JP2002040120A - Position-detecting system for radio wave source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position-detecting system for a radio wave source, which is enhanced in detection accuracy by eliminating influence of phase difference (ϕa-ϕb), that is caused from a phase shift due to multipath propagation or fading. SOLUTION: The position-detecting system for a radio wave source comprises a plurality of sensor stations (S1, S2, S3), which receive electric waves emitted by a radio wave source (unknown station) to decompose a receiving signal waveform within a prescribed period of time from a reference time into a real part and an imaginary part and then transmits complex frequency components produced by Fourier-transforming each part to a center station (C), an the center station (C), which calculates a complex conjugate product between complex frequency components received from these sensor stations (S1, S2, S3) to calculate a difference between the arrival time of each sensor station from a relation between the phase revolution quantity and the frequency of this complex conjugate product, and then detects the position of the radio wave source, based on this calculated difference of the arrival times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for detecting a radiation position of a radio wave radiated from a moving body or the like.

[0002]

2. Description of the Related Art Conventionally, as a system for detecting the position of a radio wave source called an unknown station such as a moving body that radiates radio waves,
`` Ken-ichi Itho, Soichi Watanabe, Takuro Sato and
Yoshi-saburo Hoshiko, "Radio Source Positioning Us
ing Received Time of ArrivalDifferences "Proc. VT
The method described in C 1999-Fall, pp 2062-2066, Sept. 1999 is known. According to this method, two sensor stations are set apart from each other, radio waves emitted by unknown radio wave sources are received by these sensor stations, and a received signal waveform within a predetermined time from a reference time is converted into a real part and an imaginary part. The complex frequency components are created by Fourier transforming each part, and the complex conjugate product between these multiple frequency components is calculated. Is calculated.

[0003] Here, propagation times required for a radio wave radiated from an unknown radio wave source to propagate to the two sensor stations A and B are denoted by ta and tb, respectively. Focusing on the frequency fm component contained in the radio waves emitted from this radio source and received by the sensor stations A and B, the frequency components received by the sensor stations A and B are expj
[(2πfm · ta + φa)] and exp [j (2πfm · tb + φb)].

[0004] The conjugate product of these frequency components is exp [j (2
πfm (ta−tb) + (φa−φb)]. By dividing the phase rotation amount of the conjugate product Θ = 2πfm (ta−tb) + (φa−φb) by the frequency fm, the propagation time difference τ = ta−
tb + (φa−φb) / fm is detected. Where the phase difference
(φa−φb) occurs due to multipath propagation, phase shift due to fading, and the like.

[0005]

The system for detecting the position of an unknown radio wave source has an advantage that the system can be realized at a low cost because the antenna system is simpler than the conventional system in which two direction finding devices are combined. . However, there is a problem that the calculated value of the propagation time difference of the radio wave includes the phase difference (φa−φb), and this phase difference becomes an error with respect to the propagation time difference τ.

Accordingly, an object of the present invention is to provide a position detection system with improved detection accuracy by removing the influence of a phase difference (φa−φb) caused by multipath propagation or phase shift due to fading. To provide.

[0007]

A position detecting system for a radio wave source according to the present invention for solving the above-mentioned problems of the prior art receives a radio wave emitted from the radio wave source and converts a received signal waveform within a predetermined time from a reference time. Decompose into a real part and an imaginary part, a plurality of sensor stations that transmit complex frequency components created by performing Fourier transform of each part to the center station, and a complex conjugate product between complex frequency components received from these sensor stations. Calculated,
A center station that calculates the arrival time difference between the sensor stations based on the relationship between the phase rotation amount of the complex conjugate product and the frequency, and detects the position of the radio wave source based on the calculated arrival time difference.

According to the first aspect of the present invention, the center station creates a double complex conjugate product between two different frequencies and two different sensor stations, and calculates the phase of the double complex conjugate product. By calculating the arrival time difference between the sensor stations from the relationship between the rotation amount and the frequency difference, the phase difference
(φa−φb) is canceled and erased to increase the detection accuracy.

According to the second aspect, the center station creates a complex conjugate product between two different frequencies and two different sensor stations instead of the double complex conjugate product. A sum over a predetermined frequency range is calculated while giving a phase rotation amount based on the estimated value of the arrival time difference to the complex conjugate product, and the arrival time difference estimated at the time when the sum is maximized is detected as a true arrival time difference. Thus, the phase difference and the noise are cancelled by canceling each other, and the detection accuracy is improved.

[0010]

According to a preferred embodiment of the first aspect of the present invention, the creation of the double complex conjugate product is first performed between two sensor stations for the same frequency. Is performed for two different frequencies.

[0011] According to another preferred embodiment of the second invention, two different dominant components on the frequency axis are selected as two different frequency components for generating the double complex conjugate product. You.

According to another preferred embodiment of the second invention, the center station assigns a predetermined amount of phase rotation based on the estimated value of the arrival time difference to the calculated double complex conjugate product. By calculating the sum over the frequency range and detecting the arrival time difference estimated at the time when this sum becomes the maximum as the true arrival time difference, it absorbs variations due to noise and realizes highly accurate detection. Have been.

According to the preferred embodiments of the first and second aspects of the present invention, before the calculation of the complex conjugate product, the center station performs a mutual operation on the frequency component of the complex component received from each sensor station. By performing offset compensation based on the correlation, the detection accuracy is further improved.

According to still another preferred embodiment of the first and second aspects of the present invention, the reference time is set using the GPS, thereby realizing high detection accuracy with a simple configuration. It is configured as follows.

[0015]

[Principle] According to the position detecting system of the present invention, the phase difference (φa−φb) causing the detection error of the propagation time difference is removed as follows. That is, when focusing on the component of the frequency fn contained in the radio waves emitted from the radio wave source and received by the sensor stations A and B, the above-mentioned frequency fm
The conjugate product of the received signals at the sensor stations A and B is exp [j (2πfn (ta−tb) + (φ
a −φb)].

If a mutual conjugate product is further taken between the conjugate product between the sensor stations created for the component of the frequency fn and the conjugate product between the sensor stations created for the component of the frequency fm, the double conjugate product exp [j (2π (fn −fm) (ta−tb)] is obtained.
In the process of creating this double conjugate product, the phase difference (φa−φb) is canceled and eliminated from the equation. Desired propagation time difference
(ta −tb) is the phase of this double conjugate product 2π (fn −fm)
It is detected by dividing (ta−tb) by the difference frequency δf = 2π (fn−fm). As an example of the frequency difference δf = fn−fm, a frequency between the nearest neighbor samples of the FFT is selected.

[0017]

FIG. 2 is a functional block diagram showing an entire configuration of a radio wave source position detecting system according to an embodiment of the present invention. The three sensor stations S1, S2, S3 and the center station C are installed apart from each other, and each of the sensor stations S1, S2, S3
3 and the center station C are connected by a wired or wireless transmission path. Radio waves emitted from radio sources (unknown stations) indicated by crosses are received by the sensor stations via the antennas of the sensor stations S1, S2, and S3, and complex frequency components at a reference time are created. Is transferred to the center station via.

FIG. 3 is a functional block diagram showing the configuration of the sensor stations S1, S2, S3. A radio wave transmitted from a radio source (unknown station) to be searched is received by an antenna 1 and a local oscillation signal supplied from a local oscillator 2 which is one of local oscillators installed for each of a plurality of frequency bands. Mixer 3
Mixed in. The difference frequency beat signal generated by the mixing is passed through the band-pass filter 4,
The received signal is converted into a low frequency analog signal (intermediate frequency signal or baseband signal).

The low-frequency analog signal is supplied to an A / D conversion circuit 5 where a predetermined time (for example, 0.5 seconds) from a reference time accurately determined by using a GPS receiver 6 is used as a digital signal. Is converted to This digital signal is multiplied in each of multipliers 8 and 9 by a first signal supplied from intermediate frequency signal oscillator 7 and a second signal orthogonal to the first signal. By passing through low-pass filters 10 and 11 consisting of FIR filters, real component I and imaginary component Q
Is converted into a complex baseband signal consisting of

At this time, the bandwidths of the low-pass filters 10 and 11 are set to about twice the signal bandwidth in order to suppress phase distortion. When converting the digital signal in the A / D converter 5 in the preceding stage, the low-pass filters 10 and 11 are used in order to prevent a measurement error due to aliasing.
A / D at a sampling frequency more than twice the upper limit frequency of
Conversion is performed.

