Radar device

Abstract

To provide a radar device capable of identifying a plurality of transmission signals from signals received by a receiving antenna element, while suppressing a load.SOLUTION: A radar device 1 comprises: a transmission antenna group 3; an oscillation unit 21 that generates a common signal; a modulation unit 22 that performs modulation processing to rotate a phase of a branch signal obtained by branching the common signal for each repetition period with different phase rotation amounts; a receiving antenna group 4; and a control unit 6. The control unit 6 obtains a relative velocity with respect to a target based on a reception result of reflection waves corresponding to transmission waves from some of transmission antenna elements, and obtains a shift velocity obtained by shifting a Doppler shift amount corresponding to a phase rotation amount with respect to the relative velocity. The control unit 6 uses each velocity to identify signal components corresponding to each transmission signal included in a reception signal when the reflection waves corresponding to the transmission waves from the respective transmission antenna elements are received, and generates the identified signal components as demodulated signals.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a radar device. [Background technology]

[0002] Conventionally, radar devices using virtual antennas (so-called MIMO) that combine multiple transmitting antenna elements and multiple receiving antenna elements are known. In this type of radar device, a signal in which multiple transmitting signals are multiplexed is received, so it is necessary to distinguish from the received signal which transmitting antenna element transmitted the radio wave and the reflected wave. Note that MIMO is an abbreviation for Multiple Input Multiple Output.

[0003] For example, a technique is known in which individual signals are identified from a received signal in which transmission signals simultaneously transmitted from a plurality of transmitting antenna elements are superimposed using Doppler division multiplexing (hereinafter also referred to as DDM) (see, for example, Patent Document 1). DDM is an abbreviation for Doppler Division Multiplexing.

[0004] In the DDM described in Patent Document 1, multiple transmission signals generated by modulation processing that rotates the phase by a different phase rotation amount for each predetermined repetition period are multiplexed and transmitted from multiple transmission antenna elements. When the phase rotation amount of the multiple transmission signals differs for each repetition period, the multiple transmission signals are identified from the received signal by utilizing the fact that Doppler frequency peaks corresponding to the multiple transmission signals are extracted on the velocity spectrum obtained by analyzing the received signal.

[0005] Specifically, in the DDM described in Patent Document 1, first, a signal received by a receiving antenna element is analyzed to obtain a velocity spectrum. Then, one of the peaks on the velocity spectrum is selected as a processing object, and a peak obtained by shifting the processing object by an amount of Doppler shift corresponding to the phase rotation of each transmission signal is identified as a candidate peak, and it is then determined whether or not the candidate peak actually exists on the velocity spectrum. This process is performed for all peaks on the velocity spectrum, and a processing object for which a candidate peak actually exists on the velocity spectrum is identified as a peak corresponding to the relative velocity with respect to the target. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6881177 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the DDM described in Patent Document 1, the process of determining whether or not a candidate peak actually exists on the velocity spectrum must be executed as many times as there are multiple transmitted signals. For example, if the number of transmitting antenna elements increases, the load on memory and control processing becomes significantly larger.

[0008] An object of the present disclosure is to provide a radar device capable of identifying a plurality of transmission signals from a signal received by a receiving antenna element while suppressing the load. [Means for solving the problem]

[0009] The invention described in claim 1 is A radar device, comprising: A transmitting antenna group (3) including a plurality of transmitting antenna elements (Tx); an oscillator (21) for generating a continuous wave common signal; a modulation unit (22) for performing a modulation process for rotating the phase of each of a plurality of branch signals obtained by branching a common signal into the same number as the number of transmitting antenna elements, with different phase rotation amounts for each of the branch signals at a predetermined repetition period, thereby generating a plurality of transmission signals to be input to the plurality of transmitting antenna elements; a receiving antenna group (4) including one or more receiving antenna elements (Rx); a control unit (6) that generates information about a target that has reflected a transmission wave based on a reception result at a receiving antenna element of a reflected wave corresponding to a transmission wave transmitted from a plurality of transmitting antenna elements, The control unit a relative velocity calculation unit (61) that calculates a relative velocity between the target and the target based on a reception result at a receiving antenna element of a reflected wave corresponding to a transmission wave transmitted from a part of the plurality of transmitting antenna elements; a shift speed calculation unit (62) for calculating a shift speed obtained by shifting a Doppler shift amount corresponding to a phase rotation amount with respect to a relative speed; a demodulation unit (63) that uses the relative speed and the shift speed to identify signal components corresponding to the multiple transmission signals included in a received signal when a reflected wave corresponding to a transmission wave transmitted from each of the multiple transmission antenna elements is received by a receiving antenna element, and generates the identified signal components as a demodulated signal; and a detection section (64) for determining information regarding the target using the demodulated signal.

