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 aerial relay base station and a ground base station each perform wireless communication of a service link with terminals using a time division duplex (TDD) method that uses the same frequency. The transmission timing and reception timing of wireless communication using the TDD method in the service link are reversed between the aerial relay base station and the ground base station. The aerial relay base station estimates the direction of the service link antenna of the ground base station and controls its own service link antenna such that the null of the directional beam is directed toward the estimated direction of the ground base station's service link antenna.SELECTED DRAWING: Figure 9

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 sky, 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, an aerial relay type base station 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 sky, 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. A mobile communication system is known 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, both the airborne relay base station and the ground base station cannot 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] A mobile communication system according to one 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 disposed on the ground or at sea. The airborne relay base station and the ground base station are a mobile communication system that is 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 a TDD (Time Division Duplex) method using the same frequency. The transmission timing and reception timing of the wireless communication of the TDD method in the service link are made opposite to each other between the airborne relay base station and the ground base station. The airborne relay base station estimates the direction of the service link antenna of the ground base station and controls to direct the null of the directional beam of the service link antenna of the airborne relay base station in the estimated direction of the service link antenna of the ground station.

[0008] In the mobile communication system, the airborne relay base station and the ground base station may each perform adjustment of the transmission timing to reverse the transmission using the time information acquired by a GNSS (Global Navigation Satellite System) receiver.

[0009] In the mobile communication system, the relay communication station mounted on the aircraft or the floating body may be configured as a repeater relay device (frequency conversion repeater relay device) that relays without reproducing the transmission and reception signals.

[0010] In the mobile communication system, the relay communication station mounted on the aircraft or the floating body may be configured as a base station device that reproduces the transmission and reception signals, remodulates the reproduced signals, and relays them.

[0011] In the mobile communication system, the airborne relay type base station receives 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 via a gateway device, and estimates the direction of the service link antenna of the ground base station based on the position information of the relay communication station.

[0012] In the mobile communication system, the airborne relay type 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 estimates the direction of the service link antenna of the ground base station from the measurement result.

[0013] In the mobile communication system, it further includes a base station interconnection control device that controls between the airborne relay type base station and the ground base station. The base station interconnection control device may adjust the transmission timing so that transmission and reception are reversed respectively, using the time information of GNSS (Global Navigation Satellite System) received by the airborne relay type base station via the gateway device and the time information of GNSS (Global Navigation Satellite System) received by the ground base station.

[0014] In the mobile communication system, it further includes an inter-base station cooperation control device for controlling between the aerial relay base station and the ground base station, and transfers position information acquired by a GNSS (Global Navigation Satellite System) receiver mounted on the ground base station or a service link antenna of the ground base station to the aerial relay base station via a gateway device and the inter-base station cooperation control device. 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, the ground base station may estimate the direction of the service link antenna of the aerial relay base station, and control 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 relay communication station.

[0016] In the mobile communication system, 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.

[0017] In the mobile communication system, it further includes an inter-base station cooperation control device for controlling between the aerial relay base station and the ground base station. The inter-base station cooperation control device may perform adjustment of transmission timing such that transmission and reception are reversed respectively using the time information of GNSS (Global Navigation Satellite System) received at the aerial relay base station via the gateway device and the time information of GNSS (Global Navigation Satellite System) received at the ground base station.

[0018] In the mobile communication system, a base station cooperation control device for controlling between the aerial relay base station and the terrestrial base station is further provided, and position information acquired by a GNSS (Global Navigation Satellite System) receiver mounted on the aircraft or the floating body is transferred to the terrestrial base station via the gateway device and the base station cooperation control device, and the terrestrial base station may estimate the direction of the service link antenna of the relay communication station based on the position information of its own terrestrial base station.

[0019] In the mobile communication system, 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.

[0020] According to the mobile communication system disclosed in this document, it is possible to reduce the interference caused by the downlink transmission signal from the service link antenna (aerial relay base station antenna) of the relay communication station provided on the aircraft or floating body located in the air to the reception signal of the uplink of the service link antenna (terrestrial base station antenna) of the terrestrial base station, and it is also possible to reduce the interference caused by the downlink transmission signal from the terrestrial base station antenna to the reception signal of the uplink of the aerial relay base station antenna.

