Communication system

Abstract

Provided is a communication system that is capable of fast control by using a known signal in a non-regenerative wireless relay device and furthermore is able to reduce interference in a service link by a known signal received from a base station and used for control on the wireless relay device. This communication system comprises a base station and a non-regenerative wireless relay device. The base station: sets, in an arbitrarily defined frequency range in a system bandwidth, a control frequency range to which a known signal available for use in control on the wireless relay device is allocated; multiplexes the known signal allocated to the control frequency range, and a signal for a terminal device allocated to a communication frequency range different from the control frequency range; and performs transmission of a feeder link to the wireless relay device. The wireless relay device cancels or suppresses the known signal for the control frequency range in the wireless relay device and performs transmission of a service link to the terminal device.

Description

communication systems

[0001] The present invention relates to relaying communications between a base station and a terminal device via a wireless relay device.

[0002] Conventionally, in a non-regenerative radio relay device that relays a radio signal transmitted from a base station in a mobile communication system, a gain control (AGC) is known that measures the received power of the signal transmitted from the base station and controls the gain of a power amplifier that amplifies the power of the transmission signal to be transmitted to a terminal device based on the measurement result of the received power.

[0003] Patent Document 1 discloses a device that detects a sync signal (synchronization signal) of an LTE (LONG TERM EVOLUTION) system received from a base station, measures the power size of the detected sync signal, calculates the gain of an amplifier of a repeater (wireless repeater device) based on the power size of the measured sync signal to maintain constant coverage of the repeater, and controls the amplifier of the repeater based on the calculated gain.

[0004] Special Publication No. 2015-500586

[0005] However, the known signals used in the amplifier gain control (AGC) (e.g., synchronization signals or reference signals used in fourth-generation and fifth-generation mobile communication systems) are transmitted from base stations at relatively long transmission intervals (e.g., 5 milliseconds or longer in the case of fifth-generation mobile communication systems), making them unsuitable for high-speed control of amplifier gain and unsuitable for advanced control (e.g., high-speed control of several milliseconds or less) using channel information of the feeder link between the base station and the relay station. Furthermore, a method for achieving the high-speed control described above could be considered by placing a unique known signal at an arbitrary timing, rather than the known signal used in the mobile communication system. However, such a signal is used only to control the repeater and becomes an interference signal for the mobile communication system. In particular, when the repeater is located in the sky and frequency sharing is performed between the sky and a terrestrial mobile communication system, this signal could cause interference to the terrestrial mobile communication system over a wide area.

[0006] A communication system according to one aspect of the present invention includes a base station and a non-regenerative wireless relay device that relays wireless signals between the base station and a terminal device. The base station sets a control frequency domain in an arbitrary frequency domain of a system band for allocating a known signal that can be used to control the wireless relay device, multiplexes the known signal allocated to the control frequency domain with a signal for the terminal device allocated to a communication frequency domain different from the control frequency domain, and transmits the multiplexed signal to the wireless relay device via a feeder link. The wireless relay device cancels or suppresses the known signal in the control frequency domain within the wireless relay device and transmits a service link to the terminal device.

[0007] In the communication system, the base station may have a base station device and a gateway device connected to the base station device, and the wireless relay device may relay wireless signals between the base station device and the terminal device via the gateway device.

[0008] In a communication system having the base station device and the gateway device, the base station device may set a control frequency domain in an arbitrary frequency domain of a system band for allocating a known signal usable for controlling the radio relay device, and may not allocate a signal intended for a terminal device of the mobile communication system to the control frequency domain in the system band, but may allocate the signal intended for the terminal device to a communication frequency domain different from the control frequency domain and transmit the signal. The gateway device may generate the known signal to be allocated to the control frequency domain, multiplex the known signal allocated to the control frequency domain with a signal intended for the terminal device allocated to a communication frequency domain different from the control frequency domain, and transmit the signal over a feeder link to the radio relay device. The radio relay device may cancel or suppress the known signal in the control frequency domain transmitted from the gateway device and transmit a service link to the terminal device.

[0009] In a communication system having the base station device and the gateway device, the base station device may set a control frequency domain in an arbitrary frequency domain of the system band for allocating a known signal usable for controlling the radio relay device, generate the known signal to be allocated to the control frequency domain, multiplex the known signal allocated to the control frequency domain with a signal for the terminal device allocated to a communication frequency domain different from the control frequency domain, and transmit the multiplexed signal to the gateway device. The gateway device may receive the known signal multiplexed by the base station device and the signal for the terminal device, and perform feeder link transmission to the radio relay device. The radio relay device may receive the known signal in the control frequency domain transmitted from the base station device via the gateway device, and cancel or suppress the known signal to perform service link transmission to the terminal device.

[0010] The control of the wireless relay device may be gain control for controlling a gain of a power amplifier that amplifies a service link signal received from the base station and transmitted to the terminal device, and the wireless relay device may control the gain of the power amplifier based on a reception result of the known signal (e.g., power estimated by correlation processing). Here, the wireless relay device may perform first gain control for controlling a gain of a power amplifier that amplifies a service link signal received from the base station and transmitted to the terminal device based on an observed power on a time axis in the system band, and after the first gain control, perform second gain control for controlling the gain of the power amplifier based on the reception result of the known signal.

[0011] The control frequency domain may be a frequency domain at the high-frequency end of the system band, a frequency domain at the high-frequency end of the system band, or a frequency domain at both ends of the high-frequency and low-frequency sides of the system band.

[0012] The base station may dynamically change the setting information regarding the known signal, and when changing the setting information regarding the known signal, notify the radio relay device of the change.

[0013] The base station device may dynamically change the setting information regarding the known signal, and when changing the setting information regarding the known signal, notify the gateway device and the radio relay device of the change.

[0014] The gateway device may dynamically change the setting information regarding the known signal, and when changing the setting information regarding the known signal, notify the base station device and the radio relay device of the change.

[0015] The wireless relay device may dynamically change the setting information regarding the known signal, and when changing the setting information regarding the known signal, notify the base station device and the gateway device of the change.

