JP2019039686A - Radar device and target detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection accuracy of a target. A radar device according to an embodiment includes a transmission unit, a reception unit, an analysis unit, and a derivation unit. The transmitting unit transmits the chirp wave while switching the chirp wave by a plurality of methods having different modulation frequencies and idle times. The receiving unit receives the reflected wave of the chirp wave from the target. The analysis unit frequency-analyzes the beat signal generated based on the reflected wave received by the reception unit in each of the above methods. The derivation unit searches for a correspondence relationship between the peaks extracted in each frequency spectrum for each method derived by the analysis unit, and derives a peak estimated to have the correspondence relationship. [Selection diagram] Figure 2

Description

  Embodiments disclosed herein relate to a radar apparatus and a target detection method.

  Conventionally, as a radar apparatus for detecting a target, an FCM (Fast Chirp Modulation) type radar apparatus that detects a distance and a relative speed from a target by transmitting a chirp wave whose frequency continuously increases or decreases is known. (For example, refer to Patent Document 1).

  The FCM system performs two fast Fourier transforms (FFT) on a beat signal for each chirp wave generated from a transmission signal for generating a chirp wave and a reception signal obtained by receiving a reflected wave of a chirp wave by a target. : Fast Fourier Transform) process to detect the distance and relative speed with the target.

JP, 2006-003873, A

  However, in the above-described prior art, a difference appears in the target detection characteristics due to the difference in the modulation frequency of the chirp wave. Each of these characteristic differences has advantages and disadvantages. Therefore, depending on the modulation frequency of the chirp wave, there is a possibility that the detection accuracy of the target may be lowered due to such a disadvantage.

  One embodiment of the present invention has been made in view of the above, and an object thereof is to provide a radar apparatus and a target detection method that can improve the detection accuracy of a target.

  A radar apparatus according to an aspect of an embodiment includes a transmission unit, a reception unit, an analysis unit, and a derivation unit. The transmission unit transmits the chirp wave while switching it by a plurality of methods having different modulation frequencies and idle times. The receiving unit receives a reflected wave of the chirp wave by a target. The analysis unit frequency-analyzes a beat signal generated based on the reflected wave received by the reception unit for each method. The derivation unit searches for a correspondence relationship of peaks extracted in each frequency spectrum for each of the methods derived by the analysis unit, and derives the peak estimated to have a correspondence relationship.

  According to one aspect of the embodiment, the accuracy of target detection can be improved.

FIG. 1A is a schematic explanatory diagram (part 1) of a target detection method according to an embodiment. FIG. 1B is a schematic explanatory diagram (part 2) of the target detection method according to the embodiment. FIG. 1C is a schematic explanatory diagram (part 3) of the target detection method according to the embodiment. FIG. 1D is a schematic explanatory diagram (part 4) of the target detection method according to the embodiment. FIG. 2 is a block diagram of the radar apparatus according to the embodiment. FIG. 3A is a process explanatory diagram (No. 1) from the preceding process of the signal processing unit to the frequency analysis process in the signal processing unit. FIG. 3B is a process explanatory diagram (No. 2) from the previous stage process of the signal processing unit to the frequency analysis process in the signal processing unit. FIG. 3C is a process explanatory diagram (part 1) of the peak extraction process. FIG. 3D is a process explanatory diagram (No. 2) of the peak extraction process. FIG. 4A is a process explanatory diagram (part 1) of the time difference correction process. FIG. 4B is a process explanatory diagram (part 2) of the time difference correction process. FIG. 4C is a process explanatory diagram (part 3) of the time difference correction process. FIG. 5A is a process explanatory diagram (part 1) of the correspondence determination process. FIG. 5B is a process explanatory diagram (part 2) of the correspondence determination process. FIG. 5C is a process explanatory diagram (part 3) of the correspondence determination process. FIG. 5D is a process explanatory diagram (part 4) of the correspondence determination process. FIG. 5E is a process explanatory diagram (No. 5) of the correspondence determination process. FIG. 5F is a process explanatory diagram (No. 6) of the correspondence determination process. FIG. 5G is a process explanatory diagram (part 7) of the correspondence determination process. FIG. 6 is a process explanatory diagram of the determination process of the return ghost of the distance. FIG. 7A is a flowchart illustrating a processing procedure executed by the radar apparatus according to the embodiment. FIG. 7B is a flowchart illustrating a processing procedure of derivation processing. FIG. 8 is a process explanatory diagram of an angle return ghost determination process executed by a radar apparatus according to another embodiment.

  Hereinafter, embodiments of a radar apparatus and a target detection method disclosed in the present application will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

  In the following, the outline of the target detection method according to the present embodiment will be described with reference to FIGS. 1A to 1D, and then the radar apparatus 1 to which the target detection method according to the present embodiment is applied will be described with reference to FIGS. 8 will be used for explanation. In the following description, it is assumed that the radar apparatus 1 is an FCM system. In the following, so-called aliasing that occurs when different continuous signals cannot be distinguished by sampling may be referred to as “folded ghost”.

  First, an outline of the target detection method according to the present embodiment will be described with reference to FIGS. 1A to 1D. 1A to 1D are schematic explanatory views (No. 1) to (No. 4) of a target detection method according to the present embodiment.

  In the FCM system, when the modulation frequency of the chirp wave is lowered, the maximum detection distance in distance detection can be increased. On the other hand, the distance resolution is lower (rougher) than when the modulation frequency is high. This is because when the modulation frequency of the chirp wave is low, the frequency of the beat signal, which is the difference wave between the transmitted wave and the reflected wave, becomes low, so that a peak appears in a low frequency bin in the frequency region that can be processed by the radar apparatus 1. This is because although the finite frequency region corresponding to the maximum detection distance can be widened, the interval between peaks appearing in the frequency region becomes rough. When the distance resolution is low, in the frequency spectrum derived by FFT processing, the waveform may have a spread with respect to the distance.

  Specifically, consider the situation as shown in FIG. 1A. As shown in FIG. 1A, it is assumed that there is a road side wall formed by a continuous iron pillar PL. Further, it is assumed that there is a fallen object such as a cardboard box, that is, a stationary object that does not move, in front of the vehicle. This stationary object can be said to be an obstacle on the own lane.

