Communication control method, network device, user device, chip set, communication system, and program

Abstract

To provide a network device and a communication control method for applying a minimization of drive tests (MDT) function to a user device to which a coverage extension function is applied.SOLUTION: A communication control method includes a user device transmitting, to a network, a success information stored when the user device succeeds in receiving a predetermined service from a predetermined cell. The success information includes an identifier of the predetermined cell, an identifier of the user device provided from the predetermined cell, and information indicating the number of times of trials for receiving the predetermined service.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present disclosure relates to a communication control method, a network device, a user device, a chipset, a communication system, and a program used in a mobile communication system.

Background Art

[0002] In 3GPP (Third Generation Partnership Project) (registered trademark; the same shall apply hereinafter), which is a standardization project for cellular communication systems, the function of MDT (Minimization of Drive Tests) has been specified. The MDT function enables a user device to measure a radio environment and report measurement information of the radio environment to a network together with the location information of the user device, thereby making it possible to detect, for example, coverage holes, and to optimize the network.

[0003] On the other hand, user devices for MTC (Machine Type Communication) and IoT (Internet of Things) services are known. The transmission and reception bandwidth of such user devices is limited in order to achieve cost reduction, coverage expansion, and low power consumption. In addition, a coverage expansion function including repetition is applied to such user devices so that they can be used even in a poor radio environment.

[0004] When applying the MDT function to a user device to which a coverage expansion function is applied, a new mechanism not present in the conventional MDT function is considered necessary.

Summary of the Invention

[0005] The communication control method according to an embodiment is a method executed by a user equipment. The communication control method includes transmitting, to a network, a failure report regarding a failure of a procedure related to an RRC connection executed by the user equipment when in an extended coverage of a serving cell. The failure report includes extended state information indicating a coverage extension state of the user equipment in the extended coverage, and failure count information associated with the extended state information. The failure count information indicates the number of times the user equipment has failed in the procedure in the coverage extension state.

[0006] The communication control method according to an embodiment is a method executed by a user equipment. When a procedure related to an RRC connection executed by the user equipment fails when in a serving cell, the communication control method includes saving measurement values of a radio environment of the user equipment, calculating one statistical value from the measurement values saved multiple times in the saving step when the procedure fails multiple times, and transmitting, to a network, a failure report including the calculated statistical value.

[0007] The communication control method according to an embodiment is a method executed by a user equipment. When reception of an SC-PTM for which an MBMS service is provided fails, the communication control method includes saving radio environment information regarding a radio environment of the user equipment when the reception of the SC-PTM fails, and transmitting, to a network, a failure report including the saved radio environment information. The failure report further includes a service identifier indicating the MBMS service.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

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

[0010] (Mobile Communication System) First, the configuration of a mobile communication system according to an embodiment will be described. The mobile communication system according to an embodiment is a 3GPP 5G system, but LTE may be at least partially applied to the mobile communication system.

[0011] FIG. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment.

[0012] As shown in FIG. 1, the mobile communication system includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20.

[0013] The UE 100 is a movable device. The UE 100 may be any device used by a user. For example, the UE 100 is 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 the sensor, a vehicle or a device provided in the vehicle (Vehicle UE), or an aircraft or a device provided in the aircraft (Aerial UE).

[0014] The NG-RAN 10 includes a base station (referred to as "gNB" in the 5G system) 200. The gNB 200 may also be referred to as an NG-RAN node. The gNBs 200 are interconnected 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 cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. "Cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency.

[0015] Note that the gNB may be connected to the EPC (Evolved Packet Core), which is the core network of LTE, or the base station of LTE may be connected to the 5GC. Also, the base station of LTE and the gNB may be connected via an interface between base stations.

[0016] The 5GC 20 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 information on the area where the UE 100 is located by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF are connected to the gNB 200 via the NG interface, which is an interface between the base station and the core network.

[0017] Figure 2 is a diagram showing the configuration of the UE 100 (user equipment).

[0018] As shown in Figure 2, the UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130.

[0019] The receiving unit 110 performs various receptions under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it 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 the baseband signal (transmitted 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 in the UE 100. The control unit 130 includes at least one processor and at least one memory electrically connected to the processor. The memory stores programs executed by the processor and information used for 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, etc. The CPU executes programs stored in the memory to perform various processes.

[0022] Note that the UE 100 may further include a position sensor such as a GNSS (Global Navigation Satellite System) receiver.

[0023] FIG. 3 is a diagram showing the configuration of the gNB 200 (base station).

[0024] As shown in FIG. 3, the gNB 200 includes a transmission unit 210, a reception unit 220, a control unit 230, and a backhaul communication unit 240.

[0025] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0026] The reception unit 220 performs various receptions under the control of the control unit 230. The reception unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (reception signal) and outputs it to the control unit 230.

[0027] The control unit 230 performs various controls in the gNB 200. The control unit 230 includes at least one processor and at least one memory electrically connected to the processor. The memory stores programs executed by the processor and information used for 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, etc. The CPU executes programs stored in the memory to perform various processes.

[0028] The backhaul communication unit 240 is connected to an adjacent base station via a base station interface. The backhaul communication unit 240 is connected to the AMF / UPF 300 via a base station-core network interface. Note that the gNB is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally split), and the two units may be connected by an F1 interface.

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

[0030] As shown in FIG. 4, the radio interface protocol of the user plane has a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0031] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted via a physical channel between the PHY layer of the UE 100 and the PHY layer of the gNB 200.

[0032] The MAC layer performs functions such as priority control of data, retransmission processing by Hybrid ARQ (HARQ), and random access procedures. Between the MAC layer of UE100 and the MAC layer of gNB200, data and control information are transmitted via transport channels. The MAC layer of gNB200 includes a scheduler. The scheduler determines the transport format (transport block size, modulation and coding scheme (MCS)) for uplink and downlink and the resource blocks allocated to UE100.

[0033] The RLC layer uses the functions of the MAC layer and the PHY layer to transmit data to the RLC layer on the receiving side. Between the RLC layer of UE100 and the RLC layer of gNB200, data and control information are transmitted via logical channels.

[0034] The PDCP layer performs header compression / expansion and encryption / decryption.

[0035] The SDAP layer performs the mapping between the IP flow, which is the unit for the core network to perform QoS control, and the radio bearer, which is the unit for the AS (Access Stratum) to perform QoS control. When the RAN is connected to the EPC, the SDAP may not be necessary.

[0036] Figure 5 is a diagram showing the configuration of the protocol stack of the radio interface in the control plane that handles signaling (control signals).

[0037] As shown in Figure 5, the protocol stack of the radio interface in the control plane has an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer instead of the SDAP layer shown in Figure 4.

