System with wide-area cell base station and terrestrial cell base station

Abstract

Provided is a system that makes it possible to, when forming a directional null toward an antenna or the terrestrial cell of a terrestrial cell base station from a relay communication station which is up in the sky and which forms a wide-area cell, improve frequency utilization efficiency without impairing the coverage area of the wide-area cell. A wide-area cell base station and a terrestrial cell base station perform service link communication in the same frequency band on mutually time-synchronized radio frames. The wide-area cell base station acquires information regarding the terrestrial cell base station that forms a terrestrial cell overlapping a wide-area cell, determines, on the basis of the information regarding the terrestrial cell base station, null scheduling regarding allocation of directional nulls that are formed toward an antenna or the terrestrial cell of the terrestrial cell base station on the time axis and on the frequency axis, and controls the formation of the directional nulls on the basis of information regarding the null scheduling.

Description

System Comprising a Wide-Area Cell Base Station and a Ground Cell Base Station

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

[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 sea is known. In an environment where such a wide-area cell base station communicates with a UE (terminal) via a service link (hereinafter referred to as an "upper-air system") and an existing ground cell base station communicates with a UE (terminal) via a service link (hereinafter referred to as a "ground system") coexist, when communication is performed simultaneously using the same frequency band, the signal from the relay communication station of the upper-air system becomes interference to the ground system. When this interference from the upper-air system occurs, the throughput of the ground system significantly decreases. Similarly, the signal from the ground system also becomes interference to the upper-air system. When this interference from the ground system occurs, the throughput of the upper-air system decreases.

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

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

[0005] A system according to one aspect of this disclosure is a system comprising 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, and one or more ground cell base stations that form a ground cell from an antenna located on the ground or sea. In this system, the wide-area cell base station and the one or more ground cell base stations communicate on a service link in the same frequency band using radio frames that are time-synchronized with each other. The wide-area cell base station acquires information about ground cell base stations that form ground cells overlapping with the wide-area cell, determines null scheduling regarding the time axis and frequency axis allocation of directional nulls to be formed toward the antenna of the ground cell base station or the ground cell based on the information about the ground cell base station, and controls the formation of the directional nulls based on the null scheduling information.

[0006] In the aforementioned system, the wide-area cell base station may acquire traffic information relating to at least one of the service link traffic in the wide-area cell and the service link traffic in the ground cell, and determine the null scheduling based on the traffic information and information relating to the ground cell base station.

[0007] In the above system, the wide-area cell base station may acquire user distribution information relating to at least one of the geographical distribution of user terminal devices located in the wide-area cell and the geographical distribution of user terminal devices located in the ground cell, and determine the null scheduling based on the user distribution information and information relating to the ground cell base station.

[0008] In the above system, the wide-area cell base station may calculate a selection index for each of the terminal devices of a plurality of users located in the wide-area cell to select terminal devices whose communication quality will be degraded by the formation of the null; select one or more user terminal devices to communicate with the wide-area cell base station via a service link based on the calculation results of the selection index for the plurality of user terminal devices; determine the wide-area cell's user scheduling regarding the allocation of radio resources on the time axis and frequency axis for the selected one or more user terminal devices; and communicate with the selected one or more user terminal devices via a service link based on the wide-area cell's user scheduling information.

[0009] In the aforementioned system, the selection index used by the wide-area cell base station may be an index that uses the degree of orthogonality between the channel vector between the wide-area cell base station and the terminal device of a user located in the wide-area cell, and the channel vector between the wide-area cell base station and a corresponding point on land or at sea corresponding to the direction of the null.

[0010] In the aforementioned system, the selection index used by the wide-area cell base station may be an index that uses the distance and angular direction of the user's terminal device located in the wide-area cell relative to the service link antenna of the wide-area cell base station, and the distance and angular direction of the corresponding point on land or at sea corresponding to the direction of the null relative to the service link antenna of the wide-area cell base station.

[0011] In the aforementioned system, if the spatial multiplexing rate in the radio resource to which the selected user's terminal device is assigned is less than the maximum spatial multiplexing rate of the wide-area cell, the wide-area cell base station may duplicate the communication with the terminal devices of the remaining one or more users to the radio resource.

[0012] In the aforementioned system, the wide-area cell base station may sequentially select one or more user terminal devices to communicate with the wide-area cell base station via a service link using a plurality of selection indicators for each of the plurality of user terminal devices.

[0013] In the above system, the wide-area cell base station may divide the terminal devices of multiple users located within the wide-area cell into a first group that uses radio resources to form the null and a second group that selectively uses one or more radio resources that do not form the null, and individually determine the allocation of radio resources to the user terminal devices for each group.

[0014] In the above system, the wide-area cell base station may transmit the null scheduling information to the ground cell base station, the ground cell base station may receive the null scheduling information from the wide-area cell base station, determine the ground cell user scheduling regarding the allocation of users' terminal devices in radio resources on the time axis and frequency axis based on the null scheduling information, and communicate a service link with the user terminal devices of users located in the ground cell based on the ground cell user scheduling information.

[0015] In the above system, the ground cell base station may calculate a selection index for each of the terminal devices of a plurality of users located within the ground cell, for selecting terminal devices whose communication quality will be degraded by the null formation control, and based on the calculation results of the selection index for the plurality of user terminal devices, select one or more user terminal devices to communicate with the ground cell base station via a service link, and determine the ground cell user scheduling regarding the allocation of radio resources on the time axis and frequency axis for the selected one or more user terminal devices.

[0016] In the above system, the selection index used at the ground cell base station may be an index that uses at least one of the channel state between the ground cell base station and the user's terminal device located in the ground cell, the desired signal power of the user's terminal device, and the SINR (signal-to-interference noise ratio) of the user's terminal device.

[0017] In the aforementioned system, the selection index used by the ground cell base station may be an index that uses the separation distance and angular direction of the user's terminal device located in the ground cell, with respect to the service link antenna of the ground cell base station.

[0018] In the above system, the ground cell base station may sequentially select one or more user terminal devices to communicate with the ground cell base station via a service link using a plurality of selection indicators for each of the plurality of user terminal devices.

[0019] In the above system, the ground cell base station may divide the terminal devices of multiple users located within the ground cell into a first group using radio resources for which the wide-area cell base station forms the null with respect to the base station, and a second group using radio resources for which the wide-area cell base station does not form the null with respect to the base station, partially or entirely, and individually determine the allocation of radio resources to the terminal devices of the users for each group.

[0020] In the above system, there may be a plurality of ground cell base stations, and the null scheduling information may include information on the allocation of a first radio resource that forms the null for all of the plurality of ground cell base stations, and information on the allocation of a second radio resource that selectively stops the formation of the null for each ground cell base station, and each of the plurality of ground cell base stations may preferentially allocate the first radio resource to one or more user terminal devices based on the calculation result of the selection index for the terminal devices of the plurality of users, and after the allocation of the first radio resource is completed, allocate the second radio resource to the remaining one or more user terminal devices.

[0021] In the above system, there may be a plurality of ground cell base stations, and the null scheduling information may include information on the allocation of a first radio resource that forms the null for all of the plurality of ground cell base stations, and information on the allocation of a second radio resource that selectively stops the formation of the null for each ground cell base station, and each of the plurality of ground cell base stations may preferentially allocate the first radio resource and a specific second radio resource from the second radio resource for which the null is formed for the station itself to one or more user terminal devices based on the calculation result of the selection index for the terminal devices of the plurality of users, and after the allocation of the first radio resource and the specific second radio resource is completed, the second radio resource may be allocated to the remaining one or more user terminal devices.

