Method for carrying out transfer between gNBs by using L2 U2N relay

Abstract

A base station is configured to receive a measurement report from a first user equipment (UE), the measurement report comprising a channel measurement result for a sidelink channel with at least a second UE capable of serving as a candidate relay UE for a Layer 2 (L2) UE-to-network (U2N) relay, the measurement report further comprises a relay identifier of the second UE and serving cell information for a serving cell; selecting the second UE as a target relay UE for the first UE regardless of a current radio resource control (RRC) state of the second UE and the serving cell of the second UE; and transmitting a handover preparation message to the serving cell of the target relay UE, where the serving cell of the target relay UE is a target cell for handover of the first UE, the handover preparation message including the relay identifier of the target relay UE.

Description

Technical Field

[0001] The present application generally relates to wireless communications, and in particular to a method for inter-gNB handover using L2 U2N relay. Background Art

[0002] A user equipment (UE) may be configured with multiple communication links. For example, a UE may receive a signal from a cell of a corresponding network via a downlink, and may transmit a signal to a cell of a corresponding network via an uplink. A UE may also be configured to communicate with another UE via a side link (SL). The term "side link" refers to a communication link that may be used for device-to-device (D2D) communication.

[0003] SL can be used for relay assistance to forward data / signals between the network and a remote UE that is out of range of the network and / or has poor network coverage. For example, a relay UE that is within range of the network and / or has good network coverage can relay data / signals between the network and the remote UE via a SL connection with the remote UE. After successful decoding / encoding and demodulation / modulation of the signal, the Layer 2 (L2) relay amplifies the received signal to the destination.

[0004] A typical direct network connection (without L2 relay) may be referred to as a direct network path for a UE, while a network connection employing L2 relay via SL may be referred to as an indirect network path for a (remote) UE. According to current specifications, path switching (e.g., handover) from an indirect path to a direct path is supported. However, inter-gNB path switching to a target indirect path is not currently supported. Summary of the invention

[0005] Some exemplary embodiments relate to a processor of a base station configured to perform operations. The operations include: receiving a measurement report from a first user equipment (UE), the measurement report including a channel measurement result for a sidelink channel with at least a second UE, the at least second UE being capable of being used as a candidate relay UE for a layer 2 (L2) UE to network (U2N) relay, the measurement report also including a relay identifier of the second UE and serving cell information for a serving cell; selecting the second UE as a target relay UE for the first UE regardless of a current radio resource control (RRC) state of the second UE and the serving cell of the second UE; and transmitting a handover preparation message to the serving cell of the target relay UE, wherein the serving cell of the target relay UE is a target cell for handover of the first UE, and the handover preparation message includes the relay identifier of the target relay UE.

[0006] Other exemplary embodiments relate to a processor of a base station configured to perform operations. The operations include: receiving a handover preparation message from a serving cell of a first user equipment (UE), wherein the serving cell of the first UE is a source cell for handover of the first UE, the handover preparation message including a relay identifier of a second UE, the second UE being capable of serving as a target relay UE for layer 2 (L2) UE to network (U2N) relay under the base station; identifying a current radio resource control (RRC) state of the second UE; and transmitting a handover preparation completion message to the source cell, the handover preparation completion message including an indication of whether the target relay UE is ready for handover.

[0007] Another exemplary embodiment relates to a processor of a base station, the processor being configured to perform operations. The operations include: receiving a measurement report from a first user equipment (UE), the measurement report including a channel measurement result for a sidelink channel with at least a second UE, the at least second UE being capable of being used as a candidate relay UE for a layer 2 (L2) UE to network (U2N) relay, the measurement report also including a relay identifier of the second UE and serving cell information for a serving cell; transmitting a relay query request to the serving cell of the second UE, the relay query request including the relay identifier of the second UE; and receiving a relay query response from the serving cell of the second UE, the relay query response including an indication of whether the second UE is in a first state including a radio resource control (RRC) connected state, a second state including an RRC idle or inactive state, or a third state in which the second UE is out of coverage of the serving cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1a A first exemplary handover scenario (scenario A) for a user equipment (UE) including an inter-gNB indirect to direct path handover is shown.

[0009] Figure 1b A second exemplary handover scenario (scenario B) for a UE including an inter-gNB direct to indirect path switching is shown.

[0010] Figure 1c A third exemplary handover scenario (scenario C) for a UE including an intra-gNB indirect-to-indirect path switching is shown.

[0011] Figure 1d A fourth exemplary handover scenario (scenario D) for a UE including an inter-gNB indirect to indirect path switching is shown.

[0012] Figure 2a An exemplary signaling diagram for inter-gNB handover to an indirect target path according to the first option is shown, where the target relay UE is in RRC connected state.

[0013] Figure 2b An exemplary signaling diagram for inter-gNB handover to an indirect target path according to the first option is shown, where the target relay UE is in RRC idle or inactive state.

[0014] Figure 3a An exemplary signaling diagram for inter-gNB handover to an indirect target path according to the second option is shown, where the target relay UE is in RRC connected state.

[0015] Figure 3b An exemplary signaling diagram for inter-gNB handover to an indirect target path according to the second option is shown, where the target relay UE is out of coverage with respect to the target gNB.

[0016] Figure 3c An exemplary signaling diagram for inter-gNB handover to an indirect target path according to the second option is shown, where the target relay UE is in RRC idle or inactive state.

[0017] Figure 4 An exemplary signaling diagram for inter-gNB handover to an indirect target path according to the third option is shown, where the target relay UE is in RRC connected state.

[0018] Figure 5 Exemplary network arrangements are shown according to various exemplary embodiments.

[0019] Figure 6 An exemplary UE according to various exemplary embodiments is shown.

[0020] Figure 7 An exemplary base station according to various exemplary embodiments is shown.

[0021] Figure 8 An arrangement of various protocol functions that may be implemented in a wireless communication device according to various exemplary embodiments is shown.

[0022] Fig. 9 An exemplary network diagram including a base station, a relay UE, and a remote UE is shown. DETAILED DESCRIPTION

[0023] The exemplary embodiments may be further understood with reference to the following description and associated drawings, in which like elements are provided with like reference numerals. The exemplary embodiments relate to operations for inter-gNB path switching (e.g., handover) for a user equipment (UE), wherein the target path includes a layer 2 (L2) UE to network (U2N) relay. Specifically, the exemplary embodiments relate to a process for selecting a target relay UE by a source gNB to provide an indirect network path between the target gNB and a remote UE after the handover is completed. Importantly, the radio resource control (RRC) state of one or more candidate target relay UEs under the target gNB may be provided to the source gNB and used by the source gNB to select a target relay and / or perform the handover. In some embodiments, the RRC state of the candidate UE is provided to the source gNB before selecting one of the candidate UEs as the target relay. In other embodiments, the source gNB selects the candidate UE as the target relay regardless of the RRC state of the selected target relay. In these embodiments, the RRC state is received from the target gNB before the source gNB initiates the handover process.

[0024] The exemplary embodiments are described with respect to UE. However, the use of UE is provided for illustration purposes only. The exemplary embodiments may be used with any electronic component configured with hardware, software and / or firmware for exchanging information (e.g., control information) and / or data with a network. Therefore, the UE described herein is used to represent any suitable electronic device.

[0025] Exemplary embodiments are also described with reference to a side link (SL). The term "side link" generally refers to a communication link between a UE and another UE. The SL provides direct device-to-device (D2D) communication, wherein information and / or data exchanged between the UE and another UE via the side link does not pass through a cell. In some configurations, a single SL provides two-way data communication between the UE and another UE. In other configurations, a single SL provides unidirectional data communication between the UE and another UE, but signaling may be transmitted in both directions. The term "unicast" refers to one-to-one (i.e., D2D) communication and may generally refer to two-way communication or one-way communication. Various embodiments may be applicable to one or both forms of communication as indicated below.

