Mobile communication system

Abstract

The present invention improves frequency utilization efficiency, prevents a decrease in the communication capacity of a terminal, and reduces interference in an upstream line and a downstream line of a service link of each base station in a mobile communication system provided with an airborne relay type base station having an antenna provided to an airborne flying object and the like (including a UAV, an HAPS, and a communication satellite) and a terrestrial base station. The airborne relay type base station and the terrestrial base station each perform wireless communication of the service link with the terminal by means of time division duplexing (TDD) using the same frequency. The transmission and reception timings of the TDD wireless communication in the service link are opposite between the airborne relay type base station and the terrestrial base station. The terrestrial base station suppresses an interference signal from the airborne relay type base station included in a reception signal of the upstream line. The airborne relay type base station suppresses an interference signal from the terrestrial base station included in the reception signal of the upstream line.

Description

Mobile communication systems

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

[0002] Conventionally, as flying objects or floating objects located in the sky, there are known UAVs that fly at altitudes of 18 km or less and HAPSs that fly in the stratosphere at altitudes of 18 km or more. Also known is a mobile communication system that includes an airborne relay base station as a first base station that wirelessly communicates with a terminal via a service link antenna of a relay communication station provided on the flying object or floating object such as a UAV or HAPS (airborne object) located in the sky, and a terrestrial base station as a second base station that wirelessly communicates with the terminal via an antenna located on land or sea, in which the same frequency is shared in the service link between the airborne relay base station and the terrestrial base station, enabling wireless communication between terminals of common specifications.

[0003] As a technology applicable to reducing interference between an airborne relay base station and a terrestrial base station in a mobile communication system, there is an interference control technology that adjusts and controls radio frames in the time domain (in subframe units) on the premise that the airborne relay base station and the terrestrial base station are time-synchronized with each other (see, for example, Patent Document 1 and Non-Patent Document 1). This interference control technology is a technology that complies with the LTE (Long Term Evolution)-Advanced standard, and is also called eICIC (enhanced Inter-Cell Interference Coordination).

[0004] JP 2012-129793 A

[0005] “Overview of 3GPP”, Release 10, V0.2.1 (2014-06).

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

[0007] A mobile communication system according to one aspect of the present disclosure includes an airborne relay base station that wirelessly communicates with a terminal via a service link antenna of a relay communication station installed on an aircraft or floating object located in the sky, and a terrestrial base station located on the ground or sea, where the airborne relay base station and the terrestrial base station are time-synchronized with each other. The airborne relay base station and the terrestrial base station each perform wireless communication of a service link with the terminal using a TDD (Time Division Duplex) method using the same frequency. The transmission timing and reception timing of the TDD wireless communication in the service link are reversed between the airborne relay base station and the terrestrial base station.

[0008] The terrestrial base station branches a downlink transmission signal transmitted from the terrestrial base station and forwards it to the aerial repeater base station as a transmission replica signal. The terrestrial base station performs correlation processing between the uplink reception signal of the terrestrial base station, which includes an interference signal from the aerial repeater base station that interferes with the uplink of the terrestrial base station, and the transmission replica signal forwarded from the aerial repeater base station, estimates the complex reception amplitude of the interference signal from the aerial repeater base station, generates an interference suppression signal that suppresses the interference signal from the aerial repeater base station using the estimated complex reception amplitude of the interference signal from the aerial repeater base station and the previously transmitted replica signal, and suppresses the interference signal from the aerial repeater base station included in the reception signal of the uplink of the terrestrial base station by combining the reception signal of the uplink of the terrestrial base station with the interference suppression signal.

[0009] The aerial repeater type base station branches a downlink transmission signal transmitted from the aerial repeater type base station and forwards it to the terrestrial base station as a transmission replica signal. The aerial repeater type base station performs correlation processing between an uplink reception signal of the aerial repeater type base station, which includes an interference signal from the terrestrial base station that interferes with the uplink of the aerial repeater type base station, and the transmission replica signal forwarded from the terrestrial base station, estimates the complex reception amplitude of the interference signal from the terrestrial base station, generates an interference suppression signal that suppresses the interference signal from the terrestrial base station using the estimated complex reception amplitude of the interference signal from the terrestrial base station and the transmission replica signal, and suppresses the interference signal from the terrestrial base station included in the uplink reception signal of the aerial repeater type base station by combining the uplink reception signal of the aerial repeater type base station and the interference suppression signal.

[0010] In the mobile communication system, the overhead relay base station and the terrestrial base station may adjust their transmission timings to be opposite to each other using time information acquired by a GNSS (Global Navigation Satellite System) receiver.

[0011] In the mobile communication system, the relay communication station mounted on the flying body or the floating body may be configured as a repeater relay device (frequency conversion repeater relay device) that relays transmitted and received signals without regenerating them.

[0012] In the mobile communication system, the relay communication station mounted on the flying body or the floating body may be configured as a base station device that regenerates transmitted and received signals, re-modulates the regenerated signals, and relays them.

[0013] The mobile communication system may further include an inter-base station cooperation control device that performs control between the air repeater base station and the terrestrial base station, and the inter-base station cooperation control device may transfer the transmission replica signal from the terrestrial base station to the air repeater base station, and transfer the transmission replica signal from the air repeater base station to the terrestrial base station.

[0014] In the mobile communication system, the terrestrial base station and the air repeater base station are installed in the same location or comprise a centralized base station configuration unit configured within the same device, and the centralized base station configuration unit may estimate the complex reception amplitude of an interference signal from the air repeater base station at the terrestrial base station, generate the interference suppression signal and suppress the interference signal from the air repeater base station, and estimate the complex reception amplitude of the interference signal from the terrestrial base station at the air repeater base station, generate the interference suppression signal and suppress the interference signal from the terrestrial base station.

[0015] The mobile communication system may further include an inter-base station cooperation control device that performs control between the overhead relay base station and the terrestrial base station, and the inter-base station cooperation control device may adjust the transmission timing by reversing the transmission and reception, using GNSS (Global Navigation Satellite System) time information received by the overhead relay base station and received via a gateway device, and the GNSS (Global Navigation Satellite System) time information received by the terrestrial base station.

[0016] In the mobile communication system, the flying object or the floating object may be a communication satellite, a UAV (Unmanned Aerial Vehicle) that flies at an altitude of 18 km or less, or a HAPS that flies in the stratosphere at an altitude of 18 km or more.

[0017] The mobile communication system disclosed in this specification can reduce interference caused by downlink transmission signals from a service link antenna (airborne relay base station antenna) of a relay communication station installed on an aircraft or floating body located in the sky to reception signals on the uplink of a service link antenna (terrestrial base station antenna) of a terrestrial base station, as well as reduce interference caused by downlink transmission signals from a terrestrial base station antenna to reception signals on the uplink of an airborne relay base station antenna.

