Wireless communication system, wireless communication method, network controller, and network control program

Abstract

A wireless communication system according to the present disclosure is configured to establish a low-latency communication path by link-connecting the node stations of a first group among a plurality of node stations configuring a wireless network. Further, the node stations of a second group and at least one node station of the first group among the plurality of node stations are linked to establish a high-latency communication path. The wireless communication system according to the present disclosure: transmits all traffic by using the low-latency communication path until the low-latency communication path becomes congested; and upon detecting a congested state of the low-latency communication path, transmits traffic with a long allowable latency among all traffic by using both the low-latency communication path and the high-latency communication path.

Description

[Technical field]

[0001] The present invention relates to a wireless communication system, a wireless communication method, a network controller, and a network control program. [Background technology]

[0002] In recent years, mobile communication systems have developed to the point where mobile services can be enjoyed over most of the earth. One of the requirements for the 5th generation (Beyond 5G) or 6th generation mobile communication systems, which are expected to be commercialized in the future, is ultra-coverage. Ultra-coverage refers to expanding the service area to places where the cost of laying existing base stations is high or where it is difficult to lay them, such as mountains, sea, and air. There is also a need to make the nation more resilient against natural disasters, and there is a need for a communication system that is resistant to terrestrial disasters.

[0003] As a means to realize the above requirements, non-terrestrial networks (NTNs) are attracting attention. NTNs are wireless networks that use node stations deployed in the air or in space, such as satellites, unmanned aerial vehicles (UAVs), high altitude pseudo satellites (HAPS), and drones. In NTNs, the node stations form a network by connecting with each other through communication links, and are further connected to terrestrial mobile networks via terrestrial base stations.

[0004] At NTN, the node station is equipped with a mobile base station function. Traffic packets generated by the terminal station are forwarded by the routing function to the node station connected to the terrestrial base station, and then sent to the Internet network. The same processing is also performed by the routing function for packets sent from the Internet network to the terminal station.

[0005] When routing in NTN, the node stations, terminal stations, and terrestrial base stations select the route with the shortest propagation time to the traffic destination. When comparing a communication route via a low-altitude node station with a communication route via a high-altitude node station, the communication route via the low-altitude node station has a smaller propagation delay due to its shorter distance from the ground. For this reason, traffic tends to concentrate on the communication route via the low-altitude node station. However, traffic concentration causes congestion, which leads to communication delays and packet loss and reduced throughput due to buffer overflow.

[0006] A congestion avoidance method for solving the above problem in NTN is proposed in Non-Patent Document 1. The congestion avoidance method proposed in Non-Patent Document 1 (hereinafter, referred to as the conventional method) can be explained using FIG.

[0007] In NTN, a communication route RL that passes through low-altitude node stations 7-1, 7-2, and 7-3 (hereinafter referred to as a low-altitude route) and a communication route RH that passes through a high-altitude node station 8 (hereinafter referred to as a high-altitude route) are used as communication routes from the terminal station 4 to the terrestrial base stations 3-1 and 3-2. In the low-altitude route RL, traffic passes through many node stations before reaching the terrestrial base station 3-1. For this reason, it is highly likely that multiple traffic routes share a node station, and congestion is likely to be induced at the node station.

[0008] In the conventional method disclosed in Non-Patent Document 1, a threshold is set for the propagation time, and if the propagation time is equal to or greater than the threshold, it is determined that the destination is far away, and if the propagation time is less than the threshold, it is determined that the destination is close. If it is determined that the destination is far away, the high altitude route RH is selected as the communication path for the traffic, and if it is determined that the destination is close, the low altitude route RL is selected as the communication path for the traffic to perform communication.

[0009] However, in the conventional method, the congestion status of the high altitude route RH is not taken into consideration when determining the communication route. Therefore, depending on the traffic generation situation, the high altitude route RH may become congested while the low altitude route RL may have a margin of propagation capacity. In such a situation, the throughput of the entire system decreases.

[0010] The above problem will be explained with reference to Fig. 15. The horizontal axis of the graph in Fig. 15 indicates the traffic transmission rate of the terminal station, and the vertical axis indicates the total throughput. Here, it is assumed that the high altitude route has a propagation capacity of 5 Mbps, and the low altitude route has a propagation capacity of 10 Mbps. In the example shown in Fig. 15, when the traffic transmission rate of the terminal station is 0.5 Mbps or more, congestion occurs on the high altitude route, and the throughput hits a plateau. On the other hand, the low altitude route has some propagation capacity to spare. In other words, the conventional method does not fully utilize the propagation capacity of the entire system. [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] Yuta Tada, Hiroki Nishiyama, Naoko Yoshimura, and Nei Kato, "A Study on Efficient Routing Control in Hierarchical Satellite Networks," IEICE Technical Report, Institute of Electronics, Information and Communication Engineers, September 2010, pp.45-50 Summary of the Invention [Problem to be solved by the invention]

[0012] The present disclosure has been made in light of the above-mentioned circumstances, and aims to provide technology that can prevent communication delays in NTN and a decrease in overall system throughput while satisfying traffic QoS requirements. [Means for solving the problem]

[0013] In order to achieve the above object, the present disclosure provides a wireless communication system. The wireless communication system of the present disclosure is configured to establish a low-latency communication path by linking node stations of a first group among a plurality of node stations constituting a wireless network, and to establish a high-latency communication path by linking node stations of a second group among the plurality of node stations with at least one node station of the first group. The wireless communication system of the present disclosure is configured to transmit all traffic using the low-latency communication path until the low-latency communication path becomes congested, and to transmit traffic with a long tolerable delay time among all traffic using both the low-latency communication path and the high-latency communication path upon detection of the congestion state of the low-latency communication path.

