Mobile communication system, mobile terminal, and base station

Abstract

To improve the communication performance of a communication terminal device when a large number of small cells are installed and operated in addition to a macro cell.SOLUTION: A mobile communication system includes a mobile terminal (UE) and a base station configured to be able to wirelessly communicate with the mobile terminal. In the mobile communication system, a sounding reference signal is transmitted from the mobile terminal to the base station for each mobile terminal. The sounding reference signal is used for position measurement of the mobile terminal. The position measurement of the mobile terminal is performed using the arrival angle of radio waves.SELECTED DRAWING: Figure 25

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 new communication method called Long Term Evolution (LTE) for wireless sections and System Architecture Evolution (SAE) for the overall system configuration including a core network and a wireless access network (hereinafter collectively referred to as a network) (see, for example, Non-Patent Documents 1 to 14). This communication method is also called a 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. Also, 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, which are described in Non-Patent Document 1 (Chapter 5), will be described with reference to FIG. 1. FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. In FIG. 1, one radio frame is 10 ms. The radio frame is divided into 10 subframes of equal size. The subframe is divided into two slots of equal size. The first and sixth subframes of each radio frame include a downlink synchronization signal (SS). The synchronization signal includes 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 the base station to the mobile terminal. The BCH transport block is mapped to four subframes in 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 OFDM (Orthogonal Frequency Division Multiplexing) symbols to be 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 later, resource allocation information for a Paging Channel (PCH), which is one of the transport channels described later, and Hybrid Automatic Repeat reQuest (HARQ) information for the DL-SCH. The PDCCH carries an uplink scheduling grant. The PDCCH carries Acknowledgement (Acknowledgement) / Nack (Negative Acknowledgement), which are response signals to uplink transmission. The PDCCH is also called an L1 / L2 control signal.

[0009] A 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 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 is a response signal to a downlink transmission. The PUCCH carries a CQI (Channel Quality Indicator) report. CQI is quality information that indicates the quality of received data or the quality of the communication path. The PUCCH also carries a Scheduling Request (SR).

[0012] A Physical Uplink Shared Channel (PUSCH) is a channel for uplink transmission from a mobile terminal to a base station. An 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 is a response signal to an uplink transmission. 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 Signals (CRS), MBSFN reference signals, UE-specific reference signals such as Demodulation Reference Signals (DM-RS), Positioning Reference Signals (PRS), and Channel-State Information Reference Signals (CSI-RS). Reference signal received power (RSRP) measurement is one of the physical layer measurements of a mobile terminal.

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

[0016] Retransmission control using HARQ (Hybrid ARQ) is applied to the Downlink Shared Channel (DL-SCH). 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) of mobile terminals to reduce power consumption of mobile terminals. DL-SCH is mapped to the physical downlink shared channel (PDSCH).

[0017] The Paging Channel (PCH) supports DRX of mobile terminals to enable low power consumption of the mobile terminals. The PCH is required to be 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] Here we explain HARQ. HARQ is a technology that improves the communication quality of a transmission path by combining Automatic Repeat reQuest (ARQ) and Forward Error Correction. HARQ has the advantage that error correction works effectively by retransmission even for transmission paths where communication quality changes. In particular, by combining the reception result of the initial transmission and the reception result of the retransmission when retransmitting, it is possible to obtain further quality improvement.

[0022] An example of a retransmission method will be described below. If the received data cannot be decoded correctly on the receiving side, in other words, if a CRC (Cyclic Redundancy Check) error occurs (CRC=NG), the receiving side will send a "Nack" to the transmitting side. The transmitting side that receives the "Nack" will retransmit the data. If the received data can be decoded correctly on the receiving side, in other words, if no CRC error occurs (CRC=OK), the receiving side will send an "Ack" to the transmitting side. The transmitting side that receives the "Ack" will send the next data.

[0023] The logical channel described in Non-Patent Document 1 (Chapter 6) will be explained. The Broadcast Control Channel (BCCH) is a downlink channel for broadcast system control information. The logical channel BCCH 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 changes to system information. 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 for transmission of MBMS control information for one or several MTCHs from the network to the 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. DCCH is used when a mobile terminal is in an RRC connection. 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 one-to-one 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, DTCH is mapped to a downlink shared channel (DL-SCH).

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

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

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

[0032] A CSG cell is a 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 by 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 receive calls. The area for tracking the location of a mobile terminal is called a tracking area.

[0035] In 3GPP, base stations called Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB) are under consideration. HNB in ​​UTRAN and HeNB in ​​E-UTRAN are base stations for home, corporate and commercial access services, for example. Non-Patent Document 3 discloses three different modes of access to HeNB and HNB. Specifically, an open access mode, a closed access mode and a hybrid access mode are disclosed.

[0036] Each mode has the following characteristics: In the open access mode, the HeNB and the HNB are operated as normal cells of a normal operator. In the closed access mode, the HeNB and the HNB are operated as CSG cells, which are accessible only by CSG members. In the hybrid access mode, the HeNB and the HNB are operated as CSG cells to which non-CSG members are also allowed to access at the same time. 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 (PCI), there is a PCI range reserved by the network for use in CSG cells (see Chapter 10.5.1.1 of Non-Patent Document 1). Dividing a PCI range is sometimes called PCI split. Information on PCI split (also called PCI split information) is notified by the 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 needs to perform a cell search using all PCIs, for example, all 504 codes. 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 standards for Long Term Evolution Advanced (LTE-A) as Release 10 (see Non-Patent Documents 5 and 6). LTE-A is based on the LTE wireless communication method, and is configured by adding several new technologies to it.

[0040] In the LTE-A system, carrier aggregation (CA), which aggregates two or more component carriers (CCs) (also called "aggregation"), is being considered in order to support wider frequency bandwidths (transmission bandwidths) of 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 a 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] According to the capability of the UE, a secondary cell (SCell) is configured to form a pair of a PCell and a serving cell. In the downlink, the carrier corresponding to the SCell is a downlink secondary component carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is an uplink secondary component carrier (UL SCC).

[0043] For one UE, a set of one PCell and a serving cell consisting of one or more SCells is configured.

[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] In addition, 3GPP is currently formulating Release 12 of the specifications. In this document, the use of small eNBs that configure small cells is being considered in order to handle the huge amount of traffic in the future. For example, technology is being considered that aims to increase communication capacity by improving frequency utilization efficiency by installing many small eNBs and configuring many small cells.

[0046] Mobile network traffic volume is on the rise, and communication speeds are also becoming faster. When LTE and LTE-A are fully operational, communication speeds are expected to increase further, leading to an increase in traffic volume. [Prior art documents] [Non-patent literature]

[0047] [Non-Patent Document 1] 3GPP TS36.300 V12.1.0 [Non-Patent Document 2] 3GPP TS36.304 V12.0.0 [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 TR36.842 V12.0.0 [Non-Patent Document 10] 3GPP TS23.041 V12.5.0 [Non-Patent Document 11] 3GPP R2-142471 [Non-Patent Document 12] 3GPP R2-142027 [Non-Patent Document 13] 3GPP TS23.401 V12.4.0 [Non-Patent Document 14] 3GPP TS36.211 V12.1.0 Summary of the Invention [Problem to be solved by the invention]

[0048] When a large number of small cells are installed and operated in addition to a macro cell, problems such as deterioration of mobility performance and increase in interference occur. In order to solve these problems, 3GPP is studying dual connectivity (DC) technology. In DC, it is considered that UE will communicate using macro cells and small cells. Specifically, it is considered that UE mobility performance will be ensured by the macro cell, and that throughput will be increased by using macro cell resources and small cell resources together when performing data communication.

[0049] However, there is a problem that applying DC to conventional technologies without any ingenuity will result in an impossible technology. For example, there are PWS (Public Warning System), which is a service for notifying warning information, emergency services, and UE-requested bearer modification. In PWS, it is impossible to notify UEs in DC of warning information for small cells. In emergency services, when DC is executed, a secondary eNB may reject the execution of DC in the status of its own eNB. In UE-requested bearer modification, it is not possible to modify a DCed bearer. A method for solving such problems is required.

[0050] In addition, when considering the installation and operation of many small cells in addition to the macro cell in DC, further improvement of mobility performance is desired. For example, when a UE moves within a macro cell and changes small cells, the conventional method of deriving the UE's position and moving state cannot optimally change small cells, resulting in a problem of degradation of mobility performance.

[0051] Also, 3GPP is considering technologies such as CoMP and MIMO (Multiple Input and Multiple Output) that use multiple cells (points) or multiple antennas to communicate with a UE. This technology aims to reduce the effects of interference and increase throughput by using multiple cells or multiple antennas in a coordinated manner.

[0052] However, when considering the installation and operation of a large number of small cells in addition to macro cells in technologies such as CoMP and MIMO, there is a demand for technologies that further improve mobility performance and reduce interference, as well as technologies that enable optimal scheduling in the cell to which the UE moves and increase throughput.

[0053] An object of the present invention is to improve the communication performance of a communication terminal device when a large number of small cells are installed and operated in addition to a macro cell. [Means for solving the problem]

[0054] The mobile communication system of the present invention is a mobile communication system including a mobile terminal and a base station that performs wireless communication between the mobile terminal and the mobile terminal, and is characterized in that a sounding reference signal individual for each mobile terminal is transmitted from the mobile terminal to the base station, the sounding reference signal is used for measuring the position of the mobile terminal, and the position measurement of the mobile terminal is performed using the angle of arrival of radio waves. The mobile terminal of the present invention is a mobile terminal that performs wireless communication with a base station, and is characterized in that an individual sounding reference signal is transmitted to the base station for each mobile terminal, the sounding reference signal is used to measure the position of the mobile terminal, and the position measurement of the mobile terminal is performed using the arrival angle of radio waves. The base station of the present invention is a base station that performs wireless communication with mobile terminals, and receives an individual sounding reference signal for each mobile terminal from the mobile terminal, the sounding reference signal is used for position measurement of the mobile terminal, and the position measurement of the mobile terminal is performed using the arrival angle of radio waves. Effect of the Invention

[0055] According to the present invention, it is possible to improve the communication performance of a communication terminal device when a large number of small cells are installed and operated in addition to a macro cell.

[0056] The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0057] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Diagram 2]7 is a block diagram showing the overall configuration of an LTE communication system 700 being discussed in 3GPP. [Diagram 3] FIG. 3 is a block diagram showing a 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 a configuration of a base station 72 shown in FIG. 2 which is a base station according to the present invention. [Diagram 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 performed by a mobile terminal (UE) in an LTE communication system. [Figure 7] A diagram showing the concept of a cell configuration when macro eNBs and small eNBs are mixed. [Figure 8] A figure showing an example of a cell configuration when a macro cell and a small cell are overlaid. [Figure 9] 2 is a diagram showing an example of a flow of PWS messages in the communication system of the first embodiment. FIG. [Figure 10] 11 is a diagram showing an example of a sequence of a PWS message notification process in the communication system of the first embodiment. [Figure 11] FIG. 11 is a diagram showing another example of the sequence of PWS message notification processing in the communication system of the first embodiment. [Figure 12] A figure showing an example of the flow of PWS messages in a communication system of variant 1 of embodiment 1. [Figure 13] FIG. 11 is a diagram showing an example of a sequence of a PWS message notification process in a communication system according to a first modification of the first embodiment. [Figure 14] FIG. 13 is a diagram showing another example of the sequence of PWS message notification processing in the communication system according to the first modification of the first embodiment. [Figure 15] A figure showing an example of the flow of PWS messages in a communication system of variant example 2 of embodiment 1. [Figure 16]FIG. 11 is a diagram showing an example of a sequence of a PWS message notification process in a communication system according to a second modification of the first embodiment. [Figure 17] FIG. 11 is a diagram showing another example of the sequence of PWS message notification processing in the communication system according to the second modification of the first embodiment. [Figure 18] FIG. 13 is a diagram showing an example of a sequence of a PWS message notification process in a communication system according to a third modification of the first embodiment. [Figure 19] FIG. 13 is a diagram showing another example of the sequence of PWS message notification processing in the communication system of the third modification of the first embodiment. [Figure 20] FIG. 13 is a diagram showing an example of the flow of PWS messages in a communication system according to a fourth variant of the first embodiment. [Figure 21] A figure showing an example of a sequence of DC execution processing for an emergency bearer in a communication system of embodiment 2. [Figure 22] A figure showing an example of a sequence of UE-initiated DC bearer modification processing in a communication system of embodiment 3. [Figure 23] A figure showing another example of a sequence of UE-initiated DC bearer modification processing in a communication system of embodiment 3. [Figure 24] A figure showing an example of a sequence of measurement processing of an SCG cell in a communication system of variant example 1 of embodiment 4. [Diagram 25] FIG. 1 is a diagram showing the concept of UL CoMP being considered by 3GPP. [Figure 26] FIG. 21 is a diagram showing an example of the operation of a DC in a communication system according to a first modification of the fifth embodiment. [Figure 27] FIG. 21 is a diagram showing an example of the operation of a DC in a communication system according to a first modification of the fifth embodiment. [Figure 28] FIG. 23 is a diagram illustrating the concept of the problem to be solved in the sixth embodiment. [Figure 29] FIG. 23 is a diagram showing an example of a sequence of SRS reception processing in a communication system according to a sixth embodiment. [Diagram 30]FIG. 23 is a diagram showing another example of the sequence of the SRS reception processing in the communication system of the sixth embodiment. [Diagram 31] 11 is a diagram illustrating the difference between the SRS reception start threshold and the HO start threshold for a measurement report value. [Diagram 32] FIG. 13 is a diagram illustrating an example of antenna control in a communication system according to a seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Embodiment 1 Fig. 2 is a block diagram showing the overall configuration of an LTE-based communication system 700 being discussed in 3GPP. Fig. 2 will be described. 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.

[0059] If control protocols for mobile terminal 71, such as RRC (Radio Resource Control), and user plane protocols, such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate in base station 72, E-UTRAN is composed of one or more base stations 72.

[0060] A 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.

[0061] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell re-selection, 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.

[0062] 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 including an EPC (Evolved Packet Core) core network and an E-UTRAN 70 radio access network is called 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."

[0063] The eNB76 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 eNB76 and the MME unit 73. A plurality of MME units 73 may be connected to one eNB76. The eNB76 are connected to each other via an X2 interface, and control information is communicated between the eNB76.

[0064] 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 Home-eNB GateWay (HeNBGW) 74. The Home-eNB 75 and the HeNBGW 74 are connected to each other via an S1 interface, and the HeNBGW 74 and the MME unit 73 are connected to each other via the S1 interface.

[0065] One or a plurality of Home-eNBs 75 are connected to one HeNBGW 74, and information is communicated through an S1 interface. The HeNBGW 74 is connected to one or a plurality of MME units 73, and information is communicated through an S1 interface.

[0066] The MME unit 73 and the HeNBGW 74 are upper devices, specifically, upper nodes, and control connections between the eNB 76 and the 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 the HeNBGW 74 constitute the E-UTRAN 70.

[0067] Furthermore, 3GPP is considering the following configuration. The X2 interface between Home-eNBs 75 is supported. That is, the Home-eNBs 75 are connected via the X2 interface, and control information is communicated between the Home-eNBs 75. From the MME unit 73, the HeNBGW 74 appears as the Home-eNB 75. From the Home-eNB 75, the HeNBGW 74 appears as the MME unit 73.

[0068] 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 directly connected to the MME unit 73, the interface between the Home-eNB 75 and the MME unit 73 is the same, that is, the S1 interface.

[0069] The base station device 72 may configure one cell or multiple cells. Each cell has a predetermined coverage area in 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.

[0070] FIG. 3 is a block diagram showing the configuration of the mobile terminal 71 shown in FIG. 2, which is a mobile terminal according to the present invention. The transmission process of the mobile terminal 71 shown in FIG. 3 will be described. First, the control data from the protocol processing unit 801 and the user data from the application unit 802 are stored in the transmission data buffer unit 803. The data stored in the transmission data buffer unit 803 is passed to the encoder unit 804, where encoding such as error correction is performed. There may be data that is directly output from the transmission data buffer unit 803 to the modulation unit 805 without encoding. The data that has been encoded by the encoder unit 804 is modulated by the modulation unit 805. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 806, where it is converted into a radio transmission frequency. Thereafter, a transmission signal is transmitted from the antenna 807 to the base station 72.

[0071] Moreover, the receiving process of the mobile terminal 71 is executed 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 such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 801, and the 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.

[0072] Fig. 4 is a block diagram showing the configuration of the base station 72 shown in Fig. 2 which is a base station according to the present invention. The transmission process of the base station 72 shown in Fig. 4 will be described. The EPC communication unit 901 transmits and receives data between the base station 72 and the EPC (MME unit 73, etc.), the HeNBGW 74, etc. The 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. The control data from the protocol processing unit 903, and the 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.

[0073] The data stored in the transmission data buffer unit 904 is passed to an encoder unit 905, where it undergoes encoding processing 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 processing. The encoded data is modulated in 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.

[0074] The reception process of the base station 72 is executed 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 conversion unit 907, and demodulated by a demodulation unit 909. The demodulated data is passed to a decoder unit 910, where decoding such as error correction is performed. Of the decoded data, control data is passed to a protocol processing unit 903 or an EPC communication unit 901 or an other base station communication unit 902, and user data is passed to the EPC communication unit 901 and the other base station communication unit 902. A series of processes of the base station 72 is controlled by a control unit 911. Therefore, although the control unit 911 is omitted in FIG. 4, it is connected to each unit 901 to 910.

[0075] FIG. 5 is a block diagram showing the configuration of the MME according to the present invention. FIG. 5 shows the configuration of the MME 73a included in the MME unit 73 shown in FIG. 2 described above. The PDN GW communication unit 1001 transmits and receives data between the MME 73a and the PDN GW. The base station communication unit 1002 transmits and receives data between the MME 73a and the base station 72 via the S1 interface. 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 the 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.

[0076] When 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. When 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.

[0077] 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 a control plane control unit 1005. A result of processing in the control plane control unit 1005 is transmitted to the PDN GW via a PDN GW communication unit 1001. In addition, a result of processing in the control plane control unit 1005 is transmitted to one or more base stations 72 by the S1 interface via a base station communication unit 1002, and is also transmitted to one or more HeNBGW 74 via the HeNBGW communication unit 1004.

[0078] 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, etc., and performs general 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 an idle state (also called an idle state; LTE-IDLE state, or simply idle), generation and control of paging signals in an idle state, addition, deletion, update, search, tracking area list management, etc. for one or more mobile terminals 71 under its control.

[0079] The MME 73a distributes a paging signal 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 a mobile terminal is in an idle state and in an active state. The MME 73a starts a paging protocol by transmitting a paging message to a cell belonging to a tracking area in which a UE is registered. The idle state mobility management unit 1005-3 may manage the CSG and CSG-ID of the Home-eNB 75 connected to the MME 73a, and manage the whitelist.

[0080] Next, an example of a cell search method in a communication system is shown. Fig. 6 is a flow chart showing an outline of a 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 a surrounding base station.

[0081] 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 PCI numbers are being considered. These 504 different PCIs are used to achieve synchronization and to detect (identify) the PCI of the synchronized cell.

[0082] 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 reference signal (RS) uses a code that has a one-to-one correspondence with the PCI. By correlating with the 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.

[0083] 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.

[0084] Next, in step ST4, the PBCH of the best cell is received to obtain the BCCH, which is broadcast information. The 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 DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, and SFN (System Frame Number).

[0085] Next, in step ST5, the DL-SCH of the cell is received based on the cell configuration information of 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 of other SIBs (SIBk; k is an integer ≧2). SIB 1 also includes a tracking area code (TAC).

[0086] Next, in step ST6, the mobile terminal compares the TAC of the SIB1 received in step ST5 with the TAC portion 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 a 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 code number of the tracking area.

[0087] 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 the tracking area to perform a Tracking Area Update (TAU) through the cell to a core network (EPC) including an MME, etc.

[0088] 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 (UE-ID, etc.) of a mobile terminal sent from the mobile terminal together with a 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. After that, the mobile terminal enters standby mode in the cell.

[0089] The spread of smartphones and tablet devices has led to an explosive increase in traffic via cellular wireless communications, raising concerns about a shortage of wireless resources around the world. In response to this, efforts are being made to create smaller cells and promote spatial separation in order to improve frequency utilization efficiency.

[0090] In a conventional cell configuration, a cell configured by an eNB has a relatively wide coverage area. Conventionally, a cell is configured to cover a certain area by the relatively wide coverage areas of a plurality of cells configured by a plurality of eNBs.

[0091] In the case of small cell configuration, the cell configured by the eNB has a narrower coverage range than the coverage of the cell configured by the conventional eNB. Therefore, as in the past, in order to cover a certain area, a large number of small cell eNBs are required compared to the conventional eNBs.

[0092] 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 that has been made into 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."

[0093] The macro eNB may be, for example, a “Wide Area Base Station” as described in Non-Patent Document 8.

[0094] 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.

[0095] 7 is a diagram showing the concept of a cell configuration when a macro eNB and a small eNB 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).

[0096] 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 Fig. 7, as shown by reference numerals "1304" or "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.

[0097] Also, as indicated by reference numeral "1305," the coverage of a plurality of small cells, for example, two small cells 1302, may be included in the coverage of one macro cell 1301. A mobile terminal (UE) 1303 is included, for example, in the coverage 1302 of the small cell and communicates via the small cell.

[0098] 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.

[0099] Also, as indicated by reference numeral "1307," there are cases in which 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.

[0100] Furthermore, as indicated by reference numeral "1308," there may be cases where the coverage 1302 of multiple small cells formed by multiple small eNBs is formed within the coverage 1301 of one macro cell formed by one macro eNB.

[0101] In operating small cells, there are studies underway to improve throughput by configuring small cells in areas with high traffic within the coverage of a macro cell, i.e., by overlaying small cells on top of macro cells.

[0102] Fig. 8 is a diagram showing an example of a cell configuration when a macro cell and a small cell are overlaid. In Fig. 8, similarly to Fig. 7, the coverage of the macro cell is indicated by reference symbol "1301" and the coverage of the small cell is indicated by reference symbol "1302".

[0103] In 3GPP, dual connectivity (abbreviated as DC) is being discussed in which a UE connects to both a macro cell and a small cell in a cell configuration as shown in Fig. 8 (see Non-Patent Document 9). In a control plane (C-plane) for a UE performing DC, a SeNB (Secondary eNB) is connected to an MME via an MeNB (Master eNB).

[0104] For UEs that perform DC, two architectures are mainly considered in the user plane (U-plane). One is an architecture in which the SeNB is directly connected to the S-GW (hereinafter, sometimes referred to as "architecture 1A"), and the other is an architecture in which the SeNB is connected to the S-GW via the MeNB (hereinafter, sometimes referred to as "architecture 3C").

[0105] Here, the MeNB is an eNB that configures a macro cell in the DC. The SeNB is an eNB that configures a small cell in the DC. In addition, a cell group configured by the MeNB is called an "MCG", and a cell group configured by the SeNB is called an "SCG". A cell in the MCG is called an "MCG cell", and a cell in the SCG is called an "SCG cell". A cell that transmits PUCCH in the MCG is called a "PCell". A special cell that transmits PUCCH in the SCG is called an "SPCell". The SPCell has some functions of the PCell.

[0106] The problem to be solved in the first embodiment and the solution thereto are described below. A PWS (Public Warning System) is a system that notifies UEs in a specific area of ​​a warning message (see Non-Patent Document 10). Examples of PWS include ETWS (Earthquake and Tsunami Warning System), CMAS (Commercial Mobile Alert System), EU-ALERT (European Public Warning System), and KPAS (Korean Public Alert System).

[0107] Due to the importance of the messages to be notified, PWS is supported not only for UEs in RRC_IDLE but also for UEs in RRC_CONNECTED. Furthermore, messages in PWS (hereinafter sometimes referred to as "PWS messages") are notified from MME to eNB via S1-MME, which is an interface of the control plane (C-Plane). PWS messages correspond to small cell-oriented information from higher-level devices to small cells. The higher-level devices are, for example, CBE (Cell Broadcast Entity), CBC (Cell Broadcast Centre), and MME, which will be described later.

[0108] In the DC considered by 3GPP, the SeNB is not directly connected to the MME in the control plane (C-Plane) of the UE in the DC. Therefore, when the above-mentioned PWS is applied to the DC, the UE performing the DC using the SeNB is not a notification target of the PWS message for the SeNB, and the UE cannot receive the PWS message for the SeNB.

