Wireless communication system, link control device, link control method, and link control program

Abstract

A wireless communication system according to one embodiment performs wireless communication between at least one node station that moves relative to the ground and a plurality of base stations that are provided on the ground. The wireless communication system includes: a prediction unit that predicts a CINR for a wireless communication link that varies over time between the node station and the base stations on the basis of at least weather information, time information, movement information for the node station, and position information for the base stations; a determination unit that determines whether the CINR of the wireless communication link that varies over time predicted by the prediction unit is at or above a predetermined threshold value; and a control unit that performs control that switches the wireless communication link between the node station and the base stations on the basis of the results of the determination by the determination unit.

Description

Wireless communication system, link control device, link control method, and link control program

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

[0002] In recent years, mobile communication systems have been developed, making it possible to enjoy mobile services over most of the earth. Ultra-wide coverage is 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.

[0003] Ultra-coverage refers to expanding the service area to areas where the cost of installing existing terrestrial base stations (base stations) is high or difficult, such as mountains, oceans, and the air. There is also a need to strengthen the nation's resilience against natural disasters, and there is a need for a communications system that is resistant to terrestrial disasters.

[0004] To meet these demands, expectations are growing for non-terrestrial networks (NTNs) using satellites, unmanned aerial vehicles, high-altitude platforms, drones, etc. Among these, satellites cruising in orbits lower than geostationary orbit are attracting attention due to their excellent low latency communications. In NTNs, traffic requested by each terminal is transmitted to terrestrial mobile networks via satellites, etc. and base stations.

[0005] In the NTN, the radio wave propagation environment of the wireless communication links that carry out communication between satellites and base stations fluctuates from moment to moment due to the movement of the satellites, rainfall, etc. If a communication interruption occurs in a wireless communication link, another base station that can communicate is searched for and the wireless communication link is reconnected, or traffic is transferred to another satellite that can communicate with the base station via an inter-satellite communication link, etc.

[0006] In a method of searching for a new communication path after a communication interruption occurs in a wireless communication link, a momentary interruption in communication occurs until the reconnection of the communication path is completed, so proactive control is performed to switch the communication path before a communication interruption occurs in the wireless communication link. In order to perform proactive control, it is necessary to predict the communication quality of the wireless communication link.

[0007] For example, a known conventional technique for predicting the communication quality of a wireless communication link is to periodically observe the CINR (Carrier to Interference and Noise Ratio) of the wireless communication link, predict the future CINR of the wireless communication link based on the CINR by linear interpolation, and calculate the remaining communication time (link life) of the wireless communication link (see, for example, Non-Patent Document 1).

[0008] Maurizio Mongelli, et al., "Feeder-Link Outage Prediction Algorithms for SDN-based High-Throughput Satellite Systems", IEEE ICC 2016 SAC Satellite and Space Communications

[0009] However, in the past, link lifetimes were calculated by linearly predicting future CINRs based on observed CINR values ​​up to the present time, and therefore attenuation that varies over time, such as rain attenuation, which varies independently of past CINR fluctuations, was not taken into account.Furthermore, in the past, the distance of the rain area (equivalent path length) through which radio waves actually pass and the time variation of precipitation were not taken into account in wireless communication links.

[0010] In addition, conventional methods have had large link life prediction errors, which sometimes prevent proactive control from working properly. As a result, wireless communication links are subject to momentary disconnections, which ultimately limits the communication capacity of the wireless communication links and reduces the throughput of the entire system.

[0011] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a wireless communication system, a link control device, a link control method, and a link control program that can prevent momentary interruptions in wireless communication links and suppress decreases in throughput in a wireless communication system in which one or more node stations that move relative to the earth's surface communicate with multiple base stations located on the ground.

[0012] A wireless communication system according to one embodiment of the present invention is a wireless communication system in which one or more node stations that move relative to the earth's surface communicate wirelessly with a plurality of base stations located on the ground, and is characterized by having the following: a prediction unit that predicts the CINR of a time-varying wireless communication link between the node station and the base station based on at least weather information, time information, movement information of the node station, and location information of the base station; a determination unit that determines whether the CINR of the time-varying wireless communication link predicted by the prediction unit is equal to or greater than a predetermined threshold; and a control unit that controls switching of the wireless communication link between the node station and the base station based on the result of the determination by the determination unit.

