Conditional handover procedures
A method for a conditional handover (CHO) is described in some of the present embodiments. The method may receive from a source base station (e.g., a gNB or an eNB) one or more CHO commands that each is associated with one or more triggering conditions for a CHO to a target cell associated with a target base station (e.g., a target gNB or a target eNB). The method may continuously evaluate the triggering condition(s) associated with each received (and valid) CHO command. When the method determines that at least one of the triggering conditions has been fulfilled, the method may execute the CHO command that is associated with the triggering condition in order to connect to one or more candidate target cells associated with the CHO command.
1. A method of a conditional handover (CHO) procedure for a user equipment (UE), the method comprising:
receiving, by the UE, a CHO command from a source base station, the CHO command having a CHO command identifier (ID), a first target cell configuration and at least one triggering condition;
in a case that the CHO command is received and the at least one triggering condition is fulfilled, performing a handover procedure according to the CHO command to connect to a first target cell indicated in the CHO command;
receiving, by the UE, after receiving the CHO command, a conventional handover command from the source base station, the conventional handover command having no triggering condition and indicating a second target cell; and
in a case that the CHO command is received and the at least one triggering condition is not fulfilled,
performing a handover procedure according to the conventional handover command to connect to the second target cell indicated in the conventional handover command, and
releasing the CHO command when the handover procedure according to the conventional handover command is successfully performed, wherein releasing the CHO command comprises releasing at least one of the first target cell configuration and one or more radio resources associated with the CHO command.
2. The method of claim 1 , further comprising:
performing a radio resource control (RRC) connection re-establishment procedure upon an expiry of a CHO execution timer.
3. The method of claim 1 , further comprising:
sending a CHO failure report to the source base station upon an expiry of a CHO execution timer.
4. The method of claim 1 , wherein the CHO command comprises a CHO command priority.
5. The method of claim 1 , wherein releasing the CHO command further comprises releasing the CHO ID associated with the CHO command.
6. The method of claim 1 , wherein releasing the CHO command further comprises releasing the at least one triggering condition associated with the CHO command.
7. A user equipment (UE) comprising:
one or more non-transitory computer-readable media having computer-executable instructions embodied thereon;
at least one processor coupled to the one or more non-transitory computer-readable media, and configured to execute the computer-executable instructions to:
receive a conditional handover (CHO) command from a source base station, the CHO command having a CHO command identifier (ID), a first target cell configuration and at least one triggering condition;
in a case that the CHO command is received and the at least one triggering condition is fulfilled, perform a handover procedure according to the CHO command to connect to a first target cell indicated in the CHO command;
receive, after receiving the CHO command, a conventional handover command from the source base station, the conventional handover command having no triggering condition and indicating a second target cell;
in a case that the CHO command is received and the at least one triggering condition is not fulfilled,
perform a handover procedure according to the conventional handover command to connect to the second target cell indicated in the conventional handover command, and
release the CHO command when the handover procedure according to the conventional handover command is successfully performed, wherein releasing the CHO command comprises releasing at least one of the first target cell configuration and one or more radio resources associated with the CHO command.
8. The UE of claim 7 , wherein the at least one processor is further configured to execute the computer-executable instructions to:
perform a radio resource control (RRC) connection re-establishment procedure upon an expiry of a CHO execution timer.
9. The UE of claim 7 , wherein the at least one processor is further configured to execute the computer-executable instructions to:
send a CHO failure report to the source base station upon an expiry of a CHO execution timer.
10. The UE of claim 7 , wherein the CHO command comprises a CHO command priority.
11. The UE of claim 7 , wherein releasing the CHO command further comprises releasing the CHO ID associated with the CHO command.
12. The UE of claim 7 , wherein releasing the CHO command further comprises releasing the at least one triggering condition associated with the CHO command.