Wide-area cell base station, system, null formation method, and program

Abstract

、Provide a wide-area cell base station that can cover a large number of terrestrial cells with nulls that are fewer than the number of terrestrial cell base stations (terrestrial cells) and can achieve high frequency utilization efficiency. 【Solution means】The wide-area cell base station acquires terrestrial cell-related information regarding at least one of a plurality of terrestrial cell base stations and a plurality of terrestrial cells, and based on the terrestrial cell-related information, determines the directions and number of a plurality of nulls such that the number of formed directional nulls is less than the number of a plurality of terrestrial cell base stations, calculates a weight matrix for performing formation of a plurality of nulls in an actual environment and beam formation for a terminal device connected to a wide-area cell based on the directions and number of the plurality of nulls, and applies the weight matrix to signals transmitted and received between the terminal device connected to the wide-area cell.

Description

Technical Field

[0001] The present disclosure relates to a technique for suppressing interference from a relay communication station mounted on an aerial PF such as a HAPS to a terrestrial cell.

Background Art

[0002] Conventionally, a base station (hereinafter referred to as a "wide-area cell base station") that forms a wide-area cell from a repeater-type or base station device-type relay communication station mounted on a high-altitude platform station (HAPS) (also referred to as a "high-altitude pseudo-satellite") located in the sky, a low Earth orbit (LEO) satellite, a geostationary orbit (GEO) satellite, etc. toward the ground or the sea is known. In an environment where such a wide-area cell base station communicates with a UE (terminal) through a service link (hereinafter referred to as an "aerial system") and a system where an existing terrestrial cell base station communicates with a UE (terminal) through a service link (hereinafter referred to as a "terrestrial system") coexist, when communicating simultaneously using the same frequency band, signals from the relay communication station of the aerial system become interference to the terrestrial system. When this interference from the aerial system occurs, the throughput of the terrestrial system significantly decreases. Similarly, signals from the terrestrial system also become interference to the aerial system. When this interference from the terrestrial system occurs, the throughput of the aerial system decreases.

[0003] Patent Document 1 discloses a technique for suppressing (reducing) interference to the terrestrial system by adjusting the antenna system of a high-altitude HAP (High Altitude Platform) in the sky so as to form a directive beam directed at a null to the terrestrial cell base station based on a map of the eNB (terrestrial cell base station), thereby excluding or avoiding the area covered by the terrestrial cell.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] A wide-area cell base station according to one aspect of the present disclosure is a wide-area cell base station that forms a wide-area cell from a service link antenna of a relay communication station provided on an aircraft or a floating body located in the air toward the ground or the sea. This wide-area cell base station includes a communication unit that communicates on a service link in the same frequency band with a plurality of terrestrial cell base stations that form terrestrial cells overlapping or adjacent to the wide-area cell from antennas arranged on the ground or the sea, an information acquisition unit that acquires terrestrial cell-related information regarding at least one of the plurality of terrestrial cell base stations and the plurality of terrestrial cells, and a null optimization unit that determines the directions and number of the plurality of nulls in the actual environment such that the number of the plurality of directional nulls to be formed is less than the number of the plurality of terrestrial cell base stations based on the terrestrial cell-related information acquired by the information acquisition unit, a weight calculation unit that calculates a weight matrix for performing the formation of the plurality of nulls in the actual environment and beam formation for a terminal device connected to the wide-area cell based on the directions and number of the plurality of nulls determined by the null optimization unit, and a weight control unit that applies the weight matrix calculated by the weight calculation unit to a signal transmitted and received between the wide-area cell base station and a terminal device connected to the wide-area cell.

[0006] In the wide-area cell base station, the information acquisition unit acquires traffic information of the plurality of terrestrial cell base stations, and the null optimization unit estimates a plurality of first channel vectors between the antenna of the wide-area cell base station and the antennas of the plurality of terrestrial cell base stations or the ground surface directly below the antennas or between the antenna of the wide-area cell base station and a plurality of terminal devices connected to the plurality of terrestrial cell base stations based on the traffic information of the plurality of terrestrial cell base stations, calculates the correlation between the plurality of first channel vectors and a plurality of second channel vectors corresponding to candidates for the directions of the plurality of null formations, and may determine the directions and number of the plurality of nulls based on the calculation result of the correlation.

[0007] In the wide-area cell base station, the null optimization unit may determine the directions and numbers of the plurality of nulls based on the calculation result of the correlation and the geographical distribution of the plurality of terminal devices connected to the plurality of terrestrial cell base stations.

[0008] In the wide-area cell base station, the null optimization unit may apply a priority setting weight for setting the priority of the formation of the nulls to the calculation of the correlation, and determine the directions and numbers of the plurality of nulls based on the calculation result of the correlation calculated by applying the priority setting weight.

[0009] In the wide-area cell base station, the priority setting weight may be set according to at least one of the importance of the terrestrial cell base station, the importance of the terminal device, the traffic volume of the terrestrial cell base station, the traffic volume of the terminal device, and the magnitude of the interference amount due to the positional relationship with the terrestrial cell base station or the terminal device.

[0010] In the wide-area cell base station, the null optimization unit may determine the directions and numbers of the plurality of nulls by assuming that the plurality of terminal devices connected to each of the plurality of terrestrial cell base stations are localized at the positions of the terrestrial cell base stations.

[0011] In the wide-area cell base station, the null optimization unit compares the calculated value of the correlation with a preset lower limit value, and selects, as the direction of the nulls to be formed in the actual environment, a combination of candidates for the plurality of null formation directions that satisfies the condition that the total of the calculated values of the correlation is equal to or greater than the lower limit value.

[0012] In the wide-area cell base station, for the propagation paths of the candidates for the plurality of null formation directions, the null optimization unit calculates the interference amount from the wide-area cell base station to the plurality of terrestrial cell base stations or the plurality of terminal devices connected to the plurality of terrestrial cell base stations based on the calculation result of the correlation, the transmission power of the wide-area cell base station, and the propagation loss in the propagation path, and may set the lower limit based on the calculation result of the interference amount.

[0013] In the wide-area cell base station, when the null optimization unit periodically or when a predetermined acquisition timing arrives, it updates the traffic information, re-estimates the plurality of first channel vectors based on the updated traffic information, recalculates the correlation between the plurality of first channel vectors and the plurality of second channel vectors, and may update the directions and numbers of the plurality of nulls based on the calculation result of the correlation.

[0014] In the wide-area cell base station, the null optimization unit uses the plurality of first channel vectors h b To calculate a plurality of eigenvalues λ and eigenvectors ν for the matrix A of the following formula (1) defined by, and using the eigenvectors ν with the elements rearranged in descending order of the eigenvalues λ, convert the plurality of second channel vectors, and based on the plurality of second channel vectors after the conversion, determine the directions and numbers of the plurality of nulls. Note that the right side of formula (1) may be modified in consideration of the geographical distribution of the terminal device or the priority setting weight.

Equation

[0015] In the wide-area cell base station, the null optimization unit may calculate the plurality of eigenvalues and eigenvectors from the plurality of singular values and singular vectors obtained by using singular value decomposition for the matrix defined by using the plurality of first channel vectors.

[0016] In the wide-area cell base station, the null optimization unit compares the plurality of eigenvalues in the correlation matrix after the conversion with a preset threshold value, and among the candidates for the plurality of null formation directions, selects the candidates for the null formation directions that satisfy the condition that the eigenvalue is greater than or equal to the threshold value as the directions of the nulls formed in the actual environment.

[0017] In the wide-area cell base station, the null optimization unit may select the direction of the null to be formed in the actual environment from the plurality of candidate null formation directions based on the ratio of the partial cumulative sum obtained by cumulatively adding the plurality of eigenvalues in the correlation matrix after conversion in descending order of magnitude to the total sum of all the plurality of eigenvalues.

[0018] In the wide-area cell base station, the weight calculation unit may calculate a weight matrix for performing the formation of the plurality of nulls in the actual environment and beam formation for the terminal device connected to the wide-area cell based on the calculation results of the plurality of eigenvectors.

[0019] In the wide-area cell base station, the weight calculation unit determines a plurality of second channel vectors corresponding to the directions of a plurality of (Nn) nulls to be formed in the actual environment based on the plurality of eigenvectors, and transposes the plurality of second channel vectors.

Number

Number

Number

Number

[0020] In the wide-area cell base station, the weight calculation unit uses the plurality of eigenvectors to form a weight portion W for forming a plurality of nulls in the actual environment NF and a weight portion W for forming a beam for the terminal device connected to the wide-area cellBF It may be calculated in two steps, and a weight matrix (W) for forming the plurality of nulls in the actual environment and performing beamforming on the terminal device connected to the wide-area cell may be calculated by the following formula (4).

