JP2010112879A - Radar transceiver and radar device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve, with excellent accuracy, pairing between an up-beat frequency and a down-beat frequency based on a level of a beat signal. <P>SOLUTION: A radar transceiver transmits a first transmission signal whose frequency is raised with a prescribed frequency modulation width in each modulation period, and a second transmission signal whose frequency is lowered with a prescribed frequency modulation width in each modulation period, by being switched alternately in a switching period shorter than the modulation period, and generates a first beat signal having a frequency difference between the first transmission signal in the modulation period and a reception signal corresponding thereto, and a second beat signal having a frequency difference between the second transmission signal and a reception signal corresponding thereto, and thereby can generate almost simultaneously in the same modulation period, the beat signals which have been generated hitherto in each different time zone. Consequently, a level difference resulting from a time difference is not generated between beat signals of up/down-beat frequencies to be paired, to thereby achieve the pairing with excellent accuracy. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radar apparatus that detects a relative speed or a relative distance of a target object based on a frequency difference between a frequency-modulated transmission signal and a reception signal when the transmission signal reflected by the target object is received.

  In recent years, as a means for supporting automatic control in a vehicle such as an automobile, an FM-CW (Frequency Modulated-Continuous Wave) system that can detect the relative distance and relative speed of a moving body around the own vehicle, that is, another vehicle almost simultaneously. Radar devices are widely used. As described in Patent Document 1, an FM-CW radar device transmits a frequency-modulated continuous wave as a radar signal and receives a reflected signal from a target object. Then, the relative speed and the relative distance of the target object are detected based on the frequency difference between the transmission and reception signals. Here, a method for detecting the relative speed and the relative distance of the target object by the conventional FM-CW radar device will be described with reference to FIGS.

  FIG. 1 is a diagram illustrating a transmission / reception signal and a beat signal when the FM-CW method is employed in an in-vehicle millimeter wave radar device. The transmission signal is frequency-modulated according to a triangular wave-shaped frequency modulation signal having a frequency fm (for example, 400 Hz) as shown in FIG. 1A, and the frequency is modulated by a modulation period 1 / as shown by a solid line in FIG. It rises and falls linearly at fm, center frequency f0 (for example, 76.5 GHz), and frequency modulation width ΔF (for example, 200 MHz). On the other hand, as shown by a broken line in FIG. 1B, the received signal has a time delay ΔT due to the relative distance of the target object that reflects the received signal and a frequency shift corresponding to the dopp frequency γ according to the relative speed. receive. As a result, the transmission / reception signal has a frequency difference α in the frequency increase period (up period) UP of the transmission signal and a frequency difference β in the frequency decrease period (down period) DN. At this time, the relationships shown by the following equations (1) and (2) are established between the frequency differences α and β, the relative distance R and the relative speed V of the target object (where C is the speed of light).

R = C · (α + β) / (8 · ΔF · fm) (1)
V = C · (β−α) / (4 · f0) (2)
The FM-CW radar device generates a beat signal having the frequency differences α and β as frequencies by mixing such transmission / reception signals. As shown in FIG. 1C, the beat signal has an upbeat frequency α in the up period UP and a downbeat frequency β in the down period DN.

  Here, when there are a plurality of target objects in the scanning target region, the beat signal includes an up / down beat frequency for each target object. In order to detect the relative distance and relative velocity of each target object, the FM-CW radar device performs A / D conversion on beat signals for each up period and down period, and performs FFT ( Fast Fourier transform) and detect each frequency spectrum.

  FIG. 2 shows the frequency spectrum of the beat signal in each of the up period and the down period. Here, for convenience of explanation, a case where two target objects exist in the scanning target region is shown. Then, as illustrated, two peaks corresponding to two target objects are formed in each of the frequency spectrum in the up period and the frequency spectrum in the down period.

