Mobile communication system, base station and mobile terminal

Abstract

A mobile communication system and the like is provided that can at least continue communication depending on the state of a UE that executes CoMP, and furthermore, can obtain better communication quality by executing CoMP. [Solution] A mobile communication system transmits measurement target information indicating which of the signals transmitted from multiple base stations the mobile terminal should measure from the base station to the mobile terminal, transmits measurement result information, which is the result of measuring the measurement target signals indicated by the measurement target information, from the mobile terminal to the base station, and when performing a handover, transmits a signal from the base station to the mobile terminal notifying that the measurement target signals will be removed from the measurement targets.

Description

[Technical field]

[0001] The present invention relates to a mobile communication system or the like in which wireless communication is performed between a plurality of mobile terminal devices and a base station device. [Background technology]

[0002] Among the third-generation communication methods, the Wideband Code division Multiple Access (W-CDMA) method has been available commercially in Japan since 2001. In addition, the High Speed ​​Downlink Packet Access (HSDPA) method has been launched, which realizes even faster data transmission using the downlink by adding a packet transmission channel (High Speed-Downlink Shared Channel: HS-DSCH) to the downlink (individual data channel, individual control channel). Furthermore, the High Speed ​​Uplink Packet Access (HSUPA) method has also been launched to further increase the speed of data transmission in the uplink. W-CDMA is a communication method defined by the 3rd Generation Partnership Project (3GPP), a standardization organization for mobile communication systems, and the Release 10 version of the specification has been compiled.

[0003] In addition, 3GPP is considering a new communication method other than W-CDMA, which is called Long Term Evolution (LTE) for the wireless section and System Architecture Evolution (SAE) for the overall system configuration including the core network and the wireless access network (hereinafter collectively referred to as the network). This communication method is also called the 3.9G (3.9 Generation) system.

[0004] In LTE, the access method, radio channel configuration and protocol are completely different from W-CDMA (HSDPA / HSUPA). For example, W-CDMA uses Code Division Multiple Access, whereas LTE uses OFDM (Orthogonal Frequency Division Multiplexing) for downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) for uplink. In addition, while W-CDMA uses 5MHz bandwidth, LTE allows users to select from 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz and 20MHz for each base station. Also, unlike W-CDMA, LTE does not include circuit switching and is only a packet communication method.

[0005] In LTE, the communication system is constructed using a new core network that is different from GPRS (General Packet Radio Service), which is the core network of W-CDMA, so the LTE radio access network is defined as an independent radio access network separate from the W-CDMA network.

[0006] Therefore, to distinguish it from the W-CDMA communication system, in the LTE communication system, the core network is called EPC (Evolved Packet Core) and the radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access). In the radio access network, the base station that communicates with the mobile terminal (User Equipment: UE) is called eNB (E-UTRAN NodeB). The function of the base station control device (Radio Network Controller) that exchanges control data and user data with multiple base stations is performed by the EPC. The EPC is also called aGW (Access Gateway). The system consisting of the EPC and E-UTRAN is called EPS (Evolved Packet System).

[0007] The LTE communication system provides unicast service and E-MBMS (Evolved Multimedia Broadcast Multicast Service). The E-MBMS service is a broadcast type multimedia service. The E-MBMS service is sometimes simply called MBMS. The E-MBMS service transmits large volume broadcast content such as news, weather forecasts, and mobile broadcasts to multiple mobile terminals. This is also called a point to multipoint service.

[0008] 3GPP's decisions on the overall architecture of the LTE system are described in Non-Patent Document 1 (Chapter 4). The overall architecture will be described with reference to FIG. 1. FIG. 1 is an explanatory diagram showing the configuration of an LTE-based communication system. In FIG. 1, if a control protocol for a mobile terminal 101, such as RRC (Radio Resource Control), and a user plane, such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate at a base station 102, then E-UTRAN is composed of one or more base stations 102.

[0009] The base stations 102 schedule and transmit paging signals (also called paging messages) notified from a mobility management entity (MME) 103. The base stations 102 are connected to each other via an X2 interface. The base stations 102 are also connected to an evolved packet core (EPC) via an S1 interface. More specifically, the base stations 102 are connected to a mobility management entity (MME) 103 via an S1_MME interface and to a serving gateway (S-GW) 104 via an S1_U interface.

[0010] The MME 103 distributes paging signals to a single or multiple base stations 102. The MME 103 also performs mobility control in an idle state. The MME 103 manages a tracking area list when a mobile terminal is in an idle state and when it is in an active state.

[0011] The S-GW 104 transmits and receives user data to and from one or more base stations 102. The S-GW 104 serves as a local mobility anchor point during handover between base stations. The EPC also includes a P-GW (PDN Gateway). The P-GW performs packet filtering for each user and assigns UE-ID addresses.

[0012] The control protocol RRC between the mobile terminal 101 and the base station 102 performs broadcast, paging, RRC connection management, etc. The states of the base station and mobile terminal in RRC include RRC_IDLE and RRC_CONNECTED. In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell re-selection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can transmit and receive data to and from the network. Also, in RRC_CONNECTED, handover (HO), measurement of neighbor cells, etc. are performed.

[0013] The decisions made by 3GPP regarding the frame configuration in the LTE system, which are described in Non-Patent Document 1 (Chapter 5), will be described with reference to FIG. 2. FIG. 2 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. In FIG. 2, one radio frame is 10 ms. The radio frame is divided into 10 subframes of equal size. The subframe is divided into two slots of equal size. The first and sixth subframes of each radio frame include a downlink synchronization signal (SS). The synchronization signal includes a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

[0014] Channels for MBSFN (Multimedia Broadcast multicast service Single Frequency Network) and channels for non-MBSFN are multiplexed on a subframe basis. MBSFN Transmission is a simulcast transmission technique that is realized by transmitting the same waveform from multiple cells at the same time. MBSFN transmissions from multiple cells in an MBSFN Area are recognized by mobile terminals as a single transmission. MBSFN is a network that supports such MBSFN transmissions. Hereinafter, a subframe for MBSFN transmission is referred to as an MBSFN subframe.

[0015] Non-patent document 2 describes an example of signaling when allocating MBSFN subframes. Fig. 3 is an explanatory diagram showing the configuration of an MBSFN frame. As shown in Fig. 3, a radio frame including an MBSFN subframe is allocated for each allocation period (radio frame allocation period). An MBSFN subframe is a subframe allocated for MBSFN in a radio frame defined by an allocation period and an allocation offset (radio frame allocation offset), and is a subframe for transmitting multimedia data. A radio frame that satisfies the following formula (1) is a radio frame including an MBSFN subframe. SFN mod radioFrameAllocationPeriod=radioFrameAllocationOffset …(1)

[0016] MBSFN subframe allocation is performed using 6 bits. The leftmost bit in Figure 3 defines the MBSFN allocation for the second subframe (#1). The second bit from the left defines the MBSFN allocation for the third subframe (#2), the third bit from the left defines the MBSFN allocation for the fourth subframe (#3), the fourth bit from the left defines the MBSFN allocation for the seventh subframe (#6), the fifth bit from the left defines the eighth subframe (#7), and the sixth bit from the left defines the MBSFN allocation for the ninth subframe (#8). If the bit indicates "1", it indicates that the corresponding subframe is allocated for MBSFN.

[0017] 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. The physical channel will be explained using FIG. 4. FIG. 4 is an explanatory diagram explaining the physical channel used in the LTE communication system.

[0018] In Figure 4, a Physical Broadcast Channel (PBCH) 401 is a channel for downlink transmission from a base station 102 to a mobile terminal 101. A BCH transport block is mapped to four subframes in a 40 ms interval. There is no explicit signaling of the 40 ms timing.

[0019] A Physical Control Format Indicator Channel (PCFICH) 402 is a channel for downlink transmission from the base station 102 to the mobile terminal 101. The PCFICH notifies the mobile terminal 101 of the number of OFDM symbols used for PDCCHs from the base station 102. The PCFICH is transmitted for each subframe.

[0020] The physical downlink control channel (PDCCH) 403 is a channel for downlink transmission from the base station 102 to the mobile terminal 101. The PDCCH reports resource allocation information of a downlink shared channel (DL-SCH), which is one of the transport channels shown in FIG. 5 described later, resource allocation information of a paging channel (PCH), which is one of the transport channels shown in FIG. 5, and hybrid automatic repeat reQuest (HARQ) information related to the DL-SCH. The PDCCH carries an uplink scheduling grant. The PDCCH carries Acknowledgement (Acknowledgement) / Nack (Negative Acknowledgement), which are response signals to uplink transmission. The PDCCH is also called an L1 / L2 control signal.

[0021] A physical downlink shared channel (PDSCH) 404 is a channel for downlink transmission from the base station 102 to the mobile terminal 101. A downlink shared channel (DL-SCH) which is a transport channel and a PCH which is a transport channel are mapped to the PDSCH.

[0022] A physical multicast channel (PMCH) 405 is a channel for downlink transmission from the base station 102 to the mobile terminal 101. A multicast channel (MCH), which is a transport channel, is mapped to the PMCH.

[0023] The Physical Uplink Control Channel (PUCCH) 406 is a channel for uplink transmission from the mobile terminal 101 to the base station 102. The PUCCH carries Ack / Nack, which is a response signal to a downlink transmission. The PUCCH carries a CQI (Channel Quality Indicator) report. The CQI is quality information indicating the quality of received data or the quality of a communication path. The PUCCH also carries a Scheduling Request (SR).

[0024] The Physical Uplink Shared Channel (PUSCH) 407 is a channel for uplink transmission from the mobile terminal 101 to the base station 102. The Uplink Shared Channel (UL-SCH), which is one of the transport channels shown in FIG. 5, is mapped to the PUSCH.

[0025] A physical hybrid ARQ indicator channel (PHICH) 408 is a channel for downlink transmission from the base station 102 to the mobile terminal 101. The PHICH carries Ack / Nack, which is a response signal to an uplink transmission. A physical random access channel (PRACH) 409 is a channel for uplink transmission from the mobile terminal 101 to the base station 102. The PRACH carries a random access preamble.

[0026] Downlink reference signals (RS) are symbols known in mobile communication systems. The following five types of downlink reference signals are defined: Cell-specific Reference Signals (CRS), MBSFN reference signals, UE-specific reference signals such as Demodulation Reference Signals (DM-RS), Positioning Reference Signals (PRS), and Channel-State Information Reference Signals (CSI-RS). Reference signal received power (RSRP) measurement is one of the physical layer measurements of a mobile terminal.

[0027] The transport channel described in Non-Patent Document 1 (Chapter 5) will be explained with reference to Fig. 5. Fig. 5 is an explanatory diagram explaining the transport channel used in the LTE communication system. Fig. 5(A) shows the mapping between the downlink transport channel and the downlink physical channel. Fig. 5(B) shows the mapping between the uplink transport channel and the uplink physical channel.

[0028] Among the downlink transport channels shown in Fig. 5A, 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).

[0029] Retransmission control using HARQ (Hybrid ARQ) is applied to the Downlink Shared Channel (DL-SCH). DL-SCH can be broadcast to the entire coverage of a base station (cell). DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called persistent scheduling. DL-SCH supports discontinuous reception (DRX) of mobile terminals to reduce power consumption of mobile terminals. DL-SCH is mapped to the physical downlink shared channel (PDSCH).

[0030] The Paging Channel (PCH) supports DRX of mobile terminals to enable low power consumption of the mobile terminals. The PCH is required to be broadcast to the entire coverage of the base station (cell). The PCH is mapped to physical resources such as the Physical Downlink Shared Channel (PDSCH) that can be dynamically used for traffic.

[0031] The Multicast Channel (MCH) is used for broadcasting to the entire coverage of a base station (cell). The MCH supports SFN combining of MBMS services (MTCH and MCCH) in multi-cell transmission. The MCH supports semi-static resource allocation. The MCH is mapped to the PMCH.

[0032] Among the uplink transport channels shown in FIG. 5B, 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).

[0033] The Random Access Channel (RACH) shown in FIG. 5B is limited to control information. The RACH has a risk of collision. The RACH is mapped to the Physical Random Access Channel (PRACH).

[0034] Here we explain HARQ. HARQ is a technology that improves the communication quality of a transmission path by combining Automatic Repeat reQuest (ARQ) and Forward Error Correction. HARQ has the advantage that error correction works effectively by retransmission even for transmission paths where communication quality changes. In particular, by combining the reception result of the initial transmission and the reception result of the retransmission when retransmitting, it is possible to obtain further quality improvement.

[0035] An example of a retransmission method will be described below. If the received data cannot be decoded correctly on the receiving side, in other words, if a CRC (Cyclic Redundancy Check) error occurs (CRC=NG), the receiving side will send a "Nack" to the transmitting side. The transmitting side that receives the "Nack" will retransmit the data. If the received data can be decoded correctly on the receiving side, in other words, if no CRC error occurs (CRC=OK), the receiving side will send an "Ack" to the transmitting side. The transmitting side that receives the "Ack" will send the next data.

[0036] One example of the HARQ method is Chase Combining. Chase Combining is a method in which the same data is transmitted in the initial transmission and retransmission, and the gain is improved by combining the initial transmission data and the retransmission data in the retransmission. Chase Combining is based on the idea that even if the initial transmission data contains an error, it contains partially correct data, and by combining the correct parts of the initial transmission data and the retransmission data, data can be transmitted with higher accuracy. Another example of the HARQ method is IR (Incremental Redundancy). IR increases redundancy, and by transmitting a parity bit in the retransmission, the redundancy is increased by combining it with the initial transmission, and the quality is improved by the error correction function.

[0037] The logical channels described in Non-Patent Document 1 (Chapter 6) will be explained with reference to Fig. 6. Fig. 6 is an explanatory diagram explaining logical channels used in an LTE communication system. Fig. 6(A) shows mapping between downlink logical channels and downlink transport channels. Fig. 6(B) shows mapping between uplink logical channels and uplink transport channels.

[0038] 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), which is a transport channel, or the Downlink Shared Channel (DL-SCH).

[0039] The Paging Control Channel (PCCH) is a downlink channel for transmitting paging information and changes to system information. The PCCH is used when the cell location of the mobile terminal is unknown to the network. The PCCH, which is a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

[0040] 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.

[0041] The Multicast Control Channel (MCCH) is a downlink channel for point-to-multipoint transmission. The MCCH is used for transmission of MBMS control information for one or several MTCHs from the network to the mobile terminals. The MCCH is used only by mobile terminals receiving MBMS. The MCCH is mapped to the Multicast Channel (MCH), which is a transport channel.

[0042] A Dedicated Control Channel (DCCH) is a channel that transmits dedicated control information between a mobile terminal and a network on a one-to-one basis. DCCH is used when a mobile terminal is in an RRC connection. DCCH is mapped to an uplink shared channel (UL-SCH) in the uplink and to a downlink shared channel (DL-SCH) in the downlink.

[0043] A Dedicated Traffic Channel (DTCH) is a one-to-one communication channel for transmitting user information to an individual mobile terminal. DTCH exists in both uplink and downlink. In uplink, DTCH is mapped to an uplink shared channel (UL-SCH) and in downlink, DTCH is mapped to a downlink shared channel (DL-SCH).

[0044] Multicast Traffic Channel (MTCH) is a downlink channel for transmitting traffic data from the network to the mobile terminal. MTCH is a channel used only by mobile terminals receiving MBMS. MTCH is mapped to the Multicast Channel (MCH).

[0045] CGI stands for Cell Global Identification. ECGI stands for E-UTRAN Cell Global Identification. In LTE, LTE-A (Long Term Evolution Advanced) and UMTS (Universal Mobile Telecommunication System), CSG (Closed Subscriber Group) cells are introduced. The CSG cells are described below (see Chapter 3.1 of Non-Patent Document 3).

[0046] A CSG (Closed Subscriber Group) cell is a cell for which an operator specifies available subscribers (hereinafter, may be referred to as a "cell for specific subscribers").

[0047] An identified subscriber is permitted to access one or more cells in a Public Land Mobile Network (PLMN). The cell or cells to which an identified subscriber is permitted to access are called "CSG cell(s)". However, there are access restrictions in a PLMN.

[0048] A CSG cell is a part of a PLMN that broadcasts a unique CSG identity (CSG ID; CSG-ID) and broadcasts a CSG indication of "TRUE". Members of a pre-registered and authorized subscriber group access the CSG cell using the CSG-ID, which is access permission information.

[0049] The CSG-ID is broadcast by a CSG cell or cells. There are multiple CSG-IDs in a mobile communication system. And the CSG-ID is used by a mobile terminal (UE) to facilitate the access of CSG-related members.

[0050] The location of a mobile terminal is tracked in units of an area consisting of one or more cells. Location tracking is performed to track the location of a mobile terminal even when it is in standby mode and to enable the mobile terminal to be called, in other words, to receive calls. The area for tracking the location of a mobile terminal is called a tracking area.

[0051] The CSG White List is a list that may be stored in a Universal Subscriber Identity Module (USIM) in which all CSG IDs of CSG cells to which a subscriber belongs are recorded. The CSG White List may also be simply called a white list or an allowed CSG list. The MME performs access control for access of a mobile terminal through a CSG cell (see Chapter 4.3.1.2 of Non-Patent Document 4). Specific examples of access of a mobile terminal include attach, combined attach, detach, service request, and Tracking Area Update procedure (see Chapter 4.3.1.2 of Non-Patent Document 4).

[0052] The service types of a mobile terminal in standby mode are described below (see Chapter 4.3 of Non-Patent Document 3). The service types of a mobile terminal in standby mode include limited service (also called limited service), standard service (normal service), and operator service. Limited services are emergency calls, ETWS (Earthquake and Tsunami Warning System), and CMAS (Commercial Mobile Alert System) on acceptable cells, which will be described later. Standard service (also called normal service) is a public service on an appropriate cell, which will be described later. Operator service is a service only for operators on a reserved cell, which will be described later.

[0053] The term "suitable cell" is explained below. A "suitable cell" is a cell on which a UE may camp to receive normal services. Such a cell must satisfy the following conditions (1) and (2).

[0054] (1) The cell is part of the selected PLMN or the registered PLMN, or a PLMN in the "Equivalent PLMN List".

[0055] (2) The following conditions (a) through (d) must be met in accordance with the latest information provided by the Non-Access Stratum (NAS): (a) the cell is not a barred cell; (b) The cell is part of a Tracking Area (TA) that is not part of the "Prohibited LAs for Roaming" list. In that case, the cell must satisfy (1) above. (c) the cell meets the cell selection evaluation criteria. (d) for a cell that is identified by System Information (SI) as a CSG cell, the CSG-ID is part of the UE's CSG WhiteList, i.e., is included in the UE's CSG WhiteList.

[0056] The term "acceptable cell" is explained below. An "acceptable cell" is a cell on which a UE may camp to receive limited services. Such a cell shall satisfy all of the following requirements (1) and (2).

[0057] (1) The cell is not a prohibited cell (also known as a "barred cell"). (2) The cell meets the cell selection evaluation criteria.

[0058] A "barred cell" is indicated in the system information. A "reserved cell" is indicated in the system information.

[0059] "Camping on a cell" refers to a state in which a UE completes a cell selection or cell reselection process and selects a cell for monitoring system information and paging information. A cell on which a UE camps is sometimes called a "serving cell."

[0060] In 3GPP, base stations called Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB) are under consideration. HNB in ​​UTRAN and HeNB in ​​E-UTRAN are base stations for home, corporate and commercial access services, for example. Non-Patent Document 5 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.

[0061] Each mode has the following characteristics: In the open access mode, the HeNB and the HNB are operated as normal cells of a normal operator. In the closed access mode, the HeNB and the HNB are operated as CSG cells, which are accessible only by CSG members. In the hybrid access mode, the HeNB and the HNB are operated as CSG cells to which non-CSG members are also allowed to access at the same time. In other words, a cell in the hybrid access mode (also called a hybrid cell) is a cell that supports both the open access mode and the closed access mode.

[0062] In 3GPP, among all PCIs (Physical Cell Identities), 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 on PCI splits (also called PCI split information) is notified by 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.

[0063] Non-Patent Document 6 discloses the basic operation of a mobile terminal using PCI split. A mobile terminal that does not have PCI split information needs to perform a cell search using all PCIs, for example, all 504 codes. On the other hand, a mobile terminal that has PCI split information can perform a cell search using the PCI split information.

[0064] Furthermore, 3GPP is currently formulating standards for Long Term Evolution Advanced (LTE-A) as Release 10 (see Non-Patent Documents 7 and 8).

[0065] In the LTE-A system, support for relays and relay nodes (RNs) is being considered in order to obtain high communication speeds, high throughput at cell edges, new coverage areas, and the like. The relay node, which is a relay device, is wirelessly connected to a radio access network via a cell called a donor cell (hereinafter sometimes referred to as a "donor eNB (DeNB)"). Within the range of the donor cell, the link from the network (NW) to the relay node shares the same frequency band as the link from the network to the UE. In this case, a UE compatible with 3GPP Release 8 can also be connected to the donor cell. The link between the donor cell and the relay node is called a backhaul link, and the link between the relay node and the UE is called an access link.

[0066] In the FDD (Frequency Division Duplex) backhaul link multiplexing method, transmission from DeNB to RN is performed in the downlink (DL) frequency band, and transmission from RN to DeNB is performed in the uplink (UL) frequency band. In the relay resource division method, the link from DeNB to RN and the link from RN to UE are time-division multiplexed in one frequency band, and the link from RN to DeNB and the link from UE to RN are also time-division multiplexed in one frequency band. In this way, the relay can prevent the transmission of the relay from interfering with the reception of the own relay.

[0067] In 3GPP, in addition to normal eNBs (macro cells), pico eNBs (pico cells), HeNBs (HNBs, CSG cells), nodes for hot zone cells, relay nodes, remote radio heads (RRHs), repeaters, and other so-called local nodes are being considered. A network consisting of the various types of cells mentioned above is sometimes called a heterogeneous network (HETNET).

[0068] In LTE, frequency bands available for communication (hereinafter sometimes referred to as "operating bands") are predetermined. Non-Patent Document 9 describes the frequency bands.

[0069] In the LTE-A system, carrier aggregation (CA), which aggregates two or more component carriers (CCs) (also called aggregation), is being considered in order to support wider frequency bandwidths (transmission bandwidths) of up to 100 MHz.

[0070] A UE that supports LTE, i.e. 3GPP Release 8 or 9, can transmit and receive on only one CC corresponding to one serving cell, whereas a UE that supports 3GPP Release 10 is expected to have the capability to simultaneously transmit and receive on multiple CCs corresponding to multiple serving cells, or to only receive, or to only transmit.

[0071] Each CC uses the configuration of 3GPP Release 8 or 9, and CA supports contiguous CCs, non-contiguous CCs, and CCs with different frequency bandwidths. It is not possible for a UE to configure more uplink CCs (UL CCs) than the number of downlink CCs (DL CCs). CCs configured by the same eNB do not need to provide the same coverage. CCs are compatible with 3GPP Release 8 or 9.

[0072] In CA, there is one independent HARQ entity per serving cell in both uplink and downlink. A transport block is generated per TTI per serving cell. Each transport block and HARQ retransmission is mapped to a single serving cell.

[0073] When CA is configured, the UE has only one RRC connection with the network. In the RRC connection, one serving cell provides NAS mobility information and security input. This cell is called a Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC). In the uplink, the carrier corresponding to the PCell is the Uplink Primary Component Carrier (UL PCC).

[0074] According to the capability of the UE, a secondary cell (SCell) is configured to form a pair of a PCell and a serving cell. In the downlink, the carrier corresponding to the SCell is a downlink secondary component carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is an uplink secondary component carrier (UL SCC).

[0075] For one UE, a set of one PCell and a serving cell consisting of one or more SCells is configured.

[0076] 3GPP is currently studying the aforementioned LTE Advanced (LTE-A) as a new, more advanced wireless communication method (see Non-Patent Document 7 and Non-Patent Document 8). LTE-A is based on the LTE wireless communication method, with some new technologies added to it. These new technologies include wider bandwidth extension, a technology that supports wider bandwidths, and Coordinated Multiple Point transmission and reception (CoMP). CoMP, which is being studied by 3GPP for LTE-A, is described in Non-Patent Document 10.

[0077] CoMP is a technology that aims to expand the coverage of high data rates, improve throughput at cell edges, and increase throughput in communication systems by coordinating transmission or reception between multiple geographically separated points. CoMP is divided into downlink CoMP (DL CoMP) and uplink CoMP (UL CoMP).

[0078] In DL CoMP, PDSCH to one mobile terminal (UE) is transmitted in a coordinated manner between multiple points (multipoints). PDSCH to one UE may be transmitted from one point of the multipoints, or from multiple points of the multipoints. In DL CoMP, the serving cell is a single cell that transmits resource allocation by PDCCH.

[0079] As methods for DL ​​CoMP, joint processing (JP) and coordinated scheduling (CS) or coordinated beamforming (CB) (hereinafter sometimes referred to as "CS / CB") are being considered.

[0080] In JP, data is available at each point in the CoMP cooperating set. JP includes Joint Transmission (JT) and Dynamic Point Selection (DPS). DPS includes Dynamic Cell Selection (DCS). In JT, PDSCH is transmitted from multiple points at a given time, specifically, from some or all of the CoMP cooperating set. In DPS, PDSCH is transmitted from one point in the CoMP cooperating set at a given time.

[0081] CS / CB is available only for data transmission from the serving cell, where user scheduling or beamforming decisions are made along with coordination among cells that correspond to the CoMP cooperating set.

[0082] Units and cells are considered as points for transmitting and receiving data at multiple points, and base stations (NB, eNB, HNB, HeNB), RRU (Remote Radio Unit), RRE (Remote Radio Equipment), RRH (Remote Radio Head), relay nodes (Relay Node: RN), etc. Units and cells that perform coordinated multipoint transmission are sometimes called multipoint units and multipoint cells, respectively. [Prior art documents] [Non-patent literature]

[0083] [Non-Patent Document 1] 3GPP TS36.300 V10.5.0 [Non-Patent Document 2] 3GPP TS36.331 V10.3.0 [Non-Patent Document 3] 3GPP TS36.304 V10.3.0 Chapter 3.1, Chapter 4.3, Chapter 5.2.4 [Non-Patent Document 4] 3GPP TR 23.830 V9.0.0 [Non-Patent Document 5] 3GPP S1-083461 [Non-Patent Document 6] 3GPP R2-082899 [Non-Patent Document 7] 3GPP TR 36.814 V9.0.0 [Non-Patent Document 8] 3GPP TR 36.912 V10.0.0 [Non-Patent Document 9] 3GPP TS 36.101 V10.3.0 [Non-Patent Document 10] 3GPP TR 36.819 V11.0.0 Summary of the Invention [Problem to be solved by the invention]

[0084] As mentioned above, the 3GPP is studying the CoMP (CoMP) technology. By implementing CoMP on UEs, it is possible to expand the coverage of high data rates, improve the throughput at cell edges, and increase the throughput in the communication system. However, the 3GPP has not yet fully studied the CoMP technology.

[0085] For example, it is considered to provide several sets of cells related to CoMP. However, when considering the communication quality by CoMP, the power consumption of UE, the amount of signaling between UE and serving cell, etc., the currently proposed sets may not be sufficient. Also, in the method of selecting cells in the set, if only the complex radio wave environment that varies with time is used as the selection criterion, good reception quality may not be obtained even if CoMP is performed.

[0086] Furthermore, no discussion has been made on HO processing for UEs that are running CoMP. In CoMP, cooperative processing is performed among multiple cells. Therefore, if HO processing is performed for a UE while CoMP is running, processing among multiple cells is required, so HO cannot be performed using conventional HO processing, and communication between the UE and the cell cannot be continued.

[0087] An object of the present invention is to provide a mobile communication system etc. that can at least continue communication depending on the state of a UE executing CoMP, and further, can obtain better communication quality by executing CoMP. [Means for solving the problem]

[0088] The mobile communication system of the present invention is a mobile communication system in which a plurality of base stations cooperate to perform wireless communication with a mobile terminal, and is characterized in that measurement target information indicating which of the signals transmitted from the plurality of base stations the mobile terminal should measure is transmitted from the base station to the mobile terminal, measurement result information which is the result of measuring the measurement target signals indicated by the measurement target information is transmitted from the mobile terminal to the base station, and when a handover is performed, a signal notifying the mobile terminal that the measurement target signals will be removed from the measurement targets is transmitted from the base station to the mobile terminal. Effect of the Invention

[0089] According to the mobile communication system of the present invention, at least communication can be continued depending on the state of the mobile terminal device performing cooperative communication, and further, better communication quality can be obtained by performing cooperative communication.

[0090] The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0091] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of an LTE communication system. [Diagram 2] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Diagram 3] FIG. 2 is an explanatory diagram showing the structure of an MBSFN frame. [Figure 4] FIG. 2 is an explanatory diagram illustrating physical channels used in an LTE communication system. [Diagram 5] FIG. 1 is an explanatory diagram illustrating transport channels used in an LTE communication system. [Figure 6] FIG. 2 is an explanatory diagram illustrating logical channels used in an LTE communication system. [Figure 7] 1 is a block diagram showing the overall configuration of an LTE mobile communication system being discussed in 3GPP. [Figure 8] FIG. 8 is a block diagram showing a configuration of a mobile terminal 71 shown in FIG. 7, which is a mobile terminal according to the present invention. [Figure 9] FIG. 8 is a block diagram showing a configuration of a base station 72 shown in FIG. 7 which is a base station according to the present invention. [Figure 10] 8 is a block diagram showing a configuration of an MME unit 73 shown in FIG. 7 which is an MME according to the present invention. [Figure 11] FIG. 8 is a block diagram showing a configuration of a HeNBGW 74 shown in FIG. 7 which is a HeNBGW according to the present invention. [Figure 12] 1 is a flowchart showing an outline of operations from cell search to standby performed by a mobile terminal (UE) in an LTE communication system. [Figure 13] FIG. 1 is a diagram for explaining a set of cells used to perform CoMP. [Figure 14] 1 is a diagram for explaining the inclusion relationship of a set of cells used to perform CoMP. [Figure 15] FIG. 2 is a diagram showing an example of a sequence of the mobile communication system in the first embodiment. [Figure 16] FIG. 2 is a diagram showing an example of a sequence of the mobile communication system in the first embodiment. [Figure 17] 1 is a diagram for explaining the inclusion relationship between the CoMP active set and other sets. [Figure 18] FIG. 11 is a diagram showing an example of a sequence of a mobile communication system in the second embodiment. [Figure 19] FIG. 11 is a diagram showing an example of a sequence of a mobile communication system in the third embodiment. [Figure 20] FIG. 11 is a diagram showing another example of the sequence of the mobile communication system in the third embodiment. [Figure 21] FIG. 11 is a diagram showing yet another example of the sequence of the mobile communication system in the third embodiment. [Figure 22] 1 is a diagram for explaining a set related to CoMP and an RS measured by a UE. [Figure 23] FIG. 11 is a diagram for explaining the communication quality of cells in a set regarding CoMP. [Figure 24] FIG. 13 is a diagram showing an example of a sequence of a mobile communication system in the fifth embodiment. [Diagram 25] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a second modification of the fifth embodiment. [Figure 26] FIG. 1 is a diagram illustrating ePDCCH. [Figure 27] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the sixth embodiment. [Figure 28] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the sixth embodiment. [Figure 29] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 30] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 31] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 32] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 33] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 34] A block diagram to explain a specific example of a cell unified entity. [Diagram 35] A block diagram to explain a specific example of another cell unified entity. [Diagram 36] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Figure 37] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Figure 38] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Figure 39]FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 40] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 41] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 42] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 43] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 44] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Diagram 45] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. [Figure 46] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the eighth embodiment. [Figure 47] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the eighth embodiment. [Figure 48] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the eighth embodiment. [Figure 49] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a first modification of the eighth embodiment. [Figure 50] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a first modification of the eighth embodiment. [Figure 51] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a first modification of the eighth embodiment. [Figure 52] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a first modification of the eighth embodiment. [Figure 53] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a second modification of the eighth embodiment. [Figure 54] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a second modification of the eighth embodiment. [Figure 55] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a second modification of the eighth embodiment. [Figure 56] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the ninth embodiment. [Figure 57] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the ninth embodiment. [Figure 58] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the ninth embodiment. [Figure 59] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the ninth embodiment. [Figure 60] 1 is a diagram for explaining the concept of CoMP communication between multiple sub-eNB devices and a UE. [Figure 61] 1 is a diagram for explaining the concept of CoMP communication between multiple sub-eNB devices and a UE. [Figure 62] FIG. 23 is a diagram for explaining a change of a serving cell in the tenth embodiment. [Figure 63] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the tenth embodiment. [Figure 64] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the tenth embodiment. [Figure 65] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the tenth embodiment. [Figure 66] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in the tenth embodiment. [Figure 67] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a first modification of the tenth embodiment. [Figure 68] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a first modification of the tenth embodiment. [Figure 69] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a first modification of the tenth embodiment. [Figure 70]FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a first modification of the tenth embodiment. [Figure 71] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a second modification of the tenth embodiment. [Figure 72] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a second modification of the tenth embodiment. [Figure 73] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a second modification of the tenth embodiment. [Figure 74] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in an eleventh embodiment. [Figure 75] FIG. 23 is a diagram showing an example of a sequence of a mobile communication system in a tenth modification of the eleventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0092] Embodiment 1 Fig. 7 is a block diagram showing the overall configuration of an LTE-based mobile communication system under discussion in 3GPP. In 3GPP, the overall configuration of a system including CSG (Closed Subscriber Group) cells (Home-eNodeB (Home-eNB; HeNB) of E-UTRAN, Home-NB (HNB) of UTRAN) and non-CSG cells (eNodeB (eNB) of E-UTRAN, NodeB (NB) of UTRAN, BSS of GERAN) is under consideration, and the configuration shown in Fig. 7 has been proposed for E-UTRAN (see Chapter 4.6.1 of Non-Patent Document 1).

[0093] 7 will be described. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 71 is capable of wireless communication with a base station device (hereinafter referred to as "base station") 72, and transmits and receives signals via wireless communication. The base stations 72 are classified into an eNB72-1 which is a macro cell, and a Home-eNB72-2 which is a local node. The eNB72-1 has a relatively large coverage as the coverage range in which communication with the mobile terminal (UE) 71 is possible. The Home-eNB72-2 has a relatively small coverage as its coverage.

[0094] The eNB72-1 is connected to an MME, or an 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 eNB72-1 and the MME unit 73. A plurality of MME units 73 may be connected to one eNB72-1. The MME unit 73 corresponds to a management means. The MME unit 73 is included in the EPC, which is a core network. The eNBs 72-1 are connected to each other via an X2 interface, and control information is communicated between the eNBs 72-1.

[0095] The Home-eNB72-2 is connected to the MME unit 73 via an S1 interface, and control information is communicated between the Home-eNB72-2 and the MME unit 73. A plurality of Home-eNB72-2 are connected to one MME unit 73. Alternatively, the Home-eNB72-2 is connected to the MME unit 73 via a Home-eNB GateWay (HeNBGW) 74. The Home-eNB72-2 and the HeNBGW74 are connected to each other via an S1 interface, and the HeNBGW74 and the MME unit 73 are connected to each other via the S1 interface.

[0096] One or a plurality of Home-eNBs 72-2 are connected to one HeNBGW 74, and information is communicated through an S1 interface. The HeNBGW 74 is connected to one or a plurality of MME units 73, and information is communicated through an S1 interface.

[0097] The MME unit 73 and HeNBGW 74 are upper node devices, and control connections between the eNB72-1 and Home-eNB72-2, which are base stations, and the mobile terminal (UE) 71. The MME unit 73, specifically the MME and S-GW constituting the MME unit 73, and the HeNBGW 74 correspond to management means. The MME unit 73 and HeNBGW 74 are included in the EPC, which is a core network.

[0098] Furthermore, 3GPP is considering the following configuration. The X2 interface between Home-eNBs 72-2 is supported. That is, the Home-eNBs 72-2 are connected via the X2 interface, and control information is communicated between the Home-eNBs 72-2. From the MME unit 73, the HeNBGW 74 appears as the Home-eNB 72-2. From the Home-eNB 72-2, the HeNBGW 74 appears as the MME unit 73.

[0099] In either case where the Home-eNB72-2 is connected to the MME unit 73 via the HeNBGW74 or where it is directly connected to the MME unit 73, the interface between the Home-eNB72-2 and the MME unit 73 is the same as the S1 interface. The HeNBGW74 does not support mobility to or from the Home-eNB72-2 that spans a plurality of MME units 73. The Home-eNB72-2 configures and supports only one cell.

[0100] A base station device supports only one cell, such as the Home-eNB 72-2, but is not limited to this, and one base station device may support multiple cells. When one base station device supports multiple cells, each cell functions as a base station device.

[0101] FIG. 8 is a block diagram showing the configuration of the mobile terminal 71 shown in FIG. 7, which is a mobile terminal according to the present invention. The transmission process of the mobile terminal 71 shown in FIG. 8 will be described. First, the control data from the protocol processing unit 801 and the user data from the application unit 802 are stored in the transmission data buffer unit 803. The data stored in the transmission data buffer unit 803 is passed to the encoder unit 804, where encoding such as error correction is performed. There may be data that is directly output from the transmission data buffer unit 803 to the modulation unit 805 without encoding. The data that has been encoded by the encoder unit 804 is modulated by the modulation unit 805. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 806, where it is converted into a radio transmission frequency. Thereafter, a transmission signal is transmitted from the antenna 807 to the base station 72.

[0102] Moreover, the receiving process of the mobile terminal 71 is executed as follows. A radio signal from the base station 72 is received by the antenna 807. The received signal is converted from a radio receiving frequency to a baseband signal by the frequency conversion unit 806, and demodulated by the demodulation unit 808. The demodulated data is passed to the decoder unit 809, where decoding such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 801, and the user data is passed to the application unit 802. A series of processes of the mobile terminal 71 is controlled by the control unit 810. Therefore, although the control unit 810 is omitted in FIG. 8, it is connected to each of the units 801 to 809.

[0103] Fig. 9 is a block diagram showing the configuration of the base station 72 shown in Fig. 7 which is a base station according to the present invention. The transmission process of the base station 72 shown in Fig. 9 will be described. The EPC communication unit 901 transmits and receives data between the base station 72 and the EPC (the MME unit 73, the HeNBGW 74, etc.). The other base station communication unit 902 transmits and receives data with other base stations. The EPC communication unit 901 and the other base station communication unit 902 each exchange information with a protocol processing unit 903. The control data from the protocol processing unit 903, and the user data and control data from the EPC communication unit 901 and the other base station communication unit 902 are stored in a transmission data buffer unit 904.

[0104] The data stored in the transmission data buffer unit 904 is passed to an encoder unit 905, where it undergoes encoding processing such as error correction. Some data may be output directly from the transmission data buffer unit 904 to a modulator unit 906 without undergoing encoding processing. The encoded data is modulated in the modulator unit 906. The modulated data is converted into a baseband signal, and then output to a frequency converter unit 907, where it is converted into a radio transmission frequency. The transmission signal is then transmitted from an antenna 908 to one or more mobile terminals 71.

[0105] The reception process of the base station 72 is executed as follows. A radio signal from one or more mobile terminals 71 is received by an antenna 908. The received signal is converted from a radio reception frequency to a baseband signal by a frequency conversion unit 907, and demodulated by a demodulation unit 909. The demodulated data is passed to a decoder unit 910, where decoding such as error correction is performed. Of the decoded data, control data is passed to a protocol processing unit 903 or an EPC communication unit 901 or an other base station communication unit 902, and user data is passed to the EPC communication unit 901 and the other base station communication unit 902. A series of processes of the base station 72 is controlled by a control unit 911. Therefore, although the control unit 911 is omitted in FIG. 9, it is connected to each unit 901 to 910.

[0106] The other base station communication unit 902 corresponds to a notification unit and an acquisition unit. The transmission data buffer unit 904, the encoder unit 905, the modulator unit 906, the frequency converter unit 907, the antenna 908, the demodulator unit 909, and the decoder unit 910 correspond to a communication unit.

[0107] The functions of the Home-eNB72-2 discussed in 3GPP are shown below (see Chapter 4.6.2 of Non-Patent Document 1). The Home-eNB72-2 has the same functions as the eNB72-1. In addition, when connecting to a HeNBGW74, the Home-eNB72-2 has a function of discovering an appropriate serving HeNBGW74. The Home-eNB72-2 connects to only one HeNBGW74. In other words, when connecting to a HeNBGW74, the Home-eNB72-2 does not use the Flex function in the S1 interface. When the Home-eNB72-2 is connected to one HeNBGW74, it does not connect to another HeNBGW74 or another MME unit 73 at the same time.

[0108] The TAC and PLMN ID of the Home-eNB72-2 are supported by the HeNBGW74. When the Home-eNB72-2 is connected to the HeNBGW74, the selection of the MME unit 73 in "UE attachment" is performed by the HeNBGW74 instead of the Home-eNB72-2. The Home-eNB72-2 may be deployed without network planning. In this case, the Home-eNB72-2 is moved from one geographical area to another geographical area. Therefore, the Home-eNB72-2 in this case needs to be connected to a different HeNBGW74 depending on the location.

[0109] FIG. 10 is a block diagram showing the configuration of the MME according to the present invention. FIG. 10 shows the configuration of the MME 73a included in the MME unit 73 shown in FIG. 7 described above. The PDN GW communication unit 1001 transmits and receives data between the MME 73a and the PDN GW. The base station communication unit 1002 transmits and receives data between the MME 73a and the base station 72 via the S1 interface. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 1001 to the base station communication unit 1002 via the user plane communication unit 1003, and transmitted to one or more base stations 72. If the data received from the base station 72 is user data, the user data is passed from the base station communication unit 1002 to the PDN GW communication unit 1001 via the user plane communication unit 1003, and transmitted to the PDN GW.

[0110] When the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 1001 to the control plane control unit 1005. When the data received from the base station 72 is control data, the control data is passed from the base station communication unit 1002 to the control plane control unit 1005.

[0111] The HeNBGW communication unit 1004 is provided when a HeNBGW 74 is present, and transmits and receives data via an interface (IF) between the MME 73a and the HeNBGW 74 depending on the information type. Control data received from the HeNBGW communication unit 1004 is passed from the HeNBGW communication unit 1004 to a control plane control unit 1005. A result of processing in the control plane control unit 1005 is transmitted to the PDN GW via a PDN GW communication unit 1001. In addition, a result of processing in the control plane control unit 1005 is transmitted to one or more base stations 72 by the S1 interface via a base station communication unit 1002, and is also transmitted to one or more HeNBGW 74 via the HeNBGW communication unit 1004.

[0112] 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 general processing for the control plane. The NAS security unit 1005-1 performs security for NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 1005-2 performs management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 1005-3 performs mobility management in the standby state (also called the idle state; LTE-IDLE state, or simply idle), generation and control of paging signals in the standby state, addition, deletion, update, search, and tracking area (TA) list management for one or more mobile terminals 71 under its control.

[0113] The MME 73a starts a paging protocol by transmitting a paging message to a cell belonging to a tracking area (TA) 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 72-2 connected to the MME 73a.

[0114] In the management of CSG-ID, the relationship between the mobile terminal corresponding to the CSG-ID and the CSG cell is managed (for example, added, deleted, updated, searched). This relationship may be, for example, the relationship between one or more mobile terminals registered for user access to a certain CSG-ID and the CSG cell belonging to the CSG-ID. In the management of whitelist, the relationship between the mobile terminal and the CSG-ID is managed (for example, added, deleted, updated, searched). For example, the whitelist may store one or more CSG-IDs registered by a user of a certain mobile terminal. The management of these CSGs may be performed by other parts of the MME 73a. A series of processes of the MME 73a is controlled by the control unit 1006. Therefore, although the control unit 1006 is omitted in FIG. 10, it is connected to each of the units 1001 to 1005.

[0115] The functions of the MME 73a discussed in 3GPP are as follows (see Chapter 4.6.2 of Non-Patent Document 1). The MME 73a performs access control for one or more mobile terminals that are members of a Closed Subscriber Group (CSG). The MME 73a allows the execution of paging optimization as an option.

[0116] Fig. 11 is a block diagram showing a configuration of the HeNBGW 74 shown in Fig. 7 which is a HeNBGW according to the present invention. An EPC communication unit 1101 transmits and receives data between the HeNBGW 74 and the MME 73a via the S1 interface. A base station communication unit 1102 transmits and receives data between the HeNBGW 74 and the Home-eNB 72-2 via the S1 interface. A location processing unit 1103 performs a process of transmitting registration information and the like out of the data from the MME 73a passed via the EPC communication unit 1101 to a plurality of Home-eNBs 72-2. The data processed by the location processing unit 1103 is passed to the base station communication unit 1102 and transmitted to one or a plurality of Home-eNBs 72-2 via the S1 interface.

[0117] Data that does not require processing in the location processing unit 1103 and is merely passed through (transmitted) is passed from the EPC communication unit 1101 to the base station communication unit 1102, and transmitted to one or more Home-eNBs 72-2 via the S1 interface. A series of processes in the HeNBGW 74 is controlled by a control unit 1104. Thus, although omitted in FIG. 11, the control unit 1104 is connected to each of the units 1101 to 1103.

[0118] The functions of the HeNBGW 74 discussed in 3GPP are shown below (see Chapter 4.6.2 of Non-Patent Document 1). The HeNBGW 74 relays S1 applications. Although it is part of the procedure of the MME 73a to the Home-eNB 72-2, the HeNBGW 74 terminates S1 applications that are not related to the mobile terminal 71. When the HeNBGW 74 is deployed, procedures unrelated to the mobile terminal 71 are communicated between the Home-eNB 72-2 and the HeNBGW 74, and between the HeNBGW 74 and the MME 73a. An X2 interface is not set between the HeNBGW 74 and other nodes. The HeNBGW 74 allows the execution of paging optimization as an option.

[0119] Next, an example of a cell search method in a mobile communication system is shown. Fig. 12 is a flow chart showing an outline of a 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, the mobile terminal 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.

[0120] 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 (Physical Cell Identity) assigned to each cell. 504 different PCIs are being considered. These 504 PCIs are used to achieve synchronization and to detect (identify) the PCI of the synchronized cell.

[0121] 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. A code that has a one-to-one correspondence with the PCI is used for the reference signal (RS). By correlating with the code, it is possible to separate the cell from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST1201, it is possible to detect the RS and measure the RS received power.

[0122] 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.

[0123] 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 DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, SFN (System Frame Number), and the like.

[0124] Next, in step ST1205, the DL-SCH of the cell is received based on the cell configuration information of the MIB, and SIB (System Information Block) 1 in the broadcast information BCCH is obtained. SIB 1 includes information on access to the cell, information on cell selection, and scheduling information of other SIBs (SIBk; k is an integer ≧2). SIB 1 also includes a TAC (Tracking Area Code).

[0125] Next, in step ST1206, the mobile terminal compares the TAC of the SIB1 received in step ST1205 with the TAC portion of the tracking area identity (TAI) in a tracking area (TA) list that the mobile terminal already holds. The TA (Tracking Area) list is also called a TAI list. The TAI is an identifier of a TA, 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 the code number of a TA.

[0126] If the comparison result in step ST1206 shows that the TAC received in step ST1205 is the same as the TAC included in the TA (Tracking Area) list, the mobile terminal enters standby mode in the cell. If the comparison result shows that the TAC received in step ST1205 is not included in the TA (Tracking Area) list, the mobile terminal requests a core network (Core Network, EPC) including an MME, etc., to change the TA (Tracking Area) in order to perform a TAU (Tracking Area Update) through the cell. The core network updates the TA (Tracking Area) list based on the identification number (UE-ID, etc.) of the mobile terminal transmitted from the mobile terminal together with the TAU request signal. The core network transmits the updated TA (Tracking Area) list to the mobile terminal. The mobile terminal rewrites (updates) the TAC list held by the mobile terminal based on the received TA (Tracking Area) list. After that, the mobile terminal enters standby mode in the cell.

[0127] In LTE, LTE-A and Universal Mobile Telecommunication System (UMTS), the introduction of Closed Subscriber Group (CSG) cells is being considered. As mentioned above, only one or more mobile terminals registered in a CSG cell are allowed to access it. A CSG cell and one or more registered mobile terminals constitute one CSG. A CSG thus constituted is assigned a unique identification number called a CSG-ID. One CSG may have multiple CSG cells. Once a mobile terminal registers in one CSG cell, it can access other CSG cells in the CSG to which that CSG cell belongs.

[0128] Also, Home-eNBs in LTE and LTE-A and Home-NBs in UMTS may be used as CSG cells. A mobile terminal registered in a CSG cell has a whitelist. Specifically, the whitelist is stored in a Subscriber Identity Module (SIM) or USIM. The whitelist stores CSG information of the CSG cell in which the mobile terminal has registered. Specific examples of CSG information include CSG-ID, Tracking Area Identity (TAI), and TAC. As long as CSG-ID and TAC are associated with each other, either one of them may be used. As long as CSG-ID and TAC are associated with ECGI, ECGI may be used.

[0129] From the above, a mobile terminal that does not have a whitelist (in the present invention, this also includes the case where the whitelist is empty) cannot access a CSG cell and can only access non-CSG cells. On the other hand, a mobile terminal that has a whitelist can access both the CSG cell with the registered CSG-ID and non-CSG cells.

[0130] HeNBs and HNBs are required to support various services. For example, in one service, an operator registers a mobile terminal with a certain HeNB or HNB and allows only the registered mobile terminal to access the HeNB or HNB cell, thereby increasing the wireless resources that the mobile terminal can use and enabling high-speed communication. To compensate for this, the operator sets a higher fee than usual.

[0131] In order to realize such services, CSG (Closed Subscriber Group) cells that can be accessed only by registered (subscribed, member) mobile terminals are introduced. It is required that many CSG (Closed Subscriber Group) cells are installed in shopping streets, apartment buildings, schools, companies, etc. For example, a CSG cell is installed for each store in a shopping street, for each room in an apartment building, for each classroom in a school, and for each section in a company, and a usage method is required in which only users registered in each CSG cell can use the CSG cell. HeNB / HNB is required not only to complement communication outside the coverage of a macro cell (area complementation type HeNB / HNB), but also to support various services as described above (service provision type HeNB / HNB). For this reason, there are also cases where HeNB / HNB is installed within the coverage of a macro cell.

[0132] As mentioned above, support for CoMP is being considered as a new technology for LTE-A. Also, a set of cells or points used to execute CoMP is being considered. In the present invention, the set of cells used to execute CoMP includes the following (1) to (5). It is not limited to cells, and may be a point. In the following description, a set of points or cells used to execute CoMP is collectively referred to as a "CoMP set."

[0133] (1) RRM measurement set. The RRM (Radio Resource Management) measurement set refers to a set of cells obtained by measurements described in the specifications of Releases 8 to 10, specifically, by CRS (Cell-specific Reference Signal) measurements.

[0134] (2) CoMP cooperating set: A CoMP cooperating set is a set of cells that can perform CoMP.

[0135] (3) CoMP coordination area (CoMP coordination cells) The CoMP coordination area refers to a radio area formed by cells capable of CoMP.

[0136] (4) CoMP measurement set. The CoMP measurement set is a set of cells for which CSI (Channel State Indication)-RS is measured and reported. The CoMP measurement set is selected from the RRM measurement set.

[0137] (5) CoMP transmission point. A CoMP transmission point is a cell that transmits data to a UE that is executing CoMP. The CoMP transmission point is selected from a CoMP measurement set. If there is a CoMP active set (described later), the CoMP transmission point may be selected from the CoMP active set. If there is no CoMP active set (described later), the CoMP transmission point is selected from the CoMP measurement set.

[0138] The RRM measurement set corresponds to a set of cells to be detected, and the measurements described in the aforementioned Releases 8 to 10 specifications, specifically CRS measurements, correspond to the detection process performed by the UE to determine whether wireless communication is possible or not.

[0139] The CoMP cooperating set corresponds to a cooperation-capable cell set, and is a set of candidate cells for which the UE performs detection processing for whether or not cooperative communication (CoMP communication) is possible. The CoMP measurement set corresponds to a cooperation target cell set, and is a set of target cells for which the UE performs detection processing for whether or not CoMP communication is possible.

[0140] The central entity mentioned above is an entity that centrally coordinates one or more point CoMP (see Non-Patent Document 10). The central entity corresponds to a coordinating means. The central entity is a logical entity and may be physically configured in any device. For example, the central entity may be configured in the eNB or RRH, or may be configured separately from the eNB and RRH. The central entity may also be configured in the HeNBGW.

[0141] Fig. 13 is a diagram for explaining a set of cells used to perform CoMP. In Fig. 13, an RRM measurement set 1302 is indicated by hatching with thin diagonal lines downward to the left, a CoMP cooperating set 1303 is indicated by hatching with matte lines, a CoMP measurement set 1304 is indicated by hatching with thick diagonal lines downward to the right, and a CoMP transmission point 1305 is indicated by hatching with thick diagonal lines downward to the left.

[0142] An RRM measurement set 1302, a CoMP cooperating set 1303, a CoMP measurement set 1304, and a CoMP transmission point 1305 are all configured for a UE 1301. In FIG.

[0143] Fig. 14 is a diagram for explaining the inclusion relationship of a set of cells used to execute CoMP. In Fig. 14, an RRM measurement set is represented by a circle indicated by reference symbol "1401", a CoMP measurement set is represented by a circle indicated by reference symbol "1402", and a CoMP transmission point is represented by a circle indicated by reference symbol "1403". As shown in Fig. 14, a part or all of the RRM measurement set 1401 becomes a CoMP measurement set 1402, and a part or all of the CoMP measurement set 1402 becomes a CoMP transmission point 1403.

[0144] 3GPP does not disclose any procedure for actually executing CoMP. Since it is unclear how to use the set of cells used to execute the above-mentioned CoMP, CoMP cannot be executed. In this embodiment, a method of using and configuring each set of cells, a method of notifying between the UE and the serving cell, and the procedure thereof are disclosed in order to execute CoMP.

[0145] Fig. 15 and Fig. 16 are diagrams showing an example of a sequence of a mobile communication system in the first embodiment. Fig. 15 and Fig. 16 are connected at the position of a boundary line BL1. Fig. 15 and Fig. 16 show a sequence when CoMP is executed for a desired UE when a central entity is configured in a serving cell. Since this sequence shows a case where a central entity is configured in a serving cell, the central entity and the serving cell are not particularly distinguished from each other and are referred to as a serving cell.

[0146] In step ST1501, the serving cell configures an RRM measurement configuration in order to set a range in which the desired UE is to perform RRM measurements. Here, the desired UE is assumed to be "UE1". For example, either one or both of a frequency and a reporting condition are configured as the RRM measurement configuration. For example, an event that triggers the execution of a report is configured as the reporting condition. A cell to be measured may be specified, and a cell identity (Cell-ID) such as a PCI of the cell may be configured as the RRM measurement configuration. For example, if an RRM measurement set for UE1 has already been configured on the network side, the RRM measurement set may be used. Also, a list of neighboring cells (neighbor cell list) may be the RRM measurement set.

[0147] The RRM measurement configuration, the notification and the measurement report may be for CoMP. A frequency, a reporting condition, or a cell identity suitable for CoMP is set.

[0148] As another method, the conventional RRM measurement configuration for mobility, the notification, and the measurement report may be used. In the serving cell, when the frequency, the report condition, or the cell identity set for mobility can be used for CoMP, the conventional RRM measurement configuration for mobility, the notification, and the measurement report may be used. In addition, the serving cell may be configured to set the frequency, the report condition, or the cell identity that can be used for both mobility and CoMP. This allows the RRM measurement configuration, the notification, and the measurement report to be shared, thereby reducing the amount of signaling and the control load.

[0149] In Step ST1502, the serving cell notifies UE1 of the RRM measurement configuration set in Step ST1501. Dedicated signaling is used for notifying the UE1 of the RRM measurement configuration. RRC signaling is used as the dedicated signaling.

[0150] In step ST1503, UE1 measures the CRS (hereinafter may be referred to as "CRS measurement") in accordance with the received RRM measurement configuration. Specifically, UE1 uses the frequency notified in the RRM measurement configuration as the CRS measurement to detect a cell that uses the frequency as a carrier frequency.

[0151] The CRS measurement may be performed until UE1 receives the RRM measurement configuration and then changes or releases the RRM measurement configuration. In this case, the CRS measurement may be performed periodically or periodically. In Fig. 15 and Fig. 16, the dashed line connecting ST1503 and ST1522 indicates that the CRS measurement is performed until UE1 receives the RRM measurement configuration and then changes or releases the RRM measurement configuration, as described above.

[0152] In step ST1504, when the measurement result of the CRS of the detected cell matches the reporting condition, UE1 reports the measurement result of the CRS to the serving cell by using a measurement report message. For example, UE1 notifies the serving cell of the cell identity and the RSRP of a cell whose CRS received power (RSRP) is equal to or greater than a threshold set in the RRM measurement configuration. As another example, UE1 may notify the serving cell of the cell identity and the RSRP of a cell whose difference between the CRS received power (RSRP) of the detected cell and the CRS received power (RSRP) of the serving cell is equal to or greater than a threshold set in the RRM measurement configuration. The received power of the CRS is not limited, and may be reception quality (Reference Signal Received Quality: RSRQ). Also, the report of the CRS measurement result may be performed periodically or periodically. The serving cell may be included in the RRM measurement configuration and the measurement report. In addition, the CRS measurement result of the serving cell may be always reported in the measurement report.

[0153] In Step ST1505, the serving cell creates an RRM measurement set including one or more reported cells, based on the measurement report message notified from UE1.

[0154] If an RRM measurement set already exists for UE1, a cell in the RRM measurement set may be added, deleted, or changed based on the measurement report message in step ST1504. Alternatively, for each cell in the RRM measurement set, whether the received power or received quality of the cell at that time is equal to or greater than a threshold may be recorded and managed in association with the cell identity of the cell in the RRM measurement set.

[0155] In Step ST1506, UE1 and the serving cell perform data communication in at least one of downlink (DL) and uplink (UL).

[0156] In Step ST1507, UE1 derives a CQI (Channel Quality Indicator) from the CRS and feeds it back to the serving cell.

[0157] In step ST1508, the serving cell uses the CQI received from UE1 to decide whether to execute CoMP, that is, whether to turn CoMP on or off. For example, the serving cell decides to execute CoMP when the CQI falls below a predetermined threshold (hereinafter referred to as "threshold A"), and decides to stop executing CoMP when the CQI exceeds a predetermined threshold (hereinafter referred to as "threshold B"). It is preferable to provide a predetermined offset between threshold A and threshold B to provide hysteresis. This makes it possible for the serving cell to decide whether to execute CoMP for UE1. When the processing of step ST1508 ends, the serving cell proceeds to step ST1530.

