COMMUNICATION METHOD, NETWORK NODE, AND CORE NETWORK DEVICE

Abstract

This communication method comprises: a step in which a network node transmits multicast data to a user device in a radio resource control (RCC)-connected state via a multicast session; a step in which the network node receives, from the user device and another device which is at least one of core network devices, notification information for determining whether or not to have the reception of the multicast session executed by the user device in an RRC-inactive state; and a step in which the network node determines, on the basis of the notification information, whether or not to transition the user device from the RRC-connected state to the RRC-inactive state.

Description

Communication method, base station, and user equipment

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

[0002] The 3rd Generation Partnership Project (3GPP) (registered trademark; the same applies hereinafter) defines the technical specifications for NR (New Radio), a fifth-generation (5G) wireless access technology. Compared to LTE (Long Term Evolution), a fourth-generation (4G) wireless access technology, NR has features such as high speed, large capacity, high reliability, and low latency. 3GPP defines the technical specifications for 5G / NR multicast / broadcast services (MBS) (see, for example, Non-Patent Document 1).

[0003] 3GPP Technical Specification: TS 38.300 V17.1.0

[0004] A communication method according to a first aspect is a communication method used in a mobile communication system that provides a multicast / broadcast service (MBS), and includes the steps of: a network node (or a network device) transmitting multicast data to a user equipment in a radio resource control (RRC) connected state via a multicast session; the network node receiving notification information from another device, which is at least one of the user equipment and a core network device, for determining whether to cause the user equipment to receive the multicast session in an RRC inactive state; and the network node deciding whether to transition the user equipment from the RRC connected state to the RRC inactive state based on the notification information.

[0005] A network node according to a second aspect is a network node used in a mobile communication system that provides a multicast / broadcast service (MBS), and comprises: a transmitter that transmits multicast data via a multicast session to a user equipment in a radio resource control (RRC) connected state; a receiver that receives notification information from another device, which is at least one of the user equipment and a core network device, for determining whether or not to cause the user equipment to receive the multicast session in an RRC inactive state; and a controller that determines whether or not to transition the user equipment from the RRC connected state to the RRC inactive state based on the notification information.

[0006] A user equipment according to a third aspect is a user equipment used in a mobile communication system that provides a multicast / broadcast service (MBS), and comprises: a receiving unit that receives 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 transmitting unit that transmits notification information to the network node to enable the network node to determine whether or not to cause the user equipment to receive the multicast session in an RRC inactive state.

[0007] 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram showing the configuration of a UE (user equipment) according to an embodiment. FIG. 3 is a diagram showing the configuration of a gNB (base station) according to an embodiment. FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). FIG. 6 is a diagram for explaining an operation that enables a UE in an RRC inactive state to perform multicast reception. FIG. 7 is a diagram showing an example of operation of a mobile communication system according to an embodiment. FIG. 8 is a diagram showing a modified example of the operation of FIG. 7. FIG. 9 is a diagram showing an example of operation of a mobile communication system according to a modified example. FIG. 9 is a diagram showing a modified example of the operation of FIG.

[0008] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0009] (System Configuration) Fig. 1 is a diagram showing the configuration of a mobile communication system 1 according to an embodiment. The mobile communication system 1 conforms to the 3GPP standard 5th Generation System (5GS). In the following description, 5GS is used as an example, but the mobile communication system may also be at least partially based on an LTE (Long Term Evolution) system. The mobile communication system may also be at least partially based on a 6th Generation (6G) system.

[0010] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN: Next Generation Radio Access Network) 10, and a 5G core network (5GC: 5G Core Network) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10 (or network 10). The 5GC 20 may be simply referred to as the core network (CN) 20.

[0011] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone) and / or a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0012] The NG-RAN 10 includes a base station (called a "gNB" in a 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource for wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0013] In addition, gNBs can also be connected to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also be connected to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0014] The 5GC20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0015] 2 is a diagram showing the configuration of a UE 100 (user equipment) according to an embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit that performs wireless communication with the gNB 200.

