Base station, communication device, control method, and program

Abstract

Disclosed is a base station characterized by having a control means for performing handover to another base station for a relay user equipment (UE) having a sidelink relay function under the state of being connected to a remote UE in a sidelink via the relay UE. When it is determined to perform handover to another base station for the relay UE while the remote UE is being relayed via the relay UE, the control means performs predetermined control pertaining to communication for the remote UE before performing handover for the relay UE.

Description

Base station, communication device, control method, and program

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

[0002] In recent years, the 3rd Generation Partnership Project (3GPP) (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 referred to as 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 Sidelink communication range using a Sidelink relay function that relays Sidelink communication via a relay device (relay UE). This specification defines a means 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. It also defines a means for switching from a direct path to an indirect path without disconnecting the service. Note that the indirect path refers to the communication state of a remote UE that connects to a gNB via a relay UE, and the 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 the indirect path to another gNB (Target gNB).

[0005] US Patent Publication No. 2022 / 0377822

[0006] When the relay UE is instructed to perform handover by the gNB, the relay UE operates as follows: The relay UE sets "relayUE-HO" in the IndicationType of the "NotificationMessageSidelink", which is a PC5RRC message, to the subordinate remote UE. Then, the set "NotificationMessageSidelink" is sent 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 it 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-mentioned problems, and an object of one aspect 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.

[0009] According to one aspect of the present invention, a base station has a control means for performing a handover of the relay UE to another base station when the base station is connected to a remote UE in a Sidelink via a relay UE (User Equipment) having a Sidelink relay function, and when the control means determines that a handover of the relay UE to the other base station should be performed while the remote UE is being relayed via the relay UE, the control means performs a predetermined control related to communication on the remote UE before performing a handover of the relay UE.

[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.

[0011] 1 is a diagram showing the configuration of a communication device in this embodiment. FIG. 1 is a block diagram showing an example of the functional configuration of a base station (gNB) in this embodiment. FIG. 2 is a block diagram showing an example of the functional configuration of a remote UE in this embodiment. FIG. 3 is a block diagram showing an example of the functional configuration of a remote UE in this embodiment. FIG. 4 is a sequence diagram showing path switching determination for a remote UE when a gNB determines handover of a relay UE in the first embodiment. FIG. 5 is a flowchart of gNB A in the first embodiment. FIG. 6 is a sequence diagram showing path switching determination for a remote UE when a gNB determines handover of a relay UE in the second embodiment. FIG. 7 is a flowchart of gNB A in the second embodiment. FIG. 8 is a flowchart of UE B in the second embodiment. FIG. 9 is a message format of SidelinkUEInformationNR in the second embodiment. FIG. 10 is a sequence diagram showing path switching determination for a remote UE when a gNB determines handover of a relay UE in a modified example. FIG. 11 is a flowchart of gNB A in this modified example. FIG. 12 is a sequence diagram relating to path switching to an indirect path.

[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 the 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 sending and receiving data to and from gNB A over an indirect path with UE B.

[0015] In addition, UE B (102) is also present in 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 is approaching the communication area (106) of gNB B (104) (see arrow R10). Therefore, 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 the same as that of gNB A (103) described below.

[0017] 2, 3A, and 3B may be replaced with other functional blocks that perform similar functions, some functional blocks may be omitted, or additional 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 Figure 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 the gNB A (103) (local 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 flowchart 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.

[0020] Furthermore, the hardware circuitry and a processor such as a CPU or MPU can cooperate to realize the processing described in the flowcharts below.

[0021] The memory unit 202 stores information used by the control unit 201 for control and information related to communication. The memory unit 202 may include a main memory unit and an auxiliary memory unit. The main memory unit is, for example, a read-only memory (ROM) or a random access memory (RAM). The main memory unit may store or temporarily store programs and data such as an operating system (OS), which is basic software executed by the control unit 201, and application software. The auxiliary memory unit is, for example, a hard disk drive (HDD) or a solid state drive (SSD), and may store data related to application software. For example, a control program stored in a non-volatile memory area is expanded into a random access memory (RAM) and executed by a processor constituting the control unit 201. In this way, the control unit 201 and the storage unit 202 may function as a so-called computer.

