Wireless communication system, wireless communication method, wireless communication device, and wireless communication program

Abstract

The present disclosure relates to a wireless communication system, a wireless communication method, a wireless communication device, and a wireless communication program. This wireless communication system implements communication using a non-terrestrial network, and comprises a terminal station, a terrestrial base station, a plurality of node stations constituting a non-terrestrial network, and a route control device. The route control device is configured so as to perform processing to calculate a predicted time at which a communication link interruption will occur, processing to configure a plurality of communication routes serving as switching destination candidates, processing to calculate cost values of the plurality of communication routes serving as switching destination candidates on the basis of the predicted time, and processing to compare the cost values and select, from the plurality of communication routes serving as switching destination candidates, the communication route for which the cost value is the lowest.

Description

Wireless communication system, wireless communication method, wireless communication device, and wireless communication program

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

[0002] With the recent development of mobile communication systems, mobile services can now be enjoyed over most of the earth. One of the requirements for the 5th generation and later 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 construction cost of existing base stations is high or difficult, such as mountains, oceans, or air.

[0003] To achieve the above, non-terrestrial networks (NTNs) using node stations such as satellites, unmanned aerial vehicles (UAVs), high altitude pseudo satellites (HAPS), or drones are gaining attention. In an NTN, node stations connect to each other via communication links to form a network, which is further connected to a terrestrial mobile network via a terrestrial base station. Traffic generated at terrestrial terminal stations is forwarded within the NTN to a node station that can communicate with a terrestrial base station. For example, Non-Patent Document 1 discloses a route control method for a hierarchical satellite network using an NTN.

[0004] Tada, Nishiyama, Yoshimura, and Kato, “A Study on Efficient Routing Control in Hierarchical Satellite Networks,” IEICE Technical Report SAT2010-9

[0005] However, the above-mentioned method calculates the communication path without considering the lifespan of the communication link, which is the remaining time that communication is possible through the link. As a result, a communication link failure may occur again immediately after it occurs due to node station movement or rain attenuation. This has led to the problem of frequent switching of communication paths triggered by a communication link failure.

[0006] In order to solve the above-mentioned problems, a first object of the present disclosure is to provide a wireless communication system that can avoid frequent switching of communication paths triggered by communication link disconnection.

[0007] A first aspect of the present disclosure is a wireless communication system that communicates using a non-terrestrial network, and preferably includes a terminal station, a terrestrial base station, a plurality of node stations that constitute the non-terrestrial network, and a route control device, and the route control device is configured to perform the following processes: calculating a predicted time when a communication link will be interrupted; setting a plurality of communication routes that will be candidate destinations; calculating cost values ​​of the plurality of communication routes that will be candidate destinations based on the predicted time; and comparing the cost values ​​and selecting the communication route with the smallest cost value from the plurality of candidate communication routes that will be candidate destinations.

[0008] A second aspect of the present disclosure is preferably a wireless communication method for communicating using a non-terrestrial network, comprising: calculating a predicted time when a communication link disconnection will occur; setting a plurality of communication paths as candidate destinations; calculating cost values ​​of the plurality of communication paths as candidate destinations based on the predicted time; comparing the cost values; and selecting a communication path with the smallest cost value from the plurality of candidate communication paths as candidate destinations.

[0009] A third aspect of the present disclosure is a wireless communication device that communicates using a non-terrestrial network, and is preferably configured to perform the following processes: calculating a predicted time when a communication link will be interrupted; setting multiple communication routes as candidate destinations; calculating cost values ​​of the multiple communication routes as candidate destinations based on the predicted time; and comparing the cost values ​​and selecting the communication route with the smallest cost value from the multiple communication routes as candidate destinations.

[0010] A fourth aspect of the present disclosure is preferably a wireless communication program to be executed by a wireless communication device that communicates using a non-terrestrial network, the wireless communication program including a program for causing a computer to execute the following processes: a process for calculating a predicted time at which a communication link will be interrupted; a process for setting multiple communication routes as candidate destinations; a process for calculating cost values ​​of the multiple communication routes as candidate destinations based on the predicted time; and a process for comparing the cost values ​​and selecting the communication route with the smallest cost value from the multiple communication routes as candidate destinations.

[0011] According to the first to fourth aspects of the present disclosure, it is possible to avoid frequent switching of communication paths triggered by a communication link disconnection.

