Communication method and network node

Abstract

This communication method used in a mobile communication system comprises: a step in which a relay device for changing the propagation state of a wireless signal, which is transmitted between a first cell and a user device, without demodulating and modulating the wireless signal relays the wireless signal; and a step in which a first network node corresponding to the first cell sends a message for connecting the relay device to a second cell to a second network node corresponding to the second cell on a network interface. The message includes information relating to the relay device.

Description

[Technical Field]

[0001] The present disclosure relates to a communication method and a network node for use in a mobile communication system. [Background technology]

[0002] In recent years, fifth-generation (5G) mobile communication systems have been attracting attention. NR (New Radio), the radio access technology of 5G systems, is capable of wideband transmission using higher frequency bands than LTE (Long Term Evolution), the fourth-generation radio access technology.

[0003] Radio signals (radio waves) in high frequency bands such as millimeter waves or terahertz waves have a tendency to propagate in a highly directional manner, which poses a problem of reducing the coverage of base stations. To solve this problem, repeater devices, which are a type of relay device that relays radio signals between base stations and user devices and can be controlled from a network, have attracted attention (see, for example, Non-Patent Document 1). Such repeater devices can expand the coverage of base stations while suppressing interference, for example, by amplifying radio signals received from base stations and transmitting them using directional transmission. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] 3GPP contribution: RP-213700, “New SI: Study on NR Network-controlled Repeaters” Summary of the Invention

[0005] A communication method according to a first aspect is a method for use in a mobile communication system, the communication method comprising: a step of relaying a radio signal transmitted between a first cell and a user equipment by a relay device that changes a propagation state of the radio signal without demodulating or modulating the radio signal; and a step of transmitting a message to a second network node that corresponds to the second cell via a network interface from a first network node that corresponds to the first cell, the message including information about the relay device.

[0006] A network node according to a second aspect is a device corresponding to a first cell in a mobile communication system, and includes a transmitter configured to transmit, via a network interface to a second network node corresponding to the second cell, a message for connecting a relay device that changes a propagation state of a radio signal transmitted between the first cell and a user equipment without demodulating or modulating the radio signal to the second cell, the message including information about the relay device. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. [Figure 2] FIG. 10 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. [Figure 3] FIG. 1 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). [Figure 4] FIG. 2 is a diagram illustrating an example of an application scenario of the relay device (NCR device) according to the first embodiment. [Figure 5] FIG. 2 is a diagram illustrating an example of an application scenario of the relay device (NCR device) according to the first embodiment. [Figure 6] FIG. 3 is a diagram illustrating an example of a control method for a relay device (NCR device) according to the first embodiment. [Figure 7]1 is a diagram illustrating an example of the configuration of a protocol stack in a mobile communication system having a relay device (NCR device) according to a first embodiment. [Figure 8] 1 is a diagram illustrating an example of the configuration of a relay device (NCR device) according to a first embodiment. [Figure 9] FIG. 1 is a diagram illustrating a configuration example of a base station (gNB) according to an embodiment. [Figure 10] FIG. 1 is a diagram illustrating an example of downlink signaling from a base station (gNB) to a control terminal (NCR-MT) according to the first embodiment. [Figure 11] FIG. 1 is a diagram illustrating an example of uplink signaling from a control terminal (NCR-MT) to a base station (gNB) according to the first embodiment. [Figure 12] FIG. 2 is a diagram showing an example of an overall operation sequence of the mobile communication system according to the first embodiment. [Figure 13] FIG. 2 is a diagram for explaining beam sweeping according to the first embodiment. [Figure 14] FIG. 4 is a diagram for explaining operations related to load balancing according to the first embodiment. [Figure 15] FIG. 1 is a diagram for explaining the link (connection) between the NCR device and the gNB according to the first embodiment. [Figure 16] FIG. 4 is a diagram illustrating an operation of a mobile communication system according to a first operation pattern. [Figure 17] FIG. 10 is a diagram illustrating an operation of a mobile communication system according to a second operation pattern. [Figure 18] FIG. 10 is a diagram illustrating an operation of a mobile communication system according to a third operation pattern. [Figure 19] FIG. 10 is a diagram for explaining a relay device (RIS device) according to a second embodiment. [Figure 20] FIG. 10 is a diagram for explaining a relay device (RIS device) according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] When controlling relay devices such as repeater devices from a network, the control technology for specifically controlling the relay devices has not yet been established, and it is currently difficult to efficiently extend coverage using relay devices.

[0009] Therefore, an object of the present disclosure is to enable appropriate control of a relay device that relays transmission between a base station and a user device.

[0010] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] (1) First embodiment First, a description will be given of a first embodiment. A relay device according to the first embodiment is a repeater device that can be controlled from a network.

[0012] (1.1) Overview of mobile communication systems FIG. 1 is a diagram showing the configuration of a mobile communication system according to a first embodiment. The mobile communication system 1 conforms to the 5th Generation System (5GS) standard of the 3rd Generation Partnership Project (3GPP) (registered trademark; the same applies hereinafter). In the following description, 5GS is used as an example, but the mobile communication system may also be at least partially applied to an LTE (Long Term Evolution) system. The mobile communication system may also be at least partially applied to a sixth generation (6G) system.

[0013] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10. The 5GC 20 may be simply referred to as the core network (CN) 20.

[0014] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 is 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 in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0015] The NG-RAN 10 includes a base station (called "gNB" in the 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with a UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0016] The gNB 200 may be functionally divided into a central unit (CU) and distributed units (DU). The CU controls the DU. The CU is a unit that includes upper layers included in the protocol stack described below, such as the RRC layer, SDAP layer, and PDCP layer. The CU is connected to the core network via the NG interface, which is a backhaul interface. The CU is connected to neighboring base stations via the Xn interface, which is an interface between base stations. The DU forms a cell. D U isThe DU is a unit including lower layers included in the protocol stack described below, such as the RLC layer, MAC layer, and PHY layer. The DU is connected to the CU via an F1 interface, which is a fronthaul interface.

[0017] In addition, gNBs can also connect to the Evolved Packet Core (EPC), which is the LTE core network. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via a base station-to-base station interface.

[0018] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0019] FIG. 2 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0020] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0021] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has CRC parity bits scrambled by the RNTI added.

[0022] The gNB 200 also transmits a synchronization signal block (SSB: Synchronization Signal / PBCH block). For example, the SSB is composed of four consecutive Orthogonal Frequency Division Multiplex (OFDM) symbols, and includes a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), a Physical Broadcast Channel (PBCH) / Master Information Block (MIB), and a Demodulation Reference Signal (DMRS) for the PBCH. The bandwidth of the SSB is, for example, 240 consecutive subcarriers, i.e., a bandwidth of 20 RBs.

[0023] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of UE100 and the MAC layer of gNB200 via transport channels. The MAC layer of gNB200 includes a scheduler, which determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE100.

[0024] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via logical channels.

[0025] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0026] The SDAP layer maps IP flows, which are the units for Quality of Service (QoS) control by the core network, to radio bearers, which are the units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP is not necessary.

[0027] FIG. 3 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0028] The protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer instead of the SDAP layer shown in FIG.

[0029] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0030] The NAS layer, which is located above the RRC layer, performs session management, mobility management, etc. 0's NAS signaling is transmitted between the UE 100 and the NAS layer. The UE 100 has an application layer and the like in addition to the radio interface protocol. A layer lower than the NAS layer is called an AS layer.

[0031] (1.2) Example of application scenario for relay devices 4 and 5 are diagrams showing an example of an application scenario of the NCR device according to the first embodiment.

[0032] 5G / NR enables broadband transmission using higher frequency bands than 4G / LTE. Radio signals in high frequency bands such as the millimeter wave band or terahertz wave band have high line-of-sight properties, which poses a challenge in reducing the coverage of the gNB 200. In FIG. 4, the UE 100 may be located outside the coverage area of ​​the gNB 200, for example, outside an area where a radio signal can be received directly from the gNB 200. There may be an obstruction between the gNB 200 and the UE 100, preventing the UE 100 from communicating with the gNB 200 within line-of-sight.

[0033] As shown in Fig. 4, a repeater device (500A), which is a type of relay device that relays radio signals between a gNB 200 and a UE 100 and can be controlled from a network, is introduced into the mobile communication system 1. Hereinafter, such a repeater device is referred to as an NCR (Network-Controlled Repeater) device. Such a repeater device may also be referred to as a smart repeater device.

