COMMUNICATION SYSTEM, USER EQUIPMENT AND BASE STATION

Abstract

To provide a low-latency wireless communication technique.SOLUTION: A communication system includes user equipment. The communication system also includes a base station. The base station includes a plurality of TRPs (Transmission Reception Points), and the plurality of TRPs communicate wirelessly. The user equipment includes a second time in a first time. The first time is a time from receiving a PDCCH instruction to transmitting a PRACH. The second time is a time for switching a TRP used for wireless communication.SELECTED DRAWING: Figure 2

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 19).

[0055] Also, 3GPP is considering several new technologies, such as improving communication reliability by supporting multiple TRPs (Transmission Reception Points) in a base station (see Non-Patent Document 20). [Prior art documents] [Non-patent literature]

[0056] [Non-Patent Document 1] 3GPP TS 36.300 V15.2.0 [Non-Patent Document 2] 3GPP S1-083461 [Non-Patent Document 3] 3GPP TR 36.814 V9.2.0 [Non-Patent Document 4] 3GPP TR 36.912 V15.0.0 [Non-Patent Document 5] "Scenarios, requirements and KPIs for 5G mobile and wireless system", ICT-317669-METIS / D1.1

Non-licensed Document 6

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Non-licensed literature 9

Non-licensed literature 10

Non-licensed Document 11

Non-licensed Document 12

Non-licensed Document 13

Non-licensed Document 14

Non-licensed Document 15

Non-licensed Document 16

Non-licensed Document 17

Non-licensed Document 18

Non-licensed Document 19

Non-licensed Document 20

Non-licensed Document 21

Non-licensed Document 22

[0057] When random access using PDCCH order (see Non-Patent Document 21) is used for switching the connection destination of the TRP under the base station in the UE, downlink synchronization needs to be established in the switching destination TRP during the period from PDCCH reception to PRACH transmission. Therefore, the UE cannot transmit PRACH at the first PRACH transmission opportunity after the minimum time (see Non-Patent Document 14) between PDCCH reception and PRACH transmission has elapsed, and as a result, the problem occurs that the TRP switching process in the UE cannot be performed quickly.

[0058] In view of the above problems, one object of the present invention is to provide a low-latency wireless communication technology in LTE and NR. [Means for solving the problem]

[0059] According to the present invention, a base station including a user device and a plurality of TRPs (Transmission Reception Points) that wirelessly communicate with the user device is provided, and the user device transmits a PDCCH (Physical Downlink Control Channel) After receiving instructions After the first hour PRACH (Physical Random Access Channel) Send death, Second time to switch TRP for wireless communication is included in the first time , a communication system is provided.

[0060] According to the present invention, there is provided a user device that performs wireless communication with a base station and is included in a communication system together with the base station, the base station including a plurality of TRPs that perform wireless communication with the user device, (Physical Downlink Control Channel) After receiving instructions After the first hour PRACH (Physical Random Access Channel) Send death,Second time to switch TRP for wireless communication is included in the first time , a user device is provided.

[0061] According to the present invention, a base station that performs wireless communication with a user device and is included in a communication system together with the user device includes a plurality of TRPs (Transmission Reception Points) that perform wireless communication with the user device, and the user device transmits a PDCCH (Physical Downlink Control Channel) After receiving the instruction After the first hour PRACH (Physical Random Access Channel) Send death, Second time to switch TRP for wireless communication is included in the first time , a base station is provided. Effect of the Invention

[0062] According to the present invention, it is possible to provide a low-latency wireless communication technique.

[0063] 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]

[0064] [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 sequence diagram showing an operation of a UE transmitting a PRACH after a predetermined time has elapsed since receiving a PDCCH indication, in accordance with the first embodiment. [Figure 15] FIG. 11 is a sequence diagram showing an operation of a UE discarding a PDCCH indication in accordance with the first embodiment. [Figure 16] FIG. 11 is a diagram showing switching of candidates for the number of slots from downlink data reception to HARQ response in TRP switching of a UE in accordance with a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] 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.

