Wireless communication system, main lobe direction calculation device, and main lobe direction calculation method

Abstract

To efficiently calculate a main lobe direction in wireless communication performed between a flying object and a terrestrial station.SOLUTION: A wireless communication system according to one embodiment has: a range detection part that detects such a range of azimuth angle of a directional antenna that power transmitted or received by the directional antenna exceeds predetermined power corresponding to a side lobe of the directional antenna, for each of elevation angles of the directional antenna that are sequentially changed; and a calculation part that calculates an elevation angle and an azimuth angle indicating a main lobe direction of the directional antenna on the basis of each range of azimuth angles to the respective elevation angles of the directional antenna which are detected by the range detection part and a known antenna pattern of the directional antenna.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wireless communication system, a main lobe direction calculation device, and a main lobe direction calculation method. [Background technology]

[0002] In recent years, wireless communication systems using flying objects (flying objects) as a medium, such as high altitude platform stations (HAPS) or high altitude pseudo satellites (HAPS: High Altitude Platform Stations or High Altitude Pseudo Satellites) using unmanned aerial vehicles (UAVs), have been considered.

[0003] In this type of wireless communication system, wireless devices such as terminals connect to a terrestrial base station (ground station) via the flying object, and then connect to the network. At this time, the flying object acts as a medium to relay communications between the terminals and the terrestrial base station. In other words, this wireless communication system has the advantage of making it possible to provide communication services even in places where it is difficult to install terrestrial base stations, such as oceans or mountains.

[0004] In addition, in a wireless communication system using a flying object as a medium, it is desirable to set the beam direction from the antenna with high precision.

[0005] For example, in order to measure the antenna pattern of an antenna mounted on a satellite as a flying object in a short time, a method is known in which antenna patterns are measured simultaneously at multiple points and measurement errors are corrected (for example, see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Yoshinori Suzuki and two others, "Short Time Measuring Method of Onboard Antenna Pattern and In-Orbit Test Results of Beam Forming Network on Engineering Test Satellite VIII," IEICE Transactions on Satellite Communications and Its Application Technologies for Supporting a Safe and Secure Society, 2008, Vol. J91-B, No. 12, pp. 1569-1577 Summary of the Invention [Problem to be solved by the invention]

[0007] The direction of the antenna's main beam (main lobe) may deviate from the designed direction in both elevation and azimuth due to errors in the mounting angle of the antenna to the gimbal and errors in the mounting angle of the gimbal to the aircraft.

[0008] In order to set the antenna's main beam with high precision, it is common to control the gimbal that directs the antenna, change the elevation angle and azimuth angle in a predetermined fine angle range, and measure the received power when scanning a specified range.

[0009] However, the above-mentioned method has a problem in that it takes a long time to scan a predetermined range.

[0010] An object of the present invention is to provide a wireless communication system, a main lobe direction calculation device, and a main lobe direction calculation method that can efficiently calculate the direction of a main lobe in wireless communication between an airborne vehicle and a ground station. [Means for solving the problem]

[0011] A wireless communication system according to one aspect of the present invention is a wireless communication system in which a ground station equipped with an omnidirectional antenna and a flying object equipped with a directional antenna whose elevation angle and azimuth angle are changeable and flying object flies on a horizontal circular orbit at a constant distance from the omnidirectional antenna, perform wireless communication with each other, and is characterized by having a range detection unit that detects, for each of the elevation angles of the directional antenna that are sequentially changed, a range of azimuth angles of the directional antenna in which the power transmitted or received by the directional antenna exceeds a predetermined power equivalent to a side lobe of the directional antenna, and a calculation unit that calculates the elevation angle and azimuth angle that indicate the direction of the main lobe of the directional antenna based on each of the azimuth angle ranges for each elevation angle of the directional antenna detected by the range detection unit and a known antenna pattern of the directional antenna.