[0158] In step ST1530, the serving cell determines a CoMP measurement set for UE1. That is, the serving cell selects a CoMP measurement set. Specifically, the serving cell selects a cell in the CoMP measurement set (hereinafter, may be referred to as a "cell in the CoMP measurement set"). The cell in the CoMP measurement set is selected from the cell in the RRM measurement set (hereinafter, may be referred to as a "cell in the RRM measurement set"). As an index for selection, the cell identity of the cell in the RRM measurement set, the number of cells that can be included in the CoMP measurement set, or the received power (RSRP) or received quality (RSRQ) of the reference symbol of the cell (hereinafter, may be referred to as "RSRP / RSRQ"). These may be used together with the CQI.

[0159] Also, as another index for selection, for example, the load of each cell may be used. When the load in each cell is high, it is not selected as a CoMP measurement set, and when the load is low, it is selected as a CoMP measurement set. By using the load of each cell in addition to the index, it is possible to determine whether or not to enable CoMP execution according to the load situation of each cell, and it is possible to improve the throughput of the mobile communication system.

[0160] However, the RRM measurement set may include cells that do not belong to the CoMP cooperating set. In this case, even if a cell that does not belong to the CoMP cooperating set is selected as the CoMP measurement set, CoMP cannot be performed. Therefore, selecting a cell that does not belong to the CoMP cooperating set as the CoMP measurement set is wasteful and may cause malfunction.

[0161] Therefore, in this embodiment, cells selected for the CoMP measurement set are limited to cells that belong to the CoMP cooperating set in the RRM measurement set, which makes it possible to include only cells capable of CoMP in the CoMP measurement set.

[0162] In step ST1530, when the serving cell is the only cell in the CoMP measurement set, the serving cell may determine to stop the execution of CoMP. In that case, the serving cell may decide to release the CoMP measurement configuration and notify UE1, or may proceed to the processing of step ST1527. As will be disclosed later, in a case where the serving cell is not included in the CoMP measurement set, when the CoMP measurement set has only one cell, the serving cell may determine not to stop the execution of CoMP. CoMP may be executed by the serving cell and the cell in the CoMP measurement set. When the processing of step ST1530 ends, the processing proceeds to step ST1509.

[0163] In step ST1509, the serving cell sets a CoMP measurement configuration for UE1. As the CoMP measurement configuration, for example, a cell identity of a cell in the CoMP measurement set, a CSI-RS configuration of a cell in the CoMP measurement set, or a configuration of a demodulation reference signal (DM-RS) for UE1 of a cell in the CoMP measurement set is set. As the CSI-RS configuration, a period in which CSI-RS is transmitted is set for each cell.

[0164] In step ST1510, the serving cell notifies UE1 of the CoMP measurement configuration. Dedicated signaling is used for the notification of the CoMP measurement configuration. RRC signaling is used as the dedicated signaling.

[0165] In Step ST1511, UE1, which has received the CoMP measurement configuration in Step ST1510, configures at least one of the CSI-RS configuration and the DM-RS configuration of the cell in the CoMP measurement set that is set in the CoMP measurement configuration.

[0166] In Step ST1513, the serving cell transmits CSI-RS from the CoMP measurement set.

[0167] In Step ST1512, UE1 measures the CSI-RS of the cells in the CoMP measurement set. For example, UE1 measures the RSRP / RSRQ of the CSI-RS. In this embodiment, UE1 derives CSI from the measurement value of the CSI-RS in Step ST1514. The process of deriving the CSI in Step ST1514 does not have to be performed.

[0168] The measurement of CSI-RS may be performed for each cell or each point. The measurement method of these CSI-RS may be determined in advance by a standard, or may be included in the CoMP measurement configuration and notified to UE1 from the serving cell. By including it in the CoMP measurement configuration and notifying it, it becomes possible to change the measurement method dynamically or quasi-statically. Therefore, it is possible to select a CoMP transmission point suitable for CoMP.

[0169] The measurement of the CSI-RS of the CoMP measurement set may be performed after the UE1 receives the CoMP measurement configuration until the UE1 receives a release of the CoMP measurement configuration. The measurement of the CSI-RS may be performed periodically or periodically.

[0170] In step ST1515, UE1 reports the CSI-RS measurement result (CSI-RS measurement report) of the cell in the CoMP measurement set, for example, the measurement result of RSRP / RSRQ, to the serving cell. When CSI is derived in step ST1514 as in the present embodiment, in step ST1515, UE1 reports the derivation result of CSI (CSI feedback) together with the CSI-RS measurement result to the serving cell. The reporting of the CSI-RS measurement result may be performed periodically, periodically, or when a predetermined condition is satisfied. The serving cell may be included in the CoMP measurement configuration and the CSI-RS measurement report. Also, the CSI-RS measurement result of the serving cell may always be reported in the CSI-RS measurement report.

[0171] In step ST1516, the serving cell determines the CoMP transmission point from the CSI-RS measurement result (CSI-RS measurement report) reported from UE1, for example, the measurement result of RSRP / RSRQ, and the derived result of CSI (CSI feedback). If the derived result of CSI is not reported in step ST1515, the serving cell determines the CoMP transmission point from the measurement result of CSI-RS. At this time, other indicators, for example, the load of each cell, may be used. If the load in each cell is high, the CoMP transmission point is not set, and if the load is low, the CoMP transmission point is set. In this way, by using the load of each cell in addition, it is possible to determine whether or not to enable CoMP execution according to the load situation of each cell, and the throughput of the mobile communication system can be improved. After the process of step ST1516 ends, the process proceeds to step ST1518.

[0172] In step ST1518, the serving cell performs scheduling (CoMP scheduling) by including information indicating the CoMP transmission points in a physical downlink control channel (PDCCH) for UE 1. The information indicating the CoMP transmission points may be included in downlink control information (Downlink Control Information: DCI) of the PDCCH.

[0173] The information indicating the CoMP transmission point may be a cell identity such as PCI. However, a cell identity such as PCI requires a large number of bits, and therefore, if the cell identity is included in the PDCCH, a problem occurs in that the capacity of the PDCCH is insufficient.

[0174] In order to solve the problem of insufficient capacity of the PDCCH, it is preferable to number the cells in the CoMP measurement set and indicate the CoMP transmission point by the number. Since the number is limited to the number of cells in the CoMP measurement set, it is possible to reduce the amount of information by using the number. When using the number, it is preferable to include the relationship between the cell identity of the cell in the CoMP measurement set and the numbered number in the CoMP measurement configuration set in step ST1509, and notify the UE1 from the serving cell in step ST1510.

[0175] In step ST1517, UE1 receives the PDCCH from the serving cell, obtains the CoMP transmission point information included in the DCI of the PDCCH, and receives the CoMP transmission points. To receive the CoMP transmission points, it is preferable to use the CoMP measurement configuration received in step ST1510.

[0176] In Step ST1519, UE1 and the serving cell perform transmission and reception using CoMP. Also, UE1 derives CSI from the CSI-RS and feeds it back to the serving cell.

[0177] In Step ST1520, the serving cell determines whether to change the CoMP transmission point. Specifically, the serving cell determines whether to change the CoMP transmission point by using the CSI feedback information.

[0178] When the serving cell decides to change the CoMP transmission point, it uses the measurement result of the CSI-RS of the CoMP measurement set and the other indicators mentioned above to select cells to add to the CoMP measurement set or to remove or change from the CoMP measurement set. At this time, the CSI feedback information of the CoMP transmission point and the measurement result of the CSI-RS of the CoMP measurement set may be used together.

[0179] In step ST1520, if it is determined that the CoMP transmission point is to be changed, the process returns to step ST1516 after the cell selection, and if it is determined that the CoMP transmission point is not to be changed, the process proceeds to step ST1521.

[0180] In Step ST1516, the serving cell that has selected the cell adds, deletes, or changes the CoMP transmission point, and then proceeds to Step ST1518. In Step ST1518, the serving cell includes information indicating the changed CoMP transmission point in the DCI of the PDCCH for UE1, and performs scheduling (CoMP scheduling).

[0181] In Step ST1521, UE1 and the serving cell perform transmission and reception using CoMP. Also, UE1 derives CSI from the CSI-RS and feeds it back to the serving cell.

[0182] In Step ST1522, UE1 performing CRS measurement reports the CRS measurement result to the serving cell by using a measurement report message in Step ST1523.

[0183] In step ST1524, the serving cell that has received the measurement report message changes the RRM measurement set, specifically, changes the cells in the RRM measurement set, as necessary. When the serving cell decides to change the RRM measurement set using the cell identity and CRS measurement result information received by the measurement report message, the serving cell selects a cell to be added, deleted, or changed, and adds, deletes, or changes the RRM measurement set.

[0184] When the RRM measurement set is changed in step ST1524, it may be necessary to change the CoMP measurement set selected from the RRM measurement set, specifically, to add, delete, or change a cell in the CoMP measurement set. Therefore, in step ST1525, the serving cell determines whether or not to change the CoMP measurement set. Specifically, the serving cell determines whether or not to change a cell in the CoMP measurement set.

[0185] When it is determined in Step ST1525 that the CoMP measurement set, specifically, the cell in the CoMP measurement set is to be changed, the serving cell returns to Step ST1530 and executes the process of Step ST1530. In Step ST1510, the serving cell notifies UE1 of the CoMP measurement configuration changed in Step ST1530.

[0186] At this time, all of the CoMP measurement configurations may be notified, or the difference from the most recently notified CoMP measurement configuration may be notified. By notifying all of the CoMP measurement configurations, the same CoMP measurement configuration can be used reliably on the UE and the network side, and malfunctions can be prevented. On the other hand, by notifying the difference from the most recently notified CoMP measurement configuration, the amount of signaling notified from the serving cell to the UE can be reduced.

[0187] If it is determined in Step ST1525 that the CoMP measurement set, specifically, the cells in the CoMP measurement set, are not to be changed, the mobile station proceeds to Step ST1526.

[0188] In Step ST1526, UE1 and the serving cell continue to transmit and receive using CoMP. Also, UE1 derives CSI from the CSI-RS and feeds it back to the serving cell.

[0189] In step ST1526, the serving cell performing transmission / reception to UE1 by CoMP decides whether to execute CoMP. The decision as to whether to execute CoMP may be made using the measurement result of CSI-RS. Instead of CQI in the processing of step ST1507, the same processing method may be used using CSI-RS. Also, the decision as to whether to execute CoMP may be made using the measurement result of CRS. Also, the measurement result of CSI-RS and the measurement result of CRS may be used together.

[0190] Here, consider a case where the serving cell decides to release CoMP, that is, to stop executing CoMP, in step ST1527. In this case, in step ST1528, the serving cell notifies UE1 of the release of the CoMP measurement configuration. Dedicated signaling is used for the notification of the release of the CoMP measurement configuration. RRC signaling is used as the dedicated signaling.

[0191] In step ST1528, the serving cell that has notified UE1 of the release of the CoMP measurement configuration stops executing CoMP for UE1. This stops the transmission of CSI-RS from the CoMP measurement set, the transmission of CoMP transmission point scheduling from the serving cell, and the transmission of data from the CoMP transmission point.

[0192] In step ST1529, UE1 that has received the release of the CoMP measurement configuration releases (releases) the settings of the CoMP measurement configuration, such as the CoMP measurement set. This also stops the measurement of the CoMP measurement set. Since UE1 is not notified of the scheduling of the CoMP transmission point from the serving cell, it will no longer perform transmission and reception by CoMP.

[0193] In this embodiment, a method of using each set of cells, a method of notifying between a UE and a serving cell, and the procedure thereof when CoMP is performed are disclosed. By using the method disclosed above, it becomes possible to perform CoMP.

[0194] Embodiment 2 As described in the first embodiment, the UE measures the CSI-RS of each cell in the CoMP measurement set. Therefore, when the number of cells in the CoMP measurement set is large, the power consumption of the UE increases. By reducing the number of cells in the CoMP measurement set, the power consumption of the UE can be prevented from increasing. However, when the number of cells in the CoMP measurement set is reduced, the number of cells that are candidates for the CoMP transmission point decreases, which causes a problem that the optimal CoMP transmission point is not selected.

[0195] In addition, by changing the CoMP measurement set quickly and frequently, the problem of not selecting the optimal CoMP transmission point is solved, but since the change of the cell in the CoMP measurement set is performed by RRC signaling, the change cannot be performed quickly and delays occur. In addition, since the changed CoMP measurement set must be notified to the UE frequently, the amount of RRC signaling increases, which is a problem.

[0196] In order to solve the above problems, this embodiment discloses providing a subset of cells in a CoMP measurement set. In this embodiment, a subset consisting of some or all of the cells in the CoMP measurement set is provided. Such a subset is called a CoMP active set.

[0197] 17 is a diagram for explaining the inclusion relationship between the CoMP active set and other sets. As shown in FIG. 17, the CoMP active set is configured such that a part or all of the RRM measurement set 1401 becomes the CoMP measurement set 1402, a part or all of the CoMP measurement set 1402 becomes the CoMP active set 1601, and a part or all of the CoMP active set 1601 becomes the CoMP transmission point 1403.

[0198] This paper discloses a method for selecting cells in a CoMP active set (hereinafter sometimes referred to as "cells in the CoMP active set"). Cells in the CoMP active set are selected from cells in the CoMP measurement set. The following two (1) and (2) are disclosed as indicators for determining which cell to select.

[0199] (1) The measurement results of CSI-RS by the UE are used as a judgment indicator. (2) The uplink communication quality transmitted from the UE is used as a judgment indicator.

[0200] As the measurement result of CSI-RS as the judgment index in (1), the RSRP or RSRQ of CSI-RS may be used, or CSI derived from the measurement value of CSI-RS may be used. Also, the RSRP or RSRQ of CSI-RS may be used in combination with the CSI derived from the measurement value of CSI-RS. By using the measurement result of CSI-RS as the judgment index for cell selection, the communication quality of the PDSCH region to which the data to be subjected to CoMP is mapped can be known, so that it becomes possible to select a cell suitable for performing CoMP.

[0201] As the uplink communication quality as the judgment index in (2), the measurement result of SRS (Sounding Reference Signal) may be used, or the measurement result of RS for demodulation of PUCCH or PUSCH may be used. By using the uplink communication quality as the judgment index for cell selection, the UE does not need to measure and report CSI. Therefore, the power consumption of the UE can be reduced. In addition, in Time Division Duplex (TDD), the downlink uses the same frequency band as the uplink, so that it is possible to select a cell suitable for executing CoMP even in downlink CoMP.

[0202] The judgment indicators (1) and (2) may be used together instead of using each of them individually. The cells in the CoMP active set may be selected using both of them. These judgment indicators may also be used together with the measurement result of CRS by the UE.

[0203] A method of notifying a UE of a CoMP active set is disclosed. A serving cell notifies a UE of cells in the CoMP active set. The notification of the CoMP active set may be performed as necessary. For example, when the CoMP active set is not configured, the notification of the CoMP active set may not be performed. In this case, when the CoMP active set is not notified, the UE may determine that the CoMP active set is not configured.

[0204] The notification of the CoMP active set may be performed by MAC signaling. By using MAC signaling, the CoMP active set can be notified with lower delay than when using RRC signaling. In addition, since RRC signaling is unnecessary, the amount of RRC signaling does not increase by notifying the CoMP active set.

[0205] The information indicating the cells in the CoMP active set may be a cell identity such as a PCI. However, a cell identity such as a PCI requires a large number of bits, and thus, if the cell identity is included in the MAC signaling, there is a problem that the overhead in the MAC increases.

[0206] To solve this problem, it is preferable to number the cells in the CoMP measurement set and indicate the cells in the CoMP active set by the number. Since the number is limited to the number of cells in the CoMP measurement set, it is possible to reduce the amount of information by using the number. The number may be the same as the number of the cells in the CoMP measurement set provided for the CoMP transmission point disclosed in the first embodiment.

[0207] When using the above numbers, the relationship between the cell identities of the cells in the CoMP measurement set and the numbered numbers should be included in the CoMP measurement configuration set in step ST1509, and the serving cell should notify UE1 in step ST1510.

[0208] When the notification of the CoMP active set is performed by MAC signaling, for example, the CoMP active set information may be included in a MAC CE (MAC control element) and notified. For each cell in the CoMP measurement set, a bitmap may be used in which one bit indicates whether the cell is included in the CoMP active set. The bitmap may be arranged in ascending or descending order of the number of cells in the CoMP measurement set. This allows the amount of information to be the number of bits of the number of cells in the CoMP measurement set.

[0209] The case where a cell is included in the CoMP measurement set may be referred to as "activate" (activate: act), and the case where a cell is not included in the CoMP measurement set may be referred to as "deactivate" (deactivate: deact). In other words, a set of cells to be activated in the CoMP measurement set may be referred to as a CoMP active set.

[0210] The operation of the UE when the CoMP active set is notified is disclosed. The UE measures the CSI-RS of the cells in the CoMP active set notified by MAC signaling, and reports the measurement result to the serving cell.

[0211] When the CoMP active set is set, the UE may not measure and report the CSI-RS of cells outside the CoMP active set. This eliminates the need for the UE to measure the CSI-RS of all cells in the CoMP measurement set, thereby reducing power consumption. In this case, the measurement and reporting results of the CRS by the UE or the uplink communication quality from the UE may be used as a criterion for selecting cells to be included in the CoMP active set.

[0212] As another method, when a CoMP active set is configured, the UE may make at least one of the CSI-RS measurement period and the CSI-RS report period different between cells in the CoMP active set and cells outside the CoMP active set. Specifically, the CSI-RS measurement period and the CSI-RS report period of cells outside the CoMP active set may be made longer than the CSI-RS measurement period and the CSI-RS report period of cells in the CoMP active set.

[0213] This makes it possible to use the measurement results of CSI-RS with a short period when selecting a CoMP transmission point, and to select a CoMP transmission point suitable for CoMP. On the other hand, by using the measurement results of CSI-RS with a long period when selecting a CoMP active set, it becomes possible to reduce the power consumption of the UE. Therefore, it becomes possible to reduce the power consumption of the UE while enabling the selection of a CoMP transmission point suitable for CoMP.

[0214] When the CoMP active set is set, the UE may be configured not to measure and report the CSI-RS of cells outside the CoMP active set, or the UE may be configured to make at least one of the measurement period and the report period of the CSI-RS different between the cells in the CoMP active set and the cells outside the CoMP active set. The individual signaling may be RRC signaling. For example, the individual signaling may be notified at the same time as notifying the UE of the CoMP measurement configuration. Also, the setting may be dynamically or semi-statically set.

[0215] The above-mentioned settings may be statically determined in advance by a standard, which enables the UE to determine how to measure the CSI-RS of cells outside the CoMP active set when the UE is notified of the CoMP active set by MAC signaling.

[0216] When a CoMP active set is configured, it may be possible to prevent a cell outside the CoMP active set from transmitting CSI-RS, thereby preventing unnecessary transmission from the cell.

[0217] Furthermore, when a CoMP active set is set, it may be possible to prevent CoMP from being performed by cells outside the CoMP active set for a UE that is a CoMP target.

[0218] In the CoMP measurement set, since CoMP can be performed for the UE that is the target of CoMP, the data of the UE, information related thereto, and scheduling information need to be transmitted and received between cells in the CoMP measurement set. Therefore, if the number of cells in the CoMP measurement set is large, the control load and signaling load on the network side will increase.

[0219] As described above, by preventing CoMP from being executed from cells outside the CoMP active set, it is possible to suppress such an increase in the control load and signaling load on the network side.

[0220] In this case, the CSI-RS may be transmitted from a cell outside the CoMP active set, and the UE may measure the CSI-RS from a cell outside the CoMP active set. Even if this is done, by preventing CoMP from being executed from a cell outside the CoMP active set, it becomes unnecessary to exchange data of the UE to be CoMP-targeted, information related thereto, and scheduling information on the network side. Therefore, it is possible to suppress an increase in the control load and signaling load on the network side.

[0221] A method for selecting a CoMP transmission point from a cell in a CoMP active set is disclosed. The serving cell selects a CoMP transmission point using a measurement result of CSI-RS reported from the UE. If a CoMP active set is not configured, a CoMP transmission point is selected from a cell in a CoMP measurement set. If a CoMP active set is not configured, the serving cell may select a CoMP transmission point using a measurement result of CSI-RS of a cell in a CoMP measurement set reported from the UE.

[0222] An example of a sequence for executing CoMP when a CoMP active set is provided is disclosed. The CoMP active set is determined between the determination of the CoMP measurement set and the determination of the CoMP transmission point. FIG. 18 is a diagram showing an example of a sequence of a mobile communication system in the second embodiment. The sequence shown in FIG. 18 is similar to the sequences shown in FIG. 15 and FIG. 16, so the same step numbers are used for the same steps, and common explanations are omitted. FIG. 18 shows a sequence for executing CoMP when a CoMP active set is provided.

[0223] As a first process, the UE1 and the serving cell perform the process of steps ST1501 to ST1514 and the process of step ST1530 shown in FIG. 15 and FIG.

[0224] In Step ST1515, UE1 reports the CSI-RS measurement result to the serving cell. The serving cell that receives the report of the CSI-RS measurement result from UE1 decides to configure a CoMP active set in Step ST1701. Specifically, it decides which cells in the CoMP measurement set to make active. The CSI-RS measurement result reported from the UE is used to decide which cells to make active.

[0225] In Step ST1702, the serving cell notifies the UE 1 of the CoMP active set. The serving cell notifies the UE 1 of the CoMP active set using MAC signaling.

[0226] In Step ST1703, UE1 that has received the CoMP active set measures the CSI-RS of the cells in the CoMP active set. For example, it measures the RSRP / RSRQ of the CSI-RS.

[0227] The measurement of CSI-RS in step ST1703 may be performed for each cell or for each point. The measurement method of CSI-RS may be determined in advance by a standard, or may be included in the CoMP measurement configuration and notified to the UE from the serving cell. By including it in the CoMP measurement configuration and notifying it, it becomes possible to change the measurement method dynamically or semi-statically. This makes it possible to select a CoMP transmission point suitable for CoMP.

[0228] The measurement of the CSI-RS of the CoMP active set may be performed until the UE1 receives the configuration of the CoMP active set and then receives the release of the configuration of the CoMP active set. Alternatively, the measurement may be performed until all the cells in the CoMP active set are in a deactive state. The measurement of the CSI-RS may be performed periodically or periodically.

[0229] In Step ST1704, UE1 derives CSI from the measurement value of CSI-RS. The CSI derivation process in Step ST1704 does not necessarily have to be performed.

[0230] In step ST1705, UE1 reports the CSI-RS measurement results (CSI-RS measurement report) of the cells in the CoMP active set, for example, the measurement results of RSRP / RSRQ, and the CSI derivation result (CSI feedback) to the serving cell. If the CSI derivation process of the above-mentioned step ST1704 is not performed, the CSI derivation result is not reported. The CSI-RS measurement results may be reported periodically, periodically, or when a predetermined condition is satisfied. The serving cell may be included in the CoMP active set and the CSI-RS measurement report. Also, the CSI-RS measurement result of the serving cell may always be reported in the CSI-RS measurement report.

[0231] In step ST1516, the serving cell determines the CoMP transmission point from the reported CSI-RS measurement result, for example, the RSRP / RSRQ measurement result, and the CSI derivation result. Alternatively, an index such as the cell load may be used in addition. If the CSI derivation result is not reported in the above-mentioned step ST1705, the serving cell determines the CoMP transmission point from the CSI-RS measurement result.

[0232] The UE1 which has completed the process of Step ST1705 and the serving cell which has completed the process of Step ST1516 perform the processes of Step ST1517 to Step ST1529 shown in FIG. 15 and FIG. 16 as the second process.

[0233] According to the method disclosed in this embodiment, the UE only needs to measure the CSI-RS of at least the cells in the CoMP active set, which makes it possible to reduce power consumption.

[0234] In addition, by notifying the UE through MAC signaling, the CoMP active set can be set with low latency, which makes it possible to suppress an increase in the amount of RRC signaling and to select a CoMP transmission point suitable for CoMP.

[0235] This enables CoMP implementation suitable for UE movement and rapid changes in the radio wave environment, thereby enabling the expansion of high data rate coverage, improved throughput at cell edges, and increased throughput in the communication system.

[0236] Embodiment 3 3GPP R1-113295 (hereinafter referred to as "Reference 1") discloses that in Releases 8, 9, and 10, an RRM measurement set is managed based on measurement results of a CRS from one UE.

[0237] It is also disclosed that an additional RRM measurement mechanism is required to select the CoMP measurement set.

[0238] Additionally, as additional RRM measurement mechanisms, measurements of RSRP / RSRQ using CRS, i.e., a combination of normal RRM measurements and CQI using CSI-RS, use of SRS, and measurements of RSRP / RSRQ using CSI-RS are disclosed.

[0239] 3GPP R1-113064 (hereinafter referred to as "Reference 2") discloses a method of selecting a CoMP transmission point in which the network side makes a decision based on the measurement results of the CSI-RS of each cell in the CoMP measurement set by the UE.

[0240] As described above, in CoMP, the use of the measurement results of CRS or CSI-RS by UE is being considered as a method for selecting a CoMP measurement set and a CoMP transmission point.

[0241] However, when using the measurement results of CRS or CSI-RS by UE, there is a problem that good reception quality may not be obtained depending on the location, even if CoMP is performed using MIMO (Multiple Input Multiple Output) technology with multiple antenna ports. This is because it is not possible to accurately evaluate the effects of interference from many other cells, delay, phase and power of each path, or the mutual relationship between those paths, as well as multipath, etc., due to the complex radio wave environment, and it is therefore not possible to select cells suitable for CoMP.

[0242] In order to solve the problem of being unable to select a cell suitable for CoMP as described above, in this embodiment, in a CoMP set, location information, which is information regarding the location of the UE, is used to select cells within the set (hereinafter sometimes referred to as "cells within the set").

[0243] In the following description, the location information of a UE is used to select a cell in a CoMP measurement set. The CoMP measurement set, specifically, an entity or device that selects a cell in the CoMP measurement set, acquires the location information of a UE that performs CoMP.

[0244] The CoMP measurement set is selected using the acquired location information. For example, in the sequences shown in FIG. 15 and FIG. 16, the serving cell acquires location information of UE1 before executing the process of step ST1530. In step ST1530, the serving cell selects a CoMP measurement set using the acquired location information. By acquiring the location information of the UE, it becomes possible to recognize the positional relationship between the cell and the UE. Therefore, it is possible to select a CoMP measurement set using an index that is determined geographically, that is, a positional relationship, rather than an index that varies such as the radio wave environment. This makes it possible to select a CoMP measurement set that is more suitable for CoMP.

[0245] In addition, the CoMP measurement set may be selected using not only the UE location information but also the CRS measurement results reported by the UE. Alternatively, the CSI-RS measurement results may be used together. Alternatively, an index such as the cell load may be used together. By combining the variability index and the geographical index in this way, it becomes possible to respond to dynamic time changes and to select a CoMP measurement set suitable for CoMP.

[0246] As disclosed in 3GPP TS23.271 V10.2.0 (hereinafter referred to as "Reference 3"), a mobile communication system is equipped with a function called LCS (Location Service). LCS is a function for estimating the location of a mobile terminal device for the purpose of commercial services using location information, management of a wireless communication system, location confirmation in an emergency, and location confirmation of a mobile terminal device based on legal reasons such as criminal investigation.

[0247] Furthermore, as a method for estimating the position of a mobile terminal device, for example, there is the LTE Positioning Protocol (LPP) disclosed in 3GPP TS36.305 V10.3.0 (hereinafter referred to as "Reference 4").

[0248] The method disclosed in References 3 and 4 may be used as a method for an entity that selects a CoMP measurement set to obtain location information of a UE. However, in these methods, E-SMLC (Evolved Serving Mobile Location Centre), which is an entity that manages an LCS including an LPP, manages location information of the UE. Therefore, since the location information of the UE is notified to the E-SMLC, an entity that selects a CoMP measurement set cannot normally obtain location information of the UE.

[0249] In this embodiment, a method is disclosed in which an entity that selects a CoMP measurement set acquires location information of a UE.

[0250] The entity that selects the CoMP measurement set receives a message in which the UE notifies the E-SMLC of its own location information, and extracts only the information regarding the UE's location.

[0251] Fig. 19 is a diagram showing an example of a sequence of a mobile communication system in the third embodiment. Fig. 19 shows a sequence in which an entity that selects a CoMP measurement set acquires location information of a UE. In this sequence, the entity that selects a CoMP measurement set is a serving cell.

[0252] In Step ST1801, the E-SMLC notifies the MME of a location information request message.

[0253] In Step ST1802, the MME notifies the serving cell of the received location information request message as a NAS message.

[0254] In Step ST1803, the serving cell forwards the received location information request message to the UE.

[0255] In Step ST1804, the UE notifies the serving cell of its own location information by including the location information in a provide location information message. The location information of the UE may be acquired by using, for example, a Global Positioning System (GPS).

[0256] The serving cell that receives the location information providing message extracts only the information regarding the location of the UE from the location information providing message, and may store the location information of the UE thus obtained.

[0257] In Step ST1805, the serving cell notifies the MME of the received location information provision message.

[0258] In Step ST1806, the MME notifies the E-SMLC of the received location information provision message.

[0259] The location information request message is notified to the UE via the MME and the serving cell. The location information provision message is notified to the E-SMLC via the serving cell and the MME. The NAS message is used between the MME and the serving cell and between the serving cell and the UE.

