Communication method and user device

Abstract

This communication method, which is executed by a user device in a mobile communication system that provides a multicast / broadcast service (MBS), includes: a step for receiving, from a network, information for setting a resume condition relating to multicast reception quality, the condition being a condition for starting an RRC connection resume at the time of multicast reception in a radio resource control (RRC) inactive state; a step for evaluating whether the multicast reception quality satisfies the resume condition when performing multicast reception in the RRC inactive state; a step for retaining log information relating to the multicast reception on the basis of the multicast reception quality satisfying the resume condition; and a step for transmitting the log information to the network after transitioning from the RRC inactive state to an RRC connected 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 V17.4.0

[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 the steps 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 receiving multicast in a radio resource control (RRC) inactive state; evaluating whether the multicast reception quality satisfies the resume condition when receiving multicast in the RRC inactive state; retaining log information related to the multicast reception based on whether the multicast reception quality satisfies the resume condition; and transmitting the log information to the network after transitioning from the RRC inactive state to an RRC connected 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 includes: a receiving unit that receives 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 which is used to set resume conditions related to multicast reception quality; a control unit that evaluates whether the multicast reception quality satisfies the resume conditions when receiving multicast in the RRC inactive state, and retains log information related to the multicast reception based on whether the multicast reception quality satisfies the resume conditions; and a transmitting unit that transmits the log information to the network after transitioning from the RRC inactive state to an RRC connected state.

[0007] 1 is a diagram showing an example of the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram showing an example of the configuration of a UE (user equipment) according to an embodiment. FIG. 3 is a diagram showing an example of the configuration of a gNB (base station) according to an embodiment. FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). FIG. 6 is a diagram for explaining the operation of a mobile communication system according to an embodiment. FIG. 7 is a diagram showing an example of a first operation pattern or a second operation pattern of a mobile communication system according to an embodiment. FIG. 8 is a diagram showing an example of a third operation pattern of a mobile communication system according to an embodiment. FIG. 9 is a diagram showing an example of a fourth operation pattern of a mobile communication system according to an embodiment.

[0008] Currently, 3GPP is considering extending the specifications so that a user device performing multicast reception in an RRC inactive state will resume its RRC connection if the reception quality of multicast data deteriorates below a set threshold. This will allow the user device to spontaneously transition to an RRC connected state by resuming the RRC connection when the quality of service (QoS) required for multicast reception is no longer satisfied, making it easier to satisfy the QoS required for multicast reception.

[0009] However, the current 3GPP technical specifications do not allow the network to grasp the situation when the QoS required for multicast reception is no longer met, making it difficult to optimize the network to prevent such a situation from recurring. Therefore, there is room for improvement in the conventional technology in terms of improving the QoS of MBS.

[0010] Therefore, an object of the present disclosure is to make it possible to improve the QoS of MBS.

[0011] 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.

[0012] (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.

[0013] 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.

[0014] 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).

[0015] 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").

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The UE 100 may include a positioning unit for acquiring location information indicating the geographical position (latitude, longitude, altitude) of the UE 100, for example, a GNSS (Global Navigation Satellite System) receiver.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0029] 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.

[0030] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires the successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC parity bit scrambled by the RNTI added.

[0031] 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.

[0032] 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.

[0033] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0034] 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.

[0035] 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).

[0036] 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.

[0037] 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.

[0038] 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").

[0039] (2) Overview of MBS The mobile communication system 1 can perform resource-efficient distribution using multicast / broadcast services (MBS).

[0040] (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)).

[0041] 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 (Cyclic Redundancy Code) scrambled by the G-RNTI.

[0042] 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).

[0043] 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.

[0044] (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.

[0045] 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.

[0046] 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.

[0047] (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.

[0048] 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).

[0049] (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.

[0050] 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).

[0051] 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.

[0052] By UE100 performing multicast reception in the RRC inactive state, the load (resource consumption and / or power consumption, etc.) on network 5 and UE100 can be reduced compared to when multicast reception is performed in the RRC connected state.

[0053] (3) Operation of the Mobile Communication System FIG. 6 is a diagram for explaining the operation of the mobile communication system 1 according to the embodiment.

