Wireless communication system, wireless communication method, control station, and control program

Abstract

This disclosure relates to a wireless communication system, a wireless communication method, a control station, and a control program, and aims to improve channel capacity without increasing the number of transmitting and receiving antennas. [Solution] The wireless communication system of this disclosure comprises a control station, a radio station equipped with multiple antennas, and a base station that performs MIMO communication with the radio station. The radio station has a function to vary the relative position of the multiple antennas with respect to the base station according to control information. The control station is configured to perform a process of predicting the relationship between the channel capacity formed between the radio station and the base station and the control information, a process of calculating at least one piece of control information that can improve the channel capacity based on the predicted relationship, and a process of notifying the radio station of the calculated control information. The radio station is configured to perform a process of changing its relative position based on the notified control information.

Description

[Technical Field]

[0001] This disclosure relates to a wireless communication system, a wireless communication method, a control station, and a control program. [Background technology]

[0002] MIMO communication is a communication method that uses multiple antennas to perform high-speed and highly reliable wireless communication. When MIMO communication is applied to satellites orbiting in low Earth orbit (LEO), it is known that the channel capacity fluctuates periodically. This fluctuation causes periods of time when the signals used in wireless communication completely interfere with each other.

[0003] To address this issue, Patent Document 1 discloses a technique for appropriately selecting antennas to be used for MIMO communication from among multiple transmitting antennas and multiple receiving antennas. This technique exemplifies the selection of two receiving antennas with high transmission capacity from among four fixed receiving antennas. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2021 / 251379 [Non-patent literature]

[0005] [Non-Patent Document 1] Alexei Gorokhov, Dhananjay A. Gore, and Arogyaswami J. Paulraj,"Receive Antenna Selection for MIMO Spatial Multiplexing: Theory and Algorithms",IEEE Transactions on Signal Processing,Vol.51,No.11,2003,p.2796-2807

[0006] [Non-Patent Document 2] Shahab Sanayei and Aria Nosratinia, "Antenna Selection in MIMO Systems", IEEE Communications magazine, Vol. 42, No. 10, 2004, p. 68-73

[0007] [Non-Patent Document 3] C. Kato, M. Nakadai, D. Goto, H. Shibayama and F. Yamashita, “Channel Capacity Analysis of Satellite MIMO System Depending on the Orbital Altitude," in 37th AIAA International Communication Satellite Systems Conference (ICSSC 2019), Oct. 2019. [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] In the above technology, the larger the number of antennas, the easier it is to obtain excellent communication quality under various situations. On the other hand, when the number of transmitting antennas or receiving antennas cannot be increased due to restrictions on antenna installation, there is a problem that the channel capacity cannot be improved.

[0009] In order to solve the above problems, a first object of the present disclosure is to provide a wireless communication system that can improve the channel capacity without increasing the number of transmitting antennas and receiving antennas.

[0010] Another object of the present disclosure is to provide a wireless communication method that can improve the channel capacity without increasing the number of transmitting antennas and receiving antennas.

[0011] Furthermore, a third objective of this disclosure is to provide a control station that can improve channel capacity without increasing the number of transmitting and receiving antennas.

[0012] Furthermore, a fourth objective of this disclosure is to provide a control program that can improve channel capacity without increasing the number of transmitting and receiving antennas. [Means for solving the problem]

[0013] A first aspect of this disclosure is preferably a wireless communication system comprising a control station, a radio station equipped with multiple antennas, and a base station that performs MIMO communication with the radio station, wherein the radio station has a function to vary the relative position of the multiple antennas with respect to the base station according to control information, the control station is configured to perform a process of predicting the relationship between the channel capacity formed between the radio station and the base station and the control information, a process of calculating at least one piece of control information that can improve the channel capacity based on the predicted relationship, and a process of notifying the radio station of the calculated control information, and the radio station is configured to perform a process of changing the relative position based on the notified control information.

[0014] A second aspect of this disclosure is a wireless communication method implemented by a wireless communication system comprising a control station, a radio station equipped with multiple antennas, and a base station that performs MIMO communication with the radio station, wherein the radio station has a function to vary the relative position of the multiple antennas with respect to the base station in accordance with control information, and preferably comprises predicting the relationship between the channel capacity formed between the radio station and the base station and the control information, calculating at least one piece of control information that can improve the channel capacity based on the predicted relationship, notifying the radio station of the calculated control information, and changing the relative position based on the notified control information.

[0015] A third aspect of this disclosure is a control station in a wireless communication system comprising a control station, a radio station equipped with multiple antennas, and a base station that performs MIMO communication with the radio station, wherein the radio station has a function to vary the relative positions of the multiple antennas with respect to the base station according to control information, and is configured to perform a process of predicting the relationship between the channel capacity formed between the radio station and the base station and the control information, a process of calculating at least one piece of control information that can improve the channel capacity based on the predicted relationship, and a process of notifying the radio station of the calculated control information.

