DMRS use and modulation

Hello Everyone.
I have two basic general questions.
Is DMRS in LTE used only in Uplink?
Does DMRS can be modulate rather that QPSK?

In LTE DMRS in DL as well with PDSCH channel seen in massive MIMO.
I think for reference signal we can’t use modulation, so no modulation used for DMRS… correct me if it wrong.
Modulation scheme used for Physical Channels only like PDSCH, PUSCH, PUCCH, PDCCH, PBCH, etc.

There is a modulation for since you are generating pilot signal.

That’s correct.

Ok let me check for DMRS if it’s there. :+1:

Also, it uses gold sequence 31 and generate QPSK as in release 15 introduced it.

In my knowledge for pdsch we have 2 types of DMRS ie type A and type B.

Yes, I am using type A.
At starting symbol 2.

Ok, type A for SU-MIMO.

Yes, for MU-MIMO you shall use type B.

And config there is type 1 and type 2.
In LTE, I see that they use downlink reference signals.
But, it didn’t mention that uses DMRS.

In LTE Rel 9 for 2 layers UE specific reference signal have been introduced calked demodulation reference signals (DM-RS).
DM-RS are used by UE to properly demodulate PDSCH.

@ankgitm, @baghdady.youssefrawy: Any specific reason you think Type A should be for SU-MIMO and Type B for MU-MIMO?

Type B is used because the first half symbols could be for another user for data.

Yes. In Type B, scheduling can be done on symbol level.
But MU-MIMO talks about using same resource for 2 UEs, right?
Then what is relation of MU-MIMO and TypeB?

In type A you know why is for SU-MIMO, right?

Not actually, Type A can also be use for Mu-MIMO. Please correct if i am wrong.
Difference between Type A and Type B is, slot based scheduling and Symbol based scheduling.
Type B generaly will be used for low latency services like URLLC.
But I cannot find any relation with SU/MU MIMO.
Thats why i asked…

Mmm good question here :thinking:

Yes, SU and MU is kind miss gapping here.
Even in 3GPP didn’t mentioned.
For documents.
I am now focusing on NR throughput with different parameters and configuration.
So, I am not going into details for MU, I only focusing on SU.

Let’s classify DMRS type for PDSCH.
It’s config 1 and config 2.
Now config 1 and 2 can be single or double symbols.
Single symbols for su-mimo.
Double symbols for mu-mimo.

Please tell any disconnect here…

Again, why single symbol SU and double MU here?

I got one point: config 1 have higher RE density for DMRS than config 2.
In case of MU-MIMO, scope of frequency multiplexing of DMRS of other UE is reduced.
But this doesn’t limit the use of MU-MIMO with config 1.

Config 2 better for mu-mimo with 2 symbols.
Config 1 if we use mu-mimo it lead to pdsch dmrs interference.

Maybe yes. It is just that there is no rule as such.

It can be avoided by proper parameter setting
Parameter “Antenna Ports” in DCI1_!