JP2017110937A - Radio wave arrival direction estimation device and radio wave arrival direction estimation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio wave arrival direction estimation device that can be miniaturized, has high angle resolution, is precise, and also can reduce computational complexity.SOLUTION: A radio wave arrival direction estimation device includes: a reception part 100 that includes a rotary table 112, a drive part 113 for rotating the rotary table 112 at a fixed period, and an antenna 111 that is fixed to the rotary table 112 to receive radio waves transmitted by a radio tag, and outputs a measurement signal as a signal determined based on radio waves received by the antenna 111; and a direction determination part 230 that determines an approximation model coinciding with a measurement signal by calculating a degree of coincidence between an approximation model that is a model for expressing a measurement signal by approximation with radio waves transmitted by the radio tag as planar waves, and includes an orientation angle at which radio waves arrive, a phase, and the amount of DC offset component as an unknown parameter, and a measurement signal while changing the unknown parameter of the approximation model, and an orientation angle in the determined approximation model as an orientation angle at which radio waves arrive.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radio wave arrival direction estimation device that estimates from which direction a radio wave emitted by a radio tag comes in order to estimate a direction in which the radio tag exists, and a radio wave arrival direction including the device and the radio tag It relates to an estimation system.

  The Pseudo-doppler method is known as one of the methods for estimating the radio wave arrival direction (for example, Non-Patent Document 1). In the Pseudo-doppler method, an antenna is mounted on a rotating plate or the like, and the antenna is moved to create a Doppler shift for radio waves emitted from a radio wave source. Since the signal received by the antenna changes due to the created Doppler shift, the change of the signal is analyzed to estimate the direction of the radio wave source. In Non-Patent Document 1, Fourier transform is used for analysis of a signal received by an antenna.

Chang, H.-L., Tian, J.-B., Lai, T.-T., Chu, H.-H., and Huang, P., Spinning beacons for precise indoor localization, to appear in ACM Sensys '08.

  In order to use the Pseudo-doppler method to install a device with an antenna fixed on a rotating disk indoors, it is necessary to separate the direct wave and the reflected wave caused by multipath.

  The direct wave and the reflected wave generated by multipath have different arrival directions of radio waves. That is, the direction of the radio wave source is apparently different between the direct wave and the reflected wave. A radio wave received by a moving antenna undergoes a Doppler shift reflecting the direction of the radio wave source. Therefore, the direct wave and the reflected wave can be separated by increasing the frequency resolution.

  In the Fourier transform, the frequency resolution Δf is given by the reciprocal of the window width. That is, if the window width to be analyzed is widened, the frequency resolution is high (Δf is small), and conversely if the window width is narrowed, the frequency resolution is low (Δf is large).

  Of course, the greater the frequency difference between the direct wave and the reflected wave, the easier the separation of the direct wave and the reflected wave. Therefore, it is necessary to increase the Doppler shift amount.

  For these reasons, the apparatus described in Non-Patent Document 1 rotates a large disk with a slow rotation cycle. Even if the rotation period is slow, if the disk is large, the speed of the antenna installed in the vicinity of the outer periphery of the disk increases, so the Doppler shift increases. Further, since the rotation period is slow, the time window can be widened. Therefore, the frequency resolution Δf can be increased.

  However, since a large disk is used, it cannot be easily installed in various indoor places. In order to be easily installed in various indoor places, it is desired to be small.

  To increase the Doppler shift while reducing the size of the disk, the angular velocity should be increased. However, if the angular velocity is increased, the frequency analysis window cannot be widened. This is because the time window T has a relationship of T = N / fs (N is the number of sampling points, fs is the sampling frequency), and N is reduced when the angular velocity is increased. If the angular velocity is increased, the frequency analysis window cannot be widened, so that the frequency resolution is lowered.

  Instead of frequency analysis by Fourier transform, prepare a measurement signal model and change the parameter of the model, and use a method to determine the degree of coincidence with the measurement signal. Thus, the angular resolution can be increased.

  However, the distance between the antenna and the wireless tag changes continuously due to the rotation of the antenna, and the model of the measurement signal representing the Doppler shift caused by the change in the distance becomes a complicated model when expressed strictly. As a result, the amount of calculation increases. If the model is simplified using approximation, the amount of calculation is reduced, but if the approximation is not appropriate, the estimation accuracy of the radio wave arrival direction is lowered.

  The present invention has been made based on this circumstance, and the object of the present invention is the direction of arrival of radio waves that can be downsized, have high angular resolution, high accuracy, and can reduce the amount of calculation. To provide an estimation device and a radio wave arrival direction estimation system.

  The above object is achieved by a combination of the features described in the independent claims, and the subclaims define further advantageous embodiments of the invention. Reference numerals in parentheses described in the claims indicate a correspondence relationship with specific means described in the embodiments described later as one aspect, and do not limit the technical scope of the present invention. .

方向決定部は、測定信号をＶ_ｇｅｔとしたとき、一致度として式６で表す残差ｅを算出し、残差ｅが最小となる複数の到来波の方位角の組み合わせを探索するものであって、

式６をＢで偏微分した式と、式６をＣで偏微分した式と、式６をＤで偏微分した式をそれぞれ０とすることで立式される連立方程式を解くことによりＢ、Ｃ、Ｄを算出し、算出したＢ、Ｃ、Ｄを用いて、残差ｅが最小となる複数の到来波の方位角の組み合わせを探索し、
方位角については１８０度以下の変化範囲として近似モデルの未知パラメータを変化させつつ、近似モデルと測定信号との一致度を、アンテナが３６０度回転する区間に渡り算出して、測定信号に一致する近似モデルを決定する。 The invention according to claim 1 for achieving the above object is a radio wave arrival direction estimation device for estimating the arrival direction of a radio wave of a preset constant frequency transmitted by the wireless tag (300),
A turntable (112), a drive unit (113) that rotates the turntable at a predetermined period, and a radio wave that is fixed to a position other than the center of rotation on the turntable and transmitted by the wireless tag is received. An antenna (111) and a low-frequency signal generation unit (120) that generates a low-frequency signal in which the frequency of the radio wave received by the antenna is reduced so that the center frequency becomes 0 Hz, and the low-frequency signal is used as a measurement signal. A receiving unit (100) for outputting;
A model that converts a composite wave of multiple arriving waves into a measurement signal and that represents the measurement signal using an approximation that uses the radio wave transmitted by the wireless tag as a plane wave, and the radio wave arrives as an unknown parameter. Approximation that matches the measurement signal by calculating the degree of coincidence between the approximate model that includes the azimuth angle, phase, and DC offset component amount representing the azimuth to be measured and the measurement signal while changing the unknown parameters of the approximate model A direction determining unit (230) that determines a model and determines an azimuth angle in the determined approximate model as an azimuth angle from which radio waves arrive;
The approximate model is that the frequency of the radio wave transmitted by the wireless tag is f _RF , the radius of rotation of the antenna is R, the speed of light is v _c , the time is t, the amount of DC offset component is D, the azimuth angle of each incoming wave is φ _m , When the amplitude of each incoming wave is A _m , the phase of each incoming wave is Ψ _m , the number of incoming waves is N, and the approximate model is V _ref , Equation 1 or Equation 2, Equation 3, Equation 4, and Equation 5 Model represented,

The direction determining unit calculates a residual e represented by Equation 6 as the degree of coincidence when the measurement signal is V _get and searches for a combination of azimuth angles of a plurality of incoming waves that minimize the residual e. And

By solving the simultaneous equations B and B, by substituting the equation 6 for partial differentiation with B, the equation 6 with partial differentiation with C, and the equation 6 with partial differentiation with D as 0, respectively. C, D are calculated, and the calculated B, C, D are used to search for a combination of azimuth angles of a plurality of arriving waves that minimize the residual e,
As for the azimuth angle, the unknown parameter of the approximate model is changed within a change range of 180 degrees or less, and the degree of coincidence between the approximate model and the measurement signal is calculated over the section where the antenna rotates 360 degrees to match the measurement signal. Determine the approximate model.

