Communication method and user device

Abstract

This communication method, executed by a user device in a mobile communication system that provides an MBS, includes: establishing a multicast MRB on the basis of a first MRB configuration configured from a network in an RRC connected state; receiving, from the network, a multicast session corresponding to a first MBS session ID included in the first MRB configuration by using the established multicast MRB; receiving, from the network, a second MRB configuration including a second MBS session ID, the second MRB configuration being information for configuring a multicast MRB for an RRC inactive state; and performing a configuration change related to the established multicast MRB on the basis of the second MRB configuration if the second MBS session ID matches the first MBS session ID.

Description

Communication method and user device

[0001] The present disclosure relates to a communication method and user equipment for use 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 also defines the technical specifications for 5G / NR multicast / broadcast services (MBS).

[0003] In 3GPP Release 17, reception of MBS multicast (i.e., multicast reception) is possible only for user equipment in a radio resource control (RRC) connected state (see, for example, Non-Patent Document 1). In contrast, in 3GPP Release 18, the technical specifications are planned to be extended so that user equipment in an RRC inactive state can perform multicast reception.

[0004] 3GPP Technical Specification: TS 38.300 V17.5.0

[0005] A communication method according to a first aspect is a communication method executed by a user equipment in a mobile communication system that provides a multicast broadcast service (MBS), and includes the steps of: in an RRC connected state, establishing a multicast radio bearer (MRB) based on an MRB setting configured from a network; receiving from the network, using the established multicast MRB, a multicast session corresponding to a first MBS session ID included in the MRB setting; receiving from the network a multicast setting that is information for configuring multicast reception for an RRC inactive state, the multicast setting including a second MBS session ID; and applying the multicast setting when receiving, in the RRC inactive state, the multicast session corresponding to the second MBS session ID in the same cell that received the multicast session corresponding to the first MBS session ID in the RRC connected state.

[0006] A communication method according to a second aspect is a communication method executed by a user device in a mobile communication system that provides a multicast broadcast service (MBS), and includes the steps of: in an RRC connected state, establishing a multicast radio bearer (MRB) based on a first MRB setting configured from a network; receiving from the network, using the established multicast MRB, a multicast session corresponding to a first MBS session ID included in the first MRB setting; receiving from the network a second MRB setting that is information for configuring a multicast MRB for an RRC inactive state, the second MRB setting including a second MBS session ID; and, if the second MBS session ID matches the first MBS session ID, changing the setting of the established multicast MRB based on the second MRB setting.

[0007] A user device according to a third aspect is a user device used in a mobile communication system that provides a multicast broadcast service (MBS), and is equipped with a control unit that executes the following processes: in an RRC connected state, establishing a multicast radio bearer (MRB) based on a first MRB setting configured from a network; using the established multicast MRB, receiving from the network a multicast session corresponding to a first MBS session ID included in the first MRB setting; receiving from the network a second MRB setting that is information for configuring a multicast MRB for an RRC inactive state and includes a second MRB session ID; and, if the second MBS session ID matches the first MBS session ID, changing the settings for the established multicast MRB based on the second MRB setting.

[0008] 1 is a diagram showing an example of the configuration of a mobile communication system according to an embodiment; FIG. 2 is a diagram showing an example of the configuration of a UE (user equipment) according to an embodiment; FIG. 3 is a diagram showing an example of the configuration of a gNB (network node) according to an embodiment; FIG. 4 is a diagram showing a protocol stack configuration of a radio interface of a user plane that handles data; FIG. 5 is a diagram showing a protocol stack configuration of a radio interface of a control plane that handles signaling (control signals); FIG. 6 is a diagram for explaining an assumed scenario according to an embodiment; FIG. 7 is a diagram for explaining an assumed scenario according to an embodiment; FIG. 8 is a diagram showing a first operation example of a UE according to an embodiment; FIG. 9 is a diagram showing a second operation example of a UE according to an embodiment;

[0009] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0010] (1) System Configuration Example Fig. 1 is a diagram showing a configuration example of a mobile communication system 1 according to an embodiment. The mobile communication system 1 conforms to the 3GPP standard 5th Generation System (5GS). Although 5GS will be described below as an example, the mobile communication system may be at least partially based on an LTE (Long Term Evolution) system. The mobile communication system may be at least partially based on a 6th Generation (6G) system.

[0011] 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. Furthermore, the 5GC 20 may be simply referred to as the core network (CN) 20. The RAN 10 and the CN 20 constitute a network 5 of the mobile communication system 1.

