Wireless communication system

Abstract

A wireless communication system according to the present disclosure comprises a plurality of base stations, at least one aerial wireless relay station, and a processing circuit. The processing circuit is configured to acquire, for each of the plurality of base stations, a forecast of a weather condition that affects communication quality with at least one aerial wireless relay station, and, when a decrease in communication quality is predicted for any of the plurality of base stations on the basis of the forecast of the weather condition, to transfer, in advance, an accommodation destination of a user terminal accommodated by the base station for which the decrease in communication quality is predicted, to one or more other base stations via at least one aerial wireless relay station before the decrease in communication quality occurs.

Description

Wireless communication system

[0001] This disclosure relates to a technology suitable for use in wireless communication using multiple base stations and at least one airborne radio relay station.

[0002] In recent years, mobile communication systems have advanced, making mobile services available in most areas of the land. One of the requirements for the fifth generation and beyond (Beyond 5G) mobile communication systems, which are expected to be commercialized in the future, is ultra-coverage. Ultra-coverage means expanding the service area to places where the cost of laying existing ground base stations (hereinafter referred to as ground stations) is high or difficult, such as mountainous areas, at sea, and in the air. Furthermore, there is a need to strengthen the nation's infrastructure against natural disasters, and the emergence of communication systems that are resilient to ground-based disasters is desired.

[0003] To fulfill the above requirements, there is growing interest in non-terrestrial networks (NTNs) that utilize aerial radio relay stations such as satellites, unmanned aerial vehicles, high-altitude platforms, and drones. For example, Non-Patent Document 1 discloses technology related to wireless communication using low Earth orbit (LEO) satellite constellations. In NTNs, the use of high-frequency radio waves is envisioned for the wireless communication link (feeder link) between aerial radio relay stations and ground base stations, from the perspective of increasing communication capacity.

[0004] E. Papapetrou, S. Karapantazis, G. Dimitriadis, F.-N. Pavlidou, "Satellite handover techniques for LEO networks," https: / / doi.org / 10.1002 / sat.783, 24 Feb. 2004.

[0005] However, high-frequency radio waves are significantly affected by meteorological conditions such as rainfall and clouds, resulting in deterioration of communication quality (rain attenuation, cloud attenuation), which causes a decrease in the throughput of user terminals. Therefore, it is required to proactively implement site diversity for switching communication partners to other terrestrial base stations or routing control for transferring traffic to other aerial radio relay stations in anticipation of deterioration of communication quality.

[0006] In order to solve the above problems, the present disclosure aims to provide a technology that can suppress a decrease in the throughput of user terminals due to meteorological conditions and suppress a decrease in communication capacity as a whole system by proactive control.

[0007] To achieve the above object, a wireless communication system according to an embodiment of the present disclosure includes a plurality of base stations, at least one aerial radio relay station, and a processing circuit. The processing circuit acquires a forecast of meteorological conditions that affect the communication quality between each of the plurality of base stations and at least one aerial radio relay station, and when a decrease in communication quality is predicted in any of the plurality of base stations based on the forecast of meteorological conditions, the accommodation destination of the user terminals accommodated by the base station where the decrease in communication quality is predicted is pre-transferred to one or more other base stations via at least one aerial radio relay station before the communication quality deteriorates.

[0008] According to the above technology of the present disclosure, when a decrease in communication quality is predicted in any of the plurality of base stations based on the forecast of meteorological conditions, the accommodation destination of the user terminals accommodated by the base station where the decrease in communication quality is predicted is pre-transferred to one or more other base stations via at least one aerial radio relay station before the communication quality deteriorates. By proactively selecting a base station in response to such a change in meteorological conditions, it is possible to suppress a decrease in the throughput of user terminals due to meteorological conditions and suppress a decrease in communication capacity as a whole system.

[0009] The figure shows an outline of the configuration of a wireless communication system according to an embodiment of the present disclosure. The figure shows a first switching example by switching control of a traffic transmission route executed in the wireless communication system. The figure shows a second switching example by switching control of a traffic transmission route executed in the wireless communication system. The figure shows a third switching example by switching control of a traffic transmission route executed in the wireless communication system. The figure shows a fourth switching example by switching control of a traffic transmission route executed in the wireless communication system. The flowchart shows the switching control of the traffic transmission route executed in the wireless communication system. The block diagram shows the hardware configuration of the communication quality prediction device and the switching destination base station selection device. The figure shows a first installation example of the communication quality prediction device and the switching destination base station selection device. The figure shows a second installation example of the communication quality prediction device and the switching destination base station selection device. The figure shows a third installation example of the communication quality prediction device and the switching destination base station selection device.

[0010] 1. Configuration of Wireless Communication System First, an outline of the configuration of a wireless communication system according to an embodiment of the present disclosure will be described using FIG. 1.

[0011] As shown in FIG. 1, the wireless communication system 100 is a non-terrestrial network system that connects a base station 20 and a user terminal (UE) 30 via an aerial wireless relay station 10. Typical examples of the aerial wireless relay station 10 are High Altitude Platform Station (HAPS) and LEO satellites. In the present embodiment, it is assumed that the aerial wireless relay station 10 is HAPS. There is one or more HAPS 10 that make up the wireless communication system 100. When the wireless communication system 100 includes a plurality of HAPS 10, the HAPS 10 may or may not perform link communication with each other.

