First terminal device, second terminal device, base station device, and communication system

Abstract

To improve communication quality in communication systems that utilize terminal-to-terminal communication. [Solution] The communication system comprises a plurality of terminal devices that perform sidelink communication via a PC5 interface, including a first terminal device and a second terminal device, and a network including a base station device. The second terminal device is a terminal device capable of relaying between the first terminal device and the network, or a relay terminal device that performs relaying between the first terminal device and the network. The first terminal device receives settings for measurement in sidelink communication from the base station device and uses these settings to perform measurements regarding sidelink communication from the second terminal device.

Description

Technical Field

[0001] This disclosure relates to wireless communication technologies.

Background Art

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0029] The Dedicated Traffic Channel (DTCH) is a channel for one-to-one communication to an individual communication terminal for the transmission of user information. The DTCH exists in both the uplink and the downlink. The DTCH is mapped to the UL-SCH in the uplink and to the DL-SCH in the downlink.

[0030] The Multicast Traffic Channel (MTCH) is a downlink channel for the transmission of traffic data from the network to a communication terminal. The MTCH is a channel used only for communication terminals during MBMS reception. The MTCH is mapped to the Multicast Channel (MCH).

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

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

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

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

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

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

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

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

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

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

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

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

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

[0044] To meet these requirements, 3GPP is working on the 5G standard as Release 15 (see Non-Patent Documents 6-19). The technology for the wireless portion of 5G is called "New Radio Access Technology" ("New Radio" is abbreviated as "NR").

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

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

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

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

[0049] In NR frame configurations, various subcarrier intervals, i.e., various numerologies, are supported. In NR, regardless of the numerology, one subframe is 1 millisecond, and one slot consists of 14 symbols. Furthermore, the number of slots contained in one subframe is one for a numerology with a subcarrier interval of 15 kHz, and increases proportionally with the subcarrier interval for other numerologies (see Non-Patent Document 13 (3GPP TS38.211)).

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

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

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

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

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

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

[0056] Furthermore, 3GPP is considering supporting services (or applications) using side-link (SL) communication (also known as PC5 communication) in both the Evolved Packet System (EPS) described later and the 5G core system (see Non-Patent Documents 1, 16, 20, 21, 22, and 23). Examples of services using SL communication include V2X (Vehicle-to-everything) services and proximity services.

[0057] Furthermore, 3GPP is considering several new technologies. For example, positioning technology (see Non-Patent Documents 24-27) and Integrated Access and Backhaul (IAB) are being considered (see Non-Patent Documents 16, 28, and 29).

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

[0059] The IAB is considering, for example, multiplexing within radio resources and reducing latency for access links (links between UEs and base stations) and backhaul links (links between base stations) (see Non-Patent Documents 16, 28, and 29). [Prior art documents] [Non-patent literature]

[0060] [Non-Patent Document 1] 3GPP TS 36.300 V16.2.0 [Non-Patent Document 2] 3GPP S1-083461 [Non-Patent Document 3] 3GPP TR 36.814 V9.2.0 [Non-Patent Document 4] 3GPP TR 36.912 V16.0.0 [Non-Patent Document 5] “Scenarios, requirements and KPIs for 5G mobile and wireless system”, ICT-317669-METIS / D1.1 [Non-Patent Document 6] 3GPP TR 23.799 V14.0.0 [Non-Patent Document 7] 3GPP TR 38.801 V14.0.0 [Non-Patent Document 8] 3GPP TR 38.802 V14.2.0 [Non-Patent Document 9] 3GPP TR 38.804 V14.0.0 [Non-Patent Document 10] 3GPP TR 38.912 V16.0.0 [Non-Patent Document 11] 3GPP RP-172115 [Non-Patent Document 12] 3GPP TS 37.340 V16.2.0 [Non-Patent Document 13] 3GPP TS 38.211 V16.2.0

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[0061] Support for various services using SL communication (also known 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 takes place between terminals. In SL communication, not only direct communication between terminals but also communication between the UE and the NW via a relay has been proposed (see Non-Patent Documents 20 and 23). In systems that support such relay-based communication, the problem is how to improve the communication quality between terminals and the NW.

[0062] In view of the above issues, one of the objectives of this disclosure is to improve communication quality in communication systems that utilize terminal-to-terminal communication. [Means for solving the problem]

[0063] To solve the aforementioned problems and achieve the objectives, the communication system according to this disclosure comprises a base station and a communication terminal that supports terminal-to-terminal communication between communication terminals. When a communication terminal becomes capable of terminal-to-terminal communication with another communication terminal located at a different base station than the one it is currently connected to, it notifies the connected base station of connection status information indicating that it has become capable of such communication. Upon receiving the connection status information, the base station decides, based on the connection status information, whether to change the destination of the communication terminal that notified the connection status information to another base station located at the relay communication terminal, via another communication terminal. If it decides to change the destination of the communication terminal that notified the connection status information, it requests the communication terminal to release the connection. After notifying the connected base station of connection status information, if the base station requests the release of the connection, the communication terminal releases the connection with the base station and connects to the other base station via another communication terminal. [Effects of the Invention]

[0064] According to this disclosure, it is possible to improve the communication quality in communication systems that utilize terminal-to-terminal communication.

[0065] The purpose, features, aspects, and advantages of this disclosure will become clearer from the following detailed description and accompanying drawings. [Brief explanation of the drawing]

[0066] [Figure 1] This is an explanatory diagram showing the configuration of wireless frames used in LTE communication systems. [Figure 2] This block diagram shows the overall configuration of the LTE communication system 200 as discussed in 3GPP. [Figure 3] This is a block diagram showing the overall configuration of the NR communication system 210 as discussed in 3GPP. [Figure 4] This is a diagram illustrating the configuration of a data center using eNBs and gNBs connected to the EPC. [Figure 5] This is a diagram showing the configuration of the DC using gNB connected to the NG core. [Figure 6] This is a diagram showing the configuration of the DC with eNBs and gNBs connected to the NG core. [Figure 7] This is a diagram showing the configuration of the DC with eNBs and gNBs connected to the NG core. [Figure 8] Figure 2 is a block diagram showing the configuration of the mobile terminal 202. [Figure 9] Figure 2 is a block diagram showing the configuration of base station 203. [Figure 10] This block diagram shows the configuration of MME. [Figure 11] This is a block diagram showing the configuration of the 5GC section. [Figure 12] This is a flowchart illustrating the general process from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. [Figure 13]This figure shows an example of a cell configuration in an NR system. [Figure 14] The following is a sequence diagram illustrating an example of how to set the remote UE to RRC_IDLE before it is connected to the gNB via the relay UE in Embodiment 1. [Figure 15] The following is a sequence diagram illustrating another example of how to set the remote UE to RRC_IDLE before it is connected to the gNB via the relay UE in Embodiment 1. [Figure 16] The following is a sequence diagram illustrating another example of how to set the remote UE to RRC_IDLE before it is connected to the gNB via the relay UE in Embodiment 1. [Figure 17] This sequence diagram shows an example of a method for HOing a remote UE between a gNB connected to a remote UE and a gNB connected to a relay UE, in a modified example 1 of Embodiment 1. [Figure 18] This sequence diagram shows an example of how the remote UE uses system information received from gNB#1 in Embodiment 2. [Figure 19] The second embodiment is a sequence diagram showing an example of how a gNB instructs a remote UE to receive system information. [Figure 20] This is a sequence diagram showing an example of a method in which a remote UE performs registration by changing the TA, according to a modified example 2 of Embodiment 2. [Figure 21] This sequence diagram shows an example of a method for receiving paging from a gNB belonging to a TA where a remote UE is located, as is the case with Modification 3 of Embodiment 2. [Figure 22] The sequence diagram for Embodiment 3 shows an example of how a remote UE sends an SR to gNB#1. [Figure 23] This sequence diagram shows an example of a method for making a remote UE connect from gNB#1 to gNB#2, according to Modification 1 of Embodiment 1. [Modes for carrying out the invention]

[0067] Embodiment 1. Figure 2 is a block diagram showing the overall configuration of the LTE communication system 200 being discussed in 3GPP. Figure 2 will be explained below. The radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. The mobile terminal equipment (hereinafter referred to as "User Equipment: UE") 202, which is a communication terminal device, can communicate wirelessly with the base station equipment (hereinafter referred to as "Base Station (E-UTRAN NodeB: eNB)") 203 and transmits and receives signals wirelessly.

[0068] Here, "communication terminal equipment" includes not only mobile terminal equipment such as portable mobile phone terminals, but also stationary devices such as sensors. In the following explanation, "communication terminal equipment" may sometimes be simply referred to as "communication terminal."

[0069] If the control protocol for the mobile terminal 202, such as RRC (Radio Resource Control), and the user plane (hereinafter sometimes referred to as U-Plane), such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), are terminated at base station 203, then E-UTRAN is composed of one or more base stations 203.

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

[0071] In RRC_IDLE mode, tasks such as PLMN (Public Land Mobile Network) selection, System Information (SI) notification, paging, cell re-selection, and mobility are performed. In RRC_CONNECTED mode, mobile terminals have an RRC connection and can send and receive data with the network. In RRC_CONNECTED mode, tasks such as handover (HO) and neighbor cell measurement are also performed.

[0072] Base station 203 consists of one or more eNB207 units. The system, comprising the core network EPC (Evolved Packet Core) and the wireless access network E-UTRAN201, is called EPS (Evolved Packet System). The EPC and E-UTRAN201 are sometimes collectively referred to as the "network."

[0073] The eNB207 is connected via an S1 interface to a Mobility Management Entity (MME), or a Serving Gateway (S-GW), or an MME / S-GW unit (hereinafter sometimes referred to as "MME unit") 204 that includes both an MME and an S-GW, and control information is communicated between the eNB207 and the MME unit 204. Multiple MME units 204 may be connected to a single eNB207. The eNB207s are connected to each other via an X2 interface, and control information is communicated between the eNB207s.

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

[0075] The base station 203 may constitute one cell or multiple cells. Each cell has a predetermined range called coverage, which is the range within which it can communicate with the mobile terminal 202, and wireless communication is performed with the mobile terminal 202 within that coverage. When one base station 203 constitutes multiple cells, each cell is configured to communicate with the mobile terminal 202.

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

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

[0078] The functionality of the Radio Resource Control (RRC) control protocol between UE202 and NR base station 213 is the same as in LTE. The states of NR base station 213 and UE202 in RRC are RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE.

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

[0080] The gNB217 is connected via an NG interface to an Access and Mobility Management Function (AMF), a Session Management Function (SMF), or a User Plane Function (UPF), or an AMF / SMF / UPF unit (hereinafter sometimes referred to as the "5GC unit") 214 that includes AMF, SMF, and UPF. Control information and / or user data are communicated between the gNB217 and the 5GC unit 214. The NG interface is a collective term for the N2 interface between the gNB217 and AMF, the N3 interface between the gNB217 and UPF, the N11 interface between AMF and SMF, and the N4 interface between UPF and SMF. Multiple 5GC units 214 may be connected to a single gNB217. The gNB217s are connected to each other via an Xn interface, and control information and / or user data are communicated between them.

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

[0082] Like base station 203, NR base station 213 may also consist of one or more cells. When one NR base station 213 consists of multiple cells, each cell is configured to communicate with UE 202.

[0083] The gNB217 may be divided into a Central Unit (CU) 218 ​​and a Distributed Unit (DU) 219. One CU218 is configured within the gNB217. One or more DU219s are configured within the gNB217. The CU218 is connected to the DU219 via an F1 interface, and control information and / or user data are communicated between the CU218 and the DU219.

[0084] In a 5G communication system, the Unified Data Management (UDM) function and Policy Control Function (PCF) described in Non-Patent Document 21 (3GPP TS23.501) may be included. The UDM and / or PCF may be included in the 5GC unit 214 in Figure 3.

[0085] In a 5G communication system, a Location Management Function (LMF) as described in Non-Patent Document 24 (3GPP TS38.305) may be provided. The LMF may be connected to a base station via an AMF, as disclosed in Non-Patent Document 30 (3GPP TS23.273).

[0086] In a 5G communication system, the Non-3GPP Interworking Function (N3IWF) described in Non-Patent Document 21 (3GPP TS23.501) may be included. In non-3GPP access with the UE, the N3IWF may terminate the Access Network (AN) with the UE.

[0087] Figure 4 shows the configuration of a DC with eNBs and gNBs connected to the EPC. In Figure 4, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 4, eNB223-1 acts as the master base station, and gNB224-2 acts as the secondary base station (this DC configuration is sometimes referred to as EN-DC). Figure 4 shows an example where the U-Plane connection between the MME unit 204 and gNB224-2 is made via eNB223-1, but it may also be made directly between the MME unit 204 and gNB224-2.

[0088] Figure 5 shows the configuration of a DC with gNBs connected to the NG core. In Figure 5, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 5, gNB224-1 acts as the master base station, and gNB224-2 acts as the secondary base station (this DC configuration is sometimes referred to as NR-DC). Figure 5 shows an example where the U-Plane connection between 5GC unit 214 and gNB224-2 is made via gNB224-1, but it may also be made directly between 5GC unit 214 and gNB224-2.

[0089] Figure 6 shows the configuration of a DC with eNBs and gNBs connected to the NG core. In Figure 6, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 6, eNB226-1 acts as the master base station, and gNB224-2 acts as the secondary base station (this DC configuration is sometimes referred to as NG-EN-DC). Figure 6 shows an example where the U-Plane connection between 5GC unit 214 and gNB224-2 is made via eNB226-1, but it may also be made directly between 5GC unit 214 and gNB224-2.

[0090] Figure 7 shows another configuration of a DC with eNBs and gNBs connected to the NG core. In Figure 7, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In Figure 7, gNB224-1 acts as the master base station, and eNB226-2 acts as the secondary base station (this DC configuration is sometimes referred to as NE-DC). Figure 7 shows an example where the U-Plane connection between 5GC unit 214 and eNB226-2 is made via gNB224-1, but it may also be made directly between 5GC unit 214 and eNB226-2.

[0091] Figure 8 is a block diagram showing the configuration of the mobile terminal 202 shown in Figure 2. The transmission process of the mobile terminal 202 shown in Figure 8 will now be explained. First, control data from the protocol processing unit 301 and user data from the application unit 302 are stored in the transmission data buffer unit 303. The data stored in the transmission data buffer unit 303 is passed to the encoder unit 304, where encoding processing such as error correction is performed. There may be data that is output directly from the transmission data buffer unit 303 to the modulation unit 305 without undergoing encoding processing. The data encoded by the encoder unit 304 is then modulated in the modulation unit 305. Precoding in MIMO may be performed in the modulation unit 305. The modulated data is converted into a baseband signal, then output to the frequency conversion unit 306, where it is converted to a wireless transmission frequency. After that, the transmission signal is sent from antennas 307-1 to 307-4 to the base station 203. Figure 8 illustrates the case where there are four antennas, but the number of antennas is not limited to four.

[0092] Furthermore, the reception processing of the mobile terminal 202 is performed as follows: A radio signal from the base station 203 is received by antennas 307-1 to 307-4. The received signal is converted from the radio reception frequency to a baseband signal by the frequency conversion unit 306, and demodulation processing is performed by the demodulation unit 308. Weight calculation and multiplication processing may also be performed in the demodulation unit 308. The demodulated data is passed to the decoder unit 309, where decoding processing such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 301, and the user data is passed to the application unit 302. The series of processes of the mobile terminal 202 are controlled by the control unit 310. Therefore, although the control unit 310 is omitted in Figure 8, it is connected to each of the units 301 to 309. The control unit 310 is realized by a processing circuit that includes, for example, a processor and memory. That is, the control unit 310 is realized by the processor executing a program that describes the series of processes of the mobile terminal 202. A program describing a series of processes for the mobile terminal 202 is stored in memory. Examples of memory include non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), and flash memory. The control unit 310 may be implemented using a dedicated processing circuit such as an FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), or DSP (Digital Signal Processor). In Figure 8, the number of antennas used by the mobile terminal 202 for transmission and the number of antennas used for reception may be the same or different.

[0093] Figure 9 is a block diagram showing the configuration of the base station 203 shown in Figure 2. The transmission process of the base station 203 shown in Figure 9 will now be explained. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (MME unit 204, etc.). The 5GC communication unit 412 transmits and receives data between the base station 203 and the 5GC (5GC unit 214, etc.). The other base station communication unit 402 transmits and receives data with other base stations. The EPC communication unit 401, the 5GC communication unit 412, and the other base station communication unit 402 each exchange information with the protocol processing unit 403. Control data from the protocol processing unit 403, as well as user data and control data from the EPC communication unit 401, the 5GC communication unit 412, and the other base station communication unit 402, are stored in the transmission data buffer unit 404.

[0094] The data stored in the transmission data buffer unit 404 is passed to the encoder unit 405, where it undergoes encoding processing such as error correction. Some data may be output directly from the transmission data buffer unit 404 to the modulation unit 406 without undergoing encoding processing. The encoded data is then modulated in the modulation unit 406. Precoding in MIMO may be performed in the modulation unit 406. The modulated data is converted to a baseband signal, then output to the frequency conversion unit 407, where it is converted to a wireless transmission frequency. Subsequently, the transmission signal is sent from antennas 408-1 to 408-4 to one or more mobile terminals 202. Figure 9 illustrates the case with four antennas, but the number of antennas is not limited to four.