[0013] In addition, a link control device according to one embodiment of the present invention is a link control device that controls wireless communication links between one or more node stations that move relative to the earth's surface and multiple base stations located on the ground, and is characterized by having: a prediction unit that predicts the CINR of the time-varying wireless communication link between the node station and the base station based on at least weather information, time information, movement information of the node station, and location information of the base station; a judgment unit that judges whether the CINR of the time-varying wireless communication link predicted by the prediction unit is equal to or greater than a predetermined threshold; and a control unit that controls switching of the wireless communication link between the node station and the base station based on the result of the judgment by the judgment unit.

[0014] Furthermore, a link control method according to one embodiment of the present invention is a link control method for controlling wireless communication links between one or more node stations that move relatively to the Earth's surface and a plurality of base stations located on the ground, and is characterized by including: a prediction step of predicting a CINR of a time-varying wireless communication link between the node stations and the base stations based on at least weather information, time information, movement information of the node stations, and position information of the base stations; a determination step of determining whether the CINR of the time-varying wireless communication link predicted by the prediction step is equal to or greater than a predetermined threshold; and a control step of controlling switching of the wireless communication link between the node stations and the base stations based on the result of the determination by the determination step.

[0015] According to the present invention, it is possible to prevent momentary interruptions in wireless communication links and suppress decreases in throughput in a wireless communication system in which one or more node stations that move relative to the earth's surface communicate wirelessly with multiple base stations located on the ground.

[0016] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system according to an embodiment. FIG. 2 is a functional block diagram illustrating an example of the configuration of a link control device according to an embodiment. FIG. 3 is a diagram schematically illustrating the movement of a node station and the influence of rainfall on a wireless communication link. FIG. 4 is a graph illustrating an example of fluctuations in the CINR of a wireless communication link. FIG. 5 is a graph illustrating the relationship between the CINR of a wireless communication link and the link lifespan. FIG. 6 is a diagram illustrating a first operation example of a wireless communication system. FIG. 7 is a diagram illustrating a second operation example of a wireless communication system. FIG. 8 is a diagram illustrating an example of the hardware configuration of a link control device according to an embodiment. FIG. 9 is a diagram illustrating an overview of a wireless communication system of a comparative example. FIG. 10 is a graph illustrating an example of fluctuations in the CINR of a wireless communication link over time in a wireless communication system of a comparative example. FIG. 11 is a diagram illustrating an overview of a wireless communication system of a comparative example when rainfall is occurring. FIG. 12 is a graph illustrating an example of fluctuations in the CINR of a wireless communication link in a wireless communication system of a comparative example when rainfall is occurring.

[0017] Before describing a wireless communication system according to an embodiment, the background to the invention will be described with reference to FIGS. 9 to 12. FIG. 9 is a diagram showing an overview of a wireless communication system of a comparative example. The wireless communication system of the comparative example is a wireless communication system in which wireless communication is performed between a plurality of base stations 1a and 1b located on the ground and one or more node stations 2 such as satellites that move relatively to the earth's surface. FIG. 10 is a graph showing an example of time variation of the CINR of a wireless communication link in the wireless communication system of the comparative example.

[0018] For example, in the wireless communication system of the comparative example, a wireless communication link between the base station 1a and the node station 2 is switched to a wireless communication link between the base station 1b and the node station 2 due to movement of the node station 2. At this time, the wireless communication system of the comparative example predicts the remaining communication time (link life) of the wireless communication link by linearly interpolating the future CINR based on the observation data of the CINR fluctuation up to the present time, as shown in Fig. 10 .

[0019] Fig. 11 is a diagram illustrating an overview of a wireless communication system of a comparative example when rain is occurring, and Fig. 12 is a graph illustrating an example of time variation of the CINR of a wireless communication link in the wireless communication system of the comparative example when rain is occurring.

[0020] In the wireless communication system of the comparative example, as shown in FIG. 12, if the CINR of the wireless communication link between the base station 1a and the node station 2 drops unexpectedly due to rainfall or the like, a momentary interruption occurs during the time it takes to search for and reconnect (switch to) the base station 1b as an alternative base station.

[0021] In other words, the wireless communication system of the comparative example cannot handle attenuation that varies over time, such as rain attenuation, which is unrelated to the CINR fluctuations up to the present time (the prediction error is large). Furthermore, if the prediction error of the link life is large, proactive control that switches wireless communication links in advance may not operate properly. As a result, this can lead to momentary disconnections of wireless communication links, resulting in a decrease in the throughput of the entire system.

