JP2018194527A - Distance measuring device, distance measuring method, and water level measuring system - Google Patents

Abstract

To provide a distance measuring device, a distance measuring method, and a water level measuring system, capable of appropriately measuring the distance to an object.SOLUTION: A distance measuring device according to one embodiment of the present invention comprises a transmitter, a receiver, a signal processing unit, and a distance information generation unit. The transmitter transmits a frequency-modulated transmission wave. The receiver receives a reflection wave of the transmission wave reflected by an object. The signal processing unit orthogonally detects the reception signal output from the receiver and generates an I/Q signal containing information related to an amplitude and a phase of the reception signal. The distance information generation unit generates distance information related to the distance to the object on the basis of propagation characteristics of a time region of each I/Q signal.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a distance measuring device, a distance measuring method, and a water level measuring system that measure a distance from an object using radio waves.

  FMCW (Frequency Modulation Continuous Wave) radar is known as a technique for measuring a distance from an object using radio waves (see, for example, Patent Document 1). The FMCW radar periodically transmits a radio wave whose frequency rises and falls at a constant rate, and obtains the distance to the detection target and the relative velocity from the beat component with the reflected wave.

JP-A-2015-143619

  In the FMCW radar, if a temporal change occurs in the modulation waveform of the transmission wave or the reflection surface of the transmission wave at the object, it is difficult to determine whether or not the acquired distance information is correct. The distance may not be measured correctly.

  In view of the circumstances as described above, an object of the present invention is to provide a distance measuring device, a distance measuring method, and a water level measuring system capable of appropriately measuring the distance to an object.

In order to achieve the above object, a distance measuring apparatus according to an aspect of the present invention includes a transmitter, a receiver, a signal processing unit, and a distance information generation unit.
The transmitter transmits a frequency-modulated transmission wave.
The receiver receives a reflected wave in which the transmission wave is reflected by an object.
The signal processing unit performs quadrature detection on the reception signal output from the receiver to generate an I / Q signal including information on the amplitude and phase of the reception signal.
The distance information generation unit generates distance information related to the distance to the object based on the propagation characteristics of each I / Q signal in the time domain.

  The distance measuring device is configured to generate distance information related to the distance to the object based on the propagation characteristics of two signals (I signal and Q signal) obtained by orthogonal detection of the received signal. Can be measured properly.

The distance information generation unit may be configured to evaluate a correlation between waveform peaks of each of the I / Q signals and generate the distance information based on the evaluation result.
Typically, when the waveform peaks of the respective I / Q signals match, the generated distance information is evaluated as appropriate.

Each of the I / Q signals has a plurality of peak regions having different peak levels, and the relationship between the peak levels between the peak regions in the I signal and the peak level relationship between the peak regions in the Q signal When there is a difference, the distance information generation unit may be configured to invalidate the distance information in the period with the difference.
The processing for invalidating the distance information includes processing for interrupting the generation of distance information, processing for stopping output of the generated distance information, and the like. As described above, since the suitability of the distance information is determined from the propagation characteristics of the I / Q signal, it is possible to prevent erroneous distance information from being output as a measurement value.

A distance measurement method according to an aspect of the present invention includes transmitting a frequency-modulated transmission wave.
A reflected wave in which the transmitted wave is reflected by an object is received.
By performing quadrature detection on the received signal of the reflected wave, an I / Q signal including information on the amplitude and phase of the received signal is generated.
A time domain propagation characteristic is calculated for each of the I / Q signals.
Based on the time domain propagation characteristics of each of the I / Q signals, distance information relating to the distance to the object is generated.

  The step of generating the distance information may evaluate a correlation between waveform peaks of each of the I / Q signals, and generate the distance information based on the evaluation result.

The step of generating the distance information includes:
Evaluating a plurality of waveform peaks of each of the I / Q signals;
If there is a difference between the peak level magnitude relationship between each peak area in the I signal and the peak level magnitude relation between each peak area in the Q signal, the distance information for the period in which the difference exists is invalidated. Also good.

