Wireless communication system and wireless communication control method

Abstract

In a wireless communication system according to one embodiment, a terminal station connects to one or more terrestrial base stations via a connection with any of a plurality of node stations moving in the sky. The wireless communication system comprises: a first measurement unit that measures each of communication qualities between the terminal station and the node stations; a second measurement unit that measures each of communication qualities between the node stations and the terrestrial base station; an index calculation unit that calculates each of indices, which affect the availabilities of communications between the terminal station and the node stations; a determination unit that determines, as a connection destination of the terminal station, a node station where the communication qualities measured by the first measurement unit and the second measurement unit each satisfy a predetermined condition and the index calculated by the index calculation unit is the best; and a control unit that performs control such that the terminal station is connected to the terrestrial base station via a connection with the node station determined as the connection destination by the determination unit.

Description

Wireless Communication System and Wireless Communication Control Method

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

[0002] In recent years, mobile communication systems have developed, and it has become possible to enjoy mobile services in most parts of the ground. In addition, one of the requirements for future commercialized fifth-generation (Beyond 5G) or sixth-generation mobile communication systems is ultra-coverage.

[0003] Ultra-coverage means expanding the service area to areas such as mountains, seas, and the air where the cost of laying existing base stations is high or where it is difficult to lay base stations. In addition, strengthening the country against natural disasters is also required, and the emergence of a communication system that is resistant to ground disasters is desired.

[0004] In order to realize such a wireless communication system, a non-terrestrial network (NTN) using a geostationary satellite (GEO), a medium earth orbit satellite (MEO), a low earth orbit satellite (LEO), a high altitude platform station (HAPS), an unmanned aerial vehicle (UAV), and a drone has been in the spotlight (see, for example, Non-Patent Document 1).

[0005] In NTN, a terrestrial terminal station connects to a terrestrial base station via a wireless communication device (node station) that moves non-terrestrially such as an unmanned aerial vehicle or a satellite.

[0006] Then, the traffic packet transmitted by the terminal station is packet-transferred to the satellite and HAPS connected to the terrestrial base station by the routing function and sent to the Internet. Packets transmitted from the Internet to other terminal stations are also processed similarly by the routing function.

[0007] Yuta Tada, et al., "A Study on Efficient Routing Control in Hierarchical Satellite Networks," IEICE Technical Report, Institute of Electronics, Information and Communication Engineers, 2010, pp. 45-50.

[0008] Conventional terminal stations connect their communication links to the node station where the communication environment from the terminal station to the node station is best (maximum received CNR). In NTN, for example, the frequency used for communication between terminal stations and node stations is around 2 GHz, while the frequency used for communication between ground base stations and node stations is higher, around 38 GHz, which was allocated by the WRC (World Radiocommunication Conference).

[0009] Therefore, communication between ground base stations and node stations is susceptible to weather conditions such as rainfall, which can degrade communication quality. In addition, since node stations in the air are powered by solar energy, communication quality between ground base stations and node stations can also deteriorate due to power shortages at night.

[0010] Previously, deterioration in communication quality between ground base stations and node stations could lead to reduced throughput or even complete communication failure when terminal stations sent and received traffic with networks such as the Internet.

[0011] Furthermore, the altitude of NTN can vary significantly depending on the type of node station. Therefore, the power required for communication between a terminal station and a node station differs greatly depending on the type of node station. Consequently, if a terminal station connects to a node station requiring high power when its battery level is low, it may quickly lose communication due to insufficient power.

[0012] This invention has been made in view of the above-mentioned problems, and aims to provide a wireless communication system and a wireless communication control method that can configure a non-terrestrial network with enhanced availability.

[0013] A wireless communication system according to one embodiment of the present invention is a wireless communication system in which a terminal station connects to one or more ground base stations via a connection to any of a plurality of node stations moving in the air, and is characterized by comprising: a first measurement unit that measures the communication quality between the terminal station and the node stations, a second measurement unit that measures the communication quality between the node stations and the ground base stations, an index calculation unit that calculates an index that affects the availability of communication between the terminal station and the node stations, a determination unit that determines the node station to be connected to the terminal station, where the communication quality measured by the first measurement unit and the second measurement unit each satisfies predetermined conditions and the index calculated by the index calculation unit is the best, and a control unit that controls the terminal station to connect to the ground base station via a connection to the node station determined by the determination unit.

