Synchronization priority for sidelink wireless communications

1. A method comprising:

transmitting, by a wireless node in a wireless network, a sidelink synchronization signal (S-SSB) block, including a sidelink primary synchronization signal (S-PSS), a sidelink secondary synchronization signal (S-SSS), a physical sidelink broadcast channel (PSBCH), and a demodulation reference signal (DM-RS), wherein the demodulation reference signal is based on at least a sidelink demodulation reference signal initialization value for the sidelink synchronization signal block to provide sidelink priority-related information for the sidelink synchronization signal block;

wherein the sidelink primary synchronization signal and the sidelink secondary synchronization signal are associated with a physical layer sidelink identity (SL-ID);

wherein the demodulation reference signal (DM-RS) of the sidelink synchronization signal block (S-SSB) is a pseudo-random sequence that is generated by a sequence generator, wherein the sequence generator is initialized to c init based on the following:

C init =2 11 ( i init SL +1)(└ N ID SL /4┘+1)+2 6 ( i init SL +1)+( N ID SL mod 4)

where c init is an initial state of the sequence generator to be used to generate the demodulation reference signal, and i init SL is the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block, and N ID SL is the physical layer sidelink identity for the sidelink synchronization signal block.

2. The method of claim 1 , wherein the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block indicates a sidelink synchronization priority level for the sidelink synchronization signal block.

3. The method of claim 2 , wherein each different sidelink synchronization priority level, of a plurality of sidelink synchronization priority levels, is indicated by a demodulation reference signal that is based on at least a different sidelink demodulation reference signal initialization value.

4. The method of claim 1 , wherein the sidelink primary synchronization signal and the sidelink secondary synchronization signal are associated with a physical layer sidelink identity (SL-ID); and

wherein a sidelink synchronization priority level for the sidelink synchronization signal block is associated with the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block and the physical layer sidelink identity.

5. The method of claim 1 , wherein the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block is based on at least a sidelink resource, of a plurality of sidelink resources, that is used for the transmission of the sidelink synchronization signal block.

6. The method of claim 5 , wherein different sidelink resources of the plurality of sidelink resources are provided for transmission of sidelink synchronization signal blocks having different sidelink synchronization priority levels.

7. The method of claim 1 , wherein the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block is based on at least a synchronization source type for the wireless node, wherein different synchronization source types have different sidelink synchronization priority levels.

8. The method of claim 1 , wherein the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block indicates whether a contents of physical sidelink broadcast channel (PSBCH) of the sidelink synchronization signal block is preconfigured or signaled by a base station to the wireless node.

9. The method of claim 1 , wherein the demodulation reference signal of the sidelink synchronization signal block is scrambled based on at least the sidelink demodulation reference signal initialization value.

10. The method of claim 1 , wherein the sidelink primary synchronization signal and the sidelink secondary synchronization signal are associated with a physical layer sidelink identity (SL-ID); and

wherein the demodulation reference signal of the sidelink synchronization signal block is scrambled based on at least the sidelink demodulation reference signal initialization value and the physical layer sidelink identity.

11. The method of claim 1 , wherein the demodulation reference signal of the sidelink synchronization signal block is a sequence that is generated by a sequence generator, wherein the sequence generator is initialized based on at least the sidelink demodulation reference signal initialization value, such that the demodulation reference signal indicates priority-related information for the sidelink synchronization signal block.

12. The method of claim 1 , further comprising:

determining, by the wireless node, the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block;

generating a pseudo-random sequence for demodulation reference signal that is initialized based at least on the sidelink demodulation reference signal initialization value; and

wherein the transmitting comprises transmitting the sidelink synchronization signal block including the demodulation reference signal.

13. The method of claim 12 , wherein the determining the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block is performed based on one or more of the following:

a sidelink synchronization priority level for the sidelink synchronization signal block;

a synchronization source type for the wireless node;

a sidelink resource, of a plurality of sidelink resources, that is used for the transmission of the sidelink synchronization signal block; or

whether the physical sidelink broadcast channel (PSBCH) of the sidelink synchronization signal block is preconfigured or signaled by a base station to the wireless node.