[0012] Furthermore, a main lobe direction calculation device according to one aspect of the present invention calculates the main lobe direction of a directional antenna with changeable elevation and azimuth angles provided on a flying object that flies on a horizontal circular orbit at a constant distance from an omnidirectional antenna and communicates wirelessly with a ground station equipped with the omnidirectional antenna, and is characterized in that it comprises: a range detection unit that detects, for each of the sequentially changed elevation angles of the directional antenna, a range of azimuth angles of the directional antenna in which the power transmitted or received by the directional antenna exceeds a predetermined power equivalent to a side lobe of the directional antenna; and a calculation unit that calculates the elevation angle and azimuth angle that indicate the direction of the main lobe of the directional antenna based on the ranges of azimuth angles for each of the elevation angles of the directional antenna detected by the range detection unit and a known antenna pattern of the directional antenna.

[0013] Furthermore, a main lobe direction calculation method according to one aspect of the present invention is a method for calculating the main lobe direction of a directional antenna with changeable elevation and azimuth angles provided on a flying object that flies on a horizontal circular orbit at a constant distance from an omnidirectional antenna and communicates wirelessly with a ground station equipped with the omnidirectional antenna, the method comprising the steps of: detecting, for each of the sequentially changed elevation angles of the directional antenna, a range of azimuth angles of the directional antenna in which the power transmitted or received by the directional antenna exceeds a predetermined power equivalent to a side lobe of the directional antenna; and calculating, based on the detected ranges of azimuth angles for each of the elevation angles of the directional antenna and a known antenna pattern of the directional antenna, the elevation angle and azimuth angle indicating the direction of the main lobe of the directional antenna. [Effects of the Invention]

[0014] According to the present invention, it is possible to efficiently calculate the direction of the main lobe in wireless communication between an air vehicle and a ground station. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a wireless communication system according to an embodiment. [Figure 2] (a) is a diagram showing the positional relationship between the radio waves emitted by the flying object and the antenna when the flying object's trajectory is viewed from above, and (b) is a diagram showing the positional relationship between the radio waves emitted by the flying object and the antenna when the flying object's trajectory is viewed from the side. [Figure 3] 10A and 10B are diagrams illustrating an operation of the range detection unit to detect the range of azimuth angles of the directional antenna that exceeds the power corresponding to the side lobes of the directional antenna for each elevation angle of the directional antenna. [Figure 4] 10 is a diagram illustrating an example of the magnitude of the threshold power (threshold Pth) relative to the power of the main lobe and the side lobe. FIG. [Figure 5] 10A and 10B are diagrams illustrating a method in which a calculation unit calculates an elevation angle and an azimuth angle that indicate the direction of a main lobe. [Figure 6] 10 is a flowchart illustrating a method for calculating a main lobe direction using a wireless communication system. [Figure 7] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Figure 8] FIG. 1 is a diagram showing a flying object that communicates wirelessly with a ground station, as viewed from the front. [Figure 9] 1 is a diagram illustrating a method for calculating the direction of a main lobe in wireless communication between an air vehicle and a ground station in a wireless communication system. DETAILED DESCRIPTION OF THE INVENTION

[0016] First, the background that led to the invention will be explained in more detail. Fig. 7 is a diagram showing an example of the configuration of a wireless communication system 1. In the wireless communication system 1, a terminal (or mobile station) 3 is connected to a ground station (terrestrial base station) 4 via an air vehicle (aircraft) 20. The ground station 4 is connected to a network 5 such as the Internet.

[0017] The flying object 20 is, for example, a fixed-wing unmanned aerial vehicle (UAV) or the like, and performs relay communication between the terminal 3 and the ground station 4, and is constantly connected to the network 5 via the ground station 4. The flying object 20 may also communicate with a satellite or the like.

[0018] The flying object 20 is provided with a directional antenna (see FIG. 8) on the bottom of the body, and directs radio waves toward the terminal 3 and the ground station 4, thereby establishing a communication link with each of the terminal 3 and the ground station 4.

