JP6436032B2 - Radio wave arrival direction estimation device, radio wave arrival direction estimation system - Google Patents

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. .

The present invention for achieving the above object is a radio wave arrival direction estimation device that estimates the arrival direction of a radio wave having 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 receiving unit (100) that outputs a measurement signal that is a signal determined based on radio waves received by the antenna;
A model that represents a measurement signal using an approximation in which the radio wave transmitted by the wireless tag is a plane wave, and is a differential approximation model that differentiates the approximation model that includes the azimuth angle that represents the direction in which the radio wave arrives and the phase as unknown parameters. And the degree of coincidence with the differential measurement signal obtained by differentiating the measurement signal while calculating unknown parameters of the differential approximation model, the differential approximation model that matches the differential measurement signal is determined. A direction determining unit (230) that determines an azimuth angle as an azimuth angle from which radio waves arrive.

  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, in the present invention, the azimuth angle at which the radio wave arrives is determined using the degree of coincidence between the differential measurement signal obtained by differentiating the measurement signal output from the reception unit and the differential approximation model, instead of the Fourier transform. 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 reduced in size. 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 azimuth is not determined using the approximate model itself, but is determined using a differential approximation model obtained by differentiating the approximate model. The reason for using the differential approximation model is to prevent the coincidence from fluctuating due to the influence of fluctuations in the DC offset component included in the measurement signal.

  Here, unlike the present invention, it is assumed that the amount of the DC offset component included in the measurement signal is measured in advance and the DC offset component is removed from the measurement signal. Since the magnitude of the DC offset component varies depending on environmental factors such as temperature, when removing the DC offset component from the measurement signal, it is necessary to dynamically change the amount of the DC offset component to be removed. . However, it is difficult to dynamically change the amount of the DC offset component to be removed with high accuracy. In addition, it is conceivable to add this DC offset component to the unknown parameter of the approximate model, but in this case, the amount of calculation increases due to an increase in the unknown parameter.

  On the other hand, if the differential approximation model is used, the DC offset component is removed by differentiation, so that the degree of coincidence fluctuation due to the influence of the fluctuation of the DC offset component is suppressed. Thereby, the azimuth angle can be determined with high accuracy and the amount of calculation can be reduced.

In the invention according to claim 2, the receiving unit generates a low frequency signal in which the frequency of the radio wave received by the antenna is reduced so that the center frequency is lower than the maximum Doppler shift determined by the rotation speed of the antenna. A signal generator (120) is provided to output a low frequency signal as a measurement signal,
The differential approximation model is a model obtained by differentiating a low-frequency approximation model, which is a model representing a low-frequency signal generated by a low-frequency signal generation unit, using an approximation in which a radio wave transmitted by a wireless tag is a plane wave.
The direction determining unit changes the unknown parameter of the differential approximation model within a change range of 180 degrees or less with respect to the azimuth, and the degree of coincidence between the differential approximation model and the differential measurement signal is an interval in which the antenna rotates more than 180 degrees. And a differential approximation model matching the differential measurement signal is determined.

  In the present invention, the low frequency signal generator generates the low frequency signal. Since the low frequency signal has a lower center frequency than the maximum Doppler shift determined by the rotation speed of the antenna, 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 determining unit of the present invention sets the interval for calculating the degree of coincidence as the interval in which the antenna rotates more than 180 degrees, the phase error when the frequency is positive and the phase error when the frequency is negative cancel each other. Will be. Therefore, a differential approximation model having a small phase error with respect to an actual differential measurement signal can be determined as a differential approximation model that matches the differential measurement signal. As a result, the accuracy of the azimuth angle determined from the differential approximation model is further improved.

In the invention according to claim 3, the receiving unit is an I component of a low-frequency signal obtained by lowering the frequency of the radio wave received by the antenna so that the center frequency is lower than the maximum Doppler shift determined by the rotation speed of the antenna. A low-frequency signal generation unit (120) that generates a Q component signal that is a Q component of the I component signal and the low frequency signal, and outputs the I component signal and the Q component signal as a measurement signal;
The differential approximation model is obtained by differentiating the I component signal generated by the low-frequency signal generation unit and the I component approximation model representing the Q component signal and the Q component approximation model using approximation in which the radio wave transmitted by the wireless tag is a plane wave. A differential I component approximation model and a differential Q component approximation model,
The direction determining unit changes the unknown parameters of the differential I component approximate model and the differential Q component approximate model as a change range wider than 180 degrees with respect to the azimuth, and the degree of coincidence changes the differential I component approximate model and the I component signal. This is a value that collectively represents the degree of coincidence between the differentiated differential I component signal and the degree of coincidence between the differential Q component approximate model and the differentiated Q component signal obtained by differentiating the Q component signal. And a differential I component approximation model that matches the differential I component signal and a differential Q component approximation model that matches the differential Q component signal are determined.

