Base station, communication device, control method, and program

Abstract

To provide a mechanism that reduces inconvenience that may occur in remote UE when performing a handover for relay UE.SOLUTION: A base station is disclosed that includes control means for performing a handover to another base station for relay UE (User Equipment) in a situation where the base station is connected to remote UE in a sidelink via the relay UE with a sidelink relay function. When the control means determines to perform a handover to another base station for the relay UE while the remote UE is relaying via the relay UE, the control means performs a predetermined control related to communication for the remote UE before performing a handover for the relay UE.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a base station, a communication device, a control method, and a program. [Background technology]

[0002] In recent years, the 3GPP (3rd Generation Partnership Project) (registered trademark) has been formulating specifications for LTE (Long Term Evolution) and next-generation (NR: New Radio) standards. Among these, a standard specification called Sidelink communication (hereinafter, Sidelink) has been formulated. This specification realizes direct wireless communication between devices using an interface called PC5, without going through a mobile communication network (core network).

[0003] Furthermore, 3GPP is developing specifications to expand the communication range of Sidelink by using a Sidelink relay function that relays Sidelink communication via a relay device (relay UE). In this specification, a means is specified for switching the communication state of a communication terminal (remote UE) that has the function of connecting to a base station (gNB) through a Sidelink function relay from an indirect path to a direct path without disconnecting the service. Also, a means is specified for switching from a direct path to an indirect path without disconnecting the service. Note that an indirect path refers to the communication state of a remote UE that connects to a gNB via a relay UE, and a direct path refers to the communication state of a remote UE that connects directly to a gNB.

[0004] Patent Document 1 proposes a means for a remote UE to switch from an indirect path to a direct path without disconnecting the service. It also proposes a means for handing over from an indirect path to another gNB (Target gNB). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Publication No. 2022 / 0377822 Summary of the Invention [Problem to be solved by the invention]

[0006] When the relay UE is instructed to perform handover by the gNB, the relay UE operates as follows. It sets the IndicationType of the PC5RRC message "NotificationMessageSidelink" to "relayUE-HO" for the subordinate remote UE. Then, it sends the set "NotificationMessageSidelink" to the remote UE.

[0007] In this case, the remote UE that has received the NotificationMessageSidelink transitions to RRC_IDLE. After that, the remote UE cannot communicate with the network until the remote UE releases the PC5 link and completes reselection of a cell or relay.

[0008] The present invention has been made in consideration of at least one of the above problems. As one aspect of the present invention, an object of the present invention is to provide a mechanism for reducing inconvenience that may occur in a remote UE when performing handover to a relay UE. [Means for solving the problem]

[0009] According to one aspect of the present invention, a base station has a control means for performing handover of a relay UE (User Equipment) having a sidelink relay function to another base station in a situation where the base station is connected to a remote UE in a sidelink via the relay UE, The control means is characterized in that when it determines to perform a handover of the relay UE to the other base station while the remote UE is being relayed via the relay UE, it performs a predetermined communication-related control on the remote UE before performing a handover of the relay UE. Effect of the Invention

[0010] According to one aspect of the present invention, it is possible to provide a mechanism for reducing inconvenience that may occur in a remote UE when performing handover to a relay UE. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a communication device according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a block diagram showing an example of a functional configuration of a base station (gNB) in this embodiment. [Figure 3A] 2 is a block diagram showing an example of a functional configuration of a remote UE in the present embodiment. FIG. [Figure 3B] 2 is a block diagram showing an example of a functional configuration of a remote UE in the present embodiment. FIG. [Figure 4] This is a sequence diagram of a path switching decision for a remote UE when a gNB decides to hand over a relay UE in the first embodiment. [Diagram 5] This is a flowchart of gNB A in the first embodiment. [Figure 6] This is a sequence diagram of a path switching decision for a remote UE when a gNB decides to hand over a relay UE in the second embodiment. [Figure 7] A flowchart of gNB A in the second embodiment. [Figure 8] 13 is a flowchart of a UE B in the second embodiment. [Figure 9] 13 is a message format of SidelinkUEInformationNR in the second embodiment. [Figure 10] This is a sequence diagram of a path switching decision for a remote UE when a gNB decides to hand over a relay UE in a modified example. [Figure 11] This is a flowchart of gNB A in this modified example. [Figure 12]FIG. 11 is a sequence diagram relating to path switching to an indirect path. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Each embodiment will be described in detail below with reference to the accompanying drawings.

