ASEMINAR ON

FREE SPACE OPTICAL COMMUNICATION

By T venkatesh

CONTENTS• Introduction• History• How it works• Advantages• Challenges• System design• Transmission security• Conclusion

Introduction

• Fibre less laser driven technology• No licensing and frequency coordination required• Operating wavelength range

1) 780-900 nm 2) 1500-1600nm

• Provides a line of sight link• Fso links are full duplex• Easy to install for last mile &campus

History of fso

• Greeks used sun light for messaging• In late nineteenth century graham bell

demonstrated it.• Used for defence

Last mile options

• Definition of last mile• Cable• Fiber• Licenced and unlicenced fixed wireless

Last mile solutions

• Copper based solution

1.Slower copper based solution eg. ISDN,DDS [ 56 kbps,128 kbps ] 2.Higher copper based solution eg. T-1 circuit [24 channel] T-3 circuit [28 t-1] Security is based on the burying the wires in the grounds Intrusion detection system standpoint is used for undectable purpose

• Wireless connection

1. Distribute data everyone ,security is judged by the wep2. Licence req. To planning & coordination3. Susceptible To Rain ,Link Length4. PP microwave provide higher capacityEg. LMDS• Fiber optic based solution

1.Fiber optics are two typeA) Single mode [upto 60km]

B)Multi Mode [Upto 2km]

2)Fiber Optics Are Secure Provide speed in terabyte Protected from tapping Imposible to detect light pulse• Free space optics

1)No Cables Required2)Transmitted In Atmosphere 3)Require Line Of Site Availability

4)Units are full duplex5)No requirement of the license6)Speed upto tera byte7)Simplifying Wiring And Cabeling,low Cost8)No roof space and spectrum license req.9)Low error rate, high speed

HOW IT WORKS

LASERPHOTON

DETECTORRECEIVER

DIGITAL DATA

Advantages

• Fso laser beam cannot be detected with rf meter or spectrum analyser

• Los path cannot be intercepted easily• Data can be transmitted over an encrypted

connection• Freedom from licensing and regulation• Possble to mount inside the building

Challenges

• Atmosphere• Physical obstraction• Scientillation• Solar interface

• Atmosphere challenge

1.Fog

It affect on near infrared wavelength And have same effect as rainfall have on the rf

• Physical obstructions

1.These can be removed by widely spacedRedundant transmitters and large receive optics

• Scintillation

These can be removed by automatic gain control char.,Tuned received Filtering,clock recovery phase lock Loop time constant

• Solar interference

It can be combated by 1.Long pass optical filter windo 2.Optical Narrowband Filtering

System design

• Line of sight operation• Spectral allocation• Fso link equation• Alternate routing• Network topologies• Network scalability• Coverage area• Deploymaent and installation

System performance

• Bandwidth and system capacity• Absorption and scattering losses• Rayleigh scattering• Aerosol,particles,& cloud scattering• Atmospheric scintillation• Fog• Service provider cost

• Bandwidth and system capacity

1.Fso use on\off keying for modulation eg. Light pointe giga link system 2.Speed 1gbps-160gbps On Per Link

Rayleigh scattering

It occur due to dust and moleculer particles that are small than wavelengthOf laser transmissionScattering losses decreasing by -.4 with increment in wavelength

• Scintillation

1. Due to temp.Difference b/w ground and air And the resulting heat exchange1. Index change according temp.Diff. Heat exchange cause local

index variation that affect the laser propagation

• Fog

Solution Of The Fog Is 1.Link planning2.Multipath

Transmission security

To prevent the signal interception we use

• Directional transmissionBroader signal path have chance to intercept the beam in fso beam is very Narrow

• Absense of side lobesFso have no side lobs.

Conclusion

FSO networks can be rapidly deployed to provide immediate service to the customers. Some believe that it may be the 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. FSO adds the wireless feature to the OFC and thus provides the high bandwidth requirements.

Thank You