Communication control method, user equipment and processor

Abstract

A first embodiment relates to a communication control method implemented by a user equipment in a mobile communication system providing a multicast / broadcast service (MBS). The communication control method includes receiving MBS data from a base station in a radio resource control (RRC) connected state, managing a timer for timing a time during which data and signaling transmission and reception are not performed with the base station, and transitioning from the RRC connected state to an RRC idle state in response to expiration of the timer. The managing of the timer includes controlling not to start the timer even if the MBS data is received when the MBS data transmitted via multicast or broadcast is received.

Description

Technical Field

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

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

[0003] Citation List

[0004] Non-patent literature

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

[0006] The communication control method according to the first aspect is a communication control method performed by a user equipment in a mobile communication system providing multicast / broadcast service (MBS). The communication control method includes: receiving MBS data from a base station in an RRC connected state; managing a timer that counts the time during which no data and signaling transmission and reception are performed with the base station; and transitioning from the RRC connected state to an RRC idle state in response to the expiration of the timer. Managing the timer includes: controlling not to start the timer even when MBS data is received via multicast or broadcast.

[0007] The communication control method according to the second aspect is a communication control method performed by a user equipment in a mobile communication system providing multicast broadcast service (MBS). This communication control method includes: managing a timer that counts the time during which data transmission and reception are not performed with a base station; and transitioning from an RRC connected state to an RRC idle state in response to the timer's expiration. Managing the timer includes: restarting the timer by sending or receiving a restart message before its expiration when MBS data transmitted via multicast is received from the base station.

[0008] The user equipment according to the third aspect includes a processor that executes the communication control method according to the first or second aspect. Attached Figure Description

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

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

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

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

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

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

[0015] Figure 7 This is a diagram illustrating a method for transmitting MBS data according to an embodiment.

[0016] Figure 8 This is a diagram illustrating the segmentation of the MBS bearer according to an embodiment.

[0017] Figure 9 This is a diagram illustrating an operational example of a first operating mode according to an embodiment.

[0018] Figure 10 This is a diagram illustrating an operational example of the second operating mode according to an embodiment.

[0019] Figure 11 This is a diagram illustrating an operational example of the third operating mode according to an embodiment.

[0020] Figure 12 This is a diagram illustrating an operational example of the fourth operating mode according to an embodiment. Detailed Implementation

[0021] The introduction of multicast broadcast service into 5G systems (NR) is under investigation. Compared to LTE multicast broadcast service, NR multicast broadcast service requires the provision of enhanced services.

[0022] In view of this, this disclosure provides a communication control method and user equipment for implementing enhanced multicast services.

[0023] A mobile communication system according to an embodiment is described with reference to the accompanying drawings. In the description of the drawings, the same or similar reference numerals denote the same or similar parts.

[0024] Configuration of mobile communication system

[0025] First, the configuration of the mobile communication system according to an embodiment is described. Figure 1This diagram illustrates the configuration of a mobile communication system according to an embodiment. The mobile communication system conforms to the 3GPP standard for a fifth-generation system (5GS). The following description uses 5GS as an example, but a Long Term Evolution (LTE) system can be applied at least partially to the mobile communication system. A sixth-generation (6G) system can also be applied at least partially to the mobile communication system.

[0026] like Figure 1 As shown, the mobile communication system includes user equipment (UE) 100, 5G radio access network (Next Generation Radio Access Network (NG-RAN)) 10, and 5G core network (5GC) 20.

[0027] UE 100 is a mobile wireless communication device. UE 100 can be any device, as long as it is used by a user. Examples of UE 100 include mobile phone terminals (including smartphones) and / or tablet terminals, laptop PCs, communication modules (including communication cards or chipsets), sensors or devices disposed in sensors, vehicles or devices disposed in vehicles (vehicle UE), or flying objects or devices disposed in flying objects (airborne UE).

[0028] NG-RAN 10 includes base stations (referred to as "gNBs" in 5G systems) 200. gNBs 200 are interconnected via an Xn interface, which serves as an inter-base station interface. Each gNB 200 manages one or more cells. gNBs 200 perform wireless communication with UEs 100 that have established connections to cells connected to them. gNBs 200 have Radio Resource Management (RRM) functions, functions for routing user data (hereinafter referred to as "data"), measurement and control functions for mobility control and scheduling, etc. "Cell" is used as a term to represent the smallest unit of a wireless communication area. "Cell" is also used as a term to represent the functions or resources used to perform wireless communication with UEs 100. A cell belongs to one carrier frequency.

