System for relaying communication

Abstract

To provide a system that can increase the capacity of a feeder link in a LoS environment between a relay station mounted on a communication relay device in the sky and a GW station.SOLUTION: A system comprises: a communication relay device in which a relay station using a non-regenerative relay method is mounted on a flying body or floating body located in the sky; and a gateway station which is located on the ground or sea to communicate with the communication relay device via a feeder link. The system relays communication between a user device and a base station device. The gateway station performs wireless communication of the feeder link in the MIMO transmission method using feeder link frequencies in a first frequency band with the relay station via an array antenna for feeder link. The relay station performs wireless communication of the feeder link in the MIMO transmission method using feeder link frequencies in the first frequency band with the gateway station via the array antenna for feeder link.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, a communication relay device in which a relay station is provided on an aircraft or floating body located in the sky is known (for example, see Patent Document 1). A 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2016 / 0046387 Summary of the Invention [Problem to be solved by the invention]

[0004] In a system having a communication relay device in the sky and a GW station on the ground, in order to accommodate communication traffic of a service link of mobile communication, it is an issue to increase the capacity of the feeder link in a Line of Sight (LoS) environment between the communication relay device in the sky and the GW station on the ground. In particular, when the communication relay device in the sky has a relay station of a non-regenerative relay method and relays communication of a service link of a user device in a plurality of cells in a large area, there is a high need to increase the capacity of the feeder link in the above-mentioned LoS environment. [Means for solving the problem]

[0005] A system according to one aspect of the present invention is a system that includes a communication relay device in which a non-regenerative relay type relay station is mounted on an aircraft or floating object located in the sky, and a ground or sea gateway station that performs feeder link communication with the communication relay device, and relays communication between a user device and a base station device. The gateway station performs feeder link wireless communication with the relay station via a feeder link array antenna in a MIMO transmission method using a feeder link frequency in a first frequency band. The relay station performs feeder link wireless communication with the gateway station via a feeder link array antenna in the MIMO transmission method using the feeder link frequency 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 an array antenna switching unit that switches between a plurality of sub-array antennas having different combinations of the antenna elements and that can be used for wireless communication of the feeder link, and an array antenna switching unit that 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.

[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 selected array antenna of the gateway station and a feeder link array antenna of its own station based on a predetermined known signal that differs for each cell received from the gateway station, and separates a plurality of feeder link signals multiplexed at a feeder link frequency of the first frequency band received from the gateway station based on a result of the estimation of the propagation path response, a frequency conversion unit that performs frequency conversion on a plurality of service link frequencies 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 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 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 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 gateway station 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.

[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 aircraft 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 multiple sub-array antennas in the feeder link array antenna, based on reception power of the multiple 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 propagation path response matrix between the subarray antenna and a feeder link array antenna of the communication relay device for each of the multiple 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 propagation path response matrix, and switch the selected array antenna based on an evaluation result of the singular values ​​for the multiple subarray antennas.

[0015] Here, circularly polarized radio waves may be used for wireless communication in 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 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 cross-arranged in a straight line at equal intervals in different directions.

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

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

[0019] [Figure 1] FIG. 1 is a diagram illustrating an example of an overall configuration of a system according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of frequency conversion between a feeder link frequency and a service link frequency in the system according to the embodiment. [Diagram 3]FIG. 3 is a diagram showing an example of streams 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. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between the rotation angle of the HAPS and the channel capacity when E-SDM MIMO transmission is performed between the HAPS and the GW station in a case where array antenna switching is not performed at the GW station in a system according to an embodiment. [Diagram 5] FIG. 5 is a diagram showing an example of the relationship between the rotation angle of the HAPS and the channel capacity when MIMO transmission using the ZF standard receive separation method is performed between the HAPS and the GW station when array antenna switching is not performed at the GW station in the system of the embodiment. [Figure 6] FIG. 6 is a diagram showing an example of the relationship between the rotation angle of the HAPS and the channel capacity when E-SDM MIMO transmission 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. [Figure 7] FIG. 7 is a diagram showing an example of the relationship between the rotation angle of the HAPS and the channel capacity when MIMO transmission is performed using the ZF standard receive separation method between the HAPS and the GW station when switching the array antenna at the GW station in a system according to an embodiment. [Figure 8] FIG. 8 is a diagram illustrating 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 in each of the GW station and the HAPS in the system according to the embodiment. [Figure 9] FIG. 9 is a diagram illustrating 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 in each of the GW station and the HAPS in the system according to the embodiment. [Figure 10]FIG. 10 is a diagram illustrating 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 in each of the GW station and the HAPS in the system according to the embodiment. [Figure 11] Fig. 11(a) is a diagram showing an example of rotation of a HAPS with respect to a GW station in a system according to an embodiment. Fig. 11(b) 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. [Figure 12] FIG. 12 is a block diagram showing an example of a configuration of a main part of a GW station in the system according to the embodiment. [Figure 13] FIG. 13 is a block diagram showing an example of a configuration of a main part of a HAPS in a system according to an embodiment. [Figure 14] FIG. 14 is a block diagram showing an example of a downlink radio frame from a GW station to a HAPS in the system according to the embodiment. [Figure 15] 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 the system according to the embodiment. [Figure 16] Fig. 16(a) is a diagram showing an example of a plurality of subarray antennas switchable by a GW station when linearly polarized waves are used in a system according to an embodiment. Fig. 16(b) is a diagram showing an example of a selected array antenna selected from the plurality of subarray antennas in Fig. 16(a). Fig. 16(c) is a diagram showing another example of a selected array antenna selected from the plurality of subarray antennas in Fig. 16(a). [Figure 17] Fig. 17(a) is a diagram showing an example of a plurality of subarray antennas switchable by a GW station when using circularly polarized waves in a system according to an embodiment. Fig. 17(b) is a diagram showing an example of a selected array antenna selected from the plurality of subarray antennas in Fig. 17(a). Fig. 17(c) is a diagram showing another example of a selected array antenna selected from the plurality of subarray antennas in Fig. 17(a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that each drawing merely shows the shape, size, and positional relationship in a schematic manner 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. In addition, the numerical values ​​exemplified below are merely preferred examples of the present invention, and therefore the present invention is not limited to the numerical values ​​exemplified.

[0021] The system according to the embodiment described in this specification is a system that relays communication between a user equipment (hereinafter referred to as "UE") and a base station device via a relay station of a non-regenerative relay method provided in a communication relay device such as a HAPS located in the sky and a gateway station (hereinafter referred to as a "GW station") on land or sea. The system according to the embodiment can increase the capacity of a feeder link in a line-of-sight (LoS) environment between the relay station such as a HAPS and the GW station to accommodate communication traffic of a service link for multiple cells. In particular, the system according to the embodiment is suitable for wireless communication called NR (New Radio) in a fifth generation or later generation mobile communication system.

[0022] FIG. 1 is a diagram showing an example of the overall configuration of a system according to an embodiment. In FIG. 1, the system according to the 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 aircraft or floating object located in the sky, and a GW station 20 installed on the ground or sea. The HAPS (relay station) 10 forms a plurality of cells 100(1)-100(3) facing the ground or sea via a service link antenna (for example, an array antenna), and can perform wireless communication of service links SL(1)-SL(3) with user equipment (UE) 40(1)-40(3) in each of the cells 100(1)-100(3). In addition, the HAPS (relay station) 10 can perform wireless communication of a plurality of feeder links FL(1)-FL(3) with the GW station 20 via a feeder link array antenna (hereinafter, also referred to as an "FL antenna").

[0023] The HAPS10 is equipped with at least one of a battery and a solar power generation system, for example, and can fly using electric power. The HAPS10 may be a solar plane type HAPS as shown in the figure, or an airship type HAPS. The body (main body) of the HAPS may be an artificial satellite, a balloon, or an unmanned aerial vehicle (UAV) such as a drone or an unmanned aircraft system (UAS). The HAPS10 may fly using at least one of a battery and an engine as a power source.

