Mobile communication system

Abstract

To improve frequency utilization efficiency, prevent a decrease in communication capacity of terminals, and reduce interference in the uplink and downlink service links of each base station in a mobile communication system including an aerial relay base station equipped with an antenna provided on an airborne object (including UAV, HAPS, and communication satellites) and a ground base station.SOLUTION: An airborne relay base station and a ground base station each perform wireless communication of the service link with terminals using the FDD (frequency division duplexing) method. The transmission frequency and reception frequency of wireless communication using the FDD method in the service link are reversed between the airborne relay base station and the ground base station. The ground base station estimates the direction of a service link antenna of a relay communication station and controls its own service link antenna such that the null of its directional beam is directed toward the estimated direction of the relay communication station's service link antenna.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a mobile communication system including a base station capable of wireless communication with a terminal.

Background Art

[0002] Conventionally, as a flying object or a floating object located in the air, a UAV flying at an altitude of 18 km or less and a HAPS flying in the stratosphere at an altitude of 18 km or more are known. Further, as a first base station that performs wireless communication with a terminal via a service link antenna of a relay communication station provided in a flying object or a floating object such as a UAV or a HAPS (flying object) located in the air, an aerial relay type base station, and a ground base station as a second base station that performs wireless communication with a terminal via an antenna arranged on land or at sea are provided. There is known a mobile communication system in which the same frequency is shared in the service links of the aerial relay type base station and the ground base station so that wireless communication can be performed with a terminal having a common specification.

[0003] As a technique applicable to reducing interference between an aerial relay type base station and a ground base station in a mobile communication system, there is an interference control technique for adjusting and controlling a radio frame in a time domain (subframe unit) on the premise that the aerial relay type base station and the ground base station are time synchronized with each other (see, for example, Patent Document 1 and Non-Patent Document 1). This interference control technique is a technique compliant with the LTE (Long Term Evolution)-Advanced standard and is also called eICIC (enhanced Inter-Cell Interference Coordination).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When applying the above conventional interference control technology, since the airborne relay base station and the ground base station use the frequencies assigned to the service link in a time-division manner, the radio signals used by the airborne relay base station and the ground base station are orthogonal on the time axis and no mutual interference occurs. However, due to the time-division use of frequencies, neither the airborne relay base station nor the ground base station can use all the frequencies assigned to the service link, so the communication capacity (maximum transmission rate, peak throughput) of the terminals on each service link decreases.

Means for Solving the Problems

[0007] The mobile communication system according to the first aspect disclosed in this specification includes an airborne relay base station that wirelessly communicates with a terminal via a service link antenna of a relay communication station provided on an airborne object or a floating object located in the air, and a ground base station arranged on the ground or at sea. The airborne relay base station and the ground base station are mobile communication systems that are time-synchronized with each other. The airborne relay base station and the ground base station each perform wireless communication of a service link with a terminal by an FDD (Frequency Division Duplex) method. The transmission frequency and the reception frequency of the FDD method wireless communication in the service link are opposite to each other between the airborne relay base station and the ground base station. The ground base station estimates the direction of the service link antenna of the airborne relay base station and controls to direct the null of the directivity beam of the service link antenna of the ground base station in the estimated direction of the service link antenna of the airborne relay base station.

[0008] In the mobile communication system according to the first aspect, the aerial relay base station may estimate the direction of the service link antenna of the terrestrial base station, and control to direct the null of the directional beam of the service link antenna of the aerial relay base station in the estimated direction of the service link antenna of the terrestrial base station.

[0009] The mobile communication system according to the second aspect disclosed in this specification includes an aerial relay base station that wirelessly communicates with a terminal via a service link antenna of a relay communication station provided on an aircraft or a floating body located in the air, and a terrestrial base station arranged on the ground or at sea. The aerial relay base station and the terrestrial base station are a mobile communication system that is time-synchronized with each other. The aerial relay base station and the terrestrial base station each perform wireless communication of a service link with a terminal by an FDD (Frequency Division Duplex) method. The transmission frequency and reception frequency of the wireless communication of the FDD method in the service link are opposite to each other between the aerial relay base station and the terrestrial base station. The aerial relay base station estimates the direction of the service link antenna of the terrestrial base station, and controls to direct the null of the directional beam of the service link antenna of the aerial relay base station in the estimated direction of the service link antenna of the terrestrial base station.

[0010] In the mobile communication system according to the first aspect and the second aspect, the relay communication station mounted on the aircraft or the floating body may be constituted by a repeater relay device (frequency conversion repeater relay device) that relays without regenerating the transmitted and received signals.

[0011] In the mobile communication system according to the first aspect and the second aspect, the relay communication station mounted on the aircraft or the floating body may be constituted by a base station device that regenerates the transmitted and received signals, remodulates the regenerated signals, and relays them.

[0012] In the mobile communication system according to the first aspect, the mobile communication system further includes an inter-base station control device that controls between the aerial relay base station and the ground base station, and position information acquired by a GNSS (Global Navigation Satellite System) receiver mounted on the aircraft or the floating body is transferred to the ground base station via a gateway device and the inter-base station control device, and the ground base station may estimate the direction of the service link antenna of the relay communication station based on the position information of its own ground base station.

[0013] In the mobile communication system according to the first aspect, the ground base station has an array antenna as the service link antenna, measures the direction of arrival of radio waves from the service link antenna of the relay communication station using the array antenna, and may estimate the direction of the service link antenna of the relay communication station from the measurement result.

[0014] In the mobile communication system according to the second aspect, the mobile communication system further includes an inter-base station control device that controls between the aerial relay base station and the ground base station, and position information acquired by a GNSS (Global Navigation Satellite System) receiver mounted on the ground base station or the service link antenna of the ground base station is transferred to the aerial relay base station via a gateway device and the inter-base station control device, and the aerial relay base station may estimate the direction of the service link antenna of the ground base station based on the position information of the relay communication station.

[0015] In the mobile communication system according to the second aspect, the aerial relay base station has an array antenna as the service link antenna, measures the direction of arrival of radio waves from the service link antenna of the ground base station using the array antenna, and may estimate the direction of the service link antenna of the ground base station from the measurement result.

[0016] In the mobile communication systems according to the first aspect and the second aspect, the aircraft or the floating body may be a communication satellite, a UAV (Unmanned Aerial Vehicle) flying at an altitude of 18 km or less, or a HAPS flying in the stratosphere at an altitude of 18 km or more.

[0017] According to the mobile communication system disclosed in this book, it is possible to reduce the interference caused by the downlink transmission signal from the service link antenna (upper air relay type base station antenna) of the relay communication station provided in the flying object or floating body located in the air to the reception signal of the uplink of the service link antenna (ground base station antenna) of the ground base station, and at the same time, it is possible to reduce the interference caused by the downlink transmission signal from the ground base station antenna to the reception signal of the uplink of the upper air relay type base station antenna.

Brief Explanation of Drawings

[0018]

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[0019] Hereinafter, various embodiments will be described with reference to the drawings. Note that each drawing only schematically shows the shape, size, and positional relationship to the extent that the content of the present invention can be understood. Therefore, the present invention is not limited to only the shape, size, and positional relationship illustrated in each drawing. Also, the numerical values exemplified hereinafter are only preferred examples of the present invention. Therefore, the present invention is not limited to the illustrated numerical values.

[0020] In this embodiment, an example of a mobile communication system including a HAPS base station (HAPS cellular system) as an aerial relay type base station and a terrestrial base station (terrestrial cellular system) will be mainly described. However, the present invention can also be applied to a mobile communication system in which the relay communication station of the aerial relay type base station is provided on a flying object or a floating object other than HAPS. Here, the aerial relay type base station may be an aerial communication base station used in NTN (Non-Terrestrial Network). NTN may be a network using, for example, an artificial satellite such as a communication satellite described later, and HAPS or a drone as a stratospheric communication platform capable of providing communication services in a wide area by mounting communication equipment on an unmanned aircraft flown in the stratosphere.