[0012] 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), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0013] The NG-RAN 10 includes a base station (referred to as "gNB" in the 5G system) 200, which is a type of network node. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0014] In addition, gNBs can also be connected to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also be connected to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0015] The 5GC20 includes an 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.

[0016] 2 is a diagram illustrating an example 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 configure a wireless communication unit that performs wireless communication with the gNB 200.

[0017] 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.

[0018] 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.

[0019] 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 controlled by 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.

[0020] 3 is a diagram showing an example configuration of a gNB 200 (network node) according to an embodiment. The gNB 200 has 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0026] 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.

[0027] 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 successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC (Cyclic Redundancy Code) parity bit scrambled by the RNTI added.

[0028] 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.

[0029] 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.

[0030] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0031] 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.

[0032] 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).

[0033] 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.

[0034] 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.

[0035] The NAS layer (also simply referred to as "NAS") 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 referred to as the AS layer (also simply referred to as "AS").

[0036] (2) Overview of MBS The mobile communication system 1 can perform resource-efficient distribution using multicast / broadcast services (MBS).

[0037] (2.1) MBS Broadcast 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 session in any of the following states: RRC idle state, RRC inactive state, and RRC connected state.

[0038] Point-to-Multipoint (PTM) delivery is applied to broadcast communication services. In the case of PTM transmission, the gNB 200 delivers a single copy of an MBS packet to a set (group) of multiple UEs 100. For example, the gNB 200 schedules a group-common PDSCH scrambled by a G-RNTI (Group RNTI), which is a group-common RNTI, using a group-common PDCCH having a CRC scrambled by the G-RNTI.

[0039] In the case of a broadcast communication service, the UE 100 receives a broadcast session in the following procedure. First, the UE 100 receives a system information block type 20 (SIB20) from the gNB 200. The SIB20 includes a configuration of a multicast control channel (MCCH), which is a type of logical channel. Second, the UE 100 receives the MCCH from the gNB 200 based on the SIB20. The MCCH includes a PTM configuration. The PTM configuration transmits a configuration (MTCH configuration) for a multicast traffic channel (MTCH), which is a type of logical channel, and a broadcast MRB configuration, which is a multicast radio bearer (MRB) for the broadcast session. The information transmitted by the MCCH is sometimes referred to as MBS broadcast control information. Third, the UE 100 receives the MTCH based on the MCCH. The MTCH transmits the broadcast session (specifically, MBS data belonging to the broadcast session).

[0040] The MCCH is a PTM downlink channel for transmitting MBS broadcast control information associated with one or more MTCHs from the network 5 to the UE 100. The MTCH is a PTM downlink channel for transmitting MBS data of either a multicast session or a broadcast session from the network 5 to the UE 100.

[0041] (2.2) MBS Multicast 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.

[0042] The UE 100 can receive the multicast session only after joining the multicast session (session join). Joining the multicast session may mean being registered in the network 5 (CN 20) as the UE 100 that can receive the multicast session.

[0043] In the case of a multicast communication service, only UEs 100 in an RRC connected state can receive a multicast session in 3GPP Release 17. On the other hand, in 3GPP Release 18, the standard is extended so that UEs 100 in an RRC inactive state can also receive a multicast session.

[0044] (2.2.1) Multicast reception in RRC connected state UE100 in the RRC connected state can receive a multicast session (specifically, MBS data belonging to the multicast session) using mechanisms such as PTP (Point-to-Point) and / or PTM (Point-to-Multipoint) delivery.

[0045] In the case of a multicast communication service, the UE 100 in the RRC connected state receives a multicast session in the following procedure. First, the UE 100 receives an RRC Reconfiguration message from the gNB 200. The RRC Reconfiguration message is a message transmitted on a dedicated control channel (DCCH). The RRC Reconfiguration message transmits a setting (MTCH setting) for the MTCH for receiving the multicast session and a setting of a multicast MRB, which is an MRB for the multicast session. Second, the UE 100 receives the MTCH based on the RRC Reconfiguration message. The MTCH transmits the multicast session (specifically, MBS data belonging to the multicast session).

[0046] (2.2.2) Multicast Reception in RRC Inactive State The UE 100 in the RRC inactive state can receive a multicast session (specifically, MBS data belonging to the multicast session) using the PTM distribution mechanism.