[0038] Between the RRC layer of UE100 and the RRC layer of gNB200, RRC signaling for various settings is transmitted. The RRC layer controls the logical channel, transport channel, and physical channel in response 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 the RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in the RRC idle state. Also, when the RRC connection is suspended, UE100 is in the RRC inactive state.

[0039] The NAS layer located above the RRC layer performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of UE100 and the NAS layer of AMF300.

[0040] Note that UE100 has an application layer etc. in addition to the protocol of the radio interface.

[0041] Figures 6A and 6B are diagrams showing the configuration of the downlink channels of a mobile communication system according to an embodiment. Figure 6A shows the mapping between the logical channel (Downlink Logical Channel) and the transport channel (Downlink Transport Channel).

[0042] As shown in Figure 6A, the PCCH (Paging Control Channel) is a logical channel for notifying paging information and system information changes. The PCCH is mapped to the PCH (Paging Channel), which is a transport channel.

[0043] The BCCH (Broadcast Control Channel) is a logical channel for system information. The BCCH is mapped to the BCH (Broadcast Channel) and DL-SCH (Downlink Shared Channel), which are transport channels.

[0044] The CCCH (Common Control Channel) is a logical channel for transmission control information between the UE 100 and the gNB 200. The CCCH is used when the UE 100 does not have an RRC connection with the network. The CCCH is mapped to the DL-SCH.

[0045] The DCCH (Dedicated Control Channel) is a logical channel for transmitting individual control information between the UE 100 and the network. The DCCH is used when the UE 100 has an RRC connection. The DCCH is mapped to the DL-SCH.

[0046] The DTCH (Dedicated Traffic Channel) is an individual logical channel for data transmission. The DTCH is mapped to the DL-SCH.

[0047] The SC-MTCH (Single Cell Multicast Traffic Channel) is a logical channel for SC-PTM. The SC-MTCH is a point-to-multipoint downlink channel for multicasting data (MBMS) from the network to the UE 100 using SC-PTM. Details of SC-PTM will be described later.

[0048] The SC-MCCH (Single Cell Multicast Control Channel) is a logical channel for SC-PTM. The SC-MCCH is a point-to-multipoint downlink channel for multicasting MBMS control information for one or more SC-MTCHs from the network to the UE100. The SC-MCCH is used by the UE100 that receives or is interested in receiving MBMS using SC-PTM. Also, there is only one SC-MCCH per cell.

[0049] The MCCH (Multicast Control Channel) is a logical channel for MBSFN. The MCCH is used for transmitting MBMS control information for MTCH from the network to the UE100. The MCCH is mapped to the MCH (Multicast Channel) which is a transport channel.

[0050] The MTCH (Multicast Traffic Channel) is a logical channel for MBSFN. The MTCH is mapped to the MCH.

[0051] Figure 6B shows the mapping between the Downlink Transport Channel and the Downlink Physical Channel.

[0052] As shown in Figure 6B, the BCH is mapped to the PBCH (Physical Broadcast Channel).

[0053] The MCH is mapped to the PMCH (Physical Multicast Channel). The MCH supports MBSFN by multiple cells.

[0054] PCH and DL-SCH are mapped to the PDSCH (Physical Downlink Shared Channel). DL-SCH supports HARQ, link adaptation, and dynamic resource allocation.

[0055] The PDCCH (Physical Downlink Control Channel) carries resource allocation information for the PDSCH (DL-SCH, PCH) and HARQ information related to the DL-SCH, etc. Also, the PDCCH carries an uplink scheduling grant.

[0056] (MDT function) Next, the outline of the MDT function will be described. A mobile communication system according to an embodiment supports the MDT function.

[0057] In MDT, the gNB200 sends a configuration message for setting MDT measurements to the UE100. Then, the gNB200 collects MDT measurement information from the UE100. For example, the gNB200 is directly or indirectly connected to a server for MDT. The server for MDT obtains MDT measurement information from the gNB200 and performs network optimization including coverage optimization based on the MDT measurement information.

[0058] There are two types of MDT: logged MDT and immediate MDT.

[0059] Logged MDT is where the UE100 in the RRC idle state, RRC inactive state, or RRC connected state performs radio measurements, records the measurement results together with UE location information and timestamps, and sends a report including the recorded measurement results, etc., in response to a request from the network (gNB200).

[0060] Immediate MDT is for the UE 100 in the RRC connected state to perform radio measurements and other item measurements, and send a report including the measurement results and UE location information to the network (gNB 200). The configuration message for configuring Immediate MDT may be a measurement configuration message including an information element that requires including UE location information in the measurement report.

[0061] In MDT, the UE 100 stores each of the following failure information and sends a failure report including the failure information.

[0062] (Coverage Extension Function) Next, the outline of the coverage extension function will be described. A mobile communication system according to an embodiment supports the coverage extension function.

[0063] For the UE 100 targeted for MTC (Machine Type Communications) and IoT services, the transmission and reception bandwidth is limited to only a part of the system transmission and reception band. For example, in LTE, such categories of the UE 100 are called Category M1 and Category NB (Narrow Band)-IoT. Category M1 is the category to which eMTC (enhanced MTC) UEs belong. Category NB-IoT (Category NB1) is the category to which NB-IoT UEs belong.

[0064] Category M1 limits the transmission and reception bandwidth of the UE 100 (eMTC UE) to, for example, 1.08 MHz (that is, the bandwidth of 6 resource blocks). Category NB-IoT (Category NB1) further limits the transmission and reception bandwidth of the UE 100 (NB-IoT UE) to 180 kHz (that is, the bandwidth of 1 resource block). Such narrowing of the bandwidth realizes the required cost reduction and power consumption reduction for eMTC UEs and NB-IoT UEs.

[0065] Figure 7 is a diagram showing the frequency channels handled by eMTC UEs and NB-IoT UEs.

[0066] As shown in FIG. 7, the frequency bandwidth of the system frequency band of the mobile communication system can be 10 MHz. The bandwidth of the system transmission / reception band is, for example, 50 resource blocks = 9 MHz. The bandwidth of the frequency channel that an eMTC UE can support is within 6 resource blocks = 1.08 MHz.

[0067] The frequency channel within 6 resource blocks that an eMTC UE can support is called "narrow band (NB)". The bandwidth of the frequency channel that an NB-IoT UE can support is 1 resource block = 180 kHz. The frequency channel of 1 resource block that an NB-IoT UE can support is called "carrier".

[0068] Since the UE100 of category M1 cannot receive the downlink radio signal transmitted with a bandwidth wider than 6 resource blocks, it cannot receive the normal PDCCH. For this reason, the MPDCCH (MTC-PDCCH), which is a PDCCH for MTC, is introduced. For the same reason, the NPDCCH (NB-PDCCH), which is a PDCCH for NB-IoT, is introduced.