[0012] Base stations 20 are installed at multiple locations on the ground. Each base station 20 is a ground station having one or more antennas for the base station-HAPS link. HAPS 10 establishes a feeder link 14 with base station 20. MIMO communication may be performed between HAPS 10 and base station 20. A single HAPS 10 may be connected to one or more base stations 20. Each base station 20 is also connected to the core network.

[0013] UE30 is, for example, a smartphone or IoT terminal and has one or more antennas for the UE-HAPS link. HAPS10 establishes a service link 12 with UE30. One HAPS10 can accommodate multiple UE30s. There is an upper limit on the number of UE30s that HAPS10 can accommodate, from the standpoint of communication quality. However, although the throughput per UE30 accommodated will decrease, it is possible to accommodate more UE30s than the upper limit by dynamic bandwidth management of the feeder link, etc.

[0014] Now, suppose it is raining near one of the multiple base stations 20. The rain will reduce the communication capacity of the feeder link of that base station, and decrease the throughput of the UEs that are transmitting traffic to that base station. However, if changes in weather conditions that will affect communication quality are known in advance, this can be addressed by switching the transmission route of traffic from that UE beforehand.

[0015] The wireless communication system 100 is characterized by its ability to forward or distribute traffic via a feeder link that is expected to be affected by weather conditions to other feeder links that are expected to be unaffected or less affected by weather conditions. Weather conditions differ for each base station 20, and it is not highly likely that the transmission capacity of the feeder link 14 will decrease simultaneously at all base stations 20. Therefore, by proactively switching the traffic transmission route, the wireless communication system 100 as a whole can achieve robust throughput against changes in weather conditions and suppress a decrease in communication capacity for the entire system.

[0016] As described above, in order to proactively switch the traffic transmission route in response to changes in weather conditions, it is necessary to obtain weather condition forecasts for each of the multiple base stations 20 and to select the base station 20 to which the traffic will be switched based on the weather condition forecasts. To achieve this, the wireless communication system 100 includes a communication quality forecasting device 40 and a base station selection device 42. The communication quality forecasting device 40 performs the former process, and the base station selection device 42 performs the latter process.

[0017] More specifically, the communication quality prediction device 40 is configured to acquire forecasts of weather conditions that affect communication quality between the HAPS 10 and the base station 20, and to determine, based on the weather condition forecast, whether or not a deterioration in communication quality is predicted at any of the multiple base stations 20. The switching destination base station selection device 42 is configured to, if a deterioration in communication quality is predicted at any of the base stations 20, transfer the destination of the UE 30 accommodated by the base station 20 where the deterioration in communication quality is predicted to occur to one or more other base stations 20 via at least one HAPS 10. The configuration of the communication quality prediction device 40 and the switching destination base station selection device 42, as well as specific installation examples, will be described later.

[0018] 2. Traffic Transmission Route Switching Control 2-1. First Switching Example Figure 2 shows a first switching example performed by traffic transmission route switching control in the wireless communication system 100. In Figure 2, the wireless communication system 100 is equipped with three HAPS 10A, 10B, and 10C. The wireless communication system 100 is equipped with many relay stations, but here we will explain using representative HAPS 10A, 10B, and 10C. HAPS 10A establishes a feeder link 14A with the base station 20A and establishes a service link 12A with multiple radio stations 30A. HAPS 10B establishes a feeder link 14B with the base station 20B and establishes a service link 12B with multiple radio stations 30B. HAPS 10C establishes a feeder link 14C with the base station 20C and establishes a service link 12C with multiple radio stations 30C. HAPS 10A, 10B, and 10C are connected to each other by HAPS inter-links 16AB, 16BC, and 16CA.

[0019] In Figure 2, base station 20A accommodates 100 UE30A units via HAPS 10A, base station 20B accommodates 50 UE30B units via HAPS 10B, and base station 20C accommodates 150 UE30C units via HAPS 10C. The maximum number of UE units that each base station 20A, 20B, and 20C can accommodate is assumed to be 150 units. Under these UE accommodation conditions, rainfall is predicted around base station 20A and base station 20B. The rainfall prediction is performed by the communication quality prediction device 40. The communication quality prediction device 40 predicts changes in weather conditions not only around base station 20A but also around all other base stations, based on weather forecasts obtained from external sources such as weather forecasting companies.

[0020] The communication quality prediction device 40 predicts a decline in communication quality at each base station 20A, 20B, and 20C based on changes in weather conditions. In the example shown in Figure 2, a decline in communication quality is predicted at base stations 20A and 20B. Here, communication quality typically refers to the signal CNR or the communication capacity of the feeder link. In each example, including Figure 2, communication quality refers to the communication capacity of the feeder link, and deterioration of communication quality refers to the attenuation of communication capacity.

