Communication system, base station and communication terminal

Abstract

To provide a technique that can avoid a conflict in scheduling for a communication terminal between base stations that provide dual connectivity.SOLUTION: A communication system includes a communication terminal, and a first base station and a second base station configured to be able to wirelessly communicate with the communication terminal. The first base station and the second base station are capable of providing dual connectivity to the communication terminal. The first base station notifies the second base station of information about the frame timing of the first base station.SELECTED DRAWING: Figure 15

Description

[Technical field]

[0001] The present invention relates to wireless communication technology. [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 Channel State Information (CSI). The CSI is composed of a Rank Indicator (RI), a Precoding Matrix Indicator (PMI), and a Channel Quality Indicator (CQI) report. The RI is information on the rank of a channel matrix in MIMO. The PMI is information on the precoding weight matrix used in MIMO. The 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] Similarly, the uplink reference signal is a known symbol in the LTE communication system. Two types of uplink reference signals are defined: a data demodulation reference signal (DM-RS) and a sounding reference signal (SRS).

[0016] 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).

[0017] 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).

[0018] 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.

[0019] 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.

[0020] 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).

[0021] 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).

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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).

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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).

[0031] 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).

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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).

[0036] 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).

[0037] A set of serving cells, which includes one PCell and one or more SCells, is configured for one UE.

[0038] 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.

[0039] 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.

[0040] 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)."

[0041] 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.

[0042] 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).

[0043] 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.

[0044] In order to meet such demands, 3GPP is currently working on 5G standards as Release 15 (see Non-Patent Documents 6 to 18). The technology for 5G wireless sections is called "New Radio Access Technology" ("New Radio" is abbreviated as "NR").

[0045] The NR system is being developed based on the LTE system and LTE-A system, but the following changes and additions have been made to the LTE system and LTE-A system:

[0046] The NR access method uses OFDM for the downlink and OFDM and DFT-s-OFDM (DFT-spread-OFDM) for the uplink.

[0047] NR allows the use of higher frequencies than LTE in order to improve transmission speeds and reduce processing delays.

[0048] In NR, cell coverage is ensured by forming a narrow beam-shaped transmission and reception range (beamforming) and changing the direction of the beam (beam sweeping).

[0049] In the NR frame configuration, various subcarrier intervals, i.e., various numerologies, are supported. In NR, regardless of the numerology, one subframe is 1 millisecond, and one slot is composed of 14 symbols. In addition, the number of slots included in one subframe is one in a numerology with a subcarrier interval of 15 kHz, and increases in proportion to the subcarrier interval in other numerologies (see Non-Patent Document 13 (TS38.211 v15.0.0)).

[0050] In NR, downlink synchronization signals are transmitted from base stations as synchronization signal bursts (hereinafter sometimes referred to as SS bursts) at a predetermined cycle with a predetermined duration. An SS burst is composed of synchronization signal blocks (hereinafter sometimes referred to as SS blocks) for each beam of the base station. The base station transmits the SS blocks of each beam within the duration of the SS burst by changing the beam. An SS block is composed of P-SS, S-SS, and PBCH.

[0051] In NR, the influence of phase noise is reduced by adding a Phase Tracking Reference Signal (PTRS) as a downlink reference signal for NR. PTRS is also added to the uplink reference signal in the same way as in the downlink.

[0052] In NR, in order to flexibly switch between DL and UL within a slot, slot format indication (SFI) has been added to the information contained in the PDCCH.

[0053] In addition, in NR, a base station pre-configures a portion of the carrier frequency band (hereinafter sometimes referred to as a Bandwidth Part (BWP)) for a UE, and the UE transmits and receives data to and from the base station using that BWP, thereby reducing power consumption in the UE.

[0054] In 3GPP, the following DC forms are being considered: DC by LTE base stations and NR base stations connected to the EPC, DC by NR base stations connected to the 5G core system, and DC by LTE base stations and NR base stations connected to the 5G core system (see non-patent documents 12, 16, and 23).

[0055] Also, 3GPP is considering several new technologies, such as coexistence of NR communication and LTE communication on the same frequency in DC using NR base stations and LTE base stations (hereinafter, sometimes referred to as NR-LTE coexistence) and reduction of UE power consumption by using BWP (Bandwidth Part) (see Non-Patent Documents 19 to 22).

[0056] In NR, the SRS used for uplink channel sounding is assigned within the last 6 symbols of one slot consisting of 14 symbols. The number of symbols for the SRS is either 1, 2, or 4 (see Non-Patent Documents 13 and 15). [Prior art documents] [Non-patent literature]

[0057] [Non-Patent Document 1] 3GPP TS 36.300 V14.3.0 [Non-Patent Document 2] 3GPP S1-083461 [Non-licensed document 3] 3GPP TR 36.814 V9.2.0

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Non-licensed literature 9

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[0058] In NR-LTE coexistence, an NR base station notifies an LTE base station of information about slots scheduled by the NR base station. However, since different numerologies are supported in the NR system, an LTE base station cannot know the timing of slots scheduled by the NR base station. Therefore, in NR-LTE coexistence, an NR base station and an LTE base station may schedule for the same timing. This causes a problem that a UE cannot communicate with one of the base stations, resulting in a decrease in reliability and transmission rate in communication between the UE and the base station.

[0059] In addition, in NR, the use of BWP, which uses a part of the UL carrier band, is being considered in order to reduce the power consumption of UE. However, when UE switches BWP to perform uplink transmission, the time required for BWP switching is not taken into consideration. Therefore, the base station does not appropriately perform uplink scheduling around the time of BWP switching, which results in problems such as a decrease in reliability of uplink communication and a decrease in uplink transmission rate when BWP switching occurs.

