COMMUNICATION METHOD, USER EQUIPMENT, CHIP SET, PROGRAM, AND MOBILE COMMUNICATION SYSTEM

Abstract

A communication method performed by user equipment in a mobile communication system providing a multicast / broadcast service (MBS) comprises the steps of: receiving, from a network, information for setting a condition for starting RRC connection resume during multicast reception in a radio resource control (RRC) inactive state, the condition being a resume condition related to multicast reception quality; receiving, from the network, information for setting an area condition related to an area in which the RRC connection resume based on the resume condition is permitted or prohibited; and starting the RRC connection resume when the resume condition is satisfied and the area condition is satisfied during multicast reception in the RRC inactive state.

Description

Communication Method

[0001] The present disclosure relates to a communication method for use in a mobile communication system.

[0002] The 3rd Generation Partnership Project (3GPP) has defined 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 has defined 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 V17.4.0

[0005] A communication method according to a first aspect is a communication method executed by a user device in a mobile communication system that provides a multicast / broadcast service (MBS), and includes receiving from a network a reception quality threshold associated with a multicast session for initiating RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state, and initiating the RRC connection resume in response to the reception quality falling below the reception quality threshold when receiving multicast in the RRC inactive 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 receiving, from a network, information for setting a resume condition related to multicast reception quality, which is a condition for initiating RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state; receiving, from the network, information for setting an area condition related to an area in which the RRC connection resume based on the resume condition is permitted or prohibited; and starting the RRC connection resume when the resume condition and the area condition are satisfied when receiving multicast in the RRC inactive state.

[0007] A communication method according to a third 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 receiving information from a network, which is a condition for initiating RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state and is for setting resume conditions related to multicast reception quality, the information including information for setting different resume conditions as the resume conditions for each combination of a serving cell and a neighboring cell, and starting the RRC connection resume in response to the resume condition associated with the combination of a current serving cell and a current neighboring cell being satisfied when receiving multicast in the RRC inactive state.

[0008] A communication method according to a fourth 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 receiving, from a network, information for setting a resume condition related to multicast reception quality, which is a condition for initiating RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state, wherein the resume condition includes a reception quality threshold that is compared with the multicast reception quality of a physical downlink shared channel (PDSCH) associated with a multicast traffic channel (MTCH); and starting the RRC connection resume in response to the reception quality of the PDSCH associated with the MTCH during the multicast reception when receiving multicast in the RRC inactive state.

[0009] A communication method according to a fifth 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: determining whether a resume condition related to multicast reception quality, which is a condition for initiating RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state, is set in the user device from a network; and determining, based on the result of the determination, that initiating RRC connection resume for the multicast reception is prohibited when receiving multicast in the RRC inactive state.

[0010] A communication method according to a sixth 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 receiving, from a network, information for setting a resume condition related to multicast reception quality, which is a condition for initiating RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state; initiating the RRC connection resume in response to the resume condition being satisfied when receiving multicast in the RRC inactive state; and notifying the network in the RRC connection resume procedure that the resume condition has been satisfied.

[0011] A communication method according to a seventh 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 receiving from a network information for setting a resume condition related to multicast reception quality, the resume condition being a condition for initiating an RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state, and initiating the RRC connection resume in response to the resume condition being satisfied when receiving multicast in the RRC inactive state, wherein the receiving step includes a step of receiving the information for setting a plurality of resume conditions corresponding to a plurality of multicast sessions received by the user device, and the initiating step includes a step of initiating the RRC connection resume in response to at least one of the plurality of resume conditions being satisfied.

[0012] 1 is a diagram illustrating an example of the configuration of a mobile communication system according to an embodiment. FIG. 1 is a diagram illustrating an example of the configuration of a UE (user equipment) according to an embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a gNB (base station) according to an embodiment. FIG. 3 is a diagram illustrating a protocol stack configuration of a radio interface of a user plane that handles data. FIG. 4 is a diagram illustrating a protocol stack configuration of a radio interface of a control plane that handles signaling (control signals). FIG. 5 is a diagram for explaining an operation scenario according to a first operation pattern of an embodiment. FIG. 6 is a diagram illustrating an example of the operation of a UE according to the first operation pattern of an embodiment. FIG. 7 is a diagram illustrating an example of the operation of a mobile communication system according to the first operation pattern of an embodiment. FIG. 8 is a diagram illustrating an example of the operation of a UE according to a second operation pattern of an embodiment. FIG. 9 is a diagram illustrating an example of the operation of a mobile communication system according to the second operation pattern of an embodiment. FIG. 10 is a diagram illustrating an example of the operation of a mobile communication system according to the third operation pattern of an embodiment. FIG. 11 is a diagram illustrating an example of the operation of a mobile communication system according to the third operation pattern of an embodiment. FIG. 12 is a diagram illustrating another example of the operation of a UE according to the fourth operation pattern of an embodiment. FIG. 13 is a diagram illustrating another example of the operation of a UE according to the fourth operation pattern of an embodiment. FIG. 14 is a diagram illustrating another example of the operation of a UE according to the fourth operation pattern of an embodiment. FIG. 15 is a diagram illustrating an example of the operation of a mobile communication system according to the fifth operation pattern of an embodiment. FIG. 16 is a diagram illustrating an example of the operation of a mobile communication system according to the fifth operation pattern of an embodiment. FIG. 17 is a diagram illustrating an example of the operation of a mobile communication system according to a sixth operation pattern of an embodiment. 1A and 1B show the initialization procedure for an ongoing session (left) and a stopped session (right).

[0013] 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.

[0014] (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.

[0015] 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 the network of the mobile communication system 1.

[0016] 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).

[0017] The NG-RAN 10 includes a base station (referred to as "gNB" in the 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 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 for wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 3 is a diagram showing an example of the configuration of a gNB 200 (base station) 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0035] 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.

[0036] 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).

[0037] 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.

[0038] 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.

[0039] 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").

[0040] (2) Overview of MBS The mobile communication system 1 can perform resource-efficient distribution using multicast / broadcast services (MBS).

[0041] (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 RRC idle state, RRC inactive state, and RRC connected state. Note that the MBS session can be identified by an MBS session ID (e.g., TMGI (Temporary Mobile Group Identity)).

[0042] 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.

[0043] 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 for a multicast traffic channel (MTCH), which is a type of logical channel, and a configuration of a broadcast MRB, 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).

[0044] 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. The MTCH is a PTM downlink channel for transmitting MBS data of either a multicast session or a broadcast session from the network 10 to the UE 100.

[0045] (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.

[0046] 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.

[0047] 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, this will be extended so that UEs 100 in an RRC inactive state can also receive a multicast session.

[0048] (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.

[0049] 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 for the MTCH for receiving the multicast session and a setting for 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). The settings related to MTCH (MTCH settings) are settings related to MTCH reception, and include at least one of, for example, a group identifier (G-RNTI), discontinuous reception settings (DRX settings or scheduling information: MTCH transmission ON time, MTCH transmission period, reference time and time offset, HARQ retransmission settings), Layer 2 settings (PDCP settings, RLC settings), and physical channel settings (PDCCH settings, PDSCH settings, SSB mapping settings).

[0050] (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.

[0051] 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 a "new SIB") from the gNB 200. The new SIB includes a configuration of a newly introduced MCCH (also referred to as a "multicast MCCH"). Second, the UE 100 in the RRC inactive state receives a multicast MCCH from the gNB 200 based on the new SIB. The multicast MCCH includes a PTM configuration. The PTM configuration transmits a configuration related to the MTCH for receiving the multicast session and a configuration of a multicast MRB, which is an MRB for the multicast session. Third, the UE 100 in the RRC inactive state receives the MTCH based on the multicast MCCH. The MTCH transmits the multicast session (specifically, MBS data belonging to the multicast session).

[0052] When gNB200 configures UE100 to receive multicast in the RRC inactive state, it can send PTM configuration to UE100 using an RRC Release message including a suspend configuration. In this case, when UE100 receives an RRC Release message including PTM configuration from gNB200, it transitions to the RRC inactive state and receives the multicast session in the RRC inactive state.

[0053] (3) Example of System Operation The following describes operations related to multicast reception in an RRC inactive state. In this embodiment, a scenario is assumed in which the UE 100 receives a multicast session (also referred to as "multicast reception") in an RRC inactive state. By the UE 100 performing multicast reception in the RRC inactive state, the load (resource consumption and / or power consumption, etc.) on the network 5 and the UE 100 can be reduced compared to when multicast reception is performed in an RRC connected state.

[0054] Currently, 3GPP is discussing the introduction of a function in UE 100 that transitions to an RRC connected state by initiating (triggering) RRC connection resume when the reception quality of multicast data (also referred to as "multicast reception quality") falls below a set threshold. Such a function is expected to make it easier for UE 100 to continue multicast reception. However, there is a problem in that the specific details of what measurement value should be used as the multicast reception quality and how the threshold should be set in UE 100 have not yet been determined.

[0055] The multicast reception quality falling below a set threshold and similar conditions are also referred to as "resume conditions." In the following embodiment, first to sixth operation patterns for performing appropriate control regarding RRC connection resumption based on the resume conditions will be described. The first to sixth operation patterns may be implemented independently, or two or more operation patterns may be implemented in combination.