[0022] 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 an array antenna for the service link of an aerial PF according to the embodiment. Figure 5 is a perspective view showing another example of an array antenna for the service link of an aerial PF according to the embodiment. Figure 6 is an explanatory diagram showing the challenges when beamforming is performed 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 a diagram showing an example of a coverage hole in an aerial PF cell that occurs around a terrestrial BS antenna when a directional null is formed from an aerial PF. Figure 9 is a diagram showing an example of a coverage hole in an aerial PF cell that occurs around a terrestrial BS antenna when null sweeping is performed to change the position of the directional null formed from an aerial PF toward a ground cell. Figure 10 is a diagram showing an example of the results of an area simulation including coverage holes in an aerial PF cell that occurred when a null was formed from an aerial PF toward multiple terrestrial BS antennas. Figure 11A is a diagram showing an example of switching between a wireless resource with null ON, which forms a null by the aerial PF according to the embodiment, and a wireless resource with null OFF, which does not form a null. Figure 11B is a diagram showing an example of a ground cell and an aerial PF cell when null is ON. Figure 11C is a diagram showing an example of a ground cell and an aerial PF cell when null is OFF. Figure 12 is a diagram showing an example of the results of an area simulation when null formation by the aerial PF according to the embodiment is stopped. Figure 13A is a diagram showing an example of the positional relationship between a terrestrial BS antenna and an aerial PF user's terminal device when null is ON in the on / off switching control of null formation by the aerial PF according to the embodiment. Figure 13B is a diagram showing an example of the positional relationship between a terrestrial BS antenna and an aerial PF user's terminal device when null is OFF in the on / off switching control of null formation by the aerial PF according to the embodiment.Figure 14A is a diagram showing an example of the relationship between the direction of the null formed when null is ON in the on / off switching control of null formation by the aerial PF according to the embodiment, the direction of beamforming to the aerial PF user, and the positional relationship between the terrestrial BS antenna and the terrestrial BS user's terminal device. Figure 14B is a diagram showing an example of the relationship between the null that is stopped from being formed when null is OFF in the on / off switching control of null formation by the aerial PF according to the embodiment, the relationship to beamforming to the aerial PF user, and the positional relationship between the terrestrial BS antenna and the terrestrial BS user's terminal device. Figure 15 is a diagram showing an example of the distribution of multiple terrestrial BS antennas located within the aerial PF cell and multiple aerial PF user terminal devices located around each aerial BS antenna according to the embodiment. Figure 16 is a diagram showing an example of the allocation of radio resources (null ON resources) that form nulls for all antennas of multiple terrestrial BS from the aerial PF according to the embodiment and radio resources (null OFF resources) that stop null formation for a specific terrestrial BS antenna. Figure 17 is a diagram showing an example of null scheduling that forms a null for a specific terrestrial BS antenna in the null-off resource of Figure 16. Figure 18A is a diagram showing an example of null scheduling that forms a null toward a first terrestrial BS antenna in the null-off resource of Figure 16. Figure 18B is a diagram showing an example of null scheduling that forms a null toward a second terrestrial BS antenna in the null-off resource of Figure 16. Figure 19 is a diagram showing an example of user scheduling that performs service link communication between an airborne PF and terminal devices of multiple airborne PF users in the null-off resource of Figure 16. Figure 20 is a diagram showing an example of the distribution of multiple terrestrial BS antennas located within an airborne PF cell and terminal devices of multiple terrestrial BS users located within the ground cells of each airborne BS according to the embodiment. Figure 21 is an explanatory diagram showing an example of the overall configuration of a communication system having a terrestrial BS database according to the embodiment. Figure 22 is a block diagram showing an example of the main configuration of a relay communication station mounted on an airborne PF in the communication system of Figure 21. Figure 23 is a block diagram showing an example of the main configuration of a ground cell base station in the communication system shown in Figure 21.Figure 24 is a flowchart showing an example of coordinated control between an airborne PF base station and a ground cell base station when performing beamforming control with null formation and service link communication in a communication system according to an embodiment. Figure 25A is a diagram showing an example of communication with multiple airborne PF users and resource allocation for multiple null formations in an airborne PF according to a reference example. Figure 25B is a diagram showing an example of communication with multiple airborne PF users and resource allocation for multiple null formations in an airborne PF according to an embodiment. Figure 25C is a diagram showing another example of communication with multiple airborne PF users and resource allocation for multiple null formations in an airborne PF according to an embodiment. Figure 26A is a diagram showing an example of the positional relationship between a ground BS and an airborne PF user when performing resource allocation with partial null OFF in an airborne PF according to an embodiment. Figure 26B is a diagram showing an example of the positional relationship between a ground BS and an airborne PF user when performing resource allocation with partial null OFF in an airborne PF according to an embodiment. Figure 26C is a diagram showing an example of the positional relationship between the ground BS and the aerial PF user when partial null OFF resource allocation is performed in the aerial PF according to the embodiment. Figure 27 is a diagram showing an example of an algorithm for selecting the terminal device of an aerial PF user that performs service link communication at the aerial PF base station of the communication system according to the embodiment. Figure 28 is a diagram showing another example of an algorithm for selecting the terminal device of an aerial PF user that performs service link communication at the aerial PF base station of the communication system according to the embodiment. Figure 29 is a diagram showing another example of an algorithm for selecting the terminal device of a ground BS user that performs service link communication at the ground BS of the communication system according to the embodiment.

[0023] Embodiments of the present invention will now be described 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 of a wide-area cell base station (e.g., an airborne PF base station) that forms a cell toward the ground or sea and performs MU-MIMO communication with a plurality of terminal devices (UEs) located within the cell using a multi-element array antenna. In this communication system, when a ground cell (second cell) formed by an existing ground cell base station (ground BS) using the same frequency band is located within the airborne PF cell, which is a wide-area cell (first cell), interference from the relay communication station of the airborne PF to the ground cell can be suppressed by forming a directional null from the relay communication station of the airborne PF 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 the fifth generation, which can handle simultaneous connection to a large number of terminal devices and low latency.

[0024] In particular, in the system of this embodiment, by switching the formation of a directional null from an upper-air PF relay station toward the antenna of a ground cell base station (ground cell) on or off, the occurrence of coverage holes in the upper-air PF cell (wide-area cell) when a directional null is formed from an upper-air PF relay station toward the antenna of a ground cell base station or the ground cell to suppress interference can be reduced, thereby reducing the deterioration of communication quality of user terminal equipment connected to the upper-air PF cell and improving the overall frequency utilization efficiency of the system.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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].

[0029] 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).

[0030] 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.

[0031] 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 time-synchronized radio frames and the same frequency band for wireless communication of the service link between themselves and UE 61 and 65 located in their respective cells 100C and 300C. 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 line. In this case, the RRH with the base station antenna is located at the position of the base station 30 in Figure 1.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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).

[0042] 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).

[0043] 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.

[0044] Further, the wireless communication of the service link in this embodiment has functions such as diversity coding, transmission beamforming, and spatial division multiplexing (SDM: Spatial Division Multiplexing), and uses a massive MIMO (Multiple-Input Multiple-Output) transmission method that performs 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 of the overhead PF10 to a plurality of UEs 61 within the cell, a MU-MIMO (Multi-User MIMO) technology that transmits signals to a plurality of different UEs 61 at the same time and the same frequency is used. By performing MU-MIMO transmission using an array antenna having a large number of antenna elements, it is possible to direct an appropriate beam for 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.

[0045] FIGS. 4 and 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 overhead PF10 of this embodiment.

[0046] The array antenna 130 in FIG. 4 has a flat antenna substrate, and antenna elements 130a such as a large number of patch antennas are two-dimensionally arranged in the axial directions perpendicular to each other along the planar antenna surface of the antenna substrate, and it is a planar array antenna.

[0047] 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.

[0048] 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.

[0049] 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 overhead PF10. In the service link SL between the array antenna 130 of the overhead 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.

