Communication device, control method, and program

Abstract

Disclosed is a communication device having a Mobile Base Station Relay (MBSR) operation function, the communication device being characterized by being operable in a first mode in which only another communication device having the MBSR operation function is connected to one Distribution Unit (DU) of a host station and in which communication between another communication device and an Integrated Access and Backhaul (IAB) donor is relayed.

Description

Communication device, control method, and program

[0001] The present disclosure relates to a communication device, a control method, and a program.

[0002] The Third Generation Partnership Project (3GPP (registered trademark)) has formulated cellular communication standards. In the cellular communication standards of 3GPP (hereinafter referred to as "3GPP standards"), standardization of Integrated Access and Backhaul (IAB), which integrates access lines and backhaul lines, is underway (see Patent Document 1).

[0003] In IAB, radio resources used for access lines between a base station (gNB) and a user terminal (UE, User Equipment) are also used for backhaul lines. For example, in IAB, radio resources in the millimeter wave band, such as the 28 GHz band, can be used. By using IAB, a relay device (IAB node) can relay communication between a base station device (IAB donor) and a terminal device via a wireless line, which makes it possible to expand area coverage at a lower cost than when using a wired line such as optical fiber.

[0004] Up until now, specifications have been developed for fixed base stations (IAB nodes that do not move) up to Release 17, which is the standardization phase of 3GPP.

[0005] 3GPP is currently in the Release 18 phase, where active discussions are underway on Vehicle Mounted Relay, a use case. Furthermore, active discussions are underway on Mobile IAB or Mobile Base Station Relay (MBSR) to develop specifications for the architecture and protocols to realize this use case. In IAB, which uses millimeter waves, in locations where radio waves from IAB nodes are difficult to reach due to obstructions (such as in built-up areas), MBSR has difficulty maintaining connection (communication service coverage) to IAB donors and IAB nodes.

[0006] Special Publication No. 2019-534625

[0007] In 3GPP Release 18, in order to simplify the participation of MBSR in IAB topology, the standard is being developed in a direction that restricts the connection of further IAB nodes under the MBSR. In other words, MBSR only supports single-hop. On the other hand, if it becomes possible to build a multi-hop configuration in which another MBSR is connected under the MBSR, path flexibility can be increased. In this case, it is expected that the cell coverage area can be flexibly expanded.

[0008] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a mechanism that can provide stable communication services to MBSRs that are located in areas where radio waves are difficult to reach.

[0009] A communication device according to one aspect of the present invention is a communication device having an MBSR (Mobile Base Station Relay) operation function, characterized in that the communication device is operable in a first mode in which only other communication devices having the MBSR operation function are connected to one of the communication device's DUs (Distribution Units), and in which the communication device relays communication between the other communication devices and an IAB (Integrated Access and Backhaul) donor.

[0010] According to one aspect of the present invention, it is possible to provide a mechanism that can provide stable communication services to MBSRs that are located in areas where radio waves are difficult to reach.

[0011] 1 is a diagram illustrating an example of a communication system. FIG. 2 is a diagram illustrating a software configuration of an MBSR. FIG. 3 is a diagram illustrating a hardware configuration of an MBSR. FIG. 4 is a block diagram illustrating an example of a hardware configuration of an IAB donor according to the present embodiment. FIG. 5 is a block diagram illustrating an example of a hardware configuration of an IAB donor according to the present embodiment. FIG. 6 is a flowchart illustrating a process for generating a mode change instruction to relay mode for an IAB donor according to the present embodiment. FIG. 7 is a flowchart illustrating an example of a mode determination for a relay candidate MBSR. FIG. 8 is a sequence in which an IAB donor requests relaying from a relay candidate MBSR (without UE). FIG. 9 is a relay request message format RRC (IAB donor → relay candidate MBSR). FIG. 10 is a relay request message format BAP (IAB donor → relay candidate MBSR). FIG. 11 is a flowchart illustrating an example of MBSR processing according to the present embodiment. FIG. 12 is another flowchart illustrating an example of MBSR processing according to the present embodiment. FIG. 13 is a sequence in which a disconnected MBSR requests relaying from a relay candidate MBSR (without UE). FIG. 14 is an explanatory diagram of an example of a relay request message format notification (disconnected MBSR → relay candidate MBSR). 1 is an explanatory diagram of another example of a relay request message format notification (disconnected MBSR → relay candidate MBSR). FIG. 2 is a relay request message format RRC (unicast) (disconnected MBSR → relay candidate MBSR). FIG. 3 is a sequence in which an IAB donor requests a new DU of a relay candidate MBSR (with UE) to relay. FIG. 4 is a sequence in which a disconnected MBSR requests a new DU of a relay candidate MBSR (with UE) to relay. FIG. 5 is a flowchart of another example of a mode determination of a relay candidate MBSR. FIG. 6 is a sequence in which an IAB donor requests a relay candidate MBSR (with UE) to relay. FIG. 7 is a sequence in which a disconnected MBSR requests a relay candidate MBSR (with UE) to relay.

[0012] Each embodiment will be described in detail below with reference to the accompanying drawings. In the following description, the "number ***" in TS*** represents the number of the technical specification in the 3GPP standard.

[0013] In 3GPP Release 18, the standard is being developed to restrict the connection of IAB nodes to an MBSR in order to simplify the participation of an MBSR in an IAB topology. In other words, an MBSR supports only a single hop. On the other hand, if a multi-hop configuration can be established in which another MBSR is connected to an MBSR, it is expected that path flexibility can be increased and the cell coverage area can be flexibly expanded. Therefore, the following embodiments aim to provide a specific mechanism for realizing an IAB topology with such a multi-hop configuration.

[0014] Furthermore, assuming a specific use case, when an MBSR loses connection with the IAB donor and cannot detect any other connectable nodes, it cannot connect to another MBSR even if it is nearby. This poses a problem: until the MBSR finds a parent node, UEs under the MBSR are unable to perform data communication (service is interrupted). However, the MBSR specification, which only supports single-hop, does not provide a means (trigger) for requesting relay to another MBSR. Therefore, each of the following embodiments aims to provide an operational mechanism that triggers another MBSR to start operating as a relay node for an MBSR that does not have a connectable parent node. Another aspect of each of the following embodiments aims to improve the convenience of cellular communications.

[0015] 1 illustrates a mobile wireless communication system, such as a 5G system, including an integrated wireless access and backhaul network that supports MBSR in a communication system 100. While the description here is primarily focused on 5G, it is also applicable to systems other than 5G (e.g., 5G Advanced, 6G, etc.).