Equation

[0021] A system according to another aspect of the present disclosure includes any one of the wide-area cell base stations and a plurality of terrestrial cell base stations that form terrestrial cells overlapping or adjacent to the wide-area cell from antennas arranged on the ground or at sea.

[0022] A method according to still another aspect of the present disclosure is a null formation method in a wide-area cell base station that forms a wide-area cell from a service link antenna of a relay communication station provided on an aircraft or a floating body located in the air toward the ground or the sea. This null formation method includes performing communication on a service link in the same frequency band with a plurality of terrestrial cell base stations that form terrestrial cells overlapping or adjacent to the wide-area cell from antennas arranged on the ground or at sea, obtaining terrestrial cell-related information regarding at least one of the plurality of terrestrial cell base stations and the plurality of terrestrial cells, determining the directions and number of the plurality of nulls to be formed based on the terrestrial cell-related information obtained by the information acquisition unit such that the number of the plurality of directional nulls to be formed is less than the number of the plurality of terrestrial cell base stations, calculating a weight matrix for forming the plurality of nulls in the actual environment and performing beamforming on the terminal device connected to the wide-area cell based on the directions and number of the plurality of nulls determined by the null optimization unit, and applying the weight matrix calculated by the weight calculation unit to the signals transmitted and received between the terminal device connected to the wide-area cell.

[0023] A program according to still another aspect of the present disclosure is a program executed by a computer or a processor provided in a wide-area cell base station that forms a wide-area cell from a service link antenna of a relay communication station provided in a flying object or a floating object located in the air toward the ground or the sea. This program includes program code for performing communication of a service link in the same frequency band with a plurality of terrestrial cell base stations that form terrestrial cells overlapping or adjacent to the wide-area cell from an antenna disposed on the ground or the sea, program code for acquiring terrestrial cell-related information regarding at least one of the plurality of terrestrial cell base stations and the plurality of terrestrial cells, program code for determining the directions and the number of the plurality of nulls so that the number of the plurality of formed directional nulls is less than the number of the plurality of terrestrial cell base stations based on the terrestrial cell-related information acquired by the information acquisition unit, program code for calculating a weight matrix for forming the plurality of nulls in an actual environment and performing beamforming on a terminal device connected to the wide-area cell based on the directions and the number of the plurality of nulls determined by the null optimization unit, and program code for applying the weight matrix calculated by the weight calculation unit to a signal transmitted and received between the terminal device connected to the wide-area cell.

[0024] Note that the program for performing communication, information acquisition, determination of the directions and the number of nulls, calculation of the weight matrix, and application of the weight matrix according to the present disclosure may include a learned model used in machine learning.

Brief Description of the Drawings

[0025]

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DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The system according to one embodiment described in this document is an airborne communication relay device (aerial PF) equipped with a relay communication station of a wide-area cell base station (for example, an aerial PF base station) that can form cells toward the ground or the sea and perform wireless communication with a plurality of terminal devices (UEs) located within the cells. The communication system includes an airborne communication relay device (aerial PF) that is a flying object or a floating object equipped with a relay communication station of a wide-area cell base station (for example, an aerial PF base station) that can form cells toward the ground or the sea and perform wireless communication with a plurality of terminal devices (UEs) located within the cells. The transmission method of wireless communication between the plurality of terminal devices (UEs) and the wide-area cell base station may be massive MIMO (Multiple-Input Multiple-Output) that performs multi-layer transmission using an array antenna having a large number of antenna elements described later, or MU-MIMO (Multi-User MIMO) that transmits signals to a plurality of different terminal devices (UEs) at the same time and the same frequency. Further, in the communication system of the present embodiment, when a ground cell (second cell) formed by an existing ground cell base station (ground BS) using the same frequency band is located within or around the aerial PF cell, which is a wide-area cell (first cell), interference from the relay communication station of the aerial PF to the ground cell can be suppressed by forming a null with directivity toward the antenna of the ground cell base station or the ground cell from the relay communication station of the aerial PF. The communication system according to the present embodiment is suitable for realizing a three-dimensional network of a next-generation mobile communication such as the fifth generation that can support simultaneous connection to a large number of terminal devices and low latency.

[0027] In particular, in the system of the present embodiment, the aerial PF acquires information on ground cell base stations (ground BSs) within or around the wide-area cell, and based on that information, determines the direction and number of nulls with directivity toward the antennas of the ground cell base stations or the ground cells from the relay communication station of the aerial PF, so that a large number of ground cells can be covered with fewer nulls than the number of ground cell base stations (ground cells), and high frequency utilization efficiency can be realized.

[0028] FIG. 1 is a schematic configuration diagram showing an example of the overall configuration of a communication system including an aerial PF (aerial staying type communication relay device) according to an embodiment. In FIG. 1, the aerial PF system constituting the communication system of the present embodiment is a high altitude platform station (hereinafter also referred to as "aerial platform (aerial PF)" or "HAPS"), which is an aerial staying type communication relay device (radio relay device) mounted on a flying object or a floating object equipped with a relay communication station. (Also referred to as "high altitude pseudo satellite", "stratosphere platform"). The aerial PF 10 is provided. The aerial PF 10 is located in an airspace at a predetermined altitude and forms a three-dimensional cell (hereinafter also referred to as "aerial PF cell" or "HAPS cell") 100C as a wide area cell (first cell). The aerial PF 10 is a flying object or a floating object (for example, a solar plane, a flying boat, a drone, a balloon) that is controlled to float or fly in an airspace (floating airspace) at a predetermined altitude from the ground or the sea surface by autonomous control or external control, and is equipped with a relay communication station. Note that the aerial PF 10 that can function as an aerial staying type communication relay device may be an artificial satellite such as a low earth orbit (LEO) satellite or a geostationary orbit (GEO) satellite equipped with a relay communication station. Further, the communication system of the present embodiment may include one or more terminal devices that communicate with the aerial PF 10, or may include a gateway station (feeder station) described later.

[0029] The airspace where the aerial PF 10 is located is, for example, an airspace in the stratosphere at an altitude of 11 [km] or more and 50 [km] or less above the ground (or on water such as the sea or a lake). This airspace may be an airspace at an altitude of 15 [km] or more and 25 [km] or less where the weather conditions are relatively stable, and particularly may be an airspace at an altitude of approximately 20 [km].

[0030] Since the altitude of the high-altitude PF10 is lower than that of general artificial satellites and higher than that of ground or sea-based base stations, it can ensure a high line-of-sight rate while having a smaller propagation loss than satellite communication. Due to this feature, it is also possible to provide communication services from the high-altitude PF10 to a terminal device (mobile station) 61, which is a user device such as a cellular mobile terminal on the ground or at sea. By providing communication services from the high-altitude PF10, a large area that has been covered by a large number of ground or sea-based base stations can be covered by a small number of high-altitude PF10s at once, which has the merit of being able to provide low-cost and stable communication services.

[0031] The relay communication station of the high-altitude PF10 forms a high-altitude PF cell 100C that can communicate wirelessly with the UE61 by forming a beam for wireless communication with the user's terminal device (hereinafter referred to as "UE" (user device)) towards the ground (or sea surface). The radius of the service area 100A (also referred to as the "high-altitude PF service area") 100A, which consists of the footprint 100F of this high-altitude PF cell 100C on the ground (or sea), is, for example, several tens [km] to 100 [km].

[0032] In this embodiment, the relay communication station of the high-altitude PF10 may form a plurality of three-dimensional cells (for example, 3 cells or 7 cells) and form a service area 100A consisting of a plurality of footprints of the plurality of three-dimensional cells on the ground (or sea).

[0033] The communication system of this embodiment is in an environment where an aerial PF10 equipped with a relay communication station in the sky that constitutes a wide-area cell base station (hereinafter also referred to as "aerial PF base station" or "HAPS base station") and a low-position ground cell base station (hereinafter referred to as "ground BS") 30 that forms a cell to be suppressed from interference located on the ground or at sea are mixed. In the example of FIG. 1, antennas of a plurality of low-position ground BSs 30 (hereinafter also referred to as "base station antennas") are located inside the aerial PF cell 100C, and inside a service area 100A composed of the footprint 100F of the three-dimensional cell 100C, a cell of the ground BS 30 (hereinafter also referred to as "ground cell") 300C that is smaller than the footprint 100F of the cell 100C is formed.