[0056] (3.1) First Operation Pattern FIG. 6 is a diagram for explaining an operation scenario according to the first operation pattern of the embodiment. In the illustrated example, UE 100 selects cell a of gNB 200a as its serving cell and performs multicast reception in an RRC inactive state. UE 100 is located in an overlapping area between cell a, which is the serving cell, and cell b, which is an adjacent cell. Cell b is managed by gNB 200b, which is different from gNB 200a, which is the serving gNB, but cell b may also be managed by gNB 200a. The multicast session that UE 100 in the RRC inactive state receives on the MTCH of cell a is assumed to be multicast session #1.

[0057] When cell a and cell b form a single frequency network (SFN), cell b can provide multicast session #1 on an MTCH with the same time and frequency resources as the MTCH of cell a. And / or when the same PTM configuration is applied to cell a and cell b, that is, when area-specific PTM configuration is applied to cell a and cell b, cell b can provide multicast session #1 on an MTCH with the same time and frequency resources as the MTCH of cell a. In such a case, UE 100 in an RRC inactive state can receive the MTCH of cell a and the MTCH of cell b. Therefore, even if the multicast reception quality from cell a deteriorates, the multicast reception quality from cell b can be good.

[0058] Here, it is assumed that a threshold value of reception quality for a reference signal specific to cell a, for example, a threshold value of reference signal received power (RSRP) and / or a threshold value of reference signal received quality (RSRQ), is set in UE 100 as a resume condition. The reference signal specific to cell a may be a reference signal included in the SSB (Synchronization Signal / PBCH block) of cell a. In that case, even if the multicast reception quality from cell b is good, UE 100 may start RRC connection resume for cell a in response to the multicast reception quality from cell a falling below the threshold. That is, UE 100 can receive multicast session #1 from cell b well and performs unnecessary RRC connection resume even when there is no need to perform RRC connection resume.

[0059] The first operation pattern is an operation pattern that makes it easier to prevent UE 100 from performing unnecessary RRC connection resume by limiting the start of RRC connection resume based on multicast reception quality, taking into account the area (cell) in which UE 100 is located.

[0060] FIG. 7 is a diagram illustrating an example of the operation of the UE 100 according to the first operation pattern.

[0061] In step S11, the UE 100 receives, from the network 5, information for setting a resume condition related to multicast reception quality, which is a condition for starting RRC connection resume when receiving multicast in an RRC inactive state. The information is, for example, information indicating an RSRP threshold and / or an RSRP threshold for a serving cell. The resume condition may be a condition for performing cell reselection, for example, information indicating that the reception quality of a neighboring cell has become higher than the reception quality of the serving cell.

[0062] In step S12, the UE 100 receives information for setting an area condition related to an area in which RRC connection resumption based on the resume condition is permitted or prohibited, from the network 5. Note that step S12 may be executed before step S11 or simultaneously with step S11.

[0063] The area condition may be a condition that UE 100 is not located in an area made up of a group of cells that constitute an SFN, or a condition that UE 100 is located in an area made up of a group of cells that do not constitute an SFN.

[0064] The area condition may be a condition that UE100 is not located in an area consisting of a group of cells to which a common PTM setting is applied, or a condition that UE100 is located in an area consisting of a group of cells to which a common PTM setting is not applied.

[0065] The area condition may be a condition that UE100 is located in an area consisting of a group of cells in which RRC connection resume based on the resume condition is permitted, or a condition that UE100 is not located in an area consisting of a group of cells in which RRC connection resume based on the resume condition is prohibited.

[0066] In step S13, the UE 100 that performs multicast reception in the RRC inactive state determines whether or not the resume condition is satisfied and the area condition is satisfied.

[0067] If it is determined that the resume condition is met and the area condition is met (step S13: YES), in step S14, UE 100 performing multicast reception in the RRC inactive state starts RRC connection resume and transitions to the RRC connected state.

[0068] On the other hand, if the result of step S13 is NO, in step S15, the UE 100 performing multicast reception in the RRC inactive state controls not to start the RRC connection resume. For example, even if the resume condition is set, if the area condition is not satisfied, the UE 100 controls not to start the RRC connection resume based on the resume condition.

[0069] According to this operation, even if the resume condition is satisfied, the UE 100 performing multicast reception in the RRC inactive state can maintain the RRC inactive state without starting the RRC connection resume, for example, when the UE 100 is camped on a serving cell that configures an SFN or a serving cell to which a common PTM setting is applied. This makes it easier to prevent the UE 100 from performing unnecessary RRC connection resume.

[0070] 8 is a diagram illustrating an example of the operation of the mobile communication system 1 according to the first operation pattern of the embodiment. Note that the following description of the embodiment is based on the premise that the UE 100 has already participated in a certain multicast session (hereinafter referred to as multicast session #1).

[0071] In step S101, UE100 is in an RRC connected state or an RRC inactive state in the cell (serving cell) of gNB200.

[0072] In step S102, gNB200 transmits an area setting regarding the area conditions to UE100. UE100 receives the area setting from gNB200 (current serving cell).

[0073] For a UE 100 in an RRC connected state, the gNB 200 may transmit the area setting to the UE 100 by dedicated signaling, for example, an RRC Release message or an RRC Reconfiguration message. For a UE 100 in an RRC connected state or an RRC inactive state, the gNB 200 may transmit the area setting to the UE 100 by broadcast signaling, for example, an MCCH or SIB.

[0074] The area configuration may include common PTM configuration area information indicating a common PTM configuration area to which the common PTM configuration is applied. The common PTM configuration area information may be a list of cells constituting the common PTM configuration area (cell ID list). The common PTM configuration area information transmitted by the current serving cell may be a list of other cells to which the PTM configuration provided by the current serving cell is applied (cell ID list).

[0075] The area configuration may include common MCCH configuration area information indicating a common MCCH configuration area to which the common MCCH configuration is applied. The common MCCH configuration area information may be a list of cells constituting the common MCCH configuration area (cell ID list). The common MCCH configuration area information transmitted by the current serving cell may be a list of other cells to which the MCCH configuration provided in SIB20 of the current serving cell is applied (cell ID list).

[0076] The area configuration may include SFN area information indicating an SFN area to which SFN is applied. The SFN area information may be a list of cells constituting the SFN area (cell ID list). The SFN area information transmitted by the current serving cell may be a list of other cells constituting the SFN together with the current serving cell (cell ID list).

[0077] In step S103, the gNB 200 transmits a resume condition setting for setting a resume condition to the UE 100. The UE 100 receives the resume condition setting from the gNB 200.

[0078] For a UE 100 in an RRC connected state, the gNB 200 may transmit a resume condition setting to the UE 100 by dedicated signaling, for example, an RRC Release message or an RRC Reconfiguration message. For a UE 100 in an RRC connected state or an RRC inactive state, the gNB 200 may transmit a resume condition setting to the UE 100 by broadcast signaling, for example, an MCCH or SIB.

[0079] The resume condition setting is, for example, information indicating a reception quality threshold for the serving cell (for example, an RSRP threshold and / or an RSRP threshold, etc.). The resume condition setting may be a condition for performing cell reselection, for example, information indicating that the reception quality of a neighboring cell has become higher than the reception quality of the serving cell.

[0080] The resume condition setting may include information indicating an area in which RRC connection resumption based on the resume condition is prohibited (disabled, ignored). The information may be information referring to the common PTM setting area (or common MCCH setting area) set in step S102. The information may be information referring to the SFN area set in step S102. The information may be a list of cell IDs of each cell constituting the area in which RRC connection resumption based on the resume condition is prohibited (disabled, ignored).

[0081] The resume condition setting may include information indicating an area in which RRC connection resume based on the resume condition is permitted (enabled, applied). The information may be information indicating that the cell does not belong to the common PTM setting area (or common MCCH setting area) set in step S102. The information may be information indicating that the cell does not belong to the SFN area set in step S102. The information may be a list of cell IDs of each cell constituting the area in which RRC connection resume based on the resume condition is permitted (enabled, applied).

[0082] The resume condition setting may include information indicating that RRC connection resume based on the resume condition is permitted (enabled, applied) regardless of the area.

[0083] In steps S104 and S105, UE100 in the RRC inactive state receives multicast session #1 from gNB200 on the MTCH based on the PTM setting provided by gNB200 on the MCCH. UE100 may receive multicast session #1 from gNB200 on the MTCH based on the PTM setting provided in the RRC Release message.

[0084] In step S106, the UE 100 in the RRC inactive state determines whether the resume condition is satisfied and whether the area condition is satisfied. The UE 100 may evaluate whether the resume condition is satisfied only in an area where RRC connection resume based on the resume condition is permitted (enabled, applied). The UE 100 may not evaluate whether the resume condition is satisfied in an area where RRC connection resume based on the resume condition is prohibited (disabled, ignored). Furthermore, the UE 100 may evaluate whether the resume condition is satisfied only while receiving multicast in the RRC inactive state. "Receiving multicast" may mean at least one of participating in multicast session #1, activating multicast session #1, and starting reception of multicast session #1 on the MTCH.

[0085] If it is determined that the resume condition is satisfied and the area condition is not satisfied (step S106: NO), the process returns to step S105. On the other hand, if it is determined that the resume condition is satisfied and the area condition is satisfied (step S106: YES), in step S107, RRC connection resume is performed with the gNB 200. The RRC connection resume includes transmission of an RRC Resume Request message from the UE 100 to the gNB 200 and transmission of an RRC Resume message from the gNB 200 to the UE 100.

