Method and apparatus for a relay user equipment (UE) to support direct to indirect communication path switching in a wireless communication system

1. A method for a relay User Equipment (UE), comprising:

the relay UE establishes a Radio Resource Control (RRC) connection with a network node;

the relay UE transmits a Layer 2 Identity (L2ID) of the relay UE to the network node;

the relay UE receives a local UE Identity (ID) for a remote UE and a L2ID of the remote UE from the network node;

the relay UE establishes a PC5 connection with the remote UE;

the relay UE receives a first RRC Reconfiguration Complete message from the remote UE; and

the relay UE transmits the first RRC Reconfiguration Complete message to the network node, wherein the first RRC Reconfiguration Complete message is included in an adaptation layer Protocol Data Unit (PDU) for transmission and the local UE ID for the remote UE is included in a header of the adaptation layer PDU.

2. The method of claim 1 , where the local UE ID for the remote UE and the L2ID of the remote UE are included in a RRC Reconfiguration message transmitted from the network node to the relay UE.

3. The method of claim 2 , wherein the RRC Reconfiguration message includes a Uu Radio Link Control (RLC) channel configuration and/or a PC5 or Sidelink (SL) RLC channel configuration for forwarding the first RRC Reconfiguration Complete message to the network node via the relay UE.

4. The method of claim 1 , wherein the relay UE is a Layer-2 UE-to-Network Relay.

5. The method of claim 1 , wherein the L2ID of the relay UE is transmitted to the network node via a SidelinkUEInformationNR message.

6. The method of claim 1 , wherein the network node is a gNB.

7. A relay UE (User Equipment), comprising:

a control circuit;

a processor installed in the control circuit; and

a memory installed in the control circuit and operatively coupled to the processor;

wherein the processor is configured to execute a program code stored in the memory to:

establish a Radio Resource Control (RRC) connection with a network node;

transmit a Layer 2 Identity (L2ID) of the relay UE to the network node;

receive a local UE Identity (ID) for a remote UE and a L2ID of the remote UE from the network node;

establish a PC5 connection with the remote UE;

receive a first RRC Reconfiguration Complete message from the remote UE; and

transmit the first RRC Reconfiguration Complete message to the network node, wherein the first RRC Reconfiguration Complete message is included in an adaptation layer Protocol Data Unit (PDU) for transmission and the local UE ID for the remote UE is included in a header of the adaptation layer PDU.

8. The relay UE of claim 7 , where the local UE ID for the remote UE and the L2ID of the remote UE are included in a RRC Reconfiguration message transmitted from the network node to the relay UE.

9. The relay UE of claim 8 , wherein the RRC Reconfiguration message includes a Uu Radio Link Control (RLC) channel configuration and/or a PC5 or Sidelink (SL) RLC channel configuration for forwarding the first RRC Reconfiguration Complete message to the network node via the relay UE.

10. The relay UE of claim 7 , wherein the relay UE is a Layer-2 UE-to-Network Relay.

11. The relay UE of claim 7 , wherein the L2ID of the relay UE is transmitted to the network node via a SidelinkUEInformationNR message.

12. The relay UE of claim 7 , wherein the network node is a gNB.

13. A method for a network node, comprising:

the network node establishes a Radio Resource Control (RRC) connection with a relay User Equipment (UE);

the network node receives a Layer 2 Identity (L2ID) of the relay UE from the relay UE;

the network node transmits a local UE Identity (ID) for a remote UE and a L2ID of the remote UE to the relay UE;

the network node transmits a first RRC Reconfiguration message to the remote UE for path switching the remote UE from direct to indirect communication, wherein the first RRC Reconfiguration message includes the L2ID of the relay UE; and

the network node receives a first RRC Reconfiguration Complete message from the remote UE via the relay UE, wherein the first RRC Reconfiguration Complete message is included in an adaptation layer Protocol Data Unit (PDU) and the local UE ID for the remote UE is included in a header of the adaptation layer PDU.

14. The method of claim 13 , further comprising:

the network node receives a measurement report from the remote UE, wherein the measurement report indicates one or more candidate relay UEs containing the relay UE, and wherein the measurement report includes the L2ID of the relay UE.

15. The method of claim 13 , wherein the first RRC Reconfiguration message includes a Uu Signaling Radio Bearer (SRB) configuration and/or a PC5 (or Sidelink (SL)) Radio Link Control (RLC) channel configuration for forwarding the first RRC Reconfiguration Complete message to the network node via the relay UE.

16. The method of claim 13 , wherein the L2ID of the relay UE is received from the relay UE via a first SidelinkUEInformationNR message.

17. The method of claim 13 , where the local UE ID for the remote UE and the L2ID of the remote UE are included in a second RRC Reconfiguration message transmitted from the network node to the relay UE.

18. The method of claim 17 , wherein the second RRC Reconfiguration message includes a Uu Radio Link Control (RLC) channel configuration and/or a PC5 or Sidelink (SL) RLC channel configuration for forwarding the first RRC Reconfiguration Complete message to the network node via the relay UE.

19. The method of claim 13 , further comprising:

the network node receives the L2ID of the remote UE from the remote UE.

20. The method of claim 19 , wherein the L2ID of the remote UE is transmitted to the network node via a second SidelinkUEInformationNR message.