JP4266674B2 - Radar equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radar apparatus, and more particularly to a radar apparatus suitable for in-vehicle use used for the purpose of collision prevention, auto cruise control, automatic driving, and the like.
[0002]
[Prior art]
Various radar systems such as FM-CW (Frequency Modulated-Continuous Wave), pulse Doppler, etc. are employed in a radar apparatus that measures the distance between the host vehicle and the target object and the relative speed of the target object with respect to the host vehicle. Among them, in particular, the FM-CW radar apparatus has an advantage that its inter-vehicle distance and relative speed between moving bodies can be obtained at the same time because its circuit configuration is relatively small and inexpensive. It is adopted in.
[0003]
In general, in such an FM-CW radar apparatus, for example, as shown in Patent Document 1 below, a mixer that mixes a transmission signal and a reception signal, and a beat signal (analog signal) output from the mixer are used. An AD converter (Analog-to-Digital Converter) that samples and converts it to a digital signal, and performs an analysis by applying a fast Fourier transform (FFT) process to the output of the AD converter, and the distance to the target and the target And a processor for calculating the relative speed.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-174548
[Problems to be solved by the invention]
By the way, in general, as a method for improving a signal-to-noise ratio (signal-to-noise ratio) in performing signal processing, there is a method by calculation in addition to a method by improving hardware performance. As a method for improving the S / N ratio by calculation, a method of improving the S / N ratio by performing averaging processing (averaging) on data having different acquisition times is common.
[0006]
However, in the case of radar, since the beat signal originally changes in time due to the movement of the target (target), the data cannot be simply averaged, and the averaging process (average) is performed. It is difficult to apply the SN ratio improvement method by the
[0007]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a radar apparatus capable of removing the influence of noise by signal processing calculation.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to a first aspect of the present invention, an AD converter that samples and AD-converts the signal at a sufficiently high sampling frequency with respect to the frequency band of the signal, and the AD converter Grouping means for creating a plurality of groups each consisting of a sequence of data having a fixed period by sequentially distributing data output from the data, and for each group grouped by the grouping means, the data in the group And a Fourier transform means for performing Fourier transform on the radar apparatus. Is provided.
[0009]
Further, according to the second aspect of the present invention, in the radar device according to the first aspect, the averaging processing means for performing averaging processing based on the Fourier transform result obtained for each group by the Fourier transform means is further provided. It is equipped.
[0010]
According to a third aspect of the present invention, in the radar device according to the first aspect, the sampling frequency is four times or more the maximum frequency in the signal frequency band.
[0011]
In addition, according to the fourth aspect of the present invention, an averaging process is performed on an AD converter that samples and AD-converts a signal, and a predetermined number of pieces of data continuously output from the AD converter. A radar apparatus comprising: averaging processing means for creating a time-averaged data string by performing the processing; and Fourier transform means for performing Fourier transform on the data string created by the averaging processing means Is provided.
[0012]
According to a fifth aspect of the present invention, in the radar device according to the fourth aspect, the AD converter performs sampling at a sampling frequency that is four times or more the maximum frequency in the frequency band of the beat signal. .
[0013]
According to a sixth aspect of the present invention, in the radar device according to the fourth aspect, the AD converter performs sampling a plurality of times close to each other at a constant interval equal to or less than the Nyquist interval of the beat signal. The averaging processing means executes an averaging process on the output data of the AD converter corresponding to the plurality of samplings.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an FM-CW radar apparatus will be described with reference to the accompanying drawings.
[0015]
First, the measurement principle of distance and relative velocity by FM-CW radar will be described with reference to FIGS. The FM-CW radar is a radar that transmits a continuous wave (CW) while performing frequency modulation (FM) and receives an echo (reflected wave) from a target (obstacle) in the coverage area.
[0016]
Here, if the frequency modulation (FM) is controlled using a triangular wave (which changes within a range of ± Δf / 2 around the frequency f ₀ ), the relationship between the frequency of the transmission signal and time is shown in FIG. It looks like the solid line in A).
[0017]
Then, the relationship between the frequency of the reflected signal from the target existing at a location separated by the distance R and time is as shown by the broken line in FIG. 1A if the relative speed between the target and the radar is zero. become. Accordingly, transmitted and received signals (i.e., reflection signal) and mixed (mixing) allowed is in the beat signal obtained frequency (beat frequency) f _r is as shown in FIG. 1 (B).