  When a target is detected using a chirp wave having a modulation frequency with a low distance resolution while traveling in such a situation, as shown in FIG. In other words, the sample points indicated by black circles have a wider interval than when the distance resolution is high.

  In addition, it is considered that the steel pillar PL that is continuous beside the road has a reflection level that is clearly higher than the stationary object if the stationary object in front of the vehicle is a cardboard box or the like. In the situation assumed in FIG. As shown, the waveform has a gentle shape in which it is difficult to extract the peak, and the peak corresponding to the stationary object in front of the vehicle is buried in the waveform. Therefore, there is a possibility that a stationary object in front of the vehicle cannot be detected under such a situation.

  In the FCM system, when the modulation frequency of the chirp wave is increased, the distance resolution in distance detection can be increased (finely). On the other hand, the maximum detection distance is shorter than when the modulation frequency is low. This is because when the modulation frequency of the chirp wave is high, the frequency of the beat signal becomes high, so that a peak appears in a high frequency bin in a frequency region that can be processed by the radar apparatus 1, and thus a finite frequency region corresponding to the maximum detection distance. This is because the interval between peaks appearing in such a frequency region becomes fine. That is, the characteristics of the distance resolution and the maximum detection distance are in a trade-off relationship between when the modulation frequency is low and when the modulation frequency is high.

  In the FCM method, not only for distance detection, but also in speed detection, the speed resolution is increased by increasing the idle time corresponding to the time between the chirp wave and the chirp wave. Can be lowered. On the other hand, if the idle time is lengthened, the maximum detection speed decreases, and if the idle time is shortened, the maximum detection speed increases. This is because the number of chirps of the chirp wave decreases and the number of sampling points of the relative speed also decreases as the idling time becomes longer, but the sampling frequency becomes lower and the maximum detection speed becomes lower because the high frequency is not visible, This is because the sampling interval for a finite frequency region corresponding to the maximum detection speed becomes fine. The opposite is true when the idle run time is shortened. That is, the characteristics of the speed resolution and the maximum detection speed are in a trade-off relationship between when the idle time is long and when the idle time is short.

  Therefore, using this point, in the target detection method according to the present embodiment, a chirp wave having a low modulation frequency and a chirp wave having a high modulation frequency are separately fired, and frequency analysis is performed for each, and mutual analysis is performed based on the result. The shortcomings of the characteristics in target detection were compensated.

This will be specifically described. First, in the target detection method according to the present embodiment, as shown in FIG. 1C, a chirp wave modulated by a “first modulation” method (hereinafter simply referred to as “first modulation”), and “second modulation” The chirp wave modulated by the method (hereinafter simply referred to as “second modulation”) is continuously shot. At least the modulation frequency and the idle time are different between the first modulation and the second modulation. For example, the modulation frequency Δf ₁ of the first modulation is smaller than the modulation frequency Δf ₂ of the second modulation. Further, the idle time i ₁ of the first modulation is shorter than the idle time i ₂ of the second modulation.

  When the modulation frequencies are varied in this way, the characteristics in target detection based on the respective chirp waves are as follows. As shown in FIG. 1C, the velocity resolution is “low” in the first modulation, and the maximum detection speed is “high”. The distance resolution becomes “low” and the maximum sensing distance becomes “long”. On the other hand, in the second modulation, the speed resolution becomes “high”, the maximum detection speed becomes “small”, the distance resolution becomes “high”, and the maximum detection distance becomes “short”.

  Therefore, regarding the distance, the first modulation has a disadvantage that the velocity resolution and the distance resolution are low. On the other hand, the maximum detection speed is large and the maximum detection distance is long. In the second modulation, the maximum detection speed is low and the maximum detection distance is short, but on the other hand, the speed resolution and the distance resolution are high.

  Thus, between the first modulation and the second modulation, the speed resolution and the distance resolution and the maximum detection speed and the maximum detection distance are in a trade-off relationship. For example, a target that is difficult to detect in the first modulation is selected. , And can be estimated based on the detection result based on the second modulation. Specifically, a peak that may be buried in the first modulation can be estimated from the peak of the second modulation. On the other hand, since the maximum detection speed is small in the second modulation, the “speed folding ghost” that can be detected as being different from the original speed is the peak of the first modulation in which the maximum detection speed is large and the speed folding is difficult to occur. It is possible to determine whether or not it is a ghost based on the above, and to derive an accurate speed. In the second modulation, for example, the “distance folding ghost”, which can be detected as being different from the original distance because the maximum sensing distance is short, becomes the peak of the first modulation where the maximum sensing distance is large and the distance folding is unlikely to occur. Based on this, it can be determined whether or not it is a ghost, and an accurate distance can be derived.

  More specifically, as shown in FIG. 1D, in the target detection method according to the present embodiment, the frequency spectrum based on the first modulation and the frequency spectrum based on the second modulation are collated and extracted in each frequency spectrum. Search for the correspondence between the peaks. Then, for example, a peak having a close distance and speed between the first modulation and the second modulation, that is, a peak estimated to have a correspondence relationship is derived. Then, the disadvantages of the first modulation and the second modulation are compensated by using the derived “peaks between different modulation schemes”. In other words, detection results are mutually complemented between different modulation schemes.

  For example, as shown in FIG. 1D, it is assumed that peaks P11, P12, and P13 are extracted on the first modulation side, and peaks P21a, P21b, P22, and P23 are extracted on the second modulation side. In the target detection method according to the present embodiment, first, from these peaks, a peak that is close to the distance and the speed, in other words, within a predetermined distance range and a predetermined speed range and is estimated to have a correspondence relationship is derived. For example, FIG. 1D shows an example in which it is estimated that the peaks P11, P21a, and P21b, peaks P12 and P22, and peaks P13 and P23 have a corresponding relationship as the derivation result. Although FIG. 1D shows the case of viewing from the distance side, each peak is extracted in a two-dimensional space of distance and speed. This will be described later in the description using FIGS. 3B to 3D.

