Chirp Sequence Radar Device

Abstract

To provide a chirp sequence radar device capable of accurately suppressing narrowband interference. Solution The CS device of the present embodiment includes an interference signal S g11 is received during the most recent quiet period after or before a quiet period, the DSP processes the interference signal S g3 corresponding beat signal B g frequency f Bg3 the beat signal B that can cause narrowband interference based on e (estimated frequency F i ) is estimated by a linear function. Then, the estimated beat frequency (estimated frequency F i ) power value P of the frequency spectrum at i and the power value P B1 , the power value P B2 or these power values P B1 , P B2 determines whether the difference between the average power value of and is within a predetermined range. If the difference is within the predetermined range, it is determined that a beat signal (interference signal) exists at the estimated beat frequency (estimated frequency F i ), and the beat signal of the estimated beat frequency (interference signal of estimated frequency F i ) is suppressed.

Description

Technical Field

[0001] The present invention relates to a chirp sequence radar apparatus that suppresses narrowband interference.

Background Art

[0002] As a chirp sequence radar apparatus that transmits a chirp signal modulated at a frequency that changes into a sawtooth shape at a constant sweep period, and receives a target signal obtained when the chirp signal is reflected by a target (object) and returned, there is, for example, one disclosed in the following Patent Document 1. This type of radar apparatus is also called an FMCW (Frequency Modulated Continuous Wave) radar apparatus because frequency-modulated chirp signals are continuously transmitted. It is configured to be able to detect the distance to the target and the moving speed of the target based on a beat signal generated from the difference between a received signal (target signal) reflected by the target and returned, and a transmission signal (chirp signal).

[0003] In a chirp sequence radar apparatus, when a plurality of apparatuses transmitting chirp signals with the same sweep frequency width and the same sweep period time use the same frequency band simultaneously, the one apparatus may receive both a target signal obtained when the chirp signal transmitted by the one apparatus is reflected by the target and returned, and a chirp signal transmitted from another apparatus. A chirp signal from another apparatus is difficult to distinguish from the target signal that should be originally received, and hinders target detection. In a chirp sequence radar apparatus, the chirp signals from other apparatuses can adversely affect target detection, for example, such chirp signals transmitted from other apparatuses are mistakenly identified as target signals and thus a target is falsely detected. Therefore, such a phenomenon is referred to as "narrowband interference", and the chirp signals from other apparatuses are referred to as "interference signals".

[0004] In such narrowband interference, the "chirp sequence radar device" disclosed in Patent Document 1 can improve interference suppression characteristics when an interference signal with a large signal level is received, and this device was proposed by the present inventors. In this chirp sequence radar device, interference replicas for each frequency are generated based on the frequency spectrum of the beat signal from the first received signal received during the chirp signal transmission stop period. The larger the signal level in the interference replica, the smaller the signal level of the first received signal is converted to, thereby suppressing interference from the second received signal, i.e., the interference signal, received during the chirp signal transmission period. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-108640 [Non-patent literature]

[0006] [Non-Patent Document 1] Takahiro Maruyama, Masahiro Umebira, Xiaoyan Wang, and Shigeki Takeda, "Influence of Hardware Imperfections on Chirp Sequence Radar Using Inter-Radar Interference Suppression," IEICE Technical Report, vol.122, no.151, SANE2022-45, pp.68-73, August 2022. [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, when multiple chirp sequence radar devices exist, in reality, there are considerable hardware differences between each device. For example, errors may occur in the transmitted chirp signal and chirp period between one device and another. Therefore, the beat frequency of the beat signal caused by the interference signal that generates narrowband interference is unlikely to be the same for each device, and will gradually change by different amounts depending on the magnitude of the error in the chirp rate (instantaneous rate of change of frequency) of the interference signal (chirp signal) transmitted by each device. Furthermore, as disclosed in Non-Patent Document 1 above, it has been found that spectral broadening occurs when the frequency spectrum of the beat signal caused by the interference signal is not a line spectrum.

[0008] For these reasons, the chirp sequence radar device described in Patent Document 1, which is based on the premise that the frequency spectrum of the beat signal caused by an interference signal that can cause narrowband interference without interference replicas fluctuating over time is generated as a line spectrum, has the problem that it is difficult to accurately suppress narrowband interference that occurs between real devices that have frequency fluctuations and spectral broadening of the beat signal caused by the interference signal.

[0009] This problem could potentially be solved by a method that suppresses the interfering signal using a wide frequency bandwidth that encompasses all frequency ranges in which the interfering signal may vary over time. However, since this wide frequency bandwidth includes frequencies where narrowband interference does not occur, it would uniformly suppress even the necessary signals at those frequencies. Therefore, such a method could introduce a new problem: a decrease in the probability of detecting the target signal present at surrounding frequencies where narrowband interference may occur.

[0010] The present invention has been made to solve the above-mentioned problems and aims to provide a chirp sequence radar system that can accurately suppress narrowband interference. Another object of the present invention is to provide a chirp sequence radar system that can avoid excessive suppression of narrowband interference. [Means for solving the problem]

[0011] To achieve the above object, the technical means of claim 1 recited in the claims is employed. According to this means, a chirp sequence radar apparatus comprises a transmission control section, a frequency spectrum calculation section, a signal information acquisition section, a signal source determination section, an interference signal determination section, and an interference signal suppression section. The transmission control section controls transmission of chirp signals such that transmission periods for transmitting a plurality of chirp signals and idle periods for pausing said transmission alternate. The frequency spectrum calculation section obtains frequency spectrums of two signals, which are respective beat signals of a first reception signal received during an idle period and a second reception signal received after or before said idle period.

[0012] The frequency spectrum calculation section obtains frequency spectrums of two signals, which are respective beat signals of the first reception signal and the second reception signal, by using, for example, FFT (Fast Fourier Transform). Then, the signal information acquisition section acquires, in the frequency spectrums of the two signals obtained by the frequency spectrum calculation section, each piece of information of frequency F B1 and power value P B1 corresponding to the first reception signal, and frequency F B2 and power value P B2 corresponding to the second reception signal. The signal source determination section determines whether the two signal sources of the first reception signal and the second reception signal are identical based on a difference between frequency F B1 and frequency F B2 and a difference between power value P B1 and power value P B2 . When the signal source determination section determines that the two signal sources are identical, the interference signal determination section determines whether an interference signal capable of causing narrowband interference to a signal component corresponding to a target signal in the frequency spectrum exists, and when it is determined that an interference signal exists, the interference signal suppression section suppresses the signal component corresponding to the interference signal in the frequency spectrum.

[0013] When the second reception signal is received during an immediately preceding idle period before or after the idle period, the interference signal determination section estimates estimated frequency F iThe system determines whether or not an interference signal is present, and if an interference signal is present, the interference signal suppression unit estimates the frequency F in the frequency spectrum. i The signal component corresponding to the interference signal is suppressed. That is, the interference signal determination unit determines the frequency F of the first received signal in the frequency spectrum. B1 Based on this, the estimated frequency F is estimated to be capable of causing narrowband interference. i Power value P i And, power value P B1 Power value P B2 or these P B1 ,P B2 When the difference from the average power value is within a predetermined range, the estimated frequency F i It is determined that an interference signal is present. Then, the estimated frequency F is determined. i Power value P of the frequency spectrum in i And, power value P B1 Power value P B2 Or these power values ​​P B1 ,P B2 The system determines whether the difference between the average power value of and is within a predetermined range, and if this difference is within the predetermined range, the estimated frequency F i The interference signal suppression unit determines that an interference signal is present and calculates the estimated frequency F in the frequency spectrum. i The signal component corresponding to the interference signal is suppressed. Estimated frequency F i This can be estimated using a linear function or the like, as described later.

[0014] As a result, even if hardware-specific individual differences exist in real chirp sequence radar equipment, such as errors in the transmitted chirp signal or chirp period between one device and another, which can lead to frequency fluctuations and spectral broadening of the beat signal due to the chirp signal or interference signal, one device will estimate the frequency F according to the frequency fluctuations and spectral broadening of the beat signal of each other device. i This makes it possible to determine the presence of interference signals.

[0015] Furthermore, the technical means of claim 2 described in the claims is adopted. According to this means, the chirp sequence radar device comprises a transmission control unit, a frequency spectrum calculation unit, a signal information acquisition unit, a signal source determination unit, an interference signal determination unit, and an interference signal suppression unit. The transmission control unit controls the transmission of the chirp signal so that transmission periods in which multiple chirp signals are transmitted and pause periods in which the transmission is paused alternate, and the frequency spectrum calculation unit determines the frequency spectra of two signals, which are the beat signals of a first received signal received during the pause period and a second received signal received after or before the pause period.

[0016] The frequency spectrum calculation unit uses, for example, FFT (Fast Fourier Transform) to determine the frequency spectra of the two signals, which are the beat signals of the first and second received signals. Then, the signal information acquisition unit obtains the frequency F corresponding to the first received signal in the frequency spectra of the two signals obtained by the frequency spectrum calculation unit. B1 and power value P B1 and frequency F corresponding to the second received signal B2 and power value P B2 The information for each of these is acquired, and the signal source determination unit determines the frequency F B1 and frequency F B2 The difference and power value P B1 and power value P B2 Based on the difference, it is determined whether the two signal sources of the first received signal and the second received signal are the same. If the signal source determination unit determines that the two signal sources are the same, the interference signal determination unit determines whether this same signal source is an interference signal that can cause narrowband interference with the signal component corresponding to the target signal in the frequency spectrum. The interference signal suppression unit then suppresses the signal component corresponding to the interference signal in the frequency spectrum during the transmission period and the pause period if the interference signal determination unit determines that the same signal source is an interference signal.

[0017] Then, when the second received signal is received immediately after the first received signal, for two adjacent received signals after the second received signal, such as the second received signal and the third received signal adjacent thereto, or when the second received signal is received immediately before the first received signal, for two adjacent received signals before the first received signal, such as the second received signal and the third received signal adjacent thereto, (1) calculation of the frequency spectra of the two signals by a frequency spectrum calculation unit, (2) the two frequencies F by a signal information acquisition unit Bj ,F Bk and two power values P Bj ,P Bk acquisition of information of , and (3) determination of whether the two signal sources are the same by a signal source determination unit, are sequentially performed until it is determined in (3) that the two signal sources are not the same. Thereafter, an interference signal determination unit determines that two adjacent received signals for which it has been determined that the two signal sources are the same are interference signals, and an interference signal suppression unit determines the frequency F in the frequency spectrum Bj ,F Bk suppresses the signal component corresponding to the interference signal of .

[0018] Accordingly, as individual hardware differences existing in an actual chirp sequence radar device, for example, errors may occur in transmitted chirp signals and chirp periods between one device and another device, and even if frequency fluctuation and spectral spreading of a beat signal caused by the chirp signal or the interference signal occur due to such errors, one device can determine two adjacent received signals as interference signals according to the frequency fluctuation and spectral spreading of the beat signal for each other device.

[0019] Furthermore, the technical means of claim 3 described in the claims is adopted. According to this means, the interference signal suppression unit includes a noise power estimation unit, an interference signal detection unit, and an interference signal reduction unit. The frequency F of the frequency spectrum corresponding to the first received signal among the frequency spectra of the two signals is obtained by the noise power estimation unit B1 , a frequency F separated by a predetermined frequency α forward and backward centered on B1+α and the frequency F B1-αDuring this time, (2m+1) signal components are extracted, and these extracted (2m+1) signal components are sorted in descending order of power value. Then, the (m+1)th power value located in the middle of these components is given the frequency F. B1 The noise power is estimated as an estimated value at [location]. The interference signal detection unit sets a predetermined threshold value based on the noise power estimated by the noise power estimation unit, and the frequency F of the second received signal is set based on this predetermined threshold value. B2 The system detects interference signals. The interference signal reduction unit reduces the signal level of the interference signal detected by the interference signal detection unit to an estimated value. Note that "m" is an integer greater than or equal to 1.