[0054] In STEP 1, 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. In the illustrated example, the gNB 200 transmits the resume condition setting to the UE 100 in an RRC connected state by dedicated signaling, for example, an RRC Release message or an RRC Reconfiguration message. However, the gNB 200 may transmit the resume condition setting to the UE 100 by broadcast signaling, for example, an MCCH or SIB, for a UE 100 in an RRC connected state or an RRC inactive state.

[0055] The resume condition includes a threshold value to be compared with the reception quality of the multicast data. The reception quality of the multicast data may be at least one of RSRP (Reference Signals Received Power), RSRQ (Reference Signal Received Quality), SINR (Signal-to-Interference-plus-noise ratio), BER (Bit Error Rate), BLER (Block Error Rate), and PER (Packet Error Rate). Preferably, these reception qualities are the reception qualities for the MTCH carrying the multicast session (i.e., the reception quality of the multicast data). In addition, when UE 100 receives a plurality of multicast sessions, the resume condition may be set for UE 100 for each multicast session (for each MBS session ID).

[0056] In STEP 2, UE100 in an RRC inactive state receives a multicast session (multicast data) from gNB200 on MTCH.

[0057] Here, when the resume condition setting is transmitted from gNB200 to UE100 in an RRC Reconfiguration message, UE100 receives an RRC Release message including a suspend setting from gNB200 after receiving the RRC Reconfiguration message, thereby transitioning to an RRC inactive state and performing multicast reception in the RRC inactive state. On the other hand, when the resume condition setting is transmitted from gNB200 to UE100 in an RRC Release message, UE100 receives an RRC Release message from gNB200, thereby transitioning to an RRC inactive state and performing multicast reception in the RRC inactive state.

[0058] The UE 100 performing multicast reception in the RRC inactive state measures the reception quality of multicast data (also referred to as "multicast reception quality") and evaluates whether the multicast reception quality satisfies the resume condition. When the resume condition is set as an RSRP threshold, an RSRQ threshold, or an SINR threshold, the UE 100 determines that the multicast reception quality has deteriorated below the threshold when the multicast reception quality (RSRP, RSRQ, or SINR) falls below the threshold, and determines that the multicast reception quality satisfies the resume condition.

[0059] On the other hand, when the resume condition is set as a BER threshold, a BLER threshold, or a PER threshold, if the multicast reception quality (BER, BLER, or PER) exceeds the threshold, UE100 considers that the multicast reception quality has deteriorated below the threshold, and determines that the multicast reception quality satisfies the resume condition.

[0060] In STEP 3, the UE 100 in the RRC inactive state starts RRC connection resume in response to determining that the multicast reception quality satisfies the resume condition. Specifically, the UE 100 transmits an RRC resume request (Resume Request) message to the gNB 200 (current serving cell). Here, the gNB 200 normally accepts the RRC Resume Request message and transmits an RRC Resume message to the UE 100. The UE 100 resumes the RRC connection in response to receiving the RRC Resume message, and transitions from the RRC inactive state to the RRC connected state. The UE 100 in the RRC connected state can use link adaptation and retransmission control and can perform high-quality multicast reception.

[0061] According to this procedure, when the QoS required for multicast reception is no longer satisfied, the UE 100 can spontaneously transition to the RRC connected state by resuming the RRC connection, making it easier to satisfy the QoS required for multicast reception. However, in the current 3GPP technical specifications, the network 5 cannot grasp the situation when the QoS required for multicast reception is no longer satisfied, making it difficult to perform network optimization to prevent the recurrence of such a situation.

[0062] In this embodiment, the following operation allows the network 5 to grasp the situation when the QoS required for multicast reception is no longer satisfied, thereby making it possible to improve the QoS of the MBS.

[0063] First, the UE 100 receives from the network 5 (gNB 200) information (resume condition setting) for setting a condition for starting an RRC connection resume when receiving multicast in an RRC inactive state and a resume condition related to multicast reception quality. The network 5 (gNB 200) may transmit to the UE 100, together with the resume condition setting, setting information indicating whether log information related to multicast reception should be retained. The UE 100 may retain the log information only when configured to retain the log information. Alternatively, the UE 100 may voluntarily retain the log information based on the multicast reception quality satisfying the resume condition, even without such an explicit setting.

