Unicast communication over sidelink

1. A method, comprising:

transmitting a direct communication message to one or more user equipment (UEs);

receiving a direct communication response from at least one of the one or more UEs, the direct communication response including context information and a destination sidelink ID for the at least one UE;

storing the context information of the at least one UE in association with an ID pair comprising the destination sidelink ID and a source sidelink ID; and

determining a destination for a hybrid automatic repeat request (HARQ) message based on the source sidelink ID or the destination sidelink ID.

2. The method of claim 1 , wherein the at least one UE is a vehicle-to-everything (V2X) UE.

3. The method of claim 1 , wherein the source sidelink ID comprises a per-UE ID, a per-UE pair ID, or a service ID.

4. The method of claim 1 , wherein the context information includes at least one of capability information or configuration information for the at least one UE.

5. The method of claim 1 , further comprising:

receiving a direct communication message from the at least one UE, the direct communication message including the destination sidelink ID and an indication of a V2X service;

identifying, based on the destination sidelink ID, the context information for the at least one UE; and

transmitting a direct communication response to the at least one UE to establish a link for the V2X service.

6. The method of claim 1 , further comprising transmitting the source sidelink ID to the at least one UE during a PC5-RRC connection setup procedure.

7. The method of claim 1 , wherein the destination sidelink ID is assigned by a network or self-assigned by the at least one UE.

8. The method of claim 7 , wherein the destination sidelink ID is self-assigned by the at least one UE based on one or more of a MAC layer address, a vehicle ID, or network-specific or cell-specific information.

9. The method of claim 1 , further comprising transmitting a direct communication message including a service ID during a PC5-RRC procedure.

10. The method of claim 1 , further comprising storing the context information in association with a per-UE ID, a per-UE pair ID, or a service ID.

11. The method of claim 1 , wherein the direct communication message includes information about a V2X service requesting Layer-2 link establishment, wherein the information is to allow the one or more UEs to determine whether to respond to the direct communication message.

12. The method of claim 11 , wherein the direct communication response includes an indication that the at least one UE is interested in using the V2X service announced by the direct communication message.

13. The method of claim 1 , wherein the source sidelink ID is allocated at an application layer.

14. The method of claim 13 , further comprising passing the source sidelink ID from the application layer to a lower layer.

15. The method of claim 1 , wherein the source sidelink ID is allocated at an Access Stratum (AS) layer.

16. The method of claim 1 , wherein the direct communication message is transmitted as a broadcast message.

17. The method of claim 1 , wherein the method is performed by a UE.

18. The method of claim 1 , wherein the method is performed by one or more baseband processors.

19. A device, comprising:

one or more processors; and

memory storing instructions which, when executed by the one or more processors, cause the one or more processors to perform operations comprising:

transmitting a direct communication message to one or more user equipment (UEs);

receiving a direct communication response from at least one of the one or more UEs, the direct communication response including context information and a destination sidelink ID for the at least one UE;

storing the context information of the at least one UE in association with an ID pair comprising the destination sidelink ID and a source sidelink ID; and

determining a destination for a hybrid automatic repeat request (HARQ) message based on the source sidelink ID or the destination sidelink ID.

20. A non-transitory computer readable storage medium storing instructions which, when executed by one or more processors, cause the one or more processors to perform operations comprising:

transmitting a direct communication message to one or more user equipment (UEs);

receiving a direct communication response from at least one of the one or more UEs, the direct communication response including context information and a destination sidelink ID for the at least one UE; and

storing the context information of the at least one UE in association with an ID pair comprising the destination sidelink ID and a source sidelink ID; and

determining a destination for a hybrid automatic repeat request (HARQ) message based on the source sidelink ID or the destination sidelink ID.