Communication control method and first base station

Abstract

This communication control method is used in a mobile communication system which provides a multicast / broadcast service (MBS) from a first base station to a first user device, the method comprising: collecting, by the first base station from at least one second base station within a prescribed range from the first base station, MBS interest information which the second base station has received from a second user device; and controlling, by the first base station, MBS transmission from the first base station on the basis of the collected MBS interest information.

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 first base station provides a multicast broadcast service (MBS) to a first user device, the method comprising: the first base station collecting MBS interest information received by the second base station from at least one second base station within a predetermined range of the first base station, the MBS interest information being received by the second base station from a second user device; and the first base station controlling MBS transmission of the first base station based on the collected MBS interest information.

[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 device, and includes the steps of: the user device, which is in a Radio Resource Control (RRC) idle state or an RRC inactive state, notifying the base station of MBS interest information during a random access procedure to the base station; and the user device, after notifying the MBS interest information, terminating the random access procedure without transitioning to an RRC connected state. [Brief description of the drawings]

[0006] [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. 11 is a diagram showing an example of an operation pattern 1 of an MBS interest information collecting operation according to an embodiment. [Figure 10] FIG. 11 is a diagram showing an example of an operation pattern 2 of the MBS interest information collecting operation according to an embodiment. [Figure 11]A diagram showing an example of the operation of MBS counting according to one embodiment. [Figure 12] FIG. 1 is a diagram showing two-stage configuration in LTE SC-PTM. [Figure 13] FIG. 1 illustrates a possible configuration diagram for NR MBS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] 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.

[0008] Therefore, an object of the present invention is to provide a communication control method for realizing an improved multicast / broadcast service.

[0009] 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.

[0010] (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.

[0011] 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.

[0012] 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).

[0013] 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.

[0014] 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.

[0015] 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.

[0016] FIG. 2 is a diagram showing a configuration of a UE 100 (user equipment) according to an embodiment.

[0017] As shown in FIG. 2, the UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit .

[0018] 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.

[0019] 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.

[0020] 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.

[0021] FIG. 3 is a diagram showing the configuration of a gNB 200 (base station) according to one embodiment.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The PDCP layer performs header compression / decompression and encryption / decryption.

[0033] The SDAP layer maps IP flows, which are units for QoS (Quality of Service) control by the core network, to radio bearers, which are units for QoS control by the AS (Access Stratum). Note that if the RAN is connected to the EPC, the SDAP is not necessary.

[0034] 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).

[0035] 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.

[0036] 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.

[0037] 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.

[0038] In addition, the UE 100 has an application layer and the like in addition to the protocol of the radio interface.

[0039] (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.

[0040] 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.

[0041] As shown in FIG. 6, the logical channels used for MBSFN transmission are MTCH (Multicast Traffic Channel) and MCCH (Multicast Control Channel), and the transport channel used for MBSFN transmission is MCH (Multicast Traffic Channel). t MBSFN transmission is primarily designed for multi-cell transmission, where each cell in an MBSFN area transmits the same signal (the same data) synchronously in the same MBSFN subframe.

[0042] 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.

[0043] 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.

[0044] In addition, MBS data refers to data transmitted by MBS, MBS control channel refers to MCCH or SC-MCCH, and MBS traffic channel refers to MTCH or SC-MTCH. However, MBS data may be transmitted by unicast. MBS data may also be called MBS packet or MBS traffic.

[0045] 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.

[0046] FIG. 7 is a diagram showing a method for delivering MBS data according to an embodiment.

[0047] 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.

[0048] From the 5GC20 point of view, two delivery methods are possible: Shared MBS Traffic delivery and Individual MBS Traffic delivery.

[0049] 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."

[0050] 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.

[0051] 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.

[0052] (MBS Interesting Information) Next, the MBS interest information according to an embodiment will be described. Fig. 8 is a diagram showing an operating environment according to an embodiment.

[0053] 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.

