Network device and communication control method

Abstract

To provide a network device and a communication control method that apply an MDT (Minimization of Drive Tests) function to a user device to which a coverage extension function is applied.SOLUTION: A communication control method is used in a mobile communication system and executed by a user device. The communication control method includes transmitting, to a network, a failure report related to a failure in a procedure related to RRC connection executed by the user device when the user device exists in enhanced coverage of a serving cell. The failure report includes enhancement state information indicating a coverage enhancement state of the user device in the enhanced coverage, and failure count information associated with the enhancement state information. The failure count information indicates the number of times the user device fails in the procedure in the coverage enhancement state.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present disclosure relates to a network device and a communication control method for use in a mobile communication system. [Background technology]

[0002] The Third Generation Partnership Project (3GPP) (registered trademark; the same applies below), a standardization project for cellular communication systems, has specified the MDT (Minimization of Drive Tests) function. The MDT function is a function that enables a user device to measure a radio environment and report the measurement information of the radio environment together with the location information of the user device to a network, thereby enabling detection of, for example, coverage holes and optimizing the network.

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

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

[0005] A communication control method according to an embodiment is a method executed by a user equipment. The communication control method includes transmitting a failure report to a network regarding a failure of a procedure related to an RRC connection executed by the user equipment when the user equipment is 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 fails the procedure in the coverage extension state.

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

[0007] A communication control method according to an embodiment is a method executed by a user equipment. The communication control method includes: when failing to receive an SC-PTM for providing an MBMS service, storing radio environment information related to a radio environment of the user equipment when the reception of the SC-PTM fails; and transmitting a failure report including the stored radio environment information to a network. The failure report further includes a service identifier indicating the MBMS service. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing a configuration of a mobile communication system according to an embodiment; [Diagram 2] FIG. 2 is a diagram illustrating a configuration of a user device according to an embodiment. [Diagram 3] FIG. 2 is a diagram illustrating a configuration of a base station according to an embodiment. [Figure 4]A diagram showing the configuration of a protocol stack of a user plane radio interface according to one embodiment. [Diagram 5] FIG. 2 is a diagram illustrating a configuration of a protocol stack of a radio interface of a control plane according to an embodiment. [Figure 6A] A diagram showing mapping between downlink logical channels and transport channels of a mobile communication system according to one embodiment. [Figure 6B] A diagram showing mapping between transport channels and physical channels in a mobile communication system according to one embodiment. [Figure 7] A diagram showing frequency channels handled by eMTC UE and NB-IoT UE. [Figure 8] FIG. 2 is a diagram illustrating an example of a coverage extension state in a mobile communication system according to an embodiment. [Figure 9] FIG. 11 is a diagram illustrating an example of an operation of receiving an SC-PTM. [Figure 10] FIG. 2 is a diagram showing an operation flow in the mobile communication system according to the first embodiment. [Figure 11] FIG. 11 is a diagram showing details of a part of the operational flow of FIG. [Figure 12] FIG. 11 is a diagram showing an operation flow in the mobile communication system according to the second embodiment. [Figure 13] FIG. 13 is a diagram showing details of a part of the operational flow of FIG. 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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, a 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 applied at least partially to the mobile communication system.

[0011] FIG. 1 is a diagram showing a 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 mobile 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 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).

[0014] The NG-RAN 10 includes a base station (called "gNB" in the 5G system) 200. The gNB 200 is sometimes called an NG-RAN node. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. 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.

[0015] In addition, the gNB may be connected to an EPC (Evolved Packet Core), which is a core network of LTE, and the LTE base station may be connected to 5GC. In addition, the LTE base station and the gNB may be connected via an inter-base station interface.

[0016] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various mobility controls for the UE 100. The AMF manages information on the area in which the UE 100 is located by communicating with the UE 100 using Non-Access Stratum (NAS) 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.

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

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

[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 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 transmission unit 120 performs various transmissions under the control of the control unit 130. The transmission 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 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 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 processing.

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

[0023] Figure 3 is a diagram showing the configuration of gNB200 (base station).

[0024] As shown in FIG. 3, the gNB 200 includes a transmitter 210, a receiver 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 a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

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

[0027] The control unit 230 performs various controls 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 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 processing.

[0028] The backhaul communication unit 240 is connected to adjacent base stations via an inter-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 may be configured (i.e., functionally divided) with a CU (Central Unit) and a DU (Distributed Unit), and both units may be connected with 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 user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

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

[0032] The MAC layer performs data priority control, retransmission processing using hybrid ARQ (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 assigned to the UE 100.

[0033] The RLC layer transmits data to the RLC layer on the receiving side by using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via a logical channel.

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

[0035] The SDAP layer maps IP flows, which are the units for QoS control by the core network, to radio bearers, which are the units for QoS control by the AS (Access Stratum). Note that if the RAN is connected to the EPC, the SDAP is not necessary.

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

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

[0038] Between the RRC layer of the UE 100 and the RRC layer of the gNB 200, RRC signaling for various settings is transmitted. The RRC layer controls logical channels, transport channels, and physical channels in response to establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200, the UE 100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200, the UE 100 is in an RRC idle state. Also, when the RRC connection is suspended, the UE 100 is in an RRC inactive state.

[0039] The NAS layer, which is 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 300.

[0040] In addition, the UE 100 has an application layer and the like in addition to the protocol of the radio interface.

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

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

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

[0044] The Common Control Channel (CCCH) 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] A Dedicated Control Channel (DCCH) is a logical channel for transmitting dedicated 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] A Dedicated Traffic Channel (DTCH) is a dedicated logical channel for data transmission. The DTCH is mapped to the DL-SCH.

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

[0048] The Single Cell Multicast Control Channel (SC-MCCH) is a logical channel for the SC-PTM. The SC-MCCH is a point-to-multipoint downlink channel for multicasting MBMS control information for one or more SC-MTCHs from a network to the UE 100. The SC-MCCH is used by the UE 100 that receives or is interested in receiving the MBMS using the SC-PTM. Only one SC-MCCH exists in one cell.

[0049] The MCCH (Multicast Control Channel) is a logical channel for the MBSFN. The MCCH is used for transmitting MBMS control information for the MTCH from the network to the UE 100. The MCCH is mapped to the MCH (Multicast Channel), which is a transport channel.

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

[0051] FIG. 6B shows the mapping between the transport channel (Downlink Transport Channel) and the physical channel (Downlink Physical Channel).

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

[0053] The MCH is mapped to a Physical Multicast Channel (PMCH), which supports MBSFN with multiple cells.

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

[0055] A physical downlink control channel (PDCCH) carries resource allocation information for a PDSCH (DL-SCH, PCH), HARQ information related to the DL-SCH, etc. In addition, the PDCCH carries an uplink scheduling grant.

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

[0057] In the MDT, the gNB 200 transmits a configuration message for configuring MDT measurement to the UE 100. Then, the gNB 200 collects MDT measurement information from the UE 100. For example, the gNB 200 is directly or indirectly connected to a server for MDT. The server for MDT obtains the MDT measurement information from the gNB 200, 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] In logged MDT, a UE 100 in an RRC idle state, an RRC inactive state, or an RRC connected state performs radio measurements, records the measurement results together with UE location information and a timestamp, and transmits a report including the recorded measurement results, etc., upon request from the network (gNB 200).

[0060] In the immediate MDT, the UE 100 in the RRC connected state performs radio measurements and measurements of other items, and transmits a report including the measurement results and UE location information to the network (gNB 200). The configuration message for configuring the immediate MDT may be a measurement configuration message including an information element requesting that the UE location information be included in the measurement report.

[0061] In the MDT, the UE 100 stores each piece of failure information described below, and transmits a failure report including the failure information.

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

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

[0064] Category M1 limits the transmission and reception bandwidth of UE 100 (eMTC UE) to, for example, 1.08 MHz (i.e., a bandwidth of six resource blocks). Category NB-IoT (category NB1) further limits the transmission and reception bandwidth of UE 100 (NB-IoT UE) to 180 kHz (i.e., a bandwidth of one resource block). Such narrowbanding realizes the low cost and low power consumption required for eMTC UE and NB-IoT UE.

[0065] FIG. 7 is a diagram showing frequency channels handled by eMTC UE and NB-IoT UE.

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

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

[0068] The UE 100 of category M1 cannot receive a downlink radio signal transmitted with a bandwidth wider than six resource blocks, and therefore cannot receive a 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 a mode in which it operates within the LTE transmission / reception bandwidth, a mode in which it operates in a guard band outside the LTE transmission / reception bandwidth, and a mode in which it operates within a frequency band dedicated to NB-IoT.

[0070] In order to realize coverage extension, eMTC UE and NB-IoT UE support an Enhanced Coverage (EC) function using repeated transmission, etc. The enhanced coverage is also called Coverage Enhancement (CE).

[0071] The coverage extension function may include repetition, which transmits the same signal repeatedly using multiple subframes. The more repetitions, the more coverage can be extended.

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

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

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

[0075] (How to determine coverage expansion status) 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 "CE state") may include a coverage extension level (hereinafter referred to as "CE level") and a coverage extension mode (hereinafter referred to as "CE mode").

[0077] As shown in Figure 8, the CE mode includes at least CE mode A and CE mode B. CE mode B is a state in which the coverage is further extended than CE mode A. CE mode B supports a larger number of repeated transmissions than CE mode A. A UE that supports the coverage extension function (e.g., eMTC UE) supports at least CE mode A.

[0078] The CE levels include at least four levels, level 0 to level 3. The CE modes may be associated with the CE levels. 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 modes may not be associated with the CE levels.

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

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

[0081] UE 100 measures RSRP (Reference Signal Received Power) and compares the measured RSRP with an 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 system information broadcast by a serving cell of UE 100.

[0082] The UE 100 may determine its own CE level when performing a random access procedure. When performing a random access procedure for a serving cell, the UE 100 transmits an RA preamble to the serving cell using a PRACH (Physical Random Access Channel) resource (frequency resource, time resource, preamble, etc.) corresponding to the UE 100's own CE level. The correspondence between the CE level and the PRACH resource may be set by system information. When the UE 100 cannot receive an RA (Random Access) response from the serving cell within a predetermined time, the UE 100 may transmit an RA preamble again. When the UE 100 cannot receive an RA response even if the number of times of transmission of the RA preamble reaches a predetermined number, the UE 100 may determine its own CE level as the next level. For example, when the UE 100 cannot receive an RA response even if the number of times of transmission of the RA preamble transmitted using the PRACH resource corresponding to CE level 0 reaches a predetermined number, the UE 100 determines its own CE level as CE level 1. Such a predetermined number may be set by system information. The UE 100 may then transmit an RA preamble to the serving cell using a PRACH resource corresponding to CE level 1.

[0083] The UE 100 may determine, as its own CE level, a CE level corresponding to the PRACH resource used when transmitting the RA preamble corresponding to the successfully received RA response.

[0084] The UE 100 may determine its own CE mode based on the correspondence between the CE mode and the CE level. In the example of FIG. 8, when the UE 100's CE level is level 0 or 1, the UE 100 determines its own CE mode as CE mode A, and when the UE 100's CE level is level 2 or 3, the UE 100 determines its own CE mode as CE mode B. The UE 100 may determine its own CE mode based on other criteria. For example, when the UE 100 determines that the UE 100 is in the extended coverage in response to the second cell selection criterion for CE mode A being satisfied, the UE 100 may determine its own CE mode as CE mode A.

[0085] When the UE 100 is in an RRC connected state, the UE 100 may be configured to the CE mode from a serving cell. The CE mode may be configured from the serving cell by dedicated RRC signaling.

[0086] When the UE 100 receives the RRC signaling indicating the CE mode A, the UE 100 determines its own CE mode to be the CE mode A. When the UE 100 receives the RRC signaling indicating the CE mode B, the UE 100 determines its own CE mode to be the CE mode B.

[0087] The CE state may be indicated by one of a plurality of reception power ranges (RSRP ranges). The plurality of RSRP ranges may be set by system information broadcast by the serving cell of the UE 100. The UE 100 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 the RSRP range #1, the UE 100 determines its own CE state to be the RSRP range #1.

[0088] When performing uplink (UL) communication, the UE 100 applies UL parameters according to its own CE state. The UL parameters may be set in the UE 100 by RRC signaling. The UL parameters may be set in the UE 100 by system information. The UL parameters include a UL repetition number, a transmission power, and the like. The UL repetition number may include a number of repetitions to be applied to the UL transmission. The UL repetition number may include a maximum number of repetitions to be applied to the UL transmission. The UL repetition number may be set for each UL channel. For example, the UL repetition number may include a number of repetitions of a PUCCH (Physical Uplink Control Channel), a number of repetitions of a PUSCH (Physical Uplink Shared Channel), and a number of repetitions of a PRACH. The above-mentioned predetermined number for the number of transmissions of the RA preamble may be a maximum number of repetitions of a PRACH.

[0089] When performing downlink (DL) communication, the UE 100 applies DL parameters according to its own CE state. The DL parameters may be set in the UE 100 by RRC signaling. The DL parameters may be set in the UE 100 by system information. The DL parameters include a DL repetition count, etc. The DL repetition count may include a number of repetitions to be applied to DL transmission. The DL repetition count may include a 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 a number of repetitions of PDCCH, a number of repetitions of PDSCH, etc.

[0090] (Overview of SC-PTM) Next, an overview of SC-PTM will be described. 3GPP specifies MBMS (Multimedia Broadcast Multicast Service) transmission that provides multicast / broadcast services to user devices. There are two MBMS methods: MBSFN (Multicast Broadcast Single Frequency Network) and SC-PTM (Single Cell Point-To-Multipoint). In MBSFN, data is transmitted via PMCH (Physical Multicast Channel) for each MBSFN area consisting of multiple cells. In contrast, in SC-PTM, data is transmitted via PDSCH for each cell.

[0091] The UE 100 may receive the MBMS service in an RRC connected state, or in an RRC idle state or an RRC inactive state.

[0092] Fig. 9 is a diagram showing an example of an operation of receiving SC-PTM. As shown in Fig. 9, in step S1, UE 100 acquires USD (User Service Description) from 5GC 20 via gNB 200. The USD provides basic information of each MBMS service. For each MBMS service, USD includes TMGI for identifying the MBMS service, a frequency on which the MBMS service is provided, and the start and end times of providing the MBMS service.

[0093] In step S2, UE 100 receives SIB20 from gNB 200 via BCCH (Broadcast Control Channel). SIB20 includes information (scheduling information) required for acquiring SC-MCCH. SIB20 includes sc-mcch-ModificationPeriod indicating a period during which the contents of SC-MCCH may be changed, sc-mcch-RepetitionPeriod indicating the transmission (retransmission) period of SC-MCCH by the number of radio frames, sc-mcch-Offset indicating the offset of the radio frame in which SC-MCCH is scheduled, and sc-mcch-Subframe indicating the subframe in which SC-MCCH is scheduled.

[0094] In step S3, the UE 100 receives MBMS control information from the gNB 200 via the SC-MCCH based on the SIB 20. The MBMS control information may be referred to as SC-PTM configuration information. A single cell RNTI (SC-RNTI) is used for transmitting the SC-MCCH in the physical layer. The SC-PTM configuration information includes control information applicable to an MBMS service transmitted via a single cell MBMS point to multipoint radio bearer (SC-MRB). The SC-PTM configuration information includes sc-mtch-InfoList including the configuration of each SC-MTCH in the cell transmitting the information, and scptmNeighbourCellList which is a list of neighboring cells providing the MBMS service via the SC-MRB. The sc-mtch-InfoList includes one or more SC-MTCH-Info. Each SC-MTCH-Info includes information on an ongoing MBMS session (mbmsSessionInfo) transmitted via the SC-MRB, a G-RNTI (Group RNTI) corresponding to the MBMS session, and sc-mtch-schedulingInfo, which is DRX information for the SC-MTCH. The mbmsSessionInfo includes a TMGI for identifying an MBMS service and a session ID (sessionId). The G-RNTI is an RNTI for identifying 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 an onDurationTimerSCPTM, a drx-InactivityTimerSCPTM, and a schedulingPeriodStartOffsetSCPTM. The schedulingPeriodStartOffsetSCPTM includes an SC-MTCH-SchedulingCycle and an SC-MTCH-SchedulingOffset.

[0095] In step S4, the UE 100 receives an MBMS service (MBMS data) corresponding to the TMGI that the UE 100 is interested in via the SC-MTCH based on the SC-MTCH-SchedulingInfo in the SC-PTM configuration information. In the physical layer, the gNB 200 transmits the PDCCH using the G-RNTI, and then transmits the MBMS data via the PDSCH.

[0096] When performing SC-PTM reception, the UE 100 may attempt reception by applying the repetition count (e.g., the BCCH repetition count, the SC-MCCH repetition count, the SC-MTCH repetition count, etc.) corresponding to each of the above-mentioned channels (BCCH, SC-MCCH, SC-MTCH, etc. that carry the SIB 20). The BCCH repetition count, the SC-MCCH repetition count, and the SC-MTCH repetition count may be set for each CE state.

[0097] (First embodiment) Next, an 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, the operation is performed by a UE 100 which is, for example, an eMTC UE or an NB-IoT UE.

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

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

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

[0101] In addition, the UE 100 may fail a procedure related to the RRC connection multiple times in the RRC idle state or the RRC inactive state. In this case, the UE 100 executes the processes of steps S13 and S14 multiple times and stores connection failure information related to the multiple failures (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 own CE state using the above-mentioned coverage extension state determination method. For example, UE 100 may determine its own CE level according to the measured RSRP. UE 100 may determine, as its own CE level, the CE level corresponding to the PRACH resource used when transmitting the RA preamble corresponding to the successfully received RA response. Note that, if UE 100 is not in the extended coverage (i.e., in the normal coverage), step S1301 may not be performed.

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

[0105] In step S1303, the UE 100 starts a timer in response to the transmission of an RRC request message. The timer value may be set by system information broadcast from the serving cell. The timer value may differ depending on the type of "procedure related to RRC connection" (RRC connection establishment, RRC connection resume, etc.). The timer value may differ depending on 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, the UE 100 may start a timer in response to the first transmission in the repeated transmission. The UE 100 may also start a 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 in the UE 100, the UE 100 may regard the transmission performed immediately before the maximum number of repeated transmissions is reached as the last transmission.

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

[0107] If the timer expires (step S1305: YES), the UE 100 proceeds to operation at step S14. Here, if the RRC response message is not received before the timer expires, the UE 100 assumes that the procedure regarding the RRC connection has failed, and stores failure information regarding the failure of the procedure regarding the RRC connection.

[0108] On the other hand, if the RRC response message is received before the timer expires (step S1304: YES), in step S1306, the UE 100 stops the timer, and the operation proceeds to step S1307.

[0109] In step S1307, the UE 100 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, the UE 100 succeeds in the procedure regarding the RRC connection.

[0110] On the other hand, if the RRC response message is not a positive response (step S1307: NO), the UE 100 may start the procedure related to the RRC connection again. The UE 100 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, the UE 100 stores connection failure information related to a failure of a procedure related to the RRC connection in a storage area for connection failure information. The storage area for connection failure information is provided in, for example, a memory included in the control unit 130. The connection failure information includes at least one of the following pieces of information (a) to (d).

[0112] (a) Extended State Information The UE 100 includes in the connection failure information the extended state information indicating its own CE state (the CE state determined in step S1301) when the procedure related to the RRC connection fails, and stores the information. The extended state information may indicate one of the CE level, the CE mode, and the RSRP range, or may indicate a combination of two or more of these. For example, the extended state information indicates the CE mode A and the CE level 0. The extended state information may indicate the RSRP range #1.

[0113] (b) Number of failures UE 100 stores failure count information indicating the number of times a procedure related to RRC connection has failed (hereinafter referred to as "failure count") in the connection failure information. Specifically, UE 100 holds a counter that counts the number of failures, and stores the value of the counter as failure count information. For example, UE 100 increments the counter value by 1 in response to expiration of a timer corresponding to the transmitted RRC request message (step S1305: YES), and updates the failure count information.

[0114] The UE 100 may store failure count information associated with the extended state information. That is, the UE 100 counts the failure count for each CE state. Specifically, the UE 100 holds the above-mentioned counter for each CE state, and counts the number of times that the procedure related to the RRC connection executed by the UE 100 in the same CE state has failed. For example, the UE 100 holds a counter (counter_CE0) corresponding to CE level 0, and increments the counter_CE0 by 1 when the timer corresponding to the RRC request message transmitted when the UE 100's CE level is 0 (the CE level is determined to be CE level 0 in step S1301) expires (step S1305: YES).

[0115] Although the UE 100 basically counts the number of failures for each serving cell, it may count the total number of failures of procedures related to RRC connection executed within a predetermined time (for example, 48 hours) regardless of the serving cell. In this case, the UE 100 may hold a counter_Total corresponding to the total number of failures.

[0116] (c) Failed cell identification information The UE 100 includes the cell identifier of the serving cell in which the procedure regarding the RRC connection has failed as failed cell identification information in the connection failure information and stores the same. The cell identifier may be an Evolved Cell Global Identifier (ECGI).