  Note that a plurality of peaks (for example, peaks P21a and P21b) may be detected in the second modulation with high resolution near the peak of the first modulation (for example, peak P11) with low distance and velocity resolution. If it is determined that P21a and P21b are not turned back at either speed or distance, that is, it is determined as an entity, for example, one is detected as the aforementioned iron pillar PL and the other is detected as the aforementioned obstacle. That is, in this case, the disadvantage that the resolution on the first modulation side is low is compensated by the advantage that the resolution on the second modulation side is high. Therefore, according to the target detection method according to the present embodiment, the target detection accuracy can be improved.

  In addition, as described above, on the second modulation side, the maximum detection speed is low, or the case where it is difficult to determine whether the speed or distance is a return ghost or entity, which may occur because the maximum detection distance is short, This can be determined by determining this based on the corresponding peak on the first modulation side. That is, in this case, the disadvantage that the maximum detection speed on the second modulation side is small and the maximum detection distance is short is compensated by the advantage that the maximum detection speed on the first modulation side is large and the maximum detection distance is long. Become. A specific method for determining the return of speed and distance will be described in detail with reference to FIGS. 5A to 6.

  In addition to changing the modulation frequency, for example, the wide-angle beam and the narrow-angle beam may be separately shot so that the angular resolution is different between the first modulation and the second modulation. In such a case, the case where it is difficult to determine whether the angle ghost or the ghost is actual or not, which may occur due to the narrow transmission range, can be determined by mutual complementation between the first modulation side and the second modulation side. Such a case will be described later with reference to FIG. 8 as another embodiment.

  Further, in the target detection method according to the present embodiment, when the frequency spectrum based on the first modulation and the frequency spectrum based on the second modulation are collated, the first modulated wave by the first modulation and the second spectrum by the second modulation are used. Since there is a time difference based on the modulation time of the second modulated wave between the two modulated waves, a process for correcting this is performed. Thereby, it can contribute to improving the detection accuracy of the target. This point will be described later in the description using FIGS.

  Hereinafter, the radar apparatus 1 to which the above-described target detection method is applied will be described more specifically.

  FIG. 2 is a block diagram of the radar apparatus 1 according to the present embodiment. In FIG. 2, only components necessary for explaining the features of the present embodiment are represented by functional blocks, and descriptions of general components are omitted.

  In other words, each component illustrated in FIG. 2 is functionally conceptual and does not necessarily need to be physically configured as illustrated. For example, the specific form of distribution / integration of each functional block is not limited to the one shown in the figure, and all or a part thereof is functionally or physically distributed in arbitrary units according to various loads or usage conditions.・ It can be integrated and configured.

  As shown in FIG. 2, the radar apparatus 1 includes a transmission unit 10, a reception unit 20, and a processing unit 30, and is connected to a vehicle control device 2 that controls the behavior of the host vehicle.

  The vehicle control device 2 performs vehicle control such as PCS (Pre-crash Safety System) and AEB (Advanced Emergency Braking System) based on the detection result of the target by the radar device 1. The radar device 1 may be used for various purposes other than the on-vehicle radar device (for example, monitoring of an airplane or a ship).

  The transmission unit 10 includes a signal generation unit 11, an oscillator 12, a switch 13, and a transmission antenna 14. The signal generator 11 generates a modulated signal whose voltage changes in a sawtooth waveform and supplies the modulated signal to the oscillator 12. The signal generation unit 11 generates a modulation signal by the first modulation at the transmission timing of the first modulated wave based on the control of the transmission / reception control unit 31 described later. In addition, a modulated signal by the second modulation is generated at the transmission timing of the second modulated wave.

  The oscillator 12 generates a transmission signal, which is a chirp signal whose frequency increases with the passage of time, for each predetermined period Tc (hereinafter referred to as a chirp period Tc), based on the modulation signal generated by the signal generation unit 11. To supply to the switch 13.

  The switch 13 operates under the control of the transmission / reception control unit 31, turns on the connection with one of the transmission antennas 14 at the transmission timing of the first modulated wave, and outputs a transmission signal to the one transmission antenna 14.

  Similarly, at the transmission timing of the second modulated wave, the switch 13 turns on the connection with the other transmission antenna 14 and outputs a transmission signal to the other transmission antenna 14. As shown in FIG. 2, the transmission signal generated by the oscillator 12 is also distributed to the mixer 22 described later.

  The transmission antenna 14 converts a transmission signal from the oscillator 12 via the switch 13 into a transmission wave, and outputs the transmission wave to the outside of the host vehicle. The transmission wave output from the transmission antenna 14 is a chirp wave whose frequency increases or decreases over time for each chirp period Tc. A transmission wave transmitted from the transmission antenna 14 to the outside of the host vehicle, for example, forward is reflected by a target such as another vehicle to become a reflected wave.

  The receiving unit 20 includes a plurality of receiving antennas 21 that form an array antenna, a plurality of mixers 22, and a plurality of A / D conversion units 23. The mixer 22 and the A / D conversion unit 23 are provided for each reception antenna 21.

  Each receiving antenna 21 receives a reflected wave from a target as a received wave, converts the received wave into a received signal, and outputs the received signal to the mixer 22. The number of receiving antennas 21 shown in FIG. 2 is four, but it may be three or less or five or more.

  The reception signal output from the reception antenna 21 is amplified by an amplifier (not shown) (for example, a low noise amplifier) and then input to the mixer 22. The mixer 22 mixes a part of the transmission signal distributed from the transmission unit 10 and the reception signal input from the reception antenna 21 to remove unnecessary signal components to generate a beat signal, and an A / D conversion unit To 23.

  The beat signal is a differential wave between the transmission wave and the reflected wave, and is a frequency of the transmission signal (hereinafter referred to as “transmission frequency”) and a frequency of the reception signal (hereinafter referred to as “reception frequency”). It has a beat frequency that makes a difference. The beat signal generated by the mixer 22 is converted to a digital signal by the A / D conversion unit 23 and then output to the processing unit 30.

  The processing unit 30 includes a transmission / reception control unit 31, a signal processing unit 32, and a storage unit 33. The signal processing unit 32 includes a frequency analysis unit 32a, a peak extraction unit 32b, a distance / relative speed calculation unit 32c, a derivation unit 32d, an angle estimation unit 32e, and a follow-up processing unit 32f.

