Communication method

Abstract

A communication method used in a relay apparatus, the relay apparatus including: a relay apparatus that performs a relay operation of relaying a radio signal transmitted between a network and a user equipment; and a control terminal that receives a control signal for controlling the relay device from a network, the communication method comprising the steps of: the control terminal transitioning to a radio resource control (RRC) connected state in a cell included in the network; determining whether a condition for incorporating notification information indicating that the host device is a relay device into a message to be transmitted from the control terminal to the cell is satisfied; and in response to determining that the condition is satisfied, transmitting a message including notification information from the control terminal to the cell.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a communication method for use in a mobile communication system. BACKGROUND

[0002] In recent years, a fifth generation (5G) mobile communication system has attracted attention. New radio (NR), which is a radio access technology of a 5G system, is capable of wideband transmission via a high frequency band, as compared to long term evolution (LTE), which is a fourth generation radio access technology.

[0003] Since a radio signal (radio wave) in a high frequency band such as a millimeter wave band or a terahertz wave band has high straightness, reduction in coverage of a base station is a problem. In order to solve this problem, a repeater device, which is a relay device that relays a radio signal between a network and a user equipment, and can be controlled from a network, is attracting attention (see, for example, Non-Patent Literature 1). Such a repeater device can expand the coverage of a base station while suppressing the occurrence of interference by, for example, amplifying a radio signal received from a base station and transmitting the radio signal by directional transmission. Such a repeater device is called a network-controlled repeater (NCR).

[0004] LIST OF CITATIONS

[0005] NON-PATENT LITERATURE

[0006] Non-Patent Literature 1: 3GPP Contribution: RP-213700, “New SI: Study on NR Network-controlled Repeaters” SUMMARY

[0007] The communication method according to the first aspect is a communication method for use in a relay device including a relay apparatus configured to perform a relay operation of relaying a radio signal transmitted between a network and a user equipment, and a control terminal configured to receive a control signal for controlling the relay apparatus from the network, the communication method including the steps of: the control terminal transitioning to a radio resource control (RRC) connected state in a cell included in the network; determining whether a condition for incorporating notification information indicating that the host device is the relay device into a message to be transmitted from the control terminal to the cell is satisfied; and in response to determining that the condition is satisfied, transmitting the message including the notification information from the control terminal to the cell.

[0008] The communication method according to the second aspect is a communication method used in a relay device including a relay apparatus configured to perform a relay operation of relaying radio signals transmitted between a network and a user equipment, and a control terminal configured to receive a control signal for controlling the relay apparatus from the network, the communication method including the steps of: initiating, by the control terminal in a radio resource control (RRC) connected state, an RRC connection reestablishment procedure for a cell included in the network; incorporating, into an RRC reestablishment request message, a relay device specific radio network temporary identifier (RNTI) assigned to the relay device or notification information indicating that the host device is the relay device; and transmitting the RRC reestablishment request message including the relay device specific RNTI or the notification information from the control terminal to the cell. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment.

[0010] Figure 2 is a diagram illustrating a configuration of a protocol stack of a radio interface handling a user plane of data.

[0011] Figure 3 is a diagram illustrating a configuration of a protocol stack of a radio interface handling a control plane of signaling (control signals).

[0012] Figure 4 is a diagram illustrating an example of an application scenario of an NCR device (relay device) according to a first embodiment.

[0013] Figure 5 is a diagram illustrating an example of an application scenario of an NCR device according to a first embodiment.

[0014] Figure 6 is a diagram illustrating an example of a control method of an NCR device according to a first embodiment.

[0015] Figure 7 is a diagram illustrating an example of a configuration of a protocol stack in a mobile communication system including an NCR device according to an embodiment.

[0016] Figure 8 is a diagram illustrating a specific configuration example of a mobile communication system including an NCR device according to a first embodiment.

[0017] Figure 9 is a diagram illustrating a configuration example of an NCR device according to a first embodiment.

[0018] Figure 10 is a diagram illustrating an example of a configuration of a user equipment (UE) according to an embodiment.

[0019] Figure 11 is a diagram showing an example of a configuration of a gNB (base station) according to the embodiment.

[0020] Figure 12 is a diagram showing an operation according to the first embodiment.

[0021] Figure 13 is a diagram showing an example of an operation of an NCR-MT (control terminal) according to the first embodiment.

[0022] Figure 14 is a diagram showing an example of an operation of an NCR-MT according to a variant of the first embodiment.

[0023] Figure 15 is a diagram showing RRC connection reestablishment in an NCR-MT according to the second embodiment.

[0024] Figure 16 is a diagram showing an RRC reestablishment request (RRCreestablishment request) message specified in the 3GPP RRC Technical Specification (TS 38.331).

[0025] Figure 17 is a diagram showing an example of an operation of an NCR-MT according to the second embodiment.

[0026] Figure 18 is a diagram showing an RIS device (relay device) according to the third embodiment.

[0027] Figure 19 is a diagram showing an RIS device (relay device) according to the third embodiment.

[0028] Figure 20 is a diagram showing a specific PRACH scenario (RO) for avoiding collision possibility. DETAILED DESCRIPTION

[0029] A mobile communication system according to the embodiment is described with reference to the accompanying drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0030] (1) First Embodiment

[0031] The first embodiment will be described. The relay device according to the embodiment is a repeater device that can be controlled from a network (i.e., an NCR device).

[0032] (1.1) Overview of Mobile Communication System

[0033] Figure 1 is a diagram showing a configuration of a mobile communication system according to the embodiment.

[0034] The mobile communication system 1 conforms to a fifth generation system (5GS) of the Third Generation Partnership Project (3GPP) (registered trademark; hereinafter the same) standards. Hereinafter, the 5GS will be described by way of example, but a Long Term Evolution (LTE) system can be applied at least in part to the mobile communication system. Alternatively, a sixth generation (6G) system can be applied at least in part to the mobile communication system.

[0035] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN: Next Generation Radio Access Network) 10, and a 5G core network (5GC: 5G Core Network) 20. Hereinafter, the NG-RAN 10 can be simply referred to as the RAN 10. The 5GC 20 can be simply referred to as a core network (CN) 20. The RAN 10 and the CN 20 constitute a network 5 of the mobile communication system 1.

[0036] The UE 100 is a mobile wireless communication device. As long as the UE 100 is used by a user, the UE 100 can be any device. Examples of the UE 100 include a mobile phone terminal (including a smartphone), a tablet terminal, a laptop PC, a communication module (including a communication card or a chipset), a sensor or a device provided on a sensor, a vehicle or a device provided on a vehicle (vehicle UE), or a flying object and a device provided on a flying object (aerial UE).

[0037] The NG-RAN 10 includes a base station (referred to as a "gNB" in the 5G system) 200. The gNBs 200 are interconnected via an Xn interface that is an inter-base station interface. Each gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with a cell of the gNB 200. The gNB 200 has a radio resource management (RRM) function, a function of routing user data (hereinafter, simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The "cell" is used as a term representing the smallest unit of a wireless communication area. The "cell" is also used as a term representing a function or a resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter, simply referred to as "frequency").

[0038] The gNB 200 can be functionally divided into a central unit (CU) and a distributed unit (DU). The CU controls the DU. The CU is, for example, a unit including upper layers (such as an RRC layer, an SDAP layer, and a PDCP layer) included in the following protocol stack. The CU is connected to a core network via an NG interface, which is a backhaul interface. The CU is connected to an adjacent base station via an Xn interface, which is an inter-base station interface. The DU forms a cell. The DU 202 is, for example, a unit including lower layers (such as an RLC layer, a MAC layer, and a PHY layer) included in the following protocol stack. The DU is connected to the CU via an F1 interface, which is a fronthaul interface.

[0039] The gNB can be connected to an evolved packet core (EPC) corresponding to a core network of LTE. The LTE base station can also be connected to the 5GC. The LTE base station and the gNB can be connected via an inter-base station interface.

[0040] The 5GC 20 includes an access and mobility management function (AMF) and a user plane function (UPF) 300. The AMF performs various types of mobility control and the like with respect to the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using non-access stratum (NAS) signaling. The UPF controls data transmission. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0041] Figure 2 is a diagram showing a configuration of a protocol stack of a radio interface that handles a user plane.

[0042] The user plane radio interface protocol includes a physical layer (PHY), a medium access control layer (MAC), a radio link control layer (RLC), a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP).

[0043] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted and received between the PHY layer of the UE 100 and the PHY layer of the gNB 200 via a physical channel. The PHY layer of the UE 100 receives downlink control information (DCI) transmitted from the gNB 200 through a physical downlink control channel (PDCCH). Specifically, the UE 100 performs blind decoding on the PDCCH using a radio network temporary identifier (RNTI) and acquires successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from the gNB 200 is added with cyclic redundancy code (CRC) bits scrambled by the RNTI.

[0044] The gNB 200 transmits a synchronization signal block (SSB: synchronization signal / PBCH block). The SSB includes, for example, four continuous orthogonal frequency division multiplexing (OFDM) symbols, and is arranged with 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) of the PBCH. The bandwidth of the SSB is, for example, a bandwidth of 240 continuous subcarriers, i.e., 20 RBs.

[0045] The MAC layer performs data priority control, retransmission processing using a hybrid automatic repeat request (HARQ), a random access procedure, and the like.

[0046] Data and control information are transmitted and received between the MAC layers of the UE 100 and the gNB 200 via transport channels. The MAC layer of the gNB 200 includes a scheduler. The scheduler determines the transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE 100 in the uplink and downlink.

[0047] The RLC layer transmits data to the RLC layer of the receiving side by using the functions of the MAC layer and the PHY layer. Data and control information are transmitted and received between the RLC layers of the UE 100 and the gNB 200 via logical channels.

[0048] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0049] The SDAP layer performs mapping between an IP flow, which is a unit for quality of service (QoS) control in a core network, and a radio bearer, which is a unit for QoS control in an access stratum (AS). Note that when the RAN is connected to an EPC, the SDAP does not need to be provided.

[0050] Figure 3 is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that handles signaling (control signals).

[0051] The protocol stack of the radio interface of the control plane includes a radio resource control (RRC) layer and a non-access stratum (NAS) layer, instead of Figure 2 the SDAP layer shown.

[0052] RRC signaling for various configurations is transmitted between the RRC layer of the UE 100 and the RRC layer of the gNB 200. The RRC layer controls logical channels, transport channels, and physical channels according to establishment, reestablishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200, the UE 100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200, the UE 100 is in an RRC idle state. When the connection between the RRC of the UE 100 and the RRC of the gNB 200 is suspended, the UE 100 is in an RRC inactive state.

[0053] The NAS layer located above the RRC layer performs session management, mobility management, and the like. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300A. The UE 100 includes an application layer in addition to the protocol of the radio interface. Layers lower than the NAS layer are referred to as AS layers.

[0054] (1.2) Example of application scenario of relay device

[0055] Figure 4 and Figure 5 An example of an application scenario of the NCR device according to the embodiment is shown.

