Communication method and user device

Abstract

Provided is a communication method that is executed by a user device in a mobile communication system providing a multicast broadcast service (MBS), the communication method comprising: receiving, from a network node, a threshold value setting for setting a threshold value to be compared with the reception quality at the time of reception of a multicast session in a radio resource control (RRC) inactive state, the threshold value being for use in start determination of RRC connection resume; applying the threshold value setting so as to compare the reception quality with the threshold value in the RRC inactive state; and stopping the application of the threshold value setting in response to a predetermined multicast reception-related condition being satisfied in the RRC inactive state.

Description

Communication method and user device

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

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

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

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

[0005] A communication method according to a first aspect is a communication method executed by a user device in a mobile communication system that provides a Multicast Broadcast Service (MBS), and includes receiving a threshold setting from a network node, the threshold setting setting being a threshold to be compared with a reception quality when receiving a multicast session in a Radio Resource Control (RRC) inactive state, the threshold used to determine whether to start an RRC connection resume, and applying the threshold setting to compare the reception quality with the threshold when the multicast reception is being performed in the RRC inactive state.

[0006] A user device according to a second aspect is a user device used in a mobile communication system that provides a multicast broadcast service (MBS), and comprises: a receiving unit that receives a threshold setting from a network node, the threshold setting being a threshold to be compared with a reception quality when receiving a multicast session in a radio resource control (RRC) inactive state, the threshold being used to determine whether to start an RRC connection resume; and a control unit that applies the threshold setting to compare the reception quality with the threshold when the multicast reception is being performed in the RRC inactive state.

[0007] 1 is a diagram illustrating an example of the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a UE (user equipment) according to an embodiment. FIG. 3 is a diagram illustrating an example of the configuration of a gNB (network node) according to an embodiment. FIG. 4 is a diagram illustrating a protocol stack configuration of a radio interface of a user plane that handles data. FIG. 5 is a diagram illustrating a protocol stack configuration of a radio interface of a control plane that handles signaling (control signals). FIG. 6 is a diagram illustrating an overview of the operation of a UE according to an embodiment. FIG. 7 is a diagram illustrating an overview of the operation according to a first operation pattern of an embodiment. FIG. 8 is a diagram illustrating an example of the operation according to the first operation pattern of an embodiment. FIG. 9 is a diagram illustrating an overview of the operation according to a second operation pattern of an embodiment. FIG. 10 is a diagram illustrating an example of the operation according to the second operation pattern of an embodiment. FIG. 11 is a diagram illustrating an overview of the operation according to a third operation pattern of an embodiment. FIG. 12 is a diagram illustrating an example of the operation according to the third operation pattern of an embodiment.

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

[0009] (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.

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

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

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

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

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

[0015] 2 is a diagram 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.

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

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

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

[0019] 3 is a diagram showing an example configuration of a gNB 200 (network node) according to an embodiment. The gNB 200 has a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

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

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

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

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

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

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

[0026] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires 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.

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

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

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

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

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

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

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

[0034] The NAS layer (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").

[0035] (2) Overview of MBS The mobile communication system 1 can perform resource-efficient distribution using multicast / broadcast services (MBS).

[0036] (2.1) MBS Broadcast In the case of a broadcast communication service (also referred to as "MBS Broadcast"), the same service and the same specific content data are simultaneously provided to all UEs 100 in a geographical area. That is, all UEs 100 within the broadcast service area are permitted to receive the data. The broadcast communication service is delivered to the UEs 100 using a broadcast session, which is a type of MBS session. The UEs 100 can receive the broadcast session in any of the following states: RRC idle state, RRC inactive state, and RRC connected state.

[0037] 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.

[0038] In the case of a broadcast communication service, the UE 100 receives a broadcast session in the following procedure. First, the UE 100 receives a system information block type 20 (SIB20) from the gNB 200. The SIB20 includes a configuration of a multicast control channel (MCCH), which is a type of logical channel. Second, the UE 100 receives the MCCH from the gNB 200 based on the SIB20. The MCCH includes a PTM configuration. The PTM configuration transmits a configuration (MTCH configuration) for a multicast traffic channel (MTCH), which is a type of logical channel, and a broadcast MRB configuration, which is a multicast radio bearer (MRB) for the broadcast session. The information transmitted by the MCCH is sometimes referred to as MBS broadcast control information. Third, the UE 100 receives the MTCH based on the MCCH. The MTCH transmits the broadcast session (specifically, MBS data belonging to the broadcast session).

[0039] The MCCH is a PTM downlink channel for transmitting MBS broadcast control information associated with one or more MTCHs from the network 5 to the UE 100. The MTCH is a PTM downlink channel for transmitting MBS data of either a multicast session or a broadcast session from the network 5 to the UE 100.

[0040] (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.

[0041] 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.

[0042] In the case of a multicast communication service, only UEs 100 in an RRC connected state can receive a multicast session in 3GPP Release 17. On the other hand, in 3GPP Release 18, the standard is extended so that UEs 100 in an RRC inactive state can also receive a multicast session.

[0043] (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.

[0044] In the case of a multicast communication service, the UE 100 in the RRC connected state receives a multicast session in the following procedure. First, the UE 100 receives an RRC Reconfiguration message from the gNB 200. The RRC Reconfiguration message is a message transmitted on a dedicated control channel (DCCH). The RRC Reconfiguration message transmits a setting (MTCH setting) for the MTCH for receiving the multicast session and a setting of a multicast MRB, which is an MRB for the multicast session. Second, the UE 100 receives the MTCH based on the RRC Reconfiguration message. The MTCH transmits the multicast session (specifically, MBS data belonging to the multicast session).

[0045] (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.

[0046] In the case of a multicast communication service, the UE 100 in the RRC inactive state can receive a multicast session in the following procedure. First, the UE 100 in the RRC inactive state receives a newly introduced system information block (also referred to as "SIBx") from the gNB 200. The SIBx includes a configuration of a newly introduced MCCH (also referred to as "multicast MCCH"). Second, the UE 100 in the RRC inactive state receives a multicast MCCH from the gNB 200 based on the SIBx. The multicast MCCH includes a PTM configuration. The PTM configuration transmits a configuration for an MTCH for receiving a multicast session (MTCH configuration) and a configuration of a multicast inactive MRB, which is an MRB for receiving a multicast session in the RRC inactive state (multicast inactive MRB configuration). The MTCH configuration may be included in the multicast inactive MRB configuration. Third, the UE 100 in the RRC inactive state receives the MTCH based on the multicast MCCH. The MTCH transmits the multicast session, specifically, the MBS data (i.e., multicast data) belonging to the multicast session.

[0047] When gNB200 configures UE100 to receive a multicast session in an RRC inactive state, it can send a PTM setting (multicast inactive MRB setting) to UE100 using an RRC Release message including a suspend setting. In this case, when UE100 receives an RRC Release message including a PTM setting from gNB200, it transitions to an RRC inactive state and receives the multicast session (multicast reception) in the RRC inactive state.