[0095] Furthermore, the reception processing of the base station 203 is performed as follows: A radio signal from one or more mobile terminals 202 is received by the antenna 408. The received signal is converted from the radio reception frequency to a baseband signal by the frequency conversion unit 407, and demodulation processing is performed by the demodulation unit 409. The demodulated data is passed to the decoder unit 410, where decoding processing such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 403, the 5GC communication unit 412, the EPC communication unit 401, or the other base station communication unit 402, and the user data is passed to the 5GC communication unit 412, the EPC communication unit 401, or the other base station communication unit 402. The series of processes of the base station 203 are controlled by the control unit 411. Therefore, although the control unit 411 is omitted in Figure 9, it is connected to each of the units 401-410 and 412. The control unit 411, like the control unit 310 of the mobile terminal 202 described above, is implemented as a processing circuit that includes a processor and memory, or as a dedicated processing circuit such as an FPGA, ASIC, or DSP. In Figure 9, the number of antennas used by the base station 203 for transmission and the number of antennas used for reception may be the same or different.

[0096] Figure 9 is a block diagram showing the configuration of base station 203, but base station 213 may have a similar configuration. Also, in Figures 8 and 9, the number of antennas on mobile terminal 202 and base station 203 may be the same or different.

[0097] Figure 10 is a block diagram showing the configuration of the MME. Figure 10 shows the configuration of the MME204a included in the MME unit 204 shown in Figure 2 above. The PDN GW communication unit 501 transmits and receives data between the MME204a and the PDN GW (Packet Data Network Gateway). The base station communication unit 502 transmits and receives data between the MME204a and the base station 203 via the S1 interface. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 501 to the base station communication unit 502 via the user-plane communication unit 503 and transmitted to one or more base stations 203. If the data received from the base station 203 is user data, the user data is passed from the base station communication unit 502 to the PDN GW communication unit 501 via the user-plane communication unit 503 and transmitted to the PDN GW.

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

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

[0101] The MME204a distributes paging signals to one or more base stations 203. The MME204a also performs mobility control in the idle state. The MME204a manages the tracking area list when the mobile terminal 202 is in the idle state and when it is in the active state. The MME204a initiates the paging protocol by sending a paging message to cells belonging to the tracking area where the mobile terminal 202 is registered. The management of the CSG, CSG ID, and whitelist of the eNB207 connected to the MME204a may be performed by the idle state mobility management unit 505-3.

[0102] The series of processes of the MME204a are controlled by the control unit 506. Therefore, although the control unit 506 is omitted in Figure 10, it is connected to each of the units 501 to 505. The control unit 506 is implemented as a processing circuit that includes a processor and memory, similar to the control unit 310 of the mobile terminal 202 described above, or as a dedicated processing circuit such as an FPGA, ASIC, or DSP.

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

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

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

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

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

[0108] P-SS and S-SS together are called the Synchronization Signal (SS). Each PCI assigned to a cell has a synchronization code that corresponds one-to-one with that PCI. 504 different PCI combinations are being considered. The communication terminal uses these 504 PCI combinations to synchronize and also detects (identifies) the PCI of the synchronized cell.

[0109] The communication terminal then detects the cell-specific reference signal (CRS), which is a reference signal (RS) transmitted from the base station to each cell, in step ST602 for the next synchronized cell, and measures the Reference Signal Received Power (RSRP). The reference signal (RS) uses a code that corresponds one-to-one with the PCI. By correlating with this code, it is possible to isolate it from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST601, it becomes possible to detect the RS and measure the received power of the RS.

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

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

[0112] Next, in step ST605, the communication terminal receives the DL-SCH of the cell based on the cell configuration information of the MIB and obtains SIB (System Information Block) 1 from the broadcast information BCCH. SIB1 contains information about accessing the cell, information about cell selection, and scheduling information for other SIBs (SIBk; an integer k ≥ 2). SIB1 also contains the Tracking Area Code (TAC).

[0113] Next, in step ST606, the communication terminal compares the TAC of the SIB1 received in step ST605 with the TAC portion of the Tracking Area Identity (TAI) in the Tracking Area List already held by the communication terminal. The Tracking Area List is also called the TAI list. TAI is identification information for identifying a tracking area and consists of MCC (Mobile Country Code), MNC (Mobile Network Code), and TAC (Tracking Area Code). MCC is the country code. MNC is the network code. TAC is the code number of the tracking area.

[0114] If, as a result of the comparison in step ST606, the TAC received in step ST605 is the same as a TAC included in the tracking area list, the communication terminal enters a waiting state in that cell. If, after comparison, the TAC received in step ST605 is not included in the tracking area list, the communication terminal requests a change in the tracking area through that cell to the Core Network (EPC), which includes the MME, etc., in order to perform a Tracking Area Update (TAU).

[0115] In the example shown in Figure 12, an example of the operation from cell search to standby in the LTE system is shown. However, in the NR system, in step ST603, the best beam may be selected in addition to the best cell. Also in the NR system, in step ST604, beam information, such as a beam identifier, may be obtained. Also in the NR system, in step ST604, scheduling information for the Remaining Minimum SI (RMSI) may be obtained. In the NR system, in step ST605, the RMSI may be received.

[0116] The devices constituting the core network (sometimes referred to as "core network devices") update the tracking area list based on the identification number (UE-ID, etc.) of the communication terminal sent from the communication terminal along with the TAU request signal. The core network devices send the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) its TAC list based on the received tracking area list. After that, the communication terminal enters a waiting state in that cell.

[0117] The proliferation of smartphones and tablet devices has led to an explosive increase in cellular wireless communication traffic, raising concerns about a shortage of wireless resources worldwide. To address this, efforts are being made to improve frequency utilization efficiency by reducing the number of cells and promoting spatial separation.

[0118] In conventional cell configurations, cells composed of eNBs have relatively wide coverage. Traditionally, cells are configured to cover a certain area through the relatively wide coverage of multiple cells composed of multiple eNBs.

[0119] When subdivided into smaller cells, the cells composed of eNBs have narrower coverage than cells composed of conventional eNBs. Therefore, as before, a larger number of subdivided eNBs are needed to cover a given area compared to conventional eNBs.

[0120] In the following explanation, cells with relatively high coverage, such as those composed of conventional eNBs, will be referred to as "macrocells," and the eNBs that make up macrocells will be referred to as "macro eNBs." Similarly, cells with relatively low coverage, such as those that have been resized into smaller cells, will be referred to as "small cells," and the eNBs that make up small cells will be referred to as "small eNBs."

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

[0122] A small eNB may be, for example, a low-power node, a local area node, or a hotspot. Alternatively, a small eNB may be a pico eNB constituting a picocell, a femto eNB constituting a femtocell, a HeNB, an RRH (Remote Radio Head), an RRU (Remote Radio Unit), an RRE (Remote Radio Equipment), or an RN (Relay Node). Furthermore, a small eNB may be a "Local Area Base Station" or "Home Base Station" as described in Non-Patent Document 7.

[0123] Figure 13 shows an example of a cell configuration in NR. In an NR cell, a narrow beam is formed and transmitted by changing its direction. In the example shown in Figure 13, base station 750 uses beam 751-1 to transmit and receive with a mobile terminal at a certain time. At other times, base station 750 uses beam 751-2 to transmit and receive with a mobile terminal. Similarly, base station 750 uses one or more of beams 751-3 to 751-8 to transmit and receive with a mobile terminal. In this way, base station 750 configures a wide-area cell.

[0124] Figure 13 shows an example where the base station 750 uses eight beams, but the number of beams may be different from eight. Also, in the example shown in Figure 13, the base station 750 uses one beam simultaneously, but it may use multiple beams.

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

[0126] The physical channels used in SL (see Non-Patent Document 1) are described below. The Physical Sidelink Broadcast Channel (PSBCH) carries system and synchronization-related information and is transmitted from the UE.

[0127] The Physical Sidelink Discovery Channel (PSDCH) carries sidelink discovery messages from the UE (Union Engine).

[0128] The Physical Sidelink Control Channel (PSCCH) carries control information from the UE for sidelink communication and V2X sidelink communication.

[0129] The Physical Sidelink Shared Channel (PSSCH) carries data from the UE for sidelink communication and V2X sidelink communication.

[0130] The Physical Sidelink Feedback Channel (PSFCH) carries HARQ feedback over the sidelink from the UE that received the PSSCH transmission to the UE that transmitted the PSSCH.

[0131] The transport channels used in SL (see Non-Patent Document 1) are described below. The Sidelink broadcast channel (SL-BCH) has a predetermined transport format and is mapped to the physical channel PSBCH.

[0132] The Sidelink Discovery Channel (SL-DCH) has periodic broadcast transmissions in a fixed size and predetermined format. The SL-DCH supports both UE autonomous resource selection and resource allocation scheduled by the eNB. UE autonomous resource selection carries a risk of collisions, while there are no collisions when the UE allocates resources individually via the eNB. The SL-DCH also supports HARQ combining but not HARQ feedback. The SL-DCH is mapped to the physical channel PSDCH.

[0133] Sidelink shared channels (SL-SCH) support broadcast transmission. SL-SCH supports both UE autonomous resource selection and resource allocation scheduled by the eNB. UE autonomous resource selection carries a risk of collisions, while there are no collisions when the UE allocates individual resources via the eNB. SL-SCH also supports HARQ combining but not HARQ feedback. Furthermore, SL-SCH supports dynamic link adaptation by changing transmit power, modulation, and coding. SL-SCH is mapped to the physical channel PSSCH.

[0134] This section describes the logical channels used in SL (see Non-Patent Document 1). The Sidelink Broadcast Control Channel (SBCCH) is a sidelink channel used to broadcast sidelink system information from one UE to another. The SBCCH is mapped to the transport channel SL-BCH.

[0135] A Sidelink Traffic Channel (STCH) is a one-to-many sidelink traffic channel for transmitting user information from one UE to another. STCH is used only between UEs with sidelink communication capabilities and UEs with V2X sidelink communication capabilities. One-to-one communication between two UEs with sidelink communication capabilities is also achieved via STCH. STCH is mapped to the transport channel SL-SCH.

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

[0137] 3GPP is considering supporting V2X communication in NR as well. The study of V2X communication in NR is progressing 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, SL communication was limited to broadcast only. In NR, support for unicast and groupcast in addition to broadcast is being considered for SL communication (see Non-Patent Document 22 (3GPP TS23.287)).

[0139] Support for HARQ feedback (Ack / Nack) and CSI reporting is being considered for unicast and groupcast communications.

[0140] In SL communication, in addition to broadcast, support for unicast and groupcast is being considered, and therefore support for PC5-S signaling is being explored (see Non-Patent Document 22 (3GPP TS23.287)). For example, PC5-S signaling is implemented to establish a link for SL, i.e., PC5 communication. This link is implemented at 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 UEs of their capabilities between UEs performing PC5 communication, and to notify AS layer settings for V2X communication using PC5 communication.

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

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

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

[0145] For example, if a remote UE is located at the coverage end of gNB#2, it may not be possible to obtain good communication quality. In such cases, the remote UE can obtain better communication quality by connecting to gNB#1 via a relay UE. Also, for example, if 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 reduce power consumption by communicating with gNB#1 via the relay UE, as this reduces the transmission power of the remote UE.

[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 any previously established standards, including Non-Patent Documents 20 and 23 mentioned above. Therefore, when a remote UE is connected to gNB#2, even if the situation described above occurs, the remote UE cannot connect to gNB#1 via the relay UE, which is a problem.

[0147] This embodiment discloses a method for solving these problems.

[0148] In the communication system according to this embodiment, the above problem is solved by setting the remote UE to RRC_IDLE before the remote UE is connected to gNB#1 via the relay UE. Alternatively, the remote UE may be set to RRC_IDLE before the remote UE starts the RRC connection process with gNB#1.

[0149] Furthermore, if the remote UE is connected to gNB#2 via RRC, a challenge arises in determining how to set the remote UE to RRC_IDLE. This document discloses a method for resolving this issue.

[0150] To resolve this issue, gNB#2 releases the RRC connection to the remote UE. The remote UE may also release its RRC connection to gNB#2.

[0151] For example, a remote UE performs measurements on the SL from a relay UE. The SL measurements include received quality (received power, RSSI (Received Signal Strength Indicator), SNR, SINR, and channel occupancy (which may also be CBR (Channel Busy Ratio))). That is, the remote UE measures the received quality on the SL from the relay UE (hereinafter sometimes referred to as SL received quality). The remote UE reports the SL measurement results to gNB#2. The remote UE reports the SL received quality to gNB#2. gNB#2 may use the SL received quality reported by the remote UE to decide whether or not to release the connection with the remote UE. If gNB#2 decides to release the connection with the remote UE, gNB#2 initiates the process of releasing the RRC connection to the remote UE with which it is connected via RRC. gNB#2 may also request the remote UE with which it is connected via RRC to release the RRC connection. 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 to the remote UE that is connected via RRC. The remote UE that has released the RRC connection to gNB#2 should then connect to gNB#1 via the relay UE.

[0153] This document discloses a method by which a gNB (radio network bunker) can set up SL (Single Level) measurements for a UE (Underground User). The gNB may notify the UE of the SL measurement settings. The gNB may also notify the UE performing SL communication of the SL measurement settings. SL measurement settings include the setting of the measurement target and the setting of the measurement result reporting method. Examples of measurement target settings include the frequency of the SL to be measured, the RAT (Radio Access Technology) of the SL to be measured, and the UE being measured. Alternatively, the SL measurement target may be set per beam. When SL communication is performed using beams, beam-specific SL measurement results 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. It may be possible to set whether they are the same or different. Examples of UEs to be measured for SL include different types of UEs, such as U2N relay UEs, U2U relay UEs, UEs capable of SL communication, and UEs performing SL communication. These UEs may be combined. The gNB sets the information disclosed above as the setting for the measurement target and notifies the UE.

[0155] For the SL measurement result reporting settings, for example, reporting can be done periodically, reporting when certain conditions are met (sometimes referred to as an event trigger), or reporting n times (where n is an integer greater than or equal to 1). The gNB sets the information disclosed above as the measurement result reporting method 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 exceeds a predetermined threshold. (2) When the SL reception quality falls below a predetermined threshold. (3) When the SL reception quality becomes greater than the serving cell reception quality. (4) When the SL reception quality becomes lower than the serving cell reception quality. (5) When the reception quality from a UE capable of SL communication becomes better than the reception quality from a UE performing SL communication. (6) When the reception quality from an UE capable of SL communication becomes lower than the reception quality from an UE performing SL communication. (7) A combination of (1) to (6).

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

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

[0160] The identifier of the UE itself may be notified along with the SL measurement result. The gNB will be able to recognize which UE the measurement result belongs to. The identifier of the UE itself may be notified along with the SL measurement result. The gNB will be able to recognize which UE the measurement result belongs to. The identifier of the UE being measured may be notified along with the SL measurement result. It may be notified in association with the measurement result. The gNB will be able to recognize which UE the SL measurement result belongs to. The type of the UE being measured may be notified along with the SL measurement result. The gNB will be able to recognize the type of UE the SL measurement result belongs to. Information about the group to which the UE itself belongs may be notified along with the SL measurement result. The gNB will be able to recognize which group the UE belongs to. The location information of the UE itself may be notified along with the SL measurement result. Information indicating which area it is located in may be notified as location information. The gNB will be able to recognize the location at which the reported SL measurement result was taken. The identifier of the gNB that performed the measurement may be notified along with the SL measurement result. The gNB will be able to recognize which gNB the UE's received quality measurement was taken from. The received quality measurement result from the gNB may be notified along with the SL measurement result. It may be notified in association with the identifier of the gNB that performed the measurement. The gNB can recognize which gNB the UE used to measure the received quality.

[0161] Alternatively, a Layer 3 (L3) filtering function may be added to the SL measurement and the results of L3 filtering may be reported. This would enable more accurate measurements. Alternatively, a Layer 1 (L1) filtering function may be added to the SL measurement and the results of L1 filtering may be reported. This would allow for earlier notification of measurement results.

[0162] RRC signaling may be used to notify of SL measurement settings. RRC signaling may be used to report SL measurement results. This allows for the notification of a large amount of information. L3 filtering may be used for SL measurement results reported using RRC signaling. MAC signaling may be used for reporting SL measurement results. For example, in the case of event triggering, SL measurement results can be sent and received earlier. PUCCH may be used for reporting SL measurement results. For example, in the case of event triggering, SL measurement results can be sent and received even earlier. L1 filtering may be used for SL measurement results reported using PUCCH. For example, L1 filtering and PUCCH may be used for beam-specific measurements and reporting of measurement results. This makes it possible to obtain dynamic measurement results for each beam.

[0163] This allows for the notification of SL measurement settings and results between the gNB and UE on the Uu. The gNB can notify the UE of SL measurement settings on the Uu. The UE can notify the gNB of SL measurement results on the Uu. The gNB can recognize the SL measurement results on the UE.

[0164] The measurement settings for conventional Uu may include SL measurement settings. Alternatively, the measurement settings for conventional Uu and SL measurement settings may be combined. For example, the measurement events for conventional Uu may be combined with the SL measurement events disclosed above. For example, the measurement results may be reported when the reception quality of the serving cell falls below a predetermined threshold and the SL reception quality falls above a predetermined threshold. In this way, Uu measurements and SL measurements can be combined, enabling more flexible measurement settings and the acquisition of diverse measurement results. It becomes possible to compare reception quality between a gNB and an SL-capable UE such as a relay UE.