  The invention according to claim 3 divides the low frequency signal in the invention according to claim 2 into an I component signal and a Q component signal. The differential approximation model is also a differential I component approximation model and a differential Q component approximation model. Then, the direction determining unit calculates a degree of coincidence that collectively represents the degree to which the differential I component signal and the differential I component approximate model match and the degree to which the differential Q component signal and the differential Q component approximate model match. Yes.

  The reason why the difference between the I component signal and the Q component signal is calculated and the degree of coincidence between the differentiated signal and the differential approximation model is an unknown parameter in the differential I component approximation model and the differential Q component approximation model. This is because the azimuth angle is changed over a range wider than 180 degrees. That is, the azimuth angle search range is 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. Therefore, when the search range of the azimuth is wider than 180 degrees, the azimuth is determined only by either the differential I component approximation model or the differential Q component model obtained by differentiating the I component approximation model and the Q component approximation model, respectively. I can't.

  However, if one of the differential I component approximate model and the differential Q component approximate model substitutes a parameter that becomes the same waveform as the waveform having an azimuth angle different by 180 degrees in the other approximate model, Two waveforms whose angles are different from each other by 180 degrees 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 differential I component approximate model and the differential Q component approximate model.

  According to a fourth aspect of the present invention, the low frequency signal generation unit generates a low frequency signal having a center frequency of 0 Hz, and the direction determination unit sets a section for calculating the coincidence as a section in which the antenna rotates 360 degrees. It is characterized by that.

  In the fifth aspect of the present invention, the low frequency signal generation unit generates an I component signal and a Q component signal having a center frequency of 0 Hz, and the direction determination unit rotates the 360 degrees in the interval for calculating the degree of coincidence. It is set as the area to perform.

  According to the fourth and fifth aspects of the present invention, the low-frequency signal generator generates a low-frequency signal or an I component signal and a Q component signal with a center frequency of 0 Hz. When the center frequency is 0 Hz, the absolute value of the phase error in the positive frequency section of the approximate model and the phase error in the negative frequency of the approximate model are equal to each other with the opposite sign while the antenna rotates once. . Since the section for calculating the degree of coincidence is a section in which the antenna rotates 360 degrees, the phase error can be accurately canceled. Therefore, the accuracy of the azimuth angle determined from the differential approximation model is further improved.

方向決定部は、微分測定信号をΔＶ_ｇｅｔ、微分近似モデルをＶ_ｒｅｆドットとしたとき、一致度として式６で表す微分残差ｅが最小となる複数の到来波の方位角および仰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を算出し、算出したＢ、Ｃを用いて、微分残差ｅが最小となる複数の到来波の方位角および仰角の組み合わせを探索することを特徴とする。 In the invention according to claim 6, the approximate model is a model in which a synthesized wave of a plurality of incoming waves is converted into a low frequency signal, 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 azimuth angle of each incoming wave is φ _m , the elevation angle of each incoming wave is δ _m , the amplitude of each incoming wave is A _m , the phase of each incoming wave is Ψ _m , and the number of incoming waves _Is N and the approximate model is V _ref , the model is represented by Formula 1 or Formula 2, Formula 3, Formula 4, and Formula 5,

When the differential measurement signal is ΔV _get and the differential approximation model is V _ref dot, the direction determining unit determines a combination of azimuth angles and elevation angles of a plurality of arriving waves that minimize the differential residual e represented by Equation 6 as the degree of coincidence. To explore,

B and C are calculated by solving simultaneous equations formed by partial differentiation of Equation 6 by B and partial differentiation of Equation 6 by C to 0, and calculating the calculated B and C. And searching for a combination of azimuth angles and elevation angles of a plurality of incoming waves that minimize the differential residual e.

  According to the sixth aspect of the present invention, since B and C having the amplitude A and the phase Ψ as parameters can be calculated by simultaneous equations, the amplitude A and the phase Ψ of the incoming wave can be excluded from the unknown parameters in Expression 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、微分Ｉ成分信号をΔＩ_ｇｅｔ、微分Ｑ成分信号をΔＱ_ｇｅｔ、微分Ｉ成分近似モデルをＩ_ｒｅｆドット、微分Ｑ成分近似モデルをＱ_ｒｅｆドットとしたとき、一致度として式１２で表す微分残差ｅが最小となる複数の到来波の方位角および仰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を算出し、算出したＢ、Ｃを用いて、微分残差ｅが最小となる複数の到来波の方位角および仰角の組み合わせを探索することを特徴とする。 In the invention according to claim 7, the I component approximation model and the Q component approximation model are models obtained by converting the I component and the Q component of a composite wave of a plurality of incoming waves into low frequency signals, respectively, and transmitted by the wireless tag The frequency of the radio wave to be transmitted is f _RF , the radius of rotation of the antenna is R, the speed of light is v _c , the time is t, the azimuth angle of each incoming wave is φ _m , the elevation angle of each incoming wave is δ _m , and 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, the I component approximate model is I _ref , and the Q component approximate model is Q _ref , the I component approximate models are Equations 7, 9, and 10 , And the Q component approximation model is a model represented by Equation 8, Equation 9, Equation 10, and Equation 11,

When the differential I component signal is ΔI _get , the differential Q component signal is ΔQ _get , the differential I component approximate model is I _ref dot, and the differential Q component approximate model is Q _ref dot, Searching for a combination of azimuth and elevation angles of a plurality of arriving waves for which a differential residual e is represented,

B and C are calculated by solving simultaneous equations formed by partial differentiation of Equation 12 with B and equations obtained by partial differentiation of Equation 12 with C to 0, and calculate the calculated B and C. And searching for a combination of azimuth angles and elevation angles of a plurality of incoming waves that minimize the differential residual e.