[0034] For example, the NCR device 500A amplifies a radio signal (radio wave) received from the gNB 200 and transmits it by directional transmission. Specifically, the NCR device 500A receives a radio signal transmitted by the gNB 200 by beamforming. Then, the NCR device 500A amplifies the received radio signal without demodulating or modulating it, and transmits the amplified radio signal by directional transmission. Here, the NCR device 500A may transmit the radio signal with a fixed directivity (beam). The NCR device 500A may transmit the radio signal with a variable (adaptive) directional beam. This enables the coverage of the gNB 200 to be efficiently expanded. In the first embodiment, it is mainly assumed that the NCR device 500A is applied to downlink communication from the gNB 200 to the UE 100, but the NCR device 500A can also be applied to uplink communication from the UE 100 to the gNB 200.

[0035] As shown in FIG. 5, a new UE (hereinafter referred to as "NCR-MT (Mobile termination)") 100, which is a type of control terminal for controlling the NCR device 500A, is provided. b Specifically, the NCR device 500A includes an NCR-Fwd (Forward) 510A, which is a type of repeater that relays radio signals transmitted between the gNB 200 and the UE 100, specifically, that changes the propagation state of the radio signals without demodulating or modulating the radio signals, and an NCR-MT 520A that controls the NCR-Fwd 510A by wirelessly communicating with the gNB 200. In this way, the NCR-MT 520A establishes a wireless connection with the gNB 200 and communicates wirelessly with the gNB 200, thereby controlling the NCR device 500A in cooperation with the gNB 200. This enables efficient coverage expansion using the NCR device 500A. The NCR-MT 520A controls the NCR device 500A under control from the gNB 200.

[0036] The NCR-MT520A may be configured separately from the NCR-Fwd510A. For example, the NCR-MT520A may be located near the NCR-Fwd510A and electrically connected to the NCR-Fwd510A. The NCR-MT520A may be connected to the NCR-Fwd510A via a wired or wireless connection. Alternatively, the NCR-MT520A may be configured integrally with the NCR-Fwd510A. The NCR-MT520A and the NCR-Fwd510A may be fixedly installed, for example, at the coverage edge (cell edge) of the gNB200 or on a wall or window of a building. The NCR-MT520A and the NCR-Fwd510A may be mobile, installed in a vehicle, for example. Furthermore, one NCR-MT520A may control multiple NCR-Fwd510A.

[0037] 5, the NCR device 500A (NCR-Fwd 510A) dynamically or quasi-statically changes a beam to be transmitted or received. For example, the NCR-Fwd 510A forms a beam toward each of the UE 100a and the UE 100b. The NCR-Fwd 510A may also form a beam toward the gNB 200. For example, in the communication resource between the gNB 200 and the UE 100a, the NCR-Fwd 510A transmits a radio signal received from the gNB 200 toward the UE 100a by beamforming and / or transmits a radio signal received from the UE 100a toward the gNB 200 by beamforming. In the communication resources between the gNB 200 and the UE 100b, the NCR-Fwd 510A transmits a radio signal received from the gNB 200 toward the UE 100b by beamforming, and / or transmits a radio signal received from the UE 100b by beamforming toward the gNB 200. Instead of or in addition to beamforming, the NCR-Fwd 510A may form a null (so-called null steering) toward a UE 100 (not shown) and / or a neighboring gNB 200 (not shown) that is not a communication partner, in order to suppress interference.

[0038] FIG. 6 is a diagram illustrating an example of a control method for the NCR device 500A according to the first embodiment. As illustrated in FIG. 6, the NCR-Fwd 510A relays radio signals (also referred to as "UE signals") between the gNB 200 and the UE 100. The UE signals include uplink signals (also referred to as "UE-UL signals") transmitted from the UE 100 to the gNB 200 and downlink signals (also referred to as "UE-DL signals") transmitted from the gNB 200 to the UE 100. The NCR-Fwd 510A relays UE-UL signals from the UE 100 to the gNB 200, and relays UE-DL signals from the gNB 200 to the UE 100. The radio link between the NCR-Fwd 510A and the UE 100 is also referred to as an "access link." The radio link between the NCR-Fwd 510A and the gNB 200 is also referred to as a "backhaul link."

[0039] The NCR-MT520A transmits and receives wireless signals (herein referred to as "NCR-MT signals") to and from the gNB200. The NCR-MT signals include uplink signals (herein referred to as "NCR-MT-UL signals") transmitted from the NCR-MT520A to the gNB200, and downlink signals (herein referred to as "NCR-MT-DL signals") transmitted from the gNB200 to the NCR-MT520A. The NCR-MT-UL signals include signaling for controlling the NCR device 500A. The wireless link between the NCR-MT520A and the gNB200 is also referred to as the "control link."

[0040] The gNB200 directs a beam to the NCR-MT520A based on the NCR-MT-UL signal from the NCR-MT520A. Because the NCR device 500A is co-located with the NCR-MT520A, if the backhaul link and the control link have the same frequency, when the gNB200 directs a beam to the NCR-MT520A, the beam is also directed to the NCR-Fwd510A. The gNB200 uses the beam to transmit an NCR-MT-DL signal and a UE-DL signal. The NCR-MT520A receives the NCR-MT-DL signal. Note that when the NCR-Fwd510A and the NCR-MT520A are at least partially integrated, the NCR-Fwd510A and the NCR-MT520A may be integrated with functions (e.g., antennas) for transmitting, receiving, or relaying UE signals and / or NCR-MT signals. The term "beam" includes a transmitting beam and / or a receiving beam. A beam is a general term for transmission and / or reception controlled to maximize the power of the transmitting wave and / or receiving wave in a specific direction by adjusting / adapting the antenna weight, etc.

[0041] 7 is a diagram showing an example of the configuration of a protocol stack in a mobile communication system 1 having an NCR device 500A according to the first embodiment. The NCR-Fwd 510A relays wireless signals transmitted and received between the gNB 200 and the UE 100. The NCR-Fwd 510A has an RF (Radio Frequency) function for amplifying and relaying received wireless signals, and performs directional transmission using beamforming (for example, analog beamforming).

[0042] The NCR-MT520A has at least one layer (entity) of PHY, MAC, RRC, and F1-AP (Application Protocol). The F1-AP is a type of fronthaul interface. The NCR-MT520A exchanges downlink signaling and / or uplink signaling (described below) with the gNB200 via at least one of PHY, MAC, RRC, and F1-AP. If the NCR-MT520A is a type or part of a base station, the NCR-MT520A may exchange with the gNB200 via an Xn AP (Xn-AP), which is an interface between base stations.

[0043] (1.3) Example of relay device configuration 8 is a diagram showing an example of the configuration of an NCR device 500A which is a relay device according to the first embodiment. The NCR device 500A includes an NCR-Fwd 510A, an NCR-MT 520A, and an interface 530.

[0044] The NCR-Fwd 510A includes a radio unit 511A and an NCR control unit 512A. The radio unit 511A includes an antenna unit 511a including multiple antennas (multiple antenna elements), an RF circuit 511b including an amplifier, and a directivity control unit 511c that controls the directivity of the antenna unit 511a. The RF circuit 511b amplifies and relays (transmits) radio signals transmitted and received by the antenna unit 511a. The RF circuit 511b may convert analog radio signals into digital signals and reconvert them to analog signals after digital signal processing. The directivity control unit 511c may perform analog beamforming using analog signal processing. The directivity control unit 511c may perform digital beamforming using digital signal processing. The directivity control unit 511c may perform hybrid analog and digital beamforming. The NCR control unit 512A controls the radio unit 511A in response to a control signal from the NCR-MT 520A. The NCR control unit 512A may include at least one processor. The NCR control unit 512A may output information about the capabilities of the NCR device 500A to the NCR-MT 520A.

[0045] The NCR-MT520A has a receiving unit 521, a transmitting unit 522, and a control unit 523. The receiving unit 521 performs various receptions under the control of the control unit 523. The receiving unit 521 includes an antenna and a receiver. The receiver converts a radio signal (wireless signal) received by the antenna into a baseband signal (received signal) and outputs it to the control unit 523. The transmitting unit 522 performs various transmissions under the control of the control unit 523. The transmitting unit 522 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmitted signal) output by the control unit 523 into a radio signal and transmits it from the antenna. The control unit 523 performs various controls in the NCR-MT520A. The control unit 523 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in memory to perform various processes. The control unit 523 also executes the functions of at least one of the PHY, MAC, RRC, and F1-AP layers.

[0046] The interface 530 electrically connects the NCR-Fwd 510A and the NCR-MT 520A. The control unit 523 of the NCR-MT 520A controls the NCR-Fwd 510A via the interface 530.

[0047] In the first embodiment, the receiver 521 of the NCR-MT 520A receives signaling (downlink signaling) used to control the NCR device 500A from the gNB 200 via wireless communication. The controller 523 of the NCR-MT 520A controls the NCR device 500A based on the signaling. This enables the gNB 200 to control the NCR-Fwd 510A via the NCR-MT 520A.