[0016] The communication system may further include a central control device capable of communicating with each of the base station devices, the gateway devices, and the wireless relay devices. The central control device may dynamically change the setting information regarding the known signal, and, when changing the setting information regarding the known signal, may notify the base station devices, the gateway devices, and the wireless relay devices of the change.

[0017] The central control device may receive feedback information regarding the reception result of the known signal from the wireless relay device, dynamically change the setting information regarding the known signal based on the feedback information, and, when the setting information regarding the known signal is changed, notify the base station device, the gateway device, and the wireless relay device of the change information.

[0018] The configuration information regarding the known signal may include at least one piece of information regarding the location of the control frequency domain to which the known signal is allocated, the transmission power of the known signal, the ratio of the transmission power of the known signal to the transmission power of the signal intended for the terminal device, and the signal sequence of the known signal.

[0019] The known signal may be a signal in which the signal sequence and transmission power of the signal are known, and the allocation position of the control frequency domain to which the signal is assigned. Furthermore, the known signal may not be a standard known signal such as a synchronization signal used in a mobile communication system, but may be a unique known signal that is uniquely set for use in controlling the radio relay device.

[0020] The wireless relay device may be mounted on a floating body or an air vehicle located at a predetermined altitude above the ground or sea. For example, the wireless relay device may be mounted on a drone, a balloon, an airship, a solar plane, a HAPS, an airplane, an artificial satellite, or the like located in the sky.

[0021] The programs executed in the base station, the base station device, the gateway device, and the wireless relay device may include a trained model used in machine learning, a trained model newly created by machine learning, or a trained model updated by machine learning.

[0022] According to the present invention, high-speed control using a known signal is possible in a non-regenerative wireless relay device, and interference with a service link caused by the known signal received from a base station and used to control the wireless relay device can be reduced.

[0023] FIG. 1 is an explanatory diagram showing an example of a communication system including a base station and a wireless relay device according to an embodiment. FIG. 2 is an explanatory diagram showing an example of the overall configuration of a communication system with a hierarchical cell structure including a base station according to an embodiment. FIG. 3 is an explanatory diagram showing an example of automatic gain control (AGC) of a wireless relay device in the communication system according to an embodiment. FIG. 4A is an explanatory diagram showing an example of transmission of a unique known signal from a base station to a wireless relay device and suppression of the unique known signal in the communication system according to an embodiment. FIG. 4B is an explanatory diagram showing an example of radio resources and signals in a feeder link of the communication system. FIG. 4C is an explanatory diagram showing an example of radio resources and signals in a service link of the communication system. FIG. 5A is an explanatory diagram showing another example of transmission of a unique known signal from a base station (base station device and gateway station) to a wireless relay device and cancellation of the unique known signal in the communication system according to an embodiment. FIG. 5B is an explanatory diagram showing an example of radio resources and signals in a communication line between a base station device and a gateway station in the communication system. FIG. 5C is an explanatory diagram showing an example of radio resources and signals in a feeder link of the communication system. FIG. 5D is an explanatory diagram showing an example of radio resources and signals in a service link of the communication system. Fig. 6A is an explanatory diagram showing yet another example of transmission of a unique known signal from a base station (base station device and GW station) to a wireless relay device and suppression of the unique known signal in a communication system according to an embodiment. Fig. 6B is an explanatory diagram showing an example of radio resources and signals in a communication line between a base station device and a GW station in the communication system. Fig. 6C is an explanatory diagram showing an example of radio resources and signals in a feeder link in the communication system. Fig. 6D is an explanatory diagram showing an example of radio resources and signals in a service link in the communication system. Fig. 7 is an explanatory diagram showing an example of change of setting information related to the unique known signal via a central control device (central control server) in a communication system according to an embodiment.

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Here, the embodiment of the present invention will be described on the assumption that it is applied to a 3GPP (registered trademark) LTE / LTE-Advanced mobile communication system and a next-generation NR (New Radio) mobile communication system (5th generation or later). However, the concept of the present invention can be applied to any system that uses a similar cell configuration and physical channel configuration.

[0025] 1 is an explanatory diagram showing an example of the overall configuration of a communication system (airborne wireless relay system) including a base station and a wireless relay device according to the present embodiment. The wireless relay device 10 in the communication system of the present embodiment is a non-regenerative relay station that performs automatic gain control (AGC) of a power amplifier. The communication system of the present embodiment includes a non-regenerative wireless relay device (hereinafter also referred to as a "relay station," "non-regenerative relay station," or "slave") 10 located in the sky and incorporated into a flying or floating object that moves and rotates, such as a high altitude platform station (HAPS) (also referred to as a "high altitude pseudo satellite"), drone, balloon, or artificial satellite, and a base station (hereinafter also referred to as a "HAPS base station") 35 located on land or sea. In the communication system of this embodiment, a control frequency domain for allocating a unique known signal usable for controlling the relay station 10 is set in an arbitrary frequency domain of the system band, and the unique known signal allocated to the control frequency domain is multiplexed with a signal for a terminal device (for a mobile communication system) allocated to a communication frequency domain different from the control frequency domain, and the multiplexed signal is transmitted over a feeder link FL to the relay station 10 in the sky. The relay station 10 cancels the unique known signal in the control frequency domain within the relay station 10 and transmits a service link SL to the terminal device. This enables high-speed control (e.g., high-speed control of the gain of a power amplifier on the order of several milliseconds or less) in the relay station (slave) using the unique known signal. Moreover, the unique known signal received from the base station and used to control the relay station (slave) is not re-emitted to the service link, thereby reducing interference to the service link caused by the unique known signal.

[0026] In the following embodiments, the non-regenerative wireless relay device (relay station) that relays wireless communications between the base station and the terminal device may be a device that is fixedly installed on the ground or at sea, or may be a device that is installed on a mobile object such as a vehicle or ship that can move on the ground or at sea.