[0019] 8 is a diagram showing a front view of the flying object 20 that communicates wirelessly with a ground station 4. The flying object 20 includes, for example, a vertical tail 6, wings 7, and a directional antenna 8, and establishes a communication link with the ground station 4 or the like that is located below the flying object 20 by emitting radio waves from the directional antenna 8 toward the ground station 4 or the like that is located below the flying object 20. The directional antenna 8 is disposed, for example, on the bottom of the flying object 20's fuselage.

[0020] The elevation angle and azimuth angle of the directional antenna 8 can be controlled by, for example, a two-axis gimbal. The directional antenna 8 can measure the elevation angle and azimuth angle from a reference point by an angle measuring device (not shown) attached to the two-axis gimbal, and can transmit information indicating the measured elevation angle and azimuth angle. The elevation angle and azimuth angle of the directional antenna 8 can be controlled by a command signal, which will be described later, or the like.

[0021] The flying object 20 performs relay communication between the terminal 3 and the ground station 4, and therefore needs to remain in an area in the air where it is possible to establish a communication link with each of the terminal 3 and the ground station 4. Therefore, a fixed-wing flying object such as the flying object 20 circles in the air to remain in an area in the air where it is possible to establish a communication link with each of the terminal 3 and the ground station 4.

[0022] FIG. 9 is a diagram schematically showing a method for calculating the direction of a main lobe in wireless communication between the flying object 20 and the ground station 4 in the wireless communication system 1. In FIG.

[0023] The main beam direction of the directional antenna installed on the flying object 20 may deviate from the designed direction in both elevation and azimuth due to an error in the mounting angle of the directional antenna to the gimbal or an error in the mounting angle of the gimbal to the flying object 20.

[0024] In order to calculate with high accuracy the direction of the main lobe in the wireless communication between the flying object 20 and the ground station 4, the gimbal for directing the antenna is controlled to sequentially change the elevation angle and azimuth angle in predetermined small angular increments as shown in Figure 9, and the received power is measured when scanning within a specified range.

[0025] If the direction of the main lobe deviates from the designed direction, the wireless communication system 1 feeds back to the flying object 20 the angle at which the main lobe should be corrected, and corrects the antenna angle of the flying object 20.

[0026] 1 is a diagram illustrating a 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 an air vehicle (flying object) 20 and a main lobe direction calculation device 30.

[0027] Flying object 20 is equipped with a directional antenna (see FIG. 8) on the bottom of the body, and while circling in the sky, directs radio waves toward antennas 41 and 42 connected to main lobe direction calculation device 30, thereby establishing a communication link with main lobe direction calculation device 30. For example, flying object 20 is equipped with directional antenna 8 whose elevation angle and azimuth angle are changeable, and flies on a horizontal circular orbit at a constant distance from antenna 41.

[0028] Antenna 41 is, for example, a rod-shaped antenna (omnidirectional antenna) for a relay line (millimeter wave band), and receives radio waves transmitted through the relay line by main lobe direction calculation device 30. Receiver 51 measures the received power of the radio waves received via antenna 41, and outputs the measured received power to main lobe direction calculation device 30.

[0029] Antenna 42 is, for example, a rod-shaped antenna (omnidirectional antenna) for a 169 MHz band TT&C line, and transmits and receives radio waves of telemetry signals and command signals transmitted and received over the TT&C line by main lobe direction calculation device 30. Receiver 52 acquires the elevation angle and azimuth angle of directional antenna 8 provided on flying object 20 from the radio waves received via antenna 42, and outputs the acquired elevation angle and azimuth angle to main lobe direction calculation device 30.

[0030] 1 is substantially the same as the flying object 20 described with reference to Figures 7 and 8. The main lobe direction calculation device 30 is provided, for example, inside the ground station 4 shown in Figure 7, and is capable of transmitting radio waves to the flying object 20 via a transmitter (not shown) to control each part of the flying object 20.