[0054] 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.

[0055] The gNB200A and the gNB200B 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.

[0056] In such an environment, cell C1 and cell C2 may belong to the same MBS area. An MBS area refers to an area consisting of multiple cells to 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). The gNB200A may operate as a master that manages or controls MBS transmission in the MBS area.

[0057] In one embodiment, gNB200A performs at least one of the following MBS transmission controls 1 to 3 based on whether each UE100 in its own cell C1 and its neighboring cell C2 is interested in receiving MBS.

[0058] MBS transmission control 1: The gNB200A determines whether to establish an MBS connection with a core network device (UPF300A). In order for the gNB200A to transmit MBS data in PTM, it is necessary to have an MBS connection, i.e., a connection for shared MBS data delivery (Shared MBS Traffic delivery). For example, when there are many UEs 100 interested in receiving MBS data of a certain MBS session, the gNB200A establishes an MBS connection to transmit MBS data of the MBS session in PTM. On the other hand, when there are few or no UEs 100 interested in receiving MBS data of a certain MBS session, the gNB200A does not establish an MBS connection.

[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] MBS transmission control 2: The gNB200A having an MBS connection with the core network (UPF300A) determines whether to transmit MBS data received from the core network device (UPF300A) via the MBS connection in PTP or PTM. For example, when there are many UEs 100 interested in receiving MBS data of a certain MBS session, the gNB200A transmits the MBS data of the MBS session in PTM. On the other hand, when there are few UEs 100 interested in receiving MBS data of a certain MBS session, the gNB200A transmits the MBS data of the MBS session in PTP.

[0061] MBS transmission control 3: The gNB200A determines whether to configure an SFN with its own cell and other cells. For example, when there are many UEs 100 interested in receiving the MBS of a certain MBS session, the gNB200A transmits the MBS data of the MBS session by the MBSFN. On the other hand, when there are few UEs 100 interested in receiving the MBS of a certain MBS session, the gNB200A does not transmit the MBS data of the MBS session by the MBSFN.

[0062] In order to perform at least one of the above-mentioned MBS transmission controls 1 to 3, the gNB200A collects MBS interest information received by the gNB200B from the UE100B from at least one gNB200B within a predetermined range from the gNB200A. The gNB200B within the predetermined range refers to a gNB200B that is adjacent to the gNB200B or a gNB200B that belongs to the same MBS area as the gNB200A. The gNB200A performs at least one of the MBS transmission controls 1 to 3 based on the collected MBS interest information.

[0063] In operation pattern 1 for collecting MBS interest information, the gNB 200B receives MBS interest information from the UE 100B. The MBS interest information may be an MBS interest information message spontaneously transmitted by the UE 100B or an information element included in this message, or may be an MBS counting response message transmitted by the UE 100B in response to a request from the gNB 200B or an information element included in this message.

[0064] Such a message (MBS interest information) may be, for example, an RRC message, and may include an identifier for an MBS session in which the UE 100B is interested in receiving MBS (or is receiving MBS). The identifier for the MBS session may be a message including at least one of an identifier indicating the MBS session (for example, TMGI, session ID) and / or a group RNTI (Radio Network Temporary Identifier), an identifier of a QoS flow corresponding to the MBS session, and an identifier of a frequency on which the MBS session is provided.

[0065] The gNB200A transmits a request to transmit the MBS interest information to the gNB200B. For example, the gNB200A transmits a request to transmit the MBS interest information to the gNB200B over the Xn interface.

[0066] In response to receiving a transmission request from the gNB200A, the gNB200B transmits the MBS interest information received from the UE100B to the gNB200A. For example, the gNB200B transmits the MBS interest information to the gNB200A over the Xn interface. This allows the gNB200B to grasp the MBS interest of the UE100B in the neighboring cell.

[0067] A message including MBS interest information sent from gNB200B to gNB200A may include at least one of an identifier of UE100B (e.g., an XnAP ID, which is a UE identifier used on the Xn interface), an identifier of gNB200B, and an identifier of cell C2.