[0016] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0017] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0018] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer described below. The operations of the UE 100 described above and below may be operations under the control of the control unit 230. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0019] 3 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 communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

[0020] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0021] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0022] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer described below. The operations of the gNB 200 described above and below may be operations under the control of the control unit 230. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0023] The backhaul communication unit 240 is connected to adjacent base stations via an Xn interface, which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. Note that the gNB 200 is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and the two units may be connected by an F1 interface, which is a fronthaul interface.

[0024] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0025] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0026] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires the successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC parity bit scrambled by the RNTI added.

[0027] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of the UE 100 and the MAC layer of the gNB 200 via a transport channel. The MAC layer of the gNB 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE 100.

[0028] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via a logical channel.

[0029] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0030] The SDAP layer maps IP flows, which are units for Quality of Service (QoS) control by the core network, to radio bearers, which are units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP may not be required.

[0031] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0032] The protocol stack of the radio interface of the control plane has an RRC (Radio Resource Control) layer and an NAS (Non-Access Stratum) layer instead of the SDAP layer shown in FIG.

[0033] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0034] The NAS layer, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300A. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. Also, a layer lower than the NAS layer is called an AS layer.

[0035] (Overview of MBS) The mobile communication system 1 can perform resource-efficient distribution using multicast / broadcast services (MBS).

[0036] In the case of a multicast communication service (also referred to as "MBS multicast"), the same service and the same specific content data are simultaneously provided to a specific set of UEs. That is, not all UEs 100 within a multicast service area are permitted to receive the data. The multicast communication service is delivered to the UEs 100 using a multicast session, which is a type of MBS session. The UEs 100 can receive the multicast communication service in an RRC connected state using mechanisms such as Point-to-Point (PTP) and / or Point-to-Multipoint (PTM) delivery. The UEs 100 may also receive the multicast communication service in an RRC inactive (or RRC idle) state. Such a delivery mode is also referred to as "Delivery Mode 1".

[0037] In the case of a broadcast communication service (also referred to as "MBS broadcast"), the same service and the same specific content data are simultaneously provided to all UEs 100 in a geographical area. That is, all UEs 100 within the broadcast service area are permitted to receive the data. The broadcast communication service is delivered to the UEs 100 using a broadcast session, which is a type of MBS session. The UEs 100 can receive the broadcast communication service in any of the RRC idle state, the RRC inactive state, and the RRC connected state. This delivery mode is also referred to as "delivery mode 2".

[0038] The main logical channels used for MBS delivery are the Multicast Traffic Channel (MTCH), the Dedicated Traffic Channel (DTCH), and the Multicast Control Channel (MCCH). The MTCH is a PTM downlink channel for transmitting MBS data of either a multicast or broadcast session from the network 10 to the UE 100. The DTCH is a PTP channel for transmitting MBS data of a multicast session from the network 10 to the UE 100. The MCCH is a PTM downlink channel for transmitting MBS broadcast control information associated with one or more MTCHs from the network 10 to the UE 100.

[0039] Regarding the configuration for MBS broadcast, the UE 100 in the RRC idle state, the RRC inactive state, or the RRC connected state receives the MBS configuration for the broadcast session (e.g., parameters required for MTCH reception) via the MCCH. The parameters required for MCCH reception (MCCH configuration) are provided via system information. Specifically, the system information block type 20 (SIB20) includes the MCCH configuration. Note that the SIB type 21 (SIB21) includes information on service continuity for MBS broadcast reception. The MCCH provides a list of all broadcast services, including ongoing sessions, transmitted on the MTCH. The related information for the broadcast session includes the MBS session ID (e.g., TMGI (Temporary Mobile Group Identity)), related MTCH scheduling information, and information on neighboring cells providing a specific service on the MTCH.

