JPH1020025A - Fm-cw radar device and object distance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a distance and a relative speed between a plurality of objects by circulationally transmitting a plurality of transmission waves with different repetitive modulation frequencies in time sequence. SOLUTION: A transmission wave prepared by FM modulating a carrier wave by means of a modulation signal with a triangle waveform or the like and a reflected wave reflected by an object so as to be returned are mixed together, and as a result, a beat signal with a frequency difference between both waves is generated, and then, the frequency of the beat signal is analyzed and a distance to the target or a relative speed with the target is measured. In this process, the repetitive modulation frequency of the modulation signal is switched sequently in a repeating cycle of the modulation signal by means of a modulation wave switching device 22, and between a plurality of pairs of modulation signals with different repetitive modulation frequencies, a combination of peak frequency in each section is compared mutually according to a distance calculation expression, so that a distance and a relative speed between a plurality of objects can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM-CW in which a plurality of transmission waves having different repetition modulation frequencies are circulated and transmitted in a time series, and a distance and a relative speed between a plurality of objects are simultaneously detected. The present invention relates to a radar device and an object distance measuring method.

[0002]

2. Description of the Related Art An on-vehicle radar device for measuring the distance and relative speed of an obstacle located in front of a vehicle and a running vehicle, etc., transmits radio signals in the millimeter wave band in comparison with a laser radar device using laser light. The development of the millimeter wave radar device used has been delayed, and the standardization of millimeter wave radar
The development of millimeter-wave radar equipment at z has just begun. However, a millimeter-wave radar device using a millimeter-wave charged wave has advantages over a laser radar device in that it is not affected by weather conditions such as rain and fog, and is superior to a laser system in that it can be expected to reduce costs by increasing production. A number of strengths are gaining attention.

For example, a millimeter-wave radar apparatus has a two-frequency CW system that transmits two very close continuous waves (CW) or an FM that uses a continuous wave (CW) of an FM modulated wave.
Although the -CW method and the like are known, the latter FM-CW method can be said to be particularly suitable for an on-vehicle radar device because the distance to the target and the relative speed to the target can be measured simultaneously. The FM-CW radar device 1 shown in FIG.
An FM modulated wave is transmitted from the transmitting / receiving antenna 2 toward an object such as an automobile, and a reflected wave reflected by the object and returned is received by the transmitting / receiving antenna 2 and a beat signal of the transmitted wave and the received wave is subjected to frequency analysis. It detects the distance to the target and the relative speed. The FM modulated wave is generated by the triangular wave oscillator 3 and the voltage controlled oscillator (VCO) 4 and sent to the transmission / reception antenna 2 via the circulator 6 as a transmission wave. The voltage controlled oscillator 4 converts a triangular wave having a repetition frequency fm generated by the triangular wave oscillator 3 into a frequency corresponding to the voltage value. Therefore, as shown in FIG. 16, the transmission wave has a modulation center frequency f corresponding to the center voltage Vo of the triangular wave.
FM modulation is performed with an FM modulation width of Δf around o. In this case, the modulation repetition period Tm is 1 / fm, and the first half of the modulation repetition period Tm is a modulation frequency rising period and the second half is a modulation frequency falling period.

On the other hand, as shown in FIG. 17, a reflected wave reflected by an object moving at a position of a distance R at a relative speed V is received by a transmitting / receiving antenna 2 and passed through a circulator 6 as a mixer serving as a mixing means. It is sent to 7. The mixer 7 mixes the transmitted wave and the reflected wave, and extracts a beat signal having a frequency difference between the two waves. This beat signal is supplied to the AD converter 10 via the intermediate frequency amplifier 8 and the flat amplifier 9. The A / D converter 10 converts the beat signal whose band has been limited by a built-in anti-aliasing filter (not shown) for preventing aliasing into a digital signal and supplies the digital signal to the FFT calculator 11. FFT calculator 1
1 reads the AD conversion value of the beat signal into an internal memory, divides the AD conversion value into an ascending section and a descending section of the modulation frequency, and individually performs frequency analysis to obtain a frequency spectrum. The frequency spectrum obtained by the FFT calculator 11 is supplied to a peak frequency detector 12, where the peak frequency is detected from among the frequencies exceeding the threshold value. The peak frequency in the ascending section and the peak frequency in the descending section detected in this way are determined by the object detector 1.
The distance to the object and the relative speed are calculated according to a distance calculation formula described below, and the alarm display circuit 14
Supplied to.

By the way, fo: modulation center frequency Δf: FM modulation width Tm: modulation repetition period f: transmission / reception beat frequency C: light speed T: round trip time of radio waves to the object R: distance to the object V: distance to the object Assuming that the relative speed of the object is equal to the speed of the object (relative speed V = 0)
At this time, the beat frequency f is given by f = 4Δf · R / C · Tm. On the other hand, when the relative speed V with respect to the object is other than zero, the beat frequency f is as shown in FIG.
As shown in (B), the rising section of the modulation frequency (fa)
And the descending section (fb), fa = (4Δf · R / C · Tm) − (2fo · V / C) fb = (4Δf · R / C · Tm) + (2fo · V / C) Can be Therefore, the distance to the target and the relative speed with respect to the target are given by R = C · Tm (fa + fb) / 8Δf V = C · (fa−fb) / 4fo.

