JP2003121533A - Radar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine overlapping and to surely detect a plurality of targets, even if the plurality of targets are present and the projecting section positions of the frequency spectrum of beat signals overlap. SOLUTION: A signal obtained by multiplying a beat signal, that is the difference signal between transmission and reception signals by a window function, is subjected to frequency analysis, and it is determined whether a projecting section is the one caused by a single target, depending on whether the phase before and after the projecting section in the amplitude constituent of spectrum has been inverted by 180 deg.. One-to-one pairing is made for the projecting section of the single target, while one-to-multiple pairing is made for projecting sections other than the projecting section of the single target.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar that transmits and receives a detection signal such as a millimeter wave charged wave to detect the relative position or relative speed of a target.

[0002]

2. Description of the Related Art Conventionally, an on-vehicle radar using, for example, a millimeter wave charged wave transmits a radar beam having a sharp directivity to the front or the rear of the vehicle, and transmits from a target such as a vehicle traveling in the front or the rear. Received the reflected wave of, detects the beat signal which is the frequency signal of the difference between the transmitted signal and the received signal,
The relative distance and relative speed of the target are detected from the beat signal.

Here, an FM-CW (frequency modulation continuous wave) radar in which a section in which the frequency of a transmission signal continuously rises and a section in which it continuously falls are periodically repeated,
It will be described below.

FIG. 2A shows a transmission / reception waveform when the relative velocity of the target is zero. Here, the vertical axis represents the frequency of the beat signal and the horizontal axis represents time. Further, the triangular wave indicated by the solid line indicates the frequency change of the transmission signal, and the broken line triangular wave indicates the frequency change of the reception signal over time. A time delay τ proportional to the distance to the target is generated between the transmission wave modulated by the triangular wave and the reception wave reflected by the target. Now, if the distance to the target is R and the propagation velocity of the radio wave in the atmosphere is C, then τ = 2R / C (1) The triangular wave modulation cycle of the transmission wave at this time is 1 / fm,
When the modulation width is ΔF, a beat signal (hereinafter, referred to as a frequency signal of a difference between a transmitted wave and a received wave in a section in which the frequency of the transmission signal continuously rises (hereinafter, referred to as “uplink modulation section”)) "Up-beat signal"), a beat signal (hereinafter referred to as a frequency signal of a difference between a transmitted wave and a received wave) in a section where the frequency of the transmitted signal continuously decreases (hereinafter referred to as "down-modulation section"). , “Downbeat signal”), fr = 2fm · ΔF · τ = 4R · fm · ΔF / C (2)

In the example shown in FIG. 2A, since the relative velocity of the target is 0, f1 = f2 = fr.

FIG. 2B shows a transmission / reception waveform when the relative velocity of the target is not zero. In this case, due to the Doppler effect due to the relative velocity V of the target, the frequency of the received wave is shifted by fd = 2V · f0 / C (3). Here, f0 is the center frequency of the transmitted wave. Therefore, the frequency f1 of the upbeat signal
Then, the frequency f2 of the downbeat signal is as follows: f1 = fr−fd (4) f2 = fr + fd (5) Therefore, fr and fd are calculated by fr = (f1 + f2) / 2 (6) fd = (f2-f1) / 2 (7). (6) From (7) and (2) and (3), R = C · (f1 + f2) / (8 · fm · ΔF) (8) V = C · (f2-f1) / (4 · f0) … (9) is led.

Thus, in the FMCW type radar, the frequency f1 of the upbeat signal and the frequency f2 of the downbeat signal are substituted into the equations (8) and (9) to obtain the relative distance R and the relative velocity of the target. Find V.

The above-mentioned f1 corresponds to the peak frequency of the protrusion appearing in the amplitude component of the frequency spectrum of the upbeat signal sampled in the upstream modulation section. Also, f2
Corresponds to the peak frequency of the protrusion appearing in the amplitude component of the frequency spectrum of the downbeat signal sampled in the downlink modulation section. Therefore, the beat signal is sampled in the upstream modulation section, and the peak frequency of the protruding portion appearing in the amplitude component of the frequency spectrum is obtained as f1.
Similarly, the beat signal is sampled in the downlink modulation section,
The peak frequency of the protrusion appearing in the amplitude component of the frequency spectrum is obtained as f2.

When there are a plurality of targets, protrusions appear in the frequency spectrum of the upbeat signal and the frequency spectrum of the downbeat signal by the number of the targets.

