JP2002257925A - Radar apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DBF radar apparatus of FM-CW system reduced in the amount of operation. SOLUTION: In the DBF radar apparatus of FM-CW system, a digital signal processing part includes an estimating means for estimating a beat frequency and angle about a target from a history of already acquired target information. A DBF synthesizing process is carried out within a synthesis area containing the estimated target point specified by the beat frequency and the angle which are estimated by the estimating means within a rectangular coordinate plane whose variables are the beat frequency and the angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar device suitable for a vehicle. In particular, the present invention relates to an FM-CW radar device that uses a continuous wave subjected to frequency modulation as a transmission signal and detects a target from the beat frequencies of the transmission signal and the reception signal, and also performs a DBF synthesis process (digital (Beam forming synthesis process) to form an antenna beam at a desired angle to detect the angular orientation of a target.

[0002]

2. Description of the Related Art A radar device which detects a distance and a relative speed of a target from a beat frequency with respect to a received signal using an FM-CW signal as a transmission signal, and at the same time, detects an angle (azimuth) of the target by DBF synthesis processing, For example,
It is disclosed in JP-A-11-133142.

Since this conventional radar device can detect the distance, relative speed, and angle of a relatively short-range target, the radar device can be mounted on an automobile to check the existence and behavior of a preceding vehicle. It is excellent in that.

[0004]

However, the amount of calculation required for the FFT (Fast Fourier Transform) processing for calculating the beat frequency and the DBF combining processing for obtaining an antenna beam at a desired angle is enormous. Therefore, in a small-sized radar device that can be mounted on an automobile, there is a problem that the capability of the digital signal processing unit is limited, and the calculation takes too much time.

[0005] For a radar device that can detect only the distance and the relative speed while ignoring the angle at which the target is located,
A method of estimating the power spectrum peak at the next timing from the peak of the power spectrum of the beat frequency to reduce the amount of calculation is described in, for example, JP-A-6-207979. However, an appropriate solution has not yet been obtained for a technique for reducing the amount of calculation in the DBF synthesis processing.

[0006]

SUMMARY OF THE INVENTION A radar apparatus according to the present invention is intended to solve such a problem, and includes a transmission antenna for outputting a transmission signal which is a continuous wave subjected to frequency modulation, and a plurality of element antennas. And a receiving circuit unit that obtains the beat frequency of the transmission signal and the reception signal for each element antenna, and forms an antenna beam at a desired angle by performing a DBF synthesis process on the beat frequency. A digital signal processing unit for performing detection, the digital signal processing unit includes estimation means for estimating a beat frequency and an angle related to the target from a history of the target information already acquired, and the beat frequency and the angle are determined. The beat frequency and the angle estimated by the estimating means on the orthogonal coordinate plane as variables are specified. It is characterized in that to perform the DBF synthesis process in the synthesis area including the estimated target point to be.

According to this radar device, the estimating means estimates the beat frequency and angle indicating the current position of the target from the past target information history to obtain an estimated target point, and within the combined area including the estimated target point. Since the DBF combining process is performed, the amount of DBF calculation can be significantly reduced as compared with the case where the DBF combining process is performed in all regions.

It is desirable that the digital signal processor changes the size of the synthesis area from the history of the target information that has already been acquired. Specifically, it is desirable to determine the certainty of the estimated target point from the history of the already acquired target information, and to change the size of the combined area according to the certainty.

For example, when the temporal change of past target information is small or the direction of change is stable, the certainty of the estimated target point obtained on the extension of the change is high. When the certainty of the estimated target point is high, the probability that the latest target point will fall within the combined area is sufficiently high even if the combined area is reduced. Moreover, if the combining area is made smaller, the amount of calculation in the DBF combining process can be reduced.

Conversely, for example, when the information about the past angle swings right and left over time, the certainty regarding the angle of the estimated target point is low. The probability of departure can be reduced.

[0011] The digital signal processing section may change the shape of the synthesis area from the history of the already acquired target information.

Further, the digital signal processing unit includes sub-target detecting means for performing target detection by performing DBF synthesis processing over the entire angle range with respect to the beat frequency, and the estimating means uses the target information acquired by the sub-target detecting means. It is desirable to use it.