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

[0166] (1) Commercial state. (2) RRC state. (3) Identifier of the UE. (4) Identifier of the destination UE. (5) The identifier of the RAN to connect to. (6) The identifier of the CN (Core Network) to connect to. (7) Identifier of the area in which the person resides. (8) Identifier of the service to be provided. (9) Identifier of the slice to be provided. (10) A combination of (1) to (9).

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

[0168] (3) Identifies the UE that transmits information about the UE's connection status. For example, GUTI (Globally Unique Temporary Identifier), 5G-S-TMSI (5G SAE Temporary Mobile Subscriber Identity), etc. (4) Identifies the UE that receives information about the UE's connection status. For example, GUTI, 5G-S-TMSI, etc. (5) Identifies the RAN to which the UE is connected. For example, the RAN may be a gNB, a cell, or an identifier such as a TRP (Transmission Reception Point), IAB (Integrated Access and Backhaul) donor, or IAB node. For example, the cell identifier may be an NCI (NR Cell Identifier) ​​or NCGI (NR Cell Global Identifier). (6) Identifies the CN to which the UE is connected. 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 AMF Set ID.

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

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

[0171] In this way, the receiving UE can recognize which network the UE that sent information about the UE's connection status is connected to, what the connection status is, and so on.

[0172] The information is described as being related to the UE's connection status, but it may also be related to a change in the UE's connection status. The information related to a change in the UE's connection status may include information about the connection status before the change and / or information about the connection status after the change. Information about a change in the UE's connection status may be notified between UEs performing SL communication on PC5. For example, if a relay UE changes its connection status with the NW, the relay UE may notify the remote UE of the change in the UE's connection status. For example, if a remote UE changes its connection status with the NW, the remote UE may notify the relay UE of the change in the UE's connection status. In this way, it is only necessary to notify the information when the connection status between the UE and the NW changes, which reduces the resources required for notification.

[0173] Messages may be provided to notify users of information regarding the UE's connection status or changes in the UE's connection status. These messages may contain this information. For example, a relay UE may notify a remote UE of information regarding the UE's connection status in the message. For example, a remote UE may notify a relay UE of information regarding the UE's connection status in the message.

[0174] This document discloses methods for notifying information regarding the UE's connection status and changes in the UE's connection status. Notification may be made via PC5-S signaling. This allows for early notification during PC5 connection processing. Alternatively, notification may be made via PC5-RRC signaling. For example, it may be included in an RRC message on the PC5. For instance, when notifying the RRC connection status with the network, using RRC signaling on the PC5 allows notification processing at the same RRC layer, thus reducing malfunctions. Furthermore, this information may be notified via the PC5's SRB (Signaling Radio Bearer). This allows 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 can be made earlier than with RRC signaling. The information may also be notified via PSCCH. The information may also be included in the 1st SCI (Sidelink Control Information) and notified. Doing so allows for even earlier notification. Furthermore, UEs capable of receiving PC5 communication can receive the information. The information may also be notified via PSSCH. The information may also be included in the 2nd SCI and notified. Doing so allows for earlier notification. The information may also be included in the MAC CE (Control Element) and notified via PSSCH. Doing so allows for earlier notification. Furthermore, since HARQ is applied, reception errors can be reduced.

[0176] When a remote UE establishes an RRC connection with gNB#1, the process differs from the conventional RRC connection process between a UE and a gNB, as a relay UE is interposed between the remote UE and the gNB, making the conventional method unusable. This document discloses a specific method for a remote UE to establish an RRC connection with gNB#1.

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

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

[0179] The information contained in the RRC connection request may be encapsulated. Alternatively, the information contained in the RRC connection request may be used as container information. For example, it may be encapsulated as information about the SL. It may also be encapsulated as information about the relay. The relay UE may notify the NW of the RRC connection request received from the remote UE, either encapsulated or in its container form. This simplifies and reduces the latency of receiving and transmitting RRC connection requests at the relay UE. As a result, malfunctions at the relay UE can be reduced, and RRC connection processing can be made low-latency.

[0180] Six examples of information to include in an RRC connection request are disclosed below. (1) Information indicating that it is an RRC connection request between the UE and the NW. (2) Identifier of the UE. (3) Identifier of the requesting network. (4) Identifier of the destination UE. (5) Information regarding the UE's connection status. (6) A combination of (1) to (5).

[0181] (1) may be an RRC connection request, for example, an RRC setup request. (2) Identifies the UE that sends the RRC connection request. For example, GUTI, 5G-S-TMSI, etc. (3) Identifies the RAN on which the UE makes the RRC connection request. For example, the RAN may be a gNB, a cell, or an identifier such as a TRP, IAB donor, or IAB node. For example, the cell identifier may be NCI or NCGI. (4) Identifies the UE that the RRC connection request is sent through when it is sent to the NW. For example, if a remote UE notifies the NW of an RRC connection request via a relay UE, this may be an identifier that identifies the relay UE. For example, GUTI, 5G-S-TMSI, etc. (5) may be information about the connection status of the UE as disclosed above.

[0182] In this way, a network (e.g., a gNB) that receives an RRC connection request can recognize the UE that made the connection request and the UEs that passed through the connection request. Furthermore, the UEs that passed through the connection request can recognize the destination gNB of the connection request that they received from the source UE. As a result, the gNB that receives the RRC connection request can perform RRC connection processing between the UEs that sent the RRC connection request.

[0183] When a remote UE notifies the network of an RRC connection request, it does so via a relay UE, and therefore the RRC connection request must be notified to the relay UE on PC5. As a method for notifying the RRC connection request on PC5, the method for notifying information regarding the UE's connection status on PC5 as disclosed above may be applied as appropriate. Alternatively, a message for RRC connection requests via the relay UE may be provided as RRC signaling on PC5.

[0184] A method for notifying a relay UE of an RRC connection request to a network is disclosed. The RRC signaling of the Uu 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 about the SL may be used. For example, SidelinkUEInformationNR may be used. Alternatively, a message for RRC connection requests via the relay UE may be provided. Furthermore, the RRC connection request may 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. This allows for earlier notification compared to RRC signaling. The RRC connection request may also be notified via PUCCH. The connection request may be included in the UCI for notification. This allows for even earlier notification. The RRC connection request may also be notified via PUSCH. The connection request may be included in the MAC CE and notified via PSSCH. Alternatively, it may be notified via PUSCH together with the data. This allows for earlier notification. In addition, 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. The network can then initiate the RRC connection process for the remote UE.

[0187] This document discloses another method by which a remote UE establishes an RRC connection with gNB#1. 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 different from the PC5's RRC connection request and may be an RRC connection request between the remote UE and the network. This allows the relay UE to recognize that it is different from the PC5's RRC connection request. The network may be the network to which the relay UE is connected (gNB#1). When the relay UE receives an RRC connection request from the remote UE, it notifies the network to which the relay UE is connected of an RRC connection request between the remote UE and the network.

[0188] As an example 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 in the aforementioned information (4) should be the identifier of the UE to which the RRC connection request is sent, rather than the UE through which the request is received.

[0189] In this way, the relay UE, upon receiving an RRC connection request from the remote UE, can notify gNB#1 of the RRC connection request between the remote UE and the network. Upon receiving the RRC connection request between the remote UE and the network from the relay UE, gNB#1 can then perform the RRC connection process with the remote UE.

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

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

[0192] When a remote UE notifies the relay UE of an RRC connection request to the network, the relay UE and the gNB may initiate RRC connection processing. When the relay UE receives an RRC connection request to the network from the remote UE, it may initiate RRC connection processing with gNB#1 within its coverage. The remote UE may initiate RRC connection processing for a cell that has been selected or re-selected. The remote UE notifies the relay UE of an RRC connection request to the network. The state of the remote UE may be RRC_Connected or RRC_Idle. When the relay UE receives an RRC connection request to the network, it makes an RRC connection request to the gNB (gNB#1) that has the cell that has been selected or re-selected. Once the relay UE has completed RRC connection processing with gNB#1, it may notify the remote UE of the change in RRC state.

[0193] A message requesting an RRC connection to the network may be placed on PC5. This message may also be used for relaying. The message should be a request for an RRC connection to the network to the destination UE. Seven examples of information to be included in this message are disclosed below.

[0194] (1) Information indicating a request for RRC connection to the network. (2) Identifier of the UE. (3) RRC connection status of the UE. (4) The identifier of the gNB that the user has selected or re-selected. (5) The identifier of the gNB to which the UE connects. (6) Identifier of the destination UE. (7) A combination of (1) to (6).

[0195] The method for notifying the relay UE of the RRC connection request message to the network from the remote UE may be the method described above as appropriate. The method for notifying PC5 of information regarding the UE's connection status should also be applied as appropriate.

[0196] Once the relay UE has completed the RRC connection process with gNB#1, it notifies gNB#1 of the RRC connection request message from the remote UE. This allows the remote UE to notify the network of the RRC connection request message via the relay UE. Furthermore, the relay UE does not need to be connected to the gNB in ​​advance. This enables lower power consumption for the relay UE.

[0197] gNB#1 may notify the remote UE of an RRC setup message via the relay UE. Upon receiving the RRC setup message from the remote UE via the relay UE, gNB#1 initiates the RRC connection process to the remote UE via the relay UE that received the message. gNB#1 configures the RRC for the remote UE and notifies it of an RRC setup message including the RRC configuration via the relay UE.

[0198] A method for notifying a relay UE of an RRC setup message from the network is disclosed. The RRC setup message may use the Uu's RRC signaling. The RRC setup may be used as the RRC signaling. Alternatively, an RRC message for notifying information about the service line may be used. Alternatively, a message for requesting an RRC connection via the relay UE may be provided. Furthermore, the RRC setup may be notified by the 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 method for notifying information regarding the UE's connection status on PC5 as disclosed above may be applied as appropriate. In addition, a message for RRC connection requests via the relay UE may be provided as RRC signaling on PC5.

[0200] In this way, the remote UE can receive RRC setup messages from gNB#1 via the relay UE. The remote UE can obtain the RRC settings from gNB#1 to establish an RRC connection with gNB#1. The remote UE then performs the RRC configuration using the RRC settings obtained from gNB#1.

[0201] A remote UE that has performed RRC configuration using the RRC settings obtained from gNB#1 may notify gNB#1 that the RRC setup is complete. 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 the RRC signaling for the Uu. In this way, gNB#1 will be able to receive RRC setup completion notifications from the remote UE. gNB#1 will be able to recognize that the RRC configuration has been completed by the remote UE.

[0202] This allows RRC connection processing to be performed between the remote UE and gNB#1. The remote UE can then establish an RRC connection with gNB#1.

[0203] This document discloses the resources required for communication at PC5 between the remote UE and the relay UE. If the remote UE is connected to a network, the resources required for communication at PC5 may be scheduled by the connected network. The connected network may also schedule the resources when the remote UE is transmitting. The remote UE communicates at PC5 according to the scheduling information received from the connected network. If the remote UE is not connected to a network, the resources required for communication at PC5 may be selected by the remote UE using the Resource Pool (RP) announced by the gNB#2 where the remote UE is located.

[0204] If the relay UE is connected to a network, the resources required for communication at PC5 may be scheduled by the connected network. Alternatively, the network may schedule the resources when the relay UE is transmitting. The relay UE will communicate at PC5 according to the scheduling information received from the connected network. If the relay UE is not connected to a network, the resources required for communication at PC5 may be selected by the relay UE using the RP broadcast by the gNB#1 where the relay UE is located.

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

[0206] Figure 14 is a sequence diagram showing an example of how to set the remote UE to RRC_IDLE before it is RRC-connected to the gNB via the relay UE in Embodiment 1. In step ST1401, the relay UE is in coverage of gNB#1 and is in the RRC_IDLE state. In step ST1402, the remote UE is in coverage of gNB#2 and is in the RRC_CONNECTED state. In step ST1403, gNB#2 notifies the remote UE of the setting of the SL measurement (hereinafter referred to as SL measurement setting). In step ST1404, the remote UE performs SL communication quality measurement (hereinafter sometimes referred to as SL measurement or SL measurement) according to the SL measurement setting received from gNB#2. In SL communication quality measurement, 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 results, according to the SL measurement report setting included in the SL measurement setting received from gNB#2 in step ST1403. For example, the aforementioned SL measurement event setting may be used as the SL measurement report setting. For example, if the reception quality from the UE in SL is greater than a predetermined threshold, and the reception quality from the UE is greater than the reception quality from gNB#2, that is, if the reception quality from the UE is better than the reception quality from gNB#2, the remote UE reports the SL measurement results to gNB#2. In step ST1406, gNB#2 uses the SL measurement results notified in the SL measurement report from the remote UE to determine whether or not to release the remote UE's RRC connection. If gNB#2 determines to release the remote UE's RRC connection, in step ST1407, gNB#2 notifies the remote UE of an RRC connection release request. Upon receiving the request, the remote UE performs the RRC connection release process with gNB#2 in step ST1408.

[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 with relay functionality, and in step ST1411, it performs PC5-RRC connection. Upon completion of the PC5-RRC connection, data communication between the remote UE and the relay UE becomes possible.

[0209] The relay UE connected to the remote UE initiates connection processing to the NW. The relay UE connected to the remote UE initiates RRC connection processing to gNB#1. The remote UE may request the connected relay UE to connect to the NW. For example, this request may be notified during PC5-RRC connection processing, or after PC5-RRC connection is completed, the request may be notified using PC5-RRC signaling. The relay UE that receives the request may perform connection processing to the NW. 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 configures the RRC settings for the relay UE and notifies the relay UE of the RRC setup including these settings in step ST1413. Upon receiving the RRC setup, the relay UE configures the RRC settings with gNB#1 and notifies gNB#1 of the completion of the RRC setup in step ST1414. As a result, in step ST1415, the RRC connection between the relay UE and gNB#1 is established.

[0211] In step ST1416, the relay UE connected to gNB#1 via RRC sends an RRC status change notification to the remote UE containing information about the UE's connection status with the network. Here, it is appropriate to notify that the RRC connection is active.

[0212] Upon receiving notification from the relay UE that it is connected to the NW via RRC, the remote UE notifies gNB#1 of an RRC setup request in step ST1417. This notification may also be made via the relay UE. Upon receiving the RRC setup request, gNB#1 configures the RRC settings for the remote UE and notifies the remote UE of the RRC setup, including the configuration, in step ST1418. This notification may also be made via the relay UE. Upon receiving the RRC setup, the remote UE configures the RRC settings with gNB#1 and notifies gNB#1 of the completion of the RRC setup in step ST1419. This notification may also be made via the relay UE. As a result, the RRC connection between the remote UE and gNB#1 is established in step ST1420.

[0213] This allows the remote UE, which was connected to gNB#2 via RRC, to switch to a state where it is connected to gNB#1 via RRC. As a result, the remote UE can communicate with gNB#1 via the relay UE.

[0214] In the example disclosed in Figure 14, the remote UE made an RRC connection request to gNB#1 in step ST1417. Alternatively, 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 the relay UE. Upon receiving the RRC connection request from gNB#1, the remote UE may initiate the RRC connection process for gNB#1. The remote UE may also notify gNB#1 of the RRC setup request disclosed in step ST1417 of Figure 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. Upon receiving the paging, the remote UE initiates the RRC connection process for gNB#1. This paging may be generated by gNB#1 rather than originating from the CN. The method for paging from gNB#1 to the remote UE via the relay UE may be appropriately applied from the method disclosed in Modification 4 of Embodiment 2. By using paging, gNB#1 can request the remote UE to initiate the RRC connection process.

[0216] gNB#1 may notify the remote UE of the RRC configuration without making an RRC connection request. gNB#1, having decided to establish an RRC connection with the remote UE, may also notify the remote UE of the RRC configuration via the relay UE without making an RRC connection request. This eliminates the need to send and receive RRC connection request messages from gNB#1 to the remote UE and from the remote UE to gNB#1, thereby reducing the signaling load.

[0217] The relay UE may notify gNB#1 of the connection status with the remote UE. This connection status may be information regarding the connection status in PC5, as described later. The method for notifying gNB#1 of this connection status information from the relay UE may also be the method described later as appropriate. gNB#1 may use the connection status with the relay UE and the connection status between the relay UE and the remote UE to decide whether or not to make an RRC connection request to the remote UE. If the relay UE is in an RRC connection state and an RRC connection has been 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 connection state with gNB#1 via the relay UE.

[0218] As previously mentioned, gNB#2 disclosed a method for releasing the RRC connection of a remote UE using the received quality in the SL from the remote UE. We will now disclose another method for releasing the RRC connection of a remote UE.

[0219] The remote UE reports to gNB#2 when it finds a connectable relay UE. The remote UE may also report to gNB#2 after performing the discovery process with the relay UE. The remote UE may also report to gNB#2 after establishing a PC5 connection with the relay UE. The remote UE may also report to gNB#2 when it has completed establishing the PC5-S link with the relay UE. The remote UE may also report to gNB#2 when it has completed establishing the PC5-RRC connection with the relay UE.

[0220] gNB#2 may use information received from the remote UE regarding the connection status with the relay UE to determine whether or not to release the connection with the remote UE. This information regarding the connection status between the remote UE and the relay UE may be the connection status information on PC5. If gNB#2 determines to release the connection with the remote UE, gNB#2 will start the process of releasing the RRC connection to the remote UE with which it is connected via RRC. gNB#2 may also request the remote UE with which it is connected via RRC to release the RRC connection. 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 the relay UE's connection status with the network. gNB#2 may use the information received from the remote UE regarding the relay UE's connection status with the network to decide whether or not to release the RRC connection with the remote UE. gNB#2 may also use the aforementioned information regarding the connection status between the remote UE and the relay UE, along with the information regarding the relay UE's connection status with the network, to decide whether or not to release the RRC connection with the remote UE. In this way, gNB#2 can decide whether or not 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 network via the relay UE can be performed sooner.

