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

Abstract

Provided is a wide-area cell base station that can cover numerous ground cells with fewer nulls than the number of ground cell base stations (ground cells) and can achieve high frequency utilization efficiency. This wide-area cell base station: acquires ground cell related information relating to a plurality of ground cell base stations and / or a plurality of ground cells; determines, on the basis of the ground cell related information, the directions and number of a plurality of directional nulls to be formed such that the number of directional nulls is fewer than the number of the plurality of ground cell base stations; calculates, on the basis of the directions and number of the plurality of nulls, a weight matrix for forming the plurality of nulls in a real environment and carrying out beamforming for a terminal device connected to the wide-area cell; and applies the weight matrix to signals transmitted to and received from the terminal device connected to the wide-area cell.

Description

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

[0001] This disclosure relates to a technology for suppressing interference from relay communication stations mounted on aerial PFs such as HAPS to ground cells.

[0002] Conventionally, base stations (hereinafter referred to as "wide-area cell base stations") that form wide-area cells extending to the ground or sea from repeater-type or base station equipment-type relay communication stations mounted on high-altitude platform stations (HAPS) (also called "high-altitude pseudo-satellites") located in the upper atmosphere, low Earth orbit (LEO) satellites, geostationary orbit (GEO) satellites, etc. are known. In an environment where a system in which such wide-area cell base stations communicate with UEs (terminals) via service links (hereinafter referred to as "upper-air systems") and a system in which existing ground cell base stations communicate with UEs (terminals) via service links (hereinafter referred to as "ground systems") coexist, when communication is performed simultaneously using the same frequency band, signals from the relay communication stations of the upper-air systems interfere with the ground systems. When this interference from the upper-air systems occurs, the throughput of the ground systems decreases significantly. Similarly, signals from the ground systems also interfere with the upper-air systems. When this interference from the ground systems occurs, the throughput of the upper-air systems decreases.

[0003] Patent Document 1 discloses a technique for suppressing (reducing) interference to ground systems by excluding or avoiding areas covered by ground cells, by adjusting the antenna system of an overhead High Altitude Platform (HAP) to form a directional beam by directing nulls towards ground cell base stations based on a map of eNBs (ground cell base stations).

[0004] U.S. Patent Application Publication No. 2017 / 0272131

[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 toward the ground or sea from a service link antenna of a relay communication station installed on an aircraft or floating body located in the air. The wide-area cell base station comprises: a communication unit that communicates on a service link in the same frequency band with a plurality of ground cell base stations that form ground cells overlapping with or adjacent to the wide-area cell from an antenna located on the ground or sea; 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 direction and number of the plurality of directional 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 ground cell base stations based on the ground cell-related information acquired by the information acquisition unit; a weight calculation unit that calculates a weight matrix for forming the plurality of nulls in the actual environment and beamforming toward terminal devices connected to the wide-area cell based on the direction 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 signals transmitted and received between the wide-area cell and terminal devices connected to the wide-area cell.

[0006] In the wide-area cell base station, the information acquisition unit acquires traffic information from the plurality of ground 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 ground 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 ground cell base stations, based on the traffic information from the plurality of ground cell base stations, calculates the correlation between the plurality of first channel vectors and a plurality of second channel vectors corresponding to a plurality of candidate null formation directions, and determines the direction and number of the plurality of nulls based on the result of the correlation calculation.

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

[0008] In the wide-area cell base station, the null optimization unit may apply priority setting weights to the correlation calculation to set the priority for forming the nulls, and determine the direction and number of the plurality of nulls based on the correlation calculation results calculated by applying the priority setting weights.

[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 ground cell base station, the importance of the terminal device, the traffic volume of the ground cell base station, the traffic volume of the terminal device, and the magnitude of interference due to the positional relationship between the ground cell base station and the terminal device.

[0010] In the wide-area cell base station, the null optimization unit may determine the direction and number of the plurality of nulls by assuming that for each of the plurality of ground cell base stations, the plurality of terminal devices connected to the ground cell base station are localized at the location of the ground cell base station.

[0011] In the wide-area cell base station, the null optimization unit may compare the calculated correlation value with a preset lower limit and select a combination of candidate null formation directions from among the multiple candidate null formation directions that satisfies the condition that the sum of the calculated correlation values ​​is equal to or greater than the lower limit, as the direction of the null to be formed in the actual environment.

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

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

[0014] In the wide-area cell base station, the null optimization unit performs the plurality of first channel vectors h ｂ For the matrix A of equation (1) below, defined using the above, multiple eigenvalues ​​λ and eigenvectors ν may be calculated, and the multiple second channel vectors may be transformed using the eigenvectors ν obtained by rearranging the elements in descending order of the eigenvalues ​​λ, and the direction and number of the multiple nulls may be determined based on the transformed multiple second channel vectors. Note that the right-hand side of equation (1) may be modified considering the geographical distribution of the terminal devices or the priority setting weights.

[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 singular value decomposition for a matrix defined using the plurality of first channel vectors.

[0016] In the wide-area cell base station, the null optimization unit may compare the multiple eigenvalues ​​in the transformed correlation matrix with a preset threshold, and select from the multiple candidate null formation directions a null formation direction that satisfies the condition that the eigenvalues ​​are greater than or equal to the threshold as the direction of the null to be formed in the actual environment.

[0017] In the wide-area cell base station, the null optimization unit may select a direction for null formation in the actual environment from among the candidate directions for null formation, based on the ratio of the partial cumulative sum obtained by accumulating the plurality of eigenvalues ​​in the transformed correlation matrix in order of magnitude to the total of all the plurality of eigenvalues.

[0018] In the wide area cell base station, the weight calculation section may calculate, based on the calculation results of the plurality of eigenvectors, 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.

[0019] In the wide area cell base station, the weight calculation section determines, based on the plurality of eigenvectors, a plurality of second channel vectors corresponding to directions of a plurality (Nn) of nulls formed in an actual environment, and transposes the plurality of second channel vectors to obtain and sets the transposed matrix of a channel matrix H between a service link antenna of the wide area cell base station and a target terminal device connected to the wide area cell as a column vector is selected from the following formula (3), which is a pseudo-inverse matrix of an extended channel matrix of the following formula (2) defined as, and 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 may be calculated.

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

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

[0022] A further embodiment of the present disclosure relates to a method for forming a null in a wide-area cell base station that forms a wide-area cell toward the ground or sea from a service link antenna of a relay communication station located on an aircraft or floating object in the air. This null formation method includes: communicating a service link in the same frequency band with a plurality of ground cell base stations that form ground cells overlapping with or adjacent to the wide-area cell from an antenna located on the ground or sea; acquiring ground cell-related information relating to at least one of the plurality of ground cell base stations and the plurality of ground cells; determining the direction and number of the plurality of directional nulls to be formed based on the ground cell-related information acquired 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 ground cell base stations; calculating a weight matrix for forming the plurality of nulls in a real environment and beamforming toward a terminal device connected to the wide-area cell based on the direction 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 signals transmitted and received between the terminal device connected to the wide-area cell and the network.

