System for relaying communication, communication relay device, and gateway station

Abstract

Provided is a system capable of increasing the capacity of a feeder link in an LoS environment between a GW station and a relay station that is mounted to a communication relay device in the sky. This system comprises: a communication relay device in which a relay station of a non-reproduction relay system is mounted to a flying body or a floating body located in the sky; and a gateway station on the ground or on the sea, the gateway station performing feeder link communication with the communication relay device. The system relays communication between a user device and a base station device. The gateway station performs, via a feeder link array antenna, feeder link wireless communication to the relay station by means of a MIMO transmission method using a feeder link frequency in a first frequency band. The relay station performs, via the feeder link array antenna, feeder link wireless communication to the gateway station by means of the MIMO transmission method using the feeder link frequency in the first frequency band.

Description

Communication relay system, communication relay device, and gateway station

[0001] The present invention relates to a system that relays communications between user equipment and base station equipment via a relay station mounted on a communication relay device in the air and a gateway (GW) station installed on land or at sea.

[0002] Conventionally, a communication relay device in which a relay station is provided on an air vehicle or floating body located in the sky has been known (see, for example, Patent Document 1). The communication line in the communication relay device (relay station) in the sky is composed of a feeder link between the communication relay device and a gateway (GW) station on the mobile communication network side, and a service link between the communication relay device and a terminal device.

[0003] US Patent Application Publication No. 2016 / 0046387

[0004] In a system including a communication relay device in the sky and a gateway station on the ground, in order to accommodate communication traffic of a service link of mobile communication, it is necessary to increase the capacity of the feeder link in an LoS (Line of Sight) environment between the communication relay device in the sky and the gateway station on the ground. In particular, when the communication relay device in the sky includes a relay station of a non-regenerative relay system and relays communication of the service link of user equipment in multiple cells in a large area, there is a high need for increasing the capacity of the feeder link in the LoS environment.

[0005] A system according to one aspect of the present invention is a system for relaying communications between a user equipment and a base station apparatus, comprising: a communication relay device having a non-regenerative relay station mounted on an aircraft or floating body located in the sky; and a terrestrial or marine gateway station that performs feeder link communications with the communication relay device. The gateway station performs feeder link wireless communications with the relay station via a feeder link array antenna using a MIMO transmission method using feeder link frequencies in a first frequency band. The relay station performs feeder link wireless communications with the gateway station via a feeder link array antenna using the MIMO transmission method using feeder link frequencies in the first frequency band.

[0006] In the system, the communication relay device may include a feeder link array antenna having a plurality of antenna elements, and the gateway station may include a feeder link array antenna having a greater number of antenna elements than the feeder link array antenna of the communication relay device, and may include: a feeder link array antenna that can be used for wireless communication on the feeder link by switching between a plurality of sub-array antennas having different combinations of the antenna elements; and an array antenna switching unit that selects from the plurality of sub-array antennas in the feeder link array antenna and switches a selected array antenna to be used for wireless communication on the feeder link based on a control signal received from the relay station of the communication relay device.

[0007] In the system, the communication relay device may include a service link antenna, and a received signal separation unit that estimates a propagation path response between the selection array antenna of the gateway station and its own feeder link array antenna based on a predetermined known signal that differs for each cell and is received from the gateway station, and separates a plurality of feeder link signals multiplexed at a feeder link frequency of the first frequency band and received from the gateway station based on the estimated propagation path response; a frequency conversion unit that performs frequency conversion on a plurality of service link signals at a service link frequency of a second frequency band lower than the first frequency band and received from the plurality of cells via the service link antenna to generate a plurality of feeder link signals multiplexed at the feeder link frequency of the first frequency band, and performs frequency conversion on the plurality of feeder link signals separated by the received signal separation unit to generate service link signals at the plurality of service link frequencies; and a control signal addition unit that adds the control signal to the plurality of feeder link signals to be transmitted to the gateway station.

[0008] In the system, the gateway station may include a received signal separator that estimates a propagation path response between the feeder link array antenna of the communication relay device and the selected array antenna of the gateway station based on the control signal received from the relay station of the communication relay device, and separates, based on the estimated propagation path response, a plurality of feeder link signals multiplexed at a feeder link frequency of the first frequency band received from the relay station; and a frequency converter that performs frequency conversion on service link signals of the plurality of service link frequencies in the second frequency band for the plurality of cells received from a base station device to generate a plurality of feeder link signals multiplexed at a feeder link frequency of the first frequency band, and performs frequency conversion on the plurality of feeder link signals separated by the received signal separator to generate service link signals of the plurality of service link frequencies.

[0009] In the system, the control signal may be added to and transmitted in an adjacent band adjacent to a communication band of an uplink signal from the relay station to the gateway station.

[0010] In the system, the control signal may include at least one of position information and attitude information of the air vehicle or floating body on which the relay station is mounted.

[0011] In the system, the control signal may include a plurality of reference signals that differ for each antenna port corresponding to a plurality of antenna ports in the feeder link array antenna of the communication relay device.

[0012] Here, the plurality of antenna ports may include a vertically polarized antenna port and a horizontally polarized antenna port for each of the plurality of antenna elements in the feeder link array antenna of the communication relay device.

[0013] Furthermore, the array antenna switching unit of the gateway station may switch between the plurality of sub-array antennas in the feeder link array antenna based on reception power of the plurality of reference signals that differ for each antenna port and are included in the control signal.

[0014] In the system, the array antenna switching unit of the gateway station may estimate a channel response matrix between the subarray antenna and the feeder link array antenna of the communication relay device for each of the plurality of subarray antennas based on a reception result of a reference signal included in a control signal received from the relay station, evaluate singular values ​​of the channel response matrix, and switch the selected array antenna based on the evaluation result of the singular values ​​for the plurality of subarray antennas.