[0050] 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.

[0051] 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.

[0052] Figure 7 is an explanatory diagram showing an example of a directional null formed from the aerial PF 10 toward the terrestrial 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 terrestrial BS (antenna) 30 located within the aerial PF service area 100A, interference from the aerial PF 10 toward the ground cell 300C can be reduced, and interference from the aerial PF 10 to the ground system communications can be suppressed. However, deterioration of the communication quality of the aerial PF 10 is unavoidable around the terrestrial BS 30, and there is a possibility that coverage holes 100H will occur where some UE 61' located within the aerial PF service area 100A cannot connect to the aerial PF 10.

[0053] Figure 8 shows an example of a coverage hole 100H in an upper-air PF cell (wide-area cell) 100C that occurs around the antenna of a terrestrial BS 30 when a directional null is formed from the upper-air PF 10. In the example in Figure 8, the coverage hole 100H occurs in an area wider than the terrestrial cell 300C, preventing UE61 from connecting to the upper-air PF 10 (upper-air PF cell 100C), or degrading the quality of communication (SINR) between UE61 and the upper-air PF 10. In particular, in Figure 8, UE61' located in the coverage hole 100H, which is located outside the terrestrial cell 300C, cannot connect to either the terrestrial BS 30 (terrestrial cell 300C) or the upper-air PF 10 (upper-air PF cell 100C).

[0054] Figure 9 shows an example of a coverage hole 100H in the upper air PF cell (wide-area cell) 100C that occurs around the antenna of the terrestrial BS 30 when performing null sweeping, which changes the direction of the directional null formed from the upper air PF 10 toward the ground cell 300C. When performing null sweeping, the coverage hole 100H, which is an area where connection to the upper air PF 10 (upper air PF cell 100C) is not possible or where the communication quality (SINR) has deteriorated, also changes along with the direction of the null.

[0055] Figure 10 shows an example of the results of an area simulation (computer simulation) including coverage holes in an upper-air PF cell (wide-area cell) 100C that occur when a null is formed from the upper-air PF 10 toward multiple ground BS 30(1) to 30(3) antennas. In Figure 10, the upper-air PF 10 is located above the center of the area of ​​the upper-air PF cell 100C and forms a null toward each of the multiple ground cells of BS 30(1) to 30(3) (areas of white circles in the figure). Due to this null formation, the areas shown in high density gray or black in the figure become SINR-degraded coverage holes 100H.

[0056] In this embodiment, in order to realize the sharing of the same frequency between an aerial PF system using an aerial PF 10 and a ground system using a ground BS 30, which is expected from the viewpoint of efficient frequency utilization, the aerial PF 10 and the ground BS 30 cooperate and combine switching control of null formation on the time axis, frequency axis, or both axes with resource allocation control. This improves frequency utilization efficiency without compromising the coverage area of ​​the aerial PF 10.

[0057] In the following description, we will mainly explain 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 formation switching control and resource allocation control of 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."

[0058] 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)

[0059] In the aerial PF10 according to this embodiment, for example, as shown in Figure 11A, null-ON wireless resources that form nulls on the time axis and frequency axis (hereinafter also referred to as "null-ON resources") and null-OFF wireless resources that do not form nulls (hereinafter also referred to as "null-OFF resources") are allocated to perform on / off switching control of null formation.

[0060] When a null is formed in a null-ON resource, a directional null is formed from the aerial PF 10 toward the antenna of the terrestrial BS 30 or the terrestrial cell 300C, as shown in Figure 11B. This null formation can suppress interference from the relay communication station of the aerial PF 10 toward the terrestrial cell 300C. However, the formation of the null may create a coverage hole 100H around the terrestrial BS 30. In this coverage hole 100H, there is a risk of communication degradation, such as UE61' located around the terrestrial cell 300C being unable to connect to the aerial PF 10 (aerial PF cell 100C), or a deterioration in the quality of communication (SINR) between UE61' and the aerial PF 10. In particular, if UE61' is located in an area outside the range of the terrestrial cell 300C within the coverage hole 100H, UE61' may be unable to connect to either the aerial PF cell 100C or the terrestrial cell 300C.

[0061] In this embodiment, in order to reduce the degradation of communication of UE61' located around the ground cell 300C, the system switches from a null-on resource to a null-off resource as shown in Figure 11A. When null formation is stopped in the null-off wireless resource, a wide-area aerial PF 100 is formed without the occurrence of a coverage hole 100H as shown in Figure 11C. As a result, UE61' located around the ground cell 300C can connect to the aerial PF 10 (aerial PF cell 100C), and the quality of communication (SINR) with the aerial PF 10 does not deteriorate.

[0062] Figure 12 shows an example of the results of an area simulation (computer simulation) when null formation by the upper air PF 10 according to the embodiment is stopped. As shown in Figure 12, by stopping null formation by the upper air PF 10, the occurrence of SINR-degraded coverage holes (areas shown in high-density gray or black in Figure 10) 100H around each of the multiple ground BS 30(1) to 30(3) can be suppressed.

[0063] As shown in Figures 11A to 11C and Figure 12, by allocating null ON resources and null OFF resources in the upper PF 10 and controlling the on / off switching of null formation, it is possible to improve frequency utilization efficiency without compromising the coverage area of ​​the upper PF 10, and to realize the same frequency sharing between the upper PF system using the upper PF 10 and the ground system using the ground BS 30, which is expected from the viewpoint of effective frequency utilization.

[0064] [Overview of On / Off Switching Control for Null Formation on the Upper PF Side] Figure 13A is a diagram showing an example of the positional relationship between the antenna of the ground BS 30 and the upper PF user 61 when null is ON in the on / off switching control of null formation by the upper PF 10 according to the embodiment. Figure 13B is a diagram showing an example of the positional relationship between the antenna of the ground BS 30 and the upper PF user 61 when null is OFF in the on / off switching control of null formation by the upper PF 10 according to the embodiment. In Figures 13A and 13B, the solid arrows indicate the beam direction of downlink (DL) communication from the upper PF 10 toward each of the multiple upper PF users, and the dashed arrows indicate the direction of the null formed from the upper PF 10 toward each of the multiple ground BS 30.

[0065] In the upper-air PF 10, null-ON resources and null-OFF resources are pre-configured in the wireless frame. With the null-ON resource, as shown in Figure 13A, the upper-air PF 10 forms nulls toward each of the multiple ground BS 30s, and this null formation suppresses interference from the upper-air PF 10 to the ground cell. With the null-OFF resource, as shown in Figure 13B, the upper-air PF 10 stops forming nulls so that upper-air PF users who are close to the antennas of the ground BS 30s but not within range of the ground cell 300C can communicate with the upper-air PF 10.

[0066] Furthermore, the upper-air PF10 may be controlled to stop null formation to all ground BS30 in the null OFF resource, or it may be controlled to stop null formation to only some of the ground BS30.

[0067] Furthermore, the upper-air PF 10 may calculate a selection index for each of the multiple upper-air PF users to select the upper-air PF user whose communication quality deteriorates due to the formation of nulls, and based on the calculation results of the selection index, select the upper-air PF user to communicate with the upper-air PF 10 for service link communication, and determine the user scheduling of the upper-air PF cell 100C regarding the allocation of radio resources on the time axis and frequency axis for the selected upper-air PF user.

[0068] [Coordinated control between upper-air PF and ground BS for null ON / OFF] Figure 14A is a diagram showing an example of the relationship between the direction of the null formed when null is ON in the on / off switching control of null formation by the upper-air PF according to the embodiment, the direction of beamforming to the upper-air PF user 61, and the positional relationship between the ground BS antenna and the terminal device of the ground BS user. Figure 14B is a diagram showing an example of the relationship between the null that is stopped forming when null is OFF in the on / off switching control of null formation by the upper-air PF 10 according to the embodiment, the relationship between beamforming to the upper-air PF user 61, and the positional relationship between the ground BS antenna and the terminal device of the ground BS user.