[0222] Information regarding the connection status at PC5 may be provided. The connection status may include the status of the discovery process, the status of the PC5-S link establishment process, the PC5-RRC connection status, etc. The status of the discovery process may be "discovery process in progress" or "discovery process completed." The status of the PC5-S link establishment process may be "PC5-S link establishment in progress" or "PC5-S link establishment completed." The PC5-RRC connection status may be "PC5-RRC connection in progress" or "PC5-RRC connection completed." Six examples of information regarding the connection status at PC5 are disclosed below.

[0223] (1) Connection status on PC5. (2) Identifier of the UE. (3) Identifier of the UE that will be connected to the PC5. (4) Information regarding the connection status of the UE. (5) Information on whether the UE is capable of relaying. (6) A combination of (1) to (5).

[0224] (1) may be the connection status of the UE on PC5. (2) identifies the UE that notifies the information. For example, GUTI, 5G-S-TMSI, or Layer 2 ID on PC5. (3) identifies the other UE for the PC5 connection process. For example, GUTI, 5G-S-TMSI, or Layer 2 ID on PC5. (4) is information regarding the connection status of the local UE and / or the other UE for the PC5 connection process. The information regarding the connection status of the UE disclosed above may be applied as appropriate. (5) is information regarding whether the local UE and / or the other UE for the PC5 connection process is capable of relaying. Relays include UE-to-Network relays that relay between the UE and the NW, and UE-to-UE relays that relay between UEs. This information may be provided separately. The UE may have a capability to determine whether it is capable of relaying on the SL. This capability may be used as information on whether the UE is capable of relaying.

[0225] In this way, the gNB that receives the information can recognize which UE the UE that sent information about the connection status of the UE on PC5 is connected to, what the connection status is, etc.

[0226] While the information is described as relating to the connection status on PC5, it may also be relating to changes in the connection status on PC5. This information may include information about the connection status on PC5 before the change and / or information about the connection status on PC5 after the change. By doing so, when the connection status on PC5 of the UE changes, only this information needs to be notified, reducing the resources required for notification.

[0227] Messages may be provided on the Uu to notify users of information regarding the connection status of the UE at PC5 or changes in the connection status of the UE at PC5. These messages may include this information. For example, a remote UE may notify gNB#2 of the connection status of the UE at PC5 in the message.

[0228] As a method for notifying information regarding the connection status at PC5 from the remote UE to the NW, the method for notifying RRC connection requests from the relay UE to the NW as disclosed above may be applied as appropriate.

[0229] In this way, the remote UE can notify gNB#2 of information regarding the connection status at PC5. Using this information received from the remote UE, gNB#2 can then decide whether or not to release the RRC connection with the remote UE.

[0230] In the case of UE-UE relays, information regarding the connection status at one PC5 may be notified to a UE other than the UEs that transmit and receive at that PC5. For example, if a transmitting UE, UE-TX, communicates with a receiving UE, UE-RX, via a UE-UE relay UE, the UE-UE relay UE may notify UE-RX of information regarding the connection status at the PC5 between UE-TX and the UE-UE relay UE. As a method for notifying information regarding the connection status at the PC5 between UEs, the method of notifying RRC connection requests on the PC5 via the relay UE, as disclosed above, may be applied as appropriate. In this way, even in the case of UE-UE relays, each UE can recognize the connection status at each PC5.

[0231] Figure 15 is a sequence diagram showing another example of how to set the remote UE to RRC_IDLE before it is connected to the gNB via the relay UE in Embodiment 1. In Figure 15, steps common to Figure 14 are numbered the same way, and common descriptions are omitted.

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

[0233] This allows the remote UE, which was connected to gNB#2 via RRC, to switch to an RRC connection with gNB#1. This enables 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 can release the remote UE from the RRC connection at the appropriate time.

[0234] Figure 16 is a sequence diagram showing another example of how to set the remote UE to RRC_IDLE before it is connected to the gNB via the relay UE in Embodiment 1. In Figure 16, steps common to Figure 15 are numbered the same way, and common descriptions are omitted.

[0235] Figure 16 shows the case where, in step ST1601, the relay UE is connected to gNB#1 via RRC before connecting to the remote UE and PC5.

[0236] In this case, the relay UE should notify the remote UE of information regarding its own UE's connection status. For example, the relay UE may notify the remote UE of information regarding its own UE's connection status during the PC5-RRC connection process in step ST1411. Alternatively, after the PC5-RRC connection process, it may notify the remote UE of information regarding its own UE's connection status using PC5-RRC signaling. By doing so, the remote UE can recognize the connection status between the relay UE and the network. If the remote UE has performed the RRC connection release process with gNB#2 in step ST1408, and the relay UE is in an RRC connection state with the network, it can immediately notify gNB#1 of the RRC setup request in step ST1417 and start the RRC connection process.

[0237] This allows the remote UE, which was connected to gNB#2 via RRC, to switch to an RRC connection state with gNB#1. This enables 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 can release the remote UE from the RRC connection at the appropriate time. In addition, since the remote UE can recognize the connection status of the relay UE with gNB#1, it can send an RRC setup request to gNB#1 at the appropriate time and with the appropriate processing.

[0238] This document discloses other methods for releasing the RRC connection of a remote UE.

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

[0240] gNB#2 may use the connection release request received from the remote UE to decide whether or not to release the RRC connection with the remote UE. If gNB#2 decides to release the RRC connection with the remote UE, gNB#2 will start the process of releasing the RRC connection to the connected remote UE. For example, if the remote UE notifies gNB#2 of an RRC connection release request, and gNB#2 uses the received RRC connection release request to decide to release the RRC connection with the remote UE, gNB#2 will perform the RRC connection release process to the remote UE.

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

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

[0243] This document discloses other methods for releasing the RRC connection of a remote UE.

[0244] A remote UE may release its RRC connection with the network itself. That is, the remote UE performs the process of releasing the RRC connection with the network. The determination of releasing the RRC connection may be appropriately applied to the determination method in gNB#2 described above. The network, for example gNB#2, cannot recognize whether the remote UE has released its RRC connection with its own gNB. If the network cannot recognize whether the remote UE has released its RRC connection, it will continue to hold resources for the connection with the remote UE. This results in wasted resources and a decrease in resource utilization efficiency. A method to solve this problem is disclosed.

[0245] If NW has not communicated with the remote UE for a predetermined period, it performs a connection release process with the remote UE. That is, if gNB#2 has not communicated with the RRC-connected remote UE for a predetermined period, it performs a connection release process with the remote UE in its own gNB. For example, it releases the 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. By doing so, it is possible to avoid wasteful use of resources in gNB#2.

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

[0247] Variant 1 of Embodiment 1. In this variant, another method for solving the problems shown in Embodiment 1 is disclosed.

[0248] In the communication system according to this variant, the remote UE is handed over 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 handed over between gNB#2 and gNB#1. Thereby, it is not necessary to transition the remote UE to RRC_IDLE. The connection destination can be changed from gNB#2 to gNB#1 while the remote UE remains in the RRC_CONNECTED state.

[0249] A specific method for handing over the remote UE between gNB#2 and gNB#1 is disclosed.

[0250] Figure 17 is a sequence diagram showing an example of a method for HOing a remote UE between a gNB connected to a remote UE and a gNB connected to a relay UE, in a modified example of Embodiment 1. In Figure 17, steps common to Figures 14, 15, and 16 are given the same step numbers, and common explanations are omitted.

[0251] In steps ST1403 to ST1405, gNB#2 sets up SL measurement for the remote UE. The remote UE then performs SL measurement. The remote UE reports the SL measurement results to gNB#2. For SL measurement, the method disclosed in Embodiment 1 may be applied as appropriate. In addition to SL measurement, the remote UE may also perform DL measurement. In this case, gNB#2 sets up DL measurement for the remote UE. The remote UE performs DL measurement. The remote UE reports the DL measurement results to gNB#2. For DL ​​measurement, the method described in Non-Patent Document 19 (3GPP TS38.331) may be applied as appropriate.

[0252] Upon receiving the SL measurement results, gNB#2 determines in step ST1701 whether to initiate an HO (Home Order) from gNB#2 to gNB#1 at the remote UE. In the example shown in Figure 17, it decides to initiate an HO. The SL measurement results received from the remote UE may be used in this determination. The DL (Digital Line) measurement results may also be used. For example, gNB#2 may decide to initiate an HO to gNB#1 via the relay UE if the SL reception quality from the relay UE at the remote UE is higher than the DL reception quality from gNB#2.

[0253] gNB#2 may use information on whether the remote UE is connected to the relay UE and whether the relay UE is connected to gNB#1 to determine whether the remote UE can perform a Home Order (HO) to gNB#1, or whether or not to perform a HO.

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

[0255] For example, gNB#2 may determine that it is possible to have the remote UE make an HO to gNB#1 when the PC5-RRC connection between the relay UE and the remote UE is complete and the relay UE is in an RRC connection state with gNB#1. For example, in addition to this, gNB#2 may also use the results of the communication quality measurement of the SL and DL from the remote UE as described above to determine whether to have the remote UE make an HO to gNB#1.

[0256] A remote UE may be connected to multiple relay UEs. Each relay UE may notify the remote UE of information regarding its connection status. The remote UE may also notify gNB#2 of information regarding its 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, a remote UE may measure the communication quality of the SLs of multiple relay UEs and notify gNB#2 of the measurement results. The gNB may use the communication quality measurement results of the SLs, the communication quality measurement results of the DLs, and the aforementioned connection status information to decide whether to HO the remote UE, and further, which gNB to HO to.

[0258] gNB#2 may use information about the services supported by the gNB to which the relay UE is connected (for example, a service identifier) ​​to determine which gNB to connect the remote UE to. gNB#2 may also use information about the services supported by the relay UE to determine which gNB to connect the remote UE to. In this way, for example, it becomes possible to connect the remote UE to relay UEs and gNBs that support the services performed by the remote UE.

[0259] The relay UE may notify the remote UE of the measurement result of the DL reception quality from the connected gNB. 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, which it received from the relay UE. gNB#2 may use the measurement result of the DL reception quality from the gNB to which the relay UE is connected, which it received via the remote UE, to decide which gNB to which the relay UE is connected to which the remote UE should be directed to HO. In this way, for example, the remote UE can be directed to the gNB to which the relay UE is connected, which has better communication quality. After HO, it is possible to obtain good communication quality in communication with the gNB via the relay UE.

[0260] Using the aforementioned decision-making method, gNB#2 determines which gNB to HO the remote UE. In Figure 17, this is referred to as gNB#1. In step ST1701, gNB#2 decides to HO the remote UE to gNB#1. In step ST1702, gNB#2 notifies gNB#1 of the HO request. gNB#2 may notify this request using Xn signaling. Alternatively, it may notify 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 that performs the HO. (2) Information indicating that it is an HO connected via relay UE. (3) Relay UE identifier. (4) Identifier of the original gNB. (5) The identifier of the gNB at the HO destination. (6) A combination of (1) to (5).

[0262] (1) identifies the UE performing the HO. The gNB to which the HO is directed may not be a directly connected UE. (2) This information should indicate that the requested HO is an HO to a gNB connected via a relay UE. This allows gNB#1 to recognize that the requested HO is an HO to which the UE is connected via a relay UE. (3) identifies which UE the requested HO will connect to the UE that will be HOing. This allows gNB#1 to determine which UE will connect to the UE being HOed. (4) identifies the source gNB (sometimes called the source gNB). (5) identifies the destination gNB (sometimes called the target gNB).

[0263] Upon receiving an HO request from gNB#2, gNB#1 determines in step ST1703 whether to accept the HO of the target UE. gNB#1 may also 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 to accept the target remote UE.

[0264] In this case, gNB#2 notifies gNB#1 of the connection status at PC5 between the remote UE and the relay UE. gNB#2 may also notify gNB#1 of the connection status of the relay UE. gNB#1 may use the information received from gNB#2 regarding the connection status at PC5 between the remote UE and the relay UE and / or the connection status of the relay UE to decide whether or not to accept the HO of the remote UE that is the target of the HO. gNB#1 may also determine the connection status with the relay UE itself. gNB#1 may use the identifier of the relay UE included in the HO request notified by gNB#2 to determine the connection status with the relay UE.

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

[0266] For example, when the relay UE is not in the RRC connection state with gNB#1, gNB#1 may initiate RRC connection processing for the remote UE. When gNB#1 performs RRC connection processing with the remote UE, gNB#1 may determine to accept the HO of the remote UE.

[0267] gNB#1 may determine whether to accept the HO of the remote UE by using the supported services and the reception quality between gNB#1 and the relay UE. The same effect can be obtained.

[0268] When gNB#1 determines to accept the HO of the remote UE, in step ST1704, gNB#1 notifies gNB#2 of the HO request response. In this notification, an HO request Ack message may be used. Xn signaling may also be used. When gNB#1 determines to accept the HO of the remote UE, gNB#1 may perform RRC configuration for the remote UE. gNB#1 may include the RRC configuration in the HO request response. When it is determined not to accept the HO, gNB#1 notifies gNB#2 of the HO request rejection. The HO request response and the HO request rejection may include the information included in the HO request disclosed above. By receiving the HO request response from gNB#1, gNB#2 can determine whether to transmit an HO instruction to the remote UE for gNB#1.

[0269] Upon receiving an HO request response from gNB#1, gNB#2 notifies the remote UE of an HO instruction in step ST1705. The HO instruction may include information about a change in the connection destination to gNB#1. It may also include information about a change in RRC settings associated with the change in the connection destination to gNB#1. An RRC reconfiguration notification may be used to notify the HO instruction. RRC signaling may be used. An RRCreconfiguration message may be used. The HO instruction may include the RRC setting information that gNB#1 has set for the remote UE as disclosed above. The HO instruction may also include the information to be included in the HO request as disclosed above. Upon receiving the HO instruction from gNB#2 to gNB#1, the remote UE can start processing the change of the connected gNB. The remote UE can then perform the RRC settings on gNB#1.

[0270] The remote UE, upon receiving the HO instruction from gNB#2, detaches from gNB#2 and establishes an RRC connection with gNB#1, the HO destination gNB, via a relay UE. The remote UE may perform RRC configuration using the RRC settings of gNB#1 notified by the HO instruction from gNB#2, and establish an RRC connection with gNB#1 via a relay UE. This relay UE may be the relay UE included in the HO instruction received from gNB#2. In Figure 17, the remote UE, upon receiving the HO instruction from gNB#2, detaches from gNB#2 in step ST1706, and in step ST1707, notifies gNB#1, the HO destination gNB, of the completion of RRC reconfiguration via a relay UE. This notification may use an RRC reconfiguration complete message. This establishes an RRC connection between the remote UE and gNB#1.

[0271] The method for notifying gNB#1 of the completion of RRC reconfiguration from the remote UE via the relay UE may be to appropriately apply the RRC connection request notification method and the RRC setup completion notification method disclosed in Embodiment 1 above.

[0272] This allows the remote UE to be connected 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 the RRC connection state.

[0273] This document discloses a scheduling method for SL communication resources used to notify gNB#1 of the completion of RRC reconfiguration. gNB#2 performs the scheduling of the SL communication resources. gNB#2 may notify the remote UE of the scheduling information along 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 the RRC reconfiguration completion notification to gNB#1 via the relay UE. By having gNB#2 perform the scheduling, interference with other UEs within gNB#2's coverage can be reduced.

[0274] Alternatively, gNB#1 may perform the scheduling of the SL communication resources. gNB#1 notifies the remote UE of the scheduling information of the SL communication resources via gNB#2. This notification may use an HO request response from gNB#1 to gNB#2 and 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, interference with the UE connected to gNB#1 can be reduced.

[0275] Alternatively, the remote UE may select using information about the SL from gNB#1. Information about the SL may be included in the system information. The resource pool may be used as the information about the SL. The remote UE obtains information about the SL from gNB#1. This may be done via gNB#2 or via a relay UE. As a method of obtaining it via gNB#2, for example, the information may be included in the HO request response from gNB#1 to gNB#2 and the HO instruction from gNB#2 to the remote UE, and the remote UE may obtain the information about the SL from this notification. As a method of obtaining it via a relay UE, for example, gNB#1 may notify the relay UE during the RRC connection process with the relay UE, and the relay UE may notify the relay UE during the PC5-RRC connection process with the remote UE. In this way, the remote UE can obtain information about the SL from gNB#1. It becomes possible to use the SL resource pool of gNB#1.

[0276] Alternatively, an exception resource pool for SLs may be used. This exception resource pool may be notified to the remote UE from gNB#1. It may also be notified to the remote UE by being included in the SL information from gNB#1. Or, the exception resource pool may be notified to the remote UE from gNB#2. It may also be notified to the remote UE by being included in the SL information from gNB#2. The exception resource pool for SLs is best used at the timing of such state transitions. It becomes available as a resource pool before scheduling is performed by gNB#1.

[0277] In this way, the remote UE can notify gNB#1 via the relay UE that the RRC reconfiguration is complete. gNB#1 can then recognize that the remote UE has established an RRC connection with itself.