[0018] FIG. 1 is a diagram illustrating an example of the overall configuration of a mobile communication system according to an embodiment. FIG. 2A is a diagram illustrating an example of the configuration of a relay communication station constituting an example of a HAPS base station constituting the mobile communication system according to the embodiment. FIG. 2B is a diagram illustrating an example of the configuration of a HAPS-GW corresponding to FIG. 2A. FIG. 3A is a diagram illustrating an example of the configuration of a relay communication station constituting another example of a HAPS base station constituting the mobile communication system according to the embodiment. FIG. 3B is a diagram illustrating an example of the configuration of a HAPS-GW corresponding to FIG. 3A. FIG. 4A is a diagram illustrating an example of interference from a HAPS downlink to a terrestrial base station terminal when a HAPS base station is applied to a system configuration of a reference example. FIG. 4B is a diagram illustrating an example of interference from a terrestrial base station terminal to an uplink when a HAPS base station is applied to a current configuration. FIG. 5 is a diagram illustrating an example of the arrangement of time slots of radio resources set in a HAPS base station and a terrestrial base station to which inter-cell interference control technology (eICIC) is applied when a HAPS base station is applied to the system configuration of a reference example. Fig. 6A is a diagram showing uplinks and downlinks between a terrestrial base station and a terrestrial base station terminal when a TDD (time division multiplexing) scheme is used as the transmission scheme for the service link in the mobile communication system according to the embodiment. Fig. 6B is a diagram showing an example of a frequency band in which the same frequency is shared in uplinks and downlinks between the terrestrial base station and the terrestrial base station terminal in the TDD scheme. Fig. 6C is a diagram showing an example of an arrangement of time slots in uplinks and downlinks between the terrestrial base station and the terrestrial base station terminal in the TDD scheme. Fig. 7 is a diagram showing an example of an arrangement of time slots in uplinks and downlinks when synchronization control is performed to match transmission timings and reception timings among multiple terrestrial base stations in a system configuration using a conventional TDD scheme. Fig. 8A is a diagram showing an example of downlink interference when transmission timings and reception timings among multiple terrestrial base stations are matched by synchronization control in a system configuration using a conventional TDD scheme. Fig. 8B is a diagram showing an example of uplink interference when transmission timings and reception timings among multiple terrestrial base stations are matched by synchronization control in a system configuration using a conventional TDD scheme.Fig. 9 is a diagram showing an example of time slot arrangement for uplink and downlink links when synchronization control is performed to reverse the transmission timing and reception timing between a terrestrial base station and a HAPS base station using the TDD scheme in a mobile communication system according to the embodiment. Fig. 10A is a diagram showing an example of interference from a terrestrial base station to the uplink link of a HAPS base station when synchronization control is performed to reverse the transmission timing and reception timing between the terrestrial base station and the HAPS base station. Fig. 10B is a diagram showing an example of interference from a HAPS base station to the uplink link of a terrestrial base station when synchronization control is performed to reverse the transmission timing and reception timing between the terrestrial base station and the HAPS base station. Fig. 10C is a diagram collectively showing the interference in Figs. 10A and 10B. Fig. 11A is a diagram showing reduction of interference from a HAPS base station in a terrestrial base station according to the embodiment. Fig. 11B is a diagram showing reduction of interference from a terrestrial base station in a HAPS base station according to the embodiment. Fig. 12 is a diagram showing an example of the configuration of a mobile communication system in which an interference suppression unit (interference canceller) is provided in the terrestrial base station according to the embodiment. Fig. 13 is a diagram showing an example of the configuration of the interference suppression unit (interference canceller) of the terrestrial base station of Fig. 12. Fig. 14 is a diagram showing an example of the configuration of a mobile communication system in which an interference suppression unit (interference canceller) is provided in a HAPS base station according to the embodiment. Fig. 15 is a diagram showing an example of the configuration of the interference suppression unit (interference canceller) of the HAPS base station of Fig. 14. Fig. 16 is a diagram showing an example of the configuration of a mobile communication system in which an interference suppression unit (interference canceller) is provided in a toll base station according to the embodiment. Fig. 17 is a diagram showing an example of control of transmission and reception timing between a terrestrial base station and a HAPS base station according to the embodiment. Fig. 18 is a diagram showing an example of control of transmission and reception timing between a terrestrial base station and a HAPS base station according to the embodiment.

[0019] Various embodiments will be described below with reference to the drawings. Note that each drawing merely shows a schematic representation of the shape, size, and positional relationship to the extent that the contents of the present invention can be understood, and therefore the present invention is not limited to the shape, size, and positional relationship exemplified in each drawing. Furthermore, the numerical values ​​exemplified below are merely preferred examples of the present invention, and therefore the present invention is not limited to the exemplified numerical values.

[0020] In this embodiment, an example of a mobile communication system in which a HAPS base station (HAPS cellular system) as an airborne relay 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 the relay communication station of the airborne relay base station is provided on an aircraft or floating body other than a HAPS. Here, the airborne relay base station may be an airborne communication base station used in an NTN (Non-Terrestrial Network). The NTN may be, for example, a network using artificial satellites such as the communication satellites described below, and HAPS or drones as a stratospheric communication platform that is equipped with communication equipment and the like on unmanned aircraft flown in the stratosphere and can provide communication services over a wide area.

[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 a HAPS base station (HAPS cellular system) 10 as a first base station (air relay base station) and a terrestrial base station (terrestrial cellular system) 20 as a second base station, as a plurality of base stations capable of wireless communication with a terminal 30.

[0022] The HAPS base station 10 wirelessly communicates with a terminal (hereinafter also referred to as a "HAPS base station terminal") 30(1) via a service link antenna (also referred to as a "HAPS base station antenna") 112 of a relay communication station 11 provided on a HAPS ("high altitude pseudosatellite" or "high altitude platform station") 100, which serves as an air vehicle or floating body located in the sky. The HAPS 100 is equipped with at least one of a battery and a solar power generation system, for example, and can fly using electric power. The HAPS 100 may be an airship-type HAPS as shown in the figure, or a solar plane-type HAPS. Furthermore, the air vehicle or floating body on which the relay communication station 11 is provided may be an artificial satellite (e.g., a communication satellite), a balloon, a drone, or an aircraft, in addition to a HAPS. 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 above the Earth's surface, a MEO (medium earth orbit) satellite located in an orbit at an altitude higher than 2,000 km but lower than 36,000 km, or a HEO (high earth orbit) satellite located in an orbit at an altitude near or higher than 36,000 km. The artificial satellite may also be a GEO (geostationary orbit) satellite, a quasi-geostationary satellite, a quasi-zenith satellite, or a non-geostationary satellite. The air vehicle or floating object on which the relay communication station 11 is installed may be unmanned or manned. For example, the air vehicle or 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. The air vehicle or floating body may be an unmanned aerial vehicle (UAV) such as an unmanned drone or an unmanned aircraft system (UAS). The air vehicle or floating body may be a moored type that is moored to another device (mooring device) using a mooring line such as a rope, cable, string, or wire having a predetermined strength. The purpose of mooring with the mooring line may include the purpose of power supply and signal transmission.The other device to which the tethered air vehicle or float is moored may be a device fixed on the ground, a device mounted on a vehicle capable of moving on the ground, a device mounted on a ship or float capable of moving on water, such as the sea or lake, or a device mounted on another air vehicle or float. The mooring line may include a power feeder line, a communication line such as an optical fiber, or both a power feeder line and a communication line. For example, the tethered air vehicle or float may be one or more wired-powered drones moored by one or more mooring lines (power feeders). Furthermore, air vehicles or floats such as HAPS 100, artificial satellites, drones, balloons, aircraft, and UAVs may be equipped with at least one of a battery and an engine as a power source. The UAV may be, for example, an unmanned aircraft powered by fuel or a drone powered by a battery.

[0023] The HAPS 100 equipped with the relay communication station 11 may be controlled, for example, by autonomous control or external control, to float or fly in an airspace (floating airspace) at an altitude H of 100 km or less above the ground G (or sea level). The airspace in which the HAPS 100 is located may be, for example, a stratospheric airspace at an altitude H of 18 km or more and 50 km or less. This airspace may be an airspace at an altitude of 15 km or more and 25 km or less where meteorological conditions are relatively stable, and may particularly be an airspace at an altitude of approximately 20 km. Furthermore, the airspace may be an airspace at an altitude of 0.1 km or more and 18 km or less for UAVs. Furthermore, the airspace may be an airspace at an altitude of 0.05 km or more for drones.

[0024] The relay communication station 11 includes a feeder link antenna unit (hereinafter also referred to as "FL antenna") 111 and a service link antenna unit (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 installed on the ground (or sea) via the FL antenna 111. The FL antenna 111 is, for example, an array antenna whose directivity can be controlled, as described below, and may be a massive antenna in which a large number of antenna elements are arranged two-dimensionally and whose directivity can be controlled in the horizontal and vertical directions.

[0025] Furthermore, the relay communication station 11 can communicate with the HAPS base station terminal 30(1) over a service link SL(1) via a 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 many antenna elements are arranged two-dimensionally and whose directivity can be controlled in the horizontal and vertical directions.

[0026] The HAPS-GW 12 is connected to the core network 40 of the mobile communication network via a wired or wireless communication line, and includes a feeder link antenna unit (hereinafter also referred to as "FL antenna") 121 consisting of a parabolic antenna, a massive antenna capable of controlling horizontal and vertical directivity, etc. The HAPS-GW 12 can perform feeder link FL communication with the HAPS-equipped relay communication station 11 via the FL antenna 121.

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

[0028] The HAPS-GW 12 of the HAPS base station 10 and the base station device 22 of the terrestrial base station 20 are each connected to an inter-base station cooperation control device (also referred to as an "inter-base station network cooperation control device" or "inter-system cooperation control device") 50 by a wired or wireless communication line such as optical fiber in a network cooperation control system. The HAPS base station 10 and the terrestrial base station 20 are time-synchronized with each other via the inter-base station cooperation control device 50, and timing control is performed such that the transmission and reception timing of the HAPS base station 10 is opposite to that 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 a CPU, memory, etc., an external communication interface unit for the core network 40 and the base station cooperation control device 50, and a wireless communication unit, and 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 can be performed with the core network 40 and the base station cooperation control device 50.

[0030] In the mobile communication system of this embodiment, the same wireless transmission method is used for communication of the service link SL(1) of the HAPS base station 10 and communication of the service link SL(2) of the terrestrial base station 20, and the same frequency is shared to improve frequency efficiency of the service link. The wireless transmission method is a TDD (Time Division Duplex) method that transmits and receives signals using the same frequency in a time-division manner, and can be, for example, a TDD method such as a communication method of LTE (Long Term Evolution) or LTE-Advanced, a communication method of a fourth-generation mobile phone, a communication method of a fifth-generation mobile phone, or a subsequent next-generation mobile phone.

[0031] A HAPS base station terminal 30(1) capable of connecting to and communicating with a HAPS base station 10 and a terrestrial base station terminal 30(2) capable of connecting to and communicating with a terrestrial base station 20 are mobile communication terminals 30 with the same specifications. The terminal 30 is a mobile phone, a smartphone, a portable personal computer with mobile communication capabilities, or the like, 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 into a vehicle such as an automobile or a mobile object such as a drone, or may be a terminal device for a device for the Internet of Things (IoT).

[0032] The terminal 30 is configured using hardware such as a computer device having a CPU, memory, etc., and a wireless communication unit, and by executing a predetermined program, it is possible to perform wireless communication between the HAPS base station 10 and the terrestrial base station 20.

[0033] The HAPS base station 10 of this embodiment is composed of a relay communication station 11 mounted on a HAPS 100 in the sky, or is composed of a relay communication station 11 and a HAPS-GW 12 installed on the ground (or at sea).

[0034] 2A is a diagram showing an example of the configuration of a relay communication station 11 constituting an example of a HAPS base station 10 in the mobile communication system of the embodiment. In this example configuration, the relay communication station 11 is a wireless relay device (hereinafter referred to as a "frequency conversion repeater") that converts the frequency of a feeder link, which has a different frequency from that of a service link. 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). Meanwhile, 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] In this example, the relay communication station 11 of the HAPS base station 10 is configured as a repeater relay device (frequency converting repeater) having a repeater 113 and a frequency converting device 114. The repeater 113 has a low-noise amplifier that amplifies a reception signal of the service link SL(1) received via the HAPS base station antenna 112, a power amplifier that amplifies a transmission signal of the service link SL(1) transmitted via the HAPS base station antenna (SL antenna) 12, and the like. The frequency converting device 114 converts between the frequency of the service link SL(1) and the frequency of the feeder link FL.

[0036] FIG. 2B is a diagram showing an example of the configuration of the HAPS-GW 12 corresponding to FIG. 2A . The HAPS-GW 12 in this example includes a base station device (hereinafter also referred to as a "HAPS base station device") 122 and a frequency conversion device 123. The base station device 122 includes a baseband processing device that processes baseband signals 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 converts between the frequency of the service link signal input / output to / from the base station device 122 and the frequency of the feeder link signal transmitted / received via the FL antenna 121. The HAPS-GW 12 also has a function of communicating with the base station cooperation control device 50 to adjust the transmission / reception timing of the service link SL with the terrestrial base station 20 and to transfer location information of the HAPS 100.

[0037] 3A is a diagram showing an example of the configuration of a relay communication station 11 constituting another example of the HAPS base station 10 in the mobile communication system of the embodiment. In this example configuration, the relay communication station 11 of the HAPS base station 10 is composed of a base station device similar to that of a normal terrestrial base station, and a feeder link transceiver in which the feeder link between the relay communication station 11 of the HAPS base station 10 and the HAPS-GW uses a frequency different from that of the service link. Unlike the service link, the feeder link allows the selection of an optimal wireless transmission method as appropriate.

[0038] In this example, the relay communication station 11 of the HAPS base station 10 has a base station device 115 equivalent to the base station device 22 of the terrestrial base station 20 (hereinafter also referred to as the "terrestrial base station device"), and a feeder link transceiver 116. The base station device 115 has a low-noise amplifier that amplifies a reception signal of the service link SL(1) received via the HAPS base station antenna 112, a power amplifier that amplifies a transmission signal of the service link SL(1) transmitted via the HAPS base station antenna 112, a baseband processing device that processes baseband signals of the service link, etc. The feeder link transceiver 116 transmits and receives backhaul line signals transmitted and received via the FL antenna 111 to and from the HAPS-GW 12.

