Doing a wifi long shot

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Wireless connections over 20km and more

What you need to know to successfully design and build a wifi long shot. RF Calculation. Knowledge about the Fresnel Zone. Polarisation of electromagnetic waves. Tricks to avoid interference. Timeout problems of 802.11abg and how to deal with them.

Description

Wifi is a really inexpensive way to build datalinks up to 120 kilometerdistance. Such use of Wifi is already relatively widespread in developingcountries that lack communication infrastructure. The world wide web is sofar not truly for everyone - may 1 billion people use it and about 5billions don't. It maybe unavailable, too expensive or both. Indeed,Information needs to be free - that also means that there must be cheap waysto share it. So far WiFi is the cheap way to go where no infrastructureexists - although that may change with WiMax in the future. Even if youlive in a developed country it is fun or may be necessary to build your own(community) network beyond the range a few hundred meters.

During the last months I was designing Wifi-links (long shots) in Bangladesh- mostly used for inexpensive calls with Voice over Internet Protocol sincemost people are illiterate there. The use of the network for applicationsbeside speech is slowly increasing.

If you are interested to build your own metropolitan area network - or evenbigger - with inexpensive technology for a few bucks - then this presentationmay be interesting. A brief list of the topics:

Link calculation - propagation attentuation, transmit power, receiversensitivity, antenna gain, additional losses, curvation of earth, fresnelzone, polarisation of electromagnetic waves.

Recommended hardware - Access Points, WiFi Cards, Antennae a.s.o.

Important Do's and Dont's.

Propagation delay and 802.11.

Tricks to minimize interference.

How to do long shots and stay in legal limits if you are scared. (You won'tbe able to achieve 120 km, though.)

Speakers

• Elektra Wagenrad

Schedule

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