16.14.3.2.2 Conditional Handover

The same principle as described in 9.2.3.4 applies to NTN unless hereunder specified.

NTN supports the following additional trigger conditions upon which UE may execute CHO to a candidate cell, as defined in TS 38.331 [12]:

• The RRM measurement-based event A4;
• A time-based trigger condition;
• A location-based trigger condition.

Time-based or location-based trigger conditions may be configured independently from the RRM measurement-based trigger conditions for CHO in NTN in some scenarios, e.g., when the service discontinuity gap time length is zero or negligible.

It is up to UE implementation how the UE evaluates the time- or location-based trigger condition together with the RRM measurement-based event.

When a time-based trigger condition is used, the source gNB may signal the corresponding parameters to a target gNB in an NG-C based handover, see TS 23.502 [22], or Xn based handover. The source gNB signals the corresponding CHO configuration to the UE in the RRC Reconfiguration message for handover.

When time-based trigger condition is used, the source NG-RAN node should consider the time indicated to the UE to decide when to start the early data forwarding to the target NG-RAN node.

Time-based CHO can be performed via RACH-less.