Base station, terminal, communication method, and program

Abstract

To reduce a time during which U-plane communication is stopped when handover of a master node is performed.SOLUTION: Provided is a base station including a control signal communication unit configured to receive a first message from a first base station that is a handover destination of a master node with which a terminal communicates, and a data communication unit configured to stop U-plane communication using a data radio bearer of a master cell group for the terminal and continue U-plane communication using a data radio bearer of a secondary cell group for the terminal when the first message includes information indicating that the master node with which the terminal communicates is to be handed over.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a base station, a terminal, a communication method, and a program. [Background technology]

[0002] The Third Generation Partnership Project (3GPP) has specified a technology called dual connectivity (hereinafter referred to as "DC") for fourth-generation (4G) and fifth-generation (5G) mobile communications systems, which enables communication between multiple different base stations using multiple Long Term Evolution (LTE) or New Radio (NR) carriers simultaneously. In a 5G Non-Stand Alone (NSA) architecture, which uses NR for the wireless section and the same Evolved Packet Core (EPC) as 4G for the core network, a terminal can communicate using LTE cells in an LTE area and both LTE and NR cells in areas where NR areas are overlapped, using E-UTRAN and NR - Dual Connectivity (EN-DC). On the other hand, in the 5G Stand Alone (SA) architecture, which uses NR for the radio section and 5th Generation Core Network (5GC) as the core network, NR-DC (New Radio - Dual Connectivity) enables multiple base stations to simultaneously communicate using NR cells with different frequencies in areas where the base station areas operating at different NR carrier frequencies overlap. The two types of DC in 5G, namely ENDC and NRDC, are collectively referred to as MR-DC (Multi-RAT Dual Connectivity). 5G DC also specifies a mechanism called a split bearer, which enables a single radio bearer to be divided into a bearer for a master cell group and a bearer for a secondary cell group for communication. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP TS 37.340 V18.1.0 (2024-03) Summary of the Invention [Problem to be solved by the invention]

[0004] When DC is used, a terminal communicates with two base stations called a master node (hereinafter also referred to as "MN") and a secondary node (hereinafter also referred to as "SN"). Furthermore, when the terminal moves outside the cell of the master node, the terminal must perform a master node handover (HO: Handover). Here, according to the specifications from Release 12, when DC was first specified in 3GPP, to Release 18 and earlier, when a master node handover is performed, U-plane communication must be temporarily stopped until the handover is completed, even if communication with the secondary node is possible. As a result, communication is interrupted even though communication between the terminal and the secondary node is possible.

[0005] Therefore, an object of the present invention is to provide a technology that enables reducing the time that U-plane communication is stopped when a master node handover is performed. [Means for solving the problem]

[0006] A base station according to one embodiment of the present invention has a control signal communication unit that receives a first message from a first base station that is a handover destination of the master node with which the terminal communicates, and a data communication unit that, if the first message includes information indicating that a handover of the master node with which the terminal communicates will be performed, stops U-plane communication using a data radio bearer of the master cell group for the terminal and continues U-plane communication using a data radio bearer of the secondary cell group for the terminal. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a technology that makes it possible to reduce the time that U-plane communication is stopped when a handover of a master node is performed. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating an example of a system configuration of a wireless communication system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram illustrating a split bearer. [Figure 3] FIG. 2 is a diagram illustrating an example of the hardware configuration of a terminal and a base station. [Figure 4] FIG. 2 is a diagram illustrating an example of a functional block configuration of a terminal. [Figure 5] FIG. 2 is a diagram illustrating an example of a functional block configuration of a base station. [Figure 6] FIG. 2 is a diagram illustrating an example of a functional block configuration of a base station. [Figure 7] FIG. 10 is a sequence diagram for explaining a processing procedure 1. [Figure 8] FIG. 10 is a sequence diagram for explaining a processing procedure 1. [Figure 9] FIG. 10 is a sequence diagram for explaining a processing procedure 2. [Figure 10] FIG. 10 is a sequence diagram for explaining a processing procedure 2. [Figure 11] 10 is a flowchart illustrating an example of a processing procedure performed by a base station. [Figure 12]10 is a flowchart illustrating an example of a processing procedure performed by a base station. [Figure 13] 10 is a flowchart illustrating an example of a processing procedure performed by a terminal. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the accompanying drawings, in which the same reference numerals denote the same or similar components.