The complex baseband signals I and Q output from the low-pass filters 10 and 11 are converted into parallel / serial converters 12 and
After the real part and the imaginary part are converted into serial signals arranged in front and back, they are down-sampled to about one hundredth in order to compress the amount of data, and
It is stored in the memory 14. A serial / parallel converter 15 converts the complex baseband signal read from the memory 14
Is converted again into parallel data consisting of a real part and an imaginary part, and a fast discrete Fourier transform (FFT) is performed on each of the real part and the imaginary part to convert the data into a complex frequency spectrum.

The complex frequency spectrum obtained by the FFT is subjected to signal conversion and filtering in the signal conversion / filtering unit 17 such as replacement of the positive side part with the negative side part and deletion of the outer part of the signal bandwidth. Thereafter, the data is transferred to the center station via a wired or wireless transmission path. As described above, by deleting the outer part of the signal bandwidth, the line capacity can be reduced.

Note that frequency components other than an integer multiple of the FFT frequency resolution fluctuate the phase characteristics of the FFT output and deteriorate the time difference detection accuracy. In this embodiment, rectangular windows, Bartlett windows, Blackman windows, Hanning windows, Hamming windows, Kaiser windows, and Chebyshev windows were evaluated as FFT windows for removing the unnecessary frequency components. As a result, it was confirmed that the use of the Blackman window minimized the deterioration of accuracy in a fading environment. In addition, the provision of the memory before the FFT makes it possible to cope with a sudden change in the transmission signal and the reception signal having the burst property.

In the center station, the complex frequency spectrum at the reference time transferred from each sensor station passes through a FIFO type buffer memory, so that the variation in the transfer time on the transmission path between the stations is absorbed. Transferred to device. This data processing device detects the position of the radio wave source by processing the complex frequency spectrum transferred from each sensor station according to the procedure shown in the flowchart of FIG.

Referring to the flowchart of FIG. 1, upon receiving the complex frequency spectrum from each sensor station (step 21), the data processing device first corrects the frequency offset between the sensor stations (step 22). The correction of the frequency offset is performed in order to prevent the frequency of the local oscillation signal used for the frequency conversion of the received signal from being varied for each sensor station, and preventing this from causing an error. In the data processing device, the cross-correlation between the complex frequency spectra sent from each sensor station is calculated while shifting the frequency, and so as to maximize this calculated value,
A frequency offset amount is assigned to the complex frequency spectrum of each sensor station (step 22).

Next, a complex conjugate product is calculated for the same frequency component of the complex frequency spectrum of each station to which the frequency offset has been added (step 23). That is, as illustrated in FIG. 4, a certain sensor station (for example, the sensor station S
The complex conjugate of the component S _m1 of the frequency f _m included in the complex frequency spectrum of 1) and the component S _m2 of the adjacent frequency f _m included in the complex frequency spectrum of another sensor station (for example, the sensor station S2). The product S _m1 · S _m2 ^* is calculated.

Similarly, the complex frequency spectrum of the sensor station S1 is
Other frequencies f included in the torque_nComponent S of_n1And the sensor
The corresponding frequency contained in the complex frequency spectrum of station S2
Number f _nComponent S of_n2Complex conjugate product S_n1・ S_n2 ^*Calculations such as
Is applied to all frequency components contained in the complex FFT data.
It is done about.

Next, each frequency component calculated as described above is calculated.
Dominant on the frequency axis among complex conjugate products between sensor stations
Two (higher level)
A complex conjugate product is calculated (step 24). That is,
For example, the frequency f_mAnd frequency f_nThe components of such two
In the case of
Complex conjugate product S between sensor stations_m1・ S_m2 ^*And S_n1・ S_n2 ^*With
Complex conjugate product (S_m1・ S _m2 ^*) ・ (S_n1・ S_n2 ^*)^*Calculation
Settings, resulting in different sensor stations and different frequencies.
A double complex conjugate product for is created. Remaining frequency
For the same frequency component between sensor stations
For the calculated complex conjugate product, the two dominant
Double complex conjugate product is calculated for two components
You.

In the next step 25, a metric estimation regarding the propagation time difference τ is performed. That is, each of the double complex conjugate products calculated in the preceding step 24 is multiplied by the amount of phase rotation based on the estimated value τ ₀ of the arrival time difference between the sensor stations. For example, the complex conjugate product (S _m1 · S
^{_{m2 *) · (S n1 ·}} S n2 *) ^* For the phase rotation amount based on the estimated value tau ₀ the arrival time difference _{2π (f n -f m) τ} 0
Is multiplied.

The multiplication of the amount of phase rotation based on the estimated value τ ₀ of the propagation time difference is performed for all complex conjugate products calculated in the preceding step 24, and the sum of the products is used as a metric. When the estimated value of the propagation time difference is closest to the true value, the metric takes the maximum value. In this embodiment,
Using this metric technique, an estimated value τ ₀ of the arrival time difference between the sensor stations is calculated.

Next, the estimated value τ ₀ of the arrival time difference between the two sensor stations is multiplied by the propagation speed of the radio wave to obtain the propagation path difference d.
Is calculated. Then, a hyperbola with the focus on each sensor station is calculated as a locus of the position of an unknown radio source having a propagation path difference d between two sensor stations existing at a known distance L apart. Such a hyperbola is calculated for each pair of sensor stations, and the location of the unknown radio source is calculated as the intersection of these hyperbolas (step 26). The calculated radio wave source is displayed on a screen of a display device in the center station.

As described above, in the calculation of the double complex conjugate product, the configuration in which the complex conjugate product between sensor stations is calculated for the same frequency, and then the complex conjugate product is calculated between the two frequencies has been exemplified. However, conversely, for each sensor station, the complex conjugate product is first calculated for different frequencies, and then the corresponding complex conjugate product is calculated between the two sensor stations to form a double complex conjugate product. A configuration for calculating the product may be employed.

Further, the configuration for calculating a double complex conjugate product between two dominant frequency components on the frequency axis has been exemplified.
However, if necessary, a complex conjugate product can be created for two frequency components separated from each other, such as the nearest neighbor, one jump, and two jumps.

Further, a configuration in which the detection accuracy is improved by applying a metric method in calculating the propagation time difference between the sensor stations has been exemplified. However, when not much detection accuracy is required, a configuration may be adopted in which the propagation time differences obtained from some frequency components are simply averaged.

The configuration for calculating the arrival time difference between the sensor stations from the relationship between the amount of phase rotation and the frequency difference from the double complex conjugate product has been described above. However, instead of calculating a double complex conjugate product of each frequency component, a single complex conjugate product is calculated for the same frequency component at two different sensor stations, and a metric method is employed for the single complex conjugate product. By calculating the arrival time difference between the sensor stations, the phase difference (φa−φb) between the sensor stations can be substantially removed.

That is, a plurality of frequencies m, m + 1, m +
The calculation result of the complex conjugate product between the two sensor stations 1 and 2 for 2, m + 3... Is as illustrated in FIG. The calculation result of each complex conjugate product includes a phase difference (φa−φb) between sensor stations and a fluctuation component due to noise. When the metric method is applied to these multiple conjugate products, a composite vector as shown in FIG. 6 is obtained. Although the influence of noise is removed from the phase rotation amount of the combined vector, a fixed phase rotation amount based on the phase difference (φa−φb) between the sensor stations is included.

However, the object of calculation is not the amount of phase rotation of the combined vector, but the estimated value of the propagation time difference τ given to maximize the absolute value of the combined vector. It does not depend on the phase difference (φa−φb). Thus, by employing the metric method for a single complex conjugate product of the same frequency between two sensors,
The phase difference (φa−φb) between the sensor stations can be substantially eliminated. When no noise is present, the combined vector is not a broken line but a straight line.

Further, the configuration in which the reference time is set using the GPS has been exemplified. However, the setting of the reference time can also employ an appropriate method other than GPS, for example, a synchronization operation between stations by transmitting and receiving a synchronization signal between stations.

[0039]

As described in detail above, according to the system of the first aspect of the present invention, a double complex conjugate product between two different frequencies and two different sensor stations is created, and this double complex conjugate product is created. From the relationship between the phase rotation amount of the complex conjugate product and the frequency difference, the arrival time difference between the sensor stations is calculated, so that multipath propagation or phase difference (φa−φb) caused by fading or the like is obtained. Are cancelled and eliminated, and the effect of greatly improving the detection accuracy is achieved.

According to the preferred embodiment of the present invention, by applying the metric method, variations in the detection values due to noise and the like are eliminated by averaging, and the detection accuracy is further improved.

According to the system of the second aspect,
Even if the metric method is applied to a single multiple conjugate product between two stations, the phase difference (φa − φb) and noise caused by fading etc. are canceled and eliminated, and the detection accuracy is greatly improved. The effect is achieved.