[0048] (2.2.3) Group Notification When there is temporarily no data to transmit to UE 100 in an active multicast session, gNB 200 may transition UE 100 to an RRC inactive state. When the multicast session is deactivated, gNB 200 may transition UE 100 to an RRC idle state or an RRC inactive state.

[0049] A gNB 200 that supports MBS uses a group notification mechanism to notify UEs 100 in an RRC idle state or an RRC inactive state when a multicast session is activated by CN 20. For example, a gNB 200 that supports MBS may use a group notification mechanism to notify UEs 100 in an RRC inactive state when a multicast session has been activated and there is multicast session data to be distributed in the gNB 200.

[0050] Upon receiving the group notification, the UE 100 reconnects or resumes connection to the network 5 and transitions to the RRC connected state. The group notification is processed in the paging RNTI (P-RNTI) on the PDCCH, and the paging channel is monitored by the UE 100.

[0051] The group notification paging message includes a session identifier (MBS Session ID) that is used to page all UEs 100 in RRC idle and RRC inactive states that have joined the associated MBS multicast session, i.e., the UEs 100 are not paged individually.

[0052] When UE 100 transitions to the RRC connected state, UE 100 may stop monitoring group notifications related to a particular multicast session. That is, UE 100 stops checking the MBS session ID in paging messages. UE 100 does not monitor group notifications in cases where UE 100 leaves this multicast session, network 5 requests UE 100 to leave, or network 5 releases the multicast session.

[0053] The group notification may be performed using the MCCH or may be performed using an MCCH Change Notification. When the MCCH is used, the determination may be made based on whether or not an MTCH configuration for the MBS session of interest exists in the MCCH. When the MCCH Change Notification is used, the group notification may be notified in a predetermined bit of the DCI.

[0054] (3) Operation of the Mobile Communication System The operation of the mobile communication system 1 according to the embodiment will be described.

[0055] (3.1) Operation Overview In the embodiment, a scenario is assumed in which UE 100 in an RRC inactive state starts RRC connection resume (also referred to as "RRC resume") in relation to a multicast session (multicast reception). Here, the case in which UE 100 in an RRC inactive state starts RRC connection resume in relation to a multicast session is when the reception quality (also referred to as "multicast reception quality") during multicast reception at UE 100 is poor, and / or when UE 100 needs to acquire a multicast reception setting (PTM setting) from gNB 200. In the embodiment, a scenario in which UE 100 starts RRC connection resume in response to poor reception quality during multicast reception at UE 100 in an RRC inactive state is mainly assumed.

[0056] A case where the reception quality during multicast reception at UE 100 is poor is a case where the reference signal received power (RSRP) measured by UE 100 for the serving cell is below the RSRP threshold set in UE 100 by the network 5, and / or a case where the reference signal received quality (RSRQ) measured by UE 100 for the serving cell is below the RSRQ threshold set in UE 100 by the network 5. However, a case where the reception quality during multicast reception at UE 100 is poor may also be a case where the bit error rate (BER) measured by UE 100 for the multicast session exceeds the BER threshold set in UE 100 by the network 5, and / or a case where the block error rate (BLER) measured by UE 100 for the multicast session exceeds the BLER threshold set in UE 100 by the network 5.

[0057] The threshold value (also referred to as "reception quality threshold value") to be compared with the reception quality during such multicast reception can be set by PTM setting (multicast reception setting) on ​​an MBS session basis from the network 5 (gNB 200) to the UE 100 by an RRC Release message or a multicast MCCH (multicast MCCH message). In an embodiment, the UE 100 performing multicast reception in an RRC inactive state starts an RRC connection resume procedure when the reception quality of the serving cell is worse than the threshold set by the network 5. In the embodiment, it is mainly assumed that there are two types of signaling that can set the reception quality threshold value in the UE 100: an RRC Release message and a multicast MCCH. The setting of the reception quality threshold value (threshold setting) by the RRC Release message is a dedicated setting that is set individually for each UE, and is hereinafter also referred to as a first threshold setting. The setting of the reception quality threshold by the multicast MCCH (threshold setting) is a common setting that is set in common to a plurality of UEs, and is also referred to as a second threshold setting hereinafter.

[0058] In addition, a case where UE100 needs to acquire the multicast reception setting from gNB200 is a case where UE100 has not received the multicast reception setting of the multicast session in which UE100 has joined in the RRC Release message, and the serving cell does not provide the multicast reception setting on the multicast MCCH, and UE100 may receive a paging message (group notification) indicating activation of the multicast session from the serving cell. A case where UE100 needs to acquire the multicast reception setting from gNB200 is a case where UE100 reselects a cell from the first cell to the second cell, and the second cell (reselected cell) does not provide the multicast reception setting of the multicast session in which UE100 has joined in the multicast MCCH.

[0059] Incidentally, after a reception quality threshold to be compared with the reception quality during multicast reception is set in the UE 100, the UE 100 is expected to continue to apply the setting of the reception quality threshold (threshold setting) while performing multicast reception in an RRC inactive state. However, it may be inappropriate for the UE 100 to continue to apply the same reception quality threshold setting depending on the situation of the UE 100, etc. In the embodiment, an operation for enabling the UE 100 to appropriately handle the reception quality threshold (threshold setting) will be described.

[0060] 6 is a diagram showing an overview of the operation of the UE 100 according to the embodiment. In the following description of the embodiment, it is assumed that the UE 100 has already participated in a certain multicast session. The multicast session is also referred to as a joined multicast session. "Participating in a multicast session" may mean a state in which the UE 100 is registered in the network 5 (CN 20) as the UE 100 that receives the multicast session.

[0061] In step S1, the UE 100 receives a threshold setting from the gNB 200 for setting a reception quality threshold (i.e., a reception quality threshold used to determine the start of RRC connection resume) to be compared with the reception quality at the time of reception of a multicast session (joined multicast session) in an RRC inactive state. The threshold setting may be associated with the multicast session. The UE 100 holds the received threshold setting.

[0062] In step S2, the UE 100 applies the threshold setting received in step S1 so as to compare the reception quality at the time of reception of the multicast session with the reception quality threshold in the RRC inactive state. That is, the UE 100 performs a process of comparing the reception quality with the reception quality threshold.

[0063] In step S3, in the RRC inactive state, UE 100 stops applying the threshold setting received in step S1 in response to a predetermined condition related to multicast reception being satisfied. That is, UE 100 stops the process of comparing the reception quality with the reception quality threshold. In the embodiment, an operation in which UE 100 voluntarily stops applying the threshold setting in response to a predetermined condition being satisfied is mainly assumed. Here, "stopping application of the threshold setting" may mean temporarily stopping (suspending) the use of the threshold setting (use of the reception quality threshold) while retaining the threshold setting. In this case, when the need to use the reception quality threshold again arises, UE 100 may resume use of the reception quality threshold using the retained threshold setting. Alternatively, "stopping application of the threshold setting" may mean discarding the threshold setting to make the reception quality threshold set by the threshold setting unusable. In this case, UE 100 does not need to retain the threshold setting, thereby saving memory capacity of UE 100.

[0064] In this manner, in the embodiment, the UE 100 in the RRC inactive state stops applying the threshold setting in response to the satisfaction of a predetermined condition related to multicast reception. This enables the UE 100 to appropriately handle the reception quality threshold.

