Radio wave analysis device and radio wave analysis method

Abstract

The information expression capability of radio waves is increased by using information expression based on an orthogonal basis with a high degree of freedom that allows for a large number of combinations. [Solution] The system includes a radio wave signal acquisition unit (11) that acquires the complex signal of the received electric field for each element of the array antenna as a received radio wave signal, an orthogonal basis expansion unit (12) that calculates two or more orthogonal basis components from the received radio wave signal, a reference structure acquisition unit (13) that acquires reference structure information used for modulation by the geometric structure of the radio waves, and a restructuring calculation unit (14) that uses the orthogonal basis components and the reference structure information to calculate the elevation angle, azimuth angle, and radius on a sphere (20) with the first orthogonal basis and the second orthogonal basis as poles to represent the geometric structure of the radio waves as a restructured geometric structure, and the orthogonal basis components include orbital angular momentum components.

Description

[Technical Field]

[0001] The present invention relates to a radio wave analysis device and a radio wave analysis method for performing communications, radar imaging, and object detection and recognition. [Background technology]

[0002] Methods for analyzing radio waves have been proposed for communications, radar imaging, and object detection and recognition. Patent Document 1 discloses a method in which two types of electromagnetic waves, one with an orbital angular momentum wavefront and the other with a non-orbital angular momentum wavefront, are transmitted toward a target, the returned waves are captured, two different signals are generated, and target information is calculated using the difference between the transmitted and received signals. Patent Document 2 also discloses a method in which a Poincaré sphere is constructed and polarization is observed and analyzed. The method discloses a method in which the change in the polarization state of an uplink signal during the propagation process is expressed as a change in position on the Poincaré sphere, and the polarization state of a downlink signal is optimized. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 1,179,556 [Patent Document 2] U.S. Patent No. 9,258,051 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a method for acquiring information such as the azimuth angle, range, and velocity of a target using information on each order of polarization parameters and orbital angular momentum, but does not disclose information representation on the Poincaré sphere using any orthogonal basis, limiting the ability to represent information. Furthermore, Patent Document 2 limits the orthogonal basis to only two polarization bases, limiting the ability to represent information when aiming at state representation. [Means for solving the problem]

[0005] A radio wave analysis device according to one embodiment of the present invention is a radio wave analysis device that analyzes radio waves having a geometric structure, and includes: a radio wave signal acquisition unit that acquires, as a received radio wave signal, a complex signal of the received electric field for each element of an array antenna that receives radio waves; an orthogonal basis expansion unit that calculates two or more orthogonal basis components from the received radio wave signal; a reference structure acquisition unit that acquires reference structure information that identifies the components of the radio wave corresponding to a first orthogonal basis and a second orthogonal basis that are orthogonal to each other and used for modulation by the geometric structure of the radio waves; and a restructuring calculation unit that uses the orthogonal basis components and the reference structure information to calculate the geometric structure of the radio wave as a restructured geometric structure, with the elevation angle, azimuth angle, and radius on a sphere with the first orthogonal basis and the second orthogonal basis as poles, and the orthogonal basis components include orbital angular momentum components. [Effects of the Invention]

[0006] According to the present invention, by using information representation based on an orthogonal basis with a high degree of freedom that allows for a large number of combinations, it is possible to increase the information representation capability of radio waves and improve communication capacity or object detection resolution. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Brief explanation of the drawings]

[0007] [Figure 1A] FIG. 1 is a block diagram of a radio wave analyzer according to a first embodiment. [Figure 1B] FIG. 1 is a diagram showing the geometric structure of radio waves. [Figure 2A] 3 is a flowchart of processing in the radio wave analyzer of the first embodiment. [Figure 2B] 1 is an example of a hardware configuration of a computer. [Figure 3] FIG. 10 is a block diagram of a radio wave analyzer according to a second embodiment. [Figure 4] 10 is a flowchart of a process in the radio wave analyzer of the second embodiment. [Figure 5] 10 is a configuration example of a radio signal acquisition unit. [Figure 6] 10 is a display example of a restructured geometric structure displayed on a sphere. [Figure 7] 10 is a display example showing the time change of the restructured geometric structure on a spherical surface. [Figure 8A] 10 is an example of time-varying geometric structures of a transmitted radio wave signal and a received radio wave signal. [Figure 8B] 10 is an example of time-varying geometric structures of a transmitted radio wave signal and a received radio wave signal. [Figure 8C] 10 is an example of time-varying geometric structures of a transmitted radio wave signal and a received radio wave signal. [Figure 9] FIG. 10 is a block diagram of a radio wave analyzer according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] The radio wave analysis device of this embodiment is a device that acquires and analyzes radio waves in which two or more mutually orthogonal basis components (orthogonal basis components) are superimposed (such radio waves are referred to as radio waves having a geometric structure). Here, an orthogonal basis refers to a basis in which the inner product of the basis vectors is zero. When the received radio waves have polarization components as orthogonal basis components, the radio waves having a geometric structure are polarization superimposed signals in which mutually orthogonal polarizations are superimposed. When the received radio waves have orbital angular momentum (OAM) components as orthogonal basis components, the radio waves having a geometric structure are multi-order OAM superimposed signals in which mutually orthogonal orders (or OAM modes) and rotational direction OAM components are superimposed. [Example]

[0009] FIG. 1A shows a block diagram of a radio wave analysis device 100 according to a first embodiment. The radio wave analysis device 100 is an example configuration suitable for communication applications. A transmitting unit (not shown) transmits radio waves having a geometric structure. As shown in FIG. 1B, the transmitting unit encodes the signal to be transmitted into three spherical parameters (elevation angle θ, azimuth angle φ, radius a) that indicate the geometric structure on a sphere 20 defined by two orthogonal bases 1 and 2, and transmits the encoded signal. A receiving unit including the radio wave analysis device 100 receives the radio waves having the geometric structure transmitted from the transmitting unit, analyzes the received radio waves, and restructures the geometric structure, thereby enabling decoding into the transmitted signal.

