Communication control method and relay device

Abstract

To provide a communication control method executed in a relay device included in a plurality of relay devices when a failure occurs in a backhaul link established between the relay device and a first host device in a system in which an upstream path using the plurality of relay devices is formed between a user device and a first donor device, and to provide the relay device.SOLUTION: The communication control method includes transferring data received from a lower-level device of the relay device on an upstream path to a first higher-level device of the relay device, buffering data that has not been transmitted to the first higher-level device, reestablishing a backhaul link of the relay device with a second higher-level device when a failure occurs in the backhaul link established between the relay device and the first higher-level device, and determining whether to transfer the buffered data to the second higher-level device based on whether a second donor device managing the second higher-level device is the same as the first donor device.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a communication control method and a relay device used in a mobile communication system. [Background technology]

[0002] 3GPP (3rd Generation Partnership Project) (registered trademark, hereinafter the same), a standardization project for mobile communication systems, is studying a new relay device called an IAB (Integrated Access and Backhaul) node. One or more relay devices intervene in communication between a base station, which is a donor device, and a user device, and relay this communication.

[0003] Such a relay device has user equipment functions and base station functions, and uses the user equipment functions to perform wireless communication with a higher-level device (a base station or a higher-level relay device), and uses the base station functions to perform wireless communication with a lower-level device (a user equipment or a lower-level relay device).

[0004] A wireless section between a user device and a relay device or a base station is sometimes called an access link. A wireless section between a relay device and a base station or another relay device is sometimes called a backhaul link. Non-Patent Document 1 describes a method for dynamically switching data transfer paths by integrating and multiplexing data communications on access links and data communications on backhaul links in Layer 2 and dynamically allocating radio resources to the backhaul links. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] 3GPP contribution “RP-182894” Summary of the Invention

[0006] A communication control method according to a first aspect is a method executed by a relay device included in a plurality of relay devices in a mobile communication system in which an upstream path is formed between a user device and a first donor device using the plurality of relay devices. The communication control method includes: forwarding data received from a lower-level device of the relay device in the upstream path to a first higher-level device that is higher than the relay device; buffering data that has not yet been transmitted to the first higher-level device; when a failure occurs in a backhaul link established between the relay device and the first higher-level device, re-establishing the backhaul link of the relay device with a second higher-level device; and determining whether to forward the buffered data to the second higher-level device based on whether a second donor device managing the second higher-level device is the same as the first donor device.

[0007] A relay device according to a second aspect is a relay device included in a plurality of relay devices in a mobile communication system in which an upstream path is formed between a user device and a first donor device using a plurality of relay devices. The relay device includes a control unit that executes the following processes: forwarding data received from a lower-level device of the relay device in the upstream path to a first higher-level device that is higher than the relay device; buffering data that has not yet been transmitted to the first higher-level device; re-establishing the backhaul link of the relay device with a second higher-level device when a failure occurs in the backhaul link established between the relay device and the first higher-level device; and determining whether to forward the buffered data to the second higher-level device based on whether a second donor device that manages the second higher-level device is the same as the first donor device. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating a configuration of a base station according to an embodiment. [Figure 3] FIG. 2 is a diagram illustrating a configuration of a relay device according to an embodiment. [Figure 4] FIG. 1 is a diagram illustrating a configuration of a user device according to an embodiment. [Figure 5] FIG. 2 is a diagram illustrating an example of a protocol stack configuration according to an embodiment. [Figure 6] FIG. 1 is a diagram illustrating an operation scenario of a mobile communication system according to an embodiment. [Figure 7] FIG. 10 is a flowchart illustrating an example of an operation of a relay device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] In a situation where an upstream path using multiple relay devices is formed between a user device and a first donor device, if a failure occurs in the backhaul link established between the relay device and its upper device (first upper device), it may be necessary to re-form the upstream path by re-establishing the backhaul link of the relay device with the second upper device.

