Method for performing radio link monitoring and failure procedure of multi beams operation in wireless communication system and a device therefor

1. A method performed by a user equipment (UE) operating in a wireless communication system, the method comprising:

measuring downlink radio link quality for each of multiple beams configured for the UE;

sending a first information for an out-of-sync to an upper layer of the UE based on all beams of the multiple beams meeting an out-of-sync condition; and

sending a second information for an in-sync to the upper layer of the UE based on at least one beam of the multiple beams meeting an in-sync condition,

wherein, based on downlink radio link quality of a beam becoming worse than a first threshold, the UE determines that the beam meets the out-of-sync condition,

wherein, based on downlink radio link quality of the beam becoming better than a second threshold, the UE determines that the beam meets the in-sync condition,

wherein based on the all beams of the multiple beams not meeting the out-of-sync condition and at least one beam of the multiple beams not meeting the in-sync condition, the UE does not send the first information and the second information,

wherein the multiple beams are serving beams which are currently used for beam problem detection of the UE, and

wherein based on the beam problem being detected, the UE uses candidate beams to replace the serving beams.

2. The method according to claim 1 ,

wherein the UE determines that the beam meets the out-of-sync condition within a first time period,

wherein the UE determines that the beam meets the in-sync condition within a second time period, and

wherein the first time period and the second time period are equally applied to the each of the multiple beams.

3. The method according to claim 2 , wherein even in a state in which two or more beams meet in-sync condition, only one second indication is transmitted to the upper layer of the UE within the first time period.

4. The method according to claim 1 , further comprising:

starting a timer based on sending the first information to the upper layer of the UE; and

re-sending the first information to the upper layer of the UE upon the timer expiry, based on the all beams of the multiple beams meeting the out-of-sync condition upon the timer expiry.

5. The method according to claim 2 , wherein the first time period is longer than the second time period.

6. The method according to claim 1 , further comprising:

starting a timer T 310 by a RRC layer, based on receiving N 310 consecutive first information for a cell from lower layers;

stopping the timer T 310 by a RRC layer, based on receiving N 311 consecutive second information for the cell from lower layers while the timer T 310 is running; and

considering radio link failure to be detected by a RRC layer, upon the timer T 310 expiry.

7. A User Equipment (UE) configured to operate in a wireless communication system, the UE comprising:

a Radio Frequency (RF) module; and

at least one processor; and

at least one computer memory operably coupled with the at least one processor and storing instructions that, when executed by the at least one processor, perform operations comprising:

measuring downlink radio link quality for each of multiple beams configured for the UE;

sending, through the RF module, a first information for an out-of-sync to an upper layer of the UE based on all beams of the multiple beams meeting an out-of-sync condition; and

sending, through the RF module, a second information for an in-sync to the upper layer of the UE based on at least one beam of the multiple beams meeting an in-sync condition,

wherein, based on downlink radio link quality of a beam becoming worse than a first threshold, the UE determines that the beam meets the out-of-sync condition,

wherein, based on downlink radio link quality of the beam becoming better than a second threshold, the UE determines that the beam meets the in-sync condition,

wherein based on the all beams of the multiple beams not meeting the out-of-sync condition and at least one beam of the multiple beams not meeting the in-sync condition, the UE does not send the first information and the second information,

wherein the multiple beams are serving beams which are currently used for beam problem detection of the UE, and

wherein based on the beam problem being detected, the UE uses candidate beams to replace the serving beams.

8. The UE according to claim 7 ,

wherein the UE determines that the beam meets the out-of-sync condition within a first time period,

wherein the UE determines that the beam meets the in-sync condition within a second time period, and

wherein the first time period and the second time period are equally applied to the each of the multiple beams.

9. The UE according to claim 8 , wherein even in a state in which two or more beams meet in-sync condition, only one second indication is transmitted to the upper layer of the UE within the first time period.

10. The UE according to claim 8 , wherein the first time period is longer than the second time period.

11. The UE according to claim 7 , wherein the operations further comprise:

starting a timer based on sending the first information to the upper layer of the UE, and

re-sending the first information to the upper layer of the UE upon the timer expiry, based on the all beams of the multiple beams meeting the out-of-sync condition upon the timer expiry.

12. The UE according to claim 7 , wherein the operations further comprise:

starting a timer T 310 by a RRC layer, based on receiving N 310 consecutive first information for a cell from lower layers;

stopping the timer T 310 by a RRC layer, based on receiving N 311 consecutive second information for the cell from lower layers while the timer T 310 is running; and

considering radio link failure to be detected by a RRC layer, upon the timer T 310 expiry.

13. An apparatus configured to control a User Equipment (UE) to operate in a wireless communication system, the apparatus comprising:

at least one processor; and

at least one computer memory operably coupled with the at least one processor and storing instructions that, when executed by the at least one processor, perform operations comprising:

measuring each of downlink radio link quality of multiple beams configured for the UE;

sending a first information for an out-of-sync to an upper layer of the UE based on all beams of the multiple beams meeting an out-of-sync condition; and

sending a second information for an in-sync to the upper layer of the UE based on at least one beam of the multiple beams meeting an in-sync condition,

wherein, based on downlink radio link quality of a beam becoming worse than a first threshold, the UE determines that the beam meets the out-of-sync condition,

wherein, based on downlink radio link quality of the beam becoming better than a second threshold, the UE determines that the beam meets the in-sync condition,

wherein based on the all beams of the multiple beams not meeting the out-of-sync condition and at least one beam of the multiple beams not meeting the in-sync out of sync condition, the UE does not send the first information and the second information,

wherein the multiple beams are serving beams which are currently used for beam problem detection of the UE, and

wherein based on the beam problem being detected, the UE uses candidate beams to replace the serving beams.

14. The apparatus according to claim 13 ,

wherein the UE determines that the beam meets the out-of-sync condition within a first time period,

wherein the UE determines that the beam meets the in-sync condition within a second time period, and

wherein the first time period and the second time period are equally applied to the each of the multiple beams.

15. The apparatus according to claim 14 , wherein even in a state in which two or more beams meet in-sync condition, only one second indication is transmitted to the upper layer of the UE within the first time period.

16. The apparatus according to claim 14 , wherein the first time period is longer than the second time period.

17. The apparatus according to claim 13 , wherein the operations further comprise:

Starting a timer based on sending the first information to the upper layer of the UE, and

re-sending the first information to the upper layer of the UE upon the timer expiry, based on the all beams of the multiple beams meeting the out-of-sync condition upon the timer expiry.

18. The apparatus according to claim 13 , wherein the operations further comprise:

starting a timer T 310 by a RRC layer, based on receiving N 310 consecutive first information for a cell from lower layers;

stopping the timer T 310 by a RRC layer, based on receiving N 311 consecutive second information for the cell from lower layers while the timer T 310 is running; and

considering radio link failure to be detected by a RRC layer, upon the timer T 310 expiry.