[0039] 3B is a diagram showing an example of the configuration of the HAPS-GW 12 corresponding to FIG. 3A. The HAPS-GW 12 in this example has a feeder link transceiver 124. The feeder link transceiver 124 transmits and receives backhaul line signals transmitted and received via an FL antenna 121 to and from an airborne relay communication station 11 mounted on the HAPS 100. The feeder link transceiver 124 also communicates with the core network 40 via the backhaul line. The HAPS-GW 12 also has a function of communicating with the inter-base station cooperation control device 50 to adjust the transmission and reception timing of the service link SL with the terrestrial base station 20 and to transfer location information of the HAPS 100.

[0040] In a configuration including a HAPS base station 10 and a 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 time in the FDD system or the TDD system, or if the HAPS base station terminal 30(1) and the terrestrial base station terminal 30(2) transmit signals at the same time, interference may occur between the HAPS cellular system in the sky and the terrestrial cellular system. For example, as shown in Figure 4A, when a HAPS downlink signal is transmitted from a relay communication station 11 mounted on the HAPS 100 in the sky to the HAPS base station terminal 30(1), the transmitted signal on the HAPS downlink may reach the terrestrial base station terminal 30(2) which is receiving the terrestrial downlink signal from the terrestrial base station 20, causing interference from the HAPS downlink to the terrestrial base station terminal 30(2). Furthermore, as shown in FIG. 4B , when a terrestrial base station terminal 30(2) is transmitting a terrestrial uplink signal to a terrestrial base station 20, the terrestrial uplink transmission signal may reach a relay communication station 11 of the HAPS 100 in the sky that is receiving a HAPS uplink signal from the HAPS base station terminal 30(1), and interference from the terrestrial base station terminal 30(2) may occur in the HAPS uplink of the relay communication station 11 mounted on the HAPS 100.

[0041] Conventionally, an inter-cell interference control technology called eICIC, which complies with the above-mentioned LTE-Advanced standard, has been known as a technology for controlling interference between a plurality of base stations.

[0042] 5 is a diagram showing an example of the allocation 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 to a HAPS base station in 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-divided to assign different time slots to each of the HAPS base station 10 and the terrestrial base station 20. This makes the radio resources orthogonal on the time axis, thereby enabling mutual avoidance of interference at the same frequency between the HAPS base station 10 and the terrestrial base station 20. However, in the conventional inter-cell interference control technique (eICIC), the radio resources (time slots) are time-divided and used in each of the HAPS base station 10 and the terrestrial base station 20. Therefore, all frequencies (all time) allocated to the mobile communication system of the embodiment cannot be used, and the communication capacity (maximum transmission rate, peak throughput) of the service links of each of the HAPS base station 10 and the terrestrial base station 20 decreases. In particular, the communication capacity of terrestrial base station terminals connected to a terrestrial base station 20 with a large number of terminals in its cell decreases.

[0043] In this embodiment, in order to avoid interference between the HAPS base station 10 and the terrestrial base station 20 and to prevent a decrease in the communication capacity (maximum transmission rate, peak throughput) of the service links of the HAPS base station 10 and the terrestrial base station 20, the TDD (Time Division Duplex) method adopted in standards such as the fifth generation of mobile communications is used as the transmission and reception method for the service links of each base station 10, 20.

[0044] In the TDD (Time Division Duplex) system, the same frequency is used for the uplink and downlink, and time slots are time-division multiplexed for use on the uplink and downlink. For example, in a terrestrial base station 20, as shown in Figures 6A and 6B, 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 Figure 6C, radio resources (time slots) on the time axis are time-division multiplexed for use between downlink transmission (base station transmission) from the terrestrial base station 20 to the terrestrial base station terminal 30(2) and uplink transmission (terminal transmission) from the terrestrial base station terminal 30(2) to the terrestrial base station 20.

[0045] When the HAPS base station 10 and the terrestrial base station 20 of this embodiment use a TDD (Time Division Duplex) system, the HAPS base station 10 and the terrestrial base station 20 can completely share the same frequency by applying an interference reduction technique described below that avoids interference between the HAPS base station 10 and the terrestrial base station 20. Furthermore, the HAPS base station 10 and the terrestrial base station 20 can use all frequencies (all times) allocated to the mobile communication system, preventing a decrease in the communication capacity of the service link of each base station 10, 20. In particular, a decrease in the communication capacity of terrestrial base station terminals connected to a terrestrial base station 20 with a large number of terminals in its cell can be prevented.

[0046] In a system in which the same frequency is shared by multiple base stations using the conventional TDD method, in order to avoid interference between the uplink and downlink lines of each base station, synchronization control is performed between multiple base stations 20(1) and 20(2), for example, as shown in FIG. 7, so that the transmission timing of base station transmissions on the downlink lines from the base station to the terminal is synchronized, and the transmission timing of terminal transmissions on the uplink lines from the terminal to the base station is synchronized.

[0047] When a communication method of a terrestrial cellular system using a terrestrial base station 20 (hereinafter referred to as the "terrestrial cellular system") and a communication method of a HAPS cellular system using a HAPS base station 10 (hereinafter referred to as the "HAPS cellular system") are used simultaneously, as shown in Figure 8A, interference waves from the HAPS base station 10 that transmits signals over a wide area, particularly on the downlink of the service link, may degrade the communication quality of many terrestrial base station terminals 30(2) located in the terrestrial cell 20C, and as shown in Figure 8B, signals transmitted by a large number of terrestrial base station terminals 30(2) may degrade the communication quality of the HAPS base station terminal 30(1) located in the HAPS cell 10C. Therefore, in order to use the terrestrial cellular system and the HAPS cellular system simultaneously, it is necessary to reduce interference.

[0048] In the mobile communication system of this embodiment, the transmission timing and reception timing between the HAPS base station 10 and the terrestrial base station 20 are reversed.

[0049] 9 is a diagram showing an example of the arrangement of time slots for uplink and downlink links when synchronization control is performed to reverse the transmission timing and reception timing between a terrestrial base station 20 and a HAPS base station 10 using the TDD scheme in a mobile communication system according to the embodiment. In each of a plurality of consecutive transmission / reception frames (radio frames) shown in Fig. 9, the transmission timing and transmission period of the downlink link from the terrestrial base station 20 to the terrestrial base station terminal 30(2) match the transmission timing and transmission period of the uplink link from the HAPS base station terminal 30(1) to the HAPS base station 10. On the other hand, the transmission timing and transmission period of the uplink link from the terrestrial base station terminal 30(2) to the terrestrial base station 20 match the transmission timing and transmission period of the downlink link from the HAPS base station 10 to the HAPS base station terminal 30(1).

[0050] Here, the terrestrial base station 20 and the HAPS base station 10 may adjust their transmission timings to be opposite to each other using time information acquired by a GNSS (Global Navigation Satellite System) receiver.

