Communication system and communication terminal

Abstract

This communication system comprises a base station and a communication terminal that supports inter-terminal communication. Upon entering a state of being able to perform inter-terminal communication with another communication terminal located in the range of another base station which differs from the base station to which the communication terminal is connected, the communication terminal notifies the base station, to which the communication terminal is connected, of connection status information that indicates that said state has been entered. Having received notification of the connection status information, the base station determines, on the basis of the connection status information, whether or not the connection destination of the communication terminal should be changed, via a relay communication terminal which is said another communication terminal, to said another base station having the range in which the relay communication terminal is located. If the connection destination of the communication terminal which provided notification of the connection status information is to be changed, the base station requests that the communication terminal release the connection. After the communication terminal notifies the base station, to which the communication terminal is connected, of the connection status information, if the base station requests that the connection be released, the communication terminal releases the connection to the base station and, via said another communication terminal, establishes a connection to said another base station.

Description

Communication system and communication terminal

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

[0002] The 3GPP (3rd Generation Partnership Project), a standardization organization for mobile communication systems, is considering a communication method called Long Term Evolution (LTE) for wireless sections and System Architecture Evolution (SAE) for the overall system configuration including the core network and radio access network (hereinafter collectively referred to as the network) (see, for example, Non-Patent Documents 1 to 5). This communication method is also called a 3.9G (3.9 Generation) system.

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

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

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

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

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

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

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

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

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

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

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

[0014] A downlink reference signal (RS) is a known symbol in an LTE communication system. The following five types of downlink reference signals are defined: a cell-specific reference signal (CRS), an MBSFN reference signal, a demodulation reference signal (DM-RS) which is a UE-specific reference signal, a positioning reference signal (PRS), and a channel state information reference signal (CSI-RS). Measurement of the physical layer of a communication terminal includes measurement of the reference signal received power (RSRP).

[0015] Similarly, the uplink reference signal is a symbol known in the LTE communication system. The following two types of uplink reference signals are defined: a data demodulation reference signal (DM-RS) and a sounding reference signal (SRS).

[0016] The transport channels described in Non-Patent Document 1 (Chapter 5) will be described below. Among the downlink transport channels, a broadcast channel (BCH) is broadcast to the entire coverage of the base station (cell). The BCH is mapped to a physical broadcast channel (PBCH).

[0017] Retransmission control using Hybrid ARQ (HARQ) is applied to the Downlink Shared Channel (DL-SCH). The DL-SCH can be broadcast to the entire coverage of a base station (cell). The DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called persistent scheduling. The DL-SCH supports discontinuous reception (DRX) in communication terminals to reduce power consumption of the communication terminals. The DL-SCH is mapped to the Physical Downlink Shared Channel (PDSCH).

[0018] The Paging Channel (PCH) supports DRX of communication terminals to enable low power consumption of the communication terminals. The PCH is required to broadcast to the entire coverage of the base station (cell). The PCH is mapped to physical resources such as the Physical Downlink Shared Channel (PDSCH) that can be dynamically used for traffic.

[0019] The Multicast Channel (MCH) is used for broadcasting to the entire coverage of a base station (cell). The MCH supports SFN combining of MBMS (Multimedia Broadcast Multicast Service) services (MTCH and MCCH) in multi-cell transmission. The MCH supports semi-static resource allocation. The MCH is mapped to the PMCH.

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

[0021] The Random Access Channel (RACH) is limited to control information, has a risk of collision, and is mapped to the Physical Random Access Channel (PRACH).

[0022] The following describes 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 functions effectively through retransmission even for transmission paths whose communication quality varies. In particular, by combining the reception result of the initial transmission and the reception result of the retransmission when retransmitting, it is possible to obtain further quality improvement.

[0023] An example of a retransmission method will be described below. If the receiving side is unable to decode the received data correctly, in other words, if a CRC (Cyclic Redundancy Check) error occurs (CRC=NG), the receiving side will send a "Nack" to the transmitting side. The transmitting side, having received the "Nack", will retransmit the data. If the receiving side is able to decode the received data correctly, in other words, if no CRC error occurs (CRC=OK), the receiving side will send an "Ack" to the transmitting side. The transmitting side, having received the "Ack", will send the next data.

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

[0025] The Paging Control Channel (PCCH) is a downlink channel for transmitting paging information and changes to system information. The PCCH is used when the cell location of a communication terminal is unknown to the network. The PCCH, which is a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

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

[0027] The Multicast Control Channel (MCCH) is a downlink channel for point-to-multipoint transmission. The MCCH is used to transmit MBMS control information for one or several MTCHs from the network to communication terminals. The MCCH is used only by communication terminals receiving MBMS. The MCCH is mapped to the Multicast Channel (MCH), which is a transport channel.

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

[0029] A Dedicated Traffic Channel (DTCH) is a point-to-point communication channel for transmitting user information to an individual communication terminal. DTCH exists in both uplink and downlink. In uplink, DTCH is mapped to an uplink shared channel (UL-SCH) and in downlink, it is mapped to a downlink shared channel (DL-SCH).

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

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

[0032] The location of a communication terminal is tracked in units of an area consisting of one or more cells. Location tracking is performed to track the location of the communication terminal even when it is in standby mode and to enable the communication terminal to be called, in other words, to enable the communication terminal to receive calls. The area for tracking the location of this communication terminal is called a tracking area.

[0033] 3GPP is also currently working on the development of the Long Term Evolution Advanced (LTE-A) standard as Release 10 (see Non-Patent Documents 3 and 4). LTE-A is based on the LTE wireless communication system, and is configured by adding several new technologies to it.

[0034] In the LTE-A system, in order to support wider frequency bandwidths (transmission bandwidths) up to 100 MHz, carrier aggregation (CA) is being considered, which aggregates (also referred to as "aggregation") two or more component carriers (CCs). CA is described in Non-Patent Document 1.

[0035] When CA is configured, a communication terminal (UE) has only one RRC connection with the network (NW). In the RRC connection, one serving cell provides NAS mobility information and security input. This cell is called a primary cell (PCell). In the downlink, the carrier corresponding to the PCell is the downlink primary component carrier (DL PCC). In the uplink, the carrier corresponding to the PCell is the uplink primary component carrier (UL PCC).

[0036] Depending on the UE's capabilities, a secondary cell (SCell) is configured to form a serving cell set together with the PCell. In the downlink, the carrier corresponding to the SCell is the Downlink Secondary Component Carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is the Uplink Secondary Component Carrier (UL SCC).

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

[0038] Furthermore, new technologies for LTE-A include a technology that supports wider bandwidth (Wider Bandwidth Extension) and a Coordinated Multiple Point transmission and reception (CoMP) technology. CoMP, which is being studied for LTE-A by 3GPP, is described in Non-Patent Document 1.

[0039] Furthermore, in order to handle future massive traffic volumes, 3GPP is considering the use of small eNBs (hereinafter sometimes referred to as "small-scale base station devices") that configure small cells. For example, technologies are being considered that improve frequency utilization efficiency and increase communication capacity by installing a large number of small eNBs and configuring a large number of small cells. Specifically, there is dual connectivity (abbreviated as DC), in which a UE connects to two eNBs to communicate. DC is described in Non-Patent Document 1.

[0040] Of the eNBs that perform dual connectivity (DC), one may be referred to as a "master eNB (abbreviated as MeNB)" and the other as a "secondary eNB (abbreviated as SeNB)."

[0041] Mobile network traffic volume is on the rise, and communication speeds are also increasing. Once LTE and LTE-A begin full-scale operation, communication speeds are expected to increase even further.

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

[0043] The requirements for a 5G wireless access system are that it will have 1,000 times the system capacity, 100 times the data transmission speed, one-tenth (1 / 10) the data processing delay, and 100 times the number of simultaneous connections of communication terminals compared to an LTE system, while also achieving further reductions in power consumption and lower costs for the equipment.

[0044] To meet these demands, 3GPP is currently working on 5G standards as Release 15 (see Non-Patent Documents 6 to 19). 5G wireless access technology is called "New Radio Access Technology" ("New Radio" is abbreviated as "NR").

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

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

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

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

[0049] In the NR frame structure, various subcarrier spacings, i.e., various numerologies, are supported. In NR, regardless of the numerology, one subframe is 1 millisecond, and one slot consists of 14 symbols. In addition, the number of slots included in one subframe is one in a numerology with a subcarrier spacing of 15 kHz, but in other numerologies, the number of slots increases in proportion to the subcarrier spacing (see Non-Patent Document 13 (3GPP TS38.211)).

[0050] The downlink synchronization signal in NR is transmitted from the base station as a synchronization signal burst (hereinafter sometimes referred to as an SS burst) at a predetermined cycle for a predetermined duration. The SS burst is composed of a synchronization signal block (hereinafter sometimes referred to as an SS block) for each beam of the base station.

[0051] The base station transmits the SS block of each beam by changing the beam during the duration of the SS burst. The SS block consists of the P-SS, S-SS, and PBCH.

[0052] In NR, the influence of phase noise is reduced by adding a phase tracking reference signal (PTRS) as a downlink reference signal of NR. PTRS is also added to the uplink reference signal in the same way as in the downlink.

[0053] In NR, in order to flexibly switch between DL and UL within a slot, slot format indication (SFI) has been added to the information contained in the PDCCH.

[0054] In addition, in NR, the base station pre-sets a portion of the carrier frequency band (hereinafter sometimes referred to as the Bandwidth Part (BWP)) for the UE, and the UE transmits and receives data to and from the base station using this BWP, thereby reducing power consumption in the UE.

[0055] In 3GPP, the following DC forms are being considered: DC using LTE base stations and NR base stations connected to EPC, DC using NR base stations connected to a 5G core system, and DC using LTE base stations 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 (which may be applications) using side link (SL) communication (also referred to as PC5 communication) in both the Evolved Packet System (EPS) described below and the 5G core system (see Non-Patent Documents 1, 16, 20, 21, 22, and 23). Services using SL communication include, for example, vehicle-to-everything (V2X) services and proximity services.

[0057] Additionally, 3GPP is currently studying several new technologies, such as positioning technology (see Non-Patent Documents 24 to 27) and integrated access and backhaul (IAB) (see Non-Patent Documents 16, 28, and 29).

[0058] As a positioning technology, for example, a positioning method using round trip delay times between a UE and multiple base stations (Multi-Round Trip Time: Multi-RTT) is being considered (see Non-Patent Document 24).

[0059] As IAB, for example, multiplexing within radio resources and reducing latency of access links, which are links between UEs and base stations, and backhaul links, which are links between base stations, are being considered (see Non-Patent Documents 16, 28, and 29).

[0060] 3GPP TS 36.300 V16.2.03GPP S1-0834613GPP TR 36.814 V9.2.03GPP TR 36.912 V16.0.0 “Scenarios, requirements and KPIs for 5G mobile and wireless ICT-317669-METIS / D1.13GPP TR 23.799 V14.0.03GPP TR 38.801 V14.0.03GPP TR 38.802 V14.2.03GPP TR 38.804 V14.0.03GPP TR 38.912 V16.0.03GPP RP-1721153GPP TS 37.340 V16.2.03GPP TS 38.211 V16.2.03GPP TS 38.213 V16.2.03GPP TS 38.214 V16.2.03GPP TS 38.300 V16.2.03GPP TS 38.321 V16.1.03GPP TS 38.212 V16.2.03GPP TS 38.331 V16.1.03GPP TR 23.703 V12.0.03GPP TS 23.501 V16.5.03GPP TS 23.287 V16.3.03GPP TS 23.303 V16.0.03GPP TS 38.305 V16.0.03GPP RP-2009283GPP TS 37.355 V16.0.03GPP R1-20044923GPP RP-2012933GPP TS 38.401 V16.0.03GPP TS 23.263 V16.4.03GPP TS 23.003 V16.4.03GPP TS 38.304 V16.2.0

[0061] Support for various services using SL communication (also referred to as PC5 communication) is being considered in both EPS and 5G core systems (see Non-Patent Documents 1, 16, 20, 21, 22, and 23). In SL communication, communication is performed between terminals. In SL communication, not only direct communication between terminals but also communication between a UE and a network via a relay has been proposed (see Non-Patent Documents 20 and 23). In a system that supports communication via such a relay, how to improve the communication quality between a terminal and a network becomes an issue.

[0062] In view of the above-mentioned problems, one of the objects of the present disclosure is to improve communication quality in a communication system using terminal-to-terminal communication.

[0063] In order to solve the above-mentioned problems and achieve the object, a communication system according to the present disclosure includes a base station and a communication terminal that supports terminal-to-terminal communication in which communication terminals communicate directly with each other. When a communication terminal becomes capable of terminal-to-terminal communication with another communication terminal located in a base station different from the base station to which it is currently connected, it notifies the currently connected base station of connection status information indicating that this state has occurred. The base station that has received the notification of the connection status information determines, based on the connection status information, whether to change the connection destination of the communication terminal that notified the connection status information to another base station located in the range of the relay communication terminal, which is another communication terminal. If the connection destination of the communication terminal that notified the connection status information is to be changed, it requests the communication terminal to release the connection. After notifying the currently connected base station of the connection status information, if the base station requests the communication terminal to release the connection, the communication terminal releases the connection with the base station and connects to the other base station via the other communication terminal.

[0064] According to the present disclosure, it is possible to improve communication quality in a communication system that uses terminal-to-terminal communication.

[0065] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings.

[0066] 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. FIG. 1 is a block diagram showing the overall configuration of an LTE communication system 200 being discussed in 3GPP. FIG. 2 is a block diagram showing the overall configuration of an NR communication system 210 being discussed in 3GPP. FIG. 3 is a block diagram showing the configuration of a DC by an eNB and a gNB connected to an EPC. FIG. 4 is a block diagram showing the configuration of a DC by a gNB connected to an NG core. FIG. 5 is a block diagram showing the configuration of a DC by an eNB and a gNB connected to an NG core. FIG. 6 is a block diagram showing the configuration of a mobile terminal 202 shown in FIG. 2. FIG. 7 is a block diagram showing the configuration of a base station 203 shown in FIG. 2. FIG. 8 is a block diagram showing the configuration of an MME. FIG. 9 is a block diagram showing the configuration of a 5GC unit. FIG. 10 is a flowchart showing an overview of from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. FIG. 11 is a diagram showing an example of the configuration of a cell in an NR system. FIG. 12 is a sequence diagram showing an example of a method for making a remote UE RRC_IDLE before the remote UE is RRC-connected to a gNB via a relay UE, for the first embodiment. 10 is a sequence diagram showing another example of a method for setting a remote UE to RRC_IDLE before the remote UE is RRC-connected to a gNB via a relay UE, for the first embodiment. FIG. 11 is a sequence diagram showing another example of a method for setting a remote UE to RRC_IDLE before the remote UE is RRC-connected to a gNB via a relay UE, for the first embodiment. FIG. 12 is a sequence diagram showing an example of a method for HOing a remote UE between a gNB to which the remote UE is connected and a gNB to which the relay UE is connected, for a first variant of the first embodiment. FIG. 13 is a sequence diagram showing an example of a method for a remote UE to use system information received from a gNB #1, for the second embodiment. FIG. 14 is a sequence diagram showing an example of a method for a gNB to instruct a remote UE on a gNB from which to receive system information, for the second variant of the second embodiment. FIG. 15 is a sequence diagram showing an example of a method for a remote UE to perform registration due to a TA change, for a second variant of the second embodiment. FIG. 16 is a sequence diagram showing an example of a method for receiving paging from a gNB belonging to a TA in which the remote UE is located, for a third variant of the second embodiment.10 is a sequence diagram showing an example of a method in which a remote UE transmits an SR to gNB #1 in accordance with embodiment 3. FIG. 11 is a sequence diagram showing an example of a method in which a remote UE is HO'd from gNB #1 to gNB #2 in accordance with variant 1 of embodiment 1.

[0067] First Embodiment Fig. 2 is a block diagram showing the overall configuration of an LTE communication system 200 being discussed in 3GPP. Fig. 2 will be described. The radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 202, which is a communication terminal device, is capable of wireless communication with a base station device (hereinafter referred to as "base station (E-UTRAN NodeB: eNB)") 203, and transmits and receives signals via wireless communication.

[0068] Here, the term "communication terminal device" includes not only mobile terminal devices such as mobile cell phone terminal devices, but also stationary devices such as sensors. In the following description, the term "communication terminal device" may be simply referred to as a "communication terminal."

[0069] If control protocols for mobile terminals 202, such as RRC (Radio Resource Control), and user planes (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), terminate at base stations 203, then E-UTRAN is composed of one or more base stations 203.

[0070] The control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs broadcasting, paging, RRC connection management, etc. The states of the base station 203 and the mobile terminal 202 in RRC include RRC_IDLE and RRC_CONNECTED.

[0071] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell re-selection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can transmit and receive data to and from the network. In addition, in RRC_CONNECTED, handover (HO), measurement of neighbor cells, etc. are performed.

[0072] The base station 203 is configured by one or more eNBs 207. A system configured by an EPC (Evolved Packet Core) which is a core network and an E-UTRAN 201 which is a radio access network is called an EPS (Evolved Packet System). The EPC which is a core network and the E-UTRAN 201 which is a radio access network may be collectively referred to as a "network."

[0073] The eNB 207 is connected to a Mobility Management Entity (MME), or a Serving Gateway (S-GW), or an MME / S-GW unit (hereinafter sometimes referred to as an "MME unit") 204 including an MME and an S-GW via an S1 interface, and control information is communicated between the eNB 207 and the MME unit 204. Multiple MME units 204 may be connected to one eNB 207. The eNBs 207 are connected to each other via an X2 interface, and control information is communicated between the eNBs 207.

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

[0075] The base station 203 may configure one cell or multiple cells. Each cell has a predetermined range as its coverage, which is the range within which communication with the mobile terminal 202 is possible, and wireless communication with the mobile terminal 202 is performed within the coverage. When one base station 203 configures multiple cells, each cell is configured to be able to communicate with the mobile terminal 202.

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

[0077] If control protocols for UE202, such as RRC (Radio Resource Control), and user planes (hereinafter sometimes referred to as U-Plane), such as SDAP (Service Data Adaptation Protocol), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate at the NR base station 213, the NG-RAN is composed of one or more NR base stations 213.

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

[0079] RRC_IDLE and RRC_CONNECTED are the same as those in the LTE system. RRC_INACTIVE maintains the connection between the 5G core and the NR base station 213, and performs system information (SI), paging, cell reselection, mobility, etc.

[0080] The gNB217 is connected to an AMF / SMF / UPF unit (hereinafter sometimes referred to as the "5GC unit") 214 including an Access and Mobility Management Function (AMF), a Session Management Function (SMF), or a User Plane Function (UPF), or an AMF, SMF, and UPF, via an NG interface. Control information and / or user data is communicated between the gNB217 and the 5GC unit 214. The NG interface is a collective term for the N2 interface between the gNB217 and the AMF, the N3 interface between the gNB217 and the UPF, the N11 interface between the AMF and the SMF, and the N4 interface between the UPF and the SMF. Multiple 5GC units 214 may be connected to one gNB217. The gNBs 217 are connected via an Xn interface, and control information and / or user data is communicated between the gNBs 217.

[0081] The 5GC unit 214 is an upper device, specifically an upper node, and distributes paging signals to one or more base stations 203 and / or base stations 213. The 5GC unit 214 also performs mobility control in an idle state. The 5GC unit 214 manages a tracking area list when the mobile terminal 202 is in an idle state, an inactive state, or an active state. The 5GC unit 214 initiates a paging protocol by transmitting a paging message to a cell belonging to a tracking area in which the mobile terminal 202 is registered.

[0082] The NR base station 213 may also configure one or more cells, like the base station 203. When one NR base station 213 configures multiple cells, each cell is configured to be able to communicate with the UE 202.

[0083] The gNB 217 may be divided into a central unit (hereinafter sometimes referred to as CU) 218 ​​and a distributed unit (hereinafter sometimes referred to as DU) 219. One CU 218 is configured in the gNB 217. One or more DUs 219 are configured in the gNB 217. The CU 218 is connected to the DU 219 via an F1 interface, and control information and / or user data is communicated between the CU 218 and the DU 219.

[0084] In a 5G communication system, a Unified Data Management (UDM) function and a 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 FIG. 3 .

[0085] In a 5G communication system, a Location Management Function (LMF) described in Non-Patent Document 24 (3GPP TS 38.305) may be provided. The LMF may be connected to a base station via an AMF as disclosed in Non-Patent Document 30 (3GPP TS 23.263).

[0086] A 5G communication system may include a Non-3GPP Interworking Function (N3IWF) described in Non-Patent Document 21 (3GPP TS23.501). The N3IWF may terminate an Access Network (AN) between the UE and the N3IWF in non-3GPP access between the UE and the N3IWF.

[0087] Figure 4 is a diagram showing the configuration of DC by eNB and gNB connected to EPC. In Figure 4, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 4, eNB223-1 is the master base station, and gNB224-2 is the secondary base station (this DC configuration may be referred to as EN-DC). In Figure 4, an example is shown in which U-Plane connection between the MME unit 204 and gNB224-2 is performed via eNB223-1, but it may also be performed directly between the MME unit 204 and gNB224-2.

[0088] Figure 5 is a diagram showing the configuration of DC by gNB 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 is the master base station, and gNB224-2 is the secondary base station (this DC configuration may be referred to as NR-DC). In Figure 5, an example is shown in which the U-Plane connection between the 5GC unit 214 and gNB224-2 is made via gNB224-1, but it may also be made directly between the 5GC unit 214 and gNB224-2.

[0089] Figure 6 is a diagram showing the configuration of DC by eNB and gNB connected to the NG core. In Figure 6, the solid line indicates the U-Plane connection, and the dashed line indicates the C-Plane connection. In Figure 6, eNB226-1 is the master base station, and gNB224-2 is the secondary base station (this DC configuration may be referred to as NG-EN-DC). In Figure 6, an example is shown in which the U-Plane connection between the 5GC unit 214 and the gNB224-2 is performed via eNB226-1, but it may also be performed directly between the 5GC unit 214 and the gNB224-2.

[0090] Figure 7 is a diagram showing another configuration of DC by eNB and gNB connected to the NG core. In Figure 7, the solid line indicates the U-Plane connection, and the dashed line indicates the C-Plane connection. In Figure 7, the gNB224-1 becomes the master base station, and the eNB226-2 becomes the secondary base station (this DC configuration may be referred to as NE-DC). In Figure 7, an example is shown in which the U-Plane connection between the 5GC unit 214 and the eNB226-2 is made via the gNB224-1, but it may also be made directly between the 5GC unit 214 and the eNB226-2.

[0091] FIG. 8 is a block diagram showing the configuration of mobile terminal 202 shown in FIG. 2. The transmission process of mobile terminal 202 shown in FIG. 8 will be described. First, control data from protocol processing unit 301 and user data from application unit 302 are stored in transmission data buffer unit 303. The data stored in transmission data buffer unit 303 is passed to encoder unit 304, where it undergoes encoding processes such as error correction. Some data may be output directly from transmission data buffer unit 303 to modulation unit 305 without undergoing encoding processes. The data encoded by encoder unit 304 is modulated by modulation unit 305. Precoding in MIMO may be performed by modulation unit 305. The modulated data is converted into a baseband signal, then output to frequency conversion unit 306, where it is converted to a radio transmission frequency. Then, a transmission signal is transmitted to base station 203 from antennas 307-1 to 307-4. While FIG. 8 illustrates an example in which the number of antennas is four, the number of antennas is not limited to four.

