User device, base station, and communication system

Abstract

To provide a highly reliable communication system.SOLUTION: A communication system includes a user device. The communication system also includes a base station. The base station wirelessly communicates with the user device. The user device transmits a physical uplink control channel for a scheduling request in beam failure recovery. The user device transmits a PUCCH, which is a physical uplink control channel for an SR, which is a scheduling request in BFR, which is beam failure recovery.SELECTED DRAWING: Figure 18

Description

[Technical field]

[0001] The present invention relates to a user equipment, a base station, and a communication system. [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 wireless sections and System Architecture Evolution (SAE) for the overall system configuration including a core network and a wireless access network (hereinafter collectively referred to as a network) (for example, Non-Patent Documents 1 to 5). This communication method is also called a 3.9G (3.9 Generation) system.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0037] In the LTE-A system, in order to support wider frequency bandwidths (transmission bandwidths) up to 100 MHz, Carrier Aggregation (CA) is being considered, which aggregates two or more Component Carriers (CCs) (also called "aggregation"). 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 a Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC). In the uplink, the carrier corresponding to the PCell is the Uplink Primary Component Carrier (UL PCC).

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

[0040] A set of serving cells, which includes one PCell and one or more SCells, is configured for one UE.

[0041] New technologies for LTE-A include a technology that supports wider bandwidth (Wider Bandwidth Extension) and a 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] In addition, in 3GPP, in order to handle the huge traffic in the future, the use of small eNBs (hereinafter sometimes referred to as "small-scale base station devices") that configure small cells is being considered. For example, technologies are being considered that improve frequency utilization efficiency and increase communication capacity by installing many small eNBs and configuring many small cells. Specifically, there is dual connectivity (abbreviated as DC) in which a UE connects to two eNBs to communicate. DC is described in Non-Patent Document 1.

[0043] Of the eNBs performing 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)."

[0044] Mobile network traffic is on the rise, and communication speeds are also getting faster. Once LTE and LTE-A are fully operational, communication speeds are expected to become even faster.

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

[0046] Compared to the LTE system, the 5G wireless access system requires a system capacity that is 1,000 times greater, a data transmission speed that is 100 times greater, data processing delay that is one-tenth (1 / 10), and 100 times the number of simultaneous connections of communication terminals, while also achieving further reductions in power consumption and reductions in equipment costs.

[0047] In order to meet such demands, 3GPP is currently working on 5G standards as Release 15 (see Non-Patent Documents 6 to 16). 5G wireless section technology is called "New Radio Access Technology" ("New Radio" is abbreviated as "NR"), and several new technologies are being considered (see Non-Patent Documents 11 to 16). For example, a direct SCG setting notification from a secondary base station to a UE, a beam failure recovery request using a PUCCH, etc. are being considered (see Non-Patent Documents 17 and 18). [Prior art documents] [Non-patent literature]

[0048] [Non-Patent Document 1] 3GPP TS 36.300 V14.3.0

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[0049] In NR, DC using eNB and gNB is being discussed. In addition, low-latency and high-reliability communication is required in NR. In NR, it has become possible for a secondary gNB (hereinafter sometimes referred to as SgNB) to directly notify the UE of the SCG setting. However, due to an SCG failure in DC and due to signaling between the base station and the UE in various DC procedures, there is a possibility that discrepancies in the SCG setting may occur between the UE, MeNB, and SgNB. As a result, malfunctions occur in communication systems using NR, and reliability in communication cannot be ensured.

[0050] In addition, when a beam failure occurs between a base station and a UE, the UE can transmit a beam failure recovery request signaling to the base station using PUCCH. However, since the details of the beam failure recovery request signaling are not disclosed, the communication system cannot notify the signaling using PUCCH. Therefore, a problem occurs in that a quick recovery from a beam failure cannot be achieved between the UE and the base station.

[0051] The above describes the issues when using NR, but similar issues can arise even when NR is not used.

[0052] An object of the present invention is to provide a highly reliable communication system. [Means for solving the problem]

[0053] According to the present invention, for example, a user equipment and a base station that wirelessly communicates with the user equipment are provided, and the user equipment transmits a physical uplink control channel (PUCCH) for a scheduling request (SR) in beam failure recovery (BFR). Effect of the Invention

[0054] According to the present invention, a highly reliable communication system can be provided.

[0055] The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0056] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Diagram 2] 1 is a block diagram showing the overall configuration of a communication system 200 based on the LTE standard that is being discussed in 3GPP. [Diagram 3] FIG. 3 is a block diagram showing a configuration of a mobile terminal 202 shown in FIG. [Figure 4] FIG. 3 is a block diagram showing a configuration of a base station 203 shown in FIG. [Diagram 5] FIG. 2 is a block diagram showing the configuration of an MME. [Figure 6] 1 is a flowchart showing an overview of operations from cell search to standby performed by a communication terminal (UE) in an LTE communication system. [Figure 7] A diagram showing the concept of a cell configuration when macro eNBs and small eNBs are mixed. [Figure 8] FIG. 11 is a diagram showing an example of a sequence in which an MN acquires the latest SCG setting when an SCG fails, in accordance with the first embodiment. [Figure 9] A figure showing an example of a sequence in which an MN acquires the latest SCG settings when an SN is released during SN activation, in accordance with embodiment 1. [Figure 10] A figure showing an example of a sequence in which an MN acquires the latest SCG setting when an MN activates and releases an SN, in accordance with embodiment 1. [Figure 11]FIG. 11 is a diagram showing an example of a sequence in which an MN acquires the latest SCG setting when an MN starts changing an SN, in accordance with the first embodiment. [Figure 12] FIG. 11 is a diagram showing an example of a sequence in which an MN acquires the latest SCG settings when an SN is changed upon SN activation, in accordance with the first embodiment. [Figure 13] A figure showing an example of a sequence in which a target MN acquires the latest SCG setting in an inter-MN handover that does not involve SN switching, in accordance with the first embodiment. [Figure 14] A figure showing an example of a sequence in which a target MN acquires the latest SCG setting in an inter-MN handover that does not involve SN switching, in accordance with the first embodiment. [Figure 15] FIG. 11 is a diagram showing an example of a sequence in which a source MN acquires the latest SCG configuration in switching from an MN to an eNB, in accordance with the first embodiment. [Figure 16] FIG. 11 is a diagram showing an example of a sequence in which a source MN acquires the latest SCG configuration in switching from an MN to an eNB, in accordance with the first embodiment. [Figure 17] FIG. 11 is a sequence diagram showing an example of an operation of autonomously switching a base station to which SCG failure information is notified when an SCG failure occurs, according to the second embodiment. [Figure 18] FIG. 11 is a diagram illustrating an example of a format of a PUCCH for BFRQ in accordance with a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Embodiment 1 Fig. 2 is a block diagram showing the overall configuration of an LTE-based communication system 200 being discussed in 3GPP. Fig. 2 will now be described. The radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 202, which is a communication terminal device, is capable of wireless communication with a base station device (hereinafter referred to as "base station (E-UTRAN NodeB: eNB)") 203, and transmits and receives signals via wireless communication.

[0058] Here, the term "communication terminal device" includes not only mobile terminal devices such as mobile mobile phone terminal devices, but also stationary devices such as sensors. In the following description, the "communication terminal device" may be simply referred to as a "communication terminal."

[0059] If control protocols for mobile terminals 202, such as RRC (Radio Resource Control), and user planes (hereinafter sometimes referred to as U-Planes), such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate in a base station 203, E-UTRAN is composed of one or more base stations 203.

[0060] A control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs broadcast, paging, RRC connection management, etc. The states of the base station 203 and the mobile terminal 202 in RRC include RRC_IDLE and RRC_CONNECTED.

[0061] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell re-selection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can transmit and receive data with the network. In addition, in RRC_CONNECTED, handover (HO), measurement of neighbor cells, etc. are performed.

[0062] The base station 203 is classified into an eNB 207 and a Home-eNB 206. The communication system 200 includes an eNB group 203-1 including a plurality of eNBs 207, and a Home-eNB group 203-2 including a plurality of Home-eNBs 206. A system including an EPC (Evolved Packet Core) which is a core network and an E-UTRAN 201 which is a radio access network is called an EPS (Evolved Packet System). The EPC which is a core network and the E-UTRAN 201 which is a radio access network may be collectively called a "network."

[0063] The eNB207 is connected to a Mobility Management Entity (MME), or a Serving Gateway (S-GW), or an MME / S-GW unit (hereinafter sometimes referred to as an "MME unit") 204 including an MME and an S-GW via an S1 interface, and control information is communicated between the eNB207 and the MME unit 204. A plurality of MME units 204 may be connected to one eNB207. The eNBs 207 are connected to each other via an X2 interface, and control information is communicated between the eNBs 207.

[0064] The Home-eNB 206 is connected to the MME unit 204 via an S1 interface, and control information is communicated between the Home-eNB 206 and the MME unit 204. A plurality of Home-eNBs 206 are connected to one MME unit 204. Alternatively, the Home-eNB 206 is connected to the MME unit 204 via a Home-eNB GateWay (HeNBGW) 205. The Home-eNB 206 and the HeNBGW 205 are connected to each other via an S1 interface, and the HeNBGW 205 and the MME unit 204 are connected to each other via the S1 interface.

[0065] 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.

[0066] 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.

[0067] Furthermore, 3GPP is considering the following configuration. The X2 interface between Home-eNBs 206 is supported. That is, the Home-eNBs 206 are connected via the X2 interface, and control information is communicated between the Home-eNBs 206. From the MME unit 204, the HeNBGW 205 appears as the Home-eNB 206. From the Home-eNB 206, the HeNBGW 205 appears as the MME unit 204.

[0068] In either case where the Home-eNB 206 is connected to the MME unit 204 via the HeNBGW 205 or where the Home-eNB 206 is directly connected to the MME unit 204, the interface between the Home-eNB 206 and the MME unit 204 is the same, that is, the S1 interface.

[0069] The base station 203 may configure one cell or multiple cells. Each cell has a predetermined range as a coverage area in which communication with the mobile terminal 202 is possible, and performs wireless communication with the mobile terminal 202 within the coverage area. When one base station 203 configures multiple cells, each cell is configured to be able to communicate with the mobile terminal 202.

[0070] FIG. 3 is a block diagram showing the configuration of the mobile terminal 202 shown in FIG. 2. The transmission process of the mobile terminal 202 shown in FIG. 3 will be described. First, the control data from the protocol processing unit 301 and the user data from the application unit 302 are stored in the transmission data buffer unit 303. The data stored in the transmission data buffer unit 303 is passed to the encoder unit 304, where encoding such as error correction is performed. There may be data that is directly output from the transmission data buffer unit 303 to the modulation unit 305 without being encoded. The data that has been encoded by the encoder unit 304 is modulated by the modulation unit 305. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 306, where it is converted into a radio transmission frequency. Thereafter, a transmission signal is transmitted from the antenna 307 to the base station 203.

[0071] Moreover, the receiving process of the mobile terminal 202 is executed as follows. A radio signal from the base station 203 is received by the antenna 307. The received signal is converted from a radio receiving frequency to a baseband signal by the frequency conversion unit 306, and demodulated by the demodulation unit 308. The demodulated data is passed to the decoder unit 309, where decoding such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 301, and the user data is passed to the application unit 302. A series of processes of the mobile terminal 202 is controlled by the control unit 310. Therefore, although the control unit 310 is omitted in FIG. 3, it is connected to each of the units 301 to 309.

[0072] Fig. 4 is a block diagram showing the configuration of the base station 203 shown in Fig. 2. The transmission process of the base station 203 shown in Fig. 4 will be described. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (the MME unit 204, etc.), the HeNBGW 205, etc. The other base station communication unit 402 transmits and receives data with other base stations. The EPC communication unit 401 and the other base station communication unit 402 each exchange information with a protocol processing unit 403. The control data from the protocol processing unit 403, and the user data and control data from the EPC communication unit 401 and the other base station communication unit 402 are stored in a transmission data buffer unit 404.

[0073] The data stored in the transmission data buffer unit 404 is passed to the encoder unit 405, where it is subjected to encoding processing such as error correction. Some data may be output directly from the transmission data buffer unit 404 to the modulator unit 406 without being encoded. The encoded data is modulated in the modulator unit 406. The modulated data is converted into a baseband signal, and then output to the frequency converter unit 407, where it is converted into a radio transmission frequency. The transmission signal is then transmitted from the antenna 408 to one or more mobile terminals 202.