The FM-CW radar device associates (pairs) an upbeat frequency and a downbeat frequency obtained from the same target object in order to calculate a relative speed and a relative distance for each target object. At this time, since there is a high probability that a reflected signal of the same level can be obtained from the same object, beat frequencies having equivalent level peaks, that is, an upbeat frequency α1 and a downbeat frequency β1 having a peak of level L1, The upbeat frequency α2 and the downbeat frequency β2 that form the peak of the level L2 are paired. By doing so, the relative distance and the relative speed of each target object are detected based on the above-mentioned formulas (1) and (2).
Japanese Patent Laid-Open No. 11-271433

  However, the in-vehicle FM-CW radar device moves the target object at high speed in addition to the host vehicle moving at high speed, so that the level of the received signal fluctuates due to the time difference between the up period and the down period. As a result, there may be a difference between the levels of the beat signal in the up period and the beat signal in the down period obtained from the same target object. For example, the level of the received signal increases or decreases when the angle of the reflecting surface of the target object fluctuates, or the peak is separated by receiving the reflected signal that is irregularly reflected by the unevenness of the reflecting surface. In such a case, an equivalent level peak is not formed and pairing fails.

  Then, when the pair of up period and down period is one detection cycle, the relative speed / relative distance of the target object cannot be detected within one detection cycle. In addition, in order to ensure the accuracy of the detection results output to the vehicle control device, when the detection results obtained within a certain error range in a plurality of detection cycles are output, detection is also possible due to failure of pairing. When this occurs, the output timing of the detection result is delayed. Then, the start of vehicle control may be delayed, and driving safety may be reduced.

  Accordingly, an object of the present invention made in view of the above is to provide a radar that enables accurate pairing in an FM-CW radar device that performs pairing of an upbeat frequency and a downbeat frequency based on the level of a beat signal. It is to provide a transceiver.

  In order to achieve the above object, according to a first aspect of the present invention, based on a frequency difference between a frequency-modulated transmission signal and a reception signal when the transmission signal reflected by a target object is received. A radar transceiver that outputs a beat signal having a frequency difference between the transmission and reception signals to a signal processing device that detects a relative speed or a relative distance of a target object, and the frequency increases with a predetermined frequency modulation width every modulation period. Transmitting means for alternately switching a first transmission signal and a second transmission signal whose frequency drops at the predetermined frequency modulation width every modulation period with a switching period shorter than the modulation period; and the modulation The frequency of the first beat signal having a frequency difference between the first transmission signal and the corresponding reception signal in the period, and the frequency of the second transmission signal and the corresponding reception signal Radar transceiver is provided that generates and second beat signal having a having a beat signal generating means for outputting to the signal processing device.

  According to the above aspect, the first transmission signal whose frequency increases with a predetermined frequency modulation width every modulation period, and the second transmission signal whose frequency decreases with the predetermined frequency modulation width every modulation period, The first beat signal having a frequency difference between the first transmission signal and the reception signal corresponding to the first transmission signal in the modulation period, and the second transmission are alternately switched with a switching period shorter than the modulation period. Since the second beat signal having a frequency difference between the signal and the reception signal corresponding to the signal is generated, beat signals generated in the up period and the down period in different time zones are conventionally used in the same modulation period. Can be generated almost simultaneously. Therefore, there is no level difference in the beat signal of the up / down beat frequency to be paired due to the time difference between the up period and the down period, and pairing based on the level of the beat signal can be performed with high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  FIG. 3 is a diagram for explaining a usage situation of a radar apparatus to which the present invention is applied. As an example, the FM-CW radar device 10 is mounted in a front front grill or a bumper of the vehicle 1, and transmits a radar signal (electromagnetic wave) to a scanning target area in front of the vehicle 1. The reflected signal is received. The radar apparatus 10 generates a beat signal from the transmission / reception signal and processes it by a signal processing apparatus such as a microcomputer to detect the relative distance, relative speed, or azimuth angle of the target object in the scanning target area. Here, the target object is, for example, a preceding vehicle of the vehicle 1, an oncoming vehicle, or a pedestrian or a roadside stationary object. Then, the detection result is output to the vehicle control device 100.

