COMMUNICATION CONTROL METHOD, USER EQUIPMENT, NETWORK NODE, PROCESSOR, PROGRAM, AND MOBILE COMMUNICATION SYSTEM

Abstract

To provide a communication control method capable of implementing efficient retransmission processing, and user equipment.SOLUTION: In a mobile communication system which provides multicast / broadcast services (MBS), UE 100 includes a step S105 of receiving MBS data transmitted from a gNB 200 by any transmission scheme of PTP (Point-To-Point) transmission and PTM (Point-To-Multipoint) transmission; a step S107 of triggering transmission of a status report indicating a reception state of the MBS data in a predetermined layer of the UE 100 in response to switching the transmission scheme between the PTP transmission and the PTM transmission; and a step S108 of transmitting the status report to the gNB 200.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present disclosure relates to a communication control method and a user device used 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 executed by a user device in a mobile communication system that provides a multicast broadcast service (MBS), and includes receiving MBS data transmitted from a base station using either a PTP (Point-To-Point) transmission or a PTM (Point-To-Multipoint) transmission transmission method, triggering the transmission of a status report indicating the reception status of the MBS data at a predetermined layer of the user device in response to the transmission method being switched between the PTP transmission and the PTM transmission, and transmitting the status report to the base station.

[0005] A user device according to a second aspect is a user device used in a mobile communication system that provides a multicast broadcast service (MBS), and comprises a receiving unit that receives MBS data transmitted from a base station using either a PTP (Point-To-Point) transmission or a PTM (Point-To-Multipoint) transmission transmission method, a control unit that triggers the transmission of a status report indicating the reception status of the MBS data at a specified layer of the user device in response to the transmission method being switched between the PTP transmission and the PTM transmission, and a transmitting unit that transmits the status report to the base station. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. [Figure 2] FIG. 1 is a diagram illustrating a configuration of a UE (user equipment) according to an embodiment. [Figure 3] A diagram showing the configuration of a gNB (base station) according to one embodiment. [Figure 4] FIG. 10 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. [Figure 5] FIG. 1 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 illustrating a correspondence relationship between downlink logical channels and transport channels according to an embodiment. [Figure 7] FIG. 1 is a diagram illustrating a method for distributing MBS data according to an embodiment. [Figure 8] FIG. 1 illustrates a split MBS bearer according to one embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example 1 of operations related to activation and deactivation of legs according to an embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example 2 of operations related to activation and deactivation of legs according to an embodiment. [Figure 11] FIG. 10 is a diagram illustrating an example of a MAC CE (1 octet) that stores an indication value for each bearer identifier (or logical channel identifier) according to an embodiment. [Figure 12] FIG. 10 is a diagram illustrating an example of the configuration of a PDCP status report according to one embodiment. [Figure 13] FIG. 10 is a diagram illustrating a switching operation from PTM transmission to PTP transmission according to an embodiment. [Figure 14] FIG. 10 is a diagram illustrating a switching operation from PTP transmission to PTM transmission according to an embodiment. [Figure 15] FIG. 10 is a diagram illustrating a modified example of the switching operation from PTP transmission to PTM transmission according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] The introduction of multicast and broadcast services into the 5G system (NR) is being considered. The NR multicast and broadcast services are expected to provide improved services compared to the LTE multicast and broadcast services.

[0008] Therefore, an object of the present disclosure is to realize 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, the configuration of a mobile communication system according to an embodiment will be described. Fig. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. This mobile communication system conforms to the 5th Generation System (5GS) of the 3GPP standard. In the following description, 5GS will be taken as an example, but the mobile communication system may be at least partially applied with an LTE (Long Term Evolution) system or at least partially applied with 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 a "gNB" in a 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 a 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, etc. 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 that performs wireless communication with a UE 100. One cell belongs to one carrier frequency.

[0014] In addition, gNBs can also connect to the Evolved Packet Core (EPC), which is the LTE core network. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via a base station-to-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 NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and 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 types of reception 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 transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts 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 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 processes.

[0021] FIG. 3 is a diagram showing the configuration of a gNB200 (base station) according to one embodiment.

[0022] As shown in FIG. 3, the gNB 200 includes a transmitter 210, a receiver 220, a controller 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 types of reception 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 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 processes.