[0051] As shown in Figure 9, by reversing the transmission timing and reception timing of the HAPS base station 10 and the terrestrial base station 20 for the uplink and downlink, the way in which interference is received changes significantly compared to when the transmission timing and reception timing of the HAPS base station 10 and the terrestrial base station 20 are the same for the uplink and downlink as shown in Figure 8.

[0052] 10A, the downlink of terrestrial base station 20 becomes the uplink of the service link of HAPS base station 10. Therefore, the radio waves of the downlink transmission sent from terrestrial base station antenna 21 reach HAPS base station antenna 112 as shown in the figure, and the downlink of terrestrial base station 20 causes interference with the uplink of the service link of HAPS base station 10.

[0053] In addition, the terrestrial base station terminal 30(2) and the HAPS base station terminal 30(1) are located at a relatively large distance, and since they are both located on the ground, there are many obstructions, such as buildings, between the terminals. Therefore, the interference signal power received when the uplink transmission signal of the HAPS base station terminal 30(1) reaches the terrestrial base station terminal 30(2) is generally negligibly small.

[0054] 10B, the uplink of the terrestrial base station 20 becomes the downlink of the service link of the HAPS base station 10. Therefore, the radio waves of the downlink transmission of the service link transmitted from the HAPS base station antenna 112 reach the terrestrial base station antenna 21 as shown in the figure, causing interference with the uplink of the terrestrial base station 20.

[0055] In addition, the HAPS base station terminal 30(1) and the terrestrial base station terminal 30(2) are located at a relatively large distance, and since they are both located on the ground, there are many obstructions, such as buildings, between the terminals. Therefore, the interference signal power received by the HAPS base station terminal 30(1) when the uplink transmission signal from the terrestrial base station terminal 30(2) reaches the HAPS base station terminal 30(1) is generally negligibly small.

[0056] 10A and 10B, when the terrestrial cellular system and the HAPS cellular system share the same frequency as shown in Fig. 10C, the problem can be summarized as interference between the terrestrial base station antenna 21 and the HAPS base station service link antenna 112. In other words, if the interference between the terrestrial base station antenna 21 and the HAPS base station service link antenna 112 is reduced, the terrestrial cellular system and the HAPS cellular system can share the same frequency.

[0057] In this embodiment, in order to reduce interference between the terrestrial base station antenna 21 and the service link antenna 112 of the HAPS base station, each of the terrestrial base station device 22 in the terrestrial base station 20 and the HAPS base station device 122 in the HAPS base station 10 is provided with an interference suppression unit (also referred to as an "interference canceller") that suppresses the interference. For example, as shown in FIG. 11A , the interference suppression unit (interference canceller) 220 mounted on the terrestrial base station device 22 suppresses (hereinafter also referred to as "cancellation") pre-interference from the relay communication station 11 of the HAPS base station. Also, as shown in FIG. 11B , the interference suppression unit (interference canceller) 125 mounted on the HAPS base station device 122 of the HAPS-GW 12 suppresses (cancels) pre-interference from the terrestrial base station 20.

[0058] Fig. 12 is a diagram showing an example of the configuration of a mobile communication system in which an interference suppression unit (interference canceller) 220 is provided in a terrestrial base station 20 according to the embodiment. In Fig. 12, components common to those in Figs. 1 to 3 described above are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0059] The interference suppression unit (interference canceller) 220 in this configuration example is provided in the base station device 22 of the terrestrial base station 20, and suppresses (cancels) the interference signal transmitted from the relay communication station 11 of the HAPS base station and reaching the terrestrial base station antenna 21.

[0060] In FIG. 12, a transmission signal s output from a base station device (HAPS base station device) 122 provided in a HAPS-GW 12 of a HAPS base station. Ｈ (t) is branched into two transmission signals by branching section 125 .

[0061] Of the two transmission signals branched by the branching unit 125, one transmission signal s Ｈ (t) is transmitted as a downlink signal of the service link from the HAPS base station to the HAPS base station terminal 30(1) via the FL antenna 121 and the relay communication station 11. A portion of the downlink signal transmitted from the HAPS base station antenna 112 of the relay communication station 11 reaches the terrestrial base station antenna 21 of the terrestrial base station 20 as an interference signal for the terrestrial terminal signal transmitted from the terrestrial base station terminal 30(2). In addition, the uplink signal of the service link transmitted from the terrestrial base station terminal 30(2) reaches the terrestrial base station antenna 21 of the terrestrial base station as a desired signal. The interference signal from the relay communication station 11 and the desired signal from the terrestrial base station terminal 30(2) are received by the terrestrial base station antenna 21 and input to the interference suppression unit 220 as a received signal of the uplink of the service link.

[0062] The other transmission signal s branched by the branching unit 125 Ｈ (t) is transferred as a replica of the transmission signal of the service link transmitted from the HAPS base station (hereinafter also referred to as the “transmission replica signal”) to an interference suppression unit (interference canceller) 220 provided in the base station device 22 of the terrestrial base station via a wired network (e.g., optical fiber) and the base station cooperation control device 50.

[0063] The branching unit 125 branches the transmission replica signal s s to be transferred to the inter-base station cooperation control device 50 so that the two transmission signals (interference signal, transmission replica signal) branched from the same transmission signal reach the interference suppression unit 220 at the same timing. Ｈ The delay time control is also performed to delay (t) by a predetermined delay time.

[0064] The interference suppression unit 220 of the terrestrial base station device 22 suppresses the desired signal (terrestrial terminal signal) received by the terrestrial base station antenna 21 and the interference signal h Ｈ s Ｈ (t) (transmitted signal from the HAPS base station) and the transmitted replica signal s Ｈ (t) and calculate the complex reception amplitude (hereinafter also referred to as the "path response") h of the interference signal (transmission signal from the HAPS base station). Ｈ Estimate.

[0065] Furthermore, the interference suppression unit 220 calculates the complex received amplitude h Ｈ and the replica signal s transmitted from the HAPS base station Ｈ (t) is superimposed to obtain the interference suppression signal (-h Ｈ s Ｈ The interference suppression unit 220 generates the received signal (desired signal + interference signal h Ｈ s Ｈ (t)) and interference suppression signal (-h Ｈ s Ｈ (t)) to obtain an interference signal h Ｈ s Ｈ (t) is suppressed (canceled) and only the desired signal (terrestrial terminal signal) is input to the receiver 230 of the terrestrial base station equipment 22.

[0066] Fig. 13 is a diagram showing an example of the configuration of the interference suppression unit (interference canceller) 220 of the terrestrial base station 20 of Fig. 12. In Fig. 13, components common to those in Figs. 1 to 3 and 12 are given the same reference numerals, and descriptions thereof will be omitted.

[0067] 13, the interference suppression unit (interference canceller) 220 includes an interference estimation processing unit 2201 , an interference suppression signal generation unit 2202 , a distribution unit 2203 , a delay unit 2204 , and a combination unit 2205 .

[0068] The interference estimation processing unit 2201 calculates the received signal (desired signal + interference signal) received by the terrestrial base station antenna 21 and the transmission replica signal s transferred via the inter-base station cooperation control device 50. Ｈ (t) and calculate the cross-correlation coefficient, and the interference signal h Ｈ s Ｈ Complex received amplitude (path response) h of (t) Ｈ Estimate.