[0069] The eMTC UE operates within the LTE transmission / reception bandwidth. The NB-IoT UE supports an operation mode within the LTE transmission / reception bandwidth, an operation mode in the guard band outside the LTE transmission / reception bandwidth, and an operation mode within the frequency band dedicated to NB-IoT.

[0070] The eMTC UE and the NB-IoT UE support an enhanced coverage (EC) function using repeated transmission or the like in order to achieve coverage expansion. Note that the enhanced coverage may also be called CE (Coverage Enhancement).

[0071] The coverage extension function may include repetition transmission that repeatedly transmits the same signal using a plurality of subframes. The more times of repetition transmission, the more the coverage can be extended.

[0072] The coverage extension function may include power boosting that increases the power density of the transmission signal. As an example, the power density is increased by narrowband transmission that narrows the frequency bandwidth of the transmission signal. The more the power density of the transmission signal is increased, the more the coverage can be extended. The coverage extension function may include lower MCS transmission that reduces the MCS used for the transmission signal. By performing transmission using an MCS with a low data rate and high error tolerance, the coverage can be extended.

[0073] The coverage extension function has a plurality of coverage extension states with different degrees of coverage extension. The method for determining the coverage extension state will be described later.

[0074] Note that a UE in the extended coverage may perform cell reselection by ranking based on the received power (RSRP (Reference Signal Received Power)) in the RRC idle state or the RRC inactive state. For example, the UE calculates the ranking Rs of the current serving cell and the ranking Rn of the neighboring cell, and selects a cell having a ranking Rn higher than Rs over a predetermined period (TreselectionRAT) as a new serving cell.

[0075] (Method for Determining Coverage Extension State) FIG. 8 is a diagram showing an example of a coverage extension state in a mobile communication system according to an embodiment.

[0076] The coverage extension state (hereinafter referred to as the "CE state") may include a coverage extension level (hereinafter referred to as the "CE level") and a coverage extension mode (hereinafter referred to as the "CE mode").

[0077] As shown in FIG. 8, the CE mode includes at least CE mode A and CE mode B. CE mode B is in a state where the coverage is further extended compared to CE mode A. CE mode B supports more transmission repetition times than CE mode A. A UE (e.g., an eMTC UE) that supports the coverage extension function supports at least CE mode A.

[0078] The CE level includes at least four levels: level 0 to level 3. The CE mode and the CE level may be associated. In the example of FIG. 8, CE levels 0 and 1 correspond to CE mode A, and CE levels 2 and 3 correspond to CE mode B. The CE mode and the CE level may not be associated.

[0079] When the first cell selection criterion (the first S-criteria) for normal coverage is not satisfied and the second cell selection criterion (the second S-criteria) for CE mode A is satisfied for the UE 100 in the RRC idle state or the RRC inactive state, it may be determined that it is in the extended coverage. If the UE 100 supports CE mode B, and the second S-criteria is not satisfied, and the third cell selection criterion (the third S-criteria) for CE mode B is satisfied, it may be determined that it is in the extended coverage. The "UE in the extended coverage" may mean a UE that needs to use the coverage extension function to access the cell.

[0080] After determining that it is in the extended coverage, the UE 100 determines its own CE level.

[0081] The UE 100 measures the RSRP (Reference Signal Received Power) and compares the measured RSRP with the RSRP threshold for each CE level to determine its own CE level (one of CE levels 0 to 3). The RSRP threshold for each CE level may be set by the system information broadcast by the serving cell of the UE 100.

[0082] UE100 may determine its own CE level when performing a random access procedure. When performing a random access procedure for a serving cell, UE100 transmits an RA preamble to the serving cell using a PRACH (Physical Random Access Channel) resource (frequency resource, time resource, preamble, etc.) corresponding to its own CE level. The correspondence between the CE level and the PRACH resource may be set by system information. If UE100 cannot receive an RA (Random Access) response from the serving cell within a predetermined time, it may retransmit the RA preamble. If UE100 still cannot receive an RA response even when the number of transmissions of the RA preamble reaches a predetermined number, UE100 may determine its own CE level as the next level. For example, if UE100 cannot receive an RA response even when the number of transmissions of the RA preamble transmitted using the PRACH resource corresponding to CE level 0 reaches a predetermined number, it determines its own CE level as CE level 1. Such a predetermined number may be set by system information. Thereafter, UE100 may transmit an RA preamble to the serving cell using the PRACH resource corresponding to CE level 1.

[0083] UE100 may determine the CE level corresponding to the PRACH resource used when transmitting the RA preamble corresponding to the successfully received RA response as its own CE level.

[0084] UE100 may determine its CE mode based on the correspondence between the CE mode and the CE level. In the example of FIG. 8, when the CE level of UE100 is level 0 or 1, UE100 determines its CE mode as CE mode A, and when the CE level of UE100 is level 2 or 3, UE100 determines its CE mode as CE mode B. UE100 may determine its CE mode based on other criteria. For example, when UE100 determines that it is in extended coverage in response to the satisfaction of the second cell selection criterion for CE mode A, UE100 may determine its CE mode as CE mode A.

[0085] When UE100 is in the RRC connected state, it may set the CE mode from the serving cell. The CE mode may be set by dedicated RRC signaling from the serving cell.

[0086] When UE100 receives RRC signaling indicating CE mode A, UE100 determines its CE mode as CE mode A. When UE100 receives RRC signaling indicating CE mode B, UE100 determines its CE mode as CE mode B.

[0087] The CE state may be indicated by one of a plurality of received power ranges (RSRP ranges). The plurality of RSRP ranges may be set by the system information broadcast by the serving cell of UE100. UE100 measures the RSRP and determines the RSRP range to which the measured RSRP belongs. For example, when RSRP ranges #1 to #3 are set and the measured RSRP belongs to RSRP range #1, UE100 determines its CE state as RSRP range #1.

[0088] When performing uplink (UL) communication, UE100 applies UL parameters according to its own CE state. The UL parameters may be set for UE100 by RRC signaling. The UL parameters may be set for UE100 by system information. The UL parameters include the UL repetition count, transmission power, etc. The UL repetition count may include the number of repetitions to be applied to UL transmission. The UL repetition count may include the maximum number of repetitions to be applied to UL transmission. The UL repetition count may be set for each UL channel. For example, the UL repetition count may include the repetition count of PUCCH (Physical Uplink Control Channel), the repetition count of PUSCH (Physical Uplink Shared Channel), and the repetition count of PRACH, etc. The predetermined number regarding the number of transmissions of the above RA preamble may be the maximum repetition count of PRACH.

[0089] When performing downlink (DL) communication, UE100 applies DL parameters according to its own CE state. The DL parameters may be set for UE100 by RRC signaling. The DL parameters may be set for UE100 by system information. The DL parameters include the DL repetition count, etc. The DL repetition count may include the number of repetitions to be applied to DL transmission. The DL repetition count may include the maximum number of repetitions to be applied to DL transmission. The DL repetition count may be set for each DL channel. For example, the DL repetition count may include the repetition count of PDCCH, the repetition count of PDSCH, etc.