[0109] In 3GPP, with regard to the handling of PWS in DC, only the reception of PWS messages for MeNB by UE in DC has been considered, and there has been no discussion at all about the method of receiving PWS messages for SeNB (see non-patent documents 11 and 12).

[0110] Since the PWS is targeted to a specific area, even if the SeNB and the MeNB are configured in an overlay, the PWS message for the SeNB may be different from the PWS message for the MeNB. Therefore, it is useful for a UE that is within the coverage of a SeNB to be able to receive the PWS message for the SeNB.

[0111] In the first embodiment, a method is disclosed that enables a UE performing DC using a SeNB to receive a PWS message for the SeNB.

[0112] The solution in the first embodiment is as follows. The SeNB transmits a PWS message for the SeNB to the UE in the DC. The UE performing the DC using the SeNB receives the PWS message for the SeNB.

[0113] When a PWS message is notified to one or more specific SCG cells, the SeNB used for DC transmits a PWS message for its own SCG cell to a UE performing DC using its own SCG cell. The UE performing DC using the SCG cell receives the PWS message for the SCG cell.

[0114] A method of notifying a PWS message will now be described. Fig. 9 is a diagram showing an example of the flow of a PWS message in the communication system of embodiment 1. In Fig. 9, the flow of the PWS message is indicated by bold arrows 106, 107, and 108.

[0115] The PWS message is notified from a CBE (Cell Broadcast Entity) (not shown) to a CBC (Cell Broadcast Centre) 101. The CBC 101 notifies the MME 102 of the PWS message notified from the CBE, as indicated by an arrow 106.

[0116] MME102 notifies the eNB of the PWS message notified from CBC101. Specifically, MME102 notifies SeNB104 of the PWS message as shown by arrow 107. MME102 also notifies MeNB103 of the PWS message. When the eNB's own cell is used for DC, that is, when it is SeNB104, the eNB notifies UE105 performing DC using its own cell of the PWS message notified from MME102 as shown by arrow 108.

[0117] The MME 102 and the MeNB 103 are connected by an interface 111. An S1 interface is used for the interface 111 between the MME 102 and the MeNB 103. Here, an interface for the UE 105 in the DC is shown.

[0118] The MeNB 103 and the SeNB 104 are connected by an interface 112. An X2 or Xn interface is used for the interface 112 between the MeNB 103 and the SeNB 104. Here, an interface for the UE 105 in the DC is shown.

[0119] In order for SeNB104 to notify UE105 performing DC using its own cell of a PWS message, the SCG cell may broadcast the PWS message by including it in a SIB.

[0120] A new SIB may be provided as the SIB that contains the PWS message (hereinafter, sometimes referred to as the "SIB for PWS messages"), or an existing SIB may be used. Examples of existing SIBs that contain PWS messages include SIB10 and SIB11 for ETWS and SIB12 for CMAS.

[0121] The method by which the SCG cell notifies the UE in the DC of the PWS message can be applied to the method by which the SCG cell broadcasts the PWS message to the UE under its control. The SCG cell must notify the UE under its control of the PWS message. The notification is performed by broadcasting.

[0122] Therefore, by using a method in which an SCG cell notifies a UE performing DC using its own cell of a PWS message by broadcasting the PWS message to the UE being served by the SCG cell, it is not necessary to add new processing. This prevents the functions of the SeNB from becoming complicated and reduces malfunctions.

[0123] A UE performing DC using an SCG cell receives a SIB for a PWS message broadcast from the SCG cell. Since a PWS message is broadcasted in a SIB for a PWS message, the UE receives the PWS message in the SIB for a PWS message by receiving the SIB for a PWS message.

[0124] A PWS indication may be provided to indicate to the UE in the DC that the PWS message has been broadcast. The PWS indication corresponds to broadcast instruction information indicating that information for small cells has been broadcast. The PWS indication is notified to the UE in the DC prior to the PWS message. When the UE in the DC receives the PWS indication, it receives a SIB including the PWS message of the SCG cell. In FIG. 9, the flow of the PWS indication is indicated by arrows 109 and 110.

[0125] When the SeNB 104 receives a PWS message for its own SeNB from the MME 102, the SeNB 104 notifies the UE 105 of a PWS indication. The following two methods (1) and (2) are disclosed as specific examples of a method for notifying the PWS indication.

[0126] (1) SeNB 104 directly notifies UE 105 in the DC as shown by arrow 110.

[0127] (2) As shown by arrow 109, SeNB 104 notifies UE 105 in the DC via MeNB 103.

[0128] A case where the notification method (1) above is applied as a method for notifying a PWS indication will be described. The SeNB 104 that receives a PWS message from the MME 102 identifies an SCG cell that transmits the PWS message. The SCG cell includes the PWS indication in a paging message and notifies UEs under its control. The SCG cell also notifies UEs in a DC by including the PWS indication in a paging message. The SCG cell also broadcasts the PWS message.

[0129] A UE performing DC using an SCG cell receives a paging message from the SCG cell and receives a PWS indication in the paging message.

[0130] As the PWS indication, a new indication may be provided, or an existing indication may be used. Examples of the existing indication include an ETWS indication for an ETWS and a CMAS indication for a CMAS.

[0131] When a UE performing DC using an SCG cell receives a PWS indication in a paging message, it receives a SIB including a PWS message of the SCG cell.

[0132] The SIB containing the PWS message may be statically determined in advance. Alternatively, the SIB containing the PWS message may be determined by a standard.

[0133] A UE performing DC using an SCG cell receives a SIB (SIB1) containing scheduling information in order to receive a SIB containing a PWS message. A UE in DC that receives SIB1 of an SCG cell receives a SIB containing a PWS message using the scheduling information.

[0134] Fig. 10 is a diagram showing an example of a sequence of a PWS message notification process in the communication system of embodiment 1. Fig. 10 shows an example in which the above-mentioned notification method (1) is applied as a method for notifying a PWS indication.

[0135] In Step ST1001, the UE, the MeNB, and the MME perform a registration procedure. Specifically, in the registration procedure, the UE registers with the MME via the MeNB. After completing the registration procedure, the UE transitions to an RRC_CONNECTED state with the MeNB.

[0136] In step ST1002, the MeNB activates an SeNB addition procedure (hereinafter may be referred to as "SeNB addition procedure") to execute DC for the UE. This causes the SeNB addition procedure to be performed between the MeNB, the UE, and the SeNB. Specific contents of the SeNB addition procedure are disclosed in, for example, Non-Patent Document 9. In the SeNB addition procedure, the UE synchronizes with the SCG cell to be added.

[0137] In step ST1003, the UE that has performed the SeNB addition process and has been synchronized with the SCG cell to be added receives the PCH to which the paging message of the SCG cell is mapped. In this embodiment, the UE discontinuously receives the PCH to which the paging message of the SCG cell is mapped.

[0138] The UE may receive information related to the PCH transmission timing of the SCG cell from the SeNB via the MeNB. The SeNB notifies the MeNB of information related to the PCH transmission timing of the SCG cell. The MeNB notifies the UE of information related to the PCH transmission timing of the SCG cell. These notifications may be performed in the SeNB addition process in step ST1002. The information related to the PCH transmission timing may include a DRX cycle.

[0139] Also, the SeNB recognizes the identifier of the UE in advance. The MeNB may notify the SeNB of the identifier of the UE that executes DC. This notification may be performed in the SeNB addition process in step ST1002.

[0140] As an identifier of the UE, it is preferable to use IMSI (International Mobile Subscriber Identity). By receiving the IMSI of the UE that executes DC by the SeNB, it becomes possible to derive the PCH transmission timing to the UE in the same manner as the conventional PCH transmission timing derivation method for the UE under its control. In addition, the UE in DC can also derive the PCH transmission timing from the SCG cell from the conventional derivation method based on its own IMSI.

[0141] In step ST1004, a cell broadcast centre (CBC) receives a PWS message from a cell broadcast entity (CBE) (not shown). Specifically, the CBC receives an emergency broadcast request message as the PWS message.

[0142] In step ST1005, the CBC that has received the PWS message from the CBE notifies the MME of the PWS message via the SBc interface.

[0143] In Step ST1005, the CBC notifies the MME of a tracking area ID list, warning area information, and a global eNB ID together with the PWS message. The CBC may also notify the MME of an identifier unique to the PWS message. The warning area information is composed of a list of cell identifiers, a list of tracking area identifiers, or an emergency area identifier.

[0144] A "Write-Replace Warning Request" message is used as a message for notifying the PWS message, the tracking area ID list, the warning area information, and the global eNB ID. That is, in step ST1005, the CBC notifies the MME of the PWS message, the tracking area ID list, the warning area information, and the global eNB ID by notifying the MME of the "Write-Replace Warning Request" message.

[0145] The MME that has received the PWS message identifies the eNB to which the PWS message is to be notified from a tracking area ID list. Here, a case is shown in which the SeNB is included in the tracking area ID list.

[0146] Furthermore, in step ST1006, the MME that has received the PWS message notifies the CBC of a PWS message reception confirmation message. As a message for notifying the PWS message reception confirmation message, a "Write-Replace Warning Confirm" message is used.

[0147] In step ST1007, the CBC that has received the PWS message reception confirmation message notifies the CBE of a PWS message reception response message. Specifically, the CBC notifies the CBE of an emergency broadcast response message as the PWS message reception response message.

[0148] The MME may notify the PWS message reception confirmation message in Step ST1006 after transmitting a "Write-Replace Warning Request" message in Step ST1008 described later, or after receiving a "Write-Replace Warning Response" message in Step ST1012. The MME may notify the eNB of the PWS message or after receiving a response to the PWS message notification from the eNB.

[0149] In Step ST1008, the MME notifies the SeNB of the PWS message via the S1-MME interface. In Step ST1008, the MME notifies the SeNB of warning area information together with the PWS message. The MME may also notify an identifier unique to the PWS message. As a message for notifying the PWS message and warning area information, a "Write-Replace Warning Request" message is used.

[0150] The SeNB that receives the PWS message uses warning area information to check whether the PWS message is intended for the SeNB itself. If the PWS message is intended for the SeNB itself, the SeNB uses the warning area information to identify the SCG cell that transmits the PWS message.

[0151] In step ST1009, the SeNB notifies the UE being served of a paging message including a PWS indication from the identified SCG cell. The SeNB also notifies the UE in the DC of a paging message including a PWS indication. The timing of transmitting the paging message to the UE in the DC is determined by using the IMSI of the UE acquired in the SeNB addition process in step ST1002.

[0152] In step ST1009, the UE, which is receiving the PCH in step ST1003, receives a paging message mapped to the PCH from the SCG cell and receives a PWS indication.

[0153] In step ST1010, the UE that has received the PWS indication receives SIB1 broadcast from the SCG cell and receives the scheduling information of the SIB including the PWS message. Then, in step ST1011, the UE receives the SIB including the PWS message in accordance with the scheduling information, and receives the PWS message.

[0154] In the case of an urgent PWS message, such as ETWS, the UE may receive the PWS message immediately after receiving the PWS indication.

[0155] In Step ST1012, the SeNB notifies the MME of a "Write-Replace Warning Response" message, and ends the processing procedure of the PWS message notification process.

[0156] By performing the PWS message notification process as shown in FIG. 10, a UE performing DC using a SeNB can receive a PWS message for the SeNB.

[0157] Furthermore, by setting the method of notifying a PWS indication to the notification method (1) described above, it becomes possible to notify a PWS indication in a manner similar to the conventional method of notifying a PWS indication, thereby preventing the processing in the SeNB from becoming complicated.

[0158] When there are multiple SCG cells used in DC, the UE in DC needs to receive the PCHs of multiple SCG cells. In this case, the UE in DC increases the PCH reception processing, and the power consumption increases. To avoid this, the PWS indication may be limited to only the SPCell. Also, the PWS message may be limited to only the SPCell. In this way, it is possible to prevent the power consumption of the UE in DC from increasing.

[0159] Also, when the SeNB receives a PWS message from the MME, the SCG cell that the UE performing DC using the SeNB has as its SPCell may transmit a PWS indication to the UE. The SPCell may transmit information indicating which SCG cell-destined PWS message has occurred together with the PWS indication to the UE. As a result, the UE performing DC using the SeNB only needs to receive at least the PCH of the SPCell. Also, the PWS message may be transmitted by the SCG cell that the UE performing DC using the SeNB has as its SPCell. As a result, the UE performing DC using the SeNB only needs to receive the PWS message from the SPCell. Therefore, it is possible to prevent an increase in power consumption of the UE during DC.

[0160] A case where the notification method (2) is applied as a method of notifying a PWS indication will be described with reference to Fig. 9. The SeNB 104 that receives a PWS message from the MME 102 notifies the UE 105 that is performing DC using its own SCG cell of a PWS indication via the MeNB 103.

[0161] More specifically, SeNB 104 identifies the SCG cell that transmits the PWS message, and notifies UE 105, which is performing DC using the SCG cell, of a PWS indication via MeNB 103, as shown by arrow 109.

[0162] When UE 105 performing DC using an SCG cell receives a PWS indication transmitted from MeNB 103, UE 105 receives a SIB including a PWS message of the SCG cell.

[0163] Fig. 11 is a diagram showing another example of the sequence of PWS message notification processing in the communication system of embodiment 1. Fig. 11 shows an example in which the notification method (2) described above is applied as the method for notifying a PWS indication. The sequence shown in Fig. 11 is similar to the sequence shown in Fig. 10, so the same step numbers are used for the same steps and common explanations are omitted.

[0164] First, the processes of steps ST1001 to ST1002 and steps ST1004 to ST1008 are performed in the same manner as in the case shown in Fig. 10 described above. The SeNB that receives the PWS message in step ST1008 uses warning area information to check whether the PWS message is intended for its own SeNB. If the PWS message is intended for its own SeNB, the SeNB uses the warning area information to identify the SCG cell that transmits the PWS message.

[0165] In step ST1101, the SeNB notifies the MeNB performing DC using the identified SCG cell of a PWS indication. The PWS indication is notified using the X2 interface. Alternatively, if a new Xn interface is provided between the MeNB and the SeNB for DC, it may be notified using the Xn interface. A new message may be prepared as an X2 message and the indication may be included in the message. Alternatively, the indication may be included in a message for changing the setting of the SCG cell and notified. In addition, a container for an RRC message may be provided in the X2 message or the Xn message, and the indication may be included in the container and notified. These messages may be notified by dedicated signaling.

[0166] In step ST1101, the SeNB notifies the MeNB of the SeNB identifier or the identifier of the identified SCG cell together with the PWS indication. Alternatively, if the SeNB recognizes the UE identifier in the identified SCG cell and DC, the SeNB may notify the UE identifier in the DC. As a method for the SeNB to recognize the UE identifier in the SCG cell and DC, it is preferable that the MeNB notifies the SeNB of the UE identifier in the SCG cell and DC in the SeNB addition process in step ST1002.

[0167] In step ST1101, the MeNB that has received a PWS indication for the UE in DC from the SeNB notifies the UE performing DC using the SeNB of a PWS indication in step ST1102. The notification of the PWS indication may be made using an RRC message. The RRC message may be notified by individual signaling.

[0168] In step ST1102, the MeNB may notify the UE performing DC using the SeNB of the identifier of the SCG cell transmitting the PWS message together with the PWS indication.

[0169] When the MeNB is notified of a PWS indication in a container of an RRC message from the SeNB, the MeNB may transfer the PWS indication to an RRC message and notify the container individually to the UE in the DC.

[0170] In step ST1101, the MeNB that has received the PWS indication for the UE in DC from the SeNB may notify the PWS indication only to the UE in the specified SCG cell and DC using the identifier of the specified SCG cell or the UE identifier of the specified SCG cell and DC. It is not necessary to notify the identifier of the specified SCG cell together with the PWS indication. In addition, it is not necessary to notify the UE that is performing DC with an SCG cell that does not transmit a PWS message. This makes it possible to reduce the signaling load and simplify the control.

[0171] In step ST1101, it has been disclosed that the SeNB notifies the MeNB performing DC using the identified SCG cell of the PWS indication, but the SeNB may notify the eNB capable of performing DC using its own cell or a surrounding eNB of the PWS indication. In this case, the SeNB notifies the identifier of its own SeNB or the identifier of the identified SCG cell together with the PWS indication. The eNB notified of the PWS indication uses the identifier of the SeNB or the identifier of the identified SCG cell to determine whether the eNB is performing DC using the SeNB or the SCG cell. If the SeNB or the SCG cell is used to perform DC, the PWS indication may be notified to the UE in the DC.

[0172] As another method of notifying the UE of the PWS indication, the MeNB may notify the UE by including the PWS indication in a paging message mapped to the PCH. A PWS indication of a PWS message for a SeNB in ​​a DC may be provided on the PCH. The identifier of the SCG cell transmitting the PWS message may be included together with the PWS indication. This allows the UE to identify the SCG cell transmitting the PWS message.

[0173] The MeNB may map the PCH to the PCH of the MCG cell in which the UE can receive the PCH.

[0174] Also, the MeNB may map to the PCH of the PCell. This method is applicable when the UE receives the PCH for only the PCell of the MeNB.

[0175] In Step ST1102, the UE that has received the PWS indication from the MeNB receives the identifier of the SCG cell notified along with the PWS indication, and recognizes which SCG cell the PWS message is intended for.

[0176] In step ST1010, the UE that has received the PWS indication receives SIB1 broadcast from the SCG cell and receives the scheduling information of the SIB including the PWS message. Then, in step ST1011, the UE receives the SIB including the PWS message in accordance with the scheduling information, and receives the PWS message.

[0177] In the case of an urgent PWS message, such as ETWS, the UE may receive the PWS message immediately after receiving the PWS indication.

[0178] In Step ST1012, the SeNB notifies the MME of a "Write-Replace Warning Response" message, similarly to the case shown in FIG. 10 described above, and ends the processing procedure of the PWS message notification process.

[0179] The method disclosed in the PWS indication notification method (1) when there are multiple SCG cells used for DC, or the method of notifying a PWS indication or a PWS message from an SPCell when the SeNB receives a PWS message from an MME, may be applied to the PWS indication notification method (2). This simplifies the PWS indication reception process or PWS message reception process in the UE, making it possible to reduce the power consumption of the UE.

[0180] By performing the PWS message notification process as shown in FIG. 11 above, a UE performing DC using a SeNB can receive a PWS message for the SeNB.

[0181] In addition, by using the above-mentioned (2) as the notification method for the PWS indication, the UE in the DC does not need to receive the PCH of the SCG cell, which was necessary in the above-mentioned (1) notification method. Therefore, it is possible to reduce the power consumption of the UE.

[0182] First embodiment, modified example 1 In this modified example, another method is disclosed for a SeNB to transmit a PWS message for the SeNB to a UE in a DC.

[0183] The SeNB transmits a PWS message for the SeNB to the UE in the DC via the MeNB. The UE in the DC receives a PWS message for the SeNB from the MeNB.

[0184] When a PWS message is notified to one or more specific SCG cells, the SeNB used for DC transmits a PWS message for its own SCG cell to the UE performing DC using its own SCG cell via the MeNB. The UE performing DC using the SCG cell receives a PWS message for the SCG cell from the MeNB.

[0185] A method of notifying a PWS message will now be described. Fig. 12 is a diagram showing an example of a flow of a PWS message in a communication system according to a first variation of the first embodiment. The configuration shown in Fig. 12 is similar to the configuration shown in Fig. 9, so the same reference symbols are used for the same parts and common descriptions will be omitted. In Fig. 12, the flow of the PWS message is indicated by thick arrows 106, 107, and 122.

[0186] The PWS message is notified from a CBE (not shown) to the CBC 101. The CBC 101 notifies the MME 102 of the PWS message, as indicated by an arrow 106.

[0187] MME102 notifies the eNB of the PWS message. Specifically, MME102 notifies SeNB104 of the PWS message as shown by arrow 107. MME102 also notifies MeNB103 of the PWS message. When the eNB's own cell is used for DC, that is, when it is SeNB104, the eNB notifies UE105 performing DC using its own cell of the PWS message via MeNB103 as shown by arrows 121 and 122.

[0188] The SeNB 104 that has received the PWS message from the MME 102 notifies the MeNB 103 that is performing DC using its own SeNB of the PWS message. The SeNB 104 identifies the SCG cell that transmits the PWS message, and notifies the MeNB 103 that is performing DC using the SCG cell of the PWS message.

[0189] The X2 interface 112 is used for notifying the PWS message. Alternatively, if a new Xn interface is provided between the MeNB 103 and the SeNB 104 for DC, the PWS message may be notified using the Xn interface. A new message may be provided as the X2 message, and the PWS message may be included in the message for notifying. Alternatively, the PWS message may be included in a message for changing the setting of the SCG cell for notifying. A container for the RRC message may be provided in the X2 message or the Xn message, and the RRC message may be included in the container for notifying. These messages may be notified by dedicated signaling.

[0190] The SeNB identifier or the identifier of the specified SCG cell is notified together with the PWS message. Alternatively, if the specified SCG cell and the UE identifier in the DC are recognized, the identifier of the UE in the DC may be notified. Also, an identifier unique to the PWS message may be notified.

[0191] The MeNB that has received the PWS message from the SeNB notifies the UE that is performing DC using the SeNB of the PWS message. Also, an identifier unique to the PWS message may be notified together with the PWS message. The UE that is performing DC using the SeNB receives a PWS message for the SeNB notified from the MeNB. Also, an identifier unique to the PWS message may be received together with the PWS message. In this way, the UE that is performing DC using the SeNB can obtain the PWS message for the SeNB.

[0192] As in the first embodiment, a PWS indication may be provided and notified to the UE in the DC prior to the PWS message. In this case, when the UE in the DC receives the PWS indication, it receives a PWS message for the SeNB notified from the MeNB.

[0193] In FIG. 12, the flow of PWS indications is indicated by arrows 109, 110, and 123.

[0194] When the SeNB 104 receives a PWS message for its own SeNB from the MME 102, it notifies the UE 105 of a PWS indication, as shown by the arrow 110. Alternatively, when the MeNB 103 receives a PWS message from the SeNB 104, the MeNB 103 may notify the UE 105 in the DC of a PWS indication, as shown by the arrow 123.

[0195] As specific examples of methods for notifying a PWS indication, the following three methods (1) to (3) are disclosed. (1) SeNB 104 directly notifies UE 105 in the DC as shown by arrow 110. (2) As shown by arrow 109, SeNB 104 notifies UE 105 in the DC via MeNB 103. (3) MeNB 103 notifies UE 105 in the DC, as shown by arrow 123.

[0196] The notification methods of (1) and (2) described above can be applied to the methods described in the first embodiment. As a notification method of a PWS indication, the notification method of (3) described above will be described. Having received a PWS message from SeNB104, MeNB103 notifies UE105 in DC of a PWS indication. More specifically, MeNB103 notifies UE105 performing DC using the SCG cell of a PWS indication using information received together with the PWS message, such as an SCG cell identifier, indicating which SCG cell the message is for. When UE105 performing DC using an SCG cell receives a PWS indication transmitted from MeNB103, it receives a PWS message of the SCG cell from MeNB103.

[0197] Fig. 13 is a diagram showing an example of a sequence of a PWS message notification process in a communication system according to a first modification of the first embodiment. Fig. 13 shows an example in which the notification method (3) described above is applied as a method for notifying a PWS indication. The sequence shown in Fig. 13 is similar to the sequences shown in Figs. 10 and 11 described above, so the same step numbers are used for the same steps and common explanations are omitted.

[0198] First, the processes of steps ST1001 to ST1002 and steps ST1004 to ST1008 are performed in the same manner as in the cases shown in Figures 10 and 11 described above. In step ST1008, the SeNB that has received the PWS message uses warning area information to check whether the PWS message is intended for its own SeNB. If the PWS message is intended for its own SeNB, the SeNB uses the warning area information to identify the SCG cell that transmits the PWS message.

[0199] In step ST1301, the SeNB notifies the MeNB performing DC using the identified SCG cell of a PWS message. Also, the SeNB may notify an identifier unique to the PWS message.

[0200] In step ST1302, the MeNB that has received the PWS message from the SeNB notifies the UE that is performing DC using the SeNB of a PWS indication. The notification may be performed using an RRC message. The RRC message may be notified by dedicated signaling.