Brief Description of the Drawings

[0021]

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Embodiment for Carrying Out the Invention

[0022] 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, and thus the present invention is not limited to the illustrated numerical values.

[0023] In the present embodiment, an example of a mobile communication system in which a HAPS base station (HAPS cellular system) as an aerial relay type base station and a terrestrial base station (terrestrial cellular system) share the same frequency will be mainly described. However, the present invention can also be applied to a mobile communication system in which a relay communication station of an 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 a HAPS or a drone as a stratosphere communication platform capable of providing communication services to a wide area by mounting communication devices on an unmanned aircraft flown in the stratosphere.

[0024] 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 the present 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.

[0025] 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 by power, for example, equipped with 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 provided with the relay communication station 11 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 provided with the relay communication station 11 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, a UAS (Unmanned Aircraft Systems). Further, the flying object or the floating object may be a mooring 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 the sea or a lake, or a device provided on another aircraft or floating body. The 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. The UAV may be, for example, a drone that flies with fuel or a drone that flies with a battery or the like.

[0026] 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 the weather conditions are relatively stable, and particularly an airspace with an altitude of approximately 20 [km]. Further, the above airspace may be an airspace with an altitude of 0.1 [km] or more and 18 [km] or less for the UAV. Further, the airspace for the drone may be an airspace with an altitude of 0.05 [km] or more.

[0027] 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 directivity 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 directivity in the horizontal and vertical directions can be controlled.

[0028] Also, 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 directivity can be controlled, and may be a Massive antenna in which a large number of antenna elements are two-dimensionally arranged and the directivity in the horizontal and vertical directions can be controlled.

[0029] 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 directivity in the horizontal and vertical directions, etc. 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.

[0030] The terrestrial base station 20 includes an antenna section (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 over a service link SL(2). The terrestrial base station antenna 21 can be, 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.

[0031] 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 the timing control is executed so that the transmission and reception timings of the HAPS base station 10 and the terrestrial base station 20 are opposite.

[0032] 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 section for the core network 40 and the base station interconnection control device 50, and a wireless communication section. By executing a predetermined program, wireless communication can be performed between the HAPS base station terminal 30(1) and the terrestrial base station terminal 30(2), and communication with the core network 40 and the base station interconnection control device 50 can be performed.

[0033] 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, a TDD (Time 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 as the TDD method.

[0034] The HAPS base station terminal 30(1) that can be connected to and communicate with the HAPS base station 10 and the terrestrial base station terminal 30(2) that can be connected to and communicate with the terrestrial base station 20 are mobile communication terminals 30 of the same specification. The terminal 30 is a mobile phone, a smart phone, a laptop 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.

[0035] 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.

[0036] The HAPS base station 10 of this embodiment is composed of a relay communication station 11 mounted on the HAPS 100 in the air, or is composed of the relay communication station 11 and a HAPS-GW12 provided on the ground (or at sea).

[0037] FIG. 2(a) is a diagram showing a configuration example of a relay communication station 11 that constitutes an example of a 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 into 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) into the frequency of the feeder link and transmits it to the HAPS-GW 12.

[0038] 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) 112, 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.

[0039] Figure 2(b) is a diagram showing a configuration example of HAPS-GW12 corresponding to Figure 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 HAPS 100.

[0040] Figure 3(a) is a diagram showing a configuration example of the 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.

[0041] 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.

[0042] Figure 3(b) is a diagram showing a configuration example of HAPS-GW12 corresponding to Figure 3(a). 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 with 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. 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.

[0043] 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.

[0044] Conventionally, as a technique for controlling interference between a plurality of base stations, an inter-cell interference control technique called eICIC compliant with the above-mentioned LTE-Advanced standard is known.