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

[0279] This document discloses the data forwarding of DL data. gNB#2 sends DL data to the remote UE until it notifies the remote UE of an HO instruction. When gNB#2 notifies the remote UE of an HO instruction, it buffers DL data that has not reached the remote UE. After notifying the remote UE of an HO instruction, gNB#2 buffers newly generated DL data. gNB#2 notifies gNB#1 of the SN STATUS TRANSFER. gNB#2 notifies gNB#1 of the DL data transmission status, including the SN STATUS TRANSFER. The DL data transmission status should indicate the SN that gNB#2 will assign to new data for which it does not yet have an SN (Sequence Number). gNB#2 transfers the buffered DL data and newly generated DL data to gNB#1. The last DL data sent to gNB#2 is marked with an End Marker. gNB#2 receives all DL data up to the last one and transfers it to gNB#1. gNB#1 buffers the DL data received from gNB#2.

[0280] After gNB#1 has established an RRC connection with the remote UE (or after receiving confirmation from the remote UE that the RRC has been reconfigured), it sends the buffered DL data to the remote UE. gNB#1 sends DL data to the remote UE up to the point where an End Marker is attached. If there is any new DL data for the remote UE that has been received from the UPF, gNB#1 sends this newly received DL data to the remote UE. The transmission of DL data from gNB#1 to the remote UE is performed via the relay UE connected to the remote UE.

[0281] This configuration enables data forwarding of DL data during HO (Handover) between gNB#2 and gNB#1, which is connected via a relay UE. This reduces DL data loss during HO and avoids the degradation of communication quality due to the movement of the remote UE.

[0282] This document discloses an alternative method for data forwarding DL data during HO between gNB#2 and gNB#1, which is connected via a relay UE. The main focus is on the differences from the method disclosed above.

[0283] After gNB#1 has established an RRC connection with the remote UE (or after receiving confirmation of RRC reconfiguration from the remote UE), it sends the buffered DL data to the relay UE. gNB#1 sends DL data up to the DL data with an End Marker to the relay UE. The relay UE buffers the DL data received from gNB#1. After the relay UE has established a PC5-RRC connection with the remote UE, it sends the buffered DL data to the remote UE. It sends DL data up to the DL data with an End Marker to the remote UE. After the relay UE has established an RRC connection with the remote UE (or after receiving confirmation of RRC reconfiguration from the remote UE), if there is any new DL data received from the UPF to the remote UE, it sends the newly received DL data to the relay UE. After the relay UE has established a PC5-RRC connection with the remote UE, it sends the DL data received from gNB#1 to the remote UE.

[0284] As a data forwarding method, gNB#1 is disclosed to send buffered DL data to the relay UE after completing RRC connection with the remote UE (or after receiving confirmation of RRC reconfiguration from the remote UE). However, if RA processing and / or RRC connection have already been completed between the relay UE and gNB#1, gNB#1 may immediately send the DL data transferred from gNB#2 and the DL data newly received from the UPF to the relay UE. That is, gNB#1 buffers the DL data to the remote UE transferred from gNB#2 and the DL data to the remote UE newly received from the UPF until RA processing and / or RRC connection are completed between the relay UE and gNB#1. After RA processing and / or RRC connection are completed between the relay UE and gNB#1, gNB#1 sends the buffered DL data to the relay UE.

[0285] Furthermore, as a data forwarding method, it was disclosed that the relay UE sends the DL data received from gNB#1 and buffered to the remote UE after the PC5-RRC connection with the remote UE is completed. However, if the PC5-RRC connection has already been completed between the remote UE and the relay UE, the relay UE may immediately send the DL data received from gNB#1 to the remote UE. In other words, the relay UE buffers the DL data to 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 is established, the relay UE sends the buffered DL data to the remote UE.

[0286] This allows for the early transmission of DL data from gNB#1 to the relay UE. Consequently, the transmission of DL data from the relay UE to the remote UE also becomes earlier. As a result, the delay in DL data transmission and reception by HO can be reduced.

[0287] The processing of UL data is disclosed below. The remote UE sends UL data to gNB#2 until it detaches from gNB#2. Upon detachment from gNB#2, the remote UE may notify gNB#1 of the reception status of the UL data, including the SN of the UL data that did not reach gNB#2. In this way, gNB#1 can 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 reach gNB#2. After detaching from gNB#2, the remote UE buffers newly generated UL data to gNB#1 until the RRC connection is established (or RRC reconfiguration is completed). After the RRC connection is established with gNB#1 (or RRC reconfiguration is completed), the remote UE sends the buffered UL data and newly generated UL data to gNB#1. At this time, the remote UE sends the UL data to gNB#1 via the relay UE. gNB#1 may instruct the remote UE to send the data to be retransmitted.

[0288] By doing so, during a HO (Handover) between gNB#2 and gNB#1, which is connected via a relay UE, the loss of UL data during the HO can be reduced, and the deterioration of communication quality due to the movement of the remote UE can be avoided.

[0289] This document discloses an alternative method for processing UL data during HO between gNB#2 and gNB#1, which is connected via a relay UE. The main focus is on the differences from the method disclosed above.

[0290] The remote UE buffers newly generated UL data until the PC5-RRC connection between gNB#2 and the relay UE is completed after detachment. After the PC5-RRC connection with the relay UE is completed, the remote UE sends 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 sends the buffered UL data and newly received UL data from the remote UE to gNB#1.

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

[0292] This allows for the early transmission of UL data from the remote UE to the relay UE. Consequently, the transmission of UL data from the relay UE to gNB#1 can also be done earlier. As a result, the delay in UL data transmission and reception by HO can be reduced.

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

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

[0295] Figure 23 is a sequence diagram showing an example of a method for connecting a remote UE from gNB#1 to gNB#2 in a modified example of Embodiment 1. In Figure 23, steps common to Figure 17 are given the same step numbers, and common explanations are omitted. In step ST1601, the relay UE is connected to gNB#1 via RRC. In step ST1411, the remote UE is connected to the relay UE via PC5-RRC. In step ST1420, the remote UE is connected to gNB#1 via RRC through the relay UE.

[0296] In step ST2301, gNB#1 configures the remote UE for Uu measurement. The Uu measurement may be DL measurement. It is advisable to notify gNB#1 of the Uu measurement configuration via the relay UE. This allows the remote UE, which communicates with the relay UE via SL, to notify gNB#1 of the Uu measurement results. The Uu measurement configuration and the SL measurement configuration may be combined. Alternatively, the SL measurement configuration may be included in the Uu measurement configuration. For example, an event may be provided to compare the SL measurement result and the Uu measurement result as an event for reporting the Uu measurement result. For example, an event may be provided when the SL reception quality becomes greater than the serving cell reception quality as a predetermined condition. The events for setting the SL measurement result report disclosed in Embodiment 1 may be applied as appropriate. This makes it possible to include SL measurement as part of the Uu measurement configuration. Flexible reporting of measurement results becomes possible. gNB#1 can obtain the Uu measurement result and the SL measurement result from the remote UE.

[0297] In step ST2302, the remote UE uses the Uu measurement settings and SL measurement settings notified by gNB#1 to perform Uu and SL measurements. In step ST2303, the remote UE notifies gNB#1 of the Uu and SL measurement results according to the measurement result reporting settings 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 and SL measurement results from the remote UE.

[0298] In step ST2304, gNB#1 determines whether or not to send a remote UE to gNB#1, and to which gNB to send the HO. The measurement results of Uu received from the remote UE may be used in this determination. Alternatively, the measurement results of SL may be used. For example, gNB#1 may decide to send the 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 or not the remote UE can be HO'd to gNB#2, or whether or not to HO it. For example, gNB#1 sets up Uu measurement settings 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 or not to HO' the remote UE to gNB#2. For example, gNB#1 may decide to HO' the remote UE to gNB#2 if the DL reception quality from the serving cell at the relay UE falls below a predetermined threshold. gNB#1 may also consider the DL reception quality measurement results of adjacent cells. For example, gNB#1 may decide to HO' the remote UE to gNB#2 if the DL reception quality from the serving cell and adjacent cells at the relay UE falls below a predetermined threshold. In this way, gNB#1 uses the communication quality of the Uu between itself and the relay UE, allowing it to switch the remote UE from gNB#1 to gNB#2 if the communication quality with the relay UE deteriorates. gNB#1 can then switch from communication to gNB#1 via the relay UE to direct communication to gNB#2. This makes it possible to improve the communication quality between the remote UE and the network.

[0300] In step ST2304, gNB#1 decides to have the remote UE hosted to gNB#2. In step ST2305, gNB#1 notifies gNB#2 of the HO request. This may be done via 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] Upon receiving an HO request from gNB#1, gNB#2 determines in step ST2306 whether to accept the HO of the target UE. 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 to accept the target remote UE.

[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 decide whether or not to accept the HO of the remote UE that is the target of the HO.

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

[0304] If gNB#2 decides to accept the remote UE's HO, in step ST2307, gNB#2 notifies gNB#1 of the HO request acknowledgment. This notification may use an HO request Ack message or Xn signaling. If gNB#2 decides to accept the remote UE's HO, it may configure the RRC for the remote UE. gNB#2 may include the RRC configuration in the HO request acknowledgment. If gNB#2 decides not to accept the remote UE's HO, gNB#2 notifies gNB#1 of the HO request rejection. The HO request acknowledgment and HO request rejection may include the information disclosed above that is included in the HO request. Upon receiving the HO request acknowledgment from gNB#2, gNB#1 can determine whether to send an HO instruction to gNB#2 to the remote UE.

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

[0306] Upon receiving an HO instruction from gNB#1, the remote UE notifies gNB#2, the HO target gNB, in step ST2309 that the RRC reconfiguration is complete. This notification may use the RRC reconfiguration complete message. This establishes an RRC connection between the remote UE and gNB#2. The remote UE may perform the RRC configuration using the RRC settings of gNB#2 notified by the HO instruction from gNB#1, and establish an RRC connection with gNB#2 via the relay UE. This establishes the RRC connection between the remote UE and gNB#2 in step ST2310.

[0307] A remote UE that receives an HO instruction from gNB#1 may release the resources necessary for the RRC connection with gNB#1. A remote UE that receives an HO instruction from gNB#1 may also perform the processing for the original 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 also release the radio bearer (RB) with the relay UE. In this case, processing on the remote UE's PC5 becomes unnecessary, resulting in lower power consumption. Alternatively, a remote UE that receives an HO instruction from gNB#1 does not have to release the RRC connection with the relay UE. A remote UE that receives an HO instruction from gNB#1 does not have to release the radio bearer (RB) with the relay UE. In this case, the remote UE can communicate with the relay UE earlier if communication with the relay UE is necessary.

[0309] This allows the remote UE to connect 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 connection state.

[0310] A remote UE may be connected to another gNB via a relay UE, or to another gNB via another relay UE. The methods disclosed herein may be applied as appropriate. Depending on the connectivity of the remote UE, and depending on the radio wave propagation environment of the Uu between the remote UE and the relay UE, and between 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 connect the remote UE to a gNB suitable for communication.

[0311] This document discloses the data forwarding of DL data. gNB#1 transmits DL data to the remote UE via the relay UE until it notifies the remote UE of an HO instruction. When gNB#1 notifies the remote UE of an HO instruction, it buffers DL data that did not reach the remote UE. After notifying the remote UE of an HO instruction, gNB#1 buffers newly generated DL data. gNB#1 notifies gNB#2 of the SN STATUS TRANSFER. gNB#1 notifies gNB#2 of the DL data transmission status, including it in the SN STATUS TRANSFER. The DL data transmission status should indicate the SN that gNB#1 will assign to new data that does not yet have an SN. gNB#1 forwards the buffered DL data and newly generated DL data to gNB#2. The last DL data sent to gNB#1 is marked with an End Marker. gNB#1 receives all DL data up to the last one and forwards it to gNB#2. gNB#2 buffers the DL data received from gNB#1.

[0312] After the RRC connection with the remote UE is established (or after the remote UE has received confirmation that the RRC has been reconfigured), gNB#2 sends the buffered DL data to the remote UE. gNB#2 sends DL data up to the DL data with an End Marker to the remote UE. If there is any new DL data for the remote UE that has been received from the UPF, gNB#2 sends the newly received DL data to the remote UE.

[0313] This allows for data forwarding of DL data during HO between gNB#1 and gNB#2, which are connected via a relay UE. This reduces DL data loss during HO and avoids the degradation of communication quality due to the movement of the remote UE.

[0314] The processing of UL data is disclosed below. 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 UL data, including the SN of UL data that did not reach gNB#1. gNB#2 can then 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 reach gNB#1. After receiving an HO instruction from gNB#1, the remote UE buffers newly generated UL data to gNB#2 until the RRC connection is established (or RRC reconfiguration is completed). After the RRC connection with gNB#2 is established (or RRC reconfiguration is completed), the remote UE transmits the buffered UL data and newly generated UL data to gNB#2. gNB#2 may instruct the remote UE to transmit the data to be retransmitted.

[0315] By doing so, during a HO between gNB#1 and gNB#2 connected via a relay UE, the loss of UL data during the HO can be reduced, and the deterioration of communication quality due to the movement of the remote UE can be avoided.

[0316] In the example described above, it was disclosed that the SL measurement results at the remote UE were used to determine the HO. However, the determination of the HO is not limited to the SL measurement results. For example, the HO may be determined using the load status of gNB#2. For example, the HO may be determined by a change in QoS required for communication. For example, the HO may be determined by instructions from the CN. For example, the HO may be determined by a request from gNB#1. For example, the HO may be determined by a request from the remote UE. For example, the HO may be determined by a request from the relay UE. In this way, it becomes possible to implement an HO suitable for the radio wave propagation environment between gNBs, including gNBs that can be connected via the relay UE. This makes it possible to improve the communication quality between the remote UE and the network.

[0317] In a situation where a remote UE is connected to gNB#1 via a relay UE using RRC, if an RLF (Radio Link Failure) occurs between the relay UE and gNB#1, the RRC connection between the remote UE and gNB#1 may be released. The relay UE, upon detecting the RLF with gNB#1, may notify the remote UE of a request to release the RRC connection with gNB#1. This request may include information about the cause. It is preferable to include information indicating that the RLF is between gNB#1 and the relay UE as the cause information. The remote UE, upon receiving the RRC connection release request from the relay UE, releases the settings necessary for the RRC connection with gNB#1. By doing this, when an RLF occurs between the relay UE and gNB#1, the remote UE does not need to maintain the resources necessary for the RRC connection with gNB#1, thereby improving resource utilization efficiency.

[0318] In the previous example, we assumed that an RLF (Radio Link Failure) occurred between relay UE and gNB#1, but it could also be assumed that the RRC connection between relay UE and gNB#1 was released. For example, the RRC connection would be released due to an RLF. Doing so would achieve the same effect.

[0319] If an RLC (Rapid Relay Failure) occurs between the relay UE and gNB#1, and an RRC connection can be re-established with the same gNB or another gNB before the RRC connection is released, it may be acceptable not to request the release of the RRC connection from the remote UE. This allows for early communication between the remote UE and gNB once an RRC connection is established between the relay UE and gNB.

[0320] In communication between gNB#1 and the remote UE via a relay UE, PDCP retransmission may be performed. PDCP retransmits data that could not be received. If gNB#1 sends data to the remote UE via the relay UE and the remote UE fails to receive it, gNB#1 retransmits the data to the remote UE via the relay UE. Similarly, if the remote UE sends data to gNB#1 via the relay UE and gNB#1 fails to receive it, the remote UE retransmits the data to gNB#1 via the relay UE. This improves communication quality even when communication between gNB#1 and the remote UE is conducted 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. The PDCP Status may be reported as the data reception status. 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. Similarly, 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. The PDCP SN may be used as the data reception status. When gNB#1 transmits, it is advisable to use the PDCP SN assigned by gNB#1. When a remote UE transmits, it is advisable to use the PDCP SN assigned by the remote UE. The PDCP SN may also be used to determine whether or not data has arrived. For example, the PDCP SNs of the first to last data points that have not yet arrived may be reported as the data reception status.

[0322] In this way, gNB#1 or the remote UE, upon receiving a report of data reception status, can recognize the data transmission status. gNB#1 or the remote UE can recognize data that has not arrived. Upon receiving a report of data reception status, gNB#1 or the remote UE may retransmit the data that has not arrived. In this way, by reporting the data reception status, such as a PDCP Status report, gNB#1 or the remote UE can retransmit data that has not arrived. Communication quality can be improved even when communication between gNB#1 and the remote UE is conducted via a relay UE.

[0323] Other methods for solving the problem are disclosed. Data reception status may be reported between the relay UE and the remote UE. PDCP Status may be reported as the data reception status. When the relay UE transmits, the PDCP SN assigned by the relay UE may be used. When the remote UE transmits, the PDCP SN assigned by the remote UE may be used. Upon receiving the data reception status report, the relay UE or remote UE becomes aware of the data transmission status. The relay UE or remote UE becomes aware of undelivered data. Upon receiving the data reception status report, the relay UE or remote UE may retransmit the undelivered data. In this way, by reporting the data reception status, such as PDCP Status, between the relay UE and the remote UE, the relay UE or remote UE can retransmit undelivered data. Communication quality can be improved in communication between the relay UE and the remote UE.

[0324] The relay UE may notify gNB#1 of the data reception status with the remote UE. By receiving this reception status, gNB#1 can determine whether data communication between the relay UE and the remote UE has been successfully completed. Using the data reception status between the relay UE and the remote UE received from the relay UE, gNB#1 can determine the data transmission status. gNB#1 may decide whether to retransmit data to the remote UE. For example, gNB#1 may retransmit data to the relay UE that was not sent from the relay UE to the remote UE. The relay UE can then retransmit the 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 conducted via the relay UE.