[0010] <System configuration> 1 is a diagram showing an example of the system configuration of a wireless communication system according to this embodiment. The wireless communication system 1 includes a terminal 10, a base station 20a, a base station 20b, a base station 30, and a core network (hereinafter referred to as "CN") 40.

[0011] The terminal 10 is, for example, a smartphone, a mobile phone, an IoT (Internet of Things) device, an in-vehicle terminal, or the like, and is also called UE (User Equipment).

[0012] Base station 20a and base station 20b are base stations that operate as master nodes. A master node is a base station that provides a C-plane (Control plane) connection to a core network. In the following description, when there is no need to distinguish between base station 20a and base station 20b, they will be referred to as base station 20. Furthermore, base station 30 is a base station that operates as a secondary node. A secondary node is a base station that does not provide a C-plane connection to a core network.

[0013] A group of one or more cells C20a formed by the base station 20a and one or more cells C20b formed by the base station 20b is called a master cell group (MCG). A group of one or more cells C30 formed by the base station 30 is called a secondary cell group (SCG). The base stations 20 and 30 may support wireless communication technologies such as LTE, 5G, 6G, and 6G and beyond. The base stations 20 and 30 may also be called eNBs (enhanced NodeBs), gNBs, En-gNBs, Ng-eNBs, etc.

[0014] The CN 40 is, for example, a 4G core network (Evolved Packet Core: EPC) or a 5G core network (5G Core Network: 5GC), but is not limited to these and also includes core networks of 6G and beyond. The CN 40 performs, for example, mobility management that manages the location of the terminal 10, QoS control, and path management for U-plane (User Plane) communication.

[0015] 5G(5th In the Mobile Radio Generation (MR-DC), MR-DC is introduced, in which a terminal 10 communicates simultaneously with multiple base stations 20 and 30. MR-DC defines multiple scenarios, such as EN-DC, in which the master node is LTE and the secondary node is 5G, and NR-DC, in which both the master node and the secondary node are 5G.

[0016] Figure 2 is a diagram for explaining a split bearer. As shown in Figure 2, U-plane data transmitted from CN40 is first input to base station 30, which is a secondary node. Note that U-plane data refers to data transmitted and received by users. On the other hand, C-plane data refers to control data required for communication, transmitted and received between terminal 10 and base station 20, between terminal 10 and CN40, etc.

[0017] When using a split bearer, the base station 30 decides whether to transmit downlink U-plane data to the terminal 10 via a radio bearer between the base station 30 and the terminal 10 (i.e., a data radio bearer of the secondary cell group), or via a radio bearer between the base station 20 and the terminal 10 (i.e., a data radio bearer of the master cell group). When transmitting to the terminal 10 via a radio bearer between the base station 30 and the terminal 10, the base station 30 transmits the U-plane data directly to the terminal 10. On the other hand, when transmitting to the terminal 10 via a radio bearer between the base station 20 and the terminal 10, the base station 30 transmits the U-plane data to the base station 20 via the Xn interface (or X2 interface). Subsequently, the base station 20 transmits the U-plane data received from the base station 30 to the terminal 10.

[0018] In addition, there is also a method for split bearer in which the base station 20, which is the master node, inputs and outputs U-plane data to and from the CN 40. However, in the currently widely used EN-DC, 5G base stations have higher performance. Therefore, in general, as shown in Figure 2, a method is often used in which the base station 30, which is the secondary node, inputs and outputs U-plane data.

[0019] As described above, according to the 3GPP regulations, when a handover of the master node is performed, the terminal 10 and the base station 20 must temporarily suspend U-lane communication until the handover is completed, even if they are able to communicate with the secondary node. Therefore, the wireless communication system 1 according to this embodiment makes it possible to continue U-plane communication via the secondary node while a handover of the master node is being performed.

[0020] <Hardware configuration> 3 is a diagram showing an example of the hardware configuration of the terminal 10, the base station 20, and the base station 30. The terminal 10, the base station 20, and the base station 30 each include a processor 11 such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), a memory (for example, a RAM (Random Access Memory) or a ROM (Read Only Memory)), a storage device 12 such as an HDD (Hard Disk Drive) and / or an SSD (Solid State Drive), a communication device 13 that performs wired or wireless communication, and an input / output device 14 that receives input operations and outputs information. The communication device 13 includes an antenna, an RF (Radio Frequency) circuit, a BB (Base Band) circuit, etc.

