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

Abstract

In a wireless communication system according to one embodiment, one or more node stations that move relative to the ground surface and a plurality of base stations disposed on the ground perform wireless communication. The wireless communication system is characterized by comprising: a score calculation unit that calculates scores based on a parameter related to the communication quality of wireless communication links between all the node stations and all the base stations; and a control unit that controls the wireless communication links so as to maximize the number of wireless communication links connecting the base stations and the node stations, with the highest priority placed on maximizing the total sum of the scores calculated by the score calculation 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] For example, when switching a wireless communication link to another base station, a conventional technique for selecting a base station to which the wireless communication link is to be connected is known, which uses a maximum connection time or a maximum reception strength as criteria (see, for example, non-patent document 1).

[0007] When the maximum connection time is used as a criterion for selecting a base station to connect to for a wireless communication link, even a line with extremely small communication capacity (a line whose CINR (Carrier to Interference and Noise Ratio) is fluctuating near the communication threshold) is prioritized as a connection destination if the duration is long.

[0008] On the other hand, if the maximum reception strength is used as the criterion for selecting a base station to connect to for a wireless communication link, even a line with an extremely short communication time will be prioritized as a connection destination if its reception strength is strong.

[0009] E. Papapetrou, et al., "Satellite Handover Techniques for LEO Networks"

[0010] In the past, even if the line was connected, there were cases where the throughput did not satisfy the traffic requirements, or the throughput decreased due to frequent switching of the wireless communication link.

[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 suppress 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.

[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 a score calculation unit that calculates scores based on parameters related to the communication quality of wireless communication links between all of the node stations and all of the base stations, and a control unit that controls wireless communication links so as to increase the number of wireless communication links connecting the base stations and the node stations, with the highest priority being to maximize the sum of the scores calculated by the score calculation 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 score calculation unit that calculates scores based on parameters related to the communication quality of the wireless communication links between all of the node stations and all of the base stations, and a control unit that controls the wireless communication links so as to increase the number of wireless communication links connecting the base stations and the node stations, with the highest priority being to maximize the sum of the scores calculated by the score calculation 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 relative to the earth's surface and a plurality of base stations located on the ground, and is characterized in that it includes a score calculation step for calculating scores based on parameters related to the communication quality of the wireless communication links between all of the node stations and all of the base stations, and a control step for controlling the wireless communication links so as to increase the number of wireless communication links connecting the base stations and the node stations, with the highest priority being given to maximizing the sum of the scores calculated in the score calculation step.

[0015] According to the present invention, it is possible to suppress a decrease in throughput in a wireless communication system in which one or more node stations that move relatively to the earth's surface perform wireless communication with a plurality of base stations located on the ground.

[0016] 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 a wireless communication link (switching of wireless communication links) between one node station and multiple base stations; FIG. 4 is a diagram illustrating a lookup table for presetting a base station to be connected to over time; and FIG. 5 is a graph illustrating link capacity. FIG. 6 is a diagram illustrating a first operation example of the wireless communication system. FIG. 7 is a diagram illustrating a second operation example of the wireless communication system. (a) is a diagram illustrating an operation result when a base station with the highest score is selected for a node station; (b) is a diagram illustrating an operation result when a base station is selected by giving priority to node stations with a small number of connection destination candidates. FIG. 7 is a diagram illustrating an example of the hardware configuration of a link control device according to an embodiment; (a) is a diagram illustrating an overview of a wireless communication system of a comparative example in which a base station to be connected to a wireless communication link is selected based on a maximum connection time; and (b) is a diagram illustrating an overview of a wireless communication system of a comparative example in which a base station to be connected to a wireless communication link is selected based on a maximum reception strength.

[0017] Before describing a wireless communication system according to an embodiment, the background to the invention will be described with reference to Fig. 10. Fig. 10 is a diagram illustrating an overview of a wireless communication system of a comparative example. Fig. 10(a) is a diagram illustrating an overview of a wireless communication system of a comparative example in which a base station to which a wireless communication link is connected is selected based on a maximum connection time. Fig. 10(b) is a diagram illustrating an overview of a wireless communication system of a comparative example in which a base station to which a wireless communication link is connected is selected based on a maximum reception strength.

[0018] The wireless communication system of the comparative example is a wireless communication system in which a plurality of base stations 1a and 1b located on the ground perform wireless communication with one or more node stations 2 such as satellites that move relatively to the surface of the earth.

[0019] As shown in Figure 10(a), when the wireless communication system of the comparative example selects a base station to which a wireless communication link is to be connected based on the maximum connection time, even if there is a base station 1b that can ensure communication at 1 Gbps, it selects base station 1a, which has a connection time of 6 minutes.

[0020] On the other hand, as shown in Figure 10(b), when the wireless communication system of the comparative example selects a base station to connect to a wireless communication link based on the maximum reception strength, even if there is a base station 1b with a maximum connection time of 5 minutes, the wireless communication system selects base station 1a, which has a strong reception strength and can ensure communication at 2 Gbps.