[0013] [System configuration] Fig. 1 is a diagram showing an example of the configuration of a system according to this embodiment. In Fig. 1, UE A (101) and UE B (102) are within a communication area (105) of gNB A (103).

[0014] UE A (101) operates as a remote UE that communicates with gNB A (103) using sidelink relay communication. UE B (102) operates as a relay UE that relays communication between UE A (101) and gNB A (103) using the sidelink relay function. In other words, UE A is transmitting and receiving data to and from gNB A over an indirect path with UE B.

[0015] In addition, UE B (102) is also present within the communication area (106) of gNB B (104). Here, the following situation is assumed. UE B (102) is moving away from the communication area (105) of gNB A (103) and approaching the communication area (106) of gNB B (104) (see arrow R10). For this reason, gNB A (103) is attempting to perform handover for UE B (102) with gNB B (104) as the target.

[0016] 2 is a block diagram showing an example of the functional configuration of gNB A (103) in this embodiment. Note that the functional configuration of gNB B (104) may be similar to that of gNB A (103) described below.

[0017] 2, 3A, and 3B, some or all of the functional blocks described below may be replaced with other functional blocks having similar functions, some functional blocks may be omitted, or further functional blocks may be added. Furthermore, one functional block described below may be divided into multiple functional blocks, or multiple functional blocks may be integrated into one functional block.

[0018] In the example shown in FIG. 2, gNB A (103) includes a control unit 201, a memory unit 202, a UE management unit 203, a path switching determination processing unit 204, an RRC message generation processing unit 205, an RRC message analysis processing unit 206, and a wireless communication unit 207.

[0019] The control unit 201 controls the operation of gNB A (103) (own station). The control unit 201 is configured with one or more processors such as a CPU or MPU, and controls the entire communication device by executing a control program read into the RAM, which is the storage unit 202. Note that each process performed by the control unit 201, which will be described in the flowcharts below, can also be realized using a hardware circuit such as an ASIC or FPGA. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array. In addition, the hardware circuit and a processor such as a CPU or MPU can cooperate to realize the process described in the flowcharts below.

[0020] The storage unit 202 stores information used by the control unit 201 for control and information related to communication. The storage unit 202 may include a main storage unit and an auxiliary storage unit. The main storage unit may be, for example, a ROM (Read Only Memory) or a RAM (Random Access Memory). The main storage unit may store or temporarily store programs and data such as an OS (Operating System) that is basic software executed by the control unit 201 and application software. The auxiliary storage unit may be, for example, a HDD (Hard Disk Drive) or an SSD (Solid State Drive), and may store data related to application software. For example, a control program stored in a non-volatile storage area is expanded in a RAM (Random Access Memory) and executed by a processor constituting the control unit 201. In this manner, the control unit 201 and the storage unit 202 may function as a so-called computer.

[0021] The storage unit 202 may include a recording medium for storing a predetermined program. The program stored in this recording medium may be installed via a drive device or the like, and the installed predetermined program may be executable by the control unit 201. The recording medium may be of various types. For example, the recording medium may be a recording medium that records information optically, electrically, or magnetically, such as a CD (Compact Disc)-ROM, a flexible disk, or a magneto-optical disk. The recording medium may also be a semiconductor memory that records information electrically, such as a ROM or a flash memory. Note that the recording medium does not include a carrier wave.

[0022] The UE management unit 203 manages UE information (an example of management information) within the base station area. For example, the UE management unit 203 generates and updates a management table that stores UE information for each subordinate UE (UE that communicates with gNB A (103)). The management table stores the IDs of the subordinate UEs and measurement results (such as the signal strength of a Uu link, which will be described later) reported from the subordinate UEs. The management table also stores information indicating whether the UE is operating as a relay UE, a remote UE, or neither. The management table also stores information on peer UEs. A peer UE refers to an opposing remote UE when the UE is operating as a relay UE, and refers to an opposing relay UE when the UE is operating as a remote UE.

[0023] The path switching determination processing unit 204 performs a determination process related to path switching (Switching from indirect to direct path). For example, based on UE information managed by the UE management unit 203, the path switching determination processing unit 204 determines whether to connect the UE managed by the UE management unit 203 (subordinate UE) via an indirect path or a direct path.

