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