[0092] The reception process of the mobile terminal 202 is performed as follows: Radio signals from the base station 203 are received by the antennas 307-1 to 307-4. The received signals are converted from a radio reception frequency to a baseband signal by the frequency converter 306, and demodulated by the demodulator 308. The demodulator 308 may also perform weight calculation and multiplication. The demodulated data is passed to the decoder 309, where it undergoes decoding processes such as error correction. Of the decoded data, control data is passed to the protocol processor 301, and user data is passed to the application unit 302. The series of processes of the mobile terminal 202 are controlled by the controller 310. Therefore, although not shown in FIG. 8 , the controller 310 is connected to each of the units 301 to 309. The controller 310 is implemented, for example, by a processing circuit including a processor and a memory. In other words, the controller 310 is implemented by the processor executing a program in which the series of processes of the mobile terminal 202 are described. A program describing a series of processes of 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. Control unit 310 may be realized by a dedicated processing circuit such as an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a DSP (Digital Signal Processor). In FIG. 8 , the number of antennas used by mobile terminal 202 for transmission and the number of antennas used for reception may be the same or different.

[0093] 9 is a block diagram showing the configuration of the base station 203 shown in FIG. 2. The transmission process of the base station 203 shown in FIG. 9 will be described. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (such as the MME unit 204). The 5GC communication unit 412 transmits and receives data between the base station 203 and the 5GC (such as the 5GC unit 214). The other base station communication unit 402 transmits and receives data 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, and 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.

[0094] The data stored in the transmission data buffer unit 404 is passed to the encoder unit 405, where it undergoes encoding processes such as error correction. Some data may be output directly from the transmission data buffer unit 404 to the modulator unit 406 without undergoing encoding processes. The encoded data is modulated by the modulator unit 406. The modulator unit 406 may also perform precoding in MIMO. The modulated data is converted into a baseband signal, and then output to the frequency converter unit 407, where it is converted into a radio transmission frequency. Then, the transmission signal is transmitted to one or more mobile terminals 202 from antennas 408-1 to 408-4. While FIG. 9 illustrates an example in which the number of antennas is four, the number of antennas is not limited to four.

[0095] The reception process of the base station 203 is performed as follows: A radio signal from one or more mobile terminals 202 is received by the antenna 408. The received signal is converted from a radio reception frequency to a baseband signal by the frequency conversion unit 407, and demodulated by the demodulation unit 409. The demodulated data is passed to the decoder unit 410, where decoding processes such as error correction are performed. Of the decoded data, 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 user data is passed to the 5GC communication unit 412, the EPC communication unit 401, or the other base station communication unit 402. A series of processes of the base station 203 is controlled by the control unit 411. Therefore, although the control unit 411 is omitted in FIG. 9 , it is connected to each of the units 401 to 410 and 412. Similar to the control unit 310 of the mobile terminal 202 described above, the control unit 411 is realized by a processing circuit including a processor and a memory, or a dedicated processing circuit such as an FPGA, an ASIC, or a DSP. In Fig. 9, the number of antennas used by the base station 203 for transmission and the number of antennas used for reception may be the same or different.

[0096] 9 is a block diagram showing the configuration of base station 203, but a similar configuration may also be used for base station 213. In addition, in FIGS. 8 and 9, the number of antennas of mobile terminal 202 and the number of antennas of base station 203 may be the same or different.

[0097] FIG. 10 is a block diagram showing the configuration of an MME. FIG. 10 shows the configuration of an MME 204a included in the MME unit 204 shown in FIG. 2 described above. A PDN GW communication unit 501 transmits and receives data between the MME 204a and a PDN GW (Packet Data Network Gateway). A base station communication unit 502 transmits and receives data via the S1 interface between the MME 204a and a base station 203. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 501 to the base station communication unit 502 via a user plane communication unit 503, and transmitted to one or more base stations 203. If the data received from the base station 203 is user data, the user data is passed from the base station communication unit 502 to the PDN GW communication unit 501 via the user plane communication unit 503, and transmitted to the PDN GW.

[0098] 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.

[0099] The HeNBGW communication unit 504 transmits and receives data between the MME 204a and a Home-eNB Gateway (HeNB GW). 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.

[0100] The control plane control unit 505 includes a NAS security unit 505-1, an SAE bearer control unit 505-2, an idle state mobility management unit 505-3, and the like, and performs overall processing for the control plane (hereinafter sometimes referred to as the C-Plane). The NAS security unit 505-1 performs security for NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 505-2 performs management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 505-3 performs mobility management in the idle state (idle state: also referred to as LTE-IDLE state or simply idle), generation and control of paging signals in the idle state, addition, deletion, update, search, and tracking area list management for one or more mobile terminals 202 under its control.

[0101] The MME 204a distributes paging signals to one or more base stations 203. The MME 204a also performs mobility control in an idle state. The MME 204a manages a tracking area list when the mobile terminal 202 is in an idle state and an active state. The MME 204a initiates a paging protocol by transmitting a paging message to cells belonging to a tracking area in which the mobile terminal 202 is registered. The idle state mobility management unit 505-3 may manage the CSG, CSG ID, and whitelist of the eNB 207 connected to the MME 204a.

[0102] A series of processes of the MME 204a is controlled by a control unit 506. Therefore, although not shown in Fig. 10, the control unit 506 is connected to each of the units 501 to 505. Similar to the control unit 310 of the mobile terminal 202 described above, the control unit 506 is realized by a processing circuit including a processor and a memory, or a dedicated processing circuit such as an FPGA, an ASIC, or a DSP.

[0103] FIG. 11 is a block diagram showing the configuration of the 5GC unit. FIG. 11 shows the configuration of the 5GC unit 214 shown in FIG. 3 described above. FIG. 11 shows a case where the 5GC unit 214 shown in FIG. 5 includes an AMF configuration, an SMF configuration, and a UPF configuration. The Data Network communication unit 521 transmits and receives data between the 5GC unit 214 and the Data Network. The base station communication unit 522 transmits and receives data via the S1 interface between the 5GC unit 214 and the base station 203, and / or the NG interface between the 5GC unit 214 and the base station 213. If the data received from the Data Network is user data, the user data is passed from the Data Network communication unit 521 to the base station communication unit 522 via the user plane communication unit 523 and transmitted to one or more base stations 203 and / or 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.

[0104] 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 the base station 203 and / or base station 213 is control data, the control data is passed from the base station communication unit 522 to the control plane control unit 525. The control plane control unit 525 passes the control data to the session management unit 527.

[0105] The control plane control unit 525 includes a NAS security unit 525-1, a PDU session control unit 525-2, an idle state mobility management unit 525-3, and the like, and performs overall processing for the control plane (hereinafter sometimes referred to as the C-Plane). The NAS security unit 525-1 performs security for NAS (Non-Access Stratum) messages, etc. The PDU session control unit 525-2 performs management of PDU sessions between the mobile terminal 202 and the 5GC unit 214, etc. The idle state mobility management unit 525-3 performs mobility management in the standby state (idle state: RRC_IDLE state, or simply referred to as idle), generation and control of paging signals in the standby state, addition, deletion, update, search, tracking area list management, etc. of one or more mobile terminals 202 under its control.

[0106] A series of processes of the 5GC unit 214 is controlled by a control unit 526. Therefore, although the control unit 526 is omitted in Fig. 11, it is connected to each of the units 521 to 523, 525, and 527. Similar to the control unit 310 of the mobile terminal 202 described above, the control unit 526 is realized by a processing circuit including a processor and a memory, or a dedicated processing circuit such as an FPGA, an ASIC, or a DSP.

[0107] Next, an example of a cell search method in a communication system is shown. Fig. 12 is a flowchart showing an outline of the process from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. When the communication terminal starts a cell search, in step ST601, it synchronizes slot timing and frame timing using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a surrounding base station.

[0108] P-SS and S-SS are collectively called a synchronization signal (SS). A synchronization code is assigned to the synchronization signal (SS) in one-to-one correspondence with the PCI assigned to each cell. 504 different PCIs are being considered. A communication terminal synchronizes using these 504 different PCIs and detects (identifies) the PCI of the synchronized cell.

[0109] In step ST602, for the next synchronized cell, the communication terminal detects a cell-specific reference signal (CRS), which is a reference signal (RS) transmitted from the base station for each cell, and measures the received power of the RS (Reference Signal Received Power: RSRP). A code that has a one-to-one correspondence with the PCI is used for the reference signal (RS). By correlating with this code, the cell can be separated 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.

[0110] Next, in step ST603, the communication terminal selects the cell with the best RS reception quality, for example, the cell with the highest RS reception power, that is, the best cell, from among one or more cells detected up to step ST602.

[0111] Next, in step ST604, the communication terminal receives the PBCH of the best cell and obtains the BCCH, which is broadcast information. A Master Information Block (MIB), which includes cell configuration information, is mapped to the BCCH on the PBCH. Therefore, the MIB can be obtained by receiving the PBCH and obtaining the BCCH. Examples of MIB information include the DL (downlink) system bandwidth (also called transmission bandwidth configuration: dl-bandwidth), the number of transmitting antennas, and the SFN (System Frame Number).

[0112] Next, in step ST605, the communication terminal receives the DL-SCH of the cell based on the cell configuration information in the MIB, and obtains SIB (System Information Block) 1 in the broadcast information BCCH. SIB 1 includes information on access to the cell, information on cell selection, and scheduling information for other SIBs (SIBk; k is an integer greater than or equal to 2). SIB 1 also includes a tracking area code (TAC).

[0113] Next, in step ST606, the communication terminal compares the TAC of 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 a TAI list. The TAI is identification information for identifying a tracking area, and is composed of an MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a tracking area code number.

[0114] If the comparison in step ST606 shows that the TAC received in step ST605 is the same as the TAC included in the tracking area list, the communication terminal enters standby mode in the cell. If the comparison shows that the TAC received in step ST605 is not included in the tracking area list, the communication terminal requests a core network (EPC) including an MME and the like to change the tracking area through the cell in order to perform a Tracking Area Update (TAU).

[0115] In the example shown in Fig. 12, an example of operations from cell search to standby in the LTE system is shown, but in the NR system, in step ST603, the best beam may be selected in addition to the best cell. Also, in the NR system, beam information, for example, a beam identifier, may be acquired in step ST604. Also, in the NR system, scheduling information of remaining minimum SI (RMSI) may be acquired in step ST604. In the NR system, the RMSI may be received in step ST605.

[0116] An apparatus constituting a core network (hereinafter sometimes referred to as a "core network side apparatus") updates the tracking area list based on the identification number (UE-ID, etc.) of the communication terminal sent from the communication terminal together with a TAU request signal. The core network side apparatus transmits the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) the TAC list held by the communication terminal based on the received tracking area list. Thereafter, the communication terminal enters standby mode in the cell.

[0117] The widespread use of smartphones and tablet devices has led to an explosive increase in cellular wireless communication traffic, raising concerns about a shortage of wireless resources worldwide. In response to this, efforts are being made to develop small cells and promote spatial separation in order to improve frequency utilization efficiency.

[0118] In a conventional cell configuration, a cell configured by an eNB has a relatively wide coverage area. Conventionally, a cell is configured so that a certain area is covered by the relatively wide coverage areas of multiple cells configured by multiple eNBs.

[0119] In the case of small cell configuration, a cell configured by an eNB has a narrower coverage area than a cell configured by a conventional eNB. Therefore, as in the past, a larger number of small cell configuration eNBs are required to cover a certain area than conventional eNBs.

[0120] In the following description, a cell with a relatively large coverage, such as a cell configured by a conventional eNB, is referred to as a "macro cell," and an eNB configuring a macro cell is referred to as a "macro eNB." Also, a cell with a relatively small coverage, such as a cell configured as a small cell, is referred to as a "small cell," and an eNB configuring a small cell is referred to as a "small eNB."

[0121] The macro eNB may be, for example, a "Wide Area Base Station" as described in Non-Patent Document 7.

[0122] The small eNB may be, for example, a low-power node, a local area node, a hotspot, etc. The small eNB may also be a pico eNB constituting a pico cell, a femto eNB constituting a femto cell, a HeNB, a remote radio head (RRH), a remote radio unit (RRU), a remote radio equipment (RRE), or a relay node (RN). The small eNB may also be a "local area base station" or a "home base station" as described in Non-Patent Document 7.

[0123] FIG. 13 shows an example of a cell configuration in NR. In an NR cell, narrow beams are formed and transmitted in different directions. In the example shown in FIG. 13, at a certain time, base station 750 transmits and receives signals to and from a mobile terminal using beam 751-1. At other times, base station 750 transmits and receives signals to and from a mobile terminal using beam 751-2. In a similar manner, base station 750 transmits and receives signals to and from a mobile terminal using one or more of beams 751-3 to 751-8. In this way, base station 750 forms a wide-area cell.

[0124] 13 shows an example in which the number of beams used by the base station 750 is 8, but the number of beams may be different from 8. Also, in the example shown in FIG. 13, the number of beams used simultaneously by the base station 750 is 1, but it may be multiple.

[0125] In 3GPP, a side link (SL) is supported for D2D (Device to Device) communication and V2V (Vehicle to Vehicle) communication (see Non-Patent Document 1 and Non-Patent Document 16). The SL is defined by the PC5 interface.

[0126] The physical channels used for SL (see Non-Patent Document 1) are as follows: The physical sidelink broadcast channel (PSBCH) carries information related to the system and synchronization and is transmitted from the UE.

[0127] The physical sidelink discovery channel (PSDCH) carries sidelink discovery messages from the UE.

[0128] The physical sidelink control channel (PSCCH) carries control information from the UE for sidelink and V2X sidelink communications.

[0129] The physical sidelink shared channel (PSSCH) carries data from the UE for sidelink and V2X sidelink communications.

[0130] The physical sidelink feedback channel (PSFCH) carries HARQ feedback on the sidelink from a UE that received a PSSCH transmission to the UE that transmitted the PSSCH.

[0131] The transport channel used for SL (see Non-Patent Document 1) will be described. The sidelink broadcast channel (SL-BCH) has a predetermined transport format and is mapped to the PSBCH, which is a physical channel.

[0132] The Sidelink Discovery Channel (SL-DCH) has periodic broadcast transmissions of a fixed size and a predetermined format. The SL-DCH supports both UE autonomous resource selection and eNB-scheduled resource allocation. UE autonomous resource selection involves a collision risk, whereas when the UE is allocated dedicated resources by the eNB, there is no collision. The SL-DCH supports HARQ combining but not HARQ feedback. The SL-DCH is mapped to the PSDCH, which is a physical channel.

[0133] The Sidelink Shared Channel (SL-SCH) supports broadcast transmission. The SL-SCH supports both UE autonomous resource selection and eNB-scheduled resource allocation. While UE autonomous resource selection involves a collision risk, there is no collision when the UE is allocated dedicated resources by the eNB. The SL-SCH also supports HARQ combining but not HARQ feedback. The SL-SCH also supports dynamic link adaptation by changing transmit power, modulation, and coding. The SL-SCH is mapped to the PSSCH, a physical channel.

[0134] The logical channels used for SL (see Non-Patent Document 1) will be described. The Sidelink Broadcast Control Channel (SBCCH) is a sidelink channel for broadcasting sidelink system information from one UE to other UEs. The SBCCH is mapped to the SL-BCH, which is a transport channel.

[0135] The Sidelink Traffic Channel (STCH) is a point-to-multipoint traffic channel for transmitting user information from one UE to other UEs. The STCH is used only by UEs with sidelink communication capability and UEs with V2X sidelink communication capability. Point-to-point communication between two sidelink-capable UEs is also realized using the STCH. The STCH is mapped to the SL-SCH, a transport channel.

[0136] The Sidelink Control Channel (SCCH) is a control channel for transmitting control information from one UE to another UE. The SCCH is mapped to the SL-SCH, which is a transport channel.

[0137] 3GPP is considering supporting V2X communication in NR as well. The study of V2X communication in NR is being conducted based on the LTE system and LTE-A system, but the following changes and additions have been made from the LTE system and LTE-A system.

[0138] In LTE, only broadcast was supported for SL communication. In NR, support for unicast and groupcast as SL communication in addition to broadcast is being considered (see Non-Patent Document 22 (3GPP TS23.287)).

[0139] In unicast communication and groupcast communication, support for HARQ feedback (Ack / Nack), CSI reporting, etc. is being considered.

[0140] In order to support unicast and groupcast in addition to broadcast in SL communication, support for PC5-S signaling is being considered (see Non-Patent Document 22 (3GPP TS23.287)). For example, PC5-S signaling is implemented to establish a link for implementing SL, i.e., PC5 communication. The link is implemented in the V2X layer and is also referred to as a Layer 2 link.

[0141] Furthermore, support for RRC signaling in SL communication is being considered (see Non-Patent Document 22 (3GPP TS23.287)). RRC signaling in SL communication is also referred to as PC5 RRC signaling. For example, it has been proposed to notify UE capabilities between UEs performing PC5 communication, or to notify AS layer settings for performing V2X communication using PC5 communication.

[0142] In SL communication, communication between a UE and a NW via a relay has been proposed (see Non-Patent Document 20 (3GPP TR23.703) and Non-Patent Document 23 (3GPP TS23.303)). In this disclosure, a relay between a UE and a NW may be referred to as a UE-to-NW relay or a UE-to-NW relay. In this disclosure, a UE that performs relaying between a UE and a NW may be referred to as a relay UE.

[0143] For example, there may be a need to communicate not only between UEs within the coverage of a RAN node (e.g., a gNB), which is a node constituting a RAN (Radio Access Network), but also between a UE that is farther away and the RAN node. In such cases, a method using a UE-to-NW relay may be considered. For example, communication between a gNB and a UE (sometimes referred to as a remote UE) is performed via a relay UE. Communication between the gNB and the relay UE is performed via Uu (Uu interface), and communication between the relay UE and the remote UE is performed via PC5 (PC5 interface).

[0144] For example, both the relay UE and the remote UE may be within the coverage of a gNB. The gNB in ​​which the relay UE is located (hereinafter referred to as gNB #1) may be different from the gNB in ​​which the remote UE is located (hereinafter referred to as gNB #2). In such a situation, it is possible that the remote UE communicates with the gNB in ​​which the relay UE is located via the relay UE.

[0145] For example, when a remote UE is located at the edge of the coverage of gNB #2, good communication quality may not be obtained. In such a case, the remote UE can obtain better communication quality by connecting to gNB #1 via a relay UE. Also, for example, when the distance between the remote UE and the relay UE is shorter than the distance between the remote UE and gNB #2, the remote UE can communicate with gNB #1 via the relay UE, which reduces the transmission power of the remote UE and thereby reduces power consumption.

[0146] However, when a remote UE is connected to gNB #2, no method for connecting to gNB #1 via a relay UE is disclosed in the standards established so far, including the above-mentioned Non-Patent Document 20 and Non-Patent Document 23. For this reason, when a remote UE is connected to gNB #2, even if the situation described above occurs, a problem occurs in that the remote UE cannot connect to gNB #1 via a relay UE.

[0147] In this embodiment, a method for solving such a problem will be disclosed.

[0148] In the communication system according to the present embodiment, the remote UE is set to RRC_IDLE before the remote UE is RRC-connected to the gNB #1 via the relay UE, thereby solving the above problem. The remote UE may be set to RRC_IDLE before the remote UE starts the RRC connection process with the gNB #1.

[0149] In addition, when the remote UE is RRC-connected with gNB #2, how to make the remote UE RRC_IDLE becomes an issue. Here, a method for solving such an issue is disclosed.

[0150] To solve this problem, gNB #2 releases the RRC connection of the remote UE. The remote UE may also release the RRC connection with gNB #2.

[0151] For example, the remote UE performs measurements on the SL from the relay UE. The SL measurements include reception quality (received power, RSSI (Received Signal Strength Indicator), SNR, SINR, and channel occupancy rate (CBR (Channel Busy Rate)). The remote UE measures the SL reception quality (which may be a SL Ratio). That is, the remote UE measures the reception quality in SL from the relay UE (hereinafter, may be referred to as SL reception quality). The remote UE reports the SL measurement result to gNB #2. The remote UE reports the SL reception quality to gNB #2. gNB #2 may use the SL reception quality reported from the remote UE to determine whether to release the connection with the remote UE. If gNB #2 determines to release the connection with the remote UE, gNB #2 starts a process to release the RRC connection with the RRC-connected remote UE. gNB #2 may request an RRC connection release from the RRC-connected remote UE. For example, RRC signaling may be used as the RRC connection release request. An RRC release message may be used as the RRC signaling.

[0152] In this way, gNB #2 can release the RRC connection for the remote UE that has RRC connection. The remote UE that has released the RRC connection for gNB #2 may connect to gNB #1 via the relay UE.

[0153] This specification discloses a method in which a gNB configures SL measurements for a UE. The gNB may notify the UE of the SL measurement configuration. The gNB may also notify the UE performing SL communication of the SL measurement configuration. SL measurement configuration includes configuration of measurement targets, configuration of measurement result reporting methods, etc. Measurement target configuration includes, for example, the frequency of the SL to be measured, the RAT (Radio Access Technology) of the SL to be measured, and the UE to be the SL measurement target. The SL measurement target may also be per beam. When SL communication is performed using beams, SL measurement results for each beam can be obtained.

[0154] The frequency of the SL to be measured may be the same as or different from the frequency used for communication with the serving cell. The RAT of the SL to be measured may be the same as or different from the RAT used for communication with the serving cell. Whether the RAT is the same or different may be configurable. UEs to be the target of SL measurement include, for example, UE types, such as U2N relay UEs, U2U relay UEs, UEs capable of SL communication, and UEs performing SL communication. These UEs may also be combined. The gNB sets the information disclosed above as the measurement target setting and notifies the UE.

[0155] The SL measurement result reporting setting may be, for example, periodic reporting, reporting when a predetermined condition is met (sometimes referred to as an event trigger), reporting n times (n is an integer greater than or equal to 1), etc. The gNB sets the information disclosed above as the measurement result reporting method setting and notifies the UE.

[0156] Seven examples of the aforementioned predetermined conditions (sometimes referred to as events) are disclosed below.

[0157] (1) When the SL reception quality becomes greater than a predetermined threshold. (2) When the SL reception quality becomes smaller than a predetermined threshold. (3) When the SL reception quality becomes greater than the reception quality of the serving cell. (4) When the SL reception quality becomes smaller than the reception quality of the serving cell. (5) When the reception quality from a UE capable of SL communication becomes greater than the reception quality from a UE performing SL communication. (6) When the reception quality from a UE capable of SL communication becomes smaller than the reception quality from a UE performing SL communication. (7) A combination of (1) to (6).

[0158] An offset may be provided. A predetermined offset may be added to the measurement result of the reception quality. For example, an offset may be applied to (3), and the value obtained by adding the predetermined offset to the SL reception quality may be greater than the reception quality of the serving cell. The serving cell in (3) and (4) may be, for example, a serving cell in which the UE is within coverage. The UE capable of SL communication in (5) and (6) may be, for example, a U2N relay UE. The UE capable of SL communication may be, for example, a UE capable of U2N relay communication. The above-mentioned predetermined threshold and offset may be notified from the gNB to the UE. They may also be notified by being included in the setting of the measurement result reporting method.