[0021] FIG. 1 is a diagram showing an example of the configuration of a mobile communication system (mobile phone system) according to an embodiment of the present invention. In FIG. 1, the mobile communication system of this embodiment includes, as a plurality of base stations capable of wireless communication with the terminal 30, a HAPS base station (HAPS cellular system) 10 as a first base station (aerial relay type base station) and a terrestrial base station (terrestrial cellular system) 20 as a second base station.

[0022] The HAPS base station 10 wirelessly communicates with a terminal (hereinafter also referred to as the "HAPS base station terminal") 30(1) via a service link antenna (also referred to as the "HAPS base station antenna") 112 of a relay communication station 11 provided in a HAPS (High Altitude Pseudo Satellite or High Altitude Platform Station) 100, which is a flying object or a floating object located in the sky. The HAPS 100 can fly powered by, for example, at least one of a battery and a solar power generation system. The HAPS 100 may be a solar plane type HAPS in addition to the airship type HAPS as shown in the figure. Further, the flying object or the floating object on which the relay communication station 11 is provided may be, in addition to the HAPS, an artificial satellite (for example, a communication satellite), a balloon, a drone, or an aircraft. The artificial satellite may be, for example, a LEO (Low Earth Orbit) satellite located in an orbit at an altitude of up to 2,000 km from the Earth's surface, a MEO (Medium Earth Orbit) satellite located in an orbit at an altitude higher than 2,000 km and lower than 36,000 km, or a HEO (High Earth Orbit) satellite located in an orbit at an altitude near 36,000 km or higher than 36,000 km. Further, the artificial satellite may be a GEO (Geostationary Orbit) satellite, a quasi-geostationary satellite, a quasi-zenith satellite, or a non-geostationary satellite. Further, the flying object or the floating object on which the relay communication station 11 is provided may be unmanned or manned. For example, the flying object or the floating object may be an unmanned or manned HAPS, an unmanned or manned artificial satellite, an unmanned or manned balloon, an unmanned or manned drone, an unmanned aircraft, or a manned aircraft. Further, the flying object or the floating object may be an unmanned aircraft (UAV: Unmanned Aerial Vehicle) such as an unmanned drone or a UAS (Unmanned Aircraft Systems). Further, the flying object or the floating object may be a moored type moored to another device (mooring device) using a mooring line such as a rope, a cable, a string, or a wire having a predetermined strength. The purpose of mooring with the mooring line may include the purposes of power supply and signal transmission.The other device to which the above-mentioned moored aircraft or floating body is moored may be a device fixedly arranged on the ground, a device provided on a vehicle movable on the ground, a device provided on a ship, a floating object, etc. movable on water such as on the sea or a lake, or a device provided on another aircraft or floating body. The above-mentioned mooring line may include a power supply line, a communication line such as an optical fiber, or both the power supply line and the communication line. For example, the above-mentioned moored aircraft or floating body may be one or more wired power supply drones moored by one or more mooring lines (power supply lines). Further, aircraft or floating bodies such as HAPS100, artificial satellites, drones, balloons, airplanes, and UAVs may fly with at least one of a battery and an engine as a power source. A UAV may be, for example, a drone that flies on fuel or a drone that flies on a battery or the like.

[0023] The HAPS100 equipped with the relay communication station 11 may be controlled, for example, to float or fly in an airspace (floating airspace) with an altitude H of 100 [km] or less from the ground G (or the sea surface) by autonomous control or external control. The airspace where the HAPS100 is located may be, for example, an airspace in the stratosphere with an altitude H of 18 [km] or more and 50 [km] or less. This airspace may be an airspace with an altitude of 15 [km] or more and 25 [km] or less where weather conditions are relatively stable, and particularly an airspace with an altitude of approximately 20 [km]. Further, the above-mentioned airspace may be an airspace with an altitude of 0.1 [km] or more and 18 [km] or less for UAVs. Further, the airspace may be an airspace with an altitude of 0.05 [km] or more for drones.

[0024] The relay communication station 11 includes a feeder link antenna section (hereinafter also referred to as "FL antenna") 111 and a service link antenna section (HAPS base station antenna) 112. The relay communication station 11 can perform feeder link FL communication with a HAPS gateway device (hereinafter referred to as "HAPS-GW") 12 provided on the ground (or at sea) via the FL antenna 111. The FL antenna 111 is, for example, an array antenna whose radiation direction can be controlled as described later, and may be a massive antenna in which a large number of antenna elements are two-dimensionally arranged and the directivities in the horizontal and vertical directions can be controlled.

[0025] In addition, the relay communication station 11 can perform service link SL(1) communication with the HAPS base station terminal 30(1) via the HAPS base station antenna 112. The HAPS base station antenna 112 is, for example, an array antenna whose radiation direction can be controlled, and may be a massive antenna in which a large number of antenna elements are two-dimensionally arranged and the directivities in the horizontal and vertical directions can be controlled.

[0026] The HAPS-GW 12 is connected to the core network 40 of the mobile communication network by a wired or wireless communication line, and includes a feeder link antenna section (hereinafter also referred to as "FL antenna") 121 composed of a parabolic antenna, a massive antenna capable of controlling the directivities in the horizontal and vertical directions, and the like. The HAPS-GW 12 can perform feeder link FL communication with the relay communication station 11 mounted on the HAPS via the FL antenna 121.

[0027] The terrestrial base station 20 includes an antenna unit (hereinafter also referred to as the "terrestrial base station antenna") 21 and a base station device 22 connected to the core network 40 of the mobile communication network by a wired or wireless communication line such as an optical fiber. The base station device 22 can communicate with a terminal (hereinafter also referred to as the "terrestrial base station terminal") 30(2) via the terrestrial base station antenna 21 on a service link SL(2). The terrestrial base station antenna 21 is, for example, an array antenna whose radiation direction can be controlled, and may be a Massive antenna in which a large number of antenna elements are two-dimensionally arranged and the directivities in the horizontal and vertical directions can be controlled.

[0028] The HAPS-GW12 of the HAPS base station 10 and the base station device 22 of the terrestrial base station 20 are each connected to a base station interconnection control device (also referred to as the "base station network interconnection control device" or the "inter-system interconnection control device") 50 by a wired or wireless communication line such as an optical fiber. The HAPS base station 10 and the terrestrial base station 20 are time-synchronized with each other via the base station interconnection control device 50, and timing control is executed so that the transmission and reception timings of the HAPS base station 10 are opposite to those of the terrestrial base station 20.

[0029] The HAPS base station 10 and the terrestrial base station 20 are each configured using hardware such as a computer device having, for example, a CPU and a memory, an external communication interface unit for the core network 40 and the base station interconnection control device 50, and a wireless communication unit. By executing a predetermined program, wireless communication between the HAPS base station terminal 30(1) and the terrestrial base station terminal 30(2) can be performed, or communication with the core network 40 and the base station interconnection control device 50 can be performed.

[0030] In the mobile communication system of this embodiment, the same wireless transmission method is used for the communication of the service link SL(1) of the HAPS base station 10 and the communication of the service link SL(2) of the terrestrial base station 20, and the same frequency is shared to improve the frequency efficiency of the service link. As the same wireless transmission method, the FDD (Frequency Division Duplex) method that transmits and receives by time division at the same frequency is targeted. For example, communication methods such as LTE (Long Term Evolution) and LTE-Advanced, the communication method of the fourth-generation mobile phone, the fifth-generation mobile phone, or the communication method of subsequent next-generation mobile phones can be applied to the FDD method.

