Mobile communication system, base station, and mobile

Abstract

The present invention provides a mobile communications system, base stations and mobile terminals having mobility capabilities that can support movement of the communication terminal in a configuration in which a large number of small cells are installed.SOLUTION: In a mobile communication system including a user equipment (UE) and a base station (serving cell) that performs radio communication with the user equipment (UE), the base station (serving cell) notifies the user equipment (UE) of base station group information (cell group and cell list). The base station group information includes an identifier of a base station group (cell group) and a list (cell list) of base stations constituting the base station group.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a mobile communication system in which wireless communication is performed between a communication terminal device and a base station device. [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 the wireless section and System Architecture Evolution (SAE) for the overall system configuration including the core network and radio access network (hereinafter collectively referred to as the network) (see, for example, Non-Patent Documents 1 to 12). This communication method is also called the 3.9G (3.9 Generation) system.

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

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

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

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

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

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

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

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

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

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

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

[0014] Downlink reference signals (RS) are known symbols in LTE communication systems. The following five types of downlink reference signals are defined: Cell-specific Reference 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) measurements are available as a physical layer measurement for mobile terminals.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0042] Depending on the UE's capabilities, a secondary cell (SCell) is configured to 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] Additionally, 3GPP is currently formulating Release 12 of its specifications. In this document, the use of small eNBs that configure small cells is being considered in order to handle the massive traffic volumes expected in the future. For example, technologies are being considered that would increase communication capacity by installing a large number of small eNBs to configure a large number of small cells, thereby improving frequency utilization efficiency.

[0046] Mobile network traffic volume is on the rise, and communication speeds are also increasing. When LTE and LTE-A begin full-scale operation, communication speeds are expected to increase even further, leading to an increase in traffic volume. [Prior art documents] [Non-patent literature]

[0047] [Non-Patent Document 1] 3GPP TS36.300 V11.5.0 [Non-patent document 2] 3GPP TS36.304 V11.1.0 [Non-patent document 3] 3GPP S1-083461 [Non-patent document 4] 3GPP R2-082899 [Non-patent document 5] 3GPP TR 36.814 V9.0.0 [Non-patent document 6] 3GPP TR 36.912 V10.0.0 [Non-Patent Document 7] 3GPP TR 36.819 V11.1.0 [Non-patent document 8] 3GPP TS 36.141 V11.1.0 [Non-Patent Document 9] 3GPP R1-131530 [Non-Patent Document 10] 3GPP TS36.331 V11.3.0 [Non-Patent Document 11] 3GPP TR36.842 V0.2.0 [Non-Patent Document 12] 3GPP TS37.320 V11.3.0 Summary of the Invention [Problem to be solved by the invention]

[0048] When a large number of small cells are installed, the UE must measure many cells when making measurements for cell reselection or handover, which takes a long time for measurement.

[0049] On the other hand, small cells have a smaller cell radius and coverage area than macro cells, so when a UE moves, the time the UE stays in a small cell is shorter than the time the UE stays in a macro cell.

[0050] Therefore, it is not possible to find an optimal cell as a cell reselection destination or an optimal cell as a handover destination, which increases the risk that cell reselection and handover will not be performed normally and will fail.

[0051] To ensure proper cell reselection and handover, a communication system with mobility performance capable of handling UE movement is required in a configuration in which many small cells are installed. The aforementioned Non-Patent Documents 1 to 12 do not disclose such a communication system.

[0052] An object of the present invention is to provide a communication system having mobility capabilities that can accommodate the movement of communication terminal devices in a configuration in which a large number of small cells are installed. [Means for solving the problem]

[0053] 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 with the mobile terminal, wherein the base station notifies the mobile terminal of base station group information, and the base station group information includes an identifier of a base station group and a list of the base stations that constitute the base station group. The base station of the present invention is a base station that performs wireless communication with a mobile terminal, and notifies the mobile terminal of base station group information, the base station group information including an identifier of a base station group and a list of the base stations that constitute the base station group. The mobile terminal of the present invention is a mobile terminal that performs wireless communication with a base station, receives base station group information notified from the base station, and is characterized in that the base station group information includes an identifier of a base station group and a list of the base stations that constitute the base station group. [Effects of the Invention]

[0054] According to the mobile communication system of the present invention, in a configuration in which a large number of small cells are installed, it is possible to have mobility performance that can accommodate the movement of communication terminal devices.

[0055] According to the base station of the present invention, it is possible to obtain a base station that can accommodate the movement of communication terminal devices in a configuration in which a large number of small cells are installed.

[0056] According to the mobile terminal of the present invention, it is possible to obtain a mobile terminal capable of high-speed movement in a configuration in which a large number of small cells are installed.

[0057] The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings. [Brief explanation of the drawings]

[0058] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Figure 2] FIG. 7 is a block diagram showing the overall configuration of an LTE communication system 700 being discussed in 3GPP. [Figure 3] FIG. 3 is a block diagram showing the configuration of a mobile terminal 71 shown in FIG. 2, which is a mobile terminal according to the present invention. [Figure 4] FIG. 3 is a block diagram showing the configuration of a base station 72 shown in FIG. 2, which is a base station according to the present invention. [Figure 5] FIG. 2 is a block diagram showing the configuration of an MME according to the present invention. [Figure 6] 1 is a flowchart showing an outline of operations from cell search to standby operation performed by a mobile terminal (UE) in an LTE communication system. [Figure 7] FIG. 1 is a diagram illustrating the concept of a cell configuration when macro eNBs and small eNBs are mixed. [Figure 8] FIG. 1 is a diagram illustrating the concept of transition between cell groups in which a mobile station should reside when cells are grouped. [Figure 9] FIG. 10 is a diagram showing the concept of fixing cell grouping as a system. [Figure 10] FIG. 10 is a diagram illustrating the concept of semi-statically determining cell grouping as a system. [Figure 11] FIG. 2 is a diagram showing an example of a sequence of the communication system according to the first embodiment. [Figure 12] 10 is a graph illustrating the concept of a specific example of a transition determination threshold. [Figure 13] 10 is a flowchart showing a processing procedure of a UE in an idle mode according to a first modification of the first embodiment. [Figure 14] 10 is a flowchart showing a processing procedure of a UE in an idle mode according to a first modification of the first embodiment. [Figure 15]10 is a flowchart showing a processing procedure of a UE in an idle mode according to a first modification of the first embodiment. [Figure 16] 10 is a graph illustrating the concept of a specific example of a transition determination threshold. [Figure 17] 13 is a flowchart showing a processing procedure of a UE in an idle mode according to a second modification of the first embodiment. [Figure 18] 13 is a flowchart showing a processing procedure of a UE in an idle mode according to a second modification of the first embodiment. [Figure 19] 13 is a flowchart showing a processing procedure of a UE in an idle mode according to a third modification of the first embodiment. [Figure 20] FIG. 1 is a diagram for explaining the concept of an SCG that configures a virtual macro cell. [Figure 21] FIG. 1 is a diagram illustrating an example of physical resources used in a small cell. [Figure 22] FIG. 1 is a diagram illustrating an example of the architecture of a communication system when operating in both virtual macro cell mode and individual cell mode. [Figure 23] FIG. 1 is a diagram illustrating an example of the architecture of a communication system when operating in a dedicated cell mode. [Figure 24] FIG. 10 is a diagram illustrating another example of the architecture of a communication system when operating in both the virtual macro cell mode and the individual cell mode. [Figure 25] FIG. 2 is a diagram showing an example of a sequence of an HO process in the communication system of the first embodiment. [Figure 26] FIG. 2 is a diagram showing an example of a sequence of an HO process in the communication system of the first embodiment. [Figure 27] FIG. 2 is a diagram showing an example of a sequence of an HO process in the communication system of the first embodiment. [Figure 28] FIG. 10 is a diagram for explaining the concept of an overlap area at the SCG edge when small cells are arranged at the SCG edge without overlapping. [Figure 29]FIG. 10 is a diagram for explaining the concept of an overlap area at the SCG edge when small cells are arranged at the SCG edge in an overlapping manner. [Figure 30] FIG. 10 is a diagram showing an example of a sequence of a communication system according to a second modification of the second embodiment. [Figure 31] FIG. 10 is a diagram showing an example of a sequence of a communication system according to a second modification of the second embodiment. [Figure 32] FIG. 10 is a diagram showing another example of the sequence of the communication system according to the second modification of the second embodiment. [Figure 33] FIG. 10 is a diagram for explaining a configuration in which each cell in an SCG has four antennas. [Figure 34] FIG. 1 is a diagram showing a sequence when a conventional emergency information notification system is applied to a UE having dual connectivity. [Figure 35] FIG. 11 is a diagram showing an example of a sequence of the emergency information notification system in the third embodiment. [Figure 36] FIG. 11 is a diagram showing another example of the sequence of the emergency information notification system in the third embodiment. [Figure 37] FIG. 13 is a diagram showing an example of a sequence of a communication system according to a first modification of the third embodiment. [Figure 38] FIG. 13 is a diagram showing another example of the sequence of the communication system in the first modification of the third embodiment. [Figure 39] FIG. 13 is a diagram showing an example of a sequence of a communication system in the fourth embodiment. [Figure 40] FIG. 13 is a diagram showing an example of a sequence of a communication system in a first modification of the fourth embodiment. [Figure 41] FIG. 13 is a diagram showing an example of a sequence of a communication system according to a second modification of the fourth embodiment. [Figure 42] FIG. 1 is a diagram illustrating MBMS. [Figure 43] FIG. 13 is a diagram showing an example of a sequence of a communication system in the fifth embodiment. [Figure 44]FIG. 13 is a diagram showing another example of the sequence of the communication system in the fifth embodiment. [Figure 45] 1 is a flowchart showing an outline of a conventional process from cell search to standby operation performed by a UE. [Figure 46] 13 is a flowchart showing an example of a processing procedure of the operation of the UE according to the fifth embodiment. [Figure 47] 13 is a flowchart showing an example of a processing procedure of the operation of the UE according to the fifth embodiment. [Figure 48] 13 is a flowchart showing an example of a processing procedure of the operation of the UE according to the fifth embodiment. [Figure 49] 13 is a flowchart showing another example of the processing procedure of the operation of the UE according to the fifth embodiment. [Figure 50] 13 is a flowchart showing another example of the processing procedure of the operation of the UE according to the fifth embodiment. [Figure 51] 13 is a flowchart showing another example of the processing procedure of the operation of the UE according to the fifth embodiment. [Figure 52] 13 is a flowchart showing another example of the processing procedure of the operation of the UE according to the fifth embodiment. [Figure 53] 13 is a flowchart showing another example of the processing procedure of the operation of the UE according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0059] Embodiment 1 Fig. 2 is a block diagram showing the overall configuration of an LTE communication system 700 being discussed in 3GPP. Referring to Fig. 2, the radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 70. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 71, which is a communication terminal device, is capable of wireless communication with a base station device (hereinafter referred to as "base station (E-UTRAN NodeB: eNB)") 72, and transmits and receives signals via wireless communication.

[0060] If the control protocols for the mobile terminal 71, such as RRC (Radio Resource Control), and the user plane, such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate at the base station 72, the E-UTRAN is composed of one or more base stations 72.

[0061] The control protocol RRC (Radio Resource Control) between the mobile terminal 71 and the base station 72 performs broadcasting, 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.

[0062] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell reselection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can transmit and receive data with the network. In addition, in RRC_CONNECTED, handover (HO), measurement of neighbor cells, etc. are performed.

[0063] The base stations 72 are classified into eNBs 76 and Home-eNBs 75. The communication system 700 includes an eNB group 72-1 including a plurality of eNBs 76, and a Home-eNB group 72-2 including a plurality of Home-eNBs 75. A system configured from an EPC (Evolved Packet Core) core network and an E-UTRAN 70 radio access network is referred to as an EPS (Evolved Packet System). The EPC core network and the E-UTRAN 70 radio access network may be collectively referred to as a "network."

[0064] The eNB 76 is connected to a Mobility Management Entity (MME), or a Serving Gateway (S-GW), or an MME / S-GW unit (hereinafter sometimes referred to as an "MME unit") 73 including an MME and an S-GW via an S1 interface, and control information is communicated between the eNB 76 and the MME unit 73. Multiple MME units 73 may be connected to one eNB 76. The eNBs 76 are connected to each other via an X2 interface, and control information is communicated between the eNBs 76.

[0065] The Home-eNB 75 is connected to the MME unit 73 via an S1 interface, and control information is communicated between the Home-eNB 75 and the MME unit 73. A plurality of Home-eNBs 75 are connected to one MME unit 73. Alternatively, the Home-eNB 75 is connected to the MME unit 73 via a HeNBGW (Home-eNB GateWay) 74. The Home-eNB 75 and the HeNBGW 74 are connected via an S1 interface, and the HeNBGW 74 and the MME unit 73 are connected via the S1 interface.

[0066] One or more Home-eNBs 75 are connected to one HeNBGW 74, and information is communicated through the S1 interface. The HeNBGW 74 is connected to one or more MME units 73, and information is communicated through the S1 interface.

[0067] The MME unit 73 and HeNBGW 74 are upper devices, specifically upper nodes, and control connections between the eNB 76 and Home-eNB 75, which are base stations, and the mobile terminal (UE) 71. The MME unit 73 constitutes the EPC, which is a core network. The base station 72 and HeNBGW 74 constitute the E-UTRAN 70.

[0068] Furthermore, 3GPP is considering the following configuration: The X2 interface between Home-eNBs 75 is supported. That is, Home-eNBs 75 are connected via the X2 interface, and control information is communicated between the Home-eNBs 75. From the MME unit 73, HeNBGW 74 appears as the Home-eNB 75. From the Home-eNB 75, HeNBGW 74 appears as the MME unit 73.

[0069] In either case where the Home-eNB 75 is connected to the MME unit 73 via the HeNBGW 74 or where the Home-eNB 75 is connected directly to the MME unit 73, the interface between the Home-eNB 75 and the MME unit 73 is the same, the S1 interface.

[0070] The base station device 72 may configure one cell or multiple cells. Each cell has a predetermined coverage area, which is a range within which communication with a communication terminal device is possible, and performs wireless communication with the communication terminal device within the coverage area. When one base station device configures multiple cells, each cell is configured to be able to communicate with a mobile terminal.

[0071] FIG. 3 is a block diagram showing the configuration of mobile terminal 71 shown in FIG. 2, which is a mobile terminal according to the present invention. The transmission process of mobile terminal 71 shown in FIG. 3 will be described. First, control data from protocol processing unit 801 and user data from application unit 802 are stored in transmission data buffer unit 803. The data stored in transmission data buffer unit 803 is passed to encoder unit 804, where it is subjected to encoding processes such as error correction. Some data may be output directly from transmission data buffer unit 803 to modulator unit 805 without being encoded. The data encoded by encoder unit 804 is modulated by modulator unit 805. The modulated data is converted into a baseband signal, and then output to frequency converter 806, where it is converted into a radio transmission frequency. A transmission signal is then transmitted from antenna 807 to base station 72.

[0072] Furthermore, the receiving process of the mobile terminal 71 is performed as follows. A radio signal from the base station 72 is received by the antenna 807. The received signal is converted from a radio receiving frequency to a baseband signal by the frequency conversion unit 806, and demodulated by the demodulation unit 808. The demodulated data is passed to the decoder unit 809, where decoding processes such as error correction are performed. Of the decoded data, control data is passed to the protocol processing unit 801, and user data is passed to the application unit 802. A series of processes of the mobile terminal 71 is controlled by the control unit 810. Therefore, although the control unit 810 is omitted in FIG. 3, it is connected to each of the units 801 to 809.

[0073] Figure 4 is a block diagram showing the configuration of the base station 72 shown in Figure 2, which is a base station according to the present invention. The transmission processing of the base station 72 shown in Figure 4 will be described. An EPC communication unit 901 transmits and receives data between the base station 72 and the EPC (MME unit 73, etc.), HeNBGW 74, etc. An other base station communication unit 902 transmits and receives data with other base stations. The EPC communication unit 901 and the other base station communication unit 902 each exchange information with a protocol processing unit 903. Control data from the protocol processing unit 903, and user data and control data from the EPC communication unit 901 and the other base station communication unit 902 are stored in a transmission data buffer unit 904.

[0074] The data stored in the transmission data buffer unit 904 is passed to an encoder unit 905, where it undergoes encoding processes such as error correction. Some data may be output directly from the transmission data buffer unit 904 to a modulator unit 906 without undergoing encoding processes. The encoded data is modulated by the modulator unit 906. The modulated data is converted into a baseband signal, and then output to a frequency converter unit 907, where it is converted into a radio transmission frequency. The transmission signal is then transmitted from an antenna 908 to one or more mobile terminals 71.

[0075] The reception process of the base station 72 is performed as follows: A radio signal from one or more mobile terminals 71 is received by an antenna 908. The received signal is converted from a radio reception frequency to a baseband signal by a frequency converter 907, and demodulated by a demodulator 909. The demodulated data is passed to a decoder 910, where decoding processes such as error correction are performed. Of the decoded data, control data is passed to the protocol processor 903 or the EPC communication unit 901 or other base station communication unit 902, and user data is passed to the EPC communication unit 901 and other base station communication unit 902. A series of processes of the base station 72 is controlled by a controller 911. Therefore, although the controller 911 is omitted in FIG. 4, it is connected to each of the units 901 to 910.

[0076] FIG. 5 is a block diagram showing the configuration of an MME according to the present invention. FIG. 5 shows the configuration of an MME 73a included in the MME unit 73 shown in FIG. 2 described above. A PDN GW communication unit 1001 transmits and receives data between the MME 73a and a PDN GW. A base station communication unit 1002 transmits and receives data via the S1 interface between the MME 73a and a base station 72. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 1001 to the base station communication unit 1002 via a user plane communication unit 1003, and transmitted to one or more base stations 72. If the data received from the base station 72 is user data, the user data is passed from the base station communication unit 1002 to the PDN GW communication unit 1001 via the user plane communication unit 1003, and transmitted to the PDN GW.

[0077] If the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 1001 to the control plane control unit 1005. If the data received from the base station 72 is control data, the control data is passed from the base station communication unit 1002 to the control plane control unit 1005.

[0078] The HeNBGW communication unit 1004 is provided when a HeNBGW 74 is present, and transmits and receives data via an interface (IF) between the MME 73a and the HeNBGW 74 depending on the information type. Control data received from the HeNBGW communication unit 1004 is passed from the HeNBGW communication unit 1004 to the control plane control unit 1005. The result of processing in the control plane control unit 1005 is transmitted to the PDN GW via the PDN GW communication unit 1001. In addition, the result of processing in the control plane control unit 1005 is transmitted to one or more base stations 72 via the base station communication unit 1002 by the S1 interface, and is also transmitted to one or more HeNBGWs 74 via the HeNBGW communication unit 1004.

[0079] The control plane control unit 1005 includes a NAS security unit 1005-1, an SAE bearer control unit 1005-2, an idle state mobility management unit 1005-3, and the like, and performs overall processing for the control plane. The NAS security unit 1005-1 performs security for NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 1005-2 performs management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 1005-3 performs mobility management in the idle state (also called the LTE-IDLE state or simply idle), generation and control of paging signals in the idle state, addition, deletion, update, and search of tracking areas for one or more mobile terminals 71 under its control, and tracking area list management.

[0080] The MME 73a distributes paging signals to one or more base stations 72. The MME 73a also performs mobility control in an idle state. The MME 73a manages a tracking area list when the mobile terminal is in an idle state and an active state. The MME 73a initiates a paging protocol by transmitting a paging message to a cell belonging to a tracking area in which the UE is registered. The idle state mobility management unit 1005-3 may manage the CSG, CSG-ID, and whitelist of the Home-eNB 75 connected to the MME 73a.

[0081] Next, an example of a cell search method in a communication system is shown. Fig. 6 is a flowchart showing an outline of the process from cell search to standby operation performed by a mobile terminal (UE) in an LTE communication system. When the mobile terminal starts a cell search, in step ST1201, 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.

[0082] P-SS and S-SS are collectively called the synchronization signal (SS). The synchronization signal (SS) is assigned a synchronization code that corresponds one-to-one to the PCI assigned to each cell. 504 different PCIs are being considered. These 504 different PCIs are used to achieve synchronization and to detect (identify) the PCI of the synchronized cell.

[0083] Next, in step ST1202, 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 this code, it is possible to separate the cell from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST1201, it is possible to detect the RS and measure the RS received power.

[0084] Next, in step ST1203, 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 ST1202.

[0085] Next, in step ST1204, the PBCH of the best cell is received to obtain the BCCH, which is broadcast information. A MIB (Master Information Block), which includes cell configuration information, is mapped to the BCCH on the PBCH. Therefore, the MIB can be obtained by receiving the PBCH and obtaining the BCCH. Examples of MIB information include the DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, and the SFN (System Frame Number).

[0086] Next, in step ST1205, the DL-SCH of the cell is received based on the cell configuration information in the MIB, and SIB (System Information Block) 1 is obtained from the broadcast information BCCH. SIB 1 includes information on access to the cell, information on cell selection, and scheduling information for other SIBs (SIBk; k is an integer greater than or equal to 2). SIB 1 also includes a tracking area code (TAC).

[0087] Next, in step ST1206, the mobile terminal compares the TAC of the SIB1 received in step ST1205 with the TAC part of the tracking area identity (TAI) in the tracking area list that the mobile terminal already holds. The tracking area list is also called a TAI list. The TAI is identification information for identifying a tracking area, and is composed of an MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a tracking area code number.

[0088] If the comparison in Step ST1206 shows that the TAC received in Step ST1205 is the same as the TAC included in the tracking area list, the mobile terminal enters standby mode in that cell. If the comparison shows that the TAC received in Step ST1205 is not included in the tracking area list, the mobile terminal requests a core network (EPC) including an MME, etc., to change the tracking area in order to perform a Tracking Area Update (TAU) via that cell.

[0089] An apparatus constituting a core network (hereinafter sometimes referred to as a "core network side apparatus") updates the tracking area list based on the identification number (e.g., UE-ID) of the mobile terminal sent from the mobile terminal together with the TAU request signal. The core network side apparatus transmits the updated tracking area list to the mobile terminal. The mobile terminal rewrites (updates) the TAC list held by the mobile terminal based on the received tracking area list. Thereafter, the mobile terminal enters standby mode in the cell.

[0090] The widespread use of smartphones and tablet devices has led to an explosive increase in cellular wireless communication traffic, raising concerns about a shortage of wireless resources worldwide. In response to this, efforts are being made to develop small cells and promote spatial separation in order to improve frequency utilization efficiency.

[0091] In a conventional cell configuration, a cell configured by an eNB has a relatively wide coverage area. Conventionally, a cell is configured so that a certain area is covered by the relatively wide coverage areas of multiple cells configured by multiple eNBs.

[0092] In the case of small cell configuration, a cell configured by an eNB has a narrower coverage area than a cell configured by a conventional eNB. Therefore, as in the past, a larger number of small cell configuration eNBs are required to cover a certain area compared to conventional eNBs.

[0093] In the following description, a cell that provides coverage over a relatively wide range, such as a cell configured by a conventional eNB, i.e., a cell with a relatively wide coverage area, is referred to as a "macro cell," and an eNB that configures a macro cell is referred to as a "macro eNB." Also, a cell that provides coverage over a relatively narrow range, such as a cell configured as a small cell, i.e., a cell with a relatively narrow coverage area, is referred to as a "small cell," and an eNB that configures a small cell is referred to as a "small eNB."

[0094] The macro eNB may be, for example, a "Wide Area Base Station" as described in Non-Patent Document 8.

[0095] 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.

[0096] 7 is a diagram showing the concept of a cell configuration when macro eNBs and small eNBs are mixed. A macro cell configured by a macro eNB has a relatively wide coverage area 1301. A small cell configured by a small eNB has a coverage area 1302 that is narrower than the coverage area 1301 of the macro eNB (macro cell).

[0097] When multiple eNBs are mixed, the coverage of a cell configured by one eNB may be included in the coverage of a cell configured by another eNB. In the cell configuration shown in Figure 7, as indicated by reference numerals "1304" and "1305," the coverage 1302 of a small cell configured by a small eNB may be included in the coverage 1301 of a macro cell configured by a macro eNB.

[0098] Also, as indicated by reference numeral "1305," the coverage of multiple, for example, two small cells 1302 may be included within the coverage of one macro cell 1301. A mobile terminal (UE) 1303 is included, for example, within the coverage 1302 of a small cell and communicates via the small cell.

[0099] 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.

[0100] Also, as indicated by reference numeral "1307," there may be cases where the coverage 1301 of a macro cell configured by a macro eNB and the coverage 1302 of a small cell configured by a small eNB do not overlap.

[0101] Furthermore, as indicated by reference numeral "1308," there may be cases where coverage 1302 of multiple small cells formed by multiple small eNBs is formed within coverage 1301 of one macro cell formed by one macro eNB.

[0102] The problem to be solved in the first embodiment and the solution thereto are described below. In the present embodiment, a configuration is considered in which the coverage of a macro cell formed by a macro eNB includes the coverage of a small cell formed by a small eNB.

[0103] As mentioned above, in order to cope with the huge traffic volumes that will be generated in the future, technologies are being considered that will increase frequency utilization efficiency and communication capacity, for example, by installing a large number of small eNBs and a large number of small cells.

[0104] When a large number of small cells are installed, the UE must measure many cells when making measurements for cell reselection or handover, which requires a significant amount of time for measurement. Therefore, if measurement time is limited, there is a risk that the optimal cell to use as a cell reselection destination or an optimal cell to use as a handover destination cannot be detected. If the optimal cell cannot be detected, cell reselection may be repeated, and handover may not be completed successfully, resulting in a handover failure. Thus, when a large number of small cells are installed, improving the measurement performance of the UE becomes an issue.

[0105] The solution in the first embodiment is as follows: Cells are grouped, and the UE determines whether to transition to the cell group in which it should be located.

[0106] The serving cell is the cell on which the UE is camped in the case of a UE in an idle state, and is the cell to which the UE is connected in the case of a UE in an active state (connected state).

[0107] When determining whether to transition to a cell group, a UE in standby mode (hereinafter sometimes referred to as "Idle mode") determines whether to transition to a cell belonging to a group different from the group to which the currently camped cell belongs (hereinafter sometimes referred to as "cell group"), or whether to maintain its presence in a cell belonging to the same group to which the currently camped cell belongs.

[0108] A UE in a connected state (hereinafter sometimes referred to as "Connected mode") determines whether to perform a handover to a cell belonging to a group different from that to which the currently connected cell belongs, or to perform a handover to a cell belonging to the same group as that to which the currently connected cell belongs. That is, a UE in a connected state (Connected mode) determines whether to transfer its coverage area to a cell belonging to a group different from that to which the currently connected cell belongs, or to maintain its coverage area in a cell belonging to the same group as that to which the currently connected cell belongs.

[0109] 8 is a diagram showing the concept of transition between cell groups in which a mobile station should reside when cells are grouped. Assume that cells 2101 to 2109 belong to cell group A, and cells 2110 to 2112 belong to cell group B.

[0110] Assume that the UE 2113 is in idle mode (standby state). Assume that UE 2113 is camped on cell 2109 belonging to cell group A. UE 2113 determines whether to transition its coverage area to a cell belonging to a group different from the group to which cell 2109 on which it is currently camped belongs, or whether to maintain its coverage area in a cell belonging to the same group to which cell 2109 on which it is currently camped belongs.

