Communication method, base station and user terminal

Abstract

The communication method comprises: a network node transmitting multicast data to a user equipment via a multicast session, the user equipment being in a radio resource control (RRC) connected state; the network node receives notification information for determining whether to cause the user equipment to perform reception of a multicast session from another device in an RRC inactive state, the another device being at least one of the user equipment or a core network device; and on the basis of the notification information, the network node determines whether to transition the user equipment from the RRC connected state to the RRC inactive state.

Description

Technical Field

[0001] The present disclosure relates to a communication method, a base station, and a user terminal used in a mobile communication system. Background Art

[0002] The 3rd Generation Partnership Project (3GPP; registered trademark, the same hereinafter) has defined the technical specifications of New Radio (NR) as the 5th generation (5G) radio access technology. Compared with Long Term Evolution (LTE) as the 4th generation (4G) radio access technology, NR has characteristics such as high speed, large capacity, high reliability, and low latency. 3GPP has defined the technical specifications of the Multicast / Broadcast Service (MBS) for 5G / NR (for example, see Non-Patent Document 1).

[0003] Citation List

[0004] Non-Patent Document

[0005] Non-Patent Document 1: 3GPP Technical Specification: TS 38.300 V17.1.0 Summary of the Invention

[0006] In a first aspect, a communication method is used in a mobile communication system that provides a Multicast / Broadcast Service (MBS), and the communication method includes the following steps:

[0007] A network node (or network device) sends multicast data to a user equipment via a multicast session, and the user equipment is in a Radio Resource Control (RRC) connected state; the network node receives notification information for determining whether to cause the user equipment to receive the multicast session from another device in the RRC inactive state, and the other device is at least one of the user equipment or a core network device; and based on the notification information, the network node determines whether to cause the user equipment to transition from the RRC connected state to the RRC inactive state.

[0008] In a second aspect, a network node is used in a mobile communication system that provides a Multicast / Broadcast Service (MBS), and the network node includes: a transmitter for sending multicast data to a user equipment in a Radio Resource Control (RRC) connected state via a multicast session; a receiver for receiving notification information for determining whether to cause the user equipment to receive the multicast session from another device in the RRC inactive state, and the other device is at least one of the user equipment or a core network device; and a controller for determining whether to cause the user equipment to transition from the RRC connected state to the RRC inactive state based on the notification information.

[0009] In a third aspect, a user equipment is used in a mobile communication system that provides multicast / broadcast services (MBS). The user equipment includes: a receiver for receiving multicast data from a network node via a multicast session when the user equipment is in a radio resource control (RRC) connected state; and a transmitter for sending notification information to the network node so that the network node determines whether to enable the user equipment to perform reception of the multicast session in the RRC inactive state. Description of the Drawings

[0010] Figure 1 FIG. is a diagram showing the configuration of a mobile communication system according to an embodiment.

[0011] Figure 2 FIG. is a diagram showing the configuration of a user equipment (UE) according to an embodiment.

[0012] Figure 3 FIG. is a diagram showing the configuration of a gNB (base station) according to an embodiment.

[0013] Figure 4 FIG. is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that processes data.

[0014] Figure 5 FIG. is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that processes signaling (control signals).

[0015] Figure 6 FIG. is a diagram for explaining an operation that enables a UE in the RRC inactive state to perform multicast reception.

[0016] Figure 7 FIG. is a diagram showing an operation example of a mobile communication system according to an embodiment.

[0017] Figure 8 FIG. is a diagram showing Figure 7 a modified example of the operation of

[0018] Figure 9 FIG. is a diagram showing an operation example of a mobile communication system according to a modified example.

[0019] Figure 10 FIG. is a diagram showing Figure 9 a modified example of the operation of Detailed Description of the Invention

[0020] A mobile communication system according to an embodiment is described with reference to the accompanying drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0021] System Configuration

[0022] Figure 1FIG. is a diagram showing the configuration of a mobile communication system 1 according to an embodiment. The mobile communication system 1 conforms to the fifth-generation system (5GS) of the 3GPP standard. The following description takes 5GS as an example, but the Long-Term Evolution (LTE) system can be at least partially applied to this mobile communication system. Alternatively, the sixth-generation (6G) system can be at least partially applied to this mobile communication system.

[0023] The mobile communication system includes a user equipment (UE) 100, a 5G radio access network (Next Generation Radio Access Network (NG-RAN)) 10, and a 5G core network (5GC) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10 (Network 10). The 5GC 20 may be simply referred to as the core network (CN) 20.

[0024] The UE 100 is a mobile radio communication device. As long as the UE 100 is used by a user, the UE 100 can be any device. Examples of the UE 100 include a mobile phone terminal (including a smart phone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided on the sensor, a vehicle or a device provided on the vehicle (vehicle UE), or an aircraft and a device provided on the aircraft (airborne UE).

