Mobile communication system, donor node, and communication control method

Abstract

A mobile communication system according to one aspect comprises a donor node and a plurality of relay nodes. In the mobile communication system, the donor node includes a transmission unit that uses the same frequency to simultaneously transmit specific signals addressed to respective ones of the plurality of relay nodes. The donor node also includes a reception unit that receives, from the plurality of relay nodes, signal to interference noise ratios with respect to the specific signals. Further, the donor node includes a control unit that, if it is determined on the basis of the signal to interference noise ratios that an interference is occurring in the plurality of relay nodes, sets a transmission frequency with respect to a relay node that has transmitted a smallest signal to interference noise ratio to a frequency different from the same frequency.

Description

【Technical Field】 【0001】 The present disclosure relates to a mobile communication system, a donor node, and a communication control method. 【Background Art】 【0002】 In 3GPP (Third Generation Partnership Project) (registered trademark; the same shall apply hereinafter), which is a standardization project for mobile communication systems, the introduction of a new relay node called an IAB (Integrated Access and Backhaul) node has been considered (see, for example, Non-Patent Document 1). One or more IAB nodes are interposed in the wireless communication between a base station and a user device, and relay for the wireless communication is performed. In IAB, the termination node of the NR backhaul is called a donor node. A donor node is a base station having additional functions for supporting IAB. In IAB, a network (or topology) rooted at the donor node is formed. 【Prior Art Documents】 【Non-Patent Documents】 【0003】 【Non-Patent Document 1】 3GPP TS 38.300 V17.2.0 (2022-09) 【Summary of the Invention】 【0004】 One embodiment of a mobile communication system is a mobile communication system having a donor node and a plurality of relay nodes. In the mobile communication system, the donor node has a transmitting unit that simultaneously transmits a specific signal addressed to each of the plurality of relay nodes using the same frequency. In the mobile communication system, the donor node also has a receiving unit that receives the signal-to-interference noise ratio for the specific signal from the plurality of relay nodes. Furthermore, in the mobile communication system, if the donor node determines that interference is occurring in the plurality of relay nodes based on the signal-to-interference noise ratio, it has a control unit that sets the transmission frequency to the relay node that transmitted the smallest signal-to-interference noise ratio to a frequency different from the same frequency. 【0005】 Furthermore, a donor node according to one embodiment is a donor node that performs wireless communication to multiple relay nodes. The donor node has a transmitting unit that simultaneously transmits a specific signal addressed to each of the multiple relay nodes using the same frequency. The donor node also has a receiving unit that receives the signal-to-interference noise ratio for the specific signal from the multiple relay nodes. Moreover, if the donor node determines that interference is occurring in the multiple relay nodes based on the signal-to-interference noise ratio, it has a control unit that sets the transmission frequency of the relay node that transmitted the signal with the smallest signal-to-interference noise ratio to a frequency different from the frequency. 【0006】 Furthermore, one embodiment of the communication control method is a communication control method in a mobile communication system having a donor node and a plurality of relay nodes. The communication control method includes the step of the donor node simultaneously transmitting a specific signal addressed to each of the plurality of relay nodes using the same frequency. The communication control method also includes the step of the donor node receiving the signal-to-interference noise ratio for the specific signal from the plurality of relay nodes. Furthermore, if the donor node determines that interference is occurring in the plurality of relay nodes based on the signal-to-interference noise ratio, the communication control method includes the step of setting the transmission frequency of the relay node that transmitted the smallest signal-to-interference noise ratio to a frequency different from the frequency. [Brief explanation of the drawing] 【0007】 [Figure 1] Figure 1 shows an example configuration of a mobile communication system according to the first embodiment. [Figure 2] Figure 2 shows an example of the configuration of a donor node according to the first embodiment. [Figure 3] Figure 3 shows an example of the configuration of a relay node according to the first embodiment. [Figure 4] Figure 4 shows an example configuration of a user device (UE) according to the first embodiment. [Figure 5] Figure 5 is a diagram illustrating an example of operation according to the first embodiment. [Figure 6] Figures 6(A) and 6(B) are diagrams illustrating an example of operation according to the first embodiment. [Figure 7] Figures 7(A) and 7(B) are diagrams illustrating an example of operation according to the first embodiment. [Figure 8] Figures 8(A) and 8(B) illustrate examples of measurement processes. [Figure 9] Figure 9 is a diagram illustrating an example of operation according to the first embodiment. [Figure 10] Figures 10(A) and 10(B) are diagrams illustrating an example of operation according to the first embodiment. [Modes for carrying out the invention] 【0008】 The first radio signal from the donor node to the first relay node may interfere with the second radio signal from the donor node to the second relay node. In this case, the second relay node may not be able to properly receive the second radio signal intended for its own station due to interference. Similarly, the first relay node may not be able to properly receive the first radio signal because the second radio signal interferes with it. 【0009】 Therefore, this disclosure aims to provide a mobile communication system, a donor node, and a communication control method that automatically attempt to avoid interference. 