Communication terminal device and communication system

Abstract

To provide good sidelink communication regarding sidelink communication, which is communication via a PC5 interface.SOLUTION: A communication system includes a plurality of communication terminal devices that perform sidelink communication, which is communication via a PC5 interface. A communication terminal device among the plurality of communication terminal devices is configured to transmit signaling using a default radio bearer in the sidelink communication. The default radio bearer is, for example, an SRB (Signaling Radio Bearer).SELECTED DRAWING: Figure 14

Description

Technical Field

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

Background Art

[0002] In the 3GPP (3rd Generation Partnership Project), which is 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 the radio access network (hereinafter collectively also 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 a 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, different from W-CDMA (Wideband Code Division Multiple Access), LTE does not include circuit switching and is only a packet communication method.

[0004] Regarding the decisions on frame configuration in the LTE system in 3GPP described in Non-Patent Document 1 (Chapter 5), an explanation will be given using FIG. 1. FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in a communication system of the LTE method. In FIG. 1, one radio frame is 10 ms. The radio frame is divided into 10 subframes of equal size. The subframe is divided into 2 slots of equal size. The downlink synchronization signal is included in the first and sixth subframes for each radio frame. The synchronization signal includes a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

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

[0006] The physical broadcast channel (PBCH) is a channel for downlink transmission from a base station device (hereinafter sometimes simply referred to as "base station") to a communication terminal device such as a mobile terminal device (hereinafter sometimes simply referred to as "mobile terminal") (hereinafter sometimes simply referred to as "communication terminal"). The BCH transport block is mapped to 4 subframes at intervals of 40 ms. There is no explicit signaling for the 40 ms timing.

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

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

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

[0010] The Physical Multicast Channel (PMCH) is a channel for downlink transmission from a base station to a communication terminal. The Multicast Channel (MCH), which is a transport channel, is mapped to the PMCH.

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

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

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

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

[0015] Similarly, for the uplink reference signal, it is a symbol known in the LTE communication system. The following two types of uplink reference signals are defined: the Demodulation Reference Signal (DM-RS) and the Sounding Reference Signal (SRS).

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

[0017] For the downlink shared channel (DL-SCH), retransmission control by HARQ (Hybrid ARQ) is applied. The DL-SCH can be broadcast throughout the coverage area of the base station (cell). The DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called persistent scheduling. The DL-SCH supports discontinuous reception (DRX) of the communication terminal for power consumption reduction of the communication terminal. The DL-SCH is mapped to the physical downlink shared channel (PDSCH).

[0018] The paging channel (PCH) supports DRX of the communication terminal to enable low power consumption of the communication terminal. The PCH requires broadcast throughout the coverage area of the base station (cell). The PCH is mapped to a physical resource such as the physical downlink shared channel (PDSCH) that can be dynamically used for traffic.

[0019] The multicast channel (MCH) is used for broadcast throughout the coverage area of the base station (cell). The MCH supports SFN synthesis of MBMS (Multimedia Broadcast Multicast Service) services (MTCH and MCCH) in multi-cell transmission. The MCH supports semi-static resource allocation. The MCH is mapped to the PMCH.

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

[0021] The random access channel (RACH) is limited to control information. RACH has a risk of collision. RACH is mapped to the physical random access channel (PRACH).

[0022] HARQ will be described. HARQ is a technology that improves the communication quality of the transmission path by combining automatic repeat request (ARQ) and forward error correction. HARQ has the advantage that error correction functions effectively by retransmission even for a transmission path where the communication quality changes. In particular, it is also possible to obtain further quality improvement by combining the reception result of the first transmission and the reception result of the retransmission at the time of retransmission.

[0023] An example of the retransmission method will be described. At the receiving side, when the received data cannot be decoded correctly, in other words, when a cyclic redundancy check (CRC) error occurs (CRC = NG), the receiving side sends a "Nack" to the transmitting side. The transmitting side that receives the "Nack" retransmits the data. At the receiving side, when the received data can be decoded correctly, in other words, when no CRC error occurs (CRC = OK), the receiving side sends an "Ack" to the transmitting side. The transmitting side that receives the "Ack" transmits the next data.

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

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

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

[0027] The Multicast Control Channel (MCCH) is a downlink channel for one-to-many transmission. The MCCH is used for transmitting MBMS control information for one or several MTCHs from the network to the communication terminal. The MCCH is used only for communication terminals receiving MBMS. The MCCH is mapped to the Multicast Channel (MCH), which is a 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 is in 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 by communication terminals during MBMS reception. The MTCH is mapped to the Multicast Channel (MCH).

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

[0032] The location tracking of a communication terminal is performed in units of an area composed of one or more cells. The location tracking is performed to track the location of the communication terminal even in the standby state and to enable the communication terminal to be called, in other words, to be incoming-called. The area for this location tracking of the communication terminal is called a tracking area.

[0033] Also, in 3GPP, as Release 10, the standardization of Long Term Evolution Advanced (LTE-A) is in progress (see Non-Patent Document 3 and Non-Patent Document 4). LTE-A is based on the radio interval communication method of LTE and is configured by adding several new technologies thereto.

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

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

[0036] According to the capabilities of the UE, a Secondary Cell (SCell) is configured to form a set of serving cells together with the PCell. In the downlink, the carrier corresponding to the SCell is the Downlink Secondary Component Carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is the Uplink Secondary Component Carrier (UL SCC).

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

[0038] Also, as new technologies in LTE-A, there are technologies such as Wider bandwidth extension and Coordinated Multiple Point transmission and reception (CoMP). Regarding CoMP being considered for LTE-A in 3GPP, it is described in Non-Patent Document 1.

[0039] Also, in 3GPP, in order to handle future huge traffic, it is being considered to use small eNBs (hereinafter sometimes referred to as "small base station devices") that constitute small cells. For example, technologies such as increasing the frequency utilization efficiency and increasing the communication capacity by installing a large number of small eNBs to form a large number of small cells are being considered. Specifically, there is Dual Connectivity (abbreviated as DC) where the UE connects to two eNBs for communication. Regarding DC, it is described in Non-Patent Document 1.

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

[0041] The traffic volume of mobile networks is on an increasing trend, and the communication speed is also accelerating. When LTE and LTE-A are fully launched, further increase in communication speed is expected.

[0042] Furthermore, a fifth-generation (hereinafter sometimes referred to as "5G") radio access system aiming to start services after 2020 has been studied for the increasingly advanced mobile communications. For example, in Europe, an organization called METIS has summarized the requirements for 5G (see Non-Patent Document 5).

[0043] In the 5G radio access system, compared with the LTE system, the system capacity is 1000 times, the data transmission speed is 100 times, the data processing delay is one-tenth (1 / 10), and the number of simultaneously connected communication terminals is 100 times. Further reduction in power consumption and cost of devices are required as requirements.

[0044] To meet such requirements, in 3GPP, as Release 15, the standard study of 5G is underway (see Non-Patent Documents 6 to 18). The technology of the 5G radio section is called "New Radio Access Technology" (abbreviated as "New Radio" to "NR").

[0045] The NR system is being studied based on the LTE system and the LTE-A system, but changes and additions from the LTE system and the LTE-A system are made in the following points.

[0046] As the access method of NR, OFDM is used in the downlink direction, and OFDM and DFT-s-OFDM (DFT-spread-OFDM) are used in the uplink direction.

[0047] In NR, in order to improve the transmission speed and reduce the processing delay, it is possible to use a higher frequency compared to LTE.

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

[0049] In the frame structure of NR, various subcarrier intervals, that is, various numerologies are supported. In NR, regardless of the numerology, one subframe is 1 millisecond, and one slot is composed of 14 symbols. Also, the number of slots included in one subframe is one in the numerology with a subcarrier interval of 15 kHz, and increases in proportion to the subcarrier interval in other numerologies (see Non-Patent Document 13 (TS38.211 V16.0.0)).

[0050] The downlink synchronization signal in NR is transmitted from the base station at a predetermined period with a predetermined duration as a Synchronization Signal Burst (hereinafter, may be referred to as an SS burst). The SS burst is composed of Synchronization Signal Blocks (hereinafter, may be referred to as SS blocks) for each beam of the base station. The base station transmits the SS blocks of each beam within the duration of the SS burst while changing the beam. The SS block is composed of P-SS, S-SS, and PBCH.

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

[0052] In NR, in order to flexibly perform DL / UL switching within a slot, Slot Format Indication (SFI) is added to the information included in PDCCH.

[0053] Also, in NR, the base station pre-sets a part of the carrier frequency band (hereinafter sometimes referred to as Bandwidth Part (BWP)) 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.

[0054] In 3GPP, as forms of DC, DC by an LTE base station connected to EPC and an NR base station, DC by an NR base station connected to a 5G core system, and DC by an LTE base station connected to a 5G core system and an NR base station are being studied (see Non-Patent Documents 12, 16, and 19).

[0055] Also, in 3GPP, several new technologies are being studied. For example, it is being studied to support services using Side Link (SL) communication in both EPS and 5G core systems (Non-Patent Documents 1, 20, 21, 22). Examples of services using SL communication include V2X services and proximity services.

Prior Art Documents

Non-Patent Documents

[0056]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 22

Non-Patent Document 23

Non-Patent Document 24

Non-Patent Document 25

Non-Patent Document 26

Summary of the Invention

Problems to be Solved by the Invention

[0057] It has been considered to support various services using SL communication (also referred to as PC5 communication) in both the EPS and the 5G core system (Non-Patent Documents 1, 20, 21, 22). In SL communication, communication is performed between terminals. In SL communication, it has been proposed that a terminal different from the terminals performing inter-terminal communication performs SL communication scheduling (Non-Patent Document 23). Also, in SL communication, not only direct communication between terminals but also indirect communication via a relay has been proposed (Non-Patent Document 24). In SL communication using not only terminals performing such SL communication but also other terminals, how to improve the utilization efficiency of resources used for SL communication, how to reduce the power consumption of terminals, how to satisfy the QoS required for services, and how to improve the reliability of services become problems.

[0058] In view of the above problems, an object of the present disclosure is to provide good SL communication by realizing at least one of, for example, improvement of resource utilization efficiency, reduction of power consumption of terminals, ensuring of QoS required for services, and improvement of service reliability in SL communication.

Means for Solving the Problems

[0059] The communication terminal device according to the present disclosure is a communication terminal device among a plurality of communication terminal devices provided in a communication system and performing sidelink communication, which is communication via a PC5 interface. In the sidelink communication, the communication terminal device is configured to transmit signaling using a default radio bearer.

Effect of the Invention

[0060] According to the present disclosure, good SL communication can be provided.

[0061] The object, features, aspects, and advantages of the present disclosure will become clearer from the following detailed description and the accompanying drawings.

Brief Description of the Drawings

[0062]

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Embodiments for Carrying out the Invention

[0063] Embodiment 1. FIG. 2 is a block diagram showing the overall configuration of a communication system 200 of the LTE system being discussed in 3GPP. FIG. 2 will be described. The radio access network is referred to as E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 202, which is a communication terminal device, can communicate wirelessly with a base station device (hereinafter referred to as "base station (E-UTRAN NodeB: eNB)") 203 and performs signal transmission and reception through wireless communication.

[0064] Here, the "communication terminal device" includes not only mobile terminal devices such as mobile phone terminal devices that can move, but also non-mobile devices such as sensors. In the following description, the "communication terminal device" may sometimes be simply referred to as the "communication terminal".

[0065] If a control protocol for the mobile terminal 202, for example, RRC (Radio Resource Control), and a user plane (hereinafter sometimes referred to as U-Plane), for example, PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer) are terminated at the base station 203, then the E-UTRAN is composed of one or more base stations 203.

[0066] The control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs broadcast, paging, RRC connection management, etc. As the states of the base station 203 and the mobile terminal 202 in RRC, there are RRC_IDLE and RRC_CONNECTED.

[0067] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell re-selection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can transmit and receive data with the network. Also in RRC_CONNECTED, handover (HO), measurement of neighbor cells, etc. are performed.

[0068] The base station 203 is composed of one or more eNBs 207. A system composed of the core network EPC (Evolved Packet Core) and the radio access network E-UTRAN 201 is called EPS (Evolved Packet System). The combination of the core network EPC and the radio access network E-UTRAN 201 is sometimes referred to as the "network".

[0069] The eNB 207 is connected to the Mobility Management Entity (MME), or the Serving Gateway (S-GW), or the MME / S-GW unit (hereinafter sometimes referred to as the "MME unit") 204 including the MME and the S-GW through the S1 interface, and control information is communicated between the eNB 207 and the MME unit 204. A plurality of MME units 204 may be connected to one eNB 207. The eNBs 207 are connected through the X2 interface, and control information is communicated between the eNBs 207.

[0070] The MME unit 204 is a higher-level device, specifically a higher-level node, and controls the connection between 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.

[0071] The base station 203 may constitute one cell or a plurality of cells. Each cell has a range predefined as a coverage that is a range within which communication with the mobile terminal 202 is possible, and wireless communication is performed with the mobile terminal 202 within the coverage. When one base station 203 constitutes a plurality of cells, each individual cell is configured to be able to communicate with the mobile terminal 202.

[0072] FIG. 3 is a block diagram showing the overall configuration of a 5G communication system 210 being discussed in 3GPP. FIG. 3 will be described. The radio access network is referred to as NG-RAN (Next Generation Radio Access Network) 211. The UE 202 can communicate wirelessly with an NR base station device (hereinafter referred to as "NR base station (NG-RAN NodeB: gNB)") 213 and transmit and receive signals through wireless communication. Also, the core network is referred to as 5G Core (5GC).

[0073] If the control protocol for the UE 202, 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), terminate at the NR base station 213, the NG-RAN is composed of one or more NR base stations 213.

[0074] The function of the control protocol RRC (Radio Resource Control) between the UE 202 and the NR base station 213 is the same as that of LTE. As the states of the NR base station 213 and the UE 202 in RRC, there are RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE.

[0075] RRC_IDLE and RRC_CONNECTED are the same as in the LTE mode. RRC_INACTIVE performs system information (SI) notification, paging, cell re-selection, mobility, etc. while maintaining the connection between the 5G Core and the NR base station 213.

[0076] gNB 217 is connected 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 including AMF, SMF, and UPF, via an NG interface. Control information and / or user data are communicated between gNB 217 and the 5GC unit 214. The NG interface is a general term for the N2 interface between gNB 217 and the AMF, the N3 interface between gNB 217 and the UPF, the N11 interface between the AMF and the SMF, and the N4 interface between the UPF and the SMF. A plurality of 5GC units 214 may be connected to one gNB 217. gNBs 217 are connected to each other via an Xn interface, and control information and / or user data are communicated between gNBs 217.

[0077] Similar to the base station 203, the NR base station 213 may also constitute one or more cells. When one NR base station 213 constitutes a plurality of cells, each cell is configured to be able to communicate with the UE 202.

[0078] gNB 217 may be divided into a Central Unit (hereinafter sometimes referred to as CU) 218 and a Distributed Unit (hereinafter sometimes referred to as DU) 219. One CU 218 is configured in gNB 217. One or more DUs 219 are configured in gNB 217. The CU 218 is connected to the DU 219 via an F1 interface, and control information and / or user data are communicated between the CU 218 and the DU 219.

[0079] In a 5G communication system, an integrated data management (UDM) function and a policy control function (PCF) described in Non-Patent Document 22 (3GPP TS23.501 V16.3.0) may be included. UDM and / or PCF may be included in the 5GC part in FIG. 3.

[0080] In a 5G communication system, a non-3GPP interworking function (N3IWF) described in Non-Patent Document 22 (3GPP TS23.501 V16.3.0) may be included. N3IWF may terminate the access network (AN) between the UE in non-3GPP access with the UE.

[0081] FIG. 4 is a diagram showing the configuration of DC by an eNB and a gNB connected to the EPC. In FIG. 4, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In FIG. 4, eNB223-1 becomes the master base station, and gNB224-2 becomes the secondary base station (this DC configuration may be referred to as EN-DC). In FIG. 4, an example is shown in which 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.

[0082] FIG. 5 is a diagram showing the configuration of DC by a gNB connected to the NG core. In FIG. 5, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In FIG. 5, gNB224-1 becomes the master base station, and gNB224-2 becomes the secondary base station (this DC configuration may be referred to as NR-DC). In FIG. 5, an example is shown in which the U-Plane connection between the 5GC unit 214 and gNB224-2 is made via gNB224-1, but it may also be made directly between the 5GC unit 214 and gNB224-2.

[0083] FIG. 6 is a diagram showing the configuration of DC by eNB and gNB connected to the NG core. In FIG. 6, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In FIG. 6, eNB226-1 serves as the master base station, and gNB224-2 serves as the secondary base station (this DC configuration may be referred to as NG-EN-DC). In FIG. 6, an example is shown in which the U-Plane connection between the 5GC unit 214 and gNB224-2 is made via eNB226-1, but it may also be made directly between the 5GC unit 214 and gNB224-2.

[0084] FIG. 7 is a diagram showing another configuration of DC by eNB and gNB connected to the NG core. In FIG. 7, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In FIG. 7, gNB224-1 serves as the master base station, and eNB226-2 serves as the secondary base station (this DC configuration may be referred to as NE-DC). In FIG. 7, an example is shown in which the U-Plane connection between the 5GC unit 214 and eNB226-2 is made via gNB224-1, but it may also be made directly between the 5GC unit 214 and eNB226-2.

[0085] FIG. 8 is a block diagram showing the configuration of the mobile terminal 202 shown in FIG. 2. The transmission process of the mobile terminal 202 shown in FIG. 8 will be described. First, the control data from the protocol processing unit 301 and the user data from the application unit 302 are stored in the transmission data buffer unit 303. The data stored in the transmission data buffer unit 303 is passed to the encoder unit 304, and encoding processes such as error correction are performed. There may be data that is directly output from the transmission data buffer unit 303 to the modulation unit 305 without undergoing the encoding process. The data encoded by the encoder unit 304 is subjected to modulation processing by the modulation unit 305. In the modulation unit 305, precoding in MIMO may be performed. The modulated data is converted into a baseband signal and then output to the frequency conversion unit 306, where it is converted to a wireless transmission frequency. Thereafter, transmission signals are transmitted from the antennas 307-1 to 307-4 to the base station 203. In FIG. 8, the case where the number of antennas is four is illustrated, but the number of antennas is not limited to four.

[0086] Also, the reception process of the mobile terminal 202 is executed as follows. The wireless signal from the base station 203 is received by the antennas 307-1 to 307-4. The received signal is converted from the wireless reception frequency to a baseband signal by the frequency conversion unit 306, and demodulation processing is performed in the demodulation unit 308. In the demodulation unit 308, weight calculation and multiplication processing may be performed. The demodulated data is passed to the decoder unit 309, and decoding processes such as error correction are performed. Among the decoded data, the control data is passed to the protocol processing unit 301, and the user data is passed to the application unit 302. A series of processes of the mobile terminal 202 are controlled by the control unit 310. Therefore, although omitted in FIG. 8, the control unit 310 is connected to each of the units 301 to 309. In FIG. 8, the number of antennas used for transmission and the number of antennas used for reception by the mobile terminal 202 may be the same or different.

[0087] FIG. 9 is a block diagram showing the configuration of the base station 203 shown in FIG. 2. The transmission process of the base station 203 shown in FIG. 9 will be described. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (such as the MME unit 204). The 5GC communication unit 412 transmits and receives data between the base station 203 and the 5GC (such as the 5GC unit 214). The other base station communication unit 402 transmits and receives data 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. The control data from the protocol processing unit 403, as well as the user data and control data from the EPC communication unit 401, the 5GC communication unit 412, and the other base station communication unit 402, are stored in the transmission data buffer unit 404.

[0088] The data stored in the transmission data buffer unit 404 is passed to the encoder unit 405, and encoding processes such as error correction are performed. There may be data that is directly output from the transmission data buffer unit 404 to the modulation unit 406 without undergoing the encoding process. The encoded data is subjected to modulation processing in the modulation unit 406. Precoding in MIMO may be performed in the modulation unit 406. The modulated data is converted into a baseband signal and then output to the frequency conversion unit 407, where it is converted to a radio transmission frequency. Thereafter, a transmission signal is transmitted to one or more mobile terminals 202 from the antennas 408-1 to 408-4. In FIG. 9, the case where the number of antennas is 4 is illustrated, but the number of antennas is not limited to 4.

[0089] Also, the reception processing of the base station 203 is executed as follows. A radio signal from one or more mobile terminals 202 is received by the antenna 408. The received signal is converted from 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, and decoding processing such as error correction is performed. Among 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, and the other base station communication unit 402. A series of processes of the base station 203 are controlled by the control unit 411. Therefore, although omitted in FIG. 9, the control unit 411 is connected to each unit 401 to 410. In FIG. 9, the number of antennas used for transmission and the number of antennas used for reception by the base station 203 may be the same or different.

[0090] FIG. 9 is a block diagram showing the configuration of the base station 203, but the base station 213 may have a similar configuration. Also, regarding FIGS. 8 and 9, the number of antennas of the mobile terminal 202 and the number of antennas of the base station 203 may be the same or different.

[0091] FIG. 10 is a block diagram showing the configuration of the MME. FIG. 10 shows the configuration of the MME 204a included in the MME unit 204 shown in FIG. 2 above. The PDN GW communication unit 501 transmits and receives data between the MME 204a and the PDN GW. The base station communication unit 502 transmits and receives data via the S1 interface between the MME 204a and the base station 203. When 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 plain communication unit 503 and transmitted to one or more base stations 203. When 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 plain communication unit 503 and transmitted to the PDN GW.

[0092] When the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 501 to the control plane control unit 505. When the data received from the base station 203 is control data, the control data is passed from the base station communication unit 502 to the control plane control unit 505.

[0093] The control plane control unit 505 includes an NAS security unit 505-1, an SAE bearer control unit 505-2, an idle state mobility management unit 505-3, etc., and performs overall processing for the control plane (hereinafter, may also be referred to as the C-Plane). The NAS security unit 505-1 performs security of 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 (idle state; LTE-IDLE state, or simply referred to as idle), generation and control of paging signals in the standby state, addition, deletion, update, search, tracking area list management, etc. of the tracking area of one or more mobile terminals 202 under its umbrella.

[0094] MME204a distributes paging signals to one or more base stations 203. Also, MME204a performs mobility control in the Idle State. MME204a manages the Tracking Area list when the mobile terminal is in the idle state and in the Active State. MME204a initiates the paging protocol by transmitting a paging message to a cell belonging to the tracking area (Tracking Area) in which the UE is registered. The management of the CSG of the eNB207 connected to MME204a, the management of the CSG ID, and the management of the whitelist may be performed by the idle state mobility management unit 505-3.

[0095] Figure 11 is a block diagram showing the configuration of the 5GC. In Figure 11, the configuration of the 5GC unit 214 shown in Figure 3 described above is shown. Figure 11 shows the case where the configuration of the AMF, the configuration of the SMF, and the configuration of the UPF are included in the 5GC unit 214 shown in Figure 5. 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. When 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 plain communication unit 523 and transmitted to one or more of the base stations 203 and / or the base station 213. When the data received from the base station 203 and / or the base station 213 is user data, the user data is passed from the base station communication unit 522 to the Data Network communication unit 521 via the user plain communication unit 523 and transmitted to the Data Network.

[0096] When 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 plain communication unit 523. The session management unit 527 passes the control data to the control plane control unit 525. When the data received from the base station 203 and / or the base station 213 is control data, the control data is passed from the base station communication unit 522 to the control plane control unit 525. The control plane control unit 525 passes the control data to the session management unit 527.

[0097] The control plane control unit 525 includes a NAS security unit 525-1, a PDU session control unit 525-2, an idle state mobility management unit 525-3, etc., and performs general processing for the control plane (hereinafter, may also be referred to as the C-Plane). The NAS security unit 525-1 performs security of NAS (Non-Access Stratum) messages, etc. The PDU session control unit 525-2 performs management of the PDU session between the mobile terminal 202 and the 5GC unit 214, etc. The idle state mobility management unit 525-3 performs mobility management in the standby state (idle state; RRC_IDLE state, or simply referred to as idle), generation and control of paging signals in the standby state, addition, deletion, update, search, tracking area list management, etc. of the tracking area of one or more mobile terminals 202 under its umbrella.

[0098] The 5GC unit 214 distributes paging signals to one or more base stations 203 and / or base stations 213. Also, the 5GC unit 214 performs mobility control in the idle state. When the mobile terminal is in the idle state, the 5GC unit 214 manages the tracking area list in the inactive state and the active state. The 5GC unit 214 initiates the paging protocol by transmitting a paging message to a cell belonging to the tracking area (tracking area) in which the UE is registered.

[0099] Next, an example of a cell search method in a communication system is shown. FIG. 12 is a flowchart showing an overview from cell search to standby operation performed by a communication terminal (UE) in an LTE-based communication system. When the communication terminal starts cell search, in step ST601, it synchronizes slot timing and frame timing using the first synchronization signal (P-SS) and the second synchronization signal (S-SS) transmitted from surrounding base stations.

[0100] The P-SS and S-SS are combined and called the synchronization signal (SS). The synchronization signal (SS) is assigned a synchronization code that corresponds one-to-one to the PCI assigned to each cell. 504 types of PCI are being considered. Synchronization is taken using these 504 types of PCI, and the PCI of the synchronized cell is detected (identified).

[0101] Next, for the cell that has been synchronized, in step ST602, a Cell-specific Reference Signal (CRS), which is a reference signal (Reference Signal: RS) transmitted from the base station for each cell, is detected, and the received power of the RS (Reference Signal Received Power: RSRP) is measured. A code corresponding one-to-one with the PCI is used for the reference signal (RS). By correlating with that code, it can be separated from other cells. By deriving the code for the RS of the cell from the PCI specified in step ST601, it becomes possible to detect the RS and measure the received power of the RS.

[0102] Next, in step ST603, from among the one or more cells detected up to step ST602, a cell with the best reception quality of the RS is selected, for example, a cell with the highest received power of the RS, that is, the best cell.

[0103] Next, in step ST604, the PBCH of the best cell is received to obtain the BCCH, which is the broadcast information. The MIB (Master Information Block), which contains cell configuration information, is mapped to the BCCH on the PBCH. Therefore, by receiving the PBCH and obtaining the BCCH, the MIB can be obtained. Examples of the information in the MIB include the DL (downlink) system bandwidth (also called the transmission bandwidth configuration: dl-bandwidth), the number of transmission antennas, the SFN (System Frame Number), and so on.

[0104] Next, in step ST605, based on the cell configuration information in the MIB, the DL-SCH of the cell is received to obtain the SIB (System Information Block) 1 in the broadcast information BCCH. The SIB1 contains information related to access to the cell, information related to cell selection, and scheduling information for other SIBs (SIBk; k is an integer greater than or equal to 2). In addition, the SIB1 contains the Tracking Area Code (TAC).

[0105] Next, in step ST606, the communication terminal compares the TAC of SIB1 received in step ST605 with the TAC part of the tracking area identifier (Tracking Area Identity: TAI) in the tracking area list that the communication terminal already has. The tracking area list is also referred to as the TAI list. TAI is identification information for identifying a tracking area and is composed of an MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a code number of the tracking area.

[0106] As a result of the comparison in step ST606, if the TAC received in step ST605 is the same as the TAC included in the tracking area list, the communication terminal enters the standby operation in the cell. If, after comparison, the TAC received in step ST605 is not included in the tracking area list, the communication terminal requests a change of the tracking area to perform a TAU (Tracking Area Update) to the core network (Core Network, EPC) including an MME or the like through the cell.

[0107] In the example shown in FIG. 12, an example of the operation from cell search to standby in the LTE system has been shown. In the NR system, in step ST603, in addition to the best cell, the best beam may be selected. Also, in the NR system, in step ST604, beam information, for example, a beam identifier may be acquired. Further, in the NR system, in step ST604, scheduling information of the Remaining Minimum SI (RMSI) may be acquired. In the NR system, in step ST605, it may be assumed that RMSI is received.

[0108] The device that constitutes the core network (hereinafter sometimes referred to as the "core network side device") updates the tracking area list based on the identification number (such as UE-ID) of the communication terminal sent from the communication terminal together with the TAU request signal. The core network side device transmits the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) the TAC list held by the communication terminal based on the received tracking area list. Thereafter, the communication terminal enters the standby operation in the cell.

