JP7716062B2 - Wireless communication method and radio station - Google Patents

Description

This disclosure relates to technology for wireless communication between a radio station and an air vehicle.

Currently, in order to expand communication areas, wireless communication systems using drones and other flying objects equipped with wireless communication capabilities are being studied (Non-Patent Document 1). By using such wireless communication systems, it will be possible to achieve high-quality wireless communication even in areas where radio waves cannot reach and wireless communication was previously unavailable.

In addition, the use of high-frequency bands such as millimeter waves is accelerating in order to further increase communication speeds. Generally, radio waves in high-frequency bands are more susceptible to attenuation and diffraction than radio waves in lower frequency bands. In other words, radio waves in high-frequency bands have characteristics of greater propagation loss and greater directivity. Therefore, when the distance between radio stations is great or when there are obstacles between them, it becomes difficult to provide high-quality wireless communications. Drones and other flying objects are useful in addressing these issues, and their use makes it possible to provide stable wireless communications.

Beamforming is effective in wireless communications using high-frequency bands, as it can compensate for radio wave attenuation and increase received power. There are two types of beamforming: analog beamforming, which uses analog devices, and digital beamforming, which is based on digital signal processing. Beamforming requires information such as the direction of the other wireless station and propagation channel information. For example, with analog beamforming, to determine the direction of the other wireless station, the station's own beam-stabilizing antenna is used to transmit beams in various directions, and measurement results (such as received power) of the beam in each direction are obtained. Then, based on these measurement results, the optimal beam direction aimed at the other wireless station is determined.

Silvia Sekander, Hina Tabassum, and Ekram Hossain, "Multi-Tier Drone Architecture for 5G/B5G Cellular Networks: Challenges, Trends, and Prospects," IEEE Communications Magazine 56.3 (2018): 104-111.

Let's consider the case where beamforming technology is applied to wireless communications between a wireless station and an aerial vehicle such as a drone. In wireless communications between a wireless station and an aerial vehicle, the vertical heights of the two are different, so beams must be transmitted in three-dimensional space. Therefore, compared to a two-dimensional plane, the beam transmission/measurement process required to determine the appropriate beam direction increases. This results in reduced transmission efficiency. Furthermore, transmitting radio waves in various directions can also cause interference.

One objective of the present disclosure is to provide technology that enables efficient beamforming when conducting wireless communication between a wireless station and an air vehicle.

A first aspect relates to a wireless communication method for performing wireless communication between a wireless station and an air vehicle.
The wireless communication method is
A beamforming process for forming a beam from the wireless station toward the aircraft;
and a communication process for performing communication between the radio station and the air vehicle using the beam.
The beamforming process is
a movement direction acquisition process for acquiring movement direction information indicating the movement direction of the flying object;
and a beam direction determination process for determining the beam direction of the beam within a range of a subspace intersecting with the movement direction of the aircraft based on the movement direction information.

The second aspect relates to a radio station that communicates wirelessly with an air vehicle.
The radio station includes a controller that forms a beam directed from the radio station toward the air vehicle and communicates with the air vehicle using the beam.
The controller further
a movement direction acquisition process for acquiring movement direction information indicating the movement direction of the flying object;
and a beam direction determination process for determining the beam direction of the beam within a range of a subspace intersecting with the movement direction of the aircraft based on the movement direction information.

According to the present disclosure, the direction of movement of the aircraft is taken into consideration when beamforming, which forms a beam from a wireless station toward the aircraft. The beam direction is determined within a subspace that intersects with the direction of movement of the aircraft, rather than from within the entire three-dimensional space. This reduces the processing load and processing time required to determine the beam direction. In other words, beamforming can be performed efficiently.

