# Wireless Interface

An extraction from an article :
"Try to find an unused non-overlapping channel, because each 2.4 GHz channel frequency is actually the center frequency of a channel that's 22 MHz wide. That means that an AP tuned to Channel 6 causes interference on Channels 4 through 8. In the 2.4 GHz band, Channels 1, 6, and 11 are the only non-overlapping channels. If none of those channels are unused, choose the channel with the lowest co-channel interference -- that is, the one with competing APs that have the weakest signal."

#1 What does the following mean ?
"each 2.4 GHz channel frequency is actually the center frequency of a channel that's 22 MHz wide. That means that an AP tuned to Channel 6 causes interference on Channels 4 through 8. In the 2.4 GHz band, Channels 1, 6, and 11 are the only non-overlapping channels"

#2 Does it mean AP should either set to 1, 6 or 11 for minimum interface ?

#3 How to find out non-overlapping channels ?

Tks
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Commented:
#1 What does the following mean ?
"each 2.4 GHz channel frequency is actually the center frequency of a channel that's 22 MHz wide. That means that an AP tuned to Channel 6 causes interference on Channels 4 through 8. In the 2.4 GHz band, Channels 1, 6, and 11 are the only non-overlapping channels"

It is much easier to understand if you see picture. You can see from the picture that only clean channels (non-overlapping) are 1, 6 and 11. Channels 2, 3, 4, 5 are overlapping with channels 1 and 6., just as 7, 8, 9, 10 are overlapping with channels 6 and 11.

#2 Does it mean AP should either set to 1, 6 or 11 for minimum interface ?
Yes, and if you have many APs you should set near AP to different channel. If AP1 is CH1 AP2 that is near should be set to channel 6 or channel 11, etc

#3 How to find out non-overlapping channels ?
Wireless Network analyzer tools
Or this from fluke and many more...
Author Commented:
If channel 1, 6 and 11 has already used by nearby router, should I select a channel that is never used, or I should still restrict my channel to 1, 6 ,11 ?

What is the value of RSSI ? -65dbm and -100 dbm, which one is better ?

Tks
Commented:
It's hard to get through.. problems with EE server.
:)
Here is nice article from HP - planning the site assessment
- 65 dbm is much better than -100 dbm
PrincipalCommented:
Here's an example:

Suppose that channels 1,6 and 11 are in use nearby.
(You can use something like inSSIDer to determine this).
And, say that the signal on channel 1 is the highest - so to be avoided.
And, say that the signal on channel 6 is the next highest - also to be avoided.
So, the signal on channel 11 is the least.
So, you would choose channel 9 as it's the furthest from channel 6 but still removed from channel 11.
This is a simple example but may be helpful.

The Wikipedia picture that Pedrag Jovic linked is a good one to visualize this.

Some routers have the ability to pick the best channel automatically.  Years ago I had some trouble with clients dropping off and stopped using it.  But, in crowded areas, it may be a good thing to try.  Then the channel hops around after a better one is found.

A good rule of thumb for RSSI (the signal you receive from your own router) is -70.  Toward -100 is less signal and toward zero is more signal.  A connection may work between -70 and -80 but it will be marginal.  So, for initial setups, using -70 as a rule is a good choice.  Then if you get -60 or -50 so much the better.
Well, of course, you can get this value for other signals as well and the same ideas apply.  If a signal is -95 then it's not likely to interfere much if at all.

From Wikipedia:
The 802.11 standard does not define any relationship between RSSI value and power level in mW or dBm. Vendors and chipset makers provide their own accuracy, granularity, and range for the actual power (measured as mW or dBm) and their range of RSSI values (from 0 to RSSI_Max)
Author Commented:
Tks, any free diagnosis tool that can recommend a best channel to be used in a AP / wireless router ?

I also find that my wireless control allow to set the transfer rate, should I select the maximum rate for each type. Why does it allow a range of selection although I assume the AP should try to achieve a max speed ? Any comment.

Tks again.
MandatoryRate.png
Commented:
Stronger signal strength is correlated with higher data transfer speeds, but as signal strength is getting weaker data transfer speed drops. I guess it would be best to turn all speeds on or at least all until some minimum value that you decide. If only max speed are selected many of your users will not be able to connect from places where signal is weak.

I gave you link on free tools, but I am not sure that any recommends channel to set on router (AP).

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