[0014] The present disclosure also provides a wireless communication method to achieve the above object. The wireless communication method of the present disclosure is a wireless communication method that establishes a low-latency communication path by linking node stations of a first group among a plurality of node stations constituting a wireless network, and establishes a high-latency communication path by linking node stations of a second group among the plurality of node stations with at least one node station of the first group. The wireless communication method of the present disclosure includes transmitting all traffic using the low-latency communication path until the low-latency communication path becomes congested, and transmitting traffic with a long tolerable latency among all traffic using both the low-latency communication path and the high-latency communication path upon detection of the congestion state of the low-latency communication path.

[0015] The present disclosure also provides a network controller to achieve the above object. The network controller of the present disclosure is a network controller that controls a wireless network composed of a plurality of node stations. The network controller of the present disclosure is configured to execute: establishing a low-latency communication path by link-connecting node stations of a first group among the plurality of node stations; and establishing a high-latency communication path by link-connecting node stations of a second group among the plurality of node stations with at least one node station of the first group. The network controller of the present disclosure is also configured to transmit all traffic using the low-latency communication path until the low-latency communication path becomes congested; and upon detection of the congestion state of the low-latency communication path, transmit traffic with a long allowable delay time among all traffic using both the low-latency communication path and the high-latency communication path.

[0016] Furthermore, in order to achieve the above object, the present disclosure provides a network control program. The network control program of the present disclosure includes a program for causing a computer to execute the processes performed by the network controller. That is, the network controller can be realized by a computer and a network control program. The network control program may be recorded on a computer-readable recording medium, or may be provided via a network. Effect of the Invention

[0017] According to the technology disclosed herein, it is possible to avoid congestion and prevent communication delays in NTN and a decrease in the throughput of the entire system while satisfying the QoS requirements of the traffic. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram showing a configuration of a wireless communication system according to a first embodiment of the present disclosure and a normal communication path. [Diagram 2]1 is a diagram illustrating a configuration of a wireless communication system according to a first embodiment of the present disclosure and a communication path in which a congestion state has been detected. [Diagram 3] 1 is a diagram illustrating a configuration of a node station-equipped communication device according to a first embodiment of the present disclosure. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a network controller according to the first embodiment of the present disclosure. [Diagram 5] 5 is a flowchart showing operations of a node station and a network controller according to the first embodiment of the present disclosure. [Figure 6] 1 is a diagram illustrating a relationship between a transmission rate and an overall system throughput in an example of a wireless communication system according to a first embodiment of the present disclosure. [Figure 7] 11 is a diagram showing a configuration of a wireless communication system according to a second embodiment of the present disclosure and a normal communication path. FIG. [Figure 8] 11 is a diagram illustrating a configuration of a wireless communication system according to a second embodiment of the present disclosure and a communication path in which a congestion state has been detected. FIG. [Figure 9] 11 is a flowchart showing operations of a node station and a network controller according to a second embodiment of the present disclosure. [Figure 10] FIG. 11 is a diagram showing a configuration of a wireless communication system according to a third embodiment of the present disclosure and a normal communication path. [Figure 11] 13 is a diagram illustrating a configuration of a wireless communication system according to a third embodiment of the present disclosure and a communication path in which a congestion state has been detected. FIG. [Figure 12] FIG. 11 is a diagram showing a configuration of a wireless communication system according to a fourth embodiment of the present disclosure and a normal communication path. [Figure 13] 13 is a diagram showing a configuration of a wireless communication system according to a fourth embodiment of the present disclosure and a communication path in which a congestion state has been detected. FIG. [Figure 14] FIG. 1 is a diagram illustrating a conventional method for avoiding congestion. [Figure 15] FIG. 1 is a diagram for explaining a problem with a conventional congestion avoidance method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, embodiments of a wireless communication system, a wireless communication method, a network controller, and a network control program according to the present disclosure will be described with reference to the drawings.

[0020] 1. First embodiment 1-1. Wireless communication system configuration First, the configuration of a wireless communication system according to the first embodiment will be described with reference to Fig. 1. As shown in Fig. 1, a wireless communication system 2-1 according to this embodiment includes two types of networks 17 and 18 deployed in the sky at different altitudes.

[0021] The first network is a low altitude network 17 consisting of a first group of node stations 7-1, 7-2, and 7-3 deployed at a relatively low altitude, connected by communication links. Hereinafter, the first group of node stations constituting the low altitude network 17 will be referred to as low altitude node stations. The second network is a high altitude network 18 consisting of a second group of node stations 8-1 and 8-2 deployed at a relatively high altitude, connected by communication links. Hereinafter, the second group of node stations constituting the high altitude network 18 will be referred to as high altitude node stations.

[0022] The node stations may be geostationary satellites (GEO), medium earth orbit satellites (MEO), low earth orbit satellites (LEO), high altitude pseudo satellites (HAPS), drones, unmanned aerial vehicles (UAV), or aircraft. Among these, node stations at relatively low altitudes are used as low altitude node stations 7-1 to 7-3, and node stations at relatively high altitudes are used as high altitude node stations 8-1 to 8-2. In this embodiment, the low altitude node stations 7-1 to 7-3 are LEOs, and the low altitude network 17 is a LEO network. The high altitude node stations 8-1 to 8-2 are GEOs, and the high altitude network 18 is a GEO network. Note that the number of node stations in each network 17, 18 shown in FIG. 1 is an example.