[0066] 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."

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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."

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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).

[0075] If control protocols for UE202, 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.

[0076] 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.

[0077] 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.

[0078] 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 214 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.

[0079] 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 202.

[0080] 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.

[0081] 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). In FIG. 4, an example is shown in which U-Plane connection between MME unit 204 and gNB224-2 is made via eNB223-1, but it may also be made directly between MME unit 204 and gNB224-2.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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 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.

[0088] 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.

[0089] 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 5GC communication unit 412 or the EPC communication unit 401 and the other base station communication unit 402, and the user data is passed to the 5GC communication unit 412, 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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 a 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 eNB 207 connected to the MME 204a.

[0095] 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.

[0096] 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 via the user plane control unit 523. 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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).

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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."

[0113] The macro eNB may be, for example, a “Wide Area Base Station” as described in Non-Patent Document 7.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] In a connection between a UE and an NR base station (hereinafter, sometimes referred to as a gNB), the UE may start a random access process using a random access instruction from the gNB. For example, a PDCCH may be used for the instruction. The UE may start a random access process for the gNB using a PDCCH instruction (PDCCH order) from the gNB. The PDCCH instruction may include information on a timing (PRACH transmission opportunity (PRACH occasion)) at which the UE may transmit a PRACH to the gNB. The information may be, for example, an identifier of an SS block. Information on the association between the SS block and the PRACH transmission opportunity may be notified to the UE in advance from the gNB or may be notified individually. The UE may derive a PRACH transmission opportunity using the information on the association and the information on the PRACH transmission opportunity.

[0118] A minimum time may be set for the time from when the UE receives a PDCCH instruction from the gNB to when it transmits a PRACH. The minimum time may be determined, for example, using a time required for PUSCH generation processing (hereinafter, sometimes referred to as N_T2), an uplink BWP switching time (hereinafter, sometimes referred to as Δ_BWP switching), and a predetermined delay amount (hereinafter, sometimes referred to as Δ_Delay) based on a frequency used in communication between the UE and the gNB. For example, the minimum time may be the sum of N_T2, Δ_BWP switching, and Δ_Delay. The UE may transmit the PRACH at the first PRACH transmission opportunity after the minimum time has elapsed since receiving the PDCCH instruction. The gNB may receive the PRACH from the UE at the first PRACH transmission opportunity after the minimum time has elapsed.

[0119] In addition, in the connection between the UE and the gNB, multiple TRPs (Transmission Reception Points) under the gNB may be used. The TRPs may be referred to as transmitter-receivers. The multiple UEs may be asynchronous with each other. That is, the subframe boundaries of the signals transmitted and received by each TRP may be different from each other. The gNB may switch the destination TRP under the gNB for the UE under its control. The switching of the destination TRP may be performed using an instruction from the gNB. For example, the UE may switch the destination TRP to the TRP with the improved communication quality by using the fact that the communication quality between the UE and another TRP under the same gNB is better than that of the currently connected TRP.

[0120] In the above, the following problem occurs. That is, the above-mentioned minimum time does not take into account the process associated with the switching of TRP, so the UE cannot transmit PRACH to the switching target TRP at the earliest PRACH transmission opportunity. As a result, the problem occurs that the TRP switching process in the UE cannot be performed quickly.

[0121] Solutions to the aforementioned problems are disclosed below.

[0122] The time required for synchronization with the switched TRP (hereinafter, sometimes referred to as Δ_SSB) is added to the minimum switching time for the UE to transmit the PRACH after receiving the PDCCH indication. The time required for synchronization may be, for example, a time equivalent to the SS block length (for example, 4 symbols). As another example, the time required for synchronization may be a time required for synchronization establishment processing, for example, a time required for demodulation of the SS block, a time required for synchronization code detection processing using the demodulation result, or a sum of the time required for the demodulation and synchronization code detection processing. This allows, for example, the UE to transmit the PRACH to the gNB at a PRACH transmission opportunity that arrives immediately after performing the processing for establishing synchronization with the SS block. As a result, the UE can quickly perform TRP switching.