[0201] In step ST1301, it has been disclosed that the SeNB notifies the MeNB performing DC using the identified SCG cell of a PWS message, but the SeNB may notify the eNB capable of performing DC using its own cell or a surrounding eNB of a PWS message. In this case, the SeNB notifies the identifier of its own SeNB or the identifier of the identified SCG cell together with the PWS message. The eNB notified of the PWS message uses the identifier of the SeNB or the identifier of the identified SCG cell to determine whether the eNB is performing DC using the SeNB or the SCG cell. If DC is being performed using the SeNB or the SCG cell, it is preferable to notify the UE in the DC of a PWS indication.

[0202] In step ST1302, the MeNB may use the SeNB to notify the UE in the DC of the identifier of the SCG cell that transmits the PWS message together with the PWS indication.

[0203] As another method of notifying the UE of the PWS indication, the MeNB may notify the UE by including the PWS indication in a paging message mapped to the PCH. A PWS indication of a PWS message for a SeNB in ​​a DC may be provided on the PCH. The PWS indication may include an identifier of an SCG cell that transmits the PWS message. This allows the UE to identify the SCG cell that transmits the PWS message.

[0204] The MeNB may map the PCH to the PCH of the MCG cell that the UE can receive. The MeNB may also map to the PCH of the PCell. This method can be applied when the UE receives only the PCH of the PCell of the MeNB. In this case, the UE only needs to receive the PCH of the PCell, and does not need to receive the PCH transmitted from other MCG cells. Therefore, it is possible to reduce the power consumption of the UE.

[0205] In step ST1304, the MeNB that has received the PWS message from the SeNB broadcasts the PWS message. The MeNB broadcasts the PWS message by including it in an SIB. As the SIB that includes the PWS message, a new SIB may be provided, or an SIB for a PWS message for the SeNB may be provided. An existing SIB may be used. As an existing SIB that includes a PWS message, for example, there are SIB10 and SIB11 for ETWS, and SIB12 for CMAS. As a method for the MeNB to notify a UE in a DC of a PWS message, a method in which the MeNB broadcasts a PWS message to a UE under its control may be applied.

[0206] The MeNB may broadcast a PWS message for the SeNB to the UE in the DC from the PCell. The PWS message may be included in the SIB of the PCell and broadcast.

[0207] A UE in DC only needs to receive a PWS message for SeNB transmitted from a PCell.

[0208] The UE only needs to receive the SIB of the PCell, and does not need to receive the SIB transmitted from other MCG cells, which allows for low power consumption of the UE.

[0209] The UE that has received the PWS indication from the MeNB in ​​Step ST1302 receives SIB1 broadcast from the MeNB and receives the scheduling information of the SIB including the PWS message in Step ST1303. Then, in accordance with the scheduling information, the UE receives the SIB including the PWS message in Step ST1304 and receives the PWS message.

[0210] In the case of an urgent PWS message, such as ETWS, the UE may receive the PWS message immediately after receiving the PWS indication.

[0211] By notifying a UE in a DC of a PWS indication or a PWS message from a PCell, the MeNB no longer needs to receive a PWS indication or a PWS message from a SeNB, thereby enabling the UE to consume less power.

[0212] In Step ST1012, the SeNB notifies the MME of a "Write-Replace Warning Response" message, as in the cases shown in FIGS. 10 and 11 above, and ends the processing procedure of the PWS message notification process.

[0213] In the above method, the MeNB notifies the UE in the DC of the PWS message by including it in the SIB. As another method, the MeNB may notify the UE in the DC of the PWS message by including it in the RRC message. In this case, the RRC message may be notified by individual signaling.

[0214] When the MeNB is notified of a PWS message from the SeNB in ​​a container of an RRC message, the MeNB may transfer the PWS message to an RRC message and notify the container individually to the UE in the DC.

[0215] The MeNB may notify a UE performing DC using a SeNB of the identifier of the SCG cell transmitting the PWS message together with the PWS message.

[0216] The MeNB transmits an RRC message including a PWS indication, and then transmits an RRC message including a PWS message.

[0217] In addition, the MeNB may notify the UE in the DC by including the PWS indication and the PWS message in one RRC message. In this case, it is possible to combine the messages into one, so that it is possible to reduce the amount of signaling between the MeNB and the UE.

[0218] By performing the PWS message notification process as shown in FIG. 13 above, a UE performing DC using a SeNB can receive a PWS message for the SeNB.

[0219] In addition, by notifying the UE in the DC of the PWS message from the MeNB, the UE does not need to receive the PWS message transmitted from the SeNB. This makes it possible to prevent the PWS message reception process from becoming complicated.

[0220] In addition, since there is no need to receive broadcast information from the SeNB, power consumption of the UE can be reduced.

[0221] In addition, in the above-mentioned PWS indication notification methods (2) and (3), the MeNB notifies the UE in the DC of the PWS indication. Therefore, the UE does not need to receive the PWS indication transmitted from the SeNB. This makes it possible to prevent the PWS message reception process from becoming complicated. In addition, since the UE does not need to receive the PCH of the SeNB, it is possible to reduce the power consumption of the UE.

[0222] In the example shown in Figure 13, a method is disclosed in which a PWS indication is notified to a UE in a DC prior to a PWS message, but other methods are disclosed below.

[0223] Another method is to eliminate the PWS indication for UEs in DC, in other words, to notify only PWS messages to UEs in DC.

[0224] Figure 14 is a diagram showing another example of the sequence of the PWS message notification process in the communication system of the first modification of the first embodiment. Figure 14 shows an example of the case where only the PWS message is notified to the UE in the DC. The sequence shown in Figure 14 is similar to the sequences shown in Figures 10, 11, and 13 described above, so the same step numbers are used for the same steps and common explanations are omitted.

[0225] First, the processes of steps ST1001 to ST1002 and steps ST1004 to ST1008 are performed in the same manner as in the cases shown in Fig. 10 and Fig. 11 described above. In step ST1301, the MeNB that has received a PWS message from the SeNB notifies the UE that is performing DC using the SeNB of the PWS message in step ST1401. Specifically, the MeNB notifies the UE of the PWS message by including it in an RRC message. The RRC message may be notified by UE-specific signaling.

[0226] When the MeNB is notified of a PWS message from the SeNB in ​​a container of an RRC message, the MeNB may transfer the PWS message to an RRC message and notify the container individually to the UE in the DC.

[0227] The MeNB may use the SeNB to notify the UE in the DC of the identifier of the SCG cell that transmits the PWS message together with the PWS message.

[0228] In step ST1401, the UE in the DC receives the RRC message addressed to the UE and receives a PWS message addressed to the SeNB.

[0229] In this way, the MeNB notifies the UE in the DC of the PWS message for the SeNB by including it in an RRC message for the UE. This makes it possible to notify a specific UE of the PWS message for the SeNB. Therefore, it is possible to notify the UE of the PWS message without notifying the UE of the PWS indication.

[0230] This eliminates the need for processing to send and receive PWS indications, which prevents the system from becoming complicated. Also, signaling for PWS indications is no longer necessary, which reduces the signaling load.

[0231] Modification 2 of embodiment 1 In this modification, a method is disclosed in which the MeNB transmits a PWS message for the SeNB to the UE in the DC.

[0232] In this modification, a case where the MME also notifies the MeNB of a PWS message for the SeNB will be disclosed. For example, a case where the MME also notifies the MeNB of a PWS message for the SeNB may occur when the MeNB and the SeNB are in the same TAI.

[0233] Conventionally, when an MeNB receives a PWS message from an MME, the MeNB notifies the UE served by the MeNB only if the PWS message is a PWS message for the MeNB. Therefore, if the PWS message notified from the MME is not for the MeNB, the PWS message is not notified to the UE served by the MeNB.

[0234] Even if the MME notifies the MeNB of a PWS message for the SeNB, the MeNB does not notify the PWS message to the UE under its control. That is, the MeNB does not notify the UE under its control in the DC using the SeNB of the PWS message for the SeNB.

[0235] Therefore, a problem occurs in that the UE cannot receive a PWS message for the SeNB. In this modification, a method for solving such a problem is disclosed.

[0236] The MeNB transmits a PWS message for the SeNB to the UE in the DC.

[0237] The MeNB that receives a PWS message for the SeNB from the MME notifies the UE in the DC of the PWS message for the SeNB using the SeNB.

[0238] A method of notifying a PWS message will be described. Fig. 15 is a diagram showing an example of a flow of a PWS message in a communication system according to the second modification of the first embodiment. The configuration shown in Fig. 15 is similar to the configurations shown in Figs. 9 and 12, so the same reference symbols are used for the same parts and common descriptions will be omitted. In Fig. 15, the flow of the PWS message is indicated by thick arrows 106, 151, and 152.

[0239] Upon receiving the PWS message from the CBC 101, the MME 102 notifies not only the SeNB 104 but also the MeNB 103 of the PWS message, as indicated by arrow 151.

[0240] The MeNB 103 judges whether the PWS message received from the MME 102 is intended for the SeNB 104 used for the DC. When the MeNB 103 receives a PWS message intended for the SeNB 104 used for the DC, as shown by the arrow 152, the MeNB 103 notifies the UE 105 performing the DC using the SeNB 104 of the PWS message.

[0241] UE 105, which is performing DC using SeNB 104, receives a PWS message for SeNB 104 from MeNB 103, as shown by arrow 152.

[0242] By doing this, as shown by arrow 152, UE 105 performing DC using SeNB 104 can obtain a PWS message for the SeNB.

[0243] In this modification, as in the first modification of the first embodiment, a PWS indication may be provided and notified to the UE in the DC prior to the PWS message. When the UE in the DC receives the PWS indication, it receives a PWS message for the SeNB notified from the MeNB.

[0244] The flow of the PWS indication is also shown in Fig. 15. In Fig. 15, the flow of the PWS indication is indicated by a thin arrow 123.

[0245] As shown by arrow 151, when MeNB103 receives a PWS message from MME102 for SeNB1004 used for DC, MeNB103 may notify UE105 performing DC using the SeNB104 of a PWS indication, as shown by arrow 123.

[0246] As a method for notifying a PWS indication, the method (3) for notifying a PWS indication disclosed in the first modification of the first embodiment can be applied.

[0247] Fig. 16 is a diagram showing an example of a PWS message notification processing sequence in a communication system according to Variation 2 of Embodiment 1. Fig. 16 shows an example in which the PWS indication notification method (3) disclosed in Variation 1 of Embodiment 1 is applied as a PWS indication notification method. The sequence shown in Fig. 16 is similar to the sequences shown in Figs. 10, 11, and 13, and therefore the same steps are given the same step numbers and common explanations are omitted.

[0248] First, the processes of steps ST1001, ST1002, ST1004, and ST1005 are performed in the same manner as in the cases shown in Fig. 10 and Fig. 11 described above. In step ST1005, the MME that has received the PWS message from the CBC identifies the eNB that will notify the PWS message from the tracking area ID list notified together with the PWS message. Here, a case is shown in which the tracking area ID list includes the MeNB and the SeNB.

[0249] In Step ST1008, the MME notifies the SeNB of the PWS message using the S1-MME interface. In addition, in Step ST1601, the MME also notifies the MeNB of the PWS message using the S1-MME interface. Specifically, the MME notifies the MeNB of warning area information together with the PWS message. As a message for notifying the PWS message and warning area information, a "Write-Replace Warning Request" message is used.

[0250] In Step ST1602, the MeNB that has received the PWS message in Step ST1601 uses warning area information to determine whether or not the PWS message is intended for the SeNB used for the DC.

[0251] If the PWS message is not for the SeNB used for DC, the MeNB returns to normal processing without transmitting the PWS message to the UE performing DC using the SeNB. In the case of a PWS message for the SeNB used for DC, the MeNB uses warning area information to identify the SCG cell to transmit the PWS message.

[0252] In step ST1302, the MeNB notifies the UE that is performing DC using the SeNB of a PWS indication.

[0253] The UE in the DC that has received the PWS indication receives a PWS message notified from the MeNB through the processing of steps ST1303 and ST1304. As the processing method of steps ST1303 and ST1304, the method of the first modification of the first embodiment can be applied, and therefore the description thereof will be omitted here.

[0254] In Step ST1603, the MeNB notifies the MME of a "Write-Replace Warning Response" message, and ends the processing procedure of the PWS message notification process.

[0255] By performing the PWS message notification process as shown in FIG. 16 above, a UE performing DC using a SeNB can receive a PWS message for the SeNB.

[0256] In addition, since the MeNB does not need to receive a PWS message from the SeNB, it is possible to reduce the transmission and reception processing of the PWS message between the SeNB and the MeNB. Therefore, it is possible to simplify the processing in the SeNB and the MeNB and to reduce the signaling load between the SeNB and the MeNB.

[0257] In this modified example, a method is disclosed in which a PWS indication is notified to a UE in a DC prior to a PWS message, but other methods are disclosed below.

[0258] Eliminate PWS indication for UE in DC. In other words, only PWS messages are notified to UE in DC.

[0259] Fig. 17 is a diagram showing another example of the sequence of the PWS message notification process in the communication system of the second modification of the first embodiment. Fig. 17 shows a case where only the PWS message is notified to the UE in the DC. The sequence shown in Fig. 17 is similar to the sequences shown in Figs. 10, 11, 13, 15, and 16 described above, so the same step numbers are used for the same steps and common explanations are omitted.

[0260] First, the processes of step ST1001, step ST1002, step ST1004 to step ST1008, and step ST1601 are performed in the same manner as in the case shown in Fig. 16. In step ST1601, the MeNB that has received the PWS message from the MME determines, in step ST1602, whether or not the PWS message is for the SeNB used for the DC, by using warning area information.

[0261] If the PWS message is not for the SeNB used for DC, the MeNB does not perform a PWS message transmission process to the UE performing DC using the SeNB, and returns to normal processing. In the case of a PWS message for the SeNB used for DC, the MeNB uses warning area information to identify the SCG cell to transmit the PWS message.

[0262] In step ST1401, the MeNB notifies the UE performing DC using the SeNB of a PWS message. Specifically, the MeNB notifies the UE of the PWS message by including it in an RRC message. The RRC message may be notified by UE-specific signaling.

[0263] The MeNB may notify a UE performing DC using the SeNB of the identifier of the SCG cell transmitting the PWS message together with the PWS message.

[0264] In step ST1401, the UE in the DC receives the RRC message addressed to the UE and receives a PWS message addressed to the SeNB.

[0265] In this way, the MeNB can notify a specific UE of a PWS message for the SeNB by including the PWS message for the SeNB in ​​an RRC message for the UE to notify the UE in the DC. Therefore, it is possible to notify the UE of the PWS message without notifying the UE of the PWS indication.

[0266] This eliminates the need for processing to send and receive PWS indications, which prevents the system from becoming complicated. Also, signaling for PWS indications is no longer necessary, which reduces the signaling load.

[0267] Modification 3 of embodiment 1 In this modification, another method of transmitting a PWS message for SeNB to a UE in DC by MeNB is disclosed.

[0268] In the second modification of the first embodiment, a case is disclosed in which the MME also notifies the MeNB of a PWS message for the SeNB. However, there are also cases in which the MME does not notify the MeNB of a PWS message for the SeNB. For example, this is the case in which the MeNB and the SeNB are in different TAIs. In such a case, the method disclosed in the second modification of the first embodiment cannot be applied.

[0269] In this modification, a method for solving such problems will be disclosed.

[0270] The MeNB notifies the MME of information on the SeNB used for the DC. The MeNB may perform this notification when changing the SeNB or SCG cell used for the DC. This allows the information on the SeNB held by the MME to be updated as appropriate. The notification of the information on the SeNB used for the DC may be performed in a SeNB addition process. Alternatively, it may be performed in a SeNB change process or a SeNB modification process. In addition, in a SeNB release process, the MeNB may notify the MME of information indicating that there is no SeNB used for the DC.

[0271] By doing so, the MME can associate the SeNB that transmits the PWS message with the MeNB that uses the SeNB as a DC. Therefore, the MME can notify the MeNB that uses the SeNB as a DC of the PWS message for the SeNB.

[0272] When the MME receives a PWS message, it determines whether the PWS message is for the SeNB used for the DC. When the MME receives a PWS message for the SeNB used for the DC, it notifies the MeNB of the PWS message.

[0273] The MeNB determines whether the PWS message received from the MME is for the SeNB used for DC. When the MeNB receives a PWS message for the SeNB used for DC, it notifies the UE performing DC using the SeNB of the PWS message.

[0274] A UE performing DC using the SeNB cell receives a PWS message for the SeNB cell from the MeNB.

[0275] The method of notifying a PWS message will be described below. The flow of a PWS message in this modification is the same as that in the modification 2 of the first embodiment shown in FIG.

[0276] As in the second modification of the first embodiment, a PWS indication may be provided and notified to the UE in the DC prior to the PWS message. When the UE in the DC receives the PWS indication, it receives a PWS message for the SeNB notified from the MeNB.

[0277] The flow of PWS indication in this modification is similar to that in the modification 2 of the first embodiment shown in FIG.

[0278] When the MeNB receives a PWS message for the SeNB used for DC from the MME, the MeNB may notify the UE performing DC using the SeNB of a PWS indication. As a method of notifying the PWS indication, the method of notifying the PWS indication (3) disclosed in the first modification of the first embodiment can be applied.

[0279] Fig. 18 is a diagram showing an example of a sequence of a PWS message notification process in a communication system according to Variation 3 of Embodiment 1. The sequence shown in Fig. 18 is similar to the sequence shown in Fig. 16 described above, so the same step numbers are used for the same steps and common descriptions will be omitted.

[0280] First, the process of step ST1001 is performed in the same manner as in the case shown in FIG. 16 described above. In step ST1002, the MeNB starts the SeNB addition process to execute DC for the UE. This causes the SeNB addition process to be performed between the MeNB, the UE, and the SeNB. In this SeNB addition process, the SeNB notifies the MeNB of the cell ID, TAI, or emergency area ID of its own cell.

[0281] In step ST1801, the MeNB notifies the MME of information on the added SeNB. The MeNB may also notify information on the SCG cell. As the information on the SeNB, information that can identify warning area information, specifically, the cell ID, TAI, and emergency area ID of the SeNB, may be used. As the information on the SeNB, an identifier of the MeNB performing DC using the own SeNB may also be notified. This makes it possible to recognize that the information on the SeNB is information on which SeNB is used for DC.

[0282] When the DC using the SeNB is DC architecture 1A, in the SeNB addition process for executing the DC in step ST1002, the MeNB notifies the MME of a path change of the user plane (U-plane) in the S-GW. The MeNB may use this change notification to notify the MME of information related to the added SeNB. For example, the path change notification message may include information related to the SeNB. Alternatively, in the SeNB addition process, the MeNB may notify the MME of information related to the SeNB in ​​a separate message.

[0283] In Step ST1005, the MME that has received the PWS message from the CBC identifies the eNB to which the PWS message is to be notified, from the tracking area ID list received together with the PWS message.

[0284] In Step ST1802, the MME uses the identified eNB and the information on the added SeNB received from the MeNB in ​​Step ST1801 to determine whether the eNB is a SeNB in ​​the DC. If the identified eNB is a SeNB in ​​the DC, the MME determines that the PWS message is intended for a SeNB in ​​the DC. If the identified eNB is not a SeNB in ​​the DC, the MME determines that the PWS message is not intended for a SeNB in ​​the DC.

[0285] If the PWS message is not intended for a SeNB in ​​a DC, the PWS message is not sent to the MeNB that is executing the DC using the SeNB, and normal processing is resumed.

[0286] If the PWS message is for a SeNB in ​​the DC, the MME identifies an eNB that transmits the PWS message by using the information about the added SeNB received from the MeNB in ​​step ST1801. In this case, the MeNB is used. The MME may also associate the information about the added SeNB received in step ST1801 with the MeNB that has notified the information, and identify an eNB that transmits the PWS message by using the MeNB information associated with the SeNB.

[0287] The MME, having identified the eNB that transmits the PWS message, notifies the eNB of the PWS message. The eNB is the MeNB in ​​this case. In Step ST1601, the MME also notifies the MeNB of the PWS message for the SeNB, using the S1-MME interface.

[0288] The MME notifies a tracking area ID list, warning area information, and a global eNB ID together with the PWS message. A "Write-Replace Warning Request" message is used as the notification message. An identifier unique to the PWS message may also be notified.

[0289] In Step ST1601, the MeNB that has received the PWS message determines, in Step ST1602, by using warning area information, whether or not the PWS message is intended for the SeNB used for the DC.

[0290] If the PWS message is not for the SeNB used for DC, the MeNB does not perform the PWS message transmission process to the UE performing DC using the SeNB, and returns to normal processing. In the case of a PWS message for the SeNB used for DC, the SCG cell to transmit the PWS message is identified using warning area information.

[0291] In step ST1302, the MeNB notifies the UE performing the DC using the SeNB of the PWS indication. The UE in the DC that receives the PWS indication receives the PWS message notified from the MeNB in ​​steps ST1303 and ST1304. As the method of steps ST1303 and ST1304, the method of the first modification of the first embodiment can be applied, so the description is omitted here.

[0292] When the MME determines in step ST1802 that the PWS message is intended for the SeNB in ​​the DC, the MME may notify the MeNB of information indicating that the PWS message is intended for the SeNB in ​​the DC together with the PWS message. This allows the MeNB to explicitly recognize that the received PWS message is intended for the SeNB used for the DC. The MeNB may use this information in the determination in step ST1602. This makes it possible to reduce malfunctions.

[0293] By performing the PWS message notification process as shown in FIG. 18 above, a UE performing DC using a SeNB can receive a PWS message for the SeNB.

[0294] If the MME does not notify the MeNB of a PWS message for the SeNB, for example, when the MeNB and the SeNB are in different TAIs, the MeNB can notify the UE in the DC of the PWS message for the SeNB.

[0295] A UE in DC is able to receive PWS messages for SeNB from the MeNB.

[0296] In this modified example, a method is disclosed in which a PWS indication is notified to a UE in a DC prior to a PWS message, but other methods are disclosed below.

[0297] Eliminate PWS indication for UE in DC. In other words, only PWS messages are notified to UE in DC.

[0298] Fig. 19 is a diagram showing another example of the sequence of the PWS message notification process in the communication system of the third modification of the first embodiment. Fig. 19 shows a case where only the PWS message is notified to the UE in the DC. The sequence shown in Fig. 19 is similar to Fig. 17 and Fig. 18 described above, so the same step numbers are assigned to the same steps and common explanations are omitted.

[0299] In the example shown in Fig. 19, first, the processes of steps ST1001, ST1002, ST1801, ST1004 to ST1008, ST1802, ST1601, and ST1602 are executed in the same manner as in the case shown in Fig. 18. Then, the processes of steps ST1401, ST1012, and ST1613 are executed in the same manner as in the case shown in Fig. 17.

[0300] In this way, even in this modified example, the process of transmitting and receiving a PWS indication is not required. Therefore, it is possible to prevent the processing of the system from becoming complicated. In addition, since signaling for a PWS indication is not required, it is also possible to reduce the signaling load.

[0301] Modification 4 of embodiment 1 In this modified example, another method is disclosed for a SeNB to transmit a PWS message for the SeNB to a UE in a DC.

[0302] In this modification, a case will be described in which an MME connected to an MeNB is different from an MME connected to a SeNB.

[0303] In this case, the SeNB that receives the PWS message from the MME may transmit a PWS message for the SeNB to the UE in the DC. The SeNB transmits a PWS message for the SeNB directly to the UE in the DC. Alternatively, the SeNB may transmit a PWS message for the SeNB to the UE in the DC via the MeNB.

[0304] The UE in the DC receives a PWS message for the SeNB from the SeNB or from the MeNB. As a method for this, the method disclosed in the first embodiment and the first modification of the first embodiment may be applied. The same applies when the PWS message is notified to one or more specific SCG cells.

[0305] A method of notifying a PWS message will be described. Fig. 20 is a diagram showing an example of a flow of a PWS message in a communication system according to the fourth variation of the first embodiment. The configuration shown in Fig. 20 is similar to the configurations shown in Figs. 9 and 12, so the same reference symbols are used for the same parts and common descriptions will be omitted. In Fig. 20, the flow of the PWS message is indicated by thick arrows 202, 203, 121, 122, and 108.

[0306] FIG. 20 illustrates a case where an MME 201 connected to an SeNB 104 (hereinafter may be referred to as an "MME for SeNB") and an MME 102 connected to an MeNB 103 (hereinafter may be referred to as an "MME for MeNB") are different.

