JP2015224898A - 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 capable of reducing a size, ensuring high frequency resolution, and reducing a computing volume.SOLUTION: A radio wave arrival direction estimation device estimating an arrival direction of a radio wave transmitted from a wireless tag and having a preset constant frequency over an angle range wider than 180°, comprises: an antenna 11 fixed onto a rotary table 12 rotating at the constant frequency; a quadrature signal generation unit 20 generating an I component signal and a Q component signal orthogonal to each other with a central frequency set to 0 Hz from received signals; a storage unit 32 storing first and second component signal models expressing the I and Q component signals of the received signals; a candidate determination unit 33 performing a numerical search for determining a degree of coincidence between the first component signal generated by the quadrature signal generation unit 20 and the first component signal model in a baseband signal phase range of 180°; and a phase determination unit 34 determining a degree of coincidence between the second component signal and the second component signal model while being limited to candidates of unknown parameters.

Description

  The present invention relates to a radio wave arrival direction estimation device that estimates the direction in which a radio tag exists by estimating from which direction the radio wave emitted by the radio tag comes, and a radio wave arrival comprising the device and the radio tag The present invention relates to a direction 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 circularly moved to create a Doppler shift for the radio wave emitted from the radio wave source.

  The created Doppler shift is maximized on the plus side or the minus side when the antenna velocity vector is in the direction toward the radio wave source and when the antenna speed vector is in the direction opposite to the radio wave source. . The direction of the radio wave source is estimated using such a change in Doppler shift. Therefore, the Pseudo-doppler method analyzes the frequency of the observed signal. In Non-Patent Document 1, Fourier transform is used for frequency analysis.

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, when a device having an antenna fixed on a turntable (hereinafter referred to as an antenna rotating device) is installed indoors, it is necessary to separate a direct wave and a reflected wave caused by multipath.

  The direct wave and the reflected wave generated by multipath have different radio wave arrival angles. That is, the direction of the radio wave source is apparently different between the direct wave and the reflected wave. As described above, the radio wave received by the rotating antenna rotating device undergoes a Doppler shift reflecting the direction of the radio wave transmission 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 period. 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.

  The present invention has been made based on this circumstance, and the object of the present invention is a radio wave arrival direction estimating apparatus that can be downsized, has high frequency resolution, and can reduce the amount of calculation. And providing a radio wave arrival direction estimation system.

  In order to achieve the above object, the present invention provides a radio wave arrival direction estimation device that estimates the arrival direction of a predetermined frequency radio wave transmitted by the wireless tag (100) over an angular range wider than 180 °. There is a rotating disk (12), a driving unit (13) for rotating the rotating disk at a predetermined period, and a radio wave transmitted by the wireless tag fixed at a position other than the center of rotation on the rotating disk. A quadrature signal that generates an I component signal and a Q component signal that are orthogonal to each other with a center frequency of 0 Hz from a reception signal (10) that includes an antenna (11) that receives the signal and a reception signal that represents a radio wave received by the antenna A generation unit (20) and an expression representing a first component signal that is one of an I component signal and a Q component signal of a received signal, and a baseband signal phase indicating a radio wave arrival direction from a wireless tag A first component signal model having a plurality of unknown parameters, and an expression representing a second component signal that is not the first component signal among the I component signal and the Q component signal of the received signal, A storage unit (32) storing a second component signal model having a plurality of unknown parameters including a band signal phase; a first component signal of the I component signal and the Q component signal generated by the orthogonal signal generation unit; A quadrature signal is generated by performing a numerical search for changing the unknown parameter in a range of 180 ° with respect to the baseband signal phase while determining the degree of coincidence between the first component signal model obtained by substituting the numerical value for the unknown parameter and the first component signal model. Determine a plurality of combinations of unknown parameters that become the first component signal model that most closely matches the first component signal side of the I component signal and the Q component signal generated by the unit The degree of coincidence between the complementary determination unit (33), the side that becomes the second component signal of the I component signal and the Q component signal generated by the orthogonal signal generation unit, and the second component signal model in which a numerical value is substituted for the unknown parameter Is determined only by the combination of a plurality of unknown parameters determined by the candidate determining unit, and is most consistent with the second component signal side of the I component signal and the Q component signal generated by the orthogonal signal generating unit. And a phase determination unit (34) that sets the baseband signal phase serving as the second component signal model as the baseband signal phase of the I component signal and the Q component signal generated by the quadrature signal generation unit.