[0022] The storage unit 202 may include a recording medium that stores 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. Various types of recording media can be used as the recording medium. 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.

[0023] The recording medium does not include a carrier wave.

[0024] 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 (a UE that communicates with gNB A (103)). The management table stores the IDs of the subordinate UEs and measurement results reported from the subordinate UEs (such as the signal strength of the Uu link described below). 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 about peer UEs. When a UE is operating as a relay UE, a peer UE refers to the opposite remote UE, and when a UE is operating as a remote UE, it refers to the opposite relay UE.

[0025] The path switching determination processing unit 204 performs a determination process related to path switching (switching from indirect to direct path). For example, the path switching determination processing unit 204 determines whether to connect a UE (subordinate UE) managed by the UE management unit 203 via an indirect path or a direct path, based on UE information managed by the UE management unit 203.

[0026] 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.

[0027] The RRC message analysis processing unit 206 analyzes the RRC message received from the subordinate relay UE.

[0028] In addition, the functions corresponding to the UE management unit 203, the path switching determination 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 implemented by the control unit 201.

[0029] 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 RRC messages and other necessary wireless signals from subordinate UEs.

[0030] FIG. 3A is a block diagram showing an example of the functional configuration of UE B (102) (relay UE) in this embodiment.

[0031] In the example shown in FIG. 3A , UE B (102) includes a control unit 301, a memory 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.

[0032] The control unit 301 controls the operation of the relay UE (its own device). The control unit 301 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 the 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 an FPGA. Furthermore, the processes described in the flowcharts below can also be realized by having the hardware circuit cooperate with a processor such as a CPU or an MPU.

[0033] 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.

[0034] The signal strength measurement unit 303 measures the "signal strength between remote UEs (PC5 link)" and the "signal strength between gNBs (Uu link)" as seen from the relay UE.

[0035] 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 establishing a Sidelink connection with the remote UE. That is, the Sidelink Relay processing unit 304 enables an indirect path by establishing a Sidelink connection with the remote UE. Note that, although the NR Sidelink relay function will be mainly described below, it is equally applicable to similar relay functions in 5G and later, such as 5G Advanced and 6G.

[0036] The RRC message generation processing unit 305 generates an RRC message, similar to the RRC message generation processing unit 205.

[0037] The RRC message analysis processing unit 306 analyzes the RRC messages received from the remote UE and the gNB.

[0038] The wireless communication unit 307 transmits and receives information via wireless communication with the remote UE and the base station (such as gNB A (103)). For example, the wireless communication unit 307 performs processing for transmitting the RRC message generated by the RRC message generation processing unit 305, and processing for receiving the RRC messages from the remote UE and the base station, as well as other necessary wireless communication.

[0039] 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 .

[0040] 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 the RAM, which is the storage unit 402. Note that each process performed by the control unit 401, which will be described in the flowcharts below, can also be realized using a hardware circuit such as an ASIC or an FPGA.

[0041] 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 links)," "signal strength between base stations (Uu links)," 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., via an indirect path) by establishing a Sidelink connection with the relay UE. The message generation processing unit 405 generates various messages.

[0042] The various messages include discovery signals transmitted to nearby relay UEs, RRC messages transmitted to gNB A (103), etc. 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 with nearby relay UEs and gNB A (103) via wireless communication. The wireless communication unit 407 performs transmission processing of messages generated by the RRC message generation processing unit 205 and reception processing of messages from nearby relay UEs and gNB A (103).

[0043] Next, processing examples will be described in several embodiments.

[0044] <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 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.

[0045] The operation of this embodiment will be described with reference to the sequence shown in FIG. 4 and the flowchart shown in FIG.

[0046] First, UE B (102) is transmitting and receiving user data to gNB A (103) via a direct path (F401). Also, UE A (101) is a remote UE, and is transmitting and receiving user data to 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).

[0047] 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).

[0048] Here, gNB A (103) can determine from the sl-MeasResultServingRelay in the MeasurementReport that UE A (101) is a remote UE under the relay UE B (102). From this result, gNB A (103) sets the UE B (102) management table held by the UE management unit 203 to indicate that UE B (102) is operating as a relay UE. Also, UE A (101) is added to the list of subordinate remote UEs in the management table of UE B (102) (S502).