[0016] The communication system 100 comprises multiple UEs 120-123, a core network 150, a primary base station 110, and MBSRs 101-102 mounted on vehicles 111-112. The vehicles 111-112 may be any form, such as a bus, train, taxi, or car. The vehicle 113, MBSR 103, and remote UE 123 represent the vehicle 112, MBSR 102, and remote UE 122 after they have moved. That is, the vehicle 113, MBSR 103, and remote UE 123 are identical to the vehicle 112, MBSR 102, and remote UE 122, respectively. However, this distinction is made for convenience of explanation and may not necessarily correspond to the timing of disconnection, as described below. The primary base station 110, also referred to as the IAB donor 110, is connected to the core network 150 via a wired link 140 (preferably optical fiber or other wired means). In each embodiment described below, the IAB donor 110 is a 5G base station (gNB) with additional functionality to support IAB functionality as defined in the 3GPP TS 38.300 v17.2.0 specification.

[0017] MBSRs 101 and 102, also called mobile IAB nodes, are installed in vehicles 111 and 112 and provide network coverage and capacity expansion. IAB donor 110 can communicate not only with UEs located within the vehicle, such as remote UE 121 and remote UE 122 (123), but also with UEs outside the vehicle, such as UE 120. Therefore, IAB donor 110 and MBSRs 101 and 102 form a backhaul network or IAB network, or IAB topology, accommodating UEs 121 to 122. The terms IAB network and IAB topology are used interchangeably below. IAB specifications are defined in several 3GPP standard documents, such as: -TS 38.300 RAN Architecture (V17.2.0) -TS 38.321 MAC Protocol (V17.2.0) -TS 38.331 Radio Resource Control (RRC) Protocol (V17.2.0) -TS 38.340 Backhaul Adaptation Protocol Layer (V17.2.0) -TS 38.401 RAN Architecture (V17.2.0) -TS 38.423 Xn Application Protocol (V17.2.0) -TS 38.473 F1 Application Protocol (V17.2.0) Here, with reference to Figure 1, an overview of how the problem of single-hop MBSR occurs will be described.

[0018] The IAB donor 110 is wirelessly connected to the subordinate MBSR 101 via a wireless backhaul link 141, and similarly to the subordinate MBSR 102 via a wireless backhaul link 142. Data communication is possible with a UE 121 in a vehicle 111 in which the MBSR 101 is installed, and data communication is possible with a UE 122 in a vehicle 112 in which the MBSR 102 is installed.

[0019] However, when vehicle 112 moves in the direction of arrow 160 and moves to the position of vehicle 113, MBSR 102 mounted on the vehicle moves to MBSR 103, and UE 122 in the vehicle moves to UE 123. In this case, MBSR 103 may be hidden behind a shield 130 such as a building. In this case, the radio wave strength of wireless backhaul link 142 with IAB donor 110 gradually attenuates, and eventually the wireless link is disconnected, causing a radio link failure (RLF).

[0020] After the RLF, MBSR 103 searches for and attempts to connect to the IAB donor 110 that was connected as the parent node, but is unable to do so due to obstructions 130 and 131. As a result, MBSR 103 leaves its subordinate UE 123 unable to communicate data (service interrupted). By searching for a base station (including an IAB donor or IAB node) that can be connected as a parent node, MBSR 103 may detect MBSR 101, which has high reception power, as the parent node. In this case, if MBSR 101 only supports single-hop, MBSR 101 will reject the connection request from MBSR 103. As a result, the service interruption state at MBSR 103 will continue.

[0021] Next, a mechanism that can at least partially solve this problem will be described in detail with reference to various embodiments.

[0022] 2A is a hardware functional block diagram of the MBSR 102 in each embodiment described below. Here, the configuration of the MBSR 102 will be described, but the MBSR 101 may be similar.

[0023] The MBSR 102 is configured from hardware including a control unit 201 , a storage unit 202 , a wireless communication unit 203 , and a communication antenna control unit 204 .

[0024] The control unit 201 controls the entire device by executing a control program stored in the storage unit 202. The control unit 201 is configured with one or more processors, such as a CPU or an MPU, and controls the entire communication device by executing a control program read into the RAM, which is the storage unit 202. Note that each process performed by the control unit 201, which will be described in the flowcharts below, can also be realized using a hardware circuit, such as an ASIC or an FPGA. Note that ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array. Furthermore, the processes described in the flowcharts below can also be realized by cooperation between a hardware circuit and a processor, such as a CPU or an MPU.

[0025] The memory unit 202 stores various information such as the control program executed by the control unit 201, information about the connected UE, and the connection strength with the base station and the IAB donor 110. The memory unit 202 may include a main memory unit and an auxiliary memory unit. The main memory unit is, for example, a read-only memory (ROM) or a random access memory (RAM). The main memory unit may store or temporarily store programs and data such as an operating system (OS), which is basic software executed by the control unit 201, and application software. The auxiliary memory unit is, for example, a hard disk drive (HDD) or a solid state drive (SSD), and may store data related to application software, etc. For example, the control program stored in the non-volatile storage area is expanded into a RAM (Random Access Memory) and executed by a processor constituting the control unit 201. In this way, the control unit 201 and the storage unit 202 may function as a so-called computer.

[0026] The wireless communication unit 203 performs cellular network communication such as 5G that complies with the 3GPP standard. Specifically, the cellular network communication is performed by controlling communication such as a RAN (Radio Access Network) such as 5G NR (New Radio) and controlling communication in higher layers. Note that 5G is used as an example of cellular network communication, but this is not limiting, and the control of this embodiment can also be realized based on cellular network communication such as 5G Advanced / 6G. In this case, the wireless communication unit 203 performs cellular network communication such as 5G Advanced or 6G that complies with the 3GPP standard.

[0027] The communication antenna control unit 204 controls the antenna used for wireless communication performed by the wireless communication unit 203 .

[0028] The GPS communication unit 205 receives satellite signals from GPS (Global Positioning System) satellites to acquire current location information including location identification information such as longitude and latitude information, and current time information. The GPS communication unit 205 may have a function to measure (locate) the current location based on the satellite signals. Another GNSS (Global Navigation Satellite System) may be used instead of or in addition to GPS.

[0029] The GPS antenna control unit 206 controls an antenna (not shown) for GPS communication performed by the GPS communication unit 205 .

[0030] 2B is a software functional block diagram of the MBSR in each embodiment described below. Here, the configuration of the MBSR 102 (103) will be described, but the MBSR 101 may have the same configuration.