[0020] This results in the frequency F of the frequency spectrum of the first received signal. B1 Frequency F centered around B1+α and frequency F B1-α The power value of the median of the signal components extracted during the interval is the frequency F B1 An estimated value of the noise power is calculated, and a predetermined threshold is set based on this estimated value. Then, the interference signal is detected based on this predetermined threshold. Therefore, the reduction by the interference signal reduction unit is tailored to the signal level of each individual interference signal, and is not uniformly reduced across a wide frequency range. [Effects of the Invention]

[0021] In the invention of claim 1, as hardware individual differences exist in actual chirp sequence radar devices, for example, errors may occur in the transmitted chirp signal or chirp period between one device and another, and as a result, frequency fluctuations and spectral broadening of the beat signal due to the chirp signal and interference signal may occur. However, one device will estimate the frequency F according to the frequency fluctuations and spectral broadening of the beat signal of each of the other devices. i This makes it possible to determine the presence of an interfering signal. Therefore, narrowband interference can be accurately suppressed.

[0022] In the invention of claim 2, even if hardware-related individual differences exist in actual chirp sequence radar devices, such as errors in the transmitted chirp signal or chirp period between one device and another, which may result in frequency fluctuations and spectral broadening of the beat signal due to the chirp signal or interference signal, one device can determine that two adjacent received signals are interference signals according to the frequency fluctuations and spectral broadening of the beat signal of each of the other devices. Therefore, narrowband interference can be accurately suppressed.

[0023] In the invention of claim 3, the frequency F of the frequency spectrum of the first received signal B1 Frequency F centered around B1+α and frequency F B1-α The power value of the median of the signal components extracted during the interval is the frequency F B1 An estimated value of the noise power is calculated, and a predetermined threshold is set based on this estimated value. Then, the interference signal is detected based on this predetermined threshold. Therefore, the reduction by the interference signal reduction unit is tailored to the signal level of each individual interference signal, and does not result in a uniform reduction across a wide frequency range. Consequently, excessive suppression of narrowband interference can be avoided. [Brief explanation of the drawing]

[0024] [Figure 1] Figure 1(A) is a block diagram showing an example configuration of a chirp sequence radar device (this device) according to one embodiment of the present invention. Figure 1(B) is an explanatory diagram showing an example of narrowband interference using received signals and generated beat signals received by the chirp sequence radar device. [Figure 2] These are frequency spectrum diagrams showing the frequency spectrum when narrowband interference occurs. Figure 2(A) shows the case when the measurement range (measurable distance) is 12m, and Figure 2(B) shows the case when the measurement range (measurable distance) is 40m. [Figure 3]Figure 3(A) is a schematic diagram illustrating the basic concept of the narrowband interference suppression method in this embodiment. Figure 3(B) is a schematic diagram of a chirp signal transmitted from the chirp sequence radar device of this embodiment. Figure 3(C) is a schematic diagram illustrating an example of frequency fluctuation of a beat signal obtained from the chirp sequence radar device of this embodiment. [Figure 4] This is a flowchart showing the flow of the narrowband interference suppression process (part 1) performed in the chirp sequence radar device of this embodiment. [Figure 5] Figure 4 is a flowchart showing the flow of interference signal suppression processing. [Figure 6] This is a flowchart showing the flow of the narrowband interference suppression process (part 2) performed in the chirp sequence radar device of this embodiment. [Figure 7] Figure 7(A) is an explanatory diagram showing an example of estimating the frequency characteristics of noise power by median detection in the interference signal suppression process shown in Figure 5. Figure 7(B) is a frequency spectrum diagram showing the frequency spectrum when narrowband interference occurs, with the black line representing the case when narrowband interference suppression is performed using the narrowband interference suppression process shown in Figure 4, and the gray line representing the case when it is not performed. [Modes for carrying out the invention]

[0025] Hereinafter, embodiments of the chirp sequence radar device of the present invention will be described with reference to the figures. The chirp sequence radar device 10 of this embodiment (hereinafter, the chirp sequence radar device may be referred to as the "CS device") is, for example, an on-board radar mounted on a vehicle with an autonomous driving function, and is a millimeter-wave radar in the 79 GHz band that measures the distance between the vehicle and targets (objects) such as other vehicles or pedestrians located in front of or to the side of the vehicle.

[0026] [Hardware configuration of CS device 10] As shown in Figure 1(A), the CS device 10 of this embodiment mainly consists of a DSP 11, WFG 12, VCO 13, PA 14, LNA 15, mixer 16, LPF 17, ADC 18, etc. Note that the transmitting and receiving antennas are omitted in this figure.

[0027] The DSP11 is a digital signal processing unit that generates voltage control signals to the WFG12, outputs commands to the PA14 to control whether or not high-frequency signals can be amplified, and performs Fast Fourier Transform (FFT) calculations on beat signals converted into digital signals by the ADC18. The DSP11 has on-chip memory and also has the functionality of a control unit capable of performing narrowband interference suppression processing, which will be described later. If such control unit functionality is not available, a separate CPU and semiconductor memory (not shown in the diagram) are provided in addition to the DSP11.

[0028] WFG12 is a waveform generator that generates a voltage control signal based on a command output from DSP11. In this embodiment, for example, it generates a voltage control signal that increases and decreases repeatedly at a predetermined period (e.g., 30 μs (microseconds)) in the shape of a right-angled triangle with a rising voltage (increasing linearly from the starting voltage to the right as time progresses, then rapidly decreasing back to the starting voltage), and outputs it to VCO13. Note that WFG12 is not required if DSP11 performs the function of WFG12.

[0029] VCO13 is a voltage-controlled oscillator whose oscillation frequency changes according to the voltage value of the voltage control signal output from WFG12. In this embodiment, since the voltage value of the voltage control signal changes in a right-angled triangle shape sloping upwards to the right, the oscillation frequency of VCO13 changes in a sawtooth waveform shape that increases over time. In other words, a high-frequency signal (up-chirp signal) modulated with a frequency that changes in a sawtooth waveform shape with a constant sweep period (e.g., 30 μs) is output. The high-frequency signal is branched to PA14 and mixer16 and is constantly output from VCO13. Therefore, it is possible to generate a beat signal from the received signal even during the pause period when transmission is suspended, as described later. If VCO13 cannot oscillate at the target transmission frequency (e.g., 79 GHz band), a frequency multiplier circuit (not shown in the figure) is provided on the output side.

[0030] Note that the chirp signal may also be a downward-sloping down-chirp signal. That is, the WFG12 or DSP11 may be configured to generate a voltage control signal that repeatedly decreases and increases at a predetermined period (e.g., 30 μs) in a right-angled triangle shape with a downward slope (decreasing linearly from the decreasing starting voltage over time, then rapidly increasing back to the decreasing starting voltage), and output this to the VCO13. Hereafter, when simply referred to as "chirp signal" without specifying up or down, it should be noted that both up-chirp signals and down-chirp signals may be included.

[0031] PA14 is a power amplifier that amplifies the high-frequency signal output from VCO13 to a predetermined power, and amplifies the high-frequency signal according to the command input from DSP11 to output a transmit signal, i.e., a chirp signal. Therefore, PA14 also functions as a switch to turn the transmission of the chirp signal on and off, and does not transmit the chirp signal amplified to the predetermined power during the pause period when transmission is suspended, as described later. In this embodiment, for example, a transmit signal with a transmit power of 10mW (+10dBm) is output to a transmitting antenna not shown in the figure.

[0032] LNA15 is a low-noise amplifier that amplifies the received signal output from the receiving antenna (not shown in the figure) with low noise. In this embodiment, the received signal is a target signal, such as a chirp signal transmitted toward a target that is reflected back by the target, or a chirp signal (interference signal) transmitted from another CS device.

[0033] Mixer 16 is a multiplier that generates and outputs a beat signal by mixing the amplified received signal output from LNA 15 with the high-frequency signal (chirp signal) output from VCO 13. In this case, the chirp signal from VCO 13 contributes to the generation of the beat signal as a local signal.

[0034] The LPF17 filters the beat signal output from the mixer 16 to a preset cutoff frequency (f c This is a low-pass filter that allows beat signals lower than ) to pass through. The beat frequency of the beat signal increases as the separation distance between the CS device 10 and the target increases, and decreases as the separation distance decreases. Therefore, the cutoff frequency of the LPF 17 is determined based on the measurable separation distance required for the CS device 10.

[0035] The ADC18 is an A / D converter that converts the analog beat signal output from the LPF17 into a digital signal (a digital beat signal) and outputs it to the DSP11. The digital signal input to the DSP11 is subjected to a Fast Fourier Transform by the DSP11, as described later, to determine the separation distance between the CS device 10 and the target, etc.

[0036] [Narrowband interference in CS device 10] In this embodiment, the CS device 10 is configured such that the WFG12 generates a sawtooth wave control voltage that repeats a right-angled triangle shape with a voltage value that rises (or falls) to the right. When this is input to the VCO13, the VCO13 outputs a frequency-modulated chirp signal, which is transmitted as a transmission signal via the PA14. This transmission signal (chirp signal) is reflected by the target and received by the CS device 10 as a received signal (target signal) after a delay time proportional to the distance d from the target. Then, the target signal S t When this signal is input to the mixer 16 via the LNA 15, the local signal (chirp signal S) input to the mixer 16 is then processed. s ) is multiplied by a beat signal B with a beat frequency proportional to the delay time and separation distance d. t This is output from the mixer 16.

[0037] Here, if another vehicle (another vehicle) equipped with a different CS device 100 having the same specifications as CS device 10 is driving near the vehicle equipped with CS device 10 (the vehicle itself), then the other CS device 100 will also use the same frequency band, for example, the 79GHz band, as the vehicle's CS device 10 uses. In other words, if two CS devices 10 and 100 located within a measurable separation distance use the same frequency band, the chirp signal S transmitted from the other CS device 100 will be used. g The vehicle's own CS device 10 may directly receive the chirp signal S from another CS device 100. g When the vehicle's CS device 10 receives this signal, it is also input to the mixer 16 via the LNA 15, and the local signal (chirp signal S) input to the mixer 16 is then processed. s ) is multiplied by a beat signal B with a beat frequency that is completely independent of the distance between your vehicle and other vehicles. g This will be output from the mixer 16.

[0038] And this beat signal B g The beat frequency is the cutoff frequency f of LPF17. c When the value is lower than the target signal S that should be received, t Beat signal B tSimilarly to the above, the chirp signal (interference signal) S transmitted by another CS device 100 g beat signal B g will also be input to the DSP 11 via the ADC 18. Therefore, the narrowband interference described in the "Background Art" section occurs.

[0039] That is, as shown in the upper part of FIG. 1(B), the black solid line represents the chirp signal S s , the black broken line represents the target signal S t , the gray solid line represents the interference signal S g , each of which represents a sawtooth wave, and all of them have a sweep bandwidth f s , sweep time T s , period time T p and repeats. The sawtooth wave of the target signal S t is delayed by a delay time τ with respect to the sawtooth wave of the chirp signal S s delay time τ t , and the sawtooth wave of the interference signal S g is delayed by a delay time τ with respect to the sawtooth wave of the chirp signal S s delay time τ g In this example, the target signal S t delay time τ t interference signal S is larger than g delay time τ g is larger (τ t <τ g ), and the interference signal S g is received with a delay. A beat signal having a frequency f proportional to the magnitude of these delay times B appears, an example of which is shown in the lower part of FIG. 1(B).