[Brief description of the drawings]

FIG. 1 is a flowchart for explaining the contents of a position detection process performed in a center station of a position detection system for a radio wave source according to an embodiment of the present invention.

FIG. 2 is a functional block diagram showing an entire configuration of the position detection system of the embodiment.

FIG. 3 is a functional block diagram showing a configuration of a sensor station constituting the position detection system of the embodiment.

FIG. 4 is a conceptual diagram for explaining the contents of processing performed by a center station constituting the position detection system of the embodiment.

FIG. 5 is a conceptual diagram for explaining the principle of the second invention.

FIG. 6 is a conceptual diagram for explaining the principle of the second invention.

[Explanation of symbols]

S1-S3 sensor station C center station X radio source 1 antenna 2,7 local oscillator 3,8,9 mixer 5 A / D converter 6 GPS receiver 12 parallel / serial conversion 15 serial / 3 parallel conversion 16 fast Fourier transform circuit S _{m, 1} The component of the frequency m in the reception spectrum of the sensor station 1 S _{m, 2} The component of the frequency m in the reception spectrum of the sensor station 2

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Ito 4-5-56 Urayama, Niigata City, Niigata Prefecture (72) Inventor Yoshimasa Ito 1-20-10 Higashi Tamagawa, Setagaya-ku, Tokyo (72) Inventor Yoshi Hoshiko Saburo 3-22-4 Setagaya, Setagaya-ku, Tokyo 10-22B, Tani 10B −27−503 F term (reference) 5J062 CC07 5K067 DD02 DD20 EE02 EE10 EE13 FF03 GG01 GG11 JJ53 JJ57

Claims (10)

[Claims] A complex frequency component generated by receiving a radio wave emitted by a radio wave source, decomposing a received signal waveform within a predetermined time from a reference time into a real part and an imaginary part, and performing a Fourier transform on each part. A complex conjugate product between a plurality of sensor stations to be transmitted to the station and complex frequency components received from these sensor stations is calculated. And a center station that detects the position of the radio source based on the time difference of arrival, and this center station creates a double complex conjugate product between two different frequencies and two different sensor stations, From the relationship between the phase rotation amount of this double complex conjugate product and the frequency difference,
A position detection system for a radio wave source, wherein a difference in arrival time between the sensor stations is calculated. 2. The radio wave according to claim 1, wherein the double complex conjugate product is first created between two sensor stations for the same frequency, and is created for two different frequencies. Source location system. 3. The method according to claim 1, wherein two dominant frequency components are selected as two different frequency components for generating the double complex conjugate product. A source location system. 4. The system according to claim 1, wherein the center station applies a phase rotation amount based on the estimated value of the arrival time difference to the calculated double complex conjugate product over a predetermined frequency range. A position detection system for a radio wave source, wherein a sum is calculated, and an arrival time difference estimated at a time when the sum is maximized is detected as a true arrival time difference. 5. The apparatus according to claim 1, wherein the center station performs a cross-correlation on a frequency component of a complex component received from each of the sensor stations before calculating the double complex conjugate product. A position detection system for a radio wave source, wherein offset detection is performed based on the offset. 6. The position detecting system according to claim 1, wherein the reference time is set using a GPS. 7. The radio wave source position detecting system according to claim 1, wherein the Fourier transform performed by each of the sensor stations is a discrete fast Fourier transform. 8. A complex frequency component generated by receiving a radio wave emitted by a radio wave source, decomposing a received signal waveform within a predetermined time from a reference time into a real part and an imaginary part, and performing a Fourier transform on each part. A complex conjugate product between the plurality of sensor stations to be transmitted to the station and the complex frequency components received from these sensor stations is calculated, and the arrival time difference between the sensor stations is determined from the relationship between the phase rotation amount and the frequency of the complex conjugate product. And a center station for detecting the position of the radio source based on the difference between the arrival times. The center station creates a complex conjugate product between two different frequencies and two different sensor stations, and The sum over a predetermined frequency range is calculated while giving the amount of phase rotation based on the estimated value of the arrival time difference to the product, and the arrival time difference estimated at the time when the sum is maximized is calculated as the true arrival time. The position detection system of the radio wave sources and detecting as between difference. 9. The system according to claim 8, wherein the center station calculates the complex conjugate product before
A radio wave source position detecting system, wherein offset compensation based on cross-correlation is performed on a frequency component of a complex component received from each of the sensor stations. 10. The system according to claim 8, wherein the reference time is set using a GPS.