[0069] The interference suppression signal generator 2202 generates the interference signal h estimated by the interference estimation processor 2201. Ｈ s Ｈ Complex received amplitude (path response) h of (t) Ｈ The replica signal s transmitted Ｈ (t) to obtain the interference suppression signal (-h Ｈ s Ｈ (t)).

[0070] The distributor 2203 distributes and supplies the received signal (desired signal+interference signal) received by the terrestrial base station antenna 21 to the interference estimation processor 2201 and the delay unit 2204, respectively.

[0071] The delay unit 2204 receives the received signal (desired signal + interference signal h) distributed by the distributor 2203. Ｈ s Ｈ (t)) and the interference suppression signal (-h Ｈ s Ｈ The received signal is delayed by a predetermined delay time so that the received signals (t) and (t) are input to the combiner 2205 at the same timing.

[0072] The combiner 2205 combines the interference suppression signal (-h Ｈ s Ｈ (t)) is converted into the received signal (desired signal + interference signal h Ｈ s Ｈ (t)) to obtain the interference signal h Ｈ s Ｈ (t) is suppressed (cancelled) and the desired signal is demodulated.

[0073] Fig. 14 is a diagram showing an example of the configuration of a mobile communication system in which an HAPS base station 10 according to the embodiment is provided with an interference suppression unit (interference canceller) 126. In Fig. 14, components common to those in Figs. 1 to 3 described above are given the same reference numerals, and descriptions thereof will be omitted.

[0074] The interference suppression unit (interference canceller) 126 in this configuration example is provided in the HAPS base station device 122 of the HAPS-GW 12, and suppresses (cancels) interference signals transmitted from the terrestrial base station antenna 21 and reaching the service link antenna 112 of the relay communication station 11 of the HAPS base station.

[0075] In FIG. 14, a transmission signal s output from the terrestrial base station device 22 Ｍ (t) is branched into two transmission signals by the branching unit 23 .

[0076] Of the two transmission signals branched by the branching unit 23, one transmission signal s Ｍ (t) is transmitted as a downlink signal of the service link from the terrestrial base station 20 to the terrestrial base station terminal 30(2) via the terrestrial base station antenna 21. A part of the downlink signal transmitted from the terrestrial base station antenna 21 reaches the HAPS base station antenna 112 of the relay communication station 11 of the HAPS base station as an interference signal to the HAPS terminal signal transmitted from the HAPS base station terminal 30(1). In addition, the uplink signal of the service link transmitted from the HAPS base station terminal 30(1) reaches the HAPS base station antenna 112 of the relay communication station 11 as a desired signal. The interference signal from the terrestrial base station 20 and the desired signal from the HAPS base station terminal 30(1) are received by the HAPS base station antenna 112 of the relay communication station 11 and input to the interference suppression unit 126 as a received signal of the uplink of the service link via the FL antenna 111 of the relay communication station 11 and the FL antenna 121 of the HAPS-GW 12.

[0077] The other transmission signal s branched by the branching unit 23 Ｍ(t) is transferred as a replica (transmission replica signal) of the transmission signal of the service link transmitted from the terrestrial base station device 22 to the interference suppression unit (interference canceller) 126 provided in the HAPS base station device 122 of the HAPS-GW 12 via a wired network (e.g., optical fiber) and the base station cooperation control device 50.

[0078] The branching unit 23 branches the transmission replica signal s s to be transferred to the inter-base station cooperation control device 50 so that the two transmission signals (interference signal, transmission replica signal) branched from the same transmission signal reach the interference suppression unit 126 at the same timing. Ｍ The delay time control is also performed to delay (t) by a predetermined delay time.

[0079] The interference suppression unit (interference canceller) 126 of the HAPS base station device 122 cancels the desired signal (terrestrial terminal signal) received by the HAPS base station antenna 112 and the interference signal h Ｍ s Ｍ (t) (transmitted signal from a terrestrial base station) and a transmitted replica signal s Ｍ (t) and calculate the complex reception amplitude (hereinafter also referred to as the "path response") h of the interference signal (transmission signal from the HAPS base station). Ｍ Estimate.

[0080] Furthermore, the interference suppression unit (interference canceller) 126 calculates the complex received amplitude h Ｍ and the replica signal s transmitted from the terrestrial base station Ｍ (t) is superimposed to obtain the interference suppression signal (-h Ｍ s Ｍ The interference suppression unit 126 generates the received signal (desired signal + interference signal h Ｍ s Ｍ (t)) and interference suppression signal (-h Ｍ s Ｍ (t)) to obtain an interference signal h Ｍ s Ｍ (t) is suppressed (canceled) and only the desired signal (terrestrial terminal signal) is input to the receiver 127 of the HAPS base station equipment 122.

[0081] Fig. 15 is a diagram showing an example configuration of the interference suppression unit (interference canceller) 126 of the HAPS base station 10 of Fig. 14. Note that in Fig. 15, components common to those in Figs. 1 to 3 and 14 described above are given the same reference numerals, and descriptions thereof will be omitted.

[0082] 15, the interference suppression unit (interference canceller) 126 includes an interference estimation processing unit 1261 , an interference suppression signal generation unit 1262 , a distribution unit 1263 , a delay unit 1264 , and a combination unit 1265 .

[0083] The interference estimation processing unit 1261 calculates the received signal (desired signal+interference signal) received by the FL antenna 111 of the relay communication station 11 and the FL antenna 121 of the HAPS-GW 12 and the transmission replica signal s transferred via the inter-base station cooperation control device 50. Ｍ (t) and calculate the cross-correlation coefficient, and the interference signal h Ｍ s Ｍ Complex received amplitude (path response) h of (t) Ｍ Estimate.

[0084] The interference suppression signal generator 1262 generates the interference signal h estimated by the interference estimation processor 1261. Ｍ s Ｍ Complex received amplitude (path response) h of (t) Ｍ The replica signal s transmitted Ｍ (t) to obtain the interference suppression signal (-h Ｍ s Ｍ (t)).

[0085] The distributor 1263 distributes and supplies the received signal (desired signal+interference signal) received by the FL antenna 121 of the HAPS-GW 12 to the interference estimation processor 1261 and the delay unit 1264, respectively.

[0086] The delay unit 1264 receives the received signal (desired signal + interference signal h) distributed by the distributor 1263. Ｍ s Ｍ (t)) and the interference suppression signal (-h Ｍ s Ｍ The received signal is delayed by a predetermined delay time so that the received signals (t) and (t) are input to the combiner 1265 at the same timing.

[0087] The combiner 1265 combines the interference suppression signal (-h Ｍ s Ｍ (t)) is converted into the received signal (desired signal + interference signal h Ｍ s Ｍ (t)) to obtain the interference signal h Ｍ s Ｍ (t) is suppressed (cancelled) and the desired signal is demodulated.