  In the present invention, radio waves with a constant frequency transmitted by the wireless tag are received by an antenna fixed on the rotating disk. Since the antenna repeats approaching and separating from the wireless tag by the rotation of the turntable, the reception signal representing the radio wave received by the antenna has a waveform in which a sine wave is frequency-modulated.

  The orthogonal signal generation unit generates an I component signal and a Q component signal that are orthogonal to each other with a center frequency of 0 Hz from the received signal. Since the received signal is a waveform obtained by frequency-modulating a sine wave, the I component signal and the Q component signal are also waveforms obtained by frequency-modulating the sine wave.

  A sine wave is a frequency-modulated signal, and an I component signal and a Q component signal with a center frequency of 0 Hz can be used even if the baseband signal phases indicating the direction of arrival of radio waves from the wireless tag are 180 ° different from each other. Depending on the distance between the antenna and the antenna.

  Therefore, the candidate determination unit changes the baseband signal phase of the first component signal model representing the first component signal that is one of the I component signal and the Q component signal over a range of 180 °. And the combination of the unknown parameter used as the 1st component signal model which most closely matches the 1st component signal which the orthogonal signal generation part produced | generated is determined. However, even if the baseband signal phases of the first component signal are 180 ° different from each other, depending on the distance between the wireless tag and the antenna, the same waveform is obtained. Become.

  The phase determination unit determines the degree of coincidence with the second component signal generated by the orthogonal signal generation unit by limiting to the combination of the plurality of unknown parameters determined by the candidate determination unit, and determines the combination of unknown parameters . Then, the baseband signal phase included in the determined combination of unknown parameters is set as the baseband signal phase of the I component signal and the Q component signal generated by the orthogonal signal generation unit.

  As described above, in the present invention, the range of the baseband signal phase in which the candidate determination unit performs a numerical search even though the arrival direction of the radio wave transmitted by the wireless tag is estimated over an angular range wider than 180 °. Is in the range of 180 °. Further, the combinations of unknown parameters for which the phase determination unit determines the degree of coincidence are limited to combinations of a plurality of unknown parameters determined by the candidate determination unit. Therefore, the calculation amount is reduced.

  Further, 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 rotate 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 first component signal generated by the quadrature signal generation unit or the first component signal generated by the quadrature signal generation unit using the degree of coincidence between the first component signal or the second component signal generated by the quadrature signal generation unit and the signal model, An unknown parameter of the signal model representing the second component signal is determined. 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 frequency resolution, it is only necessary to narrow the pitch for numerical search. Therefore, it is easy to increase the frequency resolution.

  The invention described in claim 2 is a radio wave arrival direction estimation system including the radio wave arrival direction estimation device according to claim 1 and a wireless tag that transmits a radio wave having a preset constant frequency.

It is a block diagram of the wireless tag reader 1 with which the radio wave arrival direction estimation system of the embodiment is provided. It is a figure which shows the velocity vector V of the antenna 11 when the antenna 11 fixed to the turntable 12 is rotating. It is a conceptual diagram of the waveform of the electric wave which the antenna 11 receives. It is a figure which shows the FM signal which FM-modulated the sine wave.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The radio wave arrival direction estimation system of the present embodiment includes a wireless tag reader 1 and a wireless tag 100 (see FIG. 2) whose configuration is shown in FIG. The wireless tag reader 1 functions as a radio wave arrival direction estimating device.

The wireless tag 100 transmits an unmodulated wave having a predetermined carrier frequency f ₀ set in advance. The wireless tag 100 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 100 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 receiving unit 10, an orthogonal signal generation unit 20, and a signal processing unit 30.

<Description of Receiving Unit 10>
The receiving unit 10 includes an antenna 11, a turntable 12, and a driving unit 13. The antenna 11 is fixed to the outer peripheral edge of the turntable 12. The shape and size of the antenna 11 are not limited as long as the antenna 11 can receive an unmodulated wave transmitted by the wireless tag 100 and can be fixed to a place other than the center of rotation on the turntable 12.

