Csi-rs beams (beamformed) versus csi-rs reference signals (from one single antenna port)

Hi Experts,
I am confused about one slide: go to slide4math.com chose beam management then chose csi-rs report 1. Then play with green arrows left and right. You will get picture like this:

My doubt is why UE1 measures rsrp of csi-rs user 2 ( blue color) and not rsrp of csi-rs user 1 ( magenta color)?
I am not clear if those are csi-rs beams (beamformed) or csi-rs reference signals (from one single antenna port).
I tend to believe are csi-rs beams as they point in different directions.

Another question: we have seen that csi-rs beams are enabled only when reportquantity=cri-RSRP for one resource nzp-csi-rs. How does Nokia deliver data when this is not active? They have to do it via Grid of beams with PMI, right?

I think these CSI_RS are in same time but different in freq-bw, UE will measure all posible CSI-RS and report RSRP.

So there are 3 options to cover the whole sector with pdsch beams:
1st one is weights based on srs.
2nd one is GoB based on csi-rs beams.
3rd one is GoB based on PMI.

1st & 2nd switching: based on UL SINR threshold?

1st & 3rd switching: based on Ul SINR threshold.
But this is only Huawei.
When srs UL SINR is lower than -10 dB it switches to PMI based weights, till then it uses srs based weights.

This parameter firstly Huawei set default -20 dB?

Yes, they even recommend -20 dB.
Not sure how GnodeB can decode something at -20 dB.
Param is called srspresinrjudgethld.
But on some projects it is -15 dB in others is -10 dB.
Hat I am trying to understand is how srs ports work. For example if csi-rs ports = 8 and UE has 4 antenna then the air interface matrix H will be 8 x 4.
But UE is 2T 4R.
How gNodeB can constitute a H matrix of 8 x 4 from srs since UE can transmit only on 2 antenna srs signals not on 4 antenna srs signals.
So gNodes B has 8 csi-rs ports to measure srs signals but UE does no have 4 srs transmitting antenna only 2 of them.
So how does gnodeB makes the matrix of 8 x 4 from 2 srs signals?
This problem does not happen in DL PMI because gnodeB has 8 antenna ports and UE has 4 rx antenna so it is easy to constitute the 8 x 4 air interface matrix from csi-rs signals.
And then UE from the air interface matrix H = 8 x 4 can calculate the PMI matrix.

What is this feature in Huawei?
Please give more details.
How are they dynamically changing PMI?
Very interesting…
Is it for NR or for LTE?

They change weight from srs based to pmi weight.
Based on ul sinr of srs.

1 Like

Crazy solution!
Hats off to huawei R&D thinking very innovative :+1:…never seen such solutions!
Even none of books mentioned it!

In this case, I think We’d better check UE capability on its layer number. Its maximum layers should be 2. Generally in this case UE has 4 rx antennas but only 2 RF trx front end chains and the smart antennas technology is used to select best two Rx antennas.

I remember they said it is based on srs if UE supports Tx antenna selection - meaning that each time UE transmit srs signal over 1 tx antenna port and turn next.

Yes but stil only 2 srs ports not 4.
So how does mimo 4 layers works with 2 srs tx antenna?

Here it says that srs ports can be 1,2 or 4:

But no UE has 4 TX antenna, or maybe I am not aware about this !?
So if no UE has 4 TX antenna how can UE transmit on 4 distinct srs ports?

Even on sharetechnote it says UE with 4 tx antenna for srs:

So again, are there UEs on the market with 4 TX antenna?

Yes, I am working now on 5G testing with mobile getting Rank4 from the field.

Can you see in UE capability what’s the value of this IE: supportedSRS-TxPortSwitch?

It is normal to get rank4 on the field.
Even for srs.
But it depends on UE capabilities.

If you get rank4 then there should be 4 antennas.

Agree for tx, how about for TX? Do you stil have 4 ant for tx?
On UE side I mean.
Do you see on UE side 4 ant for tx?

Ah okay, I got your point.
I am not focusing on UL at all.

On one UE log that I have I see supportedSRS-TxPortSwitch = 7 corresponding to 4T4R.
Meaning that now we have UE with 4T4R.
Meaning 4 srs ports are possible yet not for all UEs.

I thought there are no UEs on the market with 4T4R but I was wrong - there are.

Your UE support 2Tx 4Rx that’s why you are getting Rank 4.
But even if UE have 2 TX used for 1Tx for 4G 1Tx for 5G and how about 4TX, 2 antenna each for 4G and 5G.

Please correct if I am not right.