[0023] Note that whether a network is low altitude or high altitude is relative. Therefore, a network may be a low altitude network in one embodiment and a high altitude network in another embodiment. The same applies to a node station, and a node station may be a low altitude node station in one embodiment and a high altitude node station in another embodiment. For example, the LEO network 17 used as a low altitude network in this embodiment is used as a high altitude network in the second embodiment and as a medium altitude network in the third embodiment.

[0024] The low altitude network 17 is linked to the terrestrial base station 3-1 and connected to the mobile network 12 via the terrestrial base station 3-1. Similarly, the high altitude network 18 is linked to the terrestrial base station 3-2 and connected to the mobile network 12 via the terrestrial base station 3-2. A communication link can be established between a node station belonging to the low altitude network 17 and a node station belonging to the high altitude network 18. The two networks 17 and 18 are combined by link connection to form a non-terrestrial wireless network, i.e., NTN. All of the node stations constituting the wireless communication system 2-1 are connected to the mobile network 20 via the NTN.

[0025] Each node station has a routing function. Each node station transmits packets to a destination by transferring packets between other node stations. Each node station also has a mobile base station function. A terminal station connects to one of the node stations and connects to a mobile network 12 via an NTN. It is possible to connect to the Internet 14 via the mobile network 12. In the example shown in FIG. 1, the terminal station 4-1 connects to a low altitude node station 7-2, and the terminal station 4-2 connects to a low altitude node station 7-1. The functions of the node stations will be explained in detail later.

[0026] A network controller 20 is connected to the mobile network 12. The network controller 20 monitors the congestion state of the node stations, controls communication paths, controls link connections between the node stations, etc. The functions of the network controller 20 will be described in detail later.

[0027] In the configuration of the wireless communication system 2-1 described above, the communication links between the node stations may be realized by wireless communication using radio waves, or may be realized by other wireless communication such as optical communication. Moreover, each communication link in the wireless communication system 2-1 includes a communication line and a control line.

[0028] Further, while the wireless communication system 2-1 forms an NTN by combining two types of networks with different altitudes, it is also possible to form an NTN by combining three types of networks with different altitudes.

[0029] 1-2. Control of communication paths The wireless communication system 2-1 determines an end-to-end communication path while considering the congestion state of the network and the QoS requirements of the traffic. Figure 1 shows an example of a communication path that is usually used. When comparing a low altitude network 17 and a high altitude network 18, the low altitude network 17, which has a shorter distance from the ground to the node station, usually has a shorter propagation time to the destination. Therefore, in the basic setting, the low altitude route R11 is determined as the communication path so as to pass only through the low altitude network 17. For example, the traffic of the terminal station 4-2 is received by the nearest low altitude node station 7-1 and transmitted from the low altitude node station 7-1 to the terrestrial base station 3-1 via the low altitude network 17.

[0030] However, since the low altitude network 17 is also used by other terminal stations, traffic is likely to concentrate. For example, in the example shown in Fig. 1, traffic from the terminal station 4-2 and traffic from the terminal station 4-1 are transmitted on the low altitude route R11 at the same time. Here, it is assumed that the transmission capacity of the communication link of the low altitude network 17 is 1.0 Gbs. As in the example shown in Fig. 1, if the traffic volume from each of the terminal stations 4-1 and 4-2 is 0.4 Gbps, the total traffic volume of the low altitude node station 7-2 is within the transmission capacity of the communication link, which is 1.0 Gbs.

[0031] 2, when the traffic volume from each of the terminal stations 4-1 and 4-2 is 0.6 Gbps, the total traffic volume of the low altitude node station 7-2 becomes 1.2 Gbps, which exceeds the transmission capacity of the communication link of 1.0 Gbps. As a result, the low altitude node station 7-2 becomes congested.

[0032] When the wireless communication system 2-1 detects a congestion state in the low altitude route R11, it also uses the high altitude network 18. That is, in addition to the low altitude route R11 via the low altitude network 17, the wireless communication system 2-1 transmits traffic using the high altitude route R12 via the high altitude network 18. However, while the low altitude route R11 is a communication route with a relatively low latency, the high altitude route R12 is a communication route with a relatively high latency.

[0033] Considering that the high-altitude route R12 is a communication path with a long delay, the wireless communication system 2-1 transmits only traffic with a long tolerable delay time among all traffic, specifically, non-real-time traffic, using the high-altitude route R12 in addition. The non-real-time traffic transmitted using the high-altitude route R12 is the minimum amount of traffic that can relieve the congestion state of the low-altitude route R11, which is a communication path with a relatively low delay.

[0034] Here, we will explain the congestion state. Each node station has a transmission buffer, and stores packets waiting to be sent in the transmission buffer. The congestion state can be detected using the usage rate of the transmission buffer. In addition, the congestion state can also be detected by observing the number of packet losses at each node station, the amount of packets waiting to be sent, or the amount of traffic that has flowed in within a certain period of time.

[0035] In this embodiment, the congestion state is detected using the usage rate of the transmission buffer. If the usage rate of the transmission buffer is defined by the following formula, the congestion state can be defined as a state in which the usage rate of the transmission buffer exceeds a threshold value α.

number

[0036] According to the above definition of the congestion state, if the transmission buffer usage rate of all the low altitude node stations 7-1 to 7-3 is less than the threshold α, the wireless communication system 2-1 determines that the low altitude route R11 is not congested. Then, according to the determination result, the wireless communication system 2-1 transmits all traffic only using the low altitude route R11.