[0048] In the first embodiment, the control unit 523 of the NCR-MT 520A may transmit NCR capability information indicating the capability of the NCR device 500A to the gNB 200 via wireless communication. The NCR capability information is an example of uplink signaling from the NCR-MT 520A to the gNB 200. This allows the gNB 200 to grasp the capability of the NCR device 500A.

[0049] (1.4) Example of base station configuration 9 is a diagram showing an example of the configuration of the gNB 200 according to the first embodiment. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240.

[0050] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna. The receiving unit 220 performs various receptions under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (reception signal) and outputs it to the control unit 230. The transmitting unit 210 and the receiving unit 220 may be capable of beamforming using multiple antennas.

[0051] The control unit 230 performs various controls in the gNB 200. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0052] The backhaul communication unit 240 is connected to neighboring base stations via an inter-base station interface. The backhaul communication unit 240 is connected to the AMF / UPF 300 via a base station-core network interface. Note that the gNB is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and both units may be connected via an F1 interface.

[0053] In the first embodiment, the transmitter 210 of the gNB 200 transmits signaling (downlink signaling) used to control the NCR-Fwd 510A to the NCR-MT 520A via wireless communication. This enables the gNB 200 to control the NCR device 500A via the NCR-MT 520A. In the first embodiment, the receiver 220 of the gNB 200 may receive, via wireless communication, NCR capability information indicating the capability of the NCR device 500A from the NCR-MT 520A.

[0054] (1.5) Example of downlink signaling FIG. 10 is a diagram showing an example of downlink signaling from the gNB 200 to the NCR-MT 520A according to the first embodiment.

[0055] The gNB200 (transmitter 210) transmits downlink signaling to the NCR-MT520A. The downlink signaling may be an RRC message, which is signaling of the RRC layer (i.e., Layer 3). The downlink signaling may be a MAC CE (Control Element), which is signaling of the MAC layer (i.e., Layer 2). The downlink signaling may be downlink control information (DCI), which is signaling of the PHY layer (i.e., Layer 1). The downlink signaling may be UE-specific signaling. The downlink signaling may be broadcast signaling. The downlink signaling may be a fronthaul message (e.g., an F1-AP message). If the NCR-MT520A is a type or part of a base station, the NCR-MT520A may communicate with the gNB200 via an Xn AP (Xn-AP), which is an inter-base station interface.

[0056] For example, the gNB200 (transmitter 210) transmits an NCR control signal specifying the operation state of the NCR device 500A as downlink signaling to the NCR-MT 520A that has established a wireless connection with the gNB200 (step S1A). The NCR control signal specifying the operation state of the NCR device 500A may be MAC CE, which is signaling of the MAC layer (layer 2), or DCI, which is signaling of the PHY layer (layer 1). However, the gNB200 (transmitter 210) may also include the NCR control signal in an RRC Reconfiguration message, which is a type of RRC message individual to a UE, and transmit this to the NCR-MT 520A. The downlink signaling may be a message of a layer higher than the RRC layer (for example, an NCR application). The downlink signaling may be a message of a layer higher than the RRC layer encapsulated in a message of a layer lower than the RRC layer and transmitted. The NCR-MT 520A (transmitter 522) may transmit a response message in response to the downlink signaling from the gNB 200 via the uplink. The response message may be transmitted in response to the NCR device 500A completing the configuration specified in the downlink signaling or receiving the configuration. The NCR control signal may be referred to as Side Control Information.

[0057] The NCR control signal may include frequency control information that specifies the center frequency of a radio signal (e.g., a component carrier) to be relayed by the NCR-Fwd510A. When the NCR control signal received from the gNB200 includes frequency control information, the NCR-MT520A (control unit 523) controls the NCR-Fwd510A to relay a radio signal having a center frequency indicated by the frequency control information (step S2A). The NCR control signal may include multiple pieces of frequency control information that specify different center frequencies. By including frequency control information in the NCR control signal, the gNB200 can specify, via the NCR-MT520A, the center frequency of a radio signal to be relayed by the NCR-Fwd510A.

[0058] The NCR control signal may include mode control information that specifies an operation mode of the NCR-Fwd 510A. The mode control information may be associated with frequency control information (center frequency). The operation mode may be one of a mode in which the NCR-Fwd 510A performs omnidirectional transmission and / or reception, a mode in which the NCR-Fwd 510A performs fixed-directivity transmission and / or reception, a mode in which the NCR-Fwd 510A performs transmission and / or reception using a variable directional beam, and a mode in which the NCR-Fwd 510A performs MIMO (Multiple Input Multiple Output) relay transmission. The operation mode may be one of a beamforming mode (i.e., a mode that prioritizes improving a desired wave) and a null steering mode (i.e., a mode that prioritizes suppressing interference waves). When the NCR control signal received from the gNB 200 includes mode control information, the NCR-MT 520A (control unit 523) controls the NCR-Fwd 510A to operate in the operation mode indicated by the mode control information (step S2A). When the NCR control signal includes mode control information, the gNB 200 can specify the operation mode of the NCR-Fwd 510A via the NCR-MT 520A.

[0059] Here, the mode in which the NCR device 500A performs non-directional transmission and / or reception is a mode in which the NCR-Fwd510A performs omnidirectional relaying, and may be referred to as omni-mode. The mode in which the NCR-Fwd510A performs fixed-directivity transmission and / or reception may be a directional mode achieved by a single directional antenna. This mode may be a beamforming mode achieved by applying fixed phase and amplitude control (antenna weight control) to multiple antennas. Any of these modes may be specified (set) by the gNB200 to the NCR-MT520A. The mode in which the NCR-Fwd510A performs transmission and / or reception using a variable directional beam may be a mode in which analog beamforming is performed. This mode may be a mode in which digital beamforming is performed. This mode may be a mode in which hybrid beamforming is performed. This mode may be a mode in which an adaptive beam specific to the UE100 is formed. Any of these modes may be specified (set) by the gNB200 to the NCR-MT520A. In addition, in the operation mode in which beamforming is performed, beam control information, which will be described later, may be provided from the gNB200 to the NCR-MT520A. The mode in which the NCR device 500A performs MIMO relay transmission may be a mode in which SU (Single-User) spatial multiplexing is performed. This mode may also be a mode in which MU (Multi-User) spatial multiplexing is performed. This mode may also be a mode in which transmit diversity is performed. Any of these modes may be specified (set) by the gNB200 to the NCR-MT520A. The operation modes may include a mode in which relay transmission by the NCR-Fwd510A is turned on (activated) and a mode in which relay transmission by the NCR-Fwd510A is turned off (deactivated). Any of these modes may be specified (set) by the gNB200 to the NCR-MT520A by an NCR control signal.

[0060] The NCR control signal may include beam control information that specifies the transmission direction, transmission weight, or beam pattern when the NCR-Fwd510A performs directional transmission. The beam control information may be associated with frequency control information (center frequency). The beam control information may include a PMI (Precoding Matrix Indicator). The beam control information may include beam formation angle information. When the NCR control signal received from the gNB200 includes beam control information, the NCR-MT520A (control unit 523) controls the NCR-Fwd510A to form the transmission directivity (beam) indicated by the beam control information (step S2A). When the NCR control signal includes beam control information, the gNB200 can control the transmission directivity of the NCR device 500A via the NCR-MT520A.

[0061] The NCR control signal may include output control information that specifies the degree to which the NCR-Fwd510A amplifies the radio signal (amplification gain) or transmission power. The output control information may be information indicating a difference (i.e., a relative value) between the current amplification gain or transmission power and a target amplification gain or transmission power. When the NCR control signal received from the gNB200 includes output control information, the NCR-MT520A (control unit 523) controls the NCR-Fwd510A to change the amplification gain or transmission power to the amplification gain or transmission power indicated by the output control information (step S2A). The output control information may be associated with frequency control information (center frequency). The output control information may be information that specifies any one of the amplifier gain, beamforming gain, and antenna gain of the NCR-Fwd510A. The output control information may be information that specifies the transmission power of the NCR-Fwd510A.

[0062] When one NCR-MT 520A controls multiple NCR-Fwd 510A, the gNB 200 (transmitter 210) may transmit an NCR control signal to the NCR-MT 520A for each NCR-Fwd 510A. In this case, the NCR control signal may include an identifier (NCR identifier) ​​of the corresponding NCR-Fwd 510A. The NCR-MT 520A (controller 523) that controls multiple NCR-Fwd 510A determines the NCR-Fwd 510A to which the NCR control signal should be applied based on the NCR identifier included in the NCR control signal received from the gNB 200. Note that the NCR identifier may be transmitted from the NCR-MT 520A to the gNB 200 along with the NCR control signal, even when the NCR-MT 520A controls only one NCR-Fwd 510A.