[0031] 2A and 2B are diagrams showing a schematic representation of the positional relationship between the radio waves transmitted by the flying object 20 and the antennas 41 and 42. Fig. 2A is a diagram showing a schematic representation of the positional relationship between the radio waves transmitted by the flying object 20 and the antennas 41 and 42 when the trajectory of the flying object 20 is viewed from above. Fig. 2B is a diagram showing a schematic representation of the positional relationship between the radio waves transmitted by the flying object 20 and the antennas 41 and 42 when the trajectory of the flying object 20 is viewed from the side.

[0032] The flying object 20 flies on a circular orbit with a radius R, centered on the antenna 41 (and antenna 42). However, the direction of the main lobe of the directional antenna 8 provided on the flying object 20 may deviate from the design value in the azimuth and elevation directions.

[0033] The main lobe direction calculation device 30 (FIG. 1) is provided, for example, inside the ground station 4 as described above, and includes a storage unit 31, a range detection unit 32, a calculation unit 33, and a correction unit .

[0034] The storage unit 31 stores a threshold power value (Pth) 310 and an antenna pattern 312. The threshold power value 310 is determined in advance based on a propagation loss corresponding to a distance determined by the turning radius and altitude of the flying object 20, an antenna gain exceeding the side lobe of the antenna 41, and a transmission output from the directional antenna 8. The antenna pattern 312 is information indicating an antenna pattern including the beam width of the antenna 41, and is determined and set in advance.

[0035] The range detection unit 32 detects the range of azimuth angles of the directional antenna 8 in which the power transmitted or received by the directional antenna 8 exceeds the power corresponding to a predetermined side lobe of the directional antenna 8 for each of the elevation angles of the directional antenna 8 that are sequentially changed, and outputs the range of azimuth angles to the calculation unit 33.

[0036] FIG. 3 is a diagram showing a schematic diagram of the operation of the range detection unit 32 to detect the range of azimuth angles of the directional antenna 8 that exceeds the power corresponding to the side lobes of the directional antenna 8 for each elevation angle of the directional antenna 8.

[0037] With the elevation angle of directional antenna 8 fixed at a certain angle, main lobe direction calculation device 30 acquires received power while scanning directional antenna 8 in the azimuth direction (from start azimuth angle to end azimuth angle). After completing scanning of directional antenna 8 in the azimuth direction (from start azimuth angle to end azimuth angle), main lobe direction calculation device 30 changes the elevation angle by a predetermined width, and further acquires received power while scanning directional antenna 8 in the azimuth direction (from start azimuth angle to end azimuth angle).

[0038] For example, to detect the approximate location of the main lobe, the range detector 32 performs scanning in the azimuth direction while increasing the elevation angle by a predetermined angle dθ until the received power exceeds a threshold power Pth. The angle dθ is set to be equal to or less than half the beam width angle 2Φ from the main lobe gain to the side lobe gain in the antenna pattern.

[0039] 4 is a diagram illustrating the magnitude of the threshold power (threshold Pth) for the power of the main lobe and the side lobe. As shown in FIG. 4, threshold Pth is larger than the side lobe. For example, range detection unit 32 compares the received power with threshold power value 310 (threshold Pth) and detects the range in which the received power exceeds threshold Pth, so that the power of the side lobe is equal to or less than the threshold power, making it possible to detect the range in which only the power due to the main lobe is present.

[0040] The calculation unit 33 (Figure 1) calculates the elevation angle and azimuth angle that indicate the direction of the main lobe of the directional antenna 8 based on each of the azimuth angle ranges for each elevation angle of the directional antenna 8 detected by the range detection unit 32 and the known antenna pattern of the directional antenna 8 (antenna pattern 312).

[0041] 5 is a diagram schematically showing a method for calculating the elevation angle and azimuth angle that indicate the direction of the main lobe by the calculation unit 33. In Fig. 5, the horizontal axis represents the angle in the azimuth angle direction, and the vertical axis represents the angle in the elevation angle direction.