[0123] The time required for synchronization in the UE may be different or the same for each subcarrier interval that the UE uses for transmission and reception with the gNB. For example, the time required for demodulation of an SS block may be different or the same for each subcarrier interval. The time required for synchronization code detection processing using the demodulation result may be different or the same for each subcarrier interval. This makes it possible to prevent the time required for synchronization from being unnecessarily long when, for example, the subcarrier interval is large, that is, the symbol length is short. As a result, it becomes possible to quickly execute PRACH transmission in the UE.

[0124] As another example of the addition to the minimum switching time, the time required for the UE to switch the beam used for uplink transmission and / or downlink reception (hereinafter, sometimes referred to as Δ_beamswitch) may be added. In this way, even if the beam used by the UE is switched at the same time due to TRP switching, the UE can switch the beam within the minimum time after the addition.

[0125] As another example of addition to the minimum switching time, both Δ_SSB and Δ_beamswitch may be added. In this way, even if the beam used by the UE is switched at the same time due to TRP switching, the UE can perform the beam switching within the minimum time after addition while performing the synchronization establishment process using the SS block.

[0126] The gNB may add the above-mentioned Δ_SSB and / or Δ_beamswitch to the minimum switching time for transmitting the PRACH after receiving the PDCCH instruction, and use the result as a new minimum switching time. The gNB may start receiving the PRACH from the UE at the PRACH transmission opportunity after the new minimum switching time has elapsed from the time of transmitting the PDCCH order. The minimum switching time used in the UE and the minimum switching time used in the gNB may be set to be the same. This makes it possible to prevent, for example, discrepancies in the recognition of the PRACH transmission timing between the UE and the gNB. As a result, it is possible to improve the reliability of the communication system.

[0127] The UE may notify the gNB of information required for the above-mentioned addition in advance. For the notification of the information, for example, RRC signaling, MAC signaling, or L1 / L2 signaling may be used. The gNB may request the UE for the information required for the above-mentioned addition. For example, RRC signaling, MAC signaling, or L1 / L2 signaling may be used in the request. The information required for the above-mentioned addition may be, for example, information on the time required for synchronization establishment processing, information on the time required for beam switching in the UE, a combination of both of the above-mentioned information, or information on the time obtained by adding both of the above-mentioned times.

[0128] The UE may be provided with a function for measuring the new minimum switching time, for example, a timer for measuring the time. The same may be done in the gNB. This makes it possible to prevent malfunctions from occurring in the process from receiving the PDCCH indication to transmitting the PRACH in the UE, for example.

[0129] The UE may include information necessary for the above-mentioned addition in the UE capability and notify the gNB. This allows, for example, the UE to notify the gNB of the information together with other UE capabilities, and as a result, it is possible to avoid complexity in the communication system. As another example, the UE may notify the information using RRC signaling. This allows, for example, the UE to notify the gNB of a lot of information. As another example, the UE may notify the information using MAC signaling. This allows, for example, the UE to notify the gNB of the information quickly. As another example, the UE may notify the information using L1 / L2 signaling. This allows, for example, the UE to notify the gNB of the information even more quickly.

[0130] The UE may derive the PRACH transmission opportunity after switching the destination TRP using the frame timing in the switched TRP. In the information on the correspondence between the SS block identifier and the PRACH transmission opportunity broadcast from the gNB, the PRACH transmission timing may be based on the frame timing in the TRP in which the SS block is transmitted. This allows the UE to transmit the PRACH at the PRACH transmission opportunity in the switched TRP, for example, even if the backhaul delay between the gNB and the TRP increases or decreases before and after the TRP switching.