[0060] In view of the above problems, one object of the present invention is to provide a technology that can ensure communication reliability and transmission rate in NR. [Means for solving the problem]

[0061] The communication system of the present invention comprises a communication terminal, and a first base station and a second base station configured to be capable of wireless communication with the communication terminal, wherein the first base station and the second base station are capable of providing dual connectivity to the communication terminal, the first base station notifies the second base station of information regarding the frame timing of the first base station, the first base station further notifies the second base station of information regarding the numerology used by the first base station for communication with the communication terminal, and the first base station notifies the second base station of the information regarding the frame timing of the first base station and the information regarding the numerology used by the first base station for communication with the communication terminal by including them in the same signaling.

[0062] In addition, a base station according to the present invention is a base station configured to be capable of wireless communication with a communication terminal, and the base station can provide dual connectivity to the communication terminal together with other base stations, and the base station notifies the other base stations of information regarding the frame timing of the base station, and the base station further notifies the other base stations of information regarding the numerology used by the base station for communication with the communication terminal, and the base station notifies the other base stations of the information regarding the frame timing of the base station and the information regarding the numerology used by the base station for communication with the communication terminal by including them in the same signaling.

[0063] Moreover, a communication terminal according to the present invention is a communication terminal configured to be able to communicate with a first base station and a second base station, wherein the first base station, together with the second base station, is capable of providing dual connectivity to the communication terminal, the first base station notifies the second base station of information regarding the frame timing of the first base station, the first base station further notifies the second base station of information regarding the numerology used by the first base station for communication with the communication terminal, and the first base station notifies the second base station of the information regarding the frame timing of the first base station and the information regarding the numerology used by the first base station for communication with the communication terminal, by including them in the same signaling. Effect of the Invention

[0064] According to the present invention, it is possible to avoid a collision of scheduling for a communication terminal between base stations providing dual connectivity (for example, an LTE base station and an NR base station in NR-LTE coexistence). As a result, it is possible to ensure the reliability and communication rate of communication.

[0065] 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]

[0066] [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. 2 is a block diagram showing the overall configuration of a communication system 210 of the NR standard being discussed in 3GPP. [Figure 4] FIG. 1 is a diagram illustrating a DC configuration using eNBs and gNBs connected to an EPC. [Diagram 5] This is a diagram of a DC using gNB connected to an NG core. [Figure 6] This is a diagram showing the configuration of DC using eNBs and gNBs connected to the NG core. [Figure 7] This is a diagram showing the configuration of DC using eNBs and gNBs connected to the NG core. [Figure 8] FIG. 3 is a block diagram showing a configuration of a mobile terminal 202 shown in FIG. [Figure 9]FIG. 3 is a block diagram showing a configuration of a base station 203 shown in FIG. [Figure 10] FIG. 2 is a block diagram showing the configuration of an MME. [Figure 11] A block diagram showing the configuration of 5GC. [Figure 12] 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 13] FIG. 1 is a diagram showing an example of a cell configuration in an NR system. [Figure 14] FIG. 11 is a diagram showing the operation of notifying an LTE base station of numerology information used by an NR base station in accordance with the first embodiment. [Figure 15] A figure showing another example of the operation of notifying an LTE base station of numerology information used by an NR base station in accordance with embodiment 1. [Figure 16] FIG. 11 is a diagram illustrating an example of an operation in which a UE notifies a base station of a BWP switching time in accordance with the second embodiment. [Figure 17] FIG. 11 is a diagram showing an example of an operation for stopping upstream transmission before BWP switching earlier than the BWP switching time in the second embodiment. [Figure 18] FIG. 11 is a diagram showing an example of an operation in which, in preemption communication, upstream transmission before BWP switching is stopped earlier by an amount equivalent to the BWP switching time, in accordance with the second embodiment. [Figure 19] This figure shows an example of operation in which upstream transmission before the BWP switch is stopped earlier by an amount equivalent to the BWP switch time when the numerology is the same before and after the BWP switch in embodiment 2. [Figure 20] FIG. 11 is a diagram showing an example of an operation in which upstream transmission after BWP switching is started later than the time required for BWP switching in the second embodiment. [Figure 21] A figure showing an example of the operation of allocating a transmission suspension time equivalent to the BWP switching time after the uplink slot before the BWP switching and before the uplink slot after the BWP switching in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] 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.

[0068] 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."

[0069] 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.

[0070] 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.

[0071] 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.

[0072] The base station 203 is composed of one or more eNBs 207. A system composed of the core network EPC (Evolved Packet Core) and the radio access network E-UTRAN 201 is called an EPS (Evolved Packet System). The core network EPC and the radio access network E-UTRAN 201 are sometimes collectively called a "network."

[0073] 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.

[0074] The MME unit 204 is an upper device, specifically an upper node, and controls a connection between the eNB 207, which is a base station, and the mobile terminal (UE) 202. The MME unit 204 constitutes the EPC, which is a core network. The base station 203 constitutes the E-UTRAN 201.

[0075] 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.

[0076] FIG. 3 is a block diagram showing the overall configuration of a 5G communication system 210 being discussed in 3GPP. FIG. 3 will be described. The radio access network is called NG-RAN (Next Generation Radio Access Network) 211. The UE 202 is capable of wireless communication with an NR base station device (hereinafter referred to as "NR base station (NG-RAN NodeB: gNB)") 213, and transmits and receives signals via wireless communication. The core network is called 5G Core (5G Core: 5GC).

[0077] If control protocols for UE212, such as RRC (Radio Resource Control), and user plane (hereinafter sometimes referred to as U-Plane), such as SDAP (Service Data Adaptation Protocol), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate at the NR base station 213, the NG-RAN is composed of one or more NR base stations 213.

[0078] The function of the control protocol RRC (Radio Resource Control) between the UE 202 and the NR base station 213 is similar to that of LTE. The states of the NR base station 213 and the UE 202 in the RRC include RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE.