[0325] gNB#1 and the relay UE may report the data reception status. The PDCP Status report may be used as the data reception status report. When gNB#1 transmits, the PDCP SN assigned by gNB#1 may be used. When the 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, such as the PDCP Status report, between gNB#1 and the relay UE, gNB#1 or the relay UE can retransmit 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 with gNB#1. By receiving this reception status, the remote UE can determine whether data communication between gNB#1 and the relay UE was successfully completed. The remote UE can then use the data reception status between gNB#1 and the relay UE, received from the relay UE, to determine the data transmission status. The remote UE may decide whether to retransmit data to gNB#1. For example, the remote UE may retransmit data that was not sent from the relay UE to gNB#1. The relay UE can then retransmit the 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 conducted via the relay UE.

[0327] A method for reporting data reception status between the relay UE and the remote UE may be combined with a method for reporting data reception status between gNB#1 and the relay UE. gNB#1 or the remote UE may use the data reception status on each individual link of Uu and PC5 to decide whether to retransmit data. Alternatively, the relay UE may decide whether to retransmit data and perform the retransmission. For example, if data has not arrived on either link, the relay UE will retransmit it. If data has not arrived on both links, gNB#1 or the remote UE will retransmit it. This method makes it possible to reduce the delay in communication between gNB#1 and the remote UE via the relay UE. Even when communication between gNB#1 and the remote UE is conducted via the relay UE, it is possible to further improve the communication quality.

[0328] The method described above may be appropriately applied to the data forwarding process in the 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 in the HO.

[0329] Embodiment 2. As shown in Embodiment 1, the relay UE and the remote UE may be located within the coverage areas of different gNBs. For example, if the remote UE is located at the coverage end of gNB#2, the reception quality of the remote UE may be better with the relay UE than with gNB#2. In such cases, even if the remote UE is not connected via RRC and is in the RRC_IDLE state, its operation becomes unclear, and processing in the RRC_IDLE state cannot be performed, which is a problem.

[0330] For example, a remote UE may encounter problems where it becomes unclear whether to camp on gNB#2 or gNB#1 via a relay UE, which gNB to use for system information transmitted, or which gNB to use for SL communication resource pool (RP) transmitted, making it impossible to perform processing in the RRC_IDLE state.

[0331] This embodiment discloses a method for solving these problems.

[0332] To solve this problem, the remote UE according to this embodiment receives system information transmitted by gNB#2, which is within coverage of the remote UE. System information may include MIB, SIB, etc. System information may also 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 to gNB#2. Even if the reception quality from a relay UE that is connected to or can connect to the NW is better than the reception quality from gNB#2 at the remote UE, the remote UE still receives the system information transmitted by gNB#2. The remote UE camps on to gNB#2. If there are multiple gNBs within coverage of the remote UE, the system information of which gNB the remote UE receives can be determined using the conventional cell selection and cell re-selection method (see Non-Patent Document 32 (3GPP TS38.304)).

[0333] This allows the remote UE in RRC_IDLE to determine which gNB to use for system information. As a result, the remote UE can perform processing in RRC_IDLE.

[0334] Disclose other ways to solve the problem.

[0335] Until the relay UE's discovery process is complete, 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 to gNB#2. After the relay UE's discovery process is complete, 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 also camp on to gNB#1.

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

[0337] By receiving the system information transmitted by gNB#1 after the relay UE's discovery process is complete, the remote UE can use the system information from gNB#1 at an earlier stage.

[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 to 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 also camp on to gNB#1.

[0339] The relay UE should receive system information from gNB#1. The relay UE should then notify the remote UE of the system information received from gNB#1. During the discovery process, the relay UE may also notify the remote UE of the system information from gNB#1. During the PC5-S link establishment process, the relay UE may also notify the remote UE of the system information from gNB#1. By doing so, the remote UE can receive the system information from gNB#1 via the relay UE and use that system information.

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

[0341] Until the PC5-RRC connection 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 to gNB#2. After the PC5-RRC connection 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 also camp on to gNB#1.

[0342] The relay UE should receive system information from gNB#1. The relay UE should then notify the remote UE of the system information received from gNB#1. During the discovery process, the relay UE may also notify the remote UE of the system information of gNB#1. During the PC5-S link establishment process, the relay UE may also notify the remote UE of the system information of gNB#1. During the PC5-RRC connection process, the relay UE may also notify the remote UE of the system information of gNB#1. By doing so, the remote UE can receive the system information of gNB#1 via the relay UE and use that system information.

[0343] After the RRC connection process with the relay UE is complete, the remote UE can use the system information sent by gNB#1 once it is able to send and receive PC5-RRC messages and data on PC5 with the relay UE. If the remote UE is not yet able to send and receive PC5-RRC messages and data on PC5 with the relay UE, it can use the system information from gNB#2.

[0344] This allows the RRC_IDLE remote UE to decide which gNB to use for system information. Furthermore, the remote UE can use system information from gNB#1. The remote UE can also camp on to gNB#1.

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

[0346] In step ST1801, the remote UE is in coverage of gNB#2 and is in the 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. From steps ST1409 to ST1411, the PC5 connection is established between the remote UE and the relay UE. If the relay UE completes the PC5-RRC connection with the remote UE in step ST1411, in step ST1805, the relay UE notifies the remote UE of the system information of gNB#1. The relay UE may also broadcast the system information of gNB#1. If the remote UE completes the PC5-RRC connection with the relay UE in step ST1411, in step ST1804, the remote UE changes the system information receiving gNB from gNB#2 to gNB#1. In step ST1805, the remote UE receives the system information of gNB#1 transmitted by the relay UE. This allows the remote UE to use the system information sent from gNB#1.

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

[0348] The relay UE may store the system information received from gNB#1. For example, it may store the system information received in step ST1802. The relay UE can then send the system information to the remote UE on PC5 at any time. If the system information of gNB#1 is modified, the relay UE may store the modified system information received from gNB#1 as the updated system information. The relay UE may also notify the remote UE that the system information of gNB#1 has been modified. If the system information of gNB#1 is modified, the relay UE may also notify the remote UE of the modified system information of gNB#1.

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

[0350] As a method for the relay UE to notify the remote UE of system information, the method for notifying RRC connection requests via the relay UE on PC5, as disclosed in Embodiment 1, may be appropriately applied. As another solution, a new channel may be provided for notifying system information. By separating the channel containing system information from other channels, the remote UE can reduce malfunctions in the system information reception process.

[0351] The relay UE may notify the remote UE of system information by including it in the RRC message of PC5. The RRC message of PC5 may include a container for the Uu's RRC message. A container for system information may be included. A container for individual RRC messages may be included. By doing so, the relay UE can easily forward the RRC message received from gNB#1 as the RRC message of PC5 to the remote UE. The relay UE may make the container information transparent. By doing so, the processing of the relay UE can be made easier.

[0352] This document discloses the timing of when a relay UE notifies a remote UE of system information. The relay UE periodically notifies the remote UE of system information. This notification may be made using a physically periodic resource, or it may be made using a logically periodic resource. A logically periodic resource is defined as periodically setting resources within a resource capable of SL communication. For example, if the resources capable of SL communication are not continuous, only the resources capable of SL communication, excluding resources that cannot be communicated with SL, are counted continuously, and resources are periodically set within that count. In this way, periodicity can be obtained within the resources capable of SL communication, even if the resources capable of SL communication are discontinuous.

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

[0354] Other methods for notification timing are disclosed. The remote UE notifies the relay UE of a system information request. This system information request may be a request for system information of the gNB to which the relay UE is connected, or a request for system information stored by the relay UE. The notification of this system information request may be appropriately applied using the notification method for information regarding the connection status of the relay UE disclosed in Embodiment 1. 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 it has received from gNB#1. The remote UE can then receive the system information from gNB#1 via the relay UE.

[0356] Other methods for notifying system information between UEs on PC5 are disclosed. The relay UE broadcasts the system information received from gNB#1. Broadcast communication on the SL may be used. Notification may also be made via PC5-S signaling. This allows for early notification during PC5 connection processing. Alternatively, notification may be made via PC5-RRC signaling. For example, it may be included in an RRC message on PC5. For example, when notifying the RRC connection status with the NW, using RRC signaling on PC5 allows notification processing at the same RRC layer, thus reducing malfunctions. This information may also be notified via the SRB on PC5. This allows system information to be notified as signaling information and control information.

[0357] This information may be notified using PC5 MAC signaling. In this case, notification can be made earlier than with RRC signaling. These signalings may include information indicating that it is a broadcast. Alternatively, they may include information indicating that it is system information. Alternatively, they may include information indicating that it is 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 also be included in the 1st SCI. Doing so allows for earlier notification. The 1st SCI may include information indicating that it is a 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. Doing so allows one or more UEs capable of receiving PC5 communication to receive the information.

[0359] The information may be notified via PSSCH. The information may be included in the 2nd SCI and notified via PSSCH. The information may be included in the MAC CE and notified via PSSCH. The 2nd SCI or MAC CE of PSCCH may include information indicating that it is a 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. Furthermore, when used for broadcasting, it is preferable not to apply HARQ. In this way, one or more UEs capable of receiving PC5 communication will be able to receive the information.

[0360] This information may also be notified via PSBCH. PSBCH is a channel for broadcasting on the SL. By including this information on 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. This allows the information to be separated from other signaling and channels, thereby reducing malfunctions in the receiving process of the information at the UE.

[0362] Disclose other ways to solve the problem.

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

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

[0365] The system information of which gNB is used for a remote UE may be predetermined statically by a standard or similar document. Alternatively, it may be coordinated between gNBs. Or, the CN may decide. This allows for unified processing within the network.

[0366] Instead of receiving instructions from the gNB, the relay UE may instruct the remote UE to select a gNB that receives system information. For example, the relay UE may instruct the remote UE to select a system information receiving gNB depending on the connection status between the relay UE and gNB#1. In this way, the relay UE can instruct the remote UE to select a system information receiving gNB appropriate to its status.

[0367] Figure 19 is a sequence diagram showing an example of how a gNB instructs a remote UE to receive system information in Embodiment 2. In Figure 19, steps common to Figure 18 are given the same step numbers, and common explanations are omitted. In step ST1901, gNB#1 broadcasts an instruction for its own gNB to receive system information. The instruction for its own gNB to receive system information may be applied only to remote UEs connected via a relay UE. The instruction for its own gNB to receive system information may include information indicating that it applies only to remote UEs connected via a relay UE. The instruction for its own gNB to receive system information may be included in the system information.

[0368] Upon receiving the gNB#1 system information reception instruction broadcast by gNB#1, the relay UE executes steps ST1409 to ST1411 to complete the PC5-RRC connection with the remote UE. Then, in step ST1902, it notifies the remote UE, which is connected via PC5-RRC, of ​​the gNB#1 system information reception instruction. In step ST1805, the relay UE also notifies the remote UE of the gNB#1 system information. Upon receiving the gNB#1 system information reception instruction, the remote UE changes the gNB receiving the system information from gNB#2 to gNB#1 in step ST1804, and in step ST1805, it receives the system information from gNB#1.

[0369] The gNB#1 system information reception instruction was disclosed, but it could also be information indicating whether or not to use the gNB#1 system information. The remote UE that receives this information decides whether or not to receive the gNB#1 system information according to that information.

[0370] Although a gNB#1 system information reception instruction has been disclosed, a gNB#1 system information usage instruction may also be disclosed. A remote UE that receives such an instruction receives and uses the gNB#1 system information.

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

[0372] The choice of whether to use the system information transmitted from gNB#1 via the relay UE or the system information from gNB#2, which is in coverage, may be coordinated between the gNBs. Alternatively, the AMF may coordinate and notify each gNB. Alternatively, a node with management functions may coordinate and notify each gNB. Notification may also be sent via the AMF. Depending on the coordination result, the gNB may decide whether or not to instruct its own system information to be received and may send a system information reception instruction for its own gNB.

[0373] This allows the network side to determine which gNB's system information to receive and use at the remote UE.

[0374] The remote UE receives some 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 about the service level (SL) from gNB#2 and other system information from gNB#1. The remote UE uses the system information about the SL received from gNB#2 and other system information received from gNB#1. It is possible to configure the appropriate system information receiving gNB depending on the type of system information.

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

[0376] Disclose other ways to solve the problem.

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

[0378] Disclose other ways to solve the problem.

[0379] The remote UE receives system information from the gNB that was last connected via RRC. For example, if the last connected gNB was gNB#2, after releasing the RRC connection, the remote UE will receive system information from gNB#2. For example, if the RRC connection is released due to the termination of communication, it becomes possible to select and re-select a cell that will receive system information sooner.

[0380] The method disclosed in this embodiment enables the remote UE to receive system information. Even when a remote UE in coverage of gNB#2 is connected to a relay UE connected to gNB#1, it becomes possible to determine which gNB's system information to receive and use. This clarifies the processing performed by the remote UE in the RRC_IDLE state, thereby reducing malfunctions in that processing.

[0381] Modification 1 of Embodiment 2. In the case of the problem described in Embodiment 2, for example, the remote UE in RRC_IDLE mode performs cell selection and cell re-selection processing. However, if the remote UE considers gNB#1 via the relay UE in addition to gNB#2 which is in coverage, it becomes unclear what kind of cell selection and cell re-selection processing to perform. As a result, the remote UE is unable to perform processing in the RRC_IDLE state, which is a problem.

[0382] This modified version discloses a method for solving these problems.

[0383] In this modified version, the remote UE prioritizes the gNB in ​​coverage when selecting a cell. The remote UE may also prioritize the gNB in ​​coverage when re-selecting a cell. When the received quality from gNB#2 meets the criteria for cell selection and re-selection, the remote UE selects and re-selects gNB#2. The remote UE receives system information transmitted from the selected and re-selected gNB. The remote UE uses the system information transmitted from the selected and re-selected gNB. The remote UE may also receive paging transmitted from the selected and re-selected gNB.

[0384] Disclose other ways to solve the problem.

[0385] The remote UE prioritizes the gNB to which the relay UE is connected when selecting a cell. The remote UE may also prioritize the gNB to which the relay UE is connected when re-selecting a cell. If the SL reception quality from the relay UE exceeds a predetermined threshold, the remote UE may prioritize the gNB to which the relay UE is connected when selecting or re-selecting a cell. The remote UE receives system information transmitted from the gNB to which the cell-selected or re-selected relay UE is connected. The remote UE uses the system information transmitted from the gNB to which the cell-selected or re-selected relay UE is connected. The remote UE may also receive paging transmitted from the gNB to which the cell-selected or re-selected relay UE is connected.

[0386] By implementing this priority control, cell selection and re-selection processes in the remote UE become easier, and malfunctions in the remote UE can be reduced.

[0387] Disclose other ways to solve the problem.

[0388] The remote UE performs cell selection and cell reselection by considering the gNB in ​​coverage and the gNB to which the relay UE is connected. The remote UE measures the received quality from the gNB in ​​coverage and the SL received quality from the relay UE. Based on the received quality from the gNB in ​​coverage and the SL received quality from the relay UE, the remote UE selects the best cell or relay UE from among the cells in coverage and relay UEs that meet the criteria for cell selection and cell reselection. If a relay UE is selected, the cell of the gNB to which the relay UE is connected is designated as 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 those whose received quality from the gNB in ​​coverage meets the criteria for cell selection and cell reselection, and selects the best relay UE from among those whose received quality from the relay UE meets the criteria for cell selection and cell reselection, and designates the cell of the gNB to which the relay UE is connected as the best cell. The remote UE may also compare the received quality of the two best cells and select the better one.

[0390] The criteria for cell selection and cell re-selection may include an offset. For example, an offset may be set to compare the received quality from a gNB within coverage of the remote UE with the received SL quality from the relay UE. For example, if the offset is set to Qroffset, the best cell may be selected by comparing the received SL quality from the relay UE with the received quality from a gNB within coverage of the remote UE + Qroffset. The offset setting is not limited to this. For example, an offset may be added to the received SL quality from the relay UE. By making the offset configurable in this way, it is possible to prioritize the selection of either the gNB to which the relay UE is connected or the gNB within coverage of the remote UE.

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

[0392] Information regarding the criteria for cell selection and cell re-selection includes, for example, thresholds and offsets for the reception quality of cell selection and cell re-selection. The criteria information may be predetermined by a standard or otherwise announced by the gNB. The UE may use the criteria information announced by the gNB. Alternatively, it may be stored in the UE. For example, it may be stored in the SIM owned by the UE. The UE may use the criteria information stored in itself. Alternatively, the criteria information may be provided from the CN to the UE during the registration process. The UE may store the criteria information provided by the CN within the UE. Alternatively, the criteria information may be provided from the NW to the UE when the UE is connected to the NW. Subsequently, when the UE enters the RRC_IDLE state, it may use the said criteria information.

[0393] This method allows the remote UE to consider the gNB within coverage and the relay UE in a unified cell selection and re-selection process. This unified cell selection and re-selection process enables the remote UE to select the gNB within coverage and the gNB to which the relay UE is connected. Therefore, the cell selection and re-selection process is simplified, power consumption is reduced, and malfunctions in the remote UE are reduced.

[0394] By using the method disclosed in this modified version, cell selection and re-selection processes can be performed even when the remote UE is connected to the relay UE. The remote UE can perform processing in the RRC_IDLE state. Malfunctions can be reduced during processing by the remote UE in the RRC_IDLE state.

[0395] Modification 2 of Embodiment 2. If a remote UE in RRC_IDLE uses system information from the gNB to which the relay UE is connected, or if the gNB's cells are capable of cell selection and cell reselection, then a problem arises where the CN cannot manage the remote UE if the remote UE moves or if the surrounding radio wave propagation environment changes.