  The storage unit 33 stores history data 33a. The history data 33a is a history of processing data in a series of signal processing related to target detection that is periodically executed by the signal processing unit 32. Therefore, the previous value such as the distance and relative speed of each target data extracted as a peak by the previous cycle and determined as the target is included.

  The processing unit 30 is a microcomputer including, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory) corresponding to the storage unit 33, a RAM (Random Access Memory), a register, and other input / output ports. The entire apparatus 1 is controlled.

  The CPU of the microcomputer functions as the transmission / reception control unit 31 and the signal processing unit 32 by reading and executing the program stored in the ROM. Note that the transmission / reception control unit 31 and the signal processing unit 32 can all be configured by hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA).

  The transmission / reception control unit 31 controls the signal generation unit 11 of the transmission unit 10 and causes the signal generation unit 11 to output a modulation signal whose voltage changes in a sawtooth shape to the oscillator 12. As a result, a transmission signal whose frequency changes with the passage of time is output from the oscillator 12 to the transmission antenna 14.

  Note that the transmission / reception control unit 31 also controls the transmission timing of the first modulated wave and the second modulated wave, and causes the signal generation unit 11 to generate a modulated signal by the first modulation at the transmission timing of the first modulated wave. Similarly, at the transmission timing of the first modulated wave, the switch 13 is turned on to connect to the transmission antenna 14 on the side transmitting the first modulated wave.

  In addition, the transmission / reception control unit 31 causes the signal generation unit 11 to generate a modulated signal by the second modulation at the transmission timing of the second modulated wave. Similarly, at the transmission timing of the second modulated wave, the switch 13 is turned on with the connection with the transmission antenna 14 on the side transmitting the second modulated wave.

  The transmission / reception control unit 31 performs control so that the transmission timings of the first modulated wave and the second modulated wave are alternately switched at a predetermined cycle. The transmission / reception control unit 31 also controls the reception unit 20. The signal processing unit 32 periodically executes a series of signal processing for each scan of the radar apparatus 1.

  The frequency analysis unit 32a performs two-dimensional FFT processing based on the beat signal input from each A / D conversion unit 23, and outputs the result to the peak extraction unit 32b. The peak extraction unit 32b extracts a peak from the result of the two-dimensional FFT processing by the frequency analysis unit 32a, and outputs the extraction result to the distance / relative speed calculation unit 32c.

  Here, in order to make the explanation easy to understand, the flow of processing from the previous stage processing of the signal processing unit 32 to the peak extraction processing in the signal processing unit 32 will be described with reference to FIGS. 3A to 3D.

  FIG. 3A and FIG. 3B are explanatory diagrams (part 1) and (part 2) of processing from the previous stage processing of the signal processing unit 32 to the peak extraction processing in the signal processing unit 32. 3C and 3D are explanatory diagrams (No. 1) and (No. 2) of the peak extraction process. FIG. 3A is divided into three regions by two thick white arrows pointing downward, and these regions are described as an upper stage, a middle stage, and a lower stage in order from the top.

First, the point that the beat signal is generated by the transmission process by the transmission unit 10 and the reception process by the reception unit 20 has already been described. As a result, as shown in the upper part of FIG. 3A, a beat signal having a beat frequency f _SB (= f _ST −f _SR ) that is the difference between the transmission frequency f _ST and the reception frequency f _SR is generated for each chirp wave. The Here, the beat signal obtained by the first chirp wave is “B1”, the beat signal obtained by the second chirp wave is “B2”, and the beat signal obtained by the p-th chirp wave is “Bp”. "

In the example shown in the upper part of FIG. 3A, the transmission frequency _{f ST,} for each chirp wave, along with the reference frequency f0 time increases at a gradient θ (= (f1-f0) / Tm), to the maximum frequency f1 When it reaches, it has a sawtooth wave shape that returns to the reference frequency f0 in a short time. Further, the modulation frequency Δf of the chirp wave can be expressed by Δf = f1−f0.

Although not shown, the transmission frequency f _ST reaches the maximum frequency f1 from the reference frequency f0 in a short time for each chirp wave, and the gradient θ (= (f1−f0) with time from the maximum frequency f1. ) / Tm), and may have a sawtooth waveform that reaches the reference frequency f0.

For each beat signal generated and input in this way, the frequency analysis unit 32a first performs “first FFT processing”. As described above, the transmission wave based on the transmission signal is transmitted from the transmission antenna 14, the transmission wave is reflected by the target and becomes a reflected wave, and the reflected wave is received by the reception antenna 21 as the reception wave and received. Is output as The period from when the transmission wave is transmitted from the transmission antenna 14 until the reception signal is output increases or decreases in proportion to the distance between the target and the radar apparatus 1, and beat frequency f _SB which is the frequency of the beat signal. Is proportional to the distance between the target and the radar apparatus 1.

  Therefore, the frequency spectrum of the beat signal generated by performing the first FFT processing on the beat signal has a peak in the frequency bin corresponding to the distance from the target (hereinafter sometimes referred to as distance bin fr). Appears. Therefore, the distance to the target can be detected by specifying the distance bin fr where such a peak exists.

  By the way, when the relative velocity between the target and the radar apparatus 1 is zero, no Doppler component is generated in the received signal and the phase is the same between the received signals corresponding to each chirp wave. The phase is the same. On the other hand, when the relative velocity between the target and the radar apparatus 1 is not zero, a Doppler component is generated in the received signal, and the phase differs between the received signals corresponding to each chirp wave. A phase change corresponding to the Doppler frequency appears.

  The middle part of FIG. 3A shows an example of the first FFT processing result of beat signals (B1 to B8) that are temporally continuous and a peak phase change between beat signals. In this example, there is a peak in the same distance bin fr10, and the phase of the peak is changed.