[0111] For example, if it is determined that the UE 2113 should transfer its coverage area to a cell belonging to a group different from cell group A, which is the group to which the UE 2113 is currently camped, the UE 2113 performs measurements on cells belonging to cell group B to select a cell to reselect to, and selects a cell belonging to cell group B, such as cell 2111, as the cell to reselect to.

[0112] Also, for example, if it is determined that UE 2113 should maintain coverage of a cell belonging to the same group as cell group A, which is the group to which UE 2113 is currently camped, cell group A, UE 2113 performs measurements on cells belonging to cell group A to select a cell to reselect to, and selects another cell belonging to cell group A, for example, cell 2108, as the cell to reselect to.

[0113] In this way, when the UE 2113 is in idle mode (standby state), it selects either the group to which the cell in which the UE 2113 is located belongs or a group different from the group to which the cell in which the UE 2113 is located belongs, and performs measurements for selecting a cell to be reselected from the cells in the selected group, that is, measurements for cell reselection. Then, the UE 2113 selects a cell to be reselected based on the measurement results. Measurements for cell reselection include measurements of received power from a cell, specifically, measurements of received power of a reference signal (RS) (Reference Signal Received Power: RSRP).

[0114] Assume that the UE 2114 is in Connected mode (connected state). Assume that UE 2114 is connected to cell 2111 that belongs to cell group B. UE 2114 determines whether to transition its coverage area to a cell that belongs to a group different from the group to which currently connected cell 2111 belongs, or whether to maintain its coverage area in a cell that belongs to the same group to which currently connected cell 2111 belongs.

[0115] For example, if it is determined that the UE 2114 should transfer its coverage area to a cell belonging to a group different from cell group B, which is the group to which the currently connected cell 2111 belongs, the UE 2114 performs measurements for handover on cells 2101 to 2109 belonging to cell group A and submits a measurement report.

[0116] Also, for example, if it is determined that the UE 2114 should maintain coverage of a cell belonging to the same group as cell group B, which is the group to which the currently connected cell 2111 belongs, the UE 2114 performs measurements for handover on other cells 2110 and 2112 belonging to cell group B and submits a measurement report.

[0117] In this way, when the UE 2114 is in Connected mode (connected state), it selects either the group to which the cell to which it is connected belongs or a group different from the group to which the cell to which it is connected belongs, and performs measurements for handover on cells belonging to the selected group. Then, the UE 2114 performs a measurement report to report the measurement results. Measurements for handover include measurements of received power from cells, specifically, measurements of received power (RSRP) of reference signals (RS).

[0118] As a specific example of grouping the cells, the cells are grouped based on predetermined characteristics. As specific examples of the predetermined characteristics, the following 12 items (1) to (12) are disclosed.

[0119] (1) Grouping by cell size: The following five criteria (1-1) to (1-5) are disclosed as specific examples of criteria for determining cell size.

[0120] (1-1) The cell size is determined according to the transmission power of the cell. The higher the transmission power, the wider the range that the downlink signal from the cell can reach. Therefore, the higher the transmission power, the larger the cell size. (1-2) Determine the cell size based on the cell range. (1-3) Determine the cell size according to the coverage radius of the cell.

[0121] (1-4) Determine the cell size according to the cell type. Multiple types may be grouped together. For example, small cells, pico cells, femto cells, and hot spots are grouped as small cell sizes, and macro cells are grouped as large cell sizes. (1-5) A combination of (1-1) to (1-4) above.

[0122] (2) Grouping by frequency layer. For example, grouping by frequency layer to which carrier frequencies used by the cells belong. Or, for example, grouping by frequency band to which carrier frequencies used by the cells belong.

[0123] (3) Grouping by radio access technology (RAT) supported by the cell. As specific examples of radio access technologies, the following four (3-1) to (3-4) are disclosed. (3-1) UTRA (Universal Terrestrial Radio Access). (3-2) GERAN (GSM (registered trademark) / EDGE Radio Access Network). (3-3)CDMA2000 (Code Division Multiple Access 2000). (3-4) E-UTRAN (Evolved Universal Terrestrial Radio Access Network).

[0124] (4) Grouping by Cell Location The following two examples (4-1) and (4-2) are disclosed as specific examples of grouping by location.

[0125] (4-1) Group the cells by their installation location, regardless of the serving cell. For example, the cells installed in 1st block are grouped as Group A, and the cells installed in 2nd block are grouped as Group B.

[0126] (4-2) Grouping based on the installation location of the cell relative to the serving cell. For example, grouping based on the distance from the serving cell to the cell. Or, grouping based on the installation direction of the cell as seen from the serving cell. Specifically, grouping based on the "West area cell group," "East area cell group," etc.

[0127] (5) Grouping based on the load of the cell. For example, grouping based on the processing load of the scheduler in the cell. For example, grouping based on the amount of radio resources used or available in the cell.

[0128] (6) Grouping based on the amount of radio resources in the cells, for example, based on the bandwidth of the cells.

[0129] (7) Grouping by the type of service supported by the cell. As specific examples of supported services, the following three (7-1) to (7-3) are disclosed. (7-1) Audio support / non-support. (7-2)Data communication support / non-support. (7-3) MBMS service support / non-support.

[0130] (8) Grouping by cell delay level. For example, the backhaul link of the cell is high delay (non-ideal) or low delay (ideal). Grouping by backhaul type is also possible.

[0131] (9) Grouping according to the quality of service (QoS) supported by the cells.

[0132] (10) Group cells according to the gateway they are connected to. Cells connected to the same gateway belong to the same group.

[0133] (11) Cells are grouped according to the concentrators to which they are connected. Cells connected to the same concentrator belong to the same group. (12) A combination of (1) to (11) above.

[0134] As specific examples of methods for determining cell grouping, the following three methods (1) to (3) are disclosed.

[0135] (1) Determined fixedly as a system. Or determined statically. FIG. 9 is a diagram showing the concept of grouping cells fixedly as a system. Assume that cells 2201 to 2215 exist. For example, cells belonging to cell group A (2218) include cell 2201, cell 2202, cell 2203, cell 2204, cell 2205, cell 2206, and cell 2207. Cells belonging to cell group B (2219) include cell 2209, cell 2210, cell 2211, cell 2212, cell 2213, cell 2214, and cell 2215. This specific example (1) has a high affinity with the specific examples (1), (2), (3), (4-1), (6), (7), and (8) of the predetermined grouping feature described above, which enable cells belonging to groups to be determined fixedly as a system.

[0136] (2) Semi-static determination. Grouping is performed for each serving cell, and the cells belonging to the group are different for each serving cell. FIG. 10 is a diagram showing the concept of semi-static determination and grouping of cells as a system. Assume that cells 2201 to 2215 exist. When the serving cell is cell 2204, the cells belonging to cell group A (2216) include cell 2201, cell 2202, cell 2203, cell 2204, cell 2205, cell 2206, and cell 2207. When the serving cell is cell 2207, the cells belonging to cell group A (2217) include cell 2204, cell 2205, cell 2206, cell 2207, cell 2208, cell 2209, and cell 2210. This specific example (2) is suitable for grouping for each serving cell as a system, and has a high affinity with the specific example (4-2) of the predetermined characteristics of grouping described above.

[0137] (3) Dynamically determined. Grouping is performed over time, and the cells belonging to each group are changed over time. This specific example (3) has a strong affinity with the specific example (5) of the predetermined grouping feature, which is a feature that changes over time.

[0138] As specific examples of entities that determine cell groups, the following two (1) and (2) are disclosed.

[0139] (1) The O&M (Operation and Maintenance) decides on the group, and notifies the cell of the decided group.

[0140] (2) The cell is determined. If the cell is a small cell, the coverage macro cell may determine the group. If the small cell is installed within the coverage of another cell, the other cell is called a "coverage macro cell." If the determining cell and the cell in question are different, the determining cell notifies the cell of the determined group. In this case, the notification may be made using the X2 interface or the S1 interface.

[0141] There are the following methods for notifying a UE of a cell group. A serving cell notifies a UE being served by the serving cell of multiple cell groups. The serving cell also notifies the UE of the identification information of the groups. The serving cell may notify a list of cells constituting the group or the identification information of the cells together with the identification information of the group. The following three methods (1) to (3) are disclosed as specific examples of methods for notifying a UE of a cell group.

[0142] (1) Notifying the cell group using broadcast information The cell group may be notified using the SIB.

[0143] (2) Notifying a cell group using an individual signal. As specific examples of the individual signal, the following two examples (2-1) and (2-2) are disclosed. (2-1) Notification is made by RRC signaling, for example, by using a handover command. (2-2) Notify using measurement configuration.

[0144] (3) If the cell group and the predetermined characteristics for grouping are predetermined and each cell notifies the predetermined characteristics of its own cell by another method, it is possible to eliminate the need to notify the cell group. For example, if the predetermined characteristic for grouping is the cell size in the above-mentioned specific example (1), and if the UE can recognize the cell size of the cell by another method, it is possible to eliminate the need to notify the cell group and the cells that constitute the group. As specific examples of other methods, the following two (3-1) and (3-2) are disclosed.

[0145] (3-1) A downlink synchronization signal (SS) is used. Both the primary synchronization signal and the secondary synchronization signal may be used, or either one may be used. For example, an indicator as to whether the own cell is a small cell or an indicator indicating the set to which the own cell belongs may be mapped. For example, an indicator as to whether the own cell is a small cell or an indicator indicating the set to which the own cell belongs may be indicated using a sequence of the downlink synchronization signal.

[0146] (3-2) Discovery signal (discovery reference signal). Discovery signals are disclosed in Non-Patent Document 9. It is disclosed that discovery signals are used to discover small cells that have been switched off to reduce infrastructure power consumption (energy saving) and small cells that are operating normally (switched on). Non-Patent Document 9 also discloses that the transmission period of discovery signals is lengthened to reduce interference with other cells and reduce the transmission power of small cells. For example, an indicator as to whether the own cell is a small cell or an indicator indicating the set to which the own cell belongs may be mapped. For example, an indicator as to whether the own cell is a small cell or an indicator indicating the set to which the own cell belongs may be indicated using the sequence of the discovery signal.

[0147] A specific example of a UE's decision to transition to a cell group will be described below. The UE selects a cell group in which to reside from multiple cell groups notified by the serving cell. In the following description, selecting a cell group in which to reside from multiple cell groups notified by the serving cell may be referred to as "decision to transition to a cell group."

[0148] Also, a determination may be made as to whether or not to perform measurement. A determination as to whether or not to perform measurement may be provided. A determination as to whether or not measurement execution conditions are satisfied may be made. These may be referred to as "measurement determination" in the following description. A "measurement determination" may be made before a determination as to whether to transition to a cell group. This eliminates the need to start measurement again after a decision to transition, thereby preventing control delays.

[0149] For example, a UE in idle mode makes a measurement determination for cell reselection. If it is determined that measurement is to be performed, the UE executes the measurement for cell reselection. The UE selects a cell group for cell reselection. That is, the UE determines whether to transition to the cell group.

[0150] Furthermore, the UE in Connected mode makes a measurement determination for handover. If it is determined that measurement is to be performed, the UE executes the measurement for handover. The UE selects a cell group to handover to. In other words, it makes a determination as to whether to transition to the cell group.

[0151] After determining whether to transition to a cell group, the UE in Idle mode selects a cell to serve from among the cells belonging to the cell group to serve. The UE in Connected mode performs a measurement report when a measurement event occurs in a cell belonging to the cell group to serve (selects a candidate handover cell and performs a measurement report). In the following description, selecting a cell to serve from among the cells belonging to the cell group to serve and performing a measurement report when a measurement event occurs may be referred to as "determining whether to transition to a cell."

[0152] For example, a UE in idle mode measures cells belonging to a cell group to be served in. For example, among the cells belonging to the cell group to be served in, the UE selects a cell to be reselected to based on the cell with the highest received power, the cell with the best received quality, the best cell, or a standard cell selection criterion.

[0153] Furthermore, a UE in Connected mode measures cells belonging to a cell group in which it should reside. For example, when a measurement event occurs in a cell belonging to a cell group in which it should reside, the UE notifies the serving cell of a measurement report of the cell. A measurement event occurs when the measurement result in the UE satisfies the measurement report conditions. The serving cell uses the measurement report notified from the UE to select a cell in which the UE should reside and notifies the UE. The serving cell selects a handover destination (target cell) and notifies the UE. After that, handover processing is performed between the UE, the serving cell, the target cell, etc.

[0154] The following eight (1) to (8) are disclosed as specific examples of thresholds (indexes) for determining whether a UE should transition to a cell group. Separate thresholds for determining whether a UE should transition to a cell group may be set for a UE in idle mode and a UE in connected mode.

[0155] (1) UE movement speed. The UE uses its own movement speed to determine whether to transition to a cell group in which it should be located and selects the cell group in which it should be located. The movement speed may vary depending on the radius of the measurement target cell. For example, the movement speed may be a function of the radius of the measurement target cell.

[0156] (2) UE location and UE movement direction: The UE uses at least one of its own location and its own movement direction to determine whether to transition to a cell group in which it should be located, and selects a cell group in which it should be located.

[0157] (3) UE access class. Specific examples of access classes include AC (Access Class) and EAC (Extended Access Class) described in Non-Patent Document 10. The UE uses its own UE category in AC to determine whether to transition to a cell group in which it should be located, and selects the cell group in which it should be located. The UE also uses its own UE category in EAC to determine whether to transition to a cell group in which it should be located, and selects the cell group in which it should be located.

[0158] (4) UE Capability. The UE uses its capability to determine whether to transition to a cell group in which to serve and select the cell group in which to serve. The following three (4-1) to (4-3) are disclosed as specific examples of UE capabilities.

[0159] (4-1) Is it a high-speed, large-capacity communication terminal, or a low-speed, small-capacity communication terminal? (4-2) Is it a delay-tolerant terminal or not? There may be a level of delay. (4-3) Is it a normal UE or an MTC (Machine Type Communication)?

[0160] (5) Service type. If the UE is in Connected mode, the type of the currently connected service is used to determine whether to transition to the cell group in which the UE should be located. In other words, the cell group in which the UE should be located is selected. As specific examples of the service type, the following two (5-1) and (5-2) are disclosed. (5-1) Degree of real-time performance required. (5-2) Is it a voice service or a non-voice service?

[0161] (6) Quality of Service (QoS). If the UE is in Connected mode, the quality of the currently connected service is used to determine whether to transition to a cell group in which the UE should be located. In other words, the UE selects a cell group in which the UE should be located.

[0162] (7) Reception quality of each cell measured by the UE, the reception quality of the serving cell, and the reception quality of neighboring cells. (8) A combination of (1) to (7) above.

[0163] The following methods can be used to notify a UE of the threshold for determining whether to transition to a cell group (hereinafter sometimes referred to as the "transition determination threshold"). The serving cell notifies the UE being served of the threshold for determining whether to transition to a cell group. The serving cell may notify the threshold for determining whether to transition to a cell group together with the cell group. The serving cell may notify the threshold for determining whether to transition to a cell group in association with the cell group. The following three methods (1) to (3) are disclosed as specific examples of methods for notifying a UE of the threshold for determining whether to transition to a cell group.

[0164] (1) Notification of the transition determination threshold using broadcast information The transition determination threshold may be notified using an SIB. (2) Notification of transition determination threshold using individual signal. As specific examples of individual signal, the following two (2-1) and (2-2) are disclosed. (2-1) Notification is made by RRC signaling, for example, by using a handover command. (2-2) Notify using measurement configuration. (3) Determine statically in advance.

[0165] Next, a specific example of a sequence of a communication system in the case where the solution of the first embodiment is used will be described with reference to Fig. 11. Fig. 11 is a diagram showing an example of a sequence of a communication system in the first embodiment.

[0166] In Step ST2301, the O&M determines a cell group. In Step ST2302, the O&M notifies the serving cell of the cell group. The O&M may also notify the serving cell of a list of cells that constitute the group.

[0167] In Step ST2303, the serving cell notifies the UEs being served of the cell group. The serving cell may also notify the UEs being served of a list of cells that constitute the group.

[0168] In Step ST2304, the serving cell notifies the UE being served by the serving cell of the transition decision threshold. The transition decision threshold may be notified together with the cell group notification in Step ST2303.

[0169] In Step ST2305, the UE selects a cell group in which to serve, based on the cell group received in Step ST2303, the list of cells constituting the group, and the transition determination threshold received in Step ST2304.

[0170] In Step ST2306, the UE decides to transition to the cell group selected in Step ST2305 (hereinafter, this may be simply referred to as "transition").

[0171] The first embodiment can provide the following advantages. Measurements for selecting a cell for cell reselection or for selecting a handover destination can be limited to cells in the cell group selected by the UE. Therefore, even when a large number of small cells are installed, it is possible to limit the target cells to cells belonging to a cell group that matches the UE's decision to transition to the cell group. This makes it easier to detect the optimal cell, and improves the UE's measurement performance.

[0172] First embodiment, variant 1 The problem to be solved by the first modification of the first embodiment will be described below. When a large number of small cells are installed, cells of different cell sizes may overlap. When a UE moves, the time that the UE stays in a cell varies depending on the moving speed and the cell size. Cell reselection and handover to a cell with a short stay time causes further cell reselection and handover, which creates a problem of increased processing load on the communication system.

[0173] Furthermore, for example, even if a fast-moving UE detects a small cell as a handover destination (hereinafter sometimes referred to as a "handover destination small cell") through measurements, it may pass through the handover destination small cell while performing handover-related processing. In this case, the quality of communication with the handover destination small cell deteriorates, which may result in the handover not being performed normally and failing. Therefore, when a large number of small cells are installed, improving mobility performance becomes an issue.

[0174] The solution in Modification 1 of Embodiment 1 is described below. This modification uses the solution in Embodiment 1. Specifically, cells are grouped based on cell size, and the movement speed of the UE is used to determine whether to transition to the cell group in which the UE should reside.

[0175] In this modification, only the characteristic parts of the solution of the first embodiment will be described.

[0176] A specific example of the cell group is disclosed below: For example, a cell size group 1 (CellSizeGroup1) and a cell size group 2 (CellSizeGroup2) are provided as groups according to cell sizes.

[0177] It is assumed that cells with a large cell size, such as macro cells, belong to cell size group 1. Cell size group 1 may also be referred to as a big size cell group.

[0178] It is assumed that cells with a small cell size, for example, small cells, belong to cell size group 2. Cell size group 2 may be referred to as a small size cell group.

[0179] A specific example of the criteria for determining the cell size is the same as in the first embodiment, and therefore a description thereof will be omitted. A specific example of the method for notifying the UE of the cell group is the same as in the first embodiment, and therefore a description thereof will be omitted.

[0180] A specific example of the content of the notification of a cell group to a UE will be disclosed below. This example discloses a case where both the group identification information and the list of cells that make up the group are notified.

[0181] The group identification information is Cell Size Group 1, and if the cells that make up the cell size group are PCI#1, PCI#2, PCI#3, and PCI#4, they are notified as "CellSizeGroup1 (PCI#1, PCI#2, PCI#3, PCI#4)".

[0182] The group identification information is Cell Size Group 2, and if the cells that make up the cell size group are PCI#21, PCI#22, PCI#23, PCI#24, PCI#25, PCI#26, PCI#27, and PCI#28, they are notified as "CellSizeGroup2(PCI#21, PCI#22, PCI#23, PCI#24, PCI#25, PCI#26, PCI#27, PCI#28)".

[0183] The list of cells constituting the group may include the serving cell, for example, the identification information of the serving cell, which allows the UE to recognize the cell group to which the serving cell belongs.

[0184] The cell group to which the serving cell belongs may be separately notified to the UE being served. A specific example of a notification method is a method in which a cell notifies the UE being served of information indicating the cell group to which the cell belongs by RRC signaling or broadcast information. In this way, when the list of cells constituting the group does not include the serving cell, the cell group to which the serving cell belongs that is separately notified can be used.

[0185] A specific example of a UE's cell group transition determination is disclosed below. The UE uses its own moving speed to determine whether to transition to a cell size (inter-size) group different from the cell size group of the currently serving cell, or to maintain the same cell size (intra-size) group. This transition determination is sometimes called a "relative transition determination" because it recognizes the cell size group (cell size) of the currently serving cell.

[0186] As specific examples of how a UE can set a threshold (index) for determining whether to transition to a cell group, the following two methods (1) and (2) are disclosed.

[0187] (1) Separate thresholds are provided for determining whether to transition to the same cell group (intra cell group) and whether to transition to an inter cell group. A determination condition may be used instead of the transition threshold. A separate determination for whether to perform measurements may also be provided. Separate transition thresholds and determination for whether to perform measurements may be provided for cell reselection and handover.

[0188] (2) A threshold for determining whether to transition to an inter-cell group is set, instead of a threshold for determining whether to transition to an intra-cell group. A determination condition may be used instead of the threshold for determining whether to transition. A separate determination as to whether to perform measurement may also be set. A separate threshold for determining whether to transition and a separate determination as to whether to perform measurement may be set for cell reselection and handover.

[0189] Instead of setting a threshold for determining whether to transition to an intra-cell group, the following may be adopted: If the determination for transition to an inter-cell group is not satisfied, transition between cell groups is not performed. In other words, the mobile station maintains coverage in a cell belonging to the same cell group, and performs measurement reporting when measurement, cell selection, or a measurement event for a cell belonging to the same cell group occurs (select a candidate handover destination cell and perform a measurement reporting).

[0190] If only the determination of whether to perform measurements for determining inter-cell group transition is satisfied, transition between cell groups is not performed. Decision not to transition to an inter-cell group is made. In other words, the UE maintains coverage in a cell belonging to the same cell group, and performs measurement reporting when measurements, cell selection, or measurement events for cells belonging to the same cell group occur.

[0191] If the determination of whether to perform measurements for determining inter-cell group transition is not satisfied, transition between cell groups is not performed. Decision not to transition to an inter-cell group is made. In other words, the UE maintains coverage in a cell belonging to the same cell group, and performs measurement reporting when measurements, cell selection, or measurement events for cells belonging to the same cell group occur.

[0192] If the determination of transition to an inter cell group is satisfied, or if the determination of whether or not to perform measurements for determining transition to an inter cell group is satisfied, measurements of cells belonging to the same cell group, cell selection, and measurement reports when a measurement event occurs may or may not be performed.

[0193] In the case of specific example (2) of how to set a threshold (index) for a UE to determine whether to transition to a cell group, a specific example of a transition determination threshold for the case where a separate determination is made as to whether or not to perform measurements for transition determination, and separate thresholds are set for cell selection and handover, is disclosed below. Cell size group 1 is a large-sized cell group, and cell size group 2 is a small-sized cell group.

[0194] The following four thresholds (1) to (4) are set for cell reselection (for UEs in idle mode).

[0195] (1) A threshold value for determining whether or not to perform measurements on an inter-cell group for reselection (cell size group 2) for a UE residing in cell size group 1. For example, the moving speed is 30 km / h or less. "S1_inter_cell_size_group1: moving speed≦30 km / h".

[0196] (2) A threshold for determining whether UEs residing in cell size group 1 should transition to an inter-cell group (cell size group 2) for reselection. For example, the moving speed is less than 20 km / h. "S2_inter_cell_size_group1: moving speed<20 km / h".

[0197] (3) A threshold for determining whether to perform measurements on an inter-cell group for reselection (cell size group 1) for a UE residing in cell size group 2. For example, assume that the moving speed is higher than 30 km / h. "S1_inter_cell_size_group2: moving speed > 30 km / h".

[0198] (4) A threshold for determining whether UE residing in cell size group 2 should transition to an inter-cell group (cell size group 1) for reselection. For example, assume that the moving speed is higher than 50 km / h. "S2_inter_cell_size_group2: moving speed > 50 km / h".

[0199] The following four thresholds (1) to (4) are set for handover (for UE in Connected mode).

[0200] (1) A threshold value for determining whether to perform measurements on an inter-cell group for handover (cell size group 2) for a UE residing in cell size group 1. For example, the moving speed is 30 km / h or less. "T1_inter_cell_size_group1: moving speed≦30 km / h".

[0201] (2) A threshold value for determining whether to transition to an inter-cell group for handover (cell size group 2) for a UE currently serving in cell size group 1. For example, the moving speed is less than 20 km / h. "T2_inter_cell_size_group1: moving speed<20 km / h".

[0202] (3) A threshold value for determining whether to perform measurements in an inter-cell group for handover (cell size group 1) for a UE residing in cell size group 2. For example, assume that the moving speed is higher than 30 km / h. "T1_inter_cell_size_group2: moving speed > 30 km / h".

[0203] (4) A threshold value for determining whether to transition to an inter-cell group for handover (cell size group 1) for a UE residing in cell size group 2. For example, assume that the moving speed is higher than 50 km / h. "T2_inter_cell_size_group2: moving speed > 50 km / h".

[0204] Fig. 12 is a graph showing the concept of a specific example of a transition determination threshold. The vertical axis of Fig. 12 represents moving speed v (km / h), and the horizontal axis represents time t. Cell size group 1 (CG1) is a large-sized cell group, and cell size group 2 (CG2) is a small-sized cell group.

[0205] The UEs located in cell size group 1 will be described by classifying the moving speed v into ranges R1, R2, and R3 as indicated by reference numeral "50."

[0206] Range R1 is set to a range where the moving speed v is 30 km / h or less. Range R1 satisfies "S1_inter_cell_size_group1: moving speed≦30 km / h" and "T1_inter_cell_size_group1: moving speed≦30 km / h".

[0207] Therefore, in range R1, the UE performs measurements on the different cell group for reselection (cell size group 2: small size cell group). Also, in range R1, the UE performs measurements on the different cell group for handover (cell size group 2: small size cell group).

[0208] That is, in range R1, the UE performs measurements on the inter cell size group (small size cell group).

[0209] Range R2 is defined as a range where the moving speed v is less than 20 km / h. Range R2 satisfies "S2_inter_cell_size_group1: moving speed < 20 km / h" and "T2_inter_cell_size_group1: moving speed < 20 km / h".

[0210] Therefore, in range R2, the UE transitions to a different cell group for reselection (cell size group 2: small size cell group). If a cell belonging to another cell size group 2 meets the reselection criteria, the UE performs a reselection process.

[0211] In addition, in range R2, the UE transitions to a different cell group for handover (cell size group 2: small size cell group). If a cell belonging to another cell size group 2 satisfies the conditions for measurement reporting, the UE performs measurement reporting.

[0212] That is, in range R2, the UE performs an inter cell size group (small size cell group) transition.

[0213] Range R3 is set to a moving speed v of 20 km / h or more. Range R3 does not satisfy "S2_inter_cell_size_group1: moving speed < 20 km / h" and "T2_inter_cell_size_group1: moving speed < 20 km / h".

[0214] Since the transition to an inter-cell group is not satisfied, no transition between cell groups is performed. In other words, measurements are performed on the same cell group for reselection (cell size group 1: big size cell group). If a cell belonging to another cell size group 1 meets the reselection criteria, reselection processing is performed.

[0215] In range R3, the UE performs measurements on the same cell group for handover (cell size group 1: big size cell group). If a cell belonging to cell size group 1 satisfies the measurement report conditions, the UE performs a measurement report.

[0216] That is, in range R3, the UE performs measurement and transition of the same cell size group (Intra cell size group (Big size cell group)).

[0217] The UEs located in cell size group 2 will be described by classifying the moving speed v into ranges R4, R5, and R6 as indicated by reference numeral "51."

[0218] In range R4, the moving speed v is higher than 30 km / h. Range R4 satisfies "S1_inter_cell_size_group2: moving speed > 30 km / h" and "T1_inter_cell_size_group2: moving speed > 30 km / h".

[0219] Therefore, in range R4, the UE performs measurements on the different cell group for reselection (cell size group 1: big size cell group). Also, in range R4, the UE performs measurements on the different cell group for handover (cell size group 1: big size cell group).

[0220] That is, in range R4, the UE performs measurements on the inter cell size group (big size cell group).

[0221] In range R5, the moving speed v is higher than 50 km / h. Range R5 satisfies "S2_inter_cell_size_group2: moving speed > 50 km / h" and "T2_inter_cell_size_group2: moving speed > 50 km / h".

[0222] Therefore, in range R5, the UE transitions to a different cell group for reselection (cell size group 1: big size cell group). If a cell belonging to another cell size group 1 meets the reselection criteria, the UE performs a reselection process.

[0223] In addition, in range R5, the UE transitions to a different cell group for handover (cell size group 1: big size cell group). If a cell belonging to another cell size group 1 satisfies the measurement report condition, the UE performs a measurement report.

[0224] That is, in range R5, the UE performs an inter cell size group (big size cell group) transition.

[0225] Range R6 is set to a range where the moving speed v is equal to or less than 50 km / h. Range R6 does not satisfy "S2_inter_cell_size_group2: moving speed > 50 km / h" and "T2_inter_cell_size_group2: moving speed > 50 km / h".

[0226] Since the inter-cell group transition judgment is not satisfied, inter-cell group transition is not performed. In other words, measurements are performed on the same cell group for reselection (cell size group 2: small size cell group). If a cell belonging to another cell size group 2 meets the reselection criteria, reselection processing is performed.

[0227] In range R6, the UE performs measurements on the same cell group for handover (cell size group 2: small size cell group). If a cell belonging to cell size group 2 satisfies the measurement report conditions, the UE performs a measurement report.

[0228] That is, in range R6, the UE performs measurement and transition of the same cell size group (intra cell size group (small size cell group)).

[0229] The UE measures (estimates) its own moving speed regardless of the communication state with the cell. For example, the moving speed is measured regardless of whether the UE is in the RRC_Idle state or the RRC_Connected state. Also, the moving speed is measured regardless of whether the UE is in the ECM_Idle state or the ECM_Connected state.

[0230] The following two examples (1) and (2) are disclosed as specific examples of timing for a UE to measure its own moving speed.

[0231] (1) The UE periodically measures its speed. The serving cell notifies the UE of the time when the speed is measured.

[0232] (2) The UE periodically measures its speed. The period may vary depending on the most recent speed measurement result. It may also be a function of the most recent speed. The serving cell notifies the UE of the speed measurement period.

[0233] The timing for measuring the moving speed of the UE itself may be notified together with the information on the cell group, the transition determination threshold, and the transition determination condition.

[0234] The following three methods (1) to (3) are disclosed as specific examples of methods for notifying UE of the timing for measuring the moving speed.

[0235] (1) Notification of measurement timing is made using broadcast information. Notification may also be made using SIB.

[0236] (2) Notifying the measurement timing using an individual signal. The following two examples (2-1) and (2-2) are disclosed as specific examples of the individual signal. (2-1) Notification is made by RRC signaling, for example, by using a handover command. (2-2) Notify using measurement configuration.

[0237] (3) It may be determined in advance, which eliminates the need for notification from the serving cell, reduces the processing load of the communication system, and enables effective use of radio resources.

[0238] The following two examples (1) and (2) are disclosed as specific examples of measurement results of the moving speed used to determine the transition of the UE.

[0239] (1) Use the most recent measurement results of the UE's moving speed. (2) A moving average of values ​​measured by the UE for the movement speed is used. The moving average is taken from N (N is a natural number) measurements. The number of measurements, N, is notified to the UE from the serving cell. The method for notifying the number of measurements, N, is the same as the specific example of the method for notifying the UE of the timing for measuring the movement speed described above, so a description thereof will be omitted.

[0240] 13 to 15 are flowcharts showing the processing procedure of a UE in idle mode in Modification 1 of Embodiment 1. Fig. 13 to 15 show the processing procedure of a UE when a specific example (2) of setting a threshold for determining transition to a cell group is used.

[0241] In Step ST2401, the UE checks the group to which the serving cell belongs. In Step ST2402, the UE measures its own moving speed.

[0242] In Step ST2403, the UE judges whether or not the group to which the serving cell confirmed in Step ST2401 belongs is cell size group 2. If it is judged in Step ST2403 that the group to which the serving cell belongs is cell size group 2, it moves to Step ST2404 in FIG.14, and if it is judged that the group to which the serving cell belongs is not cell size group 2, it moves to Step ST2414 in FIG.15.

[0243] In Step ST2404 of FIG. 14, the UE decides to use a threshold for UEs residing in cell size group 2 (small size cell group) (hereinafter, may be referred to as a "second group threshold").

[0244] In Step ST2405, the UE determines whether or not the measurement execution threshold "S1_inter_cell_size_group2" (measurement execution threshold for cell selection for the second group) for determining whether or not to perform measurement on the inter-cell group for reselection (cell size group 1) for the UE residing in cell size group 2 is exceeded (whether or not the measurement execution condition for the inter-cell group is satisfied). In other words, the UE determines whether or not the measurement execution condition for the first group is satisfied. Specifically, the UE determines whether or not the moving speed is higher than 30 km / h.

[0245] In step ST2405, if it is determined that the measurement execution conditions of the first group are satisfied, i.e., if it is determined that the moving speed is higher than 30 km / h, proceed to step ST2410, and if it is determined that the measurement execution conditions of the first group are not satisfied, i.e., if it is determined that the moving speed is 30 km / h or less, proceed to step ST2406.

[0246] In Step ST2406, the UE does not measure neighboring cells that belong to an inter cell size group (big size cell group), that is, the first group, and moves to Step ST2407.

[0247] Since it is determined in Step ST2405 that the threshold for determining whether to perform measurement on an inter cell group (inter cell group) (measurement execution condition for an inter cell group) is not satisfied, the UE does not perform transition between cell groups in Step ST2407. That is, the UE does not transition to an inter cell group (inter cell size group (big size cell group)) but maintains its presence in the same cell group (intra cell size group (small size cell group)). In other words, the UE does not transition to the first group but maintains its presence in the second group.

[0248] Since it is determined in Step ST2405 that the threshold for determining whether to perform inter-cell group measurements (the measurement execution condition for inter-cell groups) is not satisfied, in Step ST2408, the UE performs measurements on cells belonging to the same cell group. That is, it performs measurements on neighboring cells belonging to the second group, which is the same cell group (intra-cell size group (small size cell group)).

[0249] Since it has been determined in Step ST2405 that the threshold for determining whether or not to perform inter cell group measurements (measurement execution condition for inter cell groups) is not satisfied, in Step ST2409, if the measurement result in Step ST2408 satisfies the reselection condition, the UE performs reselection processing to a cell belonging to the same cell group (intra cell size group (small size cell group)). The UE reselects a cell within the same cell group, i.e., within the second group. After completing the processing of Step ST2409, all processing procedures end.

[0250] In Step ST2410, the UE performs measurements on neighboring cells that belong to the first group, which is an inter-cell size group (big size cell group).

[0251] In step ST2411, the UE determines whether or not the transition determination threshold "S2_inter_cell_size_group2" (a transition condition to an inter-cell group) for transition to the reselection inter-cell group (cell size group 1) for the UE existing in cell size group 2 is satisfied. In other words, the UE determines whether or not the transition condition to the first group is satisfied. Specifically, the UE determines whether or not the moving speed is higher than 50 km / h.

[0252] In step ST2411, if it is determined that the transition conditions to the first group are satisfied, i.e., if it is determined that the moving speed is higher than 50 km / h, then proceed to step ST2412, and if it is determined that the transition conditions to the first group are not satisfied, i.e., if it is determined that the moving speed is 50 km / h or less, then proceed to step ST2407.

[0253] In Step ST2412, the UE performs inter-cell group transition, that is, transition to the first group, which is a different cell group (inter-cell size group (big size cell group)).

[0254] In Step ST2413, if the measurement result in Step ST2410 satisfies the reselection condition, the UE executes a reselection process to a cell belonging to an inter-cell size group (big size cell group). The UE reselects a cell in the inter-cell group, i.e., a cell in the first group. When the reselection is completed, the UE may change the cell group in which the UE is located to cell size group 1 (big size cell group). After completing the process of Step ST2413, all processing procedures end.

[0255] In Step ST2414 of FIG. 15, the UE decides to use a threshold for UEs residing in cell size group 1 (big size cell group) (hereinafter, may be referred to as a "first group threshold").

[0256] In step ST2415, the UE determines whether or not the measurement execution threshold "S1_inter_cell_size_group1" (measurement execution threshold for cell selection for the first group) for determining whether or not to perform measurement on the inter-cell group for reselection (cell size group 2) for the UE residing in cell size group 1 is exceeded (whether or not the measurement execution condition for the inter-cell group is satisfied). In other words, the UE determines whether or not the measurement execution condition for the second group is satisfied. Specifically, the UE determines whether or not the moving speed is 30 km / h or less.

[0257] In step ST2415, if it is determined that the measurement execution conditions of the second group are satisfied, i.e., if it is determined that the moving speed is 30 km or less, proceed to step ST2420, and if it is determined that the measurement execution conditions of the second group are not satisfied, i.e., if it is determined that the moving speed is higher than 30 km, proceed to step ST2416.

[0258] In Step ST2416, the UE does not measure neighboring cells that belong to an inter-cell size group (small size cell group), that is, the second group, and moves to Step ST2417.

[0259] Since it is determined in Step ST2415 that the threshold for determining whether to perform measurement on an inter cell group (inter cell group measurement execution condition) is not satisfied, in Step ST2417, the UE does not perform inter-cell group transition. That is, the UE does not transition to an inter-cell group (inter-cell size group (small-size cell group)) but maintains its presence in the same cell group (intra-cell size group (big-size cell group)). In other words, the UE does not transition to the second group but maintains its presence in the first group.

[0260] Since it is determined in Step ST2415 that the threshold for determining whether to perform inter cell group measurements (the measurement execution condition for inter cell groups) is not satisfied, in Step ST2418, the UE performs measurements on cells belonging to the same cell group. That is, it performs measurements on neighboring cells belonging to the first group, which is the same cell group (intra cell size group (big size cell group)).

[0261] Since it has been determined in Step ST2415 that the threshold for determining whether or not to perform inter cell group measurements (measurement execution condition for inter cell groups) is not satisfied, in Step ST2419, if the measurement result in Step ST2418 satisfies the reselection condition, the UE performs reselection processing to a cell belonging to the same cell group (intra cell size group (big size cell group)). The UE reselects a cell within the same cell group, i.e., within the first group. After completing the processing of Step ST2419, all processing procedures end.

[0262] In Step ST2420, the UE performs measurements on neighboring cells that belong to the second group, which is an inter-cell size group (small size cell group).

[0263] In step ST2421, the UE determines whether or not to satisfy the transition determination threshold "S2_inter_cell_size_group1" (a transition condition to an inter-cell group) for transition to the reselection inter-cell group (cell size group 2) for the UE currently located in cell size group 1. That is, the UE determines whether or not the transition condition to the second group is satisfied. Specifically, the UE determines whether or not the moving speed is less than 20 km / h.

[0264] In step ST2421, if it is determined that the transition conditions to the second group are met, i.e., if it is determined that the moving speed is less than 20 km / h, then proceed to step ST2422, and if it is determined that the transition conditions to the second group are not met, i.e., if it is determined that the moving speed is higher than 20 km / h, then proceed to step ST2417.

[0265] In Step ST2422, the UE performs a transition between cell groups, that is, transition to the second group, which is a different cell group (inter cell size group (small size cell group)).

[0266] In Step ST2423, if the measurement result in Step ST2420 satisfies the reselection condition, the UE executes a reselection process to a cell belonging to an inter-cell size group (small size cell group). The UE reselects a cell in the inter-cell group, i.e., a cell in the second group. When the reselection is completed, the UE may change the cell group in which the UE is located to cell size group 2 (small size cell group). After completing the process of Step ST2423, all processing procedures end.

[0267] In addition to the effects of the first embodiment, the first modification of the first embodiment can provide the following effects: By providing cell groups based on cell size and determining whether to transition to a cell group depending on the movement speed of the UE, it becomes possible to transition to a cell with a cell size that is suitable for the movement speed of the UE.

[0268] This suppresses cell reselection and handover to a cell with a short residence time, and suppresses further cell reselection and handover, thereby reducing the processing load on the communication system.Furthermore, it is possible to suppress deterioration of communication quality with the handover destination small cell caused by passing through the handover destination small cell while handover-related processing is being performed, thereby suppressing handover failures and improving mobility performance.

[0269] Embodiment 1 Variation 2 Variation 2 of Embodiment 1 solves the same problem as Variation 1 of Embodiment 1. The solution in Variation 2 of Embodiment 1 is described below. In this variation, only the characteristic parts of this variation among the solutions in Embodiment 1 and Variation 1 of Embodiment 1 described above will be described.

[0270] In this modification, the solution of the first embodiment is used, as in the first modification of the first embodiment. Specifically, cells are grouped based on cell size, and the determination of transition to the cell group in which the UE should reside is made based on the movement speed of the UE itself.

[0271] Specific examples of cell groups are the same as those in Modification 1 of Embodiment 1. For example, it is assumed that cells with large cell sizes, such as macro cells, belong to cell size group 1. Cell size group 1 may be a big size cell group. It is assumed that cells with small cell sizes, such as small cells, belong to cell size group 2. Cell size group 2 may be a small size cell group.

[0272] A specific example of the content of the notification of the cell group to the UE is the same as that of the first modification of the first embodiment, and a case will be disclosed in which both the identification information of the group and the list of cells constituting the group are notified.

[0273] The group identification information is Cell Size Group 1, and if the cells that make up the cell size group are PCI#1, PCI#2, PCI#3, and PCI#4, they are notified as "CellSizeGroup1 (PCI#1, PCI#2, PCI#3, PCI#4)".

[0274] The group identification information is Cell Size Group 2, and if the cells that make up the cell size group are PCI#21, PCI#22, PCI#23, PCI#24, PCI#25, PCI#26, PCI#27, and PCI#28, they are notified as "CellSizeGroup2(PCI#21, PCI#22, PCI#23, PCI#24, PCI#25, PCI#26, PCI#27, PCI#28)".

[0275] The list of cells constituting the group may include the own cell or may include the identification information of the own cell. If the list of cells constituting the group does not include the serving cell, the cell group to which the serving cell belongs may be notified separately to the UE being served.

[0276] A specific example of a UE's cell group transition determination is disclosed below. The UE uses its own moving speed to determine which cell size group it should reside in. This transition determination is sometimes called "absolute transition determination" because it is made based only on the group to which the target cell belongs, regardless of the cell size group (cell size) of the currently residing cell.

[0277] A specific example of how to set a threshold (index) for a UE to determine whether to transition to a cell group is disclosed below. A determination condition may be used instead of a threshold for determining transition. A separate determination as to whether to perform measurements for determining transition may also be provided. Separate determinations as to whether to perform measurements for determining transition may be provided for cell reselection and handover. In this case, cell size group 1 is a large-sized cell group, and cell size group 2 is a small-sized cell group.

[0278] The following four thresholds (1) to (4) are set for cell selection (for UEs in idle mode).

[0279] (1) A threshold value for determining whether or not to perform measurement of the reselection cell size group 1. For example, it is set to be unrelated to the moving speed. "S1_inter_cell_size_group1: moving speed<∞".

[0280] (2) A threshold value for determining whether to move to cell size group 1 for reselection. For example, this is set to be unrelated to the moving speed. "S2_inter_cell_size_group1: moving speed<∞".

[0281] (3) A threshold value for determining whether or not to perform measurements for the reselection cell size group 2. For example, the moving speed is less than 50 km / h. "S1_inter_cell_size_group2: moving speed<50 km / h".

[0282] (4) A threshold value for determining whether to transition to cell size group 2 for reselection. For example, the moving speed is less than 50 km / h. "S2_inter_cell_size_group2: moving speed<50 km / h".

[0283] The following four thresholds (1) to (4) are set for handover (for UE in Connected mode).

[0284] (1) A threshold value for determining whether or not to perform measurements on cell size group 1 for handover. For example, this is unrelated to the moving speed. "T1_inter_cell_size_group1: moving speed<∞".

[0285] (2) A threshold value for determining whether to transition to cell size group 1 for handover. For example, this is set to be unrelated to the moving speed. "T2_inter_cell_size_group1: moving speed<∞".

[0286] (3) A threshold value for determining whether or not to perform measurements on cell size group 2 for handover. For example, the moving speed is less than 50 km / h. "T1_inter_cell_size_group2: moving speed<50 km / h".

[0287] (4) A threshold value for determining whether to transition to cell size group 2 for handover. For example, the moving speed is less than 50 km / h. "T2_inter_cell_size_group2: moving speed<50 km / h".

[0288] Fig. 16 is a graph showing the concept of a specific example of a transition determination threshold. The vertical axis of Fig. 16 represents moving speed v, and the horizontal axis represents time t. Cell size group 1 is a large-sized cell group, and cell size group 2 is a small-sized cell group. The period P shown in Fig. 16 is, for example, the period at which the UE measures (estimates) moving speed v. The period does not have to be set. The moving speed v will be classified into range R11 and range R12 for explanation.

[0289] Range R11 is defined as a range where the moving speed v is less than 50 km / h. Range R11 satisfies "S1_cell_size_group2: moving speed < 50 km / h", "S2_cell_size_group2: moving speed < 50 km / h", "T1_cell_size_group2: moving speed < 50 km / h", and "T2_cell_size_group2: moving speed < 50 km / h".

[0290] Therefore, in range R11, the UE performs measurements on reselection cell size group 2 (small size cell group). The UE allows transition to reselection cell size group 2 (small size cell group). If another cell belonging to cell size group 2 meets the reselection criteria, the UE performs a reselection process.

[0291] In addition, in range R11, the UE performs measurements on handover cell size group 2 (small size cell group). The UE enables transition to handover cell size group 2 (small size cell group). If a cell belonging to another cell size group 2 satisfies the measurement report conditions, the UE performs a measurement report.

[0292] That is, in range R11, the UE performs measurements on cell size group 2 (small size cell group), and the UE is enabled to transition to cell size group 2 (small size cell group).

[0293] Range R12 is a range that does not depend on the movement speed v. In other words, the movement speed v is less than ∞. Range R12 satisfies "S1_cell_size_group1: movement speed<∞", "S2_cell_size_group1: movement speed<∞", "T1_cell_size_group1: movement speed<∞", and "T2_cell_size_group1: movement speed<∞".

[0294] Therefore, in range R12, the UE performs measurements on reselection cell size group 1 (big size cell group). The UE enables transition to reselection cell size group 1 (big size cell group). If another cell belonging to cell size group 1 meets the reselection criteria, the UE performs a reselection process.

[0295] In addition, in range R12, the UE performs measurements on handover cell size group 1 (big size cell group). The UE enables transition to handover cell size group 1 (big size cell group). If a cell belonging to another cell size group 1 satisfies the measurement report conditions, the UE performs a measurement report.

[0296] That is, in range R12, the UE performs measurements on cell size group 1 (big size cell group), and the UE enables transition to cell size group 1 (big size cell group).

[0297] In FIG. 16, points 2501, 2502, 2504, 2505, and 2506, which are indicated by white circles "◯," are included in both range R11 and range R12.

[0298] Therefore, the UE performs measurements on cell size group 2 (small size cell group) and cell size group 1 (big size cell group), and the UE allows transition to cell size group 2 (small size cell group) and cell size group 1 (big size cell group).

[0299] 16, points 2503, 2507, 2508, 2509, and 2510 indicated by black circles are included in range R12. Therefore, the UE performs measurements on cell size group 1 (big size cell group). The UE also enables transition to cell size group 1 (big size cell group).

[0300] Figures 17 and 18 are flowcharts showing the processing procedure of a UE in idle mode in Variation 2 of Embodiment 1. In addition, in the thresholds conceptually explained using Figure 16, the threshold for determining whether or not to perform measurement and the threshold for determining whether or not to perform transition are the same value. Therefore, in Figures 17 and 18, the explanation will omit the determination using the threshold for determining whether or not to perform measurement.

[0301] In Step ST2601, the UE measures its own movement speed. In Step ST2602, the UE determines whether or not the transition determination threshold for reselection cell size group 1, "S2_inter_cell_size_group1," is satisfied (whether or not the condition for transition to the first group is satisfied). Specifically, the UE determines whether or not the movement speed is less than infinity (∞).

[0302] If it is determined in step ST2602 that the condition for transitioning to the first group is satisfied, the process proceeds to step ST2603, and if it is determined that the condition for transitioning to the first group is not satisfied, the process proceeds to step ST2608 in Fig. 18. In this flowchart, the transition determination threshold "S2_inter_cell_size_group1" is "movement speed<∞", so it is not determined that this condition is not satisfied, but if it is determined that it is not satisfied, the process proceeds to step ST2608.

[0303] In Step ST2603, the UE determines whether or not the transition determination threshold for reselection cell size group 2, "S2_inter_cell_size_group2," is satisfied (whether or not the transition condition to the second group is satisfied). Specifically, the UE determines whether or not the movement speed is less than 50 km / h. If it is determined in Step ST2603 that the transition condition to the second group is not satisfied, the UE proceeds to Step ST2604, and if it is determined that the transition condition to the second group is satisfied, the UE proceeds to Step ST2606.

[0304] In Step ST2604, the UE measures cells belonging to cell size group 1. That is, the UE measures neighboring cells belonging to a big size cell group. In other words, the UE measures neighboring cells belonging to group 1.

[0305] In Step ST2605, if the measurement result in Step ST2604 satisfies the reselection condition, the UE performs a reselection process to a cell belonging to a big size cell group. That is, the UE reselects a cell in the first group. After completing the process of Step ST2605, all processing procedures end.

[0306] In Step ST2606, the UE measures cells belonging to cell size group 1 and cells belonging to cell size group 2. That is, the UE measures neighboring cells belonging to a big size cell group and neighboring cells belonging to a small size cell group. In other words, the UE measures neighboring cells belonging to the first group and neighboring cells belonging to the second group.

[0307] In Step ST2607, if the measurement result in Step ST2606 satisfies the reselection criterion, the UE performs a reselection process to a cell belonging to a big size cell group or a cell belonging to a small size cell group. In other words, the UE reselects a cell in the first group or a cell in the second group. The UE may select the best cell in the measurements of a cell belonging to cell size group 1 and a cell belonging to cell size group 2, and perform a reselection process. After completing the process of Step ST2607, all processing procedures end.

[0308] 18, the UE determines whether or not the transition determination threshold for reselection cell size group 2, "S2_inter_cell_size_group2," is satisfied (whether or not the transition condition to the second group is satisfied). Specifically, the UE determines whether or not the moving speed is less than 50 km / h.

[0309] If it is determined in step ST2608 that the condition for transitioning to the second group is not satisfied, the process proceeds to another process, but this is not a characteristic feature of the present invention, so a description thereof will be omitted.If it is determined in step ST2608 that the condition for transitioning to the second group is satisfied, the process proceeds to step ST2609.

[0310] In Step ST2609, the UE measures cells belonging to cell size group 2. That is, the UE measures neighboring cells belonging to a small size cell group. In other words, the UE measures neighboring cells belonging to group 2.

[0311] In Step ST2610, if the measurement result in Step ST2609 satisfies the reselection condition, the UE performs a reselection process to a cell belonging to a small size cell group. That is, the UE reselects a cell in the second group. After completing the process of Step ST2610, all processing procedures end.

[0312] In addition to the effects of the first embodiment and the first modification of the first embodiment, the second modification of the first embodiment can provide the following effects.

[0313] In the first modification of the first embodiment, the transition determination of the UE is a relative transition determination, and therefore, the UE needs to recognize the cell size group (cell size) of the cell in which it currently resides.

[0314] In contrast, in the second modification of the first embodiment, the transition determination of the UE is an absolute transition determination. Therefore, the UE does not need to recognize the cell size group (cell size) of the cell in which it currently resides, and the cell does not need to notify the UE being served of the cell size group to which the cell belongs. This makes it possible to effectively utilize radio resources. Furthermore, since the UE does not need to recognize the cell group to which the serving cell belongs, the processing load on the UE can be reduced.

[0315] Embodiment 1, Variation 3 In the solution of the second modification of the first embodiment, when a threshold for determining whether to perform measurements for a plurality of cell groups is satisfied, the UE performs measurements on neighboring cells belonging to the cell group for which the threshold is satisfied. Therefore, depending on the threshold for determining whether to perform measurements, the UE must measure many cells, which again results in the problem of requiring a long time for measurements.

[0316] Variation 3 of Embodiment 1 solves the same problem as Variation 2 of Embodiment 1. The solution in Variation 3 of Embodiment 1 is described below. In this variation, only the characteristic parts of this variation among the solutions in the above-mentioned Embodiment 1, Variation 1 of Embodiment 1, and Variation 2 of Embodiment 1 will be described.

[0317] In this modification, the solution of the first embodiment is used, as in the first modification of the first embodiment and the second modification of the first embodiment. Specifically, cells are grouped based on cell size, and a decision on transition to a cell group in which a UE should reside is made using the movement speed of the UE itself. The decision on transition to a cell group takes into account the priority of the cell group.

[0318] When the transition determination criteria for multiple cell groups are met, measurements are performed on cells belonging to a cell group with a higher priority, and measurements are not performed on cells belonging to a cell group with a lower priority, or are performed with a lower priority.

[0319] If the transition threshold is satisfied in multiple cell groups, transition to a cell belonging to a cell group with a higher priority is performed, and transition to a cell belonging to a cell group with a lower priority is not performed or is performed with a lower priority.

[0320] As specific examples of entities that determine priorities, the following three entities (1) to (3) are disclosed. (1) The O&M (Operation and Maintenance) decides on the priority. The O&M notifies the cells belonging to each cell group of the decided priority.

[0321] (2) The cell decides. If the cell is a small cell, the coverage macro cell may decide. If the small cell is installed within the coverage of another cell, the other cell is called a "coverage macro cell." If the determining cell and the cell in question are different, the determining cell notifies the determined priority to the cell. In this case, the notification may be made using the X2 interface or the S1 interface.

[0322] (3) Determined by the UE. Specifically, the UE determines the priority based on a predetermined threshold value that determines the priority. The predetermined threshold value is notified to the UE from the network side.

[0323] As a method of notifying a UE of priority, the serving cell notifies the UE being served by the serving cell of the priority. The serving cell notifies the priority together with the cell group. Groups are created according to cell sizes, and priorities are assigned to the groups. A specific example of the method of notifying priority is the same as the specific example of the method of notifying a cell group in the first embodiment, and therefore description thereof will be omitted.

[0324] The priority order will be explained using a specific example of how to set the threshold (index) for determining transition to a cell group disclosed in Variation 2 of Embodiment 1. Cell size group 1 is a large-sized cell group, and cell size group 2 is a small-sized cell group. The priority order of cell size group 1 is "2," and the priority order of cell size group 2 is "1." The smaller the priority order number, the higher the priority order.

[0325] The concept of a specific example of the transition determination threshold will be described using the above-mentioned Fig. 16. The explanation of range R11 and range R12 is the same as that in Modification 2 of Embodiment 1, and therefore will not be repeated.

[0326] 16, points 2501, 2502, 2504, 2505, and 2506 indicated by white circles "◯" are included in both range R11 and range R12. In other words, the criteria for performing measurements for transition determination are met in multiple cell groups, and the transition determination threshold is met in multiple cell groups.

[0327] The priority of cell size group 2 is "1," and the priority of cell size group 1 is "2." In other words, cell size group 2 has a higher priority than cell size group 1.

[0328] Therefore, the UE performs measurements on cell size group 2 (small size cell group) with priority. The UE also allows transition to cell size group 2 (small size cell group). The UE performs measurements on cell size group 1 (big size cell group) with lower priority. The UE also allows transition to cell size group 1 (big size cell group).

[0329] 16, points 2503, 2507, 2508, 2509, and 2510 indicated by black circles "●" are included in range R12. In other words, the determination of whether or not to perform measurements for transition determination is not met in multiple cell groups, and the transition determination threshold is not met in multiple cell groups.

[0330] Therefore, the UE performs measurements on cell size group 1 (Big size cell group), and the UE enables transition to cell size group 1 (Big size cell group).

[0331] Fig. 19 is a flowchart showing a processing procedure of a UE in idle mode according to Modification 3 of Embodiment 1. In the thresholds conceptually explained using Fig. 16 above, the threshold for determining whether or not to perform measurement and the threshold for determining whether or not to perform transition are the same value. Therefore, in Fig. 19, the explanation will be omitted, omitting the determination using the threshold for determining whether or not to perform measurement.

[0332] In Step ST2701, the UE measures its own movement speed. In Step ST2702, the UE checks the priority of each cell group.

[0333] In Step ST2703, the UE makes a transition decision starting from the cell group with the highest priority in the priority order confirmed in Step ST2702. In this specific example, cell group 2 has the highest priority.

[0334] Therefore, in step ST2703, the UE determines whether the transition determination threshold "S2_inter_cell_size_group2" for reselection cell size group 2 is satisfied (whether the transition condition to the cell group with the highest priority (hereinafter sometimes referred to as the "highest priority group") is satisfied). Specifically, the UE determines whether the moving speed is less than 50 km / h.

[0335] If it is determined in step ST2703 that the conditions for transitioning to the highest priority group are satisfied, the process proceeds to step ST2704, and if it is determined that the conditions for transitioning to the highest priority group are not satisfied, the process proceeds to step ST2707.

[0336] In Step ST2704, the UE measures neighboring cells that belong to cell size group 2. That is, the UE measures neighboring cells that belong to a small size cell group. In other words, the UE measures neighboring cells that belong to the highest priority group.

[0337] In Step ST2705, the UE judges whether or not there is a cell that satisfies the reselection condition based on the measurement result in Step ST2704. In other words, the UE judges whether or not there is a cell that satisfies the reselection condition in the highest priority group. If it is judged in Step ST2705 that there is a cell that satisfies the reselection condition in the highest priority group, the UE proceeds to Step ST2706, and if it is judged that there is no cell that satisfies the reselection condition in the highest priority group, the UE proceeds to Step ST2707.

[0338] In Step ST2706, the UE performs a reselection process to a cell that belongs to a small-size cell group and satisfies a reselection condition, that is, reselects a cell in the highest priority group.

[0339] In Step ST2707, the UE makes a transition decision starting with the cell group with the next highest priority in the order of priority confirmed in Step ST2702 (hereinafter, may be referred to as the "second priority group"). In this specific example, cell group 1 has the next highest priority. Therefore, in Step ST2707, the UE decides whether or not the transition decision threshold "S2_inter_cell_size_group1" for reselection cell size group 1 is met (whether or not the transition condition to the second priority group is satisfied). Specifically, the UE decides whether or not the movement speed is less than infinity (∞) per hour.

[0340] If it is determined in step ST2707 that the conditions for transitioning to the second priority group are satisfied, the process proceeds to step ST2708. In this modification, it is not determined that the conditions for transitioning to the second priority group are not satisfied, but if it is determined that the conditions are not satisfied, all processing procedures are terminated.

[0341] In Step ST2708, the UE measures cells belonging to cell size group 1. That is, the UE measures neighboring cells belonging to a big size cell group. In other words, the UE measures neighboring cells belonging to the second priority group.

[0342] In Step ST2709, the UE performs a reselection process to a cell for which the measurement result in Step ST2708 satisfies the reselection condition, that is, reselects a cell in the second priority group.

[0343] In addition to the effects of the first embodiment, the first modification of the first embodiment, and the second modification of the first embodiment, the third modification of the first embodiment can provide the following effects. Compared to the second modification of the first embodiment, it is possible to limit the cells to be measured, thereby improving measurement performance. By limiting the cells to be measured, it is possible to perform reselection processing and measurement reporting in a short time. Therefore, it is possible to prevent control delays in the communication system. Furthermore, when the network side sets priorities, the UE performs measurements according to the priorities specified by the network side, which makes it possible to adjust the load on the communication system.

[0344] First embodiment, variant 4 In the solutions of the first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, and the third modification of the first embodiment, there are cases where the load on the cell group selected by the UE or on a cell within the cell group is large. In such cases, even if the UE reselects a cell belonging to the cell group or performs handover, the user throughput of the UE is low, and a problem occurs in that high-speed, large-capacity communication cannot be performed.

[0345] The solution in Variation 4 of Embodiment 1 is shown below. Of the solutions in Embodiment 1, Variation 1 of Embodiment 1, Variation 2 of Embodiment 1, and Variation 3 of Embodiment 1, only the characteristic parts of this variation will be explained.

[0346] In this modification, load information of the cell group is taken into consideration when determining whether to transition to the cell group. This may be barring information of the cell group. The barring information of the cell group may be access class barring (ACB) information or extended access barring (EAB) information.

[0347] When the requirement for measurement execution for transition determination is satisfied for multiple cell groups, measurement is executed for cells belonging to cell groups with low load, and measurement is not executed for cells belonging to cell groups with high load, or is executed with a lower priority.

[0348] If the transition threshold is satisfied in multiple cell groups, transition to a cell belonging to a cell group with a low load is performed, and transition to a cell belonging to a cell group with a high load is not performed or is performed with a lower priority.

[0349] For example, the load levels are "1" to "3", and load level "3" prohibits UE cell reselection and handover. The larger the load level number, the higher the load.

[0350] As a method of notifying UE of load information, the serving cell notifies the UEs served by it of the load information. The serving cell notifies the load information together with the cell group. Groups are set according to cell sizes, and the load information is added. A specific example of the method of notifying load information is the same as the specific example of the method of notifying cell groups in the first embodiment, and therefore a description thereof will be omitted. Load information may be added for each cell.

[0351] The following two situations (1) and (2) are disclosed as specific examples of situations in which the fourth modification of the first embodiment is used.

[0352] (1) Group cells according to the radio access technology (RAT) they support. For example, cell group 1 is an LTE system, and cell group 2 is a wireless LAN system. For example, if the load on the LTE system is high, the load on cell group 1 is set high and the load on cell group 2 is set low.

[0353] As a result, when a determination as to whether to perform measurements for transition determination is satisfied in multiple cell groups, it becomes possible to perform measurements on cells belonging to a group of WLAN systems with low loads, and not perform measurements on cells belonging to a group of LTE systems with high loads, or perform measurements with a lower priority.Furthermore, when a threshold for transition determination is satisfied in multiple cell groups, it becomes possible to perform transition to cells belonging to a group of WLAN systems with low loads, and not perform transition to cells belonging to a cell group of LTE systems with high loads, or perform measurements with a lower priority.

[0354] (2) Group cells according to the type of backhaul link. For example, cell group 1 uses an optical network for backhaul, while cell group 2 uses a wireless network for backhaul. For example, if the load on the optical network is high, set the load on cell group 1 high and the load on cell group 2 low.

[0355] As a result, when a determination as to whether to perform measurements for transition determination is satisfied in multiple cell groups, it becomes possible for a backhaul with a low load to perform measurements on cells belonging to the wireless group, and for a backhaul with a high load to not perform measurements on cells belonging to the optical network group, or to perform them with a lower priority.Furthermore, when a threshold for transition determination is satisfied in multiple cell groups, it becomes possible for a backhaul with a low load to perform transition to cells belonging to the wireless group, and for a backhaul with a high load to not perform transition to cells belonging to the optical network cell group, or to perform them with a lower priority.

[0356] In addition to the effects of the first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, and the third modification of the first embodiment, the following effects can be obtained by the fourth modification of the first embodiment. It becomes possible to measure cells that belong to a cell group with a low load. This makes it possible to improve user throughput.

[0357] Embodiment 2 The problem to be solved in the second embodiment will be described below. The cell radius of a small cell, i.e., its coverage range, is smaller than that of a macro cell. When a UE moves, the UE stays in the small cell for a shorter period of time than in a macro cell. Therefore, a UE moving at high speed between small cells may experience a deterioration in communication quality with the HO-source small cell while HO-related processing is being performed in the HO-source small cell, resulting in an HO not being performed correctly and failing.

[0358] Furthermore, even if the UE detects an appropriate HO-target small cell through measurements, there may be cases where the UE passes through the HO-target small cell while performing HO-related processing. In this case, the communication quality with the HO-target small cell has already deteriorated, and HO may not be performed normally and may fail.

[0359] Therefore, when a large number of small cells are installed, improving mobility performance when UEs move at high speed becomes an issue.

[0360] As a solution to the above-mentioned problem, 3GPP has proposed a method called dual connectivity (see Non-Patent Document 11). In dual connectivity, a UE uses radio resources provided by at least two different network points connected by a non-ideal backhaul.

[0361] Two methods have been proposed for dual connectivity: one is inter-node radio resource aggregation, and the other is RRC diversity.

[0362] In inter-node radio resource aggregation, radio resources of two or more eNBs are aggregated for user-plane data. The two or more eNBs considered include a macro eNB and a small eNB whose coverage areas overlap in location. In this case, maintaining a mobility anchor in the macro cell is also considered. This method, in which mobility control is performed in the macro cell, can reduce HO failures due to the aforementioned short residence time of a UE in a small cell.

[0363] However, because inter-node wireless resource aggregation uses macrocells, it can only be realized in places where macrocells are overlaid on small cells. In places where only small cells are densely deployed, the above-mentioned problems arise. Also, while it is possible to install new macrocells that overlay small cells, installing macrocells would be extremely costly.

[0364] In RRC diversity, HO-related RRC signaling is transmitted from / to potential HO-target cells, allowing the UE to receive HO-related RRC signaling from the HO-source cell and / or potential HO-target cells.

[0365] However, since RRC diversity uses a cell that can be a HO target, the cell may be different from the HO target cell in the actual HO. Therefore, the UE may not always be able to receive HO-related RRC signaling from the HO target cell.

[0366] Furthermore, to perform RRC diversity using the HO-target cell, the UE must first identify the HO-target cell and then establish an RRC connection with the HO-target cell, as in the HO-related process. Therefore, it is difficult to reduce HO failures due to short residence time in the cell.

[0367] The present embodiment aims to solve the above-mentioned problem by a method different from these.

[0368] A cell (hereinafter referred to as a "virtual macro cell") that provides a coverage area larger than that of a single small cell is configured using multiple small cells.

[0369] The multiple small cells that make up a virtual macro cell are called a "small cell group" (hereinafter referred to as "SCG").

[0370] Small cells within an SCG transmit and receive the same data and signals to and from UEs. Small cells within an SCG perform the same communications.

[0371] The present invention discloses a configuration and function for each small cell in an SCG to perform the same communication. The small cells in an SCG have the same cell identifier, and the SCG has one. That is, each small cell in an SCG is identified as the same cell and performs the same communication. The SCG may be recognizable by the cell identifier between the upper entity and the SCG. The cell identifier may also be the same as that given to conventional cells. Examples of cell identifiers include CGI, ECGI, and PCI.

[0372] Conventional RRH operation is a method for increasing coverage by using multiple small cells (see Non-Patent Document 7). However, conventional RRHs are connected to a macro cell, and each RRH has a different PCI. In this embodiment, small cells have the same PCI. Therefore, in this respect, it differs from conventional methods.

[0373] Another technique using RRH is RRH in CoMP scenario 4 operation (see Non-Patent Document 7). In this technique, the macro cell and RRH are arranged so as to overlay each other, and the RRH is configured so as to have the same PCI as the macro cell. This embodiment is a method for cases where the macro cell and small cells are not overlaid, and in this respect it differs from conventional methods.

[0374] The small cells within the SCG are synchronized, and the accuracy of the synchronization should be within the range of a cyclic prefix (CP).

[0375] For downlink, it is advisable for a UE under an SCG to receive signals from small cells within the SCG within the CP range. This allows transmissions from multiple small cells to be treated as if they were from a single macrocell. Therefore, the UE can treat the signals as if they were from a single macrocell.

[0376] For uplink, it is advisable for each small cell to ensure that the received signal from the UE is within the range of the CP, which enables each small cell to treat transmissions from UEs served by the SCG in the same way as transmissions from UEs served by conventional small cells.

[0377] Synchronization between multiple small cells can be achieved using a global positioning system (GPS) or the like.

[0378] The physical resource configuration of each small cell within the SCG must be the same. The physical resource configurations in the frequency domain and time domain must be the same. The physical resource configurations, such as carrier frequency, frequency band, number of subcarriers, subframe configuration, number of symbols within a subframe, and CP length must be the same.

[0379] The protocols of each small cell within the SCG are made the same. Layer 3, layer 2, and layer 1 processing are made the same and mapped to the same physical resources. For example, physical channels and signals in layer 1 such as SS, CRS, PBCH, PDCCH, PDSCH, PUCCH, and PUSCH are mapped to the same physical resources. In addition, for layer 2 scheduling, each small cell performs scheduling for all UEs under the SCG, and the resource allocation and MCS (Modulation and Coding Scheme) for each UE are made the same for each small cell.

[0380] By having small cells within an SCG have such a configuration and function, the small cells within the SCG can perform the same communication. For UEs served by the SCG, there is no need to distinguish between each small cell, and they can be considered as one cell. In other words, the small cells within the SCG form one virtual macro cell with a wider coverage than a single small cell.

[0381] The small cells in the SCG that make up the virtual macro cell have the same PCI, and the UE cannot distinguish between the small cells, so they may be called "nodes," but in this embodiment and its variants, they will be called "cells."

[0382] A centralized control entity (hereinafter referred to as a "concentrator") may be provided for each SCG. The concentrator controls the small cells in the SCG. The concentrator is connected to each small cell in the SCG.

[0383] As described above, small cells in an SCG perform the same operations from the upper layer to the mapping to physical resources. Therefore, by controlling the concentrator to perform some or all of these operations, it is possible to simplify the configuration of each small cell.

[0384] The concentrator may be provided in one of the small cells in the SCG, or may be provided separately from the small cells.

[0385] Also, for example, the concentrator may be configured to have a modulation / demodulation unit, and each small cell may be configured to have everything from a frequency conversion unit to an antenna. The division of functions is not limited to this, and it is sufficient that each small cell can perform the same communication.

[0386] When a UE communicates with small cells in an SCG that configures a virtual macro cell, it is equivalent to communicating with a single virtual macro cell that has wider coverage than a single small cell. This reduces the number of home access failures caused by a UE's short residence time in a cell, thereby improving the UE's mobility performance.

[0387] Furthermore, some or all of the small cells in the SCG that constitutes the virtual macro cell may be provided with the functionality of individual cells, that is, cells constituted by individual eNBs, and configured to operate as individual cells. In other words, the small cells operate as cells constituted by normal eNBs.

[0388] A small cell operating as an individual cell may have a carrier frequency different from the carrier frequency when operating as a virtual macrocell. Small cells operating as individual cells may have the same carrier frequency. Alternatively, the carrier frequency when operating as a virtual macrocell may be the same as the carrier frequency of the macrocell. The frequency layer of a small cell operating as an individual cell may be different from the frequency layer when operating as a virtual macrocell. This makes it possible to eliminate interference between operation as a virtual macrocell and operation as an individual cell.

[0389] The frequency band when operating as an individual cell may be different from the frequency band when operating as a virtual macrocell, or the frequency band when operating as a virtual macrocell may be the same as the frequency band of the macrocell.

[0390] A small cell operating as an individual cell has a cell identifier when operating as an individual cell and a cell identifier when operating as a virtual macro cell. When operating as an individual cell, the small cell uses the cell identifier when operating as an individual cell, and when operating as a virtual macro cell, it uses the cell identifier when operating as a virtual macro cell. This enables the small cell to operate both as a virtual macro cell configured by small cells within an SCG and as an individual cell consisting of only the small cell.

[0391] The cell identifier of each small cell may be set by the O&M or may be set via the concentrator.

[0392] Furthermore, a PCI selection function (see Non-Patent Document 1) may be used separately to set each PCI in the small cell. The PCI when operating as a virtual macro cell may be determined using the PCI selection function in the frequency layer when operating as a virtual macro cell, and the PCI when operating as an individual cell may be determined using the PCI selection function in the frequency layer when operating as an individual cell.

[0393] Figure 20 is a diagram illustrating the concept of SCGs that make up a virtual macro cell. In Figure 20, small cells are indicated by reference numerals "4109" to "4136". Small cell groups (SCGs) are indicated by reference numerals "4105" to "4108". Each SCG is made up of seven small cells. For example, SCG 4105 is made up of small cells 4109 to 4115. Concentrators 4101 to 4104 are connected to SCGs 4105 to 4108, respectively.

[0394] Each of the SCGs 4105 to 4108 constitutes one virtual macro cell. As described above, the small cells in each SCG perform the same communication, so that the UEs served by the SCG do not need to distinguish between the small cells and can regard them as one cell. For example, in the SCG 4105, the small cells 4109 to 4115 perform the same communication. Therefore, one small cell, for example, one virtual macro cell 4105 having wider coverage than small cell 4109, is constituted.

[0395] When SCG 4108 configures a virtual macro cell, UE 4137 becomes a UE served by SCG 4108, i.e., a UE served by the virtual macro cell. When UE 4137 moves in the direction shown by the arrow, the UE stays longer in the virtual macro cell configured by SCGs 4108 and 4105 than in small cells 4136, 4131, 4113, 4112, etc.

[0396] The small cells within the SCG that make up the virtual macro cell operate as both a virtual macro cell and individual cells.

[0397] Fig. 21 is a diagram showing an example of physical resources used in a small cell. In Fig. 21, physical resources consisting of carrier frequencies and bandwidths when operating as a virtual macro cell are indicated by reference symbol "4138", and physical resources consisting of carrier frequencies and bandwidths when operating as an individual cell are indicated by reference symbol "4139".

[0398] When operating as a virtual macro cell, the physical resources 4138 are the same for each small cell in the SCG. Furthermore, each small cell in the SCG uses the physical resources 4138 to perform the same communication.

[0399] When operating as individual cells, the physical resources 4139 may be the same for each small cell in the SCG, or some or all of the physical resources may be different. Furthermore, communication is performed for each small cell using the physical resources 4139.

[0400] Among the small cells within the SCG, small cells that operate as individual cells operate both as virtual macro cells (hereinafter referred to as "virtual macro cell mode") and as individual cells (hereinafter referred to as "individual cell mode").

[0401] By doing this, an overlay structure of virtual macrocells and small cells can be created using small cells within the SCG.

[0402] Therefore, it becomes possible to achieve dual connectivity using small cells within the SCG. Conventionally, inter-node radio resource aggregation was not possible using only small cells, but by using the method disclosed in this embodiment, it becomes possible to perform this using only small cells.

[0403] It is preferable to maintain the mobility anchor using a virtual macro cell. For example, HO-related RRC signaling may be performed between the UE and a small cell in the SCG operating in virtual macro cell mode. Other signaling and data may be performed using a small cell operating in dedicated cell mode. In this way, mobility control is performed in the virtual macro cell, which has a wider coverage than the small cell, making it possible to reduce HO failures caused by the UE's short residence time in the small cell.

[0404] Alternatively, a control plane (C-plane) connection may be established using small cells in an SCG operating in virtual macro cell mode, and a user plane (U-plane) connection may be established using small cells operating in dedicated cell mode. This reduces HO failures and improves mobility performance.

[0405] By limiting communication between the virtual macrocell and the UE to predetermined signaling and control plane (C-plane) connections, or predetermined signaling and some data communication, it is possible to reduce the physical resources required for the virtual macrocell. For example, it is possible to narrow the frequency bandwidth required to operate the virtual macrocell mode.

[0406] The frequency bandwidth for operating the virtual macro cell mode may be narrower than the frequency bandwidth for operating the dedicated cell mode, thereby making it possible to suppress a decrease in frequency utilization efficiency when operating the virtual macro cell mode.

[0407] The part of data communication is assumed to require low latency, such as voice, etc. This reduces failures due to HO, and therefore reduces loss of voice data.

[0408] Fig. 22 is a diagram showing an example of the architecture of a communication system when operating in both the virtual macro cell mode and the dedicated cell mode. The communication system shown in Fig. 22 is configured with a P-GW 4201, an S-GW 4202, an MME 4203, a concentrator 4204, a first small cell (SC1) 4205, a second small cell (SC2) 4206, a third small cell (SC3) 4207, and a UE 4208.

[0409] The P-GW 4201 and the S-GW 4202 are connected by an interface 4209, such as an S5 interface. The S-GW 4202 and the MME 4203 are connected by an interface 4210, such as an S11 interface.

[0410] The MME 4203 and the concentrator 4204 are connected by an interface 4211. The MME 4203 and the first small cell (SC1) 4205 are connected by an interface 4212. The MME 4203 and the second small cell (SC2) 4206 are connected by an interface 4213. The MME 4203 and the third small cell (SC3) 4207 are connected by an interface 4214.

[0411] The interfaces 4211 to 4214 that connect the MME 4203 to the concentrator 4204 or the small cells 4205 to 4207 are, for example, S1 interfaces, specifically S1-MME interfaces.

[0412] The S-GW 4202 and the concentrator 4204 are connected by an interface 4215. The S-GW 4202 and the first small cell (SC1) 4205 are connected by an interface 4216. The S-GW 4202 and the second small cell (SC2) 4206 are connected by an interface 4217. The S-GW 4202 and the third small cell (SC3) 4207 are connected by an interface 4218.

[0413] The interfaces 4215 to 4218 that connect the S-GW 4202 to the concentrator 4204 or the small cells 4205 to 4207 are, for example, S1 interfaces, specifically S1-U interfaces.

[0414] The concentrator 4204 and the first small cell (SC1) 4205 are connected by an interface 4219, for example, an X2 interface. The concentrator 4204 and the second small cell (SC2) 4206 are connected by an interface 4220, for example, an X2 interface. The concentrator 4204 and the third small cell (SC3) 4207 are connected by an interface 4221, for example, an X2 interface.

[0415] The concentrator 4204 and the first small cell (SC1) 4205 may be connected by an interface 4222. The concentrator 4204 and the second small cell (SC2) 4206 may be connected by an interface 4223. The concentrator 4204 and the third small cell (SC3) 4207 may be connected by an interface 4224.

[0416] The first small cell (SC1) 4205 and the second small cell (SC2) 4206 are connected by an interface 4225, for example, an X2 interface. The second small cell (SC2) 4206 and the third small cell (SC2) 4207 are connected by an interface 4226, for example, an X2 interface. The first small cell (SC1) 4205 and the third small cell (SC3) 4207 are connected by an interface 4227, for example, an X2 interface.

[0417] The UE 4208 and the first small cell (SC1) 4205 are connected by an interface 4228, for example, a Uu interface which is an air interface. The UE 4208 and the second small cell (SC2) 4206 are connected by an interface 4229, for example, a Uu interface which is an air interface. The UE 4208 and the third small cell (SC3) 4207 are connected by an interface 4230, for example, a Uu interface which is an air interface.

[0418] The interfaces 4219 to 4221 and the interfaces 4222 to 4224 may be the same interface. For example, a new function may be added to the X2 interface, or a new interface may be used. By using the same interface, it is possible to simplify the control between the concentrator 4204 and each of the small cells 4205 to 4207.

[0419] A case where each of the small cells 4205 to 4207 is operated in the virtual macro cell mode will be described with reference to FIG.

[0420] In Fig. 22, a virtual macro cell is formed by each of the small cells 4205 to 4207, which are indicated by hatching, and the concentrator 4204. Each of the small cells 4205 to 4207 forms one SCG. The SCG is provided with a concentrator 4204, which is connected to each of the small cells 4205 to 4207 in the SCG using interfaces 4222 to 4224. The small cells in the SCG are controlled by the concentrator 4204 so that they all operate in the same way.

[0421] 22, a virtual macro cell is configured by connecting the interfaces indicated by the bold lines. The operations between the P-GW 4201 and the S-GW 4202 and between the MME 4203 and the S-GW 4202 are the same as those in a conventional macro cell.

[0422] In the virtual macro cell mode, the small cells in the SCG and the MME 4203 are connected via a concentrator 4204. In addition, the small cells in the SCG and the S-GW 4202 are connected via the concentrator 4204.

[0423] The concentrator 4204 may have, among other functions when a small cell in an SCG operates as a virtual macro cell, an upper layer section in particular. This eliminates the need for each small cell to connect to the MME 4203 and S-GW 4202, and allows the concentrator 4204 to connect to the MME 4203 and S-GW 4202.

[0424] In the virtual macro cell mode, each of the small cells 4205 to 4207 in the SCG communicates with the UE 4208. By configuring the architecture shown in Fig. 22, a virtual macro cell using multiple small cells is configured. This makes it possible to configure a virtual macro cell for UEs served by multiple small cells.

[0425] A case where small cells 4205 to 4207 are operated in the dedicated cell mode will be described using Figure 23. Figure 23 is a diagram showing an example of the architecture of a communication system when operating in the dedicated cell mode. Since Figure 23 is similar to Figure 22, the same parts are given the same reference numerals and their description will be omitted. Figure 23 shows a case where the second small cell (SC2) 4206 is operated in the dedicated cell mode.

[0426] The following describes a case where the second small cell (SC2) 4206 is operated in dedicated cell mode. In Fig. 23, the second small cell (SC2) 4206, shown hatched, operates as a dedicated cell. In Fig. 23, a dedicated cell is configured by being connected by an interface indicated by a thick line. Operation between the P-GW 4201 and S-GW 4202, and between the MME 4203 and S-GW 4202 is the same as in conventional macro cell operation.

[0427] The MME 4203 is directly connected to the second small cell (SC2) 4206, and the S-GW 4202 is directly connected to the second small cell (SC2) 4206. When the small cells operate in the dedicated cell mode, the small cells have the functions of conventional cells. Therefore, each of the small cells 4205 to 4207 is directly connected to the MME 4203 and the S-GW 4202. In the dedicated cell mode, communication is performed between the second small cell (SC2) 4206 and the UE 4208.

[0428] By configuring the architecture shown in FIG. 23, it becomes possible to operate small cells in the dedicated cell mode.

[0429] By using the communication system architecture shown in Figures 22 and 23 to enable small cells to operate in both virtual macro cell mode and dedicated cell mode, an overlay structure of virtual macro cells and small cells is made possible.

[0430] Therefore, it becomes possible to achieve dual connectivity using small cells within the SCG. Conventionally, inter-node radio resource aggregation was not possible using only small cells, but by using the method disclosed in this embodiment, it becomes possible to perform this using only small cells.

[0431] Figure 24 is a diagram showing another example of the architecture of a communication system when operating in both virtual macro cell mode and dedicated cell mode. Figure 24 is similar to Figure 22, so the same parts are given the same reference numerals and their descriptions will be omitted. In Figure 24, unlike Figures 22 and 23, there is no interface from the MME 4203 or S-GW 4202 to the small cells 4205 to 4207 in the SCG, and the small cells 4205 to 4207 in the SCG are connected to the MME 4203 and S-GW 4202 via a concentrator 4204.

[0432] When operated in virtual macro cell mode, the explanation will be omitted as it is the same as Fig. 22. As an example of operation in dedicated cell mode, the case where the second small cell (SC2) 4206 operates as a dedicated cell will be explained.

[0433] 24, an individual cell is configured by connecting interfaces 4209, 4210, 4211, 4215, 4220, and 4401 indicated by thick lines. The same operation as that of a conventional macro cell is performed between the P-GW 4201 and S-GW 4202 and between the MME 4203 and S-GW 4202. The concentrator 4204 may have a routing function as a function for the individual cell mode.

[0434] The second small cell (SC2) 4206 and the MME 4203 are connected via a concentrator 4204. In the downlink, the concentrator 4204 performs routing from the MME 4203 to the small cell connected to the UE 4208 that is the communication target. In the downlink, the concentrator 4204 selects the small cell connected to the UE 4208 and transfers signaling to that small cell. In the uplink, the concentrator 4204 transfers signaling from the small cell connected to the UE 4208 to the MME 4203. The concentrator 4204 may also select the MME 4203.

[0435] At least one of a destination small cell identifier, a UE identifier, and an MME identifier may be attached to or included in these signalings so that the signaling can be recognized by the concentrator 4204. This enables routing in the concentrator 4204.

[0436] Similarly, the second small cell (SC2) 4206 and the S-GW 4202 are connected via a concentrator 4204. In the downlink, the concentrator 4204 performs routing from the S-GW 4202 to the small cell connected to the UE 4208 that is the communication target. In the downlink, the concentrator 4204 selects the small cell connected to the UE 4208 and transfers data to that small cell. In the uplink, the concentrator 4204 transfers data from the small cell connected to the UE 4208 to the S-GW 4202. The concentrator 4204 may also select the S-GW 4202.

[0437] At least one of a destination small cell identifier, a UE identifier, and an MME identifier may be attached to this data so that it can be recognized by the concentrator 4204. This enables routing in the concentrator 4204.

[0438] Of the interfaces between the concentrator 4204 and each of the small cells 4205-4207, the interfaces 4219-4221 used for operation in the dedicated cell mode may be configured as a non-ideal backhaul with high latency, and the interfaces 4222-4224 used for operation in the virtual macro cell mode may be configured as an ideal backhaul with low latency or negligible latency. This makes it possible to eliminate the impact of control delays between the concentrator 4204 and each of the small cells 4205-4207 in operation in the virtual macro cell mode on the operation.

[0439] 24, it is possible to eliminate the need for interfaces that directly connect each small cell in the SCG to the MME 4203 and S-GW 4202. This eliminates the need to lay actual physical interfaces, making it possible to reduce the cost of building a communication system.

[0440] 25 to 27 are diagrams showing an example of a sequence of an HO process in the communication system according to the first embodiment. Fig. 25 and Fig. 26 are connected at the position of boundary line BL1. Fig. 26 and Fig. 27 are connected at the position of boundary line BL2.

[0441] A virtual macrocell is formed by the small cells in SCG#A. The virtual macrocell formed by the small cells in SCG#A is controlled by concentrator #A. A virtual macrocell is formed by the small cells in SCG#B. The virtual macrocell formed by the small cells in SCG#B is controlled by concentrator #B.

[0442] The small cells in SCG#A operate in both virtual macro cell mode and dedicated cell mode, and the small cells in SCG#B operate in both virtual macro cell mode and dedicated cell mode.

[0443] In step ST4501, a UE in RRC_Idle state under SCG#A performs service request processing (Service Request Procedure) between concentrator#A, MME and S-GW via a small cell in SCG#A operating in virtual macro cell mode in step ST4503.

[0444] At this time, in Step ST4502, the UE first performs an RRC connection establishment procedure to establish an RRC connection with the concentrator #A via a small cell in the SCG #A operating in the virtual macro cell mode.

[0445] In Step ST4504, the UE transitions to an RRC connected (RRC_Connected) state.

[0446] In Step ST4505, data transmission is performed between the UE, the small cell in the SCG#A operating in the virtual macro cell mode, the concentrator#A, and the S-GW.

[0447] As a result, signaling is performed between the concentrator #A and the MME via the UE and a small cell in the SCG #A operating in virtual macro cell mode. Data is performed between the concentrator #A and the S-GW via the UE and a small cell in the SCG #A operating in virtual macro cell mode. This is called communication using a virtual macro cell.

[0448] Next, a method of performing dual connectivity will be described. In Step ST4506, the concentrator #A determines a second cell to connect to the UE, specifically, an eNB constituting the second cell (hereinafter, may be referred to as a "second eNB"), in order to provide dual connectivity for the UE. The cell to perform dual connectivity may be selected from small cells in the SCG constituting the virtual macro cell to which the UE is connected. Here, the second cell may be selected from small cells in the SCG #A. The second cell may be a small cell that can be operated in a dedicated cell mode.

[0449] In Step ST4507, the concentrator #A notifies the UE, via a small cell in the SCG #A operating in virtual macro cell mode, of the configuration of the second cell (Secondary eNB) determined in Step ST4506 (Secondary eNB configuration) and of the addition of the second cell (Secondary eNB) as a radio resource.

[0450] This notification may be made using RRC signaling. For example, it may be made using RRC connection reconfiguration. It may also be made as a reconfiguration of radio resources. This notification includes the cell identifier of the small cell operated in the dedicated cell mode as the second cell. The cell identifier may be PCI, EGCI, GCI, or the like.

[0451] In Step ST4508, the UE that has received the notification of the addition of the second cell adds the second cell (secondary eNB) as radio resources by using the received configuration of the second cell.

[0452] In Step ST4509, the UE performs detection and synchronization processing of the small cell that is added as the second cell and operates in the dedicated cell mode. The notified cell identifier may be used for the detection and synchronization processing.

[0453] On the other hand, in Step ST4510, the concentrator #A performs signaling to the second cell to notify it of the addition of the second cell (Secondary eNB) using the second cell (Secondary eNB configuration). As a result, the concentrator #A notifies the second cell that the second cell has been added as a radio resource for the UE, and requests it to perform scheduling for the UE. The concentrator #A includes the identifier of the UE in this notification.

[0454] By doing this, in Step ST4511, data transmission is performed between the UE and one small cell in SCG#A that is added as the second cell and operates in the dedicated cell mode.

[0455] Therefore, the UE will be connected to both a small cell in SCG#A operating in virtual macro cell mode and one small cell in SCG#A operating in dedicated cell mode.

[0456] Next, the HO method will be described. In Step ST4512, concentrator #A notifies the measurement configuration. When notifying the measurement configuration, the concentrator #A may notify the cell identifier of the adjacent SCG when it is operated as a virtual macro cell, along with the measurement frequency. Alternatively, the concentrator #A may notify the cell identifier of the macro cell on the same frequency layer.

[0457] This enables HO with a virtual macro cell or a macro cell as the target cell. That is, HO between macro cells including a virtual macro cell is enabled. Also, since measurements of small cells operated in dedicated cell mode can be avoided, the measurement time of the UE and power consumption of the UE can be reduced.

[0458] Here, for example, the UE notifies the cell identifier of one of the small cells in SCG#B that is operated as a virtual macro cell. The UE performs measurements using the measurement configuration notified in Step ST4512.

[0459] When a predetermined event condition notified in the measurement configuration is satisfied, the UE transmits a measurement report to the concentrator #A in Step ST4513. For example, this is the case when the received power or the received quality of the virtual macro cell configured by SCG#A falls below a predetermined threshold for a predetermined period, and the received power or the received quality of the virtual macro cell configured by SCG#B exceeds the predetermined threshold for a predetermined period.

[0460] The UE notifies the concentrator #A via a small cell in the SCG #A. This notification may include the measurement results of the reception quality or reception power and the cell identifier of the virtual macro cell where the measurement was performed. The concentrator #A uses the measurement report to decide whether to perform HO.

[0461] In Step ST4514, concentrator #A, which has decided to perform HO, performs a process to terminate providing dual connectivity to the UE.

[0462] In Step ST4515, the concentrator #A notifies the UE via the small cell in the SCG #A operating in virtual macro cell mode that it will delete the radio resources of the cell providing dual connectivity.

[0463] This notification may be made using RRC signaling. For example, it may be made using RRC connection reconfiguration. It may also be made as a reconfiguration of radio resources. This notification includes the cell identifier of the small cell operated in the dedicated cell mode to be deleted. The cell identifier may be PCI, EGCI, GCI, or the like.

[0464] On the other hand, in Step ST4517, concentrator #A notifies the cell to be deleted that the cell has been deleted as a radio resource from the UE, and requests it to terminate scheduling for the UE. This notification includes the identifier of the UE.

[0465] In Step ST4516, the UE, which has received the notification that the radio resources of the cell will be deleted, performs a process of deleting the cell with which dual connectivity is being established.

[0466] This ends data transmission between the UE and one small cell in SCG#A that is operating in the dedicated cell mode and is the cell to be deleted.

[0467] Therefore, the UE returns to connecting only with small cells in SCG#A operating in virtual macro cell mode.

[0468] Concentrator #A, which has decided to perform HO in Step ST4514, notifies concentrator #B, which controls the small cell in SCG #B operating in the virtual macro cell mode and which has been decided as the HO destination, of an HO request message in Step ST4518. This notification may include the cell identifier of its own virtual macro cell and the identifier of the UE to be HO-targeted.

[0469] The concentrator #B permits admission of the UE, and in Step ST4519, notifies the concentrator #A of a response to the HO request message (HO request ack). This response includes the configuration of radio resources when the small cells in the SCG #B operate in virtual macro cell mode. A handover command may also be included.

[0470] In Step ST4520, the concentrator #A notifies the UE to be the HO target of mobility control information via a small cell in SCG #A operating in virtual macro cell mode, and issues an HO command. In the notification, the concentrator #A notifies the UE of the cell identifier of one of the small cells in SCG #B operating in virtual macro cell mode as the HO target, and the configuration of its radio resources.

[0471] The UE that has received the mobility control information in Step ST4520 performs HO in Step ST4521. In Step ST4523, the UE performs detection and synchronization processing using the information of the small cell in SCG#B that is operating in the virtual macro cell mode and that is the HO destination and that has been received in Step ST4520.

[0472] In step ST4524 of FIG. 27, the UE that has performed the synchronization process notifies the concentrator #B of the completion of the RRC connection reconfiguration (RRC connection reconfiguration complete) via the small cell in SCG #B operating in virtual macro cell mode.

[0473] In Step ST4525, the concentrator #B, which has received the notification from the UE in Step ST4524, performs a path switch process between the MME and the S-GW. The data path is changed from the concentrator #A to the concentrator #B. As a result, in Step ST4527, data transmission is performed between the concentrator #B and the S-GW via the UE and the small cell in the SCG #B operating in the virtual macro cell mode.

[0474] Furthermore, in Step ST4526, concentrator #B notifies concentrator #A of a UE context release message for the UE that is the target of HO. This allows the concentrator #A to release the radio resource configuration that it has held for the UE that is the target of HO. This makes it possible for other UEs to use the radio resources.

[0475] The concentrator #A may notify the small cells in the SCG #A of the notification. If the small cells in the SCG #A hold the radio resource configuration, the notification makes it possible to release the radio resources of the small cells in the SCG #A. In this way, the HO process is completed.

[0476] Next, a method will be described in which a UE connected to concentrator #B via a small cell in SCG #B operating in virtual macro cell mode performs dual connectivity again.

[0477] In Step ST4528, the concentrator #B determines a second cell (secondary eNB) to provide dual connectivity to the UE. The second cell may be selected from small cells in the SCG #B. The second cell may be a small cell operated in the dedicated cell mode.

[0478] In step ST4529, concentrator #B notifies the UE, via a small cell in SCG #B operating in virtual macro cell mode, of the addition of the second cell as a radio resource, along with the configuration of the second cell (Secondary eNB configuration) determined in step ST4528.

[0479] This notification may be made using RRC signaling. For example, it may be made using RRC connection reconfiguration. It may also be made as a reconfiguration of radio resources. This notification includes the cell identifier of the small cell operated in the dedicated cell mode as the second cell. The cell identifier may be PCI, EGCI, GCI, or the like.

[0480] In Step ST4530, the UE that has received the addition of the second cell in Step ST4529 adds radio resources by using the received configuration of the second cell.

[0481] In Step ST4531, the UE detects the small cell that has been added as the second cell and operates in the dedicated cell mode, and performs synchronization processing. The UE may use the notified cell identifier for the detection and synchronization processing.

[0482] On the other hand, in Step ST4532, concentrator #B notifies the second cell that the second cell has been added as a radio resource for the UE, and requests the second cell to perform scheduling for the UE. The concentrator #B includes the identifier of the UE in this notification.

[0483] As a result, in Step ST4533, data transmission is performed between the UE and one small cell in SCG#B that is added as a second cell and operates in the dedicated cell mode.

[0484] Therefore, the UE will be connected to both a small cell in SCG#B operating in virtual macro cell mode and one small cell in SCG#B operating in dedicated cell mode.

[0485] 25 to 27, dual connectivity can be achieved between small cells in an SCG that operate in virtual macro cell mode and small cells in an SCG that operate in dedicated cell mode. By operating a large number of small cells, it is possible to achieve improved user throughput.

[0486] Furthermore, by performing HO between SCGs operating in virtual macro cell mode, it is possible to reduce HO failures caused by the short residence time of UEs in each small cell, even when multiple small cells are operated, thereby improving the mobility performance of UEs.

[0487] By combining these, it is possible to improve both user throughput and mobility performance even when operating a large number of small cells.

[0488] Furthermore, by removing the second cell that is performing dual connectivity before HO is performed, the radio resources of the second cell can be allocated to other UEs. This makes it possible to improve the efficiency of radio resource usage and increase the capacity of the communication system.

[0489] Furthermore, by performing dual connectivity using a small cell belonging to the SCG of the HO destination after HO execution, it is possible to reduce connection failures with the dual connectivity cell after HO execution. Therefore, since there is no need to reconnect after a connection failure, it is possible to reduce control delays. In addition, it is possible to reduce the amount of signaling and improve throughput.

[0490] The method disclosed in this embodiment makes it possible to configure a virtual macro cell using multiple small cells. Furthermore, by using multiple small cells to operate in both virtual macro mode and dedicated cell mode, an overlay structure is possible. This makes it possible for a small cell alone to provide dual connectivity to UEs served by multiple small cells.

[0491] Therefore, it is possible to maintain the mobility anchor using the virtual macro cell, and it is possible to reduce the degradation of mobility performance between small cells.

[0492] In addition, high-capacity data communication with UEs can be performed in small cell only mode, which can improve the throughput for each UE.

[0493] Furthermore, since there is no need to install new macrocells that overlay small cells, it is possible to significantly reduce the costs of operating the communication system.

[0494] Second embodiment, variant 1 The problem to be solved by the first modification of the second embodiment will be described below. The above-mentioned Fig. 20 shows the concept of a small cell group (SCG) disclosed in the second embodiment. Small cells in an SCG that configure a virtual macro cell can configure a wider coverage area than small cells.

[0495] However, at an SCG edge where two SCGs are adjacent, a small cell in one SCG is adjacent to a small cell in another SCG, for example, small cell 4111 in SCG 4105 and small cell 4122 in SCG 4106. Ultimately, small cells are adjacent to each other at the SCG edge.

[0496] Small cells have lower transmission power than macro cells, so there are cases where the signal power at the edge of an adjacent small cell is lower than the signal power at the edge of the adjacent macro cell.

[0497] In this case, at the edge of the small cell, the distance that signal power reaches into adjacent small cells becomes shorter. That is, the coverage overlap area at the edge of the small cell becomes smaller. In other words, at the edge of the SCG, the coverage overlap area becomes smaller than at the edge of a normal macro cell.

[0498] FIG. 28 is a diagram illustrating the concept of an overlap area at an SCG edge when small cells are arranged at the SCG edge without overlapping.

[0499] In Figure 28(a), the small cells of SCG#A are indicated by reference symbols "5001" and "5002." Small cells 5001 and 5002 form coverage areas 5003 and 5004. The small cells of SCG#A are indicated by solid lines. Furthermore, the small cells of SCG#B are indicated by reference symbols "5005" and "5006." Small cells 5005 and 5006 form coverage areas 5007 and 5008. The small cells of SCG#B are indicated by dashed lines.

[0500] In Figure 28(b), the received power from small cell 5001 is indicated by reference symbol "5009." The horizontal axis of Figure 28(b) represents position, and the vertical axis represents received power (RSRP). The received power decreases as the distance from the position of small cell 5001 increases. The received power from the small cell of SCG#A is indicated by a solid line.

[0501] In Figure 28(b), the received power from small cell 5005 is indicated by reference symbol "5010." The received power decreases with increasing distance from the position of small cell 5005. The received power from the small cell of SCG#B is indicated by a dashed line.

[0502] In Figure 28(b), the predetermined reception power at which the UE can receive a signal is indicated by reference symbol "5011." The predetermined reception power at which the UE can receive a signal may be the reception sensitivity point of the UE. The UE can receive a signal when the reception power is greater than the predetermined reception power 5011.

[0503] Therefore, in Figure 28(b), in the range where both the received power 5009 from small cell 5001 and the received power 5010 from small cell 5005 are greater than the specified received power 5011, the UE can receive from both small cell 5001 and small cell 5005, and this range becomes the overlap area (OA).

[0504] In this way, the overlap area at the SCG edge becomes narrower, just like the overlap area at the small cell edge. Therefore, the residence time in the overlap area when the UE moves becomes shorter, and there are cases where there is not enough time to perform HO-related processing. When mobility is performed in virtual macro cell mode, mobility performance between SCGs, i.e., between virtual macro cells, deteriorates. The purpose of this modification is to solve these problems.

[0505] The placement of small cells in multiple SCGs is overlapped. At the edge of an SCG, the placement of small cells in adjacent SCGs is overlapped.

[0506] By doing so, it is possible to widen the area where the signal power at the SCG edge is greater than a predetermined power, and it is possible to ensure the communication quality of both adjacent SCGs in the overlap area. It is recommended to operate the virtual macro cell mode with such an SCG.

[0507] FIG. 29 is a diagram illustrating the concept of an overlap area at an SCG edge when small cells are arranged at the SCG edge in an overlapping manner.

[0508] In Figure 29(a), small cells of SCG#A are indicated by reference symbol "5101." Coverage 5103 is formed by small cells 5101. Small cells of SCG#A are indicated by solid lines. Small cells of SCG#B are indicated by reference symbol "5102." Coverage 5104 is formed by small cells 5102. Small cells of SCG#B are indicated by dashed lines.

[0509] In Figure 29(b), the received power from small cell 5101 is indicated by reference symbol "5105." The horizontal axis of Figure 29(b) represents position, and the vertical axis represents received power (RSRP). The received power decreases as the distance from the position of small cell 5101 increases. The received power from the small cell of SCG#A is indicated by a solid line.

[0510] In Figure 29(b), the received power from small cell 5102 is indicated by reference symbol "5106." The received power decreases as the distance from the position of small cell 5102 increases. The received power from the small cell of SCG#B is indicated by a dashed line.

[0511] In Figure 29(b), the predetermined reception power at which the UE can receive a signal is indicated by reference symbol "5107." The predetermined reception power at which the UE can receive a signal may be the reception sensitivity point of the UE. The UE can receive a signal when the reception power is greater than the predetermined reception power 5107.

[0512] Therefore, in Figure 29(b), in the range where both the received power from the small cells of SCG#A, including the received power 5105 from small cell 5101, and the received power from the small cells of SCG#B, including the received power 5106 from small cell 5102, are greater than the specified received power 5107, the UE can receive from both the small cells of SCG#A and the small cells of SCG#B, and this range becomes the overlap area (OA).

[0513] As shown in Figure 29, by overlapping the placement of small cells of adjacent SCGs at the SCG edge, it is possible to increase the distance that signal power reaches within the coverage of a virtual macro cell formed by adjacent SCGs. Therefore, it is possible to widen the overlap area of ​​adjacent SCGs. This makes it possible to maintain a long residence time in the overlap area when a UE moves, making it possible to secure sufficient time for performing HO-related processing.

[0514] In addition, it is possible to reduce the failure of HO between SCGs when operating in virtual macro cell mode, and improve mobility performance when a UE moves between small cells.

[0515] Another method for solving the problem shown in this modification is disclosed below. The transmission power of each small cell in the SCG may be configured to be different. It is advisable to increase the transmission power of small cells located at the edge of the SCG.

[0516] For example, it is advisable to adjust the transmission power of the small cells at the SCG edge so that the signal power at the SCG edge is approximately the same as the signal power at a normal macro cell edge.

[0517] By doing so, it is possible to enlarge the overlap area of ​​coverage in multiple adjacent small cells with increased transmission power. In other words, at the SCG edge where the small cell is located, it is possible to obtain signal power equivalent to or greater than that of a normal macro cell edge. Therefore, it is possible to widen the overlap area, which is the region up to the terminal's receiving sensitivity or a predetermined receiving power.

[0518] By operating the virtual macro cell mode in such an SCG, it is possible to reduce the failure of HO between SCGs when operating in virtual macro cell mode, and to improve mobility performance when a UE moves between small cells.

[0519] In adjacent SCGs, the transmission power of each small cell in one SCG may be configured to be different. The transmission power of the small cells located at the edge of one SCG may be increased. The density of small cells located at the edge of the SCG will differ for each SCG, but the overlap area of ​​adjacent SCGs will be wider. Therefore, the same effect as the above method can be obtained.

[0520] Second embodiment, modified example 2 As other methods for solving the problem described in the first modification of the second embodiment, the following three methods (1) to (3) are disclosed.

[0521] (1) Increase the transmission power of the signaling of the UE that is the target of HO. (2) Set the MCS (Modulation and Coding Scheme) of the signaling of the UE to be HO-targeted to a low value. (3) A combination of (1) and (2) above.

[0522] In the method (1), the signaling of the HO target UE may be signaling for a predetermined period of time.Also, the signaling for a predetermined period of time may be a period during which some or all of the HO-related processing is being performed between the HO target UE and / or the HO source cell and the HO target cell.

[0523] This allows the HO target UE to increase the transmission power of some or all of the signaling related to the HO-related process, which enables the HO target UE to receive signaling related to the HO-related process at a point farther away from the HO-source cell or the HO-target cell during the HO-related process.

[0524] Furthermore, for the HO target UE, the coverage between the HO source cell and the HO target cell appears to increase, and the overlap area expands. This allows the UE to stay in the overlap area longer during movement, ensuring sufficient time for HO-related processing.

[0525] Signaling related to HO-related processing includes signaling for measurement configuration, signaling for measurement report, RRC connection reconfiguration including mobility control information, RRC connection reconfiguration complete, etc. Signaling for transmitting scheduling information for the signaling may also be included. Signaling for responses (Ack / Nack) to these signaling may also be included.

[0526] In particular, the transmission power of the RRC connection reconfiguration signaling including mobility control information may be increased because this signaling is often the last process performed between the HO source cell and the UE in the HO-related process.

[0527] By increasing the transmission power of this signaling, the coverage of the HO source cell can be increased in appearance, the reception quality of mobility control information can be improved, and the failure of HO-related processing can be reduced.

[0528] By applying the above-mentioned method to inter-SCG HO in virtual macro cell mode operation, it is possible to reduce the failure of inter-SCG HO. At least one of the concentrators of the SCG of the HO source and the HO target increases the transmission power of signaling related to HO-related processing for the HO target UE.

[0529] Figures 30 and 31 are diagrams showing an example of a sequence of a communication system in Modification 2 of Embodiment 2. Figures 30 and 31 show an example of a sequence of the method (1) above. Figures 30 and 31 are connected at the position of boundary line BL3.

[0530] In Step ST5201, the UE is in an RRC connected (RRC_Connected) state with the virtual macro cell configured by the HO source SCG.

[0531] In Step ST5202, the concentrator of the HO source SCG performs a Radio Link Monitor (RLM) process to monitor the communication quality with the UE.

[0532] In Step ST5203, if the communication quality has deteriorated by falling below a predetermined value for a predetermined period of time, the concentrator of the HO source SCG judges whether or not to start HO-related processing with the UE. If it is judged in Step ST5203 that HO-related processing should be started, it proceeds to Step ST5204, and if it is judged not to start HO-related processing, it returns to the RLM processing of Step ST5202.

[0533] In Step ST5204, the concentrator of the HO-source SCG decides to increase the transmission power of signaling for the HO-target UE. The concentrator decides to increase the transmission power by a predetermined amount. The predetermined amount may be statically determined in advance or dynamically determined depending on the situation. In the examples shown in FIGS. 30 and 31, the concentrator decides to increase the transmission power by A decibels [dB].

[0534] The concentrator of the HO-source SCG increases the transmission power of signaling for HO-related processing to the HO-target UE by A decibels [dB] from now on. It may also increase the transmission power of signaling for HO-related processing from the HO-target UE by A decibels [dB].

[0535] To increase the transmission power of the signaling for the HO-related process from the HO target UE, the uplink (UL) scheduling information for the signaling may include information instructing an increase in transmission power. For example, information indicating the amount of transmission power increase may be included in the uplink control information (UCI). In this example, the information indicating the amount of transmission power increase is set to A decibels (dB).

[0536] A UE that receives UL scheduling information including information instructing an increase in transmission power increases transmission power by A decibels [dB] and transmits uplink signaling.

[0537] In the examples shown in Figures 30 and 31, the signaling for HO-related processing includes signaling to notify a measurement configuration message in step ST5205, signaling for uplink (UL) scheduling for measurement reporting in step ST5207, signaling for a measurement report in step ST5208, and signaling to notify a mobility control information message in step ST5214.

[0538] The concentrator of the HO source SCG, which has received the measurement report from the HO target UE in Step ST5208, decides to perform HO for the UE in Step ST5209.

[0539] After determining HO in Step ST5209, the concentrator of the HO-source SCG notifies the concentrator of the HO-target SCG of an HO request message in Step ST5210. At this time, the concentrator may notify a request to increase transmission power.

[0540] In step ST5211, the concentrator of the HO-destination SCG that has received the HO request message decides to accept the HO.

[0541] The concentrator of the HO-target SCG that has decided to accept HO in Step ST5211 decides to increase the transmission power of signaling for the UE that is the target of HO in Step ST5212 of FIG. 31. The concentrator decides to increase the transmission power by a predetermined amount. The predetermined amount may be statically determined in advance or may be dynamically determined depending on the situation. In the examples shown in FIGS. 30 and 31, the concentrator decides to increase the transmission power by B decibels [dB].

[0542] The concentrator of the HO-target SCG increases the transmission power of signaling for HO-related processing to the HO-target UE by B decibels [dB] from now on. It may also increase the transmission power of signaling for HO-related processing from the HO-target UE by B decibels [dB].

[0543] The method of increasing the transmission power of signaling for HO-related processing from the HO-targeted UE by B decibels [dB] can be a method of increasing the transmission power of signaling from the HO-targeted UE to the concentrator of the HO-source SCG.

[0544] The signaling of the HO-related process to increase the transmission power continues until the concentrator of the HO-target SCG receives an RRC connection reconfiguration complete via a small cell in the HO-target SCG, or until the UE recognizes that it has correctly received the RRC connection reconfiguration complete.

