Limiting factors for MIMO

Hi 5G Experts,
What is the maximum mMIMO configuration observed for 5G deployments till now?
What is the limiting factor here provided network have robust options like 64T64R and 128, 256 mMIMO configurations?
Is it band limitation or UE limitation?

UE Limitation.
Till now Maximum is 4x4.
3GPP supports maximum 8x8 in DL and 4x4 in UL.
But as of today phones supports 4x4 MIMO in DL.
Even in Drive Test percentage of DL MIMO 4x4 is less than 5%.
However in indoor (when antennas are separated at large distance) percentage of DL MIMO 4x4 can be very high like 90%.

So is there any MIMO config limitations specific for sub-1Ghz, Sub-6Ghz and mmWave bands?

I think there is for mmWave, it is maximum 2x2 DL MIMO.

Yes. My doubt is exactly to this point.
I have a UE capable of 4 Layers support for mmWave as per below UE cap msg (correct me if Im wrong).

So what is the limiting factor to 2x2 even though 4 Layer support is there for UE?

                                                    en-DC-r15 supported,
                                                        bandNR-r15 260
                                                        bandNR-r15 261
                                                        supportedMIMO-CapabilityDL-MRDC-r15 twoLayers
                                                        fourLayerTM3-TM4-r15 supported,
                                                        supportedMIMO-CapabilityDL-MRDC-r15 fourLayers

I think MIMO layers capabilities are per operating band.
In one band can be 4 layers in other band only 2 layers.

Yes that means it can support 4x4 MIMO right?
And both n260 and n261 are mmWave with 100 Mhz BW.

mmWave can have max 400 MHz bandwidth.

Yes, but MIMO don’t have any dependency on BW right?
Be it 100 or 400 Mhz?

This is what I know that in mmwave max mimo is 2x2 in DL.
Don’t know exactly where the limitation comes from.

Ok thanks for your inputs.
Let us try to get the limitation somehow and let me check the MIMO configs for mmwave DTs.

For MIMO configs you won’t find RR layer 3.
Only in DCI layer2 is the MIMO configuration for that transmission meaning that it could change slot by slot.

In LTE we had MxN directly from Qualcomm chipset.
Need o find something for NR.


Try PDSCH stats
There you should get MIMO config for each TB.
Weather 2 layers, 3 layers or 4 layers.
Even it is expected to change every slot it is not changed so often.

NR5G MAC PDSCH Status > Got Num Layers : Max 2 only I saw but 1 was the most used
Now the Tx antenna info, Is MIB the best one to get or some other message?
To conclude to derive MxN MIMO.

Nope there is no IE to get the number of tx antenna.
Because it is beamforming so it can be any number.
But layer = min (tx, rx)

So is it like only STBC in beamforming and no cases of Transmit diversity?
Like 4x2 MIMO used to be trasmit diversity with rank1 ,TM2 in LTE?

There is transmit diversity cases of course when there is the case of it according to PMI reporting.

Ok, let me not divert into that now.
So for me to get 5G MIMO config from UE logs, what I have now is Num layers.
Now I need to get the Tx part somehow to define MxN config.
What can be the way forward?

You can only know the number of layers.
Don’t know from where you can get the M and N.