[0047] In the case of a multicast communication service, the UE 100 in the RRC inactive state can receive a multicast session in the following procedure. First, the UE 100 in the RRC inactive state receives a newly introduced system information block (also referred to as "SIBx") from the gNB 200. The SIBx includes a configuration of a newly introduced MCCH (also referred to as "multicast MCCH"). Second, the UE 100 in the RRC inactive state receives a multicast MCCH from the gNB 200 based on the SIBx. The multicast MCCH includes a PTM configuration. The PTM configuration transmits a configuration for an MTCH for receiving a multicast session (MTCH configuration) and a configuration of an inactive MRB, which is an MRB for receiving a multicast session in the RRC inactive state (inactive MRB configuration). The MTCH configuration may be included in the multicast MRB configuration. Third, the UE 100 in the RRC inactive state receives the MTCH based on the multicast MCCH. The MTCH transmits the multicast session, specifically, the MBS data (i.e., multicast data) belonging to the multicast session.

[0048] When gNB200 configures UE100 to receive a multicast session in an RRC inactive state, it can send a PTM setting (multicast MRB setting) to UE100 using an RRC Release message including a suspend setting. In this case, when UE100 receives an RRC Release message including a PTM setting from gNB200, it transitions to an RRC inactive state and receives the multicast session (multicast reception) in the RRC inactive state.

[0049] (2.2.3) Group Notification When there is temporarily no data to transmit to UE 100 in an active multicast session, gNB 200 may transition UE 100 to an RRC inactive state. When the multicast session is deactivated, gNB 200 may transition UE 100 to an RRC idle state or an RRC inactive state.

[0050] A gNB 200 that supports MBS uses a group notification mechanism to notify UEs 100 in an RRC idle state or an RRC inactive state when a multicast session is activated by CN 20. For example, a gNB 200 that supports MBS may use a group notification mechanism to notify UEs 100 in an RRC inactive state when a multicast session has been activated and there is multicast session data to be distributed in the gNB 200.

[0051] Upon receiving the group notification, the UE 100 reconnects or resumes connection to the network 5 and transitions to the RRC connected state. The group notification is processed in the paging RNTI (P-RNTI) on the PDCCH, and the paging channel is monitored by the UE 100.

[0052] The group notification paging message includes a session identifier (MBS Session ID) that is used to page all UEs 100 in RRC idle and RRC inactive states that have joined the associated MBS multicast session, i.e., the UEs 100 are not paged individually.

[0053] When UE 100 transitions to the RRC connected state, UE 100 may stop monitoring group notifications related to a particular multicast session. That is, UE 100 stops checking the MBS session ID in paging messages. UE 100 does not monitor group notifications in cases where UE 100 leaves this multicast session, network 5 requests UE 100 to leave, or network 5 releases the multicast session.

[0054] The group notification may be performed using the MCCH or may be performed using an MCCH Change Notification. When the MCCH is used, the determination may be made based on whether or not an MTCH configuration for the MBS session of interest exists in the MCCH. When the MCCH Change Notification is used, the group notification may be notified in a predetermined bit of the DCI.

[0055] (3) Operation of the Mobile Communication System The operation of the mobile communication system 1 according to the embodiment will be described.

[0056] (3.1) Operation Overview In MBS multicast defined in 3GPP Release 17, the MRB ID of the multicast MRB is set from the gNB 200 to the UE 100, and the multicast MRB is managed by the MRB ID. The MRB ID is cell-specific. Such a multicast MRB is exclusive to the RRC connected state, and upon handover of the UE 100, the multicast MRB is reconfigured by the gNB 200 together with the MRB ID.

[0057] In the MBS broadcast defined in 3GPP Release 17, the MRB ID of the broadcast MRB is not set from the gNB 200 to the UE 100, the assignment of the MRB ID to the broadcast MRB is UE implementation dependent, and the broadcast MRB does not have an MRB ID. Therefore, the UE 100 that receives the broadcast in the RRC idle state or the RRC inactive state can perform cell reselection without considering the MRB ID.

[0058] On the other hand, in a scenario of 3GPP Release 18, that is, a scenario in which a UE 100 in an RRC inactive state performs multicast reception, the UE 100 performing multicast reception can perform cell reselection. Therefore, it is considered that an MRB ID is not set from the gNB 200 to the UE 100 for a multicast MRB for an RRC inactive state, as with a broadcast MRB. If the MRB ID is not set from the gNB 200 to the UE 100, there is a problem in that the multicast MRB cannot be managed by the MRB ID.

