Communication system, base station and communication terminal

Abstract

To improve communication performance of a communication terminal when supporting various services.SOLUTION: The communication terminal includes a narrow-band terminal that performs radio communication in a band narrower than the system band available in the cell. The terminal for narrow band recognizes the cell reselection process parameter by a predetermined method. The predetermined technique includes at least one of acquisition of a parameter predetermined in a standard as the cell reselection process parameter, reception of a MasterInformationBlock (MIB) including the cell reselection process parameter, reception of SystemInformation (SI) for a terminal for a narrow band including the cell reselection process parameter, reception of RadioResourceControl (RRC) signaling including the cell reselection process parameter, and acquisition of an indication indicating one of a plurality of candidates predetermined in the standard as the cell reselection process parameter.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to wireless communication technology. [Background technology]

[0002] 3GPP (3rd Generation Partnership Project), a standardization organization for mobile communication systems, is considering a communication method called Long Term Evolution (LTE) for the wireless section and System Architecture Evolution (SAE) for the overall system configuration including the core network and radio access network (hereinafter collectively referred to as the network) (see, for example, Non-Patent Documents 1 to 16). This communication method is also called the 3.9G (3.9 Generation) system.

[0003] LTE uses OFDM (Orthogonal Frequency Division Multiplexing) for downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) for uplink as its access method. Unlike W-CDMA (Wideband Code Division Multiple Access), LTE does not include circuit switching and is only a packet communication method.

[0004] The decisions made by 3GPP regarding the frame configuration in the LTE system, as described in Non-Patent Document 1 (Chapter 5), will be explained using Figure 1. Figure 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. In Figure 1, one radio frame is 10 ms. The radio frame is divided into 10 equally sized subframes. The subframe is divided into two equally sized slots. The first and sixth subframes of each radio frame include a downlink synchronization signal. The synchronization signals include a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

[0005] The decisions made by 3GPP regarding the channel configuration in the LTE system are described in Non-Patent Document 1 (Chapter 5). It is assumed that the same channel configuration as that of a non-CSG cell is used in a CSG (Closed Subscriber Group) cell.

[0006] The Physical Broadcast Channel (PBCH) is a channel for downlink transmission from a base station to a mobile terminal. A BCH transport block is mapped to four subframes within a 40 ms interval. There is no explicit signaling of the 40 ms timing.

[0007] The Physical Control Format Indicator Channel (PCFICH) is a channel for downlink transmission from a base station to a mobile terminal. The PCFICH informs the mobile terminal of the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols used for PDCCHs. The PCFICH is transmitted every subframe.

[0008] The Physical Downlink Control Channel (PDCCH) is a channel for downlink transmission from a base station to a mobile terminal. The PDCCH reports resource allocation information for a Downlink Shared Channel (DL-SCH), which is one of the transport channels described below, resource allocation information for a Paging Channel (PCH), which is also one of the transport channels described below, and Hybrid Automatic Repeat reQuest (HARQ) information for the DL-SCH. The PDCCH carries an uplink scheduling grant. The PDCCH carries Acknowledgement (Ack) / Negative Acknowledgement (Nack), which are response signals to uplink transmissions. The PDCCH is also called an L1 / L2 control signal.

[0009] The Physical Downlink Shared Channel (PDSCH) is a channel for downlink transmission from a base station to a mobile terminal. A Downlink Shared Channel (DL-SCH), which is a transport channel, and a PCH, which is also a transport channel, are mapped to the PDSCH.

[0010] A physical multicast channel (PMCH) is a channel for downlink transmission from a base station to a mobile terminal, and a multicast channel (MCH), which is a transport channel, is mapped to the PMCH.

[0011] The Physical Uplink Control Channel (PUCCH) is a channel for uplink transmission from a mobile terminal to a base station. The PUCCH carries Ack / Nack, which are response signals to downlink transmissions. The PUCCH also carries CQI (Channel Quality Indicator) reports. CQI is quality information that indicates the quality of received data or the quality of the communication path. The PUCCH also carries Scheduling Requests (SR).

[0012] The Physical Uplink Shared Channel (PUSCH) is a channel for uplink transmission from a mobile terminal to a base station. The Uplink Shared Channel (UL-SCH), which is one of the transport channels, is mapped to the PUSCH.

[0013] The Physical Hybrid ARQ Indicator Channel (PHICH) is a channel for downlink transmission from a base station to a mobile terminal. The PHICH carries Ack / Nack, which are response signals to uplink transmissions. The Physical Random Access Channel (PRACH) is a channel for uplink transmission from a mobile terminal to a base station. The PRACH carries a random access preamble.

[0014] Downlink reference signals (RS) are known symbols in LTE communication systems. The following five types of downlink reference signals are defined: Cell-specific Reference Signal (CRS), MBSFN reference signal, UE-specific reference signal Demodulation Reference Signal (DM-RS), Positioning Reference Signal (PRS), and Channel-State Information Reference Signal (CSI-RS). Measurement of the physical layer of a mobile terminal includes measurement of the reference signal received power (RSRP).

[0015] The transport channels described in Non-Patent Document 1 (Chapter 5) will be explained below. Among the downlink transport channels, a broadcast channel (BCH) is broadcast to the entire coverage of the base station (cell). The BCH is mapped to a physical broadcast channel (PBCH).

[0016] The Downlink Shared Channel (DL-SCH) is subject to retransmission control using Hybrid ARQ (HARQ). DL-SCH can be broadcast to the entire coverage of a base station (cell). DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called persistent scheduling. DL-SCH supports discontinuous reception (DRX) for mobile terminals to reduce power consumption. DL-SCH is mapped to the Physical Downlink Shared Channel (PDSCH).

[0017] The Paging Channel (PCH) supports DRX for mobile terminals to enable low power consumption. The PCH is required to broadcast to the entire coverage of the base station (cell). The PCH is mapped to physical resources such as the Physical Downlink Shared Channel (PDSCH) that can be dynamically used for traffic.

[0018] The Multicast Channel (MCH) is used for broadcasting to the entire coverage of a base station (cell). The MCH supports SFN combining of MBMS (Multimedia Broadcast Multicast Service) services (MTCH and MCCH) in multi-cell transmission. The MCH supports semi-static resource allocation. The MCH is mapped to the PMCH.

[0019] Among the uplink transport channels, the Uplink Shared Channel (UL-SCH) is subject to retransmission control using HARQ (Hybrid ARQ). The UL-SCH supports dynamic or semi-static resource allocation. The UL-SCH is mapped to the Physical Uplink Shared Channel (PUSCH).

[0020] The Random Access Channel (RACH) is limited to control information. The RACH is subject to collision risk. The RACH is mapped to the Physical Random Access Channel (PRACH).

[0021] We will explain HARQ. HARQ is a technology that improves the communication quality of a transmission channel by combining Automatic Repeat reQuest (ARQ) and Forward Error Correction. HARQ has the advantage that error correction works effectively by retransmission even on transmission channels where communication quality varies. In particular, by combining the reception results of the initial transmission and the retransmission when retransmitting, it is possible to obtain further quality improvement.

[0022] An example of a retransmission method will be explained below. If the receiving side is unable to decode the received data correctly, in other words, if a CRC (Cyclic Redundancy Check) error occurs (CRC=NG), the receiving side will send a "Nack" to the sending side. The sending side, having received the "Nack," will retransmit the data. If the receiving side is able to decode the received data correctly, in other words, if no CRC error occurs (CRC=OK), the receiving side will send an "Ack" to the sending side. The sending side, having received the "Ack," will send the next data.

[0023] The logical channels described in Non-Patent Document 1 (Chapter 6) will be explained below. The Broadcast Control Channel (BCCH) is a downlink channel for broadcast system control information. The BCCH, which is a logical channel, is mapped to the broadcast channel (BCH) or the downlink shared channel (DL-SCH), which are transport channels.

[0024] The Paging Control Channel (PCCH) is a downlink channel for transmitting paging information and system information changes. The PCCH is used when the cell location of the mobile terminal is unknown to the network. The PCCH, which is a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

[0025] The Common Control Channel (CCCH) is a channel for transmitting control information between a mobile terminal and a base station. The CCCH is used when the mobile terminal does not have an RRC connection with the network. In the downlink direction, the CCCH is mapped to the Downlink Shared Channel (DL-SCH), which is a transport channel. In the uplink direction, the CCCH is mapped to the Uplink Shared Channel (UL-SCH), which is a transport channel.

[0026] The Multicast Control Channel (MCCH) is a downlink channel for point-to-multipoint transmission. The MCCH is used to transmit MBMS control information for one or several MTCHs from the network to mobile terminals. The MCCH is used only by mobile terminals receiving MBMS. The MCCH is mapped to the Multicast Channel (MCH), which is a transport channel.

[0027] A Dedicated Control Channel (DCCH) is a channel that transmits dedicated control information between a mobile terminal and a network on a one-to-one basis. The DCCH is used when the mobile terminal is in an RRC connection. The DCCH is mapped to an uplink shared channel (UL-SCH) in the uplink and to a downlink shared channel (DL-SCH) in the downlink.

[0028] A Dedicated Traffic Channel (DTCH) is a point-to-point communication channel for transmitting user information to an individual mobile terminal. DTCH exists in both uplink and downlink. In uplink, DTCH is mapped to an uplink shared channel (UL-SCH) and in downlink, it is mapped to a downlink shared channel (DL-SCH).

[0029] The Multicast Traffic Channel (MTCH) is a downlink channel for transmitting traffic data from the network to mobile terminals. The MTCH is a channel used only by mobile terminals receiving MBMS. The MTCH is mapped to the Multicast Channel (MCH).

[0030] CGI stands for Cell Global Identifier. ECGI stands for E-UTRAN Cell Global Identifier. Closed Subscriber Group (CSG) cells are introduced in LTE, LTE-A (Long Term Evolution Advanced) (described below), and UMTS (Universal Mobile Telecommunication System).

[0031] A CSG (Closed Subscriber Group) cell is a cell for which an operator has identified available subscribers (hereinafter referred to as a "specific subscriber cell"). The identified subscribers are permitted to access one or more cells in a PLMN (Public Land Mobile Network). The one or more cells to which the identified subscribers are permitted to access are called "CSG cell(s)." However, there are access restrictions within the PLMN.

[0032] A CSG cell is part of a PLMN that broadcasts a unique CSG identity (CSG ID; CSG-ID) and broadcasts a CSG indication of "TRUE." Members of a pre-registered and authorized subscriber group access the CSG cell using the CSG-ID, which is access permission information.

[0033] The CSG-ID is broadcast by a CSG cell or cells. There are multiple CSG-IDs in an LTE communication system. The CSG-ID is used by a mobile terminal (UE) to facilitate access to CSG-related members.

[0034] The location of a mobile terminal is tracked in units of an area consisting of one or more cells. Location tracking is performed to track the location of a mobile terminal even when it is in standby mode and to enable the mobile terminal to be called, in other words, to allow the mobile terminal to receive calls. The area used for tracking the location of a mobile terminal is called a tracking area.

[0035] 3GPP is studying base stations called Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB). HNB in ​​UTRAN and HeNB in ​​E-UTRAN are base stations for access services for homes, businesses, and businesses, for example. Non-Patent Document 3 discloses three different modes of access to HeNB and HNB. Specifically, it discloses an open access mode, a closed access mode, and a hybrid access mode.

[0036] Each mode has the following characteristics: In the open access mode, the HeNB and HNB are operated as normal cells of a regular operator. In the closed access mode, the HeNB and HNB are operated as CSG cells, which are accessible only by CSG members. In the hybrid access mode, the HeNB and HNB are operated as CSG cells, which are simultaneously accessible by non-CSG members. In other words, a cell in the hybrid access mode (also called a hybrid cell) is a cell that supports both the open access mode and the closed access mode.

[0037] In 3GPP, among all physical cell identities (PCIs), there is a PCI range reserved by the network for use in CSG cells (see Non-Patent Document 1, Chapter 10.5.1.1). Dividing a PCI range is sometimes called PCI split. Information about PCI splits (also called PCI split information) is broadcast from a base station to mobile terminals under its control by system information. Being under the control of a base station means that the base station is the serving cell.

[0038] Non-Patent Document 4 discloses the basic operation of a mobile terminal using PCI split. A mobile terminal that does not have PCI split information must use all PCIs, for example, all 504 codes, to perform a cell search. On the other hand, a mobile terminal that has PCI split information can perform a cell search using the PCI split information.

[0039] 3GPP is also working on the development of the Long Term Evolution Advanced (LTE-A) standard as Release 10 (see Non-Patent Documents 5 and 6). LTE-A is based on the LTE wireless communication system, and is configured by adding several new technologies to it.

[0040] In the LTE-A system, carrier aggregation (CA) is being considered, which aggregates two or more component carriers (CCs) (also called "aggregation") to support wider frequency bandwidths (transmission bandwidths) up to 100 MHz.

[0041] When CA is configured, the UE has only one RRC connection with the network (NW). In the RRC connection, one serving cell provides NAS mobility information and security input. This cell is called the primary cell (PCell). In the downlink, the carrier corresponding to the PCell is the downlink primary component carrier (DL PCC). In the uplink, the carrier corresponding to the PCell is the uplink primary component carrier (UL PCC).

[0042] Depending on the UE's capabilities, a secondary cell (SCell) is configured to pair with the PCell and the serving cell. In the downlink, the carrier corresponding to the SCell is the downlink secondary component carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is the uplink secondary component carrier (UL SCC).

[0043] For one UE, a set of serving cells is configured, which includes one PCell and one or more SCells.

[0044] New technologies for LTE-A include wider bandwidth extension and Coordinated Multiple Point transmission and reception (CoMP). CoMP, which is being considered for LTE-A by 3GPP, is described in Non-Patent Document 7.

[0045] Furthermore, in order to handle the massive traffic volumes that will be generated in the future, 3GPP is considering the use of small eNBs that configure small cells. For example, technologies are being considered that aim to increase communication capacity by installing a large number of small eNBs and configuring a large number of small cells, thereby improving frequency utilization efficiency. Specifically, there is dual connectivity, in which a UE connects to two eNBs to communicate.

[0046] In addition, there is a growing demand for machine type communication (MTC), which enables communication without human operation of the UE. MTC is used for a wide range of services, such as sensing, meter monitoring, and parcel tracking monitoring.

[0047] As the demand for MTC increases, it is expected that a large number of MTC terminals (MTC UEs) will be used. Therefore, MTC terminals are required to be low cost and have a long life. 3GPP is currently studying technologies to reduce the cost of MTC terminals.

[0048] In addition, there is a growing demand for systems that use unlicensed spectrum as a complementary tool to licensed spectrum. An example of unlicensed spectrum is the ISM (Industrial, Scientific, and Medical) band, which is used for wireless local area networks (WLANs). 3GPP is studying Licensed-Assisted Access (LAA), which uses unlicensed spectrum as a complementary tool to licensed spectrum using LTE.

[0049] Mobile network traffic volume is on the rise, and communication speeds are also increasing. When LTE and LTE-A begin full-scale operation, communication speeds are expected to increase even further, leading to an increase in traffic volume. [Prior art documents] [Non-patent literature]

[0050] [Non-Patent Document 1] 3GPP TS36.300 V12.2.0 [Non-patent document 2] 3GPP TS36.304 V12.1.0 [Non-patent document 3] 3GPP S1-083461 [Non-patent document 4] 3GPP R2-082899 [Non-patent document 5] 3GPP TR 36.814 V9.0.0 [Non-patent document 6] 3GPP TR 36.912 V10.0.0 [Non-Patent Document 7] 3GPP TR 36.819 V11.2.0 [Non-patent document 8] 3GPP TS 36.141 V12.4.0 [Non-Patent Document 9] 3GPP TR36.888 V12.0.0 [Non-Patent Document 10] 3GPP R1-144563 [Non-Patent Document 11] 3GPP R1-144662 [Non-Patent Document 12] 3GPP R1-145101 [Non-Patent Document 13] 3GPP R1-143992 [Non-Patent Document 14] 3GPP TS36.213 V12.1.0 [Non-Patent Document 15] 3GPP R1-145132 [Non-Patent Document 16] 3GPP R1-144236 Summary of the Invention [Problem to be solved by the invention]

[0051] Requirements for low-cost MTC (LC-MTC) include bandwidth reduction, coverage extension, and power consumption reduction. LC-MTC UEs, which are subject to bandwidth reduction, face the problem of being unable to receive system information broadcast over the entire system bandwidth.

[0052] In addition, for LC-MTC UEs where coverage is extended, the reception quality from cells in the extended area deteriorates, so repetition transmission, which repeatedly transmits data, is being considered. However, since paging and system information have not been transmitted using repetition transmission in the past, there is a problem that there is no method for transmitting and receiving data using repetition.

[0053] Furthermore, when unlicensed spectrum is used for LTE, a fair coexistence method with other systems using unlicensed spectrum is required. Therefore, LAA is required to have a function to perform listen-before-talk (clear channel assessment) before data transmission and a function to prevent data communication from being performed continuously for a long period of time. In addition, it has been proposed to provide a signal for synchronization or measurement of unlicensed spectrum so that UE can synchronize with or measure unlicensed spectrum when no transmission is made from the cell.

[0054] However, even when transmitting such signals, it is necessary to avoid collisions with other systems, maintain fairness, and enable coexistence. There is currently no fair coexistence method for such synchronization or measurement signals in unlicensed spectrum.

[0055] An object of the present invention is to provide a communication system etc. that can improve the communication performance of a communication terminal when supporting a variety of services. [Means for solving the problem]

[0056] The communication system disclosed in the present specification is a communication system comprising a communication terminal and a base station which communicates wirelessly with the communication terminal, wherein the communication terminal includes a narrowband terminal which communicates wirelessly with the base station in a frequency band narrower than a system band which is a frequency band that can be used in wireless communication, and wherein information for the narrowband terminal is repeatedly transmitted from the base station to the communication terminal over successive subframes, and the information for the narrowband terminal is transmitted from the base station to the communication terminal using a physical downlink control channel used in narrowband resources. [Effects of the Invention]

[0057] According to the present invention, it is possible to improve the communication performance of a communication terminal when supporting a variety of services.

[0058] The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings. [Brief explanation of the drawings]

[0059] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Figure 2] FIG. 7 is a block diagram showing the overall configuration of an LTE communication system 700 being discussed in 3GPP. [Figure 3] FIG. 3 is a block diagram showing the configuration of a mobile terminal 71 shown in FIG. 2, which is a mobile terminal according to the present invention. [Figure 4] FIG. 3 is a block diagram showing the configuration of a base station 72 shown in FIG. 2, which is a base station according to the present invention. [Figure 5] FIG. 2 is a block diagram showing the configuration of an MME according to the present invention. [Figure 6] 1 is a flowchart showing an outline of operations from cell search to standby operation performed by a mobile terminal (UE) in an LTE communication system. [Figure 7] FIG. 1 is a diagram illustrating the concept of a cell configuration when macro eNBs and small eNBs are mixed. [Figure 8] 1 is a flowchart showing an example of a processing procedure in an RRC_Idle state of a UE according to the prior art. [Figure 9] 10 is a flowchart showing an example of a processing procedure in an RRC_Idle state of an LC-MTC UE according to the first embodiment. [Figure 10] 10 is a flowchart showing an example of processing in an RRC_Idle state of an LC-MTC UE according to a first modification of the first embodiment. [Figure 11] 11 is a flowchart showing an example of a process in an RRC_Idle state of an LC-MTC UE according to a second modification of the first embodiment. [Figure 12] FIG. 11 is a diagram illustrating an example of a paging repetition transmission method in the third embodiment. [Figure 13] FIG. 13 is a diagram illustrating an example of a method for transmitting paging repetitions in a first modification of the third embodiment. [Figure 14] FIG. 10 is a diagram showing an example of a sequence in which subframes in which paging repetition transmission is performed are determined from subframes excluding MBSFN subframes according to a second modification of the third embodiment. [Figure 15] FIG. 10 is a diagram illustrating an example of a frame configuration in which the subframe in which the initial transmission of an EPDCCH is performed and the subframe in which repetition transmission is performed are the same. [Figure 16]FIG. 1 is a diagram illustrating an example of a paging message in the prior art. [Figure 17] FIG. 13 is a diagram showing an example of a paging message in the fourth embodiment. [Figure 18] FIG. 20 is a diagram illustrating an example of a subframe configuration including an initial transmission and repetition transmission of an EPDCCH according to a first modification of the fourth embodiment. [Figure 19] FIG. 20 is a diagram illustrating an example of a subframe configuration including an initial transmission and repetition transmission of an EPDCCH according to a first modification of the fourth embodiment. [Figure 20] FIG. 20 is a diagram showing an example of a state of DS transmission of a cell and measurement by a UE on an unlicensed spectrum in the seventh embodiment. [Figure 21] FIG. 20 is a diagram showing an example of a state of DS transmission of a cell and measurement by a UE on an unlicensed spectrum in the seventh embodiment. [Figure 22] FIG. 20 is a diagram showing an example of a state of DS transmission of a cell and measurement by a UE on an unlicensed spectrum in a first modification of the seventh embodiment. [Figure 23] FIG. 20 is a diagram showing an example of processing up to data communication when DS transmission and UE measurement are used in the first modification of the seventh embodiment. [Figure 24] FIG. 20 is a diagram showing an example of processing up to data communication when DS transmission and UE measurement are used in the first modification of the seventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0060] Embodiment 1 Fig. 2 is a block diagram showing the overall configuration of an LTE communication system 700 being discussed in 3GPP. Referring to Fig. 2, the radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 70. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 71, which is a communication terminal device, is capable of wireless communication with a base station device (hereinafter referred to as "base station (E-UTRAN NodeB: eNB)") 72, and transmits and receives signals via wireless communication.