【0010】 [First Embodiment] For example, let's assume that the first relay node and the second relay node are installed in close proximity, below a threshold distance. In such a case, as described above, at the second relay node, the first radio signal from the donor node to the first relay node may interfere with the second radio signal from the donor node to the second relay node. Alternatively, at the first relay node, the second radio signal from the donor node to the second relay node may interfere with the first radio signal to the first relay node. 【0011】 Generally, when a donor node and multiple IAB nodes are to be installed, theoretical calculations may be performed in advance. These calculations determine the locations of the first and second relay nodes to avoid interference. 【0012】 However, performing calculations on paper can be very tedious, as it often involves considering various scenarios. 【0013】 Therefore, the objective of the first embodiment is to attempt to automatically avoid interference. 【0014】 The following describes a mobile communication system according to an embodiment, with reference to the drawings. In the drawings, identical or similar parts are denoted by the same or similar reference numerals. 【0015】 (Configuration of mobile communication systems) Figure 1 is a diagram showing the configuration of the mobile communication system 10 according to the first embodiment. The mobile communication system 10 conforms to the 5th Generation System (5GS) of the 3GPP standard. In the following explanation, 5GS will be used as an example, but the mobile communication system 10 may also have at least a portion of the LTE (Long Term Evolution) system applied to it. The mobile communication system 10 may also have at least a portion of future mobile communication systems, such as the 6th Generation (6G) system. 【0016】 As shown in FIG. 1, the mobile communication system 10 includes a 5G core network (5GC) 20, a donor node 100, relay nodes 200-N1 and 200-N2, and user equipment (UE: User Equipment) 300-1 and 300-2. 【0017】 In the following, when the relay node 200-N1 and the relay node 200-N2 are not particularly distinguished, they may be referred to as the relay node 200. Also, in the following, when the UE 300-1 and the UE 300-2 are not particularly distinguished, they may be referred to as the UE 300. 【0018】 The 5GC 20 includes core network devices such as an AMF (Access and Mobility Management Function) and a UPF (User Plane Function), and is connected to an external Internet. The AMF is a core network device that performs various mobility controls and the like for the UEs 300-1 and 300-2. The AMF can communicate with the UEs 300-1 and 300-2 using NAS (Non-Access Stratum) signaling. The UPF is a core network device that performs transfer control of user data and the like. 【0019】 The mobile communication system 10 supports IAB. Here, referring to FIG. 1, IAB will be described. 【0020】 (IAB) While the radio link between the donor node 100 and the relay node 200 is referred to as a backhaul link, the radio link between the relay node 200 and the UE 300 may be referred to as an access link. IAB is also a wireless communication method that enables wireless relay of NR access by using NR, which is a wireless access method of the 5G system, in the backhaul. 【0021】 In IAB, a network is configured with a donor node 100 as the root, and one or more relay nodes 200 included. This network is sometimes referred to as a topology (specifically, a directed acyclic graph (DAG) topology). Figure 1 shows an example where one donor node 100 is connected to two relay nodes 200-N1 and 200-N2. 【0022】 As described above, the donor node 100 is the terminating node of the NR backhaul. Furthermore, the donor node 100 is also a base station (i.e., gNB) providing network access to the UE300 via backhaul and access links. In addition, the donor node 100 is a base station with additional functions to support IAB. An example of these additional functions is the management of the routing of packet data transmitted between the donor node 100 and UE300-1 and 300-2. The donor node 100 centrally manages topology resources and route management within the network. 【0023】 In Figure 1, the backhaul link shows a single-hop example with one relay node 200 between the donor node 100 and the UE300. However, a multi-hop configuration with multiple relay nodes 200 between the donor node 100 and the UE300 is also possible. 【0024】 The donor node 100 may be a gNB. A gNB is a fixed wireless communication node that manages one or more cells. The gNB is connected to the 5GC20 via an interface called the NG interface. The gNB may be divided into a Central Unit (CU) and a Distribution Unit (DU). The CU and DU are interconnected via an interface called the F1 interface. The F1 interface has an F1-C protocol, which is the control plane protocol, and an F1-U protocol, which is the user plane protocol. 【0025】 The relay node 200 is, for example, a node that relays between the donor node 100 and the UE300 (i.e., an IAB node). In the following, relay nodes and IAB nodes may be used interchangeably. 【0026】 The relay node 200 supports the IAB-DU function. The IAB-DU function is a functional block that has functions equivalent to a base station in the relay node 200. The IAB-DU function has the function of terminating the NR access interface to the UE300 and terminating the F1 protocol to the gNB-CU of the donor node 100. 【0027】 Furthermore, relay node 200 also supports IAB-MT functionality. IAB-MT functionality is a functional block that has the equivalent functionality of UE in relay node 200, for example. IAB-MT functionality can connect to either the IAB-DU functionality of other relay nodes 200 or the gNB-DU of donor node 100 via the physical layer, MAC (Medium Access Control) layer, RLC (Radio Link Control) layer, and BAP (Backhaul Adaptation Protocol) layer. In addition, IAB-MT functionality can connect to the gNB-CU of donor node 100 via the PDCP (Packet Data Convergence Protocol) layer and RRC (Radio Resource Control) layer. Moreover, IAB-MT functionality can connect to the AMF of 5GC20 via the NAS layer. 【0028】 That concludes the explanation of IAB. 