COMMUNICATION CONTROL METHOD, BASE STATION AND SYSTEM

Abstract

A communication control method used in a mobile communication system that provides a multicast broadcast service (MBS) to user equipment from a base station, wherein: the base station receives, from a core network or another base station, a designated packet data convergence protocol (PDCP) sequence number that is designated so as to be applied to an MBS packet; the base station associates the MBS packet and the designated PDCP sequence number; and the base station transmits, to the user equipment, the MBS packet associated with the designated PDCP sequence number.

Description

[Technical field]

[0001] The present invention relates to a communication control method for use in a mobile communication system. [Background technology]

[0002] In recent years, the fifth generation (5G) mobile communication system has been attracting attention. NR (New Radio), the radio access technology (RAT) of the 5G system, has features such as high speed, large capacity, high reliability, and low latency compared to LTE (Long Term Evolution), the fourth generation radio access technology. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP technical specification "3GPP TS 38.300 V16.3.0 (2020-09)" 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 in which a base station provides a multicast broadcast service (MBS) to a user device, and includes the steps of the base station receiving a designated PDCP (Packet Data Convergence Protocol) sequence number designated to be applied to an MBS packet from a core network or another base station, the base station associating the MBS packet with the designated PDCP sequence number, and the base station transmitting the MBS packet associated with the designated PDCP sequence number to the user device.

[0005] A communication control method according to a second aspect is a communication control method used in a mobile communication system in which a base station provides a multicast broadcast service (MBS) to a user equipment, the method comprising: the base station receiving a paging message from a core network requesting paging for the user equipment in an RRC (Radio Resource Control) idle state or an RRC inactive state; and the base station performing the paging in response to receiving the paging message, the paging message including an identifier for an MBS session received by the user equipment.

[0006] A communication control method according to a 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 device, and includes the steps of: the base station transmitting MBS data received from a core network to the user device in Point To Multipoint (PTM); when the base station determines that the PTM transmission of the MBS data from the base station to the user device cannot be continued, transmitting a notification to the user device; and, in response to receiving the notification, the user device establishing a unicast session with the core network for receiving the MBS data by unicast.

[0007] A communication control method according to a fourth aspect is a communication control method used in a mobile communication system in which a base station provides a multicast broadcast service (MBS) to a user device, the method comprising: the user device receiving from a cell MBS control information used to receive MBS data and a control area identifier indicating an MBS control area range, which is an area range in which at least a part of the MBS control information is applicable; and when the user device determines that a predetermined condition regarding the MBS control area range is satisfied, re-receiving the MBS control information. [Brief description of the drawings]

[0008] [Figure 1]1 is a diagram showing a configuration of a mobile communication system according to an embodiment; [Diagram 2] FIG. 1 is a diagram illustrating a configuration of a UE (user equipment) according to an embodiment. [Diagram 3] A diagram showing the configuration of a gNB (base station) according to one embodiment. [Figure 4] A diagram showing the configuration of a protocol stack of a wireless interface of a user plane that handles data. [Diagram 5] FIG. 2 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). [Figure 6] FIG. 2 is a diagram showing a correspondence relationship between downlink logical channels and transport channels according to an embodiment. [Figure 7] FIG. 2 is a diagram illustrating a method for distributing MBS data according to an embodiment. [Figure 8] FIG. 1 illustrates an operating environment according to one embodiment. [Figure 9] FIG. 1 illustrates an operating environment according to one embodiment. [Figure 10] FIG. 11 is a diagram illustrating an operation example 1 of sequence number synchronization according to an embodiment. [Figure 11] FIG. 11 is a diagram illustrating an operation example 2 of sequence number synchronization according to an embodiment. [Figure 12] FIG. 11 is a diagram illustrating an example of a paging operation according to an embodiment. [Figure 13] FIG. 11 is a diagram illustrating an example of an operation of switching to unicast according to an embodiment. [Figure 14] FIG. 2 is a diagram illustrating an operation of a mobile communication system according to an embodiment. [Figure 15] FIG. 11 is a diagram illustrating an operation when a UE 100 according to an embodiment moves from a cell C1 to a cell C2. [Figure 16] FIG. 11 is a diagram illustrating an operation when a UE 100 according to an embodiment moves from a cell C1 to a cell C2. [Figure 17]FIG. 11 is a diagram illustrating an operation example 1 regarding re-reception of MBS control information according to an embodiment. [Figure 18] FIG. 11 is a diagram illustrating an operation example 2 regarding re-reception of MBS control information according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The introduction of multicast and broadcast services to the 5G system (NR) is being considered. It is hoped that the NR multicast and broadcast services will provide improved services compared to the LTE multicast and broadcast services.

[0010] Therefore, an object of the present invention is to provide an improved multicast / broadcast service.

[0011] A mobile communication system according to an 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.

[0012] (Configuration of a mobile communication system) First, a configuration of a mobile communication system according to an embodiment will be described. Fig. 1 is a diagram showing a configuration of a mobile communication system according to an embodiment. This mobile communication system complies with the 3GPP standard 5th Generation System (5GS). In the following description, 5GS will be taken as an example, but the mobile communication system may be at least partially applied to an LTE (Long Term Evolution) system, or at least partially applied to a 6th Generation (6G) system.

[0013] 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.

[0014] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user, and may be, for example, 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 a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0015] The NG-RAN 10 includes a base station (called "gNB" in the 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. 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 a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency.

[0016] In addition, gNBs can also be connected to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also be connected to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0017] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using Non-Access Stratum (NAS) signaling. The UPF controls data forwarding. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0018] FIG. 2 is a diagram showing a configuration of a UE 100 (user equipment) according to an embodiment.

[0019] As shown in FIG. 2, the UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit .

[0020] 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 a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0021] The transmission unit 120 performs various transmissions under the control of the control unit 130. The transmission unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0022] The control unit 130 performs various controls in the UE 100. 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 in 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 baseband signals. The CPU executes programs stored in the memory to perform various processing.

[0023] FIG. 3 is a diagram showing the configuration of a gNB 200 (base station) according to one embodiment.

[0024] As shown in FIG. 3, the gNB 200 includes a transmitter 210, a receiver 220, a control unit 230, and a backhaul communication unit 240.

[0025] 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 a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0026] The receiving unit 220 performs various receptions under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0027] 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 in 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 baseband signals. The CPU executes programs stored in the memory to perform various processing.

[0028] The backhaul communication unit 240 is connected to adjacent base stations via an inter-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) (i.e., the functions are divided), and both units may be connected to each other via an F1 interface.

[0029] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0030] As shown in FIG. 4, the user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0031] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the UE 100 and the PHY layer of the gNB 200 via a physical channel.

[0032] The MAC layer performs data priority control, retransmission processing using hybrid ARQ (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of the UE 100 and the MAC layer of the gNB 200 via a transport channel. The MAC layer of the gNB 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be assigned to the UE 100.

[0033] The RLC layer transmits data to the RLC layer on the receiving side by using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via a logical channel.

[0034] The PDCP layer performs header compression / decompression and encryption / decryption.

[0035] The SDAP layer maps IP flows, which are the units for QoS control by the core network, to radio bearers, which are the units for QoS control by the AS (Access Stratum). Note that if the RAN is connected to the EPC, the SDAP is not necessary.

[0036] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0037] As shown in FIG. 5, the protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer instead of the SDAP layer shown in FIG.

[0038] Between the RRC layer of the UE 100 and the RRC layer of the gNB 200, RRC signaling for various settings is transmitted. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200, the UE 100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200, the UE 100 is in an RRC idle state. When the connection between the RRC of the UE 100 and the RRC of the gNB 200 is suspended, the UE 100 is in an RRC inactive state.

[0039] The NAS layer, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300B.

[0040] In addition, the UE 100 has an application layer and the like in addition to the protocol of the radio interface.

[0041] (MBS) Next, an MBS according to an embodiment will be described. The MBS is a service that transmits data from the NG-RAN 10 to the UE 100 by broadcast or multicast, that is, point to multipoint (PTM). The MBS may be called an MBMS (Multimedia Broadcast and Multicast Service). Note that use cases (service types) of the MBS include public safety communication, mission critical communication, V2X (Vehicle to Everything) communication, IPv4 or IPv6 multicast distribution, IPTV, group communication, and software distribution.

[0042] There are two types of MBS transmission methods in LTE: MBSFN (Multicast Broadcast Single Frequency Network) transmission and SC-PTM (Single Cell Point To Multipoint) transmission. Fig. 6 is a diagram showing a correspondence relationship between downlink logical channels and transport channels according to one embodiment.

[0043] As shown in Figure 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 designed mainly for multi-cell transmission, and in an MBSFN area consisting of multiple cells, each cell synchronously transmits the same signal (same data) in the same MBSFN subframe.

[0044] The logical channels used for SC-PTM transmission are the SC-MTCH (Single Cell Multicast Traffic Channel) and the SC-MCCH (Single Cell Multicast Control Channel), and the transport channel used for SC-PTM transmission is the DL-SCH (Downlink Shared Channel). SC-PTM transmission is designed primarily for single-cell transmission, and transmits data by broadcast or multicast on a cell-by-cell basis. The physical channels used for SC-PTM transmission are the PDCCH (Physical Downlink Control Channel) and the PDSCH (Physical Downlink Shared It is a QoS Channel, which allows dynamic resource allocation.

[0045] In the following, an example in which an MBS is provided using the SC-PTM transmission method will be mainly described, but an MBS may also be provided using the MBSFN transmission method. Also, an example in which an MBS is provided by multicast will be mainly described. Therefore, MBS may be read as multicast. However, an MBS may also be provided by broadcast.

[0046] Moreover, MBS data refers to data transmitted by the MBS, the MBS control channel refers to the MCCH or SC-MCCH, and the MBS traffic channel refers to the MTCH or SC-MTCH. However, the MBS data may be transmitted by unicast. The MBS data may also be called MBS traffic. In the following, the MBS data handled in packet units is called an MBS packet.

[0047] A network can provide different MBS services for each MBS session. An MBS session is identified by at least one of a Temporary Mobile Group Identity (TMGI) and a session identifier, and at least one of these identifiers is called an MBS session identifier. Such an MBS session identifier may be called an MBS service identifier or a multicast group identifier.

[0048] FIG. 7 is a diagram showing a method for distributing MBS data according to an embodiment.

[0049] As shown in Fig. 7, MBS data (MBS Traffic) is distributed from a single data source (application service provider) to multiple UEs. A 5G CN (5GC) 20, which is a 5G core network, receives the MBS data from the application service provider, creates a copy (replication) of the MBS data, and distributes it.

[0050] From the 5GC20 point of view, two delivery methods are possible: Shared MBS Traffic delivery and Individual MBS Traffic delivery.

[0051] In the shared MBS data delivery, a connection is established between 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."

[0052] The MBS connection may be called a Shared MBS Traffic delivery connection or a shared transport. The MBS connection terminates in the NG-RAN 10 (i.e., the gNB 200). The MBS connection may correspond one-to-one with the 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 MBS data to the UE 100 in the selected manner.

[0053] On the other hand, in the individual MBS data delivery, a unicast session is established between the NG-RAN 10 and the UE 100, and the MBS data is delivered individually from the 5GC 20 to the UE 100. Such a unicast may be called a PDU session. The unicast (PDU session) is terminated at the UE 100.