[0014] Furthermore, a wireless communication control method according to one embodiment of the present invention is a wireless communication control method performed by a wireless communication system in which a terminal station connects to one or more ground base stations via a connection to any of a plurality of node stations moving in the air, and is characterized by including: a first measurement step of measuring the communication quality between the terminal station and the node stations, respectively; a second measurement step of measuring the communication quality between the node stations and the ground base stations, respectively; an index calculation step of calculating indices that affect the availability of communication between the terminal station and the node stations, respectively; a determination step of determining the node station to be the connection destination of the terminal station, which satisfies predetermined conditions for the communication quality measured by the first measurement step and the second measurement step, and for which the index calculated by the index calculation step is the best; and a control step of controlling the terminal station to connect to the ground base station via a connection to the node station determined as the connection destination by the determination step.

[0015] According to the present invention, it is possible to configure a non-terrestrial network with enhanced availability.

[0016] This is a diagram illustrating an overview of a wireless communication system according to one embodiment. This is a diagram specifically showing an example of the configuration of a wireless communication system according to one embodiment. This is a functional block diagram illustrating the functions of a ground base station. This is a functional block diagram illustrating the functions of a node station. This is a functional block diagram illustrating the functions of a terminal station. This is a functional block diagram illustrating the functions of a network control device according to one embodiment. This is a diagram showing an example of calculating the communication time. This is a diagram showing an example of calculating the received CNR N minutes after the ground base station to the node station. This is a diagram showing an example of calculating the total transmission capacity after N minutes. This is a diagram schematically showing a method for predicting the transmission capacity over N minutes. This is a diagram showing an example of calculating the total delay time. This is a diagram showing an example of the operation of a network control device to change the connection destination to a terminal station. This is a diagram showing an example of the operation of a wireless communication system to further change the connection destination to a terminal station based on other indicators. This is a flowchart showing an example of the operation of a wireless communication system. This is a diagram showing an example of the configuration of a wireless communication system of a comparative example.

[0017] First, the background to the present invention will be explained using Figure 15. Figure 15 is a diagram showing an example configuration of a comparative wireless communication system. As shown in Figure 15, in the comparative wireless communication system, for example, terminal station 2A connects to node station 4A or node station 5A in order to connect to base station (ground base station) 3-1A or base station (ground base station) 3-2A.

[0018] Ground base stations 3-1A and 3-2A are each connected to a network (core network) 100 such as the Internet. Node stations 4A and 5A are non-ground mobile wireless communication devices such as unmanned aerial vehicles or satellites, each equipped with mobile base station functionality, and constitute the NTN.

[0019] The comparative wireless communication system measures the communication quality (e.g., received CNR: Carrier-to-noise ratio) between terminal station 2A and node station 4A, and the communication quality between terminal station 2A and node station 5A. If the measured values ​​are above a predetermined threshold, it selects either node station 4A or 5A, which has the best communication quality, and connects the communication link.

[0020] For example, suppose the communication quality (received CNR) of the communication link between terminal station 2A and node station 4A is 8 dB, and the communication quality (received CNR) of the communication link between terminal station 2A and node station 5A is 0 dB. Furthermore, assume that the received CNR of both communication links must be -9 dB (the threshold for received CNR) or higher.

[0021] In this case, terminal station 2A connects to node station 4A and then to network 100 via ground base station 3-1A. However, if there is rainfall between node station 4A and ground base station 3-1A, the communication quality between node station 4A and ground base station 3-1A may deteriorate, potentially reducing the throughput of communications performed by terminal station 2A.

[0022] In other words, the comparative example's wireless communication system determines which node station terminal 2A connects to based solely on the communication quality of the communication link between terminal station 2A and node station 4A. NTN states that the communication quality between ground base stations 3-1A and 3-2A and node stations 4A and 5A can easily deteriorate due to weather conditions and a decrease in nighttime power supply at node stations. As a result, the comparative example's wireless communication system sometimes experienced reduced throughput or even complete loss of communication when terminal station 2A communicated with network 100 due to this deterioration in communication quality.