[0074] Moreover, the reception process of the base station 203 is executed as follows. A radio signal from one or more mobile terminals 202 is received by an antenna 408. The received signal is converted from a radio reception frequency to a baseband signal by a frequency conversion unit 407, and demodulated by a demodulation unit 409. The demodulated data is passed to a decoder unit 410, where a decoding process such as error correction is performed. Of the decoded data, the control data is passed to a protocol processing unit 403 or an EPC communication unit 401 or an other base station communication unit 402, and the user data is passed to the EPC communication unit 401 and the other base station communication unit 402. A series of processes of the base station 203 is controlled by a control unit 411. Therefore, although the control unit 411 is omitted in FIG. 4, it is connected to each unit 401 to 410.

[0075] FIG. 5 is a block diagram showing the configuration of an MME. 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 between the MME 204a and a base station 203 via an S1 interface. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 501 to the base station communication unit 502 via 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.

[0076] When the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 501 to the control plane control unit 505. When the data received from the base station 203 is control data, the control data is passed from the base station communication unit 502 to the control plane control unit 505.

[0077] The HeNBGW communication unit 504 is provided when a HeNBGW 205 is present, and transmits and receives data via an interface (IF) between the MME 204a and the HeNBGW 205 depending on the information type. Control data received from the HeNBGW communication unit 504 is passed from the HeNBGW communication unit 504 to a control plane control unit 505. A result of processing in the control plane control unit 505 is transmitted to the PDN GW via the PDN GW communication unit 501. In addition, a result of processing in the control plane control unit 505 is transmitted to one or more base stations 203 by the S1 interface via the base station communication unit 502, and is also transmitted to one or more HeNBGW 205 via the HeNBGW communication unit 504.

[0078] The control plane control unit 505 includes a NAS security unit 505-1, an SAE bearer control unit 505-2, an idle state mobility management unit 505-3, etc., and performs general processing for the control plane (hereinafter, sometimes referred to as C-Plane). The NAS security unit 505-1 performs security for NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 505-2 performs management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 505-3 performs mobility management in the idle state (also called the LTE-IDLE state or simply idle), generation and control of paging signals in the idle state, addition, deletion, update, search, and tracking area list management of one or more mobile terminals 202 under its control.

[0079] The MME 204a distributes a paging signal to one or more base stations 203. The MME 204a also performs mobility control in an idle state. The MME 204a manages a tracking area list when the mobile terminal is in an idle state and in an active state. The MME 204a initiates a paging protocol by transmitting a paging message to a cell that belongs to a tracking area in which the UE is registered. The idle state mobility management unit 505-3 may manage the CSG, CSG ID, and whitelist of the Home-eNB 206 connected to the MME 204a.

[0080] Next, an example of a cell search method in a communication system is shown. Fig. 6 is a flow chart showing an outline of a process from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. When the communication terminal starts a cell search, in step ST601, the communication terminal synchronizes slot timing and frame timing using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a surrounding base station.

[0081] 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.

[0082] Next, in step ST602, for the synchronized cell, a cell-specific reference signal (CRS), which is a reference signal (RS) transmitted from the base station for each cell, is detected and the RS received power (Reference Signal Received Power: RSRP) is measured. A code that has a one-to-one correspondence with the PCI is used for the reference signal (RS). By correlating with the code, it is possible to separate the cell from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST601, it is possible to detect the RS and measure the RS received power.

[0083] Next, in step ST603, the cell with the best RS reception quality, for example the cell with the highest RS reception power, that is, the best cell, is selected from among one or more cells detected up to step ST602.

[0084] Next, in step ST604, the PBCH of the best cell is received to obtain a BCCH, which is broadcast information. A MIB (Master Information Block), which includes cell configuration information, is mapped to the BCCH on the PBCH. Therefore, the MIB can be obtained by receiving the PBCH and obtaining the BCCH. Examples of MIB information include DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, SFN (System Frame Number), and the like.

[0085] Next, in step ST605, the DL-SCH of the cell is received based on the cell configuration information in the MIB, and SIB (System Information Block) 1 in the broadcast information BCCH is obtained. SIB 1 includes information on access to the cell, information on cell selection, and scheduling information of other SIBs (SIBk; k is an integer ≧2). SIB 1 also includes a tracking area code (TAC).

[0086] Next, in step ST606, the communication terminal compares the TAC of the SIB1 received in step ST605 with the TAC portion of the tracking area identity (TAI) in the tracking area list that the communication terminal already holds. The tracking area list is also called a TAI list. The TAI is identification information for identifying a tracking area, and is composed of a MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a code number of the tracking area.

[0087] If the TAC received in step ST605 is the same as the TAC included in the tracking area list as a result of the comparison in step ST606, the communication terminal enters standby mode in the cell. If the TAC received in step ST605 is not included in the tracking area list as a result of the comparison, the communication terminal requests a core network (EPC) including an MME, etc., to change the tracking area in order to perform a Tracking Area Update (TAU) through the cell.

[0088] An apparatus constituting a core network (hereinafter sometimes referred to as a "core network side apparatus") updates the tracking area list based on an identification number (such as a UE-ID) of a communication terminal sent from the communication terminal together with a TAU request signal. The core network side apparatus transmits the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) the TAC list held by the communication terminal based on the received tracking area list. After that, the communication terminal enters standby mode in the cell.

[0089] The spread of smartphones and tablet terminal devices has led to an explosive increase in traffic via cellular wireless communications, raising concerns about a shortage of wireless resources around the world. In response to this, efforts are being made to create smaller cells and promote spatial separation in order to improve frequency utilization efficiency.

[0090] In a conventional cell configuration, a cell configured by an eNB has a relatively wide coverage area. Conventionally, a cell is configured to cover a certain area by the relatively wide coverage areas of a plurality of cells configured by a plurality of eNBs.

[0091] In the case of small cell configuration, the cell configured by the eNB has a narrower coverage range than the coverage of the cell configured by the conventional eNB. Therefore, as in the past, in order to cover a certain area, a large number of small cell eNBs are required compared to the conventional eNBs.

[0092] 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 that has been made into 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."

[0093] The macro eNB may be, for example, a “Wide Area Base Station” as described in Non-Patent Document 7.

[0094] 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.

[0095] 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).

[0096] When multiple eNBs are mixed, the coverage of a cell configured by one eNB may be included in the coverage of a cell configured by another eNB. In the cell configuration shown in Fig. 7, as shown by reference numerals "704" and "705", the coverage 702 of a small cell configured by a small eNB may be included in the coverage 701 of a macro cell configured by a macro eNB.

[0097] Also, as indicated by reference numeral "705," the coverage of multiple, for example, two, small cells 702 may be included within the coverage of one macro cell 701. A mobile terminal (UE) 703 is included, for example, within the coverage 702 of the small cell and communicates via the small cell.

[0098] Furthermore, in the cell configuration shown in FIG. 7, as indicated by reference numeral "706," there may be cases where coverage 701 of a macro cell formed by a macro eNB and coverage 702 of a small cell formed by a small eNB overlap in a complex manner.

[0099] 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.

[0100] 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.

[0101] In dual connectivity (DC), a master base station (Master Node; hereinafter, sometimes referred to as MN) inquires of a secondary base station (Secondary Node; hereinafter, sometimes referred to as SN) about the setting of a secondary cell group (SCG) (hereinafter, sometimes referred to as SCG setting) used for communication between a UE and an SN. The SN notifies the MN of the latest SCG setting. The above-mentioned SCG inquiry and SCG notification may be used in SN change. The MN may notify the target SN of an SN addition request. The MN may include the latest SCG setting acquired from the source SN in the SN addition request. This allows the target SN to acquire the latest SCG setting, for example, even if the source SN has changed the SCG setting for the UE. Therefore, it is possible to prevent discrepancies in the SCG setting between the target SN and the UE after the secondary base station change. As a result, it is possible to prevent, for example, UE malfunction.

[0102] When the above-mentioned SCG setting inquiry and / or SCG setting notification is applied to a procedure other than SN switching, for example, when a secondary cell group failure (SCG failure; hereinafter, sometimes referred to as SCG failure) occurs, the following problem occurs. That is, since the MN is unable to detect the occurrence of an SCG failure by itself, the MN is unable to inquire about the latest SCG setting from the SN. This causes a problem that, for example, when a secondary cell group failure (SCG failure; hereinafter, sometimes referred to as SCG failure) occurs, the master base station does not know the latest SCG setting, making it impossible to take appropriate recovery measures.

[0103] Solutions to the aforementioned problems are disclosed below.

[0104] The UE notifies the MN of the latest SCG configuration. The UE may perform the notification when an SCG failure occurs. The UE may include the notification in a notification of an SCG failure. The aforementioned notification of an SCG failure may be signaling of SCG failure information (SCGfailureInformation).

[0105] The above-mentioned latest SCG setting may be information about the difference from the SCG setting from the MN to the UE. This makes it possible to reduce the amount of signaling in the Uu interface. The above-mentioned difference information may be, for example, information about the SCG setting notified directly from the SN to the UE. For example, this makes it possible to reduce the amount of processing in the UE.

[0106] The UE may hold information about the SCG setting directly set for the UE from the SN. For example, the UE may hold the information in an area different from other RRC settings. The UE may update the information. The information may be updated, for example, when the UE holds the information and receives a new SCG setting. The UE may use the information in notifying the MN of the latest SCG setting as described above. This allows, for example, the UE to quickly notify the MN of the latest SCG setting. The UE may or may not clear the information held in the UE by using the notification to the MN.

[0107] As another example of a case where an SCG failure occurs, the MN may inquire about the latest SCG configuration to the SN when the UE notifies the MN of the SCG failure. The SN may in turn inquire about the latest SCG configuration to the MN when the UE notifies the MN of the SCG failure.

[0108] The notification of the SCG setting from the SN to the MN may be, for example, information on the difference from the SCG setting from the MN to the UE. This makes it possible to reduce the amount of signaling in the interface between base stations, for example, the X2 / Xn interface. In the first embodiment, the same may be applied hereinafter.

[0109] The MN may use the SCG setting notification to update the SCG setting for the UE in the own base station. This allows the MN to appropriately execute processing for an SCG failure, for example, using the latest SCG setting.

[0110] Fig. 8 is a diagram showing an example of a sequence in which an MN acquires the latest SCG setting when an SCG failure occurs. The example of Fig. 8 shows a sequence in which a UE notifies an MN of the latest SCG setting. The example of Fig. 8 also shows a case in which an SCG setting is changed as a recovery process after an SCG failure.

[0111] In step ST801, the UE detects an SCG failure. In step ST802, the UE transmits an SCG failure notification to the MN. The UE notifies the MN of SCG setting information in communication between the UE and the SN by including the information in the notification. The above-mentioned SCG setting information may be information on a difference with respect to the SCG setting made from the MN to the UE. The above-mentioned difference information may be, for example, information on the SCG setting notified directly from the SN to the UE. The MN acquires the latest SCG setting in step ST802.

[0112] In step ST803, the MN notifies the SN of an SN modification request. The MN may include information on the SCG setting in the request. The aforementioned information on the SCG setting may be, for example, information on further changes made to the latest SCG setting. In step ST804, the SN notifies the MN of an affirmative response to the SN modification request (SN Modification Request Acknowledge). The response may include information on the modification of the SCG setting.

[0113] In Step ST805, the MN notifies the UE of an RRC connection reconfiguration. The MN may include information regarding a change in the SCG configuration in the notification. The above-mentioned information regarding a change in the SCG configuration may be information acquired from the SN in Step ST804. The UE may change the SCG configuration by using Step ST805.

[0114] In Step ST806, the UE notifies the MN of the completion of RRC connection reconfiguration (RRCConnectionReconfigurationComplete). In Step ST807, the MN notifies the SN of the completion of SN reconfiguration (SN reconfiguration complete). In Step ST808, random access processing is performed between the UE and the SN. This completes recovery from the SCG failure due to the SCG setting change.

[0115] The SN may notify the MN of information about an SCG failure. The notification may be performed, for example, when the SN detects an excessive number of downlink RLC retransmissions, or when other conditions for the SN to detect an SCG failure are satisfied. This allows the communication system to quickly detect an SCG failure, for example, when downlink communication from the SN to the UE is interrupted.

[0116] When the above-mentioned SCG setting inquiry and / or SCG setting notification is applied when an SCG failure is detected in an SN, the same problem occurs as when an SCG failure is detected in a UE. That is, since an MN cannot detect an SCG failure by itself, the MN cannot inquire about the latest SCG setting from an SN. This causes a problem that, for example, when an SN detects an SCG failure, the MN does not know the latest SCG setting and therefore cannot take appropriate recovery measures.

[0117] As a solution to the above problem, the MN may inquire about the latest SCG settings to the SN when the SN notifies the MN of an SCG failure. The SN may notify the MN of the latest SCG settings. The notification may be made after the above inquiry.