[0040] On the other hand, with regard to MBS multicast, in the current 3GPP technical specifications, UE 100 can only receive multicast session data in the RRC connected state. When UE 100 that has joined a multicast session is in the RRC connected state and the multicast session is activated, gNB 200 transmits an RRC reconfiguration message including MBS configuration for the multicast session to UE 100. Such MBS configuration is also referred to as multicast radio bearer (MRB) configuration, MTCH configuration, or multicast configuration. Such MRB configuration (MRB-ToAddMod) includes other parameters such as an MBS session ID (mbs-SessionId), an MRB ID (mrb-Identity), and a PDCP configuration (pdcp-Config) for the MRB (multicast MRB) to be configured in UE 100.

[0041] In the following embodiment, an operation that enables the UE 100 in the RRC inactive state to perform multicast reception will be mainly described. Fig. 6 is a diagram showing an overview of the operation.

[0042] Possible solutions for the UE 100 in the RRC inactive state to perform multicast reception include a distribution mode 1 based solution shown in FIG. 6( a) and a distribution mode 2 based solution shown in FIG. 6( b).

[0043] In the distribution mode 1-based solution shown in Figure 6 (a), in step S1, gNB200 transmits an RRC Reconfiguration message including an MBS setting (multicast setting) for the multicast session to UE100 in the RRC connected state. UE100 receives multicast data on the MTCH via the multicast session (multicast MRB) based on the multicast setting received in the RRC Reconfiguration message.

[0044] In step S2, the gNB 200 transmits an RRC Release message to the UE 100 in the RRC Connected state to transition the UE 100 to the RRC inactive state. The RRC Release message includes a setting (Suspend Config.) for the RRC inactive state.

[0045] In step S3, in response to the reception of the RRC Release message in step S2, the UE 100 transitions from the RRC connected state to the RRC inactive state.

[0046] In step S4, the UE 100 in the RRC inactive state continues to use the multicast setting in step S1 to receive multicast data on the MTCH via the multicast session.

[0047] This enables the UE 100 in the RRC inactive state to perform multicast reception. Note that although an example of performing multicast configuration using an RRC Reconfiguration message has been described, multicast configuration may also be performed using an RRC Release message.

[0048] The RRC Reconfiguration message and the RRC Release message are both RRC messages transmitted individually to a UE on a Dedicated Control Channel (DCCH), and are hereinafter also referred to as dedicated RRC messages.

[0049] On the other hand, in the distribution mode 2-based solution shown in FIG. 6(b), in step S11, the gNB 200 transmits an RRC Release message to the UE 100 in the RRC connected state to transition the UE 100 to the RRC inactive state. The RRC Release message includes a setting (Suspend Config.) for the RRC inactive state.

[0050] In step S12, in response to the reception of the RRC Release message in step S11, the UE 100 transitions to an RRC inactive (INACTIVE) state.

[0051] In step S13, gNB200 transmits an MCCH including an MBS setting (multicast setting) for the multicast session. UE100 receives the MCCH. Note that UE100 receives SIB20 prior to receiving the MCCH, and receives the MCCH based on SIB20. Note that MCCH transmission (and reception) may be performed before step S11 or may be performed simultaneously with step S11.

[0052] In step S14, the UE 100 in the RRC inactive state receives multicast data on the MTCH via the multicast session based on the multicast setting received on the MCCH in step S13. This enables the UE 100 in the RRC inactive state to perform multicast reception.

[0053] (System operation example) When UE100 receives multicast from gNB200 in RRC inactive state, the load on the network (particularly gNB200) and the power consumption of UE100 can be reduced compared to when UE100 receives multicast from gNB200 in RRC connected state. Therefore, from the viewpoint of efficiency, it is preferable for gNB200 to transition UE100 in RRC connected state, which is capable of receiving multicast in RRC inactive state, to RRC inactive state.

[0054] However, among the UEs 100 that perform multicast reception, there are also UEs 100 that execute group call applications such as PTT (Push to Talk). Such UEs 100 may perform multicast reception of a multicast session on the downlink (DL) while performing uplink (UL) transmission of the multicast session. If such a UE 100 is transitioned to the RRC inactive state, the UE 100 needs to transition to the RRC connected state every time it performs UL transmission, which is actually inefficient. If the gNB 200 can grasp the traffic characteristics of the multicast session, the gNB 200 can appropriately determine whether to transition the UE 100 to the RRC inactive state. However, the gNB 200 does not have an application layer, and it is difficult for the gNB 200 alone to make such an appropriate decision.