[0010]

However, the FM-
In a CW (frequency modulation continuous wave) radar, when a plurality of targets exist in the detection range, depending on the conditions of the relative distance and the relative velocity of the targets, a protruding portion generated in the frequency spectrum of the upbeat signal or the downbeat signal. There will be a state where they are extremely close to each other or completely overlap each other. When the protrusions appearing in the frequency spectrum of the beat signal overlap in this way, the amplitude components of the spectrum indicate whether the protrusions are due to a single target or multiple targets (protrusions due to multiple targets). Parts are overlapped),
Was difficult to determine.

As a result, a plurality of targets are erroneously recognized as one target, which causes a disadvantage in the operation of the radar.

Although the above-mentioned example relates to the FM-CW radar, for example, the transmitting antenna and the receiving antenna are individually provided, and a pulse wave or a continuous wave having a constant frequency is transmitted and received, and the target signal is detected from the beat signal. In a Doppler radar that detects relative speed, when there are a plurality of targets whose relative speeds are close to each other, a protrusion overlaps the frequency spectrum of the beat signal. As a result, there arises a problem that the presence of a plurality of targets cannot be detected.

An object of the present invention is to provide a radar which solves the above-mentioned problems by making it possible to determine the overlap even when there are a plurality of targets and the positions of the protruding portions of the frequency spectrum of the beat signal overlap. To provide.

[0014]

According to the present invention, based on a beat signal which is a frequency signal of a difference between a transmission signal and a reception signal,
In a radar that detects the relative position or relative velocity of a target, the frequency spectrum of the signal obtained by multiplying the window function by the beat signal is analyzed, and the predetermined frequency range centered on the peak frequency of the protrusion appearing in the amplitude component of the frequency spectrum. Then, depending on whether or not a phase inversion of approximately 180 degrees occurs in the phase component of the frequency spectrum, it is determined whether or not the received signal corresponding to the beat signal is a reflected wave from a single target. Provide unity judgment means.

In the frequency spectrum of the single target, a phase inversion of about 180 ° occurs in the phase component in a predetermined frequency range centered on the peak frequency of the protrusion of the amplitude component. The target singularity determination means positively uses the information of the phase component, which has not been used conventionally, to
The unity of the target is judged by the presence or absence of 80 ° phase inversion.

Further, according to the present invention, an up modulation section in which the frequency of the transmission signal continuously increases and a down modulation section in which the frequency of the transmission signal continuously decreases are periodically repeated. As a result, it is possible to detect the relative position and relative speed of the target by the so-called FM-CW method.

Further, according to the present invention, the protrusions appearing in the amplitude component of the frequency spectrum of the beat signal in the up modulation section and the amplitude component of the frequency spectrum of the beat signal in the down modulation section are reflected from the same target. When comparing the set of the protruding portion in the up-modulation section and the protruding portion in the down-modulation section due to the wave, regarding the protruding portion determined to be due to the single target by the target unity determination means, A collation unit is provided which collates one-to-one and collates one-to-many with respect to the protrusions determined to be overlapped by the protrusions of the plurality of targets.

As described above, in order to obtain the combination of the protrusions in the up-modulation section and the protrusions in the down-modulation section for the same target, for example, matching is performed based on the peak value of the protrusions. At this time, the protrusions caused by a single target are collated one-to-one, and the protrusions determined to be the protrusions formed by a plurality of targets are collated one-to-many. As a result, the relative speed and relative position of each of the plurality of targets are detected from the frequency of the beat signal in the up-modulation section and the frequency of the beat signal in the down-modulation section.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of a radar according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the radar. In FIG. 1, 1 is an RF block and 2 is a signal processing block.
The RF block 1 transmits and receives radio waves for radar measurement, and outputs beat signals of a transmitted wave and a received wave to the signal processing block 2. As a result, the modulation counter 11 of the signal processing block 2 performs a count for generating a triangular wave signal from the DA converter 10, and outputs the value to the DA converter 10. The DA converter 10 converts it into an analog voltage signal and supplies it to the VCO (voltage controlled oscillator) 8 of the RF block 1. As a result, the transmitted wave is FM-modulated. That is, the oscillation signal of the VCO 8 is supplied to the primary radiator 4 via the isolator 7, the coupler 6 and the circulator 5. The primary radiator 4 is located at or near the focal plane of the dielectric lens 3, and the dielectric lens 3 transmits the millimeter wave signal emitted from the primary radiator 4 as a sharp beam. When a reflected wave from a target such as a vehicle is incident on the primary radiator 4 via the dielectric lens 3, the received signal is guided to the mixer 9 via the circulator 5. In the mixer 9,
The received signal and the local signal that is a part of the transmitted signal from the coupler 6 are input, and the beat signal that is the frequency signal of the difference is output to the AD converter 12 of the signal processing block 2 as an intermediate frequency signal. AD converter 12
Converts this into digital data. The DSP (digital signal processing device) 13 performs FFT (fast Fourier transform) processing on the data string input from the AD converter 12,
As will be described later, the relative distance and relative speed of the target are calculated, and these are output to the host device via the output circuit 15.