[0079] RRC_IDLE and RRC_CONNECTED are the same as those in the LTE system. In RRC_INACTIVE, the connection between the 5G core and the NR base station 213 is maintained, and system information (SI) is reported, paging, cell re-selection, mobility, and the like are performed.

[0080] The gNB 217 is connected to an AMF / SMF / UPF unit (hereinafter sometimes referred to as a "5GC unit") 214 including an Access and Mobility Management Function (AMF), a Session Management Function (SMF), or a User Plane Function (UPF), or an AMF, SMF, and UPF, via an NG interface. Control information and / or user data are communicated between the gNB 217 and the 5GC unit 214. The NG interface is a collective term for the N2 interface between the gNB 217 and the AMF, the N3 interface between the gNB 217 and the UPF, the N11 interface between the AMF and the SMF, and the N4 interface between the UPF and the SMF. A plurality of 5GC units 204 may be connected to one gNB 217. The gNBs 217 are connected to each other via an Xn interface, and control information and / or user data are communicated between the gNBs 217.

[0081] The NR base station 213 may configure one or more cells, similar to the base station 203. When one NR base station 213 configures multiple cells, each of the cells is configured to be capable of communicating with the UE 212.

[0082] The gNB 217 may be divided into a central unit (hereinafter, sometimes referred to as CU) 218 ​​and a distributed unit (hereinafter, sometimes referred to as DU) 219. One CU 218 is configured in the gNB 217. One or more DUs 219 are configured in the gNB 217. The CU 218 is connected to the DU 219 by an F1 interface, and control information and / or user data are communicated between the CU 218 and the DU 219.

[0083] Fig. 4 is a diagram showing a configuration of DC by eNB and gNB connected to EPC. In Fig. 4, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Fig. 4, eNB223-1 is a master base station, and gNB224-2 is a secondary base station (this DC configuration may be referred to as EN-DC). Fig. 4 shows an example in which U-Plane connection between MME unit 204 and gNB224-2 is made via eNB223-1, but it may be made directly between MME unit 221 and gNB224-2.

[0084] FIG. 5 is a diagram showing a DC configuration by a gNB connected to an NG core. In FIG. 5, a solid line indicates a U-Plane connection, and a dashed line indicates a C-Plane connection. In FIG. 5, gNB 224-1 is a master base station, and gNB 224-2 is a secondary base station (this DC configuration may be referred to as NR-DC). In FIG. 5, an example is shown in which a U-Plane connection between 5GC unit 214 and gNB 224-2 is made via gNB 224-1, but it may be made directly between 5GC unit 214 and gNB 224-2.

[0085] FIG. 6 is a diagram showing a configuration of DC by eNB and gNB connected to the NG core. In FIG. 6, a solid line indicates a U-Plane connection, and a dashed line indicates a C-Plane connection. In FIG. 6, eNB226-1 becomes a master base station, and gNB224-2 becomes a secondary base station (this DC configuration may be referred to as NG-EN-DC). In FIG. 6, an example is shown in which U-Plane connection between 5GC unit 214 and gNB224-2 is made via eNB226-1, but it may be made directly between 5GC unit 214 and gNB224-2.

[0086] FIG. 7 is a diagram showing another configuration of DC by eNB and gNB connected to the NG core. In FIG. 7, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In FIG. 7, gNB224-1 is the master base station, and eNB226-2 is the secondary base station (this DC configuration may be referred to as NE-DC). In FIG. 7, an example is shown in which U-Plane connection between 5GC unit 214 and eNB226-2 is made via gNB224-1, but it may be made directly between 5GC unit 214 and eNB226-2.

[0087] FIG. 8 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. 8 will be described. First, the control data from the protocol processing unit 301 and the user data from the application unit 302 are stored in the transmission data buffer unit 303. The data stored in the transmission data buffer unit 303 is passed to the encoder unit 304, where encoding such as error correction is performed. There may be data that is directly output from the transmission data buffer unit 303 to the modulation unit 305 without encoding. The data that has been encoded by the encoder unit 304 is modulated by the modulation unit 305. Precoding in MIMO may be performed 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 antennas 307-1 to 307-4 to the base station 203. Although the case where the number of antennas is four is illustrated in FIG. 8, the number of antennas is not limited to four.

[0088] Moreover, the reception process of the mobile terminal 202 is executed as follows. Radio signals from the base station 203 are received by the antennas 307-1 to 307-4. The received signal is converted from a radio reception frequency to a baseband signal by the frequency conversion unit 306, and demodulated by the demodulation unit 308. The demodulation unit 308 may perform weight calculation and multiplication. 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. 8, it is connected to each unit 301 to 309. In FIG. 8, the number of antennas used by the mobile terminal 202 for transmission and the number of antennas used for reception may be the same or different.

[0089] FIG. 9 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. 9 will be described. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (such as the MME unit 204), the HeNBGW 205, and the like. The 5GC communication unit 412 transmits and receives data between the base station 203 and the 5GC (such as the 5GC unit 214). The other base station communication unit 402 transmits and receives data between the base station 203 and the 5GC. The EPC communication unit 401, the 5GC communication unit 412, and the other base station communication unit 402 each transmit and receive information to and from the 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, the 5GC communication unit 412, and the other base station communication unit 402 are stored in the transmission data buffer unit 404.

[0090] The data stored in the transmission data buffer unit 404 is passed to the encoder unit 405, where it is subjected to encoding such as error correction. There may be data that is directly output from the transmission data buffer unit 404 to the modulation unit 406 without being subjected to encoding. The encoded data is modulated by the modulation unit 406. The modulation unit 406 may perform precoding in MIMO. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 407, where it is converted into a radio transmission frequency. Thereafter, a transmission signal is transmitted to one or more mobile terminals 202 from the antennas 408-1 to 408-4. Although the case where the number of antennas is four is illustrated in FIG. 9, the number of antennas is not limited to four.