[0025] The NG-RAN 10 includes a base station (referred to as a "gNB" in the 5G system) 200. The gNBs 200 are interconnected via an Xn interface that is an interface between base stations. Each gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection to the cell of the gNB 200. The gNB 200 has a radio resource management (RRM) function, a function of routing user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. "Cell" is a term used to represent the smallest unit of a wireless communication area. "Cell" is also used as a term to represent a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0026] Note that the gNB can be connected to an evolved packet core (EPC) corresponding to the core network of LTE. The LTE base station can also be connected to the 5GC. The LTE base station and the gNB can be connected via an interface between base stations.

[0027] The 5GC 20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various types of mobility control, etc. for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using Non-Access Stratum (NAS) signaling. The UPF controls data transmission. The AMF and the UPF are connected to the gNB 200 via the NG interface, which is an interface between the base station and the core network.

[0028] Figure 2 FIG. is a diagram showing the configuration of a UE 100 (User Equipment) according to an embodiment. The UE 100 includes a receiver 110, a transmitter 120, and a controller 130. The receiver 110 and the transmitter 120 constitute a wireless communicator that performs wireless communication with the gNB 200.

[0029] The receiver 110 performs various types of reception under the control of the controller 130. The receiver 110 includes an antenna and receiving equipment. The receiving equipment converts the radio signal received through the antenna into a baseband signal (received signal), and outputs the resulting signal to the controller 130.

[0030] The transmitter 120 performs various types of transmission under the control of the controller 130. The transmitter 120 includes an antenna and transmitting equipment. The transmitting equipment converts the baseband signal (transmitted signal) output by the controller 130 into a radio signal, and transmits the resulting signal through the antenna.

[0031] The controller 130 performs various types of control and processing in the UE 100. Such processing includes the processing of each layer to be described later. The operations of the UE 100 described above and below can also be performed under the control of the controller 230. The 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 used for the processing performed 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, etc. of the baseband signal. The CPU executes the programs stored in the memory, thereby performing various types of processing.

[0032] Figure 3 FIG. is a diagram showing the configuration of a gNB 200 (base station) according to an embodiment. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communicator 240. The transmitter 210 and the receiver 220 constitute a wireless communicator that performs wireless communication with the UE 100. The backhaul communicator 240 constitutes a network communicator that communicates with the CN 20.

[0033] The transmitter 210 performs various types of transmissions under the control of the controller 230. The transmitter 210 includes an antenna and a transmission device. The transmission device converts the baseband signal (transmission signal) output by the controller 230 into a radio signal and transmits the obtained signal through the antenna.

[0034] The receiver 220 performs various types of receptions under the control of the controller 230. The receiver 220 includes an antenna and a reception device. The reception device converts the radio signal received through the antenna into a baseband signal (reception signal) and outputs the obtained signal to the controller 230.

[0035] The controller 230 performs various types of control and processing in the gNB 200. Such processing includes the processing of each layer to be described later. The operations of the gNB 200 described above and below can also be performed under the control of the controller 230. 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 used for the processing performed by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding, etc. of the baseband signal. The CPU executes the programs stored in the memory, thereby performing various types of processing.

[0036] The backhaul communicator 240 is connected to an adjacent base station via the Xn interface, which is an interface between base stations. The backhaul communicator 240 is connected to the AMF / UPF 300 via the NG interface between the base station and the core network. Note that the gNB 200 may include a central unit (CU) and a distributed unit (DU) (i.e., the functions are divided), and these two units may be connected via the F1 interface, which is a fronthaul interface.

[0037] Figure 4 is a diagram showing the configuration of the protocol stack of the radio interface of the user plane that processes data.

[0038] The radio interface protocol of the user plane includes a physical (PHY) layer, a media 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.

[0039] The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. Data and control information are transmitted between the PHY layer of UE 100 and the PHY layer of gNB 200 via the physical channel. Note that the PHY layer of UE 100 receives downlink control information (DCI) sent from gNB 200 through the physical downlink control channel (PDCCH). Specifically, UE 100 blindly decodes the PDCCH using a radio network temporary identifier (RNTI), and obtains the successfully decoded DCI as the DCI addressed to UE 100. The DCI sent from gNB 200 is appended with CRC parity bits scrambled by the RNTI.

[0040] The MAC layer performs priority control of data, retransmission processing through hybrid ARQ (HARQ: Hybrid Automatic Repeat reQuest), 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 the transport channel. The MAC layer of gNB 200 includes a scheduler. The scheduler determines the transmission format (transmission block size, modulation and coding scheme (MCS)) in the uplink and downlink and the resource blocks to be allocated to UE 100.

[0041] The RLC layer sends data to the RLC layer on the receiving side by using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of UE 100 and the RLC layer of gNB 200 via the logical channel.