[0024] The RRC message generation processing unit 205 generates messages used in RRC (Radio Resource Control), a protocol used for control signals between the gNB and the UE.

[0025] The RRC message analysis processing unit 206 analyzes the RRC message received from the subordinate relay UE.

[0026] In addition, functions corresponding to the UE management unit 203, the path switching decision processing unit 204, the RRC message generation processing unit 205, and / or the RRC message analysis processing unit 206 may be realized as software modules realized by the control unit 201.

[0027] The wireless communication unit 207 transmits and receives information to and from subordinate UEs via wireless communication. For example, the wireless communication unit 207 transmits an RRC message generated by the RRC message generation processing unit 205, and receives an RRC message from subordinate UEs and other necessary wireless signals.

[0028] FIG. 3A is a block diagram showing an example of the functional configuration of UE B (102) (relay UE) in this embodiment.

[0029] In the example shown in FIG. 3A, UE B (102) includes a control unit 301, a storage unit 302, a signal strength measurement unit 303, a sidelink relay processing unit 304, an RRC message generation processing unit 305, an RRC message analysis processing unit 306, and a wireless communication unit 307.

[0030] The control unit 301 controls the operation of the relay UE (own device). The control unit 301 is configured with one or more processors such as a CPU or MPU, and controls the entire communication device by executing a control program read into a RAM, which is the storage unit 302. Note that each process performed by the control unit 301, which will be described in the flowcharts below, can also be realized using a hardware circuit such as an ASIC or FPGA. Also, the hardware circuit and a processor such as a CPU or MPU can cooperate to realize the process described in the flowcharts below.

[0031] The storage unit 302 stores information used for control by the control unit 301 and information related to communication. The hardware configuration of the storage unit 302 may be the same as that of the storage unit 202 described above.

[0032] The signal strength measurement unit 303 measures the "signal strength between remote UEs (PC5 link)" and the "signal strength between gNBs (Uu link)" as viewed from the relay UE.

[0033] The Sidelink Relay processing unit 304 relays communication between the remote UE and the gNB via the NR (New Radio) Sidelink relay function of the relay UE by connecting to the remote UE via Sidelink. That is, the Sidelink Relay processing unit 304 enables an indirect path by connecting to the remote UE via Sidelink. Note that, although the NR Sidelink relay function will be mainly described below, it is also applicable to similar relay functions in 5G and beyond, such as 5G Advanced and 6G.

[0034] Similar to the RRC message generation processing unit 205, the RRC message generation processing unit 305 generates an RRC message.

[0035] The RRC message analysis processing unit 306 analyzes the RRC messages received from the remote UE and the gNB.

[0036] The wireless communication unit 307 transmits and receives information to and from the remote UE and the base station (such as gNB A (103)) via wireless communication. For example, the wireless communication unit 307 performs a transmission process of the RRC message generated by the RRC message generation processing unit 305, a reception process of the RRC message from the remote UE and the base station, and other necessary wireless communication.

[0037] In the example shown in FIG. 3B, the remote UE includes a control unit 401, a storage unit 402, a signal strength measurement unit 403, a sidelink relay processing unit 404, a message generation processing unit 405, a message analysis processing unit 406, and a wireless communication unit 407.

[0038] The control unit 401 controls the operation of the remote UE. The control unit 401 is configured with one or more processors such as a CPU or an MPU, and controls the entire communication device by executing a control program read into a RAM that is a storage unit 402. Each process performed by the control unit 401, which will be described in the flowchart below, can also be realized using a hardware circuit such as an ASIC or an FPGA.

[0039] The memory unit 402 stores information used by the control unit 401 for control and information related to communication. The signal strength measurement unit 403 measures the "signal strength between relay UEs (relay link)", "signal strength between base stations (Uu link)", and "signal strength between candidate relay UEs" as seen from the remote UE. The sidelink relay processing unit 404 enables connection to gNB A (103) via the relay function of the relay UE (i.e., indirect path) by connecting to the relay UE via sidelink. The message generation processing unit 405 generates various messages. The various messages include discovery signals transmitted to nearby relay UEs and RRC messages transmitted to gNB A (103). The message analysis processing unit 406 analyzes messages such as discovery signals and response signals transmitted from nearby relay UEs, and RRC messages transmitted from gNB A (103). The wireless communication unit 407 transmits and receives information to and from nearby relay UEs and gNB A (103) via wireless communication. The wireless communication unit 407 performs processing for transmitting messages generated by the RRC message generation processing unit 205 and processing for receiving messages from nearby relay UEs and gNB A (103).