[0029] Note that a gNB can connect to the Evolved Packet Core (EPC) corresponding to the LTE core network. LTE base stations can also connect to the 5GC. LTE base stations and gNBs can connect via an inter-base station interface.

[0030] The 5GC 20 includes Access and Mobility Management Functions (AMF) and User Plane Functions (UPF) 300. The AMF performs various types of mobility control for the UE 100. The AMF manages the mobility of the UE 100 by communicating with it using Non-Access Stratum (NAS) signaling. The UPF controls data transmission. The AMF and UPF are connected to the gNB 200 via the NG interface, which serves as the interface between the base station and the core network.

[0031] Figure 2 This is a diagram illustrating the configuration of a user equipment (UE) 100 according to an embodiment.

[0032] like Figure 2 As shown, UE 100 includes receiver 110, transmitter 120 and controller 130.

[0033] Receiver 110 performs various types of reception under the control of controller 130. Receiver 110 includes an antenna and receiving equipment. The receiving equipment converts the radio signals received through the antenna into baseband signals (received signals) and outputs the resulting signals to controller 130.

[0034] Transmitter 120 performs various types of transmissions under the control of controller 130. Transmitter 120 includes an antenna and a transmitting device. The transmitting device converts the baseband signal (transmit signal) output by controller 130 into a radio signal and transmits the obtained signal through the antenna.

[0035] Controller 130 performs various types of control within UE 100. Controller 130 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be processed by the processor. The processor may include a baseband processor and a central processing unit (CPU). The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0036] Figure 3 This is a diagram illustrating the configuration of a gNB 200 (base station) according to an embodiment.

[0037] like Figure 3 As shown, the gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communicator 240.

[0038] Transmitter 210 performs various types of transmissions under the control of controller 230. Transmitter 210 includes an antenna and a transmitting device. The transmitting device converts the baseband signal (transmit signal) output by controller 230 into a radio signal and transmits the obtained signal through the antenna.

[0039] Receiver 220 performs various types of reception under the control of controller 230. Receiver 220 includes an antenna and receiving equipment. The receiving equipment converts the radio signals received through the antenna into baseband signals (received signals) and outputs the resulting signals to controller 230.

[0040] The controller 230 performs various types of control over the gNB 200. The controller 230 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be processed by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0041] The backhaul communicator 240 is connected to the adjacent base station via the inter-base station interface. The backhaul communicator 240 is also connected to the AMF / UPF 300 via the interface between the base station and the core network. Note that the gNB may include a central unit (CU) and a distributed unit (DU) (i.e., functions are divided), and these two units may be connected via the F1 interface.

[0042] Figure 4 This is a diagram illustrating the configuration of the protocol stack for the user plane radio interface that processes data.

[0043] like Figure 4 As shown, the user plane radio interface protocol includes the physical (PHY) layer, media access control (MAC) layer, radio link control (RLC) layer, packet data convergence protocol (PDCP) layer, and service data adaptation protocol (SDAP) layer.

[0044] The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. It transmits data and control information between the PHY layer of UE 100 and the PHY layer of gNB 200 via physical channels.

[0045] The MAC layer performs data priority control, retransmission processing via Hybrid ARQ (Hybrid Automatic Repeat Request), and random access procedures. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of gNB 200 via the transport channel. The MAC layer of gNB 200 includes a scheduler. The scheduler determines the transport format (transport block size, modulation and coding scheme (MCS)) in the uplink and downlink, as well as the resource blocks to be allocated to UE 100.

[0046] The RLC layer transmits data to the RLC layer on the receiving end using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of UE 100 and the RLC layer of gNB 200 via logical channels.

[0047] The PDCP layer performs header compression and decompression, as well as encryption and decryption.

[0048] The SDAP layer performs the mapping between IP flows (as a unit of QoS (Quality of Service) control performed by the core network) and radio bearers (as a unit of QoS control performed by the access layer (AS)). Note that SDAP is not required when the RAN is connected to the EPC.

[0049] Figure 5 This is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0050] like Figure 5 As shown, the protocol stack of the control plane's radio interface includes a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer, instead of... Figure 4 The SDAP layer is shown.

[0051] RRC signaling for various configurations is transmitted between the RRC layer of UE 100 and the RRC layer of gNB 200. The RRC layer controls logical channels, transport channels, and physical channels based on the establishment, reconstruction, and release of radio bearers. When a connection exists between the RRC of UE 100 and the RRC of gNB 200 (RRC connection), UE 100 is in an RRC connected state. When no connection exists between the RRC of UE 100 and the RRC of gNB 200 (RRC connection), UE 100 is in an RRC idle state. When the connection between the RRC of UE 100 and the RRC of gNB 200 is suspended, UE 100 is in an RRC inactive state.