[0065] 6 includes a receiver 110 that receives from a gNB 200 a threshold setting for setting a reception quality threshold to be compared with the reception quality when receiving a multicast session in an RRC inactive state, and a control unit 130 that applies the threshold setting to compare the reception quality with the reception quality threshold in the RRC inactive state. The control unit 130 stops applying the threshold setting when a predetermined condition is satisfied in the RRC inactive state.

[0066] In a first operation pattern of the embodiment, in step S1, the UE 100 receives an RRC Release message including a threshold setting. In addition, in the first operation pattern, the predetermined condition is execution of cell reselection. In step S3, the UE 100 discards the threshold setting received in the RRC Release message in response to execution of cell reselection. Here, when the UE 100 performs cell reselection from the first cell to the second cell, the modulation and coding scheme (MCS) applied to multicast transmission may be different between the first cell and the second cell. In this case, the threshold setting in the first cell may be inappropriate for the second cell. Therefore, in the first operation pattern, the UE 100 discards the threshold setting received in the RRC Release message in the first cell in response to execution of cell reselection.

[0067] In a second operation pattern of the embodiment, in step S1, the UE 100 receives a first threshold setting for setting a reception quality threshold in an RRC Release message, and receives a second threshold setting for setting a reception quality threshold in a multicast MCCH. The UE 100 may receive the RRC Release message including the first threshold setting and the multicast MCCH including the second threshold setting at different times. In step S2, when the UE 100 receives both the first threshold setting and the second threshold setting, the UE 100 applies one of the first threshold setting and the second threshold setting. In step S3, the UE 100 stops applying the other of the first threshold setting and the second threshold setting, assuming that the UE 100 has received both the first threshold setting and the second threshold setting as a predetermined condition. This enables the UE 100 to appropriately handle the reception quality threshold even when different threshold settings are provided in different signalings.

[0068] In the second operation pattern, in step S2, the UE 100 may apply the first threshold setting in response to reception of the first threshold setting. In step S3, the UE 100 may start application of the second threshold setting and stop application of the first threshold setting, based on a predetermined condition that the UE 100 has received the second threshold setting after receiving the first threshold setting.

[0069] In the second operation pattern, in step S3, when the reception quality corresponding to the reception quality threshold set in the second threshold setting is better than the reception quality corresponding to the reception quality threshold set in the first threshold setting, the UE 100 may start applying the second threshold setting and stop applying the first threshold setting. This enables the UE 100 to apply a reception quality threshold that makes it easy to start the RRC connection resume procedure.

[0070] In the second operation pattern, the UE 100 may receive from the gNB 200 designation information for designating a threshold setting to be applied by the UE 100 from the first threshold setting and the second threshold setting. In step S2, when the UE 100 receives both the first threshold setting and the second threshold setting, the UE 100 may apply the threshold setting designated according to the designation information from the first threshold setting and the second threshold setting. This allows the gNB 200 to designate either threshold setting even when different threshold settings are provided by different signaling.

[0071] In a third operation pattern of the embodiment, in step S2, UE 100 applies the threshold setting received in step S1 when performing multicast reception. For example, UE 100 applies the threshold setting received in step S1 when the joined multicast session is activated and / or data (MTCH) of the multicast session is being received. In step S3, UE 100 does not apply the threshold setting received in step S1 when not performing multicast reception. For example, UE 100 may stop applying the threshold setting received in step S1 when a joined multicast session is not activated and / or data (MTCH) of the multicast session is not being received as a predetermined condition. In this case, the threshold setting may be discarded. This prevents UE 100 from performing reception quality measurement and / or threshold determination unnecessarily, thereby reducing the processing load and power consumption of UE 100.

[0072] (3.2) Specific Operation Examples First to third operation patterns will be described as specific examples of the operation of the mobile communication system 1. The first to third operation patterns may be implemented independently, or two or more operation patterns may be implemented in combination.

[0073] (3.2.1) First Operation Pattern FIG. 7 is a diagram for explaining an outline of the operation according to the first operation pattern of the embodiment.

[0074] In the first operation pattern, UE 100 performing multicast reception in the RRC inactive state discards the reception quality threshold (threshold setting) received in the RRC Release message from gNB 200 at the time of cell reselection. Specifically, UE 100 discards the reception quality threshold (threshold setting) received in the RRC Release message in the first cell at the time of cell reselection from the first cell to the second cell.

[0075] In the illustrated example, UE100 is located in an overlapping area between the first cell of gNB200a and the second cell of gNB200b, and selects the first cell as the serving cell. However, this is not limited to the case where the first cell and the second cell belong to different gNB200, and the first cell and the second cell may belong to the same gNB200. After receiving a reception quality threshold (threshold setting) in the RRC Release message in the first cell, UE100 is assumed to be receiving a joined multicast session in the first cell (i.e., multicast reception). Here, gNB200a is assumed to be transmitting multicast data, which is data of the joined multicast session, using a first MCS.

[0076] On the other hand, the second cell also provides the joined multicast session, and the gNB 200b transmits multicast data, which is data of the joined multicast session, using a second MCS. For example, the second MCS may be an MCS having lower error resilience than the first MCS.

[0077] In this way, when the MCSs for multicast transmission are different between the first cell and the second cell, the setting of the reception quality threshold set in the first cell may be inappropriate in the second cell. For example, when a low reception quality threshold is set in the RRC Release message in the first cell, if the UE 100 continues to apply such a reception quality threshold in the second cell, it is difficult to normally perform multicast reception in the second cell in the RRC inactive state.

[0078] Therefore, the UE 100 discards the reception quality threshold (threshold setting) received in the RRC Release message in the first cell when reselecting the cell from the first cell to the second cell. This makes it possible to solve such a problem. Note that the UE 100 may discard the reception quality threshold (threshold setting), acquire a new reception quality threshold (threshold setting) provided by the multicast MCCH in the second cell, and apply the acquired reception quality threshold (threshold setting) in the second cell.

[0079] FIG. 8 is a diagram illustrating an example of an operation according to the first operation pattern of the embodiment.

[0080] In step S101, UE100 is in an RRC connected state in the cell of gNB200.

[0081] In step S102, gNB200 decides to have UE100 perform multicast reception in the RRC inactive state, and transmits an RRC Release message including a suspend setting, i.e., an RRC Release message for transitioning UE100 to the RRC inactive state, to UE100. UE100 receives the RRC Release message. The RRC Release message includes a multicast reception setting (PTM setting) for multicast reception in the RRC inactive state. In the first operation pattern, the multicast reception setting includes a reception quality threshold to be compared with the multicast reception quality.

[0082] In step S103, in response to the reception of the RRC Release message in step S102, the UE 100 transitions to an RRC inactive state.

[0083] In step S104, gNB200 transmits MBS data (multicast data) of the multicast session in which UE100 has joined on MTCH.