  In the invention according to claim 7 as well, since B and C can be calculated by simultaneous equations, the amplitude A and the phase Ψ of the incoming wave can be excluded from the unknown parameters in Expression 12. Therefore, since there are fewer unknown parameters that need to be searched, the calculation can be performed quickly.

  In the invention according to claim 8, the direction determining unit removes the term of the differential measurement signal only from the formula for calculating the differential residual e, and the residual energy calculated by the formula with the sign inverted is maximized. By searching for a combination of azimuth angles and elevation angles of a plurality of incoming waves, a search is made for a combination of azimuth angles and elevation angles of a plurality of incoming waves that minimizes the differential residual e.

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

  In the invention according to claim 9, the direction determining unit calculates the differential residual e from an expression in which the differential I component signal only term and the differential Q component signal only term are excluded, and the sign is inverted. Searching for a combination of azimuth and elevation angles of a plurality of arriving waves that minimizes the differential residual e by searching for a combination of azimuth and elevation angles of the plurality of arriving waves that maximize the residual energy. Features.

  According to the ninth aspect, the calculation amount can be reduced because the combination of the azimuth angles and the elevation angles of the plurality of arrival waves that minimize the differential residual e can be searched without calculating the term of only the measurement signal.

In the invention according to claim 10, the calculation is performed by inputting a plurality of azimuth angles, elevation angles, and times into a z-factor term that is a part of an equation for calculating a differential residual and that can be calculated by determining z. a storage unit (220) that stores a calculated value of the z-factor term;
The direction determining unit uses the calculated value of the z-factor term stored in the storage unit to search for a combination of azimuth angles and elevation angles of a plurality of incoming waves that minimize the differential residual e.

  Thus, if a combination of the azimuth and elevation angles of a plurality of incoming waves that minimize the differential residual e is searched using the calculated value of the z-factor term calculated in advance, the search for the azimuth and elevation angles can be performed. Since the amount of calculation is reduced, the azimuth angle and elevation angle can be estimated quickly.

  An eleventh aspect of the invention is a radio wave arrival direction estimation system including the radio wave arrival direction estimation device according to any one of claims 1 to 10 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 patterns are opposed to each other and transmitted by radio. 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 differential residual energy E. This expression is specifically Expression 70 described later. In addition, the storage unit 220 also stores calculated values that are calculated in advance by changing the time t, the azimuth angle φ, and the elevation angle δ for the coefficient S used in the equation for calculating the differential residual energy E.

  The differential residual energy E is a value calculated by a formula obtained by removing the term of the differential measurement signal only from the formula for calculating the differential residual e. The differential residual e is a value obtained by calculating a difference between a differential measurement signal obtained by differentiating a measurement signal and a differential approximation model obtained by differentiating an approximation model obtained by modeling the differential measurement signal by plane wave approximation.

  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 obtained by modeling the I component signal and a Q component signal. It is a Q component approximation model. First, the I component approximate model and the Q component approximate model will be described.

[Explanation of I component approximate model and Q component approximate model]
In order to describe the I component approximate model and the Q component approximate model, it is first 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, and the angle formed by the line connecting the center position of the turntable 112 and the wireless tag 300 with respect to the plane including the turntable 112 is the elevation angle δ. Let radius be R.

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 and the elevation angle δ are estimated by model matching. However, exact 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 in the square root. 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 summarized phase as [psi ', has the formula 20 can get. 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 and a Q component approximate model derived based on the approximate model shown in Expression 20 are used.

  The reason why the I component approximate model and the Q component approximate model 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 between the azimuth angle φ and the elevation angle δ of the wireless tag 300 obtained using the approximate model is larger as the angle of the antenna 111 is perpendicular to the direction of arrival of radio waves, and the wireless tag 300 is closer to the antenna 111. The larger the rotation radius R of the antenna 111, the larger the antenna 111 becomes.

  The I component approximate model and the Q component approximate model used in the present embodiment are models of signals obtained by reducing 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 and a Q component approximate model.

  FIG. 7 shows a comparison between the waveform of the I component approximate model corresponding to the waveform of the approximate model of FIG. 5 and the I component signal of the waveform without approximation. FIG. 8 shows a comparison between the waveform of the approximate Q model corresponding to the waveform of the approximate model of 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 and the Q component approximate model 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 and the Q component approximate model are delayed from the waveforms without approximation, and the phases are 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 approximation model and the Q component approximation model may have the same waveform even if the azimuth angle φ is 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.