[0055] In an embodiment, the gNB200 is able to appropriately determine whether or not to transition a UE100 performing multicast reception in an RRC connected state to an RRC inactive state, thereby enabling efficient multicast reception.

[0056] Specifically, in an embodiment, a gNB 200 that transmits multicast data to a UE 100 in an RRC connected state via a multicast session receives notification information from at least one of the UE 100 and a core network device to determine whether to cause the UE 100 to receive the multicast session in an RRC inactive state. In the embodiment, an example is described in which the core network device is an AMF 300A, but the core network device may be a UPF or the like. Based on the notification information, the gNB 200 determines whether to transition the UE 100 from an RRC connected state to an RRC inactive state. The notification information may be information based on UL traffic characteristic parameters of the multicast session. For example, if there is no UL transmission or the frequency is low, the gNB 200 determines to transition the UE 100 to an RRC inactive state because there is no need for the UE 100 to frequently transition to the RRC connected state even if the UE 100 receives the multicast session in an RRC inactive state.

[0057] In an embodiment, the UE 100 or the AMF 300A identifies a UL traffic characteristic parameter of a multicast session. The UE 100 or the AMF 300A transmits, to the gNB 200, information indicating whether the UE 100 can receive the multicast session in an RRC inactive state based on the UL traffic characteristic parameter.

[0058] 7 is a diagram showing an example of operation of the mobile communication system 1 according to the embodiment. Prior to this operation, it is assumed that the UE 100 has already joined a multicast session. Furthermore, it is assumed that the UE 100 is currently receiving or will soon receive multicast data in an RRC connected state.

[0059] In step S101, the gNB 200 transmits multicast settings required for receiving a multicast session (i.e., multicast reception) to the UE 100 in the RRC connected state in a dedicated RRC message (in the illustrated example, an RRC Reconfiguration message). The UE 100 receives the multicast settings in the dedicated RRC message. Such settings may include settings that permit or request the UE 100 to transmit notification information described below.

[0060] In step S102, gNB200 transmits multicast data on MTCH via the multicast session based on the multicast setting of step S101. UE100 receives multicast data on MTCH via the multicast session based on the multicast setting of step S201.

[0061] In step S103, the UE 100 identifies UL traffic characteristic parameters of the multicast session. The UL traffic characteristic parameters include at least one of a parameter indicating whether or not UL transmission of the multicast session is performed, a parameter indicating the occurrence probability or occurrence frequency of UL transmission of the multicast session per unit time, a tolerable delay parameter of UL transmission of the multicast session, and a parameter indicating an uplink transmission data size of the multicast session.

[0062] In step S104, the UE 100 determines whether multicast reception can be performed in the RRC inactive state based on the UL traffic characteristic parameter identified in step S103. The UE 100 may determine that multicast reception can be performed in the RRC inactive state, for example, in response to the satisfaction of one or a combination of two or more of the following conditions (a) to (d):

[0063] (a) There is no UL transmission, or UL transmission is not expected for a certain period of time in the future: For example, if the service type (application type) of the multicast session is a service without UL transmission (e.g., a television broadcasting service), or if the service involves UL transmission but UL transmission is not performed for a certain period of time (e.g., 10 seconds, etc.) (e.g., the microphone is turned off in a group call), the UE 100 may determine that multicast reception can be performed in an RRC inactive state. The certain period of time may be set in the UE 100 by the gNB 200 or the AMF 300A. The UE 100 may monitor the occurrence status of UL traffic in the multicast session and make the determination by prediction based on the monitoring results.

[0064] (b) Low frequency of UL transmission: For example, if the service type (application type) of the multicast session is a service that rarely performs UL transmission, the UE 100 may determine that multicast reception can be performed in the RRC inactive state. The frequency may be set to the UE 100 by the gNB 200 or the AMF 300A. The UE 100 may monitor the frequency of UL traffic occurrence in the multicast session and make the determination by prediction based on the monitoring result.