[0059] 6 and 7 are diagrams for explaining an assumed scenario according to the embodiment. In this assumed scenario, after a UE 100 that has already participated in a multicast session transitions from an RRC connected state to an RRC inactive state in cell a, the UE 100 performs cell reselection in the RRC inactive state to reselect a serving cell from cell a to cell b, and the UE 100 transitions to an RRC connected state in cell b. In the illustrated example, an example is shown in which cells a and b belong to different gNBs 200 (gNB 200a and gNB 200b), but cells a and b may belong to a single gNB 200.

[0060] In STEP 1 shown in FIG. 6, a multicast MRB for the RRC connected state is configured by the gNB 200a for the UE 100 in the RRC connected state in cell a. Specifically, the gNB 200a transmits an RRC Reconfiguration message including a first MRB setting for setting the multicast MRB to the UE 100. The UE 100 that receives the RRC Reconfiguration message establishes a multicast MRB and receives a multicast session (multicast data) on the MTCH using the multicast MRB. Here, it is assumed that the gNB 200a sets "A" as the MRB ID of the multicast MRB.

[0061] In STEP 2 shown in FIG. 6, UE 100 transitions from the RRC connected state to the RRC inactive state in cell a. Specifically, gNB 200a transmits to UE 100 an RRC Release message (i.e., an RRC Release message including a suspend setting) for transitioning UE 100 to the RRC inactive state. The suspend setting may include information indicating which multicast service (multicast session) is receivable in the RRC inactive state. UE 100 that has received the RRC Release message transitions to the RRC inactive state. The RRC Release message may include a second MRB setting for setting a multicast MRB for the RRC inactive state. gNB 200 may transmit (broadcast) the second MRB setting for setting a multicast MRB for the RRC inactive state on the multicast MCCH. The second MRB configuration does not include the MRB ID of the multicast MRB.

[0062] Here, UE 100 can suppress interruption of reception of multicast data (i.e., packet loss) by continuously using the multicast MRB (and the PDCP entity associated with the multicast MRB) established in the RRC connected state in the RRC inactive state. UE 100 can change (reconfigure) the multicast MRB established based on the first MRB setting based on the second MRB setting by associating the multicast MRB set in the first MRB setting with the multicast MRB set in the second MRB setting, and can continuously use the multicast MRB.

[0063] However, if the second MRB configuration transmitted in the RRC Release message or the multicast MCCH does not include an MRB ID, the UE 100 cannot associate the multicast MRB configured in the first MRB configuration with the multicast MRB configured in the second MRB configuration using the MRB ID as a key. Therefore, there is a problem that it is difficult for the UE 100 to continuously use the multicast MRB established in the RRC connected state in the RRC inactive state. To solve this problem, in an embodiment, the UE 100 associates the multicast MRB configured in the first MRB configuration with the multicast MRB configured in the second MRB configuration using an MBS session ID (TMGI: Temporary Mobile Group Identity) as a key, rather than the MRB ID. As a result, the UE 100 can continuously use the multicast MRB (and the PDCP entity associated with the multicast MRB) established in the RRC connected state in the RRC inactive state.

[0064] 7, UE 100 in the RRC inactive state performs cell reselection from cell a to cell b. Here, it is assumed that UE 100 continues to use the multicast MRB established in STEP 1 in the RRC inactive state after the setting change in STEP 2, and continues to receive the multicast session in the RRC inactive state.

[0065] In STEP 4 shown in FIG. 7, UE 100 starts an RRC connection resume procedure in cell b and transitions to the RRC connected state. Specifically, UE 100 transmits an RRC Resume Request message to gNB 200b, gNB 200b transmits an RRC Resume message to UE 100, and UE 100 transmits an RRC Resume Complete message to gNB 200b, thereby completing the RRC connection resume procedure and UE 100 transitions to the RRC connected state. gNB 200b transmits an RRC Reconfiguration message to UE 100, including a third MRB setting for setting a multicast MRB for the RRC connected state. Here, it is assumed that gNB200a sets "B" as the MRB ID of the multicast MRB.

[0066] Here, UE 100 can suppress interruption of reception of multicast data (i.e., packet loss) by continuously using the multicast MRB (and the PDCP entity associated with the multicast MRB) that was used in the RRC inactive state in the RRC connected state. UE 100 can change (reconfigure) the multicast MRB in use based on the third MRB setting by associating the multicast MRB set in the second MRB setting with the multicast MRB set in the third MRB setting, and can continuously use the multicast MRB.