[0040] Next, a processing example will be described with reference to several embodiments. <First embodiment> In this embodiment, when gNB A (103) determines to hand over UE B (102), which is a relay UE, to gNB B (104), it performs a predetermined control before performing the handover. In this case, the predetermined control is related to path switching, and specifically, includes path switching from an indirect path to a direct path for UE A, which is a remote UE.

[0041] The operation of this embodiment will be described with reference to the sequence shown in FIG. 4 and the flowchart shown in FIG.

[0042] First, UE B (102) is transmitting and receiving user data to and from gNB A (103) via a direct path (F401). Also, UE A (101), as a remote UE, is transmitting and receiving user data to and from gNB A (103) via the NR Sidelink relay function of UE B (102), which is a relay UE (i.e., via an indirect path) (F402).

[0043] During user data transmission and reception, UE A (101) reports the signal strength between UE A (101) and gNB A (103) to gNB A (103) by Measurement Configuration and Reporting (F403). Such reporting is performed by UE A (101) sending a Measurement Report. gNB A (103) acquires the signal strength from the message and sets the acquired signal strength in the management table for UE A (101) held by the UE management unit 203 (S501).

[0044] Here, gNB A (103) can determine that UE A (101) is a remote UE under relay UE B (102) from sl-MeasResultServingRelay in the above-mentioned MeasurementReport. From this result, gNB A (103) sets the UE B (102) management table held by UE management unit 203 to indicate that UE B (102) is operating as a relay UE. Also, gNB A (103) adds UE A (101) to the list of remote UEs under control in the management table of UE B (102) (S502).

[0045] The UE B (102) reports by Measurement Configuration and Reporting. That is, the UE B (102) reports a Measurement Report including the signal strength between the UE B (102) and the gNB A and the signal strength between the UE B (102) and the neighboring cell, gNB B (104), to the gNB A (103) (F404). As described above with reference to FIG. 1, here, it is assumed that the gNB A (103) is attempting to perform handover for the UE B (102) with the gNB B (104) as a target. That is, the gNB A (103) determines the handover of the UE B based on the result of the Measurement Report described above (F405, S503).

[0046] At this time, gNB A (103) refers to the management table related to UE B (102) in the UE management unit 203, and determines that UE B (102) is operating as a relay UE and that a remote UE A exists under its control (S504). From this result, gNB A (103) refers to the management table of UE A (101) held by the UE management unit 203, and acquires the signal strength acquired in S501 (S506).

[0047] The gNB A (103) judges whether or not this signal strength is equal to or greater than a threshold that allows UE A (101) to be connected via a direct path (F405, S507). If the signal strength allows connection via a direct path, the gNB A (103) decides to switch UE A (101) from an indirect path via UE B (102) to a direct path (F406). As a result, the gNB A (103) executes switching for UE A (101) from the indirect path via UE B (102) to the direct path (F407, S508).

[0048] After performing path switching for UE A (101), gNB A (103) initiates a handover procedure for UE B (102) to gNB B (104) (F408 to F410, S509).

[0049] If the signal strength is not strong enough to connect via a direct path (NO in S507), the process proceeds to S509 without controlling UE A (101).

[0050] Through the above flow, when UE B (102) moves from the communication area (105) of gNB A (103) to the communication area (106) of gNB B (104), gNB A (103) can achieve the following. That is, gNB A (103) can switch UE A (101) from an indirect path to a direct path before the network disconnection of relay UE A (101) due to handover of UE B (102). This makes it possible to prevent temporary disconnection of service due to reselection of a relay UE or cell of UE A (101).

[0051] In the example shown in Fig. 5, the remote UE under the control of the relay UE B (102) is only the UE A (101), but the same applies when there is a UE other than the UE A (101) (a remote UE under the control of the relay UE B (102)). That is, in this case, the same process may be performed for each remote UE under the control of the relay UE B (102).

[0052] Second Embodiment In the first embodiment, an example is described in which a gNB identifies a remote UE under a relay UE from a Measurement Report of the remote UE. In the second embodiment, an example is described in which a gNB can identify a remote UE under a relay UE from a message from the relay UE.