[0088] FIG. 16 is a diagram showing an example of the configuration of a mobile communications system in which a toll base station (hereinafter also referred to as a "toll base station component") 60 according to the embodiment is provided with interference suppression units (interference cancellers) 220 and 126. FIG. 16 shows an example of the configuration in which a terrestrial base station device 22, a HAPS base station device 122, and a centralized interference suppression unit (centralized interference canceller) 600 are installed in the same location or configured within the same device, and the toll base station component 60 is provided. In FIG. 16, solid arrows indicate downlink transmission signals transmitted from each base station device, dashed arrows indicate interference signals, one-dot chain arrows indicate uplink reception signals received by each base station device, and two-dot chain arrows indicate transmission replica signals. Note that in FIG. 16, components common to those in FIGS. 1 to 3 and 12 to 15 described above are designated by the same reference numerals, and their description will be omitted.

[0089] 16 , the toll base station configuration unit 60, the HAPS-GW 12 of the HAPS base station 10, and the terrestrial base station antenna 21 of the terrestrial base station 20 are connected by a DAS (distributed antenna system) configured using optical cables or the like. For example, the communication path between the toll base station configuration unit 60 and the HAPS-GW 12 of the HAPS base station 10 is configured by a DAS slave unit 61(1), optical fiber 62(1), and a DAS master unit 601(1) within the toll base station configuration unit 60. Furthermore, the communication path between the toll base station configuration unit 60 and the terrestrial base station antenna 21 of the terrestrial base station 20 is configured by a DAS slave unit 61(2), optical fiber 62(2), and a DAS master unit 601(2) within the toll base station configuration unit 60.

[0090] In the toll base station configuration unit 60, the downlink transmission signal output from the HAPS base station device 122 passes through a DUP (transmitter / receiver) (also called an "antenna duplexer") 602(1), a branching unit 603(1), and a DUP 604(1), and is transmitted via a DAS master unit 601(1), an optical fiber 62(1), and a DAS slave unit 61(1), before reaching the HAPS-GW 12. The downlink transmission signal branched by the branching unit 603(1) is input to the interference suppression unit 220 of the terrestrial base station in the toll base station configuration unit 60 as a transmission replica signal of the HAPS base station.

[0091] The uplink received signal (including an interference signal from the terrestrial base station) output from the HAPS-GW 12 is transmitted via the DAS slave unit 61(1), optical fiber 62(1), and DAS master unit 601(1), and is input to the interference suppression unit 126 of the HAPS base station via the DUP 604(1). The interference suppression unit 126 outputs the uplink received signal in which the interference signal from the terrestrial base station has been suppressed. The uplink received signal after suppression of the interference signal output from the interference suppression unit 126 reaches the receiver of the HAPS base station device 122 via the DUP 602(1).

[0092] In the toll base station configuration unit 60, the downlink transmission signal output from the terrestrial base station device 22 passes through DUP 602(2), branching unit 603(2) and DUP 604(2), and is transmitted via DAS master unit 601(2), optical fiber 62(2) and DAS slave unit 61(2), before reaching the terrestrial base station antenna 21 of the terrestrial base station 20. The downlink transmission signal branched by branching unit 603(2) is input to the interference suppression unit 126 of the HAPS base station in the toll base station configuration unit 60 as a terrestrial base station transmission replica signal.

[0093] The uplink received signal (including the interference signal from the HAPS base station) output from the terrestrial base station antenna 21 of the terrestrial base station 20 is transmitted via the DAS slave unit 61(2), optical fiber 62(2), and DAS master unit 601(2), and is input to the interference suppression unit 220 of the terrestrial base station via the DUP 604(2). The interference suppression unit 220 outputs the uplink received signal in which the interference signal from the HAPS base station has been suppressed. The uplink received signal after suppression of the interference signal output from the interference suppression unit 220 reaches the receiver of the terrestrial base station device 22 via the DUP 602(2).

[0094] 16 does not require a large-scale inter-network cooperation control system that spans multiple different base stations, and it is possible to simply configure the interference suppression units (interference cancellers) of the HAPS base stations and the terrestrial base stations. Furthermore, it does not require a large-scale inter-network cooperation control system for matching the transmission and reception timing of the terrestrial base stations 20 and the HAPS base stations 10, and synchronization between the base stations can be easily established within the toll base station configuration unit 60.

[0095] 17 and 18 are diagrams showing an example of control of transmission and reception timing between the terrestrial base station 20 and the HAPS base station 10 according to the embodiment. In the mobile communication system of the present embodiment, the transmission and reception timing of the terrestrial base station 20 and the HAPS base station 10 must be reversed, so the inter-system (inter-base station) cooperation control device 50 adjusts the transmission and reception timing of the terrestrial base station 20 and the HAPS base station 10 so that the transmission and 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 and reception timing is performed by the HAPS-GW 12. In the example of FIG. 18 , the adjustment of the transmission and reception timing is performed by the relay communication station 11 mounted on the HAPS 100.

[0096] As described above, according to this embodiment, which uses the TDD method as the transmission and reception method, it is possible to share the same frequency for each service link between the terminal and the service link antenna (HAPS base station antenna) of the HAPS base station (first base station) and the service link antenna (terrestrial base station antenna) of the terrestrial base station (second base station), and it is possible to overcome the problem that the inter-cell interference control technology (eICIC) shown in FIG. 5 enables sharing of the same frequency but results in a decrease in the communication capacity of the terminal.

[0097] Furthermore, according to this embodiment, the frequency utilization rate can be doubled by sharing the frequency between the HAPS service link and the terrestrial base station.

[0098] Furthermore, according to this embodiment, this can be achieved by using a normal TDD system (5G, etc.) and changing the transmission and reception timing of the terrestrial base station 20 and the HAPS base station 10 (without any special changes).

[0099] Furthermore, according to this embodiment, the terrestrial base station interference canceller (interference suppression unit 220 of terrestrial base station device 22) and the HAPS base station interference canceller (interference suppression unit 126 of HAPS base station device 122) provided in each of the terrestrial base station 20 and the HAPS base station 10 reduce interference in the uplink and downlink of the service link of each base station, making it possible to realize frequency sharing between the terrestrial base station and the HAPS base station.

[0100] Furthermore, according to this embodiment, both the terrestrial base station 20 and the HAPS base station 10 avoid interference, so array antenna control using a massive antenna or the like is not required.

[0101] Furthermore, according to this embodiment, it is possible to realize frequency sharing in the case where the terrestrial base station antenna 21 and the HAPS base station antenna 112 are not equipped with a massive antenna, for example, and null forming is not possible.

[0102] Furthermore, according to this embodiment, both the terrestrial base station 20 and the HAPS base station 10 can suppress interference by applying a terrestrial base station interference canceller (interference suppression unit 220 of the terrestrial base station device 22) and a HAPS base station interference canceller (interference suppression unit 126 of the HAPS base station device 122) that use a network cooperation control system (inter-base station cooperation control device 50). Moreover, the terrestrial base station interference canceller and the HAPS base station interference canceller have the same configuration.

[0103] In particular, according to this embodiment, one or more terrestrial base station devices 22, a HAPS base station device 122, and a centralized interference suppression unit (centralized interference canceller) 600 are installed in the same location, or in a centralized base station configuration unit 60 configured within the same device, there is no need for a large-scale inter-network cooperation control system (inter-base station cooperation control device) that spans different base stations, and the HAPS base station interference canceller and terrestrial base station interference canceller can be easily configured.