[0022] Next, a wireless communication system according to an embodiment will be described. Fig. 1 is a diagram showing an example of the configuration of a wireless communication system 10 according to an embodiment. As shown in Fig. 1, the wireless communication system 10 according to an embodiment includes, for example, terminals 20-1 to 20-3, node stations 30-1 to 30-5, base stations 40-1 to 40-3, a link control device 50, and an external device 100. Note that when there is no need to specify one of a plurality of components, such as node stations 30-1 to 30-5, it will be simply abbreviated as node station 30.

[0023] The node stations 30-1 to 30-5 are wireless communication node stations that move relative to the Earth's surface. More specifically, the node stations 30 include all wireless communication node stations that move relative to the Earth's surface, such as low-earth orbit satellites (LEO satellites), medium-earth orbit satellites (MEO satellites), high-altitude platforms (HAPS), as well as drones, unmanned aerial vehicles (UAVs), airplanes, automobiles, etc.

[0024] Each node station 30 then establishes a wireless communication link with a base station 40 , which is a base station located on the ground, to realize communication between the terminal 20 and the base station 40 .

[0025] The link control device 50 acquires meteorological information (weather, temperature, humidity) and time information from the external device 100, which serves as an external information source, and controls the wireless communication link in the wireless communication system 10. The link control device 50 may control the wireless communication link via the external device 100, or may control the wireless communication link by directly controlling the base station 40.

[0026] For example, based on a time-varying prediction of the amount of attenuation added to the wireless communication link, the link control device 50 predicts the remaining communication time (link life) for each wireless communication link between the base station 40 and the node station 30. Then, when a wireless communication link is predicted to be disconnected, the link control device 50 performs proactive control, switching to another wireless communication link before the wireless communication link is disconnected.

[0027] The control for predicting the link life of the wireless communication links in the wireless communication system 10 may be either distributed control or centralized control. In the case of the distributed control method, these controls are performed by each base station 40 or each node station 30.

[0028] 2 is a functional block diagram illustrating an example of the configuration of a link control device 50 according to an embodiment. As shown in FIG. 2, the link control device 50 includes, for example, a communication unit 52, a control unit 54, a prediction unit 56, and a link life calculation unit 58.

[0029] The communication unit 52 acquires meteorological information such as weather, temperature, and humidity, as well as time information, from the external device 100 and outputs the information to the control unit 54 .

[0030] The control unit 54 controls each unit constituting the link control device 50. For example, the control unit 54 outputs weather information, time information, orbit information of the node station 30, position information of the base station 40, and the like to the prediction unit 56. The control unit 54 also outputs a predetermined CINR threshold to the link life calculation unit 58.

[0031] The control unit 54 also controls, via the communication unit 52, switching of the wireless communication links between the respective node stations 30 and the respective base stations 40 based on the result of a determination made by a determination unit 580, which will be described later, for example.

[0032] The prediction unit 56 predicts the CINR of the time-varying wireless communication link between the node station 30 and the base station 40 based on at least weather information, time information, movement information of each node station 30, and location information of each base station 40, and outputs the CINR to the link life calculation unit 58.

[0033] The link life calculation unit 58 includes, for example, a determination unit 580, and determines whether the CINR of the time-varying wireless communication link predicted by the prediction unit 56 is equal to or greater than a predetermined threshold (CINR threshold), and outputs the determination result to the control unit 54. At this time, the link life calculation unit 58 calculates the remaining time (link life) during which communication is possible with each of the base stations 40, based on the time-varying prediction of the amount of attenuation in the wireless communication link between the node station 30 and the base station 40.

[0034] The attenuation in the wireless communication link between the node station 30 and the base station 40 is the sum of attenuation due to various factors including rain attenuation, and is derived using orbit information of the node station 30, weather, temperature, humidity, and the like.

[0035] Here, the relationship between CINR prediction and link lifespan will be explained using Figures 3 to 5. Figure 3 is a diagram schematically showing the influence of movement of node station 30 and rainfall on a wireless communication link. Figure 4 is a graph showing an example of fluctuations in CINR of a wireless communication link. Figure 5 is a graph showing the relationship between CINR of a wireless communication link and link lifespan.

[0036] For example, the prediction unit 56 predicts the CINR using the amount of radio wave attenuation based on the distance (including the radio wave propagation path length and the equalization path length) between the node station 30 and the base station 40, which changes as the node station 30 moves, and the amount of radio wave attenuation based on the rainfall conditions in each region, which changes as the node station 30 moves. At this time, the link control device 50 may correct the prediction accuracy using weighting.