[0067] However, if the multicast MRB used in the RRC inactive state does not have an MRB ID, the UE 100 cannot associate the multicast MRB used in the RRC inactive state with the multicast MRB set in the third MRB setting using the MRB ID as a key. Therefore, there is a problem that it is difficult for the UE 100 to continue to use the multicast MRB used in the RRC inactive state in the RRC connected state. To solve this problem, in the embodiment, the UE 100 associates the multicast MRB used in the RRC inactive state with the multicast MRB set in the third MRB setting using the MBS session ID as a key, rather than the MRB ID. This allows the UE 100 to continue to use the multicast MRB used in the RRC inactive state (and the PDCP entity associated with the multicast MRB) in the RRC connected state. Furthermore, the UE 100 can apply the MRB ID "B" set in the third MRB setting to the multicast MRB.

[0068] Thus, in the embodiment, the UE 100 uses the MBS session ID instead of the MRB ID to perform configuration handover (partial handover) between the multicast MRB for the RRC connected state and the MRB for the RRC inactive state. This makes it possible to take over the MRB configuration even if the gNB 200 does not set the MRB ID to the UE 100 for the multicast MRB for the RRC inactive state. In addition, since the PDCP entity associated with the multicast MRB can be maintained without being reset, the continuity of the multicast service can be improved.

[0069] (3.2) Operation Example at the Time of Transition from RRC Connected State to RRC Inactive State Fig. 8 is a diagram showing a first operation example of the UE 100 according to the embodiment. Specifically, the first operation example is an operation example at the time of transition from the RRC Connected state to the RRC Inactive state.

[0070] In step S11, the UE 100, in the RRC connected state, establishes a multicast MRB based on the first MRB setting set from the network 5 (gNB 200). Specifically, the UE 100 receives information for setting a multicast MRB for the RRC connected state, including a first MBS session ID and an MRB ID (for example, MRB ID = A), from the network 5 (gNB 200) in an RRC RRC Reconfiguration message, thereby establishing a multicast MRB and a PDCP entity and an RLC entity corresponding to the multicast MRB. The RRC RRC Reconfiguration message may include multiple first MRB settings corresponding to multiple multicast MRBs.

[0071] In step S12, UE 100 receives a multicast session corresponding to the first MBS session ID included in the first MRB setting from network 5 (gNB 200) using the multicast MRB established in step S11. Here, UE 100 receives data (multicast data) of the multicast session on MTCH.

[0072] In step S13, the UE 100 receives, from the network 5 (gNB 200), a second MRB configuration that is information for configuring a multicast MRB for the RRC inactive state and includes a second MBS session ID. Specifically, the UE 100 receives the second MRB configuration that does not include an MRB ID but includes the second MBS session ID via a multicast MCCH or an RRC Release message. The multicast MCCH or RRC Release message may include multiple second MRB configurations corresponding to multiple multicast MRBs.

[0073] In step S14, if the second MBS session ID included in the second MRB setting matches the first MBS session ID included in the first MRB setting, UE 100 changes the setting of the multicast MRB established in the first MRB setting based on the second MRB setting. Here, if the MBS session ID corresponding to the multicast MRB for the RRC connected state matches the MBS session ID corresponding to the multicast MRB for the RRC inactive state, UE 100 identifies the setting of the multicast MRB (specifically, the first and second MRB settings having the same MBS session ID). Then, UE 100 changes the setting of the multicast MRB for the RRC connected state using the two identified MRB settings. UE 100 changes the setting while maintaining the PDCP entity associated with the multicast MRB.

[0074] For example, the UE 100 compares the two identified MRB settings (the first and second MRB settings having the same MBS session ID) and performs at least one of the following processes 1) to 5).

[0075] 1) The UE 100 may not retain the MRB ID set in the RRC Reconfiguration message (first MRB setting). The UE 100 may discard the MRB ID set in the RRC Reconfiguration message (first MRB setting). Alternatively, the UE 100 may maintain the MRB ID set in the RRC Reconfiguration message (first MRB setting).

[0076] 2) The UE 100 replaces the PDCP configuration configured in the RRC Reconfiguration message (first MRB configuration) with the second MRB configuration. However, the UE 100 maintains the PDCP entity and PDCP COUNT without resetting them. The PDCP COUNT value is composed of a hyperframe number (HFN) and a PDCP sequence number (SN). The PDCP-SN is incremented upon reception of a PDCP packet. The HFN is incremented each time the PDCP-SN circulates. Meanwhile, the PDCP entity on the receiving side performs PDCP layer processing using the PDCP COUNT. By maintaining the PDCP entity and PDCP COUNT, the continuity of multicast reception can be improved.