[0031] The software function block 301 is stored in the storage unit 202 and executed by the control unit 201. The software function block 301 includes a signal transmission unit 302, a signal reception unit 303, a data storage unit 304, a connection control unit 305, a network configuration information management unit 306, a relay request processing unit 307, and a signal generation unit 308. The software function block 301 also includes a GPS signal processing unit 309 and a mode switching unit 310.

[0032] The signal transmitting unit 302 and the signal receiving unit 303 control the wireless communication unit 203 via the control unit 201, and perform cellular network communication such as LTE and 5G that conforms to the 3GPP standard between the IAB donor 110, other MBSRs, and UE 122.

[0033] The data storage unit 304 controls and manages the storage unit 202, which is the entity, and stores and holds the software itself, connection information with the IAB donor 110, information about the UE 122, etc. Information between nodes can be collected by broadcast signals and communication packets accompanying various BAP control PDUs (hereinafter referred to as BAP control packets). Information from the UE can be collected, for example, by RRC status.

[0034] The connection control unit 305 controls the communication antenna control unit 204 via the control unit 201 during wireless communication. The connection control unit 305 generates a connection control signal based on information (described below) generated by the network configuration information management unit 306. In addition, in the MBSR 102 (103), when there is a response from another communication device (in this embodiment, the MBSR 101 described later) requesting a relay-only connection (connection in relay mode), the connection control unit 305 determines a connection to the other communication device.

[0035] The network configuration information management unit 306 manages configuration information of the IAB network including the own station. The network configuration information management unit 306 also manages type information of the UE, IAB node, and MBSR that make a connection request to the own station.

[0036] The relay request processor 307 functions in the MBSR 102 (103) (see the second, fourth, and sixth embodiments described later). The relay request processor 307 performs various processes for a relay request to be sent to another MBSR (in this embodiment, the MBSR 101 described later) when the wireless link with the parent node is disconnected. For example, the relay request processor 307 generates a relay request triggered by the disconnection of the wireless link with the parent node. At this time, the relay request processor 307 may determine another MBSR (in this embodiment, the MBSR 101 described later) to be the destination of the relay request. When notification signals are received from multiple other MBSRs before and after the disconnection of the wireless link, the relay request processor 307 may determine one MBSR from among the multiple other MBSRs as the destination of the relay request. In this case, for example, the MBSR with the highest communication quality may be determined as the destination of the relay request.

[0037] The signal generation unit 308 manages and issues various signals generated by the connection control unit 305. Furthermore, in the MBSR 102 (103), the signal generation unit 308 cooperates with the relay request processing unit 307 to generate a signal related to a relay request (described later). The relay request may be generated, for example, by adding a parameter "relay request" to a reserved field in an RRC SetUp Request message. Alternatively, the relay request may be generated by adding information indicating a relay request to broadcast information (SS / PBCH Block). This will be described later with reference to FIGS. 10A and 10B.

[0038] The GPS signal processing unit 309 performs communication in accordance with the GPS standard. The GPS signal processing unit 309 controls the antenna for GPS communication performed by the GPS communication unit 205, and calculates the current position and time from the received GPS information. The GPS signal processing unit 309 then outputs information in a format such as NMEA (National Marine Electronics Association)-0183, and stores the current position and time in the data storage unit 304 as necessary.

[0039] The mode switching unit 310 functions in the MBSR 101. The mode switching unit 310 switches the operation mode between the normal mode and the relay mode. In this embodiment, the mode switching unit 310 switches from the normal mode to the relay mode in response to a request (a request to transition to the relay mode) from the IAB donor 110, which will be described later. Alternatively, in addition to or instead of this, the mode switching unit 310 switches from the normal mode to the relay mode in response to a request from the MBSR whose wireless link with the IAB donor 110 has been disconnected.

[0040] The normal mode corresponds to a mode in which only UEs can be connected to the DU (Distributed Unit), which is the radio function part of the MBSR 101, and other IAB nodes (including the MBSR) cannot be connected to it. In other words, the normal mode corresponds to a single-hop compatible mode in which connection with UEs is possible but connection with subordinate child nodes is not possible.

[0041] The relay mode means that the MBSR is not connected to the UE and only relays other MBSRs as child nodes. The relay mode corresponds to a mode in which multi-hop is supported and only the MBSR can connect to the DU of the wireless function unit.

[0042] The normal mode may be a mode that does not allow connection of an MBSR under its control but allows connection of normal IAB nodes and UEs other than the MBSR. The relay mode may be a mode that allows connection of other IAB nodes including the MBSR. The relay mode may be a mode that allows connection of other IAB nodes and UEs including the MBSR.

[0043] Regarding the activation of a new DU (hereinafter also referred to as the "new DU") in the MBSR 101 described below, first, it confirms that the bandwidth can be allocated. After this confirmation, it creates a functional unit equivalent to the software function block 301. In this case, a new cell is formed using a different frequency than the cell formed by the original DU. In this case, the MBSR 101 dual-activates two DUs, but this method can be implemented in a variety of ways. A separate antenna and hardware mechanism for the second DU may be prepared, and the MBSR 101 processor may control the antenna and hardware mechanism to activate the new DU. Alternatively, the antenna and hardware mechanism may be shared, and multiple DUs may be activated via software. In this case, the MBSR 101 activates multiple tasks equivalent to the software function block 301 that perform control to realize the functions of the DU. The tasks activated by the MBSR 101 access the antenna and hardware mechanism using time-sharing techniques or the like, and essentially simultaneously realize the functions equivalent to the existing DU and the new DU.

[0044] FIG. 2C is a block diagram showing an example of a hardware configuration 401 of the IAB donor 110 according to this embodiment.

[0045] The hardware configuration 401 includes a control unit 402 , a storage unit 403 , a wireless communication unit 404 , and a communication antenna control unit 405 .

[0046] The control unit 402 controls the entire device by executing a control program stored in the storage unit 403. The control unit 402 is configured with one or more processors such as a CPU or MPU, and controls the entire communication device by executing a control program read into the RAM, which is the storage unit 403. Note that each process performed by the control unit 402, which will be described in the flowcharts below, can also be realized using a hardware circuit such as an ASIC or FPGA. Furthermore, the processes described in the flowcharts below can also be realized by having the hardware circuit cooperate with a processor such as a CPU or MPU.

[0047] The storage unit 403 stores a control program executed by the control unit 402, and various information such as cell information, connected terminal information, IAB routing information, and location information. The storage unit 403 may include a main storage unit and an auxiliary storage unit. The control unit 402 and the storage unit 403 may function as a so-called computer.