[0021] <Function block configuration> (Terminal) FIG. 4 is a diagram showing an example of a functional block configuration of the terminal 10. The terminal 10 includes a storage unit 100, a control signal communication unit 101, and a data communication unit 102. The storage unit 100 can be realized using a storage unit 12 included in the terminal 10. The control signal communication unit 101 and the data communication unit 102 can be realized by the processor 11 of the terminal 10 executing a program stored in the storage unit 12. The program can be stored in a storage medium. The storage medium storing the program may be a non-transitory computer-readable medium. The non-transitory storage medium is not particularly limited, and may be, for example, a storage medium such as a universal serial bus (USB) memory or a compact disc read-only memory (CD-ROM).

[0022] The storage unit 100 stores information necessary for the terminal 10 to operate and information necessary for the terminal 10 to communicate with the base station 20 or the base station 30. The information includes, for example, broadcast information, system information, and information set in the terminal 10 by individual RRC (Radio Resource Control) signaling.

[0023] The control signal communication unit 101 transmits and receives various control signals (for example, RRC messages and NAS (Network Access Stratum) messages) between the base station 20, the base station 30, and the CN 40. The control signal communication unit 101 also transmits and receives various control signals between other base stations 20 or 30 via the Uu interface.

[0024] The data communication unit 102 transmits and receives U-plane data between the base station 20 and the base station 30.

[0025] (base station) 5 is a diagram showing an example of a functional block configuration of the base station 20. The base station 20 includes a storage unit 200, a control signal communication unit 201, and a data communication unit 202. The storage unit 200 can be realized using the storage unit 12 included in the base station 20. The control signal communication unit 201 and the data communication unit 202 can be realized by the processor 11 of the base station 20 executing a program stored in the storage unit 12. The program can be stored in a storage medium. The storage medium storing the program may be a computer-readable non-transitory storage medium. The non-transitory storage medium is not particularly limited, and may be, for example, a storage medium such as a USB memory or a CD-ROM.

[0026] The storage unit 200 stores information necessary for the base station 20 to operate and information necessary for the base station 20 to communicate with the terminal 10, the base station 30, or the CN 40. The information may be written to a memory or the like of the base station 20 using, for example, a maintenance system or the like.

[0027] The control signal communication unit 201 transmits and receives various control signals (for example, X2 messages, Xn messages, RRC messages, etc.) between the terminal 10, the base station 30, and the CN 40. The control signal communication unit 101 also transmits and receives various control signals between another base station 20 or the base station 30 via the X2 interface or the Xn interface.

[0028] The data communication unit 102 transmits and receives U-plane data between the terminal 10 and the base station 30.

[0029] 6 is a diagram showing an example of a functional block configuration of the base station 30. The base station 30 includes a storage unit 300, a control signal communication unit 301, and a data communication unit 302. The storage unit 300 can be realized using the storage unit 12 included in the base station 30. The control signal communication unit 301 and the data communication unit 302 can be realized by the processor 11 of the base station 30 executing a program stored in the storage unit 12. The program can be stored in a storage medium. The storage medium storing the program may be a computer-readable non-transitory storage medium. The non-transitory storage medium is not particularly limited, and may be, for example, a storage medium such as a USB memory or a CD-ROM.

[0030] The storage unit 300 stores information necessary for the operation of the base station 30 and information necessary for the base station 30 to communicate with the terminal 10, the base station 30, or the CN 40. The information may be written to the memory of the base station 30 using a maintenance system or the like, for example.

[0031] The control signal communication unit 301 transmits and receives various control signals (for example, X2 messages, Xn messages, RRC messages, etc.) between the terminal 10, the base station 30, and the CN 40. Furthermore, the control signal communication unit 101 transmits and receives various control signals between the base station 20 or another base station 30 via the X2 interface or the Xn interface.

[0032] The data communication unit 102 transmits and receives U-plane data between the terminal 10 and the base station 30.

[0033] <Processing Procedure> Next, a description will be given of a plurality of processing procedures performed by the wireless communication system 1. In the following processing procedures, it is assumed that the terminal 10 is communicating with the base station 20a, which is the master node, and the base station 30, which is the secondary node, using MR-DC and a split bearer. It is also assumed that the terminal 10 performs handover from the cell C20a of the base station 20a to the cell C20b of the base station 20b due to movement of the terminal 10.