[0109] Due to the spread of smartphones and tablet-type terminal devices, traffic by cellular wireless communication has increased explosively, and a shortage of wireless resources is a concern worldwide. In response to this, in order to improve the frequency utilization efficiency, it has been considered to reduce the cell size and promote spatial separation.

[0110] In the configuration of a conventional cell, a cell constituted by an eNB has a relatively wide coverage area. Conventionally, cells have been configured to cover a certain area by the relatively wide coverage areas of a plurality of cells constituted by a plurality of eNBs.

[0111] When the cell size is reduced, a cell constituted by an eNB has a coverage area that is narrower than that of a cell constituted by a conventional eNB. Therefore, in order to cover a certain area as in the conventional case, a larger number of small-sized eNBs are required compared to conventional eNBs.

[0112] In the following description, a cell with a relatively large coverage area, such as a cell constituted by a conventional eNB, is referred to as a "macro cell", and an eNB that constitutes a macro cell is referred to as a "macro eNB". Also, a cell with a relatively small coverage area, such as a small-sized cell, is referred to as a "small cell", and an eNB that constitutes a small cell is referred to as a "small eNB".

[0113] The macro eNB may be, for example, the "Wide Area Base Station" described in Non-Patent Document 7.

[0114] The small eNB may be, for example, a low-power node, a local area node, a hot spot, etc. Also, the small eNB may be a pico eNB constituting a picocell, a femto eNB constituting a femtocell, a HeNB, a RRH (Remote Radio Head), a RRU (Remote Radio Unit), a RRE (Remote Radio Equipment), or an RN (Relay Node). Also, the small eNB may be the "Local Area Base Station" or the "Home Base Station" described in Non-Patent Document 7.

[0115] FIG. 13 shows an example of the configuration of a cell in NR. In an NR cell, a narrow beam is formed and transmitted while changing the direction. In the example shown in FIG. 13, the base station 750 performs transmission and reception with a mobile terminal using the beam 751-1 at a certain time. At other times, the base station 750 performs transmission and reception with the mobile terminal using the beam 751-2. Similarly hereinafter, the base station 750 performs transmission and reception with the mobile terminal using one or a plurality of the beams 751-3 to 751-8. By doing so, the base station 750 constitutes a wide range of cells.

[0116] In FIG. 13, an example in which the number of beams used by the base station 750 is 8 is shown, but the number of beams may be different from 8. Also, in the example shown in FIG. 13, the number of beams used by the base station 750 simultaneously is 1, but it may be a plurality.

[0117] In 3GPP, for D2D (Device to Device) communication and V2V (Vehicle to Vehicle) communication, a side link (SL) is supported (see Non-Patent Document 1). The SL is defined by the PC5 interface.

[0118] The physical channels used for SL (see Non-Patent Document 1) will be described. The Physical Sidelink Broadcast Channel (PSBCH) carries information related to system synchronization and is transmitted from the UE.

[0119] The Physical Sidelink Discovery Channel (PSDCH) carries sidelink discovery messages from the UE.

[0120] The Physical Sidelink Control Channel (PSCCH) carries control information from the UE for sidelink communication and V2X sidelink communication.

[0121] The Physical Sidelink Shared Channel (PSSCH) carries data from the UE for sidelink communication and V2X sidelink communication.

[0122] The transport channels used for SL (see Non-Patent Document 1) will be described. The Sidelink Broadcast Channel (SL-BCH) has a predetermined transport format and is mapped to the PSBCH, which is a physical channel.

[0123] The Sidelink Discovery Channel (SL-DCH) has periodic notification transmissions in a fixed-size pre-determined format. Also, the SL-DCH supports both UE autonomous resource selection and resource allocation scheduled by the eNB. There is a risk of collision in UE autonomous resource selection, and there is no collision when the UE is allocated individual resources by the eNB. Also, the SL-DCH supports HARQ combining but does not support HARQ feedback. The SL-DCH is mapped to the physical channel PSDCH.

[0124] The Sidelink Shared Channel (SL-SCH) supports notification transmissions. The SL-SCH supports both UE autonomous resource selection and resource allocation scheduled by the eNB. There is a risk of collision in UE autonomous resource selection, and there is no collision when the UE is allocated individual resources by the eNB. Also, the SL-SCH supports HARQ combining but does not support HARQ feedback. Also, the SL-SCH supports dynamic link adaptation by changing the transmission power, modulation, and coding. The SL-SCH is mapped to the physical channel PSSCH.

[0125] The logical channels used for SL (see Non-Patent Document 1) will be described. The Sidelink Broadcast Control Channel (SBCCH) is a sidelink channel for notifying sidelink system information from one UE to other UEs. The SBCCH is mapped to the transport channel SL-BCH.

[0126] The Sidelink Traffic Channel (STCH) is a one-to-many sidelink traffic channel for transmitting user information from one UE to other UEs. The STCH is used only by 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 realized by the STCH. The STCH is mapped to the SL-SCH, which is a transport channel.

[0127] In 3GPP, it is being considered to support V2X communication in NR as well. The study of V2X communication in NR is being carried out based on the LTE system and the LTE-A system, but changes and additions have been made from the LTE system and the LTE-A system in the following aspects.

[0128] In LTE, SL communication was only broadcast. In NR, as SL communication, in addition to broadcast, support for unicast and groupcast is being considered (see Non-Patent Document 21 (TS23.287)).

[0129] In unicast communication and groupcast communication, support for HARQ feedback (Ack / Nack), CSI reporting, etc. is being considered.

[0130] In order to support unicast and groupcast in addition to broadcast in SL communication, support for PC5-S signaling is being considered (see Non-Patent Document 21 (TS23.287)). For example, PC5-S signaling is carried out to establish a link for implementing SL, that is, PC5 communication. The link is carried out in the V2X layer and is also called a layer 2 link.

[0131] In addition, in sidelink communication (SL communication), support for RRC signaling is being considered (see Non-Patent Document 21 (TS23.287)). RRC signaling in SL communication is also referred to as PC5 RRC signaling. For example, it has been proposed to notify the capabilities of a UE between UEs performing PC5 communication, or to notify settings of the AS layer for performing V2X communication using PC5 communication.

[0132] Conventionally, in sidelink communication (SL communication), sidelink communication scheduling between a transmitting UE (referred to as UE-TX) and a receiving UE (referred to as UE-RX) has been performed by a gNB serving UE-TX or by UE-TX itself. The mode in which the gNB serving UE-TX performs scheduling is called mode-1, and the mode in which UE-TX performs scheduling itself is called mode-2 (see Non-Patent Document 23).

[0133] In 3GPP, a subdivision of mode-2, which is a method for UE-TX to perform scheduling itself, has been proposed. As the subdivided methods, it has been proposed that a UE performs resource selection for sidelink communication of another UE (mode-2(b)) or that a UE performs sidelink communication scheduling of another UE (mode-2(d)) (see Non-Patent Document 23).

[0134] In the case of methods such as mode-2(b) and mode-2(d), it is UE-TX and UE-RX that actually perform data communication for V2X services, and the UE that performs resource selection or scheduling (hereinafter sometimes referred to as the scheduling UE (S-UE)) does not perform this data communication.

[0135] Therefore, the S-UE notifies the UE-TX of resource information for SL communication for V2X services. As the resource information, in the case of mode-2(b), there is a resource pool (RP: Resource Pool), and in the case of mode-2(d), there is resource information such as scheduling information used for SL communication between the UE-TX and the UE-RX. After the S-UE notifies the UE-TX of the resource information, SL communication for V2X services is performed between the UE-TX and the UE-RX.

[0136] Nothing is disclosed regarding the connection state between the S-UE and the UE-TX in such a case.

[0137] Also, in the conventional mode-1 and mode-2, there are cases where the gNB notifies the UE-TX of resource information. In that case, the Uu interface, which is the interface between the gNB and a normal UE, is used between the gNB and the UE-TX. On the other hand, the PC5 interface, which is the interface for SL communication, is used between the S-UE and the UE-TX. Therefore, the method using the conventional Uu interface cannot be applied to the PC5 interface.

[0138] When the connection state between the S-UE and the UE-TX using the PC5 interface is unknown in a configuration using the S-UE, inconsistencies may occur between the processing between the S-UE and the UE-TX and the processing between the UE-TX and the UE-RX, resulting in malfunction.

[0139] In the first embodiment, a method for solving such problems is disclosed.

[0140] Disclosed is a method for a S-UE to notify UE-TX of resource information. The S-UE notifies the UE-TX of the resource information by means of PC5-S signaling. The S-UE may include the resource information in a PC5-S message and notify it by PC5-S signaling. The S-UE and the UE-TX may establish a PC5 unicast link. The S-UE may notify the resource information by PC5-S signaling when establishing a PC5-S connection. Alternatively, the S-UE may notify the resource information by PC5-S signaling after establishing a PC5-S connection.

[0141] The default radio bearer (RB) may be used for the notification of PC5-S signaling. The default radio bearer (RB) may be used for the notification of resource information. The RB may be a SRB or a DRB.

[0142] By doing so, the S-UE can notify the UE-TX of the resource information early. The SL communication between the UE-TX and the UE-RX can be carried out early.

[0143] Another method is disclosed. The S-UE may notify the UE-TX of the resource information by means of PC5-RRC signaling. The S-UE may include the resource information in a PC5-RRC message and notify it by PC5-RRC signaling. The S-UE and the UE-TX may establish a PC5-RRC connection. The S-UE may notify the resource information by PC5-RRC signaling when establishing a PC5-RRC connection. Alternatively, the S-UE may notify the resource information by PC5-RRC signaling after establishing a PC5-RRC connection.

[0144] For the notification of PC5-RRC signaling, a default radio bearer (RB) may be used. For the notification of resource information, a default radio bearer (RB) may be used. The RB may be a SRB or a DRB. The RB in SL may sometimes be referred to as SL RB.

[0145] As the PC5-RRC message, an AS Configuration message may be used. The AS configuration between the S-UE and the UE-TX and the AS configuration between the UE-TX and the UE-RX may be provided separately. The resource information for the SL communication between the UE-TX and the UE-RX may be included in the AS configuration between the UE-TX and the UE-RX. The AS configuration between the S-UE and the UE-TX and the AS configuration between the UE-TX and the UE-RX may be notified from the S-UE to the UE-TX in separate messages respectively.

[0146] The AS configuration between the S-UE and the UE-TX and the AS configuration between the UE-TX and the UE-RX may be included in one message and notified from the S-UE to the UE-TX. Information indicating that it is for the SL communication between the UE-TX and the UE-RX may be provided and the information may be notified in association with the AS configuration between the UE-TX and the UE-RX.

[0147] By doing so, it becomes possible to notify the resource information in the RRC layer from the S-UE to the UE-TX. The handling of the resource information in the AS layer of the S-UE and the UE-TX becomes easier. For example, it may not be necessary to notify the resource information between layers in the S-UE and the UE-TX.

[0148] The S-UE may notify the UE-TX of resource information using the radio bearers (RBs) configured for communication between the S-UE and the UE-TX. The RB may be a signaling radio bearer (SRB). By using it as a signaling RB, for example, the configuration of data radio bearers (DRBs) can be made unnecessary. The RB may also be a DRB. By using it as a data RB, for example, a desired quality of service (QoS) can be configured. By doing so, flexible notification according to the communication quality can be made possible from the S-UE to the UE-TX.

[0149] A new message may be provided for notifying resource information. By differentiating it from other messages, malfunction between the S-UE and the UE-TX can be reduced.

[0150] When the sidelink (SL) communication between the UE-TX and the UE-RX is two-way communication, data of the vehicle-to-everything (V2X) service is communicated from the UE-RX to the UE-TX. Thus, the method of the present disclosure may also be appropriately applied to the communication from the UE-RX to the UE-TX. The UE-RX and the UE-TX in the communication from the UE-RX to the UE-TX may be appropriately applied as the UE-TX and the UE-RX in the communication from the UE-TX to the UE-RX of the present disclosure. For example, as a method of notifying resource information for the communication from the UE-RX to the UE-TX, the above-described method may be appropriately applied. It may be applied as the UE-RX instead of the UE-TX.

[0151] There may be a case where the S-UE to which the UE-TX is connected is different from the S-UE to which the UE-RX is connected. In such a case, in the SL communication between the UE-TX and the UE-RX, it becomes unclear which S-UE is used.

[0152] A method for solving such problems is disclosed.

[0153] First, use an S-UE that connects to a UE that starts a PC5 connection when V2X service data is first generated. For example, when V2X service data is first generated at UE-TX, UE-TX starts PC5 connection processing with UE-RX. UE-TX may notify UE-RX of the resource information obtained from the S-UE. UE-RX uses the resource information notified by UE-TX for SL communication from UE-RX to UE-TX. In this case, the resource information notified by the S-UE to which UE-RX connects is not used for communication to the UE-TX.

[0154] By doing so, UE-RX can determine the resources to be used for SL communication to UE-TX.

[0155] The S-UE may separately provide the AS setting from UE-TX to UE-RX and the AS setting from UE-RX to UE-TX. The AS setting may be included in and notified in separate messages. Alternatively, the AS setting may be included in and notified in one message. The same effect as described above can be obtained. The AS setting from UE-TX to UE-RX and the AS setting from UE-RX to UE-TX may be associated. Examples of the AS setting include the setting of SLRB, the setting of RLC bearer, LCID (Logical Channel ID), etc.

[0156] By doing so, UE-TX can recognize the SL communication from UE-RX to UE-TX corresponding to the SL communication from UE-TX to UE-RX. Therefore, a V2X service using two-way SL communication between UE-TX and UE-RX becomes possible.

[0157] Another method is disclosed. UE-RX performs SL communication from UE-RX to UE-TX using the resource information notified by the S-UE to which UE-RX connects.

[0158] By doing so, UE-RX can determine the resources to be used for SL communication to UE-TX.

[0159] Even when using the resource information set by the S-UE to which each UE is connected, the AS settings from UE-TX to UE-RX and the AS settings from UE-RX to UE-TX may be associated. Examples of AS settings include settings of SLRB, settings of RLC bearers, LCID (Logical Channel ID), etc. UE-TX notifies UE-RX of the AS settings from UE-TX to UE-RX. Identifiers may be provided for some or all of the information within the AS settings. UE-RX assigns the identifier notified from UE-TX to the same information within the AS settings from UE-RX to UE-TX.

[0160] By doing so, UE-TX can recognize the SL communication from UE-RX corresponding to the SL communication from UE-TX to UE-RX. Therefore, a V2X service using two-way SL communication between UE-TX and UE-RX becomes possible.

[0161] UE-RX may assign an identifier different from the identifier notified from UE-TX to the same information within the AS settings from UE-RX to UE-TX. UE-RX associates and notifies UE-TX of the identifier assigned to the information within the AS settings from UE-TX to UE-RX and the identifier assigned to the information within the AS settings from UE-RX to UE-TX.

[0162] By doing so, UE-TX can recognize the SL communication from UE-RX corresponding to the SL communication from UE-TX to UE-RX. Therefore, a V2X service using two-way SL communication between UE-TX and UE-RX becomes possible.

[0163] Disclose the connection state between the S-UE and the UE-TX after the notification of resource information from the S-UE to the UE-TX. Even after the notification of resource information from the S-UE to the UE-TX, maintain the connection between the S-UE and the UE-TX. The connection between UEs over PC5 may be referred to as a PC5 connection. Maintain a PC5-S connection at the connection level. It may also be possible to maintain a PC5-RRC connection. When maintaining a PC5-RRC connection, it may be that the S-UE and the UE-TX do not release the AS configuration.

[0164] The AS configuration that is not released when maintaining a PC5-RRC connection may be, for example, the AS configuration used by the S-UE for SL communication between the UE-TX and the UE-RX. When only the notification of resource information is performed between the S-UE and the UE-TX, the AS configuration becomes the AS configuration used for the notification of resource information. When other SL communication is performed between the S-UE and the UE-TX in addition to the notification of resource information, it may be that the AS configuration does not include the AS configuration used for other SL communication.

[0165] The AS configuration may be an RB configuration. The RB configuration may be, for example, an SRB configuration, a DRB configuration, etc. The configuration of the RB may be, for example, the configuration of each protocol stack. The protocol stack may be, for example, SDAP, PDCP, RLC, MAC, PHY, etc.

[0166] By doing so, even after the notification of resource information from the S-UE to the UE-TX, the connection between the S-UE and the UE-TX can be maintained. For example, when the S-UE changes the resources for the UE-TX and notifies the UE-TX of the changed resource information, the connection process becomes unnecessary, so early notification becomes possible. The resources for SL communication between the UE-TX and the UE-RX can be changed with low latency.

[0167] PC5 connection status information indicating the connection state between UEs may be provided. UE-TX may notify S-UE of the connection state between UE-TX and UE-RX using the PC5 connection status information. The PC5 connection status information may be, for example, information indicating whether a PC5 unicast link is established. The PC5 connection status information may be information indicating whether a layer 2 link is established. The PC5 connection status information may be information indicating whether a PC5-S connection is established.

[0168] Also, the PC5 connection status information may be information indicating whether a PC5-RRC connection is established. The PC5 connection status information may be information indicating whether the AS configuration is maintained. Also, the PC5 connection status information may be information indicating RLF. Also, the PC5 connection status information may be information indicating whether a synchronization signal and / or a synchronization channel in the SL from the opposing UE is being received. The PC5 connection status information may be information indicating whether synchronization is achieved by receiving a synchronization signal and / or a synchronization channel in the SL from the opposing UE. The SS (Synchronization Signal) of the SL may be used as the synchronization signal. The SBCCH may be used as the synchronization channel.

[0169] The PC5 connection status information may be information combining the aforementioned information. For example, the PC5 connection status information may include information indicating whether a PC5-S connection is established and information indicating whether a PC5-RRC connection is established.

[0170] In this way, by providing information indicating the connection state between UEs, the connection state between UEs performing SL communication can be notified to other UEs. By using the PC5 connection status information, UE-TX performing SL communication with UE-RX can notify S-UE of the connection state between UE-TX and UE-RX.

[0171] The PC5 connection status information may include information indicating which PC5 connection it is. When multiple PC5 connections are made, it becomes possible to identify the information indicating the status of which PC5 connection.

[0172] The PC5 connection status information may be notified to the gNB or the CN node. For example, the S-UE may notify the gNB of the PC5 connection status between the S-UE and the UE-TX. For example, the UE-TX may notify the gNB of the PC5 connection status information between the UE-TX and the UE-RX via the S-UE. The gNB or the CN node can recognize the PC5 connection status between the UEs performing SL communication.

[0173] Even after the S-UE notifies the UE-TX of the resource information for SL communication between the UE-TX and the UE-RX, if the connection between the S-UE and the UE-TX is to be maintained, the problem is when to release the connection. The conditions for releasing the connection are disclosed.

[0174] When the V2X service between the UE-TX and the UE-RX ends, the connection between the S-UE and the UE-TX is released. It may be assumed that the connection between the S-UE and the UE-TX is released when all the V2X services being performed by the UE-TX end. By doing so, the connection between the S-UE and the UE-TX is maintained as long as the V2X service does not end, so that SL communication between the S-UE and the UE-TX can be performed as needed.

[0175] When the PC5 connection for SL communication between UE-TX and UE-RX is released, the connection between S-UE and UE-TX may be released. As the PC5 connection, there is a PC5-RRC connection and / or a PC5-S connection. For example, when the PC5-RRC connection and the PC5-S connection for SL communication between UE-TX and UE-RX are released, the connection between S-UE and UE-TX is released. When all the PC5 connections implemented by UE-TX are released, the connection between S-UE and UE-TX may be released. When the PC5 connection between UE-TX and UE-RX is released, the SL communication between UE-TX and UE-RX actually becomes impossible. By releasing the connection between S-UE and UE-TX when the SL communication is not required, the power consumption of S-UE and UE-TX can be reduced. Also, the resources used for the connection can be released, and the resource utilization efficiency can be improved.

[0176] When a Radio Link Failure (RLF) occurs in the SL communication between UE-TX and UE-RX, the connection between S-UE and UE-TX may be released. When all the SL communications implemented by UE-TX result in RLF and are not reconnected, the connection between S-UE and UE-TX may be released.

[0177] After RLF occurs in the SL communication between UE-TX and UE-RX and no reconnection occurs within a predetermined period, the connection between S-UE and UE-TX may be released. When all the SL communications implemented by UE-TX result in RLF and no reconnection occurs within a predetermined period, the connection between S-UE and UE-TX may be released. The predetermined period may be determined statically by a standard or the like. Alternatively, the predetermined period may be set by any one of the CN-side node, gNB, S-UE, UE-TX, UE-RX and notified to some or all of the other aforementioned nodes. The other nodes can recognize the predetermined period.

[0178] The following three methods have been proposed as methods for detecting RLF of SL (see Non-Patent Document 25).

[0179] (1) When the number of retransmissions in the RLC of the SL reaches the predetermined maximum number, it is determined as RLF.

[0180] (2) When the Nack of the HARQ of the SL continuously reaches the predetermined number of times, it is determined as RLF.

[0181] (3) When the decoding of the PSCCH of the SL fails a predetermined number of times or within a predetermined time, it is determined as RLF.

[0182] It is advisable to apply the above-mentioned method as the RLF detection method. UE-TX may perform the detection of RLF. When RLF occurs between UE-TX and UE-RX, similar to the above-mentioned method, the SL communication between UE-TX and UE-RX becomes impossible. When the SL communication is not required, by releasing the connection between S-UE and UE-TX, the power consumption of S-UE and UE-TX can be reduced, and the resources used for the connection can be released, thereby improving the resource utilization efficiency.

[0183] Among the RLF detection methods, it may be statically determined by standards or the like which method to implement. Alternatively, the RLF detection method may be settable. The node for determining the RLF detection method may be any one of the CN-side node, gNB, S-UE, UE-TX, and UE-RX. The node that determines the RLF detection method may notify the determined RLF detection method to some or all of the other nodes mentioned above. By doing so, for example, the RLF detection method can be set according to the communication quality status in each direction of the SL between UE-TX and UE-RX.

[0184] Information on the RLF detection method supported by the UE may be provided. This information may be included in the UE capabilities. The UE may notify the node that determines the RLF detection method of the information on the RLF detection method supported by it. By doing so, the node that determines the RLF detection method can recognize the RLF detection method supported by the UE and can determine the RLF detection method in consideration of this information.

[0185] In SL communication, beams may be used. To support beams in SL communication, SSB (Synchronization Signal Block) for each beam may be configured with resources for SL communication. UE-TX transmits SS with the SSB of the beam for SL communication. UE-TX may also transmit PSBCH together. UE-RX performs a reception operation during a predetermined period when the SSB is transmitted and receives the SSB transmitted from UE-TX. This makes it possible to identify the beam transmitted by UE-TX.

[0186] UE-RX may receive the SL RS (Reference Signal) transmitted from UE-TX for each beam and measure the reception quality for each beam. Also, CSI-RS corresponding to the beam may be provided and transmitted from UE-TX. UE-RX may receive the CSI-RS transmitted from UE-TX for each beam and measure the reception quality for each beam.

[0187] As a method for detecting a beam failure in SL communication, the reception results of SSB and / or SL RS for each beam and / or CSI-RS may be used. For example, when the reception of SSB fails a predetermined number of times or for a predetermined time, it is determined as RLF. By doing so, when SSB, SL RS, and CSI-RS are configured for each beam, it becomes possible to detect RLF by receiving those signals.

[0188] To detect a beam failure by UE-TX, SSB, SL RS, and CSI-RS in the beam transmitted from UE-RX to UE-TX may be used. By doing so, UE-TX can detect the beam failure of SL communication between UE-TX and UE-RX. The connection between S-UE and UE-TX can be released.

[0189] UE-TX discloses other methods for detecting beam failures. When UE-RX detects a beam failure in the beam transmitted from UE-RX to UE-TX, UE-RX may notify UE-TX of the detection of the beam failure using the beam transmitted from UE-RX to UE-TX. For example, this is effective when the communication situation is different between the beam transmitted from UE-TX to UE-RX and the beam transmitted from UE-RX to UE-TX.

[0190] When a beam failure occurs in the SL communication between UE-TX and UE-RX, the connection between S-UE and UE-TX may be released. When all SL communications performed by UE-TX become beam failures, the connection between S-UE and UE-TX may be released.

[0191] After a beam failure occurs in the SL communication between UE-TX and UE-RX and beam recovery is not performed for a predetermined period, the connection between S-UE and UE-TX may be released. When all SL communications performed by UE-TX become beam failures and beam recovery has not been performed for a predetermined period, the connection between S-UE and UE-TX may be released. The predetermined period may be determined statically by a standard or the like. Alternatively, the predetermined period may be set by any one of the CN-side node, gNB, S-UE, UE-TX, UE-RX and notified to some or all of the other foregoing nodes. The other nodes can recognize the predetermined period.

[0192] UE-TX may configure the SSB, SL RS, and CSI-RS of a plurality of beams for UE-RX. When a beam failure occurs in one beam during SL communication, UE-RX may select a beam for recovery from among the plurality of configured beams. For example, a part or all of the signals of the plurality of configured beams are received to derive the reception quality of each beam. UE-RX selects the beam with the highest reception quality.

[0193] UE-RX notifies the selected beam to UE-TX. UE-RX may notify UE-TX of information requesting SL communication on the selected beam. Such information may include information identifying the beam, for example, a beam identifier. By doing so, UE-TX can recognize the beam that UE-RX can receive. UE-TX can use the beam that UE-RX can receive for SL communication with UE-RX. UE-RX can perform SL communication with UE-TX using the beam. Beam recovery for SL communication between UE-TX and UE-RX becomes possible.

[0194] PC5-RRC signaling or MAC signaling may be used for UE-RX to notify the selected beam to UE-TX. Since HARQ retransmission is used in these signalings, a high reception probability can be obtained. As another method, the information of the selected beam may be included in the SCI for notification. It can be notified using the PSCCH, enabling early notification. Early beam recovery becomes possible.

[0195] A specific signal may be provided for UE-RX to notify the selected beam to UE-TX. A specific signal corresponding to each beam may be provided. Alternatively, the parameters constituting the specific signal may be associated with each beam. Examples of the parameters constituting the specific signal include frequency resources, time resources, sequences, or combinations thereof. These correspondence relationships may be statically determined in advance by standards or the like. Alternatively, these correspondence relationships may be notified in advance from UE-TX to UE-RX. They may be notified in association with the settings of multiple beams. Both UE-TX and UE-RX can recognize the correspondence relationships.

[0196] For example, when the timing for transmitting a specific signal is associated with each beam, UE-RX maps the specific signal on the time resource corresponding to the beam selected for recovery and notifies UE-TX. UE-TX can recognize the beam selected by UE-RX for recovery from the time resource at which the specific signal is received. SL communication using the beam can be performed between UE-TX and UE-RX.

[0197] As a method for detecting RLF in SL communication, when a beam failure is detected, it may be determined that RLF has been detected. As a method for detecting RLF in SL communication, after a beam failure occurs in SL communication and beam recovery is not performed, it may be determined that RLF has been detected. When the beam recovery is not performed for a predetermined period, it may be determined that RLF has been detected. When RLF occurs in the SL communication between UE-TX and UE-RX, the connection between S-UE and UE-TX may be released. In this way, by using beam failure as one of the methods for detecting RLF, the processing can be facilitated.

[0198] Another method for releasing the connection between S-UE and UE-TX is disclosed.

[0199] When RLF occurs in the SL communication between S-UE and UE-TX, the connection between S-UE and UE-TX may be released. When all SL communications being performed between S-UE and UE-TX result in RLF and no reconnection has occurred, the connection between S-UE and UE-TX may be released. When RLF occurs in the SL communication between S-UE and UE-TX, the SL communication between S-UE and UE-TX becomes impossible. By releasing the connection between S-UE and UE-TX when the SL communication is unnecessary, power consumption of S-UE and UE-TX can be reduced. Also, the resources used for the connection can be released, improving resource utilization efficiency.