[0048] The wireless communication unit 404 performs cellular network communication such as LTE and 5G that conform to the 3GPP (registered trademark) standard.

[0049] The communication antenna control unit 405 controls an antenna (not shown) for wireless communication performed by the wireless communication unit 404 .

[0050] FIG. 2D is a block diagram showing an example of the hardware configuration of the IAB donor 110 according to this embodiment.

[0051] The software function 501 includes a signal transmitting unit 502 , a signal receiving unit 503 , a data storage unit 504 , a connection control unit 505 , a notification information detecting unit 506 , a peripheral node determining unit 507 , and a mode change instruction generating unit 508 .

[0052] The signal transmitting unit 502 and the signal receiving unit 503 perform cellular network communication such as LTE or 5G conforming to the 3GPP standard with the terminal device. The control plane signal is received by the signal receiving unit 503.

[0053] In this embodiment, the signal transmission unit 502 transmits a transition instruction generated by a mode change instruction generation unit 508 (described later) to an MBSR that is a relay candidate (described later).

[0054] In this embodiment, the signal receiving unit 503 acquires information that can determine whether the remote communication device is an MBSR (i.e., an IAB node of a type that involves movement). Such information is arbitrary and may be, for example, information that explicitly or implies that the remote communication device is an MBSR, or information that explicitly or implies that the remote communication device is not an MBSR. In this embodiment, such information is IAB node type information, the details of which will be described later.

[0055] The data storage unit 504 stores and holds the software itself, IAB routing information, information on connected terminals, current time information, location information, movement route information, and the like.

[0056] The connection control unit 505 controls the antenna for wireless communication performed by the wireless communication unit 104 .

[0057] The broadcast information detection unit 506 detects broadcast information from surrounding base stations and MBSRs.

[0058] When the wireless link with a certain MBSR is disconnected, the peripheral node determination unit 507 determines whether or not there is another node in the vicinity of the certain MBSR that can be connected to the certain MBSR. An example of a determination method will be described later in relation to S302 in FIG. 3.

[0059] The mode change instruction generation unit 508 generates a request to transition to relay mode (an instruction to change to relay mode). The request to transition to relay mode is transmitted to an MBSR that is a relay candidate (described later). The conditions for generating the request to transition to relay mode will be described later.

[0060] <First embodiment: Relay request from IAB donor to MBSR (without UE)> FIG. 3 shows a processing flow for generating a mode change instruction to relay mode of the IAB donor 110 in this embodiment (also in the third and fifth embodiments described later).

[0061] The IAB donor 110 determines whether the connection with the subordinate MBSR has been disconnected (S300). In this example, it is assumed that the connection with the MBSR 103 has been disconnected as described above. In this case, the IAB donor 110 acquires location information of each subordinate node (e.g., IAB node and MBSR) (S301). The IAB donor 110 may acquire the location information of each subordinate node directly from each node using an RRC message. The location information may be included in a Measurement Report. Alternatively, the IAB donor 110 may acquire the location information of each node from the core network 150. Based on the location information, the IAB donor 110 determines whether there are other nodes (here, IAB nodes) or other IAB donors in the vicinity of the MBSR 103 to which the MBSR 103 can connect (S302). The vicinity of the MBSR 103 may be an area within a predetermined distance from the position of the MBSR 103 as the center, and the predetermined distance may be defined in advance.

[0062] If there is another node to which the MBSR 103 can be connected, the MBSR 103 is connected via that other node (S304). On the other hand, if there is no other node to which the MBSR 103 can be connected, the IAB donor 110 determines whether there is one or more other MBSRs to which the MBSR 103 can be connected (S303). If there is only one other MBSR to which the MBSR 103 can be connected, the process ends. On the other hand, if there is only one other MBSR to which the MBSR 103 can be connected, the IAB donor 110 transmits a request to transition to relay mode (an instruction to change to relay mode) to that other MBSR (S307). When there are multiple other MBSRs to which the MBSR 103 can be connected (S305), the process may be as follows, for example: That is, based on the Measurement Reports previously obtained from each of the other MBSRs, the other MBSR with the highest communication quality with the MBSR 103 is determined as a relay candidate (S306). The communication quality between the MBSR 103 and each other MBSR may be notified to the IAB donor 110 by each other MBSR using a reserved field "nonCriticalExtension." This reserved field is specified in the Measurement Report message format defined in Chapter 6.2.2 of TS38.331. For example, a field called "MBSR communication information" indicating communication quality may be added to the reserved field. In this case, communication status information (delay time, etc.) may be included in the MBSR communication information field.

[0063] In this case, the IAB donor 110 transmits a request to switch to relay mode (an instruction to change to relay mode) to the other MBSR with the highest communication quality (S307).

[0064] 3, step S306 may be omitted. In this case, another MBSR that is closest to the location of the MBSR 103 where disconnection was detected may be determined as a relay candidate, or another MBSR may be determined as a relay candidate based on other criteria.

[0065] FIG. 4 shows a process flow for determining an MBSR mode in this embodiment (the same applies to second to fourth embodiments described later).

[0066] The MBSR is connected to the network as an MBSR in normal mode (S401). When a mode change instruction is received from the IAB donor 110 (S402), the MBSR checks whether or not there is a UE connected to it (S403). If there is a connected UE, the MBSR starts up a new DU in relay mode (S406). If there is no connected UE, the MBSR operates in relay mode (S405). If no change instruction is received in S402, the MBSR continues to operate in normal mode (S404). At this time, multiple DUs may be started up using virtualization technology as a method for starting up a new relay mode. Furthermore, depending on the communication performance of the local station, it may be possible to provide services by dividing up the functions.

[0067] FIG. 5 is a sequence diagram showing the flow from when the IAB donor 110 detects a disconnection with the MBSR 103 until the MBSR 103 is connected to the MBSR 101 operating as a relay node.

[0068] The MBSR 101 broadcasts that it can operate as a relay node (S501). For this broadcast, an SSB (Synchronization Signal Block) message is used. However, as the information to be broadcast in S501, it is also possible to broadcast information indicating that it can operate in relay mode by newly defining rsinfo in nonCriticalExtension defined in SIB1 (or another SIB other than SIB1). Alternatively, the MBSR 101 may notify that it can operate as a relay node via an F1 message or an RRC message.

[0069] MBSR 103 receives the notification signal from MBSR 101, but does not respond at this stage because it is currently connected to its parent node (IAB donor 110). If MBSR 103 subsequently moves and becomes hidden behind an obstruction, the wireless connection with its parent node, IAB donor 110, is severed. When IAB donor 110 detects that the connection with its subordinate MBSR 103 has been severed (S502), it transmits a connection request in relay mode to the other connected child node, MBSR 101 (S503). At this time, the connection request may be transmitted on the condition that MBSR 103 can be confirmed as being connectable based on its location information, etc.

[0070] Here, the signal transmitted from the IAB donor 110 to the MBSR 101 adds a parameter "request to connect to disconnected MBSR" to the reserved field of the RRC Reconfiguration message, which is the RRC protocol shown in Fig. 6. Alternatively, the connection request may be transmitted by adding a parameter "request to connect to disconnected MBSR" to the reserved field of PDUType in S901 of the BAP message shown in Fig. 7. BAP is an abbreviation for Backhaul Adaptation Protocol.

[0071] In this embodiment, it is assumed that the MBSR 101 is not connected to a UE and is operating in relay mode in response to a response from the IAB donor 110 (see S405 in FIG. 4). Specifically, upon receiving a request from the IAB donor 110, the MBSR 101 switches from a normal mode, which supports only single hop, to relay mode (S504). That is, the MBSR 101 responds to the IAB donor 110 that it can connect in relay mode (S504) and switches from normal mode to relay mode (S505). The MBSR 101 then transmits a broadcast signal indicating that it is operating in relay mode (S505A). Alternatively, the means for notifying that it is operating in relay mode may be a unicast signal using an RRC Reconfiguration message of the RRC protocol, instead of a broadcast signal. At this time, a message format for reporting the request for relaying may be included in an RRC Reconfiguration message of the RRC protocol shown in FIG. 11, which will be described later.

[0072] Since the MBSR 103 recognizes the MBSR 101 as a connectable parent node, it decides to connect the MBSR 101 as a parent node (S506). The MBSR 103 then executes a random access procedure to connect to the MBSR 101 (S507), requests connection via an RRC SetUp Request message or the like, and completes the connection (S508). The IAB donor 110 sets up a backhaul (BH) path with the MBSR 103 via the MBSR 101, and establishes a BHRLC channel for data communication (S509). BHRLC is an abbreviation for Backhaul Radio Link Control. This series of sequences enables the UE 123 connected to the MBSR 103 to perform data communication.

[0073] <Second embodiment: Relay request to another MBSR (without UE) by a disconnected MBSR> Figure 8A shows a flowchart of MBSR 103 that has been disconnected from its parent node. After detecting the disconnection with its parent node in S801, MBSR 103 notifies other MBSRs of a relay request (S802). If a response or notification is received from an MBSR 101 that can relay (S803), MBSR 103 attempts to connect to an MBSR 101 that can relay (S804). If no other MBSR that can be connected is found in S803, another MBSR that can relay is searched for.

[0074] 8A assumes that there is only one MBSR (MBSR 101) that can be relayed, but as shown in FIG. 8B, there may be cases where multiple MBSRs have responded or notified (YES in S803A). In this case, for example, based on the responses or notifications from each MBSR, the MBSR with the highest communication quality may be determined as the relay candidate (S803B). For example, the MBSR with the highest reception strength of the received signal related to the responses or notifications from each MBSR may be determined as the relay candidate (S803B).

[0075] FIG. 9 is a sequence diagram showing the flow of a disconnected MBSR 103 requesting relay to another MBSR 101 until connection is established.

[0076] In this embodiment, as in the first embodiment described above, it is assumed that the MBSR 101 is not connected to a UE and can operate in relay mode in response to a response from the IAB donor 110 (see S405 in Figure 4).

[0077] The MBSR 101 announces that it can operate as a relay node (S901). The MBSR 103 receives the announcement signal from the MBSR 101, but does not respond at this stage because it is connected to the parent node. After that, when the MBSR 103 moves and becomes hidden behind an obstruction, the wireless connection with the parent node's IAB donor 110 is cut off, and the MBSR 103 detects that the parent node has been disconnected (S902).

[0078] Since the MBSR 103 recognizes that relaying is possible based on the broadcast signal from the MBSR 101, it sends an RRC SetUp Request message to the MBSR 101 by adding a parameter "relay request" to the reserved field of the message (S903).

[0079] Alternatively, if the MBSR 103 has not received a broadcast from the MBSR 101 in S901, it may add information indicating a relay request to the broadcast information (SS / PBCH Block) and transmit the broadcast information. At this time, a message format for broadcasting the relay request may be included in the SIB1 message shown in FIG. 10A. The SIB1 message has parameters such as SIB1-v1700-IEs, and the parameter "relay request" is added to the reserved field "Reason of NonAccess". Also, the message format for transmitting the relay request may be such that the parameter "relay request" is added to the "parameter notifying that it is an IAB node" shown in FIG. 10B.

[0080] Upon receiving the relay request from the MBSR 103, the MBSR 101 confirms (requests) with the parent node, the IAB donor 110, whether it is permitted to operate as a relay node (S904). The IAB donor 110 responds to the MBSR 101 that it is permitted to operate in relay mode (S905). Upon receiving the response from the IAB donor 110, the MBSR 101 switches from normal mode, which supports only single hop, to relay mode (S906). The MBSR 101 transmits a broadcast signal indicating that it is operating in relay mode (S907). Alternatively, instead of broadcasting, the means for notifying the MBSR 103 of its operation in relay mode may be an RRC Reconfiguration message of the RRC protocol, transmitted by unicast. In this case, the message format for broadcasting the relay request may be included in the RRC Reconfiguration message of the RRC protocol, as shown in FIG. 11 .

[0081] Since the MBSR 103 recognizes the MBSR 101 as a connectable parent node, it decides to connect to the MBSR 101 as a parent node and executes a random access procedure (S908). The MBSR 103 requests connection via an RRC SetUp Request message or the like and completes the connection (S909). The IAB donor 110 sets up a backhaul path with the MBSR 103 via the MBSR 101 and establishes a BHRLC channel for data communication (S910). This series of sequences enables the UE 123 connected to the MBSR 103 to communicate data.

[0082] In FIG. 9, MBSR 101 operates in relay mode in response to a request from IAB donor 110 (S904, S905), but in a modified example, MBSR 101 may also operate in relay mode in response to a relay request from MBSR 103 (S903).