  The I component approximation model in Equation 26 is the same as the I component approximation model in Equation 23. In other words, even if the azimuth angle φ is different by 180 degrees, the I component approximation model cannot be distinguished from each other if the phase ψ is reversed. However, since the Q component signal model in Equation 23 and the Q component signal model in Equation 26 are different, it can be seen from the Q component signal model that (φ, ψ) and (φ + π, −ψ) can be distinguished.

  However, the Q component approximation model 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.

  The Q component approximation model in Equation 30 is the same as the Q component approximation model in Equation 23. Therefore, the Q component approximate model cannot distinguish between (φ, ψ) and (φ + π, −ψ + π). However, since the I component signal model in Equation 23 and the I component signal model in Equation 30 are different, it can be seen from the I component signal model that (φ, ψ) and (φ + π, −ψ + π) can be distinguished.

  As described above, the I component approximation model and the Q component approximation model of Equation 23 cannot be distinguished from the case where the azimuth angle φ is shifted by 180 degrees by itself, and therefore, when searching over an angle range wider than 180 degrees. Requires both an I component approximation model and a Q component approximation model.

[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.

Since the I component approximate model and the Q component approximate model of the composite wave are models obtained by adding a plurality of waves of the model shown in Expression 30 to each other, they 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.

[Description of differential approximation model]
In the present embodiment, a differential I component approximate model and a differential Q component approximate model obtained by differentiating these I component approximate model and Q component approximate model are used. The reason for using the differentiated model instead of the I component approximate model and the Q component approximate model is to remove the influence of the DC offset component included in the I component signal and the Q component signal.

  The DC offset component included in the I component signal and the Q component signal is generated due to temperature characteristics of various elements constituting the receiving unit 100. On the other hand, the DC offset component is not considered in the I component approximate model and the Q component approximate model. Therefore, it is necessary to remove the influence of the DC offset component and evaluate the coincidence between the I component signal and the I component approximate model and the coincidence between the Q component signal and the Q component approximate model. Therefore, in this embodiment, these signals and models are differentiated to evaluate the degree of coincidence.

  A model obtained by differentiating the I component approximate model is referred to as a differential I component approximate model, and a model obtained by differentiating the differential Q component approximate model is referred to as a differential Q component approximate model. In order to make these differential I component approximate model and differential Q component approximate model simple to calculate, the I component approximate model and Q component approximate model are differentiated after being simplified.

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.

By differentiating Equation 37, a differential I component approximate model shown in Equation 38 and a differential Q component approximate model shown in Equation 39 are obtained.

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 waveform obtained by differentiating the I component signal and the I component approximate model, and the Q component signal are differentiated. Consider the sum of the waveform and the residual sum of squares of the Q component approximation model (hereinafter referred to as differential residual). The differential residual can be expressed by Equation 40 in a continuous time system. In Equation 40, T is a time interval (hereinafter referred to as a coincidence calculation section) in which a differential residual that 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. In the discrete time system, the differential value of the I component signal and the differential value of the Q component signal are expressed by Expression 41 and Expression 42, respectively.

By substituting Equations 41 and 42 into Equation 40, Equation 43 representing the differential residual e in the discrete time system is obtained. In Equation 43, 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 differential approximation model that minimizes the differential residual e best represents the differential waveform of the measurement signal. By replacing the characters shown in Equation 35, the unknown parameters in Equation 43 become the azimuth angle φ _m , the elevation angles δ _m , B _m , and C _m .

Here, consider obtaining B _m and C _m . When the differential residual e is partially differentiated with respect to B _n and C _n of the n-th incoming wave, Expression 44 and Expression 45 are obtained.

Further, when Equations 38 and 39 are partially differentiated by B _n and C _n , Equations 46 are obtained.

When Expression 44 is expanded and replaced with Expression 46 and Expression 38, Expression 47 is obtained. Further, when Formula 47 is rearranged, Formula 48 is obtained, and when Formula 48 is further rearranged, Formula 49 is obtained.

Similarly, for C _m , when Formula 45 is expanded and replaced by Formula 46 and Formula 39, Formula 50 is obtained. Further, when formula 50 is rearranged, formula 51 is obtained, and when formula 51 is further rearranged, formula 52 is obtained.

In order to simplify Expression 49 and Expression 52 by replacing characters, the following variables shown in Expression 53 and Expression 54 are considered.

If Formula 49 is rewritten using the variable shown in Formula 53, Formula 54 will be obtained, and if Formula 52 is rewritten using the variable shown in Formula 53, Formula 55 will be obtained.

Since we want to find B _m and C _m that minimize the differential residual e, formulas with the left side of formula 54 and formula 55 set to 0 are considered. That is, consider Equation 56.