[0021] The switching destination base station selection device 42 first uses a function f that represents the predicted communication quality per connected user terminal (predicted value of communication quality) when all UE 30A connected to base station 20A are transferred to all base stations 20A, 20B, and 20C. ｘ (p) is calculated. However, for base station 20A, the function f represents the predicted communication quality per connected user terminal if the connected UE 30A is left as is. Ｘ Calculate (p). Function f Ｘ The subscript X in (p) indicates the base station identification number. As the predicted communication quality per connected user terminal, for example, the predicted average throughput per connected user terminal can be used.

[0022] function f ｘ(p) is a function with parameters such as the predicted amount of communication quality degradation, the remaining time until communication quality degradation occurs, the maximum number of UEs that a base station can accommodate, the number of UEs accommodated by a base station, and the maximum connection time with an aerial wireless relay station. However, the number of UEs accommodated by a base station is defined as the sum of the number of UEs already accommodated by the target base station and the number of UEs transferred from the source base station. Also, whether to concentrate and transfer the UEs accommodated by the source base station to one station or disperse them among multiple base stations is also regarded as a parameter. If the predicted amount of communication quality degradation, that is, the predicted amount of attenuation due to meteorological conditions such as rain and clouds, and the remaining time until it occurs are known, it is possible to know how much communication capacity can be ensured until a certain number of minutes later and predict the communication quality for each accommodated UE.

[0023] In each example including FIG. 2, the function f ｘ (p) adopts the predicted average throughput per accommodated user terminal as the physical quantity it represents. Also, as the parameters of the function f ｘ (p), the maximum number of UEs m that can be accommodated in base station X Ｘ , the number of UEs n accommodated Ｘ , and the amount of attenuation α Ｘ are adopted. Assume that the accommodation conditions of UEs in each base station 20A, 20B, and 20C are as described above. Assume that the amount of attenuation of the feeder link 14A due to rainfall in base station ́20A is 20 dB. Also, assume that attenuation of the feeder link 14B occurs due to rainfall in base station 20B, and the amount of this attenuation is 6 dB.

[0024] Under the above conditions, when UE 30A accommodated in base station 20A remains unchanged, the predicted average throughput per accommodated user terminal in base station 20A is f Ａ (m Ａ = 150, n Ａ = 100, α ＡThe value is calculated as (=20). If the average throughput per user terminal when the number of accommodated UEs is equal to the maximum number of UEs is taken as the reference throughput, the original average throughput of base station 20A is 3 / 2 of the reference throughput. However, due to the effect of 20 dB attenuation, the predicted average throughput per user terminal will drop to about 1 / 100th. This is a level that makes communication almost impossible, so it is necessary to switch the destination of UE 30A accommodated in base station 20A to one of the other base stations 20B or 20C.

[0025] When base station 20B is used as the destination for UE 30A which is connected to base station 20A, the predicted average throughput per connected user terminal at base station 20B is f Ｂ (m Ｂ = 150, n Ｂ +n Ａ = 50 + 100, α Ｂ = This is the value calculated in 6). When the number of accommodated UEs equals the maximum number of accommodated UEs, the predicted average throughput per accommodated user terminal becomes equal to the baseline throughput. Furthermore, due to the effect of a 6 dB attenuation, the predicted average throughput per accommodated user terminal will further decrease to about one-quarter of the baseline throughput.

[0026] When base station 20C is used as the destination for UE 30A which is connected to base station 20A, the predicted average throughput per connected user terminal at base station 20C is f Ｃ (m Ｃ = 150, n Ｃ +n Ａ = 150 + 100, α Ｃ The value calculated with =0) is obtained. Since the number of accommodated UEs, 250, is an overload as it is 5 / 3 of the maximum number of UEs, the predicted average throughput per accommodated user terminal will decrease to about 3 / 5 of the standard throughput. On the other hand, unlike base station 20B, there is no decrease in predicted average throughput due to attenuation.

[0027] The switching destination base station selection device 42 uses a function f that represents the predicted communication quality per user terminal at base station 20B. ＢThe value of and the function f that represents the predicted communication quality per user terminal at base station 20C. Ｃ Compare this with the value of f. According to the calculation results above, f Ｂ The value of f is greater than the value of f Ｃ The value of is larger. The switching destination base station selection device 42 selects base station C, which has a larger value of function f, as the destination for UE30A, which is housed in base station 20A.

[0028] The selection result by the switching destination base station selection device 42 is notified to HAPS 10A and HAPS 10C. Upon receiving notification from the switching destination base station selection device 42, HAPS 10A stops transmitting traffic from UE 30A to base station 20A and forwards the traffic from UE 30A to HAPS 10C using the HAPS inter-link 16CA between HAPS 10A and HAPS 10C.

[0029] Upon receiving notification from the switching destination base station selection device 42, HAPS 10C receives traffic from UE 30A forwarded from HAPS 10A and transmits the traffic from UE 30A along with the traffic from UE 30C to base station 20C using the feeder link 14C. In this way, proactive base station selection is performed in response to changes in weather conditions, which suppresses the decrease in throughput of UE 30A due to the effects of weather conditions and suppresses the decrease in communication capacity of the wireless communication system 100 as a whole.

