JP4266029B2 - POSITIONING DEVICE AND POSITION DETERMINING METHOD IN POSITIONING DEVICE - Google Patents

Description

  The present invention receives a radio wave emitted from a radio wave source such as an RFID (Radio Frequency IDentification) tag at a plurality of base stations such as an RFID reader, and specifies the position of the radio wave source from a radio wave reception time difference at each base station. This relates to the time difference positioning method.

  There is a time difference positioning method that can determine the position of a radio wave source that is a source of direct waves from the reception times of direct waves received by a plurality of base stations (see, for example, Patent Document 1). From the difference between the direct wave reception time at the reference base station and the direct wave reception time at each base station itself, obtain the distance from each base station to the radio wave source that is the source of the radio wave, from multiple base stations The position of the radio wave source is estimated by specifying a place where the distances of the two coincide.

Japanese translation of PCT publication No. 2003-532314 (first page, FIG. 3)

  However, the prior art has the following problems. The conventional method is based on the premise that the radio wave received by each base station is known, and there is a problem that time measurement cannot be performed when an unknown radio wave is used.

The present invention has been made to solve the above-described problems. Even when an unknown radio wave is used, the time difference of the position of the radio wave source can be measured based on the measurement of the direct wave reception time at each base station. An object of the present invention is to obtain a positioning device and a position specifying method in the positioning device.

A positioning device according to the present invention receives a radio wave transmitted from a radio wave source, and measures a plurality of reception time calculation base stations that measure a radio wave reception time from a correlation between a reference signal and the received radio wave, and a plurality of reception time calculation base stations In a positioning device provided with a time difference positioning device that identifies the position of a radio wave source based on the respective radio wave reception times from the radio wave , the unknown radio wave transmitted from the radio wave source and having an unknown amplitude and phase are received and received. The base station further includes a specific base station that estimates the frequency component of the reference signal based on the frequency component included in the unknown radio wave and generates a reference signal at the reference time, and the plurality of reception time calculation base stations receive the reference signal from the specific base station The radio wave reception time is measured from the correlation between the received radio wave and the received unknown radio wave.

The position specifying method in the positioning device according to the present invention includes a step of generating a reference signal at a reference time by estimating an unknown radio wave transmitted from a radio source at a specific base station, and a plurality of reception time calculating base stations The step of measuring the radio wave reception time from the correlation between the reference signal from the base station and the received unknown radio wave, and the time difference positioner, the position of the radio wave source based on the respective radio wave reception times from the plurality of reception time calculation base stations And a step of specifying

Further, the position specifying method in the positioning device according to the present invention includes a step of transmitting a radio wave from one of a plurality of RFID reader / writers or a specific RFID reader / writer to the RFID tag, and the received power of the radio wave is detected by the RFID tag. A step of transmitting an unknown radio wave, a step of generating a reference signal at a reference time by estimating an unknown radio wave transmitted from an RFID tag with a specific RFID reader / writer, and a step of specifying with a plurality of RFID reader / writers The step of measuring the radio wave reception time from the correlation between the reference signal from the RFID reader / writer and the received unknown radio wave, and the time difference positioning device based on the radio wave reception times from a plurality of RFID readers / writers. And a step of specifying the position of the tag.

According to the present invention, unknown radio waves are estimated at a specific base station, and each base station measures the direct wave reception time based on the estimation result by the specific base station. location method in possible with the positioning device and positioning device a time difference determining the location of the radio wave sources based on the measurement of the direct wave reception time in the base station can be obtained.

Hereinafter, preferred embodiments of the positioning device of the present invention will be described with reference to the drawings.
The positioning device of the present invention measures the position of a radio wave source using an unknown radio wave, estimates the unknown radio wave by a specific base station, generates a reference signal at a reference time, and based on this reference signal, respectively The base station obtains the direct wave reception time.

Embodiment 1 FIG.
First, the basic principle of time difference positioning will be described. FIG. 15 is a diagram showing a basic configuration of a positioning device that specifies the position of a radio wave source by time difference positioning. Radio wave source 1 and K base stations 15 (1) to 15 (K) (where K is 3). And the time difference positioning device 3. FIG. 15 shows three base stations, which corresponds to the case of K = 3.

  The radio wave source 1 transmits radio waves to the base stations 15 (1) to 15 (K). On the other hand, each of the base stations 15 (1) to 15 (K) arrives via a direct wave transmitted from the radio wave source 1 and directly reaching each base station, and a route different from the direct wave due to multipath. A radio wave including an indirect wave is received, and a direct wave reception time is measured from the received radio wave.

  The time difference positioning device 3 receives the direct wave reception times measured by the respective base stations 15 (1) to 15 (K), and determines the position of the radio wave source 1 based on the position of each base station and the direct wave reception time. It is specified by the time difference positioning process.

  FIG. 16 is a diagram showing a basic configuration of a base station for measuring the direct wave reception time. Nakahara et al. “Comparison study of multiple propagation delay time resolution between FFT-MUSIC method and FFT operation type correlation method” , Shingaku Sodai, B-27, 1995. Each base station 15 (1) to 15 (K) has the basic configuration shown in FIG. 16, and can obtain the direct wave reception time based on the radio wave received by itself.

  This base station includes a passive antenna 4, a receiver 5, an A / D converter 6, FFT processors 7a and 7b, a reference signal generator 16, a correlation processor 12, and a MUSIC processor 13. Here, the FFT processors 7a and 7b correspond to frequency component calculation means, the correlation processor 12 corresponds to correlation signal generation means, and the MUSIC processor 13 corresponds to radio wave reception time estimation means.

  A radio wave transmitted from the radio wave source 1 is received by the passive antenna 4. The radio wave received by the passive antenna 4 is subjected to band limitation, phase detection, and the like by the receiver 5 and then converted from an analog signal to a digital signal by the A / D converter 5.

  The digital signal thus obtained is further subjected to FFT (Fast Fourier transform) processing by the FFT processor 7a, and converted from a time domain signal to a frequency domain signal. On the other hand, the reference signal generated by the reference signal generator 16 is also subjected to FFT (Fast Fourier transform) processing by the FFT processor 7b, and converted from a time domain signal to a frequency domain signal.

