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/s Central Hub Infinite bandwidth backbone Last mile

Solution to the Last-Mile – Optical Wireless Network To replace existing copper cable Low cost

What is Optical wireless communication? 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 propertyradioOptical BandwidthLowHigh BroadcastYesNo Data safetyNoYes Spectrum allocation YesNo Additional infrastructure YesNo

Frequently Asked Question Did atmospheric condition make line-of- sight optical communication problematic and unreliable ? 1Gb/s over 1Km though very dense fog by 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 extended 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