[0026] The backhaul communication unit 240 is connected to neighboring 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., functionally divided), and both units may be connected 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 Figure 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 UE 100 and the MAC layer of gNB 200 via a transport channel. The MAC layer of 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 allocated to UE 100.

[0031] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and 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 logical channels.

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

[0033] 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, 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] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. 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 UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0037] The NAS layer 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] The UE 100 has an application layer and the like in addition to the radio interface protocol.

[0039] (MBS) Next, an MBS according to one embodiment will be described. The MBS is a service that enables broadcast or multicast data transmission, i.e., point-to-multipoint (PTM) data transmission, from the NG-RAN 10 to the UE 100. The MBS may also be called an MBMS (Multimedia Broadcast and Multicast Service). Note that use cases (service types) of the MBS include public safety communications, mission-critical communications, V2X (Vehicle to Everything) communications, IPv4 or IPv6 multicast distribution, IPTV, group communications, 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 the correspondence relationship between downlink logical channels and transport channels according to one embodiment.

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

[0042] The logical channels used for SC-PTM transmission are the Single Cell Multicast Traffic Channel (SC-MTCH) and the Single Cell Multicast Control Channel (SC-MCCH). The transport channel used for SC-PTM transmission is the Downlink Shared Channel (DL-SCH). SC-PTM transmission is primarily designed for single-cell transmission, transmitting data by broadcast or multicast on a cell-by-cell basis. The physical channels used for SC-PTM transmission are the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Control Channel (PDSCH), which enable dynamic resource allocation.

[0043] In the following, an example in which an MBS is provided using a method similar to 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] Furthermore, MBS data refers to data provided by an MBS, an MBS control channel refers to an MCCH or SC-MCCH, and an MBS traffic channel refers to an MTCH or SC-MTCH. However, MBS data may also be transmitted via unicast. MBS data may also be referred to as an 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 also be called an MBS service identifier or a multicast group identifier.

[0046] FIG. 7 is a diagram showing a method for distributing 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 of the MBS data (replication), and distributes the data.

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

[0049] In 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) will be referred to as an "MBS connection."

[0050] The MBS connection may be referred to as 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 have a one-to-one correspondence with the MBS session.

[0051] gNB200 selects either PTP (Point-to-Point: unicast) or PTM (Point-to-Multipoint: multicast or broadcast) transmission method at its own discretion, and transmits MBS data to UE100 using the selected transmission method.

[0052] On the other hand, in 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) terminates at the UE 100.

[0053] (Split MBS bearer) Next, a split MBS bearer according to one embodiment will be described.

[0054] The gNB200 can set an MBS bearer separated into a PTP communication path and a PTM communication path (hereinafter referred to as a "split MBS bearer" as appropriate) to the UE100. This allows the gNB200 to dynamically switch the transmission of MBS data to the UE100 between PTP (PTP communication path) and PTM (PTM communication path). Alternatively, the gNB200 can improve reliability by dual-transmitting the same MBS data using both PTP (PTP communication path) and PTM (PTM communication path).

[0055] The predetermined layer that terminates splitting is the MAC layer (HARQ), the RLC layer, the PDCP layer, or the SDAP layer. In the following, an example in which the predetermined layer that terminates splitting is the PDCP layer will be mainly described, but the predetermined layer may be the MAC layer (HARQ), the RLC layer, or the SDAP layer.

[0056] 8 is a diagram showing a split MBS bearer according to one embodiment. Hereinafter, a PTP communication path is referred to as a PTP leg, and a PTM communication path is referred to as a PTM leg. Furthermore, a functional unit corresponding to each layer is referred to as an entity.

[0057] 8, each of the PDCP entity of the gNB 200 and the PDCP entity of the UE 100 separates an MBS bearer, which is a bearer (data radio bearer) used for MBS, into a PTP leg and a PTM leg. Note that a PDCP entity is provided for each bearer.

[0058] Each of the gNB 200 and the UE 100 has two RLC entities, one MAC entity, and one PHY entity, each of which is provided for each leg. A PHY entity may be provided for each leg. In the case of dual connectivity in which the UE 100 communicates with two gNBs 200, the UE 100 may have two MAC entities.

[0059] The PHY entity transmits and receives data of the PTP leg using a Cell Radio Network Temporary Identifier (C-RNTI) that is assigned one-to-one to the UE 100. The PHY entity transmits and receives data of the PTM leg using a Group Radio Network Temporary Identifier (G-RNTI) that is assigned one-to-one to the MBS session. The C-RNTI is different for each UE 100, but the G-RNTI is a common RNTI for multiple UEs 100 receiving one MBS session.