[0056] Compared with 4G / LTE, 5G / NR is capable of wideband transmission via a high frequency band. Since a radio signal in a high frequency band such as a millimeter wave band or a terahertz wave band has high straightness, reduction in coverage of the gNB 200 is a problem. In Figure 4 In the example, the UE 100 can be located outside the coverage of the gNB 200, for example, outside an area in which the UE 100 can directly receive a radio signal from the gNB 200. The UE 100 can not be able to communicate with the gNB 200 in a line-of-sight range due to the presence of an obstacle between the gNB 200 and the UE 100.

[0057] As shown in Figure 4 , a repeater device (500A) is introduced into the mobile communication system 1, which is a relay device that relays a radio signal between the gNB 200 and the UE 100, and which is an NCR device 500A that can be controlled from the network. Such a repeater device can be referred to as a smart repeater device.

[0058] For example, the NCR device 500A amplifies the radio signal (radio wave) received from the gNB 200 and transmits the radio signal by directional transmission. Specifically, the NCR device 500A receives the radio signal transmitted by the gNB 200 through beamforming. The NCR device 500A amplifies the received radio signal without demodulation or modulation and transmits the amplified radio signal by directional transmission. Here, the NCR device 500A can transmit the radio signal with a fixed directionality (beam). The NCR device 500A can also transmit the radio signal with a variable (adaptive) directional beam. This can effectively extend the coverage area of ​​the gNB 200.

[0059] In addition, such as Figure 5 As shown, a new UE (hereinafter referred to as "NCR-MT (Mobile Terminal)") 100B is introduced, which is a control terminal for controlling the NCR device 500A. Specifically, the NCR device 500A includes: an NCR-Fwd (forward) 510A, a type of relay device that relays radio signals transmitted between the gNB 200 and the UE 100, specifically by altering the propagation state of the radio signals without demodulating or modulating them; and an NCR-MT 520A, which performs wireless communication with the gNB 200 to control the NCR-Fwd 510A. Therefore, by establishing a wireless connection with the gNB 200 and performing wireless communication with it, the NCR-MT 520A cooperates with the gNB 200 to control the NCR device 500A. Thus, the NCR device 500A can be used to achieve efficient coverage extension. The NCR-MT 520A controls the NCR device 500A according to the control from the gNB 200. The NCR-MT 520A also has the same functions as the UE 100.

[0060] The NCR-MT 520A can be configured to operate independently of the NCR-Fwd 510A. For example, the NCR-MT 520A can be located near the NCR-Fwd 510A and electrically connected to it. The NCR-MT 520A can be connected to the NCR-Fwd 510A via wired or wireless connection. Alternatively, the NCR-MT 520A can be configured as an integral part of the NCR-Fwd 510A. Both the NCR-MT 520A and NCR-Fwd 510A can be permanently installed at the coverage edge (cell edge) of the gNB 200, or, for example, mounted on the wall surface or window of any building. Both the NCR-MT 520A and NCR-Fwd 510A can be installed in equipment such as vehicles and are portable. One NCR-MT 520A can control multiple NCR-Fwd 510As.

[0061] The configuration is not limited to the configuration in which the NCR-MT 520A directly controls the one or more NCR-Fwds 510A, and can be a configuration in which the NCR-MT 520A indirectly controls the one or more NCR-Fwds 510A. For example, the NCR-MT 520A can control the one or more NCR-Fwds 510A via an upper layer (e.g., an application layer).

[0062] In Figure 5 In the example shown, 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 can also form a beam toward the gNB 200. For example, in a communication resource between the gNB 200 and the UE 100a, the NCR-Fwd 510A transmits a radio signal received from the gNB 200 to the UE 100a by beamforming and / or transmits a radio signal received from the UE 100a to the gNB 200 by beamforming. In a communication resource between the gNB 200 and the UE 100b, the NCR-Fwd 510A transmits a radio signal received from the gNB 200 to the UE 100b by beamforming and / or transmits a radio signal received from the UE 100b to the gNB 200 by beamforming. Instead of or in addition to beamforming, the NCR-Fwd 510A can also perform null-forming (so-called null control) toward a UE 100 (not shown) that is not a communication partner and / or a neighboring gNB 200 (not shown) to suppress interference.

[0063] Figure 6 is a diagram showing an example of a control method for the NCR device 500A according to an embodiment. As Figure 6 shown, the NCR-Fwd 510A relays a radio signal (also referred to as a "UE signal") between the gNB 200 and the UE 100. The UE signal includes an uplink signal (referred to as a "UE-UL signal") transmitted from the UE 100 to the gNB 200 and a downlink signal (referred to as a "UE-DL signal") transmitted from the gNB 200 to the UE 100. The NCR-Fwd 510A relays the UE-UL signal from the UE 100 to the gNB 200 and relays the UE-DL signal 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".

[0064] The NCR-MT 520A transmits and receives radio signals (referred to herein as “NCR-MT signals”) to and from the gNB 200. The NCR-MT signals include uplink signals (referred to as “NCR-MT-UL signals”) transmitted from the NCR-MT 520A to the gNB 200 and downlink signals (referred to as “NCR-MT-DL signals”) transmitted from the gNB 200 to the NCR-MT 520A. The NCR-MT-DL signals include signaling (e.g., NCR control signals) for controlling the NCR device 500A. The radio link between the NCR-MT 520A and the gNB 200 is also referred to as a “control link.”

[0065] The gNB 200 directs a beam to the NCR-MT 520A based on the NCR-MT-UL signals from the NCR-MT 520A. Since the NCR device 500A and the NCR-MT 520A are co-located, when the backhaul link and the control link have the same frequency and the gNB 200 directs a beam to the NCR-MT 520A, the beam is ultimately directed to the NCR-Fwd 510A as well. The gNB 200 uses the beam to transmit NCR-MT-DL signals and UE-DL signals. The NCR-MT 520A receives the NCR-MT-DL signals. When the NCR-Fwd 510A and the NCR-MT 520A are at least partially integrated, the functionality (e.g., antennas) for transmitting or receiving or relaying UE signals and / or NCR-MT signals can be integrated in the NCR-Fwd 510A and the NCR-MT 520A. The beam includes a transmit beam and / or a receive beam. The beam is a general term for transmission and reception under control that maximizes the power of a transmit wave and / or a receive wave in a specific direction by adjusting / adapting antenna weights, etc.

[0066] Figure 7 is a diagram illustrating an example of a configuration of protocol stacks in the mobile communication system 1 having the NCR device 500A according to an embodiment. The NCR-Fwd 510A relays radio signals transmitted and received between the gNB 200 and the UE 100. The NCR-Fwd 510A has a radio frequency (RF) function of amplifying and relaying received radio signals, and performs directional transmission through beamforming (e.g., analog beamforming).

[0067] The NCR-MT 520A includes at least one layer (entity) selected from the group consisting of PHY, MAC, RRC, and an application protocol (F1-AP). F1-AP is a type of fronthaul interface. The NCR-MT 520A exchanges signaling with the gNB 200 using at least one of PHY, MAC, RRC, and F1-AP. When the NCR-MT 520A is a type of base station or is a part of a base station, the NCR-MT 520A can exchange signaling with the gNB 200 using XnAP (Xn-AP), which is an interface between base stations. The NCR-MT 520A can further include a NAS layer (entity). The NAS layer allows the NCR-MT 520A to exchange signaling with the AMF 300A. The NAS layer can constitute an upper layer of the NCR-MT 520A.

[0068] Figure 8 is a diagram illustrating a specific example of a configuration of a mobile communication system 1 including an NCR device 500A according to an embodiment.

[0069] A backhaul link is established between the gNB 200 and the NCR-Fwd 510A. An access link is established between the UE 100 and the NCR-Fwd 510A. The NCR-Fwd 510A relays radio signals transmitted between the gNB 200 and the UE 100 via the backhaul link and the access link. The NCR-Fwd 510A changes a propagation state of the radio signals without demodulating or modulating the radio signals.

[0070] Further, a control link is established between the gNB 200 and a layer 1 (L1) and / or a layer 2 (L2) of the NCR-MT 520A. The L1 / L2 of the NCR-MT 520A transmits and receives L1 / L2 signaling to and from the gNB 200 via the control link. An RRC connection is established between the gNB 200 and an RRC of the NCR-MT 520A. The RRC of the NCR-MT 520A transmits and receives RRC messages to and from the gNB 200 via the RRC connection. The NCR-MT 520A receives downlink signaling (also referred to as an “NCR control signal” or simply a “control signal”) from the gNB 200 via the RRC connection and / or the control link.

[0071] The gNB 200 (transmitter 210) transmits an NCR control signal to the NCR-MT 520A. The NCR control signal can be an RRC message, which is a control signal of the RRC layer (i.e., layer 3). The NCR control signal can be a MAC control element (CE), which is a control signal of the MAC layer (i.e., layer 2). The NCR control signal can be a downlink control information (DCI), which is a control signal of the PHY layer (i.e., layer 1). The NCR control signal can be UE-specific signaling. The NCR control signal can be broadcast signaling. The NCR control signal can be a fronthaul message (e.g., an F1-AP message). When the NCR-MT 520A is a type of base station or is a part of a base station, the NCR-MT 520A can communicate with the gNB 200 via an AP (Xn-AP) of the Xn, which is an inter-base station interface.

[0072] Hereinafter, the NCR control signal transmitted in an RRC message (and / or a MAC CE) and used to statically or semi-statically control the NCR-Fwd 510A is also referred to as “NCR configuration information” or simply “configuration information”. Here, the RRC message can be an RRC reconfiguration message. The NCR configuration information, for example, includes information for configuring the on / off of the NCR-Fwd 510A. The NCR configuration information, for example, can include information for semi-static beam configuration of the NCR-Fwd 510A.

[0073] On the other hand, the NCR control signal transmitted in L1 / L2 signaling (i.e., DCI (and / or a MAC CE)) and used to dynamically control the NCR-Fwd 510A is also referred to as “NCR control information” or simply “control information”. The NCR control information can also be referred to as secondary control information (SCI). The CRC bits of the PDCCH carrying the NCR control information are scrambled by a newly introduced dedicated RNTI. This dedicated RNTI is also referred to as “NCR-RNTI”. The NCR control information, for example, can include information for dynamic beam control of the NCR-Fwd 510A. The NCR configuration information can include information for indicating dynamic on / off of the NCR-Fwd 510A.

[0074] For example, when the NCR-MT 520A is in an RRC connected state, the NCR apparatus 500A can turn on or off the NCR-Fwd 510A according to the NCR control information (SCI) received from the gNB 200. On the other hand, after the NCR-MT 520A transitions to an RRC inactive state, the NCR apparatus 500A can turn on or off the NCR-Fwd 510A according to the latest (most recent) configuration information received from the gNB 200.

[0075] Further, the NCR control signal held by the NCR device 500A (NCR-MT 520A) (e.g., the NCR configuration information by RRC and / or the NCR control information by L1 / L2 signaling) can be referred to as an NCR-Fwd context.

