JP2743719B2 - Propagation path length measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bistatic radar for measuring a propagation path length of a radio wave transmitted from a transmitting device, reflected on a target and received by a receiving device in order to measure a target distance. Related to the device.

[0002]

2. Description of the Related Art First, a brief description will be given of a propagation path length measuring device in a conventional bistatic radar shown in FIG. As an example similar to this conventional example, Japanese Patent Application Laid-Open No. 55-5
No. 4,482. In FIG. 12, 1
Is a transmitter, a modulation signal generator 2 for generating a modulation signal,
The modulation signal generated by the modulation signal generator 2 is converted to RF (Radi
The transmitter 3 includes a transmitter 3 that converts and amplifies the frequency into a frequency, and a transmission antenna 4 that radiates the modulated signal that has been frequency-converted and amplified into RF into the air. 5 is a target, 6 is a transmitted wave emitted from the transmitting antenna, and 7 is a reflected wave of the transmitted wave 6a by the target 5. Reference numeral 10 denotes a receiving device, which includes receiving antennas 11 and 12 and RF signals received by the receiving antennas 11 and 12.
Amplify signal / IF (Intermediate Fre
(Quality), a receiver 13 for phase detection, an A / D converter 14 for converting the phase-detected signal into a digital signal, and a transmitter 1 for the reflected wave 7 in order to measure the propagation path length of the reflected wave 7. And a delay time estimator 17 for estimating the difference between the time of arrival of the transmission wave 6c transmitted directly to the receiving apparatus 10 and the time of arrival of the transmitting wave 6c.

In general, in order to uniquely determine the position of the target 5 with a bistatic radar, the transmitting antenna 4 → the target 5 →
It is necessary to calculate the distance to the receiving antenna 11. For that purpose, (a) preparing clocks that are precise and synchronized with each other in both the transmitting device 1 and the receiving device 10;
The receiving device transmits by either of (b) sending a synchronization signal from the transmitting device 1 to the receiving device 10 by wire or (c) receiving the transmission wave 6c directly emitted to the receiving device as the synchronizing signal. Synchronization with the device 1 is ensured.

[0004] Hereinafter, the transmitted waves 6b and 6c may be referred to as direct waves to emphasize that the receiving apparatus receives the reflected waves directly from the transmitting apparatus instead of the reflected waves from the target.

In the conventional example shown in FIG. 12, a synchronization signal is obtained by using the above method (c) . The target reflected wave 7 is received by the receiving antenna 11 oriented in the direction of the target 5 and subjected to amplification / conversion to IF / phase detection by the receiver 13a, and then to the digital signal by the A / D converter 14a. , And becomes a received signal u (uT). Here, T is a sampling interval in the A / D converter 14. On the other hand, the transmission wave 6c is received by another antenna 12 of the receiving device 10,
Another receiver 13b and A / D converter 14 connected to this
b, the same processing as that of the reflected wave 7 is performed, and the synchronization signal v (n
T). The delay time estimator 17 estimates the delay time difference between the received signal u (nT) and the synchronization signal v (nT) in order to calculate the propagation path length of the reflected wave.

Here, the principle of measuring the propagation path length of the reflected wave will be described. It is assumed that only the target reflected wave 7 is received by the receiving antenna 11. The target reflected wave 7 has a longer propagation distance than the direct wave 6c received by the receiving antenna 12 because the target reflected wave 7 is reflected at the target 5 and propagates from the transmitting device 1. Therefore, the received signal u (nT) is delayed from the synchronization signal v (nT) by the direct wave 6c by the time ΔT corresponding to the difference in the propagation path length.
That is,

V (nT) = A · u ((n−Δ) T) (1)

It is assumed that Δ is normalized by the sampling interval T in the A / D converter 14. Δ is not always an integer. A is a complex constant including all the attenuation during propagation, the cross-sectional area of reflection at the target 5, the gain and phase change due to passing through the antenna and the receiver, and the like.
In order to determine the arrival time difference ΔT, R. E. FIG. Boucher
and J.J. C. Hassab's paper "Analy.
sis of discrete implementation
ation of generalizedcross
correlator ”, IEEE Transac
Tionson Acoustics, Speech,
and Signal Processing, vo
l. ASSP-29, no. 3, pp. 609-61
1, 1981, etc., the received signal u
It is sufficient to calculate a cross-correlation function between (nT) and the synchronization signal v (nT), and obtain a time graph giving the maximum value of the absolute value. This is shown by the broken line in FIG. The time lag at peak A is equal to ΔT. Assuming that the speed of light is c, the difference between the propagation path lengths is d, and the sampling frequency of the A / D converter 14 is fs (= 1 / T),

D = cΔT = cΔ / fs (2)

The distance s by which the target reflected wave 7 is reflected from the transmitting apparatus 1 at the target 5 and propagates is the distance a (known) between the transmitting antenna 4 and the receiving antenna 11 plus the propagation path length difference d. Things.

S = a + d (3)

[0012] target 5, transmits the position of the receiving antenna 11 of the antenna 4 as the focus, the two focal point and the target sum of the distance to the 5 formula (3) spheroidal curved surface on such that s the Exists. If the direction of the target 5 is measured from the position of the receiving antenna 11 by another means, the position of the target 5 can be uniquely determined.

[0013]

The above measuring method is effective when the received signal u (nT) consists of only the target reflected wave 7 component. However, even if the directivity of the receiving antenna 11 is directed to the target 5, the power level of the direct wave 6b is considerably higher than the power level of the target reflected wave 7, so that
The component of the received direct wave 6b is stronger than the component of the target reflected wave 7 even if it enters from the side lobe of the receiving antenna 11. That is, the component of the direct wave 6b is mixed in the received signal u (nT) in addition to the component of the target reflected wave 7. At this time, the reception signal u (nT) and the synchronization signal v (n
The absolute value of the cross-correlation function with T) has a strong correlation between the component of the received signal u (nT) due to the direct wave 6b and the synchronization signal v (nT) due to the direct wave 6c, as shown by the solid line in FIG. , Τ = 0, the peak B is large, and the peak A indicated by the broken line is buried. Therefore, it becomes difficult to detect the time lag ΔT of the peak A, and the expressions (2) and (3)
The value of the path length s of the target reflected wave 7 obtained in step (1) cannot be calculated, or even if it can be calculated, the value becomes inaccurate. This is the same even if another method (a) or (b) for obtaining synchronization is used.

Increasing the directivity of the receiving antenna 11 and minimizing the side lobe in order to avoid the mixing of the direct wave 6b in the receiving antenna 11 can greatly increase the aperture diameter of the antenna and significantly reduce the number of elements. It is difficult to realize technically and economically because it leads to increase.

Further, the cross-correlation function in the digital signal processing system is a sample value, and the sampling interval is equal to that of the digital signal. A for various reasons
If the sampling frequency fs of the / D converter 14 cannot be increased, the sampling interval of the cross-correlation function increases. Therefore, the measurement unit (= sampling interval) of the delay time difference between the received signal u (nT) and the synchronization signal v (nT) becomes coarse, and as a result, the measurement accuracy of the propagation path length of the target reflected wave 7 deteriorates.

The present invention has been made in order to solve these problems. A means for suppressing a direct wave received by being mixed with a target reflected wave is provided, and the propagation path length of the target reflected wave 7 is reduced. It is an object of the present invention to obtain a time lag that gives the maximum value of the absolute value of the cross-correlation function between the target reflected wave reception signal and the synchronization signal in a measurement unit smaller than the sampling interval of the A / D converter for accurate measurement.

[0017]

According to a first aspect of the present invention, there is provided a propagation path length measuring apparatus in which a modulated signal is used as a transmission signal, and a transmission wave is directed to an external space via a transmission antenna. A transmitting device that radiates the transmitting device, the transmitting device is disposed at a predetermined distance from the transmitting device, and among the transmitting waves radiated from the transmitting device, a reflected echo from a target and a transmitting wave directly arriving from the transmitting device are transmitted. After receiving the same signal simultaneously with one receiving antenna and amplifying and detecting the received signal,
A first receiving means for converting to a digital signal, a second receiving antenna for receiving a transmission wave directly arriving from the transmitting device by a second receiving antenna, amplifying and phase detecting the received signal, and then converting the signal to a digital signal; Means for receiving the first receiving means output signal and the second receiving means output signal as inputs, and transmitting directly from the transmitting device included in the first receiving means output signal to the first receiving means. Means for suppressing unnecessary signals due to waves, means for delaying the output signal of the second receiving means by a predetermined time, inputting the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means, and the former delay time with respect to the latter Means for estimating the unnecessary signal, wherein the unnecessary signal suppressing means multiplies the output signal of the second receiving means by a weighting coefficient, and the output means of the multiplying means outputs the output signal of the first receiving means. Means for subtracting the signals, and inputs the above second receiving means output signal and said subtraction means output signal,
Means for calculating the weighting coefficient so as to make the average power of the subtraction means output signal minimum or close to the minimum,
The delay time estimating means calculates a cross-correlation function of the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means to obtain an absolute value thereof, from the output of the means for obtaining the cross-correlation function absolute value. A first means for obtaining and outputting a time lag giving the maximum value, a means for inputting the absolute value of the time lag and the cross-correlation function, and obtaining an interpolation value of an absolute value of the cross-correlation function near the time lag; It is provided with a second means for obtaining a time lag giving the maximum value from the output of the interpolation means of the cross-correlation function absolute value.