[0010] In this way, the radar device of the present disclosure generates a demodulated signal using the relative velocity calculated when transmitting a transmission wave from some of the multiple transmitting antenna elements, and the shift velocity calculated by shifting the Doppler shift amount corresponding to the phase rotation amount with respect to the relative velocity. This makes it possible to reduce the load on the memory and control processing of the radar device, since, unlike the conventional technology, it is not necessary to execute the process of determining whether or not a candidate peak actually exists on the velocity spectrum as many times as the multiple transmitting signals. In other words, the radar device of the present disclosure can identify multiple transmitting signals from signals received by the receiving antenna elements while reducing the load.

[0011] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of a radar device according to a first embodiment. [Diagram 2] 1 is a schematic diagram showing a transmitting antenna group including a plurality of actual transmitting antenna elements and a receiving antenna group including a plurality of actual receiving antenna elements in a radar device according to a first embodiment. FIG. [Diagram 3] 4 is an explanatory diagram for explaining a state in which a reflected wave of a transmission wave from a plurality of transmitting antenna elements is received by a receiving antenna element. FIG. [Figure 4] FIG. 2 is an explanatory diagram for explaining a modulation process in a transmission section. [Diagram 5] 5 is a flowchart showing the flow of a target detection process executed by a control unit of the radar device according to the first embodiment. [Figure 6] 5 is a flowchart showing a flow of a velocity calculation process executed by a control unit of the radar device according to the first embodiment. [Figure 7] 5 is a flowchart showing a flow of DDM processing executed by a control unit of the radar device according to the first embodiment. [Figure 8] FIG. 4 is an explanatory diagram for explaining the relationship between relative speed and shift speed. [Figure 9] 10 is an explanatory diagram for explaining the relationship between the relative velocity and the amount of phase rotation when there are multiple targets. FIG. [Figure 10] FIG. 11 is an explanatory diagram for explaining a method for setting the amount of phase rotation taking into consideration the relative speed when there are multiple targets. [Figure 11] FIG. 11 is an explanatory diagram for explaining DDM processing of a radar device serving as a comparative example. [Figure 12] FIG. 11 is an explanatory diagram for explaining a transmitting antenna element used in a speed calculation process in a radar device according to a second embodiment. [Figure 13]FIG. 1 is an explanatory diagram for explaining digital beamforming. [Figure 14] 1 is a schematic diagram showing a transmission range of a transmission wave when transmission beamforming is used. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, the same reference numerals are used for parts that are the same as or equivalent to those described in the preceding embodiments, and the description thereof may be omitted. In addition, in the embodiments, when only a part of the components is described, the components described in the preceding embodiments can be applied to the other parts of the components. In the following embodiments, each embodiment can be partially combined with each other, even if not specifically stated, as long as it does not cause any trouble in combination.

[0014] (First embodiment) The present embodiment will be described with reference to Fig. 1 to Fig. 11. In the present embodiment, an example will be described in which a radar device 1 of the present disclosure is applied to a target detection device that is mounted on a vehicle and detects various targets existing around the vehicle.

[0015] The radar device 1 emits radio waves ahead of the vehicle and receives radio waves reflected by a target ahead of the vehicle to determine the distance to the target, the relative speed with respect to the vehicle, the direction with respect to the vehicle, etc.

[0016] The radar device 1 employs the FMCW method as a signal modulation method. The radar device 1 operates at a radio frequency in a frequency band corresponding to millimeter waves (e.g., 76.5 GHz). Note that the operating frequency of the radio waves transmitted and received by the radar device 1 is not limited to a frequency corresponding to millimeter waves, and may be a frequency other than millimeter waves.

[0017] As shown in FIG. 1, the radar device 1 includes a transmitter 2, a transmitting antenna group 3 including a plurality of actual transmitting antenna elements Tx, a receiving antenna group 4 including a plurality of actual receiving antenna elements Rx, a receiver 5, and a controller 6.

[0018] The transmitting antenna group 3 has M transmitting antenna elements Tx, where M is an integer equal to or greater than 2. As shown in Fig. 2, the transmitting antenna elements Tx are arranged side by side in the horizontal direction U and the vertical direction V when the radar device 1 is mounted on a vehicle.

[0019] The transmitting antenna group 3 in this example has 24 actual transmitting antenna elements Tx. The transmitting antenna group 3 has six transmitting antenna elements Tx arranged as "vertical array elements" at an interval (1dz in this example) that is one time the predetermined vertical reference distance dz in the vertical direction V. These "vertical array elements" are arranged two by two on both sides of the receiving antenna group 4 in the horizontal direction U. The two "vertical array elements" on the outside of the receiving antenna group 4 are arranged at an interval (2dh in this example) that is twice the predetermined horizontal reference distance dh in the horizontal direction U. In addition, the "vertical array element" close to the receiving antenna group 4 is arranged at an interval (2dh in this example) that is twice the horizontal reference distance dh from the receiving antenna group 4 in the horizontal direction U.

[0020] The receiving antenna group 4 has N receiving antenna elements Rx, where N is an integer equal to or greater than 2. The receiving antenna elements Rx are arranged side by side in the horizontal direction U and the vertical direction V when the radar device 1 is mounted on a vehicle.

