Mobile communication system, first source base station, first target base station, and mobile terminal

Abstract

To enable normal transfer of a cell during communication without imposing a load on a network.SOLUTION: In a mobile communication system, a first base station and a second base station communicate with a mobile terminal in parallel, and the first base station will be changed from a first source base station to a first target base station. In a state in which the first source base station and the second base station communicate with the mobile terminal in parallel, the first source base station notifies the first target base station of a handover request. The first target base station notifies the first source base station of a handover response. The first source base station notifies the mobile terminal that the first source base station communicating with the mobile terminal will be changed to the first target base station. The system transitions to a state in which the first target base station and the second base station communicate with the mobile terminal in parallel.SELECTED DRAWING: Figure 47

Description

Technical Field

[0001] The present invention relates to a mobile communication system and the like.

Background Art

[0002] Among communication systems called the third generation, the W-CDMA (Wideband Code division Multiple Access) system has been in commercial service in Japan since 2001. In addition, by adding a channel for packet transmission (High Speed-Downlink Shared Channel: HS-DSCH) to the downlink (individual data channel, individual control channel), the HSDPA (High Speed Downlink Packet Access) service that realizes further speeding up of data transmission using the downlink has been started. Furthermore, in order to speed up data transmission in the uplink direction, the HSUPA (High Speed Uplink Packet Access) system has also been put into service. W-CDMA is a communication system defined by 3GPP (3rd Generation Partnership Project), a standardization organization for mobile communication systems, and the standard document of Release 10 has been compiled.

[0003] In addition, in 3GPP, as a communication system different from W-CDMA, the radio section is called Long Term Evolution (LTE), and a new communication system called System Architecture Evolution (SAE) is being studied for the overall system configuration including the core network and the radio access network (hereinafter, collectively referred to as the network). This communication system is also called a 3.9G (3.9 Generation) system.

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

[0005] In LTE, since a communication system is configured using a new core network different from GPRS (General Packet Radio Service), which is the core network of W-CDMA, the radio access network of 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). Also, in the radio access network, the base station that communicates with the mobile terminal (User Equipment: UE), which is a communication terminal device, is called eNB (E-UTRAN NodeB). Moreover, the function of the radio network controller, which exchanges control data and user data with multiple base stations, is assumed by the EPC. The EPC is also called aGW (Access Gateway). Further, the system composed of the EPC and the E-UTRAN is called EPS (Evolved Packet System).

[0007] In the LTE communication system, unicast services and E-MBMS services (Evolved Multimedia Broadcast Multicast Service) are provided. The E-MBMS service is a broadcast-type multimedia service. The E-MBMS service may also be simply called MBMS. In the E-MBMS service, large-capacity broadcast contents such as news, weather forecasts, and mobile broadcasts are transmitted to multiple mobile terminals. This is also referred to as a point-to-multipoint service.

[0008] Decisions regarding the overall architecture in the LTE system in 3GPP 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 a communication system using the LTE method. In FIG. 1, if the control protocol for the mobile terminal 101, for example, RRC (Radio Resource Control), and the user plane, for example, PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), PHY (Physical layer), terminate at the base station 102, then the E-UTRAN is composed of one or more base stations 102.

[0009] The base station 102 schedules and transmits a paging signal (also referred to as a paging message) notified from the Mobility Management Entity (MME) 103. The base stations 102 are connected to each other via the X2 interface. The base station 102 is also connected to the EPC (Evolved Packet Core) via the S1 interface. More specifically, the base station 102 is connected to the MME (Mobility Management Entity) 103 via the S1_MME interface and to the S-GW (Serving Gateway) 104 via the S1_U interface.

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

[0011] The S-GW 104 transmits and receives user data with one or more base stations 102. The S-GW 104 serves as a local Mobility Anchor Point during handover between base stations. There is also a P-GW (PDN Gateway) in the EPC. The P-GW performs packet filtering for each user and assigns UE-ID addresses, etc.

[0012] The control protocol RRC between the mobile terminal 101 and the base station 102 performs broadcast, paging, RRC connection management, etc. As the states of the base station and the mobile terminal in RRC, there are 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 with the network. Also in RRC_CONNECTED, handover (HO), measurement of neighbouring cells, etc. are performed.

[0013] Regarding the decisions on the frame structure in the LTE system in 3GPP described in Non-Patent Document 1 (Chapter 5), it will be described with reference to FIG. 2. FIG. 2 is an explanatory diagram showing the configuration of a radio frame used in a communication system of the LTE 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 2 slots of equal size. The first and sixth subframes of each radio frame contain downlink synchronization signals (SS). The synchronization signal includes a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

[0014] Multiplexing of a channel for MBSFN (Multimedia Broadcast multicast service Single Frequency Network) and a channel other than MBSFN is performed in units of subframes. MBSFN transmission is a simulcast transmission technique realized by transmitting the same waveform from a plurality of cells simultaneously. MBSFN transmissions from a plurality of cells in the MBSFN area are recognized as one transmission by the mobile terminal. MBSFN is a network that supports such MBSFN transmissions. Hereinafter, the subframe for MBSFN transmission is referred to as an MBSFN subframe.

[0015] Non-Patent Document 2 describes a signaling example at the time of allocation of an MBSFN subframe. 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). The 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 satisfying the following formula (1) is a radio frame including an MBSFN subframe. SFN mod radioFrameAllocationPeriod = radioFrameAllocationOffset …(1) The allocation of the MBSFN subframe is performed with 6 bits. The leftmost bit defines the MBSFN allocation of the second (#1) subframe. The second bit from the left is for the third (#2) subframe, the third bit from the left is for the fourth (#3) subframe, the fourth bit from the left is for the seventh (#6) subframe, the fifth bit from the left is for the eighth (#7) subframe, and the sixth bit from the left is for the ninth (#8) subframe. When the bit indicates "1", it indicates that the corresponding subframe is allocated for MBSFN.

[0016] Decisions regarding the channel configuration in the LTE system in 3GPP 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 even in a CSG cell (Closed Subscriber Group cell). The physical channel will be described with reference to FIG. 4. FIG. 4 is an explanatory diagram for explaining the physical channel used in the LTE communication system.

[0017] In FIG. 4, the Physical Broadcast channel (PBCH) 401 is a downlink channel from the base station 102 to the mobile terminal 101. The BCH transport block is mapped to four subframes during a 40 ms interval. There is no explicit signaling of the 40 ms timing.

[0018] The Physical Control Format Indicator Channel (PCFICH) 402 is a downlink channel from the base station 102 to the mobile terminal 101. The PCFICH notifies the mobile terminal 101 from the base station 102 about the number of OFDM symbols used for the PDCCHs. The PCFICH is transmitted for each subframe.

[0019] The Physical Downlink Control Channel (PDCCH) 403 is a downlink channel from the base station 102 to the mobile terminal 101. The PDCCH notifies resource allocation of the Downlink Shared Channel (DL-SCH), which is one of the transport channels shown in FIG. 5 below, and the Paging Channel (PCH), which is one of the transport channels shown in FIG. 5, and HARQ (Hybrid Automatic Repeat reQuest) information regarding the DL-SCH. The PDCCH carries an Uplink Scheduling Grant. The PDCCH carries an Ack (Acknowledgement) / Nack (Negative Acknowledgement), which is a response signal for uplink transmission. The PDCCH is also called an L1 / L2 control signal.

[0020] The Physical Downlink Shared Channel (PDSCH) 404 is a channel for downlink transmission from the base station 102 to the mobile terminal 101. The DL-SCH, which is a transport channel, and the PCH, which is also a transport channel, are mapped to the PDSCH.

[0021] The Physical Multicast Channel (PMCH) 405 is a channel for downlink transmission from the base station 102 to the mobile terminal 101. The Multicast Channel (MCH), which is a transport channel, is mapped to the PMCH.

[0022] 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 the Ack / Nack, which is a response signal for downlink transmission. The PUCCH also carries the CQI (Channel Quality Indicator) report. The CQI is quality information indicating the quality of the received data or the communication channel quality. Additionally, the PUCCH carries the Scheduling Request (SR).

[0023] 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 Figure 5, is mapped to the PUSCH.

[0024] The Physical Hybrid ARQ Indicator Channel (PHICH) 408 is a downlink channel from the base station 102 to the mobile terminal 101. The PHICH carries the Ack / Nack, which is a response signal for the uplink transmission. The Physical Random Access Channel (PRACH) 409 is an uplink channel from the mobile terminal 101 to the base station 102. The PRACH carries a random access preamble.

[0025] The downlink reference signal (Reference Signal: RS) is a symbol known in the LTE communication system. The following five types of downlink reference signals are defined: Cell-specific Reference Signals (CRS), MBSFN reference signals, the Demodulation Reference Signal (DM-RS) which is a UE-specific reference signal, Positioning Reference Signals (PRS), and Channel-State Information Reference Signals (CSI-RS). As a measurement of the physical layer of the mobile terminal, there is a measurement of the Reference Signal Received Power (RSRP).

[0026] 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 for 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.

[0027] Among the downlink transport channels shown in Fig. 5(A), the broadcast channel (BCH) is notified throughout the coverage area of its base station (cell). The BCH is mapped to the physical broadcast channel (PBCH).

[0028] Retransmission control by HARQ (Hybrid ARQ) is applied to the downlink shared channel (DL-SCH). The DL-SCH can be notified throughout the coverage area of the base station (cell). The DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called persistent scheduling. The DL-SCH supports discontinuous reception (DRX) of the mobile terminal for power saving of the mobile terminal. The DL-SCH is mapped to the physical downlink shared channel (PDSCH).

[0029] The paging channel (PCH) supports DRX of the mobile terminal to enable low power consumption of the mobile terminal. The PCH requires notification throughout the coverage area of the base station (cell). The PCH is mapped to a physical resource such as the physical downlink shared channel (PDSCH) that can be dynamically used for traffic.

[0030] The multicast channel (MCH) is used for notification throughout the coverage area of the base station (cell). The MCH supports SFN synthesis of MBMS services (MTCH and MCCH) in multi-cell transmission. The MCH supports semi-static resource allocation. The MCH is mapped to the PMCH.

[0031] Among the uplink transport channels shown in FIG. 5(B), for the uplink shared channel (UL-SCH), retransmission control by HARQ (Hybrid ARQ) is applied. The UL-SCH supports dynamic or semi-static resource allocation. The UL-SCH is mapped to the physical uplink shared channel (PUSCH).

[0032] The random access channel (RACH) shown in FIG. 5(B) is limited to control information. The RACH has a risk of collision. The RACH is mapped to the physical random access channel (PRACH).

[0033] An explanation of HARQ is given. HARQ is a technology that improves the communication quality of the transmission path by combining automatic repeat request (ARQ) and forward error correction. HARQ has the advantage that error correction functions effectively by retransmission even for a transmission path where the communication quality changes. In particular, it is also possible to obtain further quality improvement by combining the reception result of the first transmission and the reception result of the retransmission at the time of retransmission.

[0034] An example of the retransmission method is explained. On the receiving side, if the received data cannot be decoded correctly, in other words, if a cyclic redundancy check (CRC) error occurs (CRC = NG), the receiving side sends a "Nack" to the transmitting side. The transmitting side that receives the "Nack" retransmits the data. On the receiving side, if the received data can be decoded correctly, in other words, if no CRC error occurs (CRC = OK), the receiving side sends an "Ack" to the transmitting side. The transmitting side that receives the "Ack" transmits the next data.

[0035] As an example of the HARQ method, there is Chase Combining. Chase Combining is a method in which the same data is transmitted in the initial transmission and the 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 there are errors in the initial transmission data, it contains partially accurate data, and by combining the accurate part of the initial transmission data and the retransmission data, data can be transmitted with higher accuracy. Also, as another example of the HARQ method, there is IR (Incremental Redundancy). IR is a method that increases the redundancy. In the retransmission, parity bits are transmitted to increase the redundancy in combination with the initial transmission and improve the quality by the error correction function.

[0036] The logical channel (Logical channel) described in Non-Patent Document 1 (Chapter 6) will be described with reference to FIG. 6. FIG. 6 is an explanatory diagram for explaining the logical channel used in the LTE communication system. FIG. 6(A) shows the mapping between the downlink logical channel and the downlink transport channel. FIG. 6(B) shows the mapping between the uplink logical channel and the uplink transport channel.

[0037] 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).

[0038] The Paging Control Channel (PCCH) is a downlink channel for transmitting changes in paging information and system information. The PCCH is used when the network does not know the cell location of the mobile terminal. The PCCH, which is a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

[0039] The Common Control Channel (CCCH) is a channel for transmission control information between the mobile terminal and the 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.

[0040] The Multicast Control Channel (MCCH) is a downlink channel for one-to-many transmission. The MCCH is used for transmitting MBMS control information for one or several MTCHs from the network to the mobile terminal. The MCCH is used only for mobile terminals receiving MBMS. The MCCH is mapped to the Multicast Channel (MCH), which is a transport channel.

[0041] The Dedicated Control Channel (DCCH) is a channel for transmitting dedicated control information between the mobile terminal and the network on a one-to-one basis. The DCCH is used when the mobile terminal has an RRC connection. In the uplink, the DCCH is mapped to the Uplink Shared Channel (UL-SCH), and in the downlink, it is mapped to the Downlink Shared Channel (DL-SCH).

[0042] The Dedicated Traffic Channel (DTCH) is a one-to-one communication channel to an individual mobile terminal for the transmission of user information. The DTCH exists both in the uplink and the downlink. In the uplink, the DTCH is mapped to the Uplink Shared Channel (UL-SCH), and in the downlink, it is mapped to the Downlink Shared Channel (DL-SCH).

[0043] The Multicast Traffic Channel (MTCH) is a downlink channel for the transmission of traffic data from the network to the mobile terminal. The MTCH is a channel used only by mobile terminals during MBMS reception. The MTCH is mapped to the Multicast Channel (MCH).

[0044] CGI stands for Cell Global Identification. ECGI stands for E-UTRAN Cell Global Identification. In LTE, LTE-A (Long Term Evolution Advanced) to be described later, and UMTS (Universal Mobile Telecommunication System), a Closed Subscriber Group (CSG) cell is introduced. The CSG cell will be described below (see Section 3.1 of Non-Patent Document 3).

[0045] A Closed Subscriber Group (CSG) cell is a cell in which the operator has identified the available subscribers (hereinafter sometimes referred to as a "cell for specific subscribers"). The identified subscribers are permitted to access one or more cells of a Public Land Mobile Network (PLMN). One or more cells to which the identified subscribers are permitted access are called "CSG cell(s)". However, there is an access restriction to the PLMN.

[0046] A CSG cell is part of a PLMN that announces a unique CSG identity (CSG ID; CSG-ID) and announces "TRUE" in the CSG Indication. Members of a pre-registered and authorized subscriber group access the CSG cell using the CSG-ID, which is access permission information.

[0047] The CSG-ID is announced by the CSG cell or cell. There are multiple CSG-IDs in an LTE communication system. And the CSG-ID is used by a mobile terminal (UE) to facilitate access by CSG-related members.

[0048] The location tracking of a mobile terminal is performed in units of an area consisting of one or more cells. Location tracking is performed to track the location of the mobile terminal even in the standby state and to enable calling the mobile terminal, in other words, to enable the mobile terminal to be incoming-called. The area for this mobile terminal location tracking is called a tracking area.

[0049] A CSG White List is a list that may be stored in a USIM (Universal Subscriber Identity Module) and records all CSG IDs of the CSG cells to which a subscriber belongs. The CSG White List may also be simply called a white list or an Allowed CSG List. The access of a mobile terminal through a CSG cell is controlled by the MME performing access control (see Section 4.3.1.2 of Non-Patent Document 4). Specific examples of mobile terminal access include attach, combined attach, detach, service request, and Tracking Area Update procedure (see Section 4.3.1.2 of Non-Patent Document 4).

[0050] The service types of a mobile terminal in the standby state will be described below (see Section 4.3 of Non-Patent Document 3). The service types of a mobile terminal in the standby state include limited service (also referred to as restricted service), normal service (Normal service), and operator service. Limited service refers to emergency calls, ETWS (Earthquake and Tsunami Warning System), and CMAS (Commercial Mobile Alert System) on an acceptable cell, which will be described later. Normal service (also referred to as regular service) refers to public services on an appropriate cell, which will be described later. Operator service refers to services only for the operator on a reserved cell, which will be described later.

[0051] The "suitable cell" will be described below. A "suitable cell" is a cell on which a UE may camp on to receive normal service. Such a cell shall satisfy the following conditions (1) and (2).

[0052] (1) The cell is part of the selected PLMN or the registered PLMN, or part of the PLMN in the "Equivalent PLMN list".

[0053] (2) Based on the latest information provided by the NAS (Non-Access Stratum), it shall further satisfy the following conditions (a) to (d). (a) The cell is not a barred cell. (b) The cell is part of a tracking area that is not part of the list of "forbidden LAs for roaming". In that case, the cell shall satisfy the above (1). (c) The cell satisfies the cell selection evaluation criteria. (d) For a cell that is identified by the System Information (SI) as a CSG cell, the CSG-ID shall be part of the UE's "CSG WhiteList", i.e., it shall be included in the UE's CSG WhiteList.

[0054] The "Acceptable cell" is described as follows. An "Acceptable cell" is a cell on which the UE may camp in order to receive restricted services. Such a cell shall meet all the requirements of (1) and (2) below. (1) The cell shall not be a barred cell (also referred to as a "Barred cell"). (2) The cell shall meet the cell selection evaluation criteria.

[0055] A "Barred cell" is indicated in the system information. A "Reserved cell" is indicated in the system information.

[0056] "Camping on a cell" means that the UE has completed the cell selection or reselection process and has selected a cell on which the UE monitors the system information and paging information. The cell on which the UE camps may be referred to as the "Serving cell".

[0057] In 3GPP, base stations called Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB) are being considered. The HNB in UTRAN and the HeNB in E-UTRAN are base stations for access services for, for example, homes, corporations, and commercial use. Non-Patent Document 5 discloses three different modes of access to HeNB and HNB. Specifically, an Open access mode, a Closed access mode, and a Hybrid access mode are disclosed.

[0058] Each mode has the following characteristics. In the Open access mode, HeNB and HNB are operated as normal cells of a normal operator. In the Closed access mode, HeNB and HNB are operated as CSG cells. This CSG cell is a CSG cell that can be accessed only by CSG members. In the Hybrid access mode, HeNB and HNB are operated as CSG cells that also permit non-CSG members to access simultaneously. A cell in the Hybrid access mode (also referred to as a Hybrid cell) is, in other words, a cell that supports both the Open access mode and the Closed access mode.

[0059] In 3GPP, among all Physical Cell Identities (PCI), there is a PCI range reserved by the network for use by CSG cells (see Section 10.5.1.1 of Non-Patent Document 1). Dividing the PCI range is sometimes referred to as PCI split. Information regarding PCI split (also referred to as PCI split information) is notified from a base station to mobile terminals under its umbrella in system information. The umbrella of a base station means that the base station is a serving cell.

[0060] Non-Patent Document 6 discloses the basic operation of a mobile terminal using PCI split. A mobile terminal without PCI split information needs to perform cell search using all of the PCI, for example, all 504 codes. In contrast, a mobile terminal with PCI split information can perform cell search using the PCI split information.

[0061] Also, in 3GPP, as Release 10, the standardization of Long Term Evolution Advanced (LTE-A) is in progress (see Non-Patent Document 7 and Non-Patent Document 8).

[0062] In the LTE-A system, in order to obtain high communication speed, high throughput at the cell edge, new coverage areas, etc., it is being considered to support Relay and Relay Node (RN). The relay node, which is a relay device, is wirelessly connected to the radio access network via a cell called a donor cell (hereinafter sometimes referred to as "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 (frequency band) as the link from the network to the UE. In this case, the UE of 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.

[0063] As a multiplexing method for a backhaul link in FDD (Frequency Division Duplex), transmission from the DeNB to the RN is performed in the downlink (DL) frequency band, and transmission from the RN to the DeNB is performed in the uplink (UL) frequency band. As a method for dividing resources in a relay, the link from the DeNB to the RN and the link from the RN to the UE are time-division multiplexed in one frequency band, and the link from the RN to the DeNB and the link from the UE to the RN are also time-division multiplexed in one frequency band. By doing so, in the relay, it is possible to prevent the transmission of the relay from interfering with the reception of its own relay.

[0064] In 3GPP, not only normal eNBs (macro cells) but also so-called local nodes such as pico eNBs (pico cells), HeNBs (HNBs, CSG cells), nodes for hot zone cells, relay nodes, remote radio heads (RRHs), and repeaters are being considered. A network consisting of various types of cells as described above may also be referred to as a heterogeneous network.

[0065] In LTE, the frequency bands available for communication (hereinafter sometimes referred to as "operating bands") are predetermined. Non-Patent Document 9 describes the frequency bands.

[0066] In the LTE-A system, carrier aggregation (CA), which aggregates (also referred to as aggregating) two or more component carriers (CCs) in order to support a wider frequency bandwidth (transmission bandwidths) up to 100 MHz, is being considered.

[0067] Release 8 or 9 UEs that support LTE can only transmit and receive on one CC corresponding to one serving cell. In contrast, Release 10 UEs are considered to have the capability to simultaneously transmit and receive, or only receive, or only transmit on multiple CCs corresponding to multiple serving cells.

[0068] Each CC uses the Release 8 or 9 configuration, and CA supports contiguous CCs, non-contiguous CCs, and CCs with different frequency bandwidths. It is impossible for a UE to configure more UL CCs than the number of DL CCs. CCs configured from the same eNB do not need to provide the same coverage. CCs are compatible with Release 8 or 9.

[0069] In CA, there is one independent HARQ entity for each serving cell in both the uplink and downlink. Transport blocks are generated for each TTI for each serving cell. Each transport block and HARQ retransmission are mapped to a single serving cell.

[0070] When CA is configured, the UE has only one RRC connection with the NW. In the RRC connection, one serving cell provides NAS mobility information and security inputs. This cell is called the Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC). In the uplink, the carrier corresponding to the PCell is the Uplink Primary Component Carrier (UL PCC).

[0071] According to the capabilities of the UE, a Secondary Cell (SCell) is configured to form a set with the PCell and the serving cell. In the downlink, the carrier corresponding to the SCell is the Downlink Secondary Component Carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is the Uplink Secondary Component Carrier (UL SCC).

[0072] For one UE, a set is configured consisting of one PCell and a serving cell composed of one or more SCells.

[0073] In 3GPP, as a more advanced new radio communication method, the aforementioned LTE Advanced (LTE-A) is being studied (see Non-Patent Document 7 and Non-Patent Document 8). LTE-A is based on the LTE radio communication method and is configured by adding several new technologies thereto. Examples of the new technologies include a technology for supporting a wider bandwidth (Wider bandwidth extension) and a Coordinated Multiple Point transmission and reception (CoMP) technology. Information about CoMP being studied for LTE-A in 3GPP is described in Non-Patent Document 10.

[0074] CoMP is a technology that aims to expand high-data-rate coverage, improve throughput at the cell edge, and increase throughput in a communication system by performing coordinated transmission or reception among multiple geographically separated points. CoMP includes downlink CoMP (DL CoMP) and uplink CoMP (UL CoMP).

[0075] In DL CoMP, the PDSCH for one mobile terminal (UE) is transmitted in a coordinated manner among multiple points (multi-points). The PDSCH for one UE may be transmitted from one point of the multi-points or from multiple points of the multi-points. In DL CoMP, a serving cell is a single cell that transmits resource allocation by means of PDCCH.

[0076] As methods of DL CoMP, joint processing (JP) and coordinated scheduling (CS) or coordinated beamforming (CB) (hereinafter sometimes referred to as "CS / CB") are being studied.

[0077] In JP, data is available at each point in a CoMP cooperating set. JP includes joint transmission (JT) and dynamic point selection (DPS). DPS includes dynamic cell selection (DCS). In JT, at a certain point in time, the PDSCH is transmitted from a plurality of points, specifically, from a part or all of a CoMP cooperating set. In DPS, at a certain point in time, the PDSCH is transmitted from one point within a CoMP cooperating set.

[0078] CS / CB is only available for data transmission from a serving cell. In CS / CB, user scheduling or beamforming determination is made in combination with adjustment between cells corresponding to a CoMP cooperating set.

[0079] Units and cells that transmit and receive at multiple points include base stations (NB, eNB, HNB, HeNB), RRU (Remote Radio Unit), RRE (Remote Radio Equipment), RRH (Remote Radio Head), relay nodes (RN), etc. Units and cells that perform multi-point coordinated transmission may be referred to as multi-point units and multi-point cells, respectively.

[0080] In 3GPP, the development of the Release 12 specifications is underway. Among them, in order to cope with future huge traffic, studies have been conducted using small eNBs (cells). For example, technologies such as increasing the frequency utilization efficiency and the communication capacity by installing a large number of small eNBs (cells).

Prior Art Documents

Non-Patent Documents

[0081]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Non-Patent Document 8

Non-Patent Document 9

Non - Patent Document 10

Non - Patent Document 11

Non - Patent Document 12

Non - Patent Document 13

Non - Patent Document 14

Non - Patent Document 15

Summary of the Invention

Problems to be Solved by the Invention

[0082] Even in a small eNB (cell) (base station), for handover, it is necessary to perform the same procedure as the conventional cell transition. However, in this procedure, control of both the U - plane / C - plane is required, and there are many procedures. In an area where a plurality of small eNBs (cells) are concentrated, when a mobile station moves at a certain speed, if the handover procedure takes a long time, the mobile station may move to the next cell area before the handover procedure is completed, resulting in problems such as inappropriate handover. Also, in such a case, the frequency of handover increases, and the associated processing becomes very large, imposing a load on the network.

[0083] An object of the present invention is to provide a mobile communication system or the like that can perform cell transition of a normally communicating cell without imposing a load on the network and even when a high communication capacity is obtained, for example, by installing small eNBs (cells).

Means for Solving the Problems

[0084] The mobile communication system of the present invention is a mobile communication system in which a first base station and a second base station communicate with a mobile terminal in parallel, and the first base station is changed from a first source base station to a first target base station. In a state where the first source base station and the second base station are communicating with the mobile terminal in parallel, a handover request is notified from the first source base station to the first target base station, a handover response is notified from the first target base station to the first source base station, and changing the first source base station communicating with the mobile terminal to the first target base station is notified from the first source base station to the mobile terminal, and it is characterized in that it shifts to a state where the first target base station and the second base station communicate with the mobile terminal in parallel. The first source base station of the present invention is the first source base station in a mobile communication system in which a first base station and a second base station communicate with a mobile terminal in parallel, and the first base station is changed from a first source base station to a first target base station. In a state where it is communicating with the mobile terminal in parallel with the second base station, a handover request is notified to the first target base station, a handover response is notified from the first target base station, and changing the first base station communicating with the mobile terminal to the first target base station is notified to the mobile terminal, and it is characterized in that it shifts to a state where the first target base station and the second base station communicate with the mobile terminal in parallel. The first target base station of the present invention is the first target base station in a mobile communication system in which a first base station and a second base station communicate with a mobile terminal in parallel, and the first base station is changed from a first source base station. In a state where the first source base station and the second base station are communicating with the mobile terminal in parallel, a handover request is notified from the first source base station, a handover response is notified to the first source base station, and changing the first base station communicating with the mobile terminal from the first source base station is notified from the first source base station to the mobile terminal, and it is characterized in that it shifts to a state where it communicates with the mobile terminal in parallel with the second base station. The mobile terminal of the present invention is a mobile terminal in a mobile communication system in which a first base station and a second base station communicate in parallel, and the first base station is changed from a first source base station to a first target base station. In a state where the first source base station and the second base station are communicating with the mobile terminal in parallel, a handover request is notified from the first source base station to the first target base station, and a handover response is notified from the first target base station to the first source base station. Changing the first source base station to the first target base station is notified from the first source base station, and the mobile terminal migrates to a state of communicating in parallel with the first target base station and the second base station.

Advantages of the Invention

[0085] According to the present invention, it is possible to perform the migration of a base station that is normally communicating without imposing a load on the network.