[0545] In the examples shown in FIGS. 30 and 31, the signaling for the HO-related process includes UL scheduling in Step ST5216 and signaling for RRC connection reconfiguration complete in Step ST5217.

[0546] In step ST5213, the concentrator of the HO-destination SCG that has decided to accept the HO notifies the concentrator of the HO-source SCG of an HO request acknowledgment (HO request ack).

[0547] In Step ST5214, the concentrator of the HO source SCG notifies the HO target UE of mobility control information via a small cell in the HO source SCG.

[0548] In Step ST5215, the UE performs a process of detecting and synchronizing with small cells in the HO-target SCG.

[0549] In Step ST5216, the concentrator of the HO-target SCG transmits UL scheduling to the UE via the small cell in the HO-target SCG.

[0550] In step ST5217, the UE that has received the UL scheduling uses the scheduling information to notify the concentrator of the HO-target SCG via a small cell in the HO-target SCG of an RRC connection reconfiguration complete message indicating that the RRC connection with the concentrator has been completed.

[0551] In Step ST5218, the concentrator of the HO-target SCG performs HO completion processing with the MME and the concentrator of the HO-source SCG, such as a path switch.

[0552] Upon completing the HO completion process in Step ST5218, the concentrator of the HO-target SCG and the concentrator of the HO-source SCG stop increasing the transmission power of signaling for the HO-target UE in Steps ST5219 and ST5220.

[0553] In this way, the concentrator of the HO source SCG and the concentrator of the HO target SCG control the HO target UE to increase the transmission power of signaling between the UE and small cells in the HO source SCG or small cells in the HO target SCG from the start of HO-related processing to the HO completion processing, thereby increasing the transmission power of signaling related to HO-related processing for the HO target UE, thereby reducing the number of HO failures between SCGs.

[0554] The protocol that decides HO in the concentrator of the HO source SCG is RRC. In fact, it is the lower layer protocol, such as the PHY or PHY / MAC protocol, that increases the transmission power. Therefore, the PHY or PHY / MAC protocol needs to know which UEs should increase their transmission power and by how much.

[0555] For these reasons, RRC should notify PHY or PHY / MAC of the HO target UE's identifier for identifying the HO target UE along with the increase in transmission power of the HO target UE, which allows the PHY or PHY / MAC protocol to identify the increase in transmission power and the HO target UE for which the transmission power is to be increased.

[0556] Therefore, in the PHY protocol, it becomes possible to increase the transmission power of physical channels used for signaling of HO-related processes of HO-targeted UEs, such as PDSCH, PDCCH, PUSCH, and PUCCH.

[0557] The RRC notifies the PHY or PHY / MAC of a transmission power increase request for the HO-target UE when it starts HO-related processing for the HO-target UE, i.e., when it has performed the processing of step ST5204 in Figures 30 and 31, or when it has decided to accept HO for the HO-target UE, i.e., when it has performed the processing of step ST5212 in Figures 30 and 31. The notification may include an identifier of the HO-target UE for identifying the HO-target UE and the amount of transmission power increase. The PHY / MAC that has received the notification increases the transmission power of the signaling for the HO-target UE.

[0558] Furthermore, when the HO completion process for the HO target UE is performed, that is, when the processes of steps ST5219 and ST5220 are performed in Figures 30 and 31, the RRC notifies the PHY or PHY / MAC of a request to stop increasing the transmission power of the HO target UE. This notification may include an identifier of the HO target UE for identifying the HO target UE. The PHY / MAC that receives this notification stops increasing the transmission power of the signaling of the HO target UE.

[0559] By doing this, even if the PHY / MAC cannot recognize that the signaling is related to the HO-related process, the PHY / MAC can increase the transmission power of the signaling for the HO-related process of the UE that is the HO target. These methods can also be applied to the UE.

[0560] Fig. 32 is a diagram showing another example of the sequence of a communication system in Modification 2 of Embodiment 2. Fig. 32 shows another example of the sequence of the method (1) above. Since Fig. 32 is similar to Fig. 30 and Fig. 31 described above, the same step numbers are assigned to the steps corresponding to Fig. 30 and Fig. 31, and common explanations will be omitted. Fig. 32 shows a case where the signaling for the HO-related process to increase transmission power is a mobility control information message that is notified by the concentrator of the HO-source SCG from the small cells in the HO-source SCG to the UE that is the HO target.

[0561] In Step ST5301, the concentrator of the HO source SCG notifies the UE of a measurement configuration message.

[0562] In Step ST5302, the concentrator of the HO source SCG notifies the UE of UL scheduling. In Step ST5303, the UE notifies the concentrator of the HO source SCG of a measurement report message.

[0563] In Step ST5209, the concentrator of the HO source SCG that has received the measurement report message from the UE in Step ST5303 decides to perform HO for the UE.

[0564] After deciding to perform HO in Step ST5209, the concentrator of the HO-source SCG decides to increase the transmission power of signaling for the HO-target UE in Step ST5304. In the example shown in FIG. 32, it decides to increase the transmission power by A decibel [dB]. The signaling related to the HO-related process for increasing the transmission power is RRC connection reconfiguration including mobility control information in Step ST5307. Signaling for transmitting scheduling information for this signaling may also be included. Signaling for responding (Ack / Nack) to this signaling may also be included.

[0565] After determining HO, the concentrator of the HO-source SCG notifies the concentrator of the HO-target SCG of an HO request message in Step ST53505, without notifying a request to increase transmission power.

[0566] The concentrator of the HO-destination SCG that has received the HO request message in Step ST5305 decides to accept HO in Step ST5211.

[0567] In step ST5306, the concentrator of the HO-destination SCG that has decided to accept the HO in step ST5211 notifies the concentrator of the HO-source SCG of an HO request acknowledgement (HO request ack) message.

[0568] In Step ST5307, the concentrator of the HO source SCG notifies the HO target UE of a mobility control information message via a small cell in the HO source SCG.

[0569] When the process of Step ST5207 ends normally, the concentrator of the HO source SCG stops increasing the transmission power of signaling for the HO target UE in Step ST5308.

[0570] After that, in Steps ST5215, ST5309, ST5310, and ST5218, the UE performs HO processing between the concentrator of the HO-target SCG and the MME via a small cell in the HO-target SCG.

[0571] In this way, the concentrator of the HO source SCG controls the transmission power of the mobility control information message, i.e., the HO command message, transmitted between the HO target UE and a small cell in the HO source SCG, so as to increase the transmission power of the mobility control information message signaling of the HO target UE, thereby making it possible to increase the transmission power of the mobility control information message signaling of the HO target UE, thereby reducing the number of HO failures between SCGs.

[0572] This also makes it possible to limit signaling that increases transmission power, thereby reducing power consumption of the UE or small cells in the HO source SCG.

[0573] It is also possible to reduce interference with other cells caused by increased transmission power of the HO-source or HO-target small cell or increased transmission power of the UE, thereby increasing the throughput of the communication system.

[0574] When RRC determines HO for the HO-target UE, it notifies the PHY or PHY / MAC of a transmission power increase request for the HO-target UE, which is the process of step ST5304 in FIG. 32. The notification may include an identifier of the HO-target UE for identifying the HO-target UE and the amount of transmission power increase. Upon receiving the notification, the PHY / MAC increases the transmission power of the signaling for the HO-target UE.

[0575] Furthermore, when the notification of the mobility control information message to the HO target UE has been successfully completed, that is, when the processing of step ST5308 has been completed in FIG. 32, the RRC notifies the PHY or PHY / MAC of a request to stop increasing the transmission power of the HO target UE. The notification may include an identifier of the HO target UE for identifying the HO target UE. Upon receiving the notification, the PHY / MAC stops increasing the transmission power of the signaling of the HO target UE.

[0576] By doing so, even if the PHY / MAC cannot recognize that the signaling is related to HO, it can increase the transmission power of the mobility control information message, i.e., the HO command message, of the UE to be HO-targeted. These methods can also be applied to the UE.

[0577] In the method (2), the signaling of the HO-target UE may be signaling for a predetermined period. Furthermore, the signaling for a predetermined period may be a period during which some or all of the HO-related processing is being performed between the HO-target UE, the HO-source cell, and the HO-target cell. This allows the MCS of some or all of the signaling related to the HO-related processing of the HO-target UE to be set low.

[0578] By using the method (2) above, the reception quality of signaling related to HO-related processing at the HO-target UE is improved. This allows the HO-target UE to receive signaling related to HO-related processing at a location farther away from the HO-source cell or HO-target cell during HO-related processing. Furthermore, for the HO-target UE, the coverage between the HO-source cell and the HO-target cell appears to increase, and the overlap area expands. This allows the UE to stay in the overlap area longer when moving, ensuring sufficient time for HO-related processing.

[0579] The signaling related to the HO-related process is the same as in the method (1) above. In particular, the MCS of the signaling of the RRC connection reconfiguration including the mobility control information may be set low. This increases the apparent coverage of the HO source cell, improves the reception quality of the mobility control information, and reduces the failure of the HO-related process.

[0580] By applying the above-mentioned method to inter-SCG HO in virtual macro cell mode operation, it is possible to reduce the failure of inter-SCG HO. At least one of the concentrators of the SCG of the HO source and the HO target SCG sets a low MCS for signaling related to HO-related processing for the HO target UE. A low MCS means at least one of a low-order modulation scheme and a low coding rate.

[0581] The sequence example of the method (2) shown in Figure 32 can be obtained by replacing "increasing transmission power" with "setting MCS low" in the sequence examples of the method (1) shown in Figures 30 and 31. As a method for setting MCS low, a low MCS may be statically set in advance. Alternatively, the MCS may be set low depending on the situation.

[0582] For example, the downlink signaling may be set to an MCS n ranks lower than the MCS setting notified by the CQI from the UE. Alternatively, the MCS may be set to an MCS n ranks lower than the MCS set using a conventional method. The n ranks may be statically determined in advance as an offset value, or may be dynamically determined as appropriate depending on the type of signaling or the communication quality situation. It is preferable that the SCG concentrator determines the n ranks.

[0583] Regarding uplink signaling from a UE targeted for HO, similar to the method (1) above, uplink scheduling information for uplink signaling may include information instructing a low MCS setting. For example, information indicating an MCS offset amount may be provided in the UCI. For example, n rank may be set for the information indicating the MCS offset amount. A UE that receives UL scheduling information including information instructing a low MCS setting transmits uplink signaling with the low MCS setting.

[0584] In this way, at least one of the concentrators of the HO source SCG and the HO target SCG controls the HO target UE to set a low MCS for signaling related to HO-related processing between the UE and small cells in the HO source SCG or small cells in the HO target SCG. This allows the HO target UE to set a low MCS for signaling related to HO-related processing. This makes it possible to reduce the failure of HO between SCGs.

[0585] In the above-mentioned methods (1) and (2), the increase in transmission power or the setting of a low MCS for uplink signaling from the HO target UE is notified to the HO target UE using uplink scheduling information for the uplink signaling. Other methods are disclosed below.

[0586] At least one of the concentrators of the HO-source SCG and the HO-target SCG uses RRC signaling to notify the UE to which the HO is to be performed of an instruction to increase the transmission power of uplink signaling or to set a lower MCS. By using RRC signaling, it is possible to more reliably notify the UE of an instruction to increase the transmission power or to set a lower MCS.

[0587] As the RRC signaling, a new message may be provided, a measurement configuration may be used, or a mobility control information message may be used.

[0588] For example, if a new message is provided, at least one of the concentrators of the HO-source SCG and the HO-target SCG notifies the HO-target UE of a transmission power increase instruction message or a low MCS setting instruction message when it starts HO-related processing, i.e., when it performs the processing of step ST5204 in the above-mentioned Figures 30 and 31, or when it decides to accept HO for the HO-target UE, i.e., when it performs the processing of step ST5212 in Figures 30 and 31. The notification may include an identifier of the HO-target UE for identifying the HO-target UE and the amount of transmission power increase or MCS reduction (offset amount). The HO-target UE that receives the notification increases the transmission power of uplink signaling.

[0589] Furthermore, at least one of the concentrators of the HO source SCG and the HO target SCG notifies the HO target UE of an instruction to stop increasing the transmission power or an instruction to set a low MCS when the HO completion process for the HO target UE is performed, that is, when the processes of steps ST5219 and ST5220 are performed in Figures 30 and 31. The notification may include an identifier of the HO target UE for identifying the HO target UE. The UE that receives the notification stops increasing the transmission power or setting a low MCS for uplink signaling.

[0590] Alternatively, a measurement configuration or mobility control information message may be used to instruct an increase in transmission power or a lower MCS for uplink signaling. It is recommended to add a parameter for the amount of increase in transmission power or the amount of MCS reduction (offset amount), or a parameter for requesting such setting, to an existing message. By using an existing message, it becomes possible to notify the information together with other information, thereby reducing the amount of signaling.

[0591] Conventionally, PDCCH is used to schedule signaling for HO-related processing of UEs targeted for HO. The PDCCH includes scheduling information for all UEs served by a cell. Therefore, when the above-mentioned method is applied to scheduling signaling for HO-related processing of UEs targeted for HO, the transmission power of the PDCCH for scheduling information for all UEs served by the SCG becomes large. In this case, the setting becomes unnecessary for other UEs served by the SCG.

[0592] To solve this problem, it is preferable to use EPDCCH for scheduling signaling for HO-related processing for HO-targeted UEs.

[0593] The EPDCCH is a physical control channel transmitted to the UE using the PDSCH region. An EPDCCH can be configured for the UE that is the target of HO and used to schedule signaling for HO-related processing. This can be achieved by increasing the transmission power of the EPDCCH or by setting a lower MCS.

[0594] This makes it possible to improve the reception quality of scheduling information for HO-related process signaling for HO-target UEs, and reduce the number of HO failures between SCGs.

[0595] Furthermore, when the communication quality of the scheduling of the HO-related processing signaling deteriorates, the EPDCCH may be switched to. By increasing the transmission power of the EPDCCH or setting a low MCS, it is possible to improve the reception quality of the scheduling information of the HO-related processing signaling for the HO-target UE, thereby reducing the number of HO failures between SCGs.

[0596] On the other hand, if the communication quality of the scheduling of the signaling for the HO-related process is good, the scheduling is performed using the PDCCH. In this case, since the communication quality is good, there is no need to increase the transmission power of the PDCCH or set a low MCS. By scheduling using the PDCCH, there is no need to provide an EPDCCH, and it is possible to reduce the physical resources required for setting the EPDCCH.

[0597] By switching to EPDCCH, it is possible to optimize the physical resources used in accordance with the radio wave environment that varies over time and space due to the movement of the UE, thereby improving the efficiency of physical resource usage.

[0598] The method disclosed in this modification can be applied not only to HO between SCGs during virtual macro cell mode operation, but also to HO between normal small cells. Even when applied to HO between normal small cells, it is possible to reduce HO failures between small cells, just like this modification.

[0599] Second embodiment, variant 3 When small cells in an SCG configure a virtual macrocell, each small cell in the SCG performs the same communication. Therefore, in the uplink, the UE performs uplink transmission as if each small cell were a single cell without recognizing each small cell. In other words, uplink transmission is performed to the virtual macrocell. In this case, the method of controlling the transmission power of the UE becomes an issue.

[0600] In conventional transmission power control methods, the transmission power of a UE is determined based on the uplink communication quality of one cell that communicates with the UE. However, in the case of a virtual macro cell, since the virtual macro cell is made up of multiple cells, there is a problem that the conventional method cannot be simply applied. The purpose of this modification is to solve this problem.

[0601] The following three methods (1) to (3) are disclosed as methods for controlling the transmission power of a UE when small cells in an SCG form a virtual macrocell and communicate with a UE being served by the SCG.

[0602] (1) Selecting and combining the received power or received quality from the UE in each small cell within the SCG. (2) Equivalently combine the received power or received quality from the UE in each small cell within the SCG. (3) Maximum ratio combining of the received power or received quality from the UE in each small cell within the SCG.

[0603] The transmission power of the UE is set based on the result of combining the received power or received quality using the above method (1), (2), or (3). A specific example of the received power is the signal to interference and noise power ratio (SINR). The combination of the received power or received quality and the setting of the transmission power based on the combination should be performed by the concentrator that controls the SCG. In other words, the uplink transmission power control should be a function of the concentrator that controls the SCG.

[0604] Each small cell measures the received power or reception quality from the UE and notifies the measurement results to the concentrator. The concentrator acquires the measurement results of the received power or reception quality from each small cell for the target UE and combines the measurement results using one of the methods (1) to (3) above.

[0605] The concentrator sets the transmission power of the target UE based on the combined result. The concentrator notifies the UE of the set transmission power via the small cells in the SCG that make up the virtual macro cell. The set transmission power may be notified as uplink scheduling information.

[0606] By doing this, the UE does not need to recognize each small cell in the SCG, and can set the transmission power as if it were a single cell (virtual macro cell), making it possible to perform uplink transmission.

[0607] Furthermore, by using small cells within the SCG that configures the virtual macro cell, it becomes possible to control the uplink reception power or reception quality from the UE so as to be optimal.

[0608] Second embodiment, variant 4 In the second modification of the second embodiment, a method has been disclosed in which the MCS of signaling related to HO-related processing of HO-targeted UEs is set to a low value in order to reduce HO failures between SCGs constituting a virtual macro cell.

[0609] On the other hand, a UE may experience a sudden change in received power not only when moving between SCGs but also when moving between small cells within the SCG. In this case, the MCS selection may not be able to keep up, leading to a deterioration in communication quality or a decrease in the efficiency of radio resource usage. In such a case, since the SCG constitutes a virtual macrocell, the UE does not recognize movement between small cells within the SCG. Therefore, there is a problem in that the method of Variation 2 of Embodiment 2 cannot be applied. The present variation aims to solve this problem.

[0610] Signaling during virtual macrocell mode operation is set to a predetermined MCS. This signaling is signaling on the Uu interface. The predetermined MCS may be statically determined in advance by a standard or may be semi-statically set by the concentrator.

[0611] The predetermined MCS may be an MCS that can be received even with the lowest expected reception power. For example, the MCS may be set to a low rate. The MCS may be set to the lowest rate. Alternatively, the MCS may be set to the lowest MCS setting among the MCS settings used for the control channel or control signal.

[0612] By doing so, it is possible to suppress deterioration of communication quality due to abrupt changes in received power or a decrease in the efficiency of use of radio resources, even when moving between small cells within an SCG.

[0613] Setting a low MCS increases the amount of radio resources used, but by limiting communication between the virtual macrocell and the UE to specified signaling and control plane (C-plane) connections, or specified signaling and some data communication, it is possible to reduce the increase in radio resource use.

[0614] Second embodiment, variant 5 In the second embodiment, it is disclosed that a small cell operating as an individual cell may have a carrier frequency different from the carrier frequency when operating as a virtual macro cell. However, there may be cases where the frequency allocation situation given to an operator does not allow the small cell to have multiple carrier frequencies.

[0615] In this modification, a method of operating in the virtual macro cell mode and the dedicated cell mode using the same carrier frequency will be disclosed.

[0616] The virtual macro mode and dedicated small cell mode are performed in time division using the same frequency carrier. This method is possible because the small cells in the SCG that make up the virtual macro cell are synchronized.

[0617] The following two time-sharing methods (1) and (2) are disclosed. (1) Radio frame units. (2) In subframe units.

[0618] When the radio frame unit is used as in (1) above, the radio frame operated in the virtual macro cell mode is made different from the radio frame operated in the dedicated cell mode. The PCI setting differs between the radio frame operated in the virtual macro cell mode and the radio frame operated in the dedicated cell mode. A PCI for the virtual macro cell and a PCI for the dedicated cell are used.

[0619] The inter-mode radio frame configuration, i.e., which radio frames are used in virtual macro cell mode and which radio frames are used in dedicated cell mode, can be notified to the UE from the virtual macro cell. This is suitable when the virtual macro cell is the master cell. The inter-mode radio frame configuration can be notified to the UE along with the configuration of the second cell used for dual connectivity.

[0620] As an inter-mode radio frame configuration, it is preferable that the mode operated in each radio frame is indicated within a predetermined radio frame. The configuration of the predetermined radio frame is repeatedly set. The operation mode of each radio frame within the predetermined radio frame may be notified by a bitmap corresponding to each radio frame. For example, the predetermined radio frame is determined to be 20 radio frames, and the mode operated in each radio frame within the 20 radio frames is indicated using 20 bits. For example, "0" indicates virtual macro cell mode operation, "1" indicates dedicated cell mode operation, etc. The 20 radio frames are repeatedly set.

[0621] By setting the mode for each radio frame, it becomes possible to set the mode flexibly regardless of the subframe configuration.

[0622] When using subframe units as in (2) above, the subframes used for operation in virtual macrocell mode and the subframes used for operation in dedicated cell mode are made different. The PCI settings are different between the subframes used for operation in virtual macrocell mode and the subframes used for operation in dedicated cell mode. A PCI for the virtual macrocell and a PCI for the dedicated cell are used.

[0623] In this case, the subframe numbers to which SS and PBCH are mapped are statically determined. In this case, it is recommended that the subframe numbers to which SS and PBCH are mapped are different in each mode. Alternatively, NCT (New Carrier Type), which does not require mapping of SS and PBCH, may be used.

[0624] As an inter-mode subframe configuration, it is preferable that the mode operated in each subframe is indicated within a predetermined subframe, and the configuration of the predetermined subframe is set repeatedly.

[0625] The operation mode of each subframe within a given subframe may be notified using a bitmap corresponding to each subframe. For example, a given subframe may be determined to be 10 subframes, and the mode to be operated in each subframe within the 10 subframes may be indicated using 10 bits. For example, "0" indicates virtual macrocell mode operation, "1" indicates dedicated cell mode operation, etc. The 10 subframes are set repeatedly. Also, the subframe numbers to which the SS, PBCH, etc. are mapped are set.

[0626] As in the method (1) above, the inter-mode subframe configuration may be notified from the virtual macro cell to the UE. This method is suitable when the virtual macro cell is the master cell. The inter-mode subframe configuration may be notified to the UE along with the configuration of the second cell used for dual connectivity.

[0627] By setting the mode for each subframe, it becomes possible to set the mode in small time units, thereby improving the efficiency of use of radio resources.

[0628] Second embodiment, variant 6 In the second embodiment, since each small cell in the SCG constituting the virtual macro cell performs the same communication, it has been shown that the configuration of the physical resources of each small cell in the SCG is made the same. It has also been shown that physical channels and signals in layer 1 are mapped to the same physical resources.

[0629] However, in an SCG, there may be cases where a UE is present within the coverage of a certain small cell, but a UE is not present within the coverage of another small cell. In this case, small cells in the SCG may perform the same communication, which may result in a waste of power consumption. This modification aims to solve this problem.

[0630] Each small cell in the SCG that makes up the virtual macro cell turns transmission on and off individually.

[0631] Small cells within an SCG that configures a virtual macro cell map physical channels and signals to the same physical resources, but each small cell turns on / off transmission of the physical resources individually.

[0632] The transmission on / off may be notified from the concentrator. For example, the concentrator acquires the location information of the UE and turns off the transmission of small cells in the SCG that are not served by any UE. In this case, it may notify the small cells of a transmission off instruction to turn off transmission. Also, when a UE approaches a small cell that has its transmission turned off, it turns on the transmission of the small cell. In this case, it may notify the small cells of a transmission on instruction to turn on transmission.

[0633] In this way, each small cell in the SCG that makes up the virtual macro cell can individually turn transmission on / off, making it possible to reduce the power consumption of the entire small cells when multiple small cells are in operation.

[0634] In addition, small cells located at the edge of an SCG may not turn off transmission. This allows UEs located in an SCG adjacent to the SCG to measure the virtual macro cell configured by the SCG. Therefore, mobility such as HO to the virtual macro cell configured by the SCG can be enabled.

[0635] Furthermore, instead of turning on / off transmission of all physical resources individually for each small cell, it is also possible to turn on / off transmission of specific physical resources individually for each small cell, such as specific RBs (Resource Blocks) and physical resources to which PBCHs are mapped. Also, it is possible to turn on / off transmission of physical resources allocated to specific UEs.

[0636] This makes it possible to, for example, turn off transmission of physical resources to which PDSCH scheduled for UEs not present in a small cell served by the SCG is mapped. It also makes it possible to turn off transmission to unnecessary UEs. It also makes it possible to reduce power consumption not only when there are no UEs served by the small cell.

[0637] Also, instead of turning transmission on and off, transmission and reception may be turned on and off, which makes it possible to reduce power consumption not only on the transmitting side but also on the receiving side.

[0638] If there are UEs connected to a small cell operating in dedicated cell mode within the coverage of that small cell, the UEs may be handed over to another small cell operating in dedicated cell mode before transmission is turned off, or the UEs may be handed over to a virtual macro cell before transmission is turned off.

[0639] By handing over these UEs to a small cell operating in a dedicated cell mode that does not turn off transmission, or to a virtual macro cell, these UEs can continue communication.

[0640] It has been explained that transmission is turned off after handover, but the detailed timing of this will be disclosed below. The timing for turning off transmission of a small cell operating in a dedicated cell mode should be after transmitting mobility control information to a UE connected to the small cell.

[0641] For example, it is preferable to perform the handover after transmitting a handover command from a target small cell or virtual macro cell operating in the dedicated cell mode to the UE, because the transmission of the mobility control information is the last signaling transmitted from the source cell to the UE among the handover signaling.

[0642] By doing so, it is possible to minimize the impact on the UE to be handed over even if the transmission of the handover source cell is turned off, and therefore it is possible to reduce the occurrence of a UE connected to the small cell that turns off transmission going into HOF or RLF and being unable to maintain the connection state.

[0643] Second embodiment, variant 7 In the second embodiment, each small cell in the SCG constituting the virtual macro cell performs the same communication, and therefore the cell-specific RS of each small cell in the SCG is mapped to the same physical resource. Therefore, the RS corresponding to each antenna of each cell is mapped to the same resource and transmitted. Furthermore, when each antenna of each cell is used in transmit diversity and MIMO (Multiple Input Multiple Output), the same data from each antenna of each cell is mapped to the same physical resource and transmitted.

[0644] Fig. 33 is a diagram for explaining a configuration in which each cell in an SCG has four antennas. In Fig. 33, small cells in an SCG that configure a virtual macro cell are indicated by reference numerals "5401", "5403", "5405", and "5407".

[0645] Coverage areas 5402, 5404, 5406, and 5408 are formed by small cells 5401, 5403, 5405, and 5407, respectively. Each cell has four antennas. Small cell 5401 has four antennas 5401-1 to 5401-4. Small cell 5403 has four antennas 5403-1 to 5403-4. Small cell 5405 has four antennas 5405-1 to 5405-4. Small cell 5407 has four antennas 5407-1 to 5407-4.

[0646] In this case, the RSs corresponding to antennas 5401-1, 5403-1, 5405-1, and 5407-1 are mapped to the same resource for transmission. Furthermore, the same data is mapped to the same physical resource for transmission from these antennas 5401-1, 5403-1, 5405-1, and 5407-1.

[0647] Similarly, the transmissions from antennas 5401-2, 5403-2, 5405-2, and 5407-2, the transmissions from antennas 5401-3, 5403-3, 5405-3, and 5407-3, and the transmissions from antennas 5401-4, 5403-4, 5405-4, and 5407-4 are the same.

[0648] As a result, even if a small cell has multiple antennas, it is configured as one virtual macro cell with multiple antennas. The UE does not need to distinguish between the small cells in the SCG that configure the virtual macro cell with multiple antennas, and can regard them as one cell.