In Expression 56, 2N simultaneous equations are obtained for B _m and C _m for each n-th (n = 1 to N) incoming wave. Azimuth phi _m, phi _n, elevation [delta] _m, if Atehamere the [delta] _{n z} m, since _{z n} is obtained, the azimuth angle phi _m, phi _n, elevation [delta] _m, Applying [delta] _n, simultaneous equations 56 For each n, 2N equations are obtained for 2N unknown parameters B _m , C _m . Therefore, if the azimuth angles φ _m , φ _n , elevation angles δ _m , δ _n are applied, simultaneous equations can be solved, and unknown parameters B _m , C _m can be calculated. Since Expression 57 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 and C _m can be calculated by solving the simultaneous equations of Expression 56 in this way, a differential approximation model that minimizes the differential residual e can be obtained simply by searching for a combination of the azimuth angle φ _m and the elevation angle δ _m. Can be determined.

Further, in the present embodiment, the following equation modification is performed on Equation 43. When Expression 43 is expanded, Expression 58 is obtained.

Further, a coefficient S shown in the following formula 59 is defined.

When the coefficient S shown in Expression 59 is used, the character part of the second term on the right side of Expression 58 is expressed by Expression 60, and the character part of the fifth term on the right side of Expression 58 is expressed by Expression 61. In Equation 60, S _Ism means a product of S _I and S _sm , and S _Icm means a product of S _I and S _cm . Similarly, in Equation 61, S _qsm means the product of S _q and S _sm , and S _qcm means the product of S _q and S _cm .

Further, the square of the I _ref dot included in the third term on the right side of Expression 58 is expressed as Expression 62 using Expression 38.

When the parentheses in Expression 62 are expanded, the right side of Expression 63 is obtained.

When the third term on the right side of Expression 58 is expressed using Expression 63, Expression 64 is obtained. In the expression 64, 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 square sum of the differential Q component approximation model is also modified in the same manner as the square sum of the differential I component approximation model. First, the square of the Q _ref dot included in the sixth term on the right side of Expression 58 is expressed as Expression 65 using Expression 39.

When the inside of the parenthesis of Expression 65 is expanded, the right side of Expression 66 is obtained.

When the sixth term on the right side of Expression 58 is expressed using Expression 66, Expression 67 is obtained.

From Expression 64 and Expression 67, Expression 68 is obtained.

If Expression 60, Expression 61, and Expression 68 are used, Expression 58 can be expressed as Expression 69.

The differential residual e may be obtained by directly calculating the equation 69. However, since the first term on the right side and the second term on the right side of Equation 69 are square terms of the differential values of the I component signal and the Q component signal, they are always positive numbers and the azimuth angle φ _{m to be} searched for. And is not affected by the value of the elevation angle δ _m . Therefore, consider the differential residual energy E in which the first and second terms on the right side of Equation 69 are omitted. The differential residual energy E is expressed by Equation 70. The right side of Expression 70 is an expression obtained by omitting the first and second terms from the right side of Expression 69 and inverting the sign.

  In the present embodiment, this differential residual energy E corresponds to the degree of coincidence of claims, and the storage unit 220 stores Expression 70.

  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 71. This table is hereinafter referred to as a pre-calculation table. Each coefficient S shown in Equation 71 is a coefficient whose value can be calculated if the variable z is determined, and corresponds to a z-factor term in the claims.

As shown in Expression 33, the variable z has time t, azimuth angle φ, and elevation angle δ as variables. In the pre-calculation table, the time t is changed by 2π / ω for each sampling period, and the azimuth angle ω and the elevation angle δ are changed at an angular pitch determined based on the required angular resolution, and the time t, For each combination of the azimuth angle ω and the elevation angle δ, a calculated value obtained by calculating the coefficient S shown in Expression 71 is included.

The direction determining unit 230 determines the combination of arrival directions (that is, the azimuth angle φ _m and the elevation angle δ _m ) that minimizes the differential residual energy E, and the combination of the arrival directions is used as the arrival of actual radio waves. Suppose that it is a direction. The direction determination unit 230 performs the following steps 1 to 9 to determine a combination of arrival directions in which the differential residual energy E is minimized.

  In step 1, the I component signal and the Q component signal for the coincidence calculation section are acquired from the latest I component signal and Q component signal from the storage unit 220. 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 72. In Expression 72, 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 and the Q component approximate model are models that do not consider the change in amplitude in the non-contact portion, and therefore the I component signal and Q component signal to be compared with these models. This is because it is preferable to remove 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 the azimuth angle φ and the elevation angle δ 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 73 is calculated using the corrected I component signal I _get corrected in step 2 and the corrected Q component signal Q _get .

In step 6, the simultaneous equations shown in Expression 56 are solved for each combination of arrival directions determined in step 3, and B _m and C _m are obtained for each combination of arrival directions.