[0023] Furthermore, because the altitude of node stations varies greatly depending on the type of node station in NTN, the power required for communication between terminal stations and node stations differs depending on the type of node station. Therefore, if a terminal station has low battery power, connecting to a node station that requires a large amount of power may result in a power shortage and a short-term loss of communication.

[0024] Therefore, the wireless communication system 1 according to one embodiment described below is configured to enhance the availability of NTN.

[0025] Figure 1 is a diagram illustrating an overview of a wireless communication system 1 according to one embodiment. As shown in Figure 1, in the wireless communication system 1 according to one embodiment, for example, when a terminal station 2 connects to a ground base station 3, it does so via a link that connects to one of the following: a node station 4 such as an unmanned aerial vehicle (UAV), a node station 5 such as a low orbit satellite (LEO), or a node station 6 such as a high-altitude pseudo-satellite (HAPS). The network control device 7 performs control to determine, for example, which node station the terminal station 2 connects to. The wireless communication system 1 may also use optical wireless communication.

[0026] Figure 2 is a diagram specifically showing an example of the configuration of a wireless communication system 1 according to one embodiment. As shown in Figure 2, the wireless communication system 1 includes, for example, a terminal station 2, ground base stations 3-1 and 3-2, node stations 4 such as unmanned aerial vehicles (UAVs) at different altitudes, node station 5 such as low-earth orbit satellites (LEOs), and a network control device 7, and is configured so that the terminal station 2 can connect to the network 100. The wireless communication system 1 is configured such that the terminal station 2 connects to one or more ground base stations 3 via a connection to one of the node stations such as node station 4 or node station 5, for example, the network control device 7 controls this. Note that each function of the network control device 7 may also be provided by other devices such as the terminal station 2.

[0027] Figure 3 is a functional block diagram illustrating the functions of the ground base station 3. The ground base station 3 includes, for example, a control unit 30 and a communication unit 31.

[0028] The control unit 30 controls each component of the ground base station 3. When the wireless communication system 1 is using a centralized control method, the control unit 30 manages information indicating the communication quality of the link from node station 4 (or node station 5) to the ground base station 3 and notifies the network control device 7 of this information. When the wireless communication system 1 is using a distributed control method, the control unit 30 manages information indicating the communication quality of the link from node station 4 (or node station 5) to the ground base station 3 and notifies the terminal station 2 of this information.

[0029] The communication unit 31 connects a communication link with node station 4 (or node station 5) and performs communication.

[0030] Figure 4 is a functional block diagram illustrating the functions of node station 4 (or node station 5). Node station 4 includes, for example, a control unit 40, a first communication unit 41, and a second communication unit 42.

[0031] The control unit 40 controls each component of the node station 4. When the wireless communication system 1 is operating under a centralized control system, the control unit 40 manages information indicating the communication quality of the link from terminal station 2 to node station 4 (or node station 5), and information indicating the communication quality of the link from ground base station 3 to node station 4 (or node station 5), and notifies the network control device 7 of this information. Furthermore, when the wireless communication system 1 is operating under a distributed control system, the control unit 40 manages information indicating the communication quality of the link from terminal station 2 to node station 4 (or node station 5), and information indicating the communication quality of the link from ground base station 3 to node station 4 (or node station 5), and notifies terminal station 2 of this information.

[0032] The first communication unit 41 connects to the terminal station 2 via a communication link and performs communication. The second communication unit 42 connects to the ground base station 3 via a communication link and performs communication.

[0033] Figure 5 is a functional block diagram illustrating the functions of terminal station 2. Terminal station 2 includes a control unit 20, a communication unit 21, and a connection destination control unit 22.

[0034] The control unit 20 controls each component of the terminal station 2. When the wireless communication system 1 uses a centralized control method, the control unit 20 manages, for example, local station information (such as the remaining battery level of the local station) and information indicating the communication quality of the link from node station 4 (or node station 5) to terminal station 2, and notifies node station 4 (or node station 5) of this information. Furthermore, when the wireless communication system 1 uses a distributed control method, the control unit 20 manages the information notified by node station 4 (or node station 5), ground base station 3, and network control device 7 along with local station information, and outputs this information to the connected control unit 22.

[0035] The communication unit 21 connects a communication link to the node station 4 (or node station 5) according to the information notified by the network control device 7, and communicates with the node station 4 (or node station 5), the ground base station 3, and the network control device 7.