[0013] In order to obtain the estimated target point, the history of the target information is necessary, but the history of the target information cannot be obtained at the beginning of the target detection operation. Therefore, at the beginning of the operation, target information is acquired in advance by the sub-target detecting means, and an estimated target point is obtained based on the target information.

[0014]

FIG. 1 is a block diagram showing a radar apparatus according to an embodiment of the present invention. This radar apparatus is an FM-CW radar apparatus using a transmission signal obtained by applying frequency modulation (FM) to a continuous wave (CW). It is also a DBF radar device that forms and scans an antenna beam by digital beam forming technology to detect a target direction (angle).

Prior to describing the specific configuration and operation of the present embodiment, the detection principle of the FM-CW radar device will be described.

First, the detection principle of the FM-CW radar will be described with reference to the graphs of FIGS. FIG. 2 (A)
Is a graph in which the change in the transmission frequency is indicated by a solid line, the change in the reception frequency reflected from a target having a relative speed of zero at the position of the distance R is indicated by a broken line, and the frequency is plotted on the vertical axis and the time is plotted on the horizontal axis. Is taking.

As can be seen from this graph, a modulated signal obtained by applying a triangular frequency modulation to a continuous wave is used as a transmission signal. The center frequency of the transmission signal, that is, the carrier frequency is f0, the frequency shift width is ΔF, and the repetition frequency of the triangular wave is fm.

FIG. 3A is a graph showing a change in the received signal and a change in the transmitted signal when the relative speed of the target is not zero but at a speed V (V ≠ 0). , And the dashed line indicates the received signal frequency. Note that the meanings of the transmission signal and the coordinate axis are the same as those in FIG.

From FIG. 2A and FIG. 3A, when such a transmission signal is emitted, the reception signal has a time delay T according to the distance when the relative speed of the target is zero.
(T = 2R / C: C is the speed of light), and when the relative speed of the target is V, it is understood that a time delay T corresponding to the distance and a frequency shift D corresponding to the relative speed are received. In addition,
The example shown in FIG. 3A shows a case where the received signal frequency shifts upward in the same graph and the target approaches.

If a part of the transmission signal is mixed with the reception signal, a beat signal can be obtained. FIGS. 2B and 3B are graphs showing beat frequencies when the relative speed of the target is zero and when the relative speed is V, respectively. The time axis (horizontal axis) is shown in FIG. FIG.
The timing is matched with (A).

Here, the beat frequency when the relative speed is zero is fr, the Doppler frequency based on the relative speed is fd, and the beat frequency in the section where the frequency increases (up section) is fb.
1. Assuming that the beat frequency in the section where the frequency decreases (down section) is fb2, fb1 = fr-fd (1) fb2 = fr + fd (2) holds.

Therefore, if the beat frequencies fb1 and fb2 in the up and down sections of the modulation cycle are measured separately, fr and fd can be obtained from the following equations (3) and (4).

Fr = (fb1 + fb2) / 2 (3) fd = (fb2-fb1) / 2 (4) If fr and fd are obtained, the distance R and the velocity V of the target are calculated by the following (5) ( It can be obtained by equation (6).

R = (C / (4 · ΔF · fm)) · fr (5) V = (C / (2 · f0)) · fd (6) where C is the speed of light.

In this way, the distance R and the speed V of the target can be obtained. This is the detection principle of the FM-CW radar device.

FIG. 1 shows an FM according to an embodiment of the present invention.
The CW radar device includes a transmitting unit 1, an array antenna 2, a changeover switch 3, a receiving unit 4, and a digital signal processing unit 5.

The array antenna 2 is a receiving antenna having a plurality of element antennas ch1 to chn. An antenna beam can be formed at a desired angle by subjecting the received signals received by each of the element antennas ch1 to chn to appropriate phase shift processing and combining them. The beam scanning is achieved by sequentially shifting the desired angles. The received signal phase shifting process and the combining process for each element antenna are performed by digital operation. That is, antenna beam formation and scanning are performed by digital beam forming synthesis processing (DBF synthesis processing). However,
In the present radar apparatus, which is an FM-CW radar apparatus, a beat signal (beat frequency) obtained by mixing a transmission signal with a reception signal instead of directly performing a phase shift process and a synthesis process on the reception signal. These processings are performed for. The DBF technique is already known, and is disclosed, for example, in the above-mentioned Japanese Patent Application Laid-Open No. H11-133142.