[0045] FIG. 5 is a diagram showing an arrangement example of time slots of radio resources set in each of the HAPS base station 10 and the terrestrial base station 20 when the inter-cell interference control technique (eICIC) is applied when the HAPS base station is applied to the system configuration of the reference example. As shown in FIG. 5, in the conventional inter-cell interference control technique (eICIC), radio resources of the same frequency are time-division multiplexed, and different time slots are allocated to each of the HAPS base station 10 and the terrestrial base station 20. As a result, since the radio resources are orthogonal on the time axis, interference at the same frequency between the HAPS base station 10 and the 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 the HAPS base station 10 and the terrestrial base station 20. Therefore, the entire frequency (entire time) allocated to the mobile communication system according to the embodiment cannot be used, and the communication capacity (maximum transmission rate, peak throughput) of each service link of the HAPS base station 10 and the terrestrial base station 20 decreases. In particular, the communication capacity of the terrestrial base station terminal connected to the terrestrial base station 20 with a large number of terminals in the cell decreases.

[0046] 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 TDD (Time Division Duplex) method adopted in a standard such as the fifth generation of mobile communication is used as the transmission / reception method of the service link of each base station 10, 20.

[0047] In the TDD (Time Division Duplex) mode, the same frequency is used for the uplink and downlink, and time slots are used in a time-division manner for the uplink and downlink. For example, in the terrestrial base station 20, as shown in FIGS. 6(a) and 6(b), the same frequency is used for the uplink and downlink between the terrestrial base station 20 and the terrestrial base station terminal 30(2). Then, as shown in FIG. 6(c), between the transmission of the downlink (base station transmission) from the terrestrial base station 20 to the terrestrial base station terminal 30(2) and the transmission of the uplink (terminal transmission) from the terrestrial base station terminal 30(2) to the terrestrial base station 20, the radio resources (time slots) on the time axis are used in a time-division multiplexing manner.

[0048] When the TDD (Time Division Duplex) mode is used in the HAPS base station 10 and the terrestrial base station 20 of the present embodiment, by applying the interference reduction technique described later for avoiding interference between the HAPS base station 10 and the terrestrial base station 20, the HAPS base station 10 and the terrestrial base station 20 can completely share the same frequency. Furthermore, since the HAPS base station 10 and the terrestrial base station 20 can use all the frequencies (all times) allocated to the mobile communication system, it is possible to prevent a decrease in the communication capacity of the service link of each base station 10, 20. In particular, it is possible to prevent a decrease in the communication capacity of the terrestrial base station terminals connected to the terrestrial base station 20 where the number of terminals in the cell is large.

[0049] In a system in which a plurality of base stations using the conventional TDD mode share the same frequency, in order to avoid interference between the uplink and downlink of each base station, for example, as shown in FIG. 7, between a plurality of base stations 20(1), 20(2), the transmission timing of the base station transmission of the downlink transmitted from the base station to the terminal is made to coincide, and at the same time, synchronization control is performed so that the transmission timing of the terminal transmission of the uplink transmitted from the terminal to the base station coincides.

[0050] When simultaneously using the communication method of a terrestrial cellular system using a terrestrial base station 20 (hereinafter referred to as the "terrestrial cellular method") and the communication method of a HAPS cellular system using a HAPS base station 10 (hereinafter referred to as the "HAPS cellular method"), as shown in Fig. 8(a), especially in the downlink of the service link, due to the interference wave from the HAPS base station 10 that transmits signals over a wide area, the communication quality of many terrestrial base station terminals 30(2) located in the terrestrial cell 20C deteriorates. As shown in Fig. 8(b), in the uplink, due to the signals transmitted by a very large number of terrestrial base station terminals 30(2), the communication quality of the HAPS base station terminal 30(1) located in the 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.

[0051] In the mobile communication system of this embodiment, the transmission timing and the reception timing are reversed between the HAPS base station 10 and the terrestrial base station 20.

[0052] Fig. 9 is a diagram showing an arrangement example of time slots for the uplink and downlink when performing synchronization control to reverse the transmission timing and the reception timing between a terrestrial base station 20 and a HAPS base station 10 using the TDD method in the mobile communication system according to the embodiment. In each of the plurality of consecutive transmission and reception frames (radio frames) shown in Fig. 9, the transmission timing and the transmission period of the downlink from the terrestrial base station 20 to the terrestrial base station terminal 30(2) coincide with the transmission timing and the transmission period of the uplink from the HAPS base station terminal 30(1) to the HAPS base station 10. On the other hand, the transmission timing and the transmission period of the uplink from the terrestrial base station terminal 30(2) to the terrestrial base station 20 coincide with the transmission timing and the transmission period of the downlink from the HAPS base station 10 to the HAPS base station terminal 30(1).

