Communication control method, relay user equipment and remote user equipment

Abstract

A communication control method for use in a cellular communication system. The communication control method comprises transmitting, by a relay user equipment having a capability to relay data for a remote user equipment, a message comprising information related to the relay user equipment, receiving, by the remote user equipment, the message, and performing, by the remote user equipment, a process for establishing a sidelink connection between the remote user equipment and the relay user equipment based on the message.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a communication control method, a relay user equipment, and a remote user equipment used in a cellular communication system. BACKGROUND

[0002] In recent years, a fifth generation (5G) cellular communication system has been attracting attention. In New Radio (NR) which is a radio access technology (RAT) of a 5G system, sidelink communication in which wireless communication is directly performed between user equipments is introduced.

[0003] LIST OF CITATIONS

[0004] NON-PATENT LITERATURE

[0005] Non-Patent Literature 1: 3GPP Technical Specification "3GPP TS 38.300 V16.2.0 (2020-07)" SUMMARY

[0006] In a first aspect, a communication control method used in a cellular communication system is disclosed. The communication control method includes: transmitting, by a relay user equipment having a capability of relaying data of a remote user equipment, a message including information related to the relay user equipment; receiving, by the remote user equipment, the message; and performing, by the remote user equipment, a process for establishing a sidelink connection between the remote user equipment and the relay user equipment based on the message.

[0007] In a second aspect, a relay user equipment having a capability of relaying data of a remote user equipment in a cellular communication system is disclosed. The relay user equipment includes a transmitter configured to transmit, to the remote user equipment, a message including information related to the relay user equipment. The message is used in a process for establishing a sidelink connection between the remote user equipment and the relay user equipment.

[0008] In a third aspect, a remote user equipment used in a cellular communication system is disclosed. The remote user equipment includes a receiver configured to receive, from a relay user equipment having a capability of relaying data of the remote user equipment, a message including information related to the relay user equipment; and a controller configured to perform a process for establishing a sidelink connection between the remote user equipment and the relay user equipment based on the message. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 FIG. 1 is a diagram illustrating a structure of a cellular communication system according to an embodiment.

[0010] Figure 2 FIG. 2 is a diagram illustrating a structure of a user equipment (UE) according to an embodiment.

[0011] Figure 3 FIG. 1 is a diagram illustrating a structure of a base station (gNB) according to an embodiment.

[0012] Figure 4 FIG. 2 is a diagram illustrating a structure of a protocol stack of a radio interface processing a user plane.

[0013] Figure 5 FIG. 3 is a diagram illustrating a structure of a protocol stack of a radio interface processing a control plane.

[0014] Figure 6 FIG. 4 is a diagram illustrating sidelink relaying according to an embodiment.

[0015] Figure 7 FIG. 5 is a diagram illustrating an overall procedure related to sidelink relaying according to an embodiment.

[0016] Figure 8 FIG. 6 is a diagram illustrating a structure of a protocol stack of a sidelink processing a user plane.

[0017] Figure 9 FIG. 7 is a diagram illustrating a structure of a protocol stack of a sidelink processing a control plane.

[0018] Figure 10 FIG. 8 is a diagram illustrating relaying of UE messages according to an embodiment.

[0019] Figure 11 FIG. 9 is a diagram illustrating a sequence of a relaying UE selection procedure according to an embodiment.

[0020] Figure 12 FIG. 10 is a diagram illustrating a sequence of a relaying UE reselection procedure according to an embodiment.

[0021] Figure 13 FIG. 11 is a diagram illustrating operation mode 1 of sidelink communication control by a remote UE according to an embodiment.

[0022] Figure 14 FIG. 12 is a diagram illustrating operation mode 2 of sidelink communication control by a remote UE according to an embodiment.

[0023] Figure 15 FIG. 13 is a diagram illustrating a variation of operation mode 2 of sidelink communication control by a remote UE according to an embodiment.

[0024] Figure 16 FIG. 14 is a diagram illustrating sidelink communication control by a relaying UE according to an embodiment. DETAILED DESCRIPTION

[0025] Research has been conducted on sidelink relaying, in which a relay user equipment relays data of a remote user equipment using sidelink communication. By selecting a relay user equipment and establishing a sidelink connection with the relay user equipment, the remote user equipment is enabled to use sidelink relaying. However, if the remote user equipment cannot select a suitable relay user equipment, the remote user equipment cannot properly perform sidelink communication.

[0026] An object of the present disclosure is to enable proper sidelink communication.

[0027] A cellular communication system according to an embodiment will be described with reference to the accompanying drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0028] Structure of a cellular communication system

[0029] First, the structure of a cellular communication system according to an embodiment will be described. Figure 1 is a diagram illustrating the structure of a cellular communication system according to an embodiment. The cellular communication system conforms to the 5th generation system (5GS) of the 3GPP standard. The following description takes the 5GS as an example, but a long term evolution (LTE) system can be at least partially applied to the cellular communication system.

[0030] As Figure 1 illustrated, the cellular communication system includes a user equipment (UE) 100, a 5G radio access network (next generation radio access network (NG-RAN)) 10, and a 5G core network (5GC) 20. The radio access network and the core network are collectively referred to as a cellular communication network.

[0031] The UE 100 is a mobile wireless communication device. The UE 100 can be any device as long as it is used by a user. Examples of the UE 100 include a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided on a sensor, a vehicle or a device provided on a vehicle (a vehicle UE), or an aerial object or a device provided on an aerial object (an aerial UE).

[0032] The NG-RAN 10 includes base stations (referred to as "gNBs" in 5G systems) 200. The gNBs 200 are interconnected via an Xn interface that is an inter-base station interface. Each gNB 200 manages one or more cells. The gNB 200 performs wireless communication with UEs 100 that have established connection to cells of the gNB 200. The gNB 200 has a radio resource management (RRM) function, a function of routing user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The "cell" is used as a term representing the smallest unit of a wireless communication area, and is also used as a term representing a function or a resource for wireless communication with a UE 100. One cell belongs to one carrier frequency.

[0033] Note that the gNB can be connected to an evolved packet core (EPC) that corresponds to a core network of LTE. An LTE base station can also be connected to 5GC. The LTE base station and the gNB can be connected via an inter-base station interface.