According to the second aspect of the present invention, there is provided a propagation path length measuring apparatus.
A transmitting device that radiates a transmission wave toward an external space via a transmitting antenna by using the modulated signal as a transmission signal; and a transmission device that is disposed at a predetermined distance from the transmission device and radiates from the transmission device. First receiving means for simultaneously receiving a reflected echo from a wave target and a transmitted wave directly arriving from the transmitting device by a first receiving antenna, amplifying and phase-detecting the received signal, and converting the signal into a digital signal; A second receiving means for receiving a transmission wave directly arriving from the transmitting device by a second receiving antenna, amplifying and phase-detecting the received signal, converting the signal into a digital signal, and an output signal of the first receiving means; Using the output signal of the second receiving means as an input, an unnecessary signal caused by a transmission wave directly reaching the first receiving means from the transmitting device included in the output signal of the first receiving means is suppressed. Stage, and the second receiving means means for the output signal is delayed by a predetermined period of time, it inputs the unwanted signal suppression means output signal and said signal delay means output signal,
Means for estimating the delay time of the former with respect to the latter,
Multiplying means for multiplying the output signal of the second receiving means by a weighting coefficient, means for subtracting the output signal of the multiplying means from the output signal of the first receiving means, the output signal of the second receiving means; And the subtraction means output signal, and calculating the weighting coefficient so that the average power of the subtraction means output signal is minimum or close to the minimum. The delay time estimating means includes the unnecessary signal suppressing means. Means for calculating a discrete Fourier transform of the output signal, second means for calculating a discrete Fourier transform of the signal delay means output signal, means for taking a complex conjugate of the output of the second discrete Fourier transform calculating means, Means for multiplying the output of the complex conjugate means and the output of the first discrete Fourier transform calculation means to obtain and output cross spectrum data; To means, the number of samples of the cross spectral data N, when the a predetermined integer M, the data of the cross spectral data smoothing means output (N /
(MN−) between the (2) th and (N / 2 + 1) th samples
N) means for inserting zero-valued samples to generate data of the number of samples MN, means for inserting the zero-valued sample, means for performing an inverse discrete Fourier transform on the output, and means for obtaining the absolute value, It is provided with a means for obtaining a time lag that gives the maximum value of the output of the taking means.

According to a third aspect of the present invention, there is provided a propagation path length measuring apparatus.
A transmitting device that radiates a transmission wave toward an external space via a transmitting antenna by using the modulated signal as a transmission signal; and a transmission device that is disposed at a predetermined distance from the transmission device and radiates from the transmission device. Among the waves, a first reception antenna simultaneously receives a reflection echo from a target and a transmission wave directly arriving from the transmission device, amplifies and phase-detects the received signal, and converts the signal into a digital signal. Means for receiving a transmission wave directly arriving from the transmitting device by a second receiving antenna, amplifying and phase-detecting the received signal, and converting the signal into a digital signal; and outputting the first receiving means. A signal and the output signal of the second receiving means are input, and an unnecessary signal caused by a transmission wave directly reaching the first receiving means from the transmitting device included in the output signal of the first receiving means is suppressed. Means for delaying the output signal of the second receiving means by a predetermined time, means for receiving the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means, and estimating the former delay time with respect to the latter. Multiplying means for multiplying the output signal of the second receiving means by a weighting factor; means for subtracting the output signal of the multiplying means from the output signal of the first receiving means; and the second receiving means. Means for inputting the output signal and the output signal of the subtraction means, and calculating the weight coefficient so as to make the average power of the output signal of the subtraction means minimum or close to the minimum, wherein the delay time estimating means is unnecessary. A first means for calculating a discrete Fourier transform of an output signal of the signal suppressing means, a second means for calculating a discrete Fourier transform of an output signal of the signal delaying means, the second discrete Means for taking the complex conjugate of the output of the Fourier transform calculation means, means for multiplying the output of the complex conjugate means and the output of the first discrete Fourier transform calculation means to obtain cross spectrum data, means for smoothing the cross spectrum data, When the number of samples of the cross spectrum data, M, is a predetermined integer, (MN-N) zero value samples are added after the data of the output of the cross spectrum data smoothing means, and the number of samples M
Means for generating N data; means for performing an inverse discrete Fourier transform on the output of the zero-value sample adding means; and means for obtaining the absolute value thereof; means for obtaining a time lag for providing the maximum value of the output of the means for obtaining the absolute value of the inverse discrete Fourier transform Is provided.

According to a fourth aspect of the present invention, there is provided a propagation path length measuring apparatus.
A transmitting device that radiates a transmission wave toward an external space via a transmitting antenna by using the modulated signal as a transmission signal; and a transmission device that is disposed at a predetermined distance from the transmission device and radiates from the transmission device. Among the waves, a first reception antenna simultaneously receives a reflection echo from a target and a transmission wave directly arriving from the transmission device, amplifies and phase-detects the received signal, and converts the signal into a digital signal. Means for receiving a transmission wave directly arriving from the transmitting device by a second receiving antenna, amplifying and phase-detecting the received signal, and converting the signal into a digital signal; and outputting the first receiving means. A signal and the output signal of the second receiving means are input, and an unnecessary signal caused by a transmission wave directly reaching the first receiving means from the transmitting device included in the output signal of the first receiving means is suppressed. Means for delaying the output signal of the second receiving means by a predetermined time, means for receiving the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means, and estimating the former delay time with respect to the latter. Multiplying means for multiplying the output signal of the second receiving means by a weighting factor; means for subtracting the output signal of the multiplying means from the output signal of the first receiving means; and the second receiving means. Means for inputting the output signal and the output signal of the subtraction means, and calculating the weight coefficient so as to make the average power of the output signal of the subtraction means minimum or close to the minimum, wherein the delay time estimating means is unnecessary. A first means for generating a new signal by inserting a predetermined number of zero-valued samples between two samples adjacent to each other with respect to the output signal of the signal component suppressing means; A first low-pass digital filter having a predetermined cutoff frequency and having an output signal of the sample insertion means as an input; A second low-pass digital filter having a predetermined cutoff frequency and having as input the output signal of the second zero-value sample inserting means. Means for calculating a cross-correlation function between the output of the first low-pass digital filter and the output of the second low-pass digital filter and obtaining its absolute value; and output of the means for obtaining the absolute value of the cross-correlation function. It is provided with a means for obtaining and outputting a time lag giving the maximum value.

According to a fifth aspect of the present invention, there is provided a propagation path length measuring apparatus.
A transmitting device that radiates a transmission wave toward an external space via a transmitting antenna by using the modulated signal as a transmission signal; and a transmission device that is disposed at a predetermined distance from the transmission device and radiates from the transmission device. Among the waves, a first reception antenna simultaneously receives a reflection echo from a target and a transmission wave directly arriving from the transmission device, amplifies and phase-detects the received signal, and converts the signal into a digital signal. Means for receiving a transmission wave directly arriving from the transmitting device by a second receiving antenna, amplifying and phase-detecting the received signal, and converting the signal into a digital signal; and outputting the first receiving means. A signal and the output signal of the second receiving means are input, and an unnecessary signal caused by a transmission wave directly reaching the first receiving means from the transmitting device included in the output signal of the first receiving means is suppressed. Means for delaying the output signal of the second receiving means by a predetermined time, means for receiving the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means, and estimating the former delay time with respect to the latter. Multiplying means for multiplying the output signal of the second receiving means by a weighting factor; means for subtracting the output signal of the multiplying means from the output signal of the first receiving means; and the second receiving means. Means for inputting the output signal and the output signal of the subtraction means, and calculating the weight coefficient so as to make the average power of the output signal of the subtraction means minimum or close to the minimum, wherein the delay time estimating means is unnecessary. First means for calculating a discrete Fourier transform of an output signal of the signal component suppressing means, N is the number of samples of the first discrete Fourier transform calculating means output data, and M is a predetermined integer When, the first discrete Fourier transform computation means of the output data (N /
(MN−) between the (2) th and (N / 2 + 1) th samples
N) first means for inserting zero-valued samples to generate data of the number of samples MN; first means for calculating an inverse discrete Fourier transform of the output of the first zero-valued sample inserting means; and the signal delay means Second means for calculating a discrete Fourier transform of the output signal of the second discrete Fourier transform calculating means having the number of samples N and (N / 2) th and (N / 2 +
1) second means for inserting (MN-N) zero-valued samples between the samples to generate data of the number of samples MN, and performing inverse discrete Fourier transform of the output of the second zero-valued sample inserting means second means, said first calculates the cross-correlation function number of the inverse discrete Fourier transform computation means output and said second inverse discrete Fourier transform computing means output, means for taking the absolute value calculating, the cross-correlation It is provided with a means for calculating a time lag that gives the maximum value of the output of the means for taking the absolute value of the function.

