How UE decide SSB beam to select in 5G SA?

Hi Experts,
For SA call flow, sib1 content is very important message.
But I find under RACH config common for SA parameter RSRP SSB threshold not there.
Now query is: how UE decide to select SSB beam for SA if there are 2 SSB beams configured on site?

For NSA I’m able to find it, under RACH config common which make sense as per logic, but for SA why is it missing?

If RSRP threshold is not defined, then UE will select strongest beam.

Is it not allowed parameter for SA?
In my view some bug here…

May be. Parameter can be there if configured.

Yes, I’m checking validity for parameter is it for SA or not, but point is that without it how UE will judge? Is it blind selection of SSB beam?

Why blind selection?
Strongest one will be selected.
Even if threshold is defined, and all the beams are weaker than threshold, then also strongest beam is selected.
NSA or SA this parameter can be there if configured.

But UE need some algorithm for it.
It’s not inbulit in UE to select strongest beam, it can select week one as well my view.

What algorithm UE have when no beam satisfy the criteria?
To select strongest beam right?

3GPP TS 38.321 5.1.2 Random Access Resource selection

1> else (i.e. for the contention-based Random Access preamble selection):
2> if at least one of the SSBs with SS-RSRP above rsrp-ThresholdSSB is available:
3> select an SSB with SS-RSRP above rsrp-ThresholdSSB.
2> else:
3> select any SSB.

Hello ,

Would you mind sharing for NSA under RACH config common what parameter is there to hep UE select SSB beam?

Thanks

It is the rsrp-ThresholdSSB

1 Like