JPH07128439A - Fm-cw radar - Google Patents

Abstract

PURPOSE:To compensate the effect of the distortion of a frequency-modulated signal based on the nonlinearity of a frequency modulator by a digital signal processing for a received beat signal, regarding an FM-CW radar for enabling prevention of collision of vehicles, execution of automatic running thereof, etc. CONSTITUTION:In an FM-CW radar which receives a reflection signal from an object which is based on a transmission signal formed out of a frequency- modulated continuous signal, and calculates the distance to the object and relative speed from the frequency of a beat signal of the received signal and a branch signal of the transmission signal, a sampling means 1 is provided to sample the received beat signal, a coefficient multiplying means 2 is provided to multiply each sampled data by a coefficient corresponding to the distortion of the beat signal, a frequency discriminating means 3 is provided to determine the beat frequency from the corrected sampled data by discrete Fourier transform and a distance-speed calculating means 4 is provided to calculate the distance to the object and the relative speed from the beat frequency determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM-CW radar, and more particularly to an FM-CW radar which is mounted on a vehicle or the like, detects an object on a road and provides the information to a driver or an automatic vehicle control means of the vehicle. The present invention relates to an FM-CW radar for enabling collision prevention and automatic driving.

[0002] The FM-CW radar sends out a frequency-modulated (FM-modulated) radio wave to a target object at a predetermined repetition period, and obtains a reflected wave from the target object and a beat frequency of a transmission signal. By detecting the component, the distance to the target and the relative velocity are obtained, but if there is distortion in the frequency modulation signal due to the nonlinearity of the frequency modulator, accurate detection of the distance and relative velocity is possible. Since it becomes difficult, it is necessary to perform compensation by signal processing on the received beat signal.

[0003]

2. Description of the Related Art A radar for a vehicle is required from the viewpoint of safe driving and comfortable driving, as it enables collision prevention and automatic driving, but the FM-CW radar is composed of a transceiver. In addition, since it is simple and the distance to the object and the relative speed can be obtained by a simple signal processing device, it is about to be widely used as a radar for automobiles that requires downsizing and cost reduction.

FIG. 12 shows a basic configuration example of an FM-CW radar. Reference numeral 11 denotes a triangular wave generator, which generates a modulation signal composed of a triangular wave. A voltage-controlled oscillator 12 modulates a carrier wave with a modulation signal from the triangular wave generator 11 to generate a transmission signal frequency-modulated in a triangular wave. 13 is a directional coupler,
A part of the transmission signal is branched. Reference numeral 14 denotes a transmission antenna, which transmits a transmission wave, for example, in the traveling direction according to the transmission signal from the directional coupler 13.

A receiving antenna 15 receives a reflected wave from a preceding vehicle or the like. Reference numeral 16 denotes a mixer, which mixes a local oscillation signal composed of a transmission signal branched through the directional coupler 13 and a reception signal received through the reception antenna 15 to generate a beat frequency signal. To do. 17
Is a signal processing device that counts the output signal frequency of the mixer 16 including a pulse counter, processes the counting result, and outputs a signal of a required distance and a signal of a relative speed.

FIGS. 13A and 13B show signals of respective parts in the FM-CW radar. FIG. 13A shows a case where the relative speed is 0, and FIG. 13B shows a case where the relative speed is v. The sending and receiving frequencies, the beat frequency, and the beat signal are shown. If in FIG. 13 (a), a beat frequency _{f b = 4ΔΩf m R / c} = f r, f r is the distance frequency. In the case of FIG. 13 (b), the beat frequency _{f b = (4ΔΩf m R /} c) ± 2f 0 v / c = f r ± f
_{where d} is f _r is the range frequency and f _d is the velocity frequency. Here, f ₀ is the center frequency of the transmission signal, ΔΩ is the frequency modulation width, T is the modulation repetition period, f _m (= 1 / T) is the modulation repetition frequency, f _b is the transmission _/ reception beat frequency, and c
Is the speed of light, _tr is the round-trip time of the radio wave to the target, R is the distance to the target, and v is the relative speed to the target. Less than,
The operating principle of the FM-CW radar will be described with reference to FIGS. 12 and 13.