[0021] 10(a) and 10(b), although the communication capacity would be larger if base station 1b were selected as the destination base station for the wireless communication link, base station 1a would be selected depending on the selection criteria. Thus, in the wireless communication system of the comparative example, depending on the base station selected, the throughput of the entire system may be reduced.

[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 located on the ground, thereby realizing communication between the terminal 20 and the base station 40. Here, it is assumed that one-to-one wireless communication is performed between the multiple node stations 30 and the multiple base stations 40. Furthermore, in the wireless communication system 10, traffic accommodated in the entire system is transmitted to the base station via available wireless communication links while utilizing communication links connecting the node stations 30. Therefore, the greater the number of wireless communication links between the node stations 30 and the base stations 40, the greater the throughput of the entire system.

[0025] The link control device 50 calculates a score that serves as a criterion for determining whether to switch a wireless communication link based on (for example, all) parameters related to the communication quality of the wireless communication link. In other words, when the wireless communication system 10 needs to switch the base station 40 currently connected to the wireless communication link to another base station 40 for some reason, the wireless communication system 10 selects the base station 40 to which the wireless communication link is to be switched based on, for example, the score calculated by the link control device 50.

[0026] The wireless communication system 10 may use distributed control or centralized control for the calculation of the score and the control for selecting the base station 40 to connect to. In the case of a distributed control method, these controls are performed by each base station 40 or each node station 30. Furthermore, 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.

[0027] 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 score calculation unit 56, and a selection unit 58.

[0028] The communication unit 52 acquires external information such as time information from the external device 100 and outputs it to the control unit 54. The communication unit 52 also has a function of communicating with the base station 40.

[0029] The control unit 54 controls each unit constituting the link control device 50. For example, the control unit 54 controls the wireless communication links so as to increase the number of wireless communication links between the node stations 30 and the base stations 40, with the highest priority being to maximize the total score calculated by the score calculation unit 56 (described later).

[0030] The score calculation unit 56 calculates scores based on (e.g., all) parameters related to the communication quality of the wireless communication links between all the node stations 30 and all the base stations 40, and outputs the scores to the selection unit 58. For example, the parameters related to the communication quality of the wireless communication links include the communication capacity and the remaining time available for communication.

[0031] When the communication capacity and remaining communication time (link life) are used as parameters relating to the communication quality of the wireless communication link, the score calculation unit 56 calculates the score using the following formula (1).

[0032]

[0033] Here, the capacity of the wireless communication link is represented by C [GB], the link life is represented by tl [s], the reference value of the link life is represented by tr [s], and an arbitrary real number is represented by R.

[0034] The score is used as a criterion for selecting wireless communication links. The score is not simply calculated by multiplying the link capacity by the link lifespan, but is normalized by the reference value of the link lifespan and set as an exponent of an arbitrary real number. This prevents large differences in scores between wireless communication links whose communication time is extremely short compared to the reference value of the link lifespan. Furthermore, by selecting the real number R, it is possible to weight the link lifespan with respect to the score.

[0035] Here, the link life reference value and link capacity will be specifically explained using Figures 3 to 5. Figure 3 is a diagram showing a schematic diagram of switching of a wireless communication link between one node station 30 and multiple base stations 40. Figure 4 is a diagram showing a lookup table that sets in advance, for each time period, the base station 40 to which the wireless communication link will be connected. Figure 5 is a graph illustrating an example of link capacity.

[0036] For example, when the node station 30 moves above the base station 40-2, the score calculation unit 56 uses the remaining connection time tr in the lookup table as the reference value for the link life.

[0037] The capacity C [GB] of a wireless communication link is defined as the amount obtained by integrating the time change in the spectral efficiency that can be achieved at CINR(t) for 0≦t≦tl, where CINR(t) is the time change of the CINR of the wireless communication link, over the range 0≦t≦tl.

[0038] The link life and the change over time of the CINR of the wireless communication link are acquired by any method, and the change over time of the frequency efficiency is calculated by an appropriate method from the change over time of the CINR and an MCS table, etc.

[0039] The selection unit 58 selects a connection pair of a node station 30 and a base station 40 based on the score calculated by the score calculation unit 56 .

[0040] Then, the control unit 54 controls the wireless communication links of the node station 30 and the base station 40 via the communication unit 52 based on the result of the selection by the selection unit 58 .

[0041] Next, a first operation example of the wireless communication system 10 according to an embodiment will be described. Fig. 6 is a diagram showing the first operation example of the wireless communication system 10. Note that while the wireless communication system of the comparative example for reference performs the process of S100, the wireless communication system 10 according to an embodiment performs the processes of S200 and S202 in this order.

[0042] In step 100 (S100), the wireless communication system of the comparative example selects a base station 40 to which the node station 30 is to connect based on the maximum connection time or maximum reception strength of the wireless communication link.

[0043] In response to this, in step 200 (S200), the wireless communication system 10 calculates a score based on (e.g., all) parameters related to the communication quality of the wireless communication link, and in step 202 (S202), selects a base station 40 to which the node station 30 will connect based on the score.