[0159] The UE performs SL measurement according to the SL measurement setting notified by the gNB. The UE notifies the gNB of the SL measurement result according to the SL measurement result method notified by the gNB.

[0160] The identifier of the UE itself may be notified along with the SL measurement results. This allows the gNB to recognize which UE the measurement results are for. The identifier of the UE itself may be notified along with the SL measurement results. This allows the gNB to recognize which UE the measurement results are for. The identifier of the UE being measured may be notified along with the SL measurement results. This may be notified in association with the measurement results. The gNB will be able to recognize which UE the SL measurement results are for. The type of UE being measured may be notified along with the SL measurement results. The gNB will be able to recognize the type of UE being the target of the SL measurement results. The SL measurement results may be notified along with information about the group to which the UE itself belongs. The gNB will be able to recognize which group the UE belongs to. The SL measurement results may be notified along with the location information. Information indicating which area the UE is located in may be notified as location information. The gNB will be able to recognize at which location the reported SL measurement results are measurement results. The identifier of the gNB that performed the measurement may be notified along with the SL measurement results. The gNB can recognize which gNB the UE measured the reception quality from. The reception quality measurement result from the gNB may be notified along with the SL measurement result. The measurement may be associated with the identifier of the gNB that measured it. The gNB can recognize which gNB the UE measured the reception quality from.

[0161] A filtering function at Layer 3 (L3) may be provided for SL measurement, and the results of L3 filtering may be reported. This allows for highly accurate measurements. A filtering function at Layer 1 (L1) may be provided for SL measurement, and the results of L1 filtering may be reported. This allows for early notification of measurement results.

[0162] RRC signaling may be used to notify the SL measurement settings. RRC signaling may be used to report the SL measurement results. More information can be notified. L3 filtering may be used for the SL measurement results reported using RRC signaling. MAC signaling may be used for reporting the SL measurement results. For example, in the case of an event trigger, the SL measurement results can be transmitted and received earlier. PUCCH may be used for reporting the SL measurement results. For example, in the case of an event trigger, the SL measurement results can be transmitted and received earlier. L1 filtering may be used for the SL measurement results reported using PUCCH. For example, L1 filtering and PUCCH may be used for measurements and reporting measurement results for each beam. It is possible to obtain dynamic measurement results for each beam.

[0163] In this way, it is possible to notify the SL measurement setting and the SL measurement result between the gNB and the UE on the Uu. The gNB can notify the UE of the SL measurement setting on the Uu. The UE can notify the gNB of the SL measurement result on the Uu. The gNB can recognize the SL measurement result in the UE.

[0164] The conventional Uu measurement configuration may include the SL measurement configuration. Alternatively, the conventional Uu measurement configuration and the SL measurement configuration may be combined. For example, the conventional Uu measurement event may be combined with the SL measurement event disclosed above. For example, when the reception quality of the serving cell becomes smaller than a predetermined threshold and the SL reception quality becomes larger than a predetermined threshold, the measurement result may be reported. In this way, Uu measurement and SL measurement can be combined, enabling more flexible measurement configuration and diverse measurement results to be obtained. It is possible to compare the reception quality between a gNB and an SL-capable UE such as a relay UE.

[0165] Information regarding the connection state of the UE may be provided. Information regarding the connection state of the UE may be notified between UEs performing SL communication on the PC5. For example, a relay UE may notify a remote UE of information regarding the connection state of the UE. For example, a remote UE may notify a relay UE of information regarding the connection state of the UE. Information regarding the connection state of the UE includes a connection state with the NW. For example, the connection state with the NW may be a CM (Connection Management) state. For example, the connection state with the NW may be an RRC state. Ten examples of information regarding the connection state of the UE are disclosed below.

[0166] (1) CM state. (2) RRC state. (3) Identifier of own UE. (4) Identifier of destination UE. (5) Identifier of connecting RAN. (6) Identifier of connecting CN (Core Network). (7) Identifier of serving area. (8) Identifier of provided service. (9) Identifier of provided slice. (10) Combination of (1) to (9).

[0167] (1) specifies the connection state between the UE and the CN. For example, the CM state can be CM_Idle, CM_Connected, etc. (2) specifies the connection state between the UE and the RAN. For example, the RRC state can be RRC_IDLE, RRC_CONNECTED, RRC_INACTIVE, etc.

[0168] (3) identifies a UE that transmits information about the connection state of the UE. For example, this is a Globally Unique Temporary Identifier (GUTI) or a 5G SAE Temporary Mobile Subscriber Identity (5G-S-TMSI). (4) identifies a UE that receives information about the connection state of the UE. For example, this is a GUTI or a 5G-S-TMSI. (5) identifies a RAN to which the UE connects. For example, the RAN may be a gNB. It may also be a cell. It may also be an identifier such as a Transmission Reception Point (TRP), an Integrated Access and Backhaul (IAB) donor, or an IAB node. For example, the cell identifier may be an NR Cell Identifier (NCI) or an NR Cell Global Identifier (NCGI). (6) identifies a CN to which the UE connects. For example, the CN identifier may be an AMF identifier, an SMF identifier, or an NF (Network Function) identifier. For example, the AMF identifier may be an AMF ID or an AMF Set ID.

[0169] (7) specifies an area in which the UE is located. For example, the area in which the UE is located may be a registration area. It may also be a tracking area. It may also be an RNA (RAN Notification Area). For example, a TAC may be used as a tracking area identifier. (8) specifies a service to which the UE is provided. For example, a service area identifier may be used as a service identifier. (9) specifies a network slice to which the UE is provided. For example, a S-NSSAI (Single Network Slice Selection Assistance Information) may be used as a network slice identifier.

[0170] As the above-mentioned identifier, for example, an identifier described in Non-Patent Document 31 (3GPP TS23.003) may be used.

[0171] In this way, the UE that receives the information on the connection status of the UE can recognize which network the UE that sent the information is connected to, what the connection status is, etc.

[0172] Although the information is described as information on the connection state of the UE, it may also be information on a change in the connection state of the UE. The information on a change in the connection state of the UE may include information on the connection state before the change and / or information on the connection state after the change. Information on a change in the connection state of the UE may be notified between UEs performing SL communication on the PC 5. For example, when a relay UE changes its connection state with the NW, the relay UE may notify a remote UE of information on the change in the connection state of the UE. For example, when a remote UE changes its connection state with the NW, the remote UE may notify the relay UE of information on the change in the connection state of the UE. In this way, when the connection state between the UE and the NW is changed, it is only necessary to notify the information, thereby making it possible to reduce the resources required for notification.

[0173] A message may be provided for notifying information about the connection state of the UE or information about a change in the connection state of the UE. The message may include such information. For example, the relay UE may notify the remote UE by including information about the connection state of the UE in the message. For example, the remote UE may notify the relay UE of information about the connection state of the UE in the message.

[0174] This disclosure discloses a method for notifying information related to the connection state of a UE and information related to a change in the connection state of the UE. The information may be notified by PC5-S signaling. This enables early notification in the PC5 connection process. Alternatively, the information may be notified by PC5-RRC signaling. For example, the information may be included in an RRC message on the PC5 for notification. For example, when notifying the RRC connection state with the NW, using RRC signaling in the PC5 also enables notification processing in the same RRC layer, thereby reducing malfunctions. The information may also be notified by an SRB (Signaling Radio Bearer) of the PC5. This enables the information to be notified between UEs as signaling information and control information.

[0175] The information may be notified using PC5 MAC signaling. In this case, notification is possible earlier than with RRC signaling. The information may be notified on PSCCH. The information may be notified by being included in 1st SCI (Sidelink Control Information). In this way, notification is possible earlier. Furthermore, UEs that can receive PC5 communication can receive the information. The information may be notified on PSSCH. The information may be notified by being included in 2nd SCI. In this way, notification is possible earlier. The information may be notified on PSSCH by being included in MAC CE (Control Element). In this way, notification is possible earlier. Furthermore, since HARQ is applied, reception errors can be reduced.

[0176] When a remote UE establishes an RRC connection with gNB #1, unlike the conventional RRC connection process between a UE and a gNB, a relay UE is interposed between the remote UE and the gNB, and therefore the conventional method cannot be applied. Here, a specific method for a remote UE to establish an RRC connection with gNB #1 is disclosed.

[0177] The remote UE notifies the NW of an RRC connection request. Specifically, the remote UE notifies the NW of the RRC connection request via the relay UE. The RRC connection request may be an RRC connection request between the remote UE and the NW. The state of the remote UE making the RRC connection request may be RRC_IDLE or RRC_INACTIVE. The NW that notifies the RRC connection request may be the gNB (gNB #1) to which the relay UE is connected. An RRC setup request may be used for the RRC connection request.

[0178] When a relay UE receives an RRC connection request between the remote UE and the network from the remote UE, the relay UE notifies the network to which the remote UE is connected of the RRC connection request, or may forward the RRC connection request to the network to which the remote UE is connected.

[0179] The information included in the RRC connection request may be encapsulated. Alternatively, the information included in the RRC connection request may be container information. For example, the information may be encapsulated as information related to the SL. Alternatively, the information may be encapsulated as information related to the relay. The relay UE may notify the NW of the RRC connection request received from the remote UE while it is still encapsulated or containerized. In this way, the relay UE can easily receive and transmit the RRC connection request with low latency. This reduces malfunctions in the relay UE and enables low-latency RRC connection processing.

[0180] Six examples of information included in an RRC connection request are disclosed below: (1) Information indicating that it is an RRC connection request between a UE and a NW. (2) Identifier of the UE itself. (3) Identifier of the request destination NW. (4) Identifier of the destination UE. (5) Information about the connection state of the UE. (6) A combination of (1) to (5).

[0181] (1) may be, for example, an RRC setup request as an RRC connection request. (2) identifies the UE that transmits the RRC connection request. For example, GUTI, 5G-S-TMSI, etc. (3) identifies the RAN from which the UE makes the RRC connection request. For example, the RAN may be a gNB. It may also be a cell. It may also be an identifier such as a TRP, IAB donor, or IAB node. For example, NCI or NCGI may be used as a cell identifier. (4) identifies the UE through which the RRC connection request is transmitted to the NW. For example, when a remote UE notifies the NW of an RRC connection request via a relay UE, it may be an identifier that identifies the relay UE. For example, GUTI, 5G-S-TMSI, etc. (5) may be information regarding the connection state of the UE, as disclosed above.

[0182] By doing this, the NW (for example, a gNB) that receives the RRC connection request can recognize the UE that made the connection request and the UE through which the connection request was sent. Also, the UE through which the connection request is sent can recognize the destination gNB of the connection request received from the source UE. As a result, the gNB that receives the RRC connection request can perform RRC connection processing between the UE that sent the RRC connection request.

[0183] When a remote UE notifies a network of an RRC connection request, the RRC connection request must be transmitted to the relay UE via the PC 5. As a method for transmitting the RRC connection request via the PC 5, the method of transmitting information on the UE connection state via the PC 5, as disclosed above, may be appropriately applied. Furthermore, a message for the RRC connection request via the relay UE may be provided as RRC signaling on the PC 5.

[0184] A method for notifying an RRC connection request from a relay UE to a network is disclosed. Uu RRC signaling may be used for the RRC connection request. An RRC setup request may be used as the RRC signaling. Alternatively, an RRC message for notifying information related to an SL may be used. For example, SidelinkUEInformationNR may be used. Alternatively, a message for an RRC connection request via a relay UE may be provided. The RRC connection request may also be notified by an SRB. Signaling information and control information can be notified between the relay UE and the network.

[0185] The RRC connection request may be notified using MAC signaling. In this way, notification can be made earlier than with RRC signaling. The RRC connection request may be notified on PUCCH. The connection request may be included in UCI and notified. In this way, notification can be made earlier. The RRC connection request may be notified on PUSCH. The connection request may be included in MAC CE and notified on PSSCH. Alternatively, the connection request may be notified on PUSCH together with data. In this way, notification can be made earlier. Furthermore, since HARQ is applied, reception errors can be reduced.

[0186] In this way, the remote UE can notify the network of an RRC connection request via the relay UE, and the network can start an RRC connection process for the remote UE.

[0187] Another method for a remote UE to establish an RRC connection with gNB #1 is disclosed. The remote UE notifies the relay UE of an RRC connection request. The state of the remote UE making the RRC connection request may be RRC_IDLE or RRC_INACTIVE. The RRC connection request may be an RRC connection request between the remote UE and the NW, different from the RRC connection request of PC5. In this way, the relay UE can recognize that the RRC connection request is different from the RRC connection request of PC5. The NW may be the NW (gNB #1) to which the relay UE is connected. When the relay UE receives an RRC connection request from the remote UE, it notifies the NW to which the relay UE is connected of the RRC connection request between the remote UE and the NW.

[0188] As examples of information to be included in the RRC connection request, the examples of information disclosed above may be applied as appropriate. The identifier of the destination UE of the above-mentioned information (4) may be the identifier of the UE to which the RRC connection request is to be sent, rather than the identifier of the UE via which the request is to be sent.

[0189] In this way, the relay UE that receives the RRC connection request from the remote UE can notify the gNB #1 of the RRC connection request between the remote UE and the NW. The gNB #1 that receives the RRC connection request between the remote UE and the NW from the relay UE can perform the RRC connection process with the remote UE.

[0190] As a method for the remote UE to notify the relay UE of the RRC connection request, the above-disclosed method of notifying the PC5 of the RRC connection request via the relay UE may be appropriately applied.As a method for notifying the NW of the RRC connection request from the relay UE, the above-disclosed method of notifying the NW of the RRC connection request may be appropriately applied.

[0191] In this way, the remote UE can notify the relay UE of an RRC connection request between the remote UE and the NW, and the relay UE can notify the NW of an RRC connection request between the remote UE and the NW. The NW can then start the RRC connection process for the remote UE.

[0192] When a remote UE notifies a relay UE of an RRC connection request to the NW, the relay UE may start an RRC connection process between the relay UE and the gNB. When the relay UE receives an RRC connection request to the NW from the remote UE, the relay UE may start an RRC connection process with a gNB #1 within its coverage area. The remote UE may start an RRC connection process for a cell selected or reselected. The remote UE notifies the relay UE of an RRC connection request to the NW. The state of the remote UE may be RRC_Connected or RRC_Idle. When the relay UE receives an RRC connection request to the NW, it makes an RRC connection request to a gNB (gNB #1) having a cell selected or reselected. After completing the RRC connection process with gNB #1, the relay UE may notify the remote UE of the RRC state change.

[0193] An RRC connection request message to the network may be provided on the PC 5. The message may be for relaying. The message may be a message requesting an RRC connection to the network to the destination UE of the message. Seven examples of information to be included in the message are disclosed below.

[0194] (1) Information indicating a request for RRC connection to the network. (2) Identifier of the UE itself. (3) RRC connection status of the UE itself. (4) Identifier of the gNB for which the UE itself has selected or reselected a cell. (5) Identifier of the gNB to which the UE itself is connected. (6) Identifier of the destination UE. (7) A combination of (1) to (6).

[0195] The method of notifying the relay UE of the RRC connection request message to the network from the remote UE may be appropriately applied to the methods described above. The method of notifying the PC 5 of information related to the connection state of the UE may be appropriately applied.

[0196] The relay UE that has completed the RRC connection process with gNB #1 notifies gNB #1 of an RRC connection request message from the remote UE. In this way, the remote UE can notify the network of an RRC connection request message via the relay UE. In addition, the relay UE does not need to be connected to the gNB in ​​advance. This enables low power consumption of the relay UE.

[0197] gNB #1 may notify the remote UE of an RRC setup message via the relay UE. gNB #1, which receives the RRC setup message from the remote UE via the relay UE, starts an RRC connection process with the remote UE via the relay UE that received the message. gNB #1 performs RRC configuration for the remote UE and notifies the remote UE of an RRC setup message including the RRC configuration via the relay UE.

[0198] A method for notifying an RRC setup message from a network to a relay UE is disclosed. Uu RRC signaling may be used for the RRC setup message. RRC setup may be used as the RRC signaling. Alternatively, an RRC message for notifying information related to SL may be used. Alternatively, a message for an RRC connection request via a relay UE may be provided. Furthermore, the RRC setup may be notified by an SRB. Signaling information and control information can be notified between the network and the relay UE.

[0199] As a method for notifying the remote UE of the RRC setup message from the relay UE, the above-disclosed method of notifying the UE of the connection state information in the PC 5 may be appropriately applied. Also, as RRC signaling on the PC 5, a message for an RRC connection request via the relay UE may be provided.

[0200] In this way, the remote UE can receive an RRC setup message from gNB #1 via the relay UE. The remote UE can acquire the RRC settings for establishing an RRC connection with gNB #1 from gNB #1. The remote UE performs RRC configuration using the RRC settings acquired from gNB #1.

[0201] A remote UE that has performed RRC configuration using the RRC configuration acquired from gNB #1 may notify gNB #1 of the completion of RRC setup. The method of notification from the remote UE to gNB #1 via the relay UE may be the RRC connection request notification method disclosed above, as appropriate. RRC setup complete may be used as RRC signaling for Uu. In this way, gNB #1 can receive an RRC setup completion notification from the remote UE. gNB #1 can recognize that the RRC configuration has been completed from the remote UE.

[0202] In this way, it becomes possible to perform an RRC connection process between the remote UE and gNB #1. The remote UE can establish an RRC connection with gNB #1.

[0203] The resources required for communication in PC5 between a remote UE and a relay UE are disclosed. When a remote UE is connected to a network, the resources required for communication in PC5 may be scheduled by the connected network. When the remote UE transmits, the resources may be scheduled by the connected network. The remote UE communicates in PC5 according to scheduling information received from the connected network. When the remote UE is not connected to a network, the resources required for communication in PC5 may be selected by the remote UE using a resource pool (RP) broadcast by a gNB #2 in which the remote UE is located.

[0204] When the relay UE is connected to the NW, the resources required for communication in PC5 may be scheduled by the connected NW. The connected NW may schedule resources when the relay UE transmits. The relay UE communicates in PC5 according to scheduling information received from the connected NW. When the relay UE is not connected to the NW, the relay UE may select the resources required for communication in PC5 using the RP broadcast by the gNB #1 in which the relay UE is located.

[0205] Communication on PC5 may include not only communication after the PC5-RRC connection is completed, but also discovery processing, establishment processing of a link used for signaling on PC5 (sometimes referred to as a PC5-S link), and PC5-RRC connection processing.

[0206] 14 is a sequence diagram showing an example of a method for making a remote UE RRC_IDLE before the remote UE is RRC-connected to a gNB via a relay UE, according to the first embodiment. In step ST1401, the relay UE is in-coverage of gNB #1 and is in RRC_IDLE state. In step ST1402, the remote UE is in-coverage of gNB #2 and is in RRC_CONNECTED state. In step ST1403, gNB #2 notifies the remote UE of the SL measurement setting (hereinafter referred to as SL measurement setting). In step ST1404, the remote UE performs SL communication quality measurement (hereinafter referred to as SL measurement or SL measurement) in accordance with the SL measurement setting received from gNB #2. In measuring the communication quality of the SL, the remote UE measures, for example, the power, RSSI, SNR, SINR, etc. of the signal received from the UE.

[0207] In step ST1405, the remote UE notifies gNB #2 of an SL measurement report including the SL measurement result according to the SL measurement report configuration included in the SL measurement configuration received from gNB #2 in step ST1403. For example, the above-mentioned SL measurement event configuration may be used as the SL measurement report configuration. For example, when the reception quality from the UE in SL is greater than a predetermined threshold and the reception quality from the UE becomes greater than the reception quality from gNB #2, that is, when the reception quality from the UE becomes better than the reception quality from gNB #2, the remote UE reports the SL measurement result to gNB #2. In step ST1406, gNB #2 uses the SL measurement result notified in the SL measurement report from the remote UE to determine whether to release the RRC connection of the remote UE. When gNB #2 determines to release the RRC connection of the remote UE, in Step ST1407, gNB #2 notifies the remote UE of an RRC connection release request. In Step ST1408, the remote UE that has received the request performs an RRC connection release process with gNB #2.

[0208] In step ST1409, the remote UE performs discovery processing. In step ST1410, the remote UE performs PC5-S link establishment processing for the detected relay UE having relay function, and in step ST1411, establishes PC5-RRC connection. Completion of the PC5-RRC connection enables data communication between the remote UE and the relay UE.

[0209] The relay UE connected to the remote UE initiates connection processing to the network. The relay UE connected to the remote UE initiates RRC connection processing to gNB #1. The remote UE may request a connection to the network from the connected relay UE. For example, the request may be notified in the PC5-RRC connection processing, or the request may be notified using PC5-RRC signaling after the PC5-RRC connection is completed. The relay UE that receives the request may perform connection processing to the network. The relay UE that receives the request may perform connection processing to gNB #1.

[0210] In step ST1412, the relay UE notifies gNB #1 of an RRC setup request. Upon receiving the RRC setup request, gNB #1 performs RRC configuration for the relay UE and, in step ST1413, notifies the relay UE of the RRC setup including the configuration. Upon receiving the RRC setup, the relay UE performs RRC configuration with gNB #1 and, in step ST1414, notifies gNB #1 of the completion of RRC setup. As a result, in step ST1415, an RRC connection is established between the relay UE and gNB #1.

[0211] In step ST1416, the relay UE that has established an RRC connection with the gNB #1 transmits an RRC state change notification to the remote UE, including information about the connection state of the relay UE with the network. Here, it is preferable to notify that the relay UE is in an RRC connected state.

[0212] In Step ST1417, the remote UE that has received notification from the relay UE that it is in an RRC connected state with the network notifies the gNB #1 of an RRC setup request. This notification may be made via the relay UE. The gNB #1 that has received the RRC setup request performs RRC configuration for the remote UE, and in Step ST1418 notifies the remote UE of the RRC setup including this configuration. This notification may be made via the relay UE. The remote UE that has received the RRC setup performs RRC configuration with the gNB #1, and in Step ST1419 notifies the gNB #1 of the completion of the RRC setup. This notification may be made via the relay UE. As a result, an RRC connection is established between the remote UE and the gNB #1 in Step ST1420.

[0213] By doing this, the remote UE that was in an RRC connected state with gNB #2 can transition to an RRC connected state with gNB #1. This allows the remote UE to communicate with gNB #1 via the relay UE.

[0214] In the example disclosed in FIG. 14, the remote UE made an RRC connection request to gNB #1 in step ST1417. As an alternative method, gNB #1 may make an RRC connection request to the remote UE. gNB #1 may notify the remote UE of the RRC connection request via a relay UE. The remote UE that received the RRC connection request from gNB #1 may start an RRC connection process with gNB #1. The remote UE may notify gNB #1 of the RRC setup request disclosed in step ST1417 of FIG. 14. In this way, gNB #1 can request the remote UE to start the RRC connection process.

[0215] Paging may be used to notify the remote UE of an RRC connection request from gNB #1. When gNB #1 decides to establish an RRC connection with the remote UE, it notifies the remote UE of the paging via the relay UE. The remote UE that receives the paging initiates an RRC connection process with gNB #1. The paging may be generated by gNB #1 instead of a paging generated by the CN. The method of paging from gNB #1 to the remote UE via the relay UE may be the method disclosed in Variant 4 of Embodiment 2, as appropriate. By using paging, gNB #1 can request the remote UE to initiate an RRC connection process.