[0042] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0043] The SDAP layer performs the mapping between IP flows (as the unit of QoS (Quality of Service) control performed by the core network) and radio bearers (as the unit of QoS control performed by the access stratum (AS)). Note that when the RAN is connected to the EPC, the SDAP is not required to be provided.

[0044] Figure 5 is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0045] The protocol stack of the radio interface of the control plane includes the radio resource control (RRC) layer and the non-access stratum (NAS) layer, rather than Figure 4 the SDAP layer shown in

[0046] RRC signaling for various configurations is sent 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 according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE 100 and the RRC of gNB 200, UE 100 is in the RRC connected state. When there is no connection (RRC connection) between the RRC of UE 100 and the RRC of gNB 200, UE 100 is in the RRC idle state. When the connection between the RRC of UE 100 and the RRC of gNB 200 is suspended, UE 100 is in the RRC inactive state.

[0047] The NAS layer, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is sent between the NAS layer of UE 100 and the NAS layer of AMF300A. Note that in addition to the protocols of the radio interface, UE 100 includes an application layer. Layers lower than the NAS layer are referred to as the AS layer.

[0048] Overview of MBS

[0049] The mobile communication system 1 can perform transmission with high resource efficiency by using the multicast / broadcast service (MBS).

[0050] In the multicast communication service (also referred to as "MBS multicast"), the same service and the same specific content data are provided to a specific group of UEs simultaneously. That is, not every UE 100 in the multicast service area is allowed to receive the data. The multicast communication service is transmitted to UE 100 using a multicast session, which is a type of MBS session. UE 100 can receive the multicast communication service in the RRC connected state using mechanisms such as point-to-point (PTP) and / or point-to-multipoint (PTM) transmission. UE 100 can receive the multicast communication service in the RRC inactive (or RRC idle) state. This transmission mode is also referred to as "transmission mode 1".

[0051] In the broadcast communication service (also referred to as "MBS broadcast"), the same service and the same specific content data are provided to every UE 100 within a geographical area simultaneously. That is, every UE 100 in the broadcast service area is allowed to receive the data. The broadcast communication service is transmitted to UE 100 using a broadcast session, which is a type of MBS session. UE 100 can receive the broadcast communication service in any of the RRC idle state, RRC inactive state, and RRC connected state. This transmission mode is also referred to as "transmission mode 2".

[0052] The main logical channels for MBS transmission are the Multicast Traffic Channel (MTCH), the Dedicated Traffic Channel (DTCH), and the Multicast Control Channel (MCCH). The MTCH is a PTM downlink channel used to transmit MBS data of a multicast session or a broadcast session from the network 10 to the UE 100. The DTCH is a PTP channel used to send MBS data of a multicast session from the network 10 to the UE 100. The MCCH is a PTM downlink channel used to send MBS broadcast control information associated with one or more MTCHs from the network 10 to the UE 100.

[0053] Regarding the configuration in MBS broadcast, a UE 100 in the RRC idle state, RRC inactive state, or RRC connected state receives the MBS configuration of a broadcast session (e.g., parameters required for MTCH reception) via the MCCH. The parameters required to receive the MCCH (MCCH configuration) are provided through system information. Specifically, System Information Block Type 20 (SIB 20) includes the MCCH configuration. Note that SIB Type 21 (SIB 21) includes information related to the service continuity of MBS broadcast reception. The MCCH provides a list of all broadcast services (including ongoing sessions) transmitted on the MTCH, and the relevant information of the broadcast session includes the MBS session ID (e.g., Temporary Mobile Group Identity (TMGI)), the relevant MTCH scheduling information, and information about neighboring cells providing a specific service on the MTCH.

[0054] On the other hand, for MBS multicast, the current technical specifications of 3GPP enable the UE 100 to receive data of a multicast session only in the RRC connected state. When the UE 100 that has joined a multicast session is in the RRC connected state and the multicast session is activated, the gNB 200 sends an RRC reconfiguration message including the MBS configuration associated with the multicast session to the UE 100. This MBS configuration is also referred to as the Multicast Radio Bearer (MRB) configuration, MTCH configuration, or multicast configuration. This MRB configuration (MRB-ToAddMod) includes the MBS session ID (mbs-SessionId), the MRB ID (mrb-Identity), and other parameters of the MRB (multicast MRB) to be configured for the UE 100 (such as the PDCP configuration (pdcp-Config)).

[0055] In the following embodiments, the operations that enable a UE 100 in the RRC inactive state to perform multicast reception will be mainly described. Figure 6 An overview of the operation is shown.

[0056] As a solution for enabling a UE 100 in the RRC inactive state to perform multicast reception, consider Figure 6The solution based on Transmission Mode 1 shown in part (a) of Figure 6 and the solution based on Transmission Mode 2 shown in part (b) of

[0057] In Figure 6 the solution based on Transmission Mode 1 shown in part (a) of, in step S1, the gNB 200 sends an RRC reconfiguration message including an MBS configuration (multicast configuration) related to a multicast session to the UE 100 in the RRC connected state. The UE 100 receives multicast data on the MTCH via the multicast session (multicast MRB) based on the multicast configuration received in the RRC reconfiguration message.

[0058] In step S2, the gNB 200 sends an RRC Release message to the UE 100 in the RRC connected state to cause the UE 100 to transition to the RRC inactive state. The RRC Release message includes a configuration for the RRC inactive state (suspend configuration).

[0059] In step S3, in response to receiving the RRC Release message in step S2, the UE 100 transitions from the RRC connected state to the RRC INACTIVE state.

[0060] In step S4, the UE 100 in the RRC inactive state continues to receive multicast data on the MTCH via the multicast session using the multicast configuration in step S1.

[0061] This enables the UE 100 in the RRC inactive state to perform multicast reception. Note that although an example of using an RRC reconfiguration message to perform multicast configuration has been described, an RRC Release message can also be used to perform multicast configuration.

[0062] Both the RRC reconfiguration message and the RRC Release message are RRC messages sent for each UE on the dedicated control channel (DCCH) and are hereinafter also referred to as dedicated RRC messages.

[0063] On the other hand, in Figure 6 the solution based on Transmission Mode 2 shown in part (b) of, in step S11, the gNB 200 sends an RRC Release message to the UE 100 in the RRC connected state to cause the UE 100 to transition to the RRC inactive state. The RRC Release message includes a configuration for the RRC inactive state (suspend configuration).

[0064] In step S12, in response to receiving the RRC Release message in step S11, the UE 100 transitions to the RRC INACTIVE state.

[0065] In step S13, gNB 200 transmits an MCCH including an MBS configuration (multicast configuration) for a multicast session. UE100 receives the MCCH. Note that UE 100 receives SIB 20 before receiving the MCCH and receives the MCCH based on SIB 20. Note that the MCCH transmission (and reception) may be performed before step S11 or may be performed simultaneously with step S11.

[0066] In step S14, UE 100 in the RRC inactive state receives multicast data on the MTCH via the multicast session based on the multicast configuration received on the MCCH in step S13. This enables UE 100 in the RRC inactive state to perform multicast reception.

[0067] System operation example

[0068] When UE 100 performs multicast reception from gNB 200 in the RRC inactive state, compared with when UE 100 performs multicast reception from gNB 200 in the RRC connected state, the load on the network (specifically, gNB 200) and the power consumption of UE 100 can be reduced. Therefore, from the perspective of efficiency, it is preferable for gNB 200 to convert UE 100 in the RRC connected state that can perform multicast reception in the RRC inactive state.

[0069] However, among UEs 100 that perform multicast reception, there are also UEs 100 that execute group call applications such as Push-to-Talk (PTT). While performing multicast reception of a multicast session on the downlink (DL), such a UE 100 can perform uplink (UL) transmission of the multicast session. If such a UE 100 is converted to the RRC inactive state, then every time UE 100 performs a UL transmission, UE 100 needs to be converted to the RRC connected state, which is quite inefficient. If gNB 200 can confirm the traffic characteristics of the multicast session, then gNB 200 can appropriately determine whether to convert UE 100 to the RRC inactive state, but since gNB 200 does not have an application layer, it is difficult for gNB 200 to make such an appropriate determination alone.

[0070] In an embodiment, it enables gNB 200 to appropriately determine whether to convert UE 100 that performs multicast reception in the RRC connected state to the RRC inactive state and to achieve efficient multicast reception.

[0071] More specifically, in an embodiment, the gNB 200 (which sends multicast data to the UE 100 in the RRC connected state via a multicast session) receives notification information from another device, and this notification information is used to determine whether to cause the UE 100 to receive the multicast session from another device in the RRC inactive state, and this another device is at least one of the UE 100 or a core network device. In an embodiment, although an example where the core network device is the AMF 300A will be described, the core network device can be a UPF or the like. Based on this notification information, the gNB 200 determines whether to cause the UE 100 to transition from the RRC connected state to the RRC inactive state. This notification information can be information based on UL service characteristic parameters of the multicast session. For example, when there is no UL transmission or the frequency of UL transmission is low, even if the UE 100 attempts to receive the multicast session in the RRC inactive state, the UE 100 does not need to frequently transition to the RRC connected state, so the gNB 200 determines to cause the UE 100 to transition to the RRC inactive state.

[0072] In an embodiment, the UE 100 or the AMF 300A specifies the UL service characteristic parameters of the multicast session. The UE 100 or the AMF 300A sends information indicating whether the UE 100 can perform reception of the multicast session in the RRC inactive state to the gNB 200 based on the UL service characteristic parameters as notification information.