[0060] In order to perform PTM transmission (multicast or broadcast) of MBS data from gNB200 to UE100 using a PTM leg, a split MBS bearer must be set from gNB200 to UE100 and the PTM leg must be activated. In other words, even if a split MBS bearer is set to UE100, gNB200 cannot perform PTM transmission of MBS data using this PTM leg if the PTM leg is in a deactivation state.

[0061] Furthermore, in order for the gNB200 and the UE100 to perform PTP transmission (unicast) of MBS data using a PTP leg, a split MBS bearer must be set from the gNB200 to the UE100, and the PTP leg must be activated. In other words, even if a split MBS bearer is set to the UE100, the gNB200 cannot perform PTP transmission of MBS data using this PTP leg if the PTP leg is in an inactive state.

[0062] In a state in which the PTM leg is activated, the UE 100 monitors a PDCCH (Physical Downlink Control Channel) to which a G-RNTI associated with the MBS session is applied (i.e., the UE 100 performs blind decoding of the PDCCH using the G-RNTI). The UE 100 may monitor the PDCCH only at a scheduling opportunity for the MBS session.

[0063] When the PTM leg is deactivated, UE 100 does not monitor the PDCCH to which the G-RNTI associated with the MBS session is applied (i.e., does not perform blind decoding of the PDCCH using the G-RNTI).

[0064] UE 100 monitors a PDCCH to which a C-RNTI is applied when a PTP leg is activated. When discontinuous reception (DRX) is configured in a PTP leg, UE 100 monitors the PDCCH in a configured on duration (OnDuration). When a cell (frequency) associated with an MBS session is designated, UE 100 may monitor the PDCCH of the cell even if the cell is deactivated.

[0065] In a state in which the PTP leg is deactivated, the UE 100 may monitor a PDCCH to which a C-RNTI is applied in preparation for normal unicast downlink transmission other than MBS data. However, when a cell (frequency) associated with an MBS session is specified, the UE 100 may not monitor the PDCCH for the MBS session.

[0066] It is assumed that the split MBS bearer described above is set up by an RRC message (e.g., an RRC Reconfiguration message) sent by the RRC entity of gNB200 to the RRC entity of UE100.

[0067] (Activating and Deactivating Legs) The activation and deactivation of legs according to one embodiment will now be described.

[0068] FIG. 9 is a diagram illustrating a first example of operations related to activation and deactivation of legs according to an embodiment.

[0069] As shown in Fig. 9, in step S11, the RRC entity of the gNB 200 transmits an RRC message including the configuration of the split MBS bearer (split bearer) shown in Fig. 8 to the UE 100. The RRC message is, for example, an RRC Reconfiguration message. The RRC entity of the UE 100 establishes the split MBS bearer based on the configuration included in the RRC message received from the gNB 200. In the following, an example in which the UE 100 establishes one split MBS bearer will be mainly described, but the UE 100 may establish multiple split MBS bearers according to the configuration from the gNB 200.

[0070] When performing bearer setup using an RRC message (RRC Reconfiguration message), gNB200 may use the same message to instruct UE100 on the initial state of each leg (i.e., activation or deactivation of each leg). When transmitting an RRC message including bearer setup for a split MBS bearer to UE100, the RRC entity of gNB200 includes an instruction to activate or deactivate each leg in the RRC message along with the bearer setup.

[0071] Such an RRC message may include at least one of an identifier of the leg (PTP leg, PTM leg) that is the target of the instruction and an identifier indicating either activation or deactivation. The RRC message may also include an identifier (e.g., TMGI, G-RNTI, session identifier, QoS flow identifier, bearer identifier) associated with the MBS session (split MBS bearer) that is the target of the instruction.

[0072] In step S12, gNB200 sends instructions to UE100 to activate or deactivate the PTP leg and PTM leg individually.

[0073] Here, the MAC entity of the gNB200 may transmit a MAC control element (MAC CE) including the instruction to the UE100. The MAC entity of the UE100 receives the MAC CE from the gNB200. Alternatively, the PHY entity of the gNB200 may transmit downlink control information (DCI) including the instruction to the UE100. The PHY entity of the UE100 receives the DCI from the gNB200.