[0076] In addition, when the NCR-MT 520A detects a radio link failure (RLF) with the gNB 200, the NCR-MT 520A performs cell selection and triggers an RRC connection reestablishment (also referred to as “RRC reestablishment”). Here, when the NCR-MT 520A enters an RRC idle state due to a failure to find a suitable cell in the cell selection, the NCR device 500A turns off the NCR-Fwd 510A. During the RRC connection reestablishment procedure, the NCR-Fwd 510A is turned off.

[0077] The NCR control signal can include frequency control information for specifying a center frequency of a radio signal (e.g., a component carrier) in the NCR-Fwd 510A that is a target of relaying. When the NCR control signal received from the gNB 200 includes the frequency control information, the NCR-MT 520A (controller 523) controls the NCR-Fwd 510A so that the NCR-Fwd 510A relays a radio signal that is a target, the center frequency of which is indicated by the frequency control information (step S2A). The NCR control signal can include multiple pieces of frequency control information for specifying different center frequencies from each other. Due to the NCR control signal including the frequency control information, the gNB 200 can specify, via the NCR-MT 520A, a center frequency of a radio signal to be relayed by the NCR-Fwd 510A.

[0078] The NCR control signal can include mode control information for specifying an operation mode of the NCR-Fwd 510A. The mode control information can be associated with the frequency control information (center frequency). The operation mode can be any one of a mode in which the NCR-Fwd 510A performs non-directional transmission and / or reception, a mode in which the NCR-Fwd 510A performs fixed directional transmission and / or reception, a mode in which the NCR-Fwd 510A performs transmission and / or reception with a variable directional beam, and a mode in which the NCR-Fwd 510A performs multiple-input multiple-output (MIMO) relay transmission. The operation mode can be any one of a beamforming mode (i.e., a mode that emphasizes improvement of a desired wave) and a null steering mode (i.e., a mode that emphasizes suppression of an interfering wave). When the NCR control signal received from the gNB 200 includes the mode control information, the NCR-MT 520A (controller 523) controls the NCR-Fwd 510A so that the NCR-Fwd 510A operates in the operation mode indicated by the mode control information (step S2A). Since the NCR control signal includes the mode control information, the gNB 200 can specify the operation mode of the NCR-Fwd 510A via the NCR-MT 520A.

[0079] Here, the mode in which the NCR device 500A performs omni-directional transmission and / or reception is a mode in which the NCR-Fwd 510A performs relaying in all directions, and can be referred to as an omni-directional mode. The mode in which the NCR-Fwd 510A performs fixed directional transmission and / or reception can be a directional mode achieved through one directional antenna. The mode can be a beamforming mode achieved by applying fixed phase and amplitude control (antenna weight control) to a plurality of antennas. Any one of these modes can be designated (set) to the NCR-MT 520A from the gNB 200. The mode in which the NCR-Fwd 510A performs transmission and / or reception with a variable directional beam can be a mode for performing analog beamforming. The mode can be a mode of performing digital beamforming. The mode can be a mode of performing hybrid beamforming. The mode can be a mode for forming an adaptive beam specific to the UE 100. Any one of these modes can be designated (set) to the NCR-MT 520A from the gNB 200. In the operation mode in which beamforming is performed, beam control information to be described below can be provided to the NCR-MT 520A from the gNB 200. The mode in which the NCR device 500A performs MIMO relay transmission can be a mode for performing single-user (SU) spatial multiplexing. The mode can be a mode of performing multi-user (MU) spatial multiplexing. The mode can be a mode for performing transmission diversity. Any one of these modes can be designated (set) to the NCR-MT 520A from the gNB 200. The operation mode can include a mode in which relay transmission performed by the NCR-Fwd 510A is turned on (activated) and a mode in which relay transmission performed by the NCR-Fwd 510A is turned off (deactivated). Any one of these modes can be designated (set) to the NCR-MT 520A from the gNB 200 in the NCR control signal.

[0080] The NCR control signal can include beam control information for designating a transmission direction, a transmission weight, or a beam pattern when the NCR-Fwd 510A performs directional transmission. The beam control information can be associated with frequency control information (center frequency). The beam control information can include a precoding matrix indicator (PMI). The beam control information can include beamforming angle information. When the NCR control signal received from the gNB 200 includes the beam control information, the NCR-MT 520A (controller 523) controls the NCR-Fwd 510A to form transmission directivity (beam) indicated by the beam control information. The gNB 200 can control the transmission directivity of the NCR device 500A via the NCR-MT 520A when the NCR control signal includes the beam control information.

[0081] The NCR control signal can include output control information for specifying a degree of amplification (amplification gain) or transmission power of the NCR-Fwd 510A. The output control information can be information indicating a difference (i.e., a relative value) between a current amplification gain or transmission power and a target amplification gain or transmission power. When the NCR control signal received from the gNB 200 includes the output control information, the NCR-MT 520A (controller 523) controls the NCR-Fwd 510A so that the NCR-Fwd 510A performs a change in amplification gain or transmission power indicated by the output control information. The output control information can be associated with the frequency control information (center frequency). The output control information can be information for specifying any one of an amplification gain, a beamforming gain, an antenna gain of the NCR-Fwd 510A. The output control information can be information for specifying a transmission power of the NCR-Fwd 510A.

[0082] When one NCR-MT 520A controls a plurality of NCR-Fwds 510A, the gNB 200 (transmitter 210) can transmit the NCR control signal to the NCR-MT 520A of each NCR-Fwd 510A. In this case, the NCR control signal can include an identifier of the corresponding NCR-Fwd 510A (NCR identifier). The NCR-MT 520A (controller 523) controlling a plurality of NCR-Fwds 510A determines the NCR-Fwd 510A to which the NCR control signal is to be applied based on the NCR identifier included in the NCR control signal received from the gNB 200. Even if the NCR-MT 520A controls only one NCR-Fwd 510A, the NCR identifier can be transmitted from the NCR-MT 520A to the gNB 200 together with the NCR control signal.

[0083] Therefore, the NCR-MT 520A (controller 523) controls the NCR-Fwd 510A based on the NCR control signal from the gNB 200. This makes it possible for the gNB 200 to control the NCR-Fwd 510A via the NCR-MT 520A.

[0084] (1.3) Example of configuration of each device

[0085] An example of the configuration of each device in the mobile communication system 1 according to the embodiment will be described.

[0086] (1.3.1) Example of configuration of relay device

[0087] Figure 9An example of a configuration of the NCR device 500A (relay device) according to the embodiment is shown. The NCR device 500A includes an NCR-Fwd 510A, an NCR-MT 520A, and an interface 530.

[0088] The NCR-Fwd 510A includes a wireless unit 511A and an NCR controller 512A. The wireless unit 511A includes an antenna 511a including a plurality of antennas (a plurality of antenna elements), an RF circuit 511b including an amplifier, and a directivity controller 511c that controls the directivity of the antenna 511a. The RF circuit 511b amplifies and relays (transmits) a radio signal that is transmitted and received by the antenna 511a. The RF circuit 511b can convert a radio signal that is an analog signal into a digital signal, and reconvert the digital signal into an analog signal after digital signal processing. The directivity controller 511c can perform analog beamforming by analog signal processing. The directivity controller 511c can perform digital beamforming by digital signal processing. The directivity controller 511c can perform analog and digital hybrid beamforming. The NCR controller 512A controls the wireless unit 511A in response to a control signal from the NCR-MT 520A. The NCR controller 512A can include at least one processor.

[0089] The NCR-MT 520A includes a receiver 521, a transmitter 522, and a controller 523. The receiver 521 performs various types of reception under the control of the controller 523. The receiver 521 includes an antenna and a reception device. The reception device converts a radio wave (a radio signal) received through the antenna into a baseband signal (a reception signal), and outputs the reception signal to the controller 523. The transmitter 522 performs various types of transmission under the control of the controller 523. The transmitter 522 includes an antenna and a transmission device. The transmission device converts a baseband signal (a transmission signal) output by the controller 523 into a radio signal, and transmits the radio signal from the antenna. The controller 523 performs various types of control in the NCR-MT 520A. The operations of the NCR-MT 520A (and the NCR device 500A) described above and to be described below can be operations controlled by the controller 523. The controller 523 includes at least one processor and at least one memory. The memory stores a program to be executed by the processor and information to be used for processing by the processor. The processor can include a baseband processor and a central processing unit (CPU). The baseband processor performs modulation and demodulation, encoding and decoding, and the like of a baseband signal. The CPU executes a program stored in the memory, thereby performing various types of processing. The controller 523 performs a function of at least one layer selected from the group consisting of PHY, MAC, RRC, and F1-AP.

[0090] The interface 530 electrically or logically connects the NCR-Fwd 510A and the NCR-MT 520A. The controller 523 of the NCR-MT 520A controls the NCR-Fwd 510A via the interface 530. The interface 530 can be a logical entity of an upper layer (e.g., an application layer).

[0091] In an embodiment, the receiver 521 of the NCR-MT 520A receives signaling (NCR control signal) for controlling the NCR device 500A from the gNB 200 through wireless communication. The controller 523 of the NCR-MT 520A controls the NCR device 500A based on the signaling. This makes it possible for the gNB 200 to control the NCR-Fwd 510A via the NCR-MT 520A.

[0092] (1.3.2) Example of configuration of user equipment

[0093] Figure 10 is a diagram showing a configuration of a UE 100 (user equipment) according to an embodiment. The UE 100 includes a receiver 110, a transmitter 120, and a controller 130. The receiver 110 and the transmitter 120 constitute a wireless communicator that performs wireless communication with a gNB 200.

[0094] The receiver 110 performs various receptions under the control of the controller 130. The receiver 110 includes an antenna and a reception device. The reception device converts a radio signal received through the antenna into a baseband signal (reception signal), and outputs the resulting signal to the controller 130.

[0095] The transmitter 120 performs various transmissions under the control of the controller 130. The transmitter 120 includes an antenna and a transmission device. The transmission device converts a baseband signal (transmission signal) output by the controller 130 into a radio signal, and transmits the resulting signal through the antenna.

[0096] The controller 130 performs various controls and processing in the UE 100. Such processing includes processing of various layers to be described later. The operations of the UE 100 described above and to be described below can also be operations under the control of the controller 130. The controller 130 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be used for processing by the processor. The processor can include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding, and the like of baseband signals. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0097] (1.3.3) Example of configuration of base station

[0098] Figure 11A figure showing an example of a configuration of a gNB 200 (base station) according to the embodiment is shown. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communicator 240.

[0099] The transmitter 210 performs various types of transmission under the control of the controller 230. The transmitter 210 includes an antenna and a transmission device. The transmission device converts a baseband signal (transmission signal) output by the controller 230 into a radio signal, and transmits the resulting signal through the antenna. The receiver 220 performs various types of reception under the control of the controller 230. The receiver 220 includes an antenna and a reception device. The reception device converts a radio signal received through the antenna into a baseband signal (reception signal), and outputs the resulting signal to the controller 230. The transmitter 210 and the receiver 220 can be able to use multiple antennas for beamforming.