[0117] (d) Measurements of the wireless environment The UE 100 includes the measurement value of the radio environment of the UE 100 in the connection failure information when the procedure related to the RRC connection fails, and stores the measurement value. The measurement value may be RSRP or RSRQ (Reference Signal Received Quality). The UE 100 may include the measurement value in the connection failure information and store the measurement value only when the UE 100 is in the extended coverage.

[0118] The UE 100 measures the radio environment every time a procedure related to an RRC connection fails, and stores the measurement value.

[0119] When a procedure related to the RRC connection fails multiple times, the UE 100 may calculate one statistical value from the multiple measurement values ​​stored in the connection failure information. When the number of failures in the procedure related to the RRC connection (for example, the number of failures indicated by the failure count information) reaches a threshold, the UE 100 may start calculating the statistical value. The threshold may be set by the gNB 200. For example, the threshold may be set by the gNB 200 by an MDT measurement configuration message described later. The UE 100 may store the measurement value for each CE state.

[0120] The UE 100 may calculate an average value as a statistical value based on a plurality of measurement values ​​measured multiple times and the number of times the procedure related to the RRC connection has failed. The UE 100 may take the maximum value of the plurality of measurement values ​​as a statistical value. The UE 100 may take the minimum value of the plurality of measurement values ​​as a statistical value.

[0121] When the UE 100 calculates one statistical value from the stored measurement values, the UE 100 may store the one statistical value as a measurement value of the radio environment instead of the measurement values, thereby reducing the size of the storage area occupied by the storage of the measurement values.

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

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

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

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

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

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

[0128] In step S17, UE 100 transmits a connection failure report to gNB 200 in response to the report request message. The report request message may specify information to be included in the connection failure report (for example, the above-mentioned information (a) to (d)). UE 100 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 wireless environment.

[0129] When UE 100 stores connection failure information across a plurality of cells, UE 100 may transmit a connection failure report including connection failure information for each cell.

[0130] (Summary of the first embodiment) As described above, UE 100 transmits a failure report to the network regarding a failure of a procedure related to an RRC connection executed by UE 100 when UE 100 is in the extended coverage of a serving cell. The failure report includes extended state information indicating the CE state of UE 100 in the extended coverage and failure count information associated with the extended state information. The failure count information indicates the number of times that UE 100 fails in the procedure in the CE state. This allows the network to 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] (Modification 1 of the first embodiment) In the first embodiment, it is assumed that the UE 100 is in an RRC idle state or an RRC inactive state, but in the first modification of the first embodiment, it is assumed that the UE 100 is in an RRC connected state.

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

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

[0134] (Modification 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, but the connection failure information may include information in an area unit larger than a cell. Examples of such a larger area unit include a RAN Notification Area (RNA) which is an area unit in which paging is performed by RAN activation, an MBSFN area which is an area unit in which MBMS is provided, and a tracking area which is an area unit in which paging is performed by AMF activation. In the following, a description will be given taking a RAN notification area as an example of such a larger 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 configured by one or more cells. The RAN notification area may be set to the UE 100 by an RRC Release message in which the gNB 200 transitions the UE 100 to an RRC inactive state.

[0137] The UE 100 in the RRC inactive state does not need to notify (report) the cell reselection to the network 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 the UE 100.

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

[0140] The UE 100 may store information such as failure count information (such as the above-mentioned extended state information and radio environment measurement values) in association with the RAN notification area information. For example, the UE 100 counts the number of failures for each RAN notification area. Specifically, the UE 100 holds a counter corresponding to the RAN notification area, and counts the number of failures in the RRC connection resume procedure executed in the same RAN notification area.

[0141] The UE 100 transmits a failure report including the RAN notification area information and information such as failure count information associated with the RAN notification area information (such as the above-mentioned extended state information and the measured value of the radio environment). Therefore, the network can grasp the accessibility of each RAN notification area and set a more appropriate RAN notification area to the UE 100.

[0142] The UE 100 may store information in a unit smaller than a cell in the connection failure information. Such a unit may be a beam in a cell. One cell may include multiple beams. Each beam broadcasts a beam identifier of its own beam.

[0143] UE 100 may store information such as failure count information (extended state information, measurement values ​​of the wireless environment, etc.) in association with a beam identifier that identifies a beam.

[0144] The UE 100 transmits a failure report including a beam identifier and information such as failure count information associated with the beam identifier (extended state information, radio environment measurement values, etc.) to the network. This allows the network to grasp the accessibility of each beam and perform detailed optimization for each beam.