【0029】 The UE300 is a mobile terminal device that communicates wirelessly with the cell. The UE300 can be any device that communicates wirelessly with either the relay node 200 or the donor node 100. For example, the UE300 may be a mobile phone terminal and / or a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device attached to a sensor, a vehicle or a device attached to a vehicle, or an aircraft or a device attached to an aircraft (UAV: Unmanned Aerial Vehicle). The UE300 connects wirelessly to the relay node 200 or the donor node 100 via an access link. 【0030】 Although the UE300 may communicate directly with the donor node 100 via wireless communication, in the first embodiment, the UE300 is configured not to communicate directly with the donor node 100 via wireless communication. This allows the donor node 100 to use the resources allocated to the UE300 for its own functions as a donor node (such as resource management or route management in the topology). 【0031】 The example shown in Figure 1 illustrates a configuration where UE300-1 is connected to relay node 200-N1 and UE300-2 is connected to relay node 200-N2. The number of UE300s connected to relay node 200 can be one or multiple units. 【0032】 Furthermore, while Figure 1 shows an example where two relay nodes 200-N1 and 200-N2 are connected to the donor node 100, the number of relay nodes 200 connected to the donor node 100 may be three or more. 【0033】 Next, we will describe an example of the configuration of each device in the mobile communication system 10. 【0034】 (Example of donor node configuration) First, an example configuration of the donor node 100 according to the first embodiment will be described. Figure 2 is a diagram showing an example configuration of the donor node 100. As shown in Figure 2, the donor node 100 has a wireless communication unit 110, a network communication unit 120, and a control unit 130. 【0035】 The wireless communication unit 110 performs wireless communication with the relay node 200. The wireless communication unit 110 includes 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 130. The receiving unit 111 includes an antenna and converts the wireless signal received by the antenna into a baseband signal (received signal) (downconvert) and outputs it to the control unit 130. The transmitting unit 112 performs various types of transmission under the control of the control unit 130. The transmitting unit 112 includes an antenna and converts the baseband signal (transmitted signal) output by the control unit 130 into a wireless signal (upconvert) and transmits it from the antenna. 【0036】 The network communication unit 120 performs wired (or wireless) communication with the 5GC20. The network communication unit 120 has a receiving unit 121 and a transmitting unit 122. The receiving unit 121 performs various types of reception under the control of the control unit 130. The receiving unit 121 receives signals from the outside and outputs the received signals to the control unit 130. The transmitting unit 122 performs various types of transmission under the control of the control unit 130. The transmitting unit 122 transmits the transmission signals output by the control unit 130 to the outside. 【0037】 The control unit 130 performs various controls on the donor node 100. The control unit 130 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 processing. The processor performs processing for each layer. Processing or operation on the donor node 100, which will be described later, may also be performed by the control unit 130. 【0038】 (Example of relay node configuration) Next, an example of the configuration of a relay node according to the first embodiment will be described. Figure 3 is a diagram showing an example of the configuration of a relay node 200. As shown in Figure 3, the relay node 200 has a wireless communication unit 210 and a control unit 220. The relay node 200 may have multiple wireless communication units 210. 【0039】 The wireless communication unit 210 performs wireless communication with the donor node 100 (BH link) and wireless communication with the UE 300 (access link). The wireless communication unit 210 for BH link communication and the wireless communication unit 210 for access link communication may be provided separately. 【0040】 The wireless communication unit 210 includes 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 220. The receiving unit 211 includes an antenna and converts (downconverts) the wireless signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 220. The transmitting unit 212 performs various types of transmission under the control of the control unit 220. The transmitting unit 212 includes an antenna and converts (upconverts) the baseband signal (transmitted signal) output by the control unit 220 into a wireless signal and transmits it from the antenna. 【0041】 The control unit 220 performs various controls at the relay node 200. The control unit 220 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 processing. The processors perform processing at each layer. Processing or operation at the relay node 200, described later, may also be performed by the control unit 220. 【0042】 (Example of UE configuration) Next, an example configuration of the UE300 according to the first embodiment will be described. Figure 4 is a diagram showing an example configuration of the UE300 (user device). As shown in Figure 4, the UE300 has a wireless communication unit 310 and a control unit 320. 【0043】 The wireless communication unit 310 performs wireless communication on the access link, i.e., wireless communication with the relay node 200. The wireless communication unit 310 may also perform wireless communication on the side link, i.e., wireless communication with other UE 300s. 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 the wireless signal received by the antenna into a baseband signal (received signal) (downconvert) 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 (upconvert) and transmits it from the antenna. 【0044】 The control unit 320 performs various controls in the UE300. 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 processing for each layer described later. Note that the processing or operation in the UE300 described later may be performed by the control unit 320. 【0045】 (Example of operation according to the first embodiment) Next, an example of operation according to the first embodiment will be described. 