Any Downside To Enabling Multi-User MIMO and OFDMA/802.11ax MU-MIMO?

[HarryMuscle]

All my research so far about Multi User MIMO mentions that since most devices don't support it there's no point in enabling it. However, is there any downside to enabling these two settings (Multi-User MIMO and OFDMA/802.11ax MU-MIMO on the Wireless -> Professional page) on the off chance some of my devices do support it? By default both settings are disabled for 2.4 GHz (for 5 GHz, Multi-User MIMO is enabled and OFDMA/802.11ax MU-MIMO is set to DL OFDMA Only).

Thanks,
Harry

 

[drinkingbird]

All my research so far about Multi User MIMO mentions that since most devices don't support it there's no point in enabling it. However, is there any downside to enabling these two settings (Multi-User MIMO and OFDMA/802.11ax MU-MIMO on the Wireless -> Professional page) on the off chance some of my devices do support it? By default both settings are disabled for 2.4 GHz (for 5 GHz, Multi-User MIMO is enabled and OFDMA/802.11ax MU-MIMO is set to DL OFDMA Only).

Thanks,
Harry

You'd have to try and see. I've seen reports where it has negatively impacted performance for clients that don't support it. Similar to "airtime fairness" it may only be useful if you actually have a need for it.

I toyed with it on another brand router and seemed to have no impact. My Asus doesn't support it so can't comment on that (plus mine is AC, MIMO has been revised for AX).

 

[glens]

I'm thinking it really only comes into play if you have very many clients which are very active. In playing with it with just a few clients I saw no or slightly negative benefit.

 

[tarzan2000]

All my research so far about Multi User MIMO mentions that since most devices don't support it there's no point in enabling it. However, is there any downside to enabling these two settings (Multi-User MIMO and OFDMA/802.11ax MU-MIMO on the Wireless -> Professional page) on the off chance some of my devices do support it? By default both settings are disabled for 2.4 GHz (for 5 GHz, Multi-User MIMO is enabled and OFDMA/802.11ax MU-MIMO is set to DL OFDMA Only).

Thanks,
Harry

STA-to-STA OFDMA issue?

Good day! I did one test with a WiFi 6 router and it was very frustrating for me. I wrote about its results to the manufacturer's support, and after a long period the support answered me, that the problem was not on their side, but global - in the OFDMA technology itself. So I would really...

www.snbforums.com

 

[pgershon]

Hijacking another threat a bit, but I had experience today with GT-AX6000 router and 3 AI Mesh AX92u nodes. Many of my users saw their 5gHz speeds decline from 500 +/- to <150. I started tinkering with settings and setting "OFDMA/802.11ax MU-MIMO"to DL/UL OFDMA+MU-MIMO and set "MIMO" to disable got the speeds back. I had 4 clients each closet to a different node in the network all streaming video chats on 5gHz band.

For my experience at least, this setting was useful. But I also had to be sure "MIMO" setting itself was in disable

 

[sfx2000]

I toyed with it on another brand router and seemed to have no impact. My Asus doesn't support it so can't comment on that (plus mine is AC, MIMO has been revised for AX).

Yeah - on QCA WiFi6 - it's pretty much a non-issue with DL/UL MU-MIMO and also with OFDMA...

There's another thread that has more info and feedback on these features from a WiFi6 perspective...

Does OFDMA Really Work? Part 2

Our test of six Wi-Fi 6 routers found no significant benefit from OFDMA. Continue reading on SmallNetBuilder

www.snbforums.com

 

[Morris]

The default is disabled for both. Both MU-MIMO and OFDMA are there to help with congested networks with very large numbers of devices. You probably don't need it and by changing a default setting, you open the risk of exercising untested areas of the Asus code. You can enable and see how it goes yet you should remember you made this change and turn them off is problems develop in the future due to an Asus firmware update and/or any device on your networks with an update or a new device introduced.

In general, it's best practice to leave settings alone unless you understand what the change will do and have a good reason to change it.

 

[pgershon]

It's not clear to me what "congested" means. I have many routers but 120 total devices on my network. Maybe 16 are 5gHz while 80 or so are 2.4gHz. The 5gHz devices are phones, iPads and laptops nd are my major data users (along with one wireless Apple TV, while thmye other 4 Apple TV devices are wired). Yesterday internet speeds and performance dropped precipitously while 3 people were doing heavy work on their laptops. I corrected the problem by turning on MU-MIMO and OFDMA.

Is this where "need" comes in? Or do you think the correction was incidental and should I deactivate the settings and see if I can slow the network?

 

[Morris]

You need to determine what congested. Was it your WAN link, one of the nodes, the uplink to a node, or even your providers network.

Enabling MU-MIMO and OFDMA might have made the 3 laptops that you call heavily used have better throughput if they were indeed filling the WiFi band they are on if they were on the same node or router. You could try having the laptops do the same thing 6 time in a row alternating with MU-MIMO and OFDMA enabled and disabled and MESURE there throughput.

16 + 80 = 96 yet you state 120 devices...