[0083] <Third embodiment: Relay request from IAB donor to MBSR (with UE)> FIG. 12 is a sequence diagram showing that an IAB donor 110 that detects a disconnected MBSR 103 requests another MBSR 101 to relay.

[0084] This embodiment is based on the premise that the MBSR 101 having a relay function is connected to the UE 121 under its control (S1201). That is, unlike the first and second embodiments described above, this embodiment assumes a case in which the MBSR 101 is connected to the UE 121. In this case, the MBSR 101 can operate in relay mode while initiating a new DU in response to a response from the IAB donor 110 (see S406 in FIG. 4). Note that, unlike this assumption, if the MBSR 101 is not connected to the UE 121, the first and second embodiments described above may be used.

[0085] The MBSR 101 announces that it can operate as a relay node (S1202). The MBSR 103 receives the announcement signal from the MBSR 101, but does not respond at this stage because it is still connected to its parent node. If the MBSR 103 subsequently moves and becomes hidden behind an obstruction, its wireless connection with the parent node, the IAB donor 110, is severed. The IAB donor 110 detects that its connection with the subordinate MBSR 103 has been severed (S1203). Then, if the IAB donor 110 confirms that the other connected child node, the MBSR 101, is connectable based on the MBSR 103's location information, etc., it transmits a connection request in relay mode to the connected child node, the MBSR 101 (S1204). Here, the signal transmitted from the IAB donor 110 to the MBSR 101 adds a "connection request to disconnected MBSR" parameter to the reserved field of the RRC Reconfiguration message, which is the RRC protocol shown in FIG. 6. Alternatively, a parameter "request to connect to disconnected MBSR" may be added to the reserved area of ​​PDUType in S901 of the BAP message in FIG. 7, and a request for connection may be transmitted.

[0086] The IAB donor 110 responds to the MBSR 101 that it may operate in relay mode (S1205). Here, the MBSR 101 is connected to the UE, and simultaneously implementing a relay connection with other nodes using the same DU may lead to increased complexity. Therefore, the MBSR 101 starts a new DU2 (192) separate from the DU1 (191) currently connected to the UE 121, and uses it for relaying with the MBSR 103 (S1206). The MBSR 101 then transmits a broadcast signal indicating that it is operating in relay mode (S1207).

[0087] The MBSR 103, having recognized the MBSR 101 as a connectable parent node through the reception of the notification signal, decides to connect to the MBSR 101 as a parent node and executes a random access procedure to the MBSR 101 (S1208). Thereafter, the MBSR 103 requests connection via an RRC SetUp Request message or the like, and completes the connection (S1209). The IAB donor 110 sets up a backhaul path with the MBSR 103 via DU2 (192) of the MBSR 101, and establishes a BHRLC channel for data communication (S1210).

[0088] This series of sequences enables the UE 123 connected to the MBSR 103 to perform data communication.

[0089] <Fourth Embodiment: Relay Request to Another MBSR (with UE) by Disconnected MBSR> Figure 13 is a sequence diagram showing the flow of a disconnected MBSR 103 requesting relay to another MBSR 101, leading to connection. However, this embodiment assumes that the relaying MBSR 101 is connected to the UE 121 and is connected to the radio function unit DU1 (191) of the MBSR 101 to continue data communication (S1301). That is, unlike the first and second embodiments described above, this embodiment assumes that the MBSR 101 is connected to the UE 121. In this case, the MBSR 101 can operate in relay mode while activating a new DU in response to a response from the IAB donor 110 (see S406 in Figure 4). Note that, unlike this assumption, if the MBSR 101 is not connected to the UE 121, the first and second embodiments described above may be used.

[0090] The MBSR 101 announces that it can operate as a relay node (S1302). The MBSR 103 receives the announcement signal from the MBSR 101, but does not respond at this stage because it is connected to the parent node. After that, when the MBSR 103 moves and becomes hidden behind an obstacle, the wireless connection with the parent node's IAB donor 110 is cut off, and the MBSR 103 detects that the parent node has been disconnected (S1303).

[0091] MBSR 103 recognizes that relaying is possible based on the broadcast signal from MBSR 101. Therefore, MBSR 103 transmits an RRC SetUp Request message to MBSR 101 by adding a parameter "relay request" to the reserved field (S1304). Alternatively, similar to the third embodiment, if MBSR 103 has not received the broadcast of S1302, it may transmit information indicating a relay request by adding it to the broadcast information (SS / PBCH Block) indicating relaying is possible.

[0092] Upon receiving the relay request from the MBSR 103, the MBSR 101 checks with the parent node, the IAB donor 110, whether it is OK to operate as a relay node (S1305). The IAB donor 110 responds to the MBSR 101 that it is OK to operate in relay mode (S1306).

[0093] Here, when the MBSR 101 operates in "relay mode," the complexity increases if a connection with another node is established via the DU1 (191) currently connected to the UE 121. For this reason, a new DU2 (192) separate from the DU1 (191) currently connected to the UE 121 is newly activated and used for relaying with the MBSR 103 (S1307).

[0094] The MBSR 101 transmits a notification signal indicating that it is operating in relay mode (S1308). Alternatively, the MBSR 101 may notify the MBSR 103 of the operation in relay mode by using an RRC Reconfiguration message instead of a notification.

[0095] Since the MBSR 103 recognizes the MBSR 101 as a connectable parent node, it decides to connect to the MBSR 101 as a parent node and executes a random access procedure to the MBSR 101 (S1309). Then, it requests connection via an RRC SetUp Request message or the like, and completes the connection (S1310). The IAB donor 110 sets up a backhaul path with the MBSR 103 via DU2 (192) of the MBSR 101, and establishes a BHRLC channel for data communication (S1311). This series of sequences enables the UE 123 connected to the MBSR 103 to communicate data.

[0096] <Fifth Embodiment: Relay Request from IAB Donor to Another MBSR (with UE)> Figure 14 shows the process flow for determining the MBSR mode in this embodiment (also in the sixth embodiment described later). The MBSR is connected to the network as an MBSR in normal mode (S1401). When a mode change instruction is received from the IAB donor (S1402), the MBSR checks whether or not there is a UE connected to it (S1403). If there is a connected UE, the MBSR disconnects from the connected UE and operates in relay mode (S1406). If there is no connected UE, the MBSR operates in relay mode (S1405). If no change instruction is received in S1402, the MBSR continues to operate in normal mode (S1404).

[0097] FIG. 15 is a sequence diagram showing the flow of events from when the IAB donor detects a disconnection with the MBSR 103 to when it requests relay to another MBSR 101, resulting in connection.