[0021] The receiving antenna group 4 in this example has 24 actual receiving antenna elements Rx. The receiving antenna group 4 has 12 receiving antenna elements Rx arranged as "horizontal array elements" at intervals that are three times the horizontal reference distance dh in the horizontal direction U (3dh in this example). These "horizontal array elements" are arranged one on each side of the transmitting antenna group 3 in the vertical direction V. The "horizontal array elements" are arranged at intervals that are one time the vertical reference distance dz from the transmitting antenna group 3 in the vertical direction V (1dz in this example).

[0022] Here, the vertical reference distance dz in this example is set so as to satisfy the following formula F1 when the detection range of the radar device 1 is "±1 / 2·θvfov". In this embodiment, θvfov is set to "40°" and the vertical reference distance dz is set to "1 / 2·λ", where λ is the wavelength of the radio wave.

[0023] 1 / sin(θvfov / 180 π) 2 <dz ···(F1) The interval between the transmitting antenna elements Tx may be strictly a multiple of the vertical reference distance dz and the horizontal reference distance dh, or may include an error that is generally acceptable in the technical field to which the technology of the present disclosure belongs and does not violate the spirit of the technology of the present disclosure. The same applies to the interval between the receiving antenna elements Rx.

[0024] Furthermore, the horizontal reference distance dh in this example is set so as to satisfy the following formula F2 when the detection range of the radar device 1 is "±1 / 2·θhfov". In this embodiment, θhfov is set to "180°" and the horizontal reference distance dh is set to "1 / 2·λ", where λ is the wavelength of the radio wave.

[0025] 1 / sin(θhfov / 180 π) 2 <dh ···(F2) 3, the transmitter 2 generates a signal to be transmitted from each transmitting antenna element Tx and transmits the signal to the transmitting antenna group 3. Specifically, the transmitter 2 includes an oscillator 21 and a modulator 22 as shown in FIG.

[0026] The oscillator 21 generates a continuous wave common signal. The oscillator 21 supplies the generated common signal to the modulator 22 and also to the receiver 5 as a local signal. As shown in Fig. 4, the oscillator 21 regards a predetermined measurement period (e.g., 50 ms) as one frame, and repeatedly generates a chirp signal whose frequency changes continuously during the first measurement period (e.g., 10 ms) of each frame at each repetition period (e.g., 50 μs).

[0027] The oscillator 21 is configured to be able to change the measurement cycle, measurement period, and repetition cycle as appropriate in accordance with instructions from the controller 6. The frequency width of the chirp signal that is changed during the repetition cycle is constant regardless of the repetition cycle. In other words, the oscillator 21 is configured so that the rate of change of the frequency of the chirp signal changes by changing the repetition cycle.

[0028] The permissible range of the repetition period is set so that, when analyzing the beat signal generated by mixing the transmitted signal and the received signal, the frequency shift caused by the relative speed with respect to the target is negligibly small compared to the frequency shift caused by the distance to the object. The same applies to the permissible range of the rate of change of the frequency of the chirp signal.

[0029] The modulation unit 22 branches the common signal generated by the oscillation unit 21 to generate M branch signals, the number of which is the same as the number of transmitting antenna elements Tx constituting the transmitting antenna group 3. The modulation unit 22 performs modulation (hereinafter also referred to as phase shift keying) on ​​each of the M branch signals, rotating the phase of the branch signal for each repetition period with a different phase rotation amount for each branch signal. In this way, M transmission signals are generated to be input to the multiple transmitting antenna elements Tx. In the phase shift keying, a phase rotation amount Δφ of a different magnitude is set for each of the M branch signals, and the phase of the branch signal is rotated by that phase rotation amount Δφ for each repetition period.

[0030] Here, the number of phases used in phase shift keying is P, where P is an integer equal to or greater than M. Modulation unit 22 uses P types of phase rotation amounts expressed by Δφ=p×360° / P, where p=0, 1, 2, . . . , P-1. For example, in the case of P=4, as shown in the lower part of FIG. 4, Δφ=0° when p=0, and the phase difference of the transmission signal, which is the modulated signal, relative to the branch signal (i.e., the common signal), which is the signal before modulation, is 0° in all repetition periods. When p=1, Δφ=90°, and the phase difference of the transmission signal relative to the common signal switches every repetition period, changing in the order of 0°→90°→180°→270°→0°.

[0031] The modulation unit 22 is configured to be able to appropriately change the setting of the number of phases P, the selection of M types of phase rotation amounts Δφ to be used for phase shift keying among the P types of phase rotation amounts Δφ, and the setting of the correspondence relationship between the selected M types of phase rotation amounts and the M transmitting antenna elements Tx. The setting may be changed according to an instruction from the control unit 6, or may be automatically performed. When the setting is changed automatically, it may be changed according to a predetermined pattern or may be changed randomly.

[0032] 1, the receiving unit 5 generates a beat signal based on the reception signals received by the receiving antenna group 4 and the local signal transmitted from the transmitting unit 2, samples the beat signal, and provides it to the control unit 6. Although not shown, the receiving unit 5 is configured to include a mixer, an amplifier, an AD converter, etc.

[0033] The control unit 6 is an electronic control device mainly composed of a microcomputer equipped with a processor and a memory M. The memory M is, for example, a ROM, a RAM, etc. Various functions of the microcomputer are realized by the processor executing a program stored in a non-transient physical storage medium.

[0034] The control unit 6 detects the azimuth of the target in two mutually intersecting directions by MIMO using a plurality of transmitting antenna elements Tx and receiving antenna elements Rx aligned in the horizontal direction U and vertical direction V. For example, the control unit 6 detects the azimuth of the target in the horizontal direction U using antenna elements aligned in the horizontal direction U, and detects the azimuth in the vertical direction V based on a spectrum signal corresponding to the detected azimuth, thereby detecting the azimuth of the target in two mutually intersecting directions.

[0035] Here, in a radar device 1 that utilizes MIMO, as shown in FIG. 3, a signal in which multiple transmission signals are multiplexed is received by the receiving antenna element Rx, so it is necessary to distinguish from the received signal which transmitting antenna element transmitted the radio wave that is being reflected.

[0036] Time division multiplexing modulation (TDM) is a technique for demodulating multiplexed signals, but with time division multiplexing modulation, the number of data processed per unit time decreases, resulting in a deterioration in the S / N ratio. There is also DDM, which is described in Patent Document 1, but with DDM described in Patent Document 1, for example, if the number of transmitting antenna elements increases, the load on memory M and control processing becomes significantly large. Note that "S / N" is the ratio of signal to noise.

[0037] In consideration of these, the radar device 1 of this embodiment is configured to use DDM, which places a small load on the control unit 6, to identify a plurality of transmission signals from the signals received by the receiving antenna elements Rx in the target detection process.

[0038] The target detection process executed by the control unit 6 of the radar device 1 will be described below with reference to Fig. 5 to Fig. 7. The process shown in Fig. 5 is executed by the control unit 6 periodically or irregularly, for example, when the vehicle is in a ready state in which it can travel.

[0039] As shown in Fig. 5, in step S100, the control unit 6 executes a velocity calculation process for calculating a relative velocity with respect to a target. In this embodiment, the configuration for executing the process of step S100 in the control unit 6 corresponds to a "relative velocity calculation unit 61." Details of the velocity calculation process will be described with reference to the flowchart shown in Fig. 6.

[0040] 6, in step S110, the control unit 6 outputs a transmission wave from a part of the transmitting antenna elements Tx. Specifically, the control unit 6 outputs a transmission wave from one transmitting antenna element Tx included in the transmitting antenna group 3.

[0041] Next, in step S120, the control unit 6 receives a signal corresponding to the reflected wave from the target at the receiving antenna group 4. This signal is mixed with a local signal by the mixer of the receiving unit 5. After that, a desired frequency component is extracted by a low-pass filter, and the frequency component is provided from the receiving unit 5 to the control unit 6 as a beat signal.

[0042] Next, in step S130, the control unit 6 performs distance FFT processing. The control unit 6 obtains the distance to the target by frequency analyzing the beat signal using FFT. Note that FFT is an abbreviation for Fast Fourier Transform. Specifically, a distance spectrum is calculated for each of the N receiving antenna elements Rx. In each distance spectrum, a peak appears at a frequency corresponding to the time required for the transmission wave from the transmitting antenna element Tx to travel back and forth between the target and the target (i.e., the distance to the target).

[0043] Next, the control unit 6 performs a velocity FFT process in step S140. The control unit 6 performs frequency analysis for each beat frequency component by FFT to obtain a Doppler frequency corresponding to the relative velocity with respect to the target.

[0044] Next, in step S150, the control unit 6 calculates the relative velocity with respect to the target based on the Doppler frequency calculated by the velocity FFT process. The control unit 6 stores the relative velocity with respect to the target in the memory M. In the velocity calculation process of this embodiment, since the transmission signal is not multiplexed, the relative velocity with respect to each target can be calculated without using DDM.

[0045] This concludes the description of the speed calculation process executed in step S100 in Fig. 5. When the process in step S100 is completed, the control unit 6 executes a process in step S200 of identifying a plurality of transmission signals from the signal received by the receiving antenna element Rx using DDM (hereinafter, also referred to as DDM process).

[0046] 8, the DDM process obtains a shift speed obtained by shifting the Doppler shift amount by the phase rotation amount Δφ set in the modulation unit 22 of the transmission unit 2 with respect to the relative speed with respect to the target (i.e., the detected speed). For example, the DDM process obtains the shift speed by adding the Doppler shift amount to the relative speed obtained in the speed calculation process.

[0047] In addition, in the DDM process, the relative speed and the shift speed are used to identify signal components corresponding to a plurality of transmission signals contained in a received signal when a reflected wave corresponding to a transmission wave transmitted from each of the transmission antenna elements Tx is received by the reception antenna element Rx, and the identified signal components are generated as a demodulated signal.

