Using 40 Mhz wide channels in a 2.4 Ghz wireless network deployment

Hello everyone!

We have a site (a secondary school) where all WiFi networks are managed by us. The building should in theory have no rogue APs that introduce interference, however, other RF emitters such as microwaves, game console controllers, Bluetooth devices do exist.

I, being a young still learning network engineer wanted to follow all the best practices as detailed in online resources, as well as published books about network deployment strategies. From what I found it is generally recommended to use non-overlapping 20 MHz wide channels when deploying a network in the 2.4 GHz spectrum. Configuring APs in a manner where each AP broadcasts on a channel that is not used by any other AP nearby. I have also found a lot of resources that say that using 40 MHz wide channels is generally not recommended in the 2.4 GHz band since there are only 2 non-overlapping chunks of the available spectrum and that it would be extremely difficult to divide it in a manner where APs do not interfere with each other.

Unfortunately, our senior network engineer would like to use 20 MHz Ce channels (40 MHz effective). His logic is that we should use as much of the spectrum as possible and that the best way to get a transmitter to stop occupying the spectrum is to allow it to transmit the data at the fastest data rate possible (since a higher max speed is reachable with 40 MHz). He tells me that that I do not understand how 802.11 works and that APs operating in the same chunk of the spectrum can utilize it better if allowed to use the entire spectrum due to collision avoidance algorithms such as CSMA/CA, as opposed to dividing the spectrum into smaller chunks and having each AP use their smaller chunk.

I agree with him that his solution might “better utilize the spectrum”, however, I do not see it as bringing a better quality of service to the clients utilizing this network.

Could someone please explain why he is or isn’t correct? I cannot find a single online resource that recommends the use of 40 MHz wide channels in the 2.4Ghz spectrum unless you only have 1 or 2 transmitters each using their half of the available spectrum. However, since he is the senior network engineer we have to do things the way he says…

Not sure if you saw this, but it gives a good explanation. In short, functioning connectivity (aka, no interference) matters more than speed.

I would use channels 1,6,11 myself. The best solution would be a controller based system that can dynamically adjust channels being used.


Problem with 2.4 GHz based WiFi and the “logic” behind thinking wider is better doesn’t usually translate in real life. To sum it up

  • 2.4 GHz wireless is old and does not really meet the need of modern devices with modern needs
  • Modern typical WiFi environments are congested and 5 GHz was established to overcome the limits of 2.4 GHz
  • In 2.4 GHz environments, when a guest device is struggling to communicate, the entire WiFi AP adjusts down in performance to maintain communication with that one device. This action brings performance down for all devices on that affected AP
  • Better way for WiFi is GHz with modern standards
  • Good APs have the ability to steer clients to 5 GHz
  • Better APs have the ability to drop and limit clients using 2.4 GHz; only clients with strong signals can use 2.4 GHz
  • Suggest looking at steering and client performance thresholds if your AP system allows for it. Unifi APs do.

Good WiFi industry read is here on the subject of 2.4 Ghz. Hotels, resorts and schools have a lot in common in terms of WiFi environments.

Well that is how I started my argument with him.
I have already seen this article by CBT nugget blog as well as many others like it.
I have not seen the one by, however they are all preaching the same thing.
Every single resource I found says to use 20 MHz wide channels and to space them out so that they do not overlap.
We could do 1,6,11 but since we are in Switzerland 1, 5, 9, 14 could work too.
They also say to NOT USE 40MHz since there are only 2 non overlapping channels in Europe and 1 in the US…

Unfortunately, our senior network administrator does not like those “guides” and says that his knowledge of how 802.11 works tells him that you could easily go with 40 MHz wide channels without any issues, and that it would actually wok out better.

And I do not know what other arguments I can use to convince him.
He does have a background in radio engineering, and simply tells me that I do not understand how the technology works.
When I show online guides on best practices where it clearly states that 40 MHz wide channels are not recommended for 2.4 GHz deployments he proceeds to tell me that “there are a lot of stupid guides on the internet and that I should read a technical book about it instead”

I go on and get the O’Reilley “802.11n: A Survival Guide” by Matthew S. Gast
Find the relevant sections and tell him:
Page 62:

In the 2.4 GHz band, however, there are no good choices for where to put a 40 MHz channel. Figure 6-1 shows the difficulties of enabling a 40 MHz channel in only 83 MHz of spectrum.


Page 63:

As a general rule, 40 MHz operation in 2.4 GHz is acceptable if there are no other networks in range.
Page 105:
Do not use 40 MHz channels in the 2.4 GHz band. With only 83 MHz of spectrum, you have space for just two, and that’s only if you ignore the overlap problems. Just don’t do it.
He then proceeds on telling me that this is only applicable if there are networks not controlled by us using same spectrum. Since we manage the whole building then only our networks have to use the spectrum. If we had other people’s networks using the spectrum, then 40 MHz would not work well.

Please tell me if I am wrong, but I do not see how two of my APs using the same frequencies in the same area is not a bad idea, but if one of the APs is someone else’s on the same frequency its a totally different thing.

He then proceeds on explaining that CSMA/CA networks can easily operate in the same frequency due to collision avoidance algorithms and that since we only have one network it does not matter if a client is waiting for one AP to finish transmission or for another.

I really like my work place and it hurts me when school teachers come to me complaining that our WiFi is shitty.
If anyone with a technical background in radio engineering could explain either why he is wrong or why he is correct please let me know.
He is not taking any arguments I find on industry best practices since he says that its all fluff and that only people who understand how the physics behind radio transmission works understand how to set this up correctly.

I understand the “how” of wide banding, but suggest looking into the “why”.

The hotel best practices also says 2.4 GHz is the garbage band and on the way out (article published n 2017)

That book was published in 2012 and the info is dated by the standard that technology improvements move


Working in large wifi environments, our best practices is set the threshold for 2.4 GHz use high, steering guest devices to 5 GHz as that is a much better domain for mobile device operations and meets the overall objective to keep the experience good for the majority of users.

Also working with modern commercial grade WiFi systems, they almost always have the ability to automatically optimize channel selection. Look into a WiFi systems ability for fast roaming too

At the end of the day, do what you want with the understanding that setting the bar low for 2.4 Ghz clients will impact all the clients even with wide banding.

Another route to take is to actually work with your team to device a TEST and INTEGRATION PLAN that will measure performance and throughput of each configuration (possibly based on Customer Acceptance Criteria). Arguing (debating is a more easy word) about theoretical configuration and final implementation performance is unknown until measured.

I worked in the telephone industry (AT&T, Bell-Labs, Lucent, Nokia) managing the integration, test, and deployment of 3rd-party applications/hardware into the customer premise. Our plan always included Integration, System, and Delivery plans that included complex measurement & acceptance criteria.

May be you could take the lead to develop and implement methods and procedures (MOPs) to monitor systems to better meet the acceptance criteria customers specify?

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