[0010] The radio wave analysis device 100 comprises a radio wave signal acquisition unit 11, an orthogonal basis expansion unit 12, a reference structure acquisition unit 13, and a restructuring calculation unit 14. An overview of the processing performed by each block will be explained with reference to Fig. 2A. Note that the radio wave signals transmitted and received between the transmitting unit and the receiving unit are multiplexed radio wave signals having a geometric structure of multiple channels.

[0011] The radio signal acquisition unit 11 receives electromagnetic waves and acquires the radio signal of each channel (S01). The orthogonal basis expansion unit 12 determines the orthogonal basis components of the radio signal of each channel by orthogonal basis expansion (S02). The orthogonal basis components of the radio signal are polarization components and / or orbital angular momentum components (OAM components). If the acquired radio signal has polarization components, the orthogonal basis components are a combination of a horizontal polarization component and a vertical polarization component, or a combination of a right-handed circular polarization component and a left-handed circular polarization component. If the acquired radio signal has OAM components, the orthogonal basis components are a combination of right-handed or left-handed OAM components of any order (OAM mode).

[0012] The reference structure acquisition unit 13 acquires reference structure information of the received electromagnetic wave in advance (S03). Here, the reference structure information refers to information that identifies a combination of electromagnetic wave components corresponding to the orthogonal bases 1 and 2 used for modulation of the electromagnetic wave by a geometric structure. Multiple sets of orthogonal base components may be used simultaneously for modulation. The method by which the reference structure acquisition unit 13 acquires the reference structure information depends on the system to which this embodiment is applied. For example, the reference structure acquisition unit 13 can acquire the reference structure information by receiving control data that identifies the orthogonal bases 1 and 2 used for modulation from the transmitting unit or a higher-level system. The reference structure information only needs to be acquired before the restructuring calculation process (S04), and may be acquired at a timing unrelated to steps S01 and S02 of FIG. 2A.

[0013] The restructuring calculation unit 14 selects, for the radio wave signal of each channel, orthogonal basis components corresponding to the orthogonal basis identified by the reference structure information from the orthogonal basis components obtained by the orthogonal basis expansion unit 12, and calculates a geometric structure (spherical parameters) including the elevation angle θ, azimuth angle φ, and radius a of the sphere constructed using the selected basis. The geometric structure determined by the restructuring calculation unit 14 is called a restructured geometric structure.

[0014] For example, if the spherical parameters of the elevation angle θ, azimuth angle φ, and radius a can be transmitted and received in 10 divisions, then a pair of orthogonal bases can be used to divide the parameters into 10 3It is possible to transmit and receive information with 1000 different patterns. Analyzing radio waves using a sphere in this way allows for the expression of information using multiple combinations of orthogonal bases, resulting in a high degree of freedom. When used in communications, this facilitates multi-level modulation (the number of modulation levels can be increased), thereby increasing communication capacity. Furthermore, by increasing the order (OAM mode), the number of spatial multiplexing levels can be increased, thereby increasing communication capacity. Regarding the division of the sphere, in addition to the above, it is also possible to transmit and receive information based on the vertex positions of a polyhedron created by repeatedly dividing each face of a regular dodecahedron or icosahedron, which are regular polyhedrons close to a sphere, into equilateral triangles. This allows the distance between adjacent points to be equal at any point on the sphere, thereby equating the observation accuracy required for determining information (position on the sphere) during reception. [Example]

[0015] FIG. 3 shows a block diagram of a radio wave analysis device 101 according to a second embodiment. The radio wave analysis device 101 is an example of a configuration suitable for radar imaging and object detection and recognition applications. A transmitting unit (not shown) transmits radio waves having a geometric structure. The transmitted radio wave signal has a geometric structure (elevation angle θ, azimuth angle φ, radius a) on a sphere 20 defined by two orthogonal bases 1 and 2, as shown in FIG. 1B. A receiving unit equipped with the radio wave analysis device 101 receives the radio waves that are returned, for example, after being reflected or scattered by some object, from the transmitted radio wave signal transmitted by the transmitting unit. By analyzing the received radio waves and reconstructing their geometric structure and comparing it with the geometric structure of the transmitted radio wave signal, it becomes possible to analyze the reflector or scatterer that reflected or scattered the transmitted radio wave signal.

[0016] The radio wave analysis device 101 includes a reference radio wave signal acquisition unit 15 and a comparison operation unit 16 in addition to the radio wave signal acquisition unit 11, orthogonal basis expansion unit 12, reference structure acquisition unit 13, and restructuring operation unit 14 included in the first embodiment. An overview of the processing by each block will be described with reference to FIG. 4.

[0017] The processing of the radio wave signal acquisition unit 11, orthogonal basis expansion unit 12, reference structure acquisition unit 13, and restructuring calculation unit 14 is the same as in the first embodiment, so duplicated explanations will be omitted. The reference radio wave signal acquisition unit 15 acquires three spherical parameters that indicate the geometric structure (elevation angle θ, azimuth angle φ, radius a) of the transmitted radio wave signal transmitted by the transmitting unit (S05). The geometric structure of the transmitted radio wave signal is called the reference geometric structure. The reference geometric structure only needs to be acquired before the comparison calculation process (S06), and may be acquired at a timing unrelated to steps S01 to S04 in FIG. 4.

[0018] The comparison calculation unit 16 compares the reference geometric structure acquired by the reference radio wave signal acquisition unit 15 with the restructured geometric structure calculated by the restructuring calculation unit 14. For example, it calculates the difference between each of the spherical parameters (elevation angle θ, azimuth angle φ, radius a) constructed based on the reference structure. This difference is related to the propagation process of radio waves in the analysis target. Therefore, if the received radio wave signal is a reflection or scattering electromagnetic wave from a reflector or scatterer, it is possible to obtain information indicating the type, surface characteristics, and other characteristics of the reflector or scatterer.

[0019] For example, when the basis components are OAM components, the number of types of reference structures is equal to the number of combinations of the two orders selected as the basis, and for each of these, information on the difference between the three spherical parameters of elevation angle, azimuth angle, and radius can be obtained. For example, if the selectable radio wave geometric structures are 1st to 3rd order OAM components, it is possible to calculate changes in the geometric structure for a sphere with two orders selected from a total of six bases, with clockwise and counterclockwise rotations for each order. In this way, the ability to express information with a large number of degrees of freedom increases the information expression capabilities during analysis.

[0020] The configuration of each block of the radio wave analyzer 100 of Example 1 and the radio wave analyzer 101 of Example 2 will be described in detail below. Prior to that, the hardware configuration of the radio wave analyzer will be described. The orthogonal basis expansion unit 12, the reference structure acquisition unit 13, the restructuring calculation unit 14, the reference radio wave signal acquisition unit 15, and the comparison calculation unit 16 are executed by a computer. By applying software radio technology, part of the radio wave signal acquisition unit 11 can also be executed by a computer. FIG. 2B shows an example of the hardware configuration of a computer. The computer 30 includes, as shown in FIG. 2B, a processor (CPU) 31, a memory 32, a storage device 33, an input interface (I / F) 34, an output I / F 35, a communication I / F 36, an input / output port 37, and a bus 38 as its main components. The processor 31 functions as a functional unit (block) that provides a predetermined function by executing processing in accordance with a program loaded into the memory 32. The storage device 33 stores data and programs used by the functional units. The storage device 33 uses a non-volatile storage medium such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The input I / F 34 is an interface for connecting an input device 39 such as a keyboard or a pointing device, and the output I / F 35 is an interface for connecting a display device 40. The communication I / F 36 enables communication with a computer or the like via a network. The input / output port 37 is connected to a high-frequency circuit of the radio signal acquisition unit 11 (described later) and receives a down-converted received signal as input (when software radio technology is applied). These are connected to each other via a bus 38 so that they can communicate with each other.

[0021] The radio wave analyzers 100 and 101 of the present embodiment do not need to be implemented on a single computer, but may be implemented on multiple computers. Furthermore, some of the functional units (blocks) of the radio wave analyzers 100 and 101 may be implemented as applications on the cloud.

[0022] (Radio signal acquisition unit 11) 5 shows an example of the configuration of the radio signal acquisition unit 11. The radio signal acquisition unit 11 has a hardware configuration including an antenna 51, a high-frequency circuit 52, and an intermediate-frequency circuit 53. The intermediate-frequency circuit 53 can be processed by the computer 30 by applying software radio technology.

[0023] Antenna 51 is a circular array antenna having a total of N elements (N is an integer) arranged on the circumference. Circular array antennas are suitable for receiving radio wave signals having OAM components. Each element of the circular array antenna may be a patch antenna, a dipole antenna, a horn antenna, or the like. Note that, in order to configure antenna 51 to receive the polarized components of electromagnetic waves, it is necessary to arrange an antenna that can receive an orthogonal polarized basis pair of vertically polarized waves and horizontally polarized waves, for example.

[0024] In the high-frequency circuit 52, first, the radio wave signal received by the antenna 51 is amplified by an amplifier 61. Next, in a mixer (combiner) 63, the signal is multiplied by an oscillation signal from a local oscillator 62, thereby down-converting it to a frequency band (called an intermediate frequency) that is the difference between the frequency of the received radio wave and the oscillation frequency of the local oscillator 62, passing the signal through a low-pass filter 64, and then undergoing analog-to-digital conversion in an A / D converter 65 to obtain a down-converted signal. This frequency conversion process is called heterodyne detection.

[0025] The intermediate frequency circuit 53 uses a coherent oscillator 72 in the same band (intermediate frequency band) as the downconverted signal to extract an in-phase component and a quadrature component for the coherent oscillator 72. The in-phase component is extracted by mixing (accumulating) the downconverted signal and the oscillation signal from the coherent oscillator 72 using a mixer 71 (homodyne detection). On the other hand, the quadrature component is extracted by creating a phase-shifted signal by shifting the phase of the oscillation signal from the coherent oscillator 72 using a π / 2 phase shifter 73, and then mixing (accumulating) the downconverted signal and the phase-shifted signal using the mixer 71 (homodyne detection). The in-phase component and quadrature component are passed through a bandpass filter 74 near the intermediate frequency band and are obtained as I and Q signals, respectively. The complex signal acquisition unit 75 calculates the received electric field E = I + iQ (i is the imaginary unit) for each channel to acquire a complex signal representing the electric field.