[0034] The 5GC 20 includes an access and mobility management function (AMF) and a user plane function (UPF) 300. The AMF performs various types of mobility control and the like for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using non-access stratum (NAS) signaling. The UPF controls data transfer. The AMF and the UPF are connected to the gNB 200 via an NG interface that is an interface between a base station and a core network.

[0035] Figure 2 is a diagram illustrating a structure of a UE 100 (user equipment) according to an embodiment.

[0036] As Figure 2 indicated, the UE 100 includes a receiver 110, a transmitter 120, and a controller 130.

[0037] The receiver 110 performs various types of reception under the control of the controller 130. The receiver 110 includes an antenna and a receiving device. The receiving device converts a radio signal received through the antenna into a baseband signal (a reception signal), and outputs the resulting signal to the controller 130.

[0038] The transmitter 120 performs various types of transmission under the control of the controller 130. The transmitter 120 includes an antenna and a transmitting device. The transmitting device converts a baseband signal (a transmission signal) output by the controller 130 into a radio signal, and transmits the resulting signal through the antenna.

[0039] The controller 130 performs various types of control in the UE 100. The controller 130 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be used for processing by the processor. The processor can include a baseband processor and a central processing unit (CPU). The baseband processor performs modulation and demodulation, encoding and decoding, and the like of a baseband signal. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0040] Figure 3 is a diagram showing a structure of a gNB 200 (base station) according to an embodiment.

[0041] As Figure 3 shown, the gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communicator 240.

[0042] The transmitter 210 performs various types of transmission under the control of the controller 230. The transmitter 210 includes an antenna and a transmission device. The transmission device converts a baseband signal (transmission signal) output by the controller 230 into a radio signal and transmits the resulting signal through the antenna.

[0043] The receiver 220 performs various types of reception under the control of the controller 230. The receiver 220 includes an antenna and a reception device. The reception device converts a radio signal received through the antenna into a baseband signal (reception signal) and outputs the resulting signal to the controller 230.

[0044] The controller 230 performs various types of control with respect to the gNB 200. The controller 230 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be used for processing by the processor. The processor can include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding, and the like of a baseband signal. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0045] The backhaul communicator 240 is connected to a neighboring base station via an inter-base station interface. The backhaul communicator 240 is connected to the AMF / UPF 300 via an interface between the base station and the core network. Note that the gNB can include a central unit (CU) and a distributed unit (DU) (i.e., functions are divided), and the two units can be connected via an Fl interface.

[0046] Figure 4 is a diagram showing a structure of a protocol stack of a radio interface that processes a user plane.

[0047] As Figure 4As shown, the user plane radio interface protocol includes the physical (PHY) layer, media access control (MAC) layer, radio link control (RLC) layer, packet data convergence protocol (PDCP) layer, and service data adaptation protocol (SDAP) layer.

[0048] The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. It transmits data and control information between the PHY layer of UE 100 and the PHY layer of gNB 200 via physical channels.

[0049] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of gNB 200 via the transport channel. The MAC layer of gNB 200 includes a scheduler. The scheduler determines the transmission format (transmission block size, modulation and coding scheme (MCS)) in the uplink and downlink, as well as the resource blocks to be allocated to UE 100.

[0050] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of UE 100 and the RLC layer of gNB 200 via logical channels.

[0051] The PDCP layer performs header compression and decompression, as well as encryption and decryption.

[0052] The SDAP layer performs the mapping between IP flows, which are the unit of QoS control performed by the core network, and radio bearers, which are the unit of QoS control performed by the access layer (AS). Note that SDAP may not be provided when the RAN is connected to the EPC.

[0053] Figure 5 This is a diagram showing the structure of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0054] like Figure 5 As shown, the protocol stack of the control plane's radio interface includes a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer, instead of... Figure 4 The SDAP layer is shown.

[0055] RRC signaling for various configurations is transmitted between the RRC layer of the UE 100 and the RRC layer of the gNB 200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, reconstruction, and release of radio bearers. When a connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200 exists, the UE 100 is in an RRC connected state. When a connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200 does not exist, the UE 100 is in an RRC idle state. When a connection between the RRC of the UE 100 and the RRC of the gNB 200 is suspended, the UE 100 is in an RRC inactive state.

[0056] A NAS layer higher than the RRC layer performs session management, mobility management, and the like. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300.

[0057] Note that the UE 100 includes an application layer in addition to the protocol of the radio interface.

[0058] Overview of sidelink relay

[0059] An overview of the sidelink relay according to an embodiment will be described. Figure 6 is a diagram illustrating a sidelink relay according to an embodiment.

[0060] As Figure 6 illustrated, the sidelink relay includes two modes, that is, a UE-to-NW relay (U2N relay) and a UE-to-UE relay (U2U relay).

[0061] The U2N relay is a mode in which a relay UE 100B performs relaying between a remote UE 100A and a gNB 200 (cell). Here, a sidelink connection is established between the relay UE 100B and the remote UE 100A, and a network connection is established between the relay UE 100B and the gNB 200. Note that the sidelink is a direct link between UEs 100, and can also be referred to as a PC5 interface. The sidelink connection can be referred to as a PC5-S connection or a PC5-RRC connection. The network connection refers to a connection between a UE 100 and a cellular communication network (gNB 200), and can be referred to as a NAS connection, an RRC connection, or a Uu interface.

[0062] The relay UE 100B is located within the coverage of the cell of the gNB 200 (whose coverage is hereinafter simply referred to as "coverage"). In contrast, the remote UE 100A is located outside the coverage. According to U2N relay, the remote UE 100A, which is not within the coverage (so-called service interruption), can perform network communication via the relay UE 100B. Note that the remote UE 100A can be located within the coverage.

[0063] U2U relay is a mode in which the relay UE 100B performs relaying between the remote UE 100A and another UE 100C. Here, a sidelink connection is established between the relay UE 100B and the remote UE 100A and between the relay UE 100B and the other UE 100C. Each of the remote UE 100A, the relay UE 100B, and the other UE 100C can be located within the coverage or can be located outside the coverage. Note that the sidelink connection can be indirectly established between the remote UE 100A and the other UE 100C via the relay UE 100B.

[0064] According to U2U relay, for example, even when direct sidelink communication between the remote UE 100A and the other UE 100C cannot be performed in an area outside the coverage, the remote UE 100A can indirectly perform sidelink communication therewith via the relay UE 100B.