[0216] The gNB #1 may notify the remote UE of the RRC configuration without making an RRC connection request. The gNB #1 that has decided to establish an RRC connection with the remote UE may notify the remote UE of the RRC configuration via the relay UE without making an RRC connection request. In this way, it is possible to omit the transmission and reception of an RRC connection request from the gNB #1 to the remote UE and an RRC connection request message from the remote UE to the gNB #1. This makes it possible to reduce the signaling load.

[0217] The relay UE may notify gNB #1 of the connection status with the remote UE. The connection status may be information regarding the connection status in PC5, which will be described later. The method of notifying information regarding the connection status from the relay UE to gNB #1 may also be appropriately applied, as will be described later. gNB #1 may determine whether to make an RRC connection request to the remote UE using the connection status with the relay UE and the connection status between the relay UE and the remote UE. When the gNB #1 is in an RRC connected state with the relay UE and an RRC connection is established between the relay UE and the remote UE, gNB #1 may make an RRC connection request to the remote UE. In this way, the remote UE can transition to an RRC connected state with gNB #1 via the relay UE.

[0218] The method for gNB #2 to release the RRC connection of a remote UE using the reception quality in the SL from the remote UE has been disclosed above. Another method for releasing the RRC connection of a remote UE will now be disclosed.

[0219] When the remote UE finds a connectable relay UE, it reports it to gNB #2. When the remote UE has performed a discovery process with the relay UE, it may report this to gNB #2. When the remote UE has established a PC5 connection with the relay UE, it may report this to gNB #2. When the remote UE has completed the establishment of a PC5-S link with the relay UE, it may report this to gNB #2. When the remote UE has completed the PC5-RRC connection with the relay UE, it may report this to gNB #2.

[0220] The gNB #2 may use information regarding the connection status with the relay UE received from the remote UE to determine whether to release the connection with the remote UE. The information regarding the connection status between the remote UE and the relay UE may be information regarding the connection status in PC5. When the gNB #2 determines to release the connection with the remote UE, the gNB #2 initiates a process to release the RRC connection with the RRC-connected remote UE. The gNB #2 may request an RRC connection release from the RRC-connected remote UE. For example, RRC signaling may be used as the RRC connection release request. An RRC release message may be used as the RRC signaling.

[0221] The remote UE may notify gNB #2 of information regarding the connection status of the relay UE with the NW. gNB #2 may determine whether to release the RRC connection with the remote UE using the information regarding the connection status of the relay UE with the NW received from the remote UE. gNB #2 may determine whether to release the RRC connection with the remote UE using the information regarding the connection status between the remote UE and the relay UE and the information regarding the connection status of the relay UE with the NW. In this way, gNB #2 can determine whether to release the RRC connection with the remote UE, including the connection status of the relay UE. Furthermore, after the remote UE releases its RRC connection with gNB #2, the RRC connection process with the NW via the relay UE can be performed quickly.

[0222] Information regarding the connection state in PC5 may be provided. The connection state may be a discovery processing state, a PC5-S link establishment processing state, a PC5-RRC connection state, etc. The discovery processing state may be a discovery processing in progress or a discovery processing completed state. The PC5-S link establishment processing state may be a PC5-S link establishment processing in progress or a PC5-S link establishment completion state. The PC5-RRC connection state may be a PC5-RRC connection processing in progress or a PC5-RRC connection completion state. Six examples of information regarding the connection state in PC5 are disclosed below.

[0223] (1) Connection status in PC5. (2) Identifier of the UE itself. (3) Identifier of the UE that is the other party in the PC5 connection process. (4) Information about the connection status of the UE. (5) Information about whether the UE is capable of relaying. (6) A combination of (1) to (5).

[0224] (1) may be the connection status of the UE in PC5. (2) specifies the UE to which the information is notified. For example, GUTI, 5G-S-TMSI, Layer 2 ID on PC5, etc. (3) specifies the UE that is the other party in the PC5 connection process. For example, GUTI, 5G-S-TMSI, Layer 2 ID on PC5, etc. (4) is information regarding the connection status of the UE itself and / or the other party in the PC5 connection process. The information regarding the UE connection status disclosed above may be applied as appropriate. (5) is information regarding whether the other party in the PC5 connection process is capable of relaying. Relays include UE-to-NW relays that relay between the UE and the NW, and UE-to-UE relays that relay between UEs. These pieces of information may be provided separately. A capability may be provided for whether the UE is capable of relaying in the SL. The capability may be used as information on whether the UE can relay.

[0225] By doing this, the gNB that receives the information regarding the connection status in the UE's PC5 can recognize which UE the UE that sent the information is connected to, what the connection status is, etc.

[0226] Although the information is about the connection state in the PC 5, it may be about a change in the connection state in the PC 5. The information about a change in the connection state in the PC 5 may include information about the connection state in the PC 5 before the change and / or information about the connection state in the PC 5 after the change. In this way, when the connection state of the UE in the PC 5 is changed, it is only necessary to notify the information, and it is possible to reduce resources required for notification.

[0227] A message may be provided on Uu to notify information about the connection state of the UE in PC5 or information about changes in the connection state of the UE in PC5. This information may be included in the message. For example, the remote UE may notify gNB #2 by including information about the connection state of the UE in PC5 in the message.

[0228] As a method for notifying the NW of information relating to the connection state in the PC 5 from the remote UE, the method for notifying the NW of an RRC connection request from the relay UE disclosed above may be appropriately applied.

[0229] In this way, the remote UE can notify gNB #2 of information regarding the connection state in PC 5. gNB #2 can use the information received from the remote UE to determine whether to release the RRC connection with the remote UE.

[0230] In the case of UE-to-UE relay, information regarding the connection status in one PC 5 may be notified to a UE other than the UE that transmits and receives via that one PC 5. For example, when a transmitting UE, UE-TX, communicates with a receiving UE, UE-RX, via a UE-to-UE relay UE, the UE-to-UE relay UE may notify UE-RX of information regarding the connection status in the PC 5 between the UE-TX and the UE-to-UE relay UE. As a method for notifying information regarding the connection status in the PC 5 between UEs, the above-disclosed method of notifying the PC 5 of an RRC connection request via a relay UE may be appropriately applied. In this way, even in the case of UE-to-UE relay, each UE can recognize the connection status in each PC 5.

[0231] 15 is a sequence diagram showing another example of a method for making a remote UE RRC_IDLE before the remote UE is RRC-connected to a gNB via a relay UE, according to embodiment 1. In FIG. 15, steps common to those in FIG. 14 are assigned the same step numbers, and common descriptions will be omitted.

[0232] In steps ST1409 to ST1411, the remote UE that has established PC5-RRC connection with the relay UE notifies the gNB #2 of information regarding the connection status in PC5 with the relay UE in step ST1501. The notification may include information regarding whether the relay UE is capable of relaying. It may also include an identifier of the relay UE. In step ST1406, the gNB #2 uses the information regarding the PC5 connection status with the relay UE received from the remote UE to determine whether to release the RRC connection of the remote UE. If the gNB #2 determines to release the RRC connection of the remote UE, in step ST1407, the gNB #2 notifies the remote UE of an RRC connection release request. The remote UE that has received the request performs an RRC connection release process with the gNB #2 in step ST1408.

[0233] By doing this, a remote UE that was in an RRC connected state with gNB #2 can transition to an RRC connected state with gNB #1. This allows the remote UE to communicate with gNB #1 via the relay UE. In addition, since gNB #2 can recognize the connection state between the remote UE and the relay UE, it is possible to release the RRC connection of the remote UE at an appropriate time.

[0234] 16 is a sequence diagram showing another example of a method for making a remote UE RRC_IDLE before the remote UE is RRC-connected to a gNB via a relay UE, according to embodiment 1. In FIG. 16, steps common to those in FIG. 15 are assigned the same step numbers, and common descriptions will be omitted.

[0235] Figure 16 shows a case in which, in step ST1601, the relay UE has an RRC connection with gNB #1 before connecting with the remote UE via PC5.

[0236] In this case, the relay UE may notify the remote UE of information regarding the connection state of the relay UE. For example, the relay UE may notify the remote UE of information regarding the connection state of the relay UE in the PC5-RRC connection process of step ST1411. Alternatively, after the PC5-RRC connection process, the relay UE may notify the remote UE of information regarding the connection state of the relay UE using PC5-RRC signaling. In this way, the remote UE can recognize the connection state between the relay UE and the NW. If the remote UE that performed the RRC connection release process with the gNB #2 in step ST1408 is in an RRC-connected state with the NW, it can immediately notify the gNB #1 of an RRC setup request in step ST1417 and start the RRC connection process.

[0237] By doing this, a remote UE that was in an RRC connected state with gNB #2 can transition to an RRC connected state with gNB #1. This allows the remote UE to communicate with gNB #1 via the relay UE. Furthermore, since gNB #2 can recognize the connection status between the remote UE and the relay UE, it is possible to release the RRC connection of the remote UE at an appropriate time. Furthermore, since the remote UE can recognize the connection status of the relay UE with gNB #1, it is possible to perform an RRC setup request to gNB #1 at an appropriate time and through appropriate processing.

[0238] Another method for releasing the RRC connection of a remote UE is disclosed.

[0239] The remote UE may notify the connected network of a connection release request. If the remote UE has an RRC connection with gNB #2, it may notify gNB #2 of a connection release request. The connection release request may include information indicating that the connection to the network is being established via a relay UE. The information may be included in the connection release request as reason information. The connection release request may be, for example, an RRC connection release request and / or a CM connection release request.

[0240] gNB #2 may use the connection release request received from the remote UE to determine whether to release the RRC connection with the remote UE. If gNB #2 determines to release the RRC connection with the remote UE, gNB #2 initiates a process to release the RRC connection with the connected remote UE. For example, the remote UE notifies gNB #2 of an RRC connection release request, and gNB #2 uses the received RRC connection release request to determine to release the RRC connection with the remote UE. gNB #2 performs an RRC connection release process with the remote UE.

[0241] As a method for notifying a connection release request from a remote UE to a network, the method for notifying an RRC connection request from a relay UE to a network, as disclosed above, may be applied as appropriate.

[0242] RRC signaling may be used to initiate an RRC connection release procedure from gNB #2 to the remote UE. The RRC signaling may be an RRC release message.

[0243] Another method for releasing the RRC connection of a remote UE is disclosed.

[0244] The remote UE may release the RRC connection with the network by itself. That is, the remote UE performs an RRC connection release process with the network. The determination of the RRC connection release may be appropriately applied using the determination method in the gNB #2 described above. The network, for example, gNB #2, cannot recognize whether the remote UE has released the RRC connection with its own gNB. If the network cannot recognize whether the RRC connection with the remote UE has been released, it will continue to hold resources for the connection with the remote UE. This wastes resources and reduces resource usage efficiency. A method for solving this problem is disclosed.

[0245] If there is no communication with the remote UE for a predetermined period, the NW performs a connection release process with the remote UE. That is, if there is no communication with the remote UE connected via RRC for a predetermined period, the gNB #2 performs a connection release process with the remote UE in its own gNB. For example, it releases resources for the RRC connection with the remote UE. For example, it resets the protocol for the RRC connection with the remote UE. The predetermined period may be managed by a timer. In this way, it is possible to avoid unnecessary use of resources in the gNB #2.

[0246] By using the method disclosed in this embodiment, even when the remote UE is in an RRC connected state with gNB #2, the RRC connection state of the remote UE can be set to RRC_IDLE, and the remote UE can be RRC connected to gNB #1 via the relay UE. As a result, the remote UE can communicate with gNB #1 via the relay UE.

[0247] Modification 1 of First Embodiment In this modification, another method for solving the problem shown in the first embodiment is disclosed.

[0248] In the communication system according to this modification, the remote UE is HO (Handover) between the gNB to which the remote UE is connected and the gNB to which the relay UE is connected. That is, the remote UE is HO between gNB #2 and gNB #1. This eliminates the need to transition the remote UE to RRC_IDLE. The remote UE can change its connection destination from gNB #2 to gNB #1 while remaining in the RRC_CONNECTED state.

[0249] A specific method for HOing a remote UE between gNB #2 and gNB #1 is disclosed.

[0250] 17 is a sequence diagram showing an example of a method for HO of a remote UE between a gNB to which the remote UE is connected and a gNB to which a relay UE is connected, for Modification 1 of Embodiment 1. In FIG. 17, steps common to those in FIG. 14, FIG. 15, and FIG. 16 are assigned the same step numbers, and common descriptions will be omitted.

[0251] In steps ST1403 to ST1405, gNB #2 configures SL measurements for the remote UE. Also, the remote UE performs SL measurements. The remote UE reports the SL measurement results to gNB #2. With regard to SL measurements, the method disclosed in embodiment 1 may be applied as appropriate. Note that the remote UE may perform DL measurements in addition to SL measurements. In this case, gNB #2 configures DL measurements for the remote UE. The remote UE performs DLL measurements. The remote UE reports the DL measurement results to gNB #2. With regard to DL measurements, the method described in non-patent document 19 (3GPP TS38.331) may be applied as appropriate.

[0252] In step ST1701, gNB #2, which has received the report of the SL measurement result, determines whether to perform HO for the remote UE from gNB #2 to gNB #1, and decides to perform HO in the example shown in FIG. 17. The SL measurement result received from the remote UE may be used for this determination. The DL measurement result may also be used. For example, if the SL reception quality from the relay UE at the remote UE is higher than the DL reception quality from gNB #2, gNB #2 may decide to perform HO to gNB #1 via the relay UE.

[0253] gNB #2 may use information on whether the remote UE is connected to a relay UE and whether the relay UE is connected to gNB #1 to determine whether HO can be performed for the remote UE to gNB #1 or whether to perform HO.

[0254] In this case, the relay UE notifies the remote UE of information regarding the connection status of the relay UE. The remote UE notifies the gNB #2 of information regarding the connection status in the PC5 between the remote UE and the relay UE and / or information regarding the connection status of the relay UE. The gNB #2 may use the information regarding the connection status in the PC5 between the remote UE and the relay UE and / or information regarding the connection status of the relay UE received from the remote UE to determine whether HO can be performed for the remote UE to the gNB #1 or whether to perform HO.

[0255] For example, gNB #2 may determine that the remote UE can be HO'd to gNB #1 when the PC5-RRC connection between the relay UE and the remote UE is completed and the relay UE is in an RRC connected state with gNB #1. For example, gNB #2 may additionally determine that the remote UE can be HO'd to gNB #1 using the communication quality measurement results of SL and DL from the remote UE.

[0256] A remote UE may be connected to multiple relay UEs. Each relay UE may notify the remote UE of information regarding the connection status of the relay UE. The remote UE may notify gNB #2 of information regarding the PC5 connection status with multiple relay UEs and / or information regarding the connection status of multiple relay UEs. By receiving this information from the remote UE, gNB #2 can recognize the connection status of each relay UE to which the remote UE is connected.

[0257] For example, the remote UE may measure the SL communication quality of multiple relay UEs and notify the gNB #2 of the measurement results. The gNB may use the SL communication quality measurement results, the DL communication quality measurement results, and the above-mentioned information on the connection state to determine whether to HO the remote UE and further to which gNB to HO.

[0258] The gNB #2 may use information about the services supported by the gNB to which the relay UE is connected (e.g., a service identifier) ​​to determine to which gNB the remote UE should be HO'd. The gNB #2 may use information about the services supported by the relay UE to determine to which gNB the remote UE should be HO'd. In this way, for example, it is possible to HO the remote UE to a relay UE and a gNB that support the service provided by the remote UE.

[0259] The relay UE may notify the remote UE of the measurement result of the DL reception quality from the gNB to which it is connected. The remote UE notifies gNB #2 of the measurement result of the DL reception quality from the gNB to which the relay UE is connected, received from the relay UE. The gNB #2 may use the measurement result of the DL reception quality from the gNB to which the relay UE is connected, received via the remote UE, to determine to which gNB the remote UE should be HO'd. In this way, for example, it is possible to HO the remote UE to a gNB that has better communication quality with the gNB to which the relay UE is connected. Even after HO, it is possible to obtain good communication quality in communication with the gNB via the relay UE.

[0260] Using the above-mentioned determination method, gNB #2 determines the gNB to which the remote UE will be HO'd. In FIG. 17, this is gNB #1. In Step ST1701, gNB #2 determines to HO the remote UE to gNB #1. In Step ST1702, gNB #2 notifies gNB #1 of an HO request. gNB #2 may notify the request by Xn signaling. It may also be notified by using an HO request message.

[0261] Six examples of information to be included in the HO request are disclosed below: (1) Identifier of the UE performing the HO. (2) Information indicating that the HO is performed by connection via a relay UE. (3) Identifier of the relay UE. (4) Identifier of the gNB from which the HO is performed. (5) Identifier of the gNB to which the HO is performed. (6) A combination of (1) to (5).

[0262] (1) identifies the UE that will perform HO. This may be a UE to which the HO destination gNB is not directly connected. (2) may be information indicating that the requested HO is to a gNB that connects via a relay UE. This allows gNB #1 to recognize that the requested HO is a HO in which the UE connects via a relay UE. (3) identifies the UE through which the requested HO will connect to the UE to be HOed. This allows gNB #1 to determine the UE through which to connect to the HO target UE. (4) identifies the gNB from which the HO is originated (sometimes referred to as the source gNB). (5) identifies the gNB to which the HO is destination (sometimes referred to as the target gNB).

[0263] In step ST1703, gNB #1, which has received the HO request from gNB #2, determines whether to accept the HO of the UE that is the target of HO. gNB #1 may determine whether to accept the remote UE that is the target of HO using information on whether the remote UE is connected to a relay UE and whether the relay UE is connected to gNB #1.

[0264] In this case, gNB #2 notifies gNB #1 of information regarding the connection status in PC5 between the remote UE and the relay UE. gNB #2 may also notify gNB #1 of information regarding the connection status of the relay UE. gNB #1 may determine whether to accept the HO of the remote UE that is the HO target, using the information regarding the connection status in PC5 between the remote UE and the relay UE and / or the information regarding the connection status of the relay UE received from gNB #2. gNB #1 may also determine the connection status with the relay UE itself. gNB #1 may determine the connection status with the relay UE using the identifier of the relay UE included in the HO request notified from gNB #2.

[0265] For example, gNB #1 may decide to accept HO for the remote UE when PC5-RRC connection is completed between the relay UE and the remote UE and the relay UE is in an RRC connected state with gNB #1.

[0266] For example, gNB #1 may initiate an RRC connection process for a remote UE when the relay UE is not in an RRC connected state with gNB #1. When gNB #1 performs an RRC connection process with the remote UE, it may decide to accept HO for the remote UE.

[0267] The gNB #1 may determine whether to accept the HO of the remote UE using the services it supports and the reception quality between the gNB #1 and the relay UE. Similar effects can be obtained.

[0268] If gNB #1 decides to accept HO for the remote UE, in Step ST1704, gNB #1 notifies gNB #2 of an HO request response. This notification may use an HO request Ack message or Xn signaling. If gNB #1 decides to accept HO for the remote UE, it may perform RRC configuration for the remote UE. gNB #1 may include the RRC configuration in the HO request response. If it decides not to accept HO, gNB #1 notifies gNB #2 of an HO request rejection. The HO request response or HO request rejection may include the information included in the HO request disclosed above. When gNB #2 receives the HO request response from gNB #1, gNB #2 can determine whether to send an HO instruction to gNB #1 for the remote UE.

[0269] In step ST1705, gNB #2, which has received the HO request response from gNB #1, notifies the remote UE of an HO instruction. The HO instruction may be a notification of connection destination change information to gNB #1. The HO instruction may also be a notification of an RRC setting change associated with the connection destination change to gNB #1. An RRC reconfiguration notification may be used to notify the HO instruction. RRC signaling may be used. An RRC reconfiguration message may also be used. The HO instruction may include the RRC setting information configured by gNB #1 for the remote UE as disclosed above. The HO instruction may also include the information included in the HO request as disclosed above. By receiving an HO instruction from gNB #2 to gNB #1, the remote UE can start the process of changing the gNB to which it is connected. The remote UE can then perform RRC configuration for gNB #1.

[0270] A remote UE that receives an HO instruction from gNB #2 detaches from gNB #2 and establishes an RRC connection with gNB #1, the HO target gNB, via a relay UE. The remote UE may perform RRC configuration using the RRC configuration of gNB #1 notified in the HO instruction from gNB #2 and establish an RRC connection with gNB #1 via the relay UE. The relay UE may be the relay UE included in the HO instruction received from gNB #2. In FIG. 17, a remote UE that receives an HO instruction from gNB #2 detaches from gNB #2 in step ST1706 and notifies gNB #1, the HO target gNB, of RRC reconfiguration completion via the relay UE in step ST1707. The notification may use an RRC reconfiguration complete message. This causes the remote UE to establish an RRC connection with gNB #1.

[0271] The method for notifying gNB #1 of the completion of RRC reconfiguration from a remote UE via a relay UE may be, as appropriate, the method for notifying an RRC connection request or the method for notifying RRC setup completion disclosed in embodiment 1 above.

[0272] In this way, it is possible to HO the remote UE from gNB #2 to gNB #1. The remote UE can change its connection from gNB #2 to gNB #1 via the relay UE while remaining in an RRC connected state.

[0273] A method for scheduling SL communication resources used for RRC reconfiguration completion notification to gNB #1 is disclosed. The scheduling of the SL communication resources is performed by gNB #2. gNB #2 may notify the remote UE of the scheduling information together with the HO instruction. The scheduling information may also be included in the RRC reconfiguration notification. In this way, the remote UE can use the received SL communication resources to send an RRC reconfiguration completion notification to gNB #1 via the relay UE. By having gNB #2 perform the scheduling, interference with other UEs within the coverage of gNB #2 can be reduced.

[0274] As another method, gNB #1 may schedule the SL communication resources. gNB #1 notifies the remote UE of the scheduling information for the SL communication resources via gNB #2. This notification may be an HO request response from gNB #1 to gNB #2, or an HO instruction from gNB #2 to the remote UE. In this way, the remote UE can use the received SL communication resources to send an RRC reconfiguration completion notification to gNB #1 via the relay UE. By having gNB #1 perform the scheduling, it is possible to reduce interference with UEs connected to gNB #1.

[0275] As another method, the remote UE may make a selection using information about the SL of gNB #1. Information about the SL may be included in the system information. A resource pool may be used as the information about the SL. The remote UE acquires information about the SL from gNB #1. The information may be acquired via gNB #2 or via a relay UE. As a method of acquiring information via gNB #2, for example, the information may be included and notified in an HO request response from gNB #1 to gNB #2 or an HO instruction from gNB #2 to the remote UE, and the remote UE may acquire information about the SL from the notification. As a method of acquiring information via a relay UE, for example, gNB #1 may notify the relay UE in the RRC connection process with the relay UE, and the relay UE may notify in the PC5-RRC connection process with the remote UE. In this way, the remote UE can acquire information about the SL of gNB #1. The SL resource pool of gNB #1 can be used.

[0276] As another method, an exception resource pool for SL may be used. The exception resource pool may be notified to the remote UE from gNB #1. It may be included in information related to SL of gNB #1 and notified to the remote UE. Alternatively, the exception resource pool may be notified to the remote UE from gNB #2. It may be included in information related to SL of gNB #2 and notified to the remote UE. The exception resource pool for SL may be used at such a state transition timing. It becomes valid as a resource pool that can be used before scheduling is performed from gNB #1.