[0026] It should be noted that the circuit configuration described here is merely an example, and other configurations are possible in which the amplifier 61, band-pass filter 74, low-pass filter 64, and A / D converter 65 are present or not, or in a different order. For example, the process up to acquiring the electric field complex signal of each channel may be performed by an analog circuit, and the detected I and Q signals may be A / D converted and output.

[0027] (Formulation of OAM radio wave transmission) The orthogonal basis expansion unit 12 and the restructuring calculation unit 14 analyze the geometric structure modulated onto the transmitted radio wave signal in the transmitting unit from the received radio wave. Therefore, before describing these in detail, we will explain the modulation by the geometric structure onto the transmitted radio wave signal transmitted from the transmitting unit.

[0028] Assume that the radio waves transmitted by the transmitting unit are radio waves (radio vortex) with orbital angular momentum (OAM) simultaneously superimposed on multiple orders. Here, +lth-order and -lth-order (l is an integer) complex signals are selected as the orthogonal basis of the transmitted radio wave signal, respectively, and these are selected as the north and south poles. The sign of the order indicates the direction of rotation. The geometric structure of the transmitted radio wave signal is expressed as points on a sphere with the selected orders, i.e., ±lth-order complex signals, as the orthogonal basis. Note that there are an infinite number of orders of OAM components, such as ±1st, ±2nd, etc., and they are orthogonal to each other. Therefore, OAM components of any order and any rotation direction can be selected as orthogonal basis components. For example, the orthogonal basis components can be OAM components of the same positive or negative order, such as +1st and +2nd, or OAM components of different positive and negative orders, such as +1st and -2nd. The combination of OAM components selected as the orthogonal basis components of the transmission radio wave signal corresponds to the reference structure information acquired by the reference structure acquisition unit 13. In the following, the description will be given assuming that ±l-order OAM components (complex signals) are selected as the orthogonal basis for the reference structure.

[0029] Radius (global amplitude) a at discrete time m (m is an integer) lm , phase (global phase) ψ lm , azimuth φ lm , elevation angle θ lm , and expressed in orthogonal basis coefficients L(±l, m) (complex numbers), the transmitted radio wave signal is expressed as a 2 × 1 complex vector p lm (4 variables for each degree).

[0030]

number

[0031] The geometric structure (spherical parameters) of the radio signal are radius a lm , azimuth φ lm , elevation angle θ lm , and the global phase ψ lmIn order to transmit the three variables as information on the OAM components using a circular array antenna, the phase of each element of the circular array antenna is shifted before transmitting the signal. When transmitting radio waves with l-order OAM components (OAM radio waves), the phase shift of each of the N elements is l φ0 ,l φ1 , ···l φN-1 (φ n = 2πn / N (n = 0, 1, . . . N-1)), so when simultaneously superimposing ±lth order OAM components, an N × 2 complex vector IQ is used as a matrix to convert it into a complex signal. l is given by (Equation 2).

[0032]

number

[0033] The product of these is IQ l p lm As shown in (Equation 3), represents a complex signal obtained by phase-rotating three variables of ±lth-order OAM components in order to modulate and transmit the OAM components from each element of the circular array antenna.

[0034]

number

[0035] The real part of the complex signal is the I-axis signal of the lth (or -lth) order OAM radio wave, and the imaginary part is the Q-axis signal of the lth (or -lth) order OAM radio wave. In the multi-order simultaneous superposition method, the sum of the I-axis signals and Q-axis signals of orders 1 to l at each point in time is up-converted by an N-channel modulator. This generates the N-channel electrical signal s(t) shown in (Equation 4) to be supplied to the circular array antenna. Here, t is time, f c is the center frequency of the up-conversion [Hz].

[0036]

number

[0037] In general, the electric field E emitted by only +lth order OAM radio waves from a circular array antenna with radius b and number of elements N is expressed as (Equation 5a) at a distance r that is sufficiently large compared to radius b. Here, k is the wave number, J l ( ) is the lth-order Bessel function of the first kind, and φ and θ are the azimuth and elevation angles of the receiving point, respectively, with the transmitting circular array antenna as the origin. Similarly, in the case of only the -lth order, the electric field E is expressed as (Equation 5b).

[0038]

number

[0039] Here, the orthogonal basis coefficients L(±l, m) are transformed from (Equation 1) to (Equation 6). Note that the orthogonal basis coefficients are values ​​of orthogonal basis components.

[0040]

number

[0041] The complex signal at each time point m of the orthogonal basis coefficients L(±l, m) is modulated at a modulation frequency f c and transmitted, the electric field output by radio waves having, for example, ±lth-order OAM components can be expressed as (Equation 7a) and (Equation 7b) using the right-hand sides of (Equation 5a) and (Equation 5b) and the right-hand side of (Equation 6), respectively.

[0042]

number

[0043] Therefore, the electric field generated in the simultaneous superposition method of multiple orders from ±1 to ±n is expressed as (Equation 8).