[0086] In step S108, the UE 100 transitions from the RRC inactive state to the RRC connected state.

[0087] In step S109, the UE 100 in the RRC connected state receives the multicast session #1 on the MTCH.

[0088] As described above, according to the first operation pattern, the UE 100 performing multicast reception in the RRC inactive state can maintain the RRC inactive state without starting the RRC connection resume even when the resume condition is satisfied, for example, when the UE 100 is camped on a serving cell that constitutes an SFN or a serving cell to which a common PTM setting is applied. This makes it easier to prevent the UE 100 from performing unnecessary RRC connection resume.

[0089] Alternatively, as a modification of the first operation pattern, UE 100 may evaluate whether the resume condition is satisfied regardless of whether the area condition is satisfied. UE 100 may perform evaluation using a first reception quality threshold as the resume condition in an area where RRC connection resume based on the resume condition is permitted. UE 100 may perform evaluation using a second reception quality threshold lower than the first reception quality threshold as the resume condition in an area other than the permitted area. That is, UE 100 may change the threshold that determines the resume condition depending on the area (serving cell) in which UE 100 is located. As a result, when UE 100 is camped on a serving cell that constitutes an SFN or a serving cell to which a common PTM setting is applied, for example, the resume condition is less likely to be satisfied, making it easier to maintain the RRC inactive state. This makes it easier to prevent UE 100 from performing unnecessary RRC connection resume.

[0090] (3.2) Second Movement Pattern The second movement pattern according to the embodiment will be described, focusing on the differences from the above-described movement patterns. The second movement pattern has the same task as the first movement pattern, but the movement is different from that of the first movement pattern.

[0091] FIG. 9 is a diagram illustrating an example of an operation of the UE 100 according to the second operation pattern of the embodiment.

[0092] In step S21, the UE 100 receives information for setting a resume condition related to multicast reception quality, which is a condition for starting an RRC connection resume when receiving multicast in an RRC inactive state, from the network 5. The information includes information for setting a different resume condition (e.g., a different reception quality threshold) as the resume condition for each combination of a serving cell and a neighboring cell.

[0093] In step S22, the UE 100 determines whether or not a resume condition associated with the combination of the current serving cell and the current neighboring cell is satisfied during multicast reception in the RRC inactive state.

[0094] If it is determined that the resume condition associated with the combination of the current serving cell and the current neighboring cell is satisfied (step S22: YES), in step S23, the UE 100 starts RRC connection resume.

[0095] On the other hand, if it is determined that the resume condition associated with the combination of the current serving cell and the current neighboring cell is not satisfied (step S22: NO), in step S24, UE100 controls so as not to start RRC connection resume.

[0096] FIG. 10 is a diagram illustrating an example of the operation of the mobile communication system 1 according to the second operation pattern of the embodiment.

[0097] In step S201, UE100 is in an RRC connected state or an RRC inactive state in the cell (serving cell) of gNB200.

[0098] In step S202, the gNB 200 transmits a resume condition setting for setting a resume condition to the UE 100. The UE 100 receives the resume condition setting from the gNB 200.

[0099] For a UE 100 in an RRC connected state, the gNB 200 may transmit a resume condition setting to the UE 100 by dedicated signaling, for example, an RRC Release message or an RRC Reconfiguration message. For a UE 100 in an RRC connected state or an RRC inactive state, the gNB 200 may transmit a resume condition setting to the UE 100 by broadcast signaling, for example, an MCCH or SIB.

[0100] The resume condition setting is, for example, information indicating a reception quality threshold (for example, an RSRP threshold and / or an RSRP threshold, etc.) for the serving cell. The resume condition setting includes information for setting a different resume condition (for example, a different reception quality threshold) as a resume condition for each combination of the serving cell and the neighboring cell. That is, the gNB 200 sets a different resume condition for the UE 100 for each combination of cells.

[0101] For example, the resume condition setting includes cell information indicating a combination of cells and a resume condition (reception quality threshold) associated with the cell information. The cell information may be a combination of cell IDs, for example, a combination of cell ID #1 and cell ID #2. Alternatively, the cell information may be a cell ID of a neighboring cell. In this case, the UE 100 identifies the current serving cell and the cell ID (cell ID of the neighboring cell) as a cell combination. Note that the resume condition setting may further include a resume condition (reception quality threshold, which may be a reference threshold described later) not associated with the cell information.

[0102] In this operation pattern, the gNB200 sets the same reception quality index but different thresholds for each cell combination. For example, the gNB200 sets a different RSRP threshold for each cell combination. In this case, an offset value relative to a reference threshold (reference) may be set for each cell combination. Alternatively, the gNB200 may set a different reception quality index for each cell combination. For example, an RSRP threshold may be set for cell combination #1, and a block error rate (BLER) threshold may be set for cell combination #2.

[0103] In steps S203 and S204, UE100 in the RRC inactive state receives multicast session #1 from gNB200 on the MTCH based on the PTM setting provided by gNB200 on the MCCH. UE100 may receive multicast session #1 from gNB200 on the MTCH based on the PTM setting provided in the RRC Release message.

[0104] In step S205, the UE 100 in the RRC inactive state identifies a neighboring cell based on the received reference signal (SSB). For example, the UE 100 identifies a neighboring cell with the best reception quality.

[0105] In step S206, the UE 100 in the RRC inactive state determines whether or not a resume condition associated with the combination of the current serving cell and the current neighboring cell (the neighboring cell identified in step S205) is satisfied. Specifically, the UE 100 identifies a reception quality threshold associated with cell information that matches the combination of the current serving cell and the current neighboring cell from the resume condition setting, and determines whether or not the reception quality from the current serving cell has fallen below the identified reception quality threshold.

[0106] If it is determined that the resume condition is met (step S206: YES), that is, if it is determined that the reception quality from the current serving cell has fallen below the reception quality threshold, in step S207, UE100 in the RRC inactive state resumes RRC connection with gNB200.

[0107] In step S208, the UE 100 transitions from the RRC inactive state to the RRC connected state.

[0108] In step S209, the UE 100 in the RRC connected state receives the multicast session #1 on the MTCH.

[0109] In this operation pattern, an example in which the cell combination is a combination of a serving cell and a neighboring cell has been described, but the cell combination may be a combination of neighboring cells. For example, a resume condition may be set for the combination of neighboring cell #1 with the highest reception quality and neighboring cell #2 with the second highest reception quality.

[0110] Thus, according to the second operation pattern, UE 100 performing multicast reception in the RRC inactive state can apply a resume condition suitable for the combination of the current serving cell and the current neighboring cell. Therefore, for example, in the case of a combination of cells constituting an SFN or a combination of cells to which a common PTM setting is applied, the reception quality threshold can be set low, making it difficult to satisfy the resume condition, and making it easier to maintain the RRC inactive state. This makes it easier to prevent UE 100 from performing unnecessary RRC connection resume.

[0111] Alternatively, as a modification of the second operation pattern, the gNB 200 may set whether or not to resume the RRC connection based on the resume condition for each combination with a cell. For example, the gNB 200 may configure the UE 100 to permit the RRC connection resume based on the resume condition for cell combination #1 and prohibit the RRC connection resume based on the resume condition for cell combination #2. The UE 100 may evaluate whether or not the resume condition is satisfied only if the combination of the current serving cell and the current neighboring cell is a cell combination in which the RRC connection resume based on the resume condition is permitted.

[0112] (3.3) Third Operation Pattern The third operation pattern according to the embodiment will be described, focusing on the differences from the above-described operation patterns.

[0113] In the above-described first and second operation patterns, the operation for solving the problem when the reception quality index compared with the reception quality threshold as the resume condition is the reception quality of a single cell (serving cell) has been described. However, since the UE 100 in the RRC inactive state can receive MTCHs (multicast sessions) from both the serving cell and the neighboring cell, it is desirable to use a reception quality index that reflects the reception states of both the serving cell and the neighboring cell.

[0114] FIG. 11 is a diagram illustrating an example of an operation of the UE 100 according to the third operation pattern of the embodiment.

[0115] In step S31, the UE 100 receives, from the network 5, information for setting a resume condition related to multicast reception quality, which is a condition for starting an RRC connection resume during multicast reception in an RRC inactive state. In a third operation pattern, the resume condition includes a reception quality threshold to be compared with the reception quality of a physical downlink shared channel (PDSCH) associated with the MTCH. Here, the reception quality of the PDSCH associated with the MTCH during multicast reception is a reception quality index that reflects the reception states of both the serving cell and neighboring cells, and is also referred to as multicast data reception quality.

[0116] In step S32, the UE 100 determines whether or not the multicast data reception quality satisfies the resume condition (condition of the reception quality threshold) during multicast reception in the RRC inactive state.

[0117] If it is determined that the multicast data reception quality satisfies the resume condition (step S32: YES), in step S33, the UE 100 starts RRC connection resume.

[0118] On the other hand, if it is determined that the multicast data reception quality does not satisfy the resume condition (step S32: NO), in step S34, the UE 100 performs control so as not to start the RRC connection resume.

[0119] The multicast data reception quality may be an error rate of the multicast data, for example, a bit error rate (BER), a block error rate (BLER), or a packet error rate (PER). When such a data error rate is used as a reception quality index, the multicast data reception quality (BER / BLER / PER) satisfying the resume condition (threshold condition) may mean that the error rate is higher than a threshold, that is, the BER / BLER / PER exceed the threshold.