  In the present invention, the rotating disk can be downsized for the following reason. The frequency transmitted by the wireless tag is set to a constant frequency, but naturally, a certain amount of fluctuation occurs in the transmitted frequency in the actual device. If the magnitude of the Doppler shift caused by the rotation of the antenna is about the same as the fluctuation range of the frequency transmitted by the wireless tag, the frequency fluctuation caused by the Doppler shift cannot be distinguished from the fluctuation of the frequency transmitted by the wireless tag. Therefore, regardless of the frequency analysis method, the Pseudo-doppler method needs to move the antenna at a speed at which a certain amount of Doppler shift occurs.

  If the turntable is rotated at high speed, the window width becomes narrow. However, according to the present invention, the azimuth angle from which the radio wave arrives is determined using not the Fourier transform but the degree of coincidence between the measurement signal output from the receiving unit and the approximate model. Therefore, it is possible to increase the Doppler shift by rotating the rotating disk at high speed. That is, it is not necessary to enlarge the rotating disk in order to increase the speed of the antenna fixed to the rotating disk. Therefore, it is possible to reduce the size of the turntable. Further, in order to increase the angular resolution, it is only necessary to narrow the pitch for numerical search, so it is easy to increase the angular resolution.

  In the present invention, the azimuth angle can be accurately estimated for the following reason while reducing the amount of calculation. In the present invention, since the antenna rotates and repeats approaching and separating from the wireless tag, Doppler shift occurs in the radio wave received by the antenna. Therefore, the frequency of the radio wave received by the antenna increases with the rotational movement of the antenna. fluctuate. For this reason, if the radio wave received by the antenna is modeled strictly, a complicated model is generated and the amount of calculation increases.

  Therefore, in the present invention, an approximate model representing the measurement signal is considered. The radio wave transmitted by the wireless tag is actually a spherical wave, but the approximate model according to the present invention obtains the radio wave transmitted by the wireless tag by approximating it as a plane wave.

  The approximation as a plane wave is that the wireless tag is assumed to exist in the same direction with respect to the antenna regardless of the position of the antenna. As the distance from the antenna to the wireless tag is longer than the rotation radius of the antenna, the direction change of the wireless tag relative to the antenna is smaller even if the antenna rotates. In the present invention, as described above, the turntable can be reduced in size. If the turntable is small, the radius of rotation of the antenna is also small. If the turning radius of the antenna is reduced, the distance from the antenna to the wireless tag is likely to be longer than the turning radius of the antenna. Therefore, the approximation to the plane wave can estimate the direction of arrival of the radio wave with an accuracy close to that when the radio wave received by the antenna is strictly modeled in the present invention in which the rotating disk can be downsized. Since the arrival direction of radio waves can be estimated with an accuracy close to that of a strictly modeled model, the approximation using a plane wave can accurately estimate the azimuth angle in the present invention in which the rotating disk can be downsized.

  An approximate model using approximation as a plane wave will be described in detail later, but there is no square root that exists when it is modeled strictly. Therefore, the amount of calculation can be greatly reduced as compared with the case of strict modeling.

  Furthermore, in the present invention, the low frequency signal generator generates a low frequency signal. Since the low frequency signal has a center frequency of 0 Hz, the frequency may be negative.

  By approximating the radio wave transmitted by the wireless tag to a plane wave, a phase error occurs when the approximate model is not approximated. Here, since the frequency fluctuates due to the Doppler shift due to the rotation of the antenna, the state where the frequency is negative can be regarded as a state where the rotation direction of the antenna is reversed with respect to the state where the frequency is positive.

  The phase error generated in the approximate model is caused by a difference in distance between the distance from the wireless tag to the center of rotation of the antenna and the distance from the wireless tag to the antenna. Therefore, if the rotation direction of the antenna is reversed, a phase error also occurs in the opposite direction.

  When the frequency is positive and when the frequency is negative, the phase errors are opposite to each other. Therefore, if the interval for calculating the degree of coincidence includes the interval where the frequency is positive and the interval where the frequency is negative, The phase error can be canceled out.

  The sign of the frequency is reversed when the antenna, the rotation center of the antenna, and the wireless tag are aligned. Therefore, every time the antenna rotates 180 degrees, the positive and negative frequencies are reversed.

  Since the direction determination unit of the present invention sets the interval for calculating the degree of coincidence as the interval in which the antenna rotates 360 degrees, the phase error when the frequency is positive and the phase error when the frequency is negative are canceled out. become. Therefore, an approximate model with a small phase error with respect to the actual measurement signal can be determined as an approximate model that matches the measurement signal. As a result, the accuracy of the azimuth angle determined from the approximate model is further improved.

  In addition, the approximation model can be simplified by setting the interval for calculating the degree of coincidence as the interval in which the antenna rotates 360 degrees, and accordingly, B, C, and DC using the amplitude A and the phase Ψ as parameters. The amount D of the offset component can be calculated by simultaneous equations. Therefore, the amplitude A, the phase Ψ, and the amount D of the DC offset component of the incoming wave can be excluded from the unknown parameters in Equation 6. Therefore, since there are fewer unknown parameters that need to be searched, the calculation can be performed quickly.

方向決定部は、Ｉ成分信号をＩ_ｇｅｔ、Ｑ成分信号をＱ_ｇｅｔとしたとき、一致度として式１２で表す残差ｅが最小となる複数の到来波の方位角の組み合わせを探索するものであって、

式１２をＢで偏微分した式と、式１２をＣで偏微分した式と、式１２をＤ_Ｉで偏微分した式と、式１２をＤ_Ｑで偏微分した式をそれぞれ０とすることで立式される連立方程式を解くことによりＢ、Ｃ、Ｄ_Ｉ、Ｄ_Ｑを算出し、算出したＢ、Ｃ、Ｄ_Ｉ、Ｄ_Ｑを用いて、残差ｅが最小となる複数の到来波の方位角の組み合わせを探索し、一致度を算出する区間を、アンテナが３６０度回転する区間とする。 The invention according to claim 2 for achieving the above object is a radio wave arrival direction estimation device for estimating the arrival direction of a radio wave having a preset constant frequency transmitted by the radio tag (300),
A turntable (112), a drive unit (113) that rotates the turntable at a predetermined period, and a radio wave that is fixed to a position other than the center of rotation on the turntable and transmitted by the wireless tag is received. Generates the I component signal, which is the I component of the low frequency signal, and the Q component signal, which is the Q component of the low frequency signal, by reducing the frequency of the radio wave received by the antenna (111) so that the center frequency becomes 0 Hz. A receiving unit (100) that outputs an I component signal and a Q component signal,
A model obtained by converting the I component and Q component of a composite wave of a plurality of incoming waves into an I component signal and a Q component signal, respectively, and using an approximation in which the radio wave transmitted by the wireless tag is a plane wave, A model representing each of the Q component signals, the I component approximate model and the Q component approximate model including the amounts of azimuth, phase, amplitude, and DC offset component representing the azimuth in which the radio wave arrives as unknown parameters; The degree of coincidence representing the degree of coincidence between the component signal and the Q component signal is calculated while changing unknown parameters of the I component approximate model and the Q component approximate model, thereby matching the I component signal and the Q component signal. The I component approximate model and the Q component approximate model are determined, and the azimuth angle in the determined I component approximate model and Q component approximate model is the direction in which the radio wave arrives. Comprising a, a direction determination unit (230) for determining a,
The I component approximate model and the Q component approximate model are the frequency of the radio wave transmitted by the wireless tag is f _RF , the radius of rotation of the antenna is R, the speed of light is v _c , the time is t, and the amount of the DC offset component in the I component signal is D The amount of the DC offset component in the _I and Q component signals is D _Q , the azimuth angle of each incoming wave is φ _m , the amplitude of each incoming wave is A _m , the phase of each incoming wave is Ψ _m , the number of incoming waves is N, When the I component approximate model is I _ref and the Q component approximate model is Q _ref , the I component approximate model is a model represented by Equation 7, Equation 9, Equation 10, and Equation 11, and the Q component approximate model is Equation 8. , Equation 9, Equation 10, and Equation 11;

The direction determining unit searches for a combination of azimuth angles of a plurality of arriving waves that minimize the residual e represented by Equation 12 as the degree of coincidence when the I component signal is I _get and the Q component signal is Q _get. There,

To the expression obtained by partially differentiating Equation 12 with B, a formula obtained by partially differentiating the equation 12 in C, a formula obtained by partially differentiating Equation 12 with D _I, respectively 0 expressions obtained by partially differentiating Equation 12 with D _Q B, C, D _I , and D _Q are calculated by solving the simultaneous equations expressed by the following, and a plurality of incoming waves that minimize the residual e are calculated using the calculated B, C, D _I , and D _Q A section in which a combination of azimuth angles is searched and the degree of coincidence is calculated is defined as a section in which the antenna rotates 360 degrees.