[0068] The gNB 200B may receive MBS interest information from a plurality of UEs 100B and transmit a result of counting the received MBS interest information to the gNB 200A. The counting result may be a list of identifiers included in the message (MBS interest information) from the UE 100B and / or a count number (total value) for each of the identifiers.

[0069] However, the gNB 200B may spontaneously transmit the MBS interest information received from the UE 100B to the gNB 200A even if the gNB 200B does not receive a transmission request from the gNB 200A. For example, when the gNB 200B receives the MBS interest information from the UE 100B, the gNB 200B may transmit the received MBS interest information to the gNB 200A.

[0070] 9 is a diagram showing an example of operation pattern 1 of the MBS interest information collecting operation. In FIG. 9, non-essential steps are indicated by dashed lines.

[0071] 9, in step S101, the gNB 200A transmits a transmission request for MBS interest information to the gNB 200B. Such a transmission request may be, for example, an Xn message, and may include at least one of an identifier for an MBS session from which MBS interest is to be collected, a transmission period (report period) of MBS interest information from the gNB 200B, and an identifier of a cell from which MBS interest is to be collected.

[0072] In step S102, the gNB 200B transmits a transmission request for the MBS interest information to the UE 100B. Such a transmission request may be, for example, an RRC message, and may include an identifier (a specific example is similar to that described above) related to the MBS session from which the MBS interest is to be collected. This transmission request may be transmitted to the UE 100B by unicast, or may be transmitted to the UE 100B by multicast or broadcast.

[0073] In step S103, UE100B transmits MBS interest information regarding UE100B's MBS interest to gNB200B.

[0074] In step S104, gNB200B transmits the MBS interest information received from UE100B to gNB200A.

[0075] On the other hand, in step S105, gNB200A transmits a request to transmit MBS interest information to UE100A.

[0076] In step S106, the UE 100A transmits MBS interest information related to the MBS interest of the UE 100A to the gNB 200A. The gNB 200A may receive the MBS interest information from each of the multiple UEs 100A, and transmit the received MBS interest information or a result of the aggregation of the MBS interest information to the gNB 200A.

[0077] In step S107, the gNB 200A performs at least one of the above-mentioned MBS transmission controls 1 to 3 based on the MBS interest information received from the gNB 200B (and the MBS interest information received from the UE 100A). The gNB 200A may aggregate the MBS interest information received from the gNB 200B (and the MBS interest information received from the UE 100A) and notify the aggregation result to the gNB 200B or another gNB.

[0078] Next, an operation pattern 2 for collecting MBS interest information will be described.

[0079] When the UE 100B receiving an MBS in the cell C2 (or the UE 100B interested in receiving an MBS) is in an RRC idle state or an RRC inactive state, the UE 100B may move from the cell C2 to the cell C1 without the gNB 200B knowing. Here, a problem may occur in which the MBS session of interest to the UE 100B is not provided in the cell C1.

[0080] In operation pattern 2, when the gNB200B receives MBS interest information from the UE100B in the RRC connected state and then transitions the UE100 to the RRC idle state or the RRC inactive state, the gNB200B transmits the MBS interest information received by the gNB200B from the UE100B to the gNB200A. This enables the gNB200A to prepare MBS transmission in advance for the UE100B that may move to its own cell C1.

[0081] 10 is a diagram showing an example of operation pattern 2 of the MBS interest information collecting operation. Operation pattern 2 can be used in combination with operation pattern 1. Here, differences between operation pattern 2 and operation pattern 1 will be mainly described.

[0082] As shown in FIG. 10, in step S201, the UE 100B is in an RRC connected state.

[0083] In step S202, UE100B transmits MBS interest information to gNB200B.

[0084] In step S203, gNB200B transmits an RRC release message to UE100B, causing UE100B to transition to an RRC idle state or an RRC inactive state.