[0016] A fourth aspect of the present disclosure is a control program to be implemented by a control station in a wireless communication system comprising a control station equipped with a processor, a radio station equipped with multiple antennas, and a base station that performs MIMO communication with the radio station, wherein the radio station has a function to vary the relative positions of the multiple antennas with respect to the base station according to control information, and the control program causes the processor to perform a process of predicting the relationship between the channel capacity formed between the radio station and the base station and the control information, a process of calculating at least one piece of control information that can improve the channel capacity based on the predicted relationship, and a process of notifying the radio station of the calculated control information. [Effects of the Invention]

[0017] According to the first to fourth aspects of this disclosure, channel capacity can be improved without increasing the number of transmitting and receiving antennas. [Brief explanation of the drawing]

[0018] [Figure 1] This figure shows an overview of the radio station according to Embodiment 1 of this disclosure. [Figure 2] This is a graph showing the channel capacity related to the first comparative example. [Figure 3] This figure shows an overview of the radio station related to the second comparative example. [Figure 4] This is a graph showing the channel capacity related to the second comparative example. [Figure 5]This is a graph showing the channel capacity according to Embodiment 1 of this disclosure. [Figure 6] This figure shows an example configuration of a wireless communication system according to Embodiment 1 of this disclosure. [Figure 7] This figure shows the hardware configuration of a radio station according to Embodiment 1 of the present disclosure. [Figure 8] This is a flowchart showing the processing performed by the wireless communication system according to Embodiment 1 of this disclosure. [Figure 9] This figure shows a wireless communication system in an embodiment according to Embodiment 1 of the present disclosure. [Figure 10] This diagram shows an overview of the change in posture in the embodiment according to Embodiment 1 of the disclosure. [Figure 11] This figure shows the communication channel model in an embodiment according to Embodiment 1 of the present disclosure. [Figure 12] This graph shows the analysis results of the channel capacity in an embodiment according to Embodiment 1 of this disclosure. [Figure 13] This flowchart shows the processing performed by the wireless communication system according to Embodiment 2 of this disclosure. [Figure 14] This figure shows an example configuration of a wireless communication system according to Embodiment 3 of this disclosure. [Figure 15] This is a flowchart showing the processing performed by the wireless communication system according to Embodiment 3 of this disclosure. [Figure 16] This is a flowchart showing the processing performed by the wireless communication system according to Embodiment 4 of this disclosure. [Figure 17] This is a diagram of the Earth's inertial coordinate system. [Figure 18] This is a diagram showing the orbital coordinate system. [Modes for carrying out the invention]

[0019] Embodiment 1 Figure 1 is a diagram showing an overview of a radio station according to Embodiment 1 of this disclosure. Radio station 2 is equipped with multiple antennas and has a function to vary the relative position of the multiple antennas with respect to the base station according to control information. Note that X, Y, and Z represent a coordinate system fixed to the radio station.

[0020] Radio station 2 is a periodic mobile station that communicates wirelessly with base station 4, which will be described later. Radio station 2 is, for example, a low-energy orbiting satellite that performs MIMO communication. Base station 4 is, for example, a ground base station that performs MIMO communication.

[0021] Radio station 2 is equipped with transmitting antennas 38a and 38b. Radio station 2 rotates itself with respect to an axis of a specific coordinate system. This specific coordinate system is, for example, the orbital coordinate system described later. As a result, radio station 2 can change the relative positions of its multiple antennas with respect to the base station.

[0022] In this embodiment, the relative position of the multiple antennas with respect to the base station is described by the radio station 2 rotating itself, i.e., changing its orientation, but this is not the only way. For example, the radio station 2 may rotate only the multiple antennas while keeping itself fixed with respect to an axis of a specific coordinate system. Even in this case, the radio station 2 can change the relative position of its multiple antennas with respect to the base station. The same applies to other embodiments (embodiments 2 to 4).

[0023] Furthermore, although this embodiment describes a configuration in which the radio station 2 transmits transmission data to the base station 4 and the base station 4 receives the transmission data transmitted from the radio station 2, it is also possible for the base station 4 to transmit transmission data to the radio station 2 and for the radio station 2 to receive the transmission data transmitted from the base station 4. In this case, the multiple antennas provided by the radio station 2 function as receiving antennas, and the multiple antennas provided by the base station 4 function as transmitting antennas. The same applies to the other embodiments (embodiments 2 to 4).

[0024] Let's explain the coordinate system. Figure 17 shows the Earth's inertial coordinate system. Ix, Iy, and Iz are the X, Y, and Z axes of the Earth's inertial coordinate system, respectively. Hereafter, the Earth's inertial coordinate system will be referred to as System I. System I is a coordinate system fixed in inertial space. Inertial space is, for example, space in a state of rest or uniform motion.

[0025] Here, we show an example of System I at Earth 600. In this case, the origin I is the center of mass of Earth 600, 610. The X-axis is the axis in the direction of the vernal equinox, the Z-axis is the rotation axis of Earth 600, and the Y-axis is the axis perpendicular to the X and Z axes. For reference, the equator 620 is shown in the diagram.

[0026] Figure 18 shows the orbital coordinate system. Ox, Oy, and Oz are the X, Y, and Z axes of the orbital coordinate system, respectively. Hereafter, the orbital coordinate system may be referred to as the O system. The O system is a coordinate system that rotates with the orbital motion of the satellite.