  The invention according to claim 2 is an invention in which the measurement signal in the invention according to claim 1 is divided into an I component signal and a Q component signal. Therefore, the same effect as that of the invention according to claim 1 can be obtained.

  In addition, according to the present invention, the measurement signal is divided into an I component signal and a Q component signal, and the degree of coincidence between the I component signal and the I component approximate model and the degree of coincidence between the Q component signal and the Q component approximate model are summarized. The degree of coincidence expressed is calculated. The reason why the measurement signal is divided into the I component signal and the Q component signal is that the azimuth, which is an unknown parameter in the I component approximate model and the Q component approximate model, can be changed over a range wider than 180 degrees. This is because the azimuth angle search range can be made wider than 180 degrees.

  As will be described in detail later, the I component approximation model and the Q component approximation model may have the same waveform as a waveform having a different azimuth angle and a phase difference. For this reason, when the azimuth angle search range is wider than 180 degrees, the azimuth angle cannot be determined using only one of the I component approximate model and the Q component approximate model.

  However, if one of the I component approximation model and the Q component approximation model substitutes a parameter that becomes the same waveform as the waveform having an azimuth angle different by 180 degrees in the other approximation model, the azimuth angle in the other approximation model is Two waveforms that are 180 degrees different from each other are different waveforms. Therefore, even if the azimuth angle search range is wider than 180 degrees, the azimuth angle can be determined by using the two models of the I component approximate model and the Q component approximate model.

  In the invention according to claim 3, the direction determining unit is configured to combine the azimuth angles of a plurality of arriving waves that minimize the residual energy calculated by an expression obtained by removing the term of only the measurement signal from the expression for calculating the residual e. Is searched for a combination of azimuth angles of a plurality of incoming waves that minimize the residual e.

  In this way, it is possible to search for a combination of azimuth angles of a plurality of arriving waves that minimize the residual e, without calculating the term of only the measurement signal, thereby reducing the amount of calculation.

  In the invention according to claim 4, the direction determining unit includes a plurality of residual energy calculated by a formula obtained by removing a term of only the I component signal and a term of only the Q component signal from the formula for calculating the residual e. By searching for a combination of azimuth angles of arriving waves, a combination of azimuth angles of a plurality of arriving waves that minimize the residual e is searched.

  Even in the present invention, it is possible to search for a combination of azimuth angles of a plurality of arriving waves that minimize the residual e without calculating the term of only the measurement signal.

The invention according to claim 5 further includes a storage unit (220) that stores a calculated value of a z-factor term calculated by inputting a plurality of azimuth angles and times into a z-factor term that can be calculated by determining z. And
The direction determination unit searches for a combination of azimuth angles of a plurality of incoming waves that minimize the residual e, using the calculated value of the z-factor term stored in the storage unit.

  In this way, if a combination of azimuth angles of a plurality of incoming waves that minimize the residual e is searched using the calculated value of the z-factor term calculated in advance, the amount of calculation when searching for the azimuth angle is reduced. Therefore, the azimuth angle can be estimated quickly.

  A sixth aspect of the present invention is a radio wave arrival direction estimation system including the radio wave arrival direction estimation device of the present invention and a wireless tag.

It is a block diagram of the radio wave arrival direction estimation system of the embodiment. 6 is a diagram illustrating a relative position between an antenna 111 and a wireless tag 300. FIG. It is a figure explaining plane wave approximation. It is a figure showing the plane containing the s-axis and z-axis of FIG. It is a figure which compares and shows the waveform of an approximate model, and the waveform without approximation. It is a figure explaining the reason for which the phase of an approximate model advances. It is a figure which compares the waveform of an I component approximation model, and the I component signal of the waveform without approximation. It is a figure which compares the waveform of a Q component approximation model, and the Q component signal of the waveform without approximation. FIG. 10 is a diagram illustrating a configuration of a receiving unit 100 in Modification 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The radio wave arrival direction estimation system according to this embodiment includes the wireless tag reader 1 and the wireless tag 300 shown in FIG. The wireless tag reader 1 functions as a radio wave arrival direction estimating device.

The wireless tag 300 transmits an unmodulated wave having a predetermined carrier frequency f ₀ set in advance. The wireless tag 300 is of an active type and may transmit radio waves continuously, but it is preferable to transmit radio waves intermittently from the viewpoint of battery life. The wireless tag 300 is carried by a person and has a size that can be easily accommodated in a pocket of clothes.

  The wireless tag reader 1 includes a reception unit 100 and a signal processing unit 200, and the reception unit 100 includes an antenna unit 110 and a low frequency signal generation unit 120.

[Description of Antenna Unit 110]
The antenna unit 110 includes an antenna 111, a turntable 112, and a drive unit 113. The antenna 111 is fixed to the outer peripheral edge of the turntable 112. There is no particular limitation on the shape and size of the antenna 111 as long as it can receive an unmodulated wave transmitted by the wireless tag 300 and can be fixed to a position other than the rotation center on the turntable 112.

  The turntable 112 is rotated by the drive unit 113. The shape of the rotating disk 112 is not limited to the disk shape, but is preferably not eccentric with respect to the driving unit 113. The turntable 112 is sized so that it can easily be set indoors. For example, a disk having a diameter of 10 cm. When the turntable 112 rotates, the antenna 111 fixed on it also rotates at the same time.

  The drive unit 113 includes a motor, and rotates the turntable 112 at a constant cycle. This fixed period is determined from the rotation speed of the antenna 111 determined from the Doppler shift to be secured and the rotation radius of the antenna 111.

[Description of Low Frequency Signal Generation Unit 120]
The low frequency signal generation unit 120 includes a band pass filter 121, a local oscillator 122, a mixer 123, a low pass filter 124, an A / D converter 125, a phase shifter 126, a mixer 127, a low pass filter 128, and an A / D converter 129. I have.

  The bandpass filter 121 uses a frequency range determined from a Doppler shift generated by rotation of the antenna 111 around the frequency of the radio wave transmitted by the wireless tag 300 as a pass frequency band. The band-pass filter 121 receives a reception signal received by the antenna 111 and removes noise from the reception signal. In addition, on the transmission path where the received signal is sent from the antenna 111 to the band pass filter 121, between one end of the rotation side transmission path rotating with the turntable 112 and one end of the non-rotation side transmission path facing the one end, The antenna pattern is transmitted oppositely by facing the antenna pattern. However, a slip ring may be used instead of wireless transmission.

The local oscillator 122 generates a local oscillation signal having the same frequency as the carrier frequency f ₀ transmitted by the wireless tag 300. The mixer 123 mixes the local oscillation signal and the signal output from the band-pass filter 121, and outputs a signal having a frequency that is the sum and difference of the frequency of the local oscillation signal and the frequency output from the band-pass filter 121. .

