Method and apparatus for supporting UE-to-network relay communication in a wireless communication system
A method and device are disclosed from the perspective of a remote UE. In one embodiment, the method includes the remote UE establishing a first unicast link with a relay UE. The method also includes the remote UE establishing a Radio Resource Control (RRC) connection with a network node via the relay UE. The method further includes the remote UE establishing a second unicast link with a second UE. In addition, the method includes the remote UE detecting a sidelink radio link failure. Furthermore, the method includes the remote UE initiating or performing a RRC connection re-establishment procedure if the sidelink radio link failure occurs on the first unicast link. The method also includes the remote UE initiating or performing a Sidelink UE Information procedure if the sidelink radio link failure occurs on the second unicast link.
1. A method for a remote User Equipment (UE), comprising:
establishing a first unicast link with a relay UE;
establishing a Radio Resource Control (RRC) connection with a network node via the relay UE;
establishing a second unicast link with a second UE;
detecting a sidelink radio link failure;
initiating or performing a RRC connection re-establishment procedure in response to the sidelink radio link failure on the first unicast link, wherein the remote UE in the RRC connection re-establishment procedure performs a relay selection and/or a cell selection; and
initiating or performing a Sidelink UE Information procedure in response to the sidelink radio link failure on the second unicast link, wherein the remote UE in the Sidelink UE Information procedure sends a Sidelink UE Information message to the network node to indicate the sidelink radio link failure on the second UE.
2. The method of claim 1 , further comprising:
initiating or performing no RRC connection re-establishment procedure if the sidelink radio link failure occurs on the second unicast link.
3. The method of claim 1 , further comprising:
initiating or performing no Sidelink UE Information procedure if the sidelink radio link failure occurs on the first unicast link.
4. The method of claim 1 , wherein the first unicast link is used for forwarding traffic between the network node and the remote UE via the relay UE.
5. The method of claim 4 , wherein the network node is a base station or a gNB.
6. The method of claim 1 , wherein the second unicast link is used for transferring traffic between the remote UE and the second UE.
7. The method of claim 6 , wherein the second UE is a non-relay UE.
8. The method of claim 1 , wherein the first unicast link is associated with a Proximity-based Services (ProSe) Relay Code.
9. The method of claim 1 , wherein the second unicast link is not associated with any Proximity-based Services (ProSe) Relay Code.
10. A remote 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 first unicast link with a relay UE;
establish a Radio Resource Control (RRC) connection with a network node via the relay UE;
establish a second unicast link with a second UE;
detect a sidelink radio link failure;
initiate or perform a RRC connection re-establishment procedure in response to the sidelink radio link failure on the first unicast link, wherein the remote UE in the RRC connection re-establishment procedure performs a relay selection and/or a cell selection; and
initiate or perform a Sidelink UE Information procedure in response to the sidelink radio link failure on the second unicast link, wherein the remote UE in the Sidelink UE Information procedure sends a Sidelink UE Information message to the network node to indicate the sidelink radio link failure on the second UE.
11. The remote UE of claim 10 , further comprising:
initiating or performing no RRC connection re-establishment procedure if the sidelink radio link failure occurs on the second unicast link.
12. The remote UE of claim 10 , further comprising:
initiating or performing no Sidelink UE Information procedure if the sidelink radio link failure occurs on the first unicast link.
13. The remote UE of claim 10 , wherein the first unicast link is used for forwarding traffic between the network node and the remote UE via the relay UE.
14. The remote UE of claim 13 , wherein the network node is a base station or a gNB.
15. The remote UE of claim 10 , wherein the second unicast link is used for transferring traffic between the remote UE and the second UE.
16. The remote UE of claim 15 , wherein the second UE is a non-relay UE.
17. The remote UE of claim 10 , wherein the first unicast link is associated with a Proximity-based Services (ProSe) Relay Code.
18. The remote UE of claim 10 , wherein the second unicast link is not associated with any Proximity-based Services (ProSe) Relay Code.