Communication control method, base station, core network device, and system

Abstract

To provide a communication control method used in a mobile communication system to provide multicast broadcast services (MBS) to terminals and to provide a base station, a core network device, and a mobile communication system.SOLUTION: The communication control method includes the steps of: receiving, by a first base station gNB200A that establishes an MBS connection with a core network device UPF300A, MBS data via the MBS connection from the core network device; transmitting, by the first base station, to first user equipment UE100 in multicast or broadcast, the MBS data received from the core network device; and transmitting, by the first base station, to a second base station gNB200B, a handover request message including at least one of a first identifier that identifies the core network device and a second identifier that identifies an MBS session provided by the first base station in multicast or broadcast.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a base station, a method, and a system.

Background Art

[0002] In recent years, the fifth-generation (5G) mobile communication system has attracted attention. NR (New Radio), which is a radio access technology (RAT) of the 5G system, has characteristics such as high speed, large capacity, high reliability, and low latency compared to LTE (Long Term Evolution), which is a fourth-generation radio access technology.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

[0004] A communication control method according to a first aspect is a communication control method used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user device. A first base station that establishes an MBS connection with a core network device receives MBS data from the core network device via the MBS connection, the first base station transmits the MBS data received from the core network device to a first user device by multicast or broadcast, and the first base station transmits at least one of a first identifier that identifies the core network device and a second identifier that identifies an MBS session provided by the first base station by multicast or broadcast to a second base station.

[0005] The communication control method according to the second aspect is a communication control method used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user equipment, and includes a first base station receiving, from a core network device, a notification including a first identifier for identifying a second base station and a second identifier for identifying an MBS session provided by the second base station in multicast or broadcast.

[0006] The communication control method according to the third aspect is a communication control method used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user equipment, and includes a first base station transmitting, to a core network device, a notification indicating that a handover of the user equipment from the first base station to the second base station is a handover of the user equipment while receiving MBS when the handover is performed.

Brief Description of the Drawings

[0007]

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Mode for Carrying Out the Invention

[0008] It has been considered to introduce multicast and broadcast services into the 5G system (NR). It is desired that the multicast and broadcast service of NR provides a service improved from the multicast and broadcast service of LTE.

[0009] Therefore, an object of the present invention is to realize an improved multicast and broadcast service.

[0010] The mobile communication system according to the embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] (Configuration of Mobile Communication System) First, the configuration of the mobile communication system according to the embodiment will be described. FIG. 1 is a diagram showing the configuration of the mobile communication system according to the embodiment. This mobile communication system complies with the 5th generation system (5GS) of the 3GPP (registered trademark) standard. Hereinafter, the 5GS will be described as an example, but the LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system, or the 6th generation (6G) system may be at least partially applied.

[0012] As shown in FIG. 1, the mobile communication system includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20.

[0013] The UE 100 is a movable wireless communication device. The UE 100 can be any device used by a user. For example, the UE 100 can be a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in the sensor, a vehicle or a device provided in the vehicle (Vehicle UE), an aircraft or a device provided in the aircraft (Aerial UE).

[0014] The NG-RAN 10 includes base stations (referred to as "gNB" in the 5G system) 200. The gNBs 200 are interconnected via an Xn interface which is a base station-to-base station interface. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its own cell. The gNB 200 has functions such as a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), and / or a measurement control function for mobility control and scheduling. "Cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency.

[0015] Note that the gNB can also be connected to an Evolved Packet Core (EPC) which is the core network of LTE. The base station of LTE can also be connected to the 5GC. The base station of LTE and the gNB can also be connected via a base station-to-base station interface.

[0016] 5GC20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls for the UE100. The AMF manages the mobility of the UE100 by communicating with the UE100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF are connected to the gNB200 via the NG interface, which is an interface between the base station and the core network.

[0017] FIG. 2 is a diagram showing the configuration of a UE100 (user equipment) according to an embodiment.

[0018] As shown in FIG. 2, the UE100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130.

[0019] The receiving unit 110 performs various receptions under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130.

[0020] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmitted signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0021] The control unit 130 performs various controls in the UE100. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for the processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of the baseband signal. The CPU executes the programs stored in the memory to perform various processes.

[0022] FIG. 3 is a diagram showing the configuration of the gNB 200 (base station) according to the embodiment.

[0023] As shown in FIG. 3, the gNB 200 includes a transmission unit 210, a reception unit 220, a control unit 230, and a backhaul communication unit 240.

[0024] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0025] The reception unit 220 performs various receptions under the control of the control unit 230. The reception unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (reception signal) and outputs it to the control unit 230.

[0026] The control unit 230 performs various controls in the gNB 200. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of the baseband signal, etc. The CPU executes the programs stored in the memory to perform various processes.

[0027] The backhaul communication unit 240 is connected to an adjacent base station via a base station interface. The backhaul communication unit 240 is connected to the AMF / UPF 300 via a base station-core network interface. Note that the gNB is composed of a CU (Central Unit) and a DU (Distributed Unit) (that is, functionally divided), and the two units may be connected by an F1 interface.

[0028] FIG. 4 is a diagram showing the configuration of the protocol stack of the radio interface of the user plane that handles data.

[0029] As shown in FIG. 4, the radio interface protocol of the user plane includes a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0030] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Between the PHY layer of UE100 and the PHY layer of gNB200, data and control information are transmitted via a physical channel.

[0031] The MAC layer performs priority control of data, retransmission processing by hybrid ARQ (HARQ), and random access procedures, etc. Between the MAC layer of UE100 and the MAC layer of gNB200, data and control information are transmitted via a transport channel. The MAC layer of gNB200 includes a scheduler. The scheduler determines the uplink and downlink transport formats (transport block size, modulation and coding scheme (MCS)) and the resource blocks allocated to UE100.

[0032] The RLC layer uses the functions of the MAC layer and the PHY layer to transmit data to the RLC layer on the receiving side. Between the RLC layer of UE100 and the RLC layer of gNB200, data and control information are transmitted via a logical channel.

[0033] The PDCP layer performs header compression / decompression and encryption / decryption.

[0034] The SDAP layer performs the mapping between the IP flow, which is the unit for the core network to perform QoS control, and the radio bearer, which is the unit for the AS (Access Stratum) to perform QoS control. Note that when the RAN is connected to the EPC, the SDAP may not be necessary.

[0035] Figure 5 is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that handles signaling (control signals).

[0036] As shown in Figure 5, the protocol stack of the radio interface of the control plane has an RRC (Radio Resource Control) layer and an NAS (Non-Access Stratum) layer instead of the SDAP layer shown in Figure 4.

[0037] Between the RRC layer of UE100 and the RRC layer of gNB200, RRC signaling for various settings is transmitted. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of the radio bearer. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in the RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in the RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in the RRC inactive state.

[0038] The NAS layer located above the RRC layer performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of UE100 and the NAS layer of AMF300B.

[0039] Note that UE100 has an application layer, etc. in addition to the protocol of the radio interface.

[0040] (MBS) Next, the MBS according to the embodiment will be described. MBS is a service that performs broadcast or multicast from the NG-RAN 10 to the UE 100, that is, data transmission in a one-to-many (PTM: Point To Multipoint) manner. MBS may be called MBMS (Multimedia Broadcast and Multicast Service). Note that the use cases (service types) of MBS include public security communication, mission-critical communication, V2X (Vehicle to Everything) communication, IPv4 or IPv6 multicast distribution, IPTV, group communication, and software distribution, etc.

[0041] In LTE, there are two types of MBS transmission methods: MBSFN (Multicast Broadcast Single Frequency Network) transmission and SC-PTM (Single Cell Point To Multipoint) transmission. FIG. 6 is a diagram showing the correspondence between the downlink logical channel and the transport channel according to the embodiment.

[0042] As shown in FIG. 6, the logical channels used for MBSFN transmission are MTCH (Multicast Traffic Channel) and MCCH (Multicast Control Channel), and the transport channel used for MBSFN transmission is MCH (Multicast Control Channel). MBSFN transmission is mainly designed for multicell transmission, and in an MBSFN area composed of multiple cells, each cell synchronously transmits the same signal (the same data) in the same MBSFN subframe.

[0043] The logical channels used for SC-PTM transmission are SC-MTCH (Single Cell Multicast Traffic Channel) and SC-MCCH (Single Cell Multicast Control Channel), and the transport channel used for SC-PTM transmission is DL-SCH (Downlink Shared Channel). SC-PTM transmission is mainly designed for single cell transmission, and data transmission is performed by broadcast or multicast on a cell-by-cell basis. The physical channels used for SC-PTM transmission are PDCCH (Physical Downlink Control Channel) and PDSCH (Physical Downlink Control Channel), and dynamic resource allocation is possible.

[0044] In the following, an example of providing MBS using the SC-PTM transmission method will be mainly described, but MBS may also be provided using the MBSFN transmission method. Also, an example of providing MBS by multicast will be mainly described. Therefore, MBS may be read as multicast. However, MBS may also be provided by broadcast.

[0045] Also, MBS data refers to the data transmitted by MBS, the MBS control channel refers to MCCH or SC-MCCH, and the MBS traffic channel refers to MTCH or SC-MTCH. However, MBS data may be transmitted by unicast. MBS data may also be called MBS packets or MBS traffic.

[0046] The network can provide different MBS services for each MBS session. An MBS session is identified by at least one of TMGI (Temporary Mobile Group Identity) and a session identifier, and at least one of these identifiers is called an MBS session identifier. Such an MBS session identifier may also be called an MBS service identifier or a multicast group identifier.

[0047] Figure 7 is a diagram showing a method for delivering MBS data.

[0048] As shown in Figure 7, MBS data (MBS Traffic) is delivered from a single data source (application service provider) to a plurality of UEs. The 5G core network 5G CN (5GC) 20 receives MBS data from the application service provider, creates (Replication) a copy of the MBS data, and distributes it.

[0049] From the perspective of 5GC 20, two delivery methods are possible: shared MBS data delivery and individual MBS data delivery.

[0050] In shared MBS data delivery, a connection is established between the NG-RAN 10, which is a 5G radio access network (5G RAN), and 5GC 20, and MBS data is delivered from 5GC 20 to NG-RAN 10. Hereinafter, such a connection (tunnel) is referred to as an "MBS connection".

[0051] The MBS connection may also be referred to as a Shared MBS Traffic delivery connection or a shared transport. The MBS connection terminates at the NG-RAN 10 (i.e., gNB 200). The MBS connection may correspond one-to-one with an MBS session. The gNB 200 selects either PTP (Point-to-Point: unicast) or PTM (Point-to-Multipoint: multicast or broadcast) at its own discretion and transmits the MBS data to the UE 100 by the selected method.

[0052] In the case of unicast MBS data distribution, a unicast session is established between the NG-RAN 10 and the UE 100, and the MBS data is individually distributed from the 5GC 20 to the UE 100. Such unicast may also be referred to as a PDU Session. The unicast (PDU Session) terminates at the UE 100.

[0053] (Operation of the Mobile Communication System) Next, the operation of the mobile communication system according to the embodiment will be described.

[0054] As described above, in order for the gNB 200 to transmit MBS data in multicast or broadcast, this gNB 200 needs to have an MBS connection with the NG-RAN 10. Therefore, a problem may occur in a scenario where the UE 100 that receives MBS data in the RRC connected state performs a handover.

[0055] FIG. 8 and FIG. 9 are diagrams for explaining the operation of the mobile communication system according to the embodiment.

[0056] As shown in FIG. 8, the gNB 200A, which is the source gNB, has an MBS connection with the UPF 300A and receives MBS data from the UPF 300A via this MBS connection. The UPF 300A may also be referred to as a Multicast / Broadcast UPF (MB-UPF). The UPF 300A is an example of a core network device.

[0057] The establishment and release of the MBS connection are controlled by the AMF 300B. The AMF 300B is another example of a core network device. However, instead of the AMF 300B, the Session Management Function (SMF) may control the establishment and release of the MBS connection. The SMF is another example of a core network device. In the following description, the AMF 300B may be read as the SMF.

[0058] gNB200A transmits the MBS data received from UPF300A by multicast or broadcast. UE100 in the RRC connected state in cell C1 of gNB200A receives this MBS data. Assume that UE100 moves from cell C1 of gNB200A to cell C2 of adjacent gNB200B.

[0059] Target gNB, gNB200B, does not have an MBS connection with UPF300A. Here, when UE100 (i.e., UE100 receiving MBS data transmitted by multicast or broadcast) during MBS reception performs a handover from gNB200A to gNB200B, there is a concern that UE100 may not be able to continue receiving MBS data. For example, the MBS session received by UE100 is disconnected after the handover, and UE100 can no longer continue receiving MBS data.

[0060] Note that in the handover from gNB200A to gNB200B, handover preparation operations are performed via the Xn connection (Xn interface) between gNB200A and gNB200B. However, the communication between gNB200A and gNB200B is not limited to being performed via the Xn interface. Communication between gNB200A and gNB200B may also be performed via the NG interface, which is an interface between the base station and the core network, and a core network device. Below, an example where the communication between gNB200A and gNB200B is performed via the Xn interface will be mainly described.

[0061] As shown in FIG. 9, each of gNB200A and gNB200B has an MBS connection with UPF300A. UPF300A transmits the same MBS data to each of gNB200A and gNB200B via the MBS connection. Each of gNB200A and gNB200B transmits the MBS data received from UPF300A by multicast or broadcast.

[0062] In the situation shown in FIG. 9, even if the UE 100 receiving MBS (i.e., the UE 100 receiving MBS data transmitted by multicast or broadcast) performs a handover from gNB 200A to gNB 200B, the UE 100 can continue to receive MBS data.

[0063] Therefore, in order to improve the reception continuity of MBS data of the UE 100 in the RRC connected state, it is desirable for the gNB 200A to select a target gNB having an MBS connection for the handover of the UE 100 receiving MBS. Alternatively, it is desirable for the AMF 300B to establish an MBS connection to a target gNB not having an MBS connection for the handover of the UE 100 receiving MBS.

[0064] (1) Operation Pattern 1 FIG. 10 is a diagram showing Operation Pattern 1 according to an embodiment.

[0065] As shown in FIG. 10, in step S101, the gNB 200A establishes an MBS connection with the UPF 300A. The UE 100 in the RRC connected state establishes an MBS session via the gNB 200A.

[0066] In step S102, the UPF 300A transmits MBS data to the gNB 200A via the MBS connection.

[0067] In step S103, the gNB 200A transmits the MBS data received from the UPF 300A to the UE 100 by multicast (or broadcast).

[0068] In step S104, the gNB 200A determines a handover of the UE 100 to the gNB 200B, for example, based on a measurement report from the UE 100.

[0069] In step S105, gNB200A sends a Handover Request message to gNB200B via the Xn interface (Xn connection). The Handover Request message includes at least one of a first identifier for identifying UPF300A having an MBS connection with gNB200A and a second identifier for identifying an MBS session provided by gNB200A in multicast or broadcast (for example, the MBS session being received by UE100). The first identifier is UPF information, and the second identifier is MBS session information. If there are multiple MBS sessions provided by gNB200A in multicast or broadcast, gNB200A may include multiple second identifiers corresponding to these multiple MBS sessions in the Handover Request message.

[0070] The first identifier for identifying UPF300A includes at least one of the IP (Internet Protocol) address of UPF300A, the GTP TEID (GPRS tunneling protocol - tunnel endpoint identifier) of UPF300A, and an identifier indicating that it is UPF300A.

[0071] The second identifier for identifying an MBS session provided by gNB200A in multicast or broadcast includes at least one of a group RNTI (Radio Network Temporary Identifier), TMGI, session ID, and QoS (Quality of Service) flow ID.

[0072] When data forwarding from gNB200A to gNB200B is performed, the Handover Request message may include a data forwarding address for the MBS session. The data forwarding address for the MBS session includes at least one of the IP address of gNB200A and the GTP TEID of gNB200A.