[0027] In FIG. 1 , the communication system includes an airborne radio relay device (relay station) 10 installed on an airborne vehicle (e.g., HAPS, airship, solar plane, drone, balloon, airplane, artificial satellite, etc.) 15. The radio relay device 10 is a non-regenerative repeater type relay station (non-regenerative relay station) that wirelessly communicates with a terrestrial or marine HAPS base station 35 via a feeder link FL and with a terminal device (UE) 60 via a service link SL, relaying communication between the HAPS base station 35 and the terminal device (UE) 60. The radio relay device 10 includes a power amplifier (PA) as a power amplifier that amplifies a transmission signal of the service link SL. Note that the frequency (frequency band) of the feeder link FL and the frequency (frequency band) of the service link SL may be different from each other to prevent interference due to radio wave leakage. Furthermore, the communication system (radio relay system) may include the HAPS base station 35 in addition to the radio relay device 10, and may further include a UE 60.

[0028] The power amplifier of the wireless relay device (relay station) 10 has an automatic gain control (AGC) function that controls the gain so that the power of the transmission signal of the service link SL to the terminal device (UE) 60 is constant, based on the reception result (e.g., received power) of the unique known signal received from the HAPS base station 35.

[0029] The unique known signal in this embodiment is a signal for which, for example, the signal sequence and transmission power of the encoded signal, and the allocation position of the control frequency domain to which the signal is allocated are known.

[0030] The wireless relay device 10 has a function of detecting a synchronization signal contained in a downlink high-frequency radio (RF) signal received from a HAPS base station 35 via a feeder link FL, and can detect the frame timing of the downlink signal (hereinafter also referred to as the "downlink signal") to be relayed.

[0031] The wireless relay device 10 receives setting information related to a unique known signal used for control within the device itself (for example, gain control of a power amplifier) ​​from a HAPS base station 35 (for example, a base station device 36 or a gateway device 37 described below) or a central control server (central control device). The unique known signal is allocated to a control frequency domain set in an arbitrary frequency domain of the system band. The setting information related to the unique known signal includes at least one piece of information, for example, the location of the control frequency domain to which the unique known signal is allocated, the transmission power of the unique known signal, the ratio of the transmission power of the unique known signal to the signal for the terminal device (for the mobile communication system), and the signal sequence of the unique known signal.

[0032] In addition, the wireless relay device 10 receives base station information (e.g., base station parameters such as system bandwidth, physical cell ID, and subcarrier spacing, downlink quasi-static scheduling information including the radio resource allocation position on the time-frequency grid of the synchronization signal, or downlink and uplink quasi-static scheduling information, and a predetermined offset amount used to calculate the received power of the synchronization signal) from the HAPS base station 35 or a central control server (central control device).

[0033] The HAPS base station 35 includes, for example, a base station device 36 connected to a core network (e.g., a HAPS core network) of a mobile communication network, and a gateway device (hereinafter also referred to as a "GW station") 37 connected to the base station device 36. For example, in downlink wireless communication of the feeder link FL, the GW station 37 functions as a parent device, and the wireless relay device 10 functions as a child device.

[0034] 2 is an explanatory diagram showing an example of the overall configuration of a HAPS mobile communication system including a radio relay device 10 according to this embodiment. In FIG. 2, as a countermeasure for communication traffic during disaster response, special events, etc., wide-area large cells 10A(1), 10A(2) of multiple service links SL(1), SL(2) of a mobile communication network are deployed from an antenna 101 of a mobile flying object (or floating object) 15 located in the sky toward the ground or water (e.g., the ocean). These multiple large cells 10A(1), 10A(2) are formed by a single radio relay device and are also called "sector cells."

[0035] 2 shows an example in which the air vehicle 15 having the radio relay device 10 is an airship-type HAPS ("High Altitude Platform Station" or "High Altitude Pseudo Satellite") that can move in the sky, but the air vehicle 15 may also be other unmanned or manned air vehicles (or floating bodies) that can move or fly in the sky, such as a drone, a balloon, an airplane, a helicopter, a solar plane-type HAPS (see FIG. 1) or LAPS ("Low Altitude Platform Station" or "Low Altitude Pseudo Satellite"), an airship-type LAPS, an artificial satellite, etc. Furthermore, the air vehicle 15 may be controlled to move to a predetermined position in the sky where it will be located during radio relay operation, and then remain at that position or to fly in a circular flight within a predetermined range of flight space including that position.

[0036] The aircraft may be controlled autonomously, externally, or by a pilot on board the aircraft to fly and position in an airspace at an altitude of 100 km or less above the ground, sea level, or the surface of a body of water such as a river or lake. The flight airspace of the aircraft may also be stratospheric airspace at an altitude of 11 km or more and 50 km or less. Furthermore, the flight airspace of the aircraft 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.

[0037] The mobile communication system of this embodiment is a communication system that complies with next-generation standard specifications such as LTE (Long Term Evolution) / LTE-Advanced or fifth generation, and the radio relay device 10 has an antenna (hereinafter also referred to as an "SL antenna device") 101 for service links SL(1), SL(2) that form multiple large cells 10A(1), 10A(2), and an antenna (hereinafter also referred to as an "FL antenna device") 102 for a feeder link FL for wireless communication with a HAPS base station (e.g., eNodeB, gNodeB) 35 provided on the ground. The HAPS base station 35 is connected to a HAPS core network 30 of the mobile communication network via a communication line such as a line termination device and a dedicated line, and is capable of communicating with various nodes such as core network devices and servers via a predetermined communication interface.

[0038] The SL antenna device 101 and FL antenna device 102 of the radio relay device 10 each have multiple antenna elements (e.g., vertically polarized antennas and horizontally polarized antennas as linearly polarized antennas). The vertically polarized antenna transmits and receives radio waves in a vertically polarized plane that includes the vertical direction and the radio wave propagation direction. The horizontally polarized antenna transmits and receives radio waves in a horizontally polarized plane that is orthogonal to the vertically polarized plane and includes the radio wave propagation direction. For example, the SL antenna device 101 and the FL antenna device 102 may each be an array antenna in which antenna elements, each consisting of a pair of vertically polarized antennas and horizontally polarized antennas, are arranged one-dimensionally, two-dimensionally, or three-dimensionally.