[0006] The object detection unit 13 includes a peak frequency memory block 13a, a peak frequency prediction block 13b, and a peak frequency comparison block 13c. The peak frequency memory block 13a stores the peak frequency detected by the peak frequency detector 12 and the target information which is the output of the target detector 13, and the target frequency is already detected after the time interval T at which the next peak frequency is transmitted. The combination of the peak frequency recognized as an object and the combination of the unrecognized peak frequency is used as the peak frequency prediction block 1
3b. The peak frequency prediction block 13b
The moving amount during the time interval T is predicted from the distance and the relative speed to the object obtained from the combination of the peak frequencies from the peak frequency memory block 13a and the moving speed of the FM-CW radar device 1, and The peak frequency predicted from the movement amount is supplied to the peak frequency comparison block 13c. The distance R from the object is proportional to the arithmetic mean of the peak frequencies (fa + fb) / 2, and is obtained as R = C ・ (fa + fb) / 8Δf ・ fm, as described above. Further, the relative speed V of the target object is proportional to the difference (fa-fb) between the combinations of the peak frequencies, and is obtained as V = C ・ (fa-fb) / 4 ・ fo as described above. Peak frequency comparison block 13c
Is the current peak frequency and peak frequency prediction block 1
3c compares the predicted peak frequency with the predicted peak frequency, compares the combination of the peak frequencies recognized as the target with the predicted peak frequency, and tracks the target, and determines the peak frequency not recognized as the target as the peak frequency. Recognition of a newly appearing object is performed by comparing with a predicted value. Then, the combination of the recognized peak frequencies of the object is written into the peak frequency memory block 13a, and the distance R and the relative speed V between the object and the object are supplied to the alarm / display circuit 14 and displayed.

[0007]

When the above FM-CW radar device 1 is used as a vehicle-mounted radar device,
A transmitted wave is not always reflected from a single object, and may be reflected by a plurality of objects. For example, when a plurality of vehicles are running in front of the vehicle equipped with the FM-CW radar device 1 with an interval in the traveling direction, when the vehicles are viewed from behind, the plurality of vehicles in front of each other are mutually separated. It may appear as if you are running next to it. In such a case, the radio waves reflected by a plurality of automobiles are received by the FM-CW radar device 1. Therefore, in such a situation, a plurality of peak values appear in the frequency spectrum obtained from the reception wave and the transmission wave. Specifically, for example, when the first and second objects T1 and T2 exist on the transmission and reception waves from the transmission and reception antenna 2, the peak frequencies detected by the peak frequency detector 12 are as shown in FIG.
As shown in (B), two peak frequencies fa1 and fa2 are detected in the rising section of the modulation frequency, and two peak frequencies fb1 and fb2 are detected in the falling section of the modulation frequency.

However, as described above, the conventional FM-CW radar apparatus 1 has two or more objects T1, T2. . . Is present, a combination of a plurality of peak values in a rising section and a falling section of the modulation frequency cannot be determined by one sweep, so that the measurement is performed a plurality of times at a fixed time interval, and the past observation results are integrated. Thus, a combination of peak values is determined, and a plurality of objects are measured. For this reason, even if a new object appears on the radar transmission / reception wave, a certain period of time is required until it is detected as an object, and it is not possible to measure multiple objects in real time, and there is a certain time delay. It had problems that could not be avoided.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and a plurality of transmission waves having different repetition modulation frequencies are circulated and transmitted in a time series so that a distance and a relative speed between a plurality of objects can be simultaneously detected. It is an object of the present invention to provide an FM-CW radar device.

[0010]

In order to achieve the above-mentioned object, the present invention provides a carrier wave which is FM-modulated by a modulation signal having a triangular wave or a waveform close thereto, and is transmitted as a transmission wave to an object. Receiving the reflected wave that is reflected back, generating a beat signal having a frequency difference between the two waves by mixing the received wave with the transmitted wave, and analyzing the beat signal for frequency or distance to a target or target. FM- that measures the relative speed with the object
In the CW radar device, FM modulation wave switching means for sequentially switching a modulation repetition frequency of the modulation signal with a repetition period of the modulation signal and circulatingly generating a plurality of FM modulation waves having different modulation repetition frequencies in time series; A signal is divided into an ascending section and a descending section of the modulation frequency, Fourier-transformed, and a peak frequency detecting means for detecting a peak frequency that gives a peak position of a frequency spectrum for each section, and a peak frequency is detected in the frequency spectrum for each section. When there are a plurality of modulation repetition frequencies, a plurality of sets of modulation signals having different repetition frequencies are compared in accordance with a distance measurement formula for the combination of the peak frequencies for each section, and a distance and a relative speed between the plurality of objects are calculated. And an object detecting means for detecting

The object detection means may include a frequency difference comparison block for comparing the difference between the peak frequencies of the rising section and the falling section between a plurality of sets having different modulation repetition frequencies, and A relative speed based object detection block for detecting an object having the same relative speed from a combination of matching peak frequencies, and an addition of peak frequencies in the ascending section and the descending section between a plurality of sets having different modulation repetition frequencies. A frequency comparison block for comparing the ratio of the average ratio and the modulation repetition frequency, and a distance-based object detection block for detecting an object at the same distance from a combination of peak frequencies in which the two ratios almost match each other. Based on the combination of the peak frequency that gives almost the same distance and relative speed regardless of the wave, the distance between multiple objects It is characterized in that to detect the fine relative speed at the same time.

Further, the object detection means predicts, by calculating, from the peak frequencies in the ascending section and the descending section of a certain set of modulation frequencies, another set of peak frequencies having different modulation repetition frequencies for the same object. Then, a plurality of objects are detected simultaneously based on a combination of the peak frequency at which the predicted peak frequency value and the measured peak frequency value match.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG.
FIG. 2 is a block diagram showing an embodiment of the M-CW radar apparatus, FIG. 2 is a frequency transition diagram of an FM modulated wave by a triangular wave output from the triangular wave oscillator shown in FIG. 1, and FIG. 3 is a transmitting / receiving antenna shown in FIG. FIG. 4 is a diagram showing the positional relationship between the object and the object, FIG. 4 is a distribution diagram of the output spectrum of the FFT calculator shown in FIG. 1 when measuring a plurality of objects, and FIG. FIG. 6 is a peak frequency distribution diagram for explaining the multiple object ranging operation, FIG. 6 is an arithmetic mean distribution diagram of peak frequencies for describing the multiple object ranging operation of the object detection unit shown in FIG. 1, FIG. 7 is a flowchart for explaining a multiple object detection operation by the object detection unit shown in FIG.

