Communication control method and base station

Abstract

A communication control method for use in a mobile communication system providing a multicast broadcast service (MBS) from a base station to a user equipment, wherein a first base station establishing a MBS connection with a core network device receives MBS data from the core network device over the MBS connection, the first base station transmits the MBS data received from the core network device to a first user equipment in multicast or broadcast, and the first base station transmits at least one of a first identifier identifying the core network device and a second identifier identifying a MBS session provided by the first base station in multicast or broadcast to a second base station.

Description

Technical Field

[0001] This disclosure relates to a communication control method used in a mobile communication system. Background Technology

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

[0003] Citation List

[0004] Non-patent literature

[0005] Non-patent document 1: 3GPP technical specification "3GPP TS 38.300V16.3.0 (2020-09)" Summary of the Invention

[0006] A first aspect provides a communication control method for use in a mobile communication system that provides multicast / broadcast service (MBS) from a base station to a user equipment. The communication control method includes: receiving MBS data from a core network device via the MBS connection at a first base station that establishes an MBS connection with the core network device; transmitting the MBS data received from the core network device to a first user equipment via multicast or broadcast from the first base station; and transmitting at least one of a first identifier or a second identifier from the first base station to a second base station, the first identifier identifying the core network device and the second identifier identifying an MBS session provided by the first base station via multicast or broadcast.

[0007] A second aspect provides a communication control method for use in a mobile communication system that provides multicast / broadcast service (MBS) from a base station to a user equipment. The communication control method includes: receiving, at a first base station, a notification from a core network device including a first identifier and a second identifier, the first identifier identifying a second base station and the second identifier identifying an MBS session provided by the second base station via multicast or broadcast.

[0008] A third aspect provides a communication control method for use in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user equipment. The communication control method includes: when performing a handover of a user equipment from a first base station to a second base station, sending a notification from the first base station to a core network device indicating that the user equipment is receiving MBS. Attached Figure Description

[0009] Figure 1 This is a diagram illustrating the configuration of a mobile communication system according to an embodiment.

[0010] Figure 2 This is a diagram illustrating the configuration of a UE (User Equipment) according to an embodiment.

[0011] Figure 3 This is a diagram illustrating the configuration of a gNB (base station) according to an embodiment.

[0012] Figure 4 This is a diagram illustrating the configuration of the protocol stack for the user plane radio interface that processes data.

[0013] Figure 5 This is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0014] Figure 6 This is a diagram illustrating the correspondence between downlink logical channels and downlink transport channels according to an embodiment.

[0015] Figure 7 This is a diagram illustrating the method of delivering MBS data.

[0016] Figure 8 This is a diagram illustrating the operation of a mobile communication system according to an embodiment.

[0017] Figure 9 This is a diagram illustrating the operation of a mobile communication system according to this embodiment.

[0018] Figure 10 This is a diagram illustrating operation mode 1 according to an embodiment.

[0019] Figure 11 This is a diagram illustrating operation mode 2 according to an embodiment.

[0020] Figure 12 This is a diagram illustrating operation mode 3 according to an embodiment.

[0021] Figure 13 This is a diagram illustrating operation mode 4 according to an embodiment. Detailed Implementation

[0022] Research is underway on introducing multicast services to 5G systems (NR). Compared to LTE multicast services, NR multicast services are expected to provide enhanced services.

[0023] This invention provides enhanced multicast broadcast services.

[0024] A mobile communication system according to an embodiment is described with reference to the accompanying drawings. In the description of the drawings, the same or similar parts are indicated by the same or similar reference numerals.

[0025] Configuration of mobile communication system

[0026] First, the configuration of the mobile communication system according to an embodiment is described. Figure 1 This diagram illustrates the configuration of a mobile communication system according to an embodiment. The mobile communication system conforms to the 3GPP standard for a fifth-generation system (5GS). The following description uses 5GS as an example, but Long Term Evolution (LTE) systems or sixth-generation (6G) systems can be applied at least partially to the mobile communication system.

[0027] like Figure 1 As shown, the mobile communication system includes user equipment (UE) 100, 5G radio access network (next-generation radio access network (NG-RAN)) 10 and 5G core network (5GC) 20.

[0028] UE 100 is a mobile wireless communication device. UE 100 can be any device that is used by a user. Examples of UE 100 include mobile phone terminals (including smartphones), tablet terminals, laptop PCs, communication modules (including communication cards or chipsets), sensors or devices mounted on sensors, vehicles or devices mounted on vehicles (vehicle UE), or flying objects or devices mounted on flying objects (airborne UE).