[0061] If the control protocols for the mobile terminal 71, such as RRC (Radio Resource Control), and the user plane, such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate at the base station 72, the E-UTRAN is composed of one or more base stations 72.

[0062] The control protocol RRC (Radio Resource Control) between the mobile terminal 71 and the base station 72 performs broadcast, paging, RRC connection management, etc. The states of the base station 72 and the mobile terminal 71 in RRC include RRC_Idle and RRC_Connected.

[0063] In RRC_Idle, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell reselection, mobility, etc. are performed. In RRC_Connected, the mobile terminal has an RRC connection and can transmit and receive data with the network. In addition, in RRC_Connected, handover (HO), measurement of neighbor cells, etc. are performed.

[0064] The base stations 72 are classified into eNBs 76 and Home-eNBs 75. The communication system 700 includes an eNB group 72-1 including a plurality of eNBs 76, and a Home-eNB group 72-2 including a plurality of Home-eNBs 75. A system configured from an EPC (Evolved Packet Core) core network and an E-UTRAN 70 radio access network is referred to as an EPS (Evolved Packet System). The EPC core network and the E-UTRAN 70 radio access network may be collectively referred to as a "network."

[0065] The eNB 76 is connected to a Mobility Management Entity (MME), or a Serving Gateway (S-GW), or an MME / S-GW unit (hereinafter sometimes referred to as an "MME unit") 73 including an MME and an S-GW via an S1 interface, and control information is communicated between the eNB 76 and the MME unit 73. Multiple MME units 73 may be connected to one eNB 76. The eNBs 76 are connected to each other via an X2 interface, and control information is communicated between the eNBs 76.

[0066] The Home-eNB 75 is connected to the MME unit 73 via an S1 interface, and control information is communicated between the Home-eNB 75 and the MME unit 73. A plurality of Home-eNBs 75 are connected to one MME unit 73. Alternatively, the Home-eNB 75 is connected to the MME unit 73 via a HeNBGW (Home-eNB GateWay) 74. The Home-eNB 75 and the HeNBGW 74 are connected via an S1 interface, and the HeNBGW 74 and the MME unit 73 are connected via the S1 interface.

[0067] One or more Home-eNBs 75 are connected to one HeNBGW 74, and information is communicated through the S1 interface. The HeNBGW 74 is connected to one or more MME units 73, and information is communicated through the S1 interface.

[0068] The MME unit 73 and HeNBGW 74 are upper devices, specifically upper nodes, and control connections between the eNB 76 and Home-eNB 75, which are base stations, and the mobile terminal (UE) 71. The MME unit 73 constitutes the EPC, which is a core network. The base station 72 and HeNBGW 74 constitute the E-UTRAN 70.

[0069] Furthermore, 3GPP is considering the following configuration: The X2 interface between Home-eNBs 75 is supported. That is, Home-eNBs 75 are connected via the X2 interface, and control information is communicated between the Home-eNBs 75. From the MME unit 73, HeNBGW 74 appears as the Home-eNB 75. From the Home-eNB 75, HeNBGW 74 appears as the MME unit 73.

[0070] In either case where the Home-eNB 75 is connected to the MME unit 73 via the HeNBGW 74 or where the Home-eNB 75 is connected directly to the MME unit 73, the interface between the Home-eNB 75 and the MME unit 73 is the same, the S1 interface.

[0071] The base station device 72 may configure one cell or multiple cells. Each cell has a predetermined coverage area, which is a range within which communication with a communication terminal device is possible, and performs wireless communication with the communication terminal device within the coverage area. When one base station device configures multiple cells, each cell is configured to be able to communicate with a mobile terminal.

[0072] FIG. 3 is a block diagram showing the configuration of mobile terminal 71 shown in FIG. 2, which is a mobile terminal according to the present invention. The transmission process of mobile terminal 71 shown in FIG. 3 will be described. First, control data from protocol processing unit 801 and user data from application unit 802 are stored in transmission data buffer unit 803. The data stored in transmission data buffer unit 803 is passed to encoder unit 804, where it is subjected to encoding processes such as error correction. Some data may be output directly from transmission data buffer unit 803 to modulator unit 805 without being encoded. The data encoded by encoder unit 804 is modulated by modulator unit 805. The modulated data is converted into a baseband signal, and then output to frequency converter 806, where it is converted into a radio transmission frequency. A transmission signal is then transmitted from antenna 807 to base station 72.

[0073] Furthermore, the receiving process of the mobile terminal 71 is performed as follows. A radio signal from the base station 72 is received by the antenna 807. The received signal is converted from a radio receiving frequency to a baseband signal by the frequency conversion unit 806, and demodulated by the demodulation unit 808. The demodulated data is passed to the decoder unit 809, where decoding processes such as error correction are performed. Of the decoded data, control data is passed to the protocol processing unit 801, and user data is passed to the application unit 802. A series of processes of the mobile terminal 71 is controlled by the control unit 810. Therefore, although the control unit 810 is omitted in FIG. 3, it is connected to each of the units 801 to 809.

[0074] Figure 4 is a block diagram showing the configuration of the base station 72 shown in Figure 2, which is a base station according to the present invention. The transmission processing of the base station 72 shown in Figure 4 will be described. An EPC communication unit 901 transmits and receives data between the base station 72 and the EPC (MME unit 73, etc.), HeNBGW 74, etc. An other base station communication unit 902 transmits and receives data with other base stations. The EPC communication unit 901 and the other base station communication unit 902 each exchange information with a protocol processing unit 903. Control data from the protocol processing unit 903, and user data and control data from the EPC communication unit 901 and the other base station communication unit 902 are stored in a transmission data buffer unit 904.

[0075] The data stored in the transmission data buffer unit 904 is passed to an encoder unit 905, where it undergoes encoding processes such as error correction. Some data may be output directly from the transmission data buffer unit 904 to a modulator unit 906 without undergoing encoding processes. The encoded data is modulated by the modulator unit 906. The modulated data is converted into a baseband signal, and then output to a frequency converter unit 907, where it is converted into a radio transmission frequency. The transmission signal is then transmitted from an antenna 908 to one or more mobile terminals 71.

[0076] The reception process of the base station 72 is performed as follows: A radio signal from one or more mobile terminals 71 is received by an antenna 908. The received signal is converted from a radio reception frequency to a baseband signal by a frequency converter 907, and demodulated by a demodulator 909. The demodulated data is passed to a decoder 910, where decoding processes such as error correction are performed. Of the decoded data, control data is passed to the protocol processor 903 or the EPC communication unit 901 or other base station communication unit 902, and user data is passed to the EPC communication unit 901 and other base station communication unit 902. A series of processes of the base station 72 is controlled by a controller 911. Therefore, although the controller 911 is omitted in FIG. 4, it is connected to each of the units 901 to 910.

[0077] FIG. 5 is a block diagram showing the configuration of an MME according to the present invention. FIG. 5 shows the configuration of an MME 73a included in the MME unit 73 shown in FIG. 2 described above. A PDN GW communication unit 1001 transmits and receives data between the MME 73a and a PDN GW. A base station communication unit 1002 transmits and receives data via the S1 interface between the MME 73a and a base station 72. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 1001 to the base station communication unit 1002 via a user plane communication unit 1003, and transmitted to one or more base stations 72. If the data received from the base station 72 is user data, the user data is passed from the base station communication unit 1002 to the PDN GW communication unit 1001 via the user plane communication unit 1003, and transmitted to the PDN GW.

[0078] If the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 1001 to the control plane control unit 1005. If the data received from the base station 72 is control data, the control data is passed from the base station communication unit 1002 to the control plane control unit 1005.

[0079] The HeNBGW communication unit 1004 is provided when a HeNBGW 74 is present, and transmits and receives data via an interface (IF) between the MME 73a and the HeNBGW 74 depending on the information type. Control data received from the HeNBGW communication unit 1004 is passed from the HeNBGW communication unit 1004 to the control plane control unit 1005. The result of processing in the control plane control unit 1005 is transmitted to the PDN GW via the PDN GW communication unit 1001. In addition, the result of processing in the control plane control unit 1005 is transmitted to one or more base stations 72 via the base station communication unit 1002 by the S1 interface, and is also transmitted to one or more HeNBGWs 74 via the HeNBGW communication unit 1004.

[0080] The control plane control unit 1005 includes a NAS security unit 1005-1, an SAE bearer control unit 1005-2, an idle state mobility management unit 1005-3, and the like, and performs overall processing for the control plane. The NAS security unit 1005-1 performs security for NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 1005-2 performs management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 1005-3 performs mobility management in the idle state (also called the LTE-IDLE state or simply idle), generation and control of paging signals in the idle state, addition, deletion, update, and search of tracking areas for one or more mobile terminals 71 under its control, and tracking area list management.

[0081] The MME 73a distributes paging signals to one or more base stations 72. The MME 73a also performs mobility control in an idle state. The MME 73a manages a tracking area list when the mobile terminal is in an idle state and an active state. The MME 73a initiates a paging protocol by transmitting a paging message to a cell belonging to a tracking area in which the UE is registered. The idle state mobility management unit 1005-3 may manage the CSG, CSG-ID, and whitelist of the Home-eNB 75 connected to the MME 73a.

[0082] Next, an example of a cell search method in a communication system is shown. Fig. 6 is a flowchart showing an outline of the process from cell search to standby operation performed by a mobile terminal (UE) in an LTE communication system. When the mobile terminal starts a cell search, in step ST1, it synchronizes slot timing and frame timing using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from surrounding base stations.

[0083] P-SS and S-SS are collectively called the Synchronization Signal (SS). The Synchronization Signal (SS) is assigned a synchronization code that corresponds one-to-one to the PCI assigned to each cell. 504 different PCIs are being considered. These 504 different PCIs are used to achieve synchronization and to detect (identify) the PCI of the synchronized cell.

[0084] Next, in step ST2, for the synchronized cell, a cell-specific reference signal (CRS), which is a reference signal (RS) transmitted from the base station for each cell, is detected and the RS received power (Reference Signal Received Power: RSRP) is measured. The RS uses a code that has a one-to-one correspondence with the PCI. By correlating with this code, it is possible to separate the cell from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST1, it is possible to detect the RS and measure the RS received power.

[0085] Next, in step ST3, the cell with the best RS reception quality, for example, the cell with the highest RS reception power, that is, the best cell, is selected from one or more cells detected up to step ST2.

[0086] Next, in step ST4, the PBCH of the best cell is received to obtain the BCCH, which is broadcast information. A MIB (Master Information Block), which includes cell configuration information, is mapped to the BCCH on the PBCH. Therefore, the MIB can be obtained by receiving the PBCH and obtaining the BCCH. Examples of MIB information include the DL (downlink) system bandwidth (also called the transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, and the SFN (System Frame Number).

[0087] Next, in step ST5, the DL-SCH of the cell is received based on the cell configuration information in the MIB, and SIB (System Information Block) 1 in the broadcast information BCCH is obtained. SIB 1 includes information on access to the cell, information on cell selection, and scheduling information for other SIBs (SIBk; k is an integer greater than or equal to 2). SIB 1 also includes a Tracking Area Code (TAC).

[0088] Next, in step ST6, the mobile terminal compares the TAC of the SIB1 received in step ST5 with the TAC part of the tracking area identity (TAI) in the tracking area list already held by the mobile terminal. The tracking area list is also called a TAI list. The TAI is identification information for identifying a tracking area, and is composed of an MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a tracking area code number.

[0089] If the comparison result in step ST6 shows that the TAC received in step ST5 is the same as the TAC included in the tracking area list, the mobile terminal enters standby mode in the cell. If the comparison result shows that the TAC received in step ST5 is not included in the tracking area list, the mobile terminal requests a change of tracking area to perform a Tracking Area Update (TAU) to the core network (EPC) including the MME, etc., through the cell.

[0090] An apparatus constituting a core network (hereinafter sometimes referred to as a "core network side apparatus") updates the tracking area list based on the identification number (e.g., UE-ID) of the mobile terminal sent from the mobile terminal together with the TAU request signal. The core network side apparatus transmits the updated tracking area list to the mobile terminal. The mobile terminal rewrites (updates) the TAC list held by the mobile terminal based on the received tracking area list. Thereafter, the mobile terminal enters standby mode in the cell.

[0091] The widespread use of smartphones and tablet devices has led to an explosive increase in cellular wireless communication traffic, raising concerns about a shortage of wireless resources worldwide. In response to this, efforts are being made to develop small cells and promote spatial separation in order to improve frequency utilization efficiency.

[0092] In a conventional cell configuration, a cell configured by an eNB has a relatively wide coverage area. Conventionally, a cell is configured so that a certain area is covered by the relatively wide coverage areas of multiple cells configured by multiple eNBs.

[0093] In the case of small cell configuration, a cell configured by an eNB has a narrower coverage area than a cell configured by a conventional eNB. Therefore, as in the past, a larger number of small cell configuration eNBs are required to cover a certain area compared to conventional eNBs.

[0094] In the following description, a cell that provides coverage over a relatively wide range, such as a cell configured by a conventional eNB, i.e., a cell with a relatively wide coverage area, is referred to as a "macro cell," and an eNB that configures a macro cell is referred to as a "macro eNB." Also, a cell that provides coverage over a relatively narrow range, such as a cell configured as a small cell, i.e., a cell with a relatively narrow coverage area, is referred to as a "small cell," and an eNB that configures a small cell is referred to as a "small eNB."

[0095] The macro eNB may be, for example, a "Wide Area Base Station" as described in Non-Patent Document 8.

[0096] The small eNB may be, for example, a low-power node, a local area node, a hotspot, etc. Also, the small eNB may be a pico eNB constituting a pico cell, a femto eNB constituting a femto cell, a HeNB, a remote radio head (RRH), a remote radio unit (RRU), a remote radio equipment (RRE), or a relay node (RN). Also, the small eNB may be a "local area base station" or a "home base station" as described in Non-Patent Document 8.

[0097] 7 is a diagram showing the concept of a cell configuration when macro eNBs and small eNBs are mixed. A macro cell configured by a macro eNB has a relatively wide coverage area 1301. A small cell configured by a small eNB has a coverage area 1302 that is narrower than the coverage area 1301 of the macro eNB (macro cell).

[0098] When multiple eNBs are mixed, the coverage of a cell configured by one eNB may be included in the coverage of a cell configured by another eNB. In the cell configuration shown in Figure 7, as indicated by reference numerals "1304" and "1305," the coverage 1302 of a small cell configured by a small eNB may be included in the coverage 1301 of a macro cell configured by a macro eNB.

[0099] Also, as indicated by reference numeral "1305," the coverage of multiple, for example, two small cells 1302 may be included within the coverage of one macro cell 1301. A mobile terminal (UE) 1303 is included, for example, within the coverage 1302 of a small cell and communicates via the small cell.

[0100] Furthermore, in the cell configuration shown in FIG. 7, as indicated by reference numeral "1306," there may be cases where coverage 1301 of a macro cell configured by a macro eNB and coverage 1302 of a small cell configured by a small eNB overlap in a complex manner.

[0101] Also, as indicated by reference numeral "1307," there may be cases where the coverage 1301 of a macro cell configured by a macro eNB and the coverage 1302 of a small cell configured by a small eNB do not overlap.

[0102] Furthermore, as indicated by reference numeral "1308," there may be cases where coverage 1302 of multiple small cells formed by multiple small eNBs is formed within coverage 1301 of one macro cell formed by one macro eNB.

[0103] There is a growing demand for machine type communication (MTC), which enables communication without human operation of UE. MTC is used for a wide range of services, such as sensing, meter monitoring, and parcel tracking monitoring.

[0104] As the demand for MTC increases, it is expected that a large number of MTC terminals (MTC UEs) will be used, and therefore MTC terminals are required to be low cost and have a long lifespan.

[0105] 3GPP is currently studying technologies to reduce the cost of MTC terminals (see Non-Patent Document 9). The following three items (1) to (3) have been raised as requirements for low-cost MTC (LC-MTC):

[0106] (1) Reduced Bandwidth (2) Coverage enhancement (3) Power consumption reduction

[0107] 3GPP is studying solutions to meet these requirements. The following describes LC-MTC UE (hereinafter sometimes referred to as "LC-MTC UE"), which is a low-cost MTC terminal device.

[0108] Conventionally, system information (SI) is broadcast using PDCCH and PDSCH over the entire system band. However, an LC-MTC UE that is required to reduce its supported band cannot receive SI broadcast over the entire system band. Therefore, a new method of notifying LC-MTC UE of SI is being considered. Here, an LC-MTC UE that is required to reduce its supported band performs wireless communication over a band narrower than the system band available in a cell, and therefore corresponds to a narrowband terminal device.

[0109] Since SI must be repeatedly broadcast, it is required to reduce the SI to be notified to LC-MTC UE. The SI to be reduced includes parameters other than SIB1, SIB2, and SIB14, which are SIBs used for initial access (see Non-Patent Document 10). Therefore, the parameters to be reduced also include system information for cell reselection in SIB3, SIB4, SIB5, and SIB6.

[0110] However, a UE in the RRC_Idle state must perform a cell reselection process (see Non-Patent Document 2). Also, a UE in the RRC_Idle state can move between cells while maintaining the RRC_Idle state, without establishing an RRC connection, as long as the UE is in the same tracking area.

[0111] 8 is a flowchart showing a processing procedure of a UE in the RRC_Idle state according to the prior art. In Step ST8001, the UE in the RRC_Idle state camps on cell A.

[0112] In Step ST8002, the UE in RRC_Idle state camped on cell A performs discontinuous reception (DRX).

[0113] In Step ST8003, the UE performs a cell reselection process. Specifically, the UE receives system information related to the cell reselection process (hereinafter, may be referred to as "system information for cell reselection") broadcast by cell A, and performs the cell reselection process using the system information for cell reselection.

[0114] In Step ST8004, the UE detects cell X as a result of the cell reselection process.

[0115] In Step ST8005, the UE receives broadcast information of the detected cell X and determines, based on the received broadcast information, whether or not the TAC of SIB1 of the detected cell X is the same as the TAC received from cell A on which the UE was camped before the cell reselection process. If the TAC of SIB1 of the detected cell X is different from the TAC received from cell A, the UE proceeds to Step ST8006. If the TAC of SIB1 of the detected cell X is the same as the TAC received from cell A, the UE proceeds to Step ST8007 while remaining in the RRC_Idle state.

[0116] In Step ST8006, the UE performs a Tracking Area Update (TAU) via the detected cell X. After performing the TAU process, the UE returns to the RRC_Idle state and proceeds to Step ST8007.

[0117] In step ST8007, the UE camps on the detected cell X. When the UE camps on the detected cell X, it returns to step ST8002 and performs the processing of steps ST8002 to ST8007 described above again in accordance with the discontinuous reception cycle of the detected cell X.

[0118] If the SI notified to the LC-MTC UE is reduced and the LC-MTC UE cannot acquire system information for cell reselection, the UE will be unable to perform cell reselection processing when in RRC_Idle state.

[0119] If the cell reselection process cannot be performed, a problem occurs in that the UE moves out of range if the reception quality of the serving cell on which it is camped deteriorates.

[0120] Furthermore, when the UE transitions from the RRC_Idle state to out-of-service, settings such as the discontinuous reception (DRX) cycle are reset, which causes a problem in that the UE is no longer able to receive paging messages.

[0121] This embodiment discloses a method for solving these problems. When the timer for the discontinuous reception cycle (hereinafter sometimes referred to as the "discontinuous reception timer") expires, the LC-MTC UE synchronizes with the serving cell and performs a paging message detection operation. The LC-MTC UE keeps the discontinuous reception timer active even when it moves out of range. In other words, it maintains the discontinuous reception timer. The state in which the discontinuous reception timer is maintained while out of range may be considered a new state. Alternatively, it may be one of the RRC_Idle states.

[0122] The LC-MTC UE does not need to receive system information for cell reselection from the cell. The cell does not need to notify the LC-MTC UE of system information for cell reselection. The LC-MTC UE does not need to perform cell reselection processing when in RRC_Idle state.

[0123] In this way, the LC-MTC UE can perform discontinuous reception even without system information for cell reselection, and can receive paging messages.

[0124] FIG. 9 is a flowchart showing an example of a processing procedure in the RRC_Idle state of an LC-MTC UE according to the first embodiment.

[0125] In Step ST9001, the LC-MTC UE in the RRC_Idle state camps on cell A, for example.

[0126] In Step ST9002, the LC-MTC UE in RRC_Idle state camped on cell A performs discontinuous reception. The LC-MTC UE does not receive system information for cell reselection from cell A and does not perform cell reselection processing.

[0127] In step ST9003, the LC-MTC UE determines the reception state of a signal transmitted from cell A on which it is camped. Specifically, the LC-MTC UE determines whether the reception quality of the cell has not deteriorated and whether reception is possible. If it is determined that reception is possible, the LC-MTC UE returns to step ST9002 and continues discontinuous reception processing. If it is determined that reception is not possible, that is, reception is impossible, the LC-MTC UE determines that a predetermined transition condition is satisfied and transitions to step ST9004.

[0128] In Step ST9004, the LC-MTC UE moves out of service. The LC-MTC UE may determine to move out of service, for example, when the reception quality of the serving cell becomes equal to or lower than a predetermined threshold.

[0129] The predetermined threshold may be statically determined in advance by a standard, or may be newly established as a parameter of SI for LC-MTC UE and broadcast by the cell, or may be notified to the LC-MTC UE individually by RRC signaling by the cell. The predetermined threshold may be determined according to the terminal capability of the LC-MTC UE.

[0130] The LC-MTC UE maintains the discontinuous reception timer (DRX timer) even when it is out of range. By maintaining at least the discontinuous reception timer even when it is out of range, the LC-MTC UE can identify the discontinuous reception timing.

[0131] In Step ST9005, the LC-MTC UE determines whether the discontinuous reception timer has expired. If it determines that the discontinuous reception timer has not expired, that is, is incomplete, it performs the processing of Step ST9005 until the discontinuous reception timer expires. If it determines that the discontinuous reception timer has expired, it returns to Step ST9002, synchronizes with cell A on which the LC-MTC UE was camped before moving out of range, and performs discontinuous reception.

[0132] The LC-MTC UE should store information for synchronization with the cell it was camped on before moving out of range, as well as system information received from the cell, such as a cell identifier.

[0133] In the flowchart shown in Figure 9, when it is determined that the discontinuous reception timer has finished, the station synchronizes with the camped cell and begins discontinuous reception. Therefore, it is recommended to set the discontinuous reception timer taking into consideration the time required to achieve synchronization and the time required to begin discontinuous reception. For example, it is recommended to set the timer to a time earlier than the time when one discontinuous reception cycle has elapsed, or to a time shorter than the discontinuous reception cycle.

[0134] In this embodiment, the LC-MTC UE does not perform cell reselection processing, and therefore moves out of range if the reception quality of the serving cell, for example, the reception quality of the cell's reference signal (RS), such as RSRP (Reference Signal Received Power) or RSRQ (Reference Signal Received Quality), deteriorates.

[0135] Conventionally, when a UE moves out of range, it leaves the RRC_Idle state and resets the settings for the cell it was camped on, which also resets the discontinuous reception timer.

[0136] However, in this embodiment, even when the UE moves out of range, the discontinuous reception timer is maintained. By doing so, even if the UE moves out of range, it is possible to perform discontinuous reception again with the cell it was camped on using the discontinuous reception timer. If there is a paging message, the cell notifies the LC-MTC UE of the paging message at the discontinuous reception cycle, so that the LC-MTC UE can receive the paging message notified from the cell.

[0137] By using the method disclosed in this embodiment, an LC-MTC UE can maintain the RRC_Idle state even if it does not have information for cell reselection. Therefore, it becomes possible to receive paging messages. This allows the LC-MTC UE to receive commands and data notified from, for example, an MTC operator or an MTC server.

[0138] Furthermore, since the cell does not need to broadcast information for cell reselection to the LC-MTC UE, the amount of SI information to be broadcast can be reduced. Furthermore, since the LC-MTC UE does not perform cell reselection processing and cell selection processing, the power consumption of the LC-MTC UE can be reduced. Furthermore, since the number of processes can be reduced, the configuration is simplified and malfunctions as a system can be reduced.

[0139] It has been disclosed that a state in which the discontinuous reception timer is maintained when out of range, i.e., one of the RRC_Idle states, is provided, but in this case, the conventional process of transitioning to out of range becomes impossible.

[0140] It is preferable to newly provide a process for transitioning to a conventional out-of-service state. In an LC-MTC UE, transitioning to a conventional out-of-service state occurs when discontinuous reception has failed a predetermined number of times. If synchronization with a cell cannot be achieved at the timing of discontinuous reception, or if a control signal or a control channel cannot be received, it is preferable to determine that discontinuous reception has failed. In step ST9003 of FIG. 9, a case where reception is not possible due to deterioration of reception quality may be determined as a failure of discontinuous reception.

[0141] The case where the predetermined number of times of failure occurs may be a case where the predetermined number of times of failure occurs consecutively, or a case where the predetermined number of times of failure occurs over a predetermined period of time. Information necessary for the LC-MTC UE to move out of the conventional coverage area, such as the predetermined number of times or the predetermined period of time, may be determined in advance in a standard or the like, or may be broadcast as SI for the LC-MTC UE. Alternatively, it may be notified from the cell at the time of RRC connection at initial access.

[0142] By doing so, the LC-MTC UE does not maintain the discontinuous reception timer and does not continue the state of repeating discontinuous reception forever, which makes it possible to reduce the power consumption of the LC-MTC UE.

[0143] First embodiment, variant 1 This modification discloses another method for solving the problem described in the first embodiment. When an LC-MTC UE moves out of service area, it performs a cell selection process. Examples of triggers for starting the cell selection process may be when the UE moves out of service area, or when an intermittent reception timer expires after the LC-MTC UE moves out of service area.

[0144] The LC-MTC UE does not need to receive system information for cell reselection from the cell. The cell does not need to notify the LC-MTC of system information for cell reselection. The LC-MTC UE does not need to perform cell reselection processing when in RRC_Idle.

[0145] In this way, the LC-MTC UE is able to perform discontinuous reception and receive paging messages even if it does not have information for cell reselection.

[0146] If the trigger for starting the cell selection process is set to when the mobile station moves out of range, the cell selection process can be performed quickly, so that a good cell can be quickly detected in response to fluctuations in the radio wave propagation environment, and communication with the good cell can be quickly transitioned to.

[0147] If the trigger for starting the cell selection process is set to the completion of the discontinuous reception timer, cell detection is performed in accordance with the discontinuous reception cycle, so cell detection cannot be performed quickly and delays may occur. However, if the cell selection process selects the cell on which the LC-MTC UE was camped before moving out of range, unnecessary reception is avoided, which makes it possible to reduce the power consumption of the LC-MTC UE.

[0148] If the cell selection process is triggered by the completion of the discontinuous reception timer, the LC-MTC UE may maintain the discontinuous reception timer when moving out of range. The state in which the discontinuous reception timer is maintained while out of range may be considered a new state, or may be one of the RRC_Idle states.

[0149] When the LC-MTC UE selects a cell in the cell selection process, it is preferable that the LC-MTC UE does not necessarily perform the RRC connection establishment process.

[0150] After a cell is selected, if the selected cell belongs to the same tracking area (TA) as the cell before selection, the RRC connection establishment process is not performed, and the UE transitions to the RRC_Idle state in accordance with the broadcast information of the selected cell.

[0151] After selecting a cell, if the selected cell does not belong to the same tracking area (TA) as the cell before selection, an RRC connection establishment procedure is performed, and a TAU is performed.

[0152] By doing so, it is possible to omit the RRC connection establishment process after cell selection as necessary, thereby reducing the power consumption of the LC-MTC UE.

[0153] Although it has been disclosed that an LC-MTC UE may not necessarily perform an RRC connection establishment process when selecting a cell in a cell selection process, a periodic TAU may be performed. An RRC connection establishment process for a periodic TAU may be performed. This enables the core network to manage the mobility of the LC-MTC UE.

[0154] If the LC-MTC UE is unable to select a cell through the cell selection process, it transitions to a conventional out-of-service area.

[0155] The conventional out-of-service transition process disclosed in the first embodiment may be applied. In the LC-MTC UE, a cell selection process may be performed instead of discontinuous reception, and if the cell selection process fails a predetermined number of times, the conventional out-of-service transition may be performed. By doing so, cell selection becomes possible when there is temporary deterioration in the radio wave propagation environment.

[0156] Fig. 10 is an example of a flowchart showing processing of an LC-MTC UE in RRC_Idle mode in Modification 1 of Embodiment 1. Since the flowchart shown in Fig. 10 is similar to the flowchart shown in Fig. 9 described above, the same step numbers are assigned to the same steps, and common explanations will be omitted.

[0157] 10 shows an example in which the trigger for starting the cell selection process is when the discontinuous reception timer expires. The LC-MTC UE maintains the discontinuous reception timer even when it moves out of range.

[0158] After performing the processes of steps ST9001 to ST9004, in step ST9005, the LC-MTC UE determines whether or not the discontinuous reception timer has expired. If the discontinuous reception timer has not yet expired, the LC-MTC UE performs the process of step ST9005 until the discontinuous reception timer has expired. If the discontinuous reception timer has expired, the LC-MTC UE proceeds to step ST1001.

[0159] In Step ST1001, the LC-MTC UE starts a cell selection process.

[0160] In step ST1002, the LC-MTC UE selects cell X through a cell selection process.

[0161] In step ST1003, it is determined whether the selected cell X is the cell on which the mobile station was camped before moving out of service area. If it is determined in step ST1002 that the selected cell X is the cell on which the mobile station was camped before moving out of service area, the process returns to step ST9002 and performs discontinuous reception. Because the discontinuous reception timer is active in the cell on which the mobile station was camped before moving out of service area, discontinuous reception is immediately possible for that cell after it is determined that the discontinuous reception timer has expired.

[0162] If the selected cell X is the cell on which the LC-MTC UE was camped before moving out of service area, this makes it possible to omit the processes from step ST1004 to step ST1006, which are the processes performed after the LC-MTC UE selects a cell, thereby reducing the power consumption of the LC-MTC UE.

[0163] If it is determined in step ST1002 that the selected cell X is not the cell on which the mobile station was camped before moving out of service area, the mobile station moves to step ST1004.

[0164] In step ST1004, the UE receives broadcast information of the selected cell X and determines, based on the received broadcast information, whether the TAC of SIB1 of the selected cell X is the same as the TAC received from cell A on which the UE was camped before moving out of service area. If the TAC of SIB1 of the selected cell X is different from the TAC received from cell A, the UE proceeds to step ST1005, and if the TAC of SIB1 of the selected cell X is the same as the TAC received from cell A, the UE proceeds to step ST1006 while maintaining the RRC_Idle state.

[0165] In Step ST1005, the UE performs TAU via the selected cell X. After performing the TAU process, the UE returns to the RRC_Idle state and proceeds to Step ST1006.

[0166] In step ST1006, the UE camps on the selected cell X. When the UE camps on cell X, it returns to step ST9002 in accordance with the discontinuous reception cycle of the selected cell X and performs the processing of steps ST9002 to ST1006 described above again.

[0167] In step ST1002, if a cell cannot be selected through the cell selection process, the mobile station moves to the conventional out-of-service state.

[0168] In step ST1002, if the cell on which the mobile station was camped before moving out of service area is selected through the cell selection process, the mobile station may proceed to step ST1004 without proceeding to the discontinuous reception process of step ST9002. The determination process of step ST1003 may be omitted.

[0169] If the cell on which the mobile station was camped before moving out of range is selected, it will not be possible to immediately perform discontinuous reception, but the processing of step ST1003 can be omitted, which simplifies the control.

[0170] The LC-MTC UE should store information for synchronization with the cell it was camped on before moving out of range, as well as system information received from the cell, such as a cell identifier.

[0171] If the trigger for starting the cell selection process is the completion of the intermittent reception timer, the intermittent reception timer should be set taking into consideration the time required for the cell selection process, etc. For example, it should be set to a time earlier than the time when one intermittent reception cycle has elapsed, or to a time shorter than the intermittent reception cycle.

[0172] The method disclosed in this modification can provide the same effects as those of the first embodiment. Furthermore, since no cell reselection process is performed, it is possible to reduce the power consumption of the LC-MTC UE. Furthermore, since the number of processes can be reduced, the configuration is simplified and malfunctions of the system can be reduced.

[0173] In the method disclosed in the first embodiment, once a cell is selected at initial access, the serving cell does not change thereafter. In contrast, in this modification, when an LC-MTC UE moves out of range, a cell selection process is initiated, so that the serving cell can be changed.

[0174] Therefore, even if the radio wave propagation environment of the cell on which the mobile station was camped before moving out of service area deteriorates, a new cell can be selected, making it possible to build a stable communication system.

[0175] A new intermittent reception timer may be provided as an intermittent reception timer. This timer is an intermittent reception cycle timer that is valid when the intermittent reception timer is maintained outside the service area.

[0176] The new discontinuous reception timer may be common to the system, common to MTC or LC-MTC UEs, or per cell. Alternatively, the new discontinuous reception timer may be common to a predetermined group. Alternatively, the new discontinuous reception timer may be per LC-MTC UE.

[0177] The following five methods (1) to (5) are disclosed as specific examples of how the LC-MTC UE recognizes the new discontinuous receiving timer.

[0178] (1) It is statically determined in advance using standards, etc. It is effective to apply it when it is common to the system or common to LC-MTC UEs. It can reduce the amount of information that the cell notifies the LC-MTC UE.

[0179] (2) Notification by MIB. This is effective when applied to each cell. MIB is notified using six resource blocks (6RBs) in the center of the system band, so even LC-MTC UEs with reduced bandwidth can receive it.

[0180] (3) Notified by SI for LC-MTC UE. This is effective when applied to each cell or each LC-MTC UE. Reception is possible regardless of the RRC state of the LC-MTC UE (RRC_Idle, RRC_Connected).

[0181] (4) Notified by RRC signaling. In this case, notification may be made at the time of initial access. This may be applied to cases where notification is made for each cell or each LC-MTC UE. A larger number of parameters can be notified compared to when notifying by MIB and SI. Conversely, the amount of information notified by MIB and SI can be reduced.

[0182] (5) Multiple timer values ​​are statically determined in advance by standards, etc., and an indication corresponding to each timer value is provided. The indication can be included in the MIB or SI for the LC-MTC UE and notified to the LC-MTC UE. This is effective when applied per cell or per LC-MTC UE. The amount of information in the MIB or SI can be reduced.

[0183] Embodiment 1 Variation 2 This modification discloses another method for solving the problem described in the first embodiment. The LC-MTC UE performs cell selection processing during RRC_Idle. The cell selection processing may be performed before moving out of range. The cell selection processing may be performed instead of the conventional cell reselection processing.

[0184] The LC-MTC UE does not need to receive system information for cell reselection from the cell. The cell does not need to notify the LC-MTC of system information for cell reselection. The LC-MTC UE does not need to perform cell reselection processing when in RRC_Idle.

[0185] In this way, the LC-MTC UE is able to perform discontinuous reception and receive paging messages even if it does not have information for cell reselection.

[0186] Since there is no criteria for the cell selection process during RRC_Idle, in this modification, criteria for the cell selection process are provided. In particular, criteria for initiating the cell selection process during RRC_Idle are provided. Specifically, parameters for the criteria for initiating the cell selection process are provided. The cell notifies the LC-MTC UE of the parameters for the criteria. Examples of the parameters for the criteria include a measurement period for the reception quality of the serving cell, a measurement filter coefficient, a threshold, etc.

[0187] Only a threshold value for reception quality may be set as a parameter for the criteria. The measurement period for reception quality and the measurement filter coefficient may follow the conventional cell selection process. By setting only a threshold value for reception quality, it is possible to reduce the amount of information that the cell notifies to the LC-MTC UE. When a threshold value for cell selection process is set, the LC-MTC UE may be configured to initiate cell selection when the reception quality of the serving cell falls below the threshold value for cell selection process.

[0188] By doing so, the LC-MTC UE can start the cell selection process during RRC_Idle.

[0189] The threshold for initiating the cell selection process may be set to a value higher than the reception quality required for transitioning out of service in the past. Alternatively, the threshold may be set to a value higher than the reception quality or threshold for transitioning out of service disclosed in the first embodiment or the first modification of the first embodiment. In this way, the cell selection process can be initiated before the LC-MTC UE transitions out of service.

[0190] Conventionally, the cell reselection process is initiated using system information for the cell reselection process. However, an LC-MTC UE that cannot acquire the system information for the cell reselection process cannot perform the cell reselection process. Therefore, it is preferable that the LC-MTC UE perform the cell selection process.

[0191] However, conventionally, cell selection processing is initiated by the NAS (Non-Access Stratum). In this case, since a decision by the NAS is required during RRC_Idle, the processing becomes complicated. Therefore, it is preferable that the LC-MTC UE performs cell selection processing without requiring instructions from the NAS during RRC_Idle. The LC-MTC UE may also perform cell selection processing based on the decision of the AS (Access Stratum) during RRC_Idle.

[0192] The criteria parameters for initiating the cell selection process during RRC_Idle may be common to the system, common to MTC or LC-MTC UEs, or per cell. Alternatively, the criteria parameters may be common to a predetermined group. Alternatively, the criteria parameters may be per LC-MTC UE. Furthermore, the criteria parameters may be a combination of the above.

[0193] The following five methods (1) to (5) are disclosed as specific examples of methods by which the LC-MTC UE recognizes the parameters for criteria.

[0194] (1) It is determined statically in advance using standards, etc. It is effective when applied as a parameter common to the system or common to LC-MTC UEs. This reduces the amount of information that the cell notifies the LC-MTC UE.

[0195] (2) Notification by MIB. This is effective when applied as a parameter for each cell. MIB is notified in six resource blocks in the center of the system band, so even LC-MTC UEs with reduced bandwidth can receive it.

[0196] (3) Notified by SI for LC-MTC UE. This is effective when applied as a parameter for each cell or each LC-MTC UE. Reception is possible regardless of the RRC state of the LC-MTC UE (RRC_Idle, RRC_Connected).

[0197] (4) Notified by RRC signaling. In this case, it may be notified at the time of initial access. It is recommended to apply it as a parameter for each cell or each LC-MTC UE. It is possible to notify a larger number of parameters than when notifying by MIB and SI. Conversely, it is possible to reduce the amount of information notified by MIB and SI.

[0198] (5) Multiple parameter groups are statically determined in advance by standards, etc., and an indication corresponding to each parameter group is provided. The indication can be included in the MIB or SI for the LC-MTC UE and notified to the LC-MTC UE. This is effective when applied to parameters for each cell or each LC-MTC UE. This can reduce the amount of information in the MIB or SI.

[0199] Fig. 11 is an example of a flowchart showing processing of an LC-MTC UE in RRC_Idle mode in Modification 2 of Embodiment 1. The flowchart shown in Fig. 11 is similar to the flowchart shown in Fig. 10 described above, so the same step numbers are assigned to the same steps and common explanations will be omitted.

[0200] In Step ST1101, the LC-MTC UE receives from cell A a threshold value for initiating a cell selection process (hereinafter, may be referred to as a "cell selection activation threshold value").

[0201] In Step ST9001, the LC-MTC UE in the RRC_Idle state camps on cell A. In the example shown in FIG. 11, cell A notifies the LC-MTC UE of the system information for the LC-MTC UE.

[0202] In Step ST9002, the LC-MTC UE camped on cell A performs discontinuous reception.

[0203] In step ST1102, the LC-MTC UE determines whether the reception quality of the serving cell has fallen below the cell selection activation threshold, using the cell selection activation threshold received from cell A. If it determines that the reception quality of the serving cell has fallen below the cell selection activation threshold, it proceeds to step ST1001, and if it determines that the reception quality of the serving cell has not fallen below the cell selection activation threshold, it returns to step ST9002 and performs discontinuous reception operation.

[0204] In Step ST1001, the LC-MTC UE starts a cell selection process. In Step ST1002, the LC-MTC UE selects cell X through the cell selection process.

[0205] In step ST1103, the UE receives system information notified from the selected cell X. This system information includes a cell selection activation threshold for activating a cell selection process for cell X. That is, the UE receives the cell selection activation threshold by receiving the system information from the selected cell X.

[0206] In step ST1004, the LC-MTC UE that has received the cell selection activation threshold for cell X in step ST1103 determines whether the TAC in SIB1 of the selected cell X is the same as the TAC received from cell A on which it was camped immediately before, i.e., the cell A on which it was camped before moving out of service area. If the TAC in SIB1 of the selected cell X is different from the TAC received from cell A, the UE proceeds to step ST1005, and if the TAC in SIB1 of the selected cell X is the same as the TAC received from cell A, the UE proceeds to step ST1006 while remaining in the RRC_Idle state.

[0207] In Step ST1005, the UE performs TAU via the selected cell X. After performing the TAU process, the UE returns to the RRC_Idle state and proceeds to Step ST1006.

[0208] In step ST1006, the UE camps on the selected cell X. When the UE camps on cell X, it returns to step ST9002 in accordance with the discontinuous reception cycle of the selected cell X and performs the processing of steps ST9002 to ST1006 described above again.

[0209] In this way, the LC-MTC UE can perform cell selection processing during RRC_Idle. By performing the cell selection processing, it becomes possible to select a cell with good reception quality. By performing the cell selection processing, the LC-MTC UE in the RRC_Idle state can avoid situations where it moves out of service as much as possible.

[0210] Therefore, even if the reception quality of the serving cell continues to be poor due to changes in the radio wave propagation environment, it becomes possible to select another cell and perform communication in that cell, thereby enabling the construction of a stable communication system.