  Thus, when the relative speed between the target and the radar apparatus 1 is not zero, a phase change corresponding to the Doppler frequency appears at the peak of the same target between the beat signals. Therefore, by arranging the frequency spectrum obtained by the first FFT processing of each beat signal in time series and performing the “second FFT processing” as shown in the lower part of FIG. 3A, a peak is generated in the frequency bin with respect to the Doppler frequency. An appearing frequency spectrum can be obtained. By detecting the frequency bin in which such a peak appears, that is, the velocity bin, the relative velocity with respect to the target can be detected.

  An example of the result of the two-dimensional FFT process is shown in FIG. 3B. In the FCM method, in the result of the two-dimensional FFT processing, a combination of a distance bin and a velocity bin where a peak indicating a power value equal to or higher than a predetermined threshold exists is specified as a combination of a distance bin and a velocity bin where a peak exists. . Then, based on the combination of the distance bin and the velocity bin identified as having such a peak, the distance to the target and the relative velocity are derived.

  The peak extraction unit 32b acquires the result of such a two-dimensional FFT process from the frequency analysis unit 32a, and specifies the distance bin and the velocity bin where the peak exists based on the result of the two-dimensional FFT process.

  The peak extraction unit 32b is equal to or more than a predetermined threshold among m × n F (fr, fv), which are power values for each combination of distance bins and velocity bins, and surrounding F (fr, fv). Distance bins and velocity bins having values greater than can be distance bins and velocity bins where peaks are present. For example, in FIG. 3C, F (5, 5) is equal to or greater than a predetermined threshold, and four adjacent points F (4, 5), F (5, 4), F (5, 6), F (6, If it has a value greater than 5), the combination of distance bin fr5 and velocity bin fv5 is identified as peak position Prv.

  FIG. 3D schematically shows a case where the result of the two-dimensional FFT processing is viewed from the distance bin side or the velocity bin side. As shown in FIG. 3D, the peak extraction unit 32b estimates the peak apex by parabolic approximation and extracts the peak for the identified peak position Prv.

  Returning to the description of FIG. 2, the distance / relative speed calculator 32c will be described. The distance / relative velocity calculation unit 32c derives the distance and relative velocity with respect to the target based on the combination of the distance bin and the velocity bin corresponding to the peak position Prv identified as having a peak by the peak extraction unit 32b. . In addition, the distance / relative speed calculator 32c outputs the peak position Prv, the distance to the derived target, and the relative speed to the derivation unit 32d.

  The derivation unit 32d performs derivation processing based on the peak position Prv, the distance, and the relative speed input from the distance / relative speed calculation unit 32c. In the derivation process, the search for the corresponding peak of the first modulation and the peak of the second modulation is performed. In addition, a combination of the first modulation peak and the second modulation peak estimated to have a corresponding relationship is derived by such a search, and the second modulation peak may be folded based on the first modulation peak for the combination. Determine. Also, based on the determination result, the correspondence between the second modulation peak without aliasing and the corresponding first modulation peak is determined. In addition, the derivation unit 32d outputs the result of the derivation process to the angle estimation unit 32e.

  More specifically, it demonstrates using FIG. 4A-FIG. 4A to 4C are explanatory diagrams (part 1) to (part 3) of the time difference correction process in the derivation process. 5A to 5G are process explanatory diagrams (No. 1) to (No. 7) of the correspondence determination process in the derivation process. FIG. 6 is a process explanatory diagram of the determination process of the return ghost of the distance.

  First, in the derivation process, a time difference correction process is performed prior to the correspondence determination process. Although the outline has already been described, when comparing the frequency spectrum of the first modulation and the frequency spectrum of the second modulation for the determination of the correspondence relationship, Since there is a time difference based on the modulation time of the second modulated wave, the time difference is corrected.

  First, it is assumed that the first modulated wave is transmitted before the second modulated wave. In such a case, as shown in FIG. 4A, for example, when the peak P22 of the second modulation corresponds to a target corresponding to a stationary object or an approaching object, the target is detected with respect to the radar apparatus 1 over time. Should be approaching.

  Therefore, in such a case, the derivation unit 32d corrects, for example, the peak P22 to the side away from the radar apparatus 1. Whether the peak P22 corresponds to a target equivalent to a stationary object or an approaching object, and the correction amount, for example, can be determined based on the previous value of the target data included in the history data 33a, the above-described time difference, or the like. it can. That is, the history data 33a includes the type of the target up to the previous process, the position (distance) and the relative speed of each such target, and these are known, and the time difference between the first modulation and the second modulation. It is possible to derive how much the frequency is.

  In the same way, as shown in FIG. 4B, for example, when the peak P22 of the second modulation corresponds to a target corresponding to a separation object, the target should move away from the radar apparatus 1 with time. . Therefore, in such a case, the derivation unit 32d corrects, for example, the peak P22 toward the side closer to the radar apparatus 1.

  Further, as shown in FIG. 4C, for a target whose relative speed is 0 with respect to the host vehicle, the distance to the radar apparatus 1 does not change even after time has elapsed, so the derivation unit 32d corrects the time difference. None.

  After such time difference correction processing, the deriving unit 32d compares the frequency spectrum of the first modulation and the frequency spectrum of the second modulation, and searches for the corresponding peak of the first modulation and the peak of the second modulation.

  Specifically, as illustrated in FIG. 5A, the deriving unit 32d first “searches for a peak corresponding to between the first modulation and the second modulation” in the two-dimensional space of the distance bin and the velocity bin. Here, a combination of the first modulation peak P11 and the second modulation peaks P21a and P21b will be described as an example.

  As shown in FIG. 5A, the derivation unit 32d searches for a corresponding peak between the first modulation and the second modulation, and for example, a peak P11, a predetermined distance range (± 1 m as an example) from the peak P11, and a predetermined peak A combination with peaks P21a and P21b in the speed range (as an example, ± 1 km / h) is estimated as having a correspondence relationship.

  However, as described above, since the maximum detection speed of the second modulation is small, the peaks P21a and P21b may be a return ghost of a speed returned from a target exceeding the maximum detection speed, as shown in FIG. 5A. Thus, “only the second modulation cannot determine whether or not it is a speed ghost”.