[0040] As shown in the lower part of FIG. 1(B), the interference signal S g has a larger delay time τ than the target signal S t delay time τ g is larger, so the interference signal S g beat signal B g is higher in frequency than the beat signal B of the target signal S t beat signal B t although its frequency is higher, there are periods where it is lower than the cut-off frequency f of the LPF 17 c there is a period where it is lower than that. Therefore, the beat signal B t , B gHowever, all of these have a beat frequency f Bt ,f Bg ( <f c During the period when the sawtooth wave frequency increases linearly, that is, in the up-chirp section (or down-chirp section) where the sawtooth wave frequency increases linearly, the target signal S t and interference signal S g After both of them pass through LPF17, they are converted to digital signals by ADC18 and input to DSP11. Then these beat signals B t ,B g When subjected to a Fast Fourier Transform, it appears as a frequency spectrum as shown in Figures 2(A) and 2(B).

[0041] Figure 2(A) shows the case when the measurement range (measurable distance) is 12m, and Figure 2(B) shows the case when the measurement range (measurable distance) is 40m. In Figure 2(A), the solid black line indicates the absence of narrowband interference, i.e., the interference signal S g The gray solid line indicates the absence of interference, while the gray solid line indicates the presence of narrowband interference (ghost signal). Note that the power (dB) on the vertical axis is based on the minimum value "1" of the ADC18 output (0dB).

[0042] In Figure 2(A), where there is no narrowband interference (black solid line), the target signal S t As a frequency spectrum that can correspond to this, one target has been observed at a distance of approximately 4.2m and another at a distance of approximately 10m. In contrast, in the case of the gray solid line with narrowband interference, the interference signal S g As a frequency spectrum that may correspond to this, two ghost targets have been observed at distances of approximately 2.2m and 6.5m, which are targets that do not actually exist. In addition, the target signal S t As a frequency spectrum that could correspond to this, one target has been observed at a distance of approximately 10m, but two others at a distance of around 4.2m are mixed in with the noise level, which has been increased due to a surge in noise levels near the ghost target at a distance of approximately 6.5m.

[0043] In Figure 2(B), the interference signal S g This is a case where narrowband interference occurs due to the presence of the target signal S t As frequency spectra that may correspond to this, four targets have been observed within a distance of approximately 5-10m, and one target at a distance of approximately 30m. In addition, interference signals S g As a frequency spectrum that may correspond to this, one ghost target was observed at a distance of approximately 23m. Note that the power (dBm) on the vertical axis is based on 1mW as the reference (0dBm). From these two frequency spectrum diagrams (Figure 2(A), B)), the interference signal S g Ghost targets, as a result of this process, have frequency spectrum peaks that are significantly larger than the noise level and can also be larger than the target being observed. Therefore, even if the target is detected based on a threshold that is significantly larger than the noise level, there is a high probability of falsely detecting ghost targets.

[0044] By the way, as already mentioned in the section on [Problems the invention aims to solve], in the example above, when there are other vehicles near one's own vehicle and each is equipped with CS devices 10 and 100 with the same hardware specifications, in reality there are considerable individual differences in hardware between each device. Therefore, in this example, errors may occur in the chirp signals and their period times transmitted from the CS device 10 of the own vehicle and the CS device 100 of the other vehicle. Even if the hardware characteristics of these CS devices 10 and 100 were all the same, it is considered almost impossible for the chirp signals and their period times transmitted from both devices to perfectly match due to differences in the surrounding environment (temperature, humidity, vibration, power supply status, etc.) and changes over time.

[0045] Therefore, for example, CS devices 10 and 100 will have different chirp rates (instantaneous rate of change of frequency) in the chirp signals they transmit due to individual hardware differences. The difference in chirp rate, that is, the difference in the angle of the hypotenuse of the sawtooth wave that forms the chirp signal, results in interference signals S in narrowband interference that occur when CS device 10 receives a chirp signal transmitted from CS device 100. g and chirp signal S s Beat signal B generated by g Beat frequency f Bg It will have an impact.

[0046] Now, return to Figure 1(B) and refer to the lower part of the figure. The up-chirp section (sweep time T) in which the frequency of the transmitted signal increases. s The beat frequency f obtained from ) B f is given by the following equation (1). s is the sweep bandwidth, T s d is the sweep time, d is the distance from the target, and c is the speed of light. Therefore, (f s / T s ) is the chirp rate, and (2d / c) is the target signal S t Delay time τ t Therefore, the beat frequency f can be found by dividing twice the separation distance d by the speed of light c. B This is the chirp rate (=f s / T s ) with delay time τ t It can be found by multiplying by (=2d / c).

[0047] As mentioned above, the CS device 10,100 is a millimeter-wave radar in the 79 GHz band, so the sweep bandwidth f s It has a very wide bandwidth and can be set to, for example, 3 GHz. Also, the sweep time T s For example, it is set to 30 μs. Therefore, the chirp rate (= f s / T s ) is 3 × 10 9 / 3×10 -6 = 1 × 10 15 It becomes (Hz / s). Beat frequency f B This is the chirp rate (=f s / Ts It can be calculated by multiplying (2d / c) by (2d / c), but the speed of light c is approximately 3 × 10⁻⁶ 8 Since it is m / s, the beat frequency f B It is almost entirely dominated by the chirp rate. 7 ~10 8 It is on the order of Hz. Therefore, the difference in chirp rate between CS devices 10 and 100 due to individual hardware differences results in a beat frequency f B This has a significant impact, and it also affects the magnitude of the slope of the linear function, which will be discussed later.

[0048] f B ≒ (f s / T s )·(2d / c) … (1)

[0049] Note that this equation (1) corresponds to equation (3) disclosed in the above-mentioned Patent Document 1 (Japanese Patent Application Publication No. 2022-108640), where the sweep bandwidth f s Herein are the sweep frequency width Δf and the sweep time T. s The transmission period ΔT is represented by R, and the distance d from the target is represented by R. Furthermore, the basic operation and principles of the CS device are explained in detail in the section "(Operation of Chirp Sequence Radar Device)" of the above-mentioned Patent Document 1, so please refer to that.

[0050] [Narrowband interference suppression method] Here, referring to the schematic diagram in Figure 3, the basic concept of the narrowband interference suppression method in this embodiment will be explained. Here again, we will explain the case where other vehicles are located near the vehicle in question, and each is equipped with CS devices 10 and 100 with the same hardware specifications, as illustrated earlier. Note that CS device 100 differs from CS device 10 in this embodiment in its software configuration and settings.

[0051] The vehicle's CS device 10 sends a chirp signal S towards the target. s S chirp signal that transmits s The transmission sequence consists of seven chirp signals S s After or before continuously transmitting a chirp signal S sThe transmission is paused for the same amount of time that the first chirp signal S is transmitted. In the example shown in Figure 3(A), the CS device 10 transmits the first chirp signal S s1 Transmission is paused during the period when the signal S is transmitted, and the chirp signal S is transmitted during the 2nd to 8th periods. s2 ~S s8 It sends the 9th chirp signal S. s9 After suspending transmission during the period in which the chirp signal S is transmitted, the chirp signal S is transmitted during the 10th to 16th periods. s10 ~S s16 Send this. Repeat this from the 17th period onward.

[0052] Meanwhile, the CS device 100 of another vehicle sends a chirp signal S towards the target. g The sequence for transmitting 17 chirp signals S g After continuously transmitting the signals, the transmission is paused for a predetermined time. In the example shown in Figure 3(B), the CS device 100 transmits the 1st to 17th chirp signals S g1 ~S g17 The following signals are transmitted continuously. Then, after a predetermined pause in transmission, the 18th to 34th chirp signals S are transmitted. g18 ~S g34 After continuously transmitting, transmission is paused for a predetermined time. This is repeated from the 35th signal onward. Figure 3(B) shows the chirp signals S from the 18th signal onward. g18 These are not shown in the illustration.

[0053] In this way, CS devices 10 and 100 receive a chirp signal S s ,S g When each of these signals is transmitted, narrowband interference occurs in both CS devices 10 and 100. Here, we will describe the narrowband interference in the CS device 10 of this embodiment installed in the vehicle. As mentioned above, the CS device 10 of the vehicle transmits seven chirp signals S s After or before continuously transmitting a chirp signal S s The transmission is paused for the same amount of time that the signal S is transmitted. Therefore, during this transmission pause period, the CS device 10 itself transmits the chirp signal S sSince it is not transmitting, the chirp signal S transmitted from other CS devices 100 etc. g It will become possible to receive only that.

[0054] In other words, the CS device 10 receives the chirp signal S s As described above, the DSP11 controls the PA14 so that transmission periods in which multiple signals are transmitted consecutively and pause periods in which this transmission is paused alternate. As a result, the pause periods occur at regular intervals, and the chirp signal S transmitted from other CS devices 100 etc. g These can be received as two or more interference signals. For example, in the example shown in Figures 3(A) and 3(B), the CS device 10 receives the first chirp signal S s1 The period for transmitting the 9th chirp signal S s9 During the period when transmission was suspended, the chirp signals that were transmitted from the CS device 100 during these periods were respectively interrupted by interference signals S. g3 ,S g11 It becomes possible to receive it as such.

[0055] Then, as shown in Figure 3(C), these interference signals S g3 ,S g11 Beat signal B generated by g The frequency spectrum of the interference signal S g3 The corresponding beat frequency f Bg3 (≠f Bg11 ) and interference signal S g11 The corresponding beat frequency f Bg11 (≠f Bg3 ) These are different beat frequencies f, represented by gray-colored circles. Bg3 ,f Bg11 This has been observed as follows: This means that at least the chirp signal S s1 ,S s9 Interference signal S at each timing (period) of transmission g3 ,S g11 It can be seen that narrowband interference is occurring due to this.

[0056] Also, the beat frequency f is indicated by the gray circle.Bg3 ,f Bg11 Because the frequencies in the frequency spectrum are different, the beat frequency f B This is moving over time. Such a beat signal B g The frequency fluctuation is the beat frequency f of CS device 10 and CS device 100. B This is due to the fact that they do not match each other. Specifically, the beat signal B of the CS device 10 t Beat frequency f Bt =( f s / T s )·τ t And the beat signal B of CS device 100 g Beat frequency f Bg =( f s ' / T s ')·τ g This refers to the chirp rate (f) of both parties. s / T s )≠(f s ' / T s ') does not match due to individual hardware differences. Therefore, such differences in chirp rate affect the beat signal B of CS device 100. g Beat frequency f Bg This is the cause of the beat frequency f, which varies linearly with respect to time (as a linear function of time). Bt This changes over time.

[0057] In response, the CS device 10 transmitted a chirp signal S s2 ~S s8 ,S s10 ~S s16 The target signal S is reflected back from the target. t2 ~S t8 ,S t10 ~S t16 If the target signal is stationary, the beat signal B generated by it is... t The frequency spectra of all of them have the same beat frequency f Bt It remains stationary and does not move over time. The chirp signal S transmitted by CS device 10 s2 And so on, the target signal S that is reflected back from the target. t2Since these signals were transmitted from the same CS device 10 (the same unit), the shape of the sawtooth wave is exactly the same, even with a time delay. Therefore, the chirp signal S s2 etc. and target signal S t2 etc. are chirp rate (f s / T s )=(f s / T s ) is the same, so the beat frequency f is the same each time regardless of the passage of time. Bt It will become.

[0058] Beat signal B where narrowband interference occurs g frequency f Bg This is the chirp signal S transmitted by the CS device 10,100. s ,S g Depending on the magnitude of the difference in chirp rates, it changes gradually (over time) at different rates. In other words, the chirp signal S of the CS device 10 s and interference signal (chirp signal) S from CS device 100 g Beat signal B generated between g frequency f Bg This changes over time depending on the magnitude of the difference (error) in the chirp rate between the two. Therefore, its frequency f Bg The change in time can be represented by a linear function, and the difference in the chirp rates of the two functions becomes the slope of that linear function. Such linear functions and their slopes can be pre-defined as typical or similar examples through methods such as computer simulations or experiments.