[0084] In step S105, UE100 applies the multicast reception setting received in step S102 and performs multicast reception in the RRC inactive state. Specifically, UE100 receives MBS data (multicast data) of the multicast session in which UE100 has joined from gNB200 on MTCH. UE100 also measures the reception quality (e.g., RSRP and / or RSRQ) for gNB200 (serving cell).

[0085] In step S107, UE100 compares the measurement result of the reception quality in step S105 with the reception quality threshold set in step S102. If the measurement result of the reception quality in step S105 is worse than the reception quality threshold (step S106: YES), in step S107, UE100 starts an RRC connection resume procedure and transmits an RRC Resume Request message to gNB200. gNB200 receives the RRC Resume Request message. When the RRC connection resume procedure is completed, UE100 transitions from the RRC inactive state to the RRC connected state. In the RRC connected state, gNB200 can apply link adaptation and / or retransmission control specific to UE100, making it easy for UE100 to receive multicast even in a poor wireless environment.

[0086] If the measurement result of the reception quality in step S105 is not worse than the reception quality threshold (step S106: NO), in step S108, UE 100 determines whether to perform cell reselection. For example, UE 100 determines to perform cell reselection from the first cell to the second cell depending on whether the frequency priority of the second cell, which is a non-serving cell, is higher than that of the first cell, which is the current serving cell, and / or whether the reception quality of the second cell is higher than that of the first cell. If cell reselection is not to be performed (step S108: NO), UE 100 returns the process to step S105.

[0087] On the other hand, if cell reselection has been performed (step S108: YES), in step S109, UE 100 discards the threshold setting (reception quality threshold) received in step S102. In step S110, UE 100 may acquire a new reception quality threshold (threshold setting) provided by the multicast MCCH in the second cell, and apply the acquired reception quality threshold (threshold setting) in the second cell.

[0088] In this operation pattern, an example has been described in which the UE 100 discards the reception quality threshold (threshold setting) received in the RRC Release message from the gNB 200 (first cell) when reselecting the cell from the first cell to the second cell. However, the UE 100 may suspend (temporarily stop) the application of the reception quality threshold (threshold setting) received in the RRC Release message from the gNB 200 when reselecting the cell. Then, when the UE 100 returns from the second cell to the first cell by cell reselection, it may resume application of the suspended reception quality threshold (threshold setting).

[0089] Furthermore, in this operation pattern, the reception quality threshold (threshold setting) received in the RRC Release message is taken as an example, but the UE 100 may receive the reception quality threshold in the multicast MCCH.

[0090] (3.2.2) Second Operation Pattern FIG. 9 is a diagram for explaining an outline of an operation according to a second operation pattern of the embodiment.

[0091] In the second operation pattern, when the UE 100 performing multicast reception in the RRC inactive state receives the first threshold setting (reception quality threshold) in the RRC Release message and then receives the second threshold setting (reception quality threshold) in the multicast MCCH, the UE 100 stops applying the first threshold setting (reception quality threshold) and starts applying the second threshold setting (reception quality threshold). Here, the UE 100 may overwrite the first threshold setting (reception quality threshold) with the second threshold setting (reception quality threshold).

[0092] Here, when a threshold setting (reception quality threshold) is set on a multicast session basis, UE100 may perform the above-described operation only after receiving a first threshold setting (reception quality threshold) for a multicast session in which it has participated, and then receiving a second threshold setting (reception quality threshold) for the multicast session in which it has participated.

[0093] In the second operation pattern, the gNB200 may set, on a UE100-by-UE100 or multicast session-by-multicast session basis, designation information for specifying whether to prioritize the reception quality threshold set in the RRC Release message or the reception quality threshold set in the multicast MCCH.

[0094] In the illustrated example, UE100 is located in the cell of gNB200. gNB200 transmits a first threshold setting (reception quality threshold) to UE100 in an RRC Release message. In addition, when gNB200 changes the multicast reception setting (e.g., the MCS applied to the MTCH), it may transmit a new multicast reception setting including a second threshold setting (reception quality threshold) on the multicast MCCH. Under such an assumption, it is necessary to clarify the operation of UE100 that receives both the first threshold setting and the second threshold setting.

[0095] 10 is a diagram showing an example of an operation according to the second operation pattern of the embodiment, and the differences from the first operation pattern described above will be mainly described here.

[0096] In step S201, UE100 is in an RRC connected state in the cell of gNB200.

[0097] In step S202, gNB200 decides to have UE100 perform multicast reception in the RRC inactive state, and transmits an RRC Release message including a suspend setting, i.e., an RRC Release message for transitioning UE100 to the RRC inactive state, to UE100. UE100 receives the RRC Release message. The RRC Release message includes a multicast reception setting (PTM setting) for multicast reception in the RRC inactive state. In the second operation pattern, the multicast reception setting includes a first threshold setting that sets a reception quality threshold to be compared with the multicast reception quality.

[0098] In the second operation pattern, the RRC Release message of step S202 may include designation information indicating which threshold setting is to be prioritized, between the first threshold setting (reception quality threshold) provided in the RRC Release message and the second threshold setting (reception quality threshold) provided in the multicast MCCH of step S204. The designation information may be set for each multicast session. The designation information may be included in the multicast reception setting (PTM setting). The designation information may be information instructing that the latest threshold setting is always prioritized. Specifically, the designation information may be information specifying that the latest threshold setting in UE 100 is to be applied, between the first threshold setting (reception quality threshold) provided in the RRC Release message and the second threshold setting (reception quality threshold) provided in the multicast MCCH.

[0099] In step S203, in response to the reception of the RRC Release message in step S202, the UE 100 transitions to an RRC inactive state.

[0100] In step S204, the gNB 200 transmits a multicast MCCH (multicast MCCH message) including a multicast reception setting (PTM setting) for multicast reception in an RRC inactive state. The UE 100 receives the multicast MCCH. The multicast reception setting includes a second threshold setting that sets a reception quality threshold to be compared with the multicast reception quality.

[0101] In the second operation pattern, the multicast MCCH (multicast MCCH message) in step S204 may include designation information indicating which threshold setting is to be prioritized, between the first threshold setting (reception quality threshold) provided in the RRC Release message and the second threshold setting (reception quality threshold) provided in the multicast MCCH. The designation information may be set for each multicast session. The designation information may be included in the multicast reception setting (PTM setting). The designation information may be information instructing that the latest threshold setting is always prioritized. Specifically, the designation information may be information instructing that the latest threshold setting in UE 100 is to be applied, between the first threshold setting (reception quality threshold) provided in the RRC Release message and the second threshold setting (reception quality threshold) provided in the multicast MCCH.

[0102] In step S205, the UE 100 determines which of the first threshold setting and the second threshold setting should be applied.

[0103] The UE 100 may always prioritize the latest threshold setting. When the UE 100 receives the second threshold setting after receiving the first threshold setting, the UE 100 applies the second threshold setting. In this operation example, it is assumed that the second threshold setting is received after receiving the first threshold setting, but the UE 100 may receive the second threshold setting before the first threshold setting. When the UE 100 receives the first threshold setting after receiving the second threshold setting, the UE 100 may apply the first threshold setting.