  Therefore, as shown in FIG. 5B, for example, when the peak P21a is assumed to be a speed folding ghost, the deriving unit 32d derives a candidate to be a folding source on the same distance bin as the peak P21a. " The entity candidates can be obtained by calculation. For example, when the relative speed of the peak P21a is “−40 km / h”, the entity candidates are “± 0 km / h” and “+20 km / h”.

  Then, as illustrated in FIG. 5C, the deriving unit 32d “determines whether or not there is a corresponding peak on the first modulation side” for the derived entity candidate. Specifically, as shown in FIG. 5C, there is another peak of the first modulation in the region corresponding to the actual candidate of the peak P21a derived in FIG. 5B on the same distance bin as the peak P11 of the first modulation. It is determined whether or not.

  Here, as shown in FIG. 5D, in the case of “not present in any”, the derivation unit 32d determines that the entity is not detected even in the first modulation that is difficult to return, and the peak P21a determines “no return”. That is, the peak P21a is handled as valid target data detected by the second modulation, and is output, for example, to the angle estimation unit 32e that executes the angle estimation process of the subsequent stage process.

  On the other hand, as shown in FIG. 5E, when “exists in at least one”, the derivation unit 32d determines that the entity is detected even in the first modulation that is difficult to return, and the peak P21a determines that “there is a possibility of the return. " Then, it is handled as target data with low accuracy. For example, in the process for the current scan, it is not output to the subsequent angle estimation unit 32e.

  Note that the peak (for example, the peak P21a) determined to have a possibility of folding at the peak of the second modulation in this way has a relative speed different from that of the peak P11 of the first modulation if actually folded. As shown in 5F, “the distance increases with the passage of time” with respect to the peak P11. Therefore, when the “distance goes away with the passage of time”, the peak P21a can be “determined that there is a return”.

  Also for the peak P21b, as shown in FIG. 5G, the deriving unit 32d “derives an entity candidate” on the same distance bin as the peak P21b, for example, when the peak P21b is assumed to be a return ghost. In addition, the deriving unit 32d “determines whether or not there is a corresponding peak on the first modulation side” for the derived entity candidate.

  Thereafter, the same determination as in the case of the peak 21a shown in FIGS. 5D to 5F is performed, and it is determined that “there is a possibility of folding”, or is invalid if it is determined that “there is folding” with the passage of time. Treated as target data.

  Further, the derivation unit 32d determines that the first modulation peak P11 has a corresponding relationship with both of the second modulation peaks P21a and P21b if both of the second modulation peaks P21a and P21b are “no return”. To do. These are handled as valid target data. For example, the peak P21a is determined to be the iron pillar PL and the peak P21b is determined to be an obstacle based on the angle estimated through the subsequent angle estimation process.

  In addition, the determination process of the return ghost of the speed has been described so far, but the same determination process can be applied to the return ghost of the distance. That is, as shown in FIG. 6, when the maximum detection distance of the first modulation is long and the maximum detection distance of the second modulation is short, but there is a stationary object FO at a position exceeding the maximum detection distance of the second modulation, On the modulation side, the peak of the return ghost G of the distance may be extracted. In this case, as with the above-described folding ghost at the speed, as shown in FIG. 6, “It is impossible to determine whether the ghost G is an entity or a distance by only the second modulation”.

  However, as in the case of the return ghost of the speed, the possibility of the return of the peak of the second modulation can be determined by “determining based on the presence or absence of the corresponding peak on the first modulation side”. Specifically, after the correspondence relationship between the above-described peak P11 and peaks 21a and 21b is estimated, entity candidates when the peaks 21a and 21b are assumed to be the return ghost G of the distances are derived, respectively. If there is another peak of the first modulation at the corresponding distance, the peaks 21a and 21b are determined to be the possibility of the ghost G of the distance. On the other hand, if there is no other peak of the first modulation at the distance corresponding to the entity candidate, it can be determined that the peaks 21a and 21b are entities without aliasing, and the exact distance can be derived. Therefore, according to the radar apparatus 1 according to the present embodiment, the detection accuracy of the target can be improved.

  Returning to the description of FIG. 2, the angle estimation unit 32e will be described. The angle estimation unit 32e estimates the arrival angle of the reflected wave corresponding to each peak determined as valid target data without aliasing by the deriving unit 32d, that is, the angle at which the target exists, by a predetermined azimuth calculation process. .

  The predetermined azimuth calculation processing can be performed using a known arrival direction estimation method such as ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques), DBF (Digital Beam Forming), or MUSIC (Multiple Signal Classification). . In addition, the angle estimation unit 32e outputs the instantaneous value of the current process based on the latest scan including the estimated angle of each target, the distance to the target, the relative speed, and the like to the follow-up processing unit 32f.

  The follow-up processing unit 32f performs time series filtering on the instantaneous value from the angle estimation unit 32e using a Bayesian probability theory method or the like, and generates target data as a filter value. The target data can be followed (tracked) by such target data for each scan. The follow-up processing unit 32 f outputs the generated target data to the vehicle control device 2.

  Next, a processing procedure executed by the radar apparatus 1 according to the present embodiment will be described with reference to FIGS. 7A and 7B. FIG. 7A is a flowchart illustrating a processing procedure executed by the radar apparatus 1 according to the embodiment. FIG. 7B is a flowchart illustrating a processing procedure of derivation processing.

  Here, a processing procedure corresponding to one scan of a series of signal processing repeatedly executed for each scan cycle of the radar apparatus 1 is shown. Here, one scan corresponds to a case where the first modulated wave and the second modulated wave are continuously transmitted once.

  As shown in FIG. 7A, first, the transmission unit 10 transmits a first modulated wave and a second modulated wave (step S101). At this time, the transmission / reception control unit 31 controls the switch 13 to switch the transmission antenna 14 and continuously transmits the first modulated wave and the second modulated wave once. And the receiving part 20 receives a reflected wave (step S102).

  And the frequency analysis part 32a performs a frequency analysis process (step S103). As a result, a frequency spectrum of the first modulation and a frequency spectrum of the second modulation are obtained as a result of the two-dimensional FFT process. Subsequently, the peak extraction unit 32b executes a peak extraction process (step S104).