[0211] The LC-MTC UE maintains the RRC_Idle state during cell selection. The settings during RRC_Idle are maintained. When the LC-MTC UE selects a cell in the cell selection process, it is recommended that the LC-MTC UE does not necessarily perform the RRC connection establishment process.

[0212] After a cell is selected, if the selected cell belongs to the same TA as the cell before selection, the RRC connection establishment process is not performed, and the RRC_Idle state is maintained according to the broadcast information of the cell.

[0213] After a cell is selected, if the selected cell does not belong to the same TA as the cell before selection, an RRC connection establishment procedure is performed, and a TAU is performed.

[0214] By doing so, it is possible to omit the RRC connection establishment process after cell selection as necessary, thereby achieving low power consumption of the LC-MTC UE.

[0215] If the LC-MTC UE fails to select a cell through the cell selection process, it moves to a conventional out-of-service area. The conventional out-of-service area movement process disclosed in the first embodiment may be applied. As a cell selection process instead of discontinuous reception, the LC-MTC UE may move to a conventional out-of-service area when the cell selection process fails a predetermined number of times. This makes it possible to perform cell selection when there is temporary deterioration in the radio wave propagation environment.

[0216] Other methods of triggering the cell selection process may be to start the cell selection process at a predetermined timing or periodically. The LC-MTC UE performs the cell selection process at a predetermined cycle or at a predetermined timing. The predetermined cycle may be asynchronous with the discontinuous reception cycle, or may be an integer multiple or an integer fraction of the discontinuous reception cycle. In this way, it is possible to set the start of the cell selection process separately from the discontinuous reception cycle. Therefore, it is possible to flexibly start the cell selection process according to the installation environment and operation environment of the LC-MTC UE.

[0217] The method for setting the predetermined timing or the predetermined cycle may be the same as that for the new discontinuous reception timer disclosed in the first modification of the first embodiment. A combination of the predetermined timing or the predetermined cycle and a threshold may be used as a trigger for starting the cell selection process. This makes it possible to start the cell selection process more flexibly depending on the installation environment, operation environment, and radio wave propagation environment of the LC-MTC UE.

[0218] First embodiment, variant 3 This modification discloses another method for solving the problem shown in the first embodiment. The LC-MTC UE performs cell reselection processing during RRC_Idle. Here, the problem is how the LC-MTC UE recognizes parameters required for the cell reselection processing (hereinafter, sometimes referred to as "parameters for cell reselection processing"). This disclosure discloses a method for setting parameters for cell reselection processing of the LC-MTC UE, and a method for the LC-MTC UE to recognize parameters for cell reselection processing.

[0219] The parameters for cell reselection processing for LC-MTC UEs may be common to the system, common to MTC or LC-MTC UEs, or per cell, common to a predetermined group, or per LC-MTC UE, or a combination of the above.

[0220] The following five methods (1) to (5) are disclosed as specific examples of how an LC-MTC UE recognizes parameters for cell reselection processing.

[0221] (1) Determine statically in advance using standards, etc. This is effective when it is common across the system or common across LC-MTC UEs. This reduces the amount of information that the cell notifies the LC-MTC UE.

[0222] (2) Notification by MIB. This is effective when applied to each cell. MIB is notified in six resource blocks in the center of the system band, so even LC-MTC UEs with reduced bandwidth can receive it.

[0223] (3) Notified by SI for LC-MTC UE. This is effective when applied to each cell or each LC-MTC UE. Reception is possible regardless of the RRC state of the LC-MTC UE (RRC_Idle, RRC_Connected).

[0224] (4) Notified by RRC signaling. In this case, notification may be made at the time of initial access. This may be applied to cases where notification is made for each cell or each LC-MTC UE. A larger number of parameters can be notified than when notifying by MIB and SI. In addition, the amount of information notified by MIB and SI can be reduced.

[0225] (5) Multiple parameter groups for cell reselection processing are statically determined in advance by standards, etc., and indications corresponding to the groups are provided. The indications can be included in the MIB or SI for the LC-MTC UE and notified to the LC-MTC UE. This is effective when applied per cell or per LC-MTC UE. This can reduce the amount of information in the MIB or SI.

[0226] The above method may be applied to each parameter or each parameter group. The parameters for cell reselection processing of LC-MTC UE may be common to cells within a TA. Alternatively, the parameters for cell reselection processing of LC-MTC UE may be common to MTC or a predetermined group of LC-MTC UEs.

[0227] By doing so, when notifying by RRC signaling in the specific example (4) above, even if the LC-MTC UE performs cell reselection during RRC_Idle and selects a cell within the same TA, it becomes possible to continue using the parameters for the cell reselection process. If a cell within the same TA is selected, it becomes unnecessary to establish an RRC connection to that cell.

[0228] Therefore, the LC-MTC UE can continue to perform the cell reselection process. Also, by notifying by RRC signaling in the specific example (4), it is possible to reduce the amount of information notified by MIB and SI.

[0229] As another method, when an LC-MTC UE changes cells, an RRC connection may be established without fail. It is preferable to apply the method of notifying by RRC signaling in the specific example (4) above. By doing so, even if an LC-MTC UE performs cell reselection during RRC_Idle and selects a cell within the same TA, it is possible to establish an RRC connection and obtain the cell reselection parameters of the cell using RRC signaling.

[0230] If the LC-MTC UE needs to be notified of system information via RRC signaling in addition to cell reselection parameters, the LC-MTC UE may establish an RRC connection when changing cells. The LC-MTC UE may be notified of the system information during the RRC connection.

[0231] First embodiment, variant 4 In the first embodiment, it is disclosed that a reduction in the SI notified to the LC-MTC UE is required, and that the SI to be reduced includes parameters other than SIB1, SIB2, and SIB14, which are SIBs used for initial access.

[0232] This modification discloses another method for reducing SI. A part of the SI for cell reselection processing is reduced from the conventional SI. A part of the SI for cell reselection processing is reduced to provide the SI for cell reselection processing for the LC-MTC UE. The cell notifies the LC-MTC UE of the SI for cell reselection processing for the LC-MTC UE.

[0233] The following (1) to (7) are disclosed as examples of parameters to be reduced from among conventional parameters for cell reselection.

[0234] (1) Speed-related parameters. For example, "speedStateReselectionPars" and its parameters. Speed-related parameters are unnecessary for LC-MTC UEs that move within a predetermined cell and for LC-MTC UEs that do not move. Therefore, even if the speed-related parameters are reduced, the LC-MTC UE can still perform cell reselection processing.

[0235] (2) Parameters related to inter-frequency. For example, "cellReselectionServingFreqInfo" and its parameters, SIB5 and its parameters, etc. For LC-MTC UEs that operate at a predetermined carrier frequency, parameters related to inter-frequency are not required. Therefore, even if the parameters related to inter-frequency are reduced, the LC-MTC UEs can still perform cell reselection processing.

[0236] (3) Parameters related to inter-RAT (Radio Access Technology). For example, "cellReselectionServingFreqInfo" and its parameters, SIB6 and its parameters, etc. For an LC-MTC UE operating on a predetermined RAT, parameters related to inter-RAT are not required. Therefore, even if the number of parameters related to inter-RAT is reduced, the LC-MTC UE can still perform cell reselection processing.

[0237] (4) Priority-related parameters. For example, "cellReselectionPriority". Priority-related parameters are not required for LC-MTC UEs that operate at a predetermined carrier frequency. Therefore, even if priority-related parameters are reduced, the LC-MTC UEs can still perform cell reselection processing.

[0238] (5) Parameters related to the measurement band. For example, "q-QualMinWB". For an LC-MTC UE operating in a reduced band, the measurement band may be determined in advance to be the reduced band. In this case, parameters related to the measurement band are not required. Therefore, even if parameters related to the measurement band are reduced, the LC-MTC UE can still perform cell reselection processing.

[0239] (6) Parameters related to RSRQ. For example, "s-IntraSearchQ", "q-QualMinWB", etc. It is recommended that the LC-MTC UE decides in advance to use RSRP as the reception quality. In this case, parameters related to RSRQ are unnecessary. Therefore, even if the parameters related to RSRQ are reduced, the LC-MTC UE can still perform cell reselection processing. (7) It may be some or all of the above (1) to (6).

[0240] Of the conventional parameters for cell reselection, the following six parameters (1) to (6) are disclosed as examples of parameters that are not reduced.

[0241] (1) Parameters related to the initiation of cell reselection process. For example, "s-IntraSearchP", "s-IntraSearchQ", etc. The parameters related to the initiation of cell reselection process are parameters required to initiate the cell reselection process. By leaving the parameters related to the initiation of cell reselection process, the LC-MTC UE can initiate the cell reselection process.

[0242] (2) Parameters related to cell measurements in the cell reselection process. For example, "t-ReselectionEUTRA". The parameters related to cell measurements in the cell reselection process are parameters required to measure the reception quality of the cell in the cell reselection process. By leaving the parameters related to cell measurements in the cell reselection process, the LC-MTC UE can recognize how to perform cell measurements.

[0243] (3) Parameters related to cell selection in the cell reselection process. For example, "q-Hyst". The parameters related to cell selection in the cell reselection process are parameters required to execute the cell reselection criteria. By leaving the parameters related to cell selection in the cell reselection process, the LC-MTC UE can recognize how to select a cell.

[0244] (4) Intra-frequency parameters, such as SIB3 and its parameters. Intra-frequency parameters are required for LC-MTC UEs operating at a predetermined carrier frequency. By retaining the intra-frequency parameters, the LC-MTC UEs can perform intra-frequency cell reselection.

[0245] (5) Parameters related to a specific cell list. For example, "intraFreqNeighCellList", "intraFreqBlackCellList", "csg-PhysCellIdRange", etc. The parameters related to the specific cell list indicate whether cell reselection to a predetermined cell is possible. The parameters related to the specific cell list are also parameters required for an LC-MTC UE operating in a predetermined cell. By leaving the parameters related to the specific cell list, the LC-MTC UE can perform reselection processing to a predetermined cell. (6) It may be some or all of the above (1) to (5).

[0246] If some of the conventional SI for cell reselection processing is reduced to use it as the SI for cell reselection processing for an LC-MTC UE, it will not be possible to obtain all of the parameters required for the criteria for cell reselection processing. In this case, it is recommended to set new criteria for cell reselection processing that do not use the reduced parameters. The simplest approach is to set criteria that omit the reduced parameters.

[0247] For example, we disclose a case where the SI for the cell reselection process of an LC-MTC UE is only a parameter related to the initiation of the cell reselection process. The cell notifies the LC-MTC UE of the parameter "s-IntraSearchP" as the SI. The LC-MTC UE measures the reception quality of the serving cell, here RSRP, and initiates the cell reselection process when the measured value is equal to or less than the parameter "s-IntraSearchP". The criteria for the cell reselection process are as follows:

[0248] Rs = Qmeas,s, Rn = Qmeas,n The cell with the highest reception quality is selected from Rs and Rn, where Qmeas,s is the reception quality measurement value of the serving cell, and Qmeas,n is the reception quality measurement value of the neighboring cell.

[0249] The method by which an LC-MTC UE recognizes the SI for cell reselection processing, which is a part of the conventional SI for cell reselection processing, can be the method disclosed in the third modification of the first embodiment.

[0250] By doing so, it is possible to reduce a portion of the SI for the conventional cell reselection process and execute the cell reselection process using the SI for the cell reselection process of the LC-MTC UE. It is possible to more flexibly activate cell reselection according to the installation environment, operation environment, and radio wave propagation environment of the LC-MTC UE. By executing the cell reselection process, it is possible to eliminate situations where an LC-MTC UE in RRC_Idle state moves out of range as much as possible. Furthermore, by making it possible to reduce a portion of the SI, it is possible to reduce the required resources even when the SI is repeatedly notified.

[0251] Embodiment 2 In the cell selection process, the LC-MTC UE may select a distant cell depending on the radio wave environment. As described in the first embodiment, if the SI for cell reselection is reduced due to a request to reduce the SI of the LC-MTC UE, the cell reselection process of the LC-MTC UE will not be performed unless something is done.

[0252] In this case, the LC-MTC UE must continue camping on the previously selected distant cell until the next cell selection process is performed. In this case, the reception quality of the LC-MTC UE deteriorates, increasing the possibility of it moving out of range. When the LC-MTC UE moves out of range, it must perform a new cell selection process, establish an RRC connection, and perform an attach process or TAU process in response to instructions from the NAS. This causes a problem of increased power consumption for the LC-MTC UE.

[0253] The cell selection process has a stored information cell selection function (see Non-Patent Document 2). However, even if this function is available, if a distant cell is initially selected and no cell reselection process is performed, the information of the first distant cell is simply stored, and the distant cell will be selected in subsequent cell selection processes. Therefore, even if the stored information cell selection function is available, the problem of increased power consumption of the UE occurs.

[0254] This embodiment discloses a method for solving this problem: Priority is set in the cell selection process.

[0255] As examples of information for setting priorities, the following three items (1) to (3) will be disclosed. (1) Carrier frequency information, which may be indicated by ARFCN (Absolute Radio Frequency Channel Number). (2) Cell information. This may be a cell identifier. PCI may also be used. (3) A combination of (1) and (2) above.

[0256] It is preferable to set the information together with the priority. It becomes possible to recognize carrier information for cell selection with priority, or cell information for cell selection with priority. The priority may be common to the system, common to MTC or LC-MTC UE, or for each cell. It may be common to a predetermined group. Or it may be for each LC-MTC UE. Furthermore, a combination of the above is also possible.

[0257] The method by which the LC-MTC UE recognizes the priority may be the same as the method by which the LC-MTC UE recognizes a new discontinuous reception timer disclosed in Variant 1 of Embodiment 1. As another method, the timer may be stored in the SIM. The timer may be stored separately for each registered operator. The timer may be stored in association with the UE capability. In this way, the LC-MTC UE can recognize the priority in the cell selection process. It is advisable to set a maximum number of priority settings. This makes it possible to reduce the amount of information to be notified to the LC-MTC UE.

[0258] As examples of entities that set priorities, the following three entities (1) to (3) are disclosed. (1) eNB (cell). (2) MME. In this case, the MME notifies the eNB of the priority. It is preferable to notify using the S1 interface. (3) Operator. In this case, the operator notifies the eNB of the priority. The notification may be made via the MME. The operator may also write the priority into the SIM of the LC-MTC UE.

[0259] An example of a method for deriving the priority is disclosed below. The priority is determined according to the installation location of the LC-MTC UE. The eNB may obtain the installation location of the LC-MTC UE using a location system. Alternatively, the eNB may obtain the installation location of the LC-MTC UE using a function for MDT (minimization of drive tests). Alternatively, an operator may obtain information on the installation location of the LC-MTC UE.

[0260] Alternatively, the priority may be determined based on the measurement report results of the LC-MTC UE. For example, the eNB receiving the measurement report of the serving cell or neighboring cells of the LC-MTC UE averages or filters the measurement results for a predetermined period. From the average or filtered results, the carrier frequency or cell with the best reception quality may be derived and set as the highest priority. Priorities may also be set in descending order of reception quality.

[0261] By using the method disclosed in this embodiment, it is possible to select a cell in order of priority, instead of selecting a cell with the best reception quality in the conventional cell selection process. In this way, even if a cell reselection process is not performed in the LC-MTC UE, it is possible to reduce the power consumption of the LC-MTC UE. When performing a cell selection process, it is possible to select a cell with a high priority, so it is possible to reduce the power consumption of the LC-MTC UE.

[0262] Second embodiment, variant 1 This modification discloses another method for solving the problem shown in the second embodiment. Candidates for cell selection are provided. One or more candidates for cell selection are provided. The method disclosed in the second embodiment can be applied to examples of information for providing candidates for cell selection, a method for an LC-MTC UE to recognize candidates for cell selection, and an entity that determines candidates for cell selection. The number of candidates for cell selection may be a predetermined number in descending order of priority.

[0263] This paper discloses a method for deriving a cell to be selected from cell selection candidates. The LC-MTC UE detects cells among the candidates during cell selection. For the detected cells, the LC-MTC UE stores not only carrier frequency information or cell information but also reception quality, specifically, RS reception quality of at least one of RSRP and RSRQ. The LC-MTC UE prioritizes the cells in descending order of reception quality and performs cell selection based on the highest reception quality.

[0264] By doing this, the priority order is updated every time among the cell selection candidates, which makes it possible to flexibly respond to changes in the radio wave propagation environment and reduce the power consumption of LC-MTC UEs.

[0265] Embodiment 3 In LC-MTC, which requires an extended coverage, paging repetition is being considered. By repeating transmissions, the reception quality of LC-MTC UEs in the extended coverage area can be improved.

[0266] Conventionally, paging repetition has not been performed, so new paging repetition methods are being discussed in 3GPP. Non-Patent Document 11 discloses a paging repetition method in which paging transmission is repeated over multiple subframes.

[0267] However, no details of the subframe structure in which paging is transmitted are disclosed, so that the LC-MTC UE does not know which subframe to receive and is unable to receive paging including repetition.

[0268] This embodiment discloses a detailed method for paging repetition. Paging transmission including repetition is performed over multiple radio frames. It is preferable to transmit paging in consecutive radio frames. The initial transmission of paging should be in a radio frame and subframe derived according to a conventional method for deriving a paging frame (PF) and a paging occasion (PO) (see Non-Patent Document 2).

[0269] The PF and PO are derived using discontinuous reception (DRX) parameters such as the DRX cycle notified by higher layer signaling, and the UE identifier (UE-ID). The PO is limited to subframes with subframe numbers 0, 4, 5, and 9 in Frequency Division Duplex (FDD), and to subframes with subframe numbers 0, 1, 5, and 9 in Time Division Duplex (TDD).

[0270] The radio frames for repetitively transmitting paging are transmitted consecutively from the initial radio frame. The subframes for repetitively transmitting paging are the same as the subframe numbers derived for the initial transmission. The LC-MTC UE receives the initial and repetitive paging in the radio frames and subframes derived in this way.

[0271] This allows LC-MTC UEs to receive paging messages that include repetition, so that even LC-MTC UEs in an extended coverage area can receive paging messages.

[0272] The LC-MTC UE may not receive all of the initial transmission and repetition transmission, but may terminate reception of the repetition transmission once the desired reception quality is achieved. This reduces the reception operation of the LC-MTC UE, thereby reducing power consumption. Furthermore, paging reception can be terminated early and post-paging reception operations can be started early, thereby reducing delay time.

[0273] Fig. 12 is a conceptual diagram showing an example of a paging repetition transmission method in the third embodiment. In Fig. 12, a paging frame (PF) which is a radio frame RF in which the initial transmission of paging is performed is indicated by reference symbol "121." Furthermore, the configuration of a subframe SF in the radio frame RF is indicated by reference symbol "122."

[0274] The radio frame RF consists of 10 subframes SF numbered 0 to 9. The subframes SF hatched with diagonal lines are paging occasions (PO), which are the subframes SF in which the first transmission of paging takes place. Here, the subframe number of the PO, which is the subframe SF in which the first transmission of paging takes place, is set to "9".

[0275] In Fig. 12, the radio frame RF in which paging repetition transmission is performed is indicated by the reference symbol "123." Repetition transmission paging is transmitted consecutively for the number of repetitions starting from PF, the radio frame RF in which the initial transmission of paging is performed. Here, the number of repetitions is set to "2." The configuration of subframes SF in the radio frame RF in which paging repetition transmission is performed is the same as the configuration of subframes SF in PF, the radio frame RF in which the initial transmission of paging is performed.

[0276] Therefore, the subframe number of the subframe in which paging repetition transmission is performed is 9. The radio frame PF / PO in which the initial paging transmission is performed, and the radio frame RF and subframe SF in which repetition transmission is performed are repeatedly transmitted in an intermittent reception period T.

[0277] The number of paging repetitions may be determined for each cell or for each LC-MTC UE. The number of repetitions may be determined by the cell. The cell may determine the number of repetitions using the reception quality, CQI, CSI, etc., of the LC-MTC UE. Alternatively, the cell may acquire the capabilities of the LC-MTC UE and determine the number of repetitions using the capabilities. The following two methods (1) and (2) are disclosed as specific examples of methods for the LC-MTC UE to recognize the number of paging repetitions.

[0278] (1) Notification by SI for LC-MTC UE. This is effective when applied to each cell or each LC-MTC UE. This makes it possible to receive the number of paging repetitions regardless of the RRC state (RRC_Idle, RRC_Connected) of the LC-MTC UE.

[0279] (2) Notification by RRC signaling. In this case, notification may be performed at the time of initial access. This may be applied to cases where notification is performed for each cell or each LC-TC UE. This allows a larger number of parameters to be notified than when notifying by MIB and SI. Also, the amount of information to be notified by MIB and SI can be reduced.

[0280] In this way, the LC-MTC UE can receive the initial transmission and repetition transmission of the paging.

[0281] Although the method of transmitting paging repetitions in consecutive radio frames from the initial transmission has been described, another method will be disclosed. Repetitions of paging may be transmitted at predetermined radio frame intervals from the initial transmission.