A radar apparatus 21 shown in FIG. 1 transmits an FM modulated wave emitted from a transmitting / receiving antenna 2 toward an object such as an automobile, and receives a reflected wave reflected by the object at the transmitting / receiving antenna 2. Although the point of the CW method is the same as the conventional one, the conventional FM-wave is switched with the modulation repetition period so that a plurality of objects existing on the transmission and reception waves can be simultaneously measured. CW radar device 1
Is very different. Here, a first triangular wave W having a different modulation repetition frequency is used as a modulating wave for FM modulating a carrier having a frequency fo generated by the voltage controlled oscillator 4.
A configuration in which the first and second triangular waves W2 are alternately switched with a modulation repetition cycle is used. Specifically, a modulation wave switch 22 is connected to the triangular wave oscillator 3, and the repetition frequency fm is changed to fm1, f
The triangular wave oscillator 3 is controlled so as to oscillate different first and second triangular waves W1 and W2 such as m2. Further, the modulated wave switch 22 sends the FFT operation unit 11 and the distance-based object detection block 23d in the object detection unit 23,
The information on the repetition frequency fm is supplied.

The FM modulated wave obtained by changing the oscillation frequency of the voltage controlled oscillator 4 by the triangular wave oscillation output of the triangular wave oscillator 3 is transmitted as a transmission wave from the transmission / reception antenna 2 to the target through the circulator 6. You. However,
The frequency of the FM modulated wave can be converted when transmitting from the transmitting / receiving antenna 2. The reflected wave reflected by the target object is received by the transmitting / receiving antenna 2 and sent to the mixer 7 via the circulator 6. The mixer 7 extracts a beat signal having a frequency difference between the transmission wave and the reception wave, and outputs the beat signal to the intermediate frequency amplifier 8, the flat amplifier 9, and the AD.
The data is sent to the FFT calculator 11 via the converter 10 in the form of a digital signal. The FFT converter 11 obtains each frequency spectrum in an ascending section and a descending section of the modulation frequency for each modulation wave based on the output information from the modulation wave switching device 22, and calculates this frequency spectrum as the peak frequency detector 1.
Feed to 2. The peak frequency detector 12 detects the frequency of a plurality of peak values on the frequency spectrum, that is, the peak frequency, and supplies the detected frequency to the object detection unit 23.

The object detection unit 23 cascade-connects four blocks, namely, a frequency difference comparison block 23a, a relative speed-based object detection block 23b, a frequency comparison block 23c, and a distance-based object detection block 23d. Based on a combination of the peak frequencies that provide substantially the same distance and relative speed irrespective of the transmission wave, it functions to simultaneously detect the distance and relative speed between a plurality of objects. Specifically, the frequency difference comparison block 23a
It serves to compare the difference between the peak frequencies of the rising section and the falling section of the modulation frequency between a plurality of sets having different modulation repetition frequencies. Further, the relative speed based object detection block 23b functions to detect an object having the same relative speed from a combination of peak frequencies whose peak frequency differences substantially match. Further, the frequency comparison block 23c
The function of comparing the ratio of the arithmetic average of the peak frequency in the rising section of the modulation frequency and the peak frequency in the falling section and the ratio of the modulation repetition frequency among a plurality of sets having different modulation repetition frequencies. Further, the distance-based object detection block 23d functions to detect objects at the same distance from a combination of peak frequencies at which the two ratios substantially match. Note that the alarm display circuit 24 connected to the object detection unit 23
Based on the target information sent from the server, the target is displayed, a collision with the target is predicted, and an alarm, collision avoidance control, and the like are performed.

A description will now be given of the distance measuring operation of a plurality of objects by the object detecting section 23. Simultaneously with the start of the distance measurement, the modulation wave switch 22 switches the repetition frequency of the triangular wave output from the triangular wave oscillator 3. Therefore, as shown in FIG. 2, the transmission wave output from the voltage controlled oscillator 4 is a first triangular wave W1 (repetition frequency fm) having a different repetition frequency.
1) and a second triangular wave W2 (repetition frequency fm2) is an FM modulated wave alternately modulated. For example, when a plurality of objects T1 and T2 as shown in FIG. 3 exist on a transmission / reception wave from the transmission / reception antenna 2, the FFT calculator 11
, A frequency spectrum as shown in FIG. 4 is obtained. As a result, as shown in FIG. 5, the peak frequency detector 12 detects the same number of peak frequencies as the object in each of the rising section and the falling section of the modulation frequency.

At this time, the frequency difference detection block 23a
Calculates the respective frequency differences for all combinations of the peak frequencies in the rising section and the falling section of the modulation frequency of the first triangular wave W1 or the second triangular wave W2.
First, with respect to the first triangular wave W1, the frequency difference Vab11 is obtained from the combination of the peak frequencies fa1 and fa2 in the rising section a and the peak frequencies fb1 and fb2 in the falling section b.
(= Fa1-fb1), Vab12 (= fa1-fb)
2), Vab21 (= fa2−fb1), Vab22
(= Fa2−fb2) is obtained. Further, as for the second triangular wave W2, the peak frequencies fc1,
From the combination of fc2 and the peak frequencies fd1 and fd2 of the falling section d, the frequency difference Vcd11 (= fc1-fd
1), Vcd12 (= fc1-fd2), Vcd21
(= Fc2-fd1), Vcd22 (= fc2-fd)
2) is required. The frequency difference between the frequency peaks thus obtained is supplied to the relative speed based target detection block 23b.