  The vehicle control device 100 controls the behavior of the vehicle 1 by driving the actuator of the vehicle 1 based on the detection result by the radar device 10. For example, it tracks the preceding vehicle and follows the vehicle at a certain distance, or determines the probability of occurrence of a collision with the target object from the relative speed and relative distance, and avoids the collision when a collision is predicted Or activate an alarm device or occupant protection device.

  The usage situation shown here is an example, and the radar apparatus 10 is mounted on the front side, side, rear, or rear side of the vehicle 1, and the front side, side, rear, or rear of the vehicle 1 is mounted. It is also possible to detect the target object in the side scanning target region.

  FIG. 4 is a diagram illustrating the configuration of the radar apparatus according to this embodiment. The FM-CW radar device 10 transmits a millimeter-wave continuous wave (electromagnetic wave) subjected to frequency modulation as a transmission signal, receives the reflected signal, and generates a beat signal having a frequency corresponding to the frequency difference between the transmission and reception signals. A radar transmitter / receiver 30 to be generated and a signal processing device 14 to process a beat signal generated by the radar transmitter / receiver 30 are provided.

  First, the configuration of the radar transceiver 30 will be described with reference to FIG. 5 together with FIG. Here, FIG. 5 is a diagram illustrating various signals generated or processed in the radar transceiver 30. 5A to 5C, the horizontal axis indicates time.

  The radar transceiver 30 includes a “transmission unit” 32 including a first modulation signal generation unit 15, a second modulation signal generation unit 16, a modulation signal switching unit 17, and a voltage control oscillator 18. As shown in FIG. 5A, the first modulation signal generator 15 is a sawtooth waveform that rises linearly at a predetermined amplitude every predetermined period, in synchronization with the timing signal input from the signal processing device 14. The first modulation signal, which is a voltage signal of, is generated. Similarly, the second modulation signal generation unit 16 synchronizes with the timing signal input from the signal processing device 14 and has the same amplitude as the first modulation signal at the same period as shown in FIG. 5A. A second modulation signal which is a sawtooth voltage signal descending at is generated. Here, the first modulation signal has a rising section of the triangular wave-shaped modulation signal shown in FIG. 1A, and the second modulation signal has a falling section of the triangular wave-shaped modulation signal shown in FIG. 1A. , Corresponding to a modulation signal that repeats at half the period 1 / fm of the triangular wave, that is, at a period ((1 / fm) / 2). The period of the first and second modulation signals corresponds to the modulation period of the transmission signal generated based on this.

  As shown in FIGS. 5B and 5C, the modulation signal switching unit 17 follows a square wave signal (switching signal) having a switching period shorter than one half of the period of the first and second modulation signals. The first modulation signal is alternately switched at the same duty ratio when the switching signal is at the H level and the second modulation signal is alternately switched at the same duty ratio when the switching signal is at the L level, and the switched modulation signal is input to the voltage controlled oscillator 18. FIG. 5B shows a switching signal when the switching period is one half of the period of the first and second modulation signals and the modulation signal switched thereby, and FIG. 5C shows the switching signal. The switching signal in the case where the period is ¼ of the period of the first and second modulation signals and the modulation signal switched thereby are shown.

  The voltage controlled oscillator 18 oscillates a radar signal having a frequency corresponding to the voltage value of the modulated signal that has been switched, and outputs it as a transmission signal. This transmission signal is power-distributed by the distributor 20, and a part thereof is transmitted from the transmission antenna 11.

  Here, FIG. 6A shows a frequency change of the first transmission signal generated from the first modulation signal and a frequency change of the second transmission signal generated from the second modulation signal. Here, the first transmission signal corresponds to the transmission signal in which the up period of the transmission signal shown in FIG. 1B is repeated, and the second transmission signal is the transmission signal shown in FIG. 1B. Corresponds to a transmission signal with repeated down periods. And the frequency change of the transmission signal produced | generated from the switched modulated signal shown to FIG. 5 (B), (C) becomes as shown to FIG. 6 (B), (C). In other words, the transmission means 32 transmits, for each modulation period ((1 / fm) / 2), a first transmission signal whose frequency increases with a predetermined frequency modulation width ΔF having a center frequency f0, and each modulation period. The second transmission signal whose frequency drops with the predetermined frequency modulation width ΔF is alternately switched and transmitted at a switching cycle shorter than the modulation period.