[0015] Here, circularly polarized radio waves may be used for the radio communication of the feeder link.

[0016] In the above system, the feeder link array antenna of the communication relay device may be a linear array antenna in which a plurality of antenna elements are arranged in a straight line at equal intervals. The feeder link array antenna of the gateway station may be a two-dimensional array antenna in which a plurality of antenna elements are arranged two-dimensionally. The plurality of sub-array antennas of the gateway station may each be a plurality of linear array antennas in which a plurality of antenna elements, the same number as the feeder link array antenna of the communication relay device, are cross-arranged in a straight line at equal intervals in different directions. Furthermore, the selection array antenna of the gateway station may be a linear array antenna in which a plurality of antenna elements, the same number as the feeder link array antenna of the communication relay device, are arranged in a straight line at equal intervals.

[0017] Here, the plurality of subarray antennas of the gateway station may have an odd number of antenna elements, 3 or 5 or more, and the plurality of subarray antennas may be a first linear array antenna and a second linear array antenna, in which a central antenna element of the plurality of antenna elements is shared with another antenna element, and the plurality of antenna elements are arranged in a straight line at equal intervals in a first direction and a second direction that are orthogonal to each other.

[0018] According to the present invention, it is possible to increase the capacity of the feeder link in an LoS environment between an overhead communication relay device and a GW station, and to accommodate communication traffic of the service link for a plurality of cells.

[0019] FIG. 1 is a diagram showing an example of the overall configuration of a system according to an embodiment. FIG. 2 is a diagram showing an example of frequency conversion between a feeder link frequency and a service link frequency in a system according to an embodiment. FIG. 3 is a diagram showing an example of stream and signal separation of MIMO transmission on a propagation path between an FL antenna of a HAPS and a GW antenna of a GW station in a system according to an embodiment. FIG. 4 is a diagram showing an example of the relationship between the rotation angle of a HAPS and channel capacity when E-SDM MIMO transmission is performed between a HAPS and a GW station when array antenna switching is not performed at the GW station in a system according to an embodiment. FIG. 5 is a diagram showing an example of the relationship between the rotation angle of a HAPS and channel capacity when ZF-standard receive separation MIMO transmission is performed between a HAPS and a GW station when array antenna switching is not performed at the GW station in a system according to an embodiment. FIG. 6 is a diagram showing an example of the relationship between the rotation angle of a HAPS and channel capacity when E-SDM MIMO transmission is performed between a HAPS and a GW station when array antenna switching is performed at the GW station in a system according to an embodiment. Fig. 7 is a diagram showing an example of the relationship between the rotation angle of the HAPS and channel capacity when MIMO transmission using a ZF-standard receive separation method is performed between the HAPS and the GW station when switching the array antenna at the GW station in the system according to the embodiment. Fig. 8 is a diagram showing an example of the relationship between the rotation angle of the HAPS and the gain of each transmission stream when MIMO transmission is performed using a linear array antenna with two antenna elements at each of the GW station and the HAPS in the system according to the embodiment. Fig. 9 is a diagram showing an example of the relationship between the rotation angle of the HAPS and the gain of each transmission stream when MIMO transmission is performed using a linear array antenna with three antenna elements at each of the GW station and the HAPS in the system according to the embodiment. Fig. 10 is a diagram showing an example of the relationship between the rotation angle of the HAPS and the gain of each transmission stream when MIMO transmission is performed using a linear array antenna with four antenna elements at each of the GW station and the HAPS in the system according to the embodiment. Fig. 11A is a diagram showing an example of the rotation of the HAPS relative to the GW station in the system according to the embodiment.FIG. 11B is a diagram showing an example of the configuration of an array antenna of a GW station and an array antenna of a HAPS in a system according to an embodiment. FIG. 12 is a block diagram showing an example of the configuration of a main part of a GW station in a system according to an embodiment. FIG. 13 is a block diagram showing an example of the configuration of a main part of a HAPS in a system according to an embodiment. FIG. 14 is a block diagram showing an example of a downlink radio frame from a GW station to a HAPS in a system according to an embodiment. FIG. 15 is a block diagram showing an example of transmission of a control signal via an uplink from a HAPS to a GW station in a system according to an embodiment. FIG. 16A is a diagram showing an example of multiple subarray antennas that can be switched by a GW station when linear polarization is used in a system according to an embodiment. FIG. 16B is a diagram showing an example of a selection array antenna selected from the multiple subarray antennas of FIG. 16A. FIG. 16C is a diagram showing another example of a selection array antenna selected from the multiple subarray antennas of FIG. 16A. FIG. 17A is a diagram showing an example of multiple subarray antennas that can be switched by a GW station when circular polarization is used in a system according to an embodiment. FIG. 17B is a diagram showing an example of a selection array antenna selected from the multiple subarray antennas of FIG. 17A. FIG. 17C is a diagram showing another example of a selection array antenna selected from the plurality of subarray antennas of FIG. 17A.

[0020] Hereinafter, embodiments of the present invention will be described 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.

[0021] A system according to an embodiment described herein relays communications between a user equipment (UE) and a base station via a non-regenerative relay station provided in a communication relay device such as a HAPS located in the sky and a terrestrial or maritime gateway station (GW station). The system according to the embodiment can increase the capacity of a feeder link in a line-of-sight (LoS) environment between the HAPS relay station and the GW station to accommodate communication traffic of service links for multiple cells. In particular, the system according to the embodiment is suitable for wireless communications called New Radio (NR) in fifth-generation or later-generation mobile communication systems.