[0034] The aerial PF base station, which is a wide-area cell base station including the relay communication station mounted on the aerial PF10, and the ground BS (for example, eNodeB, gNodeB) 30 each use the same frequency band for wireless communication of the service link with the UEs 61, 65 present in their respective cells 100C, 300C. The ground BS 30 may have a configuration in which a RRH (remote radio head) having a base station antenna and a BBU (baseband unit) are connected by an optical fiber link. In this case, an RRH having a base station antenna is located at the position of the base station 30 in FIG. 1.

[0035] The relay communication station mounted on the aerial PF10 is, for example, a base station (for example, eNodeB, gNodeB) that communicates wirelessly with a gateway station (also referred to as "feeder station") 70 as a relay station having an antenna 71 facing the sky and connected to the core network of the mobile communication network 80 on the ground (or at sea) side. The relay communication station of the aerial PF10 is connected to the core network of the mobile communication network 80 via a feeder station 70 installed on the ground or at sea. The communication between the aerial PF10 and the feeder station 70 may be performed by wireless communication using radio waves such as microwaves, or may be performed by optical communication using laser light or the like.

[0036] The relay communication station (also referred to as the "wireless relay station") mounted on the upper air PF10 may be a repeater-type relay communication station or a base station device-type relay communication station. The repeater-type relay communication station is combined with the base station device mounted on the feeder station 70 to form a wide-area cell base station. The base station device-type relay communication station functions as a wide-area cell base station.

[0037] The repeater-type relay communication station has, for example, a repeater and a frequency conversion device. The repeater has a low-noise amplifier that amplifies the received signal of the service link received via the service link antenna, a power amplifier that amplifies the transmission signal transmitted via the service link antenna, etc. The frequency conversion device performs conversion between the frequency of the service link and the frequency of the feeder link. The feeder station 70 has, for example, a base station device and a frequency conversion device. The base station device has a baseband processing device that processes the baseband signal of the service link, a communication interface unit for communicating with the core network via the backhaul line, etc. The frequency conversion device performs conversion between the frequency of the service link signal input / output to / from the base station device and the frequency of the feeder link signal.

[0038] The base station device-type relay communication station has, for example, a base station device and a feeder link transceiver. The base station device has a low-noise amplifier that amplifies the received signal of the service link, a power amplifier that amplifies the transmission signal transmitted via the service link antenna, a baseband processing device that processes the baseband signal of the service link, etc. The feeder link transceiver transmits and receives the signals of the backhaul line transmitted and received with the feeder station 70. The feeder station 70 transmits and receives the signals of the backhaul line transmitted and received with the relay communication station in the upper air.

[0039] The airborne PF10 may autonomously control its floating movement (flight) and processing at the relay communication station by executing a control program with a control unit composed of a computer or the like incorporated therein. For example, each of the airborne PF10s may acquire its own current position information (e.g., GPS position information), pre-stored position control information (e.g., flight schedule information), position information of other airborne PF10s located in the vicinity, etc., and autonomously control its floating movement (flight) and processing at the relay communication station based on such information.

[0040] Also, the floating movement (flight) of the airborne PF10 and the processing at the relay communication station may be controllable by a management device (also referred to as a "remote control device") as a management device provided in a communication center or the like of the mobile communication network 80. The management device can be composed of, for example, a computer device such as a PC or a server. In this case, the airborne PF10 is incorporated with a control communication terminal device (e.g., a mobile communication module) so that it can receive control information from the management device and transmit various information such as monitoring information to the management device, and terminal identification information (e.g., IP address, telephone number, etc.) is assigned so that it can be identified by the management device. The MAC address of the communication interface may be used for identifying the control communication terminal device. Also, the airborne PF10 may transmit monitoring information such as information regarding the floating movement (flight) of itself or the surrounding airborne PF10s and the processing at the relay communication station, information regarding the state of the airborne PF10, and observation data acquired by various sensors to a predetermined transmission destination such as the management device. The control information may include the target flight route information of the airborne PF10. The monitoring information may include at least one of the current position of the airborne PF10, flight route history information, airspeed relative to the air, ground speed, and propulsion direction, the wind speed and wind direction of the airflow around the airborne PF10, and the air pressure and air temperature around the airborne PF10.

[0041] FIG. 2 is a perspective view showing an example of the airborne PF10 used in the communication system of the embodiment. The upper-air PF10 in Fig. 2 is a solar plane type HAPS, and includes a main wing part 101 with both longitudinal ends bent upward, and a plurality of motor-driven propellers 103 as propulsion devices of a bus power system at one end edge in the short direction of the main wing part 101. On the upper surface of the main wing part 101, a solar panel (hereinafter referred to as "solar panel") 102 as a solar power generation part having a solar power generation function is provided. Also, at two locations in the longitudinal direction on the lower surface of the main wing part 101, pods 105 as a plurality of equipment accommodation parts for accommodating mission equipment are connected via plate-shaped connecting parts 104. Inside each pod 105, a relay communication station 110 as mission equipment and a battery 106 are accommodated. Also, wheels 107 used at the time of takeoff and landing are provided on the lower surface side of each pod 105. The electric power generated by the solar panel 102 is stored in the battery 106, and the motor of the propeller 103 is rotationally driven by the electric power supplied from the battery 106, and the wireless relay process by the relay communication station 110 is executed.

[0042] Fig. 3 is a side view showing another example of the upper-air PF10 used in the communication system of the embodiment. The upper-air PF10 in Fig. 3 is an unmanned airship type HAPS, and since the payload is large, a large-capacity battery can be mounted. The upper-air PF10 includes an airship main body 201 filled with a gas such as helium gas for floating by buoyancy, a motor-driven propeller 202 as a propulsion device of a bus power system, and an equipment accommodation part 203 for accommodating mission equipment. Inside the equipment accommodation part 203, a relay communication station 110 and a battery 204 are accommodated. The motor of the propeller 202 is rotationally driven by the electric power supplied from the battery 204, and the wireless relay process by the relay communication station 110 is executed. Note that a solar panel having a solar power generation function may be provided on the upper surface of the airship main body 201, and the electric power generated by the solar panel may be stored in the battery 204.

[0043] In the following embodiments, an airborne communication relay device (aerial PF) that wirelessly communicates with the UE61 will be illustrated and described for the case of either the solar plane type HAPS or the unmanned airship type HAPS in FIG. 2. However, the following embodiments can be similarly applied to other airborne communication relay devices (aerial PF) other than HAPS.

[0044] Also, the links FL(F) and FL(R) between the aerial PF10 and the gateway station (hereinafter abbreviated as "GW station") 70 serving as a feeder station are referred to as "feeder links", and the link between the aerial PF10 and the UE61 is referred to as a "service link". In particular, the section between the aerial PF10 and the GW station 70 is referred to as the "radio section of the feeder link". Also, the downlink of the communication from the GW station 70 to the UE61 via the aerial PF10 is referred to as the "forward link" FL(F), and the uplink of the communication from the UE61 to the GW station 70 via the aerial PF10 is also referred to as the "reverse link" FL(R).

[0045] In the communication system of this embodiment, the duplexing method of the uplink and downlink of the wireless communication between the ground BS30 and the UE65 is not limited to a specific method. For example, it may be a time division duplex (TDD) method or a frequency division duplex (FDD) method. Also, the access method of the wireless communication between the ground BS30 and the UE65 is not limited to a specific method. For example, it may be an FDMA (Frequency Division Multiple Access) method, a TDMA (Time Division Multiple Access) method, a CDMA (Code Division Multiple Access) method, or an OFDMA (Orthogonal Frequency Division Multiple Access).

[0046] Similarly, the duplexing method for the uplink and downlink of the wireless communication with the UE 61 via the relay communication station 110 is not limited to a specific method. For example, it may be a time-division duplexing (TDD) method or a frequency-division duplexing (FDD) method. Also, the access method for the wireless communication with the UE 61 via the relay communication station 110 is not limited to a specific method. For example, it may be an FDMA method, a TDMA method, a CDMA method, or an OFDMA.

[0047] In addition, the wireless communication of the service link in this embodiment may have functions such as diversity coding, transmission beamforming, and spatial division multiplexing (SDM), and a massive MIMO transmission method may be used to perform multi-layer transmission using an array antenna having a large number of antenna elements. In particular, in this embodiment, in the downlink communication from the relay communication station in the sky PF10 to a plurality of UEs 61 within the cell, a MU-MIMO technique for transmitting signals to a plurality of different UEs 61 at the same time and the same frequency may be used. By performing MU-MIMO transmission using an array antenna having a large number of antenna elements, appropriate beams can be directed to each UE 61 according to the communication environment of each UE 61, so that the communication quality of the entire cell can be improved. Also, since communication with a plurality of UEs 61 can be performed using the same radio resources (time and frequency resources), the system capacity can be expanded.

