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 User Equipment (UE). In one embodiment, the method includes the remote UE establishing a layer-2 link with a relay UE. The method further includes the remote UE establishing a Radio Resource Control (RRC) connection with a network via the relay UE. The method also includes the remote UE initiating or performing a RRC connection re-establishment procedure, wherein the remote UE determines to keep the layer-2 link with the relay UE in the RRC connection re-establishment procedure. In addition, the method includes the remote UE starting a timer T301 in response to keeping the layer-2 link with the relay UE.
1. A method for a remote User Equipment (UE), comprising:
establishing a layer-2 link between the remote UE and a relay UE;
establishing a Radio Resource Control (RRC) connection between the remote UE and a network via the relay UE;
initiating or performing a RRC connection re-establishment procedure, wherein the remote UE, within the RRC connection re-establishment procedure, determines to keep or release the layer-2 link with the relay UE with which the remote UE initially established the layer-2 link;
starting a timer T301 in response to the determination of keeping the layer-2 link with the relay UE; and
transmitting a request message for re-establishing the RRC connection to the network via the relay UE in response to the determination of keeping the layer-2 link with the relay UE.
2. The method of claim 1 , wherein the request message for re-establishing the RRC connection is a RRCReestablishmentRequest message.
3. The method of claim 1 , further comprising:
starting a timer T311 upon initiation of the RRC connection re-establishment procedure.
4. The method of claim 3 , further comprising:
stopping the timer T311 in response to keeping the layer-2 link with the relay UE.
5. The method of claim 1 , further comprising:
stopping the timer T301 in response to reception of a RRCReestablishment message corresponding to the RRCReestablishmentRequest message from the network via the relay UE.
6. The method of claim 1 , wherein the network includes a base station or a gNB.
7. A remote User Equipment (UE), comprising:
a processor; and
a memory operatively coupled to the processor, wherein the processor is configured to execute a program code stored in the memory to:
establish a layer-2 link between the remote UE and a relay UE;
establish a Radio Resource Control (RRC) connection between the remote UE and a network via the relay UE;
initiate or perform a RRC connection re-establishment procedure, wherein the remote UE, within the RRC connection re-establishment procedure, determines to keep or release the layer-2 link with the relay UE with which the remote UE initially established the layer-2 link;
start a timer T301 in response to the determination of keeping the layer-2 link with the relay UE; and
transmit a request message for re-establishing the RRC connection to the network via the relay UE in response to the determination of keeping the layer-2 link with the relay UE.
8. The remote UE of claim 7 , wherein the request message for re-establishing the RRC connection is a RRCReestablishmentRequest message.
9. The remote UE of claim 7 , wherein the processor is further configured to execute a program code stored in the memory to:
start a timer T311 upon initiation of the RRC connection re-establishment procedure.
10. The remote UE of claim 9 , wherein the processor is further configured to execute a program code stored in the memory to:
stop the timer T311 in response to keeping the layer-2 link with the relay UE.
11. The remote UE of claim 7 , wherein the processor is further configured to execute a program code stored in the memory to:
stop the timer T301 in response to reception of a RRCReestablishment message corresponding to the RRCReestablishmentRequest message from the network via the relay UE.
12. The remote UE of claim 7 , wherein the network includes a base station or a gNB.