UE not attaching with MCS table 256QAM (only 64QAM)

Hello 5G/LTE Experts.
In SA (standalone) I see my UE isn’t attach to the cell if I configure in the cell 256qam table.
If I configure to the cell 64qam then UE attached.
Any idea what is the issue? And why the UE is not attaching with MCS table 256QAM?
My RSRP is around -70 dbm

Are you getting RRC reconfiguration fail while configuring default bearer?

Do you mean it might be because the Core isn’t static (is crashing frequently) so couldn’t attach with 256QAM?

No. Maybe UE is not behaving correctly for 256 QAM.
Try with different device also.

Where do you see failure?
In RRC Attach?

Yes. UE not attached to the cell if 256QAM configured in the cell.

Whether HARQ procedure is working properly?
If UE is not able to decode 256 QAM, it will be assigned 64 QAM in next transmission.

Yes but where do you see the failure? Not attached could mean anything.

Not attached mean like the procedure attach is failed (from msg1 to msg5).
Maybe msg3 failed or one messages from msg to msg5.

Do you mean even with 256QAM it shall be attached?
So why it is not attached when 256QAM configured In the cell but when 64QAM configured then attached?
I mean by attach I see network signals.

I mean even if UE may not have capability to decode 256QAM, it should connect as it has capability to decode 64QAM.

Since all these coding may already be configured in the gNB.

My RSRP is -55.
Mean UE see RSRP as -55.
Maybe it is too high?
That’s why UE couldn’t attach with 256QAM configured on the cell?

There is no 256QAM or UE Capability check from Msg1 to Msg5.
RRC connect phase uses QPSK or 64QAM (intentionally lower MCS for successful decoding during open loop phases).
If the UE isn’t attaching then check the failure cause first.

Got you! :wink:
I can’t lower to QPSK but to 64QAM yes.
I mean the lowest configuration in the cell is 64QAM and not QPSK.