The transmission wave sent from the transmitting antenna 14 is reflected by the target object and is received again via the receiving antenna 15 until a time delay t _r = 2R / c proportional to the distance to the target object. And undergoes a Doppler frequency shift proportional to the relative velocity. At this time, since the transmission wave is frequency-modulated by the triangular wave by the triangular wave generator 11 and the voltage controlled oscillator 12, the distance R to the target and the relative velocity v appear as a baseband frequency component.

That is, the beat frequency f _b of the transmitted _and received waves, which is obtained by mixing the received signal and the local oscillation signal from the directional coupler 13 in the mixer 16, is relative to the frequency f _r which depends on the distance. is the sum and difference of the frequencies between the frequency f _d which depends on the speed, as described above, when the relative velocity 0, a _{f b = 4ΔΩf m R / c} , when the relative velocity v, f _b = (4ΔΩf _m R / c) ± 2f ₀ / v.

That is, when a triangular wave is used as the modulation signal, when the target object approaches, that is, in the section corresponding to the rising direction of the triangular wave (the direction in which the frequency increases), the frequency corresponding to the distance and the relative speed are obtained. Is the beat frequency, and the difference between the frequency corresponding to the distance and the frequency corresponding to the relative speed is the beat frequency in the section corresponding to the descending direction (direction in which the frequency decreases). Therefore, the signal processing device 17 can detect these frequencies and calculate the distance R to the target object and the relative velocity v from the sum and difference frequencies.

[0010]

In the FM-CW radar, the frequency modulation signal is usually generated by using a voltage controlled oscillator. The voltage controlled oscillator performs a voltage-frequency conversion to generate a frequency modulation signal whose frequency changes according to the modulation signal waveform. If the voltage-frequency conversion characteristic of this voltage-controlled oscillator is linear, the generated frequency-modulated signal becomes a modulated signal without distortion.

However, the voltage-frequency characteristic of the voltage controlled oscillator is not always linear, especially at high frequencies. Moreover, the degree of the non-linearity not only varies depending on the individual oscillators, but also the respective oscillators may change greatly depending on the temperature.

If the voltage-controlled frequency conversion characteristic of the voltage-controlled oscillator is poor, the "frequency change" of the received signal and the local oscillation signal will occur.
Is a distorted version of the original modulated signal, and the received beat signal obtained by mixing both is
It has distortion as compared with the case of using a voltage controlled oscillator with good voltage-to-frequency conversion characteristics. Therefore, the information on the distance and the relative speed calculated using the frequency of the beat signal becomes erroneous.

For example, when a triangular wave is used as the modulation signal, the spectrum of the received beat signal when a voltage controlled oscillator with poor voltage-frequency conversion characteristic linearity is used,
Compared with the case of using a voltage controlled oscillator with good linearity,
It becomes wider and it becomes difficult to calculate accurate distance and relative velocity.

FIG. 14 shows the relationship between the voltage-frequency conversion characteristic and the frequency modulation characteristic. FIG. 14A shows the voltage waveform of the modulation signal. On the other hand, (b) is a voltage-frequency conversion characteristic when the voltage-frequency conversion characteristic is linear, (c) is a frequency-modulated signal when the voltage-frequency conversion characteristic is linear, and (d) is a voltage-dependent signal. The voltage-to-frequency conversion characteristic when the frequency conversion characteristic is non-linear, and (e) shows the frequency-modulated signal when the voltage-frequency conversion characteristic is non-linear.

FIG. 15 shows the relationship between the voltage-frequency conversion characteristic of the voltage-controlled oscillator and the distortion of the beat signal. In FIG. 15A, frequency modulation is performed when the voltage-frequency conversion characteristic is linear. The signal is shown, the solid line is the transmitted wave, and the dotted line is the received wave. Further, (b) shows a beat signal when the voltage-frequency conversion characteristic is linear. (C) shows a frequency-modulated signal in the case where the voltage-frequency conversion characteristic is non-linear, in which the solid line is the transmission wave and the dotted line is the reception wave. Further, (d) shows a beat signal when the voltage-frequency conversion characteristic is non-linear.

As shown in FIG. 14B, when a voltage controlled oscillator having a linear voltage-frequency conversion characteristic is used, the frequency-modulated signal has a correct triangular waveform as shown in FIG. 14C. It causes a frequency change. When the frequency-modulated signal is used as the transmission signal and the local oscillation signal, the frequencies of the resulting reception signal and the beat signal of the local oscillation signal are as shown in FIG. It is constant in the rising and falling sections of the triangular wave.