The water level measurement system according to an aspect of the present invention includes a transmission / reception unit, a signal processing unit, and a water level information generation unit.
The transmission / reception unit includes a transmitter that transmits a frequency-modulated transmission wave, and a receiver that receives a reflected wave reflected from the water surface by the transmission wave. The transmission / reception unit is installed on a bridge.
The signal processing unit performs quadrature detection on the reception signal output from the receiver to generate an I / Q signal including information on the amplitude and phase of the reception signal.
The said water level information generation part produces | generates the information regarding a water level based on the propagation characteristic of the time domain of each said I / Q signal.

  As described above, according to the present invention, the distance to the object can be appropriately measured.

It is a schematic block diagram of the water level measurement system (distance measuring device) which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the said water level measurement system. It is a figure explaining an example of operation | movement of the signal processing part in the said water level measurement system, Comprising: A is a time change of the frequency of a transmission signal, B is an output waveform of a transmission wave (transmission signal), C is reception. The output waveform of the wave (reception signal) and D indicates the output waveform of the beat component. It is a figure which shows an example of the frequency characteristic of I signal (I wave) and Q signal (Q wave) produced | generated in the said signal processing part. It is a figure which shows another example of the frequency characteristic of I signal (I wave) and Q signal (Q wave) produced | generated in the said signal processing part. It is a figure which shows an example of the propagation characteristic of the time domain of the I / Q signal acquired in the water level information generation part in the said water level measurement system. It is a figure which expands and shows the principal part of FIG. It is a figure which shows another example of the propagation characteristic of the time domain of the I / Q signal acquired in the water level information generation part in the said water level measurement system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a water level measurement system (distance measurement device) according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of the water level measurement system.

  The water level measurement system 100 of this embodiment is configured to measure the water level of rivers and lakes using radio waves. As shown in FIG. 1, the water level measurement system 100 includes a transmission / reception unit (antenna) 10, a signal processing unit 20, and a water level information generation unit 30 (distance information generation unit).

  The transmission / reception unit 10 is installed on a bridge B that is bridged over a river or lake that is a measurement target. The bridge B is typically a railway bridge or a road bridge, but is not limited thereto.

  The transmission / reception unit 10 includes a transmitter 11 and a receiver 12 (see FIG. 2). The transmission / reception unit 10 is installed at an appropriate position (for example, the center of the bottom) of the bridge B so as to transmit the radio wave EW toward the water surface Wa directly below and receive the reflected wave RW on the water surface Wa.

  The signal processing unit 20 generates a transmission signal for transmitting the radio wave EW from the transmitter 11, and orthogonally detects the reception signal output from the receiver 12 that receives the reflected wave RW, so that the amplitude of the reception signal and It is configured to generate an I / Q signal that includes information regarding the phase. Here, the I / Q signal is a general term for an I signal and a Q signal that is 90 ° out of phase with the I signal.

  As illustrated in FIG. 2, the signal processing unit 20 includes a signal generation circuit 21 and a detection circuit 22. The signal generation circuit 21 includes an oscillator 211, a triangular wave generator 212, amplifiers 213 and 214, and a mixer 215.

  3A to 3D are diagrams for explaining an example of the operation of each part of the signal generation circuit 21, where A is the time change of the frequency of the transmission signal, B is the output waveform of the transmission wave (transmission signal), and C Indicates the output waveform of the received wave (received signal), and D indicates the output waveform of the beat component. In FIG. 3, “t” represents the round trip time of the radio wave, “R” represents the distance from the transmitter / receiver 10 to the water surface Wa, and “c” represents the propagation speed (light speed) of the radio wave.

  The oscillator 211 generates a high-frequency signal having a reference frequency of, for example, 24 GHz, and outputs a transmission signal frequency-modulated with a triangular wave input from the triangular wave generator 212 to the transmitter 11 via the amplifier 213. The triangular wave generator 212 sweeps the frequency of the high-frequency signal at a constant cycle, for example, between 24.05 GHz and 24.25 GHz (see FIG. 3A). Thereby, a radio wave whose frequency rises or falls periodically at a constant rate is transmitted from the transmitter 11 toward the water surface Wa (see FIG. 3B).