【0046】 In the first embodiment, firstly, the transmitting unit (e.g., transmitting unit 112) of the donor node (e.g., donor node 100) simultaneously transmits a specific signal addressed to each of several relay nodes (e.g., relay node 200) using the same frequency. Here, simultaneous transmission means that although the start times of transmission do not have to be the same, all specific signals are transmitted in such a state that they are being transmitted at the same time. Secondly, the receiving unit (e.g., receiving unit 111) of the donor node receives the signal-to-interference-plus-noise ratio (e.g., SINR (Signal to Interference plus Noise Ratio)) for the specific signal from the several relay nodes. Thirdly, if the control unit (e.g., control unit 130) of the donor node determines that interference is occurring in a relay node based on the signal-to-interference-plus-noise ratio, it sets the transmission frequency to the relay node with the smallest signal-to-interference-plus-noise ratio to a frequency different from the aforementioned frequency. 【0047】 For example, in Figure 1, donor node 100 transmits a specific signal (hereinafter also referred to as the first specific signal) to relay node 200-N1 and a specific signal (hereinafter also referred to as the second specific signal) to relay node 200-N2, respectively, using the same frequency and timing. Relay node 200-N1 measures the SINR of the second specific signal relative to the first specific signal (hereinafter also referred to as the first SINR). Relay node 200-N2 measures the SINR of the first specific signal relative to the second specific signal (hereinafter also referred to as the second SINR). Relay node 200-N1 transmits the first SINR to donor node 100, and relay node 200-N2 transmits the second SINR to donor node 100. Here, the donor node 100 determines, based on the first and second SINRs, that interference is occurring between the communication from the donor node 100 to the relay node 200-N1 and the communication from the donor node 100 to the relay node 200-N2. If the second SINR < the first SINR, the donor node 100 sets the transmission frequency to relay node 200-N2 to a different frequency from the frequency used to transmit the second specific signal, using the SINR with the smallest second SINR. The donor node 100 sets the transmission frequency to relay node 200-N1 to the same frequency as the frequency used to transmit the first specific signal. 【0048】 Thus, in the first embodiment, when the donor node 100 detects the occurrence of interference based on the SINR, it is possible to set the transmission frequency to the relay node 200-N1 and the transmission frequency to the relay node 200-N2 to different frequencies. This makes it possible to attempt to avoid interference in, for example, wireless communication from the donor node 100 to the relay node 200-N1 and wireless communication from the donor node 100 to the relay node 200-N2. Moreover, since the donor node 100 determines the occurrence of interference based on the SINR actually measured at the relay nodes 200-N1 and 200-N2, rather than relying on theoretical calculations, and automatically sets the transmission frequency for the wireless communication subject to interference to a different frequency, there is a high probability that interference can be avoided. 【0049】 The following provides a specific example of how it works. 【0050】 Figure 5 is a diagram illustrating an example of operation according to the first embodiment. Figure 5 mainly shows an example of operation performed in the control unit 130 of the donor node 100. Figures 6(A) to 10(B) are diagrams for explaining the example of operation. The example of operation shown in Figure 5 will be explained with reference to each of the figures from 6(A) to 10(B). 【0051】 As shown in Figure 5, in step S10, the donor node 100 starts processing. 【0052】 In step S11, the donor node 100 periodically scans the area around itself. Figure 6(A) shows an example of the donor node 100 scanning the area around itself. For example, relay node 200-N1 sends an identification signal containing its own identification information (hereinafter also referred to as the first identification signal) to the donor node 100, and relay node 200-N2 sends an identification signal containing its own identification information (hereinafter also referred to as the second identification signal) to the donor node 100. Relay nodes 200-N1 and 200-N2 may also periodically send identification signals. The donor node 100 may also send an identification signal by including the identification information in an RRC message, a BAP Control PDU (Protocol Data Unit), or a MAC CE (Control Element). 【0053】 In step S12, the donor node 100 determines whether or not it has received an identification signal containing new identification information. Figure 6(B) shows an example where the relay node 200-N3, which has started operation, transmits an identification signal containing new identification information not used by the other relay nodes 200-N1 and 200-N2. In other words, the donor node 100 periodically receives identification signals from the connected relay nodes 200-N1 and 200-N2 (Figure 6(A)), but receives an identification signal containing new identification information that it has not received before from the relay node 200-N3, which has started operation (Figure 6(B)). The donor node determines whether or not it has received an identification signal containing identification information that it has not received before. 【0054】 Returning to Figure 5, if the donor node 100 receives the identification signal (Yes in step S12), the process proceeds to step S13. On the other hand, if the donor node 100 does not receive the identification signal (No in step S12), the process proceeds to step S18. 【0055】 In step S13, the donor node 100 determines that a new relay node has started operation. That is, if the donor node 100 receives an identification signal containing new identification information that has not been used before, it determines that a new relay node (for example, relay node 200-N3) has started operation. 【0056】 In step S14, the donor node 100 simultaneously transmits a specific signal to all relay nodes 200 using the same frequency. The donor node 100 may also transmit a specific signal triggered by receiving an identification signal from a relay node 200-N3 that has started operation. Specifically, the transmitting unit 112 of the donor node 100 may transmit a specific signal in response to receiving an identification signal containing identification information that identifies relay node 200-N3 from a relay node 200-N3 that has newly started operation among the multiple relay nodes 200, via the receiving unit 111. 