  Correlation calculation is performed by the correlation processor 12 on each frequency domain signal output from the FFT processors 7a and 7b. Further, the signal after the correlation calculation is subjected to MUSIC (Multiple Signal classification) processing by the MUSIC processor 13, and the direct wave reception time measured with high resolution is obtained. The direct wave reception times thus measured are transmitted from the respective base stations 15 (1) to 15 (K) to the time difference positioning device 3, and the time difference positioning device 3 is based on the respective direct wave reception times. The position of the radio wave source will be specified.

  Next, a series of operations of the positioning device and specific arithmetic expressions for positioning will be described. Each of the base stations 15 (1) to 15 (K) includes a direct wave that the radio wave transmitted from the radio wave source 1 directly reaches and an indirect wave that reaches via a different path from the direct wave due to multipath. Radio waves are received by the passive antenna 4. The reception time is measured with a preset reference time common to all base stations as zero.

Here, the processing content will be described by taking a certain k-th base station (where k is an integer of 1 ≦ k ≦ K) as an example. The time when the k-th base station receives the direct wave is τ _{1, k} and the time when the indirect wave is received is τ _{2, k} . The radio wave received by the passive antenna 4 is transmitted to the receiver 5, where band limitation and phase detection are performed. Further, the output signal from the receiver 5 is transmitted to the A / D converter 6.

The A / D converter 6 samples the received radio wave and converts it into a digital signal. Here, in the A / D converter 6, z _{1, k} ... Z _{N, k} is a digitized received signal with the sample period T _samp and the number of samples N (where N is an integer equal to or greater than 1). And Next, FFT processor 7a is calculated, the received signal z ₁ which is _digitized, k · · · z _N, the frequency components y ₁ of the received signal by performing FFT processing on the _k, k · · · y _N, the _k To do.

Here, a frequency component y ′ _{1, k} ... Obtained by adding a direct wave component and an indirect wave component transmitted from the radio wave source 1 included in the frequency component y _{1, k} ... Y _{N, k} of the received signal. y ′ _{N, k} is expressed by the following equations (1) and (2). In equations (1) and (2), Γ _{i, i} represents a frequency component of a reference signal (details will be described later). C _{1, k} represents the amplitude value of the direct wave, and c _{2, k} represents the amplitude value of the indirect wave.

The reference signal generator 16 assumes that the radio wave transmitted from the radio wave source 1 is received at time zero on the assumption that the radio wave received at each base station is known. The reference signal z0 ₁ ,. .., z0 _N is generated. Reference signal z0 _1, ···, z0 _N is, FFT processing is performed by the FFT processor 7b, the frequency component gamma _{1, 1} of the reference _signal, ···, Γ _{N, N} is generated. The correlation processor 12 uses the following equation (3) to calculate the frequency components Γ _1,1 , ..., Γ _{N, N} of the reference signal and the frequency components y _{1, k} ... Y _{N, k of the} received signal. It performs correlation calculation between the correlation signal in the frequency domain x _{1, k} ··· x _N, to produce a _k.

The correlation signal x ′ _{i, k obtained} by adding the direct wave component and the indirect wave component included in the correlation signal x _{i, k} in the frequency domain is specifically expressed by the following equation (4).

The correlation signal x _{i, k} actually output from the correlation processor 12 is expressed by the following equation (5) using the correlation signal x ′ _{i, k obtained} by adding the direct wave component and the indirect wave component. The In equation (5), n _{i, k} represents a receiver noise component superimposed on the correlation signal x ′ _{i, k} in equation (4) at the time of MUSIC processing input.

The MUSIC processor 13 takes in the correlation signal x _{i, k} (where i is an integer satisfying 1 ≦ i ≦ N) as an input signal. When the vector x _i is defined as x _i = [x _{i, k,} x _{i + 1, k} ... X _{i + M−1, k} ] ^T , the vector x _i is expressed by the following equation (6). The MUSIC processor 13 performs MUSIC processing using a (τ) as a steering vector, calculates an estimated value τ _{1, k} (tilde) of the direct wave reception time corresponding to the measurement value of the direct wave observation time, and performs time difference positioning. Is transmitted to the container 3. Note that M used here is the order of the steering vector, and is an integer smaller than the number N of samples.

  Here, when the MUSIC process is performed, two types of reception times of the direct wave and the indirect wave are measured. However, since the direct wave arrives faster than the indirect wave, The measured value τ (tilde) is estimated with the direction of arrival of the direct wave.

The time difference positioning device 3 measures the position of the radio wave source 1 based on τ (tilde) transmitted from each base station. The time difference positioning device 3 sets a specific base station (k _0th base station) and assumes a distance from the k _0th base station to the radio wave source 1 as r _k0 . At this time, the time difference positioning device 3 uniquely determines the k ₀ th position from the difference between the direct wave reception time at the k ₀ th base station and the direct wave reception time at the other base station by the following equation (10). The distance from each base station other than the base station to the radio wave source 1 can be specified. Here, c represents the speed of light.

FIG. 17 is a diagram illustrating the relationship between the distances from the base stations to the radio wave source 1 specified when the distance from the k _0th base station to the radio wave source 1 is assumed to be r _k0 . under the assumption of r _k0, it shows a state depicting respectively a circle of radius r _k around a position of a k-th base station. If, when the radio wave source 1 is present at a distance r _k, so that the radio wave source 1 is present in any point on the circumference of radius r _k.

Therefore, first we change the r _k0 assuming, when determining the respective radii r _k of the time, when a certain value r _k0, state intersect at one point, each of the circumferential occurs It will be. FIG. 18 is a diagram illustrating a state where the circumferences intersect at a certain point at a certain value r _k0 . Therefore, the time difference positioning device 3 can determine the position of the radio wave source 1 by _{obtaining rk0 in} a state as shown in FIG. 18 based on the direct wave reception time at each base station.

  Actually, the circumferences around the positions of the base stations do not completely intersect at a certain point due to measurement errors of the direct wave reception time. Therefore, the time difference positioning device 3 estimates the position of the radio wave source 1 by calculating the position where the square error of the distance is minimized using the least square method or the like.

  In the method described above, on the premise that the radio waves received by each base station are known, a reference signal is generated based on the known radio waves, and the direct wave reception time is measured. On the other hand, the present invention is characterized in that positioning based on time measurement can be performed even when an unknown radio wave is received, and details thereof will be described below.

  FIG. 1 is a configuration diagram of a positioning apparatus according to Embodiment 1 of the present invention, which includes a radio wave source 1, K unknown radio wave-compatible base stations 2 (1) to 2 (K), and a time difference positioning device 3. Is done. The radio wave source 1 and the time difference positioning device 3 are the same as those shown in the basic configuration of FIG. 15, and will be described focusing on the unknown radio wave compatible base stations 2 (1) to 2 (K).

