KR20070096009A - Target detecting device - Google Patents

Abstract

To shorten an observation time necessary for achieving an observation value with a two-frequency CW radar. Provided is a target detecting device (1) for calculating the relative velocity of a target by analyzing the frequency of a reception signal (25), which is obtained by modulating the frequency of a transmission sequentially into a plurality of step frequencies and irradiating the target with the frequency-modulated transmission signal (22) as a transmission wave (23), and by receiving the echo (24) of the transmission wave reflected from that target. The target detecting device (1) comprises frequency modulation means (2) for repeating the frequency modulating process of modulating the transmission signal (22) sequentially into the step frequency, a plurality of times within the minimum observation time for achieving a desired velocity resolution, and frequency analyzing means (6) for analyzing the frequency of the reception (25), which is obtained by receiving the echo (24) of the transmission signal (22) modulated into the same step frequency of the frequency modulating processes repeated by the frequency modulation means (2), over the frequency modulating processes.

Description

Target detection device {TARGET DETECTING DEVICE}

The present invention relates to a radar device for detecting the speed and the like of the target by irradiating the radio wave to the target.

In recent years, attempts have been actively made to increase the safety of driving by mounting a radar device in a vehicle such as an automobile to automatically detect surrounding obstacles and the like and reflecting the detection result in the driving control of the vehicle. The radar device provided for the running control of the vehicle is required to accurately detect relative speed information such as obstacles and other vehicles.

In such a radar apparatus, the received signal obtained by receiving radio waves arriving from the target is analyzed by frequency to detect the speed, position, and the like of the target. However, in order to increase the frequency resolution in the frequency resolution of the received signal, the received signal is subjected to a predetermined time. You should listen in. Taking time to observe the received wave leads to an improvement in the resolution of the frequency, thereby increasing the accuracy of the observed value output.

The minimum observation time required to achieve the desired speed resolution can be determined in principle by the frequency analysis method employed. For example, in the radar apparatus using the transmission wave of wavelength lambda, if the frequency analysis of the received signal is performed by Fourier transform, the minimum observation time T _c required for obtaining the speed resolution δV and the frequency resolution δf is It is known that 1 is satisfied.

Low price is the key to the widespread use of automobile-mounted radar, but it is slower than a pulse radar or a pulse compression radar (spectrum diffusion radar) that requires a high-performance signal processing circuit to reduce the cost of the radar device. Frequency modulated continuous wave (FMCW) or two-wave continuous wave (CW) methods that can be realized by processing are considered to be advantageous.

The FMCW method generates a bit signal of a received signal and a transmission signal obtained by receiving reflected waves from a target in two observation periods of a frequency rising period and a frequency falling period, and in the bit signal and frequency falling period obtained in the frequency rising period. It is a method of detecting the relative speed and distance of the target by combining the obtained bit signals. In this case, since the bit signal frequency needs to be obtained independently from each of the frequency rising period and the frequency falling period, both the frequency rising period and the frequency falling period must be longer than T _c . Therefore, in the FMCW method, at least 2 x T _c time is required to obtain an observation that satisfies the desired speed resolution.

On the other hand, the two-frequency CW system is a system in which transmission waves of two frequencies f1 and f2 are transmitted at regular intervals, and a target is detected from frequency and phase information of each reception wave. Also in this case, since the frequency analysis process of the reception wave with respect to the transmission wave of frequency f1 and the frequency analysis process of the reception wave with respect to the transmission wave of frequency f2 are independent, it transmits the transmission wave of frequency f1 for at least time _Tc . After receiving the reception wave, it is required to transmit the transmission wave of frequency f2 by at least time T _c to receive the reception wave. From this, even in the two-frequency CW system, at least 2 x T _c time is required to obtain an observation value satisfying the desired speed resolution as a result.

As described above, in any of the conventional FMCW system and the two-frequency CW system, an observation time of 2 × T _c or more is required in order to obtain an observation value at a desired speed resolution. As a method of obtaining an observation value in a time shorter than 2 × T _c , the phase difference of a bit signal of a reception wave obtained with respect to a transmission wave of another frequency in either of a frequency rising period and a frequency falling period in the FMCW method. Is combined to detect a relative velocity and distance of a target (for example, Patent Document 1).