[0118] As another example, the SN may include information on the latest SCG configuration in the notification of SCG failure information to the MN. The MN may use the information to update the SCG configuration held by the MN. This makes it possible to reduce, for example, the amount of signaling required for SCG configuration inquiries and / or SCG configuration notifications.

[0119] As the DC in the present embodiment 1, the MN may be an eNB or a gNB. The SN may be an eNB or a gNB. The upper NW device may be an MME or an NG-Core, for example, an AMF or an SMF. In the present embodiment 1, the following may be the same.

[0120] When the above-mentioned SCG setting inquiry and / or SCG setting notification is applied to the SN initiated SN release procedure, the following problem occurs. That is, in this procedure, the MN does not determine SN release by itself, so the MN cannot initiate an inquiry about the latest SCG setting to the SN. This causes a problem that, for example, when the SN determines to release its own SN, the MN does not know the latest SCG setting, and therefore, for example, the MN cannot perform appropriate switching processing from the SCG bearer to the MCG bearer.

[0121] As a solution to the above problem, the MN may inquire about the latest SCG settings to the SN when the SN notifies the MN that there is an SN release request (SN Release Required). The MN may include the inquiry in the SN release confirmation (SN Release Confirm) notification to the SN. This makes it possible to reduce signaling in the inter-base station interface, for example. As another example, the MN may notify the inquiry using signaling different from the SN release confirmation. This makes it possible to avoid, for example, the complexity of the design of the signaling of the SN release confirmation.

[0122] The SN may inform the MN of the latest SCG configuration, which may be done after the aforementioned inquiry.

[0123] As another example, the SN may include information about the latest SCG configuration in a notification of the SN release request (SN Release Required) to the MN. The MN may use the information to update the SCG configuration held by the MN. This makes it possible to reduce, for example, the amount of signaling required for an SCG configuration inquiry and / or an SCG configuration notification.

[0124] The above-mentioned notification of the SCG setting from the SN to the MN may be, for example, information on the difference from the SCG setting from the MN to the UE. This makes it possible to reduce the amount of signaling in an interface between base stations, for example, an X2 / Xn interface.

[0125] The MN may instruct the UE to release the SN using the SCG configuration acquired from the SN. The instruction may include, for example, information regarding a change of the bearer. The above-mentioned change of the bearer may be, for example, a switch from an SCG bearer to an MCG bearer. The MN may change the bearer using the SCG configuration acquired from the SN. This makes it possible, for example, to reduce the number of setting changes associated with a bearer change in the UE, and as a result, the amount of processing in the UE can be reduced.

[0126] Fig. 9 is a diagram showing an example of a sequence in which an MN acquires the latest SCG setting when an SN is released due to an SN activation. The example in Fig. 9 shows a case in which a notification of the presence of an SN release request from an SN to an MN and a notification of the latest SCG setting are performed by different signaling.

[0127] In step ST901, the SN transmits a notification to the MN that there is an SN release request. In step ST902, the MN makes an SCG configuration enquiry to the SN. In step ST903, the SN notifies the MN of the latest SCG configuration. In notifying the MN of the SCG configuration, the SN may transmit to the MN only the configuration contents that the SN directly notified to the UE. In step ST904, the MN notifies the SN of an SN Release Confirm.

[0128] In Step ST905, the MN notifies the UE of an RRC connection reconfiguration (RRCConnectionReconfiguration). The MN includes information on SN release in the notification. The MN may include information on bearer change in the notification. The above-mentioned bearer change may be, for example, switching from an SCG bearer to an MCG bearer, or switching from a split bearer to an MCG bearer. The UE uses Step ST905 to release the SCG configuration. The UE may use all or a part of the SCG configuration as part of the MCG configuration. In Step ST906, the UE notifies the MN of completion of RRC connection reconfiguration (RRCConnectionReconfigurationComplete).

[0129] In step ST907, the SN transfers the sequence number status to the MN (SN Status Transfer). In step ST908, the S-GW transmits user data to the SN. In step ST909, the SN transfers the user data received from the S-GW in step ST908 to the MN. In step ST910, the MN, SN, S-GW, and MME update the communication path between the S-GW and the SN to the communication path between the S-GW and the MN. In step ST911, the MN instructs the SN to release the UE context. The SN releases the UE context using step ST911.

[0130] In Fig. 9, the case where the notification of the presence of an SN release request from the SN to the MN in step ST901 and the latest SCG setting notification in step ST903 are performed by different signaling has been shown, but step ST901 and step ST903 may be performed by the same signaling. In this case, the MN may not transmit the SCG setting inquiry in step ST902 to the SN. This makes it possible to reduce the amount of signaling in the interface between base stations, for example.

[0131] In Fig. 9, the case where the SCG setting inquiry shown in step ST902 and the SN release confirmation shown in step ST904 are performed by different signaling has been shown, but step ST902 and step ST904 may be performed by the same signaling. In this case, the SN may perform the SCG setting notification shown in step ST903 after step ST904. This makes it possible to reduce the amount of signaling in the interface between base stations, for example.

[0132] Another solution is disclosed. The MN may make an SCG setting inquiry to the SN when it determines whether to release the SN. The inquiry may be executed in the MN initiated SN release procedure. The inquiry may be included in a notification of an SN release request from the MN to the SN, or may be executed by a different signaling from the notification of the SN release request. By including the inquiry in the notification of the SN release request, it is possible to reduce the amount of signaling in the interface between base stations, for example, the X2 / Xn interface. By executing the inquiry before the SN release request, for example, the MN can appropriately determine whether to release the SN using the latest SCG setting.

[0133] The notification of the SCG setting from the SN to the MN may be executed in the procedure of MN initiated SN release. The notification may be performed, for example, after an SN release request from the MN to the SN. In the above, even if the SN release request does not include information on the SCG inquiry, the SN may notify the MN of the SCG setting. This makes it possible to reduce the amount of signaling in the base station interface, for example, the X2 / Xn interface. The above-mentioned notification of the SCG setting from the SN to the MN may be, for example, information on the difference from the SCG setting from the MN to the UE. It makes it possible to reduce the amount of signaling in the base station interface, for example, the X2 / Xn interface. The MN may instruct the UE to release the SN. The instruction may be performed after the SN release request from the MN to the SN, or after the above-mentioned SCG setting notification from the SN to the MN. The UE uses the instruction to release the DC setting with the SN.

[0134] The MN may notify the SN of information regarding the cancellation of the SN release. The notification may be performed, for example, using the SCG setting that the MN receives from the SN. The SN may use the notification to stop processing required for the SN release, for example, the transfer of data from a higher-level NW device to the MN. The MN may not instruct the UE to release the SN, triggered by the SCG setting received from the SN. This allows, for example, the MN to reduce the amount of signaling and processing related to unnecessary SN release.

[0135] Fig. 10 is a diagram showing an example of a sequence in which an MN acquires the latest SCG setting when releasing an SN initiated by an MN. The example of Fig. 10 shows a case in which an SCG setting inquiry from an MN to an SN and a notification of an SN release request are performed by the same signaling. In Fig. 10, the same step numbers are assigned to signaling common to Fig. 9, and common explanations are omitted.

[0136] In step ST1001, the MN transmits an SN Release Request to the SN. The MN may include information regarding an inquiry about the latest SCG setting in the request. In step ST903, the SN notifies the MN of the latest SCG setting. In notifying the MN of the SCG setting, the SN may transmit to the MN only the setting contents notified directly from the SN to the UE.

[0137] Steps ST905 to ST911 are the same as those in FIG. 9, and therefore the description thereof will be omitted.

[0138] 10, the case where information on the latest SCG setting inquiry is included in the SN release request from the MN to the SN in step ST1001 has been shown, but the SN release request and the SCG setting inquiry may be executed by different signaling. This makes it possible to avoid, for example, complex design in the MN and SN.

[0139] Also, in Fig. 10, the case where information on the latest SCG setting inquiry is included in the SN release request from the MN to the SN in step ST1001 has been shown, but information on the SCG setting inquiry does not have to be included in step ST1001. Even if information on the SCG setting inquiry is not included in step ST1001, the SN may transmit the SCG setting notification shown in step ST903 to the MN. This makes it possible to reduce, for example, the amount of signaling in the interface between base stations.

[0140] Also, in Fig. 10, an example is shown in which SN release continues after the SCG setting notification from the SN, but SN release may be canceled. In the above, the MN may notify the SN of information regarding the cancellation of SN release. In the cancellation of SN release, the sequence after ST905 in Fig. 10 may not be executed. This makes it possible to reduce the amount of signaling and processing related to unnecessary SN release in a communication system, for example.

[0141] Another solution is disclosed. The MN may make an SCG setting inquiry to the SN when a decision is made to modify the SN. The inquiry may be executed in an MN initiated SN modification procedure. This makes it possible to prevent, for example, SCG setting discrepancies between the MN and the UE. The inquiry may be included in a notification of an SN modification request from the MN to the SN, or may be made by a different signaling from the notification of the SN modification request. By including the inquiry in the notification of the SN modification request, it is possible to reduce the amount of signaling in the interface between base stations, for example, the X2 / Xn interface. By making the inquiry by a different signaling from the SN modification request, for example, the MN can appropriately change the SCG setting using the latest SCG setting.

[0142] In a notification of an SN change request from an MN to an SN, the SCG setting changed by the MN may be stored in a different area from the SCG setting not changed by the MN. The SN may use the SCG setting stored in a different area in the notification to extract information on the SCG setting already notified to the UE from the difference between the SCG setting included in the notification and the SCG setting held by the SN. This makes it possible for the SN to distinguish, for example, the SCG setting changed by the MN from the SCG setting already notified to the UE from the SN in the SCG setting notified to the SN from the SCG setting. As a result, it is possible to prevent discrepancies in the SCG settings between the MN, the SN, and the UE, and to prevent malfunctions in the communication system.

[0143] In the above, the notification of the SN change request from the MN to the SN may include information about the SCG failure. The notification of the SCG setting inquiry may include information about the SCG failure. This allows, for example, the SN to appropriately perform recovery operations from the SCG failure.

[0144] The SCG setting notification from the SN to the MN may be executed in the procedure of MN-initiated SN change. The notification may be performed, for example, after an SN change request from the MN to the SN. Even if the change request from the MN to the SN does not include information on the SCG setting inquiry, the SCG setting notification may be performed from the SN to the MN. The notification may be included in an SN modification request acknowledgement from the SN to the MN, or may be performed by a signaling different from the SN modification request acknowledgement. The above-mentioned notification of the SCG setting from the SN to the MN may be, for example, information on the difference from the SCG setting from the MN to the UE, as shown in the MN-initiated SN release. It is possible to reduce the amount of signaling in the base station interface, for example, the X2 / Xn interface.

[0145] In the SCG setting notification from the SN to the MN, both the SCG setting already notified directly from the SN to the UE and the SCG setting to be changed in the SN change procedure may be included. Both SCG settings may be stored in different areas. In instructing the UE to change the SN, the MN may extract the SCG setting to be changed in the SN change procedure from the SCG setting notification and notify the UE. This allows, for example, the MN to quickly notify the UE of the SN change instruction.

[0146] The SN may notify the MN of information indicating that the SN change is unnecessary. The notification may be performed, for example, when the SCG setting contents included in the SN change request from the MN to the SN are the same as the SCG setting contents that the SN has directly notified to the UE. The information may be included in the SN change request acknowledgment from the SN to the MN, or may be included in the SN change request rejection from the SN to the MN. The information indicating the reason included in the SN change request rejection may include information indicating that the SCG setting has been directly notified from the SN to the UE. Alternatively, the information indicating the reason may include information indicating that the SCG setting has been configured for the UE.

[0147] The MN may instruct the UE to change the SN. The instruction may be performed using signaling of RRC connection reconfiguration. The instruction may include information on the SCG setting change content. The instruction may be performed after an SCG setting notification from the SN to the MN, or after an SN change request acknowledgment from the SN to the MN. The UE uses the instruction to change the SCG setting used for connection with the SN.

[0148] Alternatively, the MN may notify the SN of the SN change request again. For example, the above-mentioned second notification may be performed when the MN uses the SCG setting notification from the SN to change the SCG setting to be notified to the UE again. The SCG setting included in the second notification may be different from the SCG setting included in the first notification. The second notification of the SN change request from the MN to the SN may be performed after the SN notifies the MN of information indicating that the SN change is unnecessary, or after the SN notifies the MN of the SN change request acknowledgment and / or the latest SCG setting. This allows, for example, the MN to perform further SCG setting using the latest SCG setting, thereby improving the quality of the connection between the UE and the SN.

[0149] Alternatively, the MN may not instruct the UE to change the SN. After the SN notifies the MN of information indicating that the SN change is unnecessary, the MN may not instruct the UE to change the SN. This makes it possible to reduce the amount of signaling in the radio interface (e.g., Uu interface) between the MN and the UE, for example.