[0012] FIG. 1 is a diagram illustrating switching of a communication path according to a comparative example. FIG. 2 is a diagram illustrating switching of a communication path according to embodiment 1 of the present disclosure. FIG. 3 is a diagram illustrating a configuration of a wireless communication system according to embodiment 1 of the present disclosure. FIG. 4 is a diagram illustrating a configuration of a wireless communication device mounted in a node station according to embodiment 1 of the present disclosure. FIG. 5 is a diagram illustrating a configuration of a network controller according to embodiment 1 of the present disclosure. FIG. 6 is a diagram illustrating a hardware configuration of a path control device according to embodiment 1 of the present disclosure. FIG. 7 is a flowchart illustrating path switching processing according to embodiment 1 of the present disclosure. FIG. 8 is a diagram illustrating a wireless communication system according to embodiment 2 of the present disclosure.

[0013] 1 is a diagram showing switching of communication paths according to a comparative example. A wireless communication system 500 is a wireless communication system that transfers traffic transmitted from a terminal station 2 via any of node stations 6 a, 6 b, and 6 c, which are fixed node stations, and node stations 7 a, 7 b, and 7 c, which are mobile node stations.

[0014] The diagram on the left of Fig. 1 shows the first switching of communication paths. In the wireless communication system 500 shown on the left of Fig. 1, traffic transmitted from the terminal station 2 is forwarded using the communication path 14a. The communication path 14a is a communication path that passes through the node station 6a and the node station 7a.

[0015] Now, let us assume that a first communication link failure occurs between node station 6a and node station 7a. Examples of causes of the communication link failure include movement of the node station and rain attenuation. In this case, the wireless communication system 500 switches the communication path used for forwarding to communication path 14b. Communication path 14b is a communication path that passes through node station 6a, node station 6b, and node station 7b.

[0016] The right diagram of Fig. 1 shows the second switching of the communication path. In the right diagram of Fig. 1, the wireless communication system 500 transfers traffic transmitted from the terminal station 2 using the communication path 14a.

[0017] Now, let us assume that a second communication link failure occurs between node station 6b and node station 7b immediately after the first communication link failure. In this case, the wireless communication system 500 switches the communication path used for forwarding to communication path 14c. Communication path 14c is a communication path that passes through node station 6a, node station 6b, node station 6c, and node station 7c.

[0018] As described above, in the wireless communication system 500, a second communication path switch occurs immediately after a first communication path switch. That is, a problem of frequent communication path switches occurs. This problem occurs because the communication path to be used is calculated without considering the lifespan of the communication link. The present disclosure solves this problem.

[0019] [Wireless Communication System According to First Embodiment of the Present Disclosure] Fig. 2 is a diagram illustrating switching of communication paths according to the first embodiment of the present disclosure. The configuration of the wireless communication system according to this embodiment is similar to that of the wireless communication system 500. However, the wireless communication system according to this embodiment differs from the wireless communication system 500 in that the wireless communication system switches communication links in consideration of the lifespan of the communication links.

[0020] The wireless communication system 100 transfers traffic transmitted from the terminal station 2 using the communication path 14a. Assume that a first communication link disconnection occurs between the node station 6a and the node station 7a. First, the wireless communication system 100 sets up multiple communication paths as switching destination candidates. Then, using a method described later, the system calculates the cost values ​​of the switching destination candidate communication paths, and switches to the communication path with the lowest cost value. This cost value takes into account the link lifespans of the communication links included in the corresponding communication paths.

[0021] In this example, let us assume that a second communication link failure occurs between node station 6b and node station 7b immediately after the first communication link failure. In this case, the link life of the communication link connecting node station 6b and node station 7b increases, and the cost value of communication path 14b also increases. Therefore, the wireless communication system 100 selects communication path 14c instead of communication path 14b.

[0022] A detailed description will be given of a method for switching communication routes in the wireless communication system 100. First, the node station 6a calculates the cost value C of the communication route to be switched to, and switches to a communication route with a lower cost value.

[0023] This cost value includes the link life T Ｌ is taken into consideration. Ｌ is calculated by using the predicted time T' when the communication link will be down. ｓ This is expressed by Equation 1 based on the above.

[0024]

[0025] For example, the predicted time T' of a communication link interruption due to node station movement is calculated using startup information of the node station, and the predicted time T' of a communication link interruption due to rain attenuation is calculated using rainfall forecast information such as rainfall nowcast.