[0026] Both the Long Term Evolution (LTE) and 5G New Radio (NR) standards support SL communications. In some configurations, the network may provide information to the UE indicating how to establish, maintain and / or utilize the SL. Therefore, when the information and / or data exchanged through the SL does not pass through the cell, the UE and the network may exchange information associated with the SL via the network cell. In other configurations, the SL is not controlled by the network. In either configuration, the first UE and the second UE may still perform a synchronization process, a discovery process and exchange control information corresponding to the SL.

[0027] SL can be used for relay assistance to forward data / signals between the network and a remote UE that is out of range of the network and / or has poor network coverage. For example, a relay UE that is within range of the network and / or has good network coverage can relay data / signals between the network and the remote UE via a SL connection with the remote UE. After successful decoding / encoding and demodulation / modulation of the signal, the Layer 2 (L2) relay amplifies the received signal to the destination.

[0028] A typical network connection without L2 relay may be referred to as a direct network path for a UE, while an L2 relay through an SL may be referred to as an indirect network path for a (remote) UE. In Rel-17, path switching (e.g., handover) from an indirect path to a direct path under the same gNB is supported (intra-gNB handover).

[0029] In Rel-18, path switching will be supported for inter-gNB indirect to direct path switching, inter-gNB direct to indirect path switching, intra-gNB indirect to indirect path switching, and inter-gNB indirect to indirect path switching.

[0030] Figure 1a A first exemplary handover scenario 100 (scenario A) for a user equipment (UE) 102 including an inter-gNB indirect-to-direct path handover is shown. In the first scenario 100, a UE 102 (UE1) transitions from a first communication path (current path) with a first gNB 112 (gNB1) (e.g., source gNB) to a second communication path (target path) with a second gNB 114 (gNB2) (e.g., target gNB). The current path includes an indirect path, such as an L2 relay, where the second UE 104 (UE2) acts as a relay UE for a remote UE1 102. The remote UE1 102 and the relay UE2 104 communicate via a side link (SL) 116, and the relay UE2 104 and the source gNB1 108 communicate via a first direct link 118 (direct 1). The target path includes a direct path, where the UE1 102 and the target gNB2 114 communicate via a second direct link 120 (direct 2).

[0031] Figure 1bA second exemplary handover scenario 140 (scenario B) for a UE 102 including an inter-gNB direct to indirect path switch is shown. In the second scenario 140, a UE 102 (UE1) transitions from a first communication path (current path) with a first gNB 112 (gNB1) (e.g., source gNB) to a second communication path (target path) with a second gNB 114 (gNB2) (e.g., target gNB). The current path includes a direct path, in which UE1 102 and source gNB1 112 communicate via a first direct link 122 (direct 1). The target path includes an indirect path, such as L2 relay, in which a second UE 106 (UE2) acts as a relay UE for a remote UE1 102. The remote UE1 102 and the relay UE2 106 communicate via a side link (SL) 124, and the relay UE2 106 and the target gNB2 114 communicate via a second direct link 126 (direct 2).

[0032] Figure 1c A third exemplary handover scenario 150 (scenario C) for a UE 102 including an intra-gNB indirect-to-indirect path switch is shown. In the third scenario 150, a UE 102 (UE1) switches from a first communication path (current path) with a gNB 108 (gNB1) to a second communication path (target path) with gNB1 112. Similar to the first scenario 100, the current path includes a first indirect path, such as a first L2 relay, where a second UE 104 (UE2) acts as a relay UE for a remote UE1 102. The remote UE1 102 and the relay UE2 104 communicate via a first side link (SL) 116 (sidelink 1), and the remote UE2 104 and the gNB1 112 communicate via a first direct link 118 (direct 1). The target path includes a second indirect path, such as a second L2 relay, where a third UE 108 (UE3) acts as a relay UE for the remote UE1 102. Remote UE1 102 and relay UE3 106 communicate via a second side link (SL) 128 (Side Link 2), and relay UE3 108 and gNB1 112 communicate via a second direct link 130 (Direct 2).

[0033] Figure 1dA fourth exemplary handover scenario 160 (scenario D) for a UE 102 including an inter-gNB indirect-to-indirect path switch is shown. In the fourth scenario 160, the UE 102 (UE1) transitions from a first communication path (current path) with a first gNB 112 (gNB1) (e.g., source gNB) to a second communication path (target path) with a second gNB 114 (gNB2) (e.g., target gNB). Similar to the first scenario 100 and the third scenario 150, the current path includes a first indirect path, such as a first L2 relay, where the second UE 104 (UE2) acts as a relay UE for the remote UE1 102. The remote UE1 102 and the relay UE2 104 communicate via a first side link (SL) 116 (sidelink 1), and the relay UE2 104 and the source gNB1 112 communicate via a first direct link 118 (direct 1). The target path includes a second indirect path, such as a second L2 relay, in which a third UE 110 (UE3) acts as a relay UE for the remote UE1 102. The remote UE1 102 and the relay UE3 110 communicate via a second side link (SL) 132 (Side Link 2), and the relay UE3 110 and the target gNB2 110 communicate via a second direct link 134 (Direct 2).

[0034] With respect to the first handover scenario 100 (Scenario A—Inter-gNB Indirect to Direct Path Handover), existing procedures may be adapted to support this scenario. For example, a remote UE using a current communication path with a first gNB (gNB1) (e.g., source gNB) including an indirect path (L2 relay) may report neighbor cell measurements to source gNB1 via a relay UE according to currently supported UE reporting procedures. Thus, the remote UE may report channel measurements for a second gNB (gNB2) (e.g., target gNB) to source gNB1, and source gNB1 may prepare the remote UE and target gNB2 for a UE handover to target gNB2 including a direct target path.

[0035] In scenarios where the target path is an indirect path (scenario B, C, and D), it may be preferable to select the UE to act as a target relay UE when the UE is in an RRC connected state with the target gNB. For example, if a relay UE is selected that is in an RRC idle or inactive state with the target gNB, the target gNB and the relay UE must establish a dedicated RRC connection (e.g., the relay UE must enter a connected state with the target gNB) before the relay UE can relay data / signals between the target gNB and the remote UE, as will be described in more detail below. Therefore, before initiating a path switch for the UE, the source gNB may preferably know whether the target relay UE is in a connected state.

[0036] With respect to the third handover scenario 150 (Scenario C—Intra-gNB Indirect to Indirect Path Handover), where a single gNB is both the source gNB and the target gNB, the gNB has knowledge of the RRC state of the UE that may be selected as the target relay UE. The gNB may select the target relay UE based on the gNB specific implementation, and may perform different handover procedures based on whether the target relay UE is in a connected state or an idle / inactive state, which will be described in more detail below.

[0037] With respect to the second handover scenario 140 and the fourth handover scenario 160 (Scenario B—Inter-gNB direct to indirect path handover; Scenario D—Inter-gNB indirect to indirect path handover), at least two gNBs are involved in the handover, e.g., a source gNB and a target gNB. The source gNB making the path switch decision does not have direct knowledge of the RRC state of the UE that may be selected as the target relay UE under the target gNB.

[0038] As mentioned above, the handover procedure to the indirect path depends on the RRC state of the target relay UE. According to the Rel-17 procedure for intra-gNB path switching from a direct path to an indirect path (e.g., handover from a direct path under a gNB to an indirect path using a relay UE under the same gNB), the gNB and the remote UE may use a first connection establishment procedure when the target relay UE is in a connected state, and may use a second connection establishment procedure when the target relay UE is in an idle / inactive state.

[0039] In the first process, with the target relay UE in a connected state, the gNB controls the handover operation and prepares the relay UE for a remote UE handover (e.g., a gNB-controlled method). The gNB selects a relay UE and prepares the relay UE for a handover in an RRC reconfiguration message that includes, for example, P5 relay RLC channel information and bearer mapping configuration for SL communication with the remote UE. The gNB then transmits a handover command (RRC reconfiguration) to the remote UE including similar information (about the relay UE) for the remote UE to establish a SL with the relay UE. The handover command includes a dedicated RLC channel configuration so that the UE can transmit a handover complete message (RRC reconfiguration complete message) using the relay UE via the L2U2N relay. The data path is then switched to an indirect path, and the remote UE can send / receive additional data / signaling on the indirect path.