[0030] 2-2. Second Switching Example Figure 3 shows a second switching example performed by traffic transmission route switching control in the wireless communication system 100. The configuration of the wireless communication system 100 in the second switching example is the same as in the first switching example.

[0031] In Figure 3, base station 20A accommodates 100 UE30A units via HAPS 10A, base station 20B accommodates 100 UE30B units via HAPS 10B, and base station 20C accommodates 100 UE30C units via HAPS 10C. The maximum number of UE units that each base station 20A, 20B, and 20C can accommodate is assumed to be 150 units. Under these UE accommodation conditions, the communication quality prediction device 40 predicts that the communication quality at base station 20A will deteriorate due to the effects of rainfall.

[0032] The switching destination base station selection device 42 first calculates a function f representing the predicted communication quality per connected user terminal when all UEs 30A connected to base station 20A are transferred to all base stations 20A, 20B, and 20C. However, for base station 20A, it calculates a function f representing the predicted communication quality per connected user terminal when the connected UEs 30A are left as they are. The UE connection conditions at each base station 20A, 20B, and 20C are assumed to be as described above. The amount of attenuation of the feeder link 14A due to rainfall at base station 20A is assumed to be 20 dB.

[0033] If the UE30A connected to base station 20A is left as is, the predicted average throughput per connected user terminal at base station 20A is f Ａ (m Ａ = 150, n Ａ = 100, α Ａ The value will be calculated as (=20). As mentioned in the first switching example, the 20 dB attenuation will reduce the predicted average throughput per connected user terminal to a level where communication is almost impossible.

[0034] On the other hand, if base station 20B is used as the destination for UE 30A which is connected to base station 20A, the predicted average throughput per connected user terminal at base station 20B is f Ｂ (m Ｂ = 150, n Ｂ +n Ａ = 100 + 100, α ＢThe value calculated is (= 0). Since the number of UEs accommodated, 200, is an overload as it is 3 / 4 times the maximum number of UEs accommodated, the predicted average throughput per accommodated user terminal will decrease to about 3 / 4 of the standard throughput. Base stations 20B and 20C have the same maximum number of UEs accommodated and the same number of UEs accommodated, so even if base station 20C is used as the destination for UE 30A accommodated in base station 20A, the predicted average throughput per accommodated user terminal will be the same.

[0035] Next, the switching destination base station selection device 42 calculates a function f that represents the predicted communication quality per user terminal when all UE30A accommodated by base station 20A are distributed and transferred to base stations 20B and 20C. The switching destination base station selection device 42 determines the distribution ratio of UE30A so that the value of function f is the same for base stations 20B and 20C. Since base stations 20B and 20C have the same maximum number of UEs they can accommodate and the same number of UEs they can accommodate, 50 UE30A are allocated to each of them.

[0036] As described above, when UE30A is distributed between base station 20B and base station 20C, the predicted average throughput per user terminal at base station 20B is f Ｂ (m Ｂ = 150, n Ｂ +n Ａ / 2=100+50,α Ｂ The value calculated as = 0) is obtained. When the number of accommodated UEs equals the maximum number of accommodated UEs, the predicted average throughput per accommodated user terminal at base station 20B becomes equal to the reference throughput. Similarly, the predicted average throughput per accommodated user terminal at base station 20C becomes equal to the reference throughput.

[0037] The switching destination base station selection device 42 compares the maximum value of function f when all UE30A accommodated by base station 20A are transferred to either base station 20B or 20C in one go, with the value of function f when they are transferred in a distributed manner between base station 20B and base station 20C. According to the above calculation results, the value of function f is larger when the UE30A are transferred in a distributed manner between base station 20B and base station 20C than when they are transferred in one go to either base station 20B or base station 20C. Therefore, the switching destination base station selection device 42 selects base station 20B and base station 20C as destinations for the UE30A accommodated by base station 20A, and selects a distribution ratio of 50:50 for the UE30A.

[0038] Furthermore, if there are three or more base stations that serve as forwarding destinations for the UE30A accommodated by base station 20A, all of them may be designated as distribution destinations, or only some of them may be designated as distribution destinations. Which base stations are designated as distribution destinations may be predetermined based on their relationship to the source base station.

[0039] The selection result from the switching destination base station selection device 42 is notified to HAPS 10A, HAPS 10B, and HAPS 10C. Upon receiving notification from the switching destination base station selection device 42, HAPS 10A stops transmitting traffic from UE 30A to base station 20A. Then, using the inter-HAPS link 16AB between HAPS 10A and HAPS 10B, half of the traffic from UE 30A is forwarded to HAPS 10B. Additionally, using the inter-HAPS link 16CA between HAPS 10A and HAPS 10C, half of the traffic from UE 30A is forwarded to HAPS 10C.

[0040] Upon receiving notification from the switching destination base station selection device 42, HAPS 10B receives half of the traffic from UE 30A forwarded from HAPS 10A and transmits half of the traffic from UE 30A, along with the traffic from UE 30B, to base station 20B using feeder link 14B. Upon receiving notification from the switching destination base station selection device 42, HAPS 10C receives half of the traffic from UE 30A forwarded from HAPS 10A and transmits half of the traffic from UE 30A, along with the traffic from UE 30C, to base station 20C using feeder link 14C. In this way, proactive base station selection is performed in response to changes in weather conditions, which suppresses the decrease in throughput of UE 30A due to the effects of weather conditions and suppresses the decrease in communication capacity of the entire wireless communication system 100.