[0069] In the case of null ON as shown in Figure 14A, interference from the upper air PF 10 can be suppressed by null formation by the upper air PF 10. Therefore, the ground BS 30 can perform downlink (DL) communication even with the ground BS user 65 located at the edge of the ground cell 300C.

[0070] On the other hand, in the case of null OFF as shown in Figure 14B, interference from the upper air PF 10 becomes significant with null OFF resources. Therefore, the ground BS 30, through coordinated control with the upper air PF 10, also assigns ground BS users in a way that reduces the impact of interference from the upper air PF 10. For example, the ground BS 30 prioritizes assigning users who use null ON resources, and when using null OFF resources, it controls the system to select a ground BS user located in the center of the ground cell where the received power of the desired signal is high.

[0071] [An example of resource allocation control for an aerial PF] Figure 15 is a diagram showing an example of the distribution of multiple ground BS 30 antennas located within the wide-area cell (aerial PF cell) 100C of the aerial PF 10 according to the embodiment, and multiple aerial PF users 61 located around each of the aerial PF antennas. In Figure 15, the first ground cell 300C(1) of the first ground BS 30(1) (hereinafter referred to as "BS1" in the resource allocation diagram) and the second ground cell 300C(2) of the second ground BS 30(2) (hereinafter referred to as "BS2" in the resource allocation diagram) are located within the aerial PF cell 100C. Multiple aerial PF users 61(1) to 61(6) (hereinafter referred to as users 1 to 6 in the user scheduling diagram) are located around the first cell 300C(1), and multiple aerial PF users 61(7) to 61(9) (hereinafter referred to as users 7 to 9 in the user scheduling diagram) are located around the second cell 300C(2).

[0072] Figure 16 shows an example of the allocation of radio resources (null ON resources) that form nulls for all antennas of a plurality of terrestrial BSs from an aerial PF 10 according to the embodiment, and radio resources (null OFF resources) that stop forming nulls for antennas of a specific terrestrial BS. In Figure 16, a radio frame consists of a total of 24 radio resources (hereinafter also referred to as "resources"), each allocated three different frequencies on the frequency axis and eight slots on the time axis. Null OFF resources consist of a total of eight resources, each allocated eight consecutive slots on the time axis to the same first frequency on the higher frequency side, and are resources that stop forming nulls for a specific terrestrial BS among the plurality of terrestrial BSs. Null ON resources consist of a total of 16 resources, each allocated eight slots to the other second and third frequencies, and are resources that form nulls for all of the plurality of terrestrial BSs.

[0073] Figure 17 is a diagram showing an example of null scheduling that forms a null for a specific terrestrial BS antenna in the null-off resource of Figure 16. In each of the multiple resources of the null-off resource in Figure 17, the terrestrial BS that form a null from the upper PF10 are shown in high-density bold characters BS1 and BS2. Figure 18A is a diagram showing an example of null scheduling that includes a null assignment that forms a null for the antenna of the first terrestrial BS30(1) in the null-off resource of Figure 16. Figure 18B is a diagram showing an example of null scheduling that includes a null assignment that forms a null for the antenna of the second terrestrial BS30(2) in the null-off resource of Figure 16. As shown in Figures 17, 18A and 18B, for example, in the resource in the leftmost first slot of the multiple resources of the null-off resource, no null is formed for either BS1 or BS2. Also, in the resource in the second slot, a null is formed only for BS2, and no null is formed for BS1. Furthermore, the resource in the third slot creates a null only for BS1, and does not create a null for BS2.

[0074] Note that the allocation of null ON and OFF resources in Figure 16, and the null scheduling in Figures 17, 18A, and 18B are merely examples, and other allocations of null ON and OFF resources and null scheduling may be determined.

[0075] For example, the null scheduling may be determined based on traffic information relating to at least one of the service link traffic in the upper PF cell 100C and the service link traffic in the ground cells 300C(1) and 300C(2). Alternatively, the null scheduling may be determined based on user distribution information relating to at least one of the geographical distribution of upper PF users 61 located in the upper PF cell 100C and the geographical distribution of ground BS users located in the ground cells 300C(1) and 300C(2).

[0076] Figure 19 is a diagram illustrating an example of user scheduling for service link communication between the upper PF 10 and multiple upper PF users 61 in the null OFF resource shown in Figure 16. In Figure 19, for example, among the multiple resources of the null OFF resource, upper PF users 1 and 7 are assigned to the resource in the leftmost first slot, upper PF user 2 is assigned to the resource in the second slot, and upper PF user 8 is assigned to the resource in the third slot.

[0077] Here, the upper PF 10 may determine the user scheduling of the upper PF users 61 by assigning multiple upper PF users 61, who are far from both ground BS 30(1) and 30(2), to the same resource in overlapping manner, such that the spatial multiplexing of the wireless resource between the upper PF users 61 and the upper PF users 61 is less than or equal to the maximum spatial multiplexing of the upper PF cell 100C.

[0078] In this embodiment, the units of the frequency domain on the frequency axis and the time domain on the time axis for the resources in the allocation of null ON resources and null OFF resources and null allocation to each airborne BS may be the same units as those for resources in the scheduling of airborne PF users. For example, the unit of the frequency domain of the resource may be 12 subcarriers corresponding to resource blocks in a fifth-generation mobile communication system, and the unit of the time domain of the resource may be the smallest scheduling unit such as a slot or OFDM symbol in a fifth-generation mobile communication system.

[0079] Furthermore, the number of control operations and the load may be reduced by increasing the unit size of the resources in the null allocation described above. For example, the unit in the frequency domain of the resources may be a group of multiple resource blocks, and the unit in the time domain of the resources may be a group of multiple slots, a group of multiple subframes, a group of multiple wireless frames, etc. Also, the unit in the time domain of the resources may be 1 ms to 10 minutes, or 10 ms, 100 ms, or 1 s.

[0080] [Example of Terrestrial BS Resource Control] Figure 20 shows an example of the distribution of multiple terrestrial BS 30(1) and 30(2) antennas located within the wide-area cell (upper PF cell) 100C of the upper PF 10 according to the embodiment, and multiple terrestrial BS users 65 located within the terrestrial cells 300C(1) and 300C(2) of each upper BS. In Figure 20, multiple terrestrial BS users 65 are located in each of the multiple terrestrial cells 300C(1) and 300C(2).

[0081] In Figure 20, when only information about the location of null-off resources in the wireless frame is shared between the aerial PF 10 and multiple ground BS 30(1), 30(2) (in the case of sparse coordination), considering that nulls are always formed in the local cell for null-on resources, and that it is unknown at what time and frequency nulls will be directed towards the local cell for null-off resources, user scheduling is performed, for example, using the following procedure S11 to S14.

[0082] S11: Terrestrial BS 30(1) and 30(2) each determine the users to be allocated so that the number of resources allocated is less than or equal to the number of users allocated, taking into consideration traffic, channel status, etc.

[0083] S12: Terrestrial BS 30(1) and 30(2) each calculate a selection index for each terrestrial BS user 65. Here, the selection index is an index for selecting terrestrial BS users whose communication quality deteriorates due to null formation control. The selection index is, for example, an index that uses at least one of the channel state between terrestrial BS 30 and terrestrial BS user 65, the desired signal power of terrestrial BS user 65, and the SINR (signal-to-interference noise ratio) of terrestrial BS user 65. The selection index may also be an index that uses the separation distance and angular direction of the terrestrial BS user with respect to terrestrial cell BS 30.