The unknown radio wave compatible base station 2 (k ₀ ) (where k ₀ is an integer of 1 ≦ k ₀ ≦ K) estimates the unknown radio wave, generates a reference signal of the reference time as the estimation result, It is a specific base station that transmits to the unknown radio wave compatible base stations 2 (1), 2 (2), and 2 (K).

On the other hand, the unknown radio wave-corresponding base stations 2 (1), 2 (2), 2 (K) are transmitted from the radio wave source 1 using the reference signal from the unknown radio wave-corresponding base station 2 (k ₀ ). This is a reception time calculation base station that measures the reception time of a direct wave.

Thus, the positioning device of the present invention estimates the unknown radio wave by a specific base station (corresponding to the unknown radio wave compatible base station 2 (k ₀ )) to generate the reference signal of the reference time, In the base station (corresponding to unknown radio wave compatible base stations 2 (1), 2 (2), 2 (K)), the direct wave reception time is measured based on this reference signal, and the radio wave source is positioned.

FIG. 2 is a diagram showing a configuration for estimating an unknown radio wave in the specific base station according to Embodiment 1 of the present invention, and shows a configuration of the unknown radio wave corresponding base station 2 (k ₀ ) that is the specific base station. Is. The passive antenna 4, the receiver 5, the A / D converter 6, and the FFT processor 7 in FIG. 2 are the same as those shown in FIG.

  The reference signal generator 8 as reference signal generation means estimates the signal of the frequency component of the unknown radio wave subjected to the FFT process, and generates a reference signal for calculating the direct wave reception time. FIG. 3 is a configuration diagram of the reference signal generator 8 according to Embodiment 1 of the present invention. The reference signal generator 8 includes an indirect wave reception time estimator 9, an amplitude ratio estimator 10, and an initial phase estimator 11.

  The indirect wave reception time estimator 9 estimates the reception time of the indirect wave from the signal of the frequency component of the unknown radio wave subjected to the FFT process. The amplitude ratio estimator 10 estimates the amplitude ratio between the amplitude of the direct wave received at time zero and the amplitude of the indirect wave at the estimated reception time of the indirect wave. Further, the initial phase estimator 11 estimates the initial phase of the radio wave transmitted from the radio wave source.

  FIG. 4 is a configuration diagram of a base station that measures the direct wave reception time using the unknown radio wave estimation result according to Embodiment 1 of the present invention. 1) The structure of 2 (2) and 2 (K) is shown. The passive antenna 4, the receiver 5, the A / D converter 6, the FFT processor 7, the correlation processor 12, and the MUSIC processor 13 in FIG. 4 are the same as those shown in FIG.

  The reception time calculation base station having the configuration of FIG. 4 does not require the reference signal generator 16 and the FFT processor 7b as compared with the configuration of the base station shown in FIG. 16, and specifies the reference signal instead. It is configured to capture from the base station.

Next, a series of operations and specific arithmetic expressions for positioning will be described. Each of the unknown radio wave-corresponding base stations 2 (1), 2 (2), 2 (K), 2 (k ₀ ) is directly connected to the direct wave to which the radio wave transmitted from the radio wave source 1 directly reaches by multipath. The passive antenna 4 receives a radio wave including an indirect wave that reaches via a different path from the wave.

First, the unknown radio wave-compatible base station 2 (k ₀ ), which is a specific base station, generates a reference signal at a reference time with a direct wave reception time being zero, based on the received radio wave. After that, the unknown radio wave-corresponding base stations 2 (1), 2 (2), 2 (K), which are reception time calculation base stations, and the reference signal generated by the unknown radio wave-corresponding base station 2 (k ₀ ), The direct wave reception time is measured by performing a correlation operation with the frequency component of the received signal after the FFT processing generated by itself.

The unknown radio wave compatible base station 2 (k ₀ ) has a configuration for estimating an unknown radio wave as shown in FIG. A radio wave transmitted from the radio wave source 1 generates a multipath. The passive antenna 4 receives radio waves including direct waves and indirect waves. Thereafter, the processing in the receiver 5, the A / D converter 6, and the FFT processor 7 is the same as that described in FIG. 16, and the frequency components _{y1, k0,} ... y _{N, k0} is output.

The frequency components y _{1, k0} ... Y _{N, k0} of the received signal are transmitted to the reference signal generator 8. Here, the reference signal generator 8 has the processing configuration shown in FIG. The frequency components y _{1, k0} ... Y _{N, k0} of the received signal input to the reference signal generator 8 are transmitted to the indirect wave reception time estimator 9. The indirect wave reception time estimator 9 first calculates the power value Py (i) of the received signal frequency component by the following equations (11) and (12).

Further, a signal vector Py _{i, k0} is set by the following equation (13).

At this time, the signal vector Py _{i, k0} can be expressed by the following equations (14) to (16).

Further, the indirect wave reception time estimator 9 calculates the correlation matrix Rp _k0 of the signal vector Py _{i, k0} by the following equation (17) _, and the indirect wave when the reception time of the direct wave is zero by MUSIC processing. An estimated value τ _{2, k0} (tilde) of the reception time is calculated with high resolution.

The estimated value τ _{2, k0} (tilde) of the reception time output from the indirect wave reception time estimator 9 is transmitted to the amplitude ratio estimator 10. The amplitude ratio estimator 10 estimates the amplitude ratio between the direct wave and the indirect wave based on the estimated value τ _{2, k0} (tilde) of the reception time. First, an estimated value C _k0 (i) (tilde) of the amplitude ratio C _k0 (i) is calculated by the following equation (18).

Next, C _k0 (i) (tilde) is averaged, and an estimated value C _k0 (tilde) of the amplitude ratio between the direct wave and the indirect wave is calculated by the following equation (19).

The amplitude ratio estimator 10 transmits the estimated value τ _{2, k0} (tilde) of the indirect wave reception time and the estimated value C _k0 (tilde) of the amplitude ratio between the direct wave and the indirect wave to the initial phase estimator 11. Next, the initial phase estimator 11 first calculates a phase detection signal H _i represented by the following equation (20).