The low-pass filter 124 extracts a signal having a frequency that is the difference between the frequency of the local oscillation signal and the frequency output from the band-pass filter 121 from the signal output from the mixer 123. Since the frequency of the local oscillation signal is the same as the carrier frequency f ₀ transmitted by the wireless tag 300, the signal extracted by the low-pass filter 124 has a center frequency of 0 Hz. Hereinafter, the signal output from the low-pass filter 124 is referred to as an I component signal. The A / D converter 125 converts the I component signal that is an analog signal extracted by the low-pass filter 124 into a digital signal.

  The phase shifter 126 shifts the phase of the local oscillation signal by 90 °. The mixer 127 mixes the local oscillation signal whose phase is shifted by 90 ° by the phase shifter 126 and the signal output from the bandpass filter 121. The low pass filter 128 extracts a signal having a frequency that is the difference between the frequency of the local oscillation signal and the frequency output from the band pass filter 121 from the signal output from the mixer 127. However, the signal output from the low-pass filter 128 is 90 ° out of phase with the I component signal. A signal output from the low-pass filter 128 is hereinafter referred to as a Q component signal. This Q component signal also has a center frequency of 0 Hz. The A / D converter 129 converts the Q component signal, which is an analog signal extracted by the low-pass filter 128, into a digital signal. The I component signal and the Q component signal output from the A / D converters 125 and 129 correspond to the low frequency signal and the measurement signal in the claims.

[Description of Signal Processing Unit 200]
The signal processing unit 200 includes a signal acquisition unit 210, a storage unit 220, and a direction determination unit 230. The signal acquisition unit 210 acquires I component signals and Q component signals from the A / D converters 125 and 129, and stores the acquired signals in the storage unit 220.

  The wireless tag 300 transmits an unmodulated wave. However, the distance between the antenna 111 and the wireless tag 300 changes as the turntable 112 rotates. Therefore, the frequency of the radio wave received by the antenna 111 varies. Therefore, the frequency of the I component signal and the Q component signal acquired by the signal acquisition unit 210 also varies.

  The storage unit 220 stores an equation for calculating the residual energy E. This expression is specifically Expression 71 described later. In addition, the storage unit 220 also stores calculation values calculated in advance by changing the time t and the azimuth angle φ for the coefficient S used in the equation for calculating the residual energy E.

  The residual energy E is a value calculated by a formula obtained by removing the term of only the measurement signal from the formula for calculating the residual e. The residual e is a value obtained by calculating a difference between the measurement signal and an approximate model obtained by modeling the measurement signal by plane wave approximation. Since the equation for calculating the residual energy E is substantially an equation for calculating the residual e, the equation for calculating the residual energy E is also equivalent to the equation for calculating the residual e in the claims. To do.

In the present embodiment, the measurement signal is specifically an I component signal and a Q component signal. Therefore, the approximate model is also an I component approximate model I _{ref obtained by} modeling the I component signal, and the Q component signal is modeled. Q component approximate model Q _ref . First, the I component approximate model I _ref and the Q component approximate model Q _ref will be described.

[Explanation of I component approximate model and Q component approximate model]
In order to describe the I component approximate model I _ref and the Q component approximate model Q _ref , first, it is necessary to describe a model (hereinafter, a strict model) in which the received signal received by the antenna 111 is not approximated. .

FIG. 2 is a diagram illustrating the relative position between the antenna 111 and the wireless tag 300. As shown in FIG. 2, in the following description, it is assumed that the radio wave transmitted by the wireless tag 300 has a frequency f _RF , an amplitude A, and a phase Ψ _T. The rotation angular velocity of the antenna 111 is ω, and the rotation angle is θ. If time t is used, θ = ωt. Further, the azimuth angle of the wireless tag 300 with respect to the reference azimuth is φ, the angle formed by the line connecting the center position of the rotating disk 112 and the wireless tag 300 with respect to the plane including the rotating disk 112 is the elevation angle δ, and the antenna 111 Let R be the radius of rotation.

The distance between the wireless tag 300 and the center of the turntable 112 is L ₀ , the distance between the wireless tag 300 and the antenna 111 is _LR, and the position of the wireless tag 300 is P _t (x _t , y _t , z _t ), the center position of the turntable 112 is P ₀ (x ₀ , y ₀ , z ₀ ), and the position of the antenna 111 is P _R (x _R , y _R , z _R ).

If the initial angle of the antenna 111 and a x-axis direction, the position P _R of the antenna 111 can be expressed by the following equation 13.

Further, the position P _t of the wireless tag 300 can be expressed by Expression 14 using the center position P ₀ (x ₀ , y ₀ , z ₀ ), the elevation angle δ, and the azimuth angle φ of the turntable 112.

Distance _{L R} between the wireless tag 300 and the antenna 111 can be expressed by Equation 15. By substituting Equations 13 and 14 into Equation 15 and rearranging, Equation 16 is obtained.

Since Equation 16 is obtained when the velocity of light and _{v c,} the received signal _{V R} by the antenna 111 receives can be expressed by Equation 17.

Usually, the frequency of radio waves is high because it radiates into the air. Therefore, since the high frequency of the received signal V _R, lowering the frequency and local signals and mixing. Frequency _{f LO,} the mixing with the signal of the phase [psi _LO, the received signal _{V R} after mixing the formula 18. Equation 18 is an exact model.

_LR increases or decreases as the antenna 111 moves circularly. Thus, from Equation 18, the frequency of the received signal V _R after mixing, it can be seen that vary with time. Therefore, in the Fourier transform methods require a certain amount of window width to do good analysis accuracy can not be analyzed accurately received signal V _R after mixing.

  Therefore, in this embodiment, the azimuth angle φ is estimated by model matching. In the present embodiment, the elevation angle δ is assumed to be 0 degree, that is, cos δ = 1. The wireless tag reader 1 is a device that estimates the arrival direction of radio waves transmitted by the wireless tag 300, and the wireless tag 300 is carried by a person. Further, the wireless tag reader 1 is usually installed at a height that is almost the same as the height at which a person moves, such as on the ground. Therefore, the elevation angle δ can be considered to be substantially constant without estimation. Therefore, in order to simplify the calculation, in the present embodiment, the elevation angle is set to 0 degree, that is, cos δ = 1.

cos [delta] = as 1, rigorous model shown in Equation 18 includes a distance _{L R} between the wireless tag 300 and the antenna 111, the distance _{L R,} as shown in Equation 15, the entire expression is the square root Is in. Therefore, using the exact model of Equation 18 requires complex calculations. In the present embodiment, in order to simplify the calculation, an approximate model is used in which the radio wave transmitted by the wireless tag 300 is approximated as a plane wave and the exact model shown in Expression 18 is approximated.

  Considering that the radio wave transmitted by the wireless tag 300 is a plane wave, the radio wave received by the antenna 111 is parallel to the radio wave from the wireless tag 300 toward the rotation center of the antenna 111 regardless of the position of the antenna 111. Can think.

In this case, as shown in FIG. 3, the radio wave reaches the antenna 111, to the radio wave from the wireless tag 300 to the rotational center of the antenna 111 and transmitted from the approximate wave source 300a on the plane perpendicular P _L Can be considered.

In FIG. 3, L _R ′ is a distance from the approximate radio wave source 300a to the antenna 111. S is an axis representing the direction of the azimuth angle φ. FIG. 4 is a diagram showing a plane including the s-axis and the z-axis.

4 that the approximate distance L _R ′ from the approximate radio wave source 300a to the antenna 111 can be expressed by Equation 19.

'Is used in place of _{L R,} i.e., the distance _{L R} approximate distance _{L R} for formula 18' approximate distance _{L R} shown in equation 19 by substituting, further, a [delta] = 0 i.e. cos [delta] = 1, the phase Summing up as ψ ′, Equation 20 is obtained. Equation 20 is hereinafter referred to as an approximate model.

Unlike Equation 17, Equation 20 has a simple shape with no square root. In the present embodiment, an I component approximate model I _ref and a Q component approximate model Q _ref derived based on the approximate model shown in Expression 20 are used.