[0027] Here, we show an example of the O system for satellite 700. In this case, the origin C is the center of mass of satellite 700. The X-axis is the axis in the direction of satellite 700's motion, the Z-axis is the axis in the direction of Earth 600's center, and the Y-axis is the axis perpendicular to the X and Z axes. Note that in this O system, the X and Z axes change direction with respect to inertial space due to orbital angular velocity.

[0028] In this embodiment, the radio station 2 is an LEO orbiting satellite, and the base station 4 is a ground base station. As described above, the radio station 2 rotates itself with respect to the axis of the orbital coordinate system. As a result, the radio station 2 can optimize the relative positions of the transmitting antennas 38a and 38b with respect to the base station 4.

[0029] Prior to explaining the effects of this disclosure, conventional MIMO communication will be described. Figure 2 is a graph showing the channel capacity for the first comparative example.

[0030] MIMO communication is a communication method that uses multiple antennas to perform high-speed and highly reliable wireless communication. Non-patent document 1 discloses a technique for selecting a subset of receiving antennas based on CSI (Channel State Information) to maximize channel capacity in MIMO communication. This technique enables low-cost optimization of transmission capacity.

[0031] Furthermore, Non-Patent Document 2 discloses a technique for selecting a subset of antennas to be used for wireless communication using the feedbacked CSI.

[0032] Furthermore, Non-Patent Document 3 discloses that when MIMO communication is applied to LEO orbiting satellites, the channel capacity fluctuates periodically. Hereafter, this example will be referred to as the first comparative example. Figure 2 is a graph showing the channel capacity related to the first comparative example, and it shows that the channel capacity in MIMO communication decreases periodically. In this way, due to the effect of periodicity, there are times when the signals used in wireless communication completely interfere with each other. That is, there are times when the channel capacity decreases or the connection becomes unstable.

[0033] To solve this problem, Patent Document 1 discloses a technique for appropriately selecting an antenna to be used for MIMO communication from among a plurality of transmitting antennas and a plurality of receiving antennas. Hereafter, an example using this technique will be referred to as the second comparative example.

[0034] Figure 3 shows an overview of a radio station relating to the second comparative example. Radio station 2000 is a LEO orbiting satellite that performs MIMO communication. In other words, radio station 2000 is a periodic mobile station. Radio station 2000 also communicates wirelessly with a ground base station that performs MIMO communication. Radio station 2000 is equipped with transmitting antennas 38a, 38b, and 38c.

[0035] Radio station 2000 selects two transmitting antennas from among transmitting antennas 38a, 38b, and 38c to be used for MIMO communication. Furthermore, radio station 2000 switches between the two selected transmitting antennas as needed. As a result, radio station 2000 can optimize the relative positions of the two transmitting antennas with respect to the ground base station, thereby optimizing the channel capacity in MIMO communication.

[0036] Figure 4 is a graph showing the channel capacity for the second comparative example. Here, it is shown that the optimized channel capacity does not reach the maximum channel capacity. In other words, the second comparative example does not adequately solve the aforementioned problem.

[0037] The second comparative example explains why it does not adequately solve the aforementioned problems. In the second comparative example, more antennas than the number of signals are required to prevent complete interference between signals used in wireless communication. For example, when applying this technology to MIMO communication which requires two transmitting antennas and two receiving antennas, three or more transmitting antennas or three or more receiving antennas are required. Hereafter, MIMO communication which requires two transmitting antennas and two receiving antennas may be referred to as 2x2 MIMO communication.

[0038] In the second comparative example, increasing the number of antennas used can significantly improve channel capacity. In other words, it is possible to increase channel capacity or shorten the interference period.

[0039] However, in the second comparative example, channel capacity cannot be improved if the number of transmitting antennas cannot be increased. Situations where the number of transmitting antennas cannot be increased include, for example, environments with significant antenna installation constraints. Such environments with significant antenna installation constraints include, for example, satellite-based environments, especially when antennas are mounted on small satellites.

[0040] As described above, the second comparative example presented a challenge in improving channel capacity in environments with significant antenna installation constraints.

[0041] The effects of this disclosure will now be explained. Figure 5 is a graph showing the channel capacity according to Embodiment 1 of this disclosure. Here, it is shown that the optimized channel capacity is close to the maximum channel capacity. In other words, this embodiment sufficiently solves the aforementioned problems.

[0042] The reason why this embodiment is able to sufficiently solve the aforementioned problems will now be explained. In this embodiment, the radio station 2 rotates itself with respect to the axis of the orbital coordinate system. As a result, the radio station 2 can optimize the relative positions of the transmitting antennas 38a and 38b with respect to the base station 4.

[0043] Therefore, radio station 2 can optimize the channel capacity in MIMO communication without increasing the number of transmitting antennas. In other words, radio station 2 can improve the channel capacity without increasing the number of transmitting antennas.