(Patent Document 1) Japanese Patent Publication No. 2004-511783 "Method and Apparatus for Measuring Distance and Relative Speed of a Fallen Object"

(Patent Document 2) Japanese Patent Laid-Open No. 2002-71793 "Radar Device"

(Tasks to be solved by the invention)

The method of patent document 1 is based on the FMCW system. In order to realize the distance resolution generally required for automobile-mounted radar by the FMCW method, it is necessary to actually perform frequency modulation with a bandwidth of about 150 MHz. In order for a plurality of vehicles equipped with FMCW radars to coexist without interference with each other on a road, it is ideal to assign a unique frequency range to the radar apparatus of each vehicle and to perform frequency modulation within that range. However, since the width of the frequency band that can be allocated to the vehicle-mounted radar is about 1 kHz, only six FMCW radars that sweep over the frequency in the frequency range of about 150 MHz can exist at the same time. It does not become and is not practical.

The present invention has been made to solve these problems. That is, an object of the present invention is to provide a radar device capable of detecting a target object using only a two-frequency CW or a multi-frequency CW method, and achieving a desired speed resolution with only an observation time of less than half of a conventional radar device.

(Means to solve the task)

The target detection device according to the present invention sequentially modulates a frequency of a transmission signal into a plurality of step frequencies, irradiates a target signal as a transmission wave after the frequency modulation, and receives an echo of the transmission wave reflected on the target. A target detection device for calculating a relative speed of the target by frequency analysis of the received signal, wherein the frequency modulation process of sequentially modulating the transmission signal to the step frequency is performed a plurality of times within a minimum observation time for achieving a desired speed resolution. And repeating frequency modulation means and frequency analysis means for frequency analysis of the received signal corresponding to the same step frequency of the frequency modulation process over the plurality of frequency modulation processes.

The minimum observation time for achieving the desired speed resolution refers to the minimum observation time determined in principle based on the frequency analysis method employed in the radar apparatus, and in the case of Fourier transform, What is given by T _c has already been described. In the case of performing frequency analysis by a method other than a Fourier transform, for example, even when a desired speed resolution is achieved by using a super-resolution method, the lower limit of the observation time can be determined. The lower limit of the observation time in the super resolution method corresponds to the minimum observation time.

The received signal corresponding to the same step frequency of the frequency modulation process among the received signals is a received signal obtained by receiving an echo of a transmission signal modulated by the same step frequency of a plurality of frequency modulation processes repeated by frequency modulation means. It means.

(Effects of the Invention)

According to the target detection device according to the present invention, the desired speed resolution is satisfied with a shorter observation time than the conventional two-frequency CW method or the multi-frequency CW method while maintaining the characteristics of the conventional two-frequency CW method or the multi-frequency CW method. One observation can be obtained. The characteristics of the conventional two-frequency CW system or the multi-frequency CW system described herein have advantages such as that the frequency modulation bandwidth that needs to be allocated to the radar device can be reduced, or the transmission frequency modulation circuit can be simplified. have.

1 is a block diagram showing the configuration of a target detection apparatus according to Embodiment 1 of the present invention;

2 is a waveform diagram of a transmission signal in the target detection device according to the first embodiment of the present invention;

3 is a block diagram showing the configuration of the target detection apparatus according to the second embodiment of the present invention.

(Explanation of the sign)

2: transmission signal frequency modulator 3: circulator

4: transmitting and receiving antenna 5: receiving RF frequency converter

6: frequency analyzer 7: distance / speed calculator

11: reference signal generator 12: transmit RF frequency converter

13 pulser 14 A / D converter

15: reception signal storage means 16: frequency analyzer

71: speed calculator 72: distance calculator

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described using drawing.

(Example 1)

1 is a block diagram showing the configuration of a target detection apparatus according to an embodiment of the present invention. In the figure, the target detection device 1 includes a transmission signal frequency modulator 2, a circulator 3, a transmission / reception antenna 4, a reception RF frequency converter 5, a frequency analyzer 6, a distance and a speed. The calculator 7 is provided.