[0282] For example, if the number of paging repetitions is 2, the predetermined radio frame interval is 3, and the radio frame number of the radio frame in which the first paging is transmitted is 25, the first repetition is transmitted in the radio frame with radio frame number 28, and the second repetition is transmitted in the radio frame with radio frame number 31. If the predetermined radio frame interval is 1, it is preferable to transmit the paging in consecutive radio frames.

[0283] This allows flexible resource scheduling even when paging is repeated.

[0284] The predetermined radio frame interval may be statically determined in advance by a standard or the like. Alternatively, it may be determined for each cell or for each LC-MTC UE. The LC-MTC UE may recognize the predetermined radio frame interval by applying a method for recognizing the number of paging repetitions. In this way, the LC-MTC UE can recognize the predetermined radio frame interval and receive the initial transmission and repetition transmission of paging.

[0285] The period derived from the number of repetitions and the radio frame interval at which paging is transmitted may be set to be smaller than the discontinuous reception cycle T. By doing so, only the same page is transmitted within the same discontinuous reception cycle, and the LC-MTC UE does not receive multiple pages within the same discontinuous reception cycle. This makes it possible to simplify the paging process in the LC-MTC UE.

[0286] By using the method disclosed in this embodiment, the LC-MTC UE can receive the repetition transmission of the paging, and can receive the paging while satisfying the requirement of the coverage extension, thereby making it possible to build a stable communication system.

[0287] Furthermore, by performing repetition transmission of paging in consecutive radio frames or at predetermined radio frame intervals, the subframes in which repetition transmission of paging is performed can be the subframes in which conventional paging is transmitted, which allows repetition transmission of paging to be performed without affecting the MBSFN subframe settings.

[0288] In Fig. 12, the subframe in which paging repetition transmission is performed is the same as the subframe in which paging initial transmission is performed, but a case where it is a different subframe will be disclosed. The subframe in which paging repetition is performed may be derived using the repetition number. For example, in FDD, when the repetition number is 2, the first repetition transmission is performed in the subframe with subframe number 0, and the second repetition transmission is performed in the subframe with subframe number 4.

[0289] As another example, the subframe in which the nth (n is a natural number) repetition transmission is performed may be the subframe with the subframe number associated with the value obtained by "n mod 4".

[0290] For example, in the case of FDD, when the value obtained by "n mod 4" is 0, the subframe number may be 0; when the value obtained by "n mod 4" is 1, the subframe number may be 4; when the value obtained by "n mod 4" is 2, the subframe number may be 5; and when the value obtained by "n mod 4" is 3, the subframe number may be 9.

[0291] Here, "n mod 4" is the remainder when "n" is divided by "4", which is the number of subframes in which paging is repeated. The number of subframes in which paging is repeated does not have to be 4, but it should be at least 1 and at most 10.

[0292] In this way, by setting the subframes in which paging repetition transmission is performed to subframes with subframe numbers corresponding to the value obtained by "n mod 4", it becomes possible to distribute the subframes in which repetition transmission is performed among multiple subframes, thereby enabling more flexible scheduling. These derivation methods may be statically determined in advance by standards, etc.

[0293] The subframe number associated with the value obtained by "n mod 4" may be a subframe number in which conventional paging transmission is possible. By doing so, the subframe in which paging repetition transmission is performed can be the subframe in which conventional paging is transmitted, so that paging repetition transmission can be performed without affecting the MBSFN subframe setting.

[0294] Third embodiment, variant 1 In the method disclosed in the third embodiment, paging is repeatedly transmitted over multiple radio frames according to the paging repetition count. Therefore, the delay until the LC-MTC UE receives the paging increases. This causes a delay in receiving information included in the paging, such as incoming call information, SI modification, Earthquake and Tsunami Warning System (ETWS) indication, and Commercial Mobile Alert System (CMAS) indication, resulting in a control delay.

[0295] This modification discloses a method for reducing this control delay. Repetition transmission of paging is performed in subframes consecutive to the subframe in which the initial transmission of paging is transmitted. The initial transmission of paging may be performed in a radio frame and subframe derived according to the conventional method for deriving PF and PO, as in the method disclosed in the third embodiment.

[0296] In this way, the LC-MTC UE can receive paging messages including repetition with a small delay.

[0297] Fig. 13 is a conceptual diagram showing an example of a paging repetition transmission method in Modification 1 of Embodiment 3. In Fig. 13, PF, which is the radio frame RF in which the initial transmission of paging is performed, is indicated by reference symbol "131". Furthermore, the configuration of subframes SF within PF, which is the radio frame RF in which the initial transmission of paging is performed, is indicated by reference symbol "132". The first subframe SF hatched with diagonal lines is PO, which is the subframe SF in which the initial transmission of paging is performed. Here, the subframe number of PO, which is the subframe SF in which the initial transmission of paging is performed, is set to "9".

[0298] In Fig. 13, the radio frame RF in which paging repetition transmission is performed is indicated by reference symbol "133." Furthermore, the subframe SF in which paging repetition transmission is performed is indicated by reference symbol "134." Repetition transmission paging is transmitted consecutively for the repetition number (abbreviated as RPN) starting from PO, which is the subframe SF in which paging is initially transmitted. Here, the repetition number (RPN) is set to "2."

[0299] The subframe SF in which the paging repetition transmission is performed may span multiple radio frames RF. Here, among the subframes SF of the radio frame RF next to the radio frame RF131 in which the initial paging transmission is performed, the paging repetition transmission is performed in the subframes SF with subframe numbers 0 and 1. The PF / PO in which the initial paging transmission is performed, and the radio frame RF and subframe SF in which the repetition transmission is performed are repeatedly transmitted in the discontinuous reception cycle T.

[0300] In the above-described method, the repetition transmission of paging is transmitted in consecutive subframes from the initial transmission. Alternatively, the repetition transmission of paging may be transmitted at predetermined subframe intervals from the initial transmission.

[0301] For example, if the number of paging repetitions is 2, the predetermined subframe interval is 3, the radio frame number of the radio frame in which the initial paging transmission is performed is 25, and the subframe number of the subframe is 9, the first repetition is transmitted in subframe number 2 of the radio frame number 26. The second repetition is transmitted in subframe number 5 of the radio frame number 26. If the predetermined subframe interval is 1, it is preferable to transmit in consecutive subframes.

[0302] This allows flexible resource scheduling even when paging is repeated.

[0303] The predetermined radio frame interval may be statically determined in advance by a standard or the like. Alternatively, it may be determined for each cell or for each LC-MTC UE. The method by which the LC-MTC UE recognizes the predetermined radio frame interval may be the method of recognizing the number of paging repetitions disclosed in the third embodiment. In this way, the LC-MTC UE can recognize the predetermined radio frame interval and can receive the initial transmission and repetition transmission of paging.

[0304] Alternatively, the subframes in which paging repetitions are transmitted may be limited to the subframes in which conventional paging is transmitted, e.g., subframes numbered 0, 4, 5, and 9 in FDD.

[0305] For example, if the number of paging repetitions is 2, the predetermined subframe interval is 1, the radio frame number of the radio frame in which the initial paging transmission is performed is 25, and the subframe number of the subframe is 9, the first repetition is transmitted in the subframe with subframe number 0 in the radio frame with radio frame number 26. The second repetition is transmitted in the subframe with subframe number 4 in the radio frame with radio frame number 26.

[0306] By doing this, when paging is repeated, the subframe can be set to the subframe in which conventional paging is transmitted, so that repetition transmission of paging can be performed without affecting the setting of MBSFN subframes.

[0307] By using the method disclosed in this modification, the LC-MTC UE can receive repetition transmission of paging, so that it can receive paging while satisfying the requirement of coverage extension, thereby making it possible to build a stable communication system.

[0308] Furthermore, the LC-MTC UE can receive paging including repetition with a smaller delay than the method disclosed in the third embodiment. Therefore, it is possible to reduce the control delay for paging notification. This is particularly effective for notification of an ETWS indication, which has an urgent nature.

[0309] Third embodiment, variant 2 When MBSFN subframes are configured in a cell, a new problem arises: since paging cannot be transmitted or received in MBSFN subframes, conventionally, POs, which are subframes in which paging is transmitted, are limited to subframes in which MBSFN subframes cannot be configured.

[0310] In this situation where the subframes in which PO can be configured are limited, if paging repetition is performed as disclosed in the first modification of the third embodiment, a subframe in which repetition transmission is performed may collide with an MBSFN subframe. If a subframe in which repetition transmission is performed collides with an MBSFN subframe, paging cannot be transmitted in the MBSFN subframe, which causes a problem that the LC-MTC UE cannot receive paging.

[0311] This modification discloses a method for solving this problem. Paging transmission is enabled in MBSFN subframes. To enable paging transmission, control information for paging (Downlink Control Information: DCI) is transmitted in MBSFN subframes.

[0312] The control information for paging is mapped to an EPDCCH (Enhanced Physical Downlink Control Channel) or a PDCCH. The EPDCCH or PDCCH to which the control information for paging is mapped is transmitted in an MBSFN subframe. The PDSCH to which paging is mapped is transmitted in the same subframe as the subframe in which the control information for paging is transmitted.

[0313] Alternatively, the control information for paging may include information about the subframe to which the PDSCH to which the paging is mapped is mapped, thereby enabling the PDSCH to which the paging is mapped and the control information for paging to be transmitted in different subframes.

[0314] The control information for paging is masked with a Paging Indication-Radio Network Temporary Identifier (PI-RNTI), and by detecting the PI-RNTI, the LC-MTC UE can recognize the presence of paging and receive the control information for paging. By receiving the control information for paging, the LC-MTC UE can receive scheduling information for a PDSCH to which paging is mapped. The LC-MTC UE receives the PDSCH in accordance with the scheduling information for the PDSCH to which paging is mapped, and receives the paging.

[0315] In addition to the repetition transmission of paging, the initial transmission of paging may be transmitted in the MBSFN subframe. In this case, the subframe (PO) in which paging is transmitted may be set in addition to the conventional subframe number. This increases the number of subframes in which PO can be set, making it possible to handle an increased number of MTC UEs Ns in order to handle a huge number of MTCs.

[0316] Alternatively, in MBSFN subframes, paging control information may not be transmitted, and a PDSCH onto which paging is mapped may be transmitted. In MBSFN subframes, only repetition transmission may be performed, and the control information for paging repetition may be the same as the control information for the initial transmission. The scheduling information for the PDSCH onto which the initial transmission and the repetition transmission are mapped may be the same. By acquiring the scheduling information for the PDSCH onto which the initial transmission is mapped, the LC-MTC UE can receive the PDSCH onto which the repetition transmission is mapped.

[0317] Alternatively, the control information for the initial transmission of paging may include control information for paging repetition. In addition to the scheduling information for the PDSCH to which the initial transmission is mapped, the scheduling information for the PDSCH to which the repetition transmission is mapped is included. In this way, the LC-MTC UE can obtain the scheduling information for the PDSCH to which the repetition transmission is mapped by receiving the control information for the initial transmission of paging, and can receive the PDSCH.

[0318] Alternatively, the control information for the initial paging transmission may include information about the subframe in which the paging repetition transmission is performed. The subframe information may include information indicating the subframe number, information indicating the radio frame number, etc. The scheduling information of the PDSCH to which the initial paging transmission and the repetition transmission are mapped may preferably be the same.

[0319] By doing this, the LC-MTC UE can recognize the subframe in which the repetition transmission is performed by obtaining the scheduling information of the PDSCH to which the initial transmission is mapped, and can receive the PDSCH to which the repetition transmission is mapped in that subframe.

[0320] It is preferable to limit MBSFN subframes in which paging is transmitted to subframes in which PMCH is not transmitted. By doing so, it is possible to transmit paging even if there is a subframe in the MBSFN subframe in which PMCH, which is a physical channel for MBMS, is mapped. In this case, for example, it is preferable to use a method in which the eNB specifies subframes in which the above-mentioned repetition transmission is performed. It is only necessary to specify subframes in the MBSFN subframe in which PMCH is not mapped for repetition transmission.

[0321] By using the method disclosed in this modification, it is possible to transmit paging in MBSFN subframes, which solves the problem of LC-MTC UEs being unable to receive paging due to collision between subframes in which paging repetition transmissions are performed and MBSFN subframes. This allows LC-MTC UEs to receive paging repetition transmissions, which enables them to receive paging while satisfying the requirement for coverage extension. Therefore, it is possible to build a stable communication system.

[0322] Furthermore, the LC-MTC UE can receive paging including repetition with a smaller delay than the method disclosed in the third embodiment. Therefore, it is possible to reduce the control delay for paging notification. This is particularly effective for notification of an ETWS indication, which has an urgent nature.

[0323] The method disclosed in this modification may also be applied to a subframe for transmitting system information (SI) disclosed in a fifth embodiment described later. System information may be used instead of paging. DCI for SI may be masked with SI-RNTI (System Information-Radio Network Temporary Identifier). This enables SI to be transmitted in an MBSFN subframe. LC-MTC UEs can receive SI. Similar effects as those described above can be obtained.

[0324] The method disclosed in this modification may also be applied to a subframe for transmitting a random access response (RAR). RAR may be used instead of paging. DCI for RAR may be masked with a Random Access-Radio Network Temporary Identifier (RA-RNTI). This enables RAR to be transmitted in an MBSFN subframe. LC-MTC UEs can receive RAR. Similar effects to those described above can be achieved.

[0325] The number of LC-MTC UEs is expected to become enormous. Therefore, the number of subframes for transmitting paging may be increased. As described above, the conventional number is four, but it is preferable to increase this to five or more. In this case, the subframes in which PO occurs may be provided across multiple radio frames. The method disclosed below may be applied.

[0326] Another method for solving the above-described problem disclosed in this modification will be disclosed below: The subframes in which paging repetition transmission is performed are determined from subframes excluding MBSFN subframes.

[0327] FIG. 14 is a diagram showing an example of a sequence in which subframes in which paging repetition transmission is performed are determined from subframes excluding MBSFN subframes according to the second modification of the third embodiment.

[0328] In Step ST1401, the MCE notifies the eNB of MBSFN subframe configuration information.

[0329] In step ST1402, the eNB determines the MBSFN subframe configuration. At this time, the eNB may determine the MBSFN subframe configuration by taking into consideration MBSFN subframes required for purposes other than MBMS for each cell. In this manner, the MBSFN subframe configuration for the cell is determined.

[0330] In Step ST1403, the LC-MTC UE notifies the eNB of UE capability information. The UE capability information is notified by using dedicated RRC signaling. The eNB that receives the UE capability information recognizes that the UE is an LC-MTC UE.

[0331] In step ST1404, the eNB determines whether repetition is necessary based on the downlink reception quality report from the LC-MTC UE and the uplink reception quality of the LC-MTC UE. A predetermined threshold may be set and used to determine whether repetition is necessary. If it is determined that repetition is necessary, the eNB proceeds to step ST1405, and if it is determined that repetition is not necessary, the eNB proceeds to step ST1407.

[0332] In step ST1405, the eNB determines the repetition factor. In this case, too, it is preferable to set a threshold value according to the repetition factor and determine the repetition factor using the threshold value. The process of step ST1404 and the process of step ST1405 may be performed together.

[0333] In Step ST1406, the eNB determines a subframe configuration for repetition. It is preferable to select subframes equal to the number of repetitions from subframes excluding subframes configured as MBSFN subframes.

[0334] In Step ST1407, the eNB notifies the LC-MTC UE of the number of repetitions and information on the subframe configuration for repetition.

[0335] The LC-MTC UE that has received the information on the number of repetitions and the subframe configuration for repetitions performs discontinuous reception in step ST1408. In this case, it receives paging for the number of repetitions. The LC-MTC UE determines that the initial transmission of paging will be performed using PF / PO, and determines that repetitions will be performed in subframes for repetitions for the number of repetitions notified in step ST1407.

[0336] The location in the repetition subframes where paging repetition is performed may be determined in advance by a standard or the like. For example, it may be determined that repetition transmission is performed in ascending order of subframe numbers within the repetition subframes, starting from the subframe (PO) of the initial paging transmission. Alternatively, the eNB may associate the repetition numbers with the repetition subframes of the corresponding numbers and notify the UE of this association in step ST1407. If the number of repetition subframes is small and insufficient for the number of repetitions, it may be preferable to use the repetition subframes of the next radio frame.

[0337] This allows the UE to receive paging repetitions. It also prevents collisions between paging repetition transmissions and MBSFN subframes. It also allows subframes that are not actually used as MBSFN subframes to be used for repetition transmissions. This allows for early paging transmissions, enabling the UE to receive paging early, thereby reducing paging processing delays.

[0338] If the MBSFN subframe configuration is changed after the repetition subframe configuration is determined, the repetition subframe configuration should be determined again. The re-determined repetition subframe configuration should be notified to the LC-MTC UE. This allows for flexible operation of MBMS and other applications that use MBSFN subframes.

[0339] Furthermore, when the eNB configures MBSFN subframes for each cell for purposes other than MBMS, it may configure the MBSFN subframes for each cell for that purpose, taking into account the number of repetitions required for LC-MTC UEs. It is recommended to reserve the number of repetitions required for LC-MTC UEs and use the remaining subframes as MBSFN subframes. This allows for the transmission of repetitions to LC-MTC UEs to be prioritized, further reducing paging processing delays.

[0340] Third embodiment, variant 3 Conventionally, paging is received as follows: A PDCCH in a subframe (PO) in a radio frame (PF) derived using a UE identifier is received, and the PI-RNTI masked in the control information for paging (hereinafter sometimes referred to as "paging control information") is detected, thereby receiving the paging control information. An LC-MTC UE receives a PDSCH to which paging is mapped according to the received paging control information.

[0341] For LC-MTC UEs that support coverage extension, not only paging repetition but also PDCCH repetition transmission, to which paging control information is mapped, is required. By performing repeated transmission, the reception quality of the PDCCH for LC-MTC UEs in the extended coverage range is improved, enabling the LC-MTC UEs to receive the paging control information.

[0342] As a repetition transmission method of the PDCCH onto which the paging control information is mapped and a PDCCH reception method for the LC-MTC UE, the methods disclosed in the third embodiment to the second modification of the third embodiment may be applied.

[0343] The following two examples (1) and (2) are disclosed as examples of the relationship between the repetition transmission method of the PDCCH to which the paging control information is mapped and the repetition transmission method of paging.

[0344] (1) After the initial transmission and repetition transmission of the PDCCH are completed, the initial transmission and repetition transmission of the paging are performed. The initial transmission of the paging is performed in the same subframe as the last repetition transmission of the PDCCH or in a subframe k subframes later (k is an integer equal to or greater than 1).

[0345] (2) The initial transmission of the PDCCH and the initial transmission of the paging are performed in the same subframe, and each repetition transmission of the PDCCH and each repetition transmission of the paging are performed in the same subframe.

[0346] In the above-described method (1), the LC-MTC UE can start receiving paging after receiving the PDCCH to which paging control information, including repetition, is mapped. Therefore, the LC-MTC UE can acquire paging control information, such as scheduling information for resources to which paging is mapped, by receiving the PDCCH including repetition. The LC-MTC UE can receive the PDSCH to which paging is mapped using the acquired information.

[0347] In the case of the above-mentioned method (1), compared to the above-mentioned method (2), there is no need to store information about the subframes in which the initial transmission and repetition of the PDCCH are performed. Therefore, there is no need to provide a memory or buffer for storage, and the configuration of the LC-MTC UE can be simplified.

[0348] In the above-mentioned method (2), the PDCCH to which the paging control information is mapped and the paging are transmitted in the same subframe. In this case, the LC-MTC UE may store reception information for the number of subframes equal to the sum of the initial transmission and the maximum number of repetitions. If the LC-MTC UE can receive the PDCCH to which the paging control information is mapped, it can also receive the paging transmitted in the same subframe using the paging control information. The LC-MTC UE may be provided with a memory and a buffer for storage. In this case, the LC-MTC UE can receive the paging earlier than in the above-mentioned method (1), thereby reducing the control delay time.

[0349] An LC-MTC UE that supports bandwidth reduction cannot receive a conventional PDCCH transmitted across the system bandwidth, and therefore cannot receive paging using a conventional paging transmission / reception method.

[0350] This modification discloses a method for solving this problem. Paging for LC-MTC UEs is mapped to a PDSCH. Control information for paging for LC-MTC UEs, such as scheduling information for the PDSCH to which paging is mapped, is mapped to an EPDCCH. The EPDCCH is mapped to a predetermined number of resource blocks (RBs) in the PDSCH region within one subframe. This makes it possible to narrow the bandwidth of the resources to which paging control information is mapped, enabling LC-MTC UEs that support bandwidth reduction to receive paging.

[0351] The RNTI masked on the paging control information on the EPDCCH may be the PI-RNTI. Alternatively, a new RNTI may be provided for LC-MTC UEs. For example, MTC-PI-RNTI may be used. By providing a new RNTI for LC-MTC UEs, it becomes possible to distinguish them from conventional UEs. By using MTC-PI-RNTI when detecting control information, it is possible to confirm that the control information is for LC-MTC UEs, thereby reducing malfunctions.

[0352] Paging control information for conventional UEs (legacy UEs) may be transmitted using a PDCCH, and paging control information for LC-MTC UEs may be transmitted using an EPDCCH. In this case, the paging control information mapped to the EPDCCH may be masked with an MTC-PI-RNTI. When an LC-MTC UE receives an EPDCCH on a subframe of a PF / PO derived for paging and detects paging control information masked with an MTC-PI-RNTI, the LC-MTC UE receives a PDSCH in accordance with the control information to receive paging.

[0353] As described above, when the EPDCCH is used to transmit paging control information, a further problem occurs. Because the EPDCCH is transmitted in a predetermined resource block (RB), the LC-MTC UE does not know which resource in the subframe of the PF / PO derived for paging the EPDCCH is transmitted in. Therefore, the LC-MTC UE cannot receive the EPDCCH.

[0354] A solution to this problem is disclosed in Non-Patent Document 12. Specifically, Non-Patent Document 12 discloses a scheduling method for an EPDCCH for paging. This method involves mapping an EPDCCH for common messages including SIB, paging, and RAR to six resource blocks at the center of a carrier, or including information in an MIB as to whether the resource block of the EPDCCH is located at a predetermined position or whether frequency hopping is performed.

[0355] However, if the resources onto which the paging EPDCCH is mapped are fixed to the six resource blocks at the center of the carrier, the resource is susceptible to frequency fading, resulting in a problem of degradation in reception quality. Furthermore, when frequency hopping is performed, the method of notifying the frequency hopping pattern becomes an issue. If the information is included in the MIB and notified, the amount of information in the MIB increases. Furthermore, since the MIB is notified repeatedly, a large amount of resources are required. Therefore, there is a problem of reduced resource usage efficiency.

[0356] This modification discloses a method for solving such a problem. A resource for transmitting the EPDCCH, to which the paging control information is mapped, is determined in advance based on a standard or the like.

[0357] As examples of information regarding the resource on which the EPDCCH is transmitted, the following seven items (1) to (7) are disclosed. (1) Number of resource blocks (RB). (2) RB allocation. This can be the first RB number. (3) RS (Reference Signal) configuration. This can be the RS sequence or sequence number. (4) Number of repetitions. (5) Frequency hopping mode. (6) Frequency hopping pattern. (7) A combination of (1) to (6) above.

[0358] The information on the resource on which the EPDCCH is transmitted may be any information that allows the LC-MTC UE to identify the resource on which the EPDCCH is mapped. It may also be scheduling information for the EPDCCH. By determining the information in advance in a standard or the like, it is possible to prevent the amount of information in the MIB from increasing and to prevent a decrease in resource usage efficiency.

[0359] There may be a plurality of pieces of information regarding the resources of the EPDCCH to which the control information for paging is mapped. There may be a plurality of groups of information regarding the resources to which the above-mentioned EPDCCH is transmitted. By providing a plurality of pieces of information regarding the resources of the EPDCCH to which the control information for paging is mapped or a plurality of groups of information regarding the resources to which the above-mentioned EPDCCH is transmitted, the cell can change the resources to which the EPDCCH to which the control information for paging is mapped is transmitted in accordance with radio wave propagation conditions.

[0360] Therefore, it is possible to build a communication system that is robust against changes in radio wave propagation conditions. Also, when repetition reception is performed on the EPDCCH to which the paging control signal is mapped, the number of times of repetition reception can be reduced, thereby reducing the power consumption of the LC-MTC UE.

[0361] However, simply providing multiple groups does not allow the LC-MTC UE to recognize which group is being used. In this case, the LC-MTC UE may receive resources on which EPDCCHs of all groups are transmitted according to the information of all groups and detect them using the MTC-PI-RNTI. However, receiving the EPDCCHs of all groups complicates the operation of the LC-MTC UE and increases power consumption.

[0362] To solve such a problem, it is preferable to provide an indicator associated with information about each EPDCCH resource. It is also preferable to provide an indicator associated with each group of information about resources on which the EPDCCH is transmitted. The indicators and information about the EPDCCH resources of each group are determined in advance as a table in accordance with a standard or the like. The LC-MTC UE stores the table.

[0363] The cell may use the indicator to notify the LC-MTC UE of which EPDCCH resource information is valid. The cell notifies the LC-MTC UE of the indicator.

[0364] As specific examples of methods for notifying an indicator, the following three methods (1) to (3) are disclosed. (1) The indicator is included in the MIB and reported. (2) The indicator is included in the SIB including the SI information for the LC-MTC UE and notified.

[0365] By receiving the MIB or the SIB for LC-MTC UE and acquiring the indicator, the LC-MTC UE can recognize to which resource the EPDCCH to which valid paging control information is mapped is assigned. The information included in the MIB or the SIB for LC-MTC UE is only the indicator, making it possible to notify with a small amount of information. Therefore, it is possible to minimize the decrease in resource usage efficiency and build a communication system that is resistant to changes in radio wave propagation conditions.

[0366] (3) Notified by RRC signaling. In this case, notification may be performed at the time of initial access. This may be applied to cases where notification is performed for each cell or each LC-MTC UE. A larger number of parameters can be notified compared to when notifying by MIB and SI. Also, the amount of information notified by MIB and SI can be reduced. In this case, it is preferable to determine in advance in a standard, etc., that the indicator should be the same within the same TAC.

[0367] Another method for solving the above problem is disclosed. A method for deriving information about resources transmitting EPDCCHs onto which paging control information is mapped is determined in advance. The derivation method may be determined in advance in a standard or the like. A derivation function may be provided. The derivation function may be a function using at least one of PF, PO, and UE identifier (UE-ID) as an input parameter. The output parameter may be the above-mentioned information about resources transmitting EPDCCHs. Alternatively, the above-mentioned indicator may be used. The indicator and the information about resources transmitting EPDCCHs may be determined in advance in a table in a standard or the like. The LC-MTC UE stores the table.

[0368] By doing so, it is not necessary to include the above-mentioned indicator in the MIB or the SIB for LC-MTC UE, so it is possible to prevent a decrease in resource usage efficiency. Also, by using at least one of PF and PO as the input parameter of the derivation function, different resources are obtained for at least one of different PF and PO. Therefore, it is possible to prevent concentration on a specific resource. Also, by using UE-ID as the input parameter of the derivation function, different resources are obtained for each UE, so it is possible to prevent concentration on a specific resource.

[0369] If concentration occurs on a specific resource, it is possible to avoid mapping any of the paging control information to the EPDCCH. Instead, it is possible to map the paging control information to the EPDCCH of the next PF / PO. However, in this case, a problem occurs in that a delay occurs in the notification of paging. By using the method described above to prevent concentration on a specific resource, it is possible to solve this problem.

[0370] By using the method of this modification, the LC-MTC UE can receive the EPDCCH to which the control information for paging is mapped, and can detect whether or not paging is occurring. If paging is occurring, the LC-MTC UE can receive the paging.

[0371] Although the present invention discloses mapping of paging control information for LC-MTC UEs to EPDCCH, the present invention is not limited to EPDCCH and may be applied to any physical downlink control channel that uses narrowband resources, and may be applied to any physical downlink control channel that is configured within a band that can be received by LC-MTC UEs that support bandwidth reduction.

[0372] The relationship between the repetition transmission method of the EPDCCH to which the paging control information is mapped and the repetition transmission method of the paging may be the same as the relationship between the repetition transmission method of the PDCCH to which the paging control information is mapped and the repetition transmission method of the paging. LC-MTC UEs that also support coverage extension can receive the paging control information and use it to receive paging.

[0373] Embodiment 4 There are cases where the subframe in which the initial paging transmission is performed and the subframe in which the repetition transmission is performed are the same.

[0374] 15 is a conceptual diagram of a case where the subframe in which the initial paging transmission is performed and the subframe in which the repetition transmission is performed are the same. For example, the case where the repetition transmission is performed in the same subframe of consecutive radio frames as disclosed in the first modification of the third embodiment is shown.

[0375] Assume that the SFN of the radio frame in which the initial paging transmission of LC-MTC UE A is performed is 25 (SFN=25), and the subframe number of the subframe is 9. The number of repetitions is 2. In this case, for example, the initial transmission (IN(A)) is performed in radio frame (RF) 151 with SFN 25. The repetition transmissions are transmitted in the two radio frames 152 and 153 consecutive to the radio frame 151 in which the initial transmission is performed, with the same subframe number as the initial transmission, specifically, in the subframe with subframe number 9 (SF9) (RP#1(A), RP#2(A)).

[0376] The PF / PO for transmitting paging is determined by the identifier of the LC-MTC UE. Therefore, different UEs may have different PF / PO. Assume that the SFN of the radio frame in which the first paging transmission of LC-MTC UE B is performed is 26 (SFN=26), and the subframe number of the subframe is 9. The number of repetitions is 2.

[0377] In this case, for example, the initial transmission (IN(B)) is performed in a radio frame (RF) 152 with an SFN of 26. Repetition transmissions are performed in the two radio frames 153 and 154 consecutive to the radio frame 152 in which the initial transmission is performed, in the same subframe number as the initial transmission, specifically, in the subframe with subframe number 9 (SF9) (RP#1(B), RP#2(B)).

[0378] In this case, the SFN of radio frame 152 is 26, the subframe number is 9, and the initial transmission of LC-MTC UE A and the repetition transmission of LC-MTC UE B are performed. In this case, it is unclear how to multiplex the paging of the repetition transmission of LC-MTC UE A and the paging of the initial transmission of LC-MTC UE B.

[0379] This embodiment discloses a method for solving such a problem. It is preferable to create a paging message in which a paging message for initial transmission and a paging message for repetition transmission are multiplexed in the same paging message, and to map the paging message to a PDSCH. It is preferable to map the paging message for each repetition number.

[0380] The LC-MTC UE receives the paging DCI by detecting the EPDCCH to which the paging DCI is mapped using the PI-RNTI or MTC-PI-RNTI. According to the received paging DCI, the LC-MTC UE receives the PDSCH and acquires a paging message in which the initial transmission paging and the repetition transmission paging are multiplexed.

[0381] The LC-MTC UE to which the initial transmission paging is transmitted in the subframe receives the initial transmission paging in the paging message. The LC-MTC UE to which the repetition transmission paging is transmitted in the subframe receives the repetition paging according to the repetition number in the paging message.

[0382] 16 is a diagram showing an example of a paging message in the prior art. The paging message includes incoming call paging record list information (pagingRecordList), SI modification information (systemInfoModification), ETWS information (etws-Indication), CMAS information (cmas-Indication), and EAB parameter modification information (eab-ParamModification).

[0383] The paging record list information for incoming calls (pagingRecordList) includes one or more paging record information (PagingRecord). The paging record information includes a UE identifier of the UE to be called by the incoming call. Core network domain (CN domain) information may also be included. Examples of UE identifiers include s-TMSI (Serving-Temporary Mobile Subscriber Identity) and IMSI (International Mobile Subscriber Identity).

[0384] Fig. 17 is a diagram showing an example of a paging message in the fourth embodiment. The paging message includes a paging for initial transmission and a paging for repetition transmission. In Fig. 17, the part enclosed by the dashed square is a paging for repetition transmission. The repetition number is the first paging. The paging for repetition transmission may be only incoming call paging record list information (pagingRecordList_repetition#1).

[0385] The paging record list information for incoming calls for repetition transmission includes one or more paging record information for which repetition transmission is performed. The paging record information includes a UE identifier of the UE to be called by the incoming call. CN domain information may also be included. The UE identifier may be an s-TMSI, an IMSI, etc.

[0386] Paging for repetition transmission does not need to include information that is not transmitted individually to LC-MTC UEs. For example, SI modification information, ETWS information, and CMAS information. EAB parameter modification information may be applied to all LC-MTC UEs rather than to each UE, in which case it does not need to be included. In the case of per-UE paging, it may be included.

[0387] By doing this, even if the subframe in which the initial transmission paging is transmitted and the subframe in which the repetition transmission paging is transmitted are the same, the cell can transmit both the initial transmission and the repetition transmission, and the LC-MTC UE can receive either the initial transmission or the repetition transmission as appropriate.

[0388] In addition, by doing so, the paging transmission DCI for the initial transmission and the paging transmission DCI for the repetition transmission can be the same. Therefore, the EPDCCH resource to which the initial transmission DCI is mapped may be the same as the EPDCCH resource to which the repetition transmission DCI is mapped.

[0389] An LC-MTC UE can receive paging by receiving a paging PDSCH according to the paging transmission DCI mapped to the EPDCCH, and can therefore obtain either the initial transmission or the repetition transmission as appropriate.

[0390] In the above description, a paging message is multiplexed with a paging message for initial transmission and a paging message for repetition transmission. There may be one or more paging messages for repetition transmission. Paging messages for repetition transmission may also be multiplexed within a paging message. It is preferable to provide a paging message for each repetition number. This makes it possible to handle multiple numbers of repetitions.

[0391] Alternatively, multiplexing on a transport channel may be performed. A cell may multiplex a PCH for initial transmission and a PCH for repetition transmission, map the PCH to the same PDSCH, and notify the multiplexed PCH. Alternatively, a PCH for initial transmission and a PCH for repetition transmission may be coded together and mapped to a PDSCH. An LC-MTC UE can obtain either the initial transmission or the repetition transmission by receiving the PCH multiplexed with the PDSCH.

[0392] Fourth embodiment, variant 1 This modification discloses another method for solving the problem disclosed in embodiment 4. Problems arise when the method disclosed in embodiment 4 is used. For example, following the above example, a case will be described in which SFN is 26, subframe number is 9, and initial transmission and repetition transmission are performed.

[0393] In this case, the SFN is 26, the subframe number is 9, and it is assumed that the initial transmission was not actually performed, and only repetition transmission was performed. LC-MTC UE B, which may have performed the initial transmission, also detects this using the MTC-PI-RNTI and receives the EPDCCH. Then, in accordance with the paging DCI of the EPDCCH, it receives the PDSCH to which paging is mapped. However, since the initial transmission is not actually performed, the paging mapped to this PDSCH is for repetition transmission by LC-MTC UE A.

[0394] Therefore, LC-MTC UE B, which may receive the first transmission, must receive the PDSCH and acquire the paging even though the first transmission has not actually been performed. Performing this reception operation even though the first transmission has not actually been performed is wasteful. In other words, there is a problem in that the power consumption of the LC-MTC UE increases.

[0395] This modification discloses a method for solving this problem. The RNTI used for the EPDCCH for repetition transmission is made different from the RNTI used for the EPDCCH for initial transmission. The DCI for repetition transmission and the DCI for initial transmission are masked with different RNTIs.

[0396] For example, in the case of paging, it is preferable to use MTC-PI-F-RNTI for initial transmission and MTC-PI-R-RNTI for repetition transmission. An LC-MTC UE can receive paging DCI by searching for the EPDCCH using MTC-PI-F-RNTI in the subframe for initial transmission and by searching for the EPDCCH using MTC-PI-R-RNTI in the subframe for repetition transmission.

[0397] By doing this, the LC-MTC UE does not need to receive a PDSCH to which a paging message for another UE is mapped and acquire the paging even though no transmission is actually performed. This prevents an increase in power consumption of the LC-MTC UE. Here, the other UEs are UEs other than the UEs to which paging is transmitted using the same PF / PO as the LC-MTC UE (hereinafter, sometimes referred to as "UEs in a paging group").

[0398] It is recommended to set the number of RNTIs according to the number of repetitions. For example, if the number of repetitions is 4, the initial transmission should be MTC-PI-F-RNTI, the first repetition transmission should be MTC-PI-R1-RNTI, the second repetition transmission should be MTC-PI-R2-RNTI, the third repetition transmission should be MTC-PI-R3-RNTI, and the fourth repetition transmission should be MTC-PI-R4-RNTI. It is recommended to set an upper limit on the number of repetitions and determine the RNTI according to the upper limit. These RNTI values ​​may be statically determined in advance by standards, etc.

[0399] The EPDCCH resources may be different for initial transmission and repetition, or may be the same. Even if the EPDCCH resources are the same, the RNTI used for the EPDCCH for repetition transmission is made different from the RNTI used for the EPDCCH for initial transmission, and the DCI for repetition transmission and the DCI for initial transmission are masked with different RNTIs.

[0400] This allows the LC-MTC UE to receive DCI for paging when it is intended for itself. Therefore, the LC-MTC UE can receive a PDSCH to which paging intended for itself is mapped, and does not need to receive a PDSCH to which paging intended for other UEs is mapped, thereby preventing an increase in power consumption of the LC-MTC UE.

[0401] Figures 18 and 19 are conceptual diagrams of subframes including an initial transmission and repetition transmission of an EPDCCH according to Variant 1 of Embodiment 4. Following the example shown in Figure 15, the subframe has SFN 26 and subframe number 9. In Figures 18 and 19, the vertical axis represents frequency and the horizontal axis represents time. EPDCCH resources are indicated by diagonal lines. Figure 18 shows a case where the EPDCCH resources for initial transmission and the EPDCCH resources for repetition are the same. Figure 19 shows a case where the EPDCCH resources for initial transmission and the EPDCCH resources for repetition are different.

[0402] In the case of FIG. 18, both the paging initial transmission DCI (IN(B)) and the paging repetition DCI (RP#1(A)) are mapped to one EPDCCH resource (hereinafter sometimes referred to as the "paging EPDCCH") 181. The initial transmission DCI and the repetition DCI are masked with different RNTIs. The initial transmission DCI is masked with MTC-PI-F-RNTI. Since the repetition number is 1, the repetition DCI is masked with MTC-PI-R1-RNTI.

[0403] LC-MTC UE A recognizes that the transmission with SFN 26 and subframe number 9 has a repetition number of 1. Therefore, LC-MTC UE A detects the EPDCCH resource of that subframe using MTC-PI-R1-RNTI, and if DCI for repetition is present, it becomes possible to receive that DCI.

[0404] According to the received DCI, LC-MTC UE A receives a PDSCH to which paging for its own UE is mapped. By doing so, LC-MTC UE A does not need to receive a PDSCH to which paging for another UE, for example, LC-MTC UE B, is mapped. This prevents an increase in power consumption of the LC-MTC UE.

[0405] LC-MTC UE B recognizes that the transmission with SFN 26 and subframe number 9 is the first transmission. Therefore, LC-MTC UE B detects the EPDCCH resource of that subframe using MTC-PI-F-RNTI, and if DCI for repetition is present, it becomes possible to receive that DCI.

[0406] According to the received DCI, LC-MTC UE B receives a PDSCH to which paging for its own UE is mapped. By doing so, LC-MTC UE B does not need to receive a PDSCH to which paging for another UE, for example, LC-MTC UE A, is mapped. Therefore, it is possible to prevent an increase in power consumption of the LC-MTC UE.

[0407] In the case of FIG. 19, the resource of the EPDCCH for initial transmission (hereinafter sometimes referred to as the "EPDCCH for paging initial transmission") 182 is different from the resource of the EPDCCH for repetition (hereinafter sometimes referred to as the "EPDCCH for paging repetition transmission") 183. In this case as well, the DCI for initial transmission (IN(B)) and the DCI for repetition (RP#1(A)) may be masked with different RNTIs. The DCI for initial transmission is masked with MTC-PI-F-RNTI. Since the repetition number is 1, the DCI for repetition is masked with MTC-PI-R1-RNTI.

[0408] LC-MTC UE A detects the resource of the EPDCCH for transmitting repetition number 1 of its own UE in the subframe using MTC-PI-R1-RNTI, and if DCI for repetition is present, it becomes possible to receive the DCI. In accordance with the received DCI, it receives a PDSCH to which paging for its own UE is mapped. In this way, LC-MTC UE A does not need to receive a PDSCH to which paging for another UE, for example, LC-MTC UE B, is mapped. This prevents an increase in power consumption of the LC-MTC UE.

[0409] LC-MTC UE B detects the resource of its own UE's initial transmission EPDCCH in the subframe using MTC-PI-F-RNTI, and if DCI for repetition is present, it becomes possible to receive the DCI. LC-MTC UE B receives a PDSCH to which paging for its own UE is mapped according to the received DCI. This eliminates the need for LC-MTC UE B to receive a PDSCH to which paging for another UE, for example, LC-MTC UE A, is mapped. This prevents an increase in power consumption of the LC-MTC UE.

[0410] By using the method disclosed in this modification, if the subframe in which the initial paging transmission is performed and the subframe in which the repetition transmission is performed are the same, the UE receives the PDSCH to which the paging of the UE is mapped only when transmission to the UE is being performed. Therefore, it is possible to prevent an increase in power consumption of the LC-MTC UE.

[0411] If the resources to which the EPDCCH for the initial transmission and for each repetition number are mapped are clearly different within a subframe, one RNTI is sufficient. Specifically, it may be MTC-PI-RNTI. In the case of the initial transmission, the LC-MTC UE detects the EPDCCH for the predetermined resource for the initial transmission using MTC-PI-RNTI, and detects the EPDCCH for the predetermined resource for each repetition number using MTC-PI-RNTI.

[0412] Since the resource to which the EPDCCH is mapped differs for each initial transmission and repetition number, the LC-MTC UE can receive the EPDCCH depending on whether it receives the initial transmission or the repetition transmission. Therefore, only when a transmission directed to the UE is being performed, the LC-MTC UE can receive the PDSCH to which its own paging is mapped. This makes it possible to prevent an increase in power consumption of the LC-MTC UE.