[0034] Processing procedure 1 is a procedure for instructing the terminal 10 to perform a handover by using RRC signaling via an SRB2 (Signaling Radio Bearer) established between the terminal 10 and the master node. In other words, processing procedure 1 is a procedure for transmitting an RRC message instructing the terminal 10 to perform a handover from the base station 20, which is the handover source, to the terminal 10.

[0035] Processing procedure 2 is a procedure for instructing the terminal 10 to perform a handover by using RRC signaling via an SRB3 (Signaling Radio Bearer) established between the terminal 10 and a secondary node. In other words, processing procedure 2 is a procedure for transmitting an RRC message instructing the terminal 10 to perform a handover from the base station 30, which is the secondary node, to the terminal 10.

[0036] [Procedure 1] 7 and 8 are sequence diagrams for explaining processing procedure 1. In Fig. 7 and Fig. 8, base station 20a is the handover source base station (Source MN), and base station 20b is the handover destination base station (Target MN). In the following description, the RRC Reconfiguration message and the RRC Reconfiguration Complete message may be read as the RRC Connection Reconfiguration message and the RRC Connection Reconfiguration Complete message, respectively.

[0037] In step S100, the terminal 10, the base station 20a, and the base station 30 transmit and receive U-plane data using split bearers. In the case of downlink U-plane data, the U-plane data transmitted from the CN 40 to the base station 30 is transmitted to the terminal 10 via either or both of a master cell group data radio bearer (MCG DRB: Master Cell Group Data Radio Bearer) and a secondary cell group data radio bearer (SCG DRB). In addition, the terminal 10 transmits uplink U-plane data via either or both of a master cell group data radio bearer and a secondary cell group data radio bearer.

[0038] In step S101, the terminal 10 measures the reception quality of cells existing around the terminal 10, and transmits a measurement report message including the measurement result to the base station 20a.

[0039] In step S102, based on the measurement report message, the base station 20a decides to perform handover of the terminal 10. Here, it is assumed that the base station 20a has decided to change the master node of the terminal 10 to the base station 20b.

[0040] In step S103, the base station 20a transmits a handover request message (MN HO Request) to the base station 20b. The handover request message includes various information (e.g., a target cell ID of the handover destination, key information used for encryption, etc.) required for the base station 20b to process the handover of the terminal 10.

[0041] In step S104, the base station 20b checks whether or not resources necessary for accepting the terminal 10 are available and reserves them. This process is called admission control. For example, the base station 20b assigns a random access preamble to be used by the terminal 10 and reserves a C-RNTI (Cell-Radio Network Temporary Identifier).

[0042] In step S105, the base station 20b transmits a secondary node addition request message (SN Addition Request) to the base station 30 to notify the base station 30 that the base station 20b will become the master node. At this time, the base station 20b transmits the secondary node addition request message to the base station 30, including information (MN HO Admission) indicating that handover of the master node with which the terminal 10 communicates. The information indicating that handover of the master node will be performed may be expressed by a Cause value (value indicating a reason) of the secondary node addition request message. The secondary node addition request message also includes information for identifying the terminal 10 that will perform handover (for example, an identifier of the terminal 10, etc.).

[0043] In step S106, the base station 30 transmits a secondary node addition response (SN Addition Request ACK) to the base station 20b.

[0044] In step S107, the base station 30 receives from the base station 20b a secondary node addition request message including information indicating that a handover of the master node is to be performed, and temporarily suspends transmission and reception of U-plane data via the data radio bearer (MCG DRB) of the master cell group among the split bearers for the terminal 10. Furthermore, the base station 30 continues transmission and reception of U-plane data via the data radio bearer (SCG DRB) of the secondary cell group among the split bearers for the terminal 10 without suspending it.

[0045] In addition, if the base station 30 receives information indicating an abnormality in the secondary cell group from the base station 20b in the processing procedure of step S105, the base station 30 may stop both the transmission and reception of U-plane data in the master cell group and the secondary cell group in the processing procedure of step S107.

[0046] In step S108, the base station 20b transmits a handover request acknowledgement message (MN HO Request Ack) to the base station 20a in response to the handover request message (MN HO Request). Here, the base station 20b generates an RRC Reconfiguration message to be transmitted by the base station 20a to the terminal 10, stores the message in the acknowledgement message, and transmits the message to the base station 20a. The RRC Reconfiguration message generated by the base station 20b includes various pieces of information required for the terminal 10 to connect to the cell C20b of the base station 20b, such as the cell ID of the cell to which the terminal 10 should connect, RACH (Random Access Channel) resources, and the number of the random access preamble assigned to the terminal 10.

