Does a MU-MIMO router help non (SU) devices?

[Puppa]

I'm curious. Maybe this thread isn't the spot for this question, but I was under the impression that MU-MIMO, Multi-User MIMO, was supposed to accelerate conditions where there are multiple single clients, meaning that 4 standard devices connected will have better results (assuming MU-MIMO is even functional on the router) than 4 standard devices connected to a router that does not have MU-MIMO. So while a single client needs MU-MIMO for it to improve when connected alone, MU-MIMO should improve overall throughput of 4 non-MU-MIMO clients. My OnHub's Access Point performance seems to confirm this, but that may be simply due to the differing chipset altogether. Is this not true?

 

[RMerlin]

A good place to start to help understanding how MU-MIMO works is this article:

http://www.smallnetbuilder.com/wire...s-xstream-the-coming-battle-for-wi-fi-airtime

There's another article, but it reads more like marketing material from its sponsor than provide any technical explanation on the technology.

 

[RMerlin]

You'll need two to see any improvement in total bandwidth utilization from MU-MIMO.

From what I read in that article, it seems that a single MU-MIMO client would already help, no?

 

[thiggins]

A few things:

- MU-MIMO is a technology that is focused on improving total bandwidth use in 5 GHz. It does nothing to improve range.

- A MU-MIMO enabled router does nothing to improve total throughput use for non MU-MIMO (SU) devices alone. MU-MIMO uses a special form of beamforming that only MU devices can understand.

- MU-MIMO works for downlink traffic only (AP to STA)

- MU-MIMO provided improved bandwidth use by letting multiple devices share a single transmit frame. This is why you need at least two MU devices to see any benefit from MU-MIMO. One MU-MIMO client can't share a frame with SU devices.

Although the two QCA/Linksys articles are sponsored posts, the information in them is technically accurate.

The OnHub is AC1900 class and doesn't use MU-MIMO.

 

[thiggins]

From what I read in that article, it seems that a single MU-MIMO client would already help, no?

The diagram doesn't show that. If you had one MU client and two SU clients, the transmit sequence would look just like the upper part of the diagram. Neither SU client could share a frame with the MU client.

 

[sfx2000]

From what I read in that article, it seems that a single MU-MIMO client would already help, no?

There's some minor improvements to be had - current MU-MIMO routers at 4*4:4, so some precoding gain to be had at the SU-MIMO level, and the extra radio does offer additional diversity gain.

The other aspect is the scheduler improvements that are needed for MU-MIMO to be effective, and this helps all associated clients across different application flows.

 

[azazel1024]

If you have zero MU:MIMO clients, the gains are pretty much what sfx2000 mentioned, modest, but something. The big gains are if you have any MU:MIMO clients.

Generally you won't see real benefits until you have at least 2 MU:MIMO clients working at once, then the MU:MIMO clients and the SU:MIMO/SU:SISO clients all gain.

Normally what you have is time share between all clients.

So if you have 1733Mbps router, 2x433Mbps clients and an 866Mbps client, you don't get 1733Mbps of through put. What the router will do is talk to one 433Mbps client at 433Mbps for a period of time, the other 433Mbps client for a period of time and then the 867Mbps client for a period of time.

So what you might actually get is around 600Mbps of real throughput broken out between the 3 clients.

But if you have the two 433Mbps clients as MU:MIMO even with the 867Mbps client as SU:MIMO, what you'll get is the router talking to the two 433Mbps clients at the same time, for 867Mbps of bandwidth, and then talking to the 867Mbps, rinse and repeat. So you'll see roughly 867Mbps of real bandwidth broken up between the clients.

They all benefit.

Of course if all clients are MU:MIMO you'll see the most benefit, but if at least 2 are MU:MIMO and active concurrently, both they and all SU:MIMO clients will benefit to some degree.

 

[remixedcat]

Yes you also need new hardware and there's very little out there.... I'd wait to get some till all the kinks are worked out unless you live buying beta hardware