[0041] 2-3. Third Switching Example Figure 4 shows a third switching example performed by traffic transmission route switching control in the wireless communication system 100. The configuration of the wireless communication system 100 in the third switching example is the same as in the first switching example.

[0042] In Figure 4, base station 20A accommodates 150 UE30A units via HAPS 10A, base station 20B accommodates 150 UE30B units via HAPS 10B, and base station 20C accommodates 150 UE30C units via HAPS 10C. The maximum number of UE units that each base station 20A, 20B, and 20C can accommodate is assumed to be 150. Under these UE accommodation conditions, the communication quality prediction device 40 predicts that the communication quality at each of the base stations 20A, 20B, and 20C will deteriorate due to the effects of rainfall.

[0043] The switching destination base station selection device 42 uses a function f that represents the predicted communication quality per connected user terminal when all UE 30A connected to base station 20A are transferred to all base stations 20A, 20B, and 20C. ＸThe following calculation is performed. However, for base station 20A, a function f representing the predicted communication quality per connected user terminal is calculated assuming the connected UE 30A remains unchanged. The connection conditions for UEs at each base station 20A, 20B, and 20C are assumed to be as described above. The amount of attenuation in feeder links 14A, 14B, and 14C due to rainfall at each base station 20A, 20B, and 20C is assumed to be 3 dB.

[0044] If the UE30A connected to base station 20A is left as is, the predicted average throughput per connected user terminal at base station 20A is f Ａ (m Ａ = 150, n Ａ = 150, α Ａ =3) This is the value calculated in step 3). The number of accommodated UEs is equal to the maximum number of UEs, but due to the effect of a 3 dB attenuation, the predicted average throughput per accommodated user terminal will decrease to about half of the standard throughput.

[0045] On the other hand, if base station 20B is used as the destination for UE 30A which is connected to base station 20A, the predicted average throughput per connected user terminal at base station 20B is f Ｂ (m Ｂ = 150, n Ｂ +n Ａ = 150 + 150, α Ｂ =3) This is the value calculated in step 3). Since the number of UEs accommodated, 300, is an overload as it is twice the maximum number of UEs that can be accommodated, the predicted average throughput per UE will decrease to about half of the standard throughput. Furthermore, due to the effect of a 3 dB attenuation, the predicted average throughput per UE will decrease to about one-quarter of the standard throughput. Since base stations 20B and 20C have the same maximum number of UEs that can be accommodated and the same number of UEs that can be accommodated, the predicted average throughput per UE will be the same even if base station 20C is used as the destination for UE 30A that is accommodated in base station 20A.

[0046] Next, the switching destination base station selection device 42 calculates a function f that represents the predicted communication quality per user terminal when all UEs 30A accommodated by base station 20A are distributed and transferred to base stations 20B and 20C. The switching destination base station selection device 42 determines the distribution ratio of UEs 30A so that the value of function f is the same for base stations 20B and 20C. Since base stations 20B and 20C have the same maximum number of UEs they can accommodate and the same number of UEs they can accommodate, 75 UEs 30A are allocated to each of them.

[0047] As described above, when UE30A is distributed between base station 20B and base station 20C, the predicted average throughput per user terminal at base station 20B is f Ｂ (m Ｂ = 150, n Ｂ +n Ａ / 2=150+75,α Ｂ =3) This is the value calculated in the above. Since the number of UEs accommodated, 225, is an overload as it is 3 / 2 of the maximum number of UEs that can be accommodated, the predicted average throughput per UE will decrease to about 2 / 3 of the baseline throughput. Furthermore, due to the effect of a 3 dB attenuation, the predicted average throughput per UE will decrease to about 1 / 3 of the baseline throughput. Similarly, the predicted average throughput per UE at base station 20C will also be about 1 / 3 of the baseline throughput.

[0048] The switching destination base station selection device 42 uses the function f when the UE 30A accommodated by base station 20A is not transferred. Ａ The values ​​of and the function f when transferring them all at once to either base station 20B or 20C Ｂ Or function f Ｃ The values ​​of and the function f when they are distributed and transferred between base station 20B and base station 20C. Ｂ , f ＣThe value is compared with that of . According to the calculation results above, the value of function f is largest when the UE 30A accommodated by base station 20A is left at base station 20A without being moved. Therefore, the switching destination base station selection device 42 does not move the UE 30A accommodated by base station 20A to any other base station, and selects the current base station 20A as the destination for the UE 30A.

[0049] The selection result from the switching destination base station selection device 42 is notified to HAPS 10A. Upon receiving the notification from the switching destination base station selection device 42, HAPS 10A transmits the traffic from UE 30A to base station 20A using the feeder link 14A.