[0059] Therefore, in the narrowband interference suppression method of this embodiment, the beat frequency f is determined using such a linear function and its slope. B The beat signal B fluctuates. g Interference signal S in the frequency spectrum of such frequencies g The frequency is estimated to track the corresponding ghost target, and its signal level is reduced to suppress narrowband interference. In the CS device 10 of this embodiment, the DSP 11 performs narrowband interference suppression processing so that this method can be implemented.

[0060] [Narrowband interference suppression processing by CS device 10 (Part 1)] Next, we will explain the narrowband interference suppression process (part 1) executed by DSP11. The flow of this narrowband interference suppression process is shown in Figures 4 and 5, so we will explain it from here on while referring to Figures 4 and 5. This narrowband interference suppression process is performed by executing the narrowband interference suppression program (part 1) stored in the semiconductor memory such as the on-chip memory of DSP11. If it is functionally difficult for DSP11 to execute such a program, a CPU (not shown in the figure), which is provided separately from DSP11, will execute the narrowband interference suppression program (part 1) (the same applies to the narrowband interference suppression program (part 2) described later).

[0061] As shown in Figure 4, in this process (part 1), when the process starts (START), the beat signal acquisition process is first performed in step S101. The DSP11 converts the beat signal B into a digital signal (digital data) by the ADC18. t ,B g The beat signal B is input as it is received and stored in a predetermined area of ​​memory. Therefore, in this process, the beat signal B that has already been stored in the predetermined area of ​​memory is used. t ,B g The system acquires data such as the following. Strictly speaking, this data is very recent past data on the order of milliseconds, received when the CS device 10 transmitted the chirp signal or immediately before transmitting it. However, the driver of the vehicle receives the beat signal B from the CS device 10. t ,B g Data such as these is acquired and processed in real time.

[0062] In the next step, S103, beat signal FFT processing is performed. This processing is performed on the beat signal B acquired in step S101. t ,B g The Fast Fourier Transform (FFT) operation is performed on the data. The beat signal B after the Fast Fourier Transform is obtained. t ,B g The frequency spectrum of the target signal S t or interference signal S gThe frequency spectrum of the corresponding signal component appears.

[0063] In the following step S105, the frequency and power value information acquisition process is performed. This process converts the beat signal B into a frequency spectrum. t ,B g From this information, the information necessary for the determination processes in steps S107 and S109 is obtained.

[0064] For example, as mentioned above, the CS device 10 receives the first chirp signal S s1 and the 9th chirp signal S s9 Because transmission is suspended during the period when the signal is being transmitted (see Figure 3(A)), the interference signal S received during this period is not transmitted. g3 ,S g11 Two beat signals B are generated by this process. g The beat frequency f (shown by the gray circle in Figure 3(C)) Bg3 ,f Bg11 And the power value p as the signal level of that. Bg3 ,p Bg11 To obtain and

[0065] In step S107, a frequency determination process is performed. This process involves the interference signal S received during the period when transmission was suspended. g3 ,S g11 Beat signal B corresponding to g Beat frequency f Bg3 ,f Bg11 A determination is made as to whether the absolute value of the difference is less than a predetermined frequency ΔF. Beat signal B g This is because, if the interference signal source that generated these beats is the same, it is highly likely that these beat frequencies will be relatively close in value.

[0066] However, as mentioned above, the CS device 10 of the vehicle itself and the CS device 100 of the other vehicle will have their beat signals B depending on the magnitude of the difference (error) in their chirp rates. g Beat frequency f Bg3 ,f Bg11 This changes over time (as shown in the beat signal B in Figure 3(C)). gTherefore, the time-varying beat signal B g frequency f Bg While it is possible to collect a large amount of data from actual machines (real data) and, for example, apply the least squares method based on that real data to determine the linear function, in this embodiment, a function approximation can also be used, which is simpler but can be equivalent to the linear function.

[0067] Furthermore, by using a linear function obtained by applying the least squares method, etc., two beat frequencies f Bg3 ,f Bg11 The frequency difference ΔF, which is the difference between the two beat frequencies, can also be easily obtained. However, in this embodiment, for example, the average or maximum value of the data accumulated as the difference between the two beat frequencies, and the interference signal S are obtained. g Beat signal B corresponding to g The frequency fluctuation rate per unit time is calculated using the average value of accumulated data, or based on computer simulations, experiments, etc.

[0068] In the previous example, the first chirp signal S s1 The transmission was paused and the received interference signal S g3 Beat signal B corresponding to g The beat frequency is f Bg3 And the 9th chirp signal S s9 The transmission was paused and the received interference signal S g11 Beat signal B corresponding to g The beat frequency is f Bg11 Therefore, F(1)=f Bg3 ,F(9)=f Bg11 Therefore (n=1, k=8), |F(n)-F(n+k)|=|F(1)-F(9)|=|f Bg3 -f Bg11 |<ΔF is determined.

[0069] Note that the chirp signal S s Chirp signals S that arrive between the period when transmission is suspended and the period when transmission will be suspended again. s The value of k is the sum of the number of transmission periods and the number of pause periods (1 + 7 = 8).

[0070] Then, this frequency determination process determines that if the absolute value of the difference between the two beat frequencies F(n)-F(n+k) is not smaller than (larger than) a predetermined frequency difference ΔF (S107; No), then these two beat frequencies are likely from different and separate interference signal sources and not from the same CS device 100, etc. Therefore, this process (part 1) is terminated (END). On the other hand, if the absolute value of the difference between the two beat frequencies F(n)-F(n+k) is smaller than a predetermined frequency difference ΔF (S107; Yes), then these two beat frequencies may be from the same interference signal source, and the process proceeds to the determination process in step S109.

[0071] In step S109, a power value determination process is performed. This process uses the two beat frequencies f determined in step S107. Bg3 ,f Bg11 Beat signal B in g The system determines whether the absolute value of the difference in power values ​​as intensity or signal level is less than a predetermined power value ΔP. Beat signal B g If the interference signal source that generated these beat signals B is the same, then these beat signals B g The power values, which represent the intensity or signal level, are likely to be very close to the same value. ΔP is the two beat frequencies f Bg3 ,f Bg11 Beat signal B in g This is a predetermined error, expressed as the difference in power value as the intensity or signal level. For example, two beat signals B g It is determined based on the average and maximum values ​​of data accumulated as differences in power values ​​as signal intensity or signal level.

[0072] In the previous example, the first chirp signal S s1 Beat signal B corresponding to g Beat frequency f Bg3 The power value in p Bg3 And the 9th chirp signal S s9 Beat signal B corresponding to g Beat frequency f Bg11 The power value in p Bg11Therefore, P(1)=p Bg3 ,P(9)=p Bg11 Since this is the case (n=1, k=8), in step S109, |P(n)-P(n+k)|=|P(1)-P(9)|=|p Bg3 -p Bg11 |<ΔP is determined.

[0073] Then, in this power value determination process, if the absolute value of the difference between the two power values ​​P(n)-P(n+k) is not smaller than (larger than) a predetermined power value difference ΔP (S109; No), it is highly likely that these two power values ​​are from different and separate interference signal sources and are not interference signals transmitted from the same CS device 100, etc. Therefore, this process (part 1) is terminated (END). On the other hand, if the absolute value of the difference between the two power values ​​P(n)-P(n+k) is smaller than a predetermined power value difference ΔP (S109; Yes), it is highly likely that these two power values ​​are from the same interference signal source.

[0074] This allows interference signals S received during the period when transmission was suspended. g3 ,S g11 And the corresponding beat signal B g Beat frequency f Bg3 ,f Bg11 These are highly likely to have been transmitted from the same interference signal source. Therefore, we can confirm that they are a pair. Thus, the next step is to examine the interference signal S between this pair. g Beat signal B corresponding to g Beat frequency f B To obtain this information, we proceed to the next step, S111, which involves frequency estimation.

[0075] In step S111, a frequency estimation process is performed. This process involves determining the two beat frequencies f that have been determined to be a pair. Bg3 ,f Bg11 That is, interference signals S transmitted from the same interference signal source at frequencies F(2) to F(k) between F(1) and F(1+k). g4 ,S g5 ,S g6 ,Sg7 ,S g8 ,S g9 ,S g10 Beat signal B corresponding to e Beat frequency f Be The beat frequency f is estimated. Be The estimation of is performed using a function approximation that can correspond to the linear function mentioned above, F(n+1)=F(1)+(F(1+k)-F(1))×(n+1) / N. In the previous example, F(2)~F(8) are expressed as follows (N=9, n=1~7, k=8). n starts from "1" and is incremented by the increment process in step S117 (n=n+1).

[0076] F(2) = F(1)+(F(9)-F(1))×2 / 9 = f Bg3 +(f Bg11 -f Bg3 ) × 2 / 9 F(3) = F(1)+(F(9)-F(1))×3 / 9 = f Bg3 +(f Bg11 -f Bg3 ) × 3 / 9 F(4) = F(1)+(F(9)-F(1))×4 / 9 = f Bg3 +(f Bg11 -f Bg3 ) × 4 / 9 F(5) = F(1)+(F(9)-F(1))×5 / 9 = f Bg3 +(f Bg11 -f Bg3 ) × 5 / 9 F(6) = F(1)+(F(9)-F(1))×6 / 9 = f Bg3 +(f Bg11 -f Bg3 ) × 6 / 9 F(7) = F(1)+(F(9)-F(1))×7 / 9 = f Bg3 +(f Bg11 -f Bg3 ) × 7 / 9 F(8) = F(1)+(F(9)-F(1))×8 / 9 = f Bg3 +(f Bg11 -f Bg3 ) × 8 / 9

[0077] Note that interference signal S g4 ~S g10 The CS device 10 receives the signal, and the beat frequencies f estimated in F(2) to F(8) are respectively Be Beat signal B e is the interference signal S g4 ~S g10 and the chirp signal S of the CS device 10 s It is generated by the following. In Figures 3(B) and 3(C), for example, the interference signal S g4 The circle mark shown at the bottom of the page indicates that the CS device 10 receives interference signal S g4 Beat signal B generated by receiving the signal B g This indicates that...

[0078] Similarly, interference signal S g5 The circle mark shown at the bottom of the page indicates that the CS device 10 receives interference signal S g5 Beat signal B generated by receiving the signal B g The fact that, and the interference signal S g6 The circle mark shown at the bottom of the page indicates that the CS device 10 receives interference signal S g6 Beat signal B generated by receiving the signal B g This indicates that, in the direction of time progression, the interference signal S g17 The circle mark shown at the bottom of the page indicates that the CS device 10 receives interference signal S g17 Beat signal B generated by receiving the signal B g This indicates that...

[0079] In Figure 3(C), each of these beat signals B g The beat frequency f is linearly (sloping upwards to the right) along a dashed line in the direction of time progression. B The level is increasing. This is because, as will be explained later, these interference signals S g The chirp rate of the CS device 100 that transmits and these interference signals S g This is because it differs from the chirp rate of the receiving CS device 10. In this example, the beat frequency f BThese lines are arranged in a straight line that slopes upward to the right in the direction of time progression, but they can also be arranged in a straight line that slopes downward to the right in the direction of time progression. Furthermore, the angle of inclination of the lines varies, from small to large.

