UE to send PUCCH info on U slot for TDD pattern DDDSU

Hi All.

If I want my UE to send PUCCH info on U slot for TDD pattern DDDSU (S is to be used for only DL) then what shall I change on DU config side?
Do I need to change prach index?

Why would Prach index be affected?

When I do DDDSU and S slot configured for DL symbols only then I see PRACH fails but in the minute that I configure 2 Uplink symbols on S slot then UE attached.

PRACH shouldn’t be affected, but maybe PUCCH yes.

Check PRACH config index.
Basically PRACH occasion should not fall in special slot.

Yes it’s not related to PRACH index.

Weird why when configuring in S slot two UL symbols then UE attach (because it send PUCCH there) but if I don’t configure UL symbols in S slot then UE fails on RACH.

What does UE send on PUCCH?

Ack for msg4.

Yes exactly and like my UE faills on message 4.

But like my TDD pattern is having UL slot so on UL also PUCCH sent.

My confusion is why when S slot isn’t configured for any UL symbols then RACH fails.

Pucch config common in SIB1.
That’s where I remember your config would lie.
That basically has an index, which point to a table in specs to tell you how PUCCH would be configured.

Yes this is here shown.

I see in SIB1.

Not this one.

There’s an IE called PUCCH Config Common, if I’m not mistaken.

Yes I found it , it has index 0.

Read this :point_down:, it should help!


That’s right pucch is on symbol 12 & 13.

But again issue here is on S slot if not configuring any UL symbols then UE fails on RACH since I think cant send PUCCH there because no UL symbols.

But when I configure in S slot two UL symbols then RACH success.

My tdd pattern is DDDSU.

Which is expected, right?
If the slot where PUCCH is supposed to be does not have any UL symbols… It’s an issue.

I think it makes sense if you don’t config S with UL there is no chance to send ack.

But I have UL slot so PUCCH will be also there.

DDDSU so if I don’t configure in S slot UL symbol then UL slot is for PUCCH.

Can you check if the UL is sending ack?

This would depend on what your k1 is…pdsch to.ACK slot difference.

Which slot is msg4 on and which slot is ACK for you?

How can UE obtain all these configuration such as k1 if it is trying to RACH initial access?
If UE is still in RACH mode then it isn’t RRC connected to receive configurations, right?