[0649] The method of combining antennas is not limited to this, and the antennas of the small cells in the SCG that configures the virtual macro cell may be combined in any manner.

[0650] An example of the combination of antennas of each small cell in the SCG that configures the virtual macro cell will be described using Figure 33. RSs corresponding to antennas 5401-1, 5401-2, 5401-3, and 5401-4 are mapped to the same resource for transmission. Furthermore, the antenna combinations are configured so that the same data is mapped to the same physical resource for transmission from these antennas 5401-1, 5401-2, 5401-3, and 5401-4.

[0651] Similarly, transmissions from antennas 5403-1, 5403-2, 5403-3, and 5403-4, transmissions from antennas 5405-1, 5405-2, 5405-3, and 5405-4, and transmissions from antennas 5407-1, 5407-2, 5407-3, and 5407-4 are also made to be the same. By doing so, it is possible to increase the distance between antennas that perform different transmissions.

[0652] By flexibly combining antennas, the virtual macrocell can be configured with multiple antennas, making it possible to optimize gains from transmit diversity, MIMO, and the like.

[0653] In this embodiment and its variations, a small cell operated in both the virtual macro cell mode and the dedicated cell mode is referred to as a "cell," but a small cell operated in the virtual macro cell mode (hereinafter sometimes referred to as a "virtual macro cell mode operating cell") and a small cell operated in the dedicated cell mode (hereinafter sometimes referred to as a "dedicated cell mode operating cell") may also be referred to as a "cell." A small eNB may be configured to form two cells, a virtual macro cell mode operating cell and a dedicated cell mode operating cell.

[0654] The method disclosed in this embodiment and its modifications may be used in appropriate combination with the method disclosed in the first embodiment and its modifications.

[0655] For example, the methods disclosed in the first embodiment and its modifications can be applied when a small cell operating in both the virtual macro cell mode and the dedicated cell mode communicates with a UE that does not have dual connectivity. The UE that does not have dual connectivity communicates with a small cell in the SCG that configures the virtual macro cell in either the virtual macro cell mode or the dedicated cell mode.

[0656] In other words, a UE that does not perform dual connectivity communicates using either a virtual macro cell or a dedicated small cell. In such a case, the methods disclosed in the first embodiment and its modifications may be used in combination. For example, a group of virtual macro cells or macro cells and a group of dedicated small cells are provided, and the UE determines whether to transition to the group in which it should reside. The determination of the cell in which it should reside is made by the UE in the RRC_Idle state, for example, during cell selection or cell reselection, and by the cell in the RRC_Connected state, for example, during HO.

[0657] By doing so, even in a situation where only a large number of small cells are in operation, mobility to a group including a virtual macro cell is possible, and further, the measurement period for mobility can be shortened, thereby improving mobility performance.

[0658] UEs that do not perform dual connectivity include UEs that do not have dual connectivity capability and legacy UEs that are compatible with a standard that precedes the standard that supports dual connectivity.

[0659] Embodiment 3 As described in the second embodiment, dual connectivity is being studied as an operation method when a large number of small cells are installed. It is being studied that paging for a UE using dual connectivity is notified to the UE from a master cell. The master cell is a cell configured by a master eNB. The number of cells configured by the master eNB may be one or more. The master eNB is an eNB that terminates the S1-MME interface in dual connectivity.

[0660] Meanwhile, 3GPP has standardized systems (Public Warning Systems: PWS) that notify UEs of emergency information, such as the Earthquake and Tsunami Warning System (ETWS) and the Commercial Mobile Alert System (CMAS) (see Non-Patent Documents 1 and 10). In a PWS, the presence of emergency information is notified to a UE using paging. The emergency information itself is also notified as system information contained in an SIB. A UE that receives information about the presence of emergency information by paging receives an SIB containing the specified emergency information. This allows the UE to receive the emergency information.

[0661] The problem to be solved in the third embodiment will be described below. For example, when a UE served by a macrocell receives emergency information presence information by paging from the macrocell, the UE receives an SIB carrying the emergency information from the macrocell. At this time, a sudden change in the radio wave environment between the macrocell and the UE may cause a sudden deterioration in the communication quality of the downlink from the macrocell. For example, this may occur when a large bus stops between the UE and the macrocell after the UE receives the paging. In this case, the UE is unable to receive the SIB carrying the emergency information from the macrocell. The present embodiment aims to solve this problem.

[0662] A UE using dual connectivity receives emergency information presence information through paging, and if it is unable to receive the SIB containing the emergency information of the cell that notified the paging, it receives emergency information of a cell other than the cell that notified the paging.

[0663] Specifically, the UE may receive an SIB including emergency information of a cell different from the cell that notified the paging. In the 3GPP standard (see Non-Patent Document 10), for example, SIBs including emergency information of a cell different from the cell that notified the paging are SIB10, SIB11, and SIB12. SIB10 and SIB11 include emergency information of ETWS. SIB12 includes emergency information of CMAS. The UE determines which SIB to receive according to information on the presence of emergency information included in the paging. Examples of information on the presence of emergency information included in the paging include "etws-indication" and "cmas-indication."

[0664] Furthermore, since the UE receives an SIB containing emergency information for a cell different from the cell that notified the paging, the UE receives SIBs necessary for receiving the SIB. Specifically, the UE receives SIB1. SIB1 contains scheduling information for each SIB. The UE receives SIB1 and acquires the scheduling information for the SIB containing emergency information.

[0665] This allows a UE having dual connectivity to receive emergency information from a cell different from the cell that notified it of paging.

[0666] When a UE having dual connectivity receives information indicating the presence of emergency information through paging, the UE may immediately receive the emergency information from a cell different from the cell that notified the paging.

[0667] Furthermore, the reception process for the emergency information from the cell that has notified the paging and the reception process for the emergency information from a cell different from the cell that has notified the paging may be performed simultaneously.

[0668] In this way, the UE can receive the emergency information as quickly as possible.

[0669] Emergency information is notified from the MME to the eNB. Conventionally, for example, the MME notifies the emergency information only to a predetermined macro eNB. In this case, even if the macro eNB is capable of dual connectivity with a predetermined small eNB, the MME does not notify the small eNB of the emergency information. Therefore, if this continues, the UE cannot receive the emergency information from the small cell.

[0670] Therefore, when the MME notifies a specific eNB of emergency information, it may also notify eNBs that have dual connectivity with the specific eNB. This allows emergency information to be notified from all of the multiple eNBs that have dual connectivity. Therefore, a UE that has dual connectivity can receive emergency information from a cell different from the cell that notified the paging.

[0671] This method is effective when the MME knows information about the eNBs that perform dual connectivity.

[0672] The MME may acquire information about other eNBs capable of dual connectivity from the eNBs under its control in advance. For example, the eNB may notify the MME of this information using S1 signaling during setup and updates. For example, an eNB configuration update message may be used as the S1 signaling. The message includes information about eNBs capable of dual connectivity and notifies the MME. This eliminates the need to create a new message, and allows notification together with update information about the configuration of other eNBs, thereby reducing the amount of signaling.

[0673] Furthermore, the MME may acquire information about eNBs capable of dual connectivity in advance from OAM (operation, administration, and maintenance). The information about eNBs capable of dual connectivity may be a list of any eNB and eNBs that can have dual connectivity with that eNB. This is effective when OAM is made to manage information about eNBs capable of dual connectivity.

[0674] The MME may notify the eNBs under its control of information about eNBs that are capable of dual connectivity. The eNB information may be notified by S1 signaling. The eNB information may be an eNB identifier that can be recognized by the MME. An example of the eNB identifier is the "Global eNB ID."

[0675] FIG. 34 is a diagram showing a sequence when a conventional emergency information notification system is applied to a UE having dual connectivity.

[0676] In Steps ST5601 to ST5604, the UE is performing dual connectivity with a macro cell and a small cell. This shows a case where a macro eNB constituting the macro cell is a master eNB, and a small eNB constituting the small cell is a secondary eNB. The secondary eNB is a second cell that connects to the UE to perform dual connectivity. In FIG. 34, the UE is receiving paging from the macro cell.

[0677] When emergency information occurs, in Step ST5605, a cell broadcast center (CBC) notifies the MME of the emergency information. The emergency information is assumed to be ETWS.

[0678] In Step ST5606, the MME that has received the emergency information in Step ST5605 notifies a predetermined eNB under its control, in this case the master eNB which is a macro eNB constituting a macro cell, of the emergency information. A write-replace warning procedure is used to notify the emergency information. A write-replace warning request message is used as S1 signaling.

[0679] In step ST5607, the master eNB that has received the emergency information in step ST5606 notifies the UEs being served by the macrocell constituted by the eNB by including information indicating the presence of ETWS (hereinafter sometimes referred to as "ETWS presence information") in the paging.

[0680] Furthermore, in Step ST5610, the master eNB notifies the UE being served by the macro cell formed by the master eNB of emergency information (ETWS) in at least one of SIB10 and SIB11.

[0681] Furthermore, in Step ST5609, the master eNB notifies the UE being served by the macro cell constituted by the eNB of at least one of the scheduling information of SIB10 and SIB11 in SIB1.

[0682] In Step ST5608, the UE determines whether or not an ETWS exists based on the ETWS existence information included in the paging received in Step ST5607. If it is determined in Step ST5608 that an ETWS does not exist, the UE returns to the normal dual connectivity state. If it is determined in Step ST5608 that an ETWS exists, the UE receives SIB1 in Step ST5609 and obtains the scheduling information of SIB10 and SIB11. Then, in Step ST5610, the UE receives SIB10 and SIB11 and obtains the emergency information (ETWS).

[0683] In Step ST5611, the master eNB, which has notified the emergency information (ETWS) for a predetermined period at a predetermined cycle, notifies the MME of a warning response message as an emergency information end message.

[0684] In this way, a UE having dual connectivity can receive emergency information from the macro cell.

[0685] However, as described above, if the communication quality of the downlink from the macrocell suddenly deteriorates after the UE receives the paging, for example, because a large bus between the UE and the macrocell stops, the UE will be unable to receive the SIB containing the emergency information from the macrocell and the SIB containing its scheduling information in Steps ST5609 and ST5610. Therefore, a UE that receives emergency information only from the macrocell will no longer be able to receive the emergency information.

[0686] Figure 35 is a diagram showing an example of a sequence of the emergency information notification system in embodiment 3. Figure 35 is similar to the above-mentioned Figure 34, so the same step numbers are assigned to the steps corresponding to Figure 34, and common explanations will be omitted.

[0687] In Step ST5606, the MME that has received the emergency information in Step ST5605 notifies a predetermined eNB under its control, in this case, the master eNB, which is a macro eNB that constitutes a macro cell, of the emergency information. In addition, in Step ST5701, the MME notifies an eNB that is capable of dual connectivity with the predetermined eNB, in this case, a secondary eNB, which is a small eNB, of the emergency information. The write-replace warning procedure may also be used for notifying this emergency information. A write-replace warning request message may be used as S1 signaling.

[0688] In Step ST5703, the secondary eNB that has received the emergency information in Step ST5701 notifies the UE being served by the small cell configured by the eNB of the ETWS existence information included in the paging.

[0689] Furthermore, in Step ST5704, the secondary eNB notifies the UE being served by the small cell configured by the eNB of emergency information (ETWS) in at least one of SIB10 and SIB11.

[0690] Furthermore, in Step ST5703, the secondary eNB notifies the UE being served by the small cell configured by the eNB of at least one of the scheduling information of SIB10 and SIB11 in SIB1.

[0691] If it is determined in Step ST5608 that emergency information (ETWS) exists, the UE attempts to receive the emergency information from the macrocell that transmitted the paging in Step ST5607 in Steps ST5609 and ST5610.

[0692] In Step ST5702, the UE judges whether or not it has received the emergency information (ETWS) from the macro cell. If it has judged in Step ST5702 that it has received the emergency information (ETWS), it proceeds to the processing that is performed when receiving conventional emergency information. If it has judged in Step ST5702 that it has not received the emergency information from the macro cell, it receives SIB1 from the small cell in Step ST5703 and obtains the scheduling information of SIB10 and SIB11. Then, in Step ST5704, it receives SIB10 and SIB11 from the small cell and obtains the emergency information (ETWS).

[0693] In Step ST5705, the secondary eNB, which has notified the emergency information (ETWS) for a predetermined period at a predetermined cycle, notifies the MME of a warning response message as an emergency information end message.

[0694] By doing so, when a UE having dual connectivity is unable to receive emergency information from a macro cell, it becomes possible to receive emergency information from a small cell.

[0695] Another method is disclosed in which all of multiple eNBs performing dual connectivity receive emergency information from the MME.

[0696] The MME notifies a specific eNB of emergency information. The eNB that receives the emergency information from the MME may notify the eNB that has dual connectivity with the eNB of the emergency information. This allows emergency information to be notified from all of the multiple eNBs that have dual connectivity, and a UE that has dual connectivity can receive emergency information from a cell other than the cell that notified the paging.

[0697] This method is effective when an eNB recognizes information about eNBs that can establish dual connectivity with the eNB itself, and is also effective when an MME does not recognize information about eNBs that can establish dual connectivity with the eNB itself.

[0698] The eNB may acquire, in advance, information on other eNBs that are capable of dual connectivity from the MME.

[0699] For example, the MME may notify the eNB of information about eNBs that are capable of dual connectivity with the eNB along with emergency information to be notified to the eNB. This allows the eNB to notify its own eNB that is capable of dual connectivity of the emergency information. As another example, the MME may notify the eNB by S1 signaling when setting up or updating the eNB.

[0700] The eNB may acquire information about eNBs capable of dual connectivity from the OAM in advance. The information may be acquired directly from the OAM without going through the MME. This is effective when the OAM is made to manage information about eNBs capable of dual connectivity.

[0701] The information about the eNB may be an eNB identifier that can be recognized by the MME, such as a "Global eNB ID."

[0702] When emergency information is notified to an eNB, the emergency information is also notified to eNBs that are capable of dual connectivity with the eNB. The eNB that is notified of the emergency information and is capable of dual connectivity notifies the UEs being served by the eNB of the emergency information.

[0703] Specifically, emergency information is reported as system information in SIBs. For example, emergency information for ETWS may be included in SIB10 and SIB11, and emergency information for CMAS may be included in SIB12.

[0704] Furthermore, the eNB capable of dual connectivity that has received the emergency information may notify the UEs served by it of the scheduling information of the SIB containing the emergency information. Specifically, the scheduling information of the SIB containing the emergency information is broadcast as system information in the SIB. For example, it may be included in SIB1.

[0705] Figure 36 is a diagram showing another example of the sequence of the emergency information notification system in embodiment 3. Figure 36 is similar to the above-mentioned Figures 34 and 35, so the same step numbers are used for steps corresponding to Figures 34 and 35, and common explanations will be omitted.

[0706] The master eNB that has received the emergency information in Step ST5606 notifies, in Step ST5801, an eNB that has dual connectivity with the master eNB, such as a secondary eNB, of the emergency information. This notification may be performed using X2 signaling, or another new interface may be provided.

[0707] In Step ST5703, the secondary eNB that has received the emergency information in Step ST5801 notifies the UE being served by the small cell configured by the eNB of the ETWS existence information included in the paging.

[0708] Furthermore, in Step ST5704, the secondary eNB notifies the UE being served by the small cell configured by the secondary eNB of emergency information (ETWS) in at least one of SIB10 and SIB11.

[0709] Furthermore, in Step ST5703, the secondary eNB notifies the UE being served by the small cell configured by the eNB of at least one of the scheduling information of SIB10 and SIB11 in SIB1.

[0710] In Step ST5802, the secondary eNB, which has notified the emergency information (ETWS) for a predetermined period at a predetermined cycle, notifies the master eNB of a warning response message as an emergency information end message.

[0711] The master eNB, which has notified the emergency information (ETWS) at a predetermined cycle for a predetermined period in steps ST5607, ST5609, and ST5610 and has received the emergency information end message in step ST5802, notifies the MME of a warning response message as the emergency information end message in step ST5611.

[0712] By doing so, when a UE having dual connectivity is unable to receive emergency information from a macro cell, it becomes possible to receive emergency information from a small cell.

[0713] The method disclosed in this embodiment enables a UE having dual connectivity to receive emergency information from a cell configured by a secondary eNB even when the reception quality from the cell suddenly deteriorates after the UE receives emergency information by paging from the cell configured by the master eNB. Therefore, it becomes possible to notify the UE of the emergency information as quickly as possible.

[0714] Furthermore, even if a macro cell configured by a macro eNB serving as a master eNB stops operating due to a disaster or the like after the UE receives emergency information presence information through paging, the UE can still receive emergency information from a small cell configured by a small eNB serving as a secondary eNB. The UE can receive emergency information from a small cell, avoiding the macro cell that has stopped operating. This makes it possible to configure a system that can respond even in the event of a disaster.

[0715] Third embodiment, variant 1 The problem to be solved by the first modification of the third embodiment will be described below. When dual connectivity is implemented as an operation method in a case where a large number of small cells are installed, if multiple eNBs implementing dual connectivity are operated on the same frequency layer, interference may occur between the eNBs.

[0716] If emergency information is generated in these eNBs, interference will prevent the UE from receiving the emergency information. For example, when RRC diversity is performed between a macro cell configured by a master eNB and a small cell configured by a secondary eNB, when a UE served by the macro cell receives emergency information from the macro cell, the UE will be subjected to interference from the small cell that provides dual connectivity. This will degrade the reception quality from the macro cell, making it impossible to receive the emergency information. This modification aims to solve this problem.

[0717] While emergency information is being broadcast from a cell configured by the master eNB, transmission and reception operations of a cell configured by a secondary eNB that has dual connectivity with the master eNB are stopped. The transmission and reception operations may be performed over the Uu interface. Furthermore, the cell configured by the secondary eNB is a cell dedicated to dual connectivity.

[0718] Alternatively, the transmission and reception operations on the carrier frequency dedicated to dual connectivity of the cell constituted by the secondary eNB performing dual connectivity may be stopped.

[0719] By doing so, interference from the cell configured by the secondary eNB is eliminated. Therefore, the UE can receive emergency information with improved reception quality from the cell configured by the master eNB. A UE that is performing dual connectivity should receive emergency information from the cell configured by the master eNB. This allows the UE to receive emergency information with good reception quality.

[0720] The cell configured by the secondary eNB may stop transmission instead of stopping transmission and reception. Reception may continue without stopping. Also, the cell configured by the secondary eNB may transition to a dormant mode instead of stopping transmission and reception. An example of the dormant mode is a method of transmitting only specific signals at long intervals.

[0721] The following three events (1) to (3) are disclosed as triggers for the secondary eNB to stop transmission and reception.

[0722] (1) When a paging message indicating the presence of emergency information is received from the MME or the master eNB.

[0723] (2) When the master eNB receives emergency information from the MME, the master eNB notifies the secondary eNB of a message to stop transmission and reception. When the secondary eNB receives a message to stop transmission and reception from the master eNB.

[0724] (3) When the MME notifies the macro eNB of emergency information, it notifies the secondary eNB of a message to stop transmission and reception. When the secondary eNB receives a message to stop transmission and reception from the master eNB.

[0725] The following four events (1) to (4) are disclosed as triggers for the secondary eNB to resume transmission and reception.

[0726] (1) When an emergency information notification end message is sent to the MME or the master eNB.

[0727] (2) When the master eNB transmits an emergency information notification end message to the MME, the master eNB notifies the secondary eNB of a message to resume transmission and reception. When the secondary eNB receives a message to resume transmission and reception from the master eNB.

[0728] (3) When the MME receives an emergency information notification end message from the macro eNB, it notifies the secondary eNB of a message to resume transmission and reception. When the secondary eNB receives a message to resume transmission and reception from the MME.

[0729] (4) After a predetermined period of time has elapsed since the secondary eNB received a message from the MME or master eNB to stop transmission and reception.

[0730] Fig. 37 is a diagram showing an example of a sequence of a communication system in Modification 1 of Embodiment 3. Since Fig. 37 is similar to the above-mentioned Fig. 34, the same step numbers are assigned to the steps corresponding to Fig. 34, and common explanations will be omitted.

[0731] The master eNB, which has received the emergency information from the MME in Step ST5606, performs, in Step ST5901, a process to release the dual connectivity of the UEs being served by it that are performing dual connectivity, specifically, a process to remove the reconfiguration of the second cell (Secondary eNB) (Secondary eNB reconfiguration (remove) Procedure).

[0732] For example, the master eNB notifies a cell performing dual connectivity to cancel the dual connectivity process for the UE. In addition, while sending this notification, the master eNB also stops transferring data to the cell to be transmitted to the UE. The cell that has been notified of the cancellation of the dual connectivity process terminates the connection with the UE and terminates transmission to the UE.

[0733] On the other hand, the master eNB notifies the UE of the removal of the cell with which dual connectivity is being performed. This removal may be performed using an RRC connection reconfiguration message. The UE that has been notified of the removal terminates transmission and reception of the cell with which dual connectivity is being performed. By doing so, the secondary eNB terminates dual connectivity, and the UE that had been performing dual connectivity will be connected only to cells configured by the master eNB.

[0734] After canceling the dual connectivity process of the secondary eNB, in Step ST5902, the master eNB requests the secondary eNB to stop transmission and reception operations. In Step ST5903, the secondary eNB stops transmission and reception operations. By doing so, transmission and reception from the secondary eNB will no longer be performed, and it will be possible to eliminate interference with the master eNB.

[0735] After broadcasting the emergency information for a predetermined period at a predetermined cycle, the master eNB notifies the MME of an emergency information notification end message in Step ST5611, and requests the secondary eNB to start transmission and reception operation in Step ST5904. The secondary eNB that has received the request to start transmission and reception operation starts transmission and reception in Step ST5905.

[0736] Thereafter, in Step ST5906, the master eNB performs dual connectivity for a UE being served by the master eNB, as necessary, using a cell configured by the secondary eNB. For example, the master eNB notifies the cell that performs dual connectivity of a dual connectivity addition process for a desired UE. After notifying the cell of the dual connectivity addition process, the master eNB starts transferring data for the UE to the cell that performs dual connectivity. The cell that has been notified of the dual connectivity addition process performs a process to start a connection with the UE and starts transmission to the UE.

[0737] On the other hand, the master eNB notifies the UE of the addition of a cell that will provide dual connectivity. The addition of a cell that will provide dual connectivity may be performed using an RRC connection reconfiguration message. The UE that has been notified of the addition starts transmitting and receiving data to and from the cell that will provide dual connectivity. In this way, the secondary eNB can resume dual connectivity for the desired UE.

[0738] In this way, when a UE served by a cell configured by the master eNB receives emergency information from the cell, interference from a cell configured by a secondary eNB with which dual connectivity is established can be eliminated, and the emergency information can be received without degrading the reception quality from the cell.

[0739] In addition, for a UE that is using dual connectivity, the secondary eNB's dual connectivity processing is temporarily canceled, making it possible to prevent packet loss and other issues from occurring between the UE and the secondary eNB while transmission and reception operations of the secondary eNB are stopped.

[0740] Figure 38 is a diagram showing another example of the sequence of the communication system in Modification 1 of Embodiment 3. Since Figure 38 is similar to the above-mentioned Figure 34, the same step numbers are assigned to the steps corresponding to Figure 34, and common explanations will be omitted.

[0741] In Step ST6001, the master eNB that has received the emergency information from the MME in Step ST5606 requests the secondary eNB, which is performing dual connectivity, to stop transmission operation. In Step ST6002, the secondary eNB stops transmission operation. By doing so, transmission from the secondary eNB will no longer be performed, and it will be possible to eliminate interference with the master eNB.

[0742] Furthermore, the secondary eNB that stopped transmission operation in step ST6002 starts a timer for the stop period. The value of the stop period may be statically determined in advance or may be notified by the master eNB. The master eNB may set the value of the stop period in consideration of a predetermined period for notifying emergency information, and notify the secondary eNB of the set value.

[0743] In Step ST6003, the secondary eNB judges whether or not the stop period timer has expired. If it is determined in Step ST6003 that the stop period timer has expired, it proceeds to Step ST6004, and if it is determined that the stop period timer has not expired, it waits until the stop period timer has expired. The secondary eNB that has determined in Step ST6003 that the stop period timer has expired resumes transmission operation in Step ST6004. In this way, the secondary eNB can resume dual connectivity for the desired UE.

[0744] In this way, when a UE served by a cell configured by the master eNB receives emergency information from the cell, interference from a cell configured by a secondary eNB with which dual connectivity is established can be eliminated, and the emergency information can be received without degrading the reception quality from the cell.

[0745] Furthermore, compared to the sequence shown in Figure 37, the secondary eNB does not temporarily release the dual connectivity of a UE that has dual connectivity, so the master eNB can notify the UE being served of emergency information as quickly as possible. This allows the UE to receive the emergency information as quickly as possible.

[0746] Embodiment 4 As described in the second embodiment, dual connectivity is being considered as an operation method when a large number of small cells are installed.

[0747] On the other hand, 3GPP has standardized a function for restricting access when the load on a cell increases, etc. The information for restricting access is ACB (Access Class Barring) information and EAB (Extended Access Barring) information. An access class is set for a UE. The access class is stored in a SIM or the like. A cell broadcasts information about access restriction to UEs under its control as system information. The UE restricts access to the cell in accordance with the received access restriction information.

[0748] The problem to be solved in the fourth embodiment will be described below. An existing method for achieving dual connectivity is CA using a macro cell and an RRH connected to it. In such CA, the macro cell and the RRH are configured within the same eNB, and scheduling for each node is performed centrally. In addition, an ideal backhaul is configured between the nodes, in which delay can be ignored. In such CA, the eNB can adjust the load on each node, so the access restrictions for each node can be the same. In such a case, the UE only needs to be aware of the access restrictions of the cell it is camped on.

[0749] On the other hand, in the case of dual connectivity using radio resources of different eNBs, delays between eNBs cannot be ignored and non-ideal backhaul is configured, so scheduling for each eNB cannot be performed centrally. Normally, the load state of each eNB is different, so if each eNB has the same access restriction, there is a problem that the efficiency of radio resource use decreases. The present embodiment aims to solve this problem.

[0750] For a UE that performs dual connectivity, the cells configured by the master eNB set a cell having the same ACB / EAB information as the own cell as the cell for dual connectivity.

[0751] Fig. 39 is a diagram showing an example of a sequence of a communication system in Embodiment 4. Since Fig. 39 is similar to the above-mentioned Fig. 34, the same step numbers are assigned to the steps corresponding to Fig. 34, and common explanations will be omitted.

[0752] In Step ST5604, the UE that has transitioned to the RRC connected state in Steps ST5601 to ST5603 performs a secondary eNB configuration procedure as a process for configuring dual connectivity with another cell between the UE and the cell configured by the master eNB. The eNB that configures the cell becomes the secondary eNB for the UE.

[0753] Before the process of Step ST5604 is performed, the cell configured by the master eNB needs to recognize in advance the eNBs (cells) that have the same ACB / EAB information as its own cell. Therefore, the cell configured by the master eNB acquires in advance the ACB / EAB information of the cells configured by the eNBs that are capable of dual connectivity.

[0754] In Step ST6101, the master eNB notifies the eNB capable of dual connectivity of a message requesting the setting status of at least one of the ACB and EAB of the cell. A new interface may be provided for this message. Alternatively, the X2 interface may be used. For example, a resource status request message may be used. In this case, there is no need to provide a new interface, and control can be simplified. Alternatively, the S1 interface may be used. The master eNB may notify the eNB capable of dual connectivity via the MME.