[0010] Therefore, an object of the present disclosure is to provide a communication control method and a relay device that can appropriately deal with a failure in a backhaul link.

[0011] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0012] (Configuration of a mobile communication system) First, the configuration of a mobile communication system according to one embodiment will be described. Fig. 1 is a diagram showing the configuration of a mobile communication system 1 according to one embodiment. The mobile communication system 1 is a fifth-generation (5G) mobile communication system based on the 3GPP standard. Specifically, the radio access method in the mobile communication system 1 is NR (New Radio), which is a 5G radio access method. However, LTE (Long Term Evolution) may be applied at least partially to the mobile communication system 1.

[0013] 1, the mobile communication system 1 includes a 5G core network (5GC) 10, user equipment (UE) 100, a base station (referred to as a gNB) 200, and an IAB node 300. The IAB node 300 is an example of a relay device.

[0014] In one embodiment, an example in which the base station is an NR base station is mainly described, but the base station may also be an LTE base station (i.e., an eNB).

[0015] The 5GC 10 has an Access and Mobility Management Function (AMF) 11 and a User Plane Function (UPF) 12. The AMF 11 is a device that performs various mobility controls for the UE 100. The AMF 11 manages information about the area in which the UE 100 is located by communicating with the UE 100 using Non-Access Stratum (NAS) signaling. The UPF 12 is a device that performs transfer control of user data, etc.

[0016] The gNB200 is connected to the 5GC10 via an interface called an NG interface. Figure 1 illustrates three gNBs, gNB200-1 to gNB200-3, connected to the 5GC10. The gNB200 is a fixed wireless communication device that performs wireless communication with the UE100. If the gNB200 has a donor function, the gNB200 may perform wireless communication with an IAB node wirelessly connected to the gNB200.

[0017] The gNB 200 is connected to other adjacent gNBs 200 via an inter-base station interface called an Xn interface. Figure 1 shows an example in which gNB 200-1 is connected to gNB 200-2 and gNB 200-2.

[0018] Each gNB 200 manages one or more cells. A cell is used as a term indicating the smallest unit of a wireless communication area. A cell may also be used as a term indicating a function or resource for performing wireless communication with a UE 100. One cell belongs to one carrier frequency.

[0019] The UE 100 is a mobile wireless communication device that performs wireless communication with the gNB 200. The UE 100 may perform wireless communication with the IAB node 300. The UE 100 may be any device that performs wireless communication with the gNB 200 or the IAB node 300. For example, the UE 100 is a mobile phone terminal, a tablet terminal, a laptop computer, a sensor or a device provided in a sensor, or a vehicle or a device provided in a vehicle.

[0020] 1 shows an example in which UE 100-1 is wirelessly connected to gNB 200-1, UE 100-2 is wirelessly connected to IAB node 300-1, and UE 100-3 is wirelessly connected to IAB node 300-2. UE 100-1 directly communicates with gNB 200-1. UE 100-2 indirectly communicates with gNB 200-1 via IAB node 300-1. UE 100-3 indirectly communicates with gNB 200-1 via IAB node 300-1 and IAB node 300-2.

[0021] The IAB node 300 is a device (relay device) that intervenes in communication between the eNB 200 and the UE 100 and relays this communication. FIG. 1 shows an example in which the IAB node 300-1 is wirelessly connected to the gNB 200-1, which is a donor device, and the IAB node 300-2 is wirelessly connected to the IAB node 300-1. Each IAB node 300 manages a cell. The cell ID of the cell managed by the IAB node 300 may be the same as or different from the cell ID of the cell of the donor gNB 200-1.

[0022] The IAB node 300 has a UE function (user equipment function) and a gNB function (base station function). Such a UE function may be referred to as an MT, and the gNB function may be referred to as a DU.