[0036] The connection destination control unit 22 determines the node station to which it will connect based on the notified information and outputs the determined result to the control unit 20.

[0037] Figure 6 is a functional block diagram illustrating the functions of a network control device 7 according to one embodiment. When the wireless communication system 1 performs centralized control, the network control device 7 has the function of aggregating information notified from, for example, node station 4 (or node station 5), ground base station 3 and terminal station 2, as well as contract information of terminal station 2 obtained from the network (core network) 100. The network control device 7 also has the function of determining which node station 4 (or node station 5) terminal station 2 will connect to from the notified information and notifying terminal station 2 of information indicating the node station to connect to.

[0038] Furthermore, when the wireless communication system 1 is performing distributed control, the network control device 7 has a function to notify the terminal station 2 of contract information and other data obtained from the network 100.

[0039] Specifically, as shown in Figure 6, the network control device 7 includes a communication unit 71, a control unit 72, a first measurement unit 73, a second measurement unit 74, an index calculation unit 75, a prediction unit 76, and a determination unit 77.

[0040] The communication unit 71 has the function of communicating with terminal station 2, node station 4, node station 5, and ground base station 3. The communication unit 71 also communicates with the network 100.

[0041] The control unit 72 includes a CPU 720 and a memory 722, and controls each part that constitutes the network control device 7.

[0042] The first measurement unit 73 measures the communication quality between the terminal station 2 and the node stations 4 and 5, respectively.

[0043] The second measurement unit 74 measures the communication quality between node station 4 and node station 5 and ground base stations 3-1 and 3-2, respectively.

[0044] The index calculation unit 75 calculates indices that affect the availability of communication between the terminal station 2 and the node stations 4 and 5, respectively. The indices that affect the availability of communication include the remaining battery level, available communication time, transmission capacity, delay time, priority, and communication speed to be ensured, etc. of the terminal station 2.

[0045] The prediction unit 76 predicts the communication status between the terminal station 2 and the node stations 4 and 5, respectively. Then, the index calculation unit 75 may calculate indices that affect the availability of communication between the terminal station 2 and the node stations 4 and 5, respectively, based on the communication status predicted by the prediction unit 76.

[0046] The determination unit 77 determines either the node station 4 or the node station 5 as the connection destination of the terminal station 2, where the communication quality measured by the first measurement unit 73 and the second measurement unit 74 satisfies predetermined conditions respectively, and the index calculated by the index calculation unit 75 is the best.

[0047] Then, the control unit 72 controls the terminal station 2 to connect to either the ground base stations 3-1 or 3-2 through the connection with either the node station 4 or the node station 5 determined by the determination unit 77 as the connection destination.

[0048] Next, a specific operation example of the wireless communication system 1 will be described.

[0049] <First Embodiment> For example, when the network control device 7 controls the connection destination of the terminal station 2, first, the network control device 7 selects candidates for the node stations to be connected by the terminal station 2, and selects the best node station from among the selected node station candidates based on the state of the terminal station 2 so as to improve the availability.

[0050] For example, the first measurement unit 73 measures the communication quality (such as received CNR) with the terminal station 2 for all the node stations. Next, the second measurement unit 74 measures the communication quality between the selected node stations and the ground base station 3, where the measured value of the communication quality is above a predetermined threshold (reference value).

[0051] As a specific example, let's assume that the communication link between terminal station 2 and node station 4 has a received CNR of 8 dB (measured), a threshold for received CNR of -9 dB, and a communication power requirement of W / min. Also, let's assume that the communication link between terminal station 2 and node station 5 has a received CNR of 0 dB (measured), a threshold for received CNR of -9 dB, and a communication power requirement of 5 W / min.

[0052] Furthermore, the communication link between node station 4 and ground base station 3-1 is assumed to have a received CNR of -5 dB (measured) and a received CNR threshold of -9 dB. Also, the communication link between node station 5 and ground base station 3-2 is assumed to have a received CNR of 0 dB (measured) and a received CNR threshold of -9 dB.

[0053] In this case, the control unit 72 determines that the received CNR of all communication links is above a predetermined threshold and selects node station 4 and node station 5 as candidate node stations to which terminal station 2 will connect.

[0054] Then, as shown in Figure 7, the indicator calculation unit 75 calculates the available communication time for the communication link between terminal station 2 and node station 4, and the communication link between terminal station 2 and node station 5, based on the remaining battery level of terminal station 2 and the required power for communication. Here, the determination unit 77 determines node station 4 as the connection destination for terminal station 2 in such a way that the available communication time is maximized.

[0055] Furthermore, the communication quality used by the network control device 7 may not be an actual measured value, but rather a value calculated using parameters such as the location information (latitude, longitude, altitude) of terminal stations and node stations.

[0056] <Second Embodiment> The network control device 7 may also use the predicted values ​​of the communication quality of the communication links of the ground base stations 3-1 and 3-2, and node station 4 and node station 5, as parameters for selecting candidate node stations to which terminal station 2 will connect.

[0057] For example, the prediction unit 76 predicts the communication time available with ground base stations 3-1 and 3-2 for each node station whose received CNR is above a threshold. The communication time is defined as the time during which the received CNR is above a predetermined threshold. The prediction unit 76 predicts the received CNR N minutes in the future (future) as shown in Figure 8, using, for example, weather forecast data or satellite orbit information. For example, the threshold (reference value) for the communication time is set to N minutes.

[0058] As a specific example, if the communication link between node station 4 and ground base station 3-1 has a current received CNR of 8 dB (measured), a predicted received CNR of -10 dB after N minutes, and a received CNR threshold of -9 dB, then the current communication link is in good condition, but the communication link after N minutes will be degraded.

[0059] Furthermore, assuming that the communication link between node station 5 and ground base station 3-2 has a received CNR of 0 dB (measured), a predicted received CNR of 0 dB after N minutes, and a received CNR threshold of -9 dB, then the current communication link is good, and the communication link after N minutes will also be good.

[0060] Therefore, the decision unit 77 determines that the node station 4, which also has a good communication link after N minutes, will be the connection destination for the terminal station 2.

[0061] <Third Embodiment> The network control device 7 may also use a predicted value of transmission capacity as a parameter for selecting candidate node stations to which the terminal station 2 will connect.

[0062] For example, the prediction unit 76 predicts the transmission capacity for N minutes for each node station whose received CNR is above a threshold, as shown in Figure 9.

[0063] Here, the prediction unit 76 predicts the transmission capacity for N minutes using, for example, the method shown in Figure 10. As shown in Figure 10, the prediction unit 76 predicts the transmission capacity between terminal station 2 and node stations 4 and 5, respectively, assuming that the received CNR will be constant and will not change over time for N minutes from the present. At this time, the prediction unit 76 uses the current received CNR (measured value) to predict the current transmission capacity using Shannon-Hartley's theorem or an MCS (Modulation and Coding Scheme) table, etc.

[0064] Furthermore, the prediction unit 76 predicts the transmission capacity at each time point between the ground base stations 3-1 and 3-2 and node stations 4 and 5, respectively. For example, the prediction unit 76 uses the current received CNR (measured value) to predict the current transmission capacity using the Shannon-Hartley theorem. The prediction unit 76 also uses the received CNR (predicted value) N minutes later to predict the transmission capacity at N minutes later using the Shannon-Hartley theorem.

[0065] The transmission capacity across all communication paths is bottlenecked by the path with the smallest communication link capacity. In other words, in the example shown in Figure 10, the sum of the smaller capacities of each path at each time point from 0 minutes to N minutes (for example, 10M + 8M + 10M + ... + 5Mbps) represents the total transmission capacity for N minutes.

[0066] Then, if the threshold (reference value) for total transmission capacity is 20 Mbps, the determination unit 77 determines that the node station 5 with the largest total transmission capacity above that threshold will be the connection destination for the terminal station 2.

[0067] Furthermore, the transmission capacity between terminal station 2 and node stations 4 and 5 may also be calculated using Shannon's theorem or the like from the predicted value of the received CNR at each time, similar to the transmission capacity between ground base stations 3-1 and 3-2 and node stations 4 and 5, respectively. Alternatively, the transmission capacity between ground base stations 3-1 and 3-2 and node stations 4 and 5 may also be calculated by assuming that the received CNR is constant for N minutes, similar to the transmission capacity between terminal station 2 and node stations 4 and 5, respectively.