[0023] A program according to still another aspect of the present disclosure is a program executed in a computer or processor provided in a wide-area cell base station that forms a wide-area cell toward the ground or the sea from a service link antenna of a relay communication station provided on an aircraft or levitation body located in the sky. This program comprises: a program code for performing communication of a service link in the same frequency band as a plurality of terrestrial cell base stations that form terrestrial cells overlapping or adjacent to the wide-area cell from an antenna arranged on the ground or the sea; a program code for acquiring terrestrial cell-related information related to at least one of the plurality of terrestrial cell base stations and the plurality of terrestrial cells; a program code for determining the directions and the number of a plurality of directional nulls such that the number of the plurality of formed directional nulls is smaller 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 program code for calculating a weight matrix for performing the formation of the plurality of nulls in an actual environment and beamforming for 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 a program code for applying 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.

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

[0025] Figure 1 is a schematic diagram showing an example of the overall configuration of a communication system including an aerial PF according to the embodiment. Figure 2 is a perspective view showing an example of an aerial PF according to the embodiment. Figure 3 is a side view showing another example of an aerial PF according to the embodiment. Figure 4 is a perspective view showing an example of a service link array antenna of an aerial PF according to the embodiment. Figure 5 is a perspective view showing another example of a service link array antenna of an aerial PF according to the embodiment. Figure 6 is an explanatory diagram showing the challenges when performing beamforming in MU-MIMO using an array antenna of an aerial PF. Figure 7 is an explanatory diagram showing an example of a directional null formed from an aerial PF toward a terrestrial BS antenna. Figure 8 is an explanatory diagram showing the challenges when forming a directional null from an aerial PF toward multiple terrestrial BS antennas. Figure 9 is an explanatory diagram showing an example of null optimization in which fewer directional nulls are formed from an aerial PF than the number of terrestrial BS antennas according to the embodiment. Figure 10 is a flowchart showing an example of a major process including null optimization in an aerial PF according to the embodiment. Figure 11A is an explanatory diagram showing an example of the distribution of multiple ground BS in a wide-area cell formed by an upper-air PF according to the embodiment. Figure 11B is a diagram showing an example of the simulation results when nulls are formed in five directions, fewer than the number of ground BS in the wide-area cell, from the upper-air PF in Figure 11A. Figure 12 is an explanatory diagram showing an example of the overall configuration of a communication system having a ground BS database according to the embodiment. Figure 13 is a block diagram showing an example of the main configuration of a relay communication station mounted on an upper-air PF in the communication system of Figure 12. Figure 14 is a block diagram showing an example of the main configuration of a ground cell base station in the communication system of Figure 12. Figure 15 is a flowchart showing an example of processing at a relay communication station on an upper-air PF when performing beamforming control and service link communication with null formation in the communication system according to the embodiment.

[0026] Embodiments of the present invention will be described below with reference to the drawings. One embodiment of the system described herein is a communication system comprising an airborne communication relay device (airborne PF), which is an aircraft or floating object equipped with a relay communication station for a wide-area cell base station (e.g., an airborne PF base station) that forms a cell toward the ground or sea and can perform wireless communication with a plurality of terminal devices (UEs) located within the cell. The transmission method for wireless communication between the plurality of terminal devices (UEs) and the wide-area cell base station may be massive MIMO (Multi-Input Multiple-Output), which performs multi-layer transmission using an array antenna having a large number of antenna elements as described later, or MU-MIMO (Multi-User MIMO), which transmits signals to a plurality of different terminal devices (UEs) at the same time and on the same frequency. Furthermore, in this 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 an upper-air PF cell, which is a wide-area cell (first cell), the communication system of this embodiment can suppress interference from the upper-air PF relay communication station to the ground cell by forming a directional null from the upper-air PF relay communication station toward the antenna of the ground cell base station or the ground cell. The communication system according to this embodiment is suitable for realizing a 3D network for next-generation mobile communications such as fifth generation, which can handle simultaneous connection to a large number of terminal devices and low latency.

[0027] In particular, in the system of this embodiment, the aerial PF acquires information on ground cell base stations (ground BS) within or around a wide-area cell, and based on that information, determines the direction and number of directional nulls from the relay communication station of the aerial PF toward the antenna of the ground cell base station or the ground cell. This makes it possible to cover a large number of ground cells with fewer nulls than the number of ground cell base stations (ground cells), thereby achieving high frequency utilization efficiency.

[0028] Figure 1 is a schematic diagram showing an example of the overall configuration of a communication system including an upper-air PF (upper-air stationary communication relay device) according to an embodiment. In Figure 1, the upper-air PF system constituting the communication system of this embodiment includes a high-altitude platform station (hereinafter also referred to as "upper-air platform (upper-air PF)" or "HAPS") (also referred to as "high-altitude pseudo-satellite" or "stratospheric platform") 10, which is an upper-air stationary communication relay device (wireless relay device) that is an aircraft or floating body on which a relay communication station is mounted. The upper-air PF 10 is located in the airspace at a predetermined altitude and forms a three-dimensional cell (hereinafter also referred to as "upper-air PF cell" or "HAPS cell") 100C as a wide-area cell (first cell). The upper-air PF 10 is an aircraft or floating body (for example, a solar plane, airship, drone, balloon) that is controlled to float or fly in the airspace (floating airspace) at a predetermined altitude above the ground or sea surface by autonomous control or external control, and on which a relay communication station is mounted. Furthermore, the orbital PF10, which can function as an orbital 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. In addition, the communication system of this embodiment may include one or more terminal devices that the orbital PF10 communicates with, or it may include a gateway station (feeder station) as described later.

[0029] The airspace in which the upper-air PF10 is located is, for example, the stratospheric airspace at altitudes of 11 km or more and 50 km or less above the ground (or over water such as the sea or a lake). This airspace may also be the airspace at altitudes of 15 km to 25 km where meteorological conditions are relatively stable, and may be particularly the airspace at an altitude of approximately 20 km.

[0030] Because the orbiting PF10 flies at an altitude lower than that of typical artificial satellites and higher than ground or sea base stations, it can achieve high line-of-sight coverage while having less propagation loss than satellite communications. Due to this characteristic, it is also possible to provide communication services from the orbiting PF10 to user equipment such as cellular mobile terminals (mobile stations) 61 on the ground or sea. By providing communication services from the orbiting PF10, a wide area that was previously covered by numerous ground or sea base stations can be covered at once with a small number of orbiting PF10s, offering the advantage of providing low-cost and stable communication services.

[0031] The relay communication station of the upper air PF 10 forms an upper air PF cell 100C capable of wireless communication with the user's terminal equipment (hereinafter referred to as "UE" (user equipment)) by directing a beam toward the ground (or sea surface) for wireless communication with the UE 61. The radius of the service area 100A (also called the "upper air PF service area") consisting of the footprint 100F of this upper air PF cell 100C on land (or sea) is, for example, several tens [km] to 100 [km].

[0032] In this embodiment, the relay communication station in the airborne PF 10 may form a plurality of three-dimensional cells (for example, 3 cells or 7 cells), and a service area 100A consisting of a plurality of footprints of these plurality of three-dimensional cells on land (or at sea).

[0033] The communication system of this embodiment is an environment in which an aerial PF 10 equipped with an aerial relay communication station that constitutes a wide-area cell base station (hereinafter also referred to as an "aerial PF base station" or "HAPS base station") and a low-positioned ground cell base station (hereinafter referred to as a "ground BS") 30 that forms a cell that is the target of interference suppression and is located on the ground or at sea coexist. In the example of Figure 1, multiple antennas of the low-positioned ground BS 30 (hereinafter also referred to as "base station antennas") are located inside the aerial PF cell 100C, and a ground cell 300C of the ground BS 30, which is smaller than the footprint 100F of the cell 100C, is formed inside the service area 100A consisting of the footprint 100F of the three-dimensional cell 100C.