[0065] Figure 7 is a diagram illustrating an overall flow related to sidelink relaying according to an embodiment. The following description is based on an assumption that the remote UE 100A has established a network connection with the cellular communication network (gNB 200) or a sidelink connection with the other UE 100C.

[0066] As Figure 7 indicated, in step S1, the remote UE 100A and the relay UE 100B perform a relay UE discovery procedure. In the relay UE discovery procedure, there is a method in which the relay UE 100B issues a notification of the presence of the relay UE 100B itself by transmitting a discovery message, and a method in which the remote UE 100A searches for the relay UE 100B by transmitting a discovery message. The discovery message thus transmitted can be a message dedicated to discovery or an existing message for establishing a sidelink connection. Note that the remote UE 100A can transmit a discovery message indicating the presence of the remote UE 100A itself, or the relay UE 100B can transmit a discovery message for searching for the remote UE 100A. Through the relay UE discovery procedure, the remote UE 100A discovers the relay UE 100B. Here, the remote UE 100A can discover a plurality of relay UEs 100B as candidates.

[0067] In step S2, the remote UE 100A performs a relay UE selection procedure which selects a relay UE 100B for relaying data of the remote UE 100A. When only one relay UE 100B is discovered in step S1, in the relay UE selection procedure, the remote UE 100A can select the relay EU 100B depending on whether the discovered relay UE 100B satisfies a predetermined condition. In contrast, when a plurality of relay UEs 100B are discovered in step S1, in the relay UE selection procedure, the remote UE 100A can select one relay UE 100B from the discovered plurality of relay UEs 100B. The relay UE selection procedure will be described in detail below.

[0068] In step S3, the remote UE 100A and the relay UE 100B perform a sidelink connection establishment procedure which establishes a sidelink connection. For example, the sidelink connection is established by the remote UE 100A and the relay UE 100B transmitting and receiving messages of a PC5-RRC layer (e.g., RRCReconfigurationSidelink, RRCRecononfigurationCompleteSidelink) which will be described below. The sidelink connection establishment procedure can include transmitting and receiving messages of a PC5-S layer (e.g., DIRECT LINK ESTABLISHMENT REQUEST, DIRECT LINK ESTABLISHMENT ACCEPT) which will be described below.

[0069] In step S4, the remote UE 100A performs sidelink communication with the relay UE 100B and transmits data to and receives data from the relay UE 100B. The relay UE 100B relays data transmitted and received by the remote UE 100A (sidelink relaying).

[0070] In step S5, the remote UE 100A can perform another relay UE selection procedure. Specifically, the remote UE 100A can perform a relay UE reselection procedure for switching from the current relay UE 100B to another relay UE 100B.

[0071] Protocol stack of sidelink

[0072] The structure of the protocol stack of the sidelink according to the embodiment will be described.

[0073] Figure 8 is a diagram illustrating the structure of the protocol stack of the user plane of the sidelink which processes data. As Figure 8As shown, the sidelink protocol of the user plane includes a PHY layer, a MAC layer, an RLC layer, a PDCP layer, and an SDAP layer.

[0074] The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and antenna de-mapping, and resource mapping and resource de-mapping. Data and control information are transmitted between the PHY layer of the remote UE 100A and the PHY layer of the relay UE 100B via a physical channel.

[0075] The MAC layer performs priority control of data, retransmission processing of HARQ, and the like. Data and control information are transmitted between the MAC layer of the remote UE 100A and the MAC layer of the relay UE 100B via a transport channel.

[0076] The RLC layer transmits data to the RLC layer of the receiving side by using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the remote UE 100A and the RLC layer of the relay UE 100B via a logical channel. The PDCP layer performs header compression and decompression, and encryption and decryption. The SDAP layer performs mapping between an IP flow, which is a unit of QoS control performed by a core network, and a radio bearer, which is a unit of QoS control performed by an AS.

[0077] Figure 9 is a diagram showing the structure of a protocol stack of the sidelink of the control plane that handles signaling (control signals).

[0078] As Figure 9 shown, the protocol stack of the sidelink of the control plane includes a PC5-RRC layer and a PC5-S layer, instead of the SDAP layer shown in Figure 8 .

[0079] A PC5-RRC message for various configurations is transmitted between the PC5-RRC layer of the remote UE 100A and the PC5-RRC layer of the relay UE 100B. The remote UE 100A can be in a PC5-RRC connected state when a connection (PC5-RRC connection) between the PC5-RRC of the remote UE 100A and the PC5-RRC of the relay UE 100B exists. Note that the AS layer includes the PC5-RRC layer.

[0080] The PC5-S layer is located at an upper layer of the PC5-RRC layer (AS layer). A discovery message or the like PC5-S message is transmitted between the PC5-S layer of the remote UE 100A and the PC5-S layer of the relay UE 100B.

[0081] Relay UE selection procedure

[0082] A relay UE selection procedure according to an embodiment will be described.

[0083] The remote UE 100A can use sidelink relaying by selecting a relay UE 100B and establishing a sidelink connection with the relay UE 100B, but if the remote UE 100A cannot select an appropriate relay UE 100B, the remote UE 100A cannot properly perform sidelink communication. The relay UE selection procedure according to the embodiment enables the remote UE 100A to select an appropriate relay UE 100B in the relay UE selection procedure.

[0084] The relay UE selection procedure according to the embodiment includes the steps of transmitting, by a relay UE 100B having a capability of relaying data of a remote UE 100A, a message including information related to the relay UE 100B (hereinafter referred to as a "relay UE message"), receiving, by the remote UE 100A, the relay UE message, and performing, by the remote UE 100A, a process for establishing a sidelink connection between the remote UE 100A and the relay UE 100B based on the relay UE message. For example, the relay UE message is a PC5-RRC message of a PC5-RRC layer or a discovery message of a PC5-S layer.

[0085] When only one relay UE 100B is discovered, in the relay UE selection procedure, the remote UE 100A can select the relay UE 100B based on the relay UE message received from the relay UE 100B. In contrast, when a plurality of relay UEs 100B is discovered, in the relay UE selection procedure, the remote UE 100A can select one relay UE 100B based on the relay UE message of each of the plurality of relay UEs 100B.

[0086] Figure 10 FIG. 2 is a diagram illustrating a relay UE message according to an embodiment.