By the way, the above-mentioned equation for calculating the relative velocity V = V
From C · (fa−fb) / 4fo, the modulation center frequency fo
For the same transmission wave, the relative velocity V is completely independent of the modulation repetition frequency fm. Therefore, for an object having the same relative velocity V, the difference (fa-fb) between the peak frequency of the rising section and the peak section of the falling section of the modulation frequency. ) Are equal to each other. Therefore, the relative speed based object detection block 23b identifies a plurality of objects using this principle. That is, the relative speed based target detection block 23b
Is the first sent from the frequency difference comparison block 23a.
Frequency difference Vab11, Vab with respect to triangular wave W1
ab12, Vab21, Vab22 and the second triangular wave W
2 peak frequency differences Vcd11, Vcd12, Vcd
21 and Vcd22, and a combination of peak frequencies having the same frequency peak difference is detected as a combination having the same relative velocity V.

However, it is necessary to consider a measurement error or the like in the actual determination of the combination. For this reason, the target is not limited to the combination of the peak frequencies where the difference between the frequency peaks exactly matches. A combination of peak frequencies where the difference between the frequency peaks approximately matches within a certain speed error range is also supplied to the subsequent frequency comparison block 23c as a candidate object. FIG.
In the example shown in FIG. 5, Vab12, Vcd12, Vab21
And Vcd21 are selected as combinations of peak frequencies having the same frequency peak difference.

The frequency comparison block 23c calculates the arithmetic mean of the peak frequencies in the ascending and descending sections of the modulation frequency for the combination of the peak frequencies supplied from the relative speed based object detection block 23b. As a result, as shown in FIG. 6, Rab12 [= (fa1 + fb2)
/ 2], Rab21 [= (fa2 + fb1) / 2], R
cd12 [= (fc1 + fd2) / 2], Rcd21
[= (Fc2 + fd1) / 2] is obtained and supplied to the distance-based object detection block 23d.

By the way, when the same object at a distance R is measured by first and second triangular waves W1 and W2 having the same sweep bandwidth Δf and different only in the modulation repetition frequency fm like fm1 and fm2. Since the distance R = C ・ (fa + fb) / 8Δf ・ fm1 measured by the triangular wave W1 matches the distance R = C ・ (fc + fd) / 8Δf ・ fm2 measured by the triangular wave W2, C Ｃ (fa + fb) ) / 8Δf · fm1 = C · (fc + f)
d) / 8Δf · fm2 is established. This equation is: {(fa + fb) / 2)} / {(fc + fd) / 2)}
= Fm1 / fm2. As is clear from the modified formula, the ratio of the average value of the rising and falling sections of the peak frequency of the triangular wave having different modulation repetition frequencies (the value on the left side) matches the ratio of the modulation repetition frequency (the value on the right side). A combination that gives a combination for the same object. Therefore, the distance-based object detection block 23d
Focusing on this principle, objects with the same distance are specified. Specifically, in FIG. 6, the arithmetic average ratio Ra of the peak frequency supplied from the frequency comparison block 23c is shown.
b12 / Rcd12 and Rab21 / Rcd21 are compared with the modulation repetition frequency ratio fm1 / fm2, and the combination in which the ratio of the arithmetic mean of the peak frequency matches or almost matches is the combination of the same object at the distance R. We recognize that there is.

In this manner, the first and second triangular waves W1, W having the same modulation center frequency fo and different only in the repetition frequency are provided.
2, two combinations of peak frequencies at which the relative velocity V and the distance R coincide with each other are obtained.
The set is supplied to the alarm / display circuit 24 as the objects T1 and T2. In this case, the distance R to the object and the relative velocity V
Is proportional to the average value and difference of the peak frequency combination of the first triangular wave W1, and can be converted into a general physical quantity by multiplying by a known coefficient. That is, the distance R1 to the object 1 and the relative speed V1 are obtained according to the following formula: R1 = C · Rab12 / 4Δf · fm1 V1 = C · Vab12 / 4fo, and the distance R2 to the object 2 and the relative speed V2 is calculated according to the following equation: R2 = C · Rab21 / 4Δf · fm1 V2 = C · Vab21 / 4fo Note that a similar result can be obtained from a combination of frequency peaks of the second triangular wave W2. In this case, fm1 in the above equation may be replaced with fm2.

The flowchart shown in FIG. 7 shows the operation of the object detection unit 23. In the illustrated example, the modulation frequency rising section of the first triangular wave W1 is defined as section a, and its peak frequency is given by FREQ_PA (na) and FR
When EQ_PA (na) is recognized as constituting an object, the number of the object is set in TAGN_PA (na). If it is not recognized that the object is included, TAGN_PA (na) is set to -1. The number of peak frequencies in the section a is represented by na_max, and na takes a value from 0 to (na_max−1). Similarly, in section b, which is the modulation frequency falling section of the first triangular wave W1, FREQ_PB (nb) and TA
GN_PB (nb) and nb_max are used. In a section c, which is a section in which the modulation frequency of the second triangular wave W2 rises, FREQ_PC (nc) and TAGN_PC (n
c) and nc_max are used, and FREQ_PD is used in a section d that is a section in which the modulation frequency of the second triangular wave W2 falls.
(Nd), TAGN_PD (nd) and nd_max are used.

At the start of the process, first, in steps S1 to S7, TAGN_PA (na), TAGN_PA (na)
GN_PB (nb), TAGN_PC (nc), TAG
-1 is substituted for N_PD (nd). However, NP_MAX defined in step S7 represents the maximum value of the number of peak frequencies set in each section. Next, in the following step S8, n_tar representing the number of recognized objects
get is set to 0, and na is set to 0 in the following step S9.