[0131] Fig. 14 is a sequence diagram showing an example of an operation in which a UE switches a connection destination TRP after receiving a PDCCH instruction, transmits a PRACH, and receives a Random Access Response (RAR). In the example shown in Fig. 14, it is assumed that a TRP to which the UE is connected is switched from TRP#1 to TRP#2. In addition, in the example shown in Fig. 14, it is assumed that the minimum time from when the UE receives a PDCCH instruction to when it transmits a PRACH is a value obtained by adding Δ_SSB to the sum of N_T2, Δ_BWPswitching, and Δ_Delay.

[0132] In steps ST1401 and ST1402 shown in FIG. 14, the gNB transmits a PDCCH indication to the UE via TRP#1. Step ST1401 shows the indication from the gNB to TRP#1, and step ST1402 shows the indication from TRP#1 to the UE. The indication includes information indicating switching from TRP#1 to TRP#2. The indication may include information on an RA preamble used by the UE in the PRACH, information on a PRACH transmission opportunity, for example, an identifier of an SS block that the UE should receive, or both of the above.

[0133] The UE starts a timer for measuring the minimum time by receiving the PDCCH instruction in step ST1402. The UE may receive the SS block transmitted in step ST1405 before the timer expires. The UE establishes downlink synchronization with TRP#2 by receiving the SS block in step ST1405. The UE may perform step ST1405 for receiving the SS block after the timer expires. The UE transmits a PRACH to TRP#2 at the first PRACH transmission opportunity after a time equal to the sum of N_T2, Δ_BWP switching, Δ_Delay, and Δ_SSB has elapsed since receiving the PDCCH instruction and after downlink synchronization with TRP#2 has been established (step ST1407). In step ST1408, TRP#2 transmits the PRACH received from the UE to the gNB. The RA preamble in the PRACH transmission may be the RA preamble included in step ST1402 or may be different.

[0134] In steps ST1410 and ST1411 shown in FIG. 14, the gNB notifies the UE of a random access response via TRP#2. Step ST1410 shows the random access response notification from the gNB to TRP#2, and step ST1411 shows the random access response notification from TRP#2 to the UE. The UE uses the response to establish uplink synchronization with TRP#2.

[0135] In Fig. 14, an example is shown in which Δ_SSB is added to the sum of N_T2, Δ_BWPswitching, and Δ_Delay as the minimum time. The minimum time may be added with Δ_beamswitch instead of Δ_SSB, or may be added with the sum of Δ_SSB and Δ_beamswitch. This allows the UE to quickly transmit PRACH to TRP#2 even after beam switching in the UE, for example.

[0136] Another solution is disclosed. When TRP switching occurs, the gNB may not issue a PDCCH indication to the UE. For example, when switching to an asynchronous TRP, the gNB may not issue a PDCCH indication to the UE. When switching to an asynchronous TRP, the gNB may issue a random access indication to the UE by MAC signaling, or may issue a random access indication by RRC signaling. When the TRPs before and after switching are synchronous, the gNB may issue a PDCCH indication to the UE. This makes it possible to prevent, for example, discrepancies in the recognition of PRACH transmission timing between the gNB and the UE. As a result, it is possible to prevent malfunctions in the communication system.

[0137] The UE may discard the PDCCH indication instructing switching to an asynchronous TRP. The UE may notify the gNB of information indicating that the PDCCH indication has been discarded. The notification may be performed, for example, via the TRP before switching. For the notification, for example, L1 / L2 signaling may be used, MAC signaling may be used, or RRC signaling may be used. As another example, the UE may not notify the gNB of information indicating that the PDCCH indication has been discarded. For example, the UE may start a random access process for TRP#1. The random access process may be, for example, a contention-free random access process or a contention-based random access process.