[0063] In this way, the NCR-MT520A (control unit 523) controls the NCR-Fwd510A based on the NCR control signal from the gNB 200. This enables the gNB 200 to control the NCR-Fwd510A via the NCR-MT520A.

[0064] (1.6) Example of uplink signaling FIG. 11 is a diagram showing an example of uplink signaling from the NCR-MT 520A to the gNB 200 according to the first embodiment.

[0065] The NCR-MT520A (transmitter 210) transmits uplink signaling to the gNB200. The uplink signaling may be an RRC message, which is signaling of the RRC layer. The uplink signaling may be MAC CE, which is signaling of the MAC layer. The uplink signaling may be uplink control information (UCI), which is signaling of the PHY layer. The uplink signaling may be a fronthaul message (e.g., an F1-AP message). The uplink signaling may be an inter-base station message (e.g., an Xn-AP message). The uplink signaling may be a message of a layer higher than the RRC layer (e.g., an NCR application). The uplink signaling may be a message of a layer higher than the RRC layer encapsulated in a message of a layer lower than the RRC layer and transmitted. That is, the uplink signaling stores an upper layer message in a lower layer container. In addition, gNB200 (transmitter 210) may transmit a response message in response to the uplink signaling from NCR-MT520A on the downlink, and NCR-MT520A (receiver 521) may receive the response message.

[0066] For example, the NCR-MT 520A (transmitter 522), which has established a wireless connection with the gNB 200, transmits NCR capability information indicating the capabilities of the NCR device 500A to the gNB 200 as uplink signaling (step S5A). The NCR-MT 520A (transmitter 522) may include the NCR capability information in a UE Capability message or a UE Assistant Information message, which are types of RRC messages, and transmit this to the gNB 200. The NCR-MT 520A (transmitter 522) may transmit the NCR capability information (NCR capability information and / or operation status information) to the gNB 200 in response to a request or inquiry from the gNB 200.

[0067] The NCR capability information may include supported frequency information indicating frequencies supported by the NCR-Fwd 510A. The supported frequency information may be a numerical value or an index indicating a center frequency of the frequencies supported by the NCR-Fwd 510A. The supported frequency information may be a numerical value or an index indicating a range of frequencies supported by the NCR-Fwd 510A. When the NCR capability information received from the NCR-MT 520A includes supported frequency information, the gNB 200 (control unit 230) can determine the frequencies supported by the NCR-Fwd 510A based on the supported frequency information. Then, the gNB 200 (control unit 230) may set the center frequency of the radio signal targeted by the NCR device 500A within the range of frequencies supported by the NCR-Fwd 510A.

[0068] The NCR capability information may include mode capability information related to operation modes that the NCR-Fwd 510A can support or switching between operation modes. As described above, the operation mode may be at least one of a mode in which the NCR-Fwd 510A performs omnidirectional transmission and / or reception, a mode in which the NCR-Fwd 510A performs fixed-directivity transmission and / or reception, a mode in which the NCR-Fwd 510A performs transmission and / or reception using a variable directional beam, and a mode in which the NCR-Fwd 510A performs MIMO (Multiple Input Multiple Output) relay transmission. The operation mode may be either a beamforming mode (i.e., a mode that prioritizes improving a desired signal) or a null steering mode (i.e., a mode that prioritizes suppressing interference signals). The mode capability information may be information indicating which of these operation modes the NCR-Fwd 510A can support. The mode capability information may also be information indicating which of these operation modes mode switching is possible between. When the NCR capability information received from the NCR-MT520A includes mode capability information, the gNB200 (control unit 230) can determine the operation modes and mode switching supported by the NCR-Fwd510A based on the mode capability information. The gNB200 (control unit 230) may then set the operation mode of the NCR-Fwd510A within the range of the determined operation modes and mode switching.

[0069] The NCR capability information may include beam capability information indicating the beam variable range, beam variable resolution, or number of variable patterns when the NCR-Fwd510A transmits and / or receives using a variable directional beam. The beam capability information may be, for example, information indicating the variable range of the beam angle based on the horizontal or vertical direction (e.g., controllable from 30° to 90°). The beam capability information may be information indicating an absolute angle. The beam capability information may be expressed by the direction and / or elevation angle of the beam. The beam capability information may be information indicating the angle change per variable step (e.g., 5° / step horizontally, 10° / step vertically). The beam capability information may be information indicating the number of variable steps (e.g., 10 steps horizontally, 20 steps vertically). The beam capability information may be information indicating the number of variable beam patterns in the NCR-Fwd510A (e.g., beam patterns 1 to 10, a total of 10 patterns). When the NCR capability information received from the NCR-MT520A includes beam capability information, the gNB200 (control unit 230) can determine the beam angle change or beam pattern that the NCR-Fwd510A can support based on the beam capability information. The gNB200 (control unit 230) may then set the beam of the NCR-Fwd510A within the range of the determined beam angle change or beam pattern. The beam capability information may be null capability information. In the case of null capability information, the beam capability information indicates the null control capability when null steering is performed.

[0070] The NCR capability information may include control delay information indicating a control delay time in the NCR device 500A. For example, the control delay information is information indicating a delay time (e.g., 1 ms, 10 ms, etc.) from the timing when the UE 100 receives an NCR control signal or the timing when the UE 100 transmits a setting completion notice for the NCR control signal to the gNB 200 until the control (change of the operation mode and / or change of the beam) according to the NCR control signal is completed. When the NCR capability information received from the NCR-MT 520A includes control delay information, the gNB 200 (control unit 230) can ascertain the control delay time in the NCR-Fwd 510A based on the control delay information.

[0071] The NCR capability information may include amplification characteristic information relating to the amplification characteristic or output power characteristic of a radio signal in the NCR-Fwd 510A. The amplification characteristic information may be information indicating the amplifier gain (dB), beamforming gain (dB), or antenna gain (dBi) of the NCR-Fwd 510A. The amplification characteristic information may be information indicating the amplification variable range (e.g., 0 dB to 60 dB) of the NCR-Fwd 510A. The amplification characteristic information may be information indicating the number of steps (e.g., 10 steps) of the gain that the NCR-Fwd 510A can change, or the gain per variable step (e.g., 10 dB / step). The amplification characteristic information may be information indicating the variable range (e.g., 0 dBm to 30 dBm) of the output power of the NCR-Fwd 510A. The amplification characteristic information may be information indicating the number of steps (for example, 10 steps) of the output power that can be changed by the NCR-Fwd510A, or the output power per variable step (for example, 10 dBm / step or 10 dB / step).

[0072] The NCR capability information may include location information indicating the installation location of the NCR device 500A. The location information may include one or more of latitude, longitude, and altitude. The location information may include information indicating the distance and / or installation angle of the NCR device 500A relative to the gNB 200. The installation angle may be a relative angle with respect to the gNB 200, or may be a relative angle based on, for example, north, vertical, or horizontal. The installation location may be location information of the location where the antenna unit 511a of the NCR-Fwd 510A is installed.

[0073] The NCR capability information may include antenna information indicating the number of antennas possessed by the NCR-Fwd510A. The antenna information may be information indicating the number of antenna ports possessed by the NCR-Fwd510A. The antenna information may be information indicating the degrees of freedom of directivity control (beam or null formation). The degrees of freedom indicate how many beams can be formed (controlled) and are usually "(number of antennas) - 1". For example, in the case of two antennas, the degrees of freedom are 1. In the case of two antennas, a beam pattern resembling a figure eight is formed, but the degrees of freedom are 1 because directivity control is possible in only one direction.

[0074] When the NCR-MT520A controls multiple NCR-Fwds 510A, the NCR-MT520A (transmitter 522) may transmit NCR capability information for each NCR-Fwd 510A to the gNB 200. In this case, the NCR capability information may include the number of NCR-Fwds 510A and / or identifiers (NCR identifiers) of the corresponding NCR-Fwds 510A. Furthermore, when the NCR-MT520A controls multiple NCR-Fwds 510A, the NCR-MT520A (transmitter 522) may transmit information indicating at least one of the identifiers of the multiple NCR-Fwds 510A and the number of the multiple NCR-Fwds 510A. Note that the NCR identifier may be transmitted from the NCR-MT520A to the gNB 200 together with the NCR capability information, even when the NCR-MT520A controls only one NCR-Fwd 510A.

[0075] (1.7) Example of overall operation sequence Fig. 12 is a diagram showing an example of an overall operation sequence of the mobile communication system 1 according to the first embodiment. In the sequence diagrams referred to in the following embodiments, non-essential steps are indicated by dashed lines. Note that, as will be described in detail later, "NCR" in Fig. 12 may be read as "RIS."