[0048] In this embodiment, the configuration in control unit 6 that calculates the shift speed corresponds to a "shift speed calculation unit 62." Also, the configuration in control unit 6 that generates a demodulated signal corresponds to a "demodulation unit 63." Furthermore, the configuration in control unit 6 that calculates information about a target using the demodulated signal corresponds to a "detection unit 64." Details of the DDM process will be described below with reference to the flowchart shown in FIG.

[0049] 7, first, in step S210, the control unit 6 determines the amount of phase rotation Δφ used in the modulation process in the modulation unit 22 of the transmission unit 2. The amount of phase rotation Δφ is determined depending on the relative speed with respect to the target.

[0050] Here, for example, when the relative velocities with two targets are obtained, the difference between the Doppler shift amounts D1 and D2 of the phase rotation amount Δφ1 (=0°) and the phase rotation amount Δφ2 may be equal to the difference in the relative velocities with each target (the difference between the detected velocities t1 and t2), as shown in Fig. 9. In this case, the peak corresponding to the shift velocity v12 and the peak corresponding to the relative velocity v21 overlap, making it impossible to distinguish between the two.

[0051] Considering this, the control unit 6 of this embodiment determines the phase rotation amount Δφ used in the modulation process so that the speed peaks do not overlap on the speed spectrum in which multiple speed components included in the received signal are associated with frequencies. The control unit 6 of this embodiment determines the phase rotation amount Δφ used in the modulation process so that the signal component corresponding to the relative speed with the target, the signal component corresponding to the shift speed, and the aliased component of the shift speed caused by aliasing can be separated. Note that aliasing is also called aliasing distortion, and occurs when a frequency component higher than the Nyquist frequency is included in the signal before sampling.

[0052] An example of a method for determining the amount of phase rotation when three targets having velocities t1 to t3 relative to the radar device 1 are within the speed detection range of the radar device 1 will be described below with reference to Fig. 10. Since the phase is rotated in the modulation process, aliasing of the velocity occurs depending on the magnitude of the relative velocity, as shown in Fig. 10. For this reason, on the speed spectrum, folding speeds t1', t2', and t3' corresponding to the speeds t1, t2, and t3 are set not only in the speed detection range but also in the speed folding range beyond the speed detection range. These folding speeds t1', t2', and t3' are, for example, values ​​obtained by adding the maximum value of the speed detection range to the speeds t1, t2, and t3. Next, the mutual intervals in all combinations between the velocities t1, t2, t3 and the return velocities t1', t2', t3' are obtained as the Doppler shift interval Dng. Then, the phase rotation amount Δφ is determined so that the difference between the Doppler shift amounts corresponding to each phase rotation amount Δφ differs from the Doppler shift interval Dng. For example, the Doppler shift amount D2 corresponding to the phase rotation amount Δφ2 is determined so that the difference between the Doppler shift amount D1 corresponding to the reference phase rotation amount Δφ1 and the Doppler shift amount D2 is a value different from the Doppler shift interval Dng.

[0053] Next, the control unit 6 proceeds to step S220 and obtains a shift speed obtained by shifting the Doppler shift amount corresponding to the phase rotation amount Δφ determined in step S210 with respect to the relative speed with respect to the target.

[0054] Next, the control unit 6 proceeds to step S230, and causes the transmission unit 2 to output transmission waves modulated by DDM from all transmitting antenna elements based on the amount of phase rotation Δφ determined in step S210.

[0055] Next, in step S240, the control unit 6 receives a signal corresponding to the reflected wave from the target at the receiving antenna group 4. This signal is mixed with a local signal by the mixer of the receiving unit 5. After that, a desired frequency component is extracted by a low-pass filter, and the frequency component is provided from the receiving unit 5 to the control unit 6 as a beat signal.

[0056] Next, the control unit 6 performs distance FFT processing in step S250. The control unit 6 performs frequency analysis of the beat signal using FFT to obtain the distance to the target. The control unit 6 also performs speed FFT processing in step S260. The control unit 6 performs frequency analysis for each beat frequency component using FFT to obtain the Doppler frequency corresponding to the relative speed with respect to the target.

[0057] Next, in step S270, the control unit 6 uses the relative speed and the shift speed to identify signal components corresponding to a plurality of transmission signals included in a received signal when a reflected wave corresponding to a transmission wave transmitted from each of the transmitting antenna elements Tx is received by the receiving antenna element Rx. For example, when two transmitting antenna elements Tx transmit transmission waves whose phases are rotated by different phase rotation amounts, the control unit 6 identifies a signal component on the speed spectrum corresponding to a relative speed v1 as corresponding to a transmission signal from one transmitting antenna element Tx, and identifies a signal component on the speed spectrum corresponding to a shift speed v2 as corresponding to a transmission signal from the other transmitting antenna element Tx.

[0058] Here, in the velocity spectrum, when the relative velocity with respect to the target is zero, the frequency corresponding to the phase rotation amount assigned to each transmitting antenna is extracted as the Doppler frequency. For example, the frequency of the signal component corresponding to the phase rotation amount Δφ1=0° is 0 Hz. Also, in the velocity spectrum, when there is a relative velocity with respect to the object, the Doppler frequency shifts by a magnitude corresponding to the relative velocity, and frequency aliasing occurs depending on the magnitude of the relative velocity.