  The turntable 12 is rotated by the drive unit 13. The shape of the rotating disk 12 is not limited to the disk shape, but is preferably not eccentric with respect to the driving unit 13. The turntable 12 has a size that can be easily set in the room. For example, a disk having a diameter of 15 cm. When the turntable 12 rotates, the antenna 11 fixed on it rotates simultaneously.

  The drive unit 13 includes a motor, and rotates the rotating disk 12 at a constant cycle. This fixed period is determined from the rotation speed of the antenna 11 determined from the Doppler shift to be secured and the rotation radius of the antenna 11.

<Received signal characteristics>
Here, a signal (hereinafter, a received signal) received by the antenna 11 will be described. FIG. 2 shows the velocity vector V of the antenna 11 when the antenna 11 fixed to the turntable 12 is rotating. The antenna 11 is linearly approaching the wireless tag 100 when the antenna 11 is at the position a in FIG. 5 and the antenna 11 is linearly moving away from the wireless tag 100 at the position c. In addition, at the positions b and d, the velocity vectors Vb and Vd of the antenna 11 have zero components in the direction of the wireless tag 100. That is, the direction component of the wireless tag 100 of the velocity vector V of the antenna 11 periodically repeats the magnitude by the rotation of the turntable 12.

  Therefore, as shown in FIG. 3, the received signal is a frequency fluctuation signal whose frequency changes in a sine wave shape with time. Hereinafter, the frequency variation signal is referred to as an FM signal. Further, the frequency fluctuation width of the received signal is determined by the rotation speed of the antenna 11.

<Description of Orthogonal Signal Generation Unit 20>
The orthogonal signal generation unit 20 includes a band pass filter 21, a local oscillator 22, a mixer 23, a low pass filter 24, an A / D converter 25, a phase shifter 26, a mixer 27, a low pass filter 28, and an A / D converter 29. ing.

The band pass filter 21 uses a frequency range determined from a Doppler shift generated by the rotation of the antenna 11 around the frequency of the radio wave transmitted by the wireless tag 100 as a pass frequency band. The bandpass filter 21 removes noise from the reception signal received by the antenna 11. The local oscillator 22 generates a local oscillation signal having the same frequency as the carrier frequency f ₀ transmitted by the wireless tag 100.

  The mixer 23 mixes the local oscillation signal and the signal output from the bandpass filter 21, and outputs a signal having a sum frequency and a difference frequency between the frequency of the local oscillation signal and the frequency output from the bandpass filter 21. .

The low-pass filter 24 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 21 from the signal output from the mixer 23. Since the frequency of the local oscillation signal is the same frequency as the carrier frequency f ₀ transmitted by the wireless tag 100, the signal extracted by the band-pass filter 21 varies around 0 Hz. Hereinafter, the signal output from the low-pass filter 24 is referred to as an I component signal. The A / D converter 25 converts the I component signal, which is an analog signal extracted by the low-pass filter 24, into a digital signal.

  The phase shifter 26 shifts the phase of the local oscillation signal by 90 °. The mixer 27 mixes the local oscillation signal whose phase is shifted by 90 ° by the phase shifter 26 and the signal output from the bandpass filter 21. The low pass filter 28 extracts, from the signal output from the mixer 27, 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 21. However, the signal output from the low-pass filter 28 is 90 ° out of phase with the I component signal. A signal output from the low-pass filter 28 is hereinafter referred to as a Q component signal. The A / D converter 29 converts the Q component signal, which is an analog signal extracted by the low-pass filter 28, into a digital signal.

<Description of Signal Processing Unit 30>
The signal processing unit 30 includes a signal acquisition unit 31, a storage unit 32, a candidate determination unit 33, and a phase determination unit 34. The signal acquisition unit 31 acquires signals from the A / D converters 25 and 29 and stores the acquired signals in a storage unit 32 or a predetermined storage unit such as a RAM (not shown).

  As described above, the received signal is an FM signal. Therefore, the I component signal and the Q component signal, which are signals obtained by converting the center frequency of the received signal to 0 Hz and divided into the I component and the Q component, are also FM signals.

  The storage unit 32 stores an I component signal model that is an expression expressing the I component signal and a Q component signal model that is an expression expressing the Q component signal.