[0034] The aerial PF base station, which is a wide-area cell base station including a relay communication station mounted on the aerial PF 10, and the terrestrial BS (e.g., eNodeB, gNodeB) 30 each use the same frequency band for wireless communication of the service link between their respective cells 100C and 300C and UE61 and 65. The terrestrial BS 30 may be configured by connecting an RRH (remote radio head) with a base station antenna and a BBU (baseband unit) via an optical fiber line. In this case, the RRH with the base station antenna is located at the position of the base station 30 in Figure 1.

[0035] The relay communication station mounted on the airborne PF 10 is, for example, a base station (e.g., eNodeB, gNodeB) that wirelessly communicates with a gateway station (also called a "feeder station") 70, which is a relay station connected to the core network of the mobile communication network 80 on the ground (or sea) side and has an antenna 71 facing upwards. The relay communication station on the airborne PF 10 is connected to the core network of the mobile communication network 80 via the feeder station 70 installed on the ground or at sea. Communication between the airborne PF 10 and the feeder station 70 may be carried out by wireless communication using radio waves such as microwaves, or by optical communication using laser light or the like.

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

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

[0038] A base station type relay communication station includes, for example, a base station device and a feeder link transceiver. The base station device includes a low-noise amplifier for amplifying the received signal of the service link, a power amplifier for amplifying the transmitted signal transmitted via the service link antenna, and a baseband processing device for processing the baseband signal of the service link. The feeder link transceiver transmits and receives signals on the backhaul link that are transmitted and received with the feeder station 70. The feeder station 70 transmits and receives signals on the backhaul link that are transmitted and received with the relay communication station in the air.

[0039] The airborne PF10 may autonomously control its own buoyancy movement (flight) and processing at the relay communication station by having a control unit, which consists of a computer or the like built into it, execute a control program. For example, each airborne PF10 may acquire its own current position information (e.g., GPS position information), pre-stored position control information (e.g., flight schedule information), and position information of other airborne PFs located in the vicinity, and autonomously control its buoyancy movement (flight) and processing at the relay communication station based on this information.

[0040] Furthermore, the floating movement (flight) of the upper-air PF 10 and processing at the relay communication station may be controlled by a management device (also called a "remote control device") installed 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 upper-air PF 10 may be equipped 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 may be assigned terminal identification information (e.g., an IP address, a telephone number, etc.) so that it can be identified by the management device. The MAC address of the communication interface may be used to identify the control communication terminal device. In addition, the upper-air PF 10 may transmit information regarding the floating movement (flight) of itself or surrounding upper-air PFs and processing at the relay communication station, information regarding the status of the upper-air PF 10, and monitoring information such as observation data acquired by various sensors to a predetermined destination of the management device or the like. The control information may include target flight route information for the upper-air PF 10. The monitoring information may include at least one of the following: the current position of the upper-air PF10, flight route history information, airspeed, ground speed and thrust direction, wind speed and direction of the airflow around the upper-air PF10, and atmospheric pressure and temperature around the upper-air PF10.

[0041] Figure 2 is a perspective view showing an example of an aerial PF 10 used in the communication system of the embodiment. The aerial PF 10 in Figure 2 is a solar-powered HAPS, and comprises a main wing section 101 whose longitudinal ends are curved upward, and a plurality of motor-driven propellers 103 as a bus-powered propulsion system attached to one of the longitudinal ends of the main wing section 101. A solar power generation panel (hereinafter referred to as "solar panel") 102 is provided on the upper surface of the main wing section 101 as a solar power generation section having a solar power generation function. In addition, a plurality of pods 105, which serve as equipment housings for mission equipment, are connected to two longitudinal locations on the lower surface of the main wing section 101 via plate-shaped connecting sections 104. Inside each pod 105 are a relay communication station 110 and a battery 106 as mission equipment. In addition, wheels 107 used for takeoff and landing are provided on the lower side of each pod 105. The electricity generated by the solar panel 102 is stored in the battery 106, and the power supplied from the battery 106 rotates the motor of the propeller 103, which in turn enables the relay communication station 110 to perform wireless relay processing.

[0042] Figure 3 is a side view showing another example of the airborne PF10 used in the communication system of the embodiment. The airborne PF10 in Figure 3 is an unmanned airship type HAPS and can be equipped with a large-capacity battery due to its large payload. The airborne PF10 comprises an airship body 201 filled with a gas such as helium for buoyancy, a motor-driven propeller 202 as a propulsion device for the bus power system, and an equipment housing 203 that houses mission equipment. A relay communication station 110 and a battery 204 are housed inside the equipment housing 203. Power supplied from the battery 204 rotates the motor of the propeller 202, and wireless relay processing is performed by the relay communication station 110. Alternatively, a solar panel with a photovoltaic power generation function may be provided on the upper surface of the airship body 201, and the power generated by the solar panel may be stored in the battery 204.

[0043] In the following embodiments, the above-ground stationary communication relay device (aerial PF) that communicates wirelessly with UE61 will be illustrated and described in either the solar-powered plane type HAPS or the unmanned airship type HAPS shown in Figure 2. However, the following embodiments can also be similarly applied to other above-ground stationary communication relay devices (aerial PF) other than HAPS.

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

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

[0046] Similarly, the duplexing method for the uplink and downlink of the wireless communication with UE61 via the relay station 110 is not limited to a specific method, and may be, for example, a time-division duplexing (TDD) method or a frequency-division duplexing (FDD) method. Also, the access method for the wireless communication with UE61 via the relay station 110 is not limited to a specific method, and may be, for example, an FDMA method, a TDMA method, a CDMA method, or an OFDMA method.

[0047] Furthermore, the wireless communication of the service link in this embodiment may use a massive MIMO transmission method that performs multilayer transmission using an array antenna with a large number of antenna elements, and has functions such as diversity coding, transmit beamforming, and spatial division multiplexing (SDM). In particular, in this embodiment, in downlink communication from the relay communication station in the upper air PF 10 to multiple UE61s in the cell, MU-MIMO technology may be used, which transmits signals to multiple different UE61s at the same time and frequency. By performing MU-MIMO transmission using an array antenna with a large number of antenna elements, it is possible to direct an appropriate beam to each UE61 according to the communication environment of each UE61, thereby improving the overall communication quality of the cell. In addition, since communication with multiple UE61s can be performed using the same wireless resources (time and frequency resources), the system capacity can be expanded.

[0048] Figures 4 and 5 are perspective views showing examples of array antennas 130 composed of multiple elements that can be used in the MU-MIMO transmission system in the upper-air PF10 of this embodiment.

[0049] The array antenna 130 in Figure 4 is a planar array antenna having a flat antenna base, in which numerous antenna elements 130a, such as patch antennas, are arranged two-dimensionally in mutually orthogonal axial directions along the planar antenna surface of the antenna base.