[0104] Furthermore, according to this embodiment, the terrestrial base station 20 and the HAPS base station 10 do not need special devices or controls to share frequencies.

[0105] Furthermore, according to this embodiment, the transmission timing adjustment between 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 .

[0106] The present invention can improve the frequency utilization efficiency at HAPS base stations and terrestrial base stations, prevent a decrease in terminal communication capacity, and provide a system that enables frequency sharing between HAPS base stations and terrestrial base stations without adding special equipment to the HAPS base stations or terrestrial base stations, thereby contributing to the achievement of Goal 9 of the Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote industry, innovation and foster innovation."

[0107] The present invention can also be applied to cases where frequencies are shared between various systems and terrestrial base stations, as exemplified in the following (A) to (D): (A) Frequency sharing between a HAPS base station and a terrestrial base station (B) Frequency sharing between a helicopter-mounted radio relay system or a UAV-mounted radio relay system and a terrestrial base station during a disaster (C) Frequency sharing between a drone-mounted radio relay system and a terrestrial base station (D) Frequency sharing between a geostationary, medium-earth or low-earth orbit satellite communication system and a terrestrial base station

[0108] The processing steps described in this specification and the components of the mobile communication system, the airborne relay base station, the HAPS cellular system, the terrestrial base station, the terrestrial cellular system, the relay communication station, the HAPS-GW, the terminal (user equipment, mobile station, mobile machine), and the 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.

[0109] For hardware implementation, the processing units and other means used to implement the above steps and components in an entity (e.g., various wireless communication devices, wireless relay devices, Node Bs, 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 processors (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, computers, or combinations thereof.

[0110] Furthermore, with regard to firmware and / or software implementations, the means used to realize the above components may be implemented as programs (e.g., code, such as procedures, functions, modules, instructions, etc.) that perform the functions described herein. In general, any computer / processor-readable medium tangibly embodying firmware and / or software code may be used to implement means, such as a processing unit, used to realize the above steps and components described herein. For example, the firmware and / or software code may be stored in memory and executed by a computer or processor, such as in a controller. The memory may be implemented within the computer or processor, or external to the processor. The firmware and / or software code may also be stored on a computer or processor readable medium, such as, for example, random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), flash memory, floppy 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 cause the computers or processors to perform certain aspects of the functionality described herein.

[0111] Moreover, the description of the embodiments disclosed herein is provided to enable any person 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. Thus, the present disclosure is not intended to be limited to the examples and designs described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0112] 10: HAPS base station (airborne relay base station) 10C: HAPS cell 11: Relay communication station 12: HAPS-GW 15: GPS receiver 20: Terrestrial base station 20C: Terrestrial cell 21: Terrestrial base station antenna (service link antenna) 22: Base station device 23: Branching unit 30: Terminal 30(1): HAPS base station terminal 30(2): Terrestrial base station terminal 40: Core network 50: Inter-base station cooperation control device 60: Centralized base station configuration unit 600: Centralized interference suppression unit (centralized interference canceller) 100: HAPS 111: FL antenna 112: HAPS base station antenna (service link antenna) 113: Repeater 114: Frequency conversion device 115: Base station device 116: Feeder link transceiver 121: FL antenna 122: Base station device 123: Frequency conversion device 124: Feeder link transceiver 125: Branching unit 126: Interference canceller (HAPS base station) 1261: Interference estimation processing unit 1262: Interference suppression signal generation unit 1263: Distribution unit 1264: Delay unit 1265: Synthesis unit 127: Receiver 220: Interference canceller (terrestrial base station) 2201: Interference estimation processing unit 2202: Interference suppression signal generation unit 2203: Distribution unit 2204: Delay unit 2205: Synthesis unit 230: Receiver

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. 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 the terminal by a TDD (Time Division Duplex) method using the same frequency. The transmission timing and reception timing of the wireless communication in 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 terrestrial base station: Branches a downlink transmission signal transmitted from the terrestrial base station and transfers it to the aerial relay type base station as a transmission replica signal. Performs correlation processing between a reception signal of an uplink of the terrestrial base station including an interference signal from the aerial relay type base station that causes interference to the uplink of the terrestrial base station and the transmission replica signal transferred from the aerial relay type base station, estimates the complex reception amplitude of the interference signal from the aerial relay type base station. Generates an interference suppression signal for suppressing the interference signal from the aerial relay type base station using the estimation result of the complex reception amplitude of the interference signal from the aerial relay type base station and the transmission replica signal. Suppresses the interference signal from the aerial relay type base station included in the reception signal of the uplink of the terrestrial base station by synthesizing the reception signal of the uplink of the terrestrial base station and the interference suppression signal. The aerial relay type base station: Branches a downlink transmission signal transmitted from the aerial relay type base station and transfers it to the terrestrial base station as a transmission replica signal. Performs correlation processing between a reception signal of an uplink of the aerial relay type base station including an interference signal from the terrestrial base station that causes interference to the uplink of the aerial relay type base station and the transmission replica signal transferred from the terrestrial base station, estimates the complex reception amplitude of the interference signal from the terrestrial base station. Generates an interference suppression signal for suppressing the interference signal from the terrestrial base station using the estimation result of the complex reception amplitude of the interference signal from the terrestrial base station and the transmission replica signal.A mobile communication system, characterized in that an interference signal from the terrestrial base station included in the received signal of the uplink of the aerial relay type base station is suppressed by combining the received signal of the uplink of the aerial relay type base station and the interference suppression signal.

2. In the mobile communication system according to claim 1, the relay communication station mounted on the aircraft or the floating body is constituted by a repeater relay device that relays without regenerating the transmission and reception signals. A mobile communication system characterized by this.

3. In the mobile communication system according to claim 1, the relay communication station mounted on the aircraft or the floating body is constituted by a base station device that regenerates the transmission and reception signals, remodulates the regenerated signals, and relays them. A mobile communication system characterized by this.

4. In the mobile communication system according to any one of claims 1 to 3, further comprising a base station interworking control device that controls between the airborne relay type base station and the ground base station, and the base station interworking control device uses 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 to adjust the transmission timing such that transmission and reception are reversed respectively. A mobile communication system characterized by this.

5. In the mobile communication system according to any one of claims 1 to 3, further comprising a base station interworking control device that controls between the airborne relay type base station and the ground base station, and the base station interworking control device transfers the transmission replica signal from the ground base station to the airborne relay type base station and transfers the transmission replica signal from the airborne relay type base station to the ground base station. A mobile communication system characterized by this.

6. In the mobile communication system according to any one of claims 1 to 3, comprising a centralized base station configuration unit in which the ground base station and the airborne relay type base station are installed at the same location or configured within the same device, and the centralized base station configuration unit estimates the complex reception amplitude of the interference signal from the airborne relay type base station in the ground base station, generates the interference suppression signal, and suppresses the interference signal from the airborne relay type base station, and estimates the complex reception amplitude of the interference signal from the ground base station in the airborne relay type base station, generates the interference suppression signal, and suppresses the interference signal from the ground base station. A mobile communication system characterized by this.

7. 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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