[0090] (Overview of SC-PTM) Next, the overview of SC-PTM will be described. In 3GPP, Multimedia Broadcast Multicast Service (MBMS) transmission for providing multicast / broadcast services to user equipment is standardized. As MBMS methods, there are two methods: Multicast Broadcast Single Frequency Network (MBSFN) and Single Cell Point-To-Multipoint (SC-PTM). In MBSFN, data is transmitted via the Physical Multicast Channel (PMCH) in units of MBSFN areas consisting of multiple cells. On the other hand, in SC-PTM, data is transmitted via the Physical Downlink Shared Channel (PDSCH) in units of cells.

[0091] UE100 may receive the MBMS service in the RRC connected state, or may receive the MBMS service in the RRC idle state or the RRC inactive state.

[0092] FIG. 9 is a diagram showing an operation example of receiving SC-PTM. As shown in FIG. 9, in step S1, UE100 acquires a User Service Description (USD) from 5GC20 via gNB200. The USD provides basic information on each MBMS service. The USD includes, for each MBMS service, a Traffic Management and Identification (TMGI) that identifies the MBMS service, the frequency on which the MBMS service is provided, and the start / end time of the provision of the MBMS service.

[0093] In step S2, UE100 receives SIB20 from gNB200 via the BCCH (Broadcast Control Channel). SIB20 contains information (scheduling information) necessary for acquiring the SC-MCCH. SIB20 includes an sc-mcch-ModificationPeriod indicating the period during which the content of the SC-MCCH can be changed, an sc-mcch-RepetitionPeriod indicating the transmission (retransmission) period of the SC-MCCH in terms of the number of radio frames, an sc-mcch-Offset indicating the offset of the radio frame in which the SC-MCCH is scheduled, and an sc-mcch-Subframe indicating the subframe in which the SC-MCCH is scheduled, etc.

[0094] In step S3, UE100 receives MBMS control information from gNB200 via SC-MCCH based on SIB20. The MBMS control information may be referred to as SC-PTM configuration information (SCPTM Configuration). SC-RNTI (Single Cell RNTI) is used for the transmission of SC-MCCH in the physical layer. The SC-PTM configuration information includes control information applicable to the MBMS service transmitted via SC-MRB (Single Cell MBMS Point to Multipoint Radio Bearer). The SC-PTM configuration information includes an sc-mtch-InfoList that includes the settings of each SC-MTCH in the cell that transmits the information, and an scptmNeighbourCellList that is a list of adjacent cells that provide the MBMS service via SC-MRB. The sc-mtch-InfoList includes one or more SC-MTCH-Info. Each SC-MTCH-Info includes information (mbmsSessionInfo) of an ongoing MBMS session transmitted via SC-MRB, a G-RNTI (Group RNTI) corresponding to the MBMS session, and sc-mtch-schedulingInfo that is DRX information for the SC-MTCH. The mbmsSessionInfo includes a TMGI that identifies the MBMS service and a session ID (sessionId). The G-RNTI is an RNTI that identifies a multicast group (specifically, an SC-MTCH addressed to a specific group). The G-RNTI is mapped one-to-one with the TMGI. The sc-mtch-schedulingInfo includes onDurationTimerSCPTM, drx-InactivityTimerSCPTM, and schedulingPeriodStartOffsetSCPTM. The schedulingPeriodStartOffsetSCPTM includes SC-MTCH-SchedulingCycle and SC-MTCH-SchedulingOffset.

[0095] In step S4, the UE 100 receives, via the SC-MTCH, the MBMS service (MBMS data) corresponding to the TMGI of its interest based on the SC-MTCH-SchedulingInfo in the SC-PTM configuration information. At the physical layer, after transmitting the PDCCH using the G-RNTI, the gNB 200 transmits the MBMS data via the PDSCH.

[0096] When performing SC-PTM reception, the UE 100 may attempt reception by applying the number of repetitions corresponding to each of the above channels (such as the BCCH carrying SIB20, the SC-MCCH, the SC-MTCH, etc.) (for example, the BCCH repetition number, the SC-MCCH repetition number, the SC-MTCH repetition number, etc.). The BCCH repetition number, the SC-MCCH repetition number, and the SC-MTCH repetition number may be set for each CE state.

[0097] (First Embodiment) Next, the operation of the mobile communication system according to the first embodiment will be described. FIG. 10 is a diagram showing an operation flow in the mobile communication system according to the first embodiment. In this operation flow, it is executed by the UE 100 which is, for example, an eMTC UE or an NB-IoT UE.

[0098] In step S11, the gNB 200 transmits the MDT measurement configuration to the UE 100. At this point, the UE 100 is in the RRC connected state. In step S12, the UE 100 transitions from the RRC connected state to the RRC idle state or the RRC inactive state.

[0099] The operations in steps S11 to S12 may be omitted. In the following, assuming that the UE 100 is in the extended coverage area after transitioning to the RRC idle state or the RRC inactive state, the operations from step S13 will be described.

[0100] In step S13, UE 100 executes procedures related to RRC connection. If the procedure fails, in step S14, UE 100 stores connection failure information regarding the failure of the procedure. Here, the "procedure related to RRC connection" may be an RRC connection establishment procedure for establishing a new RRC connection or an RRC connection resume procedure for resuming a suspended RRC connection. In response to the success of the RRC connection establishment procedure and the RRC connection resume procedure, UE 100 transitions to the RRC connected state. The RRC connection establishment procedure and the RRC connection resume procedure may also be referred to as procedures for transitioning to the RRC connected state.

[0101] Note that UE 100 may fail multiple times in the procedure related to RRC connection in the RRC idle state or the RRC inactive state. In this case, UE 100 executes the processes of steps S13 and S14 multiple times and stores connection failure information regarding the failures for multiple times (step S14).

[0102] Details of steps S13 to S14 will be described with reference to FIG. 11. FIG. 11 is a diagram showing details of steps S13 to S14.

[0103] In step S1301, UE 100 determines its CE state using the above-described method for determining the coverage extension state. For example, UE 100 may determine its CE level according to the measured RSRP. UE 100 may determine the CE level corresponding to the PRACH resource used when transmitting the RA preamble corresponding to the successfully received RA response as its own CE level. Note that if UE 100 is not in extended coverage (i.e., if it is in normal coverage), step S1301 may not be performed.

[0104] In step S1302, UE 100 starts the procedure related to RRC connection and transmits an RRC request message corresponding to the procedure to the serving cell (gNB 200). UE 100 may transmit the RRC request message in response to receiving an RA response. When the procedure related to RRC connection is the RRC connection establishment procedure, the RRC request message is an RRC Setup Request message. When the procedure related to RRC connection is the RRC connection resume procedure, the RRC request message is an RRC Resume Request message.