[0755] The secondary eNB that has received the request for the ACB / EAB setting status in Step ST6101 notifies the master eNB of the setting information of at least one of the ACB and EAB of the cell in Step ST6102. This allows the master eNB to obtain the setting status of at least one of the ACB and EAB of the cell configured by the eNB that is capable of dual connectivity.

[0756] A new interface may be provided for this message. Alternatively, the X2 interface may be used. For example, a resource status response message may be used. In this case, there is no need to provide a new interface, which simplifies control. Alternatively, the S1 interface may be used. The secondary eNB may notify the master eNB via the MME.

[0757] In Step ST6103, the master eNB selects an eNB with the same ACB / EAB as the cell configured by its own eNB, specifically, the cell configured by this eNB.

[0758] This cell is used in the secondary eNB configuration procedure for the UE that performs dual connectivity in Step ST5604.

[0759] In this way, the UE only needs to recognize the ACB / EAB information of the cells configured by the master eNB, and does not need to recognize the ACB / EAB information of the cells configured by the secondary eNB.The cells configured by the master eNB also do not need to notify the UE of the ACB / EAB information of the cells configured by the secondary eNB.

[0760] The above-mentioned method can take into account different load conditions at each eNB, but it cannot take into account temporal fluctuations in the load conditions at each eNB. Therefore, a mechanism is provided to take into account cases where the ACB / EAB setting is changed due to fluctuations in the load conditions at each eNB.

[0761] In Step ST6104, if the ACB / EAB setting of the cell constituted by the eNB capable of dual connectivity is changed, the secondary eNB notifies the master eNB (the cell constituted by it) of the changed ACB / EAB setting information in Step ST6105.

[0762] A new interface may be provided for this message. Alternatively, the X2 interface may be used. For example, a resource status update message or an eNB configuration update message may be used. In this case, there is no need to provide a new interface, which simplifies control. Alternatively, the S1 interface may be used. The secondary eNB may notify the master eNB via the MME.

[0763] By doing so, even if the ACB / EAB setting of an eNB capable of dual connectivity is changed, the master eNB can obtain the ACB / EAB setting information after the change.

[0764] In Step ST6106, the master eNB selects (a cell configured by) an eNB with the same ACB / EAB as the cell configured by the own eNB. Then, in Step ST6107, the master eNB performs a secondary eNB change process (Secondary eNB reconfiguration (remove, add) Procedure) for the UE that performs dual connectivity. The master eNB configures the UE that performs dual connectivity to remove (a cell configured by) an eNB with an ACB / EAB different from the cell configured by the master eNB and add (a cell configured by) an eNB with the same ACB / EAB as the cell configured by the master eNB.

[0765] By doing this, even if the ACB / EAB setting of an eNB capable of dual connectivity is changed, the master eNB can take into account the changed ACB / EAB setting information and configure an appropriate eNB as the eNB (cell configured by the eNB) for dual connectivity for the UE that will perform dual connectivity.

[0766] Therefore, even if the load state of each eNB fluctuates over time, it is possible to achieve dual connectivity while suppressing a decrease in the efficiency of use of radio resources.

[0767] In the above-described method, after the secondary eNB changes the ACB / EAB setting in Step ST6104, the secondary eNB notifies the master eNB of the changed ACB / EAB setting status in Step ST6105.

[0768] In this case, even after the ACB / EAB of the secondary eNB is changed, the UE remains connected to the secondary eNB until the process of changing the secondary eNB that performs dual connectivity with the UE is performed in Step ST6107, even if the AC and EAB condition settings of the UE are different from the ACB / EAB settings of the secondary eNB after the change. If there is a large processing delay in Step ST6105 and Step ST6106, the state in which the inconsistency occurs between the settings of the UE and the settings of the secondary eNB will continue for a long time.

[0769] In order to reduce such a situation, in step ST6104, the secondary eNB may decide to change the ACB / EAB setting instead of changing the ACB / EAB setting, and if it decides to change the ACB / EAB setting, may notify the master eNB of the decided ACB / EAB setting in step ST6105.

[0770] After deciding to change the ACB / EAB settings, the secondary eNB changes the ACB / EAB settings after a predetermined period of time has elapsed. The predetermined period of time may be statically determined in advance or may be changed semi-statically. When the predetermined period of time is statically determined, control as a system can be simplified. When the predetermined period of time is changed semi-statically, it is possible to take into account the congestion status of the interface between the secondary eNB and the master eNB and time fluctuations in control delay at the master eNB.

[0771] Furthermore, the predetermined period may be different for each cell or may be the same value for all cells. If the predetermined period is different for each cell, it is possible to take into account the control delay in each cell. If the predetermined period is the same value for all cells, it is possible to simplify the control of the system.

[0772] By changing the ACB / EAB setting after the predetermined period has elapsed, it is possible to reduce the time from changing the ACB / EAB setting to processing in step ST6107. Alternatively, it is also possible to change the ACB / EAB setting after processing in step ST6107.

[0773] This makes it possible to reduce the occurrence of inconsistencies between the AC and EAB condition settings of the UE and the ACB / EAB settings of the secondary eNB.

[0774] The method disclosed in this embodiment makes it possible to perform dual connectivity while suppressing a decrease in the efficiency of use of radio resources even when the load conditions at each eNB are different and fluctuate over time, thereby increasing the system capacity.

[0775] Furthermore, it is possible to avoid situations where the server goes down due to excessive load, and therefore a stable communication system can be constructed.

[0776] Fourth embodiment, variant 1 Another method for solving the problem described in the fourth embodiment will be disclosed. For a UE that performs dual connectivity, the master eNB configures a cell that can be accessed by the UE as a dual connectivity cell.

[0777] Figure 40 is a diagram showing an example of a sequence of a communication system in Modification 1 of Embodiment 4. Figure 40 is similar to the above-mentioned Figures 34 and 39, so the same step numbers are assigned to the steps corresponding to Figures 34 and 39, and common explanations will be omitted.

[0778] In Step ST5604, the UE that has transitioned to the RRC connected state in Steps ST5601 to ST5603 performs a secondary eNB configuration procedure as a process for configuring dual connectivity with another cell between the UE and the cell configured by the master eNB. The eNB that configures the other cell becomes the secondary eNB of the UE.

[0779] Before the process of Step ST5604 is performed, the cell configured by the master eNB needs to recognize cells accessible by UEs that perform dual connectivity. Therefore, the cell configured by the master eNB acquires in advance the ACB / EAB information of cells configured by eNBs that are capable of dual connectivity, and also acquires AC setting information of the UEs.

[0780] In Step ST6201, the master eNB notifies the UE that performs dual connectivity of a message requesting AC configuration information. The message requesting AC configuration information may be notified using RRC signaling. Alternatively, the message may be notified using dedicated signaling. For example, an existing UE Capability Enquiry message may be used.

[0781] In Step ST6202, the UE that has received the request for AC configuration information notifies the master eNB (the cell configured by the master eNB) of its own UE's AC configuration information. The AC configuration information may be notified using RRC signaling. Alternatively, the AC configuration information may be notified using dedicated signaling. For example, an existing UE Capability Information message may be used. This allows the master eNB to obtain the AC configuration information of the UE that performs dual connectivity.

[0782] The process of requesting the AC configuration status in Step ST6201 may be omitted. In that case, the UE may notify the cell constituted by the master eNB of the AC configuration information in Step ST6202 when establishing an RRC connection with the cell constituted by the master eNB.

[0783] In step ST6203, the master eNB selects an ACB / EAB-configured eNB (a cell configured by the eNB) that the UE can access, using the AC configuration information of the UE that will perform dual connectivity acquired in step ST6202 and the ACB / EAB configuration information of the eNB that is capable of dual connectivity acquired in step ST6102.

[0784] This cell is used in the secondary eNB configuration procedure for the UE that performs dual connectivity in Step ST5604.

[0785] In this way, the UE only needs to recognize the ACB / EAB information of the cells configured by the master eNB, and does not need to recognize the ACB / EAB information of the cells configured by the secondary eNB.The cells configured by the master eNB also do not need to notify the UE of the ACB / EAB information of the cells configured by the secondary eNB.

[0786] In order to take into account the temporal fluctuations in the load state of each eNB, it is preferable to provide a mechanism that takes into account the case where the ACB / EAB setting is changed due to the fluctuations in the load state of each eNB disclosed in Embodiment 4. In Step ST6104 and Step ST6105, the master eNB acquires the ACB / EAB setting information of the eNB capable of dual connectivity whose ACB / EAB setting has been changed.

[0787] In Step ST6204, an ACB / EAB-configured eNB (or a cell configured by it) that the UE can access is selected using the AC configuration information of the UE that performs dual connectivity acquired in Step ST6202, the ACB / EAB configuration information of the eNB that is capable of dual connectivity acquired in Step ST6102, and the ACB / EAB configuration information of the eNB that is capable of dual connectivity and whose ACB / EAB configuration has been changed acquired in Step ST6105.

[0788] Then, in Step ST6107, the master eNB performs a secondary eNB change process for the UE that performs dual connectivity. The master eNB configures the UE that performs dual connectivity to remove (a cell configured by) an eNB with an ACB / EAB different from the cell configured by the master eNB, and to add (a cell configured by) an eNB with the same ACB / EAB as the cell configured by the master eNB.

[0789] By doing this, even if the ACB / EAB setting of an eNB capable of dual connectivity is changed, the master eNB can take into account the changed ACB / EAB setting information and configure an appropriate eNB as the eNB (cell configured by the eNB) for dual connectivity for the UE that will perform dual connectivity.

[0790] Therefore, even if the load state of each eNB fluctuates over time, it is possible to achieve dual connectivity while suppressing a decrease in the efficiency of use of radio resources.

[0791] The method disclosed in this modification can achieve the same effects as those of the fourth embodiment, and also enables the master eNB to recognize the AC configuration of the UE that performs dual connectivity. This allows more eNBs to be selected as secondary eNB candidates for dual connectivity. Therefore, it becomes possible for the UE that performs dual connectivity to perform dual connectivity in a cell that has optimal communication quality.

[0792] Fourth embodiment, variant 2 Another method for solving the problem described in the fourth embodiment will be disclosed. When the master eNB configures a cell for dual connectivity, it notifies the UE that performs dual connectivity of the ACB / EAB information of the cell for dual connectivity.

[0793] Figure 41 is a diagram showing an example of a sequence of a communication system in Modification 2 of Embodiment 4. Figure 41 is similar to the above-mentioned Figures 34 and 39, so the same step numbers are assigned to steps corresponding to Figures 34 and 39, and common explanations will be omitted.

[0794] In Steps ST5601 to ST5603, the UE transitions to an RRC connected state.

[0795] When configuring a cell for dual connectivity, the master eNB notifies the ACB / EAB information of the cell. Prior to this, the cell configured by the master eNB acquires the ACB / EAB information of the cell configured by the eNB capable of dual connectivity in advance.

[0796] Therefore, in Step ST6101, the master eNB notifies the eNB capable of dual connectivity of a message requesting the setting status of at least one of the ACB and EAB of the cell.

[0797] In Step ST6102, the eNB capable of dual connectivity that receives the request for the ACB / EAB setting status notifies the master eNB of setting information of at least one of the ACB and EAB of the cell. This allows the master eNB to obtain the setting status of at least one of the ACB and EAB of the cell configured by the eNB capable of dual connectivity.

[0798] In Step ST6302, the cell configured by the master eNB selects a cell in which dual connectivity is to be performed, using a measurement report message from the UE in Step ST6301.

[0799] In Step ST6303, the cell configured by the master eNB notifies the UE that performs dual connectivity of the configuration of the cell that performs dual connectivity. Information included in the configuration of the cell that performs dual connectivity includes the identifier of the cell, the identifier of the eNB that configures the cell, ACB / EAB setting information of the cell, etc.

[0800] In Step ST6303, the UE receives the configuration of the cell that performs dual connectivity and the ACB / EAB information of the cell, and then in Step ST6304, determines whether or not the cell is accessible. If it is determined in Step ST6304 that the cell is not accessible, the UE proceeds to Step ST6305. In Step ST6305, the UE notifies the cell configured by the master eNB that the cell is not accessible, and returns to the normal RRC_CONNECTED state. The UE may perform measurements again.

[0801] On the other hand, if it is determined in Step ST6304 that the cell is accessible, the eNB proceeds to Step ST6306. In Step ST6306, the master eNB notifies the cells that it configures that the cell is accessible.

[0802] In Step ST6307, the master eNB (a cell constituted by the master eNB) judges whether or not the UE performing dual connectivity can access the cell configured for dual connectivity. If it is judged in Step ST6307 that the UE cannot access the cell, the master eNB returns to Step ST6302 and executes the process of selecting a cell for performing dual connectivity again. When a measurement report is received from the UE again in Step ST6301, the master eNB may execute the process of selecting a cell for performing dual connectivity in Step ST6302.

[0803] If it is determined in Step ST6307 that the access is possible, the eNB proceeds to Step ST6308. In Step ST6308, the cell formed by the master eNB starts data transfer to the eNB for dual connectivity.

[0804] In Step ST6306, the UE notifies the master eNB that it can access the cell configured for dual connectivity. In Step ST6309, the UE performs detection and synchronization processing on the cell, and in Step ST6310, starts data communication.

[0805] This allows a UE having dual connectivity to recognize the ACB / EAB information of a cell configured by the secondary eNB, and the UE can determine whether it can access a cell configured by the secondary eNB separately from a cell configured by the master eNB.

[0806] Therefore, even if the load conditions in each eNB are different, it is possible to achieve dual connectivity while suppressing a decrease in the efficiency of use of radio resources, thereby enabling an increase in system capacity.

[0807] Furthermore, it is possible to avoid situations where the server goes down due to excessive load, and therefore a stable communication system can be constructed.

[0808] Since the temporal fluctuation of the load state at each eNB is taken into consideration, it is preferable to provide a mechanism that takes into consideration the case where the ACB / EAB setting is changed due to the fluctuation of the load state at each eNB disclosed in Embodiment 4. After performing the processing of the sequence shown in Fig. 41, the processing of step ST6104 and step ST6105 in Fig. 39 described above may be performed, and the processing from step ST6302 or step ST6303 may be performed again using the results.

[0809] This makes it possible to achieve dual connectivity while suppressing a decrease in the efficiency of radio resource usage, even when the load state of each eNB fluctuates over time.

[0810] The methods disclosed in the fourth embodiment and the second modification of the fourth embodiment can also be applied to the barred information of a cell. The ACB / EAB setting information of the cell may be replaced with the barred information of the cell. In the second modification of the fourth embodiment, in step ST6303 of FIG. 41, the barred information of the cell may be included as configuration information of the cell for dual connectivity and notified to the UE. In step ST6304, the UE uses the barred information to determine whether or not it is accessible.

[0811] This makes it possible to achieve dual connectivity while suppressing a decrease in the efficiency of radio resource usage even when the barred information in each eNB is different, thereby increasing the system capacity.

[0812] Embodiment 5. The problem to be solved in the fifth embodiment will be described below. When small cells are grouped together and handled, without any ingenuity, the parameters of the small cells will differ from one another even if they are included in the same group. Since small cells have narrow coverage, it is expected that many of them will be installed. Therefore, a method for setting optimal parameters for small cells will be disclosed.

[0813] The solution in the fifth embodiment is as follows: Some parameters are set to the same values ​​in small cells included in the same set. In other words, some parameters are set to common values. This is because by setting some parameters of small cells included in the same set to the same values, it is possible to build an efficient communication system.

[0814] As specific examples of sets, the following two sets (1) and (2) are disclosed. (1) Small cell cluster. In other words, small cells included in the same small cell cluster have some parameters set to the same values.

[0815] (2) When a small cell is installed within the coverage of another cell, the small cell installed within the coverage of the same other cell is called a "coverage macro cell." In other words, some parameters are set to the same values ​​for small cells installed within the coverage of the same coverage macro cell.

[0816] As specific examples of parameters that are set to the same value, the following 17 parameters (1) to (17) are disclosed.

[0817] (1) Downlink transmission bandwidth (dl-Bandwidth). This parameter is included in the MIB (see Non-Patent Document 10). By setting the downlink transmission bandwidth to the same value in small cells included in the same set, the following effects can be obtained.

[0818] Due to their narrow coverage, it is expected that many small cells will be installed. When considering the number of cells that a UE can measure from the same location, the number of small cells is likely to be greater than the number of macrocells. When measuring cells with different downlink transmission bandwidths, it may be necessary to change the UE's reception settings. For example, it may be necessary to change the settings of the frequency converter that converts the signal received by the antenna into a baseband signal according to the downlink transmission bandwidth.

[0819] According to this specific example (1), by setting the downlink transmission bandwidth (dl-Bandwidth) of small cells included in the same set to the same value, it is possible to keep the reception settings of the UE constant when measuring small cells included in the same set, without the need to change them. For example, it is possible to keep the settings of the frequency conversion unit when converting a signal received by an antenna into a baseband signal constant, without the need to change them depending on the downlink transmission bandwidth. This reduces the processing load on the UE.

[0820] Furthermore, the downlink carrier frequencies of small cells included in the same set may be included in the same frequency band. The downlink carrier frequencies of small cells included in the same set may be set to the same value. This can achieve the following effects. When measuring downlink carrier frequencies included in different frequency bands, or cells with different downlink carrier frequencies, it may be necessary to change the reception settings of the UE. For example, it is possible to change the settings of the frequency conversion unit used to convert signals received by the antenna into baseband signals, depending on the frequency band that includes the downlink carrier frequency, or depending on the downlink carrier frequency.

[0821] According to this specific example (1), by assuming that the downlink carrier frequencies of small cells included in the same set are included in the same frequency band, or by setting the downlink carrier frequencies to the same value, it is possible to keep the reception settings of the UE constant when measuring small cells included in the same set, without having to change them. For example, it is possible to keep the settings of the frequency conversion unit when converting a received signal received by an antenna into a baseband signal constant, without having to change them depending on the frequency band that includes the downlink carrier frequency or the downlink carrier frequency. This reduces the processing load on the UE.

[0822] (2) TAC. This parameter is included in SIB1 (see Non-Patent Document 10). By setting the same TAC value for small cells included in the same set, the following effects can be obtained. Small cells are likely to be installed in large numbers due to their narrow coverage. For this reason, it is likely that UEs will move frequently between small cells. Each time a UE moves between small cells with different TACs, TAU processing occurs.

[0823] This specific example (2) makes it possible to prevent TAU ​​processing from occurring when a UE moves between small cells included in the same set by setting the TAC of the small cells included in the same set to the same value. This reduces the processing load on the UE. Furthermore, since the TAU processing is reduced, the processing load on the entire system can be reduced. Furthermore, since the radio signals for TAU are reduced, radio resources can be used more effectively.

[0824] (3) CSG identity. This parameter is included in SIB1 (see Non-Patent Document 10). Small cells included in the same set may belong to the same CSG (Closed Subscriber Group). By setting the same value for the CSG identity for small cells included in the same set, the following effects can be obtained.

[0825] Since small cells have narrow coverage, it is expected that many small cells will be installed. As a result, it is expected that UEs will frequently move between small cells. Every time a UE re-selects a small cell belonging to a different CSG or a small cell with a different CSG identity, it needs to check whether the CSG cell is suitable for camping on or not (see Non-Patent Document 2). A UE can camp on a CSG cell if the UE belongs to the CSG to which the CSG cell belongs.

[0826] By setting the CSG identity to the same value for small cells included in the same set, when moving between small cells that are CSG cells included in the same set, it becomes possible for the UE to eliminate the need to check whether the CSG cell is one that can be camped on or whether it is a suitable CSG cell, thereby reducing the processing load on the UE.

[0827] (4) Uplink transmission bandwidth (UL-Bandwidth). This parameter is included in SIB2 (see Non-Patent Document 10). By setting the same value for the uplink transmission bandwidth for small cells included in the same set, the following effects can be obtained. Small cells are likely to be installed in large numbers due to their narrow coverage. This means that UEs are likely to move frequently between small cells. To support transmissions with different uplink transmission bandwidths, it may be necessary to change the transmission settings of the UE. For example, it may be possible to change the settings of the frequency conversion unit depending on the uplink transmission bandwidth.

[0828] According to this specific example (4), by setting the uplink transmission bandwidth (UL-Bandwidth) of small cells included in the same set to the same value, it is possible to keep the transmission settings of the UE constant when transmitting to small cells included in the same set, without the need to change them. For example, it is possible to keep the settings of the frequency conversion unit constant, without the need to change them depending on the uplink transmission bandwidth. This reduces the processing load on the UE.

[0829] Furthermore, the uplink carrier frequencies of small cells included in the same set may be set to be included in the same frequency band. The uplink carrier frequencies of small cells included in the same set may be set to the same value. This can achieve the following effects.

[0830] When transmitting to an uplink carrier frequency included in a different frequency band or to a cell with a different uplink carrier frequency, it may be necessary to change the transmission settings of the UE. For example, it may be necessary to change the settings of the frequency converter depending on the frequency band that includes the uplink carrier frequency or the uplink carrier frequency.

[0831] According to this specific example (4), by assuming that the uplink carrier frequencies of small cells included in the same set are included in the same frequency band, or by setting the uplink carrier frequencies to the same value, it is possible to keep the transmission settings of the UE constant when transmitting to small cells included in the same set, without the need to change them. For example, it is possible to keep the settings of the frequency conversion unit constant, without the need to change them depending on the frequency band that includes the uplink carrier frequency, or depending on the uplink carrier frequency. This reduces the processing load on the UE.

[0832] (5) SIB4. The SIB4 of small cells included in the same set is set to the same value. In other words, the neighboring cell-related information used for intra-frequency cell re-selection of small cells included in the same set is set to the same. If SIB4 transmission (configuration) is not required, then the SIB4 transmission of small cells included in the same set can be made unnecessary. By setting the SIB4 to the same value for small cells included in the same set, the following effects can be achieved.

[0833] Since small cells have narrow coverage, it is expected that many small cells will be installed. This means that UEs will likely move between small cells frequently. Each time a UE moves between small cells, a process of resetting neighboring cell-related information used for same-frequency cell reselection occurs.

[0834] In this specific example (5), by setting the SIB4 of small cells included in the same set to the same value, it becomes possible to eliminate the need for resetting the neighboring cell-related information used for same-frequency cell reselection when a UE moves between small cells included in the same set, thereby reducing the processing load on the UE.

[0835] Furthermore, the UE does not need to receive SIB4 from small cells included in the same set. In other words, if the UE reselects (or may handover to) a small cell included in the same set, it does not need to receive SIB4 again. This means that the UE does not need to perform reception processing even when SIB4 is scheduled. This makes it possible to reduce the power consumption of the UE.

[0836] Some of the parameters included in SIB4 may be set to the same value. The following four parameters (5-1) to (5-4) are disclosed as specific examples of parameters that may be set to the same value. However, this does not exclude other parameters included in SIB4 from being set to the same value.

[0837] (5-1) Same-frequency neighboring cell list (intraFreqNeighCellList). When camping on a small cell included in the same set, measurements related to same-frequency cell reselection can be performed using the same neighboring cell list. This reduces the processing load on the UE. Unlike conventional same-frequency neighboring cell lists, the list includes information about the serving cell. The serving cell information can be avoided from being used in measurements related to same-frequency cell reselection.

[0838] (5-2) PCI of neighboring cells. When camping on a small cell in the same set, measurements related to same-frequency cell reselection can be performed using the same PCI. This reduces the processing load on the UE.

[0839] (5-3) Same-frequency blacklist (intraFreqBlackCellList). Cells included in the blacklist are not candidates for cell reselection. In measurements related to same-frequency cell reselection when camping on small cells included in the same set, cells that meet the same conditions can be excluded from cell reselection candidates. An example of the same conditions is a cell included in the PCI range included in the same-frequency blacklist. This reduces the processing load on the UE. (5-4) A combination of (5-1) to (5-3).

[0840] (6) SIB5. The SIB5 of small cells included in the same set is set to the same value. In other words, the neighboring cell-related information used for inter-frequency cell re-selection of small cells included in the same set is set to the same value. If SIB5 transmission (configuration) is not required, it is sufficient to make it unnecessary for small cells included in the same set to transmit SIB5. By setting the SIB5 of small cells included in the same set to the same value, the following effects can be obtained.

[0841] Since small cells have narrow coverage, it is expected that many small cells will be installed. This means that UEs will likely move between small cells frequently. Each time a UE moves between small cells, it will have to reconfigure neighboring cell-related information used for different frequency cell reselection.

[0842] In this specific example (6), by setting the SIB5 of small cells included in the same set to the same value, it becomes possible to eliminate the need for the process of resetting neighboring cell-related information used for different frequency cell reselection when a UE moves between small cells included in the same set, thereby reducing the processing load on the UE.

[0843] Furthermore, the UE does not need to receive SIB5 from small cells included in the same set. In other words, if the UE reselects (or may handover to) a small cell included in the same set, it does not need to receive SIB5 again. This means that the UE does not need to perform reception processing even when SIB5 is scheduled. This makes it possible to reduce the power consumption of the UE.

[0844] Some of the parameters included in SIB5 may be set to the same value. The following seven parameters (6-1) to (6-7) are disclosed as specific examples of parameters that may be set to the same value. However, this does not exclude other parameters included in SIB5 from being set to the same value.

[0845] (6-1) Inter-frequency carrier frequency list (interFreqCarrierFreqList). When camping on a small cell included in the same set, measurements related to inter-frequency cell reselection can be performed using the same inter-frequency carrier frequency list. This eliminates the need for frequency settings for inter-frequency measurements, reducing the processing load on the UE.

[0846] (6-2) Downlink carrier frequency (dl-CarrierFreq). When camping on a small cell in the same set, measurements related to different frequency cell reselection can be performed using the same downlink carrier frequency. This eliminates the need for frequency settings for different frequency measurements, reducing the processing load on the UE.

[0847] (6-3) Inter-frequency neighboring cell list (interFreqNeighCellList). When camping on a small cell in the same set, measurements related to inter-frequency cell reselection can be performed using the same neighboring cell list. This reduces the processing load on the UE. ...

Claims

1. A mobile communication system including a mobile terminal and a base station that performs wireless communication with the mobile terminal, the base station notifies the mobile terminal of base station group information; A mobile communication system, wherein the base station group information includes an identifier of a base station group and a list of the base stations that constitute the base station group.

2. 2. The mobile communication system according to claim 1, wherein the base station group information is notified to the mobile terminal from the base station using a signal for notifying the mobile terminal of information individually.

3. 2. The mobile communication system according to claim 1, wherein the base station group information is notified to the mobile terminal from the base station using an RRC (Radio Resource Control) signal.

4. 4. The mobile communication system according to claim 3, wherein the list is a list of identification information indicating the base stations that constitute the base station group.

5. 2. The mobile communication system according to claim 1, wherein the base station group information is information determined by the base station.

6. 2. The mobile communication system according to claim 1, wherein the base station group information is information indicating the base station group to which the base station belongs.

7. 2. The mobile communication system according to claim 1, wherein the base station group information is notified to the mobile terminal from the base station as broadcast information.

8. A base station that performs wireless communication with a mobile terminal, notifying the mobile terminal of base station group information; The base station, wherein the base station group information includes an identifier of a base station group and a list of the base stations that constitute the base station group.

9. A mobile terminal that performs wireless communication with a base station, receiving base station group information notified from the base station; The mobile terminal, wherein the base station group information includes an identifier of a base station group and a list of the base stations that constitute the base station group.

Images