[0050] Furthermore, if transferring all UE30A accommodated by base station 20A to another base station results in a larger value of function f than not transferring them, the switching destination base station selection device 42 will transfer all UE30A accommodated by base station 20A to the other base station. In this case, the switching destination base station selection device 42 will perform a batch transfer if transferring them all at once to either base station 20B or 20C results in a larger value of function f, and will perform a distributed transfer if transferring them to both base station 20B and base station 20C results in a larger value of function f.

[0051] 2-4. Fourth Switching Example Figure 5 shows a fourth switching example performed by traffic transmission route switching control in the wireless communication system 100. In the first to third switching examples, one base station is connected to one HAPS, whereas in the fourth switching example, as shown in Figure 5, three base stations 20A, 20B, and 20C are connected to one HAPS 10D.

[0052] In Figure 5, base station 20A is assumed to accommodate 150 UEs 30A via HAPS 10D. Furthermore, each base station 20A, 20B, and 20C has a maximum capacity of 150 UEs. Under these UE accommodation conditions, the communication quality prediction device 40 predicts rainfall around each base station 20A, 20B, and 20C. The communication quality prediction device 40 predicts a decrease in communication quality due to rainfall for each base station 20A, 20B, and 20C. The prediction results show that the attenuation at base station 20A is 20 dB, at base station 20B is 3 dB, and at base station 20C is 6 dB.

[0053] The switching destination base station selection device 42 first calculates a function f representing the predicted communication quality per connected user terminal when all UEs 30A connected to base station 20A are transferred to all base stations 20A, 20B, and 20C. However, for base station 20A, it calculates a function f representing the predicted communication quality per connected user terminal when the connected UEs 30A are left as they are. The UE connection conditions at each base station 20A, 20B, and 20C are assumed to be as described above.

[0054] If the UE30A connected to base station 20A is left as is, the predicted average throughput per connected user terminal at base station 20A is f Ａ (m Ａ = 150, n Ａ = 150, α Ａ The value will be calculated as (=20). Due to the 20 dB attenuation, the predicted average throughput per connected user terminal at base station 20A will drop to about 1 / 100th of the reference throughput. This is a level that makes communication almost impossible, so it is necessary to switch the destination of UE30A connected to base station 20A to one of the other base stations 20B or 20C.

[0055] When base station 20B is used as the destination for UE 30A which is connected to base station 20A, the predicted average throughput per connected user terminal at base station 20B is f Ｂ (m Ｂ = 150, n Ａ = 150, αＢ =3) This is the value calculated in step 3). Due to the 3 dB attenuation, the predicted average throughput per user terminal will be about half of the baseline throughput.

[0056] When base station 20C is used as the destination for UE 30A which is connected to base station 20A, the predicted average throughput per connected user terminal at base station 20C is f Ｃ (m Ｃ = 150, n Ａ = 150, α ｃ = 6) This is the value calculated. Due to the effect of 6 dB attenuation, the predicted average throughput per user terminal will be about one-quarter of the baseline throughput.

[0057] Next, the switching destination base station selection device 42 calculates a function f that represents the predicted communication quality per user terminal when all UE30A accommodated by base station 20A are distributed and transferred to base stations 20B and 20C. The switching destination base station selection device 42 determines the distribution ratio of UE30A so that the value of function f is the same for base stations 20B and 20C. Based on the amount of attenuation that occurs at base stations 20B and 20C, 100 UE30A are allocated to base station 20B and 50 UE30A are allocated to base station 20C.

[0058] As described above, when UE30A is distributed between base station 20B and base station 20C, the predicted average throughput per user terminal at base station 20B is f Ｂ (m Ｂ = 150, n Ａ * 2 / 3 = 100, α Ｂ =3) This value is calculated as follows, and specifically, it is about three-quarters of the standard throughput. Similarly, the predicted average throughput per user terminal at base station 20C is also about three-quarters of the standard throughput.

[0059] The switching destination base station selection device 42 compares the maximum value of function f when all UE30A accommodated by base station 20A are transferred to either base station 20B or 20C in one go, with the value of function f when they are transferred in a distributed manner between base station 20B and base station 20C. According to the above calculation results, the value of function f is larger when the UE30A are transferred in a distributed manner between base station 20B and base station 20C than when they are transferred in one go to either base station 20B or base station 20C. Therefore, the switching destination base station selection device 42 selects base station 20B and base station 20C as destinations for the UE30A accommodated by base station 20A, and selects a distribution ratio of 100:50 for the UE30A.

[0060] The selection result by the switching destination base station selection device 42 is notified to HAPS 10D. Upon receiving notification from the switching destination base station selection device 42, HAPS 10D stops transmitting traffic from UE 30A to base station 20A. Then, using feeder link 14B, it transmits two-thirds of the traffic from UE 30A to base station 20B, and using feeder link 14C, it transmits one-third of the traffic from UE 30A to base station 20C. In this way, proactive base station selection is performed in response to changes in weather conditions, which suppresses the decrease in throughput of UE 30A due to the effects of weather conditions and suppresses the decrease in communication capacity of the wireless communication system 100 as a whole.

[0061] 2-5. Flowchart Figure 6 is a flowchart illustrating the traffic transmission route switching control performed in the wireless communication system 100. The first to fourth switching examples described above are the results of traffic transmission route switching control being performed according to this flowchart.