  Then, the distance / relative speed calculation unit 32c executes distance / relative speed calculation processing (step S105), and then the derivation unit 32d executes derivation processing (step S106). Here, as shown in FIG. 7B, in the derivation process, the derivation unit 32d first corrects the time difference between the first modulated wave and the second modulated wave (step S201).

  Subsequently, the deriving unit 32d searches for a peak having a close distance and speed between the first modulation and the second modulation (step S202). Then, the deriving unit 32d derives a combination of the first modulation peak and the second modulation peak estimated to have a correspondence as a result of the search, and sets the first modulation possibility of the second modulation peak for the first combination. A determination is made based on the modulation peak (step S203). Note that the return of step 203 includes return of speed and return of distance.

  Then, the deriving unit 32d determines the correspondence between the second modulation peak without aliasing and the first modulation peak (step S204), and ends the process.

  Returning to FIG. After step S106, the angle estimation unit 32e performs angle estimation processing (step S107). The follow-up processing unit 32f executes the follow-up process based on the processing result up to the angle estimation process (step S108), and the process corresponding to one scan is completed.

  As described above, the radar apparatus 1 according to the present embodiment includes the transmission unit 10, the reception unit 20, the frequency analysis unit 32a (corresponding to an example of “analysis unit”), and the derivation unit 32d. The transmission unit 10 transmits the chirp wave while switching it by a plurality of methods having different modulation frequencies and idle times. The receiving unit 20 receives the reflected wave of the chirp wave by the target. The frequency analysis unit 32a performs frequency analysis of the beat signal generated based on the reflected wave received by the reception unit 20 for each of the above methods. The deriving unit 32d searches for the correspondence relationship of the peaks extracted in each frequency spectrum for each of the methods derived by the frequency analysis unit 32a, and derives the peak estimated to have the correspondence relationship.

  Therefore, according to the radar apparatus 1 according to the present embodiment, the detection accuracy of the target can be improved.

  Further, the above method is a first method (first modulation method) and a second method (second modulation method) for transmitting a chirp wave at a higher modulation frequency and longer idle time than the first method, The deriving unit 32d estimates that there is a correspondence between peaks in the predetermined distance range and the predetermined speed range between the frequency spectrum of the first method and the frequency spectrum of the second method.

  Therefore, according to the radar apparatus 1 according to the present embodiment, the peak of the frequency spectrum of the first method, which has a low distance and speed resolution and is likely to be buried, is within a predetermined distance range and within a predetermined speed range. The peak of the frequency spectrum of the second method, which has a high distance and speed resolution, can be estimated to have a corresponding relationship. Therefore, for target detection, a highly accurate determination that compensates for the shortcomings due to the difference in the method. Can be done.

  Further, the derivation unit 32d determines, based on the peak of the first method, the possibility that the peak of the second method is a return ghost of speed or distance for the peaks estimated to have a correspondence relationship.

  Therefore, according to the radar apparatus 1 according to the present embodiment, it is possible to determine the possibility of the return ghost that can be detected because the maximum detection speed is low or the maximum detection distance is short in the second method.

  Further, when it is assumed that the peak according to the second method is a folded ghost, the deriving unit 32d derives an entity candidate corresponding to the folded ghost, and sets the second candidate in the region on the frequency spectrum corresponding to the entity candidate. If there is another peak due to the one method, it is determined that the peak due to the second method may be a return ghost.

  Therefore, according to the radar apparatus 1 according to the present embodiment, it is possible to accurately determine the possibility of the return ghost based on the peak of the first method having a large maximum detection speed and a long maximum detection distance.

  In addition, the derivation unit 32d determines that the peak of the second method is turned back when the peak of the second method determined to have a possibility of the return ghost of the speed is separated from the peak of the first method over time. Confirm that it is a ghost.

  Therefore, according to the radar apparatus 1 according to the present embodiment, the return ghost of the speed can be discarded as invalid target data, so that the accurate speed of the target is determined based on the valid target data that is not the return ghost. It can be derived.

  The radar apparatus 1 further includes an angle estimation unit 32e. The angle estimation unit 32e estimates the arrival angle of the reflected wave corresponding to each of the peaks having the above-described correspondence relationship that does not include a peak that may be a return ghost by a predetermined azimuth calculation process.

  Therefore, according to the radar apparatus 1 according to the present embodiment, effective target data is obtained by estimating the arrival angle for a peak with high accuracy without estimating the arrival angle for a low accuracy peak that may be a return ghost. Therefore, it is possible to perform highly accurate target determination.

  In addition, the deriving unit 32d corrects the time difference between the frequency spectra based on the modulation time on the side where the chirp wave is transmitted later in the above method.

  Therefore, according to the radar apparatus 1 according to the present embodiment, it is possible to search for a peak correspondence relationship with high accuracy in which an error due to a time difference is eliminated.

  By the way, although the case where the modulation frequency and the idle time are made different between the first modulated wave and the second modulated wave has been described so far, the angular resolution may be further varied.

(Other embodiments)
Such a case will be described as another embodiment with reference to FIG. FIG. 8 is a process explanatory diagram of the determination process for the angle return ghost G executed by the radar apparatus 1 according to another embodiment.

  A block diagram of the radar apparatus 1 according to another embodiment is the same as that in FIG. However, in the radar device 1 according to other embodiments, the angular resolution is different between one and the other of the transmission antennas 14.

  One of the transmission antennas 14 is provided so that a narrow-angle beam having a long maximum detection distance and a narrow maximum detection angle (high angular resolution) is transmitted. The other of the transmission antennas 14 is provided so that a wide-angle beam having a short maximum detection distance and a wide maximum detection angle (low angular resolution) is transmitted.

  For example, the first modulated wave is assigned to the transmission antenna 14 on the narrow-angle beam side. For example, the second modulated wave is assigned to the transmission antenna 14 on the wide-angle beam side.

  Therefore, if the relationship between the transmission ranges of the first modulated wave and the second modulated wave in such a case is schematically shown in the situation of FIG. 1A, it is as shown in FIG. In the radar apparatus 1 according to the other embodiment, based on the first modulated wave and the second modulated wave transmitted with different angular resolutions as described above, the peak of the first modulation and the first modulated wave are the same as in the above-described embodiment. Based on the combination of peaks estimated to have a correspondence relationship between the two modulation peaks, the peaks between the first modulation and the second modulation are mutually used.