[0026] Furthermore, the cost value C is expressed by equations 2 to 4 when the signal relay method of the node station is a regenerative relay method.

[0027]

[0028] ​​

[0029]

[0030] However, C ｉ is the cost value of communication link i, n is the total number of links included in the communication path, R is the link capacity, and D is the link delay time. Also, BR is the reference value of capacity, BD is the reference value of delay time, and BT ｉ is a reference value of the lifetime, which is an arbitrary value. Furthermore, α is the congestion degree of the link, and r is the traffic flow rate in the link.

[0031] Furthermore, the cost value C is expressed by equations 5 to 7 when the signal relay method of the node station is a non-regenerative relay method.

[0032]

[0033]

[0034]

[0035] where H is the number of signal relays, W is the link bandwidth utilization rate, and W Ｆ is the total bandwidth of the link, W ｕ is the allocated bandwidth of the link. BH is the reference value of the number of relays, and BW is the reference value of the utilization rate, both of which are arbitrary values.

[0036] The cost value C shown in Equation 2 and Equation 5 is calculated based on the link lifetime T Ｌ Therefore, in this embodiment, the link lifetime T Ｌ A communication path including a communication link with a longer length is selected with higher priority.

[0037] In order to continue providing communication services, it is necessary to change the communication path when a communication link is disconnected. In this embodiment, by selecting a communication path with a long communication link life, which is the remaining time available for communication, the number of times the communication path is changed can be reduced. In other words, it is possible to avoid frequent switching of communication paths triggered by communication link disconnection.

[0038] ​​​​​3 is a diagram illustrating a configuration of a wireless communication system according to the first embodiment of the present disclosure. The wireless communication system 200 illustrates an example of a wireless communication system that actually performs the switching of communication paths illustrated in the wireless communication system 100.

[0039] The wireless communication system 200 includes an NTN 30 that relays communications between a terminal station 2 and a terrestrial base station 4. The NTN 30 includes, for example, a network 32 having low-earth orbit satellites (LEO), a network 34 having medium-earth orbit satellites (MEO), and a network 36 having geostationary orbit satellites (GEO). The networks 32, 34, and 36 are networks consisting of node stations of the same type, and can form communication links with each other, with multiple networks being combined to form the NTN 30. Other examples of node stations that can be used include high-altitude pseudo satellites (HAPS), drones, unmanned aerial vehicles (UAVs), and aircraft. The communication links may be wireless or optical wireless.

[0040] In this way, the wireless communication system 200 includes a plurality of node stations in the sky, and the node stations are connected to one another via communication links. Communication links are also formed with the terrestrial base station 4, and networks are formed for each type of node station.

[0041] Furthermore, the NTN 30 is connected to a network controller 40. When the communication method of the wireless communication system 200 is a centralized control method, the network controller 40 performs processing necessary for calculating a communication path. The necessary processing is, for example, calculation of a cost value C.

[0042] When the communication method of the wireless communication system 100 is a distributed control method, the necessary processes described above are performed by each node station, eliminating the need for the network controller 40. Even when the communication method of the wireless communication system 100 is a centralized control method, the necessary processes described above are performed by each node station, eliminating the need for the network controller 40.

[0043] 4 is a diagram illustrating a configuration of a wireless communication device installed in a node station according to the first embodiment of the present disclosure. Here, an example will be described in which NTN control is performed using a distributed control method.

[0044] The wireless communication device 60 includes an inter-node communication device 62a. The inter-node communication device 62a connects a communication link with the node station 6a and performs communication. The wireless communication device 60 also includes inter-node communication devices 62b and 62c. The inter-node communication devices 62b and 62c connect communication links with the nearby node stations 6b and 7a and perform communication.

[0045] The wireless communication device 60 includes an inter-terminal station communication device 64. The inter-terminal station communication device 64 connects a communication link with the terminal station 2 and performs communication. The wireless communication device 60 also includes an inter-terrestrial base station communication device 66. The inter-terrestrial base station communication device 66 connects a communication link with the terrestrial base station 4 and performs communication.

[0046] The wireless communication device 60 includes a management device 68. The management device 68 aggregates information on each communication link obtained from the inter-node station communication devices 62a to 62c, the inter-terminal station communication device 64, and the terrestrial base station inter-communication device 66, and notifies the information to the route control device 70 and the management devices of adjacent node stations. This information includes the communication status of the communication links, such as congestion status and weather, and information necessary for calculating the cost value C.

[0047] The wireless communication device 60 also includes a prediction device 69. The prediction device 69 notifies the route control device 70 of a predicted time T' calculated by the device itself or externally.

[0048] The route control device 70 calculates a cost value C based on the notified information and determines to switch to a communication route with a lower cost value C. Then, it notifies information about the determined communication route to the management device 68. The management device 68 notifies the node station, the terminal station 2, and the terrestrial base station 4 that form the communication link selected as the communication route of the corresponding communication route.

[0049] When the NTN is controlled by a centralized control system, the wireless communication device 60 does not determine the communication path, and therefore the path control device 70 is not required. In this case, information from the management device 68 and the prediction device 69 is notified to the network controller 40, which will be described later with reference to Fig. 5. Then, the network controller 40 determines a communication path based on the notified information and notifies the management device 68.

[0050] 5 is a diagram illustrating a configuration of a network controller according to the first embodiment of the present disclosure. Here, an example in which NTN control is performed using a centralized control method will be described.

[0051] The network controller 40 includes a management device 68. The management device 68 aggregates information on each communication link notified from the node stations and notifies the route control device 70. The network controller 40 also includes a prediction device 69. The prediction device 69 notifies the route control device 70 of a predicted time T' calculated by the prediction device itself or externally.

[0052] The route control device 70 calculates a cost value C based on the notified information and determines to switch to a communication route with a lower cost value C. Then, it notifies information about the determined communication route to the management device 68. The management device 68 notifies the node station, the terminal station 2, and the terrestrial base station 4 that form the communication link selected as the communication route of the corresponding communication route.

[0053] 6 is a diagram illustrating a hardware configuration of a wireless communication device according to the first embodiment of the present disclosure. The route control device 70 includes a CPU 118. The CPU 118 is connected to a bus line 120. Memory devices such as a ROM 122, a RAM 124, and a storage 126 are connected to the bus line 120. A wireless communication program executed by the CPU 118 is stored in the memory device. The route control device 70 can realize functions specific to this embodiment by the CPU 118 executing the wireless communication program.

[0054] A communication interface 128 is also connected to the bus line 120. The route control device 70 communicates with the network via the communication interface 128. An operation unit 130 and a display unit 132 are also connected to the bus line 120. The operation unit 130 and the display unit 132 function as a user interface for operating the route control device 70.

[0055] As described above, the routing control device 70 can realize the functions specific to this embodiment by the CPU 118 executing a wireless communication program. That is, the routing control device 70 can also be realized by a computer and the program. The program can also be recorded on a recording medium or provided via a network. Note that when NTN control is a centralized control system, the wireless communication device 60 in FIG. 6 can be replaced with the network controller 40.

[0056] 7 is a flowchart illustrating the route switching process according to the first embodiment of the present disclosure. The route control device 70 starts the route switching process at a time earlier than the predicted time T′ notified by the prediction device 69 by an amount equal to the time required for the route switching process plus a margin.

[0057] First, in step 100, the predicted time T' for multiple communication paths that are candidates for switching destinations is calculated. For example, the predicted time T' for a communication link interruption due to node station movement is calculated using orbit information of the node station. The predicted time T' for a communication link interruption due to rain attenuation is calculated using rainfall forecast information such as rainfall nowcast.

[0058] Next, in step 102, link lifetimes T Ｌ Calculate the link lifetime T Ｌ is shown in Equation 1.

[0059] Next, in step 104, cost values ​​C for multiple communication paths that are candidates for switching destination are calculated. The cost values ​​C are expressed by formulas 2 to 4 when the signal relay method of the node station is a regenerative relay method, and by formulas 5 to 7 when the signal relay method of the node station is a non-regenerative relay method.

[0060] Next, in step 106, a communication route to be used for communication is selected, and the process is terminated. At this time, the communication route with the smallest cost value is selected.

[0061] As described above, in this embodiment, by selecting a communication route based on the cost value C, it is possible to avoid frequent switching of communication routes triggered by a communication link disconnection.

[0062] 8 is a diagram illustrating a wireless communication system according to a second embodiment of the present disclosure. The second embodiment differs from the first embodiment in that the communication method is a centralized control method and that the network controller is disposed in the absolute node station.