[0050] The array antenna 130 in Figure 5 is a cylindrical array antenna having a cylindrical or columnar antenna base, with numerous antenna elements 130a, such as patch antennas, arranged along the axial and circumferential directions of the circumferential surface, which serves as the first antenna surface of the antenna base. In the array antenna 130 of Figure 5, as shown in the figure, multiple antenna elements 130a, such as patch antennas, may be arranged in a circular shape along the bottom surface, which serves as the second antenna surface. Furthermore, the antenna base in Figure 5 may be a polygonal cylindrical or polygonal prism-shaped antenna base.

[0051] The shape of the array antenna 130, as well as the number, type, and arrangement of the antenna elements, are not limited to those exemplified in Figures 4 and 5.

[0052] Figure 6 is an explanatory diagram illustrating the challenges when implementing beamforming in a MU-MIMO transmission system using an array antenna 130 on an upper-air PF 10. In the service link SL between the array antenna 130 on the upper-air PF 10 and the service area 100A (footprint 100F of cell 100C) in Figure 6, communication quality can be improved by using the MU-MIMO transmission system and performing beamforming, which involves individually directing appropriate high-gain beams 100B(1) to 100B(4) to each UE61(1) to 61(4) according to the communication environment of each UE61, thereby compensating for long-distance propagation loss and enabling communication. In particular, when using a MU-MIMO transmission system that communicates with multiple UE61s using the same radio resources (e.g., resource blocks (RB) of the same time and frequency) in the service link SL, system capacity can be improved.

[0053] However, in an environment where the aerial PF10 and the ground BS30(1) and 30(2) coexist, as shown in Figure 6, if the aerial PF10 and the ground BS30(1) and 30(2) communicate simultaneously with UE61 and 65 located in each cell using the same frequency band, the downlink wireless transmission signal transmitted from the aerial PF10 may interfere with the service link communication (hereinafter also referred to as "ground system communication") between the ground BS30(1) and 30(2) and the UE65(1) and 65(2) located in the ground cells 300C(1) and 300C(2). If this interference from the aerial PF10 occurs, the throughput of communication between the ground BS30(1) and 30(2) and the UE65 will be significantly reduced.

[0054] In this embodiment, in the upper PF 10, beamforming control of the upper PF cell 100C is performed based on the position information of the base station antenna of the terrestrial BS so that the null of the beam pattern (profile of the spatial distribution of the beam) is directed toward the terrestrial BS (antenna) whose antenna is located within the upper PF cell 100C. As a result, the desired signal is transmitted by multibeam to each of the multiple UE 61 located in the upper PF cell 100C, suppressing interference that the upper PF 10 has on the ground system's communications without causing a significant decrease in communication quality.

[0055] Figure 7 is an explanatory diagram showing an example of a directional null formed from the aerial PF 10 toward the ground BS (antenna) 30. As shown in Figure 7, when a beam pattern null 100N is formed from the array antenna 130 of the aerial PF 10 toward the ground BS (antenna) 30 located within the aerial PF service area 100A, interference from the aerial PF 10 to the ground cell 300C can be reduced, and interference from the aerial PF 10 to the ground system's communications can be suppressed. However, as shown below, when a beam pattern null 100N is formed from the aerial PF 10 toward multiple ground BS (antennas) 30 located within the aerial PF service area 100A, it is desirable to cover multiple ground BS (antennas) 30 with as few nulls 100N as possible.

[0056] Figure 8 is an explanatory diagram illustrating the challenges when forming a directional null 100N from the aerial PF 10 toward multiple terrestrial BS 30 antennas. In Figure 8, by forming a null 100N from the aerial PF 10 toward multiple terrestrial BS 30 antennas, interference to all of the multiple ground cells that overlap or are adjacent to the aerial PF service area of ​​the aerial PF 10 can be reduced. However, when forming a null 100N toward all of the multiple BS 30 antennas, while the above interference can be reduced, there are challenges such as (1) to (4) below, so it is desirable to cover multiple terrestrial BS (antennas) 30 with a small null.

[0057] (1) The degrees of freedom of the array antenna 130 in the upper PF 10 are consumed. (2) The beam gain of the beam 100B from the upper PF 10 to the upper PF user (UE 61) decreases. (3) Unwanted coverage holes may occur in the upper PF service area (upper PF cell, wide area cell) 100A. (4) If the sum of the number of multiplexings for the upper PF user (UE 61) and the number of terrestrial BS 30 stations is greater than the degrees of freedom of the array antenna 130, it is not possible to form a null 100N for all terrestrial BS 30.

[0058] Figure 9 is an explanatory diagram showing an example of null optimization in which a number of directional nulls 100N are formed from the aerial PF 10 to a number of ground BS 30 that is fewer than the number of ground BS 30 according to this embodiment. In this embodiment, in order to realize the sharing of the same frequency between the aerial PF and the ground system, which is expected from the viewpoint of effective frequency utilization, the optimal direction (channel vector corresponding to the direction) and number of nulls of the nulls formed by the aerial PF 10 are determined. As shown in Figure 9, when a number of ground BS (antennas) 30 are located in the aerial PF service area 100A, the number of ground BS 30 are protected with fewer nulls than the number of ground BS (antennas) 30, thereby achieving both interference reduction to the ground BS 30 and high beam gain to the aerial PF user (UE 61). In this embodiment, a null optimization technique is provided that can reduce interference to ground cells and improve frequency utilization efficiency without impairing the coverage area 100A of the aerial PF.

[0059] The optimal null direction described above also depends on the configuration of the array antenna 130. The null optimization method of this embodiment can be applied regardless of the array configuration, and the characteristics of each array antenna 130, such as the width (null width) in the direction of elevation and azimuth of the null 100N formed from the upper air PF 10, are taken into consideration.

[0060] In the following explanation, we will mainly describe the case where the upper air PF 10 and the ground BS 30 are each performing DL (downlink) communication with the UE. However, the null optimization in this embodiment can be applied to each of the following combinations A1 to A4 of DL (downlink) and UL (uplink) communication. Hereinafter, a UE 61 of a user located in the upper air PF cell 100C and connected to the upper air PF 10 will also be referred to as an "upper air PF user," and a UE 65 of a user located in the ground cell 300C and connected to the ground BS 30 will also be referred to as a "ground BS user."

[0061] A1: When the aerial PF10 performs DL communication and the terrestrial BS30 performs DL communication (Main interference: Interference from aerial PF to terrestrial BS users, interference from terrestrial BS to aerial PF users) A2: When the aerial PF10 performs UL communication and the terrestrial BS30 performs UL communication (Main interference: Interference from aerial PF users to terrestrial BS, interference from terrestrial BS users to aerial PF) A3: When the aerial PF10 performs DL communication and the terrestrial BS30 performs UL communication (Main interference: Interference from aerial PF to terrestrial BS, interference from terrestrial BS users to aerial PF users) A4: When the aerial PF10 performs UL communication and the terrestrial BS30 performs DL communication (Main interference: Interference from terrestrial BS to aerial PF, interference from aerial PF users to terrestrial BS users)

[0062] [Main processes for null optimization] Figure 10 is a flowchart showing an example of the main processes, including null optimization, in the upper PF 10 according to the embodiment. In Figure 10, the null optimization process S110 includes an information acquisition process S111, a null optimization process S112, and an application process S113 of the null optimization results.