[0074] Such a MAC CE or DCI may include at least one of an identifier of the leg (PTP leg, PTM leg) that is the target of the instruction and an identifier indicating either activation or deactivation. The MAC CE or DCI may also include an identifier (e.g., TMGI, G-RNTI, session identifier, QoS flow identifier, bearer identifier) associated with the MBS session (split MBS bearer) that is the target of the instruction.

[0075] By using MAC CE or DCI to indicate activation and deactivation of each leg, more dynamic control is possible than when using RRC messages.

[0076] UE100 starts the process of receiving data using the C-RNTI in response to receiving an instruction to activate the PTP leg. UE100 starts the process of receiving MBS data using the G-RNTI in response to receiving an instruction to activate the PTM leg. On the other hand, UE100 ends the process of receiving data using the C-RNTI in response to receiving an instruction to deactivate the PTP leg. UE100 ends the process of receiving MBS data using the G-RNTI in response to receiving an instruction to deactivate the PTM leg.

[0077] In step S12, the gNB 200 may transmit (PTM transmission) an instruction to activate or deactivate a PTP leg to the UE 100 via the PTM leg in the activated state. This allows the PTP legs of multiple UEs 100 to be activated or deactivated collectively by PTM.

[0078] The gNB 200 may transmit (PTM transmission) an instruction to deactivate the PTM leg to the UE 100 via the activated PTM leg. This allows the PTM legs of multiple UEs 100 to be deactivated collectively by PTM.

[0079] In step S12, the gNB 200 may transmit (PTP transmission) an instruction to activate or deactivate the PTM leg to the UE 100 via the PTP leg in the activated state. This allows the PTM leg to be individually activated or deactivated for each UE 100.

[0080] The gNB 200 may transmit (PTP transmission) an instruction to deactivate the PTP leg to the UE 100 via the PTP leg in the activated state. This allows the PTP leg to be deactivated individually for each UE 100.

[0081] In step S13, in response to receiving the instruction to activate at least one of the PTP leg and the PTM leg from the gNB 200 in step S12, the UE 100 may transmit a response to the received instruction to the gNB 200. This response may be transmitted, for example, from a MAC entity of the UE 100 to the gNB 200 via the PTP leg. After transmitting the response, the UE 100 may start a data reception operation on the activated leg.

[0082] The gNB 200 transmits data through the activated leg in response to receiving the response from the UE 100. That is, after receiving the response, the gNB 200 starts a data transmission operation on the leg.

[0083] In addition, in response to receiving an instruction to deactivate at least one of the PTP leg and the PTM leg from gNB200 in step S12, UE100 may send a response to the received instruction to gNB200.

[0084] 10 is a diagram showing an operation example 2 relating to activation and deactivation of legs according to one embodiment. The basic operation of operation example 2 is similar to operation example 1, so differences from operation example 1 will be mainly described here. Note that operation example 2 can be used in combination with operation example 1.

[0085] In operation example 2, gNB200 transmits an instruction to activate or deactivate both the PTP leg and the PTM leg to UE100. For example, the MAC entity of gNB200 includes both a control instruction for the PTP leg and a control instruction for the PTM leg in a MAC CE that instructs activation or deactivation of the legs.

[0086] As shown in Fig. 10, in step S21, the RRC entity of the gNB 200 transmits an RRC message including the configuration of the split MBS bearer (split bearer) shown in Fig. 8 to the UE 100. As described above, the RRC message may include information for configuring the initial state of each leg. The information for configuring the initial state of each leg may be information similar to an instruction included in a MAC CE or DCI, which will be described later.

[0087] In step S22, the gNB 200 transmits an instruction to activate or deactivate both the PTP leg and the PTM leg to the UE 100. As described above, the instruction is included in the MAC CE or DCI.

[0088] Here, the MAC CE or DCI includes an indication of activation of both the PTP leg and the PTM leg (e.g., "1"), or deactivation of both the PTP leg and the PTM leg (e.g., "0"). Activation of both the PTP leg and the PTM leg may be activation of a split MBS bearer or activation of duplication using two legs. Also, deactivation of both the PTP leg and the PTM leg may be deactivation of a split MBS bearer or deactivation of duplication using two legs.

[0089] The MAC CE or DCI may include identifiers (e.g., TMGI, G-RNTI, session identifier, QoS flow identifier, bearer identifier) associated with the MBS session (split MBS bearer) that is the subject of the instruction. The MAC CE or DCI may include an activation or deactivation instruction for each such identifier.