1 is a conceptual diagram illustrating a wireless communication system according to an embodiment of the present disclosure. FIG. 1 is a conceptual diagram illustrating beamforming according to an embodiment of the present disclosure. FIG. 2 is a block diagram illustrating an example of a functional configuration of a wireless station according to an embodiment of the present disclosure. FIG. 1 is a block diagram illustrating a configuration example of a wireless station according to an embodiment of the present disclosure. FIG. 2 is a block diagram illustrating an example of the functional configuration of an aircraft according to an embodiment of the present disclosure. 1 is a flowchart illustrating processing in a wireless communication system according to an embodiment of the present disclosure. FIG. 2 is a block diagram illustrating an example of a functional configuration related to beamforming processing (step S100) according to an embodiment of the present disclosure. 10 is a flowchart illustrating a beamforming process (step S100) according to an embodiment of the present disclosure. 10 is a timing chart illustrating a beamforming process (step s100) according to an embodiment of the present disclosure. 10 is a flowchart illustrating a beam direction determination process (step S130) according to an embodiment of the present disclosure. FIG. 10 is a block diagram for explaining a first example of a movement direction acquisition process (step S110) according to an embodiment of the present disclosure. FIG. 10 is a block diagram illustrating a second example of the movement direction acquisition process (step S110) according to the embodiment of the present disclosure. FIG. 10 is a block diagram illustrating a third example of the movement direction acquisition process (step S110) according to the embodiment of the present disclosure. FIG. 10 is a conceptual diagram illustrating a third example of the movement direction acquisition process (step S110) according to the embodiment of the present disclosure. FIG. 10 is a conceptual diagram illustrating a third example of the movement direction acquisition process (step S110) according to the embodiment of the present disclosure. FIG. 10 is a block diagram illustrating a fourth example of the movement direction acquisition process (step S110) according to the embodiment of the present disclosure. FIG. 10 is a block diagram illustrating a fifth example of the movement direction acquisition process (step S110) according to the embodiment of the present disclosure.

Embodiments of the present disclosure will be described with reference to the accompanying drawings.

1. Overview Fig. 1 is a conceptual diagram illustrating a wireless communication system 1 according to the present embodiment. The wireless communication system 1 includes a wireless station 10 and an air vehicle 20. The wireless station 10 is located on the ground. Examples of the wireless station 10 include a wireless base station and a wireless terminal. On the other hand, the air vehicle 20 is capable of moving in the air. Examples of the air vehicle 20 include a drone. The air vehicle 20 has a wireless communication function, and wireless communication between the wireless station 10 and the air vehicle 20 is possible. For example, the air vehicle 20 functions as a relay station that relays communication between the wireless stations 10.

In this embodiment, beamforming technology is applied to wireless communication between the wireless station 10 and the air vehicle 20. At least the wireless station 10 performs beamforming and communicates with the air vehicle 20 using beams. However, in the case of wireless communication between the wireless station 10 and the air vehicle 20, the vertical heights of the two are different, so beams must be transmitted in three-dimensional space. Therefore, there is a risk that the processing load for determining an appropriate beam direction will increase compared to the case of a two-dimensional plane. Therefore, the present disclosure proposes technology that reduces the processing load for determining an appropriate beam direction and enables efficient beamforming.

Figure 2 is a conceptual diagram illustrating beamforming according to this embodiment. When wirelessly communicating with an air vehicle 20, the wireless station 10 forms a beam directed toward the air vehicle 20. In this beamforming, the wireless station 10 determines the beam direction DB taking into account the direction of movement DF of the air vehicle 20.

More specifically, the wireless station 10 acquires movement direction information indicating the movement direction DF of the flying object 20. As will be explained in detail later, various methods for acquiring movement direction information are possible. Then, based on the movement direction information, the wireless station 10 determines a beam direction DB within the range of the partial space PS that intersects with the movement direction DF of the flying object 20. The wireless station 10 does not need to search for an appropriate beam direction DB from all of three-dimensional space; it only needs to search for an appropriate beam direction DB within the range of the partial space PS that intersects with the movement direction DF of the flying object 20. For example, the space that exists in the opposite direction to the movement direction DF of the flying object 20 may be excluded from the search range of the beam direction DB. This reduces the processing load and processing time required to determine the beam direction DB.

As such, according to this embodiment, the movement direction DF of the flying object 20 is taken into consideration in beamforming, which forms a beam from the wireless station 10 directed toward the flying object 20. The beam direction DB is determined within the range of the partial space PS that intersects with the movement direction DF of the flying object 20, rather than from all of three-dimensional space. This reduces the processing load and processing time required to determine the beam direction DB. In other words, beamforming can be performed efficiently. Furthermore, because the processing load and processing time required to determine the beam direction DB are reduced, a decrease in transmission efficiency is suppressed. Furthermore, because the search range of the beam direction DB is reduced, interference occurrence is also suppressed.

The wireless communication system 1 according to this embodiment will be described in more detail below.