[0053] In the second embodiment, when the gNB A (103) determines to hand over the UE B (102) that is a relay UE to the gNB B (104), the gNB A (103) performs a predetermined control before performing the handover. In this case, the predetermined control also includes a path switch from an indirect path to a direct path for the UE A that is a remote UE.

[0054] The operation of the second embodiment will be described using the sequence shown in Figure 6, the flowchart of the gNB shown in Figure 7, the flowchart of the relay UE shown in Figure 8, and the message format shown in Figure 9.

[0055] First, the second embodiment is the same as the first embodiment in the following respects. UE A (101) transmits and receives user data to gNB A (103) on an indirect path via UE B (102), and UE B (102) transmits and receives user data to gNB A (103) on a direct path (F401, F402, S801). In addition, each reports the signal strength between gNB A (103) to gNB A (103) by Measurement Configuration and Reporting (F403, F404).

[0056] Here, upon receiving SIB12 from gNB A (103) ("YES" in S802), UE B (102) transmits SidelinkUEInformationNR to gNB A (103) (F601, F602, S803). SidelinkUEInformationNR is an RRC message, which will be described later with reference to FIG. 9. SIB12 is system information for notifying the UE of sidelink-related functions supported by the gNB, and is periodically transmitted from the gNB to the UE. Alternatively, the UE can request the gNB to transmit SIB12 to the UE by transmitting DedicatedSIBRequest to the gNB. In the second embodiment, it is assumed that gNB A (103) periodically transmits SIB12 to UE B (102).

[0057] The message format of SidelinkUEInformationNR used in the second embodiment is shown in Fig. 9. In the second embodiment, an information element called sl-PeerUE-CurrentList is added to SidelinkUEInformationNR. sl-PeerUE-CurrentList is a list that can store Source Layer-2 IDs of multiple peer UEs. sl-PeerUE-CurrentList corresponds to a list of destination IDs of peer UEs. Note that the list name "sl-PeerUE-CurrentList" is just an example and may be any name.

[0058] In addition, in Figure 9, ue-Type indicates that the UE is operating as a U2N relay UE or a U2N remote UE.

[0059] The UE B (102) adds the Source Layer-2 ID of the UE A (101) to the sl-PeerUE-CurrentList. Then, the UE B (102) creates a SidelinkUEInformationNR and transmits it to the gNB A (103) (S803).

[0060] The gNB A (103) that has received the SidelinkUEInformationNR from the UE B (102) updates the management table of the UE B (102) held by the UE management unit 203. That is, from the contents of sl-PeerUE-CurrentList, the gNB A (103) adds to the management table of the UE B (102) that the UE B (102) is operating as a relay UE (S601). Also, the gNB A (101) is added to the subordinate remote UE list in the management table of the UE B (102) (S601). Note that the fact that the UE B (102) is operating as a relay UE can be determined from the ue-Type in the SidelinkUEInformationNR.

[0061] The second embodiment may be the same as the first embodiment. First, when gNB A (103) decides to hand over UE B (102), it can identify the following from the updated management table of UE B (102) (S504). That is, gNB A (103) can identify that UE A (101) is communicating with gNB A (103) as a remote UE through the relay function of relay UE B (102) (S504).

[0062] Also, similar to the first embodiment, gNB A (103) judges whether the signal strength between UE A (101) is equal to or greater than a threshold for connection via a direct path (S507). If the signal strength is sufficient for connection via a direct path, gNB A (103) switches UE A (101) from an indirect path via UE B (102) to a direct path (F406, F407, S508). Then, it starts handover of UE B (102) (F408 to F410, S509).

[0063] Through the above flow, gNB A (103) switches UE A (101) from an indirect path to a direct path before the network disconnection of relay UE A (101) due to handover of UE B (102). This makes it possible to prevent temporary disconnection of service due to reselection of relay UE or cell of UE A (101).

[0064] Next, a modified example will be described with reference to FIGS.

[0065] In the above-described first embodiment (similar to the second embodiment), the predetermined control is path switching from an indirect path to a direct path for a remote UE under a relay UE to be handed over, but is not limited to this. For example, as in a modified example described below, the predetermined control may include path switching from an indirect path to another indirect path for a remote UE under a relay UE to be handed over, instead of or in addition to such path switching from an indirect path to a direct path.

