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 Art

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

[0003] Such a relay device has a user device function and a base station function, performs wireless communication with an upper device (base station or upper relay device) using the user device function, and performs wireless communication with a lower device (user device or lower relay device) using the base station function.

[0004] The radio section between a user device and a relay device or a base station may be called an access link. The radio section between a relay device and a base station or another relay device may be called a backhaul link. Non-Patent Document 1 describes a method of dynamically switching a data transfer path by integrating and multiplexing data communication of an access link and data communication of a backhaul link in layer 2 and dynamically allocating radio resources to the backhaul link.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

[0006] The first aspect of the communication control method is a method performed in 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 communication control method includes: transferring data received from a lower-level device of the relay device in the upstream path to a first higher-level device of the relay device; buffering data not yet transmitted to the first higher-level device; re-establishing the backhaul link of the relay device with a second higher-level device if a failure occurs in the backhaul link established between the relay device and the first higher-level device; and deciding whether or not to transfer the buffered data to the second higher-level device based on whether or not the second donor device managing the second higher-level device is the same as the first donor device.

[0007] The relay device according to the second embodiment 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 performs the following processes: transferring data received from a lower-level device of the relay device in the upstream path to a first higher-level device of the relay device; buffering data not yet transmitted to the first higher-level device; re-establishing the backhaul link of the relay device with a second higher-level device if a failure occurs in the backhaul link established between the relay device and the first higher-level device; and determining whether or not to transfer the buffered data to the second higher-level device based on whether or not the second donor device managing the second higher-level device is the same as the first donor device. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows the configuration of a mobile communication system according to one embodiment. [Figure 2] This figure shows the configuration of a base station according to one embodiment. [Figure 3] This figure shows the configuration of a relay device according to one embodiment. [Figure 4] This figure shows the configuration of a user device according to one embodiment. [Figure 5] This figure shows an example of a protocol stack configuration according to one embodiment. [Figure 6] This figure shows an operating scenario of a mobile communication system according to one embodiment. [Figure 7] This flowchart shows an example of operation of a relay device according to one embodiment. [Modes for carrying out the invention]

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

[0010] Therefore, the purpose of this disclosure is to provide a communication control method and relay device that can appropriately deal with failures in backhaul links.

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

[0012] (Configuration of mobile communication systems) First, the configuration of a mobile communication system according to one embodiment will be described. Figure 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 to the mobile communication system 1 at least partially.

[0013] As shown in Figure 1, the mobile communication system 1 includes a 5G core network (5GC) 10, user equipment (UE) 100, base stations (called gNBs) 200, and IAB nodes 300. The IAB node 300 is an example of a relay device.

[0014] In one embodiment, we will mainly describe an example where the base station is an NR base station, but the base station may also be an LTE base station (i.e., an eNB).

[0015] The 5GC10 has an AMF (Access and Mobility Management Function) 11 and a UPF (User Plane Function) 12. The AMF 11 is a device that performs various mobility controls on the UE 100. The AMF 11 manages information about the area where the UE 100 is located by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF 12 is a device that controls the transfer of user data.

[0016] The gNB200 is connected to the 5GC10 via an interface called the NG interface. Figure 1 illustrates three 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, it may also perform wireless communication with IAB nodes that are wirelessly connected to it.

[0017] gNB200 units are connected to other adjacent gNB200 units via an inter-base station interface called the Xn interface. Figure 1 shows an example where gNB200-1 is connected to gNB200-2 and gNB200-2.

[0018] Each gNB 200 manages one or more cells. A cell is a term used to indicate the smallest unit of a wireless communication area. A cell may be used as a term to indicate a function or resource for performing wireless communication with the 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 may be a mobile phone terminal, a tablet terminal, a notebook PC, a sensor or a device provided in a sensor, or a vehicle or a device provided in a vehicle.

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

[0021] The IAB node 300 is a device (relay device) that intervenes in the communication between the eNB 200 and the UE 100 and performs relaying for this communication. In FIG. 1, an example is shown in which the IAB node 300-1 is wirelessly connected to the gNB 200-1 that 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 device function) and a gNB function (base station function). Such a UE function may be called MT, and the gNB function may be called DU.