[0104] Alternatively, the UE 100 may apply a threshold setting that sets a reception quality threshold corresponding to a better reception quality between the first threshold setting and the second threshold setting. For example, when the UE 100 receives the second threshold setting after receiving the first threshold setting, if the reception quality indicated by the reception quality threshold set in the second threshold setting is better than the reception quality indicated by the reception quality threshold set in the first threshold setting, the UE 100 may apply the second threshold setting. If this is not the case, the UE 100 may continue to apply the currently applied first threshold setting. Assuming an example in which the reception quality threshold is an RSRP threshold, when the UE 100 receives the second threshold setting after receiving the first threshold setting, if the RSRP threshold set in the second threshold setting is higher than the RSRP threshold set in the first threshold setting, the UE 100 may apply the second threshold setting. If this is not the case, the UE 100 may continue to apply the currently applied first threshold setting. Such a scenario may be a scenario in which the gNB 200 changes the MCS applied to multicast transmission (MTCH transmission) of a certain multicast session to an MCS with low error resilience. For example, when performing MTCH transmission with an MCS with high error resilience, the gNB 200 sets a low reception quality threshold in the first threshold setting, and then when performing MTCH transmission with an MCS with low error resilience, sets a high reception quality threshold in the second threshold setting.

[0105] Alternatively, when UE 100 receives designation information (i.e., an explicit instruction from gNB 200) in an RRC Release message and / or a multicast MCCH, UE 100 may select the threshold setting to apply according to the designation information. The designation information may be any of 1) prioritizing the first threshold setting, 2) prioritizing the second threshold setting, or 3) always prioritizing the latest (most recently received) threshold.

[0106] In step S206, gNB200 transmits MBS data (multicast data) of the multicast session in which UE100 has joined on MTCH.

[0107] In step S207, UE100 applies the multicast reception setting and performs multicast reception in the RRC inactive state. Specifically, UE100 receives MBS data (multicast data) of the multicast session in which UE100 has joined from gNB200 on MTCH. UE100 also measures the reception quality (e.g., RSRP and / or RSRQ) for gNB200 (serving cell).

[0108] In step S208, UE100 compares the measurement result of the reception quality in step S207 with the reception quality threshold determined in step S205. If the measurement result of the reception quality is worse than the reception quality threshold (step S208: YES), in step S209, UE100 starts an RRC connection resume procedure and transmits an RRC Resume Request message to gNB200. gNB200 receives the RRC Resume Request message. When the RRC connection resume procedure is completed, UE100 transitions from the RRC inactive state to the RRC connected state.

[0109] (3.2.3) Third Operation Pattern FIG. 11 is a diagram for explaining an outline of an operation according to a third operation pattern of the embodiment.

[0110] In the third operation pattern, UE100 performing multicast reception in the RRC inactive state stops applying the threshold setting (reception quality threshold) when the multicast session (joined multicast session) is temporarily stopped (suspended), for example, when information instructing MTCH reception stop is received from gNB200. That is, when UE100 is not receiving a multicast session (MTCH), it stops applying the threshold setting (reception quality threshold). In this case, UE100 may discard the threshold setting (reception quality threshold).

[0111] When the multicast session is resumed, for example, when UE 100 receives information on the start of MTCH reception from gNB 200, the threshold setting (re-applies) is applied (re-applies). That is, when UE 100 receives a multicast session (MTCH), the threshold setting (reception quality threshold) is applied.

[0112] Note that a multicast session has two session states: an active state and an inactive state. The active state may include a state in which there is temporarily no data. When a multicast session is in an inactive state or a state in which there is temporarily no data, the UE 100 is not receiving MTCH, and therefore there is no need to start RRC resume based on a reception quality threshold. Therefore, in the third operation pattern, the UE 100 applies the threshold setting (reception quality threshold) only when the multicast session (joined multicast session) is activated and / or data of the multicast session is being received.

[0113] 12 is a diagram showing an example of an operation according to the third operation pattern of the embodiment, and the differences from the first and second operation patterns will be mainly described here.

[0114] In step S301, UE100 is in an RRC connected state in the cell of gNB200.

[0115] In step S302, gNB200 determines to have UE100 perform multicast reception in the RRC inactive state, and transmits to UE100 an RRC Release message including a suspend setting, i.e., an RRC Release message for transitioning UE100 to the RRC inactive state. UE100 receives the RRC Release message. The RRC Release message may include a multicast reception setting (PTM setting) for multicast reception in the RRC inactive state. The multicast reception setting may include a threshold setting for setting a reception quality threshold to be compared with the multicast reception quality.

[0116] In step S303, in response to the reception of the RRC Release message in step S302, the UE 100 transitions to an RRC inactive state.

[0117] In step S304, the gNB 200 may transmit a multicast MCCH (multicast MCCH message) including a multicast reception setting (PTM setting) for multicast reception in an RRC inactive state. The UE 100 may receive the multicast MCCH. The multicast reception setting may include a threshold setting for setting a reception quality threshold to be compared with the multicast reception quality.

[0118] In step S305, gNB200 transmits MBS data (multicast data) of the multicast session in which UE100 has joined on MTCH.

[0119] In step S306, UE100 applies the multicast reception setting received in step S302 or step S304 and performs multicast reception in the RRC inactive state. Specifically, UE100 receives MBS data (multicast data) of the multicast session in which UE100 has joined from gNB200 on MTCH. UE100 also measures the reception quality (e.g., RSRP and / or RSRQ) for gNB200 (serving cell).

[0120] In step S307, UE 100 compares the measurement result of the reception quality in step S306 with the reception quality threshold received in step S302 or step S304. If the measurement result of the reception quality is worse than the reception quality threshold (step S307: YES), in step S308, UE 100 starts an RRC connection resume procedure and transmits an RRC Resume Request message to gNB 200. gNB 200 receives the RRC Resume Request message. When the RRC connection resume procedure is completed, UE 100 transitions from the RRC inactive state to the RRC connected state.

[0121] On the other hand, if the measurement result of the reception quality is not worse than the reception quality threshold (step S307: NO), in step S309, UE100 determines whether to stop multicast reception. For example, UE100 determines to stop multicast reception when at least one of the following conditions is met: 1) the multicast session (MTCH) is not received, 2) the multicast session has become inactive, and 3) MTCH transmission stop information (or MTCH reception stop instruction) or session deactivation information has been received from gNB200. UE100 may determine to stop multicast reception when the condition that the multicast reception setting for the joined multicast session is no longer present in the multicast MCCH is met.

[0122] Here, not receiving the multicast session (MTCH) may mean that the UE 100 has not received the multicast session (MTCH) for a certain period of time. The certain period may be set by the gNB 200 to the UE 100 in an RRC Release or a multicast MCCH. The certain period may be a timer value (for example, milliseconds) or the number of radio frames (or the number of slots or the number of subframes).

[0123] Not receiving the multicast session (MTCH) may mean that UE 100 was unable to receive the PDSCH or PDCCH (scrambled with G-RNTI) for transmitting data of the multicast session.

[0124] The multicast session may be inactive when the UE 100 does not hold or cannot receive control information for receiving the multicast session (MTCH). For example, the multicast session may be inactive when the scheduling information of the multicast session (MTCH) of interest is removed from the multicast MCCH or is not notified.