[0059] Next, the control unit 6 proceeds to step S280, and generates the signal components corresponding to each transmitting antenna element Tx identified in step S270 as demodulated signals for each transmitting antenna element Tx.

[0060] The above is the DDM process executed in step S200 in Fig. 5. When the process in step S200 is completed, the control unit 6 proceeds to step S300 and obtains information about the target, such as its position, speed, and direction, using the demodulated signal generated in the DDM process.

[0061] The radar device 1 described above includes a transmitting antenna group 3, an oscillator 21 that generates a continuous wave common signal, a modulator 22 that generates multiple transmission signals, a receiving antenna group 4, and a controller 6 that generates information about targets that have reflected the transmission wave. The modulator 22 performs modulation processing on multiple branch signals obtained by branching a common signal into the same number of signals as the transmitting antenna elements Tx, rotating the phase of each of the branch signals by a different phase rotation amount Δφ at each predetermined repetition period. In this way, the modulator 22 generates multiple transmission signals to be input to the multiple transmitting antenna elements Tx.

[0062] The control unit 6 calculates the relative velocity with respect to the target based on the reception result at the receiving antenna element Rx of the reflected wave corresponding to the transmission wave transmitted from one of the multiple transmitting antenna elements Tx, and calculates the shift velocity obtained by shifting the Doppler shift amount corresponding to the phase rotation amount from the relative velocity.

[0063] The control unit 6 uses the relative speed and the shift speed to identify signal components corresponding to the multiple transmission signals included in the received signal when the receiving antenna element Rx receives reflected waves corresponding to the transmission waves transmitted from each of the multiple transmitting antenna elements Tx. The control unit 6 generates the identified signal components as demodulated signals and obtains information about the target using the demodulated signals.

[0064] Here, in the DDM process of Patent Document 1, a peak on the velocity spectrum is shifted by a Doppler shift corresponding to the phase rotation amount of each transmission signal, and a candidate peak is identified as being present on the velocity spectrum. This process is performed for all peaks on the velocity spectrum, and a candidate peak that actually exists on the velocity spectrum is identified as a peak corresponding to the relative velocity with respect to the target. For example, as shown in FIG. 11, when there are a first candidate and a second candidate as candidate peaks, the first candidate peak corresponds to a peak that actually exists on the velocity spectrum, and therefore the velocity v1 of the first candidate is identified as the relative velocity with respect to the target.

[0065] In contrast, the radar device 1 of this embodiment generates a demodulated signal using the relative velocity calculated when transmitting a transmission wave from some of the multiple transmitting antenna elements Tx, and the shift velocity calculated by shifting the Doppler shift amount corresponding to the phase rotation amount with respect to the relative velocity. In the DDM process of the radar device 1 of this embodiment, it is not necessary to execute the process of determining whether or not a candidate peak actually exists on the velocity spectrum the same number of times as the multiple transmitting signals, so that the load on the memory M and the control process of the radar device 1 can be reduced. In other words, the radar device 1 of this embodiment can identify multiple transmitting signals from the signal received by the receiving antenna elements Rx while reducing the load.

[0066] Moreover, the radar device 1 of this embodiment has the following features.

[0067] (1) The control unit 6 determines the amount of phase rotation used in the modulation process so that the signal component corresponding to the relative speed, the signal component corresponding to the shift speed, and the aliasing component of the shift speed caused by aliasing can be separated on the speed spectrum. Since the signal component corresponding to the relative speed and the signal component corresponding to the shift speed do not match on the speed spectrum, multiple transmission signals can be identified from the signal received by the receiving antenna element Rx.

[0068] Second embodiment Next, a second embodiment will be described with reference to Figures 12 to 14. In this embodiment, differences from the first embodiment will be mainly described.

[0069] In the radar device 1 of the present disclosure, two processes, namely, the speed calculation process and the DDM process, are executed at different timings. When the two processes are executed at different timings in this manner, the number of data processed per unit time decreases, as in the case of time division multiplexing modulation, and the S / N ratio deteriorates.

[0070] Taking this into consideration, the radar device 1 of this embodiment is configured to transmit signals with a limited transmission range by transmit beamforming from some of the multiple transmit antenna elements Tx when the relative velocity is calculated by the control unit 6. Note that transmit beamforming is a technology that uses multiple antenna elements to concentrate signals transmitted from each antenna element in a specific direction or space.

[0071] The control unit 6 realizes transmission beamforming by, for example, causing some of the "vertical array elements" constituting the transmitting antenna group 3 to simultaneously transmit phase-aligned transmission waves from the transmitting antenna elements Tx as shown in Fig. 12. This has the advantage of improving the S / N ratio of the received signal, making it easier to detect targets with low reflectivity. In other words, even if the S / N ratio decreases due to the execution of two processes, such as the speed calculation process and the DDM process, at different times, it is possible to compensate for part of the decrease by improving the S / N ratio through transmission beamforming.