[0042] If the curve (base of the main lobe) plotting the direction in which the gain of the main lobe becomes a predetermined value exceeding the threshold value Pth can be regarded as a perfect circle centered on the direction of the main lobe, the calculation unit 33 sets the elevation angle at which the received power exceeds Pth by scanning to θ1.

[0043] In addition, the calculation unit 33 sets the azimuth angle when the threshold value Pth is exceeded for the first time during scanning at the elevation angle θ1 as ψ1, and the azimuth angle when the threshold value Pth is exceeded for the first time and falls below the threshold value Pth as ψ2.

[0044] Then, the calculation unit 33 calculates the elevation angle, which is the direction of the main lobe, using the following equations (1) and (2), and calculates the azimuth angle using the following equation (3).

[0045]

number

number

number

[0046] If the curve (the base of the main lobe) plotting the direction where a predetermined value exceeds the threshold value Pth is an ellipse or other geometric shape that cannot be regarded as a perfect circle centered on the direction of the main lobe, the calculation unit 33 calculates the direction of the main lobe based on an equation that represents the geometric shape.

[0047] The correction unit 34 corrects the elevation angle and azimuth angle of the directional antenna 8 so that the preset elevation angle and azimuth angle of the directional antenna 8 (for example, the design elevation angle and azimuth angle of the directional antenna 8) match the elevation angle and azimuth angle calculated by the calculation unit 33. For example, the correction unit 34 calculates the difference between the calculated values of the elevation angle and azimuth angle of the directional antenna 8 and the design values, and sets the calculated difference as a correction value. When the correction value is transmitted (feedback) from the main lobe direction calculation device 30 (or the ground station 4) to the flying object 20, the flying object 20 corrects the elevation angle and azimuth angle of the directional antenna 8.

[0048] Next, a method for calculating the main lobe direction using the wireless communication system 10 will be described. Fig. 6 is a flowchart illustrating a method for calculating the main lobe direction using the wireless communication system 10. As shown in Fig. 6, first, the flying object 20 is caused to fly in a circle with a constant radius R around the antenna 41 (S100).

[0049] Next, the main lobe direction calculation device 30 sets the initial value of the elevation angle, the start angle of the azimuth angle, and the end angle of the azimuth angle for scanning the directional antenna 8 of the flying object 20 (S102).

[0050] The main lobe direction calculation device 30 measures the received power P by scanning in the azimuth direction at the set elevation angle (S104).

[0051] The main lobe direction calculation device 30 determines whether the received power P is greater than the threshold value Pth, and if it is greater (S106: Yes), proceeds to processing of S110, otherwise (S106: No), proceeds to processing of S108 (S106).

[0052] The main lobe direction calculation device 30 changes the elevation angle (by the change amount dθ) and returns to the process of S104 (S108).

[0053] Then, the main lobe direction calculation device 30 calculates the elevation angle and azimuth angle indicating the main beam (main lobe) direction based on the azimuth angle when the received power is greater than the threshold Pth, the azimuth angle when the received power subsequently becomes equal to or less than the threshold Pth, the elevation angle at this time, and the known antenna pattern (S110).

[0054] In this way, the wireless communication system 10 detects the range of azimuth angles of the directional antenna 8 in which the power transmitted (or received) by the directional antenna 8 exceeds the power corresponding to a predetermined side lobe of the directional antenna 8 for each of the elevation angles of the directional antenna 8 that are sequentially changed, and calculates the elevation angle and azimuth angle indicating the direction of the main lobe of the directional antenna 8 based on each of the detected azimuth angle ranges for each of the elevation angles of the directional antenna 8 and the known antenna pattern of the directional antenna 8.