Devices streaming video are not heavy users if 1080 video as they only use 5-Mb. 4K video is a bit heavier at 20-Mb each yet you did not describe your WAN speed to judge if that's an issue. Assuming your nodes are reasonably placed and a WiFi friendly environment (construction) and your home is far enough from other WiFi networks that you do not have co channel interference.

 

[pgershon]

I am pretty sure it was not my 1G WAN (fiber) that caused the congestion. I have three notes plus one router and in theory, one laptop was on the router directly and two were on different nodes. I was doing speed tests in different zones using my iPhone. And I had looked at the transmission rates the laptops were showing on the routers webpage to initially see speed issues. I suspect the nodes were all using the same channel as the router (its impossible to know what the nodes use with ASUS AI Mesh - I just assume they mimic the router's settings).

The difference between the 96 wifi devices and the 120 total devices are the 24 or so wired devices.

The nodes are probably closer together than they should be, but we get poor 5gHz speeds room to room - i assume there is WiFi interference, and also WiFi 6 range is not great. We are in the woods so interference from other networks is not as issue.

 

[Morris]

What speed are you getting on WiFi 5-Ghz?

 

[pgershon]

When things work well, I get speeds 400-700 on iPhone. When there is what I believe to be congestion, speeds drop to 150 or less. Measured from laptops or from iPhone using Speedtest

 

[Morris]

You are not testing your network alone, you are testing your ISP's WAN link to your network and all links on your ISP's network and more. You need to run speed tests between a wired computer and the wireless computer or phone to test your network. The odd are that your network is fine and the congestion is upstream of your network.

 

[pgershon]

Then why would the slowdown be toggled by changing the MU-MIMO and OFDMA setting. I demonstrated cause and effect, even if I dont have the perfect set pot speed tests to prove it. Also, the wired devices were not impacted by congestion, only the wireless ones. Demonstrated with same speedtest.

 

[Morris]

one test proves nothing. Speed test over the internet is never the same situation, way too many variables. Read my instructions to retest multiple times above.

 

[pgershon]

Thank you, but I will stick with things set up as they are now. I have MU-MIMO and OFDMA set on and nobody is complaining. It makes sense to me that if all devices are being routed on channel 100 (which, based on the GT-AX6000 web pages, seems to be what the router and nodes are doing), I would have collisions. Ideally the nodes would use different channels to avoid congestion, but that option does not seem to be available.

 

[drinkingbird]

Thank you, but I will stick with things set up as they are now. I have MU-MIMO and OFDMA set on and nobody is complaining. It makes sense to me that if all devices are being routed on channel 100 (which, based on the GT-AX6000 web pages, seems to be what the router and nodes are doing), I would have collisions. Ideally the nodes would use different channels to avoid congestion, but that option does not seem to be available.

Unfortunately a lot of mesh systems do that to minimize the impact of roaming from one node to another. I'm not a fan of that setup, I prefer to keep everything as separate devices and configure each AP as standalone. When one of the new seamless roaming standards becomes common place (and all your devices support it) mesh setups will be very different and roaming will perform much better. But they are taking their time on that. Wifi 7 may finally be the one that sees it start becoming common.

You aren't going to have "collisions" per se - modern wifi is designed to coexist with stuff on the same channel, but you'll have less total bandwidth available in theory across all nodes, and they will lose some performance from the coexistence. Ideally you'd want to change your power level so that there is minimal overlap between the nodes but I believe that is also a single setting for all devices on the master and can't do the nodes independently. But you can see if reducing the power across the board gives you good signal with less overlap (assuming you have overlap now).

But if you're happy with the performance you have now you should be fine.

 

[Morris]

Reducing power increases the chances that the APs will not hear each other and thus can not do collision avoidance. Collisions will also reduce throughput. I agree, Each AP is best on it's own channel set. It's what all enterprise controller based networks do and it's the gold design standard Asus should allow us to chose channels for every AP and also allow for automatic channel assignment. The challenge is automatic channel assignment can lead to waves of APs changing channels. The effort to avoid this known problem is probably more than they want to take on.

 

[sfx2000]

Reducing power increases the chances that the APs will not hear each other and thus can not do collision avoidance.

Reduce power enough in a mesh, and you start running into Hidden Node problems - which is a classic challenge in WiFi...

Just saying..

 

[drinkingbird]

Reducing power increases the chances that the APs will not hear each other and thus can not do collision avoidance. Collisions will also reduce throughput. I agree, Each AP is best on it's own channel set. It's what all enterprise controller based networks do and it's the gold design standard Asus should allow us to chose channels for every AP and also allow for automatic channel assignment. The challenge is automatic channel assignment can lead to waves of APs changing channels. The effort to avoid this known problem is probably more than they want to take on.

I said minimal overlap, not no overlap. Besides, if the APs can't hear each other there is really no need for them to avoid each other. In reality, in the home environment, it is unlikely you could turn these Asus routers down low enough in the GUI that they won't see each other. Your clients will lose "sight" of them long before they'll lose each other. Just as many problems can be caused by two nodes too close to each other with too much power as ones that are too far away.