[0024] For example, the HAPS10 may be controlled to float or fly in an airspace (floating airspace) with an altitude H of 100 km or less from the ground (or sea level) by autonomous control or external control. The airspace in which the HAPS10 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 the weather conditions are relatively stable, and may particularly be an airspace with an altitude of approximately 20 km. The above airspace may be an airspace with an altitude of 0.1 km or more for UAVs. It may also 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 a "GW antenna") 21 and a GW station device 22. The GW station 20 can perform wireless communication with the HAPS 10 over a plurality of feeder links FL(1) to FL(3). A plurality of base station devices 30(1) to 30(3) are connected to the GW station device 22. The GW station 20 can relay communication between the plurality of base station devices 30(1) to 30(3) and a plurality of UEs 40(1) to 40(3).

[0026] 1 shows an example in which HAPS 10 forms three cells 100(1)-100(3), 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 the system according to the embodiment. In the system according to the embodiment, in order to accommodate the 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 consideration of the trend of standardization of mobile communications, and therefore LoS-MIMO transmission is applied to the wireless transmission of the feeder links.

[0028] In the system of this embodiment, an FDD (Frequency Division Duplex) method is used as an 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 a first frequency band for wireless communication of the feeder links FL(1) to FL(3). A sub6 frequency band (reference) which is a second frequency band lower than the first frequency band is used for wireless communication of the service links SL(1) to SL(3). Here, the frequency band called sub6 is a frequency band of 6 GHz or less in the microwave band (3 GHz to 30 GHz), for example, 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 of the frequency of the first frequency band > the second frequency band is satisfied.

[0029] The relay station installed in the HAPS10 in the system of this embodiment is a non-regenerative relay type relay station, and 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 of MIMO transmission in a propagation path between the FL antenna 11 of the HAPS 10 and the GW antenna 21 of the GW station 20 in the system according to the embodiment. In FIG. 3, the wireless transmission method in 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 each of the transmitting side and the receiving side. In the MIMO transmission, spatially multiplexed streams (communication paths) 500(1) to 500(3) in the same number as the number of cells 100(1) to 100(3) are constructed in the propagation path 50. 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 downlink, the GW station 20 inputs the transmission signals of the base station devices 30(1) to 30(3) to the GW antenna 21 as is without precoding, and the receiving side HAPS 10 receiving the signals via the FL antenna 11 estimates the propagation path response in the propagation path 50 of the feeder link (channel estimation) 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, in HAPS 10, the transmission signals of UE 40(1)-40(3) are input directly to FL antenna 11 without being pre-coded, and the receiving side GW station 20, which receives the signals via GW antenna 21, estimates the propagation path response in the propagation path 50 of the feeder link (channel estimation) and separates the signals from UE 40(1)-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 by multiplying transmission weights at the transmitting array antenna and multiplying reception weights at the receiving 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 "Uniform Linear Array (ULA)") 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 among a plurality of sub-array antennas 210, each of which has a different combination of the plurality of antenna elements 211.

[0035] Each of the subarray antennas 210 is a linear array antenna (ULA) having a plurality of antenna elements 211, the same number as the FL antenna 11 of the HAPS 10, arranged in a straight 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) having a plurality of antenna elements 211, an odd number of three or five or more, in which the central antenna element of the plurality of antenna elements 211 is shared with each other, and the plurality of antenna elements 211 are arranged in a straight line at equal intervals in a first direction and a second direction orthogonal to each other. Also, a selected array antenna selected from the plurality of linear array antennas is a linear array antenna (ULA) having a plurality of antenna elements 211, the same number as the FL antenna 11 of the HAPS 10, arranged in a straight 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. In the GW antenna 21, multiple subarray antennas 210(1), 210(2) having different combinations of multiple antenna elements 211(1) to 211(5) can be switched for use in feeder link wireless communication. 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) constituting the GW antenna (UXA) 21 simultaneously in the feeder link, but selects sub-array antenna (ULA) 210(1) or sub-array antenna (ULA) 210(2) having the same number of antenna elements as 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 passing 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 of a decrease in the capacity (channel capacity) [bps / Hz] of the feeder link propagation path 50 as shown below. In this embodiment, in order to suppress capacity degradation 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 (e.g., rotation of the HAPS 10), the sub-array antennas (ULA) 210(1), 210(2) of the GW antenna (UXA) 21 are switched depending on the positional relationship between the HAPS 10 and the GW station 20 (e.g., the rotation angle of the HAPS 10 relative to the GW station 20).

[0039] Furthermore, when MIMO transmission is performed between HAPS 10 and the 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 the 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 the GW station 20.

