WO2025004154A1 - Wireless communication system, wireless communication method, wireless communication device, and wireless communication program - Google Patents

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

This disclosure relates to a wireless communication system, a wireless communication method, a wireless communication device, and a wireless communication program.

　With the development of mobile communication systems in recent years, mobile services can now be enjoyed over most of the earth. One of the requirements for mobile communication systems beyond the fifth generation, 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 installing existing base stations is high or where it is difficult to install them, such as mountains, sea, or air.

In order 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 attracting attention. In an NTN, node stations connect to each other via communication links to form a network, and are further connected to terrestrial mobile networks via terrestrial base stations. Traffic generated at terrestrial terminal stations is transferred within the NTN to node stations that can communicate with terrestrial base stations. For example, Non-Patent Document 1 discloses a route control method in a hierarchical satellite network using an NTN.

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

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 relevant link. As a result, a communication link disconnection may occur again immediately after it occurs due to the movement of the node station or rain attenuation. This poses the problem of frequent switching of communication paths triggered by communication link disconnections.

In order to solve the above-mentioned problems, the first objective of this disclosure is to provide a wireless communication system that can avoid frequent switching of communication paths triggered by communication link interruptions.

The first aspect of the present disclosure is a wireless communication system that communicates using a non-terrestrial network, and is preferably configured to include 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 disconnected; setting a plurality of communication routes that are candidates for switching destinations; calculating cost values of the plurality of communication routes that are candidates for switching destinations based on the predicted time; and comparing the cost values to select the communication route with the smallest cost value from the plurality of communication routes that are candidates for switching destinations.

A second aspect of the present disclosure is a wireless communication method for performing communication using a non-terrestrial network, which preferably includes the steps of: calculating a predicted time when a communication link will be disconnected; setting multiple communication paths as candidate destinations; calculating cost values of the multiple communication paths as candidate destinations based on the predicted time; and comparing the cost values to select the communication path with the smallest cost value from the multiple communication paths as candidate destinations.

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 disconnected; setting multiple communication paths as switchover candidate paths; calculating cost values of the multiple switchover candidate communication paths based on the predicted time; and comparing the cost values to select the communication path with the smallest cost value from the multiple switchover candidate communication paths.

A fourth aspect of the present disclosure is a wireless communication program to be executed by a wireless communication device that communicates using a non-terrestrial network, and preferably includes a program for causing a computer to execute the following processes: calculating a predicted time when a communication link will be disconnected; setting multiple communication paths as switchover candidate paths; calculating cost values of the multiple communication paths as switchover candidate paths based on the predicted time; and comparing the cost values and selecting the communication path with the smallest cost value from the multiple communication paths as switchover candidate paths.

The first to fourth aspects of the present disclosure make it possible to avoid frequent switching of communication paths triggered by a communication link interruption.

FIG. 11 is a diagram illustrating switching of a communication path according to a comparative example. FIG. 2 is a diagram illustrating switching of communication paths according to the first embodiment of the present disclosure. 1 is a diagram illustrating a configuration of a wireless communication system according to a first embodiment of the present disclosure. FIG. 2 is a diagram illustrating a configuration of a wireless communication device mounted on a node station according to a first embodiment of the present disclosure. FIG. 2 is a diagram illustrating a configuration of a network controller according to a first embodiment of the present disclosure. 1 is a diagram illustrating a hardware configuration of a route control device according to a first embodiment of the present disclosure. 4 is a flowchart showing a route switching process according to the first embodiment of the present disclosure. FIG. 11 is a diagram illustrating a wireless communication system according to a second embodiment of the present disclosure.

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

The diagram on the left in Figure 1 shows the first communication path switching. The wireless communication system 500 in the diagram on the left in Figure 1 transfers traffic sent from terminal station 2 using communication path 14a. Communication path 14a is a communication path that passes through node station 6a and node station 7a.

Now, 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.

The diagram on the right side of Figure 1 shows the second communication path switching. The wireless communication system 500 in the diagram on the right side of Figure 1 transfers traffic sent from terminal station 2 using communication path 14a.

Now, let us assume that immediately after the first communication link failure described above, a second communication link failure occurs between node station 6b and node station 7b. 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.

As described above, in wireless communication system 500, a second communication path switch occurs immediately after a first communication path switch. In other words, a problem occurs in which communication path switches occur frequently. This problem occurs because the communication path to be used is calculated without taking into account the lifespan of the communication link. The present disclosure solves this problem.

[Wireless communication system according to embodiment 1 of the present disclosure]
2 is a diagram showing switching of communication paths according to the first embodiment of the present disclosure. The configuration of the wireless communication system according to the present embodiment is similar to that of the wireless communication system 500. However, the wireless communication system according to the present embodiment differs from the wireless communication system 500 in that the wireless communication system switches communication links in consideration of the life of the communication links.