[0200] In the case where a beam failure occurs in the SL communication between the S-UE and the UE-TX, it may be possible to release the connection between the S-UE and the UE-TX. If the SL communication being performed by the S-UE and the UE-TX becomes a beam failure and beam recovery is not performed, it may be possible to release the connection between the S-UE and the UE-TX. When a beam failure occurs in the SL communication between the S-UE and the UE-TX, the SL communication between the S-UE and the UE-TX becomes impossible. By releasing the connection between the S-UE and the UE-TX when the SL communication is unnecessary, power consumption of the S-UE and the UE-TX can be reduced. Also, the resources used for the connection can be released, and the resource utilization efficiency can be improved.

[0201] As the method for detecting RLF in the SL communication described above, when detecting a beam failure, a method of determining that RLF has been detected may be used. When RLF occurs in the SL communication between the S-UE and the UE-TX, it may be possible to release the connection between the S-UE and the UE-TX. In this way, by using a beam failure as one of the methods for detecting RLF, the processing can be facilitated.

[0202] FIG. 14 and FIG. 15 are sequence diagrams showing an example of a method for maintaining the connection between the S-UE and the UE-TX even after the S-UE notifies the UE-TX of the SL communication resource information in Embodiment 1. FIGS. 14 and 15 are connected at the position of the boundary line BL1415. The S-UE notifies the UE-TX of the SL communication resource information between the UE-TX and the UE-RX. The UE-TX performs SL communication using the resource information with the UE-RX.

[0203] As an example, a case where a V2X service is performed by UE-TX using unicast communication of SL between UE-TX and UE-RX is shown. In step ST1401, UE-TX establishes a PC5-S connection with S-UE. To establish a PC5-S connection between UE-TX and S-UE, discovery processing may be performed between S-UE and UE-TX. For example, S-UE may notify a discovery announcement message for announcement. S-UE may include information indicating that it has an S-UE function in the announcement message. By receiving the announcement message, UE-TX can detect S-UE.

[0204] Alternatively, UE-TX may notify S-UE of a discovery solicitation message for solicitation. UE-TX may include information indicating that it solicits a UE having an S-UE function in the solicitation message. When S-UE having an S-UE function receives the solicitation message, it notifies a response message to UE-TX. S-UE may include information indicating that it has an S-UE function in the response message. By doing so, UE-TX can detect S-UE.

[0205] In steps ST1429, ST1402, and ST1403, S-UE and UE-TX notify each other of their UE capabilities. In step ST1402, UE-TX may include a notification of UE-TX's UE-capability and a UE-capability request to S-UE in the same message and transmit the message to S-UE. Signaling can be reduced. These notifications are notified by PC5-RRC signaling. Through these processes, S-UE and UE-TX can recognize each other's UE capabilities.

[0206] In steps ST1404, ST1405, and ST1406, the S-UE and UE-TX notify each other of the AS settings. In step ST1402, the UE-TX may include the AS setting completion notification and the AS settings for the S-UE in the same message and send the message to the S-UE, which can reduce signaling. These notifications are sent via PC5-RRC signaling. Through these processes, the S-UE and UE-TX can perform AS settings for each other.

[0207] In step ST1407, the UE-TX notifies the S-UE of the resource request for SL communication to be performed with the UE-RX. The UE-TX may notify its own UE-TX identifier, the UE-RX identifier for SL communication, and the V2X service information for SL communication together with or included in the resource request. The V2X service information may be, for example, an identifier for specifying the service or the QoS required for the V2X service. The S-UE that receives the SL communication resource request from the UE-TX sets the resources to be used for the SL communication between the UE-TX and the UE-RX. For example, the S-UE may select a resource pool or set scheduling information such as resource allocation.

[0208] In step ST1408, the S-UE notifies the UE-TX of the resource information. After notifying the resource information, the S-UE maintains the PC5 connection with the UE-TX.

[0209] The UE-TX that receives the resource information uses the resource information to establish a PC5-S connection with the UE-RX in step ST1409. Similar to the above, discovery processing may be performed.

[0210] The UE-TX that has established a PC5-S connection with the UE-RX may notify the S-UE of the PC5 connection status information in step ST1410. Here, the PC5 connection status information may include information indicating that a PC5-S connection has been established between the UE-TX and the UE-RX. The S-UE that has received the PC5 connection status information maintains the PC5 connection between the S-UE and the UE-TX.

[0211] From step ST1411 to step ST1413, the UE-TX and the UE-RX notify each other of their UE capabilities. From step ST1414 to step ST1416, the UE-TX and the UE-RX notify each other of the AS settings, and each UE performs the AS settings. By doing so, it becomes possible to implement a V2X service using SL communication between the UE-TX and the UE-RX. In step ST1417, data communication of the V2X service is performed between the UE-TX and the UE-RX.

[0212] When the V2X service between the UE-TX and the UE-RX ends, the UE-TX notifies the UE-RX of a release request for the AS settings for the V2X service in step ST1418. The UE-RX that has received the release request for the AS settings may release the PC5-RRC connection in step ST1419. The UE-RX releases the settings required for the PC5-RRC connection. The UE-RX that has released the PC5-RRX connection may release the PC5-S connection in step ST1420. The UE-RX releases the settings required for the PC5-S connection.

[0213] The UE-TX that has notified the UE-RX of the AS settings release request may release the PC5-RRC connection in step ST1421. The UE-TX releases the settings required for the PC5-RRC connection. The UE-TX that has released the PC5-RRC connection may release the PC5-S connection in step ST1422. The UE-TX releases the settings required for the PC5-S connection.

[0214] UE-TX, which has released the PC5-S connection with UE-RX, notifies the S-UE of the PC5 connection status information in step ST1423. Here, it is advisable to include in the PC5 connection status information the information indicating that the PC5-S connection between UE-TX and UE-RX has been released. The S-UE that has received the PC5 connection status information can recognize whether the PC5-S connection between UE-TX and UE-RX has been released. The S-UE that has recognized that the PC5-S connection between UE-TX and UE-RX has been released decides to release the PC5 connection between the S-UE and UE-TX.

[0215] In step ST1424, the S-UE notifies UE-TX of a request to release the AS configuration. UE-TX that has received the request to release the AS configuration may release the PC5-RRC connection with the S-UE in step ST1425. UE-TX releases the settings required for the PC5-RRC connection with the S-UE. UE-TX, which has released the PC5-RRC connection with the S-UE, may release the PC5-S connection with the S-UE in step ST1426. UE-TX releases the settings required for the PC5-S connection with the S-UE.

[0216] The S-UE that has notified UE-TX of the request to release the AS configuration may release the PC5-RRC connection in step ST1427. The S-UE releases the settings required for the PC5-RRC connection. The S-UE, which has released the PC5-RRC connection, may release the PC5-S connection in step ST1428. The S-UE releases the settings required for the PC5-S connection.

[0217] By doing so, even after the S-UE notifies the UE-TX of the resource information for SL communication between the UE-TX and the UE-RX, the connection between the S-UE and the UE-TX can be maintained. When the S-UE notifies the UE-TX of the resource information next time, the connection process between the S-UE and the UE-TX becomes unnecessary, enabling early notification. Also, when the SL communication between the UE-TX and the UE-RX becomes unnecessary, the connection between the S-UE and the UE-TX can be released. Power consumption of the S-UE and the UE-TX can be reduced. Also, the resources used for the connection can be released, improving resource utilization efficiency.

[0218] If the resources for SL communication between the UE-TX and the UE-RX are congested, the SL communication will be delayed. By using the method described above, even after the S-UE notifies the UE-TX of the resource information, the connection between the S-UE and the UE-TX can be maintained, enabling the S-UE to notify the UE-TX of the change in the resources for SL communication between the UE-TX and the UE-RX at an early stage. Therefore, the resources for SL communication between the UE-TX and the UE-RX can be changed early, reducing the occurrence of delay in the SL communication.

[0219] The UE-TX may notify the S-UE of a resource setting request or a resource change request for SL communication between the UE-TX and the UE-RX. The UE-TX may notify the S-UE of a scheduling request for SL communication between the UE-TX and the UE-RX.

[0220] The UE-TX may notify the gNB via the S-UE of a resource setting request or a resource change request for SL communication between the UE-TX and the UE-RX. The UE-TX may notify the gNB via the S-UE of a scheduling request for SL communication between the UE-TX and the UE-RX. These notifications may be used, for example, when the node for resource setting is the gNB.

[0221] UE-TX may notify the CN node via the S-UE and the gNB of a resource setting request or a resource change request for SL communication between the UE-TX and the UE-RX. UE-TX may notify the CN node via the S-UE and the gNB of a scheduling request for SL communication between the UE-TX and the UE-RX. These notifications may be used, for example, when the node that sets the resources is the CN node.

[0222] For example, when UE-TX schedules SL communication with UE-RX using resource information and fails to select the scheduling resource due to congestion with other UEs performing SL communication, a change request is notified. The resource congestion situation may be notified together with or included in the resource change request. By doing so, situations where SL communication becomes impossible or delayed due to congestion can be reduced.

[0223] For example, a resource change request may be notified according to the location of UE-TX or the area where UE-TX is located. Location information or area information may be notified together with or included in the resource change request. This is effective when resources used for each area are determined.

[0224] As described above, even after the S-UE notifies the UE-TX of the resource information, by maintaining the connection between the S-UE and the UE-TX, the resource setting / change request and the scheduling request can be notified earlier. Therefore, it becomes possible to set or change the SL communication resources and scheduling between the UE-TX and the UE-RX earlier, and the occurrence of delay in the SL communication can be reduced.

[0225] Also, by setting the condition for releasing the connection between the S-UE and the UE-TX, it becomes possible to prevent the connection between the S-UE and the UE-TX from being continuously maintained unnecessarily. Thereby, power consumption of the S-UE and the UE-TX can be reduced, and resource utilization efficiency can be improved.

[0226] After notifying the resource information from the S-UE to the UE-TX, the method of maintaining the connection between the S-UE and the UE-TX has been described above. Here, another method is disclosed. After notifying the resource information from the S-UE to the UE-TX, release the connection between the S-UE and the UE-TX. The level at which the connection is released may be the level at which the PC5-S connection is released. In addition, the PC5-RRC connection may also be released. By releasing the PC5-RRC connection, the AS configuration between the S-UE and the UE-TX may be released. When SL communication is required between the S-UE and the UE-TX, perform the PC5-S connection and the PC5-RRC connection again.

[0227] The level at which the connection is released may be the level at which the PC5-S connection is maintained and the PC5-RRC connection is released. By releasing the PC5-RRC connection, the AS configuration between the S-UE and the UE-TX may be released. When SL communication is required between the S-UE and the UE-TX, perform the PC5-RRC connection again. SL communication between the S-UE and the UE-TX can be achieved earlier.

[0228] The reconnection when SL communication is required between the S-UE and the UE-TX may be requested from the UE-TX. The UE-TX may initiate the reconnection between the S-UE and the UE-TX. For example, the UE-TX may initiate the discovery process to perform PC5 unicast communication with the S-UE. For example, the UE-TX may send a solicitation message for inviting the S-UE to initiate the discovery process. The UE-TX may notify the S-UE of the resource setting / modification request or scheduling request for SL communication between the UE-TX and the UE-RX during or after the reconnection with the S-UE.

[0229] The release of the connection between the S-UE and the UE-TX may be initiated by the UE-TX. For example, when the UE-TX receives resource information for SL communication between the S-UE and the UE-RX, the UE-TX may initiate the release of the connection between the S-UE and the UE-TX. As another method, for example, when the UE-TX establishes a PC5 connection with the UE-RX, the UE-TX may initiate the release of the connection between the S-UE and the UE-TX. By doing so, the UE-TX can release the connection with the S-UE after being able to perform SL communication with the UE-RX.

[0230] The release of the connection between the S-UE and the UE-TX may be initiated by the S-UE. The UE-TX may notify the S-UE of the PC5 connection status information between the UE-TX and the UE-RX. The S-UE may determine the release of the connection between the S-UE and the UE-TX using the PC5 connection status information between the UE-TX and the UE-RX notified by the UE-TX. For example, when the UE-TX transmits the PC5 connection status information (connection established) between the UE-TX and the UE-RX to the S-UE and the S-UE receives the information, the S-UE releases the connection with the UE-TX. By doing so, the S-UE can recognize the status of the PC5 connection between the UE-TX and the UE-RX, and the S-UE can initiate the release of the connection between the S-UE and the UE-TX.

[0231] Figures 16 and 17 are sequence diagrams showing examples of methods for releasing the connection between the S-UE and the UE-TX after the S-UE notifies the UE-TX of resource information for SL communication in Embodiment 1. Figures 16 and 17 are connected at the position of the boundary line BL1617. In Figures 16 and 17, the same step numbers are assigned to the steps common to Figures 14 and 15, and the common descriptions are omitted.

[0232] In step ST1407, UE-TX notifies S-UE of a resource request for SL communication between UE-TX and UE-RX. In step ST1408, S-UE notifies UE-TX of resource information. S-UE may release the PC5 connection with UE-TX immediately after notifying the resource information, but here, another method is exemplified.

[0233] UE-TX that has received the resource information uses the resource information to establish a PC5-S connection with UE-RX in step ST1409.

[0234] UE-TX that has established a PC5-S connection with UE-RX notifies S-UE of PC5 connection status information in step ST1410. Here, it is preferable to include information indicating that a PC5-S connection has been established between UE-TX and UE-RX in the PC5 connection status information. S-UE that has received the PC5 connection status information decides to release the PC5 connection between S-UE and UE-TX. Here, the release (connection) level of the PC5 connection is set to the level at which the AS configuration is released. It is also possible not to release the PC5-S connection.

[0235] In step ST1501, S-UE notifies UE-TX of a request to release the AS configuration. S-UE may include information indicating the release (connection) level in the request and notify it. Here, S-UE includes information requesting only the release of the AS configuration in the request and notifies it. In step ST1502, UE-TX releases the AS configuration for SL communication with S-UE. Also, in step ST1503, S-UE releases the AS configuration for SL communication with UE-TX. Thereby, when V2X service data communication using SL communication is being performed between UE-TX and UE-RX in step ST1417, the AS configuration between S-UE and UE-TX can be set to a released state.

[0236] In step ST1504, the S-UE determines a change in the resource information for SL communication between the UE-TX and the UE-RX. For example, the S-UE adjusts so that the resources used for SL communication with other UEs do not conflict with the resources for SL communication between the UE-TX and the UE-RX, and determines a change in the resources. For example, the gNB may notify the S-UE of a change in the resources. The S-UE may determine a change in the resources using the change in the resource information received from the gNB. From step ST1505 to step ST1507, the S-UE and the UE-TX notify each other of the AS settings and perform the AS settings. In step ST1508, the S-UE notifies the UE-TX of the changed resource information.

[0237] If the UE-TX changes the AS settings, it may notify the UE-RX of the changed AS settings. This notification may be applied, for example, when the UE-TX changes the AS settings using the changed resource information.

[0238] The UE-TX may notify the UE-RX of the changed resource information. If the UE-RX changes the AS settings, it may notify the UE-TX of the changed AS settings. For example, if the UE-RX receives using the changed resource information, it may notify the UE-TX of a change in the AS settings.

[0239] In step ST1509, the UE-TX reconfigures the resources for SL communication with the UE-RX using the resource information received from the S-UE. In step ST1510, the UE-TX performs communication of V2X service data using SL communication with the UE-RX using the reconfigured resources.

[0240] After notifying the UE-TX of the resource information, the S-UE determines to release the PC5 connection between the S-UE and the UE-TX. The processing from step ST1501 to step ST1503 may be performed.

[0241] When UE-TX receives the resource information changed from S-UE, it may notify the S-UE of the PC5 connection status information. Here, since the PC5 connection is not released due to the resource change, the PC5 connection status information may include information indicating that the PC5-S connection is established between UE-TX and UE-RX. When the S-UE receives the PC connection status information from UE-TX and recognizes that the PC5-S connection is established between UE-TX and UE-RX, the S-UE may decide to release the PC5 connection between the S-UE and UE-TX. The processing from step ST1501 to step ST1503 may be performed.

[0242] In this way, by adopting a method of releasing the connection between the S-UE and UE-TX after notifying the UE-TX of the resource information from the S-UE, the resources used for the SL communication between the S-UE and UE-TX can be released. Therefore, the utilization efficiency of the resources can be further improved.

[0243] A method of releasing the connection between the S-UE and UE-TX after notifying the UE-TX of the resource information from the S-UE has been described above. Here, another method is disclosed. After notifying the UE-TX of the resource information from the S-UE, the connection state between the S-UE and UE-TX and the connection state between UE-TX and UE-RX are made independent. It is also possible not to interlock the two connection states. The level of connection or the level of releasing the connection may appropriately apply the above-mentioned method.

[0244] UE-TX may notify the S-UE of the PC5 connection status information between UE-TX and UE-RX. When the connection state between UE-TX and UE-RX is changed, UE-TX may notify the PC5 connection status information. UE-TX may notify UE-RX of the PC5 connection status information between the S-UE and UE-TX. When the connection state between the S-UE and UE-TX is changed, it is also possible to notify the PC5 connection status information.

[0245] By doing so, the S-UE can recognize the connection state between the UE-TX and the UE-RX. Alternatively, the UE-RX can recognize the connection state between the S-UE and the UE-TX. For example, when the S-UE starts the connection establishment process or release process between the S-UE and the UE-TX, the S-UE can use the PC5 connection state information between the UE-TX and the UE-RX notified by the UE-TX to determine whether to start the connection establishment process or release process between the S-UE and the UE-TX. Thereby, it is possible to prevent inconsistencies from occurring between the connection state between the S-UE and the UE-TX and the connection state between the UE-TX and the UE-RX.

[0246] As disclosed in the first embodiment, by clarifying the connection state between the S-UE and the UE-TX using the PC5 interface after notifying the UE-TX of the resource information from the S-UE, it is possible to reduce malfunctions in the processing between the S-UE and the UE-TX and the processing between the UE-TX and the UE-RX. Stable SL communication can be executed in the configuration using the S-UE.

[0247] Modification Example 1 of Embodiment 1. In the configuration using the S-UE, due to the movement of each of the S-UE, UE-TX, and UE-RX and changes in the radio wave propagation environment, a situation may occur where RLF occurs only in the connection between the S-UE and the UE-TX, or the connection between the S-UE and the UE-TX is only released. Alternatively, a situation may occur where RLF occurs only in the connection between the UE-TX and the UE-RX, or the connection between the UE-TX and the UE-RX is only released. In such a situation, when the relationship between the connection state between the S-UE and the UE-TX and the connection state between the UE-TX and the UE-RX is unclear, inconsistencies may occur in the processing between the S-UE and the UE-TX and the processing between the UE-TX and the UE-RX, resulting in malfunctions.

[0248] In this first modification example of Embodiment 1, a method for solving such problems is disclosed.

[0249] Interlock the PC5 connection between the S-UE and the UE-TX and the PC5 connection between the UE-TX and the UE-RX. The PC5 connection state between the UE-TX and the UE-RX is determined according to the PC5 connection state between the S-UE and the UE-TX. For example, when the PC5 connection between the S-UE and the UE-TX is released, the PC5 connection between the UE-TX and the UE-RX is released. When the PC5 connection between the S-UE and the UE-TX is released, all PC5 connections between the UE-TX and the UE-RX may be released.

[0250] In the PC5 connection, the method disclosed in Embodiment 1 may be appropriately applied to the level of connection or the level of releasing the connection.

[0251] Instead of the release of the PC5 connection between the S-UE and the UE-TX, the above-described method may be applied when the PC5 connection between the S-UE and the UE-TX is disconnected. Instead of the release of the PC5 connection between the S-UE and the UE-TX, the above-described method may be applied when RLF is detected in the PC5 connection between the S-UE and the UE-TX. These combinations may also be possible.

[0252] FIG. 18 is a sequence diagram showing an example of a method for releasing the PC5 connection between the UE-TX and the UE-RX when the PC5 connection between the S-UE and the UE-TX is released in Modification 1 of Embodiment 1. In step ST1601, the PC5 connection is established between the S-UE and the UE-TX, and in step ST1602, the PC5 connection is also established between the UE-TX and the UE-RX. In step ST1601, the resource information for SL communication between the UE-TX and the UE-RX is notified from the S-UE to the UE-TX. Also, in step ST1602, the V2X service data using SL communication is communicated between the UE-TX and the UE-RX. After the resource information is notified from the S-UE to the UE-TX in step ST1601, the connection between the S-UE and the UE-TX is maintained.

[0253] Disclosed is the case where the S-UE releases the connection with the UE-TX. In step ST1603, the S-UE requests the UE-TX to release the PC5 connection. A disconnect request message may be used. In step ST1604, the UE-TX notifies the S-UE of a response to the release request. A disconnect response message may be used. Thereby, the PC5-S connection between the S-UE and the UE-TX is released. The PC5-S connection and the PC5-RRC connection between the S-UE and the UE-TX may be released. The AS configuration between the S-UE and the UE-TX may be released.

[0254] The PC5 connection release request may include information indicating which PC5 connection it is. In the case where multiple PC5 connections are made, the PC5 connection for which the release is requested can be specified.

[0255] The UE-TX that has released the PC5 connection with the S-UE releases the PC5 connection with the UE-RX. In step ST1605, the UE-TX requests the UE-RX to release the PC5 connection. In step ST1606, the UE-RX notifies the UE-TX of a response to the release request. Thereby, the PC5-S connection between the UE-TX and the UE-RX is released. The PC5-S connection and the PC5-RRC connection between the UE-TX and the UE-RX may be released.

[0256] The response to the release request in step ST1604 may be notified after the PC5 connection between the UE-TX and the UE-RX is released. After the UE-TX confirms in step ST1606 that the PC5 connection with the UE-RX has been released, the UE-TX may notify the S-UE of the response to the release request. The S-UE can recognize that the release of the PC5 connection between the UE-TX and the UE-RX has been executed.

[0257] By doing so, it becomes possible to interlock the PC5 connection state between the S-UE and the UE-TX and the PC5 connection state between the UE-TX and the UE-RX. When the PC5 connection between the S-UE and the UE-TX is released, the PC5 connection between the UE-TX and the UE-RX can be released.

[0258] FIG. 19 is a sequence diagram showing an example of a method for releasing the PC5 connection between the UE-TX and the UE-RX when RLF is detected in the PC5 connection between the S-UE and the UE-TX in Modification 1 of Embodiment 1. In FIG. 19, the same step numbers are assigned to the steps common to FIG. 18, and the common descriptions are omitted. In step ST1703, the UE-TX detects that RLF has occurred in the PC5 connection between the S-UE and the UE-TX. Recognizing that the PC5 connection has become impossible due to the detection of RLF, the UE-TX releases the PC5 connection with the UE-RX in steps ST1605 and ST1606.

[0259] By doing so, even when RLF occurs in the PC5 connection between the S-UE and the UE-TX, the PC5 connection between the UE-TX and the UE-RX can be released.

[0260] Another method is disclosed. The PC5 connection between the UE-TX and the UE-RX is interlocked with the PC5 connection between the S-UE and the UE-TX. The PC5 connection state between the S-UE and the UE-TX is determined according to the PC5 connection state between the UE-TX and the UE-RX. For example, when the PC5 connection between the UE-TX and the UE-RX is released, the PC5 connection between the S-UE and the UE-TX is released. When all the PC5 connections between the UE-TX and the UE-RX are released, the PC5 connection between the S-UE and the UE-TX may be released.

[0261] In the PC5 connection, the method disclosed in Embodiment 1 may be appropriately applied to the connection level or the release level of the connection.

[0262] When the PC5 connection between UE-TX and UE-RX is disconnected rather than released, the aforementioned method may be applied. When RLF is detected in the PC5 connection between UE-TX and UE-RX rather than the PC5 connection between UE-TX and UE-RX being released, the aforementioned method may be applied. These combinations may also be possible.

[0263] FIG. 20 is a sequence diagram showing an example of a method for releasing the PC5 connection between S-UE and UE-TX when the PC5 connection between UE-TX and UE-RX is released for Modification Example 1 of Embodiment 1. In FIG. 20, steps common to FIG. 18 are assigned the same step numbers, and common descriptions are omitted.

[0264] UE-TX determines to release the PC5 connection with UE-RX. In steps ST1803 and ST1804, UE-TX releases the PC5 connection with UE-RX. UE-TX that has released the PC5 connection with UE-RX releases the PC5 connection with S-UE. In steps ST1805 and ST1806, UE-TX releases the PC5 connection with S-UE.

[0265] UE-RX may determine to release the PC5 connection with UE-TX. UE-RX may request the release of the PC5 connection from UE-TX. UE-TX notifies UE-RX of a response to the release request. UE-RX and UE-TX release the PC5 connection between UE-RX and UE-TX. UE-TX that has released the PC5 connection with UE-RX releases the PC5 connection with S-UE.

[0266] By doing so, the PC5 connection state between UE-TX and UE-RX and the PC5 connection state between S-UE and UE-TX can be interlocked. When the PC5 connection between UE-TX and UE-RX is released, the PC5 connection between S-UE and UE-TX can be released.

[0267] Figure 21 is a sequence diagram showing an example of a method for releasing the PC5 connection between the S-UE and the UE-TX when RLF is detected in the PC5 connection between the UE-TX and the UE-RX for Modification Example 1 of Embodiment 1. In Figure 21, the same step numbers are assigned to the steps common to Figure 20, and the common descriptions are omitted. At step ST1903, the UE-TX detects that RLF has occurred in the PC5 connection between the UE-TX and the UE-RX. Recognizing that the PC5 connection has become impossible due to the detection of RLF, the UE-TX releases the PC5 connection with the S-UE at steps ST1805 and ST1806.

[0268] By doing so, even when the PC5 connection between the UE-TX and the UE-RX becomes RLF, the PC5 connection between the S-UE and the UE-TX can be released.

[0269] The connection state between the S-UE and the UE-TX and the connection state between the UE-TX and the UE-RX may be made independent. It is also possible not to interlock the two connection states. The method disclosed in Embodiment 1 may be appropriately applied to the level of connection or the level of releasing the connection. By deciding in advance not to interlock, each UE can recognize that the connection or release process between the S-UE and the UE-TX and the connection or release process between the UE-TX and the S-UE are performed independently. Therefore, the occurrence of inconsistencies can be reduced.

[0270] When the connection between the S-UE and the UE-TX is released and the connection between the UE-TX and the UE-RX is maintained, resources for SL communication are required between the UE-TX and the UE-RX. As the resources for SL communication, the method disclosed in Modification Example 2 of Embodiment 1 may be appropriately applied.

[0271] Also, when the connection between the S-UE and the UE-TX is released, the UE-TX may perform reselection of the S-UE. This reselection may be performed independently of the connection between the UE-TX and the UE-RX. After establishing a PC5 connection with the reselected S-UE, the UE-TX may configure or change the resources between the UE-TX and the UE-RX using the resource information notified by the S-UE. By doing so, the connection between the UE-TX and the UE-RX is maintained, enabling data communication for the V2X service.

[0272] Also, when the connection between the S-UE and the UE-TX is released, the UE-TX may select a gNB. This selection may be performed independently of the connection between the UE-TX and the UE-RX. After establishing a connection with the selected gNB, the UE-TX may configure or change the resources between the UE-TX and the UE-RX using the resource information notified by the gNB. By doing so, the connection between the UE-TX and the UE-RX is maintained, enabling data communication for the V2X service.

[0273] Also, when the connection between the S-UE and the UE-TX is released and the UE-TX fails to connect to the S-UE and the gNB, the UE-TX may configure or change the resources between the UE-TX and the UE-RX using pre-configured resources. By doing so, the connection between the UE-TX and the UE-RX is maintained, enabling data communication for the V2X service.

[0274] In the method disclosed in Modification Example 1 of Embodiment 1, the method disclosed in Embodiment 1 may be appropriately applied. For example, methods such as the UE-TX notifying the S-UE of the PC5 connection status information between the UE-TX and the UE-RX, or the UE-TX notifying the UE-RX of the PC5 connection status information between the S-UE and the UE-TX may be appropriately applied. The same effects as those of Embodiment 1 can be obtained.

[0275] For example, PC5 connection state information may be applied to a method of making the connection state between the S-UE and the UE-TX independent of the connection state between the UE-TX and the UE-RX. The UE-TX notifies the S-UE of the PC5 connection state information between the UE-TX and the UE-RX. By doing so, even if the connection state between the UE-TX and the UE-RX is independent of the connection state between the S-UE and the UE-TX, the S-UE can recognize the connection state between the UE-TX and the UE-RX. For example, when the connection between the UE-TX and the UE-RX is released or disconnected, the S-UE can recognize the state and can prevent the UE-TX from notifying the resource information between the UE-TX and the UE-RX.