The reason why the I component approximate model I _ref and the Q component approximate model Q _ref are used is that the approximate model of Expression 20 causes a phase error with respect to the actual received waveform. FIG. 5 shows a comparison between a waveform of an approximate model in which appropriate parameters are set and a waveform without approximation, that is, a waveform of an exact model.

  Compared to the waveform without approximation, the waveform of the approximate model is advanced in phase. The reason why the waveform phase of the approximate model advances is that, as shown in FIG. 6, the distance until the radio wave reaches is short in the approximate model.

6, the difference between the distance L _R and the approximate distance L _{R 'between} the wireless tag 300 and the antenna 111, the larger the perpendicular to the DOA angle of the antenna 111. In addition, the maximum value of the difference is larger as the wireless tag 300 is closer to the antenna 111, and is larger as the rotation radius R of the antenna 111 is larger. Therefore, the error of the azimuth angle φ of the wireless tag 300 obtained using the approximate model is larger as the angle of the antenna 111 is perpendicular to the radio wave arrival direction, the wireless tag 300 is closer to the antenna 111, and the antenna 111 The larger the rotation radius R, the larger.

The I component approximate model I _ref and the Q component approximate model Q _ref used in the present embodiment are models of signals obtained by dropping the center frequency of the approximate model of Expression 20 to 0 Hz and dividing it into an I component and a Q component.

In order to reduce the center frequency of the received signal V _R to 0Hz it may be mixed signals having the same frequency as the frequency f _RF of the radio tag 300 transmits the received signal V _R. An expression representing the I component of the signal after mixing is obtained by setting f _IF = 0 in Expression 18. Further, the Q component of the signal after mixing is orthogonal to the I component of the signal after mixing. Therefore, the equations representing the I component and Q component of the signal after mixing can be represented by Equation 21.

Since the phase ψ _T and the phase ψ _LO are fixed values, the equations representing the I component and the Q component of the signal after mixing can be expressed by Equation 22.

By substituting _LR ′ shown in Equation 19 for _LR in Equation 22, Equation 23 is obtained. Expression 23 is an I component approximate model I _ref and a Q component approximate model Q _ref .

FIG. 7 shows a comparison between the waveform of the I component approximate model I _ref corresponding to the waveform of the approximate model in FIG. 5 and the I component signal of the waveform without approximation. FIG. 8 shows a comparison between the waveform of the Q component approximate model Q _ref corresponding to the waveform of the approximate model in FIG. 5 and the Q component signal of the waveform without approximation. 7 and 8 are cases where the wireless tag 300 is present in the 0 degree direction.

As shown in FIGS. 7 and 8, both the I component approximate model I _ref and the Q component approximate model Q _ref have a phase error with respect to the waveform without approximation. However, unlike FIG. 5, in both the I component approximate model and the Q component approximate model, the phase is advanced or delayed with respect to the waveform without approximation.

More specifically, from 0 degrees to 180 degrees, the waveforms of the I component approximate model I _ref and the Q component approximate model Q _ref are delayed in phase from the waveform without approximation, and the phase is advanced from 180 degrees to 360 degrees. .

  The reason is as follows. Since the center frequency is set to 0 Hz, when the antenna 111 is moving away from the wireless tag 300, the I component signal and the Q component signal have negative frequencies due to Doppler shift. In the section where the frequency is negative, the rotation direction is reversed from the section where the frequency is positive. Since the rotation direction is reversed, the phase shift direction is also opposite to the section where the positive frequency is obtained.

  In this embodiment, the center frequency is set to 0 Hz in order to cause both of the phase lag and the phase advance and cancel each other out of the phase lag and the phase advance.

[Reason for using two approximate models]
However, if the center frequency is 0 Hz, the azimuth angle φ may not be uniquely determined unless the measurement signal is divided into an I component signal and a Q component signal and the I component signal and the Q component signal are not matched together.

This is because both the I component approximate model I _ref and the Q component approximate model Q _ref may have the same waveform even if the azimuth angle φ is different by 180 degrees. This will be explained by changing the formula.

In Expression 23, when φ + π is substituted for φ and −Ψ is substituted for Ψ, Expression 24 is obtained.

Since cos (a−π) = − cos (a), Expression 24 can be transformed into Expression 25.

Since cos (−a) = cos (a) and sin (−a) = − sin (a), Expression 25 can be transformed into Expression 26.

I component approximate model _{I ref} in Equation 26 is the same as the I component approximation model _{I ref} in Equation 23. In other words, even if the azimuth angle φ is different by 180 degrees, the I component approximate model I _ref cannot be distinguished from each other if the phase Ψ is reversed. However, since the Q component approximate model Q _ref in Expression 23 is different from the Q component approximate model Q _ref in Expression 26, (φ, Ψ) and (φ + π, −Ψ) can be distinguished from the Q component approximate model Q _ref. I understand.

However, the Q component approximation model Q _ref cannot distinguish between (φ, ψ) and (φ + π, −ψ + π). This will be described next.

In Expression 23, when φ + π is substituted for φ and −Ψ + π is substituted for Ψ, Expression 27 is obtained.

Since cos (a−π) = − cos (a), Expression 27 can be transformed into Expression 28.

Since cos (a + π) = − cos (a) and sin (a + π) = − sin (a), Expression 28 can be transformed into Expression 29.

Since cos (−a) = cos (a) and sin (−a) = − sin (a), Expression 29 can be transformed into Expression 30.

Q component approximate model _{Q ref} in Equation 30 is the same as the Q component approximation model _{Q ref} in Equation 23. Therefore, the Q component approximate model Q _ref cannot distinguish between (φ, ψ) and (φ + π, −ψ + π). However, since the I component approximate model I _ref in Expression 23 is different from the I component approximate model I _ref in Expression 30, (φ, Ψ) and (φ + π, −Ψ + π) can be distinguished from the I component approximate model I _ref. I understand.

As described above, the I component approximate model I _ref and the Q component approximate model Q _ref of Expression 23 cannot be individually distinguished from the case where the azimuth angle φ is shifted by 180 degrees. Therefore, when searching over an angular range wider than 180 degrees, both the I component approximate model I _ref and the Q component approximate model Q _ref are required.

[Explanation of approximate model of synthesized wave]
The approximate model shown in Equation 30 is a single wave model. In an environment where the wireless tag reader 1 estimates the arrival direction of radio waves, it is assumed that multipath occurs. Therefore, it is necessary to consider an approximate model of a combined wave in which a plurality of incoming waves generated by multipath are combined.

Hereinafter, when the I component approximate model I _ref and the Q component approximate model Q _ref are simply expressed, they mean the I component approximate model I _ref and the Q component approximate model Q _ref of the combined wave, respectively. The I component approximate model I _ref and the Q component approximate model Q _ref are models obtained by adding a plurality of waves of the model shown in Expression 23, and can be expressed by Expression 31.

When Expression 31 is generalized with N as the number of incoming waves to be combined, Expression 32 is obtained. In Equation 32, D _I and D _Q are DC offset components included in the I component signal and the Q component signal, respectively. This DC offset component is generated due to temperature characteristics of various elements constituting the receiving unit 100. Note that the DC offset component occurs even with a single wave, but has been omitted in the previous equations.

When a part of Expression 32 is replaced with a variable z shown in Expression 33, Expression 34 is obtained.

Further, when the amplitude A and the phase Ψ are converted into the variable B _m and the variable C _m shown in Expression 35, a part of Expression 34 can be converted into Expression 36.

Using Expression 36, Expression 34 can be expressed as Expression 37.

The I component signal is I _get (t), the Q component signal is Q _get (t), the degree of coincidence, the residual sum of squares of the I component signal I _get and the I component approximate model I _ref , and the Q component signal Q _get And the residual sum of squares of the Q component approximate model Q _ref (hereinafter referred to as residual e). The residual e can be expressed by Equation 38 in a continuous time system. In Equation 38, T is a time interval (hereinafter referred to as a coincidence calculation section) in which a residual e, which is a coincidence, is calculated. The coincidence degree calculation section is, for example, a time during which the antenna 111 rotates 360 degrees.