According to a sixth aspect of the present invention, there is provided a propagation path length measuring apparatus.
A transmitting device that radiates a transmission wave toward an external space via a transmitting antenna by using the modulated signal as a transmission signal; and a transmission device that is disposed at a predetermined distance from the transmission device and radiates from the transmission device. Among the waves, a first reception antenna simultaneously receives a reflection echo from a target and a transmission wave directly arriving from the transmission device, amplifies and phase-detects the received signal, and converts the signal into a digital signal. Means for receiving a transmission wave directly arriving from the transmitting device by a second receiving antenna, amplifying and phase-detecting the received signal, and converting the signal into a digital signal; and outputting the first receiving means. A signal and the output signal of the second receiving means are input, and an unnecessary signal caused by a transmission wave directly reaching the first receiving means from the transmitting device included in the output signal of the first receiving means is suppressed. Means for delaying the output signal of the second receiving means by a predetermined time, means for receiving the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means, and estimating the former delay time with respect to the latter. Multiplying means for multiplying the output signal of the second receiving means by a weighting factor; means for subtracting the output signal of the multiplying means from the output signal of the first receiving means; and the second receiving means. Means for inputting the output signal and the output signal of the subtraction means, and calculating the weight coefficient so as to make the average power of the output signal of the subtraction means minimum or close to the minimum, wherein the delay time estimating means is unnecessary. First means for calculating a discrete Fourier transform of the output signal of the signal suppressing means, N is the number of samples of the first discrete Fourier transform calculating means output data, and M is a predetermined integer. At this time, (MN-N) zero-valued samples are inserted between the (N / 2) -th and (N / 2 + 1) -th samples of the output of the first discrete Fourier transform calculating means, and the data of the sample number MN is obtained. A second means for calculating a discrete Fourier transform of an output signal of the signal delay means, and a second means for calculating the number of samples N
(MN-N) zero-valued samples are inserted between the (N / 2) -th and (N / 2 + 1) -th samples of the output of the discrete Fourier transform calculation means of the above to generate data of the number of samples MN. Means, means for obtaining a complex conjugate of the output of the second zero value sample inserting means, means for obtaining cross spectrum data by multiplying the output of the complex conjugate means and the output of the first zero value sample inserting means, the cross spectrum data Means for performing an inverse discrete Fourier transform on the output of the cross-spectral data smoothing means to obtain its absolute value, and means for obtaining a time lag for giving the maximum value of the output of the means for obtaining the absolute value of the inverse discrete Fourier transform. It is configured.

[0023]

According to the present invention, an output signal (synchronous signal) of the second receiving means for receiving a direct wave from the transmitting device.
Based on the target, to receive the reflected echo from the target
Approximately synthesizes a signal of a direct wave from the transmitting device which is mixed into the receiving means and received, and subtracts this signal from the output signal of the first receiving means to suppress an unnecessary direct wave, thereby reducing a target reflected echo. The signal can be extracted. As a result, the time delay of the extracted signal due to the reflected echo of the target with respect to the synchronization signal can be estimated without being affected by the unnecessary direct wave, so that the propagation path length of the target reflected echo can be measured without being affected by the unnecessary direct wave. .

In the delay time estimation according to the first aspect of the present invention, a cross-correlation function between the extracted signal based on the target reflected echo and the synchronization signal output from the second receiving means is calculated, and its absolute value is calculated. Find the time lag that gives the maximum value of. A time lag that gives the maximum value by interpolating the cross-correlation function absolute value at a time interval smaller than the sampling interval of the A / D converter in the first and second receiving means in the vicinity of the time lag, that is, the above two lags The delay time difference between signals can be accurately estimated.

In the delay time estimation according to the second aspect of the present invention, the extracted signal based on the target reflected echo and the synchronization signal output from the second receiving means are respectively subjected to discrete Fourier transform, and the two signals are further subjected to discrete Fourier transform. Generate and smooth cross-spectral data. In order to perform an operation corresponding to interpolation in the time domain in the frequency domain, a predetermined interval between the (N / 2) -th and (N / 2 + 1) -th samples with respect to the smoothed cross-spectral data (the number of samples N). Are inserted and inverse discrete Fourier transform is performed on them to obtain an interpolated cross-correlation function. By calculating the time lag that gives the maximum value of the interpolated cross-correlation function absolute value, the delay time difference between the two signals can be estimated with an accuracy equal to or less than the sampling interval of the A / D converter.

In the delay time estimation according to the third aspect of the present invention, a discrete Fourier transform is performed on each of the extracted signal based on the target reflected echo and the synchronization signal output from the second receiving means, and the two signals are then subjected to discrete Fourier transform. Generate and smooth cross-spectral data. A predetermined number of zero value samples are added after the Nth sample to the smoothed cross-spectral data (the number of samples N). By calculating the time lag that gives the maximum value of the result of the inverse discrete Fourier transform, the delay time difference between the two signals can be estimated with an accuracy equal to or less than the sampling interval of the A / D converter.

In the delay time estimation according to the fourth aspect of the invention, the sampling frequency of the extracted signal due to the target reflected echo and the synchronization signal output from the second receiving means is increased (interpolation is performed). By calculating a time lag that gives the maximum value of the absolute value of the cross-correlation function between these two signals, the delay time difference between the two signals can be estimated with an accuracy equal to or less than the sampling interval of the A / D converter.

In the delay time estimation according to the fifth aspect of the present invention, a discrete Fourier transform is performed on the extracted signal based on the target reflected echo and the synchronization signal output from the second receiving means. For data of the number N of samples subjected to the discrete Fourier transform, the (N / 2) th and (N / 2 +
1) Insert a predetermined number of zero value samples between the samples. When inverse discrete Fourier transform is performed on these signals, a signal having a higher sampling frequency is obtained. By calculating a time lag that gives the maximum value of the absolute value of the cross-correlation function between these two signals, the delay time difference between the two signals can be estimated with an accuracy equal to or less than the sampling interval of the A / D converter.

In the delay time estimation according to the sixth aspect of the present invention, the signal based on the extracted target reflected echo and the synchronization signal output from the second receiving means are each subjected to discrete Fourier transform. For data of the number N of samples subjected to the discrete Fourier transform, the (N / 2) th and (N / 2 +
1) Insert a predetermined number of zero value samples between the samples. From the frequency domain data thus obtained, a cross spectrum between the signal based on the extracted target reflection echo and the synchronization signal is obtained and smoothed. By performing inverse discrete Fourier processing on the smoothed cross-spectral data, an interpolated cross-correlation function between the extracted signal of the target reflected echo and the synchronization signal is obtained. By calculating the time lag that gives the maximum value of the absolute value of the cross-correlation function, the delay time difference between the two signals can be estimated with an accuracy equal to or less than the sampling interval of the A / D converter.

[0030]

【Example】

Embodiment 1 FIG. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment using a propagation path length measuring device. Reference numeral 1 denotes a transmitting device, a modulation signal generator 2 for generating a modulation signal, and an RF signal for the modulation signal generated by the modulation signal generator 2.
Transmitter 3, which converts and amplifies the frequency, converts the frequency to RF,
The transmission antenna 4 radiates the amplified modulated signal into the air. 5 is a target, 6 is a transmitted wave from the transmitting antenna 4 of the transmitting device 1, and 7 is a reflected wave of the transmitted wave 6a by the target 5. Of the transmission waves 6a, 6b, 6c, 6b is a transmission wave unintentionally received by the receiving antenna 11 of the receiving device 10,
Reference numeral 6c denotes a transmission wave transmitted toward the receiving device 10. Since the transmitted wave 6b affects the propagation path length measurement,
It becomes an interference wave for the receiving device 10. Transmitted waves 6b, 6
c may be called a direct wave.