[0062] Step S101 is performed by the communication quality forecasting device 40. The communication quality forecasting device 40 acquires weather condition forecasts for each of the multiple base stations and, based on the acquired forecasts, determines whether or not a deterioration in communication quality is predicted at a certain base station (hereinafter referred to as the target base station). If there are no base stations where a deterioration in communication quality is predicted, the switching control is terminated for the time being.

[0063] If a deterioration in communication quality is predicted at the target base station, the process from step S102 onward is executed by the switching destination base station selection device 42. First, the switching destination base station selection device 42 calculates function f for both the case where the UEs accommodated by the target base station remain within the target base station and the case where all UEs accommodated by the target base station are transferred to other base stations (step S102). Transferring UEs accommodated by the target base station to other base stations includes the case where all UEs accommodated by the target base station are centrally transferred to one station and the case where all UEs accommodated by the target base station are distributed and transferred to multiple stations. In step S102, function f is calculated for both the centralized transfer and the distributed transfer cases.

[0064] In step S103, the switching destination base station selection device 42 determines whether the value of function f is maximized when the UEs accommodated by the target base station are not transferred to other base stations but remain within the target base station. If the value of function f is larger when the UEs are not transferred to other base stations, the switching destination base station selection device 42 chooses not to transfer the UEs accommodated by the target base station to other base stations (step S104). This choice corresponds to the third switching example described above.

[0065] If transferring to another base station results in a larger value for function f, the switching destination base station selection device 42 performs the determination in step S105. In step S105, the switching destination base station selection device 42 determines whether transferring the UEs accommodated by the target base station to one base station results in a larger value for function f than distributing them. If transferring to one base station results in a larger value for function f, the switching destination base station selection device 42 selects to transfer the UEs accommodated by the target base station to one of the other base stations (step S106). This selection corresponds to the first switching example described above.

[0066] If the value of function f is larger when distributed transfer is performed, the switching destination base station selection device 42 selects to distribute the UEs accommodated by the target base station to multiple other base stations (step S107). This selection corresponds to the second and fourth switching examples described above.

[0067] 3. Hardware Configuration Diagram 7 of the Communication Quality Prediction Device and Switching Base Station Selection Device is a block diagram showing the hardware configuration of the communication quality prediction device 40 and the switching base station selection device 42 for performing the above-mentioned traffic transmission route switching control.

[0068] The communication quality prediction device 40 includes a processor 401, a program memory 402, an information memory 404, and a communication interface 405. The communication interface 405 includes an interface for communication with the switching destination base station selection device 42. The number of processors 401, program memories 402, and information memories 404 may each be multiple.

[0069] The processor 401 may be a CPU, RISC, DSP, FPGA, ASIC, PLD, or another processing unit, or a combination of two or more thereof, or it may be a dedicated processor for traffic transmission route switching control according to this embodiment. The processor 401 may also be communicatively coupled to the program memory 402 and the information memory 404, or it may have the program memory 402 and the information memory 404 built-in.

[0070] The program memory 402 stores a plurality of instructions 403 that can be executed by the processor 401. The program composed of these instructions 403 may be stored in a computer-readable non-temporary storage medium or provided via a network. At least some of the instructions 403 are configured to cause the processor 401 to execute the process shown in step S101 in Figure 6. The information memory 404 stores various information for predicting communication quality.

[0071] The switching destination base station selection device 42 comprises a processor 421, a program memory 422, an information memory 424, and a communication interface 425. The communication interface 425 includes an interface for communication with the communication quality prediction device 40 and an interface for communication with the base station or HAPS. The number of processors 421, program memories 422, and information memories 424 may each be multiple.

[0072] The processor 421 may be a CPU, RISC, DSP, FPGA, ASIC, PLD, or another processing unit, or a combination of two or more thereof, or it may be a dedicated processor for traffic transmission route switching control according to this embodiment. The processor 421 may also be communicatively coupled to the program memory 422 and the information memory 424, or it may have the program memory 422 and the information memory 424 built-in.

[0073] The program memory 422 stores a plurality of instructions 423 that can be executed by the processor 421. The program composed of these instructions 423 may be stored in a computer-readable non-temporary storage medium or provided via a network. At least some of the instructions 423 are configured to cause the processor 421 to execute the processes shown in steps S102 to S108 in Figure 6. The information memory 424 stores various information for selecting the switching destination base station.

[0074] The communication quality prediction device 40 and the switching destination base station selection device 42 may be integrated. That is, the communication quality prediction device 40 and the switching destination base station selection device 42 may be implemented in a single piece of hardware by software. Furthermore, as shown in the installation example below, it is also possible to install multiple switching destination base station selection devices 42 in a distributed manner, or to install multiple communication quality prediction devices 40 in a distributed manner. In any case, the communication quality prediction device 40 and the switching destination base station selection device 42 constitute the processing circuit of the wireless communication system 100.