The portion indicated by 16 in the RF block 1 is 1
It is a scanning unit that translates the next radiator 4 in the focal plane of the dielectric lens 3 or in a plane parallel to it. The movable part provided with the primary radiator 4 and the fixed part have 0d.
It constitutes a B coupler. The portion indicated by M indicates the driving motor.

Reference numeral 14 in the signal processing block 2 is a microprocessor for controlling the modulation counter 11 and the scan unit 16. This microprocessor 14
The beam azimuth is directed at a predetermined angle with respect to the scan unit 16, and the count cycle is determined so that the VCO 8 is modulated by a triangular wave corresponding to one peak in the up modulation section and the down modulation section within the stationary time.

FIG. 3 shows a state in which two vehicles (targets) are present in front of the host vehicle. FIG. 4 shows the frequency spectrum of the beat signal in the up-modulation section and the down-modulation section of the vehicles A and B in the state shown in FIG.
The frequency spectrum is simply called "spectrum". ) Shows the amplitude component. 4A is an amplitude component of the spectrum for the vehicle A, FIG. 4B is an amplitude component of the spectrum for the vehicle B, and FIG. 4C is a combination of A and B of an actually obtained spectrum. It is an amplitude component. In this example, the vehicle (A) traveling in front of the host vehicle is traveling at the same speed as the host vehicle, and the vehicle B is catching up from behind the vehicle A at a speed faster than the vehicle A.

At this time, since the relative speed of the vehicle A to the own vehicle is 0, as shown in (A), the peak frequency f11 of the protrusion p11 appearing in the amplitude component of the spectrum of the upbeat signal and the downbeat signal. Coincides with the peak frequency f21 of the protrusion p21 appearing in the amplitude component of the spectrum. On the other hand, since the vehicle B is faster than the host vehicle, Doppler shift occurs, and as shown in (B), the peak frequency f12 of the protrusion p12 appearing in the amplitude component of the spectrum of the upbeat signal is the spectrum of the downbeat signal. Peak frequency f22 of the protrusion p22 appearing in the amplitude component of
Will be higher than. Therefore, depending on the distance between the vehicles AB and the relative speed condition, as shown in (C), the protrusion p11 by the vehicle A included in the upbeat signal,
The protrusion p12 of the vehicle B overlaps with the protrusion p21 of the vehicle A and the vehicle B included in the downbeat signal.
Due to this, a situation occurs in which the protrusion p22 does not overlap.

FIG. 9 shows the signal processing block 2 shown in FIG.
6 is a flowchart showing a processing procedure of the DSP 13 in FIG. First, the data sampled in a predetermined cycle and AD-converted are sequentially fetched (n1) and multiplied by the window function of the Hanning window (n2). An FFT (Fast Fourier Transform) operation is performed on the data multiplied by this window function (n3). As a result, the amplitude and phase information at each discrete frequency is calculated. That is, the information of the amplitude component and the phase component is calculated from the values of the real part and the imaginary part at each discrete frequency (n
4). Then, the peak frequency of the protrusion appearing in the amplitude component is detected (n5). The processes of n1 to n5 are performed on the upbeat signal and the downbeat signal, respectively.

After that, the target unity is judged as described later (n6). That is, it is determined whether each of the detected protrusions is caused by a single target or a plurality of targets. Then, based on the protrusions detected from the upbeat signal and the protrusions detected from the downbeat signal, the protrusions of the same target are collated (hereinafter referred to as “pairing”) (hereinafter, referred to as “pairing”). n
7). After that, the paired peak frequency for the upbeat signal is f1 and the peak frequency for the downbeat signal is f2.
The relative distance and relative speed of the target are calculated by the equation (9) (n8).

Next, the above window function processing and FFT
The appearance of the frequency spectrum generated by the processing of will be described. First, a Hanning function, which is a window function used as preprocessing of FFT, is expressed by the following equation.

[0027]

[Equation 10]

However, T is a sampling period.

By using this window function, the side lobe of the spectrum after FFT can be reduced.

The Fourier transform H (f) of h (t) is expressed by the following equation.