[0260] The serving cell receives message type information of the NAS message in order to extract only information related to the UE's location from the NAS message received from the UE in step ST1804. When the message type information of the NAS message indicates that the information is related to LPP or LCS, the serving cell may receive the NAS message and extract information related to the UE's location. This eliminates the need to receive and extract all NAS messages notified from the UE, and can reduce power consumption and delay in the serving cell. As the message type information of the NAS message, information of "Generic message container type" may be used.

[0261] The provision of location information from the UE to the E-SMLC in steps ST1804 to ST1806 may be performed periodically or cyclically as shown in steps ST1807 to ST1809.

[0262] In this case, the serving cell sequentially receives information about the UE's location from the location provision message from the UE, and updates the UE's location information obtained by decoding. This allows the serving cell to always obtain the latest UE's location information. Therefore, the serving cell can always use the latest UE's location information when selecting a CoMP measurement set.

[0263] Another method for an entity that selects a CoMP measurement set to obtain location information of a UE is disclosed.

[0264] An entity that selects a CoMP measurement set is made to have an LCS client function, for example, an RRC of a serving cell may be made to have an LCS client function.

[0265] This enables the entity that selects the CoMP measurement set to obtain the location information of the desired UE from the E-SMLC as needed.

[0266] Fig. 20 is a diagram showing another example of a sequence of a mobile communication system in the third embodiment. Fig. 20 shows a sequence in which an entity that has an LCS client function and selects a CoMP measurement set acquires location information of a UE. In this sequence, it is assumed that a serving cell has an entity that selects a CoMP measurement set.

[0267] In Step ST1901, the serving cell having an LCS client function notifies the E-SMLC of a location information request message of the desired UE via the MME. The serving cell may use an S1 message for the notification to the MME. Since the serving cell has an LCS client function, it is possible for the serving cell to request the E-SMLC for location information of the desired UE.

[0268] In Step ST1902, the E-SMLC notifies the UE of the received location information request message. This notification method may be the method shown in FIG.

[0269] In Step ST1903, the UE includes its own location information in a location information provision message and notifies the E-SMLC via the serving cell and the MME. A NAS message may be used for the notification from the UE to the MME.

[0270] In Step ST1904, the E-SMLC notifies the serving cell that is the source of the location information request of the location information provision message received from the desired UE. This enables the serving cell to obtain the location information of the desired UE.

[0271] The provision of location information from the UE to the E-SMLC in Step ST1903, and the provision of location information from the E-SMLC to the serving cell in Step ST1904 may be performed regularly or periodically, as shown in Steps ST1905 and ST1906.

[0272] In this case, the serving cell may successively receive information about the UE's location from a location providing message from the UE and update the obtained UE's location information. This allows the serving cell to always obtain the latest UE's location information. Therefore, the serving cell can always use the latest UE's location information when selecting a CoMP measurement set.

[0273] Further, another method is disclosed in which an entity that selects a CoMP measurement set obtains location information of a UE.

[0274] The MME is made to have an LCS client function, and the entity that selects the CoMP measurement set is made to request information about the UE's location from the MME, which enables the entity that selects the CoMP measurement set to obtain desired UE location information from the E-SMLC as necessary.

[0275] Fig. 21 is a diagram showing yet another example of the sequence of the mobile communication system in the third embodiment. Fig. 21 shows a sequence in which an MME has an LCS client function and an entity that selects a CoMP measurement set requests information on the location of a UE from the MME and acquires the location information of the UE. In this sequence, the entity that selects a CoMP measurement set is a serving cell.

[0276] In step ST2001, the serving cell notifies the MME of a message requesting the provision of location information of the desired UE. That is, the serving cell that needs to be provided with location information of the desired UE requests the MME to provide the location information of the desired UE. The notification from the serving cell to the MME may be made using an S1 message. A message requesting the provision of location information of the desired UE may be newly provided as an S1 message.

[0277] In Step ST2002, the MME notifies the E-SMLC of a location information request message. Since the MME has an LCS client function, it is possible for the MME to request the E-SMLC for location information of a desired UE. The MME may initiate a location information request message for the desired UE to the E-SMLC by receiving a message requesting provision of location information of the desired UE from any cell.

[0278] In Step ST2003, the E-SMLC notifies the UE of a location information request message. This notification method may be the method shown in FIG.

[0279] In Step ST2004, the UE includes its own location information in a location information provision message and notifies the E-SMLC via the serving cell and the MME. A NAS message may be used for the notification from the UE to the MME.

[0280] In Step ST2005, the E-SMLC notifies the MME that originated the location information request of the location information provision message received from the desired UE.

[0281] In step ST2006, the MME notifies the cell that has requested the location information provision, that is, the serving cell here, of information regarding the location of the desired UE, which is included in the received location information provision message, as a response to the request for location information provision (hereinafter, may be referred to as a "location information response"). This enables the serving cell to obtain the location information of the desired UE.

[0282] The provision of location information from the UE to the MME in Steps ST2004 and ST2005 may be performed periodically or periodically as shown in Steps ST2007 and ST2008.

[0283] Furthermore, with the process of Step ST2005 as a trigger, a location information response from the MME to the serving cell in Step ST2006 may be performed periodically or cyclically, as shown in Step ST2009.

[0284] In this case, the serving cell may sequentially receive information about the UE's location from the location provision message from the UE and update the UE's location information obtained by decoding. This allows the serving cell to always obtain the latest UE's location information. Therefore, the serving cell can always use the latest UE's location information when selecting a CoMP measurement set.

[0285] The following four methods (1) to (4) are disclosed as methods for selecting a CoMP measurement set using location information of a UE acquired by an entity that selects a CoMP measurement set.

[0286] (1) At least, select the cell that is closest to the latest UE location. (2) Select the top k cells from among the cells that are closest to the latest UE location, where k is a natural number and may be determined in advance. (3) A cell is selected whose distance from the latest UE location is less than a predetermined threshold. The predetermined threshold may be determined in advance. (4) A combination of (1) to (3) above.

[0287] In the above methods (1) to (4), the latest location is derived based on the latest UE location information, but the current location may be derived from past and latest UE location information. The result derived in this way may be set as the UE location.

[0288] The location information of the cell may be used in the above-mentioned method. The entity that selects the CoMP measurement set may acquire location information of the neighboring cell in advance. The neighboring cell may be a neighboring CoMP-enabled cell or a cell in the CoMP cooperating set. Alternatively, it is not limited to the CoMP-enabled cell. Each cell notifies the OAM (Operation Administration and Maintenance) of the location of its own cell recognized by, for example, GPS. The entity that selects the CoMP measurement set acquires the location information of the neighboring cell from the OAM. Therefore, the entity that selects the CoMP measurement set may notify the OAM of a message requesting the location information of the neighboring cell. In addition, in a case where the E-SMLC manages the location information of the cell, the entity that selects the CoMP measurement set may acquire the location information of the neighboring cell from the E-SMLC. As a method for this, the method disclosed in this embodiment in which the entity that selects the CoMP measurement set acquires the location information of the UE can be applied. As a result, the CoMP measurement set can be selected using the location information of the UE and the location information of the cell.

[0289] In addition, when selecting a CoMP measurement set, not only the UE's location information but also the CRS measurement results reported by the UE or the CSI-RS measurement results may be used. Alternatively, an index such as the cell load may be used. By combining a variability index and a geographical index in this way, it becomes possible to respond to dynamic time changes and to select a CoMP measurement set suitable for CoMP.

[0290] The method disclosed in this embodiment can be applied to an RRM measurement set, specifically, to the selection of cells included in the RRM measurement set.

[0291] Furthermore, the method disclosed in this embodiment can be applied to a CoMP active set, specifically, to the selection of cells to be included in the CoMP active set.

[0292] The method disclosed in this embodiment can also be applied to the selection of CoMP transmission points.

[0293] Embodiment 4 Reference 1 discloses the following four methods (a) to (d) for selecting a CoMP measurement set based on which RS (Reference Signal): (a) Decision based on RRM measurement report, i.e., RSRP / RSRQ of CRS. (b) Decision based on CSI feedback information and RSRP / RSRQ of CRS. (c) Decision based on SRS / PUCCH / PUSCH. (d) Decision based on RSRP / RSRQ of CSI-RS.

[0294] Furthermore, Reference 2 discloses that cells in a CoMP measurement set are selected based on a predetermined threshold (RSRP / RSRQ) or based on a fixed measurement set size (N).

[0295] However, Reference 2 does not disclose any method for determining the value of the fixed measurement set size (N). When the measurement set size (N) is large, the number of cells that need to measure CSI-RS increases. Therefore, problems such as an increase in circuit size, power consumption, and cost arise in the UE.

[0296] In order to solve this problem, it is preferable to set the measurement set size (N) to an individual value for each UE, which makes it possible to set an optimal measurement set size for each UE.

[0297] In this case, the number of cells capable of CoMP (Nu) is included in the UE's capability, and the UE notifies the network side of the number of cells capable of CoMP (Nu) as capability information. Specifically, the number of cells capable of CoMP (Nu) may be notified by including it in an attach or TAU message. The number of cells capable of CoMP (Nu) may be the number of cells capable of measuring CSI-RS. The network side stores the number of cells capable of CoMP (Nu).

[0298] The network side notifies the central entity of the number of cells (Nu) capable of CoMP. Alternatively, the central entity may request the network side to notify the number of cells (Nu) capable of CoMP. This allows the central entity to recognize the number of cells (Nu) capable of CoMP for a desired UE.

[0299] The central entity uses the number of cells (Nu) capable of CoMP of the UE to select a desired UE CoMP measurement set. For example, the measurement set size (N) may be set to the number of cells (Nu) capable of CoMP of the UE. Alternatively, the measurement set size (N) may be set to be smaller than the number of cells (Nu) capable of CoMP of the UE.

[0300] This makes it possible to limit the cells that can use CoMP for low-cost UEs, preventing increases in circuit size, power consumption, and costs.The measurement set size can be optimized according to the UE capabilities, and CoMP can be performed without increasing circuit size, power consumption, or costs.

[0301] In the method disclosed in Reference 2, the measurement set size (N) is fixed. For example, when cells are densely installed, a UE located at the edge of coverage can obtain a desired reception quality by performing CoMP using a small number of cells.

[0302] In this way, in a situation where a desired reception quality can be obtained with a small number of cells, if a larger measurement set size (N) is set, there is a problem that power consumption is wasted in the UE, the serving cell, or the cells in the CoMP measurement set. The UE must measure the CSI-RS of unnecessary cells, which causes power consumption waste. In addition, in the cells in the CoMP measurement set, unnecessary cells must also transmit CSI-RS, which causes power consumption waste.

[0303] In order to solve the problem of such wasted power consumption, in this embodiment, the value of the measurement set size (N) (hereinafter sometimes referred to as "N value") is changed based on the reception quality. When the reception quality from the UE is good, the N value should be decreased, and when the reception quality is poor, the N value should be increased.

[0304] In order to change the N value, it is advisable to set a threshold value for reception quality. For example, thresholds A and B for reception quality are set, and if the reception quality from the UE during CoMP execution is equal to or lower than threshold A, the N value is set to the maximum value Nmax (N=Nmax) of the measurement set size (N). If the reception quality is greater than threshold A and equal to or lower than threshold B, the N value is set to an integer value obtained by dividing Nmax by 2 (N=int(Nmax / 2)). If the reception quality is greater than threshold B, the N value is set to "1" (N=1).

[0305] By doing so, it is possible to change the number of cells in the CoMP measurement set based on the reception quality from the UE, and to suppress an increase in power consumption.

[0306] In this embodiment, when the reception quality is greater than the threshold B, the N value is set to "1" (N=1), but if there is one radio link with good reception quality, CoMP can be stopped. For example, if the serving cell is the only cell in the CoMP measurement set, execution of CoMP may be stopped. If the cell is not the serving cell, CoMP may be stopped by the method disclosed in the ninth embodiment described later, and the target UE may be HO'd, that is, changed to a cell with good reception quality.

[0307] The N value may be changed based on the average value of the reception quality from the UE for a certain period of time. This makes it possible to change the N value without being affected by temporary fluctuations in reception quality. Therefore, it is possible to perform stable CoMP operation.

[0308] The method disclosed in this embodiment can be applied to a CoMP active set, specifically, to the selection of cells to be included in the CoMP active set.

[0309] The method disclosed in this embodiment can also be applied to the selection of CoMP transmission points.

[0310] The method disclosed in this embodiment can also be applied to the selection of an RRM measurement set. The UE measures the CRS in the RRM measurement set.

[0311] In Reference 2 or 3GPP, there is no discussion on whether to include the serving cell in the CoMP measurement set. Therefore, since it is unclear how to handle the serving cell, CoMP cannot be performed.

[0312] In this embodiment, the following three methods (1) to (3) for handling the serving cell are disclosed.

[0313] (1) The serving cell is also included in the handling of the CoMP measurement set. That is, the selection method of the CoMP measurement set is applied. For example, when the serving cell is included in the CoMP measurement set, if the CSI-RS measurement value of the serving cell by the UE deteriorates, the serving cell may be deleted from the CoMP measurement set. However, even if the serving cell is deleted from the CoMP measurement set, CoMP for the UE being served by the serving cell can be performed by other cells in the CoMP measurement set. Therefore, there is no problem in including the serving cell in the handling of the CoMP measurement set. Also, by including the serving cell in the handling of the CoMP measurement set, the control of the CoMP measurement set is simplified.

[0314] (2) The serving cell is not included in the CoMP measurement set. This allows the CoMP measurement set and the serving cell to be treated differently, enabling flexible control. In this case, the UE may measure the CSI-RS of the serving cell regardless of the CoMP measurement set. The serving cell may notify the UE of the CoMP measurement configuration of its own cell regardless of the CoMP measurement set. This notification may be performed using individual signaling. The individual signaling may be RRC signaling. The measurement result of the CSI-RS of the serving cell by the UE may be reported to the serving cell. The setting of the reporting method may be notified to the UE together with the CoMP measurement configuration of the own cell. This method can solve the problem in the method (1) that when the serving cell is deleted from the CoMP measurement set, measurement using the CSI-RS of the serving cell is no longer performed. In this method, the serving cell may be a cell that is not included in the CoMP measurement set but is capable of CoMP. The CoMP transmission cell may be selected from the cells in the CoMP measurement set and the serving cell. This is possible because measurements are made using the CSI-RS of the serving cell.

[0315] (3) The serving cell is always included in the CoMP measurement set. Unlike the method (1) above, the serving cell is always included in the CoMP measurement set, so that the CSI-RS of the serving cell is measured according to the handling of the CoMP measurement set. This makes it easier to control. In this case, the serving cell is not counted in the number N of the CoMP measurement set, but is always included in the CoMP measurement set. Alternatively, the serving cell is always included in the CoMP measurement set regardless of a predetermined threshold for including the cell in the CoMP measurement set. This allows the UE to perform measurements using the CSI-RS of the serving cell. In the method (1) above, it is possible to solve the problem that measurements using the CSI-RS of the serving cell are no longer performed when the serving cell is deleted from the CoMP measurement set.

[0316] The method disclosed in this embodiment can be applied to a CoMP active set, specifically, to the selection of cells to be included in the CoMP active set.

[0317] The method disclosed in this embodiment can also be applied to the selection of an RRM measurement set. The UE measures the CRS in the RRM measurement set.

[0318] Embodiment 5. When a UE executing CoMP moves, the receiving quality of the serving cell may deteriorate, and it may be better to switch the serving cell. 3GPP R1-113092 (hereinafter referred to as "Reference 5") discloses the use of RRM measurement reports for mobility control. If a UE executing CoMP moves, and the RRM measurement reports are used for mobility control, the following problems may occur.

[0319] FIG. 22 is a diagram for explaining a set related to CoMP and an RS measured by a UE. Normally, the cells in the RRM measurement set are configured by the RRM measurement by the UE, so that the CRS's RSRP / RSRQ measurement is performed. As described above, the CoMP measurement set is a set of cells whose CSI-RS is measured and reported by the UE. Therefore, for the cells in the CoMP measurement set, the CSI-RS's RSRP / RSRQ measurement is performed by the UE. Although not shown, the cells in the CoMP active set are similar to the cells in the CoMP measurement set. Since the CoMP transmission point is a cell that actually transmits data to the UE, the CSI-RS is measured by the UE. The CSI derived from the measurement result of the CSI-RS by the UE is fed back to the serving cell.

[0320] Fig. 23 is a diagram for explaining the communication quality of cells in a set for CoMP. Fig. 23 shows the numbers and communication qualities of cells in a set for each CoMP. In Fig. 23, the communication quality increases toward the top and decreases toward the bottom.

[0321] In the RRM measurement set, cells are ranked according to the communication quality of the CRS RSRP / RSRQ by the UE. In the example shown in Fig. 23, cell #11 has the highest communication quality, and cell #10 has the lowest communication quality. The cells shown with diagonal lines in Fig. 23 are cells that cannot execute CoMP with the serving cell.

[0322] In the CoMP measurement set, cells are ranked based on the communication quality of the RSRP / RSRQ of the CSI-RS by the UE. The CoMP measurement set is selected from the RRM measurement set. At this time, as disclosed in the first embodiment, the selection is limited to cells in the CoMP cooperating set. This limits the CoMP measurement set to cells capable of CoMP execution. In the example shown in FIG. 23, cell #5 (Cell #5) has the highest communication quality, and cell #6 (Cell #6) has the lowest communication quality.

[0323] The reason why the communication quality rankings are different between the RRM measurement set and the CoMP measurement set is because the indices used for communication quality are different: the RRM measurement set uses CRS RSRP / RSRQ as an index of communication quality, whereas the CoMP measurement set uses CSI-RS as an index of communication quality.

[0324] At the CoMP transmission point, cells are ranked according to the communication quality of CSI derived from the measurement of CSI-RS by the UE. The CoMP transmission point is selected from the CoMP measurement set. In the example shown in FIG. 23, cell #5 (Cell #5) has the highest communication quality, and cell #1 (Cell #1) has the lowest communication quality.

[0325] In the example shown in FIG. 23, when a UE performing CoMP moves, if the serving cell is switched based on the RRM measurement report, there is a risk that the cell will be switched to one that cannot perform CoMP. For example, cell #11 (Cell #11) is the cell with the best communication quality according to the RRM measurement report. Therefore, if the serving cell is switched to cell #11 (Cell #11) as the new serving cell, the new serving cell will not be able to perform CoMP, and a problem will occur in which good communication quality cannot be obtained.

[0326] In this embodiment, a method for solving the problem of not being able to obtain good communication quality as described above will be disclosed.

[0327] When switching the serving cell while CoMP is being performed, a cell capable of CoMP is given priority in selecting a new serving cell.

[0328] The serving cell is switched during CoMP execution by the HO (including cell change) process. When selecting a target cell in the HO decision process, a cell capable of CoMP execution is given priority.

[0329] Cells in the CoMP cooperating set may be prioritized, in other words, cells outside the CoMP cooperating set may be excluded.

[0330] Furthermore, in selecting a target cell in the HO decision process, a cell in the CoMP measurement set may be given priority.

[0331] As a result, when a UE executing CoMP moves, the new serving cell becomes a cell capable of executing CoMP, and the UE becomes able to execute CoMP in the new serving cell, thereby obtaining good communication quality.

[0332] For example, in Fig. 23, when the reception quality of the serving cell deteriorates and HO (including cell change) processing is started, in the selection of the target cell in the HO determination processing, cell #8 (Cell #8) that can execute CoMP is selected instead of cell #11 (Cell #11) that cannot execute CoMP. This enables the UE to execute CoMP in the new serving cell, and obtain good communication quality.

[0333] As another example, in Fig. 23, when the reception quality of the serving cell is degraded and HO (including cell change) processing is started, the target cell in the HO determination processing is selected as cell #5 (Cell #5) in the CoMP measurement set, not cell #11 (Cell #11) in the RRM measurement set. This can further improve the reception quality when CoMP is executed in the new serving cell.

[0334] Fig. 24 is a diagram showing an example of a sequence of a mobile communication system in the fifth embodiment. The sequence shown in Fig. 24 is similar to the sequences shown in Fig. 15 and Fig. 16, so the same step numbers are used for the same steps, and common explanations are omitted. Fig. 24 shows a sequence in which a cell capable of CoMP is given priority in the selection of a target cell in the HO decision process.

[0335] The serving cell having the function of a central entity performs the CoMP process for UE 1 as shown in steps ST1501 to ST1526 and step ST1530 in FIG. 15 and FIG.

[0336] In Step ST1526, the serving cell and UE1 perform CoMP transmission / reception and feedback of CSI.

[0337] In Step ST2301, UE1 performs RRM measurements by CRS measurement. In Step ST2302, UE1 reports the measurement results of the RRM measurements in Step ST2301 to the serving cell as a measurement report message in accordance with the reporting conditions. The measurements in Step ST2301 also include measurements of the CRS of the serving cell itself. The measurement report in Step ST2302 also includes the measurement results of the CRS of the serving cell itself.

[0338] In Step ST2303, the serving cell performs an HO decision process. The HO decision process in Step ST2303 includes the processes in Step ST2304 and Step ST2305.

[0339] In Step ST2304, the serving cell determines to perform the HO procedure for the UE 1, using the measurement report from the UE 1. For example, when the measurement result of the CRS of the serving cell becomes smaller than a predetermined threshold, the serving cell determines to perform the HO procedure for the UE 1.

[0340] In Step ST2305, the serving cell determines a target cell. The serving cell sets the cell with the best communication quality as the target cell among the cells in the CoMP measurement set. The serving cell selects the cell with the best communication quality from the CSI-RS measurement result by the UE that is the target of HO in the CoMP measurement set.

[0341] The serving cell that has performed the HO decision process in step ST2303 performs the HO process in step ST2306 with the cell selected in step ST2305 as the target cell.

[0342] In the example shown in FIG. 24, the cell with the best reception quality of CSI-RS in the CoMP measurement set is set as the target cell as the new serving cell, but the cell with the best measurement result of CSI-RS may not be selected. That is, the target cell may be selected taking into consideration other indicators, such as the load of each cell. It is sufficient that the target cell is a cell in the CoMP measurement set.

[0343] If there is no cell to be prioritized, the conventional selection method may be used to select a target cell in the HO decision process. For example, if the UE's RRM measurement report reports only the measurement results of cell #11, cell #12, and cell #13, the target cell may be selected from among those cells.

[0344] This makes it possible to switch serving cells when a UE performing CoMP moves and the reception quality of the serving cell deteriorates, making it better to switch serving cells, so that the new serving cell can continue CoMP for the UE as long as possible and provide good reception quality.

[0345] Although the cells in the CoMP measurement set are disclosed as cells capable of executing CoMP, priority may be given to cells in the CoMP active set, or to cells in the CoMP transmission point.

[0346] Priorities within these CoMP sets may be determined. For example, the priority of cells within a CoMP transmission point may be set to "1", the priority of cells within a CoMP active set may be set to "2", the priority of cells within a CoMP measurement set may be set to "3", the priority of cells within a CoMP cooperation set may be set to "4", and the priority of other cells may be set to "5".

[0347] By selecting a new serving cell (target cell) in this manner, it becomes possible to continue CoMP for the target UE in the new serving cell and obtain the best possible reception quality.

[0348] Fifth embodiment, variant 1 Reference 5 discloses the use of RRM measurement reports for mobility control. This means that the measurement results of CRS RSRP / RSRQ by the UE are used for mobility control. When a UE performing CoMP moves, if the measurement results of CRS RSRP / RSRQ by the UE are used for mobility control, the following problems will occur.

[0349] A problem occurring when using the measurement result of RSRP / RSRQ of CRS by UE for mobility control will be described using an example shown in Fig. 23. A case will be described in which a UE performing CoMP moves and the serving cell is switched based on a conventional RRM measurement report.

[0350] When the method of selecting a target cell from cells capable of executing CoMP disclosed in the fifth embodiment is applied, cell #8 (Cell #8) is the cell with the best communication quality according to the RRM measurement report. Therefore, the serving cell is switched to cell #8 (Cell #8) as the new serving cell.

[0351] However, among the CoMP measurement set, cell #8 (Cell #8) may not be the cell with the best communication quality, and may not be selected as a CoMP transmission point. That is, cell #8 (Cell #8) becomes a cell that does not transmit data to the UE by CoMP. Even though it has become the new serving cell, cell #8 (Cell #8) does not transmit or receive data by CoMP. This means that it becomes impossible to switch serving cells suitable for CoMP, such as by increasing the number of cells other than the serving cells related to CoMP.

[0352] In this way, the cell with the best communication quality according to the RRM measurement is different from the cell with the best communication quality in the CoMP measurement set or the CoMP transmission point. This is because the reception quality according to the RRM measurement uses the measurement result of the CRS existing in the area where the PDCCH is mapped, whereas the reception quality of the CoMP measurement set or the CoMP transmission point uses the measurement result of the CSI-RS existing in the area where the PDSCH is mapped. Since the data on which CoMP is performed is mapped to the symbol of the PDSCH area, the measurement of the CRS in the conventional RRM measurement does not accurately represent the quality of the PDSCH when CoMP is performed.

[0353] In this modification, a method for solving such a problem is disclosed. When switching the serving cell during CoMP execution, the measurement result of CSI-RS by the UE is used when selecting a new serving cell. The process of switching the serving cell during CoMP execution is performed by HO (including cell change) processing, and the measurement result of CSI-RS is used when selecting a target cell in the HO decision processing. The measurement result of CSI-RS may be the RSRP / RSRQ of CSI-RS, or may be CSI (CSI feedback) derived from the measurement result of CSI-RS.

[0354] For example, in Fig. 23, when the reception quality of the serving cell deteriorates and HO (including cell change) processing is initiated, in the selection of the target cell in the HO determination processing, cell #5 (Cell #5) with the best reception quality according to the CSI-RS measurement results is selected, rather than cell #8 (Cell #8) with the best reception quality according to the CRS measurement results. This allows the UE to obtain good communication quality in the new serving cell.

[0355] The sequence in this modification may be achieved by modifying part of the sequence shown in Fig. 24. That is, in this modification, in step ST2305 in Fig. 24, a process may be performed to select a cell with the best communication quality as a target cell based on the measurement result of CSI-RS by the UE that is the target of HO.

[0356] The cell with the best reception quality based on the CSI-RS measurement results may be a cell in the CoMP measurement set or a cell in the CoMP transmission point. When a UE performing CoMP moves, the new serving cell becomes a cell in the CoMP measurement set or the CoMP transmission point, so that the UE can perform CoMP including the new serving cell, and good communication quality can be obtained.

[0357] Fifth embodiment, variant 2 When a UE performing CoMP moves, the reception quality of the serving cell may deteriorate, and it may be better to switch the serving cell. In a conventional process of switching the serving cell for a UE not performing CoMP, such as a handover process, the reception quality of the serving cell is evaluated by measuring the CRS of the serving cell by the UE.

[0358] However, as disclosed in the fifth embodiment and the first modification of the fifth embodiment, for a UE executing CoMP, the measurement result of CRS does not accurately represent the communication quality during CoMP. Therefore, for a UE executing CoMP, if the measurement result of CRS of the serving cell is used to determine that the reception quality has deteriorated and the serving cell is switched as in the past, there may be cases where the communication quality during CoMP is good and there is no need to switch the serving cell. In such a case, even if the serving cell is switched, good communication quality may not be obtained in the new serving cell.

[0359] In this modification, a method for solving such a problem is disclosed. In determining whether to switch the serving cell during CoMP, the measurement result of the CSI-RS of the serving cell by the UE is used. The measurement result of the CSI-RS by the UE is used as the reception quality of the serving cell. When the UE during CoMP moves, if the reception quality of the serving cell deteriorates, the switching of the serving cell is decided. For example, if the reception quality of the serving cell falls below a predetermined threshold, it may be determined to switch the serving cell. The measurement result of CSI-RS may be the RSRP / RSRQ of CSI-RS, or may be CSI (CSI feedback) derived from the measurement result of CSI-RS.

[0360] This can solve the problem that the UE undergoing CoMP has to switch the serving cell even though the communication quality in the serving cell is good. Therefore, the UE undergoing CoMP can obtain good communication quality with the serving cell.

[0361] As a method for making a UE performing CoMP measure the CSI-RS of a serving cell, it is preferable to use the method (2) or (3) among the methods for handling the serving cell disclosed in the fourth embodiment. The UE measures the CSI-RS of the serving cell. The measurement of the CSI-RS of the serving cell may be performed periodically or periodically.

[0362] The serving cell may be switched by a HO (including cell change) process, and the measurement result of the CSI-RS of the serving cell may be used to determine whether to perform HO in the HO decision process.

[0363] Figure 25 is a diagram showing an example of a sequence of a mobile communication system in Modification 2 of the fifth embodiment. The sequence shown in Figure 25 is similar to the sequences shown in Figures 15, 16, and 24, so the same step numbers are used for the same steps, and common explanations will be omitted. Figure 25 shows a sequence in the case where the measurement result of the CSI-RS of the serving cell is used to determine whether to perform HO in the HO decision process. In this sequence, the process of Step ST2401 is performed instead of the process of Step ST2304 in Figure 24.

[0364] The serving cell having the function of a central entity performs CoMP for UE1 in the same manner as the processes of steps ST1501 to ST1526 and ST1530 in FIG. 15 and FIG. 16. In step ST1515, the measurement result of the CSI-RS of the serving cell may be included in the measurement report of the CSI-RS or the CSI feedback notified from the UE to the serving cell. Alternatively, in step ST1526, the measurement result of the CSI-RS of the serving cell may be included in the CSI feedback notified from the UE to the serving cell. Alternatively, the measurement result of the RSRP / RSRQ of the CSI-RS of the serving cell may be notified in conjunction with step ST1526. This allows the serving cell to obtain the measurement result of the CSI-RS of its own cell by UE1.