The transmission signal frequency modulation section 2 is a circuit that generates a transmission signal and modulates the frequency of the generated transmission signal into a predetermined waveform. 1, the example of the detailed structure of the transmission signal frequency modulation part 2 is also shown. The transmission signal frequency modulator 2 according to this configuration example includes a reference signal generator 11, a transmission RF frequency converter 12, and a pulser 13.

The reference signal generator 11 includes a voltage controlled oscillator (VCO), and generates a reference signal 20 periodically modulated with a frequency as a transmission signal by controlling an input voltage to the voltage controlled oscillator. Let's do it. The transmission signal RF frequency converter 12 is a circuit for frequency converting the reference signal 20 into a transmission signal 21 in a radio frequency (RF) band. The pulser 13 generates the transmission pulse signal 22 by pulsing the transmission signal 21 at a predetermined pulse repetition time.

The circulator 3 is a switch for switching the transmission signal frequency modulator 2, the reception RF frequency converter 5 and antenna 4 described later to time division. That is, at the timing of irradiating the target object with the transmission pulse signal 22 as the transmission wave, the transmission signal frequency modulator 2 and the antenna 4 are directly connected, while the transmission wave is reflected by the target and echoes the antenna 4 as an echo. At the timing of returning to, the reception RF frequency converter 5 and the antenna 4 are directly connected. By doing in this way, the antenna 4 can be used for both transmitting and receiving, the circuit scale can be made small, and the apparatus size of the target detection apparatus 1 can be made small.

The antenna 4 irradiates the target object with the transmission pulse signal 22 generated by the transmission signal frequency modulator 2 as the transmission wave 23, and further echoes the echo 24 of the transmission wave 23 reflected by the target object. ) Is received as a receive wave and output as an analog receive signal 25.

The reception RF frequency converter 5 converts the reception signal 25 in the RF band into a signal in the video signal band and performs baseband conversion in order to enable processing of the reception signal by a slower signal processing circuit. Part. The received signal after the baseband conversion is output as the received signal 26.

The frequency analyzer 6 is a part that performs frequency analysis on the received signal 26 after baseband conversion. In FIG. 1, the A / D converter 14, the reception signal storage means 15, and the frequency analyzer 16 are shown as a detailed structural example of the frequency analysis part 6. As shown in FIG. The A / D converter 14 is a circuit which converts the received signal 26 which is an analog signal into a digital signal at a predetermined sampling rate and outputs the digital received signal 27. The digital received signal 27 is stored in the received signal storage means 15.

The reception signal storage means 15 is, for example, a circuit configured to use a storage element and to store the digital reception signal 27 output from the A / D converter 14. The frequency analyzer 16 acquires the reception signal 28 from the reception signal storage means 15, and performs frequency analysis of the reception signal. The frequency analysis result 29 of the frequency analyzer 16 is output to the distance / speed calculator 7 as the output of the frequency analyzer 6.

The distance / speed calculator 7 detects a frequency component whose amplitude value is a peak from the signal that results from the frequency analysis result 29, and based on the detected frequency, the distance / speed calculator 7 to the relative speed 30 of each target and each target. It is a circuit for calculating the distance 31.

Subsequently, the operation of the target detection device 1 will be described. Initially, the speed resolution required for the target detection device 1 is δV, and the minimum observation time required for the principle of the frequency analysis process in order to satisfy this speed resolution δV is called T _C.

The reference signal generator 11 of the transmission signal frequency modulator 2 repeats the frequency modulation process of increasing the frequency of the reference signal 20 by Δf M times within T _c at the minimum observation time. Here, M is a natural number of two or more. 2 is a waveform diagram of the reference signal 20 generated in this manner. The frequency modulation process repeated by the reference signal generator 11 is to increase the frequency of the reference signal 20 by Δf over N steps (where N is a natural number of 2 or more) for each time T _PRI . The time width T _S of one frequency modulation process can be obtained as T _S = T _PRI × N. In addition, the range B of the modulated frequency is obtained as B = Δf × N.

The reference signal 20 generated in this way is converted into the transmission signal 21 in the RF band through the transmission signal RF frequency converter 12 and further converted into the transmission pulse signal 22 via the pulseizer 13. The target object is irradiated from the antenna 4 as a transmission wave 23. Part of the transmission wave 23 irradiated to the target reaches the antenna 4 again as an echo (reflection wave) 24.

