Wifi 6: Will OFDMA & MU-MIMO operate simultaneously?

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  • Updated 8 months ago
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Once OFDMA is enabled on the new WiFi 6 AP's, will OFDMA and MU-MIMO operate simultaneously? 

For example, let's say you have a factory with 100 clients connected to an R730 AP.  (For simplicity, I'll just look at the 5 GHz running 40MHz wide channels.)  The majority of the clients are lightweight and using under 500Kbps of bandwidth and, say, 10 AP's are using ~4Mbps. 
  1. Is it an either/or situation in that the AP will decide to use either use OFDMA or MU-MIMO?
  2. Or will it transmit a few frames with OFDMA and then a few frames with MU-MIMO?
  3. Or will it transmit 8 MIMO spacial streams while simultaneously splitting each stream into 18 RU's and allocating them to the clients as needed?
I've scoured the internet and can't find any answers on this.  So any insight would be appreciated.

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Paul Ainslie

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Posted 9 months ago

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Paul Ainslie

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I found this here explaining that, "...the combination of MU-MIMO and OFDMA in a single packet, while quite possible in theory, becomes complicated in practice and support is deferred to wave 2."  That should be a big improvement for high density environments!!
(Edited)
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Michael Brado, Official Rep

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Regarding OFDMA, one key point to remember about 802.11ax (or Wi-Fi 6) is it's not labeled as Extremely High Throughput (802.11ac was labeled VHT for Very High Throughput), 802.11ax is labeled as HE for High Efficiency.  The majority of frames in 802.11 are 300 Bytes or less so the theory is all of these frames can be consolidated in smaller RU's and sent at the same time, allowing more time slices for that one client that wants to download a movie.  The purpose of the client device matters just as much as the OFDMA.   If all the clients are downloading movies, then they won't request smaller spectrum chunks, they are going to request the full channel. If all of the devices are simply checking in and no demand is placed, then you won't see any increase in speed, and with only 4 clients, you won't see much improvement in anything since you can do that in 802.11ac.

For more information, there is a podcast in the US called Clear To Send that spent most of 2019 discussing Wi-Fi 6 and broke down a lot of stuff around it and I think they did a really good job.  You can find that here https://www.cleartosend.net/802-11ax-series/
(Edited)
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Paul Ainslie

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Interesting, I didn’t know that the majority of frames in 802.11 are 300 Bytes or less. In that case, the smaller RU’s will certainly improve efficiency!!


What if 95 clients are doing lightweight browsing and 4 clients are doing heavy streaming? Would/could several spatial streams be devoted to the streamers while the other spatial streams handle lightweight clients via OFDMA? Or would/could it switch between MIMO and OFDMA on a frame by frame basis?


I looked thru the cleartosend.net blogs (very well written) but couldn’t find anything about how the two can be used together.
(Edited)
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Pieter Becue

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Any idea when any of these features will be supported by Ruckus firmware? E.g. on R730 APs ?
Are we talking weeks or months ? 
Thanks, Pieter
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Paul Ainslie

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My guess, it will be months!  Do any of the big companies have fully functioning Wifi 6 AP's yet?
"...the folks writing the code for the AP airtime scheduler have a hellaciously difficult job. In the old days, all the scheduler had to do was send out packets using simple methods like round-robin. Now with AX, the scheduler has all the previous methods at hand, plus OFDMA. To complicate the scheduler's task even further, OFDMA also works in the uplink direction. So the scheduler must also decide if it wants to receive data simultaneously from multiple STAs. UL OFDMA requires precise synchronization between AP and STA, which, of course, isn't easy. Of course, all these decisions must be made for each transmit opportunity (TXOP). As I said, this is complex stuff."
Tim Higgins, Friday, 03 January 2020
https://www.smallnetbuilder.com/wireless/wireless-features/33221-what-s-missing-from-your-wi-fi-6-ro...
You could also try posting the question on a separate appropriately named thread - it should get more visibility.
(Edited)
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John D, AlphaDog

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Well the R750 already supports OFDMA in both directions with SmartZone 5.2. It is worrisome because it almost feels like the R750 might have newer components and the R730 might not be capable.
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hayk

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Yeah, I know what you mean... which also might be a reason why the R730 was orphaned from unleashed... these days I just avoid buying draft based APs.
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John D, AlphaDog

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Yeah that's unfortunate. In this case I would argue though that because OFDMA, TWT, and other specific 802.11ax features were advertised and still advertised on R730's datasheet, there's a reasonable expectation that they aren't going to just abandon those features for this AP. It would be great to have Ruckus employees chime in on the status of the R730.

Heck even TxBf and MU-MIMO are 802.11ac features and those still aren't activated on R730.

I'm okay with Unleashed not being supported mainly because it was never advertised on the datasheet. I can't say I bought the R730 having any expectation of using it with Unleashed.

I am hoping the resolution is not a quiet removal of those features from the list.
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hayk

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I'm sure they will eventually support it on the other platforms for the features.. but I believe it's on the back burner for now since their priority seems to be on the current development.