[0087] As Figure 10 indicated, when the relay UE 100B has a network connection with a cellular communication network, the relay UE message includes information indicating a network communication state between the relay UE 100B and the cellular communication network. Thereby, the remote UE 100A can select or reselect an appropriate relay UE 100B in consideration of the network communication state between the relay UE 100B and the cellular communication network.

[0088] When the relay UE 100B has a sidelink connection with another UE 100C, the relay UE message includes information indicating a sidelink communication state between the relay UE 100B and the another UE 100C. Thereby, the remote UE 100A can select or reselect an appropriate relay UE 100B in consideration of the sidelink communication state between the relay UE 100B and the another UE 100C.

[0089] The relay UE message includes information indicating a relay capability of the relay UE 100B. Thereby, the remote UE 100A can select or reselect a proper relay UE 100B taking into account the relay capability of the relay UE 100B.

[0090] In particular, the information indicating a network communication status between the relay UE 100B and the cellular communication network includes at least one of the following information elements:

[0091] - an information element indicating an RRC status (one of RRC connected, RRC inactive, and RRC idle) between the relay UE 100B and the cellular communication network;

[0092] - an information element indicating a coverage status (one of in-coverage and out-of-coverage) of the relay UE 100B;

[0093] - an information element indicating a radio status (e.g., one of RSRP, RSRQ, and SINR) between the relay UE 100B and the cellular communication network;

[0094] - an information element indicating a used frequency band between the relay UE 100B and the cellular communication network;

[0095] For example, the information element can indicate one of a Licensed spectrum as a frequency band for which a license is granted, an Unlicensed spectrum as a frequency band for which no license is needed, and a Shared spectrum as a frequency band that can be shared by multiple systems. The information element can indicate one of a Frequency Range 1 (FR1) including a frequency of 6 GHz or lower, a Frequency Range 2 (FR2) including a millimeter wave from 24.25 GHz to 52.6 GHz (although its communicable range is narrower than that of FR1, the frequency band is wider), and other frequency ranges (e.g., FR3). The information element can indicate a bandwidth (e.g., 100 MHz) of the used frequency band between the relay UE 100B and the cellular communication network;

[0096] - an information element indicating a link status (e.g., one of throughput (data rate) and delay) between the relay UE 100B and the cellular communication network;

[0097] - an information element indicating a load status (e.g., resource utilization, etc.) between the relay UE 100B and the cellular communication network.

[0098] On the other hand, the information indicating the sidelink communication state between the relay UE 100B and another UE 100C includes at least one of the following information elements:

[0099] - an information element indicating a frequency band used between the relay UE 100B and another UE 100C;

[0100] - an information element indicating a radio state between the relay UE 100B and another UE 100C;

[0101] The information element can be RSRP, RSRQ, or SINR of each such another UE 100C (per each PC5-RRC connection). The information element can be an information element indicating a measurement result of a channel busy ratio (CBR) indicating a degree of channel congestion between the relay UE 100B and another UE 100C;

[0102] - an information element indicating a link state between the relay UE 100B and another UE 100C;

[0103] - an information element indicating a load state between the relay UE 100B and another UE 100C.

[0104] On the other hand, the information indicating the relay capability of the relay UE 100B includes at least one of the following information elements. It is assumed that the upper layer (PC5-S layer) holds these information:

[0105] - an information element indicating a relay mode (one of U2N, U2U, and both) of the relay UE 100B;

[0106] The information element can be based on a mode authenticated by the network;

[0107] - an information element indicating a load state (e.g., CPU and memory utilization, etc.) of the relay UE 100B;

[0108] - an information element indicating a battery state (e.g., one of connected to a power source, using a battery, low battery) of the relay UE 100B.

[0109] Figure 11 is a diagram showing a sequence of a relay UE selection process according to an embodiment. Although this diagram is an example in which two relay UEs 100B are present as candidates, three or more relay UEs 100B can be present as candidates.

[0110] As Figure 11 shown, in step S101, the relay UE 100B#1 transmits a relay UE message to the remote UE 100A.

[0111] When the relay UE message is a discovery message of the PC5-S layer, in the relay UE 100B#1, the AS layer notifies the network link state of the AS layer or another sidelink state (with another UE 100C) to the upper layer (PC5-S layer). The upper layer (PC5-S layer) generates a discovery message by using the state information from the AS layer and the relay capability information in the upper layer (PC5-S layer), and transmits the discovery message as a relay UE message.

[0112] On the other hand, when the relay UE message is a PC5-RRC message of the PC5-RRC layer, in the relay UE 100B#1, the upper layer (PC5-S layer) notifies the relay capability state of the upper layer (PC5-S layer) to the AS layer. The AS layer generates a PC5-RRC message by using the relay capability information from the upper layer (PC5-S layer) and the link state information in the AS layer, and transmits the PC5-RRC message as a relay UE message.

[0113] The message form of the PC5-RRC message can be a PC5-RRC message broadcasted in the sidelink (e.g., an existing MasterInformationBlockSidelink or a new message). Alternatively, the message form of the PC5-RRC message can be a PC5-RRC message for sidelink connection establishment (e.g., RRCReconfigurationSidelink or RRCReconfigurationCompleteSidelink), a PC5-RRC message for inquiry and response in the sidelink (e.g., UECapabilityEnquirySidelink or UECapabilityInformationSidelink), and / or a new inquiry and response message dedicated to relaying. Regarding the inquiry and response message, the relay UE message is a response message, and the relay UE transmits the relay UE message (response message) in response to the inquiry from the remote UE.

[0114] In step S102, the relay UE 100B#2 transmits a relay UE message to the remote UE 100A.

[0115] In step S103, based on the relay UE message of each of the plurality of relay UEs 100B (relay UE 100B#1 and relay UE 100B#2), the remote UE 100A selects one relay UE 100B to establish a sidelink connection with one of the plurality of relay UEs 100B.

[0116] In such a relay UE selection process, the remote UE 100A can extract selection candidates based on radio states (e.g., sidelink RSRP) between the remote UE 100A and each relay UE 100B. The remote UE 100A can rank the candidates according to their sidelink radio states, and consider the top n (e.g., top five UEs) relay UEs 100B as candidates. Alternatively, the remote UE 100A can consider relay UEs 100B whose radio states are within a certain range (e.g., -10 dB or less) relative to the relay UE 100B with the best radio state as candidates, or consider all relay UEs 100B with a threshold or higher (e.g., -100 dBm or higher) radio state as candidates.

