between which communications links are frequently in demand .

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Cable digging, increasingly unpopular in cities, is regulated by the local authority who may restrict re-digging frequency of roads - and the cost may be prohibitive in any case, especially if a river or railway is in the way.

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Jersey City Manhattan Hudson River Merrill Lynch Office Merrill Lynch Office Merrill Lynch Office 2.6 km 1.8 km 1.6 km Merrill Lynch urgently needed additional connectivity to three locations. Terabeam installed Gig-E FSO units to build a ring topology to back up the SONET network Installation was completed within 7 days of first call Disaster Recovery – After 9/11

CHALLENGES IN FSO:

CHALLENGES IN FSO

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Challenges Environmental factors Sunlight Building Motion Alignment Window Attenuation Fog Each of these factors can “attenuate” (reduce) the signal. However, there are ways to mitigate each environmental factor . Scintillation Range Obstructions Low Clouds

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Challenges Atmospheric Attenuation - FOG Absorption or scattering of optical signals due to airborne particles Primarily FOG but can be rain, snow, smoke, dust, etc. Can result in a complete outage

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Challenges Low Clouds, Rain, Snow and Dust Low Clouds Very similar to fog Rain Drop sizes larger than fog and wavelength of light Extremely heavy rain (can’t see through it) can take a link down Heavy Snow May cause ice build-up on windows Sand Storms Likely only in desert areas; rare in the urban core

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Challenges Building Motion – Thermal Expansion 15% of buildings move more than 4 mrad 5% of buildings move more than 6 mrad 1% of buildings move more than 10 mrad

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Beam spreading and wandering due to propagation through air pockets of varying temperature, density, and index of refraction. Almost mutually exclusive with fog attenuation. Results in increased error rate but not complete outage. Challenges Scintillation

CONCLUSION:

CONCLUSION

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FSO is just starting to be applied :: to solve the Internet “last-mile” interconnectivity problem. ::some believe that it’s a unlimited bandwidth solution for the metro urban core of downtown building-to-building communication :: as well as the optimal technology for home-to-home and office-to-office connectivity.

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Requirements of a good Transmission System: High Bandwidth High BER High SNR Power efficient Provide Data Security. Low cost Easy to install and maintain .

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Reference http://www.freespaceoptic.com/ http://www.fsonews.com/ http://www.cablefreesolutions.com/ http://www.thefoa.org/ http://www.free-space-optics.org/ http://www.freespaceoptics.com/ http://www.opticsreport.com/

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