Method and apparatus for RRC connection establishment to support UE-to-network relaying in a wireless communication system
A method and device are disclosed from the perspective of a relay UE for Radio Resource Control (RRC) connection establishment to support User Equipment (UE)-to-Network relaying. In one embodiment, the method includes a relay UE establishing a PC5 RRC connection or a PC5 unicast link with a remote UE. The method also includes the relay UE receiving a RRC message from the remote UE. Furthermore, the method includes the relay UE initiating a RRC connection establishment with a network node in response to reception of the RRC message. In addition, the method includes the relay UE transmitting a Disconnect Request message to the remote UE to release the PC5 RRC connection or the PC5 unicast link or transmits a PC5 RRC message to the remote UE to inform the remote UE of a failure of the RRC connection establishment, if the RRC connection establishment fails.
1. A method for Radio Resource Control (RRC) connection establishment to support User Equipment (UE)-to-Network relaying, comprising:
a relay UE establishes a Layer-2 link with a remote UE, wherein the relay UE is a Layer-2 UE-to-Network relay;
the relay UE receives a RRC message from the remote UE;
the relay UE initiates a RRC connection establishment with a network node in response to reception of the RRC message and starts a timer;
the relay UE determines a failure of the RRC connection establishment based on reception of a RRC Reject message from the network node during the RRC connection establishment or upon expiration of the timer;
in response to determining the failure of the RRC connection establishment, the relay UE initiates a Layer-2 link release procedure and transmits a Disconnect Request message to the remote UE;
the relay UE receives a Disconnect Response message from the remote UE; and
the relay UE releases the Layer-2 link in response to reception of the Disconnect Response message.
2. The method of claim 1 , wherein the RRC message is a very first RRC message received from the remote UE after the Layer-2 link is established.
3. The method of claim 1 , wherein the RRC message is a RRC Setup Request message.
4. The method of claim 1 , wherein the RRC message is a RRC Reconfiguration Complete message.
5. The method of claim 1 , wherein the RRC message includes information to indicate the RRC connection establishment failure.
6. A relay User Equipment (UE) for UE-to-Network relaying, 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, by a UE relay, a Layer-2 link with a remote UE, wherein the UE relay is a Layer-2 UE-to-Network relay;
receive, by the UE relay, a RRC message from the remote UE;
initiate, by the UE relay, a RRC connection establishment with a network node in response to reception of the RRC message, and start a timer;
determine, by the UE relay, a failure of the RRC connection establishment based on reception of a RRC Reject message from the network node during the RRC connection establishment or upon expiration of the timer;
initiate aLayer-2 link release procedure and transmit, by the UE relay, in response to determining the failure of the RRC connection establishment, a Disconnect Request message to the remote UE;
receive, by the UE relay, a Disconnect Response message from the remote UE; and
release, by the UE relay, the Layer-2 link in response to reception of the Disconnect Response message.
7. The relay UE of claim 6 , wherein the RRC message is a very first RRC message received from the remote UE after the Layer-2 link is established.
8. The relay UE of claim 6 , wherein the RRC message is a RRC Setup Request message.
9. The relay UE of claim 6 , wherein the RRC message is a RRC Reconfiguration Complete message.
10. The relay UE of claim 6 , wherein the RRC message includes information to indicate the RRC connection establishment failure.