[0091] 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 the antenna 408. The received signal is converted from a radio reception frequency to a baseband signal by the frequency conversion unit 407, and demodulated by the demodulation unit 409. The demodulated data is passed to the decoder unit 410, where decoding such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 403 or the EPC communication unit 401 and the 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 the control unit 411. Therefore, although the control unit 411 is omitted in FIG. 4, it is connected to each unit 401 to 410. In FIG. 9, the number of antennas used by the base station 203 for transmission and the number of antennas used for reception may be the same or different.

[0092] Fig. 9 is a block diagram showing the configuration of base station 203, but base station 213 may have a similar configuration. In addition, in Fig. 8 and Fig. 9, the number of antennas of mobile terminal 202 and the number of antennas of base station 203 may be the same or different.

[0093] FIG. 10 is a block diagram showing the configuration of an MME. FIG. 10 shows the configuration of the MME 204a included in the MME unit 204 shown in FIG. 2 described above. The PDN GW communication unit 501 transmits and receives data between the MME 204a and the PDN GW. The base station communication unit 502 transmits and receives data between the MME 204a and the base station 203 via the S1 interface. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 501 to the base station communication unit 502 via the user plane communication unit 503 and transmitted to one or more base stations 203. If the data received from the base station 203 is user data, the user data is passed from the base station communication unit 502 to the PDN GW communication unit 501 via the user plane communication unit 503 and transmitted to the PDN GW.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] FIG. 11 is a block diagram showing the configuration of 5GC. FIG. 11 shows the configuration of the 5GC unit 214 shown in FIG. 3 described above. FIG. 11 shows the case where the 5GC unit 214 shown in FIG. 5 includes the AMF configuration, the SMF configuration, and the UPF configuration. The Data Network communication unit 521 transmits and receives data between the 5GC unit 214 and the Data Network. The base station communication unit 522 transmits and receives data via the S1 interface between the 5GC unit 214 and the base station 203, and / or the NG interface between the 5GC unit 214 and the base station 213. If the data received from the Data Network is user data, the user data is passed from the Data Network communication unit 521 to the base station communication unit 522 via the user plane communication unit 523, and is transmitted to one or more base stations 203 and / or base stations 213. If the data received from base station 203 and / or base station 213 is user data, the user data is passed from base station communication unit 522 to Data Network communication unit 521 via user plane communication unit 523 and transmitted to the Data Network.

[0099] If the data received from the Data Network is control data, the control data is passed from the Data Network communication unit 521 to the session management unit 527. The session management unit 527 passes the control data to the control plane control unit 525. If the data received from the base station 203 and / or base station 213 is control data, the control data is passed from the base station communication unit 522 to the control plane control unit 525. The control plane control unit 525 passes the control data to the session management unit 527.

[0100] The control plane control unit 525 includes a NAS security unit 525-1, a PDU session control unit 525-2, an idle state mobility management unit 525-3, etc., and performs general processing for the control plane (hereinafter, sometimes referred to as C-Plane). The NAS security unit 525-1 performs security for NAS (Non-Access Stratum) messages, etc. The PDU session control unit 525-2 performs management of PDU sessions between the mobile terminal 202 and the 5GC unit 214, etc. The idle state mobility management unit 525-3 performs mobility management in a standby state (also called an idle state; RRC_IDLE state, or simply idle), generation and control of paging signals in a standby state, addition, deletion, update, search, tracking area list management, etc. of one or more mobile terminals 202 under its umbrella.

[0101] The 5GC unit 214 distributes paging signals to one or more base stations 203 and / or base station 213. The 5GC unit 214 also performs mobility control in an idle state. The 5GC unit 214 manages a tracking area list when the mobile terminal is in an idle state, an inactive state, and an active state. The 5GC unit 214 initiates a paging protocol by transmitting a paging message to a cell belonging to a tracking area in which the UE is registered.

[0102] Next, an example of a cell search method in a communication system is shown. Fig. 12 is a flow chart showing an outline of a process from cell search to standby operation performed by a 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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).

[0108] 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.

[0109] 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.

[0110] In the example shown in FIG. 12, an example of operations from cell search to standby in the LTE system is shown, but in the NR system, in addition to the best cell, the best beam may be selected in step ST603. Also, in the NR system, beam information, for example, a beam identifier, may be acquired in step ST604. Also, in the NR system, scheduling information of Remaining Minimum SI (RMSI) may be acquired in step ST604. In the NR system, RMSI may be received in step ST605.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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."

[0116] The macro eNB may be, for example, a “Wide Area Base Station” as described in Non-Patent Document 7.

[0117] 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.

[0118] FIG. 13 shows an example of a cell configuration in NR. In an NR cell, a narrow beam is formed and transmitted while changing the direction. In the example shown in FIG. 13, at a certain time, the base station 750 transmits and receives with a mobile terminal using a beam 751-1. At another time, the base station 750 transmits and receives with a mobile terminal using a beam 751-2. In the same manner, the base station 750 transmits and receives with a mobile terminal using one or more of the beams 751-3 to 751-8. In this way, the base station 750 configures a wide-range cell.

[0119] 13 shows an example in which the number of beams used by the base station 750 is eight, but the number of beams may be different from eight. Also, in the example shown in FIG. 13, the number of beams used simultaneously by the base station 750 is one, but it may be more than one.

[0120] As a scheduling method by NR base stations and LTE base stations in NR-LTE coexistence, the NR base station assigns slots for transmitting and receiving with the UE, and the LTE base station assigns slots for transmitting and receiving with the UE to the slots that are free after the assignment.