Brief Description of the Drawings

[0086]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19(A)

Figure 19(B)

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Figure 27(A)

Figure 27(B)

Figure 27(C)

Figure 28

Figure 29

Figure 30

Figure 31

Figure 32

Figure 33

Figure 34

Figure 35

Figure 36

Figure 37

Figure 38

Figure 39

Figure 40

Figure 41

Figure 42

Figure 43

Figure 44

Figure 45

Figure 46

Figure 47

Figure 48

Figure 49

Figure 50

Figure 51

Figure 52

Figure 53

Figure 54

Figure 55(A)

Figure 55(B)

Figure 55(C)

Figure 55(D)

Figure 56

Figure 57

Figure 58

Figure 59

Figure 60

Figure 61

Figure 62

Figure 63

Figure 64

Figure 65

Figure 66

MODE FOR CARRYING OUT THE INVENTION

[0087] Embodiment 1. FIG. 7 is a block diagram showing the overall configuration of an LTE communication system discussed in 3GPP. In 3GPP, the overall configuration of a system including a CSG (Closed Subscriber Group) cell (Home-eNodeB (Home-eNB; HeNB) of E-UTRAN, Home-NB (HNB) of UTRAN) and a non-CSG cell (eNodeB (eNB) of E-UTRAN, NodeB (NB) of UTRAN, BSS of GERAN) has been studied, and for E-UTRAN, a configuration as shown in FIG. 7 has been proposed (see Chapter 4.6.1 of Non-Patent Document 1).

[0088] Explanation will be given for FIG. 7. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 71, which is a communication terminal device, can communicate wirelessly with a base station device (hereinafter referred to as "base station") 72 and perform signal transmission and reception through wireless communication. The base station 72 is classified into an eNB 72-1 and a Home-eNB 72-2.

[0089] eNB72-1 is connected to an MME, or an S-GW, or an MME / S-GW unit (hereinafter sometimes referred to as the "MME unit") 73 including an MME and an S-GW through 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. eNB72-1s are connected through an X2 interface, and control information is communicated between the eNB72-1s.

[0090] Home-eNB72-2 is connected to the MME unit 73 through an S1 interface, and control information is communicated between the Home-eNB72-2 and the MME unit 73. A plurality of Home-eNB72-2s may be connected to one MME unit 73. Alternatively, the Home-eNB72-2 is connected to the MME unit 73 via a HeNBGW (Home-eNB GateWay) 74. The Home-eNB72-2 and the HeNBGW74 are connected through an S1 interface, and the HeNBGW74 and the MME unit 73 are connected through an S1 interface.

[0091] One or more Home-eNB72-2s are connected to one HeNBGW74, and information is communicated through an S1 interface. The HeNBGW74 is connected to one or more MME units 73, and information is communicated through an S1 interface.

[0092] The MME unit 73 and the HeNBGW74 are upper node devices, and control the connection between the base stations eNB72-1 and Home-eNB72-2 and the mobile terminal (UE) 71. The MME unit 73, specifically the MME and the S-GW constituting the MME unit 73, and the HeNBGW74 correspond to management means. The MME unit 73 and the HeNBGW74 are included in the EPC which is a core network.

[0093] Furthermore, 3GPP is considering the following configuration. The X2 interface between Home-eNB72-2 is supported. That is, Home-eNB72-2 are connected by the X2 interface, and control information is communicated between Home-eNB72-2. From the MME unit 73, the HeNBGW74 appears as Home-eNB72-2. From Home-eNB72-2, the HeNBGW74 appears as the MME unit 73.

[0094] In both the case where Home-eNB72-2 is connected to the MME unit 73 via the HeNBGW74 and the case where it is directly connected to the MME unit 73, the interface between Home-eNB72-2 and the MME unit 73 is the same S1 interface. The HeNBGW74 does not support mobility to / from Home-eNB72-2 that spans multiple MME units 73. Home-eNB72-2 is composed of a single cell.

[0095] The base station device is composed of a single cell, such as Home-eNB72-2 for example, but is not limited thereto, and may be composed of multiple cells. When one base station device is composed of multiple cells, each cell is configured to be able to communicate with a mobile terminal.

[0096] 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, and encoding processing 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 undergoing encoding processing. The data encoded by the encoder unit 804 is subjected to modulation processing 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 wireless transmission frequency. Thereafter, a transmission signal is transmitted from the antenna 807 to the base station 72.

[0097] Also, the reception process of the mobile terminal 71 is executed as follows. A wireless signal from the base station 72 is received by the antenna 807. The received signal is converted from the wireless reception frequency to a baseband signal by the frequency conversion unit 806, and demodulation processing is performed by the demodulation unit 808. The demodulated data is passed to the decoder unit 809, where decoding processing such as error correction is performed. Among 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 are controlled by the control unit 810. Therefore, although omitted in FIG. 8, the control unit 810 is connected to each of the units 801 to 809.

[0098] 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 (MME unit 73, 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 respectively exchange information with the protocol processing unit 903. The control data from the protocol processing unit 903, as well as the user data and control data from the EPC communication unit 901 and the other base station communication unit 902, are stored in the transmission data buffer unit 904.

[0099] The data stored in the transmission data buffer unit 904 is passed to the encoder unit 905, and encoding processes such as error correction are performed. There may be data that is directly output from the transmission data buffer unit 904 to the modulation unit 906 without undergoing encoding processing. The encoded data is subjected to modulation processing in the modulation unit 906. The modulated data is converted into a baseband signal and then output to the frequency conversion unit 907, where it is converted to a radio transmission frequency. Thereafter, a transmission signal is transmitted from the antenna 908 to one or more mobile terminals 71.

[0100] Also, 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 the antenna 908. The received signal is converted from the radio reception frequency to a baseband signal in the frequency conversion unit 907, and demodulation processing is performed in the demodulation unit 909. The demodulated data is passed to the decoder unit 910, and decoding processes such as error correction are performed. Among the decoded data, the control data is passed to the protocol processing unit 903 or the EPC communication unit 901, the other base station communication unit 902, and the 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 are controlled by the control unit 911. Therefore, although omitted in FIG. 9, the control unit 911 is connected to each of the units 901 to 910.

[0101] The base station communication unit 902 corresponds to the notification unit and the acquisition unit. The transmission data buffer unit 904, the encoder unit 905, the modulation unit 906, the frequency conversion unit 907, the antenna 908, the demodulation unit 909, and the decoder unit 910 correspond to the communication unit.

[0102] The functions of the Home-eNB 72-2 being discussed in 3GPP are shown below (see Section 4.6.2 of Non-Patent Document 1). The Home-eNB 72-2 has the same functions as the eNB 72-1. In addition, when connecting to the HeNBGW 74, the Home-eNB 72-2 has the function of discovering an appropriate serving HeNBGW 74. The Home-eNB 72-2 is uniquely connected to one HeNBGW 74. That is, in the case of connection to the HeNBGW 74, the Home-eNB 72-2 does not use the Flex function in the S1 interface. When the Home-eNB 72-2 is connected to one HeNBGW 74, it does not connect to another HeNBGW 74 or another MME unit 73 at the same time.

[0103] The TAC (Tracking Area Code) and PLMN ID of the Home-eNB 72-2 are supported by the HeNBGW 74. When the Home-eNB 72-2 is connected to the HeNBGW 74, the selection of the MME unit 73 in "UE attachment" is performed by the HeNBGW 74 instead of the Home-eNB 72-2. The Home-eNB 72-2 may be deployed without a network plan. In this case, the Home-eNB 72-2 is moved from one geographical area to another geographical area. Therefore, in this case, the Home-eNB 72-2 needs to be connected to different HeNBGW 74s depending on the location.

[0104] FIG. 10 is a block diagram showing the configuration of the MME according to the present invention. In FIG. 10, the configuration of the MME 73a included in the MME unit 73 shown in FIG. 7 described above is shown. 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 via the S1 interface between the MME 73a and the base station 72. When 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 plain communication unit 1003 and transmitted to one or more base stations 72. When 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 plain communication unit 1003 and transmitted to the PDN GW.

[0105] 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 plain 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 plain control unit 1005.

[0106] The HeNBGW communication unit 1004 is provided when the HeNBGW 74 exists, and transmits and receives data via the interface (IF) between the MME 73a and the HeNBGW 74 according to the information type. The control data received from the HeNBGW communication unit 1004 is passed from the HeNBGW communication unit 1004 to the control plain control unit 1005. The result of the process in the control plain control unit 1005 is transmitted to the PDN GW via the PDN GW communication unit 1001. Further, the result processed by the control plain control unit 1005 is transmitted to one or more base stations 72 via the base station communication unit 1002 by the S1 interface, and is also transmitted to one or more HeNBGWs 74 via the HeNBGW communication unit 1004.

[0107] The control plane control unit 1005 includes an NAS security unit 1005-1, an SAE bearer control unit 1005-2, an idle state mobility management unit 1005-3, etc., and performs overall processing for the control plane. The NAS security unit 1005-1 performs security for NAS (Non-Access Stratum) messages. The SAE bearer control unit 1005-2 performs management of SAE (System Architecture Evolution) bearers. The idle state mobility management unit 1005-3 performs mobility management in the standby state (idle state; LTE-IDLE state, or simply referred to as idle), generation and control of paging signals in the standby state, addition, deletion, update, search of the tracking area of one or more mobile terminals 71 under its umbrella, and tracking area list management.

[0108] The MME 73a initiates the paging protocol by sending a paging message to a cell belonging to the tracking area (tracking area) in which the UE is registered. The management of the CSG of the Home-eNB 72-2 connected to the MME 73a, the management of the CSG-ID, and the white list management may be performed by the idle state mobility management unit 1005-3.

[0109] 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 with a certain CSG-ID and the CSG cell belonging to the CSG-ID. In the white list management, the relationship between the mobile terminal and the CSG-ID is managed (for example, added, deleted, updated, searched). For example, the white list may store one or more CSG-IDs registered by a certain mobile terminal. These CSG-related management may be performed in other parts of the MME73a. A series of processes of the MME73a are controlled by the control unit 1006. Therefore, although omitted in FIG. 10, the control unit 1006 is connected to each unit 1001 to 1005.

[0110] The functions of the MME73a discussed in 3GPP are shown below (see Section 4.6.2 of Non-Patent Document 1). The MME73a performs access control for one or more mobile terminals that are members of a CSG (Closed Subscriber Group). The MME73a optionally allows the execution of paging optimization.

[0111] FIG. 11 is a block diagram showing the configuration of the HeNBGW74 shown in FIG. 7, which is the HeNBGW according to the present invention. The EPC communication unit 1101 transmits and receives data via the S1 interface between the HeNBGW74 and the MME73a. The base station communication unit 1102 transmits and receives data via the S1 interface between the HeNBGW74 and the Home-eNB72-2. The location processing unit 1103 performs a process of transmitting registration information and the like among the data from the MME73a passed through the EPC communication unit 1101 to a plurality of Home-eNB72-2. The data processed by the location processing unit 1103 is passed to the base station communication unit 1102 and transmitted to one or more Home-eNB72-2 via the S1 interface.

[0112] Data that only needs to pass (transmit) without the need for processing in the location processing unit 1103 is passed from the EPC communication unit 1101 to the base station communication unit 1102 and transmitted to one or more Home-eNB72-2 via the S1 interface. A series of processes of the HeNBGW74 are controlled by the control unit 1104. Therefore, although omitted in FIG. 11, the control unit 1104 is connected to each of the units 1101 to 1103.

[0113] The functions of the HeNBGW74 discussed in 3GPP are shown below (see Section 4.6.2 of Non-Patent Document 1). The HeNBGW74 relays for the S1 application. Although it is a part of the procedure of the MME73a to the Home-eNB72-2, the HeNBGW74 terminates for the S1 application not related to the mobile terminal 71. When the HeNBGW74 is arranged, procedures unrelated to the mobile terminal 71 are communicated between the Home-eNB72-2 and the HeNBGW74 and between the HeNBGW74 and the MME73a. The X2 interface is not set between the HeNBGW74 and other nodes. The HeNBGW74 optionally admits the execution of paging optimization.

[0114] Next, an example of a cell search method in a communication system is shown. FIG. 12 is a flowchart showing an outline from cell search to standby operation performed by a mobile terminal (UE) in an LTE-based communication system. When starting cell search, the mobile terminal synchronizes slot timing and frame timing using the first synchronization signal (P-SS) and the second synchronization signal (S-SS) transmitted from surrounding base stations in step ST1201.

[0115] The P-SS and the S-SS are combined and 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 types of PCI are being considered. Synchronization is taken using these 504 types of PCI, and the PCI of the synchronized cell is detected (specified).

[0116] Next, for the cell that has been synchronized, in step ST1202, a cell-specific reference signal (CRS), which is a reference signal (RS) transmitted from the base station for each cell, is detected, and the received power of the RS (Reference Signal Received Power: RSRP) is measured. A code corresponding one-to-one to the PCI is used for the reference signal (RS). By correlating with that code, separation from other cells becomes possible. By deriving the code for the RS of the cell from the PCI specified in step ST1201, it becomes possible to detect the RS and measure the received power of the RS.

[0117] Next, in step ST1203, from among the one or more cells detected up to step ST1202, a cell with the best reception quality of the RS, for example, a cell with the highest received power of the RS, that is, the best cell, is selected.

[0118] Next, in step ST1204, the PBCH of the best cell is received to obtain the BCCH, which is the broadcast information. The BCCH on the PBCH has a Master Information Block (MIB) containing cell configuration information mapped thereto. Therefore, by receiving the PBCH and obtaining the BCCH, the MIB can be obtained. Examples of the information in the MIB include, for example, the DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmission antennas, the SFN (System Frame Number), and the like.

[0119] Next, in step ST1205, based on the cell configuration information of the MIB, the DL-SCH of the cell is received to obtain SIB (System Information Block) 1 in the broadcast information BCCH. SIB1 includes information related to access to the cell, information related to cell selection, and scheduling information of other SIBs (SIBk; k is an integer greater than or equal to 2). In addition, SIB1 includes a Tracking Area Code (TAC).

[0120] Next, in step ST1206, the mobile terminal compares the TAC of SIB1 received in step ST1205 with the TAC part of the Tracking Area Identity (TAI) in the tracking area list already held by the mobile terminal. The tracking area list is also referred to as the TAI list. TAI is an identifier of a tracking area and is composed of an MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). MCC is a country code. MNC is a network code. TAC is a code number of a tracking area.

[0121] If, as a result of the comparison in step ST1206, the TAC received in step ST1205 is the same as the TAC included in the tracking area list, the mobile terminal enters the standby operation in the cell. If, after comparison, the TAC received in step ST1205 is not included in the tracking area list, the mobile terminal requests a change of the tracking area to perform a Tracking Area Update (TAU) to the core network (Core Network, EPC) including the MME, etc. through the cell.

[0122] The core network updates the tracking area list based on the identification number of the mobile terminal (such as UE-ID) sent from the mobile terminal together with the TAU request signal. The core network transmits the updated tracking area list to the mobile terminal. The mobile terminal rewrites (updates) the TAC list held by the mobile terminal based on the received tracking area list. Thereafter, the mobile terminal enters the standby operation in the cell.

[0123] In LTE, LTE-A, and UMTS (Universal Mobile Telecommunication System), the introduction of CSG (Closed Subscriber Group) cells is being considered. As described above, access is permitted only to one or more mobile terminals registered in the CSG cell. One or more mobile terminals registered with the CSG cell constitute one CSG. The CSG configured in this way is assigned a unique identification number called a CSG-ID. One CSG may include a plurality of CSG cells. If a mobile terminal registers in any one CSG cell, it can access other CSG cells belonging to the CSG to which the CSG cell belongs.

[0124] In addition, Home-eNB in LTE and LTE-A and Home-NB in UMTS may be used as CSG cells. A mobile terminal registered in a CSG cell has a white list. Specifically, the white list is stored in a SIM (Subscriber Identity Module) or USIM. The white list stores the CSG information of the CSG cell registered by the mobile terminal. Specifically, as CSG information, a CSG-ID, TAI (Tracking Area Identity), TAC, etc. can be considered. If the CSG-ID and the TAC are associated, either one of them is sufficient. Also, if the CSG-ID and the TAC and the ECGI are associated, the ECGI may also be used.

[0125] From the above, a mobile terminal without a whitelist (including the case where the whitelist is empty in the present invention) cannot access a CSG cell and can only access non-CSG cells. On the other hand, a mobile terminal with a whitelist can access both the CSG cell with the registered CSG-ID and non-CSG cells.

[0126] For HeNBs and HNBs, various services need to be supported. For example, in a certain service, the operator registers a mobile terminal to certain determined HeNBs and HNBs, and by only allowing the registered mobile terminal to access the cells of the HeNBs and HNBs, the wireless resources available for the mobile terminal are increased so that high-speed communication can be performed. Accordingly, the operator sets the charging fee higher than normal.

[0127] To realize such a service, a CSG cell (Closed Subscriber Group cell) that can only be accessed by registered (subscribed, member) mobile terminals has been introduced. CSG cells (Closed Subscriber Group cells) are required to be installed in large numbers in shopping streets, condominiums, schools, companies, etc. For example, in a shopping street, a CSG cell is installed for each store, in a condominium for each room, in a school for each classroom, and in a company for each section, and a usage method is required such that only the users registered in each CSG cell can use the CSG cell.

[0128] HeNB / HNB is required not only to complement communication outside the coverage of macro cells (area-complementary HeNB / HNB), but also to support various services as described above (service-providing HeNB / HNB). For this reason, there are cases where HeNB / HNB is installed within the coverage of macro cells.

[0129] With the spread of smartphones and tablet terminals, traffic via cellular wireless communication has increased explosively, and a shortage of wireless resources is a concern worldwide. In response to this, in order to improve the frequency utilization efficiency, it has been considered to reduce the cell size and promote spatial separation.

[0130] Figure 13(A) is an image diagram of a conventional cell configuration. 1301 shows the coverage formed by a macro eNB (cell). The macro eNB (cell) forms a coverage over a relatively wide range. Conventionally, a certain area has been covered by the wide coverage of a plurality of macro eNBs (cells).

[0131] Figure 13(B) is an image diagram when cell size reduction is performed. 1302 shows the coverage formed by a small eNB (cell). The small eNB (cell) forms a coverage over a narrower range compared to the macro eNB (cell). Therefore, compared to the conventional case, a larger number of small eNBs (cells) are required to cover a certain coverage.

[0132] Figure 13(C) is an image diagram when a macro eNB (cell) and small eNBs (cells) coexist. 1303 shows the coverage formed by the macro eNB (cell), and 1304 shows the coverage formed by the small eNBs (cells). In Figure 13(C), there are cases where the coverage of a certain eNB (cell) is included within the coverage of another eNB (cell). Thus, there are cases where the coverage of the macro eNB (cell) and the coverage of the small eNBs (cells) overlap complexly. Also, there are cases where they do not overlap. Furthermore, there are cases where a large number of small eNBs (cells) are configured within the coverage of one macro eNB (cell).

[0133] Hereinafter, as in Figures 13(B) and 13(C), the case where a plurality of small eNBs (cells) are configured in the system will be described.

[0134] FIG. 14 is a diagram showing a conventional EPS architecture. 1401 is a P-GW, 1402 is an MME, 1403 is an S-GW, 1404 is an eNB, and 1405 is a UE. 1406 is an interface (S5) between the P-GW and the S-GW, 1407 is an interface (S11) between the MME and the S-GW, 1408 is an interface (S1-MME) between the MME and the eNB, 1409 is an interface (S1-U) between the S-GW and the eNB, and 1410 is an interface (Uu) between the eNB and the UE. Solid lines indicate interfaces that support user traffic (U-plane), and dashed lines indicate interfaces that support signaling (C-plane). The S5 interface 1406 and the Uu interface 1410 support both user traffic and signaling. As shown in the figure, in the conventional EPS, for one communication with a UE to be communicated with, one eNB is used to establish connections for the C-plane and the U-plane. That is, one RRC connection / S1 bearer is established using one eNB.

[0135] The problems to be solved in Embodiment 1 will be described below. Even in a small cell, for cell handover during communication, it is necessary to perform the same procedures as general cell handover shown in Section 10.1.2 of Non-Patent Document 1 (TS36.300). However, as shown in Section 10.1.2 of Non-Patent Document 1 (TS36.300), control of both the U-plane / C-Plane is required, and the procedures also increase. Also, in an area where a plurality of small cells are densely located, when moving through that area at a certain speed, if the handover procedure takes a long time, problems such as moving to the next cell area before the handover procedure is completed and being unable to perform an appropriate handover may occur. Also, in such a case, the frequency of cell handover during communication increases, and the accompanying processing becomes very large, imposing a load on the network.

[0136] The solution in Embodiment 1 is shown below. In order to solve the above problems, for one communication, it is possible to establish a plurality of RRC Connection / S1 bearers and perform cell handover without using the cell handover procedure in Chapter 10.1.2 of Non-Patent Document 1 (TS36.300).

[0137] FIG. 15 is a diagram showing the architecture of EPS according to Embodiment 1. In FIG. 15, a UE (1501) establishes an RRC Connection with three eNBs (eNB#1 (1502) / eNB#2 (1503) / eNB#3 (1504)), and each eNB establishes an S1 bearer with one S-GW. Here, the MME (1505) notifies a data distribution method and related parameters based on delivery confirmation results, quality information, received wave arrival information, UE position information, etc. at the Uu interface. Specific examples of delivery confirmation results include HARQ Ack / Nack and RLC ARQ Ack / Nack. Specific examples of quality information include CQI and CSI. A specific example of received wave arrival information is AoA (angle of arrival). A specific example of UE position information is the UE Positioning estimation result.

[0138] Note that, for the purposes of this description, the UE (1501) corresponds to a mobile station, the eNB #1 (1502) corresponds to a first base station, the eNB #2 (1503) corresponds to a second base station, and the MME (1505) and the S-GW (1506) correspond to a gateway station. Also, with respect to the C-plane signal, the RRC Connection between the UE (1501) and the eNB #1 (1502) corresponds to a first radio communication connection, and the RRC Connection between the UE (1501) and the eNB #2 (1503) corresponds to a second radio communication connection. Similarly, with respect to the C-plane signal, the S1-MME signaling connection between the MME (1505) and the eNB #1 (1502) corresponds to a first communication connection, and the S1-MME signaling connection between the MME (1505) and the eNB #2 (1503) corresponds to a second communication connection. Also, with respect to the U-plane signal, the Radio Bearer between the UE (1501) and the eNB #1 (1502) corresponds to a first radio communication connection, and the Radio Bearer between the UE (1501) and the eNB #2 (1503) corresponds to a second radio communication connection. Similarly, with respect to the U-plane signal, the S1 bearer between the S-GW (1506) and the eNB #1 (1502) corresponds to a first communication connection, and the S1 bearer between the S-GW (1506) and the eNB #2 (1503) corresponds to a second communication connection.

[0139] In this way, by establishing a first communication connection between the gateway station and the first base station, a second communication connection between the gateway station and the second base station, a first radio communication connection between the first base station and the mobile station, and a second radio communication connection between the second base station and the mobile station, respectively, one communication can be executed between the mobile station and the gateway station, and thus cell migration can be realized by adding or deleting communication connections and radio communication connections.

[0140] The U-plane signal is distributed and transmitted over a first path including the first communication connection and the first radio communication connection and a second path including the second communication connection and the second radio communication connection. The C-plane signal is distributed and transmitted over a first path including the first communication connection and the first radio communication connection and a second path including the second communication connection and the second radio communication connection.

[0141] Also, the S-GW (1506) distributes and transmits data in packet units to a plurality of eNBs for which the RRC Connection / S1 bearer has been established. This packet is, for example, an IP (internet protocol) packet. By matching the communication unit in a terminal performing IP communication, packet segmentation can be avoided, and the transmission efficiency is improved. 1507 to 1509 are the U-plane / C-plane transmission paths of eNB#1 to eNB#3 at the Uu interface. Also, 1511, 1513, and 1515 are the U-plane transmission paths between the S-GW and eNB#1 to eNB#3. Also, 1512, 1514, and 1516 are the C-plane transmission paths between the MME and eNB#1 to eNB#3.

[0142] In addition, for a specific area, it is possible to establish RRC connections / S1 bearers with a plurality of eNBs for this single communication. Examples of the specific area include within the same TA, within the same MME, within the same S-GW, etc. By being within the same MME or within the same TA, centralized control becomes possible in communication control, and communication control can be simplified. By being within the same S-GW, the distribution of U-plane data can be performed closer to the E-UTRAN, and path control can be simplified.

[0143] Regarding cell handover during communication in this specific area, the handover procedure is not performed, and it is carried out by adding / removing the RRC Connection / S1 bearer.

[0144] FIG. 16 is a diagram showing an example of a sequence for establishing communication and adding a UE-originated cell in this architecture. This sequence is configured to include a Service Request Procedure (multiple RRCs) <step ST1815> for initially establishing a bearer and a Cell Addition Procedure (eNB#2 addition) <step ST1837> for adding an RRC Connection / S1 bearer of eNB#2 to the established bearer.

[0145] In the Service Request Procedure (multiple RRCs) <step ST1815>, the UE that has established a bearer performs detection and monitoring of other neighboring cells in the same manner as normal communication operations. Using the detection and monitoring results, in step ST1836, a determination is made on whether to add the target eNB.

[0146] As a method of implementation, for example, it is determined that the quality of some reference signal of the monitored cell exceeds a certain defined threshold with respect to the level of the current cell, or the distance between the position information measured by the UE and the position information of the eNB obtained in some way in advance is calculated, and the determination is made when the distance is within a certain defined threshold. Specific examples of the reference signal include tracking RS, demodulation RS, CRS, UE-specific RS, etc. As a method of obtaining the position information of the eNB in advance, it is good to have the eNB include its own position information in the system information and notify it, or notify the UE by RRC signaling.

[0147] In this addition determination, if it is determined that addition is necessary, the Cell Addition Procedure (eNB#2 addition) <step ST1837> is performed.

[0148] Figure 17 is a sequence diagram showing the details of the service request procedure. Regarding the Service Request Procedure (multiple RRCs), it is based on the UE triggered Service Request procedure described in Section 5.3.4.1 of Non-Patent Document 11 (TS23.401). In step ST1833, after the S-GW sends a Modify Bearer Response to the MME, in step ST1834, the MME uses a message with the information identifying the target UE and the bearer information it has established as Connected UE info Report (UEID, bearer info) to notify the relevant eNB in the specific area. This is a measure to speed up the processing procedure when the UE establishes an RRC connection / S1 bearer with another eNB. If speeding up is not required, this procedure may be omitted. In that case, it is necessary to execute the Radio Bearer Establishment procedure <step ST1856> described later.

[0149] Regarding the determination of whether to execute the Service Request Procedure (multiple RRCs) or the normal UE triggered Service Request procedure, for example, the target eNB transmits information in system information or the like that can determine whether its area allows the establishment of multiple RRC connections, and the UE receives the information and determines which procedure to perform. In the determination by the UE, UE capabilities, such as the capability to establish multiple RRC connections and multiple S1 bearers with multiple eNBs, or the moving speed of the UE, etc. may be used.

[0150] Figure 18 is a sequence diagram showing the details of the cell addition procedure. The UE that has initiated the Cell Addition Procedure (addition of eNB#2) sends a request for an RRC connection (RRC connection Request (existing EPS bearer)) including information that can identify the EPS bearer to be added, which has already been established, to eNB#2 in step ST1838.

[0151] Upon receiving the RRC connection Request (existing EPS bearer), eNB#2 searches in step ST1839 for information previously notified by the MME, such as Connected UE info Report (UEID, bearer info), and checks whether the bearer information of the target UE exists. This process aims to address the case where the RRC connection Request (existing EPS bearer) is received before the notification of Connected UE info Report (UEID, bearer info) due to factors such as processing delay between MME and eNB#1, or the case where Connected UE info Report (UEID, bearer info) is not sent at all.

[0152] In the above determination, if the bearer information of the target UE can be confirmed, based on that bearer information, in step ST1841, information on the RRC connection corresponding to that bearer is sent to the UE in RRC connection setup (RAB setting equivalent to the existing bearer). The UE that has received the RRC connection setup (RAB setting equivalent to the existing bearer) performs the setting and sends RRC connection Setup complete to the eNB in step ST1842. eNB#2 that has received the RRC connection Setup complete sends Connected UE Confirmation (UE ID, existing EPS bearer) to the MME in step ST1843.

[0153] In the above determination, if the bearer information of the target UE cannot be confirmed, then, similar to the RRC Connection setup procedure in the Service Request Procedure (multiple RRCs), in step ST1845, an RRC connection setup (tentative) is transmitted. The UE that has received the RRC connection setup (tentative) performs the settings and, in step ST1846, transmits an RRC connection Setup complete to the eNB. The eNB#2 that has received the RRC connection Setup complete transmits, in step ST1847, the information for identifying the UE and the EPS bearer information for which there was a request to the MME using Connected UE Confirmation (UE ID, existing EPS bearer) for the purpose of checking the setting status of the bearer of the target UE.

[0154] The MME that has received the Initial Context Setup Complete or the Connected UE Confirmation (UE ID, existing EPS bearer) makes an additional determination for this connection in step ST1850. In the case of [1] <step ST1840>, an additional determination is made in consideration of the location information of the target eNB, the traffic situation, etc. In the case of [2] <step ST1844>, first, the existence of the existing established bearers is confirmed, and if they exist, an additional determination is made using the same criteria as in the case of [1].

[0155] In this determination, when it is determined that addition is not possible, in step ST1851, Release Reqest (UE ID, existing EPS bearer) is notified to the target eNB, and the eNB that receives this notification releases the target RRC connection in step ST1848 as necessary. In this determination, when it is determined that addition is permitted, in step ST1852, an Initial Context Setup Request is sent to the target eNB, and in step ST1853, a Modify Bearer Request is sent to the target S-GW to request the setting of S1 bearer addition.

[0156] The eNB that receives the Initial Context Setup Request performs the setting and sends Initial Context Setup Complete to the MME in step ST1859. The S-GW that receives the Modify Bearer Request performs the setting and sends a Modify Bearer Response to the MME in step ST1854. The MME that has confirmed the addition of each bearer notifies the related eNB of the bearer information update using Connected UE info Report (UEID, bearer info) in steps ST1860 to 1862.

[0157] As described above, it becomes possible to add an RRC Connection / S1 bearer.

[0158] Figure 19(A) is a diagram showing an example of a sequence for adding an RRC Connection / S1 bearer of eNB#3 starting from the UE. The procedure in Figure 19(A) is the one where, after the procedure in Figure 18, an RRC Connection / S1 bearer of eNB#3 is added starting from the UE.

[0159] Figure 19(B) is a sequence diagram showing the details of the cell addition procedure. For the added procedure, eNB#2 in Figure 18 may be replaced with eNB#3, and the description is omitted.

[0160] Figure 20 is a diagram showing an example of a sequence for adding an RRC Connection / S1 bearer to a target UE based on the determination of the eNB. Here, an example where eNB#1 makes the determination is shown. First, the UE completes the connection with eNB#1 in the Service Request Procedure (multiple RRC) <step ST1815>. The UE that has connected to eNB#1 notifies eNB#1 of the surrounding cell information in the Measurement Report at step ST2001 as usual. Here, not only the normal quality information but also the location information of the UE may be added and notified.

[0161] Upon receiving the Measurement Report, the eNB determines at step ST2002 whether to add the target eNB based on the received quality information of the surrounding cells and the location information of the UE. This may be in the same form as the existing handover determination, but it is desirable to consider that multiple connections can be established.

[0162] In this sequence example, at step ST2002, eNB#2 is determined to be added. The eNB#1 that has made the addition determination requests the addition of eNB#2 to the UE with an RRC Connection add Request (eNB2) at step ST2003. The UE that has received the RRC Connection add Request (eNB2) performs the Cell Addition Procdure (eNB#2 addition) process <step ST1837> described in Figure 18 to establish a connection with eNB#2.

[0163] After that, in step ST2005, eNB #3 is additionally determined. After that, the same processing as that for the addition of eNB #2 is performed. Note that this additional determination may be performed by eNB #2 or may be performed by only one of the eNBs. If it is performed by only one of them, it is necessary to perform a transfer process of determination authority between the eNBs using the X2 Interface or the like. If it is performed by both, the same addition request is to be discarded on the UE side.

[0164] Figure 21 is a diagram showing an example of a sequence for adding an RRC Connection / S1 bearer to a target UE according to the determination of the MME. First, the UE completes the connection with eNB #1 in the Service Request Procedure (multiple RRC) <step ST1815>. Note that, here, the notification of the Connected UE info Report (UEID, bearer info) for each eNB may be omitted. The UE that has connected to eNB #1 notifies the surrounding cell information to eNB #1 in the Measurement Report in step ST2101 as usual. Here, not only normal quality information but also the location information of the UE may be added and notified. eNB #1 that has received the Measurement Report notifies that information to the MME in the Connection Quality Report (UEID, Quality (own cell. other cell), Location) in step ST2102.

[0165] The MME that has received the Connection Quality Report (UEID, Quality (own cell. other cell), Location) determines whether to add the target eNB from the received quality information of the surrounding cells and the location information of the UE in step ST2103. In this sequence example, the case where eNB #2 is determined to be added in step ST2103 is shown.

[0166] The MME that has performed the additional determination notifies the existing bearer to eNB#2 in step ST2105 using Connected UE info Report(UEID,bearer info). If it has already been notified in the Service Request Procedure (multiple RRCs), sending this message is not necessary.

[0167] Also, the MME that has performed the additional determination notifies the addition request for eNB#2 to eNB#1 in step ST2106 using Connection add Request(eNB2). In step ST2107, eNB#1 notifies the addition request for eNB#2 to the UE using RRC Connection add Request(eNB2). The UE that has received RRC Connection add Request(eNB2) sends RRC connection Request(existing EPS bearer) to eNB#2 in step ST2108. eNB#2 that has received this sends RRC connection setup(RAB setting equivalent to the existing bearer) to the UE in step ST2109. The UE that has completed the setting sends RRC connection Setup complete to eNB#2 in step ST2110. eNB#2 that has received RRC connection Setup complete sends Connected UE Confirmation(UE ID, existing EPS bearer) to the MME in step ST2111.

[0168] After that, between eNB#2, MME, and S-GW, perform bearer configuration changes using Initial Context Setup Request <step ST2112>, Modify Bearer Request <step ST2113>, Modify Bearer Response <step ST2114>, and Initial Context Setup Complete <step ST2115> to complete the addition of the RRC Connection / S1 bearer. Additionally, afterwards, it may be possible to notify each eNB of the Connected UE info Report (UEID, bearer info).

[0169] After that, similarly to eNB#2, add eNB#3.

[0170] As described above, it becomes possible to add the RRC Connection / S1 bearer starting from the MME.

[0171] Figure 22 is a diagram showing an example of a sequence for deleting the RRC Connection / S1 bearer of eNB#1 starting from the UE. First, the UE completes the connection with eNB#1 in the Service Request Procedure (multiple RRC) <step ST1815> and adds eNB#2 in the Cell Addition Procdure (add eNB#2) <step ST1837>.

[0172] The UE that has established a bearer performs detection and monitoring of other surrounding cells in the same way as normal communication operations. In the detection and monitoring results, at step ST2201, perform a deletion determination of the target eNB. As a method of implementation, for example, the quality of some reference signal of the monitored cell is below a certain defined threshold with respect to the level of the current cell, or calculate the distance between the position information measured by the UE and the position information of the eNB obtained in some way in advance, and make a determination when the distance is outside a certain defined threshold.

[0173] In this deletion determination, if it is determined that deletion is necessary, the UE shall, in step ST2202, send a deletion request (RRC Release Request (eNB#1)) to the eNB (here eNB#2) with a good connected communication environment. The eNB#2 that has received the deletion request shall, in step ST2204, send a bearer deletion request to the MME using UE Context Release Request (eNB#1). The MME that has received the UE Context Release Request (eNB#1) shall perform a Connection deletion determination in step ST2205. This determination is made, for example, to prevent the swapping of additional processing and deletion processing due to processing delays or the like, so that not all bearers are deleted, or to reduce excessive traffic of the remaining bearers.

[0174] In the MME's Connection deletion determination, if it is determined that deletion is not possible, the MME shall, in step ST2206, notify the eNB#2 that deletion is not possible using UE Context Release Response (reject). In the MME's Connection deletion determination, if it is determined that deletion is possible, the MME shall, in step ST2209, request the release of the bearer from the eNB#1 using UE Context Release Command. The eNB#1 that has completed the release shall notify UE Context Release Complete in step ST2211. At this time, in step ST2210, an RRC Connection Release may be sent to the UE. Also, for the S-GW, in step ST2207, a deletion of the target bearer shall be requested using Modify Bearer Request (deletion), and the S-GW shall send a Modify Bearer Response in step ST2208 after the setting is completed. The MME that has confirmed the deletion of the bearer shall notify the update of the bearer to each eNB using Connected UE info Report (UEID, bearer info) in steps ST2212 to 2214.

[0175] As described above, it becomes possible to delete the RRC Connection / S1 bearer starting from the UE.

[0176] Figure 23 is a diagram showing an example of a sequence for deleting its own RRC Connection / S1 bearer starting from the eNB. First, similar to Figure 20, the UE completes the connection with eNB#1 in the Service Request Procedure (multiple RRC) <step ST1815> and adds eNB#2 in the Cell Addition Procdure (add eNB#2) <step ST1837>. The UE that has connected to eNB#1 and eNB#2 notifies the surrounding cell information to eNB#1 (and eNB#2) in the Measurement Report as usual at step ST2301. Here, not only normal quality information but also the UE's location information may be added and notified.

[0177] Upon receiving the Measurement Report, the eNB determines whether to delete its own link at step ST2302 based on the quality information of the received surrounding cells, the UE's location information, and the uplink quality information of the target UE to be measured by itself (quality of the received signal, number of L2 retransmissions, angle of arrival, etc.).

[0178] In this deletion determination, if it is determined that deletion is necessary, eNB#1 requests the deletion of the bearer from the MME in the UE Context Release Request at step ST2304. The subsequent procedures are the same as those in the RB / S1 Release Procedure2 (delete eNB#1) of Figure 20.

[0179] FIG. 24 is a diagram showing an example of a sequence for deleting the RRC Connection / S1 bearer of another eNB starting from the eNB. First, similar to FIG. 20, the UE completes the connection with eNB#1 in the Service Request Procedure (multiple RRC) <step ST1815> and adds eNB#2 in the Cell Addition Procdure (adding eNB#2) <step ST1837>. The UE that has connected to eNB#1 and eNB#2 notifies eNB#2 (and eNB#1) of the surrounding cell information in the Measurement Report as usual at step ST2401. Here, not only the normal quality information but also the location information of the UE may be added and notified.

[0180] Upon receiving the Measurement Report, eNB#2 determines at step ST2402 whether to delete another eNB (here, eNB#1) based on the received quality information of the surrounding cells and the location information of the UE.

[0181] If it is determined that deletion is necessary in this deletion determination, the RB / S1 Release Procedure2 (deleting eNB#1) <step ST2203> in FIG. 22 is activated to delete the corresponding bearer.

[0182] FIG. 25 is a diagram showing an example of a sequence for deleting the RRC Connection / S1 bearer of the eNB starting from the MME. First, similar to FIG. 20, the UE completes the connection with eNB#1 in the Service Request Procedure (multiple RRC) <step ST1815> and adds eNB#2 in the Cell Addition Procdure (add eNB#2) <step ST1837>. The UE that has connected to both eNB#1 and eNB#2 notifies the surrounding cell information to eNB#2 (and eNB#1) in the Measurement Report as usual at step ST2501. Here, not only the normal quality information but also the location information of the UE may be added and notified. eNB#2 that has received the Measurement Report notifies the information to the MME in the Connection Quality Report (UEID, Quality (own cell. other cell), Location) at step ST2102.

[0183] The MME that has received the Connection Quality Report (UEID, Quality (own cell. other cell), Location) determines whether to delete the target eNB from the received quality information of the surrounding cells and the location information of the UE at step ST2502.

[0184] In this deletion determination, if it is determined that deletion is necessary, the MME requests the S-GW to delete the target bearer in the Modify Bearer Request (deletion) at step ST2504. The subsequent procedure is the same as the RB / S1 Release Procedure2 (delete eNB#1) in FIG. 20.

[0185] Figure 26 shows an example of a sequence for deleting the RRC Connection / S1 bearer when a timeout is detected. First, similar to Figure 20, the UE completes the connection with eNB#1 in the Service Request Procedure (multiple RRC) <step ST1815> and adds eNB#2 in the Cell Addition Procdure (add eNB#2) <step ST1837>. Then, at step ST2502, when the eNB detects that there has been no data transmission in the radio section of the target UE for a long time and eNB#1 detects a data timeout (the data monitor timer expires), the procedure of RB / S1 Release Procedure1 (delete eNB#1) <step ST2603> in Figure 21 is performed to delete the target bearer. Similarly, for the UE, at step ST2601, when the UE detects that eNB#1 has detected a data timeout (the data monitor timer expires), the target bearer is deleted.

[0186] Figure 27(A) is a diagram showing an example of a sequence in data transmission when multiple RRC Connections / S1 bearers are set. In this example, it is assumed that RRC Connections / S1 bearers have already been set between the UE and eNB#1, eNB#2, and eNB#3. Here, the downlink data transmission and the uplink data transmission are described separately. Although the downlink is described first, there is no relevance between the downlink and the uplink. It is assumed that both are carried out constantly.

[0187] First, the downlink data transmission will be explained. The UE connected to eNB#1, eNB#2, and eNB#3 notifies eNB#1, eNB#2, and eNB#3 of the surrounding cell information in the Measurement Report as usual at steps ST2703 to 2705. Note that it may be only one of the eNBs. Also, here, not only the normal quality information but also the location information of the UE may be added and notified.

[0188] Three specific examples of notifying only one of the eNBs are disclosed below. (1) Notify the results of all measurements at each eNB to one of the eNBs. (2) Perform measurements according to the measurement settings of each eNB, but only one of the eNBs reports according to the settings. (3) Perform measurements according to the measurement settings of one of the eNBs, and only that one eNB reports according to the settings.

[0189] In any case, the UE will notify only one eNB, so the control can be simplified, and low power consumption can be achieved by reducing the transmission time. For (2), since the events for performing measurement reports are also limited to the measurement settings of one of the eNBs, the number of transmissions can be further reduced, the control can be further simplified, and low power consumption can be achieved. For (3), since the measurements are only performed according to the settings of one of the eNBs, the measurement process can be reduced, the control can be further simplified, and low power consumption can be achieved.

[0190] Subsequently, in step ST2706, a downlink traffic control procedure (DL Traffic Control Procedure) is executed. Subsequently, in step ST2715, an uplink traffic control procedure (UL Traffic Control Procedure) is executed.

[0191] Figure 27(B) is a sequence diagram showing the details of the downlink traffic control procedure. Each eNB that has received a Measurement Report notifies the information to the MME in a Connection Quality Report (UEID, Quality, Location) in steps ST2707 to 2709.

[0192] The MME that has received the Connection Quality Report (UEID, Quality, Location) calculates the ratio of the quality of each link from the received quality information of the surrounding cells and the location information of the UE. Considering the quality ratio and the traffic situation of each cell, in step ST2710, the final packet distribution ratio for each eNB is determined, and this ratio is notified to the S-GW in step ST2711 by Packet DL TX Racio IND (UEID, Connection1, Connection2, Connection3). The S-GW distributes the received packets to each eNB according to this ratio. (Steps ST2712 - 2714) Here, the separation, combination, etc. of the packets received by the S-GW are not performed, and it is assumed that the received packets and the packets to be transmitted to each eNB are in a one-to-one correspondence. Also, the determination of the distribution ratio is to be carried out constantly in response to the update of the quality of each link and the traffic data.

[0193] Next, the data transmission on the uplink will be described.

[0194] Figure 27(C) is a sequence diagram showing the details of the uplink traffic control procedure. The UE (AS) connected to eNB#1, eNB#2, and eNB#3 measures the quality of the links to eNB#1, eNB#2, and eNB#3 as usual in step ST2716, notifies that information to the NAS of the UE in step ST2717, and calculates the ratio of the quality of each link in step ST2718. Then, this ratio is notified to the AS in step ST2719, and according to this ratio, in steps ST2720 - 2721, the transmission packets are distributed to the links of each eNB for transmission. The UE notifies the amount of transmission data for each eNB by the buffer status report (BSR) for each eNB, and performs the transmission according to the scheduling performed using the BSR in each eNB. Here, the determination of the distribution ratio is to be carried out constantly in response to the update of the quality of each link.

[0195] All or only some of the sequence examples in the foregoing figures may be applied.

[0196] According to the above Embodiment 1, for one Connection, a plurality of RRC Connections / S1 bearers can be set, and cell handover during communication can be enabled by adding / deleting the RRC Connection / S1 bearer. Therefore, the HO procedure as shown in Section 10.1.2 of Non-Patent Document 1 (TS36.300) becomes unnecessary, and appropriate cell handover is possible even when moving at a certain speed in an area where a plurality of small cells are densely located. Also, since U-plane control becomes unnecessary, the load on the network can be reduced.

[0197] Embodiment 2. As described in Embodiment 1, an increase in communication capacity is required for the system. To increase the communication capacity, cell splitting to improve frequency utilization efficiency has been studied. In Embodiment 1, a method was disclosed that enables appropriate cell handover even in a situation where cell splitting has occurred and a plurality of small cells are densely located.

[0198] However, in the case of the method disclosed in Embodiment 1, control processing for establishing a plurality of eNBs (cells) and RRC connections is required, resulting in signaling and control delays for that purpose.

[0199] Therefore, in Embodiment 2, a method of performing communication using a plurality of eNBs (cells) without establishing RRC connections with the plurality of eNBs (cells) is disclosed.

[0200] In 3GPP, as methods for communicating using multiple cells without establishing multiple RRC connections, C / U plane split and multi-stream have been proposed (see Non-Patent Document 12 (RWS-120010) and Non-Patent Document 13 (RWS-120006)). Different from the method of establishing an RRC connection and a U-plane side bearer using one eNB (cell) in a conventional communication system, to communicate using multiple eNBs (cells) without establishing multiple eNBs (cells) and RRC connections, an architecture including MME and S-GW, a bearer establishment method, etc. are required. However, none of such architectures including MME and S-GW, bearer establishment methods, etc. have been disclosed at all.

[0201] Here, a method for communicating using multiple eNBs (cells) without establishing multiple eNBs (cells) and RRC connections will be disclosed.

[0202] For one communication, establish a C-plane connection using one eNB (cell) and establish a U-plane connection using multiple eNBs (cells). Hereinafter, the eNB (cell) that establishes the C-plane connection (including the one to be established and the established one) may be referred to as the C-plane establishment eNB (cell), and the eNB (cell) that establishes the U-plane connection (including the one to be established and the established one) may be referred to as the U-plane establishment eNB (cell). Also, the eNB (cell) that only establishes the U-plane connection may be referred to as the U-plane only establishment eNB (cell).

[0203] As the C-plane connection, establish an RRC connection, and as the U-plane connection, establish a bearer. It is preferable to use a DRB (data radio bearer) / S1 bearer as the bearer. A DRB is a radio bearer for user data.

[0204] An eNB in which only a bearer is established has at least functions related to the control of the bearer.

[0205] As a function related to bearer control, there is an E-RAB establishment / control / release function of the bearer between the S-GW and the UE. Specific examples include the establishment, configuration, maintenance, and release functions of point-to-point radio bearers (Establishment, configuration, maintenance and release of point to point Radio Bearers) and the E-RAB service management function.

[0206] As cell operation methods, a coverage cell for the purpose of providing basic coverage and a capacity cell (capacity booster cell) for the purpose of increasing communication capacity are considered (see Non-Patent Document 14 (TR36.927)). An eNB (cell) that establishes a C-plane connection may be regarded as a coverage cell, and an eNB (cell) that establishes only a U-plane connection may be regarded as a capacity cell.

[0207] Alternatively, an eNB (cell) that establishes a C-plane connection may be regarded as a macro eNB (cell), and an eNB (cell) that establishes only a U-plane connection may be regarded as a small eNB (cell).

[0208] A macro eNB is an eNB that constitutes a macro cell with a relatively large coverage area. It may be a Wide Area Base Station (see Non-Patent Document 15 (TS36.141)).

[0209] A small eNB is an eNB that constitutes a small cell with a relatively small coverage area. It may be a low-power node, a local area node, a hot spot, etc. Alternatively, it may be a pico eNB (cell), a femto eNB (cell), a HeNB, an RRH, an RRM, an RN. Alternatively, it may be a Local Area Base Station, a Home Base Station (see Non-Patent Document 15 (TS36.141)).

[0210] Note that the eNB (cell) that establishes the connection of the U-plane does not necessarily have all the functions of the eNB or the cell, so it may simply be referred to as a node.

[0211] When the eNB that only establishes the connection of the U-plane is defined as an RN, the DeNB may be defined as the C-plane establishing eNB. The method disclosed in Modification Example 2 of Embodiment 2 described later may be applied. As the interface between the C-plane establishing eNB and the U-plane establishing eNB, the backhaul link established between the DeNB and the RN may be used. In this case, the frequency layer of the link between the DeNB and the UE and the frequency layer of the link between the RN and the UE may be configured to be different. In the case of the RN, since the interface between the C-plane establishing eNB and the U-plane establishing eNB is wireless, flexible installation of a large number of U-plane establishing eNBs becomes possible.

[0212] FIG. 28 is a diagram showing the architecture of the EPS according to Embodiment 2. 2801 is the P-GW, 2802 is the S-GW, 2803 is the MME, 2804 is the C-eNB, 2805 is the U-eNB, and 2806 is the UE. The eNB that establishes the connection of the C-plane is denoted as the C-eNB, and the eNB that only establishes the connection of the U-plane is denoted as the U-eNB. The C-eNB may not only establish the connection of the C-plane but also establish the connection of the U-plane.

[0213] 2807 is the interface (S5) between the P-GW and the S-GW, 2808 is the interface (S11) between the MME and the S-GW, 2809 and 2815 are the interfaces (S1-MME) between the MME and the eNB (C-eNB, U-eNB), 2813 and 2814 are the interfaces (S1-U) between the S-GW and the eNB (C-eNB, U-eNB), 2810 and 2811 are the interfaces (Uu) between the eNB (C-eNB, U-eNB) and the UE, and 2812 is the interface between the eNBs. The interface 2812 may be X2, or a new interface may be provided. Similar to FIG. 14, solid lines indicate interfaces that support user traffic (U-plane), and dashed lines indicate interfaces that support signaling (C-plane).

[0214] The use of multiple eNBs for one communication is the same as that shown in FIG. 15 disclosed in Embodiment 1. However, in this embodiment, it is one eNB that establishes the RRC connection. That is, the connection of the C-plane is established using one eNB, and the connection of the U-plane is established using multiple eNBs. In the example of the figure, the one eNB that establishes the connection of the C-plane is the C-eNB, and the multiple eNBs that establish the connection of the U-plane are the C-eNB and the U-eNB.

[0215] In this embodiment, the RRC connection is established using the Uu (2810) interface between the C-eNB (2804) and the UE (2806) to be communicated with. That is, in the figure, the connection of the C-plane indicated by the dashed line is established between the C-eNB (2804) and the UE (2806). On the other hand, only the communication of U-plane side data (user data) is performed using the Uu (2811) interface between the U-eNB (2805) and the UE (2806) to be communicated with. That is, only the connection of the U-plane indicated by the solid line is established between the U-eNB (2805) and the UE (2806). Note that a connection of the U-plane may be established between the C-eNB (2804) and the UE (2806) as in the conventional case.

[0216] The interface 2811 for U-plane connection between the U-eNB (2805) and the UE (2806) is set as Uu, but instead of Uu, a new interface having only the U-plane connection function may be provided.

[0217] In this embodiment, for the UE (2806) to be communicated with, the communication of user data between the U-eNB (2805) and the S-GW (2802) is performed using the interface (S1-U) 2813. For the UE (2806) to be communicated with, the signaling communication between the U-eNB (2805) and the MME (2803) is performed using the interface (S1-MME) 2815. However, as will be described later, the signaling for the UE (2806) to be communicated with is limited. Any signaling necessary for at least bearer control in the U-eNB (2805) may be used.

[0218] Note that the UE (2806) here corresponds to a mobile station, the C-eNB (2804) corresponds to a first base station, the U-eNB (2805) corresponds to a second base station, and the MME (2803) and the S-GW (2802) each correspond to a gateway station. Also, regarding the C-plane signal, the RRC Connection between the UE (2806) and the C-eNB (2804) corresponds to a first radio communication connection. Similarly regarding the C-plane signal, the S1-MME signaling connection (2809) between the MME (2803) and the C-eNB (2804) corresponds to a first communication connection, and the S1-MME signaling connection (2815) between the MME (2803) and the U-eNB (2805) corresponds to a second communication connection. Also, regarding the U-plane signal, the Radio Bearer between the UE (2806) and the C-eNB (2804) corresponds to a first radio communication connection, and the Radio Bearer between the UE (2806) and the U-eNB (2805) corresponds to a second radio communication connection. Similarly regarding the U-plane signal, the S1 bearer (2814) between the S-GW (2802) and the C-eNB (2804) corresponds to a first communication connection, and the S1 bearer (2813) between the S-GW (1506) and the U-eNB (2805) corresponds to a second communication connection.

[0219] In this way, by establishing a first communication connection between the gateway station and the first base station, a second communication connection between the gateway station and the second base station, a first radio communication connection between the first base station and the mobile station, and a second radio communication connection between the second base station and the mobile station respectively, one communication is executed between the mobile station and the gateway station, so that cell migration can be realized by adding or deleting communication connections and radio communication connections.

[0220] The U-plane signal is distributed and transmitted to a first path including the first communication connection and the first radio communication connection and a second path including the second communication connection and the second radio communication connection. The C-plane signal is distributed and transmitted to a first path including the first communication connection and the first radio communication connection and a second path including the second communication connection and the first radio communication connection.

[0221] FIG. 29 is a diagram showing the protocol stack of the eNB according to Embodiment 2. 2901 is a C-eNB. It is connected to the S1-MME interface as the C-plane and to the S1-U interface as the U-plane. The dashed part of 2902 is the protocol for C-plane connection, and the dashed part of 2903 is the protocol for U-plane connection. In the C-eNB, 2904 represents the RRC protocol, 2907 represents the PDCP protocol, 2908 represents the RLC protocol, 2912 represents the MAC protocol, and 2911 represents the PHY protocol. The MAC protocol 2912 has an MPX (multiplexing) / Scheduling function 2909 and a HARQ function 2910. These protocols have functions for both the C-plane and the U-plane. In the C-plane, it has a signaling function for control information by paging, SI (system information), and an SRB (signaling radio bearer) which is a radio bearer for signaling (2905). In the U-plane, it has a user data carrying function by a DRB (data radio bearer) which is a radio bearer for user data (2906).

[0222] 2913 is a U-eNB. It is connected to the S1-MME interface as the C-plane and to the S1-U interface as the U-plane.

[0223] First, a protocol for a UE that establishes a C-plane connection to the U-eNB is shown. The dashed part of 2914 is the protocol for the C-plane connection, and the dashed part of 2915 is the protocol for the U-plane connection. In the U-eNB, 2917 represents the RRC protocol, 2920 represents the PDCP protocol, 2921 represents the RLC protocol, 2925 represents the MAC protocol, and 2924 represents the PHY protocol. The MAC protocol 2925 has an MPX (multiplexing) / Scheduling function 2922 and a HARQ function 2923. These protocols have functions for both the C-plane and the U-plane.

[0224] Next, a protocol for a UE that establishes only a U-plane connection is shown. The protocol 2914 for the C-plane connection is not configured. However, it has at least a function 2916 related to the control of the bearer. It is better to have it as an RRC function. Therefore, the PDCP protocol 2920, the RLC protocol 2921, the MAC protocol 2922, and the PHY protocol 2924 have only functions for the U-plane. In other words, they have only functions for bearer establishment.

[0225] Note that when configuring an eNB dedicated to U-plane establishment, since it is not necessary to have the protocol 2914 for establishing a C-plane connection in the U-eNB 2913, a simple configuration can be achieved.

[0226] Next, a bearer establishment method using multiple eNBs (cells) is disclosed.

[0227] In this embodiment, the MME selects an eNB for which a DRB / S1 bearer should be established for a UE to be communicated with.

[0228] As an index for selection, for example, it is advisable to use the quality information or location information notified in the measurement report of the UE disclosed in Embodiment 1.