[0023] The IAB node 300 performs wireless communication with a higher-level device (gNB 200 or a higher-level IAB node 300) through its own UE function (MT), and performs wireless communication with a lower-level device (UE 100 or a lower-level IAB node 300) through its own gNB function (DU). Here, the UE function (MT) means at least some of the functions possessed by the UE 100, and the IAB node 300 does not necessarily have all the functions of the UE 100. The gNB function (DU) means at least some of the functions of the gNB 200, and the IAB node 300 does not necessarily have all the functions of the gNB 200. For example, the gNB function (DU) may not have an RRC layer, a PDCP layer, etc.

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

[0025] It is possible to integrate and multiplex data communication of the access link and data communication of the backhaul link in layer 2, dynamically allocate radio resources to data communication of the backhaul link, and dynamically switch the relay path. Note that a millimeter wave band may be used for the access link and the backhaul link. Also, the access link and the backhaul link may be multiplexed by time division and / or frequency division.

[0026] (Configuration of the base station) Next, the configuration of the gNB 200 which is a base station according to an 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 section 210, a network communication section 220, and a control section 230.

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

[0028] The network communication unit 220 is used for wired (or wireless) communication with 5GC10 and with other adjacent gNB200 units. The network communication unit 220 has a receiving unit 221 and a transmitting unit 222. The receiving unit 221 performs various types of reception 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 types of transmission 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 gNB200. 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 for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processes. The processor performs processes described later.

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

[0031] The wireless communication unit 310 is used for wireless communication with the gNB200 (backhaul link) and wireless communication with the UE100 (access link). 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 includes 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 the wireless signal received by the antenna into a baseband signal (received signal) and outputs it 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 the baseband signal (transmitted signal) output by the control unit 320 into a wireless signal and transmits it from the antenna.

[0033] The control unit 320 performs various controls on 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 for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in the memory and performs various processes. The processor performs processes described later.

[0034] (User device configuration) Next, the configuration of UE100, a user device according to one embodiment, will be described. Figure 4 is a diagram showing the configuration of UE100. As shown in Figure 4, UE100 has a wireless communication unit 110 and a control unit 120.

[0035] The wireless communication unit 110 is used for wireless communication in the access link, specifically for wireless communication with the gNB200 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 types of reception under the control of the control unit 120. The receiving unit 111 includes an antenna and converts the wireless signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 120. The transmitting unit 112 performs various types of transmission under the control of the control unit 120. The transmitting unit 112 includes an antenna and converts the baseband signal (transmitted signal) output by the control unit 120 into a wireless signal and transmits it from the antenna.

[0036] The control unit 120 performs various controls on the UE100. 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 for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in the memory and performs various processes. The processor performs processes described later.

[0037] (An example of a protocol stack configuration) Next, an example of a protocol stack configuration in a mobile communication system 1 according to one embodiment will be described. Figure 5 is a diagram showing an example of a protocol stack configuration of the user plane. In Figure 5, an example of a protocol stack configuration for user data transmission between UE100-3 and UPF12 of 5GC10 shown in Figure 1 is shown.

[0038] As shown in Figure 5, UPF12 includes GTP-U (GPRS Tunneling Protocol for User Plane), UDP (User Datagram Protocol), IP (Internet Protocol), and Layer 1 / Layer 2 (L1 / L2). The gNB200-1 (donor gNB) is equipped with a protocol stack corresponding to these.

[0039] Furthermore, the gNB200-1 has a Central Unit (CU) and a Distributed Unit (DU). The CU holds the layers of the wireless interface protocol stack from PDCP (Packet Data Convergence Protocol) upwards, while the DU holds the layers from RLC (Radio Link Control) downwards. The CU and DU are connected via an interface called the F1 interface.

[0040] Specifically, the CU has SDAP (Service Data Adaptation Protocol), PDCP, IP, and L1 / L2. The CU's SDAP and PDCP communicate with the UE100's SDAP and PDCP via the DU, IAB node 300-1, and IAB node 300-2.

[0041] Furthermore, the DU (Device Under Unit) has the RLC (Radio Link Controller), Adaptation Layer (Adapt), MAC (Medium Access Control), and PHY (Physical Layer) as part of the wireless interface protocol stack. These protocol stacks are for gNB (Golden Network Interface). Note that the hierarchical relationship between the Adaptation Layer and RLC (S-RLC) may be reversed. The Adaptation Layer may also be called the Backhaul Adaptation Protocol (BAP) layer.