[0039] The HAPS core network 30 may be a common core network that accommodates the HAPS base stations 35 of the large cells 10A(1) and 10A(2). The frequencies used in the cells 10A(1) and 10A(2) may be, for example, microwave frequencies of 300 MHz to 30 GHz, or millimeter wave frequencies higher than 30 GHz.

[0040] In this embodiment, the wireless relay device 10 mounted on the aircraft 15 can communicate with the HAPS core network 30 of the mobile communication network, various core network devices, external networks such as the Internet, various servers such as a central control server 50, etc., via a HAPS base station 35 connected to an antenna 102 and a gateway device (hereinafter also referred to as a "GW station") which is a relay device (parent device) of the ground-side feeder link.

[0041] The central control server 50 can centrally manage base station information such as scheduling information of the HAPS base stations 35 and generate control information for controlling the base stations.

[0042] The central control server 50 also has a function of managing setting information of known signals used for AGC of the power amplifiers of the wireless relay devices 10, and notifying the setting information of known signals to the base stations 35 (the base station devices 36 and the GW stations 37 in FIG. 1 ) and the wireless relay devices 10. The central control server 50 may be installed in a remote location such as a data center, or may be installed in the HAPS core network 30.

[0043] When UE 60(1), 60(2) are present in large cells 10A(1), 10A(2), respectively, they can communicate wirelessly with a HAPS base station 35 via a radio relay device 10 in the air corresponding to the present cell, using a predetermined communication method and radio communication resources. Each of UE 60(1), 60(2) is configured using hardware such as a computer device having a CPU, memory, etc., and a radio communication unit, and can communicate with the HAPS base station 35 via the radio relay device 10 by executing a predetermined program.

[0044] The base station device 36 of the HAPS base station 35 is configured using hardware such as a computer device having a CPU, memory, etc., an external communication interface unit for the HAPS core network 30, an external communication interface unit for the central control server 50, and a wireless communication unit, and by executing a predetermined program, it is possible to perform wireless communication with UEs 60(1) and 60(2) via a GW station 37 using a predetermined communication method and wireless communication resources, to send and receive information with core network devices of the HAPS core network 30, and to send and receive information with the central control server 50.

[0045] The GW station 37 of the HAPS base station 35 is configured using hardware such as a computer device having a CPU, memory, etc., an external communication interface unit for the base station device 36, an external communication interface unit for the central control server 50, and a wireless communication unit, and by executing a predetermined program, it is possible to perform wireless communication with UEs 60(1) and 60(2) using a predetermined communication method and wireless communication resources, to send and receive information to and from the base station device 36, and to send and receive information to and from the central control server 50.

[0046] The wireless relay device 10 is configured using hardware such as a computer device having a CPU, memory, etc., and wireless communication units for the service link and feeder link. By executing a predetermined program, the wireless relay device 10 can perform wireless communication with UEs 60(1) and 60(2) using a predetermined communication method and wireless communication resources, and can send and receive information to and from the central control server 50 via the HAPS base station 35.

[0047] By executing a predetermined program, the wireless relay device 10 can perform processing to detect the frame timing of a wireless frame based on a synchronization signal included in a wireless signal received from a HAPS base station 35 .

[0048] Furthermore, by executing a predetermined program, the radio relay device 10 can control the gain of the power amplifier so that the power of the transmission signal of the service link SL to the terminal device (UE) 60 is constant, based on the reception result (e.g., measurement result of the reception power) of a known signal of the mobile communication system (e.g., a synchronization signal: SS) included in the radio signal received from the HAPS base station 35.

[0049] The HAPS base station 35 is a base station capable of downlink wireless communication using Orthogonal Frequency Division Multiplexing (OFDM) with UEs via the radio relay device 10 in the sky. The HAPS base station 35 includes, for example, an antenna, a radio signal path switching unit, a duplexer (DUP), a downlink radio receiving unit and an Orthogonal Frequency Division Multiplexing (OFDM) modulator as a downlink modulator, a control unit, an uplink radio receiving unit and an uplink demodulator (e.g., a Single-Carrier Frequency-Division Multiple Access (SC-FDMA) demodulator or an OFDM demodulator). Furthermore, the HAPS base station 35 may include a downlink radio transmitting unit and an OFDM demodulator for special purposes such as air interface-based synchronization.

[0050] The SC-FDMA demodulator performs SC-FDMA demodulation processing on the received signal received by the uplink radio receiver and passes the demodulated data to the controller. The OFDM demodulator performs OFDM demodulation processing on the received signal received by the uplink radio receiver and passes the demodulated data to the controller. The OFDM modulator modulates the downlink signal data received from the controller to be transmitted to UEs located in the base station's cell using OFDM so that the data is transmitted at a predetermined power. Furthermore, when the base station receives information on slots for which transmission is to be stopped from, for example, a server, the OFDM modulator is controlled to stop downlink transmission only for specific slots in the radio frame. The downlink radio transmitter transmits the transmission signal modulated by the OFDM modulator to the radio relay device 10 in the sky via the duplexer, the radio signal path switching unit, and the antenna.

[0051] In this embodiment, the FL antenna device of the HAPS base station 35 (GW station 37), which wirelessly communicates with the radio relay device 10 above via the feeder link FL, has multiple antenna elements (for example, a vertically polarized antenna and a horizontally polarized antenna as linearly polarized antennas). The vertically polarized antenna transmits and receives radio waves in a vertically polarized plane that includes the vertical direction and the radio wave propagation direction (antenna pointing direction). The horizontally polarized antenna transmits and receives radio waves in a horizontally polarized plane that is orthogonal to the vertical polarization plane and includes the radio wave propagation direction (antenna pointing direction). The FL antenna device of the HAPS base station 35 (GW station 37) may be an array antenna in which antenna elements, each configured as a pair of a vertically polarized antenna and a horizontally polarized antenna, are arranged one-dimensionally, two-dimensionally, or three-dimensionally.