[0049] UE B (102) reports by Measurement Configuration and Reporting. That is, UE B (102) reports to gNB A (103) a Measurement Report including the signal strength between UE B (102) and gNB A and the signal strength between UE B (102) and gNB B (104), which is a neighboring cell (F404). As described above with reference to FIG. 1, here, it is assumed that gNB A (103) is attempting to perform handover for UE B (102) with gNB B (104) as the target. That is, gNB A (103) determines handover of UE B based on the result of the Measurement Report (F405, S503).

[0050] 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). Based on 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).

[0051] The gNB A (103) determines whether 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 is sufficient to allow connection via a direct path, the gNB A (103) determines 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 an indirect path via UE B (102) to a direct path (F407, S508).

[0052] After performing path switching for UE A (101), gNB A (103) initiates a handover procedure to gNB B (104) for UE B (102) (F408 to F410, S509).

[0053] 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).

[0054] Through the above flow, gNB A (103) can achieve the following when UE B (102) moves from the communication area (105) of gNB A (103) to the communication area (106) of gNB B (104). 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 can prevent temporary disconnection of service due to reselection of a relay UE or cell by UE A (101).

[0055] In the example shown in Fig. 5, the only remote UE under the control of the relay UE B (102) is UE A (101), but the same applies when there are UEs other than UE A (101) (remote UEs 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).

[0056] <Second embodiment> In the first embodiment, an example in which a gNB identifies a subordinate remote UE of a relay UE from a Measurement Report of the remote UE is described. In the second embodiment, an example in which a gNB can identify a subordinate remote UE of a relay UE from a message from the relay UE is described.

[0057] In the second embodiment, when the gNB A (103) determines to hand over the UE B (102), which is a relay UE, to the gNB B (104), the gNB A (103) performs predetermined control before performing the handover. In this case, the predetermined control also includes path switching from an indirect path to a direct path for the UE A, which is a remote UE.

[0058] The operation of the second embodiment is explained using the sequence shown in Figure 6, the gNB flowchart shown in Figure 7, the relay UE flowchart shown in Figure 8, and the message format shown in Figure 9.

[0059] 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). Furthermore, each reports the signal strength between them to gNB A (103) by Measurement Configuration and Reporting (F403, F404).

[0060] 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).

[0061] The message format of SidelinkUEInformationNR used in the second embodiment is shown in Figure 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 the 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.

[0062] In FIG. 9, ue-Type indicates that the UE is operating as a U2N relay UE or a U2N remote UE.

[0063] 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).

[0064] The gNB A (103) that 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 the sl-PeerUE-CurrentList, it adds to the management table of the UE B (102) that the UE B (102) is operating as a relay UE (S601). Also, it adds UE A (101) 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.

[0065] The second embodiment may be the same as the first embodiment. First, when the gNB A (103) decides to hand over the UE B (102), the following can be identified from the updated management table of the UE B (102) (S504). That is, the gNB A (103) can identify that the UE A (101) is communicating with the gNB A (103) as a remote UE via the relay function of the relay UE B (102) (S504).

[0066] Also, as in the first embodiment, gNB A (103) determines whether the signal strength between UE A (101) is greater than or equal to a threshold for direct path connection (S507). If the signal strength is sufficient for direct path connection, 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).

[0067] 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 a relay UE or cell by UE A (101).

[0068] Next, a modified example will be described with reference to FIGS.

[0069] In the first embodiment (and the second embodiment) described above, the predetermined control is path switching from an indirect path to a direct path for a remote UE under the 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 the relay UE to be handed over, instead of or in addition to such path switching from an indirect path to a direct path.

[0070] 10 is a sequence diagram of a path switching determination for a remote UE when a gNB in ​​this modified example decides to hand over a relay UE. FIG. 11 is a flowchart of gNB A (103) in this modified example. FIG. 12 is a sequence diagram related to path switching to an indirect path.

[0071] 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 according to F406 and F407 are replaced by processes according 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.

[0072] 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).