[0029] NG-RAN 10 includes base stations (referred to as "gNBs" in 5G systems) 200. gNBs 200 are interconnected via the Xn interface, which is an inter-base station interface. Each gNB 200 manages one or more cells. gNBs 200 perform wireless communication with UE 100, which has established connections to the cells of gNBs 200. gNBs 200 have Radio Resource Management (RRM) functions, functions for routing user data (hereinafter referred to as "data"), measurement and control functions for mobility control and scheduling, etc. "Cell" is used as a term to represent the smallest unit of wireless communication area. "Cell" is also used as a term to represent the functions or resources used to perform wireless communication with UE 100. A cell belongs to one carrier frequency.

[0030] Note that a gNB can connect to the Evolved Packet Core (EPC) corresponding to the LTE core network. LTE base stations can also connect to the 5GC. LTE base stations and gNBs can connect via an inter-base station interface.

[0031] The 5GC 20 includes Access and Mobility Management Functions (AMF) and User Plane Functions (UPF) 300. The AMF performs various types of mobility control for the UE 100. The AMF manages the mobility of the UE 100 by communicating with it using Non-Access Stratum (NAS) signaling. The UPF controls data transmission. The AMF and UPF are connected to the gNB 200 via the NG interface, which is the interface between the base station and the core network.

[0032] Figure 2 This is a diagram illustrating the configuration of UE 100 (User Equipment) according to an embodiment.

[0033] like Figure 2 As shown, UE 100 includes receiver 110, transmitter 120 and controller 130.

[0034] Receiver 110 performs various types of reception under the control of controller 130. Receiver 110 includes an antenna and receiving equipment. The receiving equipment converts the radio signals received through the antenna into baseband signals (received signals) and outputs the resulting signals to controller 130.

[0035] Transmitter 120 performs various types of transmissions under the control of controller 130. Transmitter 120 includes an antenna and a transmitting device. The transmitting device converts the baseband signal (transmit signal) output by controller 130 into a radio signal and transmits the obtained signal through the antenna.

[0036] Controller 130 performs various types of control within UE 100. Controller 130 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor, as well as information to be processed by the processor. The processor may include a baseband processor and a central processing unit (CPU). The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0037] Figure 3 This is a diagram illustrating the configuration of a gNB 200 (base station) according to an embodiment.

[0038] like Figure 3 As shown, the gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communicator 240.

[0039] Transmitter 210 performs various types of transmissions under the control of controller 230. Transmitter 210 includes an antenna and a transmitting device. The transmitting device converts the baseband signal (transmit signal) output by controller 230 into a radio signal and transmits the obtained signal through the antenna.

[0040] Receiver 220 performs various types of reception under the control of controller 230. Receiver 220 includes an antenna and receiving equipment. The receiving equipment converts the radio signals received through the antenna into baseband signals (received signals) and outputs the resulting signals to controller 230.

[0041] The controller 230 performs various types of control over the gNB 200. The controller 230 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor, as well as information to be processed by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0042] The backhaul communicator 240 is connected to the adjacent base station via the inter-base station interface. The backhaul communicator 240 is also connected to the AMF / UPF 300 via the interface between the base station and the core network. Note that the gNB may include a central unit (CU) and a distributed unit (DU) (i.e., functions are divided), and these two units may be connected via the F1 interface.

[0043] Figure 4 This is a diagram illustrating the configuration of the protocol stack for the user plane radio interface that processes data.

[0044] like Figure 4 As shown, the user plane radio interface protocol includes the physical (PHY) layer, media access control (MAC) layer, radio link control (RLC) layer, packet data convergence protocol (PDCP) layer, and service data adaptation protocol (SDAP) layer.

[0045] The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. Data and control information are transmitted between the PHY layer of UE 100 and the PHY layer of gNB 200 via physical channels.

[0046] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of gNB 200 via the transport channel. The MAC layer of gNB 200 includes a scheduler. The scheduler determines the transmission format (transport block size, modulation and coding scheme (MCS)) in the uplink and downlink, as well as the resource blocks to be allocated to UE 100.

[0047] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC and PHY layers. Data and control information are transmitted between the RLC layer of UE 100 and the RLC layer of gNB 200 via logical channels.

[0048] The PDCP layer performs header compression and decompression, as well as encryption and decryption.

[0049] The SDAP layer performs the mapping between IP flows, which act as the core network's QoS control unit, and radio bearers, which act as the access layer (AS)'s QoS control unit. Note that SDAP may not be provided when the RAN is connected to the EPC.

[0050] Figure 5 This is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0051] like Figure 5 As shown, the protocol stack of the control plane's radio interface includes a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer, instead of... Figure 4 The SDAP layer is shown.