[0076] In step S11, the gNB200 (transmitter 210) broadcasts NCR support information indicating that the gNB200 supports the NCR-MT520A. For example, the gNB200 (transmitter 210) broadcasts a system information block (SIB) including the NCR support information. The NCR support information may be information indicating that the NCR-MT520A is accessible. Alternatively, the gNB200 (transmitter 210) may broadcast NCR non-support information indicating that the gNB200 does not support the NCR-MT520A. The NCR non-support information may be information indicating that the NCR-MT520A is inaccessible.

[0077] At this stage, the NCR-MT520A may be in an RRC idle state or an RRC inactive state. The NCR-MT520A (control unit 523), which has not established a wireless connection with the gNB200, may determine, upon receiving NCR support information from the gNB200, that access to the gNB200 is permitted, and may perform access operation to establish a wireless connection with the gNB200. The NCR-MT520A (control unit 523) may perform cell reselection, regarding the gNB200 (cell) to which access is permitted as having the highest priority.

[0078] On the other hand, if the gNB 200 does not broadcast NCR support information (or broadcasts NCR non-support information), the NCR-MT520A (control unit 523) that has not established a wireless connection with the gNB 200 may determine that it is unable to access (establish a connection with) the gNB 200. This allows the NCR-MT520A to establish a wireless connection only with gNBs 200 that can handle the NCR-MT520A.

[0079] Note that if the gNB 200 is congested, the gNB 200 may broadcast access restriction information that restricts access from the UE 100. However, unlike a normal UE 100, the NCR-MT 520A can also be considered a network-side entity. Therefore, the NCR-MT 520A may ignore the access restriction information from the gNB 200. For example, when the NCR-MT 520A (control unit 523) receives NCR support information from the gNB 200, it may perform an operation to establish a wireless connection with the gNB 200 even if the gNB 200 is broadcasting access restriction information. For example, the NCR-MT 520A (control unit 523) may not execute (or may ignore) UAC (Unified Access Control). Alternatively, a special value indicating NCR-MT access may be used for either or both of the AC / AI (Access Category / Access Identity) used in the UAC.

[0080] In step S12, the NCR-MT520A (control unit 523) initiates a random access procedure for the gNB200. In the random access procedure, the NCR-MT520A (transmitter 522) transmits a random access preamble (Msg1) and an RRC message (Msg3) to the gNB200. Also in the random access procedure, the NCR-MT520A (receiver 521) receives a random access response (Msg2) and an RRC message (Msg4) from the gNB200.

[0081] In step S13, when establishing a wireless connection with the gNB200, the NCR-MT520A (transmitter 522) may transmit NCR-MT information indicating that its own UE is an NCR-MT to the gNB200. For example, during a random access procedure with the gNB200, the NCR-MT520A (transmitter 522) includes the NCR-MT information in a random access procedure message (e.g., Msg1, Msg3, Msg5) and transmits the message to the gNB200. Based on the NCR-MT information received from the NCR-MT520A, the gNB200 (controller 230) recognizes that the accessing UE100 is the NCR-MT520A, and can, for example, remove the NCR-MT520A from the access restriction target (i.e., accept the access). When the random access procedure is completed, the NCR-MT520A transitions from the RRC idle state or the RRC inactive state to the RRC connected state.

[0082] In step S14, the gNB 200 (transmitter 522) transmits a capability inquiry message to the NCR-MT 520A to inquire about the capabilities of the NCR-MT 520A. The NCR-MT 520A (receiver 521) receives the capability inquiry message.

[0083] In step S15, the NCR-MT 520A (transmitter 522) transmits a capability information message including NCR capability information to the gNB 200. The capability information message may be an RRC message, for example, a UE Capability message. The gNB 200 (receiver 220) receives the capability information message. The gNB 200 (controller 230) determines the capabilities of the NCR device 500A based on the received capability information message.

[0084] In step S16, the gNB 200 (transmitter 522) transmits a configuration message including various settings related to the NCR device 500A to the NCR-MT 520A. The NCR-MT 520A (receiver 521) receives the configuration message. The configuration message is a type of the downlink signaling described above. The configuration message may be an RRC message, for example, an RRC Reconfiguration message.

[0085] In step S17, the gNB200 (transmitter 522) transmits a control instruction specifying the operation state of the NCR-Fwd510A to the NCR-MT520A. The control instruction may be the above-mentioned NCR control signal (e.g., L1 / L2 signaling). The NCR-MT520A (receiver 521) receives the control instruction. The NCR-MT520A (controller 523) controls the NCR-Fwd510A in accordance with the control instruction.

[0086] In step S18, the NCR-MT 520A controls the NCR device 500A in accordance with the above settings (and control instructions). Note that the NCR-MT 520A may autonomously control the NCR device 500A without relying on control instructions from the gNB 200. For example, the NCR-MT 520A may autonomously control the NCR device 500A based on the location of the UE 100 and / or information received by the NCR-MT 520A from the UE 100.

[0087] (1.8) Beam Sweeping FIG. 13 is a diagram for explaining beam sweeping according to the embodiment.

[0088] The gNB200 performs beam sweeping, sequentially switching beams in different directions while transmitting. At this time, the gNB200 transmits a different SSB for each beam. The SSBs are periodically transmitted from the gNB200 to the cell as SSB bursts consisting of multiple SSBs. Each of the multiple SSBs in an SSB burst is assigned an SSB index, which serves as an identifier. The SSBs are beamformed and transmitted in different directions. The NCR device 500A (NCR-MT520A) reports to the gNB200 during the random access channel (RACH) procedure which beam had the best reception quality. Specifically, the NCR device 500A (NCR-MT520A) transmits a random access preamble to the gNB200 in the random access channel (RACH) occasion associated with the SSB index for which the beam had the best reception quality. As a result, the gNB200 can determine the optimal beam for the NCR device 500A (NCR-MT520A).

[0089] Note that such an SSB may be transmitted in an initial BWP (initial DL BWP). When the NCR device 500A (NCR-MT520A) is in an RRC connected state, a dedicated BWP may be configured and activated in the NCR device 500A (NCR-MT520A). In the dedicated BWP, a channel state information reference signal (CSI-RS) may be used as a reference signal instead of an SSB. In the following, an example in which beam information identifying a beam is an SSB index will be mainly described, assuming that there is a one-to-one relationship between a beam and an SSB (specifically, an SSB index). However, a beam may be associated with a CSI-RS. The beam information identifying a beam may be a CSI-RS index.

[0090] (1.9) Load balancing operations FIG. 14 is a diagram for explaining the operation related to load balancing according to the first embodiment.

[0091] The NCR device 500A extends the coverage of the cell of the gNB 200S by relaying radio signals between the gNB 200S and the UE 100. In the illustrated example, there is one UE 100 connected to the gNB 200S via the NCR device 500A, but there may be multiple UEs 100.

[0092] As the coverage is expanded by the NCR device 500A, the cell of the gNB200S must accommodate more UEs, which increases the load on the cell of the gNB200S and increases the likelihood of overload.

[0093] Here, by handing over the NCR device 500A from the cell of the gNB200S (source cell) to the cell of the neighboring base station gNB200T (target cell), the load of the cell of the gNB200S can be distributed to the cell of the gNB200T. In the following, a scenario in which the NCR device 500A is handed over for the purpose of load distribution is mainly assumed. However, this is not limited to a handover of the NCR device 500A for the purpose of load distribution, and may be a handover for the purpose of improving the radio conditions of the NCR device 500A, etc. In addition, in the following, the gNB200S will also be referred to as the source gNB (source base station) 200S, and the gNB200T will also be referred to as the target gNB (target base station) 200S.

[0094] In the first embodiment, the gNB 200S corresponding to the source cell (first cell) transmits a message for connecting the NCR device 500A to the target cell (second cell) to the gNB 200T corresponding to the target cell over the Xn interface (inter-base station interface). The message includes information about the NCR device 500A. This allows the NCR device 500A to be handed over appropriately. Here, the gNB 200S is an example of a first network node, and the gNB 200T is an example of a second network node. The Xn interface is also an example of a network interface.

[0095] In the following description of the first embodiment, an example of inter-base station handover of the NCR device 500A, specifically, inter-CU handover, will be mainly described. However, the first embodiment is not limited to inter-base station handover, and may also be intra-base station handover (intra-CU handover). In the case of intra-base station handover, the first network node may be a CU or a source DU, the second network node may be a target DU, and the network interface may be an F1 interface.