[0048] FIG. 4 and FIG. 5 are perspective views showing an example of an array antenna 130 composed of multiple elements that can be used for the MU-MIMO transmission method in the sky PF10 of this embodiment.

[0049] The array antenna 130 in FIG. 4 is a planar array antenna having a flat antenna substrate, and antenna elements 130a such as a large number of patch antennas are two-dimensionally arranged in an axial direction perpendicular to each other along the planar antenna surface of the antenna substrate.

[0050] The array antenna 130 in Fig. 5 has a cylindrical or columnar antenna substrate, and a plurality of antenna elements 130a such as patch antennas are arranged along the axial direction and the circumferential direction of the circumferential side surface as the first antenna surface of the antenna substrate. It is a cylinder-type array antenna. In the array antenna 130 of Fig. 5, as shown in the figure, a plurality of antenna elements 130a such as patch antennas may be arranged in a circular shape along the bottom surface as the second antenna surface. Further, the antenna substrate in Fig. 5 may be a polygonal cylinder-shaped or polygonal column-shaped antenna substrate.

[0051] Note that the shape of the array antenna 130, as well as the number, type, and arrangement of the antenna elements, are not limited to those illustrated in Figs. 4 and 5.

[0052] Fig. 6 is an explanatory diagram showing problems in the case of performing beamforming in the MU-MIMO transmission method using the array antenna 130 of the sky PF10. In the service link SL between the array antenna 130 of the sky PF10 in Fig. 6 and the service area 100A (the footprint 100F of the cell 100C), by using the MU-MIMO transmission method and aiming appropriate high-gain beams 100B(1) to 100B(4) individually at each UE61(1) to 61(4) according to the communication environment of each UE61 to compensate for the long-distance propagation loss and performing beamforming for communication, the communication quality can be improved. In particular, when using the MU-MIMO transmission method for communicating with a plurality of UEs 61 using the same radio resource (for example, the same time-frequency resource block (RB)) in the service link SL, the system capacity can be improved.

[0053] However, in an environment where the overhead PF10 and the ground BSs 30(1) and 30(2) coexist as shown in FIG. 6, when the overhead PF10 and the ground BSs 30(1) and 30(2) communicate with the UEs 61 and 65 camping on each cell using the same frequency band simultaneously, the downlink radio transmission signal transmitted from the overhead PF10 may interfere with the communication of the service link between the ground BSs 30(1) and 30(2) and the UEs 65(1) and 65(2) camping on the ground cells 300C(1) and 300C(2) (hereinafter also referred to as "communication of the ground system"). When such interference from the overhead PF10 occurs, the throughput of the communication between the ground BSs 30(1) and 30(2) and the UE 65 is significantly reduced.

[0054] In the present embodiment, in the overhead PF10, based on the position information of the base station antennas of the ground BSs, beamforming control of the overhead PF cell 100C is performed so that the null of the beam pattern (profile of the spatial distribution of the beam) faces the ground BS (antenna) where the antenna is located within the overhead PF cell 100C. Thereby, a desired signal is transmitted to each of the plurality of UEs 61 camping on the overhead PF cell 100C by multi-beams, and the interference caused by the overhead PF10 to the communication of the ground system is suppressed without causing a significant degradation in communication quality.

[0055] FIG. 7 is an explanatory diagram showing an example of the directional null formed from the overhead PF10 toward the ground BS (antenna) 30. As shown in FIG. 7, when forming the null 100N of the beam pattern from the array antenna 130 of the overhead PF10 toward the ground BS (antenna) 30 located within the overhead PF service area 100A, the interference from the overhead PF10 to the ground cell 300C can be reduced, and the interference caused by the overhead PF10 to the communication of the ground system can be suppressed. However, as shown below, when forming the nulls 100N of the beam pattern from the overhead PF10 toward a plurality of ground BSs (antennas) 30 located in the overhead PF service area 100A, it is desirable to cover the plurality of ground BSs (antennas) 30 with as few nulls 100N as possible.

[0056] FIG. 8 is an explanatory diagram of problems when forming a directional null 100N from the sky PF10 toward antennas of a plurality of ground BSs 30. In FIG. 8, by forming the null 100N from the sky PF10 toward the antennas of the plurality of ground BSs 30, it is possible to reduce interference with all of a plurality of ground cells overlapping or adjacent to the sky PF service area of the sky PF10. However, when forming the null 100N toward all of the antennas of the plurality of BSs 30, while the above interference can be reduced, for example, there are problems as follows: (1) to (4), so it is desirable to cover a plurality of ground BSs (antennas) 30 with fewer nulls.

[0057] (1) It consumes the degrees of freedom of the array antenna 130 in the sky PF10. (2) The beam gain of the beam 100B from the sky PF10 to the sky PF user (UE61) decreases. (3) There may be unnecessary coverage holes in the sky PF service area (sky PF cell, wide area cell) 100A. (4) When the sum of the multiplicity of the sky PF user (UE61) and the number of stations of the ground BS30 is larger than the degrees of freedom of the array antenna 130, it is not possible to form the null 100N for all of the ground BSs 30.

[0058] FIG. 9 is an explanatory diagram showing an example of null optimization for forming a smaller number of directional nulls 100N from the aerial PF 10 than the plurality of terrestrial BSs 30 according to the embodiment. In the present embodiment, in order to realize co-frequency sharing between the aerial PF and the terrestrial system as expected from the viewpoint of effective frequency utilization, by determining the optimal direction (channel vector corresponding to the direction) and the number of nulls formed by the aerial PF 10, when a large number of terrestrial BSs (antennas) 30 are located in the aerial PF service area 100A, as shown in FIG. 9, by protecting a large number of terrestrial BSs 30 with fewer nulls than the terrestrial BSs (antennas) 30, both reduction of interference to the terrestrial BS 30 and high beam gain to the aerial PF user (UE61) are achieved. In the present embodiment, a technique for null optimization is provided that can reduce interference to the terrestrial cell without degrading the coverage area 100A of the aerial PF and improve the frequency utilization efficiency.

[0059] The above optimal null direction also depends on the configuration of the array antenna 130. The null optimization method of the present embodiment can be applied regardless of the array configuration, and characteristics of each array antenna 130 such as the width (null width) in the elevation angle and azimuth angle directions of the nulls 100N formed from the aerial PF 10 are considered.

[0060] In the following description, the case where the aerial PF 10 and the terrestrial BS 30 are each performing DL (downlink) communication with the UE will be mainly described, but the null optimization of the present embodiment can be applied to each of the following multiple combinations A1 to A4 of DL (downlink) communication and UL (uplink) communication. Hereinafter, the UE61 of the user who is located in the aerial PF cell 100C and connected to the aerial PF 10 is also referred to as an "aerial PF user", and the UE65 of the user who is located in the terrestrial cell 300C and connected to the terrestrial BS 30 is also referred to as a "terrestrial BS user".

[0061] A1: The case where the aerial PF 10 performs DL communication and the terrestrial BS 30 performs DL communication (Main interference: interference from the aerial PF to the terrestrial BS user, interference from the terrestrial BS to the aerial PF user) A2: The case where the aerial PF 10 performs UL communication and the terrestrial BS 30 performs UL communication (Main interference: interference from airborne PF users to terrestrial BSs, interference from terrestrial BS users to airborne PFs) A3: When airborne PF10 performs DL communication and terrestrial BS30 performs UL communication (Main interference: interference from airborne PF to terrestrial BS, interference from terrestrial BS users to airborne PF users) A4: When airborne PF10 performs UL communication and terrestrial BS30 performs DL communication (Main interference: interference from terrestrial BS to airborne PF, interference from airborne PF users to terrestrial BS users)

[0062] [Main processing of null optimization] FIG. 10 is a flowchart showing an example of main processing including null optimization in airborne PF10 according to an embodiment. In FIG. 10, the process S110 for optimizing nulls includes an information acquisition process S111, a null optimization process S112, and an application process S113 for the result of null optimization.

[0063] In the information acquisition process S111, airborne PF10 acquires terrestrial cell-related information necessary for null formation by airborne PF10. The terrestrial cell-related information is information regarding a plurality of terrestrial BSs 30, information regarding a plurality of terrestrial cells, or both types of information necessary for null formation.

[0064] In the null optimization process S112, airborne PF10 determines the directions and number of a plurality of directive nulls 100N such that the number of the plurality of directive nulls to be formed is less than the number of the plurality of terrestrial BSs 30 based on the terrestrial cell-related information acquired in the information acquisition process S111. For example, airborne PF10 estimates a first channel vector between airborne PF10 and each of the plurality of terrestrial BSs 30, a first channel vector between airborne PF10 and a plurality of terrestrial BS users (UE65) connected to the plurality of terrestrial cells 300C, or first channel vectors in both directions, and determines vectors having a large correlation with the estimated channel vectors in accordance with the number of nulls (hereinafter also referred to as "null number") to be selected by optimization.