  In step 7, using the calculated values obtained in step 4 and the calculated values calculated in steps 5 and 6, the differential residual energy E shown in equation 70 is calculated for each arrival direction of the incoming wave determined in step 3. calculate. In step 8, the maximum value of the differential residual energy E calculated in step 7 is determined. In step 9, the combination of the arrival directions corresponding to the maximum value of the differential residual energy E determined in step 8 is set as the direction in which the radio wave actually arrives. 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 this embodiment, not the Fourier transform, but the I component signal output from the receiving unit 100, the differential I component signal obtained by differentiating the Q component signal, the differential Q component signal, and the corresponding differential approximation models respectively. A differential residual energy E that expresses the degree is calculated. That is, the azimuth angle φ and the elevation angle δ are 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 and a Q component approximate model are used. The radio wave transmitted by the wireless tag 300 is actually a spherical wave, but the I component approximate model and the Q component approximate model are obtained by approximating the radio wave transmitted by the wireless tag 300 as a plane wave.

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 and the Q component approximate model of the present embodiment do not have a square root existing in the exact model as shown in Expression 23. Therefore, the amount of calculation can be greatly reduced as compared with the case where the strict model is used.

Further, in this embodiment, the azimuth angle φ and the elevation angle δ are not determined using the approximate model itself, but the differential I component approximate model and the differential Q component approximate model shown in Expressions 38 and 39 obtained by differentiating the approximate model are used. Are used to determine the azimuth angle φ _m and the elevation angle δ _m . Thereby, when the direct current offset component contained in the I component signal and the Q component signal fluctuates, it can be suppressed that the differential residual energy E fluctuates. Therefore, even if the DC offset component included in the I component signal and the Q component signal fluctuates, the azimuth angle φ _m and the elevation angle δ _m can be accurately determined, and the DC offset component is not used as an unknown parameter. An increase in the amount can also be suppressed.

Further, in the present embodiment, B _m and C _m can be calculated by the simultaneous equations shown in Expression 56, so that the amplitude A _m and the phase Ψ _m of the incoming wave are excluded from the unknown parameters that need to be searched. it can. Therefore, since there are fewer unknown parameters that need to be searched, the calculation can be performed quickly.

Further, in the present embodiment, the differential residual energy E shown in Expression 70 is calculated by removing the term of only the measurement signal V _get from the differential residual e instead of calculating the differential residual e shown in Expression 43. To do. This makes it possible to search for combinations of azimuth angles φ _m and elevation angles δ _m of a plurality of incoming waves that minimize the differential residual e without calculating the term of the measurement signal V _get alone, thereby reducing the amount of calculation. .

Furthermore, in the present embodiment, the calculated value of the coefficient S shown in Formula 71 calculated in advance by changing the time t, the azimuth angle φ _m , and the elevation angle δ _m is stored in the storage unit 220, and this calculated value is used. Then, the differential residual energy E is calculated. This also azimuth angle phi _m, since the amount of computation when estimating the elevation angle [delta] _m is reduced, the azimuth angle phi _m, the elevation angle [delta] _m can be quickly estimated.

  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, while it is difficult to accurately set the center frequency of the I component signal and the Q component signal to 0 Hz, when the reference antenna 130 is used, the center frequency of the I component signal and the Q component signal is accurately set to 0 Hz. can do.

<Modification 2>
In the above-described embodiment, the coincidence degree calculation section is a section in which the antenna 111 rotates 360 degrees. However, the coincidence degree calculation section may be a section in which the antenna 111 rotates more than 180 degrees.

  The positive and negative frequencies of the I component signal and the Q component signal are inverted when the antenna 111, the rotation center of the antenna 111, and the wireless tag 300 are aligned. Therefore, every time the antenna 111 rotates 180 degrees, the positive and negative frequencies of the I component signal and the Q component signal are inverted. In the examples of FIGS. 7 and 8, the positive and negative frequencies are inverted at 0 degrees and 180 degrees.

  If the coincidence calculation section is a section in which the antenna 111 rotates more than 180 degrees, both a section in which the frequency is positive and a section in which the frequency is negative are included. Therefore, at least the coincidence calculation section can cancel out at least a part of the phase error as long as the antenna 111 rotates more than 180 degrees.

<Modification 3>
In the above-described embodiment, two differential I component signals and differential Q component signals are used. The reason why the two differential measurement signals are used is that the I component approximate model and the Q component approximate model may have the same waveform even if the azimuth angle φ is different by 180 degrees. This is because even if φ is different by 180 degrees, the same waveform may be obtained.

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

  In addition, since only one of the differential I component signal and the differential Q component signal is sufficient, it is not necessary to divide into the I component signal and the Q component signal. When the signal is not divided into the I component signal and the Q component signal, the I component signal in the above-described embodiment is handled as the measurement signal V as it is.

Therefore, the approximate model V _ref of the measurement signal can be expressed by the following formula 74 in which I in the I component approximate model 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 is considered as an expression of the Q component approximate model shown in Expression 34. You can also. In this case, the approximate model V _ref of the measurement signal can be expressed by the following formula 75 in which Q in the Q component approximate model shown in formula 37 is replaced with V.

