Communication system

Abstract

This communication system comprises a base station (gNB), and a communication terminal (UE) connected to the base station. When a data signal is transmitted to the communication terminal, the base station reports, to the communication terminal, information relating to a demodulation reference signal that is transmitted together with the data signal, and the communication terminal transmits the data signal and the demodulation reference signal according to the information reported from the base station.

Description

Technical Field

[0001] The present disclosure relates to wireless communication technology.

Background Art

[0002] In 3GPP (3rd Generation Partnership Project), which is a standardization organization for mobile communication systems, a communication scheme referred to as Long Term Evolution (LTE) for the radio section and System Architecture Evolution (SAE) for the entire system configuration including the core network and the radio access network (hereinafter also collectively referred to as the network) is under study (for example, Non-Patent Documents 1 to 5). This communication scheme is also called a 3.9G (3.9 Generation) system.

[0003] As the access scheme for LTE, OFDM (Orthogonal Frequency Division Multiplexing) is used for the downlink direction, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is used for the uplink direction. Further, unlike W-CDMA (Wideband Code Division Multiple Access), LTE does not include circuit switching and is limited to only a packet communication scheme.

[0004] The decisions made by 3GPP regarding the frame structure in LTE systems, as described in Non-Patent Document 1 (Chapter 5), will be explained using Figure 1. Figure 1 is an explanatory diagram showing the structure of a radio frame used in an LTE communication system. In Figure 1, one radio frame is 10ms. A radio frame is divided into 10 subframes of equal size. Each subframe is divided into two slots of equal size. Downlink synchronization signals are included in the 1st and 6th subframes of each radio frame. The synchronization signals consist of a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

[0005] The 3GPP's decisions regarding channel configuration in LTE systems are described in Non-Patent Document 1 (Chapter 5). It is assumed that the same channel configuration as non-CSG cells will be used in CSG (Closed Subscriber Group) cells.

[0006] The Physical Broadcast Channel (PBCH) is a channel used for downlink transmission from base station equipment (hereinafter sometimes simply referred to as "base station") to communication terminal equipment (hereinafter sometimes simply referred to as "mobile terminal") and other such devices. A PBCH transport block is mapped to four subframes within a 40ms interval. There is no explicit signaling at 40ms timing.

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

[0008] The Physical Downlink Control Channel (PDCCH) is the channel used for downlink transmission from the base station to the communication terminal. The PDCCH notifies resource allocation information for the Downlink Shared Channel (DL-SCH), one of the transport channels described later, resource allocation information for the Paging Channel (PCH), another transport channel described later, and HARQ (Hybrid Automatic Repeat reQuest) information related to the DL-SCH. The PDCCH carries the Uplink Scheduling Grant. The PDCCH also carries Ack (Acknowledgement) / Nack (Negative Acknowledgement), which are response signals to uplink transmissions. The PDCCH is also called the L1 / L2 control signal.

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

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

[0011] The Physical Uplink Control Channel (PUCCH) is the channel used for uplink transmission from the communication terminal to the base station. The PUCCH carries the Ack / Nack response signal for downlink transmission. The PUCCH also carries Channel State Information (CSI). The CSI consists of the Rank Indicator (RI), Precoding Matrix Indicator (PMI), and Channel Quality Indicator (CQI) report. RI is the rank information of the channel matrix in MIMO. PMI is information of the precoding weight matrix used in MIMO. CQI is quality information indicating the quality of the received data or the quality of the communication channel. The PUCCH also carries a Scheduling Request (SR).

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

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

[0014] The downlink reference signal (RS) is a well-known symbol in LTE communication systems. Five types of downlink reference signals are defined: Cell-specific Reference Signal (CRS), MBSFN Reference Signal, UE-specific Reference Signal (UE-specific), Demodulation Reference Signal (DMRS), Positioning Reference Signal (PRS), and Channel State Information Reference Signal (CSI-RS). One measurement of the physical layer of a communication terminal is the Reference Signal Received Power (RSRP).

[0015] Similarly, the uplink reference signals are also known symbols for LTE communication systems. Two types of uplink reference signals are defined: the Demodulation Reference Signal (DMRS) and the Sounding Reference Signal (SRS).

[0016] This section explains the transport channel described in Non-Patent Document 1 (Chapter 5). Of the downlink transport channels, the Broadcast Channel (BCH) broadcasts to the entire coverage of the base station (cell). The BCH is mapped to the Physical Broadcast Channel (PBCH).

[0017] Downlink Shared Channels (DL-SCH) are subject to retransmission control using HARQ (Hybrid ARQ). DL-SCH can 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) for communication terminals to reduce power consumption. DL-SCH is mapped to Physical Downlink Shared Channels (PDSCH).

[0018] Paging Channels (PCHs) support DRX for communication terminals to enable low power consumption for those terminals. PCHs are required to broadcast across the entire coverage of a base station (cell). PCHs are mapped to physical resources, such as Physical Downlink Shared Channels (PDSCHs), which are dynamically available for traffic.

[0019] Multicast channels (MCHs) are used for broadcasting across the entire coverage of a base station (cell). MCHs support SFN synthesis of MBMS (Multimedia Broadcast Multicast Service) services (MTCH and MCCH) in multi-cell transmission. MCHs support quasi-static resource allocation. MCHs are mapped to PMCHs.

[0020] Among the uplink transport channels, the Uplink Shared Channel (UL-SCH) is subject to retransmission control using HARQ (Hybrid ARQ). UL-SCH supports dynamic or semi-static resource allocation. UL-SCH is mapped to the Physical Uplink Shared Channel (PUSCH).

[0021] Random Access Channels (RACHs) are limited to control information. RACHs carry a risk of collisions. RACHs are mapped to Physical Random Access Channels (PRACHs).

[0022] This section explains HARQ. HARQ is a technology that improves the communication quality of a transmission path by combining Automatic Repeat reQuest (ARQ) and Forward Error Correction. HARQ has the advantage that error correction works effectively through retransmission even on transmission paths where the communication quality changes. In particular, it is possible to achieve further quality improvement by combining the reception results of the initial transmission and the retransmission during retransmission.

[0023] Here is an example of how to retransmit data. If the receiving side is unable to correctly decode the received data, in other words, if a CRC (Cyclic Redundancy Check) error occurs (CRC=NG), the receiving side sends "Nack" to the sending side. Upon receiving "Nack," the sending side retransmits the data. If the receiving side is able to correctly decode the received data, in other words, if no CRC error occurs (CRC=OK), the receiving side sends "Ack" to the sending side. Upon receiving "Ack," the sending side sends the next data.

[0024] This section explains the logical channel described in Non-Patent Document 1 (Chapter 6). The Broadcast Control Channel (BCCH) is a downstream channel for broadcast system control information. The BCCH, being a logical channel, is mapped to the broadcast channel (BCH), which is a transport channel, or to the downstream shared channel (DL-SCH).

[0025] The Paging Control Channel (PCCH) is a downlink channel used to transmit changes to paging information and system information. The PCCH is used when the network does not know the cell location of a communication terminal. As a logical channel, the PCCH is mapped to the Paging Channel (PCH), which is a transport channel.

[0026] The Common Control Channel (CCCH) is a channel for transmit control information between a communication terminal and a base station. The CCCH is used when a communication terminal does not have an RRC connection with the network. In the downlink direction, the CCCH is mapped to the downlink common channel (DL-SCH), which is a transport channel. In the uplink direction, the CCCH is mapped to the uplink common channel (UL-SCH), which is a transport channel.

[0027] A Multicast Control Channel (MCCH) is a downlink channel for one-to-many transmission. MCCHs are used to transmit MBMS control information for one or more MCCHs from the network to communication terminals. MCCHs are only used by communication terminals receiving MBMS. MCCHs are mapped to the Multicast Channel (MCH), which is the transport channel.

[0028] A Dedicated Control Channel (DCCH) is a point-to-point channel that transmits dedicated control information between a communication terminal and a network. The DCCH is used when the communication terminal is in an RRC connection. The DCCH is mapped to an Uplink Shared Channel (UL-SCH) in the uplink, and mapped to a Downlink Shared Channel (DL-SCH) in the downlink.

[0029] A Dedicated Traffic Channel (DTCH) is a point-to-point channel for dedicated communication terminals for transmission of user information. The DTCH exists in both uplink and downlink. The DTCH is mapped to the Uplink Shared Channel (UL-SCH) in the uplink, and mapped to the Downlink Shared Channel (DL-SCH) in the downlink.

[0030] A Multicast Traffic Channel (MTCH) is a downlink channel for traffic data transmission from the network to communication terminals. The MTCH is a channel used only by communication terminals that are receiving MBMS. The MTCH is mapped to a Multicast Channel (MCH).

[0031] CGI refers to Cell Global Identifier. ECGI refers to E-UTRAN Cell Global Identifier. CSG (Closed Subscriber Group) cells are introduced in LTE, LTE-A (Long Term Evolution Advanced) described later, and UMTS (Universal Mobile Telecommunication System).

[0032] Location tracking of communication terminals is performed in units of areas consisting of one or more cells. Location tracking is performed to track the location of communication terminals even when they are in standby mode, and to enable them to be called, in other words, to allow them to receive calls. This area used for location tracking of communication terminals is called the tracking area.

[0033] Furthermore, 3GPP is working on the Long Term Evolution Advanced (LTE-A) standard as Release 10 (see Non-Patent Documents 3 and 4). LTE-A is based on the LTE wireless communication method and incorporates several new technologies.

[0034] In LTE-A systems, carrier aggregation (CA), which involves aggregating two or more component carriers (CCs) to support wider transmission bandwidths up to 100 MHz, is being considered. CA is described in Non-Patent Document 1.

[0035] When a CA (Carrier Aggregation) is configured, the UE (User Interface Device), which is a communication terminal, has a single RRC (Rapid Component Control) connection to the network (NW). In the RRC connection, one serving cell provides NAS mobility information and security input. This cell is called the Primary Cell (PCell). On the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC). On the uplink, the carrier corresponding to the PCell is the Uplink Primary Component Carrier (UL PCC).

[0036] Depending on the capabilities of the UE, secondary cells (SCells) are configured to form a set of serving cells together with PCells. On the downlink, the carrier corresponding to the SCell is the Downlink Secondary Component Carrier (DL SCC). On the uplink, the carrier corresponding to the SCell is the Uplink Secondary Component Carrier (UL SCC).

[0037] A set of serving cells consisting of one PCell and one or more SCells is configured for a single UE.

[0038] Furthermore, new technologies in LTE-A include technologies that support wider bandwidths (Wider bandwidth extension) and technologies such as Coordinated Multiple Point transmission and reception (CoMP). The CoMP technology being considered by 3GPP for LTE-A is described in Non-Patent Document 1.

[0039] Furthermore, 3GPP is considering using small eNBs (sometimes referred to as "small-scale base station equipment") that constitute small cells to cope with the enormous traffic of the future. For example, technologies are being considered to increase communication capacity by improving frequency utilization efficiency by installing a large number of small eNBs to constitute a large number of small cells. Specifically, there is dual connectivity (abbreviated as DC), in which a UE connects to and communicates with two eNBs. DC is described in Non-Patent Document 1.

[0040] In some cases, among eNBs that perform dual connectivity (DC), one is called the "master eNB (abbreviated as MeNB)" and the other is called the "secondary eNB (abbreviated as SeNB)".

[0041] Mobile network traffic is on the rise, and communication speeds are also increasing. Further speed increases are expected once LTE and LTE-A are fully operational.

[0042] Furthermore, in response to the increasing sophistication of mobile communications, a fifth-generation (sometimes referred to as "5G") wireless access system is being considered, with the goal of launching services after 2020. For example, in Europe, the METIS organization has compiled the requirements for 5G (see Non-Patent Document 5).

[0043] In 5G wireless access systems, the requirements include achieving 1000 times the system capacity, 100 times the data transmission speed, one-tenth (1 / 10) the data processing delay, and 100 times the number of simultaneous connections for communication terminals compared to LTE systems, while also achieving further reductions in power consumption and equipment costs.

[0044] To meet these requirements, 3GPP is working on the 5G standard as Release 15 (see Non-Patent Documents 6-19). The technology for the wireless portion of 5G 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 compared to the LTE system and LTE-A system.

[0046] For NR access, OFDM is used for the downstream direction, and OFDM and DFT-s-OFDM (DFT-spread-OFDM) are used for the upstream direction.

[0047] NR allows for the use of higher frequencies compared to LTE, in order to improve transmission speed and reduce processing delays.

[0048] In NR (Noise Reduction), 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 NR frame configurations, various subcarrier intervals, i.e., various numerologies, are supported. In NR, regardless of the numerology, one subframe is 1 millisecond, and one slot consists of 14 symbols. Furthermore, the number of slots contained in one subframe is one for a numerology with a subcarrier interval of 15 kHz, and increases proportionally with the subcarrier interval for other numerologies (see Non-Patent Document 13 (3GPP TS38.211)).

[0050] In NR, the downlink synchronization signal is transmitted from the base station as a synchronization signal burst (SS burst) at a predetermined period and for a predetermined duration. The SS burst consists of a synchronization signal block (SS block) for each beam of the base station.

[0051] During the duration of the SS burst, the base station transmits SS blocks of each beam, switching between beams. The SS block consists of P-SS, S-SS, and PBCH.

[0052] In noise reduction (NR), the effect of phase noise is reduced by adding a Phase Tracking Reference Signal (PTRS) as the downstream reference signal. Similarly, a PTRS is also added to the upstream reference signal.

[0053] In NR, Slot Format Indication (SFI) information has been added to the PDCCH to allow for flexible switching between DL / UL within a slot.

[0054] Furthermore, in NR, a portion of the carrier frequency band (sometimes referred to as the Bandwidth Part (BWP)) is pre-configured by the base station for the UE, and the UE performs transmission and reception with the base station in the BWP, thereby reducing the power consumption of the UE.

[0055] 3GPP is considering several data center configurations, including a data center with LTE and NR base stations connected to an EPC, a data center with NR base stations connected to a 5G core system, and a data center with LTE and NR base stations connected to a 5G core system (see Non-Patent Documents 12, 16, and 19).

[0056] Furthermore, 3GPP is considering supporting services (or applications) using side-link (SL) communication in both EPS and 5G core systems (see Non-Patent Documents 1, 16, 20, 21, 22, and 23). Examples of services using SL communication include V2X services and proximity services. [Prior art documents] [Non-patent literature]

[0057] [Non-Patent Document 1] 3GPP TS36.300 V16.2.0 [Non-Patent Document 2] 3GPP S1-083461 [Non-Patent Document 3] 3GPP TR36.814 V9.2.0 [Non-Patent Document 4] 3GPP TR36.912 V16.0.0 [Non-Patent Document 5] "Scenarios, requirements and KPIs for 5G mobile and wireless system", ICT-317669-METIS / D1.1

Non-licensed Document 6

Non-licensed Document 7

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

[0058] NR is planned to operate in higher frequency bands compared to LTE. Higher frequency bands increase path loss and degrade QoS. Therefore, coverage expansion is required. Furthermore, coverage expansion is also required to reduce capital investment in system construction and operational costs. Thus, the challenge in communication systems lies in how to expand coverage to improve communication quality and reduce costs.

[0059] In light of the above-mentioned issues, this disclosure aims, in part, to improve communication quality in communication systems. It also aims, in part, to reduce costs in communication systems. [Means for solving the problem]

[0060] The communication system relating to this disclosure comprises a base station and a communication terminal connected to the base station. When the base station causes the communication terminal to transmit a data signal, it notifies the communication terminal of information regarding a demodulation reference signal to be transmitted along with the data signal, and the communication terminal transmits the data signal and the demodulation reference signal in accordance with the information notified by the base station. [Effects of the Invention]

[0061] According to this disclosure, it is possible to realize a communication system that can improve communication quality.

[0062] The purpose, features, aspects, and advantages of this disclosure will become clearer from the following detailed description and accompanying drawings. [Brief explanation of the drawing]

[0063] [Figure 1] This is an explanatory diagram showing the configuration of wireless frames used in LTE communication systems. [Figure 2] This block diagram shows the overall configuration of the LTE communication system 200 as discussed in 3GPP. [Figure 3] This is a block diagram showing the overall configuration of the NR communication system 210 as discussed in 3GPP. [Figure 4] This is a diagram illustrating the configuration of a data center using eNBs and gNBs connected to the EPC. [Figure 5] This is a diagram showing the configuration of the DC using gNB connected to the NG core. [Figure 6] This is a diagram showing the configuration of the DC with eNBs and gNBs connected to the NG core. [Figure 7] This is a diagram showing the configuration of the DC with eNBs and gNBs connected to the NG core. [Figure 8] Figure 2 is a block diagram showing the configuration of the mobile terminal 202. [Figure 9] Figure 2 is a block diagram showing the configuration of base station 203. [Figure 10] This block diagram shows the configuration of MME. [Figure 11] This is a block diagram showing the configuration of the 5GC section. [Figure 12] This is a flowchart illustrating the general process from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. [Figure 13] This figure shows an example of a cell configuration in an NR system. [Figure 14] This is a sequence diagram showing an example of a method for performing DMRS settings during PUSCH retransmission in Embodiment 1. [Figure 15]This is a sequence diagram showing an example of a method for setting up DMRS during the initial PUSCH transmission in Embodiment 1. [Figure 16] This sequence diagram shows an example of a method for reducing DMRS during repeated PUSCH transmissions, according to a modification 1 of Embodiment 1. [Figure 17] This sequence diagram shows another example of a method for reducing DMRS during repeated PUSCH transmissions, according to Modification 1 of Embodiment 1. [Figure 18] This sequence diagram shows an example of how a UE requests a gNB to set up repeated PUSCH transmissions, as is the case with Modification 3 of Embodiment 1. [Figure 19] This diagram shows the configuration of a conventional SSB. [Figure 20] This figure shows an example of increasing the number of PBCH symbols in the SSB according to Embodiment 2. [Figure 21] This figure shows another example of increasing the number of PBCH symbols in the SSB according to Embodiment 2. [Figure 22] This sequence diagram shows an example of a modification 1 of Embodiment 2, in which the PDCCH of the RAR is transmitted multiple times using different beams during RA processing. [Figure 23] This sequence diagram shows an example of a modified example of Embodiment 2, in which a PDSCH containing a RAR message is transmitted multiple times using different beams during RA processing. [Figure 24] This sequence diagram shows an example of a modification 3 of Embodiment 2, in which the PDCCH of the RAR and the PDSCH containing the RAR message are transmitted multiple times using different beams during RA processing. [Figure 25] This is a sequence diagram showing an example of how to set up repeated transmission when retransmitting MSG3 in Embodiment 3. [Figure 26] This is a sequence diagram showing an example of an early termination method for repeated transmission of MSG3 in Embodiment 4. [Figure 27]The fourth embodiment is a sequence diagram showing another example of a method for early termination of repeated transmission of MSG3. [Figure 28] This figure shows an example of Embodiment 5 where the number of groups in the PRACH preamble is set to four. [Figure 29] The sequence diagram for Embodiment 6 shows an example of a method for notifying the UE of information regarding coverage expansion before it transitions to an abnormal state. [Modes for carrying out the invention]

[0064] Embodiment 1. Figure 2 is a block diagram showing the overall configuration of the LTE communication system 200 being discussed in 3GPP. Figure 2 will be explained below. The radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. The mobile terminal equipment (hereinafter referred to as "User Equipment: UE") 202, which is a communication terminal device, can communicate wirelessly with the base station equipment (hereinafter referred to as "Base Station (E-UTRAN NodeB: eNB)") 203 and transmits and receives signals wirelessly.

[0065] Here, "communication terminal equipment" includes not only mobile terminal equipment such as portable mobile phone terminals, but also stationary devices such as sensors. In the following explanation, "communication terminal equipment" may sometimes be simply referred to as "communication terminal."

[0066] If the control protocol for the mobile terminal 202, such as RRC (Radio Resource Control), and the user plane (hereinafter sometimes referred to as U-Plane), such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), are terminated at base station 203, then E-UTRAN is composed of one or more base stations 203.

[0067] The control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs functions such as broadcasting, paging, and RRC connection management. The states of the base station 203 and the mobile terminal 202 in RRC are RRC_IDLE and RRC_CONNECTED.

[0068] In RRC_IDLE mode, tasks such as PLMN (Public Land Mobile Network) selection, notification of system information (SI), paging, cell re-selection, and mobility are performed. In RRC_CONNECTED mode, mobile terminal 202 has an RRC connection and can send and receive data with the network. In RRC_CONNECTED mode, tasks such as handover (HO) and neighbor cell measurement are also performed.

[0069] Base station 203 consists of one or more eNB207 units. The system, comprising the core network EPC (Evolved Packet Core) and the wireless access network E-UTRAN201, is called EPS (Evolved Packet System). The EPC and E-UTRAN201 are sometimes collectively referred to as the "network."