[0077] 3) If a point-to-point (PTP) leg is configured for the multicast MRB in the RRC Reconfiguration message (first MRB configuration), the UE 100 discards or temporarily suspends the configuration of the PTP leg.

[0078] 4) When a point-to-multipoint (PTM) leg is configured in the multicast MRB in the RRC Reconfiguration message (first MRB configuration), the UE 100 changes the configuration of the PTM leg to a multicast MRB configuration for the RRC inactive state (second MRB configuration). Here, the UE 100 also changes the group DRX configuration to a multicast MRB configuration for the RRC inactive state. Furthermore, when changing the RLC configuration, the UE 100 may reset the RLC entity.

[0079] 5) If the PTM leg is not configured in the RRC Reconfiguration message (first MRB configuration), the UE 100 applies PTM reception (multicast reception) using the multicast MRB configuration for the RRC inactive state.

[0080] In step S15, after transitioning to the RRC inactive state, the UE 100 continues receiving the multicast session using the multicast MRB after the setting change in step S14.

[0081] (3.3) Operation example at the time of transition from RRC inactive state to RRC connected state Fig. 9 is a diagram showing a second operation example of the UE 100 according to the embodiment. Specifically, the second operation example is an operation example at the time of transition from the RRC inactive state to the RRC connected state. The second operation example may be an operation performed after the operation of the first operation example.

[0082] In step S21, UE 100 in the RRC inactive state receives a multicast session from network 5 (gNB 200) using a multicast MRB (specifically, a multicast MRB for the RRC inactive state) based on the second MRB setting for the RRC inactive state. Here, UE 100 receives data (multicast data) of the multicast session on MTCH.

[0083] In step S22, after the UE 100 transitions from the RRC inactive state to the RRC connected state by RRC connection resume, the UE 100 receives from the network 5 (gNB 200) a third MRB configuration including a third MBS session ID, which is information for configuring a multicast MRB for the RRC connected state. Here, the UE 100 in the RRC connected state receives the multicast MRB configuration for the RRC connected state in an RRC Reconfiguration message. Specifically, in the RRC connected state, the UE 100 receives a third MRB configuration including a third MBS session ID and an MRB ID (e.g., MRB ID = B) from the network 5 (gNB 200) in an RRC reconfiguration message. The RRC Reconfiguration message may include multiple third MRB configurations corresponding to multiple multicast MRBs.

[0084] In step S23, if the third MBS session ID received in the RRC Reconfiguration message matches the second MBS session ID corresponding to the multicast MRB in use, UE 100 in the RRC connected state changes the configuration of the multicast MRB based on the third MRB configuration. Here, if the MBS session ID corresponding to the multicast MRB for the RRC connected state matches the MBS session ID corresponding to the multicast MRB for the RRC inactive state, UE 100 identifies the configuration of the multicast MRB (specifically, the second and third MRB configurations having the same MBS session ID). Then, UE 100 changes the configuration of the multicast MRB for the RRC inactive state using the two identified MRB configurations. UE 100 changes the configuration while maintaining the PDCP entity associated with the multicast MRB. Furthermore, the UE 100 assigns the MRB ID included in the identified third MRB configuration to the multicast MRB.

[0085] For example, the UE 100 compares the two identified MRB configurations and performs at least one of the following processes 1) to 4).

[0086] 1) The UE 100 identifies the MRB ID set in the RRC Reconfiguration message (third MRB setting), and applies (holds) the identified MRB ID as the setting for the multicast MRB.

[0087] 2) The UE 100 replaces the PDCP configuration for the RRC inactive state configured in the second MRB configuration with the PDCP configuration configured in the RRC Reconfiguration message (third MRB configuration). However, the UE 100 maintains the PDCP entity and PDCP COUNT corresponding to the multicast MRB without resetting them.

[0088] 3) If a PTP leg is configured in the RRC Reconfiguration message (third MRB configuration), apply or resume application of the configuration of the PTP leg.

[0089] 4) When a PTM leg is configured in the RRC Reconfiguration message (third MRB configuration), the PTM leg configuration is changed to a multicast MRB configuration for an RRC connected state (third MRB configuration). The UE 100 also changes the group DRX configuration to a multicast MRB configuration for an RRC connected state. When changing the RLC configuration, the UE 100 may reset the RLC entity.

[0090] In step S24, the UE 100 in the RRC connected state continues receiving the multicast session by using the multicast MRB after the setting change in step S23.

[0091] (4) 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. In the RRC idle state, the above-described RRC resume (Resume) is replaced with RRC establishment (Establishment).