[0052] RRC signaling for various configurations is transmitted between the RRC layer of UE 100 and the RRC layer of gNB 200. The RRC layer controls logical channels, transport channels, and physical channels based on the establishment, reconstruction, and release of radio bearers. UE 100 is in an RRC connected state when a connection exists between the RRC of UE 100 and the RRC of gNB 200 (RRC connection). UE 100 is in an RRC idle state when a connection does not exist between the RRC of UE 100 and the RRC of gNB 200. UE 100 is in an RRC inactive state when the connection between the RRC of UE 100 and the RRC of gNB 200 is suspended.

[0053] The NAS layer, which is above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of UE 100 and the NAS layer of AMF300B.

[0054] Note that UE 100 includes the application layer in addition to the radio interface protocol.

[0055] MBS

[0056] MBS will be described according to an embodiment. MBS is a service that provides broadcast or multicast (i.e., point-to-multipoint (PTM) data transmission) from NG-RAN 10 to UE 100. MBS may be referred to as Multimedia Broadcast and Multicast Service (MBMS). Note that use cases (service types) for MBS include public communications, mission-critical communications, V2X (vehicle-to-anything) communications, IPv4 or IPv6 multicast delivery, IPTV, group communications, and software delivery.

[0057] MBS transmission in LTE includes two schemes: Multicast-Broadcast Single Frequency Network (MBSFN) transmission and Single Cell Point-to-Multipoint (SC-PTM) transmission. Figure 6This is a diagram illustrating the correspondence between downlink logical channels and downlink transport channels according to an embodiment.

[0058] like Figure 6 As shown, the logical channels used for MBSFN transmission are the Multicast Service Channel (MTCH) and the Multicast Control Channel (MCCH), and the transport channel used for MBSFN transmission is the Multicast Control Channel (MCH). MBSFN transmission is primarily designed for multi-cell transmission, and in an MBSFN area comprising multiple cells, each cell synchronously transmits the same signal (the same data) in the same MBSFN subframe.

[0059] The logical channels used for SC-PTM transmission are the Single Cell Multicast Traffic Channel (SC-MTCH) and the Single Cell Multicast Control Channel (SC-MCCH), and the transport channel used for SC-PTM transmission is the Downlink Shared Channel (DL-SCH). SC-PTM transmission is primarily designed for single-cell transmission and corresponds to broadcast or multicast data transmission on a cell-by-cell basis. The physical channels used for SC-PTM transmission are the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Control Channel (PDSCH), and dynamic resource allocation is implemented.

[0060] Although the following description primarily focuses on examples of providing MBS using the SC-PTM transport scheme, MBS can also be provided using the MBSFN transport scheme. The main example described will be using multicast to provide MBS. Therefore, MBS can be interpreted as multicast. Note that broadcast can also be used to provide MBS.

[0061] MBS data refers to data transmitted via 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 can be transmitted in unicast. MBS data can also be referred to as MBS packets or MBS traffic.

[0062] The network can provide different MBS services for each MBS session. An MBS session is identified by at least one of a Temporary Mobile Group Identifier (TMGI) or a session identifier, and at least one of these identifiers is called an MBS session identifier. Such an MBS session identifier can be referred to as an MBS service identifier or a multicast group identifier.

[0063] Figure 7 This is a diagram illustrating the method of delivering MBS data.

[0064] like Figure 7As shown, MBS data (MBS service) is delivered from a single data source (application service provider) to multiple UEs. The 5G CN (5G)20, which is the core network of the 5GC, receives MBS data from the application service provider and performs replication of the MBS data to transmit the results.

[0065] From the perspective of 5GC 20, two delivery methods are possible: shared MBS data delivery (shared MBS service delivery) and separate MBS data delivery (separate MBS service delivery).

[0066] In shared MBS data delivery, a connection is established between NG-RAN 10 and 5GC 20, which serve as the 5G radio access network (5G RAN), to deliver MBS data from 5GC 20 to NG-RAN 10. This connection (tunnel) is referred to below as the "MBS connection".

[0067] MBS connections can be referred to as shared MBS service delivery connections or shared transport. MBS connections terminate at NG-RAN 10 (i.e., gNB 200). MBS connections can correspond to MBS sessions on a one-to-one basis. gNB 200 selects either PTP (point-to-point: unicast) or PTM (point-to-multipoint: multicast or broadcast) according to its own determination and uses the selected method to send MBS data to UE 100.

[0068] On the other hand, in separate MBS data delivery, a unicast session is established between NG-RAN 10 and UE 100 to deliver MBS data separately from 5GC 20 to UE 100. This unicast can be referred to as a PDU session. The unicast (PDU session) terminates at UE 100.

[0069] Operation of mobile communication systems

[0070] The operation of the mobile communication system is described in the embodiments.