Next, the initial phase estimator 11 estimates the initial phase value φ _i (tilde) of the frequency component Γ _{i, i} of the reference signal from the real part and the imaginary part of the phase detection signal H _i calculated by the above equation (20). ) Is calculated. Further, the initial phase estimator 11 calculates an estimated value Γ _{i, i} (tilde) of the frequency component of the reference signal by the following equation (21).

The initial phase estimator 11 calculates the estimated value Γ _{i, i} (tilde) of the frequency component of the reference signal in this way for each unknown radio wave-corresponding base station 2 (1), 2 (2), 2 (K ). Each unknown radio wave-corresponding base station 2 (1), 2 (2), 2 (K) is replaced with the unknown radio wave-corresponding base station 2 (k) in place of the frequency component Γ _{i, i} of the reference signal in equation (3). ₀ ) is used to calculate the correlation signal x _{i, k} in the frequency domain using the estimated value Γ _{i, i} (tilde) of the frequency component of the reference signal sent from ₀ ).

Further, the MUSIC processor 13 uses the same procedure as that already described with reference to FIG. 16 on the assumption that the radio wave received at each base station is known, and uses the direct wave as the measurement value of the direct wave observation time. An estimated value τ _{1, k} (tilde) of the reception time is calculated.

  In addition, as an unknown radio wave transmitted from the radio wave source 1, a highly accurate positioning is possible by adopting a radio wave whose absolute value of the frequency component is constant regardless of the frequency. That is, if the specific base station uses a signal with a constant amplitude (absolute value) in the frequency domain, the unknown parameter is only the phase, and therefore the initial phase can be reliably detected.

  Further, when high-resolution processing is required according to the difference between the reception times of the direct wave and the indirect wave, the MUSIC process as described above is used. Also in this case, by adopting a radio wave whose absolute value of the frequency component is constant regardless of the frequency as the unknown radio wave, more accurate positioning is possible.

  According to the first embodiment, the specific base station can generate the reference signal at the reference time with the reception time of the direct wave being zero based on the received unknown radio wave. Further, the reception time calculation base station can measure the direct wave reception time from the unknown radio wave received by itself based on the reference signal generated by the specific base station. Thereby, even when an unknown radio wave is used, the direct wave reception time can be measured, and the time difference of the position of the radio wave source can be measured.

Embodiment 2. FIG.
In the second embodiment, another method for measuring the reception time of the direct wave using the estimation result of the unknown radio wave will be described. FIG. 5 is a configuration diagram of a base station that measures the reception time of a direct wave using the estimation result of the unknown radio wave according to Embodiment 2 of the present invention. (1) Shows the configuration of 2 (2) and 2 (K).

  The passive antenna 4, receiver 5, A / D converter 6, correlation processor 12, and MUSIC processor 13 in FIG. 5 are the same as those in FIG. 4 in the first embodiment. In the second embodiment, a filter bank 14 is used instead of the FFT processor 7, and the function of the filter bank 14 will be mainly described.

  FIG. 6 is a configuration diagram of the filter bank 14 according to the second embodiment of the present invention. The filter bank 14 is composed of N (where N is an integer equal to or greater than 2 and the same number as the number of samples N) FIR (Finite Impulse Response) type bandpass filters 14 (1) to 14 (N). . The band pass filters 14 (1) to 14 (N) have different pass bands with respect to the existence range Wp of the frequency component of the input radio wave.

Next, a series of operations and specific arithmetic expressions for positioning will be described. Each of the unknown radio wave-corresponding base stations 2 (1), 2 (2), 2 (K), 2 (k ₀ ) is directly connected to the direct wave to which the radio wave transmitted from the radio wave source 1 directly reaches by multipath. The passive antenna 4 receives a radio wave including an indirect wave that reaches via a different path from the wave.

First, the unknown radio wave compatible base station 2 (k ₀ ), which is a specific base station, generates a reference signal at the reference time based on the received radio wave. After that, the unknown radio wave-corresponding base stations 2 (1), 2 (2), 2 (K), which are reception time calculation base stations, and the reference signal generated by the unknown radio wave-corresponding base station 2 (k ₀ ), The direct wave reception time is measured by performing a correlation operation with the frequency component of the received signal after processing by the filter bank generated by itself.

The unknown radio wave compatible base station 2 (k ₀ ) has a configuration for estimating an unknown radio wave as shown in FIG. A radio wave transmitted from the radio wave source 1 generates a multipath. The passive antenna 4 receives radio waves including direct waves and indirect waves. Thereafter, the processing in the receiver 5 and the A / D converter 6 is the same as that described in FIG. 16, and the received signal z _{1, k} ... Z that has been digitized from the A / D converter 6. _{N, k} is output.

The digitized received signals z _{1, k} ... Z _{N, k} are transmitted to the filter bank 14. The filter bank 14 includes N band-pass filters 14 (1) to 14 (N), and the i-th band pass filter 14 (i) (where i is an integer of 1 ≦ i ≦ N) is Then, the signal y _{i, k} of the i-th frequency component of the received signal is output by the following equation (22).

Thereafter, the correlation processor 12 and the MUSIC processor 13 operate in the same manner as in the first embodiment, and measure the estimated value τ _{1, k} (tilde) of the direct wave reception time.

  According to the second embodiment, the unknown radio wave is estimated by specifying any one of the base stations, and at the other base station, by measuring the reception time of the direct wave based on the estimation result, Even when an unknown radio wave is received at each base station, the direct wave reception time can be measured and the time difference of the position of the radio wave source can be measured. Furthermore, in another base station which is a reception time calculation base station, it is possible to measure the direct wave reception time by using a filter bank having a plurality of band pass filters instead of the FFT processor.

Embodiment 3 FIG.
In Embodiments 1 and 2, the direct wave reception time is measured by specifying one unknown radio wave-corresponding base station 2 (k ₀ ) as a base station that estimates unknown radio waves, and the position of the radio wave source 1 is measured. The case of estimating is described. In the third embodiment, the measurement of the direct wave reception time and the calculation of the position of the radio wave source are individually performed for cases where different base stations are identified as base stations for estimating the unknown radio wave, thereby obtaining a plurality of estimation results. A case will be described in which the position of the radio wave source 1 is finally determined from the obtained and estimated results. The configuration of the positioning device in the third embodiment is the same as that in FIG.

The unknown radio wave-corresponding base stations 2 (1), 2 (2), 2 (k ₀ ), and 2 (K) in Embodiment 3 each estimate the unknown radio wave and generate a reference signal, It has a function of transmitting the reference signal to another unknown radio wave compatible base station. Further, each unknown radio wave-corresponding base station 2 (1), 2 (2), 2 (k ₀ ), 2 (K) obtains a direct wave reception time based on each reference signal, and a time difference positioning device 3 also has a function to transmit to.