[0092] The above-described operational flows are not limited to being implemented independently, but can 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. Furthermore, the order of steps in each flow may be changed as appropriate.

[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] That is, the UE 100 may be a terminal function unit (a type of communication module) for a base station to control a repeater that relays signals. Such a terminal function unit is referred to as an MT. Examples of the MT include, in addition to the IAB-MT, an NCR (Network Controlled Repeater)-MT and a RIS (Reconfigurable Intelligent Surface)-MT.

[0095] The term "network node" primarily refers to a base station, but may also refer to a core network device or a part of a base station (CU, DU, or RU). A network node may also be configured by a combination of at least a part of a core network device and at least a part of a base station.

[0096] 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).

[0097] The functions performed by the UE 100 or the gNB 200 (network node) may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may also be a programmed processor that executes a program stored in memory. In this specification, circuitry, unit, or means refers to hardware that is programmed to perform the described functions or hardware that executes them. The hardware may be any hardware disclosed herein or any hardware known to be programmed or capable of performing the described functions. If the hardware is a processor, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0098] 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.

[0099] 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.

[0100] This application claims priority from Japanese Patent Application No. 2023-164162 (filed September 27, 2023), the entire contents of which are incorporated herein by reference.

[0101] (5) Supplementary Notes The following are additional notes regarding the features of the above-described embodiment.

[0102] (Supplementary Note 1) A communication method executed by a user equipment in a mobile communication system that provides a multicast broadcast service (MBS), the communication method comprising: in an RRC connected state, establishing a multicast radio bearer (MRB) based on a first multicast MRB setting configured from a network; receiving, from the network, a multicast session corresponding to a first MBS session ID included in the first MRB setting using the established multicast MRB; receiving, from the network, a second MRB setting that is information for configuring a multicast MRB for an RRC inactive state and includes a second MBS session ID; and, if the second MBS session ID matches the first MBS session ID, changing a setting for the established multicast MRB based on the second MRB setting.

[0103] (Supplementary Note 2) The communication method according to Supplementary Note 1, wherein the performing the configuration change includes performing the configuration change while maintaining a PDCP entity associated with the multicast MRB.

[0104] (Supplementary Note 3) The communication method according to Supplementary Note 1 or 2, further comprising receiving, in the RRC connected state, from the network, the first MRB configuration, which is information for configuring a multicast MRB for the RRC connected state and includes the first MBS session ID and an MRB ID, in an RRC reconfiguration message.

[0105] (Supplementary Note 4) The communication method according to any one of Supplementary Notes 1 to 3, wherein receiving the second MRB configuration includes receiving the second MRB configuration, which does not include an MRB ID but includes the second MBS session ID, in a multicast MCCH or an RRC release message.

[0106] (Supplementary Note 5) The communication method according to any one of Supplementary Notes 1 to 4, further comprising, after transitioning to the RRC inactive state, continuing reception of the multicast session using the multicast MRB after the setting change.

[0107] (Supplementary Note 6) The communication method described in any one of Supplementary Notes 1 to 5, further comprising: after transitioning from the RRC inactive state to the RRC connected state, receiving from the network a third MRB configuration, the third MRB configuration being information for configuring a multicast MRB for the RRC connected state, the third MRB configuration including a third MBS session ID; and if the third MBS session ID matches the second MBS session ID, changing the configuration of the multicast MRB based on the third MRB configuration.

[0108] (Supplementary Note 7) The communication method according to Supplementary Note 6, further comprising, after transitioning to the RRC connected state, continuing reception of the multicast session using the multicast MRB after the setting change.

[0109] (Supplementary Note 8) The communication method according to Supplementary Note 6 or 7, wherein performing the configuration change based on the third MRB configuration includes performing the configuration change while maintaining a PDCP entity associated with the multicast MRB.

[0110] (Supplementary Note 9) The communication method according to any one of Supplementary Notes 6 to 8, further comprising receiving, in the RRC connected state, the third MRB configuration including the third MBS session ID and an MRB ID from the network in an RRC reconfiguration message.

[0111] (Supplementary Note 10) The communication method according to Supplementary Note 9, wherein performing the setting change based on the third MRB setting includes assigning the MRB ID included in the third MRB setting to the multicast MRB.

[0112] (Supplementary Note 11) A user equipment used in a mobile communication system that provides a multicast broadcast service (MBS), comprising: a control unit that executes the following processes: in an RRC connected state, establishing a multicast radio bearer (MRB) based on a first MRB setting configured from a network; receiving from the network, using the established multicast MRB, a multicast session corresponding to a first MBS session ID included in the first MRB setting; receiving from the network a second MRB setting that is information for configuring a multicast MRB for an RRC inactive state and includes a second MRB session ID; and, if the second MBS session ID matches the first MBS session ID, changing the setting of the established multicast MRB based on the second MRB setting.