[0042] IAB node 300-1 is equipped with protocol stack ST1 for UEs corresponding to these. Furthermore, IAB node 300-1 is equipped with protocol stack ST2 for gNBs. Both protocol stacks ST1 and ST2 consist of each layer (each sublayer) below layer 2. In other words, IAB node 300-1 is a Layer 2 relay device that relays user data using each layer below layer 2. IAB node 300-1 performs data relay without using layers above layer 3 (specifically, layers above PDCP). Note that IAB node 300-2 has a protocol stack configuration similar to IAB node 300-1.

[0043] This section describes the protocol stack configuration in the user plane. However, in the control plane, each of the gNB200-1, IAB node 300-1, IAB node 300-2, and UE100-3 has an RRC (Radio Resource Control) 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 sent and received using this RRC connection. Furthermore, an RRC connection is established between the RRC of gNB200-1 and the RRC of IAB node 300-2, and RRC messages are sent and received using this RRC connection. Additionally, an RRC connection is established between the RRC of gNB200-1 and the RRC of UE100-3, and RRC messages are sent 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] Figure 6 shows an operation scenario of a mobile communication system 1 according to one embodiment.

[0047] As shown in Figure 6, an upstream path is formed between UE100 and donor gNB200a using multiple relay devices (IAB node 300a, IAB node 300b, and IAB node 300c). Donor gNB200a corresponds to the first donor device.

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

[0049] Donor gNB200a manages IAB nodes 300a, 300b, 300c, and 300d, and functions as a donor for IAB nodes 300a, 300b, 300c, and 300d. In other words, IAB nodes 300a, 300b, 300c, and 300d are under the control of donor gNB200a.

[0050] Alternatively, donor gNB200b 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 gNB200b, rather than under donor gNB200a. Hereafter, the donor gNB that manages IAB node 300d will be referred to as the second donor device. The second donor device is either donor gNB200a or donor gNB200b.

[0051] UE100 transmits upstream data to donor gNB200a via the paths of IAB nodes 300a, 300b, and 300c, but bypassing IAB node 300d. In one embodiment, the upstream data is a PDCP PDU (Protocol Data Unit). However, assuming there is no segmentation (dividing) 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 donor gNB200a, and PDCP PDUs#1 and#2 have been received by IAB node 300c. PDCP PDU#3 has not yet been received by IAB node 300c and is being transmitted by the RLC layer of IAB node 300b. PDCP PDUs#4,#5, and#6 have been received by IAB node 300b, but have not yet been passed from the PDCP layer to the RLC layer at IAB node 300b. PDCP PDU#7 has been received by IAB node 300a. PDCP PDUs#8 and#9 are being buffered on the UE100 side.

[0053] Under these circumstances, a radio link failure (i.e., BH RLF) occurs between IAB node 300b and IAB node 300c in the backhaul link. IAB node 300b re-establishes the backhaul link with a new parent node (higher-level device), IAB node 300d. For example, IAB node 300b re-establishes the backhaul link with IAB node 300d by performing an RRC re-establishment process via IAB node 300d. After RRC re-establishment, the RLC entity of IAB node 300b is re-established. Here, it is assumed that IAB node 300b is buffering untransmitted PDCP PDUs #3, #4, #5, and #6 at the BAP layer, for example.

[0054] Thus, in one embodiment, when an upstream path is formed between UE100 and donor gNB200a (first donor device), if a failure occurs in the backhaul link established between IAB node 300b and IAB node 300c, IAB node 300b re-establishes its backhaul link with IAB node 300d (second upstream device). This results in the upstream path being reformed.

[0055] In one embodiment, the BAP layer of IAB node 300b may forward buffered upstream data (i.e., PDCP PDU#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 a new upstream path.

[0056] However, if IAB node 300d is not under the control of donor gNB200a, and instead is under the control of donor gNB200b, donor gNB200b cannot process the upstream data buffered by IAB node 300b, even if it receives it via IAB node 300d. Specifically, the PDCP PDU is encrypted by UE100 using a security key, the corresponding PDCP entity exists in donor 200a, and donor gNB200a performs decryption (unencryption) using a security key, but donor gNB200b does not possess this security key and therefore cannot decrypt the PDCP PDU.