[0117] In the relay UE selection process, the remote UE 100A compares information elements included in the relay UE messages of the plurality of relay UEs 100B as candidates to each other, thereby selecting one relay UE 100B. Note that which information element is used for the selection of the relay UE and the criteria (selection priority) of the selection can be configured from the gNB 200, can be defined in advance (pre-configuration), or can be configured by the user (user preference).

[0118] For example, regarding the RRC state included in the network communication state, the remote UE 100A can prefer to select a relay UE 100B in the RRC connected state rather than a relay UE 100B not in the RRC connected state. The remote UE 100A can perform relay UE selection in accordance with the priority of RRC connected state > RRC inactive state > RRC idle state.

[0119] Regarding the coverage state included in the network communication state, the remote UE 100A can exclude a relay UE 100B in-coverage or a relay UE 100B out-of-coverage from the candidates according to the use of each of U2N and U2U. The remote UE 100A can prefer to select a relay UE 100B in-coverage rather than a relay UE 100B out-of-coverage.

[0120] Regarding the radio state (RSRP, RSRQ, SINR) included in the network communication state, the remote UE 100A can prefer to select a relay UE 100B with a satisfactory radio state rather than a relay UE 100B with a poor radio state.

[0121] As for the used frequency band included in the network communication status, the remote UE 100A can prefer a relay UE 100B using a licensed spectrum over a relay UE 100B not using a licensed spectrum. The remote UE 100A can prefer a relay UE 100B using FR2 over a relay UE 100B not using FR2. The remote UE 100A can prefer a relay UE 100B using a wider bandwidth over a relay UE 100B using a narrower bandwidth. Note that each of these priority criteria can be reversed. For example, the remote UE 100A can prefer a relay UE 100B not using a licensed spectrum, or can prefer a relay UE 100B not using FR2.

[0122] As for the link status included in the network communication status, the remote UE 100A can prefer a relay UE 100B having a high throughput over a relay UE 100B having a low throughput. The remote UE 100A can prefer a relay UE 100B having a low latency over a relay UE 100B having a high latency.

[0123] As for the load status included in the network communication status, the remote UE 100A can prefer a relay UE 100B having a low load over a relay UE 100B having a high load.

[0124] The same is true for the sidelink communication status, the remote UE 100A performs relay UE selection in the same and / or similar manner as for the network communication status. Note that as for the radio status included in the sidelink communication status, the remote UE 100A can prefer a relay UE 100B having a satisfactory radio status for the communication destination of the remote UE 100A. The remote UE 100A can prefer a relay UE 100B having a low CBR measurement value over a relay UE 100B having a high CBR measurement value.

[0125] Further, as for the relay capability information, the remote UE 100A can prefer a relay UE 100B in a relay mode suitable for the use of U2N and U2U of the remote UE 100A. The remote UE 100A can prefer a relay UE 100B having a low load status (CPU and memory utilization, etc.) over a relay UE 100B having a high load status. As for the battery status, the remote UE 100A can prefer a relay UE 100B connected to a power source.

[0126] After one relay UE 100B is selected through the relay UE selection process, in step S104, the remote UE 100A performs a sidelink connection establishment process to the selected relay UE 100B (here, relay UE 100B#1).

[0127] Figure 12 is a diagram illustrating a sequence of a relay UE reselection process according to an embodiment. Here, a difference from the above-described relay UE selection process will be described.

[0128] As Figure 12 indicated, in step S151, the remote UE 100A establishes a sidelink connection with the relay UE 100B#1. The remote UE 100A can trigger the relay UE reselection in response to deterioration of the sidelink radio status with the relay UE 100B#1.

[0129] In steps S152 and S153, the remote UE 100A receives a relay UE message from each of the relay UE 100B#1 and the relay UE 100B#2.

[0130] In step S154, based on the relay UE message of each of the relay UE 100B#1 and the relay UE 100B#2, the remote UE 100A determines whether to switch to (reselect) the relay UE 100B#2. The criteria for such relay UE reselection are the same and / or similar to those for the relay UE selection described above. Here, the description will continue on the assumption that the remote UE 100A determines to perform reselection to the relay UE 100B#2 based on the remote UE 100A.

[0131] In step S154, the remote UE 100A performs a sidelink connection establishment process to the reselected relay UE 100B#2. Note that the remote UE 100A releases the sidelink connection with the relay UE 100B#1.

[0132] Sidelink communication control

[0133] Sidelink communication control in a sidelink relay process according to an embodiment will be described.

[0134] The remote UE 100A having a sidelink connection with the relay UE 100B can perform communication with a cellular communication network or another UE 100C via the relay UE 100B. However, after starting such sidelink communication, the state of the UE 100 can change, for example, a movement has occurred, which can make it difficult to properly perform sidelink communication.

[0135] The sidelink communication control according to the embodiment includes the steps of determining, by the remote UE 100A having a sidelink connection with the relay UE 100B, a network communication state between the remote UE 100A and the cellular communication network (gNB 200), and performing, by the remote UE 100A, control related to sidelink communication between the remote UE 100A and the relay UE 100B based on the network communication state. Thereby, the sidelink communication between the remote UE 100A and the relay UE 100B can be appropriately controlled.

[0136] The sidelink communication control according to the embodiment includes the steps of determining, by the relay UE 100B having a sidelink connection with the remote UE 100A, a communication state between the relay UE 100B and the cellular communication network (gNB 200) or a communication state between the relay UE 100B and another UE 100C, and performing, by the relay UE 100B, control related to sidelink communication between the relay UE 100B and the remote UE 100A based on the determined communication state. Thereby, the sidelink communication between the remote UE 100A and the relay UE 100B can be appropriately controlled.

[0137] (1) Sidelink communication control by remote UE 100A

[0138] (1.1) Operation mode 1

[0139] Operation mode 1 of the sidelink communication control by the remote UE 100A according to the embodiment will be described.

[0140] In operation mode 1 of the sidelink communication control by the remote UE 100A, the remote UE 100A having a sidelink connection with the relay UE 100B detects improvement in a network communication state between the remote UE 100A and the cellular communication network. Then, in response to the detection of the improvement, the remote UE 100A performs processing for suspending the sidelink communication between the remote UE 100A and the relay UE 100B.

