Saturday, May 16, 2009

Which Graphic Explains Co-Channel Interference Best?

I've been teaching WiFi for many years now. And one concept folks seem to have a hard time with is co-channel interference. Not that there *is* interference, that's pretty obvious, but at what level does co-channel interference actually start to 'hurt' the Wireless LAN?

I've started to call these areas 'Want' - 'Don't Want' - 'Don't Care' - but the concept is still the same.


Question: At what point does another device on the same channel equate to a 'collision domain'?


So I'm asking for the reader's help in deciding which of the following graphics make more sense?


Which should I use in classes?


Thanks for your help!


Keith


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A - Multiple small circles

B - One large circle

C - Multiple large circles

D - Wedges


4 comments:

  1. I gotta tell ya, they're all fantastic! I wouldn't cheat the students by choosing only one. Each might ring a bell for given students. These are some seriously good graphics. Kudos.

    Devinator

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  2. I agree, they all are great. As a student, I think I would catch-on the quickest with a progression of B->D->C with a final review again of D. You've used Figure D in your classes before and I've drawn it several times to (attempt to) demonstrate the concept to our sponsors, so it sticks!

    Skipper

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  3. Keith,

    The wedge is helpful, however what I am finding is that people who use the tool first need to understand how to use it correctly. Between this and SNR which is also important, that may actually open some eyes. I have a guy on staff that all he does is focus on the co-channel interference heat map and turns things way down to eliminate it even though he may be introducing other problems, like proper channel overlap, or worse yet, breaking something else that is working. My suggestion, use a couple of graphics but tie in strongly all of the things that need to be considered so that engineers do not get one minded with how to solve a problem.

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