Method and apparatus for RRC state transition

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

transitioning to a first sub-state of a radio resource control (RRC) inactive (RRC_INACTIVE) state in response to determining that the UE is in the RRC_INACTIVE state and fails to find any suitable cell during a cell reselection evaluation process;

attempting to find a suitable cell in response to determining that the UE is in the first sub-state of the RRC_INACTIVE state;

transitioning to an RRC_IDLE state in response to determining that the UE fails to find the suitable cell and camps on an acceptable cell; and

discarding RRC_INACTIVE related information in response to the transitioning to the RRC_IDLE state, wherein

the RRC_INACTIVE related information comprises a short inactive radio network temporary identifier (I-RNTI) and UE Inactive context.

2. The method of claim 1 , further comprising:

transitioning to a second sub-state of the RRC_INACTIVE state in response to determining that the UE finds the suitable cell; and

triggering a radio access network (RAN) notification area (RNA) update procedure, wherein

the suitable cell is configured by an RNA configuration.

3. The method of claim 1 , further comprising:

receiving a paging message from a second suitable cell, the paging message comprising a paging record, and the paging record comprising a UE identity; and

initiating an RRC connection resumption procedure in response to determining that the UE identity in the paging record matches an I-RNTI stored in the UE.

4. The method of claim 1 , further comprising:

receiving public land mobile network (PLMN) information from the acceptable cell, the PLMN information comprising a PLMN identity that is configured in a radio access network notification area (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.

5. The method of claim 1 , further comprising:

receiving, from a cell, a radio access network notification area (RNA) configuration in response to determining that the UE is in the RRC_INACTIVE state.

6. The method of claim 5 ,

wherein the cell and the acceptable cell are associated with a same core network.

7. The method of claim 5 , further comprising:

receiving, via one of system information from the acceptable cell or dedicated signaling of the cell, a priority order used in the cell reselection evaluation process; and

ignoring the priority order in response to determining that a timer expires.

8. The method of claim 5 , further comprising:

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

restarting the periodic RNA update timer in response to determining that the UE is in the first sub-state of the RRC_INACTIVE state and the periodic RNA update timer expires.

9. The method of claim 5 , further comprising:

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

staying in the first sub-state of the RRC_INACTIVE state in response to determining that the UE is in the first sub-state and the periodic RNA update timer expires.

10. The method of claim 1 , wherein:

the acceptable cell fulfills a minimum set of requirements to initiate an emergency call and to receive one or more Earthquake & Tsunami Warning System (ETWS) and Commercial Mobile Alert System (CMAS) notifications;

the suitable cell provides normal services; and

the acceptable cell provides limited services.

11. A user equipment (UE), comprising:

one or more processors; and

at least one memory coupled to the one or more processors, the at least one memory storing one or more computer-executable instructions that, when executed by the one or more processors, cause the UE to:

transition to a first sub-state of a radio resource control (RRC) inactive (RRC_INACTIVE) state in response to determining that the UE is in the RRC_INACTIVE state and fails to find any suitable cell during a cell reselection evaluation process;

attempt to find a suitable cell in response to determining that the UE is in the first sub-state of the RRC_INACTIVE state;

transition to an RRC_IDLE state in response to determining that the UE fails to find the suitable cell and camps on an acceptable cell; and

discard RRC_INACTIVE related information in response to the transitioning to the RRC_IDLE state, wherein

the RRC_INACTIVE related information comprises a short inactive radio network temporary identifier (I-RNTI) and UE Inactive context.

12. The UE of claim 11 , wherein the one or more computer-executable instructions, when executed by the one or more processors, further cause the UE to:

transition to a second sub-state of the RRC_INACTIVE state in response to determining that the UE finds the suitable cell; and

trigger a radio access network (RAN) notification area (RNA) update procedure, wherein

the suitable cell is configured by an RNA configuration.

13. The UE of claim 11 , wherein the one or more computer-executable instructions, when executed by the one or more processors, further cause the UE to:

receive a paging message from a second suitable cell, the paging message comprising a paging record, and the paging record comprising a UE identity; and

initiate an RRC connection resumption procedure in response to determining that the UE identity in the paging record matches an I-RNTI stored in the UE.

14. The UE of claim 11 , wherein the one or more computer-executable instructions, when executed by the one or more processors, further cause the UE to:

receive public land mobile network (PLMN) information from the acceptable cell, the PLMN information comprising a PLMN identity that is configured in a radio access network notification area (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.

15. The UE of claim 11 , wherein the one or more computer-executable instructions, when executed by the one or more processors, further cause the UE to:

receive, from a cell, a radio access network notification area (RNA) configuration in response to determining that the UE is in the RRC_INACTIVE state.

16. The UE of claim 15 ,

wherein the cell and the acceptable cell are associated with a same core network.

17. The UE of claim 15 , wherein the one or more computer-executable instructions, when executed by the one or more processors, further cause the UE to:

receive, via one of system information from the acceptable cell or dedicated signaling of the cell, a priority order used in the cell reselection evaluation process; and

ignore the priority order in response to determining that a timer expires.

18. The UE of claim 15 , wherein the one or more computer-executable instructions, when executed by the one or more processors, further cause the UE to:

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

restart the periodic RNA update timer in response to determining that the UE is in the first sub-state of the RRC_INACTIVE state and the periodic RNA update timer expires.

19. The UE of claim 15 , wherein the one or more computer-executable instructions, when executed by the one or more processors, further cause the UE to:

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

stay in the first sub-state of the RRC_INACTIVE state in response to determining that the UE is in the first sub-state and the periodic RNA update timer expires.

20. The UE of claim 11 , wherein:

the acceptable cell fulfills a minimum set of requirements to initiate an emergency call and to receive one or more Earthquake & Tsunami Warning System (ETWS) and Commercial Mobile Alert System (CMAS) notifications;

the suitable cell provides normal services; and

the acceptable cell provides limited services.