[0120] The multicast data reception quality may be the reception quality (RSRP / RSRQ / SINR) of the PDSCH carrying the MTCH. For example, the multicast data reception quality may be the reception quality of a channel state information reference signal (CSI-RS), a tracking reference signal (TRS), or a demodulation reference signal (DMRS) transmitted within the time-frequency resource of the PDSCH carrying the MTCH. In this case, the reference signal (reference signal resource) to be measured by the UE 100 may be set to the UE 100 from the gNB 200.

[0121] The reception quality threshold to be compared with the multicast data reception quality may be associated with the MBS session ID or G-RNTI and set by the gNB 200 to the UE 100. The UE 100 may measure the multicast data reception quality and compare the measurement results with the threshold for each MBS session ID or each G-RNTI.

[0122] FIG. 12 is a diagram illustrating an example of the operation of the mobile communication system 1 according to the third operation pattern of the embodiment.

[0123] In step S301, UE100 is in an RRC connected state or an RRC inactive state in the cell (serving cell) of gNB200.

[0124] In step S302, the gNB 200 transmits a resume condition setting for setting a resume condition to the UE 100. The UE 100 receives the resume condition setting from the gNB 200.

[0125] For a UE 100 in an RRC connected state, the gNB 200 may transmit a resume condition setting to the UE 100 by dedicated signaling, for example, an RRC Release message or an RRC Reconfiguration message. For a UE 100 in an RRC connected state or an RRC inactive state, the gNB 200 may transmit a resume condition setting to the UE 100 by broadcast signaling, for example, an MCCH or SIB.

[0126] In the third operation pattern, the resume condition setting includes a reception quality threshold value to be compared with the multicast data reception quality. The resume condition setting may include an MBS session ID (or G-RNTI) and a reception quality threshold value associated with the MBS session ID (or G-RNTI).

[0127] In steps S303 and S304, UE100 in the RRC inactive state receives multicast session #1 from gNB200 on the MTCH based on the PTM setting provided by gNB200 on the MCCH. UE100 may receive multicast session #1 from gNB200 on the MTCH based on the PTM setting provided in the RRC Release message.

[0128] In step S305, the UE 100 in the RRC inactive state measures the reception quality of the multicast data.

[0129] In step S306, the UE 100 in the RRC inactive state determines whether or not the multicast data reception quality satisfies the resume condition (threshold condition).

[0130] If it is determined that the multicast data reception quality satisfies the resume condition (step S306: YES), in step S307, UE100 in the RRC inactive state resumes RRC connection with gNB200.

[0131] In step S308, the UE 100 transitions from the RRC inactive state to the RRC connected state.

[0132] In step S309, the UE 100 in the RRC connected state receives the multicast session #1 on the MTCH.

[0133] (3.4) Fourth Operation Pattern A fourth operation pattern according to the embodiment will be described, focusing on differences from the above-described operation patterns.

[0134] From the viewpoint of reducing the load required for multicast reception, it is preferable that UE100 continue multicast reception in the RRC inactive state. Therefore, UE100 for which a resume condition is set may be prohibited from starting RRC connection resume for multicast reception if the resume condition is not satisfied. On the other hand, if gNB200 does not set a resume condition for UE100, UE100 can start RRC connection resume at any time.

[0135] Alternatively, if the gNB 200 does not set a resume condition for the UE 100, it may be considered that the gNB 200 does not permit the UE 100 to start an RRC connection resume for multicast reception. In this case, if the gNB 200 does not set a resume condition for the UE 100, the UE 100 may be prohibited from starting an RRC connection resume for multicast reception.

[0136] In the fourth operation pattern, the UE 100 determines whether or not a resume condition related to multicast reception quality, which is a condition for starting the RRC connection resume when receiving multicast in the RRC inactive state, is set in the UE 100 from the network 5. Based on the result of the determination, the UE 100 considers that starting the RRC connection resume for multicast reception is prohibited when receiving multicast in the RRC inactive state.

[0137] In an example of the fourth operation pattern, if a resume condition is set in the UE 100 and the resume condition is not satisfied, the UE 100 considers that initiating RRC connection resume for multicast reception is prohibited.

[0138] In another example of the fourth operation pattern, when the resume condition is not set in the UE 100, the UE 100 considers that starting the RRC connection resume for multicast reception is prohibited.

[0139] FIG. 13 is a diagram illustrating an example of an operation of the UE 100 according to the fourth operation pattern of the embodiment.

[0140] In step S41 a, the UE 100 receives the resume condition setting from the network 5.

[0141] In step S42a, the UE 100 that performs multicast reception in the RRC inactive state determines whether or not the resume condition is satisfied.

[0142] If it is determined that the resume condition is not satisfied (step S42a: NO), in step S43a, the UE 100 considers that starting the RRC connection resume for multicast reception is prohibited. In this case, the UE 100 controls not to start the RRC connection resume for multicast reception. In addition, in the UE 100, the prohibition state (and / or the subsequent permission state) may be notified from the AS to the NAS.

[0143] However, in the case of a reason other than multicast reception, for example, paging reception or uplink data generation, the UE 100 considers that it is permitted to start the RRC connection resume, and can start the RRC connection resume.

[0144] On the other hand, if it is determined that the resume condition is satisfied (step S42a: YES), in step S44a, the UE 100 starts RRC connection resume.

[0145] FIG. 14 is a diagram illustrating another example of the operation of the UE 100 according to the fourth operation pattern of the embodiment.

[0146] In step S41b, the UE 100 may receive a resume condition setting from the network 5.

[0147] In step S42b, the UE 100 that performs multicast reception in the RRC inactive state determines whether or not a resume condition is set.

[0148] If it is determined that the resume condition is set (step S42b: YES), in step S43b, the UE 100 considers that it is permitted to start the RRC connection resume for multicast reception. In this case, when the resume condition is set, the UE 100 starts the RRC connection resume for multicast reception.

[0149] If it is determined that the resume condition is not set (step S42b: NO), in step S44b, the UE 100 considers that starting the RRC connection resume for multicast reception is prohibited. In this case, the UE 100 controls not to start the RRC connection resume for multicast reception. In addition, in the UE 100, the prohibition state (and / or the subsequent permission state) may be notified from the AS to the NAS.

[0150] However, in the case of a reason other than multicast reception, for example, paging reception or uplink data generation, the UE 100 considers that it is permitted to start the RRC connection resume, and can start the RRC connection resume.

[0151] In addition, in step S44b, if it is determined that UE100 has a valid PTM setting for the RRC inactive state (and / or the MCCH of the neighboring cell includes the PTM setting for the MBS session ID of its interest) and no resume condition is set, it may be considered that UE100 is prohibited from initiating RRC connection resume for multicast reception.

[0152] (3.5) Fifth Operation Pattern A fifth operation pattern according to the embodiment will be described, focusing on differences from the above-described operation patterns.

[0153] When UE100 performing multicast reception in the RRC inactive state starts RRC connection resume in response to the resume condition being satisfied, it transmits an RRC resume request (Resume Request) message to gNB200 (current serving cell). Here, gNB200 normally accepts the RRC Resume Request message and transmits an RRC Resume message to UE100.

[0154] However, for example, when gNB200 is congested, gNB200 may reject the RRC Resume Request message and send an RRC Release message or an RRC Reject message to UE100.

[0155] When a UE 100 receiving a multicast session in an RRC inactive state performs RRC resume because the resume condition is satisfied, this means that the QoS requirements of the multicast session can no longer be satisfied. Therefore, in order to satisfy the QoS requirements, it is desirable to transition such a UE 100 to an RRC connected state with the highest priority and continue receiving the multicast session in the RRC connected state.

[0156] The fifth operating pattern is an operating pattern that makes it easier to meet the QoS requirements of a multicast session.

[0157] FIG. 15 is a diagram illustrating an example of an operation of the UE 100 according to the fifth operation pattern of the embodiment.

[0158] In step S51, the UE 100 receives, from the network 5, information for setting a resume condition related to multicast reception quality, which is a condition for starting RRC connection resume when receiving multicast in an RRC inactive state.

[0159] In step S52, the UE 100 determines whether or not a resume condition is satisfied during multicast reception in the RRC inactive state.

[0160] If it is determined that the resume condition is met (step S52: YES), in step S53, the UE 100 starts RRC connection resume. In this operation pattern, the UE 100 notifies the network 5 that the resume condition is met during the RRC connection resume procedure. For example, the UE 100 transmits an RRC Resume Request message including an information element indicating that the resume condition is met to the network 5. Alternatively, the UE 100 may perform the notification by transmitting a random access preamble to the network 5 using a physical random access channel (PRACH) resource indicating that the resume condition is met. In this case, it is assumed that the PRACH resource indicating that the resume condition is met has been notified to the UE 100 in advance from the gNB 200.

[0161] On the other hand, if it is determined that the multicast data reception quality does not satisfy the resume condition (step S52: NO), in step S55, the UE 100 performs control so as not to start the RRC connection resume.

[0162] 16 is a diagram illustrating an example of the operation of the mobile communication system 1 according to the fifth operation pattern of the embodiment. Here, a case where notification is made in an RRC Resume Request message will be described.