[0052] The NAS layer, located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of UE 100 and the NAS layer of AMF300B.

[0053] Note that in addition to the radio interface protocol, UE 100 also includes the application layer.

[0054] MBS

[0055] The MBS is described according to an embodiment. MBS is a service in which NG-RAN 10 can provide broadcast or multicast, i.e., point-to-multipoint (PTM) data transmission to UE 100. MBS may be referred to as Multimedia Broadcast and Multicast Service (MBMS). Note that examples of use cases (service types) for MBS include public safety communications, mission-critical communications, vehicle-to-everything (V2X) communications, IPv4 or IPv6 multicast delivery, Internet Protocol Television (IPTV), group communications, and software delivery.

[0056] MBS transmission in LTE includes two schemes: Multicast-Broadcast Single Frequency Network (MBSFN) transmission and Single Cell Point-to-Multipoint (SC-PTM) transmission. Figure 6 This is a diagram illustrating the correspondence between downlink logical channels and downlink transport channels according to an embodiment.

[0057] like Figure 6 As shown, the logical channels used for MBSFN transmission are the Multicast Service Channel (MTCH) and the Multicast Control Channel (MCCH), and the transport channel used for MBSFN transmission is the Multicast Channel (MCH). MBSFN transmission is mainly designed for multi-cell transmission, and in an MBSFN area that includes multiple cells, each cell synchronously transmits the same signal (the same data) in the same MBSFN subframe.

[0058] The logical channels used for SC-PTM transmission are the Single Cell Multicast Service Channel (SC-MTCH) and the Single Cell Multicast Control Channel (SC-MCCH), and the transport channel used for SC-PTM transmission is the Downlink Shared Channel (DL-SCH). SC-PTM transmission is primarily designed for single-cell transmission and corresponds to cell-by-cell broadcast or multicast data transmission. The physical channels used for SC-PTM transmission are the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Shared Channel (PDSCH), and dynamic resource allocation is possible.

[0059] Although the following descriptions will primarily focus on examples of MBS provided using the same and / or similar transmission schemes as the SC-PTM scheme, MBS can also be provided using the MBSFN transmission scheme. The descriptions will primarily focus on examples where multicast is used to provide MBS. Therefore, MBS can be interpreted as multicast. Note that MBS can also be provided via broadcast.

[0060] Assume that MBS data refers to data provided by MBS. Assume that the MBS control channel is MCCH or SC-MCCH. Assume that the MBS traffic channel is MTCH or SC-MTCH. Note that MBS data can be transmitted via unicast. MBS data can be referred to as MBS packets or MBS traffic.

[0061] The network can provide different MBS services for each MBS session. An MBS session is identified by at least one of a Temporary Mobile Group Identifier (TMGI) and a session identifier, and at least one of these identifiers is called an MBS session identifier. This MBS session identifier can be referred to as an MBS service identifier or a multicast group identifier.

[0062] MBS sessions include multicast sessions and broadcast sessions.

[0063] A multicast session is a session used to transmit multicast services. Multicast services are provided to a group of UEs 100 that have joined the multicast session for applications requiring high-reliability QoS. The multicast session is available to UEs 100 in an RRC connected state. MBS data is transmitted via multicast within the multicast session. UEs 100 will be in an RRC connected state to receive the multicast session.

[0064] A broadcast session is a session used to transmit broadcast services. Broadcast services are provided to every UE 100 within a specific service area. Broadcast sessions are available to UE 100 in all RRC states (RRC idle, RRC inactive, and RRC connected).

[0065] Figure 7 This is a diagram illustrating a method for transmitting MBS data according to an embodiment.

[0066] like Figure 7 As shown, MBS data (MBS service) is transmitted from a single data source (application service provider) to multiple UEs. The 5G CN (5GC) 20, which serves as the 5G core network, receives MBS data from the application service provider and performs replication of the MBS data to transmit the results.

[0067] From the perspective of 5GC 20, the following two transmission methods are possible: shared MBS data transmission (shared MBS service transmission) and single MBS data transmission (single MBS service transmission).

[0068] In shared MBS data transmission, a connection is established between NG-RAN 10, which serves as the 5G radio access network (5G RAN), and 5GC 20 to transmit MBS data from 5GC 20 to NG-RAN 10. This connection (tunnel) is referred to below as an "MBS connection".