[0055] Therefore, the wireless communication system 10 can reduce the number of scans in the elevation and azimuth directions, shorten the scanning time, and efficiently calculate the direction of the main lobe in wireless communication between the flying object 20 and the ground station 4 (main lobe direction calculation device 30).

[0056] Note that each function of the main lobe direction calculation device 30 may be partially or entirely configured by hardware, or may be configured as a program executed by a processor such as a CPU.

[0057] That is, the main lobe direction calculation device 30 can be realized using a computer and a program, and the program can be recorded on a storage medium or provided via a network. [Explanation of symbols]

[0058] 1, 10... wireless communication system, 3... terminal, 4... ground station, 8... directional antenna, 20... flying object (aircraft), 30... main lobe direction calculation device, 31... memory unit, 32... range detection unit, 33... calculation unit, 34... correction unit, 41, 42... antenna, 51, 52... receiver, 310... threshold power value, 312... antenna pattern

Claims

1. A wireless communication system in which a ground station equipped with an omnidirectional antenna and a flying object equipped with a directional antenna whose elevation angle and azimuth angle are changeable and flying on a horizontal circular orbit at a constant distance from the omnidirectional antenna perform wireless communication with each other, a range detection unit that detects, for each of the sequentially changed elevation angles of the directional antenna, a range of azimuth angles of the directional antenna in which power transmitted or received by the directional antenna exceeds a predetermined power corresponding to a side lobe of the directional antenna; a calculation unit that calculates an elevation angle and an azimuth angle that indicate a direction of a main lobe of the directional antenna based on each of the azimuth angle ranges for each elevation angle of the directional antenna detected by the range detection unit and a known antenna pattern of the directional antenna; A wireless communication system comprising:

2. The antenna system further includes a correction unit that corrects the elevation angle and azimuth angle of the directional antenna so that the preset elevation angle and azimuth angle of the directional antenna match the elevation angle and azimuth angle calculated by the calculation unit.

2. The wireless communication system according to claim 1, wherein:

3. A main lobe direction calculation device calculates the main lobe direction of a directional antenna with variable elevation and azimuth angles provided on a flying object that flies on a horizontal circular orbit at a constant distance from a ground station equipped with an omnidirectional antenna and performs wireless communication with the ground station, a range detection unit that detects, for each of the sequentially changed elevation angles of the directional antenna, a range of azimuth angles of the directional antenna in which power transmitted or received by the directional antenna exceeds a predetermined power corresponding to a side lobe of the directional antenna; a calculation unit that calculates an elevation angle and an azimuth angle that indicate a direction of a main lobe of the directional antenna based on each of the azimuth angle ranges for each elevation angle of the directional antenna detected by the range detection unit and a known antenna pattern of the directional antenna; A main lobe direction calculation device comprising:

4. The antenna system further includes a correction unit that corrects the elevation angle and azimuth angle of the directional antenna so that the preset elevation angle and azimuth angle of the directional antenna match the elevation angle and azimuth angle calculated by the calculation unit.

4. The main lobe direction calculation device according to claim 3, wherein:

5. A main lobe direction calculation method for calculating the main lobe direction of a directional antenna with variable elevation and azimuth angles provided on a flying object that flies on a horizontal circular orbit at a constant distance from a ground station equipped with an omnidirectional antenna and performs wireless communication with the ground station, comprising: detecting a range of azimuth angles of the directional antenna in which the power transmitted or received by the directional antenna exceeds a predetermined power corresponding to a side lobe of the directional antenna, for each of the elevation angles of the directional antenna that are sequentially changed; calculating an elevation angle and an azimuth angle indicating the direction of a main lobe of the directional antenna based on each of the detected azimuth angle ranges for each elevation angle of the directional antenna and a known antenna pattern of the directional antenna; A main lobe direction calculation method comprising:

6. The method further includes a step of calculating the difference between the elevation angle and azimuth angle of the directional antenna that are preset and the calculated elevation angle and azimuth angle.

6. The main lobe direction calculation method according to claim 5, wherein:

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