[0307] The CBC 101 is connected to the MME for SeNB 201. In Fig. 20, the flow of a PWS message from the CBC 101 to the SeNB 104 is indicated by bold arrows 202 and 203.

[0308] The PWS message is notified from a CBE (not shown) to the CBC 101, from the CBC 101 to the MME 201 for SeNB, and from the MME 201 for SeNB to the SeNB 104.

[0309] When the eNB uses its own cell for DC, that is, when it is SeNB 104, it notifies UE 105 performing DC using its own cell of a PWS message, as shown by arrow 108. In this case, the PWS indication is notified from SeNB 104 to MeNB 103 and UE 105, as shown by arrows 109 and 110.

[0310] The SeNB 104 may notify the UE 105 performing DC using its own cell of a PWS message via the MeNB 103, as shown by arrows 121 and 122. In this case, the PWS indication is notified from the SeNB 104 to the MeNB 103 and the UE 105, as shown by arrows 110, 109, and 123.

[0311] When the SeNB notifies the UE in the DC of a PWS message, the method of notifying the PWS message and the PWS indication may be the method disclosed in the above-mentioned embodiment 1. This allows the UE performing the DC using the SeNB to receive the PWS message from the SeNB.

[0312] When the SeNB notifies the UE in the DC of a PWS message for the SeNB via the MeNB, the method of notifying the PWS message and the PWS indication may be the method disclosed in the first modification of the first embodiment. This allows the UE performing the DC using the SeNB to receive the PWS message for the SeNB from the MeNB.

[0313] By doing this, even if the MME connected to the MeNB is different from the MME connected to the SeNB, a UE performing DC using the SeNB can receive a PWS message for the SeNB.

[0314] Although the MME connected to the MeNB is different from the MME connected to the SeNB, when the CBC is connected to both the MME connected to the MeNB and the MME connected to the SeNB, the method disclosed in the above-mentioned variant example 3 of the first embodiment can be applied.

[0315] In this case, the CBC notifies the MME to which the MeNB is connected of the PWS message. The method of notifying the PWS message for the SeNB between the MME notified of the PWS message and the UE in the DC may be the method disclosed in the third modification of the first embodiment.

[0316] By doing this, a UE performing DC using a SeNB can receive a PWS message for the SeNB.

[0317] Although the MME connected to the MeNB is different from the MME connected to the SeNB, a CBC is connected to both the MME connected to the MeNB and the MME connected to the SeNB, and the MeNB and SeNB are in the same tracking area (TA), the method disclosed in the above-mentioned variant 2 of embodiment 1 can be applied.

[0318] This allows a UE performing DC using an SeNB to receive a PWS message for the SeNB. This also applies when an MCG cell and an SCG cell are in the same TA.

[0319] There are cases where both the MeNB and the SeNB notify the UE under its control of the same PWS message. In other words, there are cases where the PWS message for the MeNB and the PWS message for the SeNB are the same. In such a case, if the method disclosed in the present embodiment and the modified example is used, the UE will receive the PWS message for the MeNB and the PWS message for the SeNB. That is, the UE will receive the same PWS message twice.

[0320] By making it possible for a UE to receive the same PWS message multiple times, even if it is unable to receive one PWS message, it will be able to receive the other PWS messages. This reduces the probability that a UE will be unable to receive a PWS message. This makes it possible to build a robust PWS system.

[0321] However, there is a problem in that the UE receiving the same PWS message repeatedly leads to an increase in power consumption. The following three methods (1) to (3) are disclosed as methods for solving this problem.

[0322] (1) When a UE is notified of a PWS message from both the MeNB and the SeNB, the UE judges whether the PWS message notified from the MeNB and the PWS message notified from the SeNB are the same PWS message. For this judgment, a message-specific identifier notified together with the PWS message may be used. An example of a message-specific identifier is a message ID. The UE receives the first notified PWS message. At that time, the UE records the message ID of the PWS message. The message ID of the later notified PWS message is compared with the message ID of the previously received PWS message.

[0323] If the message IDs are the same, the PWS message is not received. Alternatively, the PWS message may not be demodulated. If the message IDs are different, the PWS message is received. Also, the message ID is recorded. By repeating this process, the UE can prevent the same PWS message from being received multiple times. Therefore, an increase in power consumption of the UE can be prevented. The above method (1) may be applied when using the method disclosed in the first embodiment.

[0324] (2) When an MeNB receives a PWS message from an SeNB, the MeNB may determine whether the PWS message for the MeNB itself is the same as the PWS message for the SeNB. The method of notifying the PWS indication may be the above-mentioned method (2) or (3).

[0325] A method for the MeNB to make a judgment is disclosed. The MeNB records the message ID of the PWS message for its own MeNB, and compares the recorded message ID of the PWS message for its own MeNB with the message ID notified together with the PWS message received from the SeNB. If the message IDs are the same, the PWS message received from the SeNB is not transmitted to the UE performing DC using the SeNB. In this case, it is preferable not to notify the UE of the PWS indication either. If the message IDs are different, the MeNB transmits the PWS message received from the SeNB to the UE performing DC using the SeNB.

[0326] In this way, it is possible to prevent the UE from receiving the same PWS message twice, and therefore to prevent an increase in power consumption of the UE.

[0327] The above method (2) may be applied when the method disclosed in the first modification of the first embodiment is used.

[0328] (3) When an MeNB receives a PWS message for a SeNB from an MME, the MeNB may determine whether the PWS message for its own MeNB is the same as the PWS message for a SeNB.

[0329] A method for the MeNB to make this judgment is disclosed. The MeNB judges whether the PWS message received from the MME is intended for both the SeNB and the own MeNB. In this case, the judgment may be made using warning area information notified from the MME together with the PWS message. Specifically, the MeNB judges whether the own MeNB and the SeNB performing DC with the own MeNB are present in the warning area information as information of the eNB or cell that transmits the PWS message.

[0330] If both exist, the MeNB determines that the PWS message for its own MeNB and the PWS message for the SeNB are the same, and transmits the PWS message only once to the UE performing DC using the SeNB. In this case, the PWS indication may also be notified to the UE only once. The notification method of the PWS message for the SeNB may not be executed. If both do not exist, the PWS message is notified to the UE by the notification method of each PWS message.

[0331] In this way, it is possible to prevent the UE from receiving the same PWS message twice, and therefore to prevent an increase in power consumption of the UE.

[0332] The above method (3) may be applied when the method disclosed in the second modification of the first embodiment is used, or when the method disclosed in the third modification of the first embodiment is used.

[0333] When using the method disclosed in the fourth modification of the first embodiment, the method disclosed above can be applied appropriately according to the notification route of the PWS message, thereby obtaining the same effect.

[0334] Embodiment 2 The problem to be solved in the second embodiment and the solution thereto are described below.

[0335] It is considered that in the future, a demand for large-volume data communication such as map information will arise in emergency services such as emergency calls. Therefore, it is considered that a demand for enabling DC will arise also for emergency sessions for emergency services or emergency bearers for emergency services.

[0336] In 3GPP, standards for emergency services have been established (see Non-Patent Document 13, 4.3.12), but there has been no discussion on the introduction of DC to emergency services.

[0337] Therefore, if a process for performing DC such as the SeNB addition procedure or SeNB modification procedure (see Non-Patent Document 9) discussed in 3GPP is simply applied to the emergency bearer, there may be cases where the DC using the SeNB cannot be performed on the emergency bearer.

[0338] For example, when the MeNB performs DC for a bearer, when notifying the SeNB of a SeNB addition request, the MeNB does not notify whether the bearer is an emergency bearer or not. Therefore, the SeNB cannot recognize whether the SeNB addition request from the MeNB is for an emergency bearer or not.

[0339] In addition, the SeNB may reject a SeNB addition request received from the MeNB depending on the resource status of the SeNB itself or the SCG cell. For example, when the SeNB is overloaded, when the SeNB is notified of an overload start procedure from the MME, or when the SeNB restricts access to the UE that is the DC target, for example, when it is "not suitable". In such cases, the SeNB rejects the SeNB addition request from the MeNB.

[0340] In this way, a SeNB that does not recognize that the SeNB addition process is for an emergency bearer may reject the SeNB addition process depending on the state of its own SeNB. The rejected MeNB cannot execute DC for the emergency bearer. In other words, it is impossible to execute DC for the UE that provides emergency services.

[0341] In this embodiment, a method for enabling DC to be performed on an emergency bearer is disclosed. The solution in the second embodiment is described below.

[0342] The SeNB does not reject a processing request for performing DC from the MeNB if the request is for an emergency bearer. Processing requests for performing DC include, for example, a SeNB addition request and a SeNB modification request. When performing DC for an emergency bearer, the MeNB includes information indicating that these requests are emergency bearers in the SeNB addition request or SeNB modification request.

[0343] FIG. 21 is a diagram illustrating an example of a sequence of a DC execution process for an emergency bearer in a communication system according to a second embodiment.

[0344] MeNB and SeNB are used when DC is executed, but for the sake of simplicity, the eNBs used in DC later will be referred to as MeNB and SeNB.

[0345] First, the flow of emergency bearer-related information when an emergency bearer for emergency services is established will be described.

[0346] In Step ST2201, a UE that provides emergency services includes information indicating that the reason is an emergency (hereinafter, may be referred to as "emergency information") in an attach request or a PDN connectivity request as a NAS message and notifies the MME. In the present embodiment, the UE includes the emergency information in a PDN connectivity request and notifies the MME.

[0347] At this time, the UE includes the emergency information in an RRC connection request message related to an emergency service and notifies the MeNB of the emergency information. For example, the UE includes the emergency information in an RRC connection establishment request message as the RRC connection request message and notifies the MeNB of the emergency information.

[0348] The MeNB uses the emergency information to determine whether the request is for an emergency service. If the request is for an emergency service, the MeNB accepts the request without performing access restriction as in the case of a normal bearer.

[0349] The MeNB includes emergency information in an initial NAS message as an S1 message and notifies the MME. The MME uses the emergency information in the initial NAS message or the emergency information included in an Attach request or a PDN connectivity request to determine whether these requests are for emergency services.

[0350] If it is for emergency services, the MME selects a P-GW for emergency services (emergency P-GW), and the MME derives the address of the emergency P-GW.

[0351] In Step ST2202, the MME includes the address of the emergency P-GW in a create session request message as an S11 message and notifies the S-GW. In Step ST2203, the S-GW notifies the emergency P-GW of the create session request as an S5 message by using the address of the emergency P-GW.

[0352] In Step ST2204, the emergency P-GW obtains an emergency service ARP (Allocation and Retention Priority) value from a PCRF (Policy and Charging Rules Function).

[0353] The emergency P-GW that has obtained the ARP value for emergency services uses the ARP value to derive QoS-related information for the EPS bearer, which includes QCI, ARP, GBR, and MBR.

[0354] In Step ST2205, the emergency P-GW includes the QoS related information for the EPS bearer in a create session response message and notifies the S-GW. In Step ST2206, the S-GW includes the QoS related information for the EPS bearer in a create session response message and notifies the MME. The MME derives E-RAB (E-UTRAN Radio Access Bearer) level QoS information from the received QoS related information for the EPS bearer.

[0355] In Step ST2207, the MME includes the E-RAB level QoS information and the ARP value in an E-RAB setup request message and notifies the MeNB. An S1 message is used for the notification. Based on the received E-RAB level QoS information, the MeNB performs settings for the E-RAB provided between the S-GW and the UE via the MeNB.

[0356] In Step ST2208, the MeNB notifies the UE of the E-RAB resource configuration by including the E-RAB resource configuration in an RRC connection reconfiguration message based on the received E-RAB level QoS information.

[0357] In addition, the MME notifies the UE of the QoS-related information for the EPS bearer, excluding ARP, in an attach response message or a PDN connectivity accept message. The attach response message or the PDN connectivity accept message may be an activate dedicated EPS bearer context request message.

[0358] The UE that has received the resource configuration for E-RAB in the RRC connection reconfiguration message performs resource configuration for E-RAB, and in Step ST2209 notifies the MeNB of an RRC connection reconfiguration complete message.

[0359] In Step ST2210, the MeNB that has performed the setting for E-RAB notifies the MME of a bearer setup response message.

[0360] In addition, a UE that receives an Attach Response message or a PDN Connectivity Accept message, which are NAS messages, notifies the MME of the completion of PDN connectivity by sending a Direct Transfer message in step ST2211 and a PDN Connectivity Complete message in step ST2212.

[0361] In Step ST2213, a path setup process is performed. As a result, an emergency bearer is set up, and as shown in Step ST2214, communication of UL / DL data for the emergency bearer becomes possible.

[0362] Before disclosing how to perform DC on an emergency bearer, a method for performing conventional DC will be described.

[0363] The MeNB that has decided to perform DC for the UE requests resources from the SeNB so that the sum of the resources provided by the MeNB and the resources provided by the SeNB for the UE is equal to or exceeds the E-RAB level QoS requested by the MME.

[0364] Therefore, there may be a case where the MeNB sets a value different from the E-RAB level QoS information requested from the MME to the SeNB. The MeNB includes the E-RAB level QoS information requested to the SeNB in ​​a DC execution request message to the SeNB, for example, a SeNB addition request message, and notifies the SeNB (see Non-Patent Document 9).

[0365] The additional requirements for SeNB when implementing DC currently being discussed in 3GPP are as follows.

[0366] However, in this method, the SeNB cannot recognize whether the bearer for which the MeNB requests DC execution is for emergency services. This is because the MeNB sets the resource request for the SeNB, and it is not clear whether the MeNB includes an ARP value in the DC execution request message. In addition, even if the ARP value is included in the DC execution request message and requested, the ARP may not be the ARP value for emergency services.

[0367] In this way, an SeNB that does not recognize that this is a SeNB addition process for an emergency bearer will reject it depending on the status of its own SeNB, making it impossible to execute DC for a UE that provides emergency services.

[0368] A method for solving such problems is disclosed.

[0369] The MeNB includes information indicating that the request is a DC execution request for an emergency bearer in a DC execution request message to the SeNB. The SeNB that receives the DC execution request for the emergency bearer does not reject the DC execution request. That is, it allows the execution of DC.

[0370] An example of a method for executing DC for an emergency bearer will be described with reference to FIG.

[0371] As described above, in Step ST2214, UL / DL data communication for the emergency bearer is being performed. In Step ST2215, the MeNB notifies the SeNB of a DC execution request message to the SeNB, for example, a SeNB addition request message.

[0372] At this time, a DC execution request message for the SeNB, for example, a SeNB addition request message, is notified including information indicating that the request is for an emergency bearer. Information indicating that the request is for an emergency bearer may be included and notified together with QoS information of the E-RAB level requested to the SeNB. Alternatively, a new message for notifying information indicating that the DC execution request is for an emergency bearer may be provided.

[0373] When the MeNB requests the SeNB to execute DC for the emergency bearer, the MeNB may also notify the SeNB of the new message. The information may be notified via the X2 interface or the Xn interface. The information may be an indication or cause information.

[0374] By doing so, the SeNB can recognize that the request is a DC execution request message for the emergency bearer. In step ST2215, the SeNB that has received information indicating that the request is for the emergency bearer uses the information to determine whether the request is a DC execution request for the emergency bearer.

[0375] If the request is not a DC execution request for an emergency bearer, the SeNB decides whether to reject or accept the request according to the status of the own SeNB or SCG cell. If the request is a DC execution request for an emergency bearer, the SeNB does not reject the request. That is, the request is accepted.

[0376] FIG. 21 shows the case where the request is a DC execution request for an emergency bearer, so the SeNB does not reject the DC execution request but accepts it.

[0377] In Step ST2216, the SeNB notifies the MeNB of a DC execution request response, for example, a SeNB addition request response. In Step ST2217, the MeNB configures radio resources for executing DC for the UE by an RRC connection reconfiguration message.

[0378] In Step ST2218, the UE that has configured radio resources for the DC using the SeNB notifies the MeNB of the completion of the configuration by an RRC connection reconfiguration complete message.

[0379] In step ST2219, the MeNB notifies the SeNB that the configuration of radio resources for the DC using the SeNB has been completed by a SeNB reconfiguration complete message. By doing as described above, in step ST2202, the DC execution process for the emergency bearer is performed between the MeNB, the SeNB, and the UE.

[0380] Also, in step ST2215, the MeNB may notify the SeNB of the bearer configuration for the emergency bearer in a DC execution request message for the emergency bearer, for example, a SeNB addition request or a SeNB modification request. That is, the MeNB may request the SeNB to configure the same bearer as that configured by the MeNB itself.

[0381] In other words, the MeNB shall not set a value different from the E-RAB level QoS information requested by the MME to the SeNB for a resource request to the SeNB for an emergency bearer, i.e., set the same value to the SeNB.

[0382] For example, the MeNB sets the QoS information of the E-RAB level for the emergency bearer notified from the MME to the SeNB and makes a DC execution request. The ARP value may be included as the QoS information of the E-RAB level for the emergency bearer.

[0383] By doing so, the SeNB can recognize that it is a DC execution request for the emergency bearer, so by not rejecting the emergency bearer, it is possible to eliminate the case where it is rejected depending on the situation of the own SeNB or SCG cell. Therefore, it is possible to make DC executable for the UE that provides emergency services.

[0384] Also, in step ST2215, the MeNB may notify the SeNB of an ARP value indicating that the ARP value is for an emergency bearer when sending a DC execution request message for the emergency bearer, for example, a SeNB addition request or a SeNB modification request. The SeNB may recognize the ARP value for the emergency bearer in advance. For example, the ARP value may be statically determined in advance by a standard. Alternatively, the ARP value may be set by an operator.

[0385] Alternatively, the P-GW may obtain an ARP value for the emergency bearer from the PCRF and notify the SeNB via the MME. Alternatively, the MME may obtain an ARP value for the emergency bearer from the P-GW and notify the SeNB from the MME. The ARP value may be dedicated to the emergency bearer.

[0386] In this way, the SeNB can make a decision based on the ARP value without using information indicating that the request is for an emergency bearer. Therefore, it is not necessary for the MeNB to notify the SeNB of the information, and the amount of information between X2 or Xn can be reduced.

[0387] Second embodiment, modified example 1 There are cases where the SeNB does not permit the establishment of an emergency bearer. For example, this is due to local regulations and operator's policy. In such cases, even if the MeNB indicates to the SeNB that it is a DC execution request for an emergency bearer, the SeNB cannot accept it.

[0388] In the method disclosed in the second embodiment, a problem occurs in that the SeNB cannot reject such a case.

[0389] In this modification, a method for solving such problems will be disclosed.

[0390] When the SeNB does not permit the establishment of an emergency bearer, the SeNB rejects a DC execution request from the MeNB, for example, a SeNB addition request or a SeNB modification request, if the request is for an emergency bearer. The SeNB may notify the MeNB of a rejection message. The message may include reason information for the rejection. As reason information for the rejection, information indicating that the establishment of an emergency bearer is not permitted may be provided. When the SeNB does not permit the establishment of an emergency bearer, the SeNB may notify the MeNB of the rejection message including information indicating that the establishment of an emergency bearer is not permitted. The MeNB that receives information indicating that the establishment of an emergency bearer is not permitted does not perform DC for the UE using the SeNB.

[0391] The MeNB that receives the rejection message can determine to execute DC using another SeNB. In order to allow the MeNB that receives the rejection message to execute DC using another SeNB, the MeNB that receives the rejection message may prohibit the SeNB that notified the rejection message from making a DC execution request for a predetermined period of time. This eliminates the need to notify unnecessary DC execution request messages, thereby reducing the amount of signaling.

[0392] The predetermined period may be statically determined in advance. For example, it may be determined by a standard. By determining it in advance, it is possible to simplify the processing. Alternatively, the SeNB may include it in a rejection message and notify the MeNB. In this case, the SeNB can flexibly set the predetermined period according to the situation at that time. This enables flexible operation of the communication system. Note that the above-mentioned method can be applied not only to a rejection message due to not allowing the establishment of an emergency bearer.

[0393] Another method for solving the problem shown in this modification will be disclosed.

[0394] Even if the SeNB does not permit the establishment of an emergency bearer, the SeNB once notifies the MeNB of a DC execution request response message. The DC execution request response message includes information indicating that the establishment of an emergency bearer is not permitted. When the MeNB receives information indicating that the establishment of an emergency bearer is not permitted from the SeNB, the MeNB notifies the SeNB of a DC execution release message, for example, a SeNB release message. In addition, the MeNB does not notify the UE of an RRC connection reconfiguration message. As a result, the MeNB does not use the SeNB as a DC for an emergency bearer. This method is not limited to the method disclosed in the second embodiment, and can also be applied to a conventional case where the SeNB cannot recognize whether the bearer for which the MeNB has requested DC execution is for an emergency service or not.

[0395] Another method for solving the problem shown in this modification will be disclosed.

[0396] The SeNB may notify the surrounding eNB of information indicating that the own cell does not permit the establishment of an emergency bearer in advance. The surrounding eNB may be an eNB that may perform DC. The surrounding eNB may be notified via the MME. The MeNB uses the information to determine whether to perform DC of the emergency bearer for the SeNB. If the SeNB does not permit the establishment of an emergency bearer, the SeNB is not used to perform DC for the emergency bearer. This method is not limited to the method disclosed in the second embodiment, and can also be applied to the conventional SeNB when it cannot recognize whether the bearer requested to perform DC from the MeNB is for emergency service.

[0397] When the MME recognizes that the SeNB does not permit the establishment of an emergency bearer, the MME may notify the MeNB that may perform DC with the SeNB of the identifier of the SeNB and information indicating that the SeNB does not permit the establishment of an emergency bearer in advance. By this, the MeNB uses the information to determine whether to perform DC of the emergency bearer for the SeNB. If the SeNB does not permit the establishment of an emergency bearer, the SeNB is not used to perform DC for the emergency bearer.

[0398] These methods allow the SeNB to prevent the SeNB from allocating resources for emergency bearers when the SeNB does not permit the establishment of such bearers. A system that reflects local regulations and operator's policies can be constructed.

[0399] Second embodiment, modified example 2 If DC is to be supported for an emergency bearer, additional processing such as that shown in the second embodiment and the first modification of the second embodiment is required, and the processing becomes more complicated as a system. When the processing becomes complicated, the stability of the system deteriorates.

[0400] In this modification, a method for constructing a stable system is disclosed.

[0401] DC is not performed for emergency bearers. When determining whether to perform DC, the eNB determines whether the bearer on which DC should be performed is an emergency bearer. If it is an emergency bearer, DC is not performed. That is, the eNB does not start the DC execution process. If it is not an emergency bearer, DC is performed. That is, the eNB enables the DC execution process.

[0402] In this way, by not performing DC for emergency bearers, it is possible to build a stable system.

[0403] For emergency bearers, whether or not DC is supported may be appropriately selected depending on the status of the communication system.

[0404] For example, in places where the requirement for high throughput is low (places that are not congested), it may be better to build a stable system rather than supporting DC for emergency bearers. Therefore, in places where the requirement for high throughput is high, DC is made executable for emergency bearers, and in places where the requirement for high throughput is low, DC is not executed for emergency bearers. A threshold value may be set for the throughput requirement, and the eNB may make a judgment based on the threshold value. The threshold value may be statically determined in advance by a standard or the like, or may be notified to the eNB by the MME.

[0405] By doing this, it becomes possible to change the execution of DC for emergency bearers depending on the status of the communication system, enabling flexible operation according to the status of the communication system.

[0406] In addition, for emergency bearers, whether or not DC is supported may be appropriately selected depending on the power consumption of the UE.

[0407] For example, when DC is performed by architecture 3C, the UE needs to communicate with both the MeNB and the SeNB, which increases the power consumption of the UE. It is desirable to avoid interruption of emergency services due to the UE running out of battery. It is necessary to suppress the power consumption of the UE as much as possible depending on the situation. Therefore, when the UE battery level is high, DC can be performed for the emergency bearer, and when the UE battery level is low, DC is not performed for the emergency bearer.

[0408] The UE transmits battery remaining amount information to the eNB. The eNB may receive the battery remaining amount information of the UE and use the battery remaining amount information to determine whether to perform DC for the emergency bearer.

[0409] To obtain the remaining battery level information from the UE, the eNB may notify the UE of a battery remaining information request message. The notification may be made by an RRC message. The notification may be made by an individual UE message. For example, the eNB may include the request information for the remaining battery level information in a UE Information Request message and notify the UE. When the UE Information Request message includes the request information for the remaining battery level information, the UE notifies the eNB of the remaining battery level information by including it in a UE Information Response message.