[0150] Fig. 11 is a diagram showing an example of a sequence in which an MN acquires the latest SCG setting when an MN starts changing an SN. The example in Fig. 11 shows a case in which an SCG setting inquiry from an MN to an SN and a notification of an SN release request are performed by different signaling. In Fig. 11, the same step numbers are assigned to signaling common to Fig. 8, and common explanations are omitted.

[0151] In step ST1101, the MN notifies the SN of an SCG configuration enquiry. In step ST1102, the SN notifies the MN of SCG configuration information. The above-mentioned notification of the SCG configuration from the SN to the MN may be, for example, information regarding the difference from the SCG configuration from the MN to the UE. This makes it possible to reduce the amount of signaling in the interface between base stations, for example, the X2 / Xn interface. The MN uses the SCG configuration information to determine the changed SCG configuration.

[0152] In Step ST1103, the MN notifies the SN of an SN modification request. The request includes the changed SCG setting. In Step ST1104, the SN notifies the MN of an SN modification request acknowledgement. The request may include the changed SCG setting. Alternatively, the request may include a setting that is a further modification of the changed SCG setting determined by the MN.

[0153] In Step ST805, the MN instructs the UE to change the SN. The instruction includes the changed SCG setting. The instruction may include the setting that the SN further changes from the changed SCG setting determined by the MN.

[0154] Steps ST806 to ST808 are the same as those in FIG. 8, and therefore the description thereof will be omitted.

[0155] In Fig. 11, an example is shown in which the SCG setting inquiry shown in step ST1101 and the SN change request shown in step ST1103 are notified as different signaling, but these may be notified as the same signaling. Also, an example is shown in which the SCG setting notification shown in step ST1102 and the SN change request acknowledgment shown in step ST1104 are notified as different signaling, but these may be notified as the same signaling. This makes it possible to reduce the amount of signaling in, for example, an interface between base stations, such as an X2 / Xn interface.

[0156] Another solution is disclosed. The SCG setting notification from the SN to the MN may be triggered by the SN's decision to modify its own SN (SN Modification). It may be included in a notification of the SN modification request from the SN to the MN (SN Modification Required), or the notification of the SN modification request may be, for example, a notification in the SN-initiated SN modification procedure. This makes it possible to reduce signaling in the base station interface, for example. As another example, the MN may notify the inquiry using signaling different from the SN release confirmation. This makes it possible to avoid, for example, the complexity of the design in the signaling of the SN release confirmation. The SCG setting notification from the SN to the MN may be executed in the MN-initiated SN modification procedure.

[0157] Another solution is disclosed. The SCG setting notification from the SN to the MN may be triggered by the SN's decision to modify its own SN (SN Modification). The notification may be included in a notification of the SN modification request from the SN to the MN (SN Modification Required), or may be performed by a different signaling from the notification of the SN modification request. The notification of the SN modification request may be a signaling in the SN-initiated SN modification procedure. The MN may notify the UE of an SN modification instruction. The instruction may include the SCG setting. The UE may use the instruction to change the SCG setting.

[0158] The notification of the SCG setting from the SN to the MN may be composed of a plurality of information groups. The SN may arrange the SCG setting that has been directly notified from the SN to the UE and the SCG setting that has been decided to be changed in the SN-initiated SN change procedure in different information groups. The MN may use the information group to notify the UE of the SCG setting that has been decided to be changed in the SN-initiated SN change procedure. For example, the MN may notify the UE of only the information group including the SCG setting that has been decided to be changed in the SN. This makes it possible to reduce, for example, the amount of signaling in the SN change instruction from the MN to the UE. Also, for example, it makes it possible to reduce the amount of processing required for the MN to generate the SCG setting content to be notified to the UE.

[0159] Fig. 12 is a diagram showing an example of a sequence in which an MN acquires the latest SCG setting when an SN is changed by an SN activation. Fig. 12 shows an example in which an SCG setting notification from an SN to an MN and a notification of an SN change request are performed by the same signaling. In Fig. 12, the same step numbers are assigned to signaling common to Fig. 8, and common explanations are omitted.

[0160] In Step ST1201, the SN notifies the MN that there is an SN change request. The notification may include information on the SCG setting. The MN uses the notification to obtain the latest SCG setting.

[0161] The information on the SCG setting in step ST1201 may be composed of a plurality of information groups. The SN may arrange the SCG setting that has been directly notified from the SN to the UE and the SCG setting that has been decided to be changed in the SN change procedure initiated by the SN, in different information groups. The MN may use the information groups to issue an SN change instruction to the UE in step ST805.

[0162] Steps ST806 to ST808 are the same as those in FIG. 8, and therefore the description thereof will be omitted.

[0163] In Fig. 12, an example is shown in which the SCG setting notification from the SN to the MN and the notification of the presence of an SN change request are performed by the same signaling, but these may be performed by different signaling. For example, the MN may use both the notification of the presence of an SN change request and the SCG setting notification to issue an SN change instruction to the UE in step ST805. This enables, for example, the MN to quickly determine the change part of the SCG setting that should be notified to the UE.

[0164] Another solution is disclosed. The MN may make an SCG setting inquiry to the SN when a handover of the master base station is triggered. The handover may be, for example, an inter-MN handover without SN change. Similarly, the SCG setting information notification from the SN to the MN may be executed during the handover of the master base station. The handover may be, for example, an inter-MN handover without SN change. This allows, for example, the target MN to determine whether or not to maintain the SN using the latest SCG setting. As a result, for example, the quality of communication between the SN and the UE can be ensured.

[0165] The source MN may make this inquiry before sending a handover request to the target MN. The SN may notify the source MN of the latest SCG setting. The source MN may use the SCG setting to update the SCG setting held by the source MN. The source MN may make a handover request to the target MN. The request may include the SCG setting updated by the source MN as described above. The target MN may use the SCG setting included in the request to determine whether or not to maintain the SN.

[0166] The source MN may include information about the target MN in the inquiry to the SN. The information may be, for example, an identifier of the target MN (e.g., base station ID) or information including an identifier of the PCell of the target MN (e.g., physical cell identifier). The SN may notify the target MN of the SCG configuration using the information. The notification of the SCG configuration from the SN to the target MN may be made before the signaling of the SN Addition Acknowledge, may be included in the signaling of the SN Addition Acknowledge, or may be made after the SN Addition Acknowledge. The source MN may make a handover request to the target MN. The request may include the SCG configuration held by the source MN. The target MN may update the SCG configuration in its own MN using the SCG configuration included in the request from the source MN and the SCG configuration notified from the SN. The target MN may determine whether or not to maintain the SN using the updated SCG configuration.

[0167] As another example, the target MN may make the inquiry to the SN. The target MN may make the inquiry after a handover request from the source MN. The target MN may make the inquiry to the SN before SN addition from the target MN to the SN, may include the inquiry in the signaling of the SN addition, or may make the inquiry after the SN addition. The SN may notify the target MN of the SCG setting. The notification of the SCG setting from the SN to the target MN may be made before signaling of an SN addition acknowledgement, may be included in the signaling of the SN addition acknowledgement, or may be made after the SN addition acknowledgement. The target MN may use the notification to update the SCG setting held by the target MN. The target MN may use the updated SCG setting to determine whether or not the SN can be maintained.

[0168] In the above, even if the signaling of SN addition from the target MN to the SN does not include information on an SCG inquiry, the SN may notify the target MN of the latest SCG setting. The same may be done even if there is no inquiry of SCG setting from the target MN to the SN. This makes it possible to reduce the amount of signaling in the interface between base stations, for example, the X2 / Xn interface. The SN may determine the UE to be the target of SCG setting by using information on the UE included in the notification of SN addition from the target MN.

[0169] The target MN may notify the source MN of the SCG setting. The SCG setting may be a setting notified from the SN to the source MN or the target MN, or may be a setting that the target MN further modifies to the setting notified from the SN to the source MN or the target MN. The notification of the SCG setting from the target MN to the source MN may be notified before the signaling of the handover request acknowledgement, or may be notified after the signaling of the handover request acknowledgement. Alternatively, the notification of the SCG setting from the target MN to the source MN may be included in the signaling of the handover request acknowledgement. This makes it possible to reduce the amount of signaling due to the SCG setting notification, for example, in an interface between base stations (e.g., X2 / Xn interface).

[0170] Figures 13 and 14 are diagrams showing an example of a sequence in which a target MN acquires the latest SCG setting in an inter-MN handover that does not involve SN switching. Figures 13 and 14 are connected at the position of a border BL1314. Figures 13 and 14 show an example in which an SCG setting inquiry from the target MN to an SN and an SN addition request are performed using different signaling. Figures 13 and 14 also show an example in which an SCG setting notification from an SN to the target MN and a notification of an SN addition request acknowledgment are performed using different signaling.

[0171] In step ST1301, the source MN notifies the target MN of a handover request. In step ST1302, the target MN inquires of the SN about the latest SCG setting. In step ST1303, the SN notifies the target MN of the latest SCG setting. The target MN updates the SCG setting using step ST1301 and step ST1303 and determines whether or not to maintain the SN. The examples in Figs. 13 and 14 show the case where the SN is maintained.

[0172] In Step ST1304, the target MN notifies the SN of an SN addition request. In Step ST1305, the SN notifies the target MN of an SN addition request acknowledgment. In Step ST1306, the target MN notifies the source MN of a handover request acknowledgment. The notification in Step ST1306 may include the latest SCG setting, or may include the MCG setting used for connection between the target MN and the UE.

[0173] In Step ST1307, the source MN notifies the SN of an SN release request. The SN release request in Step ST1307 does not need to include information regarding an SCG inquiry. The SN does not need to notify the source MN of an SCG setting. This makes it possible to reduce, for example, the amount of signaling in the interface between base stations.

[0174] In step ST1308, the source MN instructs the UE to switch the MN. The instruction may use signaling for RRC connection reconfiguration. The instruction may include information on the SCG setting. The above-mentioned SCG setting may be information using an SCG setting that is further changed by the target MN in addition to the SCG setting notified from the SN to the target MN. The UE uses the instruction to switch the destination master base station from the source MN to the target MN.

[0175] In Step ST1309, the UE performs random access processing with the target MN. This establishes synchronization between the UE and the target MN. In Step ST1310, the UE notifies the target MN of completion of MN switching. For this notification, signaling of RRC connection reconfiguration completion may be used. In Step ST1311, the UE performs random access processing with the SN. This establishes synchronization between the UE and the SN. In Step ST1312, the target MN notifies the SN of SN reconfiguration complete.

[0176] In Step ST1313, the source MN transfers the sequence number status to the target MN (SN Status Transfer). In Step ST1314, the S-GW transmits user data to the source MN. In Step ST1315, the source MN transfers the user data received from the S-GW in Step ST1314 to the target MN.

[0177] Steps ST1316 to ST1319 show the procedure of path switching between the target MN, the S-GW, and the MME. In step ST1316, the target MN notifies the MME of a path switch request. In step ST1317, a bearer modification is performed between the S-GW and the MME. In step ST1318, user data is transmitted from the S-GW to the target MN via a new path. In step ST1319, the MME notifies the target MN of a path switch request acknowledgement.

[0178] In Step ST1320, the target MN instructs the source MN to release the UE context (UE context release). In Step ST1321, the source MN instructs the SN to release the UE context. The source MN uses Step ST1320 to release the UE context. The SN uses Step ST1321 to release the UE context associated with the source MN.

[0179] In Fig. 13 and Fig. 14, an example is shown in which the SCG setting inquiry from the target MN to the SN and the SN addition request are performed by different signaling, but these may be performed by the same signaling. Also, in Fig. 13 and Fig. 14, an example is shown in which the SCG setting notification from the SN to the target MN and the notification of the SN addition request acknowledgment are performed by different signaling, but these may be performed by the same signaling. This makes it possible to reduce the amount of signaling in the interface between base stations, for example.

[0180] In FIG. 13 and FIG. 14, an example of an upper NW configured using an S-GW and an MME is shown, but the sequences shown in FIG. 13 and FIG. 14 may be applied to a case where an upper NW configured using an NG core, that is, an UPF and an AMF is used. For example, in the above, the S-GW may be replaced with a UPF, and the MME may be replaced with an AMF. Also, in the above, the path switch request shown in step ST1316 may be replaced with a PDU session path switch request (PDU Session Path Switch Request). Also, in the above, the path switch request acknowledgment shown in step ST1319 may be replaced with a PDU session path switch request acknowledgment (PDU Session Path Switch Request Acknowledge). As a result, even when the upper NW device is an NG core, it is possible to obtain the same effect as in the case of an upper NW configured using an S-GW and an MME.