[0073] Figure 7 FIG. is a diagram showing an operation example of the mobile communication system 1 according to an embodiment. Before the current operation, it is assumed that the UE 100 has joined a multicast session. It is assumed that the UE 100 is performing or about to perform multicast reception in the RRC connected state.

[0074] In step S101, the gNB 200 sends the multicast configuration required for receiving the multicast session (i.e., multicast reception) to the UE 100 in the RRC connected state in a dedicated RRC message (in the example shown, it is an RRC reconfiguration message). The UE 100 receives the multicast configuration in the dedicated RRC message. Such a configuration can include a configuration for allowing or requesting the UE 100 to send the following notification information.

[0075] In step S102, the gNB 200 sends multicast data on the MTCH via the multicast session based on the multicast configuration in step S101. The UE 100 receives the multicast data on the MTCH via the multicast session based on the multicast configuration in step S201.

[0076] In step S103, the UE 100 specifies UL service characteristic parameters for the multicast session. The UL service characteristic parameters include at least one parameter selected from the group consisting of: a parameter indicating whether there is UL transmission for the multicast session, a parameter indicating the occurrence probability or occurrence frequency per unit time of the UL transmission for the multicast session, an allowable delay parameter for the UL transmission of the multicast session, and a parameter indicating the size of the uplink transmission data for the multicast session.

[0077] In step S104, the UE 100 determines whether multicast reception can be performed in the RRC inactive state based on the UL service characteristic parameters specified in step S103. For example, when one of the following conditions (a) to (d) or a combination of two or more is satisfied, the UE 100 may determine that the UE 100 can perform multicast reception in the RRC inactive state.

[0078] (a) There is no UL transmission, or it is expected that there will be no UL transmission within a certain period in the future:

[0079] For example, when the service type (application type) of the multicast session is a service without UL transmission (e.g., television broadcast service) or when the service type belongs to a service with UL transmission but no UL transmission has been performed within a certain period (e.g., 10 seconds) (e.g., the microphone is turned off in a group call), the UE 100 may determine that the UE 100 can perform multicast reception in the RRC inactive state. This certain period can be configured for the UE 100 from the gNB 200 or the AMF 300A. The UE 100 can monitor the occurrence status of the UL service in the multicast session and make this determination through prediction based on the monitoring result.

[0080] (b) The frequency of UL transmission is low:

[0081] For example, when the service type (application type) of the multicast session belongs to a service with rarely performed UL transmission, the UE 100 may determine that the UE 100 can perform multicast reception in the RRC inactive state. This frequency can be configured for the UE 100 from the gNB 200 or the AMF 300A. The UE 100 can monitor the occurrence frequency of the UL service in the multicast session and make this determination through prediction based on the monitoring result.

[0082] (c) The delay of UL transmission is allowed:

[0083] For example, when the service type (application type) of the multicast session belongs to a service that does not require UL real-time response (such as text transmission, etc.), the UE 100 may determine that the UE 100 can perform multicast reception in the RRC inactive state. The threshold (reference value) of this delay can be configured for the UE 100 from the gNB 200 or the AMF 300A.

[0084] (d) Small size of UL transmission data:

[0085] For example, when the service type (application type) of a multicast session belongs to a service that performs small data size transmissions such as only Ack and / or short text messages on the UL (e.g., only text messages on the UL in live video distribution, or only acknowledgment transmissions in upper layer retransmission functions such as FLUTE in firmware download), the UE 100 may determine that the UE 100 can perform multicast reception in the RRC inactive state. The UE 100 may monitor the occurrence status of UL traffic in the multicast session and make this determination through prediction based on the monitoring result. A threshold for determining that the data size is small can be configured for the UE 100 from the gNB 200 or the AMF 300A. Note that in this case, the UE 100 may use the small data transmission (SDT) technique for performing UL transmission during the random access procedure to perform UL transmission without transitioning to the RRC connected state. That is, this threshold may be the same as the data volume threshold of the SDT.

[0086] In step S105, the UE 100 sends an RRC message to the gNB 200, and the RRC message includes notification information indicating the determination result of step S104. The UE 100 may send an RRC message to the gNB 200 based on the determination in step S104 that the UE 100 can perform multicast reception in the RRC inactive state, and the RRC message includes notification information indicating the determination result. The gNB 200 receives the RRC message. That is, the UE 100 may notify the gNB 200 that the UE 100 can receive the multicast session in the RRC inactive state. The RRC message may include MBS session information associated with the notification information. The MBS session information is information for identifying a multicast session (multicast service), and it is, for example, the TMGI.

[0087] The RRC message may be a UE assistance information message. The "preferredRRC-State" in "ReleasePreference" in the UE assistance information message indicates the RRC state desired by the UE 100. The UE 100 sets the "preferredRRC-State" to "inactive". In an embodiment, the UE assistance information message may be able to include additional information indicating that multicast reception will continue. The UE 100 may send a UE assistance information message including a set of "preferredRRC-State" set to "inactive" and the additional information as notification information indicating that multicast sessions can be received in the RRC inactive state.