[0023] The IAB node 300 performs wireless communication with an upper device (gNB200 or upper IAB node 300) using its own UE function (MT), and also performs wireless communication with a lower device (UE100 or lower IAB node 300) using its own gNB function (DU). Note that the UE function (MT) means at least some of the functions of the UE100, and the IAB node 300 does not necessarily have all of the functions of the UE100. The gNB function (DU) means at least some of the functions of the gNB200, and the IAB node 300 does not necessarily have all of the functions of the gNB200. For example, the gNB function (DU) does not necessarily have an RRC layer, a PDCP layer, etc.

[0024] A wireless section between the UE 100 and the IAB node 300 or the gNB 200 may be referred to as an access link (or Uu). A wireless section between the IAB node 300 and the gNB 200 or another IAB node 300 may be referred to as a backhaul link (or Un). Such a backhaul link may also be referred to as a fronthaul link.

[0025] It is possible to integrate and multiplex access link data communication and backhaul link data communication in Layer 2, dynamically allocate radio resources to backhaul link data communication, and dynamically switch relay paths. The access link and backhaul link may use millimeter wave bands. The access link and backhaul link may also be multiplexed by time division and / or frequency division.

[0026] (Base station configuration) Next, the configuration of the gNB 200, which is a base station according to one embodiment, will be described. Fig. 2 is a diagram showing the configuration of the gNB 200. As shown in Fig. 2, the gNB 200 has a radio communication unit 210, a network communication unit 220, and a control unit 230.

[0027] The wireless communication unit 210 is used for wireless communication with the UE 100 and wireless communication with the IAB node 300. The wireless communication unit 210 has a receiving unit 211 and a transmitting unit 212. The receiving unit 211 performs various receptions under the control of the control unit 230. The receiving unit 211 includes an antenna, and converts a wireless signal received by the antenna into a baseband signal (received signal), and outputs the signal to the control unit 230. The transmitting unit 212 performs various transmissions under the control of the control unit 230. The transmitting unit 212 includes an antenna, and converts a baseband signal (transmitted signal) output by the control unit 230 into a wireless signal, and transmits the signal from the antenna.

[0028] The network communication unit 220 is used for wired communication (or wireless communication) with the 5GC10 and wired communication (or wireless communication) with other adjacent gNB200. The network communication unit 220 has a receiving unit 221 and a transmitting unit 222. The receiving unit 221 performs various receptions under the control of the control unit 230. The receiving unit 221 receives signals from the outside and outputs the received signals to the control unit 230. The transmitting unit 222 performs various transmissions under the control of the control unit 230. The transmitting unit 222 transmits the transmission signals output by the control unit 230 to the outside.

[0029] The control unit 230 performs various controls in the gNB 200. The control unit 230 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. The processor executes the processes described below.

[0030] (Configuration of relay device) Next, the configuration of an IAB node 300, which is a relay device according to one embodiment, will be described. Fig. 3 is a diagram showing the configuration of the IAB node 300. As shown in Fig. 3, the IAB node 300 includes a wireless communication unit 310 and a control unit 320. The IAB node 300 may include multiple wireless communication units 310.

[0031] The wireless communication unit 310 is used for wireless communication (backhaul link) with the gNB 200 and for wireless communication (access link) with the UE 100. The wireless communication unit 310 for backhaul link communication and the wireless communication unit 310 for access link communication may be provided separately.

[0032] The wireless communication unit 310 has a receiving unit 311 and a transmitting unit 312. The receiving unit 311 performs various types of reception under the control of the control unit 320. The receiving unit 311 includes an antenna, and converts a wireless signal received by the antenna into a baseband signal (received signal), and outputs the baseband signal to the control unit 320. The transmitting unit 312 performs various types of transmission under the control of the control unit 320. The transmitting unit 312 includes an antenna, and converts a baseband signal (transmitted signal) output by the control unit 320 into a wireless signal, and transmits the wireless signal from the antenna.

[0033] The control unit 320 performs various controls in the IAB node 300. The control unit 320 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes. The processor performs the processes described below.