As shown in FIG. 14 (d), when a voltage controlled oscillator having a poor linearity of voltage-frequency conversion characteristics is used, the frequency-modulated signal has a triangular wave as shown in FIG. 14 (e). Causes a distorted frequency change. When the frequency-modulated signal is used as the transmission signal and the local oscillation signal, the frequencies of the resulting reception signal and the beat signal of the local oscillation signal are as shown in FIG.
As shown in, in the rising and falling sections of the triangular wave,
Each changes. For example, the frequency in the section t is not constant and gradually increases. As a result, when the beat signal is subjected to signal processing to extract the frequency component, the spectrum spreads, and erroneous distance information and speed information are detected.

In order to solve such a problem, conventionally, a means for improving the voltage-frequency conversion characteristic of the voltage controlled oscillator itself has been taken mainly by using an analog circuit technique. For example, in Japanese Unexamined Patent Publication No. 4-291188, a detection output signal waveform by a triangular wave frequency modulation transmission signal is stored in the absence of a target, and this stored waveform is generated by a distortion wave canceling circuit in the presence of the target. Then, the difference circuit takes the difference between the detected output waveform and this stored waveform to remove the influence of distortion of the triangular wave frequency modulation transmission signal. As another method, it is described that a distortion component is removed from the detection output signal by using a bandpass filter and a band reject filter.

FIG. 16 illustrates a conventional modulation distortion correction method, in which (a) is a correction circuit application method.
(B) shows the configuration of the analog correction circuit, and (c) shows the operation of the analog correction circuit.

As shown in FIG. 16 (a), the correction circuit 18 is connected to the output of the triangular wave generator 11, and performs a necessary correction on this triangular wave output to perform the voltage controlled oscillator 1
2, which causes the voltage controlled oscillator 12 to generate a transmission signal consisting of the corrected modulation waveform.

In FIG. 16C, the voltage control signal is now generated.
The V-f characteristic of the shaker 12 has distortion as shown by A in the figure.
If it is, use the correction circuit shown in FIG.
The triangular wave generation device has a V-V characteristic such as B shown in the figure.
Correction is made by correcting the triangular wave output waveform of device 11.
It is possible to make the subsequent transmission characteristics linear as shown by C indicated by a broken line.
it can. Note that in FIG. 16B, D_1,D_2,… Ha
Iodo, R_1,R_2,… _,R₁₁, R_12,… Is resistance.

However, in the case of such a method, not only a complicated circuit technique is required, but also it is difficult to reduce variations in characteristics due to individual oscillators, and it is necessary to compensate for temperature changes. Is also difficult. Also,
A method of pre-distorting the modulation signal so as to compensate for the distortion due to the voltage-controlled oscillator is also conceivable, but the distortion to be given may differ depending on the individual oscillator, and it is difficult to uniformly compensate, There is a problem in that it is necessary to perform temperature compensation even with respect to changes due to the temperature characteristics of the analog correction circuit itself.

The present invention is intended to solve the problems of the prior art, and in the FM-CW radar, the distortion of the frequency modulation signal caused by the nonlinearity of the voltage-frequency conversion characteristic of the frequency modulator. The FM-C is designed to solve such a problem by compensating the received beat signal by digital signal processing.
The purpose is to provide a W radar.

[0024]

[Means for Solving the Problems]

(1) Receive a reflection signal from an object based on a transmission signal consisting of a frequency-modulated continuous signal, sample the beat signal of the received signal and the signal obtained by branching the transmission signal, and perform a discrete Fourier transform from this sampled data. FM-CW for calculating the beat frequency by calculating the distance to the object and the relative velocity
In the radar, by shifting the sampled data on the time axis, the distortion of the beat signal due to the distortion of the frequency modulation in the transmission signal is compensated by the digital signal processing on the receiving side.