[0065] (c) UL transmission delay is allowed: For example, if the service type (application type) of the multicast session is a service that does not require a real-time response of the UL (text transmission, etc.), the UE 100 may determine that multicast reception can be performed in the RRC inactive state. The delay threshold (reference value) may be set in the UE 100 by the gNB 200 or the AMF 300A.

[0066] (d) The size of the UL transmission data is small: For example, if the service type (application type) of the multicast session is a service that only transmits small data sizes such as ACKs and / or short text messages in the UL (for example, in live video distribution, only text messages are transmitted in the UL, or in firmware downloads, only ACKs are transmitted using an upper layer retransmission function such as FLUTE), the UE 100 may determine that multicast reception is executable in the RRC inactive state. The UE 100 may monitor the generation status of UL traffic in the multicast session and make this determination by prediction based on the monitoring results. The threshold for determining that the data size is small may be set in the UE 100 by the gNB 200 or the AMF 300A. In such a case, the UE 100 may perform UL transmission without transitioning to the RRC connected state using SDT (Small Data Transmission) technology, which performs UL transmission during a random access procedure. That is, the threshold may be the same as the data volume threshold of the SDT.

[0067] In step S105, UE100 transmits to gNB200 an RRC message including notification information indicating the determination result of step S104. In response to determining in step S104 that multicast reception is possible in the RRC inactive state, UE100 may transmit to gNB200 an RRC message including notification information indicating the determination result. gNB200 receives the RRC message. That is, UE100 may notify gNB200 that it can receive a 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 that identifies the multicast session (multicast service), and is, for example, TMGI.

[0068] The RRC message may be a UE Assistance Information message. "PreferredRRC-State" in "ReleasePreference" in the UE Assistance Information message indicates the RRC state desired by the UE 100. The UE 100 sets "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 transmit a UE Assistance Information message including a set of "preferredRRC-State" set to "inactive" and the additional information as notification information indicating that the multicast session can be received in the RRC inactive state.

[0069] The RRC message may be an MBS Interest Indication message. In the current technical specifications, the MBS Interest Indication message includes an MBS-ServiceList (specifically, a list of TMGIs) that is a list of MBS broadcast services that the UE 100 is receiving or wishes to receive. In an embodiment, the MBS-ServiceList may 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, in association with the TMGI of the MBS multicast service. Alternatively, the MBS Interest Indication message may be able to include, as a new information element, a TMGI that indicates a multicast session that can be received in an RRC inactive state.

[0070] In step S106, the gNB 200 determines whether to transition the UE 100 to the RRC inactive state based on the notification information received in step S105. Here, the description will proceed assuming that it has been determined to transition the UE 100 to the RRC inactive state.

[0071] In step S107, the gNB 200 transmits an RRC Release message including Suspend config. to the UE 100. The UE 100 receives the RRC Release message. The RRC Release message may include multicast settings required for receiving a multicast session.

[0072] In step S108, in response to the reception of the RRC Release message in step S107, the UE 100 transitions from the RRC connected state to the RRC inactive state.

[0073] In step S109, UE100 that has transitioned to the RRC inactive state receives multicast data on the MTCH via a multicast session based on the multicast setting set in step S101 or S107. UE100 may receive multicast data on the MTCH via a multicast session based on the multicast setting transmitted on the MCCH from gNB200.

[0074] In the operation example of Figure 7, an example is shown in which notification information is transmitted from UE 100 to gNB 200, but notification information may also be transmitted from AMF 300A to gNB 200. Figure 8 is a diagram showing a modified example of the operation of Figure 7. Here, differences from the operation of Figure 7 will be described, and overlapping descriptions will be omitted.

[0075] Steps S201 and S202 are the same as the operations in FIG.

[0076] In step S203, AMF300A identifies UL traffic characteristic parameters of the multicast session.

[0077] In step S204, the AMF 300A determines whether the UE 100 can perform multicast reception in the RRC inactive state based on the UL traffic characteristic parameters identified in step S203. The method of this determination is the same as the method described above.