[0100] The controller 230 performs various types of control of the gNB 200. The operations of the gNB 200 described above and to be described below can be operations under the control of the controller 230. The controller 230 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be used for processing in the processor. The processor can include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding, and the like of baseband signals. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0101] The backhaul communicator 240 is connected to neighboring base stations via an inter-base station interface. The backhaul communicator 240 is connected to the AMF / UPF 300 via an interface between the base station and the core network. The gNB can include a central unit (CU) and a distributed unit (DU) (i.e., the functions are divided), and the two units can be connected via an Fl interface.

[0102] In the embodiment, the transmitter 210 of the gNB 200 transmits, to the NCR-MT 520A, signaling (NCR control signal) for controlling the NCR-Fwd 510A through wireless communication. This makes the gNB 200 controllable of the NCR device 500A via the NCR-MT 520A.

[0103] (1.4) Operation according to the first embodiment

[0104] Figure 12 is a figure showing an operation according to the first embodiment.

[0105] First, the NCR-MT 520A (NCR device 500A) in an RRC idle state in a cell of the gNB 200 (i.e., the NCR-MT 520A camping on the cell) initiates an RRC connection establishment procedure. The RRC connection establishment procedure includes transmitting an RRC setup request message from the NCR-MT 520A to the gNB 200, transmitting an RRC setup message from the gNB 200 to the NCR-MT 520A, and transmitting an RRC setup complete message from the NCR-MT 520A to the gNB 200. The RRC setup complete message corresponds to message 5 (Msg5) in the random access procedure. The NCR-MT 520A transitions to an RRC connected state through the RRC connection establishment procedure.

[0106] Second, the NCR-MT 520A transmits a message including notification information (also referred to as "NCR node indication" or "NCR node indication IE") indicating that the host device is an NCR to the gNB 200. For example, the NCR-MT 520A transmits an RRC setup complete message (Msg5) including the NCR node indication or a UE capability response message including the NCR node indication to the gNB 200. In response to receiving the UE capability enquiry message from the gNB 200, the NCR-MT 520A transmits a UE capability response message including information about the capability of the NCR-MT 520A to the gNB 200. The UE capability response message is also referred to as a UE capability information message. When the gNB 200 receives the NCR node indication, the gNB 200 can recognize that the device connected to its own cell is the NCR-MT 520A (NCR device 500A), not the UE 100.

[0107] Third, the gNB 200 transmits an NCR control signal (specifically, NCR configuration information) to the NCR-MT 520A. The NCR-MT 520A (NCR device 500A) controls the NCR-Fwd 510A according to the received NCR control signal.

[0108] Thus, when the NCR node indication is transmitted from the NCR-MT 520A to the gNB 200, the gNB 200 can recognize that the device connected to its own cell is the NCR-MT 520A (NCR device 500A), not the UE 100. This allows the gNB 200 to transmit the NCR control signal (specifically, NCR configuration information) to the NCR-MT 520A.

[0109] However, when the desired cell is defined as a connection destination of the NCR-MT 520A, the NCR-MT 520A preferably does not receive the NCR control signal from a non-desired cell that is not the desired cell (i.e., because the NCR-Fwd 510A is to be controlled by the non-desired cell).

[0110] In particular, the setting of the prior art RF repeater is determined by network planning and / or field RF measurement. Thus, a desired cell is planned for each NCR device 500A. That is, the correspondence between a serving cell and the NCR device 500A can be determined by network planning. Such a desired cell can be configured in the NCR device 500A, for example, by a network operator entity (OAM: Operation, Administration and Maintenance).

[0111] For the NCR device 500A (NCR-MT 520A), the desired cell can be configured by, for example, the OAM. Here, the desired cell can be a cell that is planned so that the NCR-MT 520A connects to the cell. In this case, the NCR-MT 520A preferably avoids connecting to a non-desired cell that is not the desired cell. The desired cell can be referred to as a planned cell. The non-desired cell can be referred to as a non-planned cell or an unplanned cell.

[0112] Here, the desired cell can be a cell that is planned so that the NCR-MT 520A camps on and / or connects to the cell by network planning. The frequency to which the desired cell belongs is also referred to as a "desired frequency". Further, a cell that is not the desired cell is referred to as a "non-desired cell", and a frequency that is not the desired frequency is referred to as a "non-desired frequency". Information about the desired cell (e.g., a cell ID of the desired cell), information about the non-desired cell (e.g., a cell ID of the non-desired cell), information about the desired frequency (e.g., a frequency ID of the desired frequency), and / or information about the non-desired frequency (e.g., a frequency ID of the non-desired frequency) can be collectively referred to as "desired cell information". The desired cell information can include a list of cell IDs of the respective desired cell, a list of cell IDs of the respective non-desired cell, a list of frequency IDs of the respective desired frequency, and / or a list of frequency IDs of the respective desired frequency. The desired cell information can be preset for the NCR-MT 520A from the OAM. The desired cell information can be preset in the NCR-MT 520A from the gNB 200 or the AMF 300A. The NCR-MT 520A saves the preset desired cell information, and uses the saved desired cell information to determine whether to transmit the NCR node indication.

[0113] Alternatively, the desired cell can be a cell that has provided the NCR control signal to the NCR-MT 520A last time, or a cell that belongs to a frequency with which the NCR control signal has been provided to the NCR-MT 520A last time. For example, when the NCR-MT 520A receives the NCR control signal from the cell while the NCR-MT 520A is in the RRC connected state at the cell, and controls the NCR-Fwd 510A according to the received NCR control signal. The cell that has provided the NCR control signal to the NCR-MT 520A or the frequency that has provided the NCR control signal to the NCR-MT 520A can be regarded as a cell that is planned so that the NCR-MT 520A camps on the cell and / or connects to the cell. Accordingly, all cells (or all frequencies) that have provided the NCR control signal to the NCR-MT 520A can be regarded as desired cells (or desired frequencies). The NCR-MT 520A saves and manages the desired cell information related to the cell and / or the frequency that has provided the NCR control signal, and uses the saved desired cell information to determine whether to transmit the NCR node indication.

[0114] Alternatively, the desired cell can be a cell that belongs to an operating frequency of the NCR-Fwd 510A. That is, the desired cell can be a cell that belongs to a frequency that the NCR-Fwd 510A can relay. Such desired cell information can be pre-set in the NCR-MT 520A from the OAM. Such desired cell information can be pre-set in the memory of the NCR-MT 520A at the time of shipment from the factory. Such desired cell information can be pre-set in the NCR-MT 520A from the gNB 200 or the AMF 300A.

[0115] The communication method according to the first embodiment is a method used in the NCR apparatus 500A including the NCR-Fwd 510A that performs a relay operation of relaying a wireless signal transmitted between the network 5 and the UE 100, and the NCR-MT 520A that receives an NCR control signal for controlling the NCR-Fwd 510A from the network 5. First, the NCR-MT 520A transitions to the RRC connected state in a cell included in the network 5. Second, the NCR-MT 520A determines whether a condition of incorporating the NCR node indication into a message to be transmitted from the NCR-MT 520A to the cell (gNB 200) is satisfied. Third, when it is determined that the condition is satisfied, the NCR-MT 520A transmits the message including the NCR node indication from the NCR-MT 520A to the cell (gNB 200). As described above, the message can be the RRC setup complete message (Msg5) or the UE capability response message.

[0116] In the first embodiment, the NCR-MT 520A determines whether a cell to which the NCR-MT 520A is connected (also referred to as a "connected cell") is a desired cell. In response to determining that the connected cell is a desired cell, the NCR-MT 520A transmits a message including an NCR node indication to the connected cell (gNB 200). Further, the NCR-MT 520A can determine that the connected cell is a desired cell when a frequency of the cell to which the NCR-MT 520A is connected is a desired frequency. In response to determining that the connected cell belongs to a desired frequency, the NCR-MT 520A can transmit a message including an NCR node indication to the connected cell (gNB 200).

[0117] Accordingly, when it is determined that the connected cell is not a desired cell (i.e., the connected cell is a non-desired cell), the NCR-MT 520A can not transmit an NCR node indication to the connected cell (gNB 200). This makes it easier to avoid that the NCR-MT 520A receives an NCR control signal from a non-desired cell (i.e., the NCR-Fwd 510A is controlled by a non-desired cell).

[0118] In response to determining that the connected cell is not a desired cell, the NCR-MT 520A can transmit information (also referred to as "release suggestion information") for prompting the network 5 to transition from an RRC connected state to another RRC state (e.g., an RRC idle state) to the connected cell (gNB 200). This allows the gNB 200 to cause the NCR-MT 520A to transition to, for example, an RRC idle state based on the release suggestion information from the NCR-MT 520A. Thus, the NCR-MT 520A becomes easier to reselect a desired cell through cell reselection. Further, when the NCR-MT 520A can be handed over or redirected, the NCR-MT 520A can transmit desired cell information to the connected cell (gNB 200), and the gNB 200 can cause the NCR-MT 520A to perform handover or redirection to a desired cell.

[0119] Figure 13 is a diagram illustrating an operation example of the NCR-MT 520A according to the first embodiment.

[0120] In step S101, the NCR-MT 520A in an RRC idle state in the cell initiates an RRC connection establishment procedure with the cell, and establishes an RRC connection with the cell (gNB 200).

[0121] In step S102, the NCR-MT 520A determines whether the connected cell is a desired cell.

[0122] When the connected cell is the desired cell (step S102: YES), in step S103, the NCR-MT 520A incorporates the NCR node indication information into a message, and transmits the message to the connected cell (gNB 200). As described above, the message can be a Msg5. The message can be a response to the UE capability enquiry (UE capability response).

[0123] On the other hand, when the connected cell is not the desired cell (step S102: NO), in step S104, the NCR-MT 520A transmits information without NCR node indication to the connected cell (gNB 200). For example, the NCR-MT 520A does not incorporate the NCR node indication IE into the response to the UE capability enquiry (UE capability response) message.

[0124] In step S104, the NCR-MT 520A (NCR device 500A) can request the gNB 200 to release the RRC connection. For example, the NCR-MT 520A (NCR device 500A) can initiate a procedure for connection release at the NAS layer. In this procedure, the NAS layer of the NCR-MT 520A (NCR device 500A) can transmit a NAS message including information indicating connection release to the AMF 300A. Alternatively, the NCR-MT 520A can transmit a UE assistance information message including a release preference IE to the gNB 200, in which “idle”, “inactive” or “disconnected” is set as the preferred RRC state. In this procedure, the NCR-MT 520A can notify the reason for the RRC connection release. For example, the reason can be information for notifying “due to connection to a non-desired cell” and / or “due to reconnection to a desired cell”.

[0125] In the description of the operation according to the first embodiment, it is assumed that the NCR-MT 520A is transitioned from the RRC idle state to the RRC connected state. However, it can also be assumed that the NCR-MT 520A is transitioned from the RRC inactive state to the RRC connected state. In this case, the above-described RRC idle state can be understood as the RRC inactive state, and the above-described RRC connection establishment (RRC setup) can be understood as the RRC connection resume (RRC resume). The same applies to the variants to be described below.