<Description of I component signal model and Q component signal model>
FIG. 4 shows an FM signal obtained by FM-modulating a sine wave. As can be seen from FIG. 4, a signal obtained by FM-modulating a sine wave can be expressed by Equation 1. In Equation 1, f ₀ is a carrier frequency, Δf is a maximum frequency displacement, φ is an initial phase (hereinafter referred to as a baseband signal phase), and f ₁ is a baseband signal frequency.

Formula 2 is obtained by multiplying both sides of Formula 1 by 2π to convert it to angular frequency ω.

Since the phase ψ only needs to be integrated with the angular frequency ω, the phase ψ can be expressed by the equation 3 by integrating the equation 2. In Equation 3, θ is the carrier phase.

Since the phase ψ is expressed by Expression 3, when the FM signal of Expression 1 is expressed by a change in the voltage V with respect to time, the following Expression 4 is obtained. In Equation 4, α is an amplitude.

Since the received signal is an FM signal, the received signal is expressed by Equation 4 above. In the received signal, the baseband signal frequency f ₁ is the reciprocal of the rotation period of the turntable 12, and the baseband signal phase φ is the azimuth angle of the wireless tag 100 relative to the wireless tag reader 1, that is, the radio wave from the wireless tag 100. The direction of arrival.

Since the received signal is expressed by Equation 4, the I component signal and the Q component signal obtained by mixing the local oscillation signal having the carrier frequency f ₀ and reducing the center frequency to 0 Hz are expressed by Equation 5 and Equation 5, respectively. 6 can be expressed. These expressions 5 and 6 are an I component signal model and a Q component signal model, respectively.

In Equations 5 and 6, the phase θ _IF is the difference between the carrier phase θ and the phase of the local oscillation signal. This phase θ _IF is an unknown parameter because it changes depending on the distance between the wireless tag 100 and the wireless tag reader 1. The baseband signal phase φ is also an unknown parameter. On the other hand, f ₁ and Δf are known parameters.

Even if the baseband signal phase φ is shifted by 180 °, the Q component signal model of Equation 6 becomes the original equation if the sign of the phase θ _IF is also inverted. In addition, the Q component signal model of Equation 5 becomes the original equation when the phase θ _IF is changed to −θ _IF + π even if the baseband signal phase φ is shifted by 180 °. That is, both the I component signal model of Equation 5 and the Q component signal model of Equation 6 have θ _IF having the same waveform even though the baseband signal phase φ is 180 ° different.

This will be described in detail by changing the formula. In Expressions 5 and 6, when φ + π is substituted for φ and −θ _IF is substituted for θ _IF , Expressions 7 and 8 are obtained.

Since sin (a + π) = − sin (a), Expressions 7 and 8 can be transformed into Expressions 9 and 10.

Since sin (−a) = − sin (a) and cos (−a) = cos (a), Expressions 9 and 10 can be transformed into Expressions 11 and 12.

Equation 12 is the same as Equation 6. That is, even if the baseband signal phase φ is different by 180 °, the Q component signals cannot be distinguished from each other if the phase θ _IF has an opposite sign. However, since Expression 11 and Expression 5 are different, it can be seen that (φ, θ _IF ) and (φ + π, −θ _IF ) can be distinguished by the I component signal.

However, the I signal component cannot distinguish (φ, θ _IF ) from (φ + π, −θ _IF + π). This will be described next. In Expressions 5 and 6, when φ + π is substituted for φ and −θ _IF + π is substituted for θ _IF , Expressions 13 and 14 are obtained.

Since sin (a + π) = − sin (a) and cos (a + π) = − cos (a), Expressions 13 and 14 can be transformed into Expressions 15 and 16.

Since sin (−a) = − sin (a) and cos (−a) = cos (a), Expressions 15 and 16 can be transformed into Expressions 17 and 18.

Equation 17 is the same as Equation 5. That is, the I component signal cannot distinguish between (φ, θ _IF ) and (φ + π, −θ _IF + π). However, since Expression 18 and Expression 6 are different, (φ, θ _IF ) and (φ + π, −θ _IF + π) can be distinguished by the Q component signal.

  Thus, the I component signal of Equation 5 and the Q component signal of Equation 6 cannot be distinguished from the case where the baseband signal phase φ is shifted by 180 °, respectively, so that the baseband signal phase φ is determined. For this purpose, both an I component signal and a Q component signal are required.