[0044] Furthermore, radio station 2 may simultaneously apply the channel capacity optimization according to this embodiment and the channel capacity optimization according to the second comparative example. For example, if there is a range in which radio station 2, which is an LEO orbiting satellite, cannot rotate itself due to operational limitations, the channel capacity may be improved by switching the selected transmitting antenna.

[0045] Figure 6 shows an example of the configuration of a wireless communication system according to Embodiment 1 of the present disclosure. The wireless communication system 100 is shown in which a control station 6 located on the ground calculates the parameters necessary to control the rotation direction of the radio station 2.

[0046] The wireless communication system 100 includes a control station 6. The control station 6 is an uplink station that transmits parameters necessary to control the rotation direction of the radio station 2. Here, we show a configuration in which the parameters are transmitted directly from the control station 6 to the radio station 2, but it may also be a configuration in which the parameters are transmitted via a relay station, such as a relay satellite.

[0047] The control station 6 has a channel capacity prediction unit 62. The channel capacity prediction unit 62 predicts the channel capacity in MIMO communication. This prediction may be made, for example, by predicting the trend of channel capacity based on the orbital information of the radio station 2. In this case, the orbital information refers to the orbit of the orbiting satellite. Alternatively, this prediction may be made by predicting the channel capacity in real time based on the position information of the radio station 2. Furthermore, the channel capacity prediction unit 62 predicts the relationship between the channel capacity and the control information based on the calculated channel capacity.

[0048] The channel capacity prediction unit 62 transmits the relationship between the predicted channel capacity and the control information to the control information calculation unit 64. Based on the relationship between the received channel capacity and the control information, the control information calculation unit 64 calculates control information for radio station 2 that can improve the channel capacity. The control information calculation unit 64 then notifies radio station 2 of the calculated control information.

[0049] The channel capacity prediction unit 62 also transmits the predicted channel capacity to the communication method selection unit 66. Based on the received channel capacity, the communication method selection unit 66 selects a communication method that can improve the transmission speed. The communication method refers to, for example, the coding rate and the modulation method. The communication method selection unit 66 notifies the radio station 2 of the selected communication method.

[0050] Radio station 2 receives control information and communication method information in the MIMO control unit 32 included in the integrated control system 30. The MIMO control unit 32 records the control information in the control information recording unit 34. The control information recording unit 34 transmits the control information to the attitude control unit 21 included in the attitude control system 20. The attitude control unit 21 changes the attitude of radio station 2 based on the received control information. As a result of this change, radio station 2 itself rotates, which optimizes the relative position of each transmitting antenna with respect to the base station 4.

[0051] The MIMO control unit 32 also records the communication method in the communication method recording unit 36. The communication method recording unit 36 ​​transmits the received communication method to the modulation unit 27 included in the data transmission system 25.

[0052] The modulation unit 27 modulates the transmission data stored in the memory 26 based on the received communication method. The modulation unit 27 transmits the modulated transmission data to the appropriate transmitting antenna. Here, it is assumed that the radio station 2 has N transmitting antennas, namely transmitting antennas 38a to 38n.

[0053] Each transmitting antenna that receives the transmission data transmits the transmission data to base station 4. Base station 4 receives the transmission data via an appropriate receiving antenna. Here, it is assumed that base station 4 has N receiving antennas, namely receiving antennas 42a to 42n.

[0054] Each receiving antenna that receives the transmission data transmits the transmission data to the demodulation unit 44. The demodulation unit 44 demodulates and decodes the received transmission data.

[0055] Figure 7 shows the hardware configuration of the control station according to Embodiment 1 of this disclosure. Each function of the control station 6 may be partially or entirely configured by hardware such as a PLD (Programmable Logic Device) or FPGA (Field Programmable Gate Array), or it may be configured as a program executed by a processor such as a CPU.

[0056] For example, the control station 6 can be implemented using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0057] As shown in Figure 7, the control station 6 has an input unit 608, an output unit 601, a communication unit 602, a CPU 603, a memory 604, and an HDD 605 connected via a bus 606, and functions as a computer. The control station 6 is also configured to input and output data to and from a computer-readable storage medium 607.

[0058] The input unit 608 is, for example, a keyboard and mouse. The output unit 601 is, for example, a display device such as a display.

[0059] The communication unit 602 is, for example, a communication interface that communicates with the radio station 2 to be controlled.

[0060] The CPU 603 controls each component of the control station 6 and performs predetermined processing. The memory 604 and HDD 605 store data, etc.

[0061] The storage medium 607 is capable of storing programs and the like that cause the control station 6 to execute its functions. Note that the architecture of the control station 6 is not limited to the example shown in Figure 7.

[0062] Figure 8 is a flowchart showing the processing performed by the wireless communication system according to Embodiment 1 of this disclosure. Steps 100 to 114 are processes at the control station 6, and steps 116 to 128 are processes at the wireless station 2. Steps 100 to 112 are prior predictions, and steps 120 to 128 are actual MIMO communication.

[0063] First, in step 100, the pre-prediction process begins. Next, in step 101, the time t is set. Here, it is assumed that MIMO communication will be performed during the time period from 1 to T. Next, in step 102, the initial value t=1 is set.