[0126] (1.5) Variants of the operation according to the first embodiment

[0127] The variants of the first embodiment will be described mainly with respect to the differences from the above-described first embodiment. The present variants can be implemented in combination with the above-described first embodiment.

[0128] In the above first embodiment, the gNB 200 has transmitted the NCR configuration information (NCR control signal) to the NCR-MT 520A based on the NCR node indication from the NCR-MT 520A (NCR device 500A). That is, the gNB 200 uses the NCR node indication to determine whether the NCR configuration is needed. Therefore, when the new NCR configuration information is not needed (for example, when the NCR device 500A already has valid NCR configuration information), it is considered that the NCR-MT 520A can not transmit the NCR node indication to the gNB 200. This can suppress the occurrence of unnecessary signaling.

[0129] In the present embodiment, the NCR-MT 520A determines whether the NCR configuration information, which is the configuration information of the NCR device 500A, needs to be acquired from the connected cell (gNB 200). In response to determining that it is necessary to acquire the NCR configuration information, the NCR-MT 520A transmits a message including the NCR node indication to the connected cell (gNB 200).

[0130] For example, the NCR-MT 520A can determine whether the NCR device 500A has configuration information that can be used in the connected cell. In response to determining that the NCR device 500A does not have configuration information that can be used in the connected cell, the NCR-MT 520A transmits a message including the NCR node indication to the connected cell (gNB 200).

[0131] The NCR-MT 520A can determine whether the NCR-Fwd 510A is on. In response to determining that the NCR-Fwd 510A is on, the NCR-MT 520A transmits a message including the NCR node indication to the connected cell (gNB 200).

[0132] The NCR-MT 520A can determine whether to perform a relay operation that depends on the NCR control signal from the network 5. Here, the relay operation that does not depend on the NCR control signal from the network 5 can be the same as the RF repeater of the related art. In response to determining to perform the relay operation that depends on the NCR control signal from the network 5, the NCR-MT 520A can transmit a message including the NCR node indication to the connected cell (gNB 200).

[0133] Figure 14is a diagram showing an operation example of the NCR-MT 520A according to a variation of the first embodiment. Before this operation, the NCR-MT 520A can receive NCR configuration information from the network 5. The NCR configuration information can include information on a valid area, which is an area in which the NCR configuration information is valid. The valid area can be an area including one or a plurality of cells, or can be an area including one gNB 200. After receiving the NCR configuration information, the NCR-MT 520A can move to another cell (for example, by cell reselection) while keeping the NCR configuration information in the RRC idle state or the RRC inactive state.

[0134] In step S111, the NCR-MT 520A in the RRC idle state in the cell initiates an RRC connection establishment procedure with the cell, and establishes an RRC connection with the cell (gNB 200).

[0135] In step S112, the NCR-MT 520A determines whether the NCR configuration information is necessary. Specifically, the NCR-MT 520A determines whether it is necessary to acquire the NCR configuration information from the connected cell.

[0136] In step S112, the NCR-MT 520A can perform the determination based on whether the valid configuration exists. When the already received NCR configuration information is valid (for example, when the connected cell is within the valid area), the NCR-MT 520A determines that the NCR configuration information is not necessary. On the other hand, when the already received NCR configuration information is not valid, the NCR-MT 520A determines that the NCR configuration information is necessary.

[0137] In step S112, the NCR-MT 520A can perform the determination based on the relay operation state. When the NCR-Fwd 510A is off, the NCR-MT 520A determines that the NCR configuration information is necessary. For example, when the NCR-MT 520A is in the RRC idle state and the NCR-Fwd 510A is configured to be off when reselecting another cell, the NCR-Fwd 510A can be off. On the other hand, when the NCR-Fwd 510A is operating using the already received NCR configuration information, the NCR-MT 520A determines that the NCR configuration information is not necessary. For example, when the NCR-MT 520A is in the RRC inactive state, the NCR-Fwd 510A can operate according to the already received NCR configuration information.

[0138] In step S112, the NCR-MT 520A can perform the determination based on the operating state of the host device. When the NCR device 500A functions as a network control forwarder, the NCR-MT 520A determines that the NCR configuration information is necessary. On the other hand, when the NCR device 500A functions as a legacy RF forwarder without network control, the NCR-MT 520A determines that the NCR configuration information is not necessary.

[0139] When it is determined that the NCR configuration information is necessary (step S112: Yes), in step S113, the NCR-MT 520A transmits a message including the NCR node indication to the connected cell (gNB 200). When the connected cell (gNB 200) receives the NCR node indication, the connected cell can transmit the NCR configuration information to the NCR-MT 520A.

[0140] On the other hand, when it is determined that the NCR configuration information is not necessary (step S112: No), in step S114, the NCR-MT 520A does not transmit the NCR node indication to the connected cell (gNB 200). The NCR-MT 520A can transmit a message not including the NCR node indication to the connected cell (gNB 200). When the connected cell (gNB 200) does not receive the NCR node indication, the connected cell can not transmit the NCR configuration information to the NCR-MT 520A.

[0141] (2) Second Embodiment

[0142] The second embodiment will be described mainly focusing on the difference from the above-described first embodiment. The second embodiment can be implemented in combination with the first embodiment.

[0143] The second embodiment relates to RRC connection reestablishment performed by the NCR-MT 520A in the RRC connected state. Figure 15 is a diagram illustrating the RRC connection reestablishment in the NCR-MT 520A.

[0144] The NCR-MT 520A initiates an RRC connection reestablishment procedure in response to detecting (declaring) a radio link failure (RLF). In the illustrated example, the NCR-MT 520A in an RRC connected state in cell a of the gNB 200a detects (declares) an RLF in cell a. The NCR-MT 520A detects (declares) the RLF, for example, when a radio problem is detected and the radio problem is not recovered during a first timer (e.g., timer T310) expires. When the NCR-MT 520A detects the RLF, the NCR-MT 520A starts a second timer (e.g., timer T311) and attempts cell selection and RRC connection reestablishment during the second timer is operating. If the RRC connection reestablishment is not successful before the second timer expires, the NCR-MT 520A transitions to an RRC idle state.

[0145] Here, the NCR-MT 520A sends an RRC reestablishment request message to the cell b (gNB 200b) selected in the cell selection after the RLF in order to attempt the RRC connection reestablishment. Figure 16 A diagram illustrating an RRC Reestablishment Request message defined in the 3GPP RRC Technical Specification (TS 38.331) is shown. The RRC Reestablishment Request message includes a “ReestabUE-Identity” which is a transmission source identifier of the RRC Reestablishment Request message so that the gNB 200 at the receiving side identifies the UE context. In the current technical specification, the “ReestabUE-Identity” includes a cell RNTI (C-RNTI) assigned to the transmission source of the RRC Reestablishment Request message.

[0146] In a second embodiment, the NCR-MT 520A sending the RRC Reestablishment Request message incorporates an NCR-RNTI into the RRC Reestablishment Request message, which is an NCR device specific RNTI instead of the C-RNTI. Alternatively, the NCR-MT 520A sending the RRC Reestablishment Request message can incorporate the NCR-RNTI into the RRC Reestablishment Request message together with the C-RNTI. This allows the gNB 200 at the receiving side (i.e., the gNB 200 as the RRC connection reestablishment destination) to implicitly know that the transmission source of the RRC Reestablishment Request message is the NCR-MT 520A based on the NCR-RNTI. This allows the gNB 200 to perform operations such as prioritizing the RRC connection reestablishment of the NCR-MT 520A.

[0147] Alternatively, the NCR-MT 520A can incorporate the above NCR node indication into the "ReestabUE-Identity". The NCR-MT 520A can incorporate the NCR node indication into an information element other than the "ReestabUE-Identity" (e.g., "ReestablishmentCause" indicating a reestablishment cause). In other words, the information to be incorporated into the RRC reestablishment request message can be information allowing the gNB 200 at the receiving side (i.e., the gNB 200 as the RRC connection reestablishment destination) to implicitly or explicitly know that the transmission source of the RRC reestablishment request message is the NCR-MT 520A.

[0148] The communication method according to the second embodiment is a method used in the NCR apparatus 500A including: the NCR-Fwd 510A performing a relay operation of relaying a wireless signal transmitted between the network 5 and the UE 100; and the NCR-MT 520A receiving, from the network 5, an NCR control signal for controlling the NCR-Fwd 510A. First, the NCR-MT 520A in an RRC connected state initiates an RRC connection reestablishment procedure for a cell included in the network 5 (also referred to as a "reestablishment cell". Second, the NCR-MT 520A incorporates an NCR-RNTI assigned to the host apparatus (NCR apparatus) or an NCR node indication indicating that the host apparatus is the NCR apparatus into an RRC reestablishment request message. Third, the NCR-MT 520A transmits the RRC reestablishment request message including the NCR-RNTI or the NCR node indication to the reestablishment cell (gNB 200).

[0149] The NCR-MT 520A can handle a plurality of NCR-Fwds 510A to which respective NCR-RNTIs are assigned. That is, the NCR-MT 520A can include a plurality of NCR-Fwds 510A to which respective NCR-RNTIs are assigned. In this case, the NCR-MT 520A can incorporate the NCR-RNTIs of the plurality of respective NCR-Fwds 510A (the NCR-RNTIs of all the NCR-Fwds 510A) or the NCR-RNTI of a specific NCR-Fwd 510A among the plurality of NCR-Fwds 510A into the RRC reestablishment request message.

[0150] Figure 17 is a diagram illustrating an operation example of the NCR-MT 520A according to the second embodiment.

[0151] In step S201, the NCR-MT 520A in the RRC connected state detects RLF with a cell and initiates an RRC connection reestablishment procedure. The NCR-MT 520A selects a cell whose radio quality satisfies a predetermined criterion as a reestablishment cell through cell selection.

[0152] In step S202, the NCR-MT 520A incorporates (sets) the NCR-RNTI into the RRC reestablishment request message. The NCR-MT 520A can incorporate the NCR node indication into the RRC reestablishment request message. Here, the NCR-MT 520A can incorporate the NCR-RNTI (or the NCR node indication) into the RRC reestablishment request message only when the reestablishment cell broadcasts the NCR support IE (i.e., information indicating support for the NCR device) in the SIB1.

[0153] Here, when the NCR-MT 520A handles only one NCR-Fwd 510A, the NCR-MT 520A incorporates the NCR-RNTI associated with the NCR-Fwd 510A (or the NCR-MT 520A) into the RRC reestablishment request message.

[0154] On the other hand, when the NCR-MT 520A handles a plurality of NCR-Fwds 510A, a plurality of NCR-RNTIs can be configured. In this case, the NCR-MT 520A can incorporate all of the configured NCR-RNTIs into the RRC reestablishment request message. Alternatively, the NCR-MT 520A can incorporate only one (or some) of the plurality of configured NCR-RNTIs into the RRC reestablishment request message. For example, when a plurality of NCR-RNTIs are configured, the NCR-MT 520A can incorporate the NCR-RNTI of the first entry in the configuration list into the RRC reestablishment request message. In the case of carrier aggregation or dual connectivity, the NCR-MT 520A can incorporate the NCR-RNTI associated with the NCR-Fwd 510A of the cell in the primary cell (PCell) or the master cell group (MCG) of the relay NCR-MT 520A into the RRC reestablishment request message. Alternatively, the NCR-RNTI to be incorporated into the RRC reestablishment request message can be set to the NCR-MT 520A in advance from the gNB 200.