The receiving apparatus 10 is located at a predetermined distance from the transmitting apparatus 1, receives a main receiving antenna 11 for receiving the reflected wave 7 from the target 5, and transmits the reflected wave 7 from the transmitting apparatus 1 to the receiving apparatus 10. It has an auxiliary receiving antenna 12 for receiving the transmitted wave 6c. The auxiliary receiving antenna 12 is directed so as to increase the antenna gain in the direction of the transmitting device 1 in order to receive the transmission wave 6c from the transmitting device 1. 13
Is a receiver for amplifying, converting to an intermediate frequency, and detecting the phase of the transmission wave from the transmitting device 1 received by the main receiving antenna 11 and the auxiliary receiving antenna 12, and 14 converts the output of the receiver 13 to a digital signal. A / D converter for performing the operation. The sampling interval is T and the sampling frequency is f _s
(= 1 / T). Reference numeral 15 denotes an unnecessary direct wave suppressor for suppressing a component of the direct wave 6b received by the main receiving antenna 11, and reference numeral 16 denotes an output y (nT) of the unnecessary direct wave suppressor 15.
And a synchronization signal v which is an output of an A / D converter 14b connected via the auxiliary receiving antenna 12 and the receiver 13b.
(NT), a delay unit for adjusting the timing,
Is the propagation path length of the reflected wave 7 transmitted from the transmitting apparatus 1 and reflected on the target 5 and received from the transmitting apparatus 1 to the receiving apparatus 10.
The received signal u, which is the output of the A / D converter 14a due to the difference from the propagation path length of the transmission wave 6c propagating directly toward
This is a delay time estimator that estimates a delay difference between (nT) and the synchronization signal v (nT).

FIG. 2 shows an unnecessary direct wave suppressor 1 according to the present invention.
5 is an internal configuration diagram of FIG. In the figure, reference numeral 21 denotes a synchronization signal v (n
T) and a load coefficient calculation means 22 for calculating a complex load coefficient value w according to a predetermined rule based on the output signal y (nT) of the subtractor 23. The load coefficient calculation means 22 applies the load coefficient value w to the synchronization signal v (nT). Direct wave 6 multiplied and received by main receiving antenna 11
This is a multiplier that outputs a signal z (nT) that simulates a signal component due to b.

FIG. 3 is a block diagram of the delay time estimator 17a according to the first aspect of the present invention. In the figure, x (nT) is the output signal of the delay unit 16, and y (nT) is the unnecessary direct wave suppressor 1.
5, 31 are two signals x (nT) and y (n
T) a cross-correlator for calculating the cross-correlation function of T), 32 means for outputting the absolute value of the input signal, 33 a search for the maximum value of the input signal (absolute value of the cross-correlation function), and a time lag for giving the maximum value A first maximum value detector for outputting, 34 is an interpolator for interpolating the absolute value of the cross-correlation function at a predetermined time interval, and 35 is a time lag for giving the maximum value of the output of the interpolator 34, ie, delay time estimation. A second maximum value detector that outputs a value.

R (kT) is a cross-correlation function of x (nT) and y (nT) and is generally a complex number. | R (kT) | is R
The absolute value of (kT), δ _1, is the absolute value of the cross-correlation function | R of x (nT) and y (nT) which is the output of the first maximum value detector.
(KT) | is a time lag that gives the maximum value, an integer normalized by the sampling interval T, _Ra (mT / M) is an output of the interpolator 34 (M is an integer exceeding 1), and x (nT )
And a real number sequence obtained by interpolating the cross-correlation function absolute value | R (kT) | of y (nT), δ ₂ is _Ra (m · T / M) which is the output of the second maximum value detector. Is the integer value normalized by T / M, and δ ₂ T / M is the estimated delay time.

Next, the operation of the above embodiment will be described with reference to FIGS. In FIG. 1, a transmitting apparatus 1 transmits modulated signals to a target 5 and a receiving apparatus 10 by transmitting waves 6a and 6c, respectively.
Send as Among them, the reflected wave 7 from the target is received by the main receiving antenna 11 of the receiving device 10, and the transmitted wave 6 c directly transmitted to the receiving device 10 is received by the auxiliary receiving antenna 12. The receiver 13 sequentially performs amplification, conversion to an intermediate frequency, and phase detection of the received signal with the main receiving antenna 11 and the auxiliary receiving antenna 12, and converts the output signal of the receiver into an A / D converter 14.
Output to The A / D converter 14a converts the input signal into a digital signal, and outputs the received signal u (nT) to the unnecessary direct wave suppressor 15. In the unnecessary direct wave suppressor 15, a synchronization signal v (nT) which is an output of the A / D converter 14b connected via the auxiliary receiving antenna 12 and the receiver 13b.
, The component of the direct transmission wave 6b, which is an interference wave included in the received signal u (nT), is suppressed, and the component of the target reflected wave 7 is extracted and output. The synchronization signal v (nT) is supplied to the delay unit 16
Is also entered. The delay unit 16 is a delay unit for adjusting the timing of the synchronization signal v (nT) and the output signal y (nT) of the unnecessary direct wave suppressor 15, and the delay time is one sample of the signal to the unnecessary direct wave suppressor 15. Set the time from input to processing and output of that sample. Assuming that the time is DT, the output signal x (n
T) = v ((n−D) T). The reason why the delay unit 16 is necessary is that the delay time is measured by correlating the output signal x (nT) of the delay unit 16 with the output signal y (nT) of the unnecessary direct wave suppressor 15, and therefore, the timing of the two is required. Must be matched. The output signal x (nT) of the delay unit 16 and the output signal y (n) of the unnecessary direct wave suppressor 15
T) is input to the delay time estimator 17. Here, the propagation distance between the transmission wave 6a transmitted from the transmission device 1 to be reflected at the target 5 and reaching the reception device 10 and the propagation distance between the transmission wave 6c transmitted directly from the transmission device 1 to the reception device 10 Estimate the delay time of y (nT) with respect to x (nT) due to the difference. From the result, the propagation path length s is obtained using equations (2) and (3).

Next, the principle of unnecessary direct wave suppression in the unnecessary direct wave suppressor 15 shown in FIG. 2 will be described. Multiplier 2
Z (nT), which is the output of the second output signal, and the output signal y of the subtractor 23
(NT) is represented by Expression (4) and Expression (5), respectively.

Z (nT) = w · v (nT) (4) y (nT) = u (nT) −z (nT) (5)

In FIG. 1, a reception signal u (n) which is an output signal of an A / D converter 14a connected to a receiver 13a is provided.
Consider a case where T) is composed of a signal r (nT) by receiving the target reflected wave 7 and a signal j (nT) by receiving the direct wave 6b.

U (nT) = r (nT) + j (nT) (6) y (nT) = r (nT) + j (nT) −z (nT) (7)

For the sake of simplicity, it is assumed that a modulated CW (continuous wave) is used as a transmission signal, and that the transmission antenna 4, the main reception antenna 11, and the auxiliary reception antenna 12 are on the same sheet. The path length of the direct wave 6b from the transmitting antenna 4 to the main receiving antenna 11 and the auxiliary receiving antenna 1
The path length of the direct wave 6c up to 2 has the same path difference as the wavelength of the transmission wave, and the main reception antenna 11 and the receiver 13a are connected in cascade, and the auxiliary reception antenna 12 There is some difference in the transfer characteristic between the cascade and the receiver 13b, so that the direct wave 6b
There is also a difference in amplitude and phase between the signal j (nT) and the synchronization signal v (nT) due to the reception of the signal j. If H represents the difference between the amplitude and the phase between the output of the receiver 13a and the output of the receiver 13b, the following relationship is obtained (the transfer characteristics of the A / D converters 14a and 14b are the same). And).

J (nT) = H · v (nT) (8)

If the weight coefficient value w of the multiplier 22 matches the difference between the amplitude and the phase between the output of the receiver 13a and the output of the receiver 13b, that is, if w = H, the equation (4) is used.
The following equation holds from (8).

Z (nT) = j (nT) (9)

This means that the output signal z (nT) of the multiplier 22 simulates the signal j (nT) due to the reception of the direct wave 6b to be suppressed. At this time, if attention is paid to the equation (7), the output signal y (nT) of the subtractor 23 becomes the target reflected wave 7
And the signal component due to the direct wave 6b mixed into the signal received by the main receiving antenna 11 is suppressed. The method of determining the load coefficient value w will be described later.

Next, the operation of FIG. 2 will be described. The weight coefficient w is the average power E of the output signal y (nT) of the subtractor 23.
[| Y (nT) | ² ] is determined to be the minimum. Here, E [•] represents the averaging operation. In general, in a bistatic radar, the path length difference between the target reflected wave 7 and the direct waves 6b and 6c is not small, so that the signal r
(NT) and the signal j (nT) resulting from the reception of the direct wave 6b can be regarded as uncorrelated. That is, E [r (nT) j ^*
(NT)] = 0. At this time, from equation (7), the average power E [| y (nT) | ² ] is developed as in the following equation.