[0365] In Step ST2303, the serving cell performs an HO decision process. The HO decision process in Step ST2303 includes the processes in Step ST2401 and Step ST2305.

[0366] In Step ST2401, the serving cell uses the measurement result of the CSI-RS from the UE 1 to determine to perform the HO process for the UE 1. For example, when the measurement result of the CSI-RS of the serving cell becomes smaller than a predetermined threshold, the serving cell determines to perform the HO process for the UE 1.

[0367] In Step ST2305, the serving cell determines a target cell. The serving cell that has performed the HO determination process in Step ST2303 performs the HO process in Step ST2306 with the cell selected in Step ST2305 as the target cell.

[0368] The method disclosed in this modification enables a UE executing CoMP to obtain good communication quality with a serving cell.

[0369] In the present embodiment and the modification, it has been disclosed that, when switching the serving cell during execution of CoMP, the measurement result of the CSI-RS by the UE is used to select a new serving cell and to decide whether to execute HO.

[0370] In order to use the measurement result of CSI-RS by the UE, a reporting condition for CSI-RS measurement may be newly provided. Instead of the CRS measurement result, which is the reporting condition for the measurement result of CRS in the past, the measurement result of CSI-RS may be used.

[0371] The serving cell notifies the UE of the reporting conditions for measuring the CSI-RS. The serving cell may also provide and notify an indicator indicating that the measurement is for use during CoMP execution. The serving cell may include at least one of the reporting conditions and the indicator in a measurement configuration and notify the UE.

[0372] Also, it may be statically determined that measurements during CoMP are measurements of CSI-RS. For example, this may be determined in advance by a standard, etc., so that the UE and the network can share the same understanding. This eliminates the need for the indicator, and reduces the amount of information that requires signaling.

[0373] The UE may measure CSI-RS only from cells that have been notified of the CSI-RS configuration. The serving cell may also notify the UE of the CSI-RS configuration of the serving cell.

[0374] When the serving cell performs CoMP, the UE is notified of the CSI-RS configuration of the cell that measures the CSI-RS, but this should be limited to the cells that measure the CSI-RS. It is also preferable to include the CSI-RS configuration of the serving cell in this.

[0375] This allows the UE to know the CSI-RS configuration of the cell, and therefore enables it to perform measurements on the CSI-RS.

[0376] The cells to be limited may be the own cell, a cell that performs additional RRM measurements, a cell in the CoMP measurement set, or a cell in the CoMP active set.

[0377] The UE notifies the serving cell of the CSI-RS measurement result according to the CSI-RS reporting condition notified by the serving cell. This enables the serving cell to use the CSI-RS measurement result by the UE to select a new serving cell and decide whether to perform HO when switching the serving cell of the UE during CoMP execution.

[0378] In this embodiment, it has been disclosed that when switching the serving cell during CoMP execution, the measurement results of CSI-RS by the UE are used to select a new serving cell and decide whether to execute HO. However, this is not limited to this, and the following four indicators (1) to (4) may also be used.

[0379] (1) Uplink communication quality from the UE. The uplink communication quality may be the communication quality of SRS, PUCCH, and PUSCH. (2) UE location information. (3) Measurement results of the downlink demodulation reference signal (DM-RS) by the UE. (4) UE movement speed information.

[0380] By using the above-mentioned indicators (1) to (4), it becomes possible to switch the serving cell for a UE that is currently executing CoMP in a manner more suitable for CoMP, and good communication quality can be obtained.

[0381] Embodiment 6 For CoMP, CA, and the like, ePDCCH is being considered in 3GPP Release 11 as a new physical control channel (see 3GPP R1-113157 (hereinafter referred to as "Reference 6")).

[0382] 3GPP R1-114214 (hereinafter referred to as "Reference 7") discloses that ePDCCH is multiplexed with PDSCH on symbols to which PDSCH can be mapped, and that ePDCCH can be mapped even in subframes in which PDCCH does not exist.

[0383] Fig. 26 is a diagram for explaining ePDCCH. Fig. 26 shows frequency-time resources of one subframe. The vertical axis of Fig. 26 represents frequency, and the horizontal axis represents time. In Fig. 26, the area indicated by reference symbol "2501" represents symbols to which PCFICH, PHICH and PDCCH are mapped, and the area indicated by reference symbol "2502" represents symbols to which PDSCH is mapped. The area indicated by reference symbol "2503" is ePDCCH, which is multiplexed with PDSCH on symbols to which PDSCH can be mapped.

[0384] In this way, since the ePDCCH is mapped onto a symbol to which the PDSCH can be mapped, the UE cannot recognize whether the ePDCCH is mapped unless some measure is taken, and therefore the UE cannot monitor the ePDCCH.

[0385] This embodiment discloses a method for solving this problem. When ePDCCH is used, the serving cell notifies the UE of the ePDCCH configuration by dedicated signaling. As the dedicated signaling, RRC signaling may be used.

[0386] When ePDCCH is used, activation or deactivation of ePDCCH is notified by MAC signaling. For example, the notification of activation or deactivation of ePDCCH indicates the timing at which the UE starts or stops monitoring ePDCCH. The UE may use the reception of the notification of activation or deactivation of ePDCCH as a trigger to start or stop monitoring ePDCCH. This can reduce the delay time until ePDCCH monitoring is started or stopped compared to notifying activation or deactivation by RRC signaling, and can respond to changes in the surrounding radio wave environment.

[0387] As another method, information on starting or stopping the use of ePDCCH may be included in DCI mapped to PDCCH and notified to UE. Alternatively, information on starting the use may be included in DCI mapped to PDCCH, and information on stopping the use may be included in DCI mapped to ePDCCH and notified to UE. This makes it possible to set the start or stop of monitoring ePDCCH on a subframe basis. Therefore, it is possible to respond to changes in the surrounding radio wave environment in a shorter period of time.

[0388] When the serving cell notifies the UE by MAC signaling that the use of ePDCCH is to be started, the UE starts monitoring the ePDCCH.When the serving cell notifies the UE by MAC signaling that the use of ePDCCH is to be stopped, the UE stops monitoring the ePDCCH.

[0389] When ePDCCH is used for CoMP, the DCI of ePDCCH to the target UE should include CoMP transmission point information. This should be the same as the information in the case of PDCCH. The UE can recognize the CoMP transmission point by monitoring the ePDCCH.

[0390] When ePDCCH is provided for each UE, ePDCCH may be CoMP target. The serving cell can be enabled by notifying the ePDCCH of the UE of CoMP target to a cell in the CoMP measurement set or a cell in the CoMP active set. As disclosed in the embodiment described later, the scheduling information of the UE of CoMP target is notified to a cell in the CoMP measurement set or a cell in the CoMP active set. Therefore, by using the configuration information and scheduling information of the ePDCCH of the UE together, each cell in the set can make the ePDCCH of the UE a CoMP target. By CoMPing the ePDCCH, it is possible to improve the reception quality of the ePDCCH.

[0391] When ePDCCH is used, PDCCH scheduling may not be performed in subframes where ePDCCH scheduling is performed, and the UE may not monitor the PDCCH in subframes where ePDCCH is monitored.

[0392] When ePDCCH is used, PDCCH may be used for paging indication (PI). UE monitors PDCCH in an intermittent reception cycle for paging reception. When ePDCCH is mapped in a subframe in which paging indication is performed, UE monitors both PDCCH and ePDCCH. Paging is used to notify incoming calls from the network side, notify changes in system information (SI), notify PWS (Public Warning System) such as ETWS and CMAS, and the like. Therefore, by monitoring both PDCCH and ePDCCH, UE can receive notifications of incoming calls, notifications of changes in system information, PWS, and the like from the network side while performing CoMP.

[0393] When ePDCCH is used, PDCCH may be used for scheduling system information. UE monitors PDCCH at the reception timing for system information. When ePDCCH is mapped in a subframe where system information is scheduled, UE monitors both PDCCH and ePDCCH. By monitoring both PDCCH and ePDCCH, UE can receive system information while performing CoMP.

[0394] Fig. 27 and Fig. 28 are diagrams showing an example of a sequence of a mobile communication system in the sixth embodiment. Fig. 27 and Fig. 28 are connected at the position of a boundary line BL2. Fig. 27 and Fig. 28 show a sequence in the case where ePDCCH is used.

[0395] In Step ST2601, the serving cell decides to use ePDCCH for a target UE (UE1). For example, when it has decided to perform CoMP for UE1 or when it has decided to perform CA for UE1.

[0396] In step ST2602, the serving cell determines the configuration of ePDCCH for UE1. The parameters to be configured include information indicating the physical resource to which ePDCCH is mapped, the period to which ePDCCH is mapped, a UE-specific sequence used for ePDCCH, and a monitor mode. The information indicating the physical resource to which ePDCCH is mapped is, for example, a PRB number. The period to which ePDCCH is mapped is, for example, the number of subframes, the number of radio frames, and the offset of the subframe. The monitor modes include a mode of monitoring both PDCCH and ePDCCH, a mode of monitoring at least one of the PDCCH for paging notification and the PDCCH for system information scheduling and the ePDCCH, and a mode of monitoring only the ePDCCH, and the types of these modes are settable.

[0397] In Step ST2603, the serving cell notifies UE1 of the ePDCCH configuration by using RRC signaling.

[0398] In Step ST2604, UE1 sets the configuration of the received ePDCCH.

[0399] In Step ST2605, the serving cell determines scheduling for UE1 using the ePDCCH.

[0400] In Step ST2606, the serving cell notifies UE1 of the start of use of the ePDCCH (ePDCCH activation) by using MAC signaling.

[0401] In Step ST2607, the serving cell performs scheduling for UE1 using ePDCCH.

[0402] In Step ST2608, the serving cell transmits the ePDCCH to UE1 on the symbol to which the PDSCH is mapped, using the resources, period, sequence, and the like configured in Step ST2602.

[0403] Having been notified of the ePDCCH usage start signal in Step ST2606, UE1 starts monitoring the ePDCCH.

[0404] In Step ST2609, UE1 monitors the ePDCCH transmitted from the serving cell and acquires scheduling information addressed to its own UE.

[0405] In Step ST2610, UE1 communicates with the serving cell based on the received scheduling information.

[0406] Next, a case where the use of ePDCCH is deactivated will be described. In Step ST2611, the serving cell decides not to use ePDCCH for UE1. In Step ST2612, the serving cell notifies UE1 of the deactivation of ePDCCH use (ePDCCH deactivation) by using MAC signaling. This notification is performed by using the ePDCCH.

[0407] In Step ST2613, the serving cell stops scheduling for UE1 using ePDCCH, and performs scheduling for UE1 using PDCCH.

[0408] In Step ST2616, the serving cell performs scheduling for UE1 using the PDCCH.

[0409] The UE, which has been notified of the ePDCCH usage suspension signal in Step ST2612, stops monitoring the ePDCCH in Step ST2614.

[0410] In Step ST2615, UE1 starts monitoring the PDCCH transmitted from the serving cell, and acquires scheduling information addressed to its own UE.

[0411] In Step ST2617, UE1 communicates with the serving cell based on the received scheduling information.

[0412] Next, a case will be described where it is decided not to use ePDCCH for UE1. In Step ST2618, the serving cell decides not to use ePDCCH for UE1. The case where it is decided not to use ePDCCH is, for example, when execution of CoMP for UE1 is terminated or has been terminated, or when execution of CA for UE1 is terminated or has been terminated, etc.

[0413] In Step ST2619, the serving cell notifies UE1 of the release of the ePDCCH configuration. UE1 can recognize the end of use of the ePDCCH by receiving the release of the ePDCCH configuration.

[0414] The serving cell that has notified the release of the ePDCCH configuration in step ST2619 releases the ePDCCH configuration for UE1 in step ST2620. Alternatively, when the serving cell is notified of a reception response to the process of step ST2619 from UE1, the serving cell may release the ePDCCH configuration for UE1 in step ST2620. This makes it possible to release physical resources, sequences, and the like that have been reserved for UE1, thereby enabling efficient use of resources.

[0415] In Step ST2621, UE1 releases (resets) the ePDCCH configuration that it has set.

[0416] By using the method disclosed in this embodiment, the UE can recognize whether ePDCCH is mapped and can monitor ePDCCH. Therefore, communication using ePDCCH is possible. This is effective when ePDCCH is used in CoMP, CA, etc.

[0417] Embodiment 7 In the seventh embodiment, a signaling method between a serving cell and another cell different from the serving cell in the first embodiment, a data transfer method, and the like are disclosed. FIG. 29, FIG. 30, and FIG. 31 are diagrams showing an example of a sequence of a mobile communication system in the seventh embodiment. FIG. 29 and FIG. 30 are connected at the position of a boundary line BL3. FIG. 30 and FIG. 31 are connected at the position of a boundary line BL4. The sequence shown in FIG. 29 to FIG. 31 is similar to the sequence shown in FIG. 15 and FIG. 16, so the same step numbers are given to the same steps, and common explanations are omitted. FIG. 29 to FIG. 31 show a case where a central entity is configured in a serving cell, so the central entity and the serving cell are not particularly distinguished and are described as serving cells.

[0418] In step ST7101, the serving cell requests a cell other than the serving cell among the cells included in the CoMP measurement set determined in step ST1530 to join the CoMP measurement set for UE1. In the following description, a cell other than the serving cell among the cells included in the CoMP measurement set may be simply referred to as a "CoMP measurement set cell."

[0419] As a specific example, the serving cell notifies the CoMP measurement set cell of a CoMP measurement set request message. The following three items (1) to (3) are disclosed as specific examples of information indicated in the CoMP measurement set request message.

[0420] (1) Request UE1 to join the CoMP measurement set. (2) Request to start transmitting CSI-RS. (3) A combination of (1) and (2) above.

[0421] In step ST7102, the CoMP measurement set cell that has received a request for UE1 to join the CoMP measurement set from the serving cell in step ST7101 responds to the request for joining the CoMP measurement set to the serving cell. The response may be omitted. This can reduce the processing load for the response process. If the CoMP measurement set cell is able to join the CoMP measurement set for UE1 or is able to start transmitting CSI-RS to UE1, it notifies the serving cell of that effect. Specifically, the CoMP measurement set cell notifies the serving cell of a CoMP measurement set request acknowledgement (CoMP Measurement set Request Ack) message.

[0422] The CoMP measurement set cell notifies the serving cell of the fact that it is impossible to join the CoMP measurement set for UE1 or to start transmitting CSI-RS to UE1. Specifically, the CoMP measurement set cell notifies the serving cell of a CoMP measurement set request negative acknowledgement (CoMP Measurement set Request Nack) message.

[0423] A specific example of an indicator for determining that a CoMP measurement set cell cannot join the CoMP measurement set for UE1 or cannot start transmitting CSI-RS to UE1 is a high load on the CoMP measurement set cell. In this sequence, a case will be described in which the CoMP measurement set cell can join the CoMP measurement set for UE1.

[0424] In Step ST7103, the serving cell transmits CSI-RS to UE1.

[0425] The CoMP measurement set cell that has notified the serving cell in Step ST7102 that it is possible to join the CoMP measurement set starts transmitting CSI-RS to UE1 in Step ST7104.

[0426] In Step ST7105, the serving cell notifies the UE 1 of the data addressed to the UE 1. Specifically, the serving cell notifies the UE 1 of the data for CoMP.

[0427] The following three (1) to (3) are disclosed as specific examples of destinations to which the serving cell notifies data.

[0428] (1) CoMP measurement set cell. If the CoMP measurement set cell that has received the data notification is not selected as a CoMP transmission point, the CoMP measurement set cell discards the notified data. In this specific example (1), compared to a specific example (3) described later, data notification can be started regardless of whether a CoMP transmission point is determined in step ST1516, and the time available for data notification can be increased. The timing of data notification is arbitrary as long as it is after the serving cell determines the execution of CoMP in step ST1508 and before CoMP transmission and reception are performed in step ST1519. Since there is a margin in the timing of data notification, it is possible to reduce momentary high loads.

[0429] (2) A cell other than the serving cell among the cells included in the CoMP active set. In the following description, a cell other than the serving cell among the cells included in the CoMP active set may be simply referred to as a "CoMP active set cell". If a CoMP active set cell that has received a data notification is not selected as a CoMP transmission point, the CoMP active set cell discards the notified data. In this specific example (2), compared to a specific example (3) described later, data notification can be started regardless of whether a CoMP transmission point is determined in step ST1516, and the time available for data notification can be increased. The timing of data notification is arbitrary as long as it is after the serving cell determines the execution of CoMP in step ST1508 and before CoMP transmission and reception are performed in step ST1519. Since there is a margin in the timing of data notification, it is possible to reduce momentary high loads.

[0430] (3) Cells other than the serving cell among the cells included in the CoMP transmission point. In the following description, cells other than the serving cell among the cells included in the CoMP transmission point may be simply referred to as "CoMP transmission point". In this specific example (3), compared to the above specific examples (1) and (2), cells not selected as CoMP transmission points do not receive data notification, so no processing to discard data occurs. Therefore, an effect can be obtained in which no unnecessary processing occurs. The timing of data notification is arbitrary as long as it is after the serving cell determines the CoMP transmission point in step ST1516 and before CoMP transmission and reception are performed in step ST1519.

[0431] As specific examples of the types of data to be notified, the following three items (1) to (3) will be disclosed. (1) PDCP data unit, which may be PDCP PDU data or PDCP SDU data. (2) RLC data unit, which may be RLC PDU data or RLC SDU data. (3) MAC data unit. This may be MAC PDU data or MAC SDU data. Depending on the type of data to be notified, parameters required for the data may be notified together.

[0432] In Step ST7106, the serving cell notifies the CoMP transmission point of scheduling information including information indicating the CoMP transmission point determined in Step ST1516. In Step ST7106, it is preferable to notify necessary scheduling information according to the type of data notified in Step ST7105. Scheduling including information indicating the CoMP transmission point, or the scheduling information that is the result of the scheduling, is referred to as "CoMP scheduling".

[0433] After the process of step ST7106 ends, the processes of steps ST1518 to ST1529 are performed in the same manner as in the above-described embodiment 1. In Fig. 31, the processes of steps ST1519 and ST1526 are shown in more detail.

[0434] Step ST1519 includes Step ST2901 to Step ST2903. In Step ST2901, UE1 and the serving cell perform transmission and reception using CoMP. In Step ST2902, UE1 and a cell other than the serving cell included in the CoMP measurement set perform transmission and reception using CoMP. In Step ST2903, UE1 derives CSI from the CSI-RS and feeds it back to the serving cell.

[0435] Step ST1526 includes steps ST2904 to ST2906. The processes of steps ST2904 to ST2906 are performed in the same manner as the processes of steps ST2901 to ST2093.

[0436] Fig. 32 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. In the sequence shown in Fig. 32, the same steps as those in the sequences shown in Fig. 15 and Fig. 16 are given the same step numbers, and common explanations are omitted. Fig. 32 shows a sequence in which a central entity and a serving cell are distinguished and the central entity determines a CoMP transmission point. Fig. 32 shows another specific example of the processing of steps ST1515 to ST1518 in Figs. 29 to 31.

[0437] In Step ST7201, the serving cell notifies the central entity of the CSI-RS measurement result received in Step ST1515. Specific examples of the CSI-RS measurement result include a CSI-RS measurement report and CSI feedback information.

[0438] In step ST7202, the serving cell notifies the central entity of information on data to be subjected to CoMP execution (hereinafter also referred to as "data parameters"). Specific examples of data parameters include data volume, quality of service (QoS) information, etc. Alternatively, the serving cell may notify the central entity of data to be subjected to CoMP execution as data parameters.

[0439] In Step ST7204, the central entity performs adjustment between CoMP measurement sets to realize CoMP for the data that is the target of CoMP execution received in Step ST7202. Specifically, the central entity performs adjustment to determine whether the transmission of the data is acceptable in the serving cell. Since scheduling for UEs that are not the target of CoMP and are served by the serving cell is performed by the serving cell, the above adjustment can provide optimal scheduling.

[0440] In Step ST7205, the central entity performs adjustment between CoMP measurement sets to realize CoMP for the data to be subjected to CoMP execution received in Step ST7202. Specifically, the central entity performs adjustment to determine whether transmission of the data is acceptable in the CoMP measurement set cell. Since scheduling for UEs not subject to CoMP that are served by the CoMP measurement set cell is performed by the CoMP measurement set cell, optimal scheduling can be achieved by performing the above adjustment. Adjustment may be performed between CoMP active sets.

[0441] In Step ST7203, the central entity performs scheduling for UE1 based on the information on the data to be subjected to CoMP execution received in Step ST7202, the result of the coordination with the serving cell performed in Step ST7204, and the result of the coordination with the CoMP measurement set cell performed in Step ST7205. Specifically, the central entity determines a CoMP transmission point. Details of the processing in Step ST7203 are similar to the processing in Step ST1516 in FIG.15 and FIG.16.

[0442] The central entity may then again coordinate among the CoMP transmission points to determine the final CoMP scheduling.

[0443] In Step ST7207, the central entity notifies the serving cell of the CoMP scheduling determined in Step ST7203.

[0444] In Step ST7208, the serving cell notifies the CoMP measurement set cell of the scheduling received in Step ST7207. The central entity may notify the CoMP measurement set cell of the scheduling determined in Step ST7203.

[0445] Fig. 33 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. In the sequence shown in Fig. 33, the same steps as those in the sequences shown in Figs. 15, 16 and 32 are given the same step numbers, and common explanations are omitted. Fig. 33 shows a sequence in which the central entity and the serving cell are distinguished and the serving cell and the central entity jointly decide a CoMP transmission point. Fig. 33 shows another specific example of the processing of steps ST1515 to ST1518 in Figs. 29 to 31.

[0446] In Step ST7304, the serving cell decides on its own cell's independent scheduling of the data to be subjected to CoMP for UE1. The decision may be made once.

[0447] In Step ST7301, the serving cell notifies the central entity of a request for adjustment between CoMP measurement sets. When notifying the adjustment request, the serving cell may notify the scheduling determined in Step ST7304. A specific example of the scheduling is a time-frequency resource. A request for adjustment between CoMP active sets may be notified.

[0448] In Step ST7302, the central entity performs adjustment between CoMP measurement sets to realize the scheduling received in Step ST7301. Specifically, the central entity performs adjustment to determine whether the scheduling received in Step ST7301 is acceptable to the serving cell. Since scheduling for UEs that are not subject to CoMP and are served by the serving cell is performed by the serving cell, the above adjustment can provide optimal scheduling. Since the serving cell has performed scheduling in Step ST7304, the serving cell may omit this step as it is acceptable.

[0449] In Step ST7303, the central entity performs adjustment between CoMP measurement sets to realize the scheduling received in Step ST7301. Specifically, the central entity performs adjustment to determine whether the scheduling received in Step ST7301 is acceptable to the CoMP measurement set cell. Since scheduling for UEs that are not subject to CoMP and are served by the CoMP measurement set cell is performed by the CoMP measurement set cell, optimal scheduling can be achieved by performing the above adjustment. Adjustment may also be performed between CoMP active sets.

[0450] In Step ST1516, the central entity performs CoMP scheduling for UE1 based on the scheduling received in Step ST7301, the result of the coordination with the serving cell performed in Step ST7302, and the result of the coordination with the CoMP measurement set cell performed in Step ST7303. Specifically, the central entity determines a CoMP transmission point. Details of the processing are the same as those of Step ST1516 in FIG. 15 and FIG. 16.

[0451] Next, a case where a Cell Unified Entity is newly provided will be disclosed. The Cell Unified Entity is defined as an entity having any function of RRC (Radio Resource Control), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), and MAC (Medium Access Control) in a plurality of wireless areas in common. Hereinafter, in the seventh, eighth, ninth, and tenth embodiments, a Cell is defined as an entity consisting of all the functions of RRC, PDCP, RLC, MAC, and PHY (Physical layer) constituting one wireless area. Also, a Sub Cell is defined as an entity consisting of some functions of RRC, PDCP, RLC, MAC, and PHY constituting one wireless area.

[0452] The cell and the subcell having the PHY function have a function of broadcasting broadcast information and may have a function of broadcasting an identifier identifiable by the UE.

[0453] 34 is a block diagram for explaining a specific example of a cell unified entity. A cell unified entity 7416 is connected to a first subcell 7401, a second subcell 7406, and a third subcell 7411.

[0454] The first subcell 7401 configures one wireless area, and includes a MAC 7402 and a PHY 7403. The PHY 7403 includes a baseband unit (BB) 7404 and a radio frequency (RF) unit 7405.

[0455] The second subcell 7406 constitutes one wireless area, and includes a MAC 7407 and a PHY 7408. The PHY 7408 includes a BB 7409 and an RF 7410.

[0456] The third subcell 7411 constitutes one wireless area, and includes a MAC 7412 and a PHY 7413. The PHY 7413 includes a BB 7414 and an RF 7415.

[0457] The cell unified entity 7416 has functions of RRC 7417, PDCP 7418, and RLC 7419 in common in the wireless area configured by the first subcell 7401, the wireless area configured by the second subcell 7406, and the wireless area configured by the third subcell 7412. In the following description, a cell unified entity that has functions of RRC, PDCP, and RLC in common in a plurality of wireless areas, such as the cell unified entity 7416, may be referred to as a "first cell unified entity."

[0458] 35 is a block diagram for explaining a specific example of another cell unified entity. The cell unified entity 7513 is connected to the fourth subcell 7501, the fifth subcell 7505, and the sixth subcell 7509.

[0459] The fourth subcell 7501 constitutes one wireless area and includes a PHY 7502. The PHY 7502 includes a BB 7503 and an RF 7504.

[0460] The fifth subcell 7505 constitutes one wireless area and includes a PHY 7506. The PHY 7506 includes a BB 7507 and an RF 7508.

[0461] The sixth subcell 7509 constitutes one wireless area, and includes a PHY 7510. The PHY 7510 includes a BB 7511 and an RF 7512.

[0462] The cell unified entity 7513 has the functions of RRC 7514, PDCP 7515, RLC 7516, and MAC 7517 in common in the wireless area configured by the fourth subcell 7501, the wireless area configured by the fifth subcell 7505, and the wireless area configured by the sixth subcell 7509. In the following description, a cell unified entity having the functions of RRC, PDCP, RLC, and MAC in common in a plurality of wireless areas, such as the cell unified entity 7513, may be referred to as a "second cell unified entity."

[0463] As another example, a cell unified entity having in common the RRC function, the PDCP function, the RLC function, and at least the scheduling function among the MAC functions in multiple radio areas may be considered. This cell unified entity may also be called a "third cell unified entity."

[0464] FIG. 36, FIG. 37, and FIG. 38 are diagrams showing an example of a sequence of a mobile communication system in the seventh embodiment. FIG. 36 and FIG. 37 are connected at the position of a boundary line BL5. FIG. 37 and FIG. 38 are connected at the position of a boundary line BL6. The sequences shown in FIG. 36 to FIG. 38 are similar to the sequences shown in FIG. 15 and FIG. 16, so the same step numbers are given to the same steps, and common explanations are omitted. FIG. 36 to FIG. 38 show a sequence when CoMP is performed in a case where a first cell unified entity having RRC7417, PDCP7418, and RLC7419 is distinguished from a subcell. In this sequence, a case where a central entity is configured in a serving subcell is shown, so that the central entity and the serving subcell are not particularly distinguished from each other and are described as a serving cell.

[0465] In Step ST7601, the first cell unified entity configures an RRM measurement configuration. Details of the process of Step ST7601 are similar to the process of Step ST1501 in FIGS.

[0466] In Step ST7602, the first cell unified entity notifies the serving sub cell of the RRM measurement configuration set in Step ST7601.

[0467] In Step ST7603, the serving subcell notifies UE1 of the RRM measurement configuration received in Step ST7602. Details of the process of Step ST7603 are similar to the process of Step ST1502 in FIGS.

[0468] In Step ST7604, UE1 reports a measurement result of the CRS to the serving subcell. Details of the process of Step ST7604 are similar to the process of Step ST1504 in FIG.

[0469] In Step ST7605, the serving subcell notifies the first cell unified entity of the report of the measurement result received in Step ST7604.

[0470] In Step ST7606, the first cell unified entity creates an RRM measurement set. Details of the process of Step ST7606 are similar to the process of Step ST1505 in FIGS.

[0471] In Step ST7607, the first cell unified entity notifies the serving sub cell of data. Specifically, the first cell unified entity notifies the serving sub cell of data addressed to UE1. An example of the type of data to be notified is an RLC data unit. The data to be notified may be RLC PDU data. It is preferable to notify parameters required for the data together. An example of the required parameters is a parameter required for the MAC process of the serving sub cell.

[0472] In Step ST7608, the serving subcell performs scheduling of the data received in Step ST7607. MAC scheduling may be performed.

[0473] In Step ST7609, the UE1 and the serving subcell perform data communication in at least one of downlink (DL) and uplink (UL).

[0474] In Step ST7610, the serving sub cell performs data communication with the first cell unified entity regarding the DL data to be transmitted to the UE 1 and the UL data received from the UE 1. The data to be notified is similar to the process of Step ST7607.

[0475] In Step ST7611, UE1 feeds back the CQI derived from the CRS to the serving subcell.

[0476] In Step ST7612, the serving subcell notifies the first cell unified entity of the CQI feedback data received in Step ST7611.

[0477] In Step ST7613, the first cell unified entity decides whether or not to execute CoMP. Details of the process of Step ST7613 are similar to the process of Step ST1508 in FIGS.