[0054] (Sequence number synchronization) Next, sequence number synchronization according to an embodiment will be described. Figures 8 and 9 are diagrams showing an operating environment according to an embodiment.

[0055] As shown in Fig. 8, the gNB 200A manages a cell C1, and the gNB 200B manages a cell C2. A UE 100A exists in the cell C1, and a UE 100B exists in the cell C2. The UE 100A may move from the cell C1 to the cell C2. Similarly, the UE 100B may move from the cell C2 to the cell C1.

[0056] Although an example in which the cell sizes of the cells C1 and C2 are equal is illustrated, the cell sizes of the cells C1 and C2 may be different from each other. The geographical areas of the cells C1 and C2 at least partially overlap each other. Such a relationship between the cells may be called adjacent cells. The UE 100A and the UE 100B may be present in the overlapping area of ​​these cells.

[0057] The gNB200A and the gNB200B can communicate with each other via an Xn interface (Xn connection), which is an interface between base stations. However, communication between the gNB200A and the gNB200B is not limited to being performed via the Xn interface, and communication between the gNB200A and the gNB200B may be performed via an NG interface, which is an interface between a base station and a core network, and a core network device. In the following, an example in which communication between the gNB200A and the gNB200B is performed via the Xn interface will be mainly described.

[0058] Cell C1 and cell C2 may belong to the same MBS area. An MBS area is an area consisting of multiple cells in which the same MBS session is provided. Multiple cells belonging to the same MBS area may provide an MBS session at the same frequency and configure a single frequency network (SFN).

[0059] The establishment and release of the MBS connection is controlled by the AMF 300B. The AMF 300B is another example of a core network device. However, a Session Management Function (SMF) instead of the AMF 300B may control the establishment and release of the MBS connection. The SMF is another example of a core network device.

[0060] In such an environment, the gNB 200B has an MBS connection with the UPF 300A. The gNB 200B receives MBS packets from the UPF 300A via the MBS connection, and transmits the received MBS packets in cell C2 using PTM. Here, the PDCP entity of the gNB 200B assigns a PDCP header having a PDCP sequence number (PDCP SN) to the MBS packet and transmits it. The PDCP SN is counted up (incremented) for each MBS packet transmitted.

[0061] On the other hand, gNB200A does not have an MBS connection with UPF300A. Here, assuming that an SFN is configured with cells C1 and C2, gNB200A needs to establish an MBS connection with UPF300A as shown in Fig. 9. In addition, it is desirable that the PDCP SN of MBS packets transmitted by gNB200A and gNB200B is synchronized. In other words, it is desirable that MBS packets transmitted by MBS Shared Delivery are PTM-transmitted by multiple gNB200 (gNB200A and gNB200B) with synchronized PDCP SN on the air interface side.

[0062] However, gNB200B has already started PTM transmission for the target MBS session, and the PDCP SN value has increased. For this reason, if gNB200A counts up the PDCP SN from an initial value (e.g., zero), PTM transmission cannot be performed with synchronized PDCP SNs among multiple gNB200 (gNB200A and gNB200B).

[0063] Therefore, in one embodiment, the core network specifies the value of the PDCP SN of the MBS packet transmitted by the gNB200A. Here, it is assumed that the 5GC20 (core network) knows the current PDCP SN of the gNB200B. The 5GC20 specifies the value of the PDCP SN of the MBS packet transmitted by the gNB200A so that the MBS packet and its PDCP SN transmitted by the gNB200A match the MBS packet and its PDCP SN transmitted by the gNB200B.

[0064] In order for 5GC20 to know the current PDCP SN of gNB200B, 5GC20 may inquire of gNB200B about current PDCP SN information. The inquiry may include MBS session information. gNB200B may report the current PDCP SN information to 5GC20. The report may include the MBS session information. The report may be performed in response to receiving the inquiry.

[0065] In one embodiment, the gNB 200A receives an MBS packet and a designated PDCP SN designated to be applied to the MBS packet from the 5GC 20, and associates the MBS packet with the designated PDCP SN. The gNB 200A transmits the MBS packet associated with the designated PDCP SN to the UE 100. For example, the gNB 200A sets the designated PDCP SN in the PDCP header of the MBS packet, and transmits the MBS packet with the designated PDCP SN set in the PDCP header by PTM.

[0066] FIG. 10 is a diagram illustrating an operation example 1 of sequence number synchronization according to an embodiment.

[0067] 10, in step S101, the 5GC 20 (for example, the UPF 300A or the AMF 300B) transmits setting information for establishing an MBS connection (hereinafter referred to as "MBS connection setting information") to the gNB 200A. The 5GC 20 may transmit the MBS connection setting information to the gNB 200A in response to a request from the gNB 200A.

[0068] The MBS connection setting information includes a setting parameter of the MBS connection and designated PDCP SN information for the designated PDCP SN. The MBS connection setting information may include MBS session information associated with the designated PDCP SN information. The MBS session information includes an identifier for the MBS session. Such an identifier may be a session identifier (e.g., TMGI), a QoS flow identifier, and / or a G-RNTI in a PTM transmission. The gNB200A can determine the MBS session corresponding to the MBS connection to be established based on the MBS session information.

[0069] The designated PDCP SN information includes a designated PDCP SN designated to be applied to the MBS packet that the gNB200 receives first from the 5GC20 via the MBS connection. That is, the 5GC20 designates an initial value of the PDCP SN that the gNB200A should set in the MBS packet. In FIG. 10, an example is shown in which the designated PDCP SN is "10". Note that when the 5GC20 transmits the MBS connection setting information and the MBS packet to the gNB200A simultaneously, the designated PDCP SN information may be a designated PDCP SN designated to be applied to the current corresponding MBS packet.