[0113] 1: Mobile communication system 5: Network 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

Claims

1. A communication method executed by a user device in a mobile communication system that provides a multicast broadcast service (MBS), comprising: in an RRC connected state, establishing a multicast radio bearer (MRB) based on a multicast MRB setting set from a network; receiving from the network a multicast session corresponding to a first MBS session ID included in the MRB setting using the established multicast MRB; receiving from the network a multicast setting including a second MBS session ID, the multicast setting being information for setting multicast reception for an RRC inactive state; and applying the multicast setting when a multicast session corresponding to the second MBS session ID is received in the RRC inactive state in the same cell as a cell that received the multicast session corresponding to the first MBS session ID in the RRC connected state.

2. The communication method according to claim 1, further comprising: maintaining the multicast MRB and a PDCP entity associated with the multicast MRB in the RRC inactive state; and receiving the multicast session using the multicast MRB in the RRC inactive state.

3. The communication method according to claim 1, further comprising: receiving, in the RRC connected state, information for configuring a multicast MRB for the RRC connected state, the MRB configuration including the first MBS session ID and an MRB ID, from the network in an RRC reconfiguration message.

4. The method of claim 1, wherein receiving the multicast configuration includes receiving the multicast configuration in an RRC release message that does not include an MRB ID and includes the second MBS session ID.

5. A communication method executed by a user device in a mobile communication system providing a multicast broadcast service (MBS), comprising: in an RRC connected state, establishing a multicast radio bearer (MRB) based on a first multicast MRB setting configured from a network; receiving from the network, using the established multicast MRB, a multicast session corresponding to a first MBS session ID included in the first MRB setting; receiving from the network a second MRB setting, which is information for configuring a multicast MRB for an RRC inactive state, the second MRB setting including a second MBS session ID; and, if the second MBS session ID matches the first MBS session ID, changing settings for the established multicast MRB based on the second MRB setting.

6. The communication method according to claim 5, wherein performing the configuration change includes performing the configuration change while maintaining a PDCP entity associated with the multicast MRB.

7. The communication method according to claim 5, further comprising: receiving, in the RRC connected state, the first MRB configuration, which is information for configuring a multicast MRB for the RRC connected state and includes the first MBS session ID and an MRB ID, from the network in an RRC reconfiguration message.

8. The communication method of claim 5, wherein receiving the second MRB configuration includes receiving the second MRB configuration in a multicast MCCH or an RRC release message, the second MRB configuration including the second MBS session ID without including an MRB ID.

9. The communication method according to claim 5, further comprising, after transitioning to the RRC inactive state, continuing reception of the multicast session using the multicast MRB after the setting change.

10. The communication method of claim 5, further comprising: after transitioning from the RRC inactive state to the RRC connected state, receiving from the network a third MRB setting, the third MRB setting being information for setting a multicast MRB for the RRC connected state, the third MRB setting including a third MBS session ID; and if the third MBS session ID matches the second MBS session ID, changing the setting for the multicast MRB based on the third MRB setting.

11. The communication method according to claim 10, further comprising, after transitioning to the RRC connected state, continuing to receive the multicast session using the multicast MRB after the setting change.

12. The communication method according to claim 10, wherein performing the change in configuration based on the third MRB configuration includes performing the change in configuration while maintaining a PDCP entity associated with the multicast MRB.

13. The method of claim 10, further comprising: receiving, in the RRC connected state, the third MRB configuration including the third MBS session ID and an MRB ID from the network in an RRC reconfiguration message.

14. The communication method according to claim 13, wherein performing the change in setting based on the third MRB setting includes assigning the MRB ID included in the third MRB setting to the multicast MRB.

15. A user equipment used in a mobile communication system providing a multicast broadcast service (MBS), comprising: a control unit that executes the following processes: in an RRC connected state, establishing a multicast radio bearer (MRB) based on a first multicast MRB setting set from a network; receiving from the network, using the established multicast MRB, a multicast session corresponding to a first MBS session ID included in the first MRB setting; receiving from the network a second MRB setting including a second MBS session ID, which is information for setting a multicast MRB for an RRC inactive state; and, if the second MBS session ID matches the first MBS session ID, changing the settings for the established multicast MRB based on the second MRB setting.

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