The wireless communication system 100 transfers traffic sent from the terminal station 2 using the communication path 14a. Now, assume that a first communication link disconnection occurs between node station 6a and node station 7a. First, the wireless communication system 100 sets up multiple communication paths as switch destination candidates. Then, using the method described below, it calculates the cost value of the switch destination candidate communication paths and switches to the communication path with the lowest cost value. This cost value takes into account the link lifespan of the communication links included in the relevant communication path.

In this case, it is assumed that immediately after the first communication link is broken, a second communication link break occurs between node station 6b and node station 7b. In this case, the link life of the communication link connecting node station 6b and node station 7b becomes long, and the cost value of communication path 14b also becomes high. Therefore, the wireless communication system 100 selects communication path 14c instead of communication path 14b.

The method by which the wireless communication system 100 switches communication paths will now be described in detail. First, the node station 6a calculates the cost value C of the communication path to which the communication path is to be switched, and switches to the communication path with the lower cost value.

This cost value takes into consideration the link life T _L of the communication link included in the corresponding communication path. T _L is expressed by Equation 1 using a predicted time T' at which a communication link disconnection will occur, with a certain time T _S as the base time.

　

　

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

Furthermore, if the signal relay method of the node station is a regenerative relay method, the cost value C is expressed by formulas 2 to 4.

　

　

　

　

　

　

where 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. BR is the capacity reference value, BD is the delay time reference value, and BT _i is the life reference value, which are arbitrary values. Furthermore, α is the congestion degree of the link, and r is the traffic flow rate in the link.

The cost value C is expressed by formulas 5 to 7 when the signal relay method of the node station is a non-regenerative relay method.

　

　

　

　

　

　

where H is the number of relays of a signal, W is the bandwidth utilization rate of the link, _WF is the total bandwidth of the link, and _Wu is the allocated bandwidth of the link. Also, BH is the reference value of the number of relays, and BW is the reference value of the utilization rate, which are arbitrary values.

The cost value C shown in Equation 2 and Equation 5 becomes smaller as the link lifetime T _L becomes longer. Therefore, in this embodiment, a communication route including a communication link with a longer link lifetime T _L is preferentially selected.

In order to continue providing communication services, it is necessary to change the communication path when a communication link is cut off. In this embodiment, the number of times the communication path is changed can be reduced by selecting a communication path with a long communication link lifespan, which is the remaining time during which communication is possible. In other words, frequent switching of communication paths triggered by a communication link cut off can be avoided.

FIG. 3 is a diagram showing the configuration of a wireless communication system according to the first embodiment of the present disclosure. Wireless communication system 200 shows an example of a wireless communication system that actually performs the switching of communication paths shown in wireless communication system 100.

The wireless communication system 200 includes an NTN 30 that relays communication between the terminal station 2 and the 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 earth orbit satellites (GEO). The networks 32, 34, and 36 are networks made up of the same type of node stations, and can form communication links with each other, with the NTN 30 being formed by combining multiple networks. 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.

In this way, the wireless communication system 200 has multiple node stations in the sky, and the node stations are connected to each other via communication links. In addition, communication links are also formed with the terrestrial base station 4, and a network is formed for each type of node station.

The NTN 30 is also 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 the processing required to calculate the communication path. The necessary processing is, for example, the calculation of the cost value C.

If the communication method of the wireless communication system 100 is a distributed control method, the necessary processing described above is performed by each node station, and therefore the network controller 40 is not required. Also, even if the communication method of the wireless communication system 100 is a centralized control method, if the necessary processing described above is performed by each node station, the network controller 40 is not required.

FIG. 4 is a diagram showing the configuration of a wireless communication device installed in a node station according to the first embodiment of the present disclosure. Here, we will describe an example in which NTN control is performed using a distributed control method.

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

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.

The wireless communication device 60 is equipped with 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 communication device 66, and notifies the route control device 70 and the management device of the adjacent node station. This information includes the communication status of the communication link, such as congestion status and weather, and information necessary for calculating the cost value C.

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

The route control device 70 calculates a cost value C based on the notified information and decides to switch to a communication route with a lower cost value C. It then notifies the management device 68 of information about the decided communication route. The management device 68 notifies the node station, terminal station 2, and terrestrial base station 4 that form the communication link selected as the communication route of the corresponding communication route.

Note that when NTN is controlled using a centralized control method, 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 prediction device 69 is notified to the network controller 40, which will be described later in FIG. 5. The network controller 40 then determines the communication path based on the notified information and notifies the management device 68.

FIG. 5 is a diagram showing the configuration of a network controller according to the first embodiment of the present disclosure. Here, an example is described in which NTN control is performed using a centralized control method.

The network controller 40 includes a management device 68. The management device 68 consolidates 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 the predicted time T' calculated by the device itself or externally.