[0022] FIG. 1 is a diagram illustrating an example of the overall configuration of a system according to an embodiment. In FIG. 1, the system according to this embodiment includes a communication relay device (hereinafter also referred to as a HAPS (high altitude pseudo satellite) or high altitude platform station)) 10, in which a relay station is mounted on an air vehicle or floating object located in the sky, and a gateway station 20 installed on the ground or at sea. The HAPS (relay station) 10 forms multiple cells 100(1) to 100(3) facing the ground or at sea via a service link antenna (e.g., an array antenna), and can perform wireless communication over service links SL(1) to SL(3) with user equipment (UE) 40(1) to 40(3) in each of the cells 100(1) to 100(3). The HAPS (relay station) 10 can also perform wireless communication over multiple feeder links FL(1) to FL(3) with the gateway station 20 via a feeder link array antenna (hereinafter also referred to as an "FL antenna").

[0023] The HAPS 10 may be equipped with at least one of a battery and a solar power generation system and fly using electric power. The HAPS 10 may be a solar plane-type HAPS as shown in the figure, or an airship-type HAPS. The HAPS airframe (main body) may be an artificial satellite, a balloon, or an unmanned aerial vehicle (UAV) such as a drone or an Unmanned Aircraft System (UAS). The HAPS 10 may fly using at least one of a battery and an engine as a power source.

[0024] For example, HAPS 10 may be controlled 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 (or sea level). The airspace in which HAPS 10 is located may be, for example, a stratospheric airspace with an altitude H of 15 km or more and 50 km or less. This airspace may be an airspace with an altitude of 18 km or more and 25 km or less where meteorological conditions are relatively stable, and may particularly be an airspace with an altitude of approximately 20 km. Furthermore, the above airspace may be an airspace with an altitude of 0.1 km or more for UAVs. Furthermore, it may be an airspace with an altitude of 0.05 km or more for drones.

[0025] The GW station 20 includes a feeder link array antenna (hereinafter also referred to as "GW antenna") 21 and a GW station device 22. The GW station 20 can perform wireless communication with the HAPS 10 over multiple feeder links FL(1) to FL(3). Multiple base station devices 30(1) to 30(3) are connected to the GW station device 22. The GW station 20 can relay communications between the multiple base station devices 30(1) to 30(3) and multiple UEs 40(1) to 40(3).

[0026] 1 shows an example in which the HAPS 10 forms three cells 100(1) to 100(3), the HAPS 10 may form a single cell, or two or four or more cells. A single base station device, or two or four or more base station devices, may be connected to the GW station 20. The multiple base station devices connected to the GW station 20 may be multiple base station devices of the same telecommunications carrier, or multiple base station devices of different telecommunications carriers.

[0027] 2 is a diagram showing an example of frequency conversion between the frequency of the feeder link FL and the frequency of the service link SL in a system according to an embodiment. In the system according to the present embodiment, in order to accommodate traffic of the service links SL(1) to SL(3), it is necessary to increase the capacity of the feeder links FL(1) to FL(3) in an LoS environment using the millimeter wave band (first frequency band) in light of trends in standardization of mobile communications. Therefore, LoS-MIMO transmission is applied to the wireless transmission of the feeder links.

[0028] In the system of this embodiment, FDD (Frequency Division Duplex) is used as the uplink and downlink communication mode (communication multiplexing method) between the base station devices 30(1) to 30(3) and the UEs 40(1) to 40(3). A feeder link frequency in the millimeter wave band (30 GHz to 300 GHz frequency band or 28 GHz to 300 GHz frequency band) is used as the first frequency band for wireless communication over the feeder links FL(1) to FL(3). A sub6 frequency band (standard), which is a second frequency band lower than the first frequency band, is used for wireless communication over the service links SL(1) to SL(3). Here, the sub6 frequency band is a frequency band of 6 GHz or less in the microwave band (3 GHz to 30 GHz), e.g., a frequency band of 3.6 GHz to 6.0 GHz. The first frequency band of the feeder link and the second frequency band of the service link may be other frequency bands as long as the condition that the frequency of the first frequency band is greater than the frequency of the second frequency band is satisfied.

[0029] The relay station installed in the HAPS 10 in the system of this embodiment is a non-regenerative relay station that performs MIMO signal separation, amplification, and frequency conversion. The frequency conversion is, for example, as shown in Figure 2, a frequency conversion between three frequencies of the sub6 service links SL(1) to SL(3) and one frequency of the millimeter-wave feeder links FL(1) to FL(3).

[0030] 3 is a diagram showing an example of stream and signal separation in MIMO transmission on a propagation path between the FL antenna 11 of the HAPS 10 and the GW antenna 21 of the GW station 20 in a system according to an embodiment. In FIG. 3 , the wireless transmission method on the propagation path 50 between the FL antenna 11 of the HAPS 10 and the GW antenna 21 of the GW station 20 is a MIMO (Multiple Input Multiple Output) transmission method in which signals are spatially multiplexed using multiple antenna elements on both the transmitting and receiving sides. In MIMO transmission, spatially multiplexed streams (communication paths) 500(1) to 500(3) are constructed on the propagation path 50, the number of which is the same as the number of cells 100(1) to 100(3). The transmission rate can be increased by transmitting signals via these multiple streams 500(1) to 500(3).