[0121] The NR base station may notify the LTE base station of information on the slots assigned by the base station itself. The notification may be made using an inter-base station interface. The NR base station may also notify the LTE base station of information on frame timing. The LTE base station may use the information to obtain information on the difference between the frame timing in the NR base station and the frame timing in the LTE base station. The LTE base station may use the information obtained above to perform scheduling for the UE.

[0122] The configuration of the DC described above may be the configuration shown in FIG. 4, the configuration shown in FIG. 6, or the configuration shown in FIG.

[0123] The above method has the following problem. That is, since different numerologies are supported in the NR system, the LTE base station cannot know the time resources scheduled by the NR base station. Therefore, in NR-LTE coexistence, the time resources scheduled by the NR base station and the LTE base station may collide. This makes it impossible for the UE to communicate with one of the base stations, resulting in a problem of reduced reliability and transmission rate in the communication between the UE and the base station.

[0124] A method for solving the above problems is disclosed. An NR base station notifies an LTE base station of information on numerology used in communication with a UE. The LTE base station uses the information to obtain information on time resources scheduled by the NR base station.

[0125] The NR base station may notify the UE of the aforementioned information on numerology by including it in the information on the slot scheduled by the NR base station. The aforementioned slot information may include information on the scheduled symbol. This allows, for example, the LTE base station to obtain information on the time resource scheduled by the NR base station in one signaling. This allows the LTE base station to perform rapid scheduling processing in NR-LTE coexistence.

[0126] As another example, the NR base station may notify the above-mentioned information on numerology by including it in information on the frame timing of the own NR base station. The above-mentioned information on frame timing may be, for example, information on frame boundaries, information on frame numbers, or information on the difference in frame timing between the NR base station and the LTE base station. The difference may be measured by the NR base station by receiving a downlink signal from the LTE base station, or may be measured by the UE and notified to the NR base station. This makes it possible to reduce, for example, the number of times that the above-mentioned information on numerology is transmitted from the NR base station to the LTE base station. As a result, it is possible to reduce the amount of signaling in the base station-to-base station interface.

[0127] As another example, the NR base station may notify the LTE base station of the above-mentioned information on the numerology without including it in either the slot information scheduled by the NR base station or the frame timing information of the NR base station. For example, the NR base station may notify the LTE base station of the above-mentioned information on the numerology using signaling that notifies only the information. The above-mentioned signaling may be newly provided. Alternatively, the NR base station may notify the information by including it in other information. For example, the NR base station may notify the information by including it in signaling that notifies the LTE base station of the RRC setting change of the UE. This makes it possible to reduce the amount of signaling from the NR base station to the LTE base station while flexibly changing the numerology used for transmission and reception between the NR base station and the UE.

[0128] Fig. 14 is a diagram showing an operation of an NR base station notifying an LTE base station of numerology information used in communication with a UE. Fig. 14 shows a case where an NR base station notifies the LTE base station of the information by including the information in the slots assigned by the base station itself.

[0129] In step ST1501 shown in FIG. 14, the NR base station notifies the UE of information on the numerology used in communication with the UE by including the information on the slots allocated by the NR base station to the UE. In step ST1502, the same operation as in step ST1501 is performed. The above-mentioned step ST1502 is performed when updating the information on the slot allocation in step ST1501. Step ST1502 may be performed when the numerology used in communication with the UE is changed.

[0130] 15 is a diagram showing another example of an operation in which an NR base station notifies an LTE base station of numerology information used in communication with a UE. FIG. 15 shows a case in which an NR base station notifies the information by including it in information on frame timing of the base station itself.

[0131] In step ST1601 shown in FIG. 15, the NR base station notifies the NR base station of information on the numerology used in communication with the UE by including it in information on the frame timing used by the base station itself. In step ST1602, the NR base station notifies the LTE base station of information on the slots that the NR base station itself has assigned to the UE. The LTE base station derives the time resources assigned by the NR base station using the information in ST1601 and ST1602 described above. In step ST1603, the NR base station performs the same operation as in step ST1602. The LTE base station derives the time resources assigned by the NR base station using the information in ST1601 and ST1603 described above.

[0132] In the first embodiment, the NR base station notifies the LTE base station of information related to numerology, but the UE may also notify information related to the BWP used in communication with the own NR base station. The LTE base station may use the information related to the BWP to acquire the numerology used in transmission and reception between the NR base station and the UE. The NR base station may notify the LTE base station in advance of the BWP set by the UE in communication with the own NR and the numerology used in the BWP. The notification may be included, for example, in signaling that notifies the LTE base station of a change in the RRC setting of the UE. This makes it possible to reduce, for example, the amount of signaling between base stations.

[0133] According to the first embodiment, in the case of NR-LTE coexistence, the LTE base station can grasp information about time resources scheduled by the NR base station. As a result, it is possible to ensure reliability and transmission rate in communication between the UE and both base stations.

[0134] Embodiment 2 When switching the BWP in the UE, the base station notifies the UE of the information of the used BWP in the uplink scheduling grant. The UE uses the information to switch the used uplink BWP and perform uplink transmission. A predetermined time may be set in the UE, and the used BWP may be switched at the predetermined time. The above-mentioned predetermined time may be, for example, the time until the uplink transmission frequency in the UE becomes stable, or may be determined using other methods.

[0135] In the above, the following problem occurs. That is, the base station does not recognize the above-mentioned predetermined time in the UE. This causes a mismatch between the transmission timing of the UE and the reception timing of the base station in the communication between the UE and the base station before and after the BWP switching, resulting in a problem of a decrease in the reliability of communication and the communication rate.

[0136] A method for solving the above problem is disclosed. The UE notifies the base station of information regarding the BWP switching time of the UE. The information may be included in, for example, the UE capability. The UE may notify the base station of the information by including it in the UE capability. The base station may use the notification to obtain the BWP switching time of the UE. The base station may use the BWP switching time to perform scheduling for the UE. The BWP switching time may be determined, for example, by using the time when the RF (Radio Frequency) circuit of the UE becomes stable.