14. The method of claim 1 , wherein the wireless node comprises a user equipment.

15. An apparatus comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:

transmit a sidelink synchronization signal (S-SSB) block, including a sidelink primary synchronization signal (S-PSS), a sidelink secondary synchronization signal (S-SSS), a physical sidelink broadcast channel (PSBCH), and a demodulation reference signal (DM-RS), wherein the demodulation reference signal is based on at least a sidelink demodulation reference signal initialization value for the sidelink synchronization signal block to provide sidelink priority-related information for the sidelink synchronization signal block;

wherein the sidelink primary synchronization signal and the sidelink secondary synchronization signal are associated with a physical layer sidelink identity (SL-ID);

wherein the demodulation reference signal (DM-RS) of the sidelink synchronization signal block (S-SSB) is a pseudo-random sequence that is generated by a sequence generator, wherein the sequence generator is initialized to c init based on the following:

C init =2 11 ( i init SL +1)(└ N ID SL /4┘+1)+2 6 ( i init SL +1)+( N ID SL mod 4)

where c init is an initial state of the sequence generator to be used to generate the demodulation reference signal, and i init SL is the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block, and N ID SL is the physical layer sidelink identity for the sidelink synchronization signal block.

16. An apparatus comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:

receive, from a wireless node in a wireless network, a sidelink synchronization signal (S-SSB) block, including a sidelink primary synchronization signal (S-PSS), a sidelink secondary synchronization signal (S-SSS), a physical sidelink broadcast channel (PSBCH), and a demodulation reference signal (DM-RS), wherein the demodulation reference signal is based on at least a sidelink demodulation reference signal initialization value for the sidelink synchronization signal block to provide sidelink priority-related information for the sidelink synchronization signal block; and

determine, based at least in part on the demodulation reference signal, sidelink priority-related information for the sidelink synchronization signal block;

wherein the sidelink primary synchronization signal and the sidelink secondary synchronization signal are associated with a physical layer sidelink identity (SL-ID);

wherein the demodulation reference signal (DM-RS) of the sidelink synchronization signal block (S-SSB) is a pseudo-random sequence that is generated by a sequence generator, wherein the sequence generator is initialized to C init based on the following:

C init =2 11 ( i init SL +1)(└ N ID SL /4┘+1)+2 6 ( i init SL +1)+( N ID SL mod 4)

where C init is an initial state of the sequence generator to be used to generate the demodulation reference signal, and i init SL is the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block, and N ID SL is the physical layer sidelink identity for the sidelink synchronization signal block.

17. The apparatus of claim 16 , wherein the at least one processor and the computer program code configured to cause the apparatus to determine sidelink priority-related information for the sidelink synchronization signal block comprises the at least one processor and the computer program code configured to cause the apparatus to determine at least one of the following based on at least the demodulation reference signal:

a sidelink synchronization priority level for the sidelink synchronization signal block;

a synchronization source type for the wireless node;

a sidelink resource, of a plurality of sidelink resources, that is used for the transmission of the sidelink synchronization signal block; or

whether the physical sidelink broadcast channel (PSBCH) of the sidelink synchronization signal block is preconfigured or signaled by a base station to the wireless node.

18. The method of claim 16 , wherein the at least one processor and the computer program code configured to cause the apparatus to determine sidelink priority-related information comprises the at least one processor and the computer program code configured to cause the apparatus to:

determine a sidelink synchronization priority level for the sidelink synchronization signal block based on the sidelink demodulation reference signal initialization value for the sidelink synchronization signal block.

19. The apparatus of claim 16 , wherein each different sidelink synchronization priority level, of a plurality of sidelink synchronization priority levels, is determined based on at least a different sidelink demodulation reference signal initialization value.