[0080] In the next step, S113, a power value determination process is performed. This process uses the beat frequency f estimated in step S111. Be , that is, the beat signal B in F(2)~F(8) g The power value, which represents the intensity or signal level, is converted into a frequency spectrum beat signal B, similar to the frequency / power value information acquisition process in step S105. g The information is obtained from the following: Then, the beat signal B at power value P(n+1) g The system determines whether the absolute difference between the power value (as an intensity or signal level) and the power value being compared is less than a predetermined power value ΔP.

[0081] Beat signal B g If the interference signal source that generated these beat signals B is the same, then these beat signals B g The power values, which represent the intensity or signal level, are likely to be approximately the same or close to the same value. ΔP is, for example, the power values ​​of two beat signals B g This is determined based on the average and maximum values ​​of the data accumulated as the difference in power values ​​as intensity or signal level. This determination is made by |P(n+1)-(P(1)+P(1+k)) / 2|<ΔP. In other words, the two beat frequencies f used in the power value determination process in step S109 B Power value p B The determination is made by whether the absolute value of the difference from the average value (the power value being compared) is less than the power value ΔP. In the previous example, the beat frequency f Bg3 Power value p Bg3 and beat frequency f Bg11 Power value p Bg11 The determination is made by whether the absolute value of the difference with respect to the mean is less than the power value ΔP. P(2) to P(8) are expressed as follows (n=1 to 7, k=8).

[0082] |P(2)-(P(1)+P(9)) / 2| = |P(2)-(pBg3 +p Bg11 ) / 2|<ΔP |P(3)-(P(1)+P(9)) / 2| = |P(3)-(p Bg3 +p Bg11 ) / 2|<ΔP |P(4)-(P(1)+P(9)) / 2| = |P(4)-(p Bg3 +p Bg11 ) / 2|<ΔP |P(5)-(P(1)+P(9)) / 2| = |P(5)-(p Bg3 +p Bg11 ) / 2|<ΔP |P(6)-(P(1)+P(9)) / 2| = |P(6)-(p Bg3 +p Bg11 ) / 2|<ΔP |P(7)-(P(1)+P(9)) / 2| = |P(7)-(p Bg3 +p Bg11 ) / 2|<ΔP |P(8)-(P(1)+P(9)) / 2| = |P(8)-(p Bg3 +p Bg11 ) / 2|<ΔP

[0083] Then, if this power value determination process determines that the absolute value of the difference between the two power values ​​(P(n+1)-(P(1)+P(1+k)) / 2) is not smaller than (larger than) a predetermined power value difference ΔP (S113; No), then the beat signal B of that power value P(n+1) is determined. g This is likely due to another interference signal or target signal, and is not an interference signal transmitted from the same CS device 100, etc. In such cases, it is unlikely to be the cause of narrowband interference, so the next frequency F(n) is estimated without subjecting it to interference signal suppression processing in step S200. Therefore, the process proceeds to step S111 via the increment processing in step S117.

[0084] In contrast, if the absolute value of the difference between the two power values ​​(P(n+1)-(P(1)+P(1+k)) / 2) is smaller than the predetermined power value difference ΔP (S113; Yes), then the beat signal B of that power value P(n+1) gIt is highly likely that these signals were transmitted from the same interfering signal source and are also likely to cause narrowband interference. Therefore, this beat signal B g The interference signal S appearing in the frequency spectrum g The signal component corresponding to this becomes the target of suppression (suppression target) by the interference signal suppression process in step S200. Therefore, in step S113, the beat frequency f Bg3 ,f Bg11 After setting the interference signal flag and interference signal map to "1" to indicate the presence of an interference signal, the process proceeds to step S200. The interference signal flag and interference signal map are set to a predetermined value, such as the beat frequency f. Bg1 ~f Bg99 Therefore, the information for no interference signal is initially set to "0". The details of this interference signal suppression process will be explained later.

[0085] Note that the beat signal B at power value P(n+1) g The power value to be compared (the power value to be compared) to the power value as intensity or signal level is the two beat frequencies f used in the power value determination process in step S109. B Power value p B We used the mean values ​​of (P(1) and P(1+k)), but you could also use P(1) or P(1+k), for example. For example, in the previous example, P(1)=p Bg3 Or P(9)=p Bg11 It may be used as a power value to compare only one of the two.

[0086] Once the interference signal suppression processing in step S200 is complete, step S115 performs a termination determination process for this process. Specifically, it is determined whether the necessary interference signal suppression processing has been performed for the frequencies F(2) to F(k) between the two beat frequencies F(1) and F(1+k) that have been confirmed to be a pair. For example, the determination is made by whether the counter value, which starts from n=1, exceeds a termination determination value (7 in this embodiment) that is set based on the number of beat frequencies F(2) to F(k). If the termination determination value is not exceeded (S115; No), the process proceeds to the frequency estimation process in step S111 after going through the increment process (S117). As a result, the processes in steps S111 and S113 described above are performed for the next beat frequency F(3), etc. On the other hand, if the termination determination value is exceeded (S115; Yes), this process (part 1) is terminated (END).

[0087] Furthermore, in the determination processes S107, S109, and S113 of the narrowband interference suppression process (part 1) shown in Figure 4, the symbol "<" may be replaced with the symbol "≦" to change "less than" to "less than or equal to". Also, in the narrowband interference suppression process (part 1), in Figures 3(A) to (C), the direction in which time progresses, i.e., the chirp signal S s Beat signal B is transmitted sequentially in the direction of transmission. t ,B g Information processing was performed on the above, but conversely, the beat signal B was processed in the direction of time going backward. t ,B g Information processing may be performed on the following:

[0088] In the narrowband interference suppression process (part 1) described above, the first chirp signal S shown in Figure 3(A) s1 and the 9th chirp signal S s9 or interference signal S g3 ,S g11 Related to the beat frequency f Bg3 Beat signal B g and beat frequency f Bg11 Beat signal B g After performing each process according to steps S101 to S109, the interference signal Sg4 ~S g10 Each related beat signal B g Regarding interference signal S g4 ~S g10 The processes in steps S111-S113, S200, and S115 were carried out in that order. In other words, if we focus only on the interference signal, S g3 →S g11 →S g4 →S g5 →S g6 →S g7 →S g8 →S g9 →S g10 The information was processed in the order shown above, but the interference signal S was processed in the opposite order. g11 →S g3 →S g10 →S g9 →S g8 →S g7 →S g6 →S g5 →S g4 The information processing may be performed in the following order.

[0089] In this case, for example, "|F(n)-F(n+k)|<ΔF" in step S107 is replaced with "|F(nk)-F(n)|<ΔF". Also, "|P(n)-P(n+k)|<ΔP" in step S109 is replaced with "|P(nk)-P(n)|<ΔP". Furthermore, "F(n+1)=F(n)+(F(1+k)-F(1))×(n+1) / N (N=9,n=1~7,k=8)" in step S111 is replaced with "F(n-1)=F(n)-(F(1+k)-F(1))×(n-1) / N (N=9,n=9~3,k=8)". In step S113, "|P(n+1)-(P(1)+P(1+k)) / 2|<ΔP (n=1~7,k=8)" is replaced with "|P(n+1)-(P(1)+P(1+k)) / 2|<ΔP (n=7~1,k=8)", and in step S117, "n=n+1" is replaced with "n=n-1".

[0090] [Interference signal suppression processing] Here, the interference signal suppression process in step S200 will be explained with reference to Figures 5 and 7. This interference signal suppression process is performed in the narrowband interference suppression process (part 1) shown in Figure 4 and the narrowband interference suppression process (part 2) shown in Figure 6, which will be described later. In the interference signal suppression process of this embodiment, the interference signal flag and interference signal map (beat signal B) provided from the determination process (S113) in Figure 4 and the determination process (S131) ​​in Figure 6 are used. g Beat frequency f B The beat frequency f to be suppressed is determined by referring to information that explicitly indicates the presence or absence of interference signals. B Identify.

[0091] In the interference signal suppression process of this embodiment, the signal component to be suppressed included in such a frequency spectrum is reduced to, for example, the white noise level by setting an interference detection threshold (a predetermined threshold) described later using, for example, a median filter. In this embodiment, a median filter is used, but the interference detection threshold may be set using, for example, the CFAR (Constant False Alarm Rate) method or its algorithm.

[0092] As shown in Figure 5, in the interference signal suppression process, signal component rearrangement processing is first performed in step S201. This process sets a rearrangement range to positions separated by a predetermined frequency in both the increasing and decreasing directions around a certain frequency, and rearranges the signal components that exist within that range. As shown in Figure 7(A), the frequency spectrum provided in this embodiment has its horizontal axis set to the measurement range (measurable distance), but in this process, this is assumed to be the frequency axis and the rearrangement processing is performed accordingly.

[0093] In the measurement range (measurable distance) corresponding to the frequency axis of the frequency spectrum, a signal component protruding as a thin bar-shaped power value (vertical axis) exists around 23m. Since this signal component has the largest power value, a rearrangement range is set from this point to positions separated by a predetermined frequency in both the increasing frequency direction (to the right on the page) and the decreasing frequency direction (to the left on the page). In this example, a bandwidth of ±7m ((2m+1) signal components) is set as the rearrangement range centered on 23m, and the signal components are rearranged within the range of 16 to 30m. The rearrangement is performed so that the power values ​​of the signal components are ordered from largest to smallest (ascending order (small to large)) within the rearrangement range.

[0094] In the following step S203, noise power estimation processing is performed. In this process, the signal components, which have been sorted in order of power value by step S201, are subjected to median detection, and the power value of the signal component located in the middle ((m+1)th position) is estimated as the noise power estimate (median value (50th percentile ≈ mean value)). In the explanatory diagram shown in Figure 7(A), the median value estimated by the noise power estimation processing is represented by a fine dashed line.

[0095] Then, in the next step, S205, interference signal detection processing, an interference detection threshold (a predetermined threshold) is set based on this estimated value. For example, the interference detection threshold is set to a signal level 10 dB higher than the estimated median value (median value + 10 dB). In the explanatory diagram shown in Figure 7(A), the interference detection threshold estimated by the interference signal detection processing is represented by a dashed line. Then, signal components with peaks larger than this interference detection threshold are detected as interference signal components. As a result, in the measurement range, two interference signal components are detected: one with a peak significantly exceeding the interference detection threshold around 23 m, and another with a peak slightly exceeding the interference detection threshold around 35 m.

[0096] Step S207 performs interference signal reduction processing. This process reduces the signal levels of the interference signal components detected in step S205. The reduction level is set to, for example, a level equivalent to white noise. Excessive signal level reduction, such as reducing it to -110 dBm, may unnaturally lower the level to the level of noise present around the suppressed signal, even partially. Therefore, in this embodiment, the signal level to be suppressed is reduced to a level equivalent to white noise within a necessary and sufficient range and narrow bandwidth. After this processing is complete, the process returns to the narrowband interference suppression processing (part 1) shown in Figure 4 (RETURN).

[0097] By configuring the interference signal suppression process in this way, this embodiment uses a median filter and sets the interference detection threshold to a signal level 10 dB higher than the median value (median value + α (10 dB)). As a result, as shown in Figure 7(A), the median filter is effective in estimating the noise level (fine dashed line in the figure), and is particularly effective when detecting narrowband interference (dashed line in the figure). Furthermore, even if a phenomenon occurs where the noise level increases only around multiple interference signal components that are near the median, such interference signal components can be detected without being missed.

[0098] In radar technology, the CFAR method, for example, has been conventionally used as a common method for setting the detection level of targets, etc. However, as shown in Figure 7(B), which illustrates a frequency spectrum diagram comparing two states before (gray line) and after (black line) narrowband interference suppression, it can be seen that using a median filter to set a threshold for detecting ghost targets due to narrowband interference (within the dashed line in the figure), as in the interference signal suppression process (S200) of this embodiment, is effective.