[0277] In this way, the remote UE can notify the gNB #1 of the completion of RRC reconfiguration via the relay UE. The gNB #1 can recognize that the remote UE has established an RRC connection with its own gNB #1.

[0278] Data forwarding may be performed during HO between gNB #2 and gNB #1 connected via a relay UE. A data forwarding method during HO between gNB #2 and gNB #1 connected via a relay UE is disclosed.

[0279] This section discloses data forwarding of DL data. gNB #2 transmits DL data to the remote UE until it notifies the remote UE of an HO instruction. gNB #2 buffers DL data that did not arrive at the remote UE when it notifies the remote UE of an HO instruction. After notifying the remote UE of the HO instruction, gNB #2 buffers newly generated DL data. gNB #2 notifies gNB #1 of an SN STATUS TRANSFER. gNB #2 notifies gNB #1 of the DL data transmission status in the SN STATUS TRANSFER. As the DL data transmission status, it is preferable that gNB #2 indicate the SN (Sequence Number) to be assigned to new data that does not yet have an SN. gNB #2 forwards the buffered DL data and newly generated DL data to gNB #1. An End Marker is added to the last DL data to gNB #2. gNB #2 receives up to the last DL data and forwards it to gNB #1. gNB #1 buffers the DL data received from gNB #2.

[0280] After completing the RRC connection with the remote UE (or after receiving an RRC reconfiguration completion from the remote UE), gNB #1 transmits the buffered DL data to the remote UE. gNB #1 transmits up to the DL data with an End Marker attached to the remote UE. If there is newly received DL data for the remote UE from the UPF, gNB #1 transmits the newly received DL data to the remote UE. DL data transmission from gNB #1 to the remote UE is performed via a relay UE connected to the remote UE.

[0281] By doing so, data forwarding of DL data becomes possible during HO between gNB #2 and gNB #1 connected via a relay UE. This makes it possible to reduce the loss of DL data during HO and avoid deterioration of communication quality due to movement of the remote UE.

[0282] Another method for data forwarding of DL data during HO between gNB #2 and gNB #1 connected via a relay UE is disclosed. Differences from the method disclosed above are mainly disclosed.

[0283] After completing the RRC connection with the remote UE (or after receiving an RRC reconfiguration completion from the remote UE), gNB #1 transmits the buffered DL data to the relay UE. gNB #1 transmits up to the DL data with an End Marker attached to the relay UE. The relay UE buffers the DL data received from gNB #1. After completing the PC5-RRC connection with the remote UE, the relay UE transmits the buffered DL data to the remote UE. It transmits up to the DL data with an End Marker attached to the remote UE. After completing the RRC connection with the remote UE (or after receiving an RRC reconfiguration completion from the remote UE), if there is newly received DL data for the remote UE from the UPF, gNB #1 transmits the newly received DL data to the relay UE. After completing the PC5-RRC connection with the remote UE, the relay UE transmits the DL data received from gNB #1 to the remote UE.

[0284] As a data forwarding method, it has been disclosed that gNB #1 transmits buffered DL data to the relay UE after completing the RRC connection with the remote UE (which may be after receiving RRC reconfiguration completion from the remote UE). However, if the RA procedure and / or RRC connection has already been completed between the relay UE and gNB #1, gNB #1 may immediately transmit the DL data forwarded from gNB #2 and the DL data newly received from the UPF to the relay UE. That is, gNB #1 buffers the DL data for the remote UE forwarded from gNB #2 and the DL data for the remote UE newly received from the UPF until the RA procedure and / or RRC connection is completed between the relay UE and gNB #1. gNB #1 transmits the buffered DL data to the relay UE after completing the RA procedure and / or RRC connection between the relay UE and gNB #1.

[0285] Also, as a data forwarding method, it has been disclosed that the relay UE transmits to the remote UE the DL data received and buffered from gNB #1 after completing the PC5-RRC connection with the remote UE. However, if the PC5-RRC connection between the remote UE and the relay UE has already been completed, the relay UE may immediately transmit the DL data received from gNB #1 to the remote UE. That is, the relay UE buffers the DL data for the remote UE received from gNB #1 until the PC5-RRC connection with the remote UE is completed. After the PC5-RRC connection with the remote UE, the relay UE transmits the buffered DL data to the remote UE.

[0286] By doing so, it becomes possible to transmit DL data from gNB #1 to the relay UE early. Therefore, it becomes possible to transmit DL data from the relay UE to the remote UE early. As a result, it becomes possible to reduce the delay in DL data transmission and reception due to HO.

[0287] The processing of UL data will be disclosed. The remote UE transmits UL data to gNB #2 until it detaches from gNB #2. When the remote UE detaches from gNB #2, it may notify gNB #1 of the reception status of UL data, including the SN of the UL data that did not arrive at gNB #2. This allows gNB #1 to determine which UL data the remote UE needs to retransmit. When the remote UE detaches from gNB #2, it buffers the UL data that did not arrive at gNB #2. After detaching from gNB #2, the remote UE buffers newly generated UL data until RRC connection with gNB #1 is completed (or RRC reconfiguration is completed). After RRC connection with gNB #1 is completed (or RRC reconfiguration is completed), the remote UE transmits the buffered UL data and newly generated UL data to gNB #1. At this time, the remote UE transmits UL data to gNB #1 via the relay UE. gNB #1 may cause the remote UE to transmit the data to be retransmitted.

[0288] By doing this, when HO occurs between gNB #2 and gNB #1 connected via a relay UE, it is possible to reduce the loss of UL data during HO, and to avoid deterioration of communication quality due to the movement of remote UEs.

[0289] Another method for processing UL data during HO between gNB #2 and gNB #1 connected via a relay UE is disclosed. The differences from the method disclosed above are mainly disclosed.

[0290] After detaching from gNB #2, the remote UE buffers newly generated UL data until the PC5-RRC connection with the relay UE is completed. After the PC5-RRC connection with the relay UE is completed, the remote UE transmits the buffered UL data and newly generated UL data to the relay UE. The relay UE buffers the UL data received from the remote UE until the RA process with gNB #1 is completed and / or the RRC connection is completed. After the RA process with gNB #1 is completed and / or the RRC connection is completed, the relay UE transmits the buffered UL data and the newly received UL data from the remote UE to gNB #1.

[0291] As a method of processing UL data, it has been disclosed that the remote UE buffers newly generated UL data until the PC5-RRC connection with the relay UE is completed. However, if the PC5-RRC connection between the remote UE and the relay UE has already been completed, the remote UE may immediately transmit the newly generated UL data to the relay UE. That is, it has been disclosed that the relay UE buffers the UL data received from the remote UE until the RA process with the gNB #1 is completed and / or the RRC connection is completed. However, if the RA process or the RRC connection between the relay UE and the gNB #1 has already been completed, the relay UE may immediately transmit the UL data received from the remote UE to the gNB #1.

[0292] By doing so, it becomes possible to transmit UL data from the remote UE to the relay UE early. Therefore, it becomes possible to transmit UL data from the relay UE to gNB #1 early. As a result, it becomes possible to reduce the delay in UL data transmission and reception due to HO.

[0293] By using the method disclosed in this modification, a remote UE connected to gNB #2 can connect to gNB #1 via a relay UE while remaining in an RRC connected state. The remote UE can communicate with gNB #1 via the relay UE. Since HO processing between a directly connected gNB and a gNB connected via a relay UE is possible, communication continuity can be maintained during the HO. Furthermore, since the UE does not need to transition to RRC_IDLE during the HO, delays due to the HO processing can be reduced.

[0294] A remote UE connected to gNB #1 via a relay UE may be HO'd to gNB #2. This allows the remote UE to change its connection destination from gNB #1 to gNB #2 while remaining in the RRC_Connected state.

[0295] Figure 23 is a sequence diagram showing an example of a method for HO of a remote UE from gNB #1 to gNB #2 in accordance with Variant 1 of Embodiment 1. In Figure 23, steps common to those in Figure 17 are assigned the same step numbers, and common explanations will be omitted. In step ST1601, the relay UE is in an RRC connected state with gNB #1. In step ST1411, the remote UE has established a PC5-RRC connection with the relay UE. In step ST1420, the remote UE is in an RRC connected state with gNB #1 via the relay UE.

[0296] In step ST2301, gNB #1 performs Uu measurement configuration for the remote UE. The Uu measurement may be DL measurement. The Uu measurement configuration may be notified via the relay UE. In this way, a remote UE that performs SL communication with the relay UE can notify gNB #1 of the Uu measurement results. The Uu measurement configuration and SL measurement configuration may be combined. Alternatively, the Uu measurement configuration may include SL measurement configuration. For example, an event for comparing SL measurement results with Uu measurement results may be set as an event for reporting Uu measurement results. For example, an event may be set as a predetermined condition when the SL reception quality becomes greater than the reception quality of the serving cell. The event for setting SL measurement result reporting disclosed in embodiment 1 may be applied as an event. In this way, SL measurement can be included in the Uu measurement configuration. Flexible measurement result reporting is possible. gNB #1 can acquire Uu measurement results and SL measurement results from the remote UE.

[0297] In Step ST2302, the remote UE performs Uu measurement and SL measurement using the Uu measurement configuration and SL measurement configuration notified by gNB #1. In Step ST2303, the remote UE notifies gNB #1 of the Uu measurement results and SL measurement results in accordance with the measurement result report configuration notified by gNB #1 in Step ST2301. It is preferable to notify via a relay UE. In this way, gNB #1 can obtain the Uu measurement results and SL measurement results from the remote UE.

[0298] In step ST2304, gNB #1 determines whether to HO the remote UE from gNB #1 and to which gNB to HO. For this determination, the Uu measurement results received from the remote UE may be used. SL measurement results may also be used. For example, gNB #1 may determine HO to gNB #2 if the DL reception quality from gNB #2 at the remote UE is higher than the SL reception quality from the relay UE.

[0299] gNB #1 may use the communication quality with the relay UE to determine whether HO of the remote UE to gNB #2 is possible or whether to HO. For example, gNB #1 configures Uu measurements for the relay UE. gNB #1 receives a Uu measurement result report from the relay UE. The Uu measurement may be a measurement of the DL reception quality at the relay UE. gNB #1 uses the Uu measurement result received from the relay UE to determine whether to HO the remote UE to gNB #2. For example, gNB #1 may determine to HO the remote UE to gNB #2 if the DL reception quality from the serving cell at the relay UE becomes lower than a predetermined threshold. gNB #1 may also take into account the DL reception quality measurement results of neighboring cells. For example, gNB #1 may determine to HO the remote UE to gNB #2 if the DL reception quality from the serving cell and neighboring cells at the relay UE becomes lower than a predetermined threshold. In this way, by using the communication quality of Uu between gNB #1 and the relay UE, if the communication quality between gNB #1 and the relay UE deteriorates, gNB #1 can HO the remote UE from gNB #1 to gNB #2. gNB #1 can change communication from communication to gNB #1 via the relay UE to communication directly to gNB #2. It is possible to improve the communication quality between the remote UE and the NW.

[0300] In Step ST2304, gNB #1 decides to HO the remote UE to gNB #2. In Step ST2305, gNB #1 notifies gNB #2 of an HO request. The notification may be made by Xn signaling. An HO request message may also be used. The HO request may include the information to be included in the HO request disclosed above.

[0301] In step ST2306, gNB #2, which has received the HO request from gNB #1, determines whether to accept the HO of the UE that is the target of HO. gNB #2 may determine whether to accept the remote UE that is the target of HO using information on whether the remote UE is connected to a relay UE and whether the relay UE is connected to gNB #1.

[0302] gNB #1 may notify gNB #2 of information indicating that the remote UE is connected via a relay UE. gNB #2 may use the information received from gNB #1 indicating that the remote UE is connected via a relay UE to determine whether to accept HO of the remote UE that is the HO target.

[0303] gNB #2 may use the services it supports to determine whether to accept HO of the remote UE. A similar effect can be achieved.

[0304] If gNB #2 decides to accept HO for the remote UE, in Step ST2307, gNB #2 notifies gNB #1 of an HO request response. This notification may use an HO request Ack message or Xn signaling. If gNB #2 decides to accept HO for the remote UE, it may perform RRC configuration for the remote UE. gNB #2 may include the RRC configuration in the HO request response. If gNB #2 decides not to accept HO for the remote UE, gNB #2 notifies gNB #1 of an HO request rejection. The HO request response and HO request rejection may include the information included in the HO request disclosed above. When gNB #1 receives the HO request response from gNB #2, gNB #1 can determine whether to send an HO instruction to gNB #2 to the remote UE.

[0305] In step ST2308, gNB #1, which has received the HO request response from gNB #2, notifies the remote UE of an HO instruction. gNB #1 may notify the remote UE of the HO instruction via the relay UE. The HO instruction may be notification of connection destination change information to gNB #2. It may also be a change in RRC settings associated with the connection destination change to gNB #2. An RRC reconfiguration notification may be used to notify the HO instruction. RRC signaling may be used. An RRC reconfiguration message may be used. The HO instruction may include the RRC setting information configured by gNB #2 for the remote UE as disclosed above. It may also include the information included in the HO request as disclosed above. The remote UE receives the HO instruction from gNB #1 to gNB #2. The remote UE receives the HO instruction to gNB #2 from gNB #1 via the relay UE. The relay UE receives an HO instruction to gNB #2 from gNB #1 for the remote UE. The relay UE transmits the HO instruction to gNB #2 received from gNB #1 to the remote UE. The remote UE receives an HO instruction to gNB #2 from the relay UE. In this way, by receiving an HO instruction to gNB #2 from gNB #1 via the relay UE, the remote UE can start the process of changing the gNB to which it is connected. The remote UE can perform RRC configuration for gNB #2.

[0306] In Step ST2309, the remote UE that has received the HO command from gNB #1 notifies gNB #2, the HO target gNB, of the completion of RRC reconfiguration. This notification may use an RRC reconfiguration complete message. As a result, the remote UE establishes an RRC connection with gNB #2. The remote UE may perform RRC configuration using the RRC configuration of gNB #2 notified by gNB #1 in the HO command, and establish an RRC connection with gNB #1 via the relay UE. As a result, in Step ST2310, an RRC connection is established between the remote UE and gNB #2.

[0307] A remote UE that receives an HO instruction from gNB #1 may perform a process to release resources required for RRC connection with gNB #1. A remote UE that receives an HO instruction from gNB #1 may perform a process for the conventional HO source gNB.

[0308] A remote UE that receives an HO instruction from gNB #1 may release the RRC connection with the relay UE. A remote UE that receives an HO instruction from gNB #1 may release the radio bearer (RB) with the relay UE. In this case, processing on the PC5 of the remote UE is not required, and low power consumption is achieved. Alternatively, a remote UE that receives an HO instruction from gNB #1 may not release the RRC connection with the relay UE. A remote UE that receives an HO instruction from gNB #1 may not release the radio bearer (RB) with the relay UE. In this case, the remote UE can communicate with the relay UE early when communication with the relay UE is necessary.

[0309] In this way, it is possible to HO the remote UE from gNB #1 to gNB #2. The remote UE can change its connection from gNB #1 to gNB #2 via the relay UE while remaining in the RRC connected state.

[0310] The remote UE may be HO'd from a gNB via a relay UE to another gNB via the relay UE. The remote UE may be HO'd from a gNB via a relay UE to another gNB via another relay UE. The method disclosed in this specification may be applied as appropriate. Depending on the connection status of the remote UE, the radio wave propagation environment of the Uu between the remote UE and the relay UE, the remote UE and the gNB, and the radio wave propagation environment of the SL between the remote UE and the relay UE, it is possible to HO the remote UE to a gNB suitable for communication.

[0311] This section discloses data forwarding of DL data. gNB #1 transmits DL data to the remote UE until it notifies the remote UE of an HO instruction via the relay UE. gNB #1 buffers DL data that did not arrive at the remote UE when it notifies the remote UE of the HO instruction. After notifying the remote UE of the HO instruction, gNB #1 buffers newly generated DL data. gNB #1 notifies gNB #2 of an SN STATUS TRANSFER. gNB #1 notifies gNB #2 of the DL data transmission status in the SN STATUS TRANSFER. The DL data transmission status may indicate the SN to be assigned to new data that gNB #1 does not yet have an SN. gNB #1 forwards the buffered DL data and newly generated DL data to gNB #2. An End Marker is attached to the last DL data to gNB #1. gNB #1 receives up to the last DL data and forwards it to gNB #2. gNB #2 buffers the DL data received from gNB #1.

[0312] After completing the RRC connection with the remote UE (or after receiving an RRC reconfiguration completion from the remote UE), gNB #2 transmits the buffered DL data to the remote UE. gNB #2 transmits up to the DL data with an End Marker attached to the remote UE. If there is newly received DL data for the remote UE from the UPF, gNB #2 transmits the newly received DL data to the remote UE.

[0313] By doing so, data forwarding of DL data becomes possible during HO between gNB #1 and gNB #2 connected via a relay UE. It is possible to reduce the loss of DL data during HO and avoid deterioration of communication quality due to movement of the remote UE.

[0314] The processing of UL data will be disclosed. The remote UE transmits UL data to gNB #1 until it receives an HO instruction from gNB #1. The remote UE may notify gNB #2 of the reception status of the UL data, including the SN of the UL data that did not arrive at gNB #1. gNB #2 can determine which UL data the remote UE needs to retransmit. When the remote UE receives an HO instruction from gNB #1, it buffers the UL data that did not arrive at gNB #1. After receiving the HO instruction from gNB #1, the remote UE buffers newly generated UL data until RRC connection with gNB #2 is completed (or RRC reconfiguration is completed). After RRC connection with gNB #2 is completed (or RRC reconfiguration is completed), the remote UE transmits the buffered UL data and newly generated UL data to gNB #2. gNB #2 may cause the remote UE to transmit the data to be retransmitted.

[0315] By doing this, when HO occurs between gNB #1 and gNB #2, which are connected via a relay UE, it is possible to reduce the loss of UL data during HO, and to avoid deterioration of communication quality due to the movement of remote UEs.

[0316] In the above example, it has been disclosed that the SL measurement results at the remote UE are used to determine HO. The HO determination is not limited to the SL measurement results. For example, HO may be determined using the load status of gNB #2. For example, HO may be determined due to a change in the QoS required for communication. For example, HO may be determined due to an instruction from the CN. For example, HO may be determined due to a request from gNB #1. For example, HO may be determined due to a request from the remote UE. For example, HO may be determined due to a request from the relay UE. In this way, HO suitable for the radio wave propagation environment can be performed between gNBs, including gNBs that can be connected via the relay UE. It is possible to improve the communication quality between the remote UE and the NW.

[0317] In a situation where a remote UE has an RRC connection with gNB #1 via a relay UE, if a Radio Link Failure (RLF) occurs between the relay UE and gNB #1, the RRC connection between the remote UE and gNB #1 may be released. A relay UE that detects an RLF with gNB #1 may notify the remote UE of a request to release the RRC connection with gNB #1. The request may include cause information. The cause information may include information indicating an RLF between gNB #1 and the relay UE. A remote UE that receives an RRC connection release request from the relay UE releases the settings required for the RRC connection with gNB #1. In this way, if an RLF occurs between the relay UE and gNB #1, there is no need to maintain the resources required for the RRC connection with gNB #1 in the remote UE, thereby improving resource utilization efficiency.

[0318] In the above description, it is assumed that a RLF (Radio Link Failure) occurs between the relay UE and the gNB #1, but it may also be assumed that the RRC connection between the relay UE and the gNB #1 is released. For example, it may be assumed that the RRC connection is released due to an RLF. In this way, it is possible to obtain the same effect.

[0319] When an RLF occurs between the relay UE and gNB #1, if the RRC connection to the same gNB or another gNB can be established again before the RRC connection is released, the remote UE may not be requested to release the RRC connection. In this way, when the RRC connection between the relay UE and the gNB becomes possible, communication between the remote UE and the gNB can be performed quickly.

[0320] PDCP retransmission may be performed in communication between gNB #1 and a remote UE via a relay UE. PDCP retransmission of data that could not be received is performed. Regarding data transmitted to a remote UE via a relay UE, if the remote UE is unable to receive the data, gNB #1 transmits the data to the remote UE again via the relay UE. Regarding data transmitted to gNB #1 via a relay UE, if gNB #1 is unable to receive the data, the remote UE transmits the data to gNB #1 again via the relay UE. In this way, communication quality can be improved even when communication between gNB #1 and a remote UE is performed via a relay UE.

[0321] In communication between gNB #1 and a remote UE via a relay UE, the data reception status may be reported. PDCP Status may be reported as the data reception status report. For example, a remote UE that receives data from gNB #1 via a relay UE reports the data reception status to gNB #1 via the relay UE. For example, gNB #1 that receives data from a remote UE via a relay UE reports the data reception status to the remote UE via the relay UE. PDCP SN may be used as the data reception status. When gNB #1 transmits, the PDCP SN assigned by gNB #1 may be used. When a remote UE transmits, the PDCP SN assigned by the remote UE may be used. The PDCP SN may be used to determine whether data has arrived. For example, the PDCP SNs of the first to last data that have not arrived may be reported as the data reception status.

[0322] In this way, gNB #1 or a remote UE that receives a report on the data reception status can recognize the data transmission status. gNB #1 or a remote UE can recognize data that has not arrived. gNB #1 or a remote UE that receives a report on the data reception status may retransmit data that has not arrived. In this way, by reporting the data reception status, for example, by reporting a PDCP Status, gNB #1 or a remote UE can retransmit data that has not arrived. Even when communication between gNB #1 and a remote UE is performed via a relay UE, communication quality can be improved.

[0323] Another method for solving the problem is disclosed. A data reception status may be reported between a relay UE and a remote UE. A PDCP Status report may be used as the data reception status report. When a relay UE transmits, the PDCP SN assigned by the relay UE may be used. When a remote UE transmits, the PDCP SN assigned by the remote UE may be used. A relay UE or a remote UE that receives a data reception status report can recognize a data transmission status. A relay UE or a remote UE can recognize data that has not arrived. A relay UE or a remote UE that receives a data reception status report may retransmit the data that has not arrived. In this way, by reporting a data reception status between a relay UE and a remote UE, for example, a PDCP Status report, the relay UE or the remote UE can retransmit data that has not arrived. This improves communication quality in communication between a relay UE and a remote UE.

[0324] The relay UE may notify gNB #1 of the data reception status between the relay UE and the remote UE. By receiving the reception status, gNB #1 can recognize whether data communication between the relay UE and the remote UE has been performed reliably. gNB #1 can recognize the data transmission status using the data reception status between the relay UE and the remote UE received from the relay UE. gNB #1 may determine whether to retransmit data to the remote UE. For example, gNB #1 may retransmit data that was not transmitted from the relay UE to the relay UE. The relay UE can retransmit retransmitted data received from gNB #1 to the remote UE. In this way, communication quality can be improved even when communication between gNB #1 and the remote UE is performed via a relay UE.

[0325] The data reception status may be reported between gNB #1 and the relay UE. PDCP Status may be reported as the data reception status report. When gNB #1 transmits, the PDCP SN assigned by gNB #1 may be used. When a relay UE transmits, the PDCP SN assigned by the relay UE may be used. Upon receiving the data reception status report, gNB #1 or the relay UE can recognize the data transmission status. gNB #1 or the relay UE can recognize data that has not arrived. Upon receiving the data reception status report, gNB #1 or the relay UE may retransmit the data that has not arrived. In this way, by reporting the data reception status between gNB #1 and the relay UE, for example, by reporting PDCP Status, gNB #1 or the relay UE can retransmit the data that has not arrived. This improves the communication quality in communication between gNB #1 and the relay UE.