[0044] Next, a second operation example of the wireless communication system 10 according to an embodiment will be described with reference to Figs. 7 and 8. Figs. 7 and 8 are diagrams illustrating the second operation example of the wireless communication system 10. Fig. 8(a) is a diagram illustrating the operation result when selecting a base station 40 with the highest score for a node station 30. Fig. 8(b) is a diagram illustrating the operation result when selecting a base station 40 by giving priority to a node station 30 with a small number of connection destination candidates.

[0045] In the wireless communication system of the comparative example, which is used as a reference, the processes are performed in the order of S400, S402, S404, S406, and S408.

[0046] In the second operation example of the wireless communication system 10, the link control device 50 sets the number of attempts i to 0 in step 400 (S400). Here, the number of base stations 40 is assumed to be N.

[0047] In step 402 (S402), the link control device 50 determines whether or not there is a pair (connection candidate pair) of a node station 30 and a base station 40 whose score is equal to or greater than the threshold and is the maximum, excluding the node station 30 and the base station 40 that are already connected. If there is a connection candidate pair (S402: Yes), the link control device 50 proceeds to the processing of S500, and if there is no connection candidate pair (S402: No), the link control device 50 ends the processing.

[0048] In step 500 (S500), the link control device 50 determines whether or not there is a connection candidate pair that does not overlap with the base station 40. If the connection candidate pair exists (S500: Yes), the link control device 50 proceeds to processing S404. If the connection candidate pair does not exist (S500: No), the link control device 50 proceeds to processing S502.

[0049] In step 404 (S404), the link control device 50 determines the connection of the connection candidate pair.

[0050] In step 502 (S502), the link control device 50 extracts a group of nodes that are paired with the overlapping base station 40.

[0051] In step 504 (S504), the link control device 50 extracts from the node group the node station 30 (priority node) with which the number of base stations 40 with which it can communicate is the smallest.

[0052] In step 506 (S506), the link control device 50 determines whether there is one priority node, and if there is one (S506: Yes), proceeds to processing S508, and if there is not one (S506: No), proceeds to processing S510.

[0053] In step 508 (S508), the link control device 50 determines the connection of the connection candidate pair including the priority node.

[0054] In step 510 (S510), the link control device 50 determines the connection of the pair with the highest score from among the connection candidate pairs including the priority node.

[0055] In step 512 (S512), the link control device 50 determines whether the connection candidate pairs include any other overlapping base stations 40. If there are no other overlapping base stations 40 (S512: Yes), the link control device 50 proceeds to the processing of S406, and if there are other overlapping base stations 40 (S512: No), the link control device 50 returns to the processing of S502.

[0056] In step 406 (S406), the link control device 50 increments the number of trials i (i=i+1).

[0057] In step 408 (S408), the link control device 50 determines whether i=N, and if it does (S408: Yes), ends the processing, and if it does not (S408: No), returns to processing S402.

[0058] 8(a), when the base station 40 with the highest score is selected for the node station 30, the wireless communication links are the two combinations marked with circles. In this case, the base station 40-3 is not connected to any of the node stations 30, and the number of wireless communication links remains at two.

[0059] 8(b), when a node station 30 with fewer connection candidates is preferentially connected to a base station 40, the wireless communication links become the three combinations marked with circles. In this case, all base stations 40 are connected to the node station 30, and the number of wireless communication links increases to three.

[0060] However, if the total score of the wireless communication links is smaller when a node station 30 with fewer connection candidates is preferentially connected to a base station 40 than when the node station 30 is connected to the base station 40 with the highest score, the link control device 50 will connect to the base station 40 with the highest score for the node station 30, even if the number of wireless communication links is smaller.

[0061] In this way, the wireless communication system 10 preferentially connects the node stations 30 with fewer connection candidates to the base station 40, thereby making it possible to utilize as many wireless communication links as possible between the node stations 30 and the base stations 40. The wireless communication system 10 can also suppress a decrease in throughput and a decrease in the communication capacity of the entire system.

[0062] 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.

[0063] 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.

[0064] 9 is a diagram illustrating an example of the hardware configuration of a link control device 50 according to an embodiment. As shown in FIG. 9, for example, the link control device 50 has 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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...score calculation unit, 58...selection unit, 100...external device, 500...input unit, 510...output unit, 520...communication unit, 530...CPU, 540...memory, 550...HDD, 560...bus, 570...storage medium

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 score calculation unit that calculates scores based on parameters related to the communication quality of wireless communication links between all of the node stations and all of the base stations; and a control unit that controls wireless communication links so as to increase the number of wireless communication links connecting the base stations and the node stations, with the highest priority being given to maximizing the total score calculated by the score calculation unit.

2. A link control device that controls 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 score calculation unit that calculates scores based on parameters related to the communication quality of wireless communication links between all of the node stations and all of the base stations; and a control unit that controls wireless communication links so as to increase the number of wireless communication links connecting the base stations and the node stations, with the highest priority being given to maximizing the total sum of the scores calculated by the score calculation unit.

3. A link control method for controlling 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 score calculation step for calculating scores based on parameters related to the communication quality of wireless communication links between all of the node stations and all of the base stations; and a control step for controlling wireless communication links so as to increase the number of wireless communication links connecting the base stations and the node stations, with the highest priority being given to maximizing the total sum of the scores calculated in the score calculation 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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