[0037] On the other hand, if the transmission buffer usage rate of any of the low altitude node stations 7-1 to 7-3 is equal to or greater than the threshold α, the wireless communication system 2-1 determines that the low altitude route R11 is congested. Then, according to the determination result, the wireless communication system 2-1 transmits the non-real-time traffic that exceeds the threshold α using the high altitude route R12. The non-real-time traffic that falls within the threshold α is transmitted using the low altitude route R11 together with the real-time traffic.

[0038] The tolerable delay time for non-real-time traffic is longer than that for real-time traffic. Therefore, the impact of transmitting part of the non-real-time traffic using the relatively long-delay high-altitude route R12 is small. The impact of congestion caused by transmitting all traffic using the low-altitude route R11 is more serious on QoS.

[0039] As described above, when the wireless communication system 2-1 detects a congestion state on the low-altitude route R11, it transmits non-real-time traffic also via the high-altitude route R12. This makes it possible to avoid congestion on the low-altitude route R11 and prevent communication delays in the NTN and a decrease in the throughput of the entire system while satisfying the QoS requirements of the traffic.

[0040] 1-3. Node Station Configuration Next, the configuration of the node station for realizing the above-mentioned communication path control by the wireless communication system 2-1 will be described. Each node station, including the low altitude node stations 7-1 to 7-3 and the high altitude node stations 8-1 to 8-2, is equipped with a node station-mounted communication device 30 having the configuration shown in Fig. 3. The node station-mounted communication device 30 is also equipped in the node stations of the second to fourth embodiments described later.

[0041] The node station mounted communication device 30 comprises an inter-node station communication device 31, an inter-terminal station communication device 32, an inter-terrestrial base station communication device 33, and a traffic monitor 34. The inter-node station communication device 31 communicates with nearby node stations by connecting a communication link. The inter-terminal station communication device 32 communicates with terminal stations by connecting a communication link. The inter-terrestrial base station communication device 33 communicates with terrestrial base stations by connecting a communication link. The traffic monitor 34 observes the amount of traffic flowing into the device itself.

[0042] The node station mounted communication device 30 reports the traffic volume information obtained by the traffic monitor 34 to the network controller 20. The node station mounted communication device 30 may report the traffic volume information to the network controller 20 periodically or autonomously in response to the occurrence of congestion.

[0043] Each of the above-mentioned devices 31, 32, 33, and 34 of the node station-equipped communication device 30 can be configured in part or in whole by hardware such as a PLD (Programmable Logic Device) or an FPGA (Field Programmable Gate Array). The functions of the above-mentioned devices 31, 32, 33, and 34 can also be realized by a program executable by a computer. The program can be recorded on a recording medium or provided via a network.

[0044] 1-4.Network controller configuration Next, the configuration of the network controller 20 for realizing the above-mentioned communication path control by the wireless communication system 2-1 will be described with reference to Fig. 4. The configuration of the network controller 20 shown in Fig. 4 is also common to the network controllers of the second to fourth embodiments described later.

[0045] The network controller 20 includes a congestion state monitor 21, a route control device 22, and a link control device 23. The congestion state monitor 21 collects traffic volume information observed by each node station and judges the congestion state of each node station. As described above, whether or not there is a congestion state is judged based on whether or not the usage rate of the transmission buffer exceeds the threshold value α. The location of the congestion state monitor 21 is not limited to the network controller 20. A congestion state monitor may be provided for each node station, and the network controller 20 may collect the congestion state judgment results for each node station.

[0046] The route control device 22 determines an end-to-end communication path for transmitting traffic. The determination result of the congestion state monitor 21 is used to determine the communication path. Specifically, until a congestion state is detected, the low altitude route R11 is determined as the communication path for all traffic. Then, upon detection of a congestion state, the high altitude route R12 is determined as the communication path for a portion of the non-real-time traffic.

[0047] The link control device 23 performs a reconstruction process of the communication links in the NTN based on the determination result of the congestion state monitoring device 21. Specifically, upon detection of a congestion state, a communication link is constructed between a node station belonging to the low altitude network 17 and a node station belonging to the high altitude network 18 so as to establish a high altitude route R12 in addition to the low altitude route R11. However, in this embodiment, as shown in Figures 1 and 2, the communication link required to establish the high altitude route R12 is constructed in advance between the low altitude node station 7-1 and the high altitude node station 8-2 (and between the low altitude node station 7-3 and the high altitude node station 8-2).

[0048] The network controller 20 can be configured, for example, by a computer including a memory storing a program and a processor coupled to the memory. The program is executed by the processor to realize the functions of the above-mentioned devices 21, 22, and 23. The program can be recorded on a recording medium or provided via a network.

[0049] 1-5. Operation of node station and network controller The operation of each node station and the network controller 20 configured as described above will be described with reference to the flowchart of Fig. 5. The operation shown in this flowchart corresponds to the wireless communication method of the present disclosure executed by the wireless communication system 2-1.

[0050] Step S101 is an operation of each node station, more specifically, an operation executed by the node station mounted communication device 30. In step S101, the node station mounted communication device 30 of each node station uses the traffic monitor 34 to observe the amount of traffic flowing into the node station itself.