[0069] MBS connections can be referred to as shared MBS service transport connections or shared transport. MBS connections terminate at NG-RAN 10 (i.e., gNB 200). MBS connections can correspond one-to-one to MBS sessions.

[0070] The gNB 200 independently decides whether to select a point-to-point (PTP: unicast) or point-to-multipoint (PTM: multicast or broadcast) transmission scheme, and sends MBS data to the UE 100 through the selected transmission scheme.

[0071] On the other hand, in a single MBS data transmission, a unicast session is established between NG-RAN 10 and UE 100 to transmit MBS data separately from 5GC 20 to UE 100. This unicast can be referred to as a PDU session. The unicast (PDU session) terminates at UE 100.

[0072] Segmented MBS bearer

[0073] This describes the split MBS bearer according to an embodiment.

[0074] The gNB 200 can be configured for UE 100 with MBS bearers split into PTP and PTM communication paths (hereinafter appropriately referred to as "split MBS bearers"). This allows the gNB 200 to dynamically switch the transmission of MBS data to UE 100 between PTP and PTM. The gNB 200 can use both PTP and PTM to perform duplicate transmissions of the same MBS data to enhance reliability.

[0075] The predetermined layer for terminating the segmentation is the MAC layer (HARQ), RLC layer, PDCP layer, or SDAP layer. Although the following description will primarily focus on an example where the predetermined layer for terminating the segmentation is the PDCP layer, the predetermined layer can be the MAC layer (HARQ), RLC layer, or SDAP layer.

[0076] Figure 8 This diagram illustrates the segmentation of the MBS bearer according to an embodiment. In the following text, the PTP communication path is referred to as a PTP tributary, and the PTM communication path is referred to as a PTM tributary. The functional unit corresponding to each layer is referred to as an entity. Furthermore, in the PTM tributary, MBS data is transmitted via multicast.

[0077] like Figure 8 As shown, each entity in the PDCP entity of gNB 200 and UE 100 divides the MBS bearer (the bearer for MBS (data radio bearer)) into PTP tributaries and PTM tributaries. Note that a PDCP entity is provided for each bearer.

[0078] Each of the gNB 200 and UE 100 includes two RLC entities, one MAC entity, and one PHY entity for the corresponding tributary. A PHY entity may be provided for each tributary. Note that in dual connectivity where UE 100 communicates with two gNB 200s, UE 100 may include two MAC entities.

[0079] The PHY entity uses a cell RNTI (Cell Radio Network Temporary Identifier (C-RNTI)) assigned one-to-one to UE 100 to transmit and receive data in the PTP tributary. The PHY entity uses a group RNTI (Group Radio Network Temporary Identifier (G-RNTI)) assigned one-to-one to the MBS session to transmit and receive data in the PTM tributary. The C-RNTI is different for each UE 100, but the G-RNTI is a common RNTI for multiple UE 100s receiving data in one MBS session.

[0080] To perform PTM transmission (multicast or broadcast) of MBS data from gNB 200 to UE 100 using the PTM tributary, a segmented MBS bearer will be configured from gNB 200 to UE 100, and the PTM tributary will be activated. In other words, even if a segmented MBS bearer is configured for UE 100, gNB 200 cannot use the PTM tributary to perform PTM transmission of MBS data when the PTM tributary is in an inactive state.

[0081] To enable gNB 200 and UE 100 to use the PTP tributary for PTP (unicast) transmission of MBS data, a segmented MBS bearer will be configured from gNB 200 to UE 100, and the PTP tributary will be activated. In other words, even if a segmented MBS bearer is configured for UE 100, gNB 200 cannot use the PTP tributary for PTP transmission of MBS data when the PTP tributary is in an inactive state.

[0082] When the PTM tributary is active, UE 100 monitors the Physical Downlink Control Channel (PDCCH) with G-RNTI associated with the MBS session applied (i.e., blind decoding of the PDCCH is performed using G-RNTI). UE 100 can monitor the PDCCH only at the scheduling time of the MBS session.

[0083] When the PTM tributary is in a deactivated state, the UE 100 does not monitor the PDCCH that has applied G-RNTI associated with the MBS session (i.e., it does not perform blind decoding of the PDCCH using G-RNTI).

[0084] When the PTP tributary is active, UE 100 monitors the PDCCH with C-RNTI applied. When Discontinuous Receiver (DRX) is configured in the PTP tributary, UE 100 monitors the PDCCH for the configured on duration. When a cell (frequency) associated with an MBS session is specified, UE 100 can monitor the PDCCH for that cell even when that cell is deactivated.