E [| y (nT) | ² ] = E [| r (nT) | ² ] + E [| j (nT) −z (nT) | ² ] (10)

Since the weight coefficient w and the first term on the right side of the equation (10) are irrelevant, selecting a weight coefficient w that minimizes the average power E [| y (nT) | ² ] A signal z that simulates a signal component due to the direct wave 6b in the sense of mean square.
(NT) is equivalent to the signal j (nT) closest to the reception of the direct wave 6b, and the output signal y (n
Unnecessary direct wave components included in T) are minimized.

As a concrete method of determining the weighting factor value w by the weighting factor calculating means 21, for example, in the case of estimating online, the least squares mean algorithm is used.

W (n + 1) = w (n) + μ · y (nT) v ^* (nT) (11)

When averaging can be performed off-line,
By Wiener filter theory,

W = E [u (nT) v ^* (nT)] / E [| v (nT) | ² ] (12)

(For example, by Heiken, translated by Takebe: "Introduction to Adaptive Filters", Hyundai Kogakusha (19)
87)). In the equation (11), μ is an appropriate positive constant, and * is a symbol indicating complex conjugate. In each case, the average power E [| y (nT) |
² ] is the norm. In this way, the component due to the direct wave 6b included in the received signal u (nT) can be suppressed.

In the delay time estimator 17a of FIG. 3, the cross-correlator 31 has a cross-correlation function R (kT) between the output signal x (nT) of the delay unit 16 and the output signal y (nT) of the unnecessary direct wave suppressor 15. ) Is calculated by equation (13). The observed signals are x samples (nT) and y samples (nT) each of N samples,
That is, x (0), x (T), ..., x ((N-1) T)
And y (0), y (T),..., Y ((N−1) T).

[0054]

(Equation 1)

In equation (13), the cross-correlation function R (k
The range of k for calculating T) may be at least several samples larger than the delay value corresponding to the propagation path length difference predicted from k = 0.

The means 32 for obtaining an absolute value includes a cross-correlator 31
The absolute value | R (kT) | of the output R (kT) of
It is input to the first maximum value detector 33. Here, the cross-correlation function absolute value | R (kT) between the output signal x (nT) of the delay unit 16 and the output signal y (nT) of the unnecessary direct wave suppressor 15
Search for the maximum value of | and output the time lag δ ₁ T that gives it.

Using this δ ₁ , the target reflected wave 7 and the direct wave 6
When determining the propagation path length difference of c, the sampling frequency f
_{If s} is low, the propagation path length difference cannot be measured with sufficient accuracy. This is because the cross-correlation function R (kT) is a sample value with a sampling interval of T, and the propagation path length difference is measured in a distance unit determined by (light speed) × (sampling interval). Therefore, in order to more precisely estimate the delay time, the interpolator 34 interpolates the cross-correlation function absolute value | R (kT) | at a certain time interval T / M. Here, M is an integer and is called an interpolation ratio. M
Is determined by how finely the delay time is estimated. For example, if f _s = 8 kHz and M = 10, the delay time can be estimated in 12.5 μs units, and as a result, the propagation path length can be measured in 3.75 km units. It is useless to perform the interpolation over the entire time interval using all the data of the cross-correlation function absolute value | R (kT) |, and therefore, the interpolation may be performed in the vicinity of the time lag δ ₁ T given by the first maximum value detector 33. For example, the interval [(δ ₁ −3) T, (δ ₁ +3)
T] only.

The time interval for performing interpolation is [(δ ₁ -L) T,
(Δ ₁ + L) T], and when the interpolation ratio is M, Expression (14)
(P _i , q _i ) (i = 0, 1,
, 2L) by using a conventionally well-known method.

P _i = δ ₁ −L + i, q _i = | R (p _i T) | (14)

If Lagrange interpolation is performed, the interpolated cross-correlation function absolute value R _a (m · T / M) at a certain time lag m · T / M (m is an integer) in the above section is expressed by the following equation (1).
It becomes like 5).

[0061]

(Equation 2)

The interpolator 34 outputs the interpolated cross-correlation function absolute value R _a (m · T / M) thus obtained to the second maximum value detector 25. Here, similarly to the first maximum value detector 33, the interpolated cross-correlation function absolute value R
The maximum value of _a (m · T / M) is searched, and a time lag that gives the maximum value, that is, an estimated delay time δ ₂ (normalized by T / M) is obtained. From the result, ΔT = δ
The propagation path length s of the reflected wave 7 can be obtained according to the equations (2) and (3) as ₂ T / M. As described above, the propagation path length of the reflected wave 7 transmitted from the transmitting apparatus 1 and reflected on the target 5 is received with a better accuracy than the distance unit corresponding to the sampling interval of the receiving system, and furthermore, the direct wave which is an interfering wave. 6
Since the signal component b is suppressed, the peak A shown in FIG. 13 becomes clear, and accurate measurement can be performed.

Further, in the present invention, the main receiving antenna 11
Since the directivity in the target direction required for the antenna may have broader characteristics, the antenna can be cheaper, smaller, and lighter than the conventional receiving antenna. Similarly, the transmitting antenna 4 does not need to narrow down the directivity so that the direct wave does not strongly enter the side lobe of the main receiving antenna 11, so that the transmitting antenna 4 can be cheaper, smaller, and lighter than the transmitting antenna of the conventional configuration.

Although the auxiliary receiving antenna 12 has been described as an antenna having directivity in the direction of the transmitting device 1, an omni-directional antenna may be used. This is because the received power of the reflected wave 7 is sufficiently smaller than the received power of the direct wave 6c, so that the reflected wave component included in the synchronization signal v (nT) can be ignored. Omnidirectional receiving antennas are generally inexpensive, small, and lightweight.

Embodiment 2 FIG. FIG. 4 is a block diagram of the delay time estimator 17b according to the second aspect of the present invention. In the figure, x (n
T) is an output signal of the delay unit 16, y (nT) is an output signal of the unnecessary direct wave suppressor 15, and 41 is a DFT (Discrete).
e Fourier Transformation)
An arithmetic unit, means for outputting a complex conjugate of the input signal;
3, a multiplier; 44, a smoother for smoothing the cross spectrum data; 45, a zero value sample inserter for inserting a zero value sample into the smoothed cross spectrum data to increase the data length as shown in FIG. , 46 are IDFT (Inver
SE DFT calculator 32, means for outputting the absolute value of the input, 33 a maximum value detector for searching for the maximum value of the input signal (absolute value of the cross-correlation function) sequence and outputting a time lag giving the maximum value It is.

Next, the operation of the second embodiment will be described with reference to FIG. In the delay time estimator 17b, the output signal x (nT) of the delay unit 16 and the output signal y of the unnecessary direct wave suppressor 15
(NT) (n = 0, 1,..., N-1) are DFT
The frequency domain data X (k), Y (k),
(K = 0, 1,..., N−1). That is,

[0067]

(Equation 3)

The complex conjugate of X (k) (output of 42) and Y
The cross spectrum data S ′ (k) is obtained by multiplying (k) by the multiplier 43.

S ′ (k) = X ^* (k) Y (k) (k = 0, 1,..., N−1) (18)

Since the cross spectrum data S '(k) fluctuates greatly, it is smoothed by the smoother 44. Several smoothing means have been conventionally known. One of the methods is a method of taking a simple average of several terms as shown in Expression (19). S
Cross-spectral data obtained by smoothing (k) (smoothing device 4
4)

[0071]

(Equation 4)

L is a suitable positive integer. If an inverse discrete Fourier transform is performed on the smoothed cross-spectral data S (k) output from the smoother 44 thus obtained, the output signal x (nT) of the delay unit 16 and the unnecessary direct wave suppressor 1
Although 5 cross-correlation function between the output signal y (nT) of the obtained, the sampling interval is that of the A / D converter 14, when the sampling frequency f _s is low to measure accurately the propagation path length that Can not. Therefore, interpolation of the cross-correlation function is performed in the frequency domain. In this case, the first embodiment
Unlike this, interpolation is performed in all sections. R. E. FIG. C
rochiere and L.R. R. "Multirate DigitalSignal" by Rabiner
Processing "Prentice-Hall,
1983, p. 36 in FIG. As shown in 2.16, the operation of increasing the sampling frequency creates a data sequence S _I (k) of Expression (20) using the cross-spectral data S (k) smoothed in the frequency domain. Inverse discrete Fourier transform may be performed. When the M is the interpolation ratio, the sampling frequency is Mf _s in the time domain.

[0073]

(Equation 5)

As shown in FIG. 5, the smoothed cross spectrum data S (k) is divided by k = N / 2,
This is an operation of inserting (MN-N) zero-value samples between (N / 2-1) and S (N / 2). This operation is performed by the zero value sample inserter 45.

S _I (k) in equation (20) (k = 0, 1,
.., MN-1) are processed by the IDFT operator 46 in the cross-correlation function R.
_b is converted to (mT / M). The sampling interval is T / M.