[0051] Steps S102 to S104 are operations executed by the network controller 20. In step S102, the network controller 20 collects information on traffic volume observed at each node station. Then, in step S103, it is determined whether any of the low altitude node stations 7-1 to 7-3 is in a congested state based on the collected traffic volume information.

[0052] If none of the low altitude node stations 7-1 to 7-3 is in a congested state, step S105 is selected. In step S105, the network controller 20 instructs each node station to transmit all traffic via the low altitude route R11, which is a communication path with low latency.

[0053] If any of the low altitude node stations 7-1 to 7-3 is in a congested state, step S104 is selected. In step S104, the network controller 20 instructs each node station to transmit only non-real-time traffic among all traffic using the high altitude route R12, which is a communication path with a long delay.

[0054] By operating each node station and the network controller 20 according to the above flowchart, it is possible to avoid congestion and prevent communication delays in the NTN and a decrease in the throughput of the entire system.

[0055] Here, the evaluation result of one embodiment of the wireless communication system 2-1 will be described. In the embodiment, LEO is arranged as a low altitude node station, GEO is arranged as a high altitude node station, and the threshold α for judging the congestion state is set to 0.7. When non-real-time traffic that exceeds the propagation capacity of the low altitude route is transmitted using the low altitude route, packet loss occurs due to buffer overflow at the low altitude node station. In order to avoid this, the threshold α is appropriately set to control the amount of non-real-time traffic communicated on the low altitude route, and the result of improving the throughput of the entire system is shown in FIG. 6. FIG. 6 shows the relationship between the transmission rate and the throughput of the entire system according to the embodiment. In FIG. 6, the conventional technology means the use of only the low altitude route, and the inventive technology means the embodiment of the wireless communication system 2-1.

[0056] 2. Second embodiment 2-1. Wireless communication system configuration 7 shows the configuration of a wireless communication system according to the second embodiment. As shown in FIG 7, a wireless communication system 2-2 according to this embodiment includes a low altitude network 16 and a high altitude network 17.

[0057] HAPS are deployed as low altitude node stations 6-1, 6-2, and 6-3 (first group node stations) that make up the low altitude network 16. In other words, the low altitude network 16 is a HAPS network. The low altitude node station 6-1 is connected to the low altitude node station 6-2 via a communication link, and the low altitude node station 6-2 is connected to the low altitude node station 6-1 and the low altitude node station 6-3 via communication links. The low altitude node station 6-3 is connected to a terrestrial base station 3-3 via a communication link. The low altitude network 16 is connected to the mobile network 12 via the terrestrial base station 3-3.

[0058] LEOs are arranged as high altitude node stations 7-1 and 7-2 (second group node stations) that constitute the high altitude network 17. In other words, the high altitude network 17 is a LEO network. The high altitude node station 7-1 is connected to the high altitude node station 7-2 via a communication link. The high altitude node station 7-2 is connected to the terrestrial base station 3-1 via a communication link. The high altitude network 17 is connected to the mobile network 12 via the terrestrial base station 3-1. Note that the number of node stations in each of the networks 16 and 17 shown in FIG. 7 is just an example.

[0059] The high altitude network 17 and the low altitude network 16 are not previously connected by a communication link. As described below, the wireless communication system 2-2 reconstructs a link between the high altitude network 17 and the low altitude network 16 upon detection of a congestion state of any of the low altitude node stations.

[0060] The node stations 6-1 to 6-3, 7-1 to 7-2 are equipped with a node station mounted communication device 30 shown in Fig. 3. In the third and fourth embodiments described below, each node station is also equipped with a node station mounted communication device 30 shown in Fig. 3. The configuration of the node station mounted communication device 30 is as described in the first embodiment. A network controller 20 is connected to the mobile network 12. The configuration of the network controller 20 is as shown in Fig. 4. The network controller 20 in the third and fourth embodiments described below also has the configuration shown in Fig. 4.

[0061] 2-2. Control of communication paths Fig. 7 shows an example of a communication path normally used in the wireless communication system 2-2. In the basic setting, a low altitude route R21 is determined as the communication path so as to pass through only the low altitude network 16. In the example shown in Fig. 7, terminal stations 4-3 and 4-4 are connected to a low altitude node station 6-1, and terminal stations 4-1 and 4-2 are connected to a low altitude node station 6-2. The traffic of these terminal stations 4-1 to 4-4 passes through the low altitude route R21 and is transmitted to the mobile network 12 via the terrestrial base station 3-3.

[0062] However, as shown in Fig. 7, the transmission capacity of the communication link of the low altitude network 16 is 1.0 Gbps. Meanwhile, the traffic volume from each of the terminal stations 4-1 to 4-4 is 0.3 Gbps. Therefore, the total traffic volume in the low altitude node station 6-2 becomes 1.2 Gbps, which exceeds the transmission capacity of the communication link of 1.0 Gbps. As a result, the low altitude node station 6-2 becomes congested.

[0063] When the wireless communication system 2-2 detects congestion in the low altitude route R21, it establishes a communication link between the congested low altitude node station 6-2 and the high altitude node station 7-2, as shown in Fig. 8. The high altitude node station to which the communication link is to be connected is determined from the traffic observed at each high altitude node station. By reconstructing the communication link, a high altitude route R22 via the high altitude network 17 is established as a communication path from the low altitude node station 6-2 to the mobile network 12 in addition to the low altitude route R21 via the low altitude network 16. The high altitude route R22 is a communication path from the low altitude node station 6-2 to the terrestrial base station 3-1 via the high altitude node station 7-2.

[0064] The wireless communication system 2-2 divides the traffic flowing into the low altitude node station 6-2 into the low altitude route R21 and the high altitude route R22 and transmits the traffic to the mobile network 12. This eliminates the congestion state that occurred between the low altitude node station 6-2 and the low altitude node station 6-3. However, while the low altitude route R21 is a communication path with relatively low latency, the high altitude route R22 is a communication path with relatively high latency. For this reason, the wireless communication system 2-2 transmits only non-real-time traffic out of all traffic by also using the high altitude route R22.

[0065] 2-3. Operation of node station and network controller The operation of each node station and the network controller 20 in this embodiment will be described with reference to the flowchart of Fig. 9. The operation shown in this flowchart corresponds to the wireless communication method of the present disclosure executed by the wireless communication system 2-2.

[0066] Step S201 is an operation of each node station, more specifically, an operation executed by the node station mounted communication device 30 having the configuration shown in Fig. 3. In step S201, the node station mounted communication device 30 of each node station monitors the amount of traffic flowing into the node station using the traffic monitor 34.

[0067] Steps S202 to S204 are operations executed by the network controller 20. In step S202, the network controller 20 collects information on traffic volume observed at each node station. Then, in step S203, it is determined whether any of the low altitude node stations 6-1 to 6-3 is in a congested state based on the collected traffic volume information.

[0068] If any of the low altitude node stations 6-1 to 6-3 is in a congested state, step S204 is selected. In step S204, the network controller 20 instructs the congested low altitude node station to establish a communication link with a specified high altitude node station. Based on the traffic observation information of each of the high altitude node stations 7-1 to 7-2, the network controller 20 determines which high altitude node station to designate as the opposite station of the link. In the example shown in FIG. 7, the low altitude node station to be instructed to establish a communication link is the low altitude node station 6-2, and the high altitude node station to be designated as the opposite station of the link is the high altitude node station 7-2.

[0069] Step S205 is the operation of the low altitude node station that has received the instruction from the network controller 20 in step S204. In step S205, the low altitude node station that has received the instruction establishes a communication link with the specified high altitude node station in accordance with the instruction from the network controller 20. As a result, as in the example shown in Fig. 8, a communication link that connects the low altitude node station 6-2 and the high altitude node station 7-2 is established, and a high altitude route R22 that passes through the high altitude network 17 is established.

[0070] Steps S206 and S207 are operations executed by the network controller 20. If the result of the determination in step S203 is that none of the low altitude node stations 6-1 to 6-3 is in a congested state, step S207 is selected. In step S207, the network controller 20 instructs each node station to transmit all traffic via the low altitude route R21, which is a communication path with low latency.

[0071] If the high altitude route R22 is established in step S205, step S206 is selected. In step S206, the network controller 20 instructs each node station to transmit only non-real-time traffic among all traffic using the high altitude route R22, which is a communication path with a long delay, in addition.

[0072] By operating each node station and the network controller 20 according to the above flowchart, it is possible to avoid congestion and prevent communication delays in the NTN and a decrease in the throughput of the entire system while satisfying QoS requirements. Note that, although the above flowchart instructs each node station on the communication path to be used after the establishment of the communication link is completed, the communication path may be instructed at the same time as instructing the establishment of the communication link.

[0073] 3. Third embodiment 3-1. Wireless communication system configuration Fig. 10 shows the configuration of a wireless communication system according to the third embodiment. As shown in Fig. 10, a wireless communication system 2-3 according to this embodiment includes a low altitude network 16, a medium altitude network 17, and a high altitude network .

[0074] The low altitude network 16 is a HAPS network made up of HAPS deployed as low altitude node stations 6-1, 6-2, and 6-3 connected by communication links. The medium altitude network 16 is a LEO network made up of LEO deployed as medium altitude node stations 7-1 and 7-2 connected by communication links. The high altitude network 18 is a GEO network made up of GEO deployed as high altitude node station 8 connected by communication links. The propagation delay increases in proportion to the altitude of each network 16, 17, and 18. Note that the number of node stations in each network 16, 17, and 18 shown in Figure 10 is just an example.

[0075] The low altitude network 16 is connected to the mobile network 12 via a terrestrial base station 3-3. The medium altitude network 17 is connected to the mobile network 12 via a terrestrial base station 3-1. The high altitude network 18 is connected to the mobile network 12 via a terrestrial base station 3-2. However, the three networks 16, 17, and 18 are not previously connected by a communication link. Based on the traffic state of each network 16, 17, and 18, the wireless communication system 2-3 reconstructs links between the three networks 16, 17, and 18.

[0076] 3-2. Communication path control An example of a communication path used in the wireless communication system 2-3 is shown in Fig. 10. In the wireless communication system 2-3, a low altitude route R31 via the low altitude network 16 and a medium altitude route R32 via the medium altitude network 17 are used together as communication paths. However, there is no communication link between the low altitude network 16 and the medium altitude network 17, and the low altitude route R31 and the medium altitude route R32 are independent communication paths.

[0077] In the example shown in Fig. 10, terminal stations 4-3 and 4-4 are connected to a low altitude node station 6-1, and a terminal station 4-1 is connected to a low altitude node station 6-2. The traffic of these terminal stations 4-1, 4-3, and 4-4 passes through a low altitude route R31 and is transmitted to a mobile network 12 via a terrestrial base station 3-3. In addition, a terminal station 4-2 is connected to a medium altitude node station 7-1. The traffic of this terminal station 4-2 passes through a medium altitude route R32 and is transmitted to a mobile network 12 via a terrestrial base station 3-1.

[0078] 10, the transmission capacity of the communication link of the low altitude network 16 is 1.0 Gbps. On the other hand, the total traffic volume from the terminal stations 4-1, 4-3, and 4-4 is 1.2 Gbps. Therefore, the total traffic volume exceeds the transmission capacity of the communication link in the low altitude node station 6-2, and the low altitude node station 6-2 enters a congested state.

[0079] In the second embodiment, when the low altitude route becomes congested, the communication link is connected to the network of the next higher layer. However, in this embodiment, the traffic volume from the terminal station 4-2 connected to the medium altitude node station 7-1 is 0.9 Gbps, approaching the transmission capacity of the communication link of the medium altitude network 17, which is 1.0 Gbps. In other words, the medium altitude route R32 via the medium altitude network 17 does not have the capacity to accept the excess traffic from the low altitude route R31.

[0080] On the other hand, there is no traffic in the high altitude network 18, and the high altitude node station 8 has a margin of traffic volume relative to its transmission capacity. Therefore, when the wireless communication system 2-3 detects congestion in the low altitude route R31, it establishes a communication link between the low altitude node station 6-1 and the high altitude node station 8 as shown in Fig. 11. By reconstructing the communication link, a high altitude route R33 via the high altitude network 18 is established as a communication path from the low altitude node station 6-1 to the mobile network 12 in addition to the low altitude route R31 via the low altitude network 16. The high altitude route R33 is a communication path from the low altitude node station 6-1 to the terrestrial base station 3-2 via the high altitude node station 8.

[0081] The wireless communication system 2-3 divides traffic flowing into the low altitude node station 6-1 into a low altitude route R31 and a high altitude route R33 and transmits the traffic to the mobile network 12. This eliminates the congestion state that occurred between the low altitude node station 6-2 and the low altitude node station 6-3. However, while the low altitude route R31 is a communication path with relatively low latency, the high altitude route R33 is a communication path with relatively high latency. For this reason, the wireless communication system 2-3 transmits only non-real-time traffic out of all traffic by also using the high altitude route R33.

[0082] As described above, the wireless communication system and wireless communication method according to this embodiment can also avoid congestion and prevent communication delays in the NTN and a decrease in the throughput of the entire system while satisfying QoS requirements.

[0083] In the example shown in FIG. 11, a communication link is established between a low altitude node station 6-1 and a high altitude node station 8, but a communication link may also be established between a low altitude node station 6-2 that has become congested and a high altitude node station 8.

[0084] Also, when congestion is detected in the low altitude route R31, the low altitude network 16 and the medium altitude network 16 may first be connected by a communication link, and the excess traffic of the low altitude route R31 may be sent to the medium altitude route R32. Then, when congestion is detected in the medium altitude route R32, the medium altitude network 16 and the high altitude network 16 may be connected by a communication link, and the excess traffic of the medium altitude route R32 may be sent to the high altitude route R33.

[0085] 4. Fourth embodiment 4-1. Wireless communication system configuration Fig. 12 shows the configuration of a wireless communication system according to the fourth embodiment. As shown in Fig. 12, a wireless communication system 2-4 according to this embodiment has the same configuration as the wireless communication system 2-2 according to the second embodiment. However, there are differences in the connection destinations and traffic volumes of the terminal stations 4-1 to 4-4. In this embodiment, the terminal stations 4-3, 4-4, and 4-5 are connected to the low altitude node station 6-1, the terminal station 4-2 is connected to the low altitude node station 6-2, and the terminal station 4-1 is connected to the low altitude node station 6-3. The transmission capacity of the communication link of the low altitude network 16 is 1.0 Gbps, while the traffic volume from each of the terminal stations 4-1 to 4-5 is 0.4 Gbps.

[0086] 4-2. Communication path control 12 shows an example of a communication path that is normally used in the wireless communication system 2-4. In the basic setting, a low altitude route R41 is determined as the communication path so as to pass only through the low altitude network 16. Traffic of the terminal stations 4-1 to 4-5 connected to the low altitude network 16 passes through the low altitude route R41 and is transmitted to the mobile network 12 via the terrestrial base station 3-3.

[0087] However, as shown in Fig. 12, the transmission capacity of the communication link of the low altitude network 16 is 1.0 Gbps. Meanwhile, the traffic volume from each of the terminal stations 4-3 to 4-5 is 0.4 Gbps. Therefore, the total traffic volume in the low altitude node station 6-1 becomes 1.2 Gbps, which exceeds the transmission capacity of the communication link of 1.0 Gbps. As a result, the low altitude node station 6-1 becomes congested.

[0088] The low altitude node station 6-2 receives 1.4 Gbs of traffic in total, consisting of 1.0 Gbs of traffic from the low altitude node station 6-1, which is the transmission capacity of the communication link, and 0.4 Gbs of traffic from the terminal station 4-2. However, the amount of 1.4 Gbs of traffic exceeds the transmission capacity of the communication link between the low altitude node station 6-2 and the low altitude node station 6-3. As a result, the low altitude node station 6-2 also enters a congested state.

[0089] Furthermore, the low altitude node station 6-3 receives 1.0 Gbps of traffic from the low altitude node station 6-2, which is the transmission capacity of the communication link, and 0.4 Gbps of traffic from the terminal station 4-1, for a total of 1.4 Gbps of traffic. However, the amount of 1.4 Gbps of traffic exceeds the transmission capacity of the communication link between the low altitude node station 6-3 and the terrestrial base station 3-3. For this reason, the low altitude node station 6-3 also enters a congested state.