The antenna 4 receives the echo 24 and outputs an analog received signal 25. The receiving RF frequency converter 5 baseband converts the analog receive signal 25 and outputs the received signal 26 after the baseband conversion. When the number of targets is I, assuming that the received signal 26 after the baseband conversion of step n in the frequency modulation process m is X (n, m), X (n, m) is represented by Equation (2). do.

Here, σ _i , v _i , R _i are the radar reflection cross-sectional area, relative velocity, and distance of each target, and φ _i is the constant phase term of the target individual.

The received signal 26 is converted into the digital received signal 27 by the A / D converter 14 and stored in the received signal storage means 15. The frequency analyzer 16 obtains a received signal from the echo of the transmission signal modulated at the same step frequency through a plurality of frequency modulation processes from the received signal storage means 15 and analyzes the frequency. This process corresponds to acquiring X (n, m) obtained for a single n and a plurality of m from the received signal X (n, m) stored by the reception signal storage means 15 and performing frequency analysis. . If the Fourier transform is used as the frequency analysis method, the frequency analysis result 29 is expressed by equation (3).

In the following description, k in equation (3) is called a frequency component number.

The distance / speed calculator 7 calculates the relative speed and the distance of the target from the frequency analysis result 29 obtained by the equation (3). This is performed as follows. First, the distance-speed calculator 7 calculates the sum of the amplitude values of F _k (n) represented by Equation 3 as shown in Equation 4, for example.

Subsequently, the distance / speed calculator 7 calculates the frequency component number k at which the value of G _{k in} the equation (4) becomes a peak. This process is performed by detecting the frequency component number k _peak which maximizes the value of the left side G _k of the expression (4). On the other hand, the peak frequency f _peak (n) of the received signal after baseband conversion represented by Equation 2 is given by Equation 5.

Therefore, the distance / speed calculator 7 obtains the relative speed v _i of the target from the peak frequency number maximizing the equation (4) and equation (5), and outputs this v _i as the relative speed 30.

In addition, the distance / speed calculator 7 calculates the distance R of the target of the relative speed v _i . To do this, the following processing is performed. First, the distance / speed calculator 7 extracts at least two frequency components for n from the components of the peak frequencies corresponding to v _i among the frequency components represented by the equation (3). Here, for example, the frequency component f _peak (n) for n and the frequency component f _peak (n + 1) adjacent to n are extracted.

If the phase components of these frequency components are represented as Phase (f _peak (n)) and Phase (f _peak (n + 1)), the distance R to the target is expressed by Equation 6 based on the principle of the two-frequency CW method. Is calculated.

The distance R to the target calculated in this way is output as the distance 31.

As is apparent from the above, according to the target detection apparatus according to the first embodiment, the target modulation is repeatedly irradiated to the target a plurality of times between the minimum observation time T _c required to achieve the desired speed resolution δV. By analyzing the received signal for the same step frequency among the received signals obtained from the echo between different frequency modulation processes, the relative speed and distance of the target can be calculated by observing only the minimum observation time T _c .

In the above description, the Fourier transform has been described as an example of the frequency analysis method. However, it is easy to change the frequency analysis by the super resolution method to those skilled in the art.

In the frequency modulation process, the transmission signal frequency modulator 2 is configured to monotonically increase the frequency of the reference signal stepwise by Δf. However, since the configuration required here is only modulated by a plurality of frequencies, the frequency modulation may be performed by other methods such as a monotonically decreasing frequency or an arbitrary frequency modulation.

(Example 2)

In the conventional two-frequency CW radar device, there is a problem in that the distance to each target cannot be accurately separated when there are a plurality of targets having the same relative speed. On the road which is the main use place of the on-vehicle radar device, a situation in which a plurality of cars travel at substantially constant speed in the same direction appears very frequently. However, the conventional two-frequency CW radar apparatus has a problem that the distance of a target cannot be separated in such a case, and it has hindered practical use.