[0413] The methods disclosed in the fourth embodiment and the first modification of the fourth embodiment may be applied to a case where repetition is performed and a common RNTI is used in LC-MTC UEs. For example, they may be applied to notifications of SI, RAR, etc. In this case, it is possible to obtain the same effects as those of the fourth embodiment and the first modification of the fourth embodiment.

[0414] Another method for solving the above problem will be disclosed. In the above method, the number of RNTIs corresponding to the number of initial transmissions and repetitions is set. However, as another method, an RNTI dedicated to an LC-MTC UE may be set. Both the DCI for initial transmission and the DCI for repetition transmission may be masked with the RNTI dedicated to the LC-MTC UE. The LC-MTC UE may search both the EPDCCH to which the DCI for initial transmission is mapped and the EPDCCH to which the DCI for repetition transmission is mapped using its own UE's RNTI and receive the DCI. This makes it possible to receive a PDSCH and obtain paging for the UE according to the received DCI.

[0415] In the case of paging, there may be multiple UEs that have the same PF / PO as the UE itself. These are UEs within the paging group mentioned above. Therefore, an RNTI may be provided for each paging group, not for each LC-MTC UE. The DCI for paging to the paging group with the same PF / PO may be masked with the RNTI.

[0416] The following two methods (1) and (2) are disclosed as methods for an LC-MTC UE to recognize the RNTI for each UE or each paging group.

[0417] (1) Notified by RRC signaling. In this case, notification may be made at the time of initial access or TAU. The RNTI for each LC-MTC UE or the RNTI for each paging group may be common among cells within a TA.

[0418] This allows the LC-MTC UE to continue using the RNTI even when it changes the cell it camps on during RRC_Idle and selects a cell within the same TA. If a cell within a different TA is selected, initial access or TAU processing is performed in that cell, making it possible to acquire a new valid RNTI within that TA.

[0419] (2) A method for deriving an RNTI for each UE or each paging group is determined in advance. The derivation method may be determined in advance by a standard or the like. Specifically, a derivation function may be provided. The derivation function may be a function that uses at least one of the PF and the PO as an input parameter. For example, a function that uses a UE identifier such as a UE-ID, IMSI, or s-TMSI as an input parameter may be used.

[0420] In this way, the LC-MTC UE can recognize the RNTI for each UE or for each paging group. Therefore, the LC-MTC UE can search both the EPDCCH to which the DCI for initial transmission is mapped and the EPDCCH to which the DCI for repetition transmission is mapped using the RNTI of its own UE and receive the DCI. This makes it possible to receive the PDSCH and obtain paging for the UE according to the received DCI.

[0421] Embodiment 5 In the first embodiment, it was mentioned that a new method of notifying LC-MTC UE of SI that supports bandwidth reduction is being studied. As an SI transmission method for LC-MTC UE, it has been proposed to provide an MTC-SIB, which is an SIB for LC-MTC UE (see Non-Patent Document 13). As an MTC-SIB transmission method, it has been proposed to determine the resources used for transmitting the MTC-SIB to be six resource blocks at the center of the system bandwidth (see Non-Patent Documents 10 and 13).

[0422] However, if SI for LC-MTC UE is transmitted using a specific resource, it is susceptible to frequency fading, which causes a problem of degradation in reception quality.

[0423] In this embodiment, another method for transmitting SI for LC-MTC UE is disclosed.

[0424] An SIB including SI for LC-MTC UE is provided. Here, it is referred to as SIB-MTC. The SIB-MTC is mapped to a PDSCH. Control information for the PDSCH to which the SIB-MTC is mapped (hereinafter sometimes referred to as "DCI for SIB-MTC") is mapped to an EPDCCH. The DCI for SIB-MTC is, for example, scheduling information for the PDSCH to which the SIB-MTC is mapped.

[0425] The SI-RNTI may be used as the RNTI masked on the control information for the PDSCH to which the SIB-MTC on the EPDCCH is mapped. Alternatively, a new RNTI may be provided for the LC-MTC UE. For example, MTC-SI-RNTI may be used. By providing a new RNTI for the LC-MTC UE, such as MTC-SI-RNTI, it becomes possible to distinguish it from conventional UEs. By using MTC-SI-RNTI when detecting control information, it is possible to confirm that the control information is for the LC-MTC UE, thereby reducing malfunctions.

[0426] The SIB DCI for a conventional UE (legacy UE) may be transmitted using a PDCCH, and the SIB-MTC DCI for an LC-MTC UE may be transmitted using an EPDCCH. In this case, the SIB-MTC DCI mapped to the EPDCCH may be masked with the MTC-PI-RNTI.

[0427] If an EPDCCH is used to transmit DCI for SIB-MTC, it is unclear in which radio frame, in which subframe, and in which resource of the subframe the EPDCCH is transmitted. Therefore, an LC-MTC UE cannot receive the EPDCCH.

[0428] Non-Patent Document 12 discloses a solution to this problem. Specifically, it discloses a scheduling method for an EPDCCH to which DCI for SIB-MTC is mapped. The method involves mapping an EPDCCH for common messages including SIB, paging, and RAR to six resource blocks at the center of a carrier, or including information in an MIB as to whether the resource block of the EPDCCH is located at a predetermined position or whether frequency hopping is performed.

[0429] However, if the resources to which the EPDCCH for SIB-MTC is mapped are fixed to the six resource blocks at the center of the carrier, problems arise such as susceptibility to frequency fading and deterioration of reception quality. Also, when frequency hopping is performed, the method of notifying the frequency hopping pattern becomes an issue.

[0430] When MIB information is included in the notification, the amount of information in the MIB increases. Also, because the MIB is notified repeatedly, a large amount of resources are required. This results in a problem of reduced resource utilization efficiency.

[0431] This embodiment discloses a method for solving such a problem. A resource for transmitting the EPDCCH to which the DCI for SIB-MTC is mapped is determined in advance in accordance with a standard or the like.

[0432] As examples of information regarding resources on which the EPDCCH is transmitted, the following nine items (1) to (9) are disclosed. (1) Period: It is preferable to set it to a radio frame unit or a subframe unit. (2) Offset: The offset may be an offset from subframe number 0 of radio frame number 0. The offset may be in units of at least one of radio frames, subframes, and symbols. (3) Number of resource blocks (RB). (4) RB allocation. This can be the first RB number. (5) RS (Reference Signal) configuration. This can be the RS sequence or sequence number. (6) Number of repetitions. (7) Frequency hopping mode. (8) Frequency hopping pattern. (9) A combination of (1) to (8) above.

[0433] The information on the resource on which the EPDCCH is transmitted may be any information that allows the LC-MTC UE to identify the resource on which the EPDCCH is mapped. It may also be scheduling information for the EPDCCH. By determining the information in advance in a standard or the like, it is possible to prevent the amount of information in the MIB from increasing and to prevent a decrease in resource usage efficiency.

[0434] There may be a plurality of pieces of information regarding the resource of the EPDCCH to which the DCI for SIB-MTC is mapped. There may be a plurality of groups of information regarding the resource to which the above-mentioned EPDCCH is transmitted. By providing a plurality of pieces of information regarding the resource of the EPDCCH to which the DCI for SIB-MTC is mapped or a plurality of groups of information regarding the resource to which the above-mentioned EPDCCH is transmitted, the cell can change the resource to which the EPDCCH to which the DCI for SIB-MTC is mapped is transmitted in accordance with the radio wave propagation conditions.

[0435] Therefore, it is possible to build a communication system that is robust against changes in radio wave propagation conditions. Also, when repetition reception is performed on the EPDCCH to which the SIB-MTC DCI is mapped, the number of times of repetition reception can be reduced, thereby reducing the power consumption of the LC-MTC UE.

[0436] However, simply providing multiple groups does not allow the LC-MTC UE to recognize which group is being used. In this case, the LC-MTC UE may receive resources on which EPDCCHs of all groups are transmitted according to the information of all groups and detect them using the MTC-PI-RNTI. However, receiving the EPDCCHs of all groups complicates the operation of the LC-MTC UE and increases power consumption.

[0437] To solve such a problem, it is preferable to provide an indicator associated with information about each EPDCCH resource. It is also preferable to provide an indicator associated with each group of information about resources on which the EPDCCH is transmitted. The indicators and information about the EPDCCH resources of each group are determined in advance as a table in accordance with a standard or the like. The LC-MTC UE stores the table.

[0438] The method by which the cell notifies the LC-MTC UE of which EPDCCH resource-related information is valid may be the method disclosed in the third modification of the third embodiment. This makes it possible to obtain the same effect as that of the third modification of the third embodiment.

[0439] Alternatively, a method for deriving information on resources for transmitting EPDCCHs to which DCI for SIB-MTC is mapped may be determined in advance. This method can be achieved by applying the method disclosed in the third modification of the third embodiment. This can achieve the same effects as those of the third modification of the third embodiment.

[0440] Another method for an LC-MTC UE to acquire information related to the scheduling of an EPDCCH to which SIB-MTC DCI is mapped is disclosed. Among the information related to the scheduling of the EPDCCH, information related to the time direction scheduling and information related to other scheduling are handled separately.

[0441] Information about scheduling in the time direction is statically determined in advance by a standard or the like. There may be one set of information or multiple sets of information. Alternatively, the cell may notify information about scheduling in the time direction using an MIB. In the case of multiple sets of information, it is advisable to apply the method using an indicator disclosed in Variation 3 of Embodiment 3.

[0442] Other scheduling-related information may be notified as multiple pieces of information in the MIB. The method using the indicator disclosed in the third modification of the third embodiment may be applied. Alternatively, a method in which a derivation method is determined in advance may be applied. The UE identifier (UE-ID) of the LC-MTC UE may be used as an input parameter of the derivation function for derivation. Information related to scheduling in the time direction includes the aforementioned period, offset, etc.

[0443] By doing so, the same effect as that of the third modification of the third embodiment can be obtained.

[0444] By using this modification, it becomes possible for an LC-MTC UE to receive an EPDCCH to which the DCI for SIB-MTC is mapped. It is also possible to detect whether or not the DCI for SIB-MTC is present. If the DCI for SIB-MTC is present, it becomes possible to receive the DCI for SIB-MTC.

[0445] Although the present invention discloses mapping of SIB-MTC DCI for LC-MTC UE to EPDCCH, the present invention is not limited to EPDCCH and may be any physical downlink control channel using narrowband resources, or may be any physical downlink control channel configured within a band that can be received by LC-MTC UE that supports bandwidth reduction.

[0446] In the case of LC-MTC that supports coverage extension, the repetition transmission method of the EPDCCH to which the DCI for SIB-MTC is mapped, the repetition transmission method of the SIB-MTC, and the relationship between them may be the repetition transmission method of the PDCCH to which the above-mentioned paging control information is mapped, the repetition transmission method of paging, and the relationship between them.

[0447] This enables an LC-MTC UE that also supports coverage extension to receive control information for SIB-MTC, and to use this information to receive SIB-MTC.

[0448] Fifth embodiment, variant 1 The time resource of the EPDCCH onto which the DCI for paging is mapped may be the same as the time resource of the EPDCCH onto which the DCI for SIB-MTC is mapped. For example, the time resource can be indicated by a radio frame number and a subframe number. The radio frame number and subframe number of the EPDCCH onto which the DCI for paging is mapped may be the same as the radio frame number and subframe number of the EPDCCH onto which the DCI for SIB-MTC is mapped.

[0449] In addition, the number of repetitions of the EPDCCH to which the paging DCI is mapped may be the same as the number of repetitions of the EPDCCH to which the SIB-MTC DCI is mapped. For an LC-MTC UE that supports coverage extension, the number of repetitions is determined depending on its location and radio wave propagation environment.

[0450] Therefore, by transmitting the EPDCCH in the same subframe, even if the number of repetitions is the same, an LC-MTC UE can receive the EPDCCH to which both DCIs are mapped without any degradation in reception quality.

[0451] In the RRC_Idle state, the LC-MTC UE receives the EPDCCH to which the SIB-MTC DCI is mapped, and therefore can receive the EPDCCH to which the paging DCI is mapped accordingly. This makes it possible to shorten the period during which the LC-MTC UE performs reception operations, thereby achieving low power consumption.

[0452] The period of the EPDCCH onto which the paging DCI is mapped may be set to an integer fraction or an integer multiple of the period of the EPDCCH onto which the SIB-MTC DCI is mapped. This allows the LC-MTC UE to perform reception operations less frequently than when both EPDCCH transmission timings are uncorrelated, thereby shortening the reception period and reducing power consumption.

[0453] In particular, if the period of the EPDCCH to which the DCI for paging is mapped is set to an integer multiple of the period of the EPDCCH to which the DCI for SIB-MTC is mapped, it is possible to further reduce the power consumption of the LC-MTC UE. Once an LC-MTC UE receives the SIB-MTC, it does not need to receive the SIB-MTC until it is notified of an SI modification by paging.

[0454] Therefore, by setting the paging cycle to an integer multiple of the SIB-MTC cycle, it becomes unnecessary to receive SIB-MTC between paging cycles. Furthermore, it becomes possible to receive SIB-MTC simultaneously with receiving paging. Therefore, it is possible to reduce the power consumption of LC-MTC UEs.

[0455] The period may be statically determined in advance by a standard or the like. Alternatively, it may be included in the MIB and notified. The period value and an indicator indicating the period may be provided as a table, and the table may be statically determined in advance by a standard or the like, and the indicator may be included in the MIB and notified. The method of Variant 3 of Embodiment 3 or Embodiment 5 may also be applied.

[0456] The DCI for paging and the DCI for SIB-MTC may be mapped to the same EPDCCH. The EPDCCH includes multiple DCIs. The DCI for SIB-MTC is masked with the MTC-SI-RNTI and mapped to the EPDCCH. The DCI for paging is masked with the MTC-PI-RNTI and mapped to the EPDCCH.

[0457] The LC-MTC UE can acquire the SIB-MTC DCI by detecting the EPDCCH with the MTC-SI-RNTI. Also, the LC-MTC UE can acquire the paging DCI by detecting the EPDCCH with the MTC-PI-RNTI.

[0458] By doing so, it is only necessary to detect one EPDCCH resource for each RNTI at the timing when the EPDCCH is transmitted, which makes it possible to further reduce the reception period of the LC-MTC UE and achieve lower power consumption.

[0459] In this case, the timing of the EPDCCH onto which the paging DCI is mapped no longer complies with the conventional PF / PO. The timing of the EPDCCH onto which the paging DCI is mapped may be determined in advance by a standard, etc. It may be determined in advance that the time resource of the EPDCCH onto which the paging DCI is mapped is the same as the time resource of the EPDCCH onto which the SIB-MTC DCI is mapped.

[0460] In this way, the LC-MTC UE can recognize the timing of the EPDCCH to which the paging DCI is mapped.

[0461] Alternatively, a new function may be provided to derive the radio frame (PF) and subframe (PO) of the EPDCCH to which the paging DCI is mapped from the time resources of the EPDCCH to which the SIB-MTC DCI is mapped. The UE identifier (UE-ID) of the LC-MTC UE may be used as an input parameter of the derivation function. In this way, it is possible to distribute the subframes for transmitting paging to a large number of LC-MTC UEs.

[0462] Although the EPDCCH to which the DCI for paging is mapped and the EPDCC to which the DCI for SIB-MTC is mapped have been disclosed, neither of these is limited to the EPDCCH, and any physical downlink control channel using narrowband resources may be used, and any physical downlink control channel configured within a band that can be received by an LC-MTC UE that supports bandwidth reduction may be used.

[0463] Embodiment 6 The transmission power of conventional uplink channels (PUSCH, PUCCH) is derived as follows using path loss (PL) (see Non-Patent Document 14). Uplink channel transmit power = f(x), x = PL

[0464] The path loss (PL) is derived using information about transmission power notified to the UE by the cell and the received power measured by the UE. It is being considered that repetition transmission of uplink channels is performed in LC-MTC UEs that require coverage extension. This embodiment discloses a method for deriving uplink channel transmission power when LC-MTC UEs perform repetition transmission.

[0465] A new value is set by dividing the PL derived by the LC-MTC UE by the total number of transmissions on the uplink channel. Here, this value is PL-R. The total number of transmissions is the sum of the initial transmission and the number of repetition transmissions. This PL-R is used to derive the transmission power of the uplink channel in place of the conventional PL. Therefore, it is derived as follows: Uplink channel transmit power = f(x), x = PL - R = PL / total number of transmissions

[0466] When the PL is derived using the conventional method, for example, the PL value derived by an LC-MTC UE located at the extended coverage edge will be larger than the PL value derived by a UE located at the normal coverage edge. Therefore, when the uplink channel transmit power is derived using the PL derived using the conventional method, the uplink channel transmit power of an LC-MTC UE located at the extended coverage edge will be larger than the uplink channel transmit power of a UE located at the normal coverage edge. Performing repetition transmission with high uplink channel transmit power will result in excessively high received power in the cell.

[0467] Therefore, by using the method disclosed in this embodiment, when repetition transmission of the uplink channel is performed in the LC-MTC UE, it is possible to optimize the reception power of the cell. Furthermore, since the transmission power of the uplink channel can be reduced in the LC-MTC UE, it is possible to reduce power consumption.

[0468] When an LC-MTC UE performs repetition transmission of an uplink channel, the next repetition transmission may be performed without receiving an uplink channel acknowledgment response (e.g., ack / nack) for the previous transmission. This allows repetition transmission of the uplink channel without receiving an acknowledgment response for each transmission, thereby reducing control delay. In this case, the cell does not need to transmit the acknowledgment response to the LC-MTC UE.

[0469] In this case, it is advisable to use the uplink channel transmission power derivation method disclosed in this embodiment. The LC-MTC UE performs all transmissions, including the initial transmission and repetition transmissions. Therefore, the LC-MTC UE can reduce transmission power compared to when performing all transmissions with a large amount of power, thereby reducing power consumption. In addition, the cell can obtain appropriate reception power by combining the initial transmission and repetition transmissions from the LC-MTC UE.

[0470] When an LC-MTC UE performs repetition transmission of an uplink channel, it may receive an uplink channel reception acknowledgment for the previous transmission. The cell transmits the reception acknowledgment for the uplink channel transmission from the LC-MTC UE. In this case, the LC-MTC UE may use a conventional method for deriving the uplink channel transmission power. Since the LC-MTC UE can transmit with transmission power appropriate for the PL, the cell may be able to receive the uplink channel with fewer attempts. In such a case, the cell transmits the reception acknowledgment to the LC-MTC UE. Upon receiving the reception acknowledgment, the LC-MTC UE stops repetition transmission.

[0471] Therefore, the LC-MTC UE can perform uplink channel transmission with fewer repetitions, thereby improving resource usage efficiency.

[0472] A new offset value may be set for deriving the path loss of an LC-MTC UE. The offset value may be used when the LC-MTC UE derives the path loss. The offset value may be set for each cell or for each UE. When set for each cell, the cell broadcasts the offset value as SI for the LC-MTC UE. Alternatively, the offset value may be notified to the LC-MTC UE individually using RRC signaling. When set for each UE, the cell may notify the LC-MTC UE individually using RRC signaling.

[0473] As another method, a new offset value may be set for deriving the uplink channel transmission power of the LC-MTC UE. The offset value may be used when the LC-MTC UE derives the uplink channel transmission power. The offset value may be set for each cell or for each UE. A notification method from the cell to the LC-MTC UE may be applied. Alternatively, the above two methods may be used in combination.

[0474] This allows the settings for LC-MTC UE to be changed separately from those for conventional UE. Furthermore, the transmission power of LC-MTC UE can be flexibly set according to the radio wave propagation environment and interference conditions. This makes it possible to build a stable communication system even when conventional UE and LC-MTC UE coexist.

[0475] Embodiment 7 There is a growing demand for systems that use unlicensed spectrum as a complementary tool to licensed spectrum. An example of unlicensed spectrum is the ISM band used for wireless LAN. 3GPP is studying Licensed-Assisted Access (LAA) using LTE, which uses unlicensed spectrum as a complementary tool to licensed spectrum. Unlicensed spectrum can be DL only or UL and DL.

[0476] When using unlicensed spectrum, there needs to be a way to coexist fairly with other systems using unlicensed spectrum.

[0477] Therefore, an LAA is required to have at least the following five functions (1) to (5).

[0478] (1)Listen-before-talk(clear channel assessment) (2) Discontinuous transmission on a carrier with limited maximum transmission duration (3) Dynamic frequency selection for radar avoidance in certain bands / regions (4) Career selection (5) Transmission Power Control (TPC)

[0479] 3GPP is studying solutions to meet these requirements. Non-Patent Document 15, for example, discloses the following two methods (1) and (2) for transmitting data.

[0480] (1)FBE(Frame Based Equipments) A clear channel assessment (CCA) is performed at the frame boundary timing, and if the channel is clear, data transmission is carried out. If the channel is busy, a CCA is performed again at the next frame boundary timing.

[0481] (2) LBE (Load Based Equipment) CCA is performed continuously, and if it is cleared a predetermined number of times, data is transmitted immediately.