[0090] FIG. 11 is a diagram illustrating an example of a MAC CE (1 octet) that stores an indication value for each bearer identifier (or logical channel identifier) according to an embodiment. As shown in FIG. 11, in the MAC CE, M1 to M8 correspond to bearers #1 to #8 (or logical channels #1 to #8). Each field of M1 to M8 is 1 bit, and an indication value of activation (e.g., "1") or deactivation (e.g., "0") is stored in each field.

[0091] Step S23 is the same as in operation example 1. The UE 100 may transmit a response to the gNB 200.

[0092] When both the PTP leg and the PTM leg are activated, the PDCP entity of the UE 100 may perform a process of discarding duplicate packets of two identical MBS packets transmitted by duplication.

[0093] When the PTP leg is deactivated, the RRC entity of the UE 100 may transmit a message (RAI: Release Assistance Information / preference) to the gNB 200 to prompt the gNB 200 to release the RRC connection. Alternatively, the UE 100 may be permitted to transmit the RAI even when dynamic switching between the PTP leg and the PTM leg is being configured.

[0094] (Switching between PTP and PTM transmission) Next, a switching operation between PTP transmission and PTM transmission according to an embodiment will be described.

[0095] When a split MBS bearer is assumed, PTP transmission may be a method of transmitting MBS data from the gNB 200 to the UE 100 using a PTP leg (PTP communication path). PTM transmission may be a method of transmitting MBS data from the gNB 200 to the UE 100 using a PTM leg (PTM communication path).

[0096] Alternatively, a split MBS bearer need not be assumed. PTP transmission may be a method of transmitting MBS data from the gNB 200 to the UE 100 using a PTP bearer (PTP communication path) that is a first data radio bearer for PTP. PTM transmission may be a method of transmitting MBS data from the gNB 200 to the UE 100 using a PTM bearer (PTM communication path) that is a second data radio bearer for PTM.

[0097] The switching operation between PTP transmission and PTM transmission is an operation of ending MBS data transmission in one of the PTP transmission and PTM transmission transmission methods and simultaneously starting MBS data transmission in the other transmission method. During such switching, there is a concern that MBS data (MBS packets) transmitted from the gNB 200 to the UE 100 may be lost. When such packet loss occurs, it is desirable to perform retransmission in the PDCP layer (or RLC layer) to improve communication reliability.

[0098] In a UE 100 according to one embodiment, a receiver 110 receives MBS data transmitted from a gNB 200 using either a PTP (Point-To-Point) transmission or a PTM (Point-To-Multipoint) transmission method. A controller 130 of the UE 100 triggers transmission of a status report indicating a reception status of the MBS data in a predetermined layer of the UE 100 in response to switching of the transmission method between PTP transmission and PTM transmission. A transmitter 120 of the UE 100 transmits the status report to the gNB 200.

[0099] This allows the gNB 200 to grasp the reception status of MBS data from the UE 100 when switching between PTP transmission and PTM transmission. Therefore, even if an MBS packet is lost when switching between PTP transmission and PTM transmission, the gNB 200 can easily identify the lost MBS packet. Therefore, when a packet loss of an MBS packet occurs, retransmission in the PDCP layer (or RLC layer) becomes possible, thereby improving the reliability of communication.

[0100] In the following, an example will be described in which the predetermined layer is the PDCP layer and the status report transmitted from the UE 100 to the gNB 200 is a PDCP status report. However, the predetermined layer may be the RLC layer. The status report transmitted from the UE 100 to the gNB 200 may be an RLC status report (RLC Status PDU).

[0101] FIG. 12 is a diagram illustrating an example of the configuration of a PDCP status report according to an embodiment.

[0102] As shown in Figure 12, the PDCP status report has, as its main components, a 1-bit "D / C" field, a 3-bit "PDU Type" field, a 32-bit "FMC (First Missing COUNT)" field, and a variable-bit-length "Bitmap" field.

[0103] The "D / C" field indicates whether this PDCP PDU is a PDCP Data PDU or a PDCP Control PDU. The PDCP Status Report corresponds to the PDCP Control PDU.

[0104] The "PDU Type" field indicates whether this PDCP Control PDU is a "PDCP status report," "Interspersed ROHC feedback," or "EHC feedback."

