It seems that everything I read about wifi says there are only three usable channels in the 2.4 GHz band; however, there are eleven 2.4Ghz wifi channels allowed in the US.
If everyone is using 1, 6 or 11, wouldn’t it make sense to use an unused channel, say, channel 3 for my wifi infrastructure? Or to put the question differently, why can’t I use channels other than 1, 6 and 11?
The 2.4GHz band is one of many portions of radio spectrum, called the Industrial, Scientific and Medical (ISM) bands that are allocated for unlicensed use. As long as you operate within the power and antenna limits, you can pretty much do what you want. So the short answer is, you can. But there are very good reasons why you shouldn’t.
Part of the confusion regarding wifi channels comes from the allocation of the frequency spectrum. The ISM band was first allocated in 1958, before most of us were born and well before anyone even imagined wireless networking. The channel definitions were made before wifi was invented, and they assumed 5 MHz spacing.
802.11b and g transmissions require 22MHz bandwidth. Because they’re 22MHz wide, the signal covers two channels above and below the center frequency. So if you use channel 6, your signal spreads across channels 4-8. There is only room in the entire band for three 22MHz wide signals (in the US) without overlapping if they center on channels 1, 6 and 11.
If you transmit your wifi signal between two of these channels, say centered on channel 3, two things happen: your signal interferes with other wifi users on 1 and 6, and their signals interfere with you. This will greatly increase the number of data errors, which in turn will cause retransmissions and significantly reduce your throughput.
It’s as if there are a number of parallel bicycle lanes, and you try to drive a bus down one of them. Although you drive down one lane, your bus will occupy several of the adjacent lanes. If someone happens to be driving their bus in one of those adjacent lanes when your bus goes by, well…it won’t be pretty.
If you only want to use one access point in a remote area with no other wifi signals, then you can probably get a away with using a different channel. But in most urban commercial environments, the 2.4GHz band is pretty crowded. If you use an overlapping channel, you are likely to experience (and cause) interference. If your wireless system is large with many access points, then you will need all three non-overlapping channels to get good coverage. Using something other than 1, 6 or 11 will limit the density of your access points, further reducing throughput.
In summary, it’s good practice to use 1, 6 and 11 to get the maximum use of the radio spectrum with a minimum of interference.
You can use any channel you want, but as others have said channels 1, 6, and 11 are your best bet. The channels overlap each other such that 1, 6, and 11 are the only channels that don't overlap each other. A picture is worth a thousand words, this one is from the Android app Wifi Analyzer:
Notice that SSID S, centred on channel 1, gets interference from not just SSID 2412s (which is also on channel 1), but from 2417s on channel 2 and from 2422s on channel 3! However 2347s on channel 6 doesn't interfere with it at all. 2347s also does not interfere with 2362s, on channel 11.
You may need to use a wifi analyzer to find out which channel has the least interference, but bear in mind a lot of devices will change channel automagically. It is possible, though, that you're in an area where the local internet provider uses equipment that all sits on one channel, so you could get lucky. At one point I was in an apartment with 24+ different wifi networks bleeding in... all on channel 1, all gear from same ISP. There were only 3 networks elsewhere. As long as I chose a channel 6 or higher, I had no trouble.
Avoid channel 13 and 14 unless you like the idea of prison, being a prisoner, living the prison lifestyle, etc. You'll get plenty of conflicting advice, a little wifi is not worth running the risk that you have to change your definition of a good day to be "one where I didn't get assaulted until AFTER lunch."
TL;DR version: Yes, you can choose any channel, but assuming an essentially even distribution (a safe assumption in most cases), choosing 1, 6, or 11 will give you best performance since they don't overlap with each other.
The problem is, if you DO use Channel 3, you will still get interference from the channels you think you're avoiding. Channel 3 will get interference from channels 1 & 6. Interference from an adjacent channel is more disruptive to both you and your neighbours than same channel.
Channel 3 may or may not interfere with 1 & 6, it depends on where the other nodes are. If your AP is in the same room and close there will be no interference because signal strength will be high enough. In that case using 1 6 11 will cause sharing / pauses. If one person is on ch3 then throughput is increased and no pauses. In a crowded 1 6 11 there is waiting to transmit. But not for the person switched to ch3. If you could plan everybody's channel then using inbetween channels could be more efficient. However on very dense schemes.this idea may break down. It depends on signal strengths.
I don't know how so many network people parrot the "1, 6, or 11 ONLY" rule from a Cisco whitepaper that has nothing to do with a home or small office network. My AT&T Arris gateway automatically selects the "best" 2.4 GHz channel from 1, 6 or 11. It selected Ch 1,and my speed was 29 Mbps with lots of error correction on a 100 Mbps line. On a WiFi analyzer, you can clearly see the problem with using only 1, 6, or 11 "because they don't overlap" But the channels overlap by design, and various orthogonal and spread spectrum modulation methods let them coexist with little or no interference. But nothing degrades speed and causes errors as much as having multiple strong signals on a single channel. I have to go into the setup menu to change to Ch 8, (are you sure you want to make this change? Really sure?) and wireless speed is 90 Mbps.![WiFi analyzer channels]]1
Just randomly browsing the key terms "Wifi" and "Channel 3".. it's gonna be different for everyone. For me, channel 1, 6 and 11 simply do not work. There's way too much interference and my wireless mouse keeps skipping. My wireless keyboard also lags (A LOT). I set the router to channel 3 and the internet sped up about 5%, and also the wireless mouse and keyboard stopped lagging/skipping.
![![WiFi analyzer channels]](https://i.stack.imgur.com/o0dlO.jpg){kind=link}