[0037] 5, the time until the CINR predicted by the prediction unit 56 crosses a predetermined arbitrary threshold is defined as the link lifetime L(t). More specifically, the time until the CINR of the wireless communication link crosses a predetermined arbitrary threshold γ CINR CINR(t) = γ CINR The time until this occurs is defined as the link lifetime. The link lifetime can be expressed as a function that outputs two values, alive and dead, as shown in the following equation (1).

[0038]

[0039] Furthermore, the prediction unit 56 may calculate a time variation prediction CINR(t) of the CINR as follows: For example, when calculating the future line state, the prediction unit 56 calculates a time variation prediction A(t) of the total amount of attenuation (distance attenuation, atmospheric attenuation, rain attenuation, etc.) added in the wireless communication link by the following equation (2):

[0040]

[0041] where c(t) represents the radio wave propagation path between the node station 30 and the base station 40 at time t, A(t, r) represents the predicted total attenuation per unit distance at time t and position r, and A(t, r) is calculated or obtained using orbital information of the node station 30, weather, temperature, humidity, etc.

[0042] That is, the prediction unit 56 predicts the time variation of the CINR of the wireless communication link by designing the wireless communication link using the time variation of the predicted total attenuation.

[0043] Alternatively, the prediction unit 56 may calculate a time-varying prediction of CINR, CINR(t), by adding a term for predicting a time-varying rain attenuation amount to the linear estimation, which is a conventional technique. For example, the prediction unit 56 calculates a time-varying prediction of the rain attenuation amount, Arain(t), which is added by the equivalent path length of the wireless communication link, using the following equation (3):

[0044]

[0045] where c(t) represents the radio wave propagation path between the node station 30 and the base station 40 at time t, Arain(t, r) represents the predicted rain attenuation per unit distance at time t and position r, and Arain(t, r) is calculated or obtained using weather, temperature, humidity, etc. The prediction unit 56 may then calculate the time variation of the CINR of the wireless communication link by adding together the time variation of the predicted rain attenuation and the time variation of the CINR obtained by linear estimation, which is a conventional technique.

[0046] The link control device 50 then uses the link life to appropriately operate proactive control and perform control to prevent momentary disconnection of the wireless communication link.

[0047] Next, an operation example of the wireless communication system 10 according to an embodiment will be described. Fig. 6 is a diagram showing a first operation example of the wireless communication system 10. Note that in the wireless communication system of the comparative example used as a reference, processing is performed in the order of S100, S102, S104, and S106, whereas the wireless communication system 10 according to an embodiment performs processing in the order of S200, S202, S104, and S106.

[0048] The wireless communication system of the comparative example observes the CINR of a wireless communication link in step 100 (S100), and predicts time fluctuations of the CINR by performing linear interpolation based on the observed CINR values ​​in step 102 (S102).

[0049] Then, the wireless communication system of the comparative example calculates the link life in step 104 (S104), and operates the wireless communication link based on the link life in step 106 (S106).

[0050] In response to this, the wireless communication system 10 predicts (calculates) the time fluctuations of all attenuation amounts imposed on the wireless communication link in step 200 (S200), performs line design for the wireless communication link in step 202 (S202), and performs processing in steps S104 and S106.

[0051] 7 is a diagram showing a second operation example of the wireless communication system 10. Note that in the wireless communication system of the comparative example used for reference, processing is performed in the order of S300, S302, S304, and S306, but in the second operation example, the wireless communication system 10 according to one embodiment performs processing in the order of S300, S302, S400, S402, S304, and S306. The wireless communication system 10 observes the CINR of the wireless communication link in step 300 (S300), and predicts time fluctuation of the CINR by performing linear interpolation based on the observed CINR value in step 302 (S302).

[0052] In addition, in step 400 (S400), the wireless communication system 10 predicts (calculates) the time variation of the amount of rain attenuation added to the wireless communication link.

[0053] Next, in step 402 (S402), the wireless communication system 10 adds up the predicted result of the process of S302 and the predicted result of the process of S400.

[0054] Then, the wireless communication system 10 calculates the link life in step 304 (S304), and operates the wireless communication link based on the link life in step 306 (S306).

[0055] In this way, the wireless communication system 10 predicts the CINR of the wireless communication link that varies over time between the node station 30 and the base station 40, thereby preventing momentary disconnection of the wireless communication link and suppressing a decrease in throughput in a wireless communication system in which one or more node stations that move relative to the Earth's surface communicate with multiple base stations located on the ground. Furthermore, the wireless communication system 10 can suppress a decrease in the communication capacity of the entire system.