Therefore, in order to solve such a problem, the linear modulation part is provided in a part of the frequency modulation section of the transmission wave in the two-frequency CW system radar, and the same signal processing as that of the FMCW system is performed, and the distance of the plurality of targets traveling at constant speed. A method of separating is known (for example, patent document 2).

However, this method requires a more complicated transmission wave modulation circuit. For this reason, the cost reduction which is one of the main objectives of employing a 2 frequency CW system radar cannot fully be achieved. Therefore, in the second embodiment of the present invention, it is possible to separate a plurality of target distances traveling at constant speed by using the transmission wave that performs only step frequency modulation by the simple transmission signal modulation circuit as in the first embodiment. The radar apparatus will be described.

3 is a block diagram showing the configuration of a radar apparatus according to the second embodiment of the present invention. In the figure, the characteristic part compared with the radar apparatus by Example 1 is that the speed calculator 71 and the distance calculator 72 are provided. The speed calculator 71 performs speed calculation processing similar to the speed / distance calculator 7 in Embodiment 1, outputs the speed 30, and further uses frequency analysis information (used for calculating the speed 30 ( 32). On the other hand, the distance calculator 72 analyzes the frequency using a super resolution frequency estimation method and calculates the distance based on the frequency analysis. In addition, since the component which carried the same code | symbol as FIG. 1 is the same as that of Example 1, description is abbreviate | omitted.

Subsequently, the operation of the radar apparatus according to the second embodiment of the present invention will be described. Also in the radar apparatus 1 according to the second embodiment of the present invention, the reference signal generator 11 generates a reference signal 20 such as a waveform shown in FIG. 2, and therein, a frequency analyzer ( Processing up to 6) is the same as that of the first embodiment.

Subsequently, the speed calculator 71 detects the frequency at which the amplitude value becomes a peak in the same manner as the speed / distance calculator 7 of the first embodiment, calculates the relative speed of the target based on Equation 5, Output as speed 30. In addition, the peak frequency information used for calculating the relative speed is output as the frequency analysis information 32. The frequency analysis information 32 is, for example, a frequency component number that becomes a peak of the frequency analysis result 29 (expressed by Equation 3) output by the frequency analyzer 16 and the amplitude value of the frequency analysis result 29. Information containing (k to maximize the value of Equation 4).

The distance calculator 72 obtains the peak frequencies across the plurality of frequency modulation processes obtained for one n in Equation 3 for the other n, and the phase-to-phase displacement of each peak frequency (degree of change, rate of change). It is the part which separates the distance of a plurality of constant velocity targets based on. This process corresponds to obtaining a phase gradient of the peak frequency in the n direction when monotonically increasing or monotonically decreasing the step frequency in the frequency modulation process.

Specifically, the distance calculator 72 receives and receives the echo 24 of the transmission wave 23 modulated at the same step frequency in a plurality of frequency modulation processes repeated by the transmission signal frequency modulation section 2. The signal 28 is acquired from the received signal storage means 15 and subjected to frequency analysis by the super resolution frequency estimation method. Such super-resolution frequency estimation methods include MUSIC (Multiple Signal Classification), ESPRIT (Estimation of Signal Parameters via Rotational Invariance Technique), ML (Maximum Likelihood), Capon, Maximum Entropy, Linear Prediction, and Minimum Criteria ( minimum norm) method can be used, but the MUSIC method will be described as an example of specific processing.

First, one of frequencies at which the amplitude value at the Fourier transform output by the frequency analyzer 16 obtained by the speed calculator 71 becomes a peak is referred to as frequency number k _peak . In the frequency analysis result 29, the distance calculator 72 combines a frequency component corresponding to the frequency number k _peak with some frequency components before and after this frequency component, and performs a frequency averaging process.

In the following description, for example, the frequency components corresponding to the frequency number k _peak and the frequency components before and after the frequency components are used one by one. That is, three frequency components corresponding to frequency number k _peak -1, frequency components corresponding to frequency number k _peak , and frequency components corresponding to frequency number k _peak +1 are used.