[0105] In step S1303, UE 100 starts a timer in response to transmitting the RRC request message. The value of the timer may be set by the system information broadcast from the serving cell. The value of the timer may vary according to the type of the "procedure related to RRC connection" (RRC connection establishment, RRC connection resume, etc.). The value of the timer may vary according to the type of CE mode (CE mode A, CE mode B, etc.). When repeated transmission is applied to the transmission of the RRC request message, UE 100 may start the timer in response to the first transmission in the repeated transmission. Also, UE 100 may start the timer in response to the last transmission in the repeated transmission. For example, when the maximum number of repeated transmissions in the repeated transmission is set for UE 100, UE 100 may regard the transmission performed immediately before reaching the maximum number of repeated transmissions as the last transmission.

[0106] In steps S1304 to S1305, UE 100 attempts to receive an RRC response message that responds to the RRC request message before the timer expires.

[0107] When the timer expires (step S1305: YES), UE100 proceeds with the operation to step S14. Here, if the RRC response message has not been received before the timer expires, UE100 considers that the procedure related to the RRC connection has failed and stores the failure information related to the failure of the procedure related to the RRC connection.

[0108] On the other hand, if the RRC response message has been received before the timer expires (step S1304: YES), in step S1306, UE100 stops the timer and proceeds with the operation to step S1307.

[0109] In step S1307, UE100 determines whether the received RRC response message is a positive response. If the RRC response message is a positive response (step S1307: YES), in step S1308, UE100 succeeds in the procedure related to the RRC connection.

[0110] On the other hand, if the RRC response message is not a positive response (step S1307: NO), UE100 may restart the procedure related to the RRC connection. UE100 may start the procedure for the same serving cell, or may select a new serving cell and start the procedure for the new serving cell.

[0111] Here, the operation of step S14 will be described. In step S14, UE100 stores the connection failure information related to the failure of the procedure related to the RRC connection in the storage area for connection failure information. The storage area for connection failure information is provided, for example, in the memory included in the control unit 130. The connection failure information includes at least one of the following information (a) to (d).

[0112] (a) Extended state information UE100 stores the connection failure information including the extended state information indicating its CE state (the CE state determined in step S1301) when the procedure related to the RRC connection fails. The extended state information may indicate one of the CE level, CE mode, and RSRP range, or a combination of two or more of these. For example, the extended state information indicates CE mode A and CE level 0. The extended state information may indicate RSRP range #1.

[0113] (b) Failure count information UE100 stores the connection failure information including the failure count information indicating the number of times the procedure related to the RRC connection has failed (hereinafter referred to as "failure count"). Specifically, UE100 holds a counter that counts the failure count and stores the value of the counter as the failure count information. For example, UE100 increments the value of the counter by 1 and updates the failure count information in response to the expiration of the timer corresponding to the transmitted RRC request message (step S1305: YES).

[0114] UE100 may store the failure count information associated with the extended state information. That is, UE100 counts the failure count for each CE state. Specifically, UE100 holds the above-mentioned counter for each CE state and counts the number of times the procedure related to the RRC connection executed by UE100 has failed in the same CE state. For example, UE100 holds a counter corresponding to CE level 0 (counter_CE0), and when the timer corresponding to the RRC request message transmitted when its own CE level is CE level 0 (it is determined that the CE level is CE level 0 in step S1301) expires (step S1305: YES), counter_CE0 is incremented by 1.

[0115] Basically, UE100 counts the failure count for each serving cell, but it may also count the total number of failures of the procedures related to the RRC connection executed within a predetermined time (e.g., 48 h) regardless of the serving cell. In this case, UE100 may hold a counter_Total corresponding to the total failure count.

[0116] (c) Failed cell identification information When the procedure related to the RRC connection fails, UE100 saves the cell identifier of the serving cell that has failed in the connection failure information as the failed cell identification information. The cell identifier may be an ECGI (Evolved Cell Global Identifier).

[0117] (d) Measurement values of the radio environment When the procedure related to the RRC connection fails, UE100 saves the measurement values of the radio environment of UE100 in the connection failure information. The measurement values may be RSRP or RSRQ (Reference Signal Received Quality). UE100 may save the measurement values in the connection failure information only when it is in an extended coverage area.

[0118] UE100 measures the radio environment every time the procedure related to the RRC connection fails and saves the measurement values.

[0119] When the procedure related to the RRC connection fails multiple times, UE100 may calculate one statistical value from the multiple measurement values saved in the connection failure information. UE100 may start calculating the statistical value when the number of times the procedure related to the RRC connection fails (for example, the number of times indicated by the failure count information) reaches a threshold. The threshold may be set by gNB200. For example, the threshold may be set by gNB200 through the MDT measurement setting message described later. UE100 may save the measurement values for each CE state.

[0120] UE100 may calculate the average value as the statistical value based on the multiple measurement values measured multiple times and the number of times the procedure related to the RRC connection fails. UE100 may use the maximum value among the multiple measurement values as the statistical value. UE100 may use the minimum value among the multiple measurement values as the statistical value.

[0121] When calculating one statistical value from a plurality of stored measurement values, the UE 100 may store the one statistical value as a measurement value of the radio environment instead of the plurality of measurement values. By doing so, the size of the storage area occupied by storing the plurality of measurement values can be reduced.

[0122] In addition to the information of (a) to (d) described above, the connection failure information may include information related to existing MDT measurements such as location information and time stamps. The location information may be information indicating the geographical location of the UE 100 when the procedure related to the RRC connection fails. The location information may be obtained from the GNSS receiver of the UE 100.

[0123] In step S14, the UE 100 basically stores the connection failure information autonomously, but when step S11 is performed, the UE 100 may store the connection failure information according to a setting message (MDT measurement setting message) from the gNB 200. For example, when the CE state is specified by the setting message (MDT measurement setting), the UE 100 may store the failure count information associated only with the specified CE state.

[0124] Note that after step S14, the UE 100 may return the operation to step S1301 and restart the procedure related to the RRC connection.

[0125] Returning to FIG. 10, the operations after step S15 will be described. In step S15, the UE 100 transmits a notification message indicating that it has connection failure information to the gNB 200. This notification message may be called an availability indicator. The availability indicator may be a message notifying that there is connection failure information stored when the UE 100 is in extended coverage. The UE 100 may transmit the notification message when transitioning from the RRC idle state or the RRC inactive state to the RRC connected state, or during handover.

[0126] Note that the gNB200 that manages the cell in which the UE100 is located at the time of MDT measurement setting (step S11) may be different from the gNB200 that manages the cell in which the UE100 is located at the time of notification (step S15).