  It should be noted that the configuration of the transmission / reception means 32 that generates the first modulation signal and the second modulation signal separately and switches them with a switching signal is an example, and is shown in FIGS. 6B and 6C. The configuration is not limited to the above as long as such a transmission signal can be generated. For example, a modulation signal as shown in FIG. 5B or FIG. 5C is generated by DA conversion, and this is input to the voltage controlled oscillator 18 so that it is as shown in FIG. 6B or FIG. The structure which produces | generates a transmission signal may be sufficient.

  Moreover, although the switching period in the above-mentioned description illustrates the case of the half of the modulation period of the first and second modulation signals and the case of the quarter of the modulation period, it is not the example shown here. In addition, the present embodiment can be applied as long as the switching period is not more than half of the modulation period of the first and second modulation signals.

  When the first and second transmission signals are reflected by the target object, the reflected signal is received as a reception signal by the reception antenna 12. The received signal is input to the mixer 22, and the mixer 22 mixes the power-distributed transmission signal and the received signal, and generates first and second beat signals having a frequency corresponding to the frequency difference between the two. Here, the mixer 22 corresponds to beat signal generation means.

  FIG. 7 is a diagram for explaining a frequency change of a transmission / reception signal and a beat signal. First, when the frequency change of the transmission / reception signal when the first and second transmission signals are transmitted separately is shown in FIG. 7A, the center frequency is within the modulation period (1 / fm) / 2 as shown by the solid line. For a transmission signal in which the frequency linearly increases or decreases with f0 and frequency modulation width ΔF, the reception signal depends on the time delay due to the relative distance of the target object that reflects the signal and the relative velocity, as shown by the broken line. It receives a frequency shift equivalent to the dopp frequency. Therefore, the frequency difference α occurs in the transmission / reception signal in the first transmission signal, and the frequency difference β occurs in the transmission / reception signal in the second transmission signal. The frequency differences α and β correspond to the frequency difference α obtained in the transmission signal up period shown in FIG. 1B and the frequency difference β in the transmission and reception signals obtained in the down period.

  FIG. 7B shows frequency changes of the first and second transmission signals and the reception signal switched by the switching signal based on FIG. Here, first, the case where the switching cycle for switching the first and second transmission signals is one half of the modulation period is taken as an example. As illustrated, the frequency of the first transmission signal increases during the transmission period P1 of the first transmission signal, and the frequency of the second transmission signal decreases during the transmission period P2 of the second transmission signal. Here, assuming that the time delay due to the relative distance of the target object and the Doppler frequency due to the relative velocity are the same as in the case of FIG. 7A, the first and second transmission signals and the respective reception signals include the first A frequency difference α occurs in the transmission period P1 of the transmission signal, and a frequency difference β occurs in the transmission period P2 of the second transmission signal.

  FIG. 7C shows the up / down beat frequencies of the first and second beat signals generated from such transmission / reception signals. Then, as illustrated, in the transmission period P1 of the first transmission signal, a first beat signal having an upbeat frequency α is generated from the first transmission signal and the reception signal. On the other hand, in the transmission period P2 of the second transmission signal, a second beat signal having a downbeat frequency β is generated from the second transmission signal and its reception signal.

  Similarly, FIG. 7D shows the frequency change of the transmission / reception signal when the switching cycle for switching the first and second transmission signals is ¼ of the modulation period. FIG. 7E shows the frequency change of the beat signal. Again, in the transmission period P1 of the first transmission signal, a first beat signal having an upbeat frequency α is generated from the first transmission signal and its reception signal. On the other hand, in the transmission period P2 of the second transmission signal, a second beat signal having a downbeat frequency β is generated from the second transmission signal and its reception signal.

  As described above, in the present embodiment, by generating the first and second beat signals, when the transmission signal frequency-modulated according to the triangular wave modulation signal is used, the up period and the down period are separate time zones. The upbeat frequency α and the downbeat frequency β obtained in (1) can be obtained almost simultaneously within the same modulation period as the up period or the down period.