[0073] The handover request message may include an information element requesting the establishment of a data forwarding path for MBS. gNB200B may notify gNB200A of its own data forwarding address in response to the reception of this information element.

[0074] In step S106, gNB200B determines whether UE100 can be accepted based on the handover request message received from gNB200A. Here, the description will proceed assuming that gNB200B permits acceptance. If the handover request message includes a plurality of second identifiers (i.e., information on a plurality of MBS sessions), gNB200B may perform the determination of acceptance for each MBS session.

[0075] In step S107, gNB200B performs a process of establishing an MBS connection with UPF300A based on the identifier included in the handover request message from gNB200A. Here, gNB200B transmits at least one of the first identifier (UPF information) and the second identifier (MBS session information) included in the handover request message from gNB200A to AMF300B. For example, when gNB200B transmits a message for requesting the establishment of an MBS connection to AMF300B, gNB200B includes at least one of the first identifier and the second identifier in this message.

[0076] When AMF300B receives the first identifier, AMF300B can identify UPF300A to which gNB200B should establish an MBS connection based on the first identifier. When AMF300B receives the second identifier, AMF300B can identify the MBS session that gNB200B should establish based on the second identifier. If AMF300B grasps the correspondence between the MBS session and UPF300A, UPF300A may identify UPF300A to which gNB200B should establish an MBS connection based on the second identifier.

[0077] The AMF 300B may notify the gNB 200B of the specified content. For example, when the AMF 300B sends a response message to the establishment request message from the gNB 200B to the gNB 200B, the AMF 300B includes information indicating the content specified by the AMF 300B in the response message.

[0078] In step S108, the gNB 200B establishes an MBS connection (and an MBS session) with the UPF 300A under the control of the AMF 300B.

[0079] Note that the gNB 200B may perform steps S107 and S108 after step S109 described below.

[0080] In step S109, the gNB 200B sends a Handover Request Acknowledgement message indicating acceptance permission to the gNB 200A. The handover response message may include at least one of information (second identifier) of the MBS session permitted by the gNB 200B to be accepted and information (second identifier) of the MBS session rejected by the gNB 200B to be accepted.

[0081] Here, the handover response message may include a set of information (second identifier) of the MBS session permitted by the gNB 200B to be accepted and information indicating whether this MBS session (MBS connection) has been established in the gNB 200B. The handover response message may include a set of information (second identifier) of the MBS session rejected by the gNB 200B to be accepted and information indicating that the establishment of this MBS session (MBS connection) has failed in the gNB 200B.

[0082] When data forwarding from the gNB 200A to the gNB 200B is performed, the handover response message may include a data forwarding address for the MBS session. The data forwarding address for the MBS session includes at least one of the IP address of the gNB 200B and the GTP TEID of the gNB 200B.

[0083] Further, the handover response message includes radio settings for the UE 100 to receive the MBS session from the gNB 200B in multicast or broadcast.

[0084] In step S110, in response to receiving the handover response message from the gNB 200B, the gNB 200A transmits a handover command (RRC Reconfiguration) message to the UE 100. The handover command message includes at least a part of the above information (for example, information on the MBS sessions permitted by the gNB 200B to be accepted, information on the MBS sessions rejected by the gNB 200B to be accepted, and radio settings) included in the handover response message.

[0085] In step S111, in response to receiving the handover command message from the gNB 200A, the UE 100 executes a handover from the gNB 200A to the gNB 200B.

[0086] The UE 100 may identify an MBS session rejected by the gNB 200B based on the information included in the handover command message and establish a unicast (Individual MBS Traffic Delivery) connection corresponding to this MBS session. Here, in the UE 100, the information included in the handover command message may be notified from the AS layer to the NAS layer, and the NAS layer may perform the process of establishing a unicast connection. Here, the description will proceed on the assumption that the gNB 200B has permitted the acceptance of at least one MBS session.

[0087] In step S112, the UPF 300A transmits MBS data to the gNB 200B via the MBS connection.

[0088] In step S113, gNB200B transmits the MBS data received from UPF300A to UE100 by multicast (or broadcast). As a result, UE100 can continue to receive MBS data even after the handover.

[0089] (2) Operation pattern 2 Regarding operation pattern 2, the differences from the above-mentioned operation pattern 1 will be mainly described.

[0090] In the above-mentioned operation pattern 1, an example of establishing an MBS connection on gNB200B was described when UE100 receiving MBS was handed over under the situation where the target gNB, gNB200B, did not have an MBS connection (MBS session). However, gNB200B will newly start transmitting MBS data by multicast or broadcast, consuming radio resources for this transmission.

[0091] When UE100 is handed over to a target gNB that has already established an MBS connection and is transmitting MBS data by multicast or broadcast, since there are already UEs such as UE100 that are receiving this MBS data, the utilization efficiency of radio resources is good. Therefore, in operation pattern 2, gNB200A, which is the source gNB, can prioritize handing over UE100 to a target gNB that has an MBS connection by previously grasping whether an adjacent gNB has an MBS connection.

[0092] In operation pattern 2, gNB200B transmits a second identifier (the above-mentioned MBS session information) for identifying the MBS session provided by gNB200B by multicast or broadcast to gNB200A. When there are multiple MBS sessions provided by gNB200B by multicast or broadcast, gNB200B may transmit a plurality of second identifiers corresponding to these multiple MBS sessions to gNB200A.

[0093] Further, gNB200B may transmit to gNB200A a first identifier (UPF information) for identifying UPF300A having an MBS connection with gNB200B.

[0094] gNB200A determines (for example, selects a target gNB) the handover of UE100 based on at least one of the first identifier and the second identifier received from gNB200B.

[0095] FIG. 11 is a diagram showing operation pattern 2 according to an embodiment. In FIG. 11, it is assumed that UE100A is in the RRC connected state in the cell of gNB200A. It is assumed that UE100B is in the RRC connected state, the RRC idle state, or the RRC inactive state in the cell of gNB200B.

[0096] As shown in FIG. 11, in step S201, gNB200B establishes an MBS connection with UPF300A.

[0097] In step S202, gNB200B transmits to gNB200A a notification message including at least one of a first identifier (UPF information) for identifying UPF300A having an MBS connection with gNB200B and a second identifier (the above-described MBS session information) for identifying an MBS session provided by gNB200B by multicast or broadcast. This notification message is transmitted via the Xn interface (Xn connection).

[0098] gNB200B may transmit the notification message periodically (at a fixed period). gNB200B may transmit the notification message in response to a change (establishment, disconnection) in the state of the MBS connection (MBS session). gNB200B may transmit the notification message in response to receiving a transmission request for the notification message from gNB200A.

[0099] In step S203, UPF300A transmits MBS data to gNB200B via the MBS connection.

[0100] In step S204, gNB200B transmits the MBS data received from UPF300A to UE100B in a multicast (or broadcast) manner.

[0101] On the other hand, in step S205, gNB200A establishes an MBS connection with UPF300A.

[0102] In step S206, UPF300A transmits the MBS data to gNB200A via the MBS connection.

[0103] In step S207, gNB200A transmits the MBS data received from UPF300A to UE100A in a multicast (or broadcast) manner.

[0104] In step S208, gNB200A determines the handover of UE100A, for example, based on the measurement report from UE100. Here, gNB200A determines whether to select gNB200B as the target gNB for the handover of UE100A based on the notification message received from gNB200B in step S202.

[0105] If gNB200A does not have an MBS session (MBS connection) that it is providing to UE100A in a multicast (or broadcast) manner and gNB200B does not have it either, gNB200A may decide not to select gNB200B as the target gNB for the handover of UE100A.

[0106] Alternatively, if gNB200A is providing an MBS session (MBS connection) to UE100A in multicast (or broadcast) and gNB200B does not have it, gNB200A may perform handover control according to the above operation pattern 1. As a result, gNB200A can establish an MBS session (MBS connection) provided to UE100A in multicast (or broadcast) with gNB200B.

[0107] If gNB200A is providing an MBS session (MBS connection) to UE100A in multicast (or broadcast) and gNB200B has it, gNB200A may select gNB200B as the target gNB for handover of UE100A. In this case, gNB200A may perform general handover control instead of the handover control according to the above operation pattern 1.

[0108] (3) Operation pattern 3 Regarding operation pattern 3, the differences from the above operation patterns 1 and 2 will be mainly described.

[0109] In the above operation pattern 2, an example of transmitting a notification message regarding the MBS connection of gNB200B from gNB200B to gNB200A was described. In contrast, in operation pattern 3, such a notification message is transmitted from AMF300B to gNB200A. In operation pattern 3, gNB200A receives a notification message from AMF300B including an identifier for identifying gNB200B and an identifier for identifying an MBS session (MBS connection) provided by gNB200B in multicast or broadcast (the above MBS session information).

[0110] FIG. 12 is a diagram showing operation pattern 3 according to the embodiment. In FIG. 12, it is assumed that UE 100A is in the RRC connected state in the cell of gNB 200A. UE 100B is assumed to be in the RRC connected state, the RRC idle state, or the RRC inactive state in the cell of gNB 200B.

[0111] As shown in FIG. 12, in step S301, gNB 200B establishes an MBS connection with UPF 300A.

[0112] In step S302, AMF 300B transmits a notification message including an identifier for identifying gNB 200B and an identifier (the above-described MBS session information) for identifying an MBS session (MBS connection) provided by gNB 200B in multicast or broadcast to gNB 200A. The identifier for identifying gNB 200B is at least one of the gNB ID of gNB 200B and the cell ID of the cell of gNB 200B.

[0113] AMF 300B may transmit the notification message periodically (at a fixed period). AMF 300B may transmit the notification message in response to a change (establishment, disconnection) in the state of the MBS connection (MBS session). AMF 300B may transmit the notification message in response to receiving a transmission request for the notification message from gNB 200A.

[0114] In step S303, UPF 300A transmits MBS data to gNB 200B via the MBS connection.

[0115] In step S304, gNB 200B transmits the MBS data received from UPF 300A to UE 100B in multicast (or broadcast).

[0116] On the other hand, in step S305, gNB 200A establishes an MBS connection with UPF 300A.

[0117] In step S306, the UPF 300A transmits MBS data to the gNB 200A via the MBS connection.

[0118] In step S307, the gNB 200A transmits the MBS data received from the UPF 300A to the UE 100A by multicast (or broadcast).

[0119] In step S308, the gNB 200A determines the handover of the UE 100A, for example, based on the measurement report from the UE 100. Here, the gNB 200A determines whether to select the gNB 200B as the target gNB for the handover of the UE 100A based on the notification message received from the AMF 300B in step S302. Details of this operation are the same as those of the above-described operation pattern 2.

[0120] (4) Operation pattern 4 Regarding operation pattern 4, the differences from the above-described operation patterns 1 to 3 will be mainly described.

[0121] In the above-described operation pattern 1, an example in which the gNB 200A takes the lead in establishing an MBS connection with the gNB 200B was described. In operation pattern 4, the AMF 300B takes the lead in establishing an MBS connection with the gNB 200B. In operation pattern 4, when the gNB 200A performs a handover of the UE 100 from the gNB 200A to the gNB 200B, the gNB 200A transmits a notification message indicating that it is a handover of the UE 100 during MBS reception to the AMF 300B.

[0122] FIG. 13 is a diagram showing operation pattern 4 according to the embodiment.

[0123] As shown in FIG. 13, in step S401, the gNB 200A establishes an MBS connection with the UPF 300A. The UE 100 in the RRC connected state establishes an MBS session via the gNB 200A.

[0124] In step S402, UPF300A transmits MBS data to gNB200A via the MBS connection.

[0125] In step S403, gNB200A transmits the MBS data received from UPF300A to UE100 by multicast (or broadcast).

[0126] In step S404, gNB200A determines the handover of UE100 to gNB200B, for example, based on the measurement report from UE100.

[0127] In step S405, gNB200A transmits a notification message indicating that UE100 during MBS session reception is to be handed over to AMF300B. Step S405 may be performed before step S404. The notification message includes at least one identifier (or cell ID) of a gNB that is a candidate for the target gNB and the above-mentioned MBS session information. The notification message may include the identifier of UE100 during MBS session reception.

[0128] In step S406, based on the notification message from gNB200A, AMF300B may perform a process of establishing an MBS connection between a candidate gNB (gNB200B) and UPF300A as necessary.

[0129] In step S407, AMF300B may transmit a response message to gNB200A. The response message includes at least one of the identifier (or cell ID) of at least one gNB that is a candidate for the target gNB and the above-mentioned MBS session information. The identifier (or cell ID) of at least one gNB that is a candidate for the target gNB may be the identifier of a gNB for which the MBS connection has been established or is to be established. Based on the response message from AMF300B, gNB200A may reselect the target gNB for the handover of UE100.

[0130] In step S408, gNB200A transmits a handover request message for requesting a handover of UE100 to gNB200B.

[0131] (Other embodiments) Each of the above operation patterns is not limited to being implemented separately and independently, and two or more operation patterns can be combined and implemented. For example, some steps of one operation pattern may be added to another operation pattern, or some steps of one operation pattern may be replaced with some steps of another operation pattern.

[0132] In the above embodiments, an example where the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB). Further, the base station may be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may be a DU (Distributed Unit) of an IAB node.

[0133] In the above embodiments, handover between base stations has been mainly assumed, but handover within a base station may be assumed. For example, if the base station is separated into a CU and a DU, UE100 may perform a handover between two DUs belonging to one CU. In this case, the above Xn interface may be read as an F1 interface which is a CU-DU interface, and various messages and information may be transmitted and received via the F1 interface. Further, each of gNB200A and gNB200B described above may be read as a CU and / or a DU.

[0134] Furthermore, the CU is separated into a CU-CP and a CU-UP, and UE100 may perform a handover between two CU-UPs belonging to one CU-CP. In this case, the above-described Xn interface may be reinterpreted as an E1 interface, which is an interface between the CU-CP and the CU-UP, and various messages and information described above may be transmitted and received via the E1 interface. Also, each of the above-described gNB200A and gNB200B may be reinterpreted as a CU-CP and / or a CU-UP.

[0135] A program may be provided that causes a computer to execute each process performed by UE100 or gNB200. The program may be recorded on a computer-readable medium. By using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0136] Also, a circuit that executes each process performed by UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0137] As described above, the embodiments have been described in detail with reference to the drawings, but the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the gist.

[0138] This application claims the priority of Japanese Patent Application No. 2020-174886 (filed on October 16, 2020), and the entire content thereof is incorporated into this application specification.

Explanation of Reference Numerals

[0139] 10: NG-RAN (5G RAN) 20: 5GC (5G CN) 100: UE 110: Receiver unit 120: Transmitter unit 130: Control unit 200: gNB 210: Transmitter unit 220: Receiver unit 230: Control unit 240: Backhaul communication unit 300A: UPF 300B: AMF

Claims

1. A communication control method used in a mobile communication system that provides a multicast broadcast service (MBS) from a base station to a user device, comprising: The base station includes receiving a notification from a core network device, the notification including a first identifier for identifying another base station and a second identifier for identifying an MBS session provided by the other base station by multicast or broadcast. Communications control method.

2. A base station used in a mobile communication system that provides a multicast and broadcast service (MBS) from a base station to a user device, A receiving unit that receives a notification from a core network device, the notification including a first identifier that identifies another base station and a second identifier that identifies an MBS session provided by the other base station by multicast or broadcast. Base station.

3. A core network device used in a mobile communication system that provides a multicast / broadcast service (MBS) from a base station to a user device, A transmitter for transmitting a notification to the base station, the notification including a first identifier for identifying another base station and a second identifier for identifying an MBS session provided by the other base station by multicast or broadcast. Core network equipment.

4. A mobile communication system that provides a multicast and broadcast service (MBS) from a base station to a user device, comprising: The base station receives a notification from a core network device, the notification including a first identifier for identifying another base station and a second identifier for identifying an MBS session provided by the other base station by multicast or broadcast. Mobile communication system.

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