[0018]
Here, if the repetition frequency of the modulation triangular wave is f _m and the speed of light is c,
f _r / (2R / c) = (Δf / 2) / {(1 / f _m ) / 4}
∴ R = f _r c / 4f _m Δf
If the relationship is established and the beat frequency _fr is measured, the distance R can be calculated.
[0019]
When the relative speed between the target and the radar is not 0, the Doppler effect occurs, and the transmission / reception signal is as shown in FIG. Therefore, the beat frequency f _{up in the} interval in which the frequency of the transmission signal increases and the beat frequency f _{down in the} interval in which the frequency of the transmission signal decreases are as shown in FIG.
[0020]
That, f _{Stay up-and} f _down becomes shall relative velocity is superimposed Doppler frequency f _d to the beat frequency f _r in the case of 0,
f _up = f _r −f _d
f _down = f _r + f _d
It is expressed.
[0021]
As is well known, when the target moves relative to the velocity v _r , the frequency of the reflected wave received by the radar is relative to the frequency f _{0 of the} transmitted wave.
f _d = 2 · v _r · f ₀ / c
Is shifted by the Doppler frequency represented by. However, c = 3 × 10 ⁸ [m / s].
[0022]
Therefore, if f _up and f _down are measured separately and f _r and f _d are calculated based on f _up and f _down , the distance R from the radar to the object and the relative velocity v _{r of the} object with respect to the radar are calculated. Can be requested.
[0023]
FIG. 3 is a block diagram showing a configuration of an FM-CW radar apparatus according to an embodiment of the present invention. In the figure, a modulation signal generator 10 is a device that generates a triangular wave signal as a modulation signal. A voltage-controlled oscillator (Voltage-Controlled Oscillator) 12 generates a transmission signal subjected to frequency modulation (FM) based on the triangular wave signal. The transmission signal is radiated from the transmission antenna 14 as a transmission wave (radio wave).
[0024]
The receiving antenna 16 receives a reflected wave with respect to the transmitted wave, and the received signal is guided to a mixer 18. The mixer 18 mixes the reception signal and the transmission signal to generate the beat signal. The generated beat signal is input to an AD converter (Analog-to-Digital Converter) 22 through a filter 20. The AD converter 22 samples the input signal, performs AD conversion, and outputs digital data.
[0025]
Then, the output data of the AD converter 22 is guided to the processor 24. The processor 24 is composed of a microprocessor, a DSP (Digital Signal Processor), etc., performs a fast Fourier transform (FFT) process on a digital data string representing a beat signal, performs frequency analysis, and performs processing according to the measurement principle described above. And the relative speed of the object is calculated.
[0026]
By the way, the AD conversion timing in the AD converter 22, that is, the sampling period is determined in consideration of the frequency band of the input signal. That is, according to the Nyquist sampling theorem, the original signal can be restored if sampling is performed at a frequency that is twice or more the maximum frequency of the signal. This condition is called the Nyquist condition, and the lowest sampling frequency that satisfies the Nyquist condition is called the Nyquist frequency, and its reciprocal is called the Nyquist period or the Nyquist interval.
[0027]
Therefore, the sampling in the AD converter 22 is also executed with a frequency that is twice or more the maximum frequency in the frequency band of the beat signal as the sampling frequency. For example, the time chart of FIG. 4 shows an example in which the input signal voltage v is sampled at a sampling frequency four times the frequency of the beat signal as the input signal for convenience.
[0028]
By the way, at the sampling times t ₀ , t ₁ , t ₂ ,... Shown in the figure, if impulse noise is superimposed on the input signal by chance, the accuracy of the subsequent signal processing is greatly deteriorated. It becomes. Therefore, the present invention is intended to improve the SN ratio by sampling at a frequency sufficiently higher than the Nyquist frequency, that is, oversampling, against the background of recent advances in LSI technology.
[0029]
FIG. 5 is a time chart for explaining oversampling in the AD converter 22. In the example in FIG. 5, the input signal (voltage v) is sampled at a sampling frequency three times that in the case of FIG. Hereinafter, signal processing using data oversampled in this manner will be described.