[0040] In the second process, the remote UE may trigger the relay UE to enter a connected state (e.g., a UE-assisted method) while the target relay UE is in an idle or inactive state. The gNB selects the relay UE and transmits a handover command to the remote UE without first preparing the relay UE for handover. In this process, the handover command does not include a dedicated RLC channel configuration for use by the UE, so the remote UE must use the default RLC channel configuration to establish a PC5 link with the relay UE. The remote UE then transmits an RRC reconfiguration complete message to the relay UE, which triggers the relay UE to enter a connected state and relay the reconfiguration complete message to the gNB. The gNB then reconfigures the connected relay UE to establish an indirect path, and the remote UE may send / receive additional data / signaling on the indirect path via the relay UE.

[0041] Before performing the above-mentioned connection establishment process, the source gNB considers which target relay UE to select for UE handover to the indirect path. In order to provide candidate relay UEs to the source gNB, the remote UE may perform a discovery process. The discovery process may include transmitting a relay discovery message and monitoring the side link for a relay discovery message from the candidate relay UE. The discovery process may include the remote UE broadcasting a layer 2 (L2) U2N relay discovery query. The candidate UE receiving the broadcast may transmit an L2 U2N relay discovery response to the remote UE including one or more reference signals (RS), which are measured by the remote UE to determine channel state information (CSI), e.g., RSRP, for the SL channel to be used in SL communication with the candidate UE. The relay discovery response also includes serving cell information and the L2 ID of the candidate relay UE. In some scenarios, the candidate target relay UE may broadcast the L2 U2N relay announcement without first receiving a discovery query. The remote UE provides the source gNB with channel measurements, serving cell information, and L2 ID of each candidate UE in a measurement report. The source gNB selects a target relay UE taking into account the candidate UEs included in one or more measurement reports received from the remote UE. The target relay UE selection process is performed based on the gNB specific implementation and may be performed based on factors such as the RRC state of the candidate relay UE, the SL channel strength between the remote UE and the candidate relay UE, and any other factors that may be based on specific implementation details or defined in the standard.

[0042] In Rel-17, only intra-gNB direct to indirect path handover was supported. Therefore, in these procedures, the serving gNB has direct knowledge of the RRC state of all candidate relay UEs because only the serving gNB is involved in the handover. However, returning to scenario B (inter-gNB direct to indirect path handover) and scenario D (inter-gNB indirect to indirect path handover) which will be supported in Rel-18 as discussed above, at least two gNBs will be involved in the handover, e.g., the source gNB and the target gNB. The source gNB making the path switching decision has direct knowledge of the RRC state of potential UEs that may be selected as target relay UEs (under the target gNB) because the RRC state information of these UEs is not included in the relay discovery message received by the remote UE from the candidate UEs.

[0043] Note that a UE connected to a source gNB before being handed over to an indirect path on a target gNB is referred to herein as a “remote UE” even if the connection to the source gNB is a direct connection (e.g. Figure 1b The term “remote” refers to the UE after the handover when an indirect path is established with the target gNB via a relay UE, and should not be interpreted as implying that the UE must have an indirect path with the source gNB (e.g., as in Figure 1d 160).

[0044] In accordance with various exemplary embodiments described herein, a variety of approaches may be considered for an inter-gNB handover of a UE from a current path on a first (source) gNB to an indirect target path on a second (target) gNB. As described above, there is currently no process for providing the source gNB with RRC state information for candidate relay UEs served by a target gNB. Without the RRC state information for these candidate relay UEs, the source gNB cannot make a fully informed decision when selecting one of these candidate UEs as the target relay UE for a handover to an indirect path. Additionally, without first knowing the RRC state of the target relay UE, the source gNB cannot determine whether to initiate a gNB-controlled handover procedure or a UE-assisted handover procedure.

[0045] In the first option, the source gNB may select a target relay UE from one or more candidate UEs for remote UE handover regardless of the current RRC state of the candidate UEs. The source gNB may select the target relay UE based on gNB specific implementation, taking into account channel measurements for the candidate UEs provided by the remote UE in one or more measurement reports. However, once the target relay UE is selected, the source gNB must communicate with the target gNB to receive the RRC state information of the target relay UE. With the RRC state information, the source gNB knows whether the target relay UE is ready for handover and triggers the appropriate handover procedure.

[0046] Regardless of the RRC state of the selected target relay UE, the source gNB may transmit a handover prepare message identifying the target relay UE to the target gNB. If the target relay UE is in a connected state, the target gNB may reconfigure the target relay UE for L2 U2N relaying, and the source gNB may reconfigure the remote UE for handover (e.g., with a gNB-controlled handover method), as described below. Figure 2a If the target relay UE is idle or inactive, the source gNB may configure the remote UE to establish an indirect path with the target relay UE from the UE side (e.g., UE-assisted method), as described below. Figure 2b Explained in .

[0047] Figure 2a An exemplary signaling diagram 200 for an inter-gNB handover to an indirect target path according to a first option is shown, wherein the target relay UE is in an RRC connected state. In this example, the inter-gNB handover process includes handing over on a second (target) gNB 208 to a first (remote) UE 202 served by a first (source) gNB 206 for an indirect target path including a sidelink with the second (target relay) UE 204 when the target relay UE 204 is in an RRC connected state. The remote UE 202 of the signaling diagram 200 may correspond to Figure 1b , Figure 1d UE1 102 described in; Figure 5 or Figure 6 UE 510 described in; or below in Fig. 9 The target relay UE 204 of the signaling diagram 200 may correspond to the remote UE 915 described in Figure 1b UE2 106 described in or Figure 1d UE3 110 described in; hereinafter Figure 5 UE 512 described in or below in Figure 6 UE 510 described in; or below in Fig. 9 The source gNB 206 of the signaling diagram 200 may correspond to the relay UE 910 described in Figure 1b , Figure 1d gNB1 112 as described in ; or as described below in Figure 5 or Figure 7 The target gNB 208 of the signaling diagram 200 may correspond to the gNB 520A described in Figure 1b , Figure 1d gNB2 114 described in Figure 5 gNB 520B described in or below in Figure 7 or the gNB 520A described in Fig. 9Base station 905 described in.

[0048] In 212, the remote UE 202 receives a L2 U2N relay discovery message from a (candidate) target relay UE 204. The discovery message may be transmitted by the candidate UE 204 in response to a query from the remote UE 202 and / or in a relay advertisement. The remote UE 202 may measure channel quality and decode information including relay UE ID and serving cell information (e.g., for the target gNB 208) from the candidate UE 204. Note that the remote UE 202 may receive and decode multiple L2U2N relay discovery messages from multiple candidate target relay UEs.

[0049] In 214, remote UE 202 transmits a measurement report including a relay UE ID and serving cell information associated with channel measurement results for (candidate) target relay UE 204. Remote UE 202 may transmit measurement results for one or more candidate target relay UEs in one or more measurement reports. The measurement report may include measurements for candidate UEs under one or more serving cells. Source gNB 206 receives one or more measurement reports for one or more candidate UEs.

[0050] In 216, source gNB 206 evaluates the measurement results of one or more candidate target relay UEs (including (candidate) target relay UE 204), and selects relay UE 204 under gNB 208 as target relay UE 204. Source gNB 206 selects relay UE 204 as target relay regardless of the current RRC state of relay UE 204. Note that additional candidate UEs served by source gNB 206 may be available for selection. In this scenario, source gNB 206 may have RRC state information for these additional candidate UEs, and the selection of relay UE 204 as target relay may be informed by the RRC state of the additional candidate UEs under source gNB 206.