[0070] Alternatively, the designated PDCP SN information may include information associating an identifier assigned to an MBS packet received by the gNB 200 from the 5GC 20 via the MBS connection with the designated PDCP SN. The identifier assigned to the MBS packet may be a GTP SN included in a GTP header used in a GTP tunnel constituting the MBS connection and / or an SN included in an IP header of the MBS packet (IP packet). In the example of Fig. 10, the designated PDCP SN information may include a set of an identifier (e.g., "A") assigned to MBS packet A and a PDCP SN "10", and a set of an identifier (e.g., "B") assigned to MBS packet B and a PDCP SN "11".

[0071] The specified PDCP SN information may include the SN length (bit length) of the PDCP SN. The SN length is, for example, 12 bits or 18 bits. By specifying the SN length, it is possible to synchronize the timing at which the SN returns to zero (wrap around).

[0072] In step S102, gNB200A establishes an MBS connection with 5GC20 based on MBS connection setting information from 5GC20.

[0073] In step S103, the 5GC 20 transmits the MBS packet A to the gNB 200A via the MBS connection. The gNB 200A receives the MBS packet A.

[0074] In step S104, the PDCP entity of gNB200A sets the specified PDCP SN specified by 5GC20 in the PDCP header of MBS packet A based on the specified PDCP SN information from 5GC20.

[0075] In step S105, the gNB 200A transmits the MBS packet A, in which the specified PDCP SN is set in the PDCP header, to the UE 100A by PTM.

[0076] Thereafter, gNB200A updates the PDCP SN by counting it up for each MBS packet that gNB200A transmits.

[0077] For example, in step S106, the 5GC 20 transmits MBS packet B to the gNB 200A via the MBS connection. The gNB 200A receives the MBS packet B.

[0078] In step S107, the PDCP entity of gNB200A sets the updated PDCP SN (here, SN=11) in the PDCP header of MBS packet B.

[0079] In step S108, the gNB 200A transmits the MBS packet B, in which the updated PDCP SN is set in the PDCP header, to the UE 100A by PTM.

[0080] In the operation example 1, an example in which each gNB200 transmits an MBS packet using PTP has been described, but each gNB200 may also transmit an MBS packet using PTM.

[0081] Next, an operation example 2 of sequence number synchronization according to an embodiment will be described. Operation example 2 is an example in which, when UE 100 performs handover, PDCP SN is synchronized before and after the handover. Here, an example in which UE 100 in an RRC connected state performs handover from gNB 200A to gNB 200B will be described.

[0082] In the second operation example, the gNB 200B, which is the target gNB, receives a designated PDCP SN designated to be applied to an MBS packet from the gNB 200A, which is the source gNB, and associates the MBS packet with the designated PDCP SN. The gNB 200A transmits the MBS packet associated with the designated PDCP SN to the UE 100.

[0083] In operation example 2, the gNB200B receives, from the UE 100 that has performed handover from the gNB 200A to the gNB 200B, the PDCP SN of an MBS packet that the UE 100 failed to receive at the gNB 200A. The gNB 200B transmits (resends) to the UE 100 the MBS packet associated with the PDCP SN received from the UE 100.

[0084] Fig. 11 is a diagram showing an operation example 2 of sequence number synchronization according to an embodiment. In Fig. 11, each of gNB200A and gNB200B has an MBS connection with UPF300A and receives the same MBS packet from UPF300A. However, it is assumed that the PDCP SNs of the MBS packets transmitted by gNB200A and gNB200B are asynchronous.

[0085] 11, in steps S201 to S203, the gNB 200A transmits MBS packets A to C to the UE 100 by PTM. The PDCP SNs of the MBS packets A to C are "11" to "13." Here, it is assumed that the UE 100 fails to receive the MBS packet C (for example, detects a decoding error).

[0086] In step S204, gNB200A decides to handover UE100 to gNB200B.

[0087] In step S205, the gNB 200A performs handover of the UE 100. directive The gNB 200B transmits a handover request message to the gNB 200B to

[0088] The handover request message includes designated PDCP SN information. The designated PDCP SN information may include information that associates an identifier attached to an MBS packet received by the gNB 200A from the 5GC 20 via the MBS connection with a designated PDCP SN. The identifier attached to the MBS packet may be a GTP SN included in a GTP header used in a GTP tunnel constituting the MBS connection and / or an SN included in an IP header of the MBS packet (IP packet). In the example of FIG. 11, the designated PDCP SN information may include a set of an identifier (e.g., “A”) and a PDCP SN “11” attached to the MBS packet A, a set of an identifier (e.g., “B”) and a PDCP SN “12” attached to the MBS packet B, and a set of an identifier (e.g., “C”) and a PDCP SN “13” attached to the MBS packet C.

[0089] Although an example in which the handover request message includes the designated PDCP SN information has been described here, the gNB200B may obtain the designated PDCP SN information from the gNB200A by inquiring of the gNB200A. The gNB200B may obtain the designated PDCP SN information from the 5GC20. In this case, the gNB200B may obtain the designated PDCP SN information from the 5GC20 by inquiring of the 5GC20.

[0090] In step S206, the gNB200B associates each MBS packet received by the gNB200B from the 5GC20 (UPF300A) with the designated PDCP SN based on the designated PDCP SN information.

[0091] In step S207, gNB200B sends a handover response message to gNB200A.

[0092] In step S208, gNB200A sends a handover command message to UE100.

[0093] In step S209, UE100 performs handover from gNB200A to gNB200B.

[0094] In step S210, the UE 100 transmits, to the gNB 200B, a retransmission request including the PDCP SN “13” of the MBS packet C that was unsuccessfully received in step S203. This retransmission request may be a PDCP Status PDU.

[0095] In addition, in the handover request of step S205, the gNB 200A (source gNB) may notify information of the SN that is thought to have failed to be received by the UE 100 (i.e., a network-initiated retransmission request). In this case, step S210 is not essential.