[0085] When the PTP tributary is in an inactive state, UE 100 can monitor the PDCCH with C-RNTI applied to prepare for normal unicast downlink transmissions other than MBS data. Note that when specifying a cell (frequency) associated with an MBS session, UE 100 does not need to monitor the PDCCH used for that MBS session.

[0086] Note that the above-mentioned segmented MBS bearer is configured by using an RRC message (e.g., an RRC reconfiguration message) sent by the RRC entity of gNB 200 to the RRC entity of UE 100.

[0087] RRC state transition via data inactivity timer

[0088] The RRC state transition via a data inactivity timer according to an embodiment will be described.

[0089] The current 5G / NR specification defines a data inactivity timer. A data inactivity timer is a timer used to count the time during which no data and signaling transmission and reception occur between the UE 100 and gNB 200.

[0090] UE 100 in RRC connected state can be configured with a data inactivity timer from gNB 200. UE 100 transitions from RRC connected state to RRC idle state in response to the expiration of the data inactivity timer.

[0091] When a data inactivity timer is configured, the UE 100 starts the data inactivity timer in response to the transmission or reception of data or signaling. Before the data inactivity timer expires, the UE 100 restarts the data inactivity timer in response to the transmission or reception of data or signaling. Note that "restarting the data inactivity timer" means resetting and restarting the data inactivity timer.

[0092] As an example of sending or receiving data, the MAC entity of UE 100 sends or receives MAC SDUs via the Dedicated Traffic Channel (DTCH) logical channel. The DTCH logical channel is a dedicated logical channel used for data transmission.

[0093] As an example of sending or receiving signaling, the MAC entity of UE 100 sends or receives MAC SDUs via the Dedicated Control Channel (DCCH) logical channel. The DCCH logical channel is a dedicated logical channel used for signaling transmission. Note that for details on the data inactivity timer, see, for example, “5.19 Data Inactivity Monitoring” in 3GPP TS 38.321V16.3.0 and “5.3.8.5 UE Actions When the Data Inactivity Timer Expiries” in 3GPP TS 38.331V16.3.0.

[0094] First operating mode

[0095] A first operating mode according to an embodiment will be described.

[0096] The following problem occurs when UE 100 receives MBS data transmitted via multicast and applies the aforementioned data inactivity timer.

[0097] gNB 200 configures an MBS bearer for UE 100 in an RRC connected state and begins transmitting MBS data via multicast. At this time, gNB 200 recognizes UE 100 as being in an RRC connected state. Upon receiving MBS data transmitted via multicast, UE 100 starts a data inactivity timer. While the data inactivity timer is running and radio conditions in UE 100 deteriorate, UE 100 fails to successfully receive MBS data and does not restart the data inactivity timer. Subsequently, UE 100 transitions to an RRC idle state in response to the expiration of the data inactivity timer. This results in a mismatch in RRC states between gNB 200 and UE 100. Note that, as mentioned above, MBS data can be provided not only via multicast but also via broadcast.

[0098] On the other hand, when data is received via normal unicast, UE 100 typically sends feedback information (e.g., ACK / NACK) to gNB 200 regarding the received data. Therefore, as described above, even if UE 100 transitions to an RRC idle state due to deteriorating radio conditions, gNB 200 can infer that UE 100 has transitioned to an RRC idle state in response to the lack of feedback information received from UE 100. Therefore, the problem of RRC state mismatch is not significant.

[0099] However, when UE 100 receives MBS data transmitted via multicast, the transmission of feedback information may not be configured. In this case, the problem of RRC state mismatch is significant.

[0100] Note that UE 100 receiving MBS data transmitted via multicast means one of the following: 1) UE 100 is configured with an MBS bearer that includes only a PTM tributary and receives MBS data via that MBS bearer; 2) UE 100 is configured with a segmented MBS bearer that includes both a PTM tributary and a PTP tributary and receives MBS data via the PTM tributary; and 3) UE 100 uses G-RNTI to receive MBS data.

[0101] In the first operating mode according to the embodiment, UE 100 manages a data inactivity timer. In managing the data inactivity timer, even when MBS data is received via multicast, UE 100 controls the data inactivity timer not to be started. Therefore, since UE 100 does not start the data inactivity timer, it does not transition to an RRC idle state in response to the expiration of the data inactivity timer, and the aforementioned RRC state mismatch problem is resolved.

[0102] In the first operating mode, when MBS data transmitted via unicast is received, UE 100 starts or restarts the data inactivity timer in response to the receipt of MBS data. As mentioned above, since the transmission of feedback information is configured in the unicast case, the problem of RRC state mismatch is not significant.