3 is a block diagram showing an example of the functional configuration of the wireless station 10. The functional configuration particularly shows the functional configuration related to beamforming. The wireless station 10 includes a signal generation unit 11, a transmission unit 12, a beam steering antenna 13, a reception unit 14, a signal analysis unit 15, and a beam direction determination unit 16.

The signal generation unit 11 generates transmission signals to be transmitted by the radio station 10 and outputs the generated transmission signals to the transmission unit 12. The transmission signals also include measurement signals used to determine an appropriate beam direction DB (beam pattern). The transmission unit 12 converts the input transmission signals into radio signals and outputs the radio signals to the beam steering antenna 13. The beam direction determination unit 16 determines the beam direction DB and notifies the beam steering antenna 13 of the beam direction DB. The beam steering antenna 13 sets a beam in accordance with the beam direction DB notified by the beam direction determination unit 16, and transmits the radio signals input from the transmission unit 12 into the air.

The beam-variable antenna 13 also receives radio signals in the air and outputs the received radio signals to the receiver 14. The receiver 14 converts the input radio signals into received signals and outputs the received signals to the signal analyzer 15. The signal analyzer 15 extracts necessary data from the input received signals. The extracted data may be used by the beam direction determiner 16 to determine the beam direction DB.

Figure 4 is a block diagram showing an example configuration of a wireless station 10. The wireless station 10 includes a communication controller 100 that controls wireless communication. The communication controller 100 performs beamforming processing and communicates with the aircraft 20 using beams. The communication controller 100 includes one or more processors 101 (hereinafter simply referred to as "processor 101") and one or more storage devices 102 (hereinafter simply referred to as "storage device 102"). The processor 101 performs various types of information processing. For example, the processor 101 includes a CPU (Central Processing Unit). The storage device 102 stores various types of information required for processing by the processor 101. Examples of the storage device 102 include volatile memory, non-volatile memory, HDD (Hard Disk Drive), SSD (Solid State Drive), etc.

The communication control program 103 is a computer program executed by the processor 101. The functions of the communication controller 100 are realized through cooperation between the processor 101 executing the communication control program 103 and the storage device 102. The communication control program 103 is stored in the storage device 102. The communication control program 103 may also be recorded on a computer-readable recording medium. The communication control program 103 may also be provided to the communication controller 100 via a network.

As another example, the communication controller 100 may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

5 is a block diagram showing an example of the functional configuration of the aircraft 20. This diagram particularly shows the functional configuration related to beamforming. The aircraft 20 includes a notification signal generator 21, a transmitter 22, an antenna 23, a receiver 24, and a signal analyzer 25.

The antenna 23 receives radio signals transmitted from the radio station 10 and outputs the received radio signals to the receiver 24. The receiver 24 converts the input radio signals into received signals and outputs the received signals to the signal analyzer 25. The signal analyzer 25 generates reception result information based on the input received signals. Examples of reception result information include received power, received signal strength, propagation channel information (CSI: Channel State Information), etc. The signal analyzer 25 outputs the reception result information to the notification signal generator 21.

The notification signal generation unit 21 generates a notification signal including reception result information and outputs the notification signal to the transmission unit 22. Note that instead of the CSI itself, compressed CSI or conversion information obtained by singular value decomposition may be used. The transmission unit 22 converts the input notification signal into a radio signal and outputs the radio signal to the antenna 23. The antenna 23 transmits the radio signal input from the transmission unit 22 into the air.

6 is a flowchart showing processing in the wireless communication system 1 according to this embodiment. In step S100, the wireless station 10 (communication controller 100) performs beamforming processing to form a beam directed from the wireless station 10 toward the flying object 20. The beamforming processing includes at least analog beamforming. In step S200, the wireless station 10 (communication controller 100) performs wireless communication with the flying object 20 using the formed beam.

Figure 7 is a block diagram showing an example of the functional configuration related to the beamforming process (step S100). The communication controller 100 includes a moving direction acquisition unit 110, a beam direction candidate setting unit 120, a beam direction determination unit 130, and a beamforming unit 140. The moving direction acquisition unit 110, the beam direction candidate setting unit 120, the beam direction determination unit 130, and the beamforming unit 140 correspond to the beam direction determination unit 16 and the beam variable antenna 13 in Figure 3.

Figures 8 and 9 are a flowchart and a timing chart, respectively, showing the beamforming process (step S100). Below, the beamforming process (step S100) according to this embodiment will be explained with reference to Figures 7 to 9.