[0326] The relay UE may notify the remote UE of the data reception status between gNB #1 and the relay UE. By receiving the reception status, the remote UE can recognize whether data communication between gNB #1 and the relay UE has been performed reliably. The remote UE can recognize the data transmission status using the data reception status between gNB #1 and the relay UE received from the relay UE. The remote UE may determine whether to retransmit data to gNB #1. For example, the remote UE may retransmit data that was not transmitted from the relay UE to gNB #1 to the relay UE. The relay UE can retransmit retransmitted data received from the remote UE to gNB #1. In this way, communication quality can be improved even when communication between gNB #1 and the remote UE is performed via a relay UE.

[0327] The method of reporting the data reception status between the relay UE and the remote UE and the method of reporting the data reception status between the gNB #1 and the relay UE may be combined. The gNB #1 or the remote UE may determine whether to retransmit data using the data reception status of each individual link of Uu and PC5. The relay UE may also determine whether to retransmit data and perform the data retransmission. For example, if data from one link has not arrived, the relay UE retransmits the data. If data from both links has not arrived, the gNB #1 or the remote UE retransmits the data. By using this method, it is possible to reduce delays in communication between the gNB #1 and the remote UE via the relay UE. Even when communication between the gNB #1 and the remote UE is performed via the relay UE, it is possible to further improve communication quality.

[0328] The above-described method may be applied as appropriate to the data forwarding process during HO between gNB #1 and gNB #2, which are connected via a relay UE of a remote UE. This makes it possible to reduce data loss during the HO.

[0329] Embodiment 2 As shown in embodiment 1, there are cases where the relay UE and the remote UE are located within the coverage of different gNBs. For example, when the remote UE is located at the edge of the coverage of gNB #2, the remote UE may experience better reception quality with the relay UE than reception quality from gNB #2. In such a case, even if the remote UE is not RRC connected and is in an RRC_IDLE state, its operation becomes unclear, and a problem occurs in which processing in the RRC_IDLE state cannot be performed.

[0330] For example, the remote UE may not know which gNB to camp on, gNB #2 or gNB #1 via the relay UE, which gNB to use the system information transmitted from, or which gNB to use the resource pool (RP) for SL communication transmitted from, which problem arises in which processing cannot be performed in the RRC_IDLE state.

[0331] In this embodiment, a method for solving such a problem will be disclosed.

[0332] To solve this problem, a remote UE according to this embodiment receives system information transmitted by gNB #2 in which the remote UE is in coverage. Examples of system information include MIB and SIB. The system information may include system information for SL communication. The remote UE may receive all system information transmitted by gNB #2. The remote UE uses the system information received from gNB #2. The remote UE camps on gNB #2. Even if the reception quality from a relay UE that can connect to or is connected to the NW is better than the reception quality from gNB #2, the remote UE receives the system information transmitted by gNB #2. The remote UE camps on gNB #2. If there are multiple gNBs in coverage of a remote UE, the remote UE can use conventional cell selection and cell reselection methods to determine which gNB's system information it receives (see non-patent document 32 (3GPP TS38.304)).

[0333] In this way, the remote UE in RRC_IDLE can determine which gNB to use for system information transmitted from. Therefore, the remote UE can perform processing in RRC_IDLE.

[0334] Another method for solving the problem is disclosed.

[0335] Until the discovery process of the relay UE is completed, the remote UE receives system information transmitted by gNB #2, which is in coverage. The remote UE uses the system information received from gNB #2. The remote UE camps on gNB #2. After the discovery process of the relay UE is completed, the remote UE receives system information transmitted by gNB #1 via the relay UE. The remote UE uses the system information transmitted by gNB #1. The remote UE may camp on gNB #1.

[0336] The relay UE may receive system information from gNB #1. The relay UE may notify the remote UE of the system information received from gNB #1. In the discovery process, the relay UE may notify the remote UE of the system information of gNB #1. In this way, the remote UE can receive the system information of gNB #1 via the relay UE and use the system information.

[0337] By receiving the system information transmitted by gNB #1 after the relay UE has completed its discovery process, the remote UE is able to use gNB #1's system information early on.

[0338] Until the PC5-S link with the relay UE is established, the remote UE may receive system information transmitted by gNB #2. The remote UE uses the system information received from gNB #2. The remote UE camps on gNB #2. After the PC5-S link with the relay UE is established, the remote UE receives system information transmitted by gNB #1 via the relay UE. The remote UE uses the system information transmitted by gNB #1. The remote UE may camp on gNB #1.

[0339] The relay UE may receive system information from gNB #1. The relay UE may notify the remote UE of the system information received from gNB #1. In the discovery process, the relay UE may notify the remote UE of the system information of gNB #1. In the PC5-S link establishment process, the relay UE may notify the remote UE of the system information of gNB #1. In this way, the remote UE can receive the system information of gNB #1 via the relay UE and use the system information.

[0340] By receiving the system information transmitted by gNB #1 after establishing a PC5-S link with the relay UE, the remote UE can use the system information of gNB #2 when a PC5-S link with the relay UE has not yet been established.

[0341] Until the PC5-RRC connection with the relay UE is completed, the remote UE may receive system information transmitted by gNB #2. The remote UE uses the system information received from gNB #2. The remote UE camps on gNB #2. After the PC5-RRC connection with the relay UE is completed, the remote UE receives system information transmitted by gNB #1 via the relay UE. The remote UE uses the system information transmitted by gNB #1. The remote UE may camp on gNB #1.

[0342] The relay UE may receive system information from gNB #1. The relay UE may notify the remote UE of the system information received from gNB #1. In the discovery process, the relay UE may notify the remote UE of the system information of gNB #1. In the PC5-S link establishment process, the relay UE may notify the remote UE of the system information of gNB #1. In the PC5-RRC connection process, the relay UE may notify the remote UE of the system information of gNB #1. In this way, the remote UE can receive the system information of gNB #1 via the relay UE and use the system information.

[0343] By receiving the system information transmitted by gNB #1 after completing the RRC connection process with the relay UE, the remote UE can use the system information of gNB #2 when it becomes possible to send and receive data with the relay UE via PC5-RRC messages or PC5. When the remote UE is not yet able to send and receive data with the relay UE via PC5-RRC messages or PC5, it can use the system information of gNB #2.

[0344] In this way, a remote UE in RRC_IDLE can determine which gNB to use for system information transmitted from. Also, the remote UE can use system information from gNB #1. The remote UE can camp on gNB #1.

[0345] Figure 18 is a sequence diagram showing an example of a method in which a remote UE uses system information received from gNB #1 for embodiment 2. In Figure 18, steps common to those in Figure 14 are assigned the same step numbers, and common explanations are omitted. Figure 18 shows a method in which a remote UE receives and uses system information from gNB #2 or gNB #1 depending on the connection status of PC5 between the remote UE and the relay UE. In the method shown in Figure 18, the remote UE receives system information transmitted by gNB #2 and uses the system information until the PC5-RRC connection with the relay UE is completed, and after the PC5-RRC connection with the relay UE is completed, the remote UE receives system information transmitted by gNB #1 via the relay UE and uses the system information.

[0346] In Step ST1801, the remote UE is in the in-coverage area of ​​gNB #2 and is in RRC_IDLE state. In Step ST1802, the relay UE receives system information from gNB #1. In Step ST1803, the remote UE receives system information from gNB #2. In Steps ST1409 to ST1411, a PC5 connection is established between the remote UE and the relay UE. If the relay UE has completed the PC5-RRC connection with the remote UE in Step ST1411, the relay UE notifies the remote UE of the system information of gNB #1 in Step ST1805. The relay UE may also broadcast the system information of gNB #1. If the remote UE has completed the PC5-RRC connection with the relay UE in Step ST1411, the remote UE changes the gNB from which the system information is received from gNB #2 to gNB #1 in Step ST1804. In step ST1805, the remote UE receives the system information of gNB #1 transmitted by the relay UE. This enables the remote UE to use the system information transmitted from gNB #1.

[0347] In the discovery process, the remote UE may use the RP received from gNB #2, which is in coverage. This can be used in the discovery process with the first relay UE. In the discovery process, the remote UE may use the RP received from the gNB that receives system information. In the discovery process, the remote UE may use the RP received from the gNB that receives system information regarding SL. This may be used, for example, when the remote UE is connected to multiple relay UEs. When the remote UE is already connected to a relay UE, it is possible to use the system information received from gNB #1 when performing the discovery process for a new relay UE.

[0348] The relay UE may store the system information received from gNB #1. For example, it stores the system information received in step ST1802. The relay UE becomes able to transmit the system information to the remote UE on PC5 at any timing. When the system information of gNB #1 is modified, the relay UE may store the modified system information received from gNB #1 as updated system information. The relay UE may notify the remote UE that the system information of gNB #1 has been modified. When the system information of gNB #1 is modified, the relay UE may notify the remote UE of the modified system information of gNB #1.

[0349] A method for notifying system information between UEs on a PC5 is disclosed. The relay UE notifies the remote UE of the system information received from gNB#1. Unicast communication in SL may be used for the notification. Alternatively, groupcast communication in SL may be used for the notification. gNB#1 may be the gNB from which the relay UE receives the system information. gNB#1 may be the gNB on which the relay UE is camped, or may be the gNB to which the relay UE is connected.

[0350] As a method for the relay UE to notify the remote UE of the system information, the method of notifying the PC5 of the RRC connection request via the relay UE disclosed in the first embodiment may be appropriately applied. As another solution, a new channel to be used for notifying the system information may be provided. By separating the channel including the system information from other channels, the remote UE can reduce malfunctions in the reception process of the system information.

[0351] The relay UE may notify the remote UE of system information by including it in an RRC message of PC5. A container for the RRC message of Uu may be provided in the RRC message of PC5. A container for system information may be provided. A container for an individual RRC message may be provided. In this way, the relay UE can easily transfer the RRC message received from gNB #1 to the remote UE as an RRC message of PC5. The relay UE may be transparent about the container information. In this way, the processing of the relay UE can be made easier.

[0352] The timing at which a relay UE notifies a remote UE of system information is disclosed. The relay UE periodically notifies the remote UE of the system information. The notification may be performed using physically periodic resources. Alternatively, the notification may be performed using logically periodic resources. Logically periodic resources refer to periodically setting resources among resources available for SL communication. For example, if the resources available for SL communication are not continuous, only the resources available for SL communication, excluding resources not available for SL communication, are counted continuously, and resources are set periodically in this count. In this way, periodicity can be obtained within the resources available for SL communication, even if the resources available for SL communication are discontinuous.

[0353] Another method of notification timing is disclosed. When a relay UE receives system information from gNB #1, the relay UE notifies the remote UE of the system information. When a relay UE receives new or modified system information from gNB #1, the relay UE may notify the remote UE of the system information. In this way, by having the relay UE notify the remote UE of the system information triggered by the reception of the system information, it is possible to reduce waste of SL resources used for notifying the system information.

[0354] Another method of notification timing is disclosed. The remote UE notifies the relay UE of a system information request. The system information request may be a request for system information of the gNB to which the relay UE is connected, or may be a request for system information stored in the relay UE. The notification of the system information request may be appropriately applied to the notification method of information related to the connection state of the relay UE disclosed in the first embodiment. When the relay UE receives a system information request from the remote UE, it notifies the remote UE of the system information.

[0355] In this way, the relay UE can notify the remote UE of the system information received from gNB #1. The remote UE can receive the system information of gNB #1 via the relay UE.

[0356] Another method for notifying system information between UEs on PC5 is disclosed. The relay UE broadcasts the system information received from gNB #1. Broadcast communication in SL may be used. Notification may be by PC5-S signaling. In this way, notification is possible early in the PC5 connection process. Alternatively, notification may be by PC5-RRC signaling. For example, notification may be included in an RRC message on PC5. For example, when notifying the RRC connection status with the NW, by using RRC signaling in PC5 as well, notification processing can be performed in the same RRC layer, thereby reducing malfunctions. In addition, the information may be notified by the SRB of PC5. In this way, system information can be notified as signaling information and control information.

[0357] The information may be notified using PC5 MAC signaling. In this case, notification is possible earlier than RRC signaling. These signalings may include information indicating that they are broadcast. Alternatively, they may include information indicating that they are system information. Alternatively, they may include information indicating that they are system information received by the relay UE from gNB #1. In this way, one or more UEs receiving PC5 communication can receive the signaling.

[0358] The information may be notified via PSCCH. The information may be notified by including it in the 1st SCI. In this way, notification can be made earlier. The 1st SCI may include information indicating that it is broadcast. Alternatively, it may include information indicating that it is system information. It may also include information indicating that it is system information received by the relay UE from gNB #1. In this way, one or more UEs capable of receiving PC5 communication can receive the information.

[0359] The information may be notified by PSSCH. The information may be included in 2nd SCI and notified. The information may be included in MAC CE and notified by PSSCH. Information indicating that it is broadcast may be included in the 2nd SCI or MAC CE of PSCCH. Alternatively, information indicating that it is system information may be included. Information indicating that it is system information received by the relay UE from gNB #1 may be included. Furthermore, when used for broadcast, it is recommended that HARQ not be applied. In this way, one or more UEs capable of receiving PC5 communication can receive the information.

[0360] The information may be notified via PSBCH, which is a channel broadcast in SL. By including the information in this channel, the relay UE can broadcast the information, and one or more UEs capable of receiving PC5 communication can receive the information.

[0361] A channel may be provided for broadcasting the information, which can be distinguished from other signaling and channels, thereby reducing malfunctions in the reception processing of the information at the UE.

[0362] Another method for solving the problem is disclosed.

[0363] The gNB instructs the remote UE which gNB is to receive the system information. gNB #2 may instruct the remote UE which gNB is to receive the system information (hereinafter, sometimes referred to as the system information receiving gNB). The indication information of the system information receiving gNB may be included in the system information and broadcast by gNB #2. Alternatively, the indication information of the system information receiving gNB may be notified to the remote UE by gNB #2 using dedicated signaling. For example, RRC signaling, MAC signaling, or PDCCH may be used. gNB #2 may notify the remote UE to which the relay UE is connected. The indication information of the system information receiving gNB may be information indicating whether to receive system information from its own gNB or from the gNB to which the relay UE is connected.

[0364] The gNB #1 may instruct the remote UE which gNB should receive the system information. The instruction may be notified via the relay UE. The gNB #1 may include the instruction information in the system information and broadcast it to the relay UE. Alternatively, the gNB #1 may notify the relay UE using dedicated signaling. For example, RRC signaling, MAC signaling, or PDCCH may be used. The relay UE notifies the remote UE of the instruction information. The notification may be appropriately performed using the above-mentioned broadcast information transmission method. The instruction information for the system information receiving gNB may be information indicating whether to receive system information from its own gNB or from the gNB to which the remote UE is connected.

[0365] The system information of which gNB to use for the remote UE may be statically determined in advance by a standard or the like. Alternatively, it may be adjusted between gNBs. Alternatively, it may be determined by the CN. In this way, unified processing can be performed within the NW.

[0366] Instead of instructions from the gNB, the relay UE may instruct the remote UE which gNB to receive the system information. For example, the relay UE may instruct the remote UE which gNB to receive the system information from depending on the connection status between the relay UE and gNB #1. In this way, it is possible to instruct the remote UE which gNB to receive the system information from depending on the situation of the relay UE.

[0367] Figure 19 is a sequence diagram showing an example of a method in which a gNB instructs a remote UE from which gNB to receive system information, according to the second embodiment. In Figure 19, steps common to those in Figure 18 are assigned the same step numbers, and common explanations will be omitted. In step ST1901, gNB #1 broadcasts a system information reception instruction of its own gNB. The system information reception instruction of its own gNB may be applied only to remote UEs connected via a relay UE. The system information reception instruction of its own gNB may include information indicating that it is applied only to remote UEs connected via a relay UE. The system information reception instruction of its own gNB may be included in the system information.

[0368] The relay UE that has received the gNB #1 system information reception instruction broadcast from gNB #1 executes steps ST1409 to ST1411 to complete the PC5-RRC connection with the remote UE, and then in step ST1902, notifies the remote UE that is connected to the PC5-RRC of the gNB #1 system information reception instruction. Also, in step ST1805, the relay UE notifies the remote UE of the gNB #1 system information. The remote UE that has received the gNB #1 system information reception instruction changes the gNB that receives the system information from gNB #2 to gNB #1 in step ST1804, and receives the gNB #1 system information in step ST1805.

[0369] Although the system information reception instruction of gNB #1 has been disclosed, it may be information on whether to use the system information of gNB #1. The remote UE that receives the information determines whether to receive the system information of gNB #1 according to the information.

[0370] Although the system information reception instruction of gNB #1 has been disclosed, it may be an instruction to use system information of gNB #1. A remote UE that receives the instruction receives and uses the system information of gNB #1.

[0371] The system information of gNB #1 transmitted from the relay UE via SL may include an instruction to receive system information of gNB #1. It may also be an instruction to use system information of gNB #1. The remote UE receives the system information of gNB #1 transmitted from the relay UE via SL, and if the instruction to use system information of gNB #1 is included, the remote UE uses the system information of gNB #1.

[0372] The gNBs may adjust whether to use the system information transmitted from gNB #1 via the relay UE or the system information of gNB #2 in in-coverage. Alternatively, the AMF may adjust and notify each gNB. Alternatively, a node having a management function may adjust and notify each gNB. The notification may be via the AMF. Depending on the adjustment result, the gNB may decide whether to instruct its own gNB to receive system information and transmit an instruction to receive system information for its own gNB.

[0373] By doing this, the network side can determine which gNB's system information the remote UE should receive and use.

[0374] The remote UE receives some of the system information from gNB #2 and other system information from gNB #1. The remote UE uses some of the system information received from gNB #2 and other system information received from gNB #1. For example, the remote UE receives system information related to SL from gNB #2 and other system information from gNB #1. The remote UE uses system information related to SL received from gNB #2 and other system information received from gNB #1. It is possible to set an appropriate system information reception gNB depending on the type of system information.

[0375] For example, the remote UE may receive system information related to connection with the NW from gNB #2 and system information related to SL from gNB #1. The remote UE uses the system information related to connection with the NW received from gNB #2 and the system information related to SL received from gNB #1. In this way, system information related to connection on Uu can be obtained from gNB #2, which is in coverage, and system information related to connection on PC5 with the relay UE can be obtained from gNB #1, which connects via the relay UE.

[0376] Another method for solving the problem is disclosed.

[0377] The remote UE receives system information from the cell selected or reselected by the method disclosed in Variant 1 of Embodiment 2 described later. The remote UE uses the system information received from the cell selected or reselected. From the discovery process until the completion of the PC5-RRC connection, the system information may be received from gNB #2. From the discovery process until the completion of the PC5-RRC connection, the remote UE may use the system information received from gNB #2. For system information related to SL, from the discovery process until the completion of the PC5-RRC connection, the system information received from gNB #2 may be used.

[0378] Another method for solving the problem is disclosed.

[0379] The remote UE receives system information from the gNB with which it was last connected via RRC. For example, if the gNB with which it was last connected via RRC is gNB #2, after releasing the RRC connection, the remote UE receives system information from gNB #2. For example, if the RRC connection is released due to the end of communication, it becomes possible to select or reselect a cell from which to receive system information early.

[0380] By using the method disclosed in this embodiment, the remote UE can receive system information. Even if a remote UE in the in-coverage of gNB #2 connects to a relay UE connected to gNB #1, it is possible to determine which gNB's system information to receive and use. Therefore, the processing in the remote UE in the RRC_IDLE state is clarified, and malfunctions in the processing can be reduced.

[0381] Variation 1 of Embodiment 2. In the problem described in Embodiment 2, for example, a remote UE in RRC_IDLE performs cell selection and cell reselection processing. However, when considering gNB #1 via a relay UE in addition to gNB #2 in which the remote UE is in coverage, it becomes unclear what kind of cell selection and cell reselection processing to perform. As a result, a problem occurs in which the remote UE cannot perform processing in the RRC_IDLE state.

[0382] In this modification, a method for solving such a problem will be disclosed.

[0383] In this modification, the remote UE performs cell selection by prioritizing a gNB that is out of coverage. The remote UE may also perform cell reselection by prioritizing a gNB that is out of coverage. If the reception quality from gNB #2 meets the criteria for cell selection and cell reselection, the remote UE performs cell selection and cell reselection of gNB #2. The remote UE receives system information transmitted from the gNB that has selected or reselected the cell. The remote UE uses system information transmitted from the gNB that has selected or reselected the cell. The remote UE may also receive paging transmitted from the gNB that has selected or reselected the cell.

[0384] Another method for solving the problem is disclosed.

[0385] The remote UE performs cell selection by prioritizing the gNB to which the relay UE is connected. The remote UE may perform cell reselection by prioritizing the gNB to which the relay UE is connected. If the SL reception quality from the relay UE exceeds a predetermined threshold, the remote UE may perform cell selection and cell reselection by prioritizing the gNB to which the relay UE is connected. The remote UE receives system information transmitted from the gNB to which the relay UE that has selected or reselected a cell is connected. The remote UE uses system information transmitted from the gNB to which the relay UE that has selected or reselected a cell is connected. The remote UE may receive paging transmitted from the gNB to which the relay UE that has selected or reselected a cell is connected.

[0386] By performing priority control in this manner, it becomes possible to facilitate cell selection and cell reselection processes in the remote UE, and it becomes possible to reduce malfunctions in the remote UE.

[0387] Another method for solving the problem is disclosed.

[0388] The remote UE performs cell selection and cell reselection based on both the gNB in ​​coverage and the gNB to which the relay UE is connected. The remote UE measures the reception quality from the gNB in ​​coverage and the SL reception quality from the relay UE. Based on the reception quality from the gNB in ​​coverage and the SL reception quality from the relay UE, the remote UE selects the best cell or relay UE from among the cells in coverage of the remote UE and relay UEs that meet the criteria for cell selection and cell reselection. If the selected cell is a relay UE, the cell of the gNB to which the relay UE is connected is considered to be the selected cell. The remote UE receives system information transmitted from the selected best cell. The remote UE uses the system information transmitted from the best cell. The remote UE may also receive paging transmitted from the best cell.

[0389] The remote UE selects the best cell from among the cells whose reception quality from the in-coverage gNB meets the criteria for cell selection and cell reselection, and selects the best relay UE from among the relay UEs whose SL reception quality from the relay UE meets the criteria for cell selection and cell reselection, and the cell of the gNB to which the relay UE is connected is set as the best cell. The remote UE may compare the reception qualities of the two best cells and select the better one.

[0390] An offset may be included as a criterion for cell selection and cell reselection. For example, an offset may be provided to compare the reception quality from the gNB where the remote UE is in coverage with the SL reception quality from the relay UE. For example, if the offset is Qroffset, the SL reception quality from the relay UE may be compared with the reception quality from the gNB where the remote UE is in coverage + Qroffset to select the best cell. The offset setting is not limited to this. For example, an offset may be added to the SL reception quality from the relay UE. By making the offset configurable in this way, it is possible to preferentially select either the gNB to which the relay UE is connected or the gNB where the remote UE is in coverage.