[0053] Here, the terrestrial base station 20 and the HAPS base station 10 may each perform adjustment of the transmission timing to make the transmissions opposite using the time information acquired by a GNSS (Global Navigation Satellite System) receiver.

[0054] As shown in FIG. 9, by making the transmission timing and reception timing of the HAPS base station 10 and the terrestrial base station 20 opposite to each other in the uplink and downlink, the way of receiving interference changes significantly compared to the case where the transmission timing and reception timing of the HAPS base station 10 and the terrestrial base station 20 shown in FIG. 8 are the same in the uplink and downlink.

[0055] As shown in FIG. 10(a), 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.

[0056] Note that the terrestrial base station terminal 30(2) and the HAPS base station terminal 30(1) are located at a relatively far 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 received when the transmission signal of the uplink of the HAPS base station terminal 30(1) reaches the terrestrial base station terminal 30(2) is generally negligibly small.

[0057] On the other hand, as shown in FIG. 10(b), 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, and becomes interference to the uplink of the terrestrial base station 20.

[0058] Note that the HAPS base station terminal 30(1) and the terrestrial base station terminal 30(2) are located at a relatively far 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 received when the transmission signal of the uplink of the terrestrial base station terminal 30(2) reaches the HAPS base station terminal 30(1) is generally negligibly small.

[0059] When FIGS. 10(a) and 10(b) are combined, as shown in FIG. 10(c), when the terrestrial cellular system and the HAPS cellular system share the same frequency, the interference can be aggregated 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.

[0060] Therefore, in the present embodiment, the HAPS base station 10 estimates the direction of the service link antenna (terrestrial base station antenna) 21 of the terrestrial base station 20, and applies null-forming that directs the null of the directional beam of the service link antenna (HAPS base station antenna) 112 of the HAPS base station in that direction, thereby simultaneously reducing interference as shown in FIGS. 11(a) and 11(b). When FIGS. 11(a) and 11(b) are combined, FIG. 11(c) is obtained. 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 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.

[0061] FIG. 12(a) is a diagram showing an example of the service link antenna (HAPS base station antenna) 112 of the HAPS base station 10 and the relay communication station device 110 according to the embodiment. FIG. 12(b) is a diagram showing an example of beamforming in the HAPS base station 10. In the present embodiment, as shown in FIG. 12(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.

[0062] The null-forming unit 1102 generates the amplitude and phase for performing predetermined null-forming on each of the signals transmitted via the plurality of antenna elements 1120 of the HAPS base station antenna 112 (hereinafter referred to as transmission null-forming weights), and superimposes the transmission null-forming weights on the transmission signals of each antenna element 1120 output from the transceiver 1101 to generate transmission signals, and generates the amplitude and phase for performing predetermined null-forming on each of the received signals received via the plurality of antenna elements 1120 of the HAPS base station antenna 112 (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 1101. In the TDD system, the transmission null-forming weights and the reception null-forming weights may be the same.

[0063] The transmission and reception null-forming weights are calculated based on, for example, the direction of the terrestrial base station observed from the HAPS base station (horizontal angle θ in the horizontal plane, elevation angle φ in the vertical plane) based on the position information of the HAPS base station antenna 112 of its own station (position information of the HAPS 100) and the position information of the terrestrial base station antenna 21.

[0064] 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, it is possible to direct the directivity null in the direction of the terrestrial base station antenna 21 while directing the directivity beam Bnf of the HAPS base station antenna 112 in the direction of the HAPS base station terminal 30(1).

[0065] 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 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 a 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 can be used.

[0066] FIG. 13 is a diagram showing an example of beamforming control of a HAPS base station 10 by using a GPS receiver 15 mounted on a HAPS via a base station interconnection control device 50 in a mobile communication system according to an embodiment. In this example, the GNSS receiver is a GPS receiver 15 that receives signals from GPS satellites, but a GNSS receiver that receives signals from satellites of other GNSSs other than GPS may also be used.