[0127] In step S16, the gNB200 transmits a report request message to the UE100 to request the UE100 to transmit (report) a connection failure report including connection failure information based on the notification message from the UE100.

[0128] In step S17, the UE100 transmits a connection failure report to the gNB200 in response to the report request message. The report request message may specify the information to be included in the connection failure report (for example, the above-mentioned information (a) to (d)). The UE100 may transmit a connection failure report including only the information specified by the report request message. The connection failure report includes extended state information and failure count information associated with the extended state information. The connection failure report includes a statistical value calculated from measurement values of the radio environment.

[0129] When the UE100 stores connection failure information across a plurality of cells, it may transmit a connection failure report including connection failure information for each cell.

[0130] (Summary of the First Embodiment) As described above, when the UE100 is in the extended coverage of the serving cell, the UE100 transmits a failure report regarding the failure of the procedure related to the RRC connection executed by the UE100 to the network. The failure report includes extended state information indicating the CE state of the UE100 in the extended coverage and failure count information associated with the extended state information. The failure count information indicates the number of times the UE100 has failed in the procedure in the CE state. Thereby, the network can grasp the accessibility for each CE state and appropriately set transmission parameters such as the number of repeated transmissions corresponding to the CE state.

[0131] (First Modification Example of the First Embodiment) In the first embodiment, it is assumed that the UE 100 is in the RRC idle state or the RRC inactive state. However, in Modification Example 1 of the first embodiment, it is assumed that the UE 100 is in the RRC connected state.

[0132] In Modification Example 1 of the first embodiment, the UE 100 performs the operations of steps S13 to S14 in the RRC connected state. When the UE 100 is in the RRC connected state, the "procedure related to RRC connection" is the RRC connection re-establishment procedure for re-establishing the RRC connection. The RRC connection re-establishment procedure may be performed in response to the UE 100 detecting an RLF (Radio Link Failure) for the cell to which the RRC connection is established.

[0133] In step S1302, the UE 100 transmits an RRCReestablishmentRequest message as an RRC request message. In step S14, the UE 100 stores extended status information and failure count information, etc., corresponding to the RRC connection re-establishment procedure. Without performing the operations of steps S15 and S16, the UE 100 transmits a connection failure report including the extended status information and failure count information, etc., corresponding to the RRC connection re-establishment procedure in response to the success of the connection re-establishment procedure.

[0134] (Modification Example 2 of the First Embodiment) In the first embodiment, an example in which the connection failure information includes the failed cell identification information has been described. However, information in units of an area wider than a cell may be included in the connection failure information. Examples of such a wide area unit include a RAN notification area (RAN Notification Area (RNA)), which is an area unit in which paging is performed at RAN startup, an MBSFN area, which is an area unit where MBMS is provided, and a tracking area, which is an area unit in which paging is performed at AMF startup. In the following, the RAN notification area will be described as an example of such a wide area unit.

[0135] The RAN notification area is also called a RAN-based Notification Area, a RAN paging area, or a RAN location update area.

[0136] The RAN notification area may be composed of one or more cells. The RAN notification area may be set for the UE 100 by an RRC Release message in which the gNB 200 transitions the UE 100 to the RRC inactive state.

[0137] The UE 100 in the RRC inactive state does not need to notify (report) the network that it has performed cell reselection even if it moves between cells by cell reselection within the RAN notification area. When the UE 100 in the RRC inactive state reselects a cell outside the RAN notification area, it requests the network to update the RAN notification area.

[0138] The UE 100 can execute the RRC connection resume procedure in a cell belonging to the RAN notification area set for itself.

[0139] The UE 100 includes and stores the RAN notification area information that identifies the RAN notification area in the connection failure information.

[0140] UE100 may store information such as the number of failure times (such as the above-described extended state information, measurement values of the radio environment, etc.) in association with the RAN notification area information. For example, UE100 counts the number of failure times for each RAN notification area. Specifically, UE100 holds a counter corresponding to the RAN notification area and counts the number of times the RRC connection resume procedure executed in the same RAN notification area fails.

[0141] UE100 transmits a failure report including the RAN notification area information and information such as the number of failure times associated with the RAN notification area information (such as the above-described extended state information, measurement values of the radio environment, etc.) to the network. Therefore, the network can grasp the accessibility for each RAN notification area and set a more appropriate RAN notification area for UE100.

[0142] UE100 may store information in a unit narrower than a cell in the connection failure information. Such a narrow unit includes a beam within a cell. One cell may include a plurality of beams. Each beam broadcasts the beam identifier of its own beam.

[0143] UE100 may store information such as the number of failure times (extended state information, measurement values of the radio environment, etc.) in association with the beam identifier for identifying the beam.

[0144] UE100 transmits a failure report including the beam identifier and information such as the number of failure times associated with the beam identifier (extended state information, measurement values of the radio environment, etc.) to the network. Thereby, the network can grasp the accessibility for each beam and perform detailed optimization for each beam.

[0145] (Second Embodiment) Next, the operation of the mobile communication system according to the second embodiment will be described. FIG. 12 is a diagram showing an operation flow in the mobile communication system according to the second embodiment.

[0146] The second embodiment is an embodiment related to collecting data on the reception status of SC-PTM by the MDT function.

[0147] In step S21, the gNB 200 transmits an MDT measurement setting message for setting logged MDT to the UE 100 in the RRC connected state. The UE 100 receives the MDT measurement setting message and stores various setting parameters included in the received MDT measurement setting message. The setting parameters may specify the CE state. The measurement parameters may specify a specific MBMS service.

[0148] In step S22, after the communication with the gNB 200 ends, the UE 100 transitions from the RRC connected state to the RRC idle state or the RRC inactive state and starts the operation of logged MDT according to the MDT setting parameters.

[0149] Alternatively, the UE 100 may perform the operation of logged MDT according to the MDT setting parameters in the RRC connected state.

[0150] In step S23, the UE 100 attempts to receive SC-PTM. In step S24, the UE 100 stores SC-PTM failure information or SC-PTM success information regarding the reception of SC-PTM.

[0151] Details of steps S23 and S24 will be described with reference to FIG. 13. FIG. 13 is a diagram showing the details of steps S23 and S24.

[0152] In steps S2301 to S2305, the UE 100 attempts to receive SC-PTM to receive a specific MBMS service. The specific MBMS service may be an MBMS service that the UE 100 is interested in, or may be the MBMS service specified by the MDT measurement setting message in step S21.

[0153] In step S2301, UE100 attempts to perform cell reselection to a cell (SC-PTM cell) of a frequency (SC-PTM frequency) that provides a specific MBMS service using SC-PTM. The cell reselection is performed according to the cell reselection procedure defined in 3GPP. If UE100 cannot find an SC-PTM cell that meets the criteria (such as the R-criteria) related to cell reselection, it is considered that the cell reselection to the SC-PTM cell has failed.

