Method and apparatus for RRC state transition

1. A user equipment (UE), comprising:

one or more non-transitory computer-readable media having computer-executable instructions embodied thereon; and

at least one processor coupled to the one or more non-transitory computer-readable media, the at least one processor being configured to execute the computer-executable instructions to cause the UE to:

receive, from a serving cell, a radio access network (RAN) notification area (RNA) configuration when the UE is in a radio resource control (RRC) inactive (RRC_INACTIVE) state;

transition from the RRC_INACTIVE state to an RRC idle (RRC_IDLE) state when the UE finds and camps on an acceptable cell that fulfills a minimum set of requirements to initiate an emergency call and to receive Earthquake & Tsunami Warning System (ETWS) and Commercial Mobile Alert System (CMAS) notifications, wherein the UE obtains limited service within a coverage area of the acceptable cell, and the serving cell and the acceptable cell are associated with a same core network; and

discard the RNA configuration that comprises at least one of a list of tracking area identities (IDs) and a list of RAN area IDs in response to the transitioning from the RRC_INACTIVE state to the RRC_IDLE state.

2. The UE of claim 1 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

transition to a first sub-state of the RRC_INACTIVE state when the UE does not find any suitable cell during a cell reselection evaluation process; and

attempt to find a suitable cell that is configured in the RNA configuration when the UE is in the first sub-state of the RRC_INACTIVE state.

3. The UE of claim 2 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

receive, via one of system information from a camped cell and dedicated signaling of the serving cell, a priority order used in the cell reselection evaluation process.

4. The UE of claim 3 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

ignore the priority order when a timer expires.

5. The UE of claim 2 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

transition to a second sub-state of the RRC_INACTIVE state when the UE finds a suitable cell that is configured in the RNA configuration; and

trigger an RNA update procedure.

6. The UE of claim 2 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

receive, from the serving cell, a periodic RNA update timer; and

stay in the first sub-state of the RRC_INACTIVE state when the UE is in the first sub-state of the RRC_INACTIVE state and the periodic RNA update timer expires.

7. The UE of claim 2 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

receive, from the serving cell, a periodic RNA update timer; and

restart the periodic RNA update timer when the UE is in the first sub-state of the RRC_INACTIVE state and the periodic RNA update timer expires.

8. The UE of claim 2 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

receive, from the serving cell, a periodic RNA update timer;

pause the periodic RNA update timer when the UE transitions to the first sub-state of the RRC_INACTIVE state; and

resume the periodic RNA update timer when the UE leaves the first sub-state of the RRC_INACTIVE state.

9. The UE of claim 1 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

receive a paging message from a suitable cell, wherein the paging message comprises a paging record, and the paging record comprises a UE identity; and

initiate an RRC connection resumption procedure when the UE identity in the paging record matches an inactive radio network temporary identifier (I-RNTI) stored in the UE.

10. The UE of claim 1 , wherein the at least one processor is further configured to execute the computer-executable instructions to cause the UE to:

receive public land mobile network (PLMN) information from a camped cell, wherein the PLMN information comprises a PLMN identity that is configured in the RNA configuration;

report, by an access stratum (AS) layer of the UE, the PLMN identity to a non-access stratum (NAS) layer of the UE; and

perform a PLMN selection procedure.

11. A method performed by a user equipment (UE), the method comprising:

receiving, from a serving cell, a radio access network (RAN) notification area (RNA) configuration when the UE is in a radio resource control (RRC) inactive (RRC_INACTIVE) state;

transitioning from the RRC_INACTIVE state to an RRC idle (RRC_IDLE) state when the UE finds and camps on an acceptable cell that fulfills a minimum set of requirements to initiate an emergency call and to receive Earthquake & Tsunami Warning System (ETWS) and Commercial Mobile Alert System (CMAS) notifications, wherein the UE obtains limited service within a coverage area of the acceptable cell, and the serving cell and the acceptable cell are associated with a same core network; and

discarding the RNA configuration that comprises at least one of a list of tracking area identities (IDs) and a list of RAN area IDs in response to the transitioning from the RRC_INACTIVE state to the RRC_IDLE state.

12. The method of claim 11 , further comprising:

transitioning to a first sub-state of the RRC_INACTIVE state when the UE does not find any suitable cell during a cell reselection evaluation process; and

attempting to find a suitable cell that is configured in the RNA configuration when the UE is in the first sub-state of the RRC_INACTIVE state.

13. The method of claim 12 , further comprising:

receiving, via one of system information from a camped cell and dedicated signaling of the serving cell, a priority order used in the cell reselection evaluation process.

14. The method of claim 13 , further comprising:

ignoring the priority order when a timer expires.

15. The method of claim 12 , further comprising:

transitioning to a second sub-state of the RRC_INACTIVE state when the UE finds a suitable cell that is configured in the RNA configuration; and

triggering an RNA update procedure.

16. The method of claim 12 , further comprising:

receiving, from the serving cell, a periodic RNA update timer; and

staying in the first sub-state of the RRC_INACTIVE state when the UE is in the first sub-state of the RRC_INACTIVE state and the periodic RNA update timer expires.

17. The method of claim 12 , further comprising:

receiving, from the serving cell, a periodic RNA update timer; and

restarting the periodic RNA update timer when the UE is in the first sub-state of the RRC_INACTIVE state and the periodic RNA update timer expires.

18. The method of claim 12 , further comprising:

receiving, from the serving cell, a periodic RNA update timer;

pausing the periodic RNA update timer when the UE transitions to the first sub-state of the RRC_INACTIVE state; and

resuming the periodic RNA update timer when the UE leaves the first sub-state of the RRC_INACTIVE state.

19. The method of claim 11 , further comprising:

receiving a paging message from a suitable cell, wherein the paging message comprises a paging record, and the paging record comprises a UE identity; and

initiating an RRC connection resumption procedure when the UE identity in the paging record matches an inactive radio network temporary identifier (I-RNTI) stored in the UE.

20. The method of claim 11 , further comprising:

receiving public land mobile network (PLMN) information from a camped cell, wherein the PLMN information comprises a PLMN identity that is configured in the RNA configuration;

reporting, by an access stratum (AS) layer of the UE, the PLMN identity to a non-access stratum (NAS) layer of the UE; and

performing a PLMN selection procedure.