[0141] Thereby, when the network communication state between the remote UE 100A and the cellular communication network improves after the sidelink relay is started, the remote UE 100A can switch the sidelink relay communication to direct communication with the cellular communication network.

[0142] Figure 13 is a diagram illustrating operation mode 1 of the sidelink communication control by the remote UE 100A according to the embodiment. Figure 13 The case where the remote UE 100A having a sidelink connection with the relay UE 100B moves from an area outside the coverage to an area within the coverage is mainly assumed. Note that, in the following description, the case where the remote UE 100A moves from an area outside the coverage to an area within the coverage is mainly assumed.Figure 13 In the middle, the unnecessary steps are shown with dashed lines.

[0143] As Figure 13 shown, in step S201, the remote UE 100A establishes a sidelink connection with the relay UE 100B. The relay mode of the relay UE 100B can be a U2N relay or a U2U relay.

[0144] In step S202, the remote UE 100A transmits and receives data to and from the relay UE 100B.

[0145] In step S203, the relay UE 100B relays the data transmitted and received by the remote UE 100A. Although Figure 13 An example in which the relay UE 100B transmits and receives relay data to and from the gNB 200 is shown, but the relay UE 100B can transmit and receive relay data to and from another UE 100C.

[0146] In step S204, the remote UE 100A determines a network communication state between the remote UE 100A and the cellular communication network (gNB 200), and detects a change in the network communication state.

[0147] For example, in step S204, the remote UE 100A detects that the remote UE 100A has moved from an area outside the coverage to an area within the coverage. The remote UE 100A can detect the movement to the area within the coverage based on the reception power (RSRP) of a reference signal received from the cellular communication network having exceeded a threshold value. The remote UE 100A can detect the movement to the area within the coverage based on a synchronization signal received from the cellular communication network. Alternatively, in step S204, the remote UE 100A can detect that the remote UE 100A has transitioned from an RRC idle state or an RRC inactive state to an RRC connected state (step S205 described below).

[0148] Here, the threshold value to be compared with the RSRP and the network communication state to be detected by the remote UE 100A can be configured from the gNB 200 using system information (SIB) or the like, or can be a pre-defined threshold value (e.g., S-criteria) and / or a configuration (pre-configuration) written in advance in a subscriber identity module (SIM) or the like.

[0149] In step S205, the remote UE 100A establishes a network connection with the gNB 200 and transitions to an RRC connected state. Note that step S205 can be performed after step S208, which will be described below, for example, between step S208 and step S209 described below.

[0150] In response to detecting the change in the network communication state, the remote UE 100A performs processing for suspending sidelink communication between the remote UE 100A and the relay UE 100B.

[0151] As such processing, the remote UE 100A can notify the relay UE 100B of the change in the network communication state (e.g., the transition to the RRC connected state) (step S206). Here, the remote UE 100A can notify the relay UE 100B of the reception power (RSRP) of a reference signal received from the cellular communication network. Such notification can be performed using a PC5-RRC message or a PC5-S message.

[0152] Based on the notification from the remote UE 100A, the relay UE 100B can perform processing of releasing the sidelink connection with the remote UE 100A. For example, the relay UE 100B discards the PC5-RRC entity and / or the PC5-S entity and sends a PC-RRC release indication to the remote UE 100A.

[0153] In response to detecting the change in the network communication state, the remote UE 100A can suspend the sidelink communication with the relay UE 100B (step S207). For example, the remote UE 100A causes a communication timeout by not responding to the relay UE 100B, etc., thereby implicitly notifying the relay UE 100B of the release of the sidelink connection. The remote UE 100A can discard the PC5-RRC entity and / or the PC5-S entity of the remote UE 100A.

[0154] In step S208, the remote UE 100A performs processing of releasing the sidelink connection with the relay UE 100B. For example, the remote UE 100A can explicitly notify the relay UE 100B of the release of the sidelink connection by using a PC5-RRC message indicating the release of the sidelink connection.

[0155] In step S209, the remote UE 100A transmits and receives data through network communication with the gNB 200.

[0156] This operation mode describes U2N relaying, but can also be applied to U2U relaying. In this case, the gNB 200 in this operation mode can be interpreted as another UE (another remote UE) 100C, and the network communication state can be interpreted as a communication state between the remote UE 100A and the other remote UE 100C. For example, the remote UE 100A can detect the presence of another remote UE 100C in the vicinity (within a range in which direct communication can be performed) through a discovery procedure (step S204). Subsequently, in the same and / or similar manner as in this operation mode, the remote UE 100A performs an operation of releasing the sidelink connection with the relay UE 100B.

[0157] (1.2) Operation mode 2

[0158] Operation mode 2 of sidelink communication control by the remote UE 100A according to an embodiment will be described.

[0159] In operation mode 2 of sidelink communication control by the remote UE 100A, the relay UE 100B performing U2N relaying transfers first system information broadcast by a first cell of a cellular communication network to the remote UE 100A. The remote UE 100A detects an improvement in a network communication state with a second cell of the cellular communication network. In response to detecting the improvement, the remote UE 100A acquires second system information broadcast by the second cell instead of the first system information transferred from the relay UE 100B. Thereby, when the remote UE 100A moves to an area within a coverage range of the second cell different from the first cell to which the remote UE 100A is connected, the remote UE 100A can acquire system information in the second cell.

[0160] Figure 14 is a diagram illustrating operation mode 2 of sidelink communication control by the remote UE 100A according to an embodiment. Although Figure 14 An example in which the gNB 200#1 manages the cell #1 (first cell) and the gNB 200#2 manages the cell #2 (second cell) is illustrated, but one gNB 200 can manage the cell #1 and the cell #2.

[0161] As Figure 14 illustrated, in step S301, the relay UE 100B located within the coverage range of the cell #1 receives (acquires) the SIB#1 (first system information) as system information of the cell #1 from the cell #1.

[0162] In step S302, the relay UE 100B transfers the SIB#1 to the remote UE 100A. The remote UE 100A located outside the coverage range receives the SIB#1 from the relay UE 100B and applies the SIB#1.

[0163] In step S303, the remote UE 100A determines a network communication state between the remote UE 100A and the cell #2, and detects a change in the network communication state.