[0072] Specifically, the transmit beamforming may use one of the four vertically-arranged elements Tx1 to Tx4 shown in Fig. 12, or may use two or more. When two or more elements are used, multiplex transmission is performed, and therefore it is necessary to use the DDM process or the like shown in Patent Document 1. However, since not all the transmit antenna elements Tx are used, the load on the memory M and control process of the radar device 1 can be reduced. In order to reduce the load on the memory M and control process of the radar device 1, it is desirable to calculate the relative velocity using half or less of the transmit antenna elements Tx.

[0073] Here, in the DDM process described in the first embodiment, multiplex transmission is performed from all transmitting antenna elements Tx, and therefore the antenna gain is lower than when the velocity calculation process of the second embodiment is performed. Therefore, in the DDM process, there may be cases where a peak does not exist on the velocity spectrum at a position corresponding to the relative velocity with respect to the target calculated in the relative velocity calculation process.

[0074] However, even in this case, if a signal at a position corresponding to the relative speed with respect to the target obtained in the speed calculation process is selected and digital beamforming (i.e., DBF) is performed using that signal to estimate the direction in the horizontal direction U, it will be possible to properly detect the target by improving the S / N ratio.

[0075] For example, as shown in FIG. 13, when a target object is located in front of the radar device 1, the S / N ratio is improved by digitally beamforming the received signal at each receiving antenna element Rx. In FIG. 13, s1 is a signal corresponding to the detection result of the target object (a signal corresponding to the reflection intensity and phase at the target), and n1 to n4 are thermal noise. The thermal noise n1 to n4 have a Gaussian distribution, and the average approaches zero. Therefore, the S / N ratio can be improved by digitally beamforming the received signal at each receiving antenna element Rx. In this case, the improvement in S / N is 1 / 2 times the number of receiving channels n, so the more receiving antenna elements Rx there are, the more advantageous it is.

[0076] Specifically, in the target detection process, the horizontal azimuth signal estimated by MIMO is reproduced by digital beamforming. Since the signal obtained by reproduction of digital beamforming contains a phase difference component due to the difference in the position of the transmitting antenna element Tx in the vertical direction V, the signal is used to estimate the azimuth in the vertical direction V. According to such azimuth estimation, the S / N ratio is improved by digital beamforming, so that the azimuth of the target in the vertical direction V can be appropriately estimated.

[0077] Here, when transmit beam forming is used in the velocity calculation process as in this embodiment, the transmission range of the transmit beam becomes smaller than that of the DDM process, for example, as shown in Fig. 14. If there is an object outside the transmission range when using transmit beam forming, there is a risk that the velocity of the object cannot be obtained.

[0078] In an in-vehicle environment, objects that may collide with the vehicle (e.g., cars, motorcycles, pedestrians, fallen objects) are on the same road and are usually within the transmission range when using transmit beamforming, so the speed of the object can be calculated. On the other hand, objects that are outside the transmission range when using transmit beamforming tend to be stationary objects such as signs, overpasses, and ceilings installed above the road.

[0079] In consideration of this, in the control unit 6 of this embodiment, in the DDM process, demodulation process is performed by adding not only the relative speed with respect to the target calculated in the speed calculation process but also the moving speed of the host vehicle. Then, when the control unit 6 calculates information about the target using the demodulated signal, if a signal component corresponding to the moving speed of the host vehicle is detected in the speed spectrum, the control unit 6 specifies the detected signal component as corresponding to a reflected wave reflected by a stationary object. Note that, if there is no peak corresponding to the moving speed of the host vehicle in the speed spectrum, the control unit 6 discards and does not output the signal component corresponding to the moving speed.

[0080] The rest is the same as in the first embodiment. The radar device 1 of this embodiment can obtain the same effects as in the first embodiment, which are achieved by a configuration common to the first embodiment or an equivalent configuration.

[0081] Moreover, the radar device 1 of the second embodiment has the following features.

[0082] (1) When calculating the relative speed with respect to the target, the control unit 6 causes some of the transmitting antenna elements Tx to transmit transmission waves with a limited transmission range by transmission beam forming. In this way, by limiting the transmission range by transmission beam forming, the antenna gain is improved, making it easier to detect signal components corresponding to reflected waves. This greatly contributes to improving the accuracy of the relative speed with respect to the target calculated by the relative speed calculation unit 61.

[0083] (2) When the transmission range is limited by transmission beamforming to obtain the relative speed, there is a tendency that stationary objects such as traffic signs on the side of the road or above the road tend to be outside the transmission range due to the limited transmission range. For this reason, when obtaining information about a target using a demodulated signal, if a signal component corresponding to the moving speed of the host vehicle is detected in the speed spectrum, the radar device 1 is desirably configured to identify the signal component as corresponding to a reflected wave reflected by a stationary object.

[0084] (Modification of the second embodiment) The radar device 1 of the second embodiment demodulates a signal multiplexed using DDM in the speed calculation process, but is not limited to this. For example, the radar device 1 may demodulate a signal multiplexed using TDM in the speed calculation process.