[0070] The eNB207 is connected via an S1 interface to a Mobility Management Entity (MME), or a Serving Gateway (S-GW), or an MME / S-GW unit (hereinafter sometimes referred to as "MME unit") 204 that includes both an MME and an S-GW, and control information is communicated between the eNB207 and the MME unit 204. Multiple MME units 204 may be connected to a single eNB207. The eNB207s are connected to each other via an X2 interface, and control information is communicated between the eNB207s.

[0071] The MME unit 204 controls the connection between the higher-level device, specifically the higher-level node, which is the base station eNB 207, and the mobile terminal (UE) 202. The MME unit 204 constitutes the core network EPC. The base station 203 constitutes the E-UTRAN 201.

[0072] The base station 203 may constitute one cell or multiple cells. Each cell has a predetermined range called coverage, which is the range within which it can communicate with the mobile terminal 202, and wireless communication is performed with the mobile terminal 202 within that coverage. When one base station 203 constitutes multiple cells, each cell is configured to communicate with the mobile terminal 202.

[0073] Figure 3 is a block diagram showing the overall configuration of the 5G communication system 210 being discussed in 3GPP. Figure 3 will now be explained. The radio access network is called NG-RAN (Next Generation Radio Access Network) 211. UE 202 can communicate wirelessly with NR base station equipment (hereinafter referred to as "NR base station (NG-RAN NodeB: gNB)") 213 and transmits and receives signals wirelessly. The core network is called the 5G Core (5GC).

[0074] If the control protocol for UE202, such as RRC (Radio Resource Control), and the 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), are terminated at the NR base station 213, then the NG-RAN is composed of one or more NR base stations 213.

[0075] The functionality of the Radio Resource Control (RRC) control protocol between UE202 and NR base station 213 is the same as in LTE. The states of NR base station 213 and UE202 in RRC are RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE.

[0076] RRC_IDLE and RRC_CONNECTED are the same as in the LTE system. RRC_INACTIVE means that the connection between the 5G core and NR base station 213 is maintained while system information (SI) broadcasting, paging, cell re-selection, and mobility are performed.

[0077] The gNB217 is connected via an NG interface to an Access and Mobility Management Function (AMF), a Session Management Function (SMF), or a User Plane Function (UPF), or an AMF / SMF / UPF unit (hereinafter sometimes referred to as the "5GC unit") 214 that includes AMF, SMF, and UPF. Control information and / or user data are communicated between the gNB217 and the 5GC unit 214. The NG interface is a collective term for the N2 interface between the gNB217 and AMF, the N3 interface between the gNB217 and UPF, the N11 interface between AMF and SMF, and the N4 interface between UPF and SMF. Multiple 5GC units 214 may be connected to a single gNB217. The gNB217s are connected to each other via an Xn interface, and control information and / or user data are communicated between them.

[0078] The 5GC unit 214 is a higher-level device, specifically a higher-level node, and distributes paging signals to one or more base stations 203 and / or base station 213. The 5GC unit 214 also performs mobility control in the idle state. The 5GC unit 214 manages the tracking area list when the mobile terminal 202 is in the idle state, in the inactive state, and in the active state. The 5GC unit 214 initiates the paging protocol by sending a paging message to a cell belonging to the tracking area where the mobile terminal 202 is registered.

[0079] Like base station 203, NR base station 213 may also consist of one or more cells. When one NR base station 213 consists of multiple cells, each cell is configured to communicate with UE 202.

[0080] The gNB217 may be divided into a Central Unit (CU) 218 ​​and a Distributed Unit (DU) 219. One CU218 is configured within the gNB217. One or more DU219s are configured within the gNB217. The CU218 is connected to the DU219 via an F1 interface, and control information and / or user data are communicated between the CU218 and the DU219.

[0081] In a 5G communication system, the Unified Data Management (UDM) function and Policy Control Function (PCF) described in Non-Patent Document 21 (3GPP TS23.501) may be included. The UDM and / or PCF may be included in the 5GC unit 214 in Figure 3.

[0082] In a 5G communication system, a Non-3GPP Interworking Function (N3IWF) described in Non-Patent Document 21 (3GPP TS23.501) may be included. In non-3GPP access between the UE and the N3IWF, the Access Network (AN) may be terminated between the UE and the UE.

[0083] Figure 4 shows the configuration of a DC with eNBs and gNBs connected to the EPC. In Figure 4, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 4, eNB223-1 acts as the master base station, and gNB224-2 acts as the secondary base station (this DC configuration is sometimes referred to as EN-DC). Figure 4 shows an example where the U-Plane connection between the MME unit 204 and gNB224-2 is made via eNB223-1, but it may also be made directly between the MME unit 204 and gNB224-2.

[0084] Figure 5 shows the configuration of a DC with gNBs connected to the NG core. In Figure 5, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 5, gNB224-1 acts as the master base station, and gNB224-2 acts as the secondary base station (this DC configuration is sometimes referred to as NR-DC). Figure 5 shows an example where the U-Plane connection between 5GC unit 214 and gNB224-2 is made via gNB224-1, but it may also be made directly between 5GC unit 214 and gNB224-2.

[0085] Figure 6 shows the configuration of a DC with eNBs and gNBs connected to the NG core. In Figure 6, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 6, eNB226-1 acts as the master base station, and gNB224-2 acts as the secondary base station (this DC configuration is sometimes referred to as NG-EN-DC). Figure 6 shows an example where the U-Plane connection between 5GC unit 214 and gNB224-2 is made via eNB226-1, but it may also be made directly between 5GC unit 214 and gNB224-2.

[0086] Figure 7 shows another configuration of a DC with eNBs and gNBs connected to the NG core. In Figure 7, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 7, gNB224-1 acts as the master base station, and eNB226-2 acts as the secondary base station (this DC configuration is sometimes referred to as NE-DC). Figure 7 shows an example where the U-Plane connection between 5GC unit 214 and eNB226-2 is made via gNB224-1, but it may also be made directly between 5GC unit 214 and eNB226-2.

[0087] Figure 8 is a block diagram showing the configuration of the mobile terminal 202 shown in Figure 2. The transmission process of the mobile terminal 202 shown in Figure 8 will now be explained. First, control data from the protocol processing unit 301 and 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 processing such as error correction is performed. There may be data that is output directly from the transmission data buffer unit 303 to the modulation unit 305 without undergoing encoding processing. The data encoded by the encoder unit 304 is then modulated in the modulation unit 305. Precoding in MIMO may be performed in the modulation unit 305. The modulated data is converted into a baseband signal, then output to the frequency conversion unit 306, where it is converted to a wireless transmission frequency. After that, the transmission signal is sent from antennas 307-1 to 307-4 to the base station 203. Figure 8 illustrates the case where there are four antennas, but the number of antennas is not limited to four.

[0088] Furthermore, the reception processing of the mobile terminal 202 is performed as follows: A radio signal from the base station 203 is received by antennas 307-1 to 307-4. The received signal is converted from the radio reception frequency to a baseband signal by the frequency conversion unit 306, and demodulation processing is performed by the demodulation unit 308. Weight calculation and multiplication processing may also be performed in the demodulation unit 308. The demodulated data is passed to the decoder unit 309, where decoding processing 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. The series of processes of the mobile terminal 202 are controlled by the control unit 310. Therefore, although the control unit 310 is omitted in Figure 8, it is connected to each of the units 301 to 309. The control unit 310 is realized by a processing circuit that includes, for example, a processor and memory. That is, the control unit 310 is realized by the processor executing a program that describes the series of processes of the mobile terminal 202. A program describing a series of processes for the mobile terminal 202 is stored in memory. Examples of memory include non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), and flash memory. The control unit 310 may be implemented using a dedicated processing circuit such as an FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), or DSP (Digital Signal Processor). In Figure 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] Figure 9 is a block diagram showing the configuration of the base station 203 shown in Figure 2. The transmission process of the base station 203 shown in Figure 9 will now be explained. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (MME unit 204, etc.). The 5GC communication unit 412 transmits and receives data between the base station 203 and the 5GC (5GC unit 214, etc.). The other base station communication unit 402 transmits and receives data with other base stations. The EPC communication unit 401, the 5GC communication unit 412, and the other base station communication unit 402 each exchange information with the protocol processing unit 403. Control data from the protocol processing unit 403, as well as 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 undergoes encoding processing such as error correction. Some data may be output directly from the transmission data buffer unit 404 to the modulation unit 406 without undergoing encoding processing. The encoded data is then modulated in the modulation unit 406. Precoding in MIMO may be performed in the modulation unit 406. The modulated data is converted to a baseband signal, then output to the frequency conversion unit 407, where it is converted to a wireless transmission frequency. Subsequently, the transmission signal is sent from antennas 408-1 to 408-4 to one or more mobile terminals 202. Figure 9 illustrates the case with four antennas, but the number of antennas is not limited to four.

[0091] Furthermore, the reception processing of the base station 203 is performed as follows: A radio signal from one or more mobile terminals 202 is received by the antenna 408. The received signal is converted from the radio reception frequency to a baseband signal by the frequency conversion unit 407, and demodulation processing is performed by the demodulation unit 409. The demodulated data is passed to the decoder unit 410, where decoding processing such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 403, the 5GC communication unit 412, the EPC communication unit 401, or the other base station communication unit 402, and the user data is passed to the 5GC communication unit 412, the EPC communication unit 401, or the other base station communication unit 402. The series of processes of the base station 203 are controlled by the control unit 411. Therefore, although the control unit 411 is omitted in Figure 9, it is connected to each of the units 401-410 and 412. The control unit 411, like the control unit 310 of the mobile terminal 202 described above, is implemented as a processing circuit that includes a processor and memory, or as a dedicated processing circuit such as an FPGA, ASIC, or DSP. In Figure 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] Figure 9 is a block diagram showing the configuration of base station 203, but base station 213 may have a similar configuration. Also, in Figures 8 and 9, the number of antennas on mobile terminal 202 and base station 203 may be the same or different.

[0093] Figure 10 is a block diagram showing the configuration of the MME. Figure 10 shows the configuration of the MME204a included in the MME unit 204 shown in Figure 2 above. The PDN GW communication unit 501 transmits and receives data between the MME204a and the PDN GW (Packet Data Network Gateway). The base station communication unit 502 transmits and receives data between the MME204a 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] If the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 501 to the control plane control unit 505. If the data received from the base station 203 is control data, the control data is passed from the base station communication unit 502 to the control plane control unit 505.

[0095] The HeNBGW communication unit 504 transmits and receives data between the MME204a and the HeNB GW (Home-eNB Gateway). The control data received by the HeNBGW communication unit 504 from the HeNB GW is passed to the control plane control unit 505. The HeNBGW communication unit 504 transmits the control data input from the control plane control unit 505 to the HeNB GW.

[0096] The control plane control unit 505 includes the NAS security unit 505-1, the SAE bearer control unit 505-2, and the idle state mobility management unit 505-3, and performs all 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 standby state (also referred to as LTE-IDLE state or simply idle), generation and control of paging signals in the standby state, addition, deletion, updating, searching, and tracking area list management for one or more mobile terminals 202 under its umbrella.

[0097] The MME204a distributes paging signals to one or more base stations 203. The MME204a also performs mobility control in the idle state. The MME204a manages the tracking area list when the mobile terminal 202 is in the idle state and when it is in the active state. The MME204a initiates the paging protocol by sending a paging message to cells belonging to the tracking area where the mobile terminal 202 is registered. The management of the CSG, CSG ID, and whitelist of the eNB207 connected to the MME204a may be performed by the idle state mobility management unit 505-3.

[0098] The series of processes of the MME204a are controlled by the control unit 506. Therefore, although the control unit 506 is omitted in Figure 10, it is connected to each of the units 501 to 505. The control unit 506 is implemented as a processing circuit that includes a processor and memory, similar to the control unit 310 of the mobile terminal 202 described above, or as a dedicated processing circuit such as an FPGA, ASIC, or DSP.

[0099] Figure 11 is a block diagram showing the configuration of the 5GC unit. Figure 11 shows the configuration of the 5GC unit 214 shown in Figure 3. Figure 11 shows the case where the 5GC unit 214 shown in Figure 5 includes the configurations of AMF, SMF, and UPF. 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 transmitted to one or more base stations 203 and / or base station 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.

[0100] 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 communication unit 523. The session management unit 527 passes the control data to the control-plane control unit 525. If the data received from base station 203 and / or base station 213 is control data, the control data is passed from 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.

[0101] The control plane control unit 525 includes the NAS security unit 525-1, the PDU session control unit 525-2, and the idle state mobility management unit 525-3, and performs all 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 manages 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 the standby state (also referred to as RRC_IDLE state or simply idle), generation and control of paging signals in the standby state, addition, deletion, updating, searching, and tracking area list management for one or more mobile terminals 202 under its umbrella.

[0102] The series of processes in the 5GC unit 214 are controlled by the control unit 526. Therefore, although the control unit 526 is omitted in Figure 11, it is connected to each of the units 521-523, 525, and 527. The control unit 526 is implemented as a processing circuit that includes a processor and memory, similar to the control unit 310 of the mobile terminal 202 described above, or as a dedicated processing circuit such as an FPGA, ASIC, or DSP.

[0103] Next, an example of a cell search method in a communication system is shown. Figure 12 is a flowchart illustrating the process from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. When the communication terminal starts a cell search, in step ST601, it synchronizes the slot timing and frame timing using the first synchronization signal (P-SS) and the second synchronization signal (S-SS) transmitted from the surrounding base station.

[0104] P-SS and S-SS together are called the Synchronization Signal (SS). Each PCI assigned to a cell has a synchronization code that corresponds one-to-one with that PCI. 504 different PCI combinations are being considered. The communication terminal uses these 504 PCI combinations to synchronize and also detects (identifies) the PCI of the synchronized cell.

[0105] The communication terminal then detects the cell-specific reference signal (CRS), which is a reference signal (RS) transmitted from the base station to each cell, in step ST602 for the next synchronized cell, and measures the Reference Signal Received Power (RSRP). The reference signal (RS) uses a code that corresponds one-to-one with the PCI. By correlating with this code, it is possible to isolate it from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST601, it becomes possible to detect the RS and measure the received power of the RS.

[0106] Next, in step ST603, the communication terminal selects the cell with the best RS reception quality from among the one or more cells detected up to step ST602, for example, the cell with the highest RS reception power, i.e., the best cell.

[0107] Next, in step ST604, the communication terminal receives the PBCH of the best cell and obtains the BCCH, which is broadcast information. The BCCH on the PBCH is mapped to the MIB (Master Information Block), which contains cell configuration information. Therefore, by receiving the PBCH and obtaining the BCCH, the MIB can be obtained. MIB information includes, for example, the DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, and the SFN (System Frame Number).

[0108] Next, in step ST605, the communication terminal receives the DL-SCH of the cell based on the cell configuration information of the MIB and obtains SIB (System Information Block) 1 from the broadcast information BCCH. SIB1 contains information about accessing the cell, information about cell selection, and scheduling information for other SIBs (SIBk; an integer k ≥ 2). SIB1 also contains the Tracking Area Code (TAC).

[0109] 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 already held by the communication terminal. The Tracking Area List is also called the TAI list. TAI is identification information for identifying a tracking area and consists of MCC (Mobile Country Code), MNC (Mobile Network Code), and TAC (Tracking Area Code). MCC is the country code. MNC is the network code. TAC is the code number of the tracking area.

[0110] If, as a result of the comparison in step ST606, the TAC received in step ST605 is the same as a TAC included in the tracking area list, the communication terminal enters a waiting state in that cell. If, after comparison, the TAC received in step ST605 is not included in the tracking area list, the communication terminal requests a change in the tracking area through that cell to the Core Network (EPC), which includes the MME, etc., in order to perform a Tracking Area Update (TAU).

[0111] In the example shown in Figure 12, an example of the operation from cell search to standby in the LTE system is shown. However, in the NR system, in step ST603, the best beam may be selected in addition to the best cell. Also in the NR system, in step ST604, beam information, such as a beam identifier, may be obtained. Also in the NR system, in step ST604, scheduling information for the Remaining Minimum SI (RMSI) may be obtained. In the NR system, in step ST605, the RMSI may be received.

[0112] The devices constituting the core network (sometimes referred to as "core network devices") update the tracking area list based on the identification number (UE-ID, etc.) of the communication terminal sent from the communication terminal along with the TAU request signal. The core network devices send the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) its TAC list based on the received tracking area list. After that, the communication terminal enters a waiting state in that cell.

[0113] The proliferation of smartphones and tablet devices has led to an explosive increase in cellular wireless communication traffic, raising concerns about a shortage of wireless resources worldwide. To address this, efforts are being made to improve frequency utilization efficiency by reducing the number of cells and promoting spatial separation.

[0114] In conventional cell configurations, cells composed of eNBs have relatively wide coverage. Traditionally, cells are configured to cover a certain area through the relatively wide coverage of multiple cells composed of multiple eNBs.

[0115] When subdivided into smaller cells, the cells composed of eNBs have narrower coverage than cells composed of conventional eNBs. Therefore, as before, a larger number of subdivided eNBs are needed to cover a given area compared to conventional eNBs.

[0116] In the following explanation, cells with relatively high coverage, such as those composed of conventional eNBs, will be referred to as "macrocells," and the eNBs that make up macrocells will be referred to as "macro eNBs." Similarly, cells with relatively low coverage, such as those that have been resized into smaller cells, will be referred to as "small cells," and the eNBs that make up small cells will be referred to as "small eNBs."

[0117] Macro eNB may be, for example, a "Wide Area Base Station" as described in Non-Patent Document 7.

[0118] A small eNB may be, for example, a low-power node, a local area node, or a hotspot. Alternatively, a small eNB may be a pico eNB constituting a picocell, a femto eNB constituting a femtocell, a HeNB, an RRH (Remote Radio Head), an RRU (Remote Radio Unit), an RRE (Remote Radio Equipment), or an RN (Relay Node). Furthermore, a small eNB may be a "Local Area Base Station" or "Home Base Station" as described in Non-Patent Document 7.

[0119] Figure 13 shows an example of a cell configuration in NR. In an NR cell, a narrow beam is formed and transmitted by changing its direction. In the example shown in Figure 13, base station 750 uses beam 751-1 to transmit and receive with a mobile terminal at a certain time. At other times, base station 750 uses beam 751-2 to transmit and receive with a mobile terminal. Similarly, base station 750 uses one or more of beams 751-3 to 751-8 to transmit and receive with a mobile terminal. In this way, base station 750 configures a wide-area cell.

[0120] Figure 13 shows an example where the base station 750 uses eight beams, but the number of beams may be different from eight. Also, in the example shown in Figure 13, the base station 750 uses one beam simultaneously, but it may use multiple beams.

[0121] NR is planned to operate in higher frequency bands compared to LTE. Higher frequency bands increase path loss and reduce QoS. Therefore, coverage expansion is required. Furthermore, coverage expansion is needed to reduce capital investment and operating costs when building the system. 3GPP is discussing expanding PUSCH coverage by increasing or decreasing the number of DMRSs (see Non-Patent Documents 24 and 25).

[0122] However, there is no disclosure whatsoever regarding how to configure the increase or decrease in the number of DMRSs. If the method for configuring the increase or decrease in the number of DMRSs is not shared between the gNB and the UE, coordinated transmission and reception processing will become impossible, potentially leading to a deterioration in communication quality or communication interruptions due to malfunctions. As a result, coverage expansion will become impossible.

[0123] Traditionally, DMRS settings are configured via RRC signaling prior to PUSCH transmission. Therefore, the DMRS settings notified via RRC signaling are used as the DMRS settings for subsequent PUSCH transmissions. However, the radio wave propagation environment differs between the initial PUSCH transmission and subsequent PUSCH retransmissions. Consequently, even if a PUSCH retransmission is performed to recover from a communication failure during the initial transmission, it may not be possible to configure the DMRS settings for the retransmission to suit the radio wave propagation environment, resulting in a degradation of communication quality.

[0124] This embodiment discloses a method for solving these problems.

[0125] In this embodiment, the above problems are solved by dynamically configuring PUSCH. The configuration of DMRS for PUSCH may also be performed dynamically. Hereafter, the configuration of PUSCH and / or the configuration of DMRS for PUSCH may be referred to as "configuration of DMRS for PUSCH". In other words, in the communication system according to this embodiment, the configuration of DMRS for PUSCH is performed dynamically. Furthermore, the configuration of DMRS for PUSCH is enabled when PUSCH is retransmitted. When PUSCH is retransmitted, the configuration of DMRS for PUSCH is enabled for each retransmission. As for the DMRS configuration, it may be possible to switch between multiple DMRS configurations.

[0126] The gNB notifies the UE of information regarding the PUSCH's DMRS settings via PDCCH. It is preferable to notify some or all of the information regarding the PUSCH's DMRS settings, which were previously set using RRC signaling, via PDCCH. This information may also be included in the Downlink Control Information (DCI). A new DCI format that includes this information may be established. The PDCCH for retransmission of the PUSCH notifies information regarding the DMRS settings of the retransmitted PUSCH.

[0127] Information regarding the DMRS configuration of PUSCH, which is notified via PDCCH, does not need to be notified via RRC signaling. This reduces the amount of information that can be sent via RRC signaling.