[0030]
FIG. 6 is a flowchart showing a signal processing procedure by the processor 24 according to the first embodiment of the present invention. First, in step 102, the AD converter 22 oversamples and AD-converts AD converter output data as shown in FIG. 5, that is, 3N (N is a positive integer) digital data string A as a beat signal. (N) (n = 0, 1, 2,..., 3N−1) is captured.
[0031]
Next, in step 104, a fast Fourier transform (FFT) is performed on a column A (3i) (i = 0, 1, 2,..., N−1) of N pieces of data taken in 3N pieces. Is applied to perform frequency analysis. That is, frequency analysis is performed based on data collected at sampling times t ₀ , t ₃ , t ₆ , t ₉ , t ₁₂ , t ₁₅ ,.
[0032]
Next, in step 106, the fast Fourier transform is similarly performed on a column A (3i + 1) (i = 0, 1, 2,..., N−1) of N pieces of data taken in 3N pieces. (FFT) is applied to perform frequency analysis. That is, frequency analysis is performed based on data collected at sampling times t ₁ , t ₄ , t ₇ , t ₁₀ , t ₁₃ , t ₁₆ ,.
[0033]
Next, in step 108, similarly, fast Fourier transform is performed on a column A (3i + 2) (i = 0, 1, 2,..., N−1) of N pieces of data taken in 3N pieces. (FFT) is applied to perform frequency analysis. That is, the frequency analysis is performed based on the data collected at the sampling times t ₂ , t ₅ , t ₈ , t ₁₁ , t ₁₄ , t ₁₇ ,.
[0034]
As described above, in this embodiment, the data output from the AD converter 22 is sequentially distributed, and a plurality of groups each including a data row having a certain period are created. Is subjected to Fourier transform. Thus, as shown in FIGS. 7A, 7B, and 7C, three Fourier transform results are obtained.
[0035]
In the final step 110, an averaging process is performed on the Fourier transform result obtained for each group. The frequency data after the averaging processing is a beat frequency f _{up in a} section in which the frequency of the transmission signal increases or a beat frequency f _{down in a} section in which the frequency of the transmission signal decreases, and the distance R from the radar to the target. the be used to calculate the relative velocity v _r of the subject to the radar and.
[0036]
According to the first embodiment as described above, even if impulse noise is superimposed on the input signal at a certain sampling time, the accuracy of the subsequent signal processing is not greatly deteriorated, By performing the averaging process also on floor noise due to superposed thermal noise or the like, reduction is achieved and the SN ratio is improved.
[0037]
In the first embodiment, three groups are created. However, if the sampling frequency is four times or more the maximum frequency in the frequency band of the beat signal, at least two groups can be created. The present invention can be used.
[0038]
FIG. 8 is a flowchart showing a signal processing procedure by the processor 24 according to the second embodiment of the present invention. First, in step 202, the AD converter 22 over-samples and AD-converts AD converter output data as shown in FIG. 5, that is, 3N (N is a positive integer) digital data as a beat signal. Column A (n) (n = 0, 1, 2,..., 3N−1) is captured.
[0039]
Next, in step 204, averaging processing is performed for each of the three pieces of data with respect to the captured 3N pieces of data. In particular,
B (m) = [A (3m) + A (3m + 1) + A (3m + 2)] / 3
(M = 0, 1, 2, ..., N-1)
Is performed to create new N data strings B (m) (m = 0, 1, 2,..., N−1). That is, averaging is performed on the data collected at sampling times t ₀ , t ₁ and t ₂ in FIG. 5, and then averaging is performed on the data collected at sampling times t ₃ , t ₄ and t ₅ . The averaging process is performed in the same manner.
[0040]
As described above, in the second embodiment, the averaging process is performed on a certain number of pieces of data continuously output from the AD converter, and a time-averaged data string is created. In the last step 206, fast Fourier transform (FFT) is performed on the data sequence B (m) (m = 0, 1, 2,..., N−1) after the time averaging process, and frequency analysis is performed. performed, the beat frequency f _down the section where the frequency of the beat frequency f _{Stay up-or} transmit signals in the section where the frequency of the transmission signal rises is gradually lowered is obtained. Then, the value, and thus utilized for the calculation of the relative velocity v _r of the target with respect to the distance R and the radar from the radar to the object.