[0410] In this way, the eNB can receive battery remaining information from the UE, and the eNB can determine whether to support DC for the emergency bearer according to the power consumption of the UE. For the emergency bearer, whether to support DC can be appropriately used according to the power consumption of the UE.

[0411] In order to reduce the power consumption of small cells or to reduce interference when a large number of small cells are operated, turning on or off small cells is being considered. In the process of turning on a small cell for use in an emergency bearer, the small cell should not reject the process of turning on the own cell. In addition, when a small cell is used for an emergency bearer, the small cell should reject the process of turning off the own cell. As a method for this, the method disclosed in the present embodiment and the modified example may be applied as appropriate. For example, information indicating that the small cell is for use in an emergency bearer may be included in a message requesting turning on the small cell.

[0412] Embodiment 3 The problem to be solved in the third embodiment and the solution thereto are described below.

[0413] In the current standard, the UE is allowed to request modification of bearer resources (allocation or release of resources) for the configured bearer (see 3GPP TS 2013-0101122 5.4.5). The UE requests modification of the bearer to the P-GW via the MME. Since the P-GW can configure EPS bearer QoS related information, the P-GW that receives the modification request for the bearer from the UE modifies the EPS bearer QoS related information, for example, QCI, GBR, MBR, or ARP.

[0414] The MME performs bearer setup, i.e., E-RAB Setup Request, to the eNB based on the EPS bearer QoS related information notified from the P-GW via the S-GW. The MME sets up the E-RAB level QoS parameters. Therefore, when the P-GW modifies the bearer setup, the MME modifies the bearer setup for the eNB.

[0415] In this way, when DC is not performed for a certain bearer, the bearer is established using one eNB, so that the bearer can be modified by a bearer resource modification request from the UE in the conventional standard.

[0416] However, when DC is performed on a bearer, the configuration of the bearer cannot be modified by a bearer resource modification request from the UE in the conventional standard. The E-RAB configuration in the MeNB or SeNB cannot be modified.

[0417] In the discussion on DC in 3GPP, it is discussed that in the DC execution process, the MeNB derives a bearer setting to be requested to the SeNB from the bearer setting requested from the MME. In the DC execution process, the MeNB requests resources from the SeNB so that the sum of the resources provided by the MeNB and the resources provided by the SeNB is guaranteed or exceeds the QoS of the E-RAB level requested by the MME.

[0418] Therefore, there may be a case where the MeNB sets a value different from the QoS information of the E-RAB level requested by the MME to the SeNB. The MeNB includes the QoS information of the E-RAB level requested to the SeNB in ​​a DC execution request message to the SeNB, for example, a SeNB addition request message, and notifies the SeNB. In this way, the MeNB sets up a bearer for the SeNB.

[0419] In the conventional standard, a UE requests a P-GW to modify bearer resources, but there is no mechanism for the UE to request modification of the SeNB bearer settings made by the MeNB in ​​the DC. This means that a modification request cannot be made to the SeNB bearer settings or the MeNB and SeNB bearer allocation settings.

[0420] In this embodiment, a method for solving such problems is disclosed.

[0421] It is possible to modify at least one of the bearers (hereinafter referred to as "DC bearers") of the MeNB and the SeNB by UE activation. It is preferable to provide a UE-activated DC bearer modification process. It is preferable to provide a message for a UE-activated DC bearer modification request.

[0422] Disclosed is a UE-initiated DC bearer modification process. The UE makes a DC bearer modification request to the MeNB. The UE notifies the MeNB of a DC bearer modification request message.

[0423] As examples of information to be included in the DC bearer modification request message, the following eleven items (1) to (11) are disclosed. (1) Information indicating that this is a bearer modification request for DC. (2) An identifier for identifying a bearer. For example, an EPS bearer identifier, an EPS bearer ID, an E-RAB identifier, or an E-RAB ID. (3) Information indicating that the specified QoS cannot be maintained. (4) Requested E-RAB level QoS information, e.g., QCI, GBR. (5) Information indicating a request for improvement of the QoS of the SeNB, for example, information indicating a request for improvement of the QoS at the E-RAB level. (6) Information indicating a request for improvement of QoS of the MeNB. For example, information indicating a request for improvement of QoS at the E-RAB level. (7) Information indicating a packet flow ratio modification request of the MeNB and the SeNB. For example, information indicating a ratio increase request of the MeNB, information indicating a ratio increase request of the SeNB. (8) SeNB identifier, or may be an identifier of an SCG cell. (9) UE identifier. (10) UE AMBR (Aggregate Maximum Bit Rate). (11) A combination of (1) to (10) above.

[0424] The MeNB that receives the DC bearer modification request message from the UE modifies the SeNB bearer setting or the MeNB and SeNB bearer allocation setting using the information contained in the message. At this time, the MeNB may ensure that the total of the resources provided by the MeNB and the resources provided by the SeNB is equal to or greater than the E-RAB level QoS requested by the MME.

[0425] The MeNB initiates a SeNB modification procedure to execute a modified bearer setup for the SeNB. The MeNB may notify the SeNB of the QoS information of the E-RAB level requested to the SeNB.

[0426] Also, the MeNB may decide not to set up a bearer for the SeNB. In other words, the MeNB may decide to release the bearer set up for the SeNB. This increases the modification options. The MeNB may initiate a SeNB Release procedure.

[0427] Also, the MeNB may modify the packet flow ratio between the MeNB and the SeNB without modifying the DC bearer. This increases the number of modification options. For example, this may be applied when information indicating a request to modify the packet flow ratio between the MeNB and the SeNB is received from the UE. There is no need to perform a process to modify the bearer setting of at least one of the MeNB and the SeNB, and it is possible to perform a simple process.

[0428] FIG. 22 is a diagram showing an example of a sequence of a UE-initiated DC bearer modification process in a communication system of the third embodiment.

[0429] In step ST2301, a SeNB addition process is performed between the UE, the MeNB, and the SeNB, and a DC using the MeNB and the SeNB is executed for the UE (see non-patent document 9). In the case of DC architecture 1A, a SeNB addition process is performed between the UE, the MeNB, the SeNB, the MME, and the S-GW, and a DC using the MeNB and the SeNB is executed for the UE.

[0430] At this time, as described above, the MeNB performs bearer setup for the SeNB, or bearer allocation setup between the MeNB and the SeNB.

[0431] In Step ST2302, the UE determines whether or not to request modification of a bearer. It may determine whether or not a desired QoS is obtained for the bearer. Alternatively, it may determine whether or not the QoS for the bearer of the MeNB or the QoS for the bearer of the SeNB is obtained.

[0432] If the UE determines that a bearer modification request is not necessary, it continues the currently running DC.

[0433] In step ST2303, the UE that has determined to request modification of the bearer notifies the MeNB of a modification request for DC bearer. It is preferable to provide a message for the modification request for DC bearer and notify the request. It is preferable to notify the request using an RRC message. It is preferable to use UE-specific signaling. The UE may include the above-mentioned information in the modification request message for DC bearer.

[0434] In Step ST2303, the MeNB that has received the message for the DC bearer modification request modifies the resource configuration of the SeNB using the information included in the message in Step ST2304. As the modification of the resource configuration of the SeNB, the bearer configuration or the bearer allocation configuration of the MeNB and the SeNB is modified. As the bearer configuration, the QoS information of the E-RAB level may be set. In addition, at this time, the MeNB ensures that the total of the resources provided by the MeNB and the resources provided by the SeNB guarantees the QoS of the E-RAB level requested by the MME or is equal to or more than that.

[0435] In Step ST2305, the MeNB starts a SeNB modification process to execute a modified bearer setup for the SeNB. The MeNB may notify the SeNB including QoS information of the E-RAB level requested to the SeNB. As a result, the SeNB modification process is performed between the UE, MeNB, and SeNB. In the case of DC architecture 1A, the SeNB modification process is performed between the UE, MeNB, SeNB, MME, and S-GW. This SeNB modification process modifies the resource setup of the SeNB.

[0436] By doing this, it becomes possible for the UE to make a request to modify the bearer resources for DC.

[0437] If the bearer modification for DC is not performed, the MeNB notifies the UE of a rejection message.

[0438] For example, the MeNB may determine that the DC bearer modification is not performed. For example, when the MeNB receives a DC bearer modification request message from the UE, it may determine that the request from the UE indicated by the information contained in the message cannot be satisfied by modifying the SeNB resource configuration.

[0439] In such a case, the MeNB may notify the UE of a rejection message for the DC bearer modification request.

[0440] In addition, when the MeNB receives a modification rejection message from the SeNB in ​​the MeNB-initiated SeNB modification process, the MeNB may determine that the DC bearer modification request from the UE cannot be satisfied and notify the UE of a rejection message for the DC bearer modification request.

[0441] In this way, by notifying the UE of the rejection message, the UE can recognize that the DC bearer modification is not performed. The UE can use this to make a decision to execute other bearer modification means, such as a conventional UE-initiated EPS bearer modification request.

[0442] The rejection message may include reason information. The following nine examples of reason information are provided below: (1) UE initiated bearer modification for DC is not supported. (2) Total resource shortage of MeNB and SeNB. (3) Lack of resources in MeNB. (4) Lack of resources in SeNB. (5) The requested EPS level QoS is not accepted. (6) Invalid EPS bearer identifier. (7) Invalid E-RAB identifier. (8) Unsupported QCI value. (9) Rejection of the SeNB modification request, in which case the reason for the rejection may be included.

[0443] A UE that receives a rejection message may be prohibited from making a DC bearer modification request for a predetermined period of time.

[0444] This eliminates the need to notify unnecessary DC bearer modification request messages, thereby reducing the amount of signaling.

[0445] The predetermined period may be statically determined in advance. For example, it may be determined by a standard. By determining the period in advance, it is possible to simplify the process.

[0446] Alternatively, the MeNB may include the period in a rejection message and notify the UE. In this case, the MeNB can flexibly set the predetermined period according to the situation at the time, enabling flexible operation of the communication system.

[0447] It has been disclosed that when the MeNB receives an SeNB modification rejection message from the SeNB, it may determine that it cannot satisfy the DC bearer modification request from the UE and notify the UE of a rejection message for the DC bearer modification request.

[0448] As another method, when the MeNB receives a SeNB modification rejection message from the SeNB, it may determine that the DC bearer modification request from the UE cannot be satisfied and may start a change of the SeNB used for DC. If there is another SeNB capable of DC for the UE, a change process to the SeNB may be started. This makes it possible to satisfy the DC bearer modification request from the UE.

[0449] Third embodiment, variant 1 In this modification, another method for solving the problem in the third embodiment will be disclosed.

[0450] The UE performs a DC bearer modification request to the MeNB via the MME. The UE notifies the MME of a DC bearer modification request message.

[0451] As the information to be included in the DC bearer modification request message, the information disclosed in the third embodiment can be applied. Other examples of the information are disclosed below.

[0452] (1) An identifier of the MeNB that executes the DC. Alternatively, it may be an identifier of the PCell. This information may be applied in combination with the information disclosed in the third embodiment.

[0453] For example, in DC architecture 3C, the MME does not need to recognize that DC is being executed. Therefore, in such a case, even if the MME receives a DC bearer modification request message from the UE, it is not possible to perform processing accordingly.

[0454] An MME that receives a DC bearer modification request message from a UE can recognize the MeNB that is executing the DC by using the information (1) disclosed above.

[0455] The MME that receives the DC bearer modification request message from the UE notifies the MeNB that is executing the DC of the DC bearer modification request message. The information disclosed in the third embodiment can be applied as the information to be included in the DC bearer modification request message.

[0456] The MeNB that has received the DC bearer modification request message from the MME uses the information contained in the message to modify the SeNB bearer setting, or the MeNB and SeNB bearer allocation setting, etc. These processes may be performed by applying the method disclosed in the third embodiment.

[0457] Fig. 23 is a diagram showing another example of the sequence of the UE-activated DC bearer modification process in the communication system of the embodiment 3. The same steps as in Fig. 22 are assigned the same numbers and common explanations are omitted.

[0458] In Step ST2302, the UE that has determined to request modification of the bearer notifies the MME of a DC bearer modification request in Step ST2401. It is preferable to provide a message for the DC bearer modification request and notify it. The request may be a NAS message. In addition, the request may be notified to the MME via the MeNB. The UE may notify between the MeNB using an RRC message, and between the MeNB and the MME using an S1 message.

[0459] The signaling may be UE-specific. The UE may include the above-mentioned information in a DC bearer modification request message.

[0460] In step ST2401, the MME that has received the message for the bearer modification request for DC uses the information contained in the message to recognize that it is a bearer modification request for DC, and recognizes the MeNB that executes the DC, etc.

[0461] In step ST2402, the MME notifies the MeNB that executes the DC of a DC bearer modification request message. The request may be an S1 message. It may be UE-specific signaling. The MME may include the information disclosed in the third embodiment in the DC bearer modification request message.

[0462] As a result, the MeNB receives a DC bearer modification request message from the UE.

[0463] In step ST2402, the processing after the MeNB receives the modify bearer for DC request message is similar to that in embodiment 3, and therefore the description thereof will be omitted.

[0464] This enables the UE to make a request to modify the bearer resources for DC, similarly to the third embodiment.

[0465] A UE activation bearer resource modification request message notified from the UE to the MME in the conventional standard may be used as a message for a DC bearer modification request notified from the UE to the MME.

[0466] In this case, in order to distinguish from the conventional contents, the message may include information indicating that it is a DC bearer modification request and identifier information of the MeNB executing the DC. Also, the information disclosed in the third embodiment and above may be included.

[0467] Using these information, the MME may determine whether to make a bearer resource modification request to the P-GW, which is a conventional standard process, or to make a DC bearer modification request to the MeNB. For example, in the case of a DC bearer modification request, a DC bearer modification request is made to the MeNB, and if not, a bearer resource modification request is made to the P-GW.

[0468] This makes it possible to avoid the need to set up a new message from the UE to the MME, and to prevent message processing from becoming complicated.

[0469] When the MeNB notifies the UE of a rejection message, it may be notified via the MME. In this case, in addition to the information disclosed in the third embodiment, the rejection message may include information indicating a rejection of the DC bearer modification request and an identifier of the UE that made the DC bearer modification request. The MME can notify the UE of the rejection message.

[0470] In the second embodiment, a method for making DC applicable to an emergency bearer is disclosed, but in the case of an emergency bearer, a bearer change for DC may not be executed.

[0471] For example, the UE may not make a DC bearer modification request for an emergency bearer.

[0472] As another example, the MeNB may reject a request for DC bearer change for an emergency bearer even if the request is received from the UE. As the reason information, information indicating that the request is for an emergency bearer may be provided and included in the rejection message.

[0473] Embodiment 4 The problem to be solved in the fourth embodiment and the solution thereto are described below.

[0474] In the current 3GPP standard, there is a function related to UE location information. For example, there is a function of Immediate MDT (IMDT) in Minimization of Drive Test (MDT) (see 3GPP TS37.320 V12.0.0 (hereinafter sometimes referred to as "Non-Patent Document 15")). Immediate MDT is applied to UEs in RRC_Connected. Immediate MDT is performed using RRC measurement processing. In the measurement configuration, the UE is configured as to whether or not to include location information in a measurement report. If configured, the UE includes the location information in a measurement report and notifies the eNB.

[0475] In addition, when the UE receives from the eNB another setting message (OtherConfig) including specified information (obtain Location), the UE notifies the UE of detailed location information using the Global Navigation Satellite System (GNSS) in addition to the location information when transmitting a measurement report.

[0476] UE uses highly accurate GNSS to measure detailed location information. However, because GNSS is used, measurement is impossible in indoor environments, such as underground shopping malls and underground parking lots. Therefore, in such cases, other highly accurate location information is required.

[0477] In this embodiment, a method for solving such a problem will be disclosed.

[0478] When the UE executing DC is configured to include location information in the measurement report in the measurement configuration, the UE notifies the MeNB of the measurement report including the SeNB identifier as location information. The SeNB identifier may be set to a global eNB ID. Alternatively, the UE may notify the MeNB of the location information including the SCG cell identifier. The cell identifier may be set to CGI or PCI.

[0479] As specific examples of SCG cells, the following five (1) to (5) are disclosed. (1) All SCG cells configured for DC. (2) SPCell. (3) The SCG cell with the best reception quality (which may be reception power). (4) The SCG cell with the smallest path loss. (5) The cell with the smallest cell size.

[0480] In this way, the MeNB can recognize the location of the UE with an accuracy according to the coverage size of the SCG cell. As mentioned above, the coverage size of the SCG cell is relatively small. In addition, in an indoor environment, it is expected that SCG cells with particularly small coverage sizes will be used. Therefore, highly accurate location information can be obtained.

[0481] Although the notification is made to the MeNB, it is sufficient for the DC to notify an eNB having an RRC function.

[0482] Another method is disclosed.

[0483] Information indicating a report of an identifier of a SeNB or an SCG cell is newly provided. The eNB may notify the UE of the information by an RRC message. The information may be included in another configuration message (OtherConfig) and notified. When the UE executing DC is notified of information indicating a report of an identifier of a SeNB or an SCG cell by another configuration message, the UE may notify the MeNB by including the identifier of the SeNB or the SCG cell in a measurement report. By newly providing the information, the eNB can explicitly request a report of the identifier of the SeNB or the SCG cell. By using this method, the eNB can appropriately and flexibly obtain location information of the UE.

[0484] Alternatively, existing information may be used. When predetermined information (obtain location) is notified by another setting message, the UE performing DC may notify the MeNB by including the identifier of the SeNB or SCG cell in the measurement report.

[0485] In addition, when existing information is used, if the UE is unable to use GNSS, the measurement report may include an identifier of the SeNB or SCG cell and be notified to the MeNB.

[0486] By using existing information, it becomes unnecessary to provide new information, and it becomes possible to prevent the processing of the system from becoming complicated.

[0487] Also, in order to notify the MeNB including the identifier of the SeNB or SCG cell, another RRC message may be used instead of the measurement report. Also, a new RRC message may be created for notifying the information. By using a message other than the measurement report, the eNB can obtain the location information of the UE more flexibly.

[0488] By using the method disclosed in this embodiment, the eNB can obtain detailed location information of the UE. The eNB can recognize which SeNB or SCG cell the UE is located within the coverage of.

[0489] The method disclosed in this embodiment may be applied when a Radio Link Failure (RLF) or a Handover Failure (HOF) occurs.

[0490] When a UE executing DC becomes RLF or HOF, the UE may include an identifier of a SeNB or an SCG cell as location information in an RLF Report message.

[0491] When the UE receives a message including an RLF report request from the eNB, the UE may notify the eNB of an RLF report message including the location information.

[0492] For example, a UE Information Request message may be used as a message including an RLF Report request. The eNB sets RLF Report request information in the UE Information Request message and notifies the UE. The UE that receives the RLF Report request information includes location information including an identifier of the SeNB or SCG cell in a UE Information Response message and notifies the eNB.

[0493] In this way, the eNB can obtain detailed location information of the UE where the RLF or HOF has occurred.

[0494] In the current 3GPP standard, there are other functions related to UE location information. For example, UE positioning (see 3GPP TS36.305), LPP (LTE Positioning Protocol) (see 3GPP TS36.355), LCS (Location Service) (see 3GPP TS23.271), etc. In these functions, the identifier of the SeNB or SCG cell may be used as the location information of the UE. The location of the UE is derived using the identifier of the SeNB or SCG cell to which the UE in the DC is connected.

[0495] A UE performing DC using a SeNB is present within the coverage of the SeNB. Furthermore, when the SCG cell is specified, a UE performing DC using an SCG cell is present within the coverage of the SCG cell. Therefore, the location of the UE can be derived by using the identifier of the SeNB or SCG cell to which the UE in DC is connected. As mentioned above, the coverage size of the SCG cell is relatively small. Therefore, highly accurate UE location information can be obtained.

[0496] For example, there is an E-CID (Enhanced Cell ID) mechanism used in these functions. This uses information of the serving eNB or cell of the UE to obtain the location of the UE. Therefore, in the UE in the DC, information of the MeNB or PCell is used conventionally.

[0497] As a new method, in the UE in the DC, information of the SeNB or SCG cell to which the UE in the DC is connected is used to obtain the location of the UE. As the information of the SeNB or SCG cell, an eNB identifier or a cell identifier may be used. Also, time information of transmission or reception between the SeNB or SCG cell and the UE may be used. For example, the time difference between the transmission and reception of the UE (UE Tx-Rx time difference) may be used. In this way, more accurate UE location information can be obtained than the conventional E-CID method using the MeNB.

[0498] Fourth embodiment, variant 1 The problem to be solved by the first modification of the fourth embodiment and the solution thereto will be described below.

[0499] In the current 3GPP standard, there is a function related to the movement state of the UE, such as a speed dependent scaling of measurement related parameters (see 3GPP TS36.331 V12.1.0 (hereinafter sometimes referred to as "Non-Patent Document 16")).

[0500] The eNB sets, for the UE, mobility state parameters that indicate the UE's moving speed in a measurement configuration. The parameters include a measurement period, a threshold for the number of HOs, and a scaling factor. The UE that receives the measurement configuration detects the number of HOs within the measurement period. The UE derives the mobility state of the UE using the detected number of HOs and the threshold for the number of HOs. The mobility states include "high", "medium", and others (hereinafter referred to as "normal"). After deriving the mobility state of the UE, the UE derives a scaling factor according to the mobility state, and sets the value of a measurement-related parameter by multiplying the scaling factor. The measurement-related parameter includes TTT (Time To Trigger).

[0501] In this way, in the conventional standards, a UE detects the number of HOs to derive its own movement state.

[0502] In a UE executing DC, the MeNB is changed in HO, but the SeNB is not changed in HO. Therefore, the movement state of a UE executing DC is determined using the MeNB. For example, when a UE executing DC moves within the MeNB, the movement state is set to "normal".

[0503] However, small cells have a relatively small coverage. Therefore, when a UE moves between SeNBs or SCG cells, it moves in a short period of time. In such a case, the UE's movement state can no longer be called "normal".

[0504] The SCG cell measurements are used by the MeNB to determine the settings of the SeNB or SCG cell used for DC. It is insufficient to use the UE's movement state determined by the number of HOs of the MeNB to set the measurement-related parameters of the SCG cell. Measurement of the SCG cell requires more accurate settings of measurement-related parameters, in other words, suitable for the coverage of the small cell, which requires more accurate acquisition of the UE's movement state.

[0505] In this modification, a method for obtaining a more accurate movement state of a UE is disclosed.

[0506] The number of SeNB changes is used to derive the mobility state of the UE during DC execution. The UE during DC execution detects the number of SeNB changes. The UE may record the detected number of SeNB changes.

[0507] When performing an additional process of the SeNB used for DC, the MeNB instructs the UE to count the number of SeNB changes. It is preferable to notify by RRC signaling. Individual signaling may also be used.

[0508] Also, information instructing detection of the number of SeNB changes may be included in an RRC message and notified. For example, the MeNB may include the information in an RRC Connection Reconfiguration message and notify the UE. The information may be included in a "Radio Resource Configuration Dedicated" message and notified. As another example, the MeNB may include the information in a measurement configuration and notify the UE. The information may be included in a measurement report configuration and notified. The measurement configuration may be the measurement configuration of the SeNB or SCG cell used for DC.

[0509] As another example, the MeNB may notify the UE when performing RRC connection reconfiguration for the SeNB. For example, the MeNB may notify the UE of the information during a SeNB addition process. As another example, the MeNB may notify the UE of the information during a SeNB modification process or modification process. As another example, the MeNB may notify the UE of the information when changing an SPCell.

[0510] These notification methods may be used in combination, allowing for flexible operation of the system.

[0511] The UE that has received the instruction to detect the number of times the SeNB has been changed detects the number of times the SeNB has been changed, and derives the movement state of the UE using the detection result.

[0512] A specific example of a method for deriving the UE's movement state will be disclosed. The MeNB sets parameters of the movement state representing the UE's movement speed together with an instruction to detect the number of SeNB changes. The parameters are parameters related to the SeNB. The parameters include a measurement period, a threshold value for the number of SeNB changes, and a scaling factor.