[0478] In Step ST7638, the first cell unified entity selects and decides on a CoMP measurement set. Details of the process of Step ST7638 are similar to the process of Step ST1530 in FIGS.

[0479] When the first cell unified entity grasps the load status of the subcell included in the CoMP measurement set and can determine whether the CoMP measurement set subcell can join the CoMP measurement set for UE1, it is possible to omit the processes corresponding to steps ST7101 and ST7102 in Fig. 29 to Fig. 31. In this way, by providing the first cell unified entity in a mobile communication system that supports CoMP, it is possible to prevent control delays.

[0480] In Step ST7614, the first cell unified entity requests the serving subcell to start transmitting CSI-RS.

[0481] In Step ST7615, the first cell unified entity requests a cell other than the serving subcell or a subcell included in the CoMP measurement set to start transmitting CSI-RS. In the following description, a cell other than the serving subcell or a subcell included in the CoMP measurement set may be referred to as a "CoMP measurement set subcell."

[0482] In Step ST7616, the first cell unified entity configures a CoMP measurement configuration for UE 1. Details of the process of Step ST7616 are similar to the process of Step ST1509 in FIGS.

[0483] In Step ST7617, the first cell unified entity notifies the serving sub cell of the CoMP measurement configuration for UE1 configured in Step ST7616.

[0484] In Step ST7618, the serving sub cell notifies UE1 of the CoMP measurement configuration received in Step ST7617. Details of the process of Step ST7618 are similar to the process of Step ST1510 in FIGS.

[0485] In Step ST7619, the serving sub cell transmits the CSI-RS to UE1. The serving sub cell may start transmitting the CSI-RS by receiving the request to start transmitting the CSI-RS from the first cell unified entity in Step ST7614. This allows the serving sub cell to transmit the CSI-RS only when a mobile terminal being served by the serving sub cell performs measurement using the CSI-RS, thereby making it possible to reduce the power consumption of the serving sub cell.

[0486] In Step ST7620, the CoMP measurement set sub cell transmits the CSI-RS to the UE1. The CoMP measurement set sub cell may start transmitting the CSI-RS by receiving a request to start transmitting the CSI-RS from the first cell unified entity in Step ST7615. This allows the CoMP measurement set sub cell to transmit the CSI-RS only when a mobile terminal being served by the CoMP measurement set sub cell performs measurement using the CSI-RS, thereby making it possible to reduce power consumption of the CoMP measurement set sub cell.

[0487] In Step ST7621, UE1 reports the measurement result of the CSI-RS to the serving subcell. Details of the process of Step ST7621 are similar to the process of Step ST1515 in FIG.

[0488] In Step ST7622, ​​the first cell unified entity notifies the serving sub cell of the data. Details of the process of Step ST7622 are similar to the process of Step ST7607.

[0489] In Step ST7623, the serving sub cell determines a CoMP transmission point. Details of the process of determining a CoMP transmission point are similar to the process of Step ST1516 shown in FIG.

[0490] In Step ST7625, the serving sub cell notifies the CoMP measurement set sub cell of the data addressed to the UE 1. Specifically, the serving sub cell notifies the CoMP data addressed to the UE 1.

[0491] Specific examples of the type of data to be notified include MAC data units, MAC PDU data, and MAC SDU data. Also, the first cell unified entity may notify the CoMP measurement set sub cell of data addressed to UE 1. Specifically, the first cell unified entity notifies the CoMP data addressed to UE 1. As specific examples of types of data to be notified, the following three (1) to (3) are disclosed. (1) PDCP data unit, which may be PDCP PDU data or PDCP SDU data. (2) RLC data unit, which may be RLC PDU data or RLC SDU data. (3) MAC data unit, which may be MAC PDU data or MAC SDU data. In the case of the MAC data unit, the first cell unified entity may obtain a necessary MAC data unit from the serving subcell.

[0492] Parameters required for data in each layer may also be notified. Specific examples of parameters include (1) when notifying a PDCP data unit, parameters required for RLC processing and parameters required for MAC processing are notified, and (2) when notifying an RLC data unit, parameters required for MAC processing are notified.

[0493] The following two (1) and (2) are disclosed as specific examples of a cell to which the serving subcell notifies data addressed to UE1.

[0494] (1) The serving sub cell notifies the CoMP transmission sub cell determined in step ST7623 of data addressed to UE1. In this case, compared to a specific example (2) described later, although the serving sub cell is a CoMP measurement set sub cell, it is possible to reduce notification of unnecessary data to the CoMP transmission sub cell.

[0495] (2) The serving sub cell notifies the CoMP measurement set sub cell of data addressed to UE1. In this case, there is no need to wait for the determination of the CoMP transmission sub cell in step ST7623 in order to notify the data. Therefore, the timing at which the serving sub cell notifies the CoMP measurement set sub cell of data addressed to UE1 can be any timing between the determination of the CoMP measurement set in step ST7638 and before the scheduling notification in step ST7626. The first cell unified entity may notify the serving sub cell of the determined CoMP measurement set. In the CoMP measurement set sub cell that is not selected as the CoMP transmission sub cell, the data addressed to UE1 may be discarded. In this case, there is a margin in the timing of data notification compared to the specific example (1), so that momentary high loads can be reduced.

[0496] In Step ST7626, the serving sub cell may notify the CoMP transmission sub cell of the CoMP scheduling including the information indicating the CoMP transmission point determined in Step ST7323. The serving sub cell may notify the CoMP measurement set sub cell via the first cell unified entity.

[0497] In Step ST7627, the serving subcell performs CoMP scheduling including the information of the CoMP transmission point determined in Step ST7623, and notifies the UE 1. Details of the process of Step ST7627 are the same as the process of Step ST1518 in FIGS.

[0498] In Steps ST7628 and ST7629, UE1, the serving subcell, and the CoMP transmission subcell perform transmission and reception using CoMP.

[0499] In Step ST7630, UE1 derives CSI from the CSI-RS and feeds it back to the serving subcell.

[0500] In Step ST7631, UE1 reports a measurement result of the CRS to the serving subcell. Details of the process of Step ST7631 are similar to the process of Step ST1504 in FIG.

[0501] In Step ST7632, the serving sub cell notifies the first cell unified entity of the report of the CRS measurement result received in Step ST7631.

[0502] The first cell unified entity that has received the measurement report in Step ST7632 changes the RRM measurement set as necessary in Step ST7633. Details of the process of Step ST7633 are similar to the process of Step ST1524 in FIGS.

[0503] In Step ST7634, the first cell unified entity judges whether or not to change the CoMP measurement set. Details of the processing in Step ST7634 are similar to the processing in Step ST1525 in FIG. 15 and FIG. 16. If it is judged in Step ST7634 that the CoMP measurement set is to be changed, the first cell unified entity changes the cell in the CoMP measurement set and returns to the processing of Step ST7614. If it is judged in Step ST7634 that the CoMP measurement set is not to be changed, the first cell unified entity proceeds to Step ST7635.

[0504] In Step ST7635, the first cell unified entity decides to release CoMP, that is, to stop executing CoMP.

[0505] In Step ST7636, the first cell unified entity notifies the serving sub cell of the release of the CoMP measurement configuration of UE1.

[0506] In Step ST7637, the serving subcell notifies UE1 of the release of the CoMP measurement configuration of UE1 received in Step ST7636. Details of the process of Step ST7637 are similar to the process of Step ST1528 in FIGS.

[0507] Figure 39 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. In the sequence shown in Figure 39, the same steps as those in the sequence shown in Figure 38 are given the same step numbers, and common explanations will be omitted. Figure 39 shows a sequence in which the central entity and the serving sub cell are distinguished and the central entity determines the CoMP transmission point. Figure 39 shows another specific example of the processing of steps ST7621 to ST7627 in Figures 36 to 38.

[0508] In Step ST7701, the serving subcell notifies the central entity of the CSI-RS measurement result received in Step ST7621. Specific examples of the CSI-RS measurement result include a CSI-RS measurement report and CSI feedback information.

[0509] In Step ST7702, the first cell unified entity notifies the central entity of the data. Details of the process of Step ST7702 are similar to the process of Step ST7607 in FIGS.

[0510] In Step ST7704, the central entity performs adjustment between CoMP measurement sets to realize CoMP for the data that is the target of CoMP execution received in Step ST7702. Specifically, the central entity performs adjustment to determine whether the transmission of the data is acceptable in the serving sub cell. Since scheduling for UEs that are not the target of CoMP and are served by the serving sub cell is performed by the serving sub cell, the above adjustment can provide optimal scheduling.

[0511] In Step ST7705, the central entity performs adjustment between CoMP measurement sets to realize CoMP for the data to be subjected to CoMP execution received in Step ST7202. Specifically, the central entity performs adjustment to determine whether transmission of the data is acceptable in the CoMP measurement set sub cell. Since scheduling for UEs not subject to CoMP served by the CoMP measurement set sub cell is performed by the CoMP measurement set sub cell, optimal scheduling can be achieved by performing the above adjustment. Adjustment may be performed between CoMP active sets.

[0512] In Step ST7703, the central entity performs scheduling for UE1 based on the information on the data to be subjected to CoMP execution received in Step ST7702, the result of coordination with the serving sub cell performed in Step ST7704, and the result of coordination with the CoMP measurement set sub cell performed in Step ST7705. Specifically, the central entity determines a CoMP transmission point. Details of the processing in Step ST7703 are the same as those of Step ST1516 in FIG. 15 and FIG. 16.

[0513] The central entity may then again coordinate among the CoMP transmission points to determine the final CoMP scheduling.

[0514] In Step ST7707, the central entity notifies the serving sub cell and the CoMP measurement set sub cell of the data addressed to UE1. Specifically, the central entity notifies the CoMP data addressed to UE1.

[0515] In Step ST7708, the central entity notifies the serving sub cell of the CoMP scheduling including the information indicating the CoMP transmission point determined in Step ST7703. The central entity may notify the serving sub cell of the CoMP scheduling including the information indicating the CoMP transmission point determined in Step ST7703 via the first cell unified entity.

[0516] In Step ST7709, the central entity notifies the CoMP measurement set sub cell of the CoMP scheduling including the information indicating the CoMP transmission point determined in Step ST7703. The central entity may notify the CoMP measurement set sub cell via the first cell unified entity.

[0517] Figure 40 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. In the sequence shown in Figure 40, the same steps as those in the sequences shown in Figures 36 to 39 are given the same step numbers, and common explanations are omitted. Figure 40 shows a sequence in which the central entity and the serving sub cell are distinguished and the serving sub cell and the central entity jointly determine a CoMP transmission point. Figure 40 shows another specific example of the processing of steps ST7621 to ST7627 in Figures 36 to 38.

[0518] In Step ST7801, the serving subcell decides on its own cell's sole scheduling of data subject to CoMP execution for UE1. The decision may be made once.

[0519] In Step ST7802, the serving sub cell notifies the central entity of a request for coordination between CoMP measurement sets. When notifying the coordination request, the serving sub cell may notify the scheduling determined in Step ST7801. A specific example of the scheduling is a time-frequency resource. A request for coordination between CoMP active sets may be notified.

[0520] In Step ST7803, the central entity performs adjustment between the CoMP measurement sets to realize the scheduling received in Step ST7302. Specifically, the central entity performs adjustment to determine whether the scheduling received in Step ST7802 is acceptable to the serving sub cell. Since scheduling for UEs that are not subject to CoMP and are served by the serving sub cell is performed by the serving sub cell, the above adjustment can provide optimal scheduling. Since the serving sub cell has performed scheduling in Step ST7801, the serving sub cell may omit this step as it is acceptable.

[0521] In Step ST7804, the central entity performs adjustment between the CoMP measurement sets to realize the scheduling received in Step ST7302. Specifically, the central entity performs adjustment to determine whether the scheduling received in Step ST7802 is acceptable to the CoMP measurement set sub cell. Since scheduling for UEs that are not subject to CoMP and are served by the CoMP measurement set sub cell is performed by the CoMP measurement set sub cell, optimal scheduling can be achieved by performing the above adjustment. Adjustment may be performed between CoMP active sets.

[0522] In Step ST7805, the central entity performs CoMP scheduling for UE1 based on the scheduling received in Step ST7802, the result of the coordination with the serving sub cell performed in Step ST7803, and the result of the coordination with the CoMP measurement set sub cell performed in Step ST7804. Specifically, the central entity determines a CoMP transmission point. Details of the processing are the same as those of Step ST1516 in FIG. 15 and FIG. 16.

[0523] The first cell unified entity may have the function of the central entity. Alternatively, the central entity may have the function of the first cell unified entity. Alternatively, the same entity may have the function of the central entity and the function of the first cell unified entity. This makes it possible to eliminate the need for signaling and communication between the first cell unified entity and the central entity, thereby preventing control delays. Specifically, it becomes possible to omit the processing of step ST7702 in FIG. 39.

[0524] FIG. 41 to FIG. 43 are diagrams showing an example of a sequence of a mobile communication system in the seventh embodiment. FIG. 41 and FIG. 42 are connected at the position of a boundary line BL7. FIG. 42 and FIG. 43 are connected at the position of a boundary line BL8. The sequences shown in FIG. 41 to FIG. 43 are similar to the sequences shown in FIG. 15, FIG. 16, and FIG. 36 to FIG. 38, so the same step numbers are given to the same steps, and common explanations are omitted. FIG. 41 to FIG. 43 show a sequence when CoMP is performed when the second cell unified entity having RRC7514, PDCP7515, RLC7516, and MAC7517 is distinguished from the subcell. In this sequence, the central entity is configured in the second cell unified entity, so the central entity and the second cell unified entity are not particularly distinguished from each other and are described as the second cell unified entity. The same applies to the case where the central entity is configured in the third cell unified entity.

[0525] In Step ST7901, the second cell unified entity configures an RRM measurement configuration. Details of the process of Step ST7901 are similar to the process of Step ST1501 in FIGS.

[0526] In Step ST7902, the second cell unified entity notifies the serving sub cell of the RRM measurement configuration set in Step ST7901.

[0527] In Step ST7903, the serving sub cell notifies the second cell unified entity of the measurement result report received in Step ST7604.

[0528] In Step ST7904, the second cell unified entity creates an RRM measurement set. Details of the process of Step ST7904 are similar to the process of Step ST1505 in FIGS.

[0529] In Step ST7905, the second cell unified entity notifies the serving subcell of data. Specifically, the second cell unified entity notifies the serving subcell of data addressed to UE1. A specific example of the type of data to be notified is a MAC data unit. The data to be notified may be MAC PDU data or MAC SDU data. It is preferable to notify parameters required for the data together.

[0530] In Step ST7906, the second cell unified entity performs data scheduling, and may perform MAC scheduling.

[0531] In Step ST7907, the second cell unified entity notifies the serving sub cell of the scheduling performed in Step ST7906.

[0532] In Step ST7908, the serving sub cell notifies the second cell unified entity of the CQI feedback data received in Step ST7611.

[0533] In Step ST7909, the second cell unified entity decides whether or not to execute CoMP. Details of the process of Step ST7909 are the same as the process of Step ST1508 in FIGS.

[0534] In Step ST7926, the second cell unified entity selects and decides a CoMP measurement set. Details of the process of Step ST7926 are similar to the process of Step ST1530 in FIGS.

[0535] When the second cell unified entity grasps the load status of the subcell included in the CoMP measurement set and can determine whether the CoMP measurement set subcell can join the CoMP measurement set for UE1, it is possible to omit the processes corresponding to steps ST7101 and ST7102 in Figures 29 to 31. In this way, by providing the second cell unified entity in a mobile communication system that supports CoMP, it is possible to prevent control delays.

[0536] In Step ST7910, the second cell unified entity requests the serving subcell to start transmitting CSI-RS.

[0537] In Step ST7911, the second cell unified entity requests the CoMP measurement set sub cell to start transmitting the CSI-RS.

[0538] In Step ST7912, the second cell unified entity configures a CoMP measurement configuration for the UE 1. Details of the process of Step ST7912 are similar to the process of Step ST1509 in FIGS.

[0539] In Step ST7913, the second cell unified entity notifies the serving sub cell of the CoMP measurement configuration for UE1 configured in Step ST7912.

[0540] In Step ST7914, the serving sub cell transmits the CSI-RS to UE1. The serving sub cell may start transmitting the CSI-RS by receiving the request to start transmitting the CSI-RS from the second cell unified entity in Step ST7910. This allows the serving sub cell to transmit the CSI-RS only when a mobile terminal being served by the serving sub cell performs measurement using the CSI-RS, thereby making it possible to reduce the power consumption of the serving sub cell.

[0541] In Step ST7915, the CoMP measurement set sub cell transmits the CSI-RS to the UE 1. The CoMP measurement set sub cell may start transmitting the CSI-RS by receiving a request to start transmitting the CSI-RS from the second cell unified entity in Step ST7911. This allows the CoMP measurement set sub cell to transmit the CSI-RS only when a mobile terminal being served by the CoMP measurement set sub cell performs measurement using the CSI-RS, thereby making it possible to reduce power consumption of the sub cells included in the CoMP measurement set.

[0542] In Step ST7916, the serving sub cell notifies the second cell unified entity of the CSI-RS measurement result received in Step ST7621.

[0543] In Step ST7917, the second cell unified entity determines a CoMP transmission point. Details of the process of determining a CoMP transmission point are similar to the process of Step ST1516 shown in FIG.

[0544] In Step ST7918, the second cell unified entity notifies the serving sub cell and the CoMP measurement set sub cell of the data addressed to the UE 1. Specifically, the second cell unified entity notifies the UE 1 of the data for CoMP.

[0545] As specific examples of the types of data to be notified, the following three items (1) to (3) will be disclosed. (1) PDCP data unit, which may be PDCP PDU data or PDCP SDU data. (2) RLC data unit, which may be RLC PDU data or RLC SDU data. (3) MAC Data Unit, which may be MAC PDU data or MAC SDU data.

[0546] Parameters required for data in each layer may also be notified. Specific examples of parameters include (1) when notifying a PDCP data unit, parameters required for RLC processing and parameters required for MAC processing are notified, and (2) when notifying an RLC data unit, parameters required for MAC processing are notified.

[0547] A specific example of a cell to which the second cell unified entity notifies data addressed to UE1 is similar to that of the first cell unified entity in FIGS. 36 to 38, and therefore a description thereof will be omitted.

[0548] In Step ST7919, the second cell unified entity notifies the serving sub cell and the CoMP measurement set sub cell of the CoMP scheduling including the information indicating the CoMP transmission point determined in Step ST7917. Alternatively, the second cell unified entity may notify the CoMP transmission sub cell and the CoMP active set sub cell of the CoMP scheduling.

[0549] In Step ST7920, the serving sub cell notifies the second cell unified entity of the CSI feedback data received in Step ST7630.

[0550] In Step ST7921, the serving sub cell notifies the second cell unified entity of the measurement result report received in Step ST7631.

[0551] The second cell unified entity that has received the measurement report in Step ST7921 changes the RRM measurement set as necessary in Step ST7922. Details of the process of Step ST7922 are similar to the process of Step ST1524 in FIGS.

[0552] In Step ST7923, the second cell unified entity judges whether or not to change the CoMP measurement set. Details of the process of Step ST7923 are similar to the process of Step ST1525 in FIG. 15 and FIG. 16. If it is judged in Step ST7923 that the CoMP measurement set is to be changed, the second cell unified entity changes the cell in the CoMP measurement set and returns to the process of Step ST7910. If it is judged in Step ST7923 that the CoMP measurement set is not to be changed, the second cell unified entity proceeds to Step ST7924.

[0553] In Step ST7924, the second cell unified entity decides to release CoMP, that is, to stop executing CoMP.

[0554] In Step ST7925, the second cell unified entity notifies the serving sub cell of the release of the CoMP measurement configuration for UE1.

[0555] Figure 44 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. In the sequence shown in Figure 44, the same steps as those in the sequences shown in Figures 36 to 39 and Figures 41 to 43 are given the same step numbers, and common explanations are omitted. Figure 44 shows a sequence in which the central entity and the second cell unified entity are distinguished, and the central entity determines the CoMP transmission point. Figure 44 shows another specific example of the processing of steps ST7621 to ST7627 in Figures 41 to 43. The same applies to the case in which the central entity and the third cell unified entity are distinguished.

[0556] In Step ST8001, the second cell unified entity notifies the central entity of information on data to be subjected to CoMP execution (hereinafter, may be referred to as "data parameters"). Specific examples of data parameters include data volume, QoS information of a service, and the like. The second cell unified entity may notify the central entity of data to be subjected to CoMP execution.

[0557] In step ST8002, the central entity performs adjustment between the CoMP measurement sets to realize CoMP for the data to be subjected to CoMP execution received in step ST8001. Adjustment may be performed between the CoMP active sets. Specifically, the central entity performs adjustment with the second cell unified entity to determine whether the transmission of the data is acceptable in the serving subcell and the CoMP measurement set subcell. Scheduling for UEs not subject to CoMP served by the serving subcell and scheduling for UEs not subject to CoMP served by the CoMP measurement set subcell are performed by the second cell unified entity, so that optimal scheduling can be achieved by performing the above adjustment. In addition, since adjustment does not need to be performed with each subcell and adjustment can be performed collectively with the second cell unified entity, control delays can be prevented by providing the second cell unified entity in a mobile communication system supporting CoMP.

[0558] In Step ST7703, the central entity decides CoMP scheduling. The central entity performs CoMP scheduling for UE1 based on the information on the data to be subjected to CoMP execution received in Step ST8001 and the result of the coordination with the second cell unified entity performed in Step ST8002. Specifically, it decides a CoMP transmission point. Details of the processing in Step ST7703 are similar to the processing in Step ST1516 in the sequence shown in FIG.15 and FIG.16.

[0559] The central entity may then again coordinate among the CoMP transmission points to determine the final CoMP scheduling.

[0560] In Step ST8004, the central entity notifies the second cell unified entity of the CoMP scheduling determined in Step ST7703.

[0561] In Step ST8005, the second cell unified entity notifies the serving sub cell of the scheduling received in Step ST8004. The central entity may notify the serving sub cell of the scheduling determined in Step ST7703.

[0562] In Step ST8006, the second cell unified entity notifies the CoMP measurement set sub cell of the CoMP scheduling received in Step ST8004. The central entity may notify the CoMP measurement set sub cell of the CoMP scheduling determined in Step ST7703.

[0563] Figure 45 is a diagram showing an example of a sequence of a mobile communication system in the seventh embodiment. In the sequence shown in Figure 45, the same steps as those in the sequences shown in Figures 36 to 39 and Figures 41 to 43 are given the same step numbers, and common explanations are omitted. Figure 45 shows a sequence in which the central entity and the second cell unified entity are distinguished, and the second cell unified entity and the central entity jointly determine a CoMP transmission point. Figure 45 shows another specific example of the processing of steps ST7621 to ST7627 in Figures 41 to 43. The same applies to the case in which the central entity and the third cell unified entity are distinguished.

[0564] In Step ST8101, the serving sub cell notifies the second cell unified entity of the CSI-RS measurement result received in Step ST7601. Specific examples of the CSI-RS measurement result include a CSI-RS measurement report and CSI feedback information.

[0565] In Step ST8102, the second cell unified entity determines scheduling for UE1 in its own cell alone. The second cell unified entity may determine the scheduling once.

[0566] In Step ST8103, the second cell unified entity notifies the central entity of a request for adjustment between CoMP measurement sets. When notifying the adjustment request, the second cell unified entity may notify the scheduling determined in Step ST8102. A specific example of the scheduling is time-frequency resources. Adjustment between CoMP active sets may be requested.

[0567] The second cell unified entity may have the function of the central entity. Alternatively, the central entity may have the function of the second cell unified entity. Alternatively, the same entity may have the function of the central entity and the function of the second cell unified entity. Figures 41 to 43 correspond to this example.

[0568] Alternatively, the function of the central entity may be included in the third cell unified entity. Alternatively, the function of the third cell unified entity may be included in the central entity. Alternatively, the function of the central entity and the function of the third cell unified entity may be included in the same entity. Figures 41 to 43 correspond to this example.

[0569] This eliminates the need for signaling and communication between the second cell unified entity and the central entity, thereby preventing control delays. Alternatively, it eliminates the need for signaling and communication between the third cell unified entity and the central entity, thereby preventing control delays.

[0570] Specifically, it is possible to omit the processes of steps ST8001, ST8002 and ST8004 in FIG. 44, or the processes of steps ST8103, ST8002 and ST8004 in FIG.

[0571] If the central entity has a function of scheduling all UEs served by the cells included in the CoMP measurement set of the second cell unified entity, coordination between CoMP measurement sets, coordination between CoMP active sets, or coordination between CoMP transmissions is not required, which can prevent control delays and reduce processing loads.

[0572] If the central entity has a function of scheduling all UEs served by the cells included in the CoMP measurement set of the third cell unified entity, coordination between CoMP measurement sets, coordination between CoMP active sets, or coordination between CoMP transmissions is not required, which can prevent control delays and reduce processing loads.

[0573] If the MAC functions include functions that are difficult to share among multiple wireless areas, it is difficult to realize the second cell unified entity. In that case, the third cell unified entity is useful because it shares at least the scheduling function among the MAC functions among multiple wireless areas, which can prevent control delays and reduce processing loads when CoMP is executed.

[0574] Hereinafter, in the seventh, eighth, ninth and tenth embodiments, an eNB is defined as a device that implements at least one cell and related interfaces. A sub-eNB is defined as a device that implements one or more sub-cells and related interfaces. The sub-eNB also includes an RRH.

[0575] The central entity may be implemented in the eNB, the sub-eNB, the MME, and the HeNBGW, or may be implemented in a new device. Here, the new device in which the central entity is implemented is referred to as a CoMP coordinating device.

[0576] The cell unified entity may be implemented in the eNB, sub eNB, MME and HeNBGW, or may be implemented in a new device. Here, the new device in which the cell unified entity is implemented is called a cell control device. The CoMP coordinating device and the cell control device may be the same device.

[0577] The interface between each entity may differ depending on the device in which each entity is implemented. For example, an S1 interface is used between an MME and an eNB. An S1 interface is used between a HeNBGW and a HeNB. An S1 interface is used between a HeNBGW and an MME. An X2 interface is used between eNBs. A dedicated line is used between an eNB and a sub-eNB. When the sub-eNB is an RRH, the dedicated line is sometimes called an optical fiber.

[0578] According to the seventh embodiment described above, the same effects as those of the first embodiment can be obtained.

[0579] Embodiment 8 The problem to be solved in the eighth embodiment will be described below. In 3GPP, there is no disclosure about the mobility of a mobile terminal (UE Mobility) during CoMP execution. Therefore, there is a problem that CoMP cannot be executed in a mobile communication system.

[0580] A solution to this problem is given below. The serving cell before handover (hereinafter sometimes referred to as the "source cell") stops executing CoMP. Specifically, when the source cell decides to execute handover, it stops executing CoMP. The source cell stops executing CoMP before notifying the UE to be handed over of a handover instruction. In other words, the source cell does not use CoMP when notifying the UE to be handed over of an RRC connection reconfiguration message including mobility control information to which parameters required for handover are mapped, and a handover command, to the UE to be handed over.

[0581] A specific example of a method for canceling execution of CoMP is disclosed below: As a mobile communication system, the CoMP measurement configuration is released.

[0582] As specific examples of a method for canceling a CoMP measurement configuration in a mobile communication system, the following three methods (1) to (3) are disclosed.

[0583] (1) When the source cell decides to perform a handover, the source cell requests the UE to be the handover target to release the CoMP measurement configuration. After confirming that there is no ongoing HARQ process, the source cell may request the UE to be the handover target to release the CoMP measurement configuration. When requesting the UE to be the handover target to release the CoMP measurement configuration, the source cell may also notify that the reason is handover.

[0584] A UE that receives a request to release the CoMP measurement configuration may release the CoMP measurement configuration and stop measuring the CSI-RS of cells in the CoMP measurement set.

[0585] When the UE releases the CoMP measurement configuration, the UE may store radio information (RAN information) of the cells included in the CoMP measurement set. The serving cell after handover (hereinafter, sometimes referred to as the "target cell") may reconfigure the CoMP measurement set in the source cell. In such a case, the UE stores the radio information, thereby preventing control delays.

[0586] When the UE releases the CoMP measurement configuration due to handover, the UE may store the radio information. In this case, when the source cell requests the UE to be handed over to release the CoMP measurement configuration, the source cell may also notify the UE that the reason is handover.

[0587] A UE that receives a request to release the CoMP measurement configuration due to handover stores radio information of cells included in the CoMP measurement set. A UE that receives a request to release the CoMP measurement configuration due to a reason other than handover does not store radio information of cells included in the CoMP measurement set.

[0588] As specific examples of radio information of the CoMP measurement set, the following 14 items (a) to (n) are disclosed.

[0589] (a) PCI. (b) Downlink timing. (c) MIB information. (d) SIB information. (e) CSI-RS information. (f) TA. (g) Transmission-reception timing difference (TX-RX timing difference). (h) Reception MIMO information. (i) Phase difference with other cells. (j) UE location information at the time of measurement. (k) Time information at the time of measurement. (l) EDPCCH configuration. (m) Reception quality information. (n) A combination of the above (a) to (m).

[0590] (2) When the source cell decides to perform a handover, the source cell requests the cells included in the CoMP measurement set to release the CoMP measurement configuration. After confirming that there is no ongoing HARQ process, the source cell may request the cells included in the CoMP measurement set to release the CoMP measurement configuration. The cells included in the CoMP measurement set that receive the request to release the CoMP measurement configuration stop transmitting CSI-RS.