  However, as shown in FIG. 8, in this case, the first modulated wave is transmitted as a narrow-angle beam. Therefore, if a target exists at a position beyond the maximum detection angle, the angle return ghost G becomes the first. It may appear as one modulation peak. In this case, as shown in FIG. 8, “It is impossible to determine whether the ghost G is an entity or an angle folding ghost G by only the first modulation”.

  However, if there is a second modulation peak that is estimated to have a corresponding relationship and the angle indicates not the front side of the vehicle, for example, the angle in the direction of the iron pillar PL, the peak that appears on the first modulation side is It can be determined that the angle is a folded ghost G. That is, as shown in FIG. 8, “determination can be made based on the corresponding peak angle on the second modulation side”.

  As described above, in the radar apparatus 1 according to another embodiment, the transmission unit 10 transmits the chirp wave by changing the beam pattern so that the maximum detection angle is wider in the second modulation than in the first modulation. The deriving unit 32d determines whether the peak of the first modulation is a folded ghost G of the angle based on the arrival angle of the peak of the second modulation.

  Therefore, according to the radar apparatus 1 according to another embodiment, it is possible to determine whether or not there is an angle return ghost G. Contrary to what has been described, the second modulated wave may be transmitted as a narrow-angle beam and the first modulated wave may be transmitted as a wide-angle beam.

  Further, in each of the above-described embodiments, the transmission wave modulation method is the two types of the first modulation and the second modulation. However, at least the modulation frequency and the idle time may be different, and may be three or more types.

  Therefore, the number of transmission antennas 14 is not limited to two, and may be three or more. Further, instead of allocating one transmission antenna 14 to each modulated wave, all the modulated waves may be transmitted by only one transmission antenna 14.

  Further, in each of the above-described embodiments, the case of transmitting in the order of the first modulated wave and the second modulated wave has been described as an example, but the reverse order may be used. Further, in each of the above-described embodiments, the case where both the first modulated wave and the second modulated wave are a group of a plurality of chirp waves has been described as an example, but the chirp wave of the first modulated wave and the second modulated wave Chirp waves may be alternately transmitted one by one.

  Further, when the target number of stationary objects detected by the radar apparatus 1 is a predetermined number or more (for example, 20 or more), the chirp modulation frequency in the second modulated wave is higher than the chirp modulation frequency in the first modulated wave. It is preferable that the above-mentioned time is 2 times or more and that the chirp idle time in the second modulated wave is twice or more than the chirp idle time in the first modulated wave. As a result, the accurate distance and relative speed of the target can be derived in a state where the influence of folding is small.

  In the above-described embodiment, the radar apparatus 1 is provided in the vehicle. However, it goes without saying that the radar apparatus 1 may be provided in a moving body other than the vehicle, such as a ship or an aircraft.

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Radar apparatus 2 Vehicle control apparatus 10 Transmission part 14 Transmission antenna 20 Reception part 21 Reception antenna 30 Processing part 31 Transmission / reception control part 32 Signal processing part 32a Frequency analysis part 32b Peak extraction part 32c Distance / relative speed calculation part 32d Derivation part 32e Angle Estimator 32f Tracking processor 33 Storage 33a History data

Claims (9)

A transmission unit that transmits a chirp wave while switching between a plurality of methods with different modulation frequencies and idle times; and
A receiving unit for receiving the reflected wave of the chirp wave by a target;
An analysis unit that analyzes the frequency of the beat signal generated based on the reflected wave received by the reception unit for each method;
A radar comprising: a derivation unit that searches for a correspondence relationship between peaks extracted in each frequency spectrum for each of the schemes derived by the analysis unit and derives the peak estimated to have a correspondence relationship. apparatus. The method is a first method and a second method for transmitting the chirp wave with a higher modulation frequency and a longer idle time than the first method,
The derivation unit includes:
Between the frequency spectrum of the first scheme and the frequency spectrum of the second scheme, it is estimated that the peaks in the predetermined distance range and the predetermined velocity range have the correspondence. The radar apparatus according to claim 1. The derivation unit includes:
For the peaks estimated to have the correspondence, the possibility that the peak according to the second method is a speed or distance aliasing ghost is determined based on the peak according to the first method. The radar apparatus according to claim 2. The derivation unit includes:
When it is assumed that the peak according to the second scheme is the folded ghost, entity candidates corresponding to the folded ghost are derived, and the first scheme is applied to the region on the frequency spectrum corresponding to the entity candidates. The radar apparatus according to claim 3, wherein if there is another peak due to, the peak according to the second method is determined to be a possibility of the folded ghost. The derivation unit includes:
If the peak of the second method that is determined to have the possibility of the return ghost of the speed is separated from the peak of the first method over time, the peak of the second method is the return The radar apparatus according to claim 4, wherein the radar apparatus is determined to be a ghost. An angle estimation unit that estimates an arrival angle of the reflected wave corresponding to each of the peaks having the correspondence relationship that does not include the peak with the possibility of the folded ghost by a predetermined azimuth calculation process, The radar device according to claim 3, 4 or 5. The transmitter is
The chirp wave is transmitted with different beam patterns so that the maximum detection angle is wider in the second method than in the first method,
The derivation unit includes:
For the peak estimated to have the correspondence, it is determined whether the peak of the first method is the folded ghost of the angle according to the arrival angle of the peak of the second method. The radar apparatus according to claim 6. The derivation unit includes:
8. The time difference between the frequency spectra is corrected based on a modulation time on a side of the scheme in which the chirp wave is transmitted later in time. 8. Radar device. A transmission step of transmitting a chirp wave while switching between a plurality of methods having different modulation frequencies and idle times; and
A receiving step of receiving a reflected wave of the chirp wave by a target;
An analysis step of analyzing the frequency of the beat signal generated based on the reflected wave received by the reception step for each method;
And a derivation step of deriving the peak estimated to have a correspondence relationship by searching for a correspondence relationship of the peaks extracted in each frequency spectrum for each of the methods derived by the analysis step. Mark detection method.