[0096] Furthermore, although the first embodiment mainly describes handover operations, the present invention may be applied to dual connectivity (DC) operations in which the NCR device 500A simultaneously communicates with the gNB200S and the gNB200T. In this case, the first network node may be the gNB200S (master node), the second network node may be the gNB200T (secondary node), the network interface may be an F1 interface, and the message may be a secondary node addition request message.

[0097] FIG. 15 is a diagram for explaining the link (connection) between the NCR device 500A and the gNB 200S according to the first embodiment.

[0098] A backhaul link is established between the gNB 200S and the NCR-Fwd 510A of the NCR device 500A. An access link is established between the UE 100 and the NCR-Fwd 510A of the NCR device 500A. The NCR device 500A (NCR-Fwd 510A), which relays radio signals transmitted between the gNB 200S and the UE 100, changes the propagation state of the radio signals without demodulating or modulating the radio signals.

[0099] In addition, a control link is established between the gNB200S and Layer 1 and / or Layer 2 (L1 / L2) of the NCR device 500A (NCR-MT520A). An RRC connection is established between the gNB200S and the RRC of the NCR device 500A (NCR-MT520A). The RRC of the NCR device 500A (NCR-MT520A) transmits and receives RRC messages related to handover with the gNB200S via the RRC connection. The NCR device 500A (NCR-MT520A) switches the RRC connection from the source gNB200S to the target gNB200T through handover.

[0100] (1.9.1) First operation pattern In the first operation pattern, the source gNB200S notifies the target gNB200T that the handover request is for the NCR device 500A. The source gNB200S may also notify the target gNB200T that the handover is a load balancing handover. Furthermore, the source gNB200S may notify the target gNB200T of the number of UEs 100 that will subsequently be handed over to the NCR device 500A. With such notification, the target gNB200T can appropriately determine whether to accept the handover request from the source gNB200S.

[0101] FIG. 16 is a diagram showing the operation of the mobile communication system 1 according to the first operation pattern.

[0102] In step S101, the source gNB 200S decides to hand over the NCR device 500A. The source gNB 200S may decide to hand over the NCR device 500A in response to the discovery of a cell with better wireless quality based on a measurement report message from the NCR device 500A (NCR-MT 520A). The source gNB 200S may also decide to hand over the NCR device 500A in response to an increase in its own load and the need for load balancing.

[0103] In step S102, the source gNB200S transmits a handover request message to the target gNB200T over the Xn interface, requesting handover of the NCR device 500A from the source cell of the source gNB200S to the target cell of the target gNB200T. The target gNB200T receives the handover request message. The handover request message includes at least one of the following information (a1) to (c1):

[0104] (a1) Information indicating handover of NCR device 500A (i.e., NCR indication): This is flag information indicating that the target of handover is the NCR device 500A. This allows the target gNB 200T to perform control such as preferentially accepting handover of the NCR device 500A over handover of the UE 100. This flag information is defined separately from information indicating that the target of handover is an IAB (Integrated Access and Backhaul) node. As will be described later, when the relay device is a RIS device, the flag information may be information indicating that the target of handover is the RIS device. Note that the flag information may also be information indicating that the target NCR device or RIS device has been authenticated.

[0105] (b1) Information indicating that the NCR device 500A is to be handed over to distribute the load of the source gNB200S (source cell) to the target gNB200T (target cell): If the purpose of the handover is load balancing, the source gNB 200S includes information indicating that the handover is load balancing related to the NCR device 500A in the handover request. This allows the target gNB 200T to make a decision to accept the handover taking the purpose of the handover into consideration. If the purpose of the handover is to involve the movement of an NCR device or a RIS device, the information (b1) may be information indicating the movement of the device or information indicating that the device has mobility (is mobile).

[0106] (c1) Information indicating the number of UEs 100 to be handed over in association with the handover of the NCR device 500A: The information indicates, for example, the number of UEs 100 connected to the source gNB 200S via the NCR device 500A. The source gNB 200S may specify the number of UEs 100 communicating with the NCR device 500A using the same SSB as the number of UEs 100 to be handed over in conjunction with the handover of the NCR device 500A. The information may also be information on the throughput (and / or the amount of radio resources) required to accommodate the UEs 100.

[0107] In step S103, the target gNB200T determines whether to accept the handover request of step S102. That is, upon receiving the handover request message, the target gNB200T determines whether to permit handover of the NCR device 500A based on the information included in the handover request message. The target gNB200T may determine to accept the handover request if it has the ability to control the NCR device 500A and / or if it can keep its own load below a certain level even if the NCR device 500A and UE100 are handed over to it. Here, the description will proceed assuming that the target gNB200T has determined to accept (permit) the handover request.

[0108] In step S104, the target gNB200T transmits a Handover Request Acknowledge message, which is a response message indicating that the handover is permitted, to the source gNB200S over the Xn interface. The source gNB200S receives the Handover Request Acknowledge message. The target gNB200T may include in the Handover Request Acknowledge message an instruction as to whether the NCR device 500A (NCR-MT520A) should continue operating under the control of the source gNB200S during the handover. The instruction may be an instruction as to whether to continue operating under the current control after the handover.

[0109] In step S105, the source gNB200S transmits an RRC Reconfiguration message including the information in the Handover Request Acknowledge message, i.e., a handover command (Handover Command) instructing a handover to the target gNB200T (target cell), to the NCR device 500A (NCR-MT520A). The NCR device 500A (NCR-MT520A) receives the handover command. The handover command may include the instruction included in the Handover Request Acknowledge message in step S104.

[0110] In step S106, in response to receiving the handover command in step S105, the NCR device 500A (NCR-MT520A) starts accessing the target gNB 200T (target cell) specified in the handover command. During this access, the NCR device 500A (NCR-MT520A) may transmit an RRC Reconfiguration Complete message to the target gNB 200T (target cell). The NCR device 500A (NCR-MT520A) may continue to control the NCR device 500A (NCR-Fwd510A) during the handover in accordance with instructions included in the handover command.

[0111] (1.9.2) Second movement pattern As described above, when control of the NCR device 500A is transferred to another cell (target cell) due to handover, it is desirable that the other cell be able to control the NCR device 500A more quickly and accurately after the handover. In the second operation pattern, the source gNB 200S notifies the target gNB 200T of control information and / or context information of the NCR device 500A. That is, in the second operation pattern, the handover request message includes at least one of control information used to control the NCR device 500A and context information of the NCR device 500A. This allows the target gNB 200T to control the NCR device 500A more quickly and accurately after the handover. Note that the second operation pattern may be implemented in combination with the first operation pattern described above.

[0112] 17 is a diagram showing the operation of the mobile communication system 1 according to the second operation pattern. Description of operations that overlap with the operations of the first operation pattern described above will be omitted.

[0113] In step S201, the source gNB 200S decides to handover the NCR device 500A.

[0114] In step S202, the source gNB200S transmits a handover request message to the target gNB200T over the Xn interface, requesting handover of the NCR device 500A from the source cell of the source gNB200S to the target cell of the target gNB200T. The target gNB200T receives the handover request message. The handover request message includes at least one of the following information (a2) to (c2):

[0115] (a2) Control information (beam information) indicating the beam to be applied to the NCR device 500A: The control information may include the SSB index that the target gNB 200T applies to the NCR device 500A. In this case, the target gNB 200T may infer the optimal beam that the target gNB 200T applies to the NCR device 500A, for example, from the SSB index and a measurement report message from a UE 100 currently serving the target gNB 200T. The control information may include the SSB index that the target cell should apply. The source gNB 200S may identify the SSB index, for example, from a measurement report message from the NCR device 500A (NCR-MT 520A).

[0116] (b2) Control information for controlling the operation of the NCR device 500A: The control information includes NCR control information corresponding to the above-mentioned NCR control signal, for example, at least one of the weight, (output) beam angle, and transmission power (gain) applied by the source gNB 200S to the NCR device 500A. The control information may also include control time information indicating the time (timing) at which the NCR control information is applied. For example, the target gNB 200T may estimate that many UEs 100 are present in the direction of the most frequently used beam control setting and use this information as a reference when controlling the NCR device 500A.

[0117] (c2) Context information of NCR device 500A: The context information includes, for example, information indicating that the operation of the NCR device 500A has been authorized by the network (core network, radio access network, and / or network monitoring device).

[0118] In step S203, the target gNB200T determines whether to accept the handover request of step S102. Here, the description will proceed assuming that the target gNB200T has determined to accept (permit) the handover request.

[0119] The operations from step S204 to step S206 are the same as those in the first operation pattern described above.

[0120] In step S207, after the NCR device 500A connects to its own cell (target cell), the target gNB 200T performs communication control for the NCR device 500A based on the information included in the handover request message of step S202.

