Asus 2.4Ghz auto control channel chooses suboptimal channels

[MKLBNS]

This has been discussed before. I read some threads but did not find a clear explanation.

AFAIK it is common knowledge to use only channel 1/6/11 on the 2.4Ghz band. The reason for this due to 2 types of interference. Adjacent Channel Interference (ACI) & Co-Channel Interference (CCI). AFAIK CCI is better than ACI.

My Asus RT-AX88U (with latest Merlin firmware) chooses control channel 4 or 5 over the last couple of days while using auto control channel setting & 20Mhz channel-bandwidth setting. When scanning the 2.4Ghz band it shows 90% of all seen networks use channel 1/6/11. For me to use channel 4 or 5 I must suffer from a lot of ACI and at the same time creating ACI for others.

Are the best practices on ACI & CCI not applicable anymore in 2025? What could be the reason my RT-AX88U chooses those suboptimal channels?

 

[Tech9]

What could be the reason my RT-AX88U chooses those suboptimal channels?

Because the channels are not suboptimal. They are the best with most available channel bandwidth and less noise as seen from the router and calculated by the radio driver logic. If you think your manual settings are more optimal - feel free to change them. I would only lock the channel to whatever the router selects on Auto more often.

 

[MKLBNS]

This is coming from an Aerohive design document, similar information can be found in documentation from other large Wifi vendors.

Wi-Fi cells that are operating on overlapping channels (for example, channels 1 and 3) in close physical proximity to one another can result in interference between the main signal lobes of the APs. This is referred to as adjacent channel interference (ACI) and has a worse effect on performance than co-channel interference because Wi-Fi stations often cannot demodulate the signal and instead perceive it as noise. This prevents carrier detection and NAV mechanisms from properly detecting the medium as busy, forces the station to rely on raw energy detection,which is less reliable, and can result in increased frame collisions and retransmissions.

This document is from 2013 though... did the modern view on this topic change? Or is my private environment not compareable to a high density enterprise deployment and is for that reason the negative effect from ACI not as bad as the theory suggest? Do you know of any documentation from the wellknown vendors which confirm this changed view of this topic?

 

[Tech9]

The theory didn't change, but in reality in your private environment you have no control over other APs around whatsoever. Very likely most of them work on Auto and will change channel often including outside 1-6-11. If you want to play nice lock your router to whatever you believe is best from 1-6-11 and hold your ground. There is a chance the channel you lock is not the best channel in terms of available bandwidth. Modern APs filter better the noise and push more bandwidth on whatever was considered non-optimal channels in the past.

 

[MKLBNS]

but in reality in your private environment you have no control over other APs around whatsoever

Ok, this makes sense, those design documents are obviously targeted to environments where you control the entire environment.

Modern APs filter better the noise and push more bandwidth on whatever was considered non-optimal channels in the past.

Ok, this is also something I can understand.

Thanx for sharing your knowledge on this topic.

 

[Tech9]

If it makes you feel better - in my environment almost every ASUS router I ever tested was selecting Ch.4 on 2.4GHz band and it was indeed the one with the most available bandwidth most of the time. My main Ubiquiti system is set on Ch.1 and Ch.11 just because I want to play nice and I have only few devices using this band. May APs are also set at very low 40mW power on 2.4GHz band and the signal doesn't travel outside of coverage area needed.