  At this time, since the slopes of the frequency rise and fall in the first and second transmission signals are equal, the frequency differences α and β and the target object are the same as when the transmission signal frequency-modulated according to the triangular wave modulation signal is used. The relative distance R and the relative speed V are represented by the above-described equations (1) and (2). Therefore, the relative distance and relative speed of the target object can be detected based on the up / down beat frequency obtained during the modulation period by the procedure described later.

  Returning to FIG. 4, the first and second beat signals are converted into digital data by the AD converter 24 and output to the signal processing device 14. In a preferred embodiment of the present embodiment, the AD converter 24 samples the beat signal in synchronization with the switching signal.

  FIG. 8 is a diagram for explaining sampling by a switching signal. FIG. 8A schematically shows waveforms of the first and second beat signals obtained when the first and second transmission signals are transmitted alone. The waveforms of the first and second beat signals obtained from the first and second transmission signals switched by the switching signal based on FIG. 8A are shown in FIG. 8B. become.

  Here, FIG. 8C shows sampling data when the first and second beat signals are sampled in synchronization with the switching signal. As shown in the figure, sampling is performed in synchronization with the rising edge of the switching signal, so that sampling data (indicated by ●) can be reliably obtained from the first beat signal shown in FIG. By sampling in synchronism with the fall, sampling data (indicated by ◆) can be reliably obtained from the second beat signal shown in FIG. Thus, sampling data can be obtained reliably by sampling in synchronization with the switching period of the switching signal.

  Returning to FIG. 4, the signal processing device 14 will be described. The signal processing device 14 includes an arithmetic processing device such as a DSP (Digital Signal Processor) that performs FFT (Fast Fourier Transform) processing on the beat signal converted into digital data as described above and detects its frequency spectrum, and a beat signal. The microcomputer has a microcomputer for processing the frequency spectrum of the target object to determine the relative speed and relative distance of the target object. This microcomputer includes a CPU (Central Processing Unit), a ROM (Read Only Memory) in which various processing programs and control programs executed by the CPU are stored, and a RAM (Random Access Memory) in which the CPU temporarily stores various data. ).

  FIG. 9 is a diagram for explaining the operation procedure of the radar apparatus according to the present embodiment. The procedure shown in FIG. 9 is executed every cycle with the modulation period of the transmission signal as one cycle.

  First, the radar transceiver 30 performs transmission of the first and second transmission signals that are alternately switched according to the switching period and reception of the reflected signal (S2), and the first and second beat signals are transmitted from the transmission and reception signals. Is generated (S4) and A / D converted (S6).

  The signal processing device 14 performs FFT processing on the first and second beat signals subjected to A / D conversion to generate the frequency spectrum (S8), and detects an up / down beat frequency having a peak (S10). At this time, an upbeat frequency is detected from the first beat signal, and a downbeat frequency is detected from the second beat signal. The signal processing device 14 then pairs up / down beat frequencies having the same level (S12). At this time, in this embodiment, the upbeat frequency detected from the first beat signal and the downbeat frequency detected from the second beat signal are detected in the same modulation period. Can prevent the level difference. Therefore, reliable pairing is possible based on the level of the beat signal.

  Then, the signal processing device 14 detects the relative distance and relative speed of the target object based on the detected up / down beat frequency (S14). Then, the signal processing device 14 confirms the continuity in which a plurality of modulation periods (for example, three times) are continuously detected within a certain error range (S16), and determines the relative distance and relative speed at which the continuity is confirmed. It outputs to the vehicle control apparatus 100 (S18).

  Note that the azimuth angle detection method of the target object in the radar apparatus 10 can be received by a plurality of antennas even if the azimuth angle is detected from the antenna angle when the received signal is obtained by rotating the antenna. The present embodiment can also be applied to an electronic scanning method that detects the arrival direction of a received signal using phase information and amplitude information of the signal. In the above procedure, it is possible to detect the azimuth angle based on the paired beat signal after the beat signal is paired in step S12.