[0031] In the system of this embodiment, for example, in the case of a downlink, the GW station 20 inputs the transmission signals of the base station devices 30(1) to 30(3) directly to the GW antenna 21 without pre-coding them, and the HAPS 10 on the receiving side, which receives the signals via the FL antenna 11, estimates the propagation path response (channel estimation) in the feeder link propagation path 50 and separates the signals from the base station devices 30(1) to 30(3) using a weight matrix generated (determined) by a known method such as the ZF (Zero-Forcing) method or the MMSE (Minimum Mean Square Error) method. In the case of the uplink, the HAPS 10 inputs the transmission signals of the UEs 40(1) to 40(3) directly to the FL antenna 11 without pre-coding, and the receiving GW station 20, which receives the signals via the GW antenna 21, estimates the propagation path response in the feeder link propagation path 50 (channel estimation) and separates the signals from the UEs 40(1) to 40(3) using a weight matrix generated (determined) by a known method such as the ZF method or the MMSE method.

[0032] In addition, if signal separation using a weight matrix generated (determined) by the above-mentioned ZF method or the like is not performed on the receiving side, eigenbeam space division multiplexing (ESDM) (hereinafter also referred to as "E-SDM") may be performed, in which transmission weights are multiplied at the transmitting side array antenna and reception weights are multiplied at the receiving side array antenna to form optimal spatially orthogonal streams for each transmitting beam, thereby enabling signals to be transmitted to the receiving side without the streams interfering with each other.

[0033] The FL antenna 11 of the HAPS 10 is a linear array antenna (hereinafter also referred to as "ULA (Uniform Linear Array)") in which three antenna elements 111(1) to 111(3) are arranged in a straight line at equal intervals.

[0034] The GW antenna 21 of the GW station 20 has a plurality of antenna elements 211, which is greater than the FL antenna 11 of the HAPS 10, and is a two-dimensional array antenna in which the plurality of antenna elements 211 are arranged two-dimensionally. The GW antenna 21 can be used for feeder link wireless communication by switching between a plurality of sub-array antennas 210, each having a different combination of the plurality of antenna elements 211.

[0035] Each of the subarray antennas 210 is a plurality of linear array antennas (ULA) in which a plurality of antenna elements 211, the same number as the FL antennas 11 of the HAPS 10, are arranged in a line at equal intervals in different directions. For example, the subarray antennas 210 are a first linear array antenna (ULA) and a second linear array antenna (ULA) each having an odd number of antenna elements 211, three or five or more, in which the central antenna element of the plurality of antenna elements 211 is shared with another antenna element, and the plurality of antenna elements 211 are arranged in a line at equal intervals in a first direction and a second direction that are orthogonal to each other. Furthermore, a selected array antenna selected from the plurality of linear array antennas is a linear array antenna (ULA) in which a plurality of antenna elements 211, the same number as the FL antennas 11 of the HAPS 10, are arranged in a line at equal intervals.

[0036] The GW antenna 21 of the GW station 20 illustrated in FIG. 3 is a cross array antenna (hereinafter also referred to as "UXA (Uniform Cross Array)") in which five antenna elements 211(1) to 211(5) are arranged in a cross pattern at equal intervals. The GW antenna 21 can be used for feeder link wireless communication by switching between multiple subarray antennas 210(1), 210(2) (two sets in the illustrated example) each having a different combination of multiple antenna elements 211(1) to 211(5). The first subarray antenna 210(1) is a linear array antenna in which three antenna elements 211(1), 211(2), and 211(3) are arranged in a straight line at equal intervals, and the second subarray antenna 210(2) is a linear array antenna in which three antenna elements 211(4), 211(2), and 211(5) are arranged in a straight line at equal intervals. The first subarray antenna 210(1) and the second subarray antenna 210(2) share a central antenna element 211(2), and the arrangement directions of the antenna elements 211 are orthogonal to each other.

[0037] In the system of this embodiment, in order to align the number of cells and the number of streams (number of antennas), the GW station 20 does not use all of the multiple antenna elements 211(1) to 211(5) that make up the GW antenna (UXA) 21 simultaneously in the feeder link, but selects the subarray antenna (ULA) 210(1) or the subarray antenna (ULA) 210(2) that has the same number of antenna elements as the antenna elements 111(1) to 111(3) of the FL antenna (ULA) 11 of the HAPS 10 to use for the feeder link.

[0038] Furthermore, in the system of this embodiment, the rotation of the HAPS 10 in the sky changes the positional relationship between the FL antenna (ULA) 11 of the HAPS 10 and the GW antenna (UXA) 21 of the GW station 20. For example, in Fig. 3, the HAPS 10 in the sky rotates in the R direction around the Z axis that passes through the center of the FL antenna 11 of the HAPS 10 and the center of the GW antenna 21 of the GW station 20, changing the angle of the FL antenna 11 of the HAPS 10 with respect to the GW antenna 21 of the GW station 20. When the HAPS 10 in the sky rotates in this way, there is a risk that the capacity (channel capacity) [bps / Hz] of the feeder link propagation path 50 will decrease, as will be described below. In this embodiment, in order to suppress a decrease in capacity due to the positional relationship between the FL antenna (ULA) 11 of the HAPS 10 and the GW antenna (UXA) 21 of the GW station 20 (for example, rotation of the HAPS 10), the subarray antennas (ULA) 210(1) and 210(2) of the GW antenna (UXA) 21 are switched depending on the positional relationship between the HAPS 10 and the GW station 20 (for example, the rotation angle of the HAPS 10 with respect to the GW station 20).

[0039] Furthermore, when MIMO transmission is performed between HAPS 10 and GW station 20 using E-SDM on the transmitting side instead of signal separation on the receiving side, the singular values ​​(e.g., eigenvalues) of the channel response matrix (propagation path response) in the feeder link propagation path 50 vary depending on the relative positions of HAPS 10 and GW station 20. Therefore, smoothing may be performed on the transmitting side by distributing power to each antenna element depending on the relative positions of HAPS 10 and GW station 20.