【0057】 In this process, the donor node 100 transmits a specific signal containing the identification information of each relay node 200 to each relay node 200. Figure 7(A) shows an example of the transmission of specific signals. In the example shown in Figure 7(A), the donor node 100 transmits a first specific signal containing the identification information of relay node 200-N1 to relay node 200-N1. The donor node 100 also transmits a second specific signal containing the identification information of relay node 200-N2 to relay node 200-N2. Furthermore, the donor node 100 transmits a third specific signal containing the identification information of relay node 200-N3 to relay node 200-N3. The donor node 100 transmits the first to third specific signals at the same timing using the same frequency. 【0058】 The donor node 100 may also use a phased array antenna to transmit each specific signal to each relay node 200. Figure 7(B) shows an example of the configuration of a phased array antenna in the donor node 100. In Figure 7(B), the donor node 100 is shown as having four antennas, from the first antenna ANT#1 to the fourth antenna ANT#4. Each antenna ANT#1 to ANT#4 has multiple antenna elements, and by beamforming control (specifically, phase control, etc.) for each antenna element, a beam with a main lobe in a specific direction can be formed. For example, antenna ANT#1 transmits the first specific signal to relay node 200-N1 using a beam with a main lobe in the direction of relay node 200-N1. Also, for example, antenna ANT#2 transmits the second specific signal to relay node 200-N2 using a beam with a main lobe in the direction of relay node 200-N2. Furthermore, for example, antenna ANT#3 transmits a third specific signal to relay node 200-N3 using a beam with its main lobe directed towards relay node 200-N3. In this way, donor node 100 may use any of the four antennas ANT#1 to ANT#4 to transmit specific signals to each relay node 200. 【0059】 The specific signal may be a synchronization signal (SSB: Synchronization Signal Block). Alternatively, the specific signal may be a newly defined signal. In the latter case, the specific signal may be transmitted in either an RRC message, a BAP Control PDU, or a MAC CE. 【0060】 Returning to Figure 5, in step S15, the donor node 100 receives the SINR for a specific signal from all relay nodes 200. All relay nodes 200 perform a measurement process to measure the SINR using the specific signal and transmit the measured SINR to the donor node 100. 【0061】 Now, let's explain the measurement process. 【0062】 Figures 8(A) and 8(B) illustrate examples of the measurement process. Figure 8(A) shows examples of the first, second, and third specific signals. As shown in Figure 8(A), the donor node 100 transmits the first to third specific signals using the same frequency. 【0063】 In contrast, as shown in Figure 8(B), relay node 200-N1 determines the first specific signal to be the desired signal (a signal addressed to the local station) because the first specific signal contains the local station's identification information, and determines the second and third specific signals to be other signals (i.e., noise signals and interference signals) because they do not contain the local station's identification information, and measures the SINR (e.g., first SINR) which represents the ratio of the received power of the other signals (second and third specific signals) to the received power of the desired signal (first specific signal). Similarly, relay node 200-N2 determines the second specific signal, which contains the local station's identification information, to be the desired signal, and determines the first and third specific signals, which do not contain the local station's identification information, to be other signals, and measures the SINR (e.g., second SINR) which represents the ratio of the received power of the other signals (first and third specific signals) to the received power of the desired signal (second specific signal). Furthermore, relay node 200-N3 determines the third specific signal containing its own identification information as the desired signal, and the first and second specific signals, which do not contain its own identification information, as other signals. It then measures the SINR (e.g., the third SINR), which represents the ratio of the received power of the other signals (first and second specific signals) to the received power of the desired signal (third specific signal). 【0064】 Each relay node 200-N1 to 200-N3 transmits the SINR measured as described above to the donor node 100. Figure 9 shows an example where relay node 200-N1 transmits the first SINR to donor node 100, relay node 200-N2 transmits the second SINR to donor node 100, and relay node 200-N3 transmits the third SINR to donor node 100. 【0065】 Each relay node 200-N1 to 200-N3 may include each measured SINR in the measurement report and transmit it. Alternatively, each relay node 200-N1 to 200-N3 may include each measured SINR in a newly defined message and transmit it. In the latter case, each SINR may be transmitted in an RRC message, a BAP Control PDU, or a MAC CE. 【0066】 Returning to Figure 5, in step S16, the donor node 100 determines whether or not there is an SINR below the threshold. The donor node 100 determines whether or not interference is occurring at each relay node 200 by comparing the SINR with the threshold. Specifically, the donor node 100 determines that interference is occurring at at least two relay nodes 200 when the SINR is below the threshold. On the other hand, the donor node 100 determines that no interference is occurring at the relay nodes 200 when the SINR is above the threshold. 【0067】 For example, as shown in Figure 9, relay node 200-N1 is located at a predetermined distance or greater from relay nodes 200-N2 and 200-N3. Therefore, at relay node 200-N1, the difference in received power between the desired signal (first specific signal) and other signals (second specific signal or third specific signal) will be greater than or equal to a predetermined value. Consequently, the first SINR may be above the threshold. Conversely, if the first SINR is above the threshold, it is assumed that at relay node 200-N1, the second specific signal or third specific signal does not interfere with the first specific signal, and therefore no interference occurs. Consequently, at donor node 100, when the SINR is above the threshold, it is determined that no interference occurs at relay node 200, which transmitted the SINR. 