[0155] In step S203, the NCR-MT 520A transmits an RRC reestablishment request message including the NCR-RNTI (or NCR node indication) to the reestablishment cell (gNB 200). The reestablishment cell (gNB 200) recognizes that the message has been transmitted from the NCR-MT 520A based on the NCR-RNTI (or NCR node indication). The reestablishment cell (gNB 200) can perform a process such as preferentially receiving the RRC reestablishment request of the NCR-MT 520A. When the cell in which the RLF has occurred and the reestablishment cell belong to different gNBs 200, the gNB 200 managing the reestablishment cell can transmit a "RETRIEVE UE CONTEXT REQUEST" message for requesting transmission of the UE context of the NCR-MT 520A (NCR device 500A) to the gNB 200 managing the cell in which the RLF has occurred, over the Xn interface. The gNB 200 managing the reestablishment cell can incorporate the NCR-RNTI received in the RRC reestablishment request message into the "RETRIEVE UE CONTEXT REQUEST" message as the UE context ID. The gNB 200 managing the cell in which the RLF has occurred can transmit the UE context identified by the UE context ID to the gNB 200 managing the reestablishment cell. The UE context can be an NCR-MT context indicating the configuration of the NCR-MT and / or an NCR-Fwd context indicating the configuration (and / or control state) of the NCR-Fwd.

[0156] (3) Third Embodiment

[0157] Next, differences between the third embodiment and the above-described embodiments will mainly be described. As shown in FIG. 10, the relay device according to the third embodiment is a reconfigurable intelligent surface (RIS) device 500B that changes the propagation direction of an incident radio wave (radio signal) by reflection or refraction. The "NCR" in the above-described embodiments can be understood as "RIS". Figure 18

[0158] The RIS is a relay device capable of performing beamforming (directionality control) in a similar manner to the NCR by changing the characteristics of a metamaterial (hereinafter, also referred to as "RIS-Fwd"). The RIS can be capable of changing the range (distance) of a beam by controlling the reflection direction and / or refraction direction of each unit element. For example, the RIS can have a configuration capable of controlling the reflection direction and / or refraction direction of each unit element, and focus on a near UE (direct a beam) or focus on a far UE (direct a beam).

[0159] ​The RIS device 500B includes 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 cooperates with the gNB 200 to control the RIS-Fwd 510B by establishing a wireless connection with the gNB 200 and performing wireless communication with the gNB 200. The RIS-Fwd 510B can be a reflective RIS. Such a RIS-Fwd 510B reflects an incident radio wave to change the direction of propagation of the radio wave. Here, the reflection angle of the radio signal can be variably set. The RIS-Fwd 510B reflects a radio wave incident from the gNB 200 toward the UE 100. The RIS-Fwd 510B can be a transmissive RIS. Such a RIS-Fwd 510B refracts an incident radio wave to change the direction of propagation of the radio wave. Here, the refraction angle of the radio signal can be variably set.

[0160] Figure 19 is a diagram showing an example of the configuration of the RIS-Fwd (relay device) 510B and the RIS-MT (control terminal) 520B of the third embodiment. The RIS-MT 520B has a receiver 521, a transmitter 522, and a controller 523. Such a configuration is the same as that of the above-described embodiments. The RIS-Fwd 510B includes an RIS 511B and an RIS controller 512B. The RIS 511B is a metasurface configured using a structure that is extremely small with respect to the wavelength of a radio wave. For example, the RIS 511B is configured by arranging a structure that is extremely small with respect to the wavelength of a radio wave in an array, and the direction of a reflected wave and / or the beam shape can be arbitrarily designed by making the structure have different shapes depending on the arrangement position of the structure. The RIS 511B can be a transparent dynamic metasurface. The RIS 511B can be configured by stacking a transparent glass substrate on a transparent version of a metasurface substrate regularly provided with a large number of minute structures, and can be able to dynamically control the following three modes: a mode of transmitting an incident radio signal, a mode of transmitting a part of the radio signal and reflecting a part thereof, and a mode of reflecting all of the radio signal, by finely moving the stacked glass substrate. The RIS controller 512B controls the RIS 511B in response to an RIS control signal from the controller 523 in the RIS-MT 520B. The RIS controller 512B can include at least one processor and at least one actuator. The processor interprets the RIS control signal from the controller 523 in the RIS-MT 520B to drive the actuator in response to the RIS control signal.

[0161] In the third embodiment, a "RIS node indication" indicating that the host device is a RIS device can be used instead of the above-described "NCR node indication". The "RIS node indication" can be defined as information different from the "NCR node indication".

[0162] (4) Other Embodiments

[0163] In the above-described embodiments, an example in which the relay device that performs the relay transmission is the NCR device 500A or the RIS device 500B has been described. However, the relay device that performs the relay transmission is not limited to the NCR device 500A or the RIS device 500B, and can be an Integrated Access and Backhaul (IAB) node defined in the technical specification of 3GPP.

[0164] Each of the above-described operation flows is not limited to be performed individually and independently, but can be performed by combining two or more operation flows. For example, some steps in one operation flow can be added to another operation flow, or some steps in one operation flow can be replaced with some steps in another operation flow. In each flow, not all steps are necessarily performed, but only some steps can be performed.

[0165] In the above-described embodiments, an example in which the base station is an NR base station (gNB) has been described, but the base station can be an LTE base station (eNB). The base station can be a relay node such as an IAB node. The base station can be a Distributed Unit (DU) of the IAB node. Furthermore, the UE 100 can be a Mobile Terminal (MT) of the IAB node.

[0166] A program that causes a computer to perform each process performed by the communication device (for example, the UE 100 (NCR-MT 520A and RIS-MT 520B) or the gNB 200) according to the above-described embodiments can be provided. The program can be recorded in a computer-readable medium. The program is enabled to be installed on a computer using the computer-readable medium. Here, the computer-readable medium on which the program is recorded can be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and can be, for example, a recording medium such as a CD-ROM or a DVD-ROM. A circuit for performing the processing to be performed by the UE 100 or the gNB 200 can be integrated, and at least a part of the UE 100 or the gNB 200 can be implemented as a semiconductor integrated circuit (chipset, System on Chip (SoC)).

[0167] Furthermore, the term "network node" mainly refers to a base station, but can also refer to a core network device or a part (CU, DU, or RU) of a base station. The network node can be configured by a combination of at least a part of a core network device and at least a part of a base station.

[0168] A program for causing a computer to perform each processing performed by the user equipment (UE) 100, the base station (gNB) 200, or the relay device can be provided. The program can be recorded in a computer-readable medium. The program is enabled to be installed on a computer using the computer-readable medium. Here, the computer-readable medium on which the program is recorded can be a non-transitory recording medium. The non-transitory recording medium is not specifically limited, and can be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, a circuit for performing each processing performed by the UE 100, the gNB 200, or the relay device can be integrated, and at least a part of the UE 100, the gNB 200, or the relay device can be configured as a semiconductor integrated circuit (chipset or a system on chip (SoC)).

[0169] The functions implemented by the user equipment 100, the base station 200 (network node), or the relay device can be implemented in a circuit or processing circuitry including a general-purpose processor, a special purpose processor, an integrated circuit, an application-specific integrated circuit (ASIC), a central processing unit (CPU), a conventional circuit, and / or a combination thereof programmed to implement the functions. The processor can include transistors and other circuits, and can be regarded as a circuit or processing circuitry. The processor can be a programmed processor executing a program stored in a memory. The circuit, unit, and device herein are hardware programmed to implement the functions, or hardware executing the functions. The hardware can be any hardware disclosed herein, or any hardware programmed to implement or known to execute the functions. When the hardware is a processor regarded as a certain type of circuit, the circuit, device, or unit is a combination of the hardware and software for configuring the hardware and / or the processor.

[0170] The phrase "based on" and "in response to" as used in the present disclosure are not meant to exclude the existence of other elements that are not explicitly described. The phrase "based on" denotes "based on only" and "based on at least in part" both. The phrase "in response to" denotes "in response to only" and "in response to at least in part" both. The term "include" and its variations are meant to be "comprise only" unless otherwise explicitly indicated. The term "or" as used in the present disclosure is not meant to be "exclusive or". In addition, any reference in the present disclosure to names of elements using such names as "first" and "second" generally does not limit the number or order of such elements. Such names can be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to first and second elements does not mean that there can be only two elements or that a first element needs to precede a second element. For example, when English articles such as "a", "an" and "the" are added in the present disclosure by translation, these articles include plural unless the context clearly indicates otherwise.

[0171] The embodiments have been described in detail above with reference to the accompanying drawings, but the specific configurations are not limited to the above-described configurations, and various design changes can be made without departing from the gist of the present disclosure.

[0172] This application claims priority to U.S. Provisional Application No. 63 / 445103, filed February 13, 2023, the entire contents of which are incorporated herein by reference.

[0173] (5) Supplement

[0174] Features related to the above-described embodiments are described below as a supplement.

[0175] (Supplement 1)

[0176] A communication method for use in a relay device including a relay apparatus configured to perform a relay operation of relaying radio signals transmitted between a network and a user equipment, and a control terminal configured to receive a control signal for controlling the relay apparatus from the network, the communication method including the steps of:

[0177] The control terminal transitions to a radio resource control (RRC) connected state in a cell included in the network;

[0178] determining whether a condition for incorporating notification information indicating that a host device is the relay device into a message to be transmitted from the control terminal to the cell is satisfied; and

[0179] in response to determining that the condition is satisfied, transmitting the message including the notification information from the control terminal to the cell.

[0180] (Supplement 2)

[0181] The communication method according to Supplement 1, wherein the message is an RRC setup complete message or a user equipment (UE) capability response message.

[0182] (Supplement 3)

[0183] The communication method according to Supplement 1 or 2,

[0184] wherein the determining step includes steps of determining whether the cell is an expected cell defined as a connection destination of the relay device, and

[0185] the transmitting step includes a step of, in response to determining that the cell is the expected cell, transmitting the message including the notification information from the control terminal to the cell.

[0186] (Supplement 4)

[0187] The communication method according to Supplement 3, further comprising a step of:

[0188] in response to determining that the cell is not the expected cell, transmitting, from the control terminal to the cell, information for prompting the network to transition from the RRC connected state to another RRC state.

[0189] (Supplement 5)

[0190] The communication method according to any one of Supplements 1 to 4,

[0191] wherein the determining step includes steps of determining whether there is a need to acquire configuration information of the relay device from the cell, and

[0192] the transmitting step includes a step of, in response to determining that there is the need, transmitting the message including the notification information from the control terminal to the cell.