[0084] S13: Terrestrial BS 30(1) and 30(2) each allocate resources prioritizing null ON resources according to the calculation results of the selection indicators for terrestrial BS users.

[0085] S14: Once terrestrial BS 30(1) and 30(2) have completed the allocation of null ON resources, the remaining terrestrial BS users 65 will be allocated to null OFF resources. Allocating to null OFF resources increases the probability of interference, so allocation to null OFF resources will be avoided as much as possible.

[0086] In Figure 20, when null scheduling information is shared between the upper-air PF 10 and multiple ground BS 30(1), 30(2) (in the case of close coordination), considering that nulls are always formed in the cell of null-ON resources, and that it is possible to know at what time and frequency nulls will be directed towards the cell of null-OFF resources (see Figures 18A and 18B), user scheduling is performed, for example, by the following procedure S21 to S24.

[0087] S21: Terrestrial BS 30(1) and 30(2) each determine the users to be allocated so that the number of resources allocated is less than or equal to the number of users allocated, taking into consideration traffic, channel status, etc.

[0088] S22: Terrestrial BS 30(1) and 30(2) each calculate a selection index for each terrestrial BS user 65. Here, the selection index is an index for selecting terrestrial BS users whose communication quality deteriorates due to null formation control. The selection index is, for example, an index that uses at least one of the channel state between terrestrial BS 30 and terrestrial BS user 65, the desired signal power of terrestrial BS user 65, and the SINR (signal-to-interference noise ratio) of terrestrial BS user 65. The selection index may also be an index that uses the separation distance and angular direction of the terrestrial BS user relative to terrestrial cell BS 30.

[0089] S23: Terrestrial BS 30(1) and 30(2) each allocate resources in order to prioritize null-enabled resources and special resources (see Figures 18A and 18B) whose own cell has nulls, even if they are null-off resources, according to the calculation results of the selection index of terrestrial BS users.

[0090] S24: Once terrestrial BS 30(1) and 30(2) have completed the allocation of null ON resources and special resources respectively, the remaining terrestrial BS users 65 will be allocated to the remaining null OFF resources.

[0091] [Overall System Configuration] Figure 21 is an explanatory diagram showing an example of the overall configuration of a communication system having a ground base station database 82 according to the embodiment. In Figure 21, the same reference numerals are used for parts that are the same as those in Figure 1, and their descriptions are omitted. Figure 21 shows the case where the relay communication station 110 mounted on the air PF 10 is a base station equipment type relay communication station having base station equipment, but 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 on the relay communication station 110 mounted on the air PF 10 and on the ground feeder station (gateway station) 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.

[0092] In Figure 21, the aerial PF 10 can notify the ground BS 30 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 information about the ground base station 30.

[0093] The airborne PF10 and the ground-based BS30 share, for example, information I1 that is periodically notified from the airborne PF10 to the ground-based BS30 (hereinafter referred to as "notification information") and information I2 stored in the ground base station database 82 (hereinafter referred to as "DB information").

[0094] The notification information I1 depends on the user scheduling algorithm of the ground base station 30, but for example, it may include information related to nulls (I1-1) and information related to the airborne PF 10 (I1-2).

[0095] Information related to nulls (I1-1) is information about null formation related to the Ground BS30's own cell, and is, for example, the following information (I1-1-1) to (I1-1-3): (I1-1-1) A label that identifies the null (I1-1-2) Information about the location corresponding to the null, for example, the latitude and longitude of the location of the null formation target that the null is facing on land or at sea, and information such as values ​​in planar coordinates or polar coordinates (I1-1-3) The scheduling status of the null by the on / off control of null formation In the above loose coordination, only information on null-off resources is provided (resources that the null faces towards the own cell are not notified) In the above tight coordination, information on null-off resources and information on the null-off resources that stop any of the nulls and that face towards the own cell

[0096] Information regarding the PF10 in the air (I1-2) includes, for example, the following information (I1-2-1) and (I1-2-2): (I1-2-1) Information regarding the aircraft of the PF10 in the air (e.g., information on the aircraft's position and attitude) (I1-2-2) Information on the parameters related to the communication of the PF10 in the air (e.g., information on antenna configuration, beamforming and null formation)

[0097] The beamforming and null formation information mentioned above includes, for example, information on the weights to be applied to the transmitted or received signal, information on the upper-air PF user, and the codebook number if a codebook is used.

[0098] The information I2 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 demand; (I2-1) Geographic distribution of users connected to the ground BS 30 (which changes over time).

[0099] [Configuration of the relay communication station on the upper PF] Figure 22 is a block diagram showing an example of the main configuration of a base station type relay communication station 110 mounted on the upper PF 10 in the system shown in Figure 21. In Figure 22, the relay communication station 110 includes an information acquisition unit 1101, a null scheduling unit 1102, a null switching control unit 1103, a null scheduling information transmission unit 1104, and a user scheduling unit 1105 for the upper PF user 61.

[0100] The information acquisition unit 1101 accesses the ground base station database 82 via the feeder link FL and acquires information about the ground base station 30 that forms the ground cell 300C superimposed on its own service area 100A (upper PF cell 100C). The information acquisition unit 1101 may further acquire traffic information relating to at least one of the service link traffic in the upper PF cell 100C and the service link traffic in the ground cell 300C. The information acquisition unit 1101 may further acquire user distribution information relating to at least one of the geographical distribution of upper PF users 61 located in the upper PF cell 100C and the geographical distribution of ground BS users located in the ground cell 300C.

[0101] The null scheduling unit 1102 determines null scheduling for the allocation of directional nulls on the time axis and frequency axis to be formed toward the antenna or ground cell 300C of the ground base station 30, based on information of the ground base station 30 obtained from the ground base station database 82. The null scheduling unit 1102 may also determine the null scheduling based on the traffic information and the information of the ground base station 30. The null scheduling unit 1102 may also determine the null scheduling based on the user distribution information and the information of the ground base station 30.

[0102] The null switching control unit 1103 controls the formation of directional nulls based on the null scheduling information.

[0103] The null scheduling information transmission unit 1104 notifies each local base station 30 of the null scheduling information via the feeder link FL and the mobile communication network 80.

[0104] The user scheduling unit 1105 of the upper air PF 10 may calculate a selection index for each of the multiple upper air PF users 61 located in the upper air PF cell 100C to select the upper air PF user 61 whose communication quality deteriorates due to the formation of nulls. Based on the calculation results of the selection index for the multiple upper air PF users 61, it may select one or more upper air PF users 61 to communicate with the upper air PF 10 via a service link, and determine the user scheduling of the upper air PF cell 100C regarding the allocation of radio resources on the time axis and frequency axis for the selected one or more upper air PF users 61. Based on the user scheduling information of the upper air PF cell 100C, the upper air PF 10 communicates with the selected one or more upper air PF users 61 via a service link.

[0105] The selection index may, for example, be an index that uses the degree of orthogonality between the channel vector between the upper air PF 10 and the upper air PF user 61 located in the upper air PF cell 100C, and the channel vector between the upper air PF 10 and the corresponding point on the ground or at sea corresponding to the direction of the null. Alternatively, the selection index may be an index that uses the separation distance and angular direction of the upper air PF user 61 relative to the upper air PF 10 or its service link antenna, and the separation distance and angular direction of the corresponding point on the ground or at sea corresponding to the direction of the null relative to the upper air PF 10 or its service link antenna.

[0106] The user scheduling unit 1105 of the upper air PF 10 may, if the number of spatial multiplexings in the wireless resource with the selected upper air PF user 61 is less than the maximum number of spatial multiplexings in the upper air PF cell 100C, assign the remaining communication with one or more upper air PF users 61 to the wireless resource, thereby overlapping the communication with the remaining upper air PF users 61.