[0088] The RRC message can be an MBS interest indication message. In the current technical specification, the MBS interest indication message includes an MBS-ServiceList (specifically, a TMGI list), which is a list of MBS broadcast services that the UE 100 is receiving or wishes to receive. In an embodiment, the MBS-ServiceList can be a list of MBS broadcast services and MBS multicast services that the UE 100 is receiving or wishes to receive. The UE assistance information message may be able to include additional information indicating that multicast reception will continue associated with the TMGI of the MBS multicast service. The MBS interest indication message may be able to include the TMGI of a multicast session that can be received in the RRC inactive state as a new cell.

[0089] In step S106, the gNB 200 determines whether to transition the UE100 to the RRC inactive state based on the notification information received in step S105. Here, the description will continue under the assumption that it has been determined to transition the UE 100 to the RRC inactive state.

[0090] In step S107, the gNB 200 sends an RRC release message including a Suspend config. to the UE 100. The UE 100 receives the RRC release message. The RRC release message may include the multicast configuration required to receive the multicast session.

[0091] In step S108, when the UE 100 receives the RRC release message in step S107, the UE 100 transitions from the RRC connected state to the RRC inactive state.

[0092] In step S109, the UE 100 that has transitioned to the RRC inactive state receives multicast data on the MTCH via the multicast session based on the multicast configuration configured in step S101 or S107. The UE 100 may receive multicast data on the MTCH via the multicast session based on the multicast configuration sent from the gNB 200 on the MCCH.

[0093] Although Figure 7 the operation example shows an example in which the UE 100 sends notification information to the gNB 200, the AMF 300A may also send notification information to the gNB 200. Figure 8 is a flowchart showing a modified example of the Figure 7 operation. Here, the differences from the Figure 7 operation will be described, and repeated descriptions will be omitted.

[0094] Steps S201 and S202 are the same as or similar to the Figure 7 operation.

[0095] In step S203, the AMF 300A designates the UL service characteristic parameters of the multicast session.

[0096] In step S204, the AMF 300A determines whether the UE 100 can perform multicast reception in the RRC inactive state based on the UL service characteristic parameters determined in step S203. This determination method is the same as or similar to the above method.

[0097] In step S205, the AMF 300A sends an NG-Application Protocol (AP) message on the NG interface to the gNB 200. The NG-AP message includes notification information indicating the determination result of step S204. This message may include MBS session information associated with the notification information. This message may be an Initial Context Setup Request message or a UE Context Modification Request message.

[0098] In step S206, the gNB 200 determines whether to transition the UE 100 to the RRC inactive state based on the notification information received in step S205. The subsequent operations (steps S207 to S209) are the same as or similar to Figure 7 the operations of

[0099] Modified example of the operation

[0100] In this modified example, the UE 100 or the AMF 300A designates the UL service characteristic parameters of the multicast session and sends the UL service characteristic parameters to the gNB 200 as notification information. That is, in this modified example, information (materials for determination) more detailed than the information in the above embodiment is provided to the gNB 200 as notification information. The differences from the operations of the above embodiment will be described below, and repeated descriptions will be omitted.

[0101] Figure 9 is a flowchart showing an operation example of the mobile communication system 1 according to this modified example.

[0102] Steps S301 and S302 are the same as or similar to the steps of the above embodiment.

[0103] In step S303, the UE 100 designates the UL service characteristic parameters of the multicast session. The UL service characteristic parameters include at least one parameter selected from the group consisting of: a parameter indicating whether there is a UL transmission of the multicast session, a parameter indicating the occurrence probability or occurrence frequency per unit time of the UL transmission of the multicast session, an allowable delay parameter for the UL transmission of the multicast session, and a parameter indicating the size of the uplink transmission data of the multicast session.

[0104] In step S304, the UE 100 sends an RRC message including the UL service characteristic parameters specified in step S303 to the gNB 200 as notification information. The RRC message may include MBS session information associated with the notification information. As described above, the RRC message may be a UE assistance information message or an MBS interest indication message.

[0105] In step S305, the gNB 200 determines whether to transition the UE 100 to the RRC inactive state based on the notification information received in step S304. The subsequent operations (steps S306 to S308) are the same as or similar to those of the above embodiment.

[0106] Although Figure 9 the operation example shows an example in which the UE 100 sends notification information to the gNB 200, the AMF 300A may also send notification information to the gNB 200. Figure 10 shows Figure 9 a flowchart of a modified example of the operation.

[0107] Steps S401 and S402 are the same as or similar to the Figure 9 operation.

[0108] In step S403, the AMF 300A specifies the UL service characteristic parameters of the multicast session.