【0068】 On the other hand, the distance between relay node 200-N2 and relay node 200-N3 is less than a predetermined distance. Therefore, at relay node 200-N2, the difference in received power between the desired signal (second specific signal) and other signals (third specific signal) is less than a predetermined value. In other words, the second SINR may be below the threshold. In such a case, at relay node 200-N2, the third specific signal is an interfering signal of the second specific signal destined for the relay node, so the second SINR is below the threshold. Conversely, if the second SINR is below the threshold, it is assumed that the third specific signal is an interfering signal of the second specific signal destined for the relay node, and interference is occurring at relay node 200-N2. Therefore, at donor node 100, when the SINR is below the threshold, it is determined that interference is occurring at relay node 200, which transmitted the SINR. 【0069】 Similarly, at relay node 200-N3, the second specific signal is an interfering signal to the third specific signal destined for its own station, so the third SINR may fall below the threshold. Donor node 100 determines that interference is occurring at relay node 200-N3 because the third SINR is below the threshold. 【0070】 Returning to Figure 5, if there is an SINR below the threshold in step S16 (Yes in step S16), the process proceeds to step S17. On the other hand, if there is no SINR below the threshold (No in step S16), the process proceeds to step S18. 【0071】 In step S17, the donor node 100 sets the transmission frequency to the relay node 200 that transmitted the smallest SINR among those below the threshold, to a frequency different from the frequency used to transmit the specific signal. 【0072】 Figures 10(A) and 10(B) illustrate examples of transmission frequency settings. In the example shown in Figure 10(A), the donor node 100 sets the transmission frequency to the relay node 200-N2, which transmitted the second SINR, to a different frequency than the frequency used to transmit the specific signal, assuming that the second SINR is the smallest SINR. In this case, the donor node 100 sets the transmission frequency to the relay node 200-N3 to the frequency used to transmit the specific signal. 【0073】 Figure 10(B) shows an example of SINR at each of the relay nodes 200-N1 to 200-3 when the first to third specific signals are transmitted simultaneously after the transmission frequency for relay node 200-N2 has been set. As shown in Figure 10(B), the second and third specific signals transmitted from donor node 100 to the two relay nodes 200-N2 and 200-N3, respectively, are transmitted using different frequencies. Therefore, there is a high probability that interference will not occur at relay nodes 200-N2 and 200-3. In this way, this embodiment makes it possible to automatically attempt to avoid interference. 【0074】 Although the first and third specific signals are transmitted at the same frequency and timing, the SINR measured at relay node 200-N1 and the SINR measured at relay node 200-N3 are both above the threshold. Therefore, donor node 100 determines that no interference is occurring. 【0075】 Returning to Figure 5, in step S18, the donor node 100 completes the series of processes. 【0076】 (Another example of operation according to the first embodiment 1) In the first embodiment, an example was described in which each relay node 200-N1 to 200-N3 transmits SINR to the donor node 100, but the invention is not limited to this. For example, each relay node 200-N1 to 200-N3 may compare the SINR with a threshold and transmit the comparison result to the donor node 100. The comparison result may be information indicating that the SINR is greater than or equal to the threshold (or the SINR is large), or information indicating that the SINR is less than the threshold (or the SINR is small). The comparison result may also be transmitted using an RRC message, a BAP Control PDU, or a MAC CE. 【0077】 Donor node 100 may determine that interference is occurring if it receives a comparison result indicating that the SINR is below the threshold, and may determine that no interference is occurring if it receives a comparison result indicating that the SINR is above the threshold. 【0078】 (Another example of operation according to the first embodiment 2) In the first embodiment, an example was described in which a relay node 200-N3 that has started operation transmits an identification signal containing identification information. In this case, the identification information may be issued by the donor node 100. For example, the relay node 200-N3 that has started operation transmits an "IAB-indication" to the donor node 100. The "IAB-indication" is, for example, an information element that indicates that it is an IAB node. The "IAB-indication" may be transmitted using an RRC message, a BAP Control PDU, or a MAC CE. Upon receiving the "IAB-indication," the donor node 100 issues identification information to the relay node 200-N3 and transmits the identification information to the relay node 200-N3. The identification information may also be transmitted using an RRC message, a BAP Control PDU, or a MAC CE. Thereafter, as in the first embodiment, the relay node 200-N3 transmits a control signal containing the identification information. 【0079】 (Another example of operation according to the first embodiment 3) In the first embodiment, an example was described in which the relay node 200-N3 that has started operation transmits an identification signal, but the invention is not limited to this. For example, instead of transmitting an identification signal, the relay node 200-N3 may transmit information indicating that it is newly establishing a connection with the donor node 100. This information may be an "IAB-indication". This information may be transmitted in a newly defined message. In the latter case, this information may be transmitted in an RRC message, a BAP Control PDU, or a MAC CE. 