[0047] In step S109, the base station 20a extracts the RRC Reconfiguration message included in the handover request response message received from the base station 20b and transmits it to the terminal 10.

[0048] In step S110, the base station 20a sends a PDCP Serial Number Status Transfer message to the base station 20b.

[0049] In step S111, the terminal 10 that has received the RRC Reconfiguration message detaches from the base station 20a in accordance with the RRC Reconfiguration message.

[0050] In step S112, the terminal 10 and the base station 30 transmit and receive U-plane data via a data radio bearer (SCG DRB) of the secondary cell group.

[0051] In step S113, the base station 20a transmits a secondary node release request message (SN Release Request) to the base station 30 to notify the base station 30 that the base station 20a is no longer the master node.

[0052] In step S114, the base station 30 transmits a secondary node release request acknowledgement message (SN Release Request Ack) to the base station 20a.

[0053] In step S115, the terminal 10 executes a random access procedure with the base station 20b based on the RRC Reconfiguration message received in step S109, and connects to (is present in) the base station 20b.

[0054] In step S116, when the connection with the base station 20b is completed, the terminal 10 transmits an RRC Reconfiguration Complete message to the base station 20b.

[0055] In step S117, the base station 20b transmits a secondary node reconfiguration complete message (SN Reconfiguration Complete) to the base station 30 to notify the base station 30 that the handover of the master node of the terminal 10 has been completed. Note that the secondary node reconfiguration complete message may include information for identifying the terminal 10 (for example, an identifier of the terminal 10, etc.).

[0056] In step S118, upon receiving the secondary node reconfiguration completion message, the base station 30 resumes transmission and reception of U-plane data via the master cell group data radio bearer (MCG DRB) among the split bearers for the terminal 10.

[0057] In step S119, downlink U-plane data via the data radio bearer (MCG DRB) of the master cell group is first transmitted from base station 30 to base station 20a, then transmitted from base station 20a to base station 20b, and then transmitted from base station 20b to terminal 10. Meanwhile, uplink U-plane data via the data radio bearer (MCG DRB) of the master cell group is transmitted from terminal 10 to base station 30b.

[0058] In step S120, the base station 20a performs a procedure for updating the path configuration among the base station 20b, the base station 30, and the CN 40.

[0059] In step S121, since the handover of the terminal 10 is completed, the base station 20b transmits a UE context release message (UE Context Release) to the base station 20a.

[0060] In step S122, the base station 20a transmits to the base station 30 a UE context release message regarding the DC between the base station 20a of the terminal 10 and the base station 30. However, since the base station 30 is communicating as a secondary node in the DC between the terminal 10 and the base station 20a, the base station 30 does not release the UE context regarding the DC between the terminal 10 and the base station 20a.

[0061] In step S123, when the path configuration update is completed, downlink U-plane data via the data radio bearer (MCG DRB) of the master cell group is transmitted from base station 30 to base station 20b, and then transmitted from base station 20b to terminal 10. Meanwhile, uplink U-plane data via the data radio bearer (SCG DRB) of the secondary cell group is transmitted from terminal 10 to base station 30b.

[0062] [Procedure 2] 9 and 10 are sequence diagrams for explaining the processing procedure 2. FIG.

[0063] The processing procedures of steps S200 to S209 are the same as the processing procedures of steps S100 to S108 and S110 in FIG. 7, respectively, and therefore will not be described again.

[0064] In step S210, the base station 20a extracts an RRC Reconfiguration message from the handover request acknowledgement message (MN HO Request Ack) received in the processing procedure of step S208. The base station 20a also stores the extracted RRC Reconfiguration message in an RRC transfer message (RRC Transfer) and transmits the RRC Reconfiguration message to the base station 30.

[0065] In step S211, base station 30 stores the RRC Reconfiguration message extracted from the RRC transfer message in a downlink RRC transfer message (DL RRC Transfer MRDC), and transmits the message to terminal 10. The downlink RRC transfer message may be referred to as a DLInformationTransferMRDC message.

[0066] In step S212, the terminal 10 that has received the downlink RRC transfer message detaches from the base station 20a in accordance with the RRC Reconfiguration message included in the downlink RRC transfer message.

[0067] The processing procedures of steps S213 to S215 are the same as steps S112 to S114 in FIG. 7, respectively, and therefore will not be described again.