3-1. Movement direction acquisition process (step S110)
In step S110, the movement direction acquisition unit 110 acquires movement direction information 210 indicating the movement direction DF of the flying object 20. Various examples of this movement direction acquisition process will be described later. The movement direction acquisition unit 110 outputs the movement direction information 210 to the beam direction candidate setting unit 120.

3-2. Beam direction candidate setting process (step S120)
In step S120, the beam direction candidate setting unit 120 sets at least one beam direction candidate DC. The beam direction candidate DC is a candidate for the beam direction DB. The beam direction candidate setting unit 120 may set multiple beam direction candidates DC.

More specifically, the beam direction candidate setting unit 120 sets a subspace PS (see Figure 2) that intersects with the movement direction DF of the flying object 20 based on the movement direction information 210. The beam direction candidate setting unit 120 then sets at least one beam direction candidate DC within the range of that subspace PS. Note that the settable beam direction candidates DC may be predetermined across the entire space. In that case, the beam direction candidate setting unit 120 may extract only those beam direction candidates DC that exist in the subspace PS from all beam direction candidates DC.

The beam direction candidate setting unit 120 generates beam direction candidate information 220 indicating the set beam direction candidate DC, and outputs the beam direction candidate information 220 to the beam direction determination unit 130.

3-3. Beam direction determination process (step S130)
In step S130, the beam direction determination unit 130 determines an appropriate beam direction DB. Specifically, the beam direction determination unit 130 selects an appropriate beam direction DB from among the beam direction candidates DC indicated in the beam direction candidate information 220. Fig. 10 is a flowchart for explaining the beam direction determination process (step S130).

In step S131, the beam direction determination unit 130 notifies the beam forming unit 140 of each beam direction candidate DC. The beam forming unit 140 forms a beam for each beam direction candidate DC. The communication controller 100 transmits a measurement signal to the aircraft 20 using the beam for each beam direction candidate DC.

In step S132, the air vehicle 20 receives the measurement signal transmitted from the wireless station 10 and generates reception result information indicating the reception result. Examples of reception result information include received power, received signal strength, and propagation channel information (CSI). The air vehicle 20 transmits the reception result information to the wireless station 10, that is, feeds the reception result information back to the wireless station 10. Note that reception result information may be transmitted one by one for each beam direction candidate DC, or reception result information for all beam direction candidate DCs may be transmitted together. The beam direction determination unit 130 of the wireless station 10 acquires the reception result information fed back from the air vehicle 20.

In step S133, the beam direction determination unit 130 selects a beam direction candidate DC whose communication quality satisfies the conditions as the beam direction DB based on the reception result information. For example, the beam direction determination unit 130 selects the one of the multiple beam direction candidate DCs with the highest received power as the beam direction DB. If there is only one beam direction candidate DC, the beam direction determination unit 130 may select that beam direction candidate DC as the beam direction DB if the received power exceeds a predetermined power threshold.

As another example, the beam direction candidate DC with the highest received power may be selected as the beam direction DB, provided that interference with other flying objects 20 that are not the target of beamforming is kept below a predetermined threshold. This makes it possible to reduce interference power with other flying objects. As yet another example, when multiple beam direction DBs are selected, the beam direction with the highest MIMO transmission capacity may be selected.

The beam direction determination unit 130 generates beam direction information 230 that specifies the determined beam direction DB and outputs the beam direction information 230 to the beamforming unit 140.

3-4. Beamforming (Step S140)
The beam forming unit 140 receives the beam direction information 230 and forms a beam in the beam direction DB specified by the beam direction information 230. Wireless communication between the wireless station 10 and the aircraft 20 is performed based on the formed beam.

4. Various Examples of the Movement Direction Acquisition Process Various examples of the movement direction acquisition process (step S110) according to this embodiment will now be described.

4-1. First Example FIG. 11 is a block diagram illustrating a first example of the movement direction acquisition process. In the first example, the movement direction acquisition unit 110 includes a camera 111. The movement direction acquisition unit 110 captures an image of the flying object 20 using the camera 111. The movement direction acquisition unit 110 then acquires the movement direction DF of the flying object 20 based on the image capture result by the camera 111. For example, the movement direction acquisition unit 110 analyzes the image captured by the camera 111 to detect (recognize) the flying object 20. Image analysis techniques such as pattern matching are well known. The movement direction acquisition unit 110 then acquires the movement direction DF of the flying object 20 by tracing the detected position of the flying object 20.