[0057] In contrast, if IAB node 300d is under the control of donor gNB200a, donor gNB200a can process the upstream data that has been buffered by IAB node 300b when it receives it via IAB node 300d.

[0058] In one embodiment, IAB node 300b can appropriately deal with backhaul link failures by deciding whether or not to transfer buffered upstream data to IAB node 300d depending on whether or not IAB node 300d is under the control of donor gNB200a.

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

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

[0061] Thirdly, the BAP layer of IAB node 300b decides whether or not to transfer the buffered upstream data to IAB node 300d based on whether the donor device managing IAB node 300d (second donor device) is the same as donor gNB200a (first donor device).

[0062] Specifically, if the BAP layer of IAB node 300b determines that the donor device of IAB node 300d is the same as the donor gNB200a, it transfers the buffered upstream data to IAB node 300d. In this case, once the transfer of the buffered upstream data is complete, the BAP layer or RLC layer of IAB node 300b may send an ACK (e.g., an RLC ACK) corresponding to the buffered upstream data to the downstream device, IAB node 300a.

[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 the donor gNB200a (for example, if the donor device of IAB node 300d is the donor gNB200b), it discards the buffered upstream data. Alternatively, if the BAP layer or RLC layer of IAB node 300b determines that the donor device of IAB node 300d is different from the donor gNB200a, it may send a NACK (for example, an RLC NACK) corresponding to the buffered upstream data to the lower-level device, IAB node 300a.

[0064] In one embodiment, the MT of IAB node 300b may receive an identifier relating to the donor device of IAB node 300d from IAB node 300d. The MT or BAP layer of IAB node 300b may determine, based on the identifier received from IAB node 300d, whether the donor device of IAB node 300d is the same as donor gNB200a.

[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 also be sent from donor gNB200a 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 also be sent from donor gNB200a to IAB node 300b via IAB node 300c.

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

[0068] Alternatively, IAB node 300b may receive a System Information Block (SIB) from IAB node 300d that contains an identifier related to the donor device of IAB node 300d. Note that the SIB is broadcast information transmitted by IAB node 300d. The MT of IAB node 300b may retain the identifier contained 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 donor gNB200a (an identifier previously held) with the identifier for the donor device of IAB node 300d (a newly acquired identifier), and determines that the donor device managing IAB node 300d is the same as donor gNB200a only if the two match.

[0070] Alternatively, the identifier for the donor device of IAB node 300d may include at least one of the following: an identifier indicating whether the donor device of IAB node 300d is identical to donor gNB200a, and an identifier indicating whether or not it is permitted to transfer buffered upstream data to IAB node 300d. The MT or BAP layer of IAB node 300b determines, based on such identifiers, whether or not the donor device managing IAB node 300d is identical to donor gNB200a, i.e., whether or not it is permitted to transfer buffered upstream data to IAB node 300d.

[0071] Alternatively, the MT of IAB node 300b may receive a list of IAB nodes 300b under the donor gNB200a from IAB node 300c. This list may be included in the RRC Reconfiguration message sent from donor gNB200a to IAB node 300b via IAB node 300c. The MT or BAP layer of IAB node 300b determines, based on the list received from IAB node 300c, whether the donor device of IAB node 300d is the same as the donor gNB200a. For example, if the MT or BAP layer of IAB node 300b finds that the identifier for IAB node 300d is included in the list, it determines that the donor device of IAB node 300d is the same as the donor gNB200a.

[0072] Figure 7 is a flowchart 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 Figure 6 will be described. However, the operation shown in Figure 7 may also be performed by IAB node 300a shown in Figure 6. IAB node 300a is an IAB node that has an access link with UE100 and is sometimes called an access IAB node.

[0073] As shown in Figure 7, in step S1, IAB node 300b, together with IAB nodes 300a and 300c, forms an upstream path between UE100 and the first donor device (donor gNB200a).