Actual calculations are performed in a discrete time system. The residual e in the discrete time system is expressed by Equation 39. In Equation 39, k is the sampling number, K is the total number of samplings, and k and K correspond to t and T in the continuous time system, respectively.

The approximate model that minimizes the residual e best represents the waveform of the measurement signal. By replacing the characters shown in Equation 35, the unknown parameters in Equation 39 become Z _m , B _m , C _m , D _I and D _Q.

The wireless tag reader 1 of the present embodiment is a device that estimates an azimuth angle φ _m that is a radio wave arrival direction, and the azimuth angle φ _m is a search parameter. When a specific value is applied to the azimuth angle φ _m , z _m at each time t can be calculated as can be seen from Equation 33.

Equation 38 includes an I component approximate model I _ref and a Q component approximate model Q _ref , and as can be seen from Equation 37, these parameters include B _m , C _m , D in addition to z _m as parameters. _I and D _Q are included.

In the present embodiment, these B _m , C _m , D _I , and D _Q are obtained not by searching but by solving simultaneous equations. A formula modification for deriving the simultaneous equations will be described. When the equation 39 is partially differentiated by B _n , C _n , D _I , and D _Q , equations 40, 41, 42, and 43 are obtained. Note that n is a number indicating what number of incoming waves.

Further, from Expression 37, each expression shown in Expression 44 is obtained.

When the right side of Expression 40, Expression 41, Expression 42, and Expression 43 is expanded and Expression 37 and Expression 44 are substituted, Expression 45, Expression 46, Expression 47, and Expression 48 are obtained.

Here, variables determined only by the azimuth angle φ _m and the measurement signal are summarized as shown in Equation 49.

By substituting Equation 49 into Equation 45, Equation 46, Equation 47, and Equation 48, Equation 50, Equation 51, Equation 52, and Equation 53 are obtained.

Since it is desired to obtain B _m , C _m , D _I , and D _Q that minimize the residual e, formulas in which the left side of Formula 50 to Formula 53 is 0 are considered. That is, Formula 54 to Formula 57 are considered.

As shown in Equation 39, the residual e is the square of the difference between the I component signals I _get and Q _get that are measurement signals and the approximate models I _ref and Q _ref , so the residual e is B _m , C _m , D _I , D _Q are quadratic forms convex downward. Therefore, B _m , C _m , D _I , and D _Q that minimize the residual e can be obtained for each azimuth angle φ _m by solving the four simultaneous equations of Expression 54 to Expression 57.

From Equation 54 to Equation 57, for each nth (n = 1 to N) arriving wave, four simultaneous equations are obtained for each m regarding B _m , C _m , D _I , and D _Q. If the azimuth angles φ _m and φ _n are applied, z _m and z _n can be obtained. Therefore, if the azimuth angles φ _m and φ _n are applied, the simultaneous equations of Expressions 54 to 57 can be solved. That is, when the azimuth angles φ _m and φ _n are applied, the unknown parameters B _m , C _m , D _I and D _Q can be calculated. Since Expression 58 is obtained from Expression 35, when B _m and C _m are obtained, the amplitude A _m and the phase Ψ _m can also be determined.

Since B _m , C _m , D _I , and D _Q can be calculated by solving the simultaneous equations of Expression 54 to Expression 57 in this way, the search parameter is only a combination of the azimuth angles φ _m of a plurality of waves, and the residual e is The approximation model that minimizes can be determined.

Further, in the present embodiment, the following equation modification is performed on the equation 39. When Formula 39 is expanded, Formula 59 is obtained.

Further, a coefficient S shown in the following equation 60 is defined.

From Expression 37, the character part of the second term on the right side of Expression 59 is represented by Expression 61, and the character part of the fifth term on the right side of Expression 59 is represented by Expression 62.

Further, the square of I _{ref included in} the first term on the right side of Equation 59 is expressed as Equation 63 using Equation 37.

When the curly brackets in the right side of Expression 63 are expanded, the right side of Expression 64 is obtained.

When the third term on the right-hand side of Expression 59 is expressed using Expression 63, Expression 64, and Expression 60, Expression 65 is obtained.

In the expression 65, S _sij means the product of S _si and S _sj , S _sicj means the product of S _si and S _cj , S _cisj means the product of S _ci and S _sj , and S _scij is It means the product of S _ci and S _cj .

The residual sum of squares of the Q component signal Q _get and the Q component approximate model Q _ref in Equation 59 is also modified in the same manner as the residual sum of squares of the I component signal I _get and the I component approximate model I _ref . First, the square of Q _{ref included in} the sixth term on the right side of Equation 59 is expressed as Equation 66 using Equation 37.

When the curly brackets in the right side of Expression 66 are expanded, the right side of Expression 67 is obtained.

When the sixth term on the right side of Formula 59 is expressed using Formula 66, Formula 67, and Formula 60, Formula 68 is obtained.

From Expression 65 and Expression 68, Expression 69 is obtained.

Using Expression 61, Expression 62, and Expression 69, Expression 59 can be written as Expression 70.

This equation 70 may be calculated as it is to obtain the residual e. However, since the first term on the right side and the second term on the right side of Equation 70 are the square terms of the I component signal I _get and the Q component signal Q _get , they are always positive numbers and the azimuth angle φ to be searched for _{Unaffected by} the value of _m . Therefore, the residual energy E from the equation 70 excluding the first term and the second term on the right side, which are terms of only the measurement signal, that is, the I component signal I _get and the Q component signal Q _get is considered. The residual energy E is expressed by Equation 71.

  In the present embodiment, the residual energy E corresponds to the degree of coincidence of claims, and the storage unit 220 stores the formula 71.

  The storage unit 220 also stores a table of calculated values calculated by changing various values of the variable z for each coefficient S shown in Expression 72. This table is hereinafter referred to as a pre-calculation table. Each coefficient S shown in Expression 72 is a coefficient whose value can be calculated if the variable z is determined, and corresponds to a z-factor term in the claims.

The variable z has time t and azimuth angle φ as variables as shown in Expression 33. In the pre-calculation table, the time t is changed by 2π / ω for each sampling period, and the azimuth angle φ is changed at an angular pitch determined based on the required angular resolution, and the time t and the azimuth angle φ are changed. A calculated value obtained by calculating the coefficient S shown in Expression 72 is included for each combination.

The direction determining unit 230 determines a combination of arrival directions (that is, azimuth angle φ _m ) of a plurality of waves that minimize the residual energy E, and determines the combination of the arrival directions as an arrival direction in which radio waves actually arrive. Suppose there is. The direction determination unit 230 performs the following steps 1 to 9 to determine a combination of arrival directions of a plurality of waves that minimize the residual energy E.

  In step 1, the I component signal and Q component signal for the coincidence calculation section are acquired from the storage unit 220 from the latest I component signal and Q component signal. In the present embodiment, the coincidence degree calculation section is a time section in which the antenna 111 rotates 360 degrees.

In step 2, the extracted I component signal and Q component signal are corrected as shown in Expression 73. In Expression 73, I _get ′ and Q _get ′ are the I component signal and the Q component signal extracted in step 1. _Ac is the non-contact portion amplitude ratio. The non-contact portion is between one end of the rotation-side transmission path on the transmission path of the antenna 111 and one end of the non-rotation-side transmission path facing the one end, and the non-contact portion amplitude ratio is the rotation-side transmission path It is the ratio of the amplitude of the signal at one end to the amplitude at one end of the non-rotation side transmission path. This non-contact portion amplitude ratio _Ac changes with time. The reason why the non-contact portion amplitude ratio _Ac changes with time is that there is a circuit or the like around the turntable 112, and therefore the radio wave environment of the noncontact portion varies depending on the rotational position of the turntable 112. The non-contact portion amplitude ratio _Ac is measured and set in advance.