[0073] In this modification, the gNB A (103) determines whether the signal strength is equal to or greater than the threshold for connecting the UE A (101) via a direct path (F405, S507), and then operates as follows: If the signal strength is not sufficient for connecting 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 the UE A (101) (S510). For example, if there is a relay UE candidate listed in the candidate relay UE list whose signal strength with the UE A (101) is equal to or greater than the threshold, the gNB A (103) may determine whether path switching is possible using the relay UE candidate as another relay UE. Note that the signal strength between the UE A (101) and the candidate relay UEs in the candidate relay UE list may be included in the measurement report from the UE A (101) in S501. In this case, the UE A (101) may execute a discovery process to search for candidate UE relays. Specifically, when the UE A (101) receives a discovery signal or a response signal to the discovery signal from a neighboring UE, the UE A (101) analyzes the received signal. Then, the UE A (101) creates a measurement report based on the analysis result.

[0074] 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).

[0075] 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 the switching to the indirect path via another relay UE.

[0076] In the example shown in Figure 12, gNB A (103) performs RRC reconfiguration to 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 contains information used in SRAP (Sidelink Relay Adaptation Protocol) required for operation as a remote UE.

[0077] 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. As a result, gNB A (103) can notify UE A (101) that it is switching from an indirect path via UE B (102) to an indirect path via UE C (105).

[0078] UE A (101) confirms receipt of an RRC reconfiguration message from gNB A (103). At this time, the control unit 301 confirms the ID of UE C (105) from sl-PathSwitchConfig to determine that the indirect path via UE B (102) is being switched to the indirect path via UE C (105) (F1105).

[0079] 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. In other words, UE A (101) can transmit and receive data with gNB A (103) via UE C (105).

[0080] 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). That is, UE A (101) transmits the RRC reconfiguration complete message to gNB A (103) via UE C (105) instead of via UE B (102).

[0081] 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) has been completed (F1107).

[0082] 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).

[0083] On the other hand, the UE A (101) releases the PC5 link with the UE B (102) (F1109).

[0084] Then, UE A (101) continues to transmit and receive user data with 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) with gNB A (103). Note that if there is an undelivered packet that UE B (102) is currently relaying, the undelivered packet is transferred to UE C (105) as needed, and then 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). When adopting the latter method of forwarding undelivered packets via gNB A (103), if the destination of the user data is not UE A (101) but uplink communication to the core network, forwarding to UE C (105) may be omitted.

[0085] Although each embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes are possible within the scope of the claims. It is also possible to combine all or a plurality of components of the above-described embodiments.

[0086] The following additional notes are provided regarding the above-described embodiments.

[0087] [Supplementary Note 1] A base station comprising: a control means for performing handover of a relay UE (User Equipment) having a Sidelink relay function to a remote UE in Sidelink to another base station in a situation where the base station is connected to the relay UE; and when the control means determines that handover of the relay UE to the other base station should be performed in a state where the remote UE is being relayed via the relay UE, the control means performs predetermined control related to communication on the remote UE before performing handover to the relay UE.

[0088] [Supplementary Note 2] The base station according to Supplementary Note 1, further comprising a storage means for storing management information relating to a relay state of subordinate UEs including the remote UE, wherein the control means performs the predetermined control based on the management information.

[0089] [Supplementary Note 3] The base station according to Supplementary Note 2, wherein the management information includes information representing each relay UE and a remote UE connected to the corresponding relay UE.

[0090] [Supplementary Note 4] The base station according to any one of Supplementary Notes 1 to 3, characterized in that the predetermined control includes path switching 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.

[0091] [Supplementary Note 5] The base station according to Supplementary Note 4, wherein the control means executes the path switching when the signal strength between the base station and the remote UE is equal to or greater than a threshold.

[0092] [Supplementary Note 6] The base station according to Supplementary Note 2, characterized in that the control means updates the management information based on a Measurement report or a SidelinkUEInformationNR message received from the remote UE.

[0093] [Supplementary Note 7] The base station according to Supplementary Note 6, characterized in that the control means updates the management information based on a determination result, determined from sl-MeasResultServingRelay in the Measurement report, of whether the remote UE is connected via the relay UE.

[0094] [Supplementary Note 8] The base station according to Supplementary Note 6, wherein the SidelinkUEInformationNR message includes information about the remote UE connected to the relay UE.