[0229] Specific examples of the index for selection are listed in the following 11 items. (1) Communication quality information between the UE and the cell (2) Location information of the UE (3) Path loss between the UE and the cell (4) Arrival information of the received wave from the UE in the cell (5) Speed or speed class of the UE (6) Travel direction of the UE (7) Delivery confirmation result at the Uu point between the UE and the cell (8) Load status of the cell (9) Capability information of the UE (10) Type information of the UE (11) Combinations of (1) to (10) (1) Regarding this, as specific examples of communication quality information, there are RSRP, RSRQ, etc. measured by the UE. Also, the uplink communication quality measured by the cell may be used. (2) Regarding this, a UE having a GPS (Global Positioning System) or a UE connectable to a GPS can obtain the location information of the UE by positioning. It is advisable to use this location information of the UE. As another method, a location service (LCS) may be utilized. It is advisable for the network-side node to obtain the location information of the target UE from the LCS server. (3) Regarding this, when the UE can measure the path loss from the received power from the cell and the transmission power of the cell notified by the cell, it is advisable to use this path loss information. (4) Regarding this, it may be used when the cell can measure the angle of arrival (AoA) of the received wave from the UE. (5) Regarding this, a UE having a GPS or a UE connectable to a GPS may measure using the GPS. Also, it may be divided into predetermined speed classes and represented by the speed classes. As another method, the speed class may be derived from the number of HO times or connection change times of the macro cell or the number of connection change times of the small cell within a predetermined time. This derivation may be performed by the network-side node instead of the UE. (6) Regarding this as well, a UE having a GPS or a UE connectable to a GPS may measure using the GPS. As another method, the speed class may be derived from the number of HO times or connection change times of the macro cell or the number of connection change times of the small cell within a predetermined time. This derivation may be performed by the network-side node instead of the UE. The network-side node may recognize the location of the macro cell or the small cell and measure the traveling direction of the UE based on the order in which the cells are connection-changed. (7) Regarding this, it is advisable to use the data delivery confirmation result performed between the UE and the cell. Specific examples include HARQ or ARQ, etc. The eNB (cell) can obtain the delivery confirmation result at the Uu point between the UE and its own cell. (8) Regarding this, it is advisable for each cell to notify the MME or neighboring cells of the information indicating the load status of its own cell. The load status of the cell may be the traffic status of the cell.Regarding (9), the capability information of the UE is, for example, information indicating the number of eNBs capable of establishing a DRB / S1 bearer (information indicating the number of eNBs capable of establishing an RRC connection / S1 bearer when applied to Embodiment 1), etc. It may also be UE capability information defined by the standard. Regarding (10), as the UE type information, for example, it is information indicating whether it is a terminal for MTC (machine type communication) or a normal UE, etc.

[0230] Disclose a method for the MME to recognize an index when selecting a UE to communicate with and an eNB to establish a DRB / S1 bearer.

[0231] When using information measured by the UE (also referred to as UE supported information) as an index, notify this information from the UE to the C-plane establishment eNB. It is advisable to use RRC signaling for the notification.

[0232] Show three specific examples of triggers for notification as follows. (1) Instruction from the C-plnae establishment eNB (2) Periodic (3) Event occurrence In (2), for example, perform the notification according to a predetermined time period. The period may be notified from the C-plane establishment eNB to the UE in advance, or may be determined in advance by the system according to the standard, etc.

[0233] In (3), for example, notify when the measured value exceeds a predetermined threshold, etc., and notify when an event occurs according to a predetermined criterion.

[0234] As specific examples of UE supported information, (1) Information measured by the UE. (2) Cell identifier.

[0235] (1) is, for example, the information obtained by the UE through measurement among the above-mentioned indicators for selection. When it is necessary to identify which cell the information is related to, it is advisable to notify.

[0236] As a method for notifying UE-supported information, conventional measurement events may be used. As specific examples of the information notified in the measurement report, the following two are shown. (1) Communication quality information between the UE and the cell. Such as RSRP, RSRQ, etc. (2) Cell identifier.

[0237] In addition to these, it is advisable to include UE-supported information in the measurement report. The UE notifies these information to the C-plane establishment eNB through the measurement report.

[0238] The C-plane establishment eNB that receives the information notifies the information to the MME. It is advisable to use S1 signaling for the notification. At this time, it is advisable to include information that can recognize which UE the information is from. It is advisable to use a UE identifier (UE-ID) that can be recognized by the MME. Alternatively, a mobile subscriber identity that can be recognized by the MME may also be used. It is advisable to use the UE identifier, mobile subscriber identifier used within the MME, or the identifier of its own cell (the C-plane establishment eNB (cell) of the UE) and the UE identifier used within its own cell (the C-plane establishment eNB (cell)).

[0239] By using the UE-supported information received by the MME from the C-plane establishment eNB, the MME can select the eNB for which the DRB / S1 bearer should be established.

[0240] When using the information measured or acquired by the network-side node as an indicator, each node notifies the information to the MME. When the network-side node is the MME, the notification is not required. Similar to the above method, it is advisable to include information that can recognize which UE's information it is, which information is between which eNB (cell), and which eNB (cell)'s information it is.

[0241] Note that this method can also be applied when the eNB selects another eNB as disclosed in Embodiment 1. It is also applicable when the C-plane establishment RRC connected establishment eNB selects the U-plane establishment eNB from Modification Example 3 of Embodiment 2 to Modification Example 1 of Embodiment 3 described later. In this case, it is not necessary to notify the above information from the C-plnae establishment eNB to the MME.

[0242] This method can also be applied in the determination of packet allocation (packet transmission distribution determination) disclosed in Embodiment 1 or described later. Also, when the communication quality information of the uplink with each U-plane establishment eNB can be used, the packet allocation may be determined using this information. The uplink communication quality information with the UE is measured by the U-plnane establishment eNB. The U-plane establishment eNB may notify this information to the MME.

[0243] For E-RAB establishment, the MME sets the E-RAB in each selected eNB. Specific examples of E-RAB settings include the identifier of the E-RAB (E-RAB ID), QoS parameters, and the like.

[0244] If there is an eNB that has already set the E-RAB, the MME modifies the E-RAB setting for that eNB.

[0245] When there is one EPS bearer, the E-RAB settings to be set in each eNB may be the same. If there is no change in the EPS bearer, it may be the same as the E-RAB setting already set in the C-plane establishment eNB. In this case, only the E-RAB identifier may be made different. The E-RAB settings in each eNB can be individually handled using this identifier.

[0246] The MME notifies each selected eNB of information for setting up the E-RAB with the UEs to be communicated with. This includes information about the UEs to be communicated with, the E-RAB settings that the MME has set or modified for the E-RAB. For an eNB with no change in the E-RAB settings after the MME has modified the E-RAB, it may not be necessary to notify the modified E-RAB settings.

[0247] As signaling, the S1 Initial context setup request message may be used. It may be configured to notify only the information regarding the E-RAB settings within the Initial context setup request message. Also, for modifying the information about the UE, the S1 UE context modification request message may be used.

[0248] For setting up the E-RAB, the S1 E-RAB setup request message may be used. For modified E-RAB settings, the E-RAB modify request message may be used.

[0249] Additionally, a new list of the correspondence between each U-plane establishing eNB and the E-RAB settings of each U-plane establishing eNB may be provided. It may be called the E-RAB list_U-plane. The MME may notify this list to each U-plane establishing eNB. This enables each U-plane establishing eNB to recognize the E-RAB settings of other U-plane establishing eNBs.

[0250] Also, the MME may notify each U-plane establishment eNB of information regarding the C-plane establishment eNB. It may be notified together with the information for setting the E-RAB. As the information regarding the C-plane establishment eNB, it is preferable to use the identifier or address of the C-plane establishment eNB. This enables each U-plane establishment eNB to notify the C-plane establishment eNB of the necessary information. For example, in a case where the DRB setting information set by each U-plane establishment eNB described later is notified to the UE via the C-plane establishment eNB, it becomes possible to notify the DRB setting information to the C-plane establishment eNB.

[0251] Each U-plane establishment eNB performs the necessary processing for establishing the DRB / S1 bearer for the UE to be communicated with using the E-RAB setting information received from the MME. Regarding the radio section, the DRB is set. Each U-plane establishment eNB sets the DRB to be established with the UE to be communicated with using the E-RAB setting notified from the MME by the RRC function. Examples of the DRB setting include setting the DRB identifier and setting the lower layers. Examples of the lower layer setting include PDCP setting, RLC setting, MAC setting, and PHY setting.

[0252] Each U-plane establishment eNB that has set the DRB notifies the UE of the DRB setting information. It is preferable to include in the DRB setting information the identifier of its own eNB (cell) for identifying which U-plane establishment eNB's DRB setting information it is, and the identifier of the UE to be communicated with. Also, each U-plane establishment eNB may notify the system information of its own eNB (cell). Also, when each U-plane establishment eNB configures the ePDCCH, which is an extended downlink control channel, for scheduling the UE to be communicated with, it is preferable to also notify the setting information of the ePDCCH. Also, information indicating that it is a U-plane establishment request may be notified together.

[0253] Two specific examples are disclosed in which the U-plane establishment eNB notifies the UE of DRB configuration information, system information, ePDCCH configuration information, and information indicating that it is a U-plane establishment request. (1) Notify via the C-plane establishment eNB. (2) Notify via the MME and the C-plane establishment eNB.

[0254] A method of notifying via the C-plane establishment eNB in (1) is disclosed. Each U-plane establishment eNB that has configured a DRB notifies the C-plane establishment eNB of the DRB configuration information and the like. For this notification, a new interface may be provided, or the X2 interface may be used. A new message may be provided for notification.

[0255] The DRB configuration information and the like may be provided as transparent container information. In the case of transparent container information, the C-plane establishment eNB (cell) may notify the UE as it is. Information included in the AS-config message of the U-plane establishment eNB may be placed in the container information. The DRB configuration information and system information for each U-plane establishment eNB may be included in the RadioResourceConfigDedicated information in the AS-config message. It may also be a DRB list.

[0256] The C-plane establishment eNB (cell) notifies the UE of the DRB configuration information and the like of all U-plane establishment eNBs to be established with the UE.

[0257] A list (DRB list_U-plane) of each U-plane establishment eNB and each DRB configuration may be provided. The C-plane establishment eNB may notify the UE of the list.

[0258] It is advisable to use RRC signaling for this notification. A new message may be provided, or the existing RRC message may be used to notify the U-plane establishment eNB's DRB configuration information and system information. As a specific example of the existing RRC message, it is advisable to use the RRC connection reconfiguration message or the AS-config message. The DRB configuration information and system information for each U-plane establishment eNB may be included in the RadioResourceConfigDedicated information in the RRC connection reconfiguration message or the AS-config message. A DRB list may also be used.

[0259] (1)'s method can be notified without going through the MME, so the signaling volume of the system can be reduced.

[0260] A method of notifying via the MME and the C-plane establishment eNB in (2) will be disclosed. Each U-plane establishment eNB that has set a DRB notifies the MME of the DRB configuration information, etc.

[0261] It is advisable to use the S1 interface for this notification.

[0262] The MME notifies the C-plane establishment eNB of the DRB configuration information, etc. A list of each U-plane establishment eNB and its respective DRB configuration may be provided. It may also be called the DRB list_U-plane. It is advisable to use the S1 interface for this notification. A new message may be provided for notification using the S1 interface.

[0263] The C-plane establishment eNB (cell) notifies the UE to be communicated with of the DRB configuration information, etc. received from the MME. A list of each U-plane establishment eNB and its respective DRB configuration may be provided. It may also be called the DRB list_U-plane. The C-plane establishment eNB may notify this list to the UE. It is advisable to use RRC signaling for this notification. The method in (1) can be applied to this.

[0264] In addition, in (2) above, the DRB setting information and the like may be provided as container information for transparency. When it is used as container information for transparency, the MME may notify the C-plane establishment eNB of the container information as it is. Further, the C-plane establishment eNB (cell) may notify the UE of the container information as it is. Information included in the AS-config message of the U-plane establishment eNB may be placed in the container information. The DRB setting information and system information for each U-plane establishment eNB may be included in the RadioResourceConfigDedicated information in the AS-config message. It may also be used as a DRB list.

[0265] The method in (2) enables the DRB setting information to be notified to the UE even when there is no interface between the C-plane establishment eNB and the U-plane establishment eNB.

[0266] By doing so, the UE to be communicated with can recognize the DRB setting information for establishing a DRB with the eNB that establishes the U-plane. In addition, it can recognize the system information for connecting to the eNB that establishes the U-plane.

[0267] The UE to be communicated with performs DRB settings with each U-plane establishment eNB and connection processing with each U-plane establishment eNB (cell).

[0268] When the connection between the UE to be communicated with and the U-plane establishment eNB is successful, the UE may notify each U-plane establishment eNB of a connection completion message. It is advisable to include the identifier of the U-plane establishment eNB (cell) for which the connection has been completed in this message so that the identifier of the UE itself (the identifier of the UE to be communicated with) and which U-plane establishment eNB the connection has been completed with can be recognized.

[0269] Three specific examples of the notification method are disclosed below. (1) Notify each U-plane establishment eNB via the C-plane establishment eNB and the MME (2) Notify each U-plane establishment eNB via the C-plane establishment eNB (3) Notify directly to the U-plane establishment eNB (1) is disclosed. The connection completion message is notified from the UE to each U-plane establishment eNB via the C-plane establishment eNB and the MME. Since the UE has not established an RRC connection with the eNB for only U-plane establishment, the UE cannot directly notify the message to the eNB for only U-plane establishment using RRC signaling. Therefore, the method of notification via the C-plane establishment eNB disclosed in (1) is effective. It is preferable to use RRC signaling for the notification from the UE to the C-plane establishment eNB. As the RRC message, RRC connection reconfiguration complete may be used.

[0270] For the notification of this message from the C-plane establishment eNB to the MME, the S1 interface may be used. It is preferable to newly establish the S1 message. The method in (1) is also effective when there is no X2 interface.

[0271] For the notification of this message from the MME to each U-plane establishment eNB, the S1 interface may be used.

[0272] (2) is disclosed. The connection completion message is notified from the UE to each U-plane establishment eNB via the C-plane establishment eNB. It is preferable to use RRC signaling for the notification from the UE to the C-lane establishment eNB. As the RRC message, RRC connection reconfiguration complete may be used.

[0273] For the notification from the C-plane established eNB to each U-plane established eNB, a new interface may be provided, or the X2 interface may be used. If there is an X2 interface, the notification can be made without providing a new interface.

[0274] (3) is disclosed. The connection completion message is notified from the UE to each U-plane established eNB. Since the UE has not established an RRC connection with the eNB for only U-plane establishment, the UE cannot directly notify the message to the eNB for only U-plane establishment using RRC signaling.

[0275] Here, a new L1 / L2 control message is provided for the notification. The U-plane established eNB has the protocol of the L1 / L2 layer. Therefore, by newly establishing a signaling message in the L1 / L2 layer, it becomes possible to notify the message from the UE to the U-plane established eNB. It is preferable to provide it as a MAC function or a PHY function as the L1 / L2 layer. Also, the identifier of the own UE may be notified together with the L1 / L2 control message. Alternatively, a code using the identifier of the own UE may be carried on the radio resource used for the L1 / L2 control message. The U-plane established eNB (cell) can identify from which UE the message is by demodulating using the code.

[0276] Each U-plane established eNB that has received the connection completion message performs the establishment process of the DRB / S1 bearer with the UE to be communicated with.

[0277] Each U-plane established eNB may notify the MME of the completion message of the process. The UE may notify the U-plane established eNB that the setting of the DRB or the setting of the modified DRB has been completed. The S1 Initial context setup complete message may be used for the notification. Also, the E-RAB setup complete message or the E-RAB modification complete message may be notified.

[0278] It is advisable to include in the message a UE identifier (UE-ID) that can be identified by the MME for the UE to be communicated with. Alternatively, a mobile subscriber identity that can be identified by the MME may also be used. Also, the identifier of the self U-plane establishment eNB (cell) may be included. As the UE identifier that can be identified by the MME, it is advisable to use the UE identifier used within the MME. Alternatively, it may be the identifier of the C-plane establishment eNB (cell) of the UE and the UE identifier used within the C-plane establishment eNB (cell).

[0279] The MME requests the S-GW to set up an S1 bearer for the selected U-plane establishment eNB. To notify this request, the S11 interface may be used. For example, a modify bearer request message may be used. It is advisable to include in the request message the identifier of the UE to be communicated with, the identifier of the selected U-plane establishment eNB, and the E-RAB setting information of each U-plane establishment eNB. An E-RAB list_U-plane, which is a list of the correspondence between each U-plane establishment eNB and the E-RAB setting of each U-plane establishment eNB, may also be used. Also, as the identifier of each U-plane establishment eNB, the IP address set for each U-plane establishment eNB may be used.

[0280] The S-GW sets up an S1 bearer for each notified U-plane establishment eNB. If an S1 bearer has already been set up, the S1 bearer is modified.

[0281] The S-GW that has set up or modified the S1 bearer notifies the MME of a completion message for the setup or modification of the S1 bearer. It is advisable to use the S11 interface for this notification. It is advisable to use the S11 Modify bearer response message.

[0282] As a result, an S1 bearer is established between the S-GW and each U-plane establishment eNB.

[0283] Disclosed is a data transmission method in the case where a plurality of DRBs / S1 bearers are established using a plurality of eNBs. Since DRBs / S1 bearers are established using a plurality of U-plane establishment eNBs, the data transmission method disclosed in Embodiment 1 can be applied.

[0284] Regarding downlink data transmission, the MME calculates the ratio of the quality of each link. Considering the ratio of the quality and the traffic situation of each cell, the final packet distribution ratio for each eNB is determined, and this ratio is notified to the S-GW in Packet DL TX Racio IND. The S-GW distributes the received packets to each eNB according to this ratio. Here, the separation, combination, etc. of the packets received by the S-GW are not performed, and it is assumed that the received packets and the packets to be transmitted to each eNB are in a one-to-one correspondence. Also, the determination of the distribution ratio is to be constantly performed according to the update of the quality of each link and the traffic data. When calculating the ratio of the quality of each link in the MME, it is advisable to use the index for selecting the U-plane establishment eNB.

[0285] Regarding uplink data transmission, the UE measures the quality of the link with the U-plane establishment eNB and calculates the ratio of the quality of each link. Then, according to this ratio, the transmission packets are distributed to the links of each eNB for transmission. The UE notifies the amount of transmission data for each eNB by a buffer status report (BSR) for each eNB and performs transmission according to the scheduling performed using this BSR in each eNB. Also, the determination of the distribution ratio is to be constantly performed according to the update of the quality of each link.

[0286] Disclosed is a method for a U-plane establishment eNB to start data transmission to a UE that is a communication target.

[0287] Upon receiving the connection completion message from the UE to the U-plane establishment eNB, each U-plane establishment eNB may start the data transmission process to the UE. When the UE sends the connection completion message to the U-plane establishment eNB, it may start the data reception process from the U-plane establishment eNB (cell). This can reduce the deviation in the timing of starting the data transmission and reception process between the UE and the U-plane establishment eNB (cell).

[0288] Other methods are disclosed. After receiving data from the S-GW, the U-plane establishment eNB starts the data transmission process to the UE. After detecting and synchronizing with the U-plane establishment eNB (cell), the UE starts the reception process from the U-plane establishment eNB (cell). Alternatively, the UE may start the reception process from the U-plane establishment eNB (cell) after the RA procedure with the U-plane establishment eNB (cell) is successful. For example, this can be applied when there is no connection completion message from the UE to the U-plane establishment eNB. This method has the advantage that it does not require a clear trigger for starting data transmission and reception, making control easier.

[0289] In the case where there is no connection completion message from the UE to the U-plane establishment eNB, before the UE completes the connection with the U-plane establishment eNB, the S1 bearer may be set / modified at the S-GW, and downlink data may arrive at the U-plane establishment eNB. After receiving data from the S-GW, the U-plane establishment eNB will start the data transmission process to the UE. The UE has not yet completed the connection with the U-plane establishment eNB and cannot receive the data.

[0290] However, by using retransmission control at the U-plane establishment eNB, it is possible to reduce the loss of the data. Also, by increasing the maximum number of retransmissions in advance, it is possible to almost eliminate the loss of the data. Therefore, the method disclosed here can achieve the effect of facilitating control with almost no loss of data.

[0291] Disclosed is a method for a UE to transmit and receive U-plane data with a U-plane establishment eNB (cell).

[0292] The U-plane establishment eNB (cell) maps scheduling information for the UE to a Physical Downlink Control Channel (PDCCH) or an enhanced PDCCH (ePDCCH), which is a physical control channel, and notifies the UE. In the case of ePDCCH, the U-plane establishment eNB (cell) notifies the UE of the configuration information of the ePDCCH in advance. Specific examples of such information include resource (Physical Resource Block (PRB), sequence) information to be used. The configuration of the ePDCCH may be an RRC function. It may also be an RRC function of the U-plane establishment eNB. The notification of the ePDCCH may be notified to the UE to be communicated with via the C-plane establishment eNB (cell) as described above, or as another method, it may be notified from the U-plane establishment eNB (cell) to the RA procedure via the MAC.

[0293] The UE monitors the PDCCH of the U-plane establishment eNB (cell). Alternatively, if it is scheduled by the ePDCCH, it may monitor the ePDCCH. By receiving the PDCCH or ePDCCH, data scheduling information can be obtained, and the data may be received according to the scheduling information. The data is mapped to the Physical Downlink Shared Channel (PDSCH) at each U-plane establishment eNB (cell) and allocated to physical radio resources.

[0294] DRX for the U-plane establishment eNB (cell) may be configured. It is preferable that the RRC performs the configuration of DRX for the U-plane establishment eNB. If the U-plane establishment eNB performs the configuration, it may be an RRC function provided in the U-plane establishment eNB. The DRX configuration may be performed by the U-plane establishment eNB and notified to the UE via the C-plane establishment eNB (cell), or it may be notified from the U-plane establishment eNB (cell) to the RA procedure via the MAC.

[0295] The DRX setting may be performed by the C-plane establishment eNB (cell) and notified to the UE and each U-plane establishment eNB (cell).

[0296] It is preferable that the activation / deactivation of DRX is performed by the MAC. It is preferable to be the function of the MAC provided in each U-plane establishment eNB.

[0297] SPS (semi-persistent scheduling) may be set for the U-plane establishment eNB (cell). The time setting of SPS is performed by the RRC. When the U-plane establishment eNB sets it, the time setting of SPS may be the function of the RRC provided in the U-plane establishment eNB. The SPS setting may be performed by the U-plane establishment eNB (cell) and notified to the UE via the C-plane establishment eNB (cell), or may be notified by the U-plane establishment eNB (cell) to the RA procedure via the MAC.

[0298] The SPS setting may be performed by the C-plane establishment eNB (cell) and notified to the UE and each U-plane establishment eNB (cell).

[0299] It is preferable that the scheduling on the frequency axis of SPS is performed by the MAC. It is preferable to be the function of the MAC provided in each U-plane establishment eNB. The scheduling result on the frequency axis may be notified to the UE by the PDCCH or ePDCCH which is the physical control channel for scheduling.

[0300] It may be possible to shift the data scheduling timing among the eNBs (cells) that have established each U-plane. In other words, it is advisable to time-division the data transmission and reception timing among the eNBs (cells) that have established each U-plane. A UE with only one transceiver can support both communications with multiple eNBs that have established the U-plane. The DRX setting may be used to shift the data scheduling timing in multiple eNBs (cells) that have established the U-plane. Alternatively, the SPS setting may be used. The DRX setting or SPS setting of each eNB that has established the U-plane may be applied by the C-plane establishing eNB and notified to the UE and each eNB (cell) that has established the U-plane.

[0301] Also, the method disclosed in Embodiment 7 described later may be applied. In Embodiment 7, the master eNB sets the time of each slave eNB. However, the master eNB may be the C-plane establishing eNB, and each slave eNB may correspond to the eNB that has established only each U-plane.

[0302] As another method, it may be possible to set the data scheduling timing among the eNBs (cells) that have established each U-plane to be within the same period. The data scheduling and data transmission and reception of all eNBs that have established the U-plane are performed within the same period. To achieve this, the above-mentioned DRX setting or SPS setting may be used.

[0303] Alternatively, instead of all eNBs that have established the U-plane, they may be divided into a plurality of groups of eNBs that have established the U-plane, and the data scheduling timing may be set to be within the same period for each group of eNBs that have established the U-plane.

[0304] As a result, since the timing at which the UE transmits and receives is limited within a predetermined same period, power consumption of the UE can be reduced.

[0305] FIG. 30 is a diagram showing a sequence example according to Embodiment 2. It is a sequence example in the case where an RRC connection is established using one eNB and DRB / S1 bearers are established / modified using a plurality of eNBs. Processing in the P-GW and HSS is omitted.

[0306] The UE to be communicated with is in the RRC_Idle state at 3001. The UE performs service request processing at ST3002 via the C-eNB that establishes the RRC connection, between the MME and the S-GW. By this processing, a radio bearer 1 (3003) is established between the UE and the C-eNB, and an S1 bearer 1 (3004) is established between the C-eNB and the S-GW. Accordingly, an E-RAB is established between the UE and the S-GW. Using the established bearers, communication of U-plane data (user data) becomes possible between the UE and the C-eNB (ST3005) and between the C-eNB and the S-GW (ST3006).

[0307] The UE notifies the C-plane establishing eNB, i.e., the C-eNB, of a measurement report at ST3007. It is preferable to include an index for the MME to select the U-plane establishing eNB in the report.

[0308] The C-eNB that has received the measurement report from the UE notifies the MME of the information at ST3008. For example, when using communication quality information as an index, a new communication quality report message may be provided. The message may include the location information of the own UE.

[0309] The MME selects a U-plane establishing eNB for the UE to be communicated with at ST3009. The C-plane establishing eNB may be selected as the U-plane establishing eNB. It is preferable to use the index received at ST3008 for the selection.

[0310] The MME that selects the U-plane establishment eNB configures the E-RAB to be established for each U-plane establishment eNB in ST3010. Here, it is assumed that the C-plane establishment eNB also performs the establishment of the U-plane for the UE to be communicated with. Since the E-RAB has already been established for the C-eNB, the E-RAB configuration is modified. For the U-eNB, a new E-RAB configuration with the UE to be communicated with is performed.

[0311] In ST3011 and ST3012, the MME notifies each U-plane establishment eNB of an E-RAB configuration request message or an E-RAB modification request message including the E-RAB configuration information.

[0312] In ST3013, the C-eNB reconfigures the DRB for the UE to be communicated with using the E-RAB configuration modification information received from the MME.

[0313] In ST3014, the U-eNB performs the processes necessary for the establishment of the DRB / S1 bearer for the UE to be communicated with using the E-RAB configuration information received from the MME. Regarding the radio section, the DRB is configured.

[0314] The U-eNB that configured the DRB in ST3014 notifies the C-eNB of its own DRB configuration information, etc. in ST3015. In this example, a new U-plane connection configuration message is provided and notified as the message.

[0315] The C-eNB that has reset the DRB at ST3013 notifies the UE of DRB configuration information, etc. at ST3016. When receiving DRB configuration information, etc. from the U-eNB at ST3015, it notifies including the DRB configuration information, etc. of the U-plane establishment eNB at ST3016. It is preferable to notify by associating the DRB configuration information of each U-plane establishment eNB (cell), the identifier of each U-plane establishment eNB (cell), the system information of each U-plane establishment eNB (cell), and the ePDCCH configuration information. For the notification, use RRC signaling and an RRC message. Here, use the RRC connection reconfiguration message. This message may include information indicating that it is a U-plane establishment request.

[0316] When the UE that has received the RRC connection reconfiguration message at ST3016 finds information indicating that it is a U-plane establishment request in the message, it configures the DRB of each U-plane establishment eNB using the DRB configuration information of the U-plane establishment eNB in the message.

[0317] At ST3017, the UE starts the connection process with the newly established U-plane establishment eNB.

[0318] At ST3018, detect and synchronize with the U-eNB (cell). The identifier of the U-plane establishment eNB (cell) received at ST3016 may be used.

[0319] At ST3019, the UE notifies the U-eNB (cell) of the PRACH. The information regarding the PRACH in the system information of the U-plane establishment eNB (cell) received at ST3016 may be used.

[0320] With ST3020, the U-eNB (cell) notifies the UE of the TA (timing advanced) for uplink timing adjustment. Usually, since the distance between the C-eNB (cell) and the UE is different from the distance between the U-eNB (cell) and the UE, the propagation times are different. Therefore, the TA for the uplink timing adjustment of the C-eNB (cell) cannot be used for the uplink timing adjustment of the U-eNB (cell), and it is necessary to newly notify the UE from the U-eNB (cell) of the TA for the uplink timing adjustment of the U-eNB (cell).

[0321] Through the above processing, the UE completes the connection process with the U-plane establishment eNB.

[0322] The UE that has completed the connection process with the U-plane establishment eNB notifies the C-plane establishment eNB of the connection completion message at ST3021. Here, the RRC connection reconfiguration complete message is used.

[0323] At ST3021, the C-eNB that has received the connection completion message recognizes that the UE has performed the DRB setting process for its own eNB (cell). Also, it recognizes that the UE has completed the connection with another U-plane establishment eNB.