[0096] In step S211, based on the association in step S206, gNB200B transmits to UE100 MBS packet C corresponding to PDCP SN “13” for which retransmission has been requested by UE100.

[0097] In this way, according to operation example 2, even if UE 100 performs handover between gNBs whose PDCP SNs are not synchronized, MBS packets that UE 100 was unable to receive from the source gNB can be correctly transmitted (retransmitted) from the target gNB.

[0098] (paging) Next, paging according to one embodiment will be described.

[0099] When UE 100 in an RRC idle state or an RRC connected state performs MBS reception, gNB 200 may receive a paging message addressed to this UE 100 from 5GC 20 (AMF 300B). If gNB 200 pages UE 100 without considering the timing at which UE 100 performs MBS reception, there is a concern that a reception error may occur due to a conflict between the MBS reception timing and the paging reception timing in UE 100.

[0100] An operation for solving such a problem will be described. In one embodiment, the gNB 200 receives a paging message requesting paging for the UE 100 in an RRC idle state or an RRC inactive state from the 5GC 20 (AMF 300B). The paging message includes an identifier (e.g., TMGI) related to the MBS session received by the UE 100.

[0101] Specifically, AMF300B is aware of the MBS session received by UE100 in RRC idle state or RRC inactive state, and when sending a paging message addressed to this UE100 to gNB200, AMF300B notifies gNB200 of the identifier of the MBS session.

[0102] In response to receiving the paging message from the AMF 300B, the gNB 200 pages the UE 100. Specifically, the gNB 200 transmits an RRC paging message addressed to the UE 100.

[0103] Here, based on the session identifier included in the paging message from the AMF 300B, the gNB 200 performs paging (transmits an RRC paging message) at a timing different from the transmission timing of the MBS session received by the UE 100. This makes it possible to avoid a conflict between the MBS reception timing and the paging reception timing in the UE 100.

[0104] Fig. 12 is a diagram showing an example of a paging operation according to an embodiment. In Fig. 12, it is assumed that the UE 100 is in an RRC idle state or an RRC connected state.

[0105] As shown in Fig. 12, in step S301, UPF300A transmits MBS data to gNB200 via MBS connection. In step S302, gNB200 transmits the MBS data received from UPF300A to UE100 by PTM. Here, it is assumed that the timing at which gNB200 transmits MBS data by PTM is determined. For example, gNB200 notifies UE100 in advance of the timing of MBS transmission opportunities (which may be MBS transmission cycles), and UE100 performs MBS reception at the notified MBS transmission timing.

[0106] In step S303, the AMF 300B transmits a paging message addressed to the UE 100 to the gNB 200. The paging message includes a set of an identifier of the UE 100 and an identifier of an MBS session received by the UE 100 (MBS session information).

[0107] In step S304, the gNB200 determines the paging timing of the UE100 based on information included in the paging message from the AMF300B. For example, the gNB200 identifies the MBS transmission timing of the MBS session based on the MBS session information included in the paging message from the AMF300B. The gNB200 also identifies the paging opportunity (paging timing) of the UE100 based on the UE identifier included in the paging message from the AMF300B. The gNB200 then determines the paging timing that does not match the identified MBS transmission timing while avoiding the paging timing that matches the identified MBS transmission timing.

[0108] In step S305, UPF 300A transmits MBS data to gNB 200 via MBS connection. In step S306, gNB 200 transmits the MBS data received from UPF 300A to UE 100 by PTM. Note that UE 100 may prioritize MBS reception when it determines that a paging opportunity and an MBS reception opportunity collide.

[0109] In step S307, gNB200 transmits an RRC paging message to UE100 at the paging timing determined in step S304.

[0110] In this operation example, it is assumed that the UE 100 cannot simultaneously receive MBS and paging. However, it is also possible that the UE 100 has the capability to simultaneously receive MBS and paging. For this reason, the AMF 300B may further include information (capability information) on whether the UE 100 has the capability to simultaneously receive MBS and paging in the paging message. Based on the capability information, the gNB 200 may simultaneously transmit MBS data and an RRC paging message to the UE 100 having the capability.

[0111] (Switch to unicast) Next, switching to unicast according to an embodiment will be described.

[0112] For example, when performing handover of UE 100 receiving MBS data transmitted by PTM, if the target gNB 200 does not support PTM transmission (or MBS service), UE 100 will not be able to continue receiving the MBS data. Also, when gNB 200 stops PTM transmission (or MBS service), UE 100 will not be able to continue receiving the MBS data.

[0113] In this case, since the core network (5GC20) is in a state in which it can continue to provide the MBS service, the UE 100 can continue to receive the MBS data by establishing a unicast session (PDU session) as shown in Fig. 7 and switching to individual MBS data delivery (Individual MBS Traffic delivery). However, in order to establish a unicast session, it is necessary for the UE 100 to make an establishment request to the 5GC 20.

[0114] In one embodiment, the gNB200 transmits the MBS data received from the 5GC20 to the UE100 in PTM. When the gNB200 determines that the PTM transmission of the MBS data from the gNB200 to the UE100 cannot be continued, the gNB200 transmits a notification to the UE100. In response to receiving the notification, the UE100 establishes a unicast session with the 5GC20 for receiving the MBS data by unicast. In this way, the notification from the gNB200 prompts the UE100 to establish a unicast session, so that the UE100 can establish a unicast session and continue to receive the MBS data.

[0115] FIG. 13 is a diagram illustrating an example of an operation of switching to unicast according to an embodiment.

[0116] As shown in FIG. 13, in step S401, 5GC20 (UPF300A) transmits MBS data to gNB200 via an MBS connection.

[0117] In step S402, gNB200 transmits the MBS data received from 5GC20 to UE100 using PTM.