[0067] In FIG. 13, 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 stored (updated at a predetermined timing) in the HAPS base station 10 (for example, the relay communication station 11) and 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 a HAPS-GW 12 via a base station interconnection 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 a 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 acquired by the GPS receiver as the position information of the terrestrial base station 20 to the HAPS base station 10 (for example, the relay communication station 11).

[0068] FIG. 14 is a diagram showing an example of the main configuration of an antenna (HAPS base station antenna) 112 and a relay communication station device 110 when null forming of the antenna is performed by using a GPS receiver mounted on a HAPS in the HAPS base station 10 according to the embodiment. In FIG. 14, parts common to the above-described FIG. 12(a) are denoted by the same reference numerals and the description thereof is omitted.

[0069] In FIG. 14, 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 a horizontal angle θ and an 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 its own position based on its own position information and the position information of the terrestrial base station 20 transferred via the base station interconnection 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.

[0070] FIG. 15 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 arrival direction of the terrestrial base station radio wave in the HAPS base station 10 by beam scanning. This example is an example of estimating the arrival direction of the radio wave 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, and the direction (θ, φ) = (nΔθ, mΔφ) (n, m are integers) where the received power is maximum is searched for. Generally, the direction where 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. 15, parts common to the aforementioned FIGS. 12(a) and 14 are denoted by the same reference numerals and the description thereof is omitted.

[0071] In FIG. 15, 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 angle 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 the elevation angle φ of the direction of the beam B where the received power is maximum as the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the terrestrial base station 20.

[0072] FIG. 16 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 arrival direction of the terrestrial base station radio wave in the HAPS base station 10. The example in FIG. 16 is an example of estimating the arrival direction of the radio wave of the terrestrial base station by estimating the arrival angle of the radio wave. In FIG. 16, parts common to the aforementioned FIGS. 12(a) and 14 are denoted by the same reference numerals and the description thereof is omitted.

[0073] In FIG. 16, the relay communication station device 110 includes a radio wave arrival direction estimation unit 1103 and a radio wave arrival angle measurement unit 1107. When the downlink of the terrestrial base station 20 transmits, the radio wave arrival angle measurement unit 1107 uses an array antenna (Massive antenna) 112 to estimate the radio wave arrival angle direction (horizontal angle θ, elevation angle φ) of the downlink by signal processing. As an estimation technique for the radio wave arrival angle direction, for example, there is a radio wave arrival angle measurement technique called "MUSIC technique". The radio wave arrival direction estimation unit 1103 uses 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 terrestrial base station.

[0074] Regarding the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the terrestrial base station estimated in FIGS. 15 and 16 as known, the above-mentioned weight calculation unit 1104 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.

[0075] FIGS. 17 and 18 are diagrams each showing an example of control of the transmission / reception timing between the terrestrial base station 20 and the HAPS base station 10 according to the embodiment. In the mobile communication system of this embodiment, since it is necessary to reverse the transmission / reception timing between the terrestrial base station 20 and the HAPS base station 10, the system interconnection control device 50 adjusts the transmission / reception timing of the terrestrial base station 20 and the HAPS base station 10 so that the transmission / reception frame times of the terrestrial base station 20 and the HAPS base station 10 are reversed. In the example of FIG. 17, the adjustment of the transmission / reception timing is performed at the HAPS-GW12. In the example of FIG. 18, the adjustment of the transmission / reception timing is performed at the relay communication station 11 mounted on the HAPS100.

[0076] In the embodiments of FIGS. 11 to 18 described above, null forming by the terrestrial base station 20 may be further applied. For example, as shown below, the terrestrial base station 20 estimates the direction of the service link antenna (HAPS base station antenna) 112 of the HAPS base station 10, and may further apply null forming to direct the null of the directional beam of the terrestrial base station antenna 21 in that direction.

[0077] 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 10 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 to direct the null of the directional beam of the terrestrial base station antenna 21 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 to direct the null of the directional beam of the service link antenna (HAPS base station antenna) 112 of the HAPS base station in that direction. By applying these null formations, reduction of interference is simultaneously achieved as shown in FIGS. 19(a) and 19(b). FIGS. 19(a) and 19(b) are combined into FIG. 19(c), and the proposed null forming can further reduce the interference between the terrestrial base station antenna 21 and the service link antenna (HAPS base station antenna) 112 of the HAPS base station simultaneously, and the terrestrial cellular system and the HAPS cellular system can share the same frequency.