Further, in step S10, nb is set to 0, and in order to check whether FREQ_PB (nb) has already constituted the object, the following decision step S11 is performed.
It is determined whether or not TAGN_PB (nb) is 0.
If TAGN_PB (nb) is not 0, FREQ_
Since PB (nb) has already constituted the object, nb is counted up by 1 in step S33. Further, in subsequent step S34, whether nb counted up does not reach the number of peak frequencies in section b is compared with nb_max, and if so, na is counted up by 1 in step S35. The counted up na is compared with na_max in the subsequent step S36, and if na has not reached na_max, the process returns to step S10.

On the other hand, if TAGN_PB (nb) is -1, the process steps S12, S13, S13,
S31, S32 and processing step S14 relating to section d,
Steps S15, S29, and S30 are executed.

The peak frequency whose combination has been changed by the above processing is used by the frequency difference comparison block 23a in step S16 to calculate the peak frequency difference V1 of the first triangular wave W1, and further in step S17, the second triangular wave It is used to calculate the difference V2 between the peak frequencies of W2. Next, in order to compare the peak frequency differences V1 and V2,
The relative speed based object detection lock 23b is set in step S1.
At 8, the absolute value of the difference between the peak frequency differences V1 and V2 is compared with the allowable error EP_V. Therefore, when the absolute value of the difference between the peak frequency differences V1 and V2 is not smaller than the allowable error EP_V, it can be understood that the relative speeds do not match. For this reason,
It is necessary to change the combination of the peak frequencies. Here, in step S29, 1 is added to the number nd of the peak frequency in the section d. On the other hand, when the absolute value of the difference between V1 and V2 is equal to or less than the allowable error EP_V, the first triangular wave W
Since the relative speeds obtained by the combination of the peak frequencies of the first and second triangular waves W2 are equal, the distances are then compared according to the combination of the peak frequencies.

First, in steps S19 and S20,
The frequency comparison block 23c calculates the average value of the peak frequency of the first triangular wave W1 and the average value R1, R2 of the peak frequency of the second triangular wave W2, respectively. In this case, when the distances measured by the two triangular waves W1 and W2 are equal, the ratio R1 / R2 of the average value and the ratio fm1 / of the modulation repetition frequency are obtained.
fm2 matches. In other words, the ratio (R1 / R2) / (fm1 / f) between the average value ratio and the modulation repetition frequency ratio.
Since m2) becomes 1, the frequency comparison block 23c
In step S21, the absolute value | 1- (R1 / R2) / (fm1 / fm2) | of the difference between this value and 1 is compared with the allowable error EP_R. If the absolute value of the difference is not smaller than the allowable error EP, it is known that the distances do not match. Therefore, in step S29, 1 is added to the peak frequency number nd of the section d to change the combination of the peak frequencies. On the other hand, the absolute value | 1- (R1 / R2) / (fm1 /
fm2) | is equal to or smaller than the allowable error EP_V, it can be understood that the distances determined from the combination of the peak frequencies of the first triangular wave W1 and the second triangular wave W2 are equal.

Thus, the combination of the peak frequencies of the first triangular wave W1 and the second triangular wave W2 in which the relative velocity and the distance are equal to each other is recognized as an object. And step S
22 at a distance R_TARGET (n_target
t) is obtained, and in the subsequent step S23, the relative speed V
_TARGET (n_target) is obtained. Further, in subsequent steps S24 to S27, TAGN
_PA (na), TAGN_PB (nb), TAGN_
The object number is substituted for PC (nc) and TAGN_PD (nd). In this case, the object number is from 0 to (n_ta
rget-1). Next, in step S28, 1 is added to the object number n_target to change the combination of the peak frequencies, and in step S35, 1 is added to the peak frequency number na of the section a.

Thereafter, the same operation is repeated, and the transmission frequency alternately FM-modulated by the first triangular wave W1 and the second triangular wave W2 is used, and the distance between the object and the relative velocity is equal to the peak frequency. Focusing on the combination, a plurality of objects can be detected in real time. Therefore, even if a plurality of peaks appear in the frequency spectrum due to the presence of the plurality of objects, the distance R and the relative speed V between the plurality of objects can be accurately calculated. Further, since the comparison of the distances is performed by limiting only the combinations of the peak frequencies that satisfy the relationship of the relative speed, the total amount of calculation is small, and the calculation time by the object detection unit 23 can be reduced.
When it is desired to suppress the influence of an interference wave due to a transmission wave or the like from another FM-CW radar device, the repetition frequency of a triangular wave as a transmission / reception wave may be changed according to a fixed pattern or irregularly.

The FM-CW radar device 31 shown in FIG.
The configuration of the object detection unit 32 is different from that of the object detection unit 23. The object detection unit 32 includes a frequency difference comparison block 23 a and a relative speed based object detection block 2.
3b, the frequency comparison block 23c, and the distance-based object detection block 23d.
A frequency difference comparison block 23a and a relative speed-based object detection block 23b are cascade-connected to a frequency comparison block 23c and a distance-based object detection block 23d. For this reason, the distance comparison is performed by focusing only on the peak frequency combinations satisfying the relative speed relationship as in the above-described embodiment. On the contrary, the relative speed is narrowed down only by the peak frequency combinations satisfying the distance relationship. Speed comparison will be performed. However, the point that the amount of calculation itself as a whole is small is the same.