[0181] Another solution is disclosed. The MN may make an SCG setting inquiry to the SN when switching from the MN to the eNB / gNB (MN to eNB / gNB change) is triggered. Similarly, the SCG setting information notification from the SN to the MN may be executed in the procedure of switching from the MN to the eNB / gNB (MN to eNB / gNB change). For example, the procedure may be to release the DC configuration when the connection destination of the UE using the DC configuration moves from the MN to another base station by handover. This makes it possible, for example, to transfer the bearer set in the SCG to the destination base station when the SN is released. As a result, for example, it is possible to reduce the amount of processing associated with handover in the UE.

[0182] In switching from the MN to the eNB / gNB, the source MN may make the inquiry to the SN. The source MN may make the inquiry before a handover request to the destination base station. The SN may notify the source MN of the latest SCG setting. The source MN may use the SCG setting to update the SCG setting held by the source MN. The source MN may make a handover request to the destination base station. The request may include the SCG setting updated by the source MN as described above. The destination base station may use the SCG setting included in the request to determine the setting to be used for connection with the UE.

[0183] The source MN may include information on the destination base station in the inquiry to the SN. The information may be, for example, an identifier of the destination base station, or may be information including an identifier of the PCell of the destination base station (e.g., a physical cell identifier). The SN may notify the destination base station of an SCG configuration using the information. The source MN may make a handover request to the destination base station. The request may include the SCG configuration held by the source MN. The destination base station may update the SCG configuration in the MN using the SCG configuration included in the request from the source MN and the SCG configuration notified from the SN. The destination base station may determine the configuration to be used for connection with the UE using the updated SCG configuration.

[0184] As another example, the target base station may make the inquiry to the SN. The target base station may make the inquiry after a handover request from the source MN. The SN may notify the target base station of the SCG configuration. The target base station may use the notification to update the SCG configuration held by the target base station. The target base station may use the updated SCG configuration to determine the configuration to be used for connection with the UE.

[0185] The destination base station may notify the source MN of the SCG setting. The SCG setting may be a setting notified from the SN to the source MN or the destination base station, or a setting notified from the SN to the source MN or the destination base station with further changes made by the destination base station. The notification of the SCG setting from the destination base station to the source MN may be notified before the signaling of the handover request acknowledgement, or may be notified after the signaling of the handover request acknowledgement. Alternatively, the notification of the SCG setting from the destination base station to the source MN may be included in the signaling of the handover request acknowledgement. This makes it possible to reduce the amount of signaling due to the SCG setting notification, for example, in an interface between base stations (e.g., X2 / Xn interface).

[0186] Figures 15 and 16 are diagrams showing an example of a sequence in which a source MN (S-MN) acquires the latest SCG setting when switching from an MN to an eNB. Figures 15 and 16 are connected at the position of a boundary line BL1516. Figures 15 and 16 show an example in which a source MN makes an SCG setting inquiry to an SN before a handover request, and the SN notifies the source MN of the SCG setting. In Figures 15 and 16, the same step numbers are assigned to signaling common to Figures 13 and 14, and common explanations are omitted.

[0187] In Step ST1401, the source MN inquires of the SN about the latest SCG setting. In Step ST1402, the SN notifies the source MN of the latest SCG setting. The source MN updates the SCG setting by using Steps ST1401 and ST1402. In Step ST1403, the source MN notifies the target base station (T-eNB) of a handover request. In Step ST1403, the handover request may include the latest SCG setting acquired from the SN. The target base station may determine not to use a secondary base station by using the SCG setting included in Step ST1403.

[0188] Steps ST1306 and ST1307 are the same as those in FIG. 13, and therefore the description thereof will be omitted.

[0189] In step ST1408, the source MN instructs the UE to switch the base station. The instruction may use signaling for RRC connection reconfiguration. The instruction may include information on the SCG setting. The above-mentioned SCG setting may be information using an SCG setting that is further changed by the destination base station with respect to the SCG setting notified from the SN to the destination base station via the source MN. The UE uses the instruction to switch the destination base station from the source MN to the destination base station.

[0190] Steps ST1309 and ST1310 are the same as those in FIG. 14, and therefore the description thereof will be omitted.

[0191] In step ST1410, the SN transfers the sequence number status to the source MN (SN Status Transfer). The sequence number status in step ST1410 may be, for example, the sequence number status of user data transmitted and received using the SCG. In step ST1411, the source MN transfers the sequence number status to the destination base station. The sequence number status in step ST1411 may include, for example, the sequence number status in step ST1410, or may include the sequence number status of user data transmitted and received using the MCG.

[0192] In Step ST1412, the S-GW transmits user data to the SN. In Step ST1413, the SN transfers the user data received from the S-GW in Step ST1412 to the source MN. In Step ST1414, the source MN transfers the user data received from the SN in Step ST1413 to the target base station.

[0193] Steps ST1316 and ST1317 are the same as those in FIG. 14, and therefore the description thereof will be omitted.

[0194] In step ST1415, the S-GW transmits to the SN an end marker packet including information indicating that this is the last user data that uses the path using the SN. In step ST1416, the SN forwards the end marker packet received from the S-GW in step ST1415 to the source MN. In step ST1417, the source MN forwards the end marker packet received from the SN in step ST1416 to the destination base station.

[0195] Steps ST1318 to ST1320 are the same as those in FIG. 14, and therefore the description thereof will be omitted.

[0196] In Step ST1421, the source MN instructs the SN to release the UE context. The SN uses Step ST1421 to release the UE context.

[0197] 15 and 16 show an example in which the target MN makes an SCG setting inquiry, but the source base station may make an SCG setting inquiry to the SN. In the above, the SN may notify the target base station of the latest SCG setting. This allows, for example, the target base station to appropriately determine whether or not to release the SN. As a result, the efficiency of the communication system can be improved.

[0198] In FIG. 15 and FIG. 16, an example in which the destination base station is an eNB is shown, but the destination base station may be a gNB (T-gNB). In FIG. 15 and FIG. 16, an example of an upper NW configured using an S-GW and an MME is shown, but the sequences shown in FIG. 15 and FIG. 16 may be applied to a case in which an NG core, that is, an upper NW configured using a UPF and an AMF is used. For example, in the above, the S-GW may be replaced with a UPF, and the MME may be replaced with an AMF. In the above, the path switch request shown in step ST1316 may be replaced with a PDU session path switch request (PDU Session Path Switch Request). In the above, the path switch request acknowledgement shown in step ST1319 may be replaced with a PDU session path switch request acknowledgement (PDU Session Path Switch Request Acknowledge). In this way, even when the upper NW device is an NG core, it is possible to obtain the same effect as in the case of an upper NW configured using an S-GW and an MME.

[0199] Another solution is disclosed. The MN may make an SCG setting inquiry to the SN when a handover occurs in which both the MN and the SN are switched. Similarly, the SCG setting information notification from the SN to the MN may be executed during the handover. This allows, for example, the destination MN to appropriately set the SCG setting of the destination SN using the latest SCG setting. As a result, for example, it is possible to ensure the quality of communication between the destination SN and the UE.

[0200] When applying an SCG setting inquiry from an MN to an SN and / or an SCG setting information notification from an SN to an MN to a handover in which both an MN and an SN are switched, a method similar to a procedure for an inter-MN handover that does not involve SN switching may be used, or a method similar to a procedure for switching from an MN to an eNB / gNB may be used. This makes it possible to avoid, for example, the complexity of the design in a communication system.

[0201] According to the first embodiment, even when SN switching does not occur, it is possible to prevent discrepancies in SCG settings between a UE, an MN, and an SN. As a result, it is possible to prevent malfunctions in a communication system.

[0202] Embodiment 2 As a method of notifying the master base station of SCG failure information from the UE using a bearer having multiple transmission paths in the radio interface from the UE for uplink C-Plane data transmission, i.e., a UL split SRB, the UE may initiate an RRC connection re-establishment. Alternatively, the UE may autonomously switch the transmission path of the uplink split SRB1 from the SCG to the MCG. The above-mentioned method of notifying the SCG failure information may be applied when the SCG is set to be used as the transmission path of the UL split SRB1.

[0203] The above-mentioned switching of the transmission path of the uplink split bearer may be applied to the uplink split SRB2 and / or the uplink split DRB.

[0204] When applying the above-mentioned method, the following problems occur. That is, when the RRC connection is re-established, the UE re-establishes connection not only with the SCG but also with the MCG, so it takes time to complete the RRC connection re-establishment. Furthermore, during the re-establishment between the UE and the MCG, the user data communication between the UE and the MCG stops. As a result, even if the user data communication between the UE and the MCG is normally performed, the user data communication stops due to the SCG failure.

[0205] In addition, the UE autonomously switches the transmission path of the uplink split SRB1, so that all signaling transmitted using the SRB1, such as a measurement report, is transmitted to the MCG. As a result, the signaling transmitted using the SRB1 is also transmitted to the MCG, so it takes time for the UE to notify the MCG of SCG failure information. As a result, a problem occurs in that it takes time to recover from an SCG failure in the communication system.

[0206] Solutions to the aforementioned problems are disclosed below.

[0207] Only the signaling of SCG failure information enables automatic switching of the destination base station in the UE. The switching may be, for example, switching to the MCG or switching to packet duplication. As another example, the switching may be enabled according to the type of signaling of SRB1 (for example, RRC connection reconfiguration). Similarly, the switching may be enabled according to the type of signaling for SRB2. The aforementioned other signaling may be signaling using SRB1 and / or SRB2. Whether or not the destination base station can be switched in the UE may be determined for each signaling. For example, whether or not the switching can be enabled may be determined in advance by a standard for each signaling. This allows the UE to quickly notify the MCG of SCG failure information even when, for example, other signaling occurs in the UE.

[0208] For example, the UE may switch the destination of the SCG failure information from the SCG to the MCG. The above switching may be applied when the destination of the split SRB1 in the UE is set to the SCG. The UE may notify the MN of the signaling of the SCG failure information.

[0209] The MN may set the destination of the split SRB1 and / or split SRB2 in the UE to the MCG by using the signaling received from the UE. As another example, the MN may execute a procedure such as SN switching, SN release, or SN change by receiving the signaling. As another example, the MN may perform the SCG setting inquiry disclosed in the first embodiment by receiving the signaling.

[0210] Fig. 17 is a sequence diagram showing an example of an operation of autonomously switching a base station to which SCG failure information is notified when an SCG failure occurs. Fig. 17 shows an example in which an SCG is set as the transmission destination of a UL split SRB1.

[0211] In Step ST1501, it is assumed that the destination of the UL split SRB1 in the UE is set to the SCG. In Step ST1502, the UE transmits a measurement report to the SN. In Step ST1503, the SN transfers the measurement report received from the UE in Step ST1502 to the MN.

[0212] 17, it is assumed that the UE detects an SCG failure in Step ST1506. In Step ST1507, the UE switches the transmission destination of the signaling of the SCG failure information from the SCG to the MCG. In Step ST1508, the UE notifies the MN of the SCG failure information.

[0213] In Step ST1509, the MN sets the destination of the UL split SRB1 to the MCG for the UE. For example, signaling of RRC connection reconfiguration may be used for this setting. In Step ST1510, the UE switches the destination of the UL split SRB1 to the MCG. In Step ST1511, the UE notifies the MN of information indicating that switching of the destination of the UL split SRB1 has been completed. For example, signaling of RRC connection reconfiguration complete may be used for this notification. In Step ST1512, the MN notifies the SN of completion of SN reconfiguration (SN reconfiguration complete). In Step ST1513, the UE transmits a measurement result report to the MN.

[0214] In the second embodiment, the destination setting in the UL split bearer may be determined using information on the buffer accumulation amount of the UE, or may not be determined using the information. For example, the destination setting may be determined using information on the buffer accumulation amount of the PDCP and RLC layers of the UE described in Non-Patent Document 16 (3GPP TS38.323 V1.0.1), or may be determined without using the information. By using a setting in which the destination is determined without using the information, it is possible to facilitate control in the communication system, for example.

[0215] Another solution is disclosed. For signaling of SCG failure information, packet duplication in the UE is enabled. Packet duplication may be performed using DC. Packet duplication may also be enabled for other signaling. The other signaling described above may be signaling using SRB1 and / or SRB2. Whether packet duplication in the UE is possible may be determined for each signaling. For example, whether packet duplication is possible may be determined in advance by a standard for each signaling. This allows the UE to quickly notify the MN of SCG failure information even when other signaling occurs in the UE.