[0063] In the information acquisition process S111, the upper air PF10 acquires ground cell-related information necessary for null formation. The ground cell-related information is information about multiple ground BS30s, information about multiple ground cells, or both, which are necessary for null formation.

[0064] In the null optimization process S112, the upper-air PF 10 determines the direction and number of multiple nulls 100N based on the ground cell-related information acquired in the information acquisition process S111, such that the number of multiple directional nulls to be formed is less than the number of multiple ground BS 30s. For example, the upper-air PF 10 estimates a first channel vector between the upper-air PF 10 and each of the multiple ground BS 30s, a first channel vector between the upper-air PF 10 and multiple ground BS users (UE65) connected to the multiple ground cells 300C, or first channel vectors in both directions, and determines a vector with a high correlation to the estimated channel vector, in accordance with the number of nulls selected in the optimization (hereinafter also referred to as "null number").

[0065] For example, the upper-air PF 10 may estimate the multiple first channel vectors based on traffic information from multiple ground BS 30s, calculate the correlation between the multiple first channel vectors and the multiple second channel vectors corresponding to multiple candidate null formation directions, and determine the direction and number of multiple nulls to be formed during actual operation in a real environment based on the results of the correlation calculation.

[0066] Here, the above-mentioned candidate directions for null formation are candidate directions for null formation during operation in a real environment. For example, the following C1 to C5 may be set as candidate directions for null formation: C1: Direction from the aerial PF 10 toward each of the multiple terrestrial BS 30 antennas C2: Direction from the aerial PF 10 toward each of the ground surfaces directly beneath the multiple terrestrial BS 30 antennas C3: Direction from the aerial PF 10 toward each of the arbitrary points within the multiple ground cells 300C (for example, the center point of the cell, or the center point of an area where UEs (terrestrial BS users) 65 are densely located) C4: Direction from the aerial PF 10 toward each of the multiple areas within the wide-area cell 100C (aerial PF service area 100A) where multiple terrestrial BS 30s are arranged at a high density C5: Direction from the aerial PF 10 toward each of the multiple UEs (terrestrial BS users) 65 connected to the multiple ground cells 300C

[0067] The upper PF 10 may calculate a weight matrix based on the direction and number of multiple nulls 100N determined in the null optimization process S112, which is used to form multiple nulls 100N during operation in the actual environment and to form a beam 100B for upper PF users (UE61) connected to the upper PF service area (wide-area cell) 100A. The upper PF 10 may also determine whether or not to increase the number of additional nulls 100N to be formed if the number of nulls 100N determined in the null optimization process S112 does not meet predetermined conditions.

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

[0069] In beamforming control involving null formation during operation in a real environment (S120), the upper PF 10 performs null formation and beam 100B formation for the upper PF user (UE61) using channel vectors corresponding to a plurality of optimized null directions, based on the control parameter settings obtained by applying the null optimization results obtained in the null optimization process S112.

[0070] [Correlation of Channel Vectors] The channel vectors corresponding to the directions of the above-optimized plurality of nulls 100N may be determined, for example, based on the correlation of the first channel vector and the second channel vector as described above. Here, in the case of DL communication from the airborne PF 10, the first channel vector between the airborne PF 10 and the UE(u) 65 connected to the ground BS(b) 30 is, The second channel vector corresponding to the direction of the null formation candidate n formed by the upper air PF10 is, The correlation between the first channel vector and the second channel vector is given by corr(h １ , h ２ ) is defined as shown in equation (5) below. In equation (5) "(・) Ｈ The symbol '' represents the Hermitian conjugate matrix.

[0071] If the correlation corr between the first channel vector between the upper air PF10 and UE(u)65 and the second channel vector corresponding to null n is large, then the communication of UE(u)65 is more likely to be protected by the null n, resulting in a greater interference reduction effect.

[0072] When forming multiple nulls, multiple Because the parts that are correlated with each other are calculated redundantly, We find the orthogonal system and sum the correlations (corr).

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

[0074] [Estimation of channel vector] The first channel vector h between the upper air PF10 and the UE(u)65 connected to the ground BS(b)30 used in the null optimization described above. ｂ、ｕFor example, the aerial PF 10 acquires traffic information from the ground BS 30, and can perform calculation based on a model such as free space propagation. Here, the traffic information is, for example, coordinates of a ground BS user (UE 65), a statistically processed user distribution, a traffic volume, and the like. Alternatively, a relative positional relationship may be calculated from the coordinates and attitude of the aerial PF 10 and the coordinates of the ground BS user (UE 65), and a model such as free space propagation may be applied.

[0075] [Weight between user distribution and ground BS] For the sum of correlation corr of the following formula (7) included in the aforementioned formula (6), the total sum for ground BS users (UE 65) may be replaced with integration using the geographical distribution (user distribution) of the ground BS users (UE 65).

[0076] For example, a user density distribution f on a two-dimensional plane ｂ (x,y) is used, the sum of correlation corr in the aforementioned formula (6) can be rewritten as the following formula (8).

[0077] In addition, to reduce the amount of calculation, the coordinates (x of the ground BS 30 where the ground BS user (UE 65) located in the ground cell 300C ｂ , y ｂ ) is considered to be localized, and the above user density distribution f ｂ (x,y) may be simplified. δ in formula (9) is the Dirac delta function.

[0078] In this case, the second channel vector h from the aerial PF 10 to the position of the ground surface directly below the antenna of the ground BS (b) 30 (or the position of said antenna) ｂ is used to determine the direction and number of nulls so as to maximize the value of the objective function of formula (10) representing the simplified correlation.

[0079] In the objective function representing the above correlation, for example, as shown in the following weight setting examples 1 and 2, a priority setting weight w reflecting importance based on the traffic volume and interference volume of the ground BS user (UE 65) and the ground BS (b) 30 may be set.

[0080] Weight setting example 1: In this example, priority setting weights reflect the individual importance of each user. ｂ，ｕ We calculate the objective function that shows the correlation in the following equation (11) after setting the parameters.

[0081] Weight setting example 2: In this example, priority setting weights reflect the individual importance of terrestrial and BS channels. ｂ We calculate the objective function showing the correlation in equation (13) using the user distribution in equation (12) below, with the settings configured.

[0082] Furthermore, when setting the priority weights described above, a higher priority weight may be set for ground BS30s with high traffic volume to protect them. Also, since ground BS30s close to the upper-air PF10 have low propagation loss and high interference, the priority weight value may be set higher to make it easier for nulls to be directed towards those ground BS30s. In addition, the traffic information may be updated in accordance with time changes, and the priority weight values ​​may be changed to follow the changes in traffic.

[0083] [Determination of the Optimal Null Direction] To determine the optimal null direction from the above correlation, the optimal solution can be obtained by calculations similar to those used in principal component analysis, for example, as illustrated below. An example is shown for the case of objective function (10) showing a simplified correlation. However, the density distribution of users or priority setting weights may also be considered. The first channel vector and the second channel vector mentioned above are assumed to be normalized as shown in equation (14) below. Here, the first channel vector h ｂ This is the channel vector between the array antenna 130 of the upper-air PF10 and each of the multiple terrestrial BS30 antennas (or the ground directly below the antennas).

[0084] Using the normalized first and second channel vectors described above, the sum part of the correlation for terrestrial BS30 in equation (10) above can be rearranged to rewrite it as equation (15).