[0071] As mentioned above, in order for the gNB 200 to transmit MBS data via multicast or broadcast, the gNB 200 needs to have an MBS connection with the NG RAN10. Therefore, problems may occur in scenarios where a UE 100 in an RRC-connected state performing a handover while receiving MBS data.

[0072] Figure 8 and Figure 9 This is a diagram illustrating the operation of a mobile communication system according to an embodiment.

[0073] like Figure 8As shown, the gNB 200A, used as 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 can be referred to as a multicast broadcast UPF (MB-UPF). The UPF 300A is an example of a core network device.

[0074] The AMF 300B controls the establishment and release of MBS connections. The AMF 300B is another example of a core network device. Note that instead of the AMF 300B, the SMF (Session Management Function) can control the establishment and release of MBS connections. The SMF is another example of a core network device. The AMF 300B in the following description can be interpreted as the SMF.

[0075] gNB 200A transmits MBS data received from UPF 300A via multicast or broadcast. In cell C1 of gNB 200A, UE 100, in RRC connected state, receives MBS data. Assume UE 100 moves from cell C1 of gNB 200A to cell C2 of the neighboring gNB 200B.

[0076] The gNB 200B, used as the target gNB, is not connected to the MBS of the UPF 300A. Here, when the UE 100 receiving the MBS (i.e., the UE 100 receiving MBS data transmitted via multicast or broadcast) performs a handover from the gNB 200A to the gNB 200B, the UE 100 may be unable to continue receiving MBS data. For example, the MBS session received by the UE 100 may be terminated after the handover, and the UE 100 may not be able to continue receiving MBS data.

[0077] Note that during the handover from gNB 200A to gNB 200B, handover preparation is performed via the Xn connection (Xn interface) between gNB 200A and gNB 200B. Also note that communication between gNB 200A and gNB 200B is not limited to communication via the Xn interface; communication between gNB 200A and gNB 200B can also be performed via the NG interface and core network equipment. The NG interface is the interface between the base station and the core network. The following primarily describes an example of communication between gNB 200A and gNB 200B via the Xn interface.

[0078] like Figure 9As shown, each of gNB 200A and gNB 200B has an MBS connection with UPF 300A. UPF 300A sends the same MBS data to each of gNB 200A and gNB 200B via the MBS connection. Each of gNB 200A and gNB 200B transmits the MBS data received from UPF 300A via multicast or broadcast.

[0079] exist Figure 9 In the scenario shown, even if UE 100, which is receiving MBS (i.e., UE 100 receiving MBS data transmitted via multicast or broadcast), performs a handover from gNB 200A to gNB 200B, UE 100 can continue to receive MBS data.

[0080] Therefore, to improve the continuity of MBS data reception for UE 100 in RRC connection state, it is expected that gNB 200A selects a target gNB with MBS connection for handover of UE 100 receiving MBS. It is expected that AMF 300B enables a target gNB without MBS connection to establish an MBS connection for handover of UE 100 receiving MBS.

[0081] (1) Operation Mode 1

[0082] Figure 10 This is a diagram illustrating operation mode 1 according to an embodiment.

[0083] like Figure 10 As shown, in step S101, gNB 200A establishes an MBS connection with UPF 300A. UE 100, which is in RRC connection state, establishes an MBS session through gNB 200A.

[0084] In step S102, UPF 300A sends MBS data to gNB 200A via MBS connection.

[0085] In step S103, gNB 200A transmits the MBS data received from UPF 300A to UE100 via multicast (or broadcast).

[0086] In step S104, gNB 200A determines the handover from UE 100 to gNB 200B based on, for example, a measurement report from UE 100.

[0087] In step S105, gNB 200A sends a handover request message to gNB 200B via the Xn interface (Xn connection). The handover request message includes at least one of a first identifier or a second identifier. The first identifier identifies a UPF 300A with an MBS connection to gNB 200A, and the second identifier identifies an MBS session provided by gNB 200A via multicast or broadcast (e.g., an MBS session being received by UE 100). The first identifier is UPF information, and the second identifier is MBS session information. When gNB 200A provides multiple MBS sessions via multicast or broadcast, gNB 200A may include multiple second identifiers corresponding to the multiple MBS sessions in the handover request message.

[0088] The first identifier for the UPF 300A may include at least one selected from the group consisting of the IP (Internet Protocol) address of the UPF 300A, the GTP TEID (GPRS Tunneling Protocol - Tunnel Endpoint Identifier) ​​of the UPF 300A, and an identifier indicating the UPF 300A.

[0089] The second identifier that identifies an MBS session provided by the gNB 200A via multicast or broadcast may include at least one selected from the group consisting of RNTI (Radio Network Temporary Identifier), TMGI, Session ID, and QoS (Quality of Service) Stream ID.