Here, if the received signal is not reduced to 0 Hz but is reduced to the intermediate frequency f _m , neither the I component signal nor the Q component signal is the same as the signal obtained by shifting the baseband signal phase φ by 180 °. .

In detail, Q component signal of the signal decreased the FM signal of Formula 4 to an intermediate frequency f _m becomes the following equation 19.

By substituting (φ + π, −θ _IF ) for (φ, θ) in Equation 19 and transforming the equations in the same manner as Equations 6 to 12, Equation 20 is obtained.

The expression 20, since the term of the intermediate frequency f _m is left in the opposite sign to the formula 19, formula 20 and formula 19 are not identical. That is, in the case of reducing the received signal to an intermediate frequency f _m is also only the I signal component, it is possible to determine the baseband signal phase phi.

  As can be seen from the above description, the baseband signal phase φ cannot be determined for either the I component signal or the Q component signal when the center frequency is lowered to 0 Hz.

  As described above, the reason why the baseband signal phase φ cannot be determined for either the I component signal or the Q component signal is that the baseband signal phase φ is 180 °. This is because it is the same as the different signal.

  Candidate deciding unit 33 selects a first generation signal, which is one of the I component signal and the Q component signal, as an arbitrary signal, and one equation corresponding to the first generation signal among equations 5 and 6. Use to analyze. Based on this analysis, a candidate for the baseband signal phase φ that indicates the direction of arrival of radio waves from the wireless tag 100 is determined. In the following description, the first generation signal is an I component signal.

  Specifically, the analysis using the expression of the I component signal is performed by substituting a numerical value into the unknown parameter of the expression of the I component signal, and the difference from the I component signal acquired by the signal acquisition unit 31 (hereinafter referred to as residual energy E). ) Is calculated. The residual energy E represents the degree of coincidence between the signal model and the signal acquired by the signal acquisition unit 31.

  This residual energy E is calculated every time the numerical value to be substituted for the unknown parameter is changed at a pitch determined from the required resolution (here, 1 °). The process of calculating the residual energy E while changing the numerical value assigned to the unknown parameter is hereinafter referred to as a numerical search.

Wireless tag 100 is may be present in the range of 360 °, as described above, even if the I component signal is varied 180 ° baseband signal phase phi, the same waveform as the original waveform theta _IF Exists. By utilizing this, the range in which the candidate determining unit 33 performs numerical search is set to 0 ° to 179 °. A numerical search is performed every 1 ° to determine a combination of unknown parameters when the residual energy E becomes the smallest.

The presence of θ _IF having the same waveform even though the baseband signal phase φ is 180 ° is good in that the range of the numerical search can be narrowed, but the unknown parameter with the smallest residual energy E can be obtained. There will be two combinations. The two baseband signal phases φ in the combination of these two unknown parameters are different from each other. These two baseband signal phases φ are determined as candidates for the baseband signal phase φ.

  The phase determination unit 34 uses the second component signal to determine which of the two baseband signal phase φ candidates determined by the candidate determination unit 33 represents the radio wave arrival direction from the wireless tag 100. The second component signal is a signal that is not the first generation signal among the I component signal and the Q component signal. In the above description, since the first component signal is described as an I component signal, the second component signal is described as a Q component signal.

  In the phase determination unit 34, the residual energy between the Q component signal acquired by the signal acquisition unit 31 and the Q component signal model of Equation 6 for the two unknown parameter combinations determined by the candidate determination unit 33. E is calculated. Then, the two residual energies E are compared, and the baseband signal phase φ included in the unknown parameter combination that becomes the smaller residual energy E is determined as the correct baseband signal phase φ. The angle indicated by the determined baseband signal phase φ is estimated as the radio wave arrival direction from the wireless tag 100.

  As described above, in this embodiment, the candidate determination unit 33 sets the unknown parameter combination of the first component signal model (Equation 5 or 6) over a range of 180 ° with respect to the baseband signal phase φ. The residual energy E is calculated each time the combination of unknown parameters is changed. Then, an unknown parameter combination having the smallest residual energy E is set as a candidate for an unknown parameter combination including the estimated baseband signal phase φ.

  Then, the phase determination unit 34 performs a numerical search only for the candidates determined by the candidate determination unit 33 and estimates the arrival direction of radio waves from the wireless tag 100. Since the candidates determined by the candidate determination unit 33 are two sets, the phase determination unit 34 performs a numerical search by limiting to two candidates.

The reason why the numerical search for determining the unknown parameter candidates of the first component signal model may be in the range of 180 ° with respect to the baseband signal phase φ is as follows. In other words, even if the I component signal model and the Q component signal model shown in Equations 5 and 6 shift the baseband signal phase φ by 180 °, a certain phase θ _IF has the same waveform as before the shift. In other words, the I component signal model of Equation 5 and the Q component signal model of Equation 6 have uncertainty that the baseband signal phase φ is not determined even if the waveform is determined.

  The reason why the I component signal model and the Q component signal model can be expressed by Expressions 5 and 6 is that the signal received by the wireless tag reader 1 is an FM signal whose frequency changes with a sine wave, and this signal This is because the center frequency is reduced to 0 Hz and the signal divided into IQ component signals is analyzed.

  The reason why the signal received by the wireless tag reader 1 is an FM signal whose frequency changes with a sine wave is that the wireless tag 100 transmits an unmodulated wave, and the antenna 11 installed on the rotating disk 12 is the unmodulated wave. It is because it receives by.

As described above, according to the present embodiment, the wireless tag 100 transmits an unmodulated wave, and when the unmodulated wave is received by the antenna 11 installed on the turntable 12, the received signal is a sine wave and has a frequency. The FM signal changes. Then, by generating an I component signal and a Q component signal with a center frequency of 0 Hz from this received signal, the I component signal and the Q component signal are the same even if the baseband signal phase φ is 180 ° different at a certain θ _IF. It becomes a waveform. Therefore, the range for numerically searching for the unknown parameter candidates of the first component signal model is only 180 ° for the baseband signal phase φ. Then, the phase determination unit 34 searches for a numerical value limited to the combination of two unknown parameters that are candidates, and estimates the arrival direction of the radio wave from the wireless tag 100.

  Therefore, in the present embodiment, even if the wireless tag 100 may exist in a 360 ° range around the wireless tag reader 1, a numerical search for estimating the direction in which the wireless tag 100 exists is performed as a baseband signal. Since only 182 ° is required for the phase φ, the calculation amount is reduced.

  In this embodiment, the I component signal acquired by the signal acquisition unit 31 is calculated by calculating the residual energy E representing the degree of coincidence between the I component signal and the Q component signal acquired by the signal acquisition unit 31 and the signal model. The unknown parameter representing the signal model representing the Q component signal is determined. Therefore, it is possible to increase the Doppler shift by rotating the turntable 12 at a high speed. That is, it is not necessary to increase the size of the turntable 12 in order to increase the speed of the antenna 11 fixed to the turntable 12. Therefore, the size of the turntable 12 can be reduced. Further, in order to increase the frequency resolution, it is only necessary to narrow the pitch for numerical search. Therefore, it is easy to increase the frequency resolution.

  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.

  For example, in the above-described embodiment, there is one I component signal model and one Q component signal model, but two or more I component signal models and Q component signal models may be used. If two or more I component signal models and two Q component signal models are used, the incoming waves in the multipath can be specified.

  For example, it is assumed that there are two arriving waves and the range where these two waves may arrive is 360 °. Further, it is assumed that the first component signal is an I component signal. When the arrival directions of these two waves are estimated with a resolution of 1 °, there are 360 × 360 combinations of arrival directions of the arrival waves.

However, when unknown parameter candidates are determined as in the above-described embodiment, any incoming wave may be numerically searched within a range of 180 °. That is, the candidate determining unit 33, to the _I 1 + _{I 2} is the sum of the first component signal model _{I 2} to I-component signal model _{I 1} and the second wave to the first wave, the baseband signal phase phi _1, phi ₂ for may be a numerical search for ways 180 × 180. Φ ₁ and φ ₂ are the baseband signal phase of the first wave and the baseband signal phase of the second wave, respectively. Therefore, the amount of calculation is ¼ compared with the case where 360 × 360 values are numerically searched.

When two first component signal models are used on the assumption that there are two incoming waves, the number of combinations of baseband signal phases φ ₁ and φ ₂ determined by the candidate determination unit 33 is four. The phase determination unit 34 compares the second component signal acquired by the signal acquisition unit 31 with the second component signal model limited to combinations of unknown parameters including the four baseband signal phases φ ₁ and φ _2. To do.

  Comparing the calculation amount of the candidate determination unit 33 and the phase determination unit 34, the calculation amount of the candidate determination unit 33 is overwhelmingly large. Therefore, in the case of estimating two incoming waves, the amount of calculation can be reduced to approximately ¼ compared with a case where 360 × 360 patterns are numerically searched.

  For example, there are the following methods for estimating the number of incoming waves. In the first method, when the magnitude of the residual energy E calculated as one first component signal model is not less than or equal to the threshold value, it is assumed that the incoming wave is greater than or equal to the first component signal model. The number is increased, and the number of first component models when the number becomes equal to or less than the threshold is set as the number of incoming waves. The second method is a method of estimating from the position of a radio wave reflecting object in the surrounding environment where the wireless tag reader 1 is installed.

  Even in a multipath environment, it is not always necessary to use a plurality of first component signal models and second component signal models. Only one first component signal model and one second component signal model may be used in a multipath environment. In a multipath environment, when one each of the first component signal model and the second component signal model is used, the signal model of one incoming wave with the highest signal level can be determined, and the signal level is highest. This is because incoming waves are often direct waves.

DESCRIPTION OF SYMBOLS 1: Radio | wireless tag reader, 10: Receiving part, 11: Antenna, 12: Turntable, 13: Drive part, 20: Orthogonal signal generation part, 21: Band pass filter, 22: Local oscillator, 23: Mixer, 24: Low pass filter 25: A / D converter, 26: Phase shifter, 27: Mixer, 28: Low-pass filter, 29: A / D converter, 30: Signal processing unit, 31: Signal acquisition unit, 32: Storage unit, 33 : Candidate determination unit, 34: phase determination unit, 100: wireless tag

Claims (2)

A radio wave arrival direction estimation device for estimating the arrival direction of a predetermined frequency radio wave transmitted by the wireless tag (100) over an angular range wider than 180 °,
A turntable (12), a drive unit (13) that rotates the turntable at a predetermined period, and a radio wave that is fixed at a position other than the center of rotation on the turntable and transmitted by the wireless tag A receiving unit (10) including an antenna (11) to perform,
An orthogonal signal generation unit (20) for generating an I component signal and a Q component signal orthogonal to each other with a center frequency of 0 Hz from a reception signal representing a radio wave received by the antenna;
A formula expressing a first component signal that is one of an I component signal and a Q component signal of the received signal, and a plurality of unknown parameters including a baseband signal phase indicating a radio wave arrival direction from the wireless tag. A first component signal model, and an expression representing a second component signal that is not the first component signal among the I component signal and the Q component signal of the received signal, and the baseband signal phase A storage unit (32) storing a second component signal model having a plurality of unknown parameters including:
While determining the degree of coincidence between the side of the I component signal and the Q component signal generated by the orthogonal signal generation unit that is the first component signal and the first component signal model in which a numerical value is substituted for the unknown parameter The numerical search for changing the unknown parameter is performed in a range of 180 ° with respect to the baseband signal phase, and becomes the first component signal of the I component signal and the Q component signal generated by the orthogonal signal generation unit. A candidate determination unit (33) for determining a plurality of combinations of unknown parameters that become the first component signal model that most closely matches the side,
The degree of coincidence between the I component signal and the Q component signal generated by the orthogonal signal generation unit and the second component signal model obtained by assigning a numerical value to the unknown parameter is determined as the candidate. Determining only a combination of a plurality of unknown parameters determined by the determination unit, and the best match with the side that becomes the second component signal of the I component signal and the Q component signal generated by the orthogonal signal generation unit A phase determination unit (34) that sets the baseband signal phase that becomes the second component signal model as the baseband signal phase of the I component signal and the Q component signal generated by the orthogonal signal generation unit. A radio wave arrival direction estimation device.   A radio wave arrival direction estimation system comprising: the radio wave arrival direction estimation device according to claim 1; and a wireless tag that transmits a radio wave having a predetermined frequency set in advance.

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