[0128] Information regarding the DMRS settings for PUSCH, which is notified via PDCCH, may also be notified via RRC signaling. If this information is notified via PDCCH, it should take precedence over the information notified via RRC signaling. If this information is not notified via PDCCH, the information notified via RRC signaling should be used. In this way, it becomes possible to set DMRS settings suitable for PUSCH transmission by using PDCCH only when dynamic settings are required due to rapid changes in the radio wave propagation environment. In cases where the situation changes between the initial transmission and retransmission of PUSCH, it becomes possible to dynamically set DMRS settings suitable for retransmission as well.

[0129] Information regarding the DMRS settings for PUSCH, notified by PDCCH, includes information on PUSCH resource allocation, information on repeated transmissions of PUSCH, information on DMRS resource allocation for PUSCH, and information on modulation scheme. Resource allocation information includes information on resource allocation on the time axis, resource allocation on the frequency axis, and sequence information.

[0130] Here are 14 specific examples of information regarding PUSCH's DMRS configuration that is notified via PDCCH.

[0131] (1) PUSCH's UL resource allocation type. (2) PUSCH mapping type (either Type A or Type B). (3) PUSCH's time domain allocation. (4) PUSCH's time domain allocation index. (5) Information regarding the subcarrier spacing of PUSCH. (6) DMRS symbol position when the PUSCH mapping type is type A. (7) PUSCH repeat type. (8) Number of PUSCH repetitions. (9) DMRS configuration type. (10) Maximum symbol length of DMRS. (11) Symbol length of DMRS. (12) Number and / or location of additional DMRS. (13) Whether or not a transform precoder is present. (14) A combination of (1) to (13).

[0132] For example, if the gNB determines that an increase in DMRS is necessary during PUSCH retransmission, the gNB uses this information to set the number of DMRS in the PDCCH to be greater than the number set in the RRC. This improves the demodulation accuracy of PUSCH and thus improves the reception quality of PUSCH. For example, if the gNB determines that an increase in PUSCH transmission resources is necessary during PUSCH retransmission, the gNB uses this information to set the number of DMRS in the PDCCH to be less than the number set in the RRC. This allows for an increase in PUSCH resources by the amount of DMRS reduction, improving the demodulation accuracy of PUSCH and thus improving the reception quality of PUSCH.

[0133] A set of combinations of information regarding the DMRS settings of PUSCH to be notified via PDCCH may be provided. One or more sets may be designated as candidates for the information regarding the DMRS settings of PUSCH to be notified via PDCCH. Each set within these candidates may be indexed to form a candidate list.

[0134] The gNB may notify the UE of the candidate list via RRC signaling and notify via PDCCH of an index representing a set of combinations of information regarding the DMRS settings of PUSCH notified via PDCCH. The index may also be included in the DCI and notified via PDCCH. Doing so can reduce the amount of information transmitted via PDCCH.

[0135] This document discloses a method by which a gNB determines the dynamic DMRS setting for a push transmission. The gNB uses the received quality of the UL's DMRS received from the UE to determine the DMRS setting for subsequent push transmissions. For example, the gNB uses the received quality of the DMRS for the initial push transmission received from the UE to determine the DMRS setting for push retransmissions if push retransmissions are performed. Alternatively, the gNB may use the received quality of the SRS transmitted by the UE to determine the DMRS setting for subsequent push transmissions. Alternatively, the gNB may use the CSI received from the UE to determine the DMRS setting for subsequent push transmissions.

[0136] The gNB can configure the UE to transmit SRS, which can be periodic, semi-persistent, or aperiodic. Similarly, the gNB can configure the UE to report CSI, which can be periodic, semi-persistent, or aperiodic. Using these settings, the gNB utilizes the SRS and CSI received from the UE to enable DMRS configurations suitable for the radio wave propagation environment.

[0137] For example, if a gNB receives an initial PUSCH transmission but the DMRS reception quality is poor and it fails to receive the PUSCH, it is advisable to increase the number of DMRS units in the DMRS settings for retransmitting the PUSCH. This improves the reception quality of the DMRS for retransmitting the PUSCH, thereby increasing the probability of receiving the retransmission.

[0138] For example, if a gNB receives an initial PUSCH transmission, but the reception quality of the PUSCH portion is poor and the PUSCH cannot be received, it is advisable to reduce the number of DMRS in the DMRS settings for PUSCH retransmission. The UE will then increase the PUSCH resources by the amount of the reduced DMRS and send it to the UE. This makes it possible to improve the reception quality of PUSCH retransmissions and increase the probability of receiving PUSCH retransmissions.

[0139] Thus, by enabling DMRS settings during PUSCH retransmission, it becomes possible to improve the reception quality of PUSCH retransmissions and increase the probability of receiving PUSCH retransmissions. This allows for expanded PUSCH coverage.

[0140] Figure 14 is a sequence diagram showing an example of a method for performing DMRS configuration during PUSCH retransmission in Embodiment 1. In step ST1401, the gNB notifies the UE of information regarding the DMRS configuration for PUSCH. This notification is made prior to the transmission of PUSCH. RRC signaling is used to notify this information. As RRC signaling, for example, an RRCReconfiguration message may be used, or MIBs or SIBs may be used. These may be used in combination.

[0141] In step ST1402, the gNB notifies the UE of scheduling information for the initial PUSCH transmission. Along with the initial PUSCH scheduling information, or included in the PUSCH scheduling information, the gNB notifies the UL resource allocation type information (UL RA type information) and DMRS symbol length information. This information may also be included in the DCI. In step ST1403, the UE transmits the UL data via PUSCH using the information received from the gNB in ​​steps ST1401 and ST1402. The UE transmits the DMRS for PUSCH along with the PUSCH.

[0142] In step ST1404, if the gNB fails to receive the UL data, it decides to retransmit via PUSCH. Also in step ST1404, the gNB decides on the DMRS settings for the PUSCH retransmission. For example, the DMRS settings for the PUSCH retransmission may be determined using the decision method disclosed above. In step ST1405, the gNB notifies the UE of the PUSCH scheduling information for retransmission, the UL resource allocation type information, the DMRS symbol length information, as well as information regarding the PUSCH resource allocation, the PUSCH DMRS resource allocation, and the modulation scheme. This information may be included in the DCI.

[0143] In step ST1406, the UE retransmits the PUSCH signal using the information received from the gNB in ​​step ST1405 to retransmit the UL data. If the information received in step ST1405 overlaps with the information previously received by the UE in step ST1401 regarding the PUSCH DMRS settings, the UE should use the information received in step ST1405 to configure the PUSCH DMRS settings. This allows for dynamic configuration, enabling the PUSCH retransmission DMRS settings to take into account the current radio wave propagation environment.

[0144] If the DMRS settings for PUSCH retransmission do not need to be changed from the initial DMRS settings, the gNB does not need to notify the UE of the PUSCH retransmission DMRS settings. For example, in step ST1404, the gNB determines that the DMRS settings for PUSCH retransmission do not need to be changed from the initial settings. In step ST1405, the gNB notifies the UE of the PUSCH scheduling information for retransmission, but does not need to notify information regarding PUSCH resource allocation, PUSCH DMRS resource allocation, or modulation scheme. This reduces the amount of information required for signaling.

[0145] By using the sequence shown in Figure 14, it becomes possible to configure DMRS during PUSCH retransmission.

[0146] A method for dynamically configuring the DMRS of a PUSCH during PUSCH retransmission was disclosed. Here, a method for dynamically configuring the DMRS of a PUSCH during its initial transmission is disclosed. The gNB notifies the PDCCH for the initial transmission of the PUSCH with information regarding the DMRS configuration of that initial transmission.

[0147] Figure 15 is a sequence diagram showing an example of a method for setting the DMRS during the initial transmission of PUSCH according to Embodiment 1. In Figure 15, steps common to Figure 14 are given the same step numbers, and common explanations are omitted. In step ST1501, the gNB determines the DMRS settings for the initial transmission of PUSCH. The method for determining these DMRS settings may be, for example, the method disclosed above, in which the gNB determines the dynamic setting of the PUSCH's DMRS.

[0148] In step ST1502, the gNB notifies the UE of the following information for the initial transmission: PUSCH scheduling information, UL resource allocation type information, DMRS symbol length information, as well as information regarding PUSCH resource allocation, PUSCH DMRS resource allocation, and modulation scheme. This information may also be included in the DCI.

[0149] In step ST1403, the UE transmits a PUSCH for UL data transmission using the information received from the gNB in ​​step ST1502. If the information regarding the DMRS settings for the PUSCH, which the UE received in step ST1401, overlaps with the information received in step ST1502, the UE should use the information received in step ST1502 to configure the DMRS settings for the PUSCH. This allows for dynamic configuration even for the initial PUSCH transmission, enabling DMRS configuration for the initial PUSCH transmission that takes into account the most recent radio wave propagation environment, even when there is a large time interval between the initial configuration using RRC signaling and the initial PUSCH transmission.

[0150] If the gNB fails to receive the initial PUSCH transmission from the UE, it instructs the UE to retransmit the PUSCH. In this case, the method of setting the DMRS during the PUSCH retransmission, as disclosed in Figure 14, may be applied. By doing so, it becomes possible to set the DMRS for the PUSCH, taking into account the most recent radio wave propagation environment, not only for the initial transmission but also for retransmissions.

[0151] The UE may send a message to the gNB requesting a change in the PUSCH DMRS settings. For example, this message may be included in the initial PUSCH transmission, or in a retransmission of the PUSCH, or in the MAC-CE. This allows for flexible configuration of the PUSCH DMRS settings, taking into account the UE's status.

[0152] The UE may send a message to the gNB requesting a change in the PDSCH DMRS settings. For example, this could be included in the UCI and sent via PUCCH. Alternatively, it could be included in the PDSCH Ack / Nack information, or sent together with the Ack / Nack information via PUCCH. This allows for flexible configuration of the PDSCH DMRS settings, including the UE's PDSCH reception status.

[0153] In addition to PUSCH and PDSCH, messages requesting DMRS configuration changes for PUCCH and PDCCH may be provided, and these messages can be sent from the UE to the gNB. This allows for flexible configuration of DMRS for each channel, thereby improving the communication quality of each channel.

[0154] As a method for extending coverage, coverage extension in random access processing (hereinafter sometimes referred to as RA processing) is being considered. RA processing is performed by the transmission and reception of MSG1 to MSG4 between the UE and gNB. When the UE receives the RAR (Random Access Response), which is MSG2, from the gNB, it sends MSG3 to the gNB. This MSG3 is transmitted using PUSCH.

[0155] During the RA processing stage, the gNB does not configure UEs individually using RRC signaling. The DMRS settings for PUSCH for MSG3 are limited to those configured commonly for UEs in the MIB and SIB, and those configured in the RAR. For example, these include the PUSCH mapping type, PUSCH time-domain allocation, PUSCH time-domain allocation index, DMRS symbol position when the PUSCH mapping type is type A, and modulation scheme information. Other information is statically determined by standards, etc. In other words, it is common to all cells, making it impossible to configure settings suitable for the different radio wave propagation environments of each cell.

[0156] This document discloses methods for solving these problems.

[0157] To address the above issues, configuration information for the DMRS of the PUSCH for MSG3 may be provided. For example, the gNB may announce the DMRS configuration for the PUSCH for MSG3 via the MIB or SIB. The DMRS configuration information for the PUSCH for MSG3 may be part or all of the information regarding the DMRS configuration of the PUSCH notified via the PDCCH disclosed above. For example, it may include information regarding repeated transmissions of the PUSCH and information regarding the resource allocation of the PUSCH DMRS.

[0158] This information may also be part of the common configuration information for PUSCH (PUSCH-ConfigCommon). For example, this information may also be part of the common configuration information for RACH (RACH-ConfigCommon). The gNB broadcasts the PUSCH DMRS settings for MSG3 via MIB or SIB. This makes it possible to implement PUSCH DMRS settings for MSG3 that are suitable for the different radio wave propagation environments of each cell.

[0159] As a method to improve the reception quality during the initial transmission of PUSCH for MSG3, the method disclosed above that enables DMRS configuration during the initial transmission of PUSCH may be applied as appropriate. Instead of a PDCCH for scheduling PUSCH, a RAR message may be used. Alternatively, instead of a PDCCH for scheduling PUSCH, a PDCCH for scheduling RAR messages may be used.

[0160] For example, gNB notifies the UE of the DMRS settings for PUSCH for MSG3, either with a RAR message or by including it in the RAR message. PDSCH may be used for these notifications. For example, gNB may notify the UE of the DMRS settings for PUSCH for MSG3 using a PDCCH for scheduling a PDSCH containing a RAR message. gNB notifies the UE of the DMRS settings for PUSCH for MSG3, either with a scheduling DCI or by including it in the DCI.

[0161] The DMRS configuration information for PUSCH for MSG3 may be some or all of the information regarding the DMRS configuration of PUSCH that is notified via PDCCH as disclosed above. For example, it may include information regarding repeated transmissions of PUSCH and information regarding resource allocation for PUSCH's DMRS.

[0162] The DMRS configuration information for PUSCH for MSG3 may be predetermined statically by standards, etc. If this information is notified by gNB in ​​the manner disclosed above, it should take precedence over the information predetermined statically by standards, etc. If this information is not notified by gNB, the information predetermined statically by standards, etc. should be used. In this way, it becomes possible to set up DMRS suitable for transmission of PUSCH for MSG3 only when dynamic settings are required due to rapid changes in the radio wave propagation environment, etc.

[0163] This allows for dynamic settings for the initial PUSCH transmission for MSG3, enabling DMRS settings for the initial PUSCH transmission that take into account the current radio wave propagation environment.

[0164] As a method to improve the reception quality during PUSCH retransmission for MSG3, the method disclosed above that enables DMRS configuration during PUSCH retransmission may be applied as appropriate. The gNB may use the PDCCH for scheduling PUSCH retransmission for MSG3 to notify the DMRS configuration information for PUSCH for MSG3. The gNB notifies the DMRS configuration information together with, or included in, the DCI for scheduling.

[0165] This approach enables dynamic DMRS settings for PUSCH retransmissions for MSG3, allowing for DMRS settings for initial PUSCH transmissions that take into account the most recent radio wave propagation environment.

[0166] The information regarding the DMRS settings for PUSCH notified via PDCCH may be set according to the number of repetitions. Alternatively, the information regarding the DMRS settings for PUSCH notified via PDCCH may be set for each repetition. For example, for each repetition, information excluding (7) and (8) from the specific examples of information regarding the DMRS settings for PUSCH notified via PDCCH disclosed above may be set. In this way, dynamic DMRS settings become possible in PUSCH transmissions, including repetitions, and DMRS settings that take into account the most recent radio wave propagation environment become possible.

[0167] The method disclosed in this embodiment enables dynamic setting of DMRS during PUSCH retransmission. This allows for setting DMRS in accordance with the constantly changing radio wave propagation environment. For example, reducing DMRS can increase the number of REs (Resource Elements) that PUSCH can map to, thereby improving the communication quality of PUSCH. For example, increasing DMRS can improve demodulation accuracy, thereby improving the communication quality of PUSCH. Furthermore, by changing the modulation scheme between OFDM and DFT-s-OFDM, the density of DMRS in the frequency axis direction can be changed. It is also possible to obtain the same effects as when increasing or decreasing DMRS as described above.

[0168] Furthermore, dynamic DMRS settings are possible even during the initial PUSCH transmission. This allows for similar effects to be achieved when the radio wave propagation environment changes over time after RRC settings have been applied.

[0169] Furthermore, dynamic DMRS settings become possible even when transmitting via PUSCH, including MSG3. This allows for DMRS settings to be adjusted according to the constantly changing radio wave propagation environment, achieving similar effects.

[0170] This approach makes it possible to expand coverage.

[0171] Modification 1 of Embodiment 1. PUSCH is designed to be retransmitted. When PUSCH is transmitted repeatedly, DMRS is also transmitted with each retransmission. As a result, the overhead caused by DMRS increases with each repeated transmission of PUSCH, which can lead to problems in improving the communication quality of PUSCH.

[0172] This modified version discloses a method for solving these problems.

[0173] To address the above issues, the communication system of this modified version reduces DMRS during repeated transmission of PUSCH. Three methods for reducing DMRS are disclosed below.

[0174] (Method 1) Reduce the DMRS in the frequency axis direction to which the DMRS is mapped. (Method 2) Reduce the DMRS in the time axis direction to which the DMRS are mapped. (Method 3) A combination of (Method 1) and (Method 2).

[0175] A specific example of (Method 1) is disclosed. There are two types of DMRS configurations: DMRS configuration type 1 and type 2. In DMRS configuration type 1, DMRS is mapped to every two subcarriers within a single symbol. In DMRS configuration type 2, DMRS is mapped to every three pairs of two subcarriers within a single symbol.

[0176] In (Method 1), for example, DMRS can be thinned in DMRS configuration type 1. In this case, for example, DMRS can be thinned to one in two, and DMRS can be mapped every four subcarriers within one symbol. Alternatively, DMRS can be thinned in DMRS configuration type 2. DMRS can be thinned to one pair in two pairs, and DMRS can be mapped every six pairs within one symbol. The thinning interval is not limited to two. By doing so, it is possible to reduce DMRS in the frequency axis direction.

[0177] Another example of (Method 1) is to change the DMRS configuration type. As mentioned above, there are two types of DMRS configurations, and the DMRS density differs for each type. Therefore, by changing the DMRS configuration type, it is possible to reduce the number of DMRS.

[0178] As another example of (Method 1), the modulation scheme of the push transmission may be changed. By changing the modulation scheme from DFT-s-OFDM to OFDM, it is possible to reduce DMRS in the frequency axis direction.

[0179] A specific example of (Method 2) is disclosed. Conventionally, there are two types of symbols to which DMRS is mapped: one symbol and two consecutive symbols. For example, if DMRS is two symbols, it may be changed to one symbol. For example, DMRS may not be mapped at all. Also, conventionally, in addition to the normal DMRS, additional DMRS may be set for other symbols. For example, additional DMRS may not be mapped. By doing so, it is possible to reduce DMRS in the time axis direction. Furthermore, when additional DMRS is set, for example, the normal DMRS may not be mapped, or for example, both the normal DMRS and additional DMRS may be reduced. By doing so, it is possible to increase PUSCH resources while ensuring demodulation accuracy at the end of the PUSCH slot.

[0180] It is advisable to reduce DMRS according to the number of PUSCH repetitions. DMRS reduction can also be set for each repeated PUSCH transmission. For example, DMRS can be decimated for each repeated PUSCH transmission. For example, the number of DMRS to be reduced can be set for each repeated PUSCH transmission. The reduction unit can be RE units or RB (Resource Block) units. For example, the number of DMRS symbols in the time axis direction can be set for each repeated PUSCH transmission. For example, the number of DMRS symbols to be reduced can be set for each repeated PUSCH transmission. The reduction unit can be symbol units or slot units.

[0181] As part of the information regarding PUSCH's DMRS reduction, DMRS configuration type information may be provided. For example, DMRS configuration type 1, DMRS configuration type 2.

[0182] Information regarding PUSCH's DMRS reduction may include DMRS decimation information. For example, if the setting is to decimate h DMRS by i, then h and i are the DMRS decimation information. Information to identify the REs that will decimate the DMRS may be included. Information to identify the RBs that will decimate the DMRS may be included. Information indicating that all DMRS in the frequency axis direction will be reduced may be included. Such information regarding PUSCH's DMRS settings may be included, for example, in PUSCH's DMRS resource allocation information. For example, it may be included in the DMRS setting type information.

[0183] As information regarding the reduction of DMRS in PUSCH, modulation scheme information may be provided. The modulation scheme information may be OFDM or DFT-s-OFDM. As another example, the modulation scheme information may be the presence or absence of a transform precoder. If a transform precoder is present, transform precoding is performed, resulting in DFT-s-OFDM. If a transform precoder is absent, transform precoding is not performed, resulting in OFDM.

[0184] Information regarding PUSCH's DMRS reduction may include information regarding PUSCH's DMRS resource allocation. For example, DMRS symbol location information may be provided when PUSCH's mapping type is type A. By combining this with other information, flexible DMRS reduction can be configured.

[0185] Information may be provided to identify the symbols from which DMRS will be thinned. Information may be provided to identify the slots from which DMRS will be thinned. Information may be provided to indicate that all DMRS in the time axis direction will be thinned. Such information regarding PUSCH's DMRS settings may be included, for example, in PUSCH's DMRS resource allocation information. For example, it may be included in the DMRS maximum symbol length information or in the DMRS symbol length information.

[0186] It is advisable to configure information regarding PUSCH's DMRS reduction based on the number of repetitions. Alternatively, information regarding PUSCH's DMRS reduction can be configured for each repetition.

[0187] You may set a pattern for reducing DMRS in repeated PUSCH transmissions. This pattern may be set for each of multiple repeated transmissions. For example, you may reduce DMRS once every four repeated PUSCH transmissions. For example, you may reduce DMRS in the third and fourth of four repeated transmissions. Repeated transmissions are not limited to four. The pattern for reducing DMRS may be, for example, an RE pattern or an RB pattern. The pattern for reducing DMRS may be, for example, a symbol pattern or a slot pattern.