(2) A reflected signal from an object based on a transmission signal composed of a frequency-modulated continuous signal is received, a beat signal of the reception signal and a signal obtained by branching the transmission signal is sampled, and from this sampled data, In an FM-CW radar that calculates a beat frequency by a discrete Fourier transform to calculate a distance to an object and a relative velocity, the number of terms in the discrete Fourier transform is set larger than the number of terms in the sampled data, and the discrete Fourier transform of each sampled data is performed. By receiving the distortion of the beat signal based on the distortion of the frequency modulation in the transmission signal by shifting the conversion input time from the sampled time according to the distortion of the beat signal and setting the unselected discrete Fourier transform input to 0 On the side, compensation is performed by digital signal processing.

(3) A reflected signal from an object based on a transmission signal composed of a frequency-modulated continuous signal is received, a beat signal of the reception signal and a signal obtained by branching the transmission signal is sampled, and from this sampled data In an FM-CW radar that calculates a beat frequency by a discrete Fourier transform to calculate a distance to an object and a relative velocity, the number of terms in the discrete Fourier transform is set to be smaller than the number of terms in sampled data, and the discrete Fourier transform of each sampled data is performed. By shifting the transform input time from the sampled time according to the distortion of the beat signal and discarding the unselected sampling data and performing the discrete Fourier transform, the beat signal based on the distortion of frequency modulation in the transmission signal The distortion is compensated at the receiving side by digital signal processing.

(4) FIG. 1 shows the basic configuration (1) of the present invention. In the present invention, a reflection signal from an object based on a transmission signal composed of a frequency-modulated continuous signal is received, and the distance to the object and the relative speed are determined by the frequencies of the beat signals of the reception signal and the signal obtained by branching the transmission signal. In the FM-CW radar for calculating, the sampling means 1 for sampling the beat signal, the coefficient multiplying means 2 for multiplying each sampled data by the coefficient corresponding to the distortion of the beat signal,
A frequency discriminating means 3 for obtaining a beat frequency from the corrected sampled data by a discrete Fourier transform and a distance / velocity calculating means 4 for calculating a distance to an object and a relative velocity from the obtained beat frequency are provided.

(5) FIG. 2 shows the basic configuration (2) of the present invention. In the present invention, a reflection signal from an object based on a transmission signal composed of a frequency-modulated continuous signal is received, and the distance to the object and the relative speed are determined by the frequencies of the beat signals of the reception signal and the signal obtained by branching the transmission signal. In the FM-CW radar for calculating and, sampling means 1 for sampling a beat signal, and discrete Fourier transform means 5 having a larger number of terms than sampling means 1 for obtaining a beat frequency from sampled data by discrete Fourier transform. , From the input of the discrete Fourier transform means 5 corresponding to the distortion of the beat signal to input the sampling data, and to input 0 to the unselected input, and the time shift adjusting means 6 and the obtained beat frequency from the object A distance / speed calculation means 4 for calculating the distance to and the relative speed is provided.

(6) A reflected signal from an object based on a transmission signal composed of a frequency-modulated continuous signal is received, and the distance to the object and the relative distance are determined by the frequencies of the beat signals of the reception signal and the signal obtained by branching the transmission signal. FM-C to calculate speed and
In the W radar, the sampling means 1 for sampling the beat signal, the discrete Fourier transform means 5 having a smaller number of terms than the sampling means 1 for obtaining the beat frequency from the sampled data by the discrete Fourier transform, and the sampling means 1 The time shift adjusting means 6 for selecting the output corresponding to the distortion of the beat signal and inputting it to the discrete Fourier transforming means 5 and discarding the unselected output, the distance from the obtained beat frequency to the object, and the relative speed. A distance / speed calculation means 4 for calculating is provided.

[0030]

FIG. 3 shows a comparison between a distorted beat signal and an undistorted beat signal on the time axis. The thick line shows the distorted signal A and the thin line shows the undistorted signal. B
Is shown. As shown in the figure, the points of the beat signal having no distortion corresponding to the levels of the respective sampled data of the beat signal having distortion are present at positions displaced in the time axis direction.

FIG. 4 is a diagram for explaining distortion compensation on the time axis, and A shows a beat signal when the voltage-frequency conversion characteristic is poor. As shown in FIG. 4, the beat signal A when the voltage-to-frequency conversion characteristic is bad is sampled at equal time intervals, and a sampling sequence is shifted in the time axis direction, so that the voltage-to-frequency conversion characteristic is linear. It is shown that the beat signal B in the case is obtained.