[0276] By adopting the method disclosed in Modification Example 1 of Embodiment 1, malfunctions in the processing between the S-UE and the UE-TX and in the processing between the UE-TX and the UE-RX can be reduced. Stable SL communication can be executed in a configuration using the S-UE. Also, in the S-UE, the UE-TX, and the UE-RX, there is no need to maintain unnecessary connections. Therefore, power consumption of each node can be reduced. At the same time, it is possible to improve the utilization efficiency of the resources used for the SL communication between the S-UE and the UE-TX and the SL communication between the UE-TX and the S-UE.

[0277] Modification Example 2 of Embodiment 1. In Embodiment 1, it was shown that the S-UE may notify the UE-TX of a resource pool as resource information. When the UE-TX becomes unable to connect to the S-UE, for example, when the connection between the S-UE and the UE-TX is released as disclosed in Modification Example 1 of Embodiment 1 but the connection between the UE-TX and the UE-RX is maintained, it becomes unclear which RP the UE-TX should use for the SL communication with the UE-RX. For this reason, the UE-TX cannot select a resource for the SL communication, and there may be a case where the SL communication cannot be performed.

[0278] In this Modification Example 2 of Embodiment 1, a method for solving such a problem is disclosed.

[0279] While the connection between UE-TX and UE-RX is maintained, when the connection between S-UE and UE-TX is no longer maintained, pre-set the RP used for SL communication between UE-TX and UE-RX. This RP may be statically determined by standards or the like. Alternatively, a node that sets the RP, such as a CN-side node, gNB, or S-UE, may notify UE-TX of the RP setting. While the connection between S-UE and UE-TX is established, it is advisable for S-UE to notify UE-TX of the RP setting. When the connection between UE-TX and UE-RX is maintained but the connection between S-UE and UE-TX is no longer maintained, UE-TX uses the RP setting for SL communication between UE-TX and UE-RX. UE-TX may use the RP setting for SL communication between UE-TX and UE-RX when the connection between UE-TX and UE-RX is maintained but the connection between the CN-side node and UE-TX or between gNB and UE-TX is no longer maintained.

[0280] As another method, the RP setting may be pre-set within UE-TX. The RP setting may be pre-set in the (U)SIM of UE-TX. When the connection between UE-TX and UE-RX is maintained but the connection between S-UE and UE-TX is no longer maintained, UE-TX uses the RP setting for SL communication between UE-TX and UE-RX. By pre-setting within UE-TX, the signaling required for the RP setting can be reduced.

[0281] As another method, an Exceptional RP may be set. The S-UE may set an Exceptional RP used for SL communication between UE-TX and UE-RX and notify UE-TX. Alternatively, a CN-side node or gNB may set the Exceptional RP and notify UE-TX. The Exceptional RP may be set separately from the RP used when the connection between the S-UE and UE-TX is maintained. When the connection between UE-TX and UE-RX is maintained but the connection between the S-UE and UE-TX is lost, UE-TX uses this Exceptional RP setting for SL communication between UE-TX and UE-RX.

[0282] When the connection between the S-UE and UE-TX is lost, until UE-TX connects to the next destination and newly sets an RP from the next destination, the above-described RP setting may be used for SL communication between UE-TX and UE-RX.

[0283] Specific examples of situations where the connection between the S-UE and UE-TX is lost are disclosed as follows (1) to (7).

[0284] (1) Release of the PC5 connection between the S-UE and UE-TX.

[0285] (2) RLF detection between UE-TX and S-UE.

[0286] (3) Activation of the change process of the S-UE to which UE-TX connects.

[0287] (4) Activation of the change process of the gNB to which the S-UE connects.

[0288] (5) When the distance between the S-UE and UE-TX exceeds a predetermined value.

[0289] (6) When the area (zone) where UE-TX is located changes.

[0290] (7) Combinations of (1) to (6).

[0291] Regarding the above (1), as the connection level in the release of the PC5 connection, the level disclosed in Embodiment 1 may be appropriately applied.

[0292] The above (2) may be the case where UE-TX detects an RLF between UE-TX and S-UE.

[0293] The above (3) may be the case where UE-TX activates the change process of the connected S-UE. Alternatively, the change process of the S-UE connected by UE-TX may be activated by another node other than the UE-TX. Instead of the change process of the connected S-UE, it may be a reconnection process of S-UE including other S-UE.

[0294] The above (4) may be the case where S-UE activates the change process of the connected gNB. Alternatively, the change process of the gNB connected by S-UE may be activated by another node other than the S-UE. Instead of the change process of the connected gNB, it may be a reconnection process of gNB including other gNB. The change process and / or reconnection process may be activated when S-UE goes out of the coverage of gNB. The change process and / or reconnection process may be activated when S-UE fails to reconnect to gNB and there is no connected gNB.

[0295] The predetermined value in the above (5) may be the distance required for the SL communication between S-UE and UE-TX. The distance in the above (5) may be a range which is one of the QoS parameters. The predetermined value may be notified in advance to UE-TX from the node setting the RP. Alternatively, the predetermined value may be set in advance in UE-TX.

[0296] Regarding the above (6), UE-TX may perform position measurement and determine the area (zone) where the UE-TX is located. The setting of the area (zone) may be notified in advance to UE-TX from the node setting the RP. Alternatively, the setting of the area (zone) may be set in advance in UE-TX.

[0297] By adopting the method disclosed in Modified Example 2 of Embodiment 1, even when UE-TX fails to connect to S-UE, UE-TX can select resources for SL communication between UE-TX and UE-RX, enabling SL communication between UE-TX and UE-RX. It becomes possible to maintain the PC5 connection between UE-TX and UE-RX.

[0298] Embodiment 2. For example, when a pedestrian conducts SL communication with a vehicle, since the battery capacity of the UE held by the pedestrian is limited, power consumption reduction of the UE for pedestrians is required. Also, for example, when SL communication is performed between wearable devices or between small robots operating in a factory or a specific area, since the battery capacity of the UE mounted on them is limited, power consumption reduction is required. Thus, there are cases where power consumption reduction is required for UEs performing SL communication.

[0299] Regarding power consumption reduction of UEs performing SL communication, DRX in SL of LTE has been proposed (see Non-Patent Document 26). However, such a conventional DRX method does not disclose anything about cases where a plurality of services or PC5 connections are made between opposing UEs or where SL communication is performed between a plurality of opposing UEs. Also, a DRX method for unicast communication in SL supported by NR is not disclosed. For this reason, the conventional method cannot perform DRX in the above-described cases, resulting in a problem that power consumption reduction of UEs performing SL communication cannot be achieved.

[0300] In this Embodiment 2, a method for solving such problems is disclosed.

[0301] DRX is set for each pair of UEs performing SL communication. UE-TX may perform DRX setting. UE-TX may notify UE-RX of the DRX setting. The node that sets DRX (hereinafter sometimes referred to as the DRX setting node) may be UE-RX. UE-RX may notify UE-TX of the DRX setting. The DRX setting node may be gNB. Alternatively, in the case of a configuration using S-UE, the DRX setting node may be S-UE. gNB or S-UE may notify UE-TX and UE-RX of the DRX setting.

[0302] When UE-TX performs DRX setting, it may notify gNB of the DRX setting result, for example, DRX setting information. When UE-TX is connected to S-UE, it may notify S-UE of the DRX setting result. When S-UE performs DRX setting, it may notify gNB of the DRX setting result. gNB and S-UE can adjust the resources allocated to other UEs performing SL communication. Collisions with resources used for SL communication of other UEs can be reduced.

[0303] When UE-TX is not connected to gNB and is in the RRC_Idle state, or the RRC_Inactive state or out of coverage, UE-TX may perform DRX setting. When UE-TX is connected to gNB and is in the RRC_connected state, gNB may perform DRX setting. When UE-TX is not connected to gNB and is in the RRC_Idle state, or the RRC_Inactive state or out of coverage and is connected to S-UE, S-UE may perform DRX setting. DRX setting is possible regardless of the state of UE-TX.

[0304] As the method for notifying the DRX setting between UE-TX and UE-RX, the method for notifying resource information between S-UE and UE-TX disclosed in Embodiment 1 may be appropriately applied. Replace "between S-UE and UE-TX" with "between UE-TX and UE-RX" or "between UE-RX and UE-TX".

[0305] An identifier for specifying the DRX setting may be provided. The DRX setting may be associated with the DRX setting identifier. A node that sets DRX (hereinafter sometimes referred to as a DRX setting node) may notify the DRX setting, in association with the DRX setting identifier, to a node where DRX is set (hereinafter sometimes referred to as a DRX set node). By doing so, for example, as will be described later, in a case where a plurality of DRX settings are implemented for a UE performing SL communication, the UE performing SL communication can determine which DRX setting to use.

[0306] By doing so, it becomes possible to set DRX for each opposing UE performing SL communication. Even in a case where a plurality of applications (which may be services) or PC5 connections are made between opposing UEs, by setting DRX for each opposing UE performing SL communication, it is possible to unify the period during which transmission and reception are made active (on) for each opposing UE. Therefore, low power consumption of the UE can be achieved.

[0307] In some cases, one UE may perform SL communication with a plurality of UEs. Also in such a case, DRX may be set for each opposing UE. In such a case, it is preferable to associate the DRX setting with the L2ID (Layer 2 ID). The destination L2ID (destination L2ID) may be associated with the DRX setting. The source L2ID (source L2ID) may be associated with the DRX setting. Alternatively, both of these L2IDs may be associated with the DRX setting.

[0308] Associate the DRX setting with the L2ID and notify the DRX setting between UE-TX and UE-RX in each SL communication. By doing so, a UE that performs SL communication with a plurality of UEs can identify the DRX setting in the SL communication with which UE. In the case of DRX when one UE performs SL communication with a plurality of UEs, the occurrence of malfunction can be reduced.

[0309] Disclose other DRX setting methods. For each application in SL communication, DRX may be set. It is advisable to associate an identifier for identifying the application with the DRX setting. Associate the DRX setting with the application identifier and notify the DRX setting between UE-TX and UE-RX. By doing so, the UE performing SL communication can identify the DRX setting for the application. For example, in the case where multiple applications are running in a pair of opposing UEs, the DRX setting for each application can be implemented. The DRX setting suitable for the communication pattern of each application can be implemented.

[0310] For each PC5 connection in SL communication, DRX may be set. For example, set DRX for each PC5-S connection. Alternatively, DRX may be set for each L2 link. It is advisable to associate an identifier for identifying the PC5 connection with the DRX setting. Associate the DRX setting with the PC5 connection identifier and notify the DRX setting between UE-TX and UE-RX. Alternatively, notify the DRX setting between UE-TX and UE-RX by signaling at the time of PC5-S connection establishment. By doing so, the UE performing SL communication can identify the DRX setting for the PC5 connection. For example, in the case where multiple PC5 connections are running in a pair of opposing UEs, the DRX setting for each PC5 connection can be implemented. The DRX setting suitable for each PC5 connection can be implemented.

[0311] For each PC5-RRC connection in SL communication, DRX may be configured. It is advisable to associate an identifier for identifying the PC5-RRC connection with the DRX configuration. The DRX configuration is associated with the PC5-RRC connection identifier and the DRX configuration is notified between UE-TX and UE-RX. Alternatively, the DRX configuration is notified between UE-TX and UE-RX by signaling during the PC5-RRC connection. By doing so, a UE performing SL communication can identify the DRX configuration for the PC5-RRC connection. For example, in the case where multiple PC5-RRC connections are executed in a pair of opposing UEs, the DRX configuration for each PC5-RRC connection can be implemented. A DRX configuration suitable for each PC5-RRC connection can be implemented.

[0312] For each AS configuration, DRX may be configured. It is advisable to associate an identifier for identifying the AS configuration with the DRX configuration. The DRX configuration is associated with the AS configuration identifier and the DRX configuration is notified between UE-TX and UE-RX. Alternatively, the DRX configuration is notified between UE-TX and UE-RX by PC5-RRC signaling for the AS configuration. The DRX configuration may be included in the AS configuration and notified. By doing so, a UE performing SL communication can identify the DRX configuration for the AS configuration. For example, in the case where multiple AS configurations are executed in a pair of opposing UEs, the DRX configuration for each AS configuration can be implemented. A DRX configuration suitable for each AS configuration can be implemented.

[0313] For each QoS flow of PC5, DRX may be configured. It is advisable to associate an identifier for identifying the QoS flow of PC5 with the DRX configuration. The DRX configuration is associated with the QoS flow identifier of PC5, and the DRX configuration is notified between UE-TX and UE-RX. Alternatively, the DRX configuration is notified between UE-TX and UE-RX by signaling for the QoS flow configuration of PC5. By doing so, the UE performing SL communication can identify the DRX configuration for the QoS flow of PC5. For example, in the case where a plurality of QoS flows of PC5 are executed in a pair of opposing UEs, the DRX configuration for each QoS flow of PC5 can be implemented. A DRX configuration suitable for each QoS flow of PC5 can be implemented.

[0314] For each radio bearer of SL, DRX may be configured. The radio bearer may be an SRB, a DRB, or a combination of an SRB and a DRB. It is advisable to associate an identifier for identifying the radio bearer with the DRX configuration. The DRX configuration is associated with the radio bearer identifier, and the DRX configuration is notified between UE-TX and UE-RX. Alternatively, the DRX configuration is notified between UE-TX and UE-RX by PC5-RRC signaling for the radio bearer configuration. The radio bearer configuration and the DRX configuration may be included in the AS configuration and notified. By doing so, the UE performing SL communication can identify the DRX configuration for the radio bearer. For example, in the case where a plurality of radio bearers are configured in a pair of opposing UEs, the DRX configuration for each radio bearer can be implemented. A DRX configuration suitable for each radio bearer can be implemented.

[0315] For each RLC bearer of SL, DRX may be set. It is advisable to associate an identifier for identifying the RLC bearer with the DRX setting. The DRX setting is associated with the RLC bearer identifier and the DRX setting is notified between UE-TX and UE-RX. Alternatively, the DRX setting is notified between UE-TX and UE-RX by means of PC5-RRC signaling for RLC bearer setting. The RLC bearer setting and the DRX setting may be included in the AS setting and notified. By doing so, a UE performing SL communication can identify the DRX setting for the RLC bearer. For example, in a case where a plurality of RLC bearers are set in a pair of opposing UEs, the DRX setting for each RLC bearer can be implemented. A DRX setting suitable for each RLC bearer can be implemented.

[0316] For example, in a communication method in which a plurality of RLC bearers are set between opposing UEs performing SL communication and replicated packets are transmitted through the plurality of RLC bearers, by applying the DRX setting for each RLC bearer, a DRX setting corresponding to the communication status of each connection can be implemented. Thereby, improvement in communication reliability and reduction in latency can be achieved.

[0317] The number of the DRX settings described above is not limited to one and may be plural. It becomes possible to cope with various communication patterns and QoS required for services.

[0318] A plurality of DRX settings may be interlocked. For example, two DRX settings of long-cycle DRX and short-cycle DRX are interlocked. For example, the period of the long-cycle DRX is set to n times (n is a positive integer) the short-cycle DRX. The offsets of both DRXs may be the same. As an interlocking method, for example, the UE monitors at the long-cycle DRX timing and, if there is received data, shifts to the short-cycle DRX. The UE monitors at the short-cycle DRX timing and, if there is received data, receives the data. The UE monitors at the short-cycle DRX timing and, if there is no received data continuously for a predetermined number of times, shifts to the long-cycle DRX.

[0319] By doing so, when data transmission and reception are not required, the system shifts to long-cycle DRX, so that the power consumption of the receiving UE can be further reduced. Also, the resources required for DRX can be made the same as those required for short-cycle DRX, thus avoiding an increase in the resources used due to multiple DRX settings.

[0320] The offset of long-cycle DRX and the offset of short-cycle DRX may be made different. For example, the offset of long-cycle DRX may be set to a predetermined period before the offset of short-cycle DRX. As an interlocking method, for example, the UE monitors at the long-cycle DRX timing, and when there is received data, it shifts to short-cycle DRX having an offset after a predetermined period. The UE monitors at the short-cycle DRX timing and, when there is received data, receives the data. The UE monitors at the short-cycle DRX timing and, when there is no received data for a predetermined number of consecutive times, shifts to long-cycle DRX.

[0321] By doing so, as in the above-described method, when data transmission and reception are not required, the system shifts to long-cycle DRX, so that the power consumption of the receiving UE can be further reduced.

[0322] Data transmission and reception may be eliminated in long-cycle DRX. In long-cycle DRX, information indicating the presence or absence of transmitted / received data may be transmitted and received. Instead of the information indicating the presence or absence of transmitted / received data, information indicating a shift to short-cycle DRX may be used. Alternatively, information indicating monitoring at short-cycle DRX timing may be used.

[0323] A channel or signal for transmitting the information indicating the presence or absence of transmitted / received data may be provided. It is preferable to preset the configuration of the channel or signal. The channel or signal may be set, for example, using frequency resources, time resources, sequences, or a combination of some or all of them. This makes it possible to identify the channel or signal. When the receiving UE receives the preset channel or signal at the timing of long-cycle DRX, it can determine that there is transmitted / received data. The receiving UE can shift to short-cycle DRX and receive data.

[0324] By doing so, similar to the above, when data transmission and reception are not required, the system migrates to long-cycle DRX, so that the power consumption of the receiving UE can be further reduced. Also, since data transmission and reception are not performed in long-cycle DRX, the resources used for long-cycle DRX can be reduced.

[0325] Setting information necessary for the linkage of multiple DRX settings, for example, the value of n, the predetermined number of times, the offset difference (predetermined period) of each DRX, the configuration information of the channel or signal for transmitting the presence / absence information of transmitted and received data, etc., may be set in advance. The setting information necessary for the linkage of multiple DRX settings may be determined statically in advance by a standard or the like. Alternatively, the setting information necessary for the linkage of multiple DRX settings may be notified from the DRX setting node to the DRX node to be set. The DRX setting information may include the setting information necessary for the linkage of multiple DRX settings.

[0326] In this way, by linking multiple DRX settings, further power consumption reduction of the UE can be achieved. Also, it becomes possible to further improve the utilization efficiency of the resources used for SL communication.

[0327] In NR's SL unicast communication, the transmission of Ack / Nack feedback by HARQ is introduced. In the case of HARQ Nack, retransmission is performed. In SL communication, when DRX is set between UE-TX and UE-RX, the retransmission method at the time of HARQ Nack occurrence becomes a problem. Here, the retransmission method at the time of HARQ Nack occurrence is disclosed.

[0328] Apply the DRX for SL communication to the first transmission and retransmission of SL communication data. UE-TX performs the transmission operations of the first transmission data and retransmission data of SL communication at the transmission timing of the DRX set for SL communication. UE-RX performs the reception operations of the first transmission data and retransmission data of SL communication at the reception timing of the DRX set for SL communication.

[0329] As the DRX transmission and reception timing, an on-period or an on-period and an inactivity timer period may be used. It is also possible not to provide a retransmission timer period in the DRX setting information. By performing retransmission at the DRX transmission and reception timing, retransmission can be performed without providing a retransmission timer period.

[0330] If UE-RX fails to receive the first transmission data transmitted from UE-TX at the transmission timing of SL communication using DRX, UE-RX transmits a Nack for SL communication to UE-TX. When UE-TX receives a Nack for SL communication from UE-RX, UE-TX performs retransmission of SL communication. UE-TX performs the retransmission at the transmission timing of SL communication using DRX. UE-TX may transmit the retransmitted data at the same transmission timing of SL communication using DRX together with the first transmission data of the next SL communication. As multiplexing methods for retransmitted data and the next first transmission data in SL communication, time multiplexing, frequency multiplexing, and code multiplexing can be used. UE-RX performs a reception operation for the retransmission of SL communication from UE-TX at the reception timing set by DRX for SL communication. By doing so, UE-RX can receive the retransmitted data of SL communication from UE-TX.

[0331] By transmitting the retransmitted data of SL communication at the transmission timing of SL communication using DRX, it becomes unnecessary to use other resources for SL communication. For example, it becomes unnecessary to hold resources for the retransmission timer period set for retransmission in Uu. Therefore, the utilization efficiency of resources for SL communication can be improved. Also, it becomes unnecessary for UE-TX to select other resources to be used for transmitting the retransmitted data of SL communication. Therefore, power consumption of UE-TX can be reduced. Also, UE-RX only needs to perform a reception operation at the reception timing of DRX for SL communication, and it becomes unnecessary to perform a reception operation for monitoring other resources for SL communication. Therefore, power consumption of UE-RX can be reduced.

[0332] When applying SL communication DRX to the initial transmission and retransmission of data in SL communication, the retransmission will be waited until the next transmission timing. If the period of the transmission timing of SL communication DRX is long, the retransmission of SL communication will be delayed and a delay will occur. A method for solving such a problem is disclosed.

[0333] The period until retransmission may be set at an interval different from the set DRX period. UE-TX performs retransmission at the retransmission timing. UE-RX performs reception at the retransmission timing. As the different interval, n times (n is a natural number) of the set DRX period may be set. For example, set n = 2. When the DRX period is 1 s, the interval until retransmission is 2 s. When UE-RX cannot receive in the initial transmission and transmits a Nack, it starts receiving the retransmission during the DRX on period after 2 s.

[0334] By doing so, there is no need to select and hold a new resource for retransmission in SL communication. Also, if the interval of the DRX period is short, there is a high possibility that the transmission and reception will fail even if retransmission is performed in the next DRX period. By setting the period for retransmission at an interval different from the set DRX period, it becomes possible to reduce such transmission and reception failures.

[0335] The retransmission timing may be set according to the set DRX period. For example, if the DRX period is 20 ms or less, the interval until retransmission is 1 s. If the DRX period is greater than 20 ms and 1 s or less, the interval until retransmission is 3 s. If the DRX period is greater than 1 s, the interval until retransmission is 15 s. By doing so, it becomes possible to set a flexible retransmission timing according to the DRX period.

[0336] The retransmission timing may be set according to the number of retransmissions. For example, when the DRX period is 10 ms, the interval until the first retransmission is 20 ms, and the interval until the second retransmission is 40 ms. For example, when the number of retransmissions is m times, the interval until the next retransmission may be n × m times the DRX period. By doing so, the retransmission timing can be changed according to the number of transmission / reception failures, and it becomes possible to reduce the transmission / reception failures.

[0337] Multiple retransmissions may be performed during the on-period or during a plurality of retransmissions in the on-period. The number of retransmissions may be determined in advance or may be set. For example, when the DRX period is 10 ms and n = 1, the number of retransmissions is set to 2. In this case, since the interval until retransmission is 10 ms, two retransmissions are performed during the on-period 10 ms after the first transmission or during the on-period and the inactivity timer period. The retransmitted data may be the same. The Ack / Nack by HARQ may be performed for the reception results of all of the plurality of retransmissions. By doing so, it becomes possible to improve the reception success probability of the retransmitted data in UE-RX.

[0338] Multiple retransmissions may be performed during the on-periods of a plurality of DRXs. The number of retransmissions may be determined in advance or may be set. The retransmissions may be performed during a plurality of consecutive on-periods of DRX. For example, when the DRX period is 10 ms, the interval until retransmission is 10 ms, and the number of consecutive retransmissions is 3. In this case, the retransmitted data is continuously transmitted during the on-periods 10 ms, 20 ms, and 30 ms after the first transmission. The retransmitted data may be the same. The Ack / Nack by HARQ may be performed for the reception results of all of the plurality of retransmissions. In UE-RX, it becomes possible to improve the reception success establishment of the retransmitted data.

[0339] In the method described above, the on-period is described as the retransmission timing, but it may be the combination of the on-period and the inactivity timer period.

[0340] Before the retransmission is sent, the initial transmission may be sent. Initial transmissions of different HARQ processes may be sent. By doing so, it is possible to effectively utilize the resources held in DRX other than the timing at which retransmission is performed.

[0341] The DRX for SL communication is applied only to the initial transmission of the data of SL communication. UE-TX performs the transmission operation of the initial transmission data of SL communication at the transmission timing of the DRX set for SL communication. UE-RX performs the reception operation of the initial transmission data of SL communication at the reception timing of the DRX set for SL communication.

[0342] The DRX for SL communication is not applied to the retransmission of the data of SL communication. UE-TX does not perform retransmission using the transmission resources of the DRX set for SL communication. UE-TX searches for and selects SL communication resources for the retransmission data transmission of SL communication. UE-TX performs the retransmission of SL communication using the selected SL communication resources.

[0343] If UE-RX fails to receive the initial transmission data transmitted at the transmission timing of the DRX for SL communication from UE-TX, UE-RX transmits a Nack for SL communication to UE-TX. When UE-TX receives a Nack for SL communication from UE-RX, UE-TX performs the retransmission of SL communication. UE-TX searches for and selects SL communication resources and performs the retransmission of SL communication using the selected resources. When UE-RX transmits a Nack for SL communication to UE-TX, UE-RX monitors the resources for SL communication that are not the reception resources of the set DRX, detects and receives the data addressed to its own UE-RX from UE-TX.

[0344] A retransmission timer period may be provided in the DRX configuration information. Retransmission of SL communication data may be performed within the retransmission timer period. Even if the retransmission timer period is not provided, retransmission is possible when DRX is configured. In this way, by setting a specific period with the retransmission timer, for retransmission, UE-RX will perform reception only during the retransmission timer period. When the retransmission timer expires, UE-RX may go to sleep. UE-RX may go to sleep until the start of the next DRX on period.

[0345] By transmitting and receiving the retransmission of SL communication in this way, there is no need to wait until the next DRX transmission / reception timing between UE-TX and UE-RX, and the retransmitted data can be transmitted and received. Since the occurrence of delay in the retransmission transmission of SL communication can be reduced, SL communication can be carried out with low latency. Also, since the initial transmission is performed using DRX configuration, power consumption of UE-TX and UE-RX can be reduced.

[0346] DRX for retransmission may be configured. Resources different from those for the initial transmission may be configured. Retransmission is performed during the on period of the retransmission DRX or during the on period and the inactivity timer period. For example, an offset is made different between the DRX for the initial transmission and the DRX for retransmission, and other settings in the DRX configuration information are the same. Retransmission timings corresponding to each initial transmission timing may be set. By doing so, the DRX period is the same, and it is possible to set the initial transmission timing and the retransmission timing individually, and it is not necessary to use the same DRX on period for the initial transmission and the retransmission. Also, it is possible to avoid overlap of the initial transmission and the retransmission within the same resource. Since the initial transmission and the retransmission can be performed early, the delay time in SL communication can be shortened.

[0347] The above retransmission method and various settings for retransmission may be determined in advance by standards or the like. It is possible to reduce the amount of signaling required for retransmission. The gNB may perform this setting. The gNB notifies the UE-TX or UE-RX of this setting. The S-UE may perform this setting. This is effective when the S-UE is in operation. The S-UE notifies the UE-TX or UE-RX of this setting. The UE-TX may perform this setting. The UE-TX notifies the UE-RX of this setting.

[0348] When the UE-TX is not connected to the gNB and is in the RRC_Idle state, or the RRC_Inactive state, or outside the coverage area, the UE-TX may perform the retransmission setting. When the UE-TX is connected to the gNB and is in the RRC_connected state, the gNB may perform the retransmission setting. When the UE-TX is not connected to the gNB and is in the RRC_Idle state, or the RRC_Inactive state, or outside the coverage area and is connected to the S-UE, the S-UE may perform the retransmission setting. Retransmission settings can be made regardless of the state of the UE-TX.

[0349] As signaling for the retransmission setting from the UE-TX to the UE-RX, PC5-RRC signaling may be used. The DRX setting may be performed in the RRC layer of the UE, and the retransmission setting may also be performed in the RRC layer. Since the DRX setting and the retransmission setting can be set in the same layer, the occurrence of malfunction can be reduced. As signaling for the retransmission setting from the UE-TX to the UE-RX, MAC signaling may be used. The retransmission setting may be performed in the MAC layer of the UE. Retransmission can be set according to the HARQ process in the MAC layer. As signaling for the retransmission setting from the UE-TX to the UE-RX, the retransmission setting may be included in the SCI and notified on the PSCCH. The retransmission setting may be included in the SCI of the initial transmission and notified. Since the retransmission setting can be changed dynamically, it is possible to perform an optimal setting according to the communication situation such as the communication quality.