[0099] [Narrowband interference suppression processing by CS device 10 (part 2)] Next, we will explain the narrowband interference suppression process (part 2) executed by DSP11. The flow of this narrowband interference suppression process is shown in Figure 6, so we will explain it while referring to Figure 6 from here on. This narrowband interference suppression process shares information processing with the previously described narrowband interference suppression process (part 1) in steps S101 to S105, so we will omit the explanation of these parts. This process is performed by executing the narrowband interference suppression program (part 2) stored in the semiconductor memory such as the on-chip memory of DSP11. Also, the beat signal B acquired in step S101 t ,B g Similar to the narrowband interference suppression process (part 1), the data such as these is already stored in a predetermined area of ​​memory.

[0100] As shown in Figure 6, in this process (part 2), when the process starts (START), the beat signal acquisition process in step S101, the beat signal FFT processing in step S103, and the frequency and power value information acquisition process in step S105 are performed sequentially. In step S105, the beat signal B converted into a frequency spectrum is performed. t ,B g From this information, the information necessary for each judgment process in steps S121 and S123 is obtained.

[0101] For example, as mentioned above, the CS device 10 receives the first chirp signal S s1 Because transmission is suspended during the period when the signal is being transmitted (see Figure 3(A)), the interference signal S received during this period is not transmitted. g3 Beat signal B generated by g The beat frequency f (shown by the gray circle in Figure 3(C)) Bg3 And the power value p as the signal level. Bg3 And obtain the interference signal S received during the second and subsequent periods. g Beat signal B generated by g Beat frequency B (shown by the gray circle in Figure 3(C)) g And the power value p as the signal level. g To obtain the following.

[0102] In the previous example, the first chirp signal S s1 The transmission was paused and the received interference signal S g3 Beat signal B corresponding to g The beat frequency is f Bg3 And the second chirp signal S follows s2 Interference signal S received during the transmission period g4 Beat signal B corresponding to g The beat frequency is f Bg4 (Not shown in Figure 3(C)). Therefore, F(1) = f Bg3 ,F(2)=f Bg4 Therefore (n=1), |F(n)-F(n+1)|=|F(1)-F(2)|=|f Bg3 -f Bg4 The determination of |<ΔF' is made. The interference signal S received during these periods g3 ,S g4 Two beat signals B are generated by this process. g Beat frequency f Bg3 ,f Bg4 And the power value p as the signal level of those signals. Bg3 ,p Bg4 To obtain the following.

[0103] In step S121, a frequency determination process is performed. This process involves the received interference signal S g3 ,S g4 Beat signal B corresponding to g Beat frequency f Bg3 ,f Bg4 The difference is calculated, and it is determined whether the absolute value of that difference is less than a predetermined frequency ΔF'.

[0104] Beat signals B from both parties g If the interference signal source that generated the beats is the same, it is likely that these beat frequencies will be somewhat similar. However, as mentioned above, the CS device 10 of the vehicle and the CS device 100 of the other vehicle will generate beat signals B depending on the magnitude of the difference (error) in their chirp rates. g Beat frequency f Bg3 ,f Bg4 This changes over time. Therefore, the two beat frequencies fBg3 ,f Bg4 As the difference between them, the frequency ΔF' is a predetermined frequency difference, and the above function approximation, which can correspond to the linear function described in Narrowband Interference Suppression Processing (Part 1), is used: "F(2) = F(1)+(F(9)-F(1))×2 / 9 = f Bg3 +(f Bg11 -f Bg3 You may also use ") × 2 / 9". Alternatively, you may determine the frequency ΔF' based on the average or maximum value of the data accumulated as the difference between two adjacent beat frequencies.

[0105] Note that the beat frequency f Bg The allowable range of ΔF' is set to be large, taking into account the amount of fluctuation and degree of variation, and the chirp signal S transmitted by the CS device 10 s A temporally adjacent interference signal S g Beat signal B corresponding to g Beat frequency f B It may be configured to accurately detect it.

[0106] Then, this frequency determination process determines that if the absolute value of the difference between the two beat frequencies F(n)-F(n+1) is not smaller than (larger than) a predetermined frequency difference ΔF' (S121; No), then these two beat frequencies are likely from different and separate interference signal sources and not interference signals transmitted from the same CS device 100, etc. Therefore, this process (part 2) is terminated (END). On the other hand, if the absolute value of the difference between the two beat frequencies F(n)-F(n+1) is smaller than a predetermined frequency difference ΔF' (S121; Yes), then these two beat frequencies may be from the same interference signal source, and the process proceeds to the determination process in step S123.

[0107] In step S123, a power value determination process is performed. This process uses the two beat frequencies f determined in step S121. Bg3 ,f Bg4 Beat signal B in gThe difference in power values ​​as intensity or signal level is calculated, and it is determined whether the absolute value is less than a predetermined power value ΔP'. Beat signal B g If the interference signal source that generated these beat signals B is the same, then these beat signals B g The power values, which represent the intensity or signal level, are likely to be very close to the same value. ΔP' is the two beat frequencies f Bg3 ,f Bg4 Beat signal B in g This is a predetermined error, expressed as the difference in power value as the intensity or signal level. For example, two beat signals B g It is determined based on the average and maximum values ​​of data accumulated as differences in intensity and power values.

[0108] In the previous example, the first chirp signal S s1 Beat signal B corresponding to g Beat frequency f Bg3 The power value in p Bg3 And the second chirp signal S s2 Beat signal B corresponding to g Beat frequency f Bg4 The power value in p Bg4 Therefore, P(1)=p Bg3 ,P(2)=p Bg4 Since this is the case (n=1), in step S123, |P(n)-P(n+1)|=|P(1)-P(2)|=|p Bg3 -p Bg4 The determination of |<ΔP' is made.

[0109] Then, this power value determination process determines that if the absolute value of the difference between the two power values ​​P(n)-P(n+1) is not smaller than (larger than) a predetermined power value difference ΔP' (S123; No), then these two power values ​​are likely from different, separate interference signal sources and not interference signals transmitted from the same CS device 100, etc. Therefore, this process (part 2) is terminated (END). Note that the first two (1st and 2nd) beat signals B g Even if it is determined that the interference is due to a different interference signal source, the next (third) beat frequency f is used to avoid misjudgment.Bg5 If the system is configured to determine whether or not there is an interference signal that may cause narrowband interference, the process (part 2) is not terminated, and the system proceeds to step S125.

[0110] In contrast, if the absolute value of the difference between two power values ​​P(n)-P(n+1) is smaller than a predetermined power value difference ΔP' (S123; Yes), then these two power values ​​are likely to be from the same interference signal source. That is, the interference signal S received during the period when transmission was suspended. g3 ,S g4 And the corresponding beat signal B g Beat frequency f Bg3 ,f Bg4 Since it is highly likely that all of these were transmitted from the same interference signal source, in the next step S125, the beat frequency f Bg3 ,f Bg4 The interference signal flag and interference signal map, which indicate the presence of interference signals, are set to "1" to indicate the presence of interference signals. Note that these are initially set to "0" to indicate the absence of interference signals.

[0111] Also, in step S125, the third chirp signal S s3 Interference signals S received during the period when transmission was performed g5 Beat signal B corresponding to g Beat frequency f Bg5 To obtain this information, we set a counter value m (=n+1). Here, since n=1, the counter value is set to "2".

[0112] In step S127, a frequency determination process is performed. This process involves the received interference signal S g4 ,S g5 Beat signal B corresponding to g Beat frequency f Bg4 ,f Bg5 A determination is made as to whether the absolute value of the difference is less than a predetermined frequency ΔF'. ΔF' is the same as that used in the determination process in step S121.

[0113] Then, if the absolute value of the difference between the two beat frequencies F(m)-F(m+1) is not smaller than (larger than) a predetermined frequency difference ΔF' (S127; No), it is highly likely that these two beat frequencies are from different and separate interference signal sources and not interference signals transmitted from the same CS device 100, etc., so the process proceeds to the determination process in step S131. On the other hand, if the absolute value of the difference between the two beat frequencies F(m)-F(m+1) is smaller than a predetermined frequency difference ΔF' (S127; Yes), it is possible that these two beat frequencies are from the same interference signal source, so the process proceeds to the determination process in step S129.

[0114] In step S129, a power value determination process is performed. This process uses the two beat frequencies f determined in step S127. Bg4 ,f Bg5 Beat signal B in g The power value, which represents the intensity or signal level, is converted into a frequency spectrum beat signal B, similar to the frequency / power value information acquisition process in step S105. g The information is obtained from the following: Then, the beat signal B at power value P(m+1) g The system determines whether the absolute difference between the power value (as an intensity or signal level) and the power value P(m) to be compared is less than a predetermined power value ΔP'. The power value P(m) to be compared is the same as the power value P(n+1) or the power value P(m+1) obtained during the processing before incrementing the counter value m in step S135. Beat signal B g If the interference signal source that generated these beat signals B is the same, then these beat signals B g The power values, which represent the intensity or signal level, are likely to be very close to the same value. ΔP' is the two beat frequencies f Bg4 ,f Bg5 Beat signal B in g This is a predetermined error, expressed as the difference in power value as the intensity or signal level. For example, two beat signals B g It is determined based on the average and maximum values ​​of data accumulated as differences in intensity and power values.

[0115] In the previous example, the second chirp signal S s2 Beat signal B corresponding to g Beat frequency f Bg4 The power value in p Bg4 And the third chirp signal S s3 Beat signal B corresponding to g Beat frequency f Bg4 The power value in p Bg5 Therefore, P(2)=p Bg4 ,P(3)=p Bg5 Since this is the case (n=1), in step S129, |P(m)-P(m+1)|=|P(2)-P(3)|=|p Bg4 -p Bg5 The determination of |<ΔP' is made.

[0116] Then, if this power value determination process determines that the absolute value of the difference between the two power values ​​P(m)-P(m+1) is not smaller than (larger than) a predetermined power value difference ΔP' (S129; No), then it is highly likely that these two power values ​​are from different and separate interference signal sources and not interference signals transmitted from the same CS device 100, etc. Therefore, the process proceeds to the determination process in step S131.

[0117] In contrast, if the absolute value of the difference between the two power values ​​P(m)-P(m+1) is smaller than the predetermined power value difference ΔP' (S129; Yes), then these two power values ​​are likely to be from the same interfering signal source and are also likely to generate narrowband interference. Therefore, in this case, beat signal B g The interference signal S appearing in the frequency spectrum g The signal component corresponding to this becomes the target of suppression (suppression target) by the interference signal suppression process in step S200. Therefore, in step S129, the beat frequency f is entered into the interference signal flag and interference signal map. Bg4 ,f Bg5 After setting the information "1" indicating the presence of an interference signal, the process proceeds to step S131.

[0118] Step S131 performs a process to determine whether or not an interference signal is present. This process determines the presence or absence of an interference signal by referring to the aforementioned interference signal flag and interference signal map. The beat frequency f is set to "1" as information indicating the presence of an interference signal. Bg If none exist (all beat frequencies f Bg If "0" is set, then (S131; No), that is, in order to avoid misjudgment regarding the first and second in steps S121 and S123, the third beat frequency f Bg5 The result of the determination regarding the interference signal S g If the presence of such a source cannot be confirmed, it is unlikely that there is an interference signal source capable of generating narrowband interference around the CS device 10. Therefore, this process (part 2) is terminated (END).

[0119] In contrast, the beat frequency f is set to "1" as information indicating the presence of an interference signal. Bg If one or more of the above conditions are met (S131; Yes), the process moves to the next step S200 to perform interference signal suppression processing. In the interference signal suppression processing of step S200, the aforementioned signal component rearrangement processing (S201), noise power estimation processing (S203), interference signal detection processing (S205), and interference signal reduction processing (S207) are performed.