[0031] The HAPS base station terminal 30(1) that can communicate by connecting to the HAPS base station 10 and the terrestrial base station terminal 30(2) that can communicate by connecting to the terrestrial base station 20 are mobile communication terminals 30 of the same specification. The terminal 30 is a mobile phone, a smartphone, a portable computer with a mobile communication function, etc., and is also called a mobile terminal, a user equipment (UE), a mobile station, a mobile device, or a portable communication terminal. The terminal 30 may be a modular mobile station incorporated in a vehicle such as an automobile or a moving body such as a drone, or may be a terminal device of an IoT (Internet of Things) device.

[0032] The terminal 30 is configured using hardware such as a computer device having, for example, a CPU and a memory, and a wireless communication unit, and can perform wireless communication with each of the HAPS base station 10 and the terrestrial base station 20 when a predetermined program is executed.

[0033] The HAPS base station 10 of this embodiment is composed of a relay communication station 11 mounted on the HAPS 100 in the sky, or is composed of the relay communication station 11 and the HAPS-GW12 provided on the ground (or at sea).

[0034] Fig. 2(a) is a diagram showing a configuration example of the relay communication station 11 that constitutes an example of the HAPS base station 10 in the mobile communication system of the embodiment. In this configuration example, the relay communication station 11 is a radio relay device (hereinafter referred to as a "frequency conversion repeater") that converts the frequencies of a service link and a feeder link having different frequencies. In the downlink, the relay communication station 11 converts the frequency of the feeder link transmitted from the HAPS-GW 12 to the frequency of the service link and transmits it to the HAPS base station terminal 30(1). On the other hand, in the uplink, the relay communication station 11 converts the frequency of the service link transmitted from the HAPS base station terminal 30(1) to the frequency of the feeder link and transmits it to the HAPS-GW 12.

[0035] The relay communication station 11 of the HAPS base station 10 in this example is composed of a repeater relay device (frequency conversion repeater) having a repeater 113 and a frequency conversion device 114. The repeater 113 includes a low-noise amplifier that amplifies the received signal of the service link SL(1) received via the HAPS base station antenna 112, a power amplifier that amplifies the transmission signal of the service link SL(1) transmitted via the HAPS base station antenna (SL antenna) 12, and the like. The frequency conversion device 114 performs conversion between the frequency of the service link SL(1) and the frequency of the feeder link FL.

[0036] FIG. 2(b) is a diagram showing a configuration example of HAPS-GW12 corresponding to FIG. 2(a). The HAPS-GW12 in this example includes a base station device (hereinafter also referred to as “HAPS base station device”) 122 and a frequency conversion device 123. The base station device 122 includes a baseband processing device that processes the baseband signal of the service link, a communication interface unit for communicating with the core network 40 via a backhaul line, and the like. The frequency conversion device 123 performs conversion between the frequency of the service link signal input and output to and from the base station device 122 and the frequency of the feeder link signal transmitted and received via the FL antenna 121. In addition, HAPS-GW12 also has a function of communicating with the inter-base station cooperation control device 50 in order to adjust the transmission and reception timing of the service link SL with the terrestrial base station 20 or transfer the position information of the HAPS 100.

[0037] FIG. 3(a) is a diagram showing a configuration example of a relay communication station 11 that constitutes another example of the HAPS base station 10 in the mobile communication system of the embodiment. In this configuration example, the relay communication station 11 of the HAPS base station 10 includes a base station device similar to a normal terrestrial base station and a feeder link transceiver that uses a frequency different from that of the service link for the feeder link between the relay communication station 11 of the HAPS base station 10 and the HAPS-GW. In the feeder link, unlike the service link, an appropriate optimal wireless transmission method can be selected as appropriate.

[0038] The relay communication station 11 of the HAPS base station 10 in this example includes a base station device 115 equivalent to the base station device (hereinafter also referred to as “terrestrial base station device”) 22 of the terrestrial base station 20 and a feeder link transceiver 116. The base station device 115 includes a low-noise amplifier that amplifies the received signal of the service link SL(1) received via the HAPS base station antenna 112, a power amplifier that amplifies the transmission signal of the service link SL(1) transmitted via the HAPS base station antenna 112, a baseband processing device that processes the baseband signal of the service link, and the like. The feeder link transceiver 116 transmits and receives the signal of the backhaul line transmitted and received via the FL antenna 111 to and from the HAPS-GW12.

[0039] Figure 3(b) is a diagram showing a configuration example of HAPS-GW12 corresponding to Figure 3(a). The HAPS-GW12 in this example has a feeder link transceiver 124. The feeder link transceiver 124 transmits and receives signals of a backhaul line that are transmitted and received via the FL antenna 121 to and from the aerial relay communication station 11 mounted on the HAPS 100. Further, the feeder link transceiver 124 communicates with the core network 40 via the backhaul line. Also, the HAPS-GW12 has a function of communicating with the inter-base station cooperation control device 50 in order to adjust the transmission and reception timing of the service link SL with the terrestrial base station 20 or transfer the position information of the HAPS 100.

[0040] In a configuration including the HAPS base station 10 and the terrestrial base station 20 as shown in Figure 1, if the HAPS base station 10 and the terrestrial base station 20 transmit radio waves at the same timing in the FDD mode or the TDD mode, or if the HAPS base station terminal 30(1) and the terrestrial base station terminal 30(2) transmit signals at the same timing, there is a possibility of interference occurring between the aerial HAPS cellular system and the terrestrial cellular system. For example, as shown in Figure 4(a), when a signal of the HAPS downlink line is being transmitted from the relay communication station 11 mounted on the aerial HAPS 100 to the HAPS base station terminal 30(1), the transmitted signal of the HAPS downlink line may reach the terrestrial base station terminal 30(2) that is receiving a signal of the terrestrial downlink line from the terrestrial base station 20, and there is a possibility of interference from the HAPS downlink line to the terrestrial base station terminal 30(2). Also, as shown in Figure 4(b), when a signal of the terrestrial uplink line is being transmitted from the terrestrial base station terminal 30(2) to the terrestrial base station 20, the transmitted signal of the terrestrial uplink line may reach the relay communication station 11 of the aerial HAPS 100 that is receiving a signal of the HAPS uplink line from the HAPS base station terminal 30(1), and there is a possibility of interference from the terrestrial base station terminal 30(2) to the HAPS uplink line of the relay communication station 11 mounted on the HAPS 100.

[0041] Also, when simultaneously using the communication method of a terrestrial cellular system using terrestrial base station 20 (hereinafter referred to as the "terrestrial cellular method") and the communication method of a HAPS cellular system using HAPS base station 10 (hereinafter referred to as the "HAPS cellular method"), as shown in Fig. 5(a), particularly in the downlink of the service link, due to interference waves from HAPS base station 10 that transmits signals over a wide area, the communication quality of many terrestrial base station terminals 30(2) located in terrestrial cell 20C deteriorates. As shown in Fig. 5(b), in the uplink, due to signals transmitted by a very large number of terrestrial base station terminals 30(2), the communication quality of HAPS base station terminals 30(1) located in HAPS cell 10C may deteriorate. Therefore, in order to simultaneously use the terrestrial cellular method and the HAPS cellular method, it is necessary to reduce interference.

[0042] Conventionally, as a technique for controlling interference between a plurality of base stations, an inter-cell interference control technique called eICIC compliant with the aforementioned LTE-Advanced standard is known.

[0043] Fig. 6 is a diagram showing an arrangement example of time slots of radio resources set for each of HAPS base station 10 and terrestrial base station 20 when an inter-cell interference control technique (eICIC) is applied in the case where a HAPS base station is applied to a mobile communication system according to a reference example. As shown in Fig. 6, in the conventional inter-cell interference control technique (eICIC), radio resources of the same frequency are time-division multiplexed, and different time slots are assigned to each of HAPS base station 10 and terrestrial base station 20. As a result, since the radio resources are orthogonal on the time axis, interference at the same frequency between HAPS base station 10 and terrestrial base station 20 can be mutually avoided. However, in the conventional inter-cell interference control technique (eICIC), radio resources (time slots) are time-division multiplexed and used in each of HAPS base station 10 and terrestrial base station 20. Therefore, the entire frequency (entire time) allocated to the mobile communication system of the embodiment cannot be used, and the communication capacity (maximum transmission rate, peak throughput) of each service link of HAPS base station 10 and terrestrial base station 20 decreases. In particular, the communication capacity of terrestrial base station terminals connected to terrestrial base station 20 with a large number of terminals in the cell decreases.