[0350] When UE-TX performs retransmission configuration, it may notify the gNB of the retransmission configuration result. When UE-TX is connected to S-UE, it may notify S-UE of the retransmission configuration result. When S-UE performs retransmission configuration, it may notify the gNB of the retransmission configuration result. The gNB and S-UE can adjust the resources allocated to UEs performing other SL communications. Collisions with resources used for other UEs' SL communications can be reduced.

[0351] A DRX configuration request may be provided. The node where DRX is configured (DRX-configured node) may notify the node that configures DRX (DRX-configuring node) of the DRX configuration request. For example, the DRX-configured node may be UE-RX, and the DRX-configuring node may be UE-TX. In this case, UE-RX notifies UE-TX of the DRX configuration request. For example, the DRX-configuring node may be S-UE. In this case, UE-RX notifies S-UE of the DRX configuration request. UE-RX notifies UE-TX of the DRX configuration request, and UE-TX includes information on the DRX configuration in the SL communication with the UE-RX that notified the DRX configuration request (which may be referred to as DRX configuration information in this disclosure) in the DRX configuration request and notifies the DRX configuration request to S-UE. Notification of the DRX configuration information may be regarded as the DRX configuration request.

[0352] For example, the DRX-configuring node may be gNB, and UE-RX notifies gNB of the DRX configuration request. UE-RX notifies S-UE of the DRX configuration request, and S-UE includes information on the DRX configuration in the SL communication between the UE-TX and UE-RX that notified the DRX configuration request in the DRX configuration request and notifies the DRX configuration request to gNB.

[0353] The DRX-configuring node may be the UE-TX. For example, the DRX-configuring node may be the S-UE, and the UE-TX notifies the S-UE of a DRX configuration request. The UE-TX includes information on the DRX configuration in the SL communication with the UE-RX in the DRX configuration request and notifies the S-UE of the DRX configuration request. For example, the DRX-configuring node may be the gNB, and the UE-TX notifies the gNB of a DRX configuration request. The UE-TX notifies the S-UE of the DRX configuration request, and the S-UE includes information on the DRX configuration in the SL communication between the UE-TX that notified the DRX configuration request and the UE-RX in the DRX configuration request and notifies the gNB of the DRX configuration request.

[0354] As a method for notifying a DRX configuration request between the UE-RX and the UE-TX or between the UE-TX and the S-UE, the resource information notification method disclosed in Embodiment 1 may be appropriately applied. As a method for notifying a DRX configuration request between the UE-TX and the gNB or between the S-UE and the gNB, it is preferable to use the Uu interface. RRC signaling may also be used. The DRX configuration request may be included in the AS configuration for SL and notified. This is effective when the gNB implements the AS configuration for SL. As another method, MAC signaling may be used. The DRX configuration request can be notified earlier.

[0355] A message for the DRX configuration request may be provided. The message for the DRX configuration request may be notified by PC5-S signaling. The message for the DRX configuration request may be notified by PC5-RRC signaling. Reason information may be provided together with the DRX configuration request. The DRX configuration request information and the reason information may be included in the message for the DRX configuration request. The reason information may be, for example, information indicating that it is a pedestrian terminal or information indicating a power saving request. By doing so, it becomes possible to notify the DRX-configuring node of the reason for which the DRX-configured node requests the DRX configuration. The DRX-configuring node can implement the DRX configuration using the reason information.

[0356] The DRX configuration request may provide information indicating for which connection the request is made. For example, the PC5 connection identifier, PC5-RRC connection identifier, AS configuration identifier, PC5 QoS flow identifier, radio bearer identifier, RLC bearer identifier, etc. described above may be used. The DRX configuration request and the identifier may be associated with each other. The DRX configuration request and the identifier may be associated and included in a message for the DRX configuration request. By doing so, the DRX configuration node can recognize for which connection the DRX configuration is requested.

[0357] In this way, by providing the DRX configuration request, the DRX-configured node can request the DRX configuration node for DRX configuration according to its own state, such as the remaining battery capacity. It becomes possible to implement low power consumption for the UE performing SL communication.

[0358] The DRX-configured node may notify the DRX configuration node of some or all of the DRX configuration information such as the DRX cycle as a desired value (which may be a required value). Some or all of the DRX configuration information such as the DRX cycle may be notified as a DRX configuration request. Some or all of the DRX configuration information such as the DRX cycle may be included in the DRX configuration message and notified. The DRX-configured node may, for example, notify the cycle in which V2X service data using SL communication occurs as the desired DRX cycle. For example, the DRX-configured node may notify the DRX configuration node of the cycle in which V2X service data using SL communication occurs and the value obtained by statistically processing the data volume as the desired DRX cycle and the desired resource allocation amount. By doing so, the DRX-configured node can request the DRX configuration node for DRX configuration according to the state of the SL communication performed in the V2X service. It becomes possible to implement low power consumption for the UE performing SL communication according to the V2X service.

[0359] The DRX configuration information is information indicating the configuration of DRX in SL. This information is used by the DRX configuration node to perform DRX configuration in SL for the DRX-configured node.

[0360] As specific examples of the DRX setting information, the following (1) to (12) are disclosed.

[0361] (1) DRX cycle.

[0362] (2) On duration time.

[0363] (3) Inactive period.

[0364] (4) Offset.

[0365] (5) Inactivity timer.

[0366] (6) Frequency resource during the on duration.

[0367] (7) Frequency resource during the inactivity timer period.

[0368] (8) HARQ-RTT timer (HARQ-RTT-Timer).

[0369] (9) Retransmission timer.

[0370] (10) Frequency resource during the retransmission timer period.

[0371] (11) Active time.

[0372] (12) Combinations of (1) to (11).

[0373] The DRX cycle in the aforementioned (1) is the cycle when DRX is periodically performed. The DRX cycle may be the cycle at the start of the on duration or, alternatively, the cycle at the end of the inactive period.

[0374] The on-period of the foregoing (2) is the reception period at UE-RX. This period may also be the transmission period at UE-TX. The on-period may be a period during which reception or transmission is possible. The on-period starts from the beginning of the DRX cycle.

[0375] The inactive period of the foregoing (3) is the period during which reception does not occur at UE-RX. It may also be the period during which transmission does not occur at UE-TX. The inactive period may be a period during which reception or transmission is impossible. It becomes a sleep period during which transmission and reception operations are not performed at UE-RX.

[0376] The offset of the foregoing (4) is the offset period at which the DRX cycle starts.

[0377] The inactivity timer of the foregoing (5) is the period after reception of data or PSCCH indicating data. Hereinafter, this period may be referred to as the inactivity timer period. The inactivity timer is reset by reception of PSCCH and restarted. When the inactivity timer expires, the device goes to sleep. The inactivity timer is the period from reception of PSCCH until going to sleep. The data may be initial transmission data.

[0378] In the case of SL communication, it is necessary to pre-select and hold the resources used for this communication. Therefore, when an inactivity timer is set, resources for the inactivity timer period must be selected and held. For this reason, the resource utilization efficiency decreases. It may not be necessary to set an inactivity timer. The inactivity timer may be eliminated. It may be assumed that SL communication transmission and reception are performed during the on-period. In the V2X service, there may be cases where data of a predetermined capacity is generated periodically. Thus, it may also be applied to the V2X service. Since it is not necessary to select and hold resources for the inactivity timer period, the resource utilization efficiency can be improved.

[0379] The frequency resource during the on-period of the aforementioned (6) is frequency resource information that enables transmission and reception. The frequency resource during the on-period may be set in units such as, for example, subchannels, resource blocks, resource elements, subcarriers, BWPs (BandWidth Parts), etc.

[0380] The frequency resource during the inactivity timer period of the aforementioned (7) is frequency resource information that enables transmission and reception within the inactivity timer. The frequency resource during the inactivity timer period may be set using, for example, subchannels, resource blocks, resource elements, subcarriers, BWPs (BandWidth Parts), etc.

[0381] The HARQ-RTT timer of the aforementioned (8) is the period until an allocation for retransmission is transmitted. The timer may start from the symbol after the Nack transmission.

[0382] The retransmission timer of the aforementioned (9) is the period during which retransmission is transmitted. UE-RX may expect retransmitted data to be transmitted during the retransmission timer when a Nack is transmitted. The timer may start from the symbol after the expiration of the HARQ-RTT timer.

[0383] The frequency resource during the retransmission timer period of the aforementioned (10) is frequency resource information that enables transmission and reception of retransmission or an allocation for retransmission. The frequency resource during the retransmission timer period may be set using, for example, subchannels, resource blocks, resource elements, subcarriers, BWPs (BandWidth Parts), etc.

[0384] The active period of the aforementioned (11) is the period during which UE-RX receives PSCCH in DRX. This period may include part or all of the on-period, the period until the inactivity timer expires, the period until the retransmission timer expires, and the period until the HARQ-RTT timer expires.

[0385] The sum of the active period and the inactive period may be set to the DRX cycle.

[0386] Among the DRX configuration information, the time-related information may be configured in terms of time (e.g., ms), or may be configured in units of system frames, radio frames, subframes, slots, minislots, symbols, sub-symbols, etc. in SL. Also, this time information may be configured as a timer. This simplifies the time management of DRX.

[0387] With such DRX configuration information, DRX configuration in SL communication can be implemented.

[0388] In SL communication over PC5, unlike communication over Uu, it is not possible to transmit and receive in all subframes. Transmission and reception are only possible within the resource pool configured for SL communication. Therefore, the DRX configuration for Uu cannot be directly applied.

[0389] Here, a method for solving such problems is disclosed.

[0390] When performing DRX configuration in SL communication, the resources for the active period of DRX may be within the range of the RP previously configured in the SL communication. For example, when UE-TX configures DRX for UE-RX, UE-TX performs DRX configuration by selecting the resources for the active period of DRX from the RP for SL communication between UE-TX and UE-RX. The RP for SL communication between UE-TX and UE-RX may be notified by gNB, or may be notified by S-UE. As the RP for SL communication between UE-TX and UE-RX, the RP pre-configured in UE-TX may be used.

[0391] By adopting such a method, DRX can be enabled in SL communication over PC5. Also, by avoiding using resources outside the range of the RP configured for SL communication between opposing UEs, interference with other UEs can be avoided.

[0392] When DRX is configured, UE-RX does not need to monitor during all periods of the RP configured for SL communication with UE-TX, and according to the DRX configuration, it only needs to perform the reception operation during the active period. When the DRX configuration is released, UE-RX may monitor the previously configured RP.

[0393] It is disclosed that the DRX configuration information may be configured by time or by slots, symbols, etc. in SL. As described above, in SL communication, transmission and reception are possible only within the RP configured for SL communication. In the DRX configuration, if the DRX configuration method in Uu is simply used, resources outside the RP range may be configured.

[0394] Here, a method for solving such problems is disclosed.

[0395] Configure the DRX configuration information within the RP range for SL communication. For example, re-number the slots of the resources within the RP range. A reference timing may be provided. For example, starting from the beginning of radio frame 0, consecutive numbers are assigned to the slots within the RP range. Also, the symbols may be numbered consecutively. By doing so, even if the RP is composed of discontinuous resources, the resources within the RP range can be indicated by the assigned consecutive slot numbers or symbol numbers.

[0396] For example, the DRX configuration information such as the DRX period may be indicated by the assigned slot number or symbol number. UE-TX can perform SL communication transmission according to the DRX configuration information, and UE-RX can receive SL communication according to the DRX configuration information. Malfunctions in SL communication can be reduced. Also, power consumption of UE-RX can be reduced.

[0397] For example, the RP may be set periodically, and the resources of the RP within one period may be indicated by a bitmap. In the resources of the RP within one period indicated by the bitmap, DRX setting information may be set. Among the DRX setting information, the active period may be set. This setting may be performed using a bitmap. The DRX setting information included in the active period may be indicated by a bitmap in the resources of one period. Since it can be the same as the above-described RP resource setting method, DRX processing in UE-TX and UE-RX can be facilitated.

[0398] For example, among the DRX setting information, in the setting information related to frequency, the DRX setting information is set within the RP range for SL communication. For example, when a subchannel is set, the subchannels within the RP range are re-numbered. The reference subchannel may be the resource block with the lowest resource block number. For example, the subchannel having the lowest resource block number within the RP range is set as number 0, and consecutive numbers are assigned to the subchannels in the direction in which the resource block number increases. By doing so, even if the RP is composed of discontinuous resources, the resources within the RP range can be indicated by the assigned consecutive subchannel numbers.

[0399] For example, the DRX setting information related to frequency may be indicated by a bitmap for the resources within the band. Alternatively, this information may be indicated by a bitmap for the resources within the set RP range.

[0400] For example, in the DRX setting information related to frequency, the frequencies to be set may be the same. For example, the frequency resources monitored by UE-RX for the first transmission data and the retransmission data may be the same. UE-RX does not need to change the frequency to be monitored, and DRX processing can be facilitated.

[0401] A request for modifying the DRX configuration may be provided. The DRX-configured node may notify the DRX configuration node of a DRX configuration modification request. A message for the DRX configuration modification request may be provided. Reason information may be provided together with the DRX configuration modification request. The message for the DRX configuration modification request may include DRX configuration request information and reason information. The DRX configuration modification request may request to modify part or all of the DRX configuration information. Information indicating which information in the DRX configuration information is to be modified may be provided. This information may be included in the message for the DRX configuration modification request. The DRX configuration node that has received the DRX configuration modification request can perform the modification of the DRX configuration for the DRX-configured node. By doing so, power consumption of the UE performing SL communication can be reduced according to the V2X service.

[0402] The DRX configuration modification request may be provided with information indicating which DRX configuration the modification request is for. The identifier for specifying the DRX configuration described above may be used. The identifier for specifying the DRX configuration may be included in the message for the DRX configuration modification request together with the DRX configuration modification request, and the message may be notified. For example, even when multiple DRX configurations are performed for one UE, the DRX configuration node can determine which DRX configuration the DRX configuration modification request is for.

[0403] Information for assisting the SL communication settings may be notified between UEs performing SL communication. As a method for notifying the SL communication setting assistance information between UEs performing SL communication, the resource information notification method disclosed in Embodiment 1 may be appropriately applied. A message for notifying the SL communication setting assistance information may be provided. The message may be notified by PC5-S signaling. The message may be notified by PC5-RRC signaling.

[0404] Examples of information for assisting the SL communication settings are disclosed below in (1) to (10).

[0405] (1) DRX configuration.

[0406] (2) DRX setting requirements.

[0407] (3) DRX setting modification requirements.

[0408] (4) Desired DRX setting.

[0409] (5) V2X service statistical processing data.

[0410] (6) Power consumption requirements.

[0411] (7) Battery level information.

[0412] (8) Overheating state information.

[0413] (9) PC5 connection state information.

[0414] (10) Combinations of (1) to (9).

[0415] By notifying such information between UEs performing SL communication, the UEs performing SL communication can implement appropriate settings for the communication.

[0416] FIG. 22 is a sequence diagram showing an example of a method for implementing a DRX setting between UE-TX and UE-RX for Embodiment 2. In FIG. 22, steps common to FIGS. 14 and 15 are assigned the same step numbers, and common descriptions are omitted. In step ST1417, V2X service data using SL communication is transmitted and received between UE-TX and UE-RX.

[0417] Here, an example in which UE-RX notifies a DRX request message to UE-TX is shown. UE-RX, for example, evaluates the communication pattern of V2X service data communication and derives a desired DRX setting such as a desired period from the communication pattern. In step ST2001, UE-RX notifies the derived desired DRX setting to UE-TX included in a DRX setting request message.

[0418] In step ST2002, UE-TX determines the DRX setting in the SL communication with UE-RX using the DRX request message received from UE-RX and the desired DRX setting included therein.

[0419] In step ST2003, UE-TX notifies UE-RX of the determined DRX setting. In step ST2003, UE-TX that has notified UE-RX of the DRX setting performs transmission and reception of V2X service data according to the DRX setting in step ST2004. Also, UE-RX that has received the DRX setting in step ST2003 performs transmission and reception of V2X service data according to the DRX setting in step ST2004. A response message for the DRX setting in step ST2003 may be provided. By notifying UE-TX of the response message from UE-RX, UE-TX can recognize that UE-RX has performed the DRX setting.

[0420] A rejection message may be provided. Alternatively, rejection information may be included in the response message. Reason information may also be included. By notifying UE-TX of the rejection message from UE-RX, UE-TX can recognize that UE-RX was unable to perform the DRX setting. For example, UE-TX may perform a different DRX setting and notify it to UE-RX again.

[0421] By doing so, DRX transmission and reception can be implemented in the SL communication between UE-TX and UE-RX.

[0422] UE-RX may modify the DRX setting. For example, when the communication pattern of V2X service data communication changes, UE-RX may modify the DRX setting. In step ST2005, UE-RX notifies UE-TX by including the desired DRX setting in a DRX setting request message.

[0423] In step ST2006, UE-TX determines the modification of the DRX setting in the SL communication with UE-RX using the DRX request message received from UE-RX and the desired DRX setting included therein.

[0424] In step ST2007, UE-TX notifies the determined DRX setting to UE-RX. In step ST2007, UE-TX that has notified the DRX setting to UE-RX performs transmission and reception of V2X service data according to the DRX setting in step ST2008. Also, UE-RX that has received the DRX setting in step ST2007 performs transmission and reception of V2X service data according to the DRX setting in step ST2008.

[0425] By doing so, in the SL communication between UE-TX and UE-RX, the DRX setting can be flexibly modified. Transmission and reception according to the communication pattern of V2X service data can be implemented.

[0426] Disclose a method for releasing the DRX setting. The DRX setting node notifies the DRX configured node of the release of the DRX setting. The DRX setting node may notify by associating the set DRX setting with the DRX setting to be released. For example, the DRX setting node may perform the notification using the DRX setting identifier of the DRX to be released. By doing so, when releasing a plurality of DRX settings to the UE performing SL communication, it becomes possible to determine which DRX setting the UE performing SL communication releases.

[0427] Similar to the DRX setting, a response message for the release of the DRX setting may be provided. The release process of the DRX setting can be surely implemented. Also, a message for requesting the release of the DRX setting may be provided. The DRX setting can be released according to the situation of the DRX configured node. For example, when the battery of UE-RX is charged and low power consumption is no longer required, or when UE-RX wants to perform the V2X service early, UE-RX can request the release of the DRX setting, and the release of the set DRX setting becomes possible.

[0428] In SL communication, unicast communication is two-way communication. In the opposite UEs performing SL communication, DRX settings may be performed in two-way communication. For example, when unicast communication is performed between a UE-TX that first performs transmission for a V2X service and a UE-RX, DRX is set in the SL communication from UE-TX to UE-RX, and DRX is also set in the SL communication from UE-RX to UE-TX. DRX settings are performed in two-way communication in SL. By doing so, power consumption reduction of the UE and improvement of resource utilization efficiency can be achieved in two-way SL communication.

[0429] Disclose the DRX setting nodes in each direction. The transmitting-side UE in SL communication in each direction sets DRX. For example, in the SL communication from UE-TX to UE-RX, UE-TX performs DRX setting and notifies the setting to UE-RX. Also, in the SL communication from UE-RX to UE-TX, UE-RX performs DRX setting and notifies the setting to UE-TX. Each transmitting UE enables DRX setting using the timing when V2X service data is generated.

[0430] Disclose other methods. One of the opposite UEs performing two-way SL communication sets DRX in two-way SL communication. For example, the UE that first performs transmission for a V2X service may perform DRX setting in two-way SL communication. UE-TX performs DRX setting in both directions and notifies the setting to UE-RX. The signaling amount required for DRX setting can be reduced.

[0431] In two-way SL communication, the reference times in each direction may be made the same. The same synchronization source is used between opposing UEs that perform two-way SL unicast communication. Examples of the synchronization source include gNB, GNSS, and UE. The synchronization source information may be notified between the opposing UEs. The UE that receives the synchronization source information may use the same synchronization source. The UE that first transmits a V2X service may notify the opposing UE of the synchronization source information. By doing so, the reference times in each direction in two-way SL communication can be made the same.

[0432] One of the opposing UEs that perform two-way SL unicast communication may operate as a synchronization source. The opposing UEs that perform two-way SL unicast communication may transmit a synchronization signal and / or a synchronization channel. The SL SS (Synchronization Signal) may be used as the synchronization signal. The SBCCH may be used as the synchronization channel. The UE that performs two-way SL unicast communication may receive the SL SS and / or SBCCH transmitted by one of the opposing UEs and perform synchronization using them. By doing so, the reference times in each direction in two-way SL communication can be made the same.

[0433] By making the reference times in each direction the same in two-way SL communication, the time axes in each direction can be made identical. For example, it becomes possible to indicate the radio frame number, slot number, and symbol number in each direction of SL based on the same reference.

[0434] In two-way SL communication, when setting DRX in both directions of SL communication, a method of making the reference times in each direction the same in two-way SL communication may be applied. The time axes of the DRX settings in each direction can be made identical.

[0435] In two-way SL communication, the DRX timings in each direction may be aligned. The DRX timing in the communication from UE-TX to UE-RX and the DRX timing in the communication from UE-RX to UE-TX may be aligned. The DRX timing may be the on-period in the DRX setting. For example, the on-period in the communication from UE-TX to UE-RX and the on-period in the communication from UE-RX to UE-TX are provided within a predetermined period. In the present disclosure, the predetermined period may be referred to as the DRX transmission / reception period.

[0436] As a method for aligning the DRX timing in the communication from UE-TX to UE-RX and the DRX timing in the communication from UE-RX to UE-TX, the DRX cycles in each direction may be made the same. Alternatively, the DRX cycles in each direction may be in a relationship of an integer multiple or one over an integer. Also, the DRX start offset may be set so that the on-period in each direction is within the DRX transmission / reception period.

[0437] When the communication in each direction is performed in time division multiplexing, in the DRX transmission / reception period, the on-periods in each direction may be made not to overlap. For example, the DRX start offset may be set so that the on-period from UE-TX to UE-RX and the on-period from UE-RX to UE-TX are temporally continuous.

[0438] FIG. 23 is a conceptual diagram of a first example of aligning the DRX timings in each direction in two-way SL communication for Embodiment 2. The horizontal axis represents time, and the vertical axis represents frequency. The hatched portion indicates the on-period of DRX in the communication from UE-TX to UE-RX. In the hatched portion, UE-RX receives from UE-TX. The cross-hatched portion indicates the on-period of DRX in the communication from UE-RX to UE-TX. In the cross-hatched portion, UE-RX transmits to UE-TX.

[0439] Make the DRX period from UE-TX to UE-RX the same as the DRX period from UE-RX to UE-TX. Also, delay the start offset of DRX from UE-RX to UE-TX by at least the on-period of DRX in the communication from UE-TX to UE-RX compared to the start offset of DRX from UE-TX to UE-RX. FIG. 23 illustrates the case where the start offset of DRX from UE-RX to UE-TX is delayed by only the on-period of DRX. By doing so, the on-periods of DRX in the communication from UE-TX to UE-RX and the on-period of DRX in the communication from UE-RX to UE-TX can be multiplexed so that they do not overlap in the time axis direction.

[0440] By performing DRX settings in each direction in this way, it becomes possible to make the reception period and the transmission period at UE-RX continuous without overlapping. Also, it becomes possible to make the transmission period and the reception period at UE-TX continuous without overlapping.

[0441] By doing so, it becomes possible to align the transmission and reception periods in the opposing UEs that perform two-way SL communication.

[0442] In two-way SL communication, if the DRX timings in each direction are set inconsistently, the transmission and reception periods of the opposing UEs that perform SL communication will become inconsistent, and each of these UEs will repeat turning on and off for transmission and reception. Then, it becomes impossible to reduce power consumption. By aligning the transmission and reception periods in the opposing UEs that perform two-way SL communication by the method as described above, the inactive period in each UE can be lengthened. Thereby, further power consumption reduction of each UE can be achieved.

[0443] When the transmitting UE in SL communication in each direction sets DRX, one transmitting UE sets the DRX setting for one SL communication using the DRX setting set by the other transmitting UE for the other SL communication. One transmitting UE may set the DRX setting for one SL communication so that the DRX timing of the received SL communication in the other direction matches the DRX timing of the SL communication in one direction. By doing so, in two-way SL communication, even when the transmitting UE in SL communication in each direction sets DRX, the DRX timings in each direction can be aligned.

[0444] FIG. 24 is a sequence diagram showing an example of a method for aligning the DRX timings in each direction when the transmitting UE in SL communication in each direction sets DRX in Embodiment 2. In FIG. 24, steps common to FIGS. 14 and 15 are given the same step numbers, and the common descriptions are omitted. FIG. 24 illustrates a method of notifying the DRX setting when notifying each other of the AS settings between UE-TX and UE-RX.

[0445] In step ST2201, UE-TX determines the DRX setting in the SL communication from UE-TX to UE-RX. In step ST2202, UE-TX notifies UE-RX of an AS setting message. UE-TX includes the DRX setting in the SL communication from UE-TX to UE-RX in the AS setting message. By doing so, UE-RX can receive the DRX setting of the SL communication from UE-TX to UE-RX.

[0446] In step ST2203, UE-RX determines the DRX configuration for SL communication from UE-RX to UE-TX. At this time, UE-RX uses the DRX configuration for SL communication from UE-TX to UE-RX received from UE-TX. For example, UE-RX determines the DRX configuration so that the DRX period for SL communication from UE-TX to UE-RX is the same as the DRX period for SL communication from UE-RX to UE-TX. Also, UE-RX sets the offset so that the DRX on-period for SL communication from UE-TX to UE-RX is continuous with the DRX on-period for SL communication from UE-RX to UE-TX. UE-RX may set the offset so that the DRX on-period in each direction is within a predetermined DRX transmission / reception period. By doing so, the DRX timings in each direction can be aligned.

[0447] In step ST2204, UE-RX notifies UE-TX of a completion message for the AS configuration from UE-TX and an AS configuration message. UE-RX includes the DRX configuration for SL communication from UE-RX to UE-TX in the AS configuration. By doing so, UE-TX can receive with the DRX configuration for SL communication from UE-RX to UE-TX. In step ST2205, UE-TX notifies UE-RX of an AS configuration completion message.

[0448] In step ST2206, UE-TX and UE-RX perform transmission and reception of V2X service data according to the DRX configuration set for SL communication in each direction.

[0449] By doing so, the transmitting UE in SL communication in each direction can align the DRX timings in each direction. In opposite UEs performing two-way SL communication, by aligning the transmission / reception periods, the inactive periods in each UE can be lengthened. Thereby, further power consumption reduction in each UE can be achieved.

[0450] It is disclosed to include DRX settings in the AS setting message for notification. By doing so, the signaling amount can be reduced. DRX settings may be performed separately from the AS setting message. DRX settings are enabled at the timing required for SL communication in each direction. UE-TX and / or UE-RX may notify the opposing UE in SL communication in each direction of a DRX setting request. The opposing UE may perform DRX settings in response to the DRX setting request for SL communication in each direction. By doing so, DRX settings can be flexibly implemented in SL communication in each direction.

[0451] FIG. 25 is a conceptual diagram of a second example for aligning the DRX timings in each direction in two-way SL communication according to Embodiment 2. The horizontal axis represents time, and the vertical axis represents frequency. The hatched portion indicates the ON period of DRX in the communication from UE-TX to UE-RX. In the hatched portion, UE-RX receives from UE-TX. The cross-hatched portion indicates the ON period of DRX in the communication from UE-RX to UE-TX. In the cross-hatched portion, UE-RX transmits to UE-TX.

[0452] Set the DRX periods in both directions to be the same. As DRX settings, set the DRX period, offset, and DRX transmission / reception period. The communication from UE-TX to UE-RX is carried out from the beginning within the DRX transmission / reception period. This may be determined statically in a standard or the like. It is only necessary for UE-TX and UE-RX to recognize it in advance.