[0085] In step S204, the UE 100B transitions to an RRC idle state or an RRC inactive state.

[0086] In step S205, gNB200 transmits MBS interest information to gNB200A.

[0087] In step S206, the gNB 200A performs at least one of the above-mentioned MBS transmission controls 1 to 3 based on the MBS interest information received from the gNB 200B (and the MBS interest information received from the UE 100A).

[0088] (MBS Counting) Next, MBS Counting according to an embodiment will be described. MBS Counting according to an embodiment may be used in combination with the above-mentioned operation pattern 1 or 2, or may be performed separately from the above-mentioned operation pattern 1 or 2.

[0089] Generally, the UE 100 needs to be in an RRC connected state in order for the UE 100 to transmit MBS interest information to the gNB 200. However, it is inefficient for the UE 100 in the RRC idle state or the RRC inactive state to transition to the RRC connected state only to transmit the MBS interest information.

[0090] For this reason, UE 100 in the RRC idle state or the RRC inactive state notifies the gNB 200 of MBS interest information during a random access procedure to the gNB 200. After notifying the MBS interest information, UE 100 ends the random access procedure without transitioning to the RRC connected state. This allows UE 100 in the RRC idle state or the RRC inactive state to notify the gNB 200 of the MBS interest information while maintaining the RRC idle state or the RRC inactive state.

[0091] In one embodiment, the UE 100 in the RRC idle state or the RRC inactive state may receive a request message requesting transmission of MBS interest information from the gNB 200. In response to receiving the request message, the UE 100 may notify the gNB 200 of the MBS interest information during a random access procedure to the gNB 200.

[0092] The random access procedure includes a preamble transmission in which a random access preamble is transmitted from the UE 100 to the gNB 200. The UE 100 may notify the gNB 200 of MBS interest information by transmitting the preamble.

[0093] The random access procedure includes a predetermined message transmission in which the UE 100 transmits a predetermined message to the gNB 200 in response to the UE 100 receiving a random access response from the gNB 200. The UE 100 may notify the gNB 200 of the MBS interest information by transmitting the predetermined message. In this case, the UE 100 may notify the gNB 200 of the fact that the MBS interest information will be notified by transmitting the predetermined message by transmitting a preamble.

[0094] 11 is a diagram showing an example of an operation of MBS counting according to an embodiment, in which non-essential steps are indicated by dashed lines.

[0095] 11, in step S301, the UE 100 is in an RRC idle state or an RRC inactive state. It is assumed that no user data to be transmitted from the UE 100 to the gNB 200 is generated.

[0096] In step S302, the gNB 200 transmits a request message requesting transmission of MBS interest information. The gNB 200 may transmit the request message by broadcast via an MBS control channel or a broadcast control channel. The UE 100 receives the request message. The request message may include at least one of an identifier (a specific example is similar to that described above) related to an MBS session from which the MBS interest is to be collected and a transmission setting of a random access preamble. The transmission setting of the random access preamble includes information related to a specific PRACH (Physical Random Access Channel) resource described later.

[0097] In step S303, UE100 initiates a random access procedure and transmits a random access preamble to gNB200.

[0098] For such preamble transmission, the following preamble transmission method 1 or 2 may be used.

[0099] Preamble transmission method 1: The UE 100 may transmit a random access preamble by a specific PRACH resource prepared to notify the gNB 200 of the intention of transmitting MBS interest information of the UE 100 in the RRC idle state or the RRC inactive state. The PRACH resource refers to at least one of a time-frequency resource and a preamble sequence. By receiving the random access preamble by the specific PRACH resource, the gNB 200 takes into consideration the intention of the UE 100 and allocates an appropriate amount of uplink radio resources in step S304 described later.