[0044] In this embodiment, in order to avoid interference between the HAPS base station 10 and the terrestrial base station 20 and prevent a decrease in the communication capacity (maximum transmission rate, peak throughput) of each service link of the HAPS base station 10 and the terrestrial base station 20, the FDD (Frequency Division Duplex) method adopted in the standard specifications of the fifth generation of mobile communications and the like is used as the transmission and reception method of the service links of each base station 10, 20.

[0045] In the conventional FDD (Frequency Division Duplex) method, different frequencies are used for the uplink and the downlink. For example, in the terrestrial base station 20, as shown in FIGS. 7(a) and 8, the frequency F1 is used for the uplink between the terrestrial base station 20 and the terrestrial base station terminal 30(2), and the frequency F2 is used for the downlink. Also, in the HAPS base station 10, as shown in FIGS. 7(b) and 8, the frequency F1 is used for the uplink between the HAPS base station 10 and the HAPS base station terminal 30(1), and the frequency F2 is used for the downlink. Then, the same frequency F1 is used for the uplinks of the terrestrial base station 20 and the HAPS base station 10, and the same frequency F2 is used for the downlinks of the terrestrial base station 20 and the HAPS base station 10.

[0046] When the conventional FDD method is used in a mobile communication system including the HAPS base station 10 and the terrestrial base station 20, there is a possibility of interference of the same frequency occurring in each of the uplink and the downlink.

[0047] For example, as shown in Fig. 9(a), the transmission signal of the terrestrial uplink line with frequency F1 transmitted from the terrestrial base station terminal 30(2) to the terrestrial base station 20 reaches the relay communication station 11 of the HAPS base station 10 that is receiving the signal of the HAPS uplink line with frequency F1 from the HAPS base station terminal 30(1), and there is a possibility of interference from the terrestrial base station terminal 30(2) to the HAPS uplink line. Similarly, the transmission signal of the HAPS uplink line with frequency F1 transmitted from the HAPS base station terminal 30(1) to the relay communication station 11 of the HAPS base station 10 reaches the antenna 21 of the terrestrial base station 20 that is receiving the signal of the terrestrial uplink line with frequency F1 from the terrestrial base station terminal 30(2), and there is a possibility of interference from the HAPS base station terminal 30(1) to the terrestrial uplink line.

[0048] Also, as shown in Fig. 9(b), the transmission signal of the terrestrial downlink line with frequency F2 transmitted from the terrestrial base station 20 to the terrestrial base station terminal 30(2) reaches the HAPS base station terminal 30(1) that is receiving the signal of the HAPS downlink line with frequency F2 from the HAPS base station 10, and there is a possibility of interference from the terrestrial base station 20 to the HAPS downlink line. Similarly, the transmission signal of the HAPS downlink line with frequency F2 transmitted from the relay communication station 11 of the HAPS base station 10 to the HAPS base station terminal 30(1) reaches the terrestrial base station terminal 30(2) that is receiving the signal of the terrestrial downlink line with frequency F2 from the terrestrial base station 20, and there is a possibility of interference from the HAPS base station 10 to the terrestrial downlink line.

[0049] In a mobile communication system that shares the same frequency between a terrestrial base station 20 and a HAPS base station 10 using the conventional FDD method, in order to avoid interference in the uplink and downlink of each base station, for example, as shown in Fig. 7, synchronization control is performed so that the transmission timings of the base station transmissions in the downlink transmitted from the base station to the terminal are made to coincide among a plurality of base stations 20(1), 20(2), and the transmission timings of the terminal transmissions in the uplink transmitted from the terminal to the base station are made to coincide.

[0050] In the FDD system used in the mobile communication system of this embodiment, in order to suppress the co-frequency interference in each of the uplink and downlink illustrated in FIG. 9, unlike the conventional FDD system, the frequency (transmission frequency) of the downlink and the frequency (reception frequency) of the uplink in the HAPS base station 10 and the terrestrial base station 20 are reversed between the HAPS base station 10 and the terrestrial base station 20.

[0051] For example, in the terrestrial base station 20, as shown in FIGS. 10(a) and 11, the frequency F1 is used for the uplink between the terrestrial base station 20 and the terrestrial base station terminal 30(2), and the frequency F2 is used for the downlink. On the other hand, in the HAPS base station 10, as shown in FIGS. 10(b) and 11, the frequency F2 is used for the uplink between the HAPS base station 10 and the HAPS base station terminal 30(1), and the frequency F1 is used for the downlink.

[0052] By thus reversing the frequency (transmission frequency) of the downlink and the frequency (reception frequency) of the uplink in the HAPS base station 10 and the terrestrial base station 20 between the HAPS base station 10 and the terrestrial base station 20, it is possible to suppress the co-frequency interference in each of the uplink and the downlink.

[0053] As shown in FIG. 11, by reversing the frequency (transmission frequency) of the downlink and the frequency (reception frequency) of the uplink in the HAPS base station 10 and the terrestrial base station 20 between the HAPS base station 10 and the terrestrial base station 20, the way of receiving interference changes significantly compared to the case where the frequency (transmission frequency) of the downlink and the frequency (reception frequency) of the uplink in the conventional FDD system shown in FIG. 8 are the same between the HAPS base station 10 and the terrestrial base station 20.

[0054] As shown in FIG. 12(a), the uplink of the terrestrial base station 20 becomes the downlink of the service link of the HAPS base station 10. Therefore, the radio wave of the downlink transmission of the service link transmitted from the HAPS base station antenna 112 reaches the terrestrial base station antenna 21 as shown in the figure, which causes interference to the uplink of the terrestrial base station 20.

[0055] Note that the HAPS base station terminal 30(1) and the terrestrial base station terminal 30(2) are located at a relatively large distance from each other and are both located on the ground. Therefore, there are many obstacles such as buildings between these terminals, and the interference signal power of the uplink transmission signal of the terrestrial base station terminal 30(2) reaching and being received by the HAPS base station terminal 30(1) is generally negligibly small.

[0056] On the other hand, as shown in Fig. 12(b), the downlink of the terrestrial base station 20 becomes the uplink of the service link of the HAPS base station 10. Therefore, the radio wave of the downlink transmission transmitted from the terrestrial base station antenna 21 reaches the HAPS base station antenna 112 as shown in the figure, and the downlink of the terrestrial base station 20 becomes interference to the uplink of the service link of the HAPS base station 10.

[0057] Note that the terrestrial base station terminal 30(2) and the HAPS base station terminal 30(1) are located at a relatively large distance from each other and are both located on the ground. Therefore, there are many obstacles such as buildings between these terminals, and the interference signal power of the uplink transmission signal of the HAPS base station terminal 30(1) reaching and being received by the terrestrial base station terminal 30(2) is generally negligibly small.

[0058] Summarizing Fig. 12(a) and Fig. 12(b), when the terrestrial cellular system and the HAPS cellular system share the same frequency as shown in Fig. 12(c), the interference can be concentrated on the interference between the terrestrial base station antenna 21 and the service link antenna (HAPS base station antenna) 112 of the HAPS base station. That is, if the interference between the terrestrial base station antenna 21 and the service link antenna 112 of the HAPS base station is reduced, the terrestrial cellular system and the HAPS cellular system can share the same frequency.