4-2. Second Example FIG. 12 is a block diagram illustrating a second example of the movement direction acquisition process. In the second example, the movement direction acquisition unit 110 includes a ranging sensor 112. Examples of the ranging sensor 112 include LIDAR (Laser Imaging Detection and Ranging), millimeter-wave radar, and the like. The movement direction acquisition unit 110 detects the position of the flying object 20 using the ranging sensor 112. The detected position of the flying object 20 is a relative position with respect to the ranging sensor 112, and is defined by the distance and direction as seen from the ranging sensor 112. The movement direction acquisition unit 110 then acquires the movement direction DF of the flying object 20 by tracing the detected position of the flying object 20.

LIDAR is characterized by its high spatial resolution. However, with LIDAR, measurement accuracy may decrease in bad weather or in backlit environments. When millimeter-wave radar is used, the effects of weather and backlighting are reduced. It is also possible to use both LIDAR and millimeter-wave radar and combine (fuse) the measurement results from both.

It is possible that the ranging sensor 112 may also detect objects other than the flying object 20. The movement direction acquisition unit 110 may perform pattern matching based on the shape of the detected object to distinguish between the flying object 20 and other objects. The movement direction acquisition unit 110 may acquire the movement direction DF of the flying object 20 by combining the camera 111 and the ranging sensor 112.

13 is a block diagram illustrating a third example of the movement direction acquisition process. In the third example, the movement direction acquisition unit 110 includes a transmission/reception device 113. The transmission/reception device 113 transmits a radio signal to another wireless station 10 and receives a radio signal from another wireless station 10. An example of the radio signal is a wireless LAN (Local Area Network) signal.

Figure 14 is a conceptual diagram illustrating an example of a method for estimating the direction of object movement based on a wireless LAN signal. A transmitting device Tx transmits a wireless LAN signal toward a receiving device Rx. Multiple paths exist between the transmitting device Tx and the receiving device Rx. The receiving device Rx receives the wireless LAN signal via each path. The receiving device Rx monitors the features of the wireless LAN signal for each path. Examples of features include received power, received signal strength, and phase. As shown in Figure 14, when an object crosses path A, path B, and path C in that order, the features for path A, path B, and path C change in that order. Therefore, it is possible to estimate the direction of object movement based on the changes over time in the features for each path.

Figure 15 is a conceptual diagram illustrating another example of a method for estimating the direction of object movement based on wireless LAN signals. The transmitting device Tx has multiple antennas. The transmitting device Tx transmits wireless LAN signals from each of the multiple antennas. The receiving device Rx receives the wireless LAN signals transmitted from the multiple antennas. The receiving device Rx monitors the features of the wireless LAN signals for each antenna. Examples of features include received power, received signal strength, and phase. As shown in Figure 15, when an object crosses between the transmitting device Tx and the receiving device Rx, the features for each antenna change sequentially. Therefore, it is possible to estimate the direction of object movement based on the changes over time in the features for each path. The method shown in Figure 15 can also be applied to outdoor environments with little multipath.

The movement direction acquisition unit 110 estimates the movement direction DF of the flying object 20 based on the above method. That is, the movement direction acquisition unit 110 receives wireless signals (e.g., wireless LAN signals) transmitted from other wireless stations 10 via the transmission/reception device 113. The movement direction acquisition unit 110 then estimates the movement direction DF of the flying object 20 based on changes over time in the features of the received wireless signals. As mentioned above, the estimation accuracy is improved by using multiple antennas.

4-4. Fourth Example FIG. 16 is a block diagram illustrating a fourth example of the movement direction acquisition process. In the fourth example, the movement direction acquisition unit 110 includes a communication device 114 that communicates with the flying object 20. The flying object 20 is equipped with a position sensor that detects its own position. An example of the position sensor is a GPS (Global Positioning System) sensor. The flying object 20 transmits flying object position information 200 indicating its own position detected by the position sensor to the wireless station 10. The movement direction acquisition unit 110 acquires the flying object position information 200 from the flying object 20 via the communication device 114. The movement direction acquisition unit 110 then acquires the movement direction DF of the flying object 20 by tracing the position indicated by the flying object position information 200.