Also, the FM-CW radar device 4 shown in FIG.
In order to detect a plurality of objects, 1 uses an object detection unit 42 having a configuration in which a comparison of a distance and a comparison of a relative speed are processed in parallel, and the result is ANDed by an AND gate 43. In other words, the object detection unit 42 includes a frequency comparison block 23a and a frequency difference comparison block 23c connected in parallel to the peak frequency detector 12, and the output of the speed-based object detection block 23b following the frequency comparison block 23a and the frequency difference The output of the distance-based object detection block 23d subsequent to the comparison block 23c is AND-processed by the AND gate 43 and sent to the alarm display 24. For this reason, the relative speed judgment and the distance judgment can proceed simultaneously and in parallel, and the four blocks 23a to 23
The processing time can be reduced to about 、 as compared with the case where the object is detected by connecting d in tandem.

The FM-CW radar device 51 shown in FIG. 10 uses an object detection unit 52 including a peak frequency prediction block 52a and a peak frequency comparison block 52b. The peak frequency prediction block 52a predicts, by calculation, the peak frequency of the other triangular wave to be compared with respect to the same object from a combination of a plurality of peak frequencies in the ascending section and the descending section of the modulation frequency of one of the triangular waves to be compared. It is. The peak frequency comparison block 52b includes a peak frequency prediction block 52a.
Is compared with the measured peak frequency, and a plurality of objects are simultaneously detected based on the combination of the peak frequencies that match.

Here, assuming that the first triangular wave W1 is a triangular wave to be compared and the second triangular wave W2 is a triangular wave to be compared, the peak frequency of the second triangular wave W2 is predicted from the peak frequency of the first triangular wave W1. This is equivalent to measuring the same object at the relative speed V at the distance R, so that C · (fa + fb) / 8Δf · fm1 = C · (fc + f
d) / 8Δf · fm2 C · (fa−fb) / 4fo = C · (fc−fd) / 4
The two equations of fo are satisfied, and fc and fd are obtained for these two equations.
Is solved as an unknown, the frequency can be predicted.
Therefore, by adding the right sides of the left and right sides of both equations, fc = (fa + fb) fm2 / 2fm1 + (fa-f
b) / 2 is obtained, and by subtracting the right side from the left side of both equations, fd = (fa + fb) fm2 / 2fm1- (fa-f
b) / 2 is obtained. As can be seen from the solution thus obtained, it is possible to calculate the peak frequencies fc and fd in the rising section of the modulation frequency of the second triangular wave W2 from the actually measured peak frequencies fa and fb of the first triangular wave W1. And this can be used as the predicted value.

According to the above equation, the predicted values fc and fd of the plural sets of peak frequencies of the second triangular wave W2 obtained from the plural sets of peak frequencies fa and fb of the first triangular wave W1 are as follows.
In the peak frequency comparison block 52b, the peak frequency of the second triangular wave W2 detected by the peak frequency detector 12 is compared with the actually measured peak frequency. As a result of the comparison, a combination of the measured peak frequency values that is equal to or approximate to the combination of the predicted peak frequency values is specified, whereby a plurality of objects can be detected.

The FM-CW radar device 61 shown in FIG.
Has a conventional object detection unit 13 disposed between the object detection unit 23 and the peak frequency detector 12 shown in FIG. 1, disperses the object tracking process and the object discovery process, and performs pipeline processing. Is made possible. The object tracking process is performed by the object detection unit 13 detecting an object that has already been detected in the previous sweep, and the object detection process is performed by the object detection unit 23 using a newly appearing object. This is performed by detecting an object. For this reason, even when a plurality of objects exist on the transmission / reception path and a plurality of peak frequencies appear in the frequency spectrum, the distance R and the relative speed V between the plurality of objects are calculated in a short time and at high speed. be able to. In pipeline processing, processing that is continuously and repeatedly executed is decomposed for each partial processing, each processing is assigned to a special independent block specially provided, and each block is operated simultaneously with other blocks to perform processing Therefore, parallel processing and simultaneous processing of instructions are possible, and the performance improvement of the distance measurement system is obvious.

The FM-CW radar device 71 shown in FIG.
In the above embodiment, the object detection unit 32 is used instead of the object detection unit 23. Object detector 3
2, a frequency difference comparison block 23a and a relative speed-based object detection block 23b are connected in cascade to a frequency comparison block 23c and a distance-based object detection block 23d as described above, and peaks satisfying the distance relationship. The comparison of the relative speeds is limited to only the combinations of the frequencies. As in the case where the comparison of the distances is performed by narrowing down only the combinations of the peak frequencies satisfying the relation of the relative speed, there is an advantage in that the entire calculation amount itself can be reduced.

An FM-CW radar device 81 shown in FIG.
Is a conventional object detection unit 13 disposed between the peak frequency detector 12 and the object detection unit 42 shown in FIG. 9, and the object detection unit 13 has already been detected by the previous sweep. The object tracking process and the object finding process are performed by performing the object tracking process for detecting the object that is present and the object detecting unit 42 performing the object finding process for detecting the newly appearing object. Distributed pipeline processing enables short-time and high-speed ranging.

The FM-CW radar device 91 shown in FIG. 14 has a conventional object detector 13 disposed between the peak frequency detector 12 and the object detector 52 shown in FIG. The object detection unit 13 detects an object already detected in the previous sweep, and the object detection unit 52 detects a newly appearing object, thereby realizing high-speed processing by pipeline processing. ing.

In each of the above embodiments, the distance R and the relative velocity V between a plurality of objects can be calculated at a high speed. By changing the frequency irregularly, it is possible to suppress the influence of an interference wave due to a transmission wave or the like from another FM-CW radar device.