[0065] For example, the airborne PF10 may estimate the plurality of first channel vectors based on the traffic information of the plurality of ground BS30s, calculate the correlation between the plurality of first channel vectors and the plurality of second channel vectors corresponding to the candidates of the plurality of null-forming directions, and determine the directions and numbers of the plurality of nulls to be formed during actual operation in the actual environment based on the calculation results of the correlation.

[0066] Here, the candidates of the plurality of null-forming directions are candidates for the directions of the nulls to be formed during operation in the actual environment. As the candidates of the plurality of null-forming directions, for example, the following C1 to C5 may be set. C1: The directions from the airborne PF10 to each of the antennas of the plurality of ground BS30s C2: The directions from the airborne PF10 to the ground surface directly below each of the antennas of the plurality of ground BS30s C3: The directions from the airborne PF10 to each of the arbitrary points (for example, the cell center point, or the center point of the area where the UEs (ground BS users) 65 are densely present) within the plurality of ground cells 300C C4: The directions from the airborne PF10 to each of the plurality of areas where the plurality of ground BS30s are arranged at a high density within the wide-area cell 100C (airborne PF service area 100A) C5: The directions from the airborne PF10 to each of the plurality of UEs (ground BS users) 65 connected to the plurality of ground cells 300C

[0067] The airborne PF10 may calculate a weight matrix for forming the plurality of nulls 100N during operation in the actual environment and forming the beam 100B for the airborne PF user (UE61) connected to the airborne PF service area (wide-area cell) 100A based on the directions and numbers of the plurality of nulls 100N determined in the null optimization process S112. Further, when the number of the nulls 100N determined in the null optimization process S112 does not satisfy a predetermined condition, the airborne PF10 may determine whether to increase the number of the nulls 100N to be additionally formed.

[0068] In the application process S113 of the null optimization result, the null optimization result obtained in the null optimization process S112 is applied and updated to the setting of the control parameters for null formation during operation in the actual environment and for beam 100B formation for the overhead PF user (UE61).

[0069] In the beamforming control (S120) involving null formation during operation in the actual environment, the overhead PF10 performs null formation and beam 100B formation for the overhead PF user (UE61) using the channel vectors corresponding to the optimized multiple null directions based on the setting of the control parameters to which the null optimization result obtained in the null optimization process S112 is applied.

[0070] [Correlation of Channel Vectors] The channel vectors corresponding to the directions of the optimized multiple nulls 100N may be determined based on the correlation between the aforementioned first channel vector and the second channel vector as follows, for example. Here, in the case of DL communication from the overhead PF10, the first channel vector between the overhead PF10 and the UE (u) 65 connected to the ground BS (b) 30 is

Number

Number

Number

[0071] When the correlation corr between the first channel vector between the overhead PF10 and the UE(u)65 and the second channel vector corresponding to the null n is large, the communication of the UE(u)65 is likely to be protected by the null n, and the interference reduction effect is large.

[0072] When forming a plurality of nulls, a plurality of

Number

Number

[0073] Therefore, when the number of nulls to be formed is Nn, the channel vector corresponding to the direction of the null is determined from the following equation (6). δ on the right side of equation (6) n,n' is the Kronecker delta.

Number

Number

[0074] [Estimation of Channel Vector] The first channel vector h between the overhead PF10 used for the null optimization and the UE(u)65 connected to the ground BS(b)30 b、u can be calculated, for example, based on a model such as free space propagation when the overhead PF10 acquires traffic information from the ground BS30. Here, the traffic information is, for example, the coordinates of the ground BS user (UE65), the statistically processed user distribution, the traffic volume, etc. Also, the relative positional relationship can be calculated from the coordinates and attitude of the overhead PF10 and the coordinates of the ground BS user (UE65), and a model such as free space propagation may be applied.

[0075] [Weight between User Distribution and Ground BS] For the sum of the correlations corr in the following equation (7) included in the aforementioned equation (6), the sum for the ground BS users (UE65) may be replaced with an integral using the geographical distribution (user distribution) of the ground BS users (UE65). [Equation]

[0076] For example, when using the density distribution f b (x, y) of users in a two-dimensional plane, the sum of the correlations corr in the aforementioned equation (6) can be rewritten as in the following equation (8). [Equation]

[0077] Also, for reducing the computational amount, assume that the ground BS users (UE65) located in the ground cell 300C are localized at the coordinates (x b , y b ) of the ground BS 30, and the density distribution f b (x, y) of the above users may be simplified using the following equation (9). δ in equation (9) is the Dirac delta function. [Equation]

[0078] In this case, determine the null direction and number so as to maximize the value of the objective function in equation (10) showing the correlation simplified using the second channel vector h b from the upper air PF10 to the position on the ground surface directly below the antenna of the ground BS (b) 30 (or the position of the antenna). [Equation]

[0079] In the objective function showing the above correlation, for example, as shown in the following weight setting examples 1 and 2, a priority setting weight w reflecting importance may be set based on the traffic volume and interference volume of the terrestrial BS user (UE65) or the terrestrial BS (b) 30.

[0080] Weight setting example 1: In this example, the priority setting weight w reflecting the importance of each user b,u is used to calculate the objective function showing the correlation of the following equation (11).

Equation

[0081] Weight setting example 2: In this example, the priority setting weight w reflecting the importance of each terrestrial BS b is used to calculate the objective function showing the correlation of equation (13) using the user distribution of the following equation (12).

Equation

Equation

[0082] When setting the above priority setting weight, a high priority setting weight may be set to protect the terrestrial BS 30 with a large traffic volume. Also, since the propagation loss is small and the interference is large at the terrestrial BS 30 close to the upper PF10, the value of the priority setting weight may be set high so that a null is likely to be directed to the terrestrial BS 30. Further, the traffic information may be updated according to the time change, and the value of the above priority setting weight may be changed to follow the change in traffic.

[0083] [Determination of the optimal null direction] Regarding the determination of the optimal null direction from the above correlations, for example, an optimal solution can be obtained by calculations similar to principal component analysis as exemplified below. An example in the case of the objective function (10) showing the simplified correlation is shown. However, the user's density distribution or priority setting weights may be considered. It is assumed that the aforementioned first channel vector and second channel vector are normalized as shown in the following equation (14). Here, the first channel vector h b is the channel vector between the array antenna 130 of the over-air PF10 and each of the antennas of the plurality of ground BS30 (or the ground surface directly below the antenna).

Number

[0084] Using the above-normalized first channel vector and second channel vector, the sum part of the correlation of the ground BS30 in the aforementioned equation (10) can be rewritten as shown in the following equation (15).

Number

[0085] Here, the following matrix A is defined using the plurality of first channel vectors h b Calculate a plurality of eigenvalues λ and eigenvectors ν for the above matrix A, and rearrange them in descending order of eigenvalues (λ1 ≧ λ2 ≧ ···) by indexing them in descending order of the eigenvalue λ.

Number

[0086] Using the eigenvector ν that satisfies the above equation (17), a plurality of second channel vectors are determined as shown in the following equation (18).

Number

[0087]

Number

[0088] Based on the multiple second-channel vectors after the transformation of the above formula (18), the optimal solutions in the directions of multiple nulls can be determined. However, the optimal solutions in the directions of multiple nulls (second-channel vectors) are not unique and there exist equivalent transformations. Orthonormal

Number

Number

Number

[0089] From the cyclic property of the trace

Number

Number

Number

Number

Number

[0090] [Method Using Singular Value Decomposition] The above-mentioned eigenvectors may be calculated using singular value decomposition. For example, the following matrix H in equation (22) that combines all the channel vectors h1, h2, ··· between the array antenna 130 of the upper air PF10 and the antennas of a plurality of ground BS30 (or the ground surface directly below the antenna). bs is defined. For the above matrix, it may be multiplied by the square root of the priority setting weight, or the density distribution of users may be considered. [Number]

[0091] For the above matrix H bs By performing singular value decomposition on it, the following equation (23) is obtained. [Number]

[0092] For the matrix H after the above singular value decomposition bs Select the row vectors corresponding to the above N H singular values from the matrix V in n to obtain the second channel vector corresponding to the direction of the above optimal null [Number] and use it as such.

[0093] The square of the singular value corresponds to the above-mentioned eigenvalue according to the following equation (24). [Number]

[0094] [Simulation Results] FIG. 11(a) is an explanatory diagram showing an example of the distribution of a plurality of terrestrial BSs 30 in a wide area cell 100C (upper air PF service area 100A) formed by the upper air PF 10 according to the embodiment. FIG. 11(b) is a diagram showing an example of the result of the above-described correlation simulation (computer simulation) when forming nulls 100N in five directions fewer than the terrestrial BSs 30 in the wide area cell 100C (upper air PF service area 100A) from the upper air PF 10 in FIG. 11(a). As shown in FIG. 11(b), by forming nulls 100N in each of the five areas (areas with high brightness in the figure) where a plurality of terrestrial BSs 30 are arranged and the above-described correlation is high in the upper air PF service area 100A in which the wide area cell 100C is formed, interference from the upper air PF 10 to the terrestrial cell can be reduced, and communication in the terrestrial cell is protected. Moreover, since the number of nulls 100N formed in the wide area cell 100C (upper air PF service area 100A) is smaller than the number of terrestrial BSs 30 arranged in the wide area cell 100C, high frequency utilization efficiency can be realized. Also, in a portion other than the null formation area in the wide area cell 100C (upper air PF service area 100A), deterioration of the beam gain from the upper air PF 10 to the upper air PF user (UE61) can be reduced.

[0095] [Example of Method for Determining Number of Nulls] The number of nulls 100N (null number) formed in the wide area cell 100C (upper air PF service area 100A) may be determined based on the magnitude of the above-described eigenvalue. For example, a threshold value is set in advance, the plurality of eigenvalues in the above-described correlation matrix after conversion are compared with the threshold value, and among the plurality of candidates for the null formation direction, a candidate for the null formation direction that satisfies the condition that the eigenvalue is equal to or greater than the threshold value is selected as the direction of the null formed in the actual environment. Also, based on the ratio of the partial cumulative sum obtained by accumulating the plurality of eigenvalues in the above-described correlation matrix after conversion in descending order of magnitude to the total sum of all the plurality of eigenvalues, the direction of the null formed in the actual environment may be selected from the plurality of candidates for the null formation direction.

[0096] Further, compare the calculated value of the aforementioned correlation with a preset lower limit value, and among the plurality of candidate null formation directions, select a combination of candidate null formation directions that satisfy the condition that the sum of the calculated values of the correlation is equal to or greater than the lower limit value as the direction of the null to be formed in the actual environment. Also, a lower limit may be set for the calculated value of the correlation with respect to the ground BS30 (or UE65), and if the lower limit is not satisfied, the number of nulls may be increased and the direction of the null may be additionally selected.

[0097] Consider the calculated value of the aforementioned correlation, the transmission power of the overhead PF10, and the value of the propagation loss, calculate an estimated value of the interference amount from the overhead PF10 to the ground cell, and based on the estimated value of the interference amount, set a lower limit for comparison with the calculated value of the correlation. For example, for the propagation paths of the plurality of candidate null formation directions, calculate the interference amount from the overhead PF10 to the plurality of ground BS30 or the plurality of UE65 connected to the plurality of ground BS30 based on the calculation result of the correlation, the transmission power of the overhead PF10, and the propagation loss in the propagation path, and based on the calculation result of the interference amount, set the lower limit.

[0098] Also, the overhead PF10 updates the aforementioned traffic information periodically or when a predetermined acquisition timing arrives, re-estimates the plurality of first channel vectors based on the updated traffic information, recalculates the correlation between the plurality of first channel vectors and the plurality of second channel vectors, and based on the calculation result of the correlation, updates the directions and number of the plurality of nulls to be formed in the actual environment.

[0099] [Calculation Method of Beamforming Weight] The overhead PF10 may calculate a beamforming weight matrix W for performing the formation of a plurality of nulls in the actual environment and the formation of the beam 100B for the overhead PF user (UE61) connected to the wide area cell 100C based on the calculation result of the eigenvector.

[0100] For example, the weight matrix W may be calculated using the second channel vector corresponding to the direction of the null to be formed in the actual environment or the remaining eigenvectors not selected as the null direction according to the following calculation methods of B1 and B2.

[0101] B1: Method calculated from the pseudo-inverse matrix of the extended channel matrix In this method, when the channel matrix between the overhead PF10 and the UE (overhead PF user) 61 is H, the extended channel matrix H defined by the following equation (25) ex From the pseudo-inverse matrix of, as shown in the following equation (26), the weight matrix W ex is calculated.

Equation

Equation

[0102] The weight matrix W calculated by the above equation (26) ex Extracts the column vector that directs the beam 100B to the UE (overhead PF user) 61 from, and constitutes the weight matrix W.

[0103] B2: Two-stage weight calculation method In this method, the weight W of the part that performs null formation NF And the weight W of the part that performs beam formation to the UE (overhead PF user) 61 BF Are calculated separately, and as shown in the following equation (27), the weight W NF And the weight W BF Are multiplied together to obtain the weight matrix W.

Equation

[0104] The weight W of the part that performs null formation NF For example, under the condition of the following equation (28) regarding the orthogonality between the channel vector in the direction of the aforementioned null and the weight W NF Is calculated by the following equation (29) obtained under the condition that the right side of the following equation (28) is a zero matrix. Note that the right side of the following equation (28) is a zero matrix.

Equation

[0105] Also, the weight W of the part that performs null formation NF uses the orthogonality of the eigenvector ν of the aforementioned matrix A i and, among the eigenvectors ν of the matrix A i the channel vectors of the nulls to be formed [Number] can be grouped into a matrix with a user multiplicity of the sky PF or more as shown in the following equation (30). Here, N ant is the total number of elements of the array antenna. [Number]

[0106] The weight W of the part that performs beamforming BF can be calculated by any known method. For example, the weight W of the part that performs beamforming BF can be calculated by the method described in the reference (Tashiro et al., IEEE Access, vol. 10, pp. 55675 - 55693, May 2022).

[0107] FIG. 12 is an explanatory diagram showing an example of the overall configuration of a communication system having a ground BS database according to an embodiment. Note that FIG. 12 shows a case where the relay communication station 110 mounted on the sky PF10 is a base station apparatus - type relay communication station having a base station apparatus, but the relay communication station 110 mounted on the sky PF10 may be a repeater - type relay communication station. In this case, base station apparatuses are provided in the relay communication station 110 mounted on the sky PF10 and the ground feeder station (gateway station) 70, etc., and the wide - area cell base station (sky PF base station) includes the repeater - type relay communication station mounted on the sky PF10 and the ground base station apparatus.

[0108] In FIG. 12, the airborne PF10 can notify various information and the like to the ground BS30 via the feeder station (gateway station) 70, the mobile communication network 80, and the backhaul line 81. Also, the airborne PF10 can access the ground base station database 82 via the feeder station (gateway station) 70 and the mobile communication network 80, and obtain ground cell-related information such as information on the ground base station 30 and traffic information. The ground BS30 can access the ground base station database 82 via the mobile communication network 80 and the backhaul line 81 at regular intervals or at a predetermined timing, and update the ground base station database 82 in order to share ground cell-related information such as the traffic information of the ground cell 300C with the airborne PF10.

[0109] The ground cell-related information stored in the ground base station database 82 is information referred to from the airborne PF10, and is, for example, the following information (I2-1) to (I2-3). (I2-1) Station specifications such as the position coordinates, antenna height, transmission power, and cell radius of the ground BS30 (I2-2) Traffic information (I2-1) Geographical distribution of users connected to the ground BS30 (changing according to time)

[0110] [Configuration of Relay Communication Station of Airborne PF] FIG. 13 is a block diagram showing an example of the main configuration of the relay communication station 110 mounted on the airborne PF10 in the communication system of FIG. 12. In FIG. 12, the relay communication station 110 includes an information acquisition unit 1101, a channel estimation unit 1102, a null optimization unit 1103, a weight calculation unit 1104, a weight control unit 1105, and an SL communication unit 1106 that performs communication of a service link via a beam 100B with a UE (airborne PF user) 61. The channel estimation unit 1102 may be included in the null optimization unit 1103.

[0111] The information acquisition unit 1101 accesses the terrestrial base station database 82 via the feeder link FL, and acquires terrestrial cell-related information regarding at least one of the terrestrial cell 300C that overlaps with its own service area 100A (the overhead PF cell 100C) and the terrestrial base station 30 that forms the terrestrial cell 300C. The terrestrial cell-related information may include traffic information of a plurality of terrestrial BSs 30. The information acquisition unit 1101 may further acquire geographical distribution information of terrestrial BS users present in the terrestrial cell 300C.