FIG. 7 is a flowchart showing a processing procedure performed by the time difference positioning device 3 to identify the position of the radio wave source 1 in the third embodiment of the present invention. In step S701, the time difference positioning device 3 sets the number of the specific base station that estimates the unknown radio wave to k ₀ = 1. In step S702, the time difference positioning device 3 performs the same procedure as in the first embodiment based on the direct wave reception time calculated by each unknown radio wave-corresponding base station when the specific base station is k ₀ = 1. To calculate the position p1 (tilde) of the radio wave source 1.

Then, in step S703, the time difference positioning device 3, it is determined whether the number k ₀ of a particular base station is smaller than the number K of base stations. If it is determined that k ₀ <K, the time difference positioning device 3 adds 1 to the number k ₀ of the specific base station and updates k ₀ in step S704. Then, the time difference positioning device 3 repeats the processes of steps S702 and S703, so that the position pk ₀ of the radio wave source 1 when k base stations are all specified base stations (where k ₀ is 1 ≦ 1). k ₀ ≦ integer of K) is calculated.

If it is determined in step S703 that k ₀ <K is not satisfied, it means that the positions pk ₀ of the radio wave source 1 when the K units are specified base stations have been prepared, and the time difference positioning device 3 is set in step S705. The average value p (tilde) of pk ₀ (tilde) is calculated. In this way, a plurality of base stations are set as specific base stations for unknown radio wave estimation, a plurality of positioning results of the radio wave source 1 are obtained, and the position of the radio wave source 1 is set to 1 by averaging the multiple positioning results. Can be specified.

  In the description of FIG. 7, the positions of the K radio wave sources 1 in the case where all K units are specified base stations are obtained, but the present invention is not limited to this. The position of the radio wave source 1 can be specified as a single position from a plurality of measurement results even when not all K units and a plurality of two or more base stations are specified base stations.

  Further, for example, it is possible to average by deleting the maximum value and the minimum value without averaging all the positioning results, and by using various statistical methods, one positioning result can be obtained from a plurality of positioning results. The positioning result can be obtained.

  In the third embodiment, a plurality of specific base stations have an original function of generating a reference signal and a function of measuring a radio wave reception time (that is, a function that the reception time calculation base station originally has). However, the present invention is not limited to this. A base station having only the original function of generating a reference signal can be used as a plurality of specific base stations.

  According to the third embodiment, a plurality of base stations can be set as specific base stations for unknown radio wave estimation, and the position of the radio wave source can be specified based on a plurality of positioning results. As a result, it is possible to obtain a positioning result with reduced positioning error compared with the positioning result obtained by setting only one base station as a specific base station for unknown radio wave estimation, and improve the measurement accuracy. Can be planned.

Embodiment 4 FIG.
In the fourth embodiment, a case where an RFID tag is used as a radio wave source and an RFID reader / writer is used as a base station will be described. The basic configuration and operation are the same as those described in the first to third embodiments.

  The RFID tag has excellent environmental resistance and is not affected by dirt such as water, oil, chemicals, or ambient light. Further, by performing non-contact power transmission from the RFID reader / writer side, the RFID tag can be used semi-permanently without having a battery.

  The radio wave source 1 described in the first to third embodiments has its own battery (power source), actively transmits radio waves by itself, and an RFID tag can be used in the same manner. Furthermore, when an RFID tag is used as the radio wave source 1, the RFID tag itself does not have a battery and does not actively transmit radio waves by utilizing the non-contact power transmission technology described above. By detecting the reception power of the radio wave (or electromagnetic wave) transmitted from the RFID reader / writer, the radio wave (or electromagnetic wave) can be transmitted to the RFID reader / writer.

  Therefore, the RFID tag can transmit radio waves to a plurality of RFID reader / writers in the positioning device by receiving radio waves from any RFID reader / writer. On the other hand, a specific RFID reader / writer among the plurality of RFID readers / writers functions as the specific base station described in the first to third embodiments, receives a radio wave from the RFID tag as an unknown radio wave, and this unknown radio wave Can be estimated to generate a reference signal at the standard time.

  Further, a plurality of RFID readers / writers other than the specific RFID reader / writer function as the reception time calculation base station described in the first to third embodiments, and the reference signal received from the specific RFID reader / writer and the RFID The radio wave reception time is measured from the correlation with the unknown radio wave received from the tag. Then, the time difference positioning device 3 specifies the position of the RFID tag based on each radio wave reception time load measured by a plurality of RFID readers / writers other than the specific RFID reader / writer.

  According to the fourth embodiment, even when an RFID tag and an RFID reader / writer are used as a radio wave source and a base station, a positioning device that can identify the position of the RFID tag based on an unknown radio wave from the RFID tag is obtained. Can do. Further, if a non-contact power transmission technology from the RFID reader / writer side is used, the RFID tag is made battery-free, has excellent environmental resistance, and can be used semipermanently.

Embodiment 5 FIG.
In the fifth embodiment, even when the amplitude ratio of the direct wave and the indirect wave is a complex number, the reference signal at the reference time with the reception time of the direct wave being zero can be generated based on the received unknown radio wave. The base station will be described.

FIG. 8 is a diagram showing a configuration for estimating unknown radio waves in a specific base station according to Embodiment 5 of the present invention, and shows a configuration of unknown radio wave-corresponding base station 2 (k ₀ ) that is the specific base station. Is. The passive antenna 4, receiver 5, A / D converter 6, and FFT processor 7 in FIG. 8 are the same as those in FIG. 2 showing the configuration of the first embodiment.

  The complex amplitude ratio compatible reference signal generator 18 corresponds to the reference signal generator 8 in FIG. 2, and estimates a frequency component signal of an unknown radio wave subjected to FFT processing, and calculates a direct wave reception time. Is generated. Here, the complex amplitude ratio compatible reference signal generator 18 can generate a reference signal even when the amplitude ratio of the direct wave and the indirect wave is a complex number, which is different from the reference signal generator 8 in FIG.

  FIG. 9 is a configuration diagram of the complex amplitude ratio compatible reference signal generator 18 according to the fifth embodiment of the present invention. The complex amplitude ratio compatible reference signal generator 18 includes an indirect wave reception time estimator 9, a complex amplitude ratio estimator 19, and a complex amplitude ratio compatible initial phase estimator 20.