[0453] UE-RX performs a reception operation from the beginning of the DRX transmission / reception period, and enables transmission to UE-TX within the range of the DRX transmission / reception period when there is no transmission from UE-TX. UE-TX performs reception from UE-RX within the range of the DRX transmission / reception period when there is no transmission to UE-RX. UE-RX performs a reception operation from the beginning of the DRX transmission / reception period, and enables transmission to UE-TX within the range of the DRX transmission / reception period after the completion of the reception when there is a transmission from UE-TX. UE-TX performs reception from UE-RX within the range of the DRX transmission / reception period after the completion of the transmission to UE-RX when there is a transmission to UE-RX.

[0454] By doing so, it becomes possible to perform two-way SL communication during the DRX transmission / reception period. Further power consumption reduction of each UE can be achieved.

[0455] By adopting such a setting method, it is possible to reduce the signaling and the amount of information required for the DRX setting for two-way SL communication.

[0456] Such a setting method may be applied when one of the opposing UEs performing two-way SL communication performs the DRX setting in the two-way SL communication. The DRX setting process for two-way SL communication can be facilitated.

[0457] When setting DRX in each direction in two-way SL communication, one transmitting UE may perform the DRX setting for two-way SL communication. The UE may set DRX so that the DRX timings in each direction are aligned. In two-way SL communication, the DRX timings in each direction can be aligned.

[0458] FIG. 26 is a sequence diagram showing an example of a method for aligning the DRX timings in each direction when one transmitting UE sets DRX for Embodiment 2. In FIG. 26, the same step numbers are assigned to the steps common to FIGS. 14 and 15, and the common descriptions are omitted. FIG. 26 illustrates a method of notifying the DRX setting when notifying each other of the AS settings between UE-TX and UE-RX.

[0459] In step ST2401, UE-TX determines the DRX settings for SL communication from UE-TX to UE-RX and for SL communication from UE-RX to UE-TX, that is, the DRX settings for SL communication in both directions. At this time, UE-TX determines the DRX settings so that, for example, the DRX period for SL communication from UE-TX to UE-RX is the same as the DRX period for SL communication from UE-RX to UE-TX. Also, UE-TX sets an offset so that the DRX on-period for SL communication from UE-TX to UE-RX is continuous with the DRX on-period for SL communication from UE-RX to UE-TX. UE-TX may set the offset so that the DRX on-period in each direction is within a predetermined DRX transmission and reception period. By doing so, the DRX timings in each direction can be aligned.

[0460] In step ST2402, UE-TX notifies UE-RX of an AS configuration message. UE-TX includes in the AS configuration message the DRX settings for SL communication from UE-TX to UE-RX and the DRX settings for SL communication from UE-RX to UE-TX. By doing so, UE-RX can receive using the DRX settings for SL communication from UE-TX to UE-RX and can transmit using the DRX settings for SL communication from UE-RX to UE-TX.

[0461] In step ST2403, UE-RX notifies UE-TX of a completion message for the AS configuration from UE-TX and the AS configuration message. In step ST2404, UE-TX notifies UE-RX of an AS configuration completion message.

[0462] In step ST2405, UE-TX and UE-RX perform transmission and reception of V2X service data according to the DRX settings set for SL communication in each direction.

[0463] By doing so, one of the transmitting UEs performing SL communication can perform DRX settings for two-way SL communication. In the opposing UEs performing two-way SL communication, by aligning the transmission and reception periods, the inactive periods in each UE can be lengthened. Thereby, further power consumption reduction of each UE can be achieved. By one of the transmitting UEs performing DRX settings for two-way SL communication, signaling can be reduced. Also, since there is no need to perform DRX settings at UE-RX, DRX processing can be facilitated. Therefore, malfunction can be reduced.

[0464] In the case of setting a plurality of DRX settings between one pair of opposing UEs, each DRX setting may be performed so that the plurality of DRX timings are aligned. The DRX setting method described above may be applied as appropriate. Even if a plurality of DRX settings are performed, by aligning the transmission and reception periods, the inactive periods in each UE can be lengthened. Thereby, further power consumption reduction of each UE can be achieved.

[0465] A configured grant for setting in advance the resources to be used may be provided between UEs performing SL communication. The resources to be used in advance may be periodic resources. The configured grant includes allocation information of the resources. For example, UE-TX notifies UE-RX of a configured grant to set the resources to be used for SL communication. UE-RX that has received the configured grant uses the resources set by the configured grant for SL communication to UE-TX.

[0466] For the notification of configured grants between UEs performing SL communication, PC5-RRC signaling may be used. The number of configured grant settings is not limited to one and may be multiple. Also, activation / deactivation information for the configured grants may be provided. For example, the activation / deactivation information may be included in the SCI for notification. By using the SCI, it becomes possible to dynamically activate / deactivate the configured grants.

[0467] As described above in the DRX setting, in SL communication over PC5, unlike communication over Uu, it is not possible to transmit and receive in all subframes. Transmission and reception are only possible within the resource pool configured for SL communication. Therefore, the configured grants in Uu cannot be applied as they are. The method disclosed in the above DRX setting may be appropriately applied to the setting of configured grants in SL communication. It is possible to set the resources allocated by the configured grants within the range of the RP.

[0468] One transmitting UE may perform DRX setting for SL communication in one direction and set a configured grant in SL for SL communication in the other direction. For example, let one UE be UE-TX. UE-TX performs DRX setting for SL communication from UE-TX to UE-RX and sets periodic resources with a configured grant for SL communication from UE-RX to UE-TX. UE-TX may notify UE-RX of these settings. UE-RX receives SL communication from UE-TX using the DRX setting and transmits SL communication to UE-TX using the configured grant.

[0469] The one UE may be set so that the DRX timing and the timing of the periodic resources by the configured grant are aligned. In two-way SL communication, the timing at which each UE operates can be aligned. Therefore, power consumption of each UE can be reduced.

[0470] The transmitting UE in SL communication in each direction may set a configured grant. One transmitting UE uses the configured grant set for one SL communication, and the other transmitting UE uses the configured grant set for the other SL communication. The other UE may perform a configured grant for the other SL communication so that the resource timing assigned by the configured grant of the received one SL communication matches the resource timing to be assigned by the configured grant of the other SL communication. By doing so, in two-way SL communication, even when the transmitting UE in each direction of SL communication sets a configured grant, the operation timings of each UE can be aligned. Therefore, power consumption of each UE can be reduced.

[0471] In a situation where one UE performs SL communication with a plurality of UEs, the DRX timings in each SL communication may be different. In such a case, if the DRX timings in each SL communication are set non-uniformly, the transmission and reception periods of the UE become non-uniform, and the UE repeatedly turns on and off transmission and reception. Then, reduction of power consumption cannot be achieved.

[0472] Here, a method for solving such problems is disclosed.

[0473] The UE that performs SL communication with a plurality of UEs performs DTX setting so as to align the DRX timings. The UE that performs SL communication with a plurality of UEs notifies the DRX setting node of the desired DRX setting. The above-described DRX setting request message or DRX setting modification request message may be used.

[0474] Figs. 27 to 29 are sequence diagrams showing examples of a method in which a UE that performs SL communication with a plurality of UEs performs DTX setting so as to align the DRX timings in Embodiment 2. Figs. 27 to 29 are connected at the positions of boundary lines BL2728 and BL2829. In Figs. 27 to 29, steps common to Figs. 14 and 15 are given the same step numbers, and the common descriptions are omitted.

[0475] For example, a V2X service is generated that is performed by UE-TX1 using SL communication with UE-RX. In step ST1409, UE-TX1 establishes a PC5-S connection with UE-RX. In step ST2501, UE-TX1 and UE-RX mutually notify each other of UE capabilities. In step ST2502, UE-TX1 and UE-RX mutually notify each other of AS settings. By doing so, in step ST2503, it becomes possible to transmit and receive V2X service data using SL communication between UE-TX1 and UE-RX.

[0476] In step ST2505, UE-TX1 determines the DRX settings for SL communication from UE-TX1 to UE-RX and SL communication from UE-RX to UE-TX1, that is, the DRX settings for SL communication in both directions. At this time, UE-TX1 determines the DRX settings so that, for example, the DRX on-period in each direction is within a predetermined DRX transmission / reception period. By doing so, the DRX timing in each direction can be aligned.

[0477] In step ST2506, UE-TX1 notifies UE-RX of the DRX settings for SL communication in both directions between UE-TX1 and UE-RX. In step ST2507, UE-RX notifies UE-TX1 of a DRX setting completion message. By doing so, UE-RX can receive using the DRX settings for SL communication from UE-TX1 to UE-RX and can transmit using the DRX settings for SL communication from UE-RX to UE-TX1.

[0478] In step ST2508, UE-TX1 and UE-RX transmit and receive V2X service data according to the DRX settings set for SL communication in each direction.

[0479] A V2X service is generated in which UE-TX2 performs SL communication with UE-RX. Similar to steps ST1409 to ST2503 described above, UE-TX2 establishes a PC5-S connection with UE-RX and enables the transmission and reception of V2X service data using SL communication between UE-TX2 and UE-RX.

[0480] In step ST2513, UE-RX determines the desired DRX setting in the SL communication between UE-TX2 and UE-RX. At this time, UE-RX uses the DRX setting in the two-way SL communication between UE-TX1 and UE-RX received from UE-TX1. For example, UE-RX determines the desired DRX setting so that the DRX period in the SL communication from UE-TX1 to UE-RX is the same as the DRX period in the SL communication from UE-TX2 to UE-RX. Also, UE-RX may determine the desired DRX setting so that the DRX on period in the SL communication from UE-TX1 to UE-RX and the DRX on period in the SL communication from UE-TX2 to UE-RX are within a predetermined DRX transmission and reception period. By doing so, the SL connections with each UE-TX and the DRX timings in each direction can be aligned.

[0481] In step ST2514, UE-RX notifies UE-TX2 of the determined desired DRX setting. In step ST2515, UE-TX2 determines the DRX setting in the two-way SL communication between UE-TX2 and UE-RX using the desired DRX setting received from UE-RX.

[0482] In step ST2516, UE-TX2 notifies UE-RX of the DRX setting in the two-way SL communication between UE-TX2 and UE-RX. In step ST2517, UE-RX notifies UE-TX2 of a DRX setting completion message. By doing so, UE-RX can receive using the DRX setting of the SL communication from UE-TX2 to UE-RX, and can transmit using the DRX setting of the SL communication from UE-RX to UE-TX2.

[0483] In step ST2518, UE-TX2 and UE-RX perform transmission and reception of V2X service data according to the DRX settings configured for SL communication in each direction.

[0484] The same applies when a V2X service performed by UE-TX3 using SL communication with UE-RX occurs. Similar to steps ST1409 to ST2503 described above, UE-TX3 establishes a PC5-S connection with UE-RX and enables transmission and reception of V2X service data using SL communication between UE-TX3 and UE-RX.

[0485] In step ST2523, UE-RX determines the desired DRX settings for the SL communication between UE-TX3 and UE-RX. At this time, UE-RX uses the DRX settings for the two-way SL communication between UE-TX1 and UE-RX received from UE-TX1 and the DRX settings for the two-way SL communication between UE-TX2 and UE-RX received from UE-TX2. For example, UE-RX determines the desired DRX settings so that the DRX periods for the SL communication from UE-TX1 to UE-RX, the DRX periods for the SL communication from UE-TX2 to UE-RX, and the DRX periods for the SL communication from UE-TX3 to UE-RX are the same. Also, UE-RX may determine the desired DRX settings so that the DRX on-periods for the SL communication from UE-TX1 to UE-RX, the DRX on-periods for the SL communication from UE-TX2 to UE-RX, and the DRX on-periods for the SL communication from UE-TX3 to UE-RX are within a predetermined DRX transmission and reception period. By doing so, the SL connections with each UE-TX and the DRX timings in each direction can be aligned.

[0486] In step ST2526, UE-RX notifies UE-TX3 of the determined desired DRX settings. In step ST2525, UE-TX3 determines the DRX settings for the two-way SL communication between UE-TX3 and UE-RX using the desired DRX settings received from UE-RX.

[0487] In step ST2526, UE-TX3 notifies UE-RX of the DRX setting in the two-way SL communication between UE-TX3 and UE-RX. In step ST2527, UE-RX notifies UE-TX3 of a DRX setting completion message. By doing so, UE-RX can receive in accordance with the DRX setting of the SL communication from UE-TX3 to UE-RX, and can transmit in accordance with the DRX setting of the SL communication from UE-RX to UE-TX3.

[0488] In step ST2528, UE-TX3 and UE-RX transmit and receive V2X service data according to the DRX settings configured for the SL communication in each direction.

[0489] By doing so, even when a UE performs SL communication with a plurality of UEs, the SL connection with each UE-TX and the DRX timing in each direction can be aligned.

[0490] By the method as described above, in a UE that performs SL communication with a plurality of UEs, by aligning the transmission and reception periods, the inactive period can be lengthened. Thereby, power consumption of the UE can be reduced. The SL communication with a plurality of UEs may be two-way, and by appropriately combining and implementing the method disclosed in the second embodiment, power consumption of the UE can be reduced.

[0491] When DRX is set between opposing UEs, if a UE moves during the inactive period, communication with the opposing UE may become impossible. For example, UE-RX receives communication from UE-TX during the on-period of DRX. When UE-RX cannot receive communication from UE-TX during the on-period of DRX, there arises a problem that it becomes impossible to determine whether there is no transmission data from UE-TX or whether communication with UE-TX has become impossible.

[0492] Here, a method for solving such problems is disclosed. The DRX setting includes a setting to always perform transmission during the transmission on period, and the UE always performs transmission during the transmission on period according to the DRX setting. For example, the UE may transmit the RS during the transmission on period. The SL RS may be used. In order to identify the UE that has transmitted the RS, the sequence used for the RS may be a sequence using the identifier of the transmitting UE. By doing so, the UE that has received the RS can recognize that it is the RS transmitted from the transmitting UE. The UE that has received the RS can recognize that communication with the opposite UE is not impossible. The UE that has not been able to receive the RS can recognize that communication with the UE-TX has become impossible.

[0493] If the UE cannot receive the RS continuously for a predetermined number of times or for a predetermined period, the UE may determine that communication with the UE-TX has become impossible. For example, if the UE cannot receive the RS continuously for a predetermined number of times within the transmission on period, the UE may determine that communication with the UE-TX has become impossible. For example, if the transmission on periods during which the UE cannot receive the RS continue for a predetermined number of times, the UE may determine that communication with the UE-TX has become impossible. For example, it is possible to avoid determining communication as impossible in cases where the communication quality deteriorates temporarily due to communication path blocking or the like.

[0494] Also, for example, the UE may transmit the PSCCH during the transmission on period. The UE may include the identifier of the transmitting UE in the SCI, map the SCI to the PSCCH, and transmit the PSCCH. Alternatively, the identifier of the transmitting UE may be used as the code for detecting the PSCCH. By doing so, the UE that has received the PSCCH or SCI can recognize that the received PSCCH or SCI is transmitted from the transmitting UE. The UE that has received the PSCCH or SCI can recognize that communication with the opposite UE is not impossible. The UE that has not been able to receive the PSCCH or SCI can recognize that communication with the UE-TX has become impossible.

[0495] If the UE cannot receive the PSCCH or SCI continuously for a predetermined number of times or a predetermined period, the UE may determine that communication with the UE-TX has become impossible. For example, if the UE cannot receive the PSCCH or SCI continuously for a predetermined number of times within the transmission on-period, the UE may determine that communication with the UE-TX has become impossible. For example, if the number of consecutive transmission on-periods during which the UE cannot receive the PSCCH or SCI reaches a predetermined number, the UE may determine that communication with the UE-TX has become impossible. For example, it is possible to avoid determining that communication is impossible in cases where the communication quality temporarily deteriorates due to communication path blocking or the like.

[0496] By doing so, when DRX is set between opposing UEs, the receiving UE can determine whether there is no transmission data from the transmitting UE or whether communication with the transmitting UE has become impossible.

[0497] If communication with the transmitting UE becomes impossible, the receiving UE may perform the SL communication connection process again with the transmitting UE. For example, if UE-RX cannot receive a transmission from UE-TX during the on-period, it determines that SL communication with UE-TX has become impossible, and UE-RX performs the SL communication connection process with UE-TX again. Conversely, for example, if UE-TX cannot receive a transmission from UE-RX during the on-period, it determines that SL communication with UE-RX has become impossible, and UE-TX performs the SL communication connection process with UE-RX again.

[0498] By doing so, it is possible to make the SL communication between UE-TX and UE-RX possible as much as possible.

[0499] The method for determining the impossibility of communication with the opposing UE when DRX is set as described above may be appropriately applied to the method of the present disclosure. For example, the method for determining the impossibility of communication with the opposing UE when DRX is set may be appropriately applied as a method for detecting RLF at the time of DRX setting in SL. The method for determining the impossibility of communication with the opposing UE when DRX is set may be appropriately applied to the method of releasing the PC5 connection of SL communication by RLF detection. Even when DRX is set in SL communication, it is possible to execute the release process of the PC5 connection as necessary. It is possible to further improve the utilization efficiency of resources for SL communication and reduce the power consumption of the UE.

[0500] Embodiment 3. In Embodiment 1, it was disclosed that the connection between the S-UE and the UE-TX is maintained even after the S-UE notifies the UE-TX of the resource information. In this case, for example, when the S-UE changes the resources for the UE-TX, the connection process becomes unnecessary, so it is possible to notify the resource change earlier, and it was disclosed that the resource change of SL communication can be performed with low latency. However, in order to maintain the connection between the S-UE and the UE-TX, resources must be retained, which reduces the utilization efficiency of the resources. In addition, the UE requires a reception operation, increasing the power consumption of the UE.

[0501] On the other hand, in Embodiment 1, it was also disclosed that the connection between the S-UE and the UE-TX is released after the S-UE notifies the UE-TX of the resource information. In this case, it was disclosed that there is no need to retain the resources for the connection between the S-UE and the UE-TX, and the utilization efficiency of the resources can be improved. However, conversely, for example, when changing the resources used for SL communication, the connection process is required again, increasing the delay for resource change.

[0502] This Embodiment 3 discloses a method for solving such problems.

[0503] Configure DRX in the SL communication between the S-UE and the UE-TX. The S-UE may perform the DRX configuration. The UE-TX may perform the DRX configuration. It is also possible to perform the DRX configuration after notifying the UE-TX of the resource information from the S-UE. The method disclosed in Embodiment 2 may be appropriately applied.

[0504] In the SL communication between the S-UE and the UE-TX, even when V2X service data is not transmitted, the resource information used for the SL communication between the UE-TX and the UE-RX is transmitted. Conventionally, DRX is configured for the intermittent transmission and reception of U-plane data. Here, DRX configuration may be performed for the transmission and reception of C-Plane signaling.

[0505] In Embodiment 1, it was disclosed that the resource information from the S-UE to the UE-TX may be notified by PC5-S signaling. It was also disclosed that default RBs may be used for PC5-S signaling. DRX configuration may be performed for the default RBs used for the SL communication between the S-UE and the UE-TX.

[0506] By doing so, it becomes possible to implement DRX in the SL communication between the S-UE and the UE-TX while maintaining the connection without releasing the connection between the S-UE and the UE-TX after notifying the UE-TX of the resource information from the S-UE.

[0507] When two-way SL communication is performed between the S-UE and the UE-TX, the DRX timing from the S-UE to the UE-TX and the DRX timing from the UE-TX to the S-UE may be made the same. The method disclosed in Embodiment 2 may be appropriately applied. Power consumption of the S-UE and the UE-TX can be reduced.

[0508] DRX may be set between UE-TX and UE-RX. The DRX timing in the SL communication between UE-TX and UE-RX may be aligned with the DRX timing in the SL communication between S-UE and UE-TX. Since UE-TX will perform SL communication with a plurality of UEs, in such a case as well, the method disclosed in Embodiment 2 may be appropriately applied. Power consumption of S-UE, UE-TX, and UE-RX can be reduced.

[0509] According to the method disclosed in Embodiment 3, each UE performs DRX in the SL communication between S-UE and UE-TX, thereby reducing power consumption. Also, by setting resources for DRX, it is possible to improve the utilization efficiency of resources. Further, since the connection between S-UE and UE-TX is maintained, for example, when changing resources used for SL communication, reconnection processing is not required, and resource change can be implemented with low latency.

[0510] The method of determining communication impossibility with the opposing UE when DRX is set, as described above, may be appropriately applied to SL communication using S-UE. For example, the method of determining communication impossibility with the opposing UE when DRX is set may be applied as an RLF detection method at the time of DRX setting in SL, and may be appropriately applied to the methods disclosed in Embodiment 1 or Modification Example 1 of Embodiment 1. Also at the time of DRX setting in SL communication using S-UE, it is possible to execute release processing of the PC5 connection as necessary. It is possible to further improve the utilization efficiency of SL communication resources and reduce the power consumption of the UE.

[0511] In the SL communication between S-UE and UE-TX, a configured grant may be set. Instead of setting the aforementioned DRX, a configured grant may be set. For the method of setting a configured grant, the method disclosed in Embodiment 2 may be appropriately applied. The same effect can be obtained.

[0512] The method disclosed in Embodiment 3 and Modification Example 1 of Embodiment 3 may be applied to indirect communication between UEs via a relay UE. The DRX in the PC5 connection between UE-TX and UE-RX may be applied to the DRX in the PC5 connection between UE-TX and the relay UE, or the DRX in the PC5 connection between the relay UE and UE-RX. The same effect can be obtained.

[0513] For example, in Modification Example 1 of Embodiment 3, the DRX timing in the SL communication between UE-TX and the relay UE and the DRX timing in the SL communication between the relay UE and UE-RX may be made the same. The same effect can be obtained.

[0514] Embodiment 4. In SL communication, not only direct communication between UEs but also indirect communication via a relay has been proposed (see Non-Patent Document 24). A relay between UEs may be referred to as a UE-to-UE relay or an inter-UE relay. In the present disclosure, a UE that performs an inter-UE relay may be referred to as a relay UE.

[0515] For example, in a situation where a plurality of UEs traveling in a convoy approach an intersection, direct communication between UEs may become impossible due to blocking by a building or the like. Also, a UE may need to communicate not only with nearby UEs but also with a plurality of more distant UEs. In such a case, a method using an inter-UE relay can be considered. For example, the SL communication between UE-TX and UE-RX is performed via a relay UE. The SL communication between UEs via a relay UE may be referred to as indirect communication between UEs.

[0516] The radio wave propagation conditions between UE-TX and the relay UE are different from those between the relay UE and UE-RX. Therefore, the situations where SL communication between UE-TX and the relay UE becomes impossible may not match the situations where SL communication between the relay UE and UE-RX becomes impossible. If an inconsistency occurs in the connection state between UE-TX and the relay UE and the connection state between the relay UE and UE-RX, relay cannot be performed normally. As a result, problems such as the resources reserved for indirect communication between UEs via the relay UE being wasted or each UE continuing unnecessary processing may occur.

[0517] In Embodiment 4, a method for solving such problems is disclosed.

[0518] Link the PC5 connection between UE-TX and the relay UE and the PC5 connection between the relay UE and UE-RX. The PC5 connection state between the relay UE and UE-RX is determined according to the PC5 connection state between UE-TX and the relay UE. For example, when the PC5 connection between UE-TX and the relay UE is released, the PC5 connection between the relay UE and UE-RX is released.

[0519] A plurality of PC5 connections may be established between UE-TX and the relay UE, and corresponding PC5 connections may be established between the relay UE and UE-RX for each PC5 connection. In such a case, each PC5 connection between UE-TX and the relay UE and the corresponding PC5 connection between the relay UE and UE-RX may be linked. The corresponding PC5 connection state between the relay UE and UE-RX is determined according to each PC5 connection state between UE-TX and the relay UE. For example, when one PC5 connection between UE-TX and the relay UE is released, the corresponding PC5 connection between the relay UE and UE-RX is released.

[0520] One or more PC5 connections may be established between the UE-TX and the relay UE, and one or more PC5 connections may be established between the relay UE and the UE-RX corresponding to the one or more PC5 connections. In such a case, the one or more PC5 connections between the UE-TX and the relay UE and the corresponding one or more PC5 connections between the relay UE and the UE-RX may be linked. According to each PC5 connection state between the UE-TX and the relay UE, the corresponding PC5 connection state between the relay UE and the UE-RX is determined. For example, when one PC5 connection between the UE-TX and the relay UE is released, the corresponding PC5 connection between the relay UE and the UE-RX is released.

[0521] Regarding the one or more PC5 connections between the relay UE and the UE-RX, all states of the corresponding one or more PC5 connections between the relay UE and the UE-RX may be determined according to all PC5 connection states between the corresponding UE-TX and the relay UE. For example, when all PC5 connections between the UE-TX and the relay UE corresponding to the one or more PC5 connections between the relay UE and the UE-RX are released, it may be assumed that all of the corresponding one or more PC5 connections between the relay UE and the UE-RX are released.

[0522] In the PC5 connection, the method disclosed in Embodiment 1 may be appropriately applied to the level of connection or the level of releasing the connection.

[0523] When the PC5 connection between the UE-TX and the relay UE is disconnected instead of being released, the above-mentioned method may be applied. When RLF is detected in the PC5 connection between the UE-TX and the relay UE instead of being released, the above-mentioned method may be applied. These combinations may also be possible.

[0524] FIG. 30 is a sequence diagram showing an example of a method for releasing a PC5 connection between a relay UE and a UE-RX when the PC5 connection between the UE-TX and the relay UE is released in Embodiment 4. In step ST2601, a PC5 connection is established between the UE-TX and the relay UE, and in step ST2602, a PC5 connection is also established between the relay UE and the UE-RX. Discovery processing may be performed when establishing the PC5 connection. Using the PC5 connections in steps ST2601 and ST2602, V2X service data using SL communication is communicated between the UE-TX and the UE-RX.

[0525] A case where the UE-TX releases the connection with the relay UE is disclosed. In step ST2603, the UE-TX requests the relay UE to release the PC5 connection. In step ST2604, the relay UE notifies the UE-TX of a response to the release request. Thereby, the PC5-S connection between the UE-XT and the relay UE is released. The PC5-S connection and the PC5-RRC connection between the UE-TX and the relay UE may be released.

[0526] The response to the release request in step ST2604 may be notified after the PC5 connection between the UE-RX and the relay UE is released. After the relay UE confirms in step ST2606 that the PC5 connection with the UE-RX has been released, the relay UE may notify the UE-TX of a response to the release request. The UE-TX can recognize that the release of the PC5 connection between the relay UE and the UE-RX has been executed.

[0527] The relay UE that has released the PC5 connection with UE-TX releases the PC5 connection with UE-RX. In step ST2605, the relay UE requests the release of the PC5 connection from UE-RX. In step ST2606, UE-RX notifies the relay UE of a response to the release request. Thereby, the PC5-S connection between the relay UE and UE-RX is released. The PC5-S connection and the PC5-RRC connection between the relay UE and UE-RX may be released. The AS configuration between the relay UE and UE-RX may be released.

[0528] By doing so, it becomes possible to link the PC5 connection state between UE-TX and the relay UE and the PC5 connection state between the relay UE and UE-RX. When the PC5 connection between UE-TX and the relay UE is released, the PC5 connection between the relay UE and UE-RX can be released.

[0529] FIG. 31 is a sequence diagram showing an example of a method for releasing the PC5 connection between the relay UE and UE-RX when RLF is detected in the PC5 connection between UE-TX and the relay UE in Embodiment 4. In FIG. 31, the same step numbers are assigned to the steps common to FIG. 30, and the common descriptions are omitted. In step ST2701, the relay UE detects that RLF has occurred in the PC5 connection between UE-TX and the relay UE. Recognizing that the PC5 connection has become impossible due to the detection of RLF, the relay UE releases the PC5 connection with UE-RX in steps ST2605 and ST2606.

[0530] By doing so, even when RLF occurs in the PC5 connection between UE-TX and the relay UE, the PC5 connection between the relay UE and UE-RX can be released.

[0531] Another method is disclosed. The PC5 connection between the relay UE and UE-RX is interlocked with the PC5 connection between UE-TX and the relay UE. According to the PC5 connection state between the relay UE and UE-RX, the PC5 connection state between UE-TX and the relay UE is determined. For example, when the PC5 connection between the relay UE and UE-RX is released, the PC5 connection between UE-TX and the relay UE is released.