[0188] As information regarding the reduction of DMRS in PUSCH, pattern information for the DMRS to be reduced may be provided. Pattern information for the DMRS to be reduced may also be set according to the number of repetitions.

[0189] The gNB configures information for the UE regarding DMRS reduction during repeated PUSCH transmissions, enabling the UE to map a different DMRS for each repeated PUSCH transmission.

[0190] These DMRS reduction settings can be combined. In this case, flexible DMRS settings can be made in both the frequency and time axes during repeated PUSCH transmissions. This method avoids unnecessary DMRS mapping and prevents an increase in DMRS overhead. By reducing DMRS, it becomes possible to increase the resources available for mapping PUSCH, thereby improving the communication quality of PUSCH. As a result, PUSCH coverage can be expanded.

[0191] Information regarding the reduction of DMRS in PUSCH may be statically determined by standards, etc. This allows for a shared understanding between the gNB and UE. As a result, the occurrence of malfunctions can be reduced.

[0192] The gNB may notify users of information regarding PUSCH's DMRS reduction by including it in the MIB or SIB. In this case, the UE can configure it before transitioning to the RRC_CONNECTED state with the gNB. The gNB may also notify users of information regarding PUSCH's DMRS reduction through cell-common RRC signaling. For example, a cell-common parameter for uplink DMRS configuration may be provided. For example, this parameter may be included in DMRS-UplinkConfigCommon. Alternatively, information regarding PUSCH's DMRS reduction may be included in PUSCH-ConfigCommon. This allows for early notification of information regarding PUSCH's DMRS reduction.

[0193] The gNB may also notify users of information regarding PUSCH's DMRS reduction through UE-specific RRC signaling. For example, information regarding PUSCH's DMRS reduction may be included in DMRS-UplinkConfig, or in PUSCH-Config. This allows for UE-specific configuration of information regarding PUSCH's DMRS reduction.

[0194] The gNB may dynamically notify information regarding PUSCH's DMRS reduction. This information may be notified via MAC signaling. Alternatively, the information may be included in the DCI and notified via PDCCH. In this case, notification is possible only via PDCCH. This allows for dynamic configuration of information regarding PUSCH's DMRS reduction. It also allows for early configuration of information regarding PUSCH's DMRS reduction. Furthermore, it allows for early configuration in response to the constantly changing radio wave propagation environment.

[0195] Multiple candidate pieces of information regarding PUSCH's DMRS reduction may be statically defined in a standard or similar document, and the gNB may notify the UE. These multiple candidate pieces of information may be presented as a list (or table). Some or all of the information may be presented as sets, and these sets may be considered as multiple candidates. The gNB may notify the UE of which candidate piece of information to use. For example, the multiple candidates in the list may be assigned numbers, and these numbers may be used as information indicating the candidate.

[0196] For example, gNB may notify a list of multiple candidates for the information via MIB, SIB, or RRC signaling, and include a number indicating which candidate to use in MAC CE and notify via MAC signaling, or include it in DCI and notify via PDCCH. In this way, it is possible to keep the amount of information included in MAC CE and DCI to a minimum.

[0197] Figure 16 is a sequence diagram showing an example of a method for reducing DMRS during repeated PUSCH transmission in a modification 1 of Embodiment 1. In Figure 16, steps common to Figure 14 used in the description of Embodiment 1 are given the same step numbers, and common explanations are omitted. In step ST1601, the gNB decides to repeatedly transmit PUSCH to the UE. At this time, the gNB may also decide on information regarding the reduction of DMRS during repeated PUSCH transmission. In step ST1602, the gNB notifies the UE of the PUSCH scheduling information using PDCCH. Also in step ST1602, the gNB notifies the UE of the number of repeated PUSCH transmissions (Repetition count) and information regarding the reduction of DMRS for each repeated transmission. That is, the gNB notifies the UE of the number of repeated PUSCH transmissions and information regarding the reduction of DMRS for each repeated transmission using PDCCH, either together with or included in the PUSCH scheduling information.

[0198] In steps ST1603 to ST1605, the UE repeatedly transmits PUSCH using the information received from the gNB in ​​step ST1602. In each repeated transmission of PUSCH, the UE performs DMRS mapping using the DMRS reduction information received from the gNB in ​​step ST1602, and transmits PUSCH and DMRS.

[0199] Figure 17 is a sequence diagram showing another example of a method for reducing DMRS during repeated PUSCH transmissions, according to Modification 1 of Embodiment 1. In Figure 17, steps common to Figure 16 are given the same step numbers, and common explanations are omitted. In step ST1701, the gNB notifies the UE of the number of repeated PUSCH transmissions and a list of several candidate information regarding DMRS reduction for each repeated transmission (DMRS reduction information list). The gNB notifies the UE of this information via RRC signaling prior to the PUSCH transmission. For example, if uplink data occurs, in step ST1601 the gNB decides to repeatedly transmit the PUSCH. At this time, the gNB may also decide on the information regarding DMRS reduction during repeated PUSCH transmissions. In step ST1702, the gNB notifies the UE of the PUSCH scheduling information using PDCCH. Also in step ST1702, the gNB notifies the UE of index information indicating which information regarding DMRS reduction for each repeated transmission should be set. In other words, gNB notifies the UE of the index information via PDCCH, either along with the PUSCH scheduling information or by including it in the PUSCH scheduling information.

[0200] In step ST1702, the UE uses the index information received from the gNB to determine which DMRS reduction information to set from the list of multiple candidates for DMRS reduction information for each repetition received from the gNB in ​​step ST1701. In steps ST1603 to ST1605, the UE uses the determined DMRS reduction information to perform DMRS mapping for each repetition of PUSCH and then transmits PUSCH and DMRS.

[0201] Resources that have been freed up from DMRS should be mapped to PUSCH. By reducing DMRS, it becomes possible to increase the resources that can be mapped to PUSCH. The UE may use the increased PUSCH resources to determine the Transport Block (TB) size for PUSCH transmission. The data transmitted via PUSCH should be rate-matched and mapped to the increased PUSCH resources. In this way, it is possible to improve the communication quality of PUSCH.

[0202] This approach makes it possible to reduce DMRS during repeated PUSCH transmissions. As a result, the increase in overhead due to DMRS during repeated PUSCH transmissions can be suppressed, allowing for an increase in resources to map PUSCH, thereby improving the communication quality of PUSCH.

[0203] As shown in Embodiment 1, coverage expansion in RA processing is being considered. For this reason, MSG3 may be transmitted repeatedly. PUSCH containing MSG3 may be transmitted repeatedly. In this embodiment, repeated transmission of MSG3 may be repeated transmission of PUSCH containing MSG3. In repeated transmission of MSG3, the method for reducing DMRS during repeated transmission of PUSCH disclosed above may be applied as appropriate.

[0204] Information regarding DMRS reduction for PUSCH for MSG3 may be provided. Information regarding DMRS reduction for PUSCH may be set according to the number of repetitions. Information regarding DMRS reduction for PUSCH for each repetition may be set. The gNB may broadcast this information via MIB or SIB. This information may also be part of the common configuration information for PUSCH (PUSCH-ConfigCommon). For example, this information may also be part of the common configuration information for RACH (RACH-ConfigCommon). In this way, it becomes possible to reduce the DMRS for PUSCH for MSG3 and reduce the DMRS during repeated transmissions of PUSCH for MSG3, which are suitable for the different radio wave propagation environments of each cell.

[0205] Information regarding the reduction of DMRS for PUSCH for MSG3 and / or information regarding the reduction of DMRS for PUSCH based on the number of repetitions may be included in the RAR message, or it may be notified using PDCCH for scheduling the RAR message.

[0206] For example, the gNB notifies the UE of information regarding the reduction of DMRS for PUSCH for MSG3 and / or information regarding the reduction of PUSCH DMRS based on the number of repetitions, either with or included in the RAR message. PDSCH may be used for these notifications. For example, the gNB may notify the UE of information regarding the reduction of DMRS for PUSCH for MSG3 and / or information regarding the reduction of PUSCH DMRS based on the number of repetitions using a PDCCH for scheduling a PDSCH containing a RAR message. The gNB may also notify this information with or included in the DCI for scheduling.

[0207] The repeat type may be set when repeatedly transmitting a PUSCH containing MSG3. The number of repetitions may be set when repeatedly transmitting a PUSCH containing MSG3. The repeat type of the PUSCH may be applied as the repeat type. This setting may be statically determined in advance by a standard or the like. Alternatively, as a method of notifying the UE of this setting from the gNB, the notification method disclosed above, which provides information on reducing the DMRS of the PUSCH for MSG3 or information on reducing the DMRS of the PUSCH according to the number of repetitions, may be applied. In this way, it becomes possible to set up repeated transmission of the PUSCH for MSG3.

[0208] This approach makes it possible to improve the communication quality of the PUSCH for MSG3.

[0209] The method disclosed in this modified version allows for setting DMRS during repeated transmissions of PUSCH. For example, when the radio wave propagation environment is good, reducing DMRS can increase the REs that PUSCH can map, thereby improving the communication quality of PUSCH. For example, when the radio wave propagation environment is poor, not reducing DMRS can improve demodulation accuracy, thereby improving the communication quality of PUSCH.

[0210] Furthermore, DMRS settings can be configured even when repeatedly transmitting PUSCH messages, including MSG3, during RA processing. This allows for the same effects as described above to be achieved.

[0211] This approach makes it possible to expand coverage.

[0212] Embodiment 1 and Modification 1 of Embodiment 1 may be combined as appropriate. This allows for setting repeated transmissions during PUSCH retransmissions, and enables setting DMRS for each PUSCH retransmission and setting DMRS reduction for each repeated transmission during PUSCH retransmissions.

[0213] The same applies to PUSCH containing MSG3. Alternatively, in this case, the gNB may use a PDCCH for scheduling PUSCH retransmissions for MSG3 to notify information regarding DMRS reduction for PUSCH for MSG3 and / or information regarding DMRS reduction for PUSCH based on the number of retransmissions. This may be notified together with or included in the DCI for scheduling.

[0214] This allows for more flexible settings. As a result, it becomes possible to transmit PUSCH signals that are suited to the ever-changing radio wave propagation environment, thereby improving the communication quality of PUSCH. This also allows for expansion of coverage.

[0215] Modification 2 of Embodiment 1. There are two types of PUSCH repetition transmissions: PUSCH repetition type A and PUSCH repetition type B. In PUSCH repetition type A, PUSCH repetitions are set for each slot with the same start symbol and symbol length. In PUSCH repetition type B, PUSCH repetitions are set not per slot, but per PUSCH symbol length, spanning across slots. However, when spanning across slots or when symbols are used for other purposes, the PUSCH symbols that are actually repeated may be finely segmented by slot boundaries or symbols used for other purposes.

[0216] In the case of PUSCH repetition type B, if the symbols to which PUSCH is mapped are segmented finely, the DMRS settings for PUSCH configured in RRC may not be able to be implemented. For example, if the PUSCH symbol length is 4 symbols and the setting is to map DMRS to the 3rd symbol from the beginning, if the PUSCH is segmented into 2 symbols, then DMRS mapping will not be possible with this setting. In such cases, the processing of DMRS in the UE becomes unclear, which may lead to malfunctions.

[0217] This modified version discloses a method for solving these problems.

[0218] To address the above issues, the communication system in this modified version, when repeatedly transmitting PUSCH, will not map the DMRS if it cannot be mapped by the segment. It may also choose not to transmit the DMRS that cannot be mapped. For example, if the DMRS symbol length is 2 symbols and only 1 symbol cannot be mapped, the unmappable DMRS1 symbol will not be transmitted. Alternatively, it may not map to the DMRS2 symbol either, and therefore neither the DMRS1 symbol nor the DMRS2 symbol may be transmitted. This makes it possible to avoid uncertainty regarding the processing of the DMRS.

[0219] When a repeated transmission of PUSCH occurs and a DMRS is not transmitted, the gNB should use the DMRS transmitted in other repeated transmissions to demodulate the PUSCH. For example, if there are four repeated transmissions of PUSCH, and the repeated transmission numbers 2 and 3 do not transmit DMRS, the gNB will use the DMRS from repeated transmission numbers 1 and 4 to demodulate the PUSCH transmitted in repeated transmission numbers 2 and 3. In this way, the PUSCH can be received.

[0220] Another method is disclosed. In the case of repeated transmission of PUSCH repetition type B, the UE maps DMRS to the first symbol and transmits it, or maps DMRS to the first two symbols and transmits it. Alternatively, in all repeated transmissions, DMRS may be mapped to the first symbol or the first two symbols and transmitted. Alternatively, DMRS may be mapped to the first symbol or the first two symbols and transmitted only in repeated transmissions where DMRS cannot be mapped. In this way, it becomes possible to transmit DMRS even when repeated PUSCH transmissions are finely segmented. As a result, gNB can demodulate with DMRS for each repeated PUSCH transmission, and the reception quality of PUSCH can be improved.

[0221] In the case of repeated transmission of PUSCH repetition type B, PUSCH mapping type B may be set. In PUSCH mapping type B, DMRS is mapped to the first symbol or the first two symbols and transmitted. In this case, the same effect as the method disclosed above can be obtained.

[0222] The method described above should also be applied when mapping additional DMRS in addition to the regular DMRS. Alternatively, in the case of repeated transmissions of PUSCH repetition type B, additional DMRS may not be mapped or transmitted. By doing so, it is possible to avoid uncertainty regarding DMRS processing even when additional DMRS is configured.

[0223] The method for configuring DMRS in repeated PUSCH transmissions may be predetermined statically by standards or other means. This allows for common understanding between the UE and gNB. It reduces the occurrence of malfunctions in the repeated PUSCH transmission process. The gNB may notify the configuration method via MIB, SIB, or RRC signaling. In this case, the configuration method can be changed quasi-statically. The gNB may also notify the configuration method via MAC signaling by including it in MAC CE, or via PDCCH by including it in DCI. In this case, the configuration method can be changed dynamically.

[0224] The method for reducing DMRS in repeated transmissions of PUSCH, disclosed in Modification 1 of Embodiment 1, may be applied as appropriate. For example, the information regarding DMRS reduction in step ST1602 of Figure 16 may be the DMRS setting information in the method disclosed above. For example, PUSCH mapping type B may be set as the setting for each repeated transmission of PUSCH. Alternatively, additional DMRS may be set to none. In this way, even when the symbols to which PUSCH is mapped in PUSCH repetition type B are finely segmented, dynamic and flexible setting of DMRS becomes possible.

[0225] The method disclosed in this modified version eliminates inconsistencies in DMRS mapping even when the symbols to which PUSCH is mapped are finely segmented during repeated PUSCH transmissions. This reduces the occurrence of malfunctions in the repeated PUSCH transmission process. Furthermore, it enables reception of PUSCH on the gNB even when DMRS is not transmitted, and improves the reception quality of PUSCH on the gNB by mapping DMRS to the first symbol, for example. This allows for expanded PUSCH coverage.

[0226] Modification 3 of Embodiment 1. If the number of uplink retransmissions from the UE to the gNB is increasing, it may be better to improve the reception quality at the gNB by repeatedly transmitting rather than performing retransmissions that require downlink reception processing. Depending on the UE's situation, for example, if the UE's battery level is low, it may be better to improve the reception quality at the gNB by repeatedly transmitting PUSCH rather than consuming power by receiving PDCCH, which contains scheduling information for PUSCH retransmissions. For example, if the application running on the UE requires low latency, it may be better to notify the gNB quickly by repeatedly transmitting PUSCH rather than taking time by retransmitting PUSCH.

[0227] However, gNB cannot recognize this UE situation and cannot configure repeated PUSCH transmissions according to the UE situation.

[0228] This modified version discloses a method for solving these problems.

[0229] To solve the above problems, in the communication system of this modified example, the UE requests the gNB to configure the PUSCH to send repeatedly. The UE may notify the gNB of information indicating this request. The UE may also notify the gNB of information indicating this request via RRC signaling. For example, if the UE receives information regarding the DMRS settings for PUSCH from the gNB, it may notify the gNB of information indicating this request via RRC signaling. By receiving information indicating this request from the UE, the gNB can determine whether to configure the PUSCH to send repeatedly to the UE.

[0230] Furthermore, the UE may notify the gNB of the request via MAC signaling or PUCCH. This allows for dynamic notification. For example, the UE may include the information indicating the request in the SR to notify the gNB. The UE may also include the information indicating the request in the uplink scheduling request to notify the NB. By including it in the uplink scheduling request, when the gNB receives the scheduling request, it can determine whether to set a repeat transmission PUSCH for that scheduling request.

[0231] Furthermore, the UE may notify the gNB of the request by including the information indicating the request in the BSR (Buffer Status Report). By including the information in the BSR, when the gNB receives the BSR, it will be able to determine the setting for repeated PUSCH transmissions in response to the BSR.

[0232] Furthermore, the UE may notify the gNB by including information indicating the request in the PDSCH's Ack / Nack information. For example, if PDSCH retransmissions occur frequently, the UE may include information indicating the request in the PDSCH's Ack / Nack information. When downlink and uplink communication quality are related, the likelihood of frequent PUSCH retransmissions may also increase. In such cases, by including information indicating the request in the PDSCH's Ack / Nack information, the gNB can determine the PUSCH retransmission setting when it receives the Ack / Nack information.

[0233] Furthermore, the UE may notify the gNB of the information indicating the request by associating it with a PRACH. For example, when indicating the request, a predetermined PRACH setting may be used. For example, the UE may notify the gNB of the information indicating the request using an MSGA PUSCH. In a 2-step RACH, the MSGA PUSCH is sent together with the PRACH. When the gNB receives a PRACH or an MSGA PUSCH, it can determine the repeat transmission setting of the PUSCH. In this way, the gNB can determine the repeat transmission setting of the PUSCH at an early stage. In addition, the gNB can determine the repeat transmission setting of the PUSCH that sends MSG3 in RA processing.

[0234] For example, the UE may notify the gNB of the request by including information indicating the request in MSG3 during RA processing. In this case, when the gNB receives MSG3, it can determine the PUSCH recurring transmission setting. This allows the gNB to determine the PUSCH recurring transmission setting for the UE at an early stage. For example, it can determine the PUSCH recurring transmission setting that occurs after MSG3.

[0235] This document discloses a specific example of how a UE can determine whether to notify a gNB of information indicating such a request. For example, the UE may notify the gNB of information indicating such a request when the battery level in the UE falls below a predetermined threshold. Examples of battery level include a percentage of battery capacity, remaining battery capacity, or remaining operating time. For example, the UE may notify the gNB of information indicating such a request when the number of Nacks received for a PUSCH transmission or the number of times PUSCH retransmission scheduling information is received exceeds a predetermined threshold. This predetermined threshold may be statically determined in advance by a standard or the like, or it may be notified to the UE by the gNB. The predetermined threshold may be notified by the gNB via MIB or SIB, or via RRC signaling for each UE. Alternatively, the predetermined threshold may be notified by the gNB to the UE via MAC signaling or PDCCH. In this case, the predetermined threshold can be set dynamically. In this way, the UE can determine whether or not to notify the gNB of information indicating such a request. The gNB can also determine the content of the repeated PUSCH transmission settings to be made to the UE. The settings for repeated transmission of PUSCH include whether or not to allow the UE to repeatedly transmit PUSCH, and if so, the number of repetitions.

[0236] The aforementioned battery level processing in the UE may be set as a measurement event. The gNB may notify the UE of the measurement setting, including the measurement event. When the UE fulfills the measurement event, it may notify the gNB of the measurement report. In this way, the gNB can recognize the battery level of the UE.

[0237] Figure 18 is a sequence diagram showing an example of how a UE requests a PUSCH repeat transmission setting from a gNB in ​​a modification 3 of Embodiment 1. In Figure 18, steps common to Figure 17 used in the description of Modification 1 of Embodiment 1 are given the same step numbers, and common descriptions are omitted. In step ST1801, the UE notifies the gNB of information indicating a request for a PUSCH repeat transmission setting. The UE notifies this information using PUCCH. This information may also be included in the SR. In this way, the gNB can determine the content of the PUSCH repeat transmission setting from the UE.

[0238] In step ST1601, the gNB determines the content of the PUSCH repeat transmission setting to be performed on the UE, using the information indicating the request for PUSCH repeat transmission setting received in step ST1801. The example in Figure 18 shows the case where information regarding DMRS reduction (index information) is used, but it is not limited to this. For example, the gNB may not set information regarding DMRS reduction to the UE, but only set PUSCH repeat transmission and notify it in step ST1702.

[0239] By using the method disclosed in this modified version, the gNB can recognize the need for repeated transmission settings for the UE's PUSCH. That is, the gNB can implement repeated transmission settings for PUSCH depending on the UE's situation. This makes it possible to improve the communication quality of PUSCH, i.e., expand PUSCH coverage. In addition, PUSCH can be notified to the gNB in ​​a short period of time. This makes it possible to enable communication suitable for services that require low latency.