[0078] Here, the null forming in the above-mentioned terrestrial base station 20 is 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. Further, the null forming in the above-mentioned HAPS base station 10 is null forming that directs 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.

[0079] FIG. 20(a) is a diagram showing an example of an antenna (terrestrial base station antenna) 21 and a base station device 22 according to an embodiment. FIG. 20(b) is a diagram showing an example of beamforming in the same terrestrial base station 20. In the example of FIG. 20(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 device 22 includes a transceiver 221 and a null forming unit 222.

[0080] The null forming unit 222 generates an amplitude and a phase for performing predetermined null forming on each signal transmitted via a plurality of antenna elements 210 of the terrestrial base station antenna 21 (hereinafter, 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 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 of the terrestrial base station antenna 21 (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 reception signal to the transceiver 221. Note that also in the terrestrial base station 20, in the TDD system, the transmission null forming weights and the reception null forming weights may be the same.

[0081] The transmission and reception null-forming weights are calculated based on, for example, the position information of the local terrestrial base station antenna 21 and the position information of the HAPS base station antenna 112 (the position information of HAPS100), 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).

[0082] 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).

[0083] 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 receiver mounted on HAPS, or by the beamforming function of the terrestrial 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 HAPS base station, and estimating the direction of the maximum received power as the direction of HAPS to create a null-beamforming weight can be used.

[0084] FIG. 21 is a diagram showing an example of beamforming control of the terrestrial base station 20 by using the GPS receiver 15 mounted on 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.

[0085] In FIG. 21, the HAPS 100 equipped with the aerial relay communication station 11 includes a GPS receiver 15. The position information of the HAPS 100 obtained by the GPS receiver is transmitted from the relay communication station 11 to the HAPS-GW 12 via the 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 inter-base-station cooperation control device 50. At each terrestrial base station 20, the position information of the HAPS 100 received via the inter-base-station cooperation control device 50 is used for beamforming control.

[0086] In FIG. 21, similar to FIG. 13 described above, the position information of the HAPS 100 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 also used for beamforming control of the HAPS base station 10. Also, 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.

[0087] FIG. 22 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 the HAPS in the terrestrial base station 20 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.

[0088] In FIG. 22, 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 the horizontal angle θ and the elevation angle φ of the direction of the HAPS 100 (the direction of the service antenna of the HAPS 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 HAPS 100 transferred via the inter-base station cooperation control apparatus 50. The weight calculation unit 224 calculates the null-forming weight W by, for example, the direction constraint output power minimization method DCMP, which is a null-forming technique, assuming the radio wave arrival direction estimated by the radio wave arrival direction estimation unit 223 as known. The weight W calculated by the weight calculation unit 224 is set in the null-forming unit 222 and 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.

[0089] FIG. 23 is a diagram showing an example of the main configuration of the antenna (terrestrial base station antenna) 21 of the terrestrial base station 20 and the base station apparatus 22 when estimating the radio wave arrival direction of the HAPS by beam scanning in the terrestrial base station 20 according to 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. Generally, the direction in which the received power is maximum is the direction of the service antenna of the HAPS base station. In FIG. 23, parts common to FIGS. 20(a) and 22 described above are denoted by the same reference numerals and the description thereof is omitted.

[0090] In FIG. 23, 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 sky in the vertical plane with a fixed angle 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 with the maximum received power as the radio wave arrival direction (horizontal angle θ and elevation angle φ) of the HAPS.

[0091] FIG. 24 is a diagram showing another example of the main configurations of an antenna (a terrestrial base station antenna) 21 and a base station apparatus 22 of the terrestrial base station 20 when beamforming control is performed based on the estimation of the arrival direction of HAPS radio waves in the terrestrial base station 20 according to the embodiment. The example of FIG. 24 is an example of estimating the arrival direction of HAPS radio waves by estimating the arrival angle of the radio waves. In FIG. 24, parts common to the aforementioned FIGS. 20(a) and 22 are denoted by the same reference numerals and the description thereof is omitted.