[0064] Secondly, when performing multicast reception in the RRC inactive state, the UE 100 evaluates whether the multicast reception quality satisfies the resume condition.

[0065] Thirdly, the UE 100 holds log information relating to multicast reception based on the multicast reception quality satisfying the resume condition. Here, there are the following four patterns for the timing of holding the log information.

[0066] First Operation Pattern: The UE 100 holds the log information when the multicast reception quality satisfies the resume condition.

[0067] Second Operation Pattern: The UE 100 holds the log information when the UE 100 starts the RRC connection resumption after the multicast reception quality satisfies the resume condition.

[0068] Third Operation Pattern: After the multicast reception quality satisfies the resume condition, the UE 100 holds the log information when the RRC connection resume is successful.

[0069] Fourth Operation Pattern: The UE 100 holds log information when the RRC connection resume fails after the multicast reception quality satisfies the resume condition.

[0070] The log information also includes, for example, at least one of the following information 1) to 7): 1) measurement results of multicast reception quality; 2) identification information for identifying the satisfied resume conditions; 3) session identification information for identifying the multicast session whose multicast reception quality satisfied the resume conditions; 4) cell identification information for identifying the serving cell of UE100 when the multicast reception quality satisfied the resume conditions; 5) location information for identifying the geographical location of UE100 when the multicast reception quality satisfied the resume conditions; 6) time information for identifying the timing when the multicast reception quality satisfied the resume conditions; 7) identification information for identifying whether the RRC connection resume failed or succeeded.

[0071] Fourth, after UE100 transitions from the RRC inactive state to the RRC connected state, it transmits log information to network 5 (gNB200).

[0072] FIG. 7 is a diagram showing an example of the first operation pattern or the second operation pattern of the mobile communication system 1 according to the embodiment.

[0073] In step S101, the gNB 200 sets a resume condition to the UE 100. Here, the UE 100 receives from the gNB 200 information (resume condition setting) for setting a resume condition related to multicast reception quality and for starting an RRC connection resume when receiving multicast in an RRC inactive state.

[0074] In step S102, the UE 100 receives a multicast session in an RRC inactive state. When performing multicast reception in the RRC inactive state, the UE 100 measures multicast reception quality, and when performing multicast reception in the RRC inactive state, evaluates whether the multicast reception quality satisfies a resume condition.

[0075] When the UE 100 determines that the multicast reception quality satisfies the resume condition (step S103: YES), the UE 100 retains log information related to multicast reception in step S104. Furthermore, the UE 100 starts RRC connection resume. The UE 100 may retain the log information before starting the RRC connection resume. The UE 100 may retain the log information when starting the RRC connection resume.

[0076] The UE 100 may include, for example, the multicast reception quality (RSRP, RSRQ, SINR, BER, BLER, PER) measured in step S102 in the log information. The UE 100 may include, in the log information, only items for which thresholds are set as resume conditions among these reception quality indicators (RSRP, RSRQ, SINR, BER, BLER, PER). The UE 100 may include all items in the log information. When multiple resume conditions (multiple thresholds) are set in the UE 100, the UE 100 may include, in the log information, cause information indicating which resume condition (which threshold) is satisfied. For example, if the cause is that the RSRP fell below a threshold, the UE 100 records that fact.

[0077] The UE 100 may include in the log information the MBS session ID of the multicast session being received in the RRC inactive state. When the UE 100 is receiving multiple multicast sessions in the RRC inactive state and a resume condition is set for each multicast session, the UE 100 may include in the log information only the MBS session ID of the multicast session that satisfies the resume condition. The UE 100 may include in the log information the MBS session ID of each of the multiple multicast sessions.

[0078] The UE 100 may include, in the log information, a cell ID indicating the serving cell of the UE 100 when the multicast reception quality satisfies the resume condition.

[0079] The UE 100 may include, in the log information, location information indicating the geographical location of the UE 100 when the multicast reception quality satisfies the resume condition.

[0080] The UE 100 may include, in the log information, time information (for example, a timestamp) indicating the timing at which the multicast reception quality satisfied the resume condition.

[0081] In step S105, the UE 100 transitions to an RRC connected state by resuming the RRC connection.