[0112] Based on the traffic information of a plurality of terrestrial BSs 30, the channel estimation unit 1102 estimates a plurality of first channel vectors between the antenna of the overhead PF 10 and the antennas of the plurality of terrestrial BSs 30 (or the ground surface directly below the antennas) or between the antenna of the overhead PF 10 and a plurality of UEs (terrestrial cell users) 65 connected to the plurality of terrestrial BSs 30.

[0113] The null optimization unit 1103 calculates the correlation between the plurality of first channel vectors and the plurality of second channel vectors corresponding to the candidates for the plurality of null formation directions, and based on the calculation result of the correlation, determines the directions and the number of the plurality of nulls 100N in the actual environment such that the number of the plurality of directional nulls 100N formed for the overhead PF cell 100C is less than the number of the plurality of terrestrial BSs 30.

[0114] Based on the directions and the number of the plurality of nulls 100N determined by the null optimization unit 1103, the weight calculation unit 1104 calculates a weight matrix W for performing the formation of the plurality of nulls 100N in the actual environment and beamforming for the UEs (overhead cell users) 61 connected to the overhead PF cell 100C.

[0115] The weight control unit 1105 applies the weight matrix W calculated by the weight calculation unit 1104 to the signals transmitted and received between the UEs (overhead cell users) 61 connected to the overhead PF cell 100C in the SL communication unit 1106.

[0116] [Configuration of Terrestrial Base Station] FIG. 14 is a block diagram showing an example of the main configuration of a terrestrial cell base station (terrestrial BS) 30 in the communication system of FIG. 12. In FIG. 14, the terrestrial BS 30 includes a traffic information collection unit 3001 and a traffic information transmission unit 3002. The traffic information collection unit 3001 collects traffic information such as the traffic volume of service link communication between the UE (terrestrial cell user) 65 in the terrestrial cell (own cell) 300C. The traffic information includes information such as the position coordinates of the terrestrial BS 30 and the geographical distribution of the UE (terrestrial cell user) 65 in the terrestrial cell (own cell) 300C. The traffic information transmission unit 3002 transmits the traffic information collected by the traffic information collection unit 3001 to the terrestrial base station database 82 via the mobile communication network 80 and the backhaul line 81.

[0117] FIG. 15 is a flowchart showing an example of the main processing in the relay communication station 110 of the aerial PF10 when performing beamforming control involving null formation and service link communication in the communication system according to the embodiment. In FIG. 15, the relay communication station 110 of the aerial PF10 accesses the terrestrial base station database 82 via the feeder link FL, and acquires traffic information regarding the terrestrial BS 30 located around its service area 100A (aerial PF cell 100C) (S201). The traffic information to be acquired includes the coordinates of the terrestrial BS 30, the distribution of terrestrial BS users (UEs) 65, and the like.

[0118] Next, the relay communication station 110 of the aerial PF10 estimates the channel vector (first channel vector) in the direction of the terrestrial BS user (UE) 65 or the terrestrial BS 30 based on the information of the terrestrial BS 30 acquired from the terrestrial base station database 82, using a model or the like (S202).

[0119] Next, the relay communication station 110 of the aerial PF10 calculates the matrix A necessary for correlation calculation from the estimated channel vector and importance, and obtains the eigenvalues and eigenvectors of the matrix A (S203).

[0120] Next, the relay communication station 110 of the aerial PF10 selects an eigenvector with a large eigenvalue and uses it as the channel vector (second channel vector) in the null direction to be applied to the actual environment (S204).

[0121] Next, the relay communication station 110 of the aerial PF10 determines whether the calculated correlation value or eigenvalue of a plurality of channel vectors selected and determined by a preset number of eigenvectors satisfies a predetermined condition (S205). Here, if the condition is not satisfied, the eigenvector with the next largest eigenvalue is selected and added as the channel vector in the null direction to be applied to the actual environment (S206).

[0122] Next, when the selection of a predetermined number of nulls (eigenvectors, channel vectors in the null direction) of the aerial PF10 is completed, the relay communication station 110 calculates a weight matrix W for performing null formation and beam formation using the channel vector in the null direction or the eigenvector not selected in the null direction (S207).

[0123] Next, the relay communication station 110 of the aerial PF10 applies the weight matrix W and communicates with the aerial PF user 61 (S208).

[0124] As described above, according to the embodiment of the present disclosure, when the ground cell 300C formed by the antennas of the ground BS30 using the same frequency band is located within the cell 100C formed from the aerial PF10 toward the ground or the sea, interference to the ground cell 300C (ground BS30) and the ground BS user (UE) 65 connected to the ground BS30 from the aerial PF10 can be suppressed.

[0125] Also, according to the embodiment of the present disclosure, a large number of ground cells can be covered with nulls fewer than the number of ground BSs (ground cells), and high frequency utilization efficiency can be realized.

[0126] The system of the present disclosure can cover a large number of terrestrial cells with nulls that are fewer than the number of terrestrial BSs (terrestrial cells), and can provide a system that achieves high frequency utilization efficiency, thus contributing to the achievement of Goal 9, "Build the infrastructure for industry and innovation," of the Sustainable Development Goals (SDGs).

[0127] In addition, the processing steps described in this specification and the relay communication stations, feeder stations, gateway stations, management devices, monitoring devices, remote control devices, servers, terminal devices (UE: user devices, mobile stations, communication terminals), base stations, and components of base station devices of communication relay devices such as aerial PFs can be implemented by various means. For example, these steps and components may be implemented in hardware, firmware, software, or a combination thereof.

[0128] Regarding hardware implementation, means such as processing units used to realize the above steps and components in an entity (for example, a relay communication station, feeder station, gateway station, base station, base station device, relay communication station device, terminal device (UE: user device, mobile station, communication terminal), management device, monitoring device, remote control device, server, hard disk drive device, or optical disk drive device) may be implemented in one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, electronic devices, other electronic units designed to execute the functions described in this specification, computers, or a combination thereof.

[0129] Also, for firmware and / or software implementations, means such as a processing unit used to implement the above components may be implemented by a program (e.g., code such as a procedure, function, module, instruction, etc.) that executes the functions described herein. Generally, any computer / processor-readable medium that clearly embodies the firmware and / or software code may be used for implementing means such as a processing unit used to implement the above steps and components described herein. For example, the firmware and / or software code may be stored in a memory, for example, in a control device, and executed by a computer or a processor. The memory may be implemented inside the computer or the processor, or may be implemented outside the processor. Also, the firmware and / or software code may be stored in a computer- or processor-readable medium such as, for example, random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), programmable read-only memory (PROM), electrically erasable PROM (EEPROM), flash memory, floppy (registered trademark) disk, compact disk (CD), digital versatile disk (DVD), magnetic or optical data storage device, etc. The code may be executed by one or more computers or processors, and may also cause the computer or the processor to execute the functional aspects described herein.

[0130] Also, the medium may be a non-transitory recording medium. Also, the code of the program only needs to be loadable and executable by a computer, a processor, or other device or apparatus machine, and its format is not limited to a specific format. For example, the code of the program may be any of source code, object code, and binary code, or a mixture of two or more of these codes.

[0131] Also, the description of the embodiments disclosed in this specification is provided to enable those skilled in the art to manufacture or use the present disclosure. Various modifications to the present disclosure will be readily apparent to those skilled in the art, and the general principles defined herein are applicable to other variations without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure should not be limited to the examples and designs described herein, but should be accorded the widest scope that is recognized to be consistent with the principles and novel features disclosed herein.