[0103] Note that UE 100 receiving MBS data transmitted via unicast means one of the following: 1) UE 100 is configured with an MBS bearer that includes only a PTP tributary and receives MBS data via that MBS bearer; 2) UE 100 is configured with a segmented MBS bearer that includes both a PTM tributary and a PTP tributary and receives MBS data via the PTP tributary; and 3) UE 100 uses C-RNTI to receive MBS data.

[0104] Figure 9 This is a diagram illustrating an operational example of a first operating mode according to an embodiment. Figure 9 In its initial state, UE 100 is in RRC connected state and a data inactivity timer is configured from gNB 200 to UE 100.

[0105] like Figure 9 As shown, in step S101, gNB 200 transmits MBS data via multicast. UE 100 receives the MBS data transmitted via multicast.

[0106] In step S102, UE 100 receives MBS data transmitted via multicast, but controls not to start the data inactivity timer. Note that even if the data inactivity timer has already been started at this time, UE 100 controls not to restart the data inactivity timer. For example, before step S102, UE 100 starts the data inactivity timer in response to normal unicast transmission and reception of data (data other than MBS data), and in step S102, UE 100 controls not to restart the data inactivity timer.

[0107] In step S103, gNB 200 instructs UE 100 to receive MBS data via unicast. UE 100 receives instructions from gNB 200. Here, the instructions may be an RRC reconfiguration message for configuring MBS bearers that include only PTP tributaries, or instructions for activating PTP tributaries of segmented MBS bearers that have been configured for UE 100 (e.g., MAC control element (CE) or downlink control information (DCI)).

[0108] In step S104, gNB 200 sends MBS data to UE 100 via unicast. UE 100 receives the MBS data sent via unicast.

[0109] In step S105, UE 100 starts a data inactivity timer in response to receiving MBS data transmitted via unicast.

[0110] In steps S106 to S107, UE 100 restarts the data inactivity timer in response to receiving MBS data transmitted via unicast.

[0111] Second operating mode

[0112] The second operating mode according to the embodiment will be described focusing on the differences from the operating modes described above.

[0113] In the second operating mode, even when MBS data transmitted via unicast is received, UE 100 controls the data inactivity timer not to be started. Therefore, in UE 100, the process of determining whether to start the data inactivity timer can be simplified as follows.

[0114] Figure 10 This is a diagram illustrating an operational example of a second operating mode according to an embodiment. In the operational example, it is assumed that UE 100 is in an RRC connected state, and a data inactivity timer is configured from gNB 200 to UE 100.

[0115] like Figure 10As shown, in step S201, gNB 200 transmits MBS data via unicast or multicast. UE 100 receives MBS data.

[0116] In step S202, UE 100 receives MBS data but controls not to start the data inactivity timer. Note that even if the data inactivity timer has already been started at this time, UE 100 controls not to restart the data inactivity timer. For example, before step S202, UE 100 starts the data inactivity timer in response to sending and receiving data (data other than MBS data) via normal unicast, and in step S202, UE 100 controls not to restart the data inactivity timer.

[0117] Third operating mode

[0118] The third operating mode according to the embodiment will be described focusing on the differences from the operating modes described above.

[0119] In the third operating mode, the UE 100 controls whether to start or not start the data inactivity timer when it receives MBS data, based on the configuration information from the gNB 200.

[0120] Figure 11 This is a diagram illustrating an operational example of a third operating mode according to an embodiment. In the operational example, it is assumed that UE 100 is in an RRC connection state, and a data inactivity timer is configured from gNB 200 to UE 100.

[0121] like Figure 11 As shown, in step S301, gNB 200 sends configuration information to UE 100. This configuration information is used to configure whether to start a data inactivity timer when MBS data is received. UE 100 receives the configuration information from gNB 200.

[0122] This configuration information is sent to UE 100, for example, in an RRC reconfiguration message. This configuration information may also include an identifier (such as a TMGI) of the MBS session corresponding to the MBS data. For example, for each of multiple MBS sessions stopped by gNB 200, the configuration information includes a set of items: the identifier (TMGI) of the MBS session, and information for configuring whether to start a data inactivity timer when MBS data belonging to that MBS session is received.

[0123] In step S302, gNB 200 transmits MBS data. UE 100 receives MBS data.

[0124] In step S303, when UE 100 receives MBS data, it controls whether to start or not start the data inactivity timer according to the configuration information received in step S301.

