Communication system, master base station, secondary base station, and user device

Abstract

To provide a communication system capable of transmitting data from a mobile terminal device when a handover is performed between large-scale base station devices that communicate with the mobile terminal device both directly and via small-scale base station devices.SOLUTION: A communication system according to the present disclosure includes a plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station, and a user device capable of wireless communication with the plurality of base stations. In a handover process from the first master base station to the second master base station for the user device that communicates using a split bearer, which is a communication path split between the first master base station and the secondary base station, the secondary base station is not changed and the split bearer is maintained. The second master base station decides not to change the secondary base station that communicates with the user device, and the secondary base station is not changed and is maintained.SELECTED DRAWING: Figure 8

Description

[Technical field]

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

[0002] 3GPP (3rd Generation Partnership Project) (registered trademark, the same applies below), a standardization organization for mobile communication systems, is considering a communication method called Long Term Evolution (LTE) for wireless sections and System Architecture Evolution (SAE) for the overall system configuration including a core network and a radio access network (hereinafter collectively referred to as a network) (see, for example, Non-Patent Documents 1 to 11). This communication method is also called a 3.9G (3.9 Generation) system.

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

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

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

[0006] The Physical Broadcast Channel (PBCH) is a channel for downlink transmission from a base station device (hereinafter, sometimes simply referred to as a "base station") to a communication terminal device (hereinafter, sometimes simply referred to as a "communication terminal") such as a mobile terminal device (hereinafter, sometimes simply referred to as a "mobile terminal"). A BCH transport block is mapped to four subframes in a 40 ms interval. There is no explicit signaling of the 40 ms timing.

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

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

[0009] A physical downlink shared channel (PDSCH) is a channel for downlink transmission from a base station to a communication terminal. A downlink shared channel (DL-SCH), which is a transport channel, and a PCH, which is a transport channel, are mapped to the PDSCH.

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

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

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

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

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

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

[0016] Retransmission control using HARQ (Hybrid ARQ) is applied to the Downlink Shared Channel (DL-SCH). DL-SCH can be broadcast to the entire coverage of a base station (cell). DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called persistent scheduling. DL-SCH supports discontinuous reception (DRX) of communication terminals to reduce power consumption of communication terminals. DL-SCH is mapped to the physical downlink shared channel (PDSCH).

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

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

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

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

[0021] Let us explain about HARQ. HARQ is a technology that improves the communication quality of a transmission line by combining Automatic Repeat reQuest (ARQ) and Forward Error Correction. HARQ has the advantage that error correction works effectively by retransmission even for transmission lines whose communication quality changes. In particular, it is possible to obtain further quality improvement by combining the reception result of the initial transmission and the reception result of the retransmission when retransmitting.

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

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

[0024] The Paging Control Channel (PCCH) is a downlink channel for transmitting paging information and changes to system information. The PCCH is used when the network does not know the cell location of the communication terminal. The PCCH, which is a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

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

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

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

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

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

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

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

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

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

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

[0035] In 3GPP, base stations called Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB) are under consideration. HNB in ​​UTRAN and HeNB in ​​E-UTRAN are base stations for home, corporate and commercial access services, for example. Non-Patent Document 2 discloses three different modes of access to HeNB and HNB. Specifically, an open access mode, a closed access mode and a hybrid access mode are disclosed.

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

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

[0038] Non-Patent Document 3 discloses the basic operation of a communication terminal using PCI split. A communication terminal that does not have PCI split information must use all PCIs, for example, all 504 codes, to perform a cell search. In contrast, a communication terminal that has PCI split information can perform a cell search using the PCI split information.

[0039] 3GPP is also working on the development of standards for Long Term Evolution Advanced (LTE-A) as Release 10 (see Non-Patent Documents 3 and 4). LTE-A is based on the LTE wireless communication method, and is configured by adding several new technologies to it.

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

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

[0042] According to the capability of the UE, a secondary cell (SCell) is configured to form a pair of a PCell and a serving cell. In the downlink, the carrier corresponding to the SCell is a downlink secondary component carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is an uplink secondary component carrier (UL SCC).

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

[0044] New technologies for LTE-A include wider bandwidth extension and Coordinated Multiple Point transmission and reception (CoMP). CoMP, which is being considered for LTE-A by 3GPP, is described in Non-Patent Document 5.

[0045] Mobile network traffic is on the rise, and communication speeds are also getting faster. Once LTE and LTE-A are fully operational, communication speeds are expected to become even faster.

[0046] In addition, in 3GPP, in order to handle the huge traffic in the future, the use of small eNBs (hereinafter sometimes referred to as "small-scale base station devices") that configure small cells is being considered. For example, technologies are being considered that improve frequency utilization efficiency and increase communication capacity by installing many small eNBs and configuring many small cells. Specifically, there is dual connectivity (DC) in which a UE connects to two eNBs to communicate. DC is described in Non-Patent Document 6. [Prior art documents] [Non-patent literature]

[0047] [Non-Patent Document 1] 3GPP TS36.300 V13.0.0 [Non-Patent Document 2] 3GPP S1-083461 [Non-Patent Document 3] 3GPP TR 36.814 V9.0.0 [Non-Patent Document 4] 3GPP TR 36.912 V10.0.0 [Non-Patent Document 5] 3GPP TR 36.819 V11.2.0 [Non-Patent Document 6] 3GPP TR-36.842 V12.0.0 [Non-Patent Document 7] 3GPP TS 36.141 V13.0.0 [Non-Patent Document 8] 3GPP TR 36.875 V13.0.0 [Non-Patent Document 9] 3GPP R2-152359 [Non-Patent Document 10] 3GPP R2-151180 [Non-Patent Document 11] 3GPP R2-152338 Summary of the Invention [Problem to be solved by the invention]

[0048] The above-mentioned Non-Patent Document 6 does not disclose a method for enabling data transmission when handover (HO) is performed between macro cells configured with macro eNBs (hereinafter sometimes referred to as "large scale base station devices") while maintaining split bearers during dual connectivity. In addition, the conventional technology has a problem that a delay occurs in the transmission of uplink data when HO is performed between macro cells.

[0049] The object of the present invention is to provide a communication system capable of transmitting data from a mobile terminal device when a handover is performed between large-scale base station devices that communicate with the mobile terminal device both directly and via small-scale base station devices. [Means for solving the problem]

[0050] The communication system of the present invention is a communication system comprising a plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station, and a user equipment capable of wireless communication with the plurality of base stations, wherein in a handover process from the first master base station to the second master base station for the user equipment communicating using a split bearer, which is a communication path split between the first master base station and the secondary base station, the second master base station decides not to change the secondary base station communicating with the user equipment, and the secondary base station is maintained unchanged. The master base station of the present invention is a master base station in a communication system comprising a plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station, and a user device capable of wireless communication with a plurality of the base stations, wherein in a handover process from the first master base station to the second master base station for the user device communicating using a split bearer, which is a communication path split between the first master base station and the secondary base station, the secondary base station is not changed and the split bearer is maintained, and the second master base station decides not to change the secondary base station communicating with the user device, and the secondary base station is maintained without being changed. The secondary base station of the present invention is a secondary base station in a communication system comprising a plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station, and a user equipment capable of wireless communication with a plurality of the base stations, wherein in a handover process from the first master base station to the second master base station for the user equipment communicating using a split bearer, which is a communication path split between the first master base station and the secondary base station, the second master base station decides not to change the secondary base station communicating with the user equipment, and the secondary base station is maintained unchanged. The user equipment of the present invention is a user equipment in a communication system comprising a plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station, and a user equipment capable of wireless communication with a plurality of the base stations, wherein in a handover process from the first master base station to the second master base station for the user equipment communicating using a split bearer, which is a communication path split between the first master base station and the secondary base station, the second master base station decides not to change the secondary base station communicating with the user equipment, the secondary base station is maintained unchanged, and the user equipment communicates with the second master base station and the secondary base station. Effect of the Invention

[0051] According to the communication system of the present invention, the mobile terminal device maintains a connection with the secondary base station during handover processing, which allows data to be transmitted from the mobile terminal device when handover is performed between the large-scale base station device that communicates with the mobile terminal device both directly and via the small-scale base station device.

[0052] The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0053] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Diagram 2] 1 is a block diagram showing the overall configuration of a communication system 200 based on the LTE standard that is being discussed in 3GPP. [Diagram 3] FIG. 3 is a block diagram showing a configuration of a mobile terminal 202 shown in FIG. 2, which is a communication terminal according to the present invention. [Figure 4] FIG. 3 is a block diagram showing a configuration of a base station 203 shown in FIG. 2 which is a base station according to the present invention. [Diagram 5]FIG. 2 is a block diagram showing the configuration of an MME according to the present invention. [Figure 6] 1 is a flowchart showing an overview of operations from cell search to standby performed by a communication terminal (UE) in an LTE communication system. [Figure 7] A diagram showing the concept of a cell configuration when macro eNBs and small eNBs are mixed. [Figure 8] FIG. 2 is a diagram showing an example of a sequence of handover processing in the communication system of the first embodiment. [Figure 9] FIG. 2 is a diagram showing an example of a sequence of handover processing in the communication system of the first embodiment. [Figure 10] FIG. 11 is a diagram showing an example of a sequence of handover processing in a communication system according to a first modification of the first embodiment. [Figure 11] FIG. 11 is a diagram showing an example of a sequence of handover processing in a communication system according to a first modification of the first embodiment. [Figure 12] FIG. 11 is a diagram showing another example of the sequence of handover processing in the communication system according to the first modification of the first embodiment. [Figure 13] FIG. 11 is a diagram showing another example of the sequence of handover processing in the communication system according to the first modification of the first embodiment. [Figure 14] FIG. 11 is a diagram showing another example of the sequence of handover processing in the communication system according to the first modification of the first embodiment. [Figure 15] FIG. 11 is a diagram showing another example of the sequence of handover processing in the communication system according to the first modification of the first embodiment. [Figure 16] FIG. 11 is a diagram showing an example of a sequence of handover processing in a communication system according to a second modification of the first embodiment. [Figure 17] FIG. 11 is a diagram showing an example of a sequence of handover processing in a communication system according to a second modification of the first embodiment. [Figure 18] FIG. 11 is a diagram showing another example of the sequence of handover processing in the communication system according to the second modification of the first embodiment. [Figure 19]FIG. 11 is a diagram showing another example of the sequence of handover processing in the communication system according to the second modification of the first embodiment. [Figure 20] FIG. 11 is a diagram showing another example of the sequence of handover processing in the communication system according to the second modification of the first embodiment. [Figure 21] FIG. 11 is a diagram showing another example of the sequence of handover processing in the communication system according to the second modification of the first embodiment. [Figure 22] FIG. 11 is a diagram showing an example of a sequence of handover processing in a communication system according to a third modification of the first embodiment. [Figure 23] FIG. 11 is a diagram showing an example of a sequence of handover processing in a communication system according to a third modification of the first embodiment. [Figure 24] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the third modification of the first embodiment. [Diagram 25] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the third modification of the first embodiment. [Figure 26] FIG. 13 is a diagram showing an example of a sequence of handover processing in a communication system according to a fourth modification of the first embodiment. [Figure 27] FIG. 13 is a diagram showing an example of a sequence of handover processing in a communication system according to a fourth modification of the first embodiment. [Figure 28] FIG. 13 is a diagram showing an example of a sequence of handover processing in a communication system according to a fifth modification of the first embodiment. [Figure 29] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the fifth modification of the first embodiment. [Diagram 30] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the fifth modification of the first embodiment. [Diagram 31] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the fifth modification of the first embodiment. [Diagram 32]FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the fifth modification of the first embodiment. [Diagram 33] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the fifth modification of the first embodiment. [Diagram 34] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the fifth modification of the first embodiment. [Diagram 35] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the fifth modification of the first embodiment. [Diagram 36] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the fifth modification of the first embodiment. [Figure 37] FIG. 23 is a diagram showing an example of a sequence of handover processing in a communication system according to a sixth modification of the first embodiment. [Figure 38] FIG. 23 is a diagram showing an example of a sequence of handover processing in a communication system according to a sixth modification of the first embodiment. [Figure 39] FIG. 23 is a diagram showing another example of the sequence of handover processing in the communication system according to the sixth modification of the first embodiment. [Diagram 40] FIG. 23 is a diagram showing another example of the sequence of handover processing in the communication system according to the sixth modification of the first embodiment. [Diagram 41] FIG. 13 is a diagram showing an example of a sequence of handover processing in a communication system according to a seventh modification of the first embodiment. [Diagram 42] FIG. 13 is a diagram showing an example of a sequence of handover processing in a communication system according to a seventh modification of the first embodiment. [Diagram 43] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the seventh modification of the first embodiment. [Diagram 44] FIG. 13 is a diagram showing another example of the sequence of handover processing in the communication system according to the seventh modification of the first embodiment. [Diagram 45] FIG. 13 is a diagram for explaining a method of transmitting a BSR when a conventional DRAT is set. [Figure 46] FIG. 13 is a diagram for explaining a method of transmitting a BSR when a conventional DRAT is set. [Figure 47] FIG. 11 is a diagram for explaining a method of transmitting a BSR in the second embodiment. [Figure 48] FIG. 10 is a diagram for explaining a method of allocating PDCP data when a conventional DRAT is set. [Figure 49] FIG. 11 is a diagram for explaining a method of transmitting PDCP data in the third embodiment. [Figure 50] FIG. 13 is a diagram for explaining a method of uplink scheduling when a conventional DRAT is set. [Figure 51] FIG. 13 is a diagram for explaining an uplink scheduling method in embodiment 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Embodiment 1 Fig. 2 is a block diagram showing the overall configuration of an LTE-based communication system 200 being discussed in 3GPP. Fig. 2 will now be described. The radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 202, which is a communication terminal device, is capable of wireless communication with a base station device (hereinafter referred to as "base station (E-UTRAN NodeB: eNB)") 203, and transmits and receives signals via wireless communication.

[0055] Here, the term "communication terminal device" includes not only mobile terminal devices such as mobile mobile phone terminal devices, but also stationary devices such as sensors. In the following description, the "communication terminal device" may be simply referred to as a "communication terminal."

[0056] If control protocols for mobile terminals 202, such as Radio Resource Control (RRC), and user plane protocols, such as Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), and Physical layer (PHY), terminate in a base station 203, then E-UTRAN is composed of one or more base stations 203.

[0057] A control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs broadcast, paging, RRC connection management, etc. The states of the base station 203 and the mobile terminal 202 in RRC include RRC_IDLE and RRC_CONNECTED.

[0058] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell re-selection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can transmit and receive data with the network. In addition, in RRC_CONNECTED, handover (HO), measurement of neighbor cells, etc. are performed.

[0059] The base station 203 is classified into an eNB 207 and a Home-eNB 206. The communication system 200 includes an eNB group 203-1 including a plurality of eNBs 207, and a Home-eNB group 203-2 including a plurality of Home-eNBs 206. A system including an EPC (Evolved Packet Core) which is a core network and an E-UTRAN 201 which is a radio access network is called an EPS (Evolved Packet System). The EPC which is a core network and the E-UTRAN 201 which is a radio access network may be collectively called a "network."

[0060] The eNB207 is connected to a Mobility Management Entity (MME), or a Serving Gateway (S-GW), or an MME / S-GW unit (hereinafter sometimes referred to as an "MME unit") 204 including an MME and an S-GW via an S1 interface, and control information is communicated between the eNB207 and the MME unit 204. A plurality of MME units 204 may be connected to one eNB207. The eNBs 207 are connected to each other via an X2 interface, and control information is communicated between the eNBs 207.

[0061] The Home-eNB 206 is connected to the MME unit 204 via an S1 interface, and control information is communicated between the Home-eNB 206 and the MME unit 204. A plurality of Home-eNBs 206 are connected to one MME unit 204. Alternatively, the Home-eNB 206 is connected to the MME unit 204 via a Home-eNB GateWay (HeNBGW) 205. The Home-eNB 206 and the HeNBGW 205 are connected to each other via an S1 interface, and the HeNBGW 205 and the MME unit 204 are connected to each other via the S1 interface.

[0062] One or more Home-eNBs 206 are connected to one HeNBGW 205, and information is communicated through an S1 interface. The HeNBGW 205 is connected to one or more MME units 204, and information is communicated through an S1 interface.

[0063] The MME unit 204 and the HeNBGW 205 are upper devices, specifically, upper nodes, and control connections between the eNB 207 and the Home-eNB 206, which are base stations, and the mobile terminal (UE) 202. The MME unit 204 constitutes the EPC, which is a core network. The base station 203 and the HeNBGW 205 constitute the E-UTRAN 201.

[0064] Furthermore, 3GPP is considering the following configuration. The X2 interface between Home-eNBs 206 is supported. That is, the Home-eNBs 206 are connected via the X2 interface, and control information is communicated between the Home-eNBs 206. From the MME unit 204, the HeNBGW 205 appears as the Home-eNB 206. From the Home-eNB 206, the HeNBGW 205 appears as the MME unit 204.

[0065] In either case where the Home-eNB 206 is connected to the MME unit 204 via the HeNBGW 205 or where the Home-eNB 206 is directly connected to the MME unit 204, the interface between the Home-eNB 206 and the MME unit 204 is the same, that is, the S1 interface.

[0066] The base station 203 may configure one cell or multiple cells. Each cell has a predetermined range as a coverage area in which communication with the mobile terminal 202 is possible, and performs wireless communication with the mobile terminal 202 within the coverage area. When one base station 203 configures multiple cells, each cell is configured to be able to communicate with the mobile terminal 202.

[0067] FIG. 3 is a block diagram showing the configuration of the mobile terminal 202 shown in FIG. 2, which is a communication terminal according to the present invention. The transmission process of the mobile terminal 202 shown in FIG. 3 will be described. First, the control data from the protocol processing unit 301 and the user data from the application unit 302 are stored in the transmission data buffer unit 303. The data stored in the transmission data buffer unit 303 is passed to the encoder unit 304, where encoding such as error correction is performed. There may be data that is directly output from the transmission data buffer unit 303 to the modulation unit 305 without encoding. The data that has been encoded by the encoder unit 304 is modulated by the modulation unit 305. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 306, where it is converted into a radio transmission frequency. Thereafter, a transmission signal is transmitted from the antenna 307 to the base station 203.

[0068] Moreover, the receiving process of the mobile terminal 202 is executed as follows. A radio signal from the base station 203 is received by the antenna 307. The received signal is converted from a radio receiving frequency to a baseband signal by the frequency conversion unit 306, and demodulated by the demodulation unit 308. The demodulated data is passed to the decoder unit 309, where decoding such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 301, and the user data is passed to the application unit 302. A series of processes of the mobile terminal 202 is controlled by the control unit 310. Therefore, although the control unit 310 is omitted in FIG. 3, it is connected to each of the units 301 to 309.

[0069] Fig. 4 is a block diagram showing the configuration of the base station 203 shown in Fig. 2 which is a base station according to the present invention. A transmission process of the base station 203 shown in Fig. 4 will be described. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (MME unit 204, etc.), the HeNBGW 205, etc. The other base station communication unit 402 transmits and receives data with other base stations. The EPC communication unit 401 and the other base station communication unit 402 each exchange information with a protocol processing unit 403. The control data from the protocol processing unit 403, and the user data and control data from the EPC communication unit 401 and the other base station communication unit 402 are stored in a transmission data buffer unit 404.

[0070] The data stored in the transmission data buffer unit 404 is passed to the encoder unit 405, where it is subjected to encoding processing such as error correction. Some data may be output directly from the transmission data buffer unit 404 to the modulator unit 406 without being encoded. The encoded data is modulated in the modulator unit 406. The modulated data is converted into a baseband signal, and then output to the frequency converter unit 407, where it is converted into a radio transmission frequency. The transmission signal is then transmitted from the antenna 408 to one or more mobile terminals 202.

[0071] Moreover, the reception process of the base station 203 is executed as follows. A radio signal from one or more mobile terminals 202 is received by an antenna 408. The received signal is converted from a radio reception frequency to a baseband signal by a frequency conversion unit 407, and demodulated by a demodulation unit 409. The demodulated data is passed to a decoder unit 410, where a decoding process such as error correction is performed. Of the decoded data, the control data is passed to a protocol processing unit 403 or an EPC communication unit 401 or an other base station communication unit 402, and the user data is passed to the EPC communication unit 401 and the other base station communication unit 402. A series of processes of the base station 203 is controlled by a control unit 411. Therefore, although the control unit 411 is omitted in FIG. 4, it is connected to each unit 401 to 410.

[0072] FIG. 5 is a block diagram showing the configuration of the MME according to the present invention. FIG. 5 shows the configuration of the MME 204a included in the MME unit 204 shown in FIG. 2 described above. The PDN GW communication unit 501 transmits and receives data between the MME 204a and the PDN GW. The base station communication unit 502 transmits and receives data between the MME 204a and the base station 203 via the S1 interface. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 501 to the base station communication unit 502 via the user plane communication unit 503 and transmitted to one or more base stations 203. If the data received from the base station 203 is user data, the user data is passed from the base station communication unit 502 to the PDN GW communication unit 501 via the user plane communication unit 503 and transmitted to the PDN GW.

[0073] When the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 501 to the control plane control unit 505. When the data received from the base station 203 is control data, the control data is passed from the base station communication unit 502 to the control plane control unit 505.

[0074] The HeNBGW communication unit 504 is provided when a HeNBGW 205 is present, and transmits and receives data via an interface (IF) between the MME 204a and the HeNBGW 205 depending on the information type. Control data received from the HeNBGW communication unit 504 is passed from the HeNBGW communication unit 504 to a control plane control unit 505. A result of processing in the control plane control unit 505 is transmitted to the PDN GW via the PDN GW communication unit 501. In addition, a result of processing in the control plane control unit 505 is transmitted to one or more base stations 203 by the S1 interface via the base station communication unit 502, and is also transmitted to one or more HeNBGW 205 via the HeNBGW communication unit 504.

[0075] The control plane control unit 505 includes a NAS security unit 505-1, an SAE bearer control unit 505-2, an idle state mobility management unit 505-3, etc., and performs general processing for the control plane. The NAS security unit 505-1 performs security for NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 505-2 performs management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 505-3 performs mobility management in the idle state (also called the LTE-IDLE state or simply idle), generation and control of paging signals in the idle state, addition, deletion, update, search, tracking area list management, etc. for one or more mobile terminals 202 under its control.

[0076] The MME 204a distributes a paging signal to one or more base stations 203. The MME 204a also performs mobility control in an idle state. The MME 204a manages a tracking area list when the mobile terminal is in an idle state and in an active state. The MME 204a initiates a paging protocol by transmitting a paging message to a cell that belongs to a tracking area in which the UE is registered. The idle state mobility management unit 505-3 may manage the CSG, CSG-ID, and whitelist of the Home-eNB 206 connected to the MME 204a.

[0077] Next, an example of a cell search method in a communication system is shown. Fig. 6 is a flow chart showing an outline of a process from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. When the communication terminal starts a cell search, in step ST601, the communication terminal synchronizes slot timing and frame timing using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a surrounding base station.

[0078] P-SS and S-SS are collectively called the Synchronization Signal (SS). The Synchronization Signal (SS) is assigned a synchronization code that corresponds one-to-one to the PCI assigned to each cell. 504 different PCIs are being considered. These 504 different PCIs are used to achieve synchronization and to detect (identify) the PCI of the synchronized cell.

[0079] Next, in step ST602, for the synchronized cell, a cell-specific reference signal (CRS), which is a reference signal (RS) transmitted from the base station for each cell, is detected, and the RS received power (Reference Signal Received Power: RSRP) is measured. A code that has a one-to-one correspondence with the PCI is used for the reference signal (RS). By correlating with the code, it is possible to separate the cell from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST1, it is possible to detect the RS and measure the RS received power.

[0080] Next, in step ST603, the cell with the best RS reception quality, for example the cell with the highest RS reception power, that is, the best cell, is selected from among one or more cells detected up to step ST602.

[0081] Next, in step ST604, the PBCH of the best cell is received to obtain the BCCH, which is broadcast information. A MIB (Master Information Block), which includes cell configuration information, is mapped to the BCCH on the PBCH. Therefore, the MIB can be obtained by receiving the PBCH and obtaining the BCCH. Examples of MIB information include DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, SFN (System Frame Number), and the like.

[0082] Next, in step ST605, the DL-SCH of the cell is received based on the cell configuration information in the MIB, and SIB (System Information Block) 1 in the broadcast information BCCH is obtained. SIB 1 includes information on access to the cell, information on cell selection, and scheduling information of other SIBs (SIBk; k is an integer ≧2). SIB 1 also includes a tracking area code (TAC).

[0083] Next, in step ST606, the communication terminal compares the TAC of the SIB1 received in step ST605 with the TAC portion of the tracking area identity (TAI) in the tracking area list that the communication terminal already holds. The tracking area list is also called a TAI list. The TAI is identification information for identifying a tracking area, and is composed of a MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a code number of the tracking area.

[0084] If the TAC received in step ST605 is the same as the TAC included in the tracking area list as a result of the comparison in step ST606, the communication terminal enters standby mode in the cell. If the TAC received in step ST605 is not included in the tracking area list as a result of the comparison, the communication terminal requests a core network (EPC) including an MME, etc., to change the tracking area in order to perform a Tracking Area Update (TAU) through the cell.

[0085] An apparatus constituting a core network (hereinafter sometimes referred to as a "core network side apparatus") updates the tracking area list based on an identification number (such as a UE-ID) of a communication terminal sent from the communication terminal together with a TAU request signal. The core network side apparatus transmits the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) the TAC list held by the communication terminal based on the received tracking area list. After that, the communication terminal enters standby mode in the cell.

[0086] The spread of smartphones and tablet terminal devices has led to an explosive increase in traffic via cellular wireless communications, raising concerns about a shortage of wireless resources around the world. In response to this, efforts are being made to create smaller cells and promote spatial separation in order to improve frequency utilization efficiency.

[0087] In a conventional cell configuration, a cell configured by an eNB has a relatively wide coverage area. Conventionally, a cell is configured to cover a certain area by the relatively wide coverage areas of a plurality of cells configured by a plurality of eNBs.

[0088] In the case of small cell configuration, the cell configured by the eNB has a narrower coverage range than the coverage of the cell configured by the conventional eNB. Therefore, as in the past, in order to cover a certain area, a large number of small cell eNBs are required compared to the conventional eNBs.

[0089] In the following description, a cell with a relatively large coverage, such as a cell configured by a conventional eNB, is referred to as a "macro cell," and an eNB that configures a macro cell is referred to as a "macro eNB" (hereinafter sometimes referred to as a "large-scale base station device"). Also, a cell with a relatively small coverage, such as a cell that has been converted into a small cell, is referred to as a "small cell," and an eNB that configures a small cell is referred to as a "small eNB" (hereinafter sometimes referred to as a "small-scale base station device").

[0090] The macro eNB may be, for example, a “Wide Area Base Station” as described in Non-Patent Document 7.

[0091] The small eNB may be, for example, a low power node, a local area node, a hotspot, etc. Also, the small eNB may be a pico eNB constituting a pico cell, a femto eNB constituting a femto cell, a HeNB, a remote radio head (RRH), a remote radio unit (RRU), a remote radio equipment (RRE), or a relay node (RN). Also, the small eNB may be a "local area base station" or a "home base station" as described in Non-Patent Document 7.

[0092] 7 is a diagram showing the concept of a cell configuration when macro eNBs and small eNBs are mixed. A macro cell configured by a macro eNB has a relatively wide coverage area 701. A small cell configured by a small eNB has a coverage area 702 that is smaller than the coverage area 701 of the macro eNB (macro cell).

[0093] When multiple eNBs are mixed, the coverage of a cell configured by one eNB may be included in the coverage of a cell configured by another eNB. In the cell configuration shown in Fig. 7, as shown by reference numerals "704" and "705", the coverage 702 of a small cell configured by a small eNB may be included in the coverage 701 of a macro cell configured by a macro eNB.

[0094] Also, as indicated by reference numeral "705," the coverage of multiple, for example, two, small cells 702 may be included within the coverage of one macro cell 701. A mobile terminal (UE) 703 is included, for example, within the coverage 702 of the small cell and communicates via the small cell.

[0095] Furthermore, in the cell configuration shown in FIG. 7, as indicated by reference numeral "706," there may be cases where coverage 701 of a macro cell formed by a macro eNB and coverage 702 of a small cell formed by a small eNB overlap in a complex manner.

[0096] Also, as indicated by reference numeral "707," there may be cases where coverage 701 of a macro cell configured by a macro eNB and coverage 702 of a small cell configured by a small eNB do not overlap.

[0097] Furthermore, as indicated by reference numeral "708," there may be cases where the coverage 702 of multiple small cells formed by multiple small eNBs is formed within the coverage 701 of one macro cell formed by one macro eNB.

[0098] In the following description, one of the eNBs performing dual connectivity (DC) may be referred to as a "master eNB (abbreviation: MeNB)" and the other as a "secondary eNB (abbreviation: SeNB)". In addition, the HO source MeNB may be referred to as a "source MeNB (abbreviation: S-MeNB)" and the HO destination MeNB may be referred to as a "target MeNB (abbreviation: T-MeNB)".

[0099] In HO between MeNBs that are executing dual connectivity (DC), it is decided to release the SeNB. In other words, DC is terminated, communication returns to only the MeNB, and HO between MeNBs is performed.

[0100] However, in the case of HO between MeNBs, there are cases where the SeNB connected to the UE that is the target of HO is not changed before and after HO, or where it is better not to change it.

[0101] If there is no change in SeNB during HO between MeNBs, the UE can communicate with the SeNB during HO, thereby enabling data communication to be performed early and delay to be reduced.

[0102] 3GPP is studying the case where there is no change in SeNB in ​​HO between MeNBs. For example, FIG. 4.3.2.3-1 in Non-Patent Document 8 discloses a sequence of HO processing between MeNBs when there is no change in SeNB. However, Non-Patent Document 8 does not disclose in detail, particularly about user plane data, such as the timing at which to start transmitting uplink data and downlink data. In addition, there is no disclosure about HO between MeNBs when there is no change in SeNB while maintaining split bearer. Here, "split bearer" refers to a bearer split into a direct path between MeNB and UE and a path between MeNB and UE via SeNB.

[0103] In this embodiment, a method is disclosed that enables data transmission between a UE and a SeNB during HO between MeNBs while maintaining a split bearer.

[0104] In this embodiment, when performing HO between MeNBs, an MeNB maintains a split bearer for a UE that is a target of HO (hereinafter, may be referred to as a "target UE").

[0105] Fig. 8 and Fig. 9 are diagrams showing an example of a sequence of handover processing in the communication system of the first embodiment. Fig. 8 and Fig. 9 are connected by a boundary line BL1. Fig. 8 and Fig. 9 show an example of a sequence of handover processing related to transmission of uplink data and downlink data in inter-MeNB HO when there is no change in SeNB.

[0106] In FIG. 8, in step ST1011, it is shown that the UE to be the HO target is in a state of executing DC with the S-MeNB and the SeNB. In step ST1012, the UE notifies the S-MeNB of the result of measuring the connection state with the S-MeNB in ​​a state of executing DC. The measurement result of this connection state is notified by using, for example, a measurement report message disclosed in Non-Patent Document 1.

[0107] In response to the measurement result of the connection state notified in Step ST1012, the S-MeNB decides to perform HO in Step ST1013.

[0108] In Step ST1014, the S-MeNB requests the T-MeNB to become the HO target of the UE. This request to become the HO target is made by using, for example, an HO request message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8. In addition, in Step ST1014, the S-MeNB notifies the T-MeNB of SeNB configuration information, which is information on the SeNB configured by the S-MeNB.

[0109] The T-MeNB that has received the HO request in Step ST1014 decides not to change the SeNB to which the UE that is the target of HO is already connected in Step ST1015. Also, the T-MeNB decides to maintain the split bearer in Step ST1015.

[0110] In Step ST1015, the T-MeNB decides not to change the SeNB and to maintain the split bearer, based on the SeNB configuration information notified from the S-MeNB.

[0111] The SeNB configuration information may include an eNB ID of the SeNB, bearer information (E-RAB ID) using the SeNB, bearer information set for the split bearer, and setting information for the split bearer.

[0112] In Step ST1016, the T-MeNB instructs the SeNB to configure that there is no change in the SeNB while maintaining the split bearer. This instruction is performed by using, for example, an SeNB addition request message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0113] In Step ST1017, the SeNB instructed in Step ST1016 sets the SeNB to be unchanged while maintaining the split bearer, and responds to the T-MeNB that the setting is complete. This response is made by using, for example, an SeNB addition request ack message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0114] The T-MeNB that has received the response in Step ST1017 responds to the S-MeNB in ​​Step ST1018 in response to the request to become the HO target in Step ST1014. This response is made by using, for example, an HO request response (HO request Ack) message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0115] Here, the split bearer configuration information included in the SeNB addition request in Step ST1016 may be omitted partly or entirely. Alternatively, only the part of the split bearer configuration information that does not change may be omitted.