The indirect wave reception time measuring device 9 is the same as that described in the first embodiment, and estimates the reception time of the indirect wave from the signal of the frequency component of the unknown radio wave subjected to the FFT process. The complex amplitude ratio estimator 19 estimates the complex amplitude ratio between the amplitude of the direct wave received at time zero and the amplitude of the indirect wave at the estimated reception time of the indirect wave. Further, the complex amplitude ratio corresponding initial phase estimator 20 estimates the initial phase of the reference signal from the output signal of the indirect wave reception time measuring device 9 and the frequency component y _{i, k0 of the} received signal output from the FFT output device 7. To do.

Next, specific arithmetic expressions for operation and positioning will be described. The unknown radio wave compatible base station 2 (k ₀ ) has a configuration for estimating an unknown radio wave as shown in FIG. A radio wave transmitted from the radio wave source 1 generates a multipath. The passive antenna 4 receives radio waves including direct waves and indirect waves.

Thereafter, the processing in the receiver 5, the A / D converter 6, and the FFT processor 7 is the same as that described in FIG. The frequency component y _{i, k0} of the reception signal output from the FFT output unit 7 includes a frequency component y ′ _{i, k0} obtained by adding the direct wave component and the indirect wave component transmitted from the radio wave source 1. This frequency component y ′ _{i, k0} is expressed by the following equation (23).

The amplitude ratio between C ′ _{1 and k 0} that are the amplitude values of the direct wave and C ′ _{2 and k 0} that are the amplitude values of the indirect wave can be expressed by C ′ _{k 0} as shown in the following equation (24). Here, C ′ _k0 is a complex number.

The frequency component y _{i, k0} of the received signal by the unknown radio wave compatible base station 2 (k ₀ ) is transmitted to the indirect wave reception time estimator 9 in the complex amplitude ratio compatible reference signal generator 18 shown in FIG. The As described in the first embodiment, the indirect wave reception time estimator 9 uses the estimated value τ _{2, k0} (tilde) of the reception time of the indirect wave and the signal vector Py _{i, k0} represented by the equation (13). calculate.

The estimated value τ _{2, k0} (tilde) of the reception time of the indirect wave and the signal vector Py _{i, k0} are input to the complex amplitude ratio estimator 19. The complex amplitude ratio estimator 19 first obtains a signal vector _{Si, k0} (tilde) by the following equations (25) to (27).

Here, the signal vector S _{i, k0} (tilde) is composed of components as shown in the following equation (28).

Next, the complex amplitude ratio estimator 19 obtains an estimated value Arg [C ′ _k0 (tilde) (i)] of the declination value of the complex amplitude ratio C ′ _k0 (i) by the following equation (29). Here, Arg [α] represents the argument of the complex number α.

The complex amplitude ratio estimator 19 obtains an estimated value | C ′ _k0 (tilde) (i) | of the absolute value of the complex amplitude ratio C ′ _k0 (i) from the solution of the following quadratic equation (30). .

  Specifically, this solution is expressed by the following equation (31).

Further, the complex amplitude ratio estimator 19 calculates the argument estimation value Arg [C ′ _k0 (tilde) (i)] in Expression (29) and the absolute value estimation value | C ′ _k0 (tilde) in Expression (31) ( i) is used to obtain a complex amplitude ratio estimated value C ′ _k0 (tilde) by the following equation (32).

Finally, the complex amplitude ratio estimator 19 uses the estimated value τ _{2, k0} (tilde) of the reception time of the indirect wave and the complex amplitude ratio estimated value C ′ _k0 (tilde) to the complex amplitude ratio corresponding initial phase estimator 20. To communicate.

On the other hand, the complex amplitude ratio correspondence type initial phase estimator 20 receives the estimated value τ _{2, k0} (tilde) of the reception time of the indirect wave from the complex amplitude ratio estimator 19 and the complex amplitude ratio estimated value C ′ _k0 (tilde). ) And the frequency component y _{i, k0} of the received signal from the FFT processor 7. Then, the complex amplitude ratio corresponding initial phase estimator 20 first calculates a phase detection signal H _i represented by the following equation (33).

Next, the complex amplitude ratio corresponding initial phase estimator 20 calculates the initial phase estimation value φ _i (reference signal frequency component Γ _{i, j)} from the deviation angle of the phase detection signal H _i calculated by the above equation (33). (Tilde) is calculated by the following equation (34).

Further, the complex amplitude ratio corresponding initial phase estimator 20 calculates an estimated value Γ _{i, j} (tilde) of the frequency component of the reference signal by the following equation (35).

In this manner, the complex amplitude ratio compatible reference signal generator 18, like the reference signal generator 8, estimates the frequency components y _{i, k0} of the received signal to the estimated values Γ _{i, j} (tilde tilde) of the reference signal. ) Can be calculated.

Thereafter, each base station operates in the same manner as in the first embodiment, and based on the estimated values Γ _{i, i} (tilde) of the frequency components of the reference signal output from the complex amplitude ratio corresponding initial phase estimator 20, The estimated value τ _{1, k} (tilde) of the direct wave reception time is measured. Further, the time difference positioning device 3 obtains the position of the radio wave source 1 based on the estimated values τ _{1 and k} (tilde) of the direct wave reception time from each base station.

  According to the fifth embodiment, the specific base station obtains the reference signal at the reference time at which the reception time of the direct wave is zero based on the received unknown radio wave even when the amplitude ratio of the direct wave and the indirect wave is a complex number. Can be generated.

Embodiment 6 FIG.
In the sixth embodiment, an application example in which the positioning device and the position specifying method according to the present invention are applied to positioning of a vehicle position will be described. FIG. 10 is an explanatory diagram of an application example in which the position specifying method is applied to the positioning of the vehicle position in the sixth embodiment of the present invention. The vehicle position is measured using a free flow ETC (Electronic Toll Collection) system.

  In FIG. 10, a vehicle 21 includes an ETC information transmission antenna 22 that transmits information from the ETC as a radio wave. On the other hand, K roadside antennas 23 (1) to 23 (K) that receive transmission radio waves from the ETC information transmission antenna 22 are provided on the roadside.