[0109] In step S404, the AMF 300A sends an NG-application protocol (AP) message including the UL service characteristic parameters specified in step S403 to the gNB 200 on the NG interface as notification information. The message may include MBS session information associated with the notification information.

[0110] In step S405, the gNB 200 determines whether to transition the UE 100 to the RRC inactive state based on the notification information received in step S404. The subsequent operations (steps S406 to S408) are the same as or similar to the Figure 9 operation.

[0111] Other embodiments

[0112] Although multicast reception in the RRC inactive state is mainly described in the above embodiments, the operations according to the above embodiments are also applicable to multicast reception in the RRC idle state. That is, the "RRC inactive state" in the operations according to the above embodiments and their modified examples can be interpreted as the "RRC idle state". Regarding the RRC idle state, RRC resume can be interpreted as RRC establishment.

[0113] The above operation processes can be implemented separately and independently, and can also be implemented by a combination of two or more operation processes. For example, some steps in one operation process can be added to another operation process, or some steps in one operation process can be replaced by some steps in another operation process. In each process, not all steps need to be executed, but only some steps can be executed.

[0114] Although an example where the base station is an NR base station (gNB) has been described in the above embodiments and examples, the base station can be an LTE base station (eNB) or a 6G base station. The base station can be a relay node, such as an integrated access and backhaul (IAB) node. The base station can be the DU of an IAB node. The UE 100 can be the mobile terminal (MT) of an IAB node.

[0115] Although the term "network node" mainly refers to a base station, it can also refer to a device in the core network or a part of a base station (CU, DU, or RU).

[0116] A program that causes a computer to execute each process performed by the UE 100 or the gNB 200 can be provided. The program can be recorded in a computer-readable medium. Using the computer-readable medium enables the program to be installed on the computer. Here, the computer-readable medium on which the program is recorded can be a non-transitory recording medium. The non-transitory recording medium is not specifically limited, and can be, for example, a recording medium such as a CD-ROM or a DVD-ROM. The circuit for performing the process to be performed by the UE 100 or the gNB 200 can be integrated, and at least a part of the UE 100 or the gNB 200 can be implemented as a semiconductor integrated circuit (chipset, system on chip (SoC)).

[0117] Unless otherwise explicitly stated, the phrases "based on" and "depending on / responsive to" as used in this disclosure do not mean "based only on" and "depending only on / responsive only to". The phrase "based on" means both "based only on" and "based at least in part on". The phrase "depending on" means both "depending only on" and "depending at least in part on". The terms "comprising", "including" and their variants do not mean "including only the items described", but mean "may include only the items described" or "may include not only the items described but also other items". The term "or" as used in this disclosure is not intended to be an "exclusive or". Any reference to elements using names such as "first" and "second" in this disclosure generally does not limit the number or order of these elements. These names may be used herein as a convenient way to distinguish two or more elements. Thus, the reference to a first element and a second element does not mean that only two elements may be employed there or that the first element needs to be before the second element in some way. For example, when adding English articles such as "a", "an" and "the" to this disclosure through translation, these articles include the plural unless otherwise explicitly indicated in the context.

[0118] The embodiments have been described in detail above with reference to the accompanying drawings, but the specific configurations are not limited to the above configurations, and various design changes can be made without departing from the gist of this disclosure.

[0119] This application claims the priority of Japanese Patent Application No. 2022-155369 (filed on September 28, 2022), the entire content of which is incorporated herein by reference.

[0120] Supplementary Notes

[0121] The features related to the above embodiments are described below as supplements.

[0122] Supplementary Note 1

[0123] A communication method used in a mobile communication system configured to provide multicast / broadcast service (MBS), the communication method comprising the steps of:

[0124] Sending multicast data from a network node to a user equipment in a radio resource control (RRC) connected state via a multicast session;

[0125] Receiving, by the network node, notification information for determining whether to cause the user equipment to receive a multicast session from another device in an RRC inactive state, the another device being at least one of a user equipment or a core network device; and

[0126] Based on the notification information, the network node determines whether to cause the user equipment to transition from the RRC connected state to the RRC inactive state.

[0127] Supplementary Note 2

[0128] According to the communication method described in Supplementary Note 1, wherein the notification information is information based on the uplink service characteristic parameters of the multicast session.

[0129] Supplementary Note 3

[0130] According to the communication method described in Supplementary Note 2, it further includes the following steps:

[0131] The other device designates the uplink service characteristic parameters of the multicast session;

[0132] Based on the service characteristic parameters, the other device sends information indicating whether the user equipment is configured to perform reception of the multicast session in the RRC inactive state to the network node as the notification information.

[0133] Supplementary Note 4

[0134] According to the communication method described in Supplementary Note 2, it further includes the following steps:

[0135] The other device designates the uplink service characteristic parameters of the multicast session;

[0136] The other device sends the service characteristic parameters to the network node as the notification information.