[0052] The SL antenna device of the HAPS base station 35, which communicates wirelessly with the user equipment (UE) 60(1), 60(2) via the service link SL, has a plurality of antenna elements (for example, a vertically polarized antenna and a horizontally polarized antenna as linearly polarized antennas). The SL antenna device of the HAPS base station 35 may be an array antenna in which antenna elements, each consisting of a pair of a vertically polarized antenna and a horizontally polarized antenna, are arranged one-dimensionally, two-dimensionally, or three-dimensionally.

[0053] In the communication system configured as above, as shown in Fig. 3, due to loss in the radio propagation path of the feeder link FL, even if a signal is transmitted from the GW station 37 of the HAPS base station 35 at maximum transmission power, the signal power received by the radio relay device 10 is small. Therefore, the power of the signal is amplified to a predetermined power by the power amplifier of the radio relay device 10 and transmitted to the terminal device (UE) 60. By controlling the gain of the power amplifier to be determined based on the measurement result of the received power of a known signal (e.g., a synchronization signal: SS) of the mobile communication system received from the HAPS base station 35, the power of the transmission signal of the service link SL can be kept constant even if the received power of the feeder link FL of the radio relay device 10 fluctuates.

[0054] In the wireless relay system of this embodiment, a transmission signal from a HAPS base station 35 is non-regeneratively relayed by a wireless relay device (relay station) 10 mounted on an air vehicle (or floating body) 15 such as a HAPS through a feeder link FL, and can be directly received by a terminal device (UE) 60, which is widely used in terrestrial mobile communication systems. Since the received power of the feeder link signal changes as the air vehicle 15 flies, the wireless relay device (relay station) 10 in the sky amplifies the signal power using an AGC to transmit at maximum power to the service link SL. However, in mobile communication systems such as 5G NR, from the perspective of reducing power consumption and suppressing inter-cell interference, when no data signal is present, unnecessary signals are not transmitted except for certain synchronization signals (SS) that are always transmitted at predetermined timing. Therefore, a no-signal state can occur for several milliseconds to several tens of milliseconds. During this no-signal period, although it is not completely no-input due to the presence of noise power and loop interference, an unnecessarily large gain is set in the AGC. One method of controlling the AGC unit to solve this problem is to observe the received power of a specific known signal such as a synchronization signal (SS) and determine the gain to be amplified. For example, in a 5G NR wireless relay system, the AGC unit performs correlation detection processing using a replica signal of the synchronization signal (SS), thereby calculating the signal power of only the synchronization signal (SS) and determining the gain regardless of the presence or absence of a data signal.

[0055] However, in conventional mobile communication systems, known signals (e.g., synchronization signals or reference signals) used in the above-mentioned automatic gain control (AGC) are transmitted from the HAPS base station 35 at relatively long transmission intervals (e.g., 5 milliseconds to several tens of milliseconds in the case of a fifth-generation mobile communication system), making it difficult to achieve high-speed control of the gain of the power amplifier of the wireless relay device (relay station) 10 (e.g., high-speed control of several milliseconds or less).

[0056] Therefore, in this embodiment, the base station 35 multiplexes a unique known signal allocated to the control frequency domain with a signal allocated to the communication frequency domain for a terminal device (for the mobile communication system) and transmits the multiplexed signal over the feeder link. This enables high-speed gain control (e.g., high-speed control on the order of several milliseconds) in the power amplifier of the wireless relay device (relay station slave) 10 using the unique known signal. Since the unique signal is used only to control the wireless relay device, it may act as an interference signal in the service link of the mobile communication system. However, in this embodiment, the wireless relay device (relay station slave) 10 cancels the unique known signal in the control frequency domain and transmits the service link. This prevents the unique known signal received from the HAPS base station 35 and used to control the wireless relay device (relay station slave) 10 from being re-emitted over the service link, thereby reducing interference with the service link caused by the unique known signal.

[0057] 4A, 4B, and 4C are explanatory diagrams showing an example of transmission of a unique known signal from a base station 35 to a wireless relay device 10 and suppression of the unique known signal in the communication system according to the embodiment. The illustrated examples are also applicable to cases where the base station 35 does not include a gateway station or where the wireless relay device (relay station) 10 is fixedly or movably placed on land or sea.

[0058] In FIG. 4A , the base station 35 multiplexes unique known signals Sk(0) and Sk(1) assigned to a control frequency domain Fk set in an arbitrary frequency domain of the system band Fs in the mobile communication system with a signal Sm for a terminal device (for the mobile communication system) assigned to a communication frequency domain Fm different from the control frequency domain Fk, and transmits the multiplexed signals over a feeder link from the HAPS base station 35 to a radio relay device (relay station) 10 in the sky (see FIG. 4B ).

[0059] The wireless relay device (relay station) 10 performs automatic gain control (AGC) to control the gain so that the power of the transmission signal of the service link SL to the terminal device (UE) 60 is constant, for example, based on the reception result (e.g., received power) of the unique known signals Sk(0) and Sk(1) received from the HAPS base station 35.

[0060] The wireless relay device (relay station) 10 cancels the unique known signals Sk(0), Sk(1) in the control frequency domain Fk, and transmits a service link to the terminal device (UE) 60, transmitting a downlink signal including the unique known signals Sk(0), Sk(1) canceled and a signal S'm intended for the terminal device (for the mobile communication system) (see Figure 4C).

[0061] 4A to 4C, the control frequency domain Fk is set to the low-frequency end of the system band Fs (for example, the frequency domain of the first subcarrier and the second subcarrier), but the control frequency domain Fk can be set to any frequency domain of the system band Fs (for example, any subcarrier). For example, the control frequency domain Fk may be set to the high-frequency end or the frequency domain in the center of the system band Fs, or may be set to frequency domains at multiple positions in the system band Fs (for example, the frequency domains at both ends of the system band Fs on the high-frequency side and the low-frequency side).

[0062] In addition, in the examples of Figures 4A to 4C, multiple unique known signals Sk(0), Sk(1) corresponding to multiple antenna ports are assigned to the control frequency domain Fk and transmitted so that MIMO communication can be performed, but a single unique known signal or three or more unique known signals may be assigned to the control frequency domain Fk and transmitted.