[0076]

(Equation 6)

The cross-correlation function R _b (m · T / M) of the output of the IDFT calculator 46 is input to the maximum value detector 33 via the means 32 for taking an absolute value, and | R _b (m · T / M M) |
Time lag δT that searches for the maximum value of
/ M, ie, the delay time estimate. δ is normalized by the sampling interval T / M. From this result, the propagation path length s can be obtained in accordance with Equations (2) and (3) assuming that ΔT = δT / M.

Embodiment 3 FIG. FIG. 6 is a block diagram of the delay time estimator according to the third aspect of the present invention. In the drawing, reference numeral 51 denotes a zero-value sample adder for adding a zero-value sample to the smoothed cross-spectral data to increase the data length, as shown in FIG.

The operation of the above embodiment will be described with reference to FIG. In FIG. 6, the operation up to the smoother 44 is the same as that of the second embodiment, and the output of the smoother 44 is the smoothed cross-spectral data S (k) (k = 0, 1,..., N−1). .
From S (k), the output signal x of the delay unit 16 by IDFT
(NT) and the output signal y (nT) of the unnecessary direct wave suppressor 15
When obtaining the cross-correlation function with, the time variable is not an integral multiple of the normal sampling interval T, but rather is an integral multiple of the sampling interval T / M (M is an interpolation ratio).
That is, the equation (22) is used.

[0080]

(Equation 7)

In the equation (22), the time variable on the left side is not an integral multiple of T. Equation (22) can be written as follows.

[0082]

(Equation 8)

That is, a zero-value sample is added from the smoothed cross-spectral data S (k) output from the smoother 44 in accordance with the equation (24). This is shown in FIG.
This operation is performed by the zero-value sample adder 51. The output data S _J (k) of the zero-value sample adder 51 is set to an ID of 46.
If the inverse discrete Fourier transform of the number of points MN is performed by the FT arithmetic unit, the same operation as in the equation (22) is performed except for a difference of a constant multiple.

The data R _c (m ·
T / M) by the same operation as in Example 2 below | R
_{When the} time lag at which _c (mT / M) | is maximized is obtained, it becomes the estimated delay time δT / M, from which ΔT =
The propagation path length s can be obtained using Expressions (2) and (3) as δT / M.

Data R obtained according to the above method
_c (mT / M) is correctly the output signal x of the delay unit 16.
(NT) and the output signal y (nT) of the unnecessary direct wave suppressor 15
Is not a cross-correlation function interpolated with However, the estimated delay time values have been confirmed by simulations using a large number of computers that δT / M gives an almost correct delay time value.

Embodiment 4 FIG. The delay unit 1 is used in the first to third embodiments.
6 by interpolating the cross-correlation function of the output signal x (nT) of the output signal 6 and the output signal y (nT) of the unnecessary direct wave suppressor 15 to a distance unit corresponding to the sampling interval T in the A / D converter 14 ((light speed) × (sampling period)) The propagation path length could be measured with better accuracy. In the fourth and fifth embodiments to be described below, instead of interpolating the cross-correlation function, the same effect can be obtained by obtaining the cross-correlation function after interpolating the signal (increasing the sampling frequency).

FIG. 8 is a block diagram of the delay time estimator 17d according to the fourth aspect of the present invention. 9, reference numeral 61 denotes a zero-value sample inserter for inserting a zero-value sample into a signal as shown in FIG. 9, 62 denotes a low-pass digital filter, and 63 denotes output signals x _I (i · i) of two low-pass digital filters. T /
M) and a cross-correlator that calculates a cross-correlation function of y _I (i · T / M).

Next, the operation of the second embodiment will be described with reference to FIG. In the delay time estimator 17d, the output signal x (nT) of the delay unit 16 and the output signal y of the unnecessary direct wave suppressor 15 are output.
Interpolate (nT) (increase sampling frequency)
First, a zero-value sample inserter 61 intervenes between the samples as indicated by the open triangles in FIG.
M-1 samples whose value is 0 are inserted between the marks and the ● marks. Here, M is an interpolation ratio. FIG. 9 shows an example where M = 3. By this operation, the sampling frequencies of the output signals x '(iT / M) and y' (iT / M) of the two zero value sample inserters 61 are changed to the input signals x (nT) and y.
It is a factor M times of Mf _s of (nT). However, x ′ (i · T
/ M) and y ′ (i · T / M) have a frequency of f _s /
Since the 2 (M- (1/2)) are still unwanted frequency components in the range of f _s, these cut-off may have a frequency of f _s /
2 (the frequency normalized by the sampling frequency after interpolation is 1 / (2M)). The output signals x _I (iT / M) and y _I (iT / M) of the two low-pass digital filters 62
M) is a signal obtained by interpolating x (nT) and y (nT) as indicated by ● and ○ in FIG. The above process is described in R. E. FIG. Crochiere and L.A. R. R
abiner, "Multirate Digital"
SignalProcessing "Prentic
e-Hall, 1983, p. 36 in FIG. 2.16
Is shown in

The cross-correlator 63 outputs the output signals x _I (i · T / M) and y of the two low-pass digital filters 62.
Calculate the cross-correlation function R _d (m · T / M) of _I (i · T / M) (k = 0, 1,..., L−1).

[0090]

(Equation 9)

X _I (i · T / M) and y _I (i · T / M)
Sampling frequency is M
Since f _s , the sampling interval of R _d (m · T / M) is T / M. When the maximum value of the absolute value of R _d (m · T / M) is searched for by the maximum value detector 33 and the time lag that gives the maximum value is obtained, it becomes the estimated delay time δT / M (where δ is T / M normalized value). If the propagation path length s is obtained by using this δ as ΔT = δT / M in equations (2) and (3), the propagation path length can be measured in a distance unit corresponding to the sampling interval T / M after signal interpolation.

Embodiment 5 FIG. Example 5 is the same as Example 2
Interpolation (increase in sampling frequency) between two signals x (nT) and y (nT) is performed not in the time domain but in the frequency domain as in the second embodiment. FIG. 10 is a block diagram of the delay time estimator 17e according to the fifth aspect of the present invention. The operation of the fifth embodiment will be described with reference to FIG.

In the delay time estimator 17e, first, the output signal x (nT) of the delay unit 16 and the unnecessary direct wave suppressor 15
(Operation for increasing the sampling frequency) of the output signal y (nT). Two signals x (nT) and y (nT)
(N = 0, 1,..., N−1) are respectively subjected to frequency domain data X (k), Y (k) (k = 0, 1,
.., N-1). These X (k) and Y (k)
, The same zero value sample insertion as in equation (20) is performed.
This is performed by the zero value sample inserter 45. The interpolation ratio is M, the output of the two zero value sample inserters 45 is X
_I (k), and Y _I (k).

[0094]

(Equation 10)

Outputs X _{I of} two zero-value sample inserters 45
(K) and Y _I (k) are converted into time-domain signals x _I (i · T / M) and y _I (i · T / M) by the IDFT calculator 46, respectively. The sampling frequency of these signals is A / D
Mfs that is M times that in the converter 14. Output x _I (i · T / M), y of two IDFT calculators 46
_I the (i · T / M) cross-correlation function number Re of (m · T / M)
After the calculation by the cross-correlator 63 according to the equation (25), the propagation path length s is obtained in the same manner as in the fourth embodiment.

Embodiment 6 FIG. In the fifth embodiment, the interpolation (sampling frequency increase) operation is performed in the frequency domain, and the calculation of the cross-correlation function is performed in the time domain. In the sixth embodiment, the calculation of the cross-correlation function is also performed through the frequency domain.

FIG. 11 is a block diagram of the delay time estimator 17f according to the sixth aspect of the present invention. Embodiment 6 Referring to FIG.
Will be described. In the delay time estimator 17f, the output signal x (nT) of the delay unit 16 and the unnecessary direct wave suppressor 15
Of the frequency domain data X (k) and Y (k) after the DFT of the output signal y (nT) is performed by the zero-value sample inserter 45 to insert the zero-value samples of Expressions (26) and (27). Until the operation is performed, the operation is the same as that of the fifth embodiment. After taking the complex conjugate of the data X _I (k) thus obtained at 42, Y _I
(K) is multiplied by a multiplier 43 to obtain cross spectrum data S _I ′ (k).

S ₁ ′ (k) = X _I ^* (k) Y _I (k) (28) (k = 0, 1,..., MN−1)

[0099] cross-spectral data S _I 'cross-spectral is smooth (k) smoothes a smooth 44 data S _I
(K) is obtained. S _I (k) is converted by the IDFT operator 46 into MN
If the inverse discrete Fourier transform of the points is performed, the output signal x (nT) of the delay unit 16 and the output signal y of the unnecessary direct wave suppressor 15
(NT) interpolated cross-correlation function R _f (mT / M)
Is required. The sampling interval is A / D converter 1
4 is 1 / M of the sampling interval T. After the IDFT calculator 46, the propagation path length s is obtained in the same manner as in the second embodiment.