[0051] In 218, source gNB 206 transmits a handover prepare message to gNB 208, which is a target gNB 208 serving target relay UE 204. The handover prepare message includes the relay UE ID of the target relay UE 204. In addition, the handover prepare message includes the layer 2 address of the remote UE 202 and the corresponding local identifier of the remote UE 202 to be used in SRAP (Sidelink Relay Adaptation Protocol). In some embodiments, source gNB 206 may generate the local identifier so that it can be uniquely identified by the network among all remote UEs associated with layer 2 UEs to network relay UEs.

[0052] In 220, the target gNB 208 identifies the current RRC state of the target relay UE 204. In the example of the signaling diagram 200, the target relay UE 204 is in the RRC connected state.

[0053] In 222, the target gNB 208 prepares the target relay UE 204 for handover. The handover preparation includes an RRC reconfiguration message including remote UE 202 information (such as an L2 address) and relay path parameters, such as parameters for the target relay UE 204 to establish an L2U2N relay with the remote UE 202.

[0054] In 224, the target gNB 208 receives an RRC reconfiguration complete message indicating that the target relay UE 204 is prepared for handover.

[0055] At 226, the target gNB 208 transmits a handover preparation complete message to the source gNB 206 indicating that the target relay UE 204 is prepared for handover. The source gNB 206 receives the handover preparation complete message and determines that the target relay UE 204 is in the RRC connected state. Therefore, the gNB-controlled handover process can be used for the remote UE 202.

[0056] In 228, the source gNB 206 transmits a handover command (RRC reconfiguration) to the remote UE 202, the handover command including parameters for the remote UE to establish a SL with the relay UE, including a dedicated RLC channel configuration for the UE to transmit a handover complete message (RRC reconfiguration complete message) via the L2 U2N relay using the relay UE, as described above. The handover command also includes parameters for the remote UE 202 to synchronize with the target gNB 208. The data path is then switched to the indirect path, and the remote UE can send / receive additional data / signaling on the indirect path.

[0057] Figure 2b An exemplary signaling diagram 230 for an inter-gNB handover to an indirect target path according to the first option is shown, where the target relay UE is in RRC idle or inactive state. Figure 2a 200, the inter-gNB handover process includes handing over on a second (target) gNB 208 to a first (remote) UE 202 served by a first (source) gNB 206 over an indirect target path including a sidelink with a second (target relay) UE 204. Figure 2a In signaling diagram 200, remote UE 202 may correspond to UE1 102; target relay UE 204 may correspond to UE2 106 or UE3 110; source gNB 206 may correspond to gNB1112; and target gNB 208 may correspond to gNB2 114.

[0058] Steps 232 to 240 may be similar to Figure 2a 212 to 220 of the signaling diagram 230. However, in the example of the signaling diagram 230, in step 240, the target gNB 208 identifies the current RRC state of the target relay UE 204 as an RRC idle or inactive state. Therefore, in this example, the target gNB 208 cannot reconfigure the target relay UE 208 for handover until the target relay UE 208 enters the RRC connected state.

[0059] At 242, the target gNB 208 transmits a handover preparation complete message to the source gNB 206 indicating that the target relay UE 204 is not prepared for handover. The source gNB 206 receives the handover preparation complete message and determines that the target relay UE 204 is not in the RRC connected state. Therefore, the UE-assisted handover procedure can be used for the remote UE 202.

[0060] In 244, the source gNB 206 transmits a handover command (RRC reconfiguration) to the remote UE 202. Because the target relay UE 204 is not prepared for handover, the handover command to the remote UE 202 does not include a dedicated RLC channel configuration for the remote UE 202 to use for SL communication with the target relay UE 204. Therefore, the remote UE 202 uses the default RLC channel configuration to establish a PC5 link with the relay UE 204 and transmits an RRC reconfiguration complete message to the relay UE 204. In this UE-assisted handover process, the target relay UE 204 is unaware that it has been selected as the relay UE for the remote UE 202 because it is unprepared. Receiving the RRC reconfiguration complete message from the remote UE 202 triggers the relay UE 204 to enter the connected state and relay the reconfiguration complete message to the target gNB 208. After the relay UE 204 is triggered by the PC5 link establishment procedure to enter the RRC connected state, the relay UE 204 will be prepared for handover. The gNB 208 then reconfigures the connection relay UE 204 to establish an indirect path. The remote UE may send / receive additional data / signaling on the indirect path via the relay UE.

[0061] As described above, according to the first exemplary option, the gNB selects a target relay UE without knowing in advance whether the selected relay UE is already in a connected state with the target gNB. It is possible that the selection of the target relay UE is inappropriate and will result in a handover failure. For example, the target relay UE may no longer be pre-camped in the cell of the target gNB. In another example, the waiting time for handover to an idle or inactive target relay UE may be too long, and the source gNB may prefer to connect the target relay UE so that the handover waiting time is shorter.

[0062] Therefore, the source gNB may preferably know whether one or more candidate target relay UEs are in a connected state. This information may be obtained by the source gNB according to the second option, the third option and / or the fourth option described below.

[0063] In the second option, the source gNB may query one or more target gNBs for RRC state information of one or more candidate target relay UEs before selecting a target relay UE for remote UE handover. Thus, the source gNB may evaluate the candidate relay UEs in view of the RRC state information for the candidate UEs to determine a preferred candidate UE to be selected as the target relay UE.

[0064] According to the second option, the target gNB may identify one of three states for the candidate target relay UE identified in the query. The first state for the candidate target relay UE is the RRC connected state; the second state for the candidate target relay UE is the RRC idle / inactive state; the third state for the candidate target relay UE is the out of coverage state, where the candidate UE is no longer in the cell of the target gNB, for example, has been handed over to another cell.

[0065] The target gNB may transmit a response to the relay query, the response including an indication of whether the identified target relay UE is in a connected state (connected), not in a connected state (unknown), or no longer in its cell (abnormal). The source gNB may receive the response and, given knowledge of the current state of one or more candidate target relay UEs, may perform additional operations for handing over the remote UE to an indirect path, as described below in Figure 3a to Figure 3c Described in detail in .

[0066] Figure 3a An exemplary signaling diagram 300 for an inter-gNB handover to an indirect target path according to the second option is shown, wherein the target relay UE is in an RRC connected state. Figure 2a 200, the inter-gNB handover process includes handing over on a second (target) gNB 308 to a first (remote) UE 302 served by a first (source) gNB 306 including an indirect target path with a sidelink to the second (target relay) UE 304 when the target relay UE 304 is in an RRC connected state. Figure 2a to Figure 2b 200 and 230, the remote UE 302 may correspond to UE1 102; the target relay UE 304 may correspond to UE2 106 or UE3 110; the source gNB 306 may correspond to gNB1 112; and the target gNB 308 may correspond to gNB2 114.

[0067] Steps 312 to 314 may be similar to Figure 2a The remote UE 302 receives at least one L2 U2N relay discovery message from at least one (candidate) target relay UE (including the candidate target relay UE 304). Similar to the above, the remote UE 302 may receive and decode multiple L2 U2N relay discovery messages from multiple candidate target relay UEs. The remote UE 302 transmits a measurement report including a relay UE ID and serving cell information associated with channel measurement results for one or more candidate UEs including the candidate UE 304. The measurement report may include measurements for candidate UEs under one or more serving cells. The source gNB 306 receives one or more measurement reports for one or more candidate UEs.

[0068] In 316, source gNB 306 evaluates measurement results of one or more candidate target relay UEs (including (candidate) target relay UE 304) and identifies one or more candidate target relay UEs with currently unknown RRC states. For example, source gNB 306 may seek to obtain the current RRC states of all candidate UEs or a subset of candidate UEs under one or more serving cells.

[0069] In 318, the source gNB 306 transmits a relay query request to one or more serving gNBs of one or more candidate target relay UEs, including the (candidate) target gNB 308 of the (candidate) target relay 304. For example, in 316, the source gNB 306 may determine that a plurality of different candidate target relay UEs are suitable for handover of the remote UE 302 based on measurement results for these candidate UEs. Thus, the source gNB 306 may transmit the relay query request to a plurality of cells including the target gNB 308 serving the candidate target relay UE 304 selected in 324, which will be described in further detail below.