[0118] In step S403, the gNB 200 determines that the UE 100 cannot continue providing the MBS service during PTM reception. For example, the gNB 200 determines that the MBS service cannot be continued because it is necessary to hand over the UE 100 or the gNB 200 stops PTM transmission. However, the MBS service itself continues.

[0119] In step S404, gNB200 notifies UE100 to make a service request for receiving MBS via unicast.

[0120] The notification may include an identifier of the target MBS service (MBS session), for example, TMGI. The notification may be a notification that the MBS service cannot be continued by the PTM.

[0121] Assuming that the UE 100 is in an RRC connected state, the notification can be UE dedicated signaling. Assuming that the UE 100 is in an RRC idle state or an RRC inactive state, the notification can be a broadcast MBS control channel or paging (RRC paging message).

[0122] In step S405, based on the notification from gNB200, the NAS layer of UE100 sends a session establishment request for a unicast session of the receiving service (TMGI) to 5GC20.

[0123] In step S406, the UE 100 continues to receive the MBS service by unicast. The UE 100 may notify the gNB 200 that the unicast session has been established. Notify that a unicast session has been established The notification may be performed following step S405. The notification enables the gNB 200 to perform handover or stop PTM transmission at an appropriate timing.

[0124] (MBS control area range) Next, the MBS control area range according to one embodiment will be described.

[0125] A UE 100 that receives an MBS may move across cells. In order for such a UE 100 to continue receiving an MBS, it is necessary to receive an MBS control channel (MBS control information) at least in a cell to which the cell is switched when the cell is switched. This increases the load and power consumption of the UE 100, and there is a problem that it is difficult to quickly receive MBS data from a cell to which the cell is switched. The MBS control information includes setting information (MBS setting) for receiving an MBS traffic channel.

[0126] In one embodiment, a function (hereinafter referred to as a "control area function") that allows MBS control information to be shared within an area range consisting of multiple cells (hereinafter referred to as an "MBS control area range") is introduced. This allows the MBS control information to be reused across cells within the MBS control area range, thereby solving the above-mentioned problem.

[0127] That is, the gNB 200 according to one embodiment transmits MBS control information used for receiving MBS data to the UE 100 via the MBS control channel of the own cell. The gNB 200 transmits a control area identifier indicating an MBS control area range, which is an area range in which at least a part of the MBS control information is applicable, to the UE 100. This allows the UE 100 to grasp the MBS control area range in which the MBS control information of the current cell can be reused.

[0128] UE100 stores the MBS control information and the control area identifier from gNB200. Then, UE100 receives MBS data based on the stored MBS control information within the MBS control area range indicated by the stored control area identifier. In this way, within the stored area range, MBS data can be received by reusing the MBS control information even across cells, so that the load and power consumption of UE100 can be reduced, and it becomes easier to quickly receive MBS data from the switching destination cell.

[0129] FIG. 14 is a diagram showing the operation of the mobile communication system according to one embodiment.

[0130] As shown in FIG. 14, in step S501, the gNB 200 managing the cell C1 transmits MBS system information to the UE 100 via a broadcast control channel (BCCH) of the cell C1. The MBS system information is transmitted by broadcast using a predetermined RNTI. The UE 100 receives the MBS system information. Note that the system information may be referred to as a SIB (System Information Block).

[0131] The MBS system information includes scheduling information required for receiving the MBS control channel. For example, the MBS system information includes at least one of information indicating a period during which the content of the MBS control channel (MBS control information) may be changed, information indicating a time interval for transmitting the MBS control channel in terms of the number of radio frames, information indicating an offset of a radio frame in which the MBS control channel is scheduled, and information indicating a subframe in which the MBS control channel is scheduled.

[0132] In one embodiment, the MBS system information further includes an MBS control area configuration. The MBS control area configuration includes an information element (hereinafter referred to as an "applicability flag") indicating whether the control area function is applicable to the cell C1. If the control area function is applicable to the cell C1, the MBS system information includes a control area identifier. However, if the MBS system information exists, it is implicitly considered that the control area function is applicable, and the applicability flag may not exist.

[0133] The MBS control area setting may include expiration information indicating a period during which the MBS control area setting is valid (e.g., valid until a certain radio frame, valid until a certain time, valid within a certain time). After the expiration, neighboring cells constituting the MBS control area range may change their own MBS control information. Such a change may be performed by an operator's device and / or a core network. Also, such a change may be performed by signaling between gNBs 200.

[0134] The control area function may be limited to be enabled only when a single frequency network (SFN) is configured with multiple cells including the cell C1. The SFN is a network in which multiple cells operating at the same frequency transmit the same signal simultaneously. The UE 100 receives a signal (composite signal) from the multiple cells without identifying which cell transmitted the signal. The control area function may be enabled for the MBS control channel for configuring the SFN.

[0135] Furthermore, the control area identifier may be shared with a system information area identifier indicating a system information area range. The system information area range refers to an area range in which MBS system information can be reused. When the control area identifier is shared with the system information area identifier, the MBS system information may include information indicating that the MBS control information conforms to the area range setting of the MBS system information. In other words, this information is information indicating that the system information area identifier is treated as a control area identifier.

[0136] There may be multiple MBS control channels in the cell C1. For example, an MBS control channel is provided for each MBS service or for each MBS service category. In this case, the MBS system information may include an MBS control area setting for each MBS control channel. The MBS system information may include an MBS service identifier and / or an MBS control channel identifier and an MBS control area setting associated with the identifier. Instead of or in addition to the MBS control area setting, a network slice identifier associated with the MBS control channel may be included in the MBS system information.

[0137] In step S501, the UE 100 grasps the scheduling of the MBS control channel based on the MBS system information received from the gNB 200. In addition, the UE 100 stores the MBS control area setting included in this MBS system information.