[0078] In step S205, the AMF 300A transmits an NG-AP (Application Protocol) message including notification information indicating the determination result of step S204 to the gNB 200 on the NG interface. The message may include MBS session information associated with the notification information. The message may be an INITIAL CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message.

[0079] 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. Subsequent operations (steps S207 to S209) are the same as those in FIG. 7 .

[0080] (Modified Example of Operation) In this modified example, UE100 or AMF300A identifies the UL traffic characteristic parameters of the multicast session and transmits the UL traffic characteristic parameters to gNB200 as notification information. That is, in this modified example, more detailed information (determination materials) than in the above-described embodiment is provided to gNB200 as notification information. Below, differences from the operation of the above-described embodiment will be described, and overlapping descriptions will be omitted.

[0081] FIG. 9 is a diagram showing an example of the operation of the mobile communication system 1 according to this modification.

[0082] Steps S301 and S302 are the same as the operations in the above-described embodiment.

[0083] In step S303, the UE 100 identifies UL traffic characteristic parameters of the multicast session. The UL traffic characteristic parameters include at least one of a parameter indicating whether or not UL transmission of the multicast session is performed, a parameter indicating the occurrence probability or occurrence frequency of UL transmission of the multicast session per unit time, an allowable delay parameter of UL transmission of the multicast session, and a parameter indicating an uplink transmission data size of the multicast session.

[0084] In step S304, the UE 100 transmits an RRC message including the UL traffic characteristic parameters identified in step S303 as notification information to the gNB 200. 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.

[0085] 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. Subsequent operations (steps S306 to S308) are the same as those in the above-described embodiment.

[0086] In the operation example of Figure 9, an example is shown in which notification information is transmitted from UE 100 to gNB 200, but the notification information may also be transmitted from AMF 300A to gNB 200. Figure 10 is a diagram showing a modified example of the operation of Figure 9.

[0087] Steps S401 and S402 are the same as the operations in FIG.

[0088] In step S403, AMF300A identifies UL traffic characteristic parameters of the multicast session.

[0089] In step S404, the AMF 300A transmits an NG-AP (Application Protocol) message including the UL traffic characteristic parameters identified in step S403 as notification information to the gNB 200 on the NG interface. The message may include MBS session information associated with the notification information.

[0090] 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. Subsequent operations (steps S406 to S408) are the same as those in FIG. 9 .

[0091] (Other Embodiments) In the above-described embodiment, multicast reception in the RRC inactive state has been mainly described, but the operation according to the above-described embodiment may be applied to multicast reception in the RRC idle state. That is, the "RRC inactive state" in the operation according to the above-described embodiment and its modified examples may be read as the "RRC idle state." In the case of the RRC idle state, RRC restoration (Resume) is read as RRC establishment (Establishment).

[0092] The above-described operational flows are not limited to being implemented independently, but can also be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. In each flow, it is not necessary to execute all steps, and only some steps may be executed.

[0093] In the above-described embodiments and examples, an example in which the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. The base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of the IAB node. The UE 100 may also be an MT (Mobile Termination) of the IAB node.

[0094] Also, the term "network node" primarily refers to a base station, but may also refer to a device in the core network or part of a base station (CU, DU, or RU).

[0095] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. The program may be recorded on a computer-readable medium. Using a computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by the UE 100 or the gNB 200 may be integrated, and at least a portion of the UE 100 or the gNB 200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0096] As used in this disclosure, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0097] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0098] This application claims priority from Japanese Patent Application No. 2022-155369 (filed September 28, 2022), the entire contents of which are incorporated herein by reference.

[0099] (Additional Notes) Additional notes will be given regarding the features of the above-described embodiment.

[0100] (Supplementary Note 1) A communication method used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a step in which a network node transmits multicast data to a user equipment in a radio resource control (RRC) connected state via a multicast session; a step in which the network node receives notification information from another device, which is at least one of the user equipment and a core network device, for determining whether or not to cause the user equipment to receive the multicast session in an RRC inactive state; and a step in which the network node decides whether or not to transition the user equipment from the RRC connected state to the RRC inactive state based on the notification information.