[0042]

As described above, according to the present invention,
A beat signal having a frequency difference between both waves is generated by mixing a transmission wave obtained by FM-modulating a carrier wave with a modulation signal having a triangular wave or a waveform close thereto and a reflected wave that is reflected and returned by an object,
When the frequency of the beat signal is analyzed to measure the distance to the target or the relative speed to the target, the modulation repetition frequency of the modulation signal is sequentially switched with the repetition period of the modulation signal, and a plurality of modulation repetition frequencies different from each other are obtained. The FM modulation wave is circulated in a time series, the beat signal is divided into an ascending section and a descending section of the modulation frequency, Fourier-transformed, and a peak frequency which gives a peak position of a frequency spectrum is detected for each section, and each section is detected. When a plurality of peak frequencies are present in the frequency spectrum of, the combination of the peak frequency for each section between a plurality of sets of modulation signals having different modulation repetition frequencies is compared in accordance with a distance measurement formula, and a plurality of objects are compared. The distance and relative velocity between the two are detected. By finding a combination of frequency peaks in which the frequency difference between the peak values of the frequency spectrum in the section and the descending section, that is, the relative speed is equal, and the arithmetic mean of the peak frequencies, that is, the ratio of the distances, is equal to the ratio of the modulation repetition frequency, It is possible to detect the distances and relative velocities of multiple objects in a single measurement.
-When two or more objects are present on a radar transmission / reception wave as in a CW radar device, a combination of a plurality of peak values in an ascending section and a descending section of a modulation frequency cannot be determined by one sweep and is constant. This eliminates the need for complicated work such as measuring multiple times at intervals of time and determining the combination of peak values based on past observations. It can be applied to an on-vehicle rear-end collision prevention device or the like, which requires an excellent effect, and has an excellent effect such that an outstanding result can be obtained.

Further, the object detecting means includes a frequency difference comparing means for comparing the difference between the peak frequencies of the rising section and the falling section of the modulation frequency between a plurality of sets having different modulation repetition frequencies, Relative speed-based object detection means for detecting an object having the same relative speed from a combination of matching peak frequencies, and addition of peak frequencies in a rising section and a falling section of a modulation frequency between a plurality of sets having different modulation repetition frequencies. Frequency comparison means for comparing the ratio between the average ratio and the modulation repetition frequency, and distance-based object detection means for detecting objects at the same distance from a combination of peak frequencies where the two ratios substantially match, and transmitting Based on the combination of the peak frequencies that give substantially the same distance and relative speed regardless of the wave, the distance and relative speed between multiple objects are the same. Since it configured to detect the first
And a second frequency difference V1 between the peak frequency of the FM modulated wave W1
The difference V2 between the peak frequencies of the M-modulated wave W2 and the difference are obtained. If the absolute value of the difference between the peak frequency differences V1 and V2 is not smaller than the allowable error, the relative speeds do not match, so the combination of the peak frequencies may be changed. Conversely, if the absolute value of the difference between the peak frequency differences V1 and V2 is equal to or less than the allowable error, the relative speeds are known to be equal, and the distance can be compared by receiving the combination of the peak frequencies. F
Average value R1 of peak frequency of M modulated wave W1 and second FM
The average value R2 of the peak frequency of the modulated wave W2 is calculated, and when the distance measured by the modulated waves W1 and W2 is equal, the ratio of the average value (R1 / R2) to the ratio of the modulation repetition frequency (fm1 / fm2), the absolute value of the difference between the ratio between the distance ratio and the modulation repetition frequency ratio and 1 |
If 1− (R1 / R2) / (fm1 / fm2) | is equal to or less than the allowable error, the distances represented by the combination of the peak frequencies of the first triangular wave W1 and the second triangular wave W2 are equal,
In this way, a plurality of objects having the same distance and relative speed can be detected at a time. Further, the relative speed based object detection and the distance based object detection can be performed in advance, or both can be performed simultaneously. Since it may be performed in parallel,
There are effects such as that various embodiments can be selected.

Further, the object detecting means predicts, by calculating, from the peak frequencies in the ascending section and the descending section of a certain set of modulation frequencies, another set of peak frequencies having different modulation repetition frequencies for the same object. Then, based on the combination of the peak frequency at which the predicted peak frequency value and the measured peak frequency value match, a plurality of objects are detected at the same time, so that the first FM modulated wave W1
When the second FM modulated wave W2 is a triangular wave to be compared, the peak frequency of the second FM modulated wave W2 is predicted from the peak frequency of the first FM modulated wave W1. Is equivalent to measuring the same object at a relative speed V at a distance R, so that the repetition frequency fm1 (first modulation wave W1) and the repetition frequency fm2 (second modulation wave W2) The following two equations that hold for C2 (fa + fb) / 8Δf · fm1 = C · (fc + f
d) / 8Δf · fm2 C · (fa−fb) / 4fo = C · (fc−fd) / 4
From fo, a solution is obtained with fc and fd as unknowns, and fc = (fa + fb) fm2 / 2fm1 + (fa-f
b) / 2 fd = (fa + fb) fm2 / 2fm1- (fa-f
b) / 2, and the peak frequencies fc and fd in the rising section of the modulation frequency of the second triangular wave W2 can be obtained from the peak frequencies fa and fb of the first triangular wave W1 by calculation. Of the second set of peak frequencies
The plurality of sets of predicted values of the peak frequency of the modulated wave W2 are compared with the peak frequency of the second triangular wave W2 in the peak frequency comparison block, and the measured peak frequency is equal to or approximate to the combination of the peak frequency predicted values. Can be detected as a target object, and excellent effects such as efficient distance measurement with prediction prior to actual measurement can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an FM-CW radar apparatus according to the present invention.

FIG. 2 is a frequency transition diagram of an FM modulated wave by a triangular wave output from the triangular wave oscillator shown in FIG.

FIG. 3 is a diagram showing a positional relationship between a transmitting / receiving antenna shown in FIG. 1 and an object.

