For instance, a 5G Base Station(gNB) as a Master Node(MN) with the FR1 NR cells (N78, 3500 MHz) requests the UE to send the radio network capability (NR-DC capability) to setup NR-DC, i.e. add a gNB as Secondary Node(SN) with FR2 NR cells(N257, 28 GHz).
If the UE is NR-DC capable and NR-DC is operation on the MN, then the MN configures the UE an A4 measurement through the RRC Reconfiguration to determine whether the UE has suitable coverage from an FR2 NR cell/cells to set up NR-DC.
When the UE finds an FR2 NR cell that satisfies the Event A4 measurement criteria, the UE sends an Event A4 measurement report to the MN.
The MN evaluates the reported cell to determine whether it is a valid candidate for setting up NR-DC. If the reported cell is suitable, the MN initiates SN addition procedure.
Here I am trying to depict the Event A4 measurement criteria for triggering the UE to report the measurement as well as the procedure for NR-DC SN addition.
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In addition, I also prepared a video related to this topic and uploaded it on my YouTube channel, here you can find the video link: 5G NR-NR Dual Connectivity (NR-DC/NRDC) #5g #4g #telecom - YouTube