[0154] If the cell reselection by UE100 to the SC-PTM cell fails (step S2301: NO), UE100 determines that the SC-PTM reception has failed (step S2306). Then, in step S24, UE100 stores SC-PTM failure information regarding the failure of SC-PTM reception. The details of the operation in step S24 will be described later.

[0155] On the other hand, if the cell reselection by UE100 to the SC-PTM cell is successful (step S2301: YES), the operation proceeds to S2302.

[0156] In step S2302, UE100 determines its CE state using the above-described method for determining the coverage extension state. If UE100 is not in extended coverage (that is, if it is in normal coverage), step S2302 may not be performed.

[0157] In step S2303, UE100 attempts to receive SIB20. If UE100 is in extended coverage, it may attempt to receive SIB20 within the range of the set maximum number of repetitions (for example, the maximum number of repetitions of BCCH). If UE100 cannot receive SIB20 within the applied maximum number of repetitions (specifically, if the decoding of SIB20 fails), it may be determined that the reception of SIB20 has failed. If UE100 attempts to receive SIB20 within a certain period and cannot receive SIB20, it may be determined that the reception of SIB20 has failed.

[0158] If UE100 determines that reception of SIB20 has failed (step S2303: NO), it determines that SC-PTM reception has failed (step S2306).

[0159] On the other hand, if UE100 has successfully received SIB20 (step S2303: YES), it proceeds to step S2304.

[0160] In step S2304, UE100 attempts to receive SC-MCCH (SC-PTM configuration information). If UE100 is in extended coverage, it may attempt to receive SC-MCCH within the range of the set maximum number of repetitions (e.g., the number of repetitions of SC-MCCH). If UE100 cannot receive SC-MCCH within the applied maximum number of repetitions, it may determine that reception of SC-MCCH has failed. If UE100 attempts to receive SC-MCCH within a certain period and cannot receive it, it may determine that reception of SC-MCCH has failed.

[0161] If UE100 determines that reception of SC-MCCH has failed (step S2304: NO), it determines that SC-PTM reception has failed (step S2306).

[0162] On the other hand, if UE100 has successfully received SC-MCCH (step S2304: YES), it proceeds to step S2305.

[0163] In step S2305, UE100 attempts to receive SC-MTCH (MBMS data). If UE100 is in extended coverage, it may attempt to receive SC-MTCH within the range of the maximum number of repetitions (e.g., the number of repetitions of SC-MTCH). If UE100 cannot receive SC-MTCH within the applied number of repetitions, it may determine that reception of SC-MTCH has failed. If UE100 attempts to receive SC-MTCH within a certain period and cannot receive it, it may determine that reception of SC-MTCH has failed.

[0164] When the UE 100 determines that it has failed to receive the SC-MTCH (step S2305: NO), it determines that the SC-PTM reception has failed (step S2306).

[0165] On the other hand, when the UE 100 has successfully received the SC-MTCH (step S2305: YES), it determines that the SC-PTM reception has been successful (step S2307).

[0166] In step S24, when the UE 100 determines that the SC-PTM reception has failed, it stores SC-PTM failure information regarding the failure of the SC-PTM reception in a storage area for SC-PTM failure information. The storage area for SC-PTM failure information is provided in the memory included in the control unit 130. The SC-PTM failure information includes at least one of the following (a) to (k).

[0167] (a) Identification information of the SC-PTM cell The UE 100 stores the identification information of the SC-PTM cell at the time of failure of the SC-PTM in the SC-PTM failure information.

[0168] (b) MBMS service identification information The UE 100 stores the MBMS service identification information in the SC-PTM failure information. The MBMS service identification information is identification information regarding the MBMS service (the specific MBMS service described above) considered when the UE 100 has failed to receive the SC-PTM. The MBMS service identification information may include at least one of the TMGI, session ID, and G-RNTI.

[0169] (c) Radio environment information The UE 100 stores the radio environment information in the SC-PTM failure information. The radio environment information includes the measured values of the radio environment of the UE 100 when the SC-PTM reception has failed. The measured value may be the RSRP or the RSRQ.

[0170] (d) Extended state information When the UE 100 fails to receive the SC-PTM, it stores the extended state information indicating its own CE state in the SC-PTM failure information. The extended state information may indicate one of the CE level, CE mode, and RSRP range, or a combination of two or more of these.

[0171] (d) Information on the period during which the UE 100 attempted to receive the SC-PTM When the UE 100 is in extended coverage, the UE 100 stores the information on the period during which it attempted to receive the SC-PTM (hereinafter referred to as "period information") in the SC-PTM failure information. The period information includes at least one of the information on the period during which it attempted to receive SIB20, the information on the period during which it attempted to receive the SC-MCCH, and the information on the period during which it attempted to receive the SC-MTCH. The UE 100 may store the period information in association with the extended state information.

[0172] (f) Information on the number of repetitions applied to the reception of the SC-PTM When the UE 100 is in extended coverage, the UE 100 stores the information on the number of repetitions applied to the reception of the SC-PTM (hereinafter referred to as "repetition number information") in the SC-PTM failure information. The repetition number information is information on the number of repetitions applied in each of steps S2303, S2304, and S2305. The repetition number information includes at least one of the information on the number of repetitions applied to the reception of SIB20, the information on the number of repetitions applied to the reception of the SC-MCCH, and the information on the number of repetitions applied to the reception of the SC-MTCH. The UE 100 may store the repetition number information in association with the extended state information.

[0173] (h) Information on the reason (Cause) for the failure to receive the SC-PTM The UE 100 stores the Cause information on the failure to receive the SC-PTM (hereinafter referred to as "Cause information") in the SC-PTM failure information.

[0174] When the UE 100 determines that the SC-PTM reception has failed due to the failure to receive reselection to the SC-PTM cell, the UE 100 stores information indicating the reselection to the SC-PTM cell as Cause information.

[0175] When the UE 100 determines that the SC-PTM reception has failed due to the failure to receive SIB20, the UE 100 stores information indicating the reception failure of SIB20 as Cause information.

[0176] When the UE 100 determines that the SC-PTM reception has failed due to the failure to receive the SC-MCCH, the UE 100 stores information indicating the reception failure of the SC-MCCH as Cause information.

[0177] When the UE 100 determines that the SC-PTM reception has failed due to the failure to receive the SC-MTCH, the UE 100 stores information indicating the reception failure of the SC-MTCH as Cause information.

[0178] In addition to the information (a) to (k) described above, the SC-PTM failure information may include information related to existing MDT measurements such as location information and time stamps. The SC-PTM failure information may include information indicating the SC-PTM frequency.