[0105] The "FMC (First Missing COUNT)" field indicates the count value (COUNT) of the first missing PDCP SDU within the reordering window. The count value (COUNT) is composed of an HFN (Hyper Frame Number) and a PDCP sequence number.

[0106] The "Bitmap" field indicates the PDCP SDUs that were lost and the PDCP SDUs that were correctly received by the receiving PDCP entity. Specifically, the "Bitmap" field indicates the reception status of the PDCP SDUs after FMC as "0" (missing) or "1" (correctly received).

[0107] (1) Switching from PTM transmission to PTP transmission Next, a switching operation from PTM transmission to PTP transmission according to one embodiment will be described. Fig. 13 is a diagram showing a switching operation from PTM transmission to PTP transmission according to one embodiment. In the following description, it is assumed that the gNB 200 has established an MBS connection for shared MBS data delivery (Shared MBS Traffic delivery) shown in Fig. 7 with the 5GC 20.

[0108] 13, in step S101, the gNB 200 starts PTM transmission of MBS data. Specifically, the gNB 200 starts multicast transmission or broadcast transmission of MBS data belonging to a certain MBS session.

[0109] In step S102, the gNB 200 transmits MBS data belonging to a certain MBS session using PTM. The UE 100 receives the MBS data.

[0110] In step S103, the PDCP entity of UE 100 may record the sequence numbers of the MBS data that was successfully received and the sequence numbers of the MBS data that was unsuccessfully received among the MBS data (PDCP SDUs) transmitted in PTM in order to generate a PDCP status report.

[0111] In step S104, the gNB 200 transmits an instruction to the UE 100 to switch from PTM transmission to PTP transmission. This instruction may be a PTM leg deactivation instruction and / or a PTP leg activation instruction. This instruction may be an instruction to change from a PTM bearer to a PTP bearer by an RRC message (e.g., an RRC Reconfiguration message). This instruction may include an instruction to transmit or a transmission setting for a PDCP status report. However, the UE 100 may autonomously trigger (step S107) and transmit (step S108) a PDCP status report even without a PDCP status report transmission instruction or a transmission setting from the gNB 200.

[0112] In step S105, the gNB 200 and the UE 100 perform a process of switching from PTM transmission to PTP transmission. Specifically, the gNB 200 and the UE 100 end the PTM transmission of MBS data belonging to a certain MBS session and start the PTP transmission of the MBS data belonging to the MBS session.

[0113] In step S106, the gNB 200 transmits the MBS data belonging to the MBS session by PTP. The UE 100 receives the MBS data.

[0114] UE 100 may fail to receive the last MBS data (PDCP SDU) transmitted by PTM due to the process of switching from PTM transmission to PTP transmission. In this case, the PDCP entity of UE 100 records the sequence number of the MBS data (PDCP SDU) that failed to be received among the MBS data (PDCP SDU) transmitted by PTM.

[0115] UE 100 may fail to receive the first MBS data (PDCP SDU) transmitted by PTP due to the switching process from PTM transmission to PTP transmission. In this case, the PDCP entity of UE 100 records the sequence number of the MBS data (PDCP SDU) that failed to be received among the MBS data (PDCP SDU) transmitted by PTP.

[0116] In step S107, the PDCP entity of the UE 100 triggers the transmission of a PDCP status report. Specifically, the PDCP entity of the UE 100 generates a PDCP status report as shown in Fig. 12 and passes the PDCP status report to a lower layer.

[0117] Here, the PDCP entity of UE 100 may trigger the transmission of the PDCP status report when it receives the instruction in step S104, or may trigger the transmission of the PDCP status report when it performs the switching process in step S105.

[0118] The PDCP entity of the UE 100 may trigger transmission of the PDCP status report after a certain time has elapsed since receiving the instruction in step S104, or may trigger transmission of the PDCP status report after a certain time has elapsed since performing the switching process in step S105. Such a certain time (timer value) may be set in the UE 100 by the gNB 200.

[0119] The condition for triggering UE 100 to transmit a PDCP status report may be that there is a discontinuity between the sequence number of the MBS data last received by PTM and the sequence number of the MBS data first received by PTP. The PDCP entity of UE 100 triggers transmission of a PDCP status report only when it detects such a discontinuity. The condition for triggering UE 100 to transmit a PDCP status report may also be detection of a gap (discontinuity in sequence numbers) in MBS data transmitted by PTM.

