Re: Non-overlapping channel (1/6/11) isn't always optimal

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In <v1rq22tdt21v8a9cfjhtglr980ph0d0smh@xxxxxxx> on Fri, 31 Mar 2006 11:01:05
-0700, Aaron Leonard <Aaron@xxxxxxxxx> wrote:

On Thu, 30 Mar 2006 21:55:36 GMT, John Navas <spamfilter0@xxxxxxxxxxxxxx> wrote:

~ [POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]
~
~ In <91jo225f2f7i48fpv0mkkctfor8m9e8dle@xxxxxxx> on Thu, 30 Mar 2006 14:32:48
~ -0700, Aaron Leonard <Aaron@xxxxxxxxx> wrote:
~
~ >~ My point is that 1, 6, and 11 aren't necessarily optimal.
~ >~
~ >~ In fact 1, 6, and 11 are only really optimal in terms of minimizing
~ >~ interference when you control multiple overlapping access points, and even
~ >~ then they aren't necessarily optimal -- 4 channel spacing (e.g., 1, 4, 8, and
~ >~ 11) will allow 4 access points (instead of just 3) to overlap with minimal
~ >~ interference.
~ >
~ >Our test results do not concur (assuming that you control your RF
~ >environment). The interference created by using 1/4/8/11 rather
~ >than 1/6/11 channel spacing will give you less aggregate throughput
~ >throughput the 2.4GHz band. With 4 APs, you are better off having two on
~ >the same channel.
~
~ That's not my experience, which is consistent with these documents:
~
~ 4 Simultaneous Channels Okay For 802.11b
~ <http://www.extremetech.com/article2/0,3973,708876,00.asp>
~
~ The Overlapping Channel Problem
~ <http://www.ja.net/services/publications/factsheets/063-overlapping-channel-problem-v2.pdf>
~
~ WiFi was *designed* to support many interfering, overlapping networks,
~ handling the resultant packet collisions with minimum fuss.
~
~ Channel Overlap Calculations for 802.11b Networks
~ <http://www.cirond.com/whitepapers/FourPoint.pdf>
~
~ >This is because, with multiple BSSIDs on a single channel, the 802.11 MAC
~ >can (potentially) recognize the signals from the other BSSID as being valid
~ >802.11 frames, and can hence do an informed backoff/transmission. With
~ >multiple BSSIDs on adjacent overlapping channels, the other BSSID's
~ >transmissions are just perceived as noise.
~ >
~ >http://www.cisco.com/en/US/products/hw/wireless/ps430/prod_technical_reference09186a00802846a2.html
~
~ As it notes, that paper is at odds with the other authorities. In addition,
~ the only supporting test was both limited and highly artificial.
~
~ It may be that what works best is different in different types of
~ environments.

I've glanced at your references, and have this comment: ALL of them
reference 802.11b not 802.11g, and all of them point back to the original
'02 Mitch Burton paper. Note that Burton concedes that the 4-channel
allocation scheme is not well suited to 802.11g OFDM, which uses considerably
more energy at the edges of the channel.

Surely more and better testing using 802.11g is in order.

I would agree.

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