[0082] In step S106, UE 100 transmits the retained log information to network 5 (gNB 200). For example, UE 100 transmits a log retention indication (Availability Indication) indicating that log information is retained to network 5. After transmitting the log retention indication, UE 100 receives a log transmission request (UE Information Request) from network 5. In response to this, UE 100 transmits a message (UE Information Response) including the retained log information to network 5.

[0083] The network 5 may identify the location and situation of the problem and optimize the coverage area based on the log information from the UE 100. The network 5 may change the resume condition (threshold) set in the UE 100 based on the log information from the UE 100. The network 5 may transition another UE 100 that performs multicast reception in the RRC inactive state to the RRC connected state by paging (RAN Paging) based on the log information from the UE 100.

[0084] Fig. 8 is a diagram showing an example of a third operation pattern of the mobile communication system 1 according to the embodiment. Here, differences from the operation shown in Fig. 7 will be described.

[0085] The operations in steps S201 to S203 are the same as those in FIG.

[0086] When the UE 100 determines that the multicast reception quality satisfies the resume condition (step S203: YES), the UE 100 starts RRC connection resume in step S204.

[0087] In step S205, the UE 100 determines whether the RRC connection resume has been successful. For example, after transmitting an RRC Resume Request message to the gNB 200, the UE 100 determines that the RRC connection resume has been successful when receiving an RRC Resume Request message from the gNB 200; otherwise, the UE 100 determines that the RRC connection resume has failed.

[0088] When it is determined that the RRC connection resume has been successful (step S205: YES), in step S206, the UE 100 holds the log information as described above. In this operation pattern, the UE 100 may include, in the log information, information indicating that the RRC connection resume has been successful due to the multicast reception quality satisfying the resume condition.

[0089] In step S207, the UE 100 transitions to an RRC connected state by resuming the RRC connection.

[0090] In step S208, UE100 transmits the log information it holds to network 5 (gNB200).

[0091] 9 is a diagram showing an example of a fourth operation pattern of the mobile communication system 1 according to the embodiment. Here, differences from the operations shown in FIGS. 7 and 8 will be described.

[0092] The operations in steps S301 to S303 are the same as those in FIGS.

[0093] When the UE 100 determines that the multicast reception quality satisfies the resume condition (step S303: YES), the UE 100 starts RRC connection resume in step S304.

[0094] In step S305, the UE 100 determines whether or not the RRC connection resume has been successful.

[0095] If it is determined that the RRC connection resume is successful (step S305: YES), in step S306, the UE 100 transitions to an RRC connected state. Then, in step S307, if the UE 100 holds log information, the UE 100 transmits the log information to the network 5 (gNB 200).

[0096] On the other hand, if it is determined that the RRC connection resume has failed (step S305: NO), in step S308, the UE 100 retains the log information as described above. In this operation pattern, the UE 100 may include, in the log information, information indicating that the RRC connection resume has failed due to the multicast reception quality satisfying the resume condition. Thereafter, the UE 100 continues to retain the log information. When the UE 100 transitions from the RRC idle state or the RRC inactive state to the RRC connected state, the UE 100 may transmit the retained log information to the network 5.

[0097] (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.

[0098] 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).

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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).

[0104] 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.

[0105] 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.

[0106] 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.

[0107] This application claims priority from Japanese Patent Application No. 2023-101435 (filed June 21, 2023), the entire contents of which are incorporated herein by reference.

[0108] (5) Supplementary Notes The following are additional notes regarding the features of the above-described embodiment.

[0109] (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 evaluating, when receiving multicast in the RRC inactive state, whether the multicast reception quality satisfies the resume condition; a step of retaining log information related to the multicast reception based on whether the multicast reception quality satisfies the resume condition; and a step of transmitting the log information to the network after transitioning from the RRC inactive state to an RRC connected state.

[0110] (Supplementary Note 2) The communication method according to Supplementary Note 1, wherein in the storing step, the user device stores the log information when the multicast reception quality satisfies the resume condition.

[0111] (Supplementary Note 3) The communication method according to Supplementary Note 1, wherein in the storing, the user equipment stores the log information when starting the RRC connection resume after the multicast reception quality satisfies the resume condition.

[0112] (Supplementary Note 4) The communication method according to Supplementary Note 1, wherein in the storing step, the user equipment stores the log information when the RRC connection resume fails or succeeds after the multicast reception quality satisfies the resume condition.