The reason why the calculation in step 2 is performed is that the I component approximate model I _ref and the Q component approximate model Q _ref do not consider the change in amplitude in the non-contact portion, and therefore the I component signal I _get to be compared with these models, This is because the Q component signal Q _{get is} also preferably removed from the influence of the amplitude change in the non-contact portion.

  In step 3, for the incoming waves for N waves, a combination of arrival directions, that is, a combination of azimuth angles φ to be searched is determined. This combination may be determined in advance. In step 4, for each combination of arrival directions of incoming waves determined in step 3, calculated values are obtained from the pre-calculation table.

In step 5, the coefficient S shown in Equation 60 is calculated using the I component signal I _get and the Q component signal Q _get corrected in step 2.

In Step 6, for each combination of arrival directions determined in Step 3, the simultaneous equations shown in Equations 54 to 57 are solved, and B _m , C _m , D _I , and D _Q are obtained for each combination of arrival directions. .

  In step 7, using the calculated value obtained in step 4 and the calculated value calculated in steps 5 and 6, the residual energy E shown in equation 71 is calculated for each arrival direction of the incoming wave determined in step 3. To do. In step 8, the minimum value of the residual energy E calculated in step 7 is determined. In step 9, the combination of arrival directions corresponding to the minimum value of the residual energy E determined in step 8 is set as the direction in which radio waves actually arrive. Of the directions in which radio waves actually arrive, for example, the direction having the maximum amplitude is the direction in which the wireless tag 300 is present.

[Effect of the embodiment]
In the present embodiment described above, the turntable 112 can be downsized. The reason is as follows. As already described, in the Pseudo-doppler method, it is necessary to rotate the antenna 111 at a speed at which a Doppler shift having a magnitude that can be distinguished from the fluctuation of the frequency f _RF transmitted by the wireless tag 300 occurs.

  If the turntable 112 is rotated at a high speed, the window width is narrowed. However, in the present embodiment, instead of Fourier transform, a residual energy E that collectively represents the degree of coincidence between the I component signal and the Q component signal output from the receiving unit 100 and the corresponding approximate models is calculated. That is, the azimuth angle φ is obtained by a method that is not restricted by the window width. Therefore, since the rotating disk 112 can be rotated at a high speed to increase the Doppler shift, it is not necessary to increase the rotating disk 112 in order to increase the speed of the antenna 111 fixed to the rotating disk 112. Therefore, the rotating disk 112 can be downsized. Further, in order to increase the angular resolution, it is only necessary to narrow the pitch for numerical search, so it is easy to increase the angular resolution.

Further, as already described, if the radio wave received by the antenna 111 is modeled strictly, the models 18 and 16 become complicated models, and the amount of calculation increases. Therefore, in this embodiment, an I component approximate model I _ref and a Q component approximate model Q _ref are used. The radio wave transmitted by the wireless tag 300 is actually a spherical wave, but the I component approximate model I _ref and the Q component approximate model Q _ref are obtained by approximating the radio wave transmitted by the wireless tag 300 as a plane wave. Yes.

The approximation as a plane wave is that the wireless tag 300 is considered to exist in the same direction with respect to the antenna 111 regardless of the position of the antenna 111. As the distance from the antenna 111 to the wireless tag 300 is longer than the rotation radius R of the antenna 111, the direction change of the wireless tag 300 relative to the antenna 111 is smaller even if the antenna 111 rotates. In the present embodiment, as described above, the turntable 112 can be reduced in size. If the turntable 112 is small, the rotation radius R of the antenna 111 is also small. The smaller the turning radius R of the antenna 111, compared to the rotation radius R of the antenna 111, the distance _{L R} from the antenna 111 to the wireless tag 300 is likely to be longer. Therefore, in the present embodiment in which the turntable 112 can be downsized, the approximation with a plane wave is less likely to be less accurate than when the radio wave received by the antenna 111 is modeled strictly. Since there is little decrease in accuracy with respect to the case of strict modeling, the approximation to the plane wave can estimate the radio wave arrival direction with high accuracy in the present embodiment in which the turntable 112 can be reduced in size.

Further, the I component approximate model I _ref and the Q component approximate model Q _ref of the present embodiment do not have a square root that exists in the exact model, as shown in Expression 23. Therefore, the amount of calculation can be greatly reduced as compared with the case of using a strict model.

In the present embodiment, B _m , C _m , D _I , and D _Q can be calculated using the simultaneous equations shown in Expressions 54 to 57, so that the incoming wave can be calculated from unknown parameters that need to be searched. The amplitude A _m , the phase Ψ _m , and the DC offset components D _I and D _Q can be excluded. Therefore, since there are fewer unknown parameters that need to be searched, the calculation can be performed quickly.

Further, in the present embodiment, the residual e shown in Equation 70 is not calculated, but the term of only the I component signal I _get and the term of only the Q component signal Q _{get as the} measurement signal V _get are calculated from the residual e. The residual energy E shown in Equation 71 is calculated. Accordingly, since it is possible to search for a combination of azimuth angles φ _m of a plurality of arriving waves that minimize the residual e, without calculating the term of only the I component signal I _get and the term of only the Q component signal Q _get . The amount of calculation can be reduced.

Further, in the present embodiment, the calculated value of the coefficient S shown in Formula 72 calculated in advance by changing the time t and the azimuth angle φ _m is stored in the storage unit 220, and the residual is calculated using the calculated value. The energy E is calculated. This also reduces the amount of calculation when estimating the azimuth angle φ _m , so that the azimuth angle φ _m can be estimated quickly.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following modification is also contained in the technical scope of this invention, Furthermore, the summary other than the following is also included. Various modifications can be made without departing from the scope. In the following description, elements having the same reference numerals as those used so far are the same as the elements having the same reference numerals in the previous embodiments unless otherwise specified. Further, when only a part of the configuration is described, the above-described embodiment can be applied to the other parts of the configuration.

<Modification 1>
Instead of the local oscillator 122 of the above-described embodiment, the first modification includes a reference antenna 130 and a band-pass filter 131 as shown in FIG. The reference antenna 130 is fixed near the turntable 112. Further, it may be fixed to the rotation center of the turntable 112. This is because the position of the rotation center of the turntable 112 does not change even if the turntable 112 rotates.

When the local oscillator 122 is used, the frequency oscillated by the local oscillator 122 and the frequency transmitted by the wireless tag 300 do not completely match. Therefore, it is difficult to accurately set the center frequency of the I component signal I _get and the Q component signal Q _get to 0 Hz, but when the reference antenna 130 is used, the I component signal I _get and the Q component signal Q _{get are used.} Can be accurately set to 0 Hz.

<Modification 2>
In the above-described embodiment, the arrival direction of the radio wave is estimated using two measurement signals of the I component signal I _get and the Q component signal Q _get . The reason why two measurement signals are used is that the I component approximate model I _ref and the Q component approximate model Q _ref may have the same waveform even if the azimuth angle φ is 180 degrees.

Therefore, if the search range of azimuth angle φ is 180 degrees or less, azimuth angle φ may be determined using only one of I component signal I _get and Q component signal Q _get . In this case, of course, only one of the I component approximate model I _ref and the Q component approximate model Q _ref is used. The I component approximate model I _ref or the Q component approximate model Q _ref used at this time corresponds to the approximate model in the claims. Further, the I component signal I _get or the Q component signal Q _get used at this time corresponds to the low-frequency signal and the measurement signal in the claims.

Since only one of the I component signal and the Q component signal is sufficient, it is not necessary to divide into the I component signal I _get and the Q component signal Q _get . When the I component signal I _get and the Q component signal Q _get are not divided, the I component signal I _get in the above-described embodiment is treated as the measurement signal V _get as it is.

Therefore, the approximate model V _ref of the measurement signal V _get can be expressed by the following formula 74 in which I in the I component approximate model I _ref shown in formula 37 is replaced with V.

Expression 37 is an expression obtained by replacing characters in the I component approximate model shown in Expression 34. As is well known, since sin and cos are only 90 degrees out of phase with each other and have the same shape, the approximate model V _ref of the measurement signal V _get is represented by the Q component approximate model Q _ref shown in Equation 34. It can also be thought of as In this case, the approximate model V _ref of the measurement signal V _get can be expressed by the following formula 75 in which Q in the Q component approximate model Q _ref shown in formula 37 is replaced with V.