[0040] FIG. 4 is a diagram showing an example of the relationship between the rotation angle of the HAPS 10 and the channel capacity when E-SDM MIMO transmission is performed between the HAPS 10 and the GW station 20 when the subarray antenna (ULA) is 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 the channel capacity when ZF-standard reception separation MIMO transmission is performed between the HAPS 10 and the GW station 20 when the subarray antenna (ULA) is not switched at the GW station 20 in the system according to the embodiment. Note that FIG. 4 and FIG. 5 are computer simulation results for a ULA-ULA configuration using linear array antennas (ULA) having the same number of antenna elements in 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 of the linear array antenna (ULA) is 2, 3, 4, and 5, respectively (similar to FIG. 6 and FIG. 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 HAPS10 and the channel capacity when E-SDM MIMO transmission is performed between the HAPS10 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 HAPS10 and the channel capacity when ZF-standard reception separation MIMO transmission is performed between the HAPS10 and the GW station 20 when switching between the subarray antennas (ULA) at the GW station 20 in the system according to the embodiment. In FIG. 6 and FIG. 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 HAPS10 rotates 45°.

[0043] By configuring the GW antenna 21 of the GW station 20 as a UXA and switching the subarray antennas (ULA) 210(1), 210(2) that make up the UXA when the HAPS 10 rotates a specified 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 an example of the relationship between the rotation angle of HAPS10 and the gain of each transmission stream when MIMO transmission is performed using a linear array antenna (ULA) having two antenna elements, three antenna elements, and four antenna elements in the GW station 20 and the HAPS10, respectively, in the system according to the embodiment.

[0045] As shown in Figures 8, 9, and 10, when performing MIMO transmission using the ZF standard reception separation method, the variation in gain (for each transmission stream) relative to the rotation angle of HAPS10 is small at about ±1 dB compared to when performing MIMO transmission using the E-SDM method. Therefore, when performing MIMO transmission using the ZF standard reception separation method, 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 HAPS10.

[0046] FIG. 11(a) is a diagram showing an example of the rotation of the HAPS 10 with respect to the GW station 20 in the system according to the embodiment. FIG. 11(b) 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 illustrated example, the HAPS 10 rotates 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 of each array antenna 21, 11 is set so that transmission with three streams corresponding to three cells can be realized in MIMO transmission of the feeder link, and is based on the configuration of the UXA consisting of five antenna elements of the GW station 20 and the ULA consisting of three antenna elements of the HAPS 10. It should be noted that the antenna configuration and conditions in FIG. 11 are merely an example, 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 a configuration of a main part of a GW station 20 in a system according to an embodiment. In Fig. 12, the GW station 20 includes a GW antenna 21 consisting of a cross array antenna (UXA) in which the above-mentioned five antenna elements 211(1) to 211(5) are cross-arranged at equal intervals, and a GW station device 22 which is a 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 in the configuration example of Fig. 12, vertically polarized and horizontally polarized signals can be transmitted and received simultaneously in the feeder link.

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

[0049] The array switch unit 221 selects from the multiple 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 separation unit 222 estimates the propagation path response between the FL antenna 11 of HAPS10 and the selected array antenna 210(1) or 210(2) of its own station (GW station 20) based on the control signal received from the relay station of HAPS10, and separates the multiple feeder link signals multiplexed at the feeder link frequency of the first frequency band (millimeter waves) received from the relay station of HAPS10 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)-100(3) received from the multiple base station devices 30(1)-30(3) to generate multiple feeder link signals multiplexed at a feeder link frequency in the first frequency band (millimeter wave). Also, the frequency conversion unit 223 performs frequency conversion on the multiple feeder link signals separated by the received signal separation unit 222 to generate 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 a configuration of a main part of a HAPS 10 in a system according to an embodiment. In Fig. 13, the HAPS 10 includes an FL antenna 11 consisting of a linear array antenna (ULA) in which the above-mentioned 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 relay type relay station 13. In Fig. 13, the up arrows and right arrows in the antenna elements 111(1) to 111(3) indicate vertically polarized waves and horizontally polarized waves, respectively, and in the configuration example of Fig. 13, vertically polarized and horizontally polarized signals can be transmitted and received simultaneously in the feeder link.