[0034] (Configuration of user device) Next, a description will be given of a configuration of a UE 100, which is a user equipment according to an embodiment. Fig. 4 is a diagram showing the configuration of the UE 100. As shown in Fig. 4, the UE 100 includes a radio communication unit 110 and a control unit 120.

[0035] The wireless communication unit 110 is used for wireless communication in the access link, i.e., wireless communication with the gNB 200 and wireless communication with the IAB node 300. The wireless communication unit 110 has a receiving unit 111 and a transmitting unit 112. The receiving unit 111 performs various receptions under the control of the control unit 120. The receiving unit 111 includes an antenna, and converts a wireless signal received by the antenna into a baseband signal (received signal), and outputs the signal to the control unit 120. The transmitting unit 112 performs various transmissions under the control of the control unit 120. The transmitting unit 112 includes an antenna, and converts a baseband signal (transmitted signal) output by the control unit 120 into a wireless signal, and transmits the signal from the antenna.

[0036] The control unit 120 performs various controls in the UE 100. The control unit 120 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes. The processor executes the processes described below.

[0037] (An example of a protocol stack configuration) Next, an example of a protocol stack configuration in the mobile communication system 1 according to an embodiment will be described. Fig. 5 is a diagram showing an example of a protocol stack configuration of a user plane. Fig. 5 shows an example of a protocol stack configuration related to user data transmission between the UE 100-3 and the UPF 12 of the 5GC 10 shown in Fig. 1.

[0038] 5, the UPF 12 includes a GPRS Tunneling Protocol for User Plane (GTP-U), a User Datagram Protocol (UDP), an Internet Protocol (IP), and Layer 1 / Layer 2 (L1 / L2). The gNB 200-1 (donor gNB) is provided with protocol stacks corresponding to these.

[0039] The gNB200-1 also has a central unit (CU) and a distributed unit (DU). The CU has layers above the Packet Data Convergence Protocol (PDCP) in the radio interface protocol stack, and the DU has layers below the Radio Link Control (RLC). The CU and DU are connected via an interface called an F1 interface.

[0040] Specifically, the CU has a Service Data Adaptation Protocol (SDAP), a PDCP, an IP, and L1 / L2. The SDAP and PDCP of the CU communicate with the SDAP and PDCP of the UE 100 via the DU, the IAB node 300-1, and the IAB node 300-2.

[0041] The DU also has a radio interface protocol stack including RLC, an adaptation layer (Adapt), a medium access control (MAC), and a physical layer (PHY). These protocol stacks are for gNBs. The hierarchical relationship between the adaptation layer and RLC (S-RLC) may be reversed. The adaptation layer may also be called a backhaul adaptation protocol (BAP) layer.

[0042] The IAB node 300-1 is provided with a protocol stack ST1 for the UE corresponding to these. Furthermore, the IAB node 300-1 is provided with a protocol stack ST2 for the gNB. Both the protocol stack ST1 and the protocol stack ST2 are made up of layers (sublayers) below layer 2. That is, the IAB node 300-1 is a layer 2 relay device that relays user data using layers below layer 2. The IAB node 300-1 relays data without using layers above layer 3 (specifically, layers above PDCP). Note that the IAB node 300-2 has a protocol stack configuration similar to that of the IAB node 300-1.

[0043] Here, the protocol stack configuration in the user plane has been described. However, in the control plane, the gNB 200-1, the IAB node 300-1, the IAB node 300-2, and the UE 100-3 each have a Radio Resource Control (RRC) corresponding to Layer 3.

[0044] An RRC connection is established between the RRC of gNB200-1 (donor gNB) and the RRC of IAB node 300-1, and RRC messages are transmitted and received using this RRC connection. Also, an RRC connection is established between the RRC of gNB200-1 and the RRC of IAB node 300-2, and RRC messages are transmitted and received using this RRC connection. Furthermore, an RRC connection is established between the RRC of gNB200-1 and the RRC of UE 100-3, and RRC messages are transmitted and received using this RRC connection.

