Is it possible to get Rank 4 in MU-MIMO?

RAN
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21

MU-MIMO bring no benefit only marginal pre post payload gain can seen most of times throughout degrade.

22

Can you mention where in 38.214 is mentioned this?

Maybe I am wrong but even in R16 is written that for MU-MIMO max 2 layers:

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23

I read it in a recent Qualcomm report.

26

Would be great to see a 3GPP spec for this.

27

There is 2 codebook types in UL:
First support up to 4 layers but PMI matrix has only phase rotation between streams.
Second support up to 2 layers but you can also play with power of each stream, aka Waterfilling Algorithm.