[0090] When performing data forwarding from gNB 200A to gNB 200B, 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 gNB 200A or the GTPTEID of gNB 200A.

[0091] The handover request message may include information elements requesting the establishment of a data forwarding path for the MBS. In response to receiving the information elements, the gNB 200B may notify the gNB 200A of its own data forwarding address.

[0092] In step S106, gNB 200B determines whether to accept UE 100 based on the handover request message received from gNB 200A. This is described under the assumption that gNB 200B allows acceptance. When the handover request message includes multiple second identifiers (i.e., information about multiple MBS sessions), gNB 200B can determine whether to accept UE 100 for each MBS session.

[0093] In step S107, gNB 200B performs the process of establishing an MBS connection with UPF 300A based on the identifier included in the handover request message from gNB 200A. Here, gNB 200B sends at least one of a first identifier (UPF information) or a second identifier (MBS session information) included in the handover request message from gNB 200A to AMF 300B. For example, when gNB 200B sends a message to AMF 300B requesting the establishment of an MBS connection, it includes at least one of the first identifier or the second identifier in the message.

[0094] The AMF 300B, receiving the first identifier, can specify the UPF 300A with which the gNB 200B will establish an MBS connection, based on the first identifier. The AMF 300B, receiving the second identifier, can specify the MBS session that the gNB 200B wants to establish, based on the second identifier. When the AMF 300B knows the correspondence between MBS sessions and UPF 300A, the AMF 300B can specify the UPF 300A with which the gNB 200B wants to establish an MBS connection, based on the second identifier.

[0095] The AMF 300B can notify the gNB 200B of specified content. For example, when sending a response message to the gNB 200B in response to a setup request message from the gNB 200B, the AMF 300B includes information in the response message indicating the content specified by the AMF 300B.

[0096] In step S108, gNB 200B establishes an MBS connection (and MBS session) with UPF 300A under the control of AMF 300B.

[0097] Note that gNB 200B can perform steps S107 and S108 after step S109, which will be described later.

[0098] In step S109, gNB 200B sends a handover response (handover request confirmation) message to gNB 200A indicating that acceptance is permitted. The handover response message may include at least one of the following: information about the MBS session (second identifier) ​​accepted by gNB 200B or information about the MBS session (second identifier) ​​rejected by gNB 200B.

[0099] Here, the handover response message may include information (a second identifier) ​​of the MBS session that the gNB 200B allows to be accepted, and a set of information indicating whether the MBS session (MBS connection) has been established by the gNB 200B. The handover response message may also include information (a second identifier) ​​of the MBS session that the gNB 200B rejects, and a set of information indicating that the MBS session (MBS connection) failed to be established by the gNB 200B.

[0100] When performing data forwarding from gNB 200A to gNB 200B, 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 gNB 200B's IP address or gNB 200B's GTPTEID.

[0101] The handover response message includes the radio configuration for UE 100 to receive MBS sessions from gNB 200B via multicast or broadcast.

[0102] In step S110, in response to receiving a handover response message from gNB 200B, gNB 200A sends a handover instruction (RRC reconfiguration) message to UE 100. The handover instruction message may include at least a portion of the information included in the handover response message (e.g., information on MBS sessions allowed by gNB 200B, information on MBS sessions rejected by gNB 200B, and radio configuration).

[0103] In step S111, UE 100 performs a handover from gNB 200A to gNB 200B in response to receiving a handover instruction message from gNB 200A.

[0104] UE 100 can specify MBS sessions rejected by gNB 200B based on information included in the handover instruction message, in order to establish a unicast (separate MBS service delivery) connection corresponding to the MBS session. Here, in UE 100, the information included in the handover instruction message can be communicated from the AS layer to the NAS layer, and the unicast connection establishment procedure can be performed in the NAS layer. This description is based on the assumption that gNB 200B allows acceptance of at least one MBS session.

[0105] In step S112, UPF 300A sends MBS data to gNB 200B via MBS connection.

[0106] In step S113, gNB 200B transmits the MBS data received from UPF 300A to UE100 via multicast (or broadcast). This allows UE100 to continue receiving MBS data even after handover.

[0107] (2) Operation Mode 2

[0108] The description of operation mode 2 focuses primarily on its differences from operation mode 1 described above.

[0109] In the above-described operating mode 1, the following example is described: In a case where the gNB 200B, used as the target gNB, does not have an MBS connection (MBS session), the gNB 200B establishes an MBS connection during a handover of the UE 100, which is receiving MBS. However, the gNB 200B will begin to retransmit MBS data via multicast or broadcast, thereby consuming radio resources for this transmission.