[0075] 4. Installation Examples of Communication Quality Prediction Device and Switching Base Station Selection Device 4-1. First Installation Example Figure 8 shows a first installation example of the communication quality prediction device 40 and the switching base station selection device 42. In the first installation example, both the communication quality prediction device 40 and the switching base station selection device 42 are installed on the ground. The communication quality prediction device 40 and the switching base station selection device 42 are installed independently of each base station 20A, 20B, and 20C, and are connected to each base station 20A, 20B, and 20C by a land communication network. The selection result of the switching base station by the switching base station selection device 42 is notified to HAPS 10A, 10B, and 10C via base stations 20A, 20B, and 20C.

[0076] 4-2. Second Installation Example Figure 9 shows a second installation example of the communication quality prediction device 40 and the switching destination base station selection device 42. In the second installation example, the switching destination base station selection devices 42A, 42B, and 42C are distributed among the base stations 20A, 20B, and 20C. Only one communication quality prediction device 40 is provided and is connected to the switching destination base station selection devices 42A, 42B, and 42C by a land communication network. The switching destination base station selection devices 42A, 42B, and 42C select the switching destination base station while communicating with each other based on the communication quality prediction results obtained from the communication quality prediction device 40.

[0077] As a variation of the second installation example, the communication quality prediction device 40 may also be distributed and arranged for each base station 20A, 20B, and 20C.

[0078] 4-3. Third Installation Example Figure 10 shows a third installation example of the communication quality prediction device 40 and the switching destination base station selection device 42. In the third installation example, the switching destination base station selection devices 42A, 42B, 42C and the communication quality prediction devices 40A, 40B, 40C are distributed and mounted on each of the HAPS 10A, 10B, 10C. The communication quality prediction devices 40A, 40B, 40C predict the communication quality of the corresponding base stations 20A, 20B, 20C based on weather condition forecasts shared among the communication quality prediction devices 40A, 40B, 40C. The communication quality prediction results from the communication quality prediction devices 40A, 40B, 40C are shared among the switching destination base station selection devices 42A, 42B, 42C. Based on the communication quality prediction results, the switching destination base station selection devices 42A, 42B, 42C select the switching destination base station while communicating with each other.

[0079] As a variation of the third installation example, the communication quality prediction device 40 and the switching destination base station selection device 42 may be mounted on one of the HAPS units, and the selection results from the switching destination base station selection device 42 may be shared between the HAPS units via inter-HAPS link communication.

[0080] 5. The above embodiments can be modified in various ways without departing from the gist of this disclosure. That is, where the number of elements, quantities, amounts, ranges, etc., is referred to in the above embodiments, the technology of this disclosure is not limited to the number referred to, unless otherwise explicitly stated or clearly defined in principle. Also, the structures, etc., described in the above embodiments are not necessarily essential to the technology of this disclosure, unless otherwise explicitly stated or clearly defined in principle.

[0081] 10, 10A, 10B, 10C, 10D HAPS (High-Air Radio Relay Station) 12, 12A, 12B, 12C Service Link 14, 14A, 14B, 14C Feeder Link 16AB, 16BC, 16CA HAPS Inter-Link 20, 20A, 20B, 20C Base Station 30, 30A, 30B, 30C User Terminal 40, 40A, 40B, 40C Communication Quality Prediction Device 42, 42A, 42B, 42C Switching Base Station Selection Device 100 Wireless Communication System

Claims

1. A wireless communication system comprising: a plurality of base stations; at least one aerial wireless relay station; and a processing circuit, wherein the processing circuit is configured to obtain a forecast of weather conditions affecting the communication quality between each of the plurality of base stations and the at least one aerial wireless relay station, and, if a deterioration in communication quality is predicted at any of the plurality of base stations based on the forecast of weather conditions, to pre-transfer the destination of user terminals accommodated at the base station where the deterioration in communication quality is predicted to occur to one or more other base stations via the at least one aerial wireless relay station, before the deterioration in communication quality occurs.

2. A wireless communication system according to claim 1, wherein the processing circuit is configured to calculate a predicted value of communication quality per user terminal for a base station where a deterioration in communication quality is predicted, based on the weather forecast; when it is assumed that the user terminals of the base station where a deterioration in communication quality is predicted are moved to one or more other base stations, calculate a predicted value of communication quality per user terminal for one or more other base stations based on the weather forecast; and if the second predicted value calculated for one or more other base stations is greater than the first predicted value calculated for the base station where a deterioration in communication quality is predicted, the destination for user terminals accommodated by the base station where a deterioration in communication quality is predicted is moved to one or more other base stations in advance, before the communication quality deteriorates.

3. A wireless communication system according to claim 2, wherein the processing circuit is configured such that, when moving the destination of user terminals accommodated by a base station where a deterioration in communication quality is predicted to occur to another base station, it selects the base station with the largest predicted value of communication quality per user terminal after the user terminals from the base station where a deterioration in communication quality is predicted to occur to be the other base station.

4. A wireless communication system according to claim 2, wherein the processing circuit is configured such that, when transferring the destination of user terminals accommodated by a base station where a deterioration in communication quality is predicted to occur to a plurality of other base stations, the predicted value of communication quality per user terminal is the same among the plurality of other base stations.

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