[0098] In this embodiment, unlike the first and second embodiments described above, it is assumed that the MBSR 101 is connected to the UE 121. In this case, the MBSR 101 can operate in relay mode after disconnecting from the connected UE in response to a response from the IAB donor 110 (see S1406 in FIG. 14). Note that, unlike this assumption, if the MBSR 101 is not connected to the UE 121, the first and second embodiments described above may be used.

[0099] Specifically, referring to FIG. 15, in this embodiment, another MBSR has a UE 121 under its control, which is connected to the MBSR 101 and continues data communication (S1501).

[0100] The MBSR 101 announces that it can operate as a relay node (S1502). The MBSR 103 receives the announcement signal from the MBSR 101, but does not respond at this stage because it is still connected to its parent node. If the MBSR 103 subsequently moves and becomes hidden behind an obstruction, its wireless connection with the parent node, the IAB donor 110, is severed. When the IAB donor 110 detects that its connection with the subordinate MBSR 103 has been severed (S1503), it transmits a connection request in relay mode to the other connected child node, the MBSR 101 (S1504). At this time, the connection request may be transmitted on the condition that it can be confirmed that the MBSR 103 is in a connectable state based on its location information, etc. Here, the signal transmitted from the IAB donor 110 to the MBSR 101 adds a "connection request to disconnected MBSR" parameter to the reserved field of the RRC Reconfiguration message, which is the RRC protocol shown in FIG. 6. Alternatively, a parameter "request to connect to disconnected MBSR" may be added to the reserved area of ​​PDUType in S901 of the BAP message in FIG. 7, and a request for connection may be transmitted.

[0101] The IAB donor 110 responds to the MBSR 101 that it may operate in relay mode (S1505). Here, if the MBSR 101 switches from normal mode to relay mode and operates in relay mode, it would be complicated to connect to other nodes while maintaining the connection with the UE. Therefore, the MBSR 101 releases the connection with the UE 121 using an RRC Release message (or notifies other connectable IAB nodes), and operates exclusively as a relay with the MBSR 103 (S1506, S1507).

[0102] The MBSR 101 transmits a broadcast signal indicating that it will operate in relay mode (S1508). Having recognized the MBSR 101 as a connectable parent node, the MBSR 103 decides to connect to the MBSR 101 as a parent node. Then, it executes a random access procedure to connect to the MBSR 101 (S1509), requests connection via an RRC SetUp Request message or the like, and completes the connection (S1510). The IAB donor 110 sets up a backhaul path with the MBSR 103 via the MBSR 101, and establishes a BHRLC channel for data communication (S1511). This series of sequences enables the UE 123 connected to the MBSR 103 to communicate data.

[0103] <Sixth embodiment: Relay request to another MBSR (with UE) by disconnected MBSR> FIG. 16 is a sequence diagram showing the flow until connection is achieved by a disconnected MBSR 103 requesting relay to another MBSR 101.

[0104] In this embodiment, unlike the first and second embodiments described above, it is assumed that the MBSR 101 is connected to the UE 121. In this case, the MBSR 101 can operate in relay mode after disconnecting from the connected UE in response to a response from the IAB donor 110 (see S1406 in FIG. 14). Note that, unlike this assumption, if the MBSR 101 is not connected to the UE 121, the first and second embodiments described above may be used.

[0105] Specifically, referring to FIG. 16, in this embodiment, another MBSR has a UE 121 under its control, which is connected to the MBSR 101 and continues data communication (S1601).

[0106] The MBSR 101 announces that it can operate as a relay node (S1602). The MBSR 103 receives the announcement signal from the MBSR 101, but does not respond at this stage because it is connected to the parent node. After that, when the MBSR 103 moves and becomes hidden behind an obstruction, the wireless connection with the parent node's IAB donor 110 is cut off, and the MBSR 103 detects that the parent node has been disconnected (S1603).

[0107] Since MBSR 103 recognizes that relaying is possible from the broadcast signal from MBSR 101, it transmits an RRC SetUp Request message to MBSR 101 by adding a parameter "relay request" to the reserved field (S1604). Alternatively, as in the third embodiment, if S1602 (MBSR 101 can operate as a relay node) is not received, it may transmit information indicating a relay request by adding it to the broadcast information (SS / PBCH Block) that relaying is possible.

[0108] Upon receiving the relay request from MBSR 103, MBSR 101 confirms with IAB donor 110 whether it is permitted to operate as a relay node (S1605). The IAB donor 110 replies to MBSR 101 that it is permitted to operate in relay mode (S1606). Here, when MBSR 101 operates in "relay mode," maintaining a connection with the UE while connecting to other nodes increases complexity. Therefore, MBSR 101 releases its connection with UE 121 and uses it for relaying with MBSR 103 (S1607, S1608).

[0109] The MBSR 101 transmits a broadcast signal indicating that it is operating in relay mode (S1609). Alternatively, instead of broadcasting, the means for notifying the MBSR 103 of its operation in relay mode may be an RRC Reconfiguration message. Having recognized the MBSR 101 as a connectable parent node, the MBSR 103 decides to connect to the MBSR 101 as a parent node and executes a random access procedure to connect to the MBSR 101 (S1610). Thereafter, the IAB donor 110 requests connection via an RRC SetUp Request message or the like, and completes the connection (S1611). The IAB donor 110 sets up a backhaul (BH) path with the MBSR 103 via the DU2 (192) of the MBSR 101, and establishes a BHRLC channel for data communication (S1612).

[0110] This series of sequences enables the UE 123 connected to the MBSR 103 to perform data communication.

[0111] <Other Embodiments> In the above-described embodiment, an MBSR that receives a relay request starts operating in relay mode. However, the MBSR may be configured to reject the relay request as needed. The MBSR that receives a relay request can determine to reject the relay request depending on its own resource constraints, etc. If it determines to reject the relay request, it notifies the device that sent the relay request of a message indicating that the relay request is being rejected. In this case, the requesting device that receives the message indicating the rejection can transmit a relay request to another candidate device. For example, the MBSR that receives the relay request can reject the relay request if its available frequency resources are already constrained by existing communications, or if the number of UEs already connected to the MBSR is greater than a predetermined number. This process can prevent adverse effects on existing communications.

[0112] This embodiment can also be realized by supplying a program that realizes one or more of the functions of each of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC or FPGA) that realizes one or more of the functions.

[0113] Although each embodiment has been described in detail above, it is not limited to a specific embodiment, and various modifications and changes are possible within the scope of the claims. It is also possible to combine all or a plurality of components of the above-described embodiments.