[0396] This modified version discloses a method for solving these problems.

[0397] In the communication system according to this modified example, gNB#1 notifies the remote UE of the TAC via the relay UE. As the notification method, the system information notification method disclosed in Embodiment 2 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. If the remote UE moves, the remote UE may receive the TAC of a selected cell from the gNB and relay UE in coverage. 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] The remote UE performs registration if the TAC received from gNB#1 is a new TAC that differs from one or more TACs recently received from the NW. The remote UE notifies the CN of the registration request via the relay UE and gNB#1. The registration request may include information indicating that it is an update to the TAC or registration. 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) The identifier of the UE requesting registration. (2) Relay UE identifier. (3) The identifier of the gNB to which the relay UE is connected. (4) TAC received from gNB. (5) Information indicating that the registration request is made via a relay UE connection. (6) A combination of (1) to (5).

[0400] Upon receiving a registration request from a remote UE, the CN performs the registration process with 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 will 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 in a modified example 2 of Embodiment 2. In Figure 20, steps common to Figures 14 and 18 are given the same step numbers, and common explanations are omitted. In step ST2001, the relay UE receives system information from gNB#1. It also receives the PLMN identifier and TAC (let's call it TAC#1). In step ST2002, the remote UE receives system information from gNB#2. It also receives the PLMN identifier and TAC (let's call it 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 occurs after the registration processing is complete, the RRC connection is released in step ST2005.

[0403] In steps ST1409 to ST1411, the remote UE establishes an RRC connection for PC5 with the relay UE. In step ST2006, the relay UE performs the RRC connection process with gNB#1. For the RRC connection process in step ST2006, it is advisable to apply the processes from steps ST1412 to ST1414 as shown in Figure 14, etc. In step ST1804, the remote UE changes the gNB that receives system information from gNB#2 to gNB#1. In step ST2007, the relay UE transmits the system information, PLMN identifier, and TAC#1 for gNB#1 via SL. This information may also be notified to the remote UE. The remote UE receives the system information, PLMN identifier, and TAC#1 for 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 it is included, registration to the CN is not performed. If it is not included, registration to the CN is performed. Figure 20 shows the case where it is included.

[0404] In step ST2009, the remote UE performs RRC connection processing with gNB#1 via the relay UE. For the RRC connection processing performed between the remote UE and gNB#1 via the relay UE, it is recommended to apply the processes from steps ST1417 to ST1419 as shown in Figure 14, etc. In step ST2010, the remote UE performs registration processing between gNB#1, AMF#1, PCF, and UDM. After the registration processing is complete, the RRC connection may be released if no communication occurs. Figure 20 shows the case where the AMF is changed, but it is not limited to changes in the AMF. The AMF does not have to be changed.

[0405] This allows for the registration process to change the TA where the remote UE is located to the TA to which gNB#1 belongs.

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

[0407] Modification 3 of Embodiment 2. If a remote UE is within the coverage of a gNB and is also connected to a relay UE, the remote UE becomes unsure whether it should receive paging from the gNB in ​​coverage or from the relay UE. Similarly, the CN becomes unsure which source to send paging from to the remote UE. As a result, the CN cannot invoke the remote UE and cannot initiate communication with it, leading to a problem.

[0408] This modified version discloses a method for solving these problems.

[0409] In the communication system according to this modified example, if the remote UE is within coverage of gNB#2, it receives 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 connected to the relay UE has sent a new TAC, the remote UE may not need to perform registration processing via the relay UE and the gNB connected to the relay UE. This allows the CN to recognize that the remote UE only needs to send paging via the gNB within coverage. The CN sends paging to the remote UE via gNB#2.

[0410] By eliminating the need for registration processing via relay UEs and gNBs connected to them, the system's processing can be simplified. Furthermore, signaling for this registration becomes unnecessary, reducing the signaling load.

[0411] If the gNB within coverage of the remote UE changes due to the movement of the remote UE or changes in the surrounding radio wave propagation environment, and cell selection and re-selection processes are performed, the remote UE should receive paging through the gNB.

[0412] The remote UE may receive paging from the gNB that is receiving system information. Alternatively, it may receive paging from the gNB that is receiving system information related to paging. In this way, the remote UE can also receive paging from the gNB to which the relay UE is connected.

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

[0415] In this way, even in a network including relay UEs, remote UEs can receive paging from TAs or gNBs belonging to the registration area. Therefore, the processing can be the same as conventional paging processes, and malfunctions in paging processes can be reduced.

[0416] The above example showed a gNB connected to a relay UE, but a gNB where the remote UE is in coverage can also be used. The same effect can be obtained.

[0417] Figure 21 is a sequence diagram showing an example of a method for receiving paging from a gNB belonging to a TA where a remote UE is located, according to a modification 3 of Embodiment 2. In Figure 21, steps common to Figure 20 are given the same step numbers, and common explanations are omitted.

[0418] This describes the processing that occurs when data for a remote UE reaches the CN, either when the remote UE is located in the TA (TAC#2) reported by gNB#2, or in the registration area notified during 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 the data generation. In step ST2103, the SMF may notify UPF#2 of the data generation notification. In step ST2104, the SMF notifies the AMF#2 where the remote UE is registered of the data generation. In step ST2105, the AMF#2 may notify the SMF of the data generation 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. Upon receiving the paging from gNB#2, the remote UE performs service request processing and PDU (Protocol Data Unit) session establishment processing with gNB#2, AMF#2, SMF, and UPF#2 in step ST2108. In step ST2109, UPF#2 sends the generated data to gNB#2, and gNB#2 sends the data to the remote UE. In this way, data communication to the remote UE becomes possible.

[0420] For example, when communication ends, step ST2110 performs PDU session release processing between the remote UE, gNB#2, AMF#2, SMF, and UPF#2. Step ST2111 performs CM connection release processing and RRC connection release processing between the remote UE, gNB#2, and AMF#2.

[0421] This describes the process when data for the remote UE arrives at CN, assuming that the remote UE is located in the TA (TAC#1) reported by gNB#1, and that a registration process to change the TAC#1 to which gNB#1 belongs is performed in step ST2010. In step ST2112, data for the remote UE is generated at UPF#1. In step ST2113, UPF#1 notifies SMF of the data generation. In step ST2114, SMF may notify UPF#1 of the data generation notification. In step ST2115, SMF notifies AMF#1, to which the remote UE is registered, of the data generation. In step ST2116, AMF#1 may notify SMF of the data generation 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. Upon receiving the paging from the relay UE, the remote UE performs service request processing and PDU session establishment processing with the relay UE, gNB#1, AMF#1, SMF, and UPF#1 in step ST2120. In communication between the remote UE and the network 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 at the relay UE, data between the UPF and the relay UE is transferred between the relay UE and the remote 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 services communicated between the remote UE and the UPF. In a PDU session between a remote UE and a UPF, the data destination address can be either the remote UE or the UPF. This approach simplifies communication control.

[0423] The relay UE may map the SLRB (Sidelink Radio Bearer) to the Uu's RB. The relay UE transmits data from gNB#1 to the remote UE, transcribing it from the Uu RB to the SL RB. The relay UE transmits data from the remote UE to gNB#1, transcribing it from the SL RB to the Uu RB. The relay UE may also perform channel mapping. The relay UE transmits data from gNB#1 to the remote UE, transcribing it from the PUSCH to the PSSCH. The relay UE transmits data from the remote UE to gNB#1, transcribing it from the PSSCH to the PUSCH. In this way, data transmission and reception between the remote UE and gNB#1 is possible via the relay UE. In step ST2121, UPF#1 transmits the generated data to gNB#1, and gNB#1 transmits the data to the remote UE via the relay UE. In this way, data communication to the remote UE is possible.

[0424] For example, when communication ends, in step ST2122, the PDU session is released between the remote UE, relay UE, gNB#1, AMF#1, SMF, and UPF#1. In step ST2123, the CM connection is released and the RRC connection is released between the remote UE, relay UE, gNB#1, and AMF#1.

[0425] Figure 21 shows the case where AMF is changed, but it is not limited to AMF changes. AMF does not have to be changed. Figure 21 shows the case where UPF is changed, but it is not limited to UPF changes. UPF does not have to be changed. Figure 21 shows the case where SMF is the same, but it is not limited to SMF being the same. SMF may be changed.

[0426] This method allows the remote UE to know whether it should receive paging from a gNB in ​​coverage or from a relay UE, and from which gNB and relay UE it should receive the paging. Furthermore, the CN can know which gNB to send paging to for the remote UE. This enables the CN to initiate communication with the remote UE.

[0427] Other methods of paging are disclosed. A gNB connected to a relay UE and a gNB within coverage of a remote UE may send paging to the remote UE. These gNBs may send paging to the remote UE even if they belong to TAs of different TACs. The remote UE can receive paging from the gNB within coverage and the gNB connected to the relay UE. The remote UE may receive paging from the gNB within coverage and the gNB connected to the relay UE.

[0428] A specific example is disclosed. The remote UE receives the TAC from gNB#1 via the 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 remote UE performs the registration process with the CN via the relay UE and gNB. In the registration process, the CN notifies the remote UE, including the TAC of gNB#2. The registration response message in the registration process may also include the TAC of gNB#2. The TAC may also be included in the registration area information.

[0429] When paging occurs to a remote UE, the CN notifies the gNBs belonging to the TAs of the TACs included in the remote UE's registration area of ​​the paging. This means the CN notifies gNB#1 and gNB#2 of the paging. Upon receiving the paging from the CN, gNB#1 and gNB#2 send the paging to the remote UE. In this way, gNB#2, which the remote UE is in coverage of, and gNB#1, which the relay UE is connected to, are able to send the paging to the remote UE.

[0430] The remote UE waits for paging from gNB#2, which is in coverage, and gNB#1, to which the relay UE is connected. The remote UE may receive paging from either gNB#2, which is in coverage, or gNB#1, to which the relay UE is connected. This way, even if one of the paging signals cannot be sent, the other can still send it. Therefore, the remote UE can receive the sent paging signals. This improves the reliability of the paging process. In addition, the remote UE only needs to receive the first paging signal sent, allowing for early reception of paging. Therefore, the remote UE can respond quickly to paging and initiate communication with the network earlier.

[0431] Modification 4 of Embodiment 2. When sending paging from the CN to a remote UE via the gNB and relay UE, the SL must send the paging from the relay UE to the remote UE. Therefore, with conventional Uu paging processing, problems arise where the paging cannot be sent to the remote UE, or the remote UE cannot receive the paging.

[0432] This modified version discloses a method for solving these problems.

[0433] When sending paging from a CN to a remote UE via a gNB and relay UE, a challenge arises as to how the relay UE receives the paging from the gNB to the remote UE. This paper discloses a method to solve this problem.

[0434] In the communication system according to this modified example, the remote UE notifies the relay UE of information regarding its own UE identifier. This information regarding the UE identifier may be, for example, 5G-S-TMSI, or it may be a UE-ID. The UE-ID is derived from the following equation (1). Using a UE-ID reduces the amount of information required for notification. UE-ID=5G-S-TMSI mod 1024…(1)

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

[0436] Alternatively, you can set a specific value as the identifier for the UE. For example, you could set UE-ID=0.

[0437] It is advisable to notify the network, relay UE, and remote UE in advance that the identifier assigned to the remote UE by the gNB connected to the relay UE, or a 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 network, relay UE, and remote UE that the identifier assigned by gNB#1 to the remote UE will be used, and to notify the network, relay UE, and remote UE that the specific UE-ID will be used, and to notify the network, relay UE, and remote UE that the identifier used for paging will be shared.

[0438] The gNB connected to the relay UE uses the remote UE's identifier to derive the paging transmission timing and transmits the paging to the remote UE. The AMF may also derive the paging transmission timing using the remote UE's identifier. Other information regarding paging timing, such as the paging period, the number of paging occasions, and 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 determined by the AMF and notified to gNB#1 and the relay UE. The relay UE may also be notified via gNB#1.

[0439] The relay UE uses the remote UE's identifier to derive the timing for receiving paging to the remote UE. The relay UE uses the remote UE's identifier and other parameters to determine the paging timing to derive the timing for receiving paging to the remote UE. The relay UE monitors whether or not paging is transmitted from gNB#1 at the derived paging timing to the remote UE. Paging from gNB#1 to the remote UE should be included in the PCCH. The PCCH is transmitted mapped to the PDSCH. The scheduling information of the PDSCH to which the PCH is mapped is included in the DCI, and the CRC of the DCI has the P-RNTI (Paging Radio Network Temporary Identifier) ​​masked and mapped to the PDCCH.

[0440] The relay UE can detect the presence or absence of paging by monitoring the P-RNTI. If the relay UE receives a PDCCH with a masked P-RNTI, it receives a PDSCH according to the scheduling information of that PDCCH and receives paging.

[0441] Instead of the P-RNTI disclosed above, a dedicated RNTI for relays may be provided. A dedicated RNTI for relays may be used for paging from the gNB to the remote UE via the relay UE. The PDCCH to which the paging sent from gNB#1 to the relay UE is mapped is masked with the dedicated RNTI for relays. The dedicated RNTI for relays may be statically defined in a standard beforehand. This allows the gNB and the relay UE to recognize each other.

[0442] It is advisable to include the remote UE identifier in the paging. That is, the paging sent to the relay UE to the remote UE should include the remote UE identifier. When the relay UE recognizes that the paging includes the remote UE identifier, it sends the paging to the remote UE.

[0443] The paging may include information indicating that it is a paging to a remote UE via a relay UE. That is, the paging to a remote UE sent to a relay UE may include such information. When a relay UE recognizes that the paging includes such information, it sends the paging to the remote UE.

[0444] The paging may include the identifier of the relay UE. That is, this information may be included in the paging sent to the remote UE by the relay UE. When a relay UE recognizes that the paging includes its own identifier, it sends the paging to the remote UE. In this way, it becomes possible for a specific relay UE to send paging to a remote UE.

[0445] This document discloses the resources for sending paging using SL on PC5. gNB#1 schedules PC5 paging resources to the relay UE. Resources may be allocated periodically as PC5 paging resources. As a method for scheduling periodic PC5 paging resources, gNB#1 may schedule them to the relay UE using SL's CG (Configured Grant).

[0446] gNB#1 should schedule PC5 paging resources using the paging timing to the remote UE. This makes it possible to allocate periodic resources for PC5 paging. gNB#1 can then schedule PC5 paging resources to the relay UE that are appropriate for the paging timing to the remote 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 the paging from gNB#1 to the remote UE until the remote UE sends the paging may be defined as the paging processing time. The relay UE may also notify the remote UE of the paging processing time. gNB#1 may schedule PC5 paging resources at a timing that includes this processing time, in addition to the paging timing to the remote UE. In this way, it becomes possible to allocate PC5 paging resources that take into account the paging processing time at the relay UE. This makes it possible to schedule PC5 paging resources that are more suitable for the paging timing to the remote UE from gNB#1 to the relay UE.

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

[0449] When the relay UE receives paging from gNB#1 to the remote UE, it uses the PC5 paging resource to notify the remote UE.

[0450] The remote UE derives the paging timing using its own UE identifier and information about the paging timing notified by gNB#1 or AMF. If the remote UE is notified of the aforementioned paging processing time from the relay UE, it derives the paging timing considering the notified paging processing time. At the derived paging timing, the remote UE monitors the paging from the relay UE to detect whether or not paging is occurring. If paging is occurring, it uses its own UE identifier within the paging to determine if the paging is addressed to its own UE. In this way, the remote UE can receive paging addressed to its own UE via the relay UE from gNB#1.

[0451] When PC5 paging resources are allocated periodically, resources must be reserved periodically even when paging does not occur, resulting in resource waste. This paper discloses a method to solve this problem.

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

[0453] This document discloses a method for scheduling PC5 paging resources when paging to a remote UE occurs. In this method, the PCCH includes scheduling information for the PC5 paging resources. The PCCH may include scheduling information for the PC5 paging resources along 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 transmitted mapped to a PDSCH using P-RNTI as a mask. The PCCH may also be transmitted mapped to a PDSCH using relay RNTI as a mask. When paging to a remote UE occurs, gNB#1 notifies the PCCH of the paging to the remote UE, including scheduling information for the PC5 paging resources. In this way, when paging to a remote UE occurs, the relay UE can receive both the paging to the remote UE and the PC5 paging scheduling information.

[0454] Disclose other ways to solve the problem.

[0455] In this method, scheduling information for PC5 paging resources is included in the DCI and mapped to the PDCCH for notification. The DCI may also include the identifier of the relay UE. The DCI may also include the identifier of the remote UE. In this way, the relay UE can recognize which relay UE and which remote UE the message is intended for. The PDCCH may be a PDCCH using P-RNTI as a mask. Alternatively, it may be a PDCCH using a relay-specific RNTI as a mask. Alternatively, it may be a PDCCH using an RNTI for SL (SL-RNTI) as a mask. 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 PC5 paging scheduling information using the RNTI and receive the PC5 paging resource scheduling information when paging to a remote UE occurs.

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

[0457] Embodiment 3. When sending data from a remote UE to the network via a relay UE, resources for SL communication from the remote UE to the relay UE are required. Traditionally, if the remote UE is directly connected to the gNB, the remote UE can directly send an SR (Scheduling Request) to gNB#2. However, if the remote UE is not connected to gNB#2 but is connected to gNB#1 via a relay UE, the remote UE cannot directly send an SR to gNB#1. In this case, the remote UE will not have SL communication resources scheduled by gNB#1 for communication with the relay UE, and will not be able to send data to gNB#1 via the relay UE.