[0090] In this way, when the transmission capacity of the communication links between the low altitude node stations is equal, the congestion state of the upstream low altitude node station 6-1 causes the downstream low altitude node stations 6-2 and 6-3 to also become congested in a chain reaction. In this case, even if a link is established between the low altitude node station 6-3 and the high altitude network 17, the congestion state of the low altitude node stations 6-1 and 6-2 is not resolved. Also, even if a link is established between the low altitude node station 6-2 and the high altitude network 17, the congestion state of the low altitude node station 6-1 is not resolved.

[0091] Therefore, when the wireless communication system 2-4 detects congestion at a plurality of low altitude node stations, it establishes a communication link between the most upstream low altitude node station 6-1 that has become congested and the high altitude node station 7-1, as shown in FIG. 13. Which high altitude node station is to be the connection destination of the communication link is determined from the traffic observed at each high altitude node station. By reconstructing the communication link, a high altitude route R42 via the high altitude network 17 is established as a communication path from the low altitude node station 6-1 to the mobile network 12, in addition to the low altitude route R41 via the low altitude network 16. The high altitude route R42 is a communication path from the low altitude node station 6-1 to the terrestrial base station 3-1 via the high altitude node stations 7-1 and 7-2.

[0092] The wireless communication system 2-4 divides traffic flowing into the low altitude node station 6-1 into a low altitude route R41 and a high altitude route R42 and transmits the traffic to the mobile network 12. This eliminates the congestion state that occurred in the low altitude node station 6-1, and further eliminates the congestion state that occurred in the downstream low altitude node stations 6-2 and 6-3. However, while the low altitude route R41 is a communication path with a relatively low delay, the high altitude route R42 is a communication path with a relatively high delay. For this reason, the wireless communication system 2-4 transmits only non-real-time traffic out of all traffic by also using the high altitude route R42.

[0093] As described above, the wireless communication system and wireless communication method according to this embodiment can also avoid congestion and prevent communication delays in the NTN and a decrease in the throughput of the entire system while satisfying QoS requirements. [Explanation of symbols]

[0094] 2-1, 2-2, 2-3, 2-4 Wireless communication systems 4-1, 4-2, 4-3, 4-4, 4-5 Terminal Station 6-1, 6-2, 6―3 Node Station (HAPS) 7-1, 7-2, 7-3 Node Station (LEO) 8 Node Station (GEO) 3-1, 3-2, 3-3 Terrestrial base station 16 Network (HAPS Network) 17 Network (LEO Network) 18 Network (GEO Network) 12 Mobile Networks 20 Network Controller 30 Node station equipped communication device R11, R21, R31, R41 Low-latency communication routes (low-altitude routes) R12, R22, R32, R42 High latency communication routes (high altitude routes)

Claims

1. A wireless communication system configured to establish a low-latency communication path by link-connecting a first group of node stations among a plurality of node stations constituting a wireless network, and to establish a high-latency communication path by link-connecting a second group of node stations among the plurality of node stations with at least one node station of the first group, transmitting all traffic using the low-latency communication path until the low-latency communication path becomes congested; Upon detection of a congestion state of the low-latency communication path, a traffic having a long allowable delay time among all the traffic is transmitted through both the low-latency communication path and the long-latency communication path.

1. A wireless communication system comprising:

2. 2. The wireless communication system according to claim 1, and reconstructing a link between the first group and the second group upon detection of a congestion state of any one of the node stations in the first group.

1. A wireless communication system comprising:

3. 3. The wireless communication system according to claim 2, A node station in the first group that is in a congested state or has a large amount of traffic is linked to a node station in the second group that has an available transmission capacity.

1. A wireless communication system comprising:

4. 4. The wireless communication system according to claim 3, When the plurality of node stations in the first group are in a congested state, the node station in the first group that is located most upstream and in a congested state is selected as a link connection destination.

1. A wireless communication system comprising:

5. 5. The wireless communication system according to claim 1, and detecting a congestion state of the low-latency communication path by observing any one of a buffer usage rate, a packet loss count, an amount of packets waiting to be transmitted, and an amount of traffic that has flowed in within a certain period of time in each node station included in the first group.

1. A wireless communication system comprising:

6. A wireless communication method for establishing a low-latency communication path by link-connecting a first group of node stations among a plurality of node stations constituting a wireless network, and establishing a high-latency communication path by link-connecting a second group of node stations among the plurality of node stations with at least one node station of the first group, comprising: transmitting all traffic using the low-latency communication path until the low-latency communication path becomes congested; Upon detection of a congestion state of the low-latency communication path, transmitting traffic having a long tolerable delay time among all the traffic using both the low-latency communication path and the long-latency communication path.

23. A wireless communication method comprising:

7. A network controller for controlling a wireless network composed of a plurality of node stations, establishing a low-latency communication path by link-connecting a first group of node stations among the plurality of node stations; establishing a long-latency communication path by link-connecting a node station of a second group among the plurality of node stations with at least one node station of the first group; transmitting all traffic using the low-latency communication path until the low-latency communication path becomes congested; Upon detection of a congestion state of the low-latency communication path, a traffic having a long allowable delay time among all the traffic is transmitted through both the low-latency communication path and the long-latency communication path. A network controller comprising:

8. A program for causing a computer to execute the process performed by the network controller according to claim 7. A network control program comprising:

Images