MIMO Config Interpretation

RAN
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1

Hello Experts,
I have few fundamental queries on interpretation of MIMO Config.

For DL SU-MIMO, from UE logs, in LTE can we get number of Tx antenna ports config at eNB (M) and Rx antenna ports in UE (N) to conclude as MxN MIMO used by UE?

OR

Do we take it based on number of Tx antenna eNB (M) x No of layers from RI (N) as MxN?
How should I interpret MxN, for e.g. 8x2?

Note : Everything based on UE logs and no knowledge on eNB network config.
I’ll post folow up question on 5G once i get clarity on LTE above.

image

2

DCI.

https://www.sharetechnote.com/html/DCI.html#Format_2_C_RNTI

On RRC you will have antenna and TM config on the eNB as they are semi-static.

On DCI what is being effectively scheduled.

3

I couldn’t grasp everything here to get the answer for my concern. :frowning:
Can you please brief to help out with my query?

Which RRC message?

4

First RRC Connection Reconfiguration or RRC Connection Setup you can look.

5

At L1 level I tried to search, it’s showing only DCI format used which can be mapped with transmission mode, but I think it will not show no of layers used.
Example: tm3 can use 2 or 4 layer, but from DCI format we can’t judge number of layers.

For number of layers we need to check RRC message only.

6

Great.
Now, backing to my question:
What is the MIMO config interpretation

Tx side ant port.
Rx side ant port or number of layers?

7

From Tx side we can check in RRC message.

For Rx side, it depends on UE category.

But if you need to check tm mode switching, i.e. number of layers changed, then need to look at L1 message, where you can check scheduled CW, RI, CQI, etc.

With ri3 I am seeing in DL cw0 and cw1 only.
Is it like on 3rd layer, it’s copy of cw0?

Anyone having idea?

8

Nope, 3 layers means all 3 are independent layers carrying different data.

9

So it is like cw0,1, 2… Correct?

10

There can be max 2 codewords.
Crresponding to max 2 TBs.
Same in 4G and 4G but mapping to layers is different in 4G and 5G.

11

So for ri3 on 3 layer is it different cw or same?
I am seeing only 2 cw with ri3.
It’s known in LTE with MIMO we have 2 cw but what about ri3 case.

12

MIMO refers to number of TX antenna and number of RX antenna.
So you can have MIMO 8x2 with 3 layers for example.

Here is explained well:

https://www.sharetechnote.com/html/PhyProcessing_LTE.html

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13

I use to refer above picture it’s very good but if we check logs then it’s different.
Just check logs with ri3 or ri4?
What’s your observation for cw?

14

Here is a link explaining how layers are mapped to codewords for LTE ( check first table):

LTE Advanced - Layer Mapping

https://www.sharetechnote.com/html/LTE_Advanced_LayerMapping.html

So there can be max 8 layers and still have only 2 codewords.
Or 3 layers with 1 codeword or 2 codewords.
Just check that table.

15

Thanks it’s very good table. :+1::+1:
So with ri3 is it correct to have 2 cw?

16

There are 2 options of mapping: one with a single codeword and one with 2 codewords.

Check the table.

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So the order of data processing is this one: TB to codewords, codewords to layers, layers to antenna ports, antenna ports to phy antenna ports.

17

Yes agree! :+1:

@Jaeku_Ryu really works hard! Hats off! :slight_smile:

18

This is overall summary for codebook bits I used to refer.

image

According to antenna ports bits changed.

19

Here 8 is Tx antennas (ports) of eNB.
But is this 8 ports used to communicate to 2 ports at UE side?
For TM2 for Tx diversity?
Or TM9 in case of beamforming?
Since 3 layers with 8 Tx streams can still be for Tx diversity + Spatial muxing?

This is good but what I need to derive is the MxN for 5G logs.
I was trying to understand whether I could follow the LTE way but there is no clue of Tx antenna in 5G.
What I have is the RI and as you know there is no TM modes in 5G .
So i need to get M somehow

21

Usually we see
CW0 + CW1_1/2 CW1_1/2 for RI3 and RI4 CW0_1/2 + CW0_1/2 + CW1_1/2 CW1_1/2.