[0053] Relay station 13 includes a received signal separator 131, a frequency converter 132, and a control signal adder 133. Relay station 13 can process transmitted and received signals of vertical polarization and horizontal polarization.

[0054] The received signal separation unit 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 received from the GW station 20, and separates a plurality of feeder link signals multiplexed at a feeder link frequency of the first frequency band (millimeter wave) 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 the feeder link frequencies of the first frequency band (millimeter wave). Also, 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 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 conditions in which 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 Figure 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 the case of feeder link (uplink) signal separation from HAPS 10 to the GW station 20, it is difficult for the GW station 20 to detect and estimate the channel 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 in either time division or frequency division. In the case of time division, the control signal is transmitted in a period that is sufficiently short for the fluctuation of the HAPS 10, and in the case of frequency division, the control signal is transmitted in a band that can be considered as a narrowband signal. In addition, the control signal may 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 result.

[0061] The control signal may also include system information such as downlink power information, position information of HAPS10 (e.g., GNSS information such as GPS information), attitude information of HAPS10, and alive monitoring of HAPS10, and the GW antenna 21 in the GW station 20 may be switched based on any of this system information.

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

[0063] For example, if the received power at the V port of the GW antenna 21 is greater than the received power at the H port of the HAPS 10, the vertical array antenna 210(1) in Fig. 16(b) is selected. On the other hand, if the received power at the H port of the GW antenna 21 is greater than the received power at the V port of the HAPS 10, the horizontal array antenna 210(2) in Fig. 16(c) 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. However, 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 comparison result of 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 16(a) to 16(c), the GW station 20 switches between the vertical array antenna 210(1) and the horizontal array antenna 210(2) in the GW antenna 21 by comparing the received power of the control signal of the polarization that matches the arrangement direction of the array of the FL antenna 11 of HAPS 10.

[0066] FIG. 17(a) is a diagram showing an example of a plurality of subarray antennas 210(1), 210(2) switchable by the GW station 20 when circular polarization is used for the feeder link in the system according to the embodiment. As shown in FIG. 17(a), when left-handed polarization (LHP), right-handed 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, the channel capacity is calculated by singular value decomposition of the propagation path response matrix, for example, as shown in the following A to C, and the vertical array antenna (V-array) 210(1) and the horizontal array antenna (H-array) 210(2) are switched based on the calculation result.

[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 obtained 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 result of a known reference signal included in a control signal received from the HAPS10, for example.

[0068] B. Using 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 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 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 receiving side do not match.

number

[0069] C. By comparing the product of the singular values ​​of the singular value matrix Σ, it is selected which of the vertical array antenna 210(1) and the horizontal array antenna 210(2) to use.

[0070] Here, the first singular value to the third singular value of the singular value matrix Σ for the vertical array antenna (V-array) 210(1) are respectively denoted as 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 formula (2). Note that in the following formula (2), "1" is added to each singular value to accommodate low SNR.

number

[0071] In addition, the first singular value to the third singular value 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 formula (3). Note that in the following formula (3), "1" is added to each singular value to accommodate low SNR.

number

[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 evaluation value is selected.

[0073] In addition, 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 above-mentioned propagation path response matrix can also be applied to the case where linear polarization is 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 circular, rectangular, or random shape.

[0076] In addition, the present invention can increase the capacity of the feeder link in an LoS environment between the relay station and the GW station installed on a HAPS in the sky, thereby contributing to the achievement of Goal 9 of the Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote industry, innovation and infrastructure."

[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 in this specification, computers, or combinations thereof.

[0079] Also, for firmware and / or software implementation, the means such as processing units used to realize the above components may be implemented with programs (e.g., codes such as procedures, functions, modules, instructions, etc.) that execute the functions described herein. In general, any computer / processor readable medium tangibly embodying firmware and / or software codes may be used to implement the means such as processing units used to realize the above steps and components described herein. For example, the firmware and / or software codes may be stored in a memory and executed by a computer or processor, for example in a controller. The memory may be implemented within the computer or processor, or may be implemented externally to the processor. Also, the firmware and / or software codes may be stored in a computer or processor readable medium, such as a random access memory (RAM), a read-only memory (ROM), a non-volatile random access memory (NVRAM), a programmable read-only memory (PROM), an electrically erasable programmable read-only memory (EEPROM), a flash memory, a floppy disk, a compact disk (CD), a digital versatile disk (DVD), a 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 code of the program may be in any format as long as it can be read and executed by a computer, a processor, or another device or machine, and the format is not limited to a specific format. For example, the code of the program may be 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. [Explanation of symbols]