[0085] Here, the plurality of first channel vectors h ｂ We define matrix A in equation (16) below using the following.

[0086] For the matrix A above, calculate multiple eigenvalues ​​λ and eigenvectors ν, and sort them in descending order of eigenvalue (λ １ ≥λ ２ Add subscripts to the ≥ ... and rearrange them in descending order of eigenvalue λ.

[0087] Using the eigenvector ν that satisfies equation (17) above, multiple second channel vectors are determined as shown in equation (18) below.

[0088] Based on the multiple second channel vectors obtained after the transformation in equation (18) above, the optimal solution for multiple null directions can be determined. However, the optimal solution for multiple null directions (second channel vectors) is not unique; equivalent transformations exist. When these are combined as a matrix, the objective function can be rewritten as follows:

[0089] From the circulating nature of traces of It remains invariant under the unitary transformation. From the orthonormality of This is how it works. This is the identity matrix. Therefore, the orthonormality is satisfied after the transformation.

[0090] [Method using singular value decomposition] The aforementioned eigenvectors may also be calculated using singular value decomposition. For example, all channel vectors h between the array antenna 130 of the upper air PF 10 and the antennas of multiple ground BS 30 (or the ground surface directly below the antennas) １ , h ２ The following matrix H of equation (22) combines the following elements: ... ｂｓ Define the following. The above matrix may be multiplied by the square root of the priority setting weights, or the density distribution of users may be taken into consideration.

[0091] The matrix H above ｂｓ By performing singular value decomposition on , we obtain equation (23) below.

[0092] The matrix H after the singular value decomposition described above. ｂｓ Matrix V in Ｈ From the above N ｎ Select row vectors corresponding to the individual singular values, and the second channel vector corresponding to the direction of the optimal null mentioned above. Let's assume that.

[0093] The square of the singular value corresponds to the aforementioned eigenvalue according to equation (24) below.

[0094] [Simulation Results] Figure 11A is an explanatory diagram showing an example of the distribution of multiple ground BS 30 in a wide-area cell 100C (high-area PF service area 100A) formed by the upper-air PF 10 according to the embodiment. Figure 11B is a diagram showing an example of the results of the above correlation simulation (computer simulation) when nulls 100N are formed in five directions fewer than the number of ground BS 30 in the wide-area cell 100C (high-area PF service area 100A) from the upper-air PF 10 shown in Figure 11A. As shown in Figure 11B, by forming nulls 100N in each of the five ground BS surrounding areas (areas with high brightness in the figure) where multiple ground BS 30 are arranged in the upper-air PF service area 100A where the wide-area cell 100C is formed and the aforementioned correlation is high, interference from the upper-air PF 10 to the ground cell can be reduced, and communication in the ground cell is protected. Furthermore, since the number of nulls 100N formed in the wide-area cell 100C (upper PF service area 100A) is less than the number of ground BS 30s located within the wide-area cell 100C, high frequency utilization efficiency can be achieved. In addition, in areas of the wide-area cell 100C (upper PF service area 100A) other than the null formation area, the degradation of beam gain from the upper PF 10 to the upper PF user (UE 61) can be reduced.

[0095] [Example of how to determine the number of nulls] The number of nulls 100N to be formed within the wide-area cell 100C (upper PF service area 100A) (number of nulls) may be determined by the magnitude of the eigenvalues ​​mentioned above. For example, a threshold may be set in advance, and the multiple eigenvalues ​​in the transformed correlation matrix mentioned above may be compared with the threshold to select a candidate null formation direction from among the multiple candidate null formation directions that satisfies the condition that the eigenvalues ​​are greater than or equal to the threshold as the direction of the nulls to be formed in the actual environment. Alternatively, the direction of the nulls to be formed in the actual environment may be selected from the multiple candidate null formation directions based on the ratio of the partial cumulative sum obtained by accumulating the multiple eigenvalues ​​in the transformed correlation matrix mentioned above in order of magnitude to the total sum of all the multiple eigenvalues.

[0096] Alternatively, the calculated correlation values ​​mentioned above may be compared with a predetermined lower limit, and a combination of candidate null formation directions that satisfies the condition that the sum of the calculated correlation values ​​is equal to or greater than the lower limit may be selected as the null direction to be formed in the actual environment. In addition, a lower limit may be set for the calculated correlation values ​​for terrestrial BS30 (or UE65), and if the lower limit is not met, the number of nulls may be increased and additional null directions may be selected.

[0097] An estimated amount of interference from the upper-air PF10 to the ground cell may be calculated by considering the aforementioned calculated correlation values ​​and the transmission power and propagation loss values ​​of the upper-air PF10, and a lower limit may be set based on the estimated amount of interference to be compared with the calculated correlation values. For example, for the propagation paths of the multiple candidate directions for null formation, the amount of interference from the upper-air PF10 to multiple ground BS30 or multiple UE65 connected to multiple ground BS30 may be calculated based on the correlation calculation results, the transmission power of the upper-air PF10 and the propagation loss in the propagation path, and the lower limit may be set based on the calculation results of the amount of interference.

[0098] Furthermore, the upper PF 10 may periodically update the aforementioned traffic information or when a predetermined acquisition timing arrives, re-estimate the aforementioned multiple first channel vectors based on the updated traffic information, recalculate the correlation between the multiple first channel vectors and the multiple second channel vectors, and update the direction and number of multiple nulls formed in the actual environment based on the calculation result of the correlation.

[0099] [Method for calculating beamforming weights] The upper-air PF 10 may calculate a beamforming weight matrix W based on the calculation results of eigenvectors, which is used to form multiple nulls in the real environment and to form a beam 100B for the upper-air PF user (UE 61) connected to the wide-area cell 100C.

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

[0101] B1: Method of calculation from the pseudo-inverse of the extended channel matrix. In this method, when the channel matrix between the upper air PF 10 and the UE (upper air PF user) 61 is H, the extended channel matrix H is defined by equation (25) below. ｅｘ From the pseudo-inverse matrix, the weight matrix W can be obtained as shown in equation (26) below. ｅｘ Calculate.

[0102] The weight matrix W calculated using equation (26) above ｅｘ The column vectors that direct the beam 100B towards the UE (Air PF User) 61 are extracted, and a weight matrix W is constructed.

[0103] B2: Two-stage weight calculation method In this method, the weight W of the part where null formation is performed ＮＦ And the weight W of the part that forms the beam to the UE (Air PF User) 61 ＢＦ The and are calculated separately, and the weight W is shown in equation (27) below. ＮＦ and weight W ＢＦ We multiply these two factors together to obtain the weight matrix W.

[0104] Weight W of the part that performs null formation ＮＦ For example, the channel vector in the direction of null and the weight W mentioned above. ＮＦ It is calculated using equation (29) below, which is obtained under the condition of equation (28) below regarding orthogonality with respect to the matrix. Note that the right-hand side of equation (28) below is the zero matrix.

[0105] Also, the weight W of the part that performs null formation. ＮＦ This is the eigenvector ν of the aforementioned matrix A. ｉ By utilizing the orthogonality, the eigenvector ν of matrix A ｉ Among them, the channel vector of the null that is formed The elements that were not selected may be grouped together as a matrix equal to or greater than the number of users of the upper PF, as shown in equation (30) below. Here, N ａｎｔ This represents the total number of elements in the array antenna.