[0482] In unlicensed spectrum, data transmission cannot be performed continuously for long periods of time to maintain fairness and enable coexistence with other systems. It has been proposed that cells transmit data intermittently when necessary and transmit nothing when not necessary. However, if no data is transmitted from a cell, a problem arises: UEs cannot synchronize or measure the unlicensed spectrum.

[0483] For this reason, a signal for synchronization or measurement of unlicensed spectrum is required. Signals transmitted periodically in a small number of subframes are being considered as signals for synchronization or measurement of unlicensed spectrum. For example, the application of DS (Discovery Signal) used in small cells has been proposed (see Non-Patent Document 16). DS transmission is periodic, and the transmission timing is determined on a subframe-by-subframe basis. Furthermore, the eNB notifies the UE in advance of DS measurement settings such as the DS measurement period and offset. The UE receives the DS according to the DS measurement settings notified by the eNB.

[0484] However, even when transmitting synchronization or measurement signals in unlicensed spectrum, it is necessary to avoid collisions with other systems, maintain fairness, and enable coexistence. As mentioned above, fair coexistence methods have been proposed for data transmission, but there are no fair coexistence methods for such synchronization or measurement signals in unlicensed spectrum.

[0485] When no transmission is being performed from a cell, the UE does not receive the PDCCH in every subframe to detect the presence or absence of PDSCH scheduling information, as it does when receiving data, so the fair coexistence method for data transmission cannot be applied as is.

[0486] Therefore, unless some ingenuity is taken, the UE will be unable to synchronize or measure the unlicensed spectrum.

[0487] A method for solving this problem is disclosed below: A cell performs CCA before transmitting a synchronization or measurement signal in an unlicensed spectrum. The synchronization or measurement signal in an unlicensed spectrum may be a DS.

[0488] FIG. 20 is a conceptual diagram showing an example of DS transmission by a cell on an unlicensed spectrum and measurement by a UE in the seventh embodiment. The horizontal axis represents time. A DS 191 is a section (hereinafter sometimes referred to as a "DS transmission section") consisting of one or more sets of subframes. When a DS consists of multiple sets of subframes, the DS of one subframe may be repeated.

[0489] In the example shown in Figure 20, the DS transmission section is composed of two subframes. The subframes hatched with diagonal lines are the subframes in which the DS is actually transmitted. The cell periodically transmits the DS on the unlicensed spectrum at intervals of the DS transmission period (Tds).

[0490] CCA 192 must be performed before transmitting a DS. If the CCA clears the signal, DS transmission is performed. In FIG. 20, a blank CCA indicates that the signal is clear. CCA should be performed at the subframe boundary where DS transmission starts. It is recommended that DS transmission not be performed while CCA is being performed. Alternatively, the end timing of CCA may be set to coincide with the subframe boundary where DS transmission starts. In this way, the cell is able to transmit DS.

[0491] A cell notifies UEs that use unlicensed spectrum of the measurement settings for DS on the unlicensed spectrum, including the DS measurement period (Tmeas_p), offset (measurement start timing), and DS measurement duration (Tmeas_d).

[0492] The UE measures the DS from the offset to the DS measurement period (Tmeas_d). The DS measurement is repeated from the offset to the DS measurement period (Tmeas_d) at intervals of the DS measurement period (Tmeas_p). The cell configures the DS measurement on the unlicensed spectrum. The DS measurement configuration may be configured by the cell on the unlicensed spectrum or by a cell connected to the UE on the licensed spectrum.

[0493] If the configuration is performed by a cell on an unlicensed spectrum, the cell may notify the UE of the configuration, or a cell connected to the UE on a licensed spectrum may obtain the configuration from the cell on an unlicensed spectrum and notify the UE.

[0494] If the configuration is performed by a cell connecting the UE over licensed spectrum, the cell may notify the UE of the configuration, and the cell may notify the UE of the configuration together with information about the configuration of unlicensed spectrum.

[0495] The cell may notify the UE of the setting by individual signaling. RRC signaling is preferably used. This allows for individual setting for each UE. Alternatively, the setting may be broadcast as system information of the cell. This allows for setting for each cell, and when notifying a large number of UEs, the amount of information in individual signaling can be reduced.

[0496] In this way, a UE configured with unlicensed spectrum can measure the DS, and can synchronize and measure the unlicensed spectrum.

[0497] However, in this case, if the CCA determines that the DS is not clear, the UE will be unable to transmit the DS in the DS transmission period. If the DS cannot be transmitted, the UE will be unable to receive the DS during the DS measurement period (Tmeas_d) notified from the cell, which may result in problems such as loss of synchronization with the unlicensed spectrum or inability to measure the unlicensed spectrum.

[0498] A method for solving these problems is disclosed below. A second DS transmission cycle (DS transmission cycle 2 (Tds2)) is provided. If the cell is not cleared by CCA, it performs CCA again at the DS transmission timing after the second DS transmission cycle.

[0499] As specific examples of the DS transmission period 2, the following five examples (1) to (5) are disclosed. (1) Same as the DS transmission section. After the DS transmission section ends, CCA is performed again. (2) It shall be the same as the DS measurement period set in the UE. If the UE is unable to receive the DS after the DS measurement period ends, it continues measuring the DS in the DS measurement period again. (3) Within the DS transmission period. In addition, an upper limit may be set for the number of DS transmissions by CCA. The period for DS transmission by CCA when the upper limit is set may be within the DS transmission period. It may also be set to an integer fraction of the DS transmission period. (4) Make it the same as the DS transmission period. (5) A combination of (1) to (4) above.

[0500] The second DS transmission period may be set by a cell in an unlicensed spectrum or by a cell connected to the UE in a licensed spectrum, which allows for flexible setting taking into account the radio wave propagation environment and coexistence with other systems.

[0501] The UE's DS measurement method is disclosed below. Since the UE does not know when the DS will be transmitted by CCA, a CCA DS measurement window is set. The UE measures the DS assuming that the DS will be transmitted during the CCA DS measurement window. For example, a second DS measurement period (measurement period 2 (Tmeas_d2)) may be set as the CCA DS measurement window.

[0502] DS measurement period 2 should be set according to the settings of DS transmission cycle 2 and the number of DS transmissions by CCA. It should be set longer than the period for DS transmission by CCA when the number of transmissions is at the upper limit. The UE receives DS during the DS measurement period and DS measurement period 2. If the UE is unable to receive DS, it will repeat receiving the DS in the DS measurement period during DS measurement period 2.

[0503] When a UE receives a DS, it may terminate reception of the DS even if it is in the middle of reception. When a UE receives a DS and is able to perform at least one of synchronization and measurement, it may terminate reception of the DS even if it is in the middle of reception. For example, it may terminate reception of the DS even if it is in the middle of a DS transmission interval (one set of DS transmission). In addition, an offset (measurement start timing) may be set as the DS measurement window for CCA. It is preferable to set it as an offset from the beginning of the DS measurement interval. It may also be in subframe units.

[0504] A cell configures a DS measurement window for a UE that is part of an unlicensed spectrum. The DS measurement window may be configured by a cell in the unlicensed spectrum or by a cell connected to the UE in a licensed spectrum.

[0505] If the configuration is performed by a cell on an unlicensed spectrum, the cell may notify the UE of the configuration. Alternatively, a cell connected to the UE on a licensed spectrum may obtain the configuration from a cell on an unlicensed spectrum and notify the UE. If the configuration is performed by a cell connected to the UE on a licensed spectrum, the cell may notify the UE of the configuration.

[0506] The cell may notify the UE of this configuration by including it in the configuration related to measurements of DS on unlicensed spectrum. The cell may also notify the UE of information on whether CCA is to be performed for DS on unlicensed spectrum. The cell may also notify the UE of information on the CCA method to be used. The cell may also notify the UE of this information by including it in the configuration related to measurements of DS on unlicensed spectrum.

[0507] The cell may notify the UE of the setting by individual signaling. RRC signaling is preferably used. This allows for individual setting for each UE. Alternatively, the setting may be broadcast as system information of the cell. This allows for setting for each cell, and when notifying a large number of UEs, the amount of information in individual signaling can be reduced.

[0508] In this embodiment, a DS has been described, but the present invention is not limited to this and may be any signal for synchronization or measurement of an unlicensed spectrum.

[0509] 21 is a conceptual diagram showing an example of DS transmission of a cell and measurement by a UE on an unlicensed spectrum in embodiment 7. Among CCAs 201, 203, and 205, hatched with diagonal lines indicates a case where the CCAs are not clear, and unhatched CCAs indicate a case where the CCAs are clear.

[0510] Among the DSs 202, 204, and 206, the hatched areas indicate that the DSs are being transmitted, and the areas without hatching indicate that the DSs are not being transmitted.

[0511] The cell performs CCA201, and if it is not clear, it does not transmit DS202. If it is not cleared by CCA, it performs CCA203 again after DS transmission cycle 2. The cell performs CCA203, and if it is not cleared again, it does not transmit DS204, and performs CCA205 again after DS transmission cycle 2. The cell performs CCA205, and if it is clear, it transmits DS206.

[0512] A cell periodically transmits a downstream signal on the unlicensed spectrum at a downstream transmission period (Tds) interval. Before transmitting a downstream signal, the cell always performs CCA and follows the method disclosed above.

[0513] The UE measures the DS during DS measurement period 2, which is the DS measurement window for CCA. If the UE has been notified of the DS measurement period and DS transmission cycle 2, the UE may repeat the DS measurement period and DS measurement at DS transmission cycle 2 during DS measurement period 2. When the UE receives a DS, it ends DS reception even if it is in the middle of reception.

[0514] In FIG. 21, the UE receives the DS 206, performs at least one of synchronization and measurement, and ends DS reception. When the UE receives the DS, it measures the DS again after the DS measurement period (Tmeas_p). The UE measures the DS periodically at DS measurement period (Tmeas_p) intervals. The DS measurement follows the method disclosed above.

[0515] By using the method disclosed in this embodiment, when a cell transmits at least one of a synchronization signal and a measurement signal on an unlicensed spectrum, the cell can retransmit the signal even if it is no longer clear. Also, a UE can receive at least one of a synchronization signal and a measurement signal before a cell transmits a DS even if it is no longer clear in CCA.

[0516] Therefore, even in such cases, the UE can synchronize and / or measure the unlicensed spectrum, and CCA can be implemented in the unlicensed spectrum synchronization and / or measurement signals, thereby avoiding collisions with other systems on the unlicensed spectrum, ensuring fairness, and enabling coexistence.

[0517] Seventh embodiment, variant 1 In the method disclosed in the seventh embodiment, if the CCA does not result in clearing, transmission is performed in DS transmission cycle 2. Therefore, DS transmission cannot be performed during DS transmission cycle 2. If the CCA result does not result in clearing, a delay occurs before DS transmission. Therefore, the UE will experience delays in synchronization with and measurement of cells on unlicensed spectrum.

[0518] A method for solving such a problem is disclosed below. If a cell is not cleared by CCA, it continues to perform CCA continuously. If a cell is cleared by CCA, it immediately transmits a DS. Alternatively, a cell may immediately transmit a DS when CCA is cleared a predetermined number of times. It is preferable to set an upper limit on the number of DS transmissions by CCA. The period during which DS transmission by CCA is performed when the upper limit is reached may be within the DS transmission period.

[0519] The method of measuring the DS of the UE may be the same as that disclosed in the seventh embodiment. In addition, the method of setting a DS measurement window for a UE in which a cell configures an unlicensed spectrum and the method of notifying the UE of the setting may be the same as that disclosed in the seventh embodiment.

[0520] Fig. 22 is a conceptual diagram showing an example of DS transmission of a cell on an unlicensed spectrum and measurement by a UE in a first modification of the seventh embodiment. The conceptual diagram shown in Fig. 22 is similar to the conceptual diagram shown in Fig. 21 described above, and therefore the same components are given the same reference numerals and common descriptions will be omitted.

[0521] In the CCA 211, hatched areas indicate that the data is not clear, and areas without hatching indicate that the data is clear. In the DS 212, hatched areas indicate that a DS is being transmitted, and areas without hatching indicate that a DS is not being transmitted.

[0522] The cell performs CCA 213, and if it is not cleared, continues to perform CCA. The cell immediately transmits a DS when CCA is cleared a predetermined number of times. The predetermined number of times may be statically determined in advance by a standard or the like. Alternatively, it may be determined by the core network or an operator and notified to the cell in advance. In this example, the predetermined number of times is three. When CCA 214 is cleared for the third time, the cell transmits a DS 215.

[0523] A cell periodically transmits a downstream signal on the unlicensed spectrum at a downstream transmission period (Tds) interval. Before transmitting a downstream signal, the cell always performs CCA and follows the method disclosed above.

[0524] The UE measures the DS during DS measurement period 2, which is the DS measurement window for CCA. Even if the DS measurement period has been notified, the UE should measure the DS during DS measurement period 2. By doing so, even if DS transmission exceeds the UE's measurement period due to CCA, the UE can measure the DS by measuring the DS during the second DS measurement period. When the UE receives a DS, it stops receiving the DS even if it is in the middle of receiving it.

[0525] In Figure 22, the UE receives the DS 212, performs synchronization and measurement, and ends DS reception. When the UE receives the DS, it measures the DS again after the DS measurement period (Tmeas_p). The UE measures the DS periodically at DS measurement period (Tmeas_p) intervals. The DS measurement follows the method disclosed above.

[0526] By using the method disclosed in this modification, it is possible to obtain the same effect as in the seventh embodiment. Furthermore, the cell can perform CCA according to the DS transmission cycle 2 without waiting for the next DS transmission timing. Therefore, if the cell is cleared by CCA, it can immediately transmit the DS. It is possible to reduce the delay before transmitting the DS.

[0527] In addition, the UE can shorten the time it takes to synchronize with and measure cells in unlicensed spectrum, thereby reducing control delays and power consumption of the UE.

[0528] Although it has been stated that a cell immediately transmits a DS when it is cleared by CCA, it may also transmit a DS from the next subframe. DS transmission may start from the beginning of the next subframe, or after a predetermined symbol. The predetermined symbol may be notified to the UE. The method of notifying the predetermined symbol may be the method disclosed in the seventh embodiment. If there is a time between the end of CCA and the start of transmission of the next DS, a signal indicating an occupied state may be transmitted during that time.

[0529] This prevents other systems from using the unlicensed spectrum during that time, and allows the cell to transmit the next DS without collision with other systems when it starts transmitting, thereby reducing the delay before transmitting the DS.

[0530] Figures 23 and 24 are diagrams showing an example of processing up to data communication when DS transmission and UE measurement are used in Variation 1 of Embodiment 7. Figures 23 and 24 are connected at the position of boundary line BL1. The conceptual diagrams shown in Figures 23 and 24 are similar to the conceptual diagram shown in Figure 22 above, so the same reference symbols are used for the same components and common explanations will be omitted.

[0531] In the CCA 211, hatched areas indicate that the data is not clear, and areas without hatching indicate that the data is clear. In the DS 212, hatched areas indicate that a DS is being transmitted, and areas without hatching indicate that a DS is not being transmitted.

[0532] Cell #1 is a cell on a licensed spectrum, and is the cell to which the UE has an RRC connection. Cell #2 is a cell on an unlicensed spectrum. The examples shown in Figures 23 and 24 show a case where Cell #2 performs DS transmission configuration. The DS transmission configuration includes the DS transmission cycle, offset (measurement start timing), DS sequence, whether to perform CCA, and which CCA method to use.

[0533] In step ST2201, cell #2 notifies cell #1 of the DS transmission configuration. Cell #1 uses the notified DS transmission configuration to perform settings related to DS measurements on the unlicensed spectrum.

[0534] In step ST2202, cell #1 notifies the UE of the DS measurement configuration. The configuration for DS measurement on the unlicensed spectrum includes the unlicensed spectrum frequency (carrier frequency), DS measurement period (Tmeas_p), offset (measurement start timing), and DS measurement window for CCA (DS measurement period 2 (Tmeas_d2)). The DS sequence may also be included. Information on whether to perform CCA and which CCA method to use may also be included. Information on measurement reports may also be included.

[0535] When cell #2 is not transmitting data, it transmits DS according to the DS transmission configuration. The UE, which has received the configuration related to DS measurement on the unlicensed spectrum from cell #1 in Step ST2202, performs DS measurement on the notified frequency (carrier frequency) of the unlicensed spectrum in Step ST2203. The UE performs DS measurement on the frequency (carrier frequency) of the unlicensed spectrum from the measurement start timing during the DS measurement window for CCA, and repeats this measurement at the DS measurement period.

[0536] If the UE receives one or more DSs and the criteria for the measurement report are met, the UE notifies cell #1 of a measurement report in step ST2204. The measurement report reports cell identification such as PCI and reception quality such as RSRP and RSRQ. The criteria for the measurement report should be determined in advance by standards, etc. In this case, the measurement report includes the results of measuring the DS of cell #2.

[0537] Cell #1, which has received the measurement report from the UE, uses the measurement report to decide to configure cell #2 for the UE. In step ST2205, cell #1 notifies the UE of the cell addition. The cell addition includes the cell identifier and carrier frequency of the cell to be added, in this case cell #2. Cell #1 also notifies the UE of the settings related to DS measurement of the cell to be added. If the settings related to DS measurement are the same as those notified in step ST2202, this step may be omitted.

[0538] In Step ST2206, the UE that has received the configuration related to measuring the DS of cell #2 in Step ST2205 measures the DS of cell #2 using the configuration and synchronizes with cell #2. The UE continues to synchronize with cell #2 until it receives a notification from cell #1 that cell #2 has been released. It may also perform further measurements.

[0539] In step ST2207, cell #1, which has decided to communicate with the UE using cell #2, notifies the UE that cell #2 is active (cell activation). Having received this notification, the UE starts receiving data from cell #2 in step ST2210. Because data transmission from cell #2 may occur every subframe, the UE continues receiving data until it is notified by cell #1 that cell #2 is deactivated.

[0540] Furthermore, cell #1, which has decided to communicate with the UE using cell #2, notifies cell #2 of an instruction to activate data transmission (cell activation) in step ST2208. Having received this instruction, cell #2 transmits data to the UE in step ST2209. The UE receives the data transmitted from cell #2.

[0541] This allows CCA to be implemented before transmitting at least one of a synchronization signal and a measurement signal on the unlicensed spectrum when the cell on the unlicensed spectrum is not transmitting data, and allows the UE to receive at least one of the synchronization signal and the measurement signal on the unlicensed spectrum even after implementing CCA.

[0542] This also enables UEs to synchronize with and measure cells in unlicensed spectrum, and allows cells in licensed spectrum to add and activate unlicensed spectrum cells, thereby enabling data communication using cells in unlicensed spectrum.

[0543] This also enables LAA using cells on licensed spectrum and cells on unlicensed spectrum, avoiding collisions with other systems on unlicensed spectrum, ensuring fairness and coexistence with other systems.

[0544] The above-described embodiments and their modifications are merely examples of the present invention, and the embodiments and their modifications may be freely combined within the scope of the present invention. Furthermore, any component of the embodiments and their modifications may be modified or omitted as appropriate. This provides a communication system that can improve the communication performance of communication terminal devices even when supporting various services, such as MTC support and the use of unlicensed spectrum.

[0545] Although the present invention has been described in detail, the above description is illustrative in all respects and does not limit the present invention, and it is understood that countless variations not illustrated can be assumed without departing from the scope of the present invention. [Explanation of symbols]

[0546] 1301 Macro eNB (macro cell) coverage, 1302 Small eNB (small cell) coverage.

Claims

1. A communication system including a communication terminal and a base station that communicates wirelessly with the communication terminal, the communication terminal includes a narrowband terminal that wirelessly communicates with the base station using a frequency band narrower than a system band that is a frequency band that can be used in wireless communication; transmitting the information for the narrowband terminal from the base station to the communication terminal repeatedly over successive subframes; A communication system characterized in that the information for the narrowband terminal is transmitted from the base station to the communication terminal using a physical downlink control channel used in narrowband resources.

2. 2. The communication system according to claim 1, wherein the information for the narrowband terminal is system information used in the communication system.

3. 2. The communication system according to claim 1, wherein the information for the narrowband terminal is paging information for the narrowband terminal.

4. 4. The communication system according to claim 3, wherein the paging information for the narrowband terminal is timing of paging for the narrowband terminal.

5. 4. The communication system according to claim 3, wherein the paging information for the narrowband terminal is information on repeated paging.

6. 6. The communication system according to claim 5, wherein the paging repetition information is a paging repetition number.

7. A base station that wirelessly communicates with a communication terminal, the communication terminal includes a narrowband terminal that wirelessly communicates with the base station using a frequency band narrower than a system band that is a frequency band that can be used in wireless communication; repeatedly transmitting the information for the narrowband terminal to the communication terminal over successive subframes; A base station characterized in that it transmits information for the narrowband terminal to the communication terminal using a physical downlink control channel used in narrowband resources.

8. A communication terminal that wirelessly communicates with a base station, a narrowband terminal that wirelessly communicates with the base station using a frequency band narrower than a system band that is a frequency band that can be used in wireless communication; receiving information for the narrowband terminal from the base station repeatedly over successive subframes; A communication terminal characterized in that the information for the narrowband terminal is received from the base station using a physical downlink control channel used in narrowband resources.

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