[0513] The UE that receives the parameter setting detects the number of SeNB changes within the measurement period. The UE derives the mobility state of the UE by using the detected number of SeNB changes and a threshold value for the number of SeNB changes. The mobility state is defined as "high", "medium", or other (hereinafter referred to as "normal").

[0514] In this way, the UE can derive its own movement state.

[0515] The UE derives its own movement state, derives a scaling factor according to the movement state, and multiplies the measurement-related parameter by the scaling factor. An example of the measurement-related parameter is TTT.

[0516] The measurement-related parameters multiplied by the scaling factor derived using the number of SeNB changes detected by the UE are used for measurements of the SeNB or SCG cell.

[0517] In this way, the UE can detect the number of times the SeNB has been changed, and by using the detection result, the UE can derive the movement state of the UE with higher accuracy.

[0518] By using the movement state for measurements of the SCG cell, the UE can set measurement-related parameters with higher accuracy, in other words, suitable for the coverage of the small cell.

[0519] By using the method disclosed in this modification, the UE can set measurement-related parameters with higher accuracy, in other words, suitable for the coverage of the small cell. The MeNB can obtain more accurate measurement results of the SCG cell from the UE. Therefore, the MeNB can more accurately determine the setting of the SeNB or SCG cell used for DC according to the movement state of the UE.

[0520] This makes it possible to improve the throughput of the UE, and also makes it possible to improve the communication capacity of the system as a whole.

[0521] In the above-mentioned method, the MeNB notifies the UE of information instructing the UE to detect the number of times the SeNB has been changed by including the information in the RRC message, so that the UE detects the number of times the SeNB has been changed and uses the detection result for measuring the SCG cell.

[0522] Alternatively, the MeNB may notify the UE of a setting of a mobility state parameter indicating the UE's mobility speed relative to the SeNB as an instruction to detect the number of SeNB changes. When the UE receives the setting of the mobility state parameter indicating the UE's mobility speed relative to the SeNB, the UE detects the number of SeNB changes and uses the detection result for measuring the SCG cell.

[0523] In this way, it is possible to reduce the information instructing detection of the number of SeNB changes and the signaling required for that purpose.

[0524] Although it has been disclosed that the number of SeNB changes is used to derive the movement state of the UE during DC execution, the number of SPCell changes may be used. The number of SPCell changes may be used for the UE during DC execution. The UE may record the number of detected SPCell changes. This makes it possible to take into account the change of the SPcell in the SeNB, and more detailed UE movement state can be derived.

[0525] Also, the number of times the SCG cell has been changed may be used. For a UE performing DC, the number of times the SCG cell has been changed may be used. The UE may record the number of times the SCG cell has been detected. Even in the case where the SeNB is performing CA using an RRH or the like, by recording the number of times the SCG cell has been changed, it is possible to derive a more detailed UE movement state.

[0526] It may be possible to appropriately select whether to use the number of SeNB changes, the number of SPCell changes, or the number of SCG cell changes. The MeNB may instruct the UE which number of changes to use. The MeNB may notify the UE of information on which number of changes to use together with information instructing detection of the number of changes.

[0527] FIG. 24 is a diagram showing an example of a sequence of measurement processing of an SCG cell in a communication system according to the first modification of the fourth embodiment.

[0528] In Step ST2501, the MeNB notifies the SeNB (here, the S-SeNB) of an SeNB addition request message in order to execute DC for the UE.

[0529] The SeNB that receives the SeNB addition request message in Step ST2501 and determines that its own SeNB resources can be used for the DC notifies the SeNB addition request acceptance message in Step ST2502.

[0530] In Step ST2503, the MeNB that has received the SeNB addition request acceptance message notifies the UE of a setting for executing DC. For this notification, an RRC connection reconfiguration message is used. The MeNB includes in the message a setting of a mobility state parameter indicating the mobility speed of the UE with respect to the SeNB, so that the UE detects the number of SeNB changes.

[0531] The UE that has received the message in Step ST2503 performs resource configuration for DC execution.

[0532] In Step ST2504, the UE notifies the MeNB of an RRC connection reconfiguration complete message.

[0533] In Step ST2505, the MeNB notifies the SeNB of a SeNB reconfiguration message.

[0534] Accordingly, in step ST2506, DC execution processing is performed between the UE, the MeNB, and the SeNB.

[0535] In step ST2503, when the UE receives an RRC connection reconfiguration message and recognizes that the message includes a setting of a mobility state parameter indicating the UE's mobility speed with respect to the SeNB, the UE regards the message as an instruction to detect the number of SeNB changes, and in step ST2513 performs measurement processing of the SCG cell using the parameter.

[0536] Specifically, in Step ST2507, the UE detects the number of times the SeNB has been changed within the measurement period.

[0537] In Step ST2508, the UE derives a mobility state of its own UE by using the detected number of SeNB changes and a threshold value of the number of SeNB changes. The mobility state is defined as "high", "medium", or other (hereinafter referred to as "normal").

[0538] Furthermore, in Step ST2508, the UE derives a scaling factor (SF) according to the derived movement state of its own UE.

[0539] In Step ST2509, the UE multiplies a measurement-related parameter, for example, the TTT, by the derived scaling factor, sets this value to the TTT for measurement of the SCG cell, and performs measurement of the SCG cell.

[0540] In Step ST2510, the UE notifies the MeNB of measurement results, including the measurement results of the SCG cells.

[0541] In Step ST2510, the MeNB that has received the measurement result including the SCG cell from the UE decides to change the SeNB using the measurement result in Step ST2511. The MeNB that has decided to change the SeNB starts a SeNB change procedure, and accordingly, the SeNB change procedure is performed between the UE, the MeNB, the S-SeNB, and the T-SeNB. The S-SeNB is the SeNB before the change and is the source SeNB. The T-SeNB is the SeNB after the change and is the target SeNB.

[0542] Subsequently, in Step ST2513, the UE performs a measurement process of the SCG cell using a movement state parameter indicating the movement speed of the UE with respect to the SeNB.

[0543] Since the SeNB has been changed in step ST2511, the number of SeNB changes within the measurement period is incremented by one. The UE derives a new movement state of the UE by using the detected number of SeNB changes and a threshold value of the number of SeNB changes. The UE derives measurement-related parameters from the newly derived movement state of the UE, and performs measurement of the SCG cell.

[0544] In Step ST2512, the UE notifies the MeNB of the measurement results, including the measurement results of the SCG cells.

[0545] In this way, the UE detects the number of SeNB changes, and thus can derive the movement state of the UE with higher accuracy.

[0546] Furthermore, by using the movement state for measurements of the SCG cell, the UE can set measurement-related parameters with higher accuracy, in other words, suitable for the coverage of the small cell.

[0547] Therefore, the MeNB can obtain more accurate measurement results of the SCG cell from the UE, and the MeNB can more accurately determine the configuration of the SeNB or SCG cell to be used for DC depending on the movement state of the UE.

[0548] The method disclosed in this modification may be performed separately from the conventional eNB movement state derivation process. The conventional eNB, i.e., the process of deriving the movement state from the detection result of the number of HOs, and the method disclosed in this modification, i.e., the process of deriving the movement state from the detection result of the number of SeNB changes, may be performed separately or in parallel.

[0549] The movement state deriving method and the measurement method disclosed in this modification may be used exclusively for measurements of the SCG cell, enabling appropriate measurements according to the coverage range of the cell.

[0550] In addition, for the measurement of the MeNB, it is preferable to use the conventional moving state derivation method and measurement method.

[0551] The movement state derivation method and the measurement method disclosed in this modification may be used for measuring the frequency layer of an SCG cell, or may be used for measuring the frequency layer in which a small cell is operated.

[0552] This enables appropriate measurements according to the coverage range of small cells, not just SCG cells.

[0553] The source MeNB may notify the target MeNB (eNB) of the setting of a parameter of a moving state representing the moving speed of the UE with respect to the SeNB. For example, in the case of a change of the MeNB or HO of an eNB, this allows the target MeNB (eNB) to recognize the parameter setting of the moving state representing the moving speed of the UE with respect to the SeNB that was set in the source MeNB of the UE to be HOed, and can contribute to the setting of the parameter of the moving state representing the moving speed of the UE with respect to the SeNB in ​​the own MeNB (eNB).

[0554] Also, in the target MeNB (eNB), the parameter setting of the moving state representing the moving speed of the UE, which is the same as that of the source MeNB, may continue to be valid until the parameter setting of the moving state representing the new moving speed of the UE is performed. The UE continues to detect and record the number of SeNB changes using the parameter setting of the moving state representing the moving speed of the UE, which is the same as that of the source MeNB, until the parameter setting of the moving state representing the new moving speed of the UE is notified from the target MeNB (eNB). In this way, it is possible to detect the long-term moving state of the UE.

[0555] Conversely, the UE may reset the detection and recording of the SeNB change count in the HO of the MeNB (eNB). In accordance with the resetting of the detection and recording of the SeNB change count, the measurement of the SCG cell using the SeNB change count may also be reset. The UE may perform the measurement again in accordance with the reception of the measurement setting notified from the target MeNB (eNB). This eliminates the need to notify the measurement setting from the source MeNB to the target MeNB. Therefore, it is possible to prevent an increase in the amount of signaling during HO.

[0556] Although the HO of the MeNB (eNB) has been described, the present invention can also be applied to a case where the serving cell that notifies the UE of the measurement configuration is changed, such as when the MeNB is changed or the PCell is changed.

[0557] The detection and recording of the SeNB change count may be reset when the SeNB release process is performed. The UE may reset the detection and recording of the SeNB change count when the SeNB release process is notified. The UE may reset the detection and recording of the SeNB change count when the execution of the DC is completed.

[0558] In accordance with detection of the number of SeNB changes and resetting of the record, measurements of SCG cells using the number of SeNB changes may also be reset.

[0559] The method disclosed in this modification may be applied not only to TTT but also to other measurement-related parameters, and can be used when more accurate movement state is required.

[0560] Fourth embodiment, modified example 2 The problem to be solved by the second modification of the fourth embodiment and the solution thereto will be described below.

[0561] In the current 3GPP standard, there is a function related to the mobility state of a UE, for example, mobility history information (see Non-Patent Document 16).

[0562] Mobility History Information applies to UEs in RRC_Idle and RRC_Connected. When the serving cell is changed during RRC_Idle or the PCell is changed during RRC_Connected, the UE records the cell identifier of the cell (the cell before the change) and the residence time in the cell. When the UE first enters an E-UTRA cell from outside the service or from another RAT, it records only the residence time outside E-UTRA.

[0563] In response to a UE Information Request from the eNB, the UE notifies the eNB of the recorded cell identifier of the PCell or serving cell and residence time by including the cell identifier and residence time in a UE Information Response message, thereby enabling the eNB to obtain the movement state of the UE.

[0564] In this way, in the conventional standards, the target cell in the RRC_Connected state is the PCell.

[0565] The SCG cell used for DC is not a PCell, and is therefore not subject to mobility history information. The mobility state of a UE during DC execution is determined by a change in the PCell of the MeNB.

[0566] Therefore, as in the first modification of the fourth embodiment, in the conventional standards, the eNB cannot obtain highly accurate movement states of the UE suitable for the coverage of the small cell.

[0567] In this modification, a method is disclosed in which the eNB obtains a more accurate moving state of the UE.

[0568] The UE records the cell identifier of the SPCell during DC execution and the residence time in the cell. The UE during DC execution records the cell identifier of the cell (the cell before the change) and the residence time in the cell according to the change of the SPCell. The UE may also record the carrier frequency of the cell. The cell identifier may be CGI or PCI.

[0569] The UE may separately provide a list that records information of the conventional PCell and a list that records information of the SPCell. The UE records the information of the PCell and the information of the SPCell in each list.

[0570] This section discloses a method for the eNB to obtain the list recorded by the UE.

[0571] The MeNB requests a list recording SPCell information from the UE executing DC. A new RRC message for the request may be created and notified. Alternatively, an existing RRC message may be notified by including information indicating that the request is for a list recording SPCell information. It may also be notified by individual signaling.

[0572] For example, the MeNB may notify the UE of the information by including it in an RRC Connection Reconfiguration message, or may notify the UE of the information by including it in a "Radio Resource Configuration Dedicated" message.

[0573] Alternatively, the MeNB may notify the UE when performing RRC connection reconfiguration for the SeNB. For example, the MeNB may notify the UE of the information during a SeNB addition process. As another example, the MeNB may notify the UE of the information during a SeNB change process or modification process. As another example, the MeNB may notify the UE of the information when changing an SPCell.

[0574] These notification methods may be used in combination. This allows for flexible operation of the system. As another example, the information may be included in a UE Information Request message, which is the same message as in the past. Information indicating whether a list recording PCell information or a list recording SPCell information is requested may be included in the message.

[0575] When the UE receives a request for a list that records SPCell information from the MeNB, the UE notifies the MeNB of the list that records SPCell information. A new RRC message for the request may be created for notification. Alternatively, the existing RRC message may include information indicating that the request is for a list that records SPCell information. Notification may be made by individual signaling.

[0576] For example, when a UE Information Request message, which is the same as the conventional message, is used to request a list that records information on the SPCell, the notification may be made using a UE Information Response message. The UE notifies the MeNB of the list that records information on the SPCell by including it in the UE Information Response message.

[0577] The MeNB may separately request the UE for a list that records the PCell information and a list that records the SPCell information. For example, a UE Information Request message may be used for both. By including in the message information indicating whether the UE requests a list that records the PCell information or a list that records the SPCell information, the UE can recognize which information to notify the MeNB. The UE may report the corresponding list to the MeNB according to the information.

[0578] The MeNB may request both the list recording the SPCell information and the list recording the PCell information in one message. The MeNB may notify the UE of information indicating that both are requested. The UE that receives the message notifies the MeNB of both the list recording the SPCell information and the list recording the PCell information. The notification may be made using one message.

[0579] Also, one message may always be a message indicating that both are requested. It may be statically determined in advance by a standard, etc. When the MeNB notifies the UE of the message, the UE notifies the MeNB of both a list recording information on the SPCell and a list recording information on the PCell. It may be notified using one message.

[0580] This paper discloses a method for creating a list that records SPCell information.

[0581] According to the change of the SPCell during the execution of DC, the UE records the cell ID of the cell (the cell before the change) and the residence time in the cell. In addition, the carrier frequency of the cell may be recorded. The cell size of the cell may also be recorded.

[0582] The maximum number of cells to be recorded in the list may be determined. For example, the maximum number of cells may be n, and when the number of cells exceeds this number, the UE discards the oldest cells. This can prevent the UE's recording capacity from becoming too large. The maximum number of cells n may be statically determined in advance by a standard, or may be notified from the MeNB.

[0583] The UE may discard the list in which the information of the SPcell is recorded when the SeNB release procedure is executed. The UE may create a new list in which the information of the SPcell is recorded when the SeNB addition procedure is executed. The execution of the SeNB release procedure may be when the UE releases or resets resources for the SeNB.

[0584] When the SeNB release procedure is executed, the UE may hold the list recording the SPCell information for a predetermined period. When a new SeNB addition procedure is executed before the expiration of the predetermined period after the execution of the SeNB release procedure, the UE records the information in the already created list. When a new SeNB addition procedure is not executed after the execution of the SeNB release procedure and the predetermined period expires, the UE discards the list.

[0585] By doing so, even in a situation where the coverage of the SeNB is not continuous and DC is executed intermittently, the list recording the SPCell information is not discarded unnecessarily. The predetermined period may be statically determined in advance by a standard or the like. Alternatively, the predetermined period may be notified to the UE from the MeNB. As a notification method, the notification may be made using an RRC message. The notification may be made using individual signaling. Alternatively, the MeNB may notify the UEs being served by the MeNB. The predetermined period may be included in the SIB and notified.

[0586] In addition, the UE may record the time when DC is not executed during RRC_CONNECTED. For example, the time from transition to RRC_CONNECTED to execution of SeNB addition procedure, the time from execution of SeNB release procedure to execution of SeNB addition procedure, and the time from execution of SeNB release procedure to termination of RRC_CONNECTED state may be recorded. Each may be recorded separately. It may be recorded according to the occurrence of the time when DC is not executed. For the time when DC is not executed, it may be recorded as a residence time without recording the cell identifier and carrier frequency information of SPCell.

[0587] In this way, the UE can record the status of SPCell change in the RRC_CONNECTED state, including the case where the SPCell is not used. The MeNB can obtain the information from the UE, and can recognize the movement state of the UE in more detail.

[0588] Furthermore, when HO of the MeNB is performed, the UE may discard the list in which the information of the SPCell is recorded.

[0589] When the UE performs HO of the MeNB, the UE may hold the list recording the SPCell information for a predetermined period. If a new SeNB addition process or SPCell change process is performed before the expiration of the predetermined period after the HO process, the UE records the information in the already created list. If a new SeNB addition process or SPCell change process is not performed after the HO process and the predetermined period expires, the UE discards the list.

[0590] Furthermore, when HO of an MeNB is performed, the UE may notify the HO-target MeNB (eNB) of a list in which information on the SPCell is recorded, and then discard the list.

[0591] After performing the HO process, the UE may notify the HO-target MeNB (eNB) of a list in which information about the SPCell is recorded, in response to a request from the HO-target MeNB (eNB).

[0592] In the case of HO of a MeNB, the HO source MeNB may notify the HO target MeNB (eNB) of a list in which information on the SPCell acquired from the UE is recorded. If the list does not include the cell size, the MeNB may add the cell size to the list and notify it. This is effective when the MeNB recognizes the cell size of the SPCell. The notification may be made by X2 signaling. Alternatively, the notification may be made by S1 signaling via the MME.

[0593] By performing this method, the HO-target MeNB (eNB) can continue to use the information.

[0594] Also, the HO-source MeNB may notify the HO-target MeNB (eNB) of a list recording information on the SPCell acquired from the UE. The HO-source MeNB may notify the HO-target MeNB (eNB) together with the ...

[0595] In the above method, the UE records the PCell information and the SPCell information in respective lists. Alternatively, the UE may record the PCell information and the SPCell information in one list. Alternatively, the UE may include the SPcell information in the conventional PCell information list.

[0596] In this case, a parameter indicating that it is an SPCell may be provided, and a list may be created by recording the parameter in association with the SPCell.

[0597] If the cell size is already included in the list, the parameter indicating that it is an SPCell does not need to be recorded.

[0598] In this way, the UE can have one list, which reduces the storage capacity and simplifies the list creation process. In addition, it is possible to reduce the information or messages included in the list request and notification messages between the MeNB and the UE. This makes it possible to reduce the signaling load.

[0599] In the above method, the UE records the information of the SPCell and creates the list. As another method, the list may be created by recording the information of the SeNB. The UE performing DC records the eNB identifier of the SeNB (SeNB before the change) and the residence time at the eNB according to the change of the SeNB. The carrier frequency used by the eNB may also be recorded. Although the information is rougher than the information of the SPCell, it is possible to reduce the recording capacity and the signaling load.

[0600] The UE may also record information about the SCG cell to create a list. When the UE is executing DC, it records the cell identifier of the SCG cell (the SCG cell before the change) and the residence time in the cell according to the change of the SCG cell. It may also record the carrier frequency of the cell. It may also record the cell size of the cell. The MeNB can derive the moving state of the UE in more detail by acquiring the list that records information about the SCG cell.

[0601] It may be possible to select whether the list is a list that records information on SPCell, a list that records information on SeNB, or a list that records information on SCG cell. It may be statically determined in advance by a standard or the like. Alternatively, the MeNB may instruct the UE which list to create. The MeNB may notify the UE of information on which list to create. For example, the UE may be notified when it transitions to an RRC_Connected state. The MeNB may notify the UE by an RRC message. Individual signaling may be used.

[0602] Fourth embodiment, modified example 3 The problem to be solved by the third modification of the fourth embodiment and the solution thereto will be described below.

[0603] In the current 3GPP standard, there is a function related to the movement state of a UE, for example, UE History Information (see Non-Patent Document 1).

[0604] Regarding UE history information, the eNB serving the UE creates a "Last Visited Cell List" for the UE in an active state.

[0605] When a UE performs HO, the HO-source eNB adds a PCell to the "Last Visited Cell List" of the UE and notifies the HO-target eNB of the list via S1 or X2. The HO-target eNB performs the same process to the next HO-target eNB and notifies it of the list. The network side creates and maintains HO history information for the UE. Information recorded in the "Last Visited Cell List" includes a cell identifier, e.g., CGI, cell size, cell residence time, and HO reason.

[0606] Thus, in the conventional standards, the eNB records the HO history information in a list.

[0607] The SeNB used for DC is not changed in HO. Therefore, no matter how many times a UE performing DC changes its SeNB, it is not recorded in the list.

[0608] Therefore, in the conventional standards, as in the case of the second modification of the fourth embodiment, the eNB cannot obtain highly accurate movement states of the UE suitable for the coverage of the small cell.

[0609] This modification discloses another method for the eNB to obtain a more accurate movement state of the UE.

[0610] The MeNB creates a list of SPCells connected to a UE executing DC. In the following description, the list of SPCells connected to a UE executing DC may be referred to as an "SPCell change history list."

[0611] When the SPCell used for the DC is changed for the UE, the MeNB adds the pre-change SPCell to the SPCell change history list. Alternatively, when the SeNB release process is executed, the MeNB adds the SPCell connected to the UE before the release to the SPCell change history list of the UE.

[0612] Information to be recorded in the SPCell change history list includes a cell identifier, for example, CGI, cell size, cell residence time, SPCell change reason, or SeNB release reason.

[0613] In this way, the MeNB can record the history information of the SPCell of the UE during DC execution in the list. Therefore, the MeNB can obtain the movement state of the UE suitable for the coverage of the small cell.

[0614] The MeNB may separately provide a list for recording conventional HO history information and a list for recording SPCell change history information. The MeNB records the HO history information and the SPCell change history information in each list.

[0615] When the SeNB release process is performed for a UE in which DC is being executed, the MeNB may discard the list that records the SPcell change history information of the UE. When the SeNB addition process is performed for a UE, the MeNB may newly create a list that records the SPcell information of the UE. The execution of the SeNB release process may be a case where the MeNB instructs the UE to release SeNB resources.

[0616] When a SeNB release process is performed for a UE in DC execution, the MeNB may hold a list recording information on the SPCell of the UE for a predetermined period. If a new SeNB addition process is performed before the expiration of the predetermined period after the SeNB release process is performed for a UE in DC execution, the MeNB records it in the list that has already been created. If a new SeNB addition process is not performed after the SeNB release process is performed for a UE in DC execution and the predetermined period expires, the MeNB discards the list.

[0617] By doing so, even if the coverage of the SeNB is not continuous and DC is executed intermittently, the list in which the high history information is recorded in the SPCell is not discarded unnecessarily. The predetermined period may be statically determined in advance by a standard or the like. It may be semi-statically or dynamically determined. It may be determined by the MME or O&M (Operation and Maintenance) and notified to the MeNB.

[0618] Also, the MeNB may record the time when DC is not executed for the UE in RRC_Connected in the list. For example, the time from when the RRC connection establishment procedure between the UE and the MeNB is completed to when the SeNB addition procedure is executed, the time from when the SeNB release procedure is executed to when the SeNB addition procedure is executed, and the time from when the SeNB release procedure is executed to when the RRC_CONNECTED state is terminated may be recorded. Each of these may be recorded separately. It may be recorded according to the occurrence of the time when DC is not executed. For the time when DC is not executed, it is preferable to record only the residence time without recording the cell identifier and carrier frequency information of the SPCell.

[0619] In this way, the MeNB can record the status of SPCell change in the RRC_CONNECTED state, including the case where the SPCell is not used, and the MeNB can recognize the movement state of the UE in more detail.

[0620] Furthermore, when HO is performed, the MeNB may discard the list that records the SPCell change history information of the HO target UE.

[0621] When performing HO, the MeNB may hold a list recording SPCell change history information of the HO target UE for a predetermined period of time. The list can be used when the HO target UE switches back to the HO source MeNB.

[0622] In the case of HO of a MeNB, the HO-source MeNB may notify the HO-target MeNB (eNB) of a list in which SPCell change history information is recorded. The notification may be made by X2 signaling. Alternatively, the notification may be made by S1 signaling via the MME. By using this method, the HO-target MeNB (eNB) can continue to use the information.

[0623] Also, the HO-source MeNB may notify the HO-target MeNB (eNB) of a list in which HO history information of the PCell is recorded. The list may be notified together with the list in which SPCell change history information is recorded. The information may be notified by including the list in the same message.