When the approximate model V _ref shown in the equation 74 or 75 is used, the differential 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. The

<Modification 4>
In the above-described embodiment, the I component signal and the Q component signal are signals having a center frequency of 0 Hz, but the center frequency of the I component signal and the Q component signal may not be 0 Hz. However, it is preferably lower than the maximum Doppler shift. The maximum Doppler shift is a maximum value of the Doppler shift that is generated only by the rotation of the antenna 111 on the assumption that the wireless tag 300 is stationary. The maximum Doppler shift is a Doppler shift when the velocity vector of the antenna 111 is maximum in the direction toward the wireless tag 300 and maximum in the direction away from the wireless tag 300.

  If the center frequency of the I component signal and the Q component signal is lower than the maximum Doppler shift, a negative frequency is generated in the I component signal and the Q component signal. If a negative frequency occurs, the coincidence calculation section can include both a section in which the frequency is positive and a section in which the frequency is negative. Therefore, the center frequencies of the I component signal and the Q component signal need not be 0 Hz as long as they are lower than the maximum Doppler shift.

When the center frequency is not 0 Hz, if the center frequency is f _IF , the I component approximate model and the Q component approximate model are models in which the term of 2πf _IF t is placed in parentheses outside Expression 23.

<Modification 5>
The shorter the distance L _R between the antenna 111 and the wireless tag 300 with respect to the rotation radius R of the antenna 111, the phase error by using an approximation model increases. In other words, conditions for determining the azimuth angle φ of the radio tag 300 is primarily, if the distance L _R is long state between the antenna 111 and the wireless tag 300 with respect to the rotation radius R of the antenna 111, the phase error azimuth The error given to the estimation accuracy of the angle φ is small. When the influence of the phase error is small, it is not necessary to lower the center frequency so that a negative frequency is generated.

  Therefore, the receiving unit 100 may output a measurement signal whose center frequency is higher than the maximum Doppler shift, and the direction determining unit 230 may use a model obtained by differentiating the approximate model of Expression 20 as the differential approximate model. .

<Modification 6>
In the above-described embodiment, the elevation angle δ is also an unknown parameter, but the elevation angle δ is often not important when determining the direction of arrival of radio waves from the wireless tag 300 carried by a person. Therefore, the elevation angle δ may be constant, for example, 0 degrees. When the elevation angle δ is set to 0 degree, cos δ shown so far is set to 1.

<Modification 7>
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 (11)

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 receiving unit (100) that outputs a measurement signal that is a signal determined based on radio waves received by the antenna;
A model representing the measurement signal using an approximation in which a radio wave transmitted by the wireless tag is a plane wave, and differentiating an approximate model including an azimuth representing a direction in which the radio wave arrives and a phase as unknown parameters By calculating the degree of coincidence between the differential approximation model and the differential measurement signal obtained by differentiating the measurement signal while changing the unknown parameter of the differential approximation model, the differential approximation model that matches the differential measurement signal is determined. A radio wave arrival direction estimation device comprising: a direction determination unit (230) that determines the azimuth angle in the determined differential approximation model as the azimuth angle from which the radio wave arrives. In claim 1,
The reception unit generates a low-frequency signal generation unit (120) that generates a low-frequency signal in which a frequency of a radio wave received by the antenna is lowered so that a center frequency is lower than a maximum Doppler shift determined by a rotation speed of the antenna. ), And output the low frequency signal as the measurement signal,
The differential approximation model is a model obtained by differentiating a low frequency approximation model, which is a model representing a low frequency signal generated by the low frequency signal generation unit, using an approximation in which a radio wave transmitted by the wireless tag is a plane wave.
The direction determining unit changes the unknown parameter of the differential approximation model as a change range of 180 degrees or less with respect to the azimuth, and the antenna determines the degree of coincidence between the differential approximation model and the differential measurement signal. A radio wave arrival direction estimation device, wherein the differential approximation model is calculated over a section rotating more than a degree and coincides with the differential measurement signal. In claim 1,
The receiving unit includes an I component signal that is an I component of a low frequency signal obtained by reducing the frequency of the radio wave received by the antenna so that the center frequency is lower than the maximum Doppler shift determined by the rotation speed of the antenna, and A low frequency signal generator (120) for generating a Q component signal that is a Q component of the low frequency signal, and outputting the I component signal and the Q component signal as the measurement signal;
The differential approximation model uses an approximation in which a radio wave transmitted by the wireless tag is a plane wave, and an I component approximation model and a Q component approximation respectively representing the I component signal and the Q component signal generated by the low frequency signal generation unit A differential I component approximation model and a differential Q component approximation model obtained by differentiating the model,
The direction determining unit changes the unknown parameter of the differential I component approximate model and the differential Q component approximate model as a change range wider than 180 degrees with respect to the azimuth, and the coincidence degree is determined by the differential I component. A value that collectively represents the degree to which the approximate model and the differential I component signal obtained by differentiating the I component signal coincide with each other and the degree to which the differential Q component approximate model and the differential Q component signal obtained by differentiating the Q component signal coincide. Yes, the degree of coincidence is calculated over a section where the antenna rotates more than 180 degrees, and the differential I component approximate model that matches the differential I component signal and the differential Q that matches the differential Q component signal A radio wave arrival direction estimation apparatus characterized by determining a component approximation model. In claim 2,
The low frequency signal generation unit generates the low frequency signal having a center frequency of 0 Hz,
The radio wave arrival direction estimation apparatus, wherein the direction determination unit sets a section in which the degree of coincidence is calculated as a section in which the antenna rotates 360 degrees. In claim 3,
The low frequency signal generation unit generates the I component signal and the Q component signal having a center frequency of 0 Hz,
The radio wave arrival direction estimation apparatus, wherein the direction determination unit sets a section in which the degree of coincidence is calculated as a section in which the antenna rotates 360 degrees. In claim 4,
The approximate model is a model obtained by converting the composite wave of a plurality of incoming waves in the low-frequency signal, the radio tag is the frequency of the radio wave f _RF to be _transmitted, the rotation radius of the antenna R, light velocity v _c , time, t, the azimuth angle phi _m of each incoming _wave, elevation of [delta] _m of each incoming _wave, amplitude a _m of the incoming _wave, the phase [psi _m of the incoming _waves, the number of arrival waves N, wherein When the approximate model is V _ref , the model is represented by Formula 1 or Formula 2, Formula 3, Formula 4, and Formula 5,