This radar device also has lane shape obtaining means 6 as an additional component. The lane shape obtaining means 6 is additionally provided in the FM-CW radar device, and when mounted on a vehicle, obtains the shape of the lane on which the vehicle is traveling. For example, the curvature of the traveling lane can be obtained from the speed and the yaw rate obtained from the speed sensor and the yaw rate sensor mounted on the vehicle. If the curvature of the traveling lane is known, the lane shape can be known under the assumption that the lane width is a predetermined value.

The transmitting section 1 includes a voltage controlled oscillator (VCO) 11 having a center frequency of f0 (for example, 76 GHz), a buffer amplifier 12, a transmitting antenna 13, and an RF amplifier 14. The VCO 11 receives f0 ± ΔF by a control voltage output from a power supply for modulation (not shown).
/ 2 modulated wave (transmission signal) is output. The modulated wave is amplified by the buffer amplifier 12 and is radiated from the transmission antenna 13 over a wide range as an electromagnetic wave. A part of the transmission signal is amplified by the RF amplifier 14 and output as a local signal for reception detection.

The receiving array antenna 2 has n element antennas, and a changeover switch 3 is provided behind the receiving array antenna 2. The changeover switch 3 has n input terminals and one output terminal, and each of the input terminals is connected to one of n element antennas. That is,
Independent first channels to n-th channels are formed between each element antenna and the changeover switch 3 for each element antenna.

The output terminal of the changeover switch 3 is connected to any one of the n input terminals, and the connection is periodically switched by a changeover signal (clock signal). Connection switching is performed electrically on a circuit.

The receiving section 4 includes an RF amplifier 41, a mixer 4
2, an amplifier 43, a filter 44, an A / D converter 45, and a switching signal oscillator 46. Changeover switch 3
, Ie, the signal received by one of the element antennas of the array antenna 2 is R
The signal is amplified by the F amplifier 41 and the RF amplifier 14 is
Is mixed with a part of the transmission signal from. The received signal is down-converted by this mixing, and a beat signal which is a difference signal between the transmitted signal and the received signal is generated.

The received signal received in parallel for each channel is time-divided by the changeover switch 3 in a time much shorter than the beat signal period, and converted into serial data. Accordingly, the beat signal output from the mixer 42 is also a serial beat signal for each channel. This beat signal is input to the A / D converter 45 via the amplifier 43 and the low-pass filter 44, and is converted into a digital signal at the timing of the output signal of the oscillator 46, that is, the clock signal for switching the connection by the changeover switch 3. Is done.

The digital signal processing unit 5 receives the digital beat signal from the A / D converter 45. Here, the serial digital beat signal is separated for each channel and temporarily stored. The digital beat signal for each channel obtained in this manner is subjected to various processes to obtain target information, that is, the distance, relative speed, direction, and width of the target.

For the distance and the relative speed, F
It is obtained by the detection principle of the M-CW radar device. Also,
The direction is obtained by a method of forming and scanning an antenna beam by the DBF combining technique.

Next, the processing procedure in the digital signal processing unit 5 will be described with reference to the flowchart of FIG.

First, in step S1, a channel-specific beat signal, that is, a channel-specific digital beat signal in one modulation cycle (up section and down section) A / D converted by the A / D converter 45 is fetched and temporarily stored.

Then, in step S2, an FFT process is performed on the digital beat signal for each channel, and a beat frequency (beat frequency spectrum) for each channel is obtained for each of the up section and the down section.

Next, in step S3, the peak of the beat frequency (FFT peak) is detected for each channel. At this time, an appropriate channel, for example, the channel of the element antenna located at the center of the array antenna 2 ((1
By performing peak detection for both the up section and the down section for (+ n) / second element antenna channel), the distance and relative velocity of the target can be obtained from the above equations (3) to (6). However, DBF
Since the combining process has not been performed, the angle at which the target is located is unknown.