[0044]

number

[0045] (Formulation of OAM radio wave reception) The radio wave signal acquisition unit 11 receives the electric field E(r, φ, θ, m) generated by the multi-order simultaneous superposition method from ±1 to ±n orders by the antenna 51. At a certain distance r from the propagation axis of the circular array antenna, R A receiving circular array antenna (antenna 51) similar to the transmitting circular array antenna is placed opposite the transmitting circular array antenna at a distance r to receive N-channel signals and observe the entire phase plane of the radio wave vortex. R is set to a relatively short distance. The azimuth angle of the receiving circular array antenna is φ Rn =2πn / N(n=0, 1 , N-1), and the elevation angle is θ R Then, the received electric field down-converted by each element is expressed by (Equation 9).

[0046]

number

[0047] Here, from (Equation 7a), the received electric field of only the +lth order is expressed as (Equation 10).

[0048]

number

[0049] (Orthogonal basis expansion part 12) The orthogonal basis expansion unit 12 calculates the orthogonal basis coefficients L(±l, m) by orthogonal basis expansion using the received radio wave signals (complex signals of the received electric field of each channel) of the N-channel circular array antenna acquired by the radio wave signal acquisition unit 11. The spatial Fourier transform utilizes the orthogonality of complex sine waves to express the complex signals of the received electric field of each channel as a linear combination of orthogonal bases.

[0050] Specifically, to calculate the spatial frequency components in the circumference +φ direction (N divisions) of the circular array antenna, the circular harmonic function e idφA spatial Fourier transform is performed using (d=0, 1 , N-1). Here, d indicates the number of waves included in the circumferential direction, and the spatial frequency component (e idφ The component of (e) corresponds to the basis coefficient (L(+d, m)) of the d-th order OAM radio wave (m is discrete time). The basis coefficient here is a circular harmonic coefficient. By using this coefficient, a circular harmonic expansion can be performed by multiplying and adding with the circular harmonic function. Note that d can also take a negative value (written as -d, which is a spatial Fourier transform in the -φ direction (N divisions)), and the spatial frequency component (e -idφ The component of (L(-d, m)) corresponds to the basis coefficient of the -dth order OAM radio wave.

[0051] Therefore, the basis coefficient L(+l, m) can be obtained as in (Equation 11a) using the definition of the discrete Fourier transform. Similarly, the basis coefficient L(-l, m) can be obtained as in (Equation 11b). Here, the right-hand sides of (Equation 11a) and (Equation 11b) contain N 2 is multiplied, but the part inside the sigma symbol is e ilφRn and e -ilφRn This is because the same number is added N times, with the numbers and cancelling out to become 1.

[0052]

number

[0053] When a three-dimensional array antenna (including a tensegrity structure) is used as a transmitting / receiving antenna, spherical harmonics can be used.

[0054] Here, a supplementary explanation will be given regarding the relationship between antenna configuration and orthogonal basis expansion method. In the above embodiment, an example has been described in which circular harmonic function coefficients are calculated using circular harmonic functions as an orthogonal basis when the antenna 51 is a circular array antenna. The orthogonal basis expansion is performed according to the antenna shape. When the antenna 51 is an antenna with elements arranged in a one-dimensional array, orthogonal basis expansion is performed using a one-dimensional spatial Fourier transform or a one-dimensional fast Fourier transform (FFT) based on spatial frequency. Alternatively, orthogonal basis expansion is performed using a one-dimensional discrete cosine transform (DCT). Furthermore, when the antenna 51 is an antenna with elements arranged in a two-dimensional array, orthogonal basis expansion is performed using a two-dimensional spatial Fourier transform or a two-dimensional fast Fourier transform (FFT). Alternatively, orthogonal basis expansion is performed using a two-dimensional discrete cosine transform.

[0055] (Restructuring operation unit 14) The restructuring calculation unit 14 can see that the +l-th and -l-th order OAM components have been selected as the orthogonal basis components of the transmission radio wave signal from the reference structure information acquired by the reference structure acquisition unit 13. Therefore, using the orthogonal basis coefficients L(±l, m) calculated by the orthogonal basis expansion unit 12, the restructuring calculation unit 14 can find that the +l-th and -l-th order OAM components have been selected as the orthogonal basis components. lm , azimuth φ lm , elevation angle θ lm (restructured geometry).

[0056] First, (Equation 12) is established from (Equation 1), and (Equation 12) is transformed into (Equation 13) and (Equation 14), and the azimuth angle φ lm , elevation angle θ lm are required respectively.

[0057]

number

[0058]

number

[0059]

number

[0060] In addition, taking the absolute values ​​of both sides of (Equation 11a) and (Equation 11b) gives (Equation 15a) and (Equation 15b), respectively. Therefore, the radius a lm is required.