[0163] The operations in steps S501 to S505 are the same as those according to the above-described operation pattern.

[0164] If it is determined that the resume condition is satisfied (step S505: YES), the UE 100 in the RRC inactive state starts an RRC connection resume procedure. Note that the UE 100 may recognize that multicast reception in the RRC connected state is necessary. The UE 100 may recognize that a new PTM setting is necessary. The UE 100 may recognize that the QoS requirement of the multicast session will no longer be satisfied.

[0165] In step S506, the UE 100 transmits an RRC Resume Request message to the gNB 200. Here, the UE 100 sets a value (cause value) corresponding to degradation in multicast session reception quality in the Resume Cause field in the RRC Resume Request message. The value (cause value) is, for example, a value such as "deterioration in multicast reception quality," "multicast PTM setting update," or "multicast reception required in RRC connected state." The value (cause value) may be a value corresponding to a reception quality indicator that satisfies the resume condition, for example, "multicast RSRP has become worse than a threshold," "multicast BLER has become worse than a threshold," or an index value corresponding to these. Alternatively, the UE 100 may set an existing high-priority cause value (for example, emergency, mt-Access, mo-Signaling).

[0166] When gNB200 receives the RRC Resume Request message, it recognizes that the multicast session reception quality of UE100 has deteriorated based on the Resume Cause, and prioritizes processing the RRC connection resume of UE100.

[0167] In step S507, gNB200 sends an RRC Resume message to UE100.

[0168] In step S508, the UE 100 transitions from the RRC inactive state to the RRC connected state.

[0169] In step S509, the UE 100 in the RRC connected state performs multicast reception on the MTCH.

[0170] In addition, gNB200 may configure an MRB for the RRC connected state or an updated PTM configuration (MRB for inactivity) for UE100 within the RRC Resume message or after UE100 transitions to the RRC connected state.

[0171] (3.6) Sixth Operation Pattern The sixth operation pattern according to the embodiment will be described, focusing on the differences from the above-described operation patterns.

[0172] In this operation pattern, a scenario is assumed in which UE 100 is inactively receiving multiple multicast sessions. In such a scenario, network 5 (gNB 200) sets a resume condition (reception quality threshold) for each multicast session in UE 100, which is determined according to the QoS requirement of the multicast session. However, gNB 200 may not set resume conditions for some of the multiple multicast sessions that UE 100 has.

[0173] In this operation pattern, UE 100 receives, from network 5, information that sets a plurality of resume conditions corresponding to a plurality of multicast sessions that UE 100 receives. Then, UE 100 starts RRC connection resume in response to at least one of the plurality of resume conditions being satisfied. As a result, even when UE 100 receives a plurality of multicast sessions inactively, RRC connection resume based on the resume condition is possible.

[0174] 17 is a diagram illustrating an example of the operation of the mobile communication system 1 according to the sixth operation pattern of the embodiment. The UE 100 has already participated in multiple multicast sessions, and the gNB 200 is aware of the multiple multicast sessions.

[0175] In step S601, UE100 is in an RRC connected state or an RRC inactive state in the cell (serving cell) of gNB200.

[0176] In step S602, the gNB 200 transmits a resume condition setting for setting a resume condition to the UE 100. The UE 100 receives the resume condition setting from the gNB 200.

[0177] For a UE 100 in an RRC connected state, the gNB 200 may transmit a resume condition setting to the UE 100 by dedicated signaling, for example, an RRC Release message or an RRC Reconfiguration message. For a UE 100 in an RRC connected state or an RRC inactive state, the gNB 200 may transmit a resume condition setting to the UE 100 by broadcast signaling, for example, an MCCH or SIB.

[0178] In the sixth operation pattern, the resume condition is set for each session (each MBS session ID). In the resume condition setting, the resume condition may be associated with the MBS session ID. The resume condition setting may include a setting related to the number of resume conditions for performing RRC resume. The UE 100 may start RRC connection resume in response to a set number (the number of resume conditions) of multicast sessions among its own multiple multicast sessions satisfying the resume condition.

[0179] In steps S603 and S604, UE100 in an RRC inactive state receives each multicast session from gNB200 on the corresponding MTCH.

[0180] In step S605, the UE 100 in the RRC inactive state measures the reception quality of each multicast session (for example, multicast data reception quality), and determines whether or not the reception quality satisfies the corresponding resume condition.

[0181] For example, the UE 100 may start the RRC connection resume in response to the fact that a corresponding resume condition is satisfied for at least one multicast session, the fact that a corresponding resume condition is satisfied for each of a set number of multicast sessions, or the fact that a corresponding resume condition is satisfied for all multicast sessions. Note that the UE 100 may not need to evaluate the resume condition for a multicast session for which a corresponding resume condition is not set.

[0182] The gNB 200 may set a prioritized multicast session to the UE 100. When a prioritized multicast session is set and the prioritized multicast session satisfies a corresponding resume condition, the UE 100 may start RRC connection resume even if the set number of multicast sessions do not satisfy the resume condition.

[0183] In step S606, UE100 in an RRC inactive state resumes RRC connection with gNB200.

[0184] In step S607, the UE 100 transitions from the RRC inactive state to the RRC connected state.

[0185] In step S608, the UE 100 in the RRC connected state receives each multicast session on the corresponding MTCH.

[0186] (4) Other embodiments The resume conditions may be linked to the serving cell and the neighboring cell, and may be set from the gNB 200 to the UE 100. The UE 100 may perform RRC resume only if these two resume conditions are satisfied, and may not perform RRC resume in other cases. For example, if the RSRP threshold is set as the resume condition, the RRC resume is performed when the RSRP of the serving cell falls below the threshold and the RSRP of the neighboring cell falls below the threshold. Note that different values ​​may be set for these RSRP thresholds. Note that the combination of the two resume conditions may be a set that targets the serving cell and all neighboring cells, or a different combination may be set for each neighboring cell.

[0187] 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).

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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).

[0193] 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.

[0194] 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.

[0195] 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.

[0196] This application claims priority to U.S. Provisional Application No. 63 / 501,461 (filed May 11, 2023), the entire contents of which are incorporated herein by reference.

[0197] (5) Supplementary Note A The following supplementary note is provided regarding the features of the above-described embodiment.

[0198] (Supplementary Note 1) A communication method executed by a user device in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a step of receiving, from a network, information for setting a resume condition related to multicast reception quality, which is a condition for starting an RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state; a step of receiving, from the network, information for setting an area condition related to an area in which the RRC connection resume based on the resume condition is permitted or prohibited; and a step of starting the RRC connection resume when the resume condition and the area condition are satisfied when receiving multicast in the RRC inactive state.

[0199] (Supplementary Note 2) The communication method according to Supplementary Note 1, further comprising: when the resume condition is set but the area condition is not satisfied, performing control so as not to start the RRC connection resume based on the resume condition.

[0200] (Supplementary Note 3) The communication method according to Supplementary Note 1 or 2, wherein the area condition is a condition that the user equipment is not located in the area consisting of a group of cells to which a common point-to-multipoint (PTM) configuration is applied, or a condition that the user equipment is located in the area consisting of a group of cells to which the common PTM configuration is not applied.

[0201] (Supplementary Note 4) The communication method according to Supplementary Note 1 or 2, wherein the area condition is a condition that the user equipment is not located in the area consisting of a group of cells that constitute a single frequency network (SFN), or a condition that the user equipment is located in the area consisting of a group of cells that do not constitute the SFN.

[0202] (Supplementary Note 5) The communication method according to Supplementary Note 1 or 2, wherein the area condition is a condition that the user equipment is located in the area consisting of a group of cells in which the RRC connection resume based on the resume condition is permitted, or a condition that the user equipment is not located in the area consisting of a group of cells in which the RRC connection resume based on the resume condition is prohibited.

[0203] (Supplementary Note 6) A communication method executed by a user equipment in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: receiving, from a network, information for setting a resume condition related to multicast reception quality, which is a condition for initiating RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state, the information including information for setting a different resume condition as the resume condition for each combination of a serving cell and a neighboring cell; and starting the RRC connection resume in response to the resume condition associated with the combination of a current serving cell and a current neighboring cell being satisfied when receiving multicast in the RRC inactive state.

[0204] (Supplementary Note 7) A communication method executed by a user equipment in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: receiving, from a network, information for setting a resume condition related to multicast reception quality, which is a condition for initiating RRC connection resume during multicast reception in a radio resource control (RRC) inactive state, wherein the resume condition includes a reception quality threshold to be compared with the multicast reception quality of a physical downlink shared channel (PDSCH) associated with a multicast traffic channel (MTCH); and starting the RRC connection resume in response to the reception quality of the PDSCH associated with the MTCH during the multicast reception during the multicast reception in the RRC inactive state.

[0205] (Supplementary Note 8) A communication method executed by a user device in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a step of determining whether or not a resume condition related to multicast reception quality, which is a condition for initiating RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state, is set in the user device from a network; and a step of determining, based on a result of the determination, that initiating the RRC connection resume for receiving multicast when receiving multicast in the RRC inactive state is prohibited.

[0206] (Supplementary Note 9) The communication method according to Supplementary Note 8, wherein the step of determining that the RRC connection is prohibited includes the step of determining that initiation of the RRC connection resume for the multicast reception is prohibited when the resume condition is set in the user equipment and the resume condition is not satisfied.