[0100] Preamble transmission method 2: The UE 100 may transmit a random access preamble by a specific PRACH resource associated with an MBS session (e.g., TMGI) that the UE 100 is receiving or is interested in receiving. This allows the gNB 200 to know the presence of the UE 100 that is receiving or is interested in receiving a specific MBS session. However, when a specific PRACH resource is used simultaneously by multiple UEs 100, it is difficult for the gNB 200 to know the number of UEs 100 that are receiving or are interested in receiving a specific MBS session. For this reason, in step S305 described later, an indication (e.g., a 1-bit flag) indicating that the preamble has been transmitted is transmitted from the UE 100. This allows the gNB 200 to know the number of UEs 100 that are receiving or are interested in receiving a specific MBS session.

[0101] In step S304, in response to receiving the random access preamble, the gNB 200 transmits a random access response to the UE 100. The random access response includes an uplink grant for allocating an uplink radio resource (PUSCH resource) to the UE 100.

[0102] In step S305, in response to receiving the random access response, the UE 100 transmits a predetermined message to the gNB 200 by using the uplink radio resource allocated from the gNB 200. The predetermined message may be referred to as a message 3 (Msg3).

[0103] Such a predetermined message may be transmitted using any of the following message transmission methods 1 to 3.

[0104] Message sending method 1: The UE 100 transmits the MBS interest information to the gNB 200 together with an RRC Setup message or an RRC Resume Request message. The RRC Setup message is an RRC connection request message transmitted by the UE 100 in the RRC idle state. The RRC Resume Request message is an RRC connection recovery request message transmitted by the UE 100 in the RRC inactive state. The UE 100 may include the MBS interest information in the RRC Setup message or the RRC Resume Request message, or may multiplex the MBS interest information in the same transport block as the RRC Setup message or the RRC Resume Request message and transmit the same.

[0105] Message sending method 2: When using the above-described preamble transmission method 2, the UE 100 transmits the above-described indication by including it in an RRC Setup message or an RRC Resume Request message.

[0106] Message sending method 3: The UE 100 transmits only a message of MBS interest information to the gNB 200. In this case, the UE 100 does not transmit an RRC Setup message or an RRC Resume Request message.

[0107] In the message transmission methods 1 to 3, the UE 100 may include an identifier of the UE 100 (for example, 5G-S-TMSI, IMSI, etc.) in the MBS interest information (predetermined message). The UE 100 may store an identifier indicating that the message transmission is for transmitting the MBS interest information in a Cause field included in the RRC Setup message or the RRC Resume Request message. This allows the gNB 200 to decide to release the UE 100 in step S306 described later.

[0108] In step S306, the gNB 200 transmits a message (e.g., an RRC release message) to the UE 100 to keep the UE 100 in the RRC idle state or the RRC inactive state. As a result, the UE 100 ends the random access procedure without transitioning to the RRC connected state.

[0109] In this operation example, UE 100 is permitted to transmit MBS interest information only once for one request message (step S302). This is because if one UE 100 transmits MBS interest information multiple times, an error occurs in the counting result.

[0110] (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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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 (System on a chip)).

[0115] 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.

[0116] This application claims priority to U.S. Provisional Application No. 63 / 093918 (filed October 20, 2020), the entire contents of which are incorporated herein by reference.

[0117] (Additional Note) ·introduction A revised work item on NR Multicast and Broadcast Services (MBS) was approved. The objectives of the work item are to:

[0118] -Specifies basic RAN functions for broadcast / multicast for UE in RRC connected state. -Specifies a group scheduling mechanism that enables UEs to receive broadcast / multicast services. -This objective includes specifying the extensions necessary to enable simultaneous operation with unicast reception. -Provides support for dynamic change of broadcast / multicast service delivery between multicast (PTM) and unicast (PTP) with default UE service continuity. - Provide for support of basic mobility with service continuity. - Specify the necessary changes to the RAN architecture and interfaces, taking into account the consequences of SA2 SI in broadcast / multicast, assuming the necessary coordination functions (such as those hosted by the MCE) are in the gNB-CU. - Specifying the changes required to improve the reliability of broadcast / multicast services, e.g. by UL feedback. The level of reliability should be based on the requirements of the application / service provided. Study support for dynamic control of broadcast / multicast transmission areas within one gNB-DU and specify what, if anything, is needed to enable it.