In FIG. 11, the order of the complex value conjugate means 42 and the zero value sample inserter 45 having X (k) as an input may be reversed.

Embodiment 7 FIG. In the DFT calculator 41 shown in FIGS. 4, 6, 10 and 11, when the DFT calculation is performed, the number of data is an FFT (Fast Four) such as a power of two.
As long as the number of data can be used, the processing can be speeded up by replacing the data with an FFT calculator. Therefore, it is desirable to set the data number N to a power of 2 from the beginning. In addition, if the interpolation ratio M is also a power of 2, IDFT
The arithmetic unit 46 can be replaced with an IFFT (Inverse FFT) arithmetic unit, and high-speed processing can be performed similarly.

Embodiment 8 FIG. The operation of increasing (interpolating) the sampling frequency of the signal in the fourth embodiment is not limited to the method using the insertion of the zero value sample and the low-pass filtering. For example, the sampling function (s
In x) / x or a method by interpolation using a spline function can also be used.

In the first to ninth embodiments, the transmission signal waveform is not specified, but a modulated CW (continuous wave), pulse signal, chirp signal, or the like can be used. Further, in the description of the above embodiment, each signal of the receiving device 10 is taken as a complex signal, but may be a real signal.

Further, in the propagation path length measuring device of the present invention, radio waves are used to obtain information on a target.
The same effect can be obtained even with a bistatic lidar system or a bistatic sonar system using light waves and sound waves.

[0105]

As described above, the propagation path length measuring apparatus according to the present invention receives a direct wave from a receiving apparatus mixed and received in the first receiving means for receiving a reflected echo from a target. An apparatus for suppressing a signal by using an output signal (synchronous signal) of a second receiving means for receiving a direct wave from a transmitting apparatus and extracting a signal based on a target reflected echo; The delay lag, which is the time lag giving the maximum value of the absolute value of the cross-correlation function between the received signal and the synchronization signal due to the reflected echo, is calculated in a time unit shorter than the sampling interval in the A / D converters in the two receiving means. Since the apparatus is provided with an apparatus for estimating, the propagation path length of the target reflected echo can be accurately determined without being affected by the received signal due to the direct wave from the transmitting apparatus mixed and received in the first receiving means. It is possible to Ku measurement.

[Brief description of the drawings]

FIG. 1 is a first embodiment of a propagation path length measuring apparatus according to the present invention;
9 is an overall configuration diagram of No. 8 to FIG.

FIG. 2 is an internal configuration diagram of the unnecessary direct wave suppressor of FIG.

FIG. 3 is an internal configuration diagram of a delay time estimator according to the first embodiment of the present invention;

FIG. 4 is an internal configuration diagram of a delay time estimator according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a method of inserting a zero value sample by a zero value sample inserter 45 in the delay time estimator according to the second, fifth and sixth aspects of the present invention.

FIG. 6 is an internal configuration diagram of a delay time estimator according to a third embodiment of the present invention.

7 is a diagram showing a method of adding a zero value sample by a zero value sample adder 51 in the delay time estimator of FIG. 6;

FIG. 8 is an internal configuration diagram of a delay time estimator according to a fourth embodiment of the present invention.

9 is a diagram showing a method of inserting a zero value sample by a zero value sample inserter 61 in the delay time estimator of FIG. 8;

FIG. 10 is an internal configuration diagram of a delay time estimator according to a fifth embodiment of the present invention.

FIG. 11 is an internal configuration diagram of a delay time estimator according to a sixth embodiment of the present invention.

FIG. 12 is an overall configuration diagram of a conventional propagation path length measuring device.

FIG. 13 is a diagram showing a cross-correlation function between a received signal and a synchronization signal in the conventional example and the propagation path length measuring device of the present invention.

[Explanation of symbols]

1 transmitting device, 5 target, 10 receiving device, 11 main receiving antenna, 12 auxiliary receiving antenna, 13 receiver,
14 A / D converter, 15 Unwanted direct wave suppressor, 17
Delay time estimator, 21 weighting factor calculation means, 22 multiplier, 23 subtractor, 31, 63 cross-correlator, 33, 3
5 maximum value detector, 34 interpolator, 41 DFT calculator, 44 smoother, 45, 61 zero value sample inserter,
46 IDFT calculator, 51 Zero value sample adder.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-341039 (JP, A) JP-A-5-100020 (JP, A) JP-A-4-117802 (JP, A) JP-A-4- 29080 (JP, A)

Claims (6)