[0120] When the interference signal suppression process in step S200 is completed, the termination determination process for this process is performed in step S133. For example, it is determined whether or not to terminate the narrowband interference process based on a counter value that starts from m=2. The counter value starts from m=2 in step S125, but its upper limit is set based on the number of chirp signals that the CS device 10 continuously transmits. In this embodiment, the CS device 10 transmits chirp signals S with a pause period in between. s2 ~S sx Since it sends seven of these consecutively, the maximum value of the counter can be arbitrary and can be set to, for example, "16".

[0121] Therefore, for example, if the counter does not exceed "16" (S133; No), the process proceeds to the increment process in step S135, followed by the frequency determination process in step S127. On the other hand, if the counter value exceeds "16" (S133; Yes), this process (part 2) is terminated (END).

[0122] Furthermore, interference signal S from the CS device 100 of another vehicle g The signal may stop being transmitted, or interference signal S g If the power value falls below the level required to generate narrowband interference, even if such interference exists, this process (part 2) is terminated by the frequency determination process in step S127 or the power value determination process in step S129.

[0123] Furthermore, in the determination processes S121, S123, S127, and S129 of the narrowband interference suppression process (part 2) shown in Figure 6, the symbol "<" may be replaced with the symbol "≦" to change "less than" to "less than or equal to". Also, in the narrowband interference suppression process (part 2), in Figures 3(A) to (C), the direction in which time progresses, i.e., the chirp signal S s Beat signal B is transmitted sequentially in the direction of transmission. t ,B g Information processing was performed on the above, but conversely, the beat signal B was processed in the direction of time going backward. t ,B g Information processing may be performed on the following:

[0124] In the aforementioned narrowband interference suppression process (part 2), the first chirp signal S shown in Figure 3(A) s1 and the second chirp signal S s2 or interference signal S g3 ,S g4 Related to the beat frequency f Bg3 Beat signal B g and beat frequency f Bg4 Beat signal B g After performing the respective processes in steps S101-S105 and S121-S125, the interference signal S g4 ~S g10 ...Sg17 Each related beat signal B g Regarding interference signal S g4 ~S g10 ...S g17 The processes in steps S127, S129, S200, and S135 were carried out in that order. In other words, if we focus only on the interference signal, S g3 →S g4 →S g5 →S g6 →S g7 →S g8 →S g9 →S g10 →…→S g17 The information was processed in the order shown above, but the interference signal S was processed in the opposite order. g17 →S g16 →S g15 →S g14 →S g13 →S g12 →S g11 →S g10 →…→S g3 The information processing may be performed in the following order.

[0125] In this case, for example, "|F(n)-F(n+1)|<ΔF'" in step S121 is replaced with "|F(n-1)-F(n)|<ΔF'". Also, "|P(n)-P(n+1)|<ΔP'" in step S123 is replaced with "|P(n-1)-P(n)|<ΔP'". "m=n+1" in step S125 is replaced with "m=n-1". "|F(m)-F(m+1)|<ΔF'" in step S127 is replaced with "|F(m-1)-F(m)|<ΔF'". Also, "|P(m)-P(m+1)|<ΔP'" in step S129 is replaced with "|P(m-1)-P(m)|<ΔP'". In step S133, "m=m+1" is replaced with "m=m-1".

[0126] [ summary ] As described above, in this embodiment, when the DSP 11 performs narrowband interference suppression processing (part 1), the CS device 10 receives the interference signal S g11If the (second received signal) was received after or during the most recent pause period, the DSP11 performs steps S111 and S113 to determine the beat frequency f as follows: Be (Estimated frequency F i ) with beat signal B e Determine whether or not an interference signal exists, and beat signal B e If present, step S200 estimates the frequency F in the frequency spectrum. i Interference signal S g3 ,S g11 The corresponding signal component is suppressed.

[0127] That is, by step S111, the interference signal S g3 Beat signal B corresponding to g frequency f Bg3 Based on this, beat signal B can cause narrowband interference. e (Estimated frequency F i The beat frequency f is estimated using a linear function. Be (Estimated frequency F i Power value P of the frequency spectrum in ) i And, power value P B1 Power value P B2 Or these power values ​​P B1 ,P B2 Step S113 determines whether the difference between the average power value of and is within a predetermined range ΔP, and if this difference is within the predetermined range, the beat frequency f Be (Estimated frequency F i ) with beat signal B e It is determined that (interference signal) is present. Beat signal B e If present, the estimated frequency F is determined by step S200. i Interference signal S g3 ,S g11 The corresponding signal component, and the interference signal S g4 ~S g10 For the signal component corresponding to the interference signal S g3 ,S g11 ,S g4 ~S g10 The order (S g3 →S g11 →Sg4 →S g5 →S g6 →S g7 →S g8 →S g9 →S g10 The process is suppressed by performing steps S111-S113, S200, and S115.

[0128] As a result, hardware differences exist in actual chirp sequence radar equipment, for example, between CS equipment 10 and CS equipment 100, the transmitted chirp signal S s or chirp period (sweep time T) s Errors may occur in the chirp signal S, which can result in the chirp signal S s or interference signal S g Beat signal B g Even if frequency fluctuations and spectral broadening occur, the CS device 10 will receive a beat signal B for each CS device 100. g The beat frequency f changes depending on the frequency variation and spectral spread. Be (Estimated frequency F i ) with beat signal B e This makes it possible to determine the presence of interference signals. Therefore, narrowband interference can be accurately suppressed.

[0129] Note that "interference signal S g11 "The (second received signal) was received after or during the most recent pause period" means, in the example shown in Figure 3(A), (a) the chirp signal S s1 During the pause period when no transmission is made (dashed line △ in the same figure), interference signal S g3 When the (gray triangle in the same figure) is received, the chirp signal S is the next pause period after the current pause period. s9 During the pause period when no transmission is made (dashed line △ in the same figure), interference signal S g11 (The gray triangle in the same figure) was received, or (i) the chirp signal S s9 During the pause period when no transmission is made (dashed line △ in the same figure), interference signal S g11 When the (gray triangle in the same figure) is received, the chirp signal S represents the most recent pause period prior to the current pause period. s1During the pause period when no transmission is made (dashed line △ in the same figure), interference signal S g3 This indicates that the signal (gray triangle in the diagram) was received.

[0130] Furthermore, in this embodiment, when the DSP 11 performs narrowband interference suppression processing (part 2), the CS device 10 receives (f) interference signal S g12 (Second received signal) is interference signal S g11 When received immediately after the (first received signal), the interference signal S g12 and the adjacent interference signal S g13 (Third received signal) Interference signal S g11 For two adjacent received signals after that, or (k) interference signal S g10 (Second received signal) is interference signal S g11 When it is received immediately before (the first received signal), the interference signal S g10 and the adjacent interference signal S g9 (Third received signal) Interference signal S g10 For two adjacent received signals, (1) DSP11 performs the two-signal (interfering signal S) step S103. g11 and interference signal S g12 (or interference signal S) g10 and interference signal S g9 ) Each beat signal B g (2) DSP11 calculates the frequency spectrum of the two frequencies F in step S105. Bj ,F Bk and two power values ​​P Bj ,P Bk The acquisition of information, and (3) DSP11 receives two signals (interference signal S) in steps S127 and S129. g11 ,S g12 (or interference signal S) g10 ,S g9 The determination of whether the two signal sources are the same is performed sequentially until it is determined by (3) that the two signal sources are not the same (S127; No or S129; No). After that, the DSP11 interferes with the two adjacent received signals that were determined to be the same by steps S127 and S129 (S127; Yes and S129; Yes) by the interference signal Sg11 ,S g12 (or interference signal S) g10 ,S g9 It is determined that (S131; Yes), and the interference signal S is the two adjacent received signals. g11 ,S g12 (or interference signal S) g10 ,S g9 ) is suppressed by step S200.

[0131] As a result, hardware differences exist in actual chirp sequence radar equipment, for example, between CS equipment 10 and CS equipment 100, the transmitted chirp signal S s or chirp period (sweep time T) s Errors may occur in the chirp signal S, which can result in the chirp signal S s or interference signal S g Beat signal B g Even if frequency fluctuations and spectral broadening occur, the CS device 10 will receive a beat signal B for each CS device 100. g The beat frequency f changes depending on the frequency variation and spectral spread. Be (Estimated frequency F i ) with beat signal B e This makes it possible to determine the presence of interference signals. Therefore, narrowband interference can be accurately suppressed.

[0132] Note that "interference signal S g11 The two adjacent received signals after this one refer to the chirp signal S in the example shown in Figure 3(A). s9 Interference signal S received during the pause period when no transmission is being made (dashed line △ in the same figure) g11 Starting from the gray triangle (△) in the same figure, the interference signal S g11 And immediately after this, the interference signal S was received. g12 The two signals (white triangles in the same figure), and the interference signal S. g12 And immediately after this, the interference signal S was received. g13 The two signals (white triangles in the same diagram) are the interference signal S. g11 ,S g12 , interference signal S g12 ,S g13 , interference signal Sg13 ,S g14 , interference signal S g14 ,S g15 , interference signal S g15 ,S g16 or interference signal S g16 ,S g17 These are the two signals.

[0133] Also, "Interference signal S g10 "Two adjacent received signals prior to" refers to the chirp signal S in the example shown in Figure 3(A). s9 Interference signal S received during the pause period when no transmission is being made (dashed line △ in the same figure) g11 Starting from the gray triangle (△) in the same figure, the interference signal S g11 And the interference signal S received immediately before this g10 The two signals (white triangles in the same figure), and the interference signal S. g10 And the interference signal S received immediately before this g9 The two signals (white triangles in the same diagram) are the interference signal S. g11 ,S g10 , interference signal S g10 ,S g9 , interference signal S g9 ,S g8 , interference signal S g8 ,S g7 , interference signal S g7 ,S g6 , interference signal S g6 ,S g5 , interference signal S g5 ,S g4 or interference signal S g4 ,S g3 , interference signal S g3 ,S g2 or interference signal S g2 ,S g1 These are the two signals, and .

[0134] Furthermore, in the CS device 10 of this embodiment, the DSP 11 (S200) performs the following steps: step S201, the interference signal S of the frequency spectrum of the two signals g3 (or interference signal S) g11 Or interference signal S g10 The frequency F of the frequency spectrum corresponding to ) B1A frequency F is located at a predetermined frequency α before and after the center. B1+α and frequency F B1-α During this time, (2m+1) signal components are extracted, and these extracted (2m+1) signal components are sorted in descending order of power value. Then, in step S203, the (m+1)th power value located in the middle of these components is set to the frequency F. B1 The noise power in step S205 is estimated as an estimated value. A predetermined threshold is set based on the estimated noise power estimated in step S203, and the interference signal S is measured based on this predetermined threshold. g11 (or interference signal S) g12 Or interference signal S g9 ) frequency F B2 The interference signal is detected. In step S207, the signal level of the interference signal detected in step S205 is reduced to an estimated value. Note that "m" is an integer of 1 or greater.

[0135] This results in the interference signal S g3 The frequency F of the frequency spectrum B1 Frequency F centered around B1+α and frequency F B1-α The power value of the median of the signal components extracted during the interval is the frequency F B1 An estimated value of the noise power is calculated, and a predetermined threshold is set based on this estimated value. Then, the interference signal is detected based on this predetermined threshold. Therefore, the reduction in step S207 is tailored to the signal level of each individual interference signal, and does not result in a uniform reduction across a wide frequency range. Consequently, excessive suppression of narrowband interference is less likely to occur.