[0082] 10: Golden Week Station 11: Feeder link array antenna (FL antenna) 12: Service link antenna 13: Relay station 20: Golden Week Station 21: Array antenna for feeder link (GW antenna) 22:GW station equipment 30:Base station equipment 50: Propagation path 100: Cell 111: Antenna element 131: Received signal separation unit 132: Frequency conversion section 133: Control signal adding unit 210: Subarray antenna 211: Antenna element 221: Array switch section 222: Received signal separation unit 223: Frequency conversion section 500 : Stream

Claims

1. A system for relaying communication between a user device and a base station device, comprising: a communication relay device having a non-regenerative relay type relay station mounted on an aircraft or floating object located in the sky; and a ground or sea gateway station that communicates with the communication relay device via a feeder link, the gateway station performs feeder link wireless communication with the relay station via a feeder link array antenna by a MIMO transmission method using a feeder link frequency in a first frequency band; the relay station performs wireless communication of the feeder link with the gateway station via a feeder link array antenna in the MIMO transmission scheme using a feeder link frequency in the first frequency band; A system characterized by:

2. 2. The system of claim 1, the communication relay device includes a feeder link array antenna having a plurality of antenna elements; The gateway station includes: 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; an array antenna switching unit that selects 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, and switches a selected array antenna to be used for wireless communication of the feeder link, A system characterized by:

3. In the system of claim 2, The communication relay device includes: A service link antenna; a received signal separator that estimates a propagation path response between the selected array antenna of the gateway station and a feeder link array antenna of the gateway station 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 received from the gateway station based on a result of the estimation of the propagation path response; a frequency conversion unit that performs frequency conversion on service link signals of a plurality of service link frequencies in a second frequency band lower than the first frequency band received from the plurality of cells via the service link antenna, generates a plurality of feeder link signals multiplexed at the feeder link frequencies 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; a control signal adding unit that adds the control signal to the plurality of feeder link signals to be transmitted to the gateway station; The gateway station includes: 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 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 estimation result of the propagation path response; 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, generates a plurality of feeder link signals multiplexed at a feeder link frequency in 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. A system characterized by:

4. In the system of claim 2, The control signal is added to an adjacent band adjacent to a communication band of an uplink signal from the relay station to the gateway station and transmitted. A system characterized by:

5. In the system of claim 2, The control signal includes at least one of position information and attitude information of the aircraft or the floating body on which the relay station is mounted, A system characterized by:

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

7. 7. The system of claim 6, 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. A system characterized by:

8. 7. The system of claim 6, the array antenna switching unit of the gateway station switches the plurality of sub-array antennas in the feeder link array antenna based on reception powers of the plurality of reference signals, which differ for each antenna port and are included in the control signal. A system characterized by:

9. In the system of claim 2, The array antenna switching unit of the gateway station based on a reception result of a reference signal included in a control signal received from the relay station, for each of the plurality of subarray antennas, estimating a channel response matrix between the subarray antenna and a feeder link array antenna of the communication relay device, and evaluating singular values ​​of the channel response matrix; switching the selected array antenna based on the evaluation result of the singular values ​​for the plurality of subarray antennas; A system characterized by:

10. 10. The system of claim 9, A circularly polarized radio wave is used for the wireless communication of the feeder link. A system characterized by:

11. In a system according to any one of claims 2 to 10, The feeder link array antenna of the communication relay device is 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 is a two-dimensional array antenna in which a plurality of antenna elements are arranged two-dimensionally, the plurality of subarray antennas of the gateway station are each 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, the selection array antenna of the gateway station is 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; A system characterized by:

12. 12. The system of claim 11, the plurality of subarray antennas of the gateway station are a first linear array antenna and a second linear array antenna each having a plurality of antenna elements, an odd number of which is 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 orthogonal to each other; A system characterized by:

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