[0125] If the multicast reception is not to be stopped (step S309: NO), the UE 100 returns the process to step S306.

[0126] On the other hand, when multicast reception is to be stopped (step S309: YES), in step S310, UE 100 stops application of the reception quality threshold (threshold setting) received in step S302 or step S304. In this case, UE 100 may discard the reception quality threshold (threshold setting).

[0127] In step S311, UE100 determines whether to resume multicast reception. For example, UE100 determines to resume multicast reception when at least one of the following conditions is met: 1) a multicast session (MTCH) has been received, 2) the multicast session has become active, and 3) MTCH transmission start information (or MTCH reception instruction) or session activation information has been received from gNB200. UE100 may determine to resume multicast reception when the condition that a multicast reception setting for a joined multicast session exists in the multicast MCCH is met. Note that, if UE100 does not hold a reception quality threshold (threshold setting), it may acquire the reception quality threshold (threshold setting) from the multicast MCCH, for example.

[0128] If the UE 100 does not want to resume multicast reception (step S311: NO), the UE 100 returns the process to step S310. On the other hand, if the UE 100 wants to resume multicast reception (step S311: YES), the UE 100 returns the process to step S306.

[0129] (4) Other Embodiments In the above-described embodiment, an example was described in which the threshold setting (reception quality threshold) was set on a multicast session basis, but the threshold setting (reception quality threshold) may also be set in common for multiple multicast sessions.

[0130] 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 also 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), and the above-described resume cause is replaced with establishment cause.

[0131] The above-described operational flows are not limited to being implemented independently, but can be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. In each flow, it is not necessary to execute all steps, and only some steps may be executed. Furthermore, the order of steps in each flow may be changed as appropriate.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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).

[0136] 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.

[0137] 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.

[0138] 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.

[0139] This application claims priority to U.S. Provisional Application No. 63 / 540,282 (filed September 25, 2023), the entire contents of which are incorporated herein by reference.

[0140] (5) First Supplementary Note The following is a supplementary note regarding the features of the above-described embodiment.

[0141] (Supplementary Note 1) A communication method executed by a user device in a mobile communication system that provides a multicast broadcast service (MBS), comprising: receiving, from a network node, a threshold setting that sets a threshold to be compared with a reception quality at the time of reception of a multicast session in a radio resource control (RRC) inactive state, the threshold being used to determine whether to start an RRC connection resume; applying, in the RRC inactive state, the threshold setting to compare the reception quality with the threshold; and stopping application of the threshold setting in response to a predetermined condition related to multicast reception being satisfied in the RRC inactive state.

[0142] (Supplementary Note 2) The communication method according to Supplementary Note 1, wherein receiving the threshold setting includes receiving an RRC release message including the threshold setting, the predetermined condition is execution of cell reselection, and the stopping includes discarding the threshold setting received in the RRC release message in response to execution of cell reselection.

[0143] (Supplementary Note 3) The communication method according to Supplementary Note 1, wherein receiving the threshold setting includes receiving, in an RRC release message, a first threshold setting that sets a threshold to be compared with the reception quality, and receiving, on a multicast-multicast control channel (MCCH), a second threshold setting that sets a threshold to be compared with the reception quality; applying includes applying one of the first threshold setting and the second threshold setting when both the first threshold setting and the second threshold setting are received; and stopping includes stopping application of the other of the first threshold setting and the second threshold setting when both the first threshold setting and the second threshold setting are received.

[0144] (Supplementary Note 4) The communication method described in Supplementary Note 3, wherein the applying includes applying the first threshold setting in response to receiving the first threshold setting, and the stopping includes starting application of the second threshold setting and stopping application of the first threshold setting in response to receiving the second threshold setting after receiving the first threshold setting.

[0145] (Supplementary Note 4) The communication method according to Supplementary Note 4, wherein the stopping includes starting application of the second threshold setting and stopping application of the first threshold setting when a reception quality corresponding to a threshold set in the second threshold setting is better than a reception quality corresponding to a threshold set in the first threshold setting.

[0146] (Supplementary Note 5) The communication method according to any one of Supplementary Notes 3 to 4, further comprising receiving, from the network node, designation information for designating a threshold setting to be applied by the user equipment from the first threshold setting and the second threshold setting, wherein the applying includes, when both the first threshold setting and the second threshold setting are received, applying the threshold setting designated in accordance with the designation information from the first threshold setting and the second threshold setting.

[0147] (Supplementary Note 6) The communication method according to Supplementary Note 1, wherein the applying includes applying the threshold setting when the multicast reception is being performed, and the stopping includes stopping application of the threshold setting when the multicast reception is not being performed.

[0148] (Supplementary Note 7) The communication method according to Supplementary Note 6, wherein the stopping includes discarding the threshold setting if the multicast session is not activated and / or data for the multicast session is not being received.

[0149] (Supplementary Note 8) A user equipment used in a mobile communication system that provides a multicast broadcast service (MBS), comprising: a receiver unit that receives a threshold setting from a network node to set a threshold to be compared with a reception quality at the time of reception of a multicast session in a radio resource control (RRC) inactive state, the threshold being used to determine whether to start an RRC connection resume; and a controller that applies the threshold setting in the RRC inactive state to compare the reception quality with the threshold, wherein the controller stops applying the threshold setting in response to a predetermined condition related to multicast reception being satisfied in the RRC inactive state.

[0150] (6) Annex 2 1. Introduction The work item on enhanced MBS (eMBS) aims to support multicast reception by UEs in inactive state as follows: - Specify support for multicast reception by UEs in RRC inactive state [RAN2, RAN3]. - PTM configuration for UEs receiving multicast in RRC inactive state [RAN2]. - Investigate the impact of mobility and state transitions for UEs receiving multicast in RRC inactive state (seamless / lossless mobility is not mandatory) [RAN2, RAN3].

[0151] This appendix discusses the details of RRC resume due to bad quality and the causes of the resume.

[0152] 2. Discussion 2.1. RRC Resume Due to Deterioration of Reception Quality RAN2#123 agreed to introduce RSRP / RSRQ-based RRC Resume as follows.

[0153] For a UE receiving multicast in an RRC inactive state, the UE resumes the RRC connection when the RSRP or RSRQ measured based on the existing measurement requirements of the serving cell (whichever is set by the network) falls below a threshold set by the network. Whether the ping-pong issue needs to be addressed is a matter for further study.

[0154] The threshold can be PTM configured per MBS session via RRC Release or multicast MCCH messages.

[0155] Based on the agreement, remaining issues are discussed in the following sections.

[0156] 2.1.1 Ping-pong issue The agreement captures the considerations of "whether or not the ping-pong issue needs to be addressed / how to address it." Possible scenarios for resuming ping-pong include the following:

[0157] 1. A UE in an inactive state with deteriorating radio quality will initiate RRC resume when the RSRP / RSRQ falls below the threshold. 2. In response to the RRC resume request, a gNB under network congestion will send an RRC release with a suspend config. that includes the RSRP / RSRQ threshold. 3. A UE whose radio quality remains deteriorating will transition to an inactive state again, and since the RSRP / RSRQ will soon fall below the threshold, RRC resume will be initiated again.