[0138] In step S502, the gNB 200 transmits MBS control information via the MBS control channel in accordance with the scheduling according to the MBS system information transmitted in step S501. The MBS control information is transmitted by broadcast (or multicast) using a predetermined RNTI. The MBS control information may be transmitted by unicast using a C-RNTI (i.e., UE-specific configuration).

[0139] The MBS control information includes a list of scheduling information of MBS traffic channels. An MBS traffic channel is provided for each MBS service. The scheduling information of the MBS traffic channel includes, for example, an MBS service identifier (e.g., TMGI) and a group RNTI corresponding to the MBS traffic channel, and scheduling information (DRX (Discontinuous Reception) information) of the MBS traffic channel. The group RNTI is mapped one-to-one with the MBS service identifier.

[0140] In step S503, the UE 100 stores the MBS control information received from the gNB 200 in step S502 in association with the MBS control area setting (at least the control area identifier) ​​included in the MBS control information received from the gNB 200 in step S501. The UE 100 also determines the scheduling of the MBS traffic channel based on the MBS control information received from the gNB 200 in step S502. For example, the UE 100 determines the scheduling of the MBS traffic channel corresponding to an MBS service in which the UE 100 is interested, and attempts to receive this MBS traffic channel.

[0141] In step S504, the gNB 200 transmits MBS data via an MBS traffic channel according to the scheduling according to the MBS control information transmitted in step S502. The MBS data is transmitted by multicast (or broadcast) using the group RNTI. The UE 100 receives the MBS data of the MBS traffic channel corresponding to the MBS service of interest to the UE 100.

[0142] Next, a case where the UE 100 moves from the cell C1 to the cell C2, which is another cell (adjacent cell), after the above-mentioned operation will be described. Fig. 15 is a diagram showing an operation when the UE 100 according to one embodiment moves from the cell C1 to the cell C2. Fig. 15 shows an example in which the cell C1 is managed by the gNB 200A and the cell C2 is managed by the gNB 200B.

[0143] As shown in Fig. 15, the UE 100 performs handover or cell reselection when moving from a cell C1 to a cell C2. The handover refers to a cell switching operation of the UE 100 in an RRC connected state. The cell reselection refers to a cell switching operation of the UE 100 in an RRC idle state or an RRC inactive state.

[0144] In the cell C1, the UE 100 stores the MBS control information of the cell C1 in association with a control area identifier (see step S503 in FIG. 14). When switching the cell from the cell C1 to the cell C2, the UE 100 receives the MBS system information transmitted on the broadcast control channel of the cell C2 and acquires the MBS control area setting in the MBS system information.

[0145] Here, if the applicability flag in the acquired MBS control area setting is on (i.e., the control area function is applicable to cell C2), UE 100 judges whether the control area identifier in the acquired MBS control area setting (the control area identifier of cell C2) matches the control area identifier (the control area identifier of cell C1) stored in UE 100 itself. If they match, UE 100 judges that the MBS control information stored in UE 100 itself (MBS control information of cell C1) is valid, and does not receive (skips) the MBS control channel of cell C2. Then, UE 100 attempts to receive the MBS traffic channel of cell C2 based on the MBS control information stored in UE 100 itself (MBS control information of cell C1), and receives MBS data from cell C2.

[0146] In this way, when the UE 100 reads the system information of the cell C2 and the MBS control area range is the same, the UE 100 determines that the MBS control information of the cell C1 is valid in the cell C2, and does not receive the MBS control channel of the cell C2, but attempts to receive the MBS traffic channel of the cell C2. This reduces the MBS reception interruption time.

[0147] In the example of Figure 15, an example has been described in which cells C1 and C2 are managed by separate gNBs 200, but as shown in Figure 16, cells C1 and C2 may be managed by the same gNB 200.

[0148] As shown in Fig. 15 and Fig. 16, when the UE 100 moves from the cell C1 to the cell C2, the UE 100 may perform an operation of acquiring a control area identifier of the cell C2 before moving to the cell C2 while receiving an MBS from the cell C1. If the UE 100 has one receiver, such an operation may be difficult. For example, the UE 100 needs to temporarily stop receiving an MBS from the cell C1 to acquire a control area identifier of the cell C2.

[0149] For this reason, the gNB200 (cell C1) may transmit neighboring cell information to the UE100 for identifying whether or not the cell C2 (neighboring cell) belongs to the same MBS control area range as the cell C1. The UE100 can grasp whether or not the cell C2 (neighboring cell) belongs to the same MBS control area range as the cell C1 based on the neighboring cell information from the cell C1. For example, after receiving and storing the neighboring cell information, the UE100 determines whether or not it is necessary to acquire MBS control information from the neighboring cell at the time of cell switching. For example, when the cell C2 (neighboring cell) belongs to the same MBS control area range as the cell C1, the UE100 does not acquire (skips) the control area identifier of the cell C2.

[0150] gNB200 (cell C1) may transmit neighboring cell information in MBS system information via a broadcast control channel of cell C1, or may transmit neighboring cell information via an MBS control channel of cell C1.

[0151] The neighboring cell information includes a control area identifier of the neighboring cell (cell C2). The neighboring cell information may include a cell identifier and / or a frequency identifier and / or an MBS service identifier of the neighboring cell (cell C2) and a control area identifier associated with the identifier. When multiple MBS control channels exist in cell C2, the neighboring cell information may include an MBS control channel identifier and a control area identifier associated with the identifier. Alternatively, the neighboring cell information may include a cell identifier and / or a frequency identifier of the neighboring cell limited to the neighboring cell belonging to the same or different MBS control area range as cell C1. The neighboring cell information may further include a system information area identifier indicating a system information area range of the neighboring cell.

[0152] In one embodiment, after UE100 receives MBS control information used to receive MBS data and a control area identifier indicating an MBS control area range, which is an area range in which at least a portion of the MBS control information is applicable, from cell C1, if it determines that a predetermined condition regarding the MBS control area range is satisfied, UE100 re-receives the MBS control information.