[0324] The C-eNB that has recognized that the UE has completed the connection with the U-plane establishment eNB notifies the U-eNB that has completed the connection with the UE of the connection completion message at ST3022. A new U-plane connection setting completion message is provided as the message.

[0325] The C-eNB performs the process of the modified DRB setting for the UE to be communicated with, and notifies the MME of the E-RAB modification completion message at ST3037.

[0326] Upon receiving the U-plane connection setup completion message at ST3022, the U-eNB performs the establishment process of the DRB / S1 bearer with the UE to be communicated with, and at ST3023, notifies the MME of the E-RAB setup completion message. This notification may use the UE context setup complete message.

[0327] At ST3037 and ST3023, upon receiving the E-RAB setup completion message or the E-RAB modification completion message from the U-plane establishment eNB including the C-eNB, the MME can recognize that the DRB / S1 bearer setting (modification) of each U-plane establishment eNB is completed.

[0328] Upon recognizing that the E-RAB setup of each U-plane establishment eNB is completed, the MME notifies, at ST3024, the S-GW of a message requesting the setting or modification of the S1 bearer. Here, the modify bearer request message is used.

[0329] Upon receiving the message requesting the setting or modification of the S1 bearer, the S-GW performs, at ST3025, the setting or modification of the S1 bearer between itself and each U-plane establishment eNB according to the information included in the message.

[0330] After performing the setting or modification of the S1 bearer, the S-GW notifies, at ST3026, the MME of the completion message of the setting or modification of the S1 bearer. Here, the modify bearer response message is used.

[0331] Through the above processing, DRB3027 is established between the UE and the U-plane establishment eNB, and S1 bearer3028 is established between the U-plane establishment eNB and the S-GW. As a result, data communication becomes possible between the UE and the U-eNB, and between the U-eNB and the S-GW.

[0332] In ST3029, if the PDCCH or ePDCCH of the U-plane establishment eNB is configured, the UE receives the ePDCCH.

[0333] In ST3030, the U-plane establishment eNB performs multiplexing and scheduling of user data for the UE to be communicated with, and in ST3031, maps the scheduling information to the PDCCH or ePDCCH and transmits it.

[0334] In ST3032, user data is transmitted and received between the UE and the U-eNB. The user data is mapped to the PDSCH or PUSCH and allocated to physical radio resources according to the scheduling information.

[0335] In ST3033, the U-eNB transmits and receives user data with the S-GW.

[0336] Through the above processing, a DRB / S1 bearer is established between the UE and the S-GW using a plurality of eNBs (C-eNB, U-eNB), and user data can be transmitted and received.

[0337] A method for deleting an eNB that has established only a U-plane with the UE to be communicated with is disclosed. In other words, a method for releasing the E-RAB established between the UE to be communicated with by the eNB to be deleted, or a method for releasing the DRB / S1 bearer established between the UE to be communicated with by the eNB to be deleted is disclosed.

[0338] In this embodiment, the MME selects the eNB to be deleted. As a selection criterion, it is advisable to apply the above-mentioned criterion when the MME selects the eNB for which a DRB / S1 bearer should be established for the UE to be communicated with. The MME selects the eNB to be deleted using this criterion. For example, among the U-plane establishment eNBs, if the communication quality between the UE to be communicated with and the U-plane establishment eNB (cell) deteriorates and falls below a predetermined threshold, it may be selected as the eNB to be deleted.

[0339] The MME configures the E-RABs for the UEs to be communicated with by the U-plane establishment eNBs excluding the eNB to be deleted. The MME notifies each of the U-plane establishment eNBs of the E-RAB configuration.

[0340] This notification may use the S1 E-RAB modification request message. For eNBs with no change in the E-RAB configuration after the MME performs E-RAB modification, it may not be necessary to notify them of the modified E-RAB.

[0341] The MME notifies the eNB to be deleted of the release indication of the E-RAB established between the MME and the UE to be communicated with. It is advisable to use S1 signaling for this notification. It is advisable to use the S1 UE context release indication message. The S1 E-RAB release indication message may also be used for the release of the E-RAB. It is advisable to include in the release indication message the configuration information of the E-RAB to be deleted and the UE identifier for identifying which UE's E-RAB is to be released.

[0342] The U-plane establishment eNB that has received the release indication of the E-RAB established between the eNB and the UE to be communicated with performs the DRB / S1 bearer release process established between the eNB and the UE to be communicated with in the eNB itself.

[0343] For each U-plane establishment eNB that has received the E-RAB establishment request message or the modification request message, it is advisable to apply the above-described process for establishing / modifying the E-RAB.

[0344] Disclose a method for the U-plane establishment eNB to release the DRB / S1 bearer established between the eNB and the UE to be communicated with in the eNB itself.

[0345] The U-plane establishment eNB that performs the release process of the DRB / S1 bearer notifies the UE of the DRB release information. It is advisable to notify the DRB release information with the identifier of the UE to be communicated with and information for identifying which U-plane establishment eNB's DRB is to be released, for example, the identifier of the U-plane establishment eNB (cell). Also, this message may include information indicating that it is a U-plane release request.

[0346] Two specific examples of notifying the UE of DRB release information and the like are disclosed. (1) Notify via the C-plane establishment eNB. (2) Notify via the MME and the C-plane establishment eNB.

[0347] A method of notifying via the C-plane establishment eNB in (1) is disclosed. The U-plane establishment eNB that performs the release process of the DRB / S1 bearer notifies the C-plane establishment eNB of the DRB release information and the like. For this notification, a new interface may be provided, or the X2 interface may be used. A new message may be provided for the notification.

[0348] The C-plane establishment eNB (cell) notifies the UE to be communicated with of the DRB release information and the like of the U-plane establishment eNB that performs the release of the DRB.

[0349] For the UE to be communicated with, a list may be provided that associates the DRB release information of the U-plane establishment eNB to be deleted with the respective DRB setting information of each U-plane establishment eNB for each U-plane establishment eNB. It may be included in the DRB list_U-plane. The C-plane establishment eNB may notify the UE of this list.

[0350] It is advisable to apply the method of notifying the UE of DRB setting information and the like to this notification method. It is advisable to include the DRB release information and information indicating that it is a U-plane release request.

[0351] (1)'s method does not go through the MME, so the signaling volume of the system can be reduced.

[0352] Disclose a method of notifying via the MME in (2) and the C-plane establishment eNB.

[0353] The U-plane establishment eNB that performs the release process of the DRB / S1 bearer notifies the MME of DRB release information etc. It is advisable to use the S1 interface for this notification.

[0354] The MME notifies the C-plane establishment eNB of DRB release information etc. A list may be provided including the U-plane establishment eNB that releases the DRB, the DRB release information, and each U-plane establishment eNB and its respective DRB settings. It may be included in the DRB list_U-plane. It is advisable to use the S1 interface for this notification. A new message may be provided for notification using the S1 interface.

[0355] The C-plane establishment eNB (cell) notifies the UE to be communicated with of the DRB release information etc. received from the MME. A list may be provided including each U-plane establishment eNB and its respective DRB settings. It may be included in the DRB list_U-plane. The C-plane establishment eNB (cell) may notify the UE of this list.

[0356] Regarding this notification method, the method in (1) can be applied. (2)'s method enables the DRB release information to be notified to the UE even when there is no interface between the C-plane establishment eNB and the U-plane establishment eNB.

[0357] By doing so, the UE to be communicated with can recognize the release of the DRB / S1 bearer established between the U-plane establishment eNBs to be deleted.

[0358] Upon receiving DRB release information or the like, the UE performs DRB setup release processing with the U-plane establishment eNB (cell) that releases the DRB, and performs connection termination processing with the U-plane establishment eNB (cell).

[0359] As connection termination processing, for example, synchronization processing with the U-plane establishment eNB and monitoring of PDCCH or ePDCCH for scheduling from the U-plane establishment eNB are terminated.

[0360] The UE that has performed DRB release processing and connection termination with the U-plane establishment eNB may notify the U-plane establishment eNB of a connection termination message. It is preferable to include in the message a UE identifier (UE-ID) that can be identified by the MME for the UE that is the communication target. Alternatively, it may be a mobile subscriber identity that can be identified by the MME. Also, the identifier of the own U-plane establishment eNB (cell) may be included. As a UE identifier that can be identified by the MME, it is preferable to use the UE identifier used within the MME. Alternatively, it may be the identifier of the C-plane establishment eNB (cell) of the UE and the UE identifier used within the C-plane establishment eNB (cell).

[0361] Three specific examples of the notification method are disclosed below. (1) Notify each U-plane establishment eNB to be deleted via the C-plane establishment eNB and the MME (2) Notify each U-plane establishment eNB to be deleted via the C-plane establishment eNB (3) Notify each U-plane establishment eNB to be deleted directly Regarding these methods, it is preferable to apply the method of notifying each U-plane establishment eNB of the above-mentioned connection completion message.

[0362] Each U-plane establishment eNB that has received the connection termination message performs release processing of the DRB / S1 bearer established with the UE that is the communication target.

[0363] The U-plane establishment eNB that has performed the release process of the DRB / S1 bearer may notify the MME of the completion of the release. It may also notify that the release of the DRB established between the UE and the U-plane establishment eNB has been completed. The S1 UE context release complete message may be used for this notification.

[0364] The MME requests the S-GW to release the S1 bearer for the U-plane establishment eNB to be deleted. The S11 interface may be used to notify this request. For example, it is advisable to use the modify bearer request message. The communication target UE identifier, the identifier of the U-plane establishment eNB to be deleted, and the E-RAB configuration information of the U-plane establishment eNB to be deleted may be included in the request message. The E-RAB list_U-plane, which is a list of the correspondence between each U-plane establishment eNB and the E-RAB configuration of each U-plane establishment eNB, may also be used. Also, the IP address set for each U-plane establishment eNB may be used as the identifier of each U-plane establishment eNB.

[0365] The S-GW releases the S1 bearer established between the notified deleted U-plane establishment eNB and the communication target UE.

[0366] The S-GW that has released the S1 bearer notifies the MME of the S1 bearer release completion message. The S11 interface may be used for this notification. It is advisable to use the S11 Modify bearer response message.

[0367] As a result, the DRB / S1 bearer established between the S-GW and the communication target UE using the U-plane establishment eNB to be deleted is released.

[0368] Regarding the data transmission method, except for the deleted eNB, the data transmission method disclosed in Embodiment 1 may be applied using a plurality of U-plane establishment eNBs in which DRB / S1 bearer is established with the target UE.

[0369] FIG. 31 is a diagram showing a sequence example when deleting a U-plane establishment eNB according to Embodiment 2. Since the sequence shown in FIG. 31 is similar to the sequence shown in FIG. 30, the same step numbers are assigned to the same steps, and the common description is omitted.

[0370] The MME that has received the communication quality report message from the C-eNB in ST3008 determines, in ST3101, to delete one or more of the established U-plane establishment eNBs. It may be performed in combination with the selection of other U-plane establishment eNBs.

[0371] The MME that has determined the U-plane establishment eNB to be deleted in ST3101 performs, in ST3010, each E-RAB setting of the U-plane establishment eNB excluding the U-plane establishment eNB to be deleted. At this time, the newly selected U-plane establishment eNB may be included. Here, the U-plane establishment eNB to be deleted is the U-eNB, and the U-plane establishment eNB excluding the U-plane establishment eNB to be deleted is the C-eNB.

[0372] The MME that has performed each E-RAB setting of the U-plane establishment eNB notifies the C-eNB of the E-RAB modification request message in ST3011, in the same manner as described in FIG. 30. Further, the C-eNB that has received the request message reconfigures the DRB for the UE to be communicated with.

[0373] On the other hand, the MME that has determined the U-plane establishment eNB to be deleted in ST3101 notifies the U-plane establishment eNB to be deleted of the E-RAB release instruction in ST3102. The U-eNB that receives the E-RAB release instruction at ST3102 performs the release process of the DRB / S1 bearer at ST3103. For the radio section, it performs the release process of the DRB.

[0374] The U-eNB that has performed the release process of the DRB / S1 bearer at ST3103 notifies the C-eNB of the release information of the DRB configuration at ST3104. It notifies by newly providing a U-plane connection reconfiguration message as the message.

[0375] The C-eNB that receives the DRB release information from the U-eNB at ST3104 notifies the UE of the DRB configuration information at ST3105.

[0376] When the C-eNB is performing the reconfiguration of the DRB, it may notify including the DRB configuration information. It is advisable to notify by associating the DRB release information of the U-plane establishment eNB (cell) to be deleted, the DRB configuration information of the U-plane establishment eNB (cell) to be set / modified, the identifier of each U-plane establishment eNB (cell), and the system information of each U-plane establishment eNB (cell). Here, the RRC connection reconfiguration message is used for the notification.

[0377] When the UE that receives the RRC connection reconfiguration message at ST3106 includes information indicating that it is a U-plane release request in the message, it releases the DRB configuration of the U-plane establishment eNB using the DRB release information of the U-plane establishment eNB to be deleted in the message.

[0378] At ST3106, the UE performs the connection termination process with the U-plane establishment eNB to be deleted.

[0379] The UE that has completed the connection termination process with the U-plane establishment eNB to be deleted notifies the C-plane establishment eNB of the completion of the connection termination process at ST3107. Here, the RRC connection reconfiguration complete message is used as this message.

[0380] Note that this message may include the DRB setting completion information of the U-plane establishment eNB (cell) to be set / modified. Here, information indicating that the setting of the modified DRB for the C-eNB has been completed may also be included.

[0381] At ST3107, the C-eNB that has received the connection termination process completion message recognizes that the UE has completed the connection termination process with the U-plane establishment eNB. It also recognizes that the UE has performed the DRB modification process for its own eNB (cell).

[0382] The C-eNB that recognizes that the UE has completed the connection termination process with the U-plane establishment eNB notifies the U-eNB of the connection termination process completion message at ST3108. It is advisable to include the identifier of the UE to be communicated with and the identifier of its own eNB (cell) in this message. This notification uses the X2 interface or a newly provided interface and notifies by newly setting U-plane connection reconfiguration complete as the message.

[0383] The C-eNB that recognizes that the UE has performed the DRB modification process for its own eNB (cell) notifies the MME of the E-RAB modification completion message at ST3116.

[0384] At ST3108, the U-eNB that has received the U-plane connection termination process completion message performs the release process of the DRB / S1 bearer and notifies the MME of the E-RAB release completion message at ST3109. The UE context release complete message may also be used for this notification.

[0385] When the MME receives an E-RAB modification completion message or an E-RAB release completion message from the U-plane establishment eNB including the C-eNB in ST3116 and ST3109, it can recognize that the E-RAB release and E-RAB modification of each U-plane establishment eNB have been completed.

[0386] When the MME recognizes that the E-RAB release of each U-plane establishment eNB has been completed, in ST3110, it notifies the S-GW of a message requesting the release of the S1 bearer. Here, the modify bearer request message is used.

[0387] When the S-GW receives a message requesting the release of the S1 bearer, in ST3111, it uses the information included in the message to release the S1 bearer between the U-plane establishment eNB to be deleted.

[0388] The S-GW that has released the S1 bearer notifies the MME of an S1 bearer release completion message in ST3112. Here, the modify bearer response message is used.

[0389] Through the above processing, the DRB between the UE and the U-plane establishment eNB is released, and the S1 bearer between the U-plane establishment eNB and the S-GW is released. As a result, the deletion process of the U-plane establishment eNB for the UE to be communicated with is completed.

[0390] From the above, the connection of the U-plane for the UE to be communicated with is performed by the radio bearer 1 (3003) between the UE and the C-eNB and the S1 bearer 1 (3004) between the C-eNB and the S-GW. In ST3005 and ST3006, user data is transmitted and received between the UE and the S-GW through the bearer.

[0391] Disclose other methods for deleting an eNB that has established only the U-plane with a UE to be communicated with. Disclose the case of using the above-mentioned indicator (7).

[0392] When the eNB that has established only the U-plane detects a timeout because there has been no data transmission in the radio section (Uu) with the UE to be communicated with for a long time, release the DRB / S1 bearer established with the UE to be communicated with.

[0393] FIG. 32 is a diagram showing another sequence example when deleting a U-plane establishment eNB according to Embodiment 2. Since the sequence shown in FIG. 32 is similar to the sequences shown in FIGS. 30 and 31, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0394] The eNB that has established the U-plane monitors data transmission in the radio section (Uu) with the UE to be communicated with at ST3202. When it detects that there has been no data transmission for a long time and a data timeout (expiration of the data monitor timer) occurs, it releases the DRB / S1 bearer established with the UE to be communicated with.

[0395] The U-plane establishment eNB that monitors data transmission in the radio section with the UE to be communicated with and detects a data timeout notifies the MME of a request message for releasing the E-RAB established by the own eNB with the UE to be communicated with at ST3203. It is preferable to use S1 signaling for this notification. The request message may include, as reasons, that the data monitor timer has expired, the identifier of the UE that detected the data timeout, and the identifier of the own eNB.

[0396] At ST3203, the MME that has received the E-RAB release request message determines the eNB that notified it as the eNB to be deleted.

[0397] In ST3010, the MME configures the E-RABs for the UEs to be communicated with by the U-plane establishment eNBs excluding the eNB to be deleted.

[0398] Also, the MME notifies the eNB to be deleted of the release instruction for the E-RABs established between the eNB and the UEs to be communicated with. For the subsequent processing, it is advisable to perform ST3113 shown in FIG. 31.

[0399] In FIG. 31, the UE is to perform the connection termination process with the U-plane establishment eNB to be deleted upon receiving ST3105. By doing so, it is possible to avoid the misoperation due to the difference in judgment with the U-plane establishment eNB.

[0400] Not limited to this, as another method, when the UE detects a data timeout in ST3201, the UE may perform the connection termination process with the U-plane establishment eNB to be deleted. As a result, the UE can perform the connection termination process with the U-plane establishment eNB at an earlier stage, eliminating the need to perform the communication maintenance process with the unnecessary U-plane establishment eNB, such as the synchronization process and the monitoring of the PDCCH or ePDCCH for scheduling, and enabling power consumption reduction of the UE.

[0401] Another method for deleting the eNB that has established only the U-plane with the UE to be communicated with is disclosed.

[0402] The UE monitors the radio communication intervals (RLM: Radio Link Monitor) with each U-plane establishment eNB (cell).

[0403] The UE receives the RS of each U-plane establishment cell and uses the reception result of the RS to determine the deterioration of the reception quality of the radio communication interval. Five specific examples of the RS are shown below. (1) Tracking RS (2) Demodulation RS (3) CRS (4) UE-specific RS (5) Combinations of (1) to (4) Also, instead of RS, a signal equivalent to RS may be used.

[0404] When the reception quality of a wireless communication section of a UE falls below a predetermined threshold for a predetermined period, the UE determines that the reception quality has deteriorated. Alternatively, when the reception quality of a wireless communication section falls below a predetermined threshold for a predetermined period, it is preferable to reconnect to the U-plane establishment eNB (cell) again. Detection, synchronization, PRACH transmission, and TA reception of the U-plane establishment eNB (cell) are performed. A maximum value is set for the number of reconnection attempts, and when connection cannot be established even after reconnection up to the maximum value, it may be determined that the reception quality has deteriorated.

[0405] A UE that has determined that the reception quality has deteriorated notifies the C-plane establishment eNB that the reception quality of the wireless communication section has deteriorated. It is preferable to include an identifier of the U-plane establishment eNB in the notification so that it can be known which U-plane establishment eNB's wireless communication section has deteriorated reception quality.

[0406] The C-plane establishment eNB (cell) that has received the deterioration information from the UE notifies the MME of a radio link disconnection request message for the U-plane establishment eNB with deteriorated reception quality. As the radio link disconnection request message, the above-described E-RAB release request message may be used. It is preferable to use S1 signaling for the notification. It is preferable to include an identifier of the U-plane establishment eNB with deteriorated reception quality and the UE to be communicated with in the request message.

[0407] The MME that has received the request message selects an eNB that deletes the notified U-plane establishment eNB.

[0408] The MME configures the E-RABs for the UEs to be communicated with by the U-plane establishment eNBs excluding the eNB to be deleted. The MME notifies each of the U-plane establishment eNBs of the E-RAB configuration. Further, the MME notifies the eNB to be deleted of the release instruction for the E-RABs established between the MME and the UEs to be communicated with. The subsequent processing may apply the method disclosed above.

[0409] Note that the UE may perform RLM and terminate communication with the U-plane establishment eNB whose reception quality has deteriorated when it determines that the reception quality of the radio communication section has deteriorated. For example, the UE may terminate synchronization processing with the U-plane establishment eNB, or monitoring of PDCCH or ePDCCH for scheduling from the U-plane establishment eNB.

[0410] When only the U-plane establishment eNB is deleted, etc., there may be a timing deviation between the connection termination process between the UE and the U-plane establishment eNB and the switching of the S1 bearer path between the S-GWs.

[0411] For example, in the sequence example of deleting only the U-plane establishment eNB shown in FIG. 31, at ST3106, the UE performs the connection termination process with the U-eNB. From this timing, the UE can no longer receive downlink user data from the U-eNB. However, at this timing, the deletion / modification process of the S1 bearer path at the S-GW of ST3111 is not performed. That is, the user data is transmitted to the original path, i.e., the U-eNB. Therefore, the handling of the downlink user data transmitted to the U-eNB between the connection termination process of the UE with the U-eNB and the deletion / modification process of the S1 bearer path at the S-GW becomes unclear.

[0412] Here, two methods for solving this problem are disclosed below. (1) Discard it. (2) Transfer user data between the U-plane establishment eNBs.

[0413] (1) discards the user data sent to the U-plane establishment eNB to be deleted from the S-GW. Since no special control is performed for this process, there is no control delay, and it becomes possible to speed up the switching control of the S1 bearer path.

[0414] (2) transfers the user data sent to the U-plane establishment eNB to be deleted from the S-GW to the U-plane establishment eNB that does not perform deletion. It is advisable to perform transfer settings between the U-plane establishment eNBs. Transfer settings may also be performed via the C-plane establishment eNB. This enables the transfer of user data and makes it possible to speed up the switching control of the S1 bearer path without loss of user data.

[0415] FIG. 33 is a diagram showing a sequence example when data transfer is performed between U-plane establishment eNBs according to Embodiment 2. Data transfer is performed between the U-eNB and the C-eNB. Since the sequence shown in FIG. 33 is similar to the sequence shown in FIG. 31, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0416] The U-eNB that performed the DRB release setting in ST3103 buffers the downlink user data from the S-GW received in ST3301 in ST3302.

[0417] Also, the U-eNB that performed the DRB release setting in ST3103 performs transfer settings for user data with the C-eNB in ST3303.

[0418] Here, there may be a case where the C-eNB has not established a U-plane connection. The U-plane establishment eNB to be deleted may be configured to transfer user data with the U-plane establishment eNB that is not to be deleted. It is preferable that the identifier of the eNB that has established the U-plane connection is notified by the MME. For example, a list of the correspondence between each U-plane establishment eNB and the E-RAB configuration of each U-plane establishment eNB may be provided, and the MME may notify the U-plane establishment eNB to be deleted of the list. The U-plane establishment eNB to be deleted can also recognize the E-RAB configuration of other U-plane establishment eNBs.

[0419] After the transfer of user data is configured between the U-eNB and the C-eNB in ST3303, the U-eNB may transfer the user data from the S-GW to the C-eNB in ST3304. The C-eNB that has received the user data transmits the user data to the UE through the U-plane connection bearer of its own eNB (cell).

[0420] The process of ST3304 may be performed after ST3108. The U-eNB transfers the user data after recognizing the completion of the connection termination process at the UE. This can avoid the operation of transferring user data when the connection has not yet been terminated.

[0421] Also, when all the user data received from the S-GW has been transferred, it may be considered that the transfer of the user data is completed. The transfer configuration between the C-eNBs may be released.

[0422] By doing so, even if there is a timing deviation between the connection termination process between the UE and the U-plane establishment eNB and the switching of the S1 bearer path between the S-GWs, the downlink user data can be reliably processed, and malfunctions of the system can be eliminated.

[0423] When there is only one U-plane establishment cell (eNB), if no measures are taken when changing the U-plane establishment cell (eNB), the U-plane connection to the UE to be communicated with may be disconnected. For example, this occurs when the deletion process of the original U-plane establishment cell (eNB) is performed first and then the setting process of the new U-plane establishment cell (eNB) is carried out. When the U-plane connection is disconnected, the communication of user data stops, which is inconvenient for users. To solve such problems, the above-described method for transferring user data may be applied. Buffer the user data in the original U-plane establishment eNB, and after the eNB for the new U-plane connection is established, perform the transfer setting of the user data between the original U-plane establishment eNB and the new U-plane establishment eNB. Then, the user data may be transferred from the original U-plane establishment eNB to the new U-plane establishment eNB. By doing so, it is possible to avoid the stop of the communication of user data. Also, this method is effective when the UE has the ability to connect to only one U-plane establishment eNB.

[0424] When the UE has the ability to connect to multiple U-plane establishment cells (eNBs), as another method, after establishing the eNB (cell) for the new U-plane connection for the UE to be communicated with, the deletion process of the original U-plane establishment cell (eNB) may be performed. As a result, the UE to be communicated with will be connected to multiple U-plane establishment eNBs (cells), but the U-plane connection will not be disconnected, and it is possible to avoid the stop of the communication of user data.

[0425] In this method, the connection of the U-plane may be routed through the C-plane establishment eNB (cell) once. For the UE to be communicated with, the connection of the U-plane is established through the C-plane establishment eNB (cell) once. After the deletion process of the original U-plane establishment eNB (cell) is performed, the setting process of the new U-plane establishment eNB (cell) is performed. After the process is completed, the connection of the U-plane in the C-plane establishment cell (eNB) may be terminated. The same effect can be obtained. Also, by routing through the C-plane establishment cell, the selection of the new U-plane establishment eNB (cell) becomes unnecessary, and it becomes possible to change the connection of the U-plane to the C-plane establishment eNB (cell) with low latency. Therefore, when it takes time to select a new U-plane establishment cell, it is possible to reduce the deterioration and stop of communication, which is effective.

[0426] By adopting the method disclosed in this embodiment, packet data communication can be performed for the UE to be communicated with using a plurality of eNBs, so that the communication capacity of the UE can be increased.

[0427] Also, even when small cells are used, it is possible to use a plurality of eNBs, improve the frequency utilization efficiency, and increase the communication capacity as a system.

[0428] Also, the control process for establishing a plurality of RRC connections becomes unnecessary, the control process can be facilitated, and the signaling amount and the control delay amount can be reduced.

[0429] Also, since the RRC function of the U-plane establishment eNB can be limited, for example, when configuring a dedicated eNB for U-plane establishment, it can be configured more simply than a conventional eNB.

[0430] Regarding the mobility control of the UE, since no control processing is required for establishing a plurality of RRC connections, if it is within the coverage of the C-plane establishment eNB (cell), only the change (establishment / modification / deletion) of the U-plane establishment eNB is sufficient, so that low latency and high speed of the control processing can be achieved. For example, when the C-plane establishment eNB (cell) is a coverage cell and the U-plane establishment eNB (cell) is a capacity cell, etc., HO control does not need to be performed between the capacity cells, and only the change (establishment / modification / deletion) of the U-plane establishment eNB is sufficient.

[0431] Embodiment 2 Modification Example 1. In the conventional method, the control information for the UE to be communicated with is transmitted and received between the MME and one C-plane establishment eNB that has an RRC connection with the UE. However, in the case of the method disclosed in Embodiment 2, the control information for the UE to be communicated with is directly transmitted and received between the MME and each U-plane establishment eNB. Therefore, the control processing for the UE to be communicated with in the MME becomes more complicated than before.

[0432] Therefore, in Modification Example 1 of Embodiment 2, a method of performing signaling via the C-plane establishment eNB is disclosed.

[0433] For one communication, a C-plane connection is established using one eNB (cell), and a U-plane connection is established using a plurality of eNBs (cells). The signaling between the MME and the U-plane establishment eNB is performed via the C-plane establishment eNB.

[0434] Since the signaling between the MME and the U-plane establishment eNB is performed via the C-plane establishment eNB, the MME notifies the C-plane establishment eNB of the UE to be communicated with of the signaling transfer request to each U-plane establishment eNB of the UE to be communicated with. It is advisable to include the identifier (UE-ID) of the UE to be communicated with in the signaling transfer request message. Also, it is advisable to include the identifier or address of each U-plane establishment eNB (cell) to be transferred to in order to identify each U-plane establishment eNB (cell) to be transferred to.

[0435] The C-plane establishment eNB that has received the signaling transfer request performs transfer processing on the signaling for the UE to be communicated with, and transfers the signaling from the MME to each U-plane establishment eNB and the signaling from each U-plane establishment eNB to the MME.