[0110] When UE 100 performs a handover to a target gNB that has already established an MBS connection and is transmitting MBS data via multicast or broadcast, there is already a UE 100 that has received the MBS data, thus effectively utilizing radio resources. Therefore, in operating mode 2, gNB 200A, which acts as the source gNB, pre-identifies whether neighboring gNBs have MBS connections, allowing UE 100 to preferentially handover to a target gNB with an MBS connection.

[0111] In operating mode 2, gNB 200B sends a second identifier (the aforementioned MBS session information) identifying the MBS session provided by gNB 200B via multicast or broadcast to gNB 200A. When gNB 200B provides multiple MBS sessions via multicast or broadcast, gNB 200B can send multiple second identifiers corresponding to the multiple MBS sessions to gNB 200A.

[0112] The gNB 200B can send a first identifier (UPF information) to the gNB 200A, which identifies the UPF 300A that has an MBS connection with the gNB 200B.

[0113] gNB 200A can determine the handover of UE 100 (e.g., select a target gNB) based on at least one of a first identifier or a second identifier received from gNB 200B.

[0114] Figure 11 This is a diagram illustrating operation mode 2 according to an embodiment. Figure 11 In this example, assume that UE 100A is in RRC connected state in the cell of gNB 200A. UE 100B is in RRC connected state, RRC idle state, or RRC inactive state in the cell of gNB 200B.

[0115] like Figure 11 As shown, in step S201, gNB 200B establishes an MBS connection with UPF 300A.

[0116] In step S202, gNB 200B sends a notification message to gNB 200A including at least one of a first identifier (UPF information) or a second identifier (the aforementioned MBS session information). The first identifier identifies UPF 300A with an MBS connection to gNB 200B, and the second identifier identifies an MBS session provided by gNB 200B via multicast or broadcast. The notification message is sent via the Xn interface (Xn connection).

[0117] The gNB 200B can send notification messages periodically (at a constant period). The gNB 200B can send notification messages in response to changes in the state of the MBS connection (MBS session) (establishment, termination). The gNB 200B can also send notification messages in response to a request to send a notification message received from the gNB 200A.

[0118] In step S203, UPF 300A sends MBS data to gNB 200B via MBS connection.

[0119] In step S204, gNB 200B transmits the MBS data received from UPF 300A to UE100B via multicast (or broadcast).

[0120] On the other hand, in step S205, gNB 200A establishes an MBS connection with UPF 300A.

[0121] In step S206, UPF 300A sends MBS data to gNB 200A via MBS connection.

[0122] In step S207, gNB 200A transmits the MBS data received from UPF 300A to UE100A via multicast (or broadcast).

[0123] In step S208, gNB 200A determines the handover of UE 100A based on, for example, a measurement report from UE 100. Here, gNB 200A determines whether to select gNB 200B as the target gNB for the handover of UE 100A based on the notification message received from gNB 200B in step S202.

[0124] If gNB 200B does not have an MBS session (MBS connection) that gNB 200A is providing to UE 100A via multicast (or broadcast), then gNB 200A can determine not to select gNB 200B as the target gNB for UE 100A handover.

[0125] If gNB 200B does not have an MBS session (MBS connection) that gNB 200A is providing to UE 100A via multicast (or broadcast), then gNB 200A can perform handover control according to the above-described operating mode 1. This can cause gNB 200B to establish an MBS session (MBS connection) that gNB 200A is providing to UE 100A via multicast (or broadcast).

[0126] If gNB 200B has an MBS session (MBS connection) that gNB 200A is providing to UE 100A via multicast (or broadcast), then gNB 200A can select gNB 200B as the target gNB for UE 100A handover. In this case, gNB 200A can perform general handover control instead of the handover control according to the above-described operating mode 1.

[0127] (3) Operation Mode 3

[0128] The description of operation mode 3 focuses primarily on the differences from operation modes 1 and 2 mentioned above.

[0129] In the above-described operating mode 2, an example is described of sending a notification message about the MBS connection of gNB 200B to gNB 200A. Conversely, in operating mode 3, this notification message is sent from AMF 300B to gNB 200A. In operating mode 3, gNB 200A receives the notification message from AMF 300B, which includes an identifier identifying gNB 200B and an identifier identifying the MBS session (MBS connection) provided by gNB 200B via multicast or broadcast (the MBS session information described above).

[0130] Figure 12 This is a diagram illustrating operation mode 3 according to an embodiment. Figure 12 In this example, assume that UE 100A is in RRC connected state in the cell of gNB 200A. UE 100B is in RRC connected state, RRC idle state, or RRC inactive state in the cell of gNB 200B.

[0131] like Figure 12 As shown, in step S301, gNB 200B establishes an MBS connection with UPF 300A.