[0153] FIG. 17 is a diagram showing an operation example 1 regarding re-reception of MBS control information according to an embodiment.

[0154] As shown in FIG. 17, in step S601, UE 100 in an RRC idle state or an RRC inactive state performs cell reselection to another cell (cell C2) and acquires a control area identifier indicating the MBS control area range to which the other cell (cell C2) belongs.

[0155] In step S602, the UE 100 determines whether a predetermined condition regarding the MBS control area range is satisfied. In the operation example 1, the predetermined condition is that the control area identifier received from the cell C1 is different from the control area identifier received from another cell (cell C2), that is, the MBS control area range to which the cell C1 belongs is different from the MBS control area range to which the other cell (cell C2) belongs.

[0156] When it is determined that the predetermined condition is satisfied (step S602: YES), in step S603, UE 100 transitions to an RRC connected state in another cell (cell C2). Specifically, when UE 100 wants to continue receiving the currently received MBS service, UE 100 establishes an RRC connection with the other cell (cell C2). For example, when UE 100 is in an RRC idle state, UE 100 transmits an RRC Setup Request message to the other cell (cell C2). When UE 100 is in an RRC inactive state, UE 100 transmits an RRC Resume Request message to the other cell (cell C2).

[0157] In step S603, the UE 100 may notify the other cell (cell C2) of at least one of a desire to receive MBS control information (MBS setting) for the RRC idle state or the RRC inactive state and an MBS service (MBS session) that the UE 100 is interested in. Also, in step S603, the UE 100 may notify the other cell (cell C2) of a desire to transition to the RRC idle state or the RRC inactive state after receiving the MBS setting.

[0158] In step S604, the UE 100 in the RRC connected state receives (re-receives) the MBS control information from the other cell (cell C2).

[0159] FIG. 18 is a diagram showing an operation example 2 regarding re-reception of MBS control information according to an embodiment.

[0160] As shown in Fig. 18, in step S701, UE 100 receives MBS control information (MBS setting information) and information indicating the validity period of the MBS control information (expiration date information) from cell C1. By determining such a validity period, it becomes easy to change the MBS setting from the viewpoint of the network. This is because changing the MBS setting interrupts MBS reception by UE 100. Therefore, by determining the validity period, it is possible to provide the possibility of changing the MBS setting at a certain fixed period.

[0161] In step S702, the UE 100 starts a validity period that times a specified validity period.

[0162] In step S703, the UE 100 determines whether or not a predetermined condition related to the MBS control area range is satisfied. In the second operation example, the predetermined condition is that the valid period has expired in the control area range to which the cell C1 belongs.

[0163] If it is determined that the predetermined condition is satisfied (step S703: YES), in step S704, the UE 100 receives (re-receives) the MBS control information from a cell within the control area range to which the cell C1 belongs. For example, in the case of UE dedicated configuration (Dedicated config.), the UE 100 establishes an RRC connection in the same manner as in operation example 1. In the case of broadcast configuration (Broadcast config.), the UE 100 re-acquires the broadcasted MBS control channel.

[0164] (Other embodiments) In the above embodiment, an example in which the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB). The base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU (Distributed Unit) of the IAB node.

[0165] In the above-mentioned embodiment, communication between base stations is mainly assumed, but communication within a base station may also be assumed. For example, a base station may be separated into a CU and a DU, and communication may be performed between the CU and the DU. In this case, the above-mentioned Xn interface may be read as an F1 interface, which is an interface between a CU and a DU, and the above-mentioned various messages and information may be transmitted and received via the F1 interface. Also, each of the above-mentioned gNB200A and gNB200B may be read as a CU and / or a DU.

[0166] Furthermore, the CU may be separated into a CU-CP and a CU-UP, and communication may be performed between the CU-CP and the CU-UP. In this case, the above-mentioned Xn interface may be read as an E1 interface, which is an interface between the CU-CP and the CU-UP, and the above-mentioned various messages and information may be transmitted and received via the E1 interface. Also, the above-mentioned gNB200A and gNB200B may be read as a CU-CP and / or a CU-UP, respectively.

[0167] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. The program may be recorded in a computer-readable medium. Using the computer-readable medium, it is possible to install the program in the computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0168] In addition, circuits that execute 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 (chip set, SoC).

[0169] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes, etc. are possible without departing from the spirit of the invention.

[0170] This application claims priority to U.S. Provisional Application No. 63 / 094437 (filed October 21, 2020), the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0171] 10: NG-RAN (5G RAN) 20: 5GC (5G CN) 100:UE 110: Receiving unit 120: Transmitter 130: Control section 200: gNB 210: Transmission unit 220: Receiving unit 230: Control section 240: Backhaul communication unit

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 method includes receiving, by the base station, a handover request message from the other base station for handing over the user equipment from the other base station to the base station; The handover request message includes information indicating the highest PDCP sequence number of an MBS packet that the other base station has delivered to the user equipment. Communications control method.

2. A base station, A receiving unit that receives a handover request message from another base station for handing over a user equipment from the other base station to the base station, The handover request message includes information indicating the highest PDCP sequence number of a Multicast and Broadcast Service (MBS) packet that the other base station has delivered to the user equipment. Base station.

3. A base station, A transmitter configured to transmit a handover request message for handing over a user equipment from the base station to another base station to the other base station, The handover request message includes information indicating the highest PDCP sequence number of a Multicast and Broadcast Service (MBS) packet that the base station has delivered to the user equipment. Base station.

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 sends a handover request message to another base station to hand over the user equipment to the other base station; The handover request message includes information indicating the highest PDCP sequence number of an MBS packet that the base station has delivered to the user equipment. Mobile communication system.

Images