Many Devices Ignoring 40 MHz Coexistence - Wi-Fi Certified

[sfx2000]

What issues would it cause with neighboring networks? I am not aware of any.

I know it would cause issues with older 802.11 clients that are only able to to 11b, but AFAIK it'll work fine with at least 11n/ac clients and possibly 11a/g clients as well.

Or at least when I've played with it in the past, all of the 11a/n/ac clients I have had worked just fine. I don't have any b/g clients, nor did I try operating them in 11b/g mode to see if it caused any issues.

There was a long running discussion back and forth about greenfield mode in the 802.11 TGn working groups back when I was participating in the IEEE 802 sessions.

What it really comes down to is that you want all clients _and_ adjacent networks to see the beacon frames - this is so that they do not step on each other and clobber the transmissions - it's a backwards compatibility item for interoperability across chipsets and vendors.

sfx

 

[azazel1024]

Ahhh, okay.

I guess I can see where that can be an issue in some circumstances (most?). Though I'd imagine, without having any clue if it is true, that newer access points would be able to see SSID beacons transmitted at higher data rates if they are somewhat newer access points.

I would think the issue would only be if you have deployments where old access points exist which are not capable of broadcasting/receiving beacon frames transmitted at higher rates.

 

[Razor512]

Overall, isn't it a good thing that many routers are ignoring the 40 MHz coexistence?

Even in extremely crowded environments, it offers a good performance boost, especially when within 20 feet. But at longer range range, both 20 and 40 MHz offer horrible performance (possibly due to 150-160 other APs)

With these issues, 2.4 GHz should use 40 MHz unless the user specifies something different (e.g., router companies can simply add a "slow" button in the wifi settings)

 

[azazel1024]

Base on my moderate experience, I think the only times I've seen setting 20MHz mode as a benefit are in low AP situations and in long range with a lot of interferers. IE you only have a couple of surrounding access points/networks that can step on things. Otherwise, you have enough interference going on with a plethora of surrounding networks that is really doesn't matter much if you are set to 20 or 40MHz in terms of adding interference.

Close to the AP, the performance is still significantly better with 40MHz than 20MHz with lots of interferers. However, at longer range, 20MHz will perform better than 40MHz with lots of interference.

So it depends a lot on your setup. If it is a small apartment, even with a ton of surrounding SSIDs, yes you are almost deffinitely better off with 40MHz mode. In something like a townhouse, you are probably better off with 20MHz mode even though performance close to the AP is going to be better with 40MHz, because in further reaches the interferfence from nearby networks is going to cause 20MHz to perform better.

In single family homes, the distance is often enough that 40MHz is going to perform better under most circumstances.

With no interfering networks at all, 40MHz almost always performs better (with the exception of VERY extreme range).

In your own setup where you have multiple access points, you might want 20MHz mode if you have a lot of overlapping access points. If you only have 2 APs, probably better off with 40MHz on one and 20MHz on the other. Or if you have multiple access points, but there is only overlap between two APs and never more, you can probably mix and match 20/40MHz between the different APs.