[0107] The user scheduling unit 1105 of the upper-air PF 10 may greedily sequentially select one or more upper-air PF users 61 to communicate with the base station of the upper-air PF 10 via a service link, using a plurality of selection indicators for each of the plurality of upper-air PF users 61.

[0108] The user scheduling unit 1105 for the upper-air PF users may divide the multiple upper-air PF users 61 located in the upper-air PF cell 100C into a first group that uses wireless resources to form the nulls, and a second group that selectively uses one or more wireless resources that do not form the nulls, and individually determine the allocation of wireless resources to the upper-air PF users 61 for each group.

[0109] [Configuration of Ground Base Station] Figure 23 is a block diagram showing an example of the main configuration of a ground base station (ground BS) 30 in the communication system of Figure 21. In Figure 23, the ground base station 30 comprises a null scheduling information receiving unit 3001 and a ground BS user user scheduling unit 3002. The null scheduling information receiving unit 3001 receives null scheduling information for its own ground base station 30 from the air PF 10. The ground BS user user scheduling unit 3002 determines the user scheduling of the ground cell 300C regarding the allocation of ground BS users 65 in radio resources on the time axis and frequency axis, based on the null scheduling information. Based on the user scheduling information of the ground cell, the ground base station 30 communicates a service link with the ground BS users 65 located in the ground cell 300C.

[0110] The user scheduling unit 3002 of the terrestrial BS 30 may calculate a selection index for each of the multiple terrestrial BS users 65 located in the terrestrial cell 300C to select a terrestrial BS user whose communication quality will be degraded by the null formation control, and based on the calculation results of the selection index for the multiple terrestrial BS users 65, select one or more terrestrial BS users to communicate with the terrestrial BS 30 via a service link, and determine the user scheduling of the terrestrial cell regarding the allocation of wireless resources on the time axis and frequency axis for the selected one or more terrestrial BS users.

[0111] The selection index may be an index that uses at least one of the following: the channel state between the terrestrial BS 30 and the terrestrial BS user 65, the desired signal power of the terrestrial BS user 65, and the SINR (signal-to-interference noise ratio) of the terrestrial BS user 65.

[0112] The aforementioned selection index may also be an index that uses the separation distance and angular direction of the terrestrial BS user 65 relative to the service link antenna of the terrestrial BS 30.

[0113] The user scheduling unit 3002 of the terrestrial BS 30 may sequentially select one or more terrestrial BS users 65 to communicate with the terrestrial BS 30 via a service link using a plurality of selection indicators for each of the plurality of terrestrial BS users 65 in a greedy manner.

[0114] The user scheduling unit 3002 of the terrestrial BS 30 may divide the multiple terrestrial BS users 65 located in the terrestrial cell 300C into a first group that uses radio resources for which a wide-area cell base station (aerial PF base station) forms the null for their own station, and a second group that uses radio resources for which a wide-area cell base station (aerial PF base station) does not form the null for their own station, either partially or entirely, and then individually determine the allocation of radio resources to each of the two groups.

[0115] The user scheduling unit 3002 of the terrestrial BS30 may perform user scheduling according to the procedure S11 to S14 in the case of loose coordination described above, or it may perform user scheduling according to the procedure S21 to S24 in the case of tight coordination described above.

[0116] [Cooperative Control Flow] Figure 24 is a flowchart showing an example of cooperative control between the base station on the air PF 10 and the ground base station 30 when performing beamforming control with null formation and service link communication in the communication system according to the embodiment.

[0117] In Figure 24, the upper PF 10 accesses the ground base station database 82 via the feeder link FL and obtains information about ground base stations 30 located within its own service area 100A (upper PF cell 100C) (S101). The information obtained includes the coordinates of the ground base station 30, cell radius, user distribution, etc.

[0118] Next, the airborne PF 10 determines the allocation of nulls (null scheduling), including null ON / OFF information on the direction, time axis, and frequency axis, based on the information of the ground base station 30 obtained from the ground base station database 82 (S102).

[0119] Next, the airborne PF10 notifies the airborne PF10 aircraft information and null scheduling information to the airborne BS30s in each location via the feeder link FL and the mobile communication network 80 (S103).

[0120] Next, the upper-air PF 10 acquires user information necessary for selection indicators, such as channel status information with the upper-air PF user 61, location information of the upper-air PF user 61, and the angle of arrival of the received radio waves at the upper-air PF user 61 (S104).

[0121] Next, the upper-air PF 10 determines user scheduling by selecting upper-air PF users 61 who will use null OFF resources based on the aforementioned selection indicators such as orthogonality, assigning them null OFF resources (S105), excluding the upper-air PF users 61 to whom null OFF resources have been assigned from null ON resources (S106), and assigning the remaining upper-air PF users 61 to null ON resources (S107).

[0122] Next, the upper-air PF10 decides whether or not to perform other interference reduction control, taking into account the combination of UL / DL and the amount of interference between the upper-air PF10 and the ground BS30 (S108). Here, other interference reduction control is, for example, transmission power control at the uplink (UL).

[0123] Based on the null scheduling information determined above, the upper-air PF 10 controls null formation for each ground BS 30 (S109-S111), and communicates a service link with the upper-air PF user 61 based on the user scheduling information determined above (S112).

[0124] Meanwhile, the terrestrial BS 30 receives aircraft information of the upper-air PF 10 and null scheduling information related to its own cell transmitted from the upper-air PF 10 (S201), and acquires user information necessary for selection indicators, such as channel status information with the terrestrial BS user 65, location information of the terrestrial BS user 65, and the angle of arrival of the received radio waves at the terrestrial BS user 65 (S202).

[0125] Next, the terrestrial BS 30 determines user scheduling based on selection indicators such as the channel status mentioned above, prioritizing the allocation of null ON resources to its own cell's terrestrial BS users (S204) so ​​that the upper-air PF 10 can more easily occupy null OFF resources, and allocating the remaining terrestrial BS users to null OFF resources (S204).

[0126] Next, the ground BS30 decides whether or not to perform other interference reduction control, taking into account the combination of UL / DL and the amount of interference between the upper air PF10 and the ground BS30 (S205). Here, other interference reduction control includes, for example, transmission power control at the uplink (UL) and null formation by the ground BS30.

[0127] Based on the user scheduling information determined above, the terrestrial BS 30 communicates with the terrestrial BS user 65 via a service link (S206).

[0128] [Example of Null Allocation and Beam Control of Upper PF] In the system of this embodiment, null allocation and beam control of the upper PF 10 may be performed as follows. For example, the upper PF 10 forms multiple (Nn) nulls while spatially multiplexing multiple (Nu) upper PF users 61 for each radio resource. Here, a single null may cover the entire area of ​​multiple ground BS 30 (an area including multiple ground cells 300C). Alternatively, multiple nulls may be directed to the area of ​​a ground cell 300C of a single ground BS 30. Furthermore, the target area for null formation is not limited to the service area of ​​the upper PF 10. In addition, the weights for null formation may be calculated using pseudo-inverse matrix or singular value decomposition (see, for example, Tashiro et al., IEEE Access, vol. 10, pp. 55675-55693, May 2022). Furthermore, the number of spatial multiplexings (Nu) may be changed according to the communication conditions.

[0129] The upper-air PF10 may perform control to stop the formation of one or more nulls from among multiple (Nn) nulls. Also, depending on the direction of null formation, the impact on the upper-air PF10's service area may be minor, so there may be nulls for which switching control is not performed.

[0130] The upper PF10 may change the direction of the null in combination with null sweeping (see Japanese Patent Publication No. 7534460).