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

[0107] Figure 12 is an explanatory diagram showing an example of the overall configuration of a communication system having a terrestrial BS database according to the embodiment. Although Figure 12 shows the case where the relay communication station 110 mounted on the air PF 10 is a base station type relay communication station having base station equipment, the relay communication station 110 mounted on the air PF 10 may be a repeater type relay communication station. In this case, base station equipment is provided at the relay communication station 110 mounted on the air PF 10 and at ground feeder stations (gateway stations) 70, etc., and the wide-area cell base station (air PF base station) includes the repeater type relay communication station mounted on the air PF 10 and the ground base station equipment.

[0108] In Figure 12, the aerial PF 10 can notify the ground BS 30 of various information via the feeder station (gateway station) 70, the mobile communication network 80, and the backhaul line 81. The aerial PF 10 can also access the ground base station database 82 via the feeder station (gateway station) 70 and the mobile communication network 80 to obtain ground cell-related information such as ground base station 30 information and traffic information. The ground BS 30 can periodically or at predetermined intervals access the ground base station database 82 via the mobile communication network 80 and the backhaul line 81 to update the ground base station database 82 in order to share ground cell-related information such as traffic information of ground cell 300C with the aerial PF 10.

[0109] The ground cell-related information stored in the ground base station database 82 is information referenced from the airborne PF 10, and includes, for example, the following information (I2-1) to (I2-3): (I2-1) Base station specifications such as the position coordinates, antenna height, transmission power, and cell radius of the ground BS 30 (I2-2) Traffic information (I2-1) Geographic distribution of users connected to the ground BS 30 (which changes over time)

[0110] [Configuration of the relay communication station on the upper PF] Figure 13 is a block diagram showing an example of the main configuration of the relay communication station 110 mounted on the upper PF 10 in the communication system of Figure 12. In Figure 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 communicates with the UE (Upper PF user) 61 via a service link through beam 100B. The channel estimation unit 1102 may be included in the null optimization unit 1103.

[0111] The information acquisition unit 1101 accesses the ground base station database 82 via the feeder link FL and acquires ground cell-related information relating to at least one of the ground cell 300C superimposed on its own service area 100A (upper PF cell 100C) and the ground base station 30 that forms the ground cell 300C. The ground cell-related information may include traffic information of multiple ground BS 30. The information acquisition unit 1101 may further acquire geographical distribution information of ground BS users located in the ground cell 300C.

[0112] The channel estimation unit 1102 estimates multiple first channel vectors between the antenna of the aerial PF 10 and the antennas of the aerial BS 30 (or the ground directly below the antennas) or between the antenna of the aerial PF 10 and the aerial UEs (terrestrial cell users) 65 connected to the aerial BS 30, based on traffic information from the aerial BS 30.

[0113] The null optimization unit 1103 calculates the correlation between a plurality of first channel vectors and a plurality of second channel vectors corresponding to a plurality of candidate null formation directions, and based on the results of the correlation calculation, determines the direction and number of plurality of nulls 100N in the actual environment such that the number of plurality of directional nulls 100N formed for the upper air PF cell 100C is less than the number of plurality of ground BS 30.

[0114] The weight calculation unit 1104 calculates a weight matrix W based on the direction and number of multiple nulls 100N determined by the null optimization unit 1103, which is used to form multiple nulls 100N in the actual environment and to form beams for the UE (upper cell user) 61 connected to the upper 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 it and the UE (Upper Cell User) 61 connected to the upper PF cell 100C in the SL communication unit 1106.

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

[0117] Figure 15 is a flowchart illustrating an example of the main processing at the relay station 110 of the upper PF 10 when performing beamforming control with null formation and service link communication in the communication system according to the embodiment. In Figure 15, the relay station 110 of the upper PF 10 accesses the ground base station database 82 via the feeder link FL and obtains traffic information regarding the ground BS 30 located around its own service area 100A (upper PF cell 100C) (S201). The traffic information obtained includes the coordinates of the ground BS 30 and the distribution of ground BS users (UE) 65.

[0118] Next, the relay communication station 110 in the airborne PF 10 estimates the channel vector (first channel vector) in the direction of the ground BS user (UE) 65 or the ground BS 30, based on the information of the ground BS 30 obtained from the ground base station database 82, using a model or the like (S202).

[0119] Next, the relay communication station 110 in the upper air PF 10 calculates matrix A, which is necessary for correlation calculation, from the estimated channel vector and importance, and finds the eigenvalues ​​and eigenvectors of matrix A (S203).

[0120] Next, the relay communication station 110 in the upper air PF 10 selects an eigenvector with a large eigenvalue and sets it as the channel vector in the direction of null (second channel vector) to be applied to the actual environment (S204).

[0121] Next, the relay communication station 110 in the upper air PF 10 selects a predetermined number of eigenvectors and determines whether the calculated correlation value or eigenvalues ​​satisfy predetermined conditions based on the multiple channel vectors determined (S205). If the conditions are not met, the next eigenvector with the largest eigenvalue is selected and added as the channel vector in the direction of null to be applied to the actual environment (S206).

[0122] Next, once the relay communication station 110 in the upper air PF 10 has finished selecting a predetermined number of nulls (eigenvectors, channel vectors in the null direction), it calculates a weight matrix W for null formation and beam formation using the channel vectors in the null direction or eigenvectors that were not selected in the null direction (S207).

[0123] Next, the relay communication station 110 of the upper PF 10 applies the weight matrix W and communicates with the upper PF user 61 (S208).

[0124] As described above, according to the embodiments of this disclosure, when a ground cell 300C formed by an antenna of a ground BS 30 using the same frequency band is located within a cell 100C formed from an aerial PF 10 toward the ground or sea, interference from the aerial PF 10 to the ground cell 300C (ground BS 30) and the ground BS user (UE) 65 connected to the ground BS 30 can be suppressed.

[0125] Furthermore, according to the embodiments of this disclosure, a large number of terrestrial cells can be covered with fewer nulls than the number of terrestrial BS (terrestrial cells), thereby achieving high frequency utilization efficiency.

[0126] The system disclosed herein can cover a large number of terrestrial cells with fewer nulls than the number of terrestrial BS (terrestrial cells), and can provide a system that achieves high frequency utilization efficiency, thus contributing to the achievement of Sustainable Development Goal (SDG) 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0127] Furthermore, the processing steps described herein, as well as the components of communication relay equipment such as airborne PFs, including relay 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 base station equipment, can be implemented by various means. For example, these processes and components may be implemented using hardware, firmware, software, or a combination thereof.

[0128] With respect to hardware implementation, means such as processing units used to realize the above process and components in an entity (e.g., a relay station, feeder station, gateway station, base station, base station equipment, relay station equipment, terminal equipment (UE: user equipment, mobile station, communication terminal), management equipment, monitoring equipment, remote control equipment, server, hard disk drive equipment, or optical disk drive equipment) 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 perform the functions described herein, computers, or combinations thereof.