In the case where a plurality of targets exist in the frequency component of the frequency number k _peak , in order to separate each target distance, the frequency between the received signals between each step frequency portion of the frequency modulation process of the transmission signal frequency modulator 2 Must be separated. In order to make it possible to separate frequencies with different step frequencies n (n = 1 to N) in the frequency modulation process, first, a data matrix having different step frequency numbers n is defined as a sub-matrix Fq consisting of N _s

Next, the average processing of the correlation matrix of this sub-matrix Fq is performed as shown in Equation (8).

Where H denotes the complex transpose of the matrix and <*> denotes an average operation on q.

Subsequently, the distance calculator 72 intrinsically expands the correlation matrix R obtained by frequency-averaging by Equation 8, and the eigenvectors e _α (α = 1, ..., N _S -L) corresponding to the eigenvalues of the noise. Noise space consisting of E = [e ₁ … e _{Ns -L} ] Where L is the number of signals and is obtained from, for example, an eigenvalue number greater than the eigenvalue of noise.

Thereafter, the distance calculator 72 performs frequency estimation processing to calculate a plurality of target distances, respectively. This frequency estimation process is as follows. That is, the distance calculator 72 calculates a mode vector that maximizes the value of the evaluation function MUSIC (R) represented by the mode vector a (R) and the noise space E, as shown in Equation (9).

Here, the mode vector a (R) is given by equation (10).

In other words, a plurality of Rs that give the mode vector a (R) (Equation 10) that maximizes the evaluation function MUSIC (R) (Equation 9) is calculated, and the distances of the plurality of targets that run them at constant speed (31). Output as

As described above, according to the second embodiment of the present invention, distances of a plurality of constant velocity targets that cannot be separated in the conventional two-frequency CW system can be separated using the super resolution frequency estimation method.

The present invention can be applied to the radar device in general, and is particularly useful for reducing the cost and performance of the on-vehicle radar device.

Claims (4)

By sequentially modulating the frequency of the transmission signal into a plurality of step frequencies, irradiating the target object with the transmission signal after frequency modulation as a transmission wave, and frequency analysis of the received signal obtained by receiving an echo of the transmission wave reflected by the target object. In the target detection device for calculating the relative speed of the target, Frequency modulation means for repeating a frequency modulation process of sequentially modulating the transmission signal to the step frequency within a minimum observation time for achieving a desired speed resolution; Frequency analysis means for frequency analysis of the received signal corresponding to the same step frequency of the frequency modulation process of the received signal over a plurality of the frequency modulation process Target detection apparatus comprising a. The method of claim 1, The frequency analyzing means performs frequency analysis on the received signal corresponding to the first step frequency of the frequency modulation process through a plurality of the frequency modulation processes to generate a first frequency analysis result signal, and further comprises a first signal different from the first step frequency. Generating a second frequency analysis result signal by performing frequency analysis on a received signal corresponding to a two step frequency over a plurality of frequency modulation processes; Detecting a frequency component at which the amplitude value of the first frequency analysis result signal becomes a peak as a first peak frequency, and detecting a frequency component at which the amplitude value of the second frequency analysis result signal becomes a peak as a second peak frequency; Distance calculating means for calculating the distance of the target from the signal phase difference between the detected first peak frequency and the second peak frequency The target detection device further comprising. The method of claim 1, The frequency analyzing means receives the signals corresponding to the plurality of step frequencies by analyzing the received signals corresponding to the plurality of step frequencies at which the frequency modulating means modulates the transmission signal by fixing the step frequencies over a plurality of frequency modulation processes. Frequency analysis of the signal produces a signal, Speed calculating means for detecting a frequency component at which an amplitude value of the signal becomes a peak as a result of frequency analysis of the received signal corresponding to the plurality of step frequencies, and calculating a relative speed of the target from the detected frequency component; By frequency analyzing the frequency component detected by the speed calculating means over the plurality of step frequencies, the displacement of the phase components of the plurality of step frequencies is calculated, and the distance of the target is calculated based on the calculated displacement of the phase components. Distance calculating means The target detection device further comprising. The method of claim 3, wherein The distance calculating means performs frequency analysis on the frequency components detected by the speed calculating means over a plurality of step frequencies in a frequency modulation process using a super-resolution method, thereby determining the displacement of the phase components of the plurality of step frequencies. The target detection device characterized by calculating.

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