[0137] The BWP switching time may be determined, for example, in microsecond units, in a predetermined time unit (for example, Ts in LTE), or in symbol units. The BWP switching time may be determined for each numerology. This, for example, makes it easier to schedule in the base station.

[0138] An example of this will be described with reference to the drawings. Figure 16 is a diagram showing an example in which the UE notifies the base station of BWP switching time information. In the example shown in Figure 16, the UE includes the information in the UE capability and notifies the base station of the information.

[0139] When the above-mentioned method is applied, the following problem occurs. That is, the timing at which the UE switches the BWP is not determined. For example, when the time resources of the uplink transmission before the BWP switching and the uplink transmission after the BWP switching are adjacent, a discrepancy occurs in the BWP used for transmission and reception between the base station and the UE. As a result, the base station cannot receive the uplink signal before and after the BWP switching. This causes a problem that the reliability and communication rate of the uplink communication before and after the BWP switching are reduced.

[0140] A method for solving the above problem is disclosed. The UE stops uplink transmission in a slot before BWP switching by an amount equivalent to the BWP switching time earlier. The uplink transmission may be stopped by an amount equivalent to the BWP switching time or more earlier, for example, by a time obtained by rounding up the BWP switching time in symbol units before BWP switching. The above-mentioned uplink transmission stop may be performed by signaling (for example, DCI) from the base station to the UE. For example, the uplink transmission grant after BWP switching may include information regarding the above-mentioned uplink transmission stop. The signaling may include information regarding the time when the UE stops uplink transmission, for example, information equivalent to the BWP switching time, or may include information regarding the timing when the UE stops uplink transmission, for example, information regarding the symbol number at which the uplink transmission is stopped. As another example, the signaling may include information regarding the reason why the UE stops uplink transmission, for example, BWP switching. The UE may use information regarding the reason to stop the above-mentioned uplink transmission earlier by an amount equivalent to the BWP switching time. The above-mentioned uplink transmission stop time may be in symbol units, for example. Said symbol may be, for example, a symbol in the BWP before the switch.

[0141] As another example, the above-mentioned uplink transmission stop may be predefined as a standard for the operation of the UE. The UE may assume an idle schedule for the BWP switching time. That is, the UE may autonomously stop uplink transmission for the switching time and switch the BWP without signaling from the base station. This makes it possible to reduce the amount of signaling from the base station to the UE, for example.

[0142] Fig. 17 is a diagram showing an example of an operation in which a UE stops uplink transmission in a slot before switching BWPs by an amount corresponding to the BWP switching time earlier. In the example shown in Fig. 17, the BWP used first by the UE, that is, the BWP used at the left end of the figure, is BWP#1.

[0143] 17, the base station transmits an uplink grant 1701 to the UE. The uplink grant 1701 includes scheduling information for uplink transmission using a slot 1702 in BWP#1. Upon receiving the uplink grant 1701, the UE performs uplink transmission in the slot 1702 using BWP#1.

[0144] 17, the base station transmits an uplink grant 1703 to the UE. The uplink grant 1703 includes scheduling information for uplink transmission using slot 1704 in BWP#2. Upon receiving the uplink grant 1703, the UE stops uplink transmission in slot 1702 in time resource 1705 corresponding to the BWP switching time. The UE switches the BWP in use from BWP#1 to BWP#2, and performs uplink transmission in slot 1704.

[0145] The above-mentioned solution may be applied, for example, in preemption. For example, in the above-mentioned solution, the uplink transmission using the BWP before switching may be preempted, that is, the uplink transmission may have a low priority. The uplink transmission using the BWP after switching may be preempted, that is, the uplink transmission may have a high priority. The above-mentioned priority may be determined, for example, by the QCI assigned to the logical channel. This makes it possible to ensure reliability in preemption, for example.

[0146] Figure 18 is a diagram showing an example of an operation in which a UE stops uplink transmission in a slot before BWP switching earlier by an amount equivalent to the BWP switching time in preemption communication. In the example shown in Figure 18, a base station transmits a preemption message to a UE in an uplink slot before BWP switching, and the UE interrupts transmission in the uplink slot subject to preemption, switches the BWP, and then performs uplink transmission with the BWP newly assigned by the preemption message. In Figure 18, elements common to Figure 17 are given the same figure numbers, and common explanations are omitted.

[0147] The upstream grant 1701 and the slot 1702 shown in FIG. 18 are the same as those in FIG.

[0148] In FIG. 18, the base station notifies the UE of a preemption grant 1803. The preemption grant 1803 includes scheduling information for uplink preemption transmission using slot 1804 in BWP#2. The preemption grant 1803 may include a preemption indication (PI) for uplink transmission in slot 1702. The UE may use the preemption grant 1803 to stop uplink transmission using BWP#1 in time resource 1805. The time resource 1805 may include a time resource that is earlier than slot 1804 by the BWP switching time. The UE uses the preemption grant 1803 to switch the used BWP from BWP#1 to BWP#2 and performs uplink preemption transmission in slot 1704.

[0149] The above solution may be applied when the numerology before and after the switch is the same, which will provide the same effect as above.

[0150] Figure 19 is a diagram showing an example in which the transmission of the uplink slot before the BWP switch is stopped early by an amount equivalent to the BWP switch time when the numerology before and after the BWP switch is the same. In Figure 19, elements common to Figure 17 are given the same reference numbers, and common explanations are omitted.

[0151] The upstream grant 1701 and the slot 1702 shown in FIG. 19 are the same as those in FIG.

[0152] 19, the base station transmits an uplink grant 1903 to the UE. The uplink grant 1903 includes scheduling information for uplink transmission using slot 1904 in BWP#2. Upon receiving the uplink grant 1903, the UE stops uplink transmission in slot 1702 in time resource 1705 corresponding to the BWP switching time. The UE switches the BWP in use from BWP#1 to BWP#2, and performs uplink transmission in slot 1904.