[0624] When the HO-target MeNB (eNB) receives a list recording the SPCell change history information of the HO-target UE from the HO-source MeNB (eNB), the HO-target MeNB (eNB) may retain the list recording the SPCell change history information of the HO-target UE for a predetermined period of time.

[0625] After the HO process is performed, if the HO-target MeNB (eNB) newly performs a SeNB addition process or an SPCell change process before the expiration of the predetermined period, the HO-target MeNB (eNB) records the result in the list that has already been created. If the HO-target MeNB (eNB) does not newly perform a SeNB addition process or an SPCell change process and the predetermined period expires, the HO-target MeNB (eNB) discards the list.

[0626] In the above method, the MeNB records the HO history information of the PCell and the SPCell change history information in each list. As another method, the HO history information of the PCell and the SPCell change history information may be recorded in one list. Alternatively, the SPcell change history information may be included in the list of the conventional HO history information of the PCell.

[0627] In this case, a parameter indicating that it is an SPCell may be provided, and a list may be created by recording the parameter in association with the SPCell.

[0628] If the cell size is already included in the list, the parameter indicating that it is an SPCell does not need to be recorded.

[0629] By doing so, the MeNB can have one list, which reduces the storage capacity and simplifies the list creation process.

[0630] In the above method, the MeNB records the change history information of the SPCell to create the list. As another method, the list may be created by recording the change history information of the SeNB. For the UE executing the DC, the MeNB records the eNB identifier of the SeNB (SeNB before the change) and the residence time at the eNB according to the change of the SeNB. The carrier frequency used by the eNB may also be recorded. The reason for the change may also be recorded. Although the information is rougher than the information of the SPCell, it is possible to reduce the recording capacity.

[0631] The MeNB may also record change history information of the SCG cell to create a list. For a UE executing DC, the MeNB records the cell identifier of the SCG cell (SCG cell before the change) and the residence time in the cell according to the change of the SCG cell. The MeNB may also record the carrier frequency of the cell. The MeNB may also record the cell size of the cell. The MeNB may also record the reason for the change. By acquiring the list recording the change history information of the SCG cell, the MeNB becomes able to derive a more detailed moving state of the UE.

[0632] It may be possible to select whether the list is a list that records the change history information of the SPCell, a list that records the change history information of the SeNB, or a list that records the change history information of the SCG cell. It may be statically determined in advance by a standard, etc. It may be semi-statically or dynamically determined. It may be determined by the MME or O&M and notified to the MeNB.

[0633] Embodiment 5. In this embodiment, a method is disclosed for enabling communication with less waste and shortage of resources (frequency, time, transmission power) by using a Sounding Reference Signal (SRS) transmitted by a UE that is a target of Coordinated Multipoint transmission and reception (CoMP) described in Non-Patent Document 7 at the start of CoMP.

[0634] Here, the "sounding reference signal" refers to a signal of a known sequence that is constantly or intermittently transmitted even when there is no transmission data, as described in Non-Patent Document 14, for example.

[0635] First, the uplink will be described. FIG. 25 is a diagram showing the concept of UL CoMP being studied in 3GPP. In FIG. 25, eNB#1 is indicated by reference symbol "5101", eNB#2 is indicated by reference symbol "5103", the communication area, i.e., coverage, of eNB#1 is indicated by reference symbol "5102", and the communication area, i.e., coverage, of eNB#2 is indicated by reference symbol "5104". Also, a central entity or a mobile management entity (MME) is indicated by reference symbol "5106".

[0636] When performing UL CoMP, i.e., uplink multipoint coordinated reception, eNB#1 5101 and eNB#2 5103 perform inter-eNB coordinated operation via a central entity (Central Entity) or a mobile management entity (MME) 5106. For example, coordinated scheduling (CS) for multipoint coordinated scheduling is under consideration, and by scheduling communication data 5107, 5110 with a cell edge UE 5105, transmission power, etc. according to the communication status of each eNB, it is possible to improve throughput and increase system throughput. The central entity is a functional unit that performs multipoint coordination, and when performing via MME, it exchanges signals for multipoint coordination between eNBs, and actual coordinated control is performed between the eNBs.

[0637] In UL CoMP during CS, when a mobile terminal (UE) 5105 served by an eNB#1 5101 generates data 5107 to transmit to the eNB#1 5101, the mobile terminal transmits a scheduling request (SR) to the eNB#1 5101. The eNB#1 5101 checks the availability of resources, such as the communication status of other UEs, and if transmission is possible, transmits a grant signal indicating the permitted range.

[0638] Upon receiving the Grant signal, the UE 5105 transmits data 5107 that it wishes to transmit within the range permitted by the Grant signal.

[0639] When the eNB#1 5101 detects that the UE 5105 is at the cell boundary or in the vicinity of another cell, the eNB#1 5101 notifies the UE 5105 of an SRS transmission instruction using RRC (Radio Resource Control).

[0640] The UE 5105 may determine whether it is at the cell boundary based on the reported values ​​of its own cell reported in a Measurement Report message, specifically, whether the Reference Signal Received Power (RSRP) or the Reference Signal Received Quality (RSRQ), or both, are below a specific threshold.

[0641] In addition, the UE 5105 may determine whether it is in the vicinity of another cell based on whether the reported values ​​of the other cell reported by the UE 5105 in a Measurement Report message, specifically, RSRP or RSRQ, or both, are equal to or greater than a specific threshold.

[0642] In Non-Patent Document 14 (see 5.5.1.5), the parameter n RS ID is N cell IDIn the present invention, however, the SRS transmission command specifies at least one UE-specific parameter. That is, the UE 5105 transmits an SRS signal unique to the UE, not an SRS signal unique to the cell.

[0643] The SRS signal may be a UE-specific signal at all times, or may be switched from a cell-specific SRS signal to a UE-specific signal when it is detected that the UE is at a cell boundary or in the vicinity of another cell.

[0644] There are two methods for the UE to transmit data. One is a method in which the UE uses the same configuration (same PUSCH config, PUCCH config) when transmitting to eNB#1 and when transmitting to eNB#2. The other is a method in which the UE uses different configurations when transmitting to eNB#1 and when transmitting to eNB#2.

[0645] For example, in the example shown in FIG. 25, when UE 5105 transmits with different configurations for each of transmitting eNBs 5101 and 5103, eNB#2 5103 notifies eNB#1 5101 of CoMP setting parameters such as "PUCCH config" and "PUSCH config" used by eNB#2 5103 via X2 interface 5115. This may be via a central entity or MME 5106. eNB#1 5101 notifies UE 5105 of this configuration information.

[0646] As a result, when transmitting to eNB#2 5103, UE 5101 can transmit data in a configuration that can be received by eNB#2 5103. This method is effective when synchronization is not achieved between eNBs, such as when a large delay time occurs in the backhaul of the eNBs.

[0647] On the other hand, when the UE 5105 transmits with a common configuration regardless of the transmitting eNB 5101, 5103, the eNB#1 5101 notifies the eNB#2 5103 of CoMP setting parameters such as “PUCCH config” and “PUSCH config” via the X2 interface 5115. The notification may be via a central entity or the MME 5106.

[0648] This allows the eNB#2 5013 to also receive the data transmitted by the UE 5105. This method simplifies the control procedure because the UE can transmit the same data without being aware of which eNB it is transmitting to.

[0649] Furthermore, the eNB#1 5101 notifies the eNB#2 5103 adjacent to the eNB#1 5101, which may perform UL CoMP, of the SRS config 5116 directly via the X2 interface 5115. The eNB#2 5103 starts receiving the SRS from the UE 5105 in accordance with the SRS config 5116.

[0650] In this case, it is preferable to synchronize eNB#1 5101 and eNB#2 5103 in advance. Alternatively, it is preferable to synchronize them within a specific time range. It is effective to synchronize not only OFDM symbols but also subframe numbers, slot numbers, and system frame numbers (corresponding to those specified in TS36.211) that indicate a time equivalent to a length of multiple OFDM symbols.

[0651] Alternatively, the eNB can receive signals within a predetermined time range that is equal to or longer than the cyclic prefix (CP) length for the designated SRS transmission time. Alternatively, it is effective to make the CP length of only the OFDM symbol of the SRS longer than that of other data. Alternatively, it is effective to use a slot format with a long CP length including the data portion when starting SRS transmission. Alternatively, it is effective to change the reference timing that the UE transmits for each eNB, for example, the timing of the beginning of the subframe number, slot number, or system frame number.

[0652] By doing as described above, before starting UL CoMP, the eNB#2 5103 that is the target of UL CoMP knows the uplink communication quality by receiving the SRS from the UE 5105. By both the eNB#1 5101 and the eNB#2 5103 reporting the uplink reception qualities 5109 and 5112 to the central entity 5106, the central entity 5106 can perform optimal resource allocation to the two eNBs.

[0653] There is no longer any need for a delay time before starting UL CoMP (the time required to measure uplink quality after a start command is issued), so UL CoMP can be started immediately, eliminating the allocation of suboptimal frequencies, time, and transmission power that occurs due to the delay time.

[0654] In the above-mentioned method of notifying the SRS config, the notification is via the X2 interface 5115, but it may be via the central entity or the MME 5106.

[0655] At this time, the central entity notifies the selected eNB of the eNB identifier of eNB#1 5101. A plurality of eNBs may be selected.

[0656] Also, the UE 5105 may be notified of the eNB identifier of the selected eNB.

[0657] In the procedure before the start of CoMP described above, after instructing the CoMP target UE to transmit SRS, the adjacent eNB#2 5103 is notified of the SRS config 5116. However, in case the SRS resources to be allocated by the adjacent eNB#2 5103, such as the frequency, time (subframe number), and resource block number, are already in use, the adjacent eNB may be notified of the SRS config before notifying the UE.

[0658] Alternatively, eNB#2 5103 may notify a neighboring eNB (eNB#1 5101) of the usage status when eNB#2 starts using SRS so that the SRS resources of the SRS config are not the same as the SRS resources being used by eNB#2 5103. By preventing overlapping with SRS from other UEs served by eNB#2 5103, the reception quality of the SRS from the UE at eNB#2 5103 can be further improved.

[0659] In the above-mentioned example of SRS transmission start determination, eNB#1 5101 notifies UE 5105 of an SRS transmission start instruction when it detects that it is at the cell boundary, thereby minimizing SRS transmission when not in use. However, in order to save the processing time required to issue an SRS transmission start instruction when, for example, the cell radius of eNB#1 5101 is small, UE 5105 may set an SRS transmission start config in advance when it starts communicating with eNB#1 5101.

[0660] In the SRS transmission command, in addition to the information specifying the resource location, at least one UE-specific parameter is transmitted instead of a cell-specific parameter. However, an ID for identifying the UE, such as an S-TMSI (SAE (System Architecture Evolution) Temporary Mobile Station Identifier) ​​or an IMSI (International Mobile Station Identifier), may be notified (e.g., RS ID = S-TMSI, n RSID =IMSI).

[0661] In the SRS transmission command, at least one UE-specific parameter is transmitted instead of a cell-specific parameter. However, a pool of SRSs to be used commonly within a specific area, for example, within a tracking area, or within a CoMP set, or within a cluster when neighboring cells are clustered and managed, may be prepared. Even if neighboring cells are installed in places where radio waves cannot reach each other, such as an eNB installed in an underground mall and an eNB installed outdoors, a method of sharing an SRS ID for geographically close cells as one group is also effective. The IDs may be managed by a central entity or MME 5106, and the assigned ID may be notified to the UE via the serving cell by an SRS command (e.g., n RS ID =Area ID).

[0662] This makes the SRS common within a specific area, so that eNBs within that area are able to receive the SRS in advance.

[0663] In the SRS transmission command, instead of the cell-specific parameters, at least one of time multiplexing, frequency multiplexing, code multiplexing, or a combination of these may be performed to simultaneously notify a plurality of cell-specific parameters. In this case, eNB#2 5103 transmits an SRS config including at least one cell-specific parameter such as a cell ID to eNB#1 5101. eNB#1 5101 notifies this information to UE 5105. This allows UE 5105 to transmit an SRS specific to eNB#2 5103 at the same time as an SRS specific to eNB#1 5101.

[0664] Also, together with the SRS config 5116 notified from the eNB#1 5101 to the eNB#2 5103, information capable of identifying that resources used by the eNB#2 5103 are multiplexed may be notified. This enables the eNB#2 5103 to receive the SRS of the UE 5105.

[0665] Furthermore, if the number of transmission bits is reduced by changing the SRS transmission method, resulting in a shortage of SRS transmission power, a transmission power offset may be added accordingly.

[0666] In addition, in the above description, the eNB#2 5103 to which the notification is sent from the eNB#1 5101 is a neighboring eNB that may perform UL CoMP, but more specifically, the eNB may be a UL CoMP target eNB, or may be all cells in the UL CoMP set.

[0667] Although an example in which an SRS transmission command is sent to a UE using RRC is described, the command may be sent using MAC signaling or an L1 / L2 control signal (eg, PDCCH / EPDCCH).

[0668] Next, the downstream will be described.

[0669] As with the uplink, DL CoMP is being considered. For example, joint processing (JP), which transmits from both cells, and CS, which performs multipoint coordinated scheduling, are being considered. JP is classified into joint transmission (JT) and dynamic point selection (DPS). A combination method of JT and CS is also being considered. Using these methods, it is possible to improve throughput at the cell edge and increase system throughput.

[0670] In particular, when the signal used for CoMP is Time Division Duplex (TDD), the uplink and downlink have the same frequency, so the downlink transmission path can be estimated by estimating the transmission path from the uplink SRS, and therefore it can be used for DL ​​CoMP.

[0671] An example of downlink CS during TDD will be described. In DL CoMP, when data to be transmitted to a UE 5105 occurs, the eNB#1 5101 transmits the data to the UE 5105.

[0672] When the eNB#1 5101 detects that the UE 5105 is at the cell boundary, the eNB#1 5101 notifies the UE 5105 of an SRS transmission command using RRC. In Non-Patent Document 14 (see 5.5.1.5), a parameter n RS ID is N cell ID and has a value for each cell (cell ID), but in the present invention, the SRS transmission command specifies at least one UE-specific parameter. That is, the UE 5105 transmits an SRS signal unique to the UE, not an SRS signal unique to the cell.

[0673] Furthermore, eNB#1 5101 notifies eNB#2 5103 adjacent to eNB#1, which may perform DL CoMP, of the SRS config directly via X2. eNB#2 starts receiving the SRS of UE 5105 in accordance with the SRS config.

[0674] As described above, in the case of TDD, before starting DL CoMP, the eNB#2 that is the DL CoMP target knows the downlink communication quality by receiving the SRS from the UE. Both eNB#1 and eNB#2 report the uplink reception quality to the central entity 5106, so that the central entity 5106 can perform optimal resource allocation to the two eNBs.

[0675] There is no longer any delay time until DL CoMP starts, i.e., the time required for the UE to measure downlink quality after the start command is issued, so DL CoMP can start immediately, eliminating the allocation of suboptimal frequencies, time, and transmission power that occurs due to the delay time.

[0676] There are similar variations on the downward route as on the upward route.

[0677] The SRS config may be notified via S1 (via MME) or via a functional unit of a central entity that manages resource allocation for inter-eNB CoMP.

[0678] At this time, the central entity notifies the selected eNB of the eNB identifier of eNB#1 5101. A plurality of eNBs may be selected.

[0679] Also, the UE 5105 may be notified of the eNB identifier of the selected eNB.

[0680] In the procedure before the start of CoMP, the SRS config may be notified to neighboring eNBs before notifying the UE.

[0681] Alternatively, eNB#2 5103 may notify the neighboring eNB (eNB#1) of the usage status when eNB#2 starts using SRS.

[0682] In the example of SRS transmission start determination, the SRS transmission start configuration may be set in advance when the UE 5105 starts communication with the eNB#1.

[0683] At least one UE-specific parameter included in the SRS transmission instruction may be, for example, an ID for identifying the UE, such as S-TMSI or IMSI (e.g., n RS ID = S-TMSI, n RS ID =IMSI).

[0684] In the SRS transmission command, a pool of SRSs to be used commonly within a specific area, for example, within a tracking area, or within a CoMP set, or within a cluster when a group of neighboring cells is clustered and managed, may be prepared. The IDs may be managed by a central entity or the MME 5106, and the assigned ID may be notified to the UE via the serving cell by the SRS command (for example, RS ID = Pool ID for SRS).

[0685] This makes the SRS common within a specific area, so that eNBs within that area are able to receive the SRS in advance.

[0686] In the SRS transmission command, at least one UE-specific parameter is transmitted instead of a cell-specific parameter, but multiple cell-specific parameters may be notified simultaneously by performing time multiplexing, frequency multiplexing, code multiplexing, or a combination of these. In this case, information that can identify that resources used by eNB#2 5103 are multiplexed is also notified in the SRS config 5116 from eNB#1 5101 to eNB#2 5103.

[0687] In addition, in the above, the eNB#2 5103 to which the notification is sent from the eNB#1 5101 is a neighboring eNB that may perform DL CoMP, but specifically, it may be an eNB that is a DL CoMP target. Or it may be all cells in a DL CoMP set. Or, when a corresponding eNB in ​​a tracking area that supports ID management and a group of neighboring cells are clustered and managed, it may be an eNB in ​​the cluster. There may be a plurality of corresponding eNBs in the tracking area and eNBs in the cluster.

[0688] Although an example in which an SRS transmission command is sent to a UE using RRC is described, the command may be sent using MAC signaling or an L1 / L2 control signal (eg, PDCCH / EPDCCH).

[0689] When eNB#1 5101 detects that UE 5105 is away from the cell boundary or near another cell, it notifies eNB#2 5105 via X2 interface 5115 or via MME or central entity 5106 to stop receiving SRS.

[0690] It may be possible to determine that the UE is not at a cell boundary based on whether the reported values ​​of its own cell (eNB#1) reported by the UE in a Measurement Report message, specifically, RSRP, or RSRQ, or both, are above a specific threshold.

[0691] In addition, the UE may determine that it is far from the vicinity of another cell based on whether the reported values ​​of the other cell (eNB#2) reported by the UE in a Measurement Report message, specifically, RSRP, or RSRQ, or both, are below a specific threshold value.

[0692] Alternatively, when CoMP ends, eNB#2 may be notified of the stop of SRS reception.

[0693] Also, when the SRS parameters are designated as cell-specific parameters, the eNB#2 may be notified of the stop of SRS reception.

[0694] Moreover, the upstream control and the downstream control may be performed simultaneously.

[0695] Fifth embodiment, variant 1 In the fifth embodiment, an example of CoMP has been described. Similarly, by receiving SRS in DC at an adjacent eNB, the delay time after DC initiation and DC configuration change, i.e., the time required for the UE to measure downlink quality after a start instruction, is eliminated, and DC can be started immediately, eliminating the allocation of frequencies, times, and transmission power that are not optimized due to the delay time.

[0696] As described in Non-Patent Document 9 (see Chapter 8), several forms of DC are being considered, and architecture 1A and architecture 3C are being considered. An example of architecture 3C will be described below with reference to FIG. 27.

[0697] The S-GW5217 allocates two bearers per user. Bearer 1 is a bearer transmitted from the MeNB5218 to the UE5220 via the S1-U. Bearer 2 is a signal that has arrived at the MeNB5218 via the S1-U and is separated into two in the PDCP processing unit. One of the bearers is subjected to RLC (Radio Link Control) and MAC processing in the MeNB5218 and transmitted to the UE5220. The other is processed in the SeNB5219 and transmitted to the UE5220.

[0698] For example, a control signal for managing mobility is applied as bearer 1, and user packet data such as video is applied as bearer 2. This makes it possible to continue communication even with high speed movement in MeNBs with a large cell radius. Also, since SeNBs have a small cell radius, frequency bands can be used by a small number of users, enabling large-capacity communication.

[0699] 26 and 27 are diagrams showing an example of the operation of the DC in the communication system of the first modification of the fifth embodiment. The operation at the start of the DC in this modification will be described with reference to Figs. 26 and 27.

[0700] UE 5205 in communication area 5202 of MeNB 5201 communicates both control signals for mobility management and user packet data via S-GW 5206 and MeNB 5201. When UE 5205 enters communication area 5204 of SeNB 5203 and UE 5205, MeNB 5201, and SeNB 5203 are DC-enabled, they are reconfigured to DC (SeNB addition), and two bearers are set to different paths.

[0701] For example, bearer 1 is set to a path including the S-GW (5206), S1 (5214), MeNB (5201), radio propagation path (5207), and UE (5205). Bearer 2 is separated by the S-GW (5206), S1 (5214), and MeNB (5201). One of them is set to a path including the MeNB (5201), radio propagation path (5207), and UE (5205). The other is set to a path including the MeNB (5201), X2 (5215), SeNB (5203), radio propagation path (5210), and UE 5205.

[0702] Here, there is a problem that the UE 5205 cannot actually start data communication unless it establishes synchronization with the SeNB and measures communication quality. In addition, there is a problem that the communication quality of the wireless propagation path 5210 cannot be known when the bearer 2 is separated.

[0703] Therefore, by using the same method as that described in the fifth embodiment, from eNB#1 to MeNB and from eNB#2 to SeNB, it becomes possible to receive SRS in advance not only from the communicating MeNB but also from the SeNB of the neighboring cell. This enables SeNB5203 to transmit data immediately when starting DC without waiting for confirmation of the quality of the wireless propagation path.

[0704] In addition, the MeNB 5201 can start DC after determining the division ratio of Bearer 2, without waiting to confirm the quality of the wireless propagation path, taking into consideration not only the reception result of SRS 5208 that it receives itself, but also reception results 5213 such as the reception quality of SRS 5212 received by the SeNB 5203 via X2 (5215).

[0705] Also, by receiving SRS 5212, SeNB 5203 can detect the timing difference between MeNB 5201 and SeNB 5203 with high accuracy. By notifying SRS reception timing information of SeNB 5203, it is possible to set the value of the reordering waiting timer for arriving packets in uplink PDCP in MeNB 5201 taking backhaul delay into consideration at the start of DC. SRS reception timing information may be notified together with SRS reception result 5213.

[0706] In the above description, the DC start trigger is described as when UE 5205, MeNB 5201, and SeNB 5203 are DC capable. Specifically, at least one of the following four conditions (1) to (4) is required.

[0707] (1) When the UE5205 capability supports DC. (2) When both MeNB5201 and SeNB5203 are capable of DC configuration. (3) When the transmission delay of a backhaul such as an available X2 5215 is within the allowable range for DC implementation. (4) When UE 5205 detects that it is within or near the coverage areas of both MeNB 5201 and SeNB 5203.

[0708] The above explanation has been given using the example of architecture 3C, but architecture 1A also allows the SeNB to transmit data immediately when DC is started without waiting to confirm the quality of the wireless propagation path by notifying the SeNB of SRS config5216 via X2, S1 (MEE), or a central entity.

[0709] Although the above description has been given of SeNB addition, the same applies to SeNB change. By notifying the target SeNB (T-SeNB) in advance of the SRS config for setting SRS that can be received simultaneously from the MeNB, data can be transmitted immediately when the SeNB is changed without waiting for confirmation of the quality of the wireless propagation path.

[0710] In the above description, the SRS config is notified from the MeNB to the T-SeNB, but it may be notified from the source S-SeNB to the T-SeNB.

[0711] Embodiment 6 The problem to be solved in the sixth embodiment will be described with reference to Fig. 28. Fig. 28 is a diagram showing the concept of the problem to be solved in the sixth embodiment.

[0712] 28 shows a state in which, among mobile terminal devices (hereinafter referred to as "mobile terminals (User Equipment) (UE)") which are communication terminal devices, UE indicated by reference symbol "5305" is present within cell 5302 capable of transmitting and receiving radio waves of e-NB#1 (hereinafter referred to as "S-eNB") 5301 which is a handover (HO) source wireless base station device. UE 5305 performs HO 5307 and becomes present within cell 5304 of HO destination wireless base station device (hereinafter referred to as "T-eNB") 5303. The UE in this state is UE 5306 indicated by reference symbol "5306".

[0713] As described in the fifth embodiment, in the current 3GPP, the SRS is a cell-specific signal (see Non-Patent Document 14, 5.5.1.5). Therefore, the T-eNB 5303 cannot receive the SRS of the target UE until the handover is completed, and there is a problem that the start of the process (scheduling) of allocating resources such as frequency and timing to each UE based on the reception quality is delayed.

