Method and device for performing sidelink synchronization in wireless communication system

1. A method for performing wireless communication by a first device, the method comprising:

receiving a first physical sidelink control channel (PSCCH) or a first physical sidelink shared channel (PSSCH) including information related to a second synchronization source from a second device;

determining synchronization with the second device based on the information related to the second synchronization source; and

performing synchronization with the second device based on a reference signal on the first PSCCH or the first PSSCH,

wherein the second synchronization source includes a synchronization source having a highest priority pre-configured for the second device.

2. The method of claim 1 , wherein the information related to the second synchronization source includes information related to whether the second device uses the second synchronization source and information related to a synchronization quality of the second synchronization source for the second device.

3. The method of claim 2 ,

wherein the synchronization with the second device is determined based on the second device using the second synchronization source as a synchronization source.

4. The method of claim 1 , wherein the

synchronization with the second device is determined based on the number of times the second device successfully receives a synchronization signal of the second synchronization source is greater than a pre-determined threshold value.

5. The method of claim 1 , wherein the

synchronization with the second device is determined based on that a reception power level of a physical sidelink broadcast channel (PSBCH) reference signal received by the second device from the second synchronization source is higher than a pre-determined threshold level.

6. The method of claim 3 , wherein the synchronization with the second device is performed based on that a synchronization source of the highest priority pre-configured for the first device and the second synchronization source are the same.

7. The method of claim 1 , further comprising:

setting at least one of a sidelink synchronization signal (SLSS) ID value or a PSBCH field value related to a state in which the first device is directly synchronized with the second synchronization source.

8. The method of claim 1 , wherein the

synchronization with the second device is determined based on determining that a synchronization quality related to the first synchronization source is smaller than a pre-determined threshold value, and

wherein the first synchronization source includes a synchronization source of a highest priority pre-configured for the first device.

9. The method of claim 1 , further comprising:

receiving a second PSCCH or a second PSSCH including information related to a third synchronization source from a third device;

determining synchronization with the third device based on the information related to the second synchronization source and the information related to the third synchronization source; and

performing synchronization with the third device based on a reference signal on the second PSCCH or the second PSSCH,

wherein the third synchronization source includes a synchronization source having a highest priority pre-determined for the third device.

10. The method of claim 9 , wherein the information related to the third synchronization source includes information related to whether the third device uses the third synchronization source and information related to a synchronization quality of the third synchronization source for the third device.

11. The method of claim 10 , wherein the

synchronization with the third device is determined based on the third device using the third synchronization source as a synchronization source.

12. The method of claim 10 , wherein the

synchronization with the third device is determined based on that a synchronization quality related to the third synchronization source is better than a synchronization quality related to the second synchronization source.

13. The method of claim 12 , wherein

synchronization with the third device is determined based on that a difference value between a reception power level of a demodulation reference signal (DM-RS) on the first PSCCH or first PSSCH and a reception power level of a DM-RS on the second PSCCH or the second PSSCH is smaller than a pre-determined threshold value.

14. A first device for performing wireless communication, the first device comprising:

one or more memories storing instructions;

one or more transceivers; and

one or more processors connected to the one or more memories and the one or more transceivers, wherein the one or more processors execute the instructions to:

receive a first physical sidelink control channel (PSCCH) or a first physical sidelink shared channel (PSSCH) including information related to a second synchronization source from a second device,

determine synchronization with the second device based on the information related to the second synchronization source,

perform synchronization with the second device based on a reference signal on the first PSCCH or the first PSSCH,

wherein the second synchronization source includes a synchronization source having a highest priority pre-configured for the second device.

15. An device configured to control a first user equipment (UE), the device comprising:

one or more processors; and

one or more memories being operably connectable to the one or more processors and storing instructions, wherein the one or more processors execute the instructions to:

receive a first physical sidelink control channel (PSCCH) or a first physical sidelink shared channel (PSSCH) including information related to a second synchronization source from a second UE,

determine synchronization with the second UE based on the information related to the second synchronization source,

perform synchronization with the second UE based on a reference signal on the first PSCCH or the first PSSCH,

wherein the second synchronization source includes a synchronization source having a highest priority pre-configured for the second UE.