Description of Reference Numerals

[0132] 10: Aerial-stay type communication relay device (aerial PF) 30: Ground cell base station (ground base station, ground BS) 61: Aerial PF user 65: Ground BS user 70: Feeder station (GW station) 71: Antenna 80: Mobile communication network 81: Backhaul line 82: Ground base station database 100A: Service area 100B: Beam 100C: Aerial PF cell 100N: Null 110: Relay communication station 300C: Ground cell 1101: Information acquisition unit 1102: Channel estimation unit 1103: Null optimization unit 1104: Weight calculation unit 1105: Weight control unit 3001: Traffic information collection unit 3002: Traffic information transmission unit

Claims

1. A wide-area cell base station that forms a wide-area cell from a service link antenna of a relay communication station installed on an aircraft or floating object located in the sky toward the ground or sea, a communication unit that communicates with a plurality of terrestrial cell base stations that form terrestrial cells that overlap or are adjacent to the wide-area cell from an antenna installed on land or sea through a service link of the same frequency band; an information acquisition unit that acquires ground cell-related information relating to at least one of the plurality of ground cell base stations and the plurality of ground cells; a null optimization unit that determines the directions and number of the multiple nulls in a real environment based on the terrestrial cell-related information acquired by the information acquisition unit so that the number of multiple directional nulls to be formed is smaller than the number of the multiple terrestrial cell base stations; A weight calculation unit that calculates a weight matrix that forms the multiple nulls in a real environment and forms a beam for a terminal device connected to the wide-area cell based on the directions and number of the multiple nulls determined by the null optimization unit; a weight control unit that applies the weight matrix calculated by the weight calculation unit to a signal transmitted to and received from a terminal device connected to the wide-area cell; A wide-area cell base station comprising:

2. 2. The wide-area cell base station of claim 1, The information acquisition unit acquires traffic information of the plurality of terrestrial cell base stations, The null optimization unit is Based on traffic information of the plurality of terrestrial cell base stations, estimate a plurality of first channel vectors between the antenna of the wide-area cell base station and the antennas of the plurality of terrestrial cell base stations or the ground surface directly below the antennas, or between the antenna of the wide-area cell base station and a plurality of terminal devices connected to the plurality of terrestrial cell base stations; calculating correlations between the first channel vectors and a plurality of second channel vectors corresponding to a plurality of candidate null-forming directions; determining a direction and a number of the plurality of nulls based on the correlation calculation results; A wide-area cell base station comprising:

3. 3. The wide-area cell base station of claim 2, The null optimization unit determines the directions and the number of the nulls based on the correlation calculation result and a geographical distribution of a plurality of terminal devices connected to the plurality of terrestrial cell base stations. A wide area cell base station comprising:

4. 3. The wide-area cell base station of claim 2, The null optimization unit is applying a prioritization weight to the calculation of said correlation to prioritize the formation of said nulls; determining a direction and a number of the plurality of nulls based on a result of the correlation calculated by applying the priority setting weights; A wide area cell base station comprising:

5. 5. The wide-area cell base station of claim 4, a wide-area cell base station characterized in that the priority setting weight is set according to at least one of the importance of the terrestrial cell base station, the importance of the terminal device, the traffic volume of the terrestrial cell base station, the traffic volume of the terminal device, the amount of interference with the terrestrial cell base station, and the amount of interference with the terminal device.

6. 3. The wide-area cell base station of claim 2, The null optimization unit determines the directions and numbers of the nulls for each of the plurality of terrestrial cell base stations, assuming that a plurality of terminal devices connected to the terrestrial cell base station are localized at the position of the terrestrial cell base station. A wide area cell base station comprising:

7. 3. The wide-area cell base station of claim 2, The null optimization unit is comparing the calculated correlation value with a preset lower limit value; selecting, from among the plurality of null formation direction candidates, a combination of null formation direction candidates that satisfies a condition that the sum of the calculated correlation values ​​is equal to or greater than the lower limit value, as a null direction to be formed in the actual environment; A wide area cell base station comprising:

8. 8. The wide-area cell base station of claim 7, The null optimization unit is For the propagation paths of the candidates for the null formation directions, an amount of interference from the wide-area cell base station to the plurality of terrestrial cell base stations or to a plurality of terminal devices connected to the plurality of terrestrial cell base stations is calculated based on the calculation result of the correlation, the transmission power of the wide-area cell base station, and a propagation loss in the propagation path; setting the lower limit based on the calculation result of the amount of interference; A wide area cell base station comprising:

9. 3. The wide-area cell base station of claim 2, The null optimization unit is updating the traffic information periodically or at a predetermined acquisition time; re-estimating the first channel vectors based on the updated traffic information; recalculating correlations between the plurality of first channel vectors and the plurality of second channel vectors; updating the directions and the number of the plurality of nulls based on the correlation calculation results; A wide area cell base station comprising:

10. 10. The wide-area cell base station according to claim 2, The null optimization unit is Calculating a plurality of eigenvalues ​​λ and eigenvectors v for a matrix defined using the plurality of first channel vectors; Transforming the plurality of second channel vectors using the eigenvector ν whose elements are rearranged in descending order of the eigenvalue λ; determining a direction and a number of the plurality of nulls based on the transformed plurality of second channel vectors; A wide area cell base station comprising:

11. 11. The wide-area cell base station of claim 10, The null optimization unit calculates the plurality of eigenvalues ​​and eigenvectors from a plurality of singular values ​​and singular vectors obtained by using singular value decomposition on a matrix defined by using the plurality of first channel vectors. A wide area cell base station comprising:

12. 11. The wide-area cell base station of claim 10, The null optimization unit is comparing the plurality of eigenvalues ​​in the transformed correlation matrix with a preset threshold; selecting, from among the plurality of null formation direction candidates, a null formation direction candidate that satisfies the condition that the eigenvalue is equal to or greater than the threshold value as a null direction to be formed in a real environment; A wide area cell base station comprising:

13. 11. The wide-area cell base station of claim 10, the null optimization unit selects a direction of a null to be formed in a real environment from the plurality of null formation direction candidates based on a ratio between a partial cumulative sum of the plurality of eigenvalues ​​in the transformed correlation matrix in order of magnitude and a total of the plurality of eigenvalues. A wide area cell base station comprising:

14. 11. The wide-area cell base station of claim 10, The weight calculation unit calculates a weight matrix for forming the plurality of nulls in a real environment and for forming a beam for a terminal device connected to the wide-area cell based on the calculation results of the plurality of eigenvectors. A wide area cell base station comprising:

15. 15. The wide-area cell base station of claim 14, The weight calculation unit A plurality of second channel vectors corresponding to the directions of a plurality of (Nn) nulls formed in a real environment are determined based on the plurality of eigenvectors, and a transposition of the plurality of second channel vectors is performed by: [0010] The transpose matrix of the channel matrix H between the service link antenna of the wide-area cell base station and the target terminal device to be connected to the wide-area cell is expressed as follows: [0025] A column vector is selected from the following equation (3), which is a pseudo-inverse matrix of the extended channel matrix of the following equation (2) defined as follows: A wide area cell base station comprising: [0030] [0045]

16. 15. The wide-area cell base station of claim 14, The weight calculation unit A weight portion W that forms multiple nulls in a real environment using the multiple eigenvectors ＮＦ and a weight portion W that forms a beam for a terminal device that connects to the wide-area cell. ＢＦ is calculated in two stages, and a weight matrix (W) for forming the multiple nulls in a real environment and forming a beam for a terminal device connected to the wide-area cell is calculated by the following equation (4). A wide area cell base station comprising: [0050]

17. A wide-area cell base station according to any one of claims 1 to 9; A plurality of terrestrial cell base stations that form terrestrial cells overlapping or adjacent to the wide-area cell from antennas disposed on land or sea; A system comprising:

18. A null formation method in a wide-area cell base station that forms a wide-area cell from a service link antenna of a relay communication station installed on an aircraft or floating object located in the sky toward the ground or sea, comprising: performing communication of service links in the same frequency band with a plurality of terrestrial cell base stations that form terrestrial cells overlapping or adjacent to the wide-area cell from an antenna installed on land or sea; obtaining terrestrial cell related information relating to at least one of the plurality of terrestrial cell base stations and the plurality of terrestrial cells; determining the directions and the number of the plurality of directional nulls to be formed based on the acquired terrestrial cell-related information so that the number of the plurality of directional nulls to be formed is less than the number of the plurality of terrestrial cell base stations; Calculating a weight matrix for forming the plurality of nulls in a real environment and for beamforming for a terminal device connecting to the wide-area cell based on the determined directions and number of the plurality of nulls; applying the calculated weight matrix to a signal transmitted to and received from a terminal device connected to the wide-area cell; A method for forming a null, comprising:

19. A program executed on a computer or processor provided in a wide-area cell base station that forms a wide-area cell from a service link antenna of a relay communication station provided on an aircraft or floating object located in the sky toward the ground or sea, A program code for performing communication of service links in the same frequency band with a plurality of terrestrial cell base stations that form terrestrial cells overlapping or adjacent to the wide-area cell from an antenna installed on land or sea; program code for obtaining terrestrial cell related information relating to at least one of the plurality of terrestrial cell base stations and the plurality of terrestrial cells; a program code for determining directions and a number of the plurality of directional nulls based on the acquired terrestrial cell-related information such that the number of the plurality of directional nulls to be formed is less than the number of the plurality of terrestrial cell base stations; A program code for calculating a weight matrix for forming the plurality of nulls in a real environment and for beamforming for a terminal device connecting to the wide-area cell based on the determined directions and number of the plurality of nulls; A program code for applying the calculated weight matrix to a signal transmitted to and received from a terminal device connected to the wide-area cell; A program comprising:

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