[0145] Second embodiment Next, a description will be given of the operation of the mobile communication system according to the second embodiment. Fig. 12 is a diagram showing an operation flow in the mobile communication system according to the second embodiment.

[0146] The second embodiment relates to collecting data on the reception status of SC-PTM using the MDT function.

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

[0148] In step S22, after UE100 terminates communication with gNB200, it transitions from the RRC connected state to the RRC idle state or the RRC inactive state, and starts the operation of the logged MDT in accordance with the MDT configuration parameters.

[0149] Alternatively, the UE 100 may perform a logged MDT operation in accordance with the MDT configuration parameters in the RRC connected state.

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

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

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

[0153] In step S2301, UE 100 attempts cell reselection to a cell (SC-PTM cell) of a frequency (SC-PTM frequency) that provides a specific MBMS service by SC-PTM. Cell reselection is performed according to a cell reselection procedure defined in 3GPP. If UE 100 cannot find an SC-PTM cell that satisfies criteria for cell reselection (R-criteria, etc.), UE 100 considers that cell reselection to the SC-PTM cell has failed.

[0154] If the cell reselection to the SC-PTM cell fails (step S2301: NO), the UE 100 determines that the SC-PTM reception has failed (step S2306). Then, in step S24, the UE 100 stores SC-PTM failure information regarding the failure of the SC-PTM reception. The operation of step S24 will be described in detail later.

[0155] On the other hand, if the cell reselection to the SC-PTM cell is successful (step S2301: YES), the UE 100 proceeds to operation S2302.

[0156] In step S2302, the UE 100 determines its own CE state using the above-mentioned method for determining the coverage extension state. Note that, if the UE 100 is not in the extended coverage (that is, if the UE 100 is in the normal coverage), step S2302 does not need to be performed.

[0157] In step S2303, UE 100 attempts to receive SIB20. When UE 100 is in extended coverage, UE 100 may attempt to receive SIB20 within a set maximum number of repetitions (for example, the maximum number of BCCH repetitions). When UE 100 cannot receive SIB20 within the applied maximum number of repetitions (specifically, when SIB20 has failed to be decoded), UE 100 may determine that reception of SIB20 has failed. When UE 100 attempts to receive SIB20 within a certain period of time and cannot receive SIB20, UE 100 may determine that reception of SIB20 has failed.

[0158] When it is determined that reception of SIB20 has failed (step S2303: NO), UE 100 determines that reception of SC-PTM has failed (step S2306).

[0159] On the other hand, if the UE 100 has successfully received the SIB 20 (step S2303: YES), the UE 100 proceeds to step S2304.

[0160] In step S2304, UE 100 attempts to receive SC-MCCH (SC-PTM setting information). When UE 100 is in extended coverage, UE 100 may attempt to receive SC-MCCH within a set maximum number of repetitions (for example, the number of repetitions of SC-MCCH). When UE 100 cannot receive SC-MCCH within the applied maximum number of repetitions, UE 100 may determine that reception of SC-MCCH has failed. When UE 100 attempts to receive SC-MCCH within a certain period and cannot receive SC-MCCH, UE 100 may determine that reception of SC-MCCH has failed.

[0161] If UE 100 determines that reception of the SC-MCCH has failed (step S2304: NO), UE 100 determines that reception of the SC-PTM has failed (step S2306).

[0162] On the other hand, if UE 100 has successfully received the SC-MCCH (step S2304: YES), the operation proceeds to step S2305.

[0163] In step S2305, UE 100 attempts to receive SC-MTCH (MBMS data). When UE 100 is in extended coverage, UE 100 may attempt to receive SC-MTCH within a maximum number of repetitions (for example, the number of repetitions of SC-MTCH). When UE 100 cannot receive SC-MTCH within the applied number of repetitions, UE 100 may determine that reception of SC-MTCH has failed. When UE 100 attempts to receive SC-MTCH within a certain period and cannot receive SC-MTCH, UE 100 may determine that reception of SC-MTCH has failed.

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

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

[0166] In step S24, when 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 a memory included in control unit 130. The SC-PTM failure information includes at least one of the following pieces of information (a) to (g).

[0167] (A) SC-PTM cell identification information UE 100 stores the identification information of the SC-PTM cell when SC-PTM fails, by including it in SC-PTM failure information.