[0064] Next, in step 104, the control station 6 predicts the relationship between channel capacity and control information. Specifically, first the channel capacity prediction unit 62 calculates the channel capacity based on the orbital information. Then, the channel capacity prediction unit 62 predicts the relationship between channel capacity and control information based on the calculated channel capacity.

[0065] Next, in step 106, the control station 6 calculates control information for radio station 2 that can improve the channel capacity based on the relationship between the predicted channel capacity and the control information. Specifically, the control information calculation unit 64 calculates the control angle (φ) as control information that maximizes the channel capacity at time t. X ,φ Y ,φ ZThis calculation is performed, for example, based on the trajectory information of radio station 2. More specifically, this calculation is performed using, for example, the following formulas 1 to 4.

[0066]

number

[0067]

number

[0068]

number

[0069]

number

[0070] However, C is channel capacity, H is channel matrix, γ is received SNR, N is number of transmitting antennas, I N This is the N×N identity matrix. Note that the control angle of radio station 2 is determined by multiple control angles (φ X ,φ Y ,φ Z At least one of the above may be calculated, and the others may be set to predetermined values. The same applies to other embodiments (Embodiments 2 to 4).

[0071] Next, in step 108, the control station 6 selects a communication method that can improve the transmission speed based on the channel capacity trend. Specifically, the communication method selection unit 66 selects the coding rate and modulation method that maximize the transmission speed according to the channel capacity at time t.

[0072] Next, in step 110, check if control station 6 is at t=T. If not, proceed to step 111. If t=T, proceed to step 112.

[0073] In step 111, control station 6 substitutes t+1 for t and returns to step 104. In step 112, the prior prediction is completed and the process proceeds to step 114.

[0074] Next, in step 114, the control station 6 notifies the radio station 2 of the control angle and communication method. Specifically, the control information calculation unit 64 notifies the MIMO control unit 32 of the control angle that maximizes the channel capacity from t=1 to T. Furthermore, the communication method selection unit 66 notifies the MIMO control unit 32 of the coding rate and modulation method that maximizes the transmission speed according to the channel capacity from t=1 to T.

[0075] This notification may also be sent via the stored command line in the uplink.

[0076] Next, in step 116, the radio station 2 records the control angle. Specifically, the control information recording unit 34 records the control angle that maximizes the channel capacity from t=1 to T.

[0077] Also, in parallel with step 116, in step 118, the radio station 2 records the communication method. Specifically, the communication method recording unit 36 ​​records the coding rate and modulation method that maximize the transmission speed according to the channel capacity from t=1 to T.

[0078] Next, in step 120, radio station 2 starts MIMO communication. Let the time at this point be t=1.

[0079] Next, in step 122, the radio station 2 changes its attitude. Specifically, the attitude control unit 21 changes the attitude of the radio station 2 based on the received control angle. As a result of this change, the radio station 2 itself rotates, which allows for the optimization of the relative position of each transmitting antenna with respect to the base station 4.

[0080] Next, in step 124, the radio station 2 modulates the transmission data. Specifically, the modulation unit 27 modulates the transmission data stored in the memory 26 based on the received communication method.

[0081] Next, in step 126, check if radio station 2 is at t=T. If not, proceed to step 127. If t=T, proceed to step 128.

[0082] In step 127, radio station 2 substitutes t+1 for t and returns to step 122. In step 128, MIMO communication is terminated.

[0083] Next, an embodiment of this invention will be described. Figure 9 is a diagram showing a wireless communication system in an embodiment according to Embodiment 1 of this disclosure. The wireless communication system 1000 is a wireless communication system in which a base station located at Earth 600 and a radio station located on satellite 700, which is an orbiting satellite of Earth 600, perform MIMO communication.

[0084] Furthermore, satellite orbit 800 is the orbit of satellite 700. Also, the orbital coordinate system 750 for satellite 700 consists of the X' axis, which is the axis in the direction of the satellite's movement, the Z' axis, which is the axis in the direction of the center of Earth 600, and the Y' axis, which is the axis perpendicular to the X' and Z' axes.

[0085] Figure 10 is a diagram showing an overview of the attitude change in an embodiment according to Embodiment 1 of this disclosure. The upper and lower parts of Figure 10 show the satellite 700 as viewed from the Z-axis direction. In other words, the upper and lower parts of Figure 10 show the satellite 700 as seen from a base station located on Earth 600.

[0086] The upper diagram in Figure 10 shows satellite 700 before its attitude was changed. At this time, the base station can see the transmitting antennas 38a and 38b of satellite 700.

[0087] The lower part of Figure 10 shows satellite 700 after its attitude has been changed. In this example, satellite 700 is controlled at a specific angle φ relative to the Z-axis. Y It rotates itself by that amount. As a result, satellite 700 can optimize the relative positions of the transmitting antennas 38a and 38b with respect to the base station.