[0068] <Fourth Embodiment> The network control device 7 may also use delay time as a parameter for selecting candidate node stations to which terminal station 2 will connect.

[0069] For example, the prediction unit 76 predicts the transmission capacity and delay time for N minutes for each node station whose received CNR is above a threshold, as shown in Figure 11.

[0070] The communication path via node station 4 has a total delay of 1 ms, which is the sum of the delay time between terminal station 2 and node station 4 (e.g., 0.5 ms) and the delay time between node station 4 and ground base station 3-1 (e.g., 0.5 ms).

[0071] The communication path via node station 5 has a total delay of 10 ms, which is the sum of the delay time between terminal station 2 and node station 5 (e.g., 5 ms) and the delay time between node station 5 and ground base station 3-2 (e.g., 5 ms).

[0072] Here, if the threshold (reference value) for total transmission capacity is 5 Mbps and the threshold (reference value) for total delay time is 5 ms, the required transmission capacity will be met in the communication path via either node station 4 or node station 5. However, the decision unit 77 determines node station 4, whose total delay time is less than the threshold, as the connection destination for terminal station 2.

[0073] <Fifth Embodiment> Furthermore, if the number of terminals or the amount of traffic connected to the node station determined as the connection destination for terminal station 2 exceeds a threshold, the network control device 7 may change the connection destination to terminal station 2 according to the communication conditions of terminal station 2 (contract details such as best effort or high priority).

[0074] Figure 12 shows an example of the operation in which the network control device 7 changes the connection destination to a terminal station. Terminal station 2-1 is, for example, a high-priority terminal station with a high communication priority. Terminal station 2-2 is, for example, a best-effort terminal station.

[0075] As shown in Figure 12, if the number of terminals connected to node station 4 or the amount of traffic exceeds a threshold, the network control device 7 checks the communication conditions of terminal stations 2-1 and 2-2 (such as contract details like best effort or high priority) and changes the destination of the terminal stations to other node stations.

[0076] In a specific example, the network control device 7 changes the connection destination of all best-effort contract terminal stations to node station 5, which has the second longest available communication time. Furthermore, if the number of terminals or the amount of traffic exceeds the threshold even at node station 5, which has the second longest available communication time, the network control device 7 changes the connection destination to node station (not shown) with the third longest available communication time.

[0077] <Sixth Embodiment> Furthermore, if the number of terminals or the amount of traffic connected to the node station determined as the connection destination for the terminal station exceeds a threshold, the network control device 7 may change the connection destination for the terminal station based on other indicators.

[0078] Figure 13 shows an example of how the network control device 7 changes the connection destination to a terminal station based on other indicators.

[0079] For example, if terminal stations 2-1 to 2-3 are connected to node station 4, the network control device 7 may resolve the threshold exceeding situation by changing the connection destinations of some best-effort contract terminal stations, rather than changing the connection destinations of all best-effort contract terminal stations.

[0080] For example, the network control device 7 checks the status (battery level) of terminal stations 2-1 to 2-3, changes the connection destination starting with the terminal station with the highest battery level, and enables more terminal stations to communicate for a longer period of time.

[0081] Furthermore, the network control device 7 may check the status (traffic volume) of terminal stations 2-1 to 2-3 and change the connection destination in order from the terminal station with the highest traffic volume. Changing the connection destination may cause a momentary interruption of communication, so this is done to minimize the number of terminals whose connection destination is changed and to reduce the occurrence and impact of such interruptions.

[0082] Next, an example of the operation of the wireless communication system 1 will be explained using a flowchart. Figure 14 is a flowchart of an example of the operation of the wireless communication system 1. As shown in Figure 14, in step 100 (S100), the first measurement unit 73 measures the communication quality from the terminal station to the node station.

[0083] In step 102 (S102), the control unit 72 determines whether or not there are any node stations whose communication quality is above a threshold. If there are none (S102: No), the process proceeds to S108; if there are any (S102: Yes), the process proceeds to S104.

[0084] In step 104 (S104), the second measurement unit 74 measures the communication quality from the ground base station to the node station for node stations whose communication quality is above a threshold.

[0085] In step 106 (S106), the control unit 72 determines whether or not there are any node stations whose communication quality is above a threshold. If there are none (S106: No), the process proceeds to S108; if there are any (S106: Yes), the process proceeds to S110.