[0129] Furthermore, with respect to the firmware and / or software implementation, means such as processing units used to realize the aforementioned components may be implemented in the form of a program (e.g., code such as procedures, functions, modules, instructions, etc.) that performs the functions described herein. Generally, any computer / processor-readable medium that clearly embodies the firmware and / or software code may be used to implement means such as processing units used to realize the aforementioned processes and components as described herein. For example, the firmware and / or software code may be stored in memory in a control device, for example, and executed by a computer or processor. That memory may be implemented inside the computer or processor, or it may be implemented outside the processor. Furthermore, the firmware and / or software code may be stored on 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 disks, compact discs (CDs), digital versatile discs (DVDs), magnetic or optical data storage devices, etc. The code may be executed by one or more computers or processors, and the computers or processors may be made to perform functional embodiments described herein.

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

[0131] Furthermore, the descriptions of embodiments disclosed herein are provided to enable those skilled in the art to manufacture or use the disclosure. Various modifications to the 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 disclosure. Therefore, the disclosure is not limited to the examples and designs described herein, but should be accepted in the broadest sense that conforms to the principles and novel features disclosed herein.

[0132] 10: Airborne communication relay equipment (Airborne PF) 30: Ground cell base station (Ground base station, Ground BS) 61: Airborne 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: Airborne 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 toward the ground or sea from a service link antenna of a relay communication station installed on an aircraft or floating body located in the air, comprising: a communication unit that communicates on a service link in the same frequency band with a plurality of ground cell base stations that form ground cells overlapping with or adjacent to the wide-area cell from antennas located on the ground or sea; 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 direction and number of the plurality of directional 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 ground cell base stations, based on the ground cell-related information acquired by the information acquisition unit; a weight calculation unit that calculates a weight matrix for forming the plurality of nulls in the actual environment and beamforming for terminal devices connected to the wide-area cell, based on the direction 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 signals transmitted and received between the wide-area cell and terminal devices connected to the wide-area cell.

2. A wide-area cell base station according to claim 1, wherein the information acquisition unit acquires traffic information of the plurality of ground 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 ground 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 ground cell base stations, based on the traffic information of the plurality of ground cell base stations, calculates the correlation between the plurality of first channel vectors and a plurality of second channel vectors corresponding to a plurality of candidate null formation directions, and determines the direction and number of the plurality of nulls based on the result of the correlation calculation.

3. A wide-area cell base station according to claim 2, wherein the null optimization unit determines the direction and number of the plurality of nulls based on the correlation calculation result and the geographical distribution of the plurality of terminal devices connected to the plurality of ground cell base stations.

4. A wide-area cell base station according to claim 2, wherein the null optimization unit applies priority setting weights for setting the priority of null formation to the calculation of the correlation, and determines the direction and number of the plurality of nulls based on the calculation result of the correlation calculated by applying the priority setting weights.

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

6. A wide-area cell base station according to claim 2, wherein the null optimization unit determines the direction and number of the plurality of nulls by assuming that a plurality of terminal devices connected to each of the plurality of ground cell base stations are localized at the location of the ground cell base station.

7. A wide-area cell base station according to claim 2, wherein the null optimization unit compares the calculated correlation value with a preset lower limit value, and selects from among the plurality of candidate null formation directions a combination of candidate null formation directions that satisfies the condition that the sum of the calculated correlation values ​​is equal to or greater than the lower limit value, as the direction of the null to be formed in the actual environment.

8. A wide-area cell base station according to claim 7, wherein the null optimization unit calculates the amount of interference from the wide-area cell base station to the plurality of ground cell base stations or a plurality of terminal devices connected to the plurality of ground cell base stations based on the correlation calculation result, the transmission power of the wide-area cell base station, and the propagation loss in the propagation path for the plurality of candidate propagation paths for the plurality of null formation directions, and sets the lower limit based on the calculation result of the amount of interference.

9. A wide-area cell base station according to claim 2, wherein the null optimization unit updates the 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 updates the direction and number of the plurality of nulls based on the result of the correlation calculation.

10. A wide-area cell base station according to any one of claims 2 to 9, wherein the null optimization unit calculates a plurality of eigenvalues ​​λ and eigenvectors ν for a matrix defined using the plurality of first channel vectors, transforms the plurality of second channel vectors using the eigenvectors ν obtained by rearranging the elements of the eigenvalues ​​λ in descending order, and determines the direction and number of the plurality of nulls based on the transformed plurality of second channel vectors.

11. A wide-area cell base station according to claim 10, characterized in that the null optimization unit calculates the plurality of eigenvalues ​​and eigenvectors from a plurality of singular values ​​and singular vectors obtained using singular value decomposition for a matrix defined using the plurality of first channel vectors.

12. A wide-area cell base station according to claim 10, wherein the null optimization unit compares the plurality of eigenvalues ​​in the transformed correlation matrix with a preset threshold, and selects from the plurality of candidate null formation directions a candidate null formation direction that satisfies the condition that the eigenvalues ​​are greater than or equal to the threshold as the direction of the null to be formed in the actual environment.

13. A wide-area cell base station according to claim 10, wherein the null optimization unit selects a direction for null formation in the actual environment from a plurality of candidate null formation directions based on the ratio of the partial cumulative sum obtained by accumulating the plurality of eigenvalues ​​in the transformed correlation matrix in order of magnitude to the total of all the plurality of eigenvalues.

14. A wide-area cell base station according to claim 10, wherein the weight calculation unit calculates a weight matrix for forming the plurality of nulls in a real environment and beamforming for terminal devices connected to the wide-area cell, based on the calculation results of the plurality of eigenvectors.

15. In the wide-area cell base station of claim 14, the weight calculation unit determines a plurality of second channel vectors corresponding to the directions of a plurality (Nn) of nulls formed in the real environment based on the plurality of eigenvectors, and transposes the plurality of second channel vectors, 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 connected to the wide-area cell is, A wide-area cell base station characterized by selecting column vectors from equation (3) below, which is the pseudo-inverse of the extended channel matrix of equation (2) below, defined as follows, and calculating a weight matrix that performs the formation of the multiple nulls in the real environment and beamforming for terminal devices connected to the wide-area cell.

16. In the wide-area cell base station of claim 14, the weight calculation unit has a weight portion W that forms a plurality of nulls in the real environment using the plurality of eigenvectors. ＮＦ And the weight portion W that forms the beam for the terminal device connected to the wide-area cell. ＢＦ A wide-area cell base station characterized by calculating in two stages, and calculating a weight matrix (W) for forming the multiple nulls in the actual environment and beamforming for terminal devices connected to the wide-area cell using the following equation (4).

17. A system comprising a wide-area cell base station according to any one of claims 1 to 9, and a plurality of ground cell base stations that form ground cells overlapping with or adjacent to the wide-area cell from antennas located on land or at sea.

18. A method for forming a null in a wide-area cell base station that forms a wide-area cell toward the ground or sea from a service link antenna of a relay communication station installed on an aircraft or floating body located in the air, comprising: communicating a service link in the same frequency band with a plurality of ground cell base stations that form ground cells overlapping with or adjacent to the wide-area cell from an antenna located on the ground or sea; acquiring ground cell-related information relating to at least one of the plurality of ground cell base stations and the plurality of ground cells; determining the direction and number of the plurality of directional nulls to be formed based on the acquired ground 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 ground cell base stations; calculating a weight matrix for forming the plurality of nulls in a real environment and beamforming toward a terminal device connected to the wide-area cell based on the determined direction and number of the plurality of nulls; and applying the calculated weight matrix to signals transmitted and received between the terminal device connected to the wide-area cell and the network.

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

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