[0591] (3) When the source cell decides to execute handover, it stops notifying the UE1 of the data for CoMP. Specifically, it stops notifying the UE1 of the data to the cells included in the CoMP measurement set. The source cell may stop notifying the UE1 of the data for CoMP after confirming that there is no ongoing HARQ process. It may stop notifying the UE1 of the data to the cells included in the CoMP active set or notifying the UE1 of the data to the CoMP transport point.

[0592] Furthermore, when the source cell decides to execute handover, it stops notifying the CoMP scheduling for UE1. Specifically, it stops notifying the cells included in the CoMP measurement set of the CoMP scheduling for UE1. The source cell may stop notifying the CoMP scheduling for UE1 after confirming that there is no ongoing HARQ process. It may stop notifying the cells included in the CoMP active set of the CoMP scheduling for UE1 or notifying the CoMP transport point of the CoMP scheduling for UE1.

[0593] In addition, the CoMP measurement set may be managed by a serving cell or a central entity. The CoMP measurement set may be managed for each UE. The serving cell or central entity that manages the CoMP measurement set may store the CoMP measurement configuration as past information even after the CoMP measurement configuration is released.

[0594] Fig. 46 and Fig. 47 are diagrams showing an example of a sequence of a mobile communication system in the eighth embodiment. Fig. 46 and Fig. 47 are connected at the position of a boundary line BL9. Fig. 46 and Fig. 47 show a sequence in which UE1 moves from cell 1 to cell 2 when CoMP is being performed for UE1 using cell 1 and cell 2, which are serving cells. Since this sequence shows a case where a central entity is configured in a serving cell, the central entity and the serving cell are not particularly distinguished from each other and are referred to as the serving cell.

[0595] In step ST8201, cell 1 judges whether or not to hand over UE1. If cell 1 judges to hand over UE1, it stops executing CoMP for UE1. Specifically, cell 1 decides to release the CoMP measurement configuration. Furthermore, if cell 1 judges to hand over UE1, it decides a target cell that is the handover destination. In this operation example, cell 2 is selected as the target cell.

[0596] In step ST8202, cell 1 requests UE 1 to release the CoMP measurement configuration (CoMP Measurement set Release). In step ST8203, cell 2 requests UE 1 to release the CoMP measurement configuration (CoMP Measurement set Release). In this operation example, it has been disclosed that CoMP is executed using cell 1 and cell 2 when requesting release of the CoMP measurement configuration, but it is also possible to notify a release request for the CoMP measurement configuration only from cell 1 without using CoMP to release the CoMP measurement configuration.

[0597] In Step ST8204, UE1, which has received the request to cancel the CoMP measurement configuration, cancels the CoMP measurement configuration.

[0598] In Step ST8205, cell 1, which is the serving cell, requests cell 2, which is a cell included in the CoMP measurement set, to release the CoMP measurement configuration.

[0599] In Step ST8206, cell 2, which is a cell included in the CoMP measurement set, notifies the response to the request to release the CoMP measurement configuration.

[0600] In Step ST8207, Cell 2, which is a cell included in the CoMP measurement set that has received the request to release the CoMP measurement configuration in Step ST8205, stops transmitting CSI-RS.

[0601] In Step ST8208, cell 1, which is the serving cell, stops notifying cell 2, which is a cell included in the CoMP measurement set, of data addressed to UE 1. Specifically, cell 1 stops notifying data for CoMP addressed to UE 1.

[0602] In Step ST8209, cell 1 stops transmitting CSI-RS.

[0603] In Step ST8210, cell 1, which is a source cell, notifies cell 2, which is a target cell, of a handover request.

[0604] In step ST8211, cell 2, which is the target cell, determines whether or not the handover is acceptable based on resources, and if it determines that the handover is acceptable, notifies cell 1, which is the source cell, of the handover request acceptance (Handover Request Ack).

[0605] In Step ST8212, the cell 1 starts forwarding data related to the UE (data forwarding) to the cell 2. Specifically, the cell 1 notifies the cell 2 of HO data addressed to the UE 1. The HO data is notified by PDCP SDU data (see Non-Patent Document 1).

[0606] In Step ST8213, the cell 1 notifies the UE 1 of an RRC connection reconfiguration message including mobility control information to which parameters required for handover are mapped. At the same time, the cell 1 instructs the UE 1 to execute handover. The instruction to execute handover may also be referred to as a "handover command."

[0607] In Step ST8214, UE1 attempts to connect to cell 2 by using the parameters received in Step ST8213. That is, UE1 transmits a RACH to cell 2 and transmits an RRC connection request.

[0608] In Step ST8215, the cell 2 notifies the UE 1 of a timing advance (TA) in response to the process of Step ST8214.

[0609] In Step ST8216, UE1 notifies cell 2 of RRC connection reconfiguration complete.

[0610] The target cell, cell 2, which has received the RRC connection setup completion may determine that the handover process is complete. Alternatively, the target cell may determine that the serving cell change procedure is complete. The target cell, which has received the RRC connection setup completion, may re-establish multipoint communication (CoMP communication). This allows the communication quality using multiple wireless links at the cell edge to be improved after the handover.

[0611] In Step ST8217, the cell 2 which has received the notification of completion of the RRC connection reconfiguration from the UE 1 in Step ST8216 executes a path switch process.

[0612] In Step ST8218, cell 2, which has completed the path switch process, notifies cell 1 of UE context release.

[0613] In Step ST8219, the cell 1, which has received the notification of the UE context release from the cell 2 in Step ST8218, releases the radio resources for the UE 1.

[0614] The detailed operation when CoMP is performed is the same as that of the seventh embodiment. Also, as disclosed in the seventh embodiment, the central entity may determine the CoMP transmission point, or the serving cell and the central entity may jointly determine the CoMP transmission point. The detailed operation in this case is the same as that of the seventh embodiment.

[0615] Figure 48 is a diagram showing an example of a sequence of a mobile communication system in the eighth embodiment. Since the sequence shown in Figure 48 is similar to the sequences shown in Figures 46 and 47, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0616] Figure 48 shows a sequence for performing CoMP when a cell unified entity and a subcell are distinguished. This sequence shows a case where a central entity is configured in a serving subcell or in a central entity, so the central entity and the serving subcell or the central entity are not particularly distinguished from each other and are described as a serving subcell or a central entity.

[0617] FIG. 48 illustrates a sequence in which UE1 moves from subcell 1 to subcell 2 while CoMP is being performed for UE1 using subcell 1 and subcell 2, which are serving subcells.

[0618] The cell unified entity can use the sequence shown in FIG. 48 regardless of whether it is a first cell unified entity, a second cell unified entity, or a third cell unified entity.

[0619] In Step ST8301, the cell unified entity judges whether or not to hand over UE1. If the cell unified entity judges to hand over UE1, it stops the execution of CoMP for UE1. Specifically, the cell unified entity decides to release the CoMP measurement configuration. Furthermore, if the cell unified entity judges to hand over UE1, it decides a target cell that is the handover destination. In this operation example, cell 2 is selected as the target cell.

[0620] In Step ST8302, the cell unified entity requests subcell 1, which is a cell included in the CoMP measurement set, to release the CoMP measurement configuration. The request is not limited to a request to release the CoMP measurement configuration, and may be a request to stop transmitting CSI-RS. Although omitted in FIG. 48, subcell 1 may notify the cell unified entity of a response to the request to release the CoMP measurement configuration.

[0621] In Step ST8303, the cell unified entity requests subcell 2, which is a cell included in the CoMP measurement set, to release the CoMP measurement configuration. The request is not limited to a request to release the CoMP measurement configuration, and may be a request to stop transmitting CSI-RS. Although omitted in FIG. 48, subcell 2 may notify the cell unified entity of a response to the request to release the CoMP measurement configuration.

[0622] In Step ST8304, sub cell 1, which is a cell included in the CoMP measurement set that has received the request to release the CoMP measurement configuration, stops transmitting CSI-RS.

[0623] In Step ST8305, sub cell 2, which is a cell included in the CoMP measurement set that has received the request to release the CoMP measurement configuration, stops transmitting CSI-RS.

[0624] In Step ST8306, the cell unified entity stops notifying the sub cell 2 included in the CoMP measurement set of data addressed to the UE 1. Specifically, the cell unified entity stops notifying the sub cell 2 of data for CoMP addressed to the UE 1.

[0625] When the cell unified entity grasps the load situation of the subcell and can determine whether the subcell 2, which is the target cell, can accept the handover or not, it is possible to omit the processes corresponding to steps ST8210 and ST8211 in Figures 46 and 47. In this way, by providing the cell unified entity, it is possible to prevent a control delay.

[0626] Consider the case where the cell unified entity has the PDCP function in common in a plurality of wireless areas. Specifically, consider the case where the PDCP function in common in the wireless area of ​​the serving subcell and the wireless area of ​​the target subcell is provided. In this case, the data notification for HO between the serving subcell and the target subcell is not necessary. Therefore, the process corresponding to step ST8212 in FIG. 47 can be omitted. By providing the cell unified entity in this way, it is possible to prevent a control delay.

[0627] In Step ST8308, the cell unified entity notifies UE1 of an RRC connection reconfiguration message including mobility control information to which parameters required for handover are mapped. At the same time, the cell unified entity instructs UE1 to execute handover. The instruction to execute handover may also be referred to as a "handover command."

[0628] In Step ST8309, the subcell 2 notifies the cell unified entity of the RRC connection reconfiguration completion received in Step ST8216.

[0629] Consider the case where the cell unified entity has the PDCP function in common in a plurality of wireless areas. Specifically, consider the case where the PDCP function in common in the wireless area of ​​the serving subcell and the wireless area of ​​the target subcell is also considered. In this case, the path switch process from the serving subcell to the target subcell is not required. Therefore, the process corresponding to step ST8217 in FIG. 47 can be omitted. By providing the cell unified entity in this way, it is possible to prevent a control delay.

[0630] In Step ST8311, the cell unified entity, which has completed the path switch process, notifies the subcell 1 of UE context release.

[0631] The detailed operation when CoMP is executed is the same as that of the seventh embodiment. The detailed operation when CoMP is executed when the first cell unified entity is used and the detailed operation when CoMP is executed when the second cell unified entity is used are the same as that of the seventh embodiment. Also, as disclosed in the seventh embodiment, the central entity may determine the CoMP transmission point, the serving subcell and the central entity may jointly determine the CoMP transmission point, or the cell unified entity and the central entity may jointly determine the CoMP transmission point. The detailed operation in this case is the same as that of the seventh embodiment.

[0632] According to the above-described eighth embodiment, the following effects can be obtained. In this embodiment, a method of handover during execution of CoMP has been disclosed. By using the disclosed method, handover during execution of CoMP becomes possible.

[0633] Moreover, the control is easier than in the tenth embodiment described later. Moreover, compared to the tenth embodiment, the mobile communication system is prevented from becoming complicated, and the base station and the mobile terminal can operate in a unified manner with respect to the movement of the UE during CoMP execution, thereby making it possible to obtain a stable mobile communication system.

[0634] Eighth embodiment, variant 1 In this modification, a specific example of a method for canceling the execution of another CoMP different from that in the eighth embodiment will be disclosed.

[0635] The mobile communication system releases the CoMP active configuration. The mobile communication system does not release the CoMP measurement configuration, i.e., maintains it.

[0636] As specific examples of a method for releasing a CoMP active configuration in a mobile communication system, the following six methods (1) to (6) are disclosed.

[0637] (1) When the source cell decides to perform handover, the source cell requests the UE to be the handover target to release the CoMP active configuration. After confirming that there is no ongoing HARQ process, the source cell may request the UE to be the handover target to release the CoMP active configuration.

[0638] The UE that has received the request to release the CoMP active configuration releases the CoMP active configuration. The CoMP measurement configuration does not have to be released. The UE may continue measuring the CSI-RS of the cells in the CoMP measurement set.

[0639] When the UE releases the CoMP active configuration, the UE may store radio information (RAN information) of the cells included in the CoMP active set. The target cell may reconfigure the CoMP active configuration in the source cell. In such a case, the UE stores the radio information to prevent control delay.

[0640] When the UE releases the CoMP active configuration due to handover, the UE may store the radio information. In this case, when the source cell requests the UE to be handed over to release the CoMP active configuration, the source cell may also notify the UE that the reason is handover.

[0641] A UE that receives a release request for a CoMP active configuration due to handover stores radio information of cells included in the CoMP active set. A UE that receives a release request for a CoMP active configuration due to other than handover does not store radio information of cells included in the CoMP active set.

[0642] A specific example of the radio information of the CoMP active set is similar to the radio information of the CoMP measurement set in the eighth embodiment.

[0643] (2) When the source cell decides to perform a handover, the source cell does not request the cells included in the CoMP measurement set to release the CoMP measurement configuration. In other words, the cells included in the CoMP measurement set continue to transmit CSI-RS.

[0644] (3) When the source cell decides to execute handover, it stops notifying the CoMP data addressed to UE1. Specifically, it stops notifying the cells included in the CoMP measurement set of data addressed to UE1. After confirming that there is no ongoing HARQ process, the source cell may stop notifying the CoMP data addressed to UE1. It may stop notifying the cells included in the CoMP measurement set of data addressed to UE1, or notifying the cells included in the CoMP active set of data addressed to UE1, or notifying the CoMP transport point of data addressed to UE1.

[0645] (4) Explains how to handle CoMP measurement sets. (4-1) The CoMP measurement set in the source cell is continued in the target cell. Specifically, the source cell notifies the target cell of the CoMP measurement set in the source cell together with a handover request. The target cell continues to use the CoMP measurement set in the source cell notified together with the handover request as the CoMP measurement set of the UE to be handed over. At that time, if the target cell can continue to use the CoMP measurement set in the source cell, it notifies the source cell of this (Ack). The fact that the target cell can continue to use the CoMP measurement set in the source cell may be notified together with the handover request Ack.

[0646] When the target cell cannot continue to use the CoMP measurement set in the source cell, the target cell notifies the source cell of this (Nack). The target cell may notify the source cell of the fact that the CoMP measurement set in the source cell cannot be continued together with the handover request acknowledgement (Handover Request Ack).

[0647] When the target cell continues to use the CoMP measurement set in the source cell, the CoMP measurement configuration may be notified again together with an RRC connection reconfiguration message including mobility control information in which parameters required for handover are mapped. This can reduce the occurrence of state mismatch between the target cell and the UE.

[0648] Alternatively, instead of notifying again, information indicating that the CoMP measurement set in the source cell is continuously used in the target cell, such as an indicator, may be notified together with an RRC Connection Reconfiguration Message including mobility control information in which parameters required for handover are mapped. This makes it possible to reduce control information.

[0649] Alternatively, the mobile communication system may statically or semi-statically determine that the CoMP measurement set is to be continued during handover. This makes it possible to reduce control information. Also, information added to an RRC Connection Reconfiguration Message including Mobility Control Information in which parameters required for handover are mapped becomes unnecessary, making it possible to build a mobile communication system with backward compatibility.

[0650] It can be treated in the same way as the CoMP measurement set of the CoMP active set.

[0651] (4-2) The CoMP measurement set that is to be used for the UE in the target cell is notified in advance from the source cell to the UE. The notification may be made before handover.

[0652] If the target cell cannot continue to use the CoMP measurement set in the source cell, the target cell notifies the CoMP measurement set that is to be used for the UE. The CoMP measurement set that is to be used for the UE may be notified together with the handover request acknowledgement.

[0653] The CoMP measurement set intended for the UE in the target cell may be a predefined set specific to the target cell, for example a set determined by the location of the target cell rather than per UE, since the UE has not performed measurements in the target cell.

[0654] The CoMP measurement set scheduled to be used for the UE in the target cell may be notified together with an RRC Connection Reconfiguration Message including Mobility Control Information to which parameters required for handover are mapped. This allows the UE to know in advance the CoMP measurement set scheduled to be used for the UE in the target cell, thereby preventing control delays. After handover, the UE may use the CoMP measurement set scheduled to be used for the UE in the target cell.

[0655] It can be treated in the same way as the CoMP measurement set of the CoMP active set.

[0656] (5) A UE that receives a handover command may continue measuring the CSI-RS of cells in the CoMP measurement set in the target cell.

[0657] (6) Cell 1, which has been notified by the target cell that the path switch process has been completed, performs the following process. The source cell decides to cancel the CoMP measurement configuration for the UE that is the handover target. The source cell may stop transmitting CSI-RS. The source cell requests the cells included in the CoMP measurement set to cancel the CoMP measurement configuration. After confirming that there is no ongoing HARQ process, the source cell may request the cells included in the CoMP measurement set to cancel the CoMP measurement configuration.

[0658] A cell included in a CoMP measurement set that receives a request to release the CoMP measurement configuration stops transmitting CSI-RS.

[0659] FIG. 49 and FIG. 50 are diagrams showing an example of a sequence of a mobile communication system in the first modification of the eighth embodiment. FIG. 49 and FIG. 50 are connected at the position of the boundary line BL10. The sequences shown in FIG. 49 and FIG. 50 are similar to the sequences shown in FIG. 46 and FIG. 47, so the same step numbers are given to the same steps, and common explanations are omitted. FIG. 49 and FIG. 50 show a sequence in which UE1 moves from cell 1 to cell 2 when CoMP is being performed for UE1 using cell 1 and cell 2, which are serving cells. This sequence shows a case where a central entity is configured in the serving cell, so the central entity and the serving cell are not particularly distinguished and are described as serving cells.

[0660] In step ST8400, cell 1 judges whether or not to hand over UE1. If cell 1 judges to hand over UE1, it stops execution of CoMP for UE1. Specifically, cell 1 decides to release the CoMP active configuration. Furthermore, if cell 1 judges to hand over UE1, it decides a target cell that is a handover destination. In this operation example, cell 2 is selected as the target cell.

[0661] In step ST8401, cell 1 requests UE1 to release the CoMP active configuration (CoMP active set release). In step ST8402, cell 2 requests UE1 to release the CoMP active configuration (CoMP active set release). In this operation example, it has been disclosed that CoMP is executed using cell 1 and cell 2 when requesting release of the CoMP active configuration, but it is also possible to notify a release request for the CoMP measurement configuration only from cell 1 without using CoMP to release the CoMP active configuration.

[0662] In Step ST8403, UE1, which has received the request to release the CoMP active configuration, releases the CoMP active configuration.

[0663] In Step ST8404, cell 1, which has received the notification of UE context release from cell 2 in Step ST8218, decides to release the CoMP measurement configuration. Instead of releasing the CoMP measurement configuration, cell 1 may decide to release the CoMP active configuration.

[0664] In Step ST8405, cell 1, which is the serving cell, requests cell 2, which is a cell included in the CoMP measurement set, to release the CoMP measurement configuration.

[0665] In Step ST8406, cell 2, which is a cell included in the CoMP measurement set, notifies the response to the request to release the CoMP measurement configuration.

[0666] In Step ST8407, Cell 2, which is a cell included in the CoMP measurement set that has received the request to release the CoMP measurement configuration in Step ST8405, stops transmitting CSI-RS.

[0667] In Step ST8408, cell 1 that has decided to release the CoMP measurement configuration in Step ST8404 stops transmitting CSI-RS.

[0668] The detailed operation when CoMP is performed is the same as that of the seventh embodiment. Also, as disclosed in the seventh embodiment, the central entity may determine the CoMP transmission point, or the serving cell and the central entity may jointly determine the CoMP transmission point. The detailed operation in this case is the same as that of the seventh embodiment.

[0669] FIG. 51 and FIG. 52 are diagrams showing an example of a sequence of a mobile communication system in the first modification of the eighth embodiment. The sequences shown in FIG. 51 and FIG. 52 are similar to the sequences shown in FIG. 46 to FIG. 50, so the same step numbers are given to the same steps, and common explanations are omitted. FIG. 51 and FIG. 52 are connected at the position of the boundary line BL11. FIG. 51 and FIG. 52 show a sequence when CoMP is executed in a case where a cell unified entity and a subcell are distinguished. In this sequence, a case where a central entity is configured in a serving subcell or a central entity is shown, so that the central entity is not particularly distinguished and is described as a serving subcell or a central entity. FIG. 51 and FIG. 52 show a sequence when UE1 moves from subcell 1 to subcell 2 when CoMP is executed for UE1 using subcell 1 and subcell 2, which are serving subcells. The cell unified entity can use the sequences shown in Figures 51 and 52 whether it is a first cell unified entity, a second cell unified entity, or a third cell unified entity.

[0670] In Step ST8500, the cell unified entity determines whether or not to hand over UE1. If the cell unified entity determines to hand over UE1, it stops the execution of CoMP for UE1. Specifically, the cell unified entity determines to release the CoMP active configuration. Furthermore, if the cell unified entity determines to hand over UE1, it determines a target cell that is the handover destination. In this operation example, subcell 2 is selected as the target cell.

[0671] In Step ST8501, when receiving the RRC connection completion in Step ST8309, the cell unified entity decides to release the CoMP measurement configuration. Instead of releasing the CoMP measurement configuration, the cell unified entity may decide to release the CoMP active configuration.

[0672] In Step ST8502, the cell unified entity requests subcell 1, which is a cell included in the CoMP measurement set, to release the CoMP measurement configuration. The request is not limited to a request to release the CoMP measurement configuration, and may be a request to stop transmitting CSI-RS. Although omitted in Fig. 51 and Fig. 52, subcell 1 may notify the cell unified entity of a response to the request to release the CoMP measurement configuration.

[0673] In Step ST8503, the cell unified entity requests subcell 2, which is a cell included in the CoMP measurement set, to release the CoMP measurement configuration. The request is not limited to a request to release the CoMP measurement configuration, and may be a request to stop transmitting CSI-RS. Although omitted in Fig. 51 and Fig. 52, subcell 2 may notify the cell unified entity of a response to the request to release the CoMP measurement configuration.

[0674] In Step ST8504, sub cell 2, which is a cell included in the CoMP measurement set that has received the request to release the CoMP measurement configuration, stops transmitting CSI-RS.

[0675] In Step ST8505, sub cell 1, which is a cell included in the CoMP measurement set that has received the request to release the CoMP measurement configuration, stops transmitting CSI-RS.

[0676] Detailed operations when CoMP is executed are the same as those in the seventh embodiment. Detailed operations when CoMP is executed when the first cell unified entity is used and detailed operations when CoMP is executed when the second cell unified entity is used are the same as those in the seventh embodiment. Also, as disclosed in the seventh embodiment, the central entity may determine the CoMP transmission point, or the cell unified entity and the central entity may jointly determine the CoMP transmission point. Detailed operations in this case are the same as those in the seventh embodiment.

[0677] In addition to the effects of the eighth embodiment, the first modification of the eighth embodiment provides the following effects. A UE located in a location where CoMP can be performed, or a UE that has maintained reception quality by performing CoMP, can continue CoMP measurements. This allows CoMP to be started quickly even after handover, compared to the eighth embodiment. Also, it allows the source cell to notify the UE in advance of a CoMP measurement set that is scheduled to be used for the UE in the target cell. This eliminates the need for the target cell to notify the CoMP measurement set again, and allows CoMP to be started quickly even after handover, compared to the eighth embodiment.

[0678] Eighth embodiment, modified example 2 In this modification, a specific example of a method for canceling the execution of another CoMP different from that in the eighth embodiment and modification 1 of the eighth embodiment will be disclosed.

[0679] The mobile communication system may not perform CoMP scheduling and may not select CoMP transmission points.

[0680] A specific example of a method for a mobile communication system that does not perform CoMP scheduling is disclosed below.

[0681] (1) When the source cell decides to perform handover, it does not notify the UE to be handed over due to the suspension of execution of CoMP. This allows radio resources to be used more effectively than in the eighth embodiment and the first modification of the eighth embodiment. The CoMP measurement set or the CoMP active configuration does not need to be released. Measurement of the CSI-RS of the cells in the CoMP measurement set may be continued.

[0682] Other specific examples of methods for not performing CoMP scheduling in this variant are similar to specific examples (2), (3), (4), (5), and (6) of methods for releasing the CoMP active configuration in variant 1 of embodiment 8, so their explanations are omitted.

[0683] FIG. 53 and FIG. 54 are diagrams showing an example of a sequence of a mobile communication system in the second modification of the eighth embodiment. FIG. 53 and FIG. 54 are connected at the position of the boundary line BL12. The sequences shown in FIG. 53 and FIG. 54 are similar to the sequences shown in FIG. 46, FIG. 47, FIG. 49, and FIG. 50, so the same step numbers are given to the same steps, and common explanations are omitted. FIG. 53 and FIG. 54 show a sequence in which UE1 moves from cell 1 to cell 2 when CoMP is being performed for UE1 using cell 1 and cell 2, which are serving cells. This sequence shows a case where a central entity is configured in the serving cell, so the central entity and the serving cell are not particularly distinguished and are described as serving cells.

[0684] In step ST8601, cell 1 judges whether or not to hand over UE1. If cell 1 judges to hand over UE1, it stops executing CoMP for UE1. Specifically, cell 1 decides not to perform CoMP scheduling. Furthermore, if cell 1 judges to hand over UE1, it decides a target cell that is a handover destination. In this operation example, cell 2 is selected as the target cell.

[0685] In Step ST8602, cell 1, which is the serving cell, stops notifying cell 2, which is a cell included in the CoMP transmission point, of data addressed to UE 1. Specifically, it stops notifying data for CoMP addressed to UE 1.

[0686] The detailed operation when CoMP is performed is the same as that of the seventh embodiment. Also, as disclosed in the seventh embodiment, the central entity may determine the CoMP transmission point, or the serving cell and the central entity may jointly determine the CoMP transmission point. The detailed operation in this case is the same as that of the seventh embodiment.

[0687] Figure 55 is a diagram showing an example of a sequence of a mobile communication system in Modification 2 of Embodiment 8. Since the sequence shown in Figure 55 is similar to the sequences shown in Figures 46 to 48, 51 and 52, the same step numbers are assigned to the same steps, and common explanations will be omitted.

[0688] Figure 55 shows a sequence for performing CoMP when a cell unified entity and a subcell are distinguished. This sequence shows a case where a central entity is configured in a serving subcell or in a central entity, so the central entity and the serving subcell or the central entity are not particularly distinguished from each other, and are described as a serving subcell or a central entity.

[0689] Fig. 55 shows a sequence in the case where UE1 moves from subcell 1 to subcell 2 while CoMP is being performed for UE1 using subcell 1 and subcell 2, which are serving subcells. The sequence shown in Fig. 55 can be used for the cell unified entity whether it is the first cell unified entity, the second cell unified entity, or the third cell unified entity.

[0690] In Step ST8701, the cell unified entity judges whether or not to hand over UE1. If the cell unified entity judges that UE1 is to be handed over, it stops the execution of CoMP for UE1. Specifically, the cell unified entity decides not to perform CoMP scheduling. Alternatively, the serving subcell may decide not to perform CoMP scheduling. Furthermore, if the cell unified entity judges that UE1 is to be handed over, it decides a target cell that is a handover destination. In this operation example, the cell unified entity selects subcell 2 as the target cell.

[0691] In Step ST8702, the cell unified entity stops notifying subcell 2, which is a cell included in the CoMP transmission point, of data addressed to UE 1. Specifically, the cell unified entity stops notifying CoMP data addressed to UE 1.

[0692] Detailed operations when CoMP is executed are the same as those in the seventh embodiment. Detailed operations when CoMP is executed when the first cell unified entity is used and detailed operations when CoMP is executed when the second cell unified entity is used are the same as those in the seventh embodiment. Also, as disclosed in the seventh embodiment, the central entity may determine the CoMP transmission point, or the cell unified entity and the central entity may jointly determine the CoMP transmission point. Detailed operations in this case are the same as those in the seventh embodiment.

[0693] The above-described second modification of the eighth embodiment can provide the same effects as those of the eighth embodiment and the first modification of the eighth embodiment.

[0694] Embodiment 9 The problem to be solved in the ninth embodiment will be described below. In the method of the eighth embodiment, the execution of CoMP is temporarily stopped. Therefore, there is a problem that the reception quality of a link that has been maintained by executing CoMP suddenly deteriorates, causing a communication interruption. As a specific example, it is considered that the UE cannot normally receive an RRC connection reconfiguration message transmitted from a source cell, which includes mobility control information in which parameters required for handover are mapped. As a result, the UE cannot normally perform handover, and communication is interrupted.

[0695] The solution to the problem of communication interruption described above is as follows. During handover processing, the source cell continues to execute CoMP. In other words, during handover processing, the network side including the cell and subcell does not release the CoMP-related configuration. Specifically, the CoMP measurement set and the CoMP active configuration are not released. The source cell executes CoMP when notifying the UE to be handed over of an RRC connection reconfiguration message including mobility control information to which parameters required for handover are mapped, and a handover command.

[0696] Specific examples of phases during handover processing include a handover preparation phase, a handover execution phase, and a handover completion phase (see Chapter 10.1.2.1 of Non-Patent Document 1).

[0697] As specific examples of a method for continuing the execution of CoMP by a source cell, the following three methods (1) to (3) are disclosed.

[0698] (1) The source cell executes CoMP when notifying the UE to be handed over of an RRC connection reconfiguration message including mobility control information to which parameters required for handover are mapped, and a handover command.

[0699] (2) The source cell requests the UE to be handed over to release the CoMP measurement configuration together with or after an RRC connection reconfiguration message including mobility control information to which parameters required for handover are mapped. Instead of requesting the release of the CoMP measurement configuration, the source cell may request the release of the CoMP active configuration.