[0121] (1.9.3) Third movement pattern In the third operation pattern, an operation will be described in which the UE 100 is also handed over in conjunction with the handover of the NCR device 500 A. In the third operation pattern, the source gNB 200S sets a conditional handover (CHO) in the UE 100, thereby realizing the handover of the UE 100 in conjunction with the handover of the NCR device 500 A.

[0122] In CHO, the source gNB 200S transmits a handover request in advance to a candidate gNB that manages a candidate cell that is a candidate for the target cell, and also transmits configuration information for the CHO in advance to the UE 100. After receiving the configuration information, the UE 100 suspends handover until a trigger condition specified in the configuration information is satisfied, and initiates handover when the trigger condition is satisfied. The trigger condition may be that the radio quality of the candidate cell is higher than a threshold. The trigger condition may also be that the radio quality of the candidate cell is higher than the radio quality of the serving cell (source cell).

[0123] In the third operation pattern, the source gNB200S transmits a UE handover request to the target gNB200T requesting a CHO of the UE100. Here, the source gNB200S notifies the target gNB200T that the CHO is due to the handover of the NCR device 500A. That is, when requesting a CHO of the associated UE100 from the target gNB200T, the source gNB200S notifies the target gNB200T that the CHO is due to the handover of the NCR device 500A. The source gNB200S may request a handover of the group of the NCR device 500A and the user equipment from the target gNB200T by including a UE handover request in a handover request message requesting a handover of the NCR device 500A. Note that the second operation pattern may be implemented in combination with the above-described first operation pattern.

[0124] 18 is a diagram showing the operation of the mobile communication system 1 according to the third operation pattern. Description of operations that overlap with the operations of the first operation pattern described above will be omitted.

[0125] In step S301, the source gNB 200S decides to hand over the NCR device 500A.

[0126] In step S302, the source gNB200S transmits a Handover Request message to the target gNB200T over the Xn interface, requesting handover of the NCR device 500A from the source cell of the source gNB200S to the target cell of the target gNB200T. Here, the source gNB200S specifies a normal handover, not a CHO. The target gNB200T receives the Handover Request message.

[0127] The handover request message may include information indicating that a handover request message of the UE 100 will subsequently be transmitted from the source gNB 200S. In this case, the target gNB 200T may withhold transmission of a response (HO Request Ack) to the handover request of the NCR device 500A (i.e., determination of whether to accept the handover) until receiving the handover request message of the UE 100.

[0128] In the case of a group handover, the handover request message may include, as an information element, a handover request (handover request message) of the UE 100 to be subsequently handed over. The handover request includes information of the UE 100 (UE context information, etc.). If there are multiple UEs 100 to be subsequently handed over, the handover request message may include handover requests for the multiple UEs in list format. By including the handover request of the UE 100 in the handover request of the NCR device 500A, handover (i.e., group handover) can be controlled in units of groups of the NCR device 500A and UEs 100. In this case, steps S303 and S304 described below may be unnecessary.

[0129] If the handover is not a group handover, in step S303, the source gNB200S transmits a handover request message (Conditional Reconfiguration request) of the UE100 to the target gNB200T over the Xn interface. The message may include information for identifying the handover request of the NCR device 500A in step S302. From the information, the target gNB200T can know the handover timing of the corresponding NCR device 500A (the timing of transmitting the handover command, the timing of access by the NCR device 500A). The target gNB200T may perform efficient operation, for example, by preparing resources for access by the UE100 after the access by the NCR device 500A is completed.

[0130] If the handover is not a group handover and multiple UEs 100 are to be handed over, the source gNB 200S may transmit multiple handover request messages corresponding to the multiple UEs 100 to the target gNB 200T. The source gNB 200S may include information indicating that the last handover request message among the multiple handover request messages is the last message. This information allows the target gNB 200T to determine the number of HOs of the UEs 100 resulting from the handover of the NCR device 500A. The target gNB 200T may determine whether to accept the series of handover requests and return HO Request Acks for the UEs 100 and the NCR device 500A.

[0131] In step S304, the target gNB200T transmits a response (Handover Request Acknowledge) message to the handover request of UE100 in step S303 to the source gNB200S over the Xn interface. The message includes an RRC Reconfiguration (Conditional Reconfiguration) to be set in UE100. In the case of a group handover, the target gNB200T may transmit the response to the handover request of NCR device 500A and the response to the handover request of UE100 together to the source gNB200S.

[0132] In step S305, the source gNB 200S transmits a handover command including the RRC Reconfiguration (Conditional Reconfiguration) to the UE 100. The UE 100 receives the handover command and starts determining whether the CHO trigger condition is satisfied.

[0133] In step S306, the target gNB200T transmits a response (Handover Request Acknowledge) message to the handover request from the NCR device 500A to the source gNB200S over the Xn interface. The source gNB200S receives the Handover Request Acknowledge message. In the case of a group handover, the target gNB200T may include the Handover Request Acknowledge(s) of the UE 100 in the message.

[0134] In step S307, the source gNB200S sends a handover command to the NCR device 500A (NCR-MT520A) instructing a normal handover that is not CHO.

[0135] In step S308, the NCR device 500A (NCR-MT520A) accesses the target cell (target gNB200T).

[0136] In step S309, the NCR device 500A detects the target gNB 200 T( At this point, in the coverage area of ​​the NCR device 500A, the signal of the source cell is not repeated, but the signal of the target cell is repeated.

[0137] As a result, in step S310, the trigger condition of the CHO set in the UE 100 is satisfied.

[0138] In step S311, in response to the CHO trigger condition being satisfied, UE100 executes the corresponding conditional reconfiguration and starts accessing the target cell (target gNB200T).

[0139] (2) Second embodiment Next, the second embodiment will be described, focusing on the differences from the first embodiment. As shown in Fig. 19, the repeater according to the second embodiment is a Reconfigurable Intelligent Surface (RIS) device 500B that changes the propagation direction of an incident radio wave (wireless signal) by reflection or refraction. The "NCR" in the first embodiment can be read as "RIS."

[0140] RIS is a type of repeater (hereinafter also referred to as "RIS-Fwd") that can perform beamforming (directivity control) similar to NCR by changing the properties of metamaterials. In the case of RIS, the range (distance) of the beam may also be changeable by controlling the reflection direction and / or refraction direction of each unit element. For example, the RIS may be configured to be able to control the reflection direction and / or refraction direction of each unit element and to focus (direct the beam) on a nearby UE or a distant UE.

[0141] The RIS device 500B has a new UE (hereinafter referred to as "RIS-MT") 520B, which is a control terminal for controlling the RIS-Fwd 510B. The RIS-MT 520B establishes a wireless connection with the gNB 200 and performs wireless communication with the gNB 200, thereby controlling the RIS-Fwd 510B in cooperation with the gNB 200. The RIS-Fwd 510B may be a reflective RIS. Such a RIS-Fwd 510B changes the propagation direction of incident radio waves by reflecting the radio waves. Here, the reflection angle of the radio waves is variably settable. The RIS-Fwd 510B reflects radio waves incident from the gNB 200 toward the UE 100. The RIS-Fwd 510B may be a transparent RIS. Such a RIS-Fwd 510B changes the propagation direction of the radio waves by refracting the incident radio waves. Here, the refraction angle of the radio waves is variably settable.

[0142] FIG. 20 is a diagram showing an example configuration of a RIS-Fwd (repeater) 510B and a RIS-MT (control terminal) 520B according to the second embodiment. The RIS-MT 520B includes a receiver 521, a transmitter 522, and a controller 523. This configuration is similar to that of the first embodiment. The RIS-Fwd 510B includes a RIS 511B and a RIS controller 512B. The RIS 511B is a metasurface made of metamaterial. For example, the RIS 511B is configured by arranging structures that are very small compared to the wavelength of radio waves in an array. By making the structures different shapes depending on their placement, it is possible to arbitrarily design the direction and / or beam shape of the reflected waves. The RIS 511B may be a transparent dynamic metasurface. The RIS511B may be configured by overlaying a transparent glass substrate on a transparent metasurface substrate on which a large number of small structures are regularly arranged. By slightly moving the overlaid glass substrate, it may be possible to dynamically control three patterns: a mode that transmits incident radio waves, a mode that transmits some of the radio waves and reflects some of them, and a mode that reflects all of the radio waves. The RIS control unit 512B controls the RIS511B in response to a RIS control signal from the control unit 523 of the RIS-MT520B. The RIS control unit 512B may include at least one processor and at least one actuator. The processor decodes the RIS control signal from the control unit 523 of the RIS-MT520B and drives the actuator in response to the RIS control signal.

[0143] (3) Other embodiments The above-described operational flows are not limited to being implemented independently, but can also be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. In each flow, it is not necessary to execute all steps, and only some steps may be executed.