[0095] [Supplementary Note 9] A communication device having an NR (New Radio) Sidelink relay function, comprising: a transmitting means for transmitting a SidelinkUEInformationNR message, which is a Radio Resource Control (RRC) protocol message, to the base station in a situation where communication between a base station and a remote UE (User Equipment) in an NR Sidelink is being relayed; and the transmitting means includes information about the remote UE in the SidelinkUEInformationNR message.

[0096] [Supplementary Note 10] The communication device according to Supplementary Note 9, wherein the information of the remote UE includes a Source layer-2 ID of the remote UE.

[0097] [Supplementary Note 11] The communication device according to Supplementary Note 10, further comprising a control means for generating or updating a list that stores the Source Layer-2 ID of each remote UE when a PC5 link with the remote UE is established, wherein the transmission means includes the list in the SidelinkUEInformationNR message.

[0098] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0099] This application claims priority based on Japanese Patent Application No. 2023-119999, filed on July 24, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A base station having a control means for performing handover of the relay UE to another base station when connected to a remote UE in a Sidelink via a relay UE (User Equipment) having a Sidelink relay function, wherein the control means performs predetermined communication-related control on the remote UE before performing handover to the relay UE when it determines that handover of the relay UE to the other base station should be performed while the remote UE is being relayed via the relay UE.

2. The base station according to claim 1, further comprising a storage means for storing management information relating to a relay state of subordinate UEs including the remote UE, and the control means performs the predetermined control based on the management information.

3. The base station according to claim 2, wherein the management information includes information representative of each relay UE and a remote UE connected to the corresponding relay UE.

4. The base station according to claim 1, wherein the predetermined control includes path switching 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 4, wherein the control means executes the path switching when the signal strength between the base station and the remote UE is equal to or greater than a threshold.

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.

7. The base station according to claim 6, wherein the control means updates the management information based on a determination result as to whether or not the remote UE is connected via the relay UE, the determination result being determined from sl-MeasResultServingRelay in the Measurement report.

8. The base station according to claim 6, wherein the SidelinkUEInformationNR message includes information of the remote UE connected to the relay UE.

9. A communication device having an NR (New Radio) Sidelink relay function, comprising: a transmission means for transmitting a SidelinkUEInformationNR message, which is a Radio Resource Control (RRC) protocol message, to a base station in a situation where communication between a base station and a remote UE (User Equipment) in an NR Sidelink is being relayed; and the transmission means is characterized in that it includes information about the remote UE in the SidelinkUEInformationNR message.

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

11. The communication device according to claim 10, further comprising a control means for generating or updating a list that stores the Source Layer-2 ID of each remote UE when a PC5 link is established with the remote UE, wherein the transmission means includes the list in the SidelinkUEInformationNR message.

12. A control method for controlling communications, comprising a control step of performing handover of the relay UE (User Equipment) having a Sidelink relay function to another base station in a situation where a remote UE in a Sidelink is connected via the relay UE, wherein the control step includes, when it is determined that a handover should be performed for the relay UE to the other base station while the remote UE is being relayed via the relay UE, performing a predetermined control related to communications on the remote UE before performing handover to the relay UE.

13. A program for causing a computer to execute a control process for performing a handover of a relay UE (User Equipment) having a Sidelink relay function to another base station when connected to a remote UE in a Sidelink via the relay UE, the control process including, when it is determined that a handover should be performed for the relay UE to the other base station while the remote UE is being relayed via the relay UE, performing a predetermined communication-related control on the remote UE before performing a handover to the relay UE.

14. A control method for controlling communication of a communication device having an NR (New Radio) Sidelink relay function, comprising: a transmission step of transmitting a SidelinkUEInformationNR message, which is a Radio Resource Control (RRC) protocol message, to the base station in a situation where communication between a base station and a remote UE (User Equipment) in an NR Sidelink is being relayed, the SidelinkUEInformationNR message including information of the remote UE.

15. A program for controlling communication of a communication device having an NR (New Radio) Sidelink relay function, comprising: a program for causing a computer to execute a transmission step of transmitting a SidelinkUEInformationNR message, which is a Radio Resource Control (RRC) protocol message, to a base station in a situation where communication between a base station and a remote UE (User Equipment) in an NR Sidelink is being relayed, the SidelinkUEInformationNR message including information of the remote UE.

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