Communication system, base station, and user equipment

Abstract

To provide a technique that can shorten the time required for beam switching processing.SOLUTION: A communication system includes user equipment, and a first base station and a second base station, each of which is capable of forming a plurality of beams by beamforming, and communicates with the user equipment by using the plurality of beams while switching between them. When the user equipment switches its beam from a first beam formed by the first base station to a second beam formed by the second base station, setting information related to a random access process in the second beam is transmitted to the user equipment.SELECTED DRAWING: Figure 27

Description

[Technical Field]

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

[0002] 3GPP (3rd Generation Partnership Project), a standardization organization for mobile communication systems, is considering a communication method called Long Term Evolution (LTE) for the wireless section and System Architecture Evolution (SAE) for the overall system configuration including the core network and radio access network (hereinafter collectively referred to as the network) (see, for example, Non-Patent Documents 1 to 10). This communication method is also called the 3.9G (3.9 Generation) system.

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

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

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

[0006] The Physical Broadcast Channel (PBCH) is a channel for downlink transmission from a base station (hereinafter simply referred to as a "base station") to a communication terminal (hereinafter simply referred to as a "communication terminal") such as a mobile terminal (hereinafter 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 Orthogonal Frequency Division Multiplexing (OFDM) symbols used for PDCCHs. The PCFICH is transmitted every subframe.

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

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

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

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

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

[0013] The Physical Hybrid ARQ Indicator Channel (PHICH) is a channel for downlink transmission from a base station to a communication terminal. The PHICH carries Ack / Nack, which are response signals to 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 symbols known 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 Demodulation Reference Signal (DM-RS), 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 channels described in Non-Patent Document 1 (Chapter 5) will be explained below. Among the downlink transport channels, a broadcast channel (BCH) is broadcast to the entire coverage of the base station (cell). The BCH is mapped to a physical broadcast channel (PBCH).

[0016] 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) in 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 in communication terminals to enable low power consumption in communication terminals. The PCH is required to broadcast to the entire coverage of the base station (cell). The PCH is mapped to physical resources such as the Physical Downlink Shared Channel (PDSCH) that can be dynamically used for traffic.

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

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

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

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

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

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

[0024] The Paging Control Channel (PCCH) is a downlink channel for transmitting paging information and 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 Downlink Shared Channel (DL-SCH), which is a transport channel. In the uplink direction, CCCH is mapped to an Uplink Shared Channel (UL-SCH), which is a transport channel.

[0026] The Multicast Control Channel (MCCH) is a downlink channel for point-to-multipoint transmission. The MCCH is used to transmit MBMS control information for one or several MTCHs from the network to 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. The DCCH is used when the communication terminal is in an RRC connection. The DCCH is mapped to an uplink shared channel (UL-SCH) in the uplink and to a downlink shared channel (DL-SCH) in the downlink.

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

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

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

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

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

[0033] The CSG-ID is broadcast by the 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 used for tracking the location of this communication terminal is called a tracking area.

[0035] 3GPP is studying base stations called Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB). HNB in UTRAN and HeNB in E-UTRAN are base stations for access services for homes, businesses, and businesses, for example. Non-Patent Document 2 discloses three different modes of access to HeNB and HNB. Specifically, it discloses an open access mode, a closed access mode, and a hybrid access mode.

[0036] 3GPP is also working on the development of the Long Term Evolution Advanced (LTE-A) standard as Release 10 (see Non-Patent Documents 3 and 4). LTE-A is based on the LTE wireless communication system, and is configured by adding several new technologies to it.

[0037] In the LTE-A system, carrier aggregation (CA) is being considered, which aggregates two or more component carriers (CCs) (also called "aggregation") to support wider frequency bandwidths (transmission bandwidths) up to 100 MHz. CA is described in Non-Patent Document 1.

[0038] When CA is configured, the UE has only one RRC connection with the network (NW). In the RRC connection, one serving cell provides NAS mobility information and security input. This cell is called the primary cell (PCell). In the downlink, the carrier corresponding to the PCell is the downlink primary component carrier (DL PCC). In the uplink, the carrier corresponding to the PCell is the uplink primary component carrier (UL PCC).

[0039] Depending on the UE's capabilities, a secondary cell (SCell) is configured to form a pair of a PCell and a serving cell. In the downlink, the carrier corresponding to the SCell is a downlink secondary component carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is an uplink secondary component carrier (UL SCC).

[0040] For one UE, a set of one PCell and a serving cell consisting of one or more SCells is configured.

[0041] Furthermore, new technologies for LTE-A include wider bandwidth extension and Coordinated Multiple Point transmission and reception (CoMP) technology. CoMP, which is being considered for LTE-A by 3GPP, is described in Non-Patent Document 1.

[0042] Mobile network traffic volume is on the rise, and communication speeds are also increasing. Once LTE and LTE-A are fully operational, communication speeds are expected to increase even further.

[0043] Furthermore, in order to handle future massive traffic volumes, 3GPP is considering using small eNBs (hereinafter sometimes referred to as "small-scale base station devices") that configure small cells. For example, technologies are being considered that aim to increase communication capacity by installing a large number of small eNBs and configuring a large number of small cells to improve frequency utilization efficiency. Specifically, there is dual connectivity (abbreviated as DC), in which a UE connects to two eNBs to communicate. DC is described in Non-Patent Document 1.

[0044] Of the eNBs that perform dual connectivity (DC), one may be referred to as a "master eNB (abbreviated as MeNB)" and the other as a "secondary eNB (abbreviated as SeNB)."

[0045] Furthermore, in response to the increasing sophistication of mobile communications, fifth-generation (hereinafter sometimes referred to as "5G") wireless access systems are being considered, with the goal of launching services after 2020. For example, in Europe, an organization called METIS has compiled requirements for 5G (see Non-Patent Document 5).

[0046] The requirements for a 5G wireless access system are that it will have 1,000 times the system capacity, 100 times the data transmission speed, one-tenth (1 / 10) the data processing delay, and 100 times the number of simultaneous connections of communication terminals compared to an LTE system, while also achieving further reductions in power consumption and lower equipment costs.

[0047] To meet these demands, efforts are being made to increase data transmission capacity by using broadband frequencies and to increase data transmission speeds by improving frequency utilization efficiency.To achieve these goals, technologies such as MIMO (Multiple Input Multiple Output) and beamforming, which use multi-element antennas to enable spatial multiplexing, are being considered. [Prior art documents] [Non-patent literature]

[0048] [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] "Scenarios, requirements and KPIs for 5G mobile and wireless system", [online], April 30, 2013, ICT-317669-METIS / D1.1, [Retrieved January 25, 2016], Internet<https: / / www.metis2020.com / documents / deliverables / > [Non-patent document 6] 3GPP R2-144662 [Non-Patent Document 7] 3GPP R2-152359 [Non-patent document 8] 3GPP TS 36.141 V13.0.0 [Non-Patent Document 9] 3GPP TS36.321 V12.8.0 [Non-Patent Document 10] 3GPP R2-156668 Summary of the Invention [Problem to be solved by the invention]

[0049] In DC, split bearers are supported, and in the split bearers, semi-persistent scheduling (SPS) is supported not only for MeNBs but also for SeNBs (see Non-Patent Document 6).

[0050] 3GPP has proposed a method of transmitting a Buffer Status Report (abbreviated as BSR) when an uplink split bearer is being used, using a double reporting and threshold (abbreviated as DRAT) method (see Non-Patent Document 7). When DRAT is performed with an uplink split bearer, if the amount of uplink data is equal to or less than the DRAT threshold, the UE transmits data to one predetermined eNB and does not transmit data to the other eNB.

[0051] However, there are no regulations or discussions regarding the behavior of the SPS when the amount of uplink data falls below the DRAT threshold, such as whether or not the UE should transmit padding.

[0052] Without a definition of SPS operation, the implicit release function using padding transmission will not function properly, which will cause unstable operation between the eNB and the UE, and ultimately lead to malfunctions.

[0053] An object of the present invention is to provide a technique that can reduce deterioration of communication quality and communication interruptions. [Means for solving the problem]

[0054] The communication system of the present invention is a communication system comprising a user device, and a first base station and a second base station each capable of forming a plurality of beams by beamforming, the first base station and the second base station each communicating with the user device by switching between the plurality of beams, and when the user device switches beams from a first beam formed by the first base station to a second beam formed by the second base station, setting information relating to random access processing in the second beam is transmitted to the user device. The base station according to the present invention is a base station in a communication system comprising a user device, a first base station and a second base station each capable of forming a plurality of beams by beamforming, and each communicating with the user device by switching between the plurality of beams, and when the user device switches beams from a first beam formed by the first base station to a second beam formed by the second base station, the base station transmits setting information regarding random access processing in the second beam to the user device. A user device according to the present invention is a user device in a communication system comprising a first base station and a second base station, each capable of forming a plurality of beams by beamforming, and each communicating with the user device by switching between the plurality of beams, and receives setting information relating to random access processing in the second beam when switching beams from a first beam formed by the first base station to a second beam formed by the second base station. [Effects of the Invention]

[0055] According to the present invention, it is possible to reduce the time required for beam switching processing.

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

[0057] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Figure 2] 1 is a block diagram showing the overall configuration of an LTE communication system 200 being discussed in 3GPP. [Figure 3] FIG. 3 is a block diagram showing the 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 the configuration of a base station 203 shown in FIG. 2, which is a base station according to the present invention. [Figure 5]FIG. 2 is a block diagram showing the configuration of an MME according to the present invention. [Figure 6] 1 is a flowchart showing an outline of operations from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. [Figure 7] FIG. 1 is a diagram illustrating the concept of a cell configuration when macro eNBs and small eNBs are mixed. [Figure 8] A diagram explaining an example of uplink SPS operation. [Figure 9] FIG. 10 is a diagram for explaining a transmission method using DRAT. [Figure 10] FIG. 10 is a diagram for explaining a transmission method using DRAT. [Figure 11] FIG. 10 is a diagram illustrating the problem that occurs when an SPS is set up when a UL split bearer is set up. [Figure 12] FIG. 10 is a diagram illustrating a case where the DRAT threshold is set to 0 when SPS is set. [Figure 13] A diagram explaining a method of supporting implicit release when SPS is configured for a 2nd-eNB. [Figure 14] 10 is a diagram illustrating a case where upstream transmission data with a data amount smaller than the DRAT threshold occurs. FIG. [Figure 15] A diagram explaining a method for preventing the uplink SPS setting from being invalidated. [Figure 16] A diagram explaining a method of using information indicating that the uplink SPS setting is disabled. [Figure 17] 10A and 10B are diagrams illustrating a method for differentiating padding transmission when there is no uplink transmission data from padding transmission when there is uplink transmission data. [Figure 18] 10A and 10B are diagrams illustrating a method for differentiating padding transmission when there is no uplink transmission data from padding transmission when there is uplink transmission data. [Figure 19] 10A and 10B are diagrams illustrating a method for differentiating padding transmission when there is no uplink transmission data from padding transmission when there is uplink transmission data. [Figure 20] 10A and 10B are diagrams illustrating a method for differentiating padding transmission when there is no uplink transmission data from padding transmission when there is uplink transmission data. [Figure 21] FIG. 10 is a diagram illustrating a method for configuring the same SPS for a 1st-eNB as that configured for a 2nd-eNB. [Figure 22] FIG. 10 is a diagram illustrating a method for not transmitting padding when implicit release is not performed. [Figure 23] FIG. 10 is a diagram illustrating a HARQ method when padding transmission is not performed. [Figure 24] 10A and 10B are diagrams illustrating an implicit release method when padding transmission is thinned out. [Figure 25] A figure showing another example of an implicit release method when padding transmission is thinned out. [Figure 26] FIG. 1 is a diagram illustrating beamforming using a multi-element antenna. [Figure 27] FIG. 23 is a diagram showing an example of a sequence relating to a method for reducing the time required for beam switching processing in the twelfth embodiment. [Figure 28] FIG. 23 is a diagram showing an example of a sequence relating to a method for shortening the time required for beam switching processing in the thirteenth embodiment. [Figure 29] FIG. 23 is a diagram showing an example of a sequence relating to a method for reducing the time required for beam switching processing in the first modification of the thirteenth embodiment. [Figure 30] FIG. 23 is a diagram showing an example of a sequence relating to a method for reducing the time required for beam switching processing in the first modification of the thirteenth embodiment. [Figure 31] A figure showing an example of a sequence related to a method for performing HARQ processing using a target beam from the first transmission of data in variant example 2 of embodiment 13. [Figure 32] A figure showing another example of a sequence related to a method for performing HARQ processing using a target beam from the first transmission of data in variant example 2 of embodiment 13. [Figure 33]A figure showing an example of a sequence regarding a method for retransmitting data during HARQ processing using a target beam in variant example 2 of embodiment 13. [Figure 34] A figure showing an example of a sequence regarding a method performed with a target beam based on successful delivery (Ack) / failure to deliver (Nack) data during HARQ processing in variant example 2 of embodiment 13. DETAILED DESCRIPTION OF THE INVENTION

[0058] Embodiment 1 Fig. 2 is a block diagram showing the overall configuration of an LTE 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.

[0059] Here, the term "communication terminal device" includes not only mobile terminal devices such as mobile cell phone terminal devices, but also stationary devices such as sensors. In the following description, the term "communication terminal device" may be simply referred to as a "communication terminal."

[0060] If the control protocols for the mobile terminal 202, such as RRC (Radio Resource Control), and the user plane, such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate at the base station 203, the E-UTRAN is composed of one or more base stations 203.

[0061] The control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs broadcasting, 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.

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

[0063] The base stations 203 are classified into eNBs 207 and Home-eNBs 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 configured from an EPC (Evolved Packet Core) core network and an E-UTRAN 201 radio access network is called an EPS (Evolved Packet System). The EPC core network and the E-UTRAN 201 radio access network may be collectively referred to as a "network."

[0064] The eNB 207 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 eNB 207 and the MME unit 204. Multiple MME units 204 may be connected to one eNB 207. The eNBs 207 are connected to each other via an X2 interface, and control information is communicated between the eNBs 207.

[0065] 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 via an S1 interface, and the HeNBGW 205 and the MME unit 204 are connected via the S1 interface.

[0066] 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.

[0067] 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.

[0068] Furthermore, 3GPP is considering the following configuration: The X2 interface between Home-eNBs 206 is supported. That is, Home-eNBs 206 are connected via the X2 interface, and control information is communicated between the Home-eNBs 206. From the MME unit 204, HeNBGW 205 appears as Home-eNB 206. From the Home-eNB 206, HeNBGW 205 appears as MME unit 204.

[0069] 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 connected directly 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.

[0070] Base station 203 may configure one cell or multiple cells. Each cell has a predetermined range as coverage, which is the range within which communication with mobile terminal 202 is possible, and performs wireless communication with mobile terminal 202 within the coverage. When one base station 203 configures multiple cells, each cell is configured to be able to communicate with mobile terminal 202.

[0071] FIG. 3 is a block diagram showing the configuration of mobile terminal 202 shown in FIG. 2, which is a communication terminal according to the present invention. The transmission process of mobile terminal 202 shown in FIG. 3 will be described. First, control data from protocol processing unit 301 and user data from application unit 302 are stored in transmission data buffer unit 303. The data stored in transmission data buffer unit 303 is passed to encoder unit 304, where it undergoes encoding processes such as error correction. Some data may be output directly from transmission data buffer unit 303 to modulation unit 305 without undergoing encoding processes. The data encoded by encoder unit 304 is modulated by modulation unit 305. The modulated data is converted into a baseband signal, and then output to frequency conversion unit 306, where it is converted into a radio transmission frequency. A transmission signal is then transmitted from antenna 307 to base station 203.

[0072] Furthermore, the reception process of the mobile terminal 202 is performed as follows. A radio signal from the base station 203 is received by the antenna 307. The received signal is converted from a radio reception 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 processes such as error correction are 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.

[0073] Fig. 4 is a block diagram showing the configuration of base station 203 shown in Fig. 2, which is a base station according to the present invention. The transmission processing of base station 203 shown in Fig. 4 will be described. EPC communication unit 401 transmits and receives data between base station 203 and EPC (MME unit 204, etc.), HeNBGW 205, etc. Other base station communication unit 402 transmits and receives data with other base stations. EPC communication unit 401 and other base station communication unit 402 each exchange information with protocol processing unit 403. Control data from protocol processing unit 403, and user data and control data from EPC communication unit 401 and other base station communication unit 402 are stored in transmission data buffer unit 404.

[0074] The data stored in the transmission data buffer unit 404 is passed to the encoder unit 405, where it undergoes encoding processes such as error correction. Some data may be output directly from the transmission data buffer unit 404 to the modulator unit 406 without undergoing encoding processes. The encoded data is modulated by the modulator unit 406. The modulated data is converted into a baseband signal, and then output to the frequency converter 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.

[0075] The reception process of the base station 203 is performed 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 decoding processes such as error correction are performed. Of the decoded data, 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 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 of the units 401 to 410.

[0076] 5 is a block diagram showing the configuration of an MME according to the present invention. FIG. 5 shows the configuration of an MME 204a included in the MME unit 204 shown in FIG. 2 described above. A PDN GW communication unit 501 transmits and receives data between the MME 204a and a PDN GW. A base station communication unit 502 transmits and receives data via the S1 interface between the MME 204a and a base station 203. 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 a 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.

[0077] If 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. If 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.

[0078] 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 the control plane control unit 505. The 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, the 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 HeNBGWs 205 via the HeNBGW communication unit 504.

[0079] 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, and the like, and performs overall 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, and search of tracking areas for one or more mobile terminals 202 under its control, tracking area list management, etc.

[0080] The MME 204a distributes paging signals 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 an active state. The MME 204a initiates a paging protocol by transmitting a paging message to a cell belonging to a tracking area in which the UE is registered. The idle state mobility management unit 505-3 may manage the CSG, CSG-ID, and whitelist of the Home-eNB 206 connected to the MME 204a.

[0081] Next, an example of a cell search method in a communication system is shown. Fig. 6 is a flowchart showing an outline of the process from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. When the communication terminal starts a cell search, in step ST601, it synchronizes slot timing and frame timing using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a surrounding base station.

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

[0083] Next, in step 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. The RS uses a code that has a one-to-one correspondence with the PCI. By correlating with this code, it is possible to separate the cell from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST601, it is possible to detect the RS and measure the RS received power.

[0084] 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 one or more cells detected up to step ST602.

[0085] 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 the DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, and the SFN (System Frame Number).

[0086] Next, in step ST605, the DL-SCH of the cell is received based on the cell configuration information in the MIB, and SIB (System Information Block) 1 is obtained from the broadcast information BCCH. SIB 1 includes information on access to the cell, information on cell selection, and scheduling information for other SIBs (SIBk; k is an integer greater than or equal to 2). SIB 1 also includes a tracking area code (TAC).

[0087] Next, in step 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 an MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a tracking area code number.

[0088] If the comparison in step ST606 shows that the TAC received in step ST605 is the same as the TAC included in the tracking area list, the communication terminal enters standby mode in the cell. If the comparison shows that the TAC received in step ST605 is not included in the tracking area list, 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.

[0089] An apparatus constituting a core network (hereinafter sometimes referred to as a "core network side apparatus") updates the tracking area list based on the identification number (e.g., UE-ID) of the 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. Thereafter, the communication terminal enters standby operation in the cell.

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

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

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

[0093] In the following description, a cell 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 the macro cell is referred to as a "macro eNB." Also, a cell with a relatively small coverage, such as a cell configured as a small cell, is referred to as a "small cell," and an eNB that configures the small cell is referred to as a "small eNB."

[0094] The macro eNB may be, for example, a "Wide Area Base Station" as described in Non-Patent Document 7.

[0095] The small eNB may be, for example, a low-power node, a local area node, a hotspot, etc. Also, the small eNB may be a pico eNB constituting a pico cell, a femto eNB constituting a femto cell, a HeNB, a remote radio head (RRH), a remote radio unit (RRU), a remote radio equipment (RRE), or a relay node (RN). Also, the small eNB may be a "local area base station" or a "home base station" as described in Non-Patent Document 7.

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

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

[0098] 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 of a small cell 702 and communicates via the small cell.

[0099] Furthermore, in the cell configuration shown in FIG. 7, 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 overlap in a complex manner, as indicated by reference numeral "706."

[0100] 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.

[0101] 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.

[0102] Dual connectivity (DC) supports split bearers, which are bearers that are split into a direct path between the MeNB and the UE and a path between the MeNB and the UE via the SeNB.

[0103] In the split bearer, semi-persistent scheduling (SPS) is supported not only for the MeNB but also for the SeNB (see Non-Patent Document 6). SPS can be set simultaneously and independently for the MeNB and the SeNB.

[0104] SPS is a scheduling method that allows for semi-static allocation of radio resources to UEs over a long period of time, such as multiple subframes, eliminating the need for the eNB to transmit DL allocation information or UL grant information on dedicated control channels such as PDCCH and EPDCCH to the UE in each subframe.

[0105] SPS in 3GPP is described in Non-Patent Document 9.

[0106] RRC dedicated signaling notifies the UE of settings such as the SPS interval, the C-RNTI (Cell Radio Network Temporary Identifier) for the SPS, and the number of empty transmissions before implicit release of the UL (hereinafter sometimes referred to as the "number of empty transmissions before release"). This enables SPS to be executed. A parameter called "implicitReleaseAfter" is used as the number of empty transmissions before release. In the following description, the number of empty transmissions before release may be represented by the symbol "n".

[0107] Also, the SPS is disabled by RRC dedicated signaling, which causes the corresponding DL allocation information or UL grant information to be discarded. The C-RNTI for the SPS may be referred to as the SPS C-RNTI.

[0108] The SPS is activated and deactivated by the PDCCH or EPDCCH, and the SPS C-RNTI is masked in the CRC of the PDCCH or EPDCCH.

[0109] In particular, for uplink SPS, a method of terminating SPS execution called implicit release is defined. When there is no uplink transmission data, the UE transmits a MAC Protocol Data Unit (PDU) including at least one of padding bits and padding BSR. This transmission is sometimes called a null transmission or padding transmission. If this transmission is performed consecutively a number of times set as the number of null transmissions before the aforementioned UL implicit release, the uplink grant information is immediately cleared.

[0110] As a result, the eNB also disables the uplink SPS setting when it receives the transmission from the UE a number of times consecutively set as the number of idle transmissions before the UL implicit release. By disabling the SPS setting, the eNB can use the radio resources allocated by the SPS setting for other UEs.

[0111] FIG. 8 is a diagram illustrating an example of the operation of the uplink SPS.

[0112] In Step ST801, the eNB notifies the UE of the SPS resource configuration and the SPS C-RNTI to be used when receiving the PDCCH, by RRC dedicated signaling.

[0113] The UE that has received the SPS resource configuration and the SPS C-RNTI in step ST801 detects the PDCCH using the SPS C-RNTI.

[0114] In Step ST802, the eNB notifies the UE of an instruction to start (activate) SPS execution. When the UE that has received the instruction to start SPS execution in Step ST802 detects the first scheduling, the UE activates the SPS. That is, the execution of the SPS starts. Then, the scheduling continues until the UE is deactivated, that is, until the execution of the SPS is terminated.

[0115] In Steps ST803 and ST804, SPS is performed between the eNB and the UE using the scheduled SPS resources. In Steps ST803 and ST804, the UE transmits uplink data to the eNB using the configured SPS resources.

[0116] In Step ST805, when there is no more transmission data in the configured SPS resource, the UE performs padding transmission.

[0117] In steps ST805 and ST806, if the UE has continuously transmitted padding the number of times set as the number of empty transmissions before release, the UE clears the SPS in step ST807. Here, the number of empty transmissions before release is set to two.

[0118] In steps ST805 and ST806, if the eNB has received padding transmission from the UE consecutively for the number of times set as the number of null transmissions before release, the eNB also releases the uplink SPS setting in step ST807.

[0119] As mentioned above, DC supports split bearers. 3GPP has proposed a method of transmitting a buffer status report (abbreviated as BSR) when an uplink split bearer is being used, using a double reporting and threshold (abbreviated as DRAT) method (see Non-Patent Document 7).

[0120] 9 and 10 are diagrams for explaining a transmission method using DRAT. Fig. 9 shows a case where the amount of upstream PDCP data is equal to or less than a predetermined threshold (Th). Fig. 10 shows a case where the amount of upstream PDCP data is greater than a predetermined threshold (Th).

[0121] 9 , a UE 905 includes a Medium Access Control (MAC) 907, a Radio Link Control (RLC) 908, a MAC 909, an RLC 910, and a Packet Data Convergence Protocol (PDCP) 911. The MAC 907 is used for the MeNB 901. The RLC 908 is used for the MeNB 901. The MAC 909 is used for the SeNB 902. The RLC 910 is used for the SeNB 902.

[0122] 10 , the UE 906 includes a MAC 912, an RLC 913, a MAC 914, an RLC 915, and a PDCP 916. The MAC 912 is used for the MeNB 903. The RLC 913 is used for the MeNB 903. The MAC 914 is used for the SeNB 904. The RLC 915 is used for the SeNB 904.

[0123] As shown in Fig. 9, when the amount of data in PDCP 911 is equal to or less than a predetermined threshold, the DRAT reports the buffer status (abbreviated as BS) to one eNB, that is, the MeNB 901 or the SeNB 902. Whether the BS is reported to the MeNB 901 or the SeNB 902 is set by RRC signaling. The one eNB set as the eNB that reports the BS is referred to as "1st-eNB." Fig. 9 shows a case where the BS is reported to the MeNB 901.