[0132] In step S302, AMF 300B sends a notification message to gNB 200A, which includes an identifier identifying gNB 200B and an identifier identifying an MBS session (MBS connection) provided by gNB 200B via multicast or broadcast (the MBS session information mentioned above). The identifier identifying gNB 200B can be at least one of gNB ID of gNB 200B or cell ID of gNB 200B's cell.

[0133] The AMF 300B can send notification messages periodically (at a constant period). The AMF 300B can send notification messages in response to changes in the state of the MBS connection (MBS session) (establishment, termination). The AMF 300B can also send notification messages in response to a request to send a notification message received from the gNB 200A.

[0134] In step S303, UPF 300A sends MBS data to gNB 200B via MBS connection.

[0135] In step S304, gNB 200B transmits the MBS data received from UPF 300A to UE100B via multicast (or broadcast).

[0136] On the other hand, in step S305, gNB 200A establishes an MBS connection with UPF 300A.

[0137] In step S306, UPF 300A sends MBS data to gNB 200A via MBS connection.

[0138] In step S307, gNB 200A transmits the MBS data received from UPF 300A to UE100A via multicast (or broadcast).

[0139] In step S308, gNB 200A determines the handover of UE 100A based on, for example, a measurement report from UE 100. Here, gNB 200A determines whether to select gNB 200B as the target gNB for the handover of UE 100A based on the notification message received from AMF 300B in step S302. The details of this operation are the same as and / or similar to those of operation mode 2 described above.

[0140] (4) Operation Mode 4

[0141] The description of operation mode 4 focuses primarily on the differences from operation modes 1 to 3 mentioned above.

[0142] In the above-described operating mode 1, an example is described where gNB 200A actively initiates an MBS connection with gNB 200B. In operating mode 4, AMF 300B actively initiates an MBS connection with gNB 200B. In operating mode 4, when UE 100 performs a handover from gNB 200A to gNB 200B, gNB 200A sends a notification message to AMF 300B indicating that UE 100 is receiving MBS during the handover.

[0143] Figure 13 This is a diagram illustrating operation mode 4 according to an embodiment.

[0144] like Figure 13 As shown, in step S401, gNB 200A establishes an MBS connection with UPF 300A. UE 100, which is in RRC connection state, establishes an MBS session through gNB 200A.

[0145] In step S402, UPF 300A sends MBS data to gNB 200A via MBS connection.

[0146] In step S403, gNB 200A transmits the MBS data received from UPF 300A to UE100 via multicast (or broadcast).

[0147] In step S404, gNB 200A determines the handover from UE 100 to gNB 200B based on, for example, a measurement report from UE 100.

[0148] In step S405, gNB 200A sends a notification message to AMF 300B indicating that it wants to switch UE 100, which is currently receiving an MBS session. Step S405 can be performed before step S404. The notification message includes the identifier (or cell ID) of at least one gNB that is a candidate for the target gNB and the aforementioned MBS session information. The notification message may include the identifier of UE 100, which is currently receiving an MBS session.

[0149] In step S406, AMF 300B can perform the process of establishing an MBS connection between the candidate gNB (gNB 200B) and UPF 300A as needed based on a notification message from gNB 200A.

[0150] In step S407, AMF 300B may send a response message to gNB 200A. The response message includes the identifier (or cell ID) of at least one gNB that is a candidate for the target gNB, or at least one of the MBS session information mentioned above. The identifier (or cell ID) of the at least one gNB that is a candidate for the target gNB may be the identifier of a gNB that has already established or will establish an MBS connection. gNB 200A may reselect the target gNB for UE 100 handover based on the response message from AMF 300B.

[0151] In step S408, gNB 200A sends a handover request message to gNB 200B requesting UE 100 to hand over.

[0152] Other embodiments

[0153] The above-described operation modes can be implemented individually and independently, or they can be implemented in combination of two or more operation modes. For example, some steps of one operation mode can be added to another operation mode, or some steps of one operation mode can be replaced by some steps of another operation mode.

[0154] In the above embodiments, an example of an NR base station (i.e., gNB) was described; however, the base station can be an LTE base station (i.e., eNB). The base station can be a relay node, such as an Integrated Access and Backhaul (IAB) node. The base station can be a Distributed Unit (DU) of an IAB node.

[0155] While the above embodiments primarily assume inter-base station handover, intra-base station handover can also be assumed. For example, a base station can be divided into CUs and DUs, and the UE 100 can perform a handover between two DUs belonging to the same CU. In this case, the Xn interface described above can be interpreted as the F1 interface used as the CU-DU interface, and the various messages and information described above can be sent and received via the F1 interface. Each of the gNB 200A and gNB 200B described above can be interpreted as a CU and / or a DU.