[0138] The UE may determine whether the TRP after switching is synchronous or asynchronous using a notification from the gNB. The gNB may notify the UE of information regarding the synchronization / asynchronous state between the TRP after switching and the TRP before switching. The information may be, for example, an identifier indicating whether or not synchronization is established, or information regarding the difference in backhaul delay between the gNB and the TRP before and after switching. As another example, the gNB may notify the UE of information regarding the synchronization / asynchronous state between the TRPs under its control. The information may be the same as the information described above. The notification from the gNB to the UE may be made using RRC signaling, MAC signaling, or L1 / L2 signaling.

[0139] Figure 15 is a sequence diagram showing an operation of a UE discarding a PDCCH instruction to instruct switching to an asynchronous TRP. The example shown in Figure 15 shows a case where a gNB instructs a UE to switch from TRP#1 to TRP#2 that is asynchronous with TRP#1. Also, the example shown in Figure 15 shows a case where a UE notifies a gNB that it has discarded a PDCCH instruction. In Figure 15, the same numbers are assigned to parts common to Figure 14, and common explanations are omitted.

[0140] Steps ST1401 and ST1402 in FIG. 15 are the same as those in FIG.

[0141] In step ST1505 shown in Fig. 15, the UE discards the PDCCH indication received in step ST1402. In steps ST1510 and ST1511, the UE notifies the gNB via TRP#1 that it has discarded the PDCCH indication. Step ST1510 shows the notification from the UE to TRP#1, and step ST1511 shows the notification from TRP#1 to the gNB. The notification may be performed by L1 / L2 signaling, MAC signaling, or RRC signaling.

[0142] In the example illustrated in Fig. 15, the UE notifies the gNB that it has discarded the PDCCH indication in steps ST1510 and ST1511, but the notification may not be performed. This makes it possible to reduce the amount of signaling between the UE and the gNB, for example.

[0143] In the present embodiment 1, it is disclosed that, for switching TRP, the time required for synchronization with the switched TRP is added to the minimum switching time for transmitting PRACH after receiving PDCCH indication in UE. A similar method may be applied to adding a connected TRP. This allows, for example, UE to quickly connect to the added TRP.

[0144] According to the first embodiment, the UE can transmit the PRACH to the target TRP at the earliest PRACH transmission opportunity. As a result, the TRP switching process in the UE can be quickly performed.

[0145] Embodiment 2 In downlink data reception, the gNB may notify the UE of the number of slots from the reception of downlink data by the UE to the HARQ response from the UE by using L1 / L2 signaling. The gNB may notify the UE of candidates for the number of slots in advance. For example, RRC signaling may be used to notify the candidates. The gNB may select the number of slots from the candidates from the reception of downlink data by the UE to the HARQ response from the UE and notify the UE. For example, L1 / L2 signaling may be used to notify the selected number of slots. The number of slots may be notified by being included in DCI including downlink scheduling information from the gNB to the UE.

[0146] When the above-mentioned method is applied before and after TRP switching, the following problems occur. For example, switching to an asynchronous TRP changes the backhaul delay between the gNB and the TRP. This causes the time from downlink data reception to HARQ response between the UE and the gNB to vary, and as a result, the delay of downlink data transmission and reception varies before and after TRP switching.

[0147] Solutions to the aforementioned problems are disclosed below.

[0148] With the TRP switching, a candidate value of the number of slots from the reception of downlink data by the UE to the HARQ response from the UE is switched. The gNB may notify the UE of the candidate value. The notification may be performed before the TRP switching instruction from the gNB to the UE, or may be included in the switching instruction. The notification may be performed after the switching instruction. For example, RRC signaling may be used for the notification. This allows, for example, the gNB to notify the UE of a large amount of information. As another example, MAC signaling may be used. This allows, for example, quick notification from the gNB to the UE. As another example, L1 / L2 signaling may be used. This allows, for example, even quicker notification.

[0149] In the notification, the above-mentioned multiple methods may be combined. For example, one or more combinations of the candidate values ​​may be notified from the gNB to the UE in advance semi-statically (for example, by using RRC signaling), and information indicating which combination to use among the notified combinations may be notified from the gNB to the UE dynamically (for example, by using MAC signaling and / or L1 / L2 signaling). This makes it possible to flexibly control the number of slots from the reception of downlink data by the UE to the HARQ response from the UE while reducing the amount of signaling from the gNB to the UE.