The route control device 70 calculates a cost value C based on the notified information and decides to switch to a communication route with a lower cost value C. It then notifies the management device 68 of information about the decided communication route. The management device 68 notifies the node station, terminal station 2, and terrestrial base station 4 that form the communication link selected as the communication route of the corresponding communication route.

FIG. 6 is a diagram showing the 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. The memory devices store wireless communication programs executed by the CPU 118. The route control device 70 can realize functions specific to this embodiment by the CPU 118 executing the wireless communication programs.

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.

As described above, the route control device 70 can realize the functions specific to this embodiment by the CPU 118 executing the wireless communication program. In other words, the route 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 the NTN is controlled using a centralized control method, the wireless communication device 60 in FIG. 6 can be replaced with the network controller 40.

FIG. 7 is a flowchart showing the route switching process according to the first embodiment of the present disclosure. Note that 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 adding a margin to the time required for the route switching process.

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 the movement of a node station 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.

Next, in step 102, a link lifetime T _L of a plurality of communication paths that are candidates for switching destination is calculated. The link lifetime T _L is expressed by Equation 1.

Next, in step 104, cost values C for multiple communication paths that are candidates for switching destinations are calculated. 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.

Next, in step 106, the 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.

As described above, in this embodiment, by selecting a communication path based on the cost value C, it is possible to avoid frequent switching of communication paths triggered by a communication link interruption.

Embodiment 2
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 a network controller is disposed in an absolute node station.

In recent years, there has been a need to make the nation more resilient against natural disasters, and there is a demand for communication systems that are resistant to ground disasters. In this embodiment, by placing a network controller in the sky, NTN route control can be performed without being affected by ground disasters.

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 a node station that can establish 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.

Furthermore, the absolute node station 71 has a network controller 40. The network controller 40 implements a protocol for collecting information necessary to calculate the cost value C.

The node stations 6a, 6b, 7a, and 7b notify the absolute node station 71 of the information required to calculate 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 the communication path. The absolute node station 71 then notifies the node stations 6a to 6d of the information on the determined communication path.

The absolute node station 71 may exchange information by communicating directly with each node station, or may exchange information via multiple node stations.

As described above, in this embodiment, it is possible to avoid frequent switching of communication paths triggered by communication link interruptions, without being affected by ground disasters.

Reference Signs List 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 (8)

A wireless communication system for performing communication using a non-terrestrial network,
The present invention comprises a terminal station, a terrestrial base station, a plurality of node stations constituting the non-terrestrial network, and a route control device,
The route control device,
A process of calculating a predicted time when a communication link interruption will occur;
A process of setting a plurality of communication paths as switching destination candidates;
A process of calculating cost values of a plurality of communication paths that are candidates for the switching destination based on the predicted time;
comparing the cost values and selecting a communication path with a minimum cost value from the plurality of communication paths to be switching destination candidates. The signal relay method of the node station is a regenerative relay method,
The wireless communication system according to claim 1 , wherein the cost value is calculated based on a link capacity, a link delay time, and a congestion degree of a communication link included in the communication path. The signal relay method of the node station is a non-regenerative relay method,
The wireless communication system according to claim 1 , wherein the cost value is calculated based on the number of relays of a signal, a bandwidth utilization rate of a communication link included in the communication path, and a link delay time. The wireless communication system according to claim 1 , wherein the predicted time is calculated using orbit information or rainfall prediction information of the node station. An absolute node station capable of directly communicating with all node stations constituting the non-terrestrial network,
The wireless communication system according to claim 1 , wherein the absolute node station comprises the route control device. A wireless communication method for performing communication using a non-terrestrial network, comprising:
Calculating a predicted time when a communication link interruption will occur;
Setting a plurality of communication paths as switching destination candidates;
calculating cost values of the plurality of communication paths that are candidates for the switching destination based on the predicted time;
comparing the cost values and selecting a communication path with a minimum cost value from the plurality of communication paths that are candidates for switching destination. A wireless communication device for performing communication using a non-terrestrial network,
A process of calculating a predicted time when a communication link interruption will occur;
A process of setting a plurality of communication paths as switching destination candidates;
A process of calculating cost values of a plurality of communication paths that are candidates for the switching destination based on the predicted time;
comparing the cost values and selecting a communication path with the smallest cost value from the plurality of communication paths that are candidates for switching destination. A wireless communication program for causing a wireless communication device that performs communication using a non-terrestrial network to execute the program,
A process of calculating a predicted time when a communication link interruption will occur;
A process of setting a plurality of communication paths as switching destination candidates;
A process of calculating cost values of a plurality of communication paths that are candidates for the switching destination based on the predicted time;
and comparing the cost values and selecting a communication route with the smallest cost value from the plurality of communication routes that are candidates for switching.

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