Next, in step S4, a beat frequency and an angle relating to the target are estimated from the history of the target information already acquired. Further, an area including an estimated target point specified by the estimated beat frequency and angle is obtained on an orthogonal coordinate plane using the beat frequency and angle as variables. Since the DBF synthesis processing is performed later in this area, this area is called a synthesis area.

FIG. 5 is an orthogonal coordinate plane using the beat frequency and the angle as variables, and shows an example of the movement history of the target point in the up section, the estimated target point, and the combined area. A black arrow 51 indicates a past movement history of the target point. The tip is the target point obtained in the previous processing, and the rear end is the target point obtained in the processing two times before. Therefore, it can be estimated that the next target point is located at a point moved by the same length in the same direction as the arrow 51, and that point is set as the estimated target point 52. Further, an area of 5 points × 5 points centered on the estimated target point 52 is defined as a combined area 53.

Next, in step S5, DBF combining processing (first DBF combining) is performed on the combining area obtained in step S4.
In addition to performing the combining process, the DBF combining process (second DBF combining process) is performed on the beat frequency peak (FFT peak) obtained in step S3. Both DBF synthesis processes are performed for both the up section and the down section. Needless to say, the total calculation amount at this time is much smaller than the calculation amount when the DBF synthesis processing is performed for the entire angle range and the entire beat frequency range set in advance. First
The main target detecting means is constituted by the DBF synthesizing process and steps S6 to S8 to be described later.
A sub-target detecting unit is configured by the BF combining process and steps S6 to S8.

In step S6, the two-dimensional peak after the first DBF synthesis processing and the angle peak after the second DBF synthesis processing are respectively extracted. Then, in step S7, the peak extracted for the up section and the peak extracted for the down section are extracted. Perform pairing of peaks.

Pairing refers to a combination of a peak in an up section and a peak in a down section that are considered to be based on the same target. For each combination,
By applying the equations (3) to (6), the distance, relative speed, and angle of the target point corresponding to each combination can be obtained.

It is not possible to determine whether or not the point indicated by a black circle in the composite area 53 is a peak because it is in the vicinity. Therefore, peak candidates in the synthesis area 53 are only points indicated by white circles.

In step S8, the lane shape obtained by the lane shape obtaining means 6 is fetched. Further, step S
In step 9, the target is identified from the target point distance, relative speed, and angle obtained in step S7 and the lane shape captured in step S8. The type of the target, for example, whether it is a preceding vehicle, a roadside object, an obstacle on the road, and if it is a preceding vehicle, whether it is a passenger car or a large car such as a truck, is identified. .

The target information thus obtained is not only used literally as target information, but also used in the next operation cycle (steps S1 to S5).
In 9), it is used as already acquired target information.

In step S4, the beat frequency and angle at the next time are estimated from the past beat frequency and angle on the orthogonal coordinate plane using the beat frequency and angle as variables. However, a distance and a relative speed may be used instead of the beat frequency as the past target information. The target distance and relative speed
It can be obtained from the equations (3) to (6) based on the beat frequency in the up section and the beat frequency in the down section.

FIGS. 6 to 8 show the distance, the relative speed,
This shows the history of angles, and in each figure, the horizontal axis shows the operation cycle. The distance, relative speed, and angle of the same target in the next operation cycle are predicted from the history of distance, relative speed, and angle, respectively, and the beat frequency of the up section and the down section is obtained by performing backward calculation from the prediction result of the distance and the relative speed. . A point on the orthogonal coordinate plane specified by the beat frequency and the angle in the up section or the down section is an estimated target point in the up section or the down section, respectively.

In the process of determining the combination area in step S4, the size and shape of the combination area can be changed in consideration of the history of the target information.

FIG. 9 shows some examples of the movement history of the target. 10 to 13 show examples of the combination area corresponding to the movement history.

In FIG. 9, when there is little change in the movement history as indicated by an arrow 91, for example, a relatively small combined area of about 5 × 5 points as shown in FIG. 10 is sufficient. However, as shown by an arrow 92, for example, when the change in the angle is small and the change in the beat frequency is large, it is desirable that the combining area be a rectangle long in the beat frequency direction as shown in FIG. Conversely, when the change in the angle is large and the change in the beat frequency is small, as indicated by the arrow 93, it is desirable that the combining area be rectangular in the angular direction as shown in FIG. Further, when the change in the beat frequency and the angle are both large in a certain direction as indicated by an arrow 94, as shown in FIG.
It may be a special shape that is long in the direction of change.