[0056] In addition, each function possessed by the external device 100, the terminal 20, the node station 30, the base station 40, and the link control device 50 may be configured in part or in whole by hardware such as a PLD (Programmable Logic Device) or an FPGA (Field Programmable Gate Array), or may be configured as a program executed by a processor such as a CPU.

[0057] For example, the terminal 20, the node station 30, the base station 40, and the link control device 50 can be realized using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0058] 8 is a diagram illustrating an example of the hardware configuration of a link control device 50 according to an embodiment. As shown in FIG. 8, the link control device 50 has, for example, an input unit 500, an output unit 510, a communication unit 520, a CPU 530, a memory 540, and an HDD 550 connected via a bus 560, and has the functionality of a computer. The link control device 50 is also configured to be able to input and output data to and from a computer-readable storage medium 570.

[0059] The input unit 500 is, for example, a keyboard and a mouse, etc. The output unit 510 is, for example, a display device, etc. The communication unit 520 is, for example, a wireless network interface.

[0060] The CPU 530 controls each component of the link control device 50 and performs predetermined processing, etc. The memory 540 and the HDD 550 are storage units that store data, etc.

[0061] The storage medium 570 is capable of storing programs and the like that cause the link control device 50 to execute the functions of the link control device 50. The architecture that constitutes the link control device 50 is not limited to the example shown in Fig. 8. Furthermore, other components that constitute the wireless communication system 10, such as the node stations 30 and base stations 40, may also have the same hardware configuration as the link control device 50.

[0062] Although the embodiments of the present invention have been described above with reference to the drawings, it is clear that the above-described embodiments are merely examples of the present invention and that the present invention is not limited to the above-described embodiments. Therefore, addition, omission, substitution, and other modifications of components may be made without departing from the technical spirit and scope of the present invention.

[0063] The functions performed by the components described herein may be implemented in circuitry or processing circuitry, including general purpose processors, application specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a CPU (a Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to perform the described functions.

[0064] A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may be a programmed processor that executes programs stored in memory.

[0065] In this specification, a circuitry, unit, or means is hardware that is programmed to realize or performs the described functions, which may be any hardware disclosed herein or any hardware known to be programmed to realize or perform the described functions.

[0066] If the hardware is a processor considered to be a type of circuitry, the circuitry, means, or unit is a combination of the hardware and software used to configure the hardware and / or processor.

[0067] 10...wireless communication system, 20-1 to 20-3...terminals, 30-1 to 30-5...node stations, 40-1 to 40-3...base stations, 50...link control device, 52...communication unit, 54...control unit, 56...prediction unit, 58...link life calculation unit, 100...external device, 500...input unit, 510...output unit, 520...communication unit, 530...CPU, 540...memory, 550...HDD, 560...bus, 570...storage medium, 580...determination unit

Claims

1. A wireless communication system in which one or more node stations that move relative to the Earth's surface communicate wirelessly with multiple base stations located on the ground, comprising: a prediction unit that predicts the CINR of a time-varying wireless communication link between the node station and the base station based on at least weather information, time information, movement information of the node station, and location information of the base station; a determination unit that determines whether the CINR of the time-varying wireless communication link predicted by the prediction unit is equal to or greater than a predetermined threshold; and a control unit that controls switching of the wireless communication link between the node station and the base station based on the result of the determination by the determination unit.

2. A link control device that controls wireless communication links between one or more node stations that move relative to the Earth's surface and multiple base stations located on the ground, comprising: a prediction unit that predicts the CINR of the time-varying wireless communication link between the node station and the base station based on at least weather information, time information, movement information of the node station, and location information of the base station; a determination unit that determines whether the CINR of the time-varying wireless communication link predicted by the prediction unit is equal to or greater than a predetermined threshold; and a control unit that controls switching of the wireless communication link between the node station and the base station based on the result of the determination by the determination unit.

3. A link control method for controlling wireless communication links between one or more node stations that move relative to the Earth's surface and multiple base stations located on the ground, comprising: a prediction step of predicting the CINR of the time-varying wireless communication link between the node station and the base station based on at least weather information, time information, movement information of the node station, and location information of the base station; a determination step of determining whether the CINR of the time-varying wireless communication link predicted by the prediction step is equal to or greater than a predetermined threshold; and a control step of controlling switching of the wireless communication link between the node station and the base station based on the result of the determination by the determination step.

4. A link control program for causing a computer to function as each part of the link control device according to claim 2.

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