[0040] Fig. 4 is a diagram showing an example of the relationship between the rotation angle of the HAPS 10 and channel capacity when E-SDM MIMO transmission is performed between the HAPS 10 and the GW station 20 in a case where subarray antennas (ULAs) are not switched at the GW station 20 in the system according to the embodiment. Fig. 5 is a diagram showing an example of the relationship between the rotation angle of the HAPS 10 and channel capacity when ZF-standard receive separation MIMO transmission is performed between the HAPS 10 and the GW station 20 in a case where subarray antennas (ULAs) are not switched at the GW station 20 in the system according to the embodiment. 4 and 5 show the results of a computer simulation for a ULA-ULA configuration using linear array antennas (ULA) having the same number of antenna elements at each of the HAPS 10 and the GW station 20, and ULA2, ULA3, ULA4, and ULA5 in the figures indicate that the number of antenna elements in the linear array antenna (ULA) is 2, 3, 4, and 5, respectively (the same applies to FIGS. 6 and 7).

[0041] As shown in Figures 4 and 5, when the feeder link antenna configuration is a ULA-ULA configuration, a large decrease (degeneration) in channel capacity occurs when the HAPS 10 array antenna (ULA) 11 is rotated 90° with respect to the array antenna (ULA) 21 of the GW station 10.

[0042] Fig. 6 is a diagram showing an example of the relationship between the rotation angle of the HAPS 10 and channel capacity when E-SDM MIMO transmission is performed between the HAPS 10 and the GW station 20 when switching between the subarray antennas (ULA) 210(1) and 210(2) at the GW station 20 in the system according to the embodiment. Fig. 7 is a diagram showing an example of the relationship between the rotation angle of the HAPS 10 and channel capacity when ZF-standard receive separation MIMO transmission is performed between the HAPS 10 and the GW station 20 when switching between the subarray antennas (ULA) at the GW station 20 in the system according to the embodiment. Note that in Figs. 6 and 7 , switching from the subarray antenna (ULA) 210(1) to the subarray antenna (ULA) 210(2) is performed at the GW station 20 when the HAPS 10 has rotated 45°.

[0043] By configuring the GW antenna 21 of the GW station 20 in a UXA configuration and switching the subarray antennas (ULA) 210(1) and 210(2) that make up the UXA when the HAPS 10 is rotated by a predetermined angle (ideally 45°), it is possible to avoid a significant decrease (degeneration) in the channel capacity of the feeder link as shown in Figures 6 and 7. Note that if the number of antenna elements in the FL antenna 11 of the HAPS 10 and the GW antenna 21 of the GW station 20 is increased, the drop (dip) in the channel capacity at a rotation angle of 45° of the HAPS 10 becomes deeper.

[0044] 8, 9, and 10 are diagrams showing examples of the relationship between the rotation angle of the HAPS 10 and the gain of each transmission stream when MIMO transmission is performed using a linear array antenna (ULA) with two antenna elements, three antenna elements, and four antenna elements at the GW station 20 and the HAPS 10, respectively, in the system according to the embodiment.

[0045] As shown in Figures 8, 9, and 10, when MIMO transmission using the ZF standard reception separation method is performed, the variation in gain (of each transmission stream) relative to the rotation angle of HAPS 10 is small, at about ±1 dB, compared to when MIMO transmission using the E-SDM method is performed. Therefore, when MIMO transmission using the ZF standard reception separation method is performed, it is not necessary to perform power control (power allocation). If power control is performed in MIMO transmission using the ZF standard reception separation method, the amount of power control is determined from the weight matrix applied to the received signal by HAPS 10.

[0046] FIG. 11A is a diagram showing an example of the rotation of the HAPS 10 relative to the GW station 20 in the system according to the embodiment. FIG. 11B is a diagram showing an example of the configuration of the GW antenna 21 of the GW station 20 and the FL antenna 11 of the HAPS 10 in the system according to the embodiment. In the example shown, the HAPS 10 is rotating in the R direction above the GW station 20. The FL antenna 11 of the HAPS 10 uses a linear array antenna (ULA) in which three antenna elements 111(1) to 111(3) are arranged in a straight line at equal intervals. In addition, the GW antenna 21 of the GW station 20 uses a cross array antenna (UXA) in which five antenna elements 211(1) to 211(5) are arranged in a cross pattern at equal intervals. The number of antenna elements in each of the array antennas 21 and 11 is set so that transmission with three streams corresponding to three cells can be realized in MIMO transmission over the feeder link, and is based on a configuration in which the UXA is made up of five antenna elements in the GW station 20 and the ULA is made up of three antenna elements in the HAPS 10. Note that the antenna configurations and conditions in Figures 11A and 11B are examples, and the number of antenna elements in each of the array antennas 11 and 21 may be increased.

[0047] Fig. 12 is a block diagram showing an example of the configuration of the main parts of the GW station 20 in the system according to the embodiment. In Fig. 12, the GW station 20 includes a GW antenna 21 consisting of a cross array antenna (UXA) in which the five antenna elements 211(1) to 211(5) described above are cross-arranged at equal intervals, and a GW station device 22 which is the main device of the GW station 20. In Fig. 12, the up arrows and right arrows in the antenna elements 211(1) to 211(5) indicate vertically polarized waves and horizontally polarized waves, respectively, and the configuration example in Fig. 12 allows vertically polarized and horizontally polarized signals to be transmitted and received simultaneously in the feeder link.

[0048] The gateway station device 22 includes an array switch unit (array antenna switching unit) 221, a received signal separator 222, and a frequency converter 223. The gateway station device 22 can process vertically polarized and horizontally polarized transmitted and received signals.