[0458] This embodiment discloses a method for solving these problems.

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

[0460] The remote UE may be connected to the gNB that transmits the SR via RRC. Upon receiving the SR from the remote UE, gNB#1 schedules the SL communication resources with the relay UE for the remote UE. Having scheduled the SL communication resources 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] Upon receiving the SR from the remote UE, gNB#1 schedules resources for UL communication with the relay UE. Having scheduled the UL communication resources, gNB#1 notifies the relay UE of the scheduling information. This UL communication may be limited to communication from the remote UE to gNB#1 via the relay UE.

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

[0463] The remote UE may be connected to the gNB from which the relay UE transmits the SR via RRC. The remote UE may not be connected to the gNB from which the relay UE transmits the SR.

[0464] Upon receiving the SR from the relay UE, gNB#1 schedules the SL communication resources with the relay UE for the remote UE. After scheduling the SL communication resources with the relay UE for the remote UE, gNB#1 notifies the remote UE of the scheduling results. gNB#1 may also notify the remote UE of the scheduling information via the relay UE.

[0465] Upon receiving the SR from the relay UE, gNB#1 also schedules resources for UL communication with the relay UE. Having scheduled the resources for UL communication with the relay UE, gNB#1 notifies the relay UE of the scheduling results. This UL communication may be limited to communication from the remote UE to gNB#1 via the relay UE.

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

[0467] The remote UE may be connected to gNB#1 via the relay UE in an RRC (Remote Relay Control) state. The remote UE notifies gNB#1 of a scheduling request (SR) for SL (Service Level) communication resources with the relay UE. This SR may be for SL communication resources with the relay UE to communicate with gNB#1 via the relay UE.

[0468] Upon receiving the SR from the remote UE, gNB#1 schedules the resources for SL communication with the relay UE for the remote UE. After scheduling the resources for SL communication with the relay UE for the remote UE, gNB#1 notifies the remote UE of the scheduling result. 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 a 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 the Uu. A logical channel for relays may be provided, and the SR may be a scheduling request for the logical channel for relays.

[0470] Upon receiving the SR from the relay UE, gNB#1 performs scheduling of UL communication resources. After scheduling the UL communication resources to the relay UE, gNB#1 notifies the relay UE of the scheduling results. 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 a scheduling request for SL from the remote UE, it sends a scheduling request for UL to gNB#1. Alternatively, the relay UE may send a scheduling request for UL to gNB#1 when the PC5 connection between the relay UE and the remote UE is completed. This PC5 connection may be a PC5-S link establishment, or a PC5-RRC connection. Alternatively, the relay UE may send a scheduling request for UL to gNB#1 when the RRC connection between the remote UE and gNB#1 is completed. The relay UE may also send a scheduling request for UL to gNB#1 during the RRC connection process between the remote UE and gNB#1. The relay UE may also receive an RRC setup request from the remote UE, or receive confirmation of RRC setup completion from the remote UE.

[0472] As previously disclosed, a method for requesting SL communication resources from a remote UE to a relay UE was disclosed. Other methods for obtaining SL communication resources from a remote UE to a relay UE are disclosed.

[0473] The remote UE selects a resource for SL communication with the relay UE. This SL communication resource may be a resource for SL communication with the relay UE to communicate with gNB#1 via the relay UE. In this way, it becomes possible to obtain an SL communication resource from the remote UE to the relay UE. For UL communication from the relay UE to gNB#1, the method disclosed above may be applied as appropriate. In this way, it becomes possible to obtain a communication resource from the remote UE to gNB#1 via the relay UE.

[0474] The relay UE may select a resource for SL communication from the remote UE to the relay UE. This SL communication resource may be a resource for SL communication between the remote UE and the relay UE for the remote UE to communicate with gNB#1 via the relay UE.

[0475] When a relay UE receives a scheduling request for SL from a remote UE, it may select a resource for SL communication from the remote UE to the relay UE. Alternatively, the relay UE may select a resource 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. This PC5 connection may be a PC5-S link establishment, or a PC5-RRC connection. Alternatively, the relay UE may select a resource for SL communication from the remote UE to the relay UE when an RRC connection is completed between the remote UE and gNB#1. The relay UE may select a resource for SL communication from the remote UE to the relay UE during the RRC connection process between the remote UE and gNB#1. When a relay UE receives an RRC setup request from a remote UE, it may select a resource for SL communication from the remote UE to the relay UE. When a relay UE receives confirmation from the remote UE that the RRC setup is complete, it may select a resource 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. In this way, the remote UE can obtain the SL communication resource from the relay UE.

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

[0478] The method for configuring SR is disclosed. The method for configuring SL SR is disclosed. gNB#1 configures SL SR for the remote UE. As part of the SL SR configuration, the transmission timing of SL SR may be configured. The transmission timing of SL SR may be periodic. The setting information for the transmission timing of SL SR may be periodic or offset.

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

[0480] Five examples of scheduling information for SL resources used in SL SR are disclosed below. (1) Period. (2) Offset. (3) Frequency resources. (4) Activation and deactivation information. (5) A combination of (1) to (4).

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

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

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

[0484] This document discloses the method for configuring the UL SR. gNB#1 configures the UL SR for the relay UE. This UL SR may be the UL SR for which the remote UE communicates with gNB#1 via the relay UE. The UL SR configuration may include setting the transmission timing of the UL SR. The transmission timing of the UL SR may be periodic. The setting information for the transmission timing of the UL SR may be periodic or offset. Conventional SR settings defined on Uu may also be used.

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

[0486] gNB#1 performs the SL SR settings and UL SR settings together. SL SR settings include SL SR settings and / or SL SR resource settings. UL SR settings include UL SR settings and / or UL SR resource settings. gNB#1 notifies the relay UE of the SL SR settings and the UL SR settings. The SL SR settings and UL SR settings may be included in the SL setting information. gNB#1 notifies the relay UE of the SL setting information. Separate SL setting information may be provided for relays. This allows for separate notification of SL settings for other SL communications that are not relay-related. SL SR settings may be included in the SL setting information, and UL SR settings may be included in the UL setting information.

[0487] This document discloses a method for notifying the relay UE of the settings related to the service relay (SR) of the service relay (SL) and the service relay (SR) of the UL from gNB#1. RRC signaling may be used for this notification. Notification may also be made during the RRC connection process between gNB#1 and the remote UE. It may also be included in the RRC setup message or in the RRC reconfiguration message.

[0488] The relay UE notifies the remote UE of the SL's SR settings. This may be included in the SL configuration information, which is separated from the SR settings of other SLs for relay purposes. It may also be notified using PC5-RRC signaling. It may be included in the SL RRC configuration message. It may also be notified using the SL RRC reconfiguration message. Alternatively, it may be included in the SL AS configuration. It may also be included in the SL AS reconfiguration. It may also be notified during the RRC connection process performed between gNB#1 and the remote UE. It may also be included in the RRC setup message. It may also be included in the RRC reconfiguration message.

[0489] gNB#1 may notify the remote UE of both the SR settings for the SL and the SR settings for the UL. Notification may also be sent via a relay UE. The notification method should be one of the methods disclosed above as appropriate.

[0490] gNB#1 may individually notify the relay UE of the SR settings for the SL and the SR settings for the UL. The relay UE then notifies the remote UE of the SR settings for the SL. Alternatively, gNB#1 may notify the remote UE of the SR settings for the SL. This notification may be done via the relay UE. gNB#1 may also notify the relay UE of the SR settings for the UL. The SR settings for the SL and the SR settings for the UL may be notified by separate signaling. The SR settings for the SL and the SR settings for the UL may be notified by separate messages. The notification method may be appropriately applied using the methods described above.

[0491] gNB#1 may configure the SR settings for the SL and the SR settings for the UL separately. Notifications from gNB#1 to the relay UE or remote UE should be made using the individual notification methods described above as appropriate.

[0492] Notifications from gNB#1 to relay UEs or remote UEs should be sent using the aforementioned combined notification method as appropriate.

[0493] Figure 22 is a sequence diagram showing an example of how a remote UE transmits an SR to gNB#1 in Embodiment 3. In Figure 22, steps common to Figure 14 are given the same step numbers, and common explanations are omitted. In step ST1415, the relay UE is connected to gNB#1 via RRC, in step ST2201, the remote UE is connected to the relay UE via PC5-RRC, and in step ST1420, the remote UE is connected to gNB#1 via RRC.

[0494] gNB#1 configures the SR settings for the UL and SL for the relay UE, and in step ST2202, notifies the relay UE of these settings. In step ST2203, the relay UE notifies the remote UE of the SR settings for the SL. When the remote UE generates transmission data to the NW, in step ST2204, it sends the SR for the relay resource to gNB#1 via the relay UE. For sending the SR from the remote UE to the relay UE, it is preferable to use the SR settings for the SL received in step ST2203. For sending the SR from the relay UE to gNB#1, it is preferable to use the SR settings for the UL received in step ST2202. In this way, even if the remote UE is connected to gNB#1 via RRC, gNB#1 can receive SRs from the remote UE.

[0495] gNB#1 schedules relay resources for the relay UE and the remote UE. In step ST2205, gNB#1 notifies the relay UE of scheduling information for UL communication resources for relay. In step ST2206, gNB#1 notifies the remote UE of scheduling information for SL communication resources for relay via the relay UE. Upon receiving the scheduling information for SL communication resources for relay, the remote UE uses the communication resources indicated by the scheduling information to send data to gNB#1 via the relay UE in step ST2207. Upon receiving this data, the relay UE uses the communication resources indicated by the scheduling information for UL communication resources for relay to send the data received from the remote UE to gNB#1.

[0496] In this way, even when the remote UE is connected to gNB#1 via RRC, 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 send data to gNB#1 via the relay UE. In addition, in the example in Figure 22, gNB#1 schedules the SL communication resources and UL communication resources together for relay use and notifies the remote UE and relay UE. By appropriately scheduling each resource, gNB#1 can reduce the delay when the relay UE sends data received from the remote UE to gNB#1.

[0497] Resources for SL SR may be shared with other channels. For example, if the transmission timing of SL SR conflicts with the transmission timing of other channels, in part or in whole, the SL SR may be transmitted preferentially. This allows for earlier transmission of SL SR, thus enabling early acquisition of SL resource scheduling information. As a result, SL communication can be performed with low latency.

[0498] Alternatively, for example, if the transmission timing of an SL SR conflicts with the transmission timing of another channel, the higher-priority channel may be transmitted. This allows the SL SR or other channels to be transmitted using the resources allocated for the SL SR, depending on their priority.

[0499] Channels and SL SRs that could not be transmitted due to a collision may be left untransmitted or discarded. Alternatively, channels and SL SRs that could not be transmitted due to a collision may be sent using the next SL SR resource.

[0500] If the transmission timing of SL SR conflicts with the transmission timing of other channels, in part or in whole, an alternative method is to multiplex SL SR with other channels and transmit using the resources allocated for SL SR. This improves resource utilization efficiency and enables low-latency communication.

[0501] While it was disclosed that if the transmission timing of SL SR conflicts with the transmission timing of other channels, in whole or in part, resources for SL SR may be used, resources for other channels may also be used.

[0502] As disclosed in this embodiment, the gNB can set scheduling requests for relay communication to the remote UE and relay UE. The remote UE and relay UE can notify the gNB of the scheduling requests for relay communication. The gNB can perform the scheduling for relay communication to the remote UE and relay UE. The gNB can notify the remote UE and relay UE of the scheduling information for relay communication. As a result, the remote UE can communicate with the NW via the relay UE.

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

[0504] A Service Stream (SR) for CSI reporting may be provided in the Service Level (SL). The methods for setting up, sending, and scheduling the SR for CSI reporting in the SL may be appropriately applied as methods for setting up, sending, and scheduling the SR for CSI reporting in the SL. In this way, the SL's CSI reporting SR can be sent from the remote UE to gNB#1 via the relay UE. The remote UE can receive scheduling information for the SL's CSI reporting resources from gNB#1 via the relay UE. The relay UE can also receive scheduling information for the SL's CSI reporting resources on the Uu from gNB#1.

[0505] This approach makes it possible to improve the communication quality between the remote UE and the gNB.

[0506] In this disclosure, the UE from which the service data originates is designated as UE-TX. For example, if UE-TX is UE1 and UE-RX is UE2, and service data originates in UE2 and is sent to UE1, then it is preferable to designate UE2 as UE-TX and UE1 as UE-RX and apply the method described in this disclosure. This will achieve the same effect.

[0507] The embodiments and their variations described above are merely illustrative, and these embodiments and their variations can be freely combined. Furthermore, any component of each embodiment and its variations can be modified or omitted as appropriate.

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

[0509] For example, the methods disclosed in each of the embodiments and their variations described above may be applied not only to V2X (Vehicle-to-everything) services but also to services that use SL communication. For example, they may be applied to SL communication used in various services such as proximity-based services, public safety, communication between wearable devices, and communication between machines in factories.

[0510] Although this disclosure has been described in detail, the above description is illustrative and not limiting in all respects. It is understood that countless variations not illustrated are conceivable. [Explanation of symbols]

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

Claims

1. A first terminal device in a communication system, The communication system comprises a plurality of terminal devices that perform sidelink communication via a PC5 interface, including the plurality of terminal devices including the first terminal device and the second terminal device, and a network including a base station device. The second terminal device is a terminal device capable of relaying between the first terminal device and the network, or a relay terminal device that performs relaying between the first terminal device and the network. The first terminal device is The base station device receives the settings for measurement in the sidelink communication. Using the above settings, measurements are performed regarding the sidelink communication from the second terminal device. It is configured in such a way. The first terminal device.

2. The aforementioned settings include a first setting regarding the object to be measured and a second setting regarding the reporting of measurement results. The first terminal device according to claim 1.

3. The first setting is, Information indicating that the terminal device to be measured is a U2N relay UE, and Information relating to the frequency of the side link communication on which the measurement is performed, including, The first terminal device according to claim 2.

4. The first terminal device is configured to transmit the measurement result report to the base station device using the second setting. The first terminal device according to claim 2.

5. The measurement result report includes identification information for identifying the second terminal device that is the subject of measurement. The first terminal device according to claim 4.

6. The second setting includes information about an event causing the first terminal device to transmit the measurement result report, The information relating to the event includes at least one of a threshold for the event and an offset applied to the measurement result. The first terminal device according to claim 4.

7. The second terminal device is the relay terminal device, The aforementioned event includes the condition that the reception quality in the sidelink communication from the second terminal device is less than the threshold, The first terminal device is configured to transmit the measurement result report when the above conditions are met. The first terminal device according to claim 6.

8. The aforementioned event includes the condition that the reception quality in the sidelink communication from the second terminal device is greater than the threshold, The first terminal device is configured to transmit the measurement result report when the above conditions are met. The first terminal device according to claim 6.

9. If the reception quality in communication with the base station device is less than a first threshold, and the reception quality in the sidelink communication from the second terminal device is greater than a second threshold, the first terminal device is configured to transmit the measurement result report. The first terminal device according to claim 4.

10. The plurality of terminal devices further include a third terminal device capable of performing side-link communication with the first terminal device. The first terminal device is configured to transmit the measurement result report based on events related to the reception quality of the sidelink communication from the second terminal device and the reception quality of the sidelink communication from the third terminal device. The first terminal device according to claim 4.

11. The first terminal device is L3 filtering is applied to the measurement results. The measurement results report, which includes the measurement results to which the L3 filtering has been applied, is transmitted. It is configured in such a way. The first terminal device according to claim 4.

12. The second terminal device is the relay terminal device, The first terminal device is configured to receive information regarding the connection status between the second terminal device and the network from the second terminal device via a sidelink SRB (Signaling Radio Bearer). The first terminal device according to claim 1.

13. The information relating to the connection status includes information identifying the cell to which the second terminal device is connected. The first terminal device according to claim 12.

14. The connection status information further includes at least one of information identifying the tracking area and information identifying the core network. The first terminal device according to claim 13.

15. The second terminal device is the relay terminal device, The first terminal device is configured to receive information from the second terminal device indicating that the base station device to which the second terminal device is connected has been changed. The first terminal device according to claim 1.

16. A second terminal device in a communication system, The communication system comprises a plurality of terminal devices that perform sidelink communication via a PC5 interface, including the plurality of terminal devices including the first terminal device and the second terminal device, and a network including a base station device. The second terminal device is a relay terminal device that performs relaying between the first terminal device and the network. The second terminal device is configured to transmit information regarding the connection status between the second terminal device and the network to the first terminal device via a sidelink SRB (Signaling Radio Bearer). The second terminal device.

17. A base station device in a communication system, The communication system comprises a plurality of terminal devices that perform sidelink communication via a PC5 interface, including a plurality of terminal devices including a first terminal device and a second terminal device, and a network including the base station device. The base station device is configured to transmit settings for measurement in the sidelink communication from the second terminal device to the first terminal device. Base station equipment.

18. Multiple terminal devices that perform sidelink communication via a PC5 interface, including a first terminal device and a second terminal device, A network including base station equipment, A communication system comprising, The second terminal device is a terminal device capable of relaying between the first terminal device and the network, or a relay terminal device that performs relaying between the first terminal device and the network. The first terminal device is The base station device receives the settings for measurement in the sidelink communication. Using the above settings, measurements are performed regarding the sidelink communication from the second terminal device. It is configured in such a way. Communication system.

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