When you have Voice over LTE and move from a 4G LTE cell to a 5G-NR cell, the UE can be handed over to the NR cell for Voice Over 5G service.
Scenario:
- If the 5G SA supports VoNR, the 4G eNodeB sends (A1, A2) measurement configuration to the UE.
- Once the UE reports A2 events, the 4G eNodeB sends (B1 or B2) measurement configuration to the UE.
- If the 4G eNodeB receives measurement reports on event B1 or B2, it determines the target 5G cell based on signal quality and sends a Handover Command to the UE to perform the handover to the 5G cell.
Note: Through coverage-based inter-RAT mobility from E-UTRAN to NG-RAN, the coverage in areas with weak E-UTRAN coverage or coverage holes can be supplemented by inter-RAT neighboring cells, decreasing the service drop rate.
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