[0092] In FIG. 24, the base station apparatus 22 includes a radio wave arrival direction estimation unit 223 and a radio wave arrival angle measurement unit 227. When the downlink of the HAPS base station 10 is transmitting, the radio wave arrival angle measurement unit 227 estimates the radio wave arrival angle direction (horizontal angle θ, elevation angle φ) of the downlink by signal processing using an array antenna (Massive antenna) 21. 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.

[0093] Assuming that the radio wave arrival directions (horizontal angle θ and elevation angle φ) of the HAPS estimated in FIGS. 23 and 24 are known, the aforementioned weight calculation unit 224 calculates the weight W by, for example, the direction constraint output power minimization method DCMP, which is a null-forming technique.

[0094] As described above, according to this embodiment using the TDD system as the transmission / reception system, it is possible to share the same frequency in each service link between each of the service link antennas (HAPS base station antenna) of the HAPS base station (first base station) and the service link antennas (terrestrial base station antennas) of the terrestrial base station (second base station) and the terminal, and it is possible to share the same frequency as in the inter-cell interference control technique (eICIC) shown in FIG. 5, but the problem of causing a decrease in the communication capacity of the terminal can be overcome.

[0095] In addition, in the present embodiment, in each service link between the service link antenna (HAPS base station antenna) of the HAPS base station 10 and the service link antenna (ground base station antenna) of the ground base station 20 and the terminal, the same frequency is shared and the TDD method is used as the transmission / reception method. The transmission timing and reception timing of the wireless communication in the TDD method in the service link are made opposite between the HAPS base station 10 and the ground base station 20. As a result, the downlink of the service link of the ground base station 20 has the same timing as 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 only the downlink interference of the service link transmitted from the ground base station 20 remains. On the other hand, the downlink of the service link of the HAPS base station 10 has the same timing as 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 between the uplink and downlink of the service link between the HAPS base station 10 and the ground base station 20 does not cause any interference to the ground base station terminal 30(2) and the HAPS base station terminal 30(1) communicating with the respective base stations 10 and 20, and only becomes interference between the HAPS base station 10 and the ground base station 20. Therefore, in order to suppress the interference between the cell (HAPS cell) 10C configured by the HAPS base station 10 and the cell (ground cell) 20C configured by the ground base station 20, it is sufficient to only suppress the interference between the HAPS base station 10 and the ground base station 20. Therefore, in the present embodiment, by directing the null of the directional beam of the HAPS base station antenna in the direction of the ground base station antenna, it is possible to reduce the interference caused by the downlink transmission signal from the HAPS base station antenna to the reception signal of the uplink of the ground base station antenna, and 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 HAPS base station antenna.

[0096] In addition, in the present embodiment, the interference can be further reduced by directing the null of the directive beam of the terrestrial base station antenna in the direction of the HAPS base station antenna.

[0097] Moreover, according to the present embodiment, by sharing the frequencies of the HAPS service link and the terrestrial base station, the frequency utilization rate can be doubled.

[0098] Also, according to the present embodiment, it can be achieved by changing the transmission and reception timings of the terrestrial base station 20 and the HAPS base station 10 using a normal TDD system (such as 5G) without any special modification.

[0099] Furthermore, according to the present embodiment, at the terrestrial base station 20, it can be achieved by beam control that directs a null in the direction of the HAPS located above using the base station array antenna commonly 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 installed on the HAPS, null control that directs a null in that direction is easy.

[0100] Also, according to the present embodiment, at the HAPS base station 10, it can be achieved by beam control that directs a null in the direction of the terrestrial base station located below using the base station array antenna commonly used in 5G. No additional special device is required. In particular, since the direction of the terrestrial base station can be easily estimated based on information such as GPS installed on the HAPS, null control that directs a null in that direction is easy.

[0101] Moreover, according to the present embodiment, at the HAPS base station 10, no special device or control is required for frequency sharing.

[0102] Also, according to the present embodiment, the adjustment of the transmission timings of the terrestrial base station 20 and the HAPS base station 10 can be easily achieved by the inter-system (base station) cooperation control device 50.