[0063] 4A to 4C, the base station 35 may dynamically change the setting information related to the unique known signal, and when the setting information related to the unique known signal has been changed, may notify the wireless relay device 10 of the change information via a control line (e.g., an Ethernet line, a satellite communication line, a Wi-Fi line, an optical line, a mobile communication line, etc.). Furthermore, the wireless relay device 10 may dynamically change the setting information related to the unique known signal, and when the setting information related to the unique known signal has been changed, may notify the base station 35 of the change information via a control line, etc.

[0064] 5A, 5B, 5C, and 5D are explanatory diagrams showing other examples of transmission of a unique known signal from a base station 35 (base station device 36 and GW station 37) to a wireless relay device (airborne relay station) 10 and cancellation of the unique known signal in the communication system according to the embodiment. The illustrated example is an example of a communication system in which a HAPS base station 35 has a base station device 36 and a GW station 37, and the base station device 36 communicates with the wireless relay device (airborne relay station) 10 via the GW station 37.

[0065] In Figure 5A, the base station device 36 sets a control frequency domain Fk in any frequency domain of the system band Fs to allocate a unique known signal that can be used to control the wireless relay device 10, and does not allocate a signal Sm intended for the terminal device to the control frequency domain Fk in the system band Fs, but allocates and transmits the signal Sm intended for the terminal device to a communication frequency domain Fm that is different from the control frequency domain Fk (see Figure 5B).

[0066] The gateway station 37 generates unique known signals Sk(0) and Sk(1) to be assigned to the control frequency domain Fk, multiplexes the unique known signals Sk(0) and Sk(1) assigned to the control frequency domain Fk with a signal Sm for a terminal device assigned to a communication frequency domain Fm different from the control frequency domain Fk, and transmits the signal via a feeder link to the wireless relay device 10 (see FIG. 5C).

[0067] The wireless relay device (relay station) 10 performs automatic gain control (AGC) to control the gain so that the power of the transmission signal of the service link SL to the terminal device (UE) 60 is constant, for example, based on the reception result (e.g., received power) of the unique known signals Sk(0) and Sk(1) received from the HAPS base station 35.

[0068] The wireless relay device (relay station) 10 cancels the unique known signals Sk(0), Sk(1) in the control frequency domain Fk, and transmits a service link to the terminal device (UE) 60, in which the unique known signals Sk(0), Sk(1) have been canceled and the downlink signal including the signal S'm intended for the mobile communication system (for the terminal device) is transmitted (see Figure 5D).

[0069] 6A, 6B, 6C, and 6D are explanatory diagrams showing still another example of transmission of a unique known signal from a base station 35 (base station device 36 and GW station 37) to a wireless relay device 10 and suppression of the unique known signal in the communication system according to the embodiment. The illustrated example is an example of a communication system in which a HAPS base station 35 has a base station device 36 and a GW station 37, and the base station device 36 communicates with a wireless relay device (aerial relay station) 10 via the GW station 37.

[0070] 6A, the base station device 36 sets a control frequency domain Fk in an arbitrary frequency domain of the system band Fs to allocate a unique known signal that can be used to control the radio relay device 10, generates unique known signals Sk(0) and Sk(1) to be allocated to the control frequency domain Fk, multiplexes the unique known signals Sk(0) and Sk(1) allocated to the control frequency domain Fk with a signal Sm for a mobile communication system allocated to a communication frequency domain Fm different from the control frequency domain Fk, and transmits the multiplexed signal to the GW device 37 (see FIG. 6B). The signal Sm for the mobile communication system is not allocated to the control frequency domain Fk.

[0071] The GW station 37 receives the unique known signals Sk(0) and Sk(1) multiplexed by the base station device 36 and the signal Sm intended for the terminal device, and transmits the signals to the wireless relay device 10 via the feeder link (see FIG. 6C).

[0072] The wireless relay device (relay station) 10 performs automatic gain control (AGC) to control the gain so that the power of the transmission signal of the service link SL to the terminal device (UE) 60 is constant, for example, based on the reception result (e.g., received power) of the unique known signals Sk(0) and Sk(1) received from the HAPS base station 35.

[0073] The wireless relay device (relay station) 10 cancels the unique known signals Sk(0) and Sk(1) in the control frequency domain Fk, and transmits a service link to the terminal device (UE) 60, transmitting a downlink signal including the signal S'm intended for the terminal device (for the mobile communication system) with the unique known signals Sk(0) and Sk(1) canceled (see Figure 6D).

[0074] 5A to 5D and 6A to 6D, the control frequency domain Fk is set to the low-frequency end of the system band Fs (for example, the frequency domain of the first subcarrier and the second subcarrier), but the control frequency domain Fk can be set to any frequency domain of the system band Fs (for example, any subcarrier). For example, the control frequency domain Fk may be set to the high-frequency end or the frequency domain in the center of the system band Fs, or may be set to frequency domains at multiple positions in the system band Fs (for example, the frequency domains at both ends of the high-frequency side and the low-frequency side of the system band Fs).

[0075] Furthermore, in the examples of Figures 5A to 5D and Figures 6A to 6D, multiple unique known signals Sk(0), Sk(1) corresponding to multiple antenna ports are assigned to the control frequency domain Fk and transmitted so that MIMO communication can be performed, but a single unique known signal or three or more unique known signals may be assigned to the control frequency domain Fk and transmitted.

[0076] 5A to 5D and 6A to 6D, the base station device 36 may dynamically change the setting information related to the unique known signal, and when the setting information related to the unique known signal has been changed, may notify the GW station 37 and the wireless relay device 10 of the change information via a control line or the like. Also, the GW station 37 may dynamically change the setting information related to the unique known signal, and when the setting information related to the unique known signal has been changed, may notify the base station device 35 and the wireless relay device 10 of the change information via a control line or the like. Also, the wireless relay device 10 may dynamically change the setting information related to the unique known signal, and when the setting information related to the unique known signal has been changed, may notify the base station device 36 and the GW station 37 of the change information via a control line or the like.