[0391] The remote UE uses the system information transmitted from the selected best cell, and may receive paging transmitted from the best cell.

[0392] Examples of information related to the criteria for cell selection and cell reselection include thresholds for reception quality for cell selection and cell reselection, offsets, etc. The information related to the criteria may be statically determined in advance by a standard or the like, or may be broadcast by the gNB. The UE may use the information related to the criteria broadcast by the gNB. Alternatively, the information may be stored in the UE. For example, the information may be stored in a SIM possessed by the UE. The UE may use the information related to the criteria stored therein. Alternatively, the information related to the criteria may be provided to the UE by the CN during the registration process. The UE may store the information related to the criteria provided by the CN within the UE. Alternatively, the information related to the criteria may be provided to the UE from the NW when the UE is connected to the NW. Thereafter, when the UE enters the RRC_IDLE state, the information related to the criteria may be used.

[0393] By using this method, it is possible to take into account the gNB where the remote UE is out of coverage and the relay UE in a unified cell selection and reselection process. The unified cell selection and reselection process makes it possible to select the gNB where the remote UE is out of coverage and the gNB to which the relay UE is connected. This simplifies the cell selection and reselection process and enables low power consumption. It is also possible to reduce malfunctions in the remote UE.

[0394] By using the method disclosed in this modification, even when a remote UE is connected to a relay UE, it is possible to perform cell selection and reselection processes. The remote UE can perform processes in the RRC_IDLE state. It is possible to reduce malfunctions in processes of the remote UE in the RRC_IDLE state.

[0395] Modification 2 of Embodiment 2. When a remote UE in RRC_IDLE uses system information from a gNB to which a relay UE is connected or enables cell selection or cell reselection of a cell of the gNB, a problem occurs in that the CN cannot manage the remote UE when the remote UE moves or the surrounding radio wave propagation environment changes.

[0396] In this modification, a method for solving such a problem will be disclosed.

[0397] In the communication system according to this modification, gNB #1 notifies the remote UE of the TAC via the relay UE. As the notification method, the system information notification method disclosed in the second embodiment may be applied as appropriate. The TAC may be included in the system information. The remote UE receives the TAC of gNB #1 via the relay UE. When the remote UE moves, it may receive the TAC of the selected cell from the gNB in ​​coverage of the remote UE and the relay UE. The remote UE compares the received TAC with one or more TACs most recently received from the NW. The NW may be a RAN or a CN. The RAN may be a gNB. The CN may be an AMF.

[0398] If the TAC received from gNB #1 is a new TAC that is different from one or more TACs most recently received from the NW, the remote UE performs a registration process. The remote UE notifies the CN of a registration request via the relay UE and gNB #1. The registration request may include information indicating that it is a TAC or registration update. An existing Registration Request message may be used for the registration request. The Registration Type of the Registration Request message may be set to Mobility Registration Update.

[0399] Six examples of information to be included in the registration request are disclosed below: (1) Identifier of the UE requesting registration. (2) Identifier of the relay UE. (3) Identifier of the gNB to which the relay UE connects. (4) TAC received from the gNB. (5) Information indicating that the registration request is made via a connection via the relay UE. (6) A combination of (1) to (5).

[0400] Upon receiving the registration request from the remote UE, the CN performs a registration process between the relay UE and gNB #1. During the registration process, the remote UE obtains new registration area information from the CN. The registration area information may be one or more TACs.

[0401] The remote UE does not perform the registration process if the TAC received from gNB #1 is included in one or more TACs most recently received from the NW.

[0402] Figure 20 is a sequence diagram showing an example of a method by which a remote UE performs registration due to a TA change, for Variant 2 of Embodiment 2. In Figure 20, steps common to Figures 14 and 18 are assigned the same step numbers, and common descriptions are omitted. In Step ST2001, the relay UE receives system information from gNB #1. The relay UE also receives a PLMN identifier and a TAC (assumed to be TAC #1). In Step ST2002, the remote UE receives system information from gNB #2. The relay UE also receives a PLMN identifier and a TAC (assumed to be TAC #2). If TAC #2 is a new TAC, the remote UE performs RRC connection processing in Step ST2003, and performs registration processing between gNB #2, AMF #2, PCF, and UDM in Step ST2004. If no communication is performed after the registration processing is completed, the RRC connection is released in Step ST2005.

[0403] In steps ST1409 to ST1411, the remote UE establishes an RRC connection of PC5 with the relay UE. In step ST2006, the relay UE performs RRC connection processing with gNB #1. As the RRC connection processing in step ST2006, the processing of steps ST1412 to ST1414 described in FIG. 14 and the like may be applied. In step ST1804, the remote UE changes the gNB that receives the system information from gNB #2 to gNB #1. In step ST2007, the relay UE transmits the system information, PLMN identifier, and TAC #1 of gNB #1 via SL. This information may be notified to the remote UE. The remote UE receives the system information, PLMN identifier, and TAC #1 of gNB #1 transmitted by the relay UE, and in step ST2008 determines whether TAC #1 is included in the registration area information notified from the NW in the registration process of step ST2004. If included, registration is not performed with the CN. If not included, registration is performed with the CN. Figure 20 shows the case where TAC #1 is included.

[0404] In step ST2009, the remote UE performs RRC connection processing with gNB #1 via the relay UE. As the RRC connection processing performed with gNB #1 via the relay UE, it is preferable to apply the processing of steps ST1417 to ST1419 described in FIG. 14, etc. In step ST2010, the remote UE performs registration processing between gNB #1, AMF #1, PCF, and UDM. After the registration processing is completed, if no communication is performed, the RRC connection may be released. Although FIG. 20 shows a case where the AMF is changed, this is not limited to a change of the AMF. The AMF does not have to be changed.

[0405] By doing this, it becomes possible to perform registration processing to change the TA in which the remote UE exists to the TA to which gNB #1 belongs.

[0406] By using the method disclosed in this modification, even when the remote UE moves or the surrounding radio wave propagation environment changes, the CN can recognize in which TA the remote UE is located, which allows the CN to manage the remote UE.

[0407] Variant 3 of Embodiment 2. When a remote UE is in the in-coverage area of ​​a gNB and is also connected to a relay UE, it is unclear whether the remote UE should receive paging from the in-coverage gNB or from the relay UE. Also, it is unclear from the CN which side should send paging to the remote UE. As a result, the CN cannot call the remote UE, which causes a problem in that it cannot start communication with the remote UE.

[0408] In this modification, a method for solving such a problem will be disclosed.

[0409] In the communication system according to this modification, when a remote UE is out of coverage of gNB #2, it receives a paging from gNB #2. In this case, registration processing via the relay UE and the gNB connected to the relay UE may be unnecessary. Even if the gNB to which the relay UE is connected has sent a new TAC, the remote UE may not need to register via the relay UE and the gNB to which the relay UE is connected. In this way, the CN can recognize that it is sufficient to send a paging via the gNB to which the remote UE is out of coverage. The CN transmits a paging to the remote UE via gNB #2.

[0410] By eliminating the need for registration processing via the relay UE and the gNB to which the relay UE is connected, processing as a system can be simplified. In addition, signaling for the registration is no longer necessary, which reduces the signaling load.

[0411] If the gNB in ​​which the remote UE is in coverage changes due to movement of the remote UE or changes in the surrounding radio wave propagation environment, and cell selection and reselection processing is performed, the remote UE should receive paging via that gNB.

[0412] The remote UE may receive a paging from the gNB from which the remote UE has received system information. The remote UE may receive a paging from the gNB from which the remote UE has received system information related to the paging. In this way, the remote UE can also receive a paging from the gNB to which the relay UE is connected.

[0413] The remote UE may receive a paging from a gNB belonging to the TA or registration area according to the TA change process. The TA change process disclosed in Variant 2 of Embodiment 2 may be applied as appropriate. For example, when a remote UE moves and the relay UE to which it connects and the gNB to which the relay UE connects change, and the remote UE selects the new gNB, the remote UE receives a TAC from the gNB and determines whether the TAC is included in one or more TACs most recently received from the CN. If the TAC is different, the remote UE performs a registration process with the CN via the relay UE and gNB. If the remote UE performs a registration process with the CN via the relay UE and gNB, it receives a paging from the gNB. The CN transmits a paging to the remote UE via the gNB and relay UE in the new TAC.

[0414] If the TAC received from the gNB is included in one or more TACs most recently received from the CN, the remote UE does not need to perform a registration process with the CN. The remote UE receives a paging message via the relay UE and gNB. The CN transmits a paging message to the remote UE via the gNB and relay UE in the original TAC.

[0415] By doing this, even in a network including a relay UE, a remote UE can receive paging from a gNB belonging to a TA or registration area. Therefore, the same processing as conventional paging processing can be performed, and malfunctions in the paging processing can be reduced.

[0416] In the above, an example of a gNB to which a relay UE is connected is shown, but a gNB in ​​which a remote UE is in coverage may also be used. Similar effects can be obtained.

[0417] 21 is a sequence diagram showing an example of a method for receiving paging from a gNB belonging to a TA in which a remote UE exists, for Modification 3 of Embodiment 2. In FIG. 21, steps common to those in FIG. 20 are assigned the same step numbers, and common descriptions are omitted.

[0418] This shows the processing when data for the remote UE arrives at the CN when the remote UE is present in the TA (TAC #2) broadcast from gNB #2 or in the registration area notified in the registration process. In step ST2101, data for the remote UE is generated in UPF #2. In step ST2102, UPF #2 notifies the SMF of a data occurrence notification. In step ST2103, the SMF may notify the UPF #2 of a data occurrence notification response. In step ST2104, the SMF notifies the AMF #2 to which the remote UE is registered of the data occurrence notification. In step ST2105, AMF #2 may notify the SMF of the data occurrence notification response.

[0419] In step ST2106, AMF#2 notifies gNB#2 of the paging. In step ST2107, gNB#2 notifies the remote UE of the paging. In step ST2108, the remote UE that receives the paging from gNB#2 performs service request processing and PDU (Protocol Data Unit) session establishment processing with gNB#2, AMF#2, SMF, and UPF#2. In step ST2109, UPF#2 transmits the generated data to gNB#2, and gNB#2 transmits the data to the remote UE. In this way, data communication to the remote UE is possible.

[0420] For example, when communication is terminated, in step ST2110, a PDU session release procedure is performed between the remote UE, gNB #2, AMF #2, SMF, and UPF #2. In step ST2111, a CM connection release procedure and an RRC connection release procedure are performed between the remote UE, gNB #2, and AMF #2.

[0421] This shows the processing to be performed when data for the remote UE arrives at the CN when the remote UE is present in the TA (TAC #1) broadcast from gNB #1 and a registration process to change to TAC #1 to which gNB #1 belongs is performed in step ST2010. In step ST2112, data for the remote UE is generated in UPF #1. In step ST2113, UPF #1 notifies the SMF of a data occurrence notification. In step ST2114, the SMF may notify the UPF #1 of a data occurrence notification response. In step ST2115, the SMF notifies the AMF #1 to which the remote UE is registered of the data occurrence notification. In step ST2116, AMF #1 may notify the SMF of the data occurrence notification response.

[0422] In step ST2117, AMF#1 notifies gNB#1 of the paging. In step ST2118, gNB#1 notifies the relay UE of the paging. In step ST2119, the relay UE notifies the remote UE of the paging. In step ST2120, the remote UE that receives the paging from the relay UE performs service request processing and PDU session establishment processing with the relay UE, gNB#1, AMF#1, SMF, and UPF#1. In communication between the remote UE and the NW via the relay UE, a PDU session may be established between the relay UE and the UPF. A PC5 connection is established between the relay UE and the remote UE, and data between the UPF and relay UE is transferred between the relay UE and the remote UE in the relay UE, and data between the remote UE and the relay UE is transferred between the relay UE and the UPF. As another method of establishing a PDU session, a PDU session may be established between the remote UE and the UPF. A PDU session may be established for a service communicated between the remote UE and the UPF. In the PDU session between the remote UE and the UPF, the data destination addresses may be the remote UE and the UPF. This method facilitates communication control.

[0423] The relay UE may perform mapping of SLRBs (Sidelink Radio Bearers) and Uu RBs. The relay UE transfers data from gNB #1 from Uu RBs to SL RBs and transmits it to the remote UE. The relay UE transfers data from the remote UE from SL RBs to Uu RBs and transmits it to gNB #1. The relay UE may perform channel mapping. The relay UE transfers data from gNB #1 from PUSCH to PSSCH and transmits it to the remote UE. The relay UE transfers data from the remote UE from PSSCH to PUSCH and transmits it to gNB #1. In this way, data transmission and reception between the remote UE and gNB #1 is possible via the relay UE. In step ST2121, the UPF #1 transmits the generated data to the gNB #1, and the gNB #1 transmits the data to the remote UE via the relay UE. In this way, data communication to the remote UE becomes possible.

[0424] For example, when communication is terminated, in step ST2122, a PDU session release procedure is performed between the remote UE, relay UE, gNB #1, AMF #1, SMF, and UPF #1. In step ST2123, a CM connection release procedure and an RRC connection release procedure are performed between the remote UE, relay UE, gNB #1, and AMF #1.

[0425] Although Fig. 21 illustrates a case where the AMF is changed, this is not limited to a change in the AMF. The AMF does not have to be changed. Although Fig. 21 illustrates a case where the UPF is changed, this is not limited to a change in the UPF. The UPF does not have to be changed. Although Fig. 21 illustrates a case where the SMF is the same, this is not limited to a case where the SMF is the same. The SMF may be changed.

[0426] By using this method, the remote UE can recognize whether to receive paging from an in-coverage gNB or a relay UE, and which gNB or relay UE to receive paging from. Also, the CN can recognize which gNB to send paging to the remote UE. This allows the CN to start communication with the remote UE.

[0427] Another method for paging is disclosed. The gNB in ​​which the remote UE is out of coverage and the gNB to which the relay UE is connected may send a paging message to the remote UE. Even if these gNBs belong to TAs with different TACs, these gNBs may send a paging message to the remote UE. The remote UE can receive a paging message from the gNB in ​​which it is out of coverage and the gNB to which the relay UE is connected. The remote UE may receive a paging message from the gNB in ​​which it is out of coverage and the gNB to which the relay UE is connected.

[0428] A specific example will be disclosed. The remote UE receives a TAC from gNB #1 via a relay UE and determines whether it is included in one or more TACs most recently received from the CN. If the TACs are different, the CN performs a registration process with the CN via the relay UE and the gNB. In the registration process, the CN notifies the remote UE, including the TAC of gNB #2. The TAC of gNB #2 may be included in the registration response message in the registration process. The TAC may also be included in the registration area information and notified.

[0429] When paging occurs to a remote UE, the CN notifies the gNBs belonging to the TA of the TAC included in the registration area of ​​the remote UE of the paging. As a result, the CN notifies gNB #1 and gNB #2 of the paging. gNB #1 and gNB #2 that receive the paging from the CN send the paging to the remote UE. In this way, gNB #2, where the remote UE is in coverage, and gNB #1, to which the relay UE is connected, can send paging to the remote UE.

[0430] The remote UE waits for paging from the in-coverage gNB #2 and the gNB #1 to which the relay UE is connected. The remote UE may receive paging from either the in-coverage gNB #2 or the gNB #1 to which the relay UE is connected. In this way, even if one of the paging cannot be transmitted, the other paging can be transmitted. This allows the remote UE to receive the transmitted paging. This improves the reliability of the paging process. Furthermore, the remote UE only needs to receive the first transmitted paging, and can receive the paging early. This allows the remote UE to respond quickly to paging and start communication with the NW early.

[0431] Variation 4 of Embodiment 2 When transmitting paging from the CN to the remote UE via the gNB and relay UE, the paging must be transmitted from the relay UE to the remote UE via SL. For this reason, in the conventional Uu paging process, problems occur in that the paging cannot be transmitted to the remote UE or the remote UE cannot receive the paging.

[0432] In this modification, a method for solving such a problem will be disclosed.

[0433] When a paging message is sent from a CN to a remote UE via a gNB and a relay UE, a problem arises as to how the relay UE receives the paging message from the gNB to the remote UE. A method for solving this problem is disclosed.

[0434] In the communication system according to this modification, the remote UE notifies the relay UE of information relating to its own UE identifier. The information relating to the UE identifier may be, for example, 5G-S-TMSI. Alternatively, it may be UE-ID. The UE-ID is derived from the following formula (1). By using UE-ID, it is possible to reduce the amount of information required for notification. UE-ID=5G-S-TMSI mod 1024 (1)

[0435] Alternatively, the relay UE may be assigned an identifier by the gNB to which the relay UE is connected. For example, the relay UE may be assigned an Inactive Radio Network Temporary Identifier (I-RNTI). The I-RNTI may be used when the UE is in the RRC_INACTIVE state.

[0436] Alternatively, the UE identifier may be set to a specific value, for example, UE-ID=0.

[0437] It is advisable to notify in advance between the NW, the relay UE, and the remote UE that the identifier assigned to the remote UE by the gNB to which the relay UE is connected or the specific UE-ID will be used for paging. For example, during the registration process from the remote UE to the CN via the relay UE and gNB #1, it is advisable to notify the use of the identifier assigned to the remote UE by gNB #1 and the identifier, or the use of the specific UE-ID and the specific UE-ID. In this way, it is possible to share the UE identifier used for paging between the NW, the relay UE, and the remote UE.

[0438] The gNB to which the relay UE connects derives paging transmission timing using the identifier of the remote UE and transmits a paging to the remote UE. The AMF may derive the paging transmission timing using the identifier of the remote UE. Other information related to paging timing, such as the paging period, the number of paging occasions, information for obtaining the paging frame offset and the number of paging frames, may be determined by gNB #1 and notified to the AMF and the relay UE, or may be determined by the AMF and notified to gNB #1 and the relay UE. The relay UE may be notified via gNB #1.

[0439] The relay UE derives the timing of receiving paging for the remote UE using the identifier of the remote UE. The relay UE derives the timing of receiving paging for the remote UE using the identifier of the remote UE and other parameters for determining the paging timing. The relay UE monitors whether paging is transmitted from gNB #1 at the derived timing of paging for the remote UE. Paging from gNB #1 to the remote UE may be included in the PCCH. The PCCH is mapped to the PDSCH and transmitted. Scheduling information for the PDSCH to which the PCH is mapped is included in DCI, and a P-RNTI (Paging Radio Network Temporary Identifier) ​​is masked in the CRC of the DCI and mapped to the PDCCH.

[0440] The relay UE can detect whether paging is occurring by monitoring the P-RNTI. When the relay UE receives a PDCCH with a masked P-RNTI, the relay UE receives a PDSCH and paging according to the scheduling information of the PDCCH.

[0441] Instead of the P-RNTI disclosed above, a relay-dedicated RNTI may be provided. A relay-dedicated RNTI may be used for paging from the gNB to the remote UE via the relay UE. The PDCCH to which the paging transmitted from gNB #1 to the relay UE is mapped is masked with the relay-dedicated RNTI. The relay-dedicated RNTI may be statically determined in advance by a standard, etc. The gNB and relay UE can be recognized.

[0442] The paging may include an identifier of the remote UE. That is, the paging to the remote UE transmitted to the relay UE may include the identifier of the remote UE. When the relay UE recognizes that the paging includes the identifier of the remote UE, it transmits the paging to the remote UE.

[0443] The paging may include information indicating that the paging is directed to the remote UE via the relay UE. That is, the paging to the remote UE to be transmitted to the relay UE may include the information. When the relay UE recognizes that the paging includes the information, it transmits the paging to the remote UE.

[0444] The paging may include the identifier of the relay UE. That is, the paging to the remote UE transmitted to the relay UE may include this information. When the relay UE recognizes that the paging includes the identifier of its own relay UE, it transmits the paging to the remote UE. In this way, it becomes possible to transmit the paging from a specific relay UE to the remote UE.

[0445] Disclosed is a resource for transmitting paging using SL on PC5. gNB#1 schedules PC5 paging resources for relay UE. Resources may be periodically allocated as PC5 paging resources. As a scheduling method for periodic resources for PC5 paging, gNB#1 may schedule for relay UE using SL CG (Configured Grant).

[0446] gNB #1 may schedule PC5 paging resources using paging timing to the remote UE. In this way, it is possible to allocate periodic resources for PC5 paging. It is possible to schedule PC5 paging resources suitable for the paging timing to the remote UE from gNB #1 to the relay UE.

[0447] The paging processing time at the relay UE may be taken into consideration. For example, the processing time from when the relay UE receives a paging from gNB #1 to the remote UE until it transmits a paging for the remote UE may be defined as the paging processing time. The relay UE may notify the remote UE of the paging processing time. The gNB #1 may schedule PC5 paging resources at a timing that adds a time including the processing time to the paging timing for the remote UE. In this way, it becomes possible to allocate PC5 paging resources taking into consideration the paging processing time at the relay UE. It becomes possible to schedule PC5 paging resources that are more suitable for the timing of paging from gNB #1 to the relay UE to the remote UE.

[0448] If the relay UE is not connected to the gNB, the relay UE may schedule the PC5 paging resource. For example, the relay UE selects the SL resource and schedules the PC5 paging resource to the remote UE. The scheduling method may be the same as the scheduling method in the gNB #1 described above.

[0449] When the relay UE receives a paging message from gNB #1 to the remote UE, it notifies the remote UE using the PC5 paging resource.

[0450] The remote UE derives paging timing using its own UE identifier and information regarding paging timing notified from gNB #1 or AMF. When the remote UE is notified of the above-mentioned paging processing time from the relay UE, it derives paging timing taking into account the notified paging processing time. The remote UE monitors paging from the relay UE at the derived paging timing to detect the presence or absence of paging. If paging is present, it uses its own UE identifier in the paging to determine whether it is a paging addressed to the remote UE. In this way, the remote UE can receive paging addressed to the remote UE from gNB #1 via the relay UE.

[0451] If resources are periodically allocated as PC5 paging resources, periodic resources must be reserved even when paging does not occur, resulting in resource waste. A method for solving this problem is disclosed.

[0452] In order to avoid resource waste, gNB #1 dynamically schedules resources for PC5 paging. Scheduling may be performed taking into account the processing time at the relay UE. gNB #1 may dynamically schedule resources for PC5 paging for each paging timing to a remote UE. Alternatively, gNB #1 may schedule resources for PC5 paging when paging to a remote UE occurs. Since PC5 paging resource scheduling is performed only when paging occurs, resource waste can be further reduced.

[0453] A method for scheduling PC5 paging resources when paging to a remote UE occurs is disclosed. In this method, scheduling information for PC5 paging resources is included in a PCCH. The scheduling information for PC5 paging resources may be included together with the paging to the remote UE disclosed above. The scheduling information may also include the paging processing time at the relay UE. The PCCH is mapped to a PDSCH using a P-RNTI as a mask and transmitted. The PCCH may also be mapped to a PDSCH using a relay RNTI as a mask and transmitted. When paging to a remote UE occurs, gNB #1 notifies the remote UE by including scheduling information for PC5 paging resources in the PCCH together with the paging to the remote UE. In this way, when paging to the remote UE occurs, the relay UE can receive the paging to the remote UE and the PC5 paging scheduling information.

[0454] Another method for solving the problem is disclosed.