[0193] (Supplement 6)

[0194] The communication method according to Supplement 5,

[0195] the determining step includes steps of determining whether the relay device has configuration information available in the cell, and

[0196] the transmitting step includes a step of, when it is determined that the relay device does not have configuration information available in the cell, transmitting the message including the notification information from the control terminal to the cell.

[0197] (Supplement 7)

[0198] The communication method according to Supplement 5 or 6,

[0199] wherein the determining step includes a step of determining whether the relay device is on, and

[0200] The transmitting step includes a step of transmitting, from the control terminal to the cell, the message including the notification information in response to a determination that the relay device is on.

[0201] (Supplement 8)

[0202] The communication method according to any one of Supplements 5 to 7,

[0203] wherein the determining step includes a step of determining whether to perform a relay operation depending on the control signal from the network; and

[0204] The transmitting step includes a step of transmitting, from the control terminal to the cell, the message including the notification information in response to a determination that the relay operation depending on the control signal from the network is to be performed.

[0205] (Supplement 9)

[0206] A communication method for use in a relay apparatus including a relay device configured to perform a relay operation of relaying radio signals transmitted between a network and a user equipment, and a control terminal configured to receive a control signal for controlling the relay device from the network, the communication method including the steps of:

[0207] The control terminal in a radio resource control (RRC) connected state initiates an RRC connection reestablishment procedure for a cell included in the network;

[0208] incorporating, into an RRC reestablishment request message, a relay apparatus-specific radio network temporary identifier (RNTI) assigned to the relay apparatus or notification information indicating that the host apparatus is the relay apparatus; and

[0209] transmitting, from the control terminal to the cell, the RRC reestablishment request message including the relay apparatus-specific RNTI or the notification information.

[0210] (Supplement 10)

[0211] The communication method according to Supplementary Note 9, wherein, when the control terminal handles a plurality of relay devices each of which is assigned with the relay device-specific RNTI, the step of including comprises the step of incorporating the relay device-specific RNTI of each of the plurality of relay devices or the relay device-specific RNTI of a specific one of the plurality of relay devices into the RRC reestablishment request message.

[0212] (6) Supplementary Notes

[0213] 1. Introduction

[0214] In RAN #97e, an agreement has been reached on the work item of Network Controlled Relay (NCR). RAN2 #119bis-e and RAN2 #120 have made significant progress in many protocols.

[0215] In this supplementary note, the remaining issues / potential issues of RAN2 on NCR are discussed.

[0216] 2. Discussion

[0217] 2.1. NCR-Fwd on / off related matters

[0218] 2.1.1. RRC release related open issues

[0219] In RAN2 #120, the following agreements were reached.

[0220] For NCR-Fwd on / off:

[0221] NCR-Fwd can be turned on or off according to the assistance control information received from the gNB when the NCR-MT is in RRC connected mode.

[0222] NCR-Fwd can be turned on or off according to the last configuration received from the gNB after the NCR-MT enters RRC inactive mode.

[0223] For release to RRC idle state, further study is needed.

[0224] RLF of NCR-MT:

[0225] After the NCR-MT declares RLF, the NCR-MT performs cell selection and triggers RRC reestablishment;

[0226] When no suitable cell is found and the NCR-MT is in RRC idle state, NCR-Fwd is turned off; and

[0227] During the RRC reestablishment procedure, NCR-Fwd is turned off.

[0228] One open issue is whether it is reasonable for the gNB to release the NCR-MT to IDLE state. According to the discussion in RAN2 #120, there are two opinions for the RRC state of the NCR-MT:

[0229] Assumption 1: NCR-MT is basically in CONNECTED state:

[0230] Under this assumption, the gNB will not release the NCR-MT because the NCR must always be controllable by the network. Therefore, the NCR-MT can only be in IDLE state at initial access (power on) or RLF (to be precise, at RRC re-establishment failure). Since the state of NCR-Fwd due to initial access is clear (i.e., NCR-Fwd should be off) and the state due to RLF has been agreed (i.e., NCR-Fwd should also be off), there is no need to define additional NCR operation when the gNB releases the NCR-MT to IDLE state.

[0231] Assumption 2: gNB can release NCR-MT:

[0232] In this assumption, since RAN2 has already agreed on the RRC IDLE state, the gNB can release the NCR-MT for NCR power saving, signaling overhead reduction, etc. Therefore, the NCR-MT can become IDLE state due to all traditional conditions such as initial access, RLF, and RRC release. Some companies have indicated that after transitioning to IDLE state, the NCR-Fwd can fall back to a traditional RF repeater.

[0233] Observation 1: There are two controversies about whether to define the ON / OFF operation of NCR-Fwd and whether the gNB should respond to the NCR-MT returning to IDLE state.

[0234] Assumption 1 is very simple because the NCR is always under network control by assistance control information and RRC signaling, so the gNB does not need to release the NCR-MT in normal state. However, in intelligent gNB implementation, the NCR-MT can be released under certain conditions, such as for power saving and signaling overhead reduction, similar to assumption 2. Therefore, the specification should allow various gNB implementations, and in general should explicitly define the NCR operation during the IDLE state according to RRC release.

[0235] Observation 2: In normal operation, the gNB does not need to put the NCR-MT in IDLE state, but depending on the gNB implementation under certain conditions, RRC release can be allowed.

[0236] On the other hand, for the operation of NCR in inactive state, after RAN2 agreed that NCR-MT enters RRC inactive mode with WA: NCR-MT enters RRC inactive mode, NCR-Fwd can be turned on or off according to the last configuration received from gNB. That is, since gNB can always page NCR-MT by RAN paging, it is reasonable to keep the operation of NCR consistent with the operation in connected state (i.e., “no specific functional enhancements”), which RAN2 agreed. It will be understood that NCR-MT in idle state cannot be controlled by gNB since CN paging is needed to establish RRC connection for sending assistance control information and the configuration. Therefore, the operation of NCR in idle state needs to be considered separately from the inactive state.

[0237] Observation 3: The operation of NCR-Fwd in inactive state is consistent with that in connected state, and should be different from that in idle state.

[0238] In addition, as mentioned in assumption 2 above, when NCR is not controlled by gNB, the inventors believe that NCR can fall back to a legacy RF repeater. Since RAN2 agreed that “NCR-Fwd can be turned on or off according to the last configuration received from gNB”, it is clear that NCR in inactive state cannot fall back to a legacy RF repeater. In other words, it is only possible to fall back to a legacy RF repeater when NCR-MT is in idle state.

[0239] In terms of network control, a legacy RF repeater is an implementation technique. Therefore, when NCR falls back to a legacy RF repeater, it is no longer a network-controlled repeater. In other words, when a node is no longer an NCR (e.g., when NCR-MT transitions to idle state), the operation of NCR can be any operation depending on implementation.

[0240] Observation 4: According to the current protocol, NCR in inactive state cannot fall back to a legacy RF repeater. That is, the last configuration received from gNB must be followed, which RAN2 agreed.

[0241] Observation 5: When NCR is not controlled by gNB (e.g., when NCR-MT transitions to idle state), from the perspective of network control, the node can not be considered as an NCR.

[0242] As discussed in observation 2 and observation 3, the operation of NCR in idle state according to RRC release should be made clear and distinguished from that in inactive state in order to support various gNB implementations.

[0243] As mentioned above, for NCR operation due to RLF, RAN2 has agreed that "NCR-Fwd shall be turned off when no suitable cell is found and NCR-MT is in RRC idle state". Based on this agreement, there is no significant reason to differentiate the transition to idle state due to RRC release according to RLF. Therefore, when NCR-MT transitions to idle state, NCR-Fwd shall be turned off regardless of the reason of state transition.

[0244] As this operation does not exclude implementation-specific operations, the node can operate as a legacy RF repeater (i.e., "fallback" operation) even if it is not considered as an NCR (such as when NCR-MT is in idle state).

[0245] Proposal 1: RAN2 shall agree to turn off NCR-Fwd when NCR-MT is released to idle state (e.g., in case of RLF).

[0246] 2.1.2. Potential issues for RRC re-establishment

[0247] Currently, the RAN2 agreement only assumes that NCR-MT is always in the same cell. However, even if NCR mobility is not supported, NCR-MT can change the serving / resident cell due to radio conditions such as FR2 blocking. Therefore, it is worth discussing what happens when (re)selecting a cell with a different NCR-MT.

[0248] RAN2 #120 agreed the following description.

[0249] For NCR-MT RLF:

[0250] After NCR-MT declares RLF, NCR-MT performs cell selection and triggers RRC re-establishment;

[0251] When no suitable cell is found and NCR-MT is in RRC idle state, NCR-Fwd is turned off; and

[0252] During the RRC re-establishment procedure, NCR-Fwd is turned off.

[0253] For RRC re-establishment, the following steps and potential issues are determined according to the agreement:

[0254] Step 1: NCR-MT declares RLF and starts cell selection and RRC re-establishment. During these procedures, NCR-Fwd is turned off as already agreed.

[0255] Step 2a: When NCR-MT selects the same cell and successfully completes RRC re-establishment, NCR-Fwd returns to the on state according to the last configuration.

[0256] Step 2b: When the NCR-MT selects a different cell and successfully completes RRC re-establishment, determine whether NCR-Fwd should be switched off.

[0257] For potential issue of Step 2a, since the NCR has a configuration provided by the same cell, it is generally considered that NCR-Fwd is able to resume operation with the last configuration. In this case, the signaling overhead for reconfiguring the NCR can be avoided.

[0258] On the other hand, since RLF has occurred in the NCR-MT, the gNB can not prioritize this automatic resume of NCR-Fwd operation and, for example, in this case, the gNB can change the NCR configuration. Therefore, it is an option for the gNB to be explicitly instructed whether to resume NCR-Fwd operation with the last configuration or to switch off NCR-Fwd, e.g., regarding whether to perform RRC reconfiguration in advance or RRC re-establishment in time.

[0259] As another option, NCR-Fwd can be considered to be switched off even after successful RRC re-establishment with the same cell. This can be a definition that is hardcoded or an indication by the gNB as described above. In this case, when the NCR-MT declares RLF (or initiates the RRC re-establishment procedure), the last RRC configuration (and the last indication of using assistance control information) should be discarded.

[0260] Proposal 2: RAN2 should discuss whether NCR-Fwd should resume operation with the last configuration when RRC re-establishment to the same cell is successful.

[0261] For potential issue of Step 2b, the last configuration of the NCR-MT is provided by the last serving cell, not the new cell. Therefore, it is easy to provide the NCR with a new configuration from the new cell. In this case, the NCR-MT needs to discard the last RRC configuration (and the last indication of using assistance control information) when it selects a different cell (or when it sends an RRC re-establishment request to a different cell).

[0262] Proposal 3: RAN2 should discuss whether the NCR-MT will discard the last configuration when it initiates RRC re-establishment to a different cell.

[0263] 2.1.3. Potential issues of cell reselection

[0264] In RAN2 #120, the following agreements were reached.

[0265] NCR-MT basically supports cell reselection and RRM measurement in RRC idle state and RRC inactive state.

