MU on 50/50 but only SU on 75/25

Has anyone noticed this? This panel has 72 subscribers, mix of f200 and f300

On the left the AP is in 50/50 mode, right 75/25 mode

It does not appear to even try to use MU when in 75/25

(side note, 50/50 frame usage in pic is 85-95%, 75/25 is 70%)

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All my 3000's perform MU at 75/25. Only running 20Mhz channels so can't speak for other bbandwidths. They also only have 300's for SM's. No 1000's, 180's, 190's, or 200's. 

This is an interesting situation. As you probably know, MU-MIMO will only trigger with optimally spaced AC clients... 802.11n clients cannot particpate in MU-MIMO. Furthermore, MU-MIMO will only trigger when optimally placed AC clients reach bandwidth limits of the frame ratio and channel width/conditions. My guess is that the AC clients that you have are reaching the optimal bandwidth limit using a 50/50 split, and thus seeing some MU-MIMO gains... but given a 75/25 split, they have just enough downlink BW, and thus are not triggering MU-MIMO. What happens when you run some link test between groupable AC clients on the AP? Does MU-MIMO trigger?

That is interesting.  As Eric says, there are a number of factors for MU-MIMO being triggered, and one of those factors is if the AP figures it needs to use MU-MIMO or not.  So for example, you're not normally going to see MU-MIMO being triggered on a sector which is capable of 400 Mbit only has 2 users getting 10 Mbit each. The AP can deliver that without triggering MU-MIMO, and that's what it'll do.  BUT, if there are 20 users trying to pull 30 Mbit each, the AP starts to get full and approaches capacity, then that's when the AP will switch into 'high gear' and deliver some of the needed capacity via MU-MIMO.  In your particular situation, I'd guess you're not seeing MU-MIMO on the download when you're in 75%/25% because the AP can deliver the requested download without triggering MU-MIMO.

So - this is interesting.  In 50/50 mode, you are getting twice the upload potential because it's 50% upload instead of 25% upload, AND if MU-MIMO is triggering on your download, you're probably not losing any real-world download capacity vs the 75%/25% setting.  So (in your particular situation) the 50%/50% ratio is probably going to give as much download capacity (with YOUR current situation, and with MU-MIMO triggering) and is going to give more upload capacity because it's set to 50% upload.  Interesting.

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One more thing to take into account that MU-MIMO kicks in after 300 seconds of operation(connecting all the clients and finishing first round of sounding). So I wonder how it will look like in a longer term.


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ALSO keep in mind that MU-MIMO only works on downlink bandwidth with the e3k (PMP450m has uplink MU-MIMO optimization)... so with e3k there are no uplink gains in any situation. After seeing how much uplink BW is being used in your 50/50 split, and how little is used (or available) in a 75/25 split... my guess is that with 75/25 split your MU-MIMO capable clients now have enough downlink BW, and MU-MIMO is no longer being triggered because of this... but this as at the detriment of your client's uplink BW. It actually might be better for you to stay at 50/50 if you have a lot of clients with high upload bandwidth demands.


I did forget to mention this panel is on 40mhz width, and of the 72 SMs only 13 are 300's

The reason i had tried 50/50 was we had users reporting packet loss, even though 75/25 was only at 70% frame users were seeing loss similar to when the 1000 APs had hit 100%

On 50/50 there was still some loss but it was much cleaner

As far as the 300s to MU, 75/25 is what it was on historically, i had never seen the MU line until after moving it to 50/50


We are really interesting to understand what’s going on.
I would be grateful if you could send Tech Support File from AP when it’s running 50/50 and 75/25 ratio clearing Statistics after switching to new TDD ratio.

Thank you.