[0049] The array switch unit 221 selects from the plurality of sub-array antennas 210(1) and 210(2) in the GW antenna 21 based on a control signal received from the relay station of the HAPS 10, and switches the selected array antenna to be used for wireless communication of the feeder link FL.

[0050] The received signal separator 222 estimates a propagation path response between the FL antenna 11 of HAPS 10 and the selected array antenna 210(1) or 210(2) of its own station (GW station 20) based on a control signal received from the relay station of HAPS 10, and separates the multiple feeder link signals multiplexed onto the feeder link frequency of the first frequency band (millimeter waves) received from the relay station of HAPS 10 based on the estimated propagation path response.

[0051] The frequency conversion unit 223 performs frequency conversion on service link signals of multiple service link frequencies in the second frequency band (sub6) for the multiple cells 100(1) to 100(3) received from the multiple base station devices 30(1) to 30(3), and generates multiple feeder link signals multiplexed at feeder link frequencies in the first frequency band (millimeter waves).In addition, the frequency conversion unit 223 performs frequency conversion on the multiple feeder link signals separated by the received signal separation unit 222, and generates service link signals of multiple service link frequencies in the second frequency band (sub6).

[0052] Fig. 13 is a block diagram showing an example of the configuration of the main parts of a HAPS 10 in a system according to an embodiment. In Fig. 13, the HAPS 10 includes an FL antenna 11, which is a linear array antenna (ULA) in which the aforementioned three antenna elements 111(1) to 111(3) are arranged in a straight line at equal intervals, a service link antenna 12, and a non-regenerative repeater relay station 13. In Fig. 13, the up arrows and right arrows on the antenna elements 111(1) to 111(3) indicate vertically polarized and horizontally polarized waves, respectively, and the configuration example in Fig. 13 allows vertically polarized and horizontally polarized signals to be transmitted and received simultaneously in the feeder link.

[0053] The relay station 13 includes a received signal separator 131, a frequency converter 132, and a control signal adder 133. The relay station 13 can process vertically polarized and horizontally polarized transmitted and received signals.

[0054] The received signal separator 131 estimates a propagation path response between the selected array antenna of the GW station 20 and the FL antenna 11 of its own station (relay station 13) based on a predetermined known signal that differs for each cell and is received from the GW station 20, and separates the multiple feeder link signals multiplexed onto the feeder link frequency of the first frequency band (millimeter waves) received from the GW station 20 based on the estimation result of the propagation path response.

[0055] The frequency conversion unit 132 performs frequency conversion on service link signals of multiple service link frequencies in a second frequency band (sub6) lower than the first frequency band (millimeter wave) received from the multiple cells 100(1) to 100(3) via the service link antenna 12, and generates multiple feeder link signals multiplexed at feeder link frequencies in the first frequency band (millimeter wave).Furthermore, the frequency conversion unit 132 performs frequency conversion on the multiple feeder link signals separated by the received signal separation unit 131, and generates service link signals of multiple service link frequencies in the second frequency band (sub6).

[0056] The control signal adding unit 133 adds a control signal Sc to a plurality of feeder link signals to be transmitted to the GW station 20 .

[0057] The above-mentioned feeder link signal separation is performed, for example, as follows: The propagation path (channel) between the GW station 20 and the HAPS 10 is an LoS environment, under the condition that the transmission signal can be treated as a narrowband signal.

[0058] For signal separation of the feeder link (downlink) from the GW station 20 to the HAPS 10, the propagation path response (channel response) can be estimated using a known signal with a fixed pattern of the downlink signal. For example, as shown in Fig. 14, the propagation path response (channel response) is estimated using a synchronization signal (PSS, SSS) 601 specific to the cell ID (base station).

[0059] In separating the feeder link (uplink) signals from HAPS 10 to the GW station 20, it is difficult for the GW station 20 to detect and estimate the channels of the PUSCH (Physical Uplink Shared Channel), DMRS (Demodulation Reference Signal), and SRS (Sounding Reference Signal) from UEs 40(1) to 40(3). Therefore, as shown in FIG. 15 , a control signal Sc is added to an adjacent band adjacent to the communication band of the uplink signal from HAPS 10, and this control signal is used to switch the array antenna of the GW station 20.

[0060] The control signal is a signal whose number is the product of the number of antenna elements and the number of V (vertical) and H (horizontal) ports (antenna ports) of each antenna element. The control signal may be transmitted using either time division or frequency division. In the case of time division, the control signal is transmitted at a period sufficiently short to accommodate the fluctuations of the HAPS 10, while in the case of frequency division, the control signal is transmitted in a band that can be considered a narrowband signal. The control signal may also include a different reference signal for each antenna port of the FL antenna 11, and this reference signal may be used as a MIMO channel sounder. For example, a control signal including a different reference signal for each antenna port may be transmitted for six antenna ports, which is the product of the number of three antenna elements and the number of V (vertical) and H (horizontal) ports (antenna ports), to perform channel sounding of the MIMO transmission path, and the GW antenna 21 in the GW station 20 may be switched based on the results.

[0061] The control signal may also include system information such as downlink power information, position information of HAPS 10 (for example, GNSS information such as GPS information), attitude information of HAPS 10, and alive monitoring of HAPS 10, and the GW antenna 21 in the GW station 20 may be switched based on any of this system information.

[0062] Fig. 16A is a diagram showing an example of multiple subarray antennas 210(1) and 210(2) that can be switched by the GW station 20 when linear polarization is used for the feeder link in the system according to the embodiment. In Fig. 16A, the received power of the V port (vertical polarization port) and H port (horizontal polarization port) of each of the five antenna elements 211(1) to 211(5) of the GW antenna 21 is compared, and based on the comparison result, switching is performed between the vertical array antenna 210(1) in Fig. 16B and the horizontal array antenna 210(2) in Fig. 16C.