In practice, this operation may be performed by rereading the sampling time for each data of the sampling series according to the degree of distortion. For example, a certain time t
The data x (t) sampled in (3) may be processed as x (t + τ) when the corresponding shift amount is τ. Also, some complex frequency component

[Equation 1] The sampled data

[Equation 2] Is

[Equation 3] Therefore, the time axis shift for the sampled data is
It is equivalent to multiplying the coefficient corresponding to the shift amount.

In the present invention, the principle configuration is shown in FIG.
As shown in (1), sampling means 1 is used to extract the beat signal.
The synchronization signal is used to synchronize with the triangular wave generator.
, N sampled data x_0,x_1,…_,x_N-1 Ask for
The coefficient corresponding to the distortion information is calculated by the coefficient multiplying means 2.
Corrected data a by multiplying information₀ x_0,a₁ x_1,…
_,a_N-1x_N-1 From the frequency discriminating means 3
And perform a discrete Fourier transform to obtain L (L is the target
Number) frequency data f_0,f_1,…_,f_L-1 Ask for this
Distance / speed data from the distance / speed calculation means 4
(R_0,v₀ ), (R _1,v₁ )_,…_,(R_L-1,v_L-1 )
Ask.

As described above, according to the present invention, in the FM-CW radar, the discrete Fourier transform is performed by the data obtained by multiplying the sampling data of the beat signal by the coefficient corresponding to the distortion of the modulated triangular wave. By calculating the distance and relative velocity from the frequency data obtained by
Errors in speed data can be reduced.

As another method, when the frequency is extracted by using FFT (Discrete Fourier Transform), the error of the distance and velocity data based on the distortion of the modulated triangular wave can be compensated as follows. it can. There are two possible methods for this.

FIG. 5 shows a method for performing a large-sized FFT by performing normal sampling. That is, in this case, by taking the number of terms of the discrete Fourier transform larger than the number of terms of the sampled data and shifting the input time of the discrete Fourier transform for the sampled data according to the distortion, the time of the frequency modulation distortion is It realizes compensation by axis shift.

According to this method, the number of FFT terms is set large according to the fineness of the shift amount, and the sampling time of each sampling data is read according to the degree of distortion to correspond to each input term of FFT. In addition, 0 is inserted in the input term of the FFT having no corresponding sampling point, which is effective when the sampling speed is relatively slow but the FFT processing time has a margin.

FIG. 6 shows a method of performing normal FFT by performing high speed sampling. That is, in this case, by performing sampling at high speed, shifting the input time of the discrete Fourier transform of each data according to the distortion, discarding unnecessary data, and performing the discrete Fourier transform with the required number of terms, It realizes the compensation of the distortion of the modulation by shifting the time axis.

This method performs sampling at high speed and
For each input term of, the data close to the time-shifted data is selected from the sampled data, and the corresponding processing is performed. The sampling speed can be increased, but the FFT processing time This is effective when there is not enough room.

In the present invention, as shown in FIG. 2 which shows the principle configuration (2), N samplings are performed from the beat signal by the sampling means 1 and by the synchronization signal with the triangular wave generator. Data x _0, x _1, ... _, X _N−1 are obtained, and the time shift adjusting means 6 uses the coefficient information corresponding to the distortion information to obtain M pieces of time shift data y _{0 ,} y.
_1, ... _, y _M-1 is obtained, and from this, the discrete Fourier transform means 5
, L f of frequency data f _0, f _1, ... _, F _L-1 are obtained, and the distance / speed calculation means 4 calculates distance / speed data (r _0, v ₀ ), (r _1, v ₁ ). _, … _, (R _L-1, v
_L-1 ).

FIG. 7 shows the operation (1) of the time shift adjusting means.
And corresponds to the case where a large size FFT is performed by performing normal sampling. In this case, N pieces of data y ₀ = y ₀ = time shift data corresponding to N pieces of sampled data x _0, x _1, x _2, ... _, X _N−1.
x _0, y ₃ = x _1, y ₅ = x _2, ... _, y _M-1 = x _N-1 , and the remaining data y _1, y _2, y _4, ... _, y _M-2 is 0. And an example is given.