4-5. Fifth Example FIG. 17 is a block diagram illustrating a fifth example of the movement direction acquisition process. In the fifth example, the movement direction acquisition unit 110 includes a communication device 115 that communicates with an air vehicle management device 50 external to the wireless station 10. The air vehicle management device (management server) 50 manages the position, movement direction, status, etc. of each air vehicle 20. For example, the air vehicle management device 50 determines the movement direction of each air vehicle 20 using any of the methods described in the first to fourth examples above, and provides movement direction information 210 regarding each air vehicle 20. The movement direction acquisition unit 110 communicates with the air vehicle management device 50 via the communication device 115 and acquires the movement direction information 210 from the air vehicle management device 50.

1...Wireless communication system, 10...Radio station, 11...Signal generation unit, 12...Transmitter, 13...Beam variable antenna, 14...Receiver, 15...Signal analysis unit, 16...Beam direction determination unit, 20...Air vehicle, 21...Notification signal generation unit, 22...Transmitter, 23...Antenna, 24...Receiver, 25...Signal analysis unit, 50...Air vehicle management device, 100...Communication controller, 101...Processor, 102...Storage device, 103...Communication control program, 110...Movement direction acquisition unit, 120...Beam direction candidate setting unit, 130...Beam direction determination unit, 140...Beam forming unit, 200...Air vehicle position information, 210...Movement direction information, 220...Beam direction candidate information, 230...Beam direction information, DB...Beam direction, DF...Movement direction, PS...Subspace

Claims (8)

A wireless communication method for wirelessly communicating between a wireless station and an aircraft, comprising:
a beamforming process for forming a beam from the wireless station toward the aircraft;
a communication process for performing communication between the wireless station and the aircraft using the beam;
The beamforming process includes:
a movement direction acquisition process for acquiring movement direction information indicating a movement direction of the flying object;
a process of setting a partial space by excluding at least a space that exists in the opposite direction to the movement direction as seen from the aircraft from the entire three-dimensional space based on the movement direction information;
a beam direction determination process for determining a beam direction of the beam within the range of the subspace . 2. The wireless communication method according to claim 1,
The movement direction acquisition process includes:
A process of capturing an image of the flying object using a camera;
and a process of acquiring the movement direction of the flying object based on the image capture result by the camera. 2. The wireless communication method according to claim 1,
The movement direction acquisition process includes:
A process of detecting the position of the flying object using a distance measurement sensor;
and acquiring the movement direction of the aircraft based on the detected position of the aircraft. 2. The wireless communication method according to claim 1,
The movement direction acquisition process includes:
a process of receiving, at the wireless station, a wireless signal transmitted from another wireless station;
and estimating the movement direction of the aircraft based on a time change in a feature amount of the received wireless signal. 2. The wireless communication method according to claim 1,
The movement direction acquisition process includes:
A process of acquiring aircraft position information indicating the position of the aircraft detected by the aircraft;
and a process of acquiring the movement direction of the aircraft based on the aircraft position information. 6. A wireless communication method according to claim 1, further comprising:
The beamforming process further includes a process of setting at least one beam direction candidate within the range of the subspace ,
The beam direction determination process includes:
a process of transmitting a measurement signal from the wireless station to the aircraft using the beam of the at least one candidate beam direction;
a process of feeding back reception result information indicating a reception result of the measurement signal from the aircraft to the wireless station;
and selecting, as the beam direction, one of the at least one beam direction candidates that satisfies a communication quality condition based on the reception result information. A radio station that performs radio communication with an aircraft,
a controller that forms a beam from the wireless station directed to the aircraft and communicates with the aircraft using the beam;
The controller further comprises:
a movement direction acquisition process for acquiring movement direction information indicating a movement direction of the flying object;
a process of setting a partial space by excluding at least a space that exists in the opposite direction to the movement direction as seen from the aircraft from the entire three-dimensional space based on the movement direction information;
a beam direction determination process for determining a beam direction of the beam within the subspace . 8. A radio station according to claim 7,
The controller further sets at least one candidate beam direction within the subspace ;
The beam direction determination process includes:
a process of transmitting a measurement signal from the wireless station to the aircraft using the beam of the at least one candidate beam direction;
receiving, from the aircraft, reception result information indicating a reception result of the measurement signal at the aircraft;
and selecting, as the beam direction, one of the at least one beam direction candidates that satisfies a communication quality condition based on the reception result information.