[0156] Furthermore, a CU can be divided into a CU-CP and a CU-UP, and the UE 100 can perform a handover between two CU-UPs belonging to one CU-CP. In this case, the aforementioned Xn interface can be interpreted as an E1 interface used as an interface between the CU-CP and the CU-UP, and the various messages and information mentioned above can be sent and received via the E1 interface. Each of the aforementioned gNB 200A and gNB200B can be interpreted as a CU-CP and / or a CU-UP.

[0157] A program may be provided that enables the computer to execute each procedure performed by the UE 100 or gNB 200. The program may be recorded on a computer-readable medium. The use of a computer-readable medium allows the program to be installed on the computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. There are no particular limitations on the non-transitory recording medium, and it may be, for example, a recording medium such as a CD-ROM or DVD-ROM.

[0158] Circuitry for performing the processing to be performed by UE 100 or gNB 200 may be integrated, and at least a portion of UE 100 or gNB 200 may be configured as a semiconductor integrated circuit (chipset or SoC).

[0159] The embodiments have been described in detail above with reference to the accompanying drawings, but the specific configurations are not limited to those described above, and various design changes can be made without departing from the spirit of this disclosure.

[0160] This application claims priority to Japanese Patent Application No. 2020-174886 (filed on October 16, 2020), the contents of which are incorporated herein by reference in their entirety.

[0161] List of reference numerals

[0162] 10: NG-RAN (5G RAN)

[0163] 20: 5GC (5G CN)

[0164] 100:UE

[0165] 110: Receiver

[0166] 120: Transmitter

[0167] 130: Controller

[0168] 200: gNB

[0169] 210: Transmitter

[0170] 220: Receiver

[0171] 230: Controller

[0172] 240: Backhaul Communicator

[0173] 300A: UPF

[0174] 300B: AMF.

Claims

1. A communication control method used in a mobile communication system, the mobile communication system providing multicast broadcast service (MBS) from a base station to a user equipment, the communication control method comprising: At a first base station configured to establish an MBS connection with a core network device, MBS data is received from the core network device via the MBS connection. The MBS data received from the core network device is transmitted from the first base station to the first user equipment via multicast or broadcast. The first base station determines the handover of the first user equipment from the first base station to the second base station; A handover request is sent from the first base station to the second base station. The handover request includes an identifier for identifying the MBS session provided by the first base station by multicast or broadcast and data forwarding request information for the MBS session. as well as A handover response is sent from the second base station to the first base station, the handover response including an address used for data forwarding in the MBS session. The address used for data forwarding includes the GPRS Tunnel Protocol-Tunnel Endpoint Identifier (GTP-TEID) of the second base station.

2. The communication control method according to claim 1 further includes: In response to receiving the handover request, the second base station establishes an MBS connection with the core network device before sending the handover response.

3. The communication control method according to claim 2, wherein, Establishing an MBS connection with the core network device includes: establishing an MBS connection with the core network device based on the identifier.

4. The communication control method according to claim 1, wherein, The identifier is an identifier that identifies the MBS session being received by the first user equipment.

5. The communication control method according to claim 1, wherein, The switching request includes multiple of the identifiers.

6. The communication control method according to claim 1, wherein, The identifier includes at least one selected from the group consisting of the Group Radio Network Temporary Identifier (RNTI), the Temporary Mobile Group Identifier (TMGI), the Session ID, and the Quality of Service (QoS) Flow ID.

7. A base station for establishing a multicast broadcast service (MBS) connection with a core network device, the base station comprising: The receiver receives MBS data from the core network device via the MBS connection; The transmitter transmits the MBS data received from the core network device to the user equipment via multicast or broadcast. as well as The controller determines the handover of the user equipment from one base station to another. The transmitter sends a handover request to the other base station. The handover request includes an identifier for identifying the MBS session provided by the base station via multicast or broadcast, and data forwarding request information for the MBS session. The receiver receives a handover response from the other base station, the handover response including an address for data forwarding in the MBS session. The address used for data forwarding includes the GPRS Tunneling Protocol-Tunnel Endpoint Identifier (GTP-TEID) of the other base station.

8. A base station, comprising: The receiver receives a handover request from another base station that has established a multicast broadcast service (MBS) connection with the core network device, the handover request being used for the user equipment to hand over from the other base station to the base station; as well as The transmitter sends a handover response to the other base station. The handover request includes an identifier for identifying the MBS session provided by the other base station via multicast or broadcast, and data forwarding request information for the MBS session. The handover response includes an address used for data forwarding in the MBS session. The address used for data forwarding includes the GPRS Tunneling Protocol-Tunnel Endpoint Identifier (GTP-TEID) of the other base station.

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