[0070] In 320, the (candidate) target gNB 308 identifies the current state of the (candidate) target relay UE 304. As described, the current state of the candidate UE 304 can be an RRC connected state, an RRC idle or inactive state, or out of coverage. In the example of the signaling diagram 300, the target relay UE 304 is in the RRC connected state.

[0071] In 322, the (candidate) target gNB 308 transmits a relay query response to the source gNB 306 indicating that the target relay UE 304 is in the RRC connected state. The source gNB 306 receives the response message. Note that in this option, the receipt of the message indicating the connected state for the candidate UE 304 does not automatically trigger the selection of the candidate UE 304 as the target relay UE 304. Based on the responses received from one or more (candidate) target gNBs related to one or more (candidate) target relay UEs, the source gNB 302 is free to select the other candidate relay UE if it is also known that a more suitable candidate UE is in the connected state.

[0072] In 324, the source gNB 306 selects the candidate target relay UE 304 under gNB 308 as the target relay UE.

[0073] Steps 326 to 334 may be similar to Figure 2a The source gNB 306 transmits a handover preparation message to the gNB 308 which is the target gNB 308 serving the target relay UE 304. The target gNB 308 prepares the target relay UE 204 for handover, including transmitting an RRC reconfiguration and receiving an RRC reconfiguration complete message. The target gNB 308 transmits a handover preparation complete message to the source gNB 306 indicating that the target relay UE 304 is prepared for handover. Therefore, the gNB-controlled handover process is available for the remote UE 302, and the source gNB 306 transmits a handover command (RRC reconfiguration) to the remote UE 302, the handover command including parameters for the remote UE 302 to establish a SL with the relay UE, the parameters including a dedicated RLC channel configuration for the UE to transmit a handover complete message (RRC reconfiguration complete message) using the relay UE via the L2 U2N relay, as described above. The data path is then switched to the indirect path, and the remote UE may send / receive further data / signaling over the indirect path.

[0074] Figure 3b An exemplary signaling diagram 340 for an inter-gNB handover to an indirect target path according to the second option is shown, where the target relay UE is out of coverage with respect to the target gNB. Figure 3a 300, an inter-gNB handover procedure includes a first (remote) UE 302 served by a first (source) gNB 306 and a second (target relay) UE 304. However, in this example, the target relay UE 304 is no longer served by the second (target) gNB 308. For example, the target relay UE 304 may have been handed over to another cell.

[0075] Steps 342 to 350 may be similar to Figure 3a The corresponding steps 312 to 320 are performed. As described, the current state of the candidate UE 304 can be an RRC connected state, an RRC idle or inactive state, or out of coverage. In the example of the signaling diagram 340, in step 350, the target gNB 308 determines that the target relay UE 304 is out of coverage.

[0076] In 352, the (candidate) target gNB 308 transmits a relay query response indicating that the candidate target relay UE 304 is out of coverage (Relay UE ID = Abnormal) to the source gNB 306. The source gNB 306 receives the response message.

[0077] In 354, source gNB 306 performs additional handover actions based on the knowledge that candidate UE 304 is outside the coverage of candidate target gNB 308. For example, source gNB 306 may select a different candidate target relay UE than candidate UE 304, or contact a different gNB that is currently serving candidate UE 304.

[0078] Figure 3c An exemplary signaling diagram 360 for an inter-gNB handover to an indirect target path according to the second option is shown, where the target relay UE is in RRC idle or inactive state. Figure 3a 300, an inter-gNB handover process includes a first (remote) UE 302 served by a first (source) gNB 306 and a second (target relay) UE 304 served by a second (target) gNB 308. However, in this example, the candidate target relay UE 304 is in an RRC idle or inactive state under the target gNB 308.

[0079] Steps 362 to 370 may be similar to Figure 3a The corresponding steps 312 to 320 or Figure 3b 342 to 350 are performed. As described, the current state of the candidate UE 304 can be an RRC connected state, an RRC idle or inactive state, or out of coverage. In the example of the signaling diagram 360, in step 370, the target gNB 308 determines that the target relay UE 304 is in an RRC idle / inactive state.

[0080] In 372, the (candidate) target gNB 308 transmits a relay query response indicating that the candidate target relay UE 304 is in RRC idle / inactive state (Relay UE ID = unknown) to the source gNB 306. The source gNB 306 receives the response message.

[0081] In 374, source gNB 306 performs additional handover actions based on the knowledge that candidate UE 304 is in RRC idle / inactive state under candidate target gNB 308. For example, source gNB 306 may select a candidate target relay UE different from candidate UE 304, or select candidate UE 304 as the target relay UE without handover preparation. If candidate UE 304 is selected, a UE-assisted handover procedure may be initiated by source gNB 306.

[0082] As shown above, Figure 3a to Figure 3c The second option described in uses a query / response procedure to provide the source gNB with knowledge of the RRC state of the candidate target relay UEs. However, in the options to be described below, this information may be provided proactively before initiating any handover procedure.

[0083] In a third option, neighboring gNBs may proactively exchange relay UE information that includes the current RRC state of the relay UEs served by the respective gNBs. Thus, the source gNB may evaluate the candidate relay UEs in view of the RRC state information for the candidate UEs to determine a preferred candidate UE to select as the target relay UE. This may be done proactively by having each gNB advertise RRC_CONNECTED Layer 2 UEs to NW relay UEs to its neighboring gNBs. In this way, each gNB is able to maintain a list of "connected" relays in its own cell and neighboring cells.

[0084] These information exchanges for relay UEs may occur frequently or infrequently. For example, if the gNB transmits this information infrequently, this option may be used in conjunction with either the first option or the second option discussed above. If the source gNB making the handover decision determines that the information received for the relay UE from a given neighboring gNB is stale or outdated, the source gNB may implement the first option or the second option described above.

[0085] In another example, if the gNB transmits this information frequently, the source gNB may consider the relayed UE information as current and make handover decisions based on it. However, this approach may involve significantly more signaling overhead.

[0086] As described above, according to the second exemplary option and the third exemplary option, the neighboring gNBs may exchange a relatively large number of messages to provide the current RRC state information for the relay UE. Therefore, it may be preferable to use a method that reduces the message transmission overhead while still providing the source gNB with RRC state information before the target relay selection phase of the handover process.

[0087] In a fourth option, the remote UE may obtain the RRC state of the candidate target relay UE directly from the corresponding candidate UE. The candidate relay UE may provide the RRC information in the relay discovery response message, and the remote UE may include the RRC state in the measurement report to the source gNB associated with the relay UE ID and the serving cell information.

[0088] Figure 4 An exemplary signaling diagram 400 for an inter-gNB handover to an indirect target path according to the third option is shown, wherein the target relay UE is in an RRC connected state. Figure 2a 200, the inter-gNB handover process includes handing over on a second (target) gNB 408 to a first (remote) UE 402 served by a first (source) gNB 406 including an indirect target path with a sidelink to the second (target relay) UE 404 when the target relay UE 404 is in an RRC connected state. Figure 2a to Figure 2b 200 and 230, the remote UE 402 may correspond to UE1 102; the target relay UE 404 may correspond to UE2 106 or UE3 110; the source gNB 406 may correspond to gNB1 112; and the target gNB 408 may correspond to gNB2 114.

[0089] In 412 , remote UE 402 transmits a relay discovery query. The query may include a request for the current RRC state from a responding relay UE, or the inclusion of this information may be automatically triggered upon receipt of the query. The relay discovery query is received by a candidate target relay UE 404 .

[0090] In 414, the candidate target relay UE 404 transmits a relay discovery response to the remote UE 402 including an indication of the current RRC state of the candidate UE 404. In this example, the response includes an indication that the candidate target relay UE 404 is in an RRC connected state under its serving cell (e.g., the candidate target gNB 408).