[0131] Figure 25A is a diagram showing an example of resource allocation for communication with multiple upper-air PF users 61 and for the formation of multiple nulls in an upper-air PF 10 according to a reference example. Figures 25B and 25C are diagrams showing examples of resource allocation for communication with multiple upper-air PF users 61 and for the formation of multiple nulls in an upper-air PF 10 according to an embodiment, respectively. Here, in order to improve the overall communication quality and fairness of the system, the number of resources Nr that form all nulls (null ON resources) and the number Nr' that do not form all or some nulls (null OFF resources) are introduced as variable parameters.

[0132] Figure 25A is a reference example of resource allocation consisting only of null-on resources when Nu (number of users) = 6, Nn (number of nulls) = 6, Nr (number of null-on resources) = 90, and Nr' (number of null-off resources) = 10.

[0133] Figure 25B is an example of a null-off resource allocation that stops null formation all at once, where Nu (number of users) = 6, Nn (number of nulls) = 6, Nr (number of null-on resources) = 90, and Nr' (number of null-off resources) = 10. The resource allocation in Figure 25B corresponds to the positional relationship between the ground BS 30 and the airborne PF user 61 shown in Figures 13A and 13B.

[0134] The ratio of the number of null-ON resources Nr to the number of null-OFF resources Nr' may be determined based on information from the airborne PF 10, ground BS 30, airborne PF user 61, and ground BS user 65. Alternatively, the number of null-ON resources Nr and the number of null-OFF resources Nr' may be fixed, and the null selected by null ON / OFF control may be repeated in a fixed pattern. Furthermore, the resources performing null OFF control may be consecutive as shown in Figure 25B, or they may be distributed. In addition, Nr and Nr' may be changed in accordance with communication demand that changes during the day or night, or the null selected by null ON / OFF control may be changed each time.

[0135] Figure 25C is an example of a null-off resource allocation that partially stops null formation, where Nu (number of users) = 6, Nn (number of nulls) = 6, Nr (number of null-on resources) = 90, and Nr' (number of null-off resources) = 10. The resource allocation in Figure 25C corresponds to the positional relationship between the ground BS 30 and the airborne PF user 61 shown in Figures 26A, 26B, and 26C.

[0136] Disabling nulls entirely using the null OFF resource can lead to an imbalance in the utilization of the array antenna's degrees of freedom. Therefore, as shown in Figures 25C, 26A, 26B, and 26C, nulls may be partially disabled (partial null OFF). This partial null disabling can be described as null sweeping across multiple ground cells 300C.

[0137] In partial null OFF mode, the allocation of nulls may be determined by considering information such as the temporal changes or geographical distribution of traffic demand for the aerial PF 10, the ground BS 30, and both. Here, the formation or stopping of individual nulls may be controlled, for example, as follows: - Change the allocation of nulls to follow the changes in the density of aerial PF users 61 and ground BS users 65, which change over several hours, such as day and night. - If the traffic demand for ground BS 30 is high, reduce the number of times the null protecting that ground BS 30 is stopped. - Adjust so that the nulls face the direction of the densely populated ground BS users 65 many times. - If there are many aerial PF users 61 around the ground cell 300C, increase the number of times the null is stopped.

[0138] In resource allocation with partial null OFF, it is acceptable to always disable some nulls by setting the number of null ON resources Nr = 0.

[0139] Furthermore, in resource allocation with partial null-off, the number of nulls that are stopped is not necessarily constant for null-off resources.

[0140] Furthermore, in resource allocation with partial null OFF, the nulls formed by the null OFF resources may be selected in a way that minimizes degradation to the service area, taking into consideration factors such as the orthogonality of the channel vectors. Here, the nulls may be selected so that they are distributed within the area so that the channel vectors are orthogonal. In addition, to improve the communication quality of an upper-air PF user 61 surrounded by multiple nulls, the nulls formed by the null OFF resources may be selected so that multiple adjacent nulls are stopped simultaneously.

[0141] Note that in Figures 25A to 25C, even if the user number is the same across different resources, it does not necessarily mean they belong to the same user.

[0142] [Example of resource allocation control on the upper PF side] When null is OFF, the selection of upper PF users may be done as follows, for example. It is necessary to select users around the null that will be degraded by the null. Therefore, the upper PF 10 may select upper PF users when null is OFF using a selection index that uses the degree of orthogonality between the channel vector between it and the upper PF user 61 and the channel vector in the direction of null n (see equation (1) below).

[0143] Here, in equation (1) above This is the channel vector between the upper air PF and the upper air PF user u, This is the channel vector between the upper space PF and null n.

[0144] The above orthogonality formula (1) may be modified in an equivalent manner, or in a manner that does not change the magnitude relationship, such as by using a square root. Furthermore, the orthogonality with a single null may be used as the selection index, or the orthogonality with multiple nulls may be included as the selection index. In addition, when considering the orthogonality with multiple nulls, an orthonormal system may be created from the channel vectors corresponding to the multiple nulls based on the Gram-Schmidt orthonormalization method, and the orthogonality between these systems and the channel vectors of the upper PF user 61 may be used as the selection index.

[0145] Furthermore, if it is possible to obtain location information of the upper-air PF user 61 and information on the angle of arrival of the received radio waves, a selection index based on the position of the upper-air PF user 61 and the target position on the ground corresponding to the null direction may be used, such as distance and direction based on the position of the upper-air PF 10.

[0146] Furthermore, after selecting the upper-air PF users 61 around the null, if there is sufficient spatial multiplexing capacity, the remaining upper-air PF users may be selected. In this case, existing algorithms may be used in conjunction, or users may be selected using the orthogonality with the null or the selected upper-air PF users.

[0147] Also, typically, the channel vector between the above-ground PF and null n is Since this information cannot be obtained, for example, one could assume a model and estimate it from location information.

[0148] [Example of User Scheduling Algorithm for Upper PF] Upper PF 10 may greedily select Upper PF users 61 with low orthogonality to null n, as shown below. For example, in a situation where one user is selected only once (the process ends when the set of waiting users becomes an empty set), if null formation is stopped collectively when Nn (number of nulls) ≤ Nu (number of users), Upper PF users 61 may be selected using the algorithm in Figure 27, for example. If Nn (number of nulls) > Nu (number of users) and Nu null is OFF, Upper PF users 61 may be selected using the algorithm in Figure 28, for example. However, 1 ≤ r ≤ Nr is a null ON resource, and Nr < r ≤ Nr + Nr' is a null OFF resource. Here, in each algorithm... This is a collection of waiting users, is the set of users allocated resource r, and Nu is the number of users.

[0149] [Example of coordinated control between the aerial PF and ground BS for null ON / OFF] Through coordinated control between the aerial PF and ground BS, the user's selection may be made as follows, for example.

[0150] For example, the upper-air PF 10 selects the upper-air PF user 61 based on the selection criteria mentioned above.

[0151] For example, terrestrial BS 30 assigns terrestrial BS user 65 as exemplified below to reduce the impact of null formation stoppage. - Prioritize the use of null ON resources. Do not share null OFF resources depending on traffic demand. - For example, assign users with poor channel conditions from null ON resources, and assign null OFF resources only to users with relatively good conditions. - Use SINR etc. as selection criteria, taking into account channel condition, desired signal power, and interference between terrestrial BS (or between sectors). If information on the angle of arrival and location of the received radio waves can be obtained, that information may also be used as selection criteria.

[0152] Both the aerial PF10 and the ground BS30 may sequentially select users using the aforementioned selection indicators in a greedy manner.

[0153] In coordinated control between the aerial PF and the ground BS, both the aerial PF 10 and the ground BS 30 may use existing scheduling algorithms in conjunction to select users. For example, users may be divided into groups that use null ON / OFF resources based on selection criteria, and then an existing algorithm may be applied to select users. Examples of existing algorithms that can be used include proportional fairness, round robin, semi-orthogonal user selection (see Yoo and Goldsmith, IEEE J. Sel. Areas Commun., vol. 24, pp. 528-542, Mar. 2006), and angle-based user selection (see Tashiro et al., IEICE Trans. Commun., vol. E105-B, no. 4, pp. 449-460, Apr. 2022).