[0714] The S-eNB 5301 measures the reception communication quality in a cell 5302 in which the HO source UE 5305 resides, and performs scheduling within the same cell. On the other hand, the T-eNB 5303 does not receive an SRS 5309 from the UE 5305 and does not perform scheduling.

[0715] Since T-eNB 5303 can receive SRS only when UE 5306 is in a state after HO, it cannot start accurate scheduling that takes frequency characteristics into consideration early for UE 5306 that has performed HO.

[0716] In particular, when a large number of small cells are operated, the radius of each cell is small, and when a UE moves, the small cell is changed repeatedly in a short period of time. When the T-eNB executes scheduling for the UE 5306, the UE may have already moved to the area covered by another cell.

[0717] As a method for solving these problems, we propose a communication system in which the SRS is made UE-specific rather than cell-specific, as in embodiment 5, thereby enabling scheduling in T-eNB 5303 to start early.

[0718] FIG. 29 is a diagram showing an example of a sequence of an SRS reception process in the communication system according to the sixth embodiment.

[0719] In Steps ST5402 and ST5403, the UE exchanges packet data with the S-GW via the S-eNB.

[0720] In Step ST5401, the S-eNB transmits a Measurement Control (MC) message to the UE in order to know the reception quality. The UE measures the reception quality of its own cell and neighboring cells based on the information in the MC message, and transmits a Measurement Report (MR) message to the S-eNB in ​​Step ST5404.

[0721] In the sequences up to this point, the S-eNB, having received the MR message in step ST5404, performs an HO initiation decision in step ST5408, which is the process of determining whether or not to execute HO. However, in this embodiment, an SRS initiation decision is made in step ST5405 prior to the HO initiation decision in step ST5408.

[0722] If the reception quality of the CRS (RSRP, or RSRQ, or both) or the reception quality of other RSs reported by the MR message of step ST5404 is lower than threshold Th1, it is determined that the possibility of HO to an adjacent cell is low, and the MR message of step ST5404 is waited for again.

[0723] In the SRS start decision in Step ST5405, it is decided whether or not the reception quality of the neighboring cell reported by the MR message in Step ST5404 is higher than a threshold TH1. If it is higher than the threshold TH1 (Yes), it is decided that there is a possibility of HO to the cell, and in Step ST5406, the S-eNB transmits an SRS reception start instruction message including SRS Config to the T-eNB. Upon receiving the SRS reception start instruction message in Step ST5406, the T-eNB starts SRS reception in Step ST5407.

[0724] Although the above is an example of directly notifying the S-eNB to the T-eNB using X2 signaling, notification may also be made via the MME using S1 signaling.

[0725] After issuing an SRS reception start command in Step ST5406, the S-eNB determines whether to perform HO in the HO initiation decision in Step ST5408.

[0726] The sequence of subsequent HOs is the same as the current sequence.

[0727] In this embodiment, by providing an SRS start decision in step ST5405 in addition to the HO start decision in step ST5408, it is possible to start SRS reception in step ST5407 before HO.

[0728] In the SRS initiation decision of above step ST5405, if the S-eNB judges "Yes" once and then judges "HO not executed" in the HO initiation decision of step ST5408, when the S-eNB receives the MR message again in step ST5404, the S-eNB may or may not execute the SRS initiation decision of step ST5405 again and notify an SRS reception start instruction in step ST5406. By not issuing an unnecessary start instruction, it is possible to reduce the processing load on a CPU (Central Processing Unit) and the like. If the S-eNB judges "No" in the SRS initiation decision of step ST5405, the S-eNB enters a state of waiting for an MR message in step ST5405.

[0729] FIG. 31 is a diagram showing the difference between the SRS reception start threshold and the HO start threshold for the measurement report value.

[0730] In addition to the threshold value Th2 for initiating HO, a threshold value Th1 for initiating SRS according to an embodiment of the present invention is provided.

[0731] The S-eNB may set the threshold value Th1 to a value lower than the threshold value Th2, which enables the T-eNB to receive the SRS prior to HO and enables early frequency scheduling at the T-eNB.

[0732] In the above, threshold Th1 is set to a value lower than threshold Th2, but threshold Th1 and threshold Th2 may be set to the same value (Th1=Th2). In this case, an SRS reception start command (including SRS config) is notified in the SRS start determination, and an HO request is also notified. The SRS reception start command and the HO request may be in a single message.

[0733] When thresholds Th1 and Th2 are set to the same value (Th1=Th2), the T-eNB starts receiving SRS later than when threshold Th1 is set to a value lower than threshold Th2, but can start receiving SRS before HO is completed (RRC Connection Reconfiguration Complete) in step ST5414. Also, the determination process in the S-eNB can be reduced compared to when threshold Th1 is set to a value lower than threshold Th2.

[0734] When the UE 5305 moves very fast relative to the size of the cell, even if the SRS can be received at the destination T-eNB, effective scheduling may not be possible. In such a case, in order not to perform SRS reception processing, the SRS reception start instruction message transmitted from the S-eNB 5301 to the T-eNB 5303, or the HO request message, may include the speed information of the UE 5305, for example, the UE's movement state (high, medium, normal), the number of handovers or cell changes (the number of handovers or cell changes per specific time is also valid), the GPS-based location change (the location movement per specific time is also valid), and the residence time per cell. Similarly, under the control of the T-eNB 5303, it is possible to suppress the SRS 5309 during high-speed movement.

[0735] The trigger for executing the SRS reception start instruction mentioned above is a determination made by S-eNB5301 based on the reception quality reported from the UE, but it is also possible for UE5305 to make the determination and transmit the determination result to S-eNB5301 to issue an SRS reception start instruction.

[0736] For example, the UE 5305 may notify the MR of information indicating whether the reception quality for each cell is equal to or higher than a predetermined threshold.

[0737] Alternatively, when the reception quality of a neighboring cell is equal to or higher than a predetermined threshold, the UE 5305 may notify the MR by including an SRS reception request indicating that it is better to receive SRS for each cell.

[0738] Alternatively, the UE 5305 may notify, separately from the MR, that the reception quality exceeds a predetermined threshold together with an ID for identifying the target cell when the reception quality exceeds the predetermined threshold.

[0739] By doing so, it is possible to reduce the load of reception quality judgment in the MR in the S-eNB.

[0740] In the above, the start of SRS reception from another cell has been described on the assumption that the UE has already transmitted an SRS based on UE-specific parameters. Next, a process of determining whether the UE should start transmitting an SRS will be described.

[0741] Since the UE consumes transmission power to transmit an SRS, it is effective to transmit the SRS only before and after HO, or to lengthen the SRS transmission interval only before and after HO.

[0742] In addition to the above-mentioned processes, the SRS initiation determination in Step ST5405 determines whether the reception quality (RSRP or RSRQ, or both) of the CRS of the own cell (S-eNB) or the reception quality of other RSs reported by the MR message in Step ST5404 is smaller than a predetermined threshold (for example, smaller than threshold Th2), or whether the reception quality of other cells is larger than threshold Th1. If the determination result satisfies either one or both, it is determined that there is a high possibility of HO to the adjacent cell, and a transmission instruction including SRS config is notified to the UE.

[0743] For example, the S-eNB may transmit an RRC connection reconfiguration message in Step ST5417 by including the SRS config in the message. This causes the UE to start transmitting the SRS or increase the frequency of transmitting the SRS.

[0744] Regarding the timing for starting to receive SRS, T-eNB 5303 receives SRS config 5311 from UE 5305, immediately thereafter receives SRS 5309 and performs scheduling. However, it is also acceptable to receive SRS 5309 from T-eNB 5303 and UE 5305 at least once before scheduling.

[0745] Alternatively, the T-eNB 5303 may receive the SRS from the UE 5305 at least once before transmitting the HO ack.

[0746] Also, although an example in which the S-eNB instructs the UE to transmit an SRS is described using RRC, the instruction may be given using MAC signaling or an L1 / L2 control signal (for example, PDCCH / EPDCCH).

[0747] The S-eNB may instruct the UE to transmit the SRS until an SRS transmission stop instruction is sent. Alternatively, the S-eNB may instruct the UE to transmit the SRS periodically for a predetermined period of time.

[0748] Furthermore, if the UE establishes synchronization with the T-eNB after receiving MCI (Mobility Control Information), the UE may stop transmitting the SRS.

[0749] The HO sequence from S-eNB to T-eNB shown in FIG. 29 is as follows.

[0750] In Step ST5409, the S-eNB transmits an HO request to the T-eNB. In Step ST5410, the T-eNB performs admission control, and then, in Step ST5411, the T-eNB returns an "HO Request Ack" to the S-eNB.

[0751] In Step ST5412, the S-eNB that has received the Ack transmits an RRC connection reconfiguration to the UE, and then in Step ST5413 transmits an "SN Status Transfer" to the T-eNB. In Step ST5412, the UE receives the RRC connection reconfiguration, reconfigures the RRC connection, and transmits the resultant RRC connection reconfiguration complete to the T-eNB in ​​Step ST5414. This allows the UE to exchange packet data with the S-GW via the T-eNB in ​​Step ST5415 and Step ST5416.

[0752] The T-eNB may stop receiving the SRS after receiving an RRC connection reconfiguration complete in Step ST5414. Even if the HO fails, the T-eNB stops receiving the SRS.

[0753] Alternatively, it may be the timing when the T-eNB receives "SN Status Transfer" from the S-eNB in ​​Step ST5413. Furthermore, it may be the timing when the T-eNB transmits "HO Request Ack" to the S-eNB in ​​Step ST5411.

[0754] In the sequence described above, it is assumed that SRS reception is stopped after HO ends, but SRS reception may be continued even after HO fails, taking into account switchback.

[0755] In this case, the method of stopping SRS is to set a timer and secure a predetermined time before stopping SRS. After the timer expires, the threshold value may be checked again to make a judgment. Alternatively, the SRS reception may be continued until an SRS reception stop instruction is transmitted from the UE by RRC. Alternatively, the SRS reception may be continued until the serving cell issues an instruction to stop SRS reception via X2 based on neighboring cell search information from the UE.

[0756] In addition, one more determination threshold for the measurement result is added and used for determining the SRS stop command. A value that exceeds the threshold earlier than the start of HO to another cell may be set. The sequence in this case is shown in Fig. 30. Fig. 30 is a diagram showing another example of the sequence of SRS reception processing in the communication system of the sixth embodiment.

[0757] In Step ST5501, the T-eNB transmits an MC message to the UE. In Step ST5502, the UE transmits an MR message. The T-eNB receives the MR message in Step ST5502 and determines whether SRS is necessary, that is, whether to stop SRS, in Step ST5503. Specifically, the T-eNB determines whether the reception quality value of its own cell (T-eNB) reported in the MR message in Step ST5502 is smaller than threshold Th3, or whether the reception quality value of the S-eNB is smaller than a predetermined threshold. The predetermined threshold is, for example, threshold Th1. The predetermined threshold may be threshold Th4 smaller than threshold Th1.

[0758] If the reception quality value of the own cell (T-eNB) reported in the MR message of Step ST5502 is smaller than threshold Th3, or if the reception quality value of the S-eNB falls below a predetermined threshold, the mobile station judges to continue receiving SRS, returns to Step ST5502, and waits for the MR message of Step ST5502. If the reception quality value of the own cell (T-eNB) reported in the MR message of Step ST5502 is equal to or larger than threshold Th3, or if the reception quality value of the S-eNB is equal to or larger than a predetermined threshold, the mobile station stops receiving SRS in Step ST5504.

[0759] The T-eNB may determine whether or not to accept HO (Handover Request Ack) based on the SRS reception result of the target UE. In this case, it is preferable to notify "SRS reception result NG" as the reason for NG.

[0760] The T-eNB performs scheduling based on the SRS reception result of the target UE.

[0761] The uplink transmission power value is adjusted based on the SRS received value (including the initial MCS). This is effective when eNBs with different cell sizes overlap.

[0762] According to the sixth embodiment, the following effects can be obtained: Since channel estimation for the target UE becomes possible early, scheduling can be performed early, and frequency efficiency is improved.

[0763] Embodiment 7 Fig. 32 is a diagram showing an example of antenna control in a communication system according to embodiment 7. In this embodiment, as shown in Fig. 32, when a handover destination eNB#2 5704 is capable of transmitting and receiving by a plurality of antennas (MIMO), an example will be described in which antenna control such as beam forming can be performed immediately upon handover and transmission power of an eNB and a UE can be reduced by making the handover destination eNB#2 5704 capable of receiving an SRS before establishing handover.

[0764] UEs 5705 and 5706 communicating in a communication area 5701 of eNB#1 5703 are at the boundary of the area of ​​eNB#1 5703 and are moving into a communication area 5702 of eNB#2 5704.

[0765] The eNB#2 5704 has a plurality of antennas, and can form a beam 5711 with narrowed directivity by controlling the phase and amplitude of the input signal of each antenna. However, as described in the fifth embodiment, in the current 3GPP, the SRS is a cell-specific signal (see non-patent document 14, 5.5.1.5), and the SRS of the target UE cannot be received until the handover is completed, which is a problem in that a beam with narrowed directivity cannot be formed.

[0766] Therefore, as in embodiment 5, when eNB#1 5703 detects that it is at the area boundary of eNB#1 5703, eNB#1 5703 instructs UE 5705 via RRC to transmit SRS 5709, 5710 which can be received by multiple eNBs, and also transmits SRS config 5708 to eNB#2 5704 via X2 5707, thereby enabling eNB#2 5704 to receive SRS signals from UE 5705, 5706.

[0767] As a specific method for the above, the fifth embodiment or the sixth embodiment may be applied.

[0768] As a result, eNB#2 5704 has multiple antennas and can form beam 5711 with narrowed directionality by controlling the phase and amplitude of the input signal of each antenna.

[0769] To supplement, for example, the directivity of the beam is narrowed by adjusting the phase and amplitude value (=weighting coefficient) of the uplink or downlink antenna input signal that maximizes the received power of the SRS, which is a known sequence. By receiving data parts other than the known sequence or performing downlink transmission using this weighted antenna, communication can be performed using a beam with narrowed directivity. As a result, eNB#2 5704 and UE 5706 can reduce the interference power of other eNBs and UEs and can receive well, so that the transmission power can be reduced.

[0770] When UE5705 before HO transmits SRS, and when the directional antennas sequentially change direction for transmission, for example when the transmission direction is changed over time by θ(t), UE5705 before HO may include a different sequence pattern for each directional antenna so that T-eNB5704 to which the HO is to be performed can identify the directional antenna.

[0771] Alternatively, when UE5705 before HO transmits SRS, if the SRS is transmitted using directional antennas such as multiple sector antennas, UE5705 before HO may include a different sequence pattern for each directional antenna so that the directional antenna can be identified.

[0772] As an example of a method for determining the weighting coefficients, the communication area 5702 of eNB#2 5704 is divided, and the area with the maximum SRS reception power value is identified for each division. The divided area with the maximum SRS reception power is further divided, and the area with the maximum SRS reception power value is identified. The weighting coefficients may be determined by repeating the above steps.

[0773] In the case of downlink transmission, TDD is effective because the uplink and downlink have the same frequency. In the case of Frequency Division Multiplex (FDD), the uplink and downlink have different frequencies, so it is effective when the difference in propagation characteristics depending on the frequency is small.

[0774] In the above embodiment, the control for narrowing the directivity of the beam has been described, but the process of demodulating all users simultaneously by multi-user MIMO can also be executed immediately after handover. SRS ), the impulse response of the transmission path (H), noise (N), and the received signal Y are expressed as follows: Y=H×S SRS +N

[0775] For example, if noise (N) is ignored, as in the ZF (Zero Forcing) algorithm, the UE's transmitted data can be restored by finding the inverse matrix of H. In the case of TDD, the uplink and downlink propagation characteristics are the same, so by multiplying the transmitted data by the inverse matrix of H (precoding), the UE can receive a signal with reduced interference effects.

[0776] For uplink reception, the eNB may have a directional antenna / antenna group that covers the entire communication area (corresponding to communication area 5702 of eNB#2 5704), for example, an isodirectional receiving antenna with no directionality, and for downlink transmission, may have directional beamforming.

[0777] Furthermore, the receiving antenna at the eNB may have isodirectional directivity.

[0778] Alternatively, the AoA (Angle of Arrival) can be derived by receiving the SRS at a neighboring eNB that is not the serving cell. Also, by measuring the AoA at multiple eNBs that know the location of the eNB, it is possible to perform triangulation and determine the location of the UE without using the GPS (Global Positioning System).

[0779] In the above example, the X2 interface 5707 is used, but as in the fifth embodiment, the S1 interface (via MME) or the central entity may be used.

[0780] Also, although the handover destination has been described as an eNB, the same applies when a relay node (RN) or a remote radio head (RRH) has multiple antennas.

[0781] When the UEs 5705 and 5706 are mounted on trains or the like and move around bundling multiple users (moving relay nodes), it is effective to provide many antennas and perform beam forming.

[0782] For a UE equipped with multiple antennas, the following SRS transmission method is effective. The SRS is transmitted in an isotropic manner without beamforming. This allows eNB#1 and eNB#2 to receive the SRS before handover by performing the same processing as for a UE equipped with only an omni-directional antenna, and to quickly form uplink and downlink beams.

[0783] It is also effective to form a beam with narrowed directivity of the UE 5705 using a synchronization signal of the eNB that the UE 5705 can receive. The SRS is also transmitted using this beam. This makes it possible to reduce the transmission power of the SRS transmitted by the UE 5705.

[0784] In addition, since there is a possibility that the UE 5705 may not be able to receive the synchronization signal, a method may be used in which the UE 5705 uses information on the location of the eNB to transmit in the direction of the eNB even if the synchronization signal of the eNB cannot be seen.

[0785] In addition, when the UE 5705 transmits and receives multiple frequencies, the SRS may be transmitted using both an isotropic beam and a beam with narrower directivity for each frequency. This allows the eNB to quickly form uplink and downlink beams.

[0786] Furthermore, in the case of TDD, even if there is only one frequency, it is possible to transmit both isotropic beams and directional beams in each subframe.

[0787] Furthermore, in the case of FDD, even if there is only one frequency, it is possible to transmit both isotropic beams and directional beams in each subframe, just like TDD.

[0788] In addition, if the eNB is a small cell, it is also effective to use an isotropic beam. Since the radius of the cell is small, stable SRS reception is possible even when the angle of arrival changes.

[0789] Also, when the UE5705 is moving fast, such as on a bus traveling through the city, an isotropic beam may be used.

[0790] In addition, for things like the Shinkansen, where many UE5705s communicate at high volumes, a beam with narrower directionality is sufficient even if the speed of movement is fast.

[0791] If the HO-destination T-eNB5704 is FDD, after receiving the SRS5710 transmitted from the UE5705 before HO, the UE5705 feeds back the acquired terminal information to the UE5705 via the downlink channel, enabling the UE5705 to transmit uplink individual channel information via beamforming to the HO-destination T-eNB5704.

[0792] After receiving the SRS 5710 transmitted from the pre-HO UE 5705, the HO-destination T-eNB 5704 must determine whether frequency correction is necessary. If it is determined that frequency correction is not necessary, the SRS Config information received via the X2 interface 5707 can be used for beamforming of the downlink channel.

[0793] If the T-eNB5704 to which the HO is to be performed has multiple isotropic antennas such as an array antenna, the SRS Config5708 received from the S-eNB5703 before HO via communication path 5707 can be used to receive the SRS5710 of the UE5705 to be HOed, and the propagation characteristics H can be calculated.

[0794] In addition, the HO destination T-eNB5704 uses directional antennas such as multiple sector antennas (including cases where the same directivity is formed using an array antenna) to perform precoding with directivity directed to where the received power of SRS5710 is greatest, making it possible to transmit beamforming5711.

[0795] In addition, if the directional antenna of the HO-destination T-eNB5704 sequentially changes direction in accordance with the timing at which UE5705, 5706 transmit SRS, it becomes possible to calculate the direction in which the HO-destination T-eNB5704 was transmitting at the time when the received power of SRS5710 transmitted from UE5705 is at its maximum, and to transmit beamforming5711 with directivity in that direction.

[0796] Alternatively, the directional antenna of the HO-destination T-eNB 5704 may sequentially change direction in accordance with the timing that is a multiple of the timing at which the UEs 5705 and 5706 transmit SRS.

[0797] Alternatively, when SRS5710 transmitted from UE5705 is received at least once during a certain reception period in the direction in which the directional antenna of T-eNB5704 at the HO destination was transmitting, beamforming5711 transmission with directionality directed in the direction in which T-eNB5704 at the HO destination was transmitting becomes possible.

[0798] The HO destination T-eNB 5704 may obtain terminal information by a random access procedure and execute beamforming transmission 5711. The UE 5705 attempting HO transmits a PRACH to the HO destination T-eNB 5704. The HO destination T-eNB 5705 transmits a random access response to the UE 5705.

[0799] In a random access procedure, the UE 5705 performing HO notifies the T-eNB 5704 of its own location information. This enables the T-eNB 5704, which is the HO destination, to identify the location information of the UE 5705 performing HO in the random access procedure and transmit beamforming 5711 with directivity in that direction.

[0800] In addition, when the T-eNB 5704, which is the HO destination, receives the PRACH during handover, it can calculate the AoA (Angle of Arrival), and enables beamforming 5711 transmission with directivity in that direction.

[0801] Also, since it is possible to establish synchronization by receiving an SRS during handover, the RACH sequence may be omitted.

[0802] If the UE 5705 before HO moves together with other UEs, or if it is a terminal with multiple antennas, or if it has a repeater function, the location information of the UE 5705 before HO detected by the S-eNB 5703 at the source of HO is notified to the T-eNB 5704 at the destination of HO via communication path 5707 as SRS Config (setting parameter values) 5708.

[0803] As a result, the HO-destination T-eNB5704 receives the SRS5710 transmitted from the pre-HO UE5705 and uses it to derive a precoding matrix, i.e., the antenna weighting coefficient for beamforming, thereby enabling the HO-destination T-eNB5704 to transmit beamforming5711.

[0804] According to this embodiment, even in the case of MIMO, by receiving the SRS from the terminal at the HO source, it is possible to determine the beam directivity and the initial transmission power of the terminal, enabling appropriate communication from the start of HO.

[0805] Furthermore, since the reception quality at the UE during HO can be improved, it is possible to reduce handover failures (HOF) and radio link failures (RLF).

[0806] The method disclosed in this embodiment can also be applied to multi-stream beamforming.

[0807] The above-mentioned embodiments and their modifications are merely examples of the present invention, and the embodiments and their modifications can be freely combined within the scope of the present invention. In addition, any components of the embodiments and their modifications can be appropriately modified or omitted. This makes it possible to improve the communication performance of the UE even when a large number of small cells are installed and operated in addition to a macro cell.

[0808] Although the present invention has been described in detail, the above description is illustrative in all respects and does not limit the present invention. It is understood that countless variations not illustrated can be assumed without departing from the scope of the present invention. [Explanation of symbols]

[0809] 101 CBC, 102 MME, 103 MeNB, 104 SeNB, 105 UE, 1301 Macro eNB (macro cell) coverage, 1302 Small eNB (small cell) coverage.

Claims

1. A mobile communication system including a mobile terminal and a base station that performs wireless communication between the mobile terminal and the base station, transmitting a sounding reference signal, which is individual for each of the mobile terminals, from the mobile terminals to the base station; The sounding reference signal is used for position measurement of the mobile terminal; The position of the mobile terminal is measured using the angle of arrival of radio waves. A mobile communication system comprising:

2. A parameter that defines the sounding reference signal and is specific to each of the mobile terminals is notified from the base station to the mobile terminals.

2. The mobile communication system according to claim 1.

3. The parameters are signaled from the base station to the mobile terminal by Radio Resource Control (RRC) signaling.

3. The mobile communication system according to claim 2.

4. A mobile terminal that performs wireless communication with a base station, transmitting an individual sounding reference signal for each of the mobile terminals to the base station; The sounding reference signal is used for position measurement of the mobile terminal; The position of the mobile terminal is measured using the angle of arrival of radio waves. A mobile terminal comprising:

5. A base station that performs wireless communication with a mobile terminal, receiving a separate sounding reference signal for each of the mobile terminals from the mobile terminals; The sounding reference signal is used for position measurement of the mobile terminal; The position of the mobile terminal is measured using the angle of arrival of radio waves. A base station comprising:

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