[0532] When multiple PC5 connections are established between UE-TX and the relay UE and PC5 connections are established between the relay UE and UE-RX corresponding to each PC5 connection, the PC5 connection between the relay UE and UE-RX may be interlocked with the corresponding PC5 connection between UE-TX and the relay UE. According to the PC5 connection state between the relay UE and UE-RX, the corresponding PC5 connection state between UE-TX and the relay UE is determined. For example, when the PC5 connection between the relay UE and UE-RX is released, the corresponding PC5 connection between UE-TX and the relay UE is released.

[0533] When one or more PC5 connections are established between UE-TX and the relay UE and one or more PC5 connections are established between the relay UE and UE-RX corresponding to the one or more PC5 connections, the one or more PC5 connections between the relay UE and UE-RX may be interlocked with the corresponding one or more PC5 connections between UE-TX and the relay UE. According to each PC5 connection state between the relay UE and UE-RX, the corresponding PC5 connection state between UE-TX and the relay UE is determined. For example, when one PC5 connection between the relay UE and UE-RX is released, the corresponding PC5 connection between UE-TX and the relay UE is released.

[0534] One or more PC5 connections between the UE-TX and the relay UE may have all their states determined according to all the PC5 connection states between the corresponding relay UE and the UE-RX. For example, if all the PC5 connections between the relay UE and the UE-RX corresponding to one or more PC5 connections between the UE-TX and the relay UE are released, all of the corresponding one or more PC5 connections between the UE-TX and the relay UE may be released.

[0535] In the PC5 connection, the method disclosed in Embodiment 1 may be appropriately applied to the level of connection or the level of releasing the connection.

[0536] Instead of the release of the PC5 connection between the relay UE and the UE-RX, the above method may be applied when the PC5 connection between the relay UE and the UE-RX is disconnected. Instead of the release of the PC5 connection between the relay UE and the UE-RX, the above method may be applied when RLF is detected in the PC5 connection between the relay UE and the UE-RX. The above method may be applied when reconnection does not occur within a predetermined period after the occurrence of RLF in the PC5 connection between the relay UE and the UE-RX. Combinations of these may also be possible.

[0537] The method disclosed in Modification Example 1 of Embodiment 1 may be appropriately applied to the method disclosed in Embodiment 4 of the present invention. It is only necessary to replace "S-UE" and "UE-TX" in Modification Example 1 of Embodiment 1 with "UE-TX" and "relay UE", and replace "UE-TX" and "UE-RX" in Modification Example 1 of Embodiment 1 with "relay UE" and "UE-RX".

[0538] FIG. 32 is a sequence diagram showing an example of a method for releasing a PC5 connection between a UE-TX and a relay UE when the PC5 connection between the relay UE and the UE-RX is released in Embodiment 4. In FIG. 32, steps common to FIG. 31 are assigned the same step numbers, and common explanations are omitted.

[0539] The relay UE determines to release the PC5 connection with the UE-RX. In steps ST2801 and ST2802, the relay UE releases the PC5 connection with the UE-RX. The relay UE that has released the PC5 connection with the UE-RX releases the PC5 connection with the UE-TX. In steps ST2803 and ST2804, the relay UE releases the PC5 connection with the UE-TX.

[0540] By doing so, the PC5 connection state between the relay UE and the UE-RX and the PC5 connection state between the UE-TX and the relay UE can be interlocked. When the PC5 connection between the relay UE and the UE-RX is released, the PC5 connection between the UE-TX and the relay UE can be released.

[0541] FIG. 33 is a sequence diagram showing an example of a method for releasing the PC5 connection between the UE-TX and the relay UE when RLF is detected in the PC5 connection between the relay UE and the UE-RX in Embodiment 4. In FIG. 33, the same step numbers are assigned to the steps common to FIG. 32, and the common descriptions are omitted. In step ST2901, the relay UE detects that RLF has occurred in the PC5 connection between the relay UE and the UE-RX. The relay UE that has recognized that the PC5 connection has become impossible due to the detection of RLF releases the PC5 connection with the UE-TX in steps ST2803 and ST2804.

[0542] By doing so, even when RLF occurs in the PC5 connection between the relay UE and the UE-RX, the PC5 connection between the UE-TX and the relay UE can be released.

[0543] Whether to release the connection between the relay UE and the UE-RX may be determined according to the connection state between the UE-TX and the relay UE. The relay UE may make such a determination. The relay UE determines the connection state between the UE-TX and the relay UE and determines whether to release the connection between the relay UE and the UE-RX.

[0544] The UE-RX may make this decision. The UE-RX determines the connection state between the UE-TX and the relay UE, and decides whether to release the connection between the relay UE and the UE-RX. A method is required to enable the relay UE to determine the connection state between the UE-TX and the relay UE. The relay UE may detect the connection state between the UE-TX and the relay UE, and notify the UE-RX of the connection state information between the UE-TX and the relay UE. As the connection state information, the PC5 connection state information disclosed in Embodiment 1 may be used. The UE-RX uses the connection state information received from the relay UE to decide whether to release the connection between the relay UE and the UE-RX.

[0545] A PC5 connection release request may be provided. The relay UE may notify the UE-RX of the PC5 connection release request. The PC5 connection release request may include the PC5 connection state information between the UE-TX and the relay UE. The notification method may appropriately apply the resource information notification method disclosed in Embodiment 1. The UE-RX uses the PC5 connection release request received from the relay UE to decide whether to release the connection between the relay UE and the UE-RX.

[0546] If the UE-RX decides to maintain the connection between the relay UE and the UE-RX, the UE-RX may notify the relay UE to maintain the connection between the relay UE and the UE-RX. This notification may be used as a response to the PC5 connection release request. This notification may be used as a rejection response to the PC5 connection release request. Reason information may be provided and the reason information may be notified together with the rejection response.

[0547] UE-RX may notify the relay UE of a request regarding the connection between UE-TX and the relay UE. UE-RX may request a reconnection between UE-TX and the relay UE. Reconnection request information may be provided and notified together with a rejection response to the PC5 connection release request. The relay UE that has received a reconnection processing request from UE-RX performs reconnection processing with UE-TX. As the reconnection processing, a Direct Communication Request may be activated to perform reconnection processing of the PC5 connection. As the reconnection processing, discovery processing may be performed before the Direct Communication Request.

[0548] If the relay UE fails to reconnect with UE-TX, the relay UE may release the connection between the relay UE and UE-RX.

[0549] The relay UE may notify UE-RX of a PC5 connection release request. A PC5 connection release indication may be provided. The relay UE may notify UE-RX of the PC5 connection release indication. For example, the cause information may be the failure of reconnection with UE-TX. When UE-RX receives the PC5 connection release request or the PC5 connection release indication, it is advisable to release the connection with the relay UE.

[0550] By doing so, UE-RX can determine the connection state between UE-TX and the relay UE and decide whether to release the connection between the relay UE and UE-RX.

[0551] Whether to release the connection between UE-TX and the relay UE may be determined according to the connection state between the relay UE and UE-TX. The relay UE may make this determination. The relay UE determines the connection state between UE-TX and the relay UE and decides whether to release the connection between UE-TX and the relay UE.

[0552] The UE-TX may make such a decision. The UE-TX determines the connection state between the relay UE and the UE-RX, and decides whether to release the connection between the UE-TX and the relay UE. A method that enables the UE-TX to determine the connection state between the relay UE and the UE-RX is required. As this method, the method described above that enables the UE-RX to determine the connection state between the UE-TX and the relay UE may be appropriately applied. It is only necessary to replace "UE-RX" with "UE-TX" and replace "between the UE-TX and the relay UE" with "between the UE-RX and the relay UE".

[0553] By doing so, it becomes possible for the UE-TX to determine the connection state between the relay UE and the UE-RX, and decide whether to release the connection between the UE-TX and the relay UE.

[0554] FIG. 34 is a sequence diagram showing an example of a method for releasing the PC5 connection between the UE-TX and the relay UE when an RLF is detected in the PC5 connection between the relay UE and the UE-RX in Embodiment 4. FIG. 34 shows the case where the UE-TX initiates the release of the PC5 connection with the relay UE. In FIG. 34, the same step numbers are assigned to the steps common to FIG. 33, and the common descriptions are omitted. In step ST2901, the relay UE that has detected that an RLF has occurred in the PC5 connection between the relay UE and the UE-RX notifies the UE-TX of the PC5 connection state information between the relay UE and the UE-RX in step ST3001. Here, it is preferable to include in the PC5 connection state information information indicating that the PC5 connection between the relay UE and the UE-RX has been released.

[0555] The UE-TX that has received the PC5 connection state information between the relay UE and the UE-RX from the relay UE uses this information to decide whether to maintain or release the PC5 connection between the UE-TX and the relay UE. Here, since the UE-TX recognizes that the PC5 connection between the relay UE and the UE-RX has been released, in steps ST3002 and ST3003, it releases the PC5 connection with the relay UE.

[0556] By doing so, when an RLF occurs in the PC5 connection between the relay UE and UE-RX, UE-TX can determine whether to release the PC5 connection between UE-TX and the relay UE.

[0557] Modification Example 1 of Embodiment 4. Disclose another connection method in the indirect communication between UEs, which is SL communication between UEs via a relay UE.

[0558] Distinguish the individual connections between each node and the end-to-end connection. Distinguish the PC5 connection between UE-TX and the relay UE and / or the PC5 connection between the relay UE and UE-RX from the connection between UE-TX and UE-RX.

[0559] After the PC5 connection between UE-TX and the relay UE and the PC5 connection between the relay UE and UE-RX are established, establish the PC5 connection between UE-TX and UE-RX. The order of establishing the PC5 connection between UE-TX and the relay UE and the PC5 connection between the relay UE and UE-RX may be either. By establishing the PC5 connection between UE-TX and UE-RX, SL communication for V2X services is performed between UE-TX and UE-RX.

[0560] FIGs. 35 and 36 are sequence diagrams showing an example of a method for establishing the PC5 connection between UE-TX and UE-RX after the PC5 connection between UE-TX and the relay UE and the PC5 connection between the relay UE and UE-RX are established for Modification Example 1 of Embodiment 4.

[0561] As an example, the case where a V2X service occurs in which UE-TX performs SL unicast communication with UE-RX is shown. For example, UE-TX performs a process of discovering the opposing UE-RX of the V2X service. If UE-RX cannot be discovered, UE-TX performs indirect communication between UEs with UE-RX via a relay UE.

[0562] In step ST3101, UE-TX establishes a PC5-S connection with the relay UE. To establish a PC5-S connection between UE-TX and the relay UE, discovery processing may be performed between the relay UE and UE-TX. For example, the relay UE may notify a discovery announcement message for announcement. The relay UE may include in the announcement message information indicating that it has a relay function. Information indicating that it has a UE-to-UE relay function and information indicating that it has a UE-to-Network relay function may be provided separately. UE-TX can select a relay to communicate with according to the situation.

[0563] For example, here, the relay UE includes in the announcement message information indicating that it has a UE-to-UE relay function. By receiving the announcement message, UE-TX can detect a relay UE having a UE-to-UE relay function.

[0564] Alternatively, UE-TX may notify a discovery solicitation message for soliciting to the S-UE. UE-TX may include in the solicitation message information indicating that it solicits a UE having a relay UE function. Information indicating that it has a UE-to-UE relay function and information indicating that it has a UE-to-Network relay function may be provided separately. UE-TX can solicit a relay to communicate with according to the situation.

[0565] When a relay UE having a relay UE function receives the invitation message, it notifies a response message to UE-TX. The relay UE may include information indicating that it has a relay UE function in the response message. Information indicating that it has a UE-to-UE relay function and information indicating that it has a UE-to-Network relay function may be provided separately. The relay UE may include information indicating that it has a UE-to-UE relay function in the response message. By doing so, UE-TX can detect a relay UE suitable for UE-to-UE indirect communication between UE-RX via the relay UE.

[0566] From step ST3102 to step ST3104, UE-TX and the relay UE notify each other of their UE capabilities. UE capabilities required for SL communication between UE-TX and the relay UE may be notified. The methods disclosed in FIGS. 14 and 15 may be appropriately applied. Through these processes, UE-TX and the relay UE can recognize each other's UE capabilities.

[0567] From step ST3105 to step ST3107, UE-TX and the relay UE notify each other of their AS settings. AS settings required for SL communication between UE-TX and the relay UE may be notified. The methods disclosed in FIGS. 14 and 15 may be appropriately applied. Through these processes, UE-TX and the relay UE can perform each other's AS settings.

[0568] In step ST3108, UE-TX notifies a relay request to the relay UE. UE-TX may notify its own UE-TX identifier, the UE-RX identifier for performing SL communication, and the V2X service information for performing SL communication, together with or included in the relay request. The V2X service information may be, for example, an identifier for specifying the service or the QoS required for the V2X service.

[0569] Also, resource information used between the relay UE and UE-RX may be notified. The resource information may be notified by including it in the relay request. The relay UE that has received a relay request from UE-TX sets resources to be used for SL communication between the relay UE and UE-RX. For example, the relay UE may select a resource pool or set scheduling information such as resource allocation.

[0570] The relay UE that has received a relay request establishes a PC5-S connection with UE-RX in step ST3109. Similar to the above, discovery processing may be performed.

[0571] From step ST3110 to step ST3112, the relay UE and UE-RX notify each other of their UE capabilities. UE capabilities required for SL communication between the relay UE and UE-RX may be notified. From step ST3113 to step ST3115, the relay UE and UE-RX notify each other of AS configurations. AS configurations required for SL communication between the relay UE and UE-RX may be notified. Through these processes, the relay UE and UE-TX can perform AS configurations with each other.

[0572] The relay UE that has established a PC5 connection with UE-RX notifies UE-TX in step ST3116 of information indicating that relay using the PC5 connection with UE-RX has become possible. In the present disclosure, this information may be referred to as relay setup completion information. A relay setup completion message may be provided on PC5, and this information may be included in the message and notified from the relay UE to UE-TX. Instead of the relay setup completion information, PC5 connection state information may be used. It is preferable to use the PC5 connection state information between the relay UE and UE-RX.

[0573] By doing so, UE-TX recognizes that the notification of capabilities and AS settings via the PC5-S connection and the PC5-RRC connection between the relay UE and UE-RX has been completed. UE-TX can recognize that relaying is possible between the relay UE and UE-RX.

[0574] UE-TX, which recognizes that relaying is possible between the relay UE and UE-RX, performs a PC5 connection with UE-RX. UE-TX performs a PC5 connection for the V2X service between UE-TX and UE-RX via the relay UE. In step ST3117, UE-TX establishes a PC5-S connection with UE-RX. From step ST3118 to step ST3120, UE-TX and UE-RX notify each other of their UE capabilities. From step ST3121 to step ST3123, UE-TX and UE-RX notify each other of the AS settings, and each UE performs the AS setting.

[0575] By doing so, it becomes possible to establish a PC5-S connection between UE-TX and UE-RX. Each UE can recognize the information necessary for the V2X service performed between UE-TX and UE-RX. Also, each UE can recognize the capabilities of the other between UE-TX and UE-RX. Also, each UE can recognize the AS settings necessary for the V2X service between UE-TX and UE-RX. Even when using the relay UE, V2X services using SL communication become possible between UE-TX and UE-RX. In step ST3124, data communication for the V2X service is performed between UE-TX and UE-RX.

[0576] When the V2X service ends between UE-TX and UE-RX, at step ST3125, UE-TX requests UE-RX to release the PC5 connection for the V2X service. A disconnect request message may be used. At step ST3126, UE-RX notifies UE-TX of the response to the release request. A disconnect response message may be used. Thereby, the PC5-S connection between UE-TX and UE-RX is released. The PC5-S connection and the PC5-RRC connection between UE-TX and UE-RX may be released. The AS configuration between UE-TX and UE-RX may be released.

[0577] The PC5 connection between UE-TX and the relay UE and the PC5 connection between the relay UE and UE-RX are not released. If the PC5 connection between UE-TX and the relay UE or the PC5 connection between the relay UE and UE-RX is to be released, the release process may be performed individually between them.

[0578] By doing so, it is possible to distinguish between individual connections between each node and end-to-end connections. Therefore, for example, even after releasing the PC5 connection between UE-TX and UE-RX, the individual connections between each node can be maintained. When the V2X service between UE-TX and UE-RX occurs next, the connection process between UE-TX and UE-RX becomes unnecessary, enabling early notification. Also, when the SL communication between UE-TX and UE-RX becomes unnecessary, the connection between UE-TX and UE-RX can be released. The resources used for the connection can be released, improving resource utilization efficiency.

[0579] Interlock the PC5 connection between UE-TX and the relay UE, and / or the PC5 connection between the relay UE and UE-RX, and / or the PC5 connection between UE-TX and UE-RX.

[0580] For example, after the release of the PC5 connection between UE-TX and UE-RX, the PC5 connection between UE-TX and the relay UE and / or the PC5 connection between the relay UE and UE-RX may be maintained. By doing so, when V2X service data is generated between UE-TX and UE-RX, there is no need to establish a PC5 connection again between UE-TX and the relay UE and / or between the relay UE and UE-RX. Therefore, when V2X service data is generated between UE-TX and UE-RX, SL communication between UE-TX and UE-RX can be performed with low latency.

[0581] For example, when the PC5 connection between UE-TX and UE-RX is released, both the PC5 connection between UE-TX and the relay UE and the PC5 connection between the relay UE and UE-RX may be released. By doing so, the resources for the PC5 connection between UE-TX and the relay UE and the PC5 connection between the relay UE and UE-RX can be released. Therefore, it is possible to improve the resource utilization efficiency.

[0582] For example, when the PC5 connection between UE-TX and the relay UE and / or the PC5 connection between the relay UE and UE-RX is released, the PC5 connection between UE-TX and UE-RX does not have to be released. The PC5 connection may be maintained. By doing so, when V2X service data is generated between UE-TX and UE-RX, it is sufficient to establish a PC5 connection between UE-TX and the relay UE and / or between the relay UE and UE-RX, and there is no need to establish a PC5 connection again between UE-TX and UE-RX. Therefore, when V2X service data is generated between UE-TX and UE-RX, SL communication between UE-TX and UE-RX can be performed with low latency.

[0583] The foregoing method may be combined with the method disclosed in Embodiment 4. For example, when the PC5 connection between the relay UE and UE-RX is released, the PC5 connection between UE-TX and the relay UE may be released, but the PC5 connection between UE-TX and UE-RX may be maintained. For example, when the PC5 connection between UE-TX and the relay UE is released, the PC5 connection between the relay UE and UE-RX may be released, but the PC5 connection between UE-TX and UE-RX may be maintained. By doing so, when either the PC5 connection between the relay UE and UE-RX or the PC5 connection between UE-TX and the relay UE is released while maintaining the PC5 connection between UE-TX and UE-RX, the other PC5 connection can be released. Therefore, it is possible to improve the resource utilization efficiency. Also, when V2X service data is generated between UE-TX and UE-RX, SL communication between UE-TX and UE-RX can be performed with low latency.

[0584] As the connection level in the PC5 connection release, the level disclosed in Embodiment 1 may be appropriately applied. For example, as the PC5 connection release, the AS setting may be released. For example, as the PC5 connection maintenance, the AS setting may be maintained.

[0585] FIG. 37 is a sequence diagram showing an example of a method of releasing the PC5 connection between the relay UE and UE-RX while maintaining the PC5 connection between UE-TX and UE-RX when RLF is detected in the PC5 connection between UE-TX and the relay UE in Modification 1 of Embodiment 4. In FIG. 37, steps common to FIG. 30 are assigned the same step numbers, and common descriptions are omitted.

[0586] In step ST2601, a PC5 connection is established between UE-TX and the relay UE, and in step ST2602, a PC5 connection is also established between the relay UE and UE-RX. In step ST3201, the PC5 connection between UE-TX and UE-RX is established, and even when passing through the relay UE, V2X service data using SL communication is communicated.

[0587] Disclosed is a case where the relay UE releases the connection with UE-RX. In step ST3202, the relay UE detects RLF in the SL communication with UE-TX. In step ST3203, the relay UE requests the release of the PC5 connection from UE-RX. In step ST3204, UE-RX notifies the relay UE of a response to the release request. Thereby, the PC5-S connection between the relay UE and UE-RX is released. The PC5-S connection and the PC5-RRC connection between the relay UE and UE-RX may be released. The AS configuration between the relay UE and UE-RX may be released.

[0588] The PC5 connection between UE-TX and UE-RX is not released. When releasing the PC5 connection between UE-TX and UE-RX, it is advisable to perform a release process therebetween.

[0589] By doing so, it becomes possible to interlock the PC5 connection state between UE-TX and the relay UE and the PC5 connection state between the relay UE and UE-RX, and it becomes possible not to interlock each of these connection states with the PC5 connection state between UE-TX and UE-RX. When the PC5 connection between UE-TX and the relay UE is released, it becomes possible to release the PC5 connection between the relay UE and UE-RX, and it becomes possible to maintain the PC5 connection between UE-TX and the relay UE.

[0590] By doing so, it is possible to distinguish the individual connections between each node and the end-to-end connection. Therefore, for example, even after releasing the PC5 connection between each node, it becomes possible to maintain the connection between UE-TX and UE-RX. When a V2X service between UE-TX and UE-RX occurs next, after establishing the individual connections between each node, connection processes such as AS configuration by the PC5-S connection and the PC5-RRC connection between UE-TX and UE-RX become unnecessary. Therefore, data communication of the V2X service becomes possible at an early stage.

[0591] Figure 38 is a sequence diagram showing an example of a method for releasing the PC5 connection between UE-TX and the relay UE while maintaining the PC5 connection between UE-TX and UE-RX when RLF is detected in the PC5 connection between the relay UE and UE-RX for Modification Example 1 of Embodiment 4. In Figure 38, the same step numbers are assigned to the steps common to Figure 37, and the common descriptions are omitted.

[0592] In step ST3303, the relay UE detects that RLF has occurred in the PC5 connection between the relay UE and UE-RX. Upon detecting the RLF, the relay UE, recognizing that the PC5 connection has become impossible, releases the PC5 connection with UE-TX in steps ST3301 and ST3302.

[0593] The PC5 connection between UE-TX and UE-RX is not released. If it is necessary to release the PC5 connection between UE-TX and UE-RX, the release process may be carried out between them.

[0594] By doing so, it becomes possible to interlock the PC5 connection state between the relay UE and UE-RX and the PC5 connection state between UE-TX and the relay UE, and it becomes possible not to interlock each of these connection states with the PC5 connection state between UE-TX and UE-RX. When the PC5 connection between the relay UE and UE-RX is released, it becomes possible to release the PC5 connection between UE-TX and the relay UE and to maintain the PC5 connection between UE-TX and the relay UE.

[0595] For example, when releasing the PC5 connection between the relay UE and UE-RX, release the PC5 connection between UE-TX and the relay UE, and release the PC5 connection between UE-TX and UE-RX. For example, when releasing the PC5 connection between UE-TX and the relay UE, the PC5 connection between the relay UE and UE-RX may be released, and the PC5 connection between UE-TX and UE-RX may also be released. By doing so, when any of the PC5 connections between the relay UE and UE-RX or between UE-TX and the relay UE is released, all of the PC5 connections between nodes, including the end-to-end PC5 connection, can be released. Therefore, it becomes possible to further improve the resource utilization efficiency.

[0596] When the PC5 connection between UE-TX and the relay UE and / or the PC5 connection between the relay UE and UE-RX has been released, the PC5 connection release process cannot be executed between UE-TX and UE-RX. For example, problems such as the inability to notify a Disconnect Request or a Disconnect Response between UE-TX and UE-RX occur. A method for solving such problems is disclosed.

[0597] When the PC5 connection between UE-TX and the relay UE is released, the relay UE may notify UE-RX of the PC5 connection status information between UE-TX and the relay UE. By doing so, UE-RX can recognize the PC5 connection status between UE-TX and the relay UE. When the PC5 connection between UE-TX and the relay UE is released, UE-RX may release the PC5 connection with UE-TX. UE-RX may release the AS settings required for the PC5 connection. UE-RX may release the resources required for the PC connection.

[0598] When the PC5 connection between UE-TX and the relay UE is released, UE-TX may release the PC5 connection with UE-RX. UE-TX may release the AS configuration required for the PC5 connection. UE-TX may release the resources required for the PC connection.

[0599] When the PC5 connection between the relay UE and UE-RX is released, the relay UE may notify UE-TX of the PC5 connection status information between the relay UE and UE-RX. The same processing as described above may be performed.

[0600] By doing so, even when the PC5 connection between UE-TX and the relay UE and / or the PC5 connection between the relay UE and UE-RX is released, it becomes possible to release the PC5 connection between UE-TX and UE-RX. Therefore, the resources that were required for the PC5 connection between UE-TX and UE-RX can be released, making it possible to improve the resource utilization efficiency. Also, the AS configuration required for the PC5 connection between UE-TX and UE-RX can be released.

[0601] FIG. 39 is a sequence diagram showing an example of a method for releasing the PC5 connection between UE-TX and UE-RX when the PC5 connection between the relay UE and UE-RX is released, for Modification Example 1 of Embodiment 4. In FIG. 39, the same step numbers are assigned to the steps common to FIG. 37, and the common explanations are omitted.

[0602] In step ST3202, the relay UE detects RLF in the SL communication with UE-TX. In step ST3404, UE-TX detects RLF in the SL communication with the relay UE. It may be detected that the SL communication with the relay UE has become impossible. In step ST3401, the relay UE notifies UE-RX that RLF has occurred in the PC5 connection between UE-TX and the relay UE. The PC5 connection status information may be used for this notification. UE-RX that recognizes that the PC5 connection between UE-TX and the relay UE has become impossible releases the PC5 connection with the relay UE.

[0603] In step ST3402, UE-RX requests the relay UE to release the PC5 connection. In step ST3403, the relay UE notifies UE-RX of the response to the release request. Thereby, the PC5-S connection between the relay UE and UE-RX is released. The PC5-S connection and the PC5-RRC connection between the relay UE and UE-RX may be released. The AS configuration between the relay UE and UE-RX may be released.

[0604] UE-RX that recognizes that the PC5 connection between the relay UE and UE-RX has been released releases the PC5-RRC connection between UE-TX and UE-RX in step ST3405. UE-RX releases the settings required for the PC5-RRC connection. UE-RX that has released the PC5-RRC connection may release the PC5-S connection in step ST3406. UE-RX releases the settings required for the PC5-S connection. The order of releasing the PC5-RRC connection and the PC5-S connection is not limited to this.

[0605] The UE-TX that has detected RLF for SL communication with the relay UE releases the PC5-RRC connection between the UE-TX and the UE-RX in step ST3407. The UE-TX releases the settings required for the PC5-RRC connection. The UE-TX that has released the PC5-RRC connection may release the PC5-S connection in step ST3408. The UE-TX releases the settings required for the PC5-S connection. The order of releasing the PC5-RRC connection and the PC5-S connection is not limited to this.

[0606] By doing so, it becomes possible to interlock the PC5 connection state between the UE-TX and the relay UE and the PC5 connection state between the relay UE and the UE-RX, and it also becomes possible to interlock each of these connection states with the PC5 connection state between the UE-TX and the UE-RX. When the PC5 connection between the UE-TX and the relay UE is released, it becomes possible to release the PC5 connection between the relay UE and the UE-RX and to release the PC5 connection between the UE-TX and the UE-RX.

[0607] Figure 40 is a sequence diagram showing an example of a method for releasing the PC5 connection between the UE-TX and the UE-RX when RLF is detected in the PC5 connection between the relay UE and the UE-RX for Modification Example 1 of Embodiment 4. In Figure 40, steps common to Figure 39 are given the same step numbers and the common explanations are omitted.

[0608] In step ST3303, the relay UE detects RLF in the SL communication with the UE-RX. In step ST3504, the UE-RX detects RLF in the SL communication with the relay UE. It may be detected that the SL communication with the relay UE has become impossible. In step ST3501, the relay UE notifies the UE-TX that RLF has occurred in the PC5 connection between the relay UE and the UE-RX. The UE-TX that has recognized that the PC5 connection between the relay UE and the UE-TX has become impossible releases the PC5 connection with the relay UE.