[0103] The present invention can improve the frequency utilization efficiency in a HAPS base station and a terrestrial base station and can prevent a decrease in the communication capacity of a terminal, and can provide a system capable of realizing frequency sharing between a HAPS base station and a terrestrial base station without adding a special device to the HAPS base station and the terrestrial base station, thus contributing to the achievement of Sustainable Development Goal (SDG) 9, "Build the infrastructure for industry and innovation."

[0104] In addition, the present invention can also be applied when sharing frequencies between various systems exemplified in the following (A) to (D) and a terrestrial base station. (A) Frequency sharing between a HAPS base station and a terrestrial base station (B) Frequency sharing between a helicopter-mounted wireless relay system or a UAV-mounted wireless relay system in case of disaster and a terrestrial base station (C) Frequency sharing between a drone-mounted wireless relay system and a terrestrial base station (D) Frequency sharing between a satellite communication system in geostationary, medium-earth orbit or low-earth orbit and a terrestrial base station

[0105] Note that the processing steps described in this specification and the components of a mobile communication system, an aerial relay type base station, a HAPS cellular system, a terrestrial base station, a terrestrial cellular system, a relay communication station, a HAPS-GW, a terminal (user device, mobile station, mobile unit) and an inter-base station cooperation control device can be implemented by various means. For example, these processing steps and components may be implemented by hardware, firmware, software, or a combination thereof.

[0106] For hardware implementation, means such as a processing unit used to implement the above steps and components in an entity (e.g., 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 combinations thereof.

[0107] Also, for firmware and / or software implementations, 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 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 for realizing the above-described steps and components. For example, the firmware and / or software code may be stored in a memory and executed by a computer or processor, for example, in a control device. The memory may be implemented inside the computer or processor, or 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 the computer or processor may be caused to execute the functional aspects described herein.

[0108] Also, the description of the embodiments disclosed herein is provided to enable those skilled in the art to make 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 may 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 herein, but should be accorded the widest scope that recognizes the principles and novel features disclosed herein.

Description of Reference Numerals

[0109] 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 23: GPS Receiver 30: Terminal 30(1): HAPS Base Station Terminal 30(2): Ground Base Station Terminal 40: Core Network 50: Base Station Interworking 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 in 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 are a mobile communication system that is time-synchronized with each other, The aerial relay type base station and the terrestrial base station each perform wireless communication of a service link with a terminal by a TDD (Time Division Duplex) method using the same frequency, The transmission timing and reception timing of the wireless communication by the TDD 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 to direct the null of the directional beam of the service link antenna of the aerial relay type base station in the estimated direction of the service link antenna of the terrestrial base station. A mobile communication system characterized by the above.

2. In the mobile communication system of Claim 1, The relay communication station mounted on the aircraft or the floating body is composed of a repeater relay device that relays without regenerating the transmitted and received signals. A mobile communication system characterized by this.

3. In the mobile communication system of Claim 1, The relay communication station mounted on the aircraft or the floating body is composed of a base station device that regenerates the transmitted and received signals, remodulates the regenerated signals, and relays them. A mobile communication system characterized by this.

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

5. In the mobile communication system according to any one of Claims 1 to 4, It further includes a base station inter-control device that controls between the aerial relay type base station and the terrestrial base station. The inter-base station control device uses the time information of GNSS (Global Navigation Satellite System) received by the airborne relay base station and received via the gateway device and the time information of GNSS (Global Navigation Satellite System) received by the ground base station to adjust the transmission timing so that transmission and reception are reversed, respectively. A mobile communication system characterized by this.

6. In the mobile communication system according to any one of Claims 1 to 4, further comprising an inter-base station control device that controls between the airborne relay 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 base station via the gateway device and the inter-base station control device, and the airborne relay 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. A mobile communication system characterized by this.

7. In the mobile communication system according to any one of Claims 1 to 4, The airborne 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 estimates the direction of the service link antenna of the ground base station from the measurement result. A mobile communication system characterized by this.

8. In the mobile communication system according to any one of Claims 1 to 4, 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. A mobile communication system characterized by this.

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