[0154] [Example of a terrestrial BS user scheduling algorithm] Terrestrial BS 30 may select terrestrial BS users 65 greedily based on their desired power. For example, in a situation where one user is selected only once (the process terminates when the set of waiting users becomes empty), terrestrial BS users 65 may be selected using the algorithm in Figure 29. Here, Pu in the algorithm is the desired power of user u, This is the user who has allocated resource r.

[0155] 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.

[0156] Furthermore, according to the embodiments of this disclosure, when a directional null is formed from the relay communication station 110 of the upper air PF 10 toward the antenna or ground cell 300C of the ground BS 30 to suppress interference, the occurrence of coverage holes 100H in the upper air PF cell (wide-area cell) 100C can be suppressed, the deterioration of communication quality for upper air PF users 61 connected to the upper air PF cell 100C can be reduced, and the frequency utilization efficiency of the entire system can be improved.

[0157] The system disclosed herein can reduce the degradation of communication quality for airborne PF users 61 and provide a system that achieves high frequency utilization efficiency without compromising the coverage area, thus contributing to the achievement of Sustainable Development Goal (SDG) 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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 100F: Footprint 100H: Coverage hole 100N: Null 110: Relay communication station 300C: Ground cell 1101: Information acquisition unit 1102: Null scheduling unit 1103: Null switching control unit 1104: Null scheduling information transmission unit 1105: User scheduling unit 3001: Null scheduling information reception unit 3002: User Scheduling Unit

Claims

1. A system comprising: 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 object located in the air; and one or more ground cell base stations that form a ground cell from an antenna located on the ground or sea, wherein the wide-area cell base station and the one or more ground cell base stations communicate on a service link in the same frequency band using radio frames that are time-synchronized with each other; the wide-area cell base station acquires information about ground cell base stations that form ground cells overlapping with the wide-area cell; determines null scheduling regarding the allocation of directional nulls toward the antennas of the ground cell base stations or the ground cells on the time axis and frequency axis based on the information about the ground cell base stations; and controls the formation of the directional nulls based on the null scheduling information.

2. The system according to claim 1, wherein the wide-area cell base station acquires traffic information relating to at least one of the service link traffic in the wide-area cell and the service link traffic in the ground cell, and determines the null scheduling based on the traffic information and information relating to the ground cell base station.

3. The system according to claim 1, wherein the wide-area cell base station acquires user distribution information relating to at least one of the geographical distribution of user terminal devices located in the wide-area cell and the geographical distribution of user terminal devices located in the ground cell, and determines the null scheduling based on the user distribution information and information relating to the ground cell base station.

4. The system according to claim 1, wherein the wide-area cell base station calculates a selection index for each of the terminal devices of a plurality of users located in the wide-area cell to select terminal devices whose communication quality will be degraded by the formation of the null; selects one or more user terminal devices to communicate with the wide-area cell base station for a service link based on the calculation results of the selection index for the plurality of user terminal devices; determines the user scheduling of the wide-area cell regarding the allocation of radio resources on the time axis and frequency axis for the selected one or more user terminal devices; and communicates with the selected one or more user terminal devices for a service link based on the user scheduling information of the wide-area cell.

5. The system according to claim 4, wherein the selection index is an index that uses the degree of orthogonality between the channel vector between the wide-area cell base station and the terminal device of a user located in the wide-area cell and the channel vector between the wide-area cell base station and a corresponding point on land or at sea corresponding to the direction of the null.

6. The system according to claim 4, characterized in that the selection index is an index using the separation distance and angular direction of a user's terminal device located in the wide-area cell with respect to the service link antenna of the wide-area cell base station, and the separation distance and angular direction of a corresponding point on land or at sea corresponding to the direction of the null with respect to the service link antenna of the wide-area cell base station.

7. The system according to claim 4, wherein if the spatial multiplexing number in the radio resource to which the selected user's terminal device is assigned is less than the maximum spatial multiplexing number of the wide area cell, the wide area cell base station assigns the remaining one or more users' terminal devices to the radio resource in duplicate.

8. The system according to claim 4, wherein the wide-area cell base station sequentially selects one or more user terminal devices to communicate with the wide-area cell base station for a service link using a plurality of selection indicators for each of the plurality of user terminal devices.

9. The system according to claim 4, wherein the wide-area cell base station divides the terminal devices of a plurality of users located within the wide-area cell into a first group that uses radio resources to form the null and a second group that selectively uses one or more radio resources that do not form the null, and individually determines the allocation of radio resources to the terminal devices of the users for each group.

10. A system according to any one of claims 1 to 9, characterized in that: the wide-area cell base station transmits the null scheduling information to the ground cell base station; the ground cell base station receives the null scheduling information from the wide-area cell base station; determines the ground cell's user scheduling regarding the allocation of users' terminal devices in radio resources on the time axis and frequency axis based on the null scheduling information; and communicates a service link with users' terminal devices located in the ground cell based on the ground cell's user scheduling information.

11. The system according to claim 10, wherein the ground cell base station calculates a selection index for each of the terminal devices of a plurality of users located in the ground cell, for selecting terminal devices whose communication quality is degraded by the null formation control; selects one or more user terminal devices to communicate with the ground cell base station for a service link based on the calculation results of the selection index for the plurality of user terminal devices; and determines the user scheduling of the ground cell regarding the allocation of radio resources on the time axis and frequency axis for the selected one or more user terminal devices.

12. The system according to claim 11, characterized in that the selection index is an index using at least one of the channel state between the ground cell base station and the user's terminal device located in the ground cell, the desired signal power of the user's terminal device, and the SINR (signal-to-interference noise ratio) of the user's terminal device.

13. The system according to claim 11, characterized in that the selection index is an index using the separation distance and angular direction of the user's terminal device located in the ground cell, with respect to the service link antenna of the ground cell base station.

14. The system according to claim 11, wherein the ground cell base station sequentially selects one or more user terminal devices to communicate with the ground cell base station via a service link using a plurality of selection indicators for each of the plurality of user terminal devices.

15. The system according to claim 11, wherein the ground cell base station divides the terminal devices of a plurality of users located within the ground cell into a first group that uses only radio resources for which the wide-area cell base station forms the null with respect to the base station, and a second group that uses radio resources for which the wide-area cell base station does not form the null with respect to the base station, partially or entirely, and individually determines the allocation of radio resources to the terminal devices of the users for each group.

16. The system according to claim 11, comprising a plurality of ground cell base stations, wherein the null scheduling information includes information on the allocation of a first radio resource to form the null for all of the plurality of ground cell base stations, and information on the allocation of a second radio resource to selectively stop the formation of the null for each ground cell base station, wherein each of the plurality of ground cell base stations preferentially allocates the first radio resource to one or more user terminal devices based on the calculation result of the selection index for the terminal devices of the plurality of users, and after the allocation of the first radio resource is completed, allocates the second radio resource to the remaining one or more user terminal devices.

17. The system according to claim 11, comprising a plurality of ground cell base stations, wherein the null scheduling information includes information on the allocation of a first radio resource that forms the null for all of the plurality of ground cell base stations, and information on the allocation of a second radio resource that selectively stops the formation of the null for each ground cell base station, wherein each of the plurality of ground cell base stations preferentially allocates the first radio resource and a specific second radio resource from the second radio resource for which the null is formed for the station itself to one or more user terminal devices based on the calculation result of the selection index for the terminal devices of the plurality of users, and after the allocation of the first radio resource and the specific second radio resource is completed, allocates the second radio resource to the remaining one or more user terminal devices.

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