[0436] It is advisable to notify the signaling transfer request before the MME notifies each U-plane establishment eNB of the E-RAB setting of each U-plane establishment eNB. Alternatively, it may be notified together with the MME notifying each U-plane establishment eNB of the E-RAB setting of each U-plane establishment eNB. It may also be notified by including it in the signaling in which the MME notifies each U-plane establishment eNB of the E-RAB setting of each U-plane establishment eNB.

[0437] By the method disclosed in this modification example, the signaling between the MME and the U-plane establishment eNB for the UE to be communicated with can be performed via the C-plane establishment eNB.

[0438] FIG. 34 is a diagram showing the architecture according to Modification Example 1 of Embodiment 2. Since the architecture shown in FIG. 34 is similar to the architecture shown in FIG. 28, the same elements are given the same numbers and the common description is omitted.

[0439] The figure shows the architecture when an eNB dedicated to U-plane establishment is configured. Also, this architecture may be the architecture shown only for the UE to be communicated with in this modification example.

[0440] 3401 is the S1 interface established between the C-eNB and the U-eNB. The C-eNB 2804 has a function of transferring the signaling from the MME 2803 to each U-plane establishment eNB 2805 for the signaling to the UE 2806 to be communicated with, and transferring the signaling from each U-plane establishment eNB 2805 to the MME 2803.

[0441] Also, due to the architecture when an eNB dedicated to U-plane establishment is configured, it becomes possible to eliminate the interface 2815 directly connecting between the MME 2803 and the U-eNB 2805 shown in FIG. 28. This is because in this modification example, the signaling between the MME and the U-plane establishment eNB is performed via the C-plane establishment eNB.

[0442] In addition, when there is a UE having a U-eNB and a C-plane connection instead of the case where an eNB dedicated to U-plane establishment is configured, it is advisable to provide an interface 2815 directly connecting between the MME and the U-eNB.

[0443] Here, the UE (2806) corresponds to a mobile station, the C-eNB (2804) corresponds to a first base station, the U-eNB (2805) corresponds to a second base station, and the MME (2803) and S-GW (2802) correspond to a gateway station, respectively. Also, regarding the C-plane signal, the RRC Connection between the UE (2806) and the C-eNB (2804) corresponds to a first radio communication connection. Similarly, regarding the C-plane signal, the S1-MME signaling connection (2809) between the MME (2803) and the C-eNB (2804) corresponds to a first communication connection. Also, regarding the U-plane signal, the Radio Bearer between the UE (2806) and the C-eNB (2804) corresponds to a first radio communication connection, and the Radio Bearer between the UE (2806) and the U-eNB (2805) corresponds to a second radio communication connection, respectively. Similarly, regarding the U-plane signal, the S1 bearer (2814) between the S-GW (2802) and the C-eNB (2804) corresponds to a first communication connection, and the S1 bearer (2813) between the S-GW (2802) and the U-eNB (2805) corresponds to a second communication connection, respectively.

[0444] In this way, by establishing a first communication connection between the gateway station and the first base station, a second communication connection between the gateway station and the second base station, a first radio communication connection between the first base station and the mobile station, and a second radio communication connection between the second base station and the mobile station, respectively, one communication is executed between the mobile station and the gateway station, so that cell migration can be realized by adding or deleting communication connections and radio communication connections.

[0445] The U-plane signal is distributed and transmitted to a first path including a first communication connection and a first radio communication connection and a second path including a second communication connection and a second radio communication connection. The C-plane signal is distributed and transmitted to a first path including a first communication connection and a first radio communication connection and a second path including a first communication connection and a second radio communication connection.

[0446] Each U-plane establishment eNB 2805 terminates the S1 interfaces (S1-MME) 2809 and 3401, and it is also possible that the C-plane establishment eNB 2804 provides the S1 proxy function between the MME 2803 and each U-plane establishment eNB 2805. The S1 proxy function transfers the S1 signaling messages of the UE 2806 to be communicated. With this S1 proxy function, the MME 2803 can make the C-plane establishment eNB 2804 appear to each U-plane establishment eNB 2805, and each U-plane establishment eNB 2805 can make the C-plane establishment eNB 2804 appear to the MME 2803.

[0447] FIG. 35 is a diagram showing a sequence example according to Modification Example 1 of Embodiment 2. Since the sequence shown in FIG. 35 is similar to the sequence shown in FIG. 30, the same step numbers are assigned to the same steps, and the common description is omitted.

[0448] The MME that has selected the U-plane establishment eNB performs the setting of the E-RAB to be established with each U-plane establishment eNB at ST3010.

[0449] The MME performs a transfer setting request for S1 signaling to the C-plane establishment eNB (C-eNB) at ST3501. Here, it is a S1-MME proxy setting request. The C-eNB that has received the request notification performs the setting for the transfer process of the S1 signaling for the UE to be communicated between the transfer destination U-plane establishment eNB and the MME at ST3502. Thereby, the S1 message between the U-eNB and the MME is transferred via the C-eNB.

[0450] The C-eNB that has performed the transfer process settings using ST3502 may notify the MME of a message indicating the completion of the transfer process settings. The MME can be explicitly confirmed, reducing malfunction. Here, the case where there is no such message is shown. The MME notifies an E-RAB modification request message using ST3011. Also, in ST3503, the E-RAB setting request message for the U-plane establishment eNB is notified to the C-eNB by the U-plane establishment eNB. The identifier or address of the transfer destination U-plane establishment eNB may be added to or included in the request message. Assume that an S1 message is used for the request message. The C-eNB that has received the request message transfers the request message to the U-plane establishment eNB (U-eNB) in ST3504 using the transfer settings of ST3502 and the identifier or address of the transfer destination U-plane establishment eNB. As a result, the U-plane establishment eNB (U-eNB) can receive the E-RAB setting from the MME.

[0451] After this, each node performs the process of ST3035. The U-eNB that has received the U-plane connection process completion notification from the C-eNB in ST3022 performs the E-RAB setting process and notifies the MME of the E-RAB setting completion message via the C-eNB in ST3505 and ST3506. Assume that an S1 message is used. Since the transfer setting process is performed for the message to the UE, the C-eNB transfers the message received from the U-eNB in ST3505 to the MME in ST3506.

[0452] After this, the processes of ST3024 to ST3026 and ST3036 are performed.

[0453] Through the above processes, a DRB / S1 bearer is established between the UE and the S-GW using multiple eNBs (C-eNB, U-eNB), enabling the transmission and reception of user data.

[0454] By adopting the method disclosed in this modification example, it is possible to prevent control information for a UE to be communicated from being directly transmitted and received between the MME and each U-plane establishment eNB. Therefore, it is possible to suppress the complication of the control process for the UE to be communicated in the MME.

[0455] Also, when configuring an eNB dedicated to U-plane establishment, since all signaling between the MME and the U-plane establishment eNB can be performed via the C-plane establishment eNB, the IF between the MME and the U-plane establishment eNB can be eliminated. Therefore, the system configuration can be simplified. For example, it is suitable to apply when configuring a macro eNB and a node dedicated to U-plane establishment directly connected to the macro eNB.

[0456] Embodiment 2 Modification Example 2. In the conventional method, packet data for a UE to be communicated is transmitted and received between the S-GW and one C-plane establishment eNB that has an RRC connection with the UE. However, in the case of the method disclosed in Embodiment 2 or Modification Example 1 of Embodiment 2, the communication of packet data for the UE to be communicated is directly performed between the S-GW and each U-plane establishment eNB. Therefore, the control process for the UE to be communicated in the S-GW becomes more complicated than before.

[0457] Therefore, in Modification Example 2 of Embodiment 2, a method of performing packet data communication via the C-plane establishment eNB is disclosed.

[0458] For one communication, establish a C-plane connection using one eNB (cell), and establish a U-plane connection using a plurality of eNBs (cells). Data communication between the S-GW and each U-plane establishment eNB is performed via the C-plane establishment eNB.

[0459] In order to perform packet data communication between the S-GW and the U-plane establishment eNB via the C-plane establishment eNB, the MME notifies the C-plane establishment eNB of the UE to be communicated with of the packet data transfer request to each U-plane establishment eNB of the UE to be communicated with.

[0460] It is preferable to include the identifier (UE-ID) of the UE to be communicated with in the packet data transfer request message. Also, it is preferable to include the identifier or address of each U-plane establishment eNB (cell) serving as the transfer destination in order to identify each U-plane establishment eNB (cell) serving as the transfer destination.

[0461] Upon receiving the packet data transfer request, the C-plane establishment eNB transfers the packet data from the S-GW to each U-plane establishment eNB and the packet data from each U-plane establishment eNB to the S-GW for the packet data of the UE to be communicated with.

[0462] It is preferable to notify the packet data transfer request before the MME notifies each U-plane establishment eNB of the E-RAB setting of each U-plane establishment eNB. Alternatively, it may be notified together with the MME notifying each U-plane establishment eNB of the E-RAB setting of each U-plane establishment eNB. It may also be notified included in the signaling in which the MME notifies each U-plane establishment eNB of the E-RAB setting of each U-plane establishment eNB.

[0463] Also, the MME requests the S-GW to perform packet data communication with each U-plane establishment eNB via the C-plane establishment eNB for the UE to be communicated with. The MME requests the S-GW to set up an S1 bearer with each U-plane establishment eNB via the C-plane establishment eNB.

[0464] The S-GW that has received the C-plane establishment eNB via request transmits the packet data from the S-GW to each U-plane establishment eNB via the C-plane establishment eNB for the packet data for the UE to be communicated, and receives the packet data from each U-plane establishment eNB via the C-plane establishment eNB.

[0465] By the method disclosed in this modification example, the communication of the packet data between the S-GW and the U-plane establishment eNB for the UE to be communicated can be performed via the C-plane establishment eNB.

[0466] FIG. 36 is a diagram showing an architecture according to Modification Example 2 of Embodiment 2. Since the architecture shown in FIG. 36 is similar to the architecture shown in FIG. 28, the same elements are denoted by the same numbers and the common description is omitted.

[0467] The figure shows an architecture in the case of configuring an eNB dedicated to U-plane establishment. Further, this architecture may be an architecture shown only for the UE to be communicated in this modification example.

[0468] 3601 is an S1 interface established between the C-eNB and the U-eNB.

[0469] The C-eNB 2812 has a function of transferring the packet data from the S-GW 2802 to each U-plane establishment eNB 2805 and the packet data from each U-plane establishment eNB 2805 to the S-GW 2802 for the packet data for the UE 2806 to be communicated.

[0470] Further, due to the architecture in the case of configuring an eNB dedicated to U-plane establishment, it is possible to eliminate the interface 2813 directly connecting between the S-GW 2802 and the U-eNB 2805 shown in FIG. 28. This is because in this modification example, the packet data communication between the S-GW and the U-plane establishment eNB is performed via the C-plane establishment eNB.

[0471] In addition, when there is a UE having a connection to the C-plane with the U-eNB instead of configuring an eNB dedicated to establishing the U-plane, it is advisable to provide an interface 2813 for directly connecting between the S-GW and the U-eNB.

[0472] Here, the UE (2806) corresponds to a mobile station, the C-eNB (2804) corresponds to a first base station, the U-eNB (2805) corresponds to a second base station, and the MME (2803) and the S-GW (2802) correspond to a gateway station. Also, regarding the C-plane signal, the RRC Connection between the UE (2806) and the C-eNB (2804) corresponds to a first radio communication connection. Similarly, regarding the C-plane signal, the S1-MME signaling connection (2809) between the MME (2803) and the C-eNB (2804) corresponds to a first communication connection, and the S1-MME signaling connection (2815) between the MME (2803) and the U-eNB (2805) corresponds to a second communication connection. Also, regarding the U-plane signal, the Radio Bearer between the UE (2806) and the C-eNB (2804) corresponds to a first radio communication connection, and the Radio Bearer between the UE (2806) and the U-eNB (2805) corresponds to a second radio communication connection. Similarly, regarding the U-plane signal, the S1 bearer (2814) between the S-GW (2802) and the C-eNB (2804) corresponds to a first communication connection.

[0473]

[0474] ​The U-plane signal is distributed and transmitted to a first path including a first communication connection and a first wireless communication connection and a second path including a first communication connection and a second wireless communication connection. The C-plane signal is distributed and transmitted to a first path including a first communication connection and a first wireless communication connection and a second path including a second communication connection and a second wireless communication connection.

[0475] Each U-plane establishment eNB 2805 may terminate the S1 interface (S1-U) 2814, 3601, and the C-plane establishment eNB 2804 may provide an S1 proxy function between the S-GW 2802 and each U-plane establishment eNB 2805. The S1 proxy function transfers the packet data of the UE 2806 to be communicated. With this S1 proxy function, the S-GW 2802 appears to the C-plane establishment eNB 2804 as each U-plane establishment eNB 2805, and each U-plane establishment eNB 2805 appears to the C-plane establishment eNB 2804 as the S-GW 2802.

[0476] FIG. 37 is a diagram showing a sequence example according to Modification Example 2 of Embodiment 2. Since the sequence shown in FIG. 37 is similar to the sequences shown in FIGS. 30 and 35, the same step numbers are assigned to the same steps, and the common description is omitted.

[0477] The MME that has selected the U-plane establishment eNB performs the setting of the E-RAB to be established with each U-plane establishment eNB in ST3010.

[0478] In ST3701, the MME makes a transfer request for user data to the C-plane establishment eNB (C-eNB). Here, it is set as an S1-U proxy setting request. Also, here, together with the request for user data, a transfer setting request for S1 signaling is made. It is preferable to include the identifier of the UE to be communicated and the identifier of the transfer destination U-plane establishment eNB (U-eNB) in the request notification.

[0479] Upon receiving the request notification, the C-eNB performs, in ST3502, the settings for the transfer process of S1 signaling for the UE to be communicated with between the U-plane establishment eNB at the transfer destination and the MME. As a result, the S1 message between the U-eNB and the MME is transferred via the C-eNB.

[0480] Also, in ST3702, the C-eNB performs the settings for the transfer process of user data for the UE to be communicated with between the U-plane establishment eNB at the transfer destination and the S-GW. As a result, the S1 user data between the U-eNB and the S-GW is transferred via the C-eNB.

[0481] The C-eNB that has performed the settings for the transfer process of S1 signaling and S1 user data in ST3502 and ST3702 may notify the MME of a message indicating the completion of the transfer process settings. The MME can be explicitly confirmed and malfunctions can be reduced. Here, the case where there is no such message is shown as in FIG. 35.

[0482] After that, each node performs the processes from ST3011 to ST3506. Since these processes are shown in FIGS. 30 and 35, the description is omitted.

[0483] Upon recognizing that the E-RAB setting of each U-plane establishment eNB is completed, the MME notifies, in ST3703, the S-GW of a message requesting the setting or modification of the S1 bearer. At this time, it is requested to set the path of the S1 bearer via the C-plane establishment eNB. In this message, in addition to the identifier of the UE to be communicated with, the identifier of each U-plnae establishment eNB, the E-RAB setting information of each U-plane establishment eNB, it is advisable to include the identifier of the C-plane establishment eNB that performs the transfer. It is advisable to use the S11 interface for this notification. The Modify bearer request message of S11 may also be used.

[0484] Upon receiving a message requesting the setup or modification of an S1 bearer via the C-plane established eNB, the S-GW performs, in ST3704, the setup or modification of the S1 bearer between each U-plane established eNB and the C-plane established eNB according to the information contained in the message.

[0485] The S-GW that has performed the setup or modification of the S1 bearer notifies, in ST3705, the MME of the completion message of the setup or modification of the S1 bearer. It is advisable to use the S11 interface for this notification. The Modify bearer response message of S11 may also be used.

[0486] Through the above processing, DRB3027 is established between the UE and the U-plane established eNB, and S1 bearer3706 is established between the U-plane established eNB and the S-GW via the C-eNB. As a result, data communication becomes possible between the UE and the U-eNB, and between the U-eNB and the S-GW.

[0487] After that, in the UE and the U-plane established eNB, the processes of ST3029, ST3030, and ST3031 are performed.

[0488] In ST3707 and ST3708, user data is transmitted and received between the U-eNB and the S-GW via the C-eNB. At this time, it is advisable to transmit data in packet units to the C-plane established eNBs. Information (such as an identifier or an address) for identifying the destination S-GW or U-plane established eNB to which the C-plane established eNB transfers may be added to the packet. This enables easy identification of each packet in the case where there are multiple destinations.

[0489] In ST3032, user data is transmitted and received between the UE or the U-eNB.

[0490] Through the above processing, a DRB / S1 bearer is established between the UE and the S-GW using a plurality of eNBs (C-eNB, U-eNB), enabling the transmission and reception of user data.

[0491] By adopting the method disclosed in this modification example, it is possible to prevent packet data for the UE to be communicated from being directly transmitted and received between the S-GW and each U-plane establishment eNB. Therefore, it is possible to suppress the complication of the packet data transmission and reception processing for the UE to be communicated at the S-GW.

[0492] Also, when configuring an eNB dedicated to U-plane establishment, since all packet data communications between the S-GW and the U-plane establishment eNB can be performed via the C-plane establishment eNB, the IF between the S-GW and the U-plane establishment eNB can be eliminated. Therefore, the system configuration can be simplified. For example, it is suitable to apply when configuring a macro eNB and a node dedicated to U-plane establishment directly connected to the macro eNB.

[0493] Embodiment 2 Modification Example 3. In Embodiment 2, the case where the MME selects an eNB for which a DRB / S1 bearer should be established for the UE to be communicated was disclosed. In this modification example, as another method, the C-plane establishment eNB selects an eNB for which a DRB / S1 bearer should be established for the UE to be communicated. It is advisable to apply the indicators disclosed in Embodiment 2 as the indicators for selection.

[0494] A method for the C-plane establishment eNB to recognize the indicators when selecting an eNB for which a DRB / S1 bearer should be established with the UE to be communicated will be disclosed.

[0495] When using information measured by the UE (also referred to as UE supported information) as an indicator, the information is notified from the UE to the C-plane establishment eNB. It is advisable to apply the method disclosed in Embodiment 2 as the notification method.

[0496] When using information measured or obtained by a node on the network side as an indicator, each node notifies the C-plane establishment eNB of the information. If the node on the network side is the C-plane establishment eNB, notification is not required. Similar to the above method, it is advisable to include information that can identify which UE's information and which eNB's information.

[0497] The C-plane establishment eNB that receives the information selects the eNB that should establish the DRB / S1 bearer for the UE to be communicated with.

[0498] The C-plane establishment eNB notifies the MME of a message requesting the establishment of an E-RAB using the selected eNB (U-plane establishment eNB). It is advisable to include in the request message the UE identifier (UE-ID) that the MME can identify for the UE to be communicated with. Alternatively, it can also be a mobile subscriber identity that the MME can identify. Also, the identifier of its own C-plane establishment eNB (cell) can be included. As the UE identifier that the MME can identify, it is advisable to use the UE identifier used within the MME. Alternatively, it can also be the identifier of the C-plane establishment eNB (cell) of the UE and the UE identifier used within the C-plane establishment eNB (cell). It is advisable to use S1 signaling for this notification. A new message can also be provided.

[0499] The MME configures the E-RABs at each selected U-plane establishment eNB for the UE to be communicated with, notified by the C-plane establishment eNB for E-RAB establishment.

[0500] The architecture in this modification example can apply the architecture of FIG. 28 disclosed in Embodiment 2.

[0501] FIG. 38 is a diagram showing a sequence example in the case of establishing / modifying a DRB / S1 bearer using a plurality of eNBs according to Modification Example 3 of Embodiment 2. Since the sequence shown in FIG. 38 is similar to the sequence shown in FIG. 30, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0502] In ST3034, Radio Bearer 1 is established between the UE and the C-eNB, and S1 bearer 1 is established between the C-eNB and the S-GW.

[0503] The UE notifies the C-plane establishment eNB, which is the C-eNB, of the measurement report in ST3801. Regarding this, the method disclosed in Embodiment 2 can be applied.

[0504] The C-eNB that has received the measurement report selects, in ST3802, the eNB for which a DRB / S1 bearer is to be established for the UE to be communicated with.

[0505] The C-plane establishment eNB notifies, in ST3803, the MME of a message requesting the establishment of an E-RAB using the selected eNB (U-plane establishment eNB). In this example, S1 signaling is used for this notification, and an E-RAB setup request message is provided as a new message.

[0506] The MME configures, in ST3010, the E-RABs in each selected U-plane establishment eNB for the UE to be communicated with, which has been notified from the C-plane establishment eNB for E-RAB establishment.

[0507] Since the subsequent processing can apply the method disclosed in the sequence example of FIG. 30, the description is omitted.

[0508] Through the above processing, a DRB / S1 bearer is established between the UE and the S-GW using a plurality of eNBs (C-eNB, U-eNB), and user data can be transmitted and received.

[0509] FIG. 39 is a diagram showing a sequence example when deleting a U-plane establishment eNB according to Modification Example 3 of Embodiment 2. Since the sequence shown in FIG. 39 is similar to the sequence shown in FIG. 31, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0510] In ST3113, Radio Bearer 1 is established between the UE and the C-eNB, and S1 bearer1 is established between the C-eNB and the S-GW. Also, Radio Bearer 2 (DRB) is established between the UE and the U-eNB, and S1 bearer2 is established between the U-eNB and the S-GW.

[0511] The UE notifies the measurement report to the C-eNB which is the C-plane establishment eNB in ST3901. Regarding this, the method disclosed in Embodiment 2 can be applied.

[0512] The C-eNB that has received the measurement report determines, in ST3902, the U-plane establishment eNB for which the DRB / S1 bearer should be released for the UE to be communicated with. The determination method can be applied to the method disclosed in Embodiment 2 for determining the U-plane establishment eNB to be deleted by the MME.

[0513] The C-plane establishment eNB notifies, in ST3903, the MME of a message requesting the release of the E-RAB established for the UE to be communicated with by the U-plane establishment eNB determined to be deleted. In this example, S1 signaling is used for the notification, and an E-RAB release request message is provided as a new message. The request message includes the identifier of the U-plane establishment eNB determined to be deleted, the UE identifier (UE-ID) that can be identified by the MME or the mobile subscriber identity that can be identified by the MME of the UE to be communicated with, and the identifier of the self C-plane establishment eNB (cell).

[0514] The MME, at ST3010, configures the E-RABs at each U-plane establishment eNB (excluding the U-plane establishment eNB to be deleted) notified by the C-plane establishment eNB for E-RAB establishment.

[0515] Since the subsequent processing can apply the method disclosed in the sequence example of FIG. 31, the description thereof is omitted.

[0516] The MME notifies the E-RAB release request message to the U-plane establishment eNB (U-eNB) to be deleted. By having the MME perform this, the same node can control the setup / modification and release of the E-RAB, thus simplifying the control.

[0517] Through the above processing, the DRB between the UE and the U-plane establishment eNB is released, and the S1 bearer between the U-plane establishment eNB and the S-GW is released. Thereby, the deletion process of the U-plane establishment eNB for the UE to be communicated with is completed.

[0518] From the above, the connection of the U-plane for the UE to be communicated with is performed by the radio bearer 1 (3003) between the UE and the C-eNB and the S1 bearer 1 (3004) between the C-eNB and the S-GW. At ST3005 and ST3006, user data is transmitted and received between the UE and the S-GW over the bearer.

[0519] FIG. 40 is a diagram showing another sequence example when deleting the U-plane establishment eNB according to Modification Example 3 of Embodiment 2. Since the sequence shown in FIG. 40 is similar to the sequence shown in FIG. 31, the same step numbers are assigned to the same steps, and the common description is omitted.

[0520] At ST3113, the radio bearer 1 is established between the UE and the C-eNB, and the S1 bearer 1 is established between the C-eNB and the S-GW. Also, the radio bearer 2 (DRB) is established between the UE and the U-eNB, and the S1 bearer 2 is established between the U-eNB and the S-GW.

[0521] The eNB that has established the U-plane monitors, at ST4002, data transmission in the radio section (Uu) with the UE to be communicated with. When it detects that data transmission has not occurred for a long time and a data timeout (expiration of the data monitor timer) is detected, it releases the DRB / S1 bearer established with the UE to be communicated with. The U-plane establishment eNB that has detected the data timeout notifies, at ST4003, the C-eNB of a request message for releasing the E-RAB established by the self eNB with the UE to be communicated with. It is advisable to use X2 signaling for this notification. The request message may include the fact that the timer of the data monitor has expired, the identifier of the UE for which the data timeout has been detected, and the identifier of the self eNB.

[0522] At ST4003, the C-eNB that has received the E-RAB release request message determines, at ST4004, the U-plane establishment eNB for which the DRB / S1 bearer should be released for the UE to be communicated with. The C-plane establishment eNB requests, at ST4005, the MME to release the E-RAB established by the U-plane establishment eNB determined to be deleted with the UE to be communicated with. In this example, S1 signaling is used for this notification, and an E-RAB release request message is provided as a new message. The request message may include the identifier of the U-plane establishment eNB determined to be deleted, the UE identifier (UE-ID) that can be identified by the MME or the mobile subscriber identity that can be identified by the MME for the UE to be communicated with, and the identifier of the self C-plane establishment eNB (cell).

[0523] At ST4005, the MME that has received the E-RAB release request message configures, at ST3010, the E-RAB for the UE to be communicated with of the U-plane establishment eNB excluding the eNB to be deleted.

[0524] The subsequent processing can apply the method disclosed in the sequence example of FIG. 31, so the description is omitted.

[0525] The MME notifies the E-RAB release request message to the U-plane establishment eNB (U-eNB) to be deleted. By having the MME do this, the same node can control the setup / modification and release of the E-RAB, thus simplifying the control.

[0526] Through the above processing, the DRB between the UE and the U-plane establishment eNB is released, and the S1 bearer between the U-plane establishment eNB and the S-GW is released. As a result, the deletion process of the U-plane establishment eNB for the UE to be communicated with is completed.

[0527] From the above, the connection of the U-plane for the UE to be communicated with is performed by the radio bearer 1 (3003) between the UE and the C-eNB and the S1 bearer 1 (3004) between the C-eNB and the S-GW. At ST3005 and ST3006, user data is transmitted and received between the UE and the S-GW over the bearer.

[0528] FIG. 41 is a diagram showing still another sequence example in the case of deleting the U-plane establishment eNB according to Modification Example 3 of Embodiment 2. Since the sequence shown in FIG. 41 is similar to the sequence shown in FIG. 31, the same step numbers are assigned to the same steps, and the common description is omitted.

[0529] At ST3113, the radio bearer 1 is established between the UE and the C-eNB, and the S1 bearer 1 is established between the C-eNB and the S-GW. Also, the radio bearer 2 (DRB) is established between the UE and the U-eNB, and the S1 bearer 2 is established between the U-eNB and the S-GW.

[0530] The eNB that has established the U-plane monitors, at ST4102, data transmission in the radio section (Uu) with the UE to be communicated with. When it detects that data transmission has not occurred for a long time and a data timeout (expiration of the data monitoring timer) is detected, it releases the DRB / S1 bearer established with the UE to be communicated with. The U-plane establishing eNB that has detected the data timeout notifies, at ST4103, the MME of a request message for releasing the E-RAB established by the eNB itself with the UE to be communicated with. In this example, S1 signaling is used for this notification, and an E-RAB release request message is provided as a new message. The request message includes the identifier of the U-plane establishing eNB determined to be deleted, the UE identifier (UE-ID) identifiable by the MME of the UE to be communicated with or the mobile subscriber identity identifiable by the MME, and the identifier of the self C-plane establishing eNB (cell). Also, the U-eNB notifies, at ST4104, the C-eNB of the E-RAB release request message as well. This is because the C-eNB selects the U-plane establishing eNB, so the C-eNB needs to recognize the information of the U-plane establishing eNB that has released the E-RAB. It is advisable to use X2 signaling for this notification. The request message may include that the timer of the data monitor has expired, the identifier of the UE that has detected the data timeout, and the identifier of the self eNB.

[0531] At ST4103, the MME that has received the E-RAB release request message configures, at ST3010, the E-RAB of the U-plane establishing eNB excluding the eNB to be deleted for the UE to be communicated with.

[0532] The subsequent processing can apply the method disclosed in the sequence example of FIG. 30, so the description is omitted.

[0533] The MME notifies the U-plane establishment eNB (U-eNB) to be deleted of an E-RAB release request message. By having the MME perform this, the same node can control the setup / modification and release of the E-RAB, thus simplifying the control.