  In addition, the continuity check in step S16 is performed in order to ensure the accuracy of the detection result because there is a risk that the safety may decrease when the vehicle is controlled with respect to a target object that does not exist. Therefore, it is determined whether the relative velocity, the relative distance, or the azimuth detected continuously in a plurality of modulation periods is approximate to the extent that it can be determined that the target object exists. Therefore, an error range that allows such a determination is arbitrarily provided in advance, and if the detection result falls within the error range, it is confirmed that there is continuity. In addition, the number of times required for confirmation can be arbitrarily determined to the extent that the accuracy of the detection result is ensured.

  As described above, according to the present embodiment, the first transmission signal whose frequency increases with a predetermined frequency modulation width every modulation period, and the frequency decreases with the predetermined frequency modulation width every modulation period. A first beat signal having a frequency difference between the first transmission signal and the reception signal corresponding to the first transmission signal in the modulation period by alternately switching and transmitting the second transmission signal with a switching cycle shorter than the modulation period. And a second beat signal having a frequency difference between the second transmission signal and a reception signal corresponding to the second transmission signal, conventionally generated in each of an up period and a down period in different time zones. Beat signal pairs can be generated almost simultaneously within the same modulation period. Therefore, there is no level difference between beat signals due to the time difference between the up period and the down period, and pairing based on the level difference can be performed with high accuracy.

  Further, the modulation period in the present embodiment corresponds to either the conventional up period or the down period, and the target object is detected in one half of the detection cycle of the conventional pair of up period and down period. The relative distance and relative speed can be detected. Therefore, even if the number of detection cycles necessary for confirmation of continuity is taken into consideration, continuity can be confirmed at an earlier time, and the detection result can be output to the vehicle control device more quickly. Therefore, the safety of vehicle control is improved.

It is a figure explaining the transmission / reception signal and beat signal in a FM-CW system. It is a figure explaining the frequency spectrum of the beat signal in each of an up period and a down period. It is a figure explaining the use condition of the radar apparatus with which this invention is applied. It is a figure explaining the structure of the radar apparatus in this embodiment. FIG. 5 is a diagram for explaining various signals generated or processed in the radar transceiver 30. It is a figure explaining the frequency change of the 1st, 2nd transmission signal. It is a figure explaining the frequency change and beat signal of a transmission / reception signal. It is a figure explaining the sampling by a switching signal. It is a figure explaining the operation | movement procedure of the radar apparatus in this embodiment.

Explanation of symbols

10: radar device, 14: signal processing device, 15, 16: modulation signal generation unit, 17: modulation signal switching unit, 22: mixer, 24: A / D converter, 32: transmission means

Claims (5)

A signal processing device that detects a relative speed or a relative distance of the target object based on a frequency difference between the frequency-modulated transmission signal and the reception signal when the transmission signal reflected by the target object is received. A radar transceiver that outputs a beat signal having a frequency difference,
Switching a first transmission signal whose frequency is increased by a predetermined frequency modulation width every modulation period and a second transmission signal whose frequency is decreased by the predetermined frequency modulation width every modulation period are shorter than the modulation period. Transmission means for alternately switching and transmitting in a cycle;
A first beat signal having a frequency difference between the first transmission signal and the reception signal corresponding thereto in the modulation period, and a first beat signal having a frequency difference between the second transmission signal and a reception signal corresponding thereto. And a beat signal generating means for generating a beat signal and outputting the beat signal to the signal processing device. In claim 1,
The radar transceiver according to claim 1, wherein the beat signal generation means inputs the first and second beat signals sampled in synchronization with the switching period to the signal processing device. In claim 1,
The signal processing device associates the first and second beat signals having the same level, and detects the relative velocity or the relative distance based on the associated first and second beat signals. A radar transceiver characterized by that.   A radar apparatus comprising the radar transceiver according to any one of claims 1 to 3 and a signal processing apparatus. In claim 4,
When the signal processing device determines that the relative speed or relative distance detected in the plurality of modulation periods has a predetermined continuity, the signal processing device further outputs the relative speed or relative distance to another control device. A radar device characterized by the above.

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