[0074] In step S2, IAB node 300b receives a list of IAB nodes under the control of the first donor device (donor gNB200a) from IAB node 300c. This list may also be a list of identifiers for each IAB node under the control of the first donor device (donor gNB200a). This list may also be sent from the first donor device (donor gNB200a) to IAB node 300b via IAB node 300c. Note that the process in step S2 may be skipped, and the process in step S6, described later, may be executed instead.

[0075] In step S3, IAB node 300b forwards the upstream data received from its subordinate device (IAB node 300a) in the upstream path to its first superior device (IAB node 300bc). IAB node 300b also buffers any unsent upstream data to IAB node 300c.

[0076] In step S4, IAB node 300b determines whether a backhaul link failure (BH RLF) has occurred in the backhaul link established between IAB node 300b and the first higher-level device (IAB node 300c). If no BH RLF has 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, IAB node 300b re-establishes its backhaul link with the second upstream device (IAB node 300d). This reshapes the upstream path.

[0078] In step S6, the MT of IAB node 300b receives an identifier for the donor device of IAB node 300d from IAB node 300d. IAB node 300b may also receive an RRC Reconfiguration message from IAB node 300d that includes the identifier for the donor device of IAB node 300d. This RRC Reconfiguration message may also be sent from donor gNB200a to IAB node 300b via IAB node 300d. Note that if the process in step S2 described above has been executed, the process in step S6 does not need to be executed. For the determination by IAB node 300b in step S7 described below, at least one of the processes in step S2 and step S6 must be executed. Both the processes in step S2 and step S6 may be executed.

[0079] In step S7, IAB node 300b determines, based on the list received in step S2 or the identifier received in step S6, whether the second donor device managing the second higher-level device (IAB node 300d) is the same as the first donor device (donor gNB200a). In other words, IAB node 300b determines whether it is permitted to transfer the buffered upstream data to IAB node 300d.

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

[0081] On the other hand, if the second donor device managing the second higher-level device (IAB node 300d) is determined to be different from the first donor device (donor gNB200a) (step S7: NO), in step S9, IAB node 300b discards the buffered upstream data. Then, in step S10, IAB node 300b sends a NACK corresponding to the buffered upstream data to its lower-level device, IAB node 300a.

[0082] (Other embodiments) In the embodiment described above, in addition to the donor gNB200, there may be a base station (hereinafter referred to as the master base station) that manages each IAB node 300. 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): a connection to the master base station and a connection to a higher-level device (higher IAB node or donor gNB). The master base station may be the master node and its connection may be an MCG (Master Cell Group) link. The higher-level device (higher IAB node or donor gNB) may be the secondary node and its connection may be an SCG (Secondary Cell Group) link. Under these conditions, the MT of IAB node 300b may receive the list in step S3 of Figure 7 or the identifier in step S6 from the master base station via the MCG link.

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

[0084] A program is provided that causes a computer to perform each of the processes according to the embodiments described above. The program may also be recorded on a computer-readable medium. Using a computer-readable medium makes it possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or DVD-ROM. A chipset is provided that consists of a memory for storing programs for performing each of the processes performed by the UE100, gNB200, or IAB node 300, and a processor for executing the programs stored in the memory.

[0085] This application claims priority to Japanese Patent Application No. 2019-145743 (filed on August 7, 2019), and all of its contents are incorporated into the specification of this application.

Claims

1. A communication control method performed in a relay device, The relay device receives a BAP (Backhaul Adaptation Protocol) data unit from a lower-level relay device, If a failure occurs in the backhaul link between the first higher-level relay device and the relay device, the BAP data unit is transmitted via the backhaul link established between the relay device and the second higher-level relay device. The system includes receiving identification information relating to the first donor device from the first donor device, which is a donor device of the first higher-level relay device, The aforementioned transmission includes transmitting the BAP data unit based on the identification information. Communication control method.

2. It is a relay device, A receiving unit that receives BAP data units from a lower-level relay device of the relay device, The relay device has a transmission unit that transmits the BAP data unit via a backhaul link established between the relay device and the second higher-level relay device if a failure occurs in the backhaul link between the first higher-level relay device and the relay device. The receiving unit receives identification information relating to the first donor device from the first donor device, which is a donor device of the first higher-level relay device. The transmitting unit transmits the BAP data unit based on the identification information. Relay device.

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

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