[0045] (Operation according to the embodiment) Next, the operation of the mobile communication system 1 according to one embodiment will be described.

[0046] FIG. 6 is a diagram showing an operation scenario of the mobile communication system 1 according to an embodiment.

[0047] 6, an upstream path using multiple relay devices (IAB node 300a, IAB node 300b, and IAB node 300c) is formed between UE 100 and donor gNB 200a. Donor gNB 200a corresponds to a first donor device.

[0048] In the following, the IAB node 300b (relay device) on the upstream path will be mainly described. The lower device below the IAB node 300b on the upstream path is the IAB node 300a, and the first upper device above the IAB node 300b on the upstream path is the IAB node 300c. Also, it is assumed that a failure occurs in the backhaul link established between the IAB node 300b and the IAB node 300c (first upper device), and the IAB node 300b re-establishes the backhaul link with the IAB node 300d (second upper device).

[0049] The donor gNB 200a manages the IAB nodes 300a, 300b, 300c, and 300d, and functions as a donor for the IAB nodes 300a, 300b, 300c, and 300d. In other words, the IAB nodes 300a, 300b, 300c, and 300d are under the control of the donor gNB 200a.

[0050] Alternatively, donor gNB 200b may manage IAB node 300d and function as a donor for IAB node 300d. In other words, IAB node 300d may be under the control of donor gNB 200b rather than donor gNB 200a. Hereinafter, the donor gNB that manages IAB node 300d will be referred to as a second donor device. The second donor device is donor gNB 200a or donor gNB 200b.

[0051] The UE 100 transmits upstream data to the donor gNB 200a via the path of the IAB node 300a, the IAB node 300b, and the IAB node 300c, but not via the IAB node 300d. In one embodiment, the upstream data is a PDCP Protocol Data Unit (PDU). However, assuming that there is no segmentation (segmentation) of the PDCP PDU, the upstream data may be an RLC SDU. Alternatively, the upstream data may be a BAP PDU.

[0052] PDCP PDU #0 has been received by the donor gNB 200a, and PDCP PDUs #1 and #2 have been received by the IAB node 300c. PDCP PDU #3 has not yet been received by the IAB node 300c and is being transmitted by the RLC layer of the IAB node 300b. PDCP PDUs #4, #5, and #6 have been received by the IAB node 300b but have not yet been passed from the PDCP layer to the RLC layer in the IAB node 300b. PDCP PDU #7 has been received by the IAB node 300a. PDCP PDUs #8 and #9 are buffered on the UE 100 side.

[0053] Under such circumstances, a radio link failure (i.e., a BH RLF) of the backhaul link occurs between IAB node 300b and IAB node 300c. IAB node 300b reestablishes the backhaul link with IAB node 300d, which is a new parent node (upper device). For example, IAB node 300b reestablishes the backhaul link with IAB node 300d by performing an RRC reestablishment process via IAB node 300d. After the RRC reestablishment, the RLC entity of IAB node 300b is reestablished. Here, it is assumed that IAB node 300b buffers untransmitted PDCP PDUs #3, #4, #5, and #6, for example, in the BAP layer.

[0054] Thus, in one embodiment, in a situation where an upstream path is formed between the UE 100 and the donor gNB 200a (first donor device), if a failure occurs in the backhaul link established between the IAB node 300b and the IAB node 300c, the IAB node 300b re-establishes its backhaul link with the IAB node 300d (second higher-level device), thereby re-establishing the upstream path.

[0055] In one embodiment, the BAP layer of IAB node 300b may forward the buffered upstream data (i.e., PDCP PDUs #3, #4, #5, and #6) to IAB node 300d. In other words, the BAP layer of IAB node 300b may reroute the upstream data using the new upstream path.