[0534] Through the above processing, the DRB between the UE and the U-plane establishment eNB is released, and the S1 bearer between the U-plane establishment eNB and the S-GW is released. As a result, the deletion process of the U-plane establishment eNB for the UE to be communicated with is completed.

[0535] From the above, the connection of the U-plane for the UE to be communicated with is performed via radio bearer 1 (3003) between the UE and the C-eNB, and S1 bearer 1 (3004) between the C-eNB and the S-GW. At ST3005 and ST3006, user data is transmitted and received between the UE and the S-GW via this bearer.

[0536] The UE-assisted information is recognized by the C-plane establishment eNB (cell). In Embodiment 2, since the MME needs to recognize it, the control becomes complex. However, as disclosed in this modification example, since the C-plane establishment eNB selects the U-plane establishment eNB for the UE to be communicated with, there is no need for the MME to recognize the UE-assisted information that serves as an indicator at the time of this selection. Therefore, the control process is simplified and the signaling volume can be reduced.

[0537] Also, it becomes possible to perform the selection determination of the U-plane establishment eNB immediately after the UE-assisted information is notified. Therefore, there is little delay in the selection determination of the U-plane establishment eNB, and it is possible to select an appropriate eNB for communication with the UE to be communicated with.

[0538] Embodiment 3. In the modification example 3 from Embodiment 1 to Embodiment 2, in order to establish a bearer for U-plane connection using a plurality of eNBs, all of the plurality of eNBs have at least functions related to bearer control. In this embodiment, the object is to further simplify the configuration of the eNB for U-plane connection.

[0539] For one communication, establish a C-plane connection using one eNB (cell), and establish a U-plane connection using a plurality of eNBs (cells).

[0540] As the C-plane connection, establish an RRC connection, and as the U-plane connection, establish one or a plurality of individual radio bearers. It is preferable to use a DRB as the individual radio bearer.

[0541] The architecture in this embodiment can apply the architecture of FIG. 28 disclosed in Embodiment 2.

[0542] In this embodiment, an RRC connection is established using the Uu (2810) interface between the C-eNB (2804) and the UE (2806) to be communicated with. That is, in the figure, a C-plane connection indicated by a broken line is established between the C-eNB (2804) and the UE (2806). On the other hand, only data (user data) communication is performed using the Uu (2811) interface between the U-eNB (2805) and the UE (2806) to be communicated with. That is, only a U-plane connection indicated by a solid line is established between the U-eNB (2805) and the UE (2806). Note that a U-plane connection may be established between the C-eNB (2804) and the UE (2806) as in the conventional case.

[0543] The U-plane connection interface 2811 between the U-eNB (2805) and the UE (2806) is set as Uu, but a new interface having only a U-plane connection function may be provided instead of Uu.

[0544] In this embodiment, for one communication, an eNB that only establishes a U-plane connection does not have an RRC function. In other words, for a UE to be communicated with, an eNB that only establishes a U-plane connection does not have an RRC function. Therefore, for the UE (2806) to be communicated with, the signaling communication between the U-eNB (2805) where only a U-plane connection is established and the MME (2803) does not use the interface (S1-MME) 2815. Since the RRC function of the U-eNB for the UE to be communicated with can be eliminated, the configuration of the U-eNB can be simplified.

[0545] Also, for the communication of user data for the UE to be communicated with, the S1-U interface between the S-GW and the C-eNB and the interface between the C-eNB and the U-eNB may be used instead of the S1-U interface between the S-GW and the U-eNB. For the UE (2806) to be communicated with, the user data communication between the U-eNB (2805) where only a U-plane connection is established and the S-GW (2802) does not use the interface (S1-U) 2813. The interface (S1-U) 2814 between the S-GW (2802) and the C-eNB (2804) and the interface 2812 between the C-eNB (2804) and the U-eNB (2805) are used.

[0546] FIG. 42 is a diagram showing an architecture when configuring an eNB dedicated to U-plane establishment according to Embodiment 3. Since the architecture shown in FIG. 42 is similar to the architecture shown in FIG. 28, the same elements are given the same numbers and the common description is omitted. In the figure, the eNB dedicated to U-plane establishment is the U-eNB (2805). The eNB dedicated to U-plane establishment only communicates with a UE that only establishes a U-plane connection.

[0547] In the method of this embodiment, when an eNB dedicated to U-plane establishment is configured, since all signaling between the MME (2803) and the U-eNB (2805) can be performed via the C-eNB (2804), the signaling interface between the MME (2803) and the U-eNB (2805) can be eliminated.

[0548] Also, for communication of user data with a UE to be communicated with, when communication is performed using the S1-U interface between the S-GW (2802) and the C-eNB (2804) and the interface between the C-eNB (2804) and the U-eNB (2805) without using the S1-U interface between the S-GW (2802) and the U-eNB (2805), all packet data communication between the S-GW (2802) and the U-eNB (2805) can be performed via the C-eNB (2804). Therefore, the interface between the S-GW (2802) and the U-eNB (2805) can be eliminated.

[0549] By doing so, it becomes possible to simplify the configuration of the eNB dedicated to U-plane establishment. Furthermore, the interface with the MME becomes unnecessary, enabling flexible installation of the eNB dedicated to U-plane establishment. Also, since the interface with the S-GW can be made unnecessary, the interface with the node on the core network side can be eliminated, further enabling flexible installation of the eNB dedicated to U-plane establishment.

[0550] Here, the UE (2806) corresponds to a mobile station, the C-eNB (2804) corresponds to a first base station, the U-eNB (2805) corresponds to a second base station, and the MME (2803) and S-GW (2802) correspond to a gateway station, respectively. Also, regarding the C-plane signal, the RRC Connection between the UE (2806) and the C-eNB (2804) corresponds to a first radio communication connection, and the RRC Connection between the UE (2806) and the U-eNB (2805) corresponds to a second radio communication connection. Similarly, regarding the C-plane signal, the S1-MME signaling connection (2809) between the MME (2803) and the C-eNB (2804) corresponds to a first communication connection. Also, regarding the U-plane signal, the Radio Bearer between the UE (2806) and the C-eNB (2804) corresponds to a first radio communication connection, and the Radio Bearer between the UE (2806) and the U-eNB (2805) corresponds to a second radio communication connection. Similarly, regarding the U-plane signal, the S1 bearer (2814) between the S-GW (2802) and the C-eNB (2804) corresponds to a first communication connection.

[0551] In this way, by establishing a first communication connection between the gateway station and the first base station, a first radio communication connection between the first base station and the mobile station, and a second radio communication connection between the second base station and the mobile station, respectively, one communication is executed between the mobile station and the gateway station, so that cell migration can be realized by adding or deleting communication connections and radio communication connections.

[0552] The U-plane signal is distributed and transmitted to a first path including the first communication connection and the first radio communication connection and a second path including the first communication connection and the second radio communication connection. The C-plane signal is distributed and transmitted to a first path including the first communication connection and the first radio communication connection and a second path including the first communication connection and the second radio communication connection.

[0553] FIG. 43 is a diagram showing the protocol stack of the eNB according to Embodiment 3. Since the protocol stack shown in FIG. 43 is similar to the protocol stack shown in FIG. 29, the same elements are given the same numbers and the common description is omitted.

[0554] Regarding the U-eNB (2913), the protocol for a UE that establishes only a U-plane connection is shown. The protocol 2914 for C-plane connection is not configured. The PDCP protocol 2920, RLC protocol 2921, MAC protocol 2922, and PHY protocol 2923 have only functions for the U-plane. In other words, they have only functions for bearer establishment. Also, as shown by 4301, a user data transfer function between the C-eNB (2901) and the U-eNB (2913) for a UE that establishes only a U-plane connection may be provided to the C-eNB (2901) and the U-eNB (2913).

[0555] Note that when configuring an eNB dedicated to U-plane establishment, since it is not necessary to have the protocol 2914 for establishing a C-plane connection in the U-eNB 2913, a simple configuration can be achieved. Also, when communicating user data with the UE to be communicated with using the S1-U interface between the S-GW and the C-eNB and the interface between the C-eNB and the U-eNB, since it is not necessary to have the input / output function of the S1-U interface, an even simpler configuration can be achieved.

[0556] Next, a bearer establishment method using a plurality of eNBs (cells) is disclosed.

[0557] In this embodiment, the C-plane establishment eNB selects the eNB that should establish a DRB for the UE to be communicated with. As an index for selection, the index disclosed in Embodiment 2 may be applied.

[0558] Regarding the method for the C-plane establishment eNB to recognize the index when selecting the eNB that should establish a DRB with the UE to be communicated with, it is advisable to apply the method disclosed in Modification Example 3 of Embodiment 2.

[0559] The C-plane establishment eNB that has received this information selects the eNB that should establish a DRB for the UE to be communicated with.

[0560] The C-plane establishment eNB configures the DRB of the selected eNB (U-plane establishment eNB). It is advisable to newly provide this configuration function as an RRC function of the C-plane establishment eNB. The C-plane establishment eNB uses the E-RAB configuration received from the MME to configure the DRB to be established at each U-plane establishment eNB. Configure the DRB for U-plane connection to be shared among multiple U-plane establishment eNBs. It is advisable to use the above-mentioned index for this sharing. When selecting its own eNB as the U-plane establishment eNB, configure the DRB to be established at each U-plane establishment eNB including its own eNB.

[0561] If there is an eNB that has already configured a DRB, the C-plane establishment eNB modifies the DRB configuration for that eNB.

[0562] The DRB configurations set for each eNB may be the same. If there is no change in the E-RAB, it may be the same as the DRB configuration of the C-plane establishment eNB already. As the DRB configuration, the DRB identifier, PDCP configuration, RLC configuration, MAC configuration, and PHY configuration may be the same. Alternatively, the DRB identifiers may be made different. It becomes possible to handle the DRB configurations at each eNB individually.

[0563] The C-plane established eNB notifies each U-plane established eNB of a DRB setup request message. It is advisable to include DRB setup information in the request message. Additionally, it may also include the identifier of the UE to be communicated with and the identifier of the C-plane established eNB (cell). For a U-plane established eNB for which there is no change in the DRB setup after the C-plane established eNB has performed DRB modification, it may not be necessary to notify the modified DRB setup. For the notification of the DRB setup request message, the X2 interface may be used, or a new interface may be provided.

[0564] Furthermore, a list of correspondences between the DRB setups of each U-plane established eNB and each U-plane established eNB may be newly provided. It may also be referred to as the DRB list_U-plane. The C-plane established eNB may notify this list to each U-plane established eNB. Each U-plane established eNB will be able to recognize the DRB setups of other U-plane established eNBs.

[0565] Each U-plane established eNB that has received the DRB setup request message uses its own DRB setup information to perform DRB setup for the UE to be communicated with.

[0566] The C-plane established eNB notifies the UE of the DRB setup information. The C-plane established eNB (cell) may use, as the DRB setup information, information for identifying which U-plane established eNB's DRB setup, for example, the identifier of the U-plane established eNB (cell), and the DRB setup information of each U-plane established eNB. Additionally, it may also notify the system information of each U-plane established eNB (cell). Also, when each U-plane established eNB configures the ePDCCH for scheduling the UE to be communicated with, it is advisable to also notify the setup information of the ePDCCH. Additionally, information indicating that it is a U-plane establishment request may also be notified. The system information and ePDCCH configuration information of each U-plane established eNB (cell) may be notified to the C-plane established eNB in advance.

[0567] A list of each U-plane establishment eNB and each DRB setting may be provided. It may also be used as the DRB list_U-plane. The C-plane establishment eNB may notify the UE of the list.

[0568] It is advisable to use RRC signaling for this notification. A new message may be provided, or the DRB setting information and system information of the U-plane establishment eNB may be included in the existing RRC message and notified. As a specific example of the existing RRC message, it is advisable to use the RRC connection reconfiguration message or the AS-conifg message. The DRB setting information and system information for each U-plane establishment eNB may be included in the RadioResourceConfigDedicated information in the RRC connection reconfiguration message or the AS-conifg message. It may also be used as the DRB list.

[0569] By doing so, the UE to be communicated with can recognize the eNB that establishes the U-plane and the DRB setting between the UE and the eNB.

[0570] The UE to be communicated with performs DRB settings with each U-plane establishment eNB and conducts connection processing with each U-plane establishment eNB (cell).

[0571] When the connection between the UE to be communicated with and the U-plane establishment eNB is successful, the UE may notify the U-plane establishment eNB of a connection completion message. Regarding the notification method, it is advisable to apply the method disclosed in Embodiment 2. Although the application of (1) is also possible, it is advisable to apply (2) and (3) without going through the MME. The signaling volume can be reduced.

[0572] Each U-plane establishment eNB that has received a connection completion message from the UE performs the establishment process of the DRB with the UE to be communicated with. It may notify the C-plane establishment eNB of the completion message of this process. It may also notify that the setting of the DRB or the setting of the modified DRB between the UE and the U-plane establishment eNB has been completed. It is preferable to include the identifier (UE-ID) of the UE to be communicated with in this message. Also, the identifier of the self U-plane establishment eNB (cell) may be included.

[0573] As a result, the DRB between the UE to be communicated with and each U-plane establishment eNB is established.

[0574] The C-plane establishment eNB and each U-plane establishment eNB perform the setting for packet data transfer for the UE to be communicated with between the C-plane establishment eNB and the U-plane establishment eNB. For packet data transfer, the X2 interface may be used, or a new interface may be provided.

[0575] As a result, the packet data of the UE to be communicated with can be transferred between the C-plane establishment eNB and each U-plane establishment eNB.

[0576] Next, a data transmission method in the case where a plurality of DRBs are established using a plurality of eNBs is disclosed.

[0577] Regarding downlink data transmission, the C-plane establishment eNB calculates the ratio of the quality of each link. Considering the ratio of the quality and the traffic situation of each cell, the final distribution ratio of the packets to each U-plane establishment eNB is determined, and according to that ratio, the received packets are distributed to each U-plane establishment eNB. It is assumed that the determination of the distribution ratio is constantly carried out in response to the update of the quality of each link and the traffic data. When calculating the ratio of the quality of each link in the C-plane establishment eNB, the index used when selecting the U-plane establishment eNB may be used.

[0578] Disclosed is a method for packet transfer from a C-plane established eNB to each U-plane established eNB. The C-plane established eNB distributes and transfers the packets received from the S-GW to each U-plane established eNB without inputting them into the PDCP. In other words, the C-plane established eNB distributes the packets received from the S-GW to each U-plane established eNB and performs transparent transfer. In this case, the transferred packets are input into the PDCP of each U-plane established eNB, and processing by the PDCP protocol is performed. The SN (sequence number) in the PDCP is added by each U-plane established eNB.

[0579] As another method, the C-plane established eNB inputs the packets received from the S-GW into the PDCP, adds the SN, and then distributes and transfers the data unit after SN addition to each U-plane established eNB. The transferred data unit is input into the PDCP of each U-plane established eNB, and processing by the PDCP protocol is performed. The SN in the PDCP of each U-plane established eNB may or may not be added. By adding the SN by the PDCP of the C-plane established eNB, it becomes possible for the UE to recombine the user data received from each U-plane established eNB using the SN.

[0580] Regarding the data transmission in the uplink, the UE measures the quality of the link with the U-plane established eNB and calculates the ratio of the quality of each link. Then, according to the ratio, the transmission Packet is distributed to the links of each eNB for transmission. The UE notifies the amount of transmission data for each eNB by the buffer status report (BSR) for each eNB, and performs transmission according to the scheduling performed using the BSR in each eNB. It should be noted that the determination of the distribution ratio is constantly performed in response to the update of the quality of each link.

[0581] Regarding the packet transfer method from each U-plane established eNB to the C-plane established eNB, the method opposite to the downlink may be used. Each U-plane established eNB performs processing up to the PDCP protocol on the uplink data received from the UE to generate packet data, and transfers the packet data to the C-plane established eNB. In other words, the C-plane established eNB transparently transfers (transparently) the packet data from the U-plane established eNB to the S-GW for the packet data after the PDCP protocol processing. In this case, the transferred packet is not input to the PDCP of the C-plane established eNB and is transmitted to the S-GW. The S-GW that has received the packet data from the C-plane established eNB may reorder the packet data. Also, the C-plane established eNB may reorder the packet data before transmitting the packet data from each U-plane established eNB to the S-GW. The C-plane established eNB notifies the S-GW of the packet data after reordering.

[0582] As another method, each U-plane established eNB performs processing up to the PDCP protocol on the uplink data received from the UE, and transfers the data unit to the C-plane established eNB with the PDCP SN added. The C-plane established eNB inputs the transferred uplink data unit to the PDCP, uses the PDCP protocol processing to reorder using the added SN, and generates packet data. The C-plane established eNB transmits the reordered packet data to the S-GW. As a result, the S-GW does not need to reorder the packets.

[0583] Disclose the method for starting data transmission from the U-plane established eNB to the UE to be communicated with.

[0584] Upon receiving a connection completion message from the UE to the U-plane establishment eNB, or upon completion of the U-plane data transfer setting with the C-plane establishment eNB, each U-plane establishment eNB may start the data transmission process to the U-plane establishment eNB UE. The UE may start the data reception process from the U-plane establishment eNB (cell) upon transmitting the connection completion message to the U-plane establishment eNB. This can reduce the deviation in the timing of starting the data transmission and reception process between the UE and the U-plane establishment eNB (cell).

[0585] Another method is disclosed. After receiving data from the C-plane establishment eNB, the U-plane establishment eNB starts the data transmission process to the UE. After detecting and synchronizing with the U-plane establishment eNB (cell), the UE starts the reception process from the U-plane establishment eNB (cell). Alternatively, the UE may start the reception process from the U-plane establishment eNB (cell) after the success of the RA procedure with the U-plane establishment eNB (cell). For example, this can be applied when there is no connection completion message from the UE to the U-plane establishment eNB. This method has the advantage of not requiring a clear trigger for starting data transmission and reception, making control easier.

[0586] The data transfer setting between the C-plane establishment eNB and the U-plane establishment eNB may be performed when each U-plane establishment eNB receives the DRB setting information from the C-plane establishment eNB. In such a case, before the UE completes the connection with the U-plane establishment eNB, the data transfer setting may be performed between the C-plane establishment eNB and the U-plane establishment eNB, and downlink data may arrive at the U-plane establishment eNB from the C-plane establishment eNB. After receiving the data from the C-plane establishment eNB, the U-plane establishment eNB will start the data transmission process to the UE. The UE has not yet completed the connection with the U-plane establishment eNB and cannot receive the data.

[0587] However, by using retransmission control in the U-plane establishment eNB, it is possible to reduce the non-delivery of the data. Also, by increasing the maximum number of retransmissions in advance, it is possible to almost eliminate the non-delivery of the data. Therefore, the method disclosed herein can obtain the effect of facilitating control with almost no non-delivery of data.

[0588] For the method by which the UE transmits and receives U-plane data with the U-plane establishment eNB (cell), and for the method by which the UE transmits and receives C-plane data and / or U-plane data with the C-plane establishment eNB (cell), it is advisable to apply the method disclosed in Embodiment 2.

[0589] FIG. 44 is a diagram showing a sequence example in the case of establishing / modifying a DRB using a plurality of eNBs according to Embodiment 3. Since the sequence shown in FIG. 44 is similar to the sequence shown in FIG. 30, the same step numbers are assigned to the same steps, and the common explanations are omitted.

[0590] In ST3034, Radio Bearer 1 is established between the UE and the C-eNB, and S1 bearer1 is established between the C-eNB and the S-GW.

[0591] The UE notifies the C-eNB, which is the C-plane establishment eNB, of a measurement report in ST4401. Regarding this, the method disclosed in Modification Example 3 of Embodiment 2 can be applied.

[0592] The C-eNB that has received the measurement report selects, in ST4402, the eNB for which a DRB is to be established for the UE to be communicated with. As the selection method, the method disclosed in Modification Example 3 of Embodiment 2 can be applied.

[0593] The C-plane establishment eNB determines, in ST4403, the setting of the DRB using each selected eNB (U-plane establishment eNB). Also, at this time, for the U-plane establishment eNB that has already been established, the DRB setting may be modified.

[0594] The C-plane establishment eNB configures the DRBs of its own cell at ST4404. In case of modification, the modified DRBs may be configured.

[0595] The C-plane establishment eNB notifies each selected U-plane establishment eNB (U-eNB) of a DRB configuration request message at ST4405. It is advisable to include DRB configuration information in the request message. Also, the identifier of the UE to be communicated with and the identifier of the C-plane establishment eNB (cell) may be included. For the notification of the DRB configuration request message, the X2 interface may be used, or a new interface may be provided. Here, the U-plane connection configuration message is used.

[0596] Each U-eNB that has been notified of the DRB configuration request message configures the DRBs of its own eNB. Since the configuration information of the DRBs to be established at each U-eNB is included in the request message, there is no need for each U-eNB to configure the DRBs itself. Each U-eNB configures the DRBs using the notified DRB configuration information.

[0597] The C-eNB that has configured or modified the DRBs at ST4404 notifies the UE of the DRB configuration information, etc. at ST4406. Here, the RRC connection reconfiguration message is used for the notification.

[0598] If the UE that has received the RRC connection reconfiguration message at ST4406 contains information indicating that it is a U-plane establishment request in the message, it configures the DRBs of each U-plane establishment eNB using the DRB configuration information of the U-plane establishment eNB in the message.

[0599] At ST4407, the UE starts the connection process with the U-plane establishment eNB.

[0600] The processes from ST3018 to ST3022 are the same as the processes shown in Figure 30, so the description is omitted.

[0601] Each U-eNB that has received the DRB establishment completion message by ST3022 can recognize that a radio bearer (DRB2) (3027) has been configured between itself and the UE.

[0602] In ST4408, the C-eNB and each U-eNB perform settings for packet data transfer for the UE to be communicated with between the C-eNB and the U-eNB. By this process, a link for data transfer is established between the C-plane establishment eNB and the U-plane establishment eNB. Thereby, in ST4409, the packet data of the UE to be communicated with can be transferred between the C-eNB and each U-eNB.

[0603] Since the processes from ST3029 to ST3032 are the same as the processes shown in FIG. 30, the description thereof is omitted.

[0604] By the above processes, a DRB is established between the UE to be communicated with and a plurality of eNBs (C-eNB, U-eNB), and transmission and reception of user data become possible.

[0605] A method for deleting an eNB that has established only a U-plane with the UE to be communicated with is disclosed. In other words, a method for releasing the DRB established between the eNB to be deleted and the UE to be communicated with is disclosed.

[0606] In the present embodiment, the C-plane establishment eNB selects the eNB to be deleted. As an index for selection, it is preferable to apply the above-described index when the C-plane establishment eNB selects the eNB for which a DRB should be established for the UE to be communicated with. The C-plane establishment eNB selects the eNB to be deleted using this index. For example, it may be selected as the eNB to be deleted when the communication quality between the UE and the eNB (cell) falls below a predetermined threshold value.

[0607] The C-plane establishment eNB that has selected the U-plane establishment eNB to be deleted stops data transfer to the U-plane establishment eNB.

[0608] The C-plane established eNB configures the DRB for the UE to be communicated with by the U-plane established eNBs excluding the eNB to be deleted. The C-plane established eNB notifies each of the U-plane established eNBs of a DRB configuration request message. For the notification of the DRB configuration request message, the X2 interface may be used or a new interface may be provided.

[0609] For an eNB with no change in the DRB configuration after the C-plane established eNB modifies the DRB configuration, it may not be necessary to notify the modified DRB configuration request message.

[0610] Also, the C-plane established eNB notifies the eNB to be deleted of a release instruction for the DRB established between the eNB and the UE to be communicated with. The instruction message may include the identifier of the UE to be communicated with and the identifier of the C-plane established eNB (cell). For the notification of the DRB release instruction message, the X2 interface may be used or a new interface may be provided. The X2 interface may be used or a new interface may be provided.

[0611] The target eNB for deletion that has received the release instruction for the DRB established between the C-plane established eNB and the UE to be communicated with stops the scheduling for the UE. Before stopping the scheduling, it is advisable to transmit all the packet data remaining without being transmitted from the target eNB for deletion to the UE. Also, it is advisable to complete the retransmission process for all the packet data for which the retransmission process has not been completed by HARQ or ARQ.

[0612] Each U-plane established eNB that has received the DRB modification request message configures the DRB of its own eNB. Also, the U-plane established eNB that has received the release instruction for the DRB established between the eNB and the UE to be communicated with performs the release process for the DRB established between the eNB and the UE to be communicated with in its own eNB.

[0613] For each U-plane establishment eNB that has received the DRB modification request message, the method of establishing / modifying the DRB described above may be applied.

[0614] The C-plane establishment eNB notifies the UE of the DRB release information. The C-plane establishment eNB (cell) that notifies the UE of the DRB release information notifies the UE to be communicated with by RRC signaling of the DRB release information of each U-plane establishment eNB and information for identifying which U-plane establishment eNB's DRB it is, for example, the identifier of the U-plane establishment eNB. Further, it may include the DRB setting information of each U-plane establishment eNB except for the U-plane establishment eNB to be deleted by the C-eNB. Further, information indicating that it is a DRB release request for the U-plane establishment eNB determined to be deleted by the C-eNB may be notified together. Further, the system information of each U-plane establishment eNB (cell) may be notified together. Further, the ePDCCH setting information may be notified together. In the U-plane establishment eNB except for the U-plane establishment eNB to be deleted, it becomes available to the UE when the system information is changed or when a new U-plane establishment eNB is established.

[0615] It is advisable to use the RRC message. As a specific example of the RRC message, it is advisable to use the RRC connection reconfiguration message or the AS-conifg message. The RadioResourceConfigDedicated information in the RRC connection reconfiguration message or the AS-conifg message may also be used.

[0616] By doing so, the UE to be communicated with can recognize the release of the DRB established between the U-plane establishment eNBs to be deleted.

[0617] In addition, the C-plane established eNB notifies the UE of the DRB setting or modification information of the U-plane established eNB excluding the eNB to be deleted. This may be included in the above-mentioned RRC message. The DRB setting or modification information and the DRB release information may be included in one message for notification. For the subsequent DRB setting or modification process of the U-plane established eNB excluding the eNB to be deleted, the method disclosed in Embodiment 2 can be applied.

[0618] Upon receiving the DRB release information, the UE terminates the connection with each U-plane established eNB (cell) for which the DRB release is to be performed. It may be assumed that the monitoring of the PDCCH or ePDCCH of the eNB is terminated.

[0619] The UE that has performed the DRB release process and connection termination with the eNB to be deleted may notify the eNB of a connection termination message. Regarding the notification method, it is advisable to apply (2) or (3) of the method for notifying the connection completion message to each U-plane established eNB as described above.

[0620] Upon receiving the connection termination message from the UE, the eNB to be deleted activates the process of releasing the data transfer setting between the eNB to be deleted and the C-plane established eNB, and performs the process of releasing the data transfer setting between the eNB to be deleted and the C-plane established eNB. When the C-plane established eNB receives the connection termination message from the UE, the C-plane established eNB activates the process of releasing the data transfer setting between the eNB to be deleted and the C-plane established eNB, and performs the process of releasing the data transfer setting between the eNB to be deleted and the C-plane established eNB.

[0621] As a result, the DRB set between the UE to communicate with the eNB to be deleted is released.

[0622] Regarding the data transmission method, excluding the deleted eNB, the data transmission method disclosed in Embodiment 1 can be applied using a plurality of U-plane established eNBs for which the DRB is established with the target UE.

[0623] Note that no data loss occurs when deleting the U-plane establishment eNB. This is because the C-plane establishment eNB performs DRB setting, user data path switching, and data transfer control for each U-plane establishment eNB. Therefore, there is no need to perform special operations such as data loss avoidance control when deleting the U-plane establishment eNB.

[0624] FIG. 45 is a diagram showing a sequence example when deleting the U-plane establishment eNB according to Embodiment 3. Since the sequence shown in FIG. 45 is similar to the sequences shown in FIGS. 30 and 31, the same step numbers are assigned to the same steps, and the common explanations are omitted.

[0625] A radio bearer 1 (3003) is established between the UE and the C-eNB, and an S1 bearer 1 (3004) is established between the C-eNB and the S-GW. Also, a radio bearer 2 (DRB) (3027) is established between the UE and the U-eNB. In this sequence example, user data transfer settings are made between the C-eNB and the U-eNB. As a result, the user data communication between the C-eNB and the UE is performed by the direct communication between the C-eNB and the UE in ST3005, the data transfer between the C-eNB and the U-eNB in ST4409, and the user data communication between the U-eNB and the UE in ST3032. The user data communication between the C-eNB and the S-GW is performed in ST3006.

[0626] The UE notifies the measurement report to the C-eNB, which is the C-plane establishment eNB, in ST4501. Regarding this, the method disclosed in Modification Example 3 of Embodiment 2 can be applied.

[0627] The C-eNB that has received the measurement report selects, in ST4502, the U-plane establishment eNB for which the DRB should be released, that is, the U-plane establishment eNB to be deleted, for the UE to be communicated with. The selection method can be the method disclosed in Modification Example 3 of Embodiment 2.

[0628] The C-plane established eNB determines the settings of each DRB of the U-plane established eNB excluding the U-plane established eNB to be deleted in ST4503. Also, at this time, for the already established U-plane established eNB, the DRB settings may be modified.

[0629] The C-plane established eNB configures the DRBs of its own cell in ST4504. In the case of modification, the modified DRBs may be configured.

[0630] The C-plane established eNB stops the transfer of user data with the U-plane established eNB to be deleted in ST4505.

[0631] The C-plane established eNB notifies each U-plane established eNB (U-eNB) to be deleted with a DRB release indication message in ST4506. Here, the U-plane connection reconfiguration message is used.

[0632] Each U-eNB that has been notified with the DRB release indication message performs the DRB release process of its own eNB.

[0633] Each U-eNB that has been notified with the DRB release indication message stops the scheduling of user data in ST4507.

[0634] The C-eNB that has set or modified the DRB using ST4504 notifies the UE of the DRB configuration information using ST4508. At this time, information indicating that it is a DRB release request for the U-plane establishment eNB determined to be deleted by the C-eNB is included. Also, the DRB configuration information for each U-plane establishment eNB except for the U-plane establishment eNB to be deleted by the C-eNB is included. Information indicating that it is a DRB release request for the U-plane establishment eNB to be deleted, the DRB configuration information for each U-plane establishment eNB (cell), the identifier of each U-plane establishment eNB (cell), the system information of each U-plane establishment eNB (cell), and the ePDCCH configuration information are notified in association. The RRC connection reconfiguration message is used for the notification.

[0635] When the UE that has received the RRC connection reconfiguration message using ST4508 finds information indicating that it is a DRB release request for the U-plane establishment eNB in the message, it performs the release process for the DRB of the U-plane establishment eNB to be deleted in the message.

[0636] Using ST4509, the UE starts the process of ending the connection with the U-plane establishment eNB to be deleted.

[0637] The process from ST3107 to ST3108 is the same as the process shown in Figure 31, so the description is omitted.

[0638] Using ST4510, the C-eNB and each U-eNB cancel the settings for packet data transfer for the UE to be communicated between the C-eNB and the U-eNB. By this process, the link for data transfer between the C-plane establishment eNB and the U-plane establishment eNB is cancelled.

[0639] The process of ST3115 is the same as the process shown in Figure 31, so the description is omitted.

[0640] Through the above processing, the DRB between the UE and the U-plane establishment eNB is released. As a result, the deletion process of the U-plane establishment eNB for the UE to be communicated with is completed.

[0641] As described above, the connection of the U-plane for the UE to be communicated with is performed by the radio bearer 1 (3003) between the UE and the C-eNB and the S1 bearer 1 (3004) between the C-eNB and the S-GW. In ST3005 and ST3006, user data is transmitted and received between the UE and the S-GW through the bearer.

[0642] Another method for deleting the eNB that has established only the U-plane with the UE to be communicated with is disclosed. The case of using the indicator (7) disclosed in Embodiment 2 is disclosed.

[0643] When the eNB that has established only the U-plane detects a timeout because there has been no data transmission in the radio section (Uu) with the UE to be communicated with for a long time, the DRB established with the UE to be communicated with is released.

[0644] The eNB that monitors the data transmission in the radio section with the UE to be communicated with and detects a data timeout (expiration of the data monitor timer) notifies the C-plane establishment eNB of a request message for releasing the DRB established by the eNB itself with the UE to be communicated with. X2 may be used for the notification, or a new interface may be provided. The request message preferably includes the identifier of the UE that detected the data timeout and the identifier of the eNB itself.

[0645] The C-plane establishment eNB that receives the request message selects the eNB that deletes the notified U-plane establishment eNB.

[0646] The C-plane establishment eNB configures the DRB for the UE to be communicated with by the U-plane establishment eNBs excluding the eNB to be deleted. The C-plane establishment eNB notifies each of the U-plane establishment eNBs of the DRB configuration. Also, the C-plane establishment eNB notifies the eNB to be deleted of a release instruction for the DRB established between the eNB and the UE to be communicated with. For the subsequent processing, the method disclosed above may be applied.

[0647] FIG. 46 is a diagram showing another sequence example in the case of deleting a U-plane establishment eNB according to Embodiment 3. Since the sequence shown in FIG. 46 is similar to the sequence shown in FIG. 45, the same step numbers are assigned to the same steps, and the common explanations are omitted.

[0648] The eNB that has established the U-plane monitors data transmission in the radio section (Uu) with the UE to be communicated with at ST4602. When no data transmission has occurred for a long time and a data timeout (expiration of the data monitor timer) is detected, the U-plane establishment eNB stops user data scheduling at ST4603. At ST4604, it notifies the C-eNB of a request message for releasing the DRB established by the eNB itself for the UE to be communicated with. At ST4605, the C-eNB that has received the DRB release request message determines the notified U-plane establishment eNB as the eNB to be deleted, and configures or modifies the DRB for the UE to be communicated with by the U-plane establishment eNBs excluding the eNB to be deleted. The C-eNB stops user data transfer at ST4606.

[0649] For the subsequent processing, it is advisable to perform ST4512 shown in FIG. 45.

[0650] Through the above processing, the DRB between the UE and the U-plane establishment eNB is released. Thereby, the deletion process of the U-plane establishment eNB for the UE to be communicated with is completed.

[0651] As described above, the U-plane connection for the UE to be communicated with is performed via Radio Bearer 1 (3003) between the UE and the C-eNB, and S1 bearer1 (3004) between the C-eNB and the S-GW. User data is transmitted and received between the UE and the S-GW via these bearers at ST3005 and ST3006.

[0652] Not limited to this, as another method, when the UE detects a data timeout at ST4601, the UE may perform connection termination processing with the U-plane establishment eNB to be deleted. As a result, the UE can perform the connection termination processing with the U-plane establishment eNB earlier, eliminating the need to perform communication maintenance processing with the unnecessary U-plane establishment eNB, and enabling power consumption reduction of the UE.

[0653] Disclose another method for deleting an eNB that has established only the U-plane with the UE to be communicated with.

[0654] The UE monitors (RLM: Radio Link Monitor) the radio communication intervals with each U-plane establishment eNB (cell). The UE receives the RS of each U-plane establishment cell and uses the reception result of the RS to determine the deterioration of the reception quality of the radio communication interval. The specific examples of the RS can be the examples disclosed in Embodiment 2. Alternatively, a signal equivalent to the RS may be used instead of the RS.

[0655] When the reception quality of the radio communication interval falls below a predetermined threshold for a predetermined period, the UE determines that the reception quality has deteriorated. Alternatively, when the reception quality of the radio communication interval falls below a predetermined threshold for a predetermined period, it is preferable to reconnect to the U-plane establishment eNB (cell) again. Detection, synchronization, PRACH transmission, and TA reception of the U-plane establishment eNB (cell) are performed. Set a maximum value for the number of reconnection attempts, and if the connection cannot be established even after reconnection up to the maximum value, it may be determined that the reception quality has deteriorated.

[0656] The UE that has determined that the reception quality has deteriorated notifies the C-plane establishment eNB of the deterioration of the reception quality in the radio communication section. It is advisable to include the identifier of the U-plane establishment eNB in the notification so that it can be known which U-plane establishment eNB's radio communication section has deteriorated reception quality.

[0657] The C-plane establishment eNB (cell) that has received the deterioration information from the UE selects the eNB that deletes the U-plane establishment eNB with deteriorated reception quality.

[0658] The C-plane establishment eNB configures the DRB for the UE to be communicated with by the U-plane establishment eNBs excluding the eNB to be deleted. The C-plane establishment eNB notifies each of the U-plane establishment eNBs of the DRB configuration. Also, the C-plane establishment eNB notifies the eNB to be deleted of the release instruction of the DRB established between the eNB and the UE to be communicated with. The subsequent processing may apply the method disclosed above.

[0659] Note that the UE may perform RLM and terminate communication with the U-plane establishment eNB with deteriorated reception quality when it determines that the reception quality in the radio communication section has deteriorated.

[0660] By adopting the method disclosed in this embodiment, packet data communication can be performed for the UE to be communicated with using a plurality of eNBs, so that the communication capacity of the UE can be increased.

[0661] Also, even when small cells are used, it is possible to use a plurality of eNBs, improve the frequency utilization efficiency, and increase the communication capacity of the system.

[0662] In addition, control processing for establishing a plurality of RRC connections becomes unnecessary, the control processing can be facilitated, and the signaling amount and control delay amount can be reduced.

[0663] In addition, the RRC function of the U-plane establishment eNB becomes unnecessary. For example, when configuring a dedicated eNB for U-plane establishment, it is possible to configure it even more simply than a conventional eNB.

[0664] Regarding the mobility control of the UE, since control processing for establishing a plurality of RRC connections is unnecessary, within the coverage of the C-plane establishment eNB (cell), only the U-plane establishment eNB needs to be changed (established / modified / deleted). Therefore, low latency and high speed of control processing can be achieved. For example, when the C-plane establishment eNB (cell) is a coverage cell and the U-plane establishment eNB (cell) is a capacity cell, HO control does not need to be performed between capacity cells, and only the U-plane establishment eNB needs to be changed (established / modified / deleted).

[0665] In addition, since the MME does not need to recognize the U-plane establishment eNB, the signaling amount and control delay amount in the control processing on the network side can be reduced in the change of the U-plane establishment eNB. This means that even for the UE mobility control, further low latency and high speed of control processing can be achieved.

[0666] In addition, since the S-GW does not need to recognize the U-plane establishment eNB, the signaling amount and control delay amount in the control processing on the network side can be reduced in the change of the U-plane establishment eNB. This means that even for the UE mobility control, further low latency and high speed of control processing can be achieved.

[0667] In the third embodiment, a method is disclosed in which the C-plane establishment eNB selects and determines an eNB with which the target UE should establish a DRB. As another method, the MME may select and determine an eNB with which the target UE should establish a DRB.

[0668] In this case, the U-plane establishment eNB selected and determined by the MME may be notified to the C-plane establishment eNB. The C-plane establishment eNB sets the DRB configuration of the notified U-plane establishment eNB.

[0669] The subsequent processing can apply the foregoing method.

[0670] However, this method cannot achieve the effect that the MME does not need to recognize the U-plane establishment eNB. However, since other effects can be obtained, it is effective.

[0671] Embodiment 3, Variation 1. In Embodiment 3, the C-plane establishment eNB sets the DRBs of each U-plane establishment eNB for the UE to be communicated with. For this reason, there may be a conflict with the resource setting for other UEs under each U-plane establishment eNB. In this variation, a method for avoiding such a conflict is disclosed.

[0672] In a specific area, a centralized control eNB (also referred to as a Master eNB) that controls one or more specific eNBs is provided. It is preferable that the eNB having the RRC function be the centralized control eNB. In the specific area, the UE establishes an RRC connection with the centralized control eNB. The establishment of this RRC connection may be performed via other eNBs of the centralized control eNB.

[0673] It is preferable that the C-plane establishment eNB for the UE to be communicated with be the centralized control eNB, and the eNB that only establishes the U-plane be the eNB controlled by the centralized control eNB (the centralized controlled eNB, slave eNB). For the UE to be communicated with, the centralized control eNB controls all eNBs (C-plane establishment eNB + U-plane establishment eNB). Specifically, the control may be the control in each protocol of RRC, PDCP, RLC, MAC, and PHY.

[0674] When the centralized control eNB performs control, settings are made according to the priority with the DRBs of other UEs in the U-plane establishment eNB. As specific examples, three are disclosed below. (1) Give priority to the DRBs of UEs under other eNBs (cells). (2) Prioritize the DRBs of the UEs under the umbrella of the eNB (cell). (3) Prioritize the DRBs of the UEs that use the eNB (cell) as the U-plane establishment eNB.

[0675] Specific examples of DRB settings include DRB identifier settings and lower layer settings. Lower layer settings include PDCP settings, RLC settings, MAC settings, and PHY settings.

[0676] When the centralized control eNB performs control, user data on the U-plane side is transmitted between the centralized control eNB and the eNB for centralized control. Seven specific examples of the layer where this transmission occurs are disclosed below. (1) IP packet data before being input to PDCP (2) Data unit with SN added by PDCP (3) Data unit between PDCP and RLC (4) Data unit between RLC and MAC (5) Data unit after in-MAC scheduling (6) Data unit before HARQ in MAC (7) Data unit between MAC and PHY It is advisable to establish a link for these transmissions between the centralized control eNB and the eNB for centralized control. Thereby, user data on the U-plane side can be transmitted between the centralized control eNB and the eNB for centralized control.

[0677] In addition, the centralized control eNB may notify each eNB for centralized control of the settings in the necessary layers or protocols among the DRB settings in each eNB for centralized control. This can reduce the signaling volume.

[0678] The method disclosed in this modification example can also be applied to the case where instead of a plurality of eNBs, a plurality of nodes or cells are configured within a single eNB. It is advisable to provide a node or cell for centralized control within a single eNB. The node or cell for centralized control becomes the C-plane establishment eNB (cell) for the UE to be communicated with, and the nodes or cells within other eNBs become the U-plane only establishment eNBs (cells). The node or cell for centralized control may become not only the C-plane establishment eNB (cell) but also the U-plane establishment eNB (cell) for the UE to be communicated with.

[0679] FIG. 47 is a diagram showing the architecture according to Modification Example 1 of Embodiment 3. The case where a cell for centralized control is provided within a single eNB is shown.

[0680] 4701 is an eNB. 4702 is a cell that establishes a C-plane connection and is referred to as a C-cell. 4703 is a cell that establishes only a U-plane connection and is referred to as a U-cell. The C-cell and the U-cell are configured within the same eNB. 4704 is a link for user data transmission on the U-plane provided between the C-cell and the U-cell. 4705 is also provided with a signaling interface provided between the C-cell and the U-cell. This interface may use X2 or may be newly provided. The C-cell (4702) becomes the cell for centralized control and controls all cells within the same eNB (4701).

[0681] When providing a centralized control eNB within a specific area, if the eNB within 4701 represents the eNB within the specific area, the C-cell represents the centralized control eNB configured within the specific area, and the U-cell represents the eNB to be centrally controlled within the specific area, that would be fine.

[0682] By adopting the method disclosed in this modification example, in addition to the effects of Embodiment 3, the following effects can be obtained.

[0683] By providing a centralized control eNB within a specific area, it becomes possible to configure the DRB for each UE considering all the resources of all eNBs and all UEs under the umbrella of all eNBs.

[0684] It is possible to avoid conflicts between the setting of the DRB of each U-plane establishment eNB for the UE to be communicated with, which is performed by the C-plane establishment eNB, and the resource setting for other UEs under the umbrella of each U-plane establishment eNB, which is performed by each U-plane establishment eNB.

[0685] Therefore, adjustment between eNBs within a specific area becomes unnecessary, and it becomes possible to achieve low control delay and reduction of signaling volume.

[0686] In the modification example 1 from Embodiment 2 to Embodiment 3, a method for handling the U-plane when changing the C-plane establishment cell (eNB) for the UE to be communicated with is disclosed. Regarding the change of the C-plane establishment eNB, handover (HO) may be applied. The problem is when a U-plane connection eNB is established for the UE to be communicated with.

[0687] The following two methods are shown for the case where the UE to be communicated with undergoes handover between different C-plane establishment eNBs. (1) Once return the U-plane connection to the C-plane establishment eNB cell.

[0688] When the U-plane establishment eNB is different from the C-plane connection eNB, change the U-plane connection from the U-plane only establishment eNB to the C-plane establishment eNB (source C-plane establishment eNB) before handover. Establish or correct the connection between the source C-plane establishment eNB and the U-plane, and delete the U-plane only establishment eNB.

[0689] Thereby, the U-plane connection for the UE to be communicated with is also established by the source C-plane establishment eNB.

[0690] In this state, a handover (HO) is performed from the source C-plane establishment eNB to the target C-plane establishment eNB (target C-plane establishment eNB). The conventional method may be applied for this.

[0691] After the HO to the target C-plane establishment eNB is performed, a process of establishing a U-plane connection may be performed again for the UE to be communicated with, as necessary.

[0692] When X2 HO is performed between C-plane establishment eNBs, the MME does not recognize that HO is being performed at the HO preparation stage. Therefore, when the MME selects a U-plane establishment eNB, it is advisable for the source C-Plane establishment eNB that determined the HO to send a U-plane change request to the MME. It is advisable to include information indicating that it is a change request due to HO in this request message. In response to this, the MME may perform a process of setting or modifying the C-plane establishment eNB as the U-plane establishment eNB, and perform a process of deleting only the originally established U-plane establishment eNB.

[0693] By doing so, it becomes possible to change the C-plane establishment eNB without stopping the U-plane connection for the UE to be communicated with.

[0694] (2) Notify the UE from the target C-plane establishment eNB of the eNB that establishes the U-plane connection.

[0695] The source C-plane establishment eNB notifies the target C-plane establishment eNB of an HO request. Include information on the U-plane establishment eNB currently set for the UE that is currently the HO target in this message.

[0696] The target C-plane establishment eNB that received this information selects and determines the U-plane establishment eNB that establishes a U-plane connection with the UE that is the HO target. It does not have to be changed.

[0697] The target C-plane establishment eNB notifies the source C-plane establishment eNB of the HO request response message. This message includes the information of the U-plane establishment eNB set by the target C-plane establishment eNB.

[0698] The source C-plane establishment eNB notifies the UE of the HO request message together with the information.

[0699] The UE changes the connection of the C-plane to the target C-plane establishment eNB and changes the connection of the U-plane using the U-plane establishment eNB information.

[0700] On the other hand, the target C-plane establishment eNB that has selected and determined the U-plane establishment eNB notifies the MME of this information in the E-RAB setup request message. The MME uses this to perform the E-RAB setup process, or modification process, or deletion process of the U-plane establishment eNB.

[0701] By doing so, it becomes possible to change the C-plane establishment eNB and the U-plane establishment eNB for the UE to be communicated with.

[0702] Therefore, it becomes possible to change the C-plane establishment eNB for the UE to be communicated with without stopping the connection of the U-plane.

[0703] When handover is performed between cells in the C-plane establishment eNB for the UE to be communicated with, the method in the case of performing HO between different C-plane establishment eNBs may be applied between cells in the C-plane establishment eNB. The same effect can be obtained.

[0704] Embodiment 4. When a UE notifies a scheduling request (SR) for uplink transmission, conventionally, since there was only one eNB to which the UE was connected, it was sufficient to notify that single eNB. However, in the method disclosed in Modification Example 1 from Embodiment 1 to Embodiment 3, the UE is connected to a plurality of eNBs. Therefore, it becomes unclear to which eNB the UE should notify the SR.

[0705] The purpose of this embodiment is to solve this problem.

[0706] Transmit the SR for each eNB (cell) to which the UE is connected. According to the traffic control disclosed in Embodiment 1, transmit the SR as necessary for each eNB (cell). Thereby, it becomes possible to transmit UL data to each eNB (cell) according to the traffic control in the UE.

[0707] The SR setting information for the target UE in each eNB (cell) may be individually notified to the UE from each eNB (cell) in advance.

[0708] It is preferable to make the SR setting a function of RRC.

[0709] In Embodiment 1, it is preferable to include it in the RRC function possessed by each eNB. The notification to the UE can apply the conventional notification method.

[0710] In Embodiment 2, it is preferable to include it in the limited RRC function possessed by the U-plane establishment eNB. As a method of notifying the UE of the SR setting information, it is preferable to apply the method of notifying the UE of the ePDCCH configuration information.

[0711] In Embodiment 3, it is preferable to make it the RRC function possessed by the C-plane establishment eNB. The C-plane establishment eNB determines the SR setting for each U-plane establishment eNB (cell) and notifies the UE and each U-plane establishment eNB (cell).

[0712] By doing so, the UE can recognize the SR setting for each eNB and can notify the SR.

[0713] Disclose other methods. Disclose a method for handling uplink data in a UE and a method for transmitting SR.

[0714] In a UE, separate the handling of U-plane UL data and C-plane UL data.

[0715] For example, there is user data as U-plane UL data and signaling data as C-plane UL data. In a UE, determine which data to transmit.

[0716] Next, disclose the following three methods for transmitting SR. (1) In the case of C-plane UL data, transmit it to the C-plane establishment cell (eNB). (2) In the case of U-plane UL data, transmit it to the U-plane establishment cell (eNB). (3) For both types of data, transmit them to the C-plane establishment cell (eNB).

[0717] (1) In this case, a UE that determines that the uplink data is C-plane UL data transmits it to the C-plane establishment cell (eNB). The SR setting may use the SR setting in the C-plane establishment cell (eNB). If there are multiple C-plane establishment cells (eNBs), it may be possible to notify each C-plane establishment cell (eNB) related to the UL data. Alternatively, select any one C-plane establishment cell (eNB) and notify this one C-plane establishment cell (eNB). It is advisable to use a predetermined selection criterion for the selection of one C-plane establishment cell (eNB). For example, the criterion disclosed in Example 2 may be used. It is advisable to select the best cell (eNB). Thereby, the C-plane establishment cell (eNB) that receives the SR can schedule the uplink data for the UE in its own cell.

[0718] (2) In the case where the UE determines that the uplink data is the UL data of the U-plane, it transmits to the U-plane establishment cell (eNB). When the UL data of the U-plane is distributed to each U-plane establishment eNB (cell) according to data traffic control, the UE may transmit the SR to each U-plane establishment cell (eNB). The SR setting may use the SR setting in each U-plane establishment cell (eNB). As a result, each U-plane establishment cell (eNB) that receives the SR can schedule the uplink data for the UE in its own cell (eNB).

[0719] (3) In the case where the UE determines whether the uplink data is the UL data of the U-plane or the UL data of the C-plane, the UE transmits both types of data to the C-plane establishment cell (eNB). The SR setting may use the SR setting in the C-plane establishment cell (eNB), or as another method, an SR for the UL data of the U-plane and an SR for the UL data of the C-plane may be provided. In the case of the UL data of the U-plane, it is transmitted using the setting of the SR for the UL data of the U-plane. In the case of the UL data of the C-plane, it is transmitted using the setting of the SR for the UL data of the C-plane.

[0720] A method of providing an SR for the UL data of the C-plane and an SR for the UL data of the U-plane is disclosed. It is preferable to make the SR for the UL data of the C-plane and the SR for the UL data of the U-plane distinguishable. For example, the information bit string patterns used for each SR are made different. Alternatively, the identification codes or sequences multiplied by each SR are made different. Alternatively, the resources on the frequency axis and / or the time axis used for each SR notification are made different. Alternatively, as information in the SR, an identifier for identifying whether it is the UL data of the C-plane or the U-plane is provided, and so on.

[0721] As a result, the eNB notified of the SR can explicitly determine whether the SR is for the UL data of the C-plane or the UL data of the U-plane.

[0722] The setting information of each SR for the target UE in each eNB (cell) may be notified to the UE individually from each eNB (cell) in advance. It is advisable to use the method described above.

[0723] (3) By providing an SR for UL data in the C-plane and an SR for UL data in the U-plane, and having the UE transmit an SR corresponding to each uplink data, the C-plane cell (eNB) that receives the SR can determine whether it is for UL data in the C-plane or UL data in the U-plane. Therefore, it becomes possible to recognize whether scheduling should be performed on the C-plane establishment cell (eNB) or the U-plane establishment cell (eNB). In the case of the SR for UL data in the U-plane, it is advisable to notify the U-plane establishment cell (eNB) of information equivalent to the SR. A new message may be provided for this notification.

[0724] As a result, the UE can recognize which cell (eNB) it should notify the SR to for the generated data. Also, the C-plane establishment cell (eNB) and the U-plane establishment cell (eNB) can recognize what data has been generated, and the cell (eNB) that receives the SR or information equivalent to the SR can perform scheduling for uplink data.

[0725] The method of providing an SR for UL data in the C-plane and an SR for UL data in the U-plane, and having the UE transmit an SR corresponding to each uplink data may also be applied to the methods (1) and (2) described above. The eNB that receives the SR can explicitly determine which data it is based on the SR.

[0726] In the above, a method of separating the handling of UL data in the U-plane and UL data in the C-plane in the UE has been disclosed, but it is also acceptable if the UE does not separate the handling of UL data in the U-plane and UL data in the C-plane.

[0727] In this case, as a method for transmitting the SR, the UE transmits the SR to the C-plane establishment cell (eNB). Whether the uplink data is U-plane UL data or C-plane UL data, the same SR is used for transmission. For the SR configuration, the SR configuration in the C-plane establishment cell (eNB) may be used. The C-plane establishment cell (eNB) that receives the SR schedules the data using its own cell (eNB). If the U-plane is not established, it is advisable to perform U-plane establishment processing.

[0728] When the C-plane establishment cell (eNB) is able to determine whether the UL data is C-plane or U-plane UL data, if there is uplink data in the U-plane, the C-plane establishment cell (eNB) that receives the SR may notify the U-plane establishment cell (eNB) of information equivalent to the SR. A new message may be provided for this notification. It is advisable to perform scheduling from the U-plane establishment cell (eNB). The UE may transmit data from the U-plane establishment cell (eNB) to the U-plane according to the scheduling from the U-plane establishment cell (eNB).

[0729] Thereby, the UE can recognize which cell (eNB) it should notify the SR to. The cell (eNB) that receives the SR or information equivalent to the SR can perform scheduling for uplink data.

[0730] Note that the C-plane establishment cell (eNB) that receives the SR from the UE to be communicated with may request the MME to perform a new DRB configuration for the UE to be communicated with. Alternatively, a new U-plane establishment eNB may be selected and a request may be made to perform DRB configuration. The method disclosed in Modification Example 1 from Embodiment 2 to Embodiment 3 may be applied according to the situation. It becomes possible to increase the communication capacity for the UE to be communicated with.

[0731] Embodiment 5. When ...

Claims

1. A mobile communication system in which a first base station and a second base station communicate with a mobile terminal in parallel, and the first base station is changed from a first source base station to a first target base station, In a state in which the first source base station and the second base station are communicating with the mobile terminal in parallel, the first source base station notifies the first target base station of a handover request; notifying the first source base station of a handover response from the first target base station; notifying the mobile terminal from the first source base station that the first source base station communicating with the mobile terminal is changed to the first target base station; A mobile communication system, characterized in that the first target base station and the second base station transition to a state in which they communicate with the mobile terminal in parallel.

2. 2. The mobile communication system according to claim 1, wherein a handover request message for notifying the handover request includes information about the second base station.

3. 2. The mobile communication system according to claim 1, wherein a handover response message for notifying the handover response includes information about the second base station.

4. The mobile communication system according to claim 1 , wherein a base station change message for notifying that the first source base station is changed to the first target base station includes information of the second base station.

5. A first source base station in a mobile communication system in which a first base station and a second base station communicate with a mobile terminal in parallel, and the first base station is changed from a first source base station to a first target base station, notifying the first target base station of a handover request while communicating with the mobile terminal in parallel with the second base station; A handover response is notified from the first target base station; notifying the mobile terminal of a change in the first base station communicating with the mobile terminal to the first target base station; A first source base station, characterized in that the first target base station and the second base station transition to a state in which they communicate with the mobile terminal in parallel.

6. A first target base station in a mobile communication system in which a first base station and a second base station communicate with a mobile terminal in parallel and the first base station is changed from a first source base station, In a state in which the first source base station and the second base station are communicating with the mobile terminal in parallel, a handover request is notified from the first source base station; notifying the first source base station of a handover response; notifying the mobile terminal from the first source base station that the first base station communicating with the mobile terminal is to be changed from the first source base station; A first target base station that transitions to a state in which it communicates with the mobile terminal in parallel with the second base station.

7. A mobile terminal in a mobile communication system in which a first base station and a second base station communicate in parallel and the first base station is changed from a first source base station to a first target base station, In a state in which the first source base station and the second base station are communicating with the mobile terminal in parallel, a handover request is notified from the first source base station to the first target base station; A handover response is notified from the first target base station to the first source base station; A notification is received from the first source base station that the first source base station is changed to the first target base station; A mobile terminal, characterized in that it transitions to a state in which it communicates with the first target base station and the second base station in parallel.

Images