[0179] Next, returning to FIG. 12, the operations after step S25 will be described. In step S25, the UE 100 transmits a notification message indicating that it has SC-PTM failure information to the gNB 200. The UE 100 may transmit the notification message when transitioning from the RRC idle state or the RRC inactive state to the RRC connected state, or during handover, etc. The notification message may indicate that the UE 100 has SC-PTM failure information for each MBMS service.

[0180] In step S26, the gNB 200 transmits a report request message to the UE 100 to request the UE 100 to transmit (report) an SC-PTM failure report including the SC-PTM failure information based on the notification message from the UE 100.

[0181] In step S27, the UE 100 transmits an SC-PTM failure report to the gNB 200 in response to a reporting request message. The reporting request message may specify information (e.g., the above-mentioned information (a) to (k)) to be included in the SC-PTM failure report. The reporting request message may request to include SC-PTM failure information corresponding to a predetermined frequency. The reporting request message may request to include SC-PTM failure information corresponding to a predetermined cell. The reporting request message may request to include SC-PTM failure information corresponding to a predetermined MBMS identifier (TMGI).

[0182] The UE 100 may transmit an SC-PTM failure report including only the information specified by the reporting request message. The SC-PTM failure report includes radio environment information and MBMS service identification information. The SC-PTM failure report includes extended state information.

[0183] (Summary of the Second Embodiment) As described above, when the UE 100 fails to receive an SC-PTM for which an MBMS service is provided, the UE 100 stores radio environment information regarding the radio environment of the UE 100 when the reception of the SC-PTM fails. The UE 100 transmits an SC-PTM failure report including the stored radio environment information to the network. The SC-PTM failure report further includes a service identifier indicating the MBMS service. Thereby, the network can grasp the reception status of the SC-PTM for a specific MBMS service and can appropriately set the SC-PTM settings (frequency, MCS, number of repetitions, etc.) for the specific MBMS service.

[0184] (Modification Example of the Second Embodiment) In this modification example, information to be stored (SC-PTM success information) when the reception of the SC-PTM is successful will be described.

[0185] As shown in FIG. 13, when the UE 100 determines that it has successfully received the SC-PTM (step S2307), in step S24, it stores the SC-PTM success information. The SC-PTM success information includes the above-described (a) identification information of the SC-PTM cell, (b) MBMS service identification information, and (c) extended status information.

[0186] When the UE 100 is in an extended coverage area, it may store the SC-PTM success information only when it has successfully received the SC-PTM to which repeated transmission is applied.

[0187] As described above, the SC-PTM to which repeated transmission is applied includes at least one of the SIB20 to which repeated transmission is applied, the SC-MCCH to which repeated transmission is applied, and the SC-MTCH to which repeated transmission is applied.

[0188] In addition, the UE 100 further includes in the SC-PTM success information and stores the number information indicating the number of times when the SC-PTM (SIB20, SC-MCCH, SC-MTCH, etc.) was successfully received.

[0189] The UE 100 transmits an SC-PTM success report including the identification information of the SC-PTM cell, the MBMS service identification information, the extended status information, and the number information corresponding to the MBMS service identification information to the network. Thereby, the network can grasp the number information of the SC-PTM for a specific MBMS service and can appropriately set the SC-PTM setting (number of repetitions, etc.) for the specific MBMS service. For example, when the number of repetitions of the SC-MTCH set by the network (the number of repeated transmissions of the SC-MTCH) is much larger than the number information of the SC-MTCH included in the SC-PTM success information (the number of reception attempts until the UE successfully receives the SC-MTCH), the network can set the number of repetitions of the SC-MTCH smaller and can effectively utilize the transmission resources of the SC-PTM.

[0190] (Other Embodiments) In the above-described embodiment, an example in which logged MDT is applied as MDT has been mainly described, but immediate MDT may also be applied.

[0191] Also, in the above-described embodiment, the 5G system (NR) has been mainly described, but the operations according to the embodiment may be applied to LTE.

[0192] A program may be provided that causes a computer to execute each process performed by UE100 or gNB200. The program may be recorded on a computer-readable medium. By using a computer-readable medium, it is possible to install the program in 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.

[0193] Also, circuits that execute each process performed by UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0194] As described above, one embodiment has been described in detail with reference to the drawings, but the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the gist.

[0195] This application claims the priority of U.S. Provisional Application No. 62 / 884,275 (filed on August 8, 2019), and all of its contents are incorporated herein by reference.

Claims

1. A communication control method, comprising: The method comprises the steps of: transmitting success information stored by the user equipment to a network when the user equipment successfully receives a predetermined service from a predetermined cell; The success information is An identifier of the given cell; and an identifier of the user equipment provided by the given cell; and information indicating the number of attempts to receive the predetermined service. Communications control method.

2. A communication control method, comprising: The network device receives, from the user equipment, success information stored when the user equipment successfully receives a predetermined service from a predetermined cell; The success information is An identifier of the given cell; and an identifier of the user equipment provided by the given cell; and information indicating the number of attempts to receive the predetermined service. Communications control method.

3. A network device, A receiving unit that receives, from the user equipment, success information stored when the user equipment successfully receives a predetermined service from a predetermined cell, The success information is An identifier of the given cell; and an identifier of the user equipment provided by the given cell; and information indicating the number of attempts to receive the predetermined service. Network device.

4. A user device, a transmitting unit that transmits stored success information when a predetermined service is successfully received from a predetermined cell; The success information is An identifier of the given cell; and an identifier of the user equipment provided by the given cell; and information indicating the number of attempts to receive the predetermined service. User equipment.

5. A chipset, A receiving unit that receives, from the user equipment, success information stored when the user equipment successfully receives a predetermined service from a predetermined cell, The success information is An identifier of the given cell; and an identifier of the user equipment provided by the given cell; and information indicating the number of attempts to receive the predetermined service. Chipset.

6. A chipset, a transmitting unit for transmitting success information stored when a predetermined service is successfully received from a predetermined cell to a network; The success information is An identifier of the given cell; and a user equipment identifier provided by the given cell; and information indicating the number of attempts to receive the predetermined service. Chipset.

7. A communication system including a network device and a user device, a transmitting unit that transmits the stored success information when the predetermined service is successfully received from the predetermined cell; A receiving unit that receives the success information, The success information is An identifier of the given cell; and an identifier of the user equipment provided by the given cell; and information indicating the number of attempts to receive the predetermined service. Communication systems.

8. A program for causing a computer to receive, from a user device, success information stored when the user device has successfully received a predetermined service from a predetermined cell, the program comprising: The success information is An identifier of the given cell; and an identifier of the user equipment provided by the given cell; and information indicating the number of attempts to receive the predetermined service. program.

9. A program for causing a computer to transmit success information stored when a predetermined service is successfully received from a predetermined cell, The success information is An identifier of the given cell; and a user equipment identifier provided by the given cell; and information indicating the number of attempts to receive the predetermined service. program.

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