[0059] In this embodiment, the terrestrial base station 20 estimates the direction of the service link antenna (HAPS base station antenna) 112 of the HAPS base station in the sky, and applies null-forming that directs the null of the directional beam of the terrestrial base station antenna 21 in that direction, thereby simultaneously reducing interference as shown in FIGS. 13(a) and 13(b). FIGS. 13(a) and 13(b) are combined into FIG. 13(c). The proposed null-forming can simultaneously reduce the interference between the terrestrial base station antenna 21 and the service link antenna 112 of the HAPS base station, and the terrestrial cellular system and the HAPS cellular system can share the same frequency. The above null-forming is a null-forming that directs the null of the directivity of the terrestrial base station antenna 21 in the direction of the HAPS base station antenna 112 and significantly suppresses the transmission power and reception power in that direction.

[0060] FIG. 14(a) is a diagram showing an example of the antenna 21 and the base station apparatus 22 of the terrestrial base station 20 according to the embodiment. FIG. 14(b) is a diagram showing an example of beamforming in the terrestrial base station 20. In this embodiment, as shown in FIG. 14(a), a Massive antenna, which is an array antenna in which a large number of antenna elements 210 are two-dimensionally arranged, is used for the terrestrial base station antenna 21. The base station apparatus 22 includes a transceiver 221 and a null-forming unit 222.

[0061] The null-forming unit 222 generates amplitudes and phases for performing predetermined null-forming on each of the signals transmitted via the plurality of antenna elements 210 of the terrestrial base station antenna 21 (hereinafter referred to as transmission null-forming weights), and superimposes the transmission null-forming weights on the transmission signals of each antenna element 210 output from the transceiver 221 to generate transmission signals, and generates amplitudes and phases for performing predetermined null-forming on each of the received signals received via the plurality of antenna elements of the terrestrial base station antenna 21 (hereinafter referred to as reception null-forming weights), and superimposes the reception null-forming weights on the respective received signals to perform reception signal processing for generating the received signals to the transceiver 221. In the TDD system, the transmission null-forming weights and the reception null-forming weights may be the same.

[0062] The transmission and reception null-forming weights are calculated based on, for example, the position information of the own terrestrial base station antenna 21 and the position information of the HAPS base station antenna 112 (the position information of the HAPS 100), and the direction of the HAPS base station observed from the terrestrial base station (the horizontal angle θ in the horizontal plane and the elevation angle φ in the vertical plane).

[0063] When the number of antenna elements of the terrestrial base station antenna 21 is very large, for example, when it is composed of a massive antenna, by appropriately controlling the transmission and reception null-forming weights generated by the null-forming unit 222, while directing a null of directivity in the direction of the HAPS base station antenna 112, it is possible to direct the directivity beam Bnf of the terrestrial base station antenna 21 in the direction of the terrestrial base station terminal 30(2).

[0064] As beamforming control involving null-forming, for example, a method of creating a null beamforming weight using position information acquired by a GNSS (Global Navigation Satellite System) receiver mounted on a HAPS, or by the beamforming function of a terrestrial base station antenna, the beam is scanned at regular angles (Δθ, Δφ) in the horizontal and vertical planes, and the received power of the downlink signal transmitted by the service link antenna of the HAPS base station is measured. Then, the direction with the maximum received power is estimated as the direction of the HAPS, and control such as creating a null beamforming weight can be used.

[0065] FIG. 15 is a diagram showing an example of beamforming control of a terrestrial base station 20 by using a GPS receiver 15 mounted on a HAPS via a base station interworking control device 50 in a mobile communication system according to an embodiment. Note that this example is a case where the GNSS receiver is a GPS receiver 15 that receives signals from GPS satellites, but a GNSS receiver that receives signals from other GNSS satellites other than GPS may also be used.

[0066] In FIG. 15, a HAPS 100 equipped with a relay communication station 11 in the sky includes a GPS receiver 15. The position information of the HAPS 100 acquired by the GPS receiver is transmitted from the relay communication station 11 to a HAPS-GW 12 via a feeder link FL. The HAPS-GW 12 transfers the position information of the HAPS 100 received from the relay communication station 11 to each terrestrial base station 20 via the base station interworking control device 50. At each terrestrial base station 20, the position information of the HAPS 100 received via the base station interworking control device 50 is used for beamforming control.

[0067] FIG. 16 is a diagram showing an example of the main configuration of an antenna (terrestrial base station antenna) 21 and a base station device 22 when null-forming of the antenna is performed by using a GPS receiver mounted on a HAPS at a terrestrial base station 20 according to an embodiment. In FIG. 16, parts common to FIG. 14(a) described above are denoted by the same reference numerals and the description thereof is omitted.

[0068] In FIG. 16, the base station apparatus 22 includes a radio wave arrival direction estimation unit 223 and a weight calculation unit 224. The radio wave arrival direction estimation unit 223 calculates a horizontal angle θ and an elevation angle φ of the direction of the HAPS 100 with respect to the position of its own station (the direction of the service antenna of the HAPS base station) based on the position information of its own station and the position information of the HAPS 100 transferred via the inter-base station cooperation control apparatus 50. The weight calculation unit 224 calculates a null-forming weight W by, for example, the directionally constrained minimization of power (DCMP), which is a null-forming technique, with the radio wave arrival direction estimated by the radio wave arrival direction estimation unit 223 being known. The weight W calculated by the weight calculation unit 224 is set in the null-forming unit 222 and is superimposed on the transmission signal transmitted via each antenna element 210 of the terrestrial base station antenna 21 and the reception signal received via each antenna element 210 of the terrestrial base station antenna 21.

[0069] FIG. 17 is a diagram showing an example of the main configuration of the antenna (terrestrial base station antenna) 21 and the base station apparatus 22 of the terrestrial base station 20 when estimating the radio wave arrival direction of the HAPS by beam scanning in the embodiment. This example is an example of estimating the radio wave arrival direction of the HAPS by beam scanning in the elevation angle direction, which is a vertical plane. Actually, scanning is performed at regular angles (Δθ, Δφ) in both the horizontal plane and the vertical plane, and the direction (θ, φ) = (nΔθ, mΔφ) (n, m are integers) where the received power is maximum is searched for. Generally, the direction in which the received power is maximum is the direction of the service antenna (HAPS base station antenna) 112 of the HAPS base station 10. In FIG. 17, parts common to FIGS. 14(a) and 16 described above are denoted by the same reference numerals and the description thereof is omitted.

[0070] In FIG. 17, the base station apparatus 22 includes a radio wave arrival direction estimation unit 223, a beam scanning unit 225, and a received power measurement unit 226. While the beam scanning unit 225 scans the vertical plane in the sky with a fixed angular beam B, the received power measurement unit 226 measures the received power received via the antenna 21. The radio wave arrival direction estimation unit 223 sets the horizontal angle θ and the elevation angle φ of the direction of the beam B at which the received power is maximum as the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the HAPS.

[0071] FIG. 18 is a diagram showing another example of the main configuration of the antenna (ground base station antenna) 21 of the ground base station 20 and the base station apparatus 22 when performing beamforming control based on the estimation of the HAPS radio wave arrival direction in the ground base station according to the embodiment. The example of FIG. 18 is an example of estimating the radio wave arrival direction of the HAPS by estimating the radio wave arrival angle. In FIG. 18, the same reference numerals are given to the parts common to FIGS. 14(a) and 16 described above, and the description thereof is omitted.

[0072] In FIG. 18, the base station apparatus 22 includes a radio wave arrival direction estimation unit 223 and a radio wave arrival angle measurement unit 227. The radio wave arrival angle measurement unit 227 estimates the radio wave arrival angle direction (horizontal angle θ, elevation angle φ) of the downlink of the HAPS base station 10 by signal processing using the array antenna (Massive antenna) 21 during downlink transmission. As a technique for estimating the radio wave arrival angle direction, for example, there is a radio wave arrival angle measurement technique "MUSIC technique". The radio wave arrival direction estimation unit 223 sets the radio wave arrival angle direction (horizontal angle θ and elevation angle φ) estimated by the radio wave arrival angle measurement unit 227 as the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the HAPS.