[0150] After TRP switching, the UE may switch the candidate for the number of slots from downlink data reception to the HARQ response to the candidate included in the notification. After TRP switching of the UE, the gNB may select the number of slots from downlink data reception to the HARQ response from the candidates included in the notification and notify the UE. This makes it possible to reduce the delay fluctuation that occurs in the HARQ response notification from the UE to the gNB before and after TRP switching, for example.

[0151] 16 is a diagram showing switching of candidates for the number of slots from downlink data reception to HARQ response in accordance with switching of TRP. In the example of FIG. 16, it is assumed that a UE 1603 connected to a gNB 1601 switches from communication using a beam 1610 of a TRP#1 1605 to communication using a beam 1611 of a TRP#2 1607.

[0152] 16, when UE 1603 is connected to TRP#1 1605 using beam 1610, the values ​​shown in table 1615 are used as candidates for the number of slots from downlink data reception to HARQ response. In table 1615, k indicates the number of candidate slots, and index indicates an identifier for identifying the candidate.

[0153] In the example of Fig. 16, when the connection destination of UE 1603 is switched to TRP #2 1607 using beam 1611, the candidate of the number of slots from downlink data reception to HARQ response is switched to a value shown in table 1616. The candidate value shown in table 1616 may be notified from the gNB to the UE in advance, or may be notified by being included in a TRP switching instruction from the gNB to the UE.

[0154] The values ​​of k shown in Table 1615 and Table 1616 are examples, and the value of k may be different from the example in Fig. 16. In addition, the number of indexes is 8, but the number of indexes may be other numbers. This allows, for example, the gNB to flexibly schedule the UE.

[0155] In the present embodiment 2, the switching of the candidate value of the number of slots from the reception of downlink data by the UE to the HARQ response from the UE due to the switching of the TRP is disclosed. The same method may be applied to the addition of a connected TRP. For example, the value of the candidate may be added due to the addition of a connected TRP. For example, the value of the added candidate may be used in communication with the added TRP, or the value of the candidate before the addition may be used in communication with the TRP before the addition. This makes it possible to reduce the fluctuation of the delay of downlink data transmission and reception between the TRP before and after the addition.

[0156] The method disclosed in the present embodiment 2 may be applied to the transmission of SRS. The SRS may be, for example, aperiodic SRS. The method disclosed in the present embodiment 2 may be applied to the number of slots from when the UE receives an SRS transmission instruction from the gNB to when the UE transmits the SRS. This makes it possible to reduce the fluctuation in delay that occurs in the SRS transmission from the UE to the gNB before and after TRP switching, for example, in the SRS transmission from the UE.

[0157] The method disclosed in the second embodiment may be applied to the switching of BWP. For example, the candidate of the BWP setting in the UE may be switched with the TRP switching. The gNB may notify the UE of the value of the candidate of the BWP setting after the TRP switching. The notification may be performed before the TRP switching instruction from the gNB to the UE, or may be included in the switching instruction. The notification may be performed after the switching instruction. For example, the RRC signaling, the MAC signaling, or the L1 / L2 signaling may be used for the notification. This makes it possible to prevent the collision of time and / or frequency resources with other UEs with the switching of the TRP.

[0158] The above-mentioned BWP configuration may be, for example, information on the numerology of each BWP, information on the frequency and / or time resources of each BWP, information on the configured grant of each BWP, or a combination of a plurality of the above information. The above-mentioned BWP configuration may include other information. The above-mentioned operation of switching the BWP configuration candidate may be applied by replacing index in table 1615 in FIG. 16 with a BWP identifier and k with a BWP configuration. Table 1616 in FIG. 16 may be the same as Table 1615.