[0041]
In the second embodiment as described above, as in the first embodiment described above, even if impulse noise is superimposed on the input signal at a certain sampling time, the accuracy of the subsequent signal processing is greatly deteriorated. However, the floor noise due to thermal noise or the like superimposed on the signal is also reduced by performing the averaging process, and the SN ratio is improved.
[0042]
In the second embodiment, time average processing is performed for every three pieces of data. However, if the sampling frequency is four times or more the maximum frequency in the frequency band of the beat signal, every two pieces of data or more. Can be subjected to a time average process, and the present invention can be utilized.
[0043]
Further, in the case of the second embodiment, it is not always necessary to perform sampling at a constant cycle, and as shown in FIG. 9, data is collected a plurality of times in the vicinity of the original sampling time that satisfies the Nyquist condition. It may be. That is, sampling may be performed a plurality of times close to each other at a certain interval equal to or less than the Nyquist interval of the beat signal, and the averaging process may be performed on the data corresponding to the plurality of samplings.
[0044]
As mentioned above, although embodiment of this invention has been described, of course, this invention is not limited to this, It is possible to employ | adopt various embodiment.
[0045]
【The invention's effect】
As described above, according to the present invention, it is possible to remove the influence of noise by signal processing calculation in the radar apparatus, and the processing accuracy can be improved.
[Brief description of the drawings]
FIGS. 1A and 1B are characteristic diagrams respectively showing the relationship between the frequency and time of a transmission / reception signal and the relationship between a beat frequency and time when the relative speed is 0 in an FM-CW radar. is there.
FIGS. 2A and 2B are characteristic diagrams respectively showing the relationship between the frequency and time of a transmission / reception signal and the relationship between the beat frequency and time when the relative speed is not 0 in the FM-CW radar. .
FIG. 3 is a block diagram showing a configuration of an FM-CW radar apparatus according to an embodiment of the present invention.
FIG. 4 is a time chart showing an example of sampling an input signal (voltage v).
FIG. 5 is a time chart for explaining oversampling in an AD converter;
FIG. 6 is a flowchart showing a signal processing procedure by the processor according to the first embodiment of the present invention.
FIG. 7 is a diagram illustrating a Fourier transform result obtained for each group.
FIG. 8 is a flowchart showing a signal processing procedure by the processor according to the second embodiment of the present invention.
FIG. 9 is another time chart for explaining oversampling in the AD converter.
[Explanation of symbols]
10 ... Modulation signal generator 12 ... Voltage-controlled oscillator
14 ... Transmitting antenna 16 ... Receiving antenna 18 ... Mixer
20. Filter 22 ... AD converter (Analog-to-Digital Converter)
24 ... Processor

Claims (2)

A mixer for mixing a radar transmission signal and a radar reception signal and outputting a beat signal;
An AD converter that samples the beat signal at a sufficiently high sampling frequency with respect to the frequency band of the beat signal output from the mixer and performs AD conversion;
Sampling means for creating a plurality of groups of data rows having a constant period by sequentially distributing data output from the AD converter;
For each group grouped by the sampling means, Fourier transform means for performing Fourier transform on the data in the group;
Averaging processing is performed on the Fourier transform results obtained for each group by the Fourier transforming means, and the distance from the radar to the target and the relative velocity of the target with respect to the radar are calculated from the beat frequency after the averaging processing. Means,
And the sampling means shifts the sampling data by the number of groups to be created from the sampling data assigned to the group to be created among the data output from the AD converter, and sequentially assigns the data to each group. , to create two or more groups of rows of data having a predetermined period F M-CW radar apparatus. A mixer for mixing a radar transmission signal and a radar reception signal and outputting a beat signal;
An AD converter that samples the beat signal output from the mixer and performs AD conversion;
Sampling means for creating a time-averaged data string by performing averaging processing on a fixed number of pieces of data continuously output from the AD converter,
Fourier transform means for performing Fourier transform on the data string created by the sampling means;
Means for calculating the distance from the radar to the object and the relative speed of the object with respect to the radar from the beat frequency based on the Fourier transform result by the Fourier transform means;
And the AD converter performs sampling a plurality of times close to each other at a constant interval equal to or less than the Nyquist interval of the beat signal, and the sampling means includes the AD converter corresponding to the sampling of the plurality of times. F M-CW radar apparatus that perform averaging processing on the output data.

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