[0144] In the above embodiment, an example in which the base station is an NR base station (gNB) has been described, but the base station may also be an LTE base station (eNB). The base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU (Distributed Unit) of the IAB node.

[0145] A program may be provided that causes a computer to execute each process performed by UE100 (NCR-MT520A, RIS-MT520B) or gNB200. The program may be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0146] As used in this disclosure, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0147] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0148] This application claims priority from Japanese Patent Application No. 2022-136419 (filed August 30, 2022), the entire contents of which are incorporated herein by reference.

[0149] (4) Supplementary notes The following additional notes are about the features of the above-described embodiment.

[0150] (Appendix 1) A communication method used in a mobile communication system, comprising: a step of relaying a radio signal transmitted between a first cell and a user equipment by a relay device that changes a propagation state of the radio signal without demodulating or modulating the radio signal; a first network node corresponding to the first cell sending a message to a second network node corresponding to the second cell over a network interface to connect the relay device to a second cell; The message includes information about the relay device. Communication method.

[0151] (Appendix 2) the first network node is a first base station; the second network node is a second base station; The network interface is an interface between base stations. 1. A communication method as described in Appendix 1.

[0152] (Appendix 3) The message is a handover request message requesting handover of the relay device from the first cell to the second cell. 2. A communication method as described in Appendix 2.

[0153] (Appendix 4) The handover request message includes information indicating a handover of the relay device. 3. A communication method as described in Appendix 3.

[0154] (Appendix 5) The handover request message includes information indicating that the relay device is to be handed over in order to distribute the load of the first base station to the second base station. 5. A communication method according to claim 3 or 4.

[0155] (Appendix 6) The handover request message includes information indicating the number of user equipments to be handed over in association with the handover of the relay device. 6. A communication method according to any one of appendices 3 to 5.

[0156] (Appendix 7) the second base station receiving the handover request message determining whether to permit handover of the relay device based on the information included in the handover request message; If the second base station permits the handover of the relay device, the second base station transmits a response message indicating that the handover is permitted to the first base station; The first base station receiving the response message further includes a step of transmitting a handover command to the relay device. 7. A communication method according to any one of Supplementary Notes 3 to 6.

[0157] (Appendix 8) The handover request message includes at least one of control information used to control the relay device and context information of the relay device. 8. A communication method according to any one of Supplementary Notes 3 to 7.

[0158] (Appendix 9) The control information includes at least one of information indicating a beam to be applied to the relay device and information for controlling the operation of the relay device. 10. The communication method described in Appendix 8.

[0159] (Appendix 10) The method further includes a step in which the second base station, upon receiving the handover request message, performs communication control for the relay device based on the information included in the handover request message after the relay device connects to the second cell. 10. The communication method according to claim 8 or 9.

[0160] (Appendix 11) the first base station sending a user equipment handover request to the second base station, requesting a conditional handover of the user equipment from the first cell to the second cell; The step of transmitting the user equipment handover request includes the step of notifying the second base station that the conditional handover is due to a handover of the relay device. 11. A communication method according to any one of Supplementary Notes 3 to 10.

[0161] (Appendix 12) The first base station requests the second base station to hand over the group of the relay device and the user equipment by including the user equipment handover request in the handover request message requesting the handover of the relay device. 12. The communication method according to claim 11.

[0162] (Appendix 13) A network node corresponding to a first cell in a mobile communication system, comprising: a transmitter configured to transmit, via a network interface to a second network node corresponding to the second cell, a message for connecting a relay device configured to change a propagation state of a radio signal transmitted between the first cell and a user equipment without demodulating or modulating the radio signal to a second cell; The message includes information about the relay device. Network node. [Explanation of symbols]

[0163] 1: Mobile communication system 100:UE 200 :gNB 210: Transmission unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit 500A:NCR device 510A: NCR-Fwd 520A: NCR-MT 500B :RIS device 511A: Wireless unit 511a: Antenna part 511b :RF circuit 511c: Directivity control unit 512A: NCR control section 512B: RIS control unit 521: Receiving unit 522: Transmission unit 523: Control unit 530: Interface

Claims

1. A communication method used in a mobile communication system, comprising: a relay device that changes a propagation state of a radio signal transmitted between a first cell and a user equipment without demodulating or modulating the radio signal, relaying the radio signal; a first network node corresponding to the first cell transmitting a message to a second network node corresponding to the second cell over a network interface to connect the relay device to a second cell; the message is a handover request message including information about the relay device and requesting handover of the relay device from the first cell to the second cell; The handover request message includes information indicating the number of user equipments to be handed over in association with the handover of the relay device. Communication method.

2. the first network node is a first base station; the second network node is a second base station; The network interface is an interface between base stations. The communication method according to claim 1 .

3. The handover request message includes information indicating a handover of the relay device. The communication method according to claim 2 .

4. The handover request message includes information indicating that the relay device is to be handed over in order to distribute the load of the first base station to the second base station. The communication method according to claim 2 .

5. the second base station receiving the handover request message determines whether to permit handover of the relay device based on the information included in the handover request message; If the second base station permits the handover of the relay device, the second base station transmits a response message indicating that the handover is permitted to the first base station; The first base station receiving the response message transmits a handover command to the relay device. The communication method according to claim 2 .

6. A communication method for use in a mobile communication system, comprising: a relay device that changes a propagation state of a radio signal transmitted between a first cell and a user equipment without demodulating or modulating the radio signal, relaying the radio signal; a first network node corresponding to the first cell transmitting a message to a second network node corresponding to the second cell over a network interface to connect the relay device to a second cell; the message is a handover request message including information about the relay device and requesting handover of the relay device from the first cell to the second cell; the handover request message includes at least one of control information used to control the relay device and context information of the relay device; The control information includes at least one of information indicating a beam to be applied to the relay device and information for controlling the operation of the relay device. Communication method.

7. The method further includes the step of: the second network node receiving the handover request message controls communication with the relay device based on the information included in the handover request message after the relay device connects to the second cell. The communication method according to claim 6.

8. A communication method for use in a mobile communication system, comprising: a relay device that changes a propagation state of a radio signal transmitted between a first cell and a user equipment without demodulating or modulating the radio signal, relaying the radio signal; a first network node corresponding to the first cell transmitting a message to a second network node corresponding to the second cell over a network interface to connect the relay device to a second cell; the first network node is a first base station; the second network node is a second base station; the network interface is an inter-base station interface; the message is a handover request message including information about the relay device and requesting handover of the relay device from the first cell to the second cell; the first base station sending a user equipment handover request to the second base station, requesting a conditional handover of the user equipment from the first cell to the second cell; Transmitting the user equipment handover request includes notifying the second base station that the conditional handover is due to a handover of the relay device. Communication method.

9. The first base station requests the second base station to hand over the group of the relay device and the user equipment by including the user equipment handover request in the handover request message requesting the handover of the relay device. The communication method according to claim 8.

10. A network node corresponding to a first cell in a mobile communication system, comprising: a transmitter configured to transmit, via a network interface to a second network node corresponding to the second cell, a message for connecting a relay device configured to change a propagation state of a radio signal transmitted between the first cell and a user equipment without demodulating or modulating the radio signal to a second cell; the message is a handover request message including information about the relay device and requesting handover of the relay device from the first cell to the second cell; The handover request message includes information indicating the number of user equipments to be handed over in association with the handover of the relay device. Network node.

11. A network node corresponding to a first cell in a mobile communication system, comprising: a transmitter configured to transmit, via a network interface to a second network node corresponding to the second cell, a message for connecting a relay device configured to change a propagation state of a radio signal transmitted between the first cell and a user equipment without demodulating or modulating the radio signal to a second cell; the message is a handover request message including information about the relay device and requesting handover of the relay device from the first cell to the second cell; the handover request message includes at least one of control information used to control the relay device and context information of the relay device; The control information includes at least one of information indicating a beam to be applied to the relay device and information for controlling the operation of the relay device. Network node.

12. A network node corresponding to a first cell in a mobile communication system, comprising: a transmitter configured to transmit, via a network interface to a second network node corresponding to the second cell, a message for connecting a relay device configured to change a propagation state of a radio signal transmitted between the first cell and a user equipment without demodulating or modulating the radio signal to a second cell; the network node is a first base station; the second network node is a second base station; the network interface is an inter-base station interface; the message is a handover request message including information about the relay device and requesting handover of the relay device from the first cell to the second cell; the first base station sending a user equipment handover request to the second base station, requesting a conditional handover of the user equipment from the first cell to the second cell; Transmitting the user equipment handover request includes notifying the second base station that the conditional handover is due to a handover of the relay device. Network node.

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