Handling SCELL reconfiguration in LTE/NR: Sequential DL and UL configurations or Full re-addition?

5G NR
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1

Hi Experts.

In LTE or NR, if an SCELL is initially added with only DL configuration during the first reconfiguration and then UL configuration is applied to the same SCELL in a subsequent reconfiguration, is this approach correct?

Or should the SCELL first be released and then re-added later with both DL and UL configurations?

2

Your initial approach is correct and does not require releasing and re-adding the SCELL with both DL and UL.

According to the standard, it’s typical to add DL first and then apply UL through reconfiguration messages.

3

If a candidate cell is selected for both DL and UL CA, then both configurations should be added together in a single RRC reconfiguration message.

4

So if UL needs to be added later, does it require a RELEASE + ADD procedure?

5

Firstly, if UL needs to be added, it should be configured together with DL in the initial attempt. There is no separate trigger to configure the uplink independently.