[0063] For example, if the received power at the V port of the GW antenna 21 is greater than that at the H port of the HAPS 10, the vertical array antenna 210(1) in Fig. 16B is selected. On the other hand, if the received power at the H port is greater than that at the V port of the GW antenna 21 that received the signal at the V port of the HAPS 10, the horizontal array antenna 210(2) in Fig. 16C is selected.

[0064] When the GW antenna 21 receives a control signal from the HAPS 10, it is preferable to ensure the SNR of the control signal by using the combined gain of the five antenna elements 211(1) to 211(5) of the GW antenna 21, but switching between the vertical array antenna 210(1) and the horizontal array antenna 210(2) in the GW antenna 21 may be performed based on the result of comparing the received power at the V port and the H port of any one of the five antenna elements 211(1) to 211(5).

[0065] In the case of linear polarization in Figures 16A to 16C, the GW station 20 compares the received power of the control signal of the polarization that matches the direction in which the array of the FL antenna 11 of the HAPS 10 is arranged, thereby switching between the vertical array antenna 210(1) and the horizontal array antenna 210(2) in the GW antenna 21.

[0066] 17A is a diagram showing an example of multiple subarray antennas 210(1) and 210(2) that can be switched by the gateway station 20 when circular polarization is used for the feeder link in the system according to the embodiment. As shown in FIG. 17A, when left-handed circular polarization (LHP), right-handed circular polarization (RHP), or both are used for the feeder link, no polarization loss occurs, and therefore comparison of received power cannot be used. Therefore, when circular polarization is used for the feeder link, for example, as shown in the following A to C, the channel capacity is calculated by singular value decomposition of the propagation path response matrix, and switching between the vertical array antenna (V-array) 210(1) of FIG. 7B and the horizontal array antenna (H-array) 210(2) of FIG. 7C is performed based on the calculation results.

[0067] A. Using the propagation path response (channel response) of either right-hand circular polarization (RHP) or left-hand circular polarization (LHP), a propagation path response matrix (channel response matrix) H is calculated for the vertical array antenna 210(1) and the horizontal array antenna 210(2). The propagation path response (channel response) and the propagation path response matrix (channel response matrix) H can be estimated based on the reception results of a known reference signal included in a control signal received from the HAPS 10, for example.

[0068] B. By singular value decomposition, the propagation path response matrix (channel response matrix) H of the following equation (1) is obtained using the singular value matrix Σ. Note that when the number of antenna elements on the transmitting side and the receiving side are the same, the propagation path response matrix (channel response matrix) becomes a square matrix, and singular value decomposition is called eigenvalue decomposition, with the singular values ​​being called eigenvalues. Eigenvalue decomposition is limited to square matrices when the number of antenna elements on the transmitting side and the receiving side are the same, but by obtaining the propagation path response matrix (channel response matrix) H using the singular value matrix Σ as in this example, it is also possible to handle cases where the number of antenna elements on the transmitting side and the receiving side do not match.

[0069] C. Select which array antenna to use, the vertical array antenna 210(1) or the horizontal array antenna 210(2), by comparing the product of the singular values ​​of the singular value matrix Σ.

[0070] Here, the first to third singular values ​​of the singular value matrix Σ for the vertical array antenna (V-array) 210(1) are respectively λ ｖ，１ , λ ｖ，２ , λ ｖ，３ Then, the evaluation value of the product of the singular values ​​of the singular value matrix Σ of the vertical array antenna (V-array) 210(1) is expressed by the following equation (2): In the following equation (2), "1" is added to each singular value to accommodate low SNR.

[0071] Also, the first to third singular values ​​of the singular value matrix Σ for the horizontal array antenna (H-array) 210(2) are respectively denoted as λ ｈ，１ , λ ｈ，２ , λ ｈ，３ Then, the evaluation value of the product of the singular values ​​of the singular value matrix Σ of the horizontal array antenna (H-array) 210(2) is expressed by the following equation (3): Note that in the following equation (3), "1" is added to each singular value to accommodate low SNR.

[0072] Of the two evaluation values ​​of the vertical array antenna 210(1) and the horizontal array antenna 210(2), the array antenna with the larger value is selected.

[0073] The method of switching between the vertical array antenna 210(1) and the horizontal array antenna 210(2) based on the calculation result of the channel capacity calculated by the singular value decomposition of the propagation path response matrix can also be applied when linearly polarized waves are used for the feeder link.

[0074] As described above, according to this embodiment, it is possible to increase the capacity of the feeder link in an LoS environment between the HAPS 10 in the sky and the GW station 20, and to accommodate the communication traffic of the service link for the multiple cells 100(1) to 100(3).

[0075] In this embodiment, the method of selecting a subarray antenna based on the control signal or the like in the GW antenna 21 of the GW station 20 used for LoS-MIMO transmission is applicable regardless of the shape of the GW antenna 21 and the subarray antenna set in the GW antenna 21. That is, in this embodiment, the overall shape of the arrangement of antenna elements in the subarray antenna set in the GW antenna 21 is not limited to a specific shape, and may be, for example, a circle, a square, or a random shape.

[0076] Furthermore, the present invention can increase the capacity of the feeder link in an LoS environment between a relay station mounted on a HAPS in the sky and a GW station, 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 promote industrial and technological innovation."

[0077] It should be noted that the process steps and system components described herein may be implemented by various means, for example, these steps and components may be implemented in hardware, firmware, software, or a combination thereof.