[0153] In this solution, the BWP switching time may be a timing before the start timing of the scheduling after the BWP switching, or may be a timing before the end timing of the scheduling before the BWP switching. For example, when the scheduling after the BWP switching starts from a symbol in the middle of a slot, the BWP switching time may be set before the symbol. This makes it possible to apply the above-mentioned solution to the BWP switching in non-slot scheduling, for example. The above-mentioned non-slot scheduling may be non-slot scheduling in preemption, for example. This makes it possible to ensure reliability even in preemption using non-slot scheduling, for example.

[0154] Another solution is disclosed. The UE may stop uplink transmission in a slot after BWP switching until the time equivalent to the BWP switching time. The UE may stop the uplink transmission until the time equivalent to the BWP switching time or more, for example, the time obtained by rounding up the BWP switching time in symbol units before the BWP switching. The above-mentioned uplink transmission stop may be performed by signaling (for example, DCI) from the base station to the UE. For example, the uplink transmission grant after the BWP switching may include information regarding the above-mentioned uplink transmission stop. The signaling may include information regarding the time when the UE stops uplink transmission, for example, the time equivalent to the BWP switching time, or may include information regarding the timing when the UE stops uplink transmission, for example, the symbol number at which the UE stops uplink transmission. As another example, the signaling may include information regarding the reason why the UE stops uplink transmission, for example, BWP switching. The UE may start the above-mentioned uplink transmission until the time equivalent to the BWP switching time using the information regarding the reason. The uplink transmission suspension time may be, for example, in units of symbols. The symbols may be, for example, symbols in the BWP after the switch.

[0155] As another example, the above-mentioned uplink transmission stop may be predefined as a standard for the operation of the UE. The UE may assume an idle schedule for the switching time. That is, the UE may autonomously switch the BWP at the switching time without signaling from the base station and start uplink transmission. This makes it possible to reduce, for example, the amount of signaling from the base station to the UE.

[0156] In the above, the numerology before and after the BWP switching may be the same or different. The same effect as above can be obtained.

[0157] Figure 20 is a diagram showing an example in which the transmission of the uplink slot after the BWP switching is started later by an amount equivalent to the BWP switching time. Figure 20 shows the case in which the numerology is the same before and after the BWP switching. In Figure 20, the same reference numbers are given to elements common to Figure 17, and common explanations are omitted.

[0158] The upstream grant 1701 and the slot 1702 shown in FIG. 20 are the same as those in FIG.

[0159] In Fig. 20, the base station transmits an uplink grant 1903 to the UE. The uplink grant 1903 includes scheduling information for uplink transmission using slot 1904 in BWP#2. Upon receiving the uplink grant 1903, the UE switches the BWP in use from BWP#1 to BWP#2 after uplink transmission in slot 1702. The UE performs uplink transmission in slot 1904 after time resource 1705 equivalent to the BWP switching time has elapsed.

[0160] In Figure 20, the numerology is the same before and after the BWP switching, but the numerology may be different before and after the BWP switching. The same effect as described above can be obtained.

[0161] In the above, the BWP switching time may be a timing after the start timing of the scheduling after the BWP switching, or a timing after the end timing of the scheduling before the BWP switching. For example, when the scheduling after the BWP switching starts from a symbol in the middle of a slot, the BWP switching time may be provided after the symbol. This makes it possible to apply the above-mentioned solution to the BWP switching in non-slot scheduling, for example.

[0162] Another solution is disclosed. The BWP switching time may be allocated to slots before and after the BWP switching. The above allocation may be, for example, equal to the slots before and after the BWP switching. As another example, the above allocation may be different between the slots before and after the BWP switching. For example, the above allocation may be determined using the slot length. As an example in which the allocation is determined by the slot length, when the slot length before and after the BWP switching is 4:1, the allocation of the BWP switching time before and after the BWP switching may be 4:1. This makes it possible to make the ratio of the uplink transmission stop time in the scheduled time resource the same before and after the BWP switching. As a result, the base station can ensure the reliability of decoding the uplink data both before and after the BWP using error correction or the like. As another example, the amount of data to be stopped from being transmitted may be divided equally. In the above, the allocated uplink transmission stop time may be given in units of the symbol length before and after the BWP switching, respectively, or may be rounded up in units of the symbol length before and after the BWP switching, respectively.

[0163] The base station may determine the allocation. The base station may notify the UE of information regarding the allocation. For example, RRC signaling, MAC signaling, or DCI may be used for the notification. The UE may stop uplink transmission during the allocated BWP switching time. The uplink transmission stop may be performed by signaling (e.g., DCI) from the base station to the UE. For example, information regarding the uplink transmission stop may be included in the uplink transmission grant after the BWP switching. The base station may provide the uplink transmission stop time before and after the BWP switching as a time in symbol units before and after the BWP switching, respectively.

[0164] As another example, the above-mentioned allocation may be predefined as a standard. The above-mentioned allocation may be, for example, equal before and after the BWP switching, may be determined using a slot length, or may be determined using other information. The UE may use the allocation to assume empty scheduling before and after the BWP switching time. That is, the UE may autonomously perform the BWP switching at the switching time without signaling from the base station and start uplink transmission. This makes it possible to reduce, for example, the amount of signaling from the base station to the UE.

[0165] Fig. 21 is a diagram showing an example of distributing the transmission suspension time equivalent to the BWP switching time at the rear end of the uplink slot before the BWP switching and the front end of the uplink slot after the BWP switching. Fig. 21 shows an example in which the BWP switching time is equally distributed before and after the BWP switching. In Fig. 21, elements common to Fig. 17 are given the same reference numbers, and common explanations are omitted.

