Method and apparatus for radio link monitoring measurements in a system using bandwidth parts

1. A radio terminal comprising:

a memory; and

at least one processor connected to the memory,

wherein the at least one processor is configured to, when a downlink bandwidth part (BWP) is switched from a first BWP to a second BWP without a change of a cell defining synchronization signal block (SSB), if a reference signal type for Radio Link Monitoring (RLM) is set to an SSB type, continue to use for RLM measurements a first SSB associated with the first BWP after switching of the downlink BWP to the second BWP.

2. The radio terminal according to claim 1 , wherein the at least one processor is configured to determine whether to change a reference signal to be used for the RLM measurements after switching of the downlink BWP, depending on whether the reference signal type for the RLM is the SSB type or a Channel State Information Reference Signal (CSI-RS) type.

3. The radio terminal according to claim 1 , wherein the at least one processor is configured to, when the downlink BWP is switched from the first BWP to the second BWP without a change of the cell defining SSB, if the reference signal type for the RLM is set to a Channel State Information Reference Signal (CSI-RS) type, use for the RLM measurements a second CSI-RS in the second BWP, instead of a first CSI-RS in the first BWP.

4. The radio terminal according to claim 1 , wherein

the at least one processor is configured to, when the downlink BWP is switched from the first BWP to the second BWP without a change of the cell defining SSB, inherit a parameter related to the RLM, and

the parameter includes a count value of a timer to be started to determine RLF upon a specified number of consecutive occurrences of out-of-synchronization.

5. The radio terminal according to claim 1 , wherein the at least one processor is configured to, when the downlink BWP is switched from the first BWP to the second BWP without a change of the cell defining SSB, use for CSI measurements a second CSI-RS in the second BWP, instead of a first CSI-RS in the first BWP.

6. The radio terminal according to claim 1 , wherein the at least one processor is configured to, when it is instructed to switch the downlink BWP from the first BWP to the second BWP with a change of the cell defining SSB, if the reference signal type for the RLM is set to the SSB type, discontinue using the first SSB associated with the first BWP for the RLM measurements.

7. The radio terminal according to claim 1 , wherein the at least one processor is configured to, when it is instructed to switch the downlink BWP from the first BWP to the second BWP with a change of the cell defining SSB, if the reference signal type for the RLM is set to the SSB type, use for the RLM measurements a second SSB associated with the second BWP, instead of the first SSB associated with the first BWP.

8. The radio terminal according to claim 1 , wherein the at least one processor is configured to determine whether to continue to use the first SSB associated with the first BWP for the RLM measurements depending on whether switching of the downlink BWP from the first BWP to the second BWP involves a change of the cell defining SSB.

9. The radio terminal according to claim 6 , wherein

the at least one processor is configured to, when it is instructed to switch the downlink BWP from the first BWP to the second BWP with a change of the cell defining SSB, if the reference signal type for the RLM is set to the SSB type, reset a parameter related to the RLM, and

the parameter includes a count value of a timer to be started to determine RLF upon a specified number of consecutive occurrences of out-of-synchronization.

10. The radio terminal according to claim 1 , wherein the RLM measurements include measuring downlink radio quality of a serving cell when the radio terminal is in a connected mode with a view to detecting out-of-synchronization and Radio Link Failure (RLF).

11. The radio terminal according to claim 5 , wherein the CSI measurements include measuring downlink radio quality of a serving cell when the radio terminal is in a connected mode with a view to transmitting to a radio access network node a report containing a Channel Quality Indicator (CQI) to be used for at least one of scheduling and link adaptation.

12. A method performed by a radio terminal, the method comprising, when a downlink bandwidth part (BWP) is switched from a first BWP to a second BWP without a change of a cell defining synchronization signal block (SSB), if a reference signal type for Radio Link Monitoring (RLM) is set to an SSB type, continuing to use for RLM measurements a first SSB associated with the first BWP after switching of the downlink BWP to the second BWP.

13. The method according to claim 12 , further comprising determining whether to change a reference signal to be used for the RLM measurements after switching of the downlink BWP, depending on whether the reference signal type for the RLM is the SSB type or a Channel State Information Reference Signal (CSI-RS) type.

14. The method according to claim 12 , further comprising, when the downlink BWP is switched from the first BWP to the second BWP without a change of the cell defining SSB, if the reference signal type for the RLM is set to a Channel State Information Reference Signal (CSI-RS) type, using for the RLM measurements a second CSI-RS in the second BWP, instead of a first CSI-RS in the first BWP.

15. The method according to claim 12 , further comprising, when the downlink BWP is switched from the first BWP to the second BWP without a change of the cell defining SSB, inheriting a parameter related to the RLM, wherein

the parameter includes a count value of a timer that is started to determine RLF upon a specified number of consecutive occurrences of out-of-synchronization.

16. The method according to claim 12 , further comprising, when the downlink BWP is switched from the first BWP to the second BWP without a change of the cell defining SSB, using for CSI measurements a second CSI-RS in the second BWP, instead of a first CSI-RS in the first BWP.

17. The method according to claim 12 , further comprising, when it is instructed to switch the downlink BWP from the first BWP to the second BWP with a change of the cell defining SSB, if the reference signal type for the RLM is set to the SSB type, discontinuing using the first SSB associated with the first BWP for the RLM measurements.

18. The method according to claim 12 , further comprising, when it is instructed to switch the downlink BWP from the first BWP to the second BWP with a change of the cell defining SSB, if the reference signal type for the RLM is set to the SSB type, using for the RLM measurements a second SSB associated with the second BWP, instead of the first SSB associated with the first BWP.

19. The method according to claim 12 , further comprising, determining whether to continue to use the first SSB associated with the first BWP for the RLM measurements depending on whether switching of the downlink BWP from the first BWP to the second BWP involves a change of the cell defining SSB.

20. A non-transitory computer readable medium storing a program to cause a computer to perform a method for a radio terminal, wherein the method comprises, when a downlink bandwidth part (BWP) is switched from a first BWP to a second BWP without a change of a cell defining synchronization signal block (SSB), if a reference signal type for Radio Link Monitoring (RLM) is set to an SSB type, continuing to use for RLM measurements a first SSB associated with the first BWP after switching of the downlink BWP to the second BWP.