[0078] Regarding hardware implementation, means such as processing units used to realize the above steps and components in an entity (e.g., various wireless communication devices, relay stations, GW stations, base station devices, Node B, UE, 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 processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, computers, or combinations thereof.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 10: GW station 11: Feeder link array antenna (FL antenna) 12: Service link antenna 13: Relay station 20: GW station 21: Feeder link array antenna (GW antenna) 22: GW station device 30: Base station device 50: Propagation path 100: Cell 111: Antenna element 131: Received signal separator 132: Frequency converter 133: Control signal adder 210: Sub-array antenna 211: Antenna element 221: Array switch 222: Received signal separator 223: Frequency converter 500: Stream

Claims

1. A system for relaying communications between user equipment and base station equipment, comprising a communications relay device having a non-regenerative relaying relay station mounted on an aircraft or floating object located in the sky, and a ground or sea gateway station which communicates with the communications relay device via a feeder link, wherein the gateway station performs feeder link wireless communications with the relay station via a feeder link array antenna using a MIMO transmission method using a feeder link frequency in a first frequency band, and the relay station performs feeder link wireless communications with the gateway station via a feeder link array antenna using the MIMO transmission method using a feeder link frequency in the first frequency band.

2. A system according to claim 1, characterized in that the communication relay device comprises a feeder link array antenna having a plurality of antenna elements, and the gateway station comprises a feeder link array antenna having a greater number of antenna elements than the feeder link array antenna of the communication relay device, the feeder link array antenna being usable for wireless communication of the feeder link by switching between a plurality of sub-array antennas having different combinations of the antenna elements, and an array antenna switching unit which switches a selected array antenna to be used for wireless communication of the feeder link by selecting from the plurality of sub-array antennas in the feeder link array antenna based on a control signal received from the relay station of the communication relay device.

3. A system according to claim 2, wherein the communication relay device comprises a service link antenna, a received signal separation unit which estimates a propagation path response between the selected array antenna of the gateway station and its own feeder link array antenna based on a predetermined known signal different for each cell received from the gateway station, and separates a plurality of feeder link signals multiplexed at the feeder link frequency of the first frequency band received from the gateway station based on the estimated propagation path response, a frequency conversion unit which performs frequency conversion on a plurality of service link signals of a second frequency band lower than the first frequency band received from the plurality of cells via the service link antenna to generate a plurality of feeder link signals multiplexed at the feeder link frequency of the first frequency band, and which performs frequency conversion on the plurality of feeder link signals separated by the received signal separation unit to generate service link signals of the plurality of service link frequencies, and a control signal addition unit which adds the control signal to the plurality of feeder link signals to be transmitted to the gateway station, wherein the gateway station a received signal separation unit that estimates a propagation path response between the feeder link array antenna of the communication relay device and the selected array antenna of the communication relay device based on the control signal received from the relay station of the communication relay device, and separates a plurality of feeder link signals multiplexed at a feeder link frequency of the first frequency band received from the relay station based on the estimated propagation path response; and a frequency conversion unit that performs frequency conversion on service link signals of the plurality of service link frequencies in the second frequency band for the plurality of cells received from a base station device to generate a plurality of feeder link signals multiplexed at the feeder link frequency of the first frequency band, and performs frequency conversion on the plurality of feeder link signals separated by the received signal separation unit to generate service link signals of the plurality of service link frequencies.

4. A system according to claim 2, characterized in that said control signal is added to and transmitted in an adjacent band adjacent to the communication band of the uplink signal from said relay station to said gateway station.

5. A system according to claim 2, characterized in that the control signal includes at least one of position information and attitude information of the aircraft or floating body on which the relay station is mounted.

6. A system according to claim 2, characterized in that the control signal includes a plurality of reference signals which are different for each antenna port corresponding to a plurality of antenna ports in the feeder link array antenna of the communication relay device.

7. A system according to claim 6, wherein the plurality of antenna ports include a vertically polarized antenna port and a horizontally polarized antenna port for each of the plurality of antenna elements in the feeder link array antenna of the communication relay device.

8. A system according to claim 6, characterized in that the array antenna switching unit of the gateway station switches between the multiple sub-array antennas in the feeder link array antenna based on the reception power of the multiple reference signals, which differ for each antenna port and are included in the control signal.

9. A system according to claim 2, wherein the array antenna switching unit of the gateway station estimates a propagation path response matrix between the subarray antenna and the feeder link array antenna of the communication relay device for each of the plurality of subarray antennas based on a reception result of a reference signal included in a control signal received from the relay station, evaluates singular values ​​of the propagation path response matrix, and switches the selected array antenna based on the evaluation result of the singular values ​​for the plurality of subarray antennas.

10. A system according to claim 9, wherein circularly polarized radio waves are used for wireless communication in said feeder link.

11. A system according to any one of claims 2 to 10, wherein the feeder link array antenna of the communication relay device is a linear array antenna having a plurality of antenna elements arranged in a straight line at equal intervals, the feeder link array antenna of the gateway station is a two-dimensional array antenna having a plurality of antenna elements arranged two-dimensionally, the plurality of sub-array antennas of the gateway station are each a plurality of linear array antennas having a plurality of antenna elements, the same number as the feeder link array antenna of the communication relay device, cross-arranged in a straight line at equal intervals in different directions, and the selection array antenna of the gateway station is a linear array antenna having a plurality of antenna elements, the same number as the feeder link array antenna of the communication relay device, arranged in a straight line at equal intervals.

12. A system according to claim 11, characterized in that the plurality of subarray antennas of the gateway station are a first linear array antenna and a second linear array antenna each having an odd number of antenna elements, 3 or 5 or more, a central antenna element of the plurality of antenna elements being shared with each other, and the plurality of antenna elements being arranged in a straight line at equal intervals in a first direction and a second direction perpendicular to each other.

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