How 802.11 ac wave 2 MU-MIMO works

[FES]

Hi,

we have a question about how MU-MIMO works. 

In our aps infraestructure (3915 and 3912 models) we only have 20MHz channels to avoid overlaping channels. 

The aps are 2x2:2MU-MIMO. ¿our question is?

With a 20MHz using one antenna the aps can una 2 spatial streams to send trafic to 2 MU-MIMO clients? Or this only works when we have 40MHz Channel with 2 antennas working?

Sorry for the english 

[ckelly]

Ronald,

Both AP models are 11ac wave-2.  Can’t say w/o locating the spec sheet for the 3912, but the 3915 is the same hardware as the AP7632 which does support MU-MIMO - so don’t see why it wouldn’t.  If it doesn’t, it’s because of a software limitation, not hardware.

Okay….so found the spec sheet on the 3915. MU-MIMO is confirmed to be supported.

The AP3915 is built using the latest in technology, including 802.11ac Wave 2, dynamic radio management, spectrum analysis with interference classification, beamforming, multi-user MIMO, self-forming and self-healing meshing, 

[ckelly]

FES,

We only can uso different spatial streams if the users not are phisical in the same place, in order to use beanforming to use this different 2 spatial streams.

Absolutely correct.  There needs to be enough spatial diversity between two wireless clients in order make MU-MIMO work as intended. “Spatial Diversity” most of the time equates to the wireless clients being located in different physical areas.

If this case is true 802.11ac wave 2 and 802.11ax dont have more possibilities than 802.11ac wave1. Also we need that the users have devices using 802.11ac wave 2 ( more battery usage) or 802.11ax (I dont know devices in the market at now)…

Well, .11ac wave-1 did not have MU-MIMO *at all* so both wave-2 and 11ax have that difference. 🙂

And yes, the wireless clients would need to support at least 11ac wave-2 in order for MU-MIMO to function.

This thoughts are in order to have a ROI of the wifi infraestructure 802.11ac wave2.. I think is very difficult to justify in our scenario. 

In terms of ROI, are you looking to compare to an existing 802.11n infrastructure?

(You currently have 802.11n APs?)

[Ronald_Dvorak]

FYI, the APs that you’ve mentioned doesn’t support MU-MIMO.

-Ron

[ckelly]

With 11ac Wave 2 APs, you are limited to transmitting to a maximum of 4 clients at a time no matter what (but the AP can use up to eight spatial streams for those 4 clients, *if* you actually had an AP that supported 8 spatial streams) There’s also another limitation that you can only use a maximum of four spatial streams for each client. Some examples are below...if your AP supported 4 spatial streams.

• The AP can transmit to 2 different clients with 1 spatial stream each (this would consume 2 spatial streams on the AP)
• You could transmit to 4 different clients using 1 spatial stream for each client (this would consume 4 spatial streams on the AP)
• You could transmit to 2 different clients using 2 spatial streams for each client this also would consume 4 spatial streams on the AP)

 You get the idea.  But with your AP only supporting 2 spatial streams, your only possible combination is much more limited….to just the first one below.You can transmit to 2 clients with 1 spatial stream each (uses 2 spatial streams on the AP)You can transmit to 1 client with 2 spatial streams (which is technically no longer even MU-MIMO)