[0066] Fig. 10 is a sequence diagram of a path switching decision for a remote UE when a gNB in ​​this modification determines to hand over a relay UE. Fig. 11 is a flowchart of gNB A (103) in this modification. Fig. 12 is a sequence diagram related to path switching to an indirect path.

[0067] The sequence at the time of path switching determination according to this modified example shown in Fig. 10 differs from the sequence according to the first embodiment described above with reference to Fig. 4 in that the processes relating to F406 and F407 are replaced by the processes relating to F406A and F407A, respectively. Also, the flowchart according to this modified example shown in Fig. 11 differs from the flowchart according to the first embodiment described above with reference to Fig. 5 in that S502 is replaced by S502A, and S510 and S511 are added.

[0068] In this modification, gNB A (103) generates a candidate relay UE list in addition to the subordinate remote UE list from the above-mentioned Measurement Report (S502A). The candidate relay UE list is a list of UEs (relay UE candidates) that can operate as relay UEs under the control of gNB A (103).

[0069] In addition, in this modification, the gNB A (103) operates as follows after determining whether the signal strength is equal to or greater than a threshold that allows UE A (101) to be connected via a direct path (F405, S507). If the signal strength is not equal to or greater than a threshold that allows connection via a direct path ("NO" in S507), the gNB A (103) determines whether path switching to an indirect path via another relay UE is possible for UE A (101) (S510). For example, when a relay UE candidate whose signal strength between UE A (101) and the relay UE candidate is equal to or greater than a threshold is present among the relay UE candidates listed in the candidate relay UE list, the gNB A (103) may determine whether path switching is possible with the relay UE candidate as another relay UE. Note that the signal strength between UE A (101) and the candidate relay UE in the candidate relay UE list may be included in the Measurement report from UE A (101) in S501. In this case, UE A (101) may execute a discovery process to search for a candidate UE relay. Specifically, when UE A (101) receives a discovery signal or a response signal to the discovery signal from a nearby UE, UE A (101) analyzes the received signal and creates a measurement report based on the analysis result.

[0070] In this way, when gNB A (103) determines that path switching from the indirect path via UE B (102) to the indirect path via another relay UE is possible, it decides to execute such path switching (F406A). As a result, gNB A (103) executes switching for UE A (101) from the indirect path via UE B (102) to the indirect path via another relay UE (F407A, S511).

[0071] Such switching from an indirect path to an indirect path may be performed based on, for example, a sequence as shown in Fig. 12. Here, UE C (105) is assumed as another relay UE related to switching to the indirect path via another relay UE.

[0072] In the example shown in FIG. 12, gNB A (103) performs RRC reconfiguration on UE C (105) (F1104). In addition, gNB A (103) notifies UE A (101) of information necessary for establishing sidelink relay communication with UE C (105) (F1105). The necessary information includes sl-L2RemoteUE-Config. sl-L2RemoteUE-Config includes information used in SRAP (Sidelink Relay Adaptation Protocol) required for operation as a remote UE.

[0073] Furthermore, gNB A (103) adds sl-PathSwitchConfig to ReconfigurationWithSync in the RRC reconfiguration message. At this time, sl-PathSwitchConfig storing the ID of UE C (105) is used. This allows gNB A (103) to notify UE A (101) of switching from an indirect path via UE B (102) to an indirect path via UE C (105).

[0074] The UE A (101) confirms receipt of an RRC reconfiguration message from the gNB A (103). At this time, the control unit 301 confirms the ID of the UE C (105) from the sl-PathSwitchConfig, and determines that the indirect path is to be switched from the indirect path via the UE B (102) to the indirect path via the UE C (105) (F1105).

[0075] Next, UE A (101) stops data transmission and reception with UE B (102) and establishes PC5 communication (PC5 Connection) with UE C (105) (F1106). After that, UE A (101) and UE C (105) can use Sidelink relay communication based on the SRAP information acquired in the RRC reconfiguration message. That is, UE A (101) can transmit and receive data to and from gNB A (103) via UE C (105).

[0076] After establishing PC5 communication with UE C (105), UE A (101) generates an RRC reconfiguration complete message. UE A (101) transmits the RRC reconfiguration complete message to gNB A (103) via UE C (105) (F1107). In other words, UE A (101) transmits the RRC reconfiguration complete message to gNB A (103) via UE C (105) instead of via UE B (102).