[0207] (Supplementary Note 10) The communication method according to Supplementary Note 8, wherein the step of determining that the RRC connection is prohibited includes the step of determining that initiating the RRC connection resume for the multicast reception is prohibited if the resume condition is not set in the user equipment.

[0208] (Supplementary Note 11) A communication method executed by a user device in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a step of receiving, from a network, information for setting a resume condition related to multicast reception quality, the condition being a condition for initiating RRC connection resume when multicast is received in a radio resource control (RRC) inactive state; a step of initiating the RRC connection resume in response to the resume condition being satisfied when multicast is received in the RRC inactive state; and a step of notifying the network that the resume condition has been satisfied in the RRC connection resume procedure.

[0209] (Supplementary Note 12) The communication method according to Supplementary Note 11, wherein the notifying step includes a step of transmitting, to the network, an RRC Resume Request message including an information element indicating that the resume condition has been satisfied.

[0210] (Supplementary Note 13) A communication method executed by a user equipment in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a step of receiving, from a network, information for setting a resume condition related to multicast reception quality, the condition being a condition for initiating RRC connection resume when multicast is received in a radio resource control (RRC) inactive state; and a step of initiating the RRC connection resume in response to the resume condition being satisfied when multicast is received in the RRC inactive state, wherein the receiving step includes a step of receiving the information that sets a plurality of resume conditions corresponding to a plurality of multicast sessions received by the user equipment, and the initiating step includes a step of initiating the RRC connection resume in response to at least one of the plurality of resume conditions being satisfied.

[0211] (6) Appendix B 1. Introduction The work item on enhanced MBS (eMBS) aims to support multicast reception by UEs in inactive mode and is described as follows: - Specify support for multicast reception by UEs in RRC inactive mode [RAN2, RAN3]. - PTM configuration for UEs receiving multicast in RRC inactive mode [RAN2]. - Investigate the impact of mobility and state transitions for UEs receiving multicast in RRC inactive mode (seamless / lossless mobility is not mandatory) [RAN2, RAN3].

[0212] RAN2 has been discussing this goal and has reached a set of agreements. Building on these agreements, the control plane aspects regarding multicast reception in inactive mode are discussed in this appendix.

[0213] 2. Discussion 2.1. Initial Setup Procedure RAN2#120 reached a consensus to proceed with a "mixed approach."

[0214] In the mixed approach, we recommend the following: 1: If the NW configures the UE to continue multicast reception in inactive state, the NW provides PTM configuration of activated multicast sessions through RRC dedicated signaling, at least for the serving cell (other cases require further study). 2: MCCH is used when PTM configuration needs to be changed or when PTM configuration needs to be indicated during movement beyond the serving cell / gNB. Session status changes and other indications require further study. 3: It is assumed that the UE can receive multicast services only after joining the session. 4: Whether MCCH configuration is initially provided to the UE through dedicated signaling requires further study.

[0215] RAN2#121 agreed to the following: ・The UE needs to join a multicast session before receiving multicast in RR inactive. ・If the network deems it useful, it can configure the UE with the PTM configuration of a (single) serving cell before session activation and the UE can store the configuration. Once the session is activated, the UE can apply the configuration and receive multicast in inactive state without going back to RRC Connected, unless updated by MCCH after configuration. ・If the network configures the UE to receive multicast in inactive state, it can deliver the PTM configuration using an RRC Release message with suspendconfig. No other dedicated RRC message will be used to provide PTM configuration for MBS multicast in inactive. ・A new MCCH logical channel for multicast in inactive will be introduced (different from the broadcast MCCH). ・Multicast MCCH configuration will be provided via a new SIB. Alternatively, multicast MCCH configuration for the serving cell can also be provided by dedicated signaling, which is therefore not optimized for mobility.

[0216] Based on these agreements, the setup procedures for an ongoing (i.e., activated) multicast session and a deactivated (i.e., before activation) multicast session can be seen as shown in Figure 18.

[0217] 2.1.1 Ongoing (Active) Multicast Session For an ongoing multicast session, the UE configures a multicast MRB for multicast reception in Connected mode via RRC reconfiguration and starts receiving MTCH as in Rel-1. For multicast reception in Inactive mode, the UE configures a broadcast MRB (or a new "multicast inactive MRB") for multicast reception via RRC release.

[0218] Regarding the PTM settings for RRC resume, it is clear that the baseline content (IEs, etc.) is the same as that of Rel-17 MCCH (MBS Broadcast Configuration). However, since RAN2 agreed to "introduce a new MCCH logical channel," the RRC message name must also be different from that of Rel-17 MBS Broadcast Configuration. The same message is transmitted over the new MCCH logical channel.

[0219] Proposal 1: RAN2 should agree to define a new RRC message for PTM configuration in RRC release and define a new "multicast MCCH", e.g., MBSMulticastInactiveConfiguration.

[0220] Proposal 2: RAN2 should agree that the IE of the new RRC message for PTM configuration is the same as Rel-17 MBSBroadcastConfiguration as the baseline.

[0221] When the UE receives an RRCRelease with suspendConfig, the connected multicast MRBs are suspended, just like in Rel-1. The UE continues the same multicast session if the RRC release includes inactive PTM configuration. Service continuity of the multicast session needs to be ensured during / after RRC state transitions. This is similar to legacy-only configurations such as redirectedCarrierInfo, cellReselectionPriorities, deprioritizationReq, and measIdleConfig. The UE needs to start receiving broadcast MRBs as soon as it applies the PTM configuration. Whether a new procedure (i.e., the UE applies PTM configuration and starts receiving MTCH) is performed when the UE applies suspendConfig needs further study.

[0222] Proposal 3: RAN2 should agree that before suspending multicast MRBs, UEs should apply PTM configuration for broadcast MRBs (or new "multicast inactive MRBs") and start receiving the corresponding MCCH.

[0223] 2.1.2. Deactivated Multicast Session (Before Activation) In a deactivated multicast session, the UE performs PTM configuration via RRC release. If Proposal 3 above is acceptable, the UE would immediately start receiving the MTCH, but since the MTCH is not transmitted at this time, the UE should refrain from doing so. Instead, the UE should be notified via RRC release that the multicast session is still inactive, allowing the UE to wait for a multicast session activation notification without receiving the MTCH. Further study is required for detailed operation; for example, it can be decided whether to wait for session activation while applying the PTM configuration.

[0224] Proposal 4: RAN2 should agree to inform the UE via RRC release whether the multicast session has been deactivated so that the UE will not attempt to receive the corresponding MTCH.

[0225] After transitioning to inactive, the UE monitors multicast session activation notifications (i.e., group paging). Prior to multicast session activation, the gNB may change the PTM settings of the session, and such changes constitute a new "multicast MCCH" for the UE in inactive. In this case, the gNB may transmit the "multicast MCCH" before session activation.

[0226] From the UE's perspective, if the UE needs to monitor a new "multicast MCCH" for the deactivated multicast session, the UE's power consumption will increase. Therefore, it is necessary to ensure that the UE does not need to monitor the multicast MCCH before receiving the multicast session activation notification. In other words, the UE only needs to monitor the multicast MCCH once it receives the activation notification for the TMGI of interest. The same operation can be applied to new SIBs (such as SIB20) for MCCH configuration.

[0227] Proposal 5: RAN2 should agree that UEs do not need to monitor the new "multicast MCCH" or new SIBs (such as SIB20) if the corresponding multicast session is deactivated (i.e., before receiving a multicast session notification).

[0228] Upon receiving the multicast activation notification, the UE needs to check whether the MCCH configuration in the new SIB and / or the PTM configuration in the multicast MCCH have been updated if the MCCH configuration and / or the PTM configuration were provided by the RRC release. Unless the configuration has been updated, the saved configuration, i.e., the configuration provided by the RRC release, should be applied. Of course, if the configuration has been updated, the UE needs to acquire the new SIB and / or the multicast MCCH.

[0229] For the new SIB, it is expected that the UE can know whether the new SIB has been updated by checking the value tag of SIB1 as it does now. However, the UE does not know whether the multicast MCCH has been updated before receiving and decoding the MCCH. In this case, even if the MCCH has been configured by RRC release, the UE would still need to decode the MCCH once, which is also meaningless. In this sense, a value tag needs to be introduced into the MCCH so that the UE can know the PTM configuration update without decoding the MCCH. Further study is required on where the MCCH value tag should be placed, whether it should be placed in the new SIB, SIB1, or group paging, etc.

[0230] Proposal 6: RAN2 should agree that an MCCH value tag be introduced that the UE uses to know whether the PTM configuration has been updated from that set by RRC release, without having to decode the MCCH itself.

[0231] 2.2 Configuration Update in Inactivity In Rel-17, there is one MCCH in a cell. In Rel-18, RAN2 agreed to introduce a new MCCH logical channel for multicast in inactivity (different from the broadcast MCCH). The multicast MCCH is used when the PTM configuration needs to be changed or when the PTM configuration needs to be indicated during movement across the serving cell / gNB.

[0232] Observation 1: The multicast MCCH is used to update the PTM configuration of UEs in inactivity.

[0233] In other words, there are two MCCHs in Rel-18 networks: (broadcast) MCCH and multicast MCCH. The motivation for introducing separate MCCHs within a cell is thought to be to handle the different service requirements of different cast types (MBS broadcast and MBS multicast).

[0234] The question is whether different multicast sessions have different service requirements. It is considered that the service requirements for a group multimedia call service and a firmware download service are quite different. For example, the group multimedia call service is a foreground service, so it needs to frequently optimize the PTM settings, while the firmware download service is a background service, so such frequent optimization is not necessary. Considering that the initial PTM settings are provided by RRC release, updating the PTM settings via a multicast MCCH is necessary for some services but not for others. In this sense, introducing multiple multicast MCCHs is efficient for UEs and flexible for the network.

[0235] Proposal 7: RAN2 should discuss whether to introduce multiple multicast MCCHs per cell.

[0236] 2.3 UE Mobility and Service Continuity 2.3.1 Frequency Prioritization RAN2#121bis-e agreed that UE behavior during cell reselection requires further study. Similar to the Rel-17 broadcast reception procedure, the UE acquires new SIBs and multicast MCCH and PTM settings after cell reselection. If the UE reselects to a cell where PTM settings are not available on the multicast MCCH, the UE initiates the RRC resumption procedure for active multicast sessions that it is interested in receiving or continuing to receive. Frequency prioritization may be provided to the UE for cell reselection with RRC inactivity and multicast reception, but the detailed mechanism for identifying frequency information (e.g., SAI, USD, or frequency information provided directly by the network) requires further study. It is not necessary to define a mechanism other than frequency prioritization, i.e., per-cell prioritization for cell reselection, to enable the UE to select an appropriate cell. The neighbor cell list mechanism for multicast reception in RRC inactive can be configured in some aspects to be similar to the Rel-17 NCL mechanism in MBS broadcast, so that it can be used by the UE to resume RRC connection when the service is not available in the reselected cell due to NCL, without reading the MCCH in the reselected cell.

[0237] Regarding frequency information, higher layers can provide information via USD, etc. However, considering that NRMBS transmission is determined on a cell-by-cell basis, USD can only provide static information (especially for inactive UEs), while the RAN may have up-to-date information. Therefore, the RAN should also provide frequency information if possible. Therefore, like SIB21 in the Rel-17 MBS broadcast, the gNB can broadcast frequency information so that the UE can prioritize the appropriate frequency during cell reselection.

[0238] Proposal 8: RAN2 should agree that frequency information will be broadcast by the gNB.

[0239] 2.3.2 Area-Specific PTM Configuration In RAN2#121, area scope for MCCH was discussed. Some companies have proposed enabling PTM configuration in multiple cells to improve service continuity during UE mobility. In the intra-gNB case, PTM configuration for each cell can be easily coordinated (if necessary), but in the inter-gNB case, it becomes more difficult and requires negotiation with the Xn-AP. Finally, RAN2 agreed that area scope does not involve other gNBs, and the intra-gNB case requires further study. ・A serving cell does not provide PTM configuration for neighboring cells from other gNBs. ・Whether the network can provide PTM configuration to intra-gNB cells requires further study.

[0240] For this small enhancement, it is considered acceptable to limit it to the case within the gNB. Therefore, RAN2 should discuss whether the PTM configuration can be applied to multiple cells within the gNB.

[0241] Proposal 9: RAN2 should discuss whether PTM settings can be applied to multiple cells within a gNB.

[0242] 2.3.3 QoS Enforcement RAN2#119e has reached the following agreements related to Case 3: HARQ feedback and PTP are not supported for RRC inactive multicast reception.

[0243] According to the agreement, multicast reception in inactive mode is similar to MBS broadcast reception (so-called Delivery mode 2) specified in Rel-17. MBS broadcast is best-effort type.

[0244] On the other hand, guaranteeing QoS / reliability is an important issue for multicast sessions. SA2 also raised the question of whether there is a difference in quality / reliability of multicast reception between connected and inactive, and RAN2#119bis-e agreed to the following answer:

[0245] RAN2 Q1-a) If there is a large difference in the quality and reliability of MBS data reception between a UE in RRC connected state and a UE in RRC inactive state, the quality and reliability of MBS data reception between a UE in RRC connected state and a UE in RRC inactive state may be different since HARQ feedback and PTP transmission are not supported and seamless / lossless mobility is not required for multicast reception in RRC inactive.

[0246] RAN2#121bis-e agreed to introduce an event-triggered RRC restart mechanism, but the trigger conditions require further study.

[0247] The UE may trigger the resumption of the RRC connection if the reception quality of the multicast data falls below a configured threshold.

[0248] In RAN2#119e, it has been proposed to introduce thresholds for reception quality such as RSRP and BLER, which are thought to be used to ensure a certain level of QoS required for multicast reception.

[0249] Regarding the RSRP threshold, NR MBS assumes a single-cell transmission method and monitors SSB or CSI-RS instead of directly monitoring MTCH. Therefore, it is considered necessary for the UE to transition to Connected whenever it moves to the cell edge or performs cell reselection. This may not be optimal in some deployments from the perspective of network congestion and UE power saving. However, RSRP is one of the basic metrics used to evaluate reception quality and is one of the usual metrics used by gNBs when deciding on handover (i.e., handover is performed after the UE transitions to Connected due to this RSRP threshold).

[0250] Regarding the BLER threshold, it is considered to be more understandable to ensure QoS requirements since it directly monitors the quality of the MTCH, and therefore BLER is worth specifying as the metric.

[0251] Another way is to define a specific event. For example, if the event is set to cell reselection, the UE must always transition to Connected before cell reselection. However, such an event can be emulated by the RSRP threshold mentioned above. Therefore, careful consideration is required when RAN2 defines the events that will be trigger conditions.

[0252] In summary, at least the RSRP threshold and / or the MTCH BLER threshold should be used for event-triggered RRC resumption.

[0253] Proposal 10: RAN2 should agree to introduce an RSRP threshold and / or an MTCH BLER threshold to monitor multicast reception quality and trigger RRC restart.

[0254] 2.4 Notifications 2.4.1 Multicast Session Deactivation In RAN2#121bis-e, the method of notifying UEs of session deactivation is being discussed. Further study is required to determine whether the option of enhanced group paging or enhanced MCCH should be adopted to allow Rel-18 UEs to remain in RRC inactive and stop monitoring the corresponding G-RNTI in the event of session deactivation / temporary no data.

[0255] The above agreement allows for only enhanced group paging or enhanced MCCH, but does not explicitly exclude the new MAC CE. Only the key points of the analysis of these options are summarized in Table 1.

[0256] Of the three options, MAC CE is considered to be the most efficient in terms of UE power consumption (i.e., because it has the shortest latency), but email discussions have shown that this option has few supporters.

[0257] Of the two viable options, enhanced group paging has a slight advantage, even in terms of UE power consumption. Based on legacy operation, the MCCH would need to delete the PTM configuration of the deactivated session. Considering that this multicast session will become active again (because it has not been released), the enhanced MCCH would need to add back the same PTM configuration, and the UE would need to reacquire and apply this configuration. Furthermore, it is unclear what is being enhanced in the enhanced MCCH. Assuming that a deactivation notification is added to the MCCH (a similar notification is added in enhanced group paging), this notification is delayed so that the UE receives it after the session is actually deactivated. Therefore, group paging seems reasonable.

[0258] Proposal 11: RAN2 should agree to enhanced group paging for multicast session invalidation.

[0259] Regarding the details of the group paging enhancement, backward compatibility needs to be considered: since the existing paging group list (i.e., list of TMGIs) is applicable to legacy UEs, group paging needs to add a new TMGI list for invalidation notification to avoid impacting legacy UEs.

[0260] Proposal 12: If proposal 11 can be agreed upon, RAN2 will further discuss whether to create a new paging group list consisting of the TMGIs of the disabled multicast sessions.

[0261] 2.4.2 Multicast Session Activation and Selective Transition RAN2 #119e has arrived at the assumption that the gNB can select a subset of UEs to transition between inactive and connected states. It is assumed that the network can select which UEs receive in the RRC inactive and RRC connected states and can move UEs between states for multicast service reception.

[0262] RAN2#121bis-e agreed to enhance group paging for session activation notification. A Rel-18 UE can remain in RRC inactive state and start monitoring the corresponding G-RNTI when an enhanced group paging occurs (e.g., session activation or data transmission resumption). Details require further study. Legacy group paging (i.e., Rel-17 group paging) can be used to return the UE to RRC Connected state. UE-specific paging (e.g., PagingRecordList) can be used to move a specific MBS multicast UE to RRC Connected (i.e., legacy UE behavior). If a UE receives both enhanced group paging and unicast paging (and both are targeted at this UE), the UE will follow the unicast paging and transition to RRC Connected.

[0263] For the enhancement regarding group paging, considering that a subset of UEs remain in inactive while another subset transitions to Connected, the behavior of the UEs when receiving the current paging message (i.e., UE-specific paging and group paging) is as follows: UE-specific paging: The UE transitions to Connected if its UE-ID is available in the pagingRecordList. Group paging: All UEs transition to Connected when the TMGI of interest is available in the pagingGroupList. Paging messages: The pagingRecordList and pagingGroupList can be set simultaneously (i.e., in one message) from an ASN.1 perspective. In any case, all UEs transition to Connected when a TMGI of interest becomes available in the pagingGroupList, regardless of the pagingRecordList.

[0264] Therefore, the gNB cannot keep a subset of UEs in an inactive state as long as these UEs are interested in the TMGIs available in the pagingGroupList.

[0265] Therefore, the Rel-18 enhancements require a change in the UE behavior when receiving group paging. A simple solution is to cancel the legacy pagingGroupList, which is always required for Rel-17 UEs (i.e., backward compatibility). Since the cancellation needs to be per TMGI, an additional TMGI list is required (e.g., the Paging Group Cancel List is configured in TMGIs). Considering the RAN2 agreement that "if both enhanced group paging and unicast paging are received by a UE (and targeted at this UE), the UE follows unicast paging and becomes RRC connected," the behavior of a Rel-18 UE is as follows:

[0266] Step 1: The UE receives a paging message containing a pagingRecordList, pagingGroupList, and a new TMGI cancellation list. Step 2: Because the pagingGroupList contains the TMGI of interest, the UE considers it has been paged by group paging, as in Rel-17. Step 3: Because the new TMGI cancellation list contains the TMGI of interest (i.e., the same TMGI), the UE considers the group paging to have been canceled. Step 4: Because the pagingRecordList contains the UE-ID, the UE considers it has been paged by UE-specific paging and transitions to Connected, as in Rel-17. Step 5: The gNB configures the UE with multicast MRBs, as in Rel-17.

[0267] Finally, only a subset of UEs transition to Connected for multicast reception.

[0268] Proposal 13: RAN2 should agree to add a new cancellation TMGI list to group paging to cancel Rel-17 group paging.

[0269] Further study is needed for "special UEs" in RAN2#121bis-e. "Special UEs" identified by MBS assistance information from 5GC may be released to RRC inactive (e.g., when a session is deactivated). Further study is needed on how to enable the network to return to RRC connected when such UEs activate a session.

[0270] That is, the pagingRecordList contains the UE-ID of the "special UE", and the pagingGroupList and the new TMGI cancellation list contain the TMGIs of interest for the "special UE", so there is no need to extend it for this purpose.

[0271] Observation 2: The new TMGI cancellation list also works for "special UEs" at session activation.

[0272] 2.4.3. PTM Configuration Update It was agreed in RAN2#120 that MCCH should be used when PTM configuration needs to be updated. A mixed approach is recommended as follows: 5: If the NW configures the UE to continue multicast reception in inactive state, the NW provides PTM configuration for activated multicast sessions through RRC dedicated signaling, at least for the serving cell (other cases require further study). 6: MCCH is used when PTM configuration needs to be changed or when PTM configuration needs to be indicated during movement beyond the serving cell / gNB. Session status changes and other indications require further study. 7: It is assumed that the UE can receive multicast services only after joining the session. 8: Whether MCCH configuration is initially provided to the UE by dedicated signaling requires further study.

[0273] RAN2#121 agreed to use RRC release for PTM configuration (even before session activation) and to introduce a new MCCH (different from the Rel-17 MCCH).

[0274] - A UE needs to join a multicast session before receiving multicast in RRC inactive. - If the network deems it useful, it can configure the UE with the PTM configuration of a (single) serving cell before session activation, and the UE can store the configuration. Once the session is activated, the UE can apply the configuration and receive multicast in inactive state without returning to RRC connected, unless updated by MCCH after configuration. - If the network configures the UE to receive multicast in inactive state, it can deliver the PTM configuration using an RRC release message with suspendconfig. No other dedicated RRC message is used to provide PTM configuration for MBS multicast in inactive. - A new MCCH logical channel for multicast in inactive is introduced (different from broadcast MCCH).

[0275] According to these agreements, there are two cases for PTM configuration update: Case 1: UE in inactive state receiving an already activated multicast session Case 2: UE in inactive state waiting for multicast session activation Note: Case 2 may be further classified depending on whether the PTM configuration was provided by RRC release or not. In such cases, it is desirable that the solution is as common as possible.

[0276] Proposal 14: RAN2 should aim for a common solution for PTM configuration update notification that considers at least two cases: sessions that have already been activated and sessions before activation.

[0277] The motivation for using MCCH is to reduce the signaling overhead during PTM configuration updates, i.e., to allow UEs to remain inactive to obtain updated PTM configurations. Therefore, from the perspective of an inactive UE, the new PTM configuration distribution method in Rel-18 is similar to distribution mode 2 in Rel-17. In this case, it seems reasonable to reuse the existing MCCH change notification to signal PTM configuration updates.

[0278] However, MCCH Change Notification requires the UE to wake up once per MCCH change boundary, which imposes additional burden on top of monitoring paging occasions, and is not efficient, especially for case 2 above (i.e., the UE needs to monitor MCCH Change Notification even if it is only waiting for a multicast session notification to see if the PTM configuration provided by the RRC release has been updated).

[0279] To solve this problem, group paging can be enhanced for notification of PTM configuration updates. The UE only needs to monitor paging opportunities to determine whether the PTM configuration has been updated, regardless of whether the UE is receiving a multicast session or not (i.e., case 1 or case 2 above). Therefore, RAN2 needs to agree to use group paging for this notification. The details of the enhancements require further study.

[0280] Proposal 15: RAN2 should agree to use group paging for PTM configuration updates instead of the existing MCCH change notification.

[0281] 2.5 Service Continuity During RRC Resume It is necessary to consider the possibility that a UE already receiving a multicast session in Inactive (i.e., via a Broadcast MRB or a new MRB for multicast reception in Inactive) is paged and initiates an RRC Resume procedure. After transitioning to Connected, the UE would of course like to continue receiving the same multicast session. However, in this case, the UE has two MRBs for the same multicast session: the Broadcast MRB (or new MRB) configured for multicast reception in Inactive, and the resumed Multicast MRB for multicast reception in Connected.

[0282] In Rel-17, multicast sessions can only be received via multicast MRBs configured by RRC reconfiguration, whereas in Rel-18, it is expected that UEs will be able to receive multicast sessions via Broadcast MRBs (or new MRBs) configured by RRC reconfiguration or a new MCCH.

[0283] The UE should use multicast MRBs for reception after transitioning to Connected (similar to Rel-17). However, it is unclear how the UE should switch between these MRBs, when the UE should discard broadcast MRBs (or new MRBs), and how the UE should behave if the multicast MRB is an AM MRB (i.e., from the perspective of the lossless principle). Therefore, RAN2 needs to discuss the UE behavior upon RRC resumption in terms of MRB handling and service continuity of multicast sessions.

[0284] Proposal 16: RAN2 should discuss UE behavior upon RRC resumption during continuous reception of a multicast session (e.g., handling of broadcast MRBs and multicast MRBs).

[0285] 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. 1. A communication method performed by a user equipment in a mobile communication system providing a multicast / broadcast service (MBS), comprising: receiving, from a network, a plurality of reception quality thresholds associated with a plurality of multicast sessions, the reception quality thresholds being used to initiate RRC connection resume during multicast reception in a radio resource control (RRC) inactive state; identifying a reception quality threshold associated with the joined multicast session from the plurality of reception quality thresholds; and starting the RRC connection resume in response to reception quality falling below the specified reception quality threshold during multicast reception in the RRC inactive state. Communication method.

2. The communication method according to claim 1 or 2, wherein the initiating comprises sending an RRC Resume Request message including mt-Access as a Resume Cause to the network.

3. A user device for use in a mobile communication system providing a multicast / broadcast service (MBS), comprising: a receiving unit that receives from a network a plurality of reception quality thresholds associated with a plurality of multicast sessions, the reception quality thresholds being for initiating RRC connection resume during multicast reception in a radio resource control (RRC) inactive state; a control unit that identifies a reception quality threshold associated with a multicast session in which the user has participated from the plurality of reception quality thresholds; The control unit starts the RRC connection resume in response to reception quality falling below the specified reception quality threshold during multicast reception in the RRC inactive state. User equipment.

4. A chipset for user equipment used in a mobile communication system providing multicast / broadcast services (MBS), comprising: receiving, from a network, a plurality of reception quality thresholds associated with a plurality of multicast sessions, the reception quality thresholds being used to initiate RRC connection resume during multicast reception in a radio resource control (RRC) inactive state; identifying a reception quality threshold associated with a joined multicast session from the plurality of reception quality thresholds; During multicast reception in the RRC inactive state, a process of starting the RRC connection resume in response to the reception quality falling below the specified reception quality threshold is executed. Chipset.

5. A user device used in a mobile communication system providing a multicast / broadcast service (MBS), comprising: receiving, from a network, a plurality of reception quality thresholds associated with a plurality of multicast sessions, the reception quality thresholds being used to initiate RRC connection resume during multicast reception in a radio resource control (RRC) inactive state; identifying a reception quality threshold associated with a joined multicast session from the plurality of reception quality thresholds; and executing a process of starting the RRC connection resume in response to the reception quality falling below the specified reception quality threshold during multicast reception in the RRC inactive state. program.

6. A mobile communication system providing a multicast / broadcast service (MBS), comprising: a user equipment and a network node; The user equipment receives from the network node a plurality of reception quality thresholds associated with a plurality of multicast sessions, the reception quality thresholds being for initiating RRC connection resume during multicast reception in a radio resource control (RRC) inactive state; The user device identifies a reception quality threshold associated with a multicast session in which the user device has participated from the plurality of reception quality thresholds; The user equipment starts the RRC connection resume in response to reception quality falling below the specified reception quality threshold during multicast reception in the RRC inactive state. Mobile communication system.