[0164] For example, in step S303, the remote UE 100A detects that the remote UE 100A has moved from an area outside the coverage to an area within the coverage of the cell #2. The remote UE 100A detects the movement to the area within the coverage of the cell #2 based on that the received power (RSRP) of a reference signal received from the cell #2 has exceeded a threshold value. The remote UE 100A can detect the movement to the area within the coverage of the cell #2 based on that a synchronization signal is received from the cell #2. Here, the threshold value to be compared with the RSRP and the network communication state to be detected by the remote UE 100A can be configured from the gNB 200 using system information (SIB) or the like, or can be a pre-defined threshold value (e.g., S criterion) and / or a configuration (pre-configuration) written in advance in a SIM or the like.

[0165] In step S304, the remote UE 100A that has moved to the area within the coverage of the cell #2 receives (acquires) the SIB #2 (second system information) as the system information of the cell #2 from the cell #2. The remote UE 100A can discard the configuration of the SIB #1 transmitted from the relay UE 100B.

[0166] Figure 15 is a diagram illustrating a variation of operation mode 2 of the sidelink communication control by the remote UE 100A according to the embodiment. The variation assumes a case where the remote UE 100A moves from an area within the coverage to an area outside the coverage.

[0167] As Figure 15 indicated in step S351, the remote UE 100A located within the coverage of the cell #1 receives (acquires) the SIB from the cell #1.

[0168] In step S352, the remote UE 100A determines a network communication state between the remote UE 100A and the cell #1, and detects a change in the network communication state.

[0169] For example, in step S352, the remote UE 100A detects that the remote UE 100A has moved from an area within the coverage of the cell #1 to an area outside the coverage. The remote UE 100A can detect the movement to the area outside the coverage based on that the reception power (RSRP) of the reference signal received from the cell #1 has fallen below a threshold. Here, the threshold to be compared with the RSRP can be configured from the gNB 200 using system information (SIB) or the like, or can be a pre-defined threshold (e.g., S criterion) and / or a configuration (pre-configuration) written in advance in the SIM or the like.

[0170] Here, the remote UE 100A can perform the relay UE discovery procedure and / or the above-described relay UE selection procedure, and establish a sidelink connection with the relay UE 100B.

[0171] In step S353, the relay UE 100B located within the coverage of the cell #1 receives (acquires) the SIB from the cell #1.

[0172] In step S354, the relay UE 100B transfers the SIB to the remote UE 100A. The remote UE 100A located outside the coverage receives the SIB from the relay UE 100B and applies the SIB.

[0173] Note that although Figure 15 An example in which the relay UE 100B is located within the coverage of the cell #1 is shown, but the relay UE 100B can be located in another cell (cell #2). In this case, the relay UE 100B transfers the SIB of the cell #2 to the remote UE 100A outside the coverage. The remote UE 100A can discard the configuration by the SIB of the cell #1.

[0174] (2) Communication control by the relay UE 100B

[0175] The sidelink communication control by the relay UE 100B according to the embodiment will be described.

[0176] The relay UE 100B having the sidelink connection with the remote UE 100A detects deterioration of the communication state between the relay UE 100B and the cellular communication network (gNB 200), or deterioration of the communication state between the relay UE 100B and another UE 100C. In response to detecting the deterioration, the relay UE 100B performs a predetermined process for suspending the sidelink communication with the remote UE 100A.

[0177] The remote UE 100A cannot recognize the communication state between the relay UE 100B and the cellular communication network (gNB 200) or the communication state between the relay UE 100B and another UE 100C, and it is difficult to determine whether it is possible to continue sidelink relaying. When the relay UE 100B detects deterioration of the communication state, the relay UE 100B performs predetermined processing for suspending sidelink communication with the remote UE 100A, thereby enabling the remote UE 100A to perform relay UE reselection processing and the like.

[0178] In the predetermined processing, the relay UE 100B can transmit a reselection indication for causing the remote UE 100A to reselect a relay UE 100B other than the relay UE 100B to the remote UE 100A. When the relay UE 100B detects deterioration of the communication state between the relay UE 100B and another UE 100C, the relay UE 100B can notify such another UE to the remote UE 100A.

[0179] Figure 16 is a diagram illustrating sidelink communication control by the relay UE 100B according to an embodiment. Note that, in Figure 16 , steps that are not necessary are shown in dotted lines.

[0180] As Figure 16 shown, in step S401, the remote UE 100A establishes a sidelink connection with the relay UE 100B. The relay mode of the relay UE 100B can be U2N relaying or U2U relaying.

[0181] In step S402, the remote UE 100A transmits and receives data to and from the relay UE 100B.

[0182] In step S403, the relay UE 100B relays data transmitted and received by the remote UE 100A. Specifically, the relay UE 100B transmits and receives relay data to and from the gNB 200 or another UE 100C.

[0183] In step S404, the relay UE 100B determines the communication state between the relay UE 100B and the cellular communication network (gNB 200) or the communication state between the relay UE 100B and another UE 100C, and detects deterioration of the communication state.

[0184] For example, in the case of U2N relaying, the relay UE 100B can detect at least one of a radio link failure (RLF) in a network connection with the gNB 200, a recovery failure in an RRC connection, and an RRC connection release. The relay UE 100B can detect that a reception power (RSRP) of a reference signal received from the gNB 200 or a throughput of network communication with the gNB 200 has fallen below a threshold, or detect that a resource utilization (occupancy) of network communication with the gNB 200 has exceeded a threshold.

[0185] On the other hand, in the case of U2U relaying, the relay UE 100B can detect at least one of an RLF in a sidelink connection with another UE 100C, a PC5-RRC connection release, a PC5-S connection release, an establishment failure of a PC5-RRC connection, and an establishment failure of a PC5-S connection. The relay UE 100B can detect that a reception power (RSRP) of a reference signal received from the other UE 100C or a throughput of sidelink communication with the other UE 100C has fallen below a threshold, or detect that a resource utilization (occupancy) of sidelink communication with the other UE 100C has exceeded a threshold.

[0186] Note that the threshold can be configured from the gNB 200 using system information (SIB) or the like, can be a pre-defined threshold (e.g., S criterion), or can be a configuration (pre-configuration) written in advance in a SIM or the like.