[0088] FIG. 11 is a diagram showing a communication path model in an example according to Embodiment 1 of the present disclosure. T1 and T2 are positions of transmission antennas, d T is the distance between the transmission antennas, R1 and R2 are positions of reception antennas, d r is the distance between the reception antennas, r 11 (θ EL ) ~ r 22 (θ EL ) is the distance between the transmission and reception antennas, R E is the radius of the earth, h s is the satellite altitude, θ EL is the elevation angle of the satellite as seen from R1, φ P is the angle formed by the straight line connecting R1 and the center of the earth and the straight line connecting T1 and the center of the earth, φ Y is the control angle which is the control information of the transmission antenna. A method for calculating control information (control angle) using this communication path model will be specifically described.

[0089] First, a calculation formula for the channel capacity is derived. As an example, consider 2×2 MIMO communication using two transmission antennas and two reception antennas each. The channel capacity C 2×2 [bit / s / Hz] in 2×2 MIMO communication is derived as shown in Equation 5.

[0090]

Equation

[0091] However, H is a 2×2 channel matrix, H H is the Hermitian transpose of the channel matrix H, λ1 and λ2 are the eigenvalues of HH H , P T is the total transmission power of all antennas, σ 2 is the average noise power of the base station, and I2 is a 2×2 identity matrix.

[0092] Equation 5 is obtained by adding a term representing the SNR to the formula for deriving the channel capacity. In actual analysis, the G / T of the base station is calculated according to the value of the base station with the lowest G / T. Therefore, the system noise temperature of the base station with the lowest G / T is equal to the average noise power of the base station.

[0093] Furthermore, the channel model for LEO's 2x2 MIMO communication in an LOS environment is represented by equations 6 and 7.

[0094]

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[0095]

number

[0096] However, y is the received signal vector, x is the transmitted signal vector, and n is the additive white Gaussian noise (AWGN), as shown in equations 8-10.

[0097]

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[0098]

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[0099]

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[0100] Also, Γ 11 ~Γ 22 is a coefficient that includes the voltage gain and attenuation in the propagation path. Voltage gain is, for example, the gain of the transmitting and receiving antennas. Attenuation is, for example, free-space loss or atmospheric propagation loss. Furthermore, f is the frequency of the electromagnetic wave and c is the speed of light.

[0101] Here, λ1+λ2 and λ1λ2 can be rearranged as shown in equations 11 and 12.

[0102]

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[0103]

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[0104] Next, channel capacity C 2×2 The control angle φ that maximizes Y Calculate the distance d between the transmitting antennas, with the argument of cos in equation 12 being Ω, as in equation 13. T and control angle φ Y A is a function of P (d T ,φ Y ) and elevation angle θ EL ω(θ) is a function of EL Expressed as a product of ), A P (d T ,φ Y ) and ω(θ EL These are shown by equations 14 and 15, respectively.

[0105]

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[0106]

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[0107]

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[0108] Channel capacity C 2×2 The value is maximized when equation 16 is satisfied, that is, when equation 17 is satisfied.

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[0110]

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[0111] Equation 18 is derived from Equation 17.

[0112]

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[0113] Substitute equations 14 and 15 into equation 18 and rearrange. As a result, the channel capacitance C is obtained. 2×2 The control angle φ that maximizes Y This is shown by equation 19.

[0114]

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[0115] Equation 19 is the elevation angle θ EL It is a function of φ. Therefore, the control angle φ Y It can be seen that it changes depending on the elevation angle.

[0116] Therefore, in the operation of this embodiment, control information corresponding to the elevation angle (control angle φ) is used to satisfy equation 19. Y ) is controlled according to the following. As a result, channel capacitance C 2×2 This enables operation while maintaining a state where the value is maximized.

[0117] Figure 12 is a graph showing an example of the channel capacity analysis results in an embodiment according to Embodiment 1 of this disclosure. Here, the channel capacity C when the operation of this embodiment is applied is shown. 2×2 Characteristics and control angle φ Y The analysis results are shown. For comparison, the results when the operation described in this example was not applied are also shown.

[0118] In the graph, the solid line labeled "Normal" represents the channel capacity when the operation method of this embodiment is not applied. The points marked with "×" indicate the timing when the channel capacity drops to its minimum value. In other words, when the operation method of this embodiment is not applied, there are multiple instances during certain time periods when the channel capacity drops to its minimum value.

[0119] On the other hand, in the graph, the solid line shown as Optimal represents the channel capacity when the operation of this embodiment is applied, and φ Y The dotted line shown as _max represents the control angle φ. Y This is the result of the analysis. In other words, as shown in the graph, by applying the operation of this embodiment, the channel capacity can be maximized at almost all times. That is, as shown in this embodiment, the control angle φ according to the elevation angle Y By controlling posture accordingly, channel capacity can be maximized.

[0120] As described above, according to this embodiment, channel capacity can be improved without increasing the number of transmitting antennas.

[0121] However, this embodiment cannot be applied if there is a range in which the radio station 2 cannot rotate itself due to operational restrictions. In this case, channel capacity may be improved by complementaryly applying a method of switching the selected transmitting antenna.

[0122] Furthermore, although this embodiment shows a configuration using two transmitting antennas and two receiving antennas, it is not limited to this configuration. In other words, this embodiment is applicable to MIMO communication using multiple transmitting and receiving antennas.

