Any reason not use 20Mhz channel on AX devices, if stability is preferred over max speed?

RouterOS Wireless Networking
1

For years of Wi-Fi, the general recommendation is avoid large channel widths unless the spectrum is relatively clean.

But I’ve never seen that recommendation for AX devices. I know AX uses OFDMA to better handle this and large channel widths are needed to get “max speed”. But most of my use cases, I prefer minimizing latency and drops, and 20Mhz of Wi-Fi bandwidth is plenty.

I’ve generally been setting 20Mhz or 20/40Mhz channel width on AX. But with AX’s OFDMA, I’m guess I’m not sure if it’s better to use full range and let OFDMA “sort it out”.

Anyone know the best practices for AX on channel widths?

2

… so do G and N (and A) … actually only B uses DSSS with 22MHz-wide channels. So in this respect AX is nothing new. What AX adds is 1024QAM (N stops at 64QAM) so it can reach higher speeds when SINR is great. And reduces subcarrier spacing by factor of 4 (again increases speed but at the same time makes receivers sweat which usually results in slightly lower SINR). Increases max MIMO rank (not really practical) and brings MU-MIMO.

None of these give any reason why using 40MHz channels on 2.4GHz band would suddenly become a sane thing to do.

3

I have capsman setup with cAP AX devices in warehouse environment where I set the channel width to 20Mhz.
No need for more speed with warehouse scanners. I prefer stability there.

At home however (really interference-free environment “thanks to” modern building methods, not even GSM signal inside :open_mouth: :confused: ) I set my channels AWAP (As Wide As Possible).

EDIT: cross checked, it’s 20MHz. 10MHz is not possible.

4

That one I’ve never got either.

I actually been using 20Mhz on both on most of the AX devices we use. I just NEVER see anyone recommend narrowing channel width for AX… which got me questioning physics.

5

My guess: none of the vocal AX supporters considers 2.4GHz band as viable WiFi band any more (everybody is looking at 6GHz now days).

I’ve thought of a reason to go with 20MHz channels (instead of 40MHz) on 2.4GHz band: signal level. The country-regulated Tx power is spread over whole channel width and if 20MHz channel is used (as opposed to 40MHz channel), signal level is 3dB higher because Tx power is spread over half the bandwidth. Which helps to increase stability and/or coverage.

6

I set the 2.4 channel to 20 by default for compatibility.

It has served me well.

7

Yeah the 40Mhz on 2.4Ghz always seemed silly to me.

It the 5Ghz band where I just never/rarely seen anyone recommend/using 20Mhz (or even 20/40Mhz). And have wondered if either I’m missing something about AX thus the initial question… Seems I’m not alone. But do think using default 20/40/80Mhz channel width might be cause of at least some of the frequent AX complaints…

8

Even for 5GHz I use 20MHz in that setup. All cAP AX and AX3 devices.
Stable as a house AND more options to stay on below-DFS channels (scanners in use there don’t support higher channels so I had to cut down channel width to create more possibilities to avoid overlaps).

That one higher channel is for an AP in the office part :sunglasses:

2024-11-27_21-21-55.jpg

9

I don’t think that 20/40/80MHz is causing complaints. After all, this kind of channel arrangement is (supposed to be) backwards compatible with devices supporting only narrower channels. And using 20/40/80MHz on AC APs turns out just fine.
Rather I think that AX devices by MT having tendency to use frequencies in U-NII-3 (and U-NII-4) part of 5GHz band (above 5735MHz) is what causes problems: not every wireless station supports those high frequencies and many countries regulate EIRP in that part of spectrum pretty low (e.g. in ETSI region: 14dBm vs. 30dBm for lower part of 5GHz band).

10

Actualy ax hardware I tested on 7.16.2 on MikroTik have only fixed channels,
example 5500 but not 5510, and work ony on 20MHz or consecutive 20+20 or 20+20+20+20 channels.
(hAP ax², hAP ax³, wAP ax, cAP ax, mANTBox ax 15s)
2412,2417,2422,2427,2432,2437,2442,2447,2452,2457,2462,2467,2472
5180,5200,5220,5240,5260,5280,5300,5320,5500,5520,5540,5560,5580,5600,5620,5640,5660,5680,5700,5720,5745,5765,5785,5805,5825,5845,5865,5885
No one support (obviously) 2484
My hAP ax³ do not support 5845,5865 and 5885

South Korea allow also 5945-7125 indoor 24, but I do not know if actually any MikroTik ax products can use that.

2412,2417,2422,2427,2432,2437,2442,2447,2452,2457,2462 (1..11)
20

2467,2472 (12-13)
ALLOWED 20

2484 (14)
UNSUPPORTED & FORBIDDEN

5180,5200,5220,5240
indoor 23

5260,5280,5300,5320
dfs indoor 23

5500,5520,5540,5560,5580,5600,5620,5640,5660,5680,5700,5720
dfs 30

5745,5765,5785,5805,5825,5845,5865
14

5885
FORBIDDEN

5945-7125
FORBIDDEN
2412,2417,2422,2427,2432,2437,2442,2447,2452,2457,2462 (1..11)
30

2467,2472 (12-13)
FORBIDDEN

2484 (14)
UNSUPPORTED & FORBIDDEN

5180,5200,5220,5240
30

5260,5280,5300,5320
dfs 24

5500,5520,5540,5560,5580,5600,5620,5640,5660,5680,5700,5720
dfs 24

5745,5765,5785,5805,5825,5845,5865
30

5885
ALLOWED 30

5945-7125
FORBIDDEN

11

Yup, that's pretty normal on today's mainstream wireless stations (e.g. smart phones) ... they only support standard channel center frequencies. When creating MT-MT point-to-(multi)point link, this is not a problem per se, but when operating device as AP for "public" access, one really has to stick to standards. Even if one operates a "private" setup it still may be sensible to stick to standards. If not for other things to avoid excessive interference to/from innocent neighbours. E.g. using NV2 had a nice side effect that not many other WiFi gear was able to detect it (so this adds a layer of security-through-obscurity) ... but if other APs can't detect your link, it will interfere with it (without malicious intents). Similarly when using non-standard center frequencies and/or channel widths one risks of creating excessive interference with equipment which doesn't detect such "pimped up" WLAN.

12

this sounds more like Flexible Channel Utilization a feature of Wi-Fi 7 802.11be

AFAIK
channel width depends of scenario and requirements

of course, 20mhz in 2.4ghz is mandatory unless you are in a cabin in the woods without neighboring wi-fi networks