[0056] However, if the IAB node 300d is not under the control of the donor gNB 200a but is under the control of the donor gNB 200b, the donor gNB 200b cannot process the upstream data buffered by the IAB node 300b even if the donor gNB 200b receives the upstream data via the IAB node 300d. Specifically, the PDCP PDU is encrypted by the UE 100 using a security key, and the paired PDCP entity exists in the donor 200a. The donor gNB 200a decrypts (decrypts) the PDCP PDU using the security key, but the donor gNB 200b does not have this security key and cannot decrypt the PDCP PDU.

[0057] In contrast, if IAB node 300d is under the control of donor gNB 200a, donor gNB 200a can process the upstream data buffered by IAB node 300b when it receives the data via IAB node 300d.

[0058] In one embodiment, IAB node 300b can appropriately handle backhaul link failures by determining whether to forward buffered upstream data to IAB node 300d depending on whether IAB node 300d is under the control of donor gNB 200a.

[0059] First, the IAB node 300b forwards upstream data received from the IAB node 300a, which is a lower-level device of the IAB node 300b, to the IAB node 300c, which is a first higher-level device of the IAB node 300b. Also, the IAB node 300b buffers upstream data that has not yet been sent to the IAB node 300c.

[0060] Second, if a failure occurs in the backhaul link established between IAB node 300b and IAB node 300c, IAB node 300 re-establishes the backhaul link of IAB node 300b with IAB node 300d, which is the second higher-level device.

[0061] Third, the BAP layer of IAB node 300b decides whether to forward the buffered upstream data to IAB node 300d based on whether the donor device (second donor device) managing IAB node 300d is the same as donor gNB200a (first donor device).

[0062] Specifically, when the BAP layer of IAB node 300b determines that the donor device of IAB node 300d is the same as donor gNB 200a, it forwards the buffered upstream data to IAB node 300d. In this case, when the BAP layer or RLC layer of IAB node 300b completes forwarding the buffered upstream data, it may transmit an ACK (e.g., an RLC ACK) corresponding to the buffered upstream data to IAB node 300a, which is its lower-level device.

[0063] On the other hand, if the BAP layer of IAB node 300b determines that the donor device of IAB node 300d is different from donor gNB 200a (for example, if the donor device of IAB node 300d is donor gNB 200b), it discards the buffered upstream data. Also, if the BAP layer or RLC layer of IAB node 300b determines that the donor device of IAB node 300d is different from donor gNB 200a, it may transmit a NACK (for example, an RLC NACK) corresponding to the buffered upstream data to IAB node 300a, which is a lower-level device.

[0064] In one embodiment, the MT of IAB node 300b may receive an identifier for the donor device of IAB node 300d from IAB node 300d. The MT or BAP layer of IAB node 300b may determine whether the donor device of IAB node 300d is the same as donor gNB 200a based on the identifier received from IAB node 300d.

[0065] For example, IAB node 300b may receive an RRC Reconfiguration message from IAB node 300d that includes an identifier for the donor device of IAB node 300d. This RRC Reconfiguration message may be sent from donor gNB 200a to IAB node 300b via IAB node 300d.

[0066] Alternatively, IAB node 300b may receive an RRC Reconfiguration message from IAB node 300c that includes an identifier for the donor device of IAB node 300d. This RRC Reconfiguration message may be sent from donor gNB 200a to IAB node 300b via IAB node 300c.

[0067] The RRC Reconfiguration message may be an RRC Reconfiguration message for handover or an RRC Reconfiguration message for RRC re-establishment. The MT of the IAB node 300b may retain the identifier included in the received RRC Reconfiguration message.

[0068] Alternatively, the IAB node 300b may receive a System Information Block (SIB) from the IAB node 300d, the SIB including an identifier related to the donor device of the IAB node 300d. The SIB is notification information broadcast by the IAB node 300d. The MT of the IAB node 300b may hold the identifier included in the received SIB.