[0123] Embodiment 2 Figure 13 is a flowchart showing the processing performed by the wireless communication system according to Embodiment 2 of this disclosure. The processing according to this embodiment differs from Embodiment 1 in that the calculation of control information and communication method is performed in real time. Steps 120 and 101-114 are processes at the control station 6, and steps 116-128 are processes at the wireless station 2.

[0124] In the flowcharts illustrating the processes performed by the wireless communication system from this point forward, explanations for steps that represent the same process may be omitted.

[0125] First, in step 120, radio station 2 initiates MIMO communication. Next, in step 101, the time t is set. From here on, step 102 is the same as described above.

[0126] Next, in step 105, the control station 6 predicts the relationship between channel capacity and control information. Specifically, first, the channel capacity prediction unit 62 calculates the channel capacity based on the real-time location information of the radio station 2. Then, the channel capacity prediction unit 62 predicts the relationship between channel capacity and control information based on the calculated channel capacity. Steps 106 to 108 are the same as described above.

[0127] Next, in step 114, the control station 6 notifies the radio station 2 of the control information and communication method. This notification may also be made via the real-time command line in the uplink. Steps 116 to 126 are as described above.

[0128] In step 127, radio station 2 substitutes t+1 for t and returns to step 105. In step 128, MIMO communication is terminated.

[0129] As described above, according to this embodiment, channel capacity can be improved without increasing the number of transmitting antennas. Furthermore, according to this embodiment, since the process of recording pre-predicted content is unnecessary, the memory capacity can be reduced.

[0130] Embodiment 3 Figure 14 shows an example of the configuration of a wireless communication system according to Embodiment 3 of this disclosure. Wireless communication system 100a differs from wireless communication system 100 according to Embodiment 1 in that the control station 6a is contained within the radio station 2a.

[0131] The radio station 2a includes a control station 6a. The control station 6a has a channel capacity prediction unit 62.

[0132] The channel capacity prediction unit 62 transmits the trend of the relationship between the predicted channel capacity and the control information to the control information calculation unit 64a. Based on the received trend of the relationship between the channel capacity and the control information, the control information calculation unit 64a calculates control information for radio station 2a that can improve the channel capacity. The control information calculation unit 64a records the calculated control information.

[0133] The control information calculation unit 64a transmits the recorded control information to the attitude control unit 21. Based on the received control information, the attitude control unit 21 changes the attitude of the radio station 2a. As a result of this change, the radio station 2a itself rotates, which optimizes the relative position of each transmitting antenna with respect to the base station 4.

[0134] The channel capacity prediction unit 62 also transmits the predicted channel capacity trend to the communication method selection unit 66a. Based on the received channel capacity trend, the communication method selection unit 66a selects a communication method that can improve the transmission speed. The communication method selection unit 66a then records the selected communication method.

[0135] The communication method selection unit 66a transmits the recorded communication method to the modulation unit 27 included in the data transmission system 25. The modulation unit 27 modulates the transmission data stored in the memory 26 based on the received communication method.

[0136] Figure 15 is a flowchart showing the processing performed by the wireless communication system according to Embodiment 3 of this disclosure. All steps shown in Figure 15 are processes performed at the wireless station 2a.

[0137] First, in step 100a, the preliminary prediction is started. Next, in step 101a, the time t is set. Then, in step 102a, t=1 is set as the initial value.

[0138] Next, in step 104a, the radio station 2a predicts the trend in the relationship between channel capacity and control information. Specifically, first, the channel capacity prediction unit 62a calculates the channel capacity based on the orbital information. Then, the channel capacity prediction unit 62 predicts the relationship between channel capacity and control information based on the calculated channel capacity.

[0139] Next, in step 106a, radio station 2a calculates control information for radio station 2a that can improve channel capacity based on the trend of the relationship between channel capacity and control information. Specifically, the control information calculation unit 64a calculates the control angle (φ) as control information that maximizes channel capacity at time t. X ,φ Y ,φ Z Calculate the value. The more specific calculation method is the same as in step 106.

[0140] Next, in step 108a, the radio station 2a selects a communication method that can improve the transmission speed based on the channel capacity trend. Specifically, the communication method selection unit 66a selects the coding rate and modulation method that maximize the transmission speed according to the channel capacity at time t.

[0141] Next, in step 110a, check if radio station 2a is at t=T. If not, proceed to step 111a. If t=T, proceed to step 112a.

[0142] In step 111a, radio station 2a substitutes t+1 for t and returns to step 104a. In step 112a, the prior prediction is completed and the process proceeds to steps 116a and 118a.

[0143] Furthermore, this information regarding the prior prediction may be transmitted via the internal circuit of radio station 2a.

[0144] Next, in step 116a, the radio station 2a records control information. Specifically, the control information calculation unit 64a records control information that maximizes the channel capacity from t=1 to T.

[0145] Also, in parallel with step 116a, in step 118a, the radio station 2a records the communication method. Specifically, the communication method selection unit 66a records the coding rate and modulation method that maximize the transmission speed according to the channel capacity from t=1 to T. Steps 120 to 128 are the same as described above.