【0080】 (Another example of operation according to the first embodiment 4) In the first embodiment, an example was described in which the donor node 100 has "four" antennas, but the number of antennas is not limited to this. For example, the donor node 100 may have "one" or more antennas. For example, even if the number of antennas is "one," by dividing the multiple antenna elements included in the antenna into three and using the divided antenna elements to form a main lobe directed toward each relay node 200-N1 and 200-N3, a signal (e.g., a specific signal) can be transmitted toward each relay node 200 in the same way as in the case of three antennas. 【0081】 (Another example of operation according to the first embodiment 5) In the first embodiment, an example was described in which the donor node 100 transmits a specific signal triggered by receiving an identification signal from the relay node 200-N3 that has started operation. However, the trigger for transmitting the specific signal is not limited to this. For example, the donor node 100 may transmit a specific signal as appropriate. 【0082】 For example, in Figure 1, let's assume that donor node 100 uses "f1" as the transmission frequency to relay node 200-N1 and "f2" as the transmission frequency to relay node 200-N2. Let's also assume, for example, that frequency "f1" is put into use in another wireless communication system other than the mobile communication system 10 shown in Figure 1. In such a case, the SINR of the transmission frequency "f1" used by donor node 100 will be smaller than before frequency "f1" was put into use in the other wireless communication system. 【0083】 In anticipation of such a case, the donor node 100 may, as appropriate, use a specific signal at frequency "f1" and simultaneously transmit the same specific signal to the relay node 200-N2. This allows the donor node 100 to detect the presence or absence of interference as described in the first embodiment, and in some cases, to change the transmission frequency. Thus, the donor node 100 may appropriately transmit a specific signal to confirm (or improve) the transmission frequency. 【0084】 (Another example of operation according to the first embodiment 6) In the first embodiment, examples were described in which interference is detected using SINR and in which relay nodes 200 to be changed in transmission frequency are determined, but the invention is not limited to these examples. For example, indicators other than SINR may be used. Such indicators may include the signal-to-interference power ratio (SIR). Such indicators may also include the signal-to-noise power ratio (SNR). The indicator only needs to show information that represents the ratio of the desired signal to other signals (e.g., interference signal or noise signal). 【0085】 [Other embodiments] A program may be provided that causes a computer to execute each of the processes performed by the donor node 100, the relay node 200, and the UE300. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is 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. Alternatively, the circuits that execute each of the processes performed by the donor node 100, the relay node 200, and the UE300 may be integrated, and at least a portion of the donor node 100, the relay node 200, and the UE300 may be configured as a semiconductor integrated circuit (chipset, SoC: System on a chip). 【0086】 The terms "based on" and "depending on" used in this disclosure do not mean "based solely on" or "depending solely on" unless otherwise specified. "Based on" means both "based solely on" and "at least partially on." Similarly, "depending on" means both "at least partially on" and "at least partially on." Furthermore, the terms "include" and "comprise" do not mean to include only the listed items, but may include only the listed items or may include additional items in addition to the listed items. Also, the term "or" used in this disclosure is not intended to mean exclusive OR. Moreover, any reference to elements using designations such as "first," "second," etc., used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient way to distinguish between two or more elements. Therefore, references to the first and second elements do not imply that only two elements may be adopted therein, or that the first element must precede the second element in any way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall be plural unless it is clearly indicated by the context that they are not. 【0087】 Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes can be made without departing from the gist of the work. Furthermore, it is possible to combine all or part of each embodiment, each operation, each process, and each step, as long as they do not contradict each other. 【0088】 This application claims priority to Japanese Patent Application No. 2023-004242 (filed January 16, 2023), and all of its contents are incorporated into the specification of this application. 【0089】 (Note) (Note 1) A mobile communication system having a donor node and multiple relay nodes, The aforementioned donor node is A transmitting unit that simultaneously transmits a specific signal addressed to each of the multiple relay nodes using the same frequency, A receiving unit that receives the signal-to-interference noise ratio for the specified signal from the plurality of relay nodes, The control unit, when it is determined that interference is occurring at the multiple relay nodes based on the signal-to-interference noise ratio, sets the transmission frequency to the relay node that transmitted the smallest signal-to-interference noise ratio to a frequency different from the same frequency. Mobile communication system. 【0090】 (Note 2) The control unit determines that interference is occurring at the multiple relay nodes when the signal-to-interference noise ratio is below a threshold. The mobile communication system described in Appendix 1. 【0091】 (Note 3) The control unit determines that no interference is occurring at the multiple relay nodes when the signal-to-interference noise ratio is above a threshold. A mobile communication system as described in Appendix 1 or Appendix 2. 【0092】 (Note 4) The control unit sets the transmission frequency of the relay node that transmits the smallest signal-to-interference noise ratio among those below the threshold to a frequency different from the aforementioned frequency. A mobile communication system as described in any of Appendix 1 to Appendix 3. 