[0077] 7 is an explanatory diagram showing an example of changing setting information related to a unique known signal via a central control device (central control server) 50 in a communication system according to an embodiment. In FIG. 7 , the central control server 50 determines a radio resource allocation position for a signal Sm for a mobile communication system (a signal for a terminal device) and notifies the base station device 36 of the terrestrial base station of the radio resource allocation position information. Furthermore, the central control server 50 determines replica sequence information for the unique known signal Sk, the transmission power of the unique known signal Sk multiplexed by the gateway station (base station) 37, the power ratio between the unique known signal Sk and the signal Sm for the mobile communication system, and the allocation position information, and notifies the gateway station (base station) 37 and the relay station (slave station) 10 of this information. The notification method may be via Ethernet, or, for slave stations, may be multiplexed onto a separate control line using a satellite or the like.

[0078] A signal Sm for the mobile communication system (a signal for a terminal device) transmitted from a base station device 36 of a terrestrial base station is multiplexed with a unique known signal Sk generated by a known signal generating unit 371 of the gateway station (parent device) 37 and transmitted from the gateway station (parent device) 37 as a feeder link signal.

[0079] After the feeder link signal is received by the relay station (slave) 10, information such as the power, timing, and phase of the received signal of the unique known signal Sk is detected by a known signal synchronization unit 111, for example, by correlation processing. Based on the information of the obtained processing result, the known signal synchronization unit 111 calculates phase information and unique known signal power for canceling the unique known signal Sk in a cancellation processing unit 112, and notifies the cancellation processing unit 112 of the calculated phase information and unique known signal power.

[0080] The cancellation processing unit 112 cancels the unique known signal Sk based on the notified information. In addition, the received power information of the unique known signal Sk obtained by the known signal synchronization unit 111 is also notified to the subsequent gain control unit 113. The gain control unit 113 performs gain control taking into account the signal power after passing through the cancellation processing unit 112.

[0081] The known signal synchronization unit 111 can calculate an index such as SINR (Signal to Interference and Noise Ratio) as a detection result of the unique known signal Sk. The known signal synchronization unit 111 can notify the central control server 50 of this calculation result as feedback information.

[0082] Based on the obtained feedback information, the central control server 50 can, for example, change at least one of the radio resources and the known signal allocation position, change the signal sequence of the unique known signal Sk itself, or change the signal power of the unique known signal Sk and the power ratio between the unique known signal Sk and the signal Sm for the mobile communication system. For example, the central control server 50 makes the above changes when the SINR fed back from the known signal synchronizer 111 falls below a predetermined threshold. When the information is updated by the above changes, the central control server 50 re-notifies the updated information to the base station device 36 of the terrestrial base station, the GW station (parent device) 37, and the relay station (child device) 10 as needed.

[0083] In the above embodiment, the wireless relay device (relay station) 10 may execute a first gain control (first AGC) that controls the gain of the power amplifier based on the observed power on the time axis in the system band Fs, so that when an input power greater than a certain level is input to the power amplifier, the first AGC attenuates the power to a specified value, and after the first gain control, may execute a second gain control (second AGC) that controls the gain of the power amplifier based on the reception result (e.g., received power) of the unique known signal Sk.

[0084] In the above embodiment, the unique known signal Sk in the control frequency domain is cancelled, but the unique known signal Sk in the control frequency domain may be suppressed, thereby reducing re-radiation of the unique known signal Sk to the service link SL.

[0085] As described above, according to this embodiment, high-speed control (e.g., control on the order of several milliseconds or less) of the gain of the power amplifier and the like is possible using the unique known signal Sk in the non-regenerative wireless relay device (relay station) 10, and further, interference with the service link SL caused by the unique known signal Sk received from the base station 35 (base station device 36 and GW station 37) and used to control the wireless relay device 10 being re-emitted toward the service link SL can be reduced.

[0086] Furthermore, according to this embodiment, the unique known signal Sk can be continuously transmitted from the base station 35 to the wireless relay device (relay station) 10 in the control frequency domain Fk set in part of the system band Fs, so that the wireless relay device (relay station) 10 can demodulate the unique known signal Sk and acquire phase information at intervals of 1 millisecond or less. Therefore, particularly when the wireless relay device (relay station) 10 as an airborne PF performs advanced control using phase information (MIMO relay function), acquiring phase information at intervals of 1 millisecond or less can achieve higher quality communication.

[0087] Furthermore, the present invention can construct a stable high altitude platform station (HAPS) using a non-regenerative radio repeater device (non-regenerative repeater station) 10, thereby contributing to the achievement of Goal 9 of the Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation."

[0088] The processing steps and components of the communication system, mobile communication system, base station, base station device, radio relay device, and terminal device (user device, mobile station) described in this specification can be implemented by various means. For example, these steps and components may be implemented by hardware, firmware, software, or a combination thereof.

[0089] 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, Node Bs, terminals, 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.

[0090] Furthermore, with regard to firmware and / or software implementations, the means, such as a processing unit, used to realize the above components may be implemented with a program (e.g., code, such as procedures, functions, modules, instructions, etc.) that performs the functions described herein. In general, any computer / processor-readable medium tangibly embodying firmware and / or software code may be used to implement the 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 a memory and executed by a computer or processor, such as in a control device. 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.

[0091] The medium may be a non-transitory recording medium. The program code may be in any format as long as it can be read and executed by a computer, processor, or other device or machine. For example, the program code may be in any of source code, object code, and binary code, or may be a mixture of two or more of these codes.

[0092] 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.