[0069] The identifier for the donor device of IAB node 300d includes at least one of the base station identifier (gNB ID) of the donor device of IAB node 300d and the identifier of the CU (Central Unit) of the donor device of IAB node 300d. The MT or BAP layer of IAB node 300b compares the identifier for the donor gNB 200a (the identifier previously held) with the identifier for the donor device of IAB node 300d (the newly acquired identifier), and determines that the donor device managing IAB node 300d is the same as donor gNB 200a only if the two identifiers match.

[0070] Alternatively, the identifier for the donor device of IAB node 300d may include at least one of an identifier indicating whether the donor device of IAB node 300d is the same as donor gNB 200a and an identifier indicating whether the donor device is permitted to forward buffered upstream data to IAB node 300d. Based on such identifier, the MT or BAP layer of IAB node 300b determines whether the donor device managing IAB node 300d is the same as donor gNB 200a, i.e., whether the donor device is permitted to forward buffered upstream data to IAB node 300d.

[0071] Alternatively, the MT of the IAB node 300b may receive a list of IAB nodes 300b subordinate to the donor gNB 200a from the IAB node 300c. This list may be included in an RRC Reconfiguration message transmitted from the donor gNB 200a to the IAB node 300b via the IAB node 300c. The MT or BAP layer of the IAB node 300b determines whether the donor device of the IAB node 300d is the same as the donor gNB 200a based on the list received from the IAB node 300c. For example, if the identifier for the IAB node 300d is included in the list, the MT or BAP layer of the IAB node 300b determines that the donor device of the IAB node 300d is the same as the donor gNB 200a.

[0072] Fig. 7 is a flow diagram showing an example of the operation of a relay device according to one embodiment. Here, the operation of IAB node 300b in the operation scenario shown in Fig. 6 will be described. However, the operation shown in Fig. 7 may also be performed by IAB node 300a shown in Fig. 6. IAB node 300a is an IAB node having an access link with UE 100, and may be called an access IAB node.

[0073] As shown in FIG. 7, in step S1, the IAB node 300b, together with the IAB nodes 300a and 300c, forms an upstream path between the UE 100 and the first donor device (donor gNB 200a).

[0074] In step S2, the IAB node 300b receives a list of IAB nodes under the first donor device (donor gNB 200a) from the IAB node 300c. This list may be a list of identifiers of each IAB node under the first donor device (donor gNB 200a). This list may be transmitted from the first donor device (donor gNB 200a) to the IAB node 300b via the IAB node 300c. Note that the process of step S6, which will be described later, may be performed without performing the process of step S2.

[0075] In step S3, the IAB node 300b transfers the upstream data received from the lower-level device (IAB node 300a) of the IAB node 300b on the upstream path to the first upper-level device (IAB node 300bc) above the IAB node 300b. The IAB node 300b also buffers the upstream data that has not yet been sent to the IAB node 300c.

[0076] In step S4, the IAB node 300b determines whether a failure (BH RLF) has occurred in the backhaul link established between the IAB node 300b and the first higher-level device (IAB node 300c). If a BH RLF has not occurred (step S4: NO), the process returns to step S3. On the other hand, if a BH RLF has occurred (step S4: YES), the process proceeds to step S5.

[0077] In step S5, the IAB node 300b re-establishes the backhaul link of the IAB node 300b with the second upstream device (IAB node 300d), thereby re-establishing the upstream path.

[0078] In step S6, the IAB node 300b receives an identifier related to the donor device of the IAB node 300d from the MT of the IAB node 300b. The IAB node 300b may receive an RRC Reconfiguration message including an identifier related to the donor device of the IAB node 300d from the IAB node 300d. This RRC Reconfiguration message may be transmitted from the donor gNB 200a to the IAB node 300b via the IAB node 300d. Note that if the process of step S2 described above has been executed, the process of step S6 does not need to be executed. For the IAB node 300b to make a determination in step S7 described next, at least one of the processes of step S2 and step S6 needs to be executed. Both the processes of step S2 and step S6 may be executed.