(57) [Claims] 1. A transmitting device that emits a transmission wave toward an external space via a transmitting antenna by using a modulated signal as a transmitting signal, and a transmitting device that is disposed at a predetermined distance from the transmitting device. Among the radiated transmission waves, a reflected echo from a target and a transmission wave directly arriving from the transmission device are simultaneously received by a first receiving antenna, and the received signal is amplified and phase-detected, and then converted to a digital signal. First
Receiving means for receiving a transmission wave directly arriving from the transmitting device with a second receiving antenna, amplifying and phase-detecting the received signal,
A second receiving means for converting into a digital signal, the first receiving means output signal and the second receiving means output signal being input, and the second receiving means receiving the first receiving means output signal from the transmitting device included in the first receiving means output signal. Means for suppressing an unnecessary signal due to a transmission wave directly arriving at one receiving means, means for delaying the output signal of the second receiving means by a predetermined time, and outputting the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means. Means for estimating the delay time of the former with respect to the latter, wherein the unnecessary signal suppressing means comprises a multiplying means for multiplying the output signal of the second receiving means by a weighting factor; Means for subtracting the output signal of the multiplying means; inputting the output signal of the second receiving means and the output signal of the subtracting means to reduce the average power of the output signal of the subtracting means to a minimum value or a minimum value; Means for calculating the weight coefficient so as to calculate the cross-correlation function between the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means, and takes the absolute value thereof. Means, a first means for obtaining and outputting a time lag giving the maximum value from the output of the means for taking the absolute value of the cross-correlation function, and inputting the time lag and the absolute value of the cross-correlation function as inputs, and in the vicinity of the time lag, Means for obtaining an interpolated value of the absolute value of the cross-correlation function, and second means for obtaining a time lag for giving the maximum value from the output of the interpolating means for the absolute value of the cross-correlation function. Measuring device. 2. A transmitting apparatus which emits a transmission wave to an external space via a transmitting antenna by using a modulated signal as a transmitting signal, and is disposed at a predetermined distance from the transmitting apparatus. A reflected echo of the emitted transmission wave from the target and a transmission wave directly arriving from the transmission device are firstly transmitted.
At the same time, and amplify this received signal.
A first receiving means for converting to a digital signal after phase detection, a transmission wave directly arriving from the transmitting device is received by a second receiving antenna, and after amplifying and phase detecting the received signal,
A second receiving means for converting into a digital signal, the first receiving means output signal and the second receiving means output signal being input, and the second receiving means receiving the first receiving means output signal from the transmitting device included in the first receiving means output signal. Means for suppressing an unnecessary signal due to a transmission wave directly arriving at one receiving means, means for delaying the output signal of the second receiving means by a predetermined time, and outputting the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means. Means for estimating the delay time of the former with respect to the latter, wherein the unnecessary signal suppressing means comprises a multiplying means for multiplying the output signal of the second receiving means by a weighting factor; Means for subtracting the output signal of the multiplying means; inputting the output signal of the second receiving means and the output signal of the subtracting means to reduce the average power of the output signal of the subtracting means to a minimum value or a minimum value; Means for calculating the weighting factor so that the output signal of the unnecessary signal suppressing means is calculated by a discrete Fourier transform of the output signal of the unnecessary signal suppressing means. A means for calculating the complex conjugate of the output of the second discrete Fourier transform calculating means, and a cross spectrum data obtained by multiplying the output of the complex conjugate means and the output of the first discrete Fourier transform calculating means. Means for smoothing the cross-spectral data, where N is the number of samples of the cross-spectrum data, and M is a predetermined integer, the (N / 2) -th data of the cross-spectrum data smoothing means output Means for inserting (MN-N) zero-valued samples between (N / 2 + 1) -th samples to generate data of the number of samples MN; Means for performing an inverse discrete Fourier transform of the output of the sample insertion means and taking an absolute value thereof; anda means for obtaining a time lag which gives a maximum value of an output of the means for taking an absolute value of the inverse discrete Fourier transform. Propagation path length measurement device. 3. A transmitting device that emits a transmission wave toward an external space via a transmitting antenna using a modulated signal as a transmitting signal, and a transmitting device disposed at a predetermined distance from the transmitting device. Among the radiated transmission waves, a reflected echo from a target and a transmission wave directly arriving from the transmission device are simultaneously received by a first receiving antenna, and the received signal is amplified and phase-detected, and then converted to a digital signal. First
Receiving means for receiving a transmission wave directly arriving from the transmitting device with a second receiving antenna, amplifying and phase-detecting the received signal,
A second receiving means for converting into a digital signal, the first receiving means output signal and the second receiving means output signal being input, and the second receiving means receiving the first receiving means output signal from the transmitting device included in the first receiving means output signal. Means for suppressing an unnecessary signal due to a transmission wave directly arriving at one receiving means, means for delaying the output signal of the second receiving means by a predetermined time, and outputting the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means. Means for estimating the delay time of the former with respect to the latter, wherein the unnecessary signal suppressing means comprises a multiplying means for multiplying the output signal of the second receiving means by a weighting factor; Means for subtracting the output signal of the multiplying means; inputting the output signal of the second receiving means and the output signal of the subtracting means to reduce the average power of the output signal of the subtracting means to a minimum value or a minimum value; Means for calculating the weighting factor so that the output signal of the unnecessary signal suppressing means is calculated by a discrete Fourier transform of the output signal of the unnecessary signal suppressing means. Second means for calculating a Fourier transform; means for taking a complex conjugate of the output of the second discrete Fourier transform calculating means; cross-spectral data obtained by multiplying the output of the complex conjugate means and the first discrete Fourier transform calculating means Means for obtaining the cross spectrum data; means for sampling the cross spectrum data; where N is the number of samples of the cross spectrum data; and M is a predetermined integer. Means for generating data of the number of samples MN by adding zero-valued samples of the above; Means for taking the absolute value, the inverse discrete Fourier transform of the absolute value propagation path length measuring device, characterized in that configured with a means for determining the time lag which gives the maximum value of the output of the means for taking. 4. A transmitting device that emits a transmission wave toward an external space via a transmitting antenna by using a modulated signal as a transmitting signal, and is disposed at a predetermined distance from the transmitting device. Among the radiated transmission waves, a reflected echo from a target and a transmission wave directly arriving from the transmission device are simultaneously received by a first receiving antenna, and the received signal is amplified and phase-detected, and then converted to a digital signal. First
Receiving means for receiving a transmission wave directly arriving from the transmitting device with a second receiving antenna, amplifying and phase-detecting the received signal,
A second receiving means for converting into a digital signal, the first receiving means output signal and the second receiving means output signal being input, and the second receiving means receiving the first receiving means output signal from the transmitting device included in the first receiving means output signal. Means for suppressing an unnecessary signal due to a transmission wave directly arriving at one receiving means, means for delaying the output signal of the second receiving means by a predetermined time, and outputting the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means. Means for estimating the delay time of the former with respect to the latter, wherein the unnecessary signal suppressing means comprises a multiplying means for multiplying the output signal of the second receiving means by a weighting factor; Means for subtracting the output signal of the multiplying means; inputting the output signal of the second receiving means and the output signal of the subtracting means to reduce the average power of the output signal of the subtracting means to a minimum value or a minimum value; Means for calculating the weighting factor so that the delay time estimating means outputs a predetermined number of zero-valued samples between two adjacent samples with respect to the output signal of the unnecessary signal component suppressing means. First means for inserting a new signal by insertion, a first low-pass digital filter having a predetermined cutoff frequency and having an output signal of the first zero value sample insertion means as input, and the signal delay means For the output signal, two adjacent
A second means for inserting the predetermined number of zero-valued samples between two samples to generate a new signal; a predetermined cutoff frequency having an output signal of the second zero-valued sample insertion means as an input; A second low-pass digital filter having the output of the first low-pass digital filter and the second low-pass digital filter;
Means for calculating the cross-correlation function with the output of the low-pass digital filter and obtaining its absolute value; means for obtaining and outputting a time lag giving the maximum value of the output of the means for obtaining the cross-correlation function absolute value A propagation path length measuring device, characterized in that: 5. A transmitting device that radiates a transmitting wave to an external space via a transmitting antenna by using a modulated signal as a transmitting signal, and is disposed at a predetermined distance from the transmitting device. Among the radiated transmission waves, a reflected echo from a target and a transmission wave directly arriving from the transmission device are simultaneously received by a first receiving antenna, and the received signal is amplified and phase-detected, and then converted to a digital signal. First
Receiving means for receiving a transmission wave directly arriving from the transmitting device with a second receiving antenna, amplifying and phase-detecting the received signal,
A second receiving means for converting into a digital signal, the first receiving means output signal and the second receiving means output signal being input, and the second receiving means receiving the first receiving means output signal from the transmitting device included in the first receiving means output signal. Means for suppressing an unnecessary signal due to a transmission wave directly arriving at one receiving means, means for delaying the output signal of the second receiving means by a predetermined time, and outputting the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means. Means for estimating the delay time of the former with respect to the latter, wherein the unnecessary signal suppressing means comprises: a multiplying means for multiplying the output signal of the second receiving means by a weighting factor; Means for subtracting the output signal of the multiplying means; inputting the output signal of the second receiving means and the output signal of the subtracting means to minimize or minimize the average power of the output signal of the subtracting means Means for calculating the weighting factor so that the delay time estimating means calculates a discrete Fourier transform of an output signal of the unnecessary signal component suppressing means, and N denotes the first discrete Fourier. Assuming that the number of samples of the transform calculation means output data, M, is a predetermined integer, (MN−M−N) is between the (N / 2) th and (N / 2 + 1) th samples of the first discrete Fourier transform calculation means output data. N) first means for inserting zero-valued samples to generate data of the number of samples MN; first means for calculating an inverse discrete Fourier transform of the output of the first zero-valued sample inserting means; Second means for calculating a discrete Fourier transform of the output signal of the second discrete Fourier transform calculating means having the number of samples N between (N / 2) th and (N / 2 + 1) th samples of the output data. Second means for inserting NN) zero value samples to generate data of the number of samples MN; second means for calculating an inverse discrete Fourier transform of the output of the second zero value sample insertion means; 1 output of the inverse discrete Fourier transform calculating means and the second
The cross-correlation function number of the inverse discrete Fourier transform computation means outputs <br/> calculated, means for taking the absolute value, means for determining the time lag which gives the maximum value of the output of the means for taking the absolute value the correlation function A propagation path length measuring device characterized by comprising: 6. A transmitting device that emits a transmission wave toward an external space via a transmitting antenna by using a modulated signal as a transmitting signal, and a transmitting device that is disposed at a predetermined distance from the transmitting device. Among the radiated transmission waves, a reflected echo from a target and a transmission wave directly arriving from the transmission device are simultaneously received by a first receiving antenna, and the received signal is amplified and phase-detected, and then converted to a digital signal. First
Receiving means for receiving a transmission wave directly arriving from the transmitting device with a second receiving antenna, amplifying and phase-detecting the received signal,
A second receiving means for converting into a digital signal, the first receiving means output signal and the second receiving means output signal being input, and the second receiving means receiving the first receiving means output signal from the transmitting device included in the first receiving means output signal. Means for suppressing an unnecessary signal due to a transmission wave directly arriving at one receiving means, means for delaying the output signal of the second receiving means by a predetermined time, and outputting the output signal of the unnecessary signal suppressing means and the output signal of the signal delay means. Means for estimating the delay time of the former with respect to the latter, wherein the unnecessary signal suppressing means comprises a multiplying means for multiplying the output signal of the second receiving means by a weighting factor; Means for subtracting the output signal of the multiplying means; inputting the output signal of the second receiving means and the output signal of the subtracting means to reduce the average power of the output signal of the subtracting means to a minimum value or a minimum value; Means for calculating the weighting factor so that the output of the unnecessary signal suppressing means is calculated by a discrete Fourier transform of the unnecessary signal suppressing means, and N is the first discrete Fourier transform. When the number of samples of the calculation means output data, M, is a predetermined integer, the (N / 2) th and (N /
First means for inserting (MN-N) zero-valued samples between (2 + 1) -th samples to generate data of the number of samples MN; second means for calculating a discrete Fourier transform of an output signal of the signal delay means; Means (MN-N) zero-valued samples are inserted between the (N / 2) -th and (N / 2 + 1) -th samples of the output of the second discrete Fourier transform calculating means having the number of samples N A second means for generating data of the number of samples MN; a means for taking a complex conjugate of the output of the second zero-value sample inserting means; Means for obtaining spectrum data; means for smoothing the cross spectrum data; means for performing an inverse discrete Fourier transform on an output of the cross spectrum data smoothing means to obtain an absolute value; A propagation path length measuring device comprising means for obtaining a time lag that gives a maximum value of an output of a means for taking a pair value.