[0093] 10: Radio relay device 15: Aircraft (or floating body) 30: Core network 35: Base station 36: Base station device 37: GW station (gateway device) 50: Central control server 60: Terminal device (UE) 101: SL antenna device 102: FL antenna device

Claims

1. A communication system comprising a base station and a non-regenerative wireless relay device that relays wireless signals between the base station and a terminal device, wherein the base station sets a control frequency domain in an arbitrary frequency domain of the system band to allocate known signals that can be used to control the wireless relay device, multiplexes the known signals allocated to the control frequency domain with signals for the terminal device allocated to a communication frequency domain different from the control frequency domain, and transmits the signals via a feeder link to the wireless relay device, and the wireless relay device cancels or suppresses the known signals in the control frequency domain within the wireless relay device and transmits a service link to the terminal device.

2. A communication system according to claim 1, wherein the base station comprises a base station device and a gateway device connected to the base station device; the wireless relay device relays wireless signals between the base station device and the terminal device via the gateway device; the base station device sets a control frequency domain in an arbitrary frequency domain of the system band to allocate known signals that can be used to control the wireless relay device; and allocates and transmits signals intended for the terminal device in a communication frequency domain different from the control frequency domain without allocating signals intended for the terminal device in the control frequency domain in the system band; the gateway device generates the known signals to be allocated to the control frequency domain, multiplexes the known signals allocated to the control frequency domain with signals intended for the terminal device allocated in a communication frequency domain different from the control frequency domain, and transmits the multiplexed signals over a feeder link to the wireless relay device; and the wireless relay device cancels or suppresses the known signals in the control frequency domain transmitted from the gateway device and transmits the service link to the terminal device.

3. A communication system according to claim 1, wherein the base station comprises a base station device and a gateway device connected to the base station device; the wireless relay device relays wireless signals between the base station device and the terminal device via the gateway device; the base station device sets a control frequency domain in an arbitrary frequency domain of the system band for allocating known signals usable for controlling the wireless relay device, generates the known signals to be allocated to the control frequency domain, multiplexes the known signals allocated to the control frequency domain with signals destined for the terminal device allocated to a communication frequency domain different from the control frequency domain, and transmits the multiplexed signals to the gateway device; the gateway device receives the known signals multiplexed by the base station device and signals destined for the terminal device, and transmits the signals via a feeder link to the wireless relay device; and the wireless relay device receives the known signals in the control frequency domain transmitted from the base station device via the gateway device, and cancels or suppresses the known signals and transmits the signals via a service link to the terminal device.

4. A communication system according to claim 1, 2 or 3, characterized in that the control of the radio relay device is a gain control that controls the gain of a power amplifier that amplifies a service link signal received from the base station and transmitted to the terminal device, and the radio relay device controls the gain of the power amplifier based on the reception result of the known signal.

5. A communication system according to claim 4, wherein the radio relay device executes a first gain control to control the gain of the power amplifier based on the observed power on the time axis in the system band, and after the first gain control, executes a second gain control to control the gain of the power amplifier based on the reception result of the known signal.

6. A communication system according to claim 1, 2 or 3, characterized in that the control frequency domain is a frequency domain at the high frequency end of the system band, a frequency domain at the high frequency end of the system band, or a frequency domain at both ends of the high and low frequency sides of the system band.

7. A communication system according to claim 1, 2 or 3, wherein the base station dynamically changes setting information relating to the known signal, and when changing the setting information relating to the known signal, notifies the radio relay device of the change information, and the setting information relating to the known signal includes at least one piece of information regarding the allocation position of the control frequency domain to which the known signal is assigned, the transmission power of the known signal, the ratio of the transmission power of the known signal to the signal intended for the terminal device, and the signal sequence of the known signal.

8. A communication system according to claim 2 or 3, wherein the base station device dynamically changes setting information relating to the known signal, and when changing the setting information relating to the known signal, notifies the gateway device and the wireless relay device of information of the change, and the setting information relating to the known signal includes at least one piece of information regarding the allocation position of the control frequency domain to which the known signal is assigned, the transmission power of the known signal, the ratio of the transmission power of the known signal to the signal intended for the terminal device, and the signal sequence of the known signal.

9. A communication system according to claim 2 or 3, wherein the gateway device dynamically changes setting information relating to the known signal, and when changing the setting information relating to the known signal, notifies the base station device and the radio relay device of the change, and wherein the setting information relating to the known signal includes at least one piece of information regarding the allocation position of the control frequency domain to which the known signal is assigned, the transmission power of the known signal, the ratio of the transmission power of the known signal to the signal intended for the terminal device, and the signal sequence of the known signal.

10. A communication system according to claim 2 or 3, wherein the wireless relay device dynamically changes the setting information relating to the known signal, and when changing the setting information relating to the known signal, notifies the base station device and the gateway device of the change information, and the setting information relating to the known signal includes at least one piece of information regarding the allocation position of the control frequency domain to which the known signal is assigned, the transmission power of the known signal, the ratio of the transmission power of the known signal to the signal intended for the terminal device, and the signal sequence of the known signal.

11. A communication system according to claim 2 or 3, further comprising a central control unit capable of communicating with each of the base station device, the gateway device and the wireless relay device, wherein the central control unit dynamically changes setting information relating to the known signal, and when changing the setting information relating to the known signal, notifies the base station device, the gateway device and the wireless relay device of the change, and wherein the setting information relating to the known signal includes at least one piece of information regarding the allocation position of the control frequency domain to which the known signal is assigned, the transmission power of the known signal, the ratio of the transmission power of the known signal to the signal intended for the terminal device, and the signal sequence of the known signal.

12. A communication system according to claim 11, wherein the central control device receives feedback information relating to the reception results of the known signal from the wireless relay device, dynamically changes the setting information relating to the known signal based on the feedback information, and, when the setting information relating to the known signal is changed, notifies the base station device, the gateway device, and the wireless relay device of the change.

13. A communication system according to claim 1, 2 or 3, characterized in that the radio relay device performs first gain control to control the gain of a power amplifier that amplifies a service link signal received from the base station and transmitted to the terminal device, based on the observed power on the time axis in the system band, and after the first gain control, performs second gain control to control the gain of the power amplifier based on the reception result of the known signal.

14. A communication system according to claim 1, 2 or 3, characterized in that the radio repeater is mounted on a floating body or an aircraft located at a predetermined altitude above the ground or sea.

Images