[0068] In step S216, the terminal 10 executes a random access procedure with the base station 20b based on the RRC Reconfiguration message included in the downlink RRC transfer message received in step S211, and connects to (is present in) the base station 20b.

[0069] In step S217, when the connection with the base station 20b is completed, the terminal 10 transmits an RRC Reconfiguration Complete message in an uplink RRC transfer message (UL RRC Transfer MRDC) to the base station 30. The uplink RRC transfer message may be referred to as ULInformationTransferMRDC.

[0070] In step S219, when the base station 30 receives the uplink RRC transfer message from the terminal 10, it extracts the RRC Reconfiguration Complete message from the uplink RRC transfer message. The base station 30 also includes the RRC Reconfiguration Complete message in the RRC transfer message and transmits it to the base station 20b. By receiving the RRC Reconfiguration Complete message, the base station 20b recognizes that the handover of the terminal 10 has been completed.

[0071] In step S219, when the base station 30 receives the RRC transfer message including the RRC Reconfiguration Complete message, it resumes transmission and reception of U-plane data via the master cell group data radio bearer (MCG DRB) among the split bearers for the terminal 10.

[0072] The processing procedures of steps S220 to S224 are the same as the processing procedures of steps S119 to S122 in FIG. 7, respectively, and therefore will not be described again.

[0073] [Processing procedure of base station 30] 11 is a flowchart showing an example of a processing procedure performed by the base station 30. The processing procedure performed by the base station 30, which is a secondary node, will be described with reference to FIG.

[0074] In step S300, the control signal communication unit 301 of the base station 30 receives a message (first message) from the base station 20b (first base station) that is the handover destination of the master node with which the terminal 10 communicates. The message (first message) may be, but is not limited to, a secondary node addition request message (SN Addition Request) shown in step S105 of Fig. 7 or step S205 of Fig. 10. It may also be a message different from the secondary node addition request message.

[0075] In step S301, the control signal communication unit 301 checks whether the received message includes information indicating that a handover of the master node with which the terminal 10 communicates will be performed, or whether the received message includes information indicating an abnormality in the secondary cell group. If the received message includes information indicating that a handover of the master node with which the terminal 10 communicates will be performed, the process proceeds to step S302, and if the received message includes information indicating an abnormality in the secondary cell group, the process proceeds to step S303.

[0076] In step S302, if the message (first message) includes information indicating that a handover of the master node with which the terminal 10 communicates will be performed, the control signal communication unit 301 stops U-plane communication using the data radio bearer of the master cell group for the terminal 10, and continues U-plane communication using the data radio bearer of the secondary cell group for the terminal 10. Note that in this embodiment, "information indicating that a handover of the master node with which the terminal 10 communicates will be performed" may be read as "information indicating that only a handover of the master node will be performed without a handover of the secondary node with which the terminal 10 communicates."

[0077] In step S303, if the message (first message) contains information indicating an abnormality in the secondary cell group in which the terminal 10 is located, the control signal communication unit 301 stops U-plane communication using the data radio bearer of the master cell group for the terminal 10 and U-plane communication using the data radio bearer of the secondary cell group for the terminal 10.

[0078] Note that after the processing procedure of step S302, the control signal communication unit 301 may receive information instructing the terminal 10 to perform a handover of the master node from the base station 20b (first base station) or the base station 20a (second base station) which is the master node with which the terminal 10 communicates, and may transmit a message (second message) including the received information to the terminal 10. At this time, the control signal communication unit 301 may transmit the message (second message) to the terminal 10 via a control radio bearer (SRB: Signaling Radio Bearer) of the secondary node. The control radio bearer may be called SRB3. Furthermore, the message (second message) may be the message (DL RRC Transfer MRDC) shown in step S211 of FIG. 9.

[0079] [Processing procedure of base station 20b] 12 is a flowchart showing an example of a processing procedure performed by the base station 20b. The processing procedure performed by the base station 20b, which is the master node of the handover destination of the terminal 10, will be described with reference to FIG.

[0080] In step S400, the control signal communication unit 201 receives, from the base station 20a (first base station) that serves as the master node and communicates with the terminal 10, a handover request of the master node with which the terminal 10 communicates. The handover request may be the handover request shown in step S103 of Fig. 7 and step S203 of Fig. 9.

[0081] In step S401, when the control signal communication unit 201 (first transmission unit) receives a master node handover request, it transmits a message (first message) including information indicating that the master node will be handed over to the base station 20b (second base station) operating as the secondary node of the terminal 10. The message (first message) may be a secondary node addition request message (SN Addition Request) shown in step S105 of Fig. 7 or step S205 of Fig. 10, or may be a message different from the secondary node addition request message.

[0082] In step S402, the control signal communication unit 201 receives, from the base station 20b (second base station), a receipt response to a message (first message) including information indicating that a handover of the master node will be performed. The receipt response to the message (first message) may be the response message (SN Addition Request Ack) shown in step S106 of FIG. 7 or step S206 of FIG. 10.

[0083] In step S403, the control signal communication unit 201 (second transmission unit) transmits a response message to the handover request received in step S400 to the base station 20a (first base station). The response message includes information instructing the terminal 10 to perform handover of the master node to the base station 20a (first base station). The response message to the handover request may be the response message (MN HO Request Ack) shown in step S108 of FIG. 7 or step S208 of FIG. 10.

[0084] [Terminal 10 processing procedure] 13 is a flowchart showing an example of a processing procedure performed by the terminal 10. The processing procedure performed by the terminal 10 will be described with reference to FIG.

[0085] In step S500, the control signal communication unit 101 receives an RRC message from the base station 20a. The RRC message may be a message (RRC Connection Reconfiguration or RRC Reconfiguration) shown in step S109 of Fig. 7 or a message (DL RRC Transfer MRDC including RRC Connection Reconfiguration or RRC Reconfiguration) shown in step S211 of Fig. 10.

[0086] In step S501, the control signal communication unit 101 checks whether the RRC message received from the base station 20a includes information instructing a handover of the master node. If it does, the process proceeds to step S502, and if it does not, the process proceeds to step S503.

[0087] In step S502, if the RRC message contains information instructing a handover of the master node, the data communication unit 102 stops U-plane communication using the data radio bearer of the master cell group and continues U-plane communication using the data radio bearer of the secondary cell group from the time when the data communication unit 102 disconnects the connection with the base station 20a, which is the master node, until it sends a response to the RRC message to the base station 20b, which is the new master node to which the handover is to be performed.

[0088] In step S503, if the RRC message does not include information instructing to perform a handover of the master node, the control signal communication unit 101 executes processing according to the information included in the RRC message.

[0089] In the processing procedure of step S502, the control signal communication unit 101 may disconnect the connection with the base station 20a which is the master node, start communication with the base station 20b which is the new master node, and then transmit a response message to the RRC message to the base station 20b. The response message may be an RRC Reconfiguration Complete message shown in step S116 of Fig. 8.

[0090] Furthermore, in the processing procedure of step S502, the control signal communication unit 101 may disconnect the connection with the base station 20a serving as the master node, start communication with the base station 20b serving as a new master node, and then transmit a response message to the RRC message to the base station 30 operating as a secondary node corresponding to the secondary cell group. The response message may be a UL RRC Transfer MRDC message including RRC Connection Reconfiguration Complete or RRC Reconfiguration Complete, as shown in step S217 of Fig. 10.

[0091] <Summary> According to this embodiment, it is possible to provide a technology that can reduce the time that U-plane communication is stopped when a master node handover is performed. Therefore, the technology according to this embodiment can contribute to achieving Goal 9 of the Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote inclusive and sustainable industrialization, and promote innovation and infrastructure."

[0092] Furthermore, in the case of processing procedure 2, a secondary node with which communication is considered to be stable can transmit an RRC message (RRC Reconfiguration message) instructing handover to the terminal 10. This makes it possible to reduce the possibility that the terminal 10 will fail to receive the RRC message.

[0093] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The flowcharts, sequences, elements included in the embodiments, and their arrangements, materials, conditions, shapes, sizes, etc., described in the embodiments are not limited to those illustrated and can be modified as appropriate. Furthermore, configurations shown in different embodiments can be partially substituted or combined with each other. [Explanation of symbols]

[0094] 10 terminal, 11 processor, 12 storage device, 13 communication device, 14 input / output device, 20 base station, 30 base station, 40 core network, 100 storage unit, 101 control signal communication unit, 102 data communication unit, 200 storage unit, 201 control signal communication unit, 202 data communication unit, 300 storage unit, 301 control signal communication unit, 302 data communication unit

Claims

1. a control signal communication unit that receives a first message from a first base station that is a handover destination of a master node with which the terminal communicates; a data communication unit that, when the first message includes information indicating that a handover of the master node with which the terminal communicates is to be performed, stops U-plane communication using a data radio bearer of a master cell group for the terminal and continues U-plane communication using a data radio bearer of a secondary cell group for the terminal; A base station having

2. When the first message includes information indicating an abnormality in the secondary cell group in which the terminal is located, the data communication unit stops U-plane communication using a data radio bearer of the master cell group for the terminal and U-plane communication using a data radio bearer of the secondary cell group for the terminal. The base station of claim 1 .

3. The control signal communication unit receives information instructing the terminal to perform handover of the master node from the first base station or a second base station that is a master node with which the terminal communicates, and transmits a second message including the received information to the terminal. The base station of claim 1 .

4. The control signal communication unit transmits the second message to the terminal via a control radio bearer of a secondary node. The base station according to claim 3 .

5. The first message is a secondary node addition request message. The base station of claim 1 .

6. a first transmitting unit that, when receiving a handover request of the master node with which the terminal communicates from a first base station that communicates with the terminal as a master node, transmits a first message including information indicating that the master node will be handed over to a second base station that operates as a secondary node of the terminal; a second transmitting unit that transmits a response message to the handover request when a reception response to the first message is received from the second base station; A base station having

7. The second transmission unit transmits the response message to the first base station, the response message including information instructing the terminal to perform handover of the master node. The base station of claim 6.

8. The first message is a secondary node addition request message. The base station of claim 6.

9. a control signal communication unit that receives an RRC message from a base station; a data communication unit that, when the RRC message includes information instructing to perform a handover of a master node, stops U-plane communication using a data radio bearer of a master cell group and continues U-plane communication using a data radio bearer of a secondary cell group from the time when the connection with the master node is disconnected until a response to the RRC message is transmitted to a new master node that is a handover destination; and A terminal having:

10. The control signal communication unit disconnects the connection with the master node, starts communication with the new master node, and then transmits a response message to the RRC message to the new master node. The terminal according to claim 9.

11. The control signal communication unit disconnects the connection with the master node, starts communication with the new master node, and then transmits a response message to the RRC message to a base station operating as a secondary node corresponding to the secondary cell group. The terminal according to claim 9.

12. receiving a first message from a first base station that is a handover destination of a master node with which the terminal communicates; If the first message includes information indicating that a handover of the master node with which the terminal communicates is to be performed, stopping U-plane communication for the terminal using a data radio bearer of a master cell group and continuing U-plane communication for the terminal using a data radio bearer of a secondary cell group; A communication method performed by a base station, including:

13. receiving a first message from a first base station that is a handover destination of a master node with which the terminal communicates; If the first message includes information indicating that a handover of the master node with which the terminal communicates is to be performed, stopping U-plane communication for the terminal using a data radio bearer of a master cell group and continuing U-plane communication for the terminal using a data radio bearer of a secondary cell group; A program that causes a computer to execute the following.

14. When a handover request of the master node with which the terminal communicates is received from a first base station that communicates with the terminal as a master node, transmitting a first message including information indicating that handover of the master node will be performed to a second base station that operates as a secondary node of the terminal; transmitting a response message to the handover request when receiving a receipt response to the first message from the second base station; A communication method performed by a base station having the

15. When a handover request of the master node with which the terminal communicates is received from a first base station that communicates with the terminal as a master node, transmitting a first message including information indicating that handover of the master node will be performed to a second base station that operates as a secondary node of the terminal; transmitting a response message to the handover request when receiving a receipt response to the first message from the second base station; A program that causes a computer to execute the following.

16. receiving an RRC message from a base station; If the RRC message includes information instructing to perform a handover of the master node, stopping U-plane communication using the data radio bearer of the master cell group and continuing U-plane communication using the data radio bearer of the secondary cell group from the time when the connection with the master node is disconnected until a response to the RRC message is transmitted to a new master node that is a handover destination; A communication method performed by a base station having the

17. receiving an RRC message from a base station; If the RRC message includes information instructing to perform a handover of the master node, stopping U-plane communication using the data radio bearer of the master cell group and continuing U-plane communication using the data radio bearer of the secondary cell group from the time when the connection with the master node is disconnected until a response to the RRC message is transmitted to a new master node that is a handover destination; A program that causes a computer to execute the following.

Images