[0061]

number

[0062]

number

[0063] FIG. 6 shows an example of a display of a restructured geometric structure on a sphere 20 on a display device 40. When orthogonal basis 1 is a counterclockwise lth-order OAM component and orthogonal basis 2 is a clockwise lth-order OAM component, any state (geometric structure) on the Poincaré sphere given by (Equation 1) can be reconstructed. While FIG. 6 shows a cutout of a geometric structure at a certain point in time (any m), it is also possible to express the temporal change in the geometric structure as the movement and trajectory of a point on the sphere. FIG. 7 shows an example of the output of the temporal change in the restructured geometric structure. This allows the temporal change in the geometric structure of radio waves to be visualized in three dimensions, making it easier to understand the changes in the characteristics of the radio waves. Furthermore, to compare the geometric structure of the transmitted radio wave signal (reference geometric structure) with the geometric structure of the received radio wave signal (restructured geometric structure), the results of simulating the temporal change in the geometric structure of the transmitted radio wave signal and the geometric structure of the received radio wave signal for each of the azimuth angle φ, elevation angle θ, and radius a are shown in FIGS. 8A-C. The received radio wave signals shown in Figures 8A to 8C are the same as those shown in Figure 7. The units of azimuth angle φ and elevation angle θ are degrees, and the unit of radius a is an arbitrary unit. As shown in Figures 8A to 8C, the reference geometric structure of the transmitted radio wave signal and the restructured geometric structure of the received radio wave signal nearly overlap, indicating that the geometric structure of the transmitted radio wave signal can be reproduced in the received radio wave signal.

[0064] As an application of this method, the change from the reference geometric structure to the restructured geometric structure may be expressed as a trajectory on the spherical surface 20 or a multidimensional vector (for example, a three-dimensional vector on the spherical surface 20). Furthermore, by creating a feature using multiple spherical surfaces, it is possible to improve the ability to express the characteristics of the detectable radio waves or the characteristics of the target object (reflector or scatterer). For example, the displacement vector x on the first spherical surface using the orthogonal bases 1 and 2 12 and the displacement vector x on the second sphere by the orthogonal basis 3,4 34 The combined feature x 12 x 34It is also possible to generate features such as the above. This allows communication capacity to be doubled without changing the number of divisions of each spherical parameter in communications applications, and higher object recognition resolution can be achieved in radar imaging and object detection / recognition applications. The radio wave components corresponding to the multiple orthogonal bases to be combined can be combinations of polarization components, OAM components, or polarization and OAM components. Furthermore, by expressing the geometric position of the sphere as information as described above, topology information can be transmitted and received. Therefore, even if external disturbances such as phase rotation occur in the received information, the received geometric pattern is only distorted or rotated, and its structure can be easily maintained. This has the effect of realizing more robust information communication that is resistant to external disturbances.

[0065] (In the case of polarized radio waves) Although the above description has been given using an example in which the transmitted radio waves are radio wave vortices, similar processing is possible when the radio waves are radio waves with polarization components (polarized radio waves). Below, the processing of the radio wave analysis device 100 (101) will be explained using an example in which the reference structure of the transmitted radio wave signal is orthogonal base 1 for horizontal polarization and orthogonal base 2 for vertical polarization. In this case, the antenna 51 (see FIG. 5) may be an array antenna having one element that receives horizontally polarized waves and one element that receives vertically polarized waves.

[0066] The transmitted radio wave signal is expressed as a 2×1 complex vector p shown in (Equation 17) using an azimuth angle φ, an elevation angle θ, and a radius a.

[0067]

number

[0068] The matrix for converting the geometric structure shown in (Equation 17) into a complex signal is the 2 × 2 real vector IQ shown in (Equation 18). HV The product of these, IQ, shown in (Equation 19), HV p are the two complex signals of the transmitted radio wave signal.

[0069]

number

[0070]

number

[0071] In FIG. 5, if channel 1 (ch1) is configured as an antenna element that receives horizontally polarized waves and channel 2 (ch2) is configured as an antenna element that receives vertically polarized waves, the complex signals of the horizontally polarized waves and the vertically polarized waves are respectively represented by E H ,E V is expressed by (Equation 20). In the case of polarization components, the complex signals acquired by the radio wave signal acquisition unit 11 become the orthogonal basis components as they are. Therefore, the restructuring calculation unit 14 can calculate the azimuth angle φ, elevation angle θ, and radius a from (Equation 19) and (Equation 20) using (Equation 21), (Equation 22), and (Equation 23), respectively.

[0072]

number

[0073]

number

[0074]

number

[0075]

number

[0076] Even when orthogonal basis 1 is horizontally polarized and orthogonal basis 2 is vertically polarized, the geometric structure of the received radio waves can be displayed on a display device as shown in FIG.

[0077] Note that similar calculations are possible when left-handed and right-handed circular polarization are selected as the orthogonal basis pair for the polarization basis, and conversion between these orthogonal basis pairs is also possible. As described above, it is also possible to acquire the polarization component and the OAM component as separate geometric structures and display them simultaneously. When analyzing them simultaneously, it is sufficient to have an antenna configuration that can acquire both simultaneously. By analyzing both the polarization component and the OAM component and clearly visualizing the polarization status and the radio wave vortex status simultaneously, it is possible to grasp the characteristics of the target in more detail and with greater precision.

[0078] (Comparison operation unit 16) The comparison calculation unit 16 may not only calculate the difference between the reference geometric structure and the restructured geometric structure, but also, instead of calculating the difference, may calculate a transformation matrix that converts the transmitted radio wave signal (reference signal) into the received radio wave signal.