[0124] As shown in Fig. 10, if the amount of data in PDCP 916 is larger than a predetermined threshold, the BS reports the same amount of data in PDCP 916 to both eNBs, i.e., the 1st-eNB and the 2nd-eNB. In Fig. 10, the 1st-eNB is the MeNB 903, and the 2nd-eNB is the SeNB 904. The predetermined threshold is set for each radio bearer (RB).

[0125] FIG. 9 may be a case where the amount of upstream PDCP data is smaller than a predetermined threshold (Th), and FIG. 10 may be a case where the amount of upstream PDCP data is equal to or larger than a predetermined threshold (Th).

[0126] Furthermore, 3GPP proposes that the trigger for a buffer status report (BSR) and the eNB that transmits data should be aligned.

[0127] According to this, in the DRAT, if the amount of data to be transmitted is equal to or less than a threshold, the data is transmitted to one eNB (1st-eNB) that has been set, and if the amount of data to be transmitted is greater than the threshold, the data is transmitted to both eNBs (1st-eNB, 2nd-eNB).

[0128] Consider a case where an UL split bearer is configured and activated for the 2nd-eNB. When the amount of uplink data falls below a threshold, the UE will not transmit data to the 2nd-eNB due to the DRAT.

[0129] There are no regulations or discussions regarding the behavior when the amount of uplink data in the SPS resources configured for the 2nd-eNB falls below a threshold and data transmission to the 2nd-eNB is no longer performed.

[0130] Therefore, if the amount of uplink data is below a threshold, no data is transmitted to the 2nd-eNB, so there is a possibility that nothing will be transmitted using the configured SPS resource and no padding transmission will be performed.

[0131] If padding transmission is not performed, implicit release will not be performed normally, so the UE cannot determine whether to clear the SPS resources. Also, the eNB cannot determine whether to release the SPS resources. Therefore, unstable operation will occur between the eNB and the UE, which may eventually cause malfunction.

[0132] Fig. 11 is a diagram for explaining the problem that occurs when an SPS is set up when an UL split bearer is set up. The first-eNB is an MeNB, and the second-eNB is an SeNB. Fig. 11 shows a case where an SPS is set up in both the MeNB and the SeNB.

[0133] In step ST1001, the MeNB notifies the UE of activation of the uplink SPS by using the PDCCH with an uplink grant. The UE receives the PDCCH and activates the uplink SPS. That is, the UE starts executing the uplink SPS.

[0134] In Steps ST1002 to ST1007, the UE transmits uplink data to the MeNB using the uplink SPS resource configured for the MeNB.

[0135] In step ST1008, the SeNB notifies the UE of the activation of the uplink SPS by using the PDCCH in the uplink grant of the uplink SPS. The UE receives the PDCCH and activates the uplink SPS.

[0136] In step ST1009, the UE transmits uplink data to the SeNB using the uplink SPS resource configured for the SeNB. It is assumed that the amount of transmission data generated by the UE is equal to or greater than the threshold in the DRAT. Although not shown in the figure, the UE also transmits data to the MeNB.

[0137] Therefore, a part of the uplink data generated in the UE is transmitted to the MeNB, and the remaining uplink data is transmitted to the SeNB.

[0138] Consider a case where no uplink data is generated in the UE in the uplink SPS resource configured for the SeNB in step ST1010. In this case, the amount of uplink data is equal to or less than the threshold in the DRAT, so the UE determines not to transmit uplink data to the SeNB, and does not transmit padding.

[0139] In steps ST1010 and ST1011, if no uplink data is generated continuously by the UE in the uplink SPS resources configured for the SeNB, the amount of uplink data will be below the threshold in the DRAT, and the UE will determine not to transmit uplink data to the SeNB and will not transmit padding.

[0140] Even if no uplink transmission data occurs for the number of consecutive pre-release vacant transmissions (two in FIG. 11), padding transmission is not performed. Therefore, in step ST1012, the UE cannot determine whether or not to clear the SPS resources. Furthermore, the eNB cannot determine whether or not to release the SPS resources.

[0141] This may result in unstable operation between the eNB and the UE, which may in turn cause malfunctions.

[0142] For these reasons, it is necessary to provide a high-speed and stable communication system that enables SPS when DRAT is performed on an uplink split bearer.

[0143] In this embodiment, a method for solving such a problem is disclosed.

[0144] When SPS is configured, uplink data is transmitted to both the 1st-eNB and the 2nd-eNB.

[0145] As a method for doing this, for example, when SPS is set, no DRAT threshold is set. Alternatively, when SPS is set, the set DRAT threshold is invalidated. By doing this, when SPS is set, the threshold is eliminated or invalidated, and uplink data is transmitted to both the 1st-eNB and the 2nd-eNB.

[0146] A DRAT threshold for SPS may be set. By setting a DRAT threshold for SPS, the DRAT threshold for SPS can be set to a value different from the DRAT threshold for non-SPS, and the DRAT behavior for SPS can be made different from the DRAT behavior for non-SPS.

[0147] Another method for transmitting uplink data to both eNBs is to set a negative value as the DRAT threshold for SPS, which can be applied when the amount of uplink data is greater than the DRAT threshold and the data is transmitted to both eNBs.

[0148] Alternatively, the DRAT threshold for SPS is set to 0. This may be applied when the amount of uplink data is equal to or greater than the DRAT threshold and is transmitted to both eNBs.

[0149] By doing this, when SPS is set, uplink data will be transmitted to both the 1st-eNB and the 2nd-eNB.

[0150] By using these methods, when SPS is configured, uplink data is transmitted to both the 1st-eNB and the 2nd-eNB, so padding transmission is also possible. Therefore, implicit release is possible.

[0151] When SPS is configured, the transmission of uplink data to both the 1st-eNB and the 2nd-eNB may be statically determined in advance by a standard, or may be notified to the UE together with the SPS configuration. Alternatively, it may be notified to the UE together with the SPS activation.

[0152] For example, when SPS is set, it is possible to statically determine in advance by a standard or the like whether to set a DRAT threshold or to disable the set DRAT threshold or to set the DRAT threshold to a negative value or to set the DRAT threshold to 0. This allows a common understanding to be achieved between the eNB and the UE. Furthermore, since there is no need to signal this information, the signaling load can be reduced.

[0153] As another example, information for disabling the set DRAT threshold may be provided and the information may be notified to the UE together with the SPS setting. Alternatively, a negative value or 0 may be notified to the UE as the DRAT threshold together with the SPS setting.

[0154] These notifications may be sent to the UE separately from the SPS settings. By notifying the information to disable the set DRAT threshold together with the SPS settings, the signaling load can be reduced. In addition, since the timing can be synchronized with the SPS settings, the possibility of unstable operation and malfunctions can be reduced. It is recommended to use UE-specific RRC signaling for these notifications.

[0155] As another example, information to disable the set DRAT threshold may be provided and notified to the UE together with SPS activation, or a negative value or 0 may be notified to the UE together with SPS activation as the DRAT threshold.

[0156] These notifications may be sent to the UE separately from SPS activation. By notifying the UE of the information to disable the configured DRAT threshold together with SPS activation, the signaling load can be reduced. In addition, since the timing can be synchronized with SPS activation, the possibility of unstable operation or malfunction can be reduced. It is recommended to use L1 / L2 control signals for these notifications.

[0157] A method for canceling the state set as described above in which uplink data is transmitted to both the 1st-eNB and the 2nd-eNB will be disclosed.

[0158] As in the case above, if the SPS setting is cancelled, it is statically determined in advance by standards, etc., that the state will be cancelled, thereby achieving the same effect as in the case above.

[0159] Alternatively, information for validating the set DRAT threshold may be provided, and this information may be included in the signaling for disabling the SPS setting and notified to the UE. Alternatively, the DRAT threshold to be set again may be included in the signaling for disabling the SPS setting and notified to the UE. Alternatively, the signaling for disabling the SPS setting may cancel the state. This allows the DRAT threshold to return to the previous value, and the same effect as described above can be obtained.

[0160] Alternatively, information validating the set DRAT threshold may be provided, and the information may be included in the SPS deactivate and notified to the UE. Alternatively, the DRAT threshold to be reset may be included in the SPS deactivate and notified to the UE. Alternatively, the state may be canceled by SPS deactivation. This allows the DRAT threshold to be restored to the previous value, achieving the same effect as described above.

[0161] By using the method disclosed above, when SPS is configured, uplink data is transmitted to both the 1st-eNB and the 2nd-eNB, so padding transmission is also possible. Therefore, implicit release is possible.

[0162] This reduces the possibility of unstable operation between the eNB and the UE, which may result in malfunction.

[0163] 12 is a diagram illustrating a case where the DRAT threshold is set to 0 when SPS is configured. When the amount of uplink data is smaller than the DRAT threshold, it is transmitted to only the 1st-eNB, and when the amount of uplink data is equal to or greater than the DRAT threshold, it is transmitted to both the 1st-eNB and the 2nd-eNB. The 1st-eNB is the MeNB, and the 2nd-eNB is the SeNB. The figure illustrates a case where SPS is configured in both the MeNB and the SeNB.

[0164] Since FIG. 12 is similar to FIG. 11, differences will be mainly described.

[0165] The DRAT threshold 1103 is set to zero.

[0166] In step ST1008, the SeNB notifies the UE of activation by using the PDCCH with an uplink grant of uplink SPS. The notification of activation includes information for setting the DRAT threshold to 0. The UE receives the PDCCH, activates the uplink SPS, and sets the DRAT threshold to 0.

[0167] In step ST1009, the UE transmits uplink data to the SeNB using the uplink SPS resource configured for the SeNB. Since the DRAT threshold is set to 0, uplink transmission data generated in the UE can be transmitted to the SeNB. Although not shown in the figure, it is also possible to transmit data to the MeNB. Therefore, part of the uplink data generated in the UE is transmitted to the MeNB, and the remaining uplink data is transmitted to the SeNB.

[0168] In step ST1101, consider a case where no uplink data is generated in the UE in the uplink SPS resources configured for the SeNB. In this case, since the DRAT threshold is 0, even if no uplink data is generated, it is possible to transmit the data to the SeNB. Therefore, it is determined that padding transmission is also possible, and padding transmission is performed to the SeNB. In this way, padding transmission is possible even when there is no uplink transmission data between the SeNB and the UE.

[0169] In steps ST1101 and ST1102, if no uplink data is continuously generated in the UE in the uplink SPS resources configured for the SeNB, the amount of uplink data becomes equal to or greater than the DRAT threshold, and the UE is thus enabled to transmit uplink data to the SeNB. Therefore, the UE determines that padding transmission is possible and performs padding transmission.

[0170] If no uplink transmission data occurs consecutively for the number of times set as the number of empty transmissions before release and padding transmission is performed, in step ST1012, the UE clears the SPS resources, and the eNB also releases the SPS resources.

[0171] This allows the implicit release to be performed normally between the eNB and the UE.

[0172] In the method disclosed above, uplink data can be transmitted to both eNBs not only at the time when the SPS resources are allocated, but also throughout the period from when the SPS is set or activated to when it is released or deactivated.

[0173] Therefore, from the time when SPS is set or activated to the time when it is released or deactivated, even if the amount of uplink transmission data generated by the UE is small, the UE will always transmit uplink data to the 2nd-eNB, which will increase the UE's power consumption.

[0174] A method for solving such problems is disclosed.

[0175] Transmit uplink data to both the 1st-eNB and the 2nd-eNB only at the timing of SPS resource allocation. Transmit uplink data to both the 1st-eNB and the 2nd-eNB only at the timing of SPS resource allocation.

[0176] This can shorten the period for transmitting uplink data to the 2nd-eNB as well, thereby suppressing an increase in power consumption of the UE.

[0177] As described above, according to the present embodiment, when the SeNB is configured with the SPS, that is, configured to communicate with a communication terminal device using periodically allocated radio resources, if the amount of transmission data is equal to or less than the threshold Th, the threshold Th is changed so that the transmission data is transmitted to the MeNB and the SeNB. For example, as in the present embodiment, the threshold Th is set to zero (0).

[0178] This allows the SeNB to perform communication using SPS. Therefore, it is possible to provide a communication system that can stably perform communication operations between the MeNB and the SeNB and the UE. That is, since SPS is possible when DRAT is performed on an uplink split bearer, it is possible to provide a high-speed and stable communication system.

[0179] The threshold Th may be changed when the amount of transmission data is less than the threshold Th. Specifically, when the SeNB is configured with SPS, that is, configured to communicate with a communication terminal device using periodically allocated radio resources, the threshold Th may be changed so that the transmission data is transmitted to the MeNB and the SeNB when the amount of transmission data is less than the threshold Th. In this case, for example, as in the present embodiment, the threshold Th is set to zero (0).

[0180] This makes it possible to obtain the same effect as in the present embodiment. Specifically, communication by SPS can be performed in the SeNB as well. Therefore, it is possible to provide a communication system in which communication operations between the MeNB and the SeNB and the UE can be performed stably. That is, since SPS can be enabled when DRAT is performed on an uplink split bearer, it is possible to provide a high-speed and stable communication system.

[0181] Embodiment 2 When the method disclosed in the first embodiment is used, it is not possible to set a DRAT threshold value in practice, which results in an increase in the power consumption of the UE.

[0182] The DRAT threshold is used in the UE when distributing uplink transmission data from PDCP to RLC / MAC. Therefore, in order to transmit uplink data to both eNBs in accordance with the configured SPS resource allocation timing, detailed time management is required when distributing uplink transmission data in accordance with the SPS timing.

[0183] In such a case, there is a possibility that malfunctions may occur due to fluctuations in the timing of generation of upstream transmission data and fluctuations in PDCP processing time.

[0184] Therefore, in order to solve the problem described in the first embodiment, this embodiment discloses a method different from the method disclosed in the first embodiment.

[0185] Implicit release is also supported for the 2nd-eNB. When SPS is configured for the 2nd-eNB, the UE is able to transmit padding to the 2nd-eNB. When SPS is configured for the 2nd-eNB, the UE transmits padding to the 2nd-eNB even if the amount of uplink transmission data is smaller than the DRAT threshold in the configured SPS resources. This enables implicit release.

[0186] In the padding transmission, a MAC PDU including at least one of padding bits and padding BSR is transmitted as in the conventional method. By using the same padding transmission as in the conventional method, it is possible to simplify the control in the eNB and the UE.

[0187] In addition, the UE clears the SPS setting when it transmits padding to the 2nd-eNB a number of times consecutively set as the number of empty transmissions before release. The 2nd-eNB also releases the SPS resource when it receives padding transmission from the UE a number of times consecutively set as the number of empty transmissions before release.

[0188] Figure 13 is a diagram explaining a method for supporting implicit release when SPS is configured for a 2nd-eNB. The 1st-eNB is an MeNB, and the 2nd-eNB is an SeNB. This figure shows a case where SPS is configured for both the MeNB and the SeNB. Figure 13 is similar to Figures 11 and 12, so differences will mainly be described.

[0189] The DRAT threshold 1201 is set to an arbitrary value Th.

[0190] In Step ST1008, the SeNB notifies the UE of activation by using the PDCCH with an uplink grant of uplink SPS. Normal activation may be used.

[0191] Consider a case where no uplink data is generated in the UE in the uplink SPS resource configured for the SeNB in step ST1202. In this case, the amount of uplink data is smaller than the DRAT threshold. However, if SPS is configured for the SeNB, padding transmission to the SeNB is possible, so the UE transmits padding to the SeNB.

[0192] By doing so, padding transmission becomes possible even when there is no uplink transmission data between the SeNB and the UE.

[0193] In steps ST1202 and ST1203, if no uplink data is continuously generated in the UE in the uplink SPS resources configured for the SeNB, the amount of uplink data becomes equal to or greater than the DRAT threshold, and the UE is thus enabled to transmit uplink data to the SeNB. Therefore, the UE determines that padding transmission is possible and performs padding transmission.

[0194] If no uplink transmission data occurs consecutively for the number of times set as the number of empty transmissions before release and padding transmission is performed, in step ST1204, the UE clears the SPS resources, and the eNB also releases the SPS resources.

[0195] This allows the implicit release to be performed normally between the SeNB and the UE.

[0196] By using the method disclosed in this embodiment, it becomes possible to support implicit release when SPS is configured in the 2nd-eNB for a UL split bearer.

[0197] Implicit release allows the eNB and UE to make the decision to release SPS resources, thereby reducing the occurrence of unstable and malfunctioning operations.

[0198] Therefore, when SPS is configured in the 2nd-eNB for a UL split bearer, conventional SPS operation is possible.

[0199] Also, unlike the method of the first embodiment, the DRAT threshold for the 2nd-eNB can be set to any value. Therefore, even if a small amount of uplink transmission data occurs between the time SPS is set and the time it is disabled, if the amount of uplink data is smaller than the DRAT threshold, there is no need to transmit the uplink data to the 2nd-eNB. Therefore, it is possible to reduce the increase in power consumption of the UE.

[0200] Furthermore, since dynamic detailed control is no longer required in setting the DRAT threshold, it is possible to suppress the occurrence of malfunctions.

[0201] As described above, according to this embodiment, when an SeNB is configured with an SPS, i.e., configured to communicate with a communication terminal device using periodically allocated radio resources, if the amount of transmission data is equal to or less than a threshold Th, the SeNB is configured to transmit the transmission data to the MeNB and also to transmit an end signal indicating the end of communication using the periodically allocated radio resources to the SeNB, specifically to perform padding transmission.

[0202] As a result, the SeNB can terminate communication using SPS. Therefore, it is possible to provide a communication system in which communication operations between the MeNB and the SeNB and the UE can be performed stably. In other words, since SPS can be enabled when DRAT is performed on an uplink split bearer, it is possible to provide a high-speed and stable communication system.

[0203] The setting to perform the above-described padding transmission may be performed when the amount of transmission data is less than a threshold Th. Specifically, when the SeNB is configured with the SPS, that is, when the SeNB is configured to communicate with a communication terminal device using periodically allocated radio resources, when the amount of transmission data is less than a threshold Th, the SeNB may be configured to transmit the transmission data to the MeNB and to transmit an end signal indicating the end of communication using the periodically allocated radio resources to the SeNB, specifically to perform padding transmission.

[0204] This makes it possible to obtain the same effect as in the present embodiment. Specifically, the SeNB can terminate communication by SPS. Therefore, it is possible to provide a communication system in which communication operations between the MeNB and the SeNB and the UE can be performed stably. That is, since SPS can be enabled when DRAT is executed on an uplink split bearer, it is possible to provide a high-speed and stable communication system.

[0205] Second embodiment, variant 1 Another method for solving the problem described in the second embodiment is disclosed. Information indicating that there is no transmission data is provided, and the information is transmitted from the UE to the eNB using an uplink L1 / L2 control signal. For example, a PUCCH is used as the uplink L1 / L2 control signal. When there is no transmission data at the timing of the set SPS, the UE maps the information indicating that there is no transmission data onto the PUCCH and transmits it to the eNB. The eNB receives the PUCCH from the UE at the timing of the set SPS, and by obtaining the information indicating that there is no transmission data, recognizes that there is no uplink transmission data.

[0206] The UE clears the SPS resource when it transmits information indicating that there is no data to transmit for a number of consecutive times set as the number of empty transmissions before release. The eNB releases the SPS resource when it receives information indicating that there is no data to transmit from the UE for a number of consecutive times set as the number of empty transmissions before release.

[0207] By doing so, it becomes possible to support implicit release.

[0208] The PUCCH configuration, which maps information indicating that there is no data to transmit, is set by the eNB and notified to the UE in advance. The PUCCH configuration includes resources in the frequency axis direction, resources in the time axis direction, and a sequence used for the Reference Signal (RS) used for the PUCCH.

[0209] As the resource in the frequency axis direction, for example, subcarriers, resource blocks, etc. may be set. The minimum resource may also be set. The minimum resource may be the smallest unit for transmission. The smallest unit may be, for example, one physical resource block (abbreviated as PRB). As the resource in the time axis direction, the timing for transmitting the PUCCH may be set. The timing for transmitting the PUCCH may be set arbitrarily, or may be set to the timing at which the SPS resource is set. This makes it possible to simplify timing control in the UE and eNB.

[0210] The RS sequence used for the PUCCH may be for each cell or beam. By making the PUCCH frequency axis direction resources different for each UE, the eNB can receive PUCCHs even if multiple UEs transmit at the same SPS resource timing. Alternatively, the RS sequence used for the PUCCH may be UE-specific. The same PUCCH can be shared for multiple UEs using the frequency axis direction resources and the time axis direction resources. Even if multiple UEs have PUCCHs in the same resource, the eNB can receive the PUCCHs of each UE by using UE-specific RSs.

[0211] The eNB may include the PUCCH configuration in the SPS configuration and notify the UE of the PUCCH configuration. Alternatively, the eNB may include the PUCCH configuration in the SPS activation and notify the UE of the PUCCH configuration.

[0212] A conventional PUCCH configuration may be used as the PUCCH configuration for mapping information indicating that there is no transmission data. When there is no uplink transmission data at the configured SPS resource timing, the UE maps the information indicating that there is no transmission data to the PUCCH using the conventional PUCCH configuration. The UE transmits the PUCCH at the timing of the configured SPS resource. By using the conventional PUCCH configuration, the eNB does not need to configure a separate PUCCH for mapping information indicating that there is no transmission data.

[0213] Alternatively, information indicating that there is no transmission data may be mapped to the PUSCH. When there is no transmission data at the timing of the configured SPS, the UE maps the information indicating that there is no transmission data to the PUSCH and transmits it to the eNB.

[0214] The eNB receives the PUSCH from the UE at the timing of the set SPS and obtains information indicating that there is no transmission data, thereby recognizing that there is no uplink transmission data.

[0215] SPS resources have already been configured at the SPS timing. Resources for transmitting uplink data are configured as SPS resources. Since PUSCH is used for transmitting uplink data, PUSCH resources are configured.

[0216] The UE has already received an uplink grant for the PUSCH resource for the configured SPS from the eNB, so the UE can use the resource for PUSCH transmission for the configured SPS.

[0217] By using the PUSCH resources for SPS that are already set at the SPS timing, it is not necessary to separately set the PUCCH configuration, which improves resource usage efficiency and reduces signaling load.

[0218] The PUSCH resources for transmitting information indicating that there is no transmission data may be a part or all of the PUSCH resources for the SPS set at the SPS timing.

[0219] The RS sequence used for PUSCH may be the same as the method used for transmission in PUCCH described above.

[0220] As another method, an SRS (Sounding Reference Signal) may be used to indicate that there is no data to transmit. A specific SRS resource is set to indicate that there is no data to transmit. The minimum resource on the time axis may be one symbol. The eNB notifies the UE of the setting of the SRS resource. If there is no data to transmit at the timing of the set SPS, the UE transmits the SRS using the SRS resource. If the eNB receives the SRS from the UE using the SRS resource at the timing of the SPS, it can recognize that there is no data to transmit.

[0221] The RS sequence used for SRS may be the same as the method used for transmission in the PUCCH described above.

[0222] Alternatively, a sequence of RS indicating that there is no data to be transmitted may be provided, and this sequence may be used for the PUCCH, PUSCH, or SRS RS.Which of PUCCH, PUSCH, or SRS to use may be statically determined in advance, or may be notified to the UE from the eNB.In this case, the resources for this channel or signal may be individually configured for each UE.

[0223] If there is no data to transmit at the set SPS timing, the UE transmits a predetermined channel or signal using the RS sequence. If the eNB receives the predetermined channel or signal at the SPS timing, it can recognize that there is no data to transmit.

[0224] By using the method disclosed in this modification, it is possible to minimize the radio resources required for transmission. Therefore, since transmission can be performed using minimal resources, it is possible to further reduce the increase in power consumption of the UE.

[0225] Furthermore, the method disclosed in this modification may be used only when there is no transmission data at the timing of the SPS set in the 2nd-eNB. For other set SPSs, normal padding transmission may be used.

[0226] Embodiment 3 In a UL split bearer, uplink transmission data with a data amount smaller than the DRAT threshold may occur at the timing of the SPS set for the 2nd-eNB.

[0227] When the method disclosed in the second embodiment or the first modification of the second embodiment is applied, the following problems arise.

[0228] If the UE receives uplink transmission data with a data amount smaller than the DRAT threshold at the SPS timing set for the 2nd-eNB, no uplink transmission data will be generated for the 2nd-eNB despite the presence of the uplink transmission data. Therefore, the UE transmits padding to the 2nd-eNB. If such padding transmissions occur consecutively for the number of times set as the number of null transmissions before release, the SPS settings are invalidated in the UE and the 2nd-eNB by implicit release, and the SPS resources are released. In other words, even if there is uplink transmission data at the set SPS timing, the SPS resources may be released by implicit release.

[0229] After SPS resources are released by implicit release, if uplink transmission data exceeding the DRAT threshold occurs in the UE at the timing of the SPS set for the 2nd-eNB, the SPS set for the 2nd-eNB will no longer be applied.

[0230] Even if uplink transmission data occurs at the set SPS timing, the UE will no longer be able to transmit the uplink data using the SPS resource.

[0231] In this way, even though uplink transmission data occurs at the timing of the set SPS and the UE is transmitting the uplink data, the SPS resources for the 2nd-eNB are released, and the UE is no longer able to transmit uplink data to the 2nd-eNB using the set SPS resources.