FIG. 8 shows the operation (2) of the time shift adjusting means.
And corresponds to the case of performing normal FFT by performing high-speed sampling. In this case, N
Sampled data x _0, x _1, x _2, x _3, x _4, x _5, ... _, x _N-2,
From x _N-1 , M pieces of data y as time shift data
An example is shown in which ₀ = x _0, y ₁ = x _2, y ₂ = x _5, ... _, Y _M-1 = x _N-1 is selected and the remaining data is discarded.

[0043]

EXAMPLE FIG. 9 shows an example (1) of the present invention.
And the time of frequency modulation distortion by multiplication of the coefficient
The processing circuit which performs axis shift is illustrated. In the figure, 21 is
The sampling section, which samples the beat signal according to the clock
And output. 22_0,22 _1,…, 22_N-2 Is N-1
A shift register that is sampled according to the clock
The data that has been set is sequentially shifted.

23_0,22_1,…, 23_N-1 Is N multipliers
And the output x of the shift register _0,x_1,…, X_N-1 To
On the other hand, the N coefficients a from the coefficient supply unit 24_0,a_1,…_,
a_{N- 1} Are respectively multiplied. 25 is a gate part,
At the end of multiplication, the data a corrected according to the opening / closing control signal
₀ x_0,a₁ x_1,…_,a_N-1x_N-1 Is output. 26 is a lap
It is a wave number discriminator, and it is corrected by the sync signal.
Discrete Fourier transform is applied to the data to obtain L frequencies
Data f_0,f_1,…_,f_L-1 Is output.

[0045] 27 is a distance-velocity calculation unit, in response to the synchronizing signal, the frequency data f _0, f _{1, ...,} a f _L-1, distance and speed data _{(r 0, v 0),} (r _1, v ₁ ) _, … _, (r
_L-1, v _L-1 ) is output. The calculated distance and relative speed are obtained as peak values of this distance / speed data. Reference numeral 28 denotes a counter, which is a clock for the sample unit and the shift register, an opening / closing control signal for the gate unit, a synchronizing signal for the frequency discriminator and the distance / speed calculating unit,
A triangular wave synchronizing signal for a triangular wave generator (not shown) is generated in a constant synchronous relationship and supplied to each part. The configuration of FIG. 9 can also be realized by software.

FIG. 10 shows an embodiment (2) of the present invention, and exemplifies a configuration in which normal sampling is performed and a large size FFT is performed. In the figure, the same parts as those in FIG. 9 are indicated by the same numbers, and 31 is a time shift adjusting unit for adjusting the input time of the sampling data,
Reference numeral 32 is a discrete Fourier transformer that performs discrete Fourier transform to obtain frequency data.

The gate section 25 responds to the opening / closing control signal by
N sampled data x_0,x_1,…, X _N-1 Is output. Time
The inter-shift adjuster 31 determines the sampling data according to the distortion information.
Tax _0,x_1,…, X_N-1 Time shift, and y_0,
y_3,…_,y_M-1 , And other data y_1,y
_2,…_,y_M-2 0 is output to.

The discrete Fourier transformer 32 performs a discrete Fourier transform from the M pieces of data x _{0, 0,} 0, x _1, ..., X _N-1 , and the L pieces of frequency data f _0, f _{1 ,} . _, f _L-1 is output. The distance / speed calculation unit 27 uses the frequency data f _0, f _1, ...
_, f _L-1, from the distance / speed data (r _0, v ₀ ), (r _1,
v ₁ ) _, ... _, (r _L-1, v _L-1 ) are output.

FIG. 11 shows an embodiment (3) of the present invention, in which high-speed sampling is performed to obtain a normal FF.
The structure when performing T is illustrated. In the figure
The same thing as in 0 is shown with the same number.

The gate unit 25 responds to the opening / closing control signal by
N sampled data x_0,x_1,…, X _N-1 Is output. Time
The inter-shift adjuster 31 determines the sampling data according to the distortion information.
Tax _0,x_3,…, X_N-1 Time shift, M data
y_0,y_1,…_,y_M-1 Output as.

The discrete Fourier transformer 32 has M data
x_0,x_3,…, X_N-1 Discrete Fourier transform from
Frequency data f_0,f_1,…_,f_L-1 Is output. distance
-The speed calculator 27 uses the frequency data f_0,f_1,…_,f_L-1 
To distance / speed data (r _0,v₀ ), (R_1,v₁ )_,
…_,(R_L-1,v_L-1 ) Is output.