[0455] In this method, scheduling information for PC5 paging resources is included in DCI and mapped to a PDCCH for notification. The DCI may include an identifier of a relay UE. The DCI may include an identifier of a remote UE. In this way, the relay UE can recognize which relay UE and which remote UE are addressed. The PDCCH may be a PDCCH using a P-RNTI as a mask. Alternatively, a PDCCH using an RNTI dedicated to the relay as a mask may be used. Alternatively, a PDCCH using an RNTI for SL (SL-RNTI) as a mask may be used. When paging to a remote UE occurs, gNB #1 notifies the PDCCH using the RNTI as a mask, including scheduling information for PC5 paging resources. In this way, the relay UE can monitor the scheduling information for PC5 paging using the RNTI, and when paging to the remote UE occurs, it can receive the scheduling information for the PC5 paging resource.

[0456] By using the method disclosed in this modification, the relay UE can send paging to the remote UE. Also, the remote UE can receive paging from the relay UE. It is possible to send paging from the CN to the remote UE via the gNB and the relay UE. The remote UE can start communication with the NW.

[0457] Embodiment 3. When a remote UE wants to send data to a network via a relay UE, SL communication resources from the remote UE to the relay UE are required. As in the past, when a remote UE is directly connected to a gNB, the remote UE can send an SR (Scheduling Request) directly to gNB #2. However, when a remote UE is not connected to gNB #2 and is connected to gNB #1 via a relay UE, the remote UE cannot send an SR directly to gNB #1. In this case, the remote UE is not scheduled by gNB #1 for SL communication resources for communication to the relay UE, and cannot transmit data to gNB #1 via the relay UE.

[0458] In this embodiment, a method for solving such a problem will be disclosed.

[0459] In the communication system according to this embodiment, a remote UE notifies a gNB with which it is connected via RRC of a scheduling request (SR) for relay resources. The remote UE may notify a gNB with which it is connected via a relay UE of the SR for relay resources. The relay resources may be both SL communication resources and UL communication resources. The SR may be a scheduling request for all logical channels. This may include the PC5 logical channel and the Uu logical channel. A logical channel for relay may be provided, and the SR may be a scheduling request for the relay logical channel.

[0460] The remote UE may be in an RRC connection state with the gNB that transmits the SR. Upon receiving the SR from the remote UE, gNB #1 schedules resources for SL communication with the relay UE for the remote UE. After scheduling resources for SL communication with the relay UE for the remote UE, gNB #1 notifies the remote UE of the scheduling information. The remote UE may notify gNB #1 of the SR via the relay UE. gNB #1 may notify the remote UE of the scheduling information via the relay UE.

[0461] The gNB #1 that receives the SR from the remote UE schedules resources for UL communication with the relay UE. The gNB #1 that schedules resources for UL communication for the relay UE notifies the relay UE of the scheduling information. The UL communication may be limited to communication from the remote UE to the gNB #1 via the relay UE.

[0462] The relay UE notifies the gNB #1 with which it is connected via RRC of a scheduling request (SR) for relay resources. The relay resources may be UL communication resources and / or SL communication resources. The SR may be a scheduling request for all logical channels. This may include the PC5 logical channel and the Uu logical channel. A logical channel for relay may be provided, and the SR may be a scheduling request for the relay logical channel.

[0463] The remote UE may be in an RRC connected state with the gNB to which the relay UE transmits the SR. The remote UE may not be in an RRC connected state with the gNB to which the relay UE transmits the SR.

[0464] The gNB #1 that receives the SR from the relay UE schedules resources for SL communication with the relay UE for the remote UE. The gNB #1 that has scheduled resources for SL communication with the relay UE for the remote UE notifies the remote UE of scheduling information indicating the results of the scheduling. The gNB #1 may notify the remote UE of the scheduling information via the relay UE.

[0465] The gNB #1 that receives the SR from the relay UE also schedules resources for UL communication with the relay UE. After scheduling resources for UL communication with the relay UE, the gNB #1 notifies the relay UE of scheduling information indicating the results of the scheduling. The UL communication may be limited to communication from the remote UE to the gNB #1 via the relay UE.

[0466] The remote UE notifies the gNB with which it is connected via RRC of a scheduling request (SR) for resources for SL communication with the relay UE. The remote UE may notify the gNB with which it is connected via the relay UE of the SR for resources for SL communication with the relay UE. The SR may be a scheduling request for all logical channels of PC5. A logical channel for relay may be provided, and the SR may be a scheduling request for the logical channel for relay.

[0467] The remote UE may be in an RRC connection state with gNB #1 via a relay UE. The remote UE notifies gNB #1 of a scheduling request (SR) for resources for SL communication with the relay UE. This may be the SR for resources for SL communication with the relay UE for communicating with gNB #1 via the relay UE.

[0468] Upon receiving the SR from the remote UE, gNB #1 schedules resources for SL communication with the relay UE for the remote UE. After scheduling resources for SL communication with the relay UE for the remote UE, gNB #1 notifies the remote UE of scheduling information indicating the results of the scheduling. The remote UE may notify gNB #1 of the SR via the relay UE. gNB #1 may notify the remote UE of the scheduling information via the relay UE.

[0469] The relay UE notifies gNB #1 of a scheduling request (SR) for UL communication resources. This UL communication may be UL communication for a remote UE to communicate with gNB #1 via the relay UE. The SR may be a scheduling request for all logical channels of Uu. A logical channel for relay may be provided, and the SR may be a scheduling request for the logical channel for relay.

[0470] Upon receiving the SR from the relay UE, gNB #1 schedules UL communication resources. After scheduling UL communication resources for the relay UE, gNB #1 notifies the relay UE of scheduling information indicating the results of the scheduling. Upon receiving the scheduling information from gNB #1, the relay UE notifies the remote UE of the scheduling information.

[0471] When the relay UE receives an SL scheduling request from the remote UE, it transmits an UL scheduling request to the gNB #1. Alternatively, the relay UE may transmit an UL scheduling request to the gNB #1 when the PC5 connection between the relay UE and the remote UE is completed. The PC5 connection may be a PC5-S link establishment. Alternatively, it may be a PC5-RRC connection. Alternatively, the relay UE transmits an UL scheduling request to the gNB #1 when the RRC connection between the remote UE and the gNB #1 is completed. The relay UE may transmit an UL scheduling request to the gNB #1 during the RRC connection process between the remote UE and the gNB #1. The relay UE may receive an RRC setup request from the remote UE. The relay UE may receive an RRC setup completion from the remote UE.

[0472] A method for requesting resources for SL communication from a remote UE to a relay UE has been disclosed above. Another method for obtaining resources for SL communication from a remote UE to a relay UE is now disclosed.

[0473] The remote UE selects resources for SL communication with the relay UE by itself. The resources for SL communication may be resources for SL communication with the relay UE for communicating with gNB #1 via the relay UE. In this way, it is possible to obtain resources for SL communication from the remote UE to the relay UE. With regard to UL communication from the relay UE to gNB #1, the method disclosed above may be applied as appropriate. In this way, it is possible to obtain resources for communication from the remote UE to gNB #1 via the relay UE.

[0474] The relay UE may select resources for SL communication from the remote UE to the relay UE by itself. The resources for SL communication may be resources for SL communication with the relay UE for the remote UE to communicate with gNB #1 via the relay UE.

[0475] When a relay UE receives an SL scheduling request from a remote UE, the relay UE may select resources for SL communication from the remote UE to the relay UE. As an alternative, the relay UE may select resources for SL communication from the remote UE to the relay UE when a PC5 connection is completed between the relay UE and the remote UE. The PC5 connection may be a PC5-S link establishment. Alternatively, a PC5-RRC connection may be used. As an alternative, the relay UE may select resources for SL communication from the remote UE to the relay UE by itself when an RRC connection is completed between the remote UE and gNB #1. The relay UE may select resources for SL communication from the remote UE to the relay UE by itself in the RRC connection process between the remote UE and gNB #1. When a relay UE receives an RRC setup request from the remote UE, the relay UE may select resources for SL communication from the remote UE to the relay UE by itself. When the relay UE receives an RRC setup completion from the remote UE, the relay UE may select resources for SL communication from the remote UE to the relay UE.

[0476] The relay UE notifies the remote UE of the selected SL communication resource, thereby enabling the remote UE to obtain the SL communication resource from the relay UE.

[0477] Regarding UL communication from the relay UE to the gNB #1, the method disclosed above may be applied as appropriate. In this way, resources for communication from the remote UE to the gNB #1 via the relay UE can be obtained.

[0478] A method for setting an SR is disclosed. A method for setting an SL SR is disclosed. gNB #1 sets an SL SR for a remote UE. As the SL SR setting, the transmission timing of the SL SR may be set. The transmission timing of the SL SR may be periodic. The setting information for the transmission timing of the SL SR may be a period or an offset.

[0479] The gNB #1 schedules SL resources for SL SR for the remote UE. The SL resources for SL SR may be periodic. Semi-persistent scheduling (SPS) may be used for the scheduling. SL CG may be used for the scheduling. These SL resources may be dedicated to SL SR.

[0480] Five examples of scheduling information of SL resources for SL SR are disclosed below: (1) Period; (2) Offset; (3) Frequency resource; (4) Activation and deactivation information; and (5) Combination of (1) to (4).

[0481] The SL SR may be included in the PSCCH. It may be included in the 1st SCI. The SL SR may be included in the PSSCH. It may be included in the 2nd SCI. The SL SR may be included in the SL MAC CE. SL RRC may be used. PC5-RRC signaling may be used. The SL SR may be multiplexed with other data. For example, it may be multiplexed with data and included in the PSSCH. The SL SR may be included in the PSFCH. It may be multiplexed with SL Ack / Nack and / or SL CSI and included in the PSFCH. A channel for the SL SR may be provided.

[0482] A signal for SL SR may be provided. The signal may have a predetermined sequence as SL SR. The predetermined sequence may be a sequence different from that of other UEs. Alternatively, the sequence may be a sequence different from that of SL Ack / Nack or SL CSI. For example, a Zadovczu sequence may be used for SL SR, with a different cyclic shift.

[0483] The SL resource to be scheduled may be an SL SR transmission channel or an SL resource for a signal. gNB #1 may schedule an SL SR transmission channel or an SL resource for a signal for the remote UE.

[0484] A method for configuring an UL SR is disclosed. gNB #1 configures an UL SR for a relay UE. The UL SR may be an UL SR for a remote UE to communicate with gNB #1 via the relay UE. The UL SR configuration may include configuring the transmission timing of the UL SR. The transmission timing of the UL SR may be periodic. Configuration information for the transmission timing of the UL SR may include a period and an offset. The SR configuration conventionally specified on Uu may also be used.

[0485] The gNB #1 schedules SL resources for UL SR to the relay UE. The SL resources for UL SR may be periodic. The PUCCH configuration may be used as the SL resources for UL SR. Alternatively, the PUSCH configuration may be used. These SL resources may be dedicated to SL SR. Alternatively, the resource configuration for SR conventionally defined on the Uu may be used.

[0486] gNB #1 performs both SL SR configuration and UL SR configuration. SL SR configuration includes SL SR configuration and / or SL SR resource configuration. UL SR configuration includes UL SR configuration and / or UL SR resource configuration. gNB #1 notifies the relay UE of the SL SR configuration and UL SR configuration. The SL SR configuration and UL SR configuration may be included in the SL configuration information. gNB #1 notifies the relay UE of the SL configuration information. SL configuration information for relay may be provided. In this way, it is possible to notify separately from SL configuration for other SL communications that are not for relay. The SL SR configuration may be included in the SL configuration information, and the UL SR configuration may be included in the UL configuration information.

[0487] A method for notifying a relay UE of SL SR settings and UL SR settings from gNB #1 is disclosed. RRC signaling may be used for the notification. The notification may be performed during the RRC connection process between gNB #1 and the remote UE. The notification may be included in an RRC setup message. The notification may be included in an RRC reconfiguration message.

[0488] The relay UE notifies the remote UE of the SL SR settings. For relay use, the settings may be included in SL setting information separated from other SL SR settings and notified. The settings may be notified using PC5-RRC signaling. The settings may be notified by being included in an SL RRC setting message. The settings may be notified by being included in an SL RRC reconfiguration message. Alternatively, the settings may be notified by being included in an SL AS setting. The settings may be notified by being included in an SL AS reconfiguration. The settings may be notified in the RRC connection process performed between gNB #1 and the remote UE. The settings may be notified by being included in an RRC setup message. The settings may be notified by being included in an RRC reconfiguration message.

[0489] The gNB #1 may notify the remote UE of both the SL SR setting and the UL SR setting. The notification may be performed via a relay UE. The notification method may be any of the methods disclosed above.

[0490] The gNB #1 may notify the relay UE of the SL SR settings and the UL SR settings separately. The relay UE notifies the remote UE of the SL SR settings. As another method, the gNB #1 may notify the remote UE of the SL SR settings. Notification may be via the relay UE. The gNB #1 may notify the relay UE of the UL SR settings. The SL SR settings and the UL SR settings may be notified by separate signaling. The SL SR settings and the UL SR settings may be notified by separate messages. The notification method may be any of the above-mentioned methods as appropriate.

[0491] The gNB #1 may separately configure the SL SR and the UL SR. The notification from the gNB #1 to the relay UE or the remote UE may be appropriately performed by applying the above-mentioned individual notification method.

[0492] Notification from gNB #1 to relay UE or remote UE may be made by appropriately applying the aforementioned joint notification method.

[0493] Figure 22 is a sequence diagram showing an example of a method in which a remote UE transmits an SR to gNB #1 according to embodiment 3. In Figure 22, steps common to those in Figure 14 are assigned the same step numbers, and common descriptions will be omitted. In step ST1415, the relay UE is RRC-connected with gNB #1, in step ST2201, the remote UE is PC5-RRC-connected with the relay UE, and in step ST1420, the remote UE establishes RRC connection with gNB #1.

[0494] The gNB #1 configures the relay UE with UL SR settings and SL SR settings, and notifies the relay UE of these settings in step ST2202. In step ST2203, the relay UE notifies the remote UE of the SL SR settings. In step ST2204, the remote UE that has generated transmission data to the NW transmits an SR of relay resources to the gNB #1 via the relay UE. For SR transmission from the remote UE to the relay UE, the SL SR settings received in step ST2203 may be used. For SR transmission from the relay UE to the gNB #1, the UL SR settings received in step ST2202 may be used. In this way, even when the remote UE is RRC-connected with the gNB #1, the gNB #1 can receive an SR from the remote UE.

[0495] The gNB #1 schedules resources for relaying for the relay UE and the remote UE. In step ST2205, the gNB #1 notifies the relay UE of scheduling information for UL communication resources for relaying. In step ST2206, the gNB #1 notifies the remote UE of scheduling information for SL communication resources for relaying via the relay UE. Having received the scheduling information for SL communication resources for relaying, the remote UE transmits data to the gNB #1 via the relay UE in step ST2207 using the communication resources indicated by the scheduling information. Having received the data, the relay UE transmits the data received from the remote UE to the gNB #1 using the communication resources indicated by the scheduling information for UL communication resources for relaying.

[0496] By doing this, even when the remote UE is RRC connected to gNB #1, the remote UE can send an SR to gNB #1, and the remote UE and relay UE can receive scheduling information for relay resources from gNB #1. Therefore, the remote UE can transmit data to gNB #1 via the relay UE. Also, in the example of Figure 22, gNB #1 schedules SL communication resources and UL communication resources together for relaying and notifies the remote UE and relay UE. By gNB #1 appropriately scheduling each resource, it is possible to reduce the delay when the relay UE transmits data received from the remote UE to gNB #1.

[0497] The resources for SL SR may be shared with other channels. For example, if the transmission timing of the SL SR partially or completely conflicts with the transmission timing of other channels, the SL SR may be transmitted with priority. This allows the SL SR to be transmitted early, and therefore, scheduling information for SL resources can be obtained early. This allows SL communication to be performed with low latency.

[0498] Alternatively, if the transmission timing of the SL SR partially or completely conflicts with the transmission timing of another channel, a channel with a higher priority may be transmitted, which allows the SL SR or another channel to be transmitted using the resources for the SL SR according to the priority.

[0499] A channel or SL SR that cannot be transmitted due to a collision may not be transmitted, may be discarded, or may be transmitted using the next SL SR resource.

[0500] As an alternative method for when the transmission timing of the SL SR partially or completely conflicts with the transmission timing of other channels, the SL SR may be multiplexed with other channels and transmitted using the SL SR resource, thereby improving resource usage efficiency and enabling low-latency communication.

[0501] Although it has been disclosed that when the transmission timing of the SL SR partially or completely conflicts with the transmission timing of another channel, the resources for the SL SR are used, resources of the other channel may also be used.

[0502] By using the method disclosed in this embodiment, the gNB can set a scheduling request for relay communication to the remote UE and relay UE. The remote UE and relay UE can notify the gNB of a scheduling request for relay communication. The gNB can perform scheduling for relay communication to the remote UE and relay UE. The gNB can notify the remote UE and relay UE of scheduling information for relay communication. This allows the remote UE to communicate with the NW via the relay UE.

[0503] The remote UE may notify gNB #2 of the CSI report in SL. The remote UE may notify gNB #1 of the CSI report in SL via a relay UE. The remote UE may notify the gNB with which it is RRC connected of the CSI report in SL. In this way, the gNB that receives the SCI report in SL can appropriately schedule resources for SL communication.

[0504] An SR for CSI reporting in SL may be provided. The SR setting method, SR transmission method, and SL resource scheduling method disclosed above may be applied as appropriate as the SR for CSI reporting in SL, the method for transmission, and the method for scheduling CSI reporting resources. This enables the remote UE to transmit the SR for CSI reporting in SL to gNB #1 via the relay UE. The remote UE can receive scheduling information for the SL CSI reporting resources from gNB #1 via the relay UE. Furthermore, the relay UE can receive scheduling information for the SL CSI reporting resources on Uu from gNB #1.

[0505] By doing this, it is possible to improve the communication quality between the remote UE and the gNB.

[0506] In the present disclosure, the UE in which service data is generated is referred to as UE-TX. For example, if UE-TX is referred to as UE1 and UE-RX is referred to as UE2, when service data is generated in UE2 and the data is transmitted to UE1, it is advisable to apply the method of the present disclosure with UE2 as UE-TX and UE1 as UE-RX. This can achieve the same effect.

[0507] The above-described embodiments and their modifications are merely examples, and the embodiments and their modifications can be freely combined. Furthermore, any of the components of the embodiments and their modifications can be modified or omitted as appropriate.

[0508] For example, in the above-described embodiments and their modifications, a subframe is an example of a time unit for communication in a fifth-generation communication system. A subframe may be a scheduling unit. In the above-described embodiments and their modifications, the processing described as being performed in subframe units may be performed in TTI units, slot units, subslot units, or minislot units.

[0509] For example, the methods disclosed in the above-described embodiments and their modified examples may be applied to services that use SL communication, not limited to V2X (Vehicle-to-everything) services, such as proximity-based services, public safety, communication between wearable devices, and communication between devices in factories.

[0510] Although the present disclosure has been described in detail, the above description is illustrative in all respects and is not restrictive. It is understood that countless variations not illustrated can be envisioned.

[0511] 200, 210 Communication system, 202 Communication terminal device (communication terminal), 203, 207, 213, 217, 223-1, 224-1, 224-2, 226-1, 226-2, 750 Base station device (base station), 204 MME / S-GW unit (MME unit), 204a MME, 214 AMF / SMF / UPF unit (5GC unit), 218 Central unit, 219 Distributed unit, 301, 403 Protocol processing unit, 302 Application unit, 303, 404 Transmission data buffer unit, 304, 405 Encoder unit, 305, 406 Modulation unit, 306, 407 Frequency conversion unit, 307-1 to 307-4, 408-1 to 408-4 Antenna, 308, 409 Demodulation unit, 309, 410 decoder unit, 310, 411, 506, 526 control unit, 401 EPC communication unit, 402 other base station communication unit, 412 5GC communication unit, 501 PDN GW communication unit, 502, 522 base station communication unit, 503, 523 user plane communication unit, 504 HeNBGW communication unit, 505, 525 control plane control unit, 505-1, 525-1 NAS security unit, 505-2 SAE bearer control unit, 505-3, 525-3 idle state mobility management unit, 521 Data Network communication unit, 525-2 PDU session control unit, 527 session management unit, 751-1 to 751-8 beam.

Claims

1. A communication system comprising: a base station; and a communication terminal that supports terminal-to-terminal communication in which communication terminals communicate directly with each other; wherein, when the communication terminal becomes capable of terminal-to-terminal communication with another communication terminal that is located at a base station other than the currently connected base station, the communication terminal notifies the currently connected base station of connection status information indicating that this state has been achieved; the base station that has received the notification of the connection status information determines, based on the connection status information, whether to change the connection destination of the communication terminal that notified the connection status information to the other base station that is located at the relay communication terminal that is the other communication terminal, and if the connection destination of the communication terminal that notified the connection status information is to be changed, requests the communication terminal to release the connection; and when the communication terminal receives a request from the base station to release the connection after notifying the currently connected base station of the connection status information, it releases the connection with the base station and connects to the other base station via the other communication terminal.

2. The communication system described in claim 1, characterized in that the communication terminal notifies the connection status information when the communication quality of the terminal-to-terminal communication with the relay communication terminal is better than the communication quality with the currently connected base station, and the base station, upon receiving the notification of the connection status information, requests the communication terminal that notified the connection status information to release the connection.

3. The communication system according to claim 1, characterized in that the communication terminal notifies the connection status information when a connection for terminal-to-terminal communication with the relay communication terminal is completed, and the base station, upon receiving the notification of the connection status information, requests the communication terminal that notified the connection status information to release the connection.

4. A communication system according to any one of claims 1 to 3, characterized in that, when the communication terminal starts terminal-to-terminal communication with another communication terminal connected to a base station different from the base station to which it is currently connected, it notifies the currently connected base station of connection status information indicating the start of terminal-to-terminal communication and the communication quality of the terminal-to-terminal communication, and the base station that has received the notification of the connection status information and the communication quality decides based on the communication quality whether or not to change the connection destination of the communication terminal that has notified the connection status information and the communication quality to the other base station to which the other communication terminal, that is a relay communication terminal, is connected, and if the connection destination of the communication terminal that has notified the connection status information and the communication quality is to be changed, it executes a handover to change the connection destination of the communication terminal to the other base station via the relay communication terminal.

5. A communication system according to any one of claims 1 to 4, characterized in that when the communication terminal is within the range of a base station and becomes capable of terminal-to-terminal communication with another communication terminal within the range of a base station different from the one within the range of the current communication terminal, the communication terminal receives system information transmitted from the other base station within the range of the other communication terminal via the other communication terminal, and operates in accordance with the received system information.

6. A communication system according to any one of claims 1 to 5, characterized in that when the communication terminal transmits data to the core network while connected to the other base station via the relay communication terminal, the communication terminal makes a scheduling request to the other base station for resources for terminal-to-terminal communication when transmitting the data.

7. A communication terminal that supports inter-terminal communication, in which communication terminals communicate directly with each other, characterized in that when it becomes possible to perform inter-terminal communication with another communication terminal located at a base station other than the currently connected base station, it notifies the currently connected base station of connection status information indicating that this state has been achieved, and after notifying the currently connected base station of the connection status information, if the base station requests that the connection be released, it releases the connection with the base station and connects to the other base station via the other communication terminal.