[0232] 14 is a diagram illustrating a case where uplink transmission data with a data amount smaller than the DRAT threshold occurs, in which the method for supporting implicit release when SPS is configured for the 2nd-eNB, as disclosed in the second embodiment, is executed.

[0233] The 1st-eNB is an MeNB, and the 2nd-eNB is an SeNB. The example shows a case where SPS is configured in both the MeNB and the SeNB. Figure 14 is similar to Figure 13, so differences will be mainly described.

[0234] Consider a case where, in Step ST1202, uplink data with a data amount smaller than the DRAT threshold is generated in the UE in the uplink SPS resource configured for the SeNB.

[0235] In this case, in Step ST1301, the UE transmits uplink data to the MeNB.

[0236] Since no uplink transmission data occurs to the SeNB, in step ST1202, the UE transmits padding to the SeNB.

[0237] In steps ST1202 and ST1203, when uplink data with a data amount smaller than the DRAT threshold is continuously generated in the UE in the uplink SPS resource configured for the SeNB, the UE similarly transmits the uplink data to the MeNB in steps ST1301 and ST1302. The UE transmits padding to the SeNB.

[0238] If no uplink transmission data occurs for the number of consecutive times set as the number of empty transmissions before release to the SeNB and padding transmission is performed, in step ST1204, the UE clears the SPS resources by implicit release, and the eNB also releases the SPS resources.

[0239] However, consider a case where, after the implicit release, the UE generates uplink data with a data amount equal to or greater than the DRAT threshold in the uplink SPS resources configured for the SeNB in Step ST1303.

[0240] In this case, although not shown, the UE transmits uplink data to the MeNB.

[0241] Since uplink transmission data also occurs to the SeNB, the UE transmits the uplink data to the SeNB in step ST1303. However, since the SPS resource has already been released, the UE cannot use the SPS resource to transmit the uplink data.

[0242] In this case, the UE has to start by transmitting a new Scheduling Request (SR) signal because no resources for uplink transmission data to the SeNB have been allocated to the UE. The UE must transmit the SR signal to the SeNB and receive an UL grant from the SeNB.

[0243] This causes an increase in UE power consumption, a decrease in resource usage efficiency due to an increase in PDCCH resources, and an increase in delay in data transmission. This embodiment discloses a method for solving these problems.

[0244] If an uplink split bearer is configured, the uplink SPS configuration shall not be disabled. If an uplink split bearer is configured, the uplink SPS resources may not be released. If an uplink split bearer is configured, implicit release may not be performed.

[0245] When an uplink split bearer is configured, if an uplink SPS is configured in the 2nd-eNB, the UE does not clear the configured SPS resources even if it transmits padding transmissions consecutively the number of times set as the number of empty transmissions before release. The 2nd-eNB does not release the configured SPS resources even if it receives padding transmissions consecutively the number of times set as the number of empty transmissions before release.

[0246] As specific examples of methods for preventing the uplink SPS setting from being disabled, the following two methods (1) and (2) are disclosed.

[0247] (1) Determine statically in advance using standards, etc.

[0248] (2) Information indicating that the uplink SPS setting is not disabled is provided and notified to the UE from the eNB.

[0249] In the method (1) described above, it is statically determined that the uplink SPS setting will not be disabled when an uplink split bearer is set. By determining this in advance in a standard, it becomes possible for the eNB and UE to recognize this, which enables consistent operation and reduces malfunctions.

[0250] In the method (2) described above, by notifying the UE from the eNB of information indicating that the uplink SPS setting will not be disabled, it is possible to dynamically set the uplink SPS setting not to be disabled when an uplink split bearer is set, which enables flexible operation according to the communication status and load status.

[0251] The number of empty transmissions before release of UL may be used as information indicating that the uplink SPS setting is not invalidated in the method (2) above. A value indicating that the SPS setting is not invalidated may be set as the number of empty transmissions before release. Alternatively, a value indicating infinity may be set as the number of empty transmissions before release. A new value may be set separately from the existing value.

[0252] The information indicating that the uplink SPS setting in the above method (2) is not to be disabled may be notified from the eNB to the UE. The eNB that notifies may be the 1st-eNB or the 2nd-eNB. For example, when notifying the UE from the 2nd-eNB, the 2nd-eNB may notify the UE directly, or the 2nd-eNB may notify the UE via the 1st-eNB. X2 signaling may be used to notify the information between eNBs. Alternatively, S1 signaling may be used via the MME.

[0253] The following three (1) to (3) are disclosed as specific examples of signaling methods for notifying the UE of the information from the eNB.

[0254] (1) RRC signaling. For example, the signaling may be included in the signaling for setting the SPS configuration.

[0255] (2) MAC signaling For example, a MAC CE (Control Element) containing the information may be provided, and the information may be notified by MAC signaling.

[0256] (3) L1 / L2 signaling, such as PDCCH or EPDCCH, which may be included in SPS activation and notified.

[0257] In this manner, the eNB notifies the UE of information indicating that the uplink SPS configuration will not be disabled. The UE that receives this information does not disable the uplink SPS configuration. When an uplink split bearer is configured and an uplink SPS is configured in the 2nd-eNB, the UE does not perform implicit release and does not clear the configured SPS resources, even if padding transmission is performed consecutively the number of times set as the number of empty transmissions before release.

[0258] 15 is a diagram illustrating a method for preventing the uplink SPS setting from being invalidated. The method illustrates a method for notifying the SPS activation by including information indicating that the uplink SPS setting is not invalidated.

[0259] The 1st-eNB is an MeNB, and the 2nd-eNB is an SeNB. The example shows a case where SPS is configured in both the MeNB and the SeNB. Figure 15 is similar to Figure 14, so differences will be mainly described.

[0260] In Step ST1008, the SeNB notifies the UE of activation by using an uplink grant of uplink SPS over the PDCCH, and includes information indicating that the setting of uplink SPS will not be disabled in the activation.

[0261] When a UE receives SPS activation from the SeNB, it executes SPS using the configured resources and does not disable the uplink SPS setting. Even if the UE transmits padding to the SeNB a predetermined number of times, both the eNB and the UE do not perform implicit release and do not disable the SPS setting.

[0262] Consider a case where, in Step ST1202, uplink data with a data amount smaller than the DRAT threshold is generated in the UE at the SPS timing set for the SeNB.

[0263] In this case, in Step ST1301, the UE transmits uplink data to the MeNB.

[0264] Since no uplink transmission data occurs to the SeNB, in step ST1202, the UE transmits padding to the SeNB.

[0265] In steps ST1202 and ST1203, if the UE does not continuously generate uplink data with an amount of data smaller than the DRAT threshold at the timing of the SPS set for the SeNB, the UE similarly transmits uplink data to the MeNB in steps ST1301 and ST1302. The UE transmits padding to the SeNB.

[0266] Even if no uplink transmission data is generated for the number of consecutive times set as the number of empty transmissions before release for the SeNB and padding transmission is performed, the UE does not clear the SPS resources in Step ST1204 in accordance with the setting that does not invalidate the uplink SPS setting.The eNB also does not release the SPS resources.In Step ST1204, implicit release is not performed and the SPS resources are not released.

[0267] Therefore, after padding transmissions have been performed consecutively to the SeNB the number of times set as the number of pre-release empty transmissions, if uplink data with a data volume greater than or equal to the DRAT threshold is generated in the UE at the timing of the SPS set to the SeNB in step ST1204, the UE will be able to transmit uplink data to the SeNB using the set SPS resources in step ST1401.

[0268] By using the method disclosed in this embodiment, it is possible to prevent the SPS resource for the 2nd-eNB from being released even though uplink transmission data occurs at the timing of the set SPS and the UE is transmitting the uplink data. Therefore, it is possible to prevent a situation in which, when uplink data occurs in the set SPS resource, the 2nd-eNB cannot transmit the data and the UE is forced to start transmitting an SR signal.

[0269] This makes it possible to suppress an increase in UE power consumption, a decrease in resource usage efficiency due to an increase in PDCCH resources, and an increase in delay in data transmission.

[0270] As described above, in this embodiment, when the UE receives information indicating that the uplink SPS setting is not disabled, the UE stops the release of SPS resources, which are radio resources allocated by the SPS. The information indicating that the uplink SPS setting is not disabled corresponds to release stop information indicating that the release of SPS resources is stopped. In other words, when the UE receives the release stop information, the UE stops the release of SPS resources.

[0271] This prevents the SeNB from being unable to transmit uplink data when it is generated using the configured SPS resources, and eliminates the need to start with transmitting an SR signal. This makes it possible to suppress an increase in UE power consumption, a decrease in resource usage efficiency due to an increase in PDCCH resources, and an increase in data transmission delays.

[0272] Embodiment 4 In the method disclosed in embodiment 3, even if there is no actual data to be transmitted at the set SPS timing, implicit release is not performed and the SPS resources are not released.

[0273] If the SPS resources are not released, the 2nd-eNB will continue to allocate the SPS resources to the UE at the SPS timing.

[0274] In this way, continuing to allocate PUSCH resources to UEs that have run out of transmission data is wasteful and reduces resource usage efficiency. This embodiment discloses a method for solving this problem.

[0275] A timer is set for the period during which the SPS setting is not disabled. The eNB sets the period during which the SPS setting is not disabled and notifies the UE.

[0276] For example, when a setting is made not to disable the uplink SPS setting, the above-mentioned timer is used to start the implicit release function. The eNB notifies the UE of the period during which the SPS setting is not disabled, along with information indicating that the uplink SPS setting is not disabled. When the setting is made not to disable the uplink SPS setting, the UE starts the timer, and when the period during which the SPS setting is not disabled has elapsed, the UE starts implicit release and stops the timer. In this way, when padding transmission is performed consecutively the number of times set as the number of null transmissions before release, implicit release is performed, and the uplink SPS resources are released.

[0277] The period during which the SPS setting is not invalidated may be time, the number of radio frames, the number of subframes, the number of slots, or the number of symbols. The period during which the SPS setting is not invalidated may be a positive integer multiple of the set SPS timing interval. The period during which the SPS setting is not invalidated may be statically determined in advance by a standard or the like.

[0278] Alternatively, implicit release may be initiated when a predetermined number of padding transmissions are performed in succession. The predetermined number of consecutive padding transmissions disclosed in this embodiment may be different from the conventional number of empty transmissions before release.

[0279] Specifically, if the parameter representing the predetermined number of consecutive padding transmissions is set to "implicitReleaseAfter_B" and the parameter representing the number of conventional pre-release empty transmissions is set to "implicitReleaseAfter", then it is recommended that implicitReleaseAfter_B > implicitReleaseAfter.

[0280] Alternatively, implicitReleaseAfter_B=n (n is a positive integer)×implicitReleaseAfter may be used.

[0281] By doing this, it becomes possible to start implicit release depending on the period when there is no uplink transmission data. It becomes possible to set the period when the uplink SPS setting is invalid depending on the occurrence status of uplink transmission data.

[0282] By using the method disclosed in this embodiment, it is possible to eliminate a situation where the setting for uplink SPS is not disabled and implicit release is not always performed.

[0283] Therefore, it is not necessary to reserve SPS resources for a long period of time, and it is possible to reduce waste of PUSCH resources, thereby improving resource usage efficiency.

[0284] Fourth embodiment, variant 1 Another method for solving the problem described in the fourth embodiment will be disclosed. Information indicating the start of implicit release is provided and notified from the eNB to the UE. For example, in a state where it is set that the uplink SPS configuration will not be disabled, information indicating the start of implicit release is notified from the eNB to the UE. By notifying the information, both the eNB and the UE resume implicit release. In this way, when padding transmission occurs consecutively from the UE to the eNB for the number of times set as the number of null transmissions before release, implicit release is executed and the uplink SPS configuration is disabled.

[0285] By notifying the UE of the information indicating the start of implicit release from the eNB, it becomes possible to start implicit release at any timing, which enables flexible operation according to the communication status and load situation.

[0286] The number of empty transmissions before release of the UL mentioned above may be used as information indicating the start of implicit release. An existing value may be set as the number of empty transmissions before release. When the number of empty transmissions before release is set, implicit release starts.

[0287] The information indicating the start of implicit release may be notified from the eNB to the UE. The notifying eNB may be the 1st-eNB or the 2nd-eNB. For example, when notifying the UE from the 2nd-eNB, the 2nd-eNB may notify the UE directly, or the 2nd-eNB may notify the UE via the 1st-eNB. X2 signaling may be used to notify the information between eNBs. Alternatively, S1 signaling may be used via the MME.

[0288] The following three (1) to (3) are disclosed as specific examples of signaling methods for notifying the UE of information indicating the start of implicit release from the eNB.

[0289] (1) RRC signaling.

[0290] (2) MAC signaling For example, a MAC CE may be provided that includes information indicating that implicit release is to be started, and this information may be notified by MAC signaling.

[0291] (3) L1 / L2 signaling, which may be notified via, for example, the PDCCH or the EPDCCH.

[0292] By using the method disclosed in this modification, it is possible to obtain the same effects as the method disclosed in the fourth embodiment.

[0293] Furthermore, since implicit release can be started at any timing, SPS resources can be flexibly configured, which further improves the efficiency of PUSCH resource usage.

[0294] As described above, in this modification, when the UE receives information indicating the start of implicit release, it resumes the release of SPS resources. The information indicating the start of implicit release corresponds to release resume information indicating the resumption of SPS release. In other words, when the UE receives the release resume information, it resumes the release of SPS resources.

[0295] This makes it possible to obtain the same effect as in the fourth embodiment. Specifically, it is possible to eliminate a state in which implicit release is not performed while the uplink SPS setting is set not to be disabled. This eliminates the need to reserve SPS resources for a long period of time, thereby reducing waste of PUSCH resources. Therefore, it is possible to improve resource usage efficiency.

[0296] Fourth embodiment, variant 2 Another method for solving the problem described in the fourth embodiment will be disclosed. Information indicating that the uplink SPS setting is to be disabled is provided and notified from the eNB to the UE. For example, when it is set that the uplink SPS setting is not to be disabled, information indicating that the uplink SPS setting is to be disabled is notified from the eNB to the UE. The eNB determines whether to disable the uplink SPS setting. If the eNB decides to disable the uplink SPS setting, the eNB notifies the UE of information indicating that the uplink SPS setting is to be disabled, and the uplink SPS setting is disabled. The UE disables the uplink SPS setting by receiving the information indicating that the uplink SPS setting is to be disabled from the eNB. At this time, the uplink SPS setting is disabled without performing implicit release.

[0297] By notifying the UE of the information indicating that the uplink SPS setting is to be disabled from the eNB, it becomes possible to disable the uplink SPS setting at any time, which enables flexible operation according to the communication status and load status.

[0298] The aforementioned number of UL empty transmissions before release may be used as information indicating that the uplink SPS setting is disabled. An existing value may be set as the number of empty transmissions before release. When the number of empty transmissions before release is set, it may be set to indicate that the uplink SPS setting is disabled.

[0299] Information indicating that the uplink SPS setting is to be disabled may be notified from the eNB to the UE. The eNB that notifies may be the 1st-eNB or the 2nd-eNB. For example, when notifying the UE from the 2nd-eNB, the 2nd-eNB may notify the UE directly, or the 2nd-eNB may notify the UE via the 1st-eNB. X2 signaling may be used to notify information between eNBs. Alternatively, S1 signaling may be used via the MME.

[0300] The following three (1) to (3) are disclosed as specific examples of a signaling method for notifying the UE of information indicating that the uplink SPS setting is disabled from the eNB.

[0301] (1) RRC signaling.

[0302] (2) MAC signaling For example, a MAC CE including information indicating that the uplink SPS setting is disabled may be provided and notified by MAC signaling.

[0303] (3) L1 / L2 signaling, which may be notified via, for example, the PDCCH or the EPDCCH.

[0304] Figure 16 is a diagram explaining a method using information indicating that uplink SPS configuration is disabled. The 1st-eNB is an MeNB, and the 2nd-eNB is an SeNB. This shows a case where SPS is configured in both the MeNB and the SeNB. Figure 16 is similar to Figure 15, so differences will mainly be described.

[0305] In Step ST1008, the SeNB notifies the UE of activation by using an uplink grant of uplink SPS over the PDCCH, and includes information indicating that the setting of uplink SPS will not be disabled in the activation.

[0306] In steps ST1202 and ST1203, even if no uplink transmission data is generated for the number of consecutive times set as the number of empty transmissions before release to the SeNB and padding transmission is performed, the UE does not clear the SPS resources in accordance with the setting that does not invalidate the uplink SPS setting. The eNB also does not release the SPS resources. Implicit release is not performed, and the SPS resources are not released.

[0307] In Step ST1501, the SeNB sets information indicating that the uplink SPS setting is disabled and notifies the UE of this. The eNB disables the uplink SPS setting upon receiving the information indicating that the uplink SPS setting is disabled, and the UE disables the uplink SPS setting upon receiving the information indicating that the uplink SPS setting is disabled.

[0308] Since the uplink SPS configuration is disabled, the configured SPS resources are released at the subsequent SPS timing in step ST1204, which allows the eNB to allocate the SPS resources to another UE.

[0309] The following six methods (1) to (6) are disclosed as specific examples of methods by which an eNB determines whether to disable the uplink SPS setting.

[0310] (1) The period since the SPS was established.

[0311] (2) The period from when you set SPS settings not to be disabled.

[0312] (3) The number of consecutive padding transmissions received.

[0313] (4) Load at the local eNB.

[0314] (5) Communication quality with UE.

[0315] (6) Uplink transmission data generation status for 1st-eNB.

[0316] In the above-described method (1), when a predetermined period has elapsed since the uplink SPS was set, it is determined that the uplink SPS setting is invalid. The predetermined period may be a time, a number of radio frames, a number of subframes, a number of slots, or a number of symbols. The predetermined period may be a positive integer multiple of the timing interval of the set SPS.

[0317] In the above-mentioned method (2), when a predetermined period of time has elapsed since it was set that the uplink SPS setting will not be disabled, it is determined that the uplink SPS setting will be disabled.

[0318] In the above-mentioned method (3), when padding transmission is received a predetermined number of times in succession, it is determined that the uplink SPS setting is invalid. The predetermined number of times that padding transmission is received may be the above-mentioned number of empty transmissions before release. Alternatively, it may be a value greater than the number of empty transmissions before release.

[0319] In the method (4) described above, the load amount of the eNB itself is used for the judgment. If the load is equal to or greater than a predetermined value, it is determined to disable the SPS setting. If the load is lower than the predetermined value, it is determined not to disable the SPS setting. If the load is higher than the predetermined value, the resources allocated for SPS are released and made available for allocation to other UEs, thereby reducing resource shortages that occur when the load is high.

[0320] In the method (5) described above, the judgment is made using the communication quality with the UE. If the communication quality is lower than a predetermined value, it is decided to disable the SPS setting. If the communication quality is equal to or higher than a predetermined value, it is decided not to disable the SPS setting. The cause of low communication quality may be poor communication quality of already configured SPS resources. In such cases, communication quality can be improved by reallocating SPS resources. Therefore, it is advisable to disable the SPS setting when communication quality is low and enable SPS to be configured again as necessary. This can improve communication quality. Furthermore, resources with poor communication quality can be released early, thereby improving resource usage efficiency.

[0321] In the above-mentioned method (6), the 2nd-eNB recognizes the occurrence status of uplink transmission data to the 1st-eNB and determines whether to disable the uplink SPS setting.

[0322] The following two methods (6-1) and (6-2) are disclosed as specific examples of a method by which the 2nd-eNB recognizes the occurrence status of uplink transmission data to the 1st-eNB.

[0323] (6-1) The 2nd-eNB acquires information about the generation of uplink transmission data from the 1st-eNB.

[0324] The 1st-eNB may notify the 2nd-eNB whether or not uplink transmission data to the eNB (1st-eNB) has occurred at the timing of the SPS set for the 2nd-eNB.

[0325] The 2nd-eNB may notify the 1st-eNB in advance of the SPS timing set for itself. This allows the 1st-eNB to recognize whether or not it has received uplink transmission data from the UE at the SPS timing set for the 2nd-eNB. If the 1st-eNB receives uplink transmission data from the UE at the SPS timing set for the 2nd-eNB, it determines that uplink transmission data has occurred. If the 1st-eNB does not receive uplink transmission data from the UE, it determines that no uplink transmission data has occurred.

[0326] The first-eNB notifies the second-eNB whether or not there is uplink transmission data for the first-eNB. The first-eNB may notify the second-eNB only if there is no uplink transmission data for the first-eNB, or only if there is uplink transmission data for the first-eNB.

[0327] The 2nd-eNB can determine whether or not there is uplink transmission data for the 1st-eNB by receiving information on whether or not there is uplink transmission data for the local eNB. The 2nd-eNB uses the information on whether or not there is uplink transmission data for the local eNB to determine whether or not to disable the uplink SPS setting.

[0328] For example, when information indicating that there is no uplink transmission data for the 1st-eNB is received a predetermined number of times in succession, it may be determined that the uplink SPS setting is disabled.

[0329] The 2nd-eNB may notify the 1st-eNB of which bearers the 2nd-eNB has set up SPS for.

[0330] The 1st-eNB may determine whether uplink transmission data has occurred on the bearer.

[0331] This is effective because when an SPS is set for a specific bearer, the bearer can be identified.

[0332] The 1st-eNB may notify the 2nd-eNB of the number of consecutive times that no uplink transmission data has occurred.

[0333] Alternatively, the 2nd-eNB may notify the 1st-eNB of the number of consecutive failures in advance. The 1st-eNB counts the number of times that it has failed to receive uplink transmission data at the SPS timing set in the 2nd-eNB, and notifies the 2nd-eNB of that fact when the number of consecutive failures reaches the specified number.

[0334] A new message requesting the invalidation of the SPS setting may be established between eNBs. For example, the first-eNB counts the number of times that uplink transmission data cannot be received at the timing of the SPS set in the second-eNB, and when the number of consecutive times reaches the specified number, the first-eNB notifies the second-eNB of a message requesting the invalidation of the SPS setting.

[0335] The 2nd-eNB that receives the message requesting disabling of the SPS setting may decide to disable the uplink SPS setting.

[0336] The above information may be transmitted between eNBs using X2 signaling or S1 signaling. The information may be transmitted via X2 signaling or S1 signaling via MME.

[0337] (6-2) The 2nd-eNB measures and detects the uplink power at the 1st-eNB at the timing of the SPS.

[0338] The 1st-eNB may notify the 2nd-eNB of its uplink carrier frequency and bandwidth in advance. If the 1st-eNB also configures SPS at the timing of the SPS configured for the 2nd-eNB, the 1st-eNB may notify the 2nd-eNB of the SPS resource.

[0339] The 2nd-eNB measures the uplink power at the configured SPS timing using the carrier frequency and bandwidth of the 1st-eNB. If the 1st-eNB configures SPS as described above, the 2nd-eNB may measure the uplink power in the SPS resource.

[0340] To measure uplink power, it is advisable to measure the received signal strength indicator (RSSI), IoT (Interference over Thermal noise), etc.

[0341] If the measured uplink power is higher than a predetermined threshold, it is determined that data has been transmitted by the 1st-eNB. If the measured uplink power is lower than the predetermined threshold, it is determined that data has not been transmitted by the 1st-eNB.

[0342] If the 1st-eNB determines that no data has been transmitted, the 2nd-eNB may decide to disable the uplink SPS setting.

[0343] The method disclosed in this variant in which an eNB determines whether to disable the uplink SPS setting can also be applied to the method disclosed in variant 1 of embodiment 4 in which an eNB determines whether to start an implicit release.

[0344] By using the method disclosed in this modification, it is possible to obtain the same effects as the method disclosed in the first modification of the fourth embodiment.

[0345] Furthermore, it is possible to immediately disable the SPS setting and release the SPS resource without performing implicit release, thereby further improving the utilization efficiency of the PUSCH resource.

[0346] Embodiment 5. Another method for solving the problem described in embodiment 4 will be disclosed. Padding transmission when there is no uplink transmission data at the timing of the set SPS is differentiated from padding transmission when there is uplink transmission data at the timing of the set SPS.

[0347] If there is no uplink transmission data, the UE performs padding transmission for when there is no uplink transmission data. If there is uplink transmission data, the UE performs padding transmission for when there is uplink transmission data. By receiving different padding transmissions, the eNB determines whether there is uplink transmission data from the UE at the configured SPS timing. If the eNB receives padding transmission for when there is no uplink transmission data, it determines that there is no uplink transmission data and performs implicit release. If the eNB receives padding transmission for when there is uplink transmission data, it determines that there is uplink transmission data and does not count it as padding transmission for when there is no uplink transmission data. Alternatively, it may not perform uplink implicit release.

[0348] 17 and 18 are diagrams explaining a method of differentiating padding transmission when there is no uplink transmission data from padding transmission when there is uplink transmission data. The 1st-eNB is an MeNB, and the 2nd-eNB is an SeNB. The figures show a case where the amount of uplink transmission data is equal to or less than the DRAT threshold (Th). The figures show a case where SPS is set in the SeNB.

[0349] Fig. 17 shows a case where there is no uplink transmission data at the timing of the SPS set for the SeNB. Fig. 18 shows a case where there is uplink transmission data at the timing of the SPSSPS set for the SeNB. Padding transmission when there is no uplink transmission data is referred to as "padding (A) transmission." Padding transmission when there is uplink transmission data is referred to as "padding (B) transmission."

[0350] 17 and 18 are similar to FIG. 9, so differences will be mainly described.

[0351] 17, when there is no uplink transmission data at the timing of the SPS set for the SeNB 902, the UE 905 transmits padding (A) to the SeNB 902, as shown by arrow "1601." Since there is no uplink transmission data, no uplink data is transmitted from the UE 905 to the MeNB 901.

[0352] 18, when there is uplink transmission data at the timing of the SPS set for the SeNB 902, the UE 905 transmits padding (B) to the SeNB 902 as indicated by arrow "1602." Since there is uplink transmission data, the UE 905 transmits the uplink data to the MeNB 901 as indicated by arrow "1603."

[0353] 19 and 20 are diagrams explaining a method for differentiating padding transmission when there is no uplink transmission data from padding transmission when there is uplink transmission data. Padding transmission when there is no uplink transmission data is called "padding (A) transmission." Padding transmission when there is uplink transmission data is called "padding (B) transmission."

[0354] The 1st-eNB is the MeNB, and the 2nd-eNB is the SeNB. The diagram shows a case where SPS is configured in both the MeNB and the SeNB. Figure 19 is similar to Figure 13, and Figure 20 is similar to Figure 15, so differences will mainly be described.

[0355] FIG. 19 shows padding (A) transmission when there is no uplink transmission data.

[0356] In Step ST1008, the SeNB notifies the UE of activation by using the PDCCH with an uplink grant of the uplink SPS.

[0357] Upon receiving SPS activation from the SeNB, the UE executes SPS using the configured resources.

[0358] Consider a case where no uplink data is generated in the UE at the timing of the SPS set for the SeNB in Step ST1701.

[0359] In this case, in Step ST1701, the UE transmits padding (A) to the SeNB when there is no uplink transmission data.

[0360] In Steps ST1701 and ST1702, if no uplink data is generated consecutively in the UE at the timing of the SPS set for the SeNB, the UE similarly transmits padding (A) to the SeNB.

[0361] When no uplink transmission data occurs for the number of times set as the number of empty transmissions before release for the SeNB and padding (A) transmission is performed, implicit release is performed.

[0362] In Step ST1204, the eNB releases the configured SPS resources through implicit release. In Step ST1204, the UE clears the configured SPS resources.

[0363] FIG. 20 shows padding (B) transmission when there is upstream transmission data.

[0364] In Step ST1008, the SeNB notifies the UE of activation by using the PDCCH with an uplink grant of the uplink SPS.

[0365] Upon receiving SPS activation from the SeNB, the UE executes SPS using the configured resources.

[0366] In step ST1801, consider a case where uplink data is generated in the UE at the timing of the SPS set for the SeNB. Here, it is assumed that the amount of the generated uplink data is smaller than the DRAT threshold. In this case, the uplink data is transmitted to the MeNB, but not to the SeNB. The method disclosed in the third embodiment is applied, and padding transmission is performed to the SeNB.

[0367] However, in the method disclosed in this embodiment, in Step ST1801, the UE transmits padding (B) to the SeNB when there is uplink transmission data.

[0368] In steps ST1801 to ST1802, if uplink data is generated continuously in the UE at the timing of the SPS set for the SeNB, but the amount of data is smaller than the DRAT threshold and the uplink data is not transmitted to the SeNB, the UE similarly transmits padding (B) to the SeNB.

[0369] Even if padding (B) transmission is performed consecutively to the SeNB the number of times set as the number of empty transmissions before release, implicit release is not performed.

[0370] Therefore, in Step ST1204, the eNB does not release the configured SPS resources, and in Step ST1204, the UE does not clear the configured SPS resources.

[0371] Therefore, after padding (B) transmission has been performed consecutively the number of times set as the number of pre-release empty transmissions to the SeNB, if uplink data with a data volume greater than or equal to the DRAT threshold is generated in the UE at the timing of the SPS set to the SeNB in step ST1204, in step ST1401 the UE will be able to transmit uplink data to the SeNB using the SPS resources set.

[0372] This prevents implicit release from being performed even when there is uplink transmission data. When uplink transmission data equal to or greater than the DRAT threshold is generated in the UE, the SPS resource configured by the SeNB can be used to transmit the uplink data.

[0373] As mentioned above, by differentiating the padding transmission when there is no uplink transmission data from the padding transmission when there is uplink transmission data, the eNB can determine whether there is uplink transmission data from the UE at the timing of the set SPS.

[0374] When the eNB receives a padding transmission when there is no uplink transmission data, it can determine that there is no uplink transmission data. Since there is no uplink transmission data from the UE, the eNB can count it as a padding transmission when performing implicit release.

[0375] When the eNB receives padding transmission for when uplink transmission data is present, it can determine that uplink transmission data is present. Since there is uplink transmission data from the UE, the eNB does not count it as padding transmission when performing implicit release.

[0376] By counting only padding transmissions when there is no uplink transmission data from the UE, it becomes possible to perform implicit release when padding transmissions when there is actually no uplink transmission data from the UE are performed consecutively the number of times set as the number of empty transmissions before release.

[0377] A method for differentiating padding transmission when there is no uplink transmission data from padding transmission when there is uplink transmission data is disclosed.

[0378] Regarding padding transmission when there is no uplink transmission data, it is preferable to use the conventional padding transmission shown in the first embodiment, that is, to transmit a MAC PDU including at least one of padding bits and padding BSR.

[0379] To make padding transmission when there is uplink transmission data different from conventional padding transmission.

[0380] In padding transmission when uplink transmission data exists, it is preferable to perform MAC layer processing differently from the conventional method. The following three methods (1) to (3) are disclosed as specific examples of MAC PDU configuration methods different from the conventional MAC PDU for padding transmission.

[0381] (1) Establish a new MAC CE (Control Element).

[0382] (2) Set the padding bits to a specific value.

[0383] (3) Set a specific value in the header.

[0384] As the method (1) above, it is preferable to provide a MAC CE indicating that padding transmission is performed when uplink transmission data exists.

[0385] For example, a MAC CE indicating whether or not there is transmission is provided. In addition to at least one of the conventional padding bits and the padding BSR, a MAC CE indicating whether or not there is transmission may be included. A MAC CE indicating that there is transmission may also be used.

[0386] Alternatively, a MAC CE may be provided that indicates the type of padding transmission, such as whether padding transmission is performed when there is no uplink transmission data or when there is uplink transmission data.

[0387] Alternatively, a MAC CE indicating whether or not implicit release is to be performed may be provided. Padding transmission including this MAC CE indicates whether or not implicit release is to be performed.

[0388] This makes it possible to differentiate from conventional padding transmission.

[0389] As a method of (2) above, it is advisable to set a specific value to the padding bits to indicate that they are padding bits when uplink transmission data is present. Conventionally, whether or not a padding bit is a padding bit was determined by the header, so the padding bit could be anything. Here, a new specific value is set to indicate that it is padding when uplink transmission data is present. By demodulating the padding bits, the eNB can determine whether or not it is padding transmission when uplink transmission data is present.

[0390] As a method of (3) above, it is advisable to set a value in the header that indicates whether or not there is upstream transmission data. For example, a specific value indicating the presence or absence of upstream transmission data can be added to the header of the padding bits. This makes it possible to recognize that if the header indicates the presence of transmission data, it is a padding transmission when upstream transmission data is present.

[0391] Alternatively, the specific value may be added to the header of the padding BSR, which can achieve the same effect.

[0392] Alternatively, the specific value may be added to the MAC CE header, which indicates that the padding transmission is performed when uplink transmission data is present. This makes it possible to determine whether uplink transmission data is present or not using both the MAC CE and the header. This makes it possible to reduce malfunctions.

[0393] In this way, by making the MAC layer processing different from the conventional processing for padding transmission when there is uplink transmission data, it is possible to make it different from conventional padding transmission.

[0394] As another method, when there is uplink transmission data, the PHY layer processing may be made different from the conventional method for padding transmission.

[0395] For example, the reference signal used for the PUSCH that performs padding transmission when uplink transmission data is present is made different from the reference signal used for the conventional PUSCH that performs padding transmission when uplink transmission data is absent.

[0396] Alternatively, at least one of the resources on the frequency axis and the resources on the time axis onto which the PUSCH for padding transmission when uplink transmission data is present may be mapped may be made different from at least one of the resources on the frequency axis and the resources on the time axis onto which the PUSCH for padding transmission when conventional uplink transmission data is not present is mapped.

[0397] At least one of the resources on the frequency axis and the resources on the time axis may be different within at least one of the resources on the frequency axis and the resources on the time axis allocated as SPS resources. That is, the resource onto which the PUSCH for padding transmission when there is uplink transmission data is mapped and the resource onto which the PUSCH for padding transmission when there is no uplink transmission data are mapped are both present within the resources allocated as SPS resources. This eliminates the need to use resources outside the configured SPS resources, thereby suppressing an increase in the required resources.

[0398] The method of varying the SPS resource may be to vary the resource on the time axis. For example, the resource may be varied by slot. It may also be varied by symbol. Alternatively, the resource may be varied by frequency axis. For example, the resource may be varied by subcarrier. It may also be varied by resource block.

[0399] Radio resources (resources on the frequency axis - resources on the time axis) may be provided separately from the SPS resources. For example, when there is no data to transmit, padding transmission is performed using the SPS resources. When there is data to transmit, padding transmission is performed using separately configured radio resources. This makes it easier to control padding transmission because there is no need to change the mechanism for conventional padding transmission. Separately configured radio resources may be used by multiple UEs. Specifically, multiplexing is recommended. For example, time multiplexing, frequency multiplexing, and code multiplexing may be performed. Alternatively, collision-based sharing may be used. The eNB may decompose the PUSCH transmitted by the UE using the RS for each UE.

[0400] As another method, whether to perform transmission using the L1 / L2 control signal or padding transmission may be switched depending on whether uplink transmission data is present. For example, if uplink transmission data is present, transmission using the L1 / L2 control signal is performed instead of padding transmission, and if uplink transmission data is absent, conventional padding transmission is performed. The eNB can recognize whether uplink transmission data is present or absent depending on whether it is received using the L1 / L2 control signal or conventional padding transmission. For the L1 / L2 control signal when uplink transmission data is present, the method disclosed in Variation 1 of Embodiment 2 may be used.

[0401] By doing so, the 2nd-eNB can recognize whether or not there is transmission data from the UE. If there is no uplink transmission data at the SPS timing set in the 2nd-eNB, it is possible to execute implicit release. If there is uplink transmission data in the SPS resource in the 2nd-eNB, it is possible not to execute implicit release.

[0402] Therefore, as disclosed in the third embodiment, it is not necessary to reserve SPS resources for a long period of time, which occurs when implicit release is not performed in consideration of the case where uplink transmission data is present at the timing of the SPS set in the 2nd-eNB. This makes it possible to improve the utilization efficiency of PUSCH resources.

[0403] In this embodiment, a method has been disclosed in which DC is set and padding transmission is made different depending on whether or not there is uplink transmission data at the timing of SPS set in the 2nd-eNB. Not limited to this, the method disclosed in this embodiment may be applied to cases in which different padding transmissions are sent to one eNB.

[0404] For example, the UE measures the time change in the amount of uplink transmission data generated, and uses the measurement result to derive the probability that uplink transmission data will occur at the uplink transmission timing. In other words, the UE uses the measurement result of the time change in the amount of uplink transmission data generated to predict the probability that uplink transmission data will occur at the uplink transmission timing. Statistical processing may be performed to derive the probability that uplink transmission data will occur at the uplink transmission timing.

[0405] The padding transmission may be varied depending on the probability that uplink transmission data occurs at the uplink transmission timing. Measurement of the change in the amount of uplink transmission data over time may be performed for each bearer, or for each content or application.

[0406] The UE determines whether the probability of uplink transmission data occurring at the uplink transmission timing is equal to or greater than a predetermined threshold. The threshold may be predetermined as a system, or may be set by the eNB and notified by the eNB. The UE varies padding transmission depending on whether the probability of uplink transmission data occurring is equal to or greater than the predetermined threshold.

[0407] If no uplink transmission data actually occurs at the configured uplink SPS timing, the UE will perform padding transmission. At this time, if the probability of uplink transmission data occurring is greater than or equal to a threshold, padding (B) transmission will be performed. If the probability of uplink transmission data occurring is not greater than or equal to the threshold, i.e., if the probability of uplink transmission data occurring is less than the threshold, padding (A) transmission will be performed.

[0408] The eNB does not release the SPS resources even if it receives padding (B) from the UE a number of times consecutively set as the number of empty transmissions before release. Also, the UE does not clear the set SPS resources even if it transmits padding (B) to the eNB a number of times consecutively set as the number of empty transmissions before release. By doing so, it is possible to prevent the release of SPS resources when there is a high probability of uplink transmission data occurring.

[0409] For example, if upstream transmission data is supposed to occur but does not occur at the upstream transmission timing due to some delay, the SPS resource can be prevented from being released. Therefore, if upstream transmission data continues to occur, the SPS resource can be prevented from being released, and the upstream data can be transmitted using the SPS resource at the next SPS timing.

[0410] When the eNB receives padding (A) from the UE a number of times consecutively set as the number of empty transmissions before release, the eNB releases the SPS resources. Also, when the UE transmits padding (A) to the eNB a number of times consecutively set as the number of empty transmissions before release, the UE clears the set SPS resources. By doing so, when the probability of uplink transmission data occurring is low, the SPS resources can be released.

[0411] By doing so, it becomes unnecessary to reserve SPS resources for a long period of time, which makes it possible to improve the efficiency of PUSCH resource usage.

[0412] In the method disclosed above, two types of padding transmission are used, but this is not limiting, and a plurality of different padding transmissions may be provided for padding transmission. The eNB can change its operation depending on the type of padding transmission.

[0413] For example, the UE may transmit different padding depending on the downlink reception quality. Two thresholds for the downlink reception quality may be set, dividing the downlink reception quality into three reception quality states, and different padding may be transmitted depending on each of the three reception quality states. This allows the eNB to recognize the level of the downlink reception quality of the UE.

[0414] Furthermore, the eNB may schedule UL resources and notify the UE of an uplink grant even if there is no uplink scheduling request from the UE, in order to have the UE perform padding transmission. Since the UE has no uplink transmission data, the UE will perform padding transmission using the uplink resources allocated by the uplink grant. This padding transmission may be different depending on the reception quality state described above. In this way, the eNB can dynamically recognize the downlink reception quality of the UE in a timely manner. In this way, the eNB can perform diverse and flexible control over the UE.

[0415] Embodiment 6 When a UL split bearer is set for a predetermined bearer, an uplink SPS is set in the 2nd-eNB depending on the data generation status of the bearer.

[0416] When uplink transmission data occurs at the timing of the uplink SPS set on the 2nd-eNB side, not only is uplink transmission performed to the 2nd-eNB using SPS resources, but depending on the bearer setting conditions, uplink transmission will also be performed to the 1st-eNB at the timing of the SPS.

[0417] If SPS has not been configured for the 1st-eNB at the timing of the SPS, the 1st-eNB must start by transmitting an SR signal to the 1st-eNB.

[0418] Although the 1st-eNB can also be used for uplink transmission, a delay occurs with respect to the 1st-eNB, causing an increase in transmission delay time. This embodiment discloses a method for solving such a problem.

[0419] The 1st-eNB is configured with the same SPS as that configured with the 2nd-eNB. When a UL split bearer is configured, the 1st-eNB may be configured with the SPS.

[0420] A method for setting an SPS is disclosed. The SPS for the first eNB is set to the same setting as the SPS for the second eNB. It is preferable to be able to set multiple SPSs for each eNB.

[0421] The parameters do not have to be set to the same value for all parameters. The SPS interval is an example of a parameter that is set to the same value. The C-RNTI for the SPS is an example of a parameter that is set to a different value. The number of empty transmissions before UL release may be set to the same value or may be set to a different value.

[0422] When an SPS is configured in a 1st-eNB, if an SPS is configured in a 2nd-eNB, the 1st-eNB may configure the same SPS as the 2nd-eNB in addition to the SPS configuration already configured. If the SPS configuration already configured in the 1st-eNB and the SPS configuration for the 2nd-eNB are the same, for example, if the SPS timing is the same, then the configuration may be duplicated.

[0423] Alternatively, if the SPS settings already set in the 1st-eNB and the SPS settings for the 2nd-eNB are the same, for example, if the SPS timing is the same, it is better not to set them overlappingly, but to set an SPS that combines the SPS settings already set in the 1st-eNB and the SPS settings for the 2nd-eNB.

[0424] By doing this, if SPS has already been configured in the 1st-eNB, it is possible to configure the 1st-eNB with the same SPS settings as those for the 2nd-eNB without interrupting the existing SPS settings.

[0425] A method for notifying and configuring SPS settings to a UE is disclosed. The 2nd-eNB notifies the UE of the SPS settings for the 2nd-eNB. Furthermore, the 2nd-eNB notifies the 1st-eNB of the SPS settings for the 2nd-eNB. This notification may be performed using X2 signaling. Alternatively, S1 signaling via the MME may be used. This enables the 1st-eNB to recognize the SPS settings of the 2nd-eNB. The 1st-eNB applies the same parameters as those of the 2nd-eNB to the SPS settings of its own eNB. The same parameters include the SPS interval. The number of null transmissions before UL release may be the same or may be different. The C-RNTI for the SPS is independently configured by the own eNB. The 1st-eNB notifies the UE of these SPS settings.

[0426] By doing so, the 1st-eNB can set the same SPS settings for the UE as the 2nd-eNB.

[0427] Another SPS setting method is disclosed. The SPS for the first eNB is set to the same setting as the SPS for the second eNB. It is preferable to be able to set multiple SPSs for each eNB.

[0428] All parameters are to be set to the same setting: SPS interval, C-RNTI for SPS, and the number of empty transmissions before UL release.

[0429] A method for notifying and configuring the SPS settings to the UE is disclosed. The 2nd-eNB notifies the UE of the SPS settings for the 2nd-eNB. Furthermore, the 2nd-eNB notifies the 1st-eNB of the SPS settings for the 2nd-eNB. This notification may be performed using X2 signaling. Alternatively, S1 signaling via the MME may be used. This allows the 1st-eNB to recognize the SPS settings of the 2nd-eNB. The UE applies the SPS settings for the 2nd-eNB to the SPS settings for the 1st-eNB.

[0430] By doing so, the 1st-eNB can set the same SPS settings for the UE as the 2nd-eNB.

[0431] This also eliminates the need for the 1st-eNB to notify the UE of the SPS setting, thereby reducing the amount of signaling on the air interface.

[0432] A method for setting the same SPS C-RNTI between the 2nd-eNB and the 1st-eNB is disclosed. The 2nd-eNB and the 1st-eNB coordinate to set the same value in advance. For example, when the 2nd-eNB sets the SPS, it notifies the 1st-eNB in advance of the SPS C-RNTI to be used.

[0433] If the notified SPS C-RNTI can be used, the 1st-eNB notifies the 2nd-eNB of an Ack, which allows the 1st-eNB and the 2nd-eNB to use the same SPS C-RNTI.

[0434] If the notified SPS C-RNTI cannot be used, the 1st-eNB notifies the 2nd-eNB of Nack. In this case, the 2nd-eNB selects another SPS C-RNTI value and notifies the 1st-eNB. This process is repeated until an Ack is received from the 1st-eNB. By using this method, the 2nd-eNB and the 1st-eNB can use the same SPS C-RNTI.

[0435] The information may be transmitted between the 2nd-eNB and the 1st-eNB using X2 signaling, or may be transmitted via the MME using S1 signaling.

[0436] The timing of SPS activation determines the timing of SPS start, so a method is required to synchronize the SPS activation timing between both eNBs.

[0437] When the 2nd-eNB determines to notify the UE of the SPS activation, the 2nd-eNB notifies the 1st-eNB of the timing of notifying the UE of the SPS activation, or notifies the 1st-eNB of the timing of notifying the UE of the SPS activation.

[0438] The timing information may be at least one of a radio frame number and a subframe number.

[0439] The 1st-eNB uses the received timing information to derive the timing at which the SPS setting of the 2nd-eNB will be activated for the UE, and notifies the UE of SPS activation to coincide with this timing.

[0440] If the 2nd-eNB cannot notify the UE of SPS activation in time, it may notify the UE at a timing after the subsequent SPS interval. It is preferable to notify as soon as possible.

[0441] By doing so, the SPS activation timing can be synchronized between both eNBs, and the SPS timing for both eNBs can be matched.

[0442] The information may be transmitted between the 2nd-eNB and the 1st-eNB using X2 signaling, or may be transmitted via the MME using S1 signaling.

[0443] 21 is a diagram illustrating a method for configuring the same SPS for a 1st-eNB as that configured for a 2nd-eNB. The 1st-eNB is an MeNB, and the 2nd-eNB is an SeNB.

[0444] In FIG. 21, the DRAT threshold is indicated by reference symbol "1901."

[0445] The SeNB determines the SPS configuration. In Step ST1902, the SeNB notifies the UE of the SPS interval, the number of empty transmissions before release, and the SPS C-RNTI by RRC dedicated signaling.

[0446] Furthermore, in Step ST1903, the SeNB notifies the MeNB of the set SPS configuration. The set SPS configuration may be notified by X2 signaling. The SPS configuration to be notified may be the SPS interval. In addition, the number of empty transmissions before release may also be notified.

[0447] The MeNB sets the same value as the received SeNB configuration as the SPS configuration for the MeNB. The SPS C-RNTI is selected by the MeNB, without using the same value as the SeNB.

[0448] In Step ST1904, the MeNB notifies the UE of the SPS configuration for the MeNB and the SPS C-RNTI through RRC dedicated signaling.

[0449] The UE detects the PDCCH using the SPS C-RNTI notified from the SeNB and MeNB.

[0450] In Step ST1905, the SeNB notifies the MeNB of the timing of SPS activation. The MeNB that receives the timing of SPS activation becomes able to recognize the timing at which the SeNB activates the SPS.

[0451] In Steps ST1906 and ST1907, the SeNB and the MeNB each transmit an SPS activation to the UE at the activation timing determined by the SeNB. This allows both the SeNB and the MeNB to activate the SPS for the UE at the same timing.

[0452] The order of notifying the MeNB of the timing of SPS activation from the SeNB in Step ST1905 and notifying the UE of the timing of SPS activation from the SeNB in Step ST1906 may be reversed.

[0453] The SeNB notifies the MeNB of the timing at which it notified the UE of SPS activation. This makes it possible to notify the MeNB of the timing at which SPS activation was actually performed at the SeNB. By notifying the actual SPS activation timing, it becomes possible to reduce the occurrence of malfunctions such as mismatches in SPS activation timing between the SeNB and the MeNB.

[0454] The scheduling of SPS resources from the MeNB and the scheduling of SPS resources from the SeNB may be different, and the MeNB and the SeNB may perform scheduling independently.

[0455] By receiving the SPS activation, the UE recognizes that the SPS has been activated for the SeNB and the MeNB.

[0456] In steps ST1908 and ST1909, the UE transmits uplink data to the SeNB and MeNB at the timing of the set SPS.

[0457] In Step ST1910, if the amount of uplink transmission data of the UE is smaller than the DRAT threshold at the set SPS timing, the UE transmits padding to the SeNB and transmits uplink data to the MeNB.

[0458] When padding transmission to the SeNB has been performed consecutively the number of times set as the number of null transmissions before release, the eNB releases the SPS resources configured for the SeNB in Step ST1911. The UE also clears the SPS resources configured for the SeNB.

[0459] Since uplink data is being transmitted to the MeNB, the SPS resource set for the MeNB is not released in Step ST1911. If there is uplink transmission data, the uplink data is transmitted.

[0460] This section discloses the release of SPS resources. The eNB where the implicit release occurred may notify other eNBs of this. For example, if an implicit release occurs for a configured SPS in a second-eNB, the second-eNB notifies the first-eNB that an implicit release has occurred. Alternatively, the second-eNB may notify the first-eNB that the implicit release has released SPS resources or disabled the SPS settings.

[0461] The 1st-eNB that receives the release of the SPS resources of the 2nd-eNB may disable the same SPS setting as that of the 2nd-eNB that was configured in the 1st-eNB. Furthermore, the 1st-eNB may notify the UE, as appropriate, that the same SPS setting as that of the 2nd-eNB that was configured in the 1st-eNB will be disabled. By receiving this notification, the UE can disable the same SPS setting as that of the 2nd-eNB that was configured in the 1st-eNB.

[0462] By doing so, the 1st-eNB can disable the same SPS setting as the 2nd-eNB.

[0463] Furthermore, the eNB that notifies the UE of the information indicating that the uplink SPS setting disclosed in the second modification of the fourth embodiment is to be disabled may notify other eNBs to that effect. Alternatively, the eNB that notifies the UE of the information indicating that the uplink SPS setting is to be disabled may notify other eNBs to that effect in advance.

[0464] For example, when the 2nd-eNB notifies the UE of information indicating that the uplink SPS setting is to be disabled, the 2nd-eNB notifies the 1st-eNB that it has notified the UE of information indicating that the uplink SPS setting is to be disabled.

[0465] Alternatively, when the 2nd-eNB notifies the UE of information indicating that the uplink SPS setting is disabled, the 2nd-eNB notifies the 1st-eNB that it will notify the UE of information indicating that the uplink SPS setting is disabled. In this case, the 2nd-eNB may notify the 1st-eNB of the timing to disable the uplink SPS setting or the timing to notify the UE of the information indicating that the uplink SPS setting is disabled.

[0466] The 1st-eNB that has received the information indicating that the uplink SPS setting is to be disabled from the 2nd-eNB may use the information indicating that the uplink SPS setting is to be disabled to disable the same SPS setting that the 1st-eNB had set for the 2nd-eNB. Alternatively, the 1st-eNB may decide not to disable the same SPS setting that the 1st-eNB had set for the 2nd-eNB. Alternatively, the 1st-eNB may correct the same SPS setting that the 1st-eNB had set for the 2nd-eNB. For example, the 1st-eNB may return to the SPS setting that was previously set for the 1st-eNB. The 1st-eNB can flexibly change the SPS setting set for its own eNB, taking into account the load situation, etc.

[0467] Furthermore, the 1st-eNB may appropriately notify the UE that the same SPS setting as that of the 2nd-eNB that was set in the 1st-eNB will be disabled. By receiving this notification, the UE can disable the same SPS setting as that of the 2nd-eNB that was set in the 1st-eNB.

[0468] If the 1st-eNB cannot timely notify the UE of the information indicating that the uplink SPS setting is disabled by the 2nd-eNB, the 1st-eNB may notify the UE at a timing after the next SPS interval, or may notify the UE without waiting for a timing after the next SPS interval, or may notify the UE immediately.

[0469] By doing so, the 1st-eNB can disable the same SPS setting as the 2nd-eNB.

[0470] It has been stated that, at the timing of the SPS set for the 2nd-eNB, uplink data may be transmitted not only to the 2nd-eNB but also to the 1st-eNB.

[0471] By using the method disclosed in this embodiment, the SPS is configured for the 1st-eNB at the timing of the SPS configured for the 2nd-eNB. Therefore, the UE can transmit uplink data not only to the 2nd-eNB but also to the 1st-eNB at the timing of the SPS without transmitting an uplink scheduling request. This can reduce the transmission delay time for the 1st-eNB.

[0472] Embodiment 7 In the UL split bearer, if the amount of uplink transmission data is equal to or less than the DRAT threshold, the UE does not transmit uplink data to the 2nd-eNB.

[0473] Transmitting padding even when there is no uplink data to be transmitted to the 2nd-eNB results in a waste of power consumption by the UE.

[0474] In particular, if implicit release is not performed even when padding transmission occurs a predetermined number of times in succession, it is pointless to perform padding transmission because implicit release is not determined based on the number of padding transmissions.

[0475] To solve this problem, it is advisable not to send padding if an implicit release is not performed.

[0476] If there is no uplink data transmission to the 2nd-eNB at the configured SPS timing and if implicit release is not performed, the UE does not transmit padding.

[0477] Figure 22 is a diagram explaining a method for preventing padding transmission when implicit release is not performed. The 1st-eNB is the MeNB, and the 2nd-eNB is the SeNB. This shows a case where SPS is configured in both the MeNB and the SeNB. Figure 22 is similar to Figure 15, so differences will mainly be described.

[0478] In step ST1008, the SeNB notifies the UE of the activation by using the PDCCH in an uplink grant for uplink SPS. The activation includes information indicating that the uplink SPS configuration will not be disabled. This allows the UE to recognize that implicit release will not be performed and that the uplink SPS configuration will not be disabled.

[0479] A UE that receives SPS activation from the SeNB executes SPS using the configured resources, does not perform implicit release, and does not invalidate the uplink SPS setting. Even if the UE does not generate uplink transmission data for the predetermined number of times to the SeNB, both the eNB and the UE are configured not to perform implicit release and not to invalidate the uplink SPS setting.

[0480] Consider the case where, in Step ST1301, uplink data with a data amount smaller than the DRAT threshold is generated in the UE at the SPS timing set for the SeNB.

[0481] In this case, in Step ST1301, the UE transmits uplink data to the MeNB, and no uplink transmission data is generated for the SeNB.

[0482] When implicit release is not performed and no uplink transmission data occurs, padding transmission is not performed, and therefore, in step ST2001, the UE does not transmit padding to the SeNB.

[0483] In steps ST2001 to ST2002, if uplink data with a data volume smaller than the DRAT threshold is generated in the UE at the timing of the SPS set for the SeNB, similarly, in steps ST1301 to ST1302, the UE transmits uplink data to the MeNB but does not transmit padding to the SeNB.

[0484] If uplink transmission data does not occur for the number of consecutive times set as the number of empty transmissions before release to the SeNB, the UE does not transmit padding using the SPS resources. In such a case, the UE does not perform the implicit release received in Step ST1008. The UE does not clear the SPS resources in Step ST1204 in accordance with the setting that does not disable the uplink SPS setting. The eNB also does not release the SPS resources. In Step ST1204, implicit release is not performed, and the SPS resources are not released.

[0485] In step ST1204, if uplink data with a data volume greater than or equal to the DRAT threshold is generated in the UE at the timing of the SPS set for the SeNB, in step ST1401, the UE becomes able to transmit uplink data to the SeNB using the SPS resources set for it.

[0486] By doing so, if implicit release is not performed, it is possible to prevent padding transmission when no uplink transmission data is generated for the SeNB. Since the UE does not transmit padding, it is possible to reduce the power consumption of the UE. Furthermore, by preventing padding transmission when no uplink transmission data is generated for the SeNB, it is possible to reduce interference in the uplink.

[0487] When implicit release is performed, padding transmission may be performed. The method of performing implicit release may be the methods disclosed in the fourth embodiment, the first modification of the fourth embodiment, and the second modification of the fourth embodiment. The eNB may notify the UE of the start of implicit release and information indicating the start of padding transmission.

[0488] By doing so, if implicit release is not performed, padding transmission can be prevented when no uplink transmission data is generated for the 2nd-eNB.Also, if implicit release is performed, padding transmission can be performed when no uplink transmission data is generated for the 2nd-eNB.

[0489] This allows the implicit release to operate normally and also reduces the power consumption of the UE.

[0490] When implicit release is not performed, the following two methods (1) and (2) are disclosed as specific examples of a method for configuring not to transmit padding when no uplink transmission data occurs to the 2nd-eNB.

[0491] (1) Determine statically in advance using standards, etc.

[0492] (2) Information indicating that padding will not be transmitted is provided and notified to the UE from the eNB.

[0493] In the method (1) above, if implicit release is not performed, it is statically determined that padding will not be transmitted when no uplink transmission data is generated for the 2nd-eNB. By determining this in advance in a standard, it becomes possible for the eNB and UE to recognize this, which enables consistent operation and reduces malfunctions.

[0494] In the method (2) described above, by notifying the UE of information indicating that padding transmission will not be performed, it becomes possible to dynamically configure not to transmit padding when no uplink transmission data is generated for the 2nd-eNB. The eNB may notify the UE of this information when the 2nd-eNB does not perform implicit release. Upon receiving the information indicating that padding transmission will not be performed, the UE does not transmit padding when no uplink data is generated for the 2nd-eNB.

[0495] The information indicating that padding will not be transmitted as described in (2) above may be notified to the UE from the eNB. The eNB may be the 1st-eNB or the 2nd-eNB. For example, when the 2nd-eNB notifies the UE, the 2nd-eNB may notify the UE directly, or the 2nd-eNB may notify the UE via the 1st-eNB. X2 signaling may be used to notify information between eNBs. Alternatively, S1 signaling may be used via the MME.

[0496] The following three (1) to (3) are disclosed as specific examples of signaling methods for notifying the UE from the eNB of information indicating that padding transmission will not be performed.

[0497] (1) RRC signaling. For example, the signaling may be included in the signaling for setting the SPS configuration.

[0498] (2) MAC signaling: For example, a MAC CE including information indicating that padding is not transmitted may be provided and notified by MAC signaling.

[0499] (3) L1 / L2 signaling, such as PDCCH or EPDCCH, which may be included in SPS activation and notified.

[0500] Although it has been disclosed that information indicating that padding transmission will not be performed is provided and notified from the eNB to the UE, information indicating that padding transmission will be performed may also be provided. The information indicating that padding transmission will be performed may also be notified from the eNB to the UE. This makes it possible to dynamically set whether to perform padding transmission when no uplink transmission data is generated for the 2nd-eNB if implicit release is not performed, thereby enabling flexible operation according to the communication status and load status of the 2nd-eNB.

[0501] Embodiment 8 In the seventh embodiment, a method is disclosed in which padding is not transmitted if there is no uplink transmission data at the timing of the set SPS.

[0502] If padding transmission is not performed, the eNB will be unable to distinguish whether uplink data was actually transmitted but could not be received, or whether it was not received because padding transmission was not performed. This embodiment discloses a method for solving such a problem.

[0503] Even when it is configured not to transmit padding, the eNB operates HARQ. When it is configured not to transmit padding, the eNB operates HARQ. When there is uplink transmission data, the UE performs HARQ, and when there is no uplink transmission data, the UE does not transmit padding or retransmit.

[0504] Conventionally, padding transmission performed when there is no uplink transmission data at the timing of the set SPS is subject to HARQ. The eNB can determine whether uplink transmission data has been sent by receiving the padding transmission. Therefore, the UE performs padding transmission even when there is no uplink transmission data at the timing of the set SPS, and when it receives a Nack, which is a delivery and reception unsuccessful (reception unsuccessful) signal from the eNB, it retransmits the padding transmission.

[0505] In the method disclosed in this embodiment, the eNB operates HARQ, but the UE does not transmit padding if there is no uplink transmission data at the timing of the set SPS, and differs from conventional methods in that it does not retransmit padding even if it receives a Nack, which is a reception failure signal, from the eNB.

[0506] When the UE does not transmit padding, it does not retransmit the padding even if it receives a Nack from the eNB. Therefore, since there is no retransmission from the UE, the eNB determines that reception is unsuccessful and transmits a Nack again. The UE receives a Nack again from the eNB. In response to this Nack, the UE does not retransmit the padding. Since the UE does not transmit padding or retransmit the padding, this operation is repeated. Therefore, the eNB continues to transmit a Nack to the UE. A method for solving this problem is disclosed.

[0507] The eNB may set a maximum number of retransmissions. For HARQ when the initial transmission is performed on the uplink SPS resource, the eNB may set a maximum number of retransmissions.

[0508] When reception continues to be unsuccessful and the eNB continues to transmit Nack the maximum number of times without success, the eNB stops HARQ.

[0509] The maximum number of retransmissions may be statically determined in advance by a standard or the like. Alternatively, it may be determined by the eNB. This allows it to be dynamically changed depending on the communication status and load status. Alternatively, it may be determined by OAM (operation administration and maintenance). This allows it to be determined taking into account the status of multiple eNBs. Alternatively, it may be determined by the operator. It may also be determined as one of the system design parameters.

[0510] The maximum number of retransmissions disclosed in this embodiment may be set differently from the maximum number of retransmissions set in conventional HARQ. For example, the maximum number of retransmissions disclosed in this embodiment may be set smaller than the maximum number of retransmissions set in conventional HARQ. By reducing the maximum number of retransmissions disclosed in this embodiment, it becomes possible to reduce the number of NACKs transmitted from the eNB to the UE when there is no uplink transmission data and no padding transmission. This makes it possible to reduce waste of radio resources for NACKs.

[0511] FIG. 23 is a diagram explaining a HARQ method when padding transmission is not performed. The 1st-eNB is assumed to be an MeNB, and the 2nd-eNB is assumed to be an SeNB. FIG. 23 shows a case where SPS is configured in the SeNB. It shows a case where padding transmission is not performed when no uplink transmission data is generated without implicit release. In Step ST2108, the SeNB notifies the UE of activation by an uplink grant for uplink SPS, using the PDCCH. The activation includes information indicating that the uplink SPS configuration is not disabled. This allows the UE to recognize that padding transmission is not performed when no implicit release is performed and no uplink transmission data is generated.

[0512] In Step ST2101, consider a case where the UE generates uplink data with a data amount equal to or greater than the DRAT threshold at the timing of the SPS configured for the SeNB. In this case, in Step ST2101, the UE transmits the uplink data to the SeNB using the SPS resources configured for the SeNB. The eNB receives the uplink data from the UE and assumes that the reception was successful. In this case, in Step ST2102, the SeNB transmits an Ack, which is a reception success signal, to the UE. When the UE receives the Ack, it determines that the uplink data has been received by the SeNB and does not retransmit the data.

[0513] Next, in ST2103, the UE transmits uplink data to the SeNB at the timing of the set SPS. The SeNB receives the uplink data from the UE and assumes that the reception is unsuccessful. In this case, in step ST2104, the SeNB transmits a Nack to the UE.

[0514] When the UE receives a Nack, it determines that the uplink data has not been received by the SeNB, and in step ST2105, it retransmits the uplink data to the SeNB. In this way, the UE transmits the uplink data to the SeNB, and when it receives a Nack from the SeNB, it retransmits the uplink data.

[0515] In Step ST2105, it is assumed that the SeNB receives the retransmission of the uplink data from the UE and that the reception is successful. In this case, in Step ST2109, the SeNB transmits an Ack to the UE.

[0516] When the UE receives the Ack, it determines that the uplink retransmission data has been received by the eNB, and does not retransmit the data.

[0517] Next, consider a case in which uplink data with a data amount smaller than the DRAT threshold is generated in the UE at the SPS timing configured for the SeNB in Step ST2106. In this case, in Step ST2110, the UE transmits uplink data to the MeNB, but does not transmit the uplink data using the SPS resource configured for the SeNB. In Step ST2108, since it is configured not to transmit padding when no uplink transmission data is generated, the UE does not transmit padding either.

[0518] In Step ST2106, the SeNB receives the data unsuccessfully because no padding is transmitted from the UE. In this case, in Step ST2111, the SeNB transmits a Nack to the UE.

[0519] The UE may or may not receive a Nack. Even if the UE receives a Nack, the UE does not perform retransmission. Furthermore, the UE does not perform padding transmission.

[0520] In Step ST2107, the SeNB does not receive any data from the UE, and therefore reception is unsuccessful. In this case, in Step ST2112, the SeNB transmits a Nack signal to the UE again.

[0521] Similarly, the UE may or may not receive a Nack. Even if the UE receives a Nack, it does not perform retransmission. Furthermore, the UE does not perform padding transmission.

[0522] The eNB stops HARQ when the number of times Nack is transmitted reaches the maximum number of times. If the maximum number of retransmissions is not set, Nack transmission will be repeated, but in this embodiment, the maximum number of retransmissions is set, so it is possible to stop HARQ.

[0523] By using the method disclosed in this embodiment, when uplink data is transmitted from the UE, HARQ is activated, and the reception performance of the uplink data is improved.

[0524] Furthermore, when there is no uplink transmission data, the UE will not retransmit data or transmit padding even if a Nack is transmitted from the eNB. The UE only needs to retransmit data in accordance with a Nack from the eNB when it has transmitted uplink data. Therefore, the UE's transmission is limited to when uplink data is transmitted, which makes it possible to reduce increases in power consumption.

[0525] Eighth embodiment, variant 1 This modification discloses another method for solving the problem described in the eighth embodiment. The 2nd-eNB determines whether data intended for the 2nd-eNB has been generated. The 2nd-eNB uses the result to determine whether to activate HARQ.

[0526] A method for determining whether data has been generated for the 2nd-eNB is disclosed. The 2nd-eNB notifies the 1st-eNB in advance of the SPS setting of its own eNB. The SPS setting may be set at the timing of the SPS. Alternatively, the SPS interval and the timing of SPS activation may be set at the timing when the UE is notified.

[0527] This allows the 1st-eNB to recognize the timing of the SPS set by the 2nd-eNB.

[0528] The 1st-eNB determines whether the amount of uplink transmission data generated from the UE is smaller than the DRAT threshold at the timing of the SPS of the 2nd-eNB. The 1st-eNB notifies the 2nd-eNB of the determination result. The 2nd-eNB determines whether data intended for itself has been generated based on the determination result received from the 1st-eNB.

[0529] If the determination result notified by the 1st-eNB is smaller than the DRAT threshold, the 2nd-eNB determines that no data has been generated for itself.

[0530] If the determination result notified by the 1st-eNB is equal to or greater than the DRAT threshold, the 2nd-eNB determines that data intended for itself is being generated.

[0531] A method for the 2nd-eNB to determine whether to activate HARQ will be disclosed. When the 2nd-eNB determines that data intended for itself has been generated, it activates HARQ.

[0532] If the 2nd-eNB determines that no data is generated for itself, it stops HARQ.

[0533] In this method, the first eNB needs to notify the second eNB of the information. In this case, communication is performed via a backhaul interface such as the X2 interface or the S1 interface, so there are cases where the second eNB cannot immediately respond to the HARQ performed by the second eNB due to time constraints.

[0534] However, even if HARQ cannot be implemented immediately, it can be implemented after a delay due to backhaul communication, etc. Therefore, it is possible to prevent HARQ from continuing endlessly. This makes it possible to improve the resource utilization efficiency of the 2nd-eNB.

[0535] There are cases where data transmitted to the 1st-eNB is smaller than the DRAT threshold, but data is also transmitted to the 2nd-eNB. For example, when the DRAT threshold is exceeded, the scheduling ratio between the 1st-eNB and the 2nd-eNB is set to 1:2. In this case, the amount of data transmitted to the 1st-eNB is 1 / 3. In such cases, the amount of data may be smaller than the DRAT threshold.

[0536] In such a case, HARQ is not performed on the 2nd-eNB side. This causes a problem because HARQ is not performed even though data is being transmitted to the 2nd-eMB. A method for solving this problem will be disclosed.

[0537] The 1st-eNB obtains the scheduling ratio between the 1st-eNB and the 2nd-eNB. For example, if the 2nd-eNB determines the scheduling ratio, the 2nd-eNB may notify the 1st-eNB of the scheduling ratio in advance. If the 1st-eNB determines the scheduling ratio, notification is not necessary.

[0538] The 1st-eNB determines whether the scheduling ratio is smaller than the DRAT threshold, taking into account the scheduling ratio.

[0539] By doing this, it is possible to prevent HARQ from failing to operate when the scheduling ratio between the 1st-eNB and the 2nd-eNB when the DRAT threshold is exceeded results in data being transmitted to the 2nd-eNB even though the data transmitted to the 1st-eNB is smaller than the DRAT threshold.

[0540] Therefore, when there is uplink transmission data from the UE to the 2nd-eNB, the reception performance of the uplink transmission data can be improved.

[0541] Furthermore, since HARQ can be stopped, it is possible to improve the efficiency of resource usage in the 2nd-eNB.

[0542] Eighth embodiment, variant 2 Another method for solving the problem described in the eighth embodiment will be disclosed. The 2nd-eNB measures the uplink power of the SPS resource configured for the 2nd-eNB. The 2nd-eNB may measure the uplink communication quality.

[0543] The 2nd-eNB may measure, as the uplink power, received signal strength indicator (RSSI), interference over thermal noise (IOT), RSRP, signal to interference plus noise power ratio (SINR), etc. Alternatively, the 2nd-eNB may measure the received power of a PUSCH reference signal used in the configured SPS resource.

[0544] The 2nd-eNB may measure the RSRQ as the uplink communication quality, or may measure the reception quality of the PUSCH reference signal.

[0545] If the uplink power or uplink communication quality of the SPS resource configured for itself is higher than a predetermined threshold, the 2nd-eNB determines that uplink data has been transmitted to the 2nd-eNB.

[0546] If the uplink power or uplink communication quality of the SPS resources configured for the 2nd-eNB is lower than a predetermined threshold, the 2nd-eNB determines that uplink data has not been transmitted to the 2nd-eNB.

[0547] A method for the 2nd-eNB to determine whether to activate HARQ is disclosed. If the 2nd-eNB determines that data has been transmitted to the 2nd-eNB itself, it activates HARQ. If the 2nd-eNB determines that data has not been transmitted to the 2nd-eNB itself, it stops HARQ.

[0548] Because measurements are required, there are times when the 2nd-eNB cannot immediately respond to HARQ. However, even if it cannot immediately respond to HARQ, it can respond after a delay due to measurements, etc. Therefore, it is possible to prevent HARQ from continuing endlessly. This makes it possible to improve the efficiency of resource usage in the 2nd-eNB.

[0549] Furthermore, signaling between eNBs becomes unnecessary, making it possible to suppress an increase in the amount of signaling.

[0550] Embodiment 9 If the amount of uplink transmission data is equal to or less than the DRAT threshold, the UE does not transmit uplink data to the 2nd-eNB. Transmitting padding even when there is no uplink data to be transmitted to the 2nd-eNB wastes power consumption of the UE.

[0551] However, when implicit release is enabled, if padding transmission is not performed, implicit release is not performed and the configured SPS resource is not released. If the SPS resource is not released, the resource cannot be used by other UEs, and the utilization efficiency of the PUSCH resource is reduced. This embodiment discloses a method for solving such a problem.

[0552] The frequency of padding transmission when there is no uplink transmission data is changed. Specifically, padding transmission is thinned out.

[0553] In the padding transmission method disclosed above, padding is always transmitted to the 2nd-eNB when the amount of uplink transmission data is equal to or less than the DRAT threshold. In contrast, in the method disclosed in this embodiment, when the amount of uplink transmission data is equal to or less than the DRAT threshold, padding transmission to the 2nd-eNB is thinned out.

[0554] For example, a case where padding transmission is thinned out once every two times will be shown. The UE does not transmit padding at the timing of the first padding transmission. The UE transmits padding at the timing of the second padding transmission.

[0555] The number of times padding is transmitted, that is, the frequency at which padding is transmitted, is sometimes called the “padding transmission frequency.” In the above example, the padding transmission frequency is “2.”

[0556] The padding transmission frequency may be statically determined in advance by a standard or may be changed semi-statically or dynamically. The padding transmission frequency may be configured by the eNB and notified to the UE from the eNB. When notified to the UE from the eNB, the padding transmission frequency may be included in an SPS configuration message or an SPS activation message.

[0557] FIG. 24 is a diagram explaining an implicit release method when padding transmission is thinned out. The 1st-eNB is an MeNB, and the 2nd-eNB is an SeNB. This shows a case where SPS is configured in the SeNB. This shows a case where the padding transmission frequency is "2". The number of null transmissions before release for implicit release is "3". It is assumed that SPS has already been configured in the SeNB.

[0558] In Step ST2209, the SeNB notifies the UE of activation via the PDCCH in an uplink grant for uplink SPS. The activation includes information on the frequency of padding transmission. This allows the UE to know how many times to thin out padding transmission.

[0559] In Step ST2201, consider a case where uplink data with a data amount equal to or greater than the DRAT threshold is generated in the UE at the SPS timing configured for the SeNB. In this case, in Step ST2201, the UE transmits the uplink data to the SeNB using the SPS resource configured for the SeNB.

[0560] In step ST2202, if uplink data with a data volume smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that the padding transmission timing for the SeNB is the first time and does not transmit padding.

[0561] In Step ST2203, if uplink data with a data amount smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that this is the second padding transmission timing for the SeNB. Since the padding transmission frequency is "2", the UE transmits padding.

[0562] When the UE transmits padding to the SeNB, the UE resets the count of padding transmission timing.

[0563] After resetting the padding transmission timing count, in step ST2204, if uplink data with a data volume smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that the padding transmission timing for the SeNB is the first time and does not transmit padding.

[0564] In Step ST2205, if uplink data with a data amount smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that this is the second padding transmission timing for the SeNB. Since the padding transmission frequency is "2", the UE transmits padding.

[0565] When the UE transmits padding to the SeNB, the UE resets the count of padding transmission timing.

[0566] Similarly, in Step ST2206, the UE does not transmit padding to the SeNB. In Step ST2207, the UE transmits padding to the SeNB. Then, the UE resets the count of padding transmission timing.

[0567] In Step ST2203, the SeNB receives the first padding transmission from the UE, in Step ST2205, the SeNB receives the second padding transmission from the UE, and in Step ST2207, the SeNB receives the third padding transmission from the UE.

[0568] In Steps ST2203 to ST2207, the SeNB does not receive uplink data while receiving padding transmission from the UE, and has received padding transmission the number of empty transmissions before release, three times in succession in this case, so performs implicit release. Then, in Step ST2208, the SeNB releases the configured SPS resources. If the UE has transmitted padding transmission to the SeNB the number of empty transmissions before release, three times in succession in this case, in Step ST2208, the UE clears the SPS configuration.

[0569] By doing so, it is possible to reduce padding transmission when there is no uplink transmission data at the timing of the SPS set for the SeNB. By reducing padding transmission, it is possible to reduce the power consumption of the UE.

[0570] Furthermore, since padding transmission is performed, it is possible to operate implicit release, which makes it possible to suppress a decrease in the utilization efficiency of PUSCH resources.

[0571] In the example shown in Fig. 24, the UE resets the count of padding transmission timing when padding transmission is performed. As another method, the UE may reset the count of padding transmission timing when padding transmission is performed and when uplink data transmission is performed. Since the count of padding transmission timing is reset even when uplink data transmission is performed, it is possible to further reduce the number of padding transmissions.

[0572] The method for resetting the count of the padding transmission timing may be statically determined in advance by a standard or may be notified from the eNB to the UE. The notification may be included in an SPS configuration message or an SPS activation message, or may be notified together with the padding transmission frequency.

[0573] 25 is a diagram showing another example of the implicit release method when padding transmission is thinned out. The first-eNB is an MeNB, and the second-eNB is an SeNB. The example shows a case where SPS is configured in the SeNB.

[0574] Since FIG. 25 is similar to FIG. 24, differences will be mainly described.

[0575] FIG. 25 shows the case where the padding transmission frequency is "4".

[0576] Instead of the number of pre-release empty transmissions for implicit release, a predetermined number of padding transmission timings for implicit release is set. A parameter called "implicitReleaseAfter_T" is used as the predetermined number of padding transmission timings for implicit release. In the following description, the predetermined number of padding transmission timings for implicit release may be referred to as the "number of pre-release empty transmission timings." In FIG. 25, the number of pre-release empty transmission timings is set to "8." The UE may reset the padding transmission timing count when padding transmission is performed and when uplink data transmission is performed.

[0577] The number of pre-release empty transmission timings may be statically determined in advance by a standard or may be notified from the eNB to the UE. When notified from the eNB to the UE, it may be included in an SPS configuration message or an SPS activation message.

[0578] It is assumed that SPS has already been configured for the SeNB. In Step ST2310, the SeNB notifies the UE of activation by using the PDCCH with an uplink grant of uplink SPS. The activation includes information on the padding transmission frequency. The activation also includes information on the number of empty transmission timings before release. This allows the UE to recognize the number of times to thin out padding transmission and the predetermined number of padding transmission timings for implicit release.

[0579] In Step ST2311, consider a case where the UE generates uplink data with a data amount equal to or greater than the DRAT threshold at the SPS timing configured for the SeNB. In this case, in Step ST2311, the UE transmits the uplink data to the SeNB using the SPS resource configured for the SeNB.

[0580] When transmitting uplink data, the UE resets the count of padding transmission timing.

[0581] In step ST2301, if uplink data with a data amount smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that the padding transmission timing is the first time and does not transmit padding.

[0582] In step ST2302, if uplink data with a data amount smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that this is the second padding transmission timing and does not transmit padding.

[0583] In step ST2303, if uplink data with a data amount smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that this is the third padding transmission timing and does not transmit padding.

[0584] In step ST2304, if uplink data with a data volume smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that this is the fourth padding transmission timing and performs padding transmission since the padding transmission frequency is "4".

[0585] When the UE transmits padding, it resets the count of padding transmission timing.

[0586] After resetting the count of padding transmission timing, in step ST2305, if uplink data with a data amount smaller than the DRAT threshold occurs at the SPS timing set for the SeNB, the UE determines that the padding transmission timing is the first time and does not transmit padding.

[0587] Similarly, in Steps ST2306 and ST2307, the UE does not transmit padding. In Step ST2308, the UE transmits padding. Then, the UE resets the count of padding transmission timing.

[0588] In Step ST2304, the SeNB receives the first padding transmission from the UE. Since the SeNB has received the padding transmission from the UE once, it determines that the padding transmission timing has reached four or more times, taking into account that the padding transmission frequency is "4". Since the number of empty transmission timings before release is not eight or more, the SeNB maintains the SPS resources and performs reception from the UE using the SPS resources.

[0589] In Step ST2308, the SeNB receives the second padding transmission from the UE. Since the SeNB has received the padding transmission from the UE twice in succession, the SeNB determines that the number of empty transmission timings before release has reached 8 or more.

[0590] The SeNB, which has determined that the number of empty transmission timings before release has reached eight or more, performs implicit release and releases the configured SPS resources in Step ST2309.

[0591] The UE clears the SPS configuration when the padding transmission timing to the SeNB occurs consecutively for the number of empty transmission timings before release. Alternatively, since padding transmission has been performed twice consecutively, taking into consideration that the padding frequency is "4", the UE may determine that the padding transmission timing has occurred consecutively for more than the number of empty transmission timings before release, and perform implicit release and clear the configured SPS resources.

[0592] Regarding HARQ when padding transmission is not performed, the methods disclosed in the eighth embodiment to the second modification of the eighth embodiment may be applied.

[0593] By using the method disclosed in this embodiment, it is possible to reduce padding transmission when there is no uplink data transmission at the SPS timing set for the SeNB. By reducing padding transmission, it is possible to reduce the power consumption of the UE.

[0594] Furthermore, since padding transmission is performed, it is possible to operate implicit release, which makes it possible to suppress a decrease in the utilization efficiency of PUSCH resources.

[0595] In addition, by making it possible to configure the padding transmission frequency, it becomes possible to flexibly respond to requirements such as the desired communication quality, allowable delay, or desired continuous operation time of the UE for each UE or bearer for which SPS is configured for the 2nd-eNB.

[0596] Embodiment 10 In the first to ninth embodiments, problems that occur when an SPS is configured in a 2nd-eNB when a UL split bearer is configured have been described, and solutions to these problems have been disclosed. First of all, it is required to reduce the frequency with which such problems occur. In the present embodiment, a method for reducing the frequency with which such problems occur will be disclosed.

[0597] If the data generation cycles are different for multiple communications or bearers, the 1st-eNB is configured with an SPS for communications or bearers that contain data that occurs at short intervals.

[0598] It is preferable to set the SPS period of the 1st-eNB to be equal to or shorter than the SPS period of the 2nd-eNB (SPS period of the 1st-eNB≦SPS period of the 2nd-eNB).

[0599] The DRAT threshold may be set to the maximum value of the amount of data generated in a short period or more, or may be set to the minimum value of the amount of data generated in a long period or less.

[0600] By doing so, when an UL split bearer is set up and an SPS is set up in the 2nd-eNB, it is possible to reduce the number of SPS timings that occur in the 2nd-eNB. On the other hand, the 1st-eNB can always transmit uplink data, so it is possible to perform normal SPS processing. Therefore, it is possible to reduce the frequency with which the problems described in the first to ninth embodiments occur.

[0601] This makes it possible to reduce the occurrence of unstable and malfunctioning operations of eNBs and UEs, improve the efficiency of radio resource usage, and reduce the power consumption of UEs.

[0602] When there are multiple data or bearers with different communication capacities, if the larger capacity data occurs in a shorter period, the eNB suitable for the larger capacity communication may be designated as the 1st-eNB. Since the 1st-eNB can always transmit uplink data, by designating the eNB suitable for the larger capacity communication as the 1st-eNB, SPS processing suitable for the larger capacity communication becomes possible.

[0603] Embodiment 10 Variation 1 Another method for solving the problem described in the tenth embodiment will be disclosed. It is preferable that one eNB can set multiple SPSs for one UE. For example, one eNB sets an SPS for each bearer for one UE. Among bearers, there are some for which the data generation cycle and data volume for each bearer can be known to some extent. By setting an SPS for each bearer, it becomes possible to set an SPS suitable for the data generation cycle and data volume for each bearer.

[0604] In addition, the DRAT threshold is set for each bearer. Therefore, by setting the SPS for each bearer, it is possible to set the SPS suitable for the data generation period and data amount for each bearer, and to set the DRAT threshold. This makes it possible to reduce the frequency of occurrence of the problems shown in the first to ninth embodiments. In addition, it becomes possible to flexibly respond to requests such as the desired communication quality and allowable delay amount for each bearer.

[0605] The SPS may be set for each bearer group including one or more bearers, rather than for each bearer. For example, by grouping bearers with similar data generation cycles and data volumes, it becomes possible to reduce the number of SPSs that the eNB sets for one UE, thereby simplifying control.

[0606] Embodiment 10 Variation 2 Another method for solving the problem described in the tenth embodiment will be disclosed. The eNB measures the change over time of the amount of uplink transmission data from the UE, and derives the change over time of the probability that uplink transmission data will occur using the measurement result. In other words, the eNB predicts the change over time of the probability that uplink transmission data will occur using the measurement result of the change over time of the amount of uplink transmission data.

[0607] Statistical processing may be performed to derive the probability of occurrence of uplink transmission data. From the time change of the derived probability of occurrence of uplink transmission data, it is determined at which uplink transmission timing the probability of occurrence of uplink transmission data is high.

[0608] The eNB configures the SPS, schedules the SPS resources, and activates and deactivates the SPS according to the time-varying probability of the derived uplink transmission data. In this way, the eNB can configure the SPS appropriate for the time-varying amount of uplink transmission data from the UE.

[0609] Although the time change in the probability of occurrence of uplink transmission data is disclosed, the time change in the amount of data generated may also be derived. This makes it possible to derive the amount of radio resources that should be allocated as SPS resources. Therefore, it becomes possible to perform SPS resource scheduling with high accuracy.

[0610] Although a method has been disclosed in which the eNB measures the time change in the amount of uplink transmission data from the UE and derives the time change in the probability of uplink transmission data occurring using the measurement results, the UE may also measure the time change in the amount of uplink transmission data generated and derive the time change in the probability of uplink transmission data occurring using the measurement results. Statistical processing may be performed to derive the probability of uplink transmission data occurring. The UE derives at which uplink transmission timing the probability of uplink transmission data occurring is high from the derived time change in the probability of uplink transmission data occurring.

[0611] The UE notifies the eNB of the derived time variation of the probability of occurrence of uplink transmission data or information regarding which uplink transmission timing has a high probability of occurrence of uplink transmission data. This notification can be performed using RRC signaling. By using RRC signaling, it is possible to notify a large amount of information.

[0612] The notification may be made using MAC signaling or L1 / L2 control signals. When MAC signaling or L1 / L2 control signals are used, the amount of information that can be notified is smaller, but the time required for notification can be shortened. Therefore, the derived value can be reflected with low delay.

[0613] The eNB configures the SPS, schedules SPS resources, and activates and deactivates the SPS using information notified by the UE about the time change in the probability of the derived uplink transmission data occurring, or information about which uplink transmission timing has a high probability of uplink transmission data occurring.

[0614] By doing this, the UE can directly measure the time variation of the uplink transmission data generated in the UE, so it is possible to derive the time variation of the probability of the uplink transmission data occurring regardless of the radio wave propagation environment.

[0615] The UE may derive SPS configuration, SPS resource scheduling, and SPS timing according to the time change of the derived probability of occurrence of uplink transmission data. The UE notifies the eNB of information related to the derived SPS configuration, SPS resource scheduling, and SPS timing. In this way, it is possible to reduce the amount of information notified from the UE to the eNB.

[0616] Measurement of the amount of uplink transmission data or the time change in the amount of uplink transmission data generated, and derivation of the time change in the probability of uplink transmission data being generated, may be performed for each UE or bearer, or for each content or application. This makes it possible to set an SPS appropriate for each UE, bearer, content, or application.

[0617] Although the deriving of the time change in the probability of occurrence of uplink transmission data has been disclosed, it is also possible to derive the time change in the amount of uplink transmission data generated. Alternatively, it is also possible to derive the time change in the uplink throughput. By using these values, it is possible to derive the amount of radio resources that should be allocated as SPS resources. Therefore, it is possible to perform accurate scheduling of SPS resources.

[0618] By applying the above-mentioned method to the SPS configuration of the 2nd-eNB, it is possible to reduce the situation where no uplink transmission data is generated in the UE even though SPS resources are allocated in the 2nd-eNB. It may also be applied to the SPS configuration of the 1st-eNB. It is possible to configure an appropriate SPS in the 1st-eNB as well.

[0619] The above-mentioned method discloses that SPS configuration, SPS resource scheduling, and SPS timing are derived according to the time change of the probability of uplink transmission data occurring. As another method, it may be applied to setting the DRAT threshold. The DRAT threshold is set according to the time change of the probability of uplink transmission data occurring.

[0620] For example, an eNB may notify other eNBs performing DC of the results of deriving the time change in the probability of occurrence of uplink transmission data. Furthermore, the other eNBs may derive the time change in the probability of occurrence of uplink transmission data to the eNB itself. The other eNBs may use this information to set the DRAT threshold. Since the other eNBs know the time change in the probability of occurrence of uplink transmission data to each eNB, they can flexibly determine how to set the DRAT threshold.

[0621] The methods disclosed in the first and second modifications of the tenth embodiment may be applied to the 1st-eNB. In addition, they may be applied appropriately to cases other than when a DC is set. This allows for the same effects as those of the first and second modifications of the tenth embodiment to be obtained.

[0622] Embodiment 11 In 3GPP, pre-scheduling is being studied as a method for reducing delay when a UE connected to one cell starts uplink transmission. Pre-scheduling methods include a method using SPS and a method using dynamic scheduling (see Non-Patent Document 10). However, these methods are for when a UE is connected to one cell, and there has been no discussion at all about pre-scheduling methods when dual connectivity (DC) is configured.

[0623] As described above, 3GPP has introduced DC, in which a UE connects to two eNBs to communicate. DC is an important technology for increasing communication capacity. In this embodiment, a method for setting pre-scheduling when DC is set in a UE is disclosed.

[0624] The eNB that supports pre-scheduling is limited to the MeNB. The eNB that supports pre-scheduling may be statically determined in advance by a standard or the like.

[0625] If the eNB that supports pre-scheduling is not determined, for example, the SeNB may independently set pre-scheduling for the UE, but the UE may not support pre-scheduling for the SeNB. In such a case, a malfunction may occur, and DC may not be able to be executed. Therefore, by statically determining the eNB that supports pre-scheduling in advance, the method for setting pre-scheduling in DC between the UE and the eNB becomes clear, and the occurrence of malfunctions can be reduced.

[0626] In DC, data can be transmitted from both eNBs. Therefore, if only the MeNB supports pre-scheduling, the reduction in delay of uplink transmission as a bearer is small.

[0627] Therefore, in DC, it is preferable that the SeNB supports pre-scheduling. In DC, the eNBs that support pre-scheduling should be the MeNB and SeNB. Pre-scheduling may be supported simultaneously for the MeNB and SeNB. It is preferable that the pre-scheduling settings for the MeNB and SeNB be the same.

[0628] When configuring the SPS of the 2nd-eNB for a split bearer, the method disclosed in the above embodiment may be applied.

[0629] This allows pre-scheduling to be set for the SeNB as well, which in turn shortens the time it takes for the SeNB to start transmitting uplink data, thereby increasing the reduction in delay in uplink transmission as a bearer.

[0630] The pre-scheduling setting in the MeNB may be different from the pre-scheduling setting in the SeNB. Pre-scheduling may be set separately, that is, independently, for each of the MeNB and SeNB.

[0631] In DC, a split configuration can be set for each bearer, so the data to be transmitted differs for each eNB. For example, bearer #1 can be set as a split bearer using an MeNB and an SeNB, and bearer #2 can be set as a non-split bearer that is not a split bearer using an MeNB. Therefore, the data to be transmitted differs for each eNB set in DC, and the amount of delay required for each eNB set in DC also differs.

[0632] As described above, by enabling independent pre-scheduling for each eNB, it becomes possible to set pre-scheduling taking bearer settings into consideration, which makes it possible to satisfy the delay amount required for each eNB in which a DC is set.

[0633] Pre-scheduling for each eNB may be set independently for each bearer. For example, in the above example, pre-scheduling for bearer #1 for the MeNB and SeNB and pre-scheduling for bearer #2 for the MeNB may be set independently. In this way, by allowing pre-scheduling for each eNB to be set independently for each bearer, it becomes possible to satisfy different required delay amounts depending on the bearer.

[0634] The present invention discloses an entity that sets pre-scheduling and a method for notifying a UE of the pre-scheduling setting.

[0635] The MeNB configures pre-scheduling. The MeNB configures pre-scheduling for the MeNB and SeNB. The MeNB notifies the SeNB of the configuration of pre-scheduling for the SeNB. The configuration may include cancellation of the configuration. The SeNB may determine whether or not to permit (allow / disallow) the configuration of pre-scheduling notified from the MeNB. If the SeNB permits the configuration of pre-scheduling notified from the MeNB, it may notify the MeNB of information indicating permission. If the SeNB disallows the configuration of pre-scheduling notified from the MeNB, it may notify the MeNB of information indicating disallowance.

[0636] When receiving a notification of non-permission from the SeNB, the MeNB may change the pre-scheduling setting and notify the SeNB again. The MeNB may repeat the re-setting until receiving a notification of permission from the SeNB.

[0637] The X2 interface may be used to notify the setting of pre-scheduling performed between the MeNB and the SeNB. The pre-scheduling setting may be included in a message for adding, releasing, or modifying the SeNB. The X2 interface may be used to notify information indicating permission / denial performed between the SeNB and the MeNB.

[0638] The MeNB notifies the UE of the pre-scheduling configuration for at least one of the MeNB and the SeNB. The pre-scheduling configuration may be notified via the Uu interface. The pre-scheduling configuration may be notified by being included in a message for setting up a DC.

[0639] Alternatively, the SeNB may configure pre-scheduling for the SeNB, and the SeNB may notify the UE of the configuration of pre-scheduling.

[0640] Alternatively, the SeNB may notify the MeNB of the SeNB pre-scheduling configuration. The pre-scheduling configuration may be notified using the X2 interface. Upon receiving the SeNB pre-scheduling configuration from the SeNB, the MeNB may notify the UE of the configuration.

[0641] The setting of pre-scheduling is largely dependent on the setting of the bearer. Therefore, it is more preferable that the MeNB, which sets the DC using information set in the bearer, sets the pre-scheduling.

[0642] By using the method disclosed in this embodiment, it is possible to perform pre-scheduling even when a DC that connects to two eNBs and communicates with the UE is set.

[0643] This makes it possible to increase communication capacity and reduce delays in upstream transmission, enabling large-capacity communication to be carried out in a shorter period of time.

[0644] In this embodiment, a method for setting pre-scheduling when DC is set in the UE has been disclosed. Pre-scheduling may be set for the SeNB when DC is set for the UE, rather than when DC is set in the UE. The eNB may set pre-scheduling for the SeNB when adding the SeNB. The method disclosed in this embodiment may be applied as appropriate to this pre-scheduling setting.

[0645] By doing so, in the process of adding an SeNB, it is possible to omit the scheduling request process that the UE has conventionally performed to the SeNB. This makes it possible to reduce the time required for the scheduling request, and therefore the time required to set up a DC. In addition, it is possible to reduce communication delays and perform large-capacity communication in a shorter time.

[0646] The method disclosed in this embodiment is not limited to the case of adding an SeNB, but can also be applied to the case of modifying an SeNB. The pre-scheduling method disclosed in this embodiment may be applied appropriately to the modified SeNB. This makes it possible to obtain the same effects as those of this embodiment.

[0647] The above embodiment and its modified examples have disclosed cases where split bearers are supported in dual connectivity (DC). This is not limited to DC, but can also be applied to multi-connectivity, where communication is performed using multiple eNBs. This may be applied to cases where, when split bearers are performed in multi-connectivity, uplink data is not transmitted to one or more of the eNBs that make up the multi-connectivity according to a predetermined rule. This makes it possible to obtain the same effects as the above embodiment and its modified examples.

[0648] In the above embodiment and its modified examples, a case where an SPS is set when a UL split bearer is set and a DRAT is used has been disclosed, but the present invention may be applied to a case where dynamic scheduling is performed instead of a case where an SPS is set. The method for setting the DRAT threshold and the method for padding transmission when an SPS is set when a DRAT is used may also be applied to a case where dynamic scheduling is performed when a DRAT is used.

[0649] For example, when a DRAT threshold is set, if the 2nd-eNB notifies the UE of an uplink grant by dynamic scheduling, and no uplink transmission data is generated in the UE in the resources of the uplink grant, a problem similar to that when SPS is set occurs.Furthermore, when a DRAT threshold is set, and the 2nd-eNB performs dynamic scheduling by pre-scheduling, a similar problem occurs when the UE does not generate uplink transmission data in the pre-scheduled resources.

[0650] In order to solve such problems, it is advisable to apply the methods disclosed in the first embodiment, the second embodiment, the first modification of the second embodiment, the fifth embodiment, the seventh embodiment, the eighth embodiment, the first modification of the eighth embodiment, and the second modification of the eighth embodiment as appropriate. The same effect can also be obtained when dynamic scheduling is performed in the case where DRAT is used.

[0651] Embodiment 12 When an eNB communicates with a UE, the eNB uses multiple antennas to transmit signals using beamforming, which forms beams only in the direction of the UE, the terminal with which the communication is intended. One method of using beamforming to cover the eNB's service area is to arrange multiple beams with fixed directions. In this case, the eNB switches between fixed beams in accordance with the UE's movement and uses the appropriate beam.

[0652] 26 is a diagram illustrating beamforming using a multi-element antenna. The eNB configures antenna 408 shown in FIG.

[0653] The eNB forms beams in only a predetermined direction using some or all of the multiple antennas of the multi-element antenna 2401, and communicates with the UE 2402 that is the communication target. As shown in Fig. 26, the coverages 2403, 2404, and 2405 of the beams formed using beamforming are narrow coverage. The eNB covers a service area by forming multiple beams with fixed narrow coverage in different directions.

[0654] When UE2402 is in the coverage area 2403 of the first beam, the eNB communicates with UE2402 using the first beam. When UE2402 moves to the coverage area 2404 of the second beam, the eNB switches from the first beam to the second beam and communicates with UE2402. Hereinafter, the beam from which the switch is made may be referred to as the "source beam," and the beam to which the switch is made may be referred to as the "target beam."

[0655] When beamforming is used, the service area formed by the eNB is divided into narrow coverage areas formed by multiple beams, which requires high-speed beam switching processing when the UE moves between beams.

[0656] The eNB may form multiple beams for each cell using beamforming. In this case, beam switching occurs when a UE moves between beams within a single cell.

[0657] In the beam switching process, the UE must synchronize with the target beam, and the eNB must schedule the radio resources of the target beam for the UE. Therefore, it is necessary to speed up the beam switching process when the UE moves between beams, and to provide a high-speed and stable communication system.

[0658] In order to speed up the beam switching process, it is effective to reduce the time required for such synchronization process and radio resource scheduling process.

[0659] In this embodiment, a method for shortening the time required for synchronization processing with a target beam and for scheduling processing of radio resources in the target beam is disclosed.

[0660] The synchronization process with the target cell may be performed using a synchronization method with a conventional cell. The UE receives at least one of a synchronization signal, a reference signal, and a discovery signal transmitted by the target beam and synchronizes with the target beam. For example, if a synchronization signal such as P-SS or S-SS used in conventional cells is used as the synchronization signal, synchronization may be performed using the synchronization signal. In this case, a period of at least six subframes is required for synchronization.

[0661] In the synchronization signals used in conventional cells, a synchronization code is assigned that corresponds one-to-one to the PCI of each cell. However, with a PCI for each cell, the UE cannot recognize which beam it has synchronized with. To solve this problem, it is recommended to provide an identifier for each beam and assign a code that corresponds one-to-one to the identifier for each beam to the synchronization signal of each beam.

[0662] By doing so, the UE can recognize which beam it has synchronized with. The identifier for each beam may be assigned by superimposing it on the identifier for each cell. The UE can recognize which cell, and further, which beam.

[0663] Similarly, a code that corresponds one-to-one to the identifier for each beam may be assigned to the reference signal and the discovery signal. By receiving the reference signal or the discovery signal and obtaining the identifier for each beam, the UE can recognize which beam it has received.

[0664] However, when applying synchronization processing with a conventional cell, for example, when a synchronization signal is used, as described above, a period of at least six subframes is required for the UE to receive the synchronization signal. Considering the time required for synchronization processing in the UE, the time required for synchronization processing with a conventional cell becomes even longer. A method for shortening the time required for these synchronization processing is disclosed.

[0665] The eNB synchronizes beams within the same cell. Synchronization may also be performed between beams within the eNB. More specifically, synchronization of subframe timing and slot timing is performed between beams. It is also advisable to synchronize SFN (System Frame Number), radio frame number, and slot number.

[0666] By doing so, even if a beam switching process is performed for the UE, there is no need to synchronize with the target beam, which makes it possible to reduce the time required for synchronization processing.

[0667] A method for shortening the processing time for scheduling radio resources in a target beam is disclosed. Scheduling information for downlink radio resources is included in downlink control information (DCI). The downlink control information is notified to the UE by an L1 / L2 control signal. In LTE, it is mapped to a PDCCH or EPDCCH. An identifier (C-RNTI) assigned individually to each UE for each cell is masked in the CRC of the L1 / L2 control signal. By detecting its own C-RNTI, the UE can receive the L1 / L2 control signal addressed to itself and obtain the downlink control information, thereby becoming able to obtain the scheduling information for downlink radio resources.

[0668] In beams within a cell, it is recommended to use the same identifier for the UE-specific identifier masked in the CRC of the L1 / L2 control signal. It is also recommended to use an identifier assigned to each UE individually for each cell. By doing so, the UE can use the C-RNTI used in the source beam in the target beam even if a beam switching process is performed within the cell.

[0669] Therefore, after synchronization with the target beam is achieved, it is possible to receive scheduling information by immediately receiving an L1 / L2 control signal.

[0670] In inter-cell beam switching, the eNB should notify the UE of the C-RNTI in advance. The eNB should notify the UE of the C-RNTI using the source beam. By doing so, even in inter-cell beam switching, it is possible to immediately receive L1 / L2 control signals and scheduling information after synchronizing with the target cell.

[0671] As another method, an identifier (referred to as B-RNTI) may be assigned individually to each UE for each beam. The identifier assigned individually to each UE for each beam may be masked in the CRC of the L1 / L2 control signal. In the beam switching process, the eNB may notify the UE of the B-RNTI in advance. The eNB may notify the UE of the B-RNTI using the source beam. By doing so, in the beam switching process, after synchronizing with the target cell, it becomes possible to immediately receive the L1 / L2 control signal and scheduling information.

[0672] By assigning a B-RNTI to each UE individually for each beam, it becomes unnecessary to use different controls for switching beams within a cell and switching beams between cells. This makes it possible to simplify the control in the eNB and UE. Furthermore, since it becomes unnecessary to determine which control to perform, it becomes possible to reduce the time required for the determination.

