Flexible Optical Wireless Links and Nexwork
IEEE Communication Magazine . March 2003
The Last-Mile problem
• Fiber optic network exist worldwide and the amount of installed fiber will continue to grow
• Construction is prohibitively high and can take month to finish
Service provider
Fiber giga bit/s
Customer
Virtually infinite Demand end user
30k – a few Mb/sCentralHub
Infinite bandwidth backbone Last mile
Solution to the Last-Mile – Optical Wireless Network
To replace existing copper cable
Low cost
What is Optical wirelesscommunication?
Optical carrier , rather then radio/microwave (305 THz)
Outdoor link point up to 5 km Wireless network offer increase mobility Provide higher bandwidth
Optical wireless vs Radio frequency property radio Optical
Bandwidth Low High
Broadcast Yes No
Data safety No Yes
Spectrum allocation
Yes No
Additional infrastructure
Yes No
Frequently Asked Question
Did atmospheric condition make line-of-sight optical communication problematic and unreliable ?
1Gb/s over 1Km though very dense fogby use of special transmitter and receiver
Eye Safety
The maximum intensity that can enter the eye depend on the wavelength whether the laser is a small or e
xtended source and the beam divergence angle
In general OW systems operating at 1.3μm
Gaussian intensity profile : Io = 2 P/πw2
Atmospheric Turbulence On Optical Links
Problem • Diameter fluctuate
• light dance
• Scintillation
For longer ranges , in principle , turbulence effects can be mitigated by• Adaptive optic transmitter/receiver
• Delayer diversity
Atmospheric Turbulence On Optical Links cont.
Link state
In our Opacity wireless network approach responses to link state change include
• Varying the transmitter divergence , power , and/or capacity
• Varying the transmission of the link
• Redirection of laser beams
Optical link characteristics
We are investigating high-data-rate free-space optical links that can be reconfigured dynamically
Key characteristics include:• Optimal obscuration penetration
• Dynamic link acquisition , initiation , and tracking
• Topology control to provide robust quality of service
Topology reconfiguration:A Free-Space Optical Example
Experimental results
BER due to the topology control process
Summary
We present an overview of the issues affecting the implementation of an optical wireless net-working scheme
Including:• Atmospheric effect
• Eye safety
• Topology control
• Laser beam configuration
THE END
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