[0077] The gNB A (103) receives an RRC reconfiguration complete message from the UE A (101) via the UE C (105). Based on the reception of the message, the gNB A (103) can determine that the switching of the indirect path of the UE A (101) is completed (F1107).

[0078] After completing the current path switching for UE A (101), gNB A (103) performs RRC reconfiguration on UE B (102) and releases the sidelink relay function for UE A (101) (F1108).

[0079] On the other hand, UE A (101) releases the PC5 link with UE B (102) (F1109).

[0080] Then, UE A (101) continues to transmit and receive user data to and from gNB A (103) via the sidelink relay function of UE C (105) (F1110). That is, UE A (101) continues to transmit and receive user data (such as streaming data) to and from gNB A (103). If there is an undelivered packet that UE B (102) is relaying, the undelivered packet is transferred to UE C (105) as necessary, and is transmitted to the destination by UE C (105). This undelivered packet may be configured to be directly transferred from UE B (102) to UE C (105). Alternatively, the undelivered packet may be transferred from UE B (102) to gNB A (103), and then transferred from gNB A (103) to UE C (105) again. When adopting the latter method of forwarding undelivered packets via gNB A (103), if the destination of the user data is uplink communication to the core network rather than to UE A (101), forwarding to UE C (105) may be omitted.

[0081] Although each embodiment has been described above in detail, the present invention is not limited to the specific embodiment, and various modifications and changes are possible within the scope of the claims. In addition, it is also possible to combine all or a plurality of the components of the above-described embodiments.

[0082] In addition, the following supplementary notes are disclosed regarding the above embodiment.

[0083] [Appendix 1] A control unit is provided to perform handover of a relay UE (User Equipment) having a Sidelink relay function to another base station in a state where the relay UE is connected to a remote UE in Sidelink via the relay UE, The base station is characterized in that, when it is determined that a handover should be performed for the relay UE to the other base station while a remote UE is being relayed via the relay UE, the control means performs a predetermined communication-related control for the remote UE before performing a handover for the relay UE.

[0084] [Appendix 2] The method further includes a storage unit for storing management information regarding a relay state of subordinate UEs including the remote UE, The base station according to claim 1, wherein the control means performs the predetermined control based on the management information.

[0085] [Appendix 3] The base station according to claim 2, wherein the management information includes information representing each relay UE and a remote UE connected to the corresponding relay UE.

[0086] [Appendix 4] The base station according to any one of Supplementary Note 1 to 3, characterized in that the predetermined control includes path switching from an indirect path to which the remote UE connects via the relay UE to a direct path to which the remote UE connects directly.

[0087] [Appendix 5] The base station according to claim 4, wherein the control means executes the path switching when a signal strength between the base station and the remote UE is equal to or greater than a threshold.

[0088] [Appendix 6] The base station according to claim 2, wherein the control means updates the management information based on a Measurement report or a SidelinkUEInformationNR message received from the remote UE.

[0089] [Appendix 7] The base station according to claim 6, characterized in that the control means updates the management information based on a determination result of whether or not the remote UE is connected via the relay UE, the determination result being determined from an sl-MeasResultServingRelay in the Measurement report.

[0090] [Appendix 8] The base station according to claim 6, wherein the SidelinkUEInformationNR message includes information about the remote UE connected to the relay UE.

[0091] [Appendix 9] A communication device having an NR (New Radio) Sidelink relay function, A transmitting means for transmitting a SidelinkUEInformationNR message, which is a message of a Radio Resource Control (RRC) protocol, to the base station in a state where communication between the base station and a remote UE (User Equipment) in an NR Sidelink is being relayed, The communication device, wherein the transmitting means includes information of the remote UE in the SidelinkUEInformationNR message.

[0092] [Appendix 10] 10. The communications device of claim 9, wherein the information about the remote UE includes a Source layer-2 ID of the remote UE.