[0146] As described above, according to this embodiment, channel capacity can be improved without increasing the number of transmitting antennas. Furthermore, according to this embodiment, there is no need to provide a control station 6a separately from the radio station 2a, thus simplifying the configuration of the wireless communication system.

[0147] Embodiment 4 Figure 16 is a flowchart showing the processing performed by the wireless communication system according to Embodiment 4 of this disclosure. The processing according to this embodiment differs from that of Embodiment 3 in that the calculation of control information and communication method is performed in real time. All steps shown in Figure 16 are processes performed at the wireless station 2a.

[0148] First, in step 120a, radio station 2a initiates MIMO communication. Next, in step 101, the time t is set. From here on, steps 101a to 102a are the same as described above.

[0149] Next, in step 105a, the radio station 2a predicts the relationship between channel capacity and control information. Specifically, first, the channel capacity prediction unit 62 calculates the channel capacity based on the real-time location information of the radio station 2a. Then, the channel capacity prediction unit 62 predicts the relationship between channel capacity and control information based on the calculated channel capacity. From here on, steps 106a to 108a are the same as described above.

[0150] Furthermore, the transmission of control information and information regarding communication methods may be carried out via the internal lines of radio station 2a.

[0151] Next, in step 116a, radio station 2a records control information. Also, in parallel with step 116a, in step 118a, radio station 2 records the communication method.

[0152] Next, in step 122, the radio station 2a changes its attitude. Specifically, the attitude control unit 21 changes the attitude of the radio station 2a based on the received control information. Steps 124 to 128 are the same as described above.

[0153] As described above, according to this embodiment, channel capacity can be improved without increasing the number of transmitting antennas. Furthermore, according to this embodiment, since the process of recording pre-predicted content is unnecessary, memory capacity can be reduced. Moreover, according to this embodiment, since it is not necessary to provide a control station 6a separately from the radio station 2a, the configuration of the wireless communication system can be simplified. [Explanation of symbols]

[0154] 2 Radio stations 2a radio station 4 base station 6 Control Station 6a Control Station 100 Wireless Communication Systems 100a wireless communication system 604 memory 1000 Wireless Communication Systems 2000 Radio Station

Claims

1. Control station and, A radio station equipped with multiple antennas, The radio station is equipped with a base station that communicates with MIMO, The aforementioned radio station has a function to vary the relative position of the multiple antennas with respect to the base station according to control information. The aforementioned control station, A process for predicting the relationship between the channel capacity formed between the radio station and the base station and the control information, A process for calculating at least one piece of control information that can improve the channel capacity based on the predicted relationship, A process to notify the radio station of the calculated control information and It is configured to implement, The aforementioned radio station is configured to perform a process to change the relative position based on the notified control information. Wireless communication system.

2. The aforementioned radio station is a periodic mobile station, The aforementioned base station is a ground base station, The aforementioned prediction is made by predicting the trend of the channel capacity based on the orbital information of the radio station. The wireless communication system according to claim 1.

3. The aforementioned control station, Based on the improved channel capacity, a process is performed to select a communication method that can increase the transmission speed, A process of notifying the radio station of the selected communication method and It is configured to further implement, The aforementioned radio station, Based on the notified communication method, a process is performed to modulate the transmission data, The process of transmitting modulated transmission data and It is configured to further implement The wireless communication system according to claim 1.

4. The aforementioned prediction is made by predicting the channel capacity in real time based on the location information of the radio station. The wireless communication system according to claim 1.

5. The aforementioned notification is made via a relay station. The wireless communication system according to claim 1.

6. Control station and, A radio station equipped with multiple antennas, The aforementioned radio station and a base station that performs MIMO communication A wireless communication method implemented by a wireless communication system comprising: The aforementioned radio station has a function to vary the relative position of the multiple antennas with respect to the base station according to control information. To predict the relationship between the channel capacity formed between the aforementioned radio station and the aforementioned base station and the control information, Based on the predicted relationship, calculate at least one piece of control information that can improve the channel capacity, The calculated control information is notified to the radio station, Based on the control information that has been notified, the relative position is changed. A wireless communication method that includes the following features.

7. A control station in a wireless communication system comprising a control station, a radio station equipped with multiple antennas, and a base station that performs MIMO communication with the radio station, The aforementioned radio station has a function to vary the relative position of the multiple antennas with respect to the base station according to control information. A process for predicting the relationship between the channel capacity formed between the radio station and the base station and the control information, A process for calculating at least one piece of control information that can improve the channel capacity based on the predicted relationship, A process to notify the radio station of the calculated control information and It is configured to implement Control station.

8. A control program to be implemented by a control station in a wireless communication system comprising a control station equipped with a processor, a radio station equipped with multiple antennas, and a base station that performs MIMO communication with the radio station, The aforementioned radio station has a function to vary the relative position of the multiple antennas with respect to the base station according to control information. The aforementioned processor, A process for predicting the relationship between the channel capacity formed between the radio station and the base station and the control information, A process for calculating at least one piece of control information that can improve the channel capacity based on the predicted relationship, A process to notify the radio station of the calculated control information and A control program to implement the desired action.

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