[0166] The upstream grant 1701 and slot 1702 shown in FIG. 21 are the same as those in FIG.

[0167] In FIG. 21, the base station transmits an uplink grant 1903 to the UE. The uplink grant 1903 includes scheduling information for uplink transmission using slot 1904 in BWP#2. Upon receiving the uplink grant 1903, the UE stops uplink transmission in slot 1702 in time resource 2105, which corresponds to the time allocated to the slot before the BWP switching in the BWP switching time. The UE switches the BWP in use from BWP#1 to BWP#2. The UE performs uplink transmission in slot 1904 after the elapse of time resource 2106, which corresponds to the time allocated to the slot after the BWP switching in the BWP switching time.

[0168] In Fig. 21, the time resources 2105 and 2106 are equal, but the time resources 2105 and 2106 may be different. In addition, in Fig. 21, the numerology before and after the BWP switching is the same, but the numerology before and after the BWP switching may be different. The same effect as described above can be obtained.

[0169] In the above, the BWP switching time may be allocated before and after the start timing of the scheduling after the BWP switching, or before and after the end timing of the scheduling before the BWP switching. For example, when the scheduling after the BWP switching starts from a symbol in the middle of a slot, the BWP switching time may be provided after the symbol. This makes it possible to apply the above-mentioned solution to the BWP switching in non-slot scheduling, for example.

[0170] Another solution is disclosed. The BWP switching time in the UE may be predefined by a standard. The UE may perform BWP switching within the time defined by the standard. The base station may perform scheduling for the UE using the time defined by the standard. The BWP switching time may be determined, for example, by a frequency band before switching, by a frequency band after switching, or by a combination of the frequency bands before and after switching. This makes it unnecessary for the UE to notify the base station of information regarding the BWP switching time, and therefore makes it possible to reduce the amount of signaling between the UE and the base station.

[0171] The solution to be used in the second embodiment may be determined in advance by a standard, or may be determined by the base station and notified to the UE. For example, in preemption communication, the BWP switching time may be allocated within the time resource scheduled for the uplink transmission to be preempted, or in other cases, the BWP switching time may be allocated within the time resource scheduled after the BWP switching. This makes it possible to ensure reliability in communication that requires high reliability, such as URLLC.

[0172] In the second embodiment, the UE may stop uplink transmission by not transmitting data mapped to symbols in the stop period, or may stop the data by remapping to symbols excluding the period (i.e., re-encoding and re-modulation). A combination of both may be used. For example, the uplink transmission before the BWP switching may be stopped by not transmitting data mapped to symbols in the stop period. For example, the uplink transmission after the BWP switching may be stopped by remapping to symbols excluding the period. This makes it possible to suppress an increase in the amount of processing in the UE while ensuring the reliability of the uplink transmission in the UE.

[0173] The method disclosed in the second embodiment may be applied to SUL / non-SUL switching. In the above application, BWP switching in the second embodiment may be read as SUL / non-SUL switching and applied. As another example, the method disclosed in the second embodiment may be used in both BWP switching and SUL / non-SUL switching. The BWP switching time and the SUL / non-SUL switching time may be common or different. For example, by commonizing the BWP switching time and the SUL / non-SUL switching time, it is possible to reduce the size of the UE capability.

[0174] According to the second embodiment, it is possible to prevent unnecessary transmission and reception when switching BWPs, which has the effect of preventing a decrease in communication reliability and transmission rate.

[0175] 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 component of the embodiments and their modifications can be appropriately modified or omitted.

[0176] For example, in each of the above-mentioned embodiments and their modifications, a slot 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 slot unit may be performed in a TTI unit, a subframe unit, a subslot unit, or a minislot unit.

[0177] 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]

[0178] 200 communication system, 202 communication terminal device, 203 base station device.

Claims

1. a communication terminal; and a first base station and a second base station configured to be capable of wirelessly communicating with the communication terminal; The first base station and the second base station are capable of providing dual connectivity to the communication terminal; The first base station notifies the second base station of information regarding frame timing of the first base station; The first base station further notifies the second base station of information regarding a numerology used by the first base station for communication with the communication terminal; The first base station notifies the second base station of information regarding the frame timing of the first base station and information regarding the numerology used by the first base station for communication with the communication terminal, by including the information in the same signaling; Communication systems.

2. An inter-base station interface is used for reporting information regarding the frame timing of the first base station. The communication system according to claim 1 .

3. The first base station notifies the second base station of information on the slots assigned to the communication terminal. The communication system according to claim 1 .

4. The first base station is a New Radio (NR) base station, The second base station is a Long Term Evolution (LTE) base station, An interface between base stations is used for notifying the information of the slot. The communication system according to claim 3.

5. The first base station notifies the second base station of information related to the symbol. The communication system according to claim 1 .

6. A base station configured to be capable of wirelessly communicating with a communication terminal, The base station can provide dual connectivity to the communication terminal together with other base stations; The base station notifies the other base station of information regarding the frame timing of the base station; The base station further notifies the other base station of information regarding a numerology used by the base station for communication with the communication terminal, The base station notifies the other base station of information regarding the frame timing of the base station and information regarding the numerology used by the base station for communication with the communication terminal, by including the information in the same signaling; Base station.

7. A communication terminal configured to be able to communicate with a first base station and a second base station, The first base station can provide dual connectivity to the communication terminal together with the second base station, The first base station notifies the second base station of information regarding frame timing of the first base station; The first base station further notifies the second base station of information regarding a numerology used by the first base station for communication with the communication terminal; The first base station notifies the second base station of information regarding the frame timing of the first base station and information regarding a numerology used by the first base station for communication with the communication terminal, the information being included in the same signaling; the communication terminal measures a difference between frame timings of the first base station and the second base station, and notifies the first base station of the difference as information regarding the frame timing of the first base station; Communications terminal.

Images