[0125] In the third operating mode, the configuration information can be information used to configure whether to send feedback information (e.g., ACK / NACK) for MBS data. In this case, UE 100 controls to start a data inactivity timer when receiving MBS data transmissions with configured feedback information, and controls not to start a data inactivity timer when receiving MBS data transmissions without configured feedback information.

[0126] Fourth operating mode

[0127] The fourth operating mode according to the embodiment will be described focusing on the differences from the operating modes described above.

[0128] As described above, in the current 5G / NR specification, the data inactivity timer covers data and signaling transmitted and received via unicast. When UE 100 is receiving MBS data transmitted via multicast, it starts the data inactivity timer while transmitting and receiving data via normal unicast. While the data inactivity timer is running and no data transmission or reception via normal unicast is performed, UE 100 transitions to an RRC idle state upon the timer's expiration. Since UE 100 needs to be in an RRC connected state to receive MBS data transmitted via multicast, UE 100 in an RRC idle state cannot receive MBS data transmitted via multicast.

[0129] In the fourth operating mode, when MBS data is received via multicast, UE 100 restarts the data inactivity timer by sending a restart message to gNB 200 before the data inactivity timer expires. In the current specification, UE 100 is specified to restart the data inactivity timer by sending signaling. Therefore, UE 100 restarts the data inactivity timer in response to sending the restart message. Consequently, UE 100 does not transition to an RRC idle state upon the expiration of the data inactivity timer and can continuously receive MBS data via multicast.

[0130] Figure 12 This is a diagram illustrating an operational example of a fourth operating mode according to an embodiment. In the operational example, it is assumed that UE 100 is in an RRC connected state, and a data inactivity timer is configured from gNB 200 to UE 100.

[0131] like Figure 12As shown, in step S401, UE 100 starts a data inactivity timer. Here, for example, UE 100 starts the data inactivity timer in response to transmitting and receiving data (data other than MBS data) via unicast. UE 100 may start the data inactivity timer in response to transmitting and receiving signaling.

[0132] In step S402, gNB 200 transmits MBS data via multicast. UE 100 receives the MBS data transmitted via multicast.

[0133] In step S403, UE 100 determines whether the remaining time before the data inactivity timer expires is less than or equal to a threshold. This threshold can be a value configured by UE 100 itself. Alternatively, this threshold can be a value configured from gNB 200 to UE 100.

[0134] When the remaining time is less than or equal to the threshold (step S403: Yes), in step S404, UE 100 sends a restart message to gNB 200. UE 100 may send the restart message in an RRC message. Alternatively, UE 100 may send the restart message in a MACCE message. The restart message may be information used to notify gNB 200 that the data inactivity timer has been reset and restarted. The restart message may be a 1-bit flag instructing UE 100 to continue receiving MBS data. Note that gNB 200 may send a response to UE 100 regarding the restart message upon receipt.

[0135] In step S405, UE 100 responds to sending a restart message to reset and restart the data inactivity timer.

[0136] In the fourth operating mode, UE 100 can periodically send restart information before the data inactivity timer expires.

[0137] In the above description, in S403, the remaining time before the data inactivity timer expires is compared with a threshold, but this disclosure is not limited thereto. UE 100 may include a separate timer for sending restart information. When restart information is sent, UE 100 starts or restarts the timer, and sends the restart information again when the timer expires. When MBS data reception is no longer performed (when there is no interest in reception or when MBS data transmission or the MBS session ends), UE 100 stops (or discards) the timer. The value of this timer can be configured from gNB 200.

[0138] In the fourth operating mode, a restart message can be sent from gNB 200. Specifically, similar to UE 100, gNB 200 manages a data inactivity timer, and gNB 200 starts / restarts the data inactivity timer in response to sending and receiving data with UE 100 via unicast. In this case, while MBS data is being transmitted, when the remaining time of the data inactivity timer managed by gNB 200 is less than or equal to a threshold, gNB 200 sends a restart message to UE 100 via unicast. In response to receiving the restart message, UE 100 restarts the data inactivity timer managed by UE 100. Note that gNB 200 can also reset and restart the data inactivity timer managed by gNB 200 in response to receiving a restart message from UE 100.

[0139] Other embodiments

[0140] In each of the above operating modes, the processing of the timer associated with MBS data reception has been described assuming that a data inactivity timer is configured for UE 100; however, when gNB 200 transmits MBS data via multicast (PTM), the operation of not configuring a data inactivity timer for UE 100 is considered. In this case, the MBS configuration (or PTM configuration) and the data inactivity timer configuration can be configured exclusively in the RRC reconfiguration message. Alternatively, when performing MBS configuration (or PTM configuration), UE 100 can ignore the data inactivity timer even if it is configured. That is, it can be assumed that the data inactivity timer is not configured.