[0063] Recently, there has been a need to make the nation more resilient against natural disasters, etc., and the emergence of a communication system that is resistant to terrestrial disasters is desired. In this embodiment, by placing a network controller in the sky, NTN route control can be performed without being affected by terrestrial disasters.

[0064] The wireless communication system 200 includes an absolute node station 71. The absolute node station 71 is, for example, a GEO satellite. The absolute node station 71 is installed in the sky and is capable of establishing direct communication links with all node stations included in the system. The absolute node station 71 is connected to node stations 6a, 6b, 7a, and 7b via communication links 72a to 72d. The absolute node station 71 has a wide communication area and can communicate directly with all node stations that make up the NTN. This embodiment makes use of this feature.

[0065] Furthermore, the absolute node station 71 has a network controller 40. The network controller 40 implements a protocol for collecting information necessary for calculating the cost value C.

[0066] The node stations 6a, 6b, 7a, and 7b notify the absolute node station 71 of information necessary for calculating the cost value C via the communication links 72a to 72d. The absolute node station 71 calculates the cost value C based on the notified information and determines a communication route. Subsequently, the absolute node station 71 notifies the node stations 6a to 6d of information about the determined communication route.

[0067] The absolute node station 71 may exchange information by directly communicating with each node station, or may exchange information via a plurality of node stations.

[0068] As described above, in this embodiment, frequent switching of communication paths triggered by communication link disconnection can be avoided without being affected by ground disasters.

[0069] 2 Terminal station 4 Terrestrial base station 6a, 6b, 6c, 6d Node station 7a, 7b, 7c Node station 14a, 14b, 14c Communication path 32, 34, 36 Network 60 Wireless communication device 70 Route control device 71 Absolute node station 72a, 72b, 72c, 72d Communication link 100, 200, 500 Wireless communication system

Claims

1. A wireless communication system that communicates using a non-terrestrial network, comprising a terminal station, a terrestrial base station, a plurality of node stations that constitute the non-terrestrial network, and a route control device, wherein the route control device is configured to perform the following processes: calculating a predicted time when a communication link will be interrupted; setting a plurality of communication routes that are candidate destinations; calculating cost values ​​of the plurality of communication routes that are candidate destinations based on the predicted time; and comparing the cost values ​​and selecting, from the plurality of communication routes that are candidate destinations, a communication route with the smallest cost value.

2. The wireless communication system according to claim 1, wherein the signal relay method of the node station is a regenerative relay method, and the cost value is calculated based on the link capacity, link delay time and congestion degree of a communication link included in the communication path.

3. The wireless communication system according to claim 1, wherein the signal relay method of the node station is a non-regenerative relay method, and the cost value is calculated based on the number of times the signal is relayed, the bandwidth utilization rate of the communication links included in the communication path, and the link delay time.

4. The wireless communication system according to claim 1, wherein the predicted time is calculated using orbit information or rainfall forecast information of the node station.

5. The wireless communication system according to claim 1, further comprising an absolute node station capable of directly communicating with all node stations constituting said non-terrestrial network, said absolute node station comprising said route control device.

6. A wireless communication method for performing communication using a non-terrestrial network, comprising: calculating a predicted time when a communication link will be interrupted; setting a plurality of communication paths as candidate destinations; calculating cost values ​​of the plurality of communication paths as candidate destinations based on the predicted time; and comparing the cost values ​​to select a communication path with the smallest cost value from the plurality of communication paths as candidate destinations.

7. A wireless communication device that communicates using a non-terrestrial network, configured to perform the following processes: calculating a predicted time when a communication link will be interrupted; setting a plurality of communication paths as candidate destinations; calculating cost values ​​of the plurality of communication paths as candidate destinations based on the predicted time; and comparing the cost values ​​and selecting the communication path with the smallest cost value from the plurality of communication paths as candidate destinations.

8. A wireless communication program to be executed by a wireless communication device that communicates using a non-terrestrial network, the wireless communication program including a program for causing a computer to execute the following processes: calculating a predicted time when a communication link will be disconnected; setting a plurality of communication paths as candidate destinations; calculating cost values ​​of the plurality of communication paths as candidate destinations based on the predicted time; and comparing the cost values ​​and selecting the communication path with the smallest cost value from the plurality of communication paths as candidate destinations.

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