[0085] (Other embodiments) Representative embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments and can be modified in various ways, for example, as described below.

[0086] In the above embodiment, a specific antenna configuration of the radar device 1 is exemplified, but the antenna configuration of the radar device 1 is not limited to the above, and may be an antenna configuration different from the above. For example, the radar device 1 may have an antenna configuration in which the arrangement of the transmitting antenna elements Tx and the receiving antenna elements Rx is reversed. In addition, in the above embodiment, the two different directions are the horizontal direction U and the vertical direction V, but they may be directions different from these. In addition, the number of transmitting antenna elements Tx and receiving antenna elements Rx is not limited to the above.

[0087] In the above embodiment, the transmission waves are multiplexed and transmitted from all the transmitting antenna elements Tx in the DDM process, but the present invention is not limited to this. The DDM process may be, for example, a process in which the transmission waves from the transmitting antenna elements Tx are time-divided.

[0088] As in the above-described embodiment, it is preferable that the control unit 6 determines the amount of phase rotation so that the signal component corresponding to the relative speed, the signal component corresponding to the shift speed, and the aliasing component of the shift speed can be separated on the speed spectrum, but this is not necessarily required.

[0089] In the above embodiment, an example has been described in which the radar device 1 of the present disclosure is applied to a target detection device that is mounted on a vehicle and detects various targets present around the vehicle, but the application of the radar device 1 is not limited to this. The radar device 1 can also be applied to, for example, moving objects other than vehicles and stationary devices.

[0090] In the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except in cases where it is particularly expressly stated that they are essential or where they are clearly considered to be essential in principle.

[0091] In the above-described embodiments, when numerical values ​​such as the number, values, amounts, ranges, etc. of components of the embodiments are mentioned, they are not limited to the specific numbers unless it is specifically stated as required or unless it is clearly limited to a specific number in principle.

[0092] In the above-described embodiments, when referring to the shapes, positional relationships, etc. of components, etc., there is no limitation to those shapes, positional relationships, etc., unless specifically stated or in principle limited to a specific shape, positional relationship, etc.

[0093] The control unit and the method of the present disclosure may be implemented in a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. The control unit and the method of the present disclosure may be implemented in a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. The control unit and the method of the present disclosure may be implemented in one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. The computer program may also be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. [Explanation of symbols]

[0094] 1. Radar equipment 21 Oscillator 22 Modulation section 3 Transmitting antennas 4 Receiving antennas 6. Control Unit 61 Relative velocity calculation unit 62 Shift speed calculation unit 63 Demodulation section 64 Detection unit

Claims

1. A radar device, comprising: A transmitting antenna group (3) including a plurality of transmitting antenna elements (Tx); An oscillator (21) for generating a continuous wave common signal; a modulation unit (22) for performing a modulation process for rotating the phase of each of a plurality of branch signals obtained by branching the common signal into the same number as the transmitting antenna elements, with the branch signals being each rotated by a different phase rotation amount at each predetermined repetition period, thereby generating a plurality of transmission signals to be input to the plurality of transmitting antenna elements; a receiving antenna group (4) including one or more receiving antenna elements (Rx); and a control unit (6) that generates information about a target that has reflected a transmission wave based on a reception result at the receiving antenna element of a reflected wave corresponding to a transmission wave transmitted from the plurality of transmitting antenna elements, The control unit is a relative velocity calculation unit (61) for calculating a relative velocity between the target and the target based on a reception result at the receiving antenna element of a reflected wave corresponding to a transmission wave transmitted from a part of the plurality of transmitting antenna elements; a shift speed calculation unit (62) for calculating a shift speed obtained by shifting a Doppler shift amount corresponding to the phase rotation amount with respect to the relative speed; a demodulation unit (63) that uses the relative speed and the shift speed to identify signal components corresponding to the plurality of transmission signals included in a received signal when a reflected wave corresponding to a transmission wave transmitted from each of the plurality of transmission antenna elements is received by the receiving antenna element, and generates the identified signal components as a demodulated signal; a detection unit (64) that uses the demodulated signal to obtain information about the target.

2. 2. The radar device according to claim 1, wherein the control unit determines the amount of phase rotation used in the modulation process such that a signal component corresponding to the relative velocity, a signal component corresponding to the shift velocity, and an aliasing component of the shift velocity caused by aliasing can be separated from each other on a velocity spectrum in which a plurality of velocity components included in the received signal are associated with frequencies.

3. 3. The radar device according to claim 1, wherein the control unit, when calculating the relative velocity in the relative velocity calculation unit, causes some of the plurality of transmitting antenna elements to transmit a transmission wave with a transmission range limited by transmission beamforming.

4. The device is mounted on a moving body, 4. The radar device according to claim 3, wherein when a signal component corresponding to a moving speed of the moving body is detected on a speed spectrum in which a plurality of speed components included in the received signal are associated with frequencies, the control unit, when obtaining information about the target using the demodulated signal, identifies the detected signal component as corresponding to a reflected wave reflected by a stationary object.

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