[0031]

[Equation 11]

Therefore, the frequency spectrum of the beat signal generated by the reflected wave from a single target will be considered. In this case, the beat signal has a single frequency. The beat signal,

[0033]

[Equation 12]

Then, the signal obtained by multiplying the beat signal by the window function is

[0035]

[Equation 13]

Is represented by This is because the spectrum H (f) of the window function h (t) is f on the frequency axis on the frequency axis.
It means to shift by _tgt . Therefore, the spectrum X ₂ (f) of the beat signal is expressed by the following equation.

[0037]

[Equation 14]

The amplitude component and the phase component of this spectrum X ₂ (f) are as shown in FIG. However, in reality, F
Since FT is a type of discrete Fourier transform, the spectrum obtained as a result of signal processing has the frequency interval 1 shown in FIG.
/ T (T: sampling period).

[0039]

[Equation 15]

The following holds. That is, when the change in phase discretized with 1 / T is seen before and after the peak of the amplitude, it is 180
Phase inversion of ° will appear three times in a row.

On the other hand, when the protrusions caused by the reflected waves from the plurality of targets overlap, the property of phase inversion disappears due to the superposition of the plurality of protrusions.

FIG. 6 shows an example of a spectrum obtained by a single target, and FIG. 7 shows an example of a spectrum caused by a plurality of targets. In both figures, (A) is frequency on the horizontal axis,
The vertical axis represents amplitude and phase. (B) represents a vector locus of a spectrum with a frequency change on a complex plane in which the horizontal axis is the real part and the vertical axis is the imaginary part.

As shown in FIG. 6, the phase change of the spectrum caused by a single target is 18 before and after the amplitude protrusion.
Phase inversion of 0 ° occurs three times in a row. When the vector locus at this time is represented on the complex plane, it is lined up on a straight line as shown in FIG.

On the other hand, in the case of a spectrum caused by a plurality of targets, as shown in FIG.
The 80 ° phase inversion phenomenon collapses. As shown in (B) of the figure, when the vector locus is viewed on the complex plane, it is found that the vector loci are not aligned on a straight line.

FIG. 10 is a flow chart showing the processing procedure for determining the target unity in step n6 in FIG.
First, of the protrusions of the amplitude of the spectrum, which protrusion is to be used to determine the target singleness is selected (n1).
1). The phase difference between the phase at the peak frequency of the selected protrusion and the phase at the frequency immediately before that (that is, lower by the discrete frequency 1 / T) is determined. If the phase difference is about 180 °, then whether the phase difference between the phase at the center frequency and the phase at the next frequency (that is, higher by the discrete frequency 1 / T) is about 180 °. It is determined (n12 → n13). As shown in FIG. 5, the phase F (n) at the peak frequency of the amplitude
And the phase F (n-1) at discrete frequencies before and after that,
If the difference from F (n + 1) is about 180 °,
It is determined that the target that caused this protrusion is a single target (n14). If there is no phase difference of about 180 ° before and after F (n), it is determined that the protrusion is caused by a plurality of targets (n15). The above process is determined for all the protrusions appearing on the spectrum (n16 → n11).
→ ...).

The processing shown in FIG. 10 is performed for each of the upbeat signal and the downbeat signal.

Next, the pairing procedure of step n7 in FIG. 9 will be described. First, it is assumed that the amplitude components of the spectrum for the upbeat signal and the downbeat signal as shown in FIG. 8 have been obtained. Here, the protrusion p22 for the downbeat signal shown in (B)
Is determined to be a projecting portion by a plurality of targets. The other protrusions p11, p12, p13, and p21 are regarded as the protrusions of the single target. Follow the steps below for pairing.

(1) All combinations of the protrusions p11, p12, p13 for the upbeat signal and the protrusions p21, p22 for the downbeat signal are evaluated by a predetermined evaluation function.

As a result, the following evaluation value is obtained.

[0050] As the above-mentioned evaluation function, with respect to the two protrusions to be collated, the evaluation value is higher as the amplitude value is closer, and the evaluation value is greatly reduced if the peak frequencies are separated by a frequency which is not normally possible. Use an evaluation function.

In the case of the evaluation values shown in Table 1, first, p11 and p21 having the highest evaluation value are determined as a pair.

(3) Next, the remaining protrusions p12 and p1
Out of 3, p22, the second highest evaluation value (p12,
p22) is selected as a pair. Here, since it is determined that p22 is a protrusion due to a plurality of targets, it is left as a pairing target with another protrusion even after the pairing with p12.

(4) Since the remaining (p13, p22) also have a high evaluation value, they are selected as a pair.