FIG. 11 is an explanatory diagram of time difference positioning in an application example of the sixth embodiment of the present invention. The time difference positioning device 3 measures the time difference of the vehicle 21 from the estimated values τ _{1 and k} (tilde) of the direct wave reception times from the roadside antennas 23 (1) to 23 (K). The functions of the unknown radio wave compatible base station 2 and the time difference positioning device 3 are the same as those described in the first embodiment.

  FIG. 12 is a configuration diagram of an ETC including an ETC information transmission antenna 22 mounted on the vehicle 21 in an application example of the sixth embodiment of the present invention. The ETC information storage 24 stores information necessary for performing ETC processing. The transmitter 25 transmits information stored in the ETC information storage 24 as a radio wave via the ETC information transmission antenna 22.

  Next, the operation will be described. Information transmitted via the ETC information transmitting antenna 22 is received by the roadside antennas 23 (1) to 23 (K). The radio waves received by the roadside antennas 23 (1) to 23 (K) are transmitted to the unknown radio wave compatible base stations 2 (1) to 2 (K).

Similarly to the fifth embodiment, the k _0th unknown radio wave-corresponding base station 2 (k ₀ ) obtains the estimated values Γ _{i, i} (tilde) of the frequency components of the reference signal, and each unknown radio wave-corresponding base station Transmit to stations 2 (1) -2 (K). Each unknown radio wave-corresponding base station 2 (1) to 2 (K) measures the estimated value τ _{1, k} (tilde) of the direct wave reception time and transmits it to the time difference positioner 3. The time difference positioning device 3 measures the position of the vehicle 21 using the estimated time τ _{1, k} (tilde) of the direct wave reception time.

  Here, when a vehicle not equipped with an ETC passes under the roadside antennas 23 (1) to 23 (K), there arises a problem that a toll cannot be collected. Therefore, it is necessary to discriminate vehicles that are not equipped with ETC.

  According to the application example of the sixth embodiment, the position of the vehicle on which the ETC is mounted can be specified. Therefore, when a vehicle equipped with an ETC and a vehicle not equipped with an ETC pass under the roadside antennas 23 (1) to 23 (K) at the same time, the information on the specified vehicle position is used. Whether or not the vehicle is equipped with ETC can be determined.

  According to the sixth embodiment, the positioning of the vehicle position can be easily realized by applying the positioning device and the position specifying method of the present invention to the ETC system.

Embodiment 7 FIG.
In the seventh embodiment, another application example in which the positioning device and the position specifying method according to the present invention are applied to positioning of a vehicle position will be described. FIG. 13 is an explanatory diagram of an application example in which the position specifying method is applied to positioning of the vehicle position in the seventh embodiment of the present invention. The positioning of the vehicle position is realized using a smart plate.

  Here, the smart plate is an IC chip on which various information such as automobile registration information related to the vehicle is recorded on the license plate of the vehicle and has a function of transmitting various information. is there.

  In FIG. 13, a vehicle 21 includes a smart plate transmission antenna 24 that transmits information from an IC chip of a smart plate as a radio wave. On the other hand, K roadside antennas 23 (1) to 23 (K) that receive transmission radio waves from the smart plate transmission antenna 24 are provided on the roadside.

  FIG. 14 is a configuration diagram of a smart plate including a smart plate transmission antenna 24 mounted on a vehicle 21 in an application example of the seventh embodiment of the present invention. The vehicle information storage 26 corresponds to an IC chip that records various information. The transmitter 25 transmits information stored in the vehicle information storage 26 as radio waves via the smart plate transmission antenna 24.

  Next, the operation will be described. Information transmitted via the smart plate transmission antenna 24 is received by the roadside antennas 23 (1) to 23 (K). The radio waves received by the roadside antennas 23 (1) to 23 (K) are transmitted to the unknown radio wave compatible base stations 2 (1) to 2 (K).

Similar to the sixth embodiment, the k _0th unknown radio wave-corresponding base station 2 (k ₀ ) obtains the estimated values Γ _{i, i} (tilde) of the frequency components of the reference signal, and each unknown radio wave-corresponding base station Transmit to stations 2 (1) -2 (K). Each unknown radio wave-corresponding base station 2 (1) to 2 (K) measures the estimated value τ _{1, k} (tilde) of the direct wave reception time and transmits it to the time difference positioner 3. The time difference positioning device 3 measures the position of the vehicle 21 using the estimated time τ _{1, k} (tilde) of the direct wave reception time.

  According to the seventh embodiment, the positioning of the vehicle position can be easily realized by applying the positioning device and the position specifying method of the present invention to the smart plate system. Since the position of the vehicle on which the smart plate is mounted can be specified, there is an advantage that the vehicle that has entered the restricted area can be found.

It is a block diagram of the positioning apparatus in Embodiment 1 of this invention. It is the figure which showed the structure which estimates the unknown radio wave in the specific base station of Embodiment 1 of this invention. It is a block diagram of the reference signal generator in Embodiment 1 of this invention. It is a block diagram of the base station which measures a direct wave reception time using the estimation result of the unknown radio wave in Embodiment 1 of this invention. It is a block diagram of the base station which measures the reception time of a direct wave using the estimation result of the unknown radio wave in Embodiment 2 of this invention. It is a block diagram of the filter bank in Embodiment 2 of this invention. It is the flowchart which showed the process sequence which a time difference positioning device performs in order to identify the position of a radio wave source in Embodiment 3 of this invention. It is the figure which showed the structure which estimates the unknown radio wave in the specific base station of Embodiment 5 of this invention. It is a block diagram of the complex amplitude ratio corresponding | compatible type reference signal generator in Embodiment 5 of this invention. It is explanatory drawing of the application example which applied the position specific method to the positioning of a vehicle position in Embodiment 6 of this invention. It is explanatory drawing of the time difference positioning in the application example of Embodiment 6 of this invention. It is a block diagram of ETC including the ETC information transmission antenna mounted in the vehicle in the application example of Embodiment 6 of the present invention. It is explanatory drawing of the example of application which applied the position specific method to positioning of a vehicle position in Embodiment 7 of this invention. It is a block diagram of the smart plate containing the smart plate transmission antenna mounted in the vehicle in the application example of Embodiment 7 of this invention. It is the figure which showed the basic composition of the positioning apparatus which pinpoints the position of a radio wave source by time difference positioning. It is a figure which shows the basic composition for measuring a direct wave reception time. It is a figure which shows the relationship of the distance from each base station specified to the radio wave source when the distance from the k _0th base station to the radio wave source is assumed to be r _k0 . It is a figure which shows the state where each circumference _| intersection crossed at one certain point in _rk0 of a certain value.