[0158] To avoid ping-pong in the above scenario, the gNB may keep the UE in a connected state or set appropriate RSRP / RSRQ thresholds for the UE.

[0159] To support such a decision, the gNB may need to know the radio conditions and / or the reason for RRC resume (in this case, due to deterioration in radio quality) as soon as the UE requests RRC resume.

[0160] Observation 1: In order to guarantee QoS requirements, the gNB may need to know the UE's radio conditions when the UE requests RRC resume and the reason for RRC resume.

[0161] It should be noted that, according to the RAN2 discussions in the early stages of Release 18, the two main motivations for supporting multicast reception in the inactive state are network congestion mitigation and UE power consumption. Therefore, it is not reasonable for the gNB to always keep the UE in the connected state and configure measurement reporting every time the UE requests RRC resume.

[0162] Observation 2: Since the motivation for supporting multicast reception in the inactive state is to reduce network congestion and save UE power, it is not reasonable to rely on measurement reports to guarantee QoS requirements.

[0163] Considering the above observations, when the UE initiates RRC resume due to a deterioration in reception quality during the RRC resume procedure, it is useful for the UE to report the measurement results in the RRC resume request or RRC resume complete. Another option is for the UE to indicate the deterioration in radio conditions in the resume cause. With such information, the gNB can make an appropriate decision on whether to keep the UE in connected state for QoS guarantees.

[0164] Proposal 1: RAN2 should agree that the measurement results are reported within the RRC resume procedure or a new resume cause "Multicast quality" is introduced.

[0165] 2.1.2 Validity of RSRP / RSRQ Thresholds Configured by RRC Release RAN2 agreed that "thresholds can be configured by RRC release or by PTM configuration per MBS session via multicast MCCH messages." For dedicated configurations provided by RRC release, many settings remain valid until the corresponding timer expires. For example, dedicated frequency priority remains valid until T320 expires. This occurs regardless of cell reselection; dedicated settings provided by the source cell remain valid even after the UE reselects the target cell.

[0166] Observation 3: According to the current specification, many dedicated settings remain valid until a timer expires, regardless of cell reselection.

[0167] Regarding the RSRP / RSRQ thresholds, if they are valid after cell reselection, problems may occur assuming the following conditions: - In the source cell, PTM is transmitted with a low MCS, so the UE sets a low RSRP threshold to ensure a certain reception quality. - In the target cell after cell reselection, PTM is transmitted with a higher MCS, but the UE still applies the old RSRP threshold. - As a result, the UE will experience MTCH reception errors even though the RSRP is still better than the old threshold.

[0168] To avoid this problem, the RSRP / RSRQ thresholds should be cell-specific, considering that the PTM transmission of NR MBS is cell-specific, i.e., if the UE reselects a different cell, the old RSRP / RSRQ thresholds should be discarded.

[0169] Proposal 2: RAN2 should agree to discard the RSRP / RSRQ thresholds upon cell reselection.

[0170] Another possible issue in handling RSRP / RSRQ thresholds is which threshold should the UE apply when thresholds are provided by both RRC release and multicast MCCH. In the current specification, dedicated settings provided by RRC release generally take precedence over settings provided by SIB. However, for inactive multicast reception, RAN2 agreed that "if the PTM setting needs to be changed, RAN2 will use the MCCH to indicate it," meaning that the PTM setting provided by RRC release may be changed by the PTM setting provided by multicast MCCH. This means that the RSRP / RSRQ thresholds cannot be UE-specific, i.e., TMGI-specific, because they are overwritten by the multicast MCCH.

[0171] Proposal 3: RAN2 should ensure that the PTM configuration including RSRP / RSRQ thresholds provided by RRC release is always overridden by the configuration provided by multicast MCCH, i.e. there is no UE-specific configuration for inactive multicast reception.

[0172] 2.1.3 Other Confirmations RAN2#123 agreed that "for a UE receiving multicast in an RRC inactive state, the UE resumes the RRC connection when the measured RSRP or RSRQ [...] of the serving cell falls below a threshold [...]." The RSRP / RSRQ threshold is introduced to guarantee QoS for multicast reception in an inactive state.

[0173] On the other hand, if the multicast session is deactivated by the network, a UE in an inactive state may not receive the MTCH (or temporarily not receive data) when the session is deactivated. In this case, the UE is considered the same as a legacy UE in an inactive state, so RRC resume due to quality deterioration (RSRP / RSRQ threshold) is not required. As already implied in the above agreement, a UE in an inactive state must ensure that it does not initiate RRC resume if the multicast session is deactivated (or there is temporarily no data), even if the RSRP / RSRQ deteriorates below the threshold.

[0174] Proposal 4: RAN2 needs to ensure that inactive UEs do not initiate RRC resume when the multicast session is disabled (or there is temporarily no data), even if the RSRP / RSRQ becomes worse than the threshold.

[0175] In RAN2#123, RAN2 discussed whether the threshold could be based on BLER, but ultimately RAN2 decided to adopt RSRP / RSRQ.

[0176] On the other hand, in Release 17, it was a common understanding in RAN2 that SFN (single frequency network) can only be deployed depending on the network implementation, e.g., within a DU. In inter-cell SFN, reception quality is stable even at the cell edge by combining reception from MTCHs of different cells. However, RSRP / RSRQ are cell-specific and degrade at the cell edge when moving away from SFN. Therefore, RSRP / RSRQ thresholds do not work well in SFN deployments, but BLER thresholds can avoid such issues.

[0177] Proposal 5: RAN2 should ensure that the NW implementation of SFN (Single Frequency Network) allowed in Release 17 does not operate at the RSRP / RSRQ threshold in Release 18.

[0178] RAN2#123 agreed to reuse existing resume causes for RRC resume due to several reasons other than the deterioration of reception quality discussed in the previous section in Release 18. However, it is still necessary to analyze which existing resume causes are applicable and whether new resume causes are really unnecessary.

[0179] No new resume causes are introduced for UEs receiving inactive MC when resuming due to quality degradation or incorrect SIBx / PTM configuration, unless a problem is identified with using one of the existing resume causes.

[0180] Currently, 11 resumes are defined, along with five spare fields: ResumeCause ::= ENUMERATED {emergency, highPriorityAccess, mt-Access, mo-Signalling, mo-Data, mo-VoiceCall, mo-VideoCall, mo-SMS, rna-Update, mps-PriorityAccess, mcs-PriorityAccess, spare1, spare2, spare3, spare4, spare5}

[0181] Similar to observation 2 above, one of the motivations for inactive multicast reception is to alleviate network congestion, so the analysis must consider the case when the network is congested.

[0182] Observation 4: The mapping of RRC resume and existing resume causes for multicast reception needs to take into account the congestion state of the network.