[0086] In step 108 (S108), the terminal station does not connect to any node station.

[0087] In step 100 (S110), the control unit 72 determines a candidate node station to connect to the terminal station from among the node stations whose communication quality is above a threshold.

[0088] In step 112 (S112), the index calculation unit 75 calculates indices that affect the availability of communication between the terminal station and the node station.

[0089] In step 114 (S114), the prediction unit 76 determines the node station to connect to the terminal station from among the candidate node stations that connect to the terminal station.

[0090] In step 116 (S116), the control unit 72 controls the terminal station to connect to the ground base station via a connection with the node station determined by the determination unit 77 as the connection destination.

[0091] Thus, in one embodiment, the wireless communication system 1 determines the node station to be connected to as the terminal station if the communication quality measured by the first measurement unit 73 and the second measurement unit 74 each meet predetermined conditions, and the index calculated by the index calculation unit 75 is the best. This enables the configuration of a non-terrestrial network with enhanced availability.

[0092] Furthermore, the functions of each terminal station 2, ground base station 3, node station 4, node station 5, node station 6, and network control device 7 may be partially or entirely comprised of hardware such as a PLD (Programmable Logic Device) or FPGA (Field Programmable Gate Array), or they may be comprised of programs executed by a processor such as a CPU.

[0093] For example, a network control device 7 according to one embodiment can be implemented using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0094] The functions realized by the components described herein may be implemented in a circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and / or combinations thereof, programmed to realize the functions described herein.

[0095] A processor includes transistors and other circuits and is considered circuitry or processing circuitry. A processor may also be a programmed processor that executes programs stored in memory.

[0096] In this specification, circuitry, unit, and means are hardware programmed to perform or execute the functions described herein. Such hardware may be any hardware disclosed herein, or any hardware known to be programmed to perform or execute the functions described herein.

[0097] If the hardware is a processor that is considered to be a type of circuitry, then the circuitry, means, or unit is a combination of hardware and software used to constitute the hardware and / or processor.

[0098] 1... Wireless communication system, 2, 2-1 to 2-3... Terminal station, 3, 3-1, 3-2... Ground base station, 4, 5, 6... Node station, 7... Network control device, 71... Communication unit, 72... Control unit, 73... First measurement unit, 74... Second measurement unit, 75... Indicator calculation unit, 76... Prediction unit, 77... Determination unit

Claims

1. A wireless communication system in which a terminal station connects to one or more ground base stations via a connection to one of a plurality of node stations moving in the air, comprising: a first measurement unit that measures the communication quality between the terminal station and the node stations; a second measurement unit that measures the communication quality between the node stations and the ground base stations; an index calculation unit that calculates an index affecting the availability of communication between the terminal station and the node stations; a determination unit that determines the node station to be connected to as the connection destination of the terminal station, such that the communication quality measured by the first measurement unit and the second measurement unit each satisfies predetermined conditions and the index calculated by the index calculation unit is the best; and a control unit that controls the terminal station to connect to the ground base station via a connection to the node station determined by the determination unit.

2. The wireless communication system according to claim 1, further comprising a prediction unit that predicts the communication status between the terminal station and the node station, wherein the index calculation unit calculates an index that affects the availability of communication between the terminal station and the node station based on the communication status predicted by the prediction unit.

3. A wireless communication control method performed by a wireless communication system in which a terminal station connects to one or more ground base stations via a connection to any of a plurality of node stations moving in the air, comprising: a first measurement step of measuring the communication quality between the terminal station and the node stations; a second measurement step of measuring the communication quality between the node stations and the ground base stations; an index calculation step of calculating an index that affects the availability of communication between the terminal station and the node stations; a determination step of determining the node station as the connection destination for the terminal station, such that the communication quality measured by the first measurement step and the second measurement step each satisfies predetermined conditions and the index calculated by the index calculation step is the best; and a control step of controlling the terminal station to connect to the ground base station via a connection to the node station determined as the connection destination by the determination step.

4. The wireless communication control method according to claim 3, further comprising a prediction step of predicting the communication status between the terminal station and the node station, wherein the index calculation step calculates an index that affects the availability of communication between the terminal station and the node station based on the communication status predicted by the prediction step.

Images