[0159] According to the second embodiment, it is possible to reduce the time fluctuation from downlink data reception to HARQ response even before and after TRP switching. As a result, it is possible to reduce the delay fluctuation of downlink data transmission and reception before and after TRP switching.

[0160] Embodiment 3 The UE may transmit an SRS of multiple symbols in one subframe. The SRS transmission may be used in LTE. The base station may configure the UE to transmit multiple SRS symbols. The UE may transmit the multiple SRS symbols using the configuration.

[0161] In the above, the following problem occurs. That is, in the conventional SRS configuration disclosed in Non-Patent Document 22 (see Non-Patent Document 22), the SRS is only configured to be transmitted in one symbol at the end of a subframe. As a result, the base station cannot configure the UE to transmit multiple SRS symbols in one subframe, and the UE cannot transmit multiple SRS symbols in one subframe.

[0162] A method for solving the aforementioned problems is disclosed.

[0163] Information on SRS transmission symbols is added to the SRS setting. The information may include information on the first symbol among the symbols through which the SRS is transmitted, or may include information on the number of symbols through which the SRS is transmitted. Information on the last symbol among the symbols through which the SRS is transmitted may or may not be included. As another example, information on the symbol number through which the SRS is transmitted may be included. The information on the symbol number through which the SRS is transmitted may be in the form of, for example, a bitmap. In the bitmap, each bit may correspond to a symbol number in one subframe.

[0164] As another example, information about the slot in which the SRS is transmitted may be included. The information about the SRS transmission symbol may be information about the symbol in which the SRS is transmitted in the slot, for example, information indicating whether the SRS is transmitted in the first half or second half of the slot. This makes it possible to reduce the amount of information about the SRS transmission symbol when, for example, the SRS is transmitted in only one of the subframes.

[0165] Another solution is disclosed. SRS configuration can be set in units of one slot, that is, in units of half a subframe. In the above, one subframe, which is the setting unit in the SRS configuration identifier, for example, the SRS transmission period and / or SRS transmission offset in srs-ConfigIndex in Non-Patent Document 22, may be read as one slot and applied. This makes it possible to avoid, for example, the complexity of communication system design regarding settings from a base station to a UE.

[0166] According to the third embodiment, a UE can transmit an SRS of a plurality of symbols in one subframe. As a result, sounding can be quickly performed even for a UE at a cell edge, for example.

[0167] 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.

[0168] 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.

[0169] 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]

[0170] 200 communication system, 202 communication terminal device, 203 base station device.

Claims

1. A user device; a base station including a plurality of TRPs (Transmission Reception Points) that wirelessly communicate with the user equipment; Equipped with The user equipment transmits a PRACH (Physical Random Access Channel) a first time after receiving a PDCCH (Physical Downlink Control Channel) indication; A communication system, wherein the first time includes a second time for switching a TRP used for wireless communication.

2. A user device that performs wireless communication with a base station and is included in a communication system together with the base station, The base station includes a plurality of TRPs (Transmission Reception Points) that wirelessly communicate with the user equipment, Transmitting a PRACH (Physical Random Access Channel) a first time after receiving a PDCCH (Physical Downlink Control Channel) instruction; A user device, wherein the first time is included in a second time for switching the TRP used for wireless communication.

3. A user device according to claim 2, A user device that transmits information related to the second time in capability information.

4. A user device according to claim 2, The second time is a time for synchronizing with the TRP to be a new connection destination, the user device.

5. A user device according to claim 2, A user device, wherein the second time is an addition time applied when adding a TRP to be a new connection destination.

6. A base station that performs wireless communication with a user device and is included in a communication system together with the user device, A plurality of TRPs (Transmission Reception Points) that wirelessly communicate with the user equipment, The user equipment transmits a PRACH (Physical Random Access Channel) a first time after receiving a PDCCH (Physical Downlink Control Channel) indication; A base station, wherein the first time is included in a second time for switching a TRP used for wireless communication.

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