[0119] -Specifies basic RAN functions for broadcast / multicast for UEs in RRC idle / RRC inactive state. -Specifies the changes required to enable reception of Point to Multipoint transmissions by UEs in RRC Idle / RRC Inactive state with the aim of maintaining maximum commonality between the RRC Connected state and the RRC Idle / RRC Inactive state for PTM reception configuration.

[0120] In RAN2#111-e, many companies proposed reusing the LTE SC-PTM mechanism for idle / inactive UEs, but as the chair summarized: - Chair: Many companies believe there is a big difference between idle and connected solutions. What that ultimately means needs further consideration. - Chair's view: Many proposals to reuse (to a large extent or 100%) LTE SC-PTM for idle / inactive NR. Some companies are proposing to connect and control etc. for idle / inactive distributions too.

[0121] This appendix discusses control plane considerations for NR MBS.

[0122] Discussion In LTE SC-PTM, configuration is provided by two messages: SIB20 and SC-MCCH. SIB20 provides SC-MCCH scheduling information, and SC-MCCH provides SC-MTCH scheduling information including G-RNTI and TMGI, and neighbor cell information.

[0123] The advantage of the LTE two-stage configuration as shown in Figure 12 was that the SC-MCCH scheduling was independent from the SIB20 scheduling in terms of repetition period, duration, modification period etc. This facilitated frequent scheduling / updating of the SC-MCCH, especially for delay-sensitive services and / or UEs that join the session late. According to WID, this is also the case for NR MBS, since one of the applications is group communication etc.

[0124] Observation 1: In LTE, the two-stage configuration with SIB20 and SC-MCCH lends itself to different scheduling of these control channels, which also lends itself to NR MBS.

[0125] Proposal 1: RAN2 should agree to use a two-stage configuration with different NR MBS messages, such as SIB20 in SC-PTM and SC-MCCH.

[0126] In addition to Proposal 1, NR MBS is envisioned to support the various types of use cases outlined in the WID. It is noted that NR MBS should be appropriately designed for a variety of requirements ranging from delay-sensitive applications such as mission-critical and V2X to delay-tolerant applications such as IoT, in addition to other aspects of requirements ranging from lossless applications such as software distribution to UDP-type streaming such as IPTV.

[0127] Therefore, the design of the control channel should consider its flexibility and resource efficiency, otherwise, for example, when delay-tolerant and delay-sensitive services are configured together in one control channel, the control channel needs to be scheduled frequently to satisfy the delay requirements from the delay-sensitive services, which may cause more signaling overhead.

[0128] Objective A of the SA2 SI is about enabling general MBS services over 5GS and identified use cases that may benefit from this capability include (but are not limited to) public safety, mission critical, V2X applications, transparent IPv4 / IPv6 multicast distribution, IPTV, over-the-air software distribution, group communications, and IoT applications.

[0129] Observation 2: The NR MBS control channel needs to be flexible and resource efficient for different types of use cases.

[0130] One possibility is to consider whether it is necessary to separate the configuration channels for different use cases, as shown in Figure 13. For example, one control channel provides frequent delay-sensitive services, and another control channel provides sparse delay-tolerant services. In LTE SC-PTM, there is a restriction that a cell can have only one SC-MCCH. However, considering that there are more use cases than in LTE, NR MBS should remove such a restriction. If multiple SC-MCCHs are allowed in a cell, each SC-MCCH has different scheduling configurations, such as repetition period, that can be optimized for a specific service. How a UE identifies the SC-MCCH that provides the service it is interested in needs further consideration.

[0131] Proposal 2: RAN2 should discuss whether multiple control channels will be supported in cells in NR MBS, like multiple SC-MCCHs that were not present in LTE.

[0132] Furthermore, a new paradigm in NR is the support of on-demand SI transmission. This concept can be reused for the SC-MCCH of NR MBS, i.e., on-demand SC-MCCH. For example, the SC-MCCH for delay-tolerant services is provided on-demand, so that signaling resource consumption can be optimized. Of course, the network has other options to provide the SC-MCCH periodically, i.e., not on-demand, for delay-sensitive services, etc.

[0133] Proposal 3: RAN2 should discuss the option of a control channel being provided on an on-demand basis, such as the on-demand SC-MCCH that was not available in LTE.

[0134] Another possibility could be further considered to merge these messages, i.e. one-stage configuration, as shown in Fig. 13. For example, the SIB provides SC-MTCH scheduling information directly, i.e. without SC-MCCH. This would provide optimization for delay-tolerant services and / or power-sensitive UEs. For example, the UE may request the SIB (on-demand) and the gNB may start providing the SIB and corresponding services after requests from multiple UEs. These UEs do not need to monitor the repeatedly broadcasted SC-MCCH.

[0135] Proposal 4: RAN2 should discuss options such as the SIB providing traffic channel configuration directly if multicast reception without SC-MCCH (i.e., one-stage configuration) is supported.

[0136] (dedicated signaling based configuration) Some companies have proposed that MBS configuration be provided only by dedicated signaling. For UEs in RRC connected state with multicast services such as group communication, dedicated signaling is easy, but it means that UEs in idle / inactive state must always transition to RRC connected state before receiving MBS services, even if these UEs are only interested in broadcast services. This may result in unnecessary power consumption of UEs and may also be less future-proof, such as free broadcast services being supported in future releases. Therefore, we believe that MBS configuration via broadcast signaling should be the baseline, as in LTE SC-PTM, proposals 1 to 4.

[0137] However, it is considered that flexibility in network implementation and deployment policies is gained if the control channel can be provided via RRC reconfiguration as shown in Figure 13. For example, the network may decide not to broadcast the MBS control channel and only provide the configuration via dedicated signaling when necessary, e.g. for operators that do not offer broadcast services. As another example, it is beneficial for service continuity during handover if the target cell provides the MBS configuration via a handover command.

[0138] Therefore, RAN2 needs to consider whether the RRC reconfiguration provides an MBS control channel.

[0139] Proposal 5: RAN2 needs to consider the option of providing SC-MCCH when RRC reconfiguration was not available in LTE.

[0140] (Indication of Interest / Counting) In LTE eMBMS, two methods are specified for the network to collect the UE's receiving / interested services in order to make appropriate decisions on MBMS data delivery including starting / stopping MBMS sessions: MBMS Interest Indication (MII) and MBMS Counting. The MII triggered by the UE contains information related to the interested MBMS frequencies, the interested MBMS services, MBMS priority, and MBMS ROM (receive only mode). The counting response triggered by the network via a counting request for a particular MBMS service contains information related to the interested MBSFN areas and MBMS services.

[0141] These methods were introduced for different purposes: MII is primarily used by the network to ensure that the UE can continue to receive the services it is interested in while in the Connected state, while Counting is used to allow the network to determine whether a sufficient number of UEs are interested in receiving the service.

[0142] Observation 3: In LTE e MBMS, two kinds of UE assistance information are introduced for different purposes: MBMS interest indication is introduced for scheduling in NB, and MBMS counting is introduced for session control in MCE.

[0143] For NR MBS, multicast services such as group communication use cases are expected and the network has full knowledge of MBS services that UEs in connected state are receiving / interested in, so no assistance information from the UE is required, e.g. network PTP / PTM distribution decisions. However, in our understanding, this is not the case for broadcast services or UEs in idle / inactive state. Especially for broadcast services, the same problem solved by counting with MII in LTE eMBMS, i.e. observation 3, still exists in NR MBS. Therefore, RAN2 needs to consider whether assistance information such as MII and counting can be useful for NR MBS.