[0216] Another solution is disclosed. Signaling of SCG failure information is transmitted using another SRB. For example, SRB0 or ​​SRB2 may be used to transmit signaling of SCG failure information. SRB2 may be a split SRB2 or a non-split SRB2. The use of the split SRB2 described above may be applied, for example, when MCG is set as the destination of the split SRB2. The other SRB that can transmit the signaling of SCG failure information described above may be predefined in a standard. This allows the UE to quickly notify the MN of the signaling, for example, even when the transmission buffer accumulation amount for SRB1 in the UE is large.

[0217] Another solution is disclosed. The UE may include information about the SCG failure in the signaling of the RRC connection re-establishment. The information may include, for example, an identifier indicating that an SCG failure has occurred, or may include part or all of the information of the signaling of the SCG failure information. The UE may notify the MN of the signaling after detecting the SCG failure. The signaling may include information indicating that the connection between the UE and the MCG is maintained. The MN may re-establish only the connection between the UE and the SCG using the information about the SCG failure in the signaling. The MN may maintain the connection between the UE and the MCG using the information. This makes it possible to quickly restore the connection between the UE and the SCG while maintaining the connection between the UE and the MCG, for example.

[0218] Another solution is disclosed. The UE may transmit information indicating the SCG failure to the MN using RACH or using MAC signaling. The UE may transmit information indicating the SCG failure to the MN using L1 / L2 signaling. In the above transmission, a DRB or an SRB may be used. The MN may use the information to, for example, switch the destination of the UL split bearer. This allows, for example, the UE to quickly notify information indicating the SCG failure.

[0219] Another solution is disclosed. A PDCP status PDU including information indicating an SCG failure may be provided. The UE may transmit the PDCP status PDU to the MCG. The UE may transmit the PDCP status PDU using an SRB or a DRB. The SRB and / or the DRB may be a bearer for transmitting the MCG. This allows, for example, the UE to quickly notify the MN of an SCG failure.

[0220] Another solution is disclosed. The size of the signaling of the SCG failure information is set to a predetermined threshold or more. The predetermined threshold may be a threshold related to the buffer accumulation amount of the PDCP and RLC layers of the UE described in Non-Patent Document 16 (3GPP TS 38.323 V1.0.1). This allows, for example, the UE to promptly notify the MN of the signaling.

[0221] For example, the UE may add padding to the signaling of the SCG failure information. As another example, the UE may include information on the SCG configuration disclosed in the first embodiment in the signaling of the SCG failure information. This makes it possible to reduce wasteful communication, and also enables the UE to promptly notify the MN of the signaling.

[0222] As another example, a plurality of the above-mentioned predetermined thresholds may be provided. The plurality of thresholds may be, for example, a threshold used by the UE in normal times and a threshold used by the UE when an SCG failure is detected. For example, when the UE detects an SCG failure, the UE may use a value different from the threshold used in normal times, for example, a value smaller than the threshold used in normal times, as the threshold. The threshold when an SCG failure is detected may be, for example, 0 or may not be 0. For example, when an SCG failure is detected, the UE may transmit uplink data using a split bearer to either the MCG or the SCG by using the fact that the accumulated amount of an L2 buffer, for example, a buffer of the PDCP layer and the RLC layer, is equal to or greater than the threshold used when an SCG failure is detected. In the above, the UE may transmit the uplink data to the MCG. This allows, for example, the UE to quickly notify the MCG of SCG failure information.

[0223] The above-mentioned multiple thresholds may be defined in advance by a standard, or may be determined by the MN and notified in advance or individually to the UE. For example, signaling of RRC connection reconfiguration may be used, or signaling of RRC connection setup (RRCConnectionSetup) may be used. Both of the above may be used. For example, the threshold used by the UE when detecting an SCG failure may be defined as 0 in the standard, and the threshold used in normal times may be determined and notified in advance to the UE by the MN.

[0224] The UE may restore the destination of the split SRB1 to the original setting when recovering from the SCG failure. The UE may use a newly set destination as the destination of the split SRB1 when recovering from the SCG failure. The operation using the newly set destination may be applied, for example, when the destination of the split SRB1 is newly set in the process of recovering from the SCG failure. This allows, for example, efficient operation of the communication system. The same may be applied to the split SRB2 and / or split DRB.

[0225] Another solution is disclosed. The UE may transmit the notification of SCG failure information with priority over other signaling. For example, the UE may clear a layer 2 buffer provided for the UL split SRB1. The UE may clear the aforementioned buffer when detecting an SCG failure. The notification of the SCG failure information in the UE may be performed after the aforementioned buffer is cleared. The buffer may be a buffer for initial transmission of the PDCP layer. The buffer may include a buffer for retransmission of the PDCP layer, a buffer for initial transmission and / or retransmission of the RLC layer, or a buffer for initial transmission and / or retransmission of the MAC layer.

[0226] As another example, when the UE detects an SCG failure, the UE may transmit data waiting to be transmitted stored in a buffer of the PDCP layer for the uplink split SRB1 to the RLC layer for the SCG. The UE may transmit the SCG failure information from the RRC layer to the PDCP layer after transmitting the stored data waiting to be transmitted to the RLC layer for the SCG. This allows the UE to quickly notify the MN of the SCG failure information, for example.

[0227] As another example, the UE may transmit the notification of the SCG failure information in the MAC layer for the MCG with priority over other signaling and / or other user data. For example, in the MAC layer, the priority of the logical channel for transmitting the SCG failure information may be set higher than that of other logical channels. The above-mentioned operation of increasing the priority may be performed, for example, when an SCG failure is detected. This allows, for example, the UE to quickly notify the MN of the SCG failure information.

[0228] The above-mentioned buffer clearing may be combined with the method disclosed in the second embodiment. For example, the above-mentioned buffer clearing may be combined with a method in which the UE autonomously switches the transmission path of the uplink split SRB1 from the SCG to the MCG. As another example, the above-mentioned buffer clearing may be combined with switching of the destination base station in the signaling of SCG failure information, with packet duplication in the signaling of SCG failure information, or with the signaling of SCG failure information using another SRB. When the above-mentioned buffer clearing is combined with the signaling of SCG failure information using another SRB, the SRB for clearing the buffer may be SRB0 or ​​SRB2. As another example, the above-mentioned buffer clearing may be combined with a method of setting the size of the signaling of SCG failure information to a predetermined threshold or more. This makes it possible, for example, to quickly notify the MN of the signaling of SCG failure information from the UE. Similarly, the operation of transmitting data awaiting transmission stored in the buffer of the PDCP layer for the uplink split SRB1 to the RLC layer for the SCG, and / or the operation of increasing the priority of the logical channel for notifying SCG failure information in the MAC layer for the MCG may be combined with the method disclosed in the second embodiment.

[0229] As an uplink packet duplication operation when an SCG failure is detected, the UE may continue to transmit uplink data to the MN. The UE may stop transmitting uplink data to the SN. The uplink data may be transmitted using a DRB or an SRB. In the above, the SRB may be SRB0, SRB1, SRB2, or SRB3. The stop of the uplink data transmission to the SN in the UE may be, for example, the stop of the transmission from the PDCP layer to the RLC layer, the stop of the transmission from the RLC layer to the MAC layer, the stop of the transmission from the MAC layer to the PHY layer, or the stop of the radio transmission in the PHY layer. In each of the above-mentioned layers, the retransmission of the data that has been stopped may not be performed, or may be performed. The above-mentioned retransmission may be performed, for example, after recovery from the SCG failure. This makes it possible to avoid, for example, the complexity of the design in the communication system.

[0230] This embodiment 2 may be combined with embodiment 1. For example, the notification of SCG failure information from the UE disclosed in this embodiment 2 may include information on the SCG setting disclosed in embodiment 1. As another example, upon receiving the SCG failure information disclosed in this embodiment 2, the MN may make an SCG setting inquiry to the SN disclosed in embodiment 1. In the above, the SN may notify the MN of the SCG setting. This makes it possible to prevent, for example, discrepancies in the SCG settings between the MN and the UE after the MN receives SCG failure information. As a result, it becomes possible to prevent malfunctions in the communication system.

[0231] According to the second embodiment, when an SCG failure is detected, it becomes possible to quickly perform signaling from the UE to the MN. As a result, the MN can quickly perform SCG recovery processing.

[0232] Embodiment 3 In a beam failure recovery request (hereinafter, sometimes referred to as BFRQ) using a PUCCH, the PUCCH for SR may be used for transmission. As another example, a PUCCH for beam measurement result reporting may be used. The base station may configure the PUCCH for BFRQ for the UE. For example, RRC signaling may be used for the configuration.

[0233] However, in the BFRQ using PUCCH, details of RRC signaling used for setting the PUCCH are not disclosed, and the format of the PUCCH for transmitting the BFRQ is not disclosed. As a result, the UE cannot notify the base station of the BFRQ using the PUCCH. In addition, it is not disclosed how to ensure reliability in the PUCCH for BFRQ. As a result, reliability cannot be ensured in the notification of the BFRQ from the UE to the base station.

[0234] Solutions to the aforementioned problems are disclosed below.

[0235] The UE transmits the PUCCH for BFRQ using a predetermined sequence. The application of the predetermined sequence may be performed, for example, when the BFRQ information includes only information on the occurrence or non-occurrence of beam failure. The predetermined sequence may be, for example, a ZC sequence. This allows, for example, the base station to quickly detect the PUCCH. In the PUCCH for BFRQ, parameters related to the sequence, for example, a root index and / or a cyclic shift amount, may be made different from the sequence of the PUCCH for SR and / or ACK / NACK. Alternatively, the parameters in the PUCCH for BFRQ may be the same as those in the PUCCH for SR and / or ACK / NACK. When the parameters are the same as those in the PUCCH for SR and / or ACK / NACK, the frequency and / or time resource of the PUCCH for BFRQ may be made different from those in the PUCCH for ACK / NACK. In the base station, the PUCCH for BFRQ and the PUCCH for SR and / or ACK / NACK can be distinguished from each other.

[0236] As another example, the UE may transmit the PUCCH for BFRQ using PSK and / or QAM modulation (hereinafter, sometimes referred to as PSK / QAM modulation). The PSK may be BPSK, QPSK, or other PSK methods. The QAM may be 16QAM, 64QAM, 256QAM, or other QAM methods. The same may be applied to the PSK and QAM below. The application of PSK / QAM modulation may be performed, for example, when the BFRQ is composed of multiple bits, for example, when the BFRQ includes information about a beam, which will be described later.

[0237] The UE may transmit the PSK / QAM modulated PUCCH for BFRQ together with the DMRS. The UE may frequency-multiplex or time-multiplex the PUCCH for BFRQ and the DMRS.

[0238] The UE may transmit the PUCCH for BFRQ as a short PUCCH, for example to obtain a frequency diversity effect, or as a long PUCCH, for example to obtain a time diversity effect.

[0239] Fig. 18 is a diagram showing an example of a format of a PUCCH for BFRQ. Fig. 18 shows an example in which PSK / QAM modulation is used as a modulation scheme for a PUCCH for BFRQ. Fig. 18 also shows an example in which a short PUCCH of one symbol is used as a PUCCH.

[0240] 18, BFRQ information is PSK / QAM modulated and mapped to PUCCH 1601. To demodulate PUCCH 1601, DMRS 1602 is frequency-multiplexed and mapped to the same symbol as PUCCH 1601.

[0241] 18 shows an example in which a short PUCCH of one symbol is used, but a short PUCCH of two or more symbols may be used, or a long PUCCH may be used. Also, although an example in which DMRS 1602 is FDM-multiplexed with PUCCH 1601 is shown, TDM may be used.

[0242] The PUCCH for BFRQ may include information on the presence or absence of BFRQ. For example, the UE may determine that BFRQ is present by transmitting the PUCCH, or may determine that BFRQ is not present by not transmitting the PUCCH. As another example, the UE may use a different sequence for the PUCCH for BFRQ depending on the presence or absence of BFRQ. As another example, an identifier indicating the presence or absence of BFRQ may be included in the PUCCH. As another example, the modulation method of the PUCCH may be different depending on the presence or absence of BFRQ. For example, when BFRQ is present, the PUCCH may be PSK and / or QAM modulated, and when BFRQ is not present, the PUCCH may be configured with a predetermined sequence (e.g., ZC sequence).

[0243] The PUCCH for BFRQ may include information about the beam that has failed. For example, the identifier of the downlink beam may be included, or information about the measurement result of the downlink beam by the UE may be included. The base station may use, for example, the information about the measurement result to increase the transmission power of the downlink beam. This allows, for example, the UE to quickly restore the beam.