[0073] Assuming that the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the HAPS estimated in each of FIGS. 17 and 18 is known, the above-described weight calculation unit 224 calculates the weight W by, for example, the direction constraint output power minimization method DCMP (Directionally Constrained Minimization of Power), which is a null-forming technique.

[0074] In the embodiments of FIGS. 13 to 18 described above, null forming by the terrestrial base station 20 is applied. However, instead of or in addition to the null forming by the terrestrial base station 20, null forming by the HAPS base station 10 may be applied. For example, instead of or in addition to the null forming by the terrestrial base station 20, as shown below, the HAPS base station 10 estimates the direction of the antenna (terrestrial base station antenna) 21 of the terrestrial base station 20, and applies null forming in which the null of the directional beam of the service link antenna (HAPS base station antenna) 112 of the HAPS base station is directed in that direction.

[0075] FIG. 19(a) is a diagram showing reduction of interference from the terrestrial base station 20 to the uplink of the HAPS base station when null forming is applied to beamforming in the respective antennas of the HAPS base station 10 and the terrestrial base station 20 according to the embodiment. FIG. 19(b) is a diagram showing reduction of interference from the HAPS base station to the uplink of the terrestrial base station 20 when null forming is applied to beamforming in the respective antennas of the HAPS base station 10 and the terrestrial base station 20 according to the embodiment. The terrestrial base station 20 estimates the direction of the service link antenna (HAPS base station antenna) 112 of the HAPS base station in the sky, and applies null forming in which the null of the directional beam of the terrestrial base station antenna 21 is directed in that direction. Further, the HAPS base station 10 estimates the direction of the antenna 21 of the terrestrial base station 20, and applies null forming in which the null of the directional beam of the service link antenna (HAPS base station antenna) 112 of the HAPS base station is directed in that direction. By applying these null formings, reduction of interference is simultaneously realized as shown in FIGS. 19(a) and 19(b). FIGS. 19(a) and 19(b) are combined into FIG. 19(c), and the interference between the terrestrial base station antenna 21 and the service link antenna (HAPS base station antenna) 112 of the HAPS base station can be further reduced simultaneously by the proposed null forming, and the terrestrial cellular system and the HAPS cellular system can share the same frequency.

[0076] Here, the null forming in the terrestrial base station 20 is null forming that turns the null of the directivity of the terrestrial base station antenna 21 in the direction of the HAPS base station antenna 112 and significantly suppresses the transmission power and reception power in that direction. Further, the null forming in the HAPS base station 10 is null forming that turns the null of the directivity of the HAPS base station antenna 112 in the direction of the terrestrial base station antenna 21 and significantly suppresses the transmission power and reception power in that direction.

[0077] FIG. 20(a) is a diagram showing an example of a service link antenna (HAPS base station antenna) 112 of the HAPS base station 10 and a relay communication station device 110 according to the embodiment. FIG. 20(b) is a diagram showing an example of beam forming in the HAPS base station 10. In the present embodiment, as shown in FIG. 20(a), a Massive antenna, which is an array antenna in which a large number of antenna elements 1120 are two-dimensionally arranged, is used for the HAPS base station antenna 112. The relay communication station device 110 includes a transmission / reception device 1101 and a null forming unit 1102.

[0078] The null forming unit 1102 generates an amplitude and a phase for performing predetermined null forming on each signal transmitted via a plurality of antenna elements 1120 of the HAPS base station antenna 112 (hereinafter, transmission null forming weights), and superimposes the transmission null forming weights on the transmission signals of each antenna element 1120 output from the transmission / reception device 1101 to generate a transmission signal, and generates an amplitude and a phase for performing predetermined null forming on each received signal received via a plurality of antenna elements 1120 of the HAPS base station antenna 112 (hereinafter, reception null forming weights), and superimposes the reception null forming weights on the respective received signals to perform reception signal processing for generating a received signal to the transmission / reception device 1101. In the TDD system, the transmission null forming weights and the reception null forming weights may be the same.

[0079] The transmission and reception null-forming weights are calculated based on, for example, the position information of the HAPS base station antenna 112 of the local station (the position information of the HAPS 100) and the position information of the terrestrial base station antenna 21, and the direction of the terrestrial base station observed from the HAPS base station (the horizontal angle θ in the horizontal plane and the elevation angle φ in the vertical plane).

[0080] When the number of antenna elements of the HAPS base station antenna 112 is very large, for example, when it is composed of a massive antenna, by appropriately controlling the transmission and reception null-forming weights generated by the null-forming unit 1102, while directing a null with directivity in the direction of the terrestrial base station antenna 21, it is possible to direct the directivity beam Bnf of the HAPS base station antenna 112 in the direction of the HAPS base station terminal 30(1).

[0081] As the beamforming control involving the above null-forming, for example, a method of creating a null-beamforming weight using the position information obtained by a GNSS (Global Navigation Satellite System) receiver mounted on the HAPS, or by the beamforming function of the HAPS base station antenna, scanning the beam at regular angles (Δθ, Δφ) in the horizontal and vertical planes, measuring the received power of the downlink signal transmitted by the service link antenna of the terrestrial base station, and estimating the direction of the maximum received power as the direction of the terrestrial base station to create a null-beamforming weight, etc. can be used.

[0082] FIG. 21 is a diagram showing an example of beamforming control of the HAPS base station 10 by using the GPS receiver 15 mounted on the HAPS via the base station interconnection control device 50 in the mobile communication system according to the embodiment. Note that this example is an example when the GNSS receiver is the GPS receiver 15 that receives signals from GPS satellites, but a GNSS receiver that receives signals from other GNSS satellites other than GPS may also be used.

[0083] In FIG. 21, the HAPS 10 equipped with the airborne relay communication station 11 includes a GPS receiver 15. The position information of the HAPS 10 obtained by the GPS receiver is stored (updated at a predetermined timing) in the HAPS base station 10 (for example, the relay communication station 11) and is used for beamforming control of the HAPS base station 10. The position information of each terrestrial base station 20 is transmitted from each terrestrial base station 20 to the HAPS-GW 12 via the inter-base station cooperation control device 50. The HAPS-GW 12 transfers the position information of each terrestrial base station 20 received from each terrestrial base station 20 to the HAPS base station 10 (for example, the relay communication station 11) via the feeder link FL. Note that the terrestrial base station 20 or the terrestrial base station antenna 21 may include a GPS receiver 15, and transfer the position information obtained by the GPS receiver to the HAPS base station 10 (for example, the relay communication station 11) as the position information of the terrestrial base station 20.

[0084] FIG. 22 is a diagram showing an example of the main configuration of the antenna (HAPS base station antenna) 112 and the relay communication station device 110 when null-forming of the antenna is performed by using the HAPS-mounted GPS receiver in the HAPS base station 10 according to the embodiment. In FIG. 22, parts common to FIG. 20(a) described above are denoted by the same reference numerals and the description thereof is omitted.

[0085] In FIG. 22, the relay communication station device 110 includes a radio wave arrival direction estimation unit 1103 and a weight calculation unit 1104. The radio wave arrival direction estimation unit 1103 calculates the horizontal angle θ and the elevation angle φ of the direction of the terrestrial base station 20 (the direction of the service antenna of the terrestrial base station) with respect to the position of its own station based on the position information of its own station and the position information of the terrestrial base station 20 transferred via the base station interworking control device 50. The weight calculation unit 1104 calculates a null-forming weight W by, for example, the directionally constrained minimization of power (DCMP), which is a null-forming technique, assuming that the radio wave arrival direction estimated by the radio wave arrival direction estimation unit 1103 is known. The weight W calculated by the weight calculation unit 1104 is set in the null-forming unit 1102 and superimposed on the transmission signal transmitted via each antenna element 1120 of the HAPS base station antenna 112 and the reception signal received via each antenna element 1120 of the HAPS base station antenna 112.