[0079] The electric field for each element of a circular array antenna when +lth-order OAM radio waves are transmitted and received is expressed by (Equation 7a). Therefore, by determining the values ​​of the three spherical parameters, the electric field due to +lth-order OAM radio waves can be expressed as a single complex signal with real and imaginary parts. Here, for example, if a two-dimensional vector (equivalent to a complex signal with two parameters, real and imaginary parts) that represents the state of the incident wave, which is a +1th-order radio wave vortex, is expressed as x i , the two-dimensional vector representing the state of the reflected wave is y o These are connected by the transformation matrix of SU(2) (a group consisting of second-order unitary matrices with determinant 1, also known as the second-order special unitary group), which is in the relationship of a unitary transformation (a transformation in which the value of the dot product of two vectors remains unchanged before and after the transformation), as shown in (Equation 24). Note that a to d of the transformation matrix are real numbers.

[0080]

number

[0081] The comparison calculation unit 16 uses the complex signal of the wave incident on a known object (reference signal (transmitted signal)) and the complex signal of the wave reflected from the object (received signal) to inversely calculate the transformation matrix. As shown in (Equation 24), the transformation matrix has four elements, which correspond to a rotation matrix that converts the incident wave into a reflected wave, and essentially represents the characteristics of the reflector or scatterer or the propagation path. In other words, it can be treated as a feature that represents the characteristics of the target object. Because there are four elements, the inverse calculation of the transformation matrix requires measurements of the incident wave and reflected wave under at least two conditions.

[0082] Here, the incident wave vectors under observation condition 1 and observation condition 2 are x i1 =[x1, x2] T , x i2 =[x3, x4] T , the reflected wave vectors under observation condition 1 and observation condition 2 are y o1 =[y1, y2] T , y o2 =[y3, y4] T In this case, (Equation 25) holds true from (Equation 24).

[0083]

number

[0084]

number

[0085] Elements a to d of the transformation matrix can be calculated by multiplying both sides of (Equation 25) from the left with the inverse matrix (Equation 26). These are used to create the following equations. Observation condition 1 and observation condition 2 can be set to have different geometric structures with different azimuth angles φ and elevation angles θ, for example.

[0086] Since the number of elements in the transformation matrix is ​​four, it can be obtained by performing measurements at least twice under different observation conditions. However, to obtain a more robust solution, it is also effective to perform measurements N times (three or more times) under different observation conditions. The incident wave and reflected wave under each observation condition are respectively x iN =[x 2N-1 , x 2N ] T , y oN =[y 2N-1 , y 2N ] T Then, the elements of the transformation matrix can be expressed as (Equation 27) using a pseudo-inverse matrix equivalent to the least squares approximation.

[0087]

number

[0088] In this case, elements a to d of the transformation matrix can be determined more robustly. As a result, even under noisy observation conditions, by repeating measurements under multiple observation conditions, the elements of the transformation matrix, i.e., the feature quantities that represent the characteristics of the target object and propagation path, can be determined with higher accuracy.

[0089] Furthermore, by performing such calculations for each order of the radio wave vortex, it becomes possible to determine the dependence of the elements of the transformation matrix that are reflected in the reflection and propagation characteristics on the order of the radio wave vortex. By obtaining characteristics that depend on the order of the radio wave vortex and the orthogonal basis components of the superimposed radio wave vortices, it becomes possible to obtain more detailed characteristics of reflectors and scatterers. [Example]

[0090] 9 shows a block diagram of a radio wave analysis device 102 according to a third embodiment. Changes in the geometric structure of radio waves reflect the characteristics of the target object (reflector or scatterer). Therefore, the radio wave analysis device 102 learns the change patterns of the spherical parameters and stores them in a database, thereby enabling estimation of target object information from limited information, leading to a reduction in measurement time and an improvement in analysis accuracy.

[0091] The learning device 17 classifies the change patterns of the spherical parameters between the geometric structure of the transmitted radio wave signal (reference geometric structure) output by the comparison operation unit 16 and the geometric structure of the received radio wave signal (restructured geometric structure) into a plurality of classes in advance. The classes may be based on, for example, the type of object, reflection characteristics, density, etc. The relationship between the change patterns of the spherical parameters learned by the learning device 17 and the classes is stored in a database 18. The classification unit 19 refers to the database 18 and classifies new outputs from the comparison operation unit 16 into one of the classes.

[0092] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments and modifications have been described in detail to make the present invention easier to understand, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment or modification with the configuration of another embodiment or modification, and it is also possible to add the configuration of another embodiment or modification to the configuration of one embodiment or modification. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment or modification with other configurations. [Explanation of symbols]

[0093] 11: Radio wave signal acquisition unit, 12: Orthogonal basis expansion unit, 13: Reference structure acquisition unit, 14: Restructuring calculation unit, 15: Reference radio wave signal acquisition unit, 16: Comparison calculation unit, 17: Learning device, 18: Database, 19: Classification unit, 20: Sphere, 30: Computer, 31: Processor, 32: Memory, 33: Storage device, 34: Input I / F, 35: Output I / F, 36: Communication I / F, 37: Input / output port , 38: bus, 39: input device, 40: display device, 51: antenna, 52: high frequency circuit, 53: intermediate frequency circuit, 61: amplifier, 62: local oscillator, 63: mixer, 64: low pass filter, 65: A / D converter, 71: mixer, 72: coherent oscillator, 73: π / 2 phase shifter, 74: band pass filter, 75: complex signal acquisition unit, 100, 101, 102: radio wave analysis device.