FIG. 4 is an output spectrum distribution diagram of the FFT calculator shown in FIG. 1 at the time of distance measurement of a plurality of objects.

FIG. 5 is a peak frequency distribution diagram for explaining a multiple object distance measuring operation of the object detection unit shown in FIG. 1;

FIG. 6 is an arithmetic mean distribution diagram of peak frequencies for explaining a multiple object distance measuring operation of the object detection unit shown in FIG. 1;

FIG. 7 is a flowchart illustrating a multiple object detection operation performed by the object detection unit illustrated in FIG. 1;

8 is a block diagram showing a modified example of the FM-CW radar device shown in FIG.

9 is a block diagram showing a modified example of the FM-CW radar device shown in FIG.

FIG. 10 is a block diagram showing a modified example of the FM-CW radar device shown in FIG. 1 which is different from FIG. 8;

FIG. 11 is a block diagram showing still another modification of the FM-CW radar device shown in FIG. 1;

FIG. 12 is a block diagram showing a modified example of the FM-CW radar device shown in FIG. 11;

FIG. 13 is a block diagram showing a modification of the FM-CW radar device shown in FIG. 9;

FIG. 14 is a block diagram showing a modified example of the FM-CW radar device shown in FIG. 10;

FIG. 15 is a block diagram showing an example of a conventional FM-CW radar device.

16 is a frequency transition diagram of an FM modulated wave by a triangular wave output from the triangular wave oscillator shown in FIG.

17 is a diagram showing a positional relationship between the transmitting / receiving antenna shown in FIG. 15 and an object.

FIG. 18 is an output spectrum distribution diagram of the FFT calculator shown in FIG.

19 is an output spectrum distribution diagram of the FFT calculator shown in FIG. 15 during distance measurement of a plurality of objects.

[Explanation of symbols]

Reference Signs List 2 transmitting / receiving antenna 3 triangular wave oscillator 4 voltage controlled oscillator 6 circulator 7 mixer 8 intermediate frequency amplifier 9 flat amplifier 10 AD converter 11 FFT operator 12 peak frequency detector 21, 31, 41, 51, 61, 71, 81, 91F
M-CW radar device 22 Modulated wave switch 23, 32, 42, 52 Object detector 24 Alarm display circuit 43 AND gate 52a Peak frequency prediction block 52b Peak frequency comparison block

Claims (4)

[Claims] 1. A carrier wave is FM-modulated with a modulation signal having a triangular wave or a waveform close thereto, transmitted as a transmission wave toward an object, receives a reflected wave reflected back from the object, and receives the received wave. An FM- which mixes with the transmission wave to generate a beat signal having a frequency difference between the two waves and analyzes the beat signal to measure the distance to the target or the relative speed with respect to the target.
In the CW radar apparatus, FM modulation wave switching means for sequentially switching a modulation repetition frequency of the modulation signal with a repetition period of the modulation signal and circulatingly generating a plurality of FM modulation waves having different modulation repetition frequencies in time series; A signal is divided into an ascending section and a descending section of the modulation frequency, Fourier-transformed, and a peak frequency detecting means for detecting a peak frequency that gives a peak position of a frequency spectrum for each section, and a peak frequency is detected in the frequency spectrum for each section. When there are a plurality of modulation repetition frequencies, a plurality of sets of modulation signals having different repetition frequencies are compared in accordance with a distance measurement formula for the combination of the peak frequencies for each section, and a distance and a relative speed between the plurality of objects are calculated. FM-CW comprising: an object detecting means for detecting
Radar equipment. 2. A frequency difference comparison block for comparing a difference between peak frequencies of the ascending section and the descending section between a plurality of sets having different modulation repetition frequencies, wherein the peak frequency difference is substantially the same. A relative speed based object detection block for detecting an object having the same relative speed from a combination of matching peak frequencies, and an addition of peak frequencies in the ascending section and the descending section between a plurality of sets having different modulation repetition frequencies. A frequency comparison block for comparing the ratio of the average ratio and the modulation repetition frequency, and a distance-based object detection block for detecting an object at the same distance from a combination of peak frequencies in which the two ratios almost match each other. Based on the combination of the peak frequencies that give substantially the same distance and relative speed regardless of the wave, the distance and phase between multiple objects are determined. The FM-CW radar device according to claim 1, wherein the anti-velocity is simultaneously detected. 3. The object detecting means calculates and calculates another set of peak frequencies having different modulation repetition frequencies for the same object from the peak frequencies in the ascending section and the descending section of a certain set of modulation frequencies. An FM-CW radar device, wherein a plurality of objects are simultaneously detected based on a combination of a peak frequency at which a predicted peak frequency value and an actual measured peak frequency match. 4. A carrier wave is FM-modulated with a modulation signal having a triangular wave or a waveform close thereto, transmitted as a transmission wave toward an object, receives a reflected wave reflected by the object, and receives the reflected wave. A beat signal having a frequency difference between the two waves is generated by mixing with the transmission wave, and the beat signal is subjected to frequency analysis to measure a distance to a target or a relative speed with the target, in an object distance measuring method, The modulation repetition frequency of the modulation signal is sequentially switched with the repetition cycle of the modulation signal, a plurality of FM modulation waves having different modulation repetition frequencies are circulated in a time series, and the beat signal is generated in a rising section and a falling section of the modulation frequency. Fourier transform is performed, and a peak frequency that gives a peak position of a frequency spectrum is detected for each section, and a plurality of peak frequencies exist in the frequency spectrum for each section. In this case, a plurality of sets of modulated signals having different modulation repetition frequencies are compared with each other in accordance with a distance measurement formula for a combination of the peak frequencies in each section to detect a distance and a relative speed between the plurality of sets of modulated signals. A distance measuring method for an object.