[0093] [Appendix 11] The present invention further includes a control means for generating or updating a list storing a Source Layer-2 ID of each remote UE when a PC5 link is established with the remote UE; The communication device described in Supplementary Note 10, characterized in that the transmitting means includes the list in the SidelinkUEInformationNR message. [Explanation of symbols]

[0094] 101UEA 102UEB 103 gNB A 104 gNB B 105 gNB A communication area 106 gNB B coverage area

Claims

1. A base station capable of communication as defined by the 3GPP (3rd Generation Partnership Project) standard, A decision means for determining whether to hand over a relay UE (User Equipment) with Sidelink relay functionality to another base station, while connected to a remote UE in Sidelink via the relay UE, A transmission means for transmitting a handover request to the aforementioned other base station, When it is decided to hand over the relay UE to the other base station, the transmission means performs predetermined communication-related control on the remote UE before sending a handover request to the other base station, A base station characterized by having the following features.

2. The system further includes a storage means for storing management information relating to the relay status of subordinate UEs, including the aforementioned remote UE. The base station according to claim 1, characterized in that the control means performs the predetermined control based on the management information.

3. The base station according to claim 2, characterized in that the management information includes information representing each relay UE and a remote UE connected to the corresponding relay UE.

4. The base station according to claim 1, characterized in that the predetermined control includes switching the path from an indirect path to which the remote UE is connected via the relay UE to a direct path to which the remote UE is directly connected.

5. The base station according to claim 1, characterized in that the predetermined control includes switching paths from an indirect path to which the remote UE is connected via the relay UE to an indirect path to which the remote UE is connected via another relay UE.

6. The base station according to claim 4, characterized in that the control means performs the path switching when the signal strength between it and the remote UE is greater than or equal to a threshold.

7. The base station according to claim 1, further comprising receiving means for receiving a Measurement report or a SidelinkUEInformationNR message from the remote UE.

8. The base station according to claim 7, characterized in that the Measurement report includes sl-MeasResultServingRelay.

9. The base station according to claim 7, wherein the SidelinkUEInformationNR message includes information about the remote UE connected to the relay UE.

10. A communication device having a Sidelink relay function as defined in the 3GPP (3rd Generation Partnership Project) standard, The system includes a transmission means for transmitting a SidelinkUEInformationNR message, which is a Radio Resource Control (RRC) message, to the base station while relaying communication between the base station and a remote UE (User Equipment). The transmission means is a communication device characterized by including information of the remote UE in the SidelinkUEInformationNR message.

11. The communication device according to claim 10, characterized in that the information of the remote UE includes the Source layer-2 ID of the remote UE.

12. The system further includes control means for generating or updating a list that stores the Source Layer-2 IDs of each remote UE when a PC5 link is established with a remote UE. The communication device according to claim 11, characterized in that the transmission means includes the list in the SidelinkUEInformationNR message.

13. A control method for controlling communication at a base station capable of communication as defined in the 3GPP (3rd Generation Partnership Project) standard, A decision step of deciding to hand over the relay UE (User Equipment) having Sidelink relay functionality to another base station while connected to a remote UE in Sidelink, A transmission step of sending a handover request to the aforementioned other base station, When it is decided to hand over the relay UE to the other base station, the transmission step includes a control step in which predetermined communication-related controls are performed on the remote UE before sending a handover request to the other base station, A control method characterized by including

14. A program for controlling communication at a base station capable of communication as defined in the 3GPP (3rd Generation Partnership Project) standard, wherein a computer provides: A decision step of deciding to hand over the relay UE (User Equipment) having Sidelink relay functionality to another base station while connected to a remote UE in Sidelink, A transmission step of sending a handover request to the aforementioned other base station, When it is decided to hand over the relay UE to the other base station, the transmission step includes a control step in which predetermined communication-related controls are performed on the remote UE before sending a handover request to the other base station, A program characterized by causing something to be executed.

15. A control method for controlling communication of a communication device having a Sidelink relay function as defined in the 3GPP (3rd Generation Partnership Project) standard, A control method characterized by including a transmission step of transmitting a SidelinkUEInformationNR message, which is a Radio Resource Control (RRC) message containing information about the remote UE, to the base station while relaying communication between the base station and a remote UE (User Equipment).

16. A program for controlling communication of a communication device having a Sidelink relay function as defined in the 3GPP (3rd Generation Partnership Project) standard, wherein a computer provides: A program characterized by causing a transmission step to be executed in which, while relaying communication between a base station and a remote UE (User Equipment), the program transmits a SidelinkUEInformationNR message, which is a Radio Resource Control (RRC) message, containing information about the remote UE, to the base station.

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