Idle UE in high mobility and beam update

Specs & Protocol Testing
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1

Hi folks,
As you know, gNB selects the best Tx beam based on the RACH resources used by UE which correspond to a particular SSB time index.
Suppose there is a high mobility UE in idle condition.
For such UE, for every beam switch in idle mode, UE needs to do a RACH to indicate the updated best beam?
Please let me know if my understanding is correct.

2

Idle mode only for SA mode.
It’s by beam switching using tci I think.

3

I think, UE sticks to SSB beams for idle mode.
There is no reason to continue to scan to narrower CSI-RS beams.

4

Will it not do idle mode reselection in mobility?
If cell change within same cell it should beam switching for idle mode.

5

If cell change within same cell it should beam switching for idle mode → I understand that UE has to beam switch in idle mode. So, everytime it does a beam switch, gNB to be notified of it through RACH? That’s my question.
Or when paging is done, it is done across all SSBs?

6

In Idle mode no need to update beam change.
Paging always happen on cell/gNB basis not at beam level.

7

Ok.
So, you mean, during paging occasion, gNB will sweep the entire cell with paging info?

8

Samsung have concept of common beam which always spans entire cell area.
Broadcast messages generally transmitted by common beam.
But your question is interesting…let us see for others opinion.

9

Good to know… thanks for the info :+1: