Abstract: A method and apparatus are disclosed from the perspective of a first device. In one embodiment, the method includes the first device performs sensing on a data resource pool, and the first device selects/derives at least a first data resource from the data resource pool based on the sensing result of the data resource pool. The method further includes the first device transmits a first control information on a first control resource, wherein the first control information allocates or indicates the first data resource. The method also includes the first device performs a first data transmission on the first data resource to at least one second device.

Abstract: A method and apparatus are disclosed from the perspective of a first UE (User Equipment) to update Layer-2 Identities (IDs). In one embodiment, the method includes the first UE establishing a unicast link with a second UE, wherein a first Layer-2 ID of the first UE and a second Layer-2 ID of the second UE are used for data transmission and reception on the unicast link. The method further includes the first UE transmitting a Link Identifier Update Request message for the unicast link to the second UE, wherein the Link Identifier Update Request message includes a new first Layer-2 ID of the first UE. The method also includes the first UE receiving a Link Identifier Update Accept message for the unicast link from the second UE, wherein the Link Identifier Update Accept message includes a new second Layer-2 ID of the second UE.

Abstract: A method and device are disclosed for a remote User Equipment (UE) to support UE-to-Network relay communication. The remote UE establishes a PC5 connection with a first relay UE for a relay communication with a first network node. The remote UE also performs a Radio Resource Control (RRC) connection establishment procedure with the first network node via the first relay UE. Furthermore, the remote UE transmits a first RRC message to a second network node via a second relay UE for requesting RRC connection re-establishment, wherein the first RRC message includes a first Cell Radio Network Temporary Identifier (C-RNTI) of the remote UE. Also, the remote UE receives a second RRC message from the second network node via the second relay UE for re-establishing a RRC connection between the second network node and the remote UE, wherein the second RRC message includes a second C-RNTI of the remote UE.

Abstract: A method and apparatus are disclosed from the perspective of a first UE (User Equipment) in RRC_CONNECTED to detect configuration failure. In one embodiment, the method includes the first UE transmitting a first PC5 RRC (Radio Resource Control) message to a second UE, wherein the first PC5 RRC message includes an AS (Access Stratum)-layer configuration for a unicast link established with the second UE. The method also includes the first UE transmitting a fourth RRC message to a network node if a configuration failure of the AS-layer configuration is detected, wherein the fourth RRC message indicates the configuration failure occurs.

Abstract: A method and device are disclosed for Sidelink Relay Adaptation Protocol (SRAP) Data Protocol Data Unit (PDU) discarding. In one embodiment, the method includes a relay UE establishing a PC5 connection with a remote UE. The method further includes the relay UE receiving a SRAP Data PDU from the remote UE. The method also includes the relay UE preventing from discarding the SRAP Data PDU if the SRAP Data PDU is the first SRAP Data PDU received from the remote UE via SL-RLC1, wherein a header of the first SRAP Data PDU contains a UE Identity/Identifier (ID) of the remote UE, and the UE ID of the remote UE is not included in any SRAP configuration of the relay UE.

Abstract: 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.

Abstract: 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.

Abstract: 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 unicast 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, wherein a first Radio Link Control (RLC) entity is created and used for transmitting a first RRC message for request of establishing the RRC connection to the network via the relay UE. The method also includes the remote UE selecting a suitable cell. In addition, the method includes the remote UE releasing the first RLC entity in response to selection of the suitable cell. Furthermore, the method includes the remote UE transmitting a second RRC message to the network directly.

Abstract: A method and device are disclosed from the perspective of a first UE (User Equipment) for changing sidelink identity for a sidelink unicast link associated with a second UE. In one method, the method includes the first UE establishing the sidelink unicast link with the second UE, wherein a first lower-layer identity of the first UE and a second lower-layer identity of the second UE are used for communicating between the first UE and the second UE via the sidelink unicast link. The method also includes the first UE transmitting a Link Identifier Update Request message to the second UE, wherein the Link Identifier Update Request message includes a new first lower-layer identity of the first UE or information for deriving the new first lower-layer identity. The method further includes the first UE receiving a Link Identifier Update Response message from the second UE.

Abstract: A method and apparatus are disclosed from the perspective of a first UE (User Equipment) to update Layer-2 Identities (IDs). In one embodiment, the method includes the first UE establishing a unicast link with a second UE, wherein a first Layer-2 ID of the first UE and a second Layer-2 ID of the second UE are used for data transmission and reception on the unicast link. The method further includes the first UE transmitting a Link Identifier Update Request message for the unicast link to the second UE, wherein the Link Identifier Update Request message includes a new first Layer-2 ID of the first UE. The method also includes the first UE receiving a Link Identifier Update Accept message for the unicast link from the second UE, wherein the Link Identifier Update Accept message includes a new second Layer-2 ID of the second UE.

Abstract: A method and apparatus are disclosed. In an example from the perspective of a device, a grant is received on a first interface. The grant is associated with transmission on a second interface. A first resource and/or a second resource are derived based upon the grant. A first transmission for delivering a transport block is performed on the first resource on a first transmission beam. The first transmission is on the second interface. A second transmission for delivering the transport block is performed on the second resource on a second transmission beam. The second transmission is on the second interface.

Abstract: A method and device are disclosed from the perspective of a remote UE. In one embodiment, the remote UE establishes a Radio Resource Control (RRC) connection with a network node. The remote UE also transmits a Layer 2 Identity (L2ID) of the remote UE to the network node. The remote UE further receives a first RRC Reconfiguration message from the network node for path switching from direct to indirect communication, wherein the first RRC Reconfiguration message indicates a relay UE for the path switching. In addition, the remote UE establishes a PC5 connection with the relay UE. Furthermore, the remote UE transmits a first RRC Reconfiguration Complete message corresponding to the first RRC Reconfiguration message to the network node via the relay UE.

Abstract: A method and device are disclosed from the perspective of a remote UE. In one embodiment, the remote UE establishes a Radio Resource Control (RRC) connection with a network node. The remote UE also transmits a Layer 2 Identity (L2ID) of the remote UE to the network node. The remote UE further receives a first RRC Reconfiguration message from the network node for path switching from direct to indirect communication, wherein the first RRC Reconfiguration message indicates a relay UE for the path switching. In addition, the remote UE establishes a PC5 connection with the relay UE. Furthermore, the remote UE transmits a first RRC Reconfiguration Complete message corresponding to the first RRC Reconfiguration message to the network node via the relay UE.

Abstract: A method and apparatus are disclosed. In an example from the perspective of a first device, a grant is received from a network node. The grant allocates a set of sidelink data resources. One or more sidelink data transmissions are performed on the set of sidelink data resources. A second feedback information associated with the one or more sidelink data transmissions is received and/or detected. An uplink resource is derived. A first feedback information is transmitted on the uplink resource to the network node. The first feedback information is set based upon the second feedback information.

Abstract: A method and device are disclosed from the perspective of a first User Equipment (UE) to support Sidelink (SL) Discontinuous Reception (DRX). In one embodiment, the method includes the first UE establishing a unicast link with a second UE. The method further includes the first UE receiving a SL DRX configuration associated with the second UE from the second UE. The method also includes the first UE transmitting the SL DRX configuration to a network node. In addition, the method includes the first UE receiving a sidelink grant from the network node, wherein the sidelink grant indicates sidelink resources. Furthermore, the method includes the first UE performing a sidelink transmission to the second UE based on the sidelink resources.

Abstract: A method and apparatus are disclosed from the perspective of a network node. In one embodiment, the method includes receiving a resource request to allocate SPS resource from a UE, wherein the resource request indicates a first logical channel. The method also allocating the UE with a first SPS resource and a second SPS resource for the first logical channel and a second logical channel associated with the first logical channel based on the resource request.

Abstract: A method and apparatus are disclosed from the perspective of a first UE (User Equipment) to request SLRB (Sidelink Radio Bearer) configuration for a unicast link with a second UE. In one embodiment, the method includes the first UE receiving a first message from the second UE, wherein the first message includes a first SLRB configuration for the unicast link. The method further includes the first UE transmitting a second message to a network node to request a second SLRB configuration for the unicast link when the first message is received or a successful transmission of a complete message associated with the first message to the second UE is confirmed.

Abstract: A method and apparatus are disclosed from the perspective of a first User Equipment (UE) in RRC_CONNECTED to request sidelink resources. In one embodiment, the method transmits a first RRC (Radio Resource Control) message to a network node, wherein a presence of a sidelink QoS (Quality of Service) information list in the first RRC message is optional.

Abstract: A method and apparatus are disclosed. In an example from the perspective of a User Equipment (UE), if sidelink packet duplication is configured or enabled for a Sidelink Radio Bearer (SLRB), a first Packet Data Convergence Protocol (PDCP) Protocol Data Unit (PDU), corresponding to a first PDCP Service Data Unit (SDU), and a duplicate of the first PDCP PDU, are transmitted. A first PDCP Sequence Number (SN) of the first PDCP PDU is set based upon one or more state variables used for sidelink transmission on the SLRB. If the sidelink packet duplication is de-configured or disabled for the SLRB, a second PDCP PDU, corresponding to a second PDCP SDU, is transmitted. Noduplicate of the second PDCP PDU is transmitted. A second PDCP SN of the second PDCP PDU is set based upon the one or more state variables used for sidelink transmission on the SLRB.

Abstract: A method and apparatus are disclosed from the perspective of a UE (User Equipment) to handle a sidelink buffer status report (SL BSR). In one embodiment, the method includes the UE transmitting a SL BSR to a network node, wherein a format of the SL BSR includes at least one field of buffer size associated with HARQ (Hybrid Automatic Repeat Request) feedback enabled and one field of buffer size associated with HARQ feedback disabled. The method also includes the UE receiving a sidelink grant from the network node. The method further includes the UE selecting data from a logical channel for transmission according to a HARQ feedback mode of the logical channel and whether the sidelink grant is associated with a HARQ feedback resource or not.