[0168] (a) MBMS service identification information The UE 100 includes the MBMS service identification information in the SC-PTM failure information and stores it. The MBMS service identification information is identification information related to the MBMS service (the above-mentioned specific MBMS service) considered when the UE 100 fails to receive the SC-PTM. The MBMS service identification information may include at least one of the TMGI, the session ID, and the 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 a measurement value of the radio environment of the UE 100 when the SC-PTM reception fails. The measurement value may be RSRP or RSRQ.

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

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

[0172] (F) Information on the number of repetitions applied to receiving SC-PTM When UE 100 is in the extended coverage, UE 100 stores information on the number of repetitions applied to SC-PTM reception (hereinafter referred to as "repetition number information") in 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 information on the number of repetitions applied to SIB20 reception, information on the number of repetitions applied to SC-MCCH reception, and information on the number of repetitions applied to SC-MTCH reception. UE 100 may store the repetition number information in association with extended state information.

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

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

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

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

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

[0178] The SC-PTM failure information may include, in addition to the above-mentioned information (A) to (G), information regarding existing MDT measurements such as location information, timestamp, etc. The SC-PTM failure information may include information indicating the SC-PTM frequency.

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

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

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

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

[0183] (Summary of the second embodiment) As described above, when UE 100 fails to receive SC-PTM in which an MBMS service is provided, UE 100 stores radio environment information related to the radio environment of UE 100 at the time when the reception of SC-PTM fails. 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. This allows the network to grasp the reception status of SC-PTM for a specific MBMS service and to appropriately set the SC-PTM settings (frequency, MCS, number of repetitions, etc.) for the specific MBMS service.

[0184] (Modification of the second embodiment) In this modified example, the information (SC-PTM success information) that is saved when the SC-PTM is successfully received will be described.

[0185] 13, when UE 100 determines that it has successfully received the SC-PTM (step S2307), it stores the SC-PTM success information in step S24. The SC-PTM success information includes the above-mentioned (A) SC-PTM cell identification information, (B) MBMS service identification information, and (D) extended state information.

[0186] UE 100 may store SC-PTM success information only when UE 100 successfully receives SC-PTM to which repeated transmission is applied when UE 100 is in extended coverage.

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

[0188] Furthermore, UE 100 further includes in the SC-PTM success information information the number of times that an SC-PTM (SIB20, SC-MCCH, SC-MTCH, etc.) was transmitted before it was successfully received, and stores the information.

[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 state information, and the number information corresponding to the MBMS service identification information to the network. This allows the network to grasp the number information of SC-PTM for a specific MBMS service, and to appropriately set the SC-PTM setting (repetition number, etc.) for the specific MBMS service. For example, if the number of repetitions of SC-MTCH set by the network (number of repeated transmissions of SC-MTCH) is much larger than the number information of SC-MTCH included in the SC-PTM success information (number of receptions attempted by the UE until it successfully receives SC-MTCH), the network can set the number of repetitions of SC-MTCH to be small, and the transmission resources of SC-PTM can be effectively utilized.

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

[0191] In addition, in the above-described embodiment, the 5G system (NR) has been mainly described, but the operation 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 the UE 100 or the gNB 200. The program may be recorded in a computer-readable medium. Using the computer-readable medium, it is possible to install the program in the computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0193] In addition, 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 (chip set, SoC).

[0194] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes, etc. are possible without departing from the spirit and scope of the present invention.

[0195] This application claims priority to U.S. Provisional Application No. 62 / 884,275, filed August 8, 2019, the entire contents of which are incorporated herein by reference.

Claims

1. A network device, A receiving unit that receives, from the user equipment, a failure report including a measurement value of a radio environment of the user equipment stored when a timer started in response to a start of a procedure related to an RRC connection executed by the user equipment expires, the failure report includes beam identifiers of a plurality of beams belonging to a cell that failed the procedure and the measurement values ​​associated with the beams identified by the beam identifiers; The receiving unit 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 made until the predetermined service was successfully received. Network device.

2. A communication control method executed by a network device, comprising: receiving a failure report from the user equipment, the failure report including measurements of a radio environment of the user equipment stored upon expiration of a timer started in response to initiation of an RRC connection procedure performed by the user equipment; receiving, from the user equipment, success information stored when the user equipment successfully receives a predetermined service from a predetermined cell; Including, the failure report includes beam identifiers of a plurality of beams belonging to a cell that failed the procedure and the measurement values ​​associated with the beams identified by the beam identifiers; 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 made until the predetermined service was successfully received. Communications control method.

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