[0266] In Rel-18, NCR-MT does not support handover and RRM measurement in RRC connected state.

[0267] One potential issue with cell reselection is the priority handling for specific cells. For legacy RF repeaters, the deployment is determined by network planning and / or field RF measurements. Therefore, it is assumed that for each NCR, the desired cells are planned, i.e., the network planning determines the relationship between serving cells and NCRs. These desired cells are likely to be set to the NCR by OAM.

[0268] Observation 6: NCRs can be configured with desired cells, e.g., by OAM.

[0269] In this case, the NCR-MT should avoid camping on (or connecting to) non-desired cells. Therefore, the NCR-MT should prioritize desired cells over non-desired cells. While cell selection generally allows implementation-specific operations (i.e., IAB-MT selects any suitable cell as long as the cell is appropriate), cell reselection consists of a set of deterministic operations according to the specification (inter-frequency cell reselection criteria, ranking, etc.). Therefore, standard support is needed to ensure the network planning of NCRs.

[0270] The simplest approach is to enhance the priority handling of cell reselection. The NCR-MT can prioritize desired cells similar to MBS frequencies or sidelink frequencies (the priority can vary depending on the UE’s preference). This enhancement allows the NCR-MT to continuously perform measurements to attempt to reselect a desired cell and minimizes the likelihood of camping on / connecting to a non-desired cell.

[0271] Another approach is to define NCR-specific offsets for intra-frequency cell reselection (i.e., within the R standard). This is because, when the inventors believe that NCRs are likely to be deployed at the cell edge (i.e., the coverage of a macro cell can be extended), the ranking can lead the NCR-MT to reselect a non-desired cell on the same frequency.

[0272] Proposal 4: RAN2 should discuss whether to allow NCR-MT to prioritize desired cells (i.e., cells of interest) in the cell reselection procedure.

[0273] Another potential issue is mobility in inactive mode. RAN2 agreed that “after the NCR-MT transitions to RRC inactive mode, NCR-Fwd can be turned on or off according to the last configuration received from the gNB”. Based on this agreement, after the NCR-MT becomes inactive, the NCR-MT can reselect to a different cell due to, e.g., obstruction of FR2. When NCR-Fwd is off, there is no issue, but when NCR-Fwd is on, the same issue as described in Section 2.1.2 can occur.

[0274] Observation 7: When NCR-MT is in non-active state with NCR-Fwd turned on, it is possible to reselect to a different cell.

[0275] In this scenario, it is necessary to clarify how NCR should behave. Possible options are as follows:

[0276] Option 1: Based on current protocol agreements, NCR-Fwd remains turned on with the last configuration.

[0277] Option 2: Turn off NCR-Fwd (or NCR-MT discard the last configuration), similar to suggestion 3 above.

[0278] Since Option 1 is the same as the protocol agreement “NCR-Fwd can be turned on or off based on the last configuration received from gNB after NCR-MT has entered non-active mode”, and “Any support of WA:RRC inactive mode without specific functional enhancements”, Option 1 is likely to be valid as the standardization effort is minimized.

[0279] From a technical point of view, Option 2 is considered as a reasonable behavior. This is because the configuration has already been provided by another cell (i.e., the last serving cell), and it is somewhat unnatural for NCR-Fwd to operate without recognizing the configuration of the current cell. This is because the reselected cell can have different resources available for NCR. Therefore, since RAN2 also agrees that cell reselection is mandatory to support, it can be said that adopting Option 2 is a kind of fail-safe mechanism.

[0280] Based on the above discussion, Option 2 is more desirable from the point of view of technical reasonableness.

[0281] Suggestion 5: RAN2 should discuss whether NCR-Fwd should be turned off when NCR-MT reselects to a different cell.

[0282] Another potential issue is when NCR-MT connects to an unexpected cell after cell reselection or RRC reestablishment. It is necessary for NCR to reconnect to the desired cell. From the gNB’s point of view, the RRC connection with NCR-MT eventually makes no sense. RAN2 has agreed that “NCR-MT does not support handover”. Therefore, the only way the gNB can perform is to release NCR-MT, but since NCR-MT will follow the cell reselection procedure after transitioning to the idle state, it cannot be guaranteed that NCR-MT will camp on / reconnect to the desired cell. In this case, redirection can be enhanced to make NCR-MT camp on the desired cell. However, whether the gNB can acquire the desired cell of NCR (e.g., a cell set by OAM) is still a problem.

[0283] Proposal 6: RAN2 should discuss whether to enhance redirection in order to move NCR-MT from a desired cell to a desired cell (instead of handover).

[0284] 2.2. Access control issues

[0285] 2.2.1. Open issues regarding NPN support

[0286] In RAN2 #120, it was agreed to consider the following:

[0287] Introduce NCR support indication per PLMN in SIB1.

[0288] The inventors believe that NCR deployment in NPN is also beneficial and has potential market demand. For example, in Japan, it is planned to plan NPN frequencies in high frequency bands of FR1 (4.9 GHz) and FR2 (28 GHz). At such frequencies, coverage extension of NCR is usually very important. As another example, due to the local / closed nature of NPN, NPN can exhibit higher performance in URLLC use cases such as smart factories. In this case, a low-latency repeater is more suitable than a high-latency repeater.

[0289] From a specification perspective, the NCR support indication is assumed to be a 1-bit indication added to each entry of the PLMN identification information list in SIB1, similar to the IAB support indication. In order to support NCR in NPN, it is only necessary to add the same indication to each entry of the NPN identification information list, similar to IAB. Therefore, the standardization effort is expected to be minimal (close to zero). In addition, in a PLMN network, no signaling overhead occurs (i.e., since the NPN identification information list is an arbitrary IE, the list is not present in such a network).

[0290] In addition, RAN2 has agreed to the following statement, which explicitly indicates that NCR is supported in NPN.

[0291] NCR-MT supporting NPN should consider using cellReservedForOtherUse for NPN-only cell determination.

[0292] In view of the above, the inventors believe that there is no need to impose an “artificial” restriction on the introduction of NCR in NPN. Therefore, RAN2 should confirm that NCR is supported in NPN, which will resolve the previous consideration.

[0293] Proposal 7: RAN2 should confirm that NCR is supported in NPN. Therefore, the NCR support indication is also added to each entry of the NPN identification list in SIB1.

[0294] 2.2.2. Potential issues with PRACH resources

[0295] In IAB, specific PRACH scenarios (ROs) can be provided to avoid possible collisions. Such opportunities are defined in the following IEs to extend the generic configuration of UEs.

[0296] Since NCRs are considered as network nodes such as IAB nodes, PRACH collisions with UEs should also be avoided. For UEs in the extended coverage provided by NCRs, the preamble sent by the UE is forwarded by the NCR to the gNB, while in the case of IAB, the preamble sent by the UE is terminated by the IAB node. Therefore, the inventors consider this as a more serious issue for NCRs. Thus, the inventors consider this as a more serious issue for NCRs in terms of PRACH collisions on the gNB reception side.

[0297] Therefore, it is worth considering whether separate PRACH resources should be provided to NCR-MTs from UEs. When this is necessary, further consideration is needed whether the separate PRACH resources are defined by separate ROs (as in Release 16 IAB) or by PRACH partitioning (i.e., as part of the preamble defined for the combination of features of Release 17 RedCap, SDT, slicing, and coverage extension).

[0298] Proposal 8: RAN2 should discuss whether to define separate PRACH resources specific to NCR-MTs.

[0299] Reference Signs

[0300] 1: Mobile communication system

[0301] 100: UE

[0302] 200: gNB

[0303] 210: Transmitter

[0304] 220: Receiver

[0305] 230: Controller

[0306] 240: Backhaul communicator

[0307] 500A: NCR apparatus

[0308] 510A: NCR-Fwd

[0309] 520A: NCR-MT

[0310] 500B: RIS apparatus

[0311] 510B: RIS-Fwd

[0312] 520B: RIS-MT

[0313] 511A: wireless unit

[0314] 511a: antenna

[0315] 511b: RF circuitry

[0316] 511c: directivity controller

[0317] 512A: NCR controller

[0318] 512B: RIS controller

[0319] 521: receiver

[0320] 522: transmitter

[0321] 523: controller

[0322] 530: interface

Claims

1. A communication method used in a relay device, the relay device comprising: A relay device is configured to perform relay operations to relay radio signals transmitted between a network and user equipment. And a control terminal, configured to receive control signals from the network for controlling the relay device, the communication method comprising: The control terminal is converted to Radio Resource Control (RRC) connection state in the cells included in the network; Determine whether the conditions for incorporating notification information indicating that the host device is the relay device into the message to be sent from the control terminal to the cell are met; and In response to determining that the condition is met, the control terminal sends the message including the notification information to the cell.

2. The communication method according to claim 1, wherein, The message is either an RRC establishment completion message or a UE capability response message.

3. The communication method according to claim 1 or 2, in, The determination includes: determining whether the cell is a desired cell defined as the connection destination of the relay device; and The sending includes: in response to determining that the cell is the desired cell, sending the message including the notification information from the control terminal to the cell.

4. The communication method according to claim 3 further includes: In response to determining that the cell is not the desired cell, the control terminal sends information to the cell to prompt the network to switch from the RRC connection state to another RRC state.

5. The communication method according to claim 1 or 2, in, The determination includes: determining whether there is a need to obtain the configuration information of the relay device from the cell, and The sending includes: in response to determining that the need exists, sending a message including the notification information from the control terminal to the cell.

6. The communication method according to claim 5, in, The determination includes: determining whether the relay device includes configuration information available in the cell, and The sending includes: when it is determined that the relay device does not include configuration information available in the cell, sending the message including the notification information from the control terminal to the cell.

7. The communication method according to claim 5, in, The determination includes: determining whether the relay device is turned on; and The sending includes: in response to determining that the relay device is turned on, sending a message including the notification information from the control terminal to the cell.

8. The communication method according to claim 5, in, The determination includes: determining whether to perform a relay operation depending on the control signals from the network; and The transmission includes: in response to determining that a relay operation dependent on the control signal from the network is to be performed, sending the message including the notification information from the control terminal to the cell.

9. A communication method used in a relay device, the relay device comprising: A relay device is configured to perform relay operations to relay radio signals transmitted between a network and user equipment. And a control terminal, configured to receive control signals from the network for controlling the relay device, the communication method comprising: The control terminal in the Radio Resource Control (RRC) connection state initiates an RRC connection reconstruction process for the cells included in the network; The Relay Device Dedicated Radio Network Temporary Identifier (RNTI) assigned to the relay device, or notification information indicating that the host device is the relay device, is incorporated into the RRC Re-establishment Request message; and The control terminal sends an RRC reconstruction request message to the cell, which includes the relay device's dedicated RNTI or the notification information.

10. The communication method according to claim 9, wherein, When the control terminal processes multiple relay devices, each of which is assigned a dedicated RNTI for the relay device, the merging includes: merging the dedicated RNTI for the relay device of each of the multiple relay devices or the dedicated RNTI for the relay device of a specific relay device among the multiple relay devices into the RRC rebuild request message.

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