[0673] Scheduling information for uplink radio resources is also included in downlink control information (DCI), and therefore the methods disclosed above can be applied.

[0674] In the uplink, the UE needs to request radio resources from the eNB. In conventional cells, the request for radio resources is made via a scheduling request (SR) or PRACH. In the beam switching process, the UE requests radio resources from the target beam.

[0675] However, SR and PRACH cannot be performed at any timing, but must be performed at a predetermined timing set by the eNB. Therefore, the UE must wait until the predetermined timing set by the eNB, which causes a delay. In the case of a narrow-coverage beam switching process, this delay is likely to lead to communication failure.

[0676] A method for solving such a problem will be disclosed. The eNB schedules uplink radio resources in a target beam for the UE in advance. The eNB may schedule uplink radio resources in a target beam for the UE in advance using a source beam.

[0677] For example, SPS may be used as a scheduling method for uplink radio resources of a target beam. The eNB may notify the UE of the uplink SPS setting in the target beam using the source beam. The notification of the uplink SPS setting may be performed before the UE synchronizes with the target beam. After receiving the uplink SPS setting in the target beam, the UE synchronizes with the target beam and then performs uplink transmission using the notified uplink SPS setting in the target beam.

[0678] The SPS configuration may include not only the time interval of the SPS resource but also an offset and scheduling information. The offset may be specified as a radio frame number or a subframe number.

[0679] This paper describes how to set up SPS in the target beam and how to activate it. The time interval of the SPS resource can be set in the source beam. Setting the time interval of the SPS resource in the source beam eliminates the need for setting it from the target beam when switching beams, and shortens the time required for the switching process.

[0680] The scheduling information for SPS resources may be set in the source beam. By setting the scheduling information for SPS resources in the source beam, it is possible to eliminate the need for setting from the target beam when switching beams, thereby shortening the time required for the switching process.

[0681] Alternatively, the scheduling information for SPS resources may be set in the target beam, which allows for the setting of scheduling information such as resource allocation according to the load situation in the target beam.

[0682] Activation and deactivation of the SPS may be performed in the source beam. By performing activation and deactivation of the SPS in the source beam, setting from the target beam is not required when switching beams, and the time required for the switching process can be shortened.

[0683] Alternatively, SPS resource activation and deactivation may be performed in the target beam. This allows activation and deactivation to be performed according to the load situation in the target beam. Furthermore, resource utilization efficiency can be improved compared to when activation and deactivation are performed in advance in the source beam. This is because when activation and deactivation are performed in advance in the source beam, SPS resources must be continuously allocated to the target UE from the time when activation and deactivation are performed in advance in the source beam until the target beam is switched to and SPS is actually performed, resulting in waste of radio resources.

[0684] The aforementioned methods of setting the SPS and activating and deactivating the SPS on the source beam or the target beam may be combined as appropriate, allowing for configuration based on the load situation and delay tolerance of the target beam.

[0685] This eliminates the need for the UE to request uplink radio resources from the eNB using the target beam after beam switching, thereby reducing delays and shortening the time required for beam switching processing.

[0686] Although the use of uplink SPS as a scheduling method for uplink radio resources of a target beam has been disclosed here, downlink SPS may also be used as a scheduling method for downlink radio resources of a target beam. The eNB may notify the UE of the downlink SPS configuration in the target beam using the source beam. In this way, after switching to the target beam, the UE can receive the configured SPS resources according to the downlink SPS configuration.

[0687] Dynamic scheduling may be used as another method for scheduling uplink radio resources of a target beam. The eNB transmits radio resource scheduling information to the UE in any subframe using the target beam without receiving a scheduling request from the UE. After synchronizing with the target beam, the UE receives an L1 / L2 control signal in every subframe, thereby enabling it to receive the scheduling information of the radio resources transmitted by the eNB in any subframe. This allows the UE to perform uplink transmission using the received scheduling information of the uplink radio resources.

[0688] This eliminates the need for the UE to request uplink radio resources from the eNB, thereby reducing delays and shortening the time required for beam switching processing.

[0689] Fig. 27 is a diagram showing an example of a sequence relating to a method for reducing the time required for beam switching processing in Embodiment 12. Fig. 27 shows a case where a source beam (S-Bm) is switched to a target beam (T-Bm).

[0690] In step ST2501, the eNB communicates with the UE using a source beam. The eNB synchronizes the source beam and target beam in advance. The eNB synchronizes the subframe timing and slot timing between the source beam and target beam. The SFN (System Frame Number), radio frame number, and slot number are also synchronized. By doing this, in step ST2502, if the UE is synchronized with the source beam, it is also synchronized with the target beam. In step ST2502, the UE indicates that it has also synchronized with the target beam.

[0691] In step ST2503, the eNB notifies the UE of uplink scheduling information in the target beam using the source beam. Here, the uplink scheduling information in the target beam is the uplink SPS configuration information in the target beam. The SPS configuration information includes not only the time interval of the SPS resource but also the offset and scheduling information.

[0692] Information about the target beam may be notified together with uplink scheduling information for the target beam. Information about the target beam may include, for example, an identifier of the target beam. In addition, when an identifier assigned individually to each UE for each beam is used, the identifier may be notified. RRC signaling may be used to notify the uplink scheduling information for the target beam and the information about the target beam.

[0693] In Step ST2504, the eNB notifies the UE of a beam switching instruction using the source beam. Beam switching instruction information may be provided and notified. The beam switching instruction information is information that triggers beam switching. In other words, it is information that triggers the UE to receive an L1 / L2 control signal of the target beam. RRC signaling may be used to notify the beam switching instruction information.

[0694] The UE that has received the beam switching command information has already synchronized with the target beam in step ST2502, and therefore receives downlink control information of the target beam in step ST2505. The UE receives the PDCCH or EPDCCH in every subframe. By receiving the downlink control information of the target beam, the UE can obtain downlink scheduling information and can receive downlink data in accordance with the scheduling information.

[0695] If there is uplink transmission data, in step ST2506, the UE transmits the uplink data to the eNB using the SPS resource configured for the target beam.

[0696] By doing so, in step ST2507, communication between the UE and the eNB becomes possible using the target beam.

[0697] By using the method disclosed in this embodiment, when a UE moves between beams that have narrow coverage due to beamforming and switches beams, it is possible to reduce the deterioration of communication quality and communication interruptions caused by the time required for synchronization processing and radio resource scheduling processing.

[0698] If the position of an antenna consisting of multiple antenna elements forming a beam is the same for each beam, the path distance from the antenna to the UE will be approximately the same. Therefore, there is no need to change the uplink transmission timing between the source beam and the target beam. However, if the antenna position differs for each beam, the UE may need to synchronize the uplink with the target beam.

[0699] A method for performing uplink synchronization is disclosed. An eNB instructs a UE to perform a random access (RA) process in a target beam. The instruction to perform the RA process in the target beam may be performed using an L1 / L2 control signal in the target beam. Alternatively, the instruction may be performed using a PDCCH or EPDCCH in the target beam.

[0700] When the UE receives an instruction to perform RA processing in the target beam, the UE may perform RA processing in the target beam. By performing RA processing in the target beam, the eNB can adjust the uplink transmission timing of the UE. Specifically, in the RA processing, the eNB notifies the UE of the uplink transmission timing. This is also called timing advance.

[0701] In this way, the UE can achieve uplink synchronization on the target beam.

[0702] A method for an eNB to determine whether to perform uplink synchronization is disclosed. The eNB acquires information about the location of the antenna. For example, each antenna acquires information about its own antenna location using a Global Positioning System (GPS) or the like, and notifies the eNB of the information about its own antenna location. Alternatively, an operator may set information about the antenna location in the eNB. Alternatively, the operator may set information about the antenna location in the OAM, and the OAM may notify the eNB of the information.

[0703] The eNB uses the acquired information about the antenna position to determine whether uplink synchronization is required for the UE that is the target of communication using the target beam.

[0704] When the eNB determines that uplink synchronization is necessary, it may instruct the UE to perform RA processing in the target beam.

[0705] In this way, the eNB can determine whether or not to perform uplink synchronization as needed. If uplink synchronization is not required, it is possible to avoid performing RA processing. Even if uplink synchronization is required, the RA processing is performed in accordance with an instruction from the eNB, so that the RA processing is collision-free, and control can be simplified.

[0706] In the example shown in Figure 27, the uplink scheduling information in the target beam and the instruction to switch to the target beam are notified by separate signaling. As another example, the uplink scheduling information in the target beam and the instruction to switch to the target beam may be notified by the same signaling. This makes it possible to obtain the same effect.

[0707] Embodiment 13 In the twelfth embodiment, it is disclosed that the eNB notifies the UE of a beam switching instruction for switching the beam. For example, the process of step ST2504 in FIG. 27 is shown.

[0708] In the twelfth embodiment, it has been disclosed that RRC signaling is used to notify beam switching instruction information. However, when RRC signaling is used, the signal is divided into multiple transport blocks, and is transmitted at multiple transmission time intervals (TTIs). Furthermore, retransmission is applied for each transport block. Therefore, the time required for transmitting and receiving RRC signaling increases. In the present embodiment, a method for shortening the time required for notifying a beam switching instruction in beam switching processing is disclosed.

[0709] Beam switching commands are sent via MAC signaling or L1 / L2 signaling. A dedicated control channel, such as PDCCH or EPDCCH, is used for L1 / L2 signaling. Both MAC signaling and L1 / L2 signaling are performed in one TTI, which makes it possible to shorten the time required to send a beam switching command compared to RRC signaling.

[0710] In the case of MAC signaling, HARQ is applied, which has the effect of lowering the reception error rate compared to when L1 / L2 signaling is used.

[0711] In the case of L1 / L2 signaling, HARQ is not applied, so beam switching instructions can be sent with less delay than when MAC signaling is used.

[0712] Whether to use MAC signaling or L1 / L2 signaling may be determined statically by a standard or the like. Alternatively, both methods may be supported and used semi-statically or dynamically. For example, MAC signaling or L1 / L2 signaling may be used depending on the radio wave propagation environment. When the radio wave propagation environment is good, L1 / L2 signaling may be used, and when the radio wave propagation environment is not good, MAC signaling may be used.

[0713] The entity that determines beam switching is disclosed. The MAC protocol in the eNB should determine beam switching. By having MAC make the decision instead of RRC, it becomes possible to determine which beam to use together with or be included in scheduling. Each beam should be treated as a radio resource configured on the same time-frequency axis. Multiple beams may be treated as multiple radio resources, and scheduling may be performed using the multiple radio resources.

[0714] In addition, having MAC determine whether to switch beams is suitable for transmitting beam switching instructions using signaling below MAC. By having MAC determine whether to switch beams, it is possible to shorten the processing time from determining whether to switch beams to transmitting a beam switching instruction.

[0715] In addition to the beam switching instruction, the following three items (1) to (3) are disclosed as specific examples of information used when causing a UE to switch a beam. Hereinafter, the information used when causing a UE to switch a beam may be referred to as "beam switching related information."

[0716] (1) Information on which beam to switch to, e.g., the target beam identifier.

[0717] (2) Information on the reset of each protocol of the source beam and the setting of each protocol of the target beam.

[0718] (3) Information to enable communication with the target beam.

[0719] The above-mentioned specific example (1) will now be explained in more detail. The beam identifier may be assigned for each predetermined range of the network. For example, the beam identifier may be assigned for each MME. Alternatively, the beam identifier may be assigned for each eNB. Alternatively, a predetermined number of beam identifiers may be prepared in advance and assigned from among them.

[0720] By allocating beam identifiers in a narrow range of the network, it is possible to reduce the amount of information required for the beam identifier, for example, the number of bits. For example, by allocating beam identifiers for each cell, it is possible to reduce the amount of information required for beam switching-related information, for example, the number of bits.

[0721] The above specific example (2) will be explained in more detail. The same PDCP is used between beams within the same cell. Therefore, information on whether or not to reset and / or reconfigure PDCP when switching beams is not required. It may be decided in advance by standards, etc., that neither resetting nor reconfiguring is to be performed. When switching beams within the same cell, the UE should retain the PDCP setting of the source beam.

[0722] The same RLC is used between beams within the same cell. Therefore, there is no need for information on whether or not to reset and / or reconfigure the RLC when switching beams. It may be decided in advance by standards, etc., that neither resetting nor reconfiguring is to be performed. When switching beams within the same cell, the UE should retain the RLC settings of the source beam.

[0723] Beams within the same cell differ only in some of the MAC settings. Therefore, there is no need for information on whether or not to reset and / or reconfigure the MAC when switching beams. In other words, resetting is not necessary, and only the different settings should be reconfigured. It may be decided in advance by standards, etc., that only the different settings should be reconfigured. In beam switching processing within the same cell, the UE should only retain the MAC settings that are the same as those of the source beam.

[0724] Beams within the same cell have different PHY settings, some or all of which are different. Information on whether to reset and / or reconfigure the PHY is required.

[0725] As specific examples of information for enabling communication with the target beam in the above-mentioned specific example (3), the following three items (3-1) to (3-3) are disclosed.

[0726] (3-1) UE identifier in the target beam, for example, C-RNTI or B-RNTI.

[0727] (3-2) Information about the MAC and PHY of the target beam. For example, there are common radio resource settings, MAC main settings, and individual PHY settings. "radioResourceConfigCommon" is used as a parameter for common radio resource settings. "mac-MainConfig" is used as a parameter for MAC main settings. "physicalConfigDedicated" is used as a parameter for individual PHY settings.

[0728] (3-3) Information about SCells in the target beam.

[0729] The information (3-1) to (3-3) described above may be omitted if there is no change from the source beam setting. Alternatively, only the information that has changed from the source beam setting may be notified. This reduces the amount of information.

[0730] In addition to the beam switching instruction, the eNB notifies the UE of information to be used when causing the UE to switch beams, so that the UE that receives the beam switching instruction information can communicate using the target beam.

[0731] The eNB notifies the UE of beam switching related information in order to cause the UE to switch the beam. A method for notifying the beam switching related information will be disclosed.

[0732] The eNB notifies the UE of beam switching related information using the source beam. The beam switching related information is notified before notifying the UE of the beam switching instruction. The beam switching related information may be notified by RRC signaling. A new message may be created for notifying the beam switching related information.

[0733] A message may be provided to notify configuration information for beam measurement (hereinafter sometimes referred to as "beam measurement configuration information"). The beam measurement configuration information may be configuration information for CSI measurement.

[0734] The UE measures the beam using the beam measurement configuration information notified by the eNB. The UE measures the beam included in the beam measurement configuration information. The UE reports the beam measurement results to the eNB. The eNB may also notify the UE of the settings for reporting. The settings may be notified together with the beam measurement configuration information or may be included in the beam measurement configuration information. The eNB receives the beam measurement result report from the UE and determines the beam to use for the UE.

[0735] This paper discloses a method for reporting beam measurement results by a UE to an eNB. As a beam measurement, the received power of a reference signal or discovery signal transmitted for each beam may be measured. Alternatively, the received power may be measured as reception quality. Alternatively, a quantity including interference power and noise power may be measured. For example, the signal to noise ratio (SNR) or the signal to interference plus noise power ratio (SINR) may be measured.

[0736] Conventionally, the measurement results of a cell are reported by RRC signaling. Although the RRC signaling may be used, as described above, the time required for transmitting and receiving the RRC signaling increases.

[0737] Alternatively, the notification may be made by MAC or L1 / L2 signaling, or by using MAC CE, or by mapping to PUCCH and notifying, or by mapping to PUSCH and notifying, or by using CQI reporting or CSI reporting.

[0738] This allows the UE to report the beam measurement results to the eNB earlier, thereby shortening the time from beam measurement to beam switching processing, allowing the eNB to select a more appropriate target beam.

[0739] Figure 28 is a diagram showing an example of a sequence relating to a method for shortening the time required for beam switching processing in embodiment 13. Figure 28 shows a case where switching is performed from a source beam (S-Bm) to a target beam (T-Bm). It shows a case where synchronization is achieved between the source beam and the target beam. It shows a case where scheduling information for radio resources in the target beam is notified in advance using the source beam. The sequence shown in Figure 28 is similar to the sequence shown in Figure 27, so the same steps are given the same step numbers and common explanations will be omitted. Here, the differences will mainly be explained.

[0740] In step STST2601, the eNB notifies the UE of beam measurement configuration information using the source beam. The beam measurement configuration information is notified using RRC signaling.

[0741] In Step ST2602, the UE that has acquired the beam measurement configuration information from the eNB measures the reference signal transmitted for each beam for measurement included in the beam measurement configuration information.

[0742] In Step ST2603, the UE notifies the eNB of the measurement result obtained in Step ST2602 using the source beam. The measurement result may be reported using L1 / L2 signaling. For example, the measurement result may be reported using the PUCCH, which is an uplink control channel. This makes it possible to speed up signaling.

[0743] In Step ST2603, the UE does not need to report all of the measurement results obtained in Step ST2602. It may report only the measurement results of beams for which reporting is triggered according to predetermined criteria. The eNB notifies the UE of these settings together with beam measurement configuration information in Step ST2601.

[0744] The eNB that has received the report of the beam measurement result in Step ST2603 decides whether or not to switch the beam for the UE in Step ST2604. For example, if the reception quality of the source beam deteriorates below a predetermined threshold and a beam with better reception quality than the source beam exists, the eNB decides to switch to the beam with better reception quality.

[0745] In Step ST2605, the eNB that has decided to switch the beam for the UE in Step ST2604 notifies the UE of beam switching related information of the target beam using the source beam. RRC signaling may be used to notify the UE of the beam switching related information.

[0746] In step ST2503, if the eNB has notified the UE of scheduling information for uplink radio resources in the target beam using the source beam, the eNB may notify the UE using the same signaling as the notification.

[0747] In Step ST2606, the eNB notifies the UE of beam switching instruction information to switch to the target beam using the source beam. The eNB uses MAC signaling to notify the UE of the beam switching instruction information. This makes it possible to speed up signaling.

[0748] In Step ST2605, the UE receives the beam switching related information of the target beam, and in Step ST2606, the UE receives the beam switching instruction information and receives the L1 / L2 control signal of the target beam.

[0749] In Step ST2606, the eNB that has transmitted the beam switching instruction information to the UE to switch to the target beam performs scheduling for the UE using the target beam.

[0750] In the sequence shown in FIG. 28, the beam switching related information and the message notifying the beam measurement configuration information are notified separately. As an alternative method, the beam switching related information may be notified by being included in the message notifying the beam measurement configuration information. It is preferable to include the beam switching related information of the beam included in the beam measurement configuration information. In this case, the information is notified to the UE before the eNB determines the target beam. Therefore, the target beam included in the beam switching related information has not yet been determined. Therefore, it is preferable to include information about the beam for beam measurement instead of the target beam. There may be one or more beams for beam measurement. A source beam may also be included.

[0751] Also, for example, if the target beam cannot be determined by the first beam measurement configuration information, the eNB may notify the UE of another beam measurement configuration information again. The beam measurement configuration information may be notified by including beam switching related information in the message notifying the beam measurement configuration information.

[0752] Although the use of RRC signaling for notifying beam switching related information from the eNB to the UE has been disclosed, MAC signaling may also be used as another method. The information may be notified by the MAC CE. A new MAC CE may be provided and may contain information necessary for executing beam switching. The information may also be notified together with beam switching instruction information.

[0753] The information notified by RRC signaling and the information notified by MAC signaling may be separated. For example, information with a large amount of information may be notified by RRC signaling, and information with a small amount of information may be notified by MAC signaling. Configuration information for enabling communication using the target beam in the above-mentioned specific example (3) may be notified by RRC signaling, and the identifier of the target beam in the above-mentioned specific example (1) may be notified by MAC signaling. By notifying information with a small amount of information by MAC signaling, it becomes possible to transmit the beam switching instruction information as well in one transport block.

[0754] When beam switching instruction information is notified by MAC signaling, MAC signaling is performed in one TTI. As described above, RRC signaling is divided into multiple transport blocks and transmitted, so it is performed over multiple TTIs. Furthermore, even when retransmission is taken into consideration, by using MAC signaling, it is possible to shorten the time required to notify beam switching instruction information compared to when using RRC signaling.

[0755] Therefore, by using the method disclosed in this embodiment, when a UE moves between beams that have narrow coverage due to beamforming and switches beams, it is possible to reduce the deterioration of communication quality and communication interruptions caused by signaling times.

[0756] In addition, by using L1 / L2 signaling to report the beam measurement results, the time from beam measurement to beam switching can be shortened, which enables beam switching to a more optimal beam and reduces communication delays and interruptions due to degradation of communication quality and switching failures.

[0757] Embodiment 13 Variation 1 In the thirteenth embodiment, a method for shortening the time required to notify beam switching instruction information is disclosed. In this modification, another method is disclosed.

[0758] The eNB determines one or more beams that are candidates for the target beam for the UE to communicate with. The source beam may be included in the candidate target beams. Hereinafter, the beams that are candidates for the target beam may be referred to as "target candidate beams."

[0759] The eNB decides to activate or deactivate some or all of the target candidate beams.

[0760] The eNB notifies the UE of the activation or deactivation instructions for some or all of the target candidate beams using the source beam, preferably via MAC signaling or L1 / L2 signaling.

[0761] The UE synchronizes with the beam for which activation has been instructed and receives downlink control information (DCI). It may also receive an L1 / L2 control signal. For example, it receives a PDCCH or EPDCCH. The UE receives the PDCCH or EPDCCH and detects DCI addressed to the UE using the C-RNTI or B-RNTI.

[0762] If activation instructions are received for multiple beams, the UE will receive downlink control information for multiple beams.

[0763] The eNB determines the beam to be used for the UE from among the activated beams and switches from the source beam to the determined beam. The eNB communicates with the UE using the switched beam. At this time, the eNB does not need to notify the UE of beam switching instruction information. This is because the UE has received downlink control information for the beam that has been instructed to be activated, and therefore can obtain scheduling information for the communication regardless of which beam the communication is started on.

[0764] This eliminates the need to notify the beam switching instruction information. After determining to switch the beam for the UE, the eNB can immediately communicate with the UE using the switched beam. Therefore, it is possible to shorten the time required for the beam switching process.

[0765] After determining the target candidate beam, the eNB may notify the UE of beam switching related information of the target candidate beam. The method disclosed in the twelfth embodiment can be applied to notify the beam switching related information.

[0766] The target candidate beam is determined as appropriate. The target candidate beam may be determined periodically or in response to a report of the UE's beam measurement results. When the target candidate beam is changed, the UE may be notified again of the beam switching related information of the target candidate beam. Only the beam switching related information of the beam to be changed, deleted, or added may be notified. For the beam to be deleted, only the beam identifier may be notified.

[0767] The beam to be activated or deactivated is determined as needed. The determination of the beam to be activated or deactivated may be performed periodically or based on the UE's beam measurement results. When the beam to be activated or deactivated is changed, the UE may be notified again of the instruction to activate or deactivate the beam. Alternatively, only the beam to be changed may be notified.

[0768] The beam to be used for the UE is determined as needed. The beam to be used for the UE may be determined periodically or in response to a report of the beam measurement results from the UE. This eliminates the need to notify the UE of beam switching instruction information even if the beam to be used is changed.

[0769] 29 and 30 are diagrams showing an example of a sequence relating to a method for shortening the time required for beam switching processing in Variation 1 of Embodiment 13. Figures 29 and 30 are connected at the boundary line BL1. Figures 29 and 30 show a case where a source beam (S-Bm) is switched to a first target beam (T-Bm1). They also show a case where a first target beam (T-Bm1) is switched to a second target beam (T-Bm2). They also show a case where synchronization is not achieved between the source beam and the target beam. They also show a case where scheduling information for radio resources in the target beam is not performed in advance using the source beam. The sequences in Figures 29 and 30 are similar to the sequence shown in Figure 28, so the same step numbers are assigned to the same steps, and common explanations will be omitted. Here, differences will be mainly described.

[0770] The eNB that has received the report of the beam measurement results in Step ST2603 uses the report of the beam measurement results from the UE to determine beams that will be candidate target beams for the UE in Step ST2801. For example, the eNB selects the top two beams whose UE's beam reception quality measurement results are equal to or higher than a predetermined threshold, and determines these three beams, including the source beam, as target candidate beams. The eNB may consider other information in addition to the report of the beam measurement results when determining target candidate beams.

[0771] In Step ST2802, the eNB that has determined a target candidate beam for the UE in Step ST2801 notifies the UE of beam switching related information of the target candidate beam using the source beam. The beam switching related information of the target candidate beam is notified using, for example, RRC signaling.

[0772] In Step ST2820, the eNB determines, from among the target candidate beams, a beam to be activated and / or deactivated for the UE. For this determination, the eNB may use the most recently received report of the beam measurement result from the UE.

[0773] In Step ST2803, the eNB notifies the UE of the beams to be activated and / or deactivated. The beams to be activated and / or deactivated are notified, for example, using MAC signaling. Here, the beams to be activated are the source beam (S-Bm), the first target beam (T-Bm1), and the second target beam (T-Bm2).

[0774] A UE that receives a beam for at least one of activation and deactivation in Step ST2803 synchronizes with the beam to be activated in Steps ST2804, ST2805, and ST2806.

[0775] Furthermore, in steps ST2807, ST2808, and ST2809, the UE receives downlink control information for the beam to be activated. For example, the UE receives EPDCCHs for the source beam, the first target beam, and the second target beam. For this reception, the UE may use the beam switching related information for the target candidate beam acquired in step ST2802.