Claims

1. A radio wave analysis device for analyzing radio waves having a geometric structure, a radio wave signal acquisition unit that acquires, as a received radio wave signal, a complex signal of a received electric field for each element of an array antenna that receives the radio waves; an orthogonal basis expansion unit that calculates two or more orthogonal basis components from the received radio wave signal; a reference structure acquisition unit that acquires reference structure information that identifies components of the radio wave corresponding to a first orthogonal basis and a second orthogonal basis that are orthogonal to each other and that are used for modulating the radio wave by a geometric structure; a restructuring calculation unit that calculates the geometric structure of the radio wave as a restructured geometric structure by using the orthogonal basis components and the reference structure information, the elevation angle, the azimuth angle, and the radius on a sphere with the first orthogonal basis and the second orthogonal basis as poles, A radio wave analysis device including orbital angular momentum components as the orthogonal basis components.

2. In claim 1, a reference radio wave signal acquisition unit that acquires, as a reference geometric structure, an elevation angle, an azimuth angle, and a radius on the spherical surface, which is a geometric structure based on the reference structure information at the time of transmitting the radio wave; a comparison calculation unit that compares the restructured geometric structure with the reference geometric structure and outputs a comparison result.

3. In claim 2, the comparison calculation unit calculates a transformation matrix that transforms a complex signal of a transmission electric field at the time of transmission of the radio wave into a complex signal of the reception electric field; A radio wave analysis device, wherein the transformation matrix is ​​a transformation matrix of SU(2).

4. In claim 1 or 2, A radio wave analysis device further including polarized wave components as the orthogonal basis components.

5. In claim 4, When the orthogonal basis components are polarization components, the components of the radio wave corresponding to the first orthogonal basis and the second orthogonal basis are a combination of a horizontal polarization component and a vertical polarization component, or a combination of a right-handed circular polarization component and a left-handed circular polarization component, A radio wave analysis device in which, when the orthogonal basis components are orbital angular momentum components, the components of the radio wave corresponding to the first orthogonal basis and the second orthogonal basis are a combination of clockwise or counterclockwise orbital angular momentum components of any order or OAM mode.

6. In claim 1, the array antenna is a circular array antenna in which the elements are arranged on a circumference, The orthogonal basis expansion unit performs a spatial Fourier transform using a circular harmonic function as an orthogonal basis to calculate spatial frequency components as the orbital angular momentum components.

7. In claim 1 or 2, A radio wave analysis device in which the geometric structure of the radio waves is expressed as a combination of an elevation angle, an azimuth angle, and a radius on a sphere whose poles are the first orthogonal base and the second orthogonal base, and an elevation angle, an azimuth angle, and a radius on a sphere whose poles are a third orthogonal base and a fourth orthogonal base different from the first orthogonal base and the second orthogonal base.

8. In claim 7, A radio wave analysis device, wherein the components of the radio wave corresponding to the first orthogonal basis and the second orthogonal basis are orbital angular momentum components, and the components of the radio wave corresponding to the third orthogonal basis and the fourth orthogonal basis are polarization components.

9. In claim 1 or 2, A radio wave analysis device that displays the restructured geometric structure calculated by the restructuring calculation unit on a display device as a time trajectory of positions on a spherical surface.

10. In claim 2, a learner that learns a relationship between a change pattern of the restructured geometric structure relative to the reference geometric structure and a class; a database that stores the relationship between the change patterns learned by the learning device and the classes; a classification unit that refers to the database and classifies the comparison result output from the comparison operation unit into one of the classes, the class is a class of an object, A radio wave analysis device in which the radio waves are radio waves reflected or scattered by the object.

11. A radio wave analysis method for analyzing radio waves having a geometric structure, comprising: acquiring a complex signal of a received electric field for each element of an array antenna that receives the radio waves as a received radio wave signal; calculating two or more orthogonal basis components from the received radio wave signal; acquiring reference structure information that identifies components of the radio wave corresponding to a first orthogonal basis and a second orthogonal basis that are orthogonal to each other and that are used for modulating the radio wave with a geometric structure; Using the orthogonal basis components and the reference structure information, calculate the geometric structure of the radio wave as a restructured geometric structure, which is an elevation angle, an azimuth angle, and a radius on a sphere having the first orthogonal basis and the second orthogonal basis as poles; A radio wave analysis method in which the orthogonal basis components include orbital angular momentum components.

12. In claim 11, acquiring, as a reference geometric structure, an elevation angle, an azimuth angle, and a radius of the spherical surface, which is a geometric structure based on the reference structure information at the time of transmitting the radio wave; A radio wave analysis method that compares the restructured geometric structure with the reference geometric structure and outputs a comparison result.

13. In claim 12, calculating a transformation matrix that transforms a complex signal of a transmission electric field at the time of transmission of the radio wave into a complex signal of the reception electric field; The radio wave analysis method, wherein the transformation matrix is ​​a transformation matrix of SU(2).

14. In claim 11 or 12, A radio wave analysis method further including polarized wave components as the orthogonal basis components.

15. In claim 12, learning in advance a relationship between a change pattern of the restructured geometric structure relative to the reference geometric structure and a class, and storing the learned relationship between the change pattern and the class in a database; classifying the comparison result between the restructured geometric structure and the reference geometric structure into one of the classes by referring to the database; the class is a class of an object, A radio wave analysis method, wherein the radio waves are radio waves reflected or scattered by the object.

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