[0113] (Supplementary Note 5) The communication method according to any one of Supplementary Notes 1 to 4, wherein the log information includes a measurement result of the multicast reception quality.

[0114] (Supplementary Note 6) The communication method according to any one of Supplementary Notes 1 to 5, wherein the log information includes identification information for identifying the satisfied resume condition.

[0115] (Supplementary Note 7) The communication method according to any one of Supplementary Notes 1 to 6, wherein the log information includes session identification information for identifying a multicast session whose multicast reception quality satisfies the resume condition.

[0116] (Supplementary Note 8) The communication method according to any one of Supplementary Notes 1 to 7, wherein the log information includes cell identification information for identifying a serving cell of the user equipment when the multicast reception quality satisfies the resume condition.

[0117] (Supplementary Note 9) The communication method according to any one of Supplementary Notes 1 to 8, wherein the log information includes location information for identifying a geographical location of the user device when the multicast reception quality satisfies the resume condition.

[0118] (Supplementary Note 10) The communication method according to any one of Supplementary Notes 1 to 9, wherein the log information includes time information for identifying a timing at which the multicast reception quality satisfied the resume condition.

[0119] (Supplementary Note 11) The communication method according to any one of Supplementary Notes 4 to 10, wherein the log information includes identification information for identifying whether the RRC connection resume has failed or succeeded.

[0120] (Supplementary Note 12) A user equipment used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: a receiving unit that receives, from a network, information for setting a resume condition related to multicast reception quality, the condition being a condition for starting an RRC connection resume when receiving multicast in a radio resource control (RRC) inactive state; a control unit that evaluates whether the multicast reception quality satisfies the resume condition when receiving multicast in the RRC inactive state, and holds log information related to the multicast reception based on whether the multicast reception quality satisfies the resume condition; and a transmitting unit that transmits the log information to the network after transitioning from the RRC inactive state to an RRC connected state.

[0121] 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 node, information for setting a condition for initiating RRC connection resume during multicast reception in a radio resource control (RRC) inactive state and for setting a resume condition related to multicast reception quality; When performing multicast reception in the RRC inactive state, evaluating whether the multicast reception quality satisfies the resume condition; storing log information regarding the multicast reception based on whether the multicast reception quality satisfies the resume condition; and transmitting the log information to the network node after transitioning from the RRC inactive state to an RRC connected state. Communication method.

2. In the storing, the user device stores the log information when the multicast reception quality satisfies the resume condition. The communication method according to claim 1 .

3. In the storing, the user equipment stores the log information when the RRC connection resume is started after the multicast reception quality satisfies the resume condition. The communication method according to claim 1 .

4. In the storing, the user equipment stores the log information when the RRC connection resume fails or succeeds after the multicast reception quality satisfies the resume condition. The communication method according to claim 1 .

5. The log information includes the measurement result of the multicast reception quality. The communication method according to claim 1 .

6. The log information includes identification information for identifying the satisfied resume condition. The communication method according to claim 1 .

7. The log information includes session identification information for identifying a multicast session whose multicast reception quality satisfies the resume condition. The communication method according to claim 1 .

8. The log information includes cell identification information for identifying a serving cell of the user equipment when the multicast reception quality satisfies the resume condition. The communication method according to claim 1 .

9. The log information includes location information for identifying a geographical location of the user device when the multicast reception quality satisfies the resume condition. The communication method according to claim 1 .

10. The log information includes time information for identifying the timing at which the multicast reception quality satisfied the resume condition. The communication method according to claim 1 .

11. The log information includes identification information for identifying whether the RRC connection resume has failed or succeeded. The communication method according to claim 4.

12. A user equipment for use in a mobile communication system providing a multicast / broadcast service (MBS), comprising: a receiving unit configured to receive, from a network node, information for setting a condition for initiating RRC connection resume during multicast reception in a radio resource control (RRC) inactive state and for setting a resume condition related to multicast reception quality; a control unit that evaluates whether the multicast reception quality satisfies the resume condition when multicast reception is performed in the RRC inactive state, and stores log information related to the multicast reception based on whether the multicast reception quality satisfies the resume condition; a transmitter that transmits the log information to the network node after transitioning from the RRC inactive state to an RRC connected state. User equipment.