[0091] In 416, the remote UE 402 transmits a measurement report to the source gNB 406, the measurement report including the relay UE ID, serving cell information, and current RRC state associated with the channel measurement results for the (candidate) target relay UE 404. Similar to the above, one or more measurement reports for one or more candidate target relay UEs may be transmitted.

[0092] Steps 418 to 420 may be similar to Figure 3aThe source gNB 402 selects the candidate UE 404 as the target relay UE and transmits a handover preparation command including the relay UE ID of the target relay UE 404 to the target gNB 408. In 422, the target gNB 408 identifies the target relay UE 404. In 424, the target gNB 408 reconfigures the target relay UE 404 for handover.

[0093] Figure 5 An exemplary network arrangement 500 according to various exemplary embodiments is shown. The exemplary network arrangement 500 includes UEs 510, 512. Those skilled in the art will appreciate that UEs 510, 512 may be any type of electronic component configured to communicate via a network, such as a mobile phone, a tablet computer, a desktop computer, a smart phone, a tablet phone, an embedded device, a wearable device (e.g., HMD, AR glasses, etc.), an Internet of Things (IoT) device, etc. It should also be understood that an actual network arrangement may include any number of UEs used by any number of users. Therefore, an example with two UEs 510, 512 is provided for illustrative purposes only.

[0094] UE 510, 512 can communicate directly with one or more networks. In the example of network configuration 500, the network with which UE 510, 512 can wirelessly communicate is 5G NR radio access network (5GNR-RAN) 520, LTE radio access network (LTE-RAN) 522 and wireless local area network (WLAN) 524. These types of networks support side link (SL) communication. In the exemplary network arrangement 500, UE 510 and UE 512 can be connected via SL. However, UE 510, 512 can also communicate with other types of networks, and UE 510, 512 can also communicate with the network through a wired connection. Therefore, UE 510, 512 may include a 5G NR chipset communicating with 5G NR-RAN 520, an LTE chipset communicating with LTE-RAN 522, and an ISM chipset communicating with WLAN 524.

[0095] 5G NR-RAN 520 and LTE-RAN 522 may be part of a cellular network that may be deployed by a network operator (e.g., Verizon, AT&T, T-Mobile, etc.). These networks 520, 522 may include, for example, cells or base stations (NodeB, eNodeB, HeNB, eNBS, gNB, gNodeB, macrocell, microcell, small cell, femtocell, etc.) configured to send and receive traffic from UEs equipped with appropriate cellular chipsets. WLAN 524 may include any type of wireless local area network (WiFi, hotspot, IEEE 802.11x network, etc.).

[0096] UE 510, 512 may be connected to 5G NR-RAN via gNB 520A or gNB 520B. Reference to two gNBs 520A, 520B is for illustrative purposes only. Exemplary embodiments may apply to any appropriate number of gNBs. UE 510, 512 may also be connected to LTE-RAN 522 via eNBs 522A, 522B. Those skilled in the art will appreciate that any association process may be performed for UE 510, 512 to connect to 5G NR-RAN 520 and LTE-RAN 522. For example, as discussed above, 5G NR-RAN 520 and LTE-RAN 522 may be associated with a particular cellular provider at which UE 510, 512 and / or its user has contract and credential information (e.g., stored on a SIM card). Upon detecting the presence of 5G NR-RAN 520, UE 510, 512 may transmit corresponding credential information to associate with 5G NR-RAN 520. More specifically, UE 510, 512 may associate with a specific base station (e.g., gNB 520A of 5G NR-RAN 520, eNB 522A of LTE-RAN 522).

[0097] UE 510, 512 may also communicate directly with each other using SL. SL is a direct device-to-device (D2D) communication link. Therefore, information and / or data transmitted directly to another endpoint (e.g., UE 510 or UE 512) does not pass through the cell (e.g., gNB 520A, eNB 522A). In some embodiments, UE 510, 512 may receive information from the cell about how to establish, maintain and / or utilize SL. Therefore, the network (e.g., 5G NR-RAN 520, LTE-RAN 522) may control SL. In other embodiments, UE 510, 512 may control SL. Regardless of how SL is controlled, UE 510, 512 may simultaneously maintain downlink / uplink to the currently occupied cell (e.g., gNB 520A, eNB 522A) and SL to another UE.

[0098] In some scenarios, a UE (e.g., UE 510) may not have a direct connection to a cell, and another UE (e.g., UE 512) may be used as a relay UE to forward data / signals to / from UE 510 and / or 5G NR-RAN 520. SL may be used for relay assistance to forward data / signals between 5G NR-RAN 520 and a remote UE 510 that is out of range of the network and / or has poor network coverage. After successful decoding / encoding and demodulation / modulation of the signal, the Layer 2 (L2) UE-to-Network (U2N) relay amplifies the received signal to the destination.

[0099] In addition to the networks 520, 522, and 524, the network arrangement 500 also includes a cellular core network 530, the Internet 540, an IP multimedia subsystem (IMS) 550, and a network service backbone 560. The cellular core network 530 can be viewed as a collection of interconnected components that manage the operation of the cellular network and traffic. The cellular core network 530 also manages traffic flowing between the cellular network and the Internet 540. The IMS 550 can generally be described as an architecture for delivering multimedia services to UEs 510, 512 using IP protocols. The IMS 550 can communicate with the cellular core network 530 and the Internet 540 to provide multimedia services to the UEs 510, 512. The network service backbone 560 communicates directly or indirectly with the Internet 540 and the cellular core network 530. The network service backbone 560 can generally be described as a set of components (e.g., servers, network storage arrangements, etc.) that implement a set of services that can be used to extend the functionality of the UEs 510, 512 to communicate with various networks.

[0100] Figure 6 An exemplary UE 510 is shown according to various exemplary embodiments. The UE 510 sends Figure 5 UE 510 may also represent any of the UEs 102-110 described above with respect to FIGS. 1 to 4. UE 510 may include a processor 605, a memory arrangement 610, a display device 615, an input / output (I / O) device 620, a transceiver 625, and other components 630. Other components 630 may include, for example, an audio input device, an audio output device, a power supply, a data acquisition device, a port for electrically connecting UE 510 to other electronic devices, and the like.

[0101] The processor 605 may be configured to execute a number of engines of the UE 510. For example, the engines may include a L2 U2N relay engine 635 for performing various operations related to the handover process to the indirect path, as described above.

[0102] The engine 635 described above is provided as an application (e.g., a program) executed by the processor 605 for illustrative purposes only. The functions associated with the engine 635 may also be represented as independent combined components of the UE 510, or may be modular components coupled to the UE 510, for example, an integrated circuit with or without firmware. For example, the integrated circuit may include an input circuit system for receiving a signal and a processing circuit system for processing signals and other information. The engine may also be embodied as one application or multiple separate applications. In addition, in some UEs, the functions described for the processor 605 are split between two or more processors (such as a baseband processor and an application processor). The exemplary implementation scheme may be implemented in any of these or other configurations of the UE.

[0103] The memory arrangement 610 may be a hardware component configured to store data related to operations performed by the UE 510. The display device 615 may be a hardware component configured to display data to a user, and the I / O device 620 may be a hardware component that enables a user to enter input. The display device 615 and the I / O device 620 may be separate components, or may be integrated together (such as a touch screen). The transceiver 625 may be a hardware component configured to establish a connection with the 5G NR-RAN 520 and / or any other appropriate type of network. Thus, the transceiver 625 may operate on a variety of different frequencies or channels (e.g., a set of contiguous frequencies).

[0104] Figure 7 An exemplary base station 520A is shown in accordance with various exemplary embodiments. The base station 520A will Figure 5 The network arrangement 500 is described in detail. The base station 520A may represent any access node through which the UE 510 can establish a connection and manage network operations. The base station 520A may also represent Figure 5 Base station 520B or the above-mentioned Figures 1 to Figure 4 Described gNB 112, 114.