[0079] In step S7, the IAB node 300b determines whether the second donor device managing the second upstream device (IAB node 300d) is the same as the first donor device (donor gNB 200a) based on the list received in step S2 or the identifier received in step S6. In other words, the IAB node 300b determines whether it is permitted to forward the buffered upstream data to the IAB node 300d.

[0080] If it is determined that the second donor device managing the second upstream device (IAB node 300d) is the same as the first donor device (donor gNB200a) (step S7: YES), in step S8, the IAB node 300b transfers the buffered upstream data to the second upstream device (IAB node 300d).

[0081] On the other hand, if it is determined that the second donor device managing the second higher-level device (IAB node 300d) is different from the first donor device (donor gNB 200a) (step S7: NO), in step S9, the IAB node 300b discards the buffered upstream data. Then, in step S10, the IAB node 300b transmits a NACK corresponding to the buffered upstream data to the IAB node 300a, which is the lower-level device.

[0082] (Other embodiments) In the above-described embodiment, a base station (hereinafter referred to as a master base station) that manages each IAB node 300 may exist in addition to the donor gNB 200. The master base station may be an LTE base station. The MT of each IAB node 300 may have two connections (i.e., dual connections): one with the master base station and one with an upper device (upper IAB node or donor gNB). The master base station may be the master node, and the connection may be a Master Cell Group (MCG) link. The upper device (upper IAB node or donor gNB) may be a secondary node, and the connection may be a Secondary Cell Group (SCG) link. Under such assumptions, the MT of the IAB node 300b may receive the list of step S3 or the identifier of step S6 of FIG. 7 from the master base station via the MCG link.

[0083] In the above-described embodiment, an example in which the mobile communication system 1 is a 5G mobile communication system has been mainly described. However, the base station in the mobile communication system 1 may be an eNB, which is an LTE base station. Furthermore, the core network in the mobile communication system 1 may be an EPC (Evolved Packet Core). Furthermore, the gNB may be connected to the EPC, and the eNB may be connected to the 5GC, and the gNB and eNB may be connected via an inter-base station interface (Xn interface, X2 interface).

[0084] A program that causes a computer to execute each process according to the above-described embodiments may be provided. The program may also be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. A chipset may also be provided, which is configured by a memory that stores a program for executing each process performed by the UE 100, the gNB 200, or the IAB node 300, and a processor that executes the program stored in the memory.

[0085] This application claims priority from Japanese Patent Application No. 2019-145743 (filed August 7, 2019), the entire contents of which are incorporated herein by reference.

Claims

1. A communication control method executed in a relay device, comprising: receiving a BAP (Backhaul Adaptation Protocol) data unit from a lower relay device of the relay device; When a failure occurs in a backhaul link between a first upper relay device of the relay device and the relay device, transmitting the BAP data unit via a backhaul link established between the relay device and a second upper relay device; receiving, from a first donor device that is a donor device of the first higher level relay device, identification information relating to the first donor device; The transmitting step includes transmitting the BAP data unit based on the identification information. Communication control method.

2. A relay device, a receiving unit for receiving a BAP data unit from a lower relay device of the relay device; a transmitter that transmits the BAP data unit via a backhaul link established between the relay device and a second upper relay device when a failure occurs in a backhaul link between the relay device and a first upper relay device of the relay device, the receiving unit receives, from a first donor device that is a donor device of the first higher level relay device, identification information regarding the first donor device; The transmitting unit transmits the BAP data unit based on the identification information. Relay device.

3. A processor for controlling a relay device, A process of receiving a BAP (Backhaul Adaptation Protocol) data unit from a lower relay device of the relay device; When a failure occurs in a backhaul link between a first upper relay device of the relay device and the relay device, a process of transmitting the BAP data unit via a backhaul link established between the relay device and a second upper relay device; receiving, from a first donor device that is a donor device of the first higher-level relay device, identification information relating to the first donor device; The transmitting step includes transmitting the BAP data unit based on the identification information. Processor.

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