When the approximate model V _ref shown in the equation 74 or 75 is used, the residual e is expressed by the equation 76 because the right side shown in the equation 43 is only the first term or the second term. .

<Modification 3>
Direction decision unit 230 of the above embodiment, I component signal extracted in the step 1 by a non-contact area amplitude ratio A _c in step 2, had been corrected Q component signal, must be omitted this step 2 If accurate direction estimation accuracy is obtained, step 2 may be omitted.

1: wireless tag reader, 100: receiving unit, 110: antenna unit, 111: antenna, 112: turntable, 113: driving unit, 120: low frequency signal generating unit, 121: bandpass filter, 122: local oscillator, 123: Mixer, 124: Low-pass filter, 125: A / D converter, 126: Phase shifter, 127: Mixer, 128: Low-pass filter, 129: A / D converter, 130: Reference antenna, 131: Band-pass filter, 200 : Signal processing unit, 210: signal acquisition unit, 220: storage unit, 230: direction determination unit, 300: wireless tag, 300a: approximate radio wave source

Claims (6)

A radio wave arrival direction estimation device for estimating the arrival direction of a predetermined frequency radio wave transmitted by the wireless tag (300),
A turntable (112), a drive unit (113) for rotating the turntable at a predetermined fixed period, and a radio wave transmitted by the wireless tag that is fixed at a position other than the center of rotation on the turntable. And a low-frequency signal generation unit (120) that generates a low-frequency signal obtained by lowering the frequency of the radio wave received by the antenna so that the center frequency becomes 0 Hz. A receiving unit (100) for outputting as a measurement signal;
A model obtained by converting a composite wave of a plurality of incoming waves into the measurement signal, and a model representing the measurement signal using an approximation in which a radio wave transmitted by the wireless tag is a plane wave, and as an unknown parameter, By calculating the degree of coincidence between the approximate signal containing the amount of azimuth angle, phase, and DC offset component representing the direction in which the radio wave arrives, and the measurement signal while changing unknown parameters of the approximate model, A direction determining unit (230) that determines the approximate model that matches the measurement signal, and determines the azimuth angle in the determined approximate model as the azimuth angle from which the radio wave has arrived,
The approximate model includes a frequency of a radio wave transmitted by the wireless tag as f _RF , a radius of rotation of the antenna as R, a speed of light as v _c , a time as t, the amount of the DC offset component as D, and the azimuth angle of each incoming wave. Is φ _m , the amplitude of each incoming wave is A _m , the phase of each incoming wave is ψ _m , the number of incoming waves is N, and the approximate model is V _ref , Equation 1 or Equation 2, Equation 3, Equation 3 4 is a model represented by Equation 5,

When the measurement signal is V _get , the direction determination unit calculates a residual e represented by Equation 6 as the degree of coincidence, and the combination of the azimuth angles of the plurality of incoming waves that minimizes the residual e To search for,

Simultaneous equations obtained by substituting 0 for the equation obtained by partial differentiation of the equation 6 by B, the equation obtained by partial differentiation of the equation 6 by C, and the equation obtained by partial differentiation of the equation 6 by D. The B, C, and D are calculated by solving, and the calculated B, C, and D are used to search for the combination of the azimuth angles of the plurality of arriving waves that minimize the residual e,
As for the azimuth angle, the unknown parameter of the approximate model is changed within a change range of 180 degrees or less, and the degree of coincidence between the approximate model and the measurement signal is calculated over a section where the antenna rotates 360 degrees. The radio wave arrival direction estimation device, wherein the approximate model that matches the measurement signal is determined. A radio wave arrival direction estimation device for estimating the arrival direction of a predetermined frequency radio wave transmitted by the wireless tag (300),
A turntable (112), a drive unit (113) for rotating the turntable at a predetermined fixed period, and a radio wave transmitted by the wireless tag that is fixed at a position other than the center of rotation on the turntable. Antenna (111), an I component signal which is an I component of a low frequency signal obtained by reducing the frequency of a radio wave received by the antenna so that a center frequency becomes 0 Hz, and a Q component which is a Q component of the low frequency signal A low-frequency signal generator (120) that generates a signal, and a receiver (100) that outputs the I component signal and the Q component signal;
The model is obtained by converting the I component and Q component of a plurality of incoming waves into the I component signal and the Q component signal, respectively, and using the approximation in which the radio wave transmitted by the wireless tag is a plane wave. An I component approximate model and a Q component, each of which represents a component signal and the Q component signal, and includes, as unknown parameters, the amount of azimuth, phase, amplitude, and DC offset component representing the azimuth from which the radio wave arrives By calculating the degree of coincidence that collectively represents the degree to which the approximate model matches the I component signal and the Q component signal while changing unknown parameters of the I component approximate model and the Q component approximate model, Determining the I component approximation model and the Q component approximation model that match the I component signal and the Q component signal, and determining the determined I component approximation model and Serial the azimuth angle in the Q component approximate model, the direction determination unit for determining the azimuth angle of the radio wave has arrived (230) comprises a,
The I-component approximate model and the Q-component approximate model are such that the frequency of the radio wave transmitted by the wireless tag is f _RF , the radius of rotation of the antenna is R, the speed of light is v _c , the time is t, and the direct current in the I component signal is The amount of the offset component is D _I , the amount of the DC offset component in the Q component signal is D _Q , the azimuth angle of each incoming wave is φ _m , the amplitude of each incoming wave is A _m , and the phase of each incoming wave is Ψ _m When the number of incoming waves is N, the I component approximate model is I _ref , and the Q component approximate model is Q _ref , the I component approximate model is expressed by Equation 7, Equation 9, Equation 10, and Equation 11. The Q component approximation model is a model represented by Formula 8, Formula 9, Formula 10, Formula 11;

The direction determining unit has the azimuth angle of the plurality of arriving waves that minimizes the residual e expressed by Equation 12 as the degree of coincidence when the I component signal is I _get and the Q component signal is Q _get . Search for combinations,

And expressions obtained by partially differentiating the equation 12 in the B, a formula obtained by partially differentiating the equation 12 in the C, a formula obtained by partially differentiating the equation 12 by the D _I, partially differentiating the above formula 12 in the D _Q The B, C, D _I and D _Q are calculated by solving simultaneous equations formed by setting each of the formulas to 0, and using the calculated B, C, D _I and D _Q , Searching for a combination of the azimuth angles of the plurality of incoming waves with the smallest residual e, and setting the interval for calculating the degree of coincidence as an interval in which the antenna rotates 360 degrees apparatus. In claim 1,
The direction determining unit searches for a combination of the azimuth angles of the plurality of arriving waves with the smallest residual energy calculated by an expression obtained by removing the term of only the measurement signal from the expression for calculating the residual e. Thus, the radio wave arrival direction estimation device searching for a combination of the azimuth angles of the plurality of arrival waves that minimizes the residual e. In claim 2,
The direction determining unit is configured to obtain the plurality of arriving waves having minimum residual energy calculated by an expression obtained by removing the term of only the I component signal and the term of only the Q component signal from the expression for calculating the residual e. By searching for a combination of the azimuth angles, a radio wave arrival direction estimation device that searches for the combination of the azimuth angles of the plurality of incoming waves that minimize the residual e. In any one of Claims 1-4,
A storage unit (220) that stores a calculated value of the z-factor term calculated by inputting a plurality of the azimuth angles and the time into a z-factor term that can be calculated by determining z.
The direction determining unit uses the calculated value of the z-factor term stored in the storage unit to search for a combination of the azimuth angles of the plurality of arriving waves with the smallest residual e. Radio wave arrival direction estimation device.   A radio wave arrival direction estimation system comprising the radio wave arrival direction estimation device according to any one of claims 1 to 5 and the wireless tag.

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