When the differential measurement signal is ΔV _get and the differential approximation model is V _ref dot, the direction determination unit is configured to determine the direction of the plurality of arriving waves that minimizes the differential residual e expressed by Equation 6 as the degree of coincidence. Searching for a combination of angles and elevation angles,

The B and C are calculated by solving the simultaneous equations formed by subtracting the expression 6 obtained by partial differentiation of the expression 6 from the B and the expression obtained by partially differentiating the expression 6 from the C by 0. A radio wave arrival direction estimation device that searches for a combination of the azimuth angle and the elevation angle of the plurality of incoming waves that minimizes the differential residual e using the B and C. In claim 5,
The I component approximate model and the Q component approximate model are models obtained by converting the I component and the Q component of a composite wave of a plurality of incoming waves into the low frequency signal, respectively, and the frequency of the radio wave transmitted by the wireless tag F _RF , the radius of rotation of the antenna is R, the speed of light is v _c , the time is t, the azimuth angle of each incoming wave is φ _m , the elevation angle of each incoming wave is δ _m , the amplitude of each incoming wave is A _m , When the phase of the incoming wave is Ψ _m , 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 Equations 7, 9, and 10 The Q component approximate model is a model represented by Equation 8, Equation 9, Equation 10, and Equation 11,

When the differential I component signal is ΔI _get , the differential Q component signal is ΔQ _get , the differential I component approximate model is I _ref dot, and the differential Q component approximate model is Q _ref dot, Searching for a combination of the azimuth angle and the elevation angle of the plurality of arriving waves that minimizes the differential residual e represented by Equation 12 as the degree of coincidence,

B and C are calculated by solving simultaneous equations formed by subtracting the equation 12 from the partial differentiation of the equation 12 by B and the equation 12 by partially differentiating the equation 12 by the C, respectively. A radio wave arrival direction estimation device that searches for a combination of the azimuth angle and the elevation angle of the plurality of incoming waves that minimizes the differential residual e using the B and C. In claim 6,
The direction determining unit removes the term of only the differential measurement signal from the equation for calculating the differential residual e, and the plurality of arriving waves with the maximum residual energy calculated by the equation with the sign inverted. A search for a combination of the azimuth angle and the elevation angle of the plurality of arrival waves that minimizes the differential residual e by searching for a combination of the azimuth angle and the elevation angle of the radio wave. apparatus. In claim 7,
The direction determining unit removes a term of only the differential I component signal and a term of only the differential Q component signal from an equation for calculating the differential residual e, and a residual calculated by an equation having a sign inverted. By searching for the combination of the azimuth angle and the elevation angle of the plurality of arriving waves having the maximum energy, the combination of the azimuth angle and the elevation angle of the plurality of arriving waves that minimizes the differential residual e is searched. A radio wave arrival direction estimating device. In claim 6 or 7,
The z calculated by inputting a plurality of the azimuth angle, the elevation angle, and the time into a z-factor term that is a part of an expression for calculating the differential residual e and that can be calculated by determining the z. A storage unit (220) storing the calculated values of the factor terms;
The direction determining unit searches for a combination of the azimuth angle and the elevation angle of the plurality of arriving waves that minimizes the differential residual e using the calculated value of the z-factor term stored in the storage unit. A radio wave arrival direction estimation device characterized by the above.   A radio wave arrival direction estimation system comprising the radio wave arrival direction estimation device according to any one of claims 1 to 10 and the wireless tag.

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