[0136] In this embodiment, the CS device 10 uses, for example, seven chirp signals S s After or before continuously transmitting a chirp signal S s The transmission sequence for the chirp signal was configured to pause transmission for the same amount of time as the transmission of the chirp signal S, but this is not the only configuration. sThe number of chirp signals is not limited, as long as there are multiple signals. Also, the time during which transmission is paused is limited to one or more chirp signals S s There is no limit to the number of items that can be sent within the time frame.

[0137] Furthermore, in the CS device 10 of the above-described embodiment, in the narrowband interference suppression processing (part 2), the interference signal S is treated as two adjacent received signals (two signals). g11 ,S g12 , interference signal S g12 ,S g13 , interference signal S g13 ,S g14 And so on, interference signal S g11 ,S g10 , interference signal S g10 ,S g9 , interference signal S g9 ,S g8 In this configuration, the two adjacent signals (one and the other) are set up so that the other signal in the first pair and the one signal in the second pair are the same signal (they differ in part), but this is not the only way. For example, interference signal S g11 ,S g12 , interference signal S g13 ,S g14 Yes, interference signal S g11 ,S g10 , interference signal S g9 ,S g8 In this way, two adjacent signals (one and the other) may be configured to be completely different in the previous set and the following set. In this case, the interference signal S is changed to "m=n+2" in step S125 and "m=m+2" in S135. g Some changes to the processing content will be necessary due to the specification and selection of certain parameters. This will reduce the total time required for decision processing in steps S121, S123, S127, S129, etc., and thus reduce the information processing time in the narrowband interference suppression processing (part 2).

[0138] Furthermore, in the CS device 10 of the above-described embodiment, in the narrowband interference suppression processing (part 2), the interference signal S is treated as two adjacent received signals (two signals). g11 ,S g12 , interference signal S g12 ,Sg13 , interference signal S g13 ,S g14 And so on, interference signal S g11 ,S g10 , interference signal S g10 ,S g9 , interference signal S g9 ,S g8 As shown above, we have constructed combinations of two adjacent signals that are in the immediate vicinity, but we are not limited to this. For example, interference signal S g11 ,S g13 , interference signal S g12 ,S g14 Yes, interference signal S g11 ,S g9 , interference signal S g10 ,S g8 In this way, two signals can be constructed using the next adjacent combination with a return signal, skipping one signal. Also, interference signal S g11 ,S g13 , interference signal S g15 ,S g17 And so on, interference signal S g11 ,S g9 , interference signal S g7 ,S g5 In this way, two signals can also be constructed using the next adjacent combination with one signal skipped between them and no return signal. In these cases as well, the interference signal S g Some changes to the processing content will be necessary when specifying or selecting. In the case of the next adjacent combination without return, the specified or selected interference signal S g By halving the number of such elements, it becomes possible to significantly reduce the information processing time in narrowband interference suppression processing (part 2).

[0139] Furthermore, in the CS device 10 of the above-described embodiment, in the narrowband interference suppression process (part 2), the interference signal suppression process by step S200 is performed in the middle of repeating the loop process as follows: steps S127→S129→S131→S200→S133→S135→S127→… thereby detecting and successively suppressing narrowband interference from two adjacent received signals. However, instead of providing the interference signal suppression process by step S200 in the middle of such loop processing, two adjacent received signals that need to be suppressed outside the loop processing may be suppressed together in one go.

[0140] Furthermore, in the CS device 10 of the embodiment described above, the narrowband interference suppression process (1) and the narrowband interference suppression process (2) were configured as separate algorithms, but an algorithm that combines both may also be configured. For example, if we focus only on the interference signal shown in Figure 3(A), S g3 →S g11 →S g4 →S g5 →S g6 →S g7 →S g8 →S g9 →S g10 →S g11 →S g12 →S g13 →S g14 →S g15 As shown above, the information processing algorithm may be configured to execute the process (1) first, followed by the process (2). This allows for a reduction in overall processing time compared to executing the process (2) for all interference signals from the beginning, by executing the process (1) first, which allows for some degree of foresight in suppressing interference signals.

[0141] In the above-described embodiment of the CS device 10, the configuration was explained using a 79GHz band millimeter-wave radar as an example, but it is also possible to configure chirp sequence radar devices in the 76GHz band, 24GHz band, 26GHz band, and other frequency bands as described above.

[0142] Furthermore, although the above-described embodiment illustrated the case where the CS device 10 is mounted as an in-vehicle radar in a vehicle with an autonomous driving function, the CS device 10 can also be used in other applications, such as a vital sensor that can monitor heart rate and respiration without touching the patient for medical purposes, a sensor for monitoring elderly people at home with consideration for privacy for nursing care purposes, and a sensor for detecting the approach of construction vehicles and automated guided vehicles for industrial machinery purposes.

[0143] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples described above. Furthermore, the technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Moreover, the technologies illustrated in this specification or drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness. Note that the terms in parentheses in the [Explanation of Symbols] section may indicate the correspondence between the terms used in each of the embodiments described above and the terms described in the claims. [Explanation of Symbols]

[0144] 10... Chirp sequence radar system, vehicle's CS system (device 1) 11…DSP (Transmission Control Unit, Frequency Spectrum Calculation Unit, Signal Information Acquisition Unit, Signal Source Determination Unit, Interference Signal Determination Unit, Interference Signal Suppression Unit) 100...CS equipment (other equipment) on other vehicles S103 (Frequency Spectrum Calculation Unit) S107, S109, S121, S123, S127, S129 (signal source determination section) S111, S113, S133 (Interference signal determination unit) S200 (Interference signal suppression unit) S201, S203 (Noise power estimation section) S205 (Interference signal detection unit) S207 (Interference signal reduction unit) B e ,B g ,B t ...beat signal f B ,f Bg ,f Bt ...beat frequency f Be ...Beat frequency (estimated frequency F that is estimated to cause narrowband interference) i ) f Bg3...Beat frequency (F, the frequency in the frequency spectrum of the beat signal corresponding to the first received signal) B1 ) f Bg11 ...Beat frequency (F, the frequency in the frequency spectrum of the beat signal corresponding to the second received signal) B2 ) f c ...cutoff frequency f s ...Sweep bandwidth p g ...power value p Bg3 ...Power value (Power value P corresponding to the first received signal in the frequency spectrum of the beat signal) B1 ) p Bg11 ...Power value (Power value P corresponding to the second received signal in the frequency spectrum of the beat signal) B1 ) S g ...interference signal S g3 ...Interference signal (first received signal) S g4 ,S g2 ...Interference signal (third received signal) S g11 ...Interference signal (second received signal) S s ,S s2 ~S s8 ,S s10 ~S s16 ...chirp signal S t ...target signal T p …cycle time T s ... sweeping time τ g ,τ t ...delay time

Claims

1. A chirp sequence radar device that transmits a chirp signal modulated with a frequency that changes in a sawtooth waveform with a constant sweep period, and detects an object based on a beat signal obtained by mixing the chirp signal with a target signal received when the chirp signal is reflected from the object, A transmission control unit controls the transmission of the chirp signals such that transmission periods in which multiple chirp signals are transmitted and pause periods in which the transmission is suspended alternate. A frequency spectrum calculation unit that calculates the frequency spectra of two signals, which are the beat signals of a first received signal received during the aforementioned pause period and a second received signal received after or before the aforementioned pause period. The frequency F corresponding to the first received signal in the frequency spectrum of the two signals obtained by the frequency spectrum calculation unit is B1 and power value P B1 and the frequency F corresponding to the second received signal B2 and power value P B2 A signal information acquisition unit that acquires information for each of these, The aforementioned frequency F B1 and the aforementioned frequency F B2 The difference and the power value P B1 and the aforementioned power value P B2 A signal source determination unit determines whether the two signal sources of the first received signal and the second received signal are the same based on the difference between them, If the signal source determination unit determines that the two signal sources are the same, an interference signal determination unit determines whether or not there is an interference signal that can cause narrowband interference with the signal component corresponding to the target signal in the frequency spectrum. The system includes an interference signal suppression unit that suppresses the signal component in the frequency spectrum corresponding to the interference signal when the interference signal determination unit determines that the interference signal is present, When the second received signal was received after or during the most recent pause period prior to the pause period, Said interference signal determining unit is configured to determine the frequency F of said first received signal in said frequency spectrum B1 an estimated frequency F estimated to be capable of causing said narrowband interference based on i has a power value P i and said power value P B1 , power value P B2 or these P B1 , P B2 when the difference from the average power value of is within a predetermined range, the estimated frequency F i is determined to have said interference signal present, The interference signal suppression unit performs the estimated frequency F in the frequency spectrum. i A chirp sequence radar device characterized by suppressing the signal component corresponding to the aforementioned interference signal.

2. A chirp sequence radar device that transmits a chirp signal modulated with a frequency that changes in a sawtooth waveform with a constant sweep period, and detects an object based on a beat signal obtained by mixing the chirp signal with a target signal received when the chirp signal is reflected from the object, A transmission control unit controls the transmission of the chirp signals such that transmission periods in which multiple chirp signals are transmitted and pause periods in which the transmission is suspended alternate. A frequency spectrum calculation unit that calculates the frequency spectra of two signals, which are the beat signals of a first received signal received during the aforementioned pause period and a second received signal received after or before the aforementioned pause period. The frequency F corresponding to the first received signal in the frequency spectrum of the two signals obtained by the frequency spectrum calculation unit is B1 and power value P B1 and the frequency F corresponding to the second received signal B2 and power value P B2 A signal information acquisition unit that acquires information for each of these, The aforementioned frequency F B1 and the aforementioned frequency F B2 The difference and the power value P B1 and the aforementioned power value P B2 A signal source determination unit determines whether the two signal sources of the first received signal and the second received signal are the same based on the difference between them, If the signal source determination unit determines that the two signal sources are the same, the interference signal determination unit determines whether or not this same signal source is an interference signal that can cause narrowband interference with the signal component corresponding to the target signal in the frequency spectrum. The system includes an interference signal suppression unit that suppresses the signal component in the frequency spectrum corresponding to the interference signal when the interference signal determination unit determines that the same signal source is the interference signal during the transmission period and the pause period. When the second received signal is received immediately after the first received signal, the second received signal and the adjacent third received signal, or two other received signals that are adjacent to the second received signal, or When the second received signal was received immediately before the first received signal, the second received signal and the third received signal adjacent to it, and other two received signals that precede the first received signal, (1) The frequency spectrum calculation unit calculates the frequency spectra of the two signals, (2) The signal information acquisition unit calculates the two frequencies F Bj , F Bk and the two aforementioned power values ​​P Bj , P Bk The acquisition of information and (3) the determination by the signal source determination unit as to whether the two signal sources are the same are performed sequentially until (3) determines that the two signal sources are not the same. The interference signal determination unit determines that the two adjacent received signals, which are determined to be from the same signal source, are the interference signals. The interference signal suppression unit controls the frequency F in the frequency spectrum. Bj , F Bk A chirp sequence radar device characterized by suppressing the signal component corresponding to the aforementioned interference signal.

3. The aforementioned interference signal suppression unit is The frequency F of the frequency spectrum of the two signals that corresponds to the first received signal B1 A frequency F is located at a predetermined frequency α before and after the center. B1+α and frequency F B1-α After sorting the (2m+1) signal components extracted during this period in descending order of power value, the (m+1)th power value located in the middle of them is given the frequency F B1 A noise power estimation unit that estimates the noise power in the given state, A predetermined threshold is set based on the estimated value of the noise power estimated by the noise power estimation unit, and the frequency F of the second received signal is set based on this predetermined threshold. B2 An interference signal detection unit for detecting the interference signal in the above, The system includes an interference signal reduction unit that reduces the signal level of the interference signal detected by the interference signal detection unit to the estimated value. A chirp sequence radar apparatus according to claim 1 or 2, characterized by the features described above.

Images