【0093】 (Note 5) The transmitting unit transmits the specific signal in response to the receiving unit receiving an identification signal from a relay node that has newly started operation among the plurality of relay nodes, which identifies that relay node. A mobile communication system as described in any of the appendices 1 through 4. 【0094】 (Note 6) The transmitting unit transmits the specific signal, which includes the identification information of each relay node, to each relay node. A mobile communication system as described in any of Appendix 1 to Appendix 5. 【0095】 (Note 7) The aforementioned specific signal is a synchronization signal or a newly defined signal. A mobile communication system as described in any of Appendix 1 to Appendix 6. 【0096】 (Note 8) The aforementioned signal-to-interference noise ratio is included in the measurement report or a newly defined message. A mobile communication system as described in any of Appendix 1 to Appendix 7. 【0097】 (Note 9) A donor node that performs wireless communication to multiple relay nodes, A transmitting unit that simultaneously transmits a specific signal addressed to each of the multiple relay nodes using the same frequency, A receiving unit that receives the signal-to-interference noise ratio for the specified signal from the plurality of relay nodes, The set includes a control unit that, when it is determined that interference is occurring at the multiple relay nodes based on the signal-to-interference noise ratio, sets the transmission frequency of the relay node that transmitted the smallest signal-to-interference noise ratio to a frequency different from the same frequency. Donor node. 【0098】 (Note 10) A communication control method in a mobile communication system having a donor node and multiple relay nodes, The donor node simultaneously transmits a specific signal addressed to each of the multiple relay nodes using the same frequency. The donor node receives the signal-to-interference noise ratio for the specific signal from the plurality of relay nodes, If the donor node determines, based on the signal-to-interference noise ratio, that interference is occurring in the multiple relay nodes, the donor node has the step of setting the transmission frequency of the relay node that transmitted the smallest signal-to-interference noise ratio to a frequency different from the same frequency. Communication control method. [Explanation of symbols] 【0099】 10: Mobile communication systems 20:5GC 100: Donor Nodes 110: Wireless Communication Section 111: Receiving unit 112: Transmitter 130: Control Unit 200: Relay node 210: Wireless Communication Section 211: Receiving Unit 212: Transmitter 220: Control Unit 300:UE 320: Control Unit

Claims

[Claim 1] A mobile communication system having a donor node and multiple relay nodes, The aforementioned donor node is A transmitting unit that simultaneously transmits a specific signal addressed to each of the multiple relay nodes using the same frequency, A receiving unit that receives the signal-to-interference noise ratio for the specified signal from the plurality of relay nodes, The control unit, when it is determined that interference is occurring at the multiple relay nodes based on the signal-to-interference noise ratio, sets the transmission frequency to the relay node that transmitted the smallest signal-to-interference noise ratio to a frequency different from the same frequency. Mobile communication system. [Claim 2] The control unit determines that interference is occurring at the multiple relay nodes when the signal-to-interference noise ratio is below a threshold. The mobile communication system according to claim 1. [Claim 3] The control unit determines that no interference is occurring at the multiple relay nodes when the signal-to-interference noise ratio is above a threshold. The mobile communication system according to claim 1. [Claim 4] The control unit sets the transmission frequency of the relay node that transmits the smallest signal-to-interference noise ratio among those below the threshold to a frequency different from the aforementioned frequency. The mobile communication system according to claim 2. [Claim 5] The transmitting unit transmits the specific signal in response to the receiving unit receiving an identification signal from a relay node that has newly started operation among the plurality of relay nodes, which identifies that relay node. The mobile communication system according to claim 1. [Claim 6] The transmitting unit transmits the specific signal, which includes the identification information of each relay node, to each relay node. The mobile communication system according to claim 5. [Claim 7] The aforementioned specific signal is a synchronization signal or a newly defined signal. The mobile communication system according to claim 1. [Claim 8] The aforementioned signal-to-interference noise ratio is included in the measurement report or a newly defined message. The mobile communication system according to claim 2 or claim 3. [Claim 9] A donor node that performs wireless communication to multiple relay nodes, A transmitting unit that simultaneously transmits a specific signal addressed to each of the multiple relay nodes using the same frequency, A receiving unit that receives the signal-to-interference noise ratio for the specified signal from the plurality of relay nodes, The set includes a control unit that, when it is determined that interference is occurring at the multiple relay nodes based on the signal-to-interference noise ratio, sets the transmission frequency of the relay node that transmitted the smallest signal-to-interference noise ratio to a frequency different from the same frequency. Donor node. [Claim 10] A communication control method in a mobile communication system having a donor node and multiple relay nodes, The donor node simultaneously transmits a specific signal addressed to each of the multiple relay nodes using the same frequency. The donor node receives the signal-to-interference noise ratio for the specific signal from the multiple relay nodes, If the donor node determines, based on the signal-to-interference noise ratio, that interference is occurring in the multiple relay nodes, it sets the transmission frequency of the relay node that transmitted the smallest signal-to-interference noise ratio to a frequency different from the same frequency. Communication control method.

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