[0776] In Step ST2810, the eNB decides to switch beams. Specifically, the eNB decides to switch from the source beam to the first target beam. This decision may be made using the most recently received report of the beam measurement result from the UE.

[0777] In Step ST2810, the eNB decides to switch the beam to the first target beam, and in Step ST2811, the eNB transmits scheduling information for the UE to the UE using the first target beam. The scheduling information may include DCI. The DCI includes at least one of downlink scheduling information and uplink scheduling information. Furthermore, downlink data may be transmitted in the same subframe as the downlink scheduling information.

[0778] In Step ST2811, the UE that has received the downlink control information of the first target beam in Step ST2808 acquires the scheduling information transmitted using the first target beam.

[0779] The UE that has acquired the scheduling information of the first target beam in step ST2811 receives downlink data in accordance with the downlink scheduling information if the scheduling information includes downlink scheduling information.

[0780] If the scheduling information of the first target beam that has been acquired in Step ST2811 includes uplink scheduling information, the UE transmits uplink data to the eNB in accordance with the uplink scheduling information in Step ST2812. Alternatively, the UE may transmit a scheduling request or a buffer status report (BSR).

[0781] In this way, in step ST2813, the UE and the eNB are able to communicate using the first target beam.

[0782] 29 and 30 further disclose a method for switching the target beam. In step ST2813, communication with the UE is performed using the first target beam. Therefore, the first target beam becomes the source beam for the UE, but will continue to be referred to as the first target beam here.

[0783] In Step ST2814, the UE performs beam measurement. For this beam measurement, the UE uses the measurement configuration of the beam included in the beam measurement configuration information notified in Step ST2601. Although not shown in the figure, if a new measurement configuration of a beam is notified using the first target beam, the UE may perform measurement using the measurement configuration of the beam.

[0784] The UE that has measured the beam in Step ST2814 reports the beam measurement results to the eNB in Step ST2815. The reporting is performed using the first target beam. The reporting may be performed using L1 / L2 signaling, which can speed up signaling.

[0785] In Step ST2816, the eNB that has received the report of the beam measurement results in Step ST2815 decides to switch the beam. The beam is switched from among the beams to be activated and notified to the UE in Step ST2803.

[0786] In Step ST2817, the eNB that has decided to switch the beam to the second target beam in Step ST2816 transmits scheduling information for the UE to the UE using the second target beam. The scheduling information includes DCI, etc. The DCI includes at least one of downlink scheduling information and uplink scheduling information. Furthermore, downlink data may be transmitted in the same subframe as the downlink scheduling information.

[0787] In step ST2817, the UE that has received the downlink control information of the second target beam in step ST2809 acquires the scheduling information transmitted using the second target beam.

[0788] The UE that has acquired the scheduling information of the second target beam in ST2817 receives downlink data in accordance with the downlink scheduling information if the scheduling information includes downlink scheduling information.

[0789] If the scheduling information of the second target beam that has been acquired in Step ST2817 includes uplink scheduling information, the UE transmits uplink data to the eNB in accordance with the uplink scheduling information in Step ST2818. Alternatively, the UE may transmit a scheduling request or a buffer status report (BSR).

[0790] In this way, in step ST2819, the UE and the eNB are able to communicate using the second target beam.

[0791] By doing so, it becomes possible to switch beams without notifying the UE of beam switching instruction information.

[0792] Therefore, it is possible to shorten the time from when the eNB decides to switch beams to when the UE switches to the decided beam and becomes able to communicate.

[0793] This makes it possible to switch to a more optimal beam in a short time, even in situations where beam switching occurs frequently, thereby reducing communication quality degradation and communication delays and interruptions due to switching failures.

[0794] In addition, by notifying the UE of candidate beams for the target beam, the UE can synchronize and limit the number of beams with which it receives control information. Therefore, the method disclosed above can reduce the processing load on the UE, thereby enabling lower power consumption, smaller size, lighter weight, and lower cost.

[0795] In the examples disclosed above, the beams to be activated or deactivated are some or all of the target candidate beams.

[0796] Alternatively, the beam to be activated may be the same as the target candidate beam, in which case the process of determining the beam to be activated in the eNB is not required.

[0797] In this case, notification of switching-related information for the target candidate beam may also be notification of activation of the target candidate beam.

[0798] The UE regards the beam notified in the switching-related information of the target candidate beam as an activated beam, synchronizes with the beam, and receives downlink control information.

[0799] For example, the processes of steps ST2820 and ST2803 in FIGS. 29 and 30 are omitted.

[0800] This makes it possible to reduce the amount of signaling from the eNB to the UE, and also to simplify control between the eNB and the UE.

[0801] The UE may set the maximum number of receivable beams. The maximum number of receivable beams may be determined according to the UE capability. Alternatively, the maximum number of receivable beams may be set as a parameter of the UE capability.

[0802] It is advisable for the UE to notify the eNB in advance of the maximum number of beams that the UE can receive. Alternatively, the UE may notify the eNB of its capabilities.

[0803] By doing this, the eNB can set the number of target candidate beams or beams to be activated to be less than or equal to the maximum number of beams that the UE can receive.

[0804] The downlink control information of a beam may include scheduling information of other beams, for example, the downlink control information of a source beam may include scheduling information of a target beam.

[0805] For example, in Figures 29 and 30, in step ST2811, the eNB notifies the downlink scheduling information or uplink scheduling information of the first target beam using the source beam. In step ST2811, the UE receives the downlink scheduling information or uplink scheduling information of the first target beam using the source beam. If the scheduling information is of the first target beam, the UE receives the radio resources of the first target beam in accordance with the downlink scheduling information. Alternatively, if the scheduling information is of the first target beam, the UE transmits the uplink scheduling information using the radio resources of the first target beam in accordance with the uplink scheduling information.

[0806] This allows for flexible use of multiple beams if the UE is capable of using multiple beams.

[0807] For example, it is possible to use different beams for transmitting control information and for data communication. This allows for operation in which control information is transmitted using one of multiple beams and data communication is performed using another of multiple beams. The eNB can use each beam taking into consideration the coverage, load, and radio wave propagation conditions of each beam. For example, it is preferable to transmit control information using a beam with wide coverage and data communication using a beam with narrow coverage. This allows for operation of beams suited to the characteristics of each beam.

[0808] Embodiment 13 Variation 2 If a beam switching process occurs when the UE moves between beams while communication has not yet been successful in the source beam, the question arises as to how to handle data that has not yet been successfully delivered.

[0809] This modification discloses a method for handling unsuccessfully delivered data during beam switching processing. Data that was unsuccessfully delivered using a source beam is transmitted using a target beam. This may be done for both uplink and downlink.

[0810] In PDCP, data that was not successfully transmitted using the source beam is discarded and retransmitted from the target cell. This makes it possible to reduce data loss when switching beams.

[0811] When a UE moves between narrow-coverage beams formed by beamforming technology, beam switching may occur frequently. In such cases, using the method disclosed above results in repeated retransmission of PDCP data. In some cases, the same PDCP data may be retransmitted multiple times. This causes problems such as delays in data communication and failure to meet the required QoS. A method for solving such problems is disclosed.

[0812] When switching beams, the data being processed by HARQ on the source beam is retransmitted on the target beam. When the UE receives a beam movement instruction, it retransmits the data being processed by HARQ on the source beam on the target beam. When the eNB sends a beam movement instruction to the UE, it retransmits the data being processed by HARQ on the source beam on the target beam.

[0813] As specific examples of methods for retransmitting data undergoing HARQ processing in a source beam using a target beam, the following two methods (1) and (2) are disclosed.

[0814] (1) The target beam is used from the first transmission of data during HARQ processing.

[0815] (2) HARQ is performed using the source beam and the target beam.

[0816] A specific example of a method for using a target beam from the first transmission of data during HARQ processing in the above-mentioned specific example (1) will be disclosed. Figure 31 is a diagram showing an example of a sequence related to a method for using a target beam from the first transmission of data during HARQ processing in a second modification of the thirteenth embodiment. This shows a method performed by a UE from a scheduling request (SR) when transmitting uplink data using a target beam.

[0817] In step ST2901, the UE receives downlink data from the eNB via the source beam.

[0818] In step ST2902, the UE transmits uplink data to the eNB using the source beam.

[0819] In Step ST2903, the eNB decides to switch the beam for the UE.

[0820] In step ST2904, the eNB provides unreached downlink data information, which is information about downlink data undergoing HARQ processing in the source beam, to the target beam. If the source beam and the target beam are the same eNB, this is performed within the same eNB. In this case, the information about the downlink data undergoing HARQ processing may be applied from the source beam to the target beam.

[0821] The information regarding the downlink data undergoing HARQ processing in the source beam may be information that enables identification of the data to be transmitted in the target beam.

[0822] In Step ST2905, the eNB notifies the UE of beam switching instruction information using the source beam.

[0823] In Step ST2906, the UE that has received the beam switching instruction information synchronizes with the target beam.

[0824] In Step ST2907, the eNB performs downlink scheduling to the UE to transmit downlink data that was undergoing HARQ processing in the source beam using the target beam from the initial transmission. At this time, the eNB may use the information regarding the downlink data that was undergoing HARQ processing in the source beam received in Step ST2904. The notification may use the target beam.

[0825] In step ST2907, the eNB that has notified the UE of the scheduling information in the target beam for the initial data transmission transmits downlink data being HARQ processed in the source beam to the UE using the target beam in accordance with the scheduling information.

[0826] In Step ST2908, the UE that has received the downlink scheduling information in Step ST2907 receives, in accordance with the scheduling information, downlink data being HARQ processed in the source beam in the target beam.

[0827] By doing this, it becomes possible to communicate downlink data undergoing HARQ processing in the source beam using the target beam.

[0828] Next, the uplink data will be described. In Step ST2909, the UE that has received the beam switching command information in Step ST2905 transmits a scheduling request (SR) to the eNB using the target beam. The SR is transmitted to transmit the uplink data currently being HARQ processed in the source beam.

[0829] The eNB that has received the SR in Step ST2909 determines uplink scheduling, and in Step ST2910 notifies the UE of the uplink scheduling information using the target beam.

[0830] In Step ST2911, the UE that has received the uplink scheduling information in Step ST2910 transmits UL data to the eNB in accordance with the scheduling information. Transmission begins with the first transmission of uplink data currently being HARQ processed in the source beam.

[0831] By doing so, it becomes possible to communicate data undergoing HARQ processing in the source beam using the target beam. Therefore, it is not necessary to start with retransmission of PDCP data in the target beam. This makes it possible to reduce the occurrence of situations in which PDCP data retransmission is repeated many times even when beam switching occurs frequently.

[0832] Another method will be disclosed. Figure 32 is a diagram showing another example of a sequence relating to a method for performing an initial transmission of data during HARQ processing using a target beam in Variant 2 of Embodiment 13. Figure 32 shows a sequence of a method for making SR transmission unnecessary for a UE when performing uplink data transmission using a target beam. The sequence shown in Figure 32 is similar to the sequence shown in Figure 31, so the same step numbers are assigned to the same steps and common explanations will be omitted. Here, differences will be mainly explained. As the downlink data is the same as in Figure 31, explanations will be omitted and only uplink data will be explained.

[0833] In Step ST2903, the eNB that has decided to switch the beam for the UE provides information about the uplink data undergoing HARQ processing in the source beam to the target beam in Step ST3001. If the source beam and the target beam are the same eNB, this is performed within the same eNB. In this case, the information about the uplink data undergoing HARQ processing may be applied from the source beam to the target beam.

[0834] The information regarding the uplink data undergoing HARQ processing in the source beam may be information that enables identification of the data to be transmitted in the target beam.

[0835] The eNB that transmitted the beam switching instruction information to the UE in Step ST2905 performs uplink scheduling in Step ST3002 to have the UE transmit the uplink data that was undergoing HARQ processing in the source beam to the UE using the target beam from the initial transmission. At this time, the eNB may use the information regarding the uplink data that was undergoing HARQ processing in the source beam received in Step ST3001. The notification may use the target beam.

[0836] In step ST3002, the UE that has received the scheduling information for the target beam for the initial transmission of uplink data transmits the uplink data being HARQ processed in the source beam to the eNB using the target beam in accordance with the scheduling information, starting from the initial transmission.

[0837] By doing this, it is possible to communicate uplink data undergoing HARQ processing in the source beam using the target beam without transmitting an SR from the UE in the target beam.

[0838] Since the UE does not need to transmit SR, the power consumption of the UE can be reduced, and the time required from beam switching to transmission of uplink data by the UE can be shortened.

[0839] A specific example of a method for performing the HARQ of the above-mentioned specific example (2) using a source beam and a target beam will be disclosed. Figure 33 is a diagram showing an example of a sequence relating to a method for performing retransmission of data during HARQ processing using a target beam in Variation 2 of Embodiment 13. Figure 33 shows a sequence of a method for eliminating the need for a UE to transmit an SR when transmitting uplink data using a target beam. The sequence shown in Figure 33 is similar to the sequence shown in Figure 32, so the same step numbers are assigned to the same steps and common explanations will be omitted. Here, the differences will mainly be described.

[0840] The UE that has failed to receive downlink data from the eNB in Step ST2901 transmits a Nack, which is delivery failure (delivery unsuccessful) information, to the eNB using the source beam in Step ST3101 through HARQ processing.

[0841] In Step ST2903, the eNB decides to switch the beam for the UE.

[0842] In step ST3103, the eNB provides unreached downlink data information, which is information about downlink data undergoing HARQ processing in the source beam, to the target beam. If the source beam and the target beam are the same eNB, this is performed within the same eNB. In this case, the information about the downlink data undergoing HARQ processing may be applied from the source beam to the target beam.

[0843] The information about the downlink data undergoing HARQ processing in the source beam may be information that can identify the data to be transmitted in the target beam. In this case, since NACK has been received from the UE, the information may be information that can identify the data to be retransmitted.

[0844] In Step ST2905, the eNB notifies the UE of beam switching instruction information using the source beam.

[0845] In Step ST2906, the UE that has received the beam switching instruction information synchronizes with the target beam.

[0846] In Step ST3105, the eNB performs downlink scheduling for the UE to transmit the downlink data that was undergoing HARQ processing in the source beam using the target beam from the retransmission. At this time, the eNB may use the information regarding the downlink data that was undergoing HARQ processing in the source beam that was received in Step ST3103. The notification may use the target beam.

[0847] In step ST3105, the eNB that has notified the UE of scheduling information for retransmission in the target beam for the initial transmission of data transmits retransmission data of downlink data being HARQ processed in the source beam to the UE using the target beam in accordance with the scheduling information.

[0848] In step ST3106, the UE that has received the downlink scheduling information in step ST3105 receives, in accordance with the scheduling information, retransmission data of downlink data being HARQ processed in the source beam in the target beam.

[0849] By doing this, it becomes possible to communicate downlink data undergoing HARQ processing in the source beam using the target beam.

[0850] In Figure 33, the case where the eNB transmits the first retransmission data of downlink data using the target beam has been disclosed, but this is not limited to the first time. The same can be done for any number of times. If NACK continues in the source beam, the retransmission data at the time beam switching is executed is transmitted using the target beam.

[0851] The eNB that has failed to receive uplink data from the UE in Step ST2902 transmits a Nack, which is delivery failure (delivery unsuccessful) information, to the UE through HARQ processing in Step ST3102. At this time, the eNB notifies the UE of uplink scheduling information for retransmission data.

[0852] In Step ST2903, the eNB decides to switch the beam for the UE.

[0853] In Step ST2903, the eNB that has decided to switch the beam for the UE provides, in Step ST3104, unaccomplished uplink data information, which is information about uplink data undergoing HARQ processing in the source beam, to the target beam. If the source beam and the target beam are the same eNB, this is performed within the same eNB. In this case, the information about the uplink data undergoing HARQ processing may be applied from the source beam to the target beam.

[0854] The information about the uplink data undergoing HARQ processing in the source beam may be information that can identify the data to be transmitted in the target beam. Here, since NACK is being transmitted to the UE, it is preferable to include information that can identify scheduling information for the uplink retransmission data.

[0855] In step ST2905, the UE receives beam switching instruction information from the eNB and, in step ST3107, retransmits uplink data to the eNB using the target beam in accordance with the scheduling information for retransmission of uplink data received using the source beam in step ST3102.

[0856] The uplink scheduling information for retransmission data that the eNB notifies to the UE using the source beam in Step ST3102 may be the uplink scheduling information for retransmission data when the target beam is used.

[0857] 33, in Step ST3102, the eNB transmits NACK to the UE using a source beam and notifies the UE of uplink scheduling information for retransmission data. As another method, the uplink scheduling information for retransmission data may be notified using a target beam.

[0858] The eNB, which has transmitted the beam switching instruction information to the UE in Step ST2905, transmits uplink scheduling information for the retransmission data to the UE using the target beam in order to cause the UE to transmit the retransmission data using the target beam.

[0859] At this time, the eNB may use the information regarding the uplink data undergoing HARQ processing in the source beam received in step ST3104.

[0860] In step ST3107, the UE that has received the uplink scheduling information for the uplink retransmission data transmits, to the eNB, using the target beam, starting with the retransmission of the uplink data currently being HARQ processed in the source beam, in accordance with the scheduling information.

[0861] By doing this, if the reception quality of the source beam deteriorates, it becomes possible to communicate by retransmission using the target beam.

[0862] Therefore, it is possible to improve communication quality even earlier than in a method in which communication is performed using a target beam from the first transmission.

[0863] Another method will be disclosed. Figure 34 is a diagram showing an example of a sequence relating to a method performed using a target beam from successful delivery (Ack) / failure to deliver (Nack) of data during HARQ processing in a second variant of the thirteenth embodiment. Figure 34 shows a sequence of a method that allows the UE to avoid transmitting an SR when transmitting uplink data using a target beam. The sequence shown in Figure 34 is similar to the sequence shown in Figure 33, so the same step numbers are assigned to the same steps and common explanations will be omitted. Here, the differences will mainly be explained.

[0864] In Step ST2901, the eNB transmits downlink data to the UE. It is assumed that the UE fails to receive the downlink data.

[0865] In Step ST2903, the eNB decides to switch beams for the UE. In Step ST3201, the eNB provides unreached downlink data information, which is information about downlink data undergoing HARQ processing in the source beam, to the target beam. If the source beam and the target beam are the same eNB, this is performed within the same eNB. In this case, the information about the downlink data undergoing HARQ processing may be applied from the source beam to the target beam.

[0866] The information on the downlink data undergoing HARQ processing in the source beam may be information that can identify the data to be transmitted in the target beam. If a Nack is subsequently received from the UE, the information may be information that can identify the data to be retransmitted.

[0867] A UE that fails to receive downlink data from the eNB in step ST2901 needs to transmit an Ack / Nack to the eNB at a predetermined timing using HARQ processing. However, here, it is assumed that the UE receives beam switching instruction information from the eNB in step ST2905 before transmitting the Ack / Nack.

[0868] In Step ST2906, the UE that has received the beam switching instruction information synchronizes with the target beam.

[0869] In Step ST3203, the UE transmits a Nack to the eNB using the target beam. If the UE has successfully received the downlink data in Step ST2901, it transmits an Ack. Here, the reception has failed, i.e., the delivery has failed, so it transmits a Nack. The timing of transmitting the Ack / Nack should be a predetermined timing that is determined by the timing of receiving the downlink data in the source beam.

[0870] The eNB derives the timing at which an Ack / Nack is transmitted, using information about downlink data undergoing HARQ processing in the source beam received in Step ST3201. In Step ST3203, the eNB receives a Nack from the UE at the derived timing.

[0871] In Step ST3204, the eNB that has received Nack from the UE in Step ST3203 performs downlink scheduling for the UE using the target beam to transmit, from retransmission, downlink data that was undergoing HARQ processing in the source beam using the target beam. At this time, the eNB may use the information regarding the downlink data that was undergoing HARQ processing in the source beam that was received in Step ST3201.

[0872] In step ST3204, the eNB that has notified the UE of scheduling information for retransmission in the target beam transmits retransmission data of downlink data being HARQ processed in the source beam to the UE using the target beam in accordance with the scheduling information.

[0873] In Step ST3205, the UE that has received the downlink scheduling information in Step ST3204 receives, in accordance with the scheduling information, retransmission data of downlink data being HARQ processed in the source beam in the target beam.

[0874] By doing this, it becomes possible to communicate downlink data undergoing HARQ processing in the source beam using the target beam.

[0875] The following describes uplink data. In Step ST2902, the eNB fails to receive the uplink data from the UE.

[0876] In Step ST2903, the eNB decides to switch the beam for the UE.

[0877] In Step ST2903, the eNB that has decided to switch the beam for the UE provides, in Step ST3202, unaccomplished uplink data information, which is information about uplink data undergoing HARQ processing in the source beam, to the target beam. If the source beam and the target beam are the same eNB, this is performed within the same eNB. In this case, the information about the uplink data undergoing HARQ processing may be applied from the source beam to the target beam.

[0878] The information on the uplink data undergoing HARQ processing in the source beam may be information that can identify the data to be transmitted in the target beam. When a NACK is subsequently transmitted to the UE, the information may be information that can identify the data to be retransmitted.

[0879] An eNB that fails to receive uplink data from the UE in step ST2902 needs to transmit an Ack / Nack to the UE at any timing using HARQ processing, but here it is assumed that the eNB transmitted beam switching instruction information to the UE in step ST2905 before transmitting the Ack / Nack.

[0880] In Step ST2906, the UE that has received the beam switching instruction information synchronizes with the target beam.

[0881] In Step ST3206, the eNB transmits a Nack to the UE using the target beam. If the uplink data is successfully received in Step ST2902, the eNB transmits an Ack. Here, the reception has failed, that is, the delivery has failed, so the eNB transmits a Nack. The timing of transmitting the Ack / Nack may be any timing.

[0882] In Step ST3206, the eNB transmits, to the UE, uplink scheduling information, together with NACK, for causing the UE to transmit, using the target beam, the uplink data that was undergoing HARQ processing in the source beam from the retransmission. At this time, the eNB may use the information regarding the uplink data that was undergoing HARQ processing in the source beam, received in Step ST3202.

[0883] Although it has been disclosed that uplink scheduling information is transmitted together with NACK, it is also possible to transmit only uplink scheduling information. NACK may also be generated by the uplink scheduling information. It is preferable that the scheduling information includes information indicating that it is a retransmission.

[0884] In step ST2905, the UE receives beam switching instruction information from the eNB, and in step ST3207, retransmits uplink data to the eNB using the target beam in accordance with the scheduling information for uplink data retransmission received using the target beam in step ST3206.

[0885] By doing so, when the reception quality of the source beam deteriorates, it becomes possible to use the target beam to communicate starting from the transmission of Ack / Nack.

[0886] Therefore, it is possible to improve communication quality even earlier than in a method in which communication is performed using a target beam from the first transmission.

[0887] By using the method disclosed in this modification, it is possible to transmit data that has not been successfully delivered using a source beam using a target beam.

[0888] By appropriately combining the methods disclosed above, it becomes possible to use a target beam for initial transmission, retransmission, or Ack / Nack transmission.

[0889] By appropriately combining these methods depending on the timing of beam switching, it is possible to switch beams at the optimal timing depending on the radio wave environment, etc.

[0890] Therefore, even in situations where beam switching occurs frequently, it is possible to switch to a more optimal beam at the appropriate time, thereby reducing communication quality degradation and communication delays and interruptions due to switching failures.

[0891] In the twelfth embodiment to the thirteenth embodiment, the beam switching has been disclosed. As the beam switching, it is preferable to apply the methods disclosed in the above-mentioned embodiments in appropriate combination to the beam switching between beams in the same cell, between beams in different cells, or between beams in different eNBs. This makes it possible to reduce the deterioration of communication quality due to the beam switching process and the communication delay and communication interruption due to the switching failure.

[0892] 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. Furthermore, any component of the embodiments and their modifications can be modified or omitted as appropriate.

[0893] Although the present invention has been described in detail, the above description is illustrative in all respects and does not limit the present invention, and it is understood that countless variations not illustrated can be assumed without departing from the scope of the present invention. [Explanation of symbols]

[0894] 901,903 MeNB, 902,904 SeNB, 905,906,2402 UE, 907,909,912,914 MAC, 908,910,913,915 RLC, 911,916 PDCP, 2401 Multi-element antenna, 2403,2404,2405 Coverage.

Claims

1. a user device; A communication system including a first base station and a second base station, each capable of forming a plurality of beams by beamforming, and each communicating with a user device by switching between the plurality of beams, When the user equipment performs beam switching from a first beam formed by the first base station to a second beam formed by the second base station, setting information regarding a random access process in the second beam is transmitted to the user equipment. Communication system.

2. a user device; A base station in a communication system including a first base station and a second base station, each capable of forming a plurality of beams by beamforming, and each communicating with a user device by switching between the plurality of beams, When the user equipment performs beam switching from a first beam formed by the first base station to a second beam formed by the second base station, transmitting setting information related to a random access process in the second beam to the user equipment; Base station.

3. a user device; A user device in a communication system including a first base station and a second base station, each capable of forming a plurality of beams by beamforming, the first base station and the second base station communicating with the user device by switching between the plurality of beams, receiving setting information regarding a random access process in the second beam when performing beam switching from a first beam formed by the first base station to a second beam formed by the second base station; User equipment.

Images