JP2018179914A - Radar device and target detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve target detection performance.SOLUTION: A radar device according to an embodiment includes a transmitting unit, a receiving unit, and a transceiving control unit. The transmitting unit transmits a chirp wave whose frequency is continuously increasing or decreasing. The receiving unit receives a reflection wave of the chirp wave by a target. The transceiving control unit controls the transmitting unit and the receiving unit. In addition, the transceiving control unit has the transmitting unit modulate the chirp wave so that a modulation frequency of the chirp wave is changed for each chirp wave.SELECTED DRAWING: Figure 2

Description

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

  Conventionally, a so-called FM-CW (mounted on a vehicle etc.) derives the distance and relative velocity of a target from the frequency difference between a transmission wave frequency-modulated by a triangular wave and a reflected wave that the transmission wave hits the target. A radar apparatus of the Frequency Modulated Continuous Wave method is known (see, for example, Patent Document 1).

JP 2004-198438 A

  However, the above-mentioned prior art has room for further improvement in improving the detection performance of the target.

  Specifically, in the FM-CW method, peak frequencies are extracted for each of the "UP section" and "DN section" of the beat signal indicating the frequency difference between the transmit signal and the receive signal, and reflections corresponding to the respective peak frequencies Calculate the wave arrival angle and its power value. And based on the calculation result, it is necessary to execute pairing which combines the peak frequency of each of "UP section" and "DN section".

  However, pairing may cause an incorrect combination, which may reduce the detection performance of the target. Further, in the FM-CW method, it is difficult to expand both the detectable distance range and the speed range, and there is a problem that the detection performance of the short distance is poor.

  One aspect of the embodiment is made in view of the above, and it is an object of the present invention to provide a radar apparatus and a target detection method capable of improving the detection performance of a target.

  A radar device according to an aspect of the embodiment includes a transmission unit, a reception unit, and a transmission / reception control unit. The transmitter transmits a chirp wave whose frequency increases or decreases continuously. The receiving unit receives a reflected wave of the chirp wave by a target. The transmission / reception control unit controls the transmission unit and the reception unit. Further, the transmission / reception control unit causes the transmission unit to modulate the modulation frequency of the chirp wave so as to be changed for each of the chirp waves.

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

FIG. 1 is a schematic explanatory view of a target detection method according to the embodiment. FIG. 2 is a block diagram of the radar device according to the embodiment. FIG. 3A is an explanatory view (No. 1) of processes from pre-stage processing of the signal processing unit to frequency analysis processing in the signal processing unit. FIG. 3B is an explanatory view (No. 2) of processes from pre-processing of the signal processing unit to frequency analysis processing in the signal processing unit. FIG. 4 is an explanatory diagram of a first modulation scheme according to the embodiment. FIG. 5A is an explanatory diagram of a second modulation scheme according to the embodiment. FIG. 5B is a supplementary explanatory view (part 1) of FIG. 5A. FIG. 5C is a supplementary explanatory view (part 2) of FIG. 5A. FIG. 6A is a flowchart (part 1) illustrating a processing procedure executed by the radar device according to the embodiment. FIG. 6B is a flowchart (part 2) illustrating a processing procedure performed by the radar device according to the embodiment.

  Hereinafter, embodiments of a radar device and a target detection method disclosed in the present application will be described in detail with reference to the attached drawings. Note that the present invention is not limited by the embodiments described below.

  Moreover, in the following, after the outline of the target detection method according to the present embodiment is described with reference to FIG. 1, the radar device 1 to which the target detection method according to the present embodiment is applied is illustrated in FIGS. To explain. The radar device 1 according to the present embodiment is assumed to be an on-vehicle radar device adopting an FCM (Fast Chirp Modulation) method.

  First, an outline of a target detection method according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic explanatory view of a target detection method according to the present embodiment. The upper part of FIG. 1 shows an outline and problems of the FM-CW radar apparatus as a comparative example.

  As shown in the upper part of FIG. 1, in the FM-CW radar apparatus as the comparative example, the transmission signal fs (t) is frequency-modulated by a so-called triangular wave, and is transmitted as a transmission wave from the transmission antenna. Then, the transmitted wave transmitted is reflected at the target and arrives as a reflected wave, and is received as a received signal fr (t) at the receiving antenna.

  At this time, as shown in the upper part of FIG. 1, the reception signal fr (t) is delayed by a time difference τ with respect to the transmission signal fs (t) according to the distance between the radar device and the target. The beat signal has the frequency fup of the "UP section" where the frequency rises and the frequency fdn of the "DN section" where the frequency falls due to the time difference τ and the Doppler effect based on the relative velocity of the radar device and the target It is obtained as a repeated signal.

  The beat signal is frequency-analyzed using fast Fourier transform (FFT) or the like to extract peak frequencies that become peaks on the “UP section” side and the “DN section” side.

  Then, the peak frequencies extracted on each of the “UP interval” side and the “DN interval” side are subjected to azimuth calculation using a known direction of arrival estimation method such as, for example, ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques). .

  In the azimuth calculation result, the arrival angle and the power value corresponding to the peak frequency are shown, and pairing is performed to combine each peak with a similar arrival angle and power value on the “UP section” side and the “DN section” side. Become.

  However, the FM-CW method may reduce the detection performance of the target at such a point that "pairing is necessary". This is because an incorrect combination (misparing) may be made depending on the calculated arrival angle and the value indicated by the power value as long as the combination is performed. Mispairing leads to false detection of the target.

  Further, the FM-CW method is said to be "difficult to expand distance range and speed range". For example, in the FM-CW method, when priority is given to the maximum detection distance, the detectable speed range tends to be narrowed accordingly.

  In addition, the FM-CW system has a "short-distance detection performance poor" aspect because the transmission (TX) and reception (RX) switching intervals are relatively long.

  Therefore, in order to solve the problems in the FM-CW method, in the target detection method according to the present embodiment, as shown in the lower part of FIG.

  The FCM method is for beat signals for each chirp wave generated from a transmission signal that generates a chirp wave whose frequency continuously increases or decreases and a reception signal obtained by receiving a reflection wave of a chirp wave from a target. This is a method of detecting the distance to the target and the relative velocity by performing two FFTs (hereinafter sometimes referred to as “two-dimensional FFT processing”). In the following, “chirp wave” may be simply referred to as “chirp”.

  In the FCM method, the above-mentioned pairing becomes unnecessary, so that it is possible to prevent false detection of a target based on mispairing.

  Further, as shown in the lower part of FIG. 1, in the target detection method according to the present embodiment, “the modulation frequency is changed for each chirp wave”. For example, the distance resolution can be increased by gradually increasing the modulation frequency. Thereby, the detection performance of a target can be improved.

  Also, as shown in the lower part of FIG. 1, in the target detection method according to the present embodiment, “adjustment of chirp time and total chirp time” is performed. Thereby, the maximum detection speed can be expanded and the speed resolution can be improved. That is, the detection performance of the target can be improved.

  In addition, as shown in the lower part of FIG. 1, in the target detection method according to the present embodiment, “switching of transmission / reception timing in chirp” is performed. Thereby, the short distance detection performance can be improved. That is, the detection performance of the target can be improved.

  The outline of the FCM method in the target detection method according to the present embodiment and an example of the generated waveform will be described later with reference to FIG. 3A and later.

  Hereinafter, the radar device 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 device 1 according to the present embodiment. In FIG. 2, only components necessary to explain 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 have to be physically configured as illustrated. For example, the specific form of the distribution and integration of each functional block is not limited to that shown in the drawings, and all or a part thereof may be functionally or physically distributed in any unit depending on various loads, usage conditions, etc. It is possible to integrate and configure.

  As shown in FIG. 2, the radar device 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) or 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 applications (for example, monitoring of an airplane or a ship) other than the on-vehicle radar device.

  Subsequently, the transmitting unit 10 and the receiving unit 20 will be described, but first, the basic behavior in the FCM method will be described. The transmission unit 10 includes a signal generation unit 11, an oscillator 12, a transmission antenna 13, and a switch 14.

  The signal generation unit 11 generates a modulation signal whose voltage changes in a sawtooth waveform, and supplies the modulation signal to the oscillator 12. The oscillator 12 is a chirp signal whose frequency increases with the passage of time based on the modulation signal generated by the signal generation unit 11. The pulse repetition interval PRI (hereinafter, “chirp period PRI”) ) And supply to the switch 14. The switch 14 operates under the control of a transmission / reception control unit 31 described later, and outputs a transmission signal to the transmission antenna 13 when the switch 14 is turned on. As shown in FIG. 2, the transmission signal generated by the oscillator 12 is also distributed to a mixer 22 described later.

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

  The receiving unit 20 includes a plurality of receiving antennas 21 forming an array antenna, a plurality of mixers 22, a plurality of A / D converting units 23, and a switch 24. The mixer 22 and the A / D converter 23 are provided for each of the receiving antennas 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 supplies the signal to the switch 24. The switch 24 operates under the control of the transmission / reception control unit 31 and outputs a reception signal to the mixer 22 when it is turned on. The number of receiving antennas 21 shown in FIG. 2 is four, but may be three or less or five or more.

  The received signal output from the receiving antenna 21 is amplified by an amplifier (not shown) (for example, a low noise amplifier) and then input to the mixer 22 via the switch 24. 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, thereby generating an A / D conversion unit. Output to 23.

  The beat signal is a differential wave between the transmission wave and the reflection wave, and is composed of the frequency of the transmission signal (hereinafter referred to as "transmission frequency") and the frequency of the reception signal (hereinafter referred to as "reception frequency"). It has a beat frequency that is 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, an angle estimation unit 32c, a distance / relative velocity calculation unit 32d, and a follow-up processing unit 32e.

  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 detection of a target periodically executed by the signal processing unit 32.

  The processing unit 30 is, for example, a microcomputer including a central processing unit (CPU), a read only memory (ROM) corresponding to the storage unit 33, a random access memory (RAM), a register, other input / output ports, etc. The entire apparatus 1 is controlled.

  The CPU of the microcomputer reads and executes the program stored in the ROM to function as the transmission / reception control unit 31 and the signal processing unit 32. 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 to the oscillator 12 a modulation signal whose voltage changes in a sawtooth shape. As a result, a transmission signal whose frequency changes as time passes is output from the oscillator 12 to the transmission antenna 13. The transmission / reception control unit 31 controls the signal generation unit 11 to change the modulation frequency stepwise for each chirp wave, or adjust the chirp time Td and the total chirp time Tr (all will be described later). be able to. This point will be described later in the description using FIG.

  The transmission / reception control unit 31 also controls the reception unit 20. The transmission / reception control unit 31 controls the switching of the switch 14 and the switch 24 to control the transmission timing of the transmission unit 10 and the reception timing of the reception unit 20. For example, the transmission / reception control unit 31 can switch the transmission timing and the reception timing of the reception unit 20 a plurality of times within the transmission period of one chirp wave. This point will be described later in the description using FIG. 5A.

  The signal processing unit 32 periodically executes a series of signal processing for each scan of the radar device 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 angle estimation unit 32c.

  Here, in order to make the description easy to understand, the flow of basic processing from the pre-stage processing of the signal processing unit 32 to the peak extraction processing in the signal processing unit 32 will be described using FIGS. 3A and 3B.

  FIGS. 3A and 3B are process explanatory diagrams (1) and (2) from the pre-stage processing of the signal processing unit 32 to the peak extraction processing in the signal processing unit 32. FIGS. Although FIG. 3A is divided into three regions by two thick downward white arrows, these regions are described as an upper stage, a middle stage, and a lower stage in order from the top. Also, the upper part of FIG. 3A shows a basic chirp waveform.

First, it has already been described that the beat signal is generated by the transmission process by the transmission unit 10 and the reception process by the reception unit 20. Thereby, as shown in the upper part of FIG. 3A, a beat signal having a beat frequency f _SB (= f _ST −f _SR ) which is a difference between the transmission frequency f _ST and the reception frequency f _SR is generated for each chirp wave. Ru. 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". "

Further, in the example shown in the upper part of FIG. 3A, the transmission frequency f _ST increases from the reference frequency f0 with time with a gradient θ (= (f1−f0) / Td) for each chirp wave and reaches the maximum frequency f1. When it reaches it, it has a sawtooth shape that returns to the reference frequency f0 in a short time. Further, the modulation width Δf of the chirp wave can be expressed by Δf = f1−f0.

Although not shown, the transmission frequency f _ST arrives from the reference frequency f 0 to the maximum frequency f 1 in a short time for each chirp wave, and the slope θ (= (f 1 −f 0 from the maximum frequency f 1 with time) It may be sawtooth wave shape which is reduced by) / Td) and reaches the reference frequency f0.

The frequency analysis unit 32 a first performs “first FFT processing” on each beat signal generated and input in this manner. As described above, the transmission wave based on the transmission signal is transmitted from the transmission antenna 13, and the transmission wave is reflected by the target to be a reflected wave, and the reflection wave is received as the reception wave by the reception antenna 21 and the reception signal Is output as The period from when the transmission wave is transmitted from the transmission antenna 13 to when the reception signal is output increases or decreases in proportion to the distance between the target and the radar device 1, and the beat frequency f _SB which is the frequency of the beat signal Is proportional to the distance between the target and the radar device 1.

  Therefore, in the frequency spectrum of the beat signal generated by performing the first FFT processing on the beat signal, the frequency bin corresponding to the distance to the target (hereinafter sometimes referred to as "distance bin") is A peak appears. Therefore, the distance to the target can be detected by specifying the distance bin in which such a peak exists.

  By the way, when the relative velocity between the target and the radar device 1 is zero, no Doppler component occurs in the received signal, and the phases of the received signals corresponding to the respective chirp waves are the same. The phase is also the same. On the other hand, when the relative velocity between the target and the radar device 1 is not zero, a Doppler component occurs in the received signal, and the phases of the received signals corresponding to the respective chirp waves are different. Changes in phase according to the Doppler frequency appear.

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

  Thus, when the relative velocity between the target and the radar device 1 is not zero, a change in phase corresponding to the Doppler frequency appears at the peak of the same target between beat signals. Therefore, the frequency spectrum obtained by the first FFT processing of each beat signal is arranged in time series, and the “second FFT processing” is performed as shown in the lower part of FIG. An emerging frequency spectrum can be obtained. The relative velocity with the target can be detected by detecting the frequency bin in which such a peak appears, that is, the velocity bin.

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

  The peak extraction unit 32b acquires the result of such two-dimensional FFT processing from the frequency analysis unit 32a, and specifies the distance bin and the velocity bin in which the peak is present based on the result of the two-dimensional FFT processing.

  Returning to the description of FIG. 2, the angle estimation unit 32 c will be described. The angle estimation unit 32c estimates the arrival angle of the reflected wave corresponding to each of the peaks extracted by the peak extraction unit 32b, that is, the angle at which the target is present, by predetermined azimuth calculation processing.

  The predetermined direction calculation processing can be performed using a known direction-of-arrival estimation method such as ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques), DBF (Digital Beam Forming), or MUSIC (Multiple Signal Classification). . Further, the angle estimation unit 32c outputs the estimated angle of each target to the distance / relative velocity calculation unit 32d.

  The distance / relative velocity calculation unit 32 d derives the distance to the target and the relative velocity based on the combination of the distance bin and the velocity bin identified as having a peak by the peak extraction unit 32 b.

  Further, the distance / relative velocity calculation unit 32 d outputs the instantaneous value in the latest scan, such as the distance and relative velocity with the derived target, the angle of the target estimated by the angle estimation unit 32 c, to the following processing unit 32 e Do.

  The follow-up processing unit 32e performs time-series filtering on the instantaneous value from the distance / relative velocity calculation unit 32d using a Bayesian probability theory method or the like, and generates target data as a filter value. Such target data for each scan makes it possible to track the target. The follow-up processing unit 32 e outputs the generated target data to the vehicle control device 2.

  Next, based on the basic waveform of the chirp wave in the FCM method described above, the radar device 1 according to the present embodiment adopts a modulation method of changing the basic waveform to improve the detection performance of the target. explain.

  FIG. 4 is an explanatory diagram of a first modulation scheme according to the present embodiment. As shown in FIG. 4, in the first modulation method, the radar apparatus 1 shifts the chirp waves CP1, CP2,... CPn to the high frequency side along the time axis while maintaining the modulation width Δf. Generate a modulation waveform. The chirp time Td corresponding to the transmission period of one chirp wave is constant.

  In other words, while maintaining the modulation width Δf, the radar device 1 increases the shift amount Δfr of the modulation width Δf stepwise for each of the chirp waves CP1, CP2,... CPn along the time axis. Generate a modulation waveform. By increasing the shift amount Δfr stepwise, the distance resolution becomes high. In the example shown in FIG. 4, the modulation width Δf is constant, and the constant modulation width Δf + shift amount Δfr = modulation frequency.

  As the switching signal in the figure shows, the timing of transmission (TX) and reception (RX) is switched for each chirp wave. Such control is performed by the transmission / reception control unit 31 controlling the switching of the switch 14 and the switch 24 as described above.

  That is, the transmission / reception control unit 31 controls the modulation scheme such that the modulation frequency (here, the shift amount Δfr) is changed stepwise for each of the chirp waves CP1, CP2,. Thereby, distance resolution can be improved. Also, the switching of transmission / reception timing is performed for each chirp wave, that is, the switch 14 is kept in the on state and the switch 24 is kept in the off state during the chirp time Td, and the switching is performed so Because control is performed, the number of switching operations can be reduced, and the burden on hardware can be reduced.

  In addition, since the transmission timing and the reception timing are different due to switching, it is possible to suppress short-range clutter caused by a part of the transmission wave being reflected and received by the radome.

  Next, the second modulation method will be described. FIG. 5A is an explanatory diagram of a second modulation scheme according to the present embodiment. 5B and 5C are supplementary explanatory views (part 1) and (part 2) of FIG. 5A.

  In the second modulation method, basically, as in the first modulation method, a chirp in which the shift amount Δfr of the modulation width Δf increases stepwise along the time axis while maintaining the modulation width Δf. Suppose waves CP1, CP2,... CPn.

  However, in the second modulation scheme, the radar apparatus 1 further modulates the transmission (TX) and reception (RX) timings to be switched multiple times within one transmission period of one chirp wave (that is, the chirp time Td). The point of generating a waveform is different from the first modulation scheme.

Therefore, in the second modulation method, as shown in FIG. 5A, three transmission frequencies f _{ST1 to} f _ST3 exist in the chirp waves CP1, CP2,... CPn, and three reception frequencies f _SR1 corresponding to these. .About.f _SR3 and reflection frequencies f _{RF1 to} f _RF3 are observed. The modulation time of each of the transmission frequencies f _{ST1 to} f _ST3 corresponding to the transmission timing of transmission (TX) is the same.

A more specific description will be given using FIG. 5B. FIG. 5B is an enlarged view of the chirp wave CP1 of FIG. 5A. The reception frequencies f _{SR1 to} f _SR3 and the reflection frequencies f _{RF1 to} f _RF3 are omitted for easy understanding of the drawing. Further, although the chirp wave CP1 is taken as an example in FIG. 5B, the same applies to the chirp waves CP2,.

As described above, in the second modulation scheme, as shown in FIG. 5B, three transmission frequencies f _{ST1 to} f _ST3 exist in the chirp wave CP1. These are so-called "sub-chirp waves", so-called "sub-chirp waves", generated by switching in one chirp wave CP1 and equally spaced in time (the modulation time is the same).

As shown in FIG. 5B, these transmission frequencies f _ST1 , f _ST2 and f _ST3 are sequentially referred to as sub-chirp waves CP1-1, CP1-2 and CP1-3. The two-dimensional FFT process described above is performed for each of the sub-chirp waves CP1-1, CP1-2, and CP1-3.

The modulation widths Δf are different in the sub-chirp waves CP1-1 to CP1-3. As shown in FIG. 5B, for example, assuming that the modulation widths of the sub-chirp waves CP1-1, CP1-2, CP1-3 are Δf ₁ , Δf ₂ , Δf ₃ in order, the comparison relationship between them is Δf ₁ <Δf ₂ It is <Δf ₃ and Δf ₃ = Δf.

  Here, as shown in FIG. 5C, when the modulation width Δf is different, the distance resolution derived from the beat signal becomes higher as the modulation width Δf becomes larger. In the case of the example shown in FIG. 5C, the contrast of the distance resolution is (1) <(2) <(3). The smaller the modulation width Δf, the larger the maximum detection distance derived from the beat signal. In the case of the example shown in FIG. 5C, the comparison relationship of the maximum detection distance is (1)> (2)> (3). By using a plurality of chirp waves (including sub-chirp waves) having different modulation widths Δf in this way, for example, from a position of a predetermined distance or more by the chirp wave having the lowest distance resolution and the largest maximum detection distance. It can detect approaching vehicles. In addition, it is possible to detect a motorcycle near a predetermined distance by the chirp wave of (2) in which the distance resolution and the maximum detection distance are medium. Furthermore, the pedestrian in the vicinity of the vehicle can be detected at a predetermined distance or less by the chirp wave (3) having the highest distance resolution and the smallest maximum detection distance. In this manner, various targets present at positions from near distance to long distance can be detected with high accuracy.

It returns to the explanation of FIG. 5B. Further, in the sub-chirp waves CP1-1 to CP1-3, the shift amount Δfr is also different. Therefore, in the chirp wave CP1, the modulation frequency (modulation width Δf ₁ + shift amount Δfr) of the sub-chirp wave CP1-1 is the smallest, and the modulation frequency (modulation width Δf ₃ + shift amount Δfr) of the sub-chirp wave CP1-3 is the largest. Become. Returning to the explanation of FIG. 5A, the modulation frequency (modulation width Δf ₃ + shift amount Δfr) of the sub-chirp wave CPn-3 of the chirp wave CPn is the largest when the chirp wave CPn is included. As described above, in the second modulation method, the radar device 1 generates a modulation waveform so that the modulation frequency increases stepwise for each sub-chirp wave of the chirp waves CP1, CP2,... CPn along the time axis. .

  Further, in the second modulation method, the chirp time Td which is a parameter in the time direction, the total chirp time Tr, and the modulation width Δf which is a parameter in the frequency direction and the shift amount Δfr are adjusted to meet the vehicle condition and the like. It is possible to improve the detection performance of the target.

  Specifically, when c is the light velocity, and fc is the center frequency, the maximum detection velocity Vmax can be obtained by the equation (1) Vmax = c / (4 × Td × fc). Therefore, it is possible to expand the maximum detection speed Vmax by adjusting the chirp time Td to be smaller.

  Further, the velocity resolution Δv can be obtained by the equation (2) Δv = c / (2 × Tr × fc). Therefore, by adjusting the total chirp time Tr to be large, it is possible to improve the velocity resolution Δv.

  Further, the maximum detection distance Rmax can be obtained by the equation (3) Rmax = c × Tr / (4 × Td × Δfr). Further, the distance resolution ΔR can be obtained by the equation (4) ΔR = c / (2 × Δfr). Therefore, by adjusting (chirp total time Tr / chirp time Td) and the shift amount Δfr, the maximum detection distance Rmax can be expanded or the distance resolution ΔR can be improved.

  By adjusting the above parameters so that, for example, the maximum detected velocity Vmax is increased and the distance resolution ΔR is improved according to the vehicle condition, for example, it is possible to move a high speed moving object through the blind spot position by the own vehicle. It becomes possible to detect well.

  Here, the vehicle status is acquired based on various sensors and the like mounted on the host vehicle, the acquired acquisition status is analyzed, and the transmission / reception control unit 31 automatically adjusts the parameters according to the analysis result. Moreover, the modulation waveform may be generated by the first modulation method or the second modulation method.

  Next, the processing procedure executed by the radar device 1 according to the present embodiment will be described using FIGS. 6A and 6B. FIG. 6A and FIG. 6B are flowcharts (part 1) and (part 2) showing the processing procedure executed by the radar device 1 according to the present embodiment. Here, a processing procedure corresponding to one scan, which is repeatedly executed for each scan cycle of the radar device 1, is shown.

  As shown in FIG. 6A, first, the transmission / reception control unit 31 controls the transmission unit 10 and the reception unit 20 to execute FCM transmission / reception processing (step S101). Here, the FCM transmission and reception process will be described.

  As shown in FIG. 6B, in the FCM transmission / reception process, the transmission unit 10 performs waveform modulation so as to change the modulation frequency for each chirp wave based on the control of the transmission / reception control unit 31 (step S201).

  Then, based on the control of the transmission / reception control unit 31, the transmission unit 10 adjusts parameters relating to the speed performance (maximum detected speed, speed resolution) and the distance performance (maximum detected distance, distance resolution) as necessary (step S202) ).

  Further, the transmission / reception control unit 31 sets switching of transmission / reception in the chirp wave as needed (step S203).

  Then, the transmitting unit 10 transmits a radio wave (step S204), the receiving unit 20 receives a reflected wave (step S205), and the process ends.

  It returns to the explanation of FIG. 6A. Subsequently, the frequency analysis unit 32a executes frequency analysis processing based on the processing result of the FCM transmission and reception processing (step S102). Then, the peak extraction unit 32b executes peak extraction processing based on the processing result of the frequency analysis processing (step S103).

  Then, the angle estimation unit 32c executes the angle estimation processing based on the processing result of the peak extraction processing (step S104). Then, the distance / relative velocity calculation unit 32d executes distance / relative velocity calculation processing based on the processing result of the angle estimation processing (step S105).

  Then, the follow-up processing unit 32e executes the follow-up processing based on the processing result of the distance / relative velocity calculation processing (step S106), and the processing corresponding to one scan is completed.

  As described above, the radar device 1 according to the present embodiment includes the transmission unit 10, the reception unit 20, and the transmission / reception control unit 31. The transmission unit 10 transmits a chirp wave whose frequency continuously increases or decreases. The receiving unit 20 receives the reflected wave of the chirp wave by the target. The transmission / reception control unit 31 controls the transmission unit 10 and the reception unit 20. Further, the transmission / reception control unit 31 causes the transmission unit 10 to modulate the modulation frequency of the chirp wave so as to be changed for each of the chirp waves.

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

  Further, the transmission / reception control unit 31 causes the transmission unit 10 to modulate the chirp waves CP1, CP2,... CPn so as to shift to the high frequency side while maintaining the modulation width.

  Therefore, according to the radar apparatus 1 which concerns on this embodiment, distance resolution can be improved.

  Further, the transmission / reception control unit 31 does not switch between the transmission timing and the reception timing of the reception unit 20 within the transmission period of one chirp wave by the transmission unit 10.

  Therefore, according to the radar device 1 according to the present embodiment, switching of transmission and reception timing is performed for each chirp wave, so the number of switchings can be reduced, and the burden on hardware can be reduced. In addition, since the transmission timing and the reception timing are different from each other, it is possible to suppress short range clutter caused by a part of the transmission wave being reflected and received by the radome.

  Further, the transmission / reception control unit 31 switches the transmission timing and the reception timing of the reception unit 20 a plurality of times within the transmission period of one chirp wave by the transmission unit 10.

  Therefore, according to the radar device 1 according to the present embodiment, by using a plurality of sub-chirp waves having different modulation widths Δf, it is possible to detect various objects present at positions from a short distance to a long distance with high accuracy. Can.

  Further, the transmission / reception control unit 31 controls the transmission timing of the transmission unit 10 so that the chirp time Td of the chirp wave (corresponding to an example of the “modulation time”) becomes the same.

  Therefore, the radar device 1 according to the present embodiment can contribute to the improvement of the distance resolution.

  In addition, the transmission / reception control unit 31 adjusts the chirp time Td of the chirp wave to be smaller, thereby expanding the detection maximum speed.

  Therefore, according to the radar device 1 according to the present embodiment, the detection maximum speed can be expanded by adjusting the chirp time Td. That is, the detection performance of the target can be improved.

  In addition, the transmission / reception control unit 31 improves the speed resolution by adjusting the total chirp time Tr corresponding to one scan period of a plurality of chirp waves to be large.

  Therefore, according to the radar device 1 according to the present embodiment, the speed resolution can be improved by adjusting the total chirp time Tr. That is, the detection performance of the target can be improved.

  In the embodiment described above, as shown in FIG. 4 and FIG. 5A, for example, the chirp waves CP1 to CPn shift to the high frequency side along the time axis, but the shift to the high frequency side infinitely If it reaches the upper limit frequency, it returns to the original frequency. In FIG. 5A, for example, the shift from the chirp wave CP1 to the chirp wave CPn is repeated every chirp total time Tr corresponding to one scan period.

  Also, in the second modulation scheme of the above-described embodiment, an example in which three sub-chirp waves are generated from one chirp wave has been described, but two or four or more may be generated. .

  In the above-described embodiment, the radar device 1 is provided on the host vehicle, but it is needless to say that the radar device 1 may be provided on a mobile 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 invention are not limited to the specific details and representative embodiments represented and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Reference Signs List 1 radar device 10 transmission unit 20 reception unit 31 transmission / reception control unit Rmax maximum detection distance Td chirp time Tr total chirp time Vmax maximum detection speed ΔR distance resolution Δf modulation width Δfr shift amount Δv speed resolution

Claims (8)

A transmitter for transmitting a chirp wave whose frequency continuously increases or decreases;
A receiving unit for receiving the reflected wave of the chirp wave by a target;
A transmission / reception control unit that controls the transmission unit and the reception unit;
The transmission / reception control unit
A radar apparatus characterized in that the transmission section modulates the modulation frequency of the chirp wave so as to be changed for each chirp wave. The transmission / reception control unit
The radar apparatus according to claim 1, wherein the transmitter modulates the chirp wave so that the chirp wave shifts toward the high frequency side along the time axis while maintaining the modulation width. The transmission / reception control unit
The radar apparatus according to claim 1 or 2, wherein the transmission timing and the reception timing of the reception unit are not switched within the transmission period of one chirp wave by the transmission unit. The transmission / reception control unit
The radar apparatus according to claim 1, wherein the transmission timing and the reception timing of the reception unit are switched a plurality of times within a transmission period of one chirp wave by the transmission unit. The transmission / reception control unit
The transmission timing of the said transmission part is controlled so that the modulation time of the said chirp wave becomes the same. The radar apparatus as described in any one of Claims 1-4 characterized by the above-mentioned. The transmission / reception control unit
The radar apparatus according to any one of claims 1 to 5, wherein the detection maximum velocity is expanded by adjusting the modulation time of the chirp wave to be smaller. The transmission / reception control unit
The radar apparatus according to any one of claims 1 to 6, wherein speed resolution is improved by adjusting the total chirp time corresponding to one scan period of the plurality of chirp waves to be large. . A target detection method using a radar device comprising: a transmitter configured to transmit a chirp wave whose frequency is continuously increased or decreased; and a receiver configured to receive a reflected wave of the chirp wave by the target.
A control step of controlling the transmitting unit and the receiving unit;
The control step
A target detection method, comprising: modulating the transmission section so that the modulation frequency of the chirp wave is changed for each of the chirp waves.

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