[0086] FIG. 23 is a diagram showing an example of the main configuration of the antenna (HAPS base station antenna) 112 of the HAPS base station 10 and the relay communication station device 110 when estimating the radio wave arrival direction of the terrestrial base station by beam scanning in the HAPS base station 10 according to the embodiment. This example is an example of estimating the radio wave arrival direction from the terrestrial base station 20 by beam scanning in the elevation angle direction, which is a vertical plane. Actually, scanning is performed at regular angles (Δθ, Δφ) in both the horizontal and vertical planes to search for the direction (θ, φ) = (nΔθ, mΔφ) (n, m are integers) where the received power is maximum. Generally, the direction in which the received power is maximum is the direction of the service link antenna (terrestrial base station antenna) 21 of the terrestrial base station 20. In FIG. 23, the same reference numerals are given to the parts common to FIGS. 20(a) and 22 described above, and the description thereof is omitted.

[0087] In FIG. 23, the relay communication station device 110 includes a radio wave arrival direction estimation unit 1103, a beam scanning unit 1105, and a received power measurement unit 1106. While the beam scanning unit 1105 scans the vertical plane in the sky with a fixed angular beam B, the received power measurement unit 1106 measures the received power received via the antenna 112. The radio wave arrival direction estimation unit 1103 sets the horizontal angle θ and elevation angle φ of the direction of the beam B at which the received power is maximum as the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the ground base station 20.

[0088] FIG. 24 is a diagram showing another example of the main configuration of the antenna (HAPS base station antenna) 112 of the HAPS base station 10 and the relay communication station device 110 when performing beamforming control based on the estimation of the radio wave arrival direction of the ground base station in the HAPS base station 10 according to the embodiment. The example of FIG. 24 is an example of estimating the radio wave arrival direction of the ground base station by estimating the radio wave arrival angle. In FIG. 24, the same reference numerals are given to the parts common to the above-described FIGS. 20(a) and 22, and the description thereof is omitted.

[0089] In FIG. 24, the relay communication station device 110 includes a radio wave arrival direction estimation unit 1103 and a radio wave arrival angle measurement unit 1107. The radio wave arrival angle measurement unit 1107 estimates the radio wave arrival angle direction (horizontal angle θ, elevation angle φ) of the downlink of the ground base station 20 by signal processing using the array antenna (Massive antenna) 112 during the downlink transmission of the ground base station 20. As a technique for estimating the radio wave arrival angle direction, for example, there is a radio wave arrival angle measurement technique "MUSIC technique". The radio wave arrival direction estimation unit 1103 sets the radio wave arrival angle direction (horizontal angle θ and elevation angle φ) estimated by the radio wave arrival angle measurement unit 1107 as the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the ground base station.

[0090] With the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the ground base station estimated in each of FIGS. 23 and 24 being known, the above-described weight calculation unit 1104 calculates the weight W by, for example, the directionally constrained minimization of power method DCMP (Directionally Constrained Minimization of Power), which is a null-forming technique.

[0091] According to this embodiment that uses the FDD mode as the transmission / reception mode, it is possible to share the same frequency in each service link between each of the service link antennas (HAPS base station antennas) of the HAPS base station (first base station) and the terminal, and between each of the service link antennas (ground base station antennas) of the ground base station (second base station) and the terminal. It is possible to share the same frequency like the inter-cell interference control technology (eICIC) shown in FIG. 6, but the problem of causing a decrease in the communication capacity of the terminal can be overcome.

[0092] Also, in this embodiment, in each service link between each of the service link antennas (HAPS base station antennas) of the HAPS base station 10 and the terminal, and between each of the service link antennas (ground base station antennas) of the ground base station 20 and the terminal, the same frequency is shared and the FDD mode is used as the transmission / reception mode. Between the HAPS base station 10 and the ground base station 20, the transmission frequency and the reception frequency of the wireless communication in the FDD mode in the service link are made opposite to each other. As a result, the frequency F2 of the downlink of the service link of the ground base station 20 becomes the same as the frequency F2 of the uplink of the service link of the HAPS base station 10, and there is no interference from the terminal (ground base station terminal) 30(2) communicating with the ground base station 20 to the uplink of the service link of the HAPS base station 10, and there is only the downlink interference of the service link transmitted from the ground base station 20. On the other hand, the frequency F1 of the downlink of the service link of the HAPS base station 10 becomes the same as the frequency F1 of the uplink of the service link of the ground base station 20, and the downlink of the service link of the HAPS base station 10 has no interference to the downlink of the ground base station terminal 30(2), and becomes interference to the uplink of the service link of the ground base station 20. From the above, the interference in the uplink and downlink of the service link between the HAPS base station 10 and the terrestrial base station 20 does not cause any interference to the terrestrial base station terminals 30(2) and the HAPS base station terminals 30(1) that are communicating with the respective base stations 10 and 20, and it is only the interference between the HAPS base station 10 and the terrestrial base station 20. That is, by reversing the transmission frequency and the reception frequency between the terrestrial base station 20 and the HAPS base station 10, the interference relationship between transmission and reception can be extremely simplified to "the interference between the terrestrial base station and the HAPS base station". Therefore, in order to suppress the interference between the cell (HAPS cell) 10C composed of the HAPS base station 10 and the cell (terrestrial cell) 20C composed of the terrestrial base station 20, it is sufficient to only suppress the interference between the HAPS base station 10 and the terrestrial base station 20. Therefore, in this embodiment, by directing the null of the directional beam of the terrestrial base station antenna in the direction of the HAPS base station antenna, the interference caused by the downlink transmission signal from the HAPS base station antenna to the uplink reception signal of the terrestrial base station antenna can be reduced, and the interference caused by the downlink transmission signal from the terrestrial base station antenna to the uplink reception signal of the HAPS base station antenna can be reduced. That is, the line-of-sight propagation is basically between the terrestrial base station 20 and the relay communication station 11 of the HAPS base station 10, the arrival angle of the radio wave is extremely narrow, and by directing the null of the terrestrial base station antenna 21 in the direction of the HAPS base station, the interference can be suppressed. Furthermore, by directing the null of the HAPS base station antenna 112 in the direction of the terrestrial base station, the interference can be further suppressed.

[0093] Also, according to this embodiment, by only the null-forming control of the terrestrial base station antenna 21, the interference in both directions between the terrestrial base station 20 and the relay communication station 11 of the HAPS base station 10 can be suppressed.

[0094] Also, according to this embodiment, it can be realized by changing the transmission frequency and the reception frequency between the terrestrial base station 20 and the HAPS base station 10 using the normal FDD method (such as 5G) without any special changes.

[0095] Further, according to the present embodiment, at the terrestrial base station 20, it can be realized by beam control that nulls are directed upward in the direction of the HAPS using a base station array antenna generally used in 5G. No additional special device is required. In particular, since the direction of the HAPS can be easily estimated based on information such as GPS mounted on the HAPS, null control for directing nulls in that direction is easy.

[0096] Further, according to the present embodiment, at the HAPS base station 10, no special device or control is required to share frequencies.

[0097] Further, according to the present embodiment, adjustment of the transmission timings of the terrestrial base station 20 and the HAPS base station 10 can be easily realized by the inter-system (base station) cooperation control device 50.

[0098] The present invention can improve the frequency utilization efficiency at the HAPS base station and the terrestrial base station and prevent a decrease in the communication capacity of the terminal, and can realize frequency sharing between the HAPS base station and the terrestrial base station without adding special devices to the HAPS base station and the terrestrial base station. Therefore, it can contribute to the achievement of Sustainable Development Goal (SDG) 9, "Build the infrastructure for industry and innovation."

[0099] Further, the present invention can also be applied when sharing frequencies between the various systems exemplified in the following (A) to (D) and the terrestrial base station. (A) Frequency sharing between the HAPS base station and the terrestrial base station (B) Frequency sharing between a helicopter-mounted wireless relay system or a UAV-mounted wireless relay system during a disaster and the terrestrial base station (C) Frequency sharing between a drone-mounted wireless relay system and the terrestrial base station (D) Frequency sharing between a satellite communication system in a geostationary, medium-earth orbit, or low-earth orbit and the terrestrial base station

[0100] In addition, the processing steps, mobile communication systems, aerial relay base stations, HAPS cellular systems, terrestrial base stations, terrestrial cellular systems, relay communication stations, HAPS-GWs, terminals (user devices, mobile stations, mobile units), and the constituent elements of the base station interworking control devices described in this specification can be implemented by various means. For example, these processing steps and constituent elements may be implemented by hardware, firmware, software, or a combination thereof.

[0101] Regarding hardware implementation, means such as processing units used to realize the above steps and constituent elements in an entity (for example, various wireless communication devices, wireless relay devices, NodeB, servers, gateways, switches, computers, hard disk drive devices, or optical disk drive devices) may be implemented in one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, electronic devices, other electronic units designed to execute the functions described in this specification, computers, or a combination thereof.

[0102] Also, regarding firmware and / or software implementation, the means used to implement the above components may be implemented by a program (e.g., code such as procedures, functions, modules, instructions, etc.) that executes the functions described in this specification. Generally, any computer / processor-readable medium that clearly embodies the firmware and / or software code may be used for the implementation of means such as processing units for realizing the above steps and components described in this specification. For example, the firmware and / or software code may be stored in a memory, for example, in a control device, and executed by a computer or a processor. The memory may be implemented inside the computer or the processor, or may be implemented outside the processor. Also, the firmware and / or software code may be stored in a computer or processor-readable medium such as, for example, random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), programmable read-only memory (PROM), electrically erasable PROM (EEPROM), FLASH memory, floppy (registered trademark) disk, compact disk (CD), digital versatile disk (DVD), magnetic or optical data storage device, etc. The code may be executed by one or more computers or processors, and may also cause the computer or processor to execute the functional aspects described in this specification.

[0103] Also, the description of the embodiments disclosed in this specification is provided to enable those skilled in the art to manufacture or use the present disclosure. Various modifications to the present disclosure will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other variations without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure should not be limited to the examples and designs described in this specification, but should be recognized in the broadest scope consistent with the principles and novel features disclosed herein.

Description of Reference Numerals

[0104] 10: HAPS Base Station (High Altitude Relay Type Base Station) 10C: HAPS Cell 11: Relay Communication Station 12: HAPS-GW 15: GPS Receiver 20: Ground Base Station 20C: Ground Cell 21: Ground Base Station Antenna (Service Link Antenna) 22: Base Station Equipment 30: Terminal 30(1): HAPS Base Station Terminal 30(2): Ground Base Station Terminal 40: Core Network 50: Base Station Interconnection Control Device 100: HAPS 110: Relay Communication Station Equipment 1101: Transceiver 1102: Null Forming Unit 1103: Radio Wave Arrival Direction Estimation Unit 1104: Weight Calculation Unit 1105: Beam Scanning Unit 1106: Received Power Measurement Unit 1107: Radio Wave Arrival Angle Measurement Unit 111: FL Antenna 112: HAPS Base Station Antenna (Service Link Antenna) 1120: Antenna Element 113: Repeater 114: Frequency Conversion Device 115: Base Station Equipment 116: Feeder Link Transceiver 121: FL Antenna 122: Base Station Equipment 123: Frequency Conversion Device 124: Feeder Link Transceiver 210: Antenna Element 221: Transceiver 222: Null Forming Unit 223: Radio Wave Arrival Direction Estimation Unit 224: Weight calculation unit 225: Beam scanning unit 226: Received power measurement unit 227: Radio wave arrival angle measurement unit

Claims

1. An aerial relay type base station that performs wireless communication with a terminal via a service link antenna of a relay communication station provided on an aircraft or a floating body located in the air, and one or more terrestrial base stations that perform wireless communication with the terminal via a service link antenna arranged on the ground or at sea, wherein: The aerial relay type base station and the terrestrial base station each perform wireless communication of a service link with the terminal by an FDD (Frequency Division Duplex) method. The transmission frequency and the reception frequency of the wireless communication by the FDD method in the service link are opposite to each other between the aerial relay type base station and the terrestrial base station. The terrestrial base station estimates the direction of the service link antenna of the aerial relay type base station and controls the null of the directional beam of the service link antenna of the terrestrial base station to be directed in the estimated direction of the service link antenna of the aerial relay type base station. A mobile communication system characterized by the above.

2. In the mobile communication system according to Claim 1, The aerial relay type base station estimates the direction of the service link antenna of the terrestrial base station and controls the null of the directional beam of the service link antenna of the aerial relay type base station to be directed in the estimated direction of the service link antenna of the terrestrial base station. A mobile communication system characterized by the above.

3. An aerial relay type base station that performs wireless communication with a terminal via a service link antenna of a relay communication station provided on an aircraft or a floating body located in the air, and one or more terrestrial base stations that perform wireless communication with the terminal via a service link antenna arranged on the ground or at sea, wherein: The aerial relay type base station and the terrestrial base station each perform wireless communication of a service link with the terminal by an FDD (Frequency Division Duplex) method. The transmission frequency and the reception frequency of the wireless communication by the FDD method in the service link are opposite to each other between the aerial relay type base station and the terrestrial base station. The aerial relay type base station estimates the direction of the service link antenna of the terrestrial base station and controls the null of the directional beam of the service link antenna of the aerial relay type base station to be directed in the estimated direction of the service link antenna of the terrestrial base station. A mobile communication system characterized by the above.

4. In the mobile communication system according to any one of Claims 1 to 3, The mobile communication system is characterized in that the relay communication station mounted on the flying object or the floating object is composed of a repeater relay device that relays the transmission and reception signals without regenerating them.

5. In the mobile communication system according to any one of Claims 1 to 3, the relay communication station mounted on the flying object or the floating object is composed of a base station device that regenerates the transmission and reception signals, remodulates the regenerated signals, and relays them, which is a feature of the mobile communication system.

6. In the mobile communication system according to Claim 1 or 2, it further includes a base station inter-control device for controlling between the airborne relay type base station and the ground base station, the position information acquired by a GNSS (Global Navigation Satellite System) receiver mounted on the flying object or the floating object is transferred to the ground base station via a gateway device and the base station inter-control device, the ground base station estimates the direction of the service link antenna of the relay communication station based on the position information of its own ground base station, which is a feature of the mobile communication system.

7. In the mobile communication system according to Claim 1 or 2, the ground base station has an array antenna as the service link antenna, measures the radio wave arrival direction from the service link antenna of the relay communication station using the array antenna, and estimates the direction of the service link antenna of the relay communication station from the measurement result, which is a feature of the mobile communication system.

8. In the mobile communication system according to Claim 2 or 3, it further includes a base station inter-control device for controlling between the airborne relay type base station and the ground base station, the position information acquired by a GNSS (Global Navigation Satellite System) receiver mounted on the ground base station or the service link antenna of the ground base station is transferred to the airborne relay type base station via a gateway device and the base station inter-control device, and the airborne relay type base station estimates the direction of the service link antenna of the ground base station based on the position information of the relay communication station, which is a feature of the mobile communication system.

9. In the mobile communication system according to Claim 2 or 3, the airborne relay type base station has an array antenna as the service link antenna, measures the radio wave arrival direction from the service link antenna of the ground base station using the array antenna, and estimates the direction of the service link antenna of the ground base station from the measurement result, which is a feature of the mobile communication system.

10. In the mobile communication system according to any one of claims 1 to 3, the aircraft or the floating body is a communication satellite, a UAV (Unmanned Aerial Vehicle) flying at an altitude of 18 km or less, or a HAPS flying in the stratosphere at an altitude of 18 km or more, and the mobile communication system is characterized by this.

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