[0120] In step S108, the lower layers (RLC entity, MAC entity, and PHY entity) of the UE 100 transmit a PDCP status report to the gNB 200. The gNB 200 receives the PDCP status report.

[0121] In step S109, the gNB 200 retransmits the missing MBS data to the UE 100 by PTP based on the missing packet information (FMC and Bitmap) included in the PDCP status report. The UE 100 receives the retransmitted MBS data by PTP.

[0122] In this way, even if MBS data is lost in UE 100 when switching from PTM transmission to PTP transmission, the lost MBS data can be identified based on the PDCP status report and complemented by retransmission in the PDCP layer.

[0123] (2) Switching from PTP transmission to PTM transmission Next, a switching operation from PTP transmission to PTM transmission according to an embodiment will be described below. Fig. 14 is a diagram showing a switching operation from PTP transmission to PTM transmission according to an embodiment.

[0124] 14, in step S201, the gNB 200 starts PTP transmission of MBS data. Specifically, the gNB 200 starts unicast transmission of MBS data belonging to a certain MBS session.

[0125] In step S202, the gNB 200 transmits MBS data belonging to a certain MBS session using PTM. The UE 100 receives the MBS data.

[0126] In step S203, the PDCP entity of UE 100 may record the sequence numbers of MBS data that were successfully received and the sequence numbers of MBS data that were unsuccessfully received among the MBS data (PDCP SDUs) transmitted via PTP in order to generate a PDCP status report.

[0127] In step S204, the gNB 200 transmits an instruction to the UE 100 to switch from PTP transmission to PTM transmission. This instruction may be a deactivation instruction for a PTP leg and / or an activation instruction for a PTM leg. This instruction may be an instruction to change from a PTP bearer to a PTM bearer by an RRC message (e.g., an RRC Reconfiguration message). This instruction may include an instruction to transmit or a transmission setting for a PDCP status report. However, the UE 100 may autonomously trigger (step S207) and transmit (step S208) a PDCP status report even without a transmission instruction or a transmission setting for a PDCP status report from the gNB 200.

[0128] In step S205, the gNB 200 and the UE 100 perform a process of switching from PTP transmission to PTM transmission. Specifically, the gNB 200 and the UE 100 end the PTP transmission of MBS data belonging to a certain MBS session and start the PTM transmission of the MBS data belonging to the MBS session.

[0129] In step S206, the gNB 200 transmits the MBS data belonging to the MBS session in PTM. The UE 100 receives the MBS data.

[0130] UE 100 may fail to receive the last MBS data (PDCP SDU) transmitted by PTP due to the switching process from PTP transmission to PTM transmission. In this case, the PDCP entity of UE 100 records the sequence number of the MBS data (PDCP SDU) that failed to be received among the MBS data (PDCP SDU) transmitted by PTP.

[0131] UE 100 may fail to receive the first MBS data (PDCP SDU) transmitted in PTM due to the process of switching from PTP transmission to PTM transmission. In this case, the PDCP entity of UE 100 records the sequence number of the MBS data (PDCP SDU) that failed to be received among the MBS data (PDCP SDU) transmitted in PTM.

[0132] In step S207, the PDCP entity of the UE 100 triggers the transmission of a PDCP status report. Specifically, the PDCP entity of the UE 100 generates a PDCP status report as shown in Fig. 12 and passes the PDCP status report to a lower layer.

[0133] Here, the PDCP entity of UE 100 may trigger the transmission of the PDCP status report when it receives the instruction in step S204, or may trigger the transmission of the PDCP status report when it performs the switching process in step S205.

[0134] The PDCP entity of the UE 100 may trigger transmission of the PDCP status report after a certain time has elapsed since receiving the instruction in step S204, or may trigger transmission of the PDCP status report after a certain time has elapsed since performing the switching process in step S205. Such a certain time (timer value) may be set in the UE 100 by the gNB 200.

[0135] The condition for triggering UE 100 to transmit a PDCP status report may be that there is a discontinuity between the sequence number of the MBS data last received via PTP and the sequence number of the MBS data first received via PTM. The PDCP entity of UE 100 triggers transmission of a PDCP status report only when it detects such a discontinuity. The condition for triggering UE 100 to transmit a PDCP status report may also be detection of a gap (discontinuity in sequence numbers) in MBS data transmitted via PTP.

[0136] In step S208, the lower layers (RLC entity, MAC entity, and PHY entity) of the UE 100 transmit a PDCP status report to the gNB 200. The gNB 200 receives the PDCP status report.