  The reflected wave RW of the radio wave EW reflected by the water surface Wa is received by the receiver 12, and the received signal is input to the mixer 215 via the amplifier 214 (see FIG. 3C). The mixer 215 mixes (multiplies) the high-frequency signal of the reference frequency generated by the oscillator 211 and the reception signal output from the receiver 12, and outputs the beat component (beat signal) (see FIG. 3D).

  The detection circuit 22 includes a distributor 221, a phase shifter 222, an I signal generator 223, and a Q signal generator 224.

  The distributor 221 distributes the beat signal output from the mixer 215 to the I signal generator 223 and the Q signal generator 224, respectively. The phase shifter 222 inputs the 0 ° component of the reference signal to the I signal generator 223 and the 90 ° component of the reference signal to the Q signal generator 224 using the high frequency signal generated by the oscillator 211 as a reference signal. The I signal generator 223 generates an I signal by mixing (multiplying) the beat signal and the 0 ° component of the reference signal, and the Q signal generator 224 mixes the beat signal and the 90 ° component of the reference signal. A Q signal is generated by (multiplication).

  Here, the square sum of the I signal and the Q signal corresponds to the intensity of the received signal, the square root of the square sum of the I signal and the Q signal corresponds to the amplitude of the received signal, and the arctangent of the I signal and the Q signal corresponds to the phase. Equivalent to. An example of frequency characteristics of the I signal (I wave) and the Q signal (Q wave) is shown in FIG.

  The water level information generation unit 30 is configured to generate information on the water level based on the propagation characteristics of each I / Q signal in the time domain. The water level information generation unit 30 may be electrically connected to the signal processing unit 20 by wire or may be electrically connected wirelessly. In the latter case, the water level information generating unit 30 can be installed at a place other than the measurement place, which is advantageous in terms of manageability, installation cost, and the like.

  Information about the water level is typically used to determine flood risk. The information related to the water level may include not only the water level but also the amount of change (increase amount) or the rate of change (increase rate) of the water level based on the normal water surface height. In addition, a determination result as to which level among a plurality of preset water level levels may be included.

  The water level information generation unit 30 is connected to an external device such as a display device or a storage device (not shown). These external devices display monitoring data such as the time change of the measured water level information and the rising rate of the water level, or store these measured values. The water level measurement system 100 may further include a camera for photographing the water surface, a temperature sensor or a humidity sensor for detecting the temperature or humidity of the outside air, and the like.

  As shown in FIG. 2, the water level information generation unit 30 includes A / D converters 31 and 32, an FFT (Fast Fourier Transform) calculator 33, and a determination unit 34.

  The A / D converters 31 and 32 convert each I / Q signal from an analog signal to a digital signal and output the converted signal to the FFT calculator 33. The FFT calculator 33 performs the inverse Fourier transform on each of the I / Q signals, thereby acquiring the time domain propagation characteristics of each of the I and Q components of the beat signal. At this time, for example, as shown in FIG. 5, a frequency function of a predetermined frequency or more may be discarded data (both the real part and the imaginary part are 0), thereby improving the resolution.

  An example of the time domain propagation characteristics of the I / Q signal calculated by the FFT calculator 33 is shown in FIG. 6, and details of the vicinity of the waveform peak portion of each I / Q signal in FIG. 7 are shown. In the figure, the horizontal axis represents the distance calculated based on the propagation time of the received signal, and the vertical axis represents the amplitude level (arbitrary unit) (same for FIG. 8).

  As shown in FIGS. 6 and 7, typically, the peak positions of the I / Q signals coincide with each other. In this case, the position where each peak level is maximum is determined as the distance to the object (water surface Wa in this example).