[0244] The PUCCH for BFRQ may include information about a beam measured by the UE. For example, an identifier of a downlink beam may be included, or information about a measurement result of the downlink beam by the UE may be included. The beam information included in the information may be, for example, information about a beam whose measurement result by the UE is equal to or greater than a predetermined threshold. The threshold may be determined in advance by a standard, or may be notified or individually notified to the UE by the base station in advance. The beam information included in the information may be information about a plurality of beams. The base station may use the information to restore the downlink beam. This allows, for example, a UE to quickly restore from a beam failure.

[0245] The setting required for the transmission of the PUCCH for BFRQ from the UE may be determined by a standard. This, for example, makes it possible to reduce the amount of signaling required for the setting. As another example, the information may be notified in advance from the base station to the UE, or may be notified individually. As the individual notification, for example, RRC signaling may be used. The RRC signaling may be, for example, RRC connection reconfiguration. This, for example, makes it possible to perform flexible control using the usage status of the UE, other UEs, and other base stations in a communication system. As another example, the information may be notified from the base station to the UE by MAC signaling, or may be notified from the base station to the UE by L1 / L2 signaling. This, for example, makes it possible to quickly notify the information to the UE. The above-mentioned combination may be used for the setting. For example, the use of sequence modulation for the PUCCH may be determined by a standard, and information regarding the sequence may be notified from the base station to the UE individually.

[0246] The settings required for transmitting a PUCCH for BFRQ from a UE are disclosed below as (1) to (4).

[0247] (1) Information regarding PUCCH transmission resources.

[0248] (2) Information about the modulation method.

[0249] (3) Information regarding notifications from UE.

[0250] (4) A combination of (1) to (3) above.

[0251] The above (1) may include, for example, information on the transmission timing of the PUCCH for BFRQ. The information may include information on the period and offset of the transmission of the PUCCH for BFRQ, or information on the number of transmission symbols. The above (1) may include information on the frequency resource of the PUCCH, or information indicating whether the PUCCH is a long PUCCH or a short PUCCH.

[0252] The above (2) may be, for example, modulation using PSK and / or QAM, or modulation using a sequence (eg, ZC sequence).

[0253] In the above (2), in the case of modulation using PSK and / or QAM, information on DMRS may be included. The information on DMRS may include, for example, information on the root index of the DMRS or information on the amount of cyclic shift of the DMRS. Information on a multiplexing method of the DMRS and PUCCH may be included. The multiplexing method may be, for example, FDM or TDM.

[0254] In the above (2), in the case of modulation using a sequence, information on the root index of the sequence may be included, or information on the amount of cyclic shift of the sequence may be included.

[0255] The above (3) may include, for example, information on whether or not information on a beam is notified. The beam may be a beam that has failed, may be a beam that the UE has measured, or may be both of the above.

[0256] The above (3) may include information about the signal that the UE uses in measuring the beam, such as CSI-RS, SS (synchronization signal), or both of the above.

[0257] The above (3) may include information regarding whether or not the measurement results have been notified.

[0258] Some or all of the information related to the above items (1) to (4) may be defined in advance by a standard, which may reduce the amount of signaling required for the notification from the base station to the UE, for example.

[0259] The UE may notify the BFRQ at the earliest PUCCH transmission timing for BFRQ after detecting a beam failure. This allows, for example, the UE to promptly notify the base station of the BFRQ. As another example, the UE may notify the BFRQ at the earliest PUCCH transmission timing for BFRQ after detecting a new beam. This allows, for example, prompt recovery from a beam failure.

[0260] Another solution is disclosed. The UE may transmit the BFRQ using the PUCCH for SR. The SR and BFRQ information may be multiplexed in the same PUCCH. In multiplexing the SR and the BFRQ, the BFRQ may not include beam information. For example, the BFRQ information may be only an identifier indicating that a beam failure has occurred.

[0261] A predetermined sequence may be used in the PUCCH in which the multiplexing is performed. The application of the predetermined sequence may be performed, for example, when the BFRQ information includes only information on the occurrence or non-occurrence of beam failure. A different sequence may be used for each of the cases where only SR is present, only BFRQ is present, and both SR and BFRQ are present. When neither SR nor BFRQ is present, PUCCH may not be transmitted. As the above-mentioned different sequence, for example, the root index of the sequence may be different, the cyclic shift amount may be different, or the sequence itself may be different, for example, an m-sequence may be used when BFRQ is present. A combination of the above-mentioned sequences may be used. This allows, for example, the base station to easily obtain information on SR and / or BFRQ. The base station may obtain information on SR and information on BFRQ from the sequence of the PUCCH.

[0262] As another example, PSK / QAM modulation may be used in the PUCCH to be multiplexed. The application of PSK / QAM modulation may be performed, for example, when the BFRQ is composed of multiple bits, for example, when the BFRQ includes information about a beam. The PUCCH may include, for example, information about the presence or absence of SR, or information about the BFRQ (e.g., the presence or absence of BFRQ, information about a beam).

[0263] In applying PSK / QAM modulation to the PUCCH to be multiplexed, the UE may multiplex the PSK / QAM modulated PUCCH and the DMRS and transmit the multiplexed PUCCH. The multiplexing may be, for example, FDM or TDM. The base station may determine the presence or absence of BFRQ using a signal received from the UE. For example, the base station may determine the presence or absence of BFRQ by using the fact that the QPSK signal and the DMRS signal are FDM-modulated. This allows, for example, the base station to easily determine the presence or absence of BFRQ.

[0264] In applying PSK / QAM modulation to the PUCCH to which the multiplexing is performed, information regarding the presence or absence of SR may be included in the DMRS. For example, different DMRS sequences (e.g., root index, cyclic shift) may be used depending on the presence or absence of SR. This makes it possible to increase the amount of information that can be included in the PUCCH, for example.

[0265] In applying PSK / QAM modulation to the multiplexed PUCCH, the PUCCH of other UEs may not be transmitted in the time-frequency resource in which the multiplexed PUCCH is transmitted, thereby making it possible to prevent interference with the PUCCH of other UEs.

[0266] As another example, in application of PSK / QAM modulation to the PUCCH to be multiplexed, the PUCCH of another UE may be transmitted in the time-frequency resource in which the PUCCH is transmitted. The UE may transmit the PUCCH on a contention-based basis. The UE may retransmit the PUCCH to the base station by using the fact that beam recovery is not performed within a predetermined period and / or that no uplink grant is received from the base station. The aforementioned predetermined period may be determined by a standard, or may be notified or notified in advance from the base station to the UE. This enables multiplexing with the PUCCH of another UE, thereby enabling an increase in the capacity of the communication system.

[0267] The above-mentioned determination as to whether or not the PUCCH of another UE can be transmitted in the time-frequency resource in which the PUCCH is transmitted may also be applied to the PUCCH for another UCI.

[0268] In the PUCCH to which the multiplexing is performed, both a predetermined sequence and PSK / QAM modulation may be used. For example, in a PUCCH without BFRQ, i.e., a PUCCH with only SR, a predetermined sequence may be used, and in a PUCCH with BFRQ, PSK / QAM modulation may be used. In the absence of both SR and BFRQ, the PUCCH may not be transmitted. This allows, for example, the conventional SR PUCCH to continue to be used in the communication system, thereby making it possible to avoid complexity in the design of the communication system.

[0269] As another example of the method of transmitting BFRQ using PUCCH for SR, multiple arrangements of PUCCH may be used. For example, different arrangements may be used as the arrangement of PUCCH depending on the presence or absence of SR. Different PUCCH arrangements according to SR may be performed, for example, when BFRQ is composed of multiple bits, for example, when BFRQ includes information about beam. As another example, different arrangements may be used as the arrangement of PUCCH depending on the presence or absence of BFRQ. Different PUCCH arrangements according to the presence or absence of BFRQ may be performed, for example, when information about BFRQ includes only information about the occurrence or absence of beam failure. The different arrangements may be, for example, signals being swapped between symbols, between subcarriers, or a combination of both. The above-mentioned swap between symbols may be swap between groups of a plurality of symbols. The above-mentioned swap between subcarriers may be swap between groups of a plurality of subcarriers. This makes it possible to multiplex BFRQ information without changing the sequence or modulation method, for example, and therefore makes it possible to avoid complexity in the design of the communication system.

[0270] The information regarding the above-mentioned multiple locations may be defined by a standard, or may be notified in advance from the base station to the UE or notified individually.

[0271] The information included in the PUCCH in which SR and BFRQ are multiplexed may include a part or all of the information of BFRQ included in the PUCCH for BFRQ described above. It may also include information on SR, for example, information on the presence or absence of SR. For example, when a sequence is used in the PUCCH in which SR and BFRQ are multiplexed, the PUCCH may only have information on the presence or absence of SR and information on the presence or absence of BFRQ.

[0272] In the transmission of BFRQ using the PUCCH for SR, only one of SR and BFRQ may be transmitted in one PUCCH. That is, either SR or BFRQ may be prioritized. In the above, the format of the PUCCH may be the same as the conventional format of the PUCCH for SR or the format of the PUCCH for BFRQ described above. This makes it possible to avoid, for example, the complexity of the design in the communication system.

[0273] Regarding the prioritization between SR and BFRQ, for example, the preferred UCI may be statically determined in the standard, or may be notified or semi-statically from the base station to the UE. The semi-static notification may be, for example, RRC dedicated signaling. Alternatively, the base station may dynamically notify the UE using MAC signaling or L1 / L2 signaling.

[0274] As another example of the prioritization, the UCI that was generated first in the UE may be given priority, and as another example, the UCI that was not transmitted in the immediately preceding PUCCH may be given priority.

[0275] The settings required for transmitting BFRQ using the PUCCH for SR may be defined by a standard, similar to the settings required for transmitting the PUCCH for BFRQ, or may be notified in advance from the base station to the UE or notified individually.

[0276] In the notification of the setting from the base station to the UE using RRC dedicated signaling, the setting content may be included in the SR setting content, for example. This allows the base station to notify the UE of the SR setting and the BFRQ setting at the same time, for example, so that the setting process in the UE can be quickly performed.

[0277] The settings (1) to (6) required for transmitting BFRQ using the PUCCH for SR are disclosed below.

[0278] (1) Information regarding PUCCH transmission resources.

[0279] (2) Information about the modulation method.

[0280] (3) Information regarding notifications from UE.

[0281] (4) Information regarding multiplexing of SR and BFRQ.

[0282] (5) Information regarding PUCCH placement.

[0283] (6) A combination of (1) to (5) above.

[0284] The above (1) may be the same as the setting (1) required for transmitting PUCCH for BFRQ.

[0285] In the above (1), the information on the transmission timing of the PUCCH may be the same as the information on the transmission timing of the SR, which makes it easier for the base station to schedule the PUCCH.

[0286] The above (2) may be the same as the setting (2) required for transmitting PUCCH for BFRQ.

[0287] In the above (2), the information on the DMRS in modulation using PSK and / or QAM may include information on the sequence of the DMRS with / without SR, and may include information on the difference in the sequence of the DMRS (e.g., root index, cyclic shift amount) between with SR and without SR.

[0288] In the above (2), in the case of modulation using a sequence, information on the sequence in each of the cases where only SR is present, only BFRQ is present, and both SR and BFRQ are present may be included. Information on the difference in sequence between the above three may also be included.

[0289] The above (3) may include information similar to the setting (3) required for transmitting PUCCH for BFRQ, or may include information regarding SR notification.

[0290] The above (4) may include, for example, information on whether SR and BFRQ can be multiplexed on one PUCCH. If the multiplexing is not possible, the information may indicate which of PUCCH and SR is to be prioritized.

[0291] The above (5) may include, for example, information regarding whether different PUCCH arrangements are supported, information indicating whether the signals are to be swapped between symbols or between subcarriers, or information regarding the number of symbols and / or subcarriers to be grouped together.

[0292] The UE may detect a beam for downlink communication. The detection may be performed after the UE detects a beam failure. A signal used for beam detection in the UE may be determined in advance by a standard, or may be notified or individually notified to the UE from the base station. The signal may be, for example, a CSI-RS or a synchronization signal (SS). As another example, the UE may not perform a detection operation for a beam for downlink communication.

[0293] The transmission timing of the PUCCH transmitted from the UE to the base station, for example, the period and offset, should be the same regardless of the presence or absence of the BFRQ, which allows the base station to detect the BFRQ by receiving the PUCCH.

[0294] The UE may notify the BFRQ at the earliest PUCCH for SR transmission timing after detecting a beam failure. This allows, for example, the UE to promptly notify the base station of the BFRQ. As another example, the UE may notify the BFRQ at the earliest PUCCH for SR transmission timing after detecting a new beam. This allows, for example, prompt recovery from a beam failure.

[0295] The base station may use BFRQ to change the downlink beam for the UE. The base station may use BFRQ to transmit CSI-RS to other beams as well. The arrangement of CSI-RS in other beams may be the same as that of the original beam. This allows, for example, the UE to detect other beams with the same arrangement as the original beam. As a result, the UE can quickly perform beam detection to recover from a beam failure.