Although not shown, only the size may be changed in accordance with the history of the target information without changing the shape of the synthesis area. When the movement history of the target has little change or when the change direction of the movement history is constant over a relatively long period, the reliability of the estimated target point is high. In such a case, there is almost no possibility that the target will deviate from the synthesis area even if the synthesis area is reduced. Conversely, when the change in the movement history is large or when the change direction is unstable, the certainty of the estimated target point is low. In such a case, by increasing the combining area, omission of peak detection can be prevented. In this case, the amount of calculation increases with the enlargement of the synthesis area, but the amount of calculation is much smaller than that of the conventional whole-area calculation.

[0054]

As described above, according to the radar apparatus of the present invention, which is both an FM-CW radar apparatus and a DBF radar apparatus, without reducing the target detection capability,
The amount of calculation can be greatly reduced. Therefore, a high detection capability can be provided even when used in a case where the calculation processing capacity of the calculation means is limited for miniaturization, such as a vehicle-mounted radar device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a radar device according to an embodiment of the present invention.

FIG. 2 is a graph for explaining a detection principle of the FM-CW radar device.

FIG. 3 is a graph for explaining a detection principle of the FM-CW radar device.

FIG. 4 is a flowchart showing an operation procedure of the embodiment.

FIG. 5 is a diagram showing an orthogonal coordinate plane in which a beat frequency and an angle are variables.

FIG. 6 is a diagram showing a history of a distance of a target.

FIG. 7 is a diagram showing a history of a relative speed of a target.

FIG. 8 is a diagram showing a history of target angles.

FIG. 9 is a rectangular coordinate plan view showing several examples of a movement history of a target and using beat frequency and angle as variables.

FIG. 10 is a diagram showing an example of a combining area.

FIG. 11 is a diagram showing an example of a combining area.

FIG. 12 is a diagram showing an example of a combining area.

FIG. 13 is a diagram illustrating an example of a combining area.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transmission part, 2 ... Array antenna, 3 ... Changeover switch,
4 ... Reception unit, 5 ... Digital signal processing unit, 6 ... Lane shape acquisition unit, 11 ... Voltage controlled oscillator, 13 ... Transmission antenna, 41 ... RF amplifier, 42 ... Mixer, 45 ... A / D converter, 46 ... Switching signal generator, 52 ... estimated target point, 53 ... composite area.

Claims (6)

[The claims] 1. A transmission antenna for outputting a transmission signal which is a continuous wave subjected to frequency modulation, a reception antenna including a plurality of element antennas, and a beat frequency of the transmission signal and the reception signal for each of the element antennas A radar circuit comprising: a receiving circuit unit that performs a DBF synthesis process on the beat frequency to form an antenna beam at a desired angle to detect a target; Is provided with estimating means for estimating a beat frequency and an angle relating to the target from the history of the already acquired target information, and the beat frequency and the angle estimated by the estimating means in a rectangular coordinate plane having the beat frequency and the angle as variables, respectively. Within the synthesis area containing the estimated target point specified by Radar apparatus and executes the serial DBF synthesis process. 2. The radar apparatus according to claim 1, wherein the digital signal processing unit changes the size of the synthesis area based on a history of the target information that has already been acquired. 3. The method according to claim 2, wherein the digital signal processing unit obtains the certainty of the estimated target point from the history of the previously acquired target information, and changes the size of the combined area according to the certainty. The radar device according to claim 2. 4. The radar device according to claim 1, wherein the digital signal processing unit changes the shape of the synthesis area based on a history of already acquired target information. 5. The digital signal processing unit includes a sub-target detecting unit that performs a target detection by performing a DBF combining process on an entire angle range with respect to a beat frequency, and the estimating unit acquires the sub-target detecting unit. The radar device according to any one of claims 1 to 4, wherein the target information is used as needed. 6. The sub-target detecting means detects a beat frequency peak, and then performs target detection by performing a DBF combining process on the entire angle range for a beat frequency range including the beat frequency peak. The radar device according to claim 5, wherein: