the digital inquisition

How to chose the right WiFi channel

By  , in , posted: 26-May-2007 20:58

With increasing density of WiFi networks we're facing more and more WiFi networks popping up in our neighbourhoods, which may impact performance on your WiFi network, if frequencies interfere.

To scan your neighbourhood for active WiFi networks use "Netstumbler", an easy-to-use WiFi scanner for Windows. After starting Netstumbler will show you all discovered networks inlcuding the used channels.

Two WiFi networks operating on the same channel are forced to share bandwidth, as they can't "talk" simultaneously, which halves each network's bandwidth. In order to evade this effect, you need to change your access point's channel, but taking the adjacent one won't do it, as WiFi channels are arranged in an overlapping pattern, as you can see from this scheme:

Channel 1 overlaps channels 2 to 5, which therefore may not be used for a neighbouring WiFi network. If channel 1 is used, you should switch to channel >=6.

There must be a spacing of at least 5 channels (or more) between each WiFi network in order to avoid interferences.

Further, if all your WiFi-devices support 802.11g (the 54 MBit/s WiFi-variant), you should set your router to 802.11g-only mode, as the 802.11b-compatibility impacts on bandwidth and range even among 802.11g-devices. Another possible cause of low performance may be proprietary WiFi acceleration modes like "SuperG", "MAXg", "125 High Speed Mode" or "SpeedBooster", if not all devices in your network support the very same mode, why you should disable those.

Also note that a lot of cordless phones in NZ operate at the 2.4 GHz band like Wifi and so most of them cause interferences WiFi, that can't be avoided by a channel change, since those phones use a very broad spectrum or perform permanent frequency hopping.
If you own a 2.4 GHz phone, try switching it off and removing the power supply of it's base station. In case your wireless signal improves, replace your cordless phone with a new one operating at 1.8 GHz or 5.8 GHz.

Other related posts:
NZ's hopeless wireless market

Comment by juha, on 27-May-2007 10:47

Very useful graph that.

Comment by hellonearthisman, on 27-May-2007 21:33

Nice Info. Thanks.

Comment by wangvivian, on 22-Sep-2008 21:04

Thanks very much for kind sharing.
But how about a wifi phone support 802.11b/g?

Comment by Lobotom, on 27-Nov-2008 06:07

Nice and neat, clear and short.

Thanks for the tips.

Just out of curiosity, the frequencies above are unique world-wide right ? Or due to local laws, does the 802.11G standard itself include variants ?

Comment by Lobotom, on 27-Nov-2008 22:27

I wish to add for Vista users that Netstumbler won't work.

I suggest using inSSIDer instead.

Author's note by inquisitor, on 5-Jan-2009 05:37

"Just out of curiosity, the frequencies above are unique world-wide right ? Or due to local laws, does the 802.11G standard itself include variants ?"

Channels 1-11 are in use worldwide, while 12 and 13 may be used only outside the US and 14 seems to be utilized only in Japan. Therefore WiFi-devices sold in the US are limited to channels 1-11 by hard- or software. So if you're a hotspot operator, you should chose a channel American visitors can use, too. Also when purchasing WiFi-hardware from the US, check out if you can replace drivers or firmware by an international version in order to gain full channel capability.

For details check Wikipedia:

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