Wireless channels in congested environments

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yanko
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PostPosted: Sat Jul 11, 2015 15:11    Post subject: Wireless channels in congested environments Reply with quote
I have two wireless access points. I've been reading much advice on choosing channels and everyone says use 1, 6, or 11 to avoid interference, since frequency bands overlap. That much I understand. My question is, if everyone near me uses these three channels, is it better for me to use them too, or should I use 3 and 9 instead?

In other words, will I get more interference from other traffic on the same channel or on a neighboring channel? I can see valid arguments for both, but it seems to come down to subtleties on how the protocol handles conflicts. A neighboring channel may garble my packet but the same channel might land a packet on top of my own.

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Murrkf
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PostPosted: Sat Jul 11, 2015 17:26    Post subject: Reply with quote
No. 3 will usually overlap with both 1 and 6, and 9 will overlap with both 6 and 11, so they are actually the worst channels to use.
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raqua
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PostPosted: Sat Jul 11, 2015 19:56    Post subject: Reply with quote
I live in a big block of flats and wifi situation is pretty difficult here. I have tested all channels and 8 works significantly better that 1,6 or 11. There are at least three nearby networks on each of those channels. I get double speed on channel 8.
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js1662
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PostPosted: Wed Jul 15, 2015 10:30    Post subject: Reply with quote
I found this article that talks on this subject: http://www.smallnetbuilder.com/wireless/wireless-howto/31656-it-takes-a-neighborhood-to-fix-bad-wireless
yanko
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PostPosted: Sun Jul 19, 2015 17:49    Post subject: Test results: ch.3 is best Reply with quote
Thanks for all your help. The article was especially helpful explaining the physics of it.

However, I did some testing, and here are the results. For context, mine is an B/G only router and the neighbors are all on 1, 6, and 11, with 11 being the busiest and 6 being the least busy:

write/read in Mbps
1: 17.1/17.6
2: 18.3/17.7
3: 19.4/19.9
4: 18.6/18.8
5: not done
6: 17.1/17.9
7: not done
8: 14.9/16.1
9: 7.8/11.4
10: not done
11: 10.3/14.8

3 is the clear winner, with performance gradually decreasing on either side with 1 and 6 being about the same. Above 6 performance continues to fall with 9 being the worst, but 11 not much better.

So it seems like in practice, in spite the theory, the best channel is one that's half way between busy channels.

I imagine N may be different due to wider frequency band. I'll redo the test when I get one; until then I'm sticking to 3.

Y
js1662
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PostPosted: Mon Jul 20, 2015 1:32    Post subject: Reply with quote
You have to consider your neighbors as channel 3 is an overlapping channel to those who is using channel 1 or 6. BTW, try your test on other locations in your home and see if you get the same result.
mightybonus
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PostPosted: Sat Mar 12, 2016 15:20    Post subject: Reply with quote
[quote="js1662"]I found this article that talks on this subject: http://www.smallnetbuilder.com/wireless/wireless-howto/31656-it-takes-a-neighborhood-to-fix-bad-wireless[/quote]

Wow -- I had always been under the impression to scan your area with inSSIDer... then choose the most "open/unused" channel. In my neighborhood everyone seems to be on 1, 2, 3, 6 and 11. So I have had myself on 8. Interesting article, but it really goes against everything I had believed. I may have a hard time changing. Shocked
mightybonus
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PostPosted: Sat Mar 12, 2016 23:57    Post subject: Reply with quote
...and sure enough, there's plenty of conflicting information even among the reliable sources. Some say to share channels, some say to find an unused (or least used) channel. Overall the tone of the latest articles I read seem to imply the "everyone on 1, 6, 11" advice is outdated and may no longer be necessary with modern routers and devices.
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