[0141] The above-described operation modes can be implemented individually and independently, or they can be combined in combination. For example, some steps in one operation mode can be added to another. Additionally, some steps in one operation mode can be replaced by steps in another.

[0142] In the above embodiments, an example in which the base station is an NR base station (i.e., a gNB) is described; however, the base station can be an LTE base station (i.e., an eNB). The base station can be a relay node, such as an Integrated Access and Backhaul (IAB) node. The base station can be a Distributed Unit (DU) of an IAB node.

[0143] A program may be provided that enables the computer to perform each process executed by the UE 100 or gNB 200. This program may be recorded on a computer-readable medium. The computer-readable medium allows the program to be installed on the computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not specifically limited and may, for example, be a recording medium such as a CD-ROM or DVD-ROM.

[0144] The circuitry used to perform the processing to be performed by UE 100 or gNB 200 can be integrated, and at least a portion of UE 100 or gNB 200 can be implemented as a semiconductor integrated circuit (chipset, system-on-chip (SoC)).

[0145] Unless otherwise expressly stated, the descriptions of “based on” and “depending on” as used in this disclosure do not mean “based on only” or “depending on only”. The phrase “based on” means both “based on only” and “at least partially based on”. The phrase “depending on / responding to” means both “depending on / responding to only” and “at least partially dependent on / responding to”. Additionally, “obtaining / acquiring” can mean obtaining information from stored information, can mean obtaining information from information received from another node, or can mean obtaining information by generating information. The terms “comprising,” “including,” and variations thereof do not mean “including only the said items,” but rather mean “may include only the said items” or “may include not only the said items but also other items.” The term “or” as used in this disclosure is not intended to be an “exclusive or.” Any reference to elements in this disclosure using names such as “first” and “second” does not generally limit the number or order of these elements. These names may be used herein as a convenient way to distinguish two or more elements. Therefore, a reference to a first element and a second element does not mean that only the two elements can be used there or that the first element needs to precede the second element in some way. For example, when English articles such as “a,” “one,” and “the” are added in this disclosure by translation, these articles include plural forms unless otherwise explicitly stated in the context.

[0146] The embodiments have been described in detail above with reference to the accompanying drawings, but the specific configurations are not limited to those described above, and various design changes can be made without departing from the spirit of this disclosure.

[0147] This application claims priority to Japanese Patent Application No. 2021-079265 (filed on May 7, 2021), the entire contents of which are incorporated herein by reference.

[0148] Figure Labels

[0149] 10: NG-RAN (5G RAN)

[0150] 20: 5GC (5G CN)

[0151] 100:UE

[0152] 110: Receiver

[0153] 120: Transmitter

[0154] 130: Controller

[0155] 200: gNB

[0156] 210: Transmitter

[0157] 220: Receiver

[0158] 230: Controller

[0159] 240: Backhaul communicator.

Claims

1. A communication control method executed by a user equipment in a mobile communication system configured to provide multicast broadcast service (MBS), the communication control method comprising: Receive MBS data from the base station while in Radio Resource Control (RRC) connection state; A data inactivity timer is used to monitor data inactivity. as well as In response to the expiration of the data inactivity timer, the system transitions from the RRC connected state to the RRC idle state. The management of the data inactivity timer includes: when MBS data transmitted via broadcast is received, controlling the data inactivity timer not to be started even if MBS data is received.

2. The communication control method according to claim 1, in, Managing the timer also includes: when MBS data is received via unicast, starting or restarting the data inactivity timer in response to receiving the MBS data.

3. A user equipment in a mobile communication system providing multicast broadcast service (MBS), the user equipment comprising: The receiver receives MBS data from the base station while in Radio Resource Control (RRC) connected state; as well as The controller manages a data inactivity timer, which is used to monitor data inactivity. The controller: In response to the expiration of the data inactivity timer, the system transitions from the RRC connected state to the RRC idle state. When the MBS data is received via broadcast, the control does not start the data inactivity timer even if the MBS data is received.

4. A processor for controlling user equipment in a mobile communication system, the mobile communication system providing a multicast broadcast service (MBS), the processor performing the following processing: Receive MBS data from the base station while in Radio Resource Control (RRC) connection state; A data inactivity timer is used to monitor data inactivity. In response to the expiration of the data inactivity timer, the system transitions from the RRC connected state to the RRC idle state; as well as When the MBS data is received via broadcast, the control does not start the data inactivity timer even if the MBS data is received.

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