[0700] The UE that has received the request to release the CoMP measurement configuration may release the CoMP measurement configuration and stop measuring the CSI-RS of the cells in the CoMP measurement set. The UE may release the CoMP measurement configuration in the source cell and stop measuring the CSI-RS of the cells in the CoMP measurement set in the source cell.

[0701] Alternatively, as a mobile communication system, an RRC connection reconfiguration message including mobility control information in which parameters required for handover are mapped during CoMP execution may also include a request to release the CoMP measurement configuration or a request to release the CoMP active configuration. This can reduce control information. In this case, a UE that receives an RRC connection reconfiguration message including mobility control information in which parameters required for handover are mapped during CoMP execution may cancel the CoMP measurement configuration, cancel the CoMP active configuration, or stop measuring the CSI-RS of cells in the CoMP measurement set.

[0702] The UE may store the radio information when releasing the CoMP measurement configuration due to handover. A specific example is the same as that in the eighth embodiment, and therefore a description thereof will be omitted.

[0703] (3) Cell 1, which has received a notification from the target cell that the path switch process has been completed, performs the following process. A specific example of the notification that the path switch process has been completed is a notification of UE context release. The source cell stops notifying CoMP data addressed to UE1. Specifically, it stops notifying cells included in the CoMP measurement set of data addressed to UE1. After confirming that there is no ongoing HARQ process, the source cell may stop notifying UE1 of data for CoMP. It may stop notifying cells included in the CoMP measurement set of data addressed to UE1, or notifying cells included in the CoMP active set of data addressed to UE1, or notifying a CoMP transport point of data addressed to UE1.

[0704] Other specific examples of the method for continuing CoMP execution by the source cell in this variant are similar to specific examples (4), (5), and (6) of the method for releasing the CoMP active configuration in variant 1 of embodiment 8, so their explanations are omitted.

[0705] FIG. 56 and FIG. 57 are diagrams showing an example of a sequence of a mobile communication system in the ninth embodiment. FIG. 56 and FIG. 57 are connected at the position of the boundary line BL13. The sequences shown in FIG. 56 and FIG. 57 are similar to the sequences shown in FIG. 46, FIG. 47, FIG. 49, and FIG. 50, so the same step numbers are given to the same steps, and common explanations are omitted. FIG. 56 and FIG. 57 show a sequence in which UE1 moves from cell 1 to cell 2 when CoMP is being performed for UE1 using cell 1 and cell 2, which are serving cells. Since this sequence shows a case where a central entity is configured in a serving cell, the central entity and the serving cell are not particularly distinguished from each other and are described as serving cells.

[0706] In step ST8801, cell 1 judges whether or not to hand over UE1. If cell 1 judges to hand over UE1, it decides to continue executing CoMP for UE1 by the source cell during the handover process. Also, if cell 1 judges to hand over UE1, it decides a target cell that is a handover destination. In this operation example, cell 2 is selected as the target cell.

[0707] In Step ST8802, cell 1 notifies UE1 of an RRC connection reconfiguration message including mobility control information to which parameters required for handover are mapped. In Step ST8803, cell 2 notifies UE1 of an RRC connection reconfiguration message including mobility control information to which parameters required for handover are mapped. In addition, cell 1 instructs UE1 to execute handover. In this operation example, CoMP is executed using cell 1 and cell 2 in notifying the RRC connection reconfiguration message.

[0708] In Step ST8804, UE1, which has received the request to cancel the CoMP measurement configuration, cancels the CoMP measurement configuration.

[0709] In Step ST8805, Cell 1, which has received the UE context release in Step ST8218, stops notifying cells included in the CoMP measurement set of data addressed to UE 1. Specifically, Cell 1 stops notifying data for CoMP addressed to UE 1.

[0710] The detailed operation when CoMP is performed is the same as that of the seventh embodiment. Also, as disclosed in the seventh embodiment, the central entity may determine the CoMP transmission point, or the serving cell and the central entity may jointly determine the CoMP transmission point. The detailed operation in this case is the same as that of the seventh embodiment.

[0711] Figures 58 and 59 are diagrams showing an example of a sequence of a mobile communication system in the ninth embodiment. Figures 58 and 59 are connected at the position of boundary line BL14. The sequences shown in Figures 58 and 59 are similar to the sequences shown in Figures 46 to 48, 51, 52, 56 and 57, so the same step numbers are used for the same steps and common explanations will be omitted.

[0712] 58 and 59 show a sequence for performing CoMP when a cell unified entity and a subcell are distinguished. In this sequence, a case where a central entity is configured in a serving subcell or in a central entity is shown, so that the central entity and the serving subcell or the central entity are not particularly distinguished from each other and are described as a serving subcell or a central entity.

[0713] 58 and 59 show a sequence in which UE1 moves from subcell 1 to subcell 2 when CoMP is being performed for UE1 using subcell 1 and subcell 2, which are serving subcells. The sequences shown in FIG. 58 and FIG. 59 can be used for the cell unified entity whether it is the first cell unified entity, the second cell unified entity, or the third cell unified entity.

[0714] In Step ST8901, the cell unified entity judges whether or not to hand over UE1. If the cell unified entity judges to hand over UE1, it decides to continue executing CoMP for UE1 by the source cell during the handover process. Furthermore, if the cell unified entity judges to hand over UE1, it decides a target cell that is a handover destination. In this operation example, subcell 2 is selected as the target cell.

[0715] In Step ST8902, the cell unified entity that has received the RRC connection completion in Step ST8309 stops notifying the cells included in the CoMP measurement set of data addressed to UE1. Specifically, it stops notifying the CoMP data addressed to UE1.

[0716] The detailed operation when CoMP is performed is the same as that of the seventh embodiment. Also, as disclosed in the seventh embodiment, the central entity may determine the CoMP transmission point, or the serving cell and the central entity may jointly determine the CoMP transmission point. The detailed operation in this case is the same as that of the seventh embodiment.

[0717] In addition to the effects of the eighth embodiment and the first modification of the eighth embodiment, the ninth embodiment described above can provide the following effects. The handover process does not cause a sudden deterioration in reception quality in the source cell. As a specific example, the RRC connection reconfiguration message transmitted from the source cell includes mobility control information to which parameters required for handover are mapped, and is transmitted using CoMP, so that the UE can normally receive the RRC connection reconfiguration message.

[0718] Ninth embodiment, variant 1 The problem to be solved by the first modification of the ninth embodiment will be described below. 3GPP discloses the following operation when a radio link failure occurs (see Non-Patent Document 1, Chapter 10.1.6). Radio link failure includes handover failure. The conditions for successful reconnection of a UE when a radio link failure occurs are disclosed. One of the conditions for successful reconnection is when the UE selects an eNB that stores the UE's context as a reconnection destination.

[0719] When a handover failure occurs, the target cell does not notify the source cell of the UE context release. Therefore, the context of the UE to be handed over is not released in the source cell. Also, when a handover failure occurs, if the UE selects the source cell as a reconnection destination, the condition for the reconnection to be successful is met.

[0720] When a UE moves while CoMP is being performed, it is possible that the reception quality is maintained by performing CoMP in the source cell. Therefore, if a handover fails, even if the source cell is selected as the reconnection destination, the reception quality of the link is poor, and there is a high possibility that the reconnection will fail.

[0721] The solution to the problem of the increased possibility of reconnection failure as described above is shown below. When a UE detects a handover failure during movement of the UE while CoMP is being performed and selects the source cell as the reselection destination, the UE resets the CoMP measurement set in the source cell. Measurement of CSI-RS of cells in the CoMP measurement set in the source cell may be resumed. Also, the CoMP active set in the source cell is reset.

[0722] In the first modification of the ninth embodiment, the source cell cancels the CoMP measurement configuration for the UE to be handed over after receiving a notification from the target cell that the path switch process has been completed. If a handover failure occurs, there is no notification from the target cell that the path switch process has been completed. Therefore, in the case of a handover failure, the source cell does not cancel the CoMP measurement configuration for the UE to be handed over. This prevents inconsistency in the CoMP measurement set between the UE and the network side including the cell and the subcell.

[0723] In this case, the UE may store radio information when releasing the CoMP measurement configuration due to handover. A specific example is the same as that in the eighth embodiment, and therefore a description thereof will be omitted.

[0724] The above-described first modification of the ninth embodiment provides the following advantages: When a handover fails and a source cell is selected as a reconnection destination, the reception quality of the link can be maintained by executing CoMP, and the reconnection can be more likely to be successful.

[0725] Embodiment 10 The problem to be solved by the tenth embodiment will be described below. In the above-mentioned eighth embodiment and its modification, and ninth embodiment and its modification, when a handover is performed in a UE performing multipoint communication (CoMP communication) in a set CoMP active set or CoMP measurement set, that is, when a serving cell is changed, the UE is configured to stop the CoMP communication, switch to single-point communication with the serving cell, and re-establish the multipoint communication after the procedure for changing the serving cell is completed.

[0726] Fig. 60 and Fig. 61 are diagrams for explaining the concept of CoMP communication between multiple sub-eNB devices and UEs. Fig. 60 shows a case where three sub-eNB (Sub-eNB) devices, namely a first sub-eNB device (Sub-eNB1) 10104, a second sub-eNB device (Sub-eNB2) 10105, and a third sub-eNB device (Sub-eNB3) 10106, and a first UE (UE1) 10107 are performing CoMP communication. Three cell areas 10101 to 10103 are realized by the three sub-eNB devices 10104 to 10106.

[0727] Fig. 61 shows a case where a first UE (UE1) moves from a position indicated by reference symbol "10207" to a position indicated by reference symbol "10208." In Fig. 61, a first UE (UE1) 10207, 10208 corresponds to the first UE (UE1) 10107 in Fig. 60, a first to third sub-eNB apparatus (Sub-eNB1 to Sub-eNB3) 10204 to 10206 correspond to the first to third sub-eNB apparatus (Sub-eNB1 to Sub-eNB3) 10104 to 10106 in Fig. 60, and cell areas 10201 to 10203 of the sub-eNB apparatuses 10204 to 10206 correspond to cell areas 10101 to 10103 in Fig. 60.

[0728] When the first UE (UE1) moves from the position indicated by reference symbol "10207" to the position indicated by reference symbol "10208", the CoMP communication is stopped due to the accompanying serving cell change process. At this time, the first UE (UE1) 10208 communicates with, for example, the first sub-eNB device (Sub-eNB1) 10204.

[0729] As shown in Figure 61, the serving cell is often changed when the UE is located at the cell edge of the serving cell. In such a positional relationship, the communication quality of the communication link between the serving cell and the UE is considered to be degraded due to the distance. In addition, the serving cell change itself can be considered to be performed for the purpose of changing to a cell with better communication quality of the communication link.

[0730] As shown in Fig. 61, when the CoMP communication is stopped when the serving cell is changed, the gain in communication quality of the multipoint communication (CoMP communication) over the single-point communication cannot be obtained during the stop period, and communication with low communication quality is unavoidable. This may cause a situation in which the procedure for changing the serving cell itself cannot be completed.

[0731] In addition, one of the objectives of CoMP communication is to improve communication quality using multiple wireless links at the cell edge, so the above problem is also an important issue.

[0732] Furthermore, the following problem can be cited as another problem: In the process of changing the serving cell of a UE disclosed in Non-Patent Document 1 and the like, although there is a recovery process by upper layer retransmission, the loss of some Layer 2 packets is permitted during the procedure.

[0733] However, packet loss causes an increase in unnecessary communication traffic due to a change in the serving cell. In addition, when considering the impact of quality degradation due to the stop of CoMP communication, the impact of packet loss may become even greater.

[0734] The solution to the problem in the tenth embodiment is described below. In order to solve the problem, in the present embodiment, the serving cell is changed while continuing the CoMP communication. FIG. 62 is a diagram for explaining the change of the serving cell in the tenth embodiment. FIG. 62 shows a case where the first UE (UE1) moves from the position indicated by the reference code "10307" to the position indicated by the reference code "10308" while continuing the CoMP communication.

[0735] The target cells included in the CoMP active set or CoMP measurement set of CoMP are likely to be geographically adjacent cells, and the serving cell to be changed to is very likely to be selected from among those cells. In Fig. 62, the CoMP active set shows an example in which the serving cell is changed from the cell including the first sub-eNB apparatus (Sub-eNB1) 10304 to the cell including the second sub-eNB apparatus (Sub-eNB2) 10305 among the cells including the first to third sub-eNB apparatuses (Sub-eNB1 to Sub-eNB3) 10304 to 10306.

[0736] At this time, the communication link quality of the cell from which the serving cell is changed (hereinafter referred to as the "source cell") is likely to be insufficient due to the movement of the UE, and the communication link quality of the cell to which the serving cell is changed (hereinafter referred to as the "target cell") is likely to be good as the distance has become closer. Therefore, changing the serving cell while continuing CoMP communication is highly effective because it is consistent with the purpose of CoMP communication and allows the serving cell to be changed in a good environment.

[0737] In addition, because the serving cell is changed while continuing CoMP communication, it is expected that the conventional physical layer interruption can be minimized. Therefore, by linking the layer 2 of the source cell and the layer 2 of the target cell, it is possible to minimize the packet loss of the existing layer 2 and suppress the increase in unnecessary traffic caused by the change of the serving cell.

[0738] To achieve this, the following four processes (1) to (4) are added to the serving cell change procedure.

[0739] (1) Notifying the CoMP set from the source cell to the target cell. (2) Data units (RLC SDUs, RLC PDUs, and other data units in the middle of processing) before, during, or after Layer 2 (PDCP / RLC) processing, excluding PDCP SDUs, must not be discarded, and must be forwarded from the source cell to the target cell together with related parameters.

[0740] (3) At least for layer 2 processing, processing related to physical layer processing such as HARQ processing, is to be completed on the source cell side, and switching to the target cell is to be performed.

[0741] (4) In data transmission of Layer 2 (PDCP / RLC), a procedure for maintaining the transmission order between the source cell and the target cell is added (not performing RLC re-establishment described in 3GPP TS36.322 V10.0.0 (hereinafter referred to as "Reference 8")).

[0742] Although the transfer of MAC data units is not described in this embodiment, it is also possible to transfer data units before the start of HARQ processing in the MAC layer to a target cell in the same manner as RLC / PDCP.

[0743] Fig. 63 to Fig. 66 are diagrams showing an example of a sequence of a mobile communication system in the tenth embodiment. Fig. 63 and Fig. 64 are connected at the position of boundary line BL15. Fig. 64 and Fig. 65 are connected at the position of boundary line BL16. Fig. 65 and Fig. 66 are connected at the position of boundary line BL17.

[0744] This sequence is an example of a case where the UE performs CoMP communication with three cells as a CoMP active set or a CoMP measurement set in communication between the UE and the E-UTRAN, and the serving cell is changed between the cells. Although not shown in Figures 63 to 66, scheduling notification from the cell to the UE is performed using the PDCCH, etc.

[0745] Here, among the cells in the CoMP active set or CoMP measurement set, the serving cell before the serving cell change is defined as the source cell, the serving cell after the change is defined as the target cell, and the remaining cell that does not become the serving cell in this sequence is defined as a non-serving cell.

[0746] Each cell is made up of PHY, MAC, RLC, PDCP, and RRC layers, and each layer basically has at least the functions described in the 3GPP standard.

[0747] First, at the beginning of the sequence, it is assumed that the UE is performing CoMP communication with three cells as a CoMP active set or a CoMP measurement set. In this case, in steps ST10401 to ST10404, between the source cell and the target cell and between the source cell and the non-serving cell, there are links for transmitting MAC data units and links for notifying scheduling information related to the data units scheduled by the MAC of the source cell. These links may be collectively referred to as "MAC data unit-related transmission links."

[0748] The links shown here are described in a logical sense, and the realization form differs depending on the actual implementation. For example, when the source cell and the target cell are implemented as different eNBs, the communication interface may be an X2 interface. In addition, it is assumed that logical links exist not only for MAC data unit-related transmission links but also for communication paths for communication between each cell, as described above.

[0749] In Step ST10405, the source cell performs an HO decision process. Specifically, the source cell determines to perform HO to the target cell.

[0750] After that, in step ST10406, the RRC of the source cell makes an HO request. Specifically, the RRC of the source cell notifies the RRC of the target cell of the necessity (proposal) of continuing CoMP currently operating in communication with the target UE, the CoMP active set and the CoMP measurement set, and measurement information related to communication with the cell. Here, the necessity (proposal) of continuing CoMP is determined from the CoMP set, and does not need to be explicitly notified.

[0751] In Steps ST10407 to ST10408, the RRC of the target cell that has received the HO request in Step ST10406 ​​determines CoMP set candidates in the target cell based on the information included in the HO request, the traffic situation of its own cell, CoMP cooperating set information, and the like.

[0752] Then, in steps ST10408 and ST10455, the RRC of the target cell notifies the cells included in the CoMP active set or CoMP measurement set of the CoMP set candidate, in this example, the source cell and non-serving cells, of a request for CoMP communication (CoMP Request) for the target UE.

[0753] The source cell and non-serving cell that receive the request in steps ST10408 and ST10455 check the status of their own traffic and other communication resources, and notify the target cell of the results as a CoMP response in steps ST10409 and ST10456.

[0754] The target cell that has received the CoMP responses in Step ST10409 and Step ST10456 determines a CoMP set based on the results in Step ST10410.

[0755] After that, in step ST10411, the target cell notifies the source cell of a response including information on whether HO is possible, whether CoMP is to be continued, and a compatible CoMP set, as an HO response, based on the CoMP set determination result. Here, whether CoMP is possible or not does not need to be explicitly notified, since it is determined from the CoMP set. Also, if the target cell continues the CoMP set in the source cell received in step ST10406, it does not need to notify the compatible CoMP set.

[0756] In step ST10412, the source cell that has received the HO possible response (OK) transmits a message indicating CoMP continuation and serving cell change including information on the CoMP set as an RRC connection reconfiguration to the UE. By transmitting this message, the UE that has received the message can perform an operation different from that when it has received "RRC Connection Reconfiguration" described in Non-Patent Document 1, Reference Document 1, and the like.

[0757] As specific examples of operations different from those when "RRC Connection Reconfiguration" is received, the following three (1) to (3) are disclosed. (1) RLC “Re-establishment” will not be conducted. (2) Do not reset the MAC. (3) There will be no “re-establishment” of the PDCP.

[0758] As specific examples of messages indicating a serving cell change for CoMP continuation, the following six messages (1) to (6) are disclosed. (1) Indicates whether CoMP is to continue or not. (2) Indicates whether or not to re-establish RLC. (3) Indicates whether to reset the MAC. (4) Indicate whether or not to re-establish the PDCP. (5) A combination of (1) to (4) above. (6) "RRC Connection Reconfiguration" during CoMP execution or during CoMP set configuration is statically determined to indicate the above (1) to (5). This makes it unnecessary to create new messages compared to the above (1) to (5), and makes it possible to avoid the mobile communication system becoming complicated.

[0759] As specific examples of a method for notifying a message indicating a serving cell change for CoMP continuation, the following three methods (1) to (3) are disclosed. (1) Add a new RRC Connection Reconfiguration indicator or information element. (2) Add a new indicator or information element to Mobility Control Information. (3) Create a new message.

[0760] In addition to step ST10412, in steps ST10413 and ST10414, the RRC of the source cell issues a PDCP processing stop and forward request (PDCP stop and forward request) and an RLC processing stop and forward request (RLC stop and forward request) to the target PDCP and RLC to stop processing unprocessed data units and stop transmission to the downlink MAC and RLC, and also issues an instruction to transmit "untransmitted data units and related parameters to the higher layer for uplink and to the lower layer for downlink" to the target cell. By newly establishing the RLC processing stop and forward request (RLC stop and forward request) in step ST10414, it becomes possible to forward the data units and related parameters of the layer 2 (RLC) from the source cell to the target cell. In addition, data forwarding of RLC data becomes possible.

[0761] The PDCP and RLC of the source cell that has received this instruction stop the above-mentioned processing and transfer in steps ST10417 to ST10422, and also continue to transfer to the target cell in steps ST10423 and ST10425 data units received in each layer after this instruction. The method of stopping this transfer may be determined by managing a timer for each layer, or may be synchronized with expiration of a MAC timer, which will be described later. In addition, when a notification of HO completion of the UE is given in step ST10457, which will be described later, it is also possible to determine the stop based on that instruction.

[0762] In this transfer, the data unit level, PDU or SDU, and the packet to be transferred are transmitted to the target cell so that the order in which they would have been processed if there was no HO can be known. For example, the processing order and the transmission order can be made to match, or information on the processing order can be added.

[0763] Also, for retransmission packets of the RLC shown in Reference 8, information indicating this is the case is added to the PDU, and the packets are transmitted to the target cell in the order of processing, for example, in the order of the RLC or SN numbers.

[0764] In addition, in the transmission process in each layer, a data unit for which the transmission process has not been completed in the lower layer (RLC for PDCP, MAC for RLC) may be transmitted together with the data unit. In this case, when the completion of the data unit transmission process in the corresponding lower layer is confirmed in the target cell, the data unit is not transmitted but is discarded.

[0765] Furthermore, the RRC of the source cell notifies the MAC that HO has been started in Step ST10415. Specifically, the RRC of the source cell notifies the MAC of the start of HO (HO ind).

[0766] The MAC of the source cell that has received the notification of the start of HO continues the process for the downlink until the currently held data unit transfer is completed. A timer may be set to determine whether to stop the process and to specify the maximum processing completion time. In this case, the process is stopped when the process is completed or the timer expires.

[0767] At this time, it is necessary to take into consideration the HARQ process (see 3GPP TS36.321 V10.4.0 (hereinafter referred to as "Reference 9")). Since the HARQ process is a stop-and-wait method with N processes, it is necessary to set the timer value taking into consideration this retransmission.

[0768] For the uplink, the reception process of the data unit from the UE is continued. To determine whether to stop the process, a timer different from the timer is provided, and the process is stopped after waiting for the completion period of the MAC process on the UE side. As with the downlink, the time until the timer expires must take into account the HARQ process. To simplify the implementation, the same timer may be used for the uplink and downlink. In addition, when the UE is notified of the completion of HO, which will be described later, the instruction can be used as the decision to stop.

[0769] The UE that has received the RRC connection reconfiguration message in Step ST10412 also stops the UL RLC and PDCP processing in the UL RLC / PDCP stop processing in Step ST10416, similar to the cell.

[0770] As for MAC, like the cell, the UE continues the process until the transfer of the currently held data unit is completed for the uplink. To determine whether to stop the process, a timer is provided, and in Step ST10424, the UE determines whether the MAC process is completed or the process timer has expired.

[0771] For downlink, the reception process of the data unit from the cell is continued. To determine whether to stop the process, a timer different from the timer is provided, and the process is stopped after waiting for the completion period of the MAC process on the cell side. As with the uplink, the time until the timer expires must take into account the HARQ process. As in this embodiment, the same timer may be used for uplink and downlink to simplify the implementation.

[0772] When the MAC process is completed or the process timer expires in Step ST10424, the UE transmits an RRC connection reconfiguration complete message corresponding to the RRC connection reconfiguration to the target cell in Step ST10428. If necessary, the UE performs a synchronization process in Step ST10426 and a TA notification process in Step ST10427.

[0773] After that, the UE performs communication according to the MAC scheduling of the target cell with the target cell as the serving cell. Whether or not the message of the serving cell change procedure such as step ST10427 becomes CoMP communication depends on whether or not the process of step ST10429 described later is executed and the completion status of the process of step ST10442. If the process of step ST10429 is not executed and the process of step ST10442 is completed, CoMP communication is possible.

[0774] The RRC of the target cell that has received the RRC connection Reconfiguration Complete message in Step ST10428 notifies the source cell of the completion of the serving cell change of the UE (UE HO Complete Ind) in Step ST10457 of Step ST10429. In addition, the RRC of the target cell notifies non-serving cells of the completion of the serving cell change of the UE (UE HO Complete Ind) in Step ST10430.

[0775] The source cell that recognizes the completion of the serving cell change in the notification of completion of the serving cell change of the UE in Step ST10457 completes the MAC, RLC, and PDCP processes of the target UE in Step STST10433. After completing the processes, the source cell notifies the target cell of the completion of the source cell process (Source cell process complete) in Step ST10458.

[0776] The non-serving cell that recognizes the completion of the serving cell change in the notification of completion of the serving cell change of the UE in Step ST10430 completes the MAC processing of the target UE in Steps ST10431, ST10432, and ST10435. After completing the processing, the non-serving cell notifies the target cell of source cell process complete in Step ST10434.

[0777] The series of processes in Step ST10429 is a procedure aimed at strictly eliminating discrepancies in the completion of processes between the UE and each cell, and can be applied to the process completion procedure in the source cell when changing the serving cell during CoMP execution. The process in Step ST10429 may not be performed if the purpose is to simplify the process procedure and speed up the change of the serving cell.

[0778] In step ST10442, the target cell that has transmitted an HO response in step ST10411 performs the processes of steps ST10436 and ST10437. After that, in steps ST10438 and ST10440, the target cell sets up data unit links between its own MAC and the MAC of the source cell and between its own MAC and the MAC of the non-serving cell, and in steps ST10439 and ST10441, sets up a scheduling information link.

[0779] A series of processes in step ST10442 may be executed at any timing between the transmission of an HO response in step ST10411 and the transmission of a data request in step ST10449. If the data unit link between the MACs of the source cell, the scheduling information link, and the target cell in steps ST10401 to ST10404 cannot be opened simultaneously, the links may be opened from the completion of HO, as shown in Figs.

[0780] The RRC of the target cell that has received the RRC connection reconfiguration complete notification in Step ST10428 notifies its own MAC, RLC and PDCP of the completion of the serving cell change, that is, UE HO complete indication, in Steps ST10443, ST10444 and ST10445. After that, the processes of Steps ST10446 to ST10454 are performed.

[0781] The MAC of the target cell that has received the HO completion notification of the UE in step ST10443 checks whether the target MAC transmission link is open, and if it is open, performs processing according to the request of the UE for the uplink, and for the downlink, requests data from the RLC and performs MAC processing of the data transmitted from the RLC. Communication with the cell in which the MAC transmission link is open is also started. If the target MAC transmission link is not open, the MAC of the target cell opens the target MAC transmission link and then performs the above processing.

[0782] The RLC of the target cell that has received the HO completion notification from the UE in step ST10444 first processes the transferred data units in the transmission order using the parameters transmitted along with them, and then sequentially processes the uplink RLC PDUs transmitted from the MAC.

[0783] In addition, for the downlink, when data transmission is requested by a data transmission request (DATA request) in step ST10449, the RLC of the target cell processes the transferred retransmission data units in order and transmits the RLC PDU to the MAC, and then processes the transferred initial transmission data units and transmits the RLC PDU to the MAC.

[0784] After completing the processing of the transferred data unit, the RLC requests the PDCP to transmit data in step ST10453, and then processes the data received from the PDCP.

[0785] The PDCP of the target cell that has received the HO completion notification of the UE in Step ST10445 performs an S1 interface path switch process and sets a switch in the target cell in Step ST10446. For uplink, the PDCP of the target cell first processes the transferred data units in the order of transmission using the parameters transmitted along with them, and then sequentially processes the uplink PDCP PDUs transmitted from the RLC.

[0786] Furthermore, in downlink, when data transmission is requested by the data request in Step ST10453, the PDCP of the target cell processes the transferred data unit and transmits the PDCP PDU to the RLC.

[0787] In this embodiment, data units in each layer are transmitted between cells with the processing order assumed by the source cell clarified. Then, in the target cell, data units are processed in the processing order, and then data unit processing from the upper and lower layers is performed. In addition, in the downlink, data transmission is started according ...

Claims

1. A mobile communication system in which a plurality of base stations cooperate to perform wireless communication with a mobile terminal, transmitting measurement target information indicating which of the signals transmitted from the plurality of base stations the mobile terminal should measure from the base station to the mobile terminal; Transmitting measurement result information, which is a result of performing measurement on the measurement target signal indicated by the measurement target information, from the mobile terminal to the base station; A mobile communication system comprising: when performing a handover, the base station transmits to the mobile terminal a signal notifying that the measurement target signal is to be removed from the measurement target.

2. 2. The mobile communication system according to claim 1, wherein the measurement target signal is a reference signal for acquiring a state of a transmission path by measurement by the mobile terminal.

3. 2. The mobile communication system according to claim 1, wherein the measurement target information is transmitted to the mobile terminal using a signal provided for individual communication.

4. The mobile communication system according to claim 1, wherein the measurement target information is transmitted using an RRC (Radio Resource Control) signal.

5. 2. The mobile communication system according to claim 1, wherein the measurement result information is periodically transmitted from the mobile terminal to one of the plurality of base stations.

6. A base station that performs wireless communication between a mobile terminal and another base station in cooperation with the other base stations, Transmitting measurement target information to the mobile terminal, the measurement target information indicating which of the signals transmitted from the base station and the other base station the mobile terminal should measure; receiving, from the mobile terminal, measurement result information which is a result of performing measurement on the measurement target signal indicated by the measurement target information; A base station characterized in that, when performing a handover, a signal notifying the mobile terminal that the measurement target signal is to be removed from the measurement target is transmitted to the mobile terminal.

7. A mobile terminal that performs wireless communication with a plurality of base stations that operate in coordination, receiving measurement target information indicating which of the signals transmitted from the plurality of base stations the mobile terminal should measure from the base station; Transmitting measurement result information, which is a result of performing measurement on the measurement target signal indicated by the measurement target information, to the base station; When performing a handover, the mobile terminal receives from the base station a signal notifying that the signal to be measured is to be removed from the measurement targets.

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