[0105] Base station 520A may include a processor 705, a memory arrangement 710, an input / output (I / O) device 715, a transceiver 720, and other components 725. Other components 725 may include, for example, a battery, a data acquisition device, ports for electrically connecting base station 700 to other electronic devices, and the like.

[0106] The processor 705 may be configured to execute a number of engines of the base station 520A. For example, the engines may include the L2 U2N relay engine 730 for performing various operations related to the handover process to the indirect path, as described above.

[0107] The engine 730 described above as an application (e.g., a program) executed by the processor 705 is merely exemplary. The functions associated with the engine 730 may also be represented as a separate combined component of the base station 700, or may be a modular component coupled to the base station 700, such as an integrated circuit with or without firmware. For example, the integrated circuit may include an input circuit system for receiving signals and a processing circuit system for processing signals and other information. In addition, in some base stations, the functions described for the processor 705 are split between multiple processors (e.g., baseband processors, application processors, etc.). The exemplary embodiments may be implemented in any of these or other configurations of the base station.

[0108] The memory 710 may be a hardware component configured to store data related to operations performed by the base station 700. The I / O device 715 may be a hardware component or port that enables a user to interact with the base station 700. The transceiver 720 may be a hardware component configured to exchange data with the UE 510 and any other UE in the system 500. The transceiver 720 may operate on a variety of different frequencies or channels (e.g., a set of continuous frequencies). Therefore, the transceiver 720 may include one or more components (e.g., radio devices) to enable data exchange with various networks and UEs.

[0109] Figure 8 800 illustrates an arrangement of various protocol functions that may be implemented in a wireless communication device according to various exemplary embodiments. Figure 8 An example of a MAC layer 805, an RLC layer 810, and a PDCP layer 815 is shown, which may be collectively referred to as layer 2 (L2) of the protocol stack.

[0110] An instance of MAC 805 may process requests from an instance of RLC 810 via one or more MAC Service Access Points (SAPs) and provide indications thereto. These requests and indications transmitted via the MAC-SAP may include one or more logical channels. MAC 805 may perform mapping between logical channels and transport channels, multiplexing MAC service data units (SDUs) from one or more logical channels onto transport blocks (TBs) delivered to the PHY via transport channels, demultiplexing MAC SDUs from TBs delivered from the PHY via transport channels to one or more logical channels, multiplexing MAC SDUs onto TBs, scheduling information reporting, error correction via HARQ, and logical channel prioritization.

[0111] An instance of RLC 810 may process requests from an instance of PDCP 815 via one or more radio link control service access points (RLC-SAPs) and provide indications thereto. These requests and indications transmitted via the RLC-SAPs may include one or more RLC channels. RLC 810 may operate in a variety of operating modes, including: transparent mode (TM), unacknowledged mode (UM), and acknowledged mode (AM). RLC 810 may perform transfer of upper layer protocol data units (PDUs), error correction through automatic repeat request (ARQ) for AM data transfer, and concatenation, segmentation, and reassembly of RLC SDUs for UM and AM data transfers. RLC 810 may also perform re-segmentation of RLC data PDUs for AM data transfers, reorder RLC data PDUs for UM and AM data transfers, detect duplicate data for UM and AM data transfers, discard RLC SDUs for UM and AM data transfers, detect protocol errors for AM data transfers, and perform RLC re-establishment.

[0112] An instance of PDCP 815 may process requests from an instance of RRC and / or an instance of SDAP via one or more Packet Data Convergence Protocol Service Access Points (PDCP-SAPs) and provide instructions thereto. These requests and instructions transmitted via PDCP-SAPs may include one or more radio bearers. PDCP 815 may perform header compression and decompression of IP data, maintain PDCP sequence numbers (SNs), perform sequential delivery of upper layer PDUs when the lower layer is reestablished, eliminate duplication of lower layer SDUs when the lower layer is reestablished for a radio bearer mapped on RLC AM, encrypt and decrypt control plane data, perform integrity protection and integrity verification on control plane data, control timer-based data discard, and perform security operations (e.g., encryption, decryption, integrity protection, integrity verification, etc.).

[0113] Layer 2 (L2) User Device to Network (U2N) relay enables a remote device (eg, a wearable device such as a watch) to access a cellular network via a relay device (eg, a wireless phone).

[0114] Fig. 9An exemplary network diagram 900 is shown including a base station 905, a relay UE 910, and a remote UE 915. The relay UE 910 is shown as being within the coverage area of ​​the base station 905 and being able to exchange signaling / data with the base station 905, while the remote UE 915 is shown as not being in the service of the base station 905. However, in some exemplary embodiments described herein, the remote UE 915 may be within the coverage area of ​​the base station 905 and exchange signaling / data with it. The relay UE 910 and the remote UE 915 may be connected via a SL configured as an L2 relay by the network.

[0115] Relaying is performed above the RLC sublayer for both user plane and control plane protocol architectures. The Uu interface for PDCP and RRC terminates between the remote UE and the gNB, while the RLC, MAC and PHY and non-3GPP transport layers terminate in each link (remote UE to relay UE, and relay UE to network).

[0116] Example

[0117] In a first embodiment, a processor of a base station is configured to perform operations including: receiving a relay query request from a serving cell of a first user equipment (UE), wherein the serving cell of the first UE is a source cell for handover of the first UE, the relay query request including a relay identifier of a second UE indicated as a target relay UE for layer 2 (L2) UE to network (U2N) relay under the base station; identifying whether the second UE is in a first state including a radio resource control (RRC) connected state, a second state including an RRC idle or inactive state, or a third state in which the second UE is outside the coverage of the base station; and transmitting a relay query response to the serving cell of the first UE, the relay query response including an indication of whether the second UE is in the first state, the second state, or the third state.

[0118] In a second embodiment, according to the processor of the first embodiment, the relay query response indicates that the second UE is in the RRC connected state under the serving cell.

[0119] In a third embodiment, the processor according to the second embodiment, wherein the operations further comprise receiving a handover prepare message from the serving cell of the source UE, the handover prepare message comprising the relay identifier of the second UE.

[0120] In a fourth embodiment, according to the processor of the first embodiment, the relay query response indicates that the second UE is in the RRC idle or inactive state under the serving cell.

[0121] In a fifth embodiment, the processor according to the first embodiment, wherein the relay query response indicates that the second UE is out of coverage of the serving cell.

[0122] In a sixth embodiment, according to the processor of the first embodiment, the operation further comprises: periodically transmitting information for the relay UE in the RRC connected state under the base station to a neighboring base station.

[0123] In a seventh embodiment, according to the processor of the first embodiment, the operation further comprises: periodically receiving information for the relay UE in the RRC connected state under the base station from a neighboring base station.

[0124] In an eighth embodiment, a processor of a user equipment (UE) is configured to perform operations including: a transport layer 2 (L2) UE to network (U2N) relay discovery query; receiving a L2U2N discovery response from another UE that can serve as a target relay UE for L2 U2N relay under a target serving cell, the discovery response including a first indication of a current radio resource control (RRC) state of the other UE under the target serving cell; and transmitting a measurement report to a serving cell, the measurement report including a channel measurement result for a side link channel with the other UE and a second indication of the current RRC state of the other UE under the target serving cell.

[0125] In a ninth embodiment, a processor of a base station is configured to perform operations including: receiving a measurement report from a first user equipment (UE), the measurement report including a channel measurement result for a side link channel with at least a second UE, the at least second UE being capable of being used as a candidate relay UE for a layer 2 (L2) UE to network (U2N) relay, the measurement report also including a relay identifier of the second UE and service cell information for a service cell, the measurement report also including a current radio resource control (RRC) state of the second UE and the service cell of the second UE; selecting the second UE as a target relay UE for the first UE based on the current RRC state; and transmitting a handover preparation message to the target service cell of the target relay UE, wherein the service cell of the target relay UE is a target cell for handover of the first UE, and the handover preparation message includes the relay identifier of the second UE.