[0609] In step ST3502, UE-TX requests the relay UE to release the PC5 connection. In step ST3503, the relay UE notifies UE-TX of the response to the release request. Thereby, the PC5-S connection between UE-TX and the relay UE is released. The PC5-S connection and the PC5-RRC connection between UE-TX and the relay UE may be released. The AS configuration between UE-TX and the relay UE may be released.

[0610] By doing so, it becomes possible to interlock the PC5 connection state between the relay UE and UE-RX, and the PC5 connection state between UE-TX and the relay UE, and it also becomes possible to interlock each of these connection states with the PC5 connection state between UE-TX and UE-RX. When the PC5 connection between the relay UE and UE-RX is released, it becomes possible to release the PC5 connection between UE-TX and the relay UE, and it becomes possible to release the PC5 connection between UE-TX and UE-RX.

[0611] If the PC5 connection release between UE-TX and the relay UE and / or the PC5 connection release between the relay UE and UE-RX is performed, and the PC5 connection between UE-TX and UE-RX is maintained indefinitely, then inter-UE indirect communication will be impossible while the PC5 connection is maintained. For this reason, resources and AS configurations will be wasted. A method for solving such problems is disclosed.

[0612] It may be good to set a period until releasing the PC5 connection between UE-TX and UE-RX. A timer until releasing the PC5 connection between UE-TX and UE-RX may be provided. The setting of the period (which may be a timer) may be notified by PC5-S signaling or PC5-RRC signaling. The setting of the period (which may be a timer) may be notified including in the AS setting. The timer may be notified by UE-TX to UE-RX. Alternatively, UE-TX may notify the relay UE and UE-RX of the timer. Similarly, UE-RX may notify UE-TX of the timer. Alternatively, UE-RX may notify the relay UE and UE-TX of the timer. Alternatively, the timer may be statically determined by a standard or the like. By doing so, the PC5 connection between UE-TX and UE-RX can be released according to the timer.

[0613] When communication cannot be performed between UE-TX and UE-RX for a predetermined time, the PC5 connection between UE-TX and UE-RX may be released. The above-mentioned timer may be used. UE-TX and UE-RX each start the timer in the last communication between UE-TX and UE-RX. When communication occurs during the timer period, the timer is reset. When there is no communication and the timer expires, the PC5 connection between UE-TX and UE-RX is released. For example, the longest communication interval assumed for the V2X service using SL communication may be set as the timer. By doing so, when communication cannot be performed due to some problem, the PC5 connection between UE-TX and UE-RX can be released.

[0614] When the PC5 connection between the UE-RX and the relay is released, or when the reconnection process of the PC5 connection is started in the situation where the PC5 connection between the UE-RX and the relay is released, the aforementioned timer may be started. If the PC5 connection between the UE-RX and the relay is reconnected within the timer, the timer is reset. When the timer expires, the UE-RX may release the PC5 connection between the UE-TX and the UE-RX. Alternatively, in the situation where the PC5 connection between the UE-TX and the relay UE is maintained and the timer expires, the relay UE may notify the UE-TX of a release request or a release instruction for the PC5 connection between the UE-TX and the UE-RX. The UE-TX may release the PC5 connection between the UE-TX and the UE-RX by receiving a PC5 connection release request or a PC5 connection release instruction from the relay UE.

[0615] When the PC5 connection between the relay UE and the UE-TX is released, or when the reconnection process of the PC5 connection is started in the situation where the PC5 connection between the relay UE and the UE-TX is released, the aforementioned timer may be started. If the PC5 connection between the relay UE and the UE-TX is reconnected within the timer, the timer is reset. When the timer expires, the UE-TX may release the PC5 connection between the UE-TX and the UE-RX. Alternatively, in the situation where the PC5 connection between the relay UE and the UE-RX is maintained and the timer expires, the relay UE may notify the UE-RX of a release request for the PC5 connection between the UE-TX and the UE-RX. The UE-RX may release the PC5 connection between the UE-TX and the UE-RX by receiving a PC5 connection release request or a PC5 connection release instruction from the relay UE.

[0616] When RLF is detected in the PC5 connection instead of when the PC5 connection is released, the aforementioned various methods may be applied as appropriate.

[0617] When the reconnection of the PC5 connection between UE-TX and the relay UE and / or the reconnection of the PC5 connection between the relay UE and UE-RX fails, the PC5 connection between UE-TX and UE-RX can be released. When the direct communication between UEs via the relay between UE-TX and UE-RX is not possible, the PC5 connection can be released. Therefore, unnecessary AS settings can be released, and it becomes possible to improve the resource utilization efficiency.

[0618] Embodiment 5. When the S-UE is within the coverage of the gNB (IC: In Coverage) and when it is out of the coverage (OOC: Out of Coverage), the resource setting methods are different. When the S-UE is in the IC, after connecting to the gNB, the resource setting is notified from the gNB. When the S-UE is in the OOC, the S-UE uses the resources set by the NW or pre-configured for the S-UE in advance.

[0619] When UE-TX selects the S-UE, selecting the S-UE in the IC can reduce the collision of resources used for SL by the adjustment of the gNB. On the other hand, selecting the S-UE in the OOC enables the S-UE to perform the setting without waiting for the setting from the gNB, and enables the SL communication to be performed with lower latency. However, in the conventional method, since UE-TX selects the S-UE with better communication quality in the selection of the S-UE, it was impossible for UE-TX to determine whether it is in the IC or the OOC.

[0620] In this Embodiment 5, a method for solving such problems is disclosed.

[0621] Provide information indicating whether it is IC or OOC. Information indicating whether it is connected to a gNB may be provided. Information indicating which gNB it is connected to may be provided. The information indicating whether it is connected to a gNB may include the information indicating which gNB it is connected to. In the present disclosure, it may be referred to as IC / OOC information. The S-UE notifies the UE-TX of this information. For example, when establishing a PC5 connection with the UE-TX, the S-UE may notify the UE-TX of this information. The UE-TX may select the S-UE using this information when establishing a PC5 connection.

[0622] For example, the S-UE may notify the IC / OOC information during discovery. For example, when the S-UE transmits a discovery announcement, the S-UE includes the IC / OOC information in the announcement and transmits it. For example, when the UE-TX transmits a discovery invitation message, the S-UE will notify the UE-TX of a response message to the received invitation message, but the S-UE may include the IC / OOC information in the response message and notify it.

[0623] By doing so, the UE-TX can receive the IC / OOC information transmitted from the S-UE, and by using the IC / OOC information when selecting the S-UE, it becomes possible to determine whether the S-UE is IC or OOC.

[0624] The UE-TX may preferentially select an S-UE that is IC. When there are multiple S-UEs with a reception quality equal to or higher than a predetermined level, the UE-TX may preferentially select an S-UE that is IC. For example, in a case where reliability is required for a V2X service using SL communication between the UE-TX and the UE-RX, the UE-TX may preferentially select an S-UE that is IC. By doing so, the gNB can avoid a collision between the resources used for SL communication between the UE-TX and the UE-RX and the resources used for SL communication between other UEs. Thereby, it becomes possible to improve the communication quality of the SL communication between the UE-TX and the UE-RX. For this reason, it is possible to improve the reliability of the V2X service using the SL communication between the UE-TX and the UE-RX.

[0625] When the UE-TX is connected to the gNB, it may preferentially select an S-UE that is connected to the same gNB. When there are multiple S-UEs with a reception quality equal to or higher than a predetermined value, it may preferentially select an S-UE that is connected to the same gNB. For example, when the gNB determines the SL communication resources between the UE-TX and the UE-RX, the UE-TX may preferentially select an S-UE that is connected to the same gNB. By doing so, for example, it is possible to prevent a situation where the resource setting notified to the UE-TX via the S-UE from the gNB is different from the resource setting directly notified to the UE-TX from the gNB. Thereby, the occurrence of malfunction can be reduced. For this reason, the reliability of the V2X service using the SL communication between the UE-TX and the UE-RX can be improved.

[0626] The UE-TX may preferentially select an out-of-coverage (OOC) S-UE. When there are multiple S-UEs with a reception quality equal to or higher than a predetermined value, it may preferentially select an OOC S-UE. For example, when low latency characteristics are required for the V2X service using the SL communication between the UE-TX and the UE-RX, the UE-TX may preferentially select an OOC S-UE. By doing so, the SL communication between the UE-TX and the UE-RX can be carried out earlier. For this reason, the V2X service using the SL communication between the UE-TX and the UE-RX can be carried out with low latency.

[0627] The UE-TX may select an in-coverage (IC) S-UE or an OOC S-UE according to the QoS required for the V2X service using the SL communication. It becomes possible to select an appropriate S-UE according to the V2X service.

[0628] The UE-TX may notify the S-UE of the information. For example, the UE-TX may notify the information when establishing a PC5 connection with the S-UE. The S-UE may use the information to determine whether it can connect to the UE-TX when establishing the PC5 connection.

[0629] For example, UE-TX may notify IC / OOC information during discovery. For example, in the case of IC, UE-TX includes information of the connected gNB, such as an identifier for identifying the gNB, in the IC / OOC information and notifies it. For example, when UE-TX transmits a discovery invitation message, UE-TX includes the IC / OOC information in the invitation message and transmits it. By receiving the invitation message, S-UE can recognize whether there is a gNB to which UE-TX is connected, and if so, which gNB it is connected to.

[0630] S-UE can determine whether it is possible to become S-UE for UE-TX by using the gNB information to which UE-TX is connected. For example, if UE-TX is connected to the same gNB, S-UE determines that it is possible to become S-UE for the UE-TX. In this case, S-UE notifies a response message to UE-TX. S-UE may include the gNB information to which S-UE is connected in the response message and notify it. If UE-TX is not connected to the same gNB, S-UE determines that it is impossible to become S-UE for the UE-TX. In this case, S-UE does not transmit a response message to UE-TX.

[0631] By doing so, it is possible to reduce the occurrence of malfunction that occurs when UE-TX and S-UE are connected to different gNBs as described above. Therefore, the reliability of the V2X service using the SL communication between UE-TX and UE-RX can be improved.

[0632] In the foregoing, an example in which S-UE and UE-TX are connected to the same one gNB has been disclosed, but the number of gNBs is not limited to one and may be plural. A group of gNBs may be provided. Specific examples of the gNB group are disclosed as follows (1) to (9).

[0633] (1) Base stations of the same RAT.

[0634] (2) Base stations within the same PLMN.

[0635] (3) Base stations within the same NPN (NPN may be, for example, CAG).

[0636] (4) Base stations within the same network slice.

[0637] (5) Base stations within the same TA.

[0638] (6) Base stations within the same RNA (RAN-based Notification Area).

[0639] (7) Base stations within the same system information area. It may also be base stations within an area where the system information used for SL communication is the same.

[0640] (8) Base stations that can support the same QoS requirements.

[0641] (9) Combinations of (1) to (8).

[0642] The method disclosed above may be applied to the gNB group. For example, UE-TX may preferentially select and connect to an S-UE that connects to another gNB belonging to the gNB group to which the gNB to which UE-TX connects belongs. For example, if the gNB to which the S-UE connects belongs to the same gNB group as the gNB to which UE-TX connects, UE-TX may be able to select the S-UE.

[0643] Information regarding S-UE, UE-TX, and UE-RX may be notified between gNB groups. By doing so, coordinated processing over a wider range becomes possible. For example, information such as UE capabilities and AS settings between S-UE and UE-TX, and UE capabilities and AS settings between UE-TX and UE-RX may be notified in advance between gNB groups. For example, this information may be notified in advance between the gNB group and the S-UE connected thereto.

[0644] When UE-TX changes the connected S-UE to another S-UE that is connected to the same or a different gNB within the same gNB group, the S-UE after the change can recognize the information between the S-UE before the change and UE-TX, and the information between UE-TX and UE-RX. As a result, it is not necessary to newly notify the information between the S-UE after the change and UE-TX. Also, the S-UE after the change can recognize the information between UE-TX and UE-RX. The S-UE can set and notify resource information to UE-TX earlier. The same applies when the gNB sets the resource information.

[0645] The PC5 connection between UEs may be prohibited by the connected gNB or gNB group. For example, when the gNB to which the S-UE is connected is different from the gNB to which UE-TX is connected, the PC5 connection between the UEs may be prohibited.

[0646] The gNB group information may be statically determined in advance by standards or the like. Alternatively, the gNB group information may be semi-statically notified from the node that sets the gNB group to the UEs performing SL communication. In Uu, RRC signaling may be used. In PC5, PC5-S signaling or PC5-RRC signaling may be used. For example, the range of the gNB group can be set according to the radio wave propagation situation and the load situation. The gNB group information may be dynamically notified from the node that sets the gNB group to the UEs performing SL communication. In Uu, DCI may be used. In PC5, SCI may be used. The range of the gNB group can be dynamically set.

[0647] Examples of the node that sets the gNB group include RAN nodes, CN nodes, etc.

[0648] By doing so, it is possible to prohibit a gNB outside the gNB group from making a PC5 connection with a UE in a specific area. As a result, SL communication can be limited to UEs connected to the desired gNB. As a result, for example, interference with UEs connected to other than the gNB can be reduced.

[0649] Also, for each UE performing SL communication, the corresponding RAT (Radio Access Technology) may be different. For example, for each S-UE, the RAT for which resources can be configured may be different. Examples of RATs include NR and LTE that support SL communication. In such a case, it is necessary for the S-UE to select an S-UE whose corresponding RAT is the same as the RAT for SL communication supported by UE-TX. However, in the conventional method, UE-TX may not be able to select an S-UE corresponding to the same RAT.

[0650] Here, a method for solving such problems is disclosed.

[0651] Provide information indicating the corresponding RAT. Information on the RAT for which resources can be configured may also be provided. In the present disclosure, these types of information may sometimes be referred to as RAT information. The S-UE notifies the UE-TX of the RAT information corresponding to the S-UE. For example, the S-UE may notify the RAT information when establishing a PC5 connection with the UE-TX. The UE-TX may select the S-UE using the RAT information when establishing the PC5 connection.

[0652] For example, the UE-TX selects an S-UE for which resources can be configured using the RAT for SL communication supported by itself.

[0653] The UE-TX may also notify the S-UE of the RAT information for SL communication supported by the UE-TX. For example, the UE-TX may notify the information when establishing a PC5 connection with the S-UE. The S-UE may use the information to determine whether it can connect to the UE-TX when establishing the PC5 connection.

[0654] For example, if the resource can be set in the RAT for SL communication supported by UE-TX, the S-UE determines that it is possible to become the S-UE. In this case, the S-UE notifies a response message to UE-TX. The S-UE may include the corresponding RAT information of the S-UE in the response message and then notify it. If the resource cannot be set in the RAT for SL communication supported by UE-TX, the S-UE determines that it is impossible to become the S-UE. In this case, the S-UE does not send a response message to UE-TX.

[0655] As an example of the method for notifying the RAT information, the method described above may be appropriately applied.

[0656] The number of corresponding RATs is not limited to one and may be plural.

[0657] By doing so, UE-TX can select the S-UE corresponding to the RAT for SL communication between UE-TX and UE-RX. The S-UE can notify UE-TX of the resource information suitable for the RAT for SL communication between UE-TX and UE-RX. By doing so, even in the case where SL communication is supported by a plurality of RATs, SL communication between UE-TX and UE-RX using the S-UE becomes possible.

[0658] Also, for each UE performing SL communication, the PLMN to be connected may be different. For example, for each S-UE, the PLMN to be connected may be different. However, in the conventional method, UE-TX may not be able to select the S-UE connected to the same PLMN in some cases.

[0659] Here, a method for solving such problems is disclosed.

[0660] Provide information indicating the PLMN to which it is connected. Information on the PLMN that has received authentication for the V2X service may be provided. In the present disclosure, such information may sometimes be referred to as PLMN information. As the PLMN information, for example, a PLMN identifier may be used. The S-UE notifies the UE-TX of the PLMN information to which the S-UE is connected. For example, the S-UE may notify the PLMN information when establishing a PC5 connection with the UE-TX. The UE-TX may select the S-UE using the PLMN information when establishing a PC5 connection.

[0661] For example, the UE-TX selects an S-UE that is connected to the PLMN to which it is connected.

[0662] The UE-TX may notify the S-UE of the PLMN information to which the UE-TX is connected. For example, the UE-TX may notify the information when establishing a PC5 connection with the S-UE. The S-UE may use the information to determine whether it can connect to the UE-TX when establishing a PC5 connection.

[0663] For example, if the S-UE is connected to the same PLMN as the UE-TX, the S-UE determines that it is possible to become the S-UE. In this case, the S-UE notifies the UE-TX of a response message. The S-UE may include the PLMN information to which the S-UE is connected in the response message and notify it. If the S-UE is connected to a PLMN different from the PLMN to which the UE-TX is connected, the S-UE determines that it is impossible to become the S-UE. In this case, the S-UE does not send a response message to the UE-TX.

[0664] The method described above may be appropriately applied as an example of the method for notifying PLMN information.

[0665] The number of PLMNs to which it is connected or the PLMNs that have received authentication for the V2X service is not limited to one and may be plural.

[0666] By doing so, UE-TX can select an S-UE that connects to the same PLMN as the PLMN to which it is connected. UE-TX can select an S-UE that is authenticated with the same PLMN as the PLMN that has been authenticated for the desired V2X service. By doing so, even when SL communication is supported by multiple PLMNs, SL communication between UE-TX and UE-RX using the S-UE becomes possible.

[0667] Disclosed is a method that enables SL communication even when the PLMN to which the S-UE is connected is different from the PLMN to which the UE-TX is connected. It is preferable to determine in advance by a standard or the like the resources used for SL communication between the S-UE and the UE-TX. Alternatively, the resources used for SL communication between the S-UE and the UE-TX may be notified from the CN node when the S-UE and the UE-TX are connected to the CN node for authentication of the V2X service. By doing so, SL communication between the S-UE and the UE-TX becomes possible even when the PLMN to which the S-UE is connected is different from the PLMN to which the UE-TX is connected.

[0668] It is preferable to determine in advance by a standard or the like the resources used for SL communication between the UE-TX and the UE-RX. Alternatively, the resources used for SL communication between the UE-TX and the UE-RX may be notified from the CN node when the S-UE is connected to the CN node for authentication of the V2X service. By doing so, SL communication between the UE-TX and the UE-RX becomes possible even when the PLMN to which the S-UE is connected is different from the PLMN to which the UE-TX is connected.

[0669] The S-UE notifies the UE-TX of the resources preset for SL communication between the UE-TX and the UE-RX or the resources notified from the CN node. The UE-TX may perform SL communication with the UE-RX using the resources.

[0670] By doing so, SL communication between the UE-TX and the UE-RX becomes possible even when the PLMN to which the S-UE is connected is different from the PLMN to which the UE-TX is connected.

[0671] The UE may connect to a NPN (Non Public Network) (see Non-Patent Document 22). The NPN may be a Private NW. When SL communication is supported in the NPN, for each UE that performs SL communication, the NPN to which it connects may be different. For example, for each S-UE, the NPN to which it connects may be different. However, in the conventional method, the UE-TX may not be able to select an S-UE that connects to the same NPN.

[0672] As a method for solving such a problem, the method of providing the information indicating the PLMN to be connected described above may be appropriately applied. "PLMN" may be replaced with "NPN". "PLMN information" may be replaced with "NPN information" or "information for specifying the NPN". When the NPN is configured as a CAG (Closed Access Group), the information for specifying the CAG may be used. Alternatively, instead of the information indicating the PLMN, information including the PLMN and the NPN and indicating them may be used.

[0673] By doing so, the UE-TX can, for example, select an S-UE that connects to the same NPN as the NPN to which it connects. The UE-TX can select an S-UE that has been authenticated with the same NPN as the NPN that has been authenticated for the desired V2X service. By doing so, even when SL communication is supported in a plurality of NPNs, or a plurality of NPNs and PLMNs, SL communication between the UE-TX and the UE-RX using the S-UE becomes possible.

[0674] Regarding the method that enables SL communication even when the NPN to which the S-UE is connected is different from the NPN to which the UE-TX is connected, the above-described method may be appropriately applied. Even when the NPN or PLMN to which the S-UE is connected is different from the NPN or PLMN to which the UE-TX is connected, SL communication between the UE-TX and the UE-RX becomes possible. Also, even when the NPN or PLMN to which the S-UE is connected is different from the NPN or PLMN to which the UE-TX is connected, SL communication between the UE-TX and the UE-RX is enabled.

[0675] In a 5G core system, network slices are supported (see Non-Patent Document 22). When network slices are supported in a network including the PC5 interface, different slices may be used for each service that performs SL communication. In such a case, for example, the S-UE itself may be used in a specific one or more slices. There may be a case where the S-UE does not hold resource information used in a slice corresponding to the V2X service using SL communication between the UE-TX and the UE-RX. However, in the conventional method, the UE-TX may not be able to select an S-UE used in a slice corresponding to the V2X service using SL communication or an S-UE that holds resource information used in the slice.

[0676] Here, a method for solving such problems is disclosed.

[0677] Provide information indicating a slice. For example, information indicating the slice used by the UE may be provided. Information indicating the slice in which the resource information held by the UE is used may also be provided. In the present disclosure, these pieces of information may be referred to as slice correspondence information. As the slice correspondence information, information for specifying a network slice may be used. In a 5G core system, as an identifier for specifying a network slice, S-NSSAI (Single Network Slice Selection Assistance Information) is used. S-NSSAI may be used as the information for specifying a network slice.

[0678] The S-UE notifies the UE-TX of the slice correspondence information of the S-UE. For example, when establishing a PC5 connection with the UE-TX, the S-UE may notify its own slice correspondence information of the S-UE. The UE-TX may select the S-UE using the slice correspondence information of the S-UE when establishing a PC5 connection.

[0679] For example, the UE-TX selects an S-UE corresponding to a slice corresponding to the V2X service performed in SL communication.

[0680] The UE-TX may notify the S-UE of the slice correspondence information of the UE-TX. The UE-TX may also notify information indicating the slice corresponding to the V2X service using the SL communication performed by the UE-TX. For example, when establishing a PC5 connection with the S-UE, the UE-TX may notify the slice correspondence information. The S-UE may determine whether it can connect to the UE-TX using the slice correspondence information when establishing a PC5 connection.

[0681] For example, when the S-UE has the resource information of the slice corresponding to the V2X service performed by the UE-TX using SL communication, it is determined that the S-UE can become the S-UE. In this case, the S-UE notifies the UE-TX of a response message. The S-UE may include the slice correspondence information of the S-UE in the response message and notify it. When the S-UE does not have the resource information of the slice corresponding to the V2X service performed by the UE-TX using SL communication, it is determined that the S-UE cannot become the S-UE. In this case, the S-UE does not send a response message to the UE-TX.

[0682] As an example of the method for notifying the slice correspondence information, the method described above may be appropriately applied.

[0683] The number of the slices is not limited to one and may be plural.

[0684] By doing so, the UE-TX can obtain the resource information of the slice corresponding to the V2X service using SL communication from the S-UE. The UE-TX can execute the desired V2X service in the corresponding slice. By doing so, when network slicing is supported in a network including the PC5 interface, the V2X service using SL communication can be implemented using the desired slice. By performing SL communication in the slice corresponding to the V2X service, resource collisions between SL communications can be avoided. Therefore, even when many V2X services using SL communication are implemented, it is possible to satisfy the QoS required for each V2X service.

[0685] In various services using SL communication, the QoS required for each service is different. The QoS that can be supported may be different for each S-UE. When implementing a service such as V2X using SL communication, in the conventional method, the UE-TX may not be able to select an S-UE that satisfies the QoS required for the service to be implemented.

[0686] Here, a method for solving such problems is disclosed.

[0687] Provide information indicating the QoS that can be supported. In the present disclosure, this information may sometimes be referred to as S-UE supported QoS information. As the S-UE supported QoS information, for example, one or more parameters characterizing the QoS may be used. Alternatively, for example, QCI (QoS Class Identifier) may be used. For example, when establishing a PC5 connection with UE-TX, the S-UE may notify the S-UE supported QoS information. UE-TX may select the S-UE using the S-UE supported QoS information when establishing a PC5 connection.

[0688] For example, UE-TX selects an S-UE that supports the QoS required for the service it performs using SL communication. UE-TX selects an S-UE that may be able to achieve the QoS required for the service it performs using SL communication.

[0689] UE-TX may notify the S-UE of information regarding the QoS required for the service that UE-TX performs. For example, UE-TX may notify this information when establishing a PC5 connection with the S-UE. The S-UE may use this information to determine whether it can connect to UE-TX when establishing a PC5 connection.

[0690] For example, when the S-UE supports the QoS required by UE-TX, it determines that it is possible to become an S-UE. In this case, the S-UE notifies a response message to UE-TX. The S-UE may include the S-UE supported QoS information in the response message and notify it. When the S-UE does not support the QoS required by UE-TX, it determines that it is impossible to become an S-UE. In this case, the S-UE does not send a response message to UE-TX.

[0691] As an example of the method for notifying the S-UE supported QoS information, the method described above may be appropriately applied.

[0692] The number of QoSs that an S-UE can support is not limited to one and may be plural.

[0693] By doing so, UE-TX can select an S-UE that can support the QoS required for the service it performs using SL communication. It becomes possible to perform a service using SL communication between UE-TX and UE-RX using the S-UE.

[0694] Also, an S-UE may be provided for each predetermined area (which may be a zone). The S-UEs in each area may perform resource setting and resource allocation for the SL communication performed by the UE-TX in the same area. In such a case, when selecting an S-UE, UE-TX needs to select an S-UE in the same area. However, in the conventional method, since UE-TX selects an S-UE with better communication quality in the selection of the S-UE, there may be a case where an S-UE in the same area cannot be selected.

[0695] Here, a method for solving such problems is disclosed.

[0696] Information indicating the area where the S-UE is located is provided. Information indicating the area where the S-UE function of the S-UE is valid may be provided. An area identifier indicating which area may be provided. The S-UE notifies the UE-TX of the information. For example, the S-UE may notify the information when establishing a PC5 connection with the UE-TX. UE-TX may select the S-UE using the information when establishing the PC5 connection.

[0697] This area may be TA, and the identifier of TA may be used as the area information. This area may be RNA, and the identifier of RNA may be used as the area information. This area may be an area delimited by longitude and latitude, and longitude and latitude may be used as the area information. This area may be an area consisting of three-dimensional space, and for example, longitude, latitude, and altitude may be used as the area information. The NW node may set the area information. The NW node may notify the S-UE of the area information.

[0698] For example, the S-UE may notify the area information during discov...

Claims

1. A communication terminal device among a plurality of communication terminal devices provided in a communication system and performing side link communication, which is communication via a PC5 interface, The communications terminal device is configured to transmit signaling using a default radio bearer in the sidelink communication.

2. 2. The communication terminal device according to claim 1, A communications terminal device, wherein the default radio bearer is a Signaling Radio Bearer (SRB).

3. 3. The communication terminal device according to claim 2, The communication terminal device is configured to transmit PC5-S signaling using the SRB.

4. 3. The communication terminal device according to claim 2, The communication terminal device is configured to transmit PC5-RRC (Radio Resource Control) signaling using the SRB.

5. 5. The communication terminal device according to claim 4, The communication terminal device is configured to transmit capability information of the communication terminal device to another communication terminal device among the plurality of communication terminal devices using the PC5-RRC signaling.

6. 5. The communication terminal device according to claim 4, The communication terminal device is configured to transmit, to another communication terminal device among the plurality of communication terminal devices, an AS (Access Stratum) setting for unicast communication with the other communication terminal device, using the PC5-RRC signaling.

7. 7. The communication terminal device according to claim 6, The communication terminal device is configured to transmit a release request to the other communication terminal device to request release of the AS setting.

8. 7. The communication terminal device according to claim 6, The communication terminal device is configured to, when changing the AS setting, transmit the changed AS setting to the other communication terminal device.

9. 2. The communication terminal device according to claim 1, The communication terminal device is configured to set DRX (Discontinuous reception) for transmitting and receiving signaling of the C-Plane, which is a control plane, for unicast communication using the default radio bearer.

10. A communication system including a plurality of communication terminal devices that perform sidelink communication, which is communication via a PC5 interface, A communication system, wherein a communication terminal device among the plurality of communication terminal devices is configured to transmit signaling using a default radio bearer in the sidelink communication.

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