[0137] In step S209, the gNB 200 retransmits the missing MBS data in PTM to the UE 100 based on the missing packet information (FMC and Bitmap) included in the PDCP status report. The UE 100 receives the MBS data retransmitted in PTM.

[0138] In this way, even if MBS data is lost in UE 100 when switching from PTP transmission to PTM transmission, the lost MBS data can be identified based on the PDCP status report and complemented by retransmission in the PDCP layer.

[0139] (3) Example of change in switching behavior from PTP transmission to PTM transmission Next, a modified example of the switching operation from PTP transmission to PTM transmission according to an embodiment will be described. Fig. 15 is a diagram showing a modified example of the switching operation from PTP transmission to PTM transmission according to an embodiment.

[0140] As shown in Fig. 15, the operations of steps S301 to S308 are the same as those of Fig. 14. However, in steps S304 and S305, the gNB 200 and the UE 100 do not deactivate the PTP communication path (PTP leg) and maintain the active state.

[0141] In step S309, the gNB 200 retransmits the missing MBS data to the UE 100 by PTP based on the missing packet information (FMC and Bitmap) included in the PDCP status report. The UE 100 receives the retransmitted MBS data by PTP.

[0142] In this way, the gNB 200 and the UE 100 perform the initial transmission process of the MBS data using PTM, while performing the retransmission process of the MBS data using PTP. This allows the MBS data to be retransmitted using PTP only to the UE 100 in which the MBS data has been lost, thereby realizing efficient retransmission process. Note that the UE 100 may voluntarily stop the reception process using PTP when the lost MBS data has been compensated for by retransmission.

[0143] (Other embodiments) In the above embodiment, an example has been described in which a PTP communication path is configured with a PTP leg and a PTM communication path is configured with a PTM leg using a split MBS bearer. However, two radio bearers (data radio bearers) may be used to configure a PTP communication path with a first radio bearer for PTP and a PTM communication path with a second radio bearer for PTM.

[0144] In the above-described embodiment, an example has been described in which the predetermined layer is the PDCP layer and the status report transmitted from the UE 100 to the gNB 200 is a PDCP status report. However, the PDCP entity in the above-described embodiment may be read as an RLC entity, and the PDCP status report may be read as an RLC status report (RLC Status PDU).

[0145] The above-mentioned operational flows are not limited to being implemented independently, but can also be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow.

[0146] 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 also 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.

[0147] 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 on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0148] 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 (chipset, SoC).

[0149] 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 can be made within the scope that does not deviate from the gist of the invention.

[0150] This application claims priority from Japanese Patent Application No. 2020-214243 (filed December 23, 2020), the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0151] 10:NG-RAN (5G RAN) 20:5GC(5G CN) 100:UE 110: Receiving unit 120: Transmitter 130: Control unit 200 :gNB 210: Transmission unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit

Claims

1. A communication control method executed by a user device in a mobile communication system that provides a multicast broadcast service (MBS), receiving an RRC message from a network node; triggering transmission of a status report indicating a reception status of MBS data in a predetermined layer of the user equipment based on information included in the RRC message; and The RRC message includes a bearer identifier associated with the MBS bearer. Communication control method.

2. The predetermined layer is a Packet Data Convergence Protocol (PDCP) layer, The status report is a PDCP status report. The communication control method according to claim 1 .

3. The RRC message is an RRC Reconfiguration message. The communication control method according to claim 1.

4. A user equipment for use in a mobile communication system providing a multicast broadcast service (MBS), comprising: a receiver for receiving an RRC message from a network node; a control unit that triggers transmission of a status report indicating a reception status of MBS data in a predetermined layer of the user equipment based on information included in the RRC message; Equipped with The RRC message includes a bearer identifier associated with the MBS bearer. User equipment.

5. A network node for providing a multicast and broadcast service (MBS), comprising: a transmitter for transmitting an RRC message to a user equipment, the RRC message including information for triggering transmission of a status report indicating a reception status of MBS data in a predetermined layer of the user equipment; The RRC message includes a bearer identifier associated with the MBS bearer. Network node.

6. A device for use in a user device for carrying out the communication method according to claim 1. Processor.

7. The communication method according to claim 1 is executed by a user device. program.

8. A user equipment according to claim 4 and a network node. Mobile communication system.

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