[0114] In addition, the following supplementary notes are disclosed regarding the above-described embodiment.

[0115] [Supplementary Note 1] A communication device having an operation function of MBSR (Mobile Base Station Relay), characterized in that the communication device is operable in a first mode in which only other communication devices having the operation function of MBSR are connected to one of the communication device's DU (Distribution Unit), and in which the communication device relays communication between the other communication devices and an IAB (Integrated Access and Backhaul) donor.

[0116] [Supplementary Note 2] The communication device according to Supplementary Note 1, characterized in that it comprises a mode switching means for switching the operation mode between a second mode in which only a UE (User Equipment) is connected to one DU of the own station, and the first mode.

[0117] [Supplementary Note 3] The communication device according to Supplementary Note 1 or 2, characterized in that when operating in the first mode, only a connection from another MBSR out of the UE and the other MBSR is permitted.

[0118] [Supplementary Note 4] The communication device according to Supplementary Note 2, characterized in that when switching from the second mode to the first mode while connected to a UE, a new DU is activated.

[0119] [Supplementary Note 5] The communication device according to Supplementary Note 2 or 4, characterized in that the mode switching means switches from the second mode to the first mode in response to a relay request from an IAB donor or a relay request from the other communication device.

[0120] [Supplementary Note 6] The communication device according to any one of Supplementary Notes 1 to 5, further comprising a transmitting means for transmitting to an IAB donor or the other communication device that the communication device is operable in the first mode or that the communication device is operating in the first mode.

[0121] [Supplementary Note 7] The communication device according to any one of Supplementary Notes 1 to 6, wherein the transmitting means uses an SSB (Synchronization Signal Block) message or an RRC message.

[0122] [Supplementary Note 8] A communication device having an operation function of MBSR (Mobile Base Station Relay), which, in response to a relay request from an IAB (Integrated Access and Backhaul) donor, relays the other communication device having the operation function of MBSR so that the other communication device can communicate with the IAB donor via the node itself.

[0123] [Supplementary Note 9] The communication device according to Supplementary Note 8, which changes the relay method of the other communication device depending on whether or not the other communication device is connected to a UE (User Equipment) when the relay request is received.

[0124] [Supplementary Note 10] The communication device according to Supplementary Note 9, wherein, if the communication device is connected to a UE when the relay request is received, the communication device starts a new Distributed Unit (DU) in response to the relay request, and relays the other communication device using the started new DU.

[0125] [Supplementary Note 11] The communication device according to Supplementary Note 9 or 10, wherein, if the communication device is connected to a UE when the relay request is received, the communication device releases the connection with the connected UE in response to the relay request, and then relays the other communication device.

[0126] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0127] This application claims priority based on Japanese Patent Application No. 2023-216606, filed December 22, 2023, the entire contents of which are incorporated herein by reference.

[0128] 100 Communication system 101 MBSR 102 MBSR 103 MBSR 110 IAB donor (primary base station) 111 Vehicle 112 Vehicle 113 Vehicle 130 Shield 131 Shield 140 Wired link 141 Wireless backhaul link 142 Wireless backhaul link 150 Core network 201 Control unit 202 Storage unit 203 Wireless communication unit 204 Communication antenna control unit 205 GPS communication unit 206 GPS antenna control unit 302 Signal transmission unit (an example of a transmission means) 303 Signal reception unit 304 Data storage unit 305 Connection control unit 306 Network configuration information management unit 307 Relay request processing unit 308 Signal generation unit 309 GPS signal processing unit 310 Mode switching unit (an example of a mode switching means) 402 Control unit 403 Storage unit 404 Wireless communication unit 405 Communication antenna control unit 502 Signal transmission unit 503 Signal reception unit 504 Data storage unit 505 Connection control unit 506 Notification information detection unit 507 Peripheral node determination unit 508 Mode change instruction generation unit

Claims

1. A communication device having an MBSR (Mobile Base Station Relay) operation function, characterized in that the communication device is operable in a first mode in which only other communication devices having the MBSR operation function are connected to one of the communication devices' DUs (Distribution Units), and in which the communication device is operable in a first mode in which the communication device relays communication between the other communication devices and an IAB (Integrated Access and Backhaul) donor.

2. A communication device as described in claim 1, characterized in that it is provided with a mode switching means for switching the operating mode between a second mode in which only UE (User Equipment) is connected to one DU of the station and the first mode.

3. The communication device according to claim 1, characterized in that when operating in the first mode, only a connection from another MBSR among the UE and the other MBSR is permitted.

4. The communication device according to claim 2, characterized in that when switching from the second mode to the first mode while connected to a UE, a new DU is initiated.

5. The communication device according to claim 2, wherein the mode switching means switches from the second mode to the first mode in response to a relay request from an IAB donor or a relay request from the other communication device.

6. A communication device as claimed in any one of claims 1 to 5, further comprising a transmitting means for transmitting to an IAB donor or the other communication device that it is operable in the first mode or that it is operating in the first mode.

7. The communication device according to claim 6, wherein the transmission means uses an SSB (Synchronization Signal Block) message or an RRC message.

8. A communication device having an MBSR (Mobile Base Station Relay) operation function, which, in response to a relay request from an IAB (Integrated Access and Backhaul) donor or a relay request from another communication device having an MBSR operation function, relays the other communication device so that the other communication device can communicate with the IAB donor via its own node.

9. The communication device according to claim 8, wherein the relay method of the other communication device is changed depending on whether or not the other communication device is connected to a UE (User Equipment) when the relay request is received.

10. The communication device according to claim 9, which, if connected to a UE when receiving the relay request, starts a new Distributed Unit (DU) in response to the relay request, and relays the other communication device using the new DU that has been started.

11. The communication device according to claim 9, which, if connected to a UE when the relay request is received, responds to the relay request by disconnecting the connected UE and then relaying to the other communication device.

12. A control method for a communication device having an MBSR (Mobile Base Station Relay) operation function, comprising the step of forming a first mode in which only other communication devices having the MBSR operation function are connected to one of the station's DUs (Distribution Units), and in which the first mode relays communications between the other communication devices and an IAB (Integrated Access and Backhaul) donor.

13. A program for causing a computer of a communication device having an MBSR (Mobile Base Station Relay) operating function to execute a process of forming a first mode in which only other communication devices having an MBSR operating function are connected to one of the station's DUs (Distribution Units), and in which the first mode relays communications between the other communication devices and an IAB (Integrated Access and Backhaul) donor.

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