[0101] (Supplementary Note 2) The communication method according to Supplementary Note 1, wherein the notification information is information based on uplink traffic characteristic parameters of the multicast session.

[0102] (Supplementary Note 3) The communication method according to Supplementary Note 2, further comprising the steps of: the other device identifying uplink traffic characteristic parameters of the multicast session; and the other device transmitting, to the network node, information indicating whether the user equipment is able to receive the multicast session in the RRC inactive state based on the traffic characteristic parameters, as the notification information.

[0103] (Supplementary Note 4) The communication method according to Supplementary Note 2, further comprising the steps of: the other device identifying uplink traffic characteristic parameters of the multicast session; and the other device transmitting the traffic characteristic parameters to the network node as the notification information.

[0104] (Supplementary Note 5) The communication method according to any one of Supplementary Notes 2 to 4, wherein the traffic characteristic parameter includes at least one of a parameter indicating whether or not uplink transmission of the multicast session is performed, a parameter indicating an occurrence probability or occurrence frequency of uplink transmission of the multicast session per unit time, an allowable delay parameter for uplink transmission of the multicast session, and a parameter indicating an uplink transmission data size of the multicast session.

[0105] (Supplementary Note 6) A network node used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a transmitter that transmits multicast data via a multicast session to a user equipment in a radio resource control (RRC) connected state; a receiver that receives notification information from another device that is at least one of the user equipment and a core network device, for determining whether or not to cause the user equipment to receive the multicast session in an RRC inactive state; and a controller that determines whether or not to transition the user equipment from the RRC connected state to the RRC inactive state based on the notification information.

[0106] (Supplementary Note 7) A user equipment used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a receiver that receives 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 that transmits notification information to the network node, for the network node to determine whether or not to cause the user equipment to receive the multicast session in an RRC inactive state.

[0107] 1: Mobile communication system 10: RAN 20: CN 100: UE (user equipment) 110: Receiving unit 120: Transmitting unit 130: Control unit 200: gNB (base station) 210: Transmitting unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit 300A: AMF

Claims

1. A communication method for use in a mobile communication system providing a multicast / broadcast service (MBS), comprising: a network node transmitting multicast data to a user equipment in a Radio Resource Control (RRC) Connected state via a multicast session; The network node determines whether to cause the user equipment to receive the multicast session in an RRC inactive state; and determining, based on the determination, whether to transition the user equipment from the RRC connected state to the RRC inactive state; The determination includes determining, by the network node, whether to cause the user equipment to receive the multicast session in the RRC inactive state based on notification information provided by a core network device; The notification information includes information regarding an uplink transmission frequency of the user equipment in the multicast session. Communication methods.

2. The notification information includes information indicating whether the user equipment is capable of receiving the multicast session in the RRC inactive state. The communication method according to claim 1 .

3. The determination includes determining, by the network node, whether or not the user equipment is able to receive the multicast session in the RRC inactive state based on an allowable delay of the multicast session provided by the core network device. The communication method according to claim 1 .

4. A network node for use in a mobile communication system providing a multicast / broadcast service (MBS), comprising: A transmitter that transmits multicast data via a multicast session to a user equipment in a radio resource control (RRC) connected state; A control unit that determines whether to cause the user equipment to receive the multicast session in an RRC inactive state. The control unit determines whether to transition the user equipment from the RRC connected state to the RRC inactive state based on the determination, The determination includes determining whether to cause the user equipment to receive the multicast session in the RRC inactive state based on notification information provided from a core network device; The notification information includes information regarding an uplink transmission frequency of the user equipment in the multicast session. Network node.

5. A core network device for use in a mobile communication system providing a multicast / broadcast service (MBS), comprising: A transmitting unit configured to transmit notification information to a network node for the network node to determine whether or not to cause a user equipment that is in a radio resource control (RRC) connected state and that receives multicast data from a network node via a multicast session to receive the multicast session in an RRC inactive state, The notification information includes information regarding an uplink transmission frequency of the user equipment in the multicast session. Core network equipment.