Does MU-MIMO APs will require new client MU-MIMO aware or it work with existing legacy 11a/b/g/n and wave 1 11ac client

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I read various information online, some contradictory on the subject and some other not clearly answering that question. Also read 802.11ac: A Survival Guide while being very informative this question is not realy answer there too.

So I would like to know if current wireless client (like 4x good old Galaxy S2 phone without software update) will be able to receive downstream simultaneously from an APs supporting MU-MIMO.

Base on info from Aruba:
"The one catch with MU-MIMO is that it will require new client hardware since both the AP and client need to be designed with the MU-MIMO capability."

Further info from Aruba forum also say Wave 1 802.11ac client chipset won't support MU-MIMO

While a whitepaper from Meru say legacy client will work with MU-MIMO fine with 11a and 11n client in 5GHz band (meaning it won't for 11b/g/n in 2.4GHz???)

I hope you can help me with this question!!!
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Jacques Gagnon

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Posted 4 years ago

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Nick Lowe, Official Rep

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Official Response
 802.11ac beamforming uses explicit channel measurement which will require client support. Without the sounding frames in the expected format (the explicit part), it won't work.
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Roberto Casula, Champ

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Official Response
Hi Jacques,

MU-MIMO is dependent on a training/feedback process between the AP and prospective clients (just like explicit beamforming - the mechanism is very similar). The AP needs CSI feedback from the client to determine how to construct the transmission steering matrices for MU transmission. Support for this at the physical level has to be available in the client's chipset and therefore legacy clients (including wave 1 802.11ac clients) cannot participate in the process. (At the protocol level, there are new frame formats that a legacy client wouldn't understand anyway).

This will simply mean that legacy clients will not be grouped for MU-MIMO transmission, so the direct answer to your question as to whether you could have a couple of Samsung Galaxy S2s taking advantage of MU-MIMO is "no".

Looking at Meru's document, it's as if the paragraph you cite has been pasted into the wrong section! It seems to me that the statement that the sentence "802.11a and 802.11n 5GHz clients will be supported with no upgrade required" should have gone at the top of the section on 802.11ac, not in the specific paragraph about MU-MIMO! I think it's a cut and paste error.

By the way, it's still far from clear exactly how much benefit MU-MIMO will give in real-world deployments. There are many factors that impact how much benefit you get, including client density and mix, their relative locations, type of traffic, channel width...

It depends on how much airtime can be "saved" compared with the extra air-time overhead required for MU-MIMO to operate (the channel state information training and feedback process requires airtime to operate...and this is airtime that can't be used for sending "real" data) and the "loss" caused by the inevitable interference between MU-MIMO clients. Even with near-real-time channel state information, there will be some interference between clients - it's just the way the (complicated) maths works there is a trade-off in that each client might be able to realise slightly lower speeds individually packet-by-packet, but the sharing of the medium gives them a higher aggregate. Many many factors!

Hope this helps!