[0187] In step S405, the relay UE 100B determines a deterioration of a communication state between the relay UE 100B and the cellular communication network (gNB 200) or a communication state between the relay UE 100B and the other UE 100C, and transmits a message indicating the deterioration of the communication state to the remote UE 100A. The message can be a PC5-RRC message transmitted by unicast, or can be a message transmitted by broadcast.

[0188] For example, the message of step S405 can be a reselection indication instructing the remote UE 100A to perform a relay UE reselection process. In the case of U2U relaying, the message can include a destination ID indicating the other UE 100C having a deteriorated sidelink communication state. The message can include information indicating whether the deterioration of the communication state is a deterioration of a network communication state or a deterioration of a sidelink communication state.

[0189] The message of step S405 can be a suspend indication indicating temporary suspension of sidelink communication with the remote UE 100A. In this case, when the communication state between the relay UE 100B and the cellular communication network (gNB 200) or the communication state between the relay UE 100B and another UE 100C improves, the relay UE 100B can transmit a resume indication indicating resumption of sidelink communication with the remote UE 100A to the remote UE 100A. These indications can include information indicating the cause (based on the above-described detection result).

[0190] The message of step S405 can be a discovery message. The discovery message includes a list of identifiers of other UEs 100C with which the relay UE 100B has a sidelink connection. When the relay UE 100B detects that the communication state with any one of the UEs 100C in the list deteriorates, the relay UE 100B updates the list to eliminate the identifier of that UE 100C and notifies the remote UE 100A of the discovery message including the updated list. Thereby, the remote UE 100A is able to correctly identify other UEs 100C capable of sidelink relay communication. Note that when the list includes an identifier of the gNB 200 (i.e., in the case of U2N relay), the identifier (cell ID, identifier indicating network connection, etc.) can be deleted from the list.

[0191] The message of step S405 can be the above-described relay UE message. In other words, in response to a change (determination) in the communication state with the gNB 200 or another UE 100C, the relay UE 200B triggers transmission of the above-described relay UE message.

[0192] In step S406, the relay UE 100B can perform processing for suspending sidelink communication with the remote UE 100A. For example, the relay UE 100B can cause a communication timeout by not giving a response to the remote UE 100A, etc., thereby implicitly notifying the remote UE 100A of release of the sidelink connection. The relay UE 100B can explicitly notify the remote UE 100A of release of the connection by using a PC5-RRC message indicating release of the sidelink connection.

[0193] In step S407, for example, the remote UE 100A can trigger the relay UE reselection process based on the message received from the relay UE 100B in step S405. Here, the remote UE 100A can perform the relay UE reselection process after excluding the relay UE 100B that has transmitted the message from the reselection candidates. In the remote UE 100A, the AS layer can notify the upper layer (PC5-S, etc.) of the reception of the message (and the content of the message). In this case, the upper layer can exclude the relay UE 100B that has transmitted the message from the objects to be discovered in the relay UE discovery process.

[0194] Other Embodiments

[0195] The above-described sequence can be implemented not only individually and independently but also in a combination of two or more steps of different sequences.

[0196] A program that causes a computer to execute each of the processes performed by the UE 100 or the gNB 200 can be provided. The program can be recorded in a computer-readable medium. The use of the computer-readable medium enables the program to be installed on the computer. Here, the computer-readable medium in which the program is recorded can be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and can be, for example, a recording medium such as a CD-ROM, a DVD-ROM.

[0197] Circuitry for executing the processes to be performed by the UE 100 or the gNB 200 can be integrated, and at least a part of the UE 100 or the gNB 200 can be configured as a semiconductor integrated circuit (chipset or SoC).

[0198] Embodiments have been described in detail above with reference to the accompanying drawings, but the specific configurations are not limited to the above and various design changes can be made without departing from the gist of the present disclosure.

[0199] This application claims priority to U.S. Provisional Application No. 63 / 086,146 filed October 1, 2020, the entire contents of which are incorporated herein by reference.

Claims

1.A communication control method for use in a cellular communication system, the communication control method comprising: transmitting, by a relay user equipment having a capability of relaying data of a remote user equipment, a message including information related to the relay user equipment; receiving, by the remote user equipment, the message; and performing, by the remote user equipment, a process configured to establish a sidelink connection between the remote user equipment and the relay user equipment based on the message, the message including an information element indicating a usage frequency between the relay user equipment and a network. 2.The communication control method according to claim 1, further comprising: detecting, by the relay user equipment, a radio link failure (RLF) between the relay user equipment and the network; and transmitting, by the relay user equipment to the remote user equipment, a PC5-RRC message including information representing the RLF. 3.The communication control method according to claim 1, wherein the transmitting includes transmitting, by each of a plurality of relay user equipments, the message, and the performing includes selecting or reselecting, from the plurality of relay user equipments, one relay user equipment to establish the sidelink connection based on the message of each of the plurality of relay user equipments. 4.The communication control method according to claim 1, wherein the message is a PC5-Radio Resource Control (RRC) message of a PC5-RRC layer or a discovery message of a PC5-S layer. 5.The communication control method according to claim 1, wherein when the relay user equipment has a network connection with a cellular communication network, the message includes information indicating a network communication status between the relay user equipment and the cellular communication network. 6.The communication control method according to claim 1, wherein when the relay user equipment has a sidelink connection with a different user equipment, the message includes information indicating a sidelink communication status between the relay user equipment and the different user equipment. 7.The communication control method according to claim 1, wherein the message includes information indicating a relay capability of the relay user equipment. 8.The communication control method according to claim 7, wherein the information indicating the relay capability of the relay user equipment includes information related to a load of the relay user equipment. 9.A relay user equipment having a capability of relaying data of a remote user equipment in a cellular communication system, the relay user equipment comprising: a transmitter configured to transmit, to the remote user equipment, a message including information related to the relay user equipment, wherein the message is used in a process configured to establish a sidelink connection between the remote user equipment and the relay user equipment, the message including an information element indicating a usage frequency between the relay user equipment and a network. 10.A remote user equipment for use in a cellular communication system, the remote user equipment comprising: ​ ​ a receiver configured to receive, from a relay user equipment having a capability to relay data for a remote user equipment, a message comprising information related to the relay user equipment; and a controller configured to perform, based on the message, a process configured to establish a sidelink connection between the remote user equipment and the relay user equipment, the message comprising an information element indicating a usage frequency between the relay user equipment and a network.

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