[0116] In Step ST1019, the S-MeNB that has received the response in Step ST1018 requests the SeNB to release the SeNB. This request is made by using, for example, an SeNB release request message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0117] The SeNB release request of Step ST1019 is a release request for the bearer configuration of the SeNB configured by the S-MeNB.

[0118] The SeNB that has received the SeNB release request in Step ST1019 releases the bearer configuration configured by the S-MeNB. At this time, the split bearer configuration configured by the T-MeNB is not released, including the omitted configuration.

[0119] In Step ST1020, the S-MeNB notifies the target UE of the maintenance of the split bearer using the same SeNB. In accordance with the notified information, the target UE maintains the already set split bearer configuration without going through the process of changing the configuration to the MeNB bearer configuration once and then changing it to the split bearer configuration again.

[0120] A method for notifying a target UE of the maintenance of a split bearer using the same SeNB is disclosed. Information indicating that the split bearer is maintained may be provided. Also, information indicating that the same SeNB is used may be provided.

[0121] The notification of the target UE to maintain the split bearer using the same SeNB may be sent from the S-MeNB to the target UE, or the T-MeNB may notify the S-MeNB of the setting information, and the S-MeNB may notify the target UE.

[0122] The information indicating the use of the same SeNB may have a size of 1 bit. The information indicating the maintenance of the split bearer may have a size of 1 bit. The information indicating the maintenance of the split bearer using the same SeNB may have a size of 1 bit.

[0123] In Step ST1020, the information indicating the maintenance of the split bearer using the same SeNB is notified by adding it to, for example, an RRC Connection Reconfiguration message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8. Also, it may be notified together with Mobility Control Information (MCI) of the RRC Connection Reconfiguration message.

[0124] In Step ST1020, when the information indicating the maintenance of the split bearer is notified, the detailed configuration of the split bearer may be changed, or information on the detailed configuration of the split bearer may be notified.

[0125] Another method for notifying the target UE of maintaining the split bearer with the same SeNB is disclosed. The T-MeNB notifies the target UE of the re-establishment of the split bearer.

[0126] The notification to the target UE is performed by notifying the S-MeNB of SeNB configuration information from the T-MeNB, and then notifying the target UE from the S-MeNB. The information to be notified is the addition of SeNB and split bearer configuration. This notification may be notified in step ST1020 by adding it to an RRC connection reconfiguration message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8. It may also be notified together with the MCI of the RRC connection reconfiguration message.

[0127] The information that the T-MeNB notifies the target UE is set to the same setting as the bearer configuration information of the SeNB that the S-MeNB set. In this case, some or all of the SeNB settings and split bearer configuration information may be omitted. Or, only the unchanged information may be omitted.

[0128] When part or all of the SeNB configuration and split bearer configuration information is omitted, the S-MeNB may determine the information to be omitted using information from the T-MeNB, or the T-MeNB may determine the information to be omitted using information from the S-MeNB.

[0129] In step ST1021, the target UE judges whether or not it is possible to set up a split bearer configuration for the notified SeNB. If it is judged that the setting is possible, the target UE proceeds to step ST1022. If it is judged that the setting is not possible, the HO process between MeNBs in the case where the SeNB is not changed while maintaining the split bearer is not possible, and therefore the process disclosed in FIG. 4.3.2.3-1 of non-patent document 8 is performed as another HO process.

[0130] If it is determined in Step ST1021 that a split bearer configuration for the SeNB can be set and the process proceeds to Step ST1022, in Step ST1022, the target UE sets a split bearer configuration for the corresponding SeNB and T-MeNB.

[0131] In particular, the configuration for the SeNB is disclosed. When the configuration is for maintaining a split bearer using the same SeNB, the target UE does not need to reset the MAC of the SeNB (SCG (Secondary Cell Group) in Non-Patent Document 1), and reconfigures the MAC. Reconfigures the RLC of the SeNB (SCG). Reconfigures the PDCP of the SeNB (SCG).

[0132] In Step ST1023, the target UE performs RA processing with the T-MeNB and synchronizes with the T-MeNB.

[0133] In Step ST1024, the target UE that has performed the RA process notifies the T-MeNB of the completion of the configuration of the T-MeNB configuration and the SeNB configuration. This notification is performed using, for example, an RRC Connection Reconfiguration Complete message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0134] The target UE that has completed the connection transmits uplink data to the T-MeNB in ​​step ST1025 shown in Fig. 9. The transmission of the uplink data in step ST1025 is performed after the notification of the completion of the setting in step ST1024, which indicates the completion of the connection, as shown in Figs. 8 and 9.

[0135] In step ST1026, the T-MeNB, having received the uplink data, transmits the received uplink data to the S-GW.

[0136] The T-MeNB that has received the notification of completion of configuration of the T-MeNB configuration and the SeNB configuration in step ST1024 shown in Fig. 8 notifies the SeNB that the SeNB configuration in the UE has been completed in step ST1027 shown in Fig. 9. This notification is performed by using, for example, a SeNB reconfiguration complete message disclosed in Fig. 4.3.2.3-1 of Non-Patent Document 8.

[0137] The SeNB that has been notified in Step ST1027 that the SeNB configuration in the UE has been completed performs RA processing with the target UE in Step ST1028. As a result, the target UE is synchronized with the SeNB.

[0138] In step ST1029, the target UE that has performed the RA process transmits uplink data to the SeNB.

[0139] In step ST1030, the SeNB that has received the uplink data transmits the received uplink data to the T-MeNB.

[0140] The T-MeNB that has received the uplink data in Step ST1030 transmits the received uplink data to the S-GW in Step ST1031. As a result of this process, DC is being executed for the uplink data.

[0141] In Step ST1032, the T-MeNB that has completed the connection with the target UE makes a path switch request to the MME to change the destination of downlink data from the S-GW from the S-MeNB to the T-MeNB. This request is made using, for example, a path switch request message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0142] In Step ST1033, the MME that has received the path switch request requests the S-GW to modify the bearer. This request is made by using, for example, a modify bearer request message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0143] The S-GW that has received the bearer change request performs path switching in Step ST1034. The path switching is a process of changing a path, which is a communication path between the UE and the MeNB, from a path formed by the S-MeNB and the UE to a path formed by the T-MeNB and the UE.

[0144] Specifically, in Step ST1034, the S-GW changes the transmission destination of the downlink data to the T-MeNB. In Step ST1035, the S-GW transmits the downlink data to the T-MeNB.

[0145] The T-MeNB that has received the downlink data starts transmission through the split bearer with the SeNB. In Step ST1036, the T-MeNB transmits the downlink data to the target UE.

[0146] Furthermore, in Step ST1037, the T-MeNB transmits downlink data to the SeNB. In Step ST1038, the SeNB that has received the downlink data transmits the downlink data to the target UE.

[0147] In Step ST1039, the S-GW that has changed the destination of the downlink data to the T-MeNB responds to the MME that it has received the bearer modification request. This response is made by using, for example, a modify bearer request ack message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0148] In Step ST1039, the MME that has received the bearer change request response transmits a path switch request response to the T-MeNB in ​​Step ST1040. This response is performed by using, for example, a path switch request Ack message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0149] In Step ST1041, the T-MeNB that has received the path switch request response in Step ST1040 notifies the S-MeNB of the release of the UE context. This notification is performed by using, for example, a UE context release message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0150] In Step ST1042, the S-MeNB that has received the UE context release notification requests the SeNB to release the UE context. This notification is performed, for example, by using a UE context release message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8. The SeNB that has received the UE context release request releases the UE context.

[0151] As described above, in this embodiment, a method for enabling data transmission between a UE and a SeNB during HO between MeNBs while maintaining a split bearer has been disclosed. Specifically, in this embodiment, transmission of uplink data is started before a path switch process by an S-GW. That is, in this embodiment, the UE maintains a connection with the SeNB during the HO process, and starts transmitting data to the SeNB in ​​step ST1029 before the path switch in step ST1034 is performed.

[0152] This allows data to be transmitted from the UE when HO is performed between MeNBs that communicate with the UE both directly and via SeNBs, thereby reducing the delay in transmitting uplink data.

[0153] First embodiment, modified example 1 As another example of the RA process with the SeNB and the transmission of uplink data in the first embodiment, a first modification of the first embodiment will be disclosed.

[0154] Figures 10 and 11 are diagrams showing an example of a sequence of handover processing in a communication system according to the first modification of the first embodiment. Figures 10 and 11 are connected by a boundary line BL2. Figures 10 and 11 show an example of a sequence of transmission of uplink data and downlink data in inter-MeNB HO when there is no change in SeNB, as a handover processing. Since the handover processing in this modification is similar to the handover processing in the first embodiment shown in Figures 9 and 10 described above, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0155] The processes of steps ST1011 to ST1026 and steps ST1051 to ST1053 are performed in the same manner as in the above-described first embodiment. In step ST1024, the T-MeNB that has received the notification of the completion of the configuration of the T-MeNB configuration and the SeNB configuration notifies the SeNB that the configuration of the SeNB in ​​the UE has been completed in step ST1027. This notification is performed by using, for example, a SeNB reconfiguration complete message disclosed in FIG. 4.3.2.3-1 of non-patent document 8.

[0156] In step ST1028B1, the target UE that has transmitted uplink data in step ST1025 performs RA processing with the SeNB and synchronizes with the SeNB. In step ST1029B1, the target UE that has synchronized with the SeNB transmits uplink data to the SeNB. The SeNB that has received the uplink data may provide a buffer for the received uplink data. This may buffer the received data.

[0157] In this modification, as shown in FIG. 11, before the SeNB receives a notification that the SeNB configuration in the UE has been completed in Step ST1027, the RA process in Step ST1028B1 and the transmission of uplink data in Step ST1029B1 are performed.

[0158] Thereafter, the processes of steps ST1030 to ST1042 are performed in the same manner as in the above-described embodiment 1. In this manner, the UE can transmit uplink data to the SeNB early without waiting for the process of step ST1027. In addition, when it becomes possible to transmit uplink data from the SeNB to the T-MeNB, the uplink data is immediately transmitted, so that it is possible to reduce a delay in transmitting uplink data during HO.

[0159] Figures 12 and 13 are diagrams showing another example of the sequence of handover processing in a communication system according to the first modification of the first embodiment. Figures 12 and 13 are connected by a boundary line BL3. Figures 12 and 13 show an example of a sequence of transmission of uplink data in inter-MeNB HO when there is no change in SeNB, as the handover processing. The handover processing in this modification is similar to the handover processing in the first embodiment shown in Figures 9 and 10 described above, so the same step numbers are used for the same steps, and common explanations will be omitted.

[0160] The processes of steps ST1011 to ST1022 and steps ST1051 to ST1053 are performed in the same manner as in the above-described embodiment 1. Next, in step ST1023, the target UE performs RA processing with the T-MeNB and synchronizes with the T-MeNB.

[0161] In Step ST1028C1, the target UE that has been synchronized with the T-MeNB in ​​the RA process in Step ST1023 performs RA process with the SeNB and synchronizes with the SeNB.

[0162] In Step ST1029C1, the target UE synchronized with the SeNB transmits uplink data to the SeNB. The SeNB that receives the uplink data may provide a buffer for the received uplink data. This may buffer the received data.

[0163] In Step ST1024, the target UE that has transmitted the uplink data notifies the T-MeNB of the completion of the configuration of the T-MeNB configuration and the SeNB configuration. This notification is performed by using, for example, an RRC Connection Reconfiguration Complete message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0164] In Step ST1025, the target UE that has completed the connection transmits uplink data to the T-MeNB. In this manner, the transmission of uplink data in Step ST1025 is performed, for example, after the notification of the completion of setting in Step ST1024, which indicates the completion of the connection.

[0165] In step ST1026, the T-MeNB, having received the uplink data, transmits the received uplink data to the S-GW.

[0166] The T-MeNB that has received the notification of completion of the configuration of the T-MeNB configuration and the SeNB configuration in Step ST1024 notifies the SeNB that the configuration of the SeNB in ​​the UE has been completed in Step ST1027. This notification is performed by using, for example, a SeNB reconfiguration complete message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0167] Thereafter, the processes of steps ST1030 to ST1042 are performed in the same manner as in the above-described embodiment 1. In this manner, the UE can transmit uplink data to the SeNB early without waiting for the process of step ST1024. In addition, when it becomes possible to transmit uplink data from the SeNB to the T-MeNB, the uplink data is immediately transmitted, so that it is possible to reduce a delay in transmitting uplink data during HO.

[0168] Figures 14 and 15 are diagrams showing another example of the sequence of handover processing in a communication system according to the first modification of the first embodiment. Figures 14 and 15 are connected by a boundary line BL4. Figures 14 and 15 show another example of the sequence of transmission of uplink data in an inter-MeNB uplink HO as handover processing when there is no change in SeNB. The handover processing in this modification is similar to the handover processing in the first embodiment shown in Figures 9 and 10 described above, so the same step numbers are used for the same steps and common explanations are omitted.

[0169] The processes of steps ST1011 to ST1020 and steps ST1051 to ST1053 are performed in the same manner as in the above-mentioned first embodiment. In step ST1021, the target UE judges whether or not it is possible to set up a split bearer configuration for the notified SeNB. If it is judged that the setting is possible, it proceeds to step ST1022. If it is judged that the setting is not possible, it is not possible to perform HO processing between MeNBs in the case where the SeNB is not changed while maintaining the split bearer, and therefore, the process disclosed in FIG. 4.3.2.3-1 of non-patent document 8 is performed as another HO processing.

[0170] In Step ST1022, the target UE sets a split bearer configuration for the corresponding SeNB and T-MeNB.

[0171] In particular, the configuration for the SeNB is disclosed. If the target UE is configured to maintain the split bearer using the same SeNB, it does not need to reset the MAC of the SeNB (SCG), and reconfigures the MAC. Reconfigures the RLC of the SeNB (SCG). Reconfigures the PDCP of the SeNB (SCG).

[0172] The target UE that has set a split bearer configuration for the relevant SeNB and T-MeNB in ​​ST 1022 performs RA processing with the SeNB in ​​Step ST 1028D1. As a result, the target UE is synchronized with the SeNB.

[0173] In Step ST1029D1, the target UE synchronized with the SeNB transmits uplink data to the SeNB. The SeNB that receives the uplink data may provide a buffer for the received uplink data. This may buffer the received data.

[0174] In Step ST1023, the target UE that has transmitted the uplink data in Step ST1029D1 performs RA processing with the T-MeNB and synchronizes with the T-MeNB.

[0175] In Step ST1024, the target UE that has performed the RA process notifies the T-MeNB of the completion of the configuration of the T-MeNB configuration and the SeNB configuration. This notification is performed using, for example, an RRC Connection Reconfiguration Complete message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0176] The target UE that has completed the connection transmits uplink data to the T-MeNB in ​​Step ST1025. In this manner, the transmission of uplink data in Step ST1025 is performed, for example, after the notification of the completion of setting in Step ST1024, which indicates the completion of the connection.

[0177] In step ST1026, the T-MeNB, having received the uplink data, transmits the received uplink data to the S-GW.

[0178] The T-MeNB that has received the notification of completion of the configuration of the T-MeNB configuration and the SeNB configuration in Step ST1024 notifies the SeNB that the configuration of the SeNB in ​​the UE has been completed in Step ST1027. This notification is performed by using, for example, a SeNB reconfiguration complete message disclosed in FIG. 4.3.2.3-1 of Non-Patent Document 8.

[0179] The SeNB that has received the uplink data in step ST1029D1 transmits the received uplink data to the T-MeNB in ​​step ST1030. Thereafter, the processes of steps ST1031 to ST1042 are performed in the same manner as in the above-described first embodiment. In this manner, the UE can transmit uplink data to the SeNB early without waiting for the process of step ST1023. Furthermore, when it becomes possible to transmit uplink data from the SeNB to the T-MeNB, the uplink data is immediately transmitted, so that it is possible to reduce a delay in transmitting uplink data during HO.

[0180] As described above, in this modified example, in any of the examples shown in Figures 10 to 15, transmission of uplink data from the target UE of steps ST1029B1, ST1029C1, and ST1029D1 to the SeNB is performed after completion of RA processing between the target UE and the SeNB of steps ST1028B1, ST1028C1, and step ST1028D1.

[0181] The timing of the RA process between the target UE and the SeNB in ​​Steps ST1028B1, ST1028C1, and ST1028D1 is earlier in the sequence than in Embodiment 1. The timing of the transmission of uplink data from the SeNB to the T-MeNB in ​​Steps ST1029B1, ST1029C1, and ST1029D1 is earlier in the sequence than in Embodiment 1.

[0182] In this way, during HO of the MeNB, the target UE can transmit uplink data to the SeNB early. Also, when the transmission of uplink data from the SeNB to the T-MeNB becomes possible, the uplink data is transmitted immediately, so that the delay in the transmission of uplink data during HO can be reduced.

[0183] Modification 2 of embodiment 1 As another example of transmission of uplink data between a SeNB and a T-MeNB after the RA process with the SeNB in ​​the first embodiment, a second modification of the first embodiment will be disclosed.

[0184] Figures 16 and 17 are diagrams showing an example of a sequence of handover processing in a communication system according to the second modification of the first embodiment. Figures 16 and 17 are connected by a boundary line BL5. Figures 16 and 17 show an example of a sequence of transmission of uplink data and downlink data in an inter-MeNB uplink HO as a handover processing in the case where there is no change in the SeNB in ​​this modification. The handover processing in this modification is similar to the handover processing in the first modification of the first embodiment shown in Figures 11 and 12 described above, so the same step numbers are assigned to the same steps and common explanations are omitted.

[0185] 10 and 11 in the first modification of the first embodiment described above, the processes of steps ST1011 to ST1026, steps ST1028B1, ST1029B1, and steps ST1051 to ST1053 are performed. The SeNB that has received the uplink data in step ST1029B1 transmits the uplink data received in step ST1029B1 to the T-MeNB in ​​step ST1030B2 immediately after step ST1029B1 before being notified in step ST1027 that the SeNB configuration in the UE has been completed.

[0186] In step ST1031 immediately after step ST1030B2, the T-MeNB that has received the uplink data transmitted in step ST1030B2 transmits the uplink data received in step ST1030B2 to the S-GW. Alternatively, a buffer for uplink data may be provided. This may allow the received data to be buffered.

[0187] Next, in step ST1027, the T-MeNB notifies the SeNB that the SeNB configuration in the UE has been completed. Thereafter, the processes of steps ST1032 to ST1042 are performed in the same manner as in the first modification of the first embodiment described above. In this manner, the S-eNB can transmit uplink data to the T-MeNB and from the T-MeNB to the S-WG promptly without waiting for the process of step ST1027. This makes it possible to reduce the delay in transmitting uplink data during HO.

[0188] Figures 18 and 19 are diagrams showing another example of the sequence of handover processing in a communication system according to the second modification of the first embodiment. Figures 18 and 19 are connected by a boundary line BL6. Figures 18 and 19 show another example of the sequence of the handover processing relating to the transmission of uplink data in an inter-MeNB uplink HO when there is no change in the SeNB in ​​this modification. The handover processing shown in Figures 18 and 19 is similar to the handover processing according to the first modification of the first embodiment shown in Figures 12 and 13 described above, so the same step numbers are used for the same steps, and common explanations will be omitted.

[0189] 12 and 13 in the first modification of the first embodiment described above, the processes of steps ST1011 to ST1023, steps ST1028C1, steps ST1029C1, and steps ST1051 to ST1053 are performed. In this modification, the SeNB that has received the uplink data transmitted in step ST1029C1 transmits the uplink data received in step ST1029C1 to the T-MeNB in ​​step ST1030C2 immediately after step ST1029C1.

[0190] That is, the T-MeNB receives uplink data from the SeNB in ​​step ST1030C2 before receiving a notification of completion of setting the T-MeNB configuration and the SeNB configuration in step ST1024. The T-MeNB may be provided with a buffer for the received uplink data. This may buffer the received data.

[0191] Next, in step ST1024, the target UE notifies the T-MeNB of the completion of setting the T-MeNB configuration and the SeNB configuration. In addition, the target UE transmits uplink data to the T-MeNB in ​​step ST1025. The T-MeNB that has received the uplink data transmits the uplink data to the S-GW in step ST1026.

[0192] After receiving the notification of completion of setting up the T-MeNB configuration and the SeNB configuration in Step ST1024, in Step ST1026, the T-MeNB transmits the uplink data received in Step ST1030C2 and Step ST1025 to the S-GW.

[0193] Thereafter, the processes of steps ST1027 to ST1042 are performed in the same manner as in the first modification of the first embodiment described above. In this manner, the S-eNB can transmit uplink data to the T-MeNB early without waiting for the process of step ST1024. Also, when it becomes possible to transmit uplink data from the T-MeNB to the S-GW, it becomes possible to transmit the uplink data immediately, and it becomes possible to reduce a delay in transmitting the uplink data during HO.

[0194] Figures 20 and 21 are diagrams showing another example of the sequence of handover processing in a communication system according to the second modification of the first embodiment. Figures 20 and 21 are connected by a boundary line BL7. Figures 20 and 21 show another example of the sequence of transmission of uplink data in an inter-MeNB uplink HO as handover processing when there is no change in the SeNB in ​​this modification. The handover processing shown in Figures 20 and 21 is similar to the handover processing according to the first modification of the first embodiment shown in Figures 14 and 15 described above, so the same step numbers are used for the same steps and common explanations are omitted.

[0195] The processes of steps ST1011 to ST1022 and steps ST1051 to ST1053 are performed in the same manner as in the example shown in Fig. 14 and Fig. 15 in the first modification of the first embodiment described above. In step ST1022, the target UE that has set a split bearer configuration for the relevant SeNB and T-MeNB performs RA processing with the SeNB in ​​step ST1028D1. As a result, the target UE is synchronized with the SeNB.

[0196] In Step ST1029D1, the target UE transmits uplink data to the SeNB. When the SeNB receives the uplink data transmitted from the target UE in Step ST1029D1, in Step ST1030D2 immediately after Step ST1029D1, the SeNB transmits the uplink data received in Step ST1029D1 to the T-MeNB.

[0197] That is, the T-MeNB receives uplink data from the SeNB in ​​Step ST1030D2 before the RA process in Step ST1023. The T-MeNB may provide a buffer for the received uplink data. This may buffer the received data.

[0198] Next, in Step ST1023, the target UE performs RA processing with the T-MeNB. As a result, the target UE is synchronized with the T-MeNB.

[0199] Next, in step ST1024, the target UE notifies the T-MeNB of the completion of setting the T-MeNB configuration and the SeNB configuration. In addition, the target UE transmits uplink data to the T-MeNB in ​​step ST1025. The T-MeNB that has received the uplink data transmits the uplink data to the S-GW in step ST1026.

[0200] After receiving the notification of completion of the configuration of the T-MeNB configuration and the SeNB configuration in Step ST1024, in Step ST1026, the T-MeNB transmits the uplink data received in Step ST1030D2 and Step ST1025 to the S-GW.

[0201] Thereafter, the processes of steps ST1027 to ST1042 are performed in the same manner as in the first modification of the first embodiment described above.

[0202] As described above, in this modification, when the SeNB receives the uplink data transmitted from the target UE in steps ST1029B1, ST1029C1, and ST1029D1, the SeNB immediately transmits the received uplink data to the T-MeNB in ​​the immediately following steps ST1030B2, ST1030C2, and ST1030D2. This allows the uplink data to be transmitted to the T-MeNB via the SeNB early during HO of the MeNB. In addition, when it becomes possible to transmit the uplink data from the T-MeNB to the S-GW, the uplink data is transmitted immediately, so that it is possible to reduce the delay in transmitting the uplink data during HO.

[0203] Modification 3 of embodiment 1 As another example of transmission of uplink data received from a SeNB between the T-MeNB and the S-GW in the first embodiment, a third variant of the first embodiment will be disclosed.

[0204] Fig. 22 and Fig. 23 are diagrams showing an example of a sequence of handover processing in a communication system according to the third modification of the first embodiment. Fig. 22 and Fig. 23 are connected by a boundary line BL8. Fig. 22 and Fig. 23 show an example of a sequence of transmission of uplink data in an inter-MeNB uplink HO as a handover processing in the case where there is no change in the SeNB in ​​this modification. Since the handover processing in this modification is similar to the handover processing in the second modification of the first embodiment shown in Figs. 18 and 19 described above, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0205] Similar to the second modification of the first embodiment shown in FIG. 18 and FIG. 19, the processes of steps ST1011 to ST1023, step ST1028C1, step ST1029C1, step ST1030C2, and step ST1051 to ST1053 are performed.

[0206] When the T-MeNB receives the uplink data transmitted from the target UE in Step ST1030C2, the T-MeNB immediately transmits the uplink data to the S-GW in Step ST1031C3 before receiving a setting completion notification of the T-MeNB configuration and the SeNB configuration in Step ST1024. After that, the processes of Steps ST1024 to ST1042 are performed in the same manner as in the above-mentioned first embodiment.

[0207] Figures 24 and 25 are diagrams showing another example of the sequence of handover processing in a communication system according to the third modification of the first embodiment. Figures 24 and 25 are connected by a boundary line BL9. Figures 24 and 25 show an example of a sequence of transmission of uplink data in an inter-MeNB uplink HO as handover processing when there is no change in the SeNB in ​​this modification. The handover processing in this modification is similar to the handover processing in the second modification of the first embodiment shown in Figures 20 and 21 described above, so the same step numbers are used for the same steps and common explanations are omitted.

[0208] Similar to the second modification of the first embodiment shown in FIG. 20 and FIG. 21, the processes of steps ST1011 to ST1022, step ST1028D1, step ST1029D1, step ST1030D2, and step ST1051 to ST1053 are performed.

[0209] When the T-MeNB receives the uplink data transmitted from the target UE in Step ST1030D2, the T-MeNB immediately transmits the uplink data to the S-GW in Step ST1031D3 before the RA process in Step ST1023. In addition, the T-MeNB notifies the target UE via the SeNB that the uplink data has been transmitted.

[0210] The UE that has received the notification discards the buffer for the uplink data transmitted in step ST1029D1. After that, the process of steps ST1032 to ST1042 is performed in the same manner as in the first modification of the first embodiment described above.

[0211] As described above, in this modification, when the T-MeNB receives uplink data transmitted from the SeNB in ​​steps ST1030C2 and ST1030D2, the T-MeNB immediately transmits the received uplink data to the S-GW in subsequent steps ST1031C3 and ST1031D3. This enables data transmitted to the T-MeNB via the SeNB to be transmitted to the S-GW early during HO of the MeNB.

[0212] In this way, even during HO of the MeNB, uplink data can be transmitted by transmitting data via the SeNB, so it is possible to reduce the delay in delivery of uplink data during HO. In addition, since the target UE can transmit uplink data to the S-GW early, it is possible to reduce the buffer for uplink data.

[0213] Modification 4 of embodiment 1 As another example of a case where synchronization is established between a target UE and a SeNB during HO between MeNBs, a fourth modification of the first embodiment will be disclosed.

[0214] Figures 26 and 27 are diagrams showing an example of a sequence of handover processing in a communication system according to the fourth modification of the first embodiment. Figures 26 and 27 are connected by a boundary line BL10. Figures 26 and 27 show an example of a sequence of transmission of uplink data in an inter-MeNB uplink HO as a handover processing in the case where there is no change in the SeNB in ​​this modification. The handover processing shown in Figures 26 and 27 is similar to the handover processing according to the third modification of the first embodiment shown in Figures 24 and 25 described above, so the same step numbers are used for the same steps, and common explanations are omitted.

[0215] The processes of steps ST1011 to ST1022 and steps ST1051 to ST1053 are performed in the same manner as in the third modification of the first embodiment shown in FIGS. 24 and 25 described above.

[0216] During HO between MeNBs, the SeNB is not changed, so it is considered that the target UE and the SeNB are synchronized. In this way, when the target UE and the SeNB are synchronized, the RA process in step ST1028D1 shown in FIG. 24 may be omitted.

[0217] Therefore, in this embodiment, as shown in FIG. 26, after the target UE sets a split bearer configuration for the corresponding SeNB and T-MeNB in ​​step ST1022, the target UE transmits uplink data to the SeNB in ​​the subsequent step ST1029D1. In step ST1029D1, the target UE may transmit a scheduling request (SR) to the SeNB. After transmitting the SR, the UE transmits uplink data according to the uplink scheduling from the SeNB.

[0218] In Step ST1029D1, the SeNB receives the uplink data from the UE, and in Step ST1030D2, transmits the uplink data to the T-MeNB. After that, the processes of Steps ST1023 to ST1042 are performed in the same manner as in the third modification of the first embodiment described above.

[0219] As described above, in this modification, when the target UE is synchronized with the SeNB during HO of the MeNB, the target UE sets a split bearer configuration for the corresponding SeNB and T-MeNB in ​​step ST1022, and then immediately transmits the uplink data received in step ST1029D1 to the SeNB in ​​step ST1029D1. This makes it possible to transmit the uplink data to the SeNB more quickly.

[0220] Modification 5 of embodiment 1 In this modification, an example of processing when a handover failure (abbreviation: HOF) occurs during HO between MeNBs without changing SeNB while a split bearer is being executed in DC will be disclosed.

[0221] In the conventional method, for example, the sequence shown in Figure 4.3.2.3-1 of Non-Patent Document 8, when HOF occurs between MeNBs, there is a problem that the SeNB cannot release the resources reserved by the SeNB in ​​response to the SeNB addition request message transmitted from the T-MeNB to the SeNB. For example, there is a problem that the SeNB UE X2AP ID, bearer setting, UE context, etc. cannot be released. If the resources cannot be released, the resources will be exhausted as HOF is repeated, and communication will become impossible.

[0222] Therefore, in this modified example, when HOF is detected, a message to release these resources configured in the SeNB is notified in the process corresponding to the SeNB addition request message sent by the T-MeNB to the SeNB.

[0223] A desirable method for detecting HOF is to start a timer after permitting HO in the T-MeNB, and stop the timer when it is determined that the UE and SeNB are synchronized.

[0224] Fig. 28 is a diagram showing an example of a sequence of handover processing in a communication system according to Modification 5 of Embodiment 1. Since the handover processing in this modification is similar to the handover processing in Embodiment 1 shown in Figs. 9 and 10 described above, the same step numbers are assigned to the same steps, and common explanations will be omitted.

[0225] The processes of steps ST1011 to ST1017 are performed in the same manner as in the first embodiment shown in the above-described Figures 9 and 10. In this embodiment, when the process of step ST1017 ends, the process proceeds to steps ST1061 and ST1062.

[0226] In Step ST1062, the T-MeNB transmits an HO request response (HO request ack) to the S-MeNB. The T-MeNB determines that the HO request response has been transmitted in this manner as an HO permission for the UE, and starts a timer in Step ST1061. When the T-MeNB receives an RRC connection reconfiguration complete message from the UE, it is desirable to determine that the UE and the SeNB are synchronized, and stop the timer.

[0227] When synchronization between the UE and the SeNB fails in the RA process and HOF is detected as in step ST1063, for example, when the T-MeNB cannot receive an RRC connection reconfiguration complete message from the UE, the T-MeNB sets a timer to expire in step ST1064. At that time, the T-MeNB transmits a message for releasing resources to the SeNB in ​​step ST1065.

[0228] In Step ST1066, the SeNB that has received the resource release message releases the resources that it has secured in response to the SeNB addition request message. For example, the SeNB UE X2AP ID, bearer settings, UE context, etc. are released. In addition, if there are resources secured for a connection between the T-MeNB and the SeNB that are set up from the S-MeNB, it is desirable to release those settings as well.

[0229] A new message such as a SeNB configuration release message may be provided as a message for releasing resources from the T-MeNB to the SeNB. Alternatively, reject information may be provided as information of the SeNB reconfiguration complete message, and HOF may be added as a cause.

[0230] As described above, according to this modification, resources secured in the SeNB can be released, so that resource depletion can be prevented even when HOF is repeated.

[0231] Next, a function related to the handling of uplink data in a T-MeNB will be mentioned with reference to Fig. 29 and Fig. 30. Fig. 29 and Fig. 30 are diagrams showing another example of a sequence of handover processing in a communication system according to the fifth modification of the first embodiment. Fig. 29 and Fig. 30 are connected by a boundary line BL11. Fig. 29 and Fig. 30 show an example of a sequence related to the transmission of uplink data in an inter-MeNB uplink HO as a handover processing in the case where there is no change in the SeNB in ​​this modification. The handover processing in this modification is similar to the handover processing in the first embodiment shown in Figs. 9 and 10 and the fifth modification of the first embodiment shown in Fig. 28, and therefore the same step numbers are assigned to the same steps, and common explanations are omitted.

[0232] The processes of steps ST1011 to ST1022 and steps ST1051 to ST1053 are performed in the same manner as in the first embodiment shown in Fig. 8 and Fig. 9. In this modification, when the process of step ST1022 ends, the processes of steps ST1028 to ST1030 are performed.

[0233] As described in the first embodiment, it is also effective for the SeNB to have a function of transmitting uplink data to the T-MeNB as soon as synchronization with the UE is established. It is also effective for the T-MeNB to have a function of storing data and waiting for the S-GW to become in a state where it can receive data, such as a path switch in the S-GW.

[0234] In this case, synchronization cannot be established between the UE and the T-MeNB, the RA process between the UE and the SeNB in ​​Step ST1028 is performed earlier than the timer expires, and HOF may be detected in the T-MeNB in ​​Step ST1063 without synchronization being established between the UE and the T-MeNB. In this case, the SeNB has already transmitted some PDCP packets to the T-MeNB.

[0235] For such a case, the T-MeNB may have a function of discarding uplink data received from the SeNB before the detection of HOF when the timer expires in step ST1064, i.e., when the HOF is detected. This makes it possible to release resources, and therefore to prevent the exhaustion of resources for the data buffer of the T-MeNB while repeating HOF.

[0236] Thereafter, the processes of steps ST1065 and ST1066 are carried out in the same manner as in the case shown in FIG.

[0237] Next, a function related to the handling of uplink data in the T-MeNB will be described with reference to Figures 31 and 32. Figures 31 and 32 are diagrams showing another example of the sequence of handover processing in the communication system of the fifth modification of the first embodiment. Figures 31 and 32 are connected by a boundary line BL12. Figures 31 and 32 show an example of the sequence related to the transmission of uplink data in an inter-MeNB uplink HO as the handover processing when there is no change in the SeNB in ​​this modification. The handover processing in this modification is similar to the handover processing in the first embodiment shown in Figures 9 and 10 and the fifth modification of the first embodiment shown in Figure 28, so that the same step numbers are assigned to the same steps and common explanations are omitted.

[0238] As described in the first embodiment, the SeNB transmits uplink data to the T-MeNB as soon as synchronization with the UE is established. For example, when the S-GW can always receive data from either the T-MeNB or the S-MeNB, it is effective for the T-MeNB to have a function of promptly transmitting the received uplink data to the S-GW. In that case, when synchronization cannot be established between the UE and the T-MeNB and the RA process between the UE and the SeNB is earlier than the expiration of the timer, the SeNB has transmitted some PDCP packets to the T-MeNB before HOF detection. Similarly, the T-MeNB has transmitted some data, for example, GTP (GPRS (General Packet Radio Service) Tunneling Protocol) packets, to the S-GW.

[0239] For such a case, it is preferable that the T-MeNB has a function to transmit uplink data received from the SeNB before the HOF was detected to the S-GW when the timer expires, i.e., when the HOF is detected. This prevents the uplink data received by the SeNB from being discarded and eliminates the need for retransmission from the UE, enabling efficient transmission.

[0240] Also, as described in Modification Example 3 of Embodiment 1, the T-MeNB may transmit, to the UE, an uplink data reception success response from the UE via the SeNB. The UE that has received the uplink data reception success response from the T-MeNB may discard the uplink data. As described above, the UE can discard the successfully transmitted uplink data at an earlier stage, and can reduce the buffer capacity of the uplink data.

[0241] Next, three examples in which a timer for determining synchronization establishment is also provided in the SeNB will be described with reference to FIGS. 33 to 36.

[0242] FIG. 33 shows an example in a case where the measurement time (Ts) of the SeNB timer is smaller than the measurement time (Tm) of the T-MeNB timer (Ts < Tm). FIG. 34 shows an example in a case where the measurement time (Ts) of the SeNB timer is greater than or equal to the measurement time (Tm) of the T-MeNB timer (Ts ≧ Tm). FIGS. 35 and 36 show an example of the handling of uplink data transmission in a case where the measurement time (Ts) of the SeNB timer is greater than or equal to the measurement time (Tm) of the T-MeNB timer (Ts ≧ Tm).

[0243] FIG. 33 is a diagram showing another example of the handover process sequence in the communication system of Modification Example 5 of Embodiment 1. In FIG. 33, as the handover process, an example of the sequence of uplink data transmission in the MeNB uplink HO without SeNB change in this modification example is shown. Since the handover process in this modification example is similar to the handover processes of Embodiment 1 shown in FIGS. 9 and 10 and Modification Example 5 of Embodiment 1 shown in FIG. 28, the same step numbers are assigned to the same steps, and the common description is omitted.

[0244] FIG. 34 is a diagram showing another example of the sequence of handover processing in the communication system according to Modification Example 5 of Embodiment 1. In FIG. 34, as an example of the handover processing, a sequence related to the transmission of uplink data in the MeNB uplink HO when there is no change in the SeNB in this modification example is shown. Since the handover processing in this modification example is similar to the handover processing in Embodiment 1 shown in FIGS. 9 and 10 and Modification Example 5 of Embodiment 1 shown in FIG. 28, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0245] FIGS. 35 and 36 are diagrams showing another example of the sequence of handover processing in the communication system according to Modification Example 5 of Embodiment 1. FIGS. 35 and 36 are connected by a boundary line BL13. In FIGS. 35 and 36, as an example of the handover processing, a sequence related to the transmission of uplink data in the MeNB uplink HO when there is no change in the SeNB in this modification example is shown. Since the handover processing in this modification example is similar to the handover processing in Embodiment 1 shown in FIGS. 9 and 10 and Modification Example 5 of Embodiment 1 shown in FIG. 28, the same step numbers are assigned to the same steps, and common explanations are omitted.

[0246] First, as shown in FIG. 33, when the timer measurement time (Ts) of the SeNB is set such that Ts<Tm, where Ts is less than the timer measurement time (Tm) of the T-MeNB, the SeNB may start the timer as in step ST1072 when it transmits a SeNB addition request Ack message to the T-MeNB in step ST1071. Similarly, the SeNB may stop the timer when it receives a SeNB reconfiguration Complete message from the T-MeNB.

[0247] When the timer expires in Step ST1072, the SeNB releases resources secured by the SeNB in ​​response to the SeNB addition request message, such as the SeNB UE X2AP ID, bearer settings, UE context, etc. In addition, if there are resources secured for a connection between the T-MeNB and the SeNB that are set by the S-MeNB, it is desirable to release those settings as well.

[0248] Also, it is effective for the SeNB to have a function of notifying the T-MeNB to release the SeNB configuration when the timer expires in Step ST1072. For example, it is effective for the SeNB to transmit a SeNB release request message (SeNB release required) to the T-MeNB in ​​Step ST1073 when the timer expires in Step ST1072. This message enables the T-MeNB to promptly stop and terminate the SeNB configuration for the target UE.

[0249] Furthermore, the T-MeNB that has received the SeNB release required message in step ST1073 may notify the SeNB of a SeNB release confirm message in step ST1074. In this case, it is effective for the SeNB not to release the SeNB configuration when the timer expires in step ST1072, but to release the SeNB configuration after receiving the SeNB release confirm message in step ST1074. This makes it possible to avoid a mismatch in the states of the SeNB and the T-MeNB, i.e., to avoid a state where the SeNB is in HOF and the T-MeNB is waiting for HO establishment, thereby enabling stable operation.

[0250] The T-MeNB that has been notified of the release of the SeNB configuration resets the HOF timer (Tm) in Step ST1075. Also, the T-MeNB terminates the SeNB configuration for the target UE. If the timer is not reset, the HOF timer of the T-MeNB expires in Step ST1076.

[0251] Next, a case will be described in which the measurement time (Ts) of the timer of the SeNB is set to be equal to or longer than the measurement time (Tm) of the timer of the T-MeNB (Ts≧Tm) as shown in FIG.

[0252] When the timer of the T-MeNB expires in Step ST1064, in Step ST1065, the T-MeNB notifies the SeNB of resource release. A new message such as a SeNB configuration release message may be provided as a message for releasing resources from the T-MeNB to the SeNB. Alternatively, reject information may be provided as information of SeNB reconfiguration complete, and HOF may be added as a cause. In Step ST1066, the SeNB releases resources secured by the SeNB in ​​response to the SeNB addition request message, such as a SeNB UE X2AP ID, a bearer configuration, and a UE context.

[0253] The SeNB that has received the resource release from the T-MeNB resets the timer (Ts) set by the SeNB in ​​Step ST1081. If the timer is not reset, the timer of the SeNB expires in Step ST1082.

[0254] As described in the example shown in FIG. 33 above, since no SeNB release required message from the SeNB that becomes valid when the SeNB timer (Ts) < T-MeNB timer (Tm) causes no state inconsistency, it is more desirable that the SeNB timer (Ts) ≥ T-MeNB timer (Tm). Therefore, it is effective to set the timer value to SeNB timer (Ts) ≥ T-MeNB timer (Tm) in OAM (Operation Administration and Maintenance).

[0255] Also, it is effective to set the SeNB timer (Ts) ≥ T-MeNB timer (Tm) as a value predetermined by the operator in the non-volatile memories of the SeNB device and the T-MeNB device, etc.

[0256] Also, it is effective to notify the timer value from the SeNB to the T-MeNB and have the T-MeNB set the SeNB timer (Ts) ≥ T-MeNB timer (Tm). For the notification of the timer value from the SeNB to the T-MeNB, for example, a SeNB addition request Ack message is used.

[0257] Also, it is effective to notify the T-MeNB from the S-MeNB of the source of HO of a set value that satisfies the SeNB timer (Ts) ≥ T-MeNB timer (Tm). For the notification of the set value that satisfies the SeNB timer (Ts) ≥ T-MeNB timer (Tm), an HO request message or an SN status transfer message is used.

[0258] Finally, the handling of the uplink data transmission when the SeNB timer (Ts) ≥ T-MeNB timer (Tm) will be described with reference to FIGS. 35 and 36.

[0259] As in the cases of Fig. 31 and Fig. 32, the T-MeNB may transmit uplink data to the S-GW before HOF detection. The T-MeNB may transmit an uplink data reception success response from the UE to the UE via the SeNB. The UE that has received the uplink data reception success response from the T-MeNB may discard the uplink data. As a result, the UE can discard successfully transmitted uplink data early, and the buffer capacity of the uplink data can be reduced.

[0260] The SeNB that has received the resource release from the T-MeNB resets the timer (Ts) set by the SeNB in ​​Step ST1081. If the timer is not reset, the timer of the SeNB expires in Step ST1082.

[0261] Although not shown in the figure, regardless of the magnitude relationship between Ts and Tm, the T-MeNB may determine the expiration time of the timer for the SeNB and notify the SeNB, and the SeNB may start the timer with that value.

[0262] Alternatively, the timer value set in the T-MeNB may be notified to the SeNB, and the SeNB may set the timer value for the SeNB.

[0263] Modification 6 of embodiment 1 In the above-described embodiment and modification, the processing of uplink data (UL U-plane data) is disclosed. In this modification, in addition to the above-described embodiment and modification, the processing of downlink data (DL U-plane data) is additionally disclosed.

[0264] In the conventional method, for example, in the sequence shown in Figure 4.3.2.3-1 of Non-Patent Document 8, there is no provision for the start timing of forwarding of downlink data, and transmission cannot start unless a path switch is performed from the S-MeNB to the T-MeNB. In addition, since there is no provision for the start timing of forwarding of downlink data, it depends on the construction of the T-MeNB, and when a SeNB connects to various T-MeNBs, there is a problem that the number of connection test cases increases and development costs increase. In addition, in a SeNB that is simultaneously connected to multiple T-MeNBs, for example, resources of the transmission data buffer from the T-MeNB are controlled early and in large quantities, resulting in waste.

[0265] In order to solve this problem, a method of performing downlink data forwarding at an appropriate timing will be described with reference to Figures 37 and 38. Figures 37 and 38 are diagrams showing an example of a sequence of handover processing in a communication system according to the sixth modification of the first embodiment. Figures 37 and 38 are connected by a boundary line BL14. Figures 37 and 38 show an example of a sequence of transmission of uplink data in an inter-MeNB uplink HO as handover processing when there is no change in the SeNB in ​​this modification. The handover processing in this modification is similar to the handover processing in the first embodiment shown in Figures 9 and 10 described above, so the same step numbers are assigned to the same steps and common descriptions are omitted.

[0266] Only the differences from the first embodiment will be described. In this modification, the T-MeNB detects transmission of a SeNB reconfiguration complete message, and performs downlink data forwarding to the SeNB in ​​step ST1092. Also, it is desirable to transmit an SN status transfer message from the T-MeNB to the SeNB in ​​step ST1091 before the downlink data forwarding in step ST1092.

[0267] Alternatively, the T-MeNB may effectively forward downlink data to the SeNB when it detects receipt of an RRC Connection Reconfiguration Complete message from the UE.

[0268] After completing the RA process with the UE in step ST1028, the SeNB transmits the downlink data transferred from the T-MeNB to the UE in step ST1029A. In step ST1029A, similar to step ST1029 in the above-described first embodiment, uplink data is also transmitted from the UE to the SeNB. It is desirable for the SeNB to have a function of buffering the downlink data. This makes it possible to accumulate data until the RA process is completed.

[0269] Also, for example, it is desirable for the SeNB to provide a buffer for the length of the path for forwarding downlink data. For example, it is desirable to provide a buffer for the length of the path from the S-GW to the S-MeNB, SeNB to the path from the S-GW to the S-MeNB, T-MeNB, SeNB. This makes it possible to transmit data in order from the oldest to the newest when the path is changed again, for example, when the path from the S-GW to the S-MeNB, T-MeNB, SeNB is changed again to the path from the S-GW to the T-MeNB, SeNB.

[0270] As described above, by performing downlink data forwarding, it is possible to transmit downlink data forwarded from the S-MeNB before the path switch of the S-GW is performed during HO between MeNBs.

[0271] FIG. 39 and FIG. 40 show an example of a case where the RA process between the UE and the SeNB is performed before the RA process between the UE and the T-MeNB. FIG. 39 and FIG. 40 are diagrams showing another example of the sequence of the handover process in the communication system of the sixth modification of the first embodiment. FIG. 39 and FIG. 40 are connected by the boundary line BL15. FIG. 39 and FIG. 40 show an example of the sequence of the handover process related to the transmission of uplink data in the inter-MeNB uplink HO in the case where the SeNB is not changed in this modification. The handover process in this modification is similar to the handover process in the first embodiment shown in the above-mentioned FIG. 9 and FIG. 10 and the sixth modification of the first embodiment shown in FIG. 37 and FIG. 38, so that the same step numbers are assigned to the same steps, and the common description is omitted.

[0272] 39 and 40, after downlink data forwarding is performed in step ST1092, the SeNB transmits uplink data to the T-MeNB in ​​step ST1030. Next, the SeNB transmits downlink data to the UE in step ST1093.

[0273] 39 and 40, as soon as the T-MeNB receives an RRC connection reconfiguration complete message from the UE in Step ST1024, it becomes possible to transmit uplink data to the S-GW in Steps ST1025 and ST1026. This allows the downlink data transferred from the S-MeNB in ​​Steps ST1092 and ST1093 to be transmitted for both uplink and downlink before the path switch of the S-GW is performed in Step ST1034 during HO between MeNBs.

[0274] Modification 7 of embodiment 1 In the sixth variant of the first embodiment, an example has been shown in which downlink data forwarding is performed after transmitting an SeNB reconfiguration complete message or upon receiving an RRC connection reconfiguration complete message. However, in this variant, a method for performing downlink data forwarding earlier is disclosed.

[0275] Figures 41 and 42 are diagrams showing an example of a sequence of handover processing in a communication system according to the seventh modification of the first embodiment. Figures 41 and 42 are connected by a boundary line BL16. Figures 41 and 42 show an example of a sequence of transmission of uplink data in an inter-MeNB uplink HO as handover processing when there is no change in the SeNB in ​​this modification. The handover processing in this modification is similar to the handover processing in the first embodiment shown in Figures 9 and 10 described above, so the same step numbers are used for the same steps and common explanations are omitted.

[0276] As shown in FIG. 41 and FIG. 42, in this modification, the T-MeNB has a function of performing downlink data forwarding before receiving a SeNB reconfiguration complete message in step ST1024. For example, the T-MeNB has a function of detecting the completion of connection between the SeNB and the UE, and when detecting the completion of connection between the SeNB and the UE in step ST1101, it is preferable to perform downlink data forwarding to the SeNB in ​​step ST1092. Specifically, the T-MeNB has a function of determining reception of uplink data from the SeNB in ​​step ST1030, and after receiving the uplink data in step ST1030, it is effective to perform downlink data forwarding to the SeNB in ​​step ST1092.

[0277] Furthermore, it is desirable that the T-MeNB transmits an SN status transfer message to the SeNB in ​​Step ST1091 before forwarding downlink data in Step ST1092.

[0278] After completing the RA process with the UE in Step ST1028, the SeNB that has received the downlink data from the T-MeNB transmits the downlink data to the UE in Step ST1093. After that, the processes of Steps ST1023 to ST1042 are performed in the same manner as in the first embodiment.

[0279] By having the above functions, it is possible to transmit downlink data transferred from the S-MeNB to the UE without waiting for the transmission of the SeNB reconfiguration complete message. In other words, it is possible to perform communication between the UE, SeNB, T-MeNB, and S-GW for both uplink and downlink.

[0280] Figures 43 and 44 are diagrams showing another example of the sequence of handover processing in a communication system according to the seventh modification of the first embodiment. Figures 43 and 44 are connected by a boundary line BL17. Figures 43 and 44 show an example of a sequence of transmission of uplink data in an inter-MeNB uplink HO as a handover processing in the case where there is no change in the SeNB in ​​this modification. The handover processing in this modification is similar to the handover processing in the first embodiment shown in the above-mentioned Figures 9 and 10 and the sixth modification of the first embodiment shown in Figures 37 and 38, so that the same step numbers are assigned to the same steps and common explanations are omitted.

[0281] As shown in Figures 43 and 44, instead of the function of forwarding downlink data before SeNB reconfiguration Complete, the T-MeNB may have the function of forwarding downlink data to the SeNB as soon as it receives data forwarded downlink from the S-MeNB.

[0282] This function is particularly effective when the SeNB continues downlink synchronization with the UE or can instantly establish synchronization. For example, a function of transmitting information indicating whether the SeNB can continue synchronization with the UE in an SeNB addition request Ack message transmitted from the SeNB to the T-MeNB in ​​step ST1017 may be provided. When the SeNB can continue synchronization, it is desirable for the T-MeNB to forward downlink data to the SeNB in ​​step ST1092 as soon as it receives data forwarded in downlink from the S-MeNB in ​​steps ST1052 and ST1053.

[0283] Before forwarding downlink data in step ST1092, it is effective to perform SN status transfer in step ST1091.

[0284] After completing the RA process with the UE in Step ST1028, the SeNB that has received the downlink data from the T-MeNB in ​​Step ST1092 transmits the downlink data to the UE in Step ST1029A.

[0285] As a result, downlink data transferred from the S-MeNB can be transmitted to the UE without waiting for the transmission of the SeNB reconfiguration complete message, which is faster than in the cases of Figures 41 and 42. That is, both uplink and downlink communications can be performed between the UE, SeNB, T-MeNB, and S-GW.

[0286] Embodiment 2 In embodiment 1 and its variants, a method for transmitting and receiving uplink data and downlink data between a UE and a network side node when HO occurs between MeNBs while a split bearer is being executed and there is no change in SeNB has been disclosed.

[0287] It has been disclosed that in the case of HO when there is no change in SeNB, the UE may already connect to the SeNB before connecting to the T-MeNB. During the HO, the UE transmits uplink data to the SeNB after connecting to the SeNB. During the HO, the UE does not transmit uplink data to the T-MeNB. During the HO, the UE transmits uplink data to the SeNB after completing RA processing for the SeNB. During the HO, if the UE is synchronized with the SeNB, the UE may transmit uplink data to the SeNB after setting the SeNB configuration. Also, during the HO, the UE does not transmit uplink data to the T-MeNB until completing RA processing for the T-MeNB. During the HO, the UE transmits uplink data only to the SeNB after completing RA processing for the SeNB until completing RA processing for the T-MeNB.

[0288] In this way, during HO when there is no change in the SeNB, uplink data can be transmitted and received between the UE and the SeNB before the UE connects to the T-MeNB. Therefore, uplink data can be transmitted and received between the UE and the SeNB at an earlier stage. This makes it possible to reduce delays in data transmission and reception due to HO.

[0289] During HO when there is no change in SeNB while maintaining the split bearer, if an attempt is made to transmit and receive uplink data between the UE and the SeNB before the UE connects to the T-MeNB, the following problems may occur.

[0290] 3GPP has proposed a method of transmitting a Buffer Status Report (BSR) when an uplink split bearer is being executed, using a double reporting and threshold (abbreviated as DRAT) method (see Non-Patent Document 9). In the DRAT, when the amount of PDCP data is equal to or less than a predetermined threshold, the buffer status (abbreviated as BS) is reported to one eNB, i.e., the MeNB or the SeNB. When the amount of PDCP data is greater than a predetermined threshold, the BS of the same amount of PDCP data is reported to both eNBs, i.e., the MeNB and the SeNB. When the amount of PDCP data is less than a predetermined threshold, RRC signaling is used to indicate to which of the MeNB and the SeNB the BS is to be reported. The predetermined threshold is set for each resource block (RB).

[0291] In this way, in the DRAT, the BSR is triggered to both eNBs, i.e., the MeNB and the SeNB, with the same amount of PDCP data, and the BSR is transmitted. If HO occurs in this state, the UE triggers the BSR to both the MeNB and the SeNB with the same amount of PDCP data. However, since HO is in progress, the UE cannot actually send a BSR to the T-MeNB until the UE synchronizes with the T-MeNB and connects. Furthermore, the UE cannot transmit data to the T-MeNB. Therefore, triggering a BSR to the T-MeNB before the UE synchronizes with the T-MeNB during HO is pointless and may cause malfunction. For example, if a BSR is triggered to the T-MeNB, the UE will attempt to transmit a BSR even though it is not yet connected to the T-MeNB. The UE will not know how to operate, and will cause malfunction.

[0292] In addition, other problems arise. In 3GPP, it is proposed that the trigger of BSR and the eNB that transmits data should be the same. According to this, even during HO, if the UE triggers the BSR, the UE cannot ignore the BSR and transmits data to the T-MeNB. Even if the UE triggers the BSR on the T-MeNB side before connecting to the T-MeNB during HO, the UE cannot transmit data to the T-MeNB. Therefore, after connecting to the T-MeNB, the UE transmits the BSR to the T-MeNB and transmits data. As a result, when the UE transmits data to the T-MeNB, a delay in transmission occurs. In this embodiment, a method for solving such a problem is disclosed.

[0293] During HO between MeNBs, if a BSR is triggered to the MeNB side before connecting to the T-MeNB, the UE ignores the trigger of the BSR. The UE may determine whether or not it has connected to the T-MeNB based on whether or not RA processing has been performed with the T-MeNB. The UE may determine whether or not it has connected to the T-MeNB based on whether or not an RRC Connection Reconfiguration Complete message has been notified.

[0294] In the case of the method disclosed here, the triggering of the BSR to the T-MeNB in ​​the UE becomes useless. Other methods are disclosed below. The UE triggers a BSR to the SeNB during HO between MeNBs. The UE does not trigger a BSR to the MeNB during HO between MeNBs. The UE may be after the UE connects to the SeNB or before the UE connects to the T-MeNB during HO between MeNBs. The UE may determine whether or not it has connected to the SeNB based on whether or not RA processing has been performed with the SeNB. The UE may determine whether or not it has connected to the SeNB based on whether or not it is synchronized with the SeNB. The UE transmits a BSR to the eNB for which the BSR has been triggered.

[0295] The UE may be configured to perform the method when performing HO between MeNBs when there is no change in SeNB. The UE may be configured to perform the method when performing HO between MeNBs when there is no change in SeNB while maintaining split bearer. The UE may reset DRAT even if it is set and perform the method. The UE may reset DRAT and perform the method even if an eNB that transmits uplink data at or below a threshold is set to the MeNB when DRAT is set.

[0296] By doing so, the method can be performed whether the amount of PDCP data is equal to or less than the threshold or equal to or more than the threshold.

[0297] Although the above method is performed, it is also possible to switch to the above method. Even if a method other than the above method is set in the BSR trigger method and BSR transmission method, the method is switched to the above method.

[0298] When performing HO between MeNBs without changing the SeNB, the UE may be synchronized with the SeNB during HO since the UE is already connected to the SeNB before HO.

[0299] The UE may perform RLC retransmission of uplink data transmitted to the SeNB before HO by ARQ (Automatic Repeat reQuest) processing. In HO between MeNBs when there is no change in SeNB, if the UE is synchronized with the SeNB during HO, the UE may continue to transmit uplink data to the SeNB, and may also continue to transmit uplink RLC retransmission data. In this way, taking into account the data for which RLC retransmission of uplink data to the SeNB is being performed, not only PDCP data but also the RLC retransmission data may be included in the BSR.

[0300] FIG. 45 and FIG. 46 are diagrams for explaining a method of transmitting a BSR when a conventional DRAT is set. FIG. 45 shows a case where the amount of PDCP data is equal to or less than a threshold. FIG. 46 shows a case where the amount of PDCP data is greater than a threshold. The UE 2013 is connected to both the MeNB 2011 and the SeNB 2012, and an uplink split bearer is established. The PDCP 2014 is a protocol stack that performs PDCP processing for the UE 2013. The RLC 2015 for MeNB is a protocol stack that performs RLC processing for the MeNB 2011. The MAC 2016 for MeNB is a protocol stack that performs MAC processing for the MeNB 2011. The RLC 2017 for SeNB is a protocol stack that performs RLC processing for the SeNB 2012. The MAC 2018 for SeNB is a protocol stack that performs MAC processing for the SeNB 2012.

[0301] 45 and 46, when the amount of PDCP data is equal to or less than a threshold, a BSR is set to be transmitted to the MeNB 2011. The threshold is notified from the MeNB 2011 to the UE 2013. The MeNB 2011 may notify the UE 2013 of the threshold by RRC signaling together with a parameter for setting which of the eNBs, the MeNB 2011 or the SeNB 2012, to notify when the amount of PDCP data is equal to or less than the threshold.

[0302] When the amount of PDCP data is equal to or less than the threshold, as shown in Fig. 45, the UE 2013 triggers a BSR to the MeNB 2011, and transmits a BSR to the MeNB 2011, as shown by an arrow 2019 in Fig. 45. When the amount of PDCP data is greater than the threshold, as shown in Fig. 46, the UE 2013 triggers a BSR to both the MeNB 2011 and the SeNB 2012, and transmits a BSR to both the MeNB 2011 and the SeNB 2012, as shown by arrows 2020 and 2021 in Fig. 46. Non-Patent Document 9 discloses that the same amount of PDCP data is notified to both the MeNB 2011 and the SeNB 2012, but different values ​​may be notified to each of the eNBs 2011 and 2012.

[0303] Fig. 47 is a diagram for explaining a method of transmitting a BSR in embodiment 2. Since Fig. 47 is similar to the above-mentioned Fig. 45 and Fig. 46, the same components are given the same reference symbols and common descriptions are omitted.

[0304] After connecting to the SeNB 2012 in the HO between the MeNB 2011 and before connecting to the T-MeNB, the UE 2013 triggers a BSR to the SeNB 2012 and does not trigger a BSR to the MeNB 2011. As shown by an arrow 2022 in Fig. 47, the UE 2013 transmits a BSR only to the eNB for which the BSR is triggered, that is, the SeNB 2012 in this case. After connecting to the SeNB 2012 in the HO between the MeNB 2011 and before connecting to the T-MeNB, the UE 2013 transmits a BSR only to the SeNB 2012 by performing the above-mentioned method, regardless of whether the amount of PDCP data is equal to or less than the threshold or equal to or more than the threshold.

[0305] In this way, even if the uplink bearer split is maintained and the DRAT is set in the HO between the MeNBs 2011, the BSR is not triggered and the BSR is not transmitted to the MeNB 2011 after the connection with the SeNB 2012 and before the connection with the T-MeNB. Therefore, the MeNB 2011 does not transmit the uplink scheduling for the PDCP data to the UE 2013, and the UE 2013 does not transmit the PDCP data to the MeNB 2011. Therefore, the UE 2013 can eliminate the transmission of unnecessary data to the unconnected T-MeNB, and it is possible to reduce the transmission delay and the power consumption of the UE 2013. The MeNB 2011 may be either an S-MeNB or a T-MeNB.

[0306] A method for a UE to transition to the method disclosed in this embodiment is disclosed. A UE that receives an instruction for HO between MeNBs when there is no change in SeNB performs the method disclosed in this embodiment. In addition, a UE that has an uplink split bearer set or has an uplink split bearer maintenance set in the HO instruction may perform the method disclosed in this embodiment. MCI (Mobility Control Information) may include information indicating HO between MeNBs when there is no change in SeNB, information indicating uplink split bearer setting, or information indicating setting of uplink split bearer maintenance. When a UE receives MCI including these pieces of information as a HO instruction, the method disclosed in this embodiment may be performed.

[0307] In this manner, the UE can perform the method disclosed in this embodiment without providing new information and notifying the UE of the information, thereby reducing the amount of signaling.

[0308] In HO between MeNBs, it is possible not to trigger a BSR to the MeNB even if dual connectivity (DC) is set or even if an uplink split bearer is set.

[0309] Another method for the UE to transition to the method disclosed in this embodiment is disclosed. Information indicating a transition to the method disclosed in this embodiment is newly provided. When the T-MeNB determines that the UE should perform HO while maintaining the uplink split bearer, it notifies the UE of the information. The notification may be made via the S-MeNB. For example, the T-MeNB notifies the S-MeNB by including the information in the HO request response. X2 signaling may be used for this notification. Alternatively, S1 signaling may be used via the MME. The S-MeNB that receives the information notifies the UE that is the target of HO of the information. RRC signaling may be used for this notification. The UE that receives the information performs the method disclosed in this embodiment. The information may be included in the MCI, or may be notified separately without being included in the MCI.

[0310] This allows the notification to be sent to the UE separately from the HO request, enabling flexible notification according to the situation.

[0311] Another method for the UE to transition to the method disclosed in this embodiment is disclosed. The MeNB sets the threshold value set in the DRAT to the maximum configurable value and notifies the UE. Furthermore, the MeNB sets the eNB that triggers or transmits the BSR set in the DRAT to the SeNB and notifies the UE. The maximum configurable value should be set to a value equal to or greater than the amount of PDCP data that the UE can handle. In this way, when uplink pair splitting is set, the amount of PDCP data generated in the UE is always equal to or less than the threshold. Since it is set to trigger or transmit the BSR to the SeNB when the amount is equal to or less than the threshold, the UE can trigger or transmit the BSR only to the SeNB.

[0312] The setting may be changed by using the DRAT setting. For example, when returning the notification to only the SeNB to the normal DRAT, the threshold is set again, and the eNB that triggers or transmits the BSR below the threshold as necessary is set, so that the UE can perform the normal DRAT. In this way, the UE can perform the method disclosed in this embodiment without providing new information and notifying the UE. This makes it possible to reduce the amount of signaling.

[0313] Alternatively, a threshold indicating that the BSR is to be triggered or transmitted to only one eNB may be set. The MeNB sets the threshold set in the DRAT to the threshold and notifies the UE. Furthermore, the MeNB sets the eNB that triggers or transmits the BSR set in the DRAT to the SeNB and notifies the UE. This is effective when the amount of PDCP data generated in the UE is unknown. For example, the threshold is set to 0. When the MeNB wants the UE to perform the method disclosed in this embodiment, it sets the threshold set in the DRAT to 0 and notifies the UE. Since the threshold "0" indicates that the BSR is to be triggered or transmitted to only one eNB, the UE triggers or transmits the BSR to only one eNB regardless of the amount of PDCP data. It is possible to recognize which eNB, the MeNB or the SeNB, to notify by receiving information on the eNB that triggers or transmits the BSR.

[0314] A threshold value indicating that the BSR is triggered or transmitted only to the SeNB may be set. This makes it possible to omit information on the eNB that triggers or transmits the BSR. Similarly, a threshold value indicating that the BSR is triggered or transmitted only to the MeNB may be set. This is effective when it is desired to set the BSR to be triggered or transmitted only to the MeNB. The information may be included in the MCI, or may be notified separately without being included in the MCI.

[0315] Processing after completing HO between MeNBs when there is no change in SeNB will be disclosed. After completing HO between MeNBs when there is no change in SeNB, the UE returns to normal DRAT from triggering or transmitting BSR only to the SeNB. The time after completing HO may be after completing connection between the UE and the T-MeNB. Alternatively, it may be after completing synchronization between the UE and the T-MeNB, after completing RA processing between the UE and the T-MeNB, or after the UE transmits an RRC Connection Reconfiguration Complete message to the T-MeNB.

[0316] After completing HO when there is no change in SeNB, the UE can connect to both the T-MeNB and the SeNB. By doing so, the UE can trigger BSR and transmit BSR to both the eNBs of the T-MeNB and the SeNB. After completing the HO, it becomes possible to transmit uplink PDCP data not only to the SeNB but also to the MeNB, so that the transmission delay can be reduced.

[0317] By using the method disclosed in this embodiment, it becomes possible to transmit uplink data to the SeNB during HO between MeNBs when there is no change in SeNB. In addition, since the BSR is not triggered or transmitted to the MeNB, the MeNB does not transmit uplink scheduling (uplink grant) and does not transmit PDCP data to the MeNB. This prevents the UE from performing unnecessary transmission to the MeNB, and reduces transmission delays and UE power consumption. In addition, since the UE triggers or transmits a BSR to the SeNB, uplink scheduling is transmitted from the SeNB to the UE, and the UE transmits PDCP data to the SeNB. Therefore, even during HO, the UE is able to transmit data only to the SeNB, making it possible to reduce delays in data transmission due to HO.

[0318] The method disclosed in this embodiment can be applied to a case where, during HO between MeNBs when there is no change in SeNB with a split bearer maintained, uplink data is not transmitted from the UE to the T-MeNB, but is transmitted from the UE to the SeNB. For example, Figs. 12 and 13, Figs. 14 and 15, Figs. 26 and 27, etc., disclosed in the first and fourth modifications of the first embodiment.

[0319] Embodiment 3 During HO when there is no change in SeNB while maintaining the split bearer, if an attempt is made to transmit and receive uplink data between the UE and the SeNB before the UE connects to the T-MeNB, the following problems may occur.

[0320] When performing uplink split bearer, the UE must determine whether to send PDCP data to the RLC for the MeNB or to the RLC for the SeNB. For example, when the amount of PDCP data is greater than a predetermined threshold, the UE sends the PDCP data to the RLC for both eNBs that report the BSR. For example, Non-Patent Document 10 discloses that the allocation ratio for the MeNB and the SeNB is determined in advance, and the data generated by PDCP is sent to the RLC for the MeNB and the RLC for the SeNB according to the allocation ratio.

[0321] If HO occurs in this state, the UE will send data generated by PDCP to both the RLC for MeNB and the RLC for SeNB during HO. However, since HO is in progress, the UE cannot actually send a BSR to the T-MeNB, and further cannot send data to the T-MeNB, until the UE synchronizes with the T-MeNB and connects. Therefore, during HO, it is pointless for the UE to send PDCP data to the RLC for T-MeNB before synchronizing with the T-MeNB. In addition, data may accumulate in at least one of the buffers of the RLC and MAC for the T-MeNB, causing problems such as overflow. In this embodiment, a method for solving such problems is disclosed.

[0322] During HO between MeNBs, the UE sends uplink PDCP data to the RLC for the SeNB. During HO between MeNBs, the UE does not send uplink PDCP data to the RLC for the MeNB. The PDCP data may be a PDCP PDU.

[0323] The HO between MeNBs may be after the UE connects to the SeNB and before the UE connects to the T-MeNB. The UE may determine whether or not the UE has connected to the SeNB based on whether or not the RA process has been performed with the SeNB. The UE may determine whether or not the UE has connected to the SeNB based on whether or not the UE has been synchronized with the SeNB.

[0324] The UE may perform the method when performing HO between MeNBs when there is no change in SeNB. The UE may perform the method when performing HO between MeNBs when there is no change in SeNB while maintaining split bearer. The UE may reset DRAT and perform the method even if DRAT is set. The UE may reset DRAT and perform the method even if an eNB that transmits uplink data below a threshold is set to the MeNB when DRAT is set.

[0325] By doing so, the above method is performed whether the amount of PDCP data is equal to or less than the threshold value or equal to or more than the threshold value.

[0326] Although the above method is performed, it is also possible to switch to the above method. Even if a method other than the above method is set as the data distribution method of the PDCP, the method is switched to the above method.

[0327] Fig. 48 is a diagram for explaining a method of allocating PDCP data when a conventional DRAT is set. Fig. 48 shows a case where the amount of PDCP data is greater than a threshold. Fig. 48 is similar to Fig. 45 and Fig. 46 described above, so the same reference symbols are used for the same configurations and common descriptions are omitted.

[0328] When the amount of PDCP data is larger than the threshold, the UE 2013 transmits the PDCP 2014 data to both the RLC 2015 for the MeNB 2011 and the RLC 2017 for the SeNB 2012, as shown by arrows 2031 and 2032 in Fig. 48. The allocation ratio of the PDCP data for the MeNB 2011 and the SeNB is notified in advance to the UE 2013 by the MeNB 2011. The MeNB 2011 may notify the UE 2013 by RRC signaling. The MeNB 2011 may also notify the UE 2013 together with the DRAT setting.

[0329] Fig. 49 is a diagram for explaining a method of transmitting PDCP data in the embodiment 3. Since Fig. 49 is similar to the above-mentioned Fig. 45 and Fig. 46, the same components are given the same reference symbols and common descriptions will be omitted.

[0330] In the HO between the MeNBs 2011, after connecting to the SeNB 2012 and before connecting to the T-MeNB 2011, the UE 2013 transmits uplink PDCP data to the RLC 2017 for the SeNB, as shown by an arrow 2041 in Fig. 49. The UE 2013 does not transmit uplink PDCP data to the RLC 2015 for the MeNB. In other words, the UE 2013 transmits uplink PDCP data only to the RLC 2017 for the SeNB.

[0331] The method disclosed in this embodiment may be applied not only when the amount of PDCP data is greater than a threshold, but also when the amount of PDCP data is equal to or less than a threshold. When the eNB that transmits uplink data when the amount of PDCP data is equal to or less than a threshold is the MeNB2011, the method disclosed in this embodiment is applied, so that the UE2013 transmits uplink PDCP data only to the RLC2017 for SeNB after connecting to the SeNB2012 in HO between the MeNB2011 and before connecting to the T-MeNB. In this way, the uplink PDCP data is transmitted only to the SeNB2012, whether the amount of PDCP data is equal to or less than a threshold or equal to or more than a threshold.

[0332] A method for the UE to transition to the method disclosed in this embodiment will be disclosed. The MeNB 2011 notifies the UE 2013 that uplink PDCP data will be transmitted only to the RLC 2017 for SeNB during HO between the MeNBs 2011. This notification may be sent from the T-MeNB or S-MeNB to the UE 2013. When the T-MeNB notifies the UE 2013, the notification may be sent via the S-MeNB.

[0333] As a notification method, the method disclosed in the second embodiment can be applied. A method of instructing a transition to the method disclosed in this embodiment based on an HO instruction to a UE that is a target of HO may be applied. Also, a method of newly providing information indicating a transition to the method disclosed in this embodiment and notifying the UE may be applied.

[0334] Alternatively, the MeNB may set the threshold value in the DRAT to the maximum value that can be set, and notify the UE of the set threshold value.

[0335] When this is applied, in the DRAT, if the amount of PDCP data is equal to or less than a predetermined threshold, PDCP data is sent only to the RLC for the eNB that transmits the BSR. This may be determined in advance in a standard, or may be notified to the UE in advance when performing DC. It may be notified to the UE in advance as a setting parameter of the DRAT.

[0336] By setting the threshold value in the DRAT to the maximum value possible, the amount of PDCP data generated by the UE is always below the threshold. The MeNB is configured to trigger or transmit a BSR to the SeNB when the amount is below the threshold. This enables the UE to send PDCP data only to the RLC for the SeNB.

[0337] Processing after completion of HO between MeNBs when there is no change in SeNB will be disclosed. After completion of HO between MeNBs when there is no change in SeNB, the UE sends PDCP data to both RLC for T-MeNB and RLC for SeNB instead of only RLC for SeNB. Completion of HO may be completion of connection between the UE and T-MeNB. Alternatively, completion of synchronization between the UE and T-MeNB, completion of RA processing between the UE and T-MeNB, or transmission of an RRC Connection Reconfiguration Complete message by the UE to the T-MeNB may be performed.

[0338] In this way, the UE can transmit PDCP data to RLC for both the eNBs of the T-MeNB and the SeNB. After completing HO when there is no change in the SeNB, the UE can connect to both the T-MeNB and the SeNB. Therefore, after completing the HO, it becomes possible to transmit uplink PDCP data not only to the SeNB but also to the MeNB, thereby reducing the transmission delay.

[0339] By using the method disclosed in this embodiment, during HO between MeNBs when there is no change in SeNB, uplink PDCP data is not sent to the RLC for the MeNB, so all uplink PDCP data is sent only to the RLC for the SeNB. Therefore, it becomes possible to transmit uplink PDCP data only to the SeNB.

[0340] In addition, during HO, while the UE is not connected to the T-MeNB, uplink data is not stored in at least one of the RLC and MAC buffers for the MeNB of the UE. Therefore, it is possible to suppress the occurrence of overflow of these buffers. In addition, it is possible to reduce the capacity of at least one of the RLC and MAC buffers for the MeNB of the UE.

[0341] Embodiment 4 During HO when there is no change in SeNB while maintaining the split bearer, if an attempt is made to transmit and receive uplink data between the UE and the SeNB before the UE connects to the T-MeNB, the following problems may occur.

[0342] In 3GPP, a method is proposed for uplink scheduling (uplink grant) from the MeNB and SeNB to the UE when an uplink split bearer is being executed, which is different from the method of simply performing uplink scheduling based on the value of the BSR from the UE (see Non-Patent Document 11). This is done to avoid over-scheduling and under-scheduling from the MeNB and SeNB to the UE.

[0343] For example, when the PDCP data in the DRAT becomes larger than a predetermined threshold, the UE transmits a BSR including the same amount of PDCP data to both the MeNB and the SeNB. If the MeNB and the SeNB schedule the BSR transmitted from the UE by the value of the BSR, the amount of resources secured by the scheduling becomes twice the amount of PDCP data transmitted by the UE. In other words, overscheduling occurs.

[0344] In order to reduce such over-scheduling, for example, there is a method in which both the MeNB and SeNB perform uplink scheduling by multiplying the BSR received from the UE by a predetermined ratio (including 1). If the predetermined ratio is 0.7, the MeNB schedules the amount obtained by multiplying the value of the BSR received by the MeNB by 0.7 for the UE. The SeNB also schedules the amount obtained by multiplying the value of the BSR received by the SeNB by 0.7 for the UE. By doing so, it is possible to reduce over-scheduling.

[0345] In addition, there is a method in which a ratio between the MeNB and the SeNB is determined in advance, and uplink scheduling is performed according to that ratio. For example, the ratio between the MeNB and the SeNB is 4:6. The MeNB schedules the UE with the amount obtained by multiplying the BSR value received from the UE by 0.4, and the SeNB schedules the UE with the amount obtained by multiplying the BSR value received from the UE by 0.6.

[0346] In addition, in the DRAT, the MeNB performs uplink scheduling for an amount equal to or greater than a threshold for the BSR value notified from the UE, and the SeNB performs uplink scheduling for an amount equal to the threshold.

[0347] In this way, a method is proposed for uplink scheduling from the MeNB and SeNB to a UE when an uplink split bearer is being executed, which is different from the method of simply performing uplink scheduling based on the BSR value from the UE.

[0348] If no effort is made to address this issue, during HO when the SeNB is not changed while the split bearer is maintained, even before the UE connects to the T-MeNB, it is assumed that the T-MeNB will perform scheduling, and since scheduling from the SeNB is restricted, scheduling efficiency will deteriorate. This embodiment discloses a method for solving this issue.

[0349] During HO between MeNBs, the SeNB performs uplink scheduling (uplink grant) that can be assigned to the BSR received from the UE to the maximum extent possible. Also, during HO between MeNBs, uplink scheduling from the MeNB may not be performed.

[0350] The period during HO between MeNBs may be after the UE connects to the SeNB and before the UE connects to the T-MeNB. The SeNB may determine that the UE has connected to the T-MeNB by judging whether or not a SeNB reconfiguration complete message has been received from the T-MeNB. When the SeNB receives a SeNB reconfiguration complete message from the T-MeNB, the SeNB judges that the UE has connected to the T-MeNB. In this manner, the SeNB can judge that the UE has connected to the T-MeNB.

[0351] A scheduling method for SeNB is disclosed, which can be applied when RA procedure is performed between SeNB and UE during HO.

[0352] The SeNB does not perform uplink scheduling for the UE after performing SeNB addition setting processing for the T-MeNB and the UE and before connecting to the UE. Instead of the above-mentioned "after performing SeNB addition setting processing", it may be "after receiving a SeNB addition request message" or "after transmitting a SeNB addition request ack message". The SeNB may determine whether or not it has connected to the UE based on whether or not it has performed RA processing with the UE. The SeNB may determine whether or not it has connected to the UE based on whether or not it is synchronized with the UE.

[0353] As a method for preventing the SeNB from performing uplink scheduling for the UE, the SeNB may not perform uplink scheduling when it does not receive a BSR from the UE.

[0354] Alternatively, the SeNB may set the GR (grant ratio) to 0 (0%). The GR is the ratio of uplink scheduling to the BSR. By setting the GR to 0, even if the BSR cannot be received from the UE and the BSR value is indefinite, or even if some BSR value exists, the amount of uplink scheduling becomes 0 in the processing inside the SeNB, and uplink scheduling can be prevented from being performed.

[0355] The SeNB performs maximum scheduling for the UE after connecting to the UE until receiving a message from the T-MeNB indicating that the SeNB reconfiguration is complete. Although it is said that the schedule is performed after connecting to the UE, it may be said that the schedule is performed when the BSR is received after connecting to the UE.

[0356] The message indicating that SeNB reconfiguration has been completed may be a SeNB Reconfiguration Complete message.

[0357] As a method for the SeNB to perform maximum scheduling for the UE, uplink scheduling may be performed with a GR of 1 (100%) for the BSR from the UE.

[0358] After receiving a message from the T-MeNB indicating that the SeNB reconfiguration has been completed, the SeNB performs uplink scheduling for the BSR from the UE using a normal uplink scheduling method. If the DRAT is equal to or greater than a threshold, the SeNB performs uplink scheduling using a pre-configured uplink scheduling method. Alternatively, the SeNB may perform uplink scheduling using a GR that is set when the DRAT is equal to or greater than a threshold.

[0359] In this way, during HO between MeNBs, the SeNB can perform uplink scheduling (uplink grant) that can be assigned to the maximum extent possible for the BSR received from the UE.

[0360] A scheduling method of the T-MeNB is disclosed. After the T-MeNB transmits an HO request response to the S-MeNB and before connecting to the UE, the T-MeNB does not perform uplink scheduling for the UE.

[0361] The determination as to whether the T-MeNB is connected to the UE may be made based on whether an RRC Connection Reconfiguration Complete message is received from the UE. Alternatively, the determination as to whether the T-MeNB is connected to the UE may be made based on whether an RA process is performed between the T-MeNB and the UE. Alternatively, the determination as to whether the T-MeNB is connected to the UE may be made based on whether synchronization with the UE is achieved.

[0362] As a method for preventing the T-MeNB from performing uplink scheduling for the UE, the T-MeNB may not perform uplink scheduling if it does not receive a BSR from the UE. Alternatively, the T-MeNB may set the GR to 0 (0%). By setting the GR to 0, even if the BSR cannot be received from the UE and the BSR value is indefinite or some BSR value exists, the uplink scheduling amount becomes 0 in the internal processing of the T-MeNB, and uplink scheduling can be prevented from being performed.

[0363] After the T-MeNB is connected to the UE, the T-MeNB performs uplink scheduling for the BSR from the UE until the T-MeNB notifies the SeNB of the completion of the reconfiguration. Although the term "after the T-MeNB is connected to the UE" is used, the term "after the T-MeNB is connected to the UE" may be used instead.

[0364] Although uplink scheduling is performed for the BSR from the UE in the above embodiment, maximum scheduling may be performed for the BSR from the UE. As a method for the T-MeNB to perform maximum scheduling for the UE, uplink scheduling may be performed with a GR of 1 (100%) for the BSR from the UE.

[0365] Alternatively, the T-MeNB may perform uplink scheduling in response to a BSR from the UE in the manner of normal uplink scheduling.

[0366] If the DRAT is greater than or equal to the threshold, the T-MeNB may perform uplink scheduling for the BSR from the UE at the configured GR or a GR greater than the configured GR.

[0367] Alternatively, the T-MeNB may perform uplink scheduling in response to a BSR from the UE so that the UE can transmit uplink data with an amount at least greater than 0.

[0368] After transmitting a message to the SeNB indicating that the reconfiguration is complete, the T-MeNB performs uplink scheduling using a normal uplink scheduling method for the BSR from the UE. If the DRAT is equal to or greater than a threshold, uplink scheduling is performed using a pre-configured uplink scheduling method. Alternatively, uplink scheduling may be performed using a GR that is set when the DRAT is equal to or greater than a threshold.

[0369] By doing this, uplink scheduling from the MeNB is not performed during HO between MeNBs, and uplink scheduling from the T-MeNB can be performed after the UE and the T-MeNB are connected.

[0370] Furthermore, by doing this, even if the UE connects to the T-MeNB before connecting to the SeNB, it is possible to transmit uplink data via the T-MeNB.

[0371] In uplink scheduling, for example, there is a method in which both the MeNB and the SeNB perform uplink scheduling by multiplying the BSR received from the UE by a predetermined ratio, and a method in which uplink scheduling is performed according to a predetermined ratio between the MeNB and the SeNB. In such a case, it is necessary to adjust which scheduling method to use between the MeNB and the SeNB. Here, the adjustment method is disclosed.

[0372] The MeNB performs this adjustment. In the case of HO between MeNBs, it may be performed by the T-MeNB. The MeNB notifies the SeNB of information on the uplink scheduling method. When the MeNB configures a GR in the SeNB, the MeNB may notify the SeNB of the GR.

[0373] As a method of notification from the MeNB to the SeNB, the notification may be made during SeNB addition processing, or may be made by including the notification in a SeNB addition request message, or may be made during SeNB modification processing, or may be made by including the notification in a SeNB modification request message. In response to the notification, the SeNB may notify the MeNB of Ack, which is a response signal indicating that the setting is possible.

[0374] Alternatively, the notification may be sent together with a SeNB reconfiguration complete message, or may be sent by being included in the SeNB reconfiguration complete message.

[0375] In this way, it becomes possible to adjust the scheduling method between the MeNB and the SeNB.

[0376] Figure 50 is a diagram for explaining a method of uplink scheduling when a conventional DRAT is set. Figure 50 shows a case where the amount of PDCP data is greater than a threshold. Figure 50 is similar to the above-mentioned Figures 45 and 46, so the same reference symbols are used for the same configurations and common descriptions are omitted.

[0377] When the amount of PDCP data is larger than the threshold, the MeNB 2011 and the SeNB 2012 notify the UE 2013 of uplink scheduling (uplink grant) as indicated by arrows 2051 and 2052 in Fig. 50. Normally, uplink scheduling from the MeNB 2011 and the SeNB 2012 to the UE 2013 when an uplink split bearer is being executed is performed according to the value of the BSR from the UE 20113.

[0378] Concerning uplink scheduling, the adjustment between the MeNB2011 and the SeNB2012 is not disclosed in the above-mentioned Non-Patent Documents 1 to 11. For the adjustment, the above-mentioned method may be applied. For example, when the DRAT is equal to or greater than a threshold, the MeNB2011 sets a GR and notifies the SeNB2012 of the GR as shown by the arrow 2053. In this way, it becomes possible to adjust the scheduling between the MeNB2011 and the SeNB2012 when the DRAT is set.

[0379] By using this method, uplink scheduling becomes possible, and the UE 2013 becomes able to transmit uplink data to the MeNB 2011 and the SeNB 2012 in accordance with the received uplink scheduling.

[0380] Fig. 51 is a diagram for explaining an uplink scheduling method in the fourth embodiment. Since Fig. 51 is similar to the above-mentioned Fig. 45 and Fig. 46, the same components are given the same reference symbols and common descriptions are omitted.

[0381] During HO between the MeNBs 2011, as indicated by an arrow 2061 in Fig. 51, the SeNB 2012 performs uplink scheduling (uplink grant) that can be assigned to the maximum extent possible for the BSR received from the UE 2013. Furthermore, during HO between the MeNBs 2011, no uplink scheduling is performed from the MeNB 2011.

[0382] In this way, during HO between MeNBs 2011, the SeNB 2012 can perform uplink scheduling that can be assigned to the BSR transmitted by the UE 2013 to the maximum extent possible. Since the UE 2013 performs uplink scheduling that can be assigned to the BSR transmitted to the SeNB 2012 to the maximum extent possible, during HO between MeNBs 2011, it becomes possible to transmit uplink data to the maximum extent possible when connected to the SeNB 2012. It becomes possible to transmit uplink data without being restricted by the GR set in the DRAT. Therefore, during HO between MeNBs 2011, even if the MeNB 2011 and the UE 2013 are not connected, the UE 2013 can transmit uplink data to the SeNB 2012.

[0383] The above-mentioned method can be applied to the coordination of information regarding uplink scheduling between the MeNB 2011 and the SeNB 2012.

[0384] By using the method disclosed in this embodiment, scheduling from the SeNB is no longer restricted, and deterioration of scheduling efficiency can be suppressed.

[0385] As described above, even when the MeNB and SeNB perform non-normal uplink scheduling for a UE that is running an uplink split bearer, the scheduling from the SeNB is no longer restricted, and deterioration in scheduling efficiency can be suppressed.

[0386] During HO between MeNBs when there is no change in SeNB, the UE is able to transmit uplink data to the SeNB early, thereby making it possible to reduce delays in transmission of uplink data.

[0387] Another method for scheduling the SeNB is disclosed, which can be applied when the SeNB and the UE are already synchronized during HO.

[0388] The SeNB does not perform uplink scheduling for the UE until it receives an SR (scheduling request) from the UE after performing SeNB additional configuration processing for the T-MeNB and the UE.

[0389] After receiving an SR from the UE, the SeNB performs maximum scheduling for the UE until receiving a message from the T-MeNB indicating that SeNB reconfiguration is complete. Although it is described as after receiving an SR from the UE, it may be after receiving an SR from the UE and when receiving a BSR.

[0390] After receiving a message from the T-MeNB indicating that the SeNB reconfiguration has been completed, the SeNB performs uplink scheduling for the BSR from the UE using a normal uplink scheduling method. If the DRAT is equal to or greater than a threshold, the SeNB performs uplink scheduling using a pre-configured uplink scheduling method. Alternatively, the SeNB may perform uplink scheduling using the GR that is set when the DRAT is equal to or greater than a threshold.

[0391] By doing this, during HO between MeNBs, if the SeNB has already been synchronized with the UE, the SeNB can perform uplink scheduling (uplink grant) that can be assigned to the maximum extent possible for the BSR received from the UE.

[0392] In the HO between MeNBs when there is no change in the SeNB, the connection between the SeNB and the UE may be continued, and this method may be applied in such a case. During the HO, the UE can transmit uplink data to the SeNB early.

[0393] Another method for scheduling the SeNB is disclosed. This method can be applied to the case where the SeNB receives a message indicating that the SeNB reconfiguration is completed from the T-MeNB before the SeNB connects to the UE or receives an SR during HO.

[0394] When the SeNB receives a message indicating that the SeNB reconfiguration is complete from the T-MeNB before connecting to the UE or before receiving an SR, the SeNB performs uplink scheduling using a normal uplink scheduling method for the BSR from the UE after receiving the message indicating that the SeNB reconfiguration is complete. If the DRAT is equal to or greater than a threshold, uplink scheduling is performed using a pre-set uplink scheduling method. Alternatively, uplink scheduling may be performed using a GR that is set when the DRAT is equal to or greater than a threshold.

[0395] By doing so, even when a message indicating that SeNB reconfiguration has been completed is received from the T-MeNB before the SeNB connects to the UE or receives an SR during HO, it is possible to clarify control and reduce malfunctions.

[0396] Pre-scheduling (hereinafter referred to as "PS") is being considered in 3GPP. PS is a method of scheduling resources for uplink data to a UE in advance without receiving a BSR from the UE.

[0397] Here, a method of performing PS for the SeNB in ​​the DC is disclosed. PS in the SeNB is performed from the MeNB to the UE. The MeNB performs PS in the SeNB to the UE.

[0398] The PS configuration of the SeNB is set between the MeNB and the SeNB. The PS configuration includes scheduling information, a scheduling period, etc. A setting method is disclosed. A PS setting request of the SeNB is made from the MeNB to the SeNB. The setting request may include the ID of the target UE, the setting of the target bearer, information about QoS (Quality of Service), etc. The SeNB that receives the PS setting request sets the PS configuration for the target UE. The SeNB notifies the MeNB of the PS configuration set for the target UE. In this way, the PS configuration of the SeNB is set between the MeNB and the SeNB.

[0399] In the SeNB addition process between the MeNB and the SeNB, the PS configuration may be set. The MeNB sends a PS setting request to the SeNB by using a SeNB addition request message. The SeNB that sets the PS configuration in response to the request notifies the MeNB of the PS configuration by using a SeNB addition request Ack message.

[0400] Alternatively, the PS configuration may be set in a SeNB modification process between the MeNB and the SeNB. The MeNB sends a SeNB PS configuration request to the SeNB using a SeNB modification request message. The SeNB that has set the PS configuration in response to the request notifies the MeNB of the SeNB PS configuration using a SeNB modification request Ack message.

[0401] In this way, there is no need to provide a new message for PS setup between the MeNB and the SeNB, and setup can be performed using existing messages, which simplifies PS setup control.

[0402] The PS configuration of the SeNB is set between the MeNB and the UE. The MeNB notifies the UE of the PS configuration set between the MeNB and the UE. The UE sets the PS configuration of the SeNB notified from the MeNB. RRC signaling may be used for the notification from the MeNB to the UE. The notification from the MeNB to the UE may be included in the RRC signaling used for the SeNB configuration. This makes it possible to reduce the amount of signaling. Also, by notifying together with the SeNB configuration, it is possible to simplify the control of the SeNB configuration in the UE.

[0403] Alternatively, MAC signaling may be used for the notification, which is effective when scheduling is performed by MAC.

[0404] Alternatively, the PDCCH may be used for the notification. Scheduling information for the UE is transmitted on the PDCCH. By including the PS configuration in the PDCCH and notifying it, it becomes easier to control the setting of the scheduling configuration in the UE.

[0405] Alternatively, the above three notification methods may be used in combination. For example, a part of the PS configuration is notified by one of the above three notification methods, and the other part of the PS configuration is notified by another notification method. For example, the scheduling information is notified by PDCCH, and the scheduling period is notified by RRC signaling. In this way, it is possible to adopt the optimal notification method for each piece of PS configuration information.

[0406] By doing so, it becomes possible for the DC to perform PS with respect to the SeNB.

[0407] Here, a method of performing PS for a SeNB in ​​HO between MeNBs is disclosed. PS in the SeNB is performed from the T-MeNB to the UE. The T-MeNB performs PS in the SeNB to the UE. The PS configuration of the SeNB is set between the T-MeNB and the SeNB. The setting method can be the method described above.

[0408] The T-MeNB notifies the UE of the PS configuration set with the SeNB. The T-MeNB may notify the UE via the S-MeNB. X2 signaling may be used for the notification from the T-MeNB to the S-MeNB. For example, the notification may be included in an HO request ack message. The notification from the S-MeNB to the UE may be by RRC signaling. For example, the notification may be included in an RRC Connection Reconfiguration message. Also, for example, the notification may be included in an RRC Connection Reconfiguration message together with the MCI. The UE sets the PS configuration of the SeNB received from the T-MeNB.

[0409] During HO, after connecting to the SeNB, the UE transmits uplink data using resources configured by the received SeNB configuration, and may also transmit BSR using the resources.

[0410] In this way, it becomes possible to perform PS with respect to the SeNB. The UE becomes able to transmit uplink data to the SeNB using the PS configuration.

[0411] This paper discloses an uplink scheduling method when PS is set for SeNB in ​​HO between MeNBs with no change of SeNB while maintaining split bearer.

[0412] The SeNB follows the configured PS in uplink scheduling for the UE after performing SeNB additional configuration processing for the T-MeNB and the UE, until receiving an SR from the UE. After receiving an SR from the UE, the SeNB performs maximum scheduling for the UE until receiving a message from the T-MeNB indicating that SeNB reconfiguration is complete. Although it is described as after receiving an SR from the UE, it may be when receiving a BSR after receiving an SR from the UE.

[0413] After receiving a message from the T-MeNB indicating that the SeNB reconfiguration has been completed, the SeNB performs uplink scheduling using a normal uplink scheduling method for the BSR from the UE. If the DRAT is equal to or greater than a threshold, the SeNB performs uplink scheduling using a pre-configured uplink scheduling method. Alternatively, the SeNB may perform uplink scheduling using a GR that is set when the DRAT is equal to or greater than a threshold.

[0414] In this way, in the case where the SeNB is not changed while the split bearer is maintained during HO between MeNBs, if a PS is set for the SeNB, the UE can transmit uplink data to the SeNB early by following the PS. Alternatively, the UE can transmit a BSR to the SeNB early, and can then transmit uplink data. This makes it possible to reduce the delay in transmitting uplink data.

[0415] The above-described embodiments and their modifications are merely examples of the present invention, and the embodiments and their modifications can be freely combined within the scope of the present invention. In addition, any of the components of the embodiments and their modifications can be appropriately modified or omitted.

[0416] Although the present invention has been described in detail, the above description is illustrative in all respects and does not limit the present invention. It is understood that countless variations not illustrated can be assumed without departing from the scope of the present invention. [Explanation of symbols]

[0417] 701 Macro eNB (macro cell) coverage, 702 Small eNB (small cell) coverage, 703,2013 Mobile terminal (UE), 2011 MeNB, 2012 SeNB, 2014 PDCP, 2015,2017 RLC, 2016,2018 MAC.

Claims

1. A plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station; A communication system including a user device capable of wirelessly communicating with a plurality of the base stations, In a handover process from the first master base station to the second master base station for the user equipment that communicates using a split bearer, which is a communication path split between the first master base station and the secondary base station, the second master base station determines not to change the secondary base station that communicates with the user equipment; The secondary base station is maintained unchanged; Communication systems.

2. The communication system according to claim 1 , wherein the first master base station notifies the user equipment to maintain the split bearer via the second master base station.

3. 2. The communication system according to claim 1, wherein the first master base station notifies the user equipment that the split bearer is maintained via the second master base station together with mobility control information (MCI) included in an RRC connection reconfiguration message.

4. The communication system according to claim 1 , wherein in the handover process, the second master base station notifies the user equipment via the first master base station of reconfiguration of the split bearer while maintaining the secondary base station.

5. The communication system according to claim 1 , wherein in the handover process, the first master base station notifies the user equipment of a part of the configuration information of the secondary base station transmitted from the second master base station.

6. A plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station; A master base station in a communication system including a plurality of base stations and a user device capable of wireless communication with the base stations, In a handover process from the first master base station to the second master base station for the user equipment that communicates using a split bearer, which is a communication path split between the first master base station and the secondary base station, the secondary base station is not changed and the split bearer is maintained; The second master base station determines not to change the secondary base station communicating with the user equipment; The secondary base station is maintained unchanged; Master base station.

7. A plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station; A secondary base station in a communication system including a plurality of user equipment capable of wireless communication with the base stations, In a handover process from the first master base station to the second master base station for the user equipment that communicates using a split bearer, which is a communication path split between the first master base station and the secondary base station, the second master base station determines not to change the secondary base station that communicates with the user equipment; The secondary base station is maintained unchanged; Secondary base station.

8. A plurality of base stations including a plurality of master base stations including a first master base station and a second master base station and at least one secondary base station; A user device in a communication system including a plurality of user devices capable of wireless communication with the base stations, In a handover process from the first master base station to the second master base station for the user equipment that communicates using a split bearer, which is a communication path split between the first master base station and the secondary base station, the second master base station determines not to change the secondary base station that communicates with the user equipment; The secondary base station is maintained unchanged; The user equipment communicates with the second master base station and the secondary base station. User equipment.

Images