Claims (16)

A plurality of reception time calculation base stations that receive radio waves transmitted from radio sources and measure radio reception times from the correlation between reference signals and received radio waves;
A positioning device comprising: a time difference positioning device that specifies a position of the radio wave source based on the radio wave reception times from the plurality of reception time calculation base stations;
An unknown radio wave having an unknown amplitude and phase transmitted from the radio wave source is received, a frequency component of the reference signal is estimated based on a frequency component included in the received unknown radio wave, and a reference signal at a reference time is generated A specific base station,
The plurality of reception time calculation base stations are positioning devices that measure radio wave reception times from a correlation between the reference signal from the specific base station and a received unknown radio wave. The positioning device according to claim 1,
The radio wave source is an RFID tag,
The plurality of reception time calculation base stations are a plurality of RFID readers / writers,
The specific base station is a specific RFID reader / writer. The positioning device according to claim 2,
The RFID tag is a positioning device that transmits radio waves by detecting reception power of radio waves from any of the plurality of RFID reader / writers or the specific RFID reader / writer. The positioning device according to claim 2,
The RFID tag transmits a radio wave in which the absolute value of a frequency component is constant regardless of the frequency as an unknown radio wave,
The specific RFID reader / writer generates a reference signal at a standard time by obtaining a phase of the unknown radio wave. The positioning device according to claim 2,
The specific RFID reader / writer is
A receiver for receiving radio waves transmitted from the RFID tag;
A frequency component calculating means for converting a received radio wave from the receiver into a frequency signal of a plurality of frequency components;
A positioning device comprising: reference signal generating means for generating a reference signal corresponding to each frequency component based on the frequency signal from the frequency component calculating means. The positioning device according to claim 5,
The reference signal generation means includes
Based on the frequency signal from the frequency component calculation means, an indirect wave reception time estimation means for estimating the reception time of the indirect wave received via the multipath when the direct wave reception time is zero, and
Amplitude ratio estimating means for estimating an amplitude ratio between the amplitude of the direct wave at time zero and the amplitude of the indirect wave at the estimated reception time of the indirect wave;
Initial phase estimation means for estimating an initial phase of a frequency component of a radio wave transmitted from the RFID tag based on the reception time of the indirect wave and the amplitude ratio and generating a reference signal corresponding to each frequency component. Positioning device. The positioning device according to claim 5,
The reference signal generation means includes
Based on the frequency signal from the frequency component calculation means, an indirect wave reception time estimation means for estimating the reception time of the indirect wave received via the multipath when the direct wave reception time is zero, and
Complex amplitude ratio estimation means for estimating a complex amplitude ratio between the amplitude of the direct wave at time zero and the amplitude of the indirect wave at the estimated reception time of the indirect wave;
Complex that generates a reference signal corresponding to each frequency component by estimating the initial phase of the frequency component of the radio wave transmitted from the RFID tag based on the reception time of the indirect wave, the complex amplitude ratio, and the frequency signal. A positioning device comprising: an amplitude ratio compatible initial phase estimating means. The positioning device according to claim 6 or 7,
The indirect wave reception time estimation means is a positioning device that estimates the reception time of the indirect wave using MUSIC processing. The positioning device according to claim 2,
The RFID reader / writer is
A receiver for receiving radio waves transmitted from the RFID tag;
A frequency component calculating means for converting a received radio wave from the receiver into a frequency signal of a plurality of frequency components;
Correlation signal generation means for generating a correlation signal for each frequency component based on a reference signal from the specific RFID reader / writer and a frequency signal from the frequency component calculation means;
A positioning apparatus comprising: radio wave reception time estimation means for measuring radio wave reception time of an unknown radio wave based on the correlation signal from the correlation signal generation means. The positioning device according to claim 9,
The radio wave reception time estimation means is a positioning device that estimates the radio wave reception time using MUSIC processing. The positioning device according to any one of claims 5 to 10,
The frequency component calculation means is a positioning device which is FFT processing means for calculating frequency signals of the plurality of frequency components from the received radio wave by performing FFT processing. The positioning device according to any one of claims 5 to 10,
The frequency component calculating means is a positioning device that is a filter bank that calculates a frequency signal of the plurality of frequency components from the received radio wave by using a band-pass filter. The positioning device according to any one of claims 2 to 10,
The positioning device includes a plurality of specific RFID reader / writers as the specific RFID reader / writer,
The plurality of RFID readers / writers measure the radio wave reception time for each reference signal from the correlation between each reference signal from the plurality of specific RFID reader / writers and the received unknown radio wave,
The time difference positioning device specifies the position of the RFID tag for each reference signal based on the reception time of each radio wave from the plurality of RFID readers / writers, and further determines the position of the RFID tag from the position of the RFID tag specified for each reference signal. A positioning device that identifies the location of RFID tags. The positioning device according to claim 13,
Each of the plurality of specific RFID readers / writers measures the radio wave reception time for each reference signal from the correlation between each reference signal from the other specific RFID reader / writer and the received unknown radio wave,
The time difference positioning device specifies the position of the RFID tag for each reference signal based on the reception times of the radio waves from the plurality of RFID reader / writers and the plurality of specific RFID reader / writers, and further specifies for each reference signal A positioning device that identifies the position of the RFID tag from the position of the RFID tag. Estimating a unknown radio wave transmitted from a radio wave source at a specific base station and generating a reference signal at a base time;
In a plurality of reception time calculation base stations, measuring a radio wave reception time from a correlation between the reference signal from the specific base station and the received unknown radio wave,
In the time difference positioning device, location method in a positioning device that includes a step of identifying the location of the radio wave source based on each of the radio reception time from the plurality of reception time calculation base station. Transmitting radio waves from one of a plurality of RFID readers / writers or a specific RFID reader / writer to an RFID tag;
Transmitting an unknown radio wave by detecting the received power of the radio wave with the RFID tag;
Generating a reference signal at a standard time by estimating the unknown radio wave transmitted from the RFID tag with the specific RFID reader / writer;
A step of measuring a radio wave reception time from a correlation between the reference signal from the specific RFID reader / writer and the received unknown radio wave in the plurality of RFID reader / writers;
A method for specifying a position in a positioning device, comprising: a step of determining a position of the RFID tag on the basis of each radio wave reception time from the plurality of RFID readers / writers with a time difference positioning device.

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