In this way, the projection p1 of the single target is
One-to-one pairing is performed for 1, p12, and p13, and one-to-many pairing is performed for the projecting portion p22 formed by a plurality of targets.

As a condition for ending the pairing, for example, (1) When pairing for all protrusions is completed (2) When there is no pair whose evaluation value exceeds a certain value And two.

In the embodiment described above, FM-
Although the CW type radar has been described, it may be similarly applied to a Doppler radar in which a pulse wave or a continuous wave having a constant frequency is transmitted and received and the relative velocity of the target is detected from the beat signal. That is, the relative speed is calculated from the peak frequency of the protruding portion appearing in the amplitude component of the frequency spectrum of the beat signal.
If there is no phase reversal of 0 degree, it may be treated as if there are a plurality of targets having substantially the same relative velocity.

[0057]

According to the present invention, based on the phase information of the frequency spectrum of the beat signal, which is the frequency signal of the difference between the transmission signal and the reception signal, a single protrusion is formed in the amplitude component of the frequency spectrum. By providing the target unity determination means for determining whether or not it is due to the reflected wave from the target,
The problem that a plurality of targets are erroneously recognized as one target can be solved.

Further, according to the present invention, an up-modulation section in which the frequency of the transmission signal continuously rises and a down-modulation section in which the frequency of the transmission signal continuously descends are periodically repeated, whereby The relative position and relative speed of the target can be detected at the same time.

Further, according to the present invention, the combination of the protruding portion appearing in the amplitude component of the frequency spectrum in the up modulation section and the protruding portion appearing in the amplitude component of the frequency spectrum in the down modulation section for the same target is obtained. At this time, the protrusions caused by a single target are collated on a one-to-one basis, and the protrusions determined by a plurality of targets are collated on a one-to-many basis. The relative speed and relative position of the target can be detected without error.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a radar according to an embodiment.

FIG. 2 is a diagram showing a waveform of a frequency change of a beat signal in the radar.

FIG. 3 is a diagram showing a relationship between a host vehicle and another vehicle in front of the host vehicle.

FIG. 4 is a diagram showing an example of a spectrum in the situation shown in FIG.

FIG. 5 is a diagram showing an example of a phase change before and after a peak on a frequency spectrum due to a single target.

FIG. 6 is a diagram showing an example of a phase change before and after a peak on a frequency spectrum due to a single target.

FIG. 7 is a diagram showing an example of a phase change before and after a peak on a frequency spectrum caused by a plurality of targets.

FIG. 8 shows a spectrum as an example of pairing.

FIG. 9 is a flowchart showing a signal processing procedure in the radar.

FIG. 10 is a flowchart showing the procedure of target unityness determination processing.

[Explanation of symbols]

1-RF block 2-Signal processing block 3-dielectric lens 4-1 primary radiator 5-circulator 6-coupler 7-isolator 8-VCO 9-mixer 15-output circuit 16-scan unit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Motoki Nakanishi             2-10-10 Tenjin, Nagaokakyo, Kyoto Stock             Murata Manufacturing Co., Ltd. (72) Inventor Ikuo Takakuwa             2-10-10 Tenjin, Nagaokakyo, Kyoto Stock             Murata Manufacturing Co., Ltd. F-term (reference) 5J070 AB17 AB24 AC01 AC06 AD01                       AH35

Claims (3)

[Claims] 1. A radar for detecting a relative position or a relative velocity of a target based on a beat signal which is a frequency signal of a difference between a transmission signal and a reception signal, wherein a frequency of a signal obtained by multiplying the beat signal by a window function. The beat signal is analyzed depending on whether or not the phase component of the frequency spectrum is inverted by about 180 degrees in a predetermined frequency range centered on the peak frequency of the protrusion appearing in the amplitude component of the frequency spectrum. A target singleness determining means for determining whether or not the received signal corresponding to is due to a reflected wave from a single target. 2. The transmission signal is one in which an upstream modulation section in which the frequency of the transmission signal continuously rises and a downstream modulation section in which the frequency of the transmission signal continuously falls are periodically repeated. The radar according to 1. 3. A reflected wave from the same target with respect to protrusions appearing in the amplitude component of the frequency spectrum of the beat signal in the up modulation section and the amplitude component of the frequency spectrum of the beat signal in the down modulation section, respectively. According to the above, when collating a set of the protrusion in the up-modulation section and the protrusion in the down-modulation section, regarding the protrusion determined to be due to a single target by the target unity determination means. 3. The radar according to claim 2, further comprising a collating unit that collates one-to-one with each other, and collates one-to-many with respect to the protrusions that are determined to overlap with each other by a plurality of targets.