[0296] Another solution is disclosed. The UE may transmit the BFRQ using a PUCCH for beam measurement result reporting. That is, the UE may include information of the BFRQ in the beam measurement result report. The PUCCH may be a PUCCH for reporting the measurement result of the SS (synchronization signal) to the base station. The PUCCH may be newly provided.

[0297] The information on the BFRQ included in the beam measurement result report may include information on the presence or absence of the BFRQ (e.g., a flag indicating the presence or absence of the BFRQ), may include information using the beam identifier, or may include information on the beam measurement result. As the information using the beam identifier, for example, the beam identifier may be associated with a predetermined special value (e.g., all bits '0', all bits '1') of the beam identifier, which may be associated with the BFRQ. As the information on the beam measurement result, for example, the measurement result being equal to or less than a predetermined threshold may be associated with the BFRQ. As another example, the measurement result may be associated with a predetermined special value (e.g., all bits '0', all bits '1') of the measurement result, which may be associated with the BFRQ. This allows, for example, the information on the presence or absence of the BFRQ and the information on the beam measurement result report to be shared. As a result, it is possible to avoid complexity in the design of the UE and the base station regarding the BFRQ.

[0298] The beam identifier and / or the beam measurement result included in the BFRQ information included in the beam measurement result report PUCCH may be the beam identifier and / or the beam measurement result for CSI-RS. This enables, for example, the base station to quickly recover from a beam failure by using information on the beam for CSI-RS.

[0299] Alternatively, the BFRQ information included in the beam measurement result report PUCCH may be only information regarding the presence or absence of BFRQ. The base station may perform a recovery operation from a beam failure using the beam information included in the beam measurement result report. This makes it possible to suppress an increase in the amount of signaling of the beam measurement result report PUCCH, including the BFRQ, for example.

[0300] As another example, the DMRS in the PUCCH for beam measurement result report may be changed using information of the BFRQ. The change may be, for example, a change in the sequence of the DMRS. The change in the sequence may be, for example, a change in the root index, a change in the amount of cyclic shift, or a combination of both. This allows, for example, the UE to quickly notify the base station of the PUCCH including the BFRQ.

[0301] As another example, the beam measurement result report PUCCH does not need to include information on the beam measurement result. The PUCCH may include only information on the BFRQ. The information on the BFRQ may be the same as that in the case where the BFRQ information is multiplexed on the beam measurement result report PUCCH described above.

[0302] In the case where only information related to the BFRQ is included in the PUCCH, the modulation using the sequence may be performed. The modulation using the sequence may be performed in the same manner as the PUCCH for SR. This allows, for example, the base station to quickly detect the BFRQ.

[0303] As another example of the transmission method of BFRQ using PUCCH for SR, multiple arrangements of PUCCH may be used. The above-mentioned multiple arrangements may be the same as the example of the transmission method of BFRQ using PUCCH for SR. For example, different arrangements may be used as the arrangement of PUCCH depending on the presence or absence of BFRQ. Different PUCCH arrangements depending on the presence or absence of BFRQ may be performed, for example, when the information on BFRQ includes only the information on the occurrence or absence of beam failure.

[0304] The settings required for transmitting the BFRQ using the PUCCH for beam measurement results report may be determined in advance by a standard, or may be notified from the base station to the UE, or may be notified individually, similar to the settings required for transmitting the BFRQ using the PUCCH for SR described above. For example, RRC signaling, MAC signaling, or L1 / L2 signaling may be used as the individual notification. This can provide the same effect as multiplexing SR and BFRQ.

[0305] The settings (1) to (6) required for transmitting BFRQ using the PUCCH for reporting beam measurement results described above are disclosed below.

[0306] (1) Information regarding PUCCH transmission resources.

[0307] (2) Information about the modulation method.

[0308] (3) Information regarding notifications from UE.

[0309] (4) Beam measurement results and BFRQ multiplexing information.

[0310] (5) Information regarding PUCCH placement.

[0311] (6) A combination of (1) to (5) above.

[0312] The above (1) may be the same as the setting (1) required for transmitting BFRQ using PUCCH for SR. Information regarding the transmission timing of PUCCH for beam measurement result report, including BFRQ, may be the same as information regarding the transmission timing of beam measurement result report. Scheduling of PUCCH in the base station becomes easy.

[0313] The above-mentioned (2) may be the same as the setting (2) required for transmitting BFRQ using the PUCCH for SR.

[0314] In the above (2), the information on the DMRS in modulation using PSK and / or QAM may include information on the sequence of the DMRS with / without BFRQ. Information on the difference in the sequence of the DMRS (e.g., root index, cyclic shift amount) between with and without BFRQ may also be included.

[0315] In the above (2), in the case of modulation using a sequence, information on the sequence in the case where only BFRQ is present may be included.

[0316] The above-mentioned (3) may be the same as the setting (3) required for transmitting BFRQ using the PUCCH for SR. Information regarding the beam measurement result report may be included.

[0317] The above-mentioned (4) may be the same as the setting (4) required for transmitting BFRQ using the PUCCH for SR.

[0318] The above-mentioned (5) may be the same as the setting (5) required for transmitting BFRQ using the PUCCH for SR.

[0319] The operation of the UE in transmitting the BFRQ using the PUCCH for beam measurement result report may be the same as the operation of the UE in transmitting the BFRQ using the PUCCH for SR. The operation of the base station may also be the same.

[0320] The beam measurement result report PUCCH in the third embodiment may be periodic, semi-persistent, or non-periodic. For example, the UE may notify the BFRQ at the earliest PUCCH transmission timing for beam measurement result report after a beam failure is detected. This allows, for example, the UE to promptly notify the base station of the BFRQ. As another example, the UE may notify the BFRQ at the earliest PUCCH transmission timing for beam measurement result report after a new beam is detected. This allows, for example, a prompt recovery from a beam failure.

[0321] The PUCCH for beam measurement result report in the third embodiment may be a PUCCH for CSI. The UE may transmit a BFRQ using the PUCCH for CSI. When transmitting a BFRQ using the PUCCH for CSI, a method similar to the method of transmitting a BFRQ using the PUCCH for beam measurement result report may be used. This provides the same effect as multiplexing the beam measurement result and the BFRQ.

[0322] In the third embodiment, the BFRQ may be multiplexed with other UCI. The other UCI may be, for example, Ack / Nack. For the BFRQ transmission using the PUCCH for Ack / Nack, a method similar to the BFRQ transmission using the PUCCH for SR may be used, or a method similar to the BFRQ transmission using the beam measurement result report PUCCH may be used. This allows, for example, flexible setting regarding the PUCCH.

[0323] BFRQ transmission using PUCCH for each UCI disclosed in the third embodiment may be combined. The above-mentioned PUCCH may be periodic, semi-persistent, or aperiodic. A combination of periodic, semi-persistent, and aperiodic PUCCHs may be used. For example, the UE may notify the BFRQ at the earliest PUCCH transmission timing regardless of the UCI. This enables, for example, a quick notification from the UE to the base station.

[0324] The PUCCH including the BFRQ disclosed in the third embodiment may not be used for the beam failure judgment in the base station. The base station may judge the beam failure in the UE by using the reception status for each PUCCH transmission timing type from the UE. The PUCCH transmission timing type may be a periodic PUCCH, a semi-persistent PUCCH, or an aperiodic PUCCH. For example, when the base station receives a periodic PUCCH from the UE but cannot receive an aperiodic PUCCH from the UE, the base station may judge the beam failure in the UE. As another example, when the base station cannot receive an aperiodic PUCCH from the UE, the base station may judge the beam failure in the UE. In the above, information on the presence or absence of reception of a plurality of PUCCHs may be used. For example, when the base station cannot receive an aperiodic PUCCH consecutively for a predetermined number of times or more, the base station may judge the beam failure in the UE. In the above, the base station may judge the PUCCH cannot be received by using the reception quality of the PUCCH in the base station falling below a predetermined quality. This makes it possible to reduce, for example, the amount of signaling in the radio interface.

[0325] The base station may transmit a PDCCH to the UE using information about the beam included in the BFRQ. In transmitting the PDCCH, the base station may use a beam acquired from the information. After transmitting the BFRQ, the UE may detect the PDCCH within a predetermined time window. This allows, for example, a quick recovery from a beam failure to be performed.

[0326] The UE may transmit the PUCCH including the BFRQ using multiple beams. The PUCCH may be a PUCCH for BFRQ, a PUCCH for SR, a PUCCH for beam measurement result report, or a PUCCH for other UCI. This, for example, makes it possible to ensure the reliability of the BFRQ notification from the UE. As another example, the UE may transmit the PUCCH including the BFRQ multiple times. The multiple transmissions may be, for example, transmitting the same PUCCH with different symbols, transmitting the same PUCCH with different slots, or transmitting the same PUCCH in units of the PUCCH transmission period of each UCI. This, for example, makes it possible to improve the reliability of the BFRQ notification from the UE.

[0327] As another example, the UE may transmit a PUCCH including a BFRQ as a long PUCCH. The PUCCH may be a PUCCH for a BFRQ, a PUCCH for an SR, a PUCCH for a beam measurement result report, or a PUCCH for another UCI. This may ensure, for example, time diversity. As another example, the UE may transmit a PUCCH as a short PUCCH. Frequency diversity may be ensured. As another example, the UE may use a PUCCH in combination with a short PUCCH and a long PUCCH. Time and frequency diversity may be ensured. The combination of a short PUCCH and a long PUCCH may be, for example, a UE using both a short PUCCH and a long PUCCH in the same slot.

[0328] The base station may instruct the UE in advance which method to send the PUCCH as a short PUCCH, a long PUCCH, or both the short PUCCH and the long PUCCH. For example, the instruction may be made using RRC dedicated signaling, MAC signaling, or L1 / L2 signaling.

[0329] According to the third embodiment, the UE can transmit the BFRQ by using the PUCCH. Also, the UE can quickly recover from a beam failure.

[0330] The above-described embodiments and their modifications are merely examples of the present invention, and the embodiments and their modifications can be freely combined within the scope of the present invention. In addition, any of the components of the embodiments and their modifications can be appropriately modified or omitted.

[0331] For example, in each of the above-mentioned embodiments and their modifications, a subframe is an example of a time unit of communication in a fifth generation base station communication system. It may be a scheduling unit. In each of the above-mentioned embodiments and their modifications, the processing described as a subframe unit may be performed in a TTI unit, a slot unit, a subslot unit, or a minislot unit.

[0332] Although the present invention has been described in detail, the above description is illustrative in all respects and does not limit the present invention. It is understood that countless variations not illustrated can be assumed without departing from the scope of the present invention. [Explanation of symbols]

[0333] 200 communication system, 202 communication terminal device, 203 base station device.

Claims

1. A communication unit for wirelessly communicating with a base station, The communication unit transmits a physical uplink control channel (PUCCH) for a scheduling request (SR) in beam failure recovery (BFR).

2. The user equipment of claim 1, wherein a first resource configuration of the physical uplink control channel for the scheduling request in the beam failure recovery is configured separately from a second resource configuration of the physical uplink control channel for a signal different from the scheduling request in the beam failure recovery.

3. The user equipment according to claim 2 , wherein the first resource configuration includes at least one of first information on a transmission resource of the physical uplink control channel related to the first resource configuration and second information on a modulation scheme.

4. 4. The user equipment according to claim 3, wherein the first information includes at least any of information on a transmission timing of the physical uplink control channel, information on a number of transmission symbols of the physical uplink control channel, information on a transmission frequency of the physical uplink control channel, and information indicating whether the physical uplink control channel is a long physical uplink control channel or a short physical uplink control channel.

5. The user equipment according to claim 3 , wherein the second information includes information related to a data demodulation reference signal (DMRS).

6. The user equipment of claim 1 , wherein a cyclic shift of the physical uplink control channel for the scheduling request in the beam failure recovery is different from a cyclic shift for other signals.

7. The user equipment of claim 1 , wherein the physical uplink control channel for the scheduling request in the beam failure recovery is multiplexed with a physical uplink control channel for a signal different from the scheduling request in the beam failure recovery.

8. The user equipment according to claim 7 , wherein the signal is a signal indicating Ack / Nack.

9. A communication unit for wirelessly communicating with a user device, A base station, wherein the communication unit receives a physical uplink control channel (PUCCH) for a scheduling request (SR) in beam failure recovery (BFR) from the user equipment.

10. A user device; a base station that wirelessly communicates with the user equipment; A communication system, wherein the user equipment transmits a physical uplink control channel (PUCCH) for a scheduling request (SR) in beam failure recovery (BFR).

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