In FIGS. 10 and 11, the internal connection of the time shift adjusting section can be changed by the distortion information from the outside. For example, when the temperature characteristic of the oscillator is known, the distortion characteristic of the oscillator is sequentially known by a method such as sequentially monitoring the temperature of the oscillator, and the time shift amount is adjusted adaptively by adjusting the time shift amount based on the information. The distortion can be corrected.

[0053]

As described above, according to the present invention, F
In the M-CW radar, the distortion of the frequency modulation signal caused by the nonlinearity of the voltage-frequency conversion characteristic in the frequency modulator can be compensated by the digital signal processing on the received beat signal.

Since the present invention uses the method based on digital signal processing, it has the following various advantages. It is possible to perform a stable operation over time without being affected by temperature fluctuations. Even if the degree of distortion varies with time due to temperature characteristics and the like, it is possible to adapt adaptively. When the compensating circuit is configured using PLA, DSP, etc., the parameters and algorithm can be easily modified by software. The combination with other analog means and digital signal processing means can be easily performed. In the future, it will be possible to manufacture a higher quality and cheaper distortion compensator by realizing higher speed and lower price of digital elements.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration (1) of the present invention.

FIG. 2 is a diagram showing a basic configuration (2) of the present invention.

FIG. 3 is a diagram showing a time-axis comparison between a distorted beat signal and an undistorted beat signal.

FIG. 4 is a diagram illustrating distortion compensation on the time axis.

FIG. 5: Regular sampling is performed to obtain a large size F.
It is a figure which shows the method of performing FT.

FIG. 6 is a diagram showing a method of performing normal FFT by performing high-speed sampling.

FIG. 7 is a diagram showing an operation (1) of the time shift adjusting means.

FIG. 8 is a diagram showing an operation (2) of the time shift adjusting means.

FIG. 9 is a diagram showing an embodiment (1) of the present invention.

FIG. 10 is a diagram showing an embodiment (2) of the present invention.

FIG. 11 is a diagram showing an embodiment (3) of the present invention.

FIG. 12 is a diagram showing a basic configuration example of an FM-CW radar.

13A and 13B are diagrams showing respective signals in the FM-CW radar, where FIG. 13A shows a case where the relative speed is 0, and FIG. 13B shows a case where the relative speed is v.

FIG. 14 is a diagram showing a relationship between a voltage-frequency conversion characteristic and a frequency characteristic, wherein (a) shows a voltage waveform of a modulation signal, and (b) shows a voltage pair when the voltage-frequency conversion characteristic is linear. Frequency conversion characteristic, (c) a frequency-modulated signal when the voltage-frequency conversion characteristic is linear, (d) a voltage-frequency conversion characteristic when the voltage-frequency conversion characteristic is non-linear,
(E) shows a frequency-modulated signal when the voltage-frequency conversion characteristic is non-linear.

FIG. 15 is a diagram showing the relationship between the voltage-frequency conversion characteristic of the voltage-controlled oscillator and the distortion of the beat signal, wherein (a) is a frequency-modulated signal when the voltage-frequency conversion characteristic is linear; ) Is a beat signal when the voltage-frequency conversion characteristic is linear, (c) is a frequency-modulated signal when the voltage-frequency conversion characteristic is nonlinear, and (d) is a beat when the voltage-frequency conversion characteristic is nonlinear. Signals are shown respectively.

16A and 16B are views illustrating a conventional modulation distortion correction method, wherein FIG. 16A shows a method of applying a correction circuit, FIG. 16B shows a configuration of an analog correction circuit, and FIG. 16C shows an operation of the analog correction circuit. .

[Explanation of symbols]

 1 sampling means 2 coefficient multiplication means 3 frequency discrimination means 4 distance / speed calculation means 5 discrete Fourier transform means 6 time shift adjustment means

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Masahiko Shimizu Inventor Masahiko Shimizu 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (72) Inventor, Osamu Isaji 1-228 Gosho-dori, Hyogo-ku, Hyogo Prefecture Fujitsu Within Ten Co., Ltd.