  By the way, the measurement of the water level of a river or the like using radio waves is easily affected by vibrations and wind and rain of the bridge B where the transmission / reception unit 10 is installed, and foreign objects such as floating substances exist on the water surface Wa which is the object. If so, the reflected wave RW on the water surface Wa may not be properly received. In this case, for example, as shown in FIG. 8, the peak position shift and the level difference between the I signal and the Q signal increase, or a plurality of significant waveform peaks are mixed for each signal. In such a case, it is difficult to obtain appropriate water level information (distance information), which causes erroneous measurement.

  Therefore, the water level information generation unit 30 of the present embodiment evaluates the propagation characteristics in the time domain of each I / Q signal output from the FFT calculator 33 and determines whether the propagation characteristics of these I / Q signals are appropriate. It has the judgment part 34 to do.

  The determination unit 34 is configured by a computer including a CPU (Central Processing Unit), a memory, and the like. The determination unit 34 acquires the propagation characteristics of each I / Q signal at a predetermined period, evaluates the correlation of each waveform peak, and generates water level information (distance information) based on the evaluation result. The predetermined period is not particularly limited, and is, for example, several minutes, several tens of minutes, or several hours.

  For example, as shown in FIGS. 6 and 7, when the peak positions of the I / Q signals coincide with each other, the determination unit 34 receives the reception signal based on the appropriate reflected wave RW from the object (water surface Wa). Judge as a signal. Then, the determination unit 34 outputs the position where the peak level of each of the I / Q signals is maximum to an external device such as a display as the distance to the object (water surface Wa).

  On the other hand, as shown in FIG. 8, the determination unit 34 has a difference in the peak position or level of each I / Q signal, or a plurality of significant waveform peaks are mixed in each I / Q signal. When the following conditions are satisfied, the received signal is determined to be inappropriate.

  That is, each of the I / Q signals has a plurality of peak areas having different peak levels, and the peak level magnitude relationship between the peak areas in the I signal and the peak level magnitude relation between the peak areas in the Q signal If there is a difference between the two, the determination unit 34 invalidates the distance information for the period in which the difference exists.

That each I / Q signal has a plurality of peak areas having different peak levels means that each of the I signal and the Q signal has two or more peak areas as shown in FIG.
Moreover, the magnitude relationship of the peak levels between the peak areas in the I signal is, for example, the magnitude relationship between the levels of the first waveform peak I (1) and the second waveform peak I (2) of the I signal in FIG. In the illustrated example, I (1) <I (2).
Similarly, the magnitude relationship of the peak levels between the peak areas in the Q signal is the magnitude relationship between the levels of the first waveform peak Q (1) and the second waveform peak Q (2) of the Q signal in FIG. In the illustrated example, Q (1)> Q (2).

  Here, the first waveform peaks I (1) and Q (1) of the I signal and the Q signal are waveform peaks corresponding to each other. Similarly, the second waveform peaks I (2) and Q ( 2) is also a waveform peak corresponding to each other. Then, when the corresponding waveform peaks are compared with each other, in the example of FIG. 8, it can be determined that the two are in different levels.

  When there is a difference in the magnitude relationship between the waveform peak levels between the I / Q signals as described above, the determination unit 34 determines that the acquired reception signal is an inappropriate signal for calculating appropriate distance information, Water level information (distance information) acquired during a period (timing) where the difference exists is invalidated. As a result, it is possible to prevent the inappropriate water level information from being output to the external device, so that only highly reliable measurement values can be provided.

  The process for invalidating the distance information in the determination unit 34 may be a process for interrupting the generation of the distance information or a process for stopping the output of the generated distance information. Since there is often a temporary state where there is a difference in the magnitude relationship between the waveform peak levels between the I / Q signals, the determination unit 34 continues to propagate the I / Q signal when the distance information is invalidated. The distance information may be generated by acquiring the characteristics.

  The two waveform peaks of each of the I / Q signals to be compared in the determination unit 34 are not particularly limited, and typically, the waveform peak having the highest peak level and the second highest waveform peak are referred to. Further, the number of waveform peaks to be compared is not limited to two, and may be three or more.

  As described above, according to the water level measurement system 100 of the present embodiment, the distance information related to the distance to the object is generated based on the propagation characteristics of the two signals (I signal and Q signal) obtained by orthogonal detection of the received signal. Therefore, it is possible to appropriately measure the distance to the object.

  Moreover, since the water level information generation unit 30 is configured to evaluate the correlation between the waveform peaks of each of the I / Q signals and generate the distance information based on the evaluation result, it occurs due to the measurement environment. The fluctuation of the obtained I / Q signal can be appropriately evaluated. Therefore, it is possible to stably acquire appropriate water level information even under measurement conditions that are easily influenced by the external environment, such as river water level measurement.

  As mentioned above, although embodiment of this invention was described, this invention is not limited only to the above-mentioned embodiment, Of course, a various change can be added.

  For example, in the above embodiment, an example in which the present invention is applied to water level measurement of a river or the like has been described. However, the present invention is not limited to this, and the distance from an object other than the water surface, such as an on-vehicle collision prevention radar, may be measured. The present invention can also be applied to measurement.

  In the above embodiment, the transmission / reception unit 10 is configured with two antennas for transmission (transmitter 11) and reception (receiver 12). However, the transmission / reception unit 10 is configured with one antenna for both transmission and reception. It may be configured.

DESCRIPTION OF SYMBOLS 10 ... Transmission / reception part 11 ... Transmitter 12 ... Receiver 20 ... Signal processing part 21 ... Signal generation circuit 22 ... Detection circuit 30 ... Water level information generation part 34 ... Judgment part 211 ... Oscillator 223 ... I signal generator 224 ... Q signal generation vessel

Claims (7)

A transmitter for transmitting a frequency-modulated transmission wave;
A receiver for receiving a reflected wave reflected by the object from the transmitted wave;
A signal processing unit that performs quadrature detection on the reception signal output from the receiver and generates an I / Q signal including information on the amplitude and phase of the reception signal;
A distance information generating unit that generates distance information related to a distance to the object based on propagation characteristics of each of the I / Q signals in a time domain. The distance measuring device according to claim 1,
The distance information generation unit evaluates a correlation between waveform peaks of the I / Q signals, and generates the distance information based on the evaluation result. The distance measuring device according to claim 2,
Each of the I / Q signals has a plurality of peak regions having different peak levels, and the relationship between the peak levels between the peak regions in the I signal and the peak level relationship between the peak regions in the Q signal When there is a difference, the distance information generation unit invalidates the distance information in the period with the difference. Transmit a frequency-modulated transmission wave,
Receiving the reflected wave reflected from the object by the transmitted wave;
By performing quadrature detection on the received signal of the reflected wave, an I / Q signal including information on the amplitude and phase of the received signal is generated,
Calculating propagation characteristics in the time domain for each of the I / Q signals;
A distance measurement method that generates distance information related to a distance to the object based on propagation characteristics of each of the I / Q signals in a time domain. The distance measuring method according to claim 4,
The step of generating the distance information evaluates the correlation between the waveform peaks of each of the I / Q signals, and generates the distance information based on the evaluation result. The distance measuring method according to claim 5,
The step of generating the distance information includes:
Evaluating a plurality of waveform peaks of each of the I / Q signals;
If there is a difference between the peak level magnitude relationship between each peak area in the I signal and the peak level magnitude relation between each peak area in the Q signal, the distance information for the period in which the difference exists is invalidated. Yes Distance measurement method. A transmitter for transmitting a frequency-modulated transmission wave; and a receiver for receiving a reflected wave reflected by the water surface of the transmission wave; a transmission / reception unit installed on a bridge;
A signal processing unit that performs quadrature detection on the reception signal output from the receiver and generates an I / Q signal including information on the amplitude and phase of the reception signal;
A water level measurement system comprising: a water level information generation unit that generates information on a water level based on propagation characteristics of each of the I / Q signals in a time domain.

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