[0144] Note that MBMS ROM information in MII and information on MBSFN area in counting response are not required in Rel-17 since ROM and SFN are not supported as described in WID.

[0145] Proposal 6: RAN2 needs to agree to introduce UE assistance information for NR MBS, e.g. MBMS interest indication and / or MBMS counting.

[0146] If you agree with Proposal 6, it is worth considering an extension on top of LTE eMBMS. In LTE eMBMS, even if a large portion of UEs are in RRC idle state and receiving broadcast services, neither MII nor counting can collect information from idle UEs. In our understanding, this is one of the problems of LTE eMBMS from the perspective of session control and resource efficiency.

[0147] In NR MBS, the same problem may exist for idle / inactive UEs. For example, the network cannot know if idle / inactive UEs are not receiving / interested in the broadcast service. Therefore, PTM transmission may continue even if no UEs are receiving the service. If the gNB is aware of the interest of idle / inactive UEs, such unnecessary PTM can be avoided. Conversely, if PTM stops while there are still idle / inactive UEs receiving the service, multiple UEs may request a connection at the same time.

[0148] It is therefore worth considering whether to introduce mechanisms to collect UE assistance information, specifically for MBMS counting, from idle / inactive UEs. Obviously, it would be desirable for idle / inactive UEs to be able to report information without transitioning to RRC Connected. For example, this could be achieved if PRACH resource partitioning associated to MBS services were introduced for such reporting.

[0149] Proposal 7: RAN2 should consider whether UE assistance information such as MBMS counting is also collected from UEs in idle / inactive state.

Claims

1. A communication control method used in a mobile communication system that provides a multicast broadcast service (MBS) from a first base station to a first user device, comprising: The first base station collects, from at least one second base station belonging to the same MBS area as the first base station, MBS interest information received by the second base station from a second user device; The first base station controls MBS transmission of the first base station based on the collected MBS interest information; The MBS area is an area consisting of multiple cells in which the same MBS session is provided. Communications control method.

2. The collecting step includes: the second base station receiving the MBS interest information from the second user equipment; The first base station transmits a request to transmit the MBS interest information to the second base station; and transmitting, by the second base station, the MBS interest information to the first base station in response to receiving the transmission request from the first base station. The communication control method according to claim 1 .

3. The collecting step includes: The second base station receives the MBS interest information from the second user equipment in a Radio Resource Control (RRC) connected state; The second base station transitions the second user equipment to an RRC idle state or an RRC inactive state; and transmitting, by the second base station, the MBS interest information received by the second base station from the second user device to the first base station. The communication control method according to claim 1 .

4. Controlling the MBS transmission of the first base station includes: and determining whether the first base station establishes an MBS connection with a core network device, or whether the first base station transmits MBS data received from the core network device in PTP or PTM based on the collected MBS interest information. The communication control method according to any one of claims 1 to 3.

5. The collecting step includes receiving, by the first base station, from the second base station, a total number of MBS session identifiers included in the MBS interest information received by the second base station from a plurality of user devices. The communication control method according to claim 1 .

6. The transmission request includes an identifier for an MBS session to be collected. The communication control method according to claim 2.

7. Determining based on the collected MBS interest information, The first base station determines that, when there are many user devices interested in receiving MBS data of the MBS session, the MBS data of the MBS session is transmitted in the PTM; The first base station determines, when a small number of user devices are interested in receiving MBS data of the MBS session, to transmit MBS data of the MBS session by the PTP. The communication control method according to claim 4.

8. A first base station providing a multicast and broadcast service (MBS) to a first user device, comprising: a control unit that collects MBS interest information received from a second user device by at least one second base station that belongs to the same MBS area as the first base station; The control unit controls MBS transmission of the first base station based on the collected MBS interest information; The MBS area is an area consisting of multiple cells in which the same MBS session is provided. First base station.

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