[0126] In a tenth embodiment, a processor of a base station is configured to perform operations including: receiving a measurement report from a first user equipment (UE), the measurement report including a channel measurement result for a side link channel with at least a second UE, the at least second UE being capable of being used as a candidate relay UE for a layer 2 (L2) UE to network (U2N) relay, the measurement report also including a relay identifier of the second UE and service cell information for a service cell; periodically receiving information from one or more neighboring base stations indicating that the relay UE is in a radio resource control (RRC) connected state under the one or more neighboring base stations; determining from the received information that the second UE is in the RRC connected state under one of the neighboring base stations; and selecting the second UE as a target relay UE for the first UE based on the second UE being in the RRC connected state.

[0127] Those skilled in the art will appreciate that the exemplary embodiments described above may be implemented with any suitable software configuration or hardware configuration or combination thereof. Exemplary hardware platforms for implementing the exemplary embodiments may include, for example, Intel x86-based platforms with compatible operating systems, Windows OS, Mac platforms and MAC OS, mobile devices with operating systems such as iOS, Android, etc. In other examples, the exemplary embodiments of the above methods may be embodied as a program including lines of code stored on a non-transitory computer-readable storage medium, which, when compiled, may be executed on a processor or microprocessor.

[0128] Although this application describes various embodiments, each having different features in various combinations, those skilled in the art will understand that any feature of one embodiment may be combined with features of other embodiments in any manner that is not expressly negated or that is not functionally or logically inconsistent with the operation of the device or the prescribed function of the disclosed embodiment.

[0129] It is understood that the use of personally identifiable information should be subject to privacy policies and practices that are generally recognized to meet or exceed industry or government requirements for maintaining user privacy. Specifically, personally identifiable information data should be managed and processed to minimize the risk of unintentional or unauthorized access or use, and the nature of the authorized use should be clearly stated to users.

[0130] It will be apparent to those skilled in the art that various modifications may be made to the present disclosure without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is intended to cover modifications and variations of the present disclosure, provided that these modifications and variations are within the scope of the appended claims and their equivalents.

Claims

1. A processor of a base station, the processor being configured to perform operations including: receiving a measurement report from a first user equipment (UE), the measurement report including a channel measurement result for a sidelink channel with at least a second UE, the second UE being capable of serving as a candidate relay UE for a layer 2 (L2) UE-to-network (U2N) relay, the measurement report also including a relay identifier of the second UE and serving cell information for a serving cell; selecting the second UE as a target relay UE for the first UE regardless of a current radio resource control (RRC) state of the second UE and the serving cell of the second UE; and A handover preparation message is transmitted to the serving cell of the target relay UE, wherein the serving cell of the target relay UE is a target cell for handover of the first UE, and the handover preparation message includes the relay identifier of the target relay UE.

2. The processor of claim 1, wherein the handover prepare message further comprises a layer 2 address of the first UE and a corresponding local identifier of the first UE to be used in a Sidelink Relay Adaptation Protocol (SRAP).

3. The processor of claim 1 , wherein the operations further comprise: A handover preparation complete message is received from the target cell, wherein the handover preparation complete message includes an indication of whether the target relay UE is ready for handover.

4. The processor of claim 3, wherein when the RRC state of the target relay UE is an RRC connected state and the target cell reconfigures the target relay UE to act as the L2 U2N relay with the first UE, the handover preparation complete message indicates that the target relay UE is ready for handover.

5. The processor of claim 4, wherein the operations further comprise: Transmitting a handover command to the first UE, the handover command including parameters for establishing a side link with the target relay UE to establish an indirect path to the target gNB.

6. The processor of claim 4, wherein the parameters comprise a dedicated radio link control (RLC) channel configuration for the first UE to transmit a handover complete message to the target gNB via the target relay UE.

7. The processor of claim 3, wherein when the RRC state of the target relay UE is an RRC idle or inactive state and the target cell has not reconfigured the target relay UE for the L2 U2N relay with a remote UE, the handover preparation complete message indicates that the target relay UE is not ready for handover.

8. The processor of claim 7, wherein the operations further comprise: A handover command is transmitted to the first UE, the handover command including parameters for establishing a side link with the target relay UE, wherein the parameters include not including a dedicated radio link control (RLC) channel configuration, and the first UE uses a default RLC channel configuration to transmit a handover complete message to the target gNB via the target relay UE and trigger the target relay UE to enter the connected state.

9. A processor of a base station, the processor being configured to perform operations including: receiving a handover preparation message from a serving cell of a first user equipment (UE), wherein the serving cell of the first UE is a source cell for handover of the first UE, the handover preparation message including a relay identifier of a second UE capable of serving as a target relay UE for layer 2 (L2) UE-to-network (U2N) relay under the base station; identifying a current radio resource control (RRC) state of the second UE; as well as A handover preparation complete message is transmitted to the source cell, wherein the handover preparation complete message includes an indication of whether the target relay UE is ready for handover.

10. The processor of claim 9, wherein the operations further comprise: When the target relay UE is in an RRC connected state, transmitting to the target relay UE an RRC reconfiguration for the L2 U2N relay with the first UE; and An RRC reconfiguration complete message is received from the target relay UE.

11. The processor of claim 9, wherein the handover preparation complete message transmitted to the source cell indicates that the target relay UE is ready for handover.

12. The processor of claim 9, wherein when the target relay UE is in an RRC idle or inactive state, the handover preparation complete message transmitted to the source cell indicates that the target relay UE is not ready for handover.

13. A processor of a base station, the processor being configured to perform operations comprising: receiving a measurement report from a first user equipment (UE), the measurement report including a channel measurement result for a sidelink channel with at least a second UE, the second UE being capable of serving as a candidate relay UE for a layer 2 (L2) UE-to-network (U2N) relay, the measurement report also including a relay identifier of the second UE and serving cell information for a serving cell; transmitting a relay query request to the serving cell of the second UE, the relay query request including the relay identifier of the second UE; and A relay query response is received from the serving cell of the second UE, the relay query response comprising an indication of whether the second UE is in a first state comprising a radio resource control (RRC) connected state, a second state comprising an RRC idle or inactive state, or a third state wherein the second UE is out of coverage of the serving cell.

14. The processor of claim 13, wherein the relay query response indicates that the second UE is in the RRC connected state under the serving cell.

15. The processor of claim 14, wherein the operations further comprise: selecting the second UE as a target relay UE for the first UE based on the second UE being in the RRC connected state; as well as A handover preparation message is transmitted to the serving cell of the target relay UE, wherein the serving cell of the target relay UE is a target cell for handover of the first UE, and the handover preparation message includes the relay identifier of the second UE, the layer 2 address of the first UE, and the corresponding local identifier of the first UE to be used in a sidelink relay adaptation protocol (SRAP).

16. The processor of claim 13, wherein the relay query response indicates that the second UE is in the RRC idle or inactive state under the serving cell.

17. The processor of claim 16, wherein the operations further comprise: Another UE different from the second UE is selected as a target relay UE for the first UE based on the second UE being in the RRC idle or inactive state.

18. The processor of claim 16, wherein the operations further comprise: The second UE is selected as a target relay UE for the first UE and a UE-assisted handover process is implemented.

19. The processor of claim 13, wherein the relay query response indicates that the second UE is out of coverage of the serving cell.

20. The processor of claim 19, wherein the operations further comprise: Another UE different from the second UE is selected as a target relay UE for the first UE based on the second UE being out of coverage.

21. The processor of claim 19, wherein the operations further comprise: A further relay query request is transmitted to a further serving cell of the second UE, the relay query request including the relay identifier of the second UE.

22. The processor of claim 13, wherein the operations further comprise: The information for the relay UE in the RRC connected state under the base station is periodically transmitted to a neighboring base station.

23. The processor of claim 13, wherein the operations further comprise: Information for the relay UE in the RRC connected state under the base station is periodically received from a neighboring base station.

Images