[0137] Supplementary Note 5

[0138] According to the communication method described in any one of Supplementary Notes 2 to 4,

[0139] wherein the service characteristic parameters include at least one parameter selected from the group consisting of: a parameter indicating the existence of the uplink transmission of the multicast session, a parameter indicating the probability or frequency of occurrence of the uplink transmission of the multicast session per unit time, an allowable delay parameter of the uplink transmission of the multicast session, and a parameter indicating the size of the uplink transmission data of the multicast session.

[0140] Supplementary Note 6

[0141] A network node used in a mobile communication system, the mobile communication system being configured to provide multicast / broadcast services (MBS), the network node comprising:

[0142] A transmitter, configured to transmit multicast data to a user equipment in a Radio Resource Control (RRC) connected state via a multicast session;

[0143] A receiver, configured to receive notification information for determining whether to cause the user equipment to receive a multicast session from another device in an RRC inactive state, the another device being at least one of a user equipment or a core network device; and

[0144] A controller, configured to determine whether to cause the user equipment to transition from an RRC connected state to an RRC inactive state based on the notification information.

[0145] Supplementary Note 7

[0146] A user equipment used in a mobile communication system, the mobile communication system being configured to provide a Multicast / Broadcast Service (MBS), the user equipment comprising:

[0147] A receiver, configured to: when the user equipment is in a Radio Resource Control RRC connected state, receive multicast data from a network node via a multicast session; and

[0148] A transmitter, configured to send notification information to the network node so that the network node determines whether to cause the user equipment to receive the multicast session in an RRC inactive state.

[0149] Reference Numerals

[0150] 1: Mobile communication system

[0151] 10: RAN

[0152] 20: CN

[0153] 100: User Equipment (UE)

[0154] 110: Receiver

[0155] 120: Transmitter

[0156] 130: Controller

[0157] 200: gNB (Base Station)

[0158] 210: Transmitter

[0159] 220: Receiver

[0160] 230: Controller

[0161] 240: Backhaul Communicator

[0162] 300A: AMF.

Claims

1. A communication method used in a mobile communication system, the mobile communication system being configured to provide a multicast / broadcast service MBS, the communication method comprising the following steps: Sending multicast data from a network node to a user equipment via a multicast session, the user equipment being in a radio resource control RRC connected state; Determining, by the network node, whether to cause the user equipment to perform reception of the multicast session in the RRC inactive state; And Based on the determination, determining, by a base station, whether to cause the user equipment to transition from the RRC connected state to the RRC inactive state.

2. The communication method according to claim 1, wherein, The determination includes: determining, by the network node based on notification information provided by a core network device, whether to cause the user equipment to perform reception of the multicast session in the RRC inactive state.

3. The communication method according to claim 2, wherein, The notification information includes information indicating whether the user equipment is configured to perform reception of the multicast session in the RRC inactive state.

4. The communication method according to claim 2, wherein, The notification information is information based on uplink traffic characteristic parameters of the multicast session.

5. The communication method according to claim 2, further comprising the following steps: Specifying, by the core network device, uplink traffic characteristic parameters of the multicast session; Based on the traffic characteristic parameters, sending, by the core network device to the network node, information indicating whether the user equipment is configured to perform reception of the multicast session in the RRC inactive state as the notification information.

6. The communication method according to claim 2, further comprising the following steps: Specifying, by the core network device, uplink traffic characteristic parameters of the multicast session; Sending, by the core network device to the network node, the traffic characteristic parameters as the notification information.

7. The communication method according to any one of claims 4 to 6, Among them, The traffic characteristic parameters include at least one parameter selected from the group consisting of: a parameter indicating the existence of uplink transmission of the multicast session, a parameter indicating the probability or frequency of occurrence of uplink transmission of the multicast session per unit time, an allowable delay parameter for uplink transmission of the multicast session, a parameter indicating the size of uplink transmission data of the multicast session.

8. A network node used in a mobile communication system, the mobile communication system being configured to provide a multicast / broadcast service MBS, the network node comprising: A transmitter configured to send multicast data to a user equipment in a radio resource control RRC connected state via a multicast session; And A controller configured to determine whether to cause the user equipment to perform reception of the multicast session in the RRC inactive state, wherein the controller is configured to determine whether to cause the user equipment to transition from the RRC connected state to the RRC inactive state based on the determination.

9. A user equipment used in a mobile communication system, the mobile communication system being configured to provide a multicast / broadcast service MBS, the user equipment comprising: A receiver configured to receive multicast data from a network node via a multicast session when the user equipment is in a radio resource control RRC connected state; and a transmitter, configured to send notification information to the network node so that the network node determines whether to cause the user equipment to perform reception of the multicast session in the RRC inactive state.

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