[0183] Typical gNB decisions when receiving an RRC Resume request during network congestion can be classified as follows: - Always accept emergency situations; - Prioritize highPriorityAccess, mps-PriorityAccess, and mcs-PriorityAccess; - Accept mt-Access and mo-Signalling (as much as possible); - May reject mo-Data, mo-VoiceCall, mo-VideoCall, and mo-SMS; - In the case of rna-Update, respond with an RRC release with a new RNA.

[0184] Observation 5: Resume allows the gNB to decide whether to accept, reject, or release with a new RNA in response to an RRC resume request, especially in the case of NW congestion.

[0185] RAN2 has agreed that the UE will initiate RRC resume in two cases: due to quality degradation or insufficient SIBx / PTM configuration. From the perspective of the impact on network load, these reasons are characterized as follows:

[0186] As discussed in Section 2.1.1, in the case of RRC resume due to quality deterioration, the UE must remain connected because if the UE is released again while in inactive, QoS requirements will no longer be guaranteed. Considering that the UE must remain connected, the UE does not consume additional downlink resources (since it only receives PTMs already sent to other UEs), but it does consume uplink resources (e.g., HARQ ACKs). In times of network congestion, this consumes slightly more resources compared to multicast reception in inactive state, but may still be prioritized over resume requests for unicast services. In other words, the gNB may prioritize RRC resume requests for multicast reception over RRC resume requests for unicast reception, but may still reject the RRC resume request due to high congestion.

[0187] In the case of RRC resume due to incomplete SIBx / PTM configuration, if the radio conditions are good, the UE is released with PTM configuration, i.e., RRC resume, and can receive the multicast session. Therefore, in terms of network congestion, it is "light," i.e., it consumes almost no downlink / uplink resources. In other words, the NW can immediately accept the RRC resume request, assuming the RRC release with PTM configuration of RRC resume.

[0188] Observation 6: In order to keep the UE connected when the network is congested, the gNB may reject RRC resume due to quality degradation, which may have some impact on the network congestion.

[0189] Observation 7: Due to SIBx / PTM configuration deficiency, the gNB can accept RRC resume and immediately release UEs with PTM configuration, as this does not affect network congestion.

[0190] Considering the above discussion, RRC resume due to bad quality may be mapped to either mo-Data, mo-VoiceCall, mo-VideoCall, or mo-SMS. However, since multicast reception in Connected does not require additional PDSCH resources (i.e., PTM is already provided for other UEs), current gNB implementations for these existing resume causes may be affected if a different type of communication (i.e., multicast reception only) is mapped to an existing resume cause.

[0191] For RRC resume due to lack of SIBx / PTM settings, there is no mapped resume cause because there is a new intent of RRC resume with PTM settings. For rna-Update, a similar gNB decision is assumed, but the gNB provides RNA instead of PTM settings for RRC resume. This means that the gNB cannot send an RRC release with PTM settings in response to an RRC resume request, and the gNB may mistakenly reject the UE's request even though the UE is only requesting a PTM setting update, which has no impact on network congestion.

[0192] Observation 8: There is no existing resume cause that matches the gNB's expected decision in the case of an RRC resume request, either due to quality degradation or insufficient SIBx / PTM configuration.

[0193] RAN2 has indeed identified new possible resume causes with the following discussion: Resume Causes: 1. Multicast Quality 2. Multicast Configuration

[0194] These two resume causes can easily solve all the problems discussed above without potentially impacting current gNB implementations. As discussed above, the two resume causes are useful for gNBs to appropriately guide different results. Therefore, two new resume causes should be introduced accordingly.

[0195] Since 3GPP is likely to begin considering 6G from Release 20, 5G NR is expected to evolve over only the next two releases (i.e., up to Release 20 at most). Given the history of additional resumes in past releases, three resumes in Release 18 will be sufficient.

[0196] Proposal 6: RAN2 should agree on a new resume cause "Multicast Quality" to be set when RRC resume is initiated due to quality degradation. Expected gNB decisions take priority over MO data, etc.

[0197] Proposal 7: RAN2 should agree on a new resume cause "multicast configuration" that is set when RRC resume is initiated due to SIBx / PTM misconfiguration. The expected gNB decision is to respond with an RRC release with PTM configuration.

[0198] 1: Mobile communication system 5: Network 10: RAN 20: CN 100: UE (user equipment) 110: Receiving unit 120: Transmitting unit 130: Control unit 200: gNB (base station) 210: Transmitting unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit

Claims

1. A communication method executed by a user device in a mobile communication system providing a Multicast Broadcast Service (MBS), comprising: receiving a threshold setting from a network node, the threshold setting setting being a threshold to be compared with a reception quality when receiving a multicast session in a Radio Resource Control (RRC) inactive state, the threshold used to determine whether to start an RRC connection resume; and applying the threshold setting to compare the reception quality with the threshold when the multicast reception is being performed in the RRC inactive state.

2. The communication method according to claim 1, further comprising: ceasing application of the threshold setting in response to a predetermined condition relating to multicast reception being satisfied in the RRC inactive state.

3. The communication method according to claim 2, wherein receiving the threshold setting includes receiving an RRC release message including the threshold setting, the predetermined condition is execution of cell reselection, and stopping includes discarding the threshold setting received in the RRC release message in response to the execution of cell reselection.

4. The communication method according to claim 2, wherein receiving the threshold setting includes receiving a first threshold setting in an RRC release message, the first threshold setting setting a threshold to be compared with the reception quality, and receiving a second threshold setting on a multicast-multicast control channel (MCCH), the second threshold setting setting a threshold to be compared with the reception quality; applying includes applying one of the first threshold setting and the second threshold setting when both the first threshold setting and the second threshold setting are received; and stopping includes stopping application of the other of the first threshold setting and the second threshold setting when both the first threshold setting and the second threshold setting are received.

5. The communication method described in claim 4, wherein the applying includes applying the first threshold setting in response to receiving the first threshold setting, and the stopping includes starting application of the second threshold setting and stopping application of the first threshold setting in response to receiving the second threshold setting after receiving the first threshold setting.

6. The communication method of claim 5, wherein the stopping includes starting application of the second threshold setting and stopping application of the first threshold setting when the reception quality corresponding to the threshold set in the second threshold setting is better than the reception quality corresponding to the threshold set in the first threshold setting.

7. The communication method according to claim 4, further comprising receiving designation information from the network node for designating which of the first threshold setting and the second threshold setting is to be applied by the user equipment, and said applying includes, when both the first threshold setting and the second threshold setting are received, applying the threshold setting designated in accordance with the designation information from among the first threshold setting and the second threshold setting.

8. The communication method according to claim 1, wherein the step of stopping includes stopping application of the threshold setting when the multicast reception is not being performed.

9. The method of claim 8, wherein the stopping includes discarding the threshold setting if the multicast session is not activated and / or data for the multicast session is not being received.

10. A user equipment used in a mobile communication system that provides a multicast broadcast service (MBS), comprising: a receiving unit that receives a threshold setting from a network node, the threshold setting being a threshold to be compared with a reception quality when receiving a multicast session in a radio resource control (RRC) inactive state, the threshold setting being used to determine whether to start an RRC connection resume; and a control unit that applies the threshold setting to compare the reception quality with the threshold when the multicast reception is being performed in the RRC inactive state.

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