[0240] Embodiment 2. In NR, expansion of coverage in initial access, such as expansion of coverage in SSB (SS block), and expansion of coverage in RA processing are being considered. In RA processing, the gNB uses a beam to transmit SSB and a beam to receive PRACH from the UE. Since these beams use relatively wide beams, wide beams are also used in RA processing. However, with wide beams, there is a problem in that wide coverage cannot be obtained.

[0241] This embodiment discloses a method for solving these problems.

[0242] In this embodiment, the above problems are solved by changing the number of symbols constituting the PBCH from the conventional method. For example, the SS and PBCH are not configured with the same symbols. The number of symbols for the PBCH within the SSB may be different from the conventional method. The frequency domain of the PBCH may be different from the conventional method. The number of symbols for the SSB may be increased.

[0243] Furthermore, in this embodiment, the above problems are solved by repeatedly transmitting PBCH. For example, PBCH is repeatedly transmitted for each symbol. PBCH may be transmitted multiple times for each symbol, with each symbol transmitted on a different beam. Different beams may be used for SS transmission and PBCH transmission. PBCH may be transmitted multiple times on a narrow beam. SS may be transmitted on a wide beam, and PBCH on a narrow beam.

[0244] Figure 19 shows the configuration of a conventional SSB. A conventional SSB consists of four symbols, with SS (PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal)) in the first and third symbols, and PBCH in the second through fourth symbols.

[0245] Figure 20 shows an example of increasing the number of PBCH symbols in the SSB according to Embodiment 2. In the example shown in Figure 20, the SSB is composed of 4 symbols. The SS (PSS and SSS) are mapped to the 1st and 3rd symbols, and the PBCH is mapped to the 2nd and 4th symbols. In the conventional SSB shown in Figure 19, the PBCH is also mapped to the 3rd symbol, but in this embodiment, the PBCH is not mapped to the 3rd symbol. That is, the SS and PBCH are not mapped to the same symbol. By doing so, the SS and PBCH can be transmitted on different beams.

[0246] The PBCH is transmitted twice using the second and fourth symbols. It is preferable to transmit the PBCH using a different beam each time. This makes it possible to transmit the PBCH using a narrow beam. The resources in the frequency axis direction of the PBCH may be different from conventional methods. The resources in the frequency axis direction of the PBCH may be increased. This ensures that the necessary resource capacity for mapping one PBCH is secured.

[0247] Figure 21 shows another example of increasing the number of PBCH symbols within the SSB for Embodiment 2. In the example shown in Figure 21, the SSB consists of 6 symbols. The SS (PSS and SSS) are mapped to the 2nd and 4th symbols, and the PBCH is mapped to the 1st, 3rd, 5th, and 6th symbols. The SS and PBCH are not mapped to the same symbol. This makes it possible to transmit the SS and PBCH on different beams.

[0248] In the example shown in Figure 21, the PBCH transmits four times using symbols 1, 3, 5, and 6. It is preferable to transmit using a different beam each time the PBCH is transmitted. In this way, it becomes possible to transmit the PBCH using a narrow beam with an even narrower beam width than the narrow beam used in the example shown in Figure 20. The resources in the frequency axis direction of the PBCH may be different from conventional methods. The resources in the frequency axis direction of the PBCH may be increased. In this way, the resource capacity necessary to map one PBCH can be secured.

[0249] An identifier for a beam transmitting PBCH may be provided. Hereinafter, this identifier may be referred to as a PBCH beam identifier. Conventionally, a beam identifier corresponding to SSB is provided, but in the present embodiment, a beam identifier corresponding to PBCH (PBCH beam identifier) is provided. With this configuration, when a gNB transmits PBCH multiple times using different beams, a UE can identify each beam on which PBCH is transmitted.

[0250] A PBCH beam identifier may be associated with one or a plurality of PRACH configurations. The PRACH configurations may be made into a list. The PRACH configuration may include resources on the time axis and / or the frequency axis for transmitting PRACH. The PBCH beam identifier may be associated with one or a plurality of PRACH preambles. These associations may be statically determined in advance by standards or the like. As another method, the gNB may notify these associations by including them in MIB or SIB. This configuration enables the UE to perform RA processing.

[0251] The UE receives PBCH transmitted on different beams, and for example, identifies the beam identifier of the received PBCH. The UE may identify, as a PBCH beam, a beam on which a PBCH with reception quality equal to or higher than a predetermined threshold is received. A beam on which a PBCH that first achieves reception quality equal to or higher than the predetermined threshold is received may be set as the PBCH beam. The predetermined threshold may be statically determined in advance by standards or the like. As another method, the UE may receive PBCH of all beams transmitted a plurality of times, and identify the beam identifier of the PBCH with the best reception quality. In this way, the UE can identify the PBCH beam. The reception quality in the present disclosure may be received power or a signal-to-interference-plus-noise ratio. For example, the reception quality of DMRS may be measured. For example, another RS (e.g., RS for channel state measurement) may be provided in PBCH, and the reception quality of the RS may be measured.

[0252] The UE selects the PRACH configuration corresponding to the identified PBCH beam. The UE may select the PRACH preamble corresponding to the identified PBCH beam. The UE may transmit the PRACH using the PRACH configuration and / or PRACH preamble corresponding to the identified beam.

[0253] The gNB uses the PRACH configuration and / or PRACH preamble received from the UE to identify the receive beam corresponding to the PBCH beam identified by the UE. In subsequent processes, the gNB may use the optimal transmit beam and receive beam for the UE. By doing so, the gNB can identify the optimal transmit beam and receive beam for the UE. For example, using a narrow beam for PBCH transmission enables coverage extension.

[0254] With such a method, it is possible to use narrow beams from PBCH reception to RA processing, and to obtain wide coverage.

[0255] Another method for solving the aforementioned problem is disclosed.

[0256] In another solution, the number of SSBs is increased within one SS burst. The number of SSBs may be increased within 5 ms. For example, when the carrier frequency band is greater than 3 GHz and 6 GHz or less, and the SCS is 30 kHz, conventionally 8 SSBs could be configured, but 16 SSBs are now configurable. An integer multiple of 5 ms may be defined as the SS burst period. This makes it possible to configure more SSBs within the SS burst. The UE preferably receives SSBs at intervals that are an integer multiple of 5 ms. For example, even when the carrier frequency band is as high as 6 GHz or more, a large number of SSBs can be configured. By doing so, the gNB can transmit more SSBs. Therefore, it becomes possible to transmit SSBs using narrower beams than in the conventional art.

[0257] The number of SSBs within one repetition period of an SSB can be increased. For example, if the carrier frequency band is 6 GHz or higher, the SCS is 120 kHz, and the repetition period of one SSB is 20 ms, conventionally it was possible to configure 64 SSBs, but it is now possible to configure 128 SSBs. In this way, the gNB can transmit more SSBs. As a result, it becomes possible to transmit SSBs using a narrower beam than before.

[0258] The beam identifier should be set to SSB as before. The beam identifier should be associated with one or more PRACH settings. The UE should select the PRACH setting corresponding to the identified SSB beam and transmit the PRACH. By making the SSB a narrow beam, the gNB can transmit and receive using the optimal narrow beam for the UE even in RA processing after PRACH.

[0259] This method makes it possible to use narrow beams in SSB and RA processing, thereby achieving wider coverage.

[0260] This document discloses other methods for extending SSB coverage.

[0261] Another way to extend coverage is to repeatedly transmit SSB signals from the same beam. SSB signals from the same beam may be transmitted repeatedly within a single SS burst. SSB signals from the same beam may be transmitted repeatedly within 5ms. SSB signals from the same beam may be transmitted repeatedly within one SSB repetition period. It is recommended that the beam identifiers for the repeatedly transmitted SSB signals from the same beam remain the same.

[0262] The period during which SSB from the same beam is repeatedly transmitted may be predetermined statically by standards or other means. The UE receives the SSB during this period. Receiving the SSB from the same beam multiple times can improve the quality of SSB reception.

[0263] This method makes it possible to improve the reception quality of SSB and expand SSB coverage.

[0264] Modification 1 of Embodiment 2. In this modified example, similar to Embodiment 2 described above, a method is disclosed to solve the problem that wide beams are used in RA processing, making it impossible to obtain broad coverage.

[0265] In this modified example, the above problem is solved by transmitting the RAR multiple times. The RAR consists of scheduling information for the PDSCH transmitted by the PDCCH and the RAR message transmitted by the PDSCH. To solve the above problem, it is good to transmit the RAR PDCCH multiple times. In this modified example, the RAR is transmitted multiple times using different beams. More specifically, the RAR PDCCH is transmitted multiple times using different beams. For example, the beam from which the RAR PDCCH is transmitted may be a narrow beam. In this way, the coverage of the RAR PDCCH can be extended.

[0266] The gNB may transmit multiple different narrow beams within the beam range identified by the UE upon receiving the SSB. The gNB may transmit multiple different narrow beams so as to include the beam range identified by the UE upon receiving the SSB. Even if a wide beam is used for SSB transmission, it is preferable to transmit the RAR's PDCCH with a narrow beam. In this way, the coverage of the RAR's PDCCH can be expanded while including the SSB coverage.

[0267] Furthermore, in this modified version, a RAR window is provided that allows for multiple RAR transmissions. The duration of the conventional RAR window may be extended. The maximum duration of the conventional RAR window is 80 slots. The duration of the RAR window may be longer than 80 slots. The duration of the RAR window may be continuous or non-continuous. The duration of the RAR window may be set according to the number of RAR transmissions. The gNB transmits multiple RAR PDCCHs within the RAR window duration.

[0268] The RAR window period may be statically determined by a standard or similar. The number of RAR PDCCH transmissions may be associated with the RAR window period. This association may be presented as a list. An index may be assigned to each association. The gNB may notify the UE of the RAR window period via MIB or SIB. Notification may be made using SIB1. Notification may also be made as information other than the PBCH MIB.

[0269] The gNB may notify the number of RAR PDCCH transmissions. Upon receiving this notification, the UE may, for example, derive the RAR window period using a list defined in the standard. The gNB may also notify the index of the association between the number of RAR PDCCH transmissions and the RAR window period. Upon receiving this notification, the UE may, for example, derive the RAR window period using a list defined in the standard.

[0270] The UE receives the RAR PDCCH within the RAR window range. The UE may receive the RAR PDCCH multiple times. In this way, the UE can receive the RAR PDCCH even if it is transmitted multiple times.

[0271] The gNB notifies the UE of the scheduling information of the PDSCH containing the RAR message via the PDCCH of each beam's RAR. This scheduling information may also be included in the DCI and notified via the PDCCH. It is preferable to use only one resource for the PDSCH of the RAR message. Using a single resource improves resource utilization efficiency. The scheduling information notified via the PDCCH of each beam's RAR will indicate the same resource. If the gNB has not yet identified the narrow beam to transmit to the UE, it may use a wide beam to transmit the PDSCH containing the RAR message. This allows the UE to receive the RAR message.

[0272] The gNB includes the beam identifier of each beam in the DCI of the PDCCH of the RAR. A sequence using the beam identifier may be used for the DMRS of the PDCCH of the RAR of each beam. These may be combined. This enables the UE that has received the PDCCH of the RAR to identify the beam on which the PDCCH of the RAR is transmitted.

[0273] The gNB includes scheduling information for MSG3 of RA processing in the RAR message scheduled by the PDCCH of the RAR. This allows the UE to receive the RAR message using the scheduling information of the PDCCH of the RAR, and to obtain the scheduling information of MSG3 to be transmitted to the gNB.

[0274] The UE measures the reception quality of the PDCCH of the RAR for each beam. The UE may measure the reception quality of the RS of the PDCCH of the RAR for each beam. For example, the reception quality of the DMRS may be measured. For example, another RS (e.g., RS for channel state measurement) may be provided in the PDCCH, and the reception quality of said RS may be measured. L1-RSRP may be measured as the reception quality. The UE may store the reception quality information of each beam. The UE may identify the beam having the best reception quality among the PDCCHs of the RAR transmitted a plurality of times. The UE may store the identifier of the beam having the best reception quality.

[0275] Furthermore, the UE receives a RAR message (MSG2) using the scheduling information for the RAR's PDCCH. The UE also sends MSG3 using the scheduling information contained in the RAR message. MSG3 may include reception quality information for each beam transmitting the RAR's PDCCH and / or the identifier of the beam with the best reception quality. The reception quality information for each beam may be associated with a beam identifier. It may also be a list of reception quality information for each beam. As reception quality information for each beam, MSG3 may include reception quality information for the top n beams with the best reception quality (n is an integer greater than or equal to 1). In this way, the UE can notify the gNB of the reception quality of the RAR's PDCCH transmitted by the gNB, or the beam with the best reception quality.

[0276] The UE may measure the reception quality of the RAR PDCCH for each beam and, if it exceeds a predetermined threshold, may choose not to receive subsequent RAR PDCCHs. In other words, the UE identifies beams that have exceeded the predetermined threshold. The predetermined threshold and the value of n above may be determined in advance by standards, etc. Alternatively, the gNB may notify the UE in advance. For example, it may be notified by including it in the MIB or SIB.

[0277] The UE receives a RAR message using the PDCCH scheduling information of the RAR transmitted for beams that exceed a predetermined threshold. The UE then transmits an MSG3 using the scheduling information of the MSG3 included in the RAR message. The MSG3 may include reception quality information and / or an identifier for the beam that exceeds the predetermined threshold. The MSG3 may also include reception quality information and / or identifiers for the top n beams with good reception quality that exceed the predetermined threshold. In this way, the UE can notify the gNB of beams whose reception quality exceeds a predetermined threshold.

[0278] The gNB may use a wide beam to receive MSG3 transmitted from the UE. The gNB receives MSG3 from the UE and, using the reception quality information of each beam and / or the identifier of the beam with the best reception quality, can identify the beam to be used for transmission to the UE. For example, the beam with the best reception quality is used for transmission to the UE. The gNB may then transmit the RA-processed MSG4 to the UE using the identified beam.

[0279] Figure 22 is a sequence diagram showing an example of a method for transmitting the RAR PDCCH multiple times using different beams in RA processing, according to Modification 1 of Embodiment 2. In step ST2201, the UE sends a PRACH to the gNB to initiate access to the gNB. More specifically, the UE sends a PRACH preamble to the gNB as MSG1. The PRACH is sent with settings corresponding to the SSB received by the UE. This allows the gNB to recognize which SSB the UE has received.

[0280] Upon receiving the PRACH, the gNB transmits the RAR PDCCH in steps ST2202 to ST2204. The gNB transmits the RAR PDCCH multiple times using different beams. The RAR PDCCH transmitted by the gNB contains scheduling information for the PDSCH containing the RAR message. The scheduling information announced in the RAR PDCCH for each beam contains information indicating the same resource.

[0281] The beam transmitting the RAR PDCCH may be different from the SSB beam received by the UE. Multiple beams transmitting RAR PDCCHs are configured to cover the SSB beam received by the UE. By transmitting the RAR PDCCH multiple times in this way, it becomes possible to use a narrow beam for RAR PDCCH transmission.

[0282] The RAR PDCCH shown in steps ST2202 to ST2204 is transmitted within the RAR window period. The UE receives the RAR PDCCH transmitted in steps ST2202 to ST2204. The UE should receive it within the RAR window period. The RAR window period may be an extension of the conventional RAR window period. Multiple RAR PDCCHs can be sent and received. The CRC of the DCI of the RAR PDCCH is scrambled with RA-RNTI (Random Access - Radio Network Temporary Identifier), and the UE can receive the RAR PDCCH by using RA-RNTI.

[0283] The UE receives the PDCCH of the RAR transmitted in steps ST2202 to ST2204, measures the received quality of each beam, and identifies the beam with the best received quality.

[0284] In step ST2205, the gNB transmits a PDSCH containing the RAR message, MSG2, on a single beam, according to the scheduling information transmitted on the RAR's PDCCH. This beam may be a wide beam. It is preferable to use the same beam as for SSB transmission. In step ST2205, the UE receives the PDSCH according to the scheduling information received on the RAR's PDCCH and receives the RAR message. The RAR message, MSG2, contains the scheduling information MSG3.

[0285] In step ST2206, the UE transmits a PUSCH containing MSG3, using the scheduling information of MSG3 included in the received RAR message. The MSG3 may also include the best beam information of the PDCCH received in steps ST2202 to ST2204. The best beam information may include a beam identifier. In step ST2206, the gNB receives a PUSCH from the UE containing MSG3 according to the scheduling information of MSG3 included in the RAR message. The beam receiving the PUSCH may be a wide beam. It is preferable to use a receiving beam corresponding to the transmitting beam of the RAR message or the transmitting beam of the SSB.

[0286] In step ST2206, the gNB, upon receiving a PUSCH containing MSG3, acquires MSG3 and the best beam information of PDCCH, enabling it to identify the optimal beam for the UE from among the beams transmitted in steps ST2202 to ST2204.

[0287] In step ST2207, the gNB notifies the UE of the scheduling information for the PDSCH containing MSG4 in the PDCCH. The best beam indicated by the best beam information received in step ST2206 should be used for this transmit beam. In step ST2208, the gNB transmits the PDSCH containing MSG4 to the UE according to the scheduling information for the PDSCH containing MSG4. Similarly, the best beam indicated by the best beam information received in step ST2206 should be used for this transmit beam. In this way, the gNB can use the optimal narrow beam for the UE based on the scheduling information for MSG4 and the transmission of MSG4.

[0288] In step ST2207, the UE receives a PDCCH containing scheduling information for the PDSCH that includes MSG4, and uses this scheduling information to receive the PDSCH in step ST2208 and acquire MSG4. This makes RA processing possible. In addition, the gNB can use a narrow beam for processing from MSG4 onward for the UE.

[0289] By using the method disclosed in this modified version, the gNB can transmit the PDCCH of the RAR in a narrow beam. The gNB can identify the narrow beam with the best reception quality at the UE by receiving MSG3. Therefore, it becomes possible to use the optimal narrow beam for transmission and reception from MSG4 onward for the UE, thereby expanding coverage.

[0290] Modification 2 of Embodiment 2. This modified version discloses another method to solve the problem that wide beams are used in RA processing, similar to Modification 1 of Embodiment 2 described above, and that wide coverage cannot be obtained.

[0291] In this modified example, the above problem is solved by transmitting RAR multiple times, similar to Modified Example 1 described above, but the details of the RAR transmission operation are different. To solve the above problem, it is good to transmit PDSCH containing the RAR message multiple times. In this embodiment as well, RAR is transmitted multiple times using different beams. More specifically, PDSCH containing the RAR message is transmitted multiple times using different beams. For example, the beam from which PDSCH containing the RAR message is transmitted may be a narrow beam. In this way, the coverage of PDSCH containing the RAR message can be expanded.

[0292] The gNB may transmit multiple different narrow beams within the beam range identified by the UE upon receiving the SSB. The gNB may transmit multiple different narrow beams so as to include the beam range identified by the UE upon receiving the SSB. Even if a wide beam is used for transmitting the SSB and RAR PDCCH, it is preferable to transmit the PDSCH containing the RAR message using a narrow beam. In this way, the coverage of the PDSCH containing the RAR message can be expanded while including the SSB coverage.

[0293] RAR does not need to send PDCCH multiple times. Therefore, the conventional method can be applied to the RAR window.

[0294] The number of times a PDSCH containing a RAR message is transmitted may be determined statically by a standard or similar. The gNB may notify the number of times a PDSCH containing a RAR message is transmitted. The gNB may notify the number of times a PDSCH containing a RAR message is transmitted via MIB or SIB. It may also be notified using SIB1. It may also be notified as information other than the MIB of the PBCH. The gNB may notify the number of times a PDSCH containing a RAR message is transmitted via the RAR PDCCH. It may be notified together with, or included in, the scheduling information of the PDSCH containing the RAR message. In this way, the UE can recognize the number of times a PDSCH containing a RAR message is transmitted.

[0295] The gNB notifies the UE of scheduling information for multiple PDSCHs containing RAR messages via the RAR's PDCCH. This scheduling information may also be included in the DCI and notified via the PDCCH. The scheduling information for each PDSCH containing a RAR message may be different. The resource allocation on the time axis may be different for each PDSCH containing a RAR message. This makes it possible to transmit multiple PDSCHs containing RAR messages using different beams. Narrow beams may be used for each beam.

[0296] The DCI included in the RAR's PDCCH may include the identifier of the beam from which the RAR message is transmitted. The scheduling information of the PDSCH containing the RAR message for each beam may also include the beam identifier. Alternatively, the beam identifier may be included in the RAR message itself. A sequence using the beam identifier may be used in the DMRS of the PDSCH containing the RAR message for each beam. These methods may be combined. In this way, a UE receiving a PDSCH containing a RAR message can identify the beam from which the PDSCH containing the RAR message is transmitted.

[0297] The gNB includes scheduling information for MSG3 of the RA processing in the RAR message for each beam. The information included in the RAR message may be scheduling information for each beam that transmits MSG3, scheduling information for each beam that receives MSG3, or scheduling information for MSG3 for each beam identifier as disclosed above. Resource allocation information may be included as the scheduling information for MSG3. This resource allocation information may be resource allocation information on the time axis and / or frequency axis.

[0298] The time-axis resource allocation of MSG3 in the RAR message for each beam may be the same. The time-axis resource allocation of MSG3 may be indicated by an offset from the reception timing of the PDSCH containing the RAR message or the PDSCH scheduling the PDSCH. In this way, even if the offset is set to the same, the transmission timing of MSG3 will be different. Therefore, UEs can transmit MSG3 on different beams and / or gNBs can receive MSG3 on different beams.

[0299] The time-axis resource allocation of MSG3 in the RAR message for each beam may be different. In this case, it is advisable to set the transmission timing of MSG3 to be different. This allows UEs to transmit MSG3 on different beams and / or gNBs to receive MSG3 on different beams.

[0300] The resource allocation on the frequency axis for MSG3 in the RAR message of each beam may be the same or different. If they are the same, transmission and reception processing at the UE and gNB can be made easier.

[0301] As scheduling information for MSG3, an offset value for each beam (for example, Kbeam) may be provided. Kbeam may be statically determined by standards, etc. Kbeam may be notified by gNB via MIB or SIB. Kbeam may be notified by gNB via RRC signaling. Kbeam may be notified by gNB by including it in a RAR message.

[0302] It is preferable to add beam-specific offset information (Kbeam) to the offset information from the reception timing of the PDSCH containing the RAR message or the PDSCH scheduling the said PDSCH to obtain the beam-specific offset. In this way, even if the aforementioned offsets are set to the same value, the transmission timing of MSG3 will be different. Therefore, UEs can transmit MSG3 on different beams and / or gNBs can receive MSG3 on different beams.

[0303] Multiple MSG3 scheduling information entries may be created and listed. Multiple MSG3 resource allocation information entries may be created and listed. An index may be added to the list. The list of MSG3 scheduling information may be statically defined by a standard or the like. The gNB may notify the list of MSG3 scheduling information via MIB or SIB. The gNB may notify the list of MSG3 scheduling information via RRC signaling.

[0304] The gNB may include an index indicating the scheduling information of MSG3 in the RAR message for each beam. This reduces the amount of information in the RAR message, reduces the resources used by the PDSCH, which includes RAR messages sent multiple times, and improves resource utilization efficiency.

[0305] Since this list contains scheduling information for MSG3 corresponding to each beam's RAR message, it may require more information than before. For this reason, an offset value from the reception timing of the PDSCH containing the RAR message or the PDSCH scheduling the PDSCH is added to the list. The start symbol value and / or symbol length value of the PUSCH that transmits the MSG3 may also be added to the list. In this way, scheduling of MSG3 corresponding to the RAR message for each beam becomes possible.

[0306] The UE receives the RAR's PDCCH. The UE also receives a PDSCH containing RAR messages that are transmitted multiple times, using the scheduling information of the RAR's PDCCH. The UE also measures the reception quality of each beam. The UE may measure the reception quality of the RS of each beam's PDSCH. For example, the reception quality of the DMRS may be measured. For example, another RS ​​(e.g., a channel state measurement RS) may be provided in the PDSCH, and the reception quality of that RS may be measured. L1-RSRP may be measured as reception quality. The UE may store the reception quality information for each beam. In a PDSCH containing RAR messages transmitted multiple times, the UE uses the reception quality of each beam to identify one beam. The UE may store the identifier of the identified beam. For example, in a PDSCH containing RAR messages transmitted multiple times, the UE may identify the beam with the best reception quality. The UE may store the identifier of the beam with the best reception quality.

[0307] The gNB receives MSG3s from the UE using the scheduling information of MSG3s included in the RAR messages for each beam. The UE then transmits an MSG3 using the scheduling information of MSG3s included in the RAR message sent by a single identified beam, for example, the beam with the best reception quality. In this way, the gNB can identify the beam with the best reception quality received by the UE.

[0308] MSG3 may include reception quality information for each beam transmitting a PDSCH containing a RAR message and / or the identifier of the beam with the best reception quality. The reception quality information for each beam may be associated with a beam identifier. It may also be in the form of a list. As reception quality information for each beam, MSG3 may include reception quality information for the top n beams with the best reception quality and / or the identifiers of the top n beams with the best reception quality. As reception quality information for each beam, MSG3 may include reception quality information for the top n beams with the best reception quality that exceed a predetermined threshold and / or the identifiers of the top n beams with the best reception quality that exceed a predetermined threshold. In this way, the gNB can recognize the reception quality of each beam at the UE.

[0309] The gNB receives MSG3 on the beam corresponding to each beam in the PDSCH containing the RAR message. The gNB may also use a narrow beam to receive MSG3 transmitted from the UE. By using a narrow beam for transmitting the PDSCH containing the RAR message, it becomes possible to use a narrow beam to receive MSG3. The gNB may transmit the RA processing MSG4 to the UE using a beam that has been identified. The gNB can then transmit MSG4 using a narrow beam.

[0310] Figure 23 is a sequence diagram showing an example of a method for transmitting a PDSCH containing a RAR message multiple times using different beams in RA processing, according to Modification 2 of Embodiment 2. Steps common to Figure 22 used in the description of Modification 1 of Embodiment 2 are given the same step numbers, and the common explanations are omitted. After step ST2201 is executed and the gNB receives a PRACH from the UE, it transmits the RAR PDCCH in step ST2301. The gNB transmits the RAR PDCCH with a single beam. It is preferable to use the same beam as the SSB received by the UE.

[0311] The RAR PDCCH includes scheduling information for a PDSCH containing multiple RAR messages. This allows the gNB to transmit multiple PDSCHs containing subsequent RAR messages using different beams. The RAR PDCCH in step ST2301 is transmitted within the RAR window period. The UE should receive the RAR PDCCH within the RAR window period. The RAR window period may be the conventional RAR window period. In this case, one RAR PDCCH can be sent and received. The DCI CRC of the RAR PDCCH is scrambled with RA-RNTI, and the UE can receive the RAR PDCCH using RA-RNTI.

[0312] In steps ST2302 to ST2304, the gNB transmits multiple PDSCHs containing RAR messages according to the scheduling information transmitted in the RAR PDCCH. The gNB uses a different beam for each transmission. This beam may be a narrow beam. In this case, the beam is configured to cover the SSB beam received by the UE. This makes it possible to use a narrow beam for PDSCH transmissions containing RAR messages. The RAR message contained in each PDSCH contains scheduling information for MSG3 corresponding to the beam transmitting each PDSCH.

[0313] In steps ST2302 to ST2304, the UE receives multiple PDSCHs according to the scheduling information received in the RAR's PDCCH. The UE receives the PDSCHs containing the RAR messages transmitted in steps ST2302 to ST2304, measures the reception quality of each beam, and identifies the beam with the best reception quality. The UE receives the RAR message for the PDSCH of the identified beam.

[0314] In step ST2305, the UE uses the scheduling information for MSG3 included in the received RAR message to transmit a PUSCH containing MSG3. In this way, the UE can transmit a PUSCH containing MSG3 with a resource allocation corresponding to the beam of the PDSCH with the best received quality. The gNB receives the PUSCH according to the scheduling information for MSG3 included in each of the multiple RAR messages. The beam receiving the PUSCH may be a narrow beam. It is preferable to use a received beam corresponding to the transmitted beam of each RAR message. In step ST2305, by receiving the PUSCH containing MSG3 transmitted from the UE, the gNB can acquire MSG3 and identify the beam with the best received quality for the UE. In other words, the gNB can recognize the optimal beam for the UE from among the beams transmitted in steps ST2302 to ST2304.

[0315] In step ST2207, the gNB notifies the UE of the scheduling information for the PDSCH containing MSG4 in the PDCCH. The beam identified by reception in step ST2305 is preferably used for this transmission beam. In step ST2208, the gNB transmits the PDSCH containing MSG4 to the UE according to the scheduling information for the PDSCH containing MSG4. Similarly, the best beam identified by reception in step ST2305 is preferably used for this transmission beam. In this way, the gNB can use the optimal narrow beam for the UE for both the scheduling information of MSG4 and the transmission of MSG4.

[0316] By using the method disclosed in this modified version, the gNB can transmit the PDSCH containing the RAR message using a narrow beam. Furthermore, the gNB can receive MSG3 with the receiving beam corresponding to the transmitting beam with the best reception quality at the UE. Therefore, the gNB can receive MSG3 using the optimal narrow beam. Additionally, the gNB can use the optimal narrow beam for transmission and reception of MSG4 and beyond for the UE. By using a narrow beam from the PDSCH containing the RAR message to processing MSG4 and beyond, coverage can be expanded.

[0317] Modification 3 of Embodiment 2. This modified version discloses another method to solve the problem that wide beams are used in RA processing, similar to the modified versions 1 and 2 of Embodiment 2 described above, and that wide coverage cannot be obtained.

[0318] In this modified example, the above problem is solved by transmitting the RAR multiple times, similar to Modified Examples 1 and 2 described above, but the details of the RAR transmission operation are different. To solve the above problem, it is good to transmit the RAR PDCCH and the PDSCH containing the RAR message multiple times. In this embodiment as well, the RAR is transmitted multiple times using different beams. More specifically, the RAR PDCCH and the PDSCH containing the RAR message are transmitted multiple times using different beams. For example, the beam from which the RAR PDCCH and the PDSCH containing the RAR message are transmitted may be a narrow beam. In this way, coverage of the RAR PDCCH and the PDSCH containing the RAR message can be expanded.

[0319] The gNB may transmit multiple different narrow beams within the beam range identified by the UE upon receiving the SSB. The gNB may transmit multiple different narrow beams so as to include the beam range identified by the UE upon receiving the SSB. Even if a wide beam is used for transmitting the SSB and RAR PDCCH, it is preferable to transmit the RAR PDCCH and the PDSCH containing the RAR message using a narrow beam. In this way, the coverage of the RAR PDCCH and the PDSCH containing the RAR message can be expanded while including the coverage of the SSB.

[0320] With respect to the RAR window, the method disclosed in Modification 1 of Embodiment 2 may be applied as appropriate. The gNB transmits multiple RAR PDCCHs within the RAR window period.

[0321] Regarding the number of transmissions of the RAR PDCCH and the PDSCH containing the RAR message, and the method for notifying them, the method disclosed in Modification 2 of Embodiment 2 may be applied as appropriate. Instead of the PDSCH containing the RAR message shown in Modification 2 of Embodiment 2, it may be used to have both the RAR PDCCH and the PDSCH containing the RAR message. In this way, the UE can recognize the number of transmissions of the RAR PDCCH and the PDSCH containing the RAR message.

[0322] The gNB notifies the UE of the scheduling information for the PDSCH containing the corresponding RAR message at the RAR's PDCCH. This scheduling information may also be included in the DCI and notified at the PDCCH. The scheduling information for the PDSCH containing the RAR message notified at each RAR's PDCCH may be different. The resource allocation on the time axis may also be different as part of the scheduling information for the PDSCH containing the RAR message. In this way, it becomes possible to transmit the PDSCH containing the RAR message using the beam corresponding to the beam transmitting the RAR's PDCCH. Narrow beams may be used for each beam.

[0323] The resource allocation information on the time axis of the PDSCH containing the RAR message may be represented by an offset from the transmission or reception timing of the RAR PDCCH. In this case, the offset information on the time axis of the PDSCH containing the RAR message may be the same for each beam. In this way, even if the offset is set to be the same, the transmission or reception timing of each PDSCH containing the RAR message will be different. Therefore, the gNB can transmit each PDSCH containing the RAR message on a different beam.

[0324] The DCI included in the RAR's PDCCH may include the beam identifier for each beam. The scheduling information of the PDSCH containing the RAR message for each beam may include the beam identifier for each beam. A sequence using the beam identifier may be used in the DMRS of the RAR's PDCCH for each beam. The beam identifier may be included in the RAR message. A sequence using the beam identifier may be used in the DMRS of the PDSCH containing the RAR message for each beam. These may be combined. In this way, a UE that receives the RAR's PDCCH and the PDSCH containing the RAR message can identify the beam from which the RAR's PDCCH and the PDSCH containing the RAR message are transmitted.

[0325] Regarding the method for notifying scheduling information of MSG3 for RA processing, the method disclosed in Modification 2 of Embodiment 2 may be applied as appropriate. In this case, the same effects as in Modification 2 of Embodiment 2 can be obtained.

[0326] The UE receives PDCCHs of multiple RARs. The UE also receives PDSCHs containing the corresponding RAR messages using the scheduling information of each RAR's PDCCH. The UE also measures the reception quality of each beam. The UE may measure the reception quality of the RS of each beam's PDCCH. The UE may measure the reception quality of the RS of each beam's PDSCH. For example, the reception quality of the DMRS may be measured. For example, other RSs (e.g., RSs for channel state measurement) may be provided on the PDCCH and / or PDSCH, and the reception quality of these RSs may be measured. The UE may measure the reception quality of the RSs of each beam's PDCCH and PDSCH. L1-RSRP may be measured as reception quality. The UE may store the reception quality information for each beam. In a PDSCH containing RAR messages transmitted multiple times, the UE uses the reception quality of each beam to identify one beam. The UE may store the identifier of the identified beam. For example, the UE may identify the beam with the best reception quality in the PDCCH and PDSCH containing the RAR message that has been transmitted multiple times. The UE may store an identifier for the beam with the best reception quality.

[0327] The gNB receives MSG3s from the UE using the scheduling information of MSG3s included in the RAR messages for each beam. The UE then transmits MSG3s using the PDCCH of the RAR transmitted on one identified beam, for example, the beam with the best reception quality, and the scheduling information of MSG3s included in the RAR message. In this way, the gNB can identify the beam with the best reception quality received by the UE.

[0328] MSG3 may include reception quality information for each beam and / or the identifier of the beam with the best reception quality. The reception quality information for each beam may be associated with a beam identifier. It may also be in the form of a list. As reception quality information for each beam, MSG3 may include reception quality information for the top n beams with the best reception quality and / or the identifiers of the top n beams with the best reception quality. As reception quality information for each beam, MSG3 may include reception quality information for the top n beams with the best reception quality that exceed a predetermined threshold and / or the identifiers of the top n beams with the best reception quality that exceed a predetermined threshold. In this way, the gNB can recognize the reception quality of each beam at the UE.

[0329] The gNB receives MSG3 on the beam corresponding to each beam in the PDSCH containing the RAR message. The gNB may also use a narrow beam to receive MSG3 transmitted from the UE. By using a narrow beam for transmitting the RAR PDCCH and the PDSCH containing the RAR message, it becomes possible to use a narrow beam to receive MSG3. The gNB may transmit the RA processing MSG4 to the UE using a beam that is specifically identified. The gNB can then transmit MSG4 using a narrow beam.

[0330] Figure 24 is a sequence diagram showing an example of a method for transmitting the RAR PDCCH and the PDSCH containing the RAR message multiple times using different beams in the RA processing of Modification 3 of Embodiment 2. Steps common to Figure 22 used in the description of Modification 1 of Embodiment 2 are given the same step numbers, and the common explanations are omitted. When step ST2201 is executed and the gNB receives the PRACH from the UE, it transmits the RAR PDCCH and the PDSCH containing the RAR message multiple times using different beams in steps ST2401 and ST2302, ST2402 and ST2303, and ST2403 and ST2304.

[0331] For transmitting the RAR PDCCH and the corresponding RAR message-containing PDSCH, for example, steps ST2401 and ST2302 should use the same beam. The same applies to steps ST2402 and ST2303, and ST2403 and ST2304. This beam may be different from the SSB beam received by the UE. The beam transmitting multiple RAR PDCCHs and RAR message-containing PDSCHs is configured to cover the SSB beam received by the UE. By transmitting the RAR PDCCH and RAR message-containing PDSCH multiple times in this way, it becomes possible to use a narrow beam for each transmission.

[0332] Each RAR's PDCCH includes scheduling information for the PDSCH containing the corresponding RAR message. For example, the RAR's PDCCH transmitted in step ST2401 includes scheduling information for the PDSCH containing the RAR message transmitted in step ST2302. This allows the gNB to transmit not only the RAR's PDCCH but also the PDSCH containing the RAR message using different beams. By transmitting multiple times using different beams, these beams can be made into narrow beams.

[0333] The RAR PDCCHs in steps ST2401 to ST2403 are transmitted within the RAR window period. The UE should receive the RAR PDCCHs within the RAR window period. The RAR window period may be an extension of the conventional RAR window period. Multiple RAR PDCCHs can be sent and received. The CRC of the DCI of the RAR PDCCHs is scrambled with RA-RNTI, and the UE can receive the RAR PDCCHs by using RA-RNTI.

[0334] Each PDSCH contains a RAR message that includes scheduling information for the MSG3 corresponding to the beam transmitting each PDSCH.

[0335] The UE receives the RAR PDCCH and the PDSCH containing the RAR message multiple times in steps ST2401 and ST2302, ST2402 and ST2303, and ST2403 and ST2304. The UE may receive the RAR PDCCH transmitted in steps ST2401 to ST2403, measure the reception quality of each beam, and identify the beam with the best reception quality. The UE may receive the PDSCH containing the RAR message transmitted in steps ST2302 to ST2304 and identify the beam with the best reception quality. The UE may receive the RAR PDCCH and the PDSCH containing the RAR message transmitted in steps ST2401 and ST2302, ST2402 to ST2303, and ST2403 to ST2304, measure the reception quality of each beam, and identify the beam with the best reception quality.

[0336] The UE receives the PDCCH of the identified beam and receives the RAR message of the PDSCH according to the scheduling information contained in the PDCCH.

[0337] In step ST2305, the UE uses the scheduling information for MSG3 included in the received RAR message to send a PUSCH containing MSG3. The gNB receives the PUSCH according to the scheduling information for MSG3 included in each of the multiple RAR messages. In step ST2305, by receiving the PUSCH containing MSG3 sent from the UE, the gNB can acquire MSG3 and identify the beam with the best reception quality for the UE. In other words, the gNB can recognize the optimal beam for the UE from among the beams sent in steps ST2401 and ST2302, steps ST2402 and ST2303, and steps ST2403 and ST2304.

[0338] By using the method disclosed in this modified version, the gNB can transmit the PDCCH of the RAR and the PDSCH containing the RAR message in a narrow beam. Furthermore, the gNB can receive MSG3 with the receiving beam corresponding to the transmitting beam with the best reception quality at the UE. Therefore, the gNB can receive MSG3 in an optimal narrow beam. Additionally, the gNB can use the optimal narrow beam for transmission and reception of MSG4 and beyond for the UE. By using a narrow beam from the RAR's PDCCH to processing MSG4 and beyond, coverage can be expanded.

[0339] In Modification 2 and Modification 3 of Embodiment 2, it was disclosed that the scheduling information for MSG3 included in the RAR message of each PDSCH is set so that the transmission timing of MSG3 is different. Alternatively, the scheduling information for MSG3 included in the RAR message of each PDSCH may be information indicating the same resource. There may be only one resource for the PUSCH containing MSG3. In this way, the UE can transmit the PUSCH containing MSG3 with the single beam, and therefore the gNB can receive the PUSCH with the single beam. The single beam may be a wide beam. In this way, the resources used can be reduced, and the reception processing of the PUSCH containing MSG3 in the gNB can be simplified, thereby reducing the power consumption of the gNB.

[0340] Upon receiving MSG3 from the UE, the gNB uses the reception quality information for each beam contained in MSG3 and / or the identifier information for the beam with the best reception quality to identify the beam to be used by the UE. The gNB should then transmit MSG4 for RA processing to the UE using the identified beam. The gNB can then transmit MSG4 using a narrow beam. In this way, it becomes possible to use a narrow beam for processing from MSG4 onward.

[0341] Embodiment 3. As disclosed in Embodiment 2, the expansion of coverage in RA processing has been considered. This embodiment discloses another method for expanding MSG3 coverage.

[0342] Retransmission is supported for MSG3 in RA processing. If the gNB cannot receive MSG3 from the UE, it will schedule another MSG3 transmission to the UE. The UE will retransmit the MSG3 according to the scheduling information sent by the gNB. It is recommended to set up repeated transmission for MSG3 retransmission. The number of repeated transmissions may be increased along with the number of retransmissions. By enabling repeated transmission for MSG3 retransmission in this way, it is possible to improve the reception quality of MSG3 at the gNB. This allows for expansion of MSG3 coverage.

[0343] For MSG3, the scheduling method differs between the initial transmission and retransmissions. For the initial transmission of MSG3, the scheduling information is included in the RAR message. This scheduling information is notified via PDSCH. For retransmissions of MSG3, the scheduling information is notified via PDCCH. Thus, the scheduling method differs between the initial transmission and retransmissions of MSG3.

[0344] In the communication system according to this embodiment, the number of retransmissions of MSG3 and the number of repeated transmissions are set in association. Alternatively, the number of repeated transmissions for each retransmission of MSG3 may be set in association. For example, the first retransmission may be set to 2 repeated transmissions, the second retransmission to 4 repeated transmissions, and so on. The association information may also include an increase or decrease in the number of repeated transmissions or a difference (step) for each retransmission. For example, the number of repetitions may increase by 2 for every increase of 1 in the retransmission count. The number of repetitions is not limited to an increase. Multiple such associations may be set as a list. An index may be assigned to each association in the list.

[0345] Information linking the initial transmission of MSG3 to the number of repeated transmissions may be provided. While information linking the number of retransmissions of MSG3 to the number of repeated transmissions has been disclosed, as an alternative, the number of repeated transmissions of the initial transmission of MSG3 may also be included in this information. In this way, it becomes possible to set the number of repeated transmissions from the initial transmission of MSG3.

[0346] This association information may be statically defined by standards, etc. The gNB may notify this association information via MIB or SIB. The gNB may also notify this association information via RRC signaling.

[0347] Alternatively, the gNB may include the association information in the MAC CE and notify it via MAC signaling. The gNB may also include the association information in the RAR message containing the scheduling information for the initial transmission of MSG3 and notify it via PDSCH. The association information may be notified via PDSCH together with, or included in, the scheduling information for the initial transmission of MSG3. Upon receiving the RAR message, the UE can recognize the number of repetitions for MSG3 transmission. When the UE transmits MSG3, it uses the association information to transmit the MSG3.

[0348] In this way, gNB can determine the number of repetitions corresponding to the number of transmissions, including retransmissions, of MSG3, taking into account the radio wave propagation environment when scheduling the initial transmission of MSG3. Therefore, it is possible to consider the radio wave propagation environment close to the transmission timing of MSG3, which makes it possible to improve the reception quality of MSG3, including retransmissions.

[0349] Alternatively, the gNB may include the association information in the DCI containing the MSG3 retransmission scheduling information and notify it via the PDCCH. The association information may be notified via the PDCCH together with the MSG3 retransmission scheduling information, or included in the MSG3 retransmission scheduling information. The UE can recognize the number of retransmissions for the MSG3 by receiving the DCI containing the MSG3 retransmission scheduling information. When the UE retransmits the MSG3, it uses the association information to perform the retransmission.

[0350] In this way, gNB can determine the number of MSG3 retransmissions and repetitions by considering the radio wave propagation environment when scheduling MSG3 retransmissions. Therefore, it is possible to consider the radio wave propagation environment closer to the MSG3 retransmission timing, thereby improving the reception quality during MSG3 retransmissions.

[0351] Alternatively, information may be provided regarding whether or not to perform repeated transmission. This information may be activation or deactivation information for repeated transmission. The information regarding whether or not to perform repeated transmission may simply indicate that it should be performed. If this information is not present, repeated transmission should not be performed. Alternatively, the information regarding whether or not to perform repeated transmission may simply indicate that it should not be performed. If this information is not present, repeated transmission should be performed.

[0352] The gNB may include this information in the RAR message containing the scheduling information for the initial transmission of MSG3 and notify it via PDSCH. Alternatively, the gNB may include an index indicating the association information of the association list in the DCI containing the scheduling information for the retransmission of MSG3 and notify it via PDCCH. This allows for dynamic configuration of repeated transmissions.

[0353] The UE determines whether to perform repeated transmissions during the initial transmission or retransmission, depending on the setting. If repeated transmissions are to be performed, the UE may use the number of repetitions set in the association information between the number of transmissions and the number of repeated transmissions of MSG3 disclosed above to perform repeated transmissions of MSG3.

[0354] Alternatively, the gNB may send the number of repetitions to the UE along with information indicating whether or not to perform repeated transmissions. Or, it may send the number of repetitions along with information indicating that repeated transmissions will be performed. If the repetition information indicates that it will be performed, the UE may use the repetition count information sent together to perform repeated transmissions of MSG3.

[0355] By doing so, it becomes possible to consider a radio wave propagation environment that is closer to the transmission timing of MSG3, thereby improving the reception quality when transmitting MSG3.

[0356] Figure 25 is a sequence diagram showing an example of how to set up repeated transmission when MSG3 is retransmitted, according to Embodiment 3. Steps common to Figure 22 used in the description of Modification 1 of Embodiment 2 are given the same step numbers, and the common descriptions are omitted. In step ST2501, the gNB transmits information relating the number of MSG3 retransmissions and the number of repetitions. The gNB includes this information in the SIB and transmits it. In step ST2201, the UE sends a PRACH to the gNB in ​​order to access the gNB. In step ST2502, the gNB receives the PRACH from the UE, decides to transmit MSG2, and decides to set up repeated transmission of MSG3. In step ST2503, the gNB sends a RAR PDCCH to the UE. The PDCCH contains scheduling information for the PDSCH to which the RAR message is transmitted.

[0357] In step ST2504, the gNB sends information indicating whether or not to perform repeated transmission, either with or included in the RAR message. Upon receiving this information in step ST2504, if the information indicates that repeated transmission should be performed, the UE determines the number of repeated transmissions (n1) of the initial transmission of MSG3 using the association information between the number of retransmissions and the number of repeated transmissions of MSG3 notified in step ST2501. In steps ST2505 to ST2506, the UE sends a PUSCH containing the determined number of repeated transmissions and MSG3.

[0358] In step ST2507, the gNB decides to retransmit MSG3 to the UE. The gNB also decides to set up repeated transmission for the UE. In step ST2508, the gNB sends the RAR PDCCH to the UE.

[0359] In step ST2509, the gNB transmits information indicating whether or not to perform repeated transmission, along with or included in the scheduling information for retransmitting MSG3. In step ST2509, the UE, upon receiving this information, determines the number of repeated transmissions (n2) for the first retransmission of MSG3, using the association information between the number of MSG3 retransmissions and the number of repeated transmissions notified in step ST2501, if the information indicates that repeated transmission will be performed. In steps ST2510 to ST2511, the UE transmits a PUSCH containing the determined number of repeated transmissions and MSG3.

[0360] In step ST2512, the gNB successfully demodulates MSG3 received from the UE. After successfully demodulating MSG3, the gNB executes steps ST2207 and ST2208 to send MSG4 to the UE.

[0361] The method disclosed in this embodiment enables repeated transmission of MSG3 during RA processing. This improves the reception quality of MSG3 in gNB and expands MSG3 coverage.

[0362] Modification 1 of Embodiment 3. This modified example discloses another method for extending MSG3 coverage.

[0363] In this modified example, MSG3 coverage is extended by setting the transmit power during retransmission. The transmit power may be increased along with the number of retransmissions. By making it possible to set the transmit power during MSG3 retransmission in this way, it is possible to improve the reception quality of MSG3 in gNB. Therefore, MSG3 coverage can be extended.

[0364] In this modified example, the number of retransmissions of MSG3 is associated with the transmission power. Alternatively, the transmission power for each retransmission of MSG3 may be associated with the setting. For example, the first retransmission may be set to transmission power P1, the second retransmission to transmission power P2, and so on. P1 and P2 may be power values. P1 and P2 may be offset values ​​from a predetermined power value. The predetermined power value may be a power value derived by the UE using path loss.

[0365] The association information may include the increase or decrease in transmission power or the difference (step) for each retransmission. For example, the power may increase by ΔP each time the retransmission count increases by one. For example, if the transmission power for the initial transmission is P0, then for the first retransmission it is P0+ΔP, and for the second retransmission it is P0+ΔP+ΔP. The transmission power is not limited to an increase. The increase or decrease in transmission power may differ for each retransmission. For example, for the first retransmission it is ΔP1, for the second retransmission it is ΔP2, and so on. Multiple such associations may be presented as a list of the association information. Each association in the list may be assigned an index.

[0366] An upper limit may be set for the transmission power. The upper limit for transmission power may be set for each retransmission of MSG3. Alternatively, it may be set for the transmission of MSG3 rather than for each retransmission. For example, if the transmission power increases in response to MSG3 retransmissions and exceeds the upper limit for transmission power, it is advisable to set the transmission power to that upper limit. Doing so can reduce interference.

[0367] Information relating the initial transmission of MSG3 to the transmission power may be provided. While information relating the number of retransmissions of MSG3 to the transmission power has been disclosed, as an alternative, the transmission power of the initial transmission of MSG3 may also be included in this information. In this way, the transmission power can be set from the initial transmission of MSG3.

[0368] The method for setting the transmission power during MSG3 retransmission can be appropriately applied to the method for setting information relating the number of MSG3 retransmissions and the number of repeated transmissions disclosed in Embodiment 3. This makes it possible to set the transmission power during MSG3 retransmission.

[0369] By using the method disclosed in this modified version, it becomes possible to set the transmission power during retransmission of MSG3 in RA processing. This makes it possible to improve the reception quality of MSG3 in gNB and expand the coverage of MSG3.

[0370] The transmission power may be set during repeated transmissions when retransmitting MSG3. In this case, the method for setting repeated transmissions during MSG3 retransmission disclosed in Embodiment 3 and the method for setting the transmission power during MSG3 retransmission in this modified example can be appropriately combined and applied. For example, the transmission power can be set for each repeated transmission during MSG3 retransmission. The method for setting the transmission power during MSG3 retransmission in this modified example can be appropriately applied as such. In this way, even when repeated transmission is possible during MSG3 retransmission, the transmission power can be set for each repeated transmission. This makes it possible to improve the reception quality of MSG3 in gNB and expand the coverage of MSG3.

[0371] Embodiment 4. Embodiment 3 disclosed a method for achieving coverage expansion by combining retransmission and repeated transmission of MSG3. When applying such a method, for example, gNB may be able to demodulate correctly after receiving repeated transmissions of several MSG3s. In such cases, it is a waste of resources for the UE to transmit all the set number of repeated transmissions of the MSG3, reducing resource utilization efficiency. It also increases unnecessary power consumption in the UE. To solve these problems, it is required to stop repeated transmission of MSG3 early.

[0372] MSG3 is sent via PUSCH. The method for canceling repeated PUSCH transmissions has already been standardized. However, the standardized method for canceling repeated PUSCH transmissions cannot be applied to UEs that are not in the RRC_CONNECTED state. An UE sending MSG3 has not yet reached the RRC_CONNECTED state. Therefore, the standardized method for canceling repeated PUSCH transmissions cannot be applied as a method to stop repeated transmissions of MSG3.

[0373] In light of these circumstances, this embodiment discloses a method for early termination of repeated transmission of MSG3.

[0374] In this embodiment, information regarding stopping (or canceling) the repeated transmission of MSG3 is provided so that the repeated transmission of PUSCH can be stopped before the state becomes RRC_CONNECTED. This information may hereafter be referred to as MSG3 stop information. In the communication system according to Embodiment 4, the gNB notifies the UE of information regarding stopping the repeated transmission of MSG3. This notification may be made between the setting of repeated transmission of MSG3 and the end of the last repeated transmission of MSG3 at the UE. The notification of MSG3 stop information may be made once or multiple times. The gNB may continue to notify until it recognizes that the repeated transmission of MSG3 has been stopped by the UE.

[0375] MSG3 stop information is notified from the gNB to the UE using downlink symbols. If the repeated transmission of MSG3 is PUSCH repetition type A, the MSG3 stop information may be notified in the slot containing the downlink symbols. If the repeated transmission of MSG3 is PUSCH repetition type B, the notification may be made using downlink symbols. The gNB may notify the UE of MSG3 stop information multiple times within a single slot.

[0376] In this way, gNB can notify the UE of MSG3 failure information.

[0377] When the UE receives a setting from the gNB to repeatedly transmit MSG3, it begins monitoring for MSG3 stop information from the gNB. The UE may also begin monitoring for MSG3 stop information from the gNB after the first transmission of MSG3. The UE monitors for MSG3 stop information from the gNB until repeated transmission of MSG3 is completed or until MSG3 stop information is received. The UE monitors for MSG3 stop information from the gNB using downlink symbols. The UE may also monitor for MSG3 stop information from the gNB using downlink symbols for each slot or each mini-slot. When the UE receives MSG3 stop information, it stops repeatedly transmitting MSG3. The UE may also terminate monitoring for MSG3 stop information after receiving MSG3 stop information.

[0378] The gNB may notify the UE of MSG3 stop information via PDCCH. In this case, the UE monitors PDCCH. Alternatively, MSG3 stop information may be included in DCI and notified via PDCCH. MSG3 stop information may be included in DCI Format0_0. Or, a new DCI format may be created to include MSG3 stop information. This is effective when using a small number of bits for MSG3 stop information.

[0379] Therefore, it is advisable to configure PDCCH to include MSG3 stop information.

[0380] The gNB scrambles the CRC of DCIs containing MSG3 stop information using TC-RNTI (Temporary Cell - Radio Network Temporary Identifier). In this case, the TC-RNTI is notified to the UE in a RAR message containing MSG3 scheduling information from the gNB. The CRC of DCIs containing MSG3 stop information is scrambled using TC-RNTI. In this way, the UE can quickly and easily determine whether a DCI contains MSG3 stop information by determining whether or not it is scrambled with TC-RNTI included in the RAR message.

[0381] Alternatively, the CRC of the DCI containing MSG3 stop information can be scrambled with RA-RNTI (Random Access - RNTI). In this case, the DCI containing the scheduling information for the RAR message is notified to the UE from the gNB after being scrambled with RA-RNTI. The UE is aware of RA-RNTI before sending the MSG3. The CRC of the DCI containing MSG3 stop information is scrambled with RA-RNTI. When using RA-RNTI, DCI Format1_0 may be used for the DCI. In this way, the UE can quickly and easily determine whether the PDCCH contains MSG3 stop information by determining whether the DCI has been scrambled with RA-RNTI.

[0382] Alternatively, a new RNTI may be added to scramble the CRC of the DCI containing the MSG3 stop information. For example, CI2-RNTI. In this case, the gNB may notify the UE by including CI2-RNTI in the RAR message. The UE can then recognize CI2-RNTI before sending the MSG3. Therefore, when repeatedly sending MSG3, by determining whether the DCI containing the MSG3 stop information sent from the gNB is scrambled with CI2-RNTI, it becomes possible to quickly and easily determine whether or not the PDCCH contains the MSG3 stop information.

[0383] Alternatively, the RNTI for scrambling the DCI's CRC containing the MSG3 stop information may be derived from another RNTI. For example, it may be derived from the RA-RNTI. In this case, it becomes unnecessary to separately notify the UE of the RNTI for scrambling the DCI's CRC containing the MSG3 stop information. In other words, the amount of information required for notifying the MSG3 stop information can be reduced.

[0384] Alternatively, MSG3 stop information may not be required. The UE may determine whether to stop repeated transmission of MSG3 based on whether or not it has received DCI scrambled with the aforementioned RNTI. The UE may determine that MSG3 has stopped if it receives PDCCH scrambled with the aforementioned RNTI. The UE may determine that MSG3 has not stopped if it does not receive PDCCH scrambled with the aforementioned RNTI.

[0385] In this way, the UE can receive MSG3 stop information from the gNB. If the gNB can demodulate the repeated transmission of PUSCH containing MSG3 from the UE, it can stop the repeated transmission of MSG3 from the UE earlier. This assumes that the gNB can demodulate the repeated transmission of PUSCH containing MSG3 from the UE, but it could also be the case that the gNB can decode the repeated transmission of MSG. In this way, it is possible to improve the efficiency of resource utilization for repeated transmission of MSG3. In addition, it is possible to reduce unnecessary power consumption at the UE.

[0386] Figure 26 is a sequence diagram showing an example of an early termination method for repeated transmission of MSG3 in Embodiment 4. Steps common to Figure 25 used in the description of Embodiment 3 are given the same step numbers, and the common explanations are omitted. In step ST2601, the gNB transmits RACH setting information. The gNB transmits this information in the SIB. In step ST2201, the UE starts RA processing to access the gNB.

[0387] In step ST2602, the gNB sends the number of repetitions of MSG3 and the CI2-RNTI along with the RAR message, or included in the RAR message. Upon receiving this information in step ST2602, the UE begins repeatedly sending MSG3 from step ST2603. Upon receiving this information, the UE also begins detecting PDCCHs with scrambled CI2-RNTI in the DCI's CRC. The UE continues repeatedly sending MSG3 until it receives a PDCCH with scrambled CI2-RNTI in the DCI's CRC, or until it reaches the number of repetitions of MSG3.

[0388] In step ST2604, the UE sends a second repeated transmission of MSG3. Having received the second repeated transmission in step ST2604, the gNB successfully decodes MSG3 in step ST2512. Having successfully decoded MSG3, the gNB sends MSG3 stop information to the UE in step ST2605. The gNB includes the MSG3 stop information in the DCI, which has its CRC scrambled by CI2-RNTI, and transmits it via PDCCH.

[0389] A UE that has started detecting a PDCCH with CI2-RNTI scrambled in the DCI's CRC can receive the PDCCH transmitted from the gNB in ​​step ST2605. In step ST2605, the UE obtains the MSG3 stop information contained in the PDCCH. In step ST2606, the UE stops the repeated transmission of MSG3. In this way, the UE stops repeated transmission without transmitting the remaining MSG3, even if the number of repeated transmissions of MSG3 has not been reached.

[0390] Having sent MSG3 stop information to the UE in step ST2605, the gNB executes steps ST2207 and ST2208 to send MSG4 to the UE.

[0391] This approach allows for the early termination of repeated transmissions of MSG3 by the UE, for example, if the gNB correctly decodes the MSG3 from the UE.

[0392] Figure 27 is a sequence diagram showing another example of an early termination method for repeated transmission of MSG3 in Embodiment 4. Steps common to Figure 26 are given the same step numbers, and common explanations are omitted. In step ST2701, the gNB transmits the number of repeated transmissions of MSG3 and the TC-RNTI together with or included in the RAR message. Upon receiving this information in step ST2701, the UE starts repeatedly transmitting MSG3 from step ST2603. The UE also starts detecting the PDCCH with the TC-RNTI scrambled in the DCI's CRC. The UE continues to repeatedly transmit MSG3 until it receives the PDCCH with the TC-RNTI scrambled in the DCI's CRC, or until it reaches the number of repeated transmissions of MSG3.

[0393] If the gNB successfully decodes MSG3, in step ST2702, it sends the PDSCH scheduling information, including MSG4, to the UE via PDCCH, including it in the DCI. The gNB then sends this scheduling information via PDCCH, including it in the DCI, which has been scrambled with CRC by TC-RNTI.

[0394] A UE that has started detecting a PDCCH with TC-RNTI scrambled into the DCI's CRC can receive the PDCCH sent from the gNB in ​​step ST2702. Upon receiving the PDCCH with TC-RNTI scrambled into the DCI's CRC, the UE stops repeatedly transmitting MSG3 in step ST2606. In other words, the UE determines that MSG3 has been successfully decoded by the gNB upon receiving the PDCCH with TC-RNTI scrambled into the DCI's CRC. Thus, even if the number of repeated transmissions of MSG3 has not been reached, the UE stops repeatedly transmitting without sending the remaining MSG3.

[0395] If the gNB sent PDSCH scheduling information including MSG4 to the UE in step ST2702, it sends MSG4 in step ST2208.

[0396] This approach allows for the early termination of repeated transmissions of MSG3 by the UE, for example, when the gNB correctly decodes MSG3 from the UE. Furthermore, since there is no need to transmit MSG3 termination information, the amount of signaling can be reduced.

[0397] The method disclosed in this embodiment makes it possible to stop repeated transmission of MSG3 from the UE early, for example, when the gNB correctly decodes MSG3 from the UE. This expands MSG3 coverage and improves resource utilization efficiency. It also helps to suppress unnecessary increases in power consumption of the UE.

[0398] Information regarding the reduction in the number of MSG3 repetitions may be provided. This information may be the number of MSG3 repetitions after notification of the information. Alternatively, it may be the number of repetitions reduced from the already set number of MSG3 repetitions. For example, if the gNB is likely to be able to correctly decode the MSG3 from the UE, it will notify the UE of the MSG3 repetition reduction information. The notification method may be appropriately applied using the method disclosed above.

[0399] Information regarding the extension of the number of MSG3 repetitions may be provided. This information may be the number of MSG3 repetitions after notification of the information. Alternatively, it may be the extension from the already set number of MSG3 repetitions. For example, if the gNB is unlikely to be able to correctly decode the MSG3 from the UE, it will notify the UE of the MSG3 repetition extension information. The notification method may be appropriately applied using the method disclosed above.

[0400] This approach allows for appropriate control of the number of repeated transmissions based on the MSG3 reception status in the gNB. This expands MSG3 coverage and improves resource utilization efficiency. It also helps to suppress unnecessary power consumption increases in the UE.

[0401] Embodiment 5. As mentioned above, coverage can be expanded by increasing the number of times MSG3 is sent repeatedly. However, setting an unnecessarily large number of repetitions can lead to wasted resources. It can also increase unnecessary power consumption in the UE. Therefore, a more efficient setting of the number of times MSG3 is sent repeatedly is required.

[0402] This embodiment discloses a method for solving these problems.

[0403] To solve the above problems, the gNB of the communication system according to this embodiment sets repeated transmission of MSG3 according to the group of the PRACH preamble in RA processing. Here, in NR, the PRACH preamble is divided into two groups, Group A and Group B. For example, the gNB sets repeated transmission when it is Group B. When it is Group A, repeated transmission may not be set. The UE uses Group B for the PRACH preamble when the size of MSG3 is larger than a predetermined amount. If the size of MSG3 is large, not enough resources can be allocated to the transmission of the MSG3, which may degrade the communication quality. When the PRACH preamble selected by the UE is Group B, the gNB can improve the communication quality of MSG3 by setting repeated transmission of MSG3.

[0404] The gNB may set the number of times MSG3 is repeated depending on the group in the PRACH preamble. This allows for more flexible repetition settings.

[0405] In this way, by configuring the repetition of MSG3 transmission according to the group used in the PRACH preamble, it is possible to improve the communication quality of MSG3 and expand MSG3 coverage. Furthermore, since the repetition of MSG3 transmission can be configured according to the size of MSG3, it becomes possible to set a more efficient number of MSG3 repetitions.

[0406] The number of groups in the PRACH preamble may be increased. While there were traditionally two groups, there may be three or more. There may also be three or more groups for the contention base. These may be subgroups of the traditional groups. For example, group A may be divided into two groups, A1 and A2. For example, group B may be divided into two groups, B1 and B2.

[0407] Figure 28 shows an example of Embodiment 5 where the number of PRACH preamble groups is set to four. Group A for the contention base is divided into two groups, A1 and A2, and group B is divided into two groups, B1 and B2. That is, four groups are formed: A1, A2, B1 and B2.

[0408] Each group may correspond to the number of times MSG3 is repeatedly transmitted. For example, the conventional group A can be divided into groups A1 and A2, and group B can be divided into groups B1 and B2. Groups A1 and A2 are set to correspond to the number of times MSG3 is repeatedly transmitted. For example, for group A1, the number of times MSG3 is repeatedly transmitted may be Ra1 or less, and for group A2, the number of times MSG3 is repeatedly transmitted may be greater than Ra1. Groups B1 and B2 are set to correspond to the number of times MSG3 is repeatedly transmitted. Similarly, for group B1, the number of times MSG3 is repeatedly transmitted may be Rb1 or less, and for group B2, the number of times MSG3 is repeatedly transmitted may be greater than Rb1.

[0409] The number of times each group and its corresponding MSG3 message is sent may be predetermined by a standard or other static setting. Alternatively, the CN may set it and notify the gNB. The CN may be OAM (Operations, Administration and Maintenance), which may set it and notify the gNB. The CN may be a node (or function) with orchestration capabilities, which may set it and notify the gNB. Alternatively, the gNB may decide it. In this way, the gNB can set the number of times MSG3 is sent based on the group of PRACH preamble sent from the UE.

[0410] The UE may select a group corresponding to the number of times MSG3 has been sent. The UE selects and sends a PRACH preamble from the selected group.

[0411] The UE may select a group using the path loss value. A predetermined threshold may be set for path loss for group selection. This predetermined threshold may be statically determined by a standard or the like. The gNB may notify this via MIB or SIB. This predetermined threshold is used to select a group corresponding to the number of times MSG3 has been repeatedly transmitted.

[0412] For example, introduce path loss as a criterion for group selection when MSG3 is CCCH. The UE uses the size of MSG3 and the path loss to select the group corresponding to the number of times MSG3 has been transmitted. For example, set a predetermined threshold for the size of MSG3, and if it is greater than or equal to this threshold, the size of MSG3 is set to L. If it is less than the threshold, the size of MSG3 is set to S. For example, if the path loss is greater than or equal to a predetermined threshold, the path loss is set to L. If it is less than the threshold, the path loss is set to S.

[0413] For example, if the size of MSG3 is S and the path loss is S, the UE uses group A1. If the size of MSG3 is S and the path loss is L, it uses group A2. If the size of MSG3 is L and the path loss is S, it uses group B1. If the size of MSG3 is L and the path loss is L, it uses group B2. In this way, the UE evaluates the size and path loss of MSG3 and decides which group to use for the PRACH preamble, as described above. The UE sends the PRACH using the PRACH preamble from the determined group.

[0414] The gNB identifies groups of PRACH preambles using the PRACH preambles sent from the UE. The gNB then determines whether or not to repeatedly send MSG3 from the identified groups. The gNB may also determine the number of times to repeatedly send MSG3 from the identified groups.

[0415] A group may be created for the UE to request the setting of repeated transmission of MSG3. The group may be based on the number of times MSG3 is to be repeated. For example, groups A1, A2 and B1, B2 as disclosed in the above example. The UE determines the group of PRACH preambles corresponding to the number of times MSG3 is to be repeated, for example, based on the status of its own UE or the SSB reception quality. The UE transmits PRACH using the preamble in the determined group. The gNB determines the number of times MSG3 is to be repeated using the group of PRACH preambles received from the UE.

[0416] This allows the UE to request the setting for repeated transmission of MSG3. For example, the gNB can set the number of times MSG3 is repeated depending on the UE's status and the SSB reception quality at the UE.

[0417] By using the method disclosed in this embodiment, the gNB can determine the setting for repeated transmission of MSG3 based on the group of PRACH preambles selected by the UE. The gNB can determine the setting for repeated transmission of MSG3 depending on the size of MSG3, path loss at the UE, SSB reception quality, etc. Since the gNB can appropriately set the repeated transmission of MSG3 for the UE, coverage expansion is possible, and wasted resources are reduced, improving resource utilization efficiency.

[0418] Embodiment 6. In NR, contention-based RA processing may be performed in abnormal conditions. Abnormal conditions include, for example, BFR (Beam Failure Recovery) and Out of Sync detection. The method for configuring initial access processing such as SSB transmission / reception and RA processing in such abnormal conditions is not disclosed at all in the standards established to date, including the aforementioned Non-Patent Documents 1 to 25.

[0419] This embodiment discloses a method for setting up initial access processing in such an abnormal state.

[0420] The gNB notifies the UE of information regarding coverage expansion before it transitions to an abnormal state. The gNB may also notify the UE of information regarding coverage expansion when it is in the RRC_CONNECTED state. The information regarding coverage expansion may be the information disclosed in Embodiments 1 to 5. Twenty specific examples of information regarding coverage expansion are disclosed below.

[0421] (1) Information regarding the DMRS settings for PUSCH. (2) The number of times PUSCH is repeatedly transmitted. (3) The number of repeated transmissions when retransmitting via PUSCH. (4) Information regarding DMRS reduction when PUSCH is repeatedly transmitted. (5) A list of information regarding DMRS reduction when repeatedly transmitting PUSCH. (6) Information regarding repeated transmissions of PBCH. (7) Information regarding the number of SSBs. (8) Information regarding SS burst intervals. (9) Information regarding RAR windows. (10) The number of times MSG3 is sent repeatedly. (11) Number of repeated transmissions when resending MSG3. (12) Information regarding DMRS reduction when repeatedly sending MSG3. (13) Information list regarding DMRS reduction when repeatedly sending MSG3. (14) Information regarding the transmission power when MSG3 is repeatedly transmitted. (15) Information list regarding the transmission power during repeated transmission of MSG3. (16) RNTI information for receiving MSG3 stop information. (17) Information regarding the group of PRACH preambles. (18) Information regarding repeated transmission of PRACH. (19) Information regarding repeated transmissions of MSGA PUSCH. (20)(1)~(19) combinations.

[0422] The gNB notifies the UE of information about coverage expansion using individual signaling. It may also use RRC signaling. For example, it may be included in the RRC Reconfiguration. It may also be included in the BFR configuration. For example, it may be included in the BeamFailureRecoveryConfig.

[0423] When the UE performs initial access processing in an abnormal state, it uses the coverage expansion information most recently obtained from the gNB. The UE may also use the received coverage expansion information if the gNB performing initial access processing in the abnormal state is the same gNB that received the coverage expansion information. Since the UE can obtain coverage information in advance, it is possible to improve the robustness of the recovery process from the abnormal state. In addition, since there is no need to send or receive coverage expansion information from the cell in the abnormal state, it is possible to recover from the abnormal state more quickly.

[0424] The UE performs the initial access process when transitioning from the RRC_INACTIVE state to the RRC_CONNECTED state using the coverage expansion information most recently obtained from the gNB. The UE retains the coverage expansion information in the RRC_INACTIVE state. The coverage expansion information may be enabled in the RNA (RAN Notification Area). This improves the robustness of the transition process from the RRC_INACTIVE state to the RRC_CONNECTED state. Furthermore, since there is no need to receive coverage expansion information from the cell when transitioning to the RRC_CONNECTED state, it is possible to return to the RRC_CONNECTED state quickly.

[0425] The gNB may notify the UE of information regarding coverage extensions for adjacent cells before the UE transitions to an abnormal state. The gNB may also notify the UE of information regarding coverage extensions for adjacent cells when the UE is in the RRC_CONNECTED state. The information regarding coverage extensions may be associated with the identifier of the adjacent cell. This is useful when setting information regarding coverage extensions for each cell. The identifier of the adjacent cell may be PCI. The UE can recognize the PCI by receiving the cell's SS, thus enabling early cell identification. The information regarding coverage extensions may be associated with the beam identifier. This is useful when setting information regarding coverage extensions for each beam.

[0426] gNBs may notify each other of information regarding the coverage expansion of the cells they comprise. This notification may be made using the Xn interface or by Xn signaling. In this way, gNBs can obtain information regarding the coverage expansion of neighboring cells.

[0427] Furthermore, in NR, gNB may be separated into CU and DU. In such cases, information regarding coverage expansion for each cell may be communicated between the CU and DU. If multiple DUs constitute multiple cells, information regarding coverage expansion for the cells corresponding to the DUs may be communicated between the CU and DU. The F1 interface may be used for this communication. Communication may also be done via F1 signaling. In this way, even when gNB is separated into CU and DU, information regarding coverage expansion can be managed appropriately.

[0428] The method for notifying information regarding coverage extensions from gNB to UE should be the method disclosed above, as appropriate.

[0429] When performing initial access processing in an abnormal state, the UE uses the coverage expansion information of the adjacent cell most recently obtained from the gNB to perform RA processing. Even if the gNB performing initial access processing in the abnormal state is different from the gNB that received the information on the adjacent cell's coverage expansion, the UE may still use the received information on the adjacent cell's coverage expansion to perform initial access processing. By doing so, the UE can obtain information on the coverage of adjacent cells in advance, thereby improving the robustness of the return process to other cells from the abnormal state. Furthermore, since there is no need to receive information on coverage expansion from cells in the abnormal state, the UE can return from the abnormal state more quickly.

[0430] When transitioning from the RRC_INACTIVE state to the RRC_CONNECTED state, the UE performs RA processing using information about the coverage expansion of adjacent cells most recently obtained from the gNB. In the RRC_INACTIVE state, the UE retains information about the coverage expansion of adjacent cells. This information may be enabled in the RNA (RAN Notification Area). This information may be enabled only for adjacent cells where the information exists. This allows the UE to perform initial access processing even when transitioning to the RRC_CONNECTED state in a different cell than the one it was in before entering the RRC_INACTIVE state. It also improves the robustness of the transition process from the RRC_INACTIVE state to the RRC_CONNECTED state. Furthermore, since there is no need to send or receive information about coverage expansion from the cell when transitioning to the RRC_CONNECTED state, it is possible to return to the RRC_CONNECTED state quickly.

[0431] When transitioning from the RRC_IDLE state to the RRC_CONNECTED state, the UE performs the initial access using information about coverage expansion for its own cell and / or adjacent cells, which was most recently obtained from the gNB. The UE retains this coverage expansion information while in the RRC_IDLE state. This allows the UE to perform the initial access even when transitioning to the RRC_CONNECTED state in the same cell as before or a different cell. It also improves the robustness of the transition process from the RRC_IDLE state to the RRC_CONNECTED state. Furthermore, since there is no need to send or receive information about coverage expansion from the cell when transitioning to the RRC_CONNECTED state, it can return to the RRC_CONNECTED state more quickly.

[0432] The method disclosed above may also be applied to initial access processing performed in two steps. Information regarding repeated transmissions of MSGA PUSCH may be used as information regarding coverage expansion. In this way, the same effect can be obtained even in initial access processing performed in two steps.

[0433] Figure 29 is a sequence diagram illustrating an example of a method for notifying a UE of coverage expansion information before it transitions to an abnormal state, according to Embodiment 6. In the example shown in Figure 29, while the UE is in the RRC_CONNECTED state, in step ST2901, the gNB notifies the UE of coverage expansion information. The gNB may notify the UE of this information through individual RRC signaling. For example, the information may be included in an RRCReconfiguration message. If the UE receives this information, in step ST2902, it may notify the gNB of a configuration response message. This ensures that the gNB can reliably determine whether or not the UE has received information about coverage expansion. If the gNB does not receive a configuration response message from the UE, it may notify the UE of coverage expansion information again.

[0434] A predetermined period may be set as a method for determining whether the gNB cannot receive a configuration response message regarding coverage expansion from the UE. This predetermined period may be managed by a timer. For example, the gNB may start a timer when it receives notification of a message containing information about coverage expansion, and if it receives a configuration response message regarding coverage expansion within the timer, i.e., within the predetermined period, it will determine that the configuration response message has been received. If it fails to receive a configuration response message regarding coverage expansion within the timer, it will determine that the configuration response message could not be received.

[0435] In this way, the UE can receive information about coverage expansion when it is in the RRC_CONNECTED state. The UE can receive information about coverage expansion when it is in a state where communication is functioning normally.

[0436] In step ST2903, the UE enters an abnormal state, such as the occurrence of a beam failer. The UE performs BFR processing due to the occurrence of the beam failer. In step ST2904, the UE initiates initial access processing to the gNB. In this initial access processing, the UE uses the coverage expansion information received in step ST2901. This improves the robustness of the transition process to the RRC_CONNECTED state. Furthermore, since there is no need to send or receive coverage expansion information from the cell when transitioning to the RRC_CONNECTED state, the UE can return to the RRC_CONNECTED state more quickly.

[0437] For example, as the processing in step ST2904, the setting of the number of repetitions when transmitting MSG3, as disclosed in Figure 25 used in the description of Embodiment 3, may be performed. In this case, as the processing in step ST2904, SSB transmission and reception and the processing of steps ST2201 to ST2208 in Figure 25 are performed. In step ST2901, the gNB includes information relating the number of retransmissions and the number of repeated transmissions of MSG3 in the coverage expansion information for the UE. The UE uses this information to perform the processing of steps ST2201 to ST2208. In this way, repeated transmission of MSG3 is possible in the initial access processing of step ST2904. Therefore, it is possible to improve the reception quality of MSG3 in the gNB and expand the coverage of MSG3.

[0438] In Figure 29, the same gNB is accessed before and after the beam failer, but the accessed gNB may be different before and after the beam failer. If they are different, it is advisable to use information about coverage expansion of adjacent cells.

[0439] As mentioned above, it was assumed that the gNB accessed before and after the beam failer is different, but it is also possible that what differs before and after the beam failer is the cells that make up the gNB.

[0440] By using the method disclosed in this embodiment, coverage can be expanded when performing initial access processing in an abnormal state, and the robustness of the transition process to the RRC_CONNECTED state can be improved. Furthermore, it becomes possible to transition to the RRC_CONNECTED state at an earlier stage.

[0441] The embodiments and their variations described above are merely illustrative, and these embodiments and their variations can be freely combined. Furthermore, any component of each embodiment and its variations can be modified or omitted as appropriate.

[0442] The methods disclosed in the above-described embodiments and their modifications may be appropriately applied to a communication system using a gNB configured to be divided into a CU and a DU. For example, in Embodiment 1, the CU notifies the DU of information regarding the DMRS settings of the PUSCH to be notified via PDCCH. F1 signaling may be used for notification from the CU to the DU. The DU includes the information regarding the DMRS settings of the PUSCH received from the CU in the DCI and notifies the UE via PDCCH. If the CU determines the DMRS settings for PUSCH retransmission, it is advisable to notify the DU of information regarding the DMRS settings of the PUSCH to be notified via PDCCH. The DU can then perform dynamic DMRS settings for PUSCH for the UE. In this way, the effects shown in the above-described embodiments and their modifications can be obtained even in a communication system using a gNB configured to be divided into a CU and a DU.

[0443] For example, in the embodiments and their modifications described above, a subframe is an example of a communication time unit in a fifth-generation communication system. The communication time unit may also be a scheduling unit. Furthermore, in the embodiments and their modifications described above, the processing described as being performed in subframe units may also be performed in TTI units, slot units, sub-slot units, or mini-slot units.

[0444] Although this disclosure has been described in detail, the above description is illustrative and not limiting in all respects. It is understood that countless variations not illustrated are conceivable. [Explanation of Symbols]

[0445] 200,210 Communication system, 202 Communication terminal equipment (communication terminal), 203,207,213,217,223-1,224-1,224-2,226-1,226-2,750 Base station equipment (base station), 204 MME / S-GW section (MME section), 204a MME, 214 AMF / SMF / UPF section (5GC section), 218 Central unit, 219 Distributed unit, 301,403 Protocol processing section, 302 Application section, 303,404 Transmit data buffer section, 304,405 Encoder section, 305,406 Modulation section, 306,407 Frequency conversion section, 307-1~307-4,408-1~408-4 Antenna, 308,409 Demodulation section, 309,410 Decoder section, 310, 411, 506, 526 Control section, 401 EPC communication section, 402 Other base station communication section, 412 5GC communication section, 501 PDN GW communication section, 502, 522 Base station communication section, 503, 523 User plane communication section, 504 HeNBGW communication section, 505, 525 Control plane control section, 505-1, 525-1 NAS security section, 505-2 SAE bearer control section, 505-3, 525-3 Idle state mobility management section, 521 Data Network communication section, 525-2 PDU session control section, 527 Session management section, 751-1~751-8 Beam.

Claims

1. Base station and A communication terminal connected to the aforementioned base station, Equipped with, When the base station causes the communication terminal to transmit a data signal, it notifies the communication terminal of information regarding the demodulation reference signal to be transmitted along with the data signal. The communication terminal transmits a data signal and a demodulation reference signal in accordance with the information notified from the base station. When the base station causes the communication terminal to perform the initial transmission of a data signal, and when the communication terminal causes the data signal to perform a retransmission, it notifies the communication terminal of information regarding the demodulation reference signal to be transmitted along with the data signal. Based on the reception quality of the demodulation reference signal or data signal in the initial transmission, the base station notifies the communication terminal of information regarding the number of demodulation reference signals in the retransmission. The base station reduces the number of demodulation reference signals in the frequency axis direction such that, when the communication terminal repeatedly transmits a data signal, the number of demodulation reference signals transmitted with the data signal from the second time onward is less than the number of demodulation reference signals transmitted with the data signal the first time. A communication system characterized by the following features.

2. The base station reduces the number of demodulation reference signals in the frequency axis direction and reduces the number of demodulation reference signals in the time axis direction. The communication system according to feature 1.

3. If the communication terminal is unable to place the demodulation reference signal on the physical uplink shared channel in accordance with the information notified by the base station, it transmits a physical uplink shared channel that does not include the demodulation reference signal. When the base station receives a data signal on a physical uplink shared channel that does not include a demodulation reference signal, it performs demodulation processing of the received data signal using the already received demodulation reference signal. The communication system according to claim 1 or 2, characterized in that it is the same as described in claim 1 or 2.

4. When the base station receives a request from the communication terminal for repeated transmission of a data signal, it determines the content of the repeated transmission of the data signal to be performed by the communication terminal based on the content of the request. A communication system according to any one of the features 1 to 3.

5. The base station transmits the synchronization signal and the physical broadcast channel by assigning them to different symbols. The communication system according to any one of features 1 to 4.

6. The base station repeatedly transmits a symbol on which the physical broadcast channel is located. The communication system according to claim 5, characterized in that it is the same as described in claim 5.

7. The base station, in random access processing for the communication terminal to connect to the base station, repeatedly transmits scheduling information for allocating resources to the communication terminal using different beams. A communication system according to any one of claims 1 to 6.

8. The base station, in random access processing for the communication terminal to connect to the base station, repeatedly sends a response message to the communication terminal using different beams. A communication system according to any one of features 1 to 7.

9. The base station instructs the communication terminal on the number of times to resend a message in the random access process for the communication terminal to connect to the base station, and the number of times to repeatedly send the message in each of the message transmission processes. The communication system according to any one of the features 1 to 8.

10. If the base station meets a predetermined condition while the communication terminal is repeatedly transmitting the message, it instructs the communication terminal to terminate the repeated transmission. The communication system according to feature 9.

11. The base station determines the number of times to repeat the transmission based on which predetermined group the message sent from the communication terminal at the start of the random access processing belongs. The communication system according to claim 9 or 10, characterized by the features described above.

12. The base station instructs the communication terminal on the transmission power to retransmit a message during random access processing for the communication terminal to connect to the base station. The communication system according to any one of features 1 to 11.

13. The base station notifies the communication terminal of information regarding coverage expansion at a predetermined time. The communication terminal, upon receiving notification of information regarding the coverage expansion from the base station, retains the information, and, if initial access processing to the base station is required, uses the retained information to perform the initial access processing. The communication system according to any one of features 1 to 12.

Images