Claims (6)

[Claims] 1. A reflected signal from an object based on a transmission signal composed of a frequency-modulated continuous signal is received, a beat signal between the reception signal and a signal obtained by branching the transmission signal is sampled, and the sampled data is sampled. In an FM-CW radar for calculating a distance to an object and a relative velocity by obtaining a beat frequency by a discrete Fourier transform from the above, by shifting the sampling data on the time axis, it is based on the distortion of frequency modulation in the transmission signal. An FM-CW radar, characterized in that distortion of a beat signal is compensated by digital signal processing on the receiving side. 2. A reflected signal from an object based on a transmission signal composed of a frequency-modulated continuous signal is received, a beat signal of the reception signal and a signal obtained by branching the transmission signal is sampled, and the sampled data is sampled. In the FM-CW radar that calculates the beat frequency by the discrete Fourier transform from and calculates the distance to the object and the relative velocity, the number of terms of the discrete Fourier transform is made larger than the number of terms of the sampling data, and The discrete Fourier transform input time is shifted from the sampled time according to the distortion of the beat signal, and the unselected discrete Fourier transform input is set to 0.
The FM-C is characterized in that the distortion of the beat signal due to the distortion of the frequency modulation in the transmission signal is compensated by the digital signal processing on the receiving side.
W radar. 3. A reflected signal from an object based on a transmission signal composed of a frequency-modulated continuous signal is received, a beat signal between the reception signal and a signal obtained by branching the transmission signal is sampled, and the sampled data is sampled. In the FM-CW radar that calculates the beat frequency by the discrete Fourier transform from and calculates the distance to the object and the relative velocity, the number of terms of the discrete Fourier transform is set to be smaller than the number of terms of sampling data, and Discrete Fourier Transform The input time is shifted from the sampled time according to the distortion of the beat signal, and the discrete Fourier transform is performed by discarding the unselected sampling data, and the beat based on the distortion of the frequency modulation in the transmitted signal. An FM-CW radar characterized in that signal distortion is compensated by digital signal processing on the receiving side. 4. A distance to an object by receiving a reflection signal from an object based on a transmission signal composed of a frequency-modulated continuous signal, and by the frequency of a beat signal of the reception signal and a signal obtained by branching the transmission signal. FM to calculate relative velocity
-In a CW radar, sampling means (1) for sampling the beat signal, coefficient multiplication means (2) for multiplying each of the sampled data by a coefficient corresponding to the distortion of the beat signal, and the corrected A frequency discriminating means (3) for obtaining a beat frequency from the sampled data by a discrete Fourier transform and a distance / velocity calculating means (4) for computing a distance to the object and a relative velocity from the obtained beat frequency are provided. An FM-CW radar characterized by the following. 5. A distance to an object is obtained by receiving a reflection signal from an object based on a transmission signal composed of a frequency-modulated continuous signal, and by a frequency of a beat signal of the reception signal and a signal obtained by branching the transmission signal. FM to calculate relative velocity
-In a CW radar, sampling means (1) for sampling the beat signal, and discrete Fourier transform means having a larger number of terms than the sampling means (1) for obtaining a beat frequency from the sampled data by discrete Fourier transform (5) and a time shift adjusting means for inputting the sampling data by selecting corresponding to the distortion of the beat signal from the input of the discrete Fourier transforming means (5) and inputting 0 to an unselected input ( An FM-CW radar comprising: 6) and a distance / speed calculation means (4) for calculating a distance to an object and a relative speed from the obtained beat frequency. 6. A distance to an object is obtained by receiving a reflection signal from an object based on a transmission signal composed of a frequency-modulated continuous signal and by a frequency of a beat signal of the reception signal and a signal obtained by branching the transmission signal. FM to calculate relative velocity
-In a CW radar, sampling means (1) for sampling the beat signal, and discrete Fourier transform means having a smaller number of terms than the sampling means (1) for obtaining beat frequencies from the sampled data by discrete Fourier transform (5) and a time shift adjusting means for selecting an output from the sampling means (